AGMA 923-C22
(Revision of AGMA 923-B05)
AGMA Information Sheet
AGMA 923-C22
Metallurgical Specifications
for Steel and Cast Iron
Gearing
AMERICAN GEAR MANUFACTURERS ASSOCIATION
American
Gear
Manufacturers
Association
AGMA 923-C22
Metallurgical Specifications for Steel and Cast Iron Gearing
AGMA 923-C22
(Revision of AGMA 923-B05)
CAUTION NOTICE: AGMA technical publications are subject to constant
improvement, revision or withdrawal as dictated by experience. Any person who
refers to any AGMA Technical Publication should be sure that the publication is the
latest available from the Association on the subject matter.
[Tables or other self-supporting sections may be referenced. Citations should read:
See AGMA 923-C22, Metallurgical Specifications for Steel and Cast Iron Gearing,
published by the American Gear Manufacturers Association, 1001 N. Fairfax Street,
Suite 500, Alexandria, Virginia 22314, http://www.agma.org.]
Approved August 2022
ABSTRACT
This document identifies metallurgical quality characteristics which are important to the performance of
steel and cast iron gearing. The AGMA gear rating standards identify performance levels of gearing by
heat treatment method and grade number. For each heat treatment method and AGMA grade number,
acceptance criteria are given for various metallurgical characteristics identified in this document.
Published by
American Gear Manufacturers Association
1001 N. Fairfax Street, Suite 500, Alexandria, Virginia 22314
Copyright © 2022 by American Gear Manufacturers Association
All rights reserved.
No part of this publication may be reproduced in any form, in an electronic
retrieval system or otherwise, without prior written permission of the publisher.
Printed in the United States of America
ISBN: 978-1-64353-119-9
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AGMA 923-C22
Contents
Foreword ................................................................................................................................................ iv
1 Scope ................................................................................................................................................. 1
2 Normative references.......................................................................................................................... 1
3 Definitions ........................................................................................................................................... 3
4 Procedures ....................................................................................................................................... 16
4.1 Recommended test methods..................................................................................................... 16
4.2 Test coupons ............................................................................................................................ 25
4.2.1 Process control test coupons.......................................................................................... 25
4.2.2 Representative test coupon ............................................................................................ 25
5 Metallurgical requirements ................................................................................................................ 26
5.1
5.2
5.3
5.4
5.5
5.6
5.7
Through hardened gearing ........................................................................................................ 26
Carburized and hardened gearing ............................................................................................. 29
Induction or flame hardened gearing ......................................................................................... 36
Nitrided gearing......................................................................................................................... 41
Gray iron gearing ...................................................................................................................... 46
Ductile iron gearing ................................................................................................................... 47
Austempered ductile iron gearing, ADI ...................................................................................... 48
Annexes
Annex A Bibliography ............................................................................................................................ 50
Tables
Table 1 – Metallurgical characteristics for through hardened gearing...................................................... 27
Table 2 – Metallurgical characteristics for carburized and hardened gearing .......................................... 30
Table 3 – Metallurgical characteristics for induction or flame hardened gearing ...................................... 36
Table 4 – Metallurgical characteristics for nitrided gearing...................................................................... 42
Table 5 – Metallurgical characteristics for gray iron gearing ................................................................... 46
Table 6 – Metallurgical characteristics for ductile iron gearing ................................................................ 47
Table 7 – Metallurgical characteristics for austempered ductile iron gearing ........................................... 48
Figures
Figure 1 – Continuous carbide network .................................................................................................... 4
Figure 2 – Semi-continuous carbide network............................................................................................ 5
Figure 3 – Discontinuous carbides ........................................................................................................... 5
Figure 4 – Dispersed carbides ................................................................................................................. 6
Figure 5 – Solid on shaft pinion blank ...................................................................................................... 8
Figure 6 – Bore style gearing blank .......................................................................................................... 8
Figure 7 – Disc style gearing blank .......................................................................................................... 8
Figure 8 – Web style gear blank............................................................................................................... 9
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Figure 9 – Intergranular oxidation in carburized gearing ......................................................................... 11
Figure 10 – Microcracks. Original magnification: 1000X, bright field ....................................................... 12
Figure 11 – Microcracks. Original magnification: 1000X, dark field ......................................................... 12
Figure 12 – Non-martensitic transformation products in carburized gearing ............................................ 13
Figure 13 – Tempered martensite and 5% retained austenite in carburized gearing ............................... 14
Figure 14 – Tempered martensite and 20% retained austenite in carburized gearing ............................. 15
Figure 15 – Tempered martensite and 30% retained austenite in carburized gearing ............................. 15
Figure 16 – Case depth measurement locations .................................................................................... 17
Figure 17 – Examples of ingot, bloom, billet/bar, and shaft forgings ....................................................... 20
Figure 18 – Example of upset disk forging ............................................................................................. 21
Figure 19 – Example of closed die forging ............................................................................................. 22
Figure 20 – Example of seamless rolled ring forging .............................................................................. 23
Figure 21 – Example bevel gearing blank .............................................................................................. 24
Figure 22 – Variations in hardening pattern obtainable on gear teeth with flame or induction hardening . 41
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AGMA 923-C22
Foreword
[The foreword, footnotes and annexes, if any, in this document are provided for informational purposes
only and are not to be construed as a part of AGMA 923-C22, Metallurgical Specifications for Steel and
Cast Iron Gearing.]
In November 1984, an ad hoc Metallurgy and Gear Rating Committee met to define the factors required
to qualify the various metallurgical quality grades that were to be introduced into the gear rating standard
that eventually became ANSI/AGMA 2001-B88, Fundamental Rating Factors and Calculation Methods for
Involute Spur and Helical Gear Teeth.
In May 1988, ANSI/AGMA 6033-A88, Standard for Marine Propulsion Gear Units – Part 1, Materials, was
published using a short list of metallurgical factors in table form.
In September 1988, ANSI/AGMA 2001-B88 was published using metallurgical factors in table form.
Starting in July 1992, AGMA representatives participated in writing ISO 6336-5, Calculation of Load
Capacity of Spur and Helical Gears – Part 5: Strength and Quality of Materials, which was a modification
of the tables in ANSI/AGMA and DIN Standards.
In February 1993, AGMA 6002-B93, Design Guide for Vehicle Spur and Helical Gears, was published
using a modified version of the tables used in ANSI/AGMA 2001-B88.
In September 1993, the AGMA Metallurgy and Materials Committee accepted the task of consolidating
the various tables to avoid redundancies and conflicting requirements, and started work on AGMA
923-A00, Metallurgical Specifications for Steel Gearing.
In January 1995, a revised ANSI/AGMA 2001-C95 was published using a version of the ANSI/AGMA
2001-B88 tables as revised by the AGMA Helical Gear Rating Committee.
In November 1997, a revised ANSI/AGMA 2003-B97, Rating the Pitting Resistance and Bending Strength
of Generated Straight Bevel, Zerol Bevel and Spiral Bevel Gear Teeth, was published using a version of
the ANSI/AGMA 2001-B88 tables as revised by the AGMA Bevel Gearing Committee.
The committee reviewed all metallurgical tables of the gear rating standards ANSI/AGMA 2001-B88,
ANSI/AGMA 2003-A86, and ISO 6336-5:1996 and their proposed revisions to develop consolidated
tables describing the metallurgical characteristics associated with each specific type of heat treatment
and metallurgical quality grade. Effort was made to reference ISO specifications where possible. The
consolidated tables were submitted to the gear rating committees for their agreement and are published
here for reference by other standards.
AGMA’s goal is to develop a consistent metallurgical specification which reflects the quality requirements
for steel gearing. AGMA 923-A00 was such a document and was intended to be consistent with the
applicable portions of ISO 6336-5:1996, to the extent possible while the two standards were in parallel
development. The AGMA Technical Division Executive Committee approved the publication of AGMA
923-A00 in August 2000.
AGMA 923-B05 incorporated changes to Item 8, microstructure, of Table 1, metallurgical characteristics
for through hardened gearing. The balance of the document remains unchanged. The AGMA Technical
Division Executive Committee approved the publication of AGMA 923-B05 in May 2005.
AGMA 923-C22 replaces AGMA 923-B05. This edition of the information sheet was developed to be
consistent with ISO 6336-5:2016. An expanded reduction ratio calculation methodology with new figures
has been added to the procedures section. In addition, metallurgical tables have been updated as follows:
a) listing of requirements sequentially;
b) chemistry and cleanliness requirements were added;
c) footnotes were reworded and renumbered for uniformity;
d) new metallurgical tables were added for gray cast iron, ductile iron, and austempered
ductile iron.
The first draft of AGMA 923-C22 was created in November 2013. It was approved by the Technical
Division Executive Committee (TDEC) in August 2022.
Suggestions for improvement of this information sheet will be welcome. They should be sent to
tech@agma.org.
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AMERICAN GEAR MANUFACTURERS ASSOCIATION
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PERSONNEL of the AGMA Metallurgy and Materials Committee
Chair: Carl R. Ribaudo........................................Timken Company, Retired
Vice Chair: Liam Joseph Coen............................INNIO Waukesha Gas Engines, Inc
ACTIVE MEMBERS
D. Antos .............................................................Canton Drop Forge
J. Bishar .............................................................GE Transportation, a Wabtec Company
R. Errichello........................................................Geartech
M. He .................................................................Scot Forge Company
J. Lefevre ...........................................................Applied Process Inc.
D. McLain ...........................................................General Motors LLC
W. Skrzypek .......................................................Twin Disc, Incorporated
A. Swiglo ............................................................Northern Illinois University
T. Tressler ..........................................................Ellwood City Forge
D. Weires ...........................................................Boeing Rotorcraft – Philadelphia
F. Uherek ...........................................................Regal Rexnord Corporation
D. Yatzook..........................................................Artec Machine Systems
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AGMA 923-C22
American Gear Manufacturers Association –
Metallurgical Specifications for Steel and Cast Iron
Gearing
1
Scope
Metallurgical quality characteristics for use in conjunction with AGMA gear rating standards are
recommended. Three different metallurgical quality grades: grade 1, grade 2, and grade 3 are defined.
Characteristics include raw material, heat treatment, post heat treat processing, and associated
inspections. Gear design and rating, case depth, allowable stress numbers, and quality control sampling
plans are not included.
2
Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of
this document. At the time of initial development, the editions shown were valid. All standards are subject
to revision, and parties to agreements based on this document are encouraged to investigate the
possibility of applying the most recent editions of the standards shown below.
AGMA 904, Metric Usage
ANSI/AGMA 1010, Appearance of Gear Teeth – Terminology of Wear and Failure
ANSI/AGMA 1012, Gear Nomenclature, Definitions of Terms with Symbols
ANSI/AGMA 2001, Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical
Gear Teeth
ANSI/AGMA 2003, Rating the Pitting Resistance and Bending Strength of Generated Straight Bevel,
Zerol Bevel and Spiral Bevel Gear Teeth
ANSI/AGMA 2004, Gear Materials and Heat Treatment Manual
ANSI/AGMA ISO 14104, Gears – Surface Temper Etch Inspection After Grinding – Chemical Method
ANSI/AGMA 6002, Design Guide for Vehicle Spur and Helical Gears
ASTM A29/A29M, Specification for Steel Bars, Carbon and Alloy, Hot-Wrought, General Requirements
ASTM A148/A148M, Specification for Steel Castings, High Strength, for Structural Purposes
ASTM A247, Standard Test Method for Evaluating the Microstructure of Graphite in Iron Castings
ASTM A255, Standard Test Methods for Determining Hardenability of Steel
ASTM A275/A275M, Test Method for Magnetic Particle Examination of Steel Forgings
ASTM A370, Standard Test Methods and Definitions for Mechanical Testing of Steel Products
ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings
ASTM A519/A519M, Standard Specification for Seamless Carbon and Alloy Steel Mechanical Tubing
ASTM A534, Standard Specification for Carburizing Steels for Anti-Friction Bearings
ASTM A536, Standard Specification for Ductile Iron Castings
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ASTM A609/A609M, Standard Practice for Castings, Carbon, Low-Alloy, and Martensitic Stainless
Steel, Ultrasonic Examination Thereof
ASTM A751, Test Methods, Practices, and Terminology for Chemical Analysis of Steel Products
ASTM A866-18, Standard Specification for Medium Carbon Anti-Friction Bearing Steel
ASTM A897, Standard Specification for Austempered Ductile Iron Castings
ASTM A941, Standard Terminology Relating to Steel, Stainless Steel, Related Alloys, and Ferroalloys
ASTM A956, Standard Test Method for Leeb Hardness Testing of Steel Products
ASTM A1038, Standard Test Method for Portable Hardness Testing by the Ultrasonic Contact
Impedance Method
ASTM E3, Practice for Preparation of Metallographic Specimens
ASTM E8/E8M, Standard Test Methods for Tension Testing of Metallic Materials
ASTM E10, Standard Test Method for Brinell Hardness of Metallic Materials
ASTM E18, Standard Test Methods for Rockwell Hardness of Metallic Materials 1, 2
ASTM E23, Standard Test Methods for Notched Bar Impact Testing of Metallic Materials
ASTM E45, Standard Test Methods for Determining the Inclusion Content of Steel
ASTM E92, Standard Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials
ASTM E110, Standard Test Method for Indentation Hardness of Metallic Materials by Portable
Hardness Testers
ASTM E112, Standard Test Methods for Determining Average Grain Size
ASTM E125, Standard Reference Photographs for Magnetic Particle Indications on Ferrous Castings
ASTM E140, Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness,
Vickers Hardness, Rockwell Hardness, Rockwell Superficial Hardness, Knoop Hardness, Scleroscope
Hardness, and Leeb Hardness
ASTM E350, Standard Test Methods for Chemical Analysis of Carbon Steel, Low-Alloy Steel, Silicon
Electrical Steel, Ingot Iron, and Wrought Iron
ASTM E351, Standard Test Methods for Chemical Analysis of Cast Iron – All Types
ASTM E407, Standard Practice for Microetching Metals and Alloys
ASTM E1077, Standard Test Methods for Estimating the Depth of Decarburization of Steel Specimens
ASTM E1444, Practice for Magnetic Particle Examination
ISO 185, Grey Cast Irons – Classification
ISO 642, Steel – Hardenability test by end quenching (Jominy test)
ISO 643, Steels – Micrographic determination of the ferritic or austenitic grain size
ISO 683-1, Heat-treatable steels, alloy steels and free-cutting steels – Part 1: Direct-hardening
unalloyed and low-alloyed wrought steel in form of different black products
ISO 683-11, Heat-treatable steels, alloy steels and free-cutting steels – Part 11: Wrought casehardening steels
ISO 945, Microstructure Of Cast Irons
ISO 1083, Spheroidal Graphite Cast Irons – Classification
ISO 4967, Steel – Determination of content of non-metallic inclusions – micrographic method using
standard diagrams
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ISO 6336-5, Calculation of load capacity of spur and helical gears – Part 5: Strength and quality
of materials
ISO 17804, Founding – Ausferritic spheroidal graphite cast irons – Classification
ISO 18265, Metallic Materials – Conversion of Hardness Values
SAE/AMS 2300, Premium Aircraft-Quality Steel Cleanliness, Magnetic Particle Inspection Procedure
SAE/AMS 2301, Cleanliness, Aircraft Quality Steel Magnetic Particle Inspection Procedure
SAE/AMS 2304, Special Aircraft-Quality Steel Cleanliness, Magnetic Particle Inspection Procedure
SAE/AMS-S-13165, Shot Peening of Metal Parts
SAE J419, Methods of Measuring Decarburization
SAE J423, Methods of Measuring Case Depth
SAE J864, Surface Hardness Testing with Files
3
Definitions
The terms used in this document, wherever applicable, conform to AGMA 904 and ANSI/AGMA 1012, but
they have been modified to cover only those concepts applicable to this document. For definitions of
technical terms not included in this clause, see ANSI/AGMA 1012, ANSI/AGMA 2004, and ASTM A941.
Key terms used in this document are defined as follows:
NOTE: The definitions used in this information sheet may differ from other AGMA publications. The user should
assure themselves that they fully understand the terms, definitions, and symbols as contained in this publication.
alloy steel: A steel containing specified quantities of alloying elements (other than carbon and the
commonly accepted amounts of manganese, copper, silicon, sulfur, and phosphorus) added to increase
hardenability and to affect changes in mechanical properties.
annealing: Without an adjective annealing is assumed to mean full annealing.
