H13 Steel Acceptance and Heat Treat Criteria — 2005 • i
i • H13 Steel Acceptance and Heat Treat Criteria — 2005
Special Premium and Superior Quality
Die H13 Steel and Heat Treatment
Acceptance Criteria for Pressure Die
Casting Dies
NADCA #207-200X3 (Premium and Superior)
Contents
Page
Abstract
Statement of Purpose
I. Material Quality Requirements
II. Material Quality Certification of Conformance
III. Heat Treatment Quality Requirements
IV. Heat Treatment Quality Testing Requirements
V. Heat Treatment Quality Certification of Conformance
Acknowledgements
Appendix 1: Guide to Sample Preparation Techniques
Appendix 2: Practical Guide to Steel and Heat
Treatment Quality
Appendix 3: Welding Die Casting Die Materials
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by:
NADCA DIE MATERIALS COMMITTEE
ASTM Standards referred to in this document may be obtained from:
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North America Die Casting Association
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Rosemont, IL 60018-4733
Phone:
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Fax:
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E-mail:
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Copyright © 200x 3
North American Die Casting Association
Wheeling Rosemont, Illinois 60018-4733
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Neither the North American Die Casting Association, nor the authors of this work:
• Makes any warranty or representation, express or implied, with respect to the
accuracy, completeness, or usefulness of the information contained in this
document;
• Assumes any liability with respect to the use of, or for damages resulting from the
use of, any information, method, process or equipment described in this
document.
ABSTRACT
An agreement has been reached with NADCA member firms that are major material suppliers and/or
heat treaters of H13 die steel to the die casting industry. Acceptance criteria, restrictive specifications
as noted, and a certification plan have been developed for both the Material Quality and the Heat
Treatment Quality of Special Premium and Superior Quality Grade H13 die steels. By specifying die
H13 steels produced to these specifications, improved levels of cleanliness, a reduction in micro and
macro banding, and impact toughness capabilities are certified. These This steels will respond more
uniformly and predictably to heat treatment, thus reducing the risk of excessive distortion and
cracking during heat treatment and giving longer and more consistent die life.
When dealing with premium grade H13 neither the steel making process nor the forging practices are
stipulated by this specification, provided that all quality requirements in this specification are met.
When dealing with superior grade H13 With the exception of Grade A (“Premium H13”) die steel,
the steel making process shall include secondary refining, either ESR (electro-slag remelt) or VAR
(vacuum arc remelt). However, small round stock less than 3” diameter may not be available by these
remelt process. Regardless of the steel making process or the forging practices, material covered by
this specification must meet all quality requirements in this specification.
The heat treatment quality requirements in this specification pertain to the vacuum hardening and
high-pressure gas quenching process. While NADCA recognizes the viability of other heat treatment
methods, the scope of the procedures within this specification are exclusively vacuum austenitizing
and pressurized gas quenching.
STATEMENT OF PURPOSE
These acceptance criteria and specifications are not intended for all die casting applications. They
apply where high volume production or critical performance is required. Die casters and tool builders
should insist that certification of the Material Quality accompany each piece of Special Quality
Premium or Superior H13 die steel purchased for use in die casting dies and that certification of the
Heat Treatment Quality accompany each furnace load of Special Quality die H13 steel hardened in
accordance with this protocol.
For certain applications requiring a higher level of Material Quality and Heat Treatment Quality, Superior Grade H13 is a variety of Special Quality die steels are listed in this specification as Grades B H that are commercially available and should meet the appropriate specification requirements of
NADCA #207-200 3 Superior.
For applications requiring a lesser level of Material Quality and/or Heat Treatment Quality, Grade A
(“Premium H13”) die steel Premium Grade H13 is is available and should meet the appropriate
specification requirements of NADCA # 207-200X 3 Premium.
It should be noted that die performance is a complex combination of many factors including die size
& design, casting alloy, operational procedures, steel composition, austenitizing temperature, impact
toughness and hardness. Other factors such as temper resistance, hot strength, and fatigue
resistance also effect die performance and should be considered when specifying steel grade, heat
treatment parameters. Final hardness should be selected based upon steel grade, size, and die design.
Consult your steel supplier and/or heat treater for guidance.
NOTE: Every effort has been made to assure information contained in these procedures is correct. However,
NADCA does not accept responsibility for damage, injury or costs incurred by using these procedures.
Check the suppliers’ instructions for specific directions on products used. Be sure to comply with all
applicable safety codes and regulations.
I. Material Quality Requirements
A. Chemical composition (% by weight) of Critical Alloying Elements &
Impurities
Special Quality Both Premium and Superior grades of die H13 steel must conform to the Chemical
Requirements of Table 1 ASTM A681 (latest revision) Section 6 with the following modifications, or
emphasis.
PREMIUM GRADE A
MIN.
MAX.
0.37 *
0.42 *
0.20
0.50
—
0.025 *
—
0.005 *
0.80
1.20
5.00 *
5.50 *
0.80
1.20
1.20 *
1.75 *
ELEMENTS
Carbon
Manganese
Phosphorus
Sulfur
Silicon
Chromium
Vanadium
Molybdenum
* Modifications from ASTM A681 for premium quality
SUPERIOR ALL OTHER GRADES
MIN.
MAX.