− full annealing: The heating to and holding at a suitable temperature above the upper
transformation temperature and then cooling, typically in the furnace at a suitable rate, for reducing
hardness, improving machinability, producing a desired microstructure, or obtaining desired
mechanical properties.
− subcritical annealing: Reheating to a temperature below the lower transformation temperature.
For carburized gearing the temperature is typically 1200–1250°F (650–675°C) and is done after
carburizing and before hardening.
ausferrite: a cast iron matrix microstructure, produced by a controlled thermal process, which consists of
predominantly acicular ferrite and high carbon austenite.
austempering: Austempering is an isothermal heat treatment process that can be applied to ferrous
materials to increase strength and toughness. Austempering consists of austenitizing, rapid quenching to
avoid the formation of high temperature transformation products to a temperature above the martensite
start temperature, and then holding to allow isothermal formation of either ausferrite in cast iron, or lower
bainite in steel. A ferrous material heat treated by austempering is referred to as austempered.
austenite: A solid solution of one or more elements in face-centered cubic iron. In carbon and low alloy
steels this phase is stable only at elevated temperatures and is non-magnetic.
austempered ductile iron: Also known as ADI or ausferritic ductile iron, is produced by giving
conventional ductile iron an austempering heat treatment.
austenitizing: The forming of austenite by heating a ferrous material into the transformation range
(partial austenitizing) or above the transformation range (complete austenitizing).
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bainite: An aggregate of ferrite and cementite resulting from the transformation of austenite at
temperatures below the pearlite range but above the martensite start temperature. Its appearance is
feathery if formed in the upper part of the bainite transformation range (upper bainite) and acicular,
resembling tempered martensite, if formed in the lower part (lower bainite).
banding: Banding is alternating areas of different microstructures typically seen as metallographic dark
and light etching areas as the result of localized chemical microsegregation. Elements which tend to
segregate are sulfur, phosphorus, carbon, silicon, and manganese. Microsegregation is nonuniform
distribution of alloying elements.
base hardness: See hardness, base.
bending strength: The strength of gear teeth related to their resistance to gear tooth bending failure.
Bending failure is a fatigue phenomenon usually resulting in cracking at the tooth root fillet. Typical cracks
and fractures are illustrated in ANSI/AGMA 1010. See standards such as ANSI/AGMA 2001 and
ANSI/AGMA 2003.
capable of: The producer documents that the material was produced with the processing steps and
controls that the producer has established to assure compliance with the specification, but the testing to
confirm compliance is not required.
carbide: A microstructural phase which is a compound of metal (M) and carbon (C) having the chemical
formula of MxCy. See Figure 1 through Figure 4 for photomicrographs of various classifications of carbide
distribution (white constituent) in tempered martensite.
5% nital etch
400 X mag.
Figure 1 – Continuous carbide network
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20 µm
Figure 2 – Semi-continuous carbide network
20 µm
Figure 3 – Discontinuous carbides
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20 µm
Figure 4 – Dispersed carbides
carbon potential: A measure of the ability of a furnace environment containing active carbon to alter or
maintain, under prescribed conditions, the carbon content of the steel.
carbon restoration: Carburizing to replace the carbon lost in the surface layer due to previous thermal
processing.
carbon steel: A steel having no specified minimum quantity of alloying elements except manganese
and silicon.
carbonitriding: A modified form of gas carburizing, in which steel (typically plain carbon and very low
alloy) is austenitized in an ammonia enriched carburizing atmosphere. This results in simultaneous
adsorption of carbon and nitrogen bearing gases, the dissociation of these gases, and diffusion of carbon
and nitrogen atoms into the steel, which results in the formation of complex nitrides in a high carbon case.
carburizing: A heat treatment process in which an austenitized steel is brought into contact with a
carbonaceous atmosphere of sufficient carbon potential to cause adsorption of carbon bearing gases at
the surface where they dissociate and by diffusion to create a carbon concentration gradient. Carburizing
is generally followed by quenching and reheating (tempering) of an item to produce a hardened and
tempered case.
carburized and austempered: A heat treatment for carburizing grades of steels which produces a high
carbon, hard bainitic case, and a softer tempered martensite or bainite core.
case: The outer portion that has been made harder than the inner portion (see core hardness) as a result
of altered composition, microstructure, or both, by treatments such as carburize and hardening, induction
hardening, flame hardening, and nitriding.
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case depth, effective: The distance from the finished tooth surface to a specific sub-surface hardness
value. Stock removal done after heat treating will reduce the as heat treated effective case depth and
potentially the surface hardness.
− carburized and hardened: The effective case depth is measured normal to the finished gear
surface to a location where the hardness number is 50 HRC (542 HK500 or 515 HV500) minimum by
conversion from a microhardness test result. Note that ISO 6336-5 uses 550 HV minimum, which
converts to 52.4 HRC or 583 HK, as its criterion for determining the effective case depth. It is
recognized that the effective case depth of carburized and hardened gear teeth varies with location
on the gear tooth.
− induction and flame hardened: For Grades 1 and 2 gearing, the effective hardened depth is
measured from the finished surface to a location where the hardness number is equivalent to 10
HRC numbers below the specified minimum surface hardness. Grade 3 induction hardened gearing
uses the carburized and hardened definition for its effective hardened depth definition. Note that
ISO 6336-5 uses the distance from the surface to the location where the hardness is equal to 80%
of the specified minimum surface hardness as its criterion for determining the effective hardened
depth.
− nitrided: The effective case depth is measured from the finished surface to a location where the
hardness number is equivalent to 40.8 HRC (421 HK500 or 400 HV500) minimum by conversion from
a microhardness test result. If the core hardness is more than 38.9 HRC (391 HK500 or 380 HV500),
core hardness plus 54 HK500 or 50 HV500 (4.6 HRC) minimum may be used as the definition of
nitrided effective case depth. Note that this is the same definition used in ISO 6336-5.
case depth, total: For carburized gearing the maximum depth of diffused carbon.
The total case depth for induction or flame hardened gearing is usually assumed to be the same as the
hardened and effective case depths.
The total case depth for nitrided gearing is the distance from the surface to the depth at which the HRC
hardness number is 110% of the hardness number for the core
case hardening: The generic terminology covering carburize and nitride hardening processes applicable
to steel that change the chemical composition and microstructure of the surface layer by adsorption of
carbon, nitrogen, or a mixture of the two and by diffusion, create a chemical composition gradient.
Adsorption of carbon processes involve a subsequent quenching to harden, while adsorption of nitrogen
does not require quenching to harden.
case hardness: See hardness, case.
cast iron: A family of alloys composed primarily of iron, carbon, and silicon, where the carbon exists in
amounts higher than that which can remain in solid solution in austenite at eutectic temperature.
cementite: A hard compound of iron and carbon, known chemically as iron carbide, having the chemical
formula Fe3C.
cold treatment: The preferred terminology for cooling carburized and hardened parts to temperatures
typically below minus 80°F (minus 60°C) to reduce retained austenite. Cold treatment is also known as
sub-zero treatment or deep freezing. If cooled to below minus 300°F (minus 185°C), the correct
terminology is deep cryogenic treatment.
controlling section: Controlling section is the diameter of the largest sphere that can be inscribed within
the section of the pinion or gear containing teeth.
Controlling section has the greatest effect in determining the rate of cooling during quenching at a
location where the specified hardness is required. Figure 5 through Figure 8 illustrate the controlling
section size for various gearing configurations whose teeth are machined after heat treatment and whose
hardness should be maintained at the roots of the teeth. The maximum permitted section size for an alloy
steel increases with the hardenability of the alloy steel.
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Note that a flat plate with thickness equal to the diameter of a round bar will cool slower than the bar. The
thickness of a plate equivalent in cooling rate to that of a round bar (equivalent controlling section size) is
approximately 0.7 times the bar diameter.
The controlling section size for the selection of an appropriate type of steel and specified hardness
combination should consider part configuration at the time of heat treatment. Special stock additional
allowances, such as those used to minimize distortion during heat treatment, should be considered.
Figure 5 – Solid on shaft pinion blank
NOTE: If the bore diameter is less than 20% of the length
of the bore, then the controlling section is determined by
Figure 5 or Figure 7.
Figure 6 – Bore style gearing blank
Figure 7 – Disc style gearing blank
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Figure 8 – Web style gear blank
converted hardness: See hardness, converted.
core hardness: See hardness, core.
crack: Separation of a material matrix to form a linear discontinuity with a sharp tip; not to be confused
with microcrack.
decarburization: The loss of carbon from the near-surface of a ferrous material.
deep freeze treatment: See cold treatment.
deoxidizing: The removal of oxygen from molten steel by addition of suitable elements, such as silicon
and aluminum which react with oxygen, primarily forming discard slag.
DI (ideal critical diameter): DI is the diameter of a given steel that will produce 50% martensite at its
center when quenched at an ideal quench severity of H = ∞. DI can be calculated per ASTM A255. An
actual critical diameter for a given steel and quench rate can be determined by quenching a series of long
round bars of increasing diameters in a given quench medium and measuring a hardness profile across
the bar diameter on a transverse section taken from the mid-length of the bar. The bar with center
hardness corresponding to the critical level for hardening, usually the 50% martensite level, determines
the critical diameter.
direct quenching: The quenching of carburized gearing directly after the carburizing operation, generally
from a reduced temperature within the austenitic range.
ductile iron: A cast iron which is treated with a nodularizing agent, typically Mg, in the molten state
causing the graphitic carbon to precipitate out preferentially into spheroids. These graphite spheroids are
commonly referred to as nodules.
effective case depth: See case depth, effective.
ferrite: A solid solution of one or more elements in body-centered cubic iron. In carbon and alloy steels
this phase is stable at room temperature.
flame hardening: A surface hardening process in which only the surface layer of the work piece is
heated by a flame to above the upper transformation temperature and immediately quenched.
free ferrite: The ferrite that is formed directly during cooling without simultaneous formation of carbide.
full annealing: see annealing.
grain size: The dimensions of the grains, or crystals, in a polycrystalline metal exclusive of twinned
regions and sub-grains when present. The ASTM grain size is a designation bearing a relationship to
number of grains per square inch at 100 times magnification. Commercial grain size is categorized as
either coarse (grain size 1–4) or fine (grain size 5 or finer).
graphite flake: The predominate form of graphitic carbon in gray iron having a curved plate-like structure.
graphite nodule: The predominate form of graphitic carbon in ductile iron having a polycrystalline radial
structure commonly referred to as a spheroid or nodule.
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gray iron: Cast iron that has graphitic carbon predominately in the form of flakes.
hardenability: The property of a ferrous alloy that determines the depth and distribution of hardness
induced by quenching.
hardened depth: For induction or flame hardened gearing, alternative terminology for effective case
depth.
hardened zone: The area hardened by a surface hardening process.
hardness, base: The surface hardness in the tooth area that was developed by through hardening and
not changed by subsequent heat treatments. If the material selected has adequate hardenability for the
required hardness and section size combination, this surface hardness represents the expected hardness
at the intersection of the root circle and the centerline of the tooth at mid-face width. Base hardness is
applicable to through hardened, induction hardened, flame hardened, and nitrided gearing, but not to
carburized and hardened gearing.
hardness, case: For carburized and hardened gearing and induction or flame hardened gearing the
hardness is measured at 0.002–0.004 inches (0.05–0.10 mm) below the surface using a microhardness
test technique.
For nitriding specifications, surface hardness is typically used rather than case hardness. Case hardness
is not to be confused with surface hardness.
hardness, converted: The hardness number reported on a scale different from the scale used for
hardness testing. For example, an actual microhardness test reading of 542 HK500 has a converted
hardness of 50 HRC and would be properly reported as 50 HRC (542 HK500) with the hardness number
and scale in parentheses representing the actual testing result and method.
hardness, core: The hardness at the intersection of the root circle and the centerline of the tooth at midface width that was developed during the hardening of carburized gearing. An alternative location is given
by ISO 18265. See relevant application standards for additional guidance.
The material should have adequate hardenability for the required hardness and section size combination
for the required core hardness to be achieved. The quench severity should also be adequate in order to
achieve the required core hardness.
The term core hardness is applicable to carburized and hardened gearing. Induction, flame, and nitride
hardened gearing may use the term base hardness.
The core hardness of non-tooth portions, such as journal areas of carburized and hardened gearing, is
the hardness at a specified location such as surface, quarter radius, mid-radius, or centerline.
hardness, surface: The hardness measured directly on the functional surface, after appropriate surface
preparation. Surface hardness is not to be confused with case hardness, which is taken on a
metallographic cross-section using a microhardness tester. In cases where teeth are small such that
surface hardness measurements are impractical, a microhardness measurement within 0.004 inches
(100 micrometers) depth below the surface may be used to qualify surface hardness.
hardness conversion chart: A published document for use in converting from one hardness testing
scale to another.
Hardness conversion charts should be used with great caution since discrepancies of 0.3 HRC numbers
at 30 HRC to 3.9 HRC numbers at 60 HRC have been noted between various published conversion
charts. Therefore, it is suggested that the conversion chart used for testing and reporting be specified.
Some of the more popular hardness conversion charts are found in ASTM A370, ASTM E140,
ISO 6336-5, and certain individual corporate documents and standards. For this document, ASTM E140
is used and should be used whenever no other document is specified.
induction hardening: A surface hardening process in which only the surface layer of the work piece is
heated by electrically induced currents to above the upper transformation temperature and immediately
quenched.
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intergranular oxidation (IGO): The preferential oxidization of certain alloying elements along grain
boundaries during gas carburizing. See Figure 9 for a photomicrograph of intergranular oxides (black
constituent).
Figure 9 – Intergranular oxidation in carburized gearing
linear indication: An indication with length at least three times its width.
macropitting resistance: Endurance limit adequate to resist contact fatigue. Initial pitting and
progressive macropitting are illustrated and discussed in ANSI/AGMA 1010. See standards such as
ANSI/AGMA 2001 and ANSI/AGMA 2003.
marquench: Quenching into a liquid media whose temperature is above the martensite start
transformation temperature, typically 300–500°F (150–260°C), held at this temperature until temperature
is uniform throughout, and then cooled to form martensite. Marquenching is used to achieve reduced
distortion when compared to conventional quenching.
martensite: A generic term for microstructures formed by the diffusionless phase transformation of
austenite. Martensite is characterized by an acicular or needle-like pattern in the microstructure and is the
hardest of the austenitic transformation products in steel.
metallurgical notch: If an induction or flame hardened gear with type B flank hardening has a pattern
that terminates (runs out) at the surface of the root fillet it is accompanied by tensile residual stress that
adds to the bending stress, which greatly reduces the bending fatigue resistance. This is known as a
“metallurgical notch.”
microcracks: Microscopic discontinuities that specifically occur only across or alongside martensite
plates. Some prefer to call these discontinuities broken martensitic needles or platelets. They are a
quantifiable feature of the martensitic case microstructure of carburized parts. The use of microcrack
measurements in critical crack size calculations is considered inappropriate. Microcracks may be
associated with reduced macropitting resistance resulting from cold treating which may be prohibited to
avoid the potential problem. See Figure 10 and Figure 11.
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Figure 10 – Microcracks. Original magnification: 1000X, bright field.
Field area = 11000 µm2 (0.011 mm2)
Figure 11 – Microcracks. Original magnification: 1000X, dark field.
Field area = 11047.5 µm2 (0.011 mm2 )
nitriding: The introduction of nascent nitrogen into a suitable solid ferrous alloy by holding at a suitable
temperature in contact with a nitrogenous material. Adsorption of nascent nitrogen produces case
hardening without quenching.
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nitrocarburizing: A heat treating process in which carbon and nitrogen bearing gases are absorbed on
the surface of a ferrous material, the gases dissociate, and carbon and nitrogen atoms diffuse into the
metal to produce case hardening without quenching. This modified nitriding process can be performed in
either ferritic or austenitic temperature ranges.
nodularity: The unit of measure for the volumetric proportion of spheroidal graphite to all graphite in a
ductile iron. Type I and Type II graphite as defined by ASTM A247 of the graphite nodules in ductile iron.
nodule: See graphite nodule.
nodule count: The measurement of the number of nodules in a given section of ductile iron, in nodules
per unit area. The nodule count influences the strength and toughness of the iron.
non-martensitic structures: Inclusive terminology for ferrite, carbide, retained austenite, pearlite, and
bainite due to incomplete transformation to martensite or incomplete austenization. Retained austenite is
not included in the quantitative metallographic measurement of non-martensitic structures.
non-martensitic transformation products (NMTP): Inclusive terminology for ferrite, carbide, pearlite,
and upper bainite in the surface microstructure of carburize hardened gearing due to incomplete
transformation to martensite. See Figure 12 for a photograph of non-martensitic transformation products
in martensite.
5% nital etch
400 X mag.
Figure 12 – Non-martensitic transformation products in carburized gearing
normalizing: The heating of a ferrous alloy to a suitable temperature above the upper transformation
temperature and then cooling, in air or vacuum, until transformation is complete.
pearlite: A microstructural constituent consisting of lamellar ferrite and cementite resulting from the
transformation of austenite at temperatures above the bainite range.
process control test coupon: For carburized and hardened gearing or nitrided gearing, a test coupon
used primarily to monitor the consistency of the heat treatment process in terms of carbon or nitrogen
penetration and case microstructure. Sometimes called a standardized test coupon. For procedures
associated with process control test coupons, see 4.2.1.
Due to differences in quench cooling rates and hardenability, the microstructure and hardness of process
control test coupons used for carburized and hardened gearing is likely to not be the same as that of the
finished gear tooth.
quench and temper: Austenitizing, followed by rapid cooling (quenching) and reheating (tempered) to a
temperature generally below 1275°F (690°C).
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reduction ratio: In forging and rolling, the total reduction ratio is the product of all steps used to produce
a forging or bar. Depending on the type of deformation, the total reduction can be any combination of the
following:
− changing cross-sectional area by elongating: the ratio of initial cross-sectional area and the final
cross-sectional area.
− upset: the ratio of initial height and the final height.
− ring rolling: ratio of initial wall cross-sectional area and the final wall cross-sectional area.
For tapered ingots or any other non-uniform as-cast starting stock, the mean cross-sectional area is
typically used to calculate the reduction.
Unless otherwise specified, when a multiple cross-sectional area forging is produced, the reduction ratio
of the largest diameter where the gear teeth will be machined should be used.
reheat quenching: The quenching of carburized gearing after the carburizing operation, by first slow
cooling below the austenitic range, then re-austentizing and quenching.
representative test coupon: A test coupon designed to represent the quenching rate of the finished
gearing tooth. If the coupon is to be used only to determine the case properties, it can be smaller than
one used to determine the core properties of the gear tooth. A representative test coupon sized for
determining the core hardness and microstructure can also be used for determining the case properties
or as a process control test coupon. A representative test coupon sized for determining the case
properties can also be used as a process control test coupon but not for determining core properties
unless substantiated by documented test data. For procedures associated with representative test
coupons, see 4.2.2.
retained austenite: The metastable austenite contained within a quenched microstructure. The amount
of retained austenite is a function of carbon content, alloy content (especially nickel and manganese),
quench temperature and subsequent thermal or mechanical treatments. See Figure 13 through Figure 15
for examples of visual estimates of retained austenite (white constituent) in tempered martensite. More
precise measurements of retained austenite can be obtained by X-ray diffraction techniques.
5% nital etch
400 X mag.
Figure 13 – Tempered martensite and 5% retained austenite in carburized gearing
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5% nital etch
400 X mag.
Figure 14 – Tempered martensite and 20% retained austenite in carburized gearing
5% nital etch
400 X mag.
Figure 15 – Tempered martensite and 30% retained austenite in carburized gearing
shot peening: A cold working process performed by bombarding the surface of a part with small
spherical media. This results in a thin layer of high magnitude residual surface compressive stress and
generally improves the bending strength in the roots of gear teeth. Shot peening should not be confused
with grit blasting or shot blasting which are cleaning operations.
specialty nitriding steel: A steel typically alloyed with 1% aluminum to provide higher surface hardness
after nitriding than normally attained with nitrided through hardening steels.
standardized test coupon: Alternate terminology for a process control test coupon.
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sub-zero treatment: See cold treatment.
subcritical anneal: See anneal, subcritical.
surface hardening: The generic terminology for selective induction or flame heating of a surface layer
and then quenching that layer to produce a hardened surface layer that may be thinner than the heated
area but is harder than the unheated base material. With induction or flame hardening there is no
significant alteration of the chemical composition of the surface layer.
surface hardness: See hardness, surface.
surface temper: Localized overheating on ground surfaces. Can be detected and classified using a
chemical etch method.
tempering: The reheating of a hardened ferrous alloy part to a temperature below the transformation
range and holding at temperature followed by cooling it at any rate.
test bar: A sample used for tensile or impact strength testing. Also used as alternate terminology for a
test coupon used for hardness and microstructure testing.
test coupon: See specific type of test coupon, such as process control or representative.
through hardening: The process of using a rapid quench to increase hardness throughout a steel alloy
for the purpose of increasing its strength. Through hardening typically consists of three steps: the heating
of an alloy above critical temperature to alter its mechanical properties, a rapid quench in a medium, such
as oil, salt or caustic, and a reheating, or tempering, to eliminate excess brittleness from the treated alloy.
total case depth: See case depth, total.
total nominal alloy content: The sum of the mid-points of the specified ranges for all alloying elements
added to increase hardenability (e.g., Mn, Cr, Ni, Mo).
transformation temperature: The temperature at which a phase change occurs.
traveling indication: An uninterrupted ultrasonic testing signal on the display which moves horizontally
on the sweep line as the transducer is moved on the scanning surface. Travel of the signal indicates
varied depth of the discontinuity from the scanning surface, often indicative of a crack.
4
Procedures
In order to have comparable test results between inspectors and evaluators, a consistent set of test
methods and procedures is necessary to comply with the definitions, requirements, recommendations,
and considerations contained in this document.
4.1 Recommended test methods
The test methods listed in this clause are to be used when no other method is clearly defined or specified.
These are the methods to be used for evaluations to the requirements of Clause 5.
Testing of the actual part is preferred and should always be used whenever practical. However, properly
selected test coupons can also be used. The dimensions in this document are always to be measured
normal (not oblique) to the surface.
banding: The coupons should be hardened and evaluated in the as-quenched condition. Microhardness
indentations should be taken per ASTM E384 Vickers using loads of 200g or higher.
carbon: See surface carbon.
case hardness: For carburized and hardened gearing, unless otherwise specified, the case hardness is
determined at a location 1/2 of tooth height at least midway between the end faces (or from a
representative test coupon).
For induction or flame hardened gearing, unless otherwise specified, the case hardness is determined at
a location 1/4 of tooth height above the root at least midway between the end faces.
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For nitrided gearing, unless otherwise specified, the case hardness is determined at a location 1/2 of
tooth height at least midway between the end faces (or from a process control or representative test
coupon).
chemistry: Analyzed per ASTM A751 for steels.
core hardness: Per a standard or superficial hardness testing method listed under “hardness” see Figure
16 for test location.
decarburization: Per any of three methods:
− Method 1: File hardness. The flanks of a tooth are file hardness tested per SAE J864 or
ISO 6336-5, Annex D with lack of file hardness indicating possible decarburization or nonmartensitic structures.
− Method 2: Reduction of hardness. Surface hardness readings are taken in the same area using two
different hardness testing loads, such as HRC and HR15N with major loads of 150 kg and 15 kg
respectively. The two sets of readings are compared using a standard hardness conversion chart,
such as ASTM E140. Decarburization is indicated by a lower converted hardness for the lighter
load compared to that from the heavier load, presuming that proper hardness testing techniques
were used for both sets of tests.
− Method 3: Metallographic evaluation. A metallographic specimen is prepared per ASTM E3, etched
per ASTM E407, and evaluated per ASTM E1077 or SAE J419.
effective case depth: Per SAE J423 microhardness test method. For carburized and hardened gearing,
Figure 16 indicates where to measure case depth and core hardness. It is based on reference [6] for
carburized gearing. The 30° line defines the approximate location for effective case depth measurement
at the root fillet.
Figure 16 – Case depth measurement locations
− Location A, at approximately mid-height of the tooth, is the location for measuring case depth and
case hardness at the flank.
− Location B is the location for measuring case depth and case hardness at approximately 30°
normal to the root fillet.
− Location C is the location for measuring case depth and case hardness at the tooth tip.
− Location D is the location at the root diameter for measuring core hardness.
For nitrided gearing, unless otherwise specified, the effective case depth is determined at a location 1/2 of
tooth height (or from a representative test coupon).
For induction or flame hardened gearing, unless otherwise specified, the effective case depth or
hardened depth is determined at a location 1/4 of tooth height above the root.
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grain size: Per ASTM E112 or ISO 643. For carburized parts see Table 2, notes.
hardenability: Per ASTM A255 or ISO 642 end-quench test or by hardenability calculation per
ASTM A255.
hardness: Listed below are each method and the associated processes which are tested by that method.
− ASTM E10, Brinell hardness testing
o
o
Through hardened gearing
Base hardness of flame, induction, or nitride hardened gearing
− ASTM E18, Rockwell hardness testing
o
Through hardened gearing
o
Carburized and hardened gearing
o
Flame and induction hardened gearing
o
Nitrided gearing
− ASTM E92, Vickers hardness testing
o
Through hardened gearing
o
Carburized and hardened gearing
o
Flame and induction hardened gearing
o
Nitrided gearing
− ASTM E384, Microhardness testing
o
Carburized and hardened gearing
o
Flame and induction hardened gearing
o
Nitrided gearing
If standard hardness testing per ASTM E10 or ASTM E18 is not practical due to size of gearing and test
location, portable testing may be accomplished by ASTM E110. If ASTM E110 is not appropriate,
alternative portable methods are ASTM A956 and ASTM A1038.
Measurement of surface hardness per ASTM E18 is used as a nondestructive method to evaluate the
conformity of individual work pieces to the surface hardness requirements. The measurement method
should be appropriate for the size and configuration of the work pieces. The teeth area requirements for
hardness measurements include the root of the tooth. Alternate methods of hardness measurement,
including file testing in accordance with SAE J864 or ISO 6336-5, Annex D, may be used.
Due to the state of the art of alternate microhardness testing methods, results may vary by the equivalent
of three points HRC from actual HRC measurements per ASTM E18. The significance and interpretation
of those results should be agreed upon between the parties.
intergranular oxides: In the unetched condition, see metallography and Figure 9.
magnetic particle: Per ASTM E1444 regardless of form, or alternatively ASTM E125 for castings or
ASTM A275 for forgings.
mechanical testing: Per ASTM E8 for tensile testing and ASTM E23 for impact testing (also see
hardness).
metallography: Performed at a magnification of 400–600 diameters. Metallographic samples should be
prepared per ASTM E3 and etched per ASTM E407, except for intergranular oxidation which should be
evaluated in the unetched condition.
microhardness: See hardness.
microstructure: See metallography.
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nodularity: Analyzed per ASTM A247 or ISO 945.
nodule count: Analyzed per ASTM A247 or ISO 945.
nonmetallic inclusions: Per any of the following methods:
− SAE/AMS 2301, for aircraft steels
− SAE/AMS 2300, for premium aircraft quality
− SAE/AMS 2304, for special aircraft quality
− ASTM A534, for carburizing bearing steels
− ASTM A866, for through hardening bearing steels
− ASTM E45, for inclusion count
− ISO 4967, by comparison to micrographic diagrams, Method A
− SAE J422, by comparison to micrographic diagrams
reduction ratio: The reduction ratio can be calculated by the following equations; other appropriate
methods exist and may be used with best engineering judgement. For tapered ingots or any other nonuniform as-cast starting stock, unless otherwise specified the mean cross-sectional area should be used
to calculate the reduction ratio. When a multiple cross-sectional area forging is produced, the reduction
ratio in the area of the largest diameter where the gear teeth will be machined should be used. For
forgings with varying reductions along the tooth profile, the portion with the least reduction in the teeth
area should be used for the calculation of reduction ratio. Piercing operations and any associated
expansion do not contribute to the reduction ratio. The total reduction from the as-cast dimension to the
final forged dimension is the mathematical product of all the individual applicable forging steps. These
calculation steps are examples of hot working sequence for a given final shape, other forging sequences
are possible, the reduction calculation should be based on the actual reduction sequence employed.
RR = R1R 2 R3 R 4 R5 ...R x : 1
(1)
where
RR
is reduction ratio;
Rx
is the mechanical reduction of each individual forging step.
Sample reduction ratio calculation methods are shown below. Other forging sequences are possible.
For bar stock and shaft forgings produced by axial elongation such as in Figure 17:
A 
R1 =  i 
 Af 
where
(2)
Ai
is the initial cross-sectional area of the as-cast material, in2 (mm2);
Af
is the final cross-sectional area at the largest forged diameter in the area where the teeth will be,
in2 (mm2); and
R2, R3, R4, and R5 = 1
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Figure 17 – Examples of ingot, bloom, billet/bar, and shaft forgings
For disks produced by axial elongation and upsetting such as in Figure 18:
RR = R1 R 2 : 1
(3)
A 
R1 =  i 
 Af 
(4)
D 
R 2 =  i 
 Df 
(5)
where
Ai
is the initial cross-sectional area of the as-cast material, in2 (mm2);
Af
is the final cross-sectional area of the axially elongated material prior to upsetting, in2 (mm2);
Di
is the initial height of the cutoff forged material prior to upsetting, inch (mm);
is the final height of the finish forged upset disk in the area where the teeth will be, inch (mm);
and
R3, R4, and R5 = 1.
Df
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Figure 18 – Example of upset disk forging
For closed die forgings with a portion that is raised such as in Figure 19:
RR = R1 R 2 R3 : 1
(6)
A 
R1 =  i 
 Af 
(7)
D 
R 2 =  i 
 Df 
(8)
H 
R3 =  f 
 Hi 
(9)
where
Ai
is the initial cross-sectional area of the as-cast material, in2 (mm2);
Af
is the final cross-sectional area of the axially elongated material prior to upsetting, in2 (mm2);
Di
is the initial height of the cutoff forged material prior to upsetting, inch (mm);
Df
is the final height of the disk prior to raising, inch (mm);
Hf
is the final height of the finished closed die forging in the raised area where the teeth will be, inch
(mm);
Hi
is the initial disk height prior to the raising, inch (mm); and
R4 and R5 = 1.
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Figure 19 – Example of closed die forging
For forged or rolled rings such as in Figure 20:
RR = R1 R 2 R4 : 1
(10)
A 
R1 =  i 
 Af 
(11)
D 
R 2 =  i 
 Df 
(12)
 WA i 
R 4 = 

 WAf 
(13)
where
Ai
is the initial cross-sectional area of the as-cast material, in2 (mm2);
Af
is the final cross-sectional area of the axially elongated material prior to upsetting, in2 (mm2);
Di
is the initial height of the cutoff forged material prior to upsetting, inch (mm);
Df
is the final height of the upset blank after upsetting before any piercing, inch (mm);
WAi is the initial wall cross-sectional area of the upset disk after piercing, disregarding any expansions
associated with piercing, in2 (mm2);
WAf is the final wall cross-sectional area of the finish forging or rolled ring in the area where the teeth
will be, in2 (mm2); and
R3 and R5 = 1.
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Figure 20 – Example of seamless rolled ring forging
For gearing blanks where the pitch line of the teeth is not parallel to the forging centerline (such as for
bevel gearing) as in Figure 21:
RR = R1 R 2 R3 R5 : 1
(14)
A 
R1 =  i 
 Af 
(15)
D 
R 2 =  i 
 Df 
(16)
B 
R5 =  i 
 Bf 
(17)
where
Ai
is the initial cross-sectional area of the as-cast material, in2 (mm2);
Af
is the final cross-sectional area of the axially elongated material prior to upsetting, in2 (mm2);
Di
is the initial height of the cutoff forged material prior to upsetting, inch (mm);
Df
is the final height of the finish forged upset disk, inch (mm);
Bi
is the initial cross-sectional area of the teeth portion of blank before additional mechanical
working;
Bf
is the cross-sectional area of the portion of blank receiving additional mechanical working where
the teeth will be; and
R3, R4 = 1.
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Figure 21 – Example bevel gearing blank
surface carbon: Per one of the following methods:
− Method 1: Spectrometric. Per ASTM E415.
− Method 2: Combustion. The combustion method utilizes chips from a machining cut of 0.001–0.004
inch (0.02–0.10 mm) in thickness on a carbon control specimen. The chips from this cut are
collected and analyzed by combustion for carbon content per ASTM E350. The specimen should be
machined dry with high-speed steel cutting tools on centers, and at least one gram of clean chips
free of contamination should be used for analysis.