0.37
0.42
0.20
0.50
—
0.015 ‡
—
0.003 ‡
0.80
1.20
5.00
5.50
0.80
1.20
1.20
1.75
‡ Modifications from NADCA Premium Quality for Superior Quality
B. Hardness
1. Both Premium and Superior Qualities: Annealed hardness of Special Quality steel, as received,
shall not exceed 235 HBW.
C. Microcleanliness
The permissible limits of microcleanliness (severity levels of non metallic inclusion content) shall be
determined by ASTM E45, Method A (latest revision). Plate I-r should be used to obtain rating increments of 0.5. The maximum allowable limits are as follows.
INCLUSION TYPE
A (sulfide)
B (aluminide)
C (silicate)
D (globular oxides)
GRADE A PREMIUM
THIN
HEAVY
1.0
0.5
1.5
1.0
1.0
1.0
2.0
1.0
ALL OTHER GRADES SUPERIOR
THIN
HEAVY
0.5 ‡
0.5
1.5
1.0
0.5 ‡
0.5 ‡
1.5 ‡
1.0
‡ Modifications from NADCA Premium Quality for Superior Quality
D. Ultrasonic quality (ASTMA-681 S1.1)
Appropriate ultrasonic inspection techniques shall be performed to assure soundness. All blocks shall
be free from internal defects such as stringers, oxides, porosity, bursts, heavy segregation, etc., as
indicated by ultrasonic testing. Ultrasonic examination of the original steel stock shall be conducted
in accordance with ASTM recommended practices A388 and E114 (latest revision). Acceptance
criteria are as agreed upon between supplier and vendor.
E. Impact Capability Testing
Impact capability testing pertains to all mill product forms with a thickness greater or equal to 2-1/2
inches. Specimen blanks shall be removed from the short transverse orientation corresponding to the
center location of the parent block of steel (see Fig. 1 and 2). A minimum of one set of 5 impact
specimens shall be tested per lot of material produced. A lot shall consist of all the product of a single
ingot, which is forged or rolled via a common procedure to one size and annealed in a single furnace
charge. Multiple starting ingots, variations in forging or rolling size or procedure, or variations in
annealing furnace charge are defined as a multiple lots and shall require additional sets of tests.
Fig. 1. Schematic diagram illustrating the removal of capability Charpy V-notch specimens from the short
transverse orientation corresponding to the center location of a parent block of steel that has a
rectangular/square cross-section.
NOTE: The base of the notch shall be parallel to the longitudinal direction of the parent block or slab, See
Charpy V-notch samples per ASTM A370, latest revision.
Fig. 2 Schematic diagram illustrating the removal of capability Charpy V-notch specimens from the transverse
(radial) orientation corresponding to the center location of a parent bar of steel that has a circular
cross-section.
NOTE: The base of the notch shall be parallel to the longitudinal direction of the parent bar. See Charpy Vnotch samples per ASTM A370, latest revision.
Individual specimens shall be machined oversize to be nominally 1/2” x 1/2” x 2-1/2”each.
Specimens are to be hardened and tempered before machining to final dimensions. Specimens shall
be heat treated, machined, and tested as follows (see Table 2 for designated autenitizing /
tempering temperatures and final hardness):
1. Austenitize at 1885°F (1030°C) for 30 minutes;
2. Oil quench. Oil temperature 120°F (50°C) maximum;
3. Minimum double temper at a temperature of at least 1100°F (590°C) for 2 hours minimum each temper to achieve a final hardness of 44/46 HRC;
4. Air cool to room temperature between each temper;
5. Following the preceding laboratory hardening process, the samples shall be machined to
final size and finish ground. See Charpy full size test impact specimen per ASTM
A370, Fig. 11a:
• adjacent sides shall be at 90 degrees ±10 minutes
• cross section dimensions shall be ±0.100 mm (±0.004 in.)
• length of specimen shall be 55 ±1 mm (2.165 ± 0.040 in.)
• surface finish shall be 63 micro inch (1.6 micro meter) max. on the 55 x 10
mm faces.
6. Five impact specimens shall be tested at room temperature on test machines that meet
the calibration requirements of ASTM E23 or ISO 148/R442 (latest revision). The
values of the highest and lowest specimens shall be discarded and the average of the
remaining three results shall be computed. Testing shall yield the following specified
values.
?
7. Acceptance Criteria:
a) Premium Quality is 8 ft. lbs. (11 J) average with 6 ft. lbs. (8 J) single minimum
value.
b) Superior Quality is 10 ft. lbs. average (14 J) with 8 ft. lbs. (11 J) single
minimum value.
see Table 2 for capability impact toughness acceptance criteria
NOTE: These impact toughness values apply only to impact specimens that are individually heat treated prior
to final machining in accordance with the method prescribed above. Charpy impact specimens are to
be notched after final machining. Ground notches are preferred and shall be used for referee
purposes. EDM notches are not allowed.
F. Grain Size:
Grain size shall be developed using the Direct Quench method per ASTM E112 by austenitizing at
1885°F (1030°C) for 30 minutes, quench at a moderate or rapid rate and temper at 1100°F minimum.
Hardening should be in a protective media or by using an appropriately oversize sample in a nonprotective media. Grain size to be measured by using the ASTM comparative method and shall be
predominately ASTM No. 7 or finer.