Both methods require that prior to carburizing the process control specimen, sufficient stock be machined
from the surface to be carburized, in order to remove all material with non-uniform surface chemistry.
surface temper: Per ANSI/AGMA ISO 14104.
test coupons: Microstructure and microhardness can be determined from either actual parts or test
coupons. Core hardness can be determined from either actual parts or representative coupons. See 4.2
for the specific type of test coupon (process control or representative).
ultrasonic inspection: Ultrasonic inspection is recommended for large parts to detect flaws before
incurring the expense of machining. When ultrasonic inspection is specified, the following guidelines
should apply:
− For wrought products the straight beam procedures described in ASTM A388 should apply. Either
the flat bottom hole or back reflection method may be used.
The sensitivity for the flat bottom hole method should utilize standard test blocks per ASTM E428
with the reflector size as specified in Table 1 through Table 4 of this information sheet. The metal
test distance for the blocks should be 4.000 inches (101.6 mm). This sensitivity should be used
when radially scanning the portion of the wrought material that will comprise the tooth area. The
tooth area includes only those portions of the gearing material where the teeth will be located to a
depth below the finished tooth tips of at least 1.5 times the tooth height. The balance of the part
may be scanned using a distance amplitude correction curve (DAC) whose construction is detailed
in ASTM A388.
− For cast products, the straight beam procedures described in ASTM A609 should apply. The back
reflection method should be used.
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4.2 Test coupons
4.2.1
Process control test coupons
Process control test coupons are used to monitor various heat treatment process parameters, their
variation, their interactions, and to verify that these parameters are maintained within their expected
control range. The process control test coupons may be made of various steel grades, different sizes, and
differing geometry depending on the parameter to be monitored and the heat treat facility’s quality control
plan. Process control test coupons are not intended to be used for final acceptance.
The properties of a process control coupon may be correlated by experience to the properties of the
finished gearing with regard to hardness and case depth. The process control test coupon microstructure
may be correlated to the condition of the finished gear. The method of correlation should be documented.
Process control test coupons may be used to determine surface carbon concentration, carbon
penetration, carbon gradients, nitride depth, white layer thickness, intergranular oxidation depth, and
process repeatability. Shim stock is often used to monitor atmospheric carbon potential. Variations from
expected process control limits are used as indicators of unacceptable heat treat process variations. As
long as the process control test coupons are within expected control limits, the parts being heat treated
should have the expected metallurgical properties.
The process control test coupon for carburize and hardening should have minimum dimensions of
5/8 inch (16 mm) diameter by 2 inches (50 mm) long and is suitable for gearing 4.5 normal diametral pitch
(module 5.6) and finer. A 1-inch (25 mm) diameter by 2 inches (50 mm) long coupon may be used for
coarser pitch (module) carburized gearing to 1.5 normal diametral pitch (module 17). The size of the
coupon for coarser than 1.5 normal diametral pitch (module 17) gearing should be agreed upon and
should approximate the inscribed diameter at mid height of the tooth cross section. The coupon length
should be a minimum of 2 times the diameter. Test disks or plates may be used whose minimum
thickness is 70% of the appropriate test bar diameter. The minimum inscribed diameter on a test disc
(or plate dimensions) should be three times its thickness.
For determination of case hardness, case depth, and case microstructure, the process control test
coupon should be examined on a section normal to its axis and at least one diameter from the end of the
test coupon. Case hardness is to be measured by a microhardness method at a depth 0.002 to 0.004
inch (0.05 to 0.10 mm) below the surface. Any post-heat treat stock removal should be considered.
4.2.2
Representative test coupon
The representative test coupon should be from the same grade of alloy steel with similar hardenability as
the production part but need not necessarily be from the same heat of steel. Representative test coupon
proportions of a minimum diameter of 6 divided by the normal diametral pitch (6 times module) but not
less than 5/8-inch diameter (16 mm), and a minimum length 2 times its diameter, as used in ISO 6336-5,
are recommended. A representative test coupon may contain a tooth form that will be used to verify the
heat treat process.
With customer approval, representative test coupon proportions of a minimum diameter of 3 divided by
the normal diametral pitch (3 times module) but not less than 5/8-inch diameter (16 mm), and a minimum
length 2 times its diameter, as used in ISO 6336-5, may be used.
A representative test coupon should have the same heat treat condition prior to carburizing as the part(s)
represented. This coupon should remain with the part(s) represented throughout the entire heat treat
process, with the possible exception of heat treatments prior to carburizing.
The representative test coupon, when positioned in a heat treat load in the same general area but
separate from the piece part, is intended to represent the metallurgy of the heat-treated tooth section.
The microstructure at the center of the minimum size representative test coupon approximates the core
microstructure of the tooth section.
©AGMA 2022 – All rights reserved
25
AMERICAN GEAR MANUFACTURERS ASSOCIATION
5
AGMA 923-C22
Metallurgical requirements
Metallurgical characteristics defined in the tables of this clause are intended to assure the quality of the
finished gear teeth.
Individual AGMA rating standards may have specific modifications to the metallurgical characteristics
grading. Users of this document should be aware that the Grade 1, Grade 2, and Grade 3 gearing
produced by different heat treatment processes have different ratings. In addition, the definition of Grade
1, 2, and 3 differs between AGMA standards. Refer to the applicable gear rating standards for specific
gear ratings.
Individual customers and manufacturers may have specific modifications to the metallurgical grade
requirements or special material and processing conditions that are not covered in these tables. These
modifications and special conditions are permissible with mutual agreement.
The following tables suggest limits on metallurgical characteristics to differentiate materials between
different grades. As individual gearing designs increase in size and complexity of features, they become
more difficult to manufacture, heat treat, and inspect. This document, as a general rule, does not
differentiate based on gearing size. However, where necessary, specific notation is made to reflect the
special processing methods, techniques and inspections required for large gear manufacturing.
All requirements for a metallurgical quality grade should be met in order to use the stress value, from the
AGMA rating standard, for that grade. This can be accomplished by specifically certifying each
requirement where necessary, or by establishing practices and procedures to obtain the requirements on
a production basis, see Clause 3 for the definition of “capable of” as used in following tables. It is not the
intent of this document that all requirements for metallurgical quality grade be certified, but that practices
and procedures be established for their compliance on a production basis. Intermediate values are not
classified since the effect of deviations from the quality standards cannot be evaluated easily. Specific
sampling plans and test methods should be addressed by either the manufacturer, the customer, or both.
The various characteristics are listed in the order in which that characteristic is typically evaluated during
the manufacturing sequence. Each individual characteristic has the same item number in Table 1 through
Table 7 whenever it is used, regardless of which table it appears. Some characteristics are only
applicable to specific heat treat methods. Therefore, some item numbers are not used in some tables.
Characteristics that are typically evaluated at the same time are grouped by having the same number
before the decimal point and modified with different numbers after the decimal point for the individual
characteristics evaluated at that time.
5.1 Through hardened gearing
The major metallurgical characteristics that affect through hardened gearing performance are shown in
Table 1. Suggested minimum characteristics are noted that would normally apply to differentiate materials
between different grades. Consult the specific product or application standard for actual requirements. It
is expected that all criteria in a specific grade should be met for the material to be considered meeting the
grade requirements.
©AGMA 2022 – All rights reserved
26
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 1 – Metallurgical characteristics for through hardened gearing
TH Item
#
1
1.1
Characteristic 1) 2)
Material chemistry
Wrought product
Grade 1
Grade 2
A material grade chemistry that is adequate to achieve the desired hardenability should be
specified with the following additional requirements.
Not specified
Alloy steel
Alloy steel
0.25–0.60% Carbon
0.30–0.60% Carbon
0.025% Sulfur max
0.015% Sulfur max
Maximums:
25 ppm Calcium
25 ppm Oxygen
2.0 ppm Hydrogen
100 ppm Nitrogen
1.2
Cast product
2
Grain size
3
Hardenability 3)
4
Non-metallic inclusions
(cleanliness,
steelmaking) 4)
Wrought product
4.1
Grade 3
Not specified
5 or finer
Verification not
required
Not specified
Not specified
Maximums:
10 ppm Calcium
25 ppm Oxygen
2.0 ppm Hydrogen
100 ppm Nitrogen
Alloy steel
Not applicable
0.30–0.60% Carbon
0.025% Sulfur Max
5 or finer. Test report per ASTM E112 or certified by ASTM A29.
A minimum hardenability which is appropriate for part size and quench
severity should be specified.
Alternative A:
Alternative A:
− Capable of meeting bearing quality − Certified ASTM A866
per ASTM A866
Alternative B, all of the following:
Alternative B, all of the following:
− The steel should be certified:
− The steel should be certified:
o electric furnace practice
o electric furnace practice
o ladle refined
o ladle refined
o deoxidized
o deoxidized
o vacuum degassed
o vacuum degassed
o bottom poured ingot
o bottom poured ingot or strand
o protected from re-oxidation
cast
during teeming or casting
o protected from re-oxidation
o certified cleanliness by
during
either ASTM E45 or ISO
o teeming or casting
4967 Method A. Acceptable
o Capable of cleanliness
if does not exceed:
confirmation by either
Type
Fine Thick
ASTM E45 or ISO 4967 Method A (sulfide)
2.5
1.5
A. Acceptable if does not
B (alumina)
2.0
1.0
exceed:
C (silicate)
0.5
0.5
Type
Fine Thick
D (globular oxide) 1.0
1.0
2.0
A (sulfide)
3.0
3.0
DS 6)
B (alumina)
2.5
1.5
Alternative C:
C (silicate)
2.5
1.5
− Certified SAE/AMS 2300
D (globular oxide) 2.0
1.5
or/AMS 2304
Alternative C:
− Capable of meeting SAE/AMS
2301
4.2
Cast product
5
5.1
Material form
Wrought product
Not specified
©AGMA 2022 – All rights reserved
Alternative D 5)
− Magnetic particle inspection of
finished gearing to the
requirements of Item 22, Grade 3
Only permissible if primarily round
(Type 1) 7) sulfide inclusions
Not applicable
Forgings per ASTM A788 or equivalent
Bar stock per ASTM A29 or equivalent or ISO 683-1
Tubing per ASTM A519 or equivalent
27
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 1 – Metallurgical characteristics for through hardened gearing (continued)
TH Item
#
5.2
5.3
6
7
8
9
9.1
9.2
12
Characteristic 1) 2)
Grade 1
Grade 2
Grade 3
− At least 7 to 1 for strand or continuous cast 8)
− At least 3 to 1 for ingot cast 8)
Castings per ASTM A781
Not applicable
Not specified
Quench and temper
900°F (482°C) minimum temper.
Mechanical properties
Hardness testing is required. Other mechanical testing is required only if specified. See
after heat treatment 9)
applicable rating standard for location of required hardness value.
Microstructure 4)
Sound metallurgical practice dictates that the microstructure should be commensurate with
steel grade, section size and sampling location. Unless otherwise specified, non-martensitic
transformation products within the microstructure are not a reason for rejection if the
hardness complies with the specified values.
Ultrasonic inspection and In addition to ultrasonic inspection and when specified by the customer, magnetic particle
magnetic particle
inspection may be used to detect laps, cracks, and seams. The limits for the inspection
inspection 4) 8) 10)
should be agreed upon with the purchaser.
Ultrasonic inspection 8)
Inspection recommended to the
Inspection required to the
Wrought material.
following limits:
following limits:
− Flat bottom hole (FBH)
Not specified
− No indications giving a signal
− No indications giving a signal
technique
response greater than an 8/64-inch
response greater than a 5/64o The test includes a
(3.18 mm) reference standard.
inch (1.98 mm) reference
− No indications giving a signal
radial scan from the
standard.
− No indications giving a signal
response greater than 50% of the
outside diameter
response greater than 50% of
reference standard if accompanied
using a 4.00-inch test
the reference standard if
by a 50% loss of back reflection.
metal distance, which
accompanied by a 50% loss of
− No indications which are
is described in
back reflection.
continuous over an area twice the
Clause 4.
o Areas beyond the
− No indications which are
diameter of the search unit.
tooth area are subject
continuous over an area twice
to agreement between
the diameter of the search unit.
the purchaser and
manufacturer.
Wrought product
Material reduction ratio
Cast product
Heat treatment 3)
Not specified
− Back reflection
technique
o The test includes a
radial scan from the
outside diameter
using a 4.00-inch test
metal distance, which
is described in
Clause 4.
o It is recommended
that the FBH method
be used to evaluate
indications found that
do not meet the
criteria of the table.
Castings
− Back reflection
technique
Not specified
Surface hardness in tooth
area (or on a
representative surface) 9)
− No indications giving a signal
− No indications giving a signal
response greater than 10% of back
response greater than 5% of
reflection.
back reflection.
− No multiple indications that lower
− No multiple indications that
the amplitude of the first back
lower the amplitude of the first
reflection by more than 40%.
back reflection by more than
− No traveling indications whose
20%.
amplitude is greater than 5% of
− No traveling indications whose
back reflection and length is
amplitude is greater than 5%
greater than 0.75 inch (19 mm).
of back reflection and length
is greater than 0.50 inch
(13 mm).
Not specified
− ASTM A609 Level 1 from outside
Not applicable
surface to the lesser of 1.5 times
tooth height below finished tooth
tips or 1 inch below the tooth root.
− ASTM A609 Level 2 greater than
the lesser of 1.5 times tooth height
below finished tooth tips or 1 inch
below the tooth root.
Hardness testing is recommended. See applicable rating standard for required
hardness value.
Hardness should be obtained at roots with 900°F (482°C) minimum temper.
©AGMA 2022 – All rights reserved
28
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 1 – Metallurgical characteristics for through hardened gearing (concluded)
TH Item
#
16
16.3
21
22
Characteristic 1) 2)
Surface microstructure
considering subsequent
stock removal
Decarburization. Any of
the following methods are
acceptable:
− Method 1. File testing
Grade 1
Grade 2
Grade 3
Should meet the following surface related characteristic:
Not applicable
Not applicable
− Method 2. Reduction of
surface hardness by two
load method 9)
Not specified
Maximum 2 HRC points or equivalent by conversion
− Method 3.
Metallographic
evaluation
Surface cracks 10)
Not specified
No total or partial decarburization apparent on the finished gear tooth
Magnetic particle
inspection of finished
gearing 8) 10) 11)
22.1
Below mid tooth height
22.2
Above mid tooth height
23
Normal
diametral
pitch
Module
≤3
≥8
>3 to 10
>2.5 to <8
≥10
≤ 2.5
Shot peening 13)
Cracks, bursts, seams, and laps are not permissible in the exposed surface bounded by the
outside diameter of the teeth, the root diameter of the teeth, and the face width of the teeth
including all chamfers, reliefs, filets, and ends of the teeth. Cracks in other areas of the part
require engineering disposition.
Not specified
Inspection recommended to the following limits:
If Alternative D is selected in 4.1 Non-metallic inclusions, magnetic
particle inspection is required using the acceptance criteria from
Table 2 item 22 Grade 3.
Not specified
No indications
Indication, maximum 12)
inch
mm
1/8
3.2
3/32
2.4
1/16
1.6
Shot peening per SAE/AMS-S-13165 and AGMA 938 may be used to increase surface
residual compressive stress.
Not specified
NOTES:
1)
See Clause 3 for definitions and Clause 4 for test methods.
2)
The metallurgical requirements assume homogeneous composition. In practice, microsegregation and banding occurs in steels.
This microsegregation can produce variations in microstructure and properties that should be assessed.
3)
Specifying “H” grades of alloys will assure hardenability values are reported (either calculated or measured) The controlling
section size, diametral pitch (module) and DI should be considered. The designer should specify hardenability values.
4)
The grade requirements for non-metallic inclusion, ultrasonic and microstructure characteristics apply only to those portions of
the gearing material where the teeth will be located to a depth below the finished tooth tip of at least 1.5 times the tooth height.
5)
Care should be exercised when using Alternative D because of the risk of rejection after the expense of further manufacturing
processes.
6)
DS is only applicable to certification in accordance with ISO 4967.
7)
Sims and Dhale Morphology of MnS per [1].
8)
In-process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to detect
flaws before incurring the expense of further machining.
9)
See ASTM A370 or ASTM E140 for hardness conversion tables.
10)
Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised.
11)
Cracks in non-functional areas require engineering disposition.
12)
Limits: Maximum of one indication in any inch (25 mm) of face width with a maximum of five such indications per any 5 inches
(125 mm) of face width of any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered.
13)
It is recommended that ANSI/AGMA 2004 be reviewed to determine if the benefits of surface residual compressive stress
achieved by shot peening may be beneficial to the particular application. Shot peening of the flanks of gear teeth should be
reviewed to ensure that no detrimental effects are caused to the gear set.
5.2 Carburized and hardened gearing
The major metallurgical characteristics that affect carburized and hardened gearing performance are
shown in Table 2. Carburizing in this document does not include carbonitriding. Suggested minimum
characteristics are noted that would normally apply to differentiate materials between different grades.
Consult the specific product or application standard for actual requirements. It is expected that all criteria
in a specific grade should be met for the material to be considered meeting the grade requirements.
©AGMA 2022 – All rights reserved
29
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 2 – Metallurgical characteristics for carburized and hardened gearing
CH Item
Characteristic 1) 2)
#
1
Material chemistry
1.1
1.2
Wrought product
Cast product
2
3
Initial grain size
Hardenability 4)
4
Non-metallic inclusions
(cleanliness,
steelmaking) 5)
Wrought product
4.1
4.2
Cast product
5
5.1
Material form
Wrought product
5.2
Wrought product
Material reduction ratio
Cast product
5.3
Grade 1
Grade 2
Grade 3
A material grade chemistry that is adequate to achieve the desired hardenability should be
specified with the following additional requirements
Specified
Alloy steel
Alloy steel
0.30% Carbon max
0.30% Carbon max
0.025% Sulfur max
0.015% Sulfur max
0.025% Phosphorus max
0.025% Phosphorus max
Recommended Maximums:
Maximums:
25 ppm Calcium 3)
10 ppm Calcium 3)
25 ppm Oxygen
25 ppm Oxygen
2.0 ppm Hydrogen
2.0 ppm Hydrogen
100 ppm Nitrogen
100 ppm Nitrogen
Specified
Alloy steel
0.30% Carbon max
Not permitted
0.025% Sulfur max
0.025% Phosphorus max
5 or finer. Test report per ASTM E112 or certified by ASTM A29.
Not specified
A minimum hardenability which is appropriate for part size and quench
severity should be specified.
Not specified
Not specified
Alternative A:
− Capable of meeting bearing quality
per ASTM A534 or ASTM A1089
Alternative A:
− Certified ASTM A534 or
ASTM A1089
Alternative B:
The steel should be certified:
− electric furnace practice
− ladle refined
− deoxidized
− vacuum degassed
− bottom poured ingot or strand
casted
− protected from re-oxidation during
teeming or casting
− capable of cleanliness confirmation
by either ASTM E45 or ISO 4967
Method B Plate II
Acceptable if does not exceed:
Type
Fine
Thick
A (sulfide)
3.0
3.0
B (alumina)
2.5
1.5
C (silicate)
2.5
1.5
D (globular oxide) 2.0
1.5
Alternative B:
The steel should be certified:
− electric furnace practice
− ladle refined
− deoxidized
− vacuum degassed
− bottom poured ingot
− protected from re-oxidation
during teeming or casting
− certified cleanliness by either
ASTM E45 or ISO 4967
Method A. Acceptable if does
not exceed:
Type
Fine Thick
A (sulfide)
2.5 1.5
B (alumina)
2.0 1.0
C (silicate)
0.5 0.5
D (globular oxide) 1.0 1.0
DS 7)
2.0
Alternative C:
Alternative C:
− Capable of meeting SAE/AMS 2301 − Certified SAE/AMS 2300 or
SAE/AMS 2304
Alternative D 6) :
− Magnetic particle inspection of
finished gearing to the requirements
of Item 22, Grade 3.
Only permissible if primarily round
Not applicable
(Type 1) sulfide inclusions 8)
Forgings per ASTM A788 or equivalent
Bar stock per ASTM A29 or ISO 683-11
Tubing per ASTM A519 or equivalent
Not specified
− At least 7 to 1 for strand or continuous cast 9)
− At least 3 to 1 for ingot cast 9)
Castings per ASTM A148 or ASTM A781
©AGMA 2022 – All rights reserved
Not applicable
30
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 2 – Metallurgical characteristics for carburized and hardened gearing (continued)
CH Item
Characteristic 1) 2)
#
8
Microstructure 5)
9
9.1
Grade 1
Grade 2
Grade 3
Sound metallurgical practice dictates that the microstructure should be commensurate with
steel grade, section size and sampling location. Unless otherwise specified, non-martensitic
transformation products within the microstructure are not a reason for rejection if the
hardness complies with the specified values.
Ultrasonic inspection 5) 9) 10) In addition to ultrasonic inspection and when specified by the customer, magnetic particle
inspection may be used to detect laps, cracks and seams. The limits for the inspection
should be agreed upon with the purchaser.
Ultrasonic inspection 9)
Inspection recommended to the
Inspection required to the
Wrought product
following limits:
following limits:
− Flat bottom hole (FBH)
Not specified
− No indications giving a signal
− No indications giving a signal
technique.
response greater than an 8/64-inch
response greater than a 5/64o The test includes a
(3.18 mm) reference standard.
inch (1.98 mm) reference
− No indications giving a signal
radial scan from the
standard.
− No indications giving a signal
response greater than 50% of the
outside diameter using
response greater than 50% of
same reference standard if
a 4.00-inch test metal
the reference standard if
accompanied by a 50% loss of back
distance, which is
accompanied by a 50% loss
reflection.
described in Clause 4.
o Areas beyond the
of back reflection.
− No indications which are continuous
− No indications which are
tooth area are subject
over an area twice the diameter of
continuous over an area twice
to agreement between
the search unit.
the diameter of the search
the purchaser and
manufacturer.
unit.
− Back reflection technique
o It is recommended
that the FBH method
be used to evaluate
indications found that
do not meet the
criteria of the table.
Not specified
− No indications giving a signal
response greater than 10% of back
reflection.
− No multiple indications that lower
the amplitude of the first back
reflection by more than 40%.
− No traveling indications whose
amplitude is greater than 5% of
back reflection and length is greater
than 0.75 inch (19 mm).
9.2
Cast product
− Back reflection technique
Not specified
− ASTM A609 Level 1 from outside
surface to 1.5 times tooth height
below finished tooth tips
− ASTM A609 Level 2 greater than
1.5 times tooth height below
finished tooth tips
11
Tempering after case
Recommended
Required
hardening
Surface hardness in tooth
area. Alternative method of
Hardness testing is recommended and surface hardness should meet the following
inspection is case
hardness 11) 12) 13)
characteristics:
Tooth flank
55-64 HRC or
58-64 HRC or equivalent
58-64 HRC or equivalent
equivalent
Tooth root
− Normal diametral pitch 3 53 HRC minimum
56 HRC minimum or equivalent
58 HRC minimum or equivalent
(module 8) and coarser
or equivalent
12
12.1
12.2
13
13.1
13.2
− Normal diametral pitch
finer than 3 (module 8)
Case properties
considering subsequent
stock removal, see
Figure 16 11) 12)
Effective case depth in
finished condition 14)
Effective case depth
minimum at root radius, as
determined by bending
strength rating 14)
55 HRC minimum
or equivalent
58 HRC minimum or equivalent
− No indications giving a signal
response greater than 5% of
back reflection.
− No multiple indications that
lower the amplitude of the first
back reflection by more than
20%.
− No traveling indications
whose amplitude is greater
than 5% of back reflection
and length is greater than
0.50 inch (13 mm).
Not applicable
58 HRC minimum or equivalent
Should meet the following characteristics when inspected per ASTM E-384 or SAE J423:
Minimum and maximum effective case depth requirements for the finished gear tooth
should be specified in accordance with the appropriate rating standard.
Minimum effective case depth requirements at the root radius should be specified in
accordance with the appropriate rating standard.
©AGMA 2022 – All rights reserved
31
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 2 – Metallurgical characteristics for carburized and hardened gearing (continued)
CH Item
Characteristic 1) 2)
#
13.5
Case hardness as
determined on a
representative test
specimen using a 500gram minimum load
13.6
Case hardness near
surface within 0.004-in
(0.05–0.10 mm)
14
Core hardness after case
hardening 11) 12) 15)
14.1
For macropitting
resistance rating,
14.2
For bending strength
rating,
15
Surface carbon (typical) 17)
15.1
15.2
15.3
16
16.1
16.2
16.2.1
16.2.2
For up to 2.5% total
nominal alloy content
2.5% to 3.5% total nominal
alloy content
Over 3.5% total nominal
alloy content
Surface microstructure
considering subsequent
stock removal 12) 18)
Intergranular oxidation
(IGO), see Figure 9
Minimum specified
effective case depth
inch
(mm)
<0.030
<(0.75)
0.030/0.059 (0.76/1.50)
0.060/0.089 (1.51/2.25)
0.090/0.120 (2.26/3.00)
>0.120
>(3.00)
Non-martensitic
transformation products
(NMTP), see Figure 12 19)
Minimum specified
effective case depth
inch
(mm)
<0.030
<(0.75)
0.030/0.059 (0.76/1.50)
0.060/0.089 (1.51/2.25)
0.090/0.120 (2.26/3.00)
>0.120
>(3.00)
NMTP requirements on
flank for macropitting
resistance rating
NMTP requirements on
root for bending strength
rating
Grade 1
Grade 2
Grade 3
55-64 HRC or
equivalent
58-64 HRC or equivalent
58-64 HRC or equivalent
Should meet
surface hardness
No partial decarburization apparent at
400X minimum, except in unground
roots
No partial decarburization
apparent at 400X minimum
Not specified
21 HRC minimum
21 HRC minimum
21 HRC minimum
25 HRC minimum
30 HRC minimum 16)
Some alloys may have desired case carbon content outside of these ranges; therefore, the
range should be specified by the gear designer
0.60–1.10%C
0.60–1.10%C
0.60–1.00%C
0.60–1.10%C
0.60–1.00%C
0.60–1.00%C
0.60–1.10%C
0.65–0.95%C
0.65–0.95%C
The first 0.002–0.003 inch (0.05–0.08 mm) of case microstructure in the tooth area should
meet the surface hardness requirement of the specific grade and also meet the following
surface related characteristics and the requirements of Item 17.
Not specified
Maximum allowable IGO depth
inch
0.0007
0.0010
0.0014
0.0018
0.0025
(µm)
(17)
(25)
(35)
(45)
(60)
Maximum allowable IGO depth
inch
0.0005
0.0008
0.0008
0.0010
0.0012
(µm)
(12)
(20)
(20)
(25)
(30)
Not specified
Maximum allowable NMTP depth
Not specified
Not specified
©AGMA 2022 – All rights reserved
inch
(µm)
0.0007
(17)
0.0010
(25)
0.0014
(35)
0.0018
(45)
0.0025
(60)
5% maximum within allowable NMTP
depth
10% maximum within allowable
NMTP depth, except in unground
roots
Maximum allowable NMTP
depth
inch
(µm)
0.0005
(12)
0.0008
(20)
0.0008
(20)
0.0010
(25)
0.0012
(30)
Trace amount within allowable
NMTP depth
5% maximum within allowable
NMTP depth
32
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 2 – Metallurgical characteristics for carburized and hardened gearing (continued)
CH Item
Characteristic 1) 2)
#
16.3
Decarburization. Any of
the following methods are
acceptable.
− Method 1. File testing.
Grade 1
− Method 3. Metallographic
evaluation.
16.3.1
16.3.2
In root for bending strength
rating
17
Case microstructure
considering subsequent
stock removal,
disregarding corner
effects 12)
Carbide precipitation in the
case
17.1
17.2
Retained austenite in the
case 20)
17.3
Microstructure limits for
macropitting resistance
rating.
Microstructure of the case
to a depth of 0.010 inch
(0.25 mm) or the first 20%
of the minimum specified
effective case depth,
whichever is smaller, along
the flank.21)
Grade 3
Not specified, but
should meet
surface hardness
− Method 2. Reduction of
surface hardness by two
load method or reduction
of case hardness.11)
Minimum specified
effective case depth
inch
(mm)
<0.030
<(0.75)
0.030/0.059 (0.76/1.50)
0.060/0.089 (1.51/2.25)
0.090/0.120 (2.26/3.00)
>0.120
>(3.00)
On flank for pitting
resistance rating
Grade 2
Should meet
surface hardness
Not specified
Gear tooth surfaces should be file hard to the minimum surface
hardness.
Maximum 3 HRC points or equivalent Maximum 1.5 HRC points or
below maximum measured hardness equivalent below maximum
by conversion but measuring at least measured hardness by
58 HRC or equivalent by conversion
conversion but measuring at
in the finished state.
least 58 HRC or equivalent by
conversion in the finished state.
No partial decarburization apparent
No partial decarburization
on active tooth profile. No ferrite (total apparent on the gear tooth
decarburization) is permissible in the including the root. No ferrite
case microstructure of the gear tooth. (total decarburization) is
permissible in the case
microstructure of the gear
tooth.
Maximum allowable decarb. depth
in root
inch
(µm)
0.0007
(17)
0.0010
(25)
0.0015
(38)
0.0020
(50)
0.0025
(60)
No partial decarburization apparent
No partial decarburization
within allowable depth
apparent within allowable depth
No partial decarburization apparent
within allowable depth, except in
unground roots
No partial decarburization
apparent within allowable depth
The microstructure of the first 20% of the minimum specified effective case depth should be
predominantly tempered martensite. Additional requirements for the case microstructure
are given in Item 16 and the following case related characteristics:
Continuous
Semi-continuous carbide network per Discontinuous carbides per
carbide network
Figure 2 is not acceptable.
Figure 3 are not acceptable.
per Figure 1 is not Discontinuous carbides per Figure 3
Dispersed carbides per Figure
acceptable. Semi- are acceptable. Maximum acceptable 4 are acceptable. Maximum
continuous
dimension of any carbide, in any
acceptable dimension of any
carbide network
direction, is 0.0008 inch (0.02 mm).
carbide, in any direction, is
per Figure 2 is
0.0004 inch (0.01 mm).
acceptable.
Not specified
Retained austenite 30% maximum determined metallographically by
comparison with Figure 15. Rejection of piece parts should only be
based on case hardness. The minimum microhardness at 0.004 inch
(0.1 mm) or through the area of highest retained austenite should be
58 HRC (690 HK500).11) 18)
Not specified.
Primarily tempered martensite with
Primarily tempered martensite
Untempered
5% maximum non-martensitic
with only trace non-martensitic
martensite is
structures, carbide precipitation per
structures permissible, carbide
acceptable.
Item 17.1, retained austenite per Item precipitation per Item 17.1,
17.2, and other surface
retained austenite per Item
microstructures as defined under
17.2, and other surface
Items 16.1 through 16.3.
microstructures as defined
under Items 16.1 through 16.3.
©AGMA 2022 – All rights reserved
33
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 2 – Metallurgical characteristics for carburized and hardened gearing (continued)
CH Item
Characteristic 1) 2)
#
17.4
Additional microstructure
limits for macropitting
resistance rating.
Microstructure of the case
from a depth of 0.010 inch
(0.25 mm) or the first 20%
of the minimum specified
effective case depth,
whichever is smaller, to a
depth equal to 40% of the
minimum specified
effective case depth along
the flank.14)
− Normal diametral pitch 3
(module 8) and coarser.
− Normal diametral pitch
finer than 3 (module 8).
17.5
Additional microstructure
limits for bending strength
rating.
Microstructure of the case
to a depth of 0.010 inch
(0.25 mm) or the first 20%
of the minimum specified
effective case depth,
whichever is smaller, at
the root fillet.21)
17.6
Additional microstructure
limits for bending strength
rating.
Microstructure of the case
from a depth of 0.010 inch
(0.25 mm) or the first 20%
of the minimum specified
effective case depth,
whichever is smaller, to a
depth equal to 40% of the
minimum specified
effective case depth at the
root fillet.14)
Normal diametral pitch 3
(module 8) and coarser.
Normal diametral pitch
finer than 3 (module 8).
17.7
Microcracks in case
(cracks across more than
one platelet)
18
Core microstructure 5) 11)
18.1
Final grain size
18.2
Non-martensitic
transformation products
Grade 1
Grade 2
Grade 3
Not specified
Not specified
Not specified
Not specified
5% maximum non-martensitic
structures
Primarily tempered martensite with
10% maximum non-martensitic
structures, carbide precipitation per
Item 17.1, retained austenite per Item
17.2, and other surface
microstructures as defined under
Items 16.1 through 16.3.