An alternative method to rate the grain size may be used. The Shepherd Fracture Grain Size shall be
predominantly No. 7 or finer when made on a hardened (air cooled after heating for 30 minutes at
1885° F (1030° C), in a protective media or using an appropriately oversize sample in a non protective media) and untempered specimen taken from a representative sample.
G. Annealed Microstructure:
The annealed microstructure of the as-received steel shall consist essentially of a ferritic matrix with
a homogeneous distribution of spheriodized carbides when examined at 500X, after being polished
and etched with 5% Nital. Acceptable microstructures for annealed die steels H13 steel are shown in
the NADCA Annealed Microstructure Reference Chart.
H: Banding Segregation:
The annealed microstructure shall be free of excessive banding by conformance with the NADCA
Banding Segregation Reference Chart for levels of microbanding or microchemical segregation. For
sizes 4” and below, banding segregation shall not be cause for rejection unless excessive primary carbides are present.
II. Material Quality - Certification of Conformance:
Material that has been designated as NADCA Special Premium
Quality or Superior Quality H13 die steel in accordance with
this specification shall be accompanied by a Certificate of
Conformance from the steel supplier that includes the following data and information:
A.
NADCA Grade (A – H)
B.
Supplier Heat Designation
C.
Annealed Brinell Hardness
D.
Chemical Analysis
E.
F.
G.
H.
I.
J.
NOTE
Microcleanliness levels
Confirmation that Ultrasonic
Inspection has been performed
Grain Size Number
Annealed Microstructure Rating
Number
Microbanding Designation Levels
Impact capability test results: shall
include three individual results of
specimens and average result, heat
treatment and final hardness.
The laboratory capability austenitizing
temperature must be stated
III. Heat Treatment Quality Requirements
Vacuum Heat Treatment Process Requirements
The most critical parameters in the heat treatment of Special Premium and Superior Quality H13 die
steels are the austenitizing treatment and the quench rate from the austenitizing temperature. The
quench rate must be controlled to provide optimum metallurgical properties while minimizing
distortion and risk of cracking. A more detailed discussion of the heat treatment process is included in
Appendix 2: Practical Guide to Steel and Heat Treatment Quality.
NOTE for SUPERIOR QUALITY: Except for Premium H13 Grade A, a test coupon must be
attached to the workpiece prior to hardening. See Section IV-L for details.
NOTE: ALL Special Quality Die Steels can be certified as either “Class 1” or “Class 2”
Heat Treatment Quality. Certification as Class 1 Heat Treatment Quality requires that a test
coupon must be attached to the workpiece prior to hardening. See Section IV-L for details.
A. Equipment
Premium
• Vacuum furnace with a minimum 2 bar backfill capability and a programmable furnace controller
linked to multiple load thermocouples.
• Sufficient cooling capability to cool die surface from 1885° F (1030 °C) at a minimum rate of
50°F/min. (28°C/min.). See Section III F.
• Furnace must be capable of isothermal hold during quench based on input from surface and core
thermocouples where interrupted quench is required.
Superior
• Vacuum furnace with high-pressure gas quenching capability and a programmable furnace controller
linked to multiple load thermocouples.
• Sufficient backfill pressure and cooling capability to cool die surface from the designated
austenitizing temperature 1885°F (1030°C) at a minimum rate of 50°F/min. (28°C/min.). See
Section III F.
• Furnace must be capable of isothermal hold during quench based on input from surface and core
thermocouples where interrupted quench is required.
‡ Modifications from NADCA Premium Quality for Superior Quality
B. Furnace Loading
• Pieces in the load shall be placed and distributed to allow for uniform heating and quenching.
• The geometry of the pieces must be considered to insure uniform heat treatment and crack
prevention.
• The furnace must not be overloaded, so that the minimum quench rate can be achieved.
C. Thermocouple Placement
• A dedicated thermocouple hole for placement of the surface thermocouple (Ts) is recommended. Hole
should typically be 1/8” to 1/4” (3.175mm to 6.35mm) diameter, depending on thermocouple wire used
and should be 0.625” ± 0.125” (15.87mm ± 3.175mm) deep.
• The surface thermocouple (Ts) hole should be located in the center of the largest area of the die in the
backside and should be at least 1/4T x 1/4W or mid-radius from the nearest corner.
• The core thermocouple (Tc) should be placed as close to the center of mass as possible using existing
coolant holes. In cases where core thermocouple placement is not possible, the furnace load shall
be controlled from a load block that represents the maximum thickness of the die with a
thermocouple at the center of mass.
• All thermocouple holes shall be packed with a fiber refractory material to prevent direct contact with
quenchant.
• Thermocouple wires must be secured to prevent movement during quenching.
• If multiple blocks are hardened in the same load, thermocouples should be placed in the block with
the largest cross section.
D. Preheating Practice
• Load work into cold furnace and heat at a rate not to exceed 400°F/hour (220°C/hour) as measured
by Tc.
• Heat to 1000°F to 1250°F (540°C to 675°C) furnace temperature and hold until Ts-Tc<200°F
(110°C).
• Heat to 1550°F ± 50°F (845°C ± 10°C) and hold until Ts - Tc < 100°F (60°C).