Only trace non-martensitic
structures
Primarily tempered martensite
with 5% maximum nonmartensitic structures, carbide
precipitation per Item 17.1,
retained austenite per Item
17.2, and other surface
microstructures as defined
under Items 16.1 through 16.3.
Not specified
Not specified
Not specified
Not specified
10% maximum non-martensitic
structures
Not specified
5% maximum non-martensitic
structures
10 maximums per 0.0001 in2
(0.064 mm2) field.20) 22)
Untempered
martensite is
acceptable.
Untempered
martensite is
acceptable.
Untempered
martensite is
acceptable.
Sound metallurgical practice dictates that the microstructure should be commensurate with
steel grade, section size and sampling location.
5 or finer,
5 or finer, test report per ASTM E112 23)
verification not
required
Not specified
Sound metallurgical practice dictates that the core microstructure
requirements are maintained in the tooth area to a depth of twice the
minimum specified effective case depth or 0.100 inch (2.5 mm),
whichever is less, below the minimum specified effective case depth.
The microstructure in this zone should be predominantly tempered
martensite. This microstructure zone should be free of ferrite, pearlite,
and measurable bainite. Unless otherwise specified by agreement, nonmartensitic transformation products within the microstructure are not a
reason for rejection if the hardness complies with its specified values.
Below this zone the core microstructure should be free of ferrite and be
primarily tempered martensite with some acicular ferrite and bainite
permissible.
©AGMA 2022 – All rights reserved
34
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 2 – Metallurgical characteristics for carburized and hardened gearing (continued)
CH Item
Characteristic 1) 2)
#
18.3
Banding in flank/tooth area
at a depth of 2.0 to 2.5
times the specified
effective case depth.
20
Surface temper etch
inspection of ground teeth
21
Surface cracks 10)
22
Magnetic particle
inspection of finished
gearing 9) 10) 24)
22.1
22.2
23
Below mid tooth height
Above mid tooth height
Normal
diametral
pitch
Module
≤3
≥8
>3 to 10
>2.5 to <8
≥10
≤2.5
Shot peening 26)
Grade 1
Grade 2
Grade 3
Not specified
Microhardness readings of
alternating dark and light areas
should not vary by more than
5 HRC points by conversion.
Not specified
FB2, which allows light tempering on FB1, which allows light
25% of functional area.
tempering on 10% of functional
area.
Cracks, bursts, seams and laps are not permissible in the exposed surface bounded by the
outside diameter of the teeth, the root diameter of the teeth, and the face width of the teeth
including all chamfers, reliefs, fillets, and ends of the teeth. Cracks in other areas of the part
require engineering disposition.
Not specified
Not specified
Inspection recommended to the
following limits:
If Alternative D is selected in
4.1 Non-metallic inclusions,
magnetic particle inspection is
required using the following
acceptance criteria.
Not specified
No indications
No Indications
Indication, maximum 25)
Indication, maximum 25)
Not specified
inch
mm
inch
mm
1/8
3.2
3/32
2.4
3/32
2.4
1/16
1.6
1/16
1.6
1/32
0.8
Shot peening per SAE/AMS-S-13165 or AGMA 938 may be used to increase surface
residual compressive stress.
NOTES:
1)
See Clause 3 for definitions and Clause 4 for test methods.
2)
The metallurgical requirements assume homogeneous composition. In practice, microsegregation and banding occurs in steels.
This microsegregation can produce variations in microstructure and properties that should be assessed.
3)
Intentional additions of calcium or calcium alloys for deoxidation or inclusion and shape control are not permitted unless
specifically approved by the purchaser. The use of lime or fluorspar, or both, in the steelmaking slag is acceptable.
4)
Specifying “H” grades of alloys will assure hardenability values are reported (either calculated or measured). The controlling
section size, diametral pitch (module) and DI should be considered. The designer should specify hardenability values.
5)
The grade requirements for non-metallic inclusion, ultrasonic, and microstructure characteristics apply only to those portions of
the gearing material where the teeth will be located to a depth below the finished tooth tip of at least 1.5 times the tooth height.
6)
Care should be exercised when using Alternative D because of the risk of rejection after the expense of further manufacturing
processes.
7)
DS type inclusion is only applicable to certification in accordance with ISO 4967.
8)
Sims and Dhale Morphology of MnS per [1].
9)
In-process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to detect
flaws before incurring the expense of further machining.
10)
Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised.
11)
See ASTM A370 or ASTM E140 for hardness conversion tables.
12)
See Clause 3 and Clause 4 for a discussion of test coupons.
13)
Root hardness may be less than flank hardness, depending on the size of the gear and the quench process.
14)
When specifying minimum case depth, note that the “optimum” values for macropitting resistance and bending strength
capacity are not the same. A maximum case depth is prescribed in order to minimize the risk of embrittlement in the tooth area,
including the tips.
15)
Core hardness requirements for macropitting resistance and bending strength are considered independently. The gear rating
may be limited by either macropitting resistance or bending strength for the selected metallurgical quality grade and its core
hardness requirement.
16)
Minimum hardness of 30 HRC for Grade 3 may be difficult to achieve on coarse pitch gearing. Due to the tooth section size of
3 normal diametral pitch (module 8) gearing and coarser, the alternate (ISO 6336-5) core hardness test location may be used
provided documented testing or experience is available.
17)
Optimum macropitting resistance is best achieved at surface carbon levels above the eutectoid carbon for a given alloy
chemistry.
18)
If excessive, salvage may be possible by processes such as shot peening per Item 23 or by grinding provided the integrity of
the gearing is not compromised.
19)
At maximum allowable depths, the surface may not be file hard and may not have the expected residual stress profile.
©AGMA 2022 – All rights reserved
35
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 2 – Metallurgical characteristics for carburized and hardened gearing (concluded)
NOTES (concluded):
20)
21)
22)
23)
24)
25)
26)
If cold treatment is performed, it is recommended that it be preceded by tempering at 300°F (150°C) minimum in order to
minimize formation of microcracks. Retempering is required after cold treatment. Cold treatment should not be used to
transform large amounts of retained austenite (e.g., 50%) to gain excessive improvements in hardness, even with prior
tempering.
Bainite, observable at 200X, that extends from the core microstructure into the case area is considered a ratable characteristic.
This bainite is the result of slower heat extraction rates due to part section size, mass of furnace load, marginal agitation,
elevated quenchant temperatures, and generally follows alloy segregation and material flow lines. The bainite that results in a
fine pepper structure at 400–600X, but is still not resolvable at 800X, is considered non-ratable (trace).
Maximum limit of microcracks (Item 17.5) for Grade 3 gearing may be difficult to achieve if cold treatment is used to transform
the retained austenite level to 30% maximum.
Report the as-carburized/hardened grain size, the specimen should not be re-austenitized as part of sample preparation for
grain size determination that could change the as-carburized/hardened grain size.
Cracks in nonfunctional areas require engineering disposition.
Limits: Maximum of one indication in any inch (25 mm) of face width with a maximum of five such indications per any 5 inches
(125 mm) of face width of any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered.
It is recommended that ANSI/AGMA 2004 be reviewed to determine if the benefits of surface residual compressive stress
achieved by shot peening may be beneficial to the particular application. Shot peening of the flanks of gear teeth should be
reviewed to ensure that no detrimental effects are caused to the gear set.
5.3 Induction or flame hardened gearing
The major metallurgical characteristics that affect induction or flame hardened gearing performance are
shown in Table 3. Suggested minimum characteristics are noted that would normally apply to differentiate
materials between different grades. Consult the specific product or application standard for actual
requirements. It is expected that all criteria in a specific grade should be met for the material to be
considered meeting the grade requirements.
Table 3 – Metallurgical characteristics for induction or flame hardened gearing
Item
1
1.1
1.2
Characteristic
Material chemistry
1) 2)
Wrought product
Cast product
2
Grain size
3
Hardenability 3)
4
Non-metallic inclusions
(cleanliness,
steelmaking) 4)
Grade 3
Spin induction Type A
Grade 1
Grade 2
(Contour) only
A material grade chemistry that is adequate to achieve the desired hardenability should be
specified with the following additional requirements
Not specified
Alloy steel
Alloy steel
0.25 – 0.60% Carbon
0.30 – 0.60% Carbon
0.025% Sulfur max
0.015% Sulfur max
Not specified
5 or finer.
Verification not
required.
Not specified
©AGMA 2022 – All rights reserved
Maximums:
Maximums:
25 ppm Calcium
10 ppm Calcium
25 ppm Oxygen
25 ppm Oxygen
2.0 ppm Hydrogen
2.0 ppm Hydrogen
100 ppm Nitrogen
100 ppm Nitrogen
Alloy steel 0.30 – 0.60% Carbon
Not applicable
0.025% Sulfur max
5 or finer. Test report per ASTM E112 or certified by ASTM A29.
A minimum hardenability which is appropriate for part size and quench
severity should be specified.
36
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 3 – Metallurgical characteristics for induction or flame hardened gearing (continued)
Item
4.1
Characteristic
Wrought product
1) 2)
4.2
Cast product
5.1
Material form
5.2
8
Wrought product
Material reduction ratio
Cast product
Heat treatment prior to
surface hardening
Mechanical properties
prior to surface
hardening.9) See also Item
14.
Hardness – flank
Hardness – root
Other mechanical
properties
Microstructure 4)
9
Ultrasonic inspection 4) 8) 10)
5.3
6
7
7.1
7.2
7.3
Grade 1
Not specified
Grade 2
Alternative A:
− Capable of meeting bearing
quality per ASTM A534
Grade 3
Spin induction Type A
(Contour) only
Alternative A:
− Certified ASTM A534
Alternative B, all of the following:
The steel should be certified:
− electric furnace practice
− ladle refined
− deoxidized
− vacuum degassed
− bottom poured ingot or strand
casted
− protected from re-oxidation
during teeming or casting
− capable of cleanliness
confirmation by either ASTM
E45 or ISO 4967 Method B
Plate II. Acceptable if does not
exceed:
Type
Fine Thick
A (sulfide)
3.0
3.0
B (alumina)
2.5
1.5
C (silicate)
2.5
1.5
D (globular oxide) 2.0
1.5
Alternative B, all of the following:
The steel should be certified:
− electric furnace practice
− ladle refined
− deoxidized
− vacuum degassed
− bottom poured ingot
− protected from re-oxidation during
teeming or casting
− certified cleanliness by either
ASTM E45 or ISO 4967 Method A.
Acceptable if does not exceed:
Alternative C:
Capable of meeting SAE/AMS
2301
Alternative C:
Certified SAE/AMS 2300 or/AMS
2304.
Type
A (sulfide)
B (alumina)
C (silicate)
D (globular oxide)
DS 6)
Fine
2.5
2.0
0.5
1.0
2.0
Thick
1.5
1.0
0.5
1.0
Alternative D 5)
Magnetic particle inspection of
finished gearing to the
requirements of Item 22,
Grade 3.
Not specified
Only permissible if primarily
Not applicable
round (Type 1) 7) sulfide
inclusions.
Forgings per either ASTM A788 or equivalent.
Bar stock per ASTM A29 or equivalent or ISO 683-1.
Tubing per ASTM A519 or equivalent.
Not specified
− At least 7 to 1 for strand or continuous cast.8)
− At least 3 to 1 for ingot cast.8)
Castings per ASTM A781
Not Applicable
Not specified
Quench and temper
900°F (480°C) minimum temper.
Not specified
Not specified
28 HRC minimum
30 HRC minimum
28 HRC minimum
30 HRC minimum
Other mechanical testing is required only if specified
Sound metallurgical practice dictates that the microstructure should be commensurate with
steel grade, section size and sampling location. Unless otherwise specified, non-martensitic
transformation products within the microstructure are not a reason for rejection if the
hardness complies with the specified values.
In addition to ultrasonic inspection and when specified by the customer, magnetic particle
inspection may be used to detect laps, cracks, and seams. The limits for the inspection
should be agreed upon with the purchaser.
©AGMA 2022 – All rights reserved
37
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 3 – Metallurgical characteristics for induction or flame hardened gearing (continued)
Item
9.1
9.2
10
11
12
13
13.1
13.2
1) 2)
Characteristic
Ultrasonic inspection 8)
Wrought material.
− Flat bottom hole (FBH)
technique
o The test includes a
radial scan from the
outside diameter
using a 4.00 inch test
metal distance, which
is described in
Clause 4.
o Areas beyond the
tooth area are subject
to agreement between
the purchaser and
manufacturer.
− Back reflection technique
o The test includes a
radial scan from the
outside diameter
using a 4.00 inch test
metal distance, which
is described in
Clause 4.
o It is recommended
that the FBH method
be used to evaluate
indications found that
do not meet the
criteria of the table.
Cast product
− Back reflection technique
Overheating, especially at
the tooth tips and end
faces 11) 12)
Tempering after surface
hardening
Surface hardness on a
representative surface.
Alternative method of
inspection is hardened
zone hardness 9) 11)
Hardened depth
considering subsequent
stock removal. Also see
Item 19.9) 11) 12)
Hardened depth in
finished condition
Hardened depth minimum
at root radius, or on
representative sample with
same geometry and
material as work piece, as
determined by bending
strength rating.
Grade 1
Not specified
Grade 2
Inspection recommended to the
following limits:
− No indications giving a signal
response greater than an
8/64 inch (3.18 mm) reference
standard.
− No indications giving a signal
response greater than 50% of
the same reference standard if
accompanied by a 50% loss of
back reflection.
− No indications which are
continuous over an area twice
the diameter of the search unit.
Grade 3
Spin induction Type A
(Contour) only
Inspection required to the following
limits:
− No indications giving a signal
response greater than a 5/64 inch
(1.98 mm) reference standard.
− No indications giving a signal
response greater than 50% of the
reference standard if accompanied
by a 50% loss of back reflection
− No indications which are
continuous over an area twice the
diameter of the search unit.
− No indications giving a signal
− No indications giving a signal
response greater than 10% of
response greater than 5% of back
back reflection.
reflection.
− No multiple indications that
− No multiple indications that lower
lower the amplitude of the first
the amplitude of the first back
back reflection by more than
reflection by more than 20%.
40%.
− No traveling indications whose
− No traveling indications whose
amplitude is greater than 5% of
amplitude is greater than 5% of
back reflection and length is
back reflection and length is
greater than 0.50 inch (13 mm).
greater than 0.75 inch
(19 mm).
Not specified
− ASTM A609 Level 1 from
Not applicable
outside surface to 1.5 times
tooth height below finished
tooth tips.
− ASTM A609 Level 2 greater
than 1.5 times tooth height
below finished tooth tips.
Avoid surface temperatures that result in grain growth, incipient melting or unfavorable
residual stresses. Larger chamfers minimize this problem.
1 hour minimum at temperature; furnace temper is required 13)
50 HRC minimum or 54 HRC minimum as required
by rating standard
Should meet the following characteristics:
Minimum and maximum hardened depth should be
specified in accordance with the rating standard. A
hardening pattern per Figure 22 should be specified.
Not specified
©AGMA 2022 – All rights reserved
50% of minimum specified
hardened depth at 1/4 tooth
height above the root
recommended.
58–64 HRC or equivalent
Minimum and maximum hardened
depth should be specified in
accordance with the rating standard.
Figure 22 Type A contour pattern
only should be specified.
100% of minimum specified
hardened depth at 1/4 tooth height
above the root recommended, and
66% of minimum specified hardened
depth at the root.
38
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 3 – Metallurgical characteristics for induction or flame hardened gearing (continued)
Item
14
14.1
14.2
16
16.2
16.3
17
17.3
Grade 1
Grade 2
Grade 3
Spin induction Type A
(Contour) only
Not specified
28 HRC minimum
30 HRC minimum
Not specified
28 HRC minimum
30 HRC minimum
1) 2)
Characteristic
Base hardness after
surface hardening.
Also see Item 7.9) 11) 14)
Base/core hardness for
macropitting resistance
rating.
Base/core hardness for
bending strength rating
Surface microstructure
considering subsequent
stock removal 11) 15)
Flank for macropitting
resistance rating.
Non-martensitic
transformation products,
see Figure 12.16)
Minimum specified
hardened depth
inch
(mm)
<0.030
<(0.75)
0.030/0.059 (0.76/1.50)
0.060/0.089 (1.51/2.25)
0.090/0.120 (2.26/3.00)
0.120
>(3.00)
Root for bending
resistance rating 9)
Case microstructure
considering subsequent
stock removal,
disregarding corner
effects 11)
Microstructure of case
along flank (for
macropitting resistance
rating).