• Additional preheating steps may be used at the discretion of the heat treater or toolmaker.
E. Austenitizing
• Rapidly heat from final preheating temperature to the designated austenitizing temperture (see Table
2) 1885°F ± 10°F (1030°C ± 5°C).
• Soak time shall be 30 minutes after Ts - Tc< 25°F or 90 minutes maximum afterTs = the designated
austenitizing temperture 1885°F (1030°C) whichever occurs first.
F. Quenching
• Quench as rapidly as possible to 300ºF (150ºC) as measured by the core thermocouple, Tc.
• Minimum quenching rate shall be: 50°F/minute (28°C/minute) between the designated austenitizing
temperture 1885°F and 1000°F (1030°C and 540°C), measured by Ts (in other words Ts shall
reach 1000°F (590°C) in less than 18 minutes).
NOTE: This definition of how to measure the cooling rate is necessary to prevent discrepancies. In dies
with ruling sections greater than about 12” (300mm), it may not be possible to achieve the
recommended quench rate with all equipment.
• The quench may be interrupted when Ts is between 850° F and 750° F (455°C and 400°C).
NOTE: An interrupted quench is recommended when the difference between the surface (Ts) and core
thermocouple (Tc), exceeds 200°F (90°C). If interrupted, rapid pressurized gas quenching
must be resumed when either: 1.) Tc – Ts <= 200ºF (95ºC); 2.) Ts reaches 750ºF (400ºC);
OR 3.) total interrupt time reaches 30 minutes maximum. Maintain pressurized gas
quenching until Tc < 300ºF (150ºC).
• Continue rapid pressurized gas quenching when Tc - Ts<200°F (110°C) or 30 minutes maximum
after Ts reaches interrupt temperature.
• Maintain pressurized gas quenching until Tc<300°F (150°C).
• Die shall be cooled in still air until surface temperature Ts< = 120°F (50°C ) prior to tempering.
• Die shall be immediately loaded for the first temper.
G. Tempering
• A minimum of two tempering cycles are required before finishing operations.
• Cool to ambient temperature between temper cycles.
• Stress temper finished dies in air at 50°F (25°C) below highest tempering temperature or1000°F
(565°C) minimum. (This practice results in a minimum of three tempering cycles.)
• Tempering and stress temper cycles shall be held for one hour per inch of thickness based on the
furnace thermocouple, two hours minimum.
H. Rehardening
• If rehardening is required, the workpiece shall be reannealed at 1550°F–1600°F (840°C - 870°C) for
1 hour per inch of thickness followed by slow cooling at less than 60°F (33°C)/hour to1100°F
(540°C), then furnace cooled.
NOTE: Dies Must Not Be Rehardened Without Customer Approval.
IV. Heat Treatment Quality – Testing Requirements:

REQUIRED FOR CLASS 1 & CLASS 2 HEAT TREATMENT
QUALITY CERTIFICATION
I. Hardness
• The recommended hardness range shall be within the range of 42 to 52 HRC. The lower end of the
hardness range is recommended for dies where gross cracking is of concern whereas the high end
of the range is recommended for improved heat checking resistance.
• Specific hardness range must be specified by the customer, stated as a 3-point range; eg. 44-46 HRC.
• Hardness testing shall be conducted following the latest revisions of ASTM E10, ASTM E18, ASTM
A956 or ASTM E384.
• A minimum of five hardness readings is preferred (four corners and center face) at positions agreed
by customer.
• Any deviation from the specified hardness range shall be referred to the customer.
J. Furnace Chart Data
• A copy of the furnace chart data produced from contact thermocouples in accordance with III. C
above and representing the actual load shall be available from the heat treater for 7 years
minimum.
• The furnace chart data shall be presented in a legible manner documenting the thermal cycle
experienced by the workpiece including preheating steps, austenitizing, and the quench from the
hardening temperature to Tc<300°F (150°C).
• The minimum quenching rate, measured by Ts, shall be 50°F/minute (28°C/minute) between the
designated austenitizing temperture 1885°F and 1000° F (1030°C and 540°C).
K. Hardened Microstructure
• The microstructure of a specimen representing the hardened detail shall be examined.
• The specimen shall be either 1) cut from a corner or edge of the hardened detail or 2) cut from a
coupon that was attached flush to the detail throughout the hardening process. For Superior
Quality see section IV L for test coupon details.
• The specimen shall be prepared in accordance with ASTM E3 and etched with a 5% Nital solution.
(See Appendix 1.)
• The hardened microstructure of the specimen shall consist essentially of tempered martensite with
some bainite.
• There shall be no evidence of pearlite, retained austenite, decarburization, carburization, or excessive
intergranular precipitation.
• Unacceptable microstructures for hardened material are shown in NADCA Heat Treated Microstructure Reference Chart. (See inside back cover.)
REQUIRED FOR CLASS 1 HEAT TREATMENT QUALITY
CERTIFICATION
L. Impact Toughness
• A coupon approximately 2 ½” x 3 ½” x ½” thick shall be prepared from a sample preferably from the
same Grade/block of Special Quality die steel of known “annealed capability” impact toughness
such that the 2 ½” dimension represents the thickness direction, the 3 ½” dimension represents
width direction, and the ½” dimension represents the length direction of the parent material.

Surogate coupons are allowed and may be substituted.
• The coupon shall be attached to each workpiece away from edges and corners such that a 2 ½”” x 3
½” face of the coupon is in intimate contact with the workpiece. If tack welds are used, the welds
should be placed along the 3 ½” dimension.
• The coupon shall accompany the workpiece through the preheating, austenitizing, quenching, and
first temper of the hardening procedure.
• The coupon may be removed from the die after the first temper and separately tempered to 44/46
HRC.
• Test coupon must be tempered 44/46 HRC.
• From the coupon, three 10mm x 10mm Charpy impact specimens shall be machined and notched and
tested at room temperature in accordance with ASTM A370. The base of the V-notch shall be parallel
to the longitudinal direction of the parent material. The samples shall be machined to final size and
finish ground. See Charpy V-notch per ASTM A370 latest revision, Fig. 11a.
 Adjacent sides shall be at 90 degrees ±10 minutes
 Cross section dimensions shall be ±0.100 mm (±0.004 in.)
 Length of specimen shall be 55 ±1 mm (2.165 ± 0.040 in.)
 Surface finish shall be 63 micro inch (1.6 micro meter) max. on the 55 x 10 mm faces.
 Ground notches are preferred; EDM notches are not allowed.
• Testing shall be conducted at room temperature on test machines that meet the calibration
requirements of ASTM E23 or ISO 148/R442 (latest revision).
• Acceptance criteria: 8 ft-lbs (11 J) average with 6 ft-lbs. (8 J) single minimum value at
44/46 HRC. The three individual results and the average shall be reported.
NOTE: These toughness criteria are from specimens removed from a required test coupon of
Special Superior Quality material that was attached to the workpiece during hardening
and is meant to represent the properties of the workpiece itself.
V. Heat Treatment Quality - Certification of Conformance:
NADCA Special Premium and Superior Quality H13 die steel that has been hardened in accordance
with this specification shall be accompanied by a Certificate of Conformance from the heat treater
that includes the following data and information:
A. Heat Treat Source
B. Item Identification
X. Heat Treatment Quality Class (1 or 2)
X. NADCA Steel Grade
C. Material Heat Number
D. Shipping Weight
E. Specified Hardness
F. Pre-Heat: Step 1 Temperature & Time
G. Pre-Heat: Step 2 Temperature & Time
H. Pre-Heat: Step 3 Temperature & Time
I. Hardening: Temperature & Soak Time
J. Quench Rate
K. Quench Pressure
L. Interrupt: Temperature & Hold Time
M. 1st Temper: Temperature, Soak Time, Hardness
N. 2nd Temper: Temperature, Soak Time, Hardness
O. 3rd Temper: Temperature, Soak Time, Hardness
P. Final Hardness
Q. *Hardened Microstructure
R. *ALL Special Die Steels except Premium H13 Grade A:
Hardened Impact Toughness; shall include three individual results and
average results.
* Test results can be provided by a heat treater or testing facility.
Example
HEAT TREATMENT QUALITY
Certification of Conformance
Heat Treatment Quality Class
NADCA Steel Grade
Heat Treat Source:
Item Identification:
Material Ht. No.:
Required Hardness:
Material Brand:
Ship Wt. Ea.:
Ship Date:
Operation
Anneal
Stress Relieve
Pre-Heat: Step 1
Pre-Heat: Step 2
Pre-Heat: Step 3
High Heat
Quench Rate
Quench Pressure
Interrupt Temp.
Temper: Draw 1
Temper: Draw 2
Temper: Draw 3
Final Temp.
Stress Temper
Final Hardness:
Temperature
Time
Furnace
Hardness
Hardened Microstructure:
Required for Class 1 Heat treatment superior quality:
Test Coupons Attached: YES
NO 

Impact Toughness: 3 Individual Values-
ft.-lbs,
ft.-lbs,
ft.-lbs
Average ft.-lbs
We certify that the above statements are true and correct and that all temperatures were obtained with standard and
approved equipment.
Work or Shop Order No.:
Authorized Signature:
Date:
ACKNOWLEDGMENTS:
NADCA acknowledges the technical support and contributions of the following individuals and
companies:
Die Materials Specification Task Group
Chairman: Corwyn Berger Bodycote Materials Testing, Inc.
Jesse Adamson A. Finkl & Sons Co.
Terry Bachmeier ThyssenKrupp Specialty Steels NA
Guy Brada Bodycote Taussig, Inc.
Carl J Dorsch Timken Latrobe Steel
Rudiger Ehrhardt ThyssenKrupp Specialty Steels EWK
Edward Flynn GM Powertrain
Patricia Miller Bohler Uddeholm NA
Ed Severson Crucible Materials Corp.
Die Materials Heat Treatment Task Group
Chairman: John Fitzgerald FPM Heat Treating
Vince Adkar ThyssenKrupp Heat Treatment NA
Mark Baleja Century Sun Metal Treating
Gene Hainault Therm-Tech of Waukasha
Mark E. McCormick Paulo Products Co.
Iqbal Shahid Bohler Uddeholm North America
Craig Zimmerman Bodycote Thermal Processing
Cover pictures provided by Bohler Uddeholm and FPM Heat Treating.