17.6
Microstructure at root (for
bending strength rating).
18
18.1
Core microstructure 11)
Final grain size
18.2
Non-martensitic
transformation products
(NMTP)
18.3
Banding in flank/tooth area
at a depth of 2.0 to 2.5
times the specified
hardened depth.
The first 0.002–0.003 inch (0.05–0.08 mm) of hardened zone microstructure in the tooth
area should meet the surface hardness requirement of the specific grade and also meet the
following surface related characteristics and the requirements of Item 17.
Should meet
Should meet specified hardness
Should meet specified hardness
specified
hardness
Maximum allowable depth
Maximum allowable depth
inch
(µm)
inch
(µm)
0.0007
(17)
0.0005
(12)
0.0010
(25)
0.0008
(20)
0.0015
(38)
0.0008
(20)
0.0020
(50)
0.0010
(25)
0.0025
(60)
0.0012
(30)
Should meet
No partial decarburization
No partial decarburization apparent
specified
apparent at 400X, except in
at 400X
hardness
unground roots
The first 20% of the case microstructure should be predominantly tempered martensite. The
microstructure should be free of undissolved pearlite observable at 100X and measurable
bainite observable at 400–600X.
The following case microstructure characteristics for each grade should be met:
Primarily fine
acicular
martensite
Primarily fine acicular tempered
martensite. Non-martensitic
structures anywhere in the case
should not exceed 5%.
Primarily fine acicular tempered
martensite with no non-martensitic
structures.
Primarily fine
acicular
martensite
Primarily fine acicular tempered
martensite. Non-martensitic
structures anywhere in the case
should not exceed 10%.
Primarily fine acicular tempered
martensite. Non-martensitic
structures anywhere in the case
should not exceed 5%.
5 or finer,
verification not
required
Not specified
©AGMA 2022 – All rights reserved
5 or finer, test report per ASTM E112 17)
Sound metallurgical practice dictates that the core microstructure
requirements are maintained in the tooth area to a depth of twice the
minimum specified effective case depth or 0.100 inch (2.5 mm),
whichever is less, below the minimum specified effective case depth.
The microstructure in this zone should be predominantly tempered
martensite. This microstructure zone should be free of ferrite, pearlite,
and measurable bainite. Unless otherwise specified by agreement, nonmartensitic transformation products within the microstructure are not a
reason for rejection if the hardness complies with its specified values.
Below this zone the core microstructure should be free of ferrite and be
primarily tempered martensite with some acicular ferrite and bainite
permissible.
Not specified
Microhardness readings of
alternating dark and light areas
should not vary by more than 5 HRC
points by conversion.
39
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 3 – Metallurgical characteristics for induction or flame hardened gearing (concluded)
Item
19
1) 2)
Characteristic
Heat affected zone. Also
see Item 13.11) 12)
20
Surface temper etch
inspection of ground teeth
21
Surface cracks 10)
22
Magnetic particle
inspection of finished
gearing 8) 10) 18)
22.1
22.2
23
Below mid tooth height
Above mid tooth height
Normal
diametral Module
pitch
≤3
≥8
>3 to 10
>2.5 to <8
≥10
≤ 2.5
Shot peening 20)
Grade 3
Spin induction Type A
Grade 1
Grade 2
(Contour) only
Induction and flame hardening heat treatments have a characteristic heat affected zone that
is caused by the surface heating process. This zone can have lower hardness and different
microstructure than the base material. The case depth specification should be established
to avoid gear failure which might initiate in this zone.
Not specified
FB2, which allows light
FB1, which allows light tempering on
tempering on 25% of functional
10% of functional area.
area.
Cracks, bursts, seams and laps are not permissible in the exposed surface bounded by the
outside diameter of the teeth, the root diameter of the teeth, and the face width of the teeth
including all chamfers, reliefs, fillets, and ends of the teeth. Cracks in other areas of the part
require engineering disposition.
Not specified
Inspection recommended to the following limits:
If Alternative D is selected in 4.1 Non-metallic inclusions, magnetic
particle inspection is required using the acceptance criteria from Table
2 item 22 Grade 3.
Not specified
No indications
Indication, maximum 19)
Indication, maximum 19)
inch
mm
inch
mm
1/8
3.2
3/32
2.4
3/32
2.4
1/16
1.6
1/16
1.6
1/32
0.8
Shot peening per SAE/AMS-S-13165 or AGMA 938-A05 may be used to increase surface
residual compressive stress.
Not specified
NOTES:
1)
See Clause 3 for definitions and Clause 4 for test methods.
2)
The metallurgical requirements assume homogeneous composition. In practice, microsegregation and banding occurs in steels.
This microsegregation can produce variations in microstructure and properties that should be assessed.
3)
Specifying “H” grades of alloys will assure hardenability values are reported (either calculated or measured) The controlling
section size, diametral pitch (module) and DI should be considered. The designer should specify hardenability values.
4)
The grade requirements for non-metallic inclusion, ultrasonic, and microstructure characteristics apply only to those portions of
the gear material where the teeth will be located to a depth below the finished tooth tip of at least 1.5 times the tooth height.
5)
Care should be exercised when using Alternative D because of the risk of rejection after the expense of further manufacturing
processes.
6)
DS is only applicable to certification in accordance with ISO 4967.
7)
Sims and Dhale Morphology of MnS per [1].
8)
In-process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to detect
flaws before incurring the expense of further machining.
9)
See ASTM E140 or ASTM E140 for hardness conversion tables.
10)
Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised.
11)
See Clause 3 and Clause 4 for a discussion on test coupons.
12)
The hardness pattern, depth, facilities and process method should be established, documented and verified to be repeatable.
The process equipment and methods should be sufficiently accurate to reproduce the specified results. Excessive case depth
can generate unfavorable residual stress conditions.
13)
Induction tempering is recommended for Grade 3 as a crack preventing stress relief heat treatment prior to furnace tempering.
14)
Mechanical properties, including core hardness, may not be the same after induction or flame hardening as they were before
induction or flame hardening.
15)
Microstructure analysis of induction hardened test specimens have shown indications of undissolved pearlite or “ghost pearlite.”
This is especially true with rapid (short) heating cycles. This “ghost pearlite” should not be present.
16)
At maximum allowable depths, the surface may not be file hard and may not have the expected residual stress profile.
17)
Report the as-carburized/hardened grain size, the specimen should not be re-austenitized as part of sample preparation for
grain size determination that could change the as-carburized/hardened grain size.
18)
Cracks in non-functional areas require engineering disposition.
19)
Limits: Maximum of one indication in any inch (25 mm) of face width with a maximum of five such indications per any 5 inches
(125mm) of face width of any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered.
20)
It is recommended that ANSI/AGMA 2004 and AGMA 938 be reviewed to determine if the benefits of surface residual
compressive stress achieved by shot peening may be beneficial to the particular application. Shot peening of the flanks of gear
teeth should be reviewed to ensure that no detrimental effects are caused to the gear set.
©AGMA 2022 – All rights reserved
40
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
NOTES:
−
−
−
−
Type A indicates that flanks and roots are hardened for contour or non-contour patterns.
Only spin hardening Type A (Contour) is applicable to Grade 3.
Type B indicates that the flanks are hardened only to the form diameter.
For Type B, the full active profile should be hardened with the transition zone not in the root fillet area.
Figure 22 – Variations in hardening pattern obtainable on gear teeth
with flame or induction hardening
5.4 Nitrided gearing
The major metallurgical characteristics that affect nitrided gearing performance are shown in Table 4.
Suggested minimum characteristics are noted that would normally apply to differentiate materials
between different grades. Consult the specific product or application standard for actual requirements. It
is expected that all criteria in a specific grade should be met for the material to be considered meeting the
grade requirements.
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AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 4 – Metallurgical characteristics for nitrided gearing
Item
1
1.1
1.2
Characteristic 1) 2)
Material chemistry 3)
Wrought product
Cast product
2
Grain size
3
Hardenability 3) 4)
4
Non-metallic inclusions
(cleanliness, steelmaking) 5)
Wrought product
4.1
4.2
Cast product
5
5.1
Material form
Wrought product
5.2
Wrought product
Material reduction ratio
©AGMA 2022 – All rights reserved
Grade 1
Grade 2
Grade 3
A material grade chemistry that is adequate to achieve the desired hardenability
should be specified with the following additional requirements:
Not specified
Alloy steel
Alloy steel
0.25–0.60% Carbon
0.30–0.60% Carbon
0.025% Sulfur max
0.015% Sulfur max
Maximums:
Maximums:
25 ppm Calcium
10 ppm Calcium
25 ppm Oxygen
25 ppm Oxygen
2.0 ppm Hydrogen
2.0 ppm Hydrogen
100 ppm Nitrogen
100 ppm Nitrogen
Not specified
Alloy steel
Not applicable
0.30–0.60% Carbon
0.025% Sulfur Max
5 or finer
5 or finer. Test report per ASTM
Verification not required
E112 or certified by ASTM A29.
Not specified
A minimum hardenability which is appropriate for part size and
quench severity should be specified.
Not specified
Not specified
Alternative A:
− Capable of meeting
bearing quality per ASTM
A866
Alternative A:
− Certified ASTM A866
Alternative B, all of the
following:
− The steel should be
certified:
o electric furnace practice
o ladle refined
o deoxidized
o vacuum degassed
o bottom poured ingot or
strand cast
o protected from reoxidation during
o teeming or casting
o capable of cleanliness
confirmation by either
ASTM E45 or ISO 4967
Method A. Acceptable if
does not exceed:
Type
Fine Thick
A (sulfide)
3.0 3.0
B (alumina)
2.5 1.5
C (silicate)
2.5 1.5
D (globular oxide) 2.0 1.5
Alternative B, all of the following:
− The steel should be certified:
o electric furnace practice
o ladle refined
o deoxidized
o vacuum degassed
o bottom poured ingot
o protected from re-oxidation
during teeming or casting
o certified cleanliness by either
ASTM E45 or ISO 4967
Method A. Acceptable if
does not exceed:
Type
Fine Thick
A (sulfide)
2.5 1.5
B (alumina)
2.0 1.0
C (silicate)
0.5 0.5
D (globular oxide) 1.0 1.0
2.0
DS 7)
Alternative C:
− Capable of meeting
SAE/AMS 2301
Alternative C:
− Certified SAE/AMS 2300
or/AMS 2304
Alternative D 6)
− Magnetic particle
inspection of finished
gearing to the
requirements of Item 22,
Grade 3
Only permissible if primarily
round (Type 1) 8) sulfide
inclusions
Not applicable
Forgings per ASTM A788 or equivalent
Bar stock per ASTM A29 or equivalent or ISO 683-1
Tubing per ASTM A519 or equivalent
Not specified
At least 7 to 1 for strand or continuous cast 9)
At least 3 to 1 for ingot cast 9)
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AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 4 – Metallurgical characteristics for nitrided gearing (continued)
Item
6
7
7.3
8
Characteristic 1) 2)
Heat treatment prior to case
hardening
Mechanical properties prior to
surface hardening.10) See also
Item 14.
Other mechanical properties
Microstructure 5)
9
Ultrasonic inspection and magnetic
particle inspection 5) 9) 11)
9.1
Ultrasonic inspection 9)
Wrought material.
− Flat bottom hole (FBH) technique
o The test includes a radial scan
from the outside diameter
using a 4.00-inch test metal
distance, which is described in
Clause 4.
o Areas beyond the tooth area
are subject to agreement
between the purchaser and
manufacturer.
− Back reflection technique
o The test includes a radial scan
from the outside diameter
using a 4.00-inch test metal
distance, which is described in
Clause 4.
o It is recommended that the
FBH method be used to
evaluate indications found that
do not meet the criteria of the
table.
12
Surface hardness on a
representative surface. Alternative
method of inspection is case
hardness.10) 12)
− Specialty nitriding steels 3)
− Through hardening steels
Case depth considering
subsequent stock removal 11)
Effective case depth in finished
condition
Total case depth in finished
condition
Core hardness after case
hardening. Also see Item 7.10) 12) 13)
Surface microstructure considering
subsequent stock removal 12)
13
13.1
13.4
14
16
©AGMA 2022 – All rights reserved
Grade 1
Grade 2
Grade 3
Quench and temper with tempering temperature at least 50°F (28°C) above the
nitriding temperature. Tempering temperature at least 900°F (482°C).
Other mechanical testing is required only if specified
Sound metallurgical practice dictates that the microstructure should be commensurate
with steel grade, section size and sampling location. Unless otherwise specified, nonmartensitic transformation products within the microstructure are not a reason for
rejection if the hardness complies with the specified values.
In addition to ultrasonic inspection and when specified by the customer, magnetic
particle inspection may be used to detect cracks and seams. The limits for the
inspection should be agreed upon with the purchaser.
Not specified
Inspection recommended to Inspection required to the
the following limits:
following limits:
− No indications giving a
− No indications giving a signal
signal response greater
response greater than a 5/64than an 8/64-inch
inch (1.98 mm) reference
(3.18 mm) reference
standard.
standard.
− No indications giving a signal
− No indications giving a
response greater than 50% of
signal response greater
the reference standard if
than 50% of the reference
accompanied by a 50% loss of
standard if accompanied
back reflection.
by a 50% loss of back
− No indications which are
reflection.
continuous over an area twice
− No indications which are
the diameter of the search unit.
continuous over an area
− No indications giving a signal
twice the diameter of the
response greater than 5% of
search unit.
back reflection.
− No indications giving a
− No multiple indications that
signal response greater
lower the amplitude of the first
than 10% of back
back reflection by more than
reflection.
20%.
− No multiple indications that − No traveling indications whose
lower the amplitude of the
amplitude is greater than 5% of
first back reflection by
back reflection and length is
more than 40%.
greater than 0.50 inch (13 mm).
− No traveling indications
whose amplitude is greater
than 5% of back reflection
and length is greater than
0.75 inch (19 mm).
− No indications which are
continuous over an area
twice the diameter of the
search unit.
Either 89–93 HR15N, 650–900 HV or 690–900 HK
Either 83 min HR15N, 450 min HV or 470 min HK
Should meet either of the following characteristics:
Minimum effective case depth requirements for the tooth should be specified in
accordance with the appropriate rating standard.
Minimum total case depth requirements for the tooth should be specified in
accordance with the appropriate rating standard.
28 HRC minimum
32 HRC minimum
The first 0.002–0.003 inch (0.05–0.08 mm) of case microstructure in the tooth area
should meet the surface hardness requirement of the specific grade and also meet the
following surface related characteristics and the requirements of Item 17.
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AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 4 – Metallurgical characteristics for nitrided gearing (continued)
Item
16.3
Characteristic 1) 2)
Decarburization.
− Method 1. Not applicable.
− Method 2. Reduction of hardness
by two load method.10)
− Method 3. Metallographic
evaluation.
16.4
18
18.2
Not specified
Not specified
Grade 3
Maximum 2 HRC points or
equivalent below maximum
measured hardness by
conversion.
No partial decarburization
apparent except in unground
roots.
No reduction in hardness below
maximum measured hardness by
conversion is permissible.
Maximum allowable depth
Maximum allowable depth
No partial decarburization
apparent.
Epsilon (ε) nitride (white layer) 14)
along flank or in root
Minimum specified effective
case depth
inch
17
Grade 1
Grade 2
No decarburization permitted on surface to be nitrided.
(mm)
less
less
at least
than
at least
than
-0.015
-(0.38)
0.015
-(0.38)
-Case microstructure considering
subsequent stock removal,
disregarding corner effects
Core microstructure 12)
Non-martensitic transformation
products
20
Surface temper inspection
21
Surface cracks 11)
©AGMA 2022 – All rights reserved
Maximum allowable
depth
inch
(mm)
inch
(mm)
inch
(mm)
0.0010
(0.025)
0.0008
(0.02)
0.0005
(0.013)
0.0010
(0.025)
0.0008
(0.02)
0.0008
(0.02)
The microstructure of the first 20% of the minimum specified effective case depth
should be predominantly tempered martensite with interspersed Εpsilon (ε) nitride.
Additional requirements for the case microstructure are given in Item 16 and the
following case related characteristics. The microstructure should be free of ferrite,
pearlite, and measurable bainite.
Not specified
Sound metallurgical practice
dictates that the core
microstructure requirements are
maintained in the tooth area to a
depth of twice the minimum
specified effective case depth or
0.100 inch (2.5 mm), whichever
is less, below the minimum
specified effective case depth.
The microstructure in this zone
should be predominantly
tempered martensite. This
microstructure zone should be
free of ferrite, pearlite, and
measurable bainite. Unless
otherwise specified by
agreement, non-martensitic
transformation products within
the microstructure are not a
reason for rejection if the
hardness complies with its
specified values.
Below this zone the core
microstructure should be free of
ferrite and be primarily tempered
martensite with some acicular
ferrite and bainite permissible.
The normal inspection methods, as defined in ANSI/AGMA ISO 14104, are not
applicable to nitrided gearing. Care should be taken when grinding nitrided surfaces to
ensure that no harmful surface conditions are produced in the grinding process.
Cracks, bursts, seams and laps are not permissible in the exposed surface bounded
by the outside diameter of the teeth, the root diameter of the teeth, and the face width
of the teeth including all chamfers, reliefs, fillets, and ends of the teeth. Cracks in other
areas of the part require engineering disposition.
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AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 4 – Metallurgical characteristics for nitrided gearing (concluded)
Item
22
Characteristic 1) 2)
Magnetic particle inspection of
finished gearing 9) 11) 15)
Grade 1
Not specified
22.1
22.2
Below mid tooth height
Above mid tooth height
Normal
diametral pitch
Module
Not specified
Grade 2
Grade 3
Inspection recommended to the following limits:
If Alternative D is selected in 4.1 Non-metallic inclusions,
magnetic particle inspection is required using the acceptance
criteria from Table 2 item 22 Grade 3.
No Indications
Indication, maximum 16)
inch mm
1/8 3.2
3/32 2.4
1/16 1.6
Not specified
≤3
≥8
>3 to 10
>2.5 to <8
≥10
≤ 2.5
23
Shot peening
Shot peening is not recommended 14)
NOTES:
1)
See Clause 3 for definitions and Clause 4 for test methods.
2)
The metallurgical requirements assume homogeneous composition. In practice, microsegregation and banding occurs in steels.
This microsegregation can produce variations in microstructure and properties that should be assessed.
3)
Chemistry should include adequate alloying elements such as chromium, molybdenum, or vanadium. Nitriding steels such as
Nitralloy 135M and Nitralloy N are typically alloyed with 1% aluminum to provide higher surface hardness after nitriding than
normally attained with nitrided through hardening steel.
4)
The controlling section size, diametral pitch (module) and DI should be considered. The designer should specify hardenability
values. Specifying “H” grades of alloys will assure hardenability values are reported (either calculated or measured).
5)
The grade requirements for nonmetallic inclusion, ultrasonic and microstructure characteristics apply only to those portions of
the gearing material where the teeth will be located to a depth below the finished tooth tip of at least 1.5 times the tooth height
6)
Care should be exercised when using Alternative D because of the risk of rejection after the expense of further manufacturing
processes.
7)
DS is only applicable to certification in accordance with ISO 4967.
8)
Sims and Dhale Morphology of MnS per [1].
9)
In-process ultrasonic or magnetic particle, or both, inspection of gearing blanks is recommended for large diameter parts to
detect flaws before incurring the expense of further machining.
10)
See ASTM A370 or ASTM E140 for hardness conversion tables.
11)
Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised.
12)
For a discussion of test coupons see Clause 3 and Clause 4.
13)
Mechanical properties including core hardness may not be the same.
14)
Low intensity glass bead blasting or isotropic superfinishing to remove epsilon (ε) nitride (white layer) is acceptable.
15)
Cracks in non-functional areas require engineering disposition.
16)
Limits: Maximum of one indication in any inch (25 mm) of face width with a maximum of five such indications per any 5 inches
(125 mm) of face width of any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered.
©AGMA 2022 – All rights reserved
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AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
5.5 Gray iron gearing
The major metallurgical characteristics that affect gray iron gearing performance are shown in Table 5.
The minimum acceptable requirements for each factor for metallurgical quality Grades 1, 2, and 3 are
specified. All criteria in any given grade should be met to qualify for the stress number associated with
that metallurgical quality grade.
Table 5 – Metallurgical characteristics for gray iron gearing
Item
1
Characteristic 1), 2)
Material chemistry
3
4
Material form
As cast microstructure
5
Weld repair 3)
7
7.1
Mechanical properties
Hardness
7.2
Other properties
10
Surface cracks 4)
11
Magnetic particle inspection of
finished gearing 3) 4) 5)
11.1
11.2
Below mid tooth height
Above mid tooth height
Normal
diametral pitch
Module
≤3
>3 to 10
≤10
≤8
2.5 to 8
≤2.5
Grade 1
Certification not
required
Grade 2
Certification not
required
Grade 3
If agreed upon between supplier
and 100% verified per foundry
ladle. Foundry test report only per
ASTM E351.
Casting per ASTM A48 or ISO 185; or by contractual agreement
Specified but not verified. Gray iron should be free of cementite and steadite and
should consist of flake graphite in a matrix of pearlite. Unless otherwise specified,
the graphite structure should be primarily type 7, distribution A in accordance with
ASTM A247.
Weld repair of iron castings is not permitted in the near tooth region and is permissible
only with customer approved processes.
Hardness testing is required on semi-finished gear blanks, 1/8 inch (3.2 mm) maximum
machining stock and using only Brinell or Leeb rebound hardness testers. The
minimum measured hardness value should meet the specified design requirement.
A maximum range of 40 Brinell numbers or equivalent, by conversion, in measured
hardness values is recommended.
Not verified
Not verified
The tensile test requirements
should be met for the grade as
specified by ASTM A48 or ISO 185.
Physical testing of a representative
coupon which is cast in the same
lot and heat treated with the same
parts is acceptable.
Cracks, bursts, and seams are not permissible in the exposed surface bounded by the
outside diameter of the teeth, the root diameter of the teeth, and the face width of the
teeth including all chamfers, reliefs, fillets, and ends of the teeth. Cracks in other areas
of the part require engineering disposition.
Not specified
Inspection
recommended to the
Inspection recommended to the
following limits:
following limits:
Not specified
No indications
No indications
Not specified
Indication, maximum 6)
inch
mm
1/8
3.2
3/32
2.4
1/16
1.6
Indication, maximum 6)
inch
mm
3/32
2.4
1/16
1.6
1/32
0.8
NOTES:
1)
See Clause 3 for definitions and Clause 4 for test methods.
2)
The metallurgical requirements assume homogeneous composition. In practice, microsegregation can produce variations in
microstructure and properties that should be assessed.
3)
In-process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to detect
flaws before incurring the expense of further machining.
4)
Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised.
5)
Cracks in non-functional areas require engineering disposition.
6)
Limits: Maximum of one indication in any inch (25 mm) of face width with a maximum of five such indications per any 5 inches
(125 mm) of face width of any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered.
©AGMA 2022 – All rights reserved
46
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
5.6 Ductile iron gearing
The major metallurgical characteristics that affect ductile iron gearing performance are shown in Table 6.
The minimum acceptable requirements for each factor for metallurgical quality Grades 1, 2, and 3 are
specified. All criteria in any given grade should be met to qualify for the stress number associated with
that metallurgical quality grade.
Table 6 – Metallurgical characteristics for ductile iron gearing
Item
1
Characteristic 1), 2)
Material chemistry
3
4
Material form
As cast microstructure
5
Weld repair 3)
6
Heat treatment
7
7.1
Mechanical properties
Hardness
7.2
Other properties
10
Surface cracks 4)
11
Magnetic particle inspection of
finished gearing 3) 4) 5)
11.1
11.2
Below mid tooth height
Above mid tooth height
Normal
diametral
pitch
Module
≤3
>3 to 10
≥10
≥8
2.5 to 8
≤2.5
Grade 1
Certification not
required
Grade 2
Certification not
required
Grade 3
If agreed upon between
supplier and 100% verified per
foundry ladle. Foundry test
report only per ASTM E351,
including as a minimum; C, Si,
S, P, and Mn.
ASTM A536 or ISO 1083; or by contractual agreement
Specified but not verified
The graphite structure should
consist primarily of at least
80% types I and II greater.
In mold treated castings
require 100% ultrasonic
inspection per Table 7 Items 9
and 9.2
Weld repair of iron castings is not permitted in the near tooth region and is
permissible only with customer approved processes.
Not specified. Grade 60-40-18 may require a ferritizing anneal. Grade 100-70-03
may require a normalize and temper. Grade 120-90-02 requires a quench and
temper.
Hardness testing is required on semi-finished gear blanks, 1/8 inch (3.2 mm)
maximum machining stock and using only Brinell or Leeb rebound hardness
testers. The minimum measured hardness value should meet the specified design
requirement. A maximum range of 40 Brinell numbers or equivalent, by
conversion, in measured hardness values is recommended.
Not verified
Not verified
The tensile, yield, and
elongation test requirements
should be met for the grade as
specified by ASTM A536 or
ISO 1083.
Cracks, bursts, seams, and laps are not permissible in the exposed surface
bounded by the outside diameter of the teeth, the root diameter of the teeth, and
the face width of the teeth including all chamfers, reliefs, fillets, and ends of the
teeth. Cracks in other areas of the part require engineering disposition.
Not specified
Inspection
recommended to the
Inspection recommended to
following limits:
the following limits:
Not specified
No indications
No indications
Not specified
Indication, maximum 6)
inch
mm
1/8
3.2
3/32
2.4
1/16
1.6
Indication, maximum 6)
inch
mm
3/32
2.4
1/16
1.6
1/32
0.8
NOTES:
1)
See Clause 3 for definitions and Clause 4 for test methods.
2)
The metallurgical requirements assume homogeneous composition. In practice, microsegregation can produce variations in
microstructure and properties that should be assessed.
3)
In-process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to
detect flaws before incurring the expense of further machining.
4)
Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised.
5)
Cracks in non-functional areas require engineering disposition.
6)
Limits: Maximum of one indication in any inch (25 mm) of face width with a maximum of five such indications per any
5 inches (125 mm) of face width of any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered.
©AGMA 2022 – All rights reserved
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AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
5.7 Austempered ductile iron gearing, ADI
The major metallurgical characteristics that affect austempered ductile iron gearing performance are
shown in Table 7. The minimum acceptable requirements for each factor for metallurgical quality
Grades 1, 2, and 3 are specified. All criteria in any given grade should be met to qualify for the stress
number associated with that metallurgical quality grade. For additional information, see AGMA 939.
Table 7 – Metallurgical characteristics for austempered ductile iron gearing
Item
1
Characteristic 1)
Material chemistry
2
Hardenability
3
4
Material form
As cast microstructure 2)
5
Weld repair 3)
6
7
7.2
9
Heat treatment
Mechanical properties
Other properties
Ultrasonic inspection and
magnetic particle inspection 2) 3) 4)
9.2
Castings
− Back reflection technique
10
Surface cracks 4)
11
Magnetic particle inspection of
finished gearing 3) 4) 5)
Below mid tooth height
11.1
©AGMA 2022 – All rights reserved
Grade 1
Not verified
Grade 2
Not verified
Grade 3
Chemistry to provide sufficient
hardenability should be agreed
upon between the manufacturer
and purchaser. 100% verified per
foundry ladle. Foundry test report
only per ASTM E351.
For ADI, the chemistry should provide sufficient hardenability to produce a
substantially ausferritic microstructure in the part
ASTM A897 or ISO 17804 or by contractual agreement
Specified but not
Specified but not verified The graphite component of the
verified
microstructure should consist of
80% type I and II or greater per
ASTM A247. Graphite form min
80% type V and VI and no coarser
than nodule size 5 if tested per ISO
945. Ultrasonic methods may be
used per agreement between the
manufacturer and purchaser. Inmold treated castings require
100% ultrasonic testing.
Weld repair of iron castings is not permitted in Weld repair is not allowed
the near tooth region and is permissible only
with customer approved processes prior to
heat treatment.
Austenitizing followed by austempering treatment (isothermal quenching)
See AGMA 939 for additional information
Not verified
Not verified
The minimum tensile, yield,
elongation and impact property
requirements should be met for the
grade as specified by ASTM A536
or ISO 1083. Properties are to be
confirmed by testing a specimen
representative of the controlling
section. Test specimens should
undergo the heat treatment with
the gear(s) they represent.
In addition to ultrasonic inspection and when specified by the customer, magnetic
particle inspection may be used to detect cracks and seams. The limits for the
inspection should be agreed upon with the purchaser.
Not specified
ASTM A609 Level 1 from outside surface to the lesser of 1.5
times tooth height below finished tooth tips or 1 inch below the
tooth root.
ASTM A609 Level 2 greater than the lesser of 1.5 times tooth
height below finished tooth tips or 1 inch below the tooth root.
Cracks, bursts, seams, and laps are not permissible in the exposed surface
bounded by the outside diameter of the teeth, the root diameter of the teeth, and
the face width of the teeth including all chamfers, reliefs, fillets, and ends of the
teeth. Cracks in other areas of the part require engineering disposition.
Not specified
Inspection recommended Inspection recommended to the
to the following limits:
following limits:
Not specified
No indications
No Indications
48
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Table 7 – Metallurgical characteristics for austempered ductile iron gearing (concluded)
Item
11.2
12
Characteristic 1)
Above mid tooth height
Normal
diametral
pitch
≤3
>3 to 10
≥10
Shot peening 7)
Grade 1
Grade 2
Grade 3
Indication, maximum 6)
inch
mm
Indication, maximum 6)
inch
mm
Module
Not specified
≥8
>2.5 to 8
≤ 2.5
1/8
3.2
3/32
2.4
3/32
2.4
1/16
1.6
1/16
1.6
1/32
0.8
Shot peening per SAE/AMS-S-13165 or AGMA 938 may be used to increase
surface residual compressive stress.
NOTES:
1)
See Clause 3 for definitions and Clause 4 for test methods.
2)
The grade requirements for non-metallic inclusion, ultrasonic and microstructure characteristics apply only to those portions
of the gearing material where the teeth will be located to a depth below the finished tooth tip of at least 1.5 times the tooth
height.
3)
In-process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to
detect flaws before incurring the expense of further machining.
4)
Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised.
5)
Cracks in non-functional areas require engineering disposition.
6)
Limits: Maximum of one indication in any inch (25 mm) of face width with a maximum of five such indications per any
5 inches (125 mm) of face width of any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered.
7)
It is recommended that ANSI/AGMA 2004 be reviewed to determine if the benefits of surface residual compressive stress
achieved by shot peening may be beneficial to the particular application. Shot peening of the flanks of gear teeth should be
reviewed to ensure that no detrimental effects are caused to the gear set.
©AGMA 2022 – All rights reserved
49
AMERICAN GEAR MANUFACTURERS ASSOCIATION
AGMA 923-C22
Annex A
Bibliography
The following documents are either referenced in the text of AGMA 923-C22, Metallurgical Specifications for Steel
and Cast Iron Gearing, or indicated for additional information.
[1]
Sims, C. E., and Dahle, F. B., 1938, “Effect of aluminum on the properties of medium carbon cast
steel,” Transactions of the American Foundrymen's Society, 46, p. 65.
ANSI/AGMA 6033, Materials for Marine Propulsion Gearing
ASM Handbook, Volume 1 – Properties and selection: Irons, steels and high-performance alloys, ASM
International, Materials Park, Ohio, 1990
ASM Handbook, Volume 4 – Heat treating, ASM International, Materials Park, Ohio, 1991
Boyer, Howard E., Ed., Hardness Testing, ASM International, Materials Park, Ohio, 1987
Doane, D.V. and Semchyshen, M., Modern carburized nickel alloy steel, Nickel Development Institute,
Toronto, 1990
Heat Treater’s Guide – Practices and procedures for irons and steels, ASM International, Materials Park,
Ohio, 1995
Kern, Roy F. and Suess, Manfred E., Steel Selection – A guide for improving performance and profits,
John Wiley & Sons, New York, 1979
Krauss, G., Steels: Heat Treatment and Processing Principles, ASM International, Materials Park, Ohio,
1996
Parish, Geoffrey, Carburizing: Microstructures and Properties, ASM International, Materials Park, Ohio,
1999
Practical Data for Metallurgists, 14th edition, The Timken Company, Canton, Ohio, 1999
Reed-Hill, R.E., Physical Metallurgy Principles, D. Van Nostrand, New York, 1973
Totten, G.E., and Howes, M.A.H., Steel Heat Treatment Handbook, Marcel Dekker, New York, 1997
©AGMA 2022 – All rights reserved
50