Appendix 1 
Appendix 1:
Guide to Sample Preparation Techniques
When taking samples for Impact Testing and Metallographic Examination, the location from which
the test material is removed is important. Likewise, the direction and orientation of the test
specimens can have a significant influence on the test results. Accordingly, it is imperative that
samples be produced in strict accordance with the following guidelines.
Impact Capability Testing –
As required by Section I.E., all mill product forms with a thickness greater or equal to 21⁄2 inches
must be subjected to an Impact Capability test. A sample of test material, at least 21⁄2” x 31⁄2” x 1⁄2”
is to be removed from the center location of the parent block of steel. The 21⁄2” dimension is to be
parallel to the thickness dimension of the parent block; the 31⁄2” dimension is to be parallel to the
width of the parent material; the 1⁄2” dimension represents the length direction of the parent material.
See Figure 1a. Five Charpy V-notch (CVN) specimen blanks shall be removed from the short
transverse orientation from the test material. See Figure 1b.
Figure 1a. and Figure 1b. Location & Orientation of Test Material and Charpy Impact Test Samples.
Individual CVN specimens shall be rough machined oversize to be nominally 1/2” x 1/2” x 2-
1/2”each. The specimens are then to be hardened and tempered in accordance with the procedure
listed in Section I.E. before machining to final dimensions. After final machining to 10mm x 10mm x
55mm per ASTM A370 Figure 11a, each specimen is to be notched in the Short Transverse (ST)
orientation such that the base of the V-notch is parallel to the longitudinal direction of the parent
material per Figure 1b above.
Impact Toughness; Required for Class 1 Heat Treatment Quality
CertificationClass 1 Heat Treatment Superior Quality material is required to have a special test coupon attached to
the workpiece prior to hardening. See Section IV.L. The coupon is identical to the sample of test
material used for Impact Capability testing described above. A coupon approximately 2 ½” x 3 ½” x
½” thick shall be prepared from a sample of Special Quality H13 die steel of known “annealed
capability” impact toughness such that the 2 ½” dimension represents the thickness direction, the 3
½” dimension represents width direction, and the ½” dimension represents the length direction of the
parent material. The coupon shall be attached to the workpiece away from edges and corners such
that a 2 ½” x 3 ½” face of the coupon is in intimate contact with the workpiece. See Figures 2a & 2b.
After the completion of the hardening and tempering heat treatment (see Section IV.L.), three 10mm
x 10mm x 55mm CVN specimens are to be finish machined from the test coupon per ASTM A370
Figure 11a, and notched in the ST orientation such that the base of the V-notch is parallel to the
thickness direction of the test coupon (i.e. longitudinal direction of the parent material) per Figure 1b
above.
Metallographic Examinations –
A variety of Metallographic Examinations are required by this specification. For some of the
required tests, if properly selected, a single specimen may be used for multiple requirements. The
samples for Metallographic Examinations on Annealed Material should be taken from the test
material cut for the Impact Capability testing. A single specimen can be used to evaluate the
banding, microcleanliness, and annealed structure. A separate specimen is required to evaluate the
grain size of the material. This sample may be taken from a broken CVN specimen after completing
the Impact Capability testing or may be taken from a specimen hardened in accordance with Section
I.F. using the Direct Quench method per ASTM E112.
Samples for examination of annealed material must be taken such that the surface to be examined is
parallel to the principal direction of deformation. Preferably, specimens should be taken from the
near-center of the width and thickness of an end face of the block. See Figures 3a and 3b.
Fig 3a & 3b: Sketches showing location and orientation of metallographic specimens removed from block and
round stock for determination of microcleanliness, banding, grain size, and microstructure of annealed material. The shaded faces in the figures are the faces which should be polished and etched for
the metallographic examinations.
Specimens should be mounted, ground, and polished in accordance with standard metallographic
procedures and ASTM E3. Examination for microcleanliness shall be conducted in the unetched condition in accordance with ASTM E45, Method A, Plate 1-r. Examination for Banding/Segregation
and for rating the Annealed Microstructure shall be conducted in the etched condition. The
specimens should be etched immediately after polishing by immersion in a 5% Nital solution for
approximately 30 seconds to obtain a properly developed microstructure. The Banding/Segregation
shall be evaluated and rated by metallographic examination at a magnification of 50X; the Annealed
Microstructure shall be evaluated and rated at a magnification of 500X.
Grain Size determination shall be conducted on a properly prepared metallographic specimen of a
laboratory quenched sample in the etched condition at a magnification of 100X. Due to the typically
fine grain size, examination may be made at a higher magnification using the formula presented in
ASTM E112 Comparison Method.
Samples for evaluation of the hardened microstructure shall be made on a specimen taken from commercially heat treated material and must include an as-hardened surface; i.e. not ground or otherwise
machined after hardening. The sample should be taken from the hardened coupon used for Impact
Toughness testing for Special Quality material or from a sample cut from a corner or edge of a hardened workpiece of Premium Quality material if no test sample was attached to the workpiece.
Specimens shall be mounted, ground, and polished in accordance with standard metallographic
procedures. The specimens shall be etched by immersion in a 5% Nital solution for approximately 30
seconds to obtain a properly developed microstructure. See Figures 4a,b,c,d.
The microstructure shall be examined and rated at 500X. The hardened microstructure of the specimen shall consist essentially of martensite with some bainite. There shall be no evidence of pearlite,
retained austenite, decarburization, carburization, or excessive intergranular precipitation.
Figure 4a,b,c,d. Microstructures of hardened Special Quality die steel Premium H13 showing the effects of
sample preparation and etching techniques. Fig 4a: This image shows a die steel an H13
microstructure that has been properly ground, polished, and etched. Fig. 4b: This image shows
polishing scratches, a pulled-out inclusion, surface dust particles and etch stains. All of these features
are polishing artifacts, and are not indicative of poor heat treatment. Fig 4c: This image shows the
microstructure of the same specimen in Fig 4a, but in this case, the specimen has been overetched
after polishing. The overetching masks critical details of the microstructure. The overetched
condition can be the result of an incorrect acid concentration in the etchant, or an etching time that
was too long. Fig 4d: This image shows the microstructure of the same specimen in Fig 4a, but in this
case, the specimen has been underetched after polishing. The underetching makes critical details of
the microstructure difficult or impossible to discern. The underetched condition can be the result of
an oxidized specimen surface (too much time between polishing and etching), incorrect acid
concentration in the etchant, or etchant that is too old.
Appendix 2:
Practical Guide to Steel and Heat Treatment Quality
Introduction: Preparations, Instructions
Aim:
This Appendix gives practical guidance for stress relieving, hardening and tempering processes applicable to hot work die steels H13 steel for use as die casting or squeeze casting tools, inserts, cores,
etc. The main purpose is to provide optimum metallurgical properties while minimizing distortion
and risk of cracking.
Written Instructions:
It is strongly recommended that written instructions be given to the heat treater that itemize the
requirements of the customer and take into account the requirements of the preceding specification.
Such written instructions may include or exclude information given here. Where a difference occurs,
the customer’s instructions shall take precedence.
Liaison:
Close liaison between the customer and heat treater (over details such as required properties, permissible size change, etc.) will assist the heat treater in achieving the best results with the least risk.
Preparation For Heat Treatment:
It is the tool maker’s responsibility to prepare the tool such that the risk of cracking, distortion and
surface effects are minimized.
Examine material certification for statement of conformance to NADCA #207-200X 3
Grade Name & Heat
Supplier
Number
of Ultrasonic
Confirmation
Inspection
Annealed
Hardness
Microcleanliness/Inclusion
Content
Banding/Microsegregation
Rating
Chemical
Composition
Annealed Microstructure Rating Impact Capability Test Results
Size
Grain
Number
Avoid stress risers – check for:
Sharp inside corners
Deep tool & stamp marks
Weak, thin sections
Very deep cavities
Ensure tool is not cracked before heat treatment:
Use dye penetrant, ultrasonic testing, magnetic particle
Notify heat treater if EDM is used prior to hardening
Ensure surfaces are free from dirt, rust, oxides, grease & cutting fluids
If die has been welded, mark the weld and notify the heat treater.
Steel grade
Burrs
NADCA Grade H13, Premium, Superior)
Manufacturer & designation
Heat or batch number
Present Condition
after previous
Annealed
hardening
Hardened & tempered
Stress relieved
Annealed
Surface Condition
Nitrided (specify type & depth)
Other surface treatment (type & depth)
Welded
Allowance for Distortion & Growth
Sufficient metal is left on tool (review stock allowance and critical dimensions w/ heat treater)
Identify critical dimension(s)
Final Hardness
Specify exact range (42-50 HRC for finished tools,
higher values for smaller tools)
Specify location of test on tool
Review Records/Certification
Certification of compliance
charts of temperature
Furnace
& times (see page 11)
Instrument
calibration
records
Test Results Requested
Hardness check
Quench rate
Impact test
Micro-examination of sample taken from die
Heat Treatment Guidelines
Instructions:
• Heat treater must contact the customer if written instruction differs from
these recommended procedures
• Furnace load size and placement must be appropriate to assure conformance to recommended procedures
• Must avoid change in surface composition e.g. decarburization, oxidation,
etc.
• Maintain temperature controllers to AMS 2750 or latest revisions.
• Maintain instrument calibration records
• Use thermocouples in the furnace load per procedure, additional thermocouples may be used
• Maintain accurate, traceable records of all technical details such as temperatures, soak times, cooling rates and hardness
• Conditions must be controlled to limit surface effects such as decarburization, carburization or nitriding
• Hardening vacuum furnaces, with positive pressure capability of at least 2
bar on premium quality and 5 bar on superior quality.
• Tempering/stress relieving: air, atmosphere or vacuum is allowed.
• Stress tempering/oxide treatment: air
• Annealing: vacuum or atmosphere
• Accurate temperature control is important.
• Every tool shall be hardness tested and reported using Rockwell C scale
• A minimum of five hardness readings is preferred (four corners and center) at positions agreed by customer.
• If decarburization, etc. is suspected, this may be checked by using Rockwell superficial or microhardness testing.
• A test coupon can be attached to the die prior to hardening to evaluate
microstructure, toughness, etc. as requested by the customer. This is a
mandatory requirement for Class1 Heat Treatment Quality certification
Superior Quality H13.
NOTE: Dies Must Not Be Rehardened Without Customer Approval.
Stress Relieving After Rough Machining
The stress relieving treatment may be performed to reduce the likelihood of distortion during subsequent machining or heat treatment.
Rough Machining
• The rough machining operation can introduce high levels of residual stress (heavy grinding may also
produce a hardened skin due to the high temperatures generated).
• If not relieved, this stress may cause distortion during final machining or during the hardening
operation.
• Leave sufficient stock on all surfaces at the rough machining stage to be removed using lighter cuts
after the stress relieving operation - and before final hardening
Heating Temperatures and Soak
• Charge into cool furnace (less than 500° F [260° C]). Heat to 1050° F - 1250° F (560°
C - 675°C) in a vacuum, electric or gas furnace.
• Tools should be well supported and allow free circulation of the heating medium so
that they are heated uniformly.
• Allow 20 min. per inch of section thickness for heating. Hold for a minimum of 1/2
hour per inch of section thickness or a minimum of two hours, once the furnace
reaches operating temperature.
• Where feasible, use a thermocouple in the center of the tool (e.g. in an ejector hole or
waterline) to indicate when the center of the tool reaches temperature, then hold for
2 hours minimum.
Cooling
Simple shapes: may be taken out and air cooled. Charge into cool furnace (less than
500° F [260° C]).
Complex shapes: (e.g. where section thickness varies by more than 3 inches) should
be furnace cooled to 800° F (430° C) maximum to reduce the cooling stress before air
cooling.
In both cases, cool as uniformly as possible in still air away from drafts to prevent
reintroduction of thermal stress.
Annealing
Annealing involves heating the tool slowly to a high temperature, then
cooling slowly to develop the softest condition possible with this grade of
steel. A tool which was incorrectly hardened or has softened in service may
be annealed to reduce the risk of cracking and distorting during heating for
hardening. The treatment may take over 24 hours. There is a risk of
distortion, scaling and decarburization.
Heat: Slowly - Maximum rate of 400° F (220°C) per hour to a
temperature of 1550°F – 1600°F. (840°C – 870°C).
Hold: Preferably until the center of die is up to temperature as
indicated by a thermocouple in a hole in the die;
OR
For one hour per inch of thickness after furnace temperature stabilizes,
two hours minimum.
Cool: Slowly - Maximum rate of 60°F (33°C) per hour to 1100° F
(590°C) maximum. Then furnace cool.
Practical Details
Atmosphere Control
Notes & Precautions
Above 1100° F (590°C) Vacuum 100
microns min.
Support well to prevent sagging. Separate work to aid uniform
heating.
Below 1100°F (590°C) Air cool or
vacuum backing pump or inert gas at 1
bar
Endothermic gas mixture Nitrogen +
hydrocarbon gas Nitrogen + hydrogen
May use thermocouple attached to the tool.
Control atmosphere by dew point, CO2, or oxygen probe to
carbon potential of 0.4%. Surface discoloration will occur.
Inspection
Hardness: 235 HBW maximum
Surface Layers: If little or no material is to be machined from the surface, check for decarb
or carburization on a corner taken from the tool or on a sample of Special Quality die steel
H13 included with the load.
Austenitizing: Heating For Hardening
Three phases must be controlled: heating rate, hardening temperature and soaking time. All three will
depend on the equipment used, the geometry and size of the tool and mechanical properties aimed
for. The information below is in three parts. In the left column, the normal optimum aim values. In
the center column is more detailed information, ranges and alternative variations. The right column
gives technical details, precautions, etc.
Step Heating
• Load work into cold furnace, and heat at a rate not to exceed 400°F/hr.
(220°C/hr.)
• Heat to 1000° F to 1250° F (540°C-675°C)
• Hold until Ts-Tc < 200°F (110°C)
• Heat to 1550° F ± 50°F (845°C ± 25°C )
• Hold until Ts-Tc < 100°F ± (60°C) heat in “steps” holding
• Alternative preheating steps may be used at the discretion of heat treater or
toolmaker.
• Rapidly heat to a designated autenitizing temperature 1885°F ± 10°F (1030°C
± 5°C)
• The outside of the tool heats up faster than the inside. This creates stress due
to thermal expansion and phase changes.
• Aim to reach austenitizing temperature with the outside and inside temperatures as close as possible.
• This can be achieved by heating slowly but it is more efficient to heat in
“steps” holding temperature constant so that equalization can occur.
• Use the heating cycle which gives the least risk and is compatible the equipment available.
• The most sensitive temperatures are when the temperature reaches the
“critical” temperature of 1560°F (850°C) and close to austenitizing
temperature where grain growth can occur.
Austenitizing
1925°F
(1050°C)
1900°F
(1040°C)
High
Temperatures
• Better carbide
solution
• Risk of grain growth
• More temperature
resistance
• Less heat checking
• Lower impact
toughness
Choice of austenitizing temperature is a compromise
High temperatures give good carbide solution. The
alloy absorbed gives resistance to tempering in service
and a reduced rate of heat checking.
1885°F
(1030°C)
1875°F
(1025°C)
1850°F(1010°C)
1825°F
(995°C)
Normal Range
Low
Temperatures
Lower temperatures give less carbide and alloy
solution, less resistance to softening and heat checking.
• Less temper
resistance
• More heat checking
• Higher impact
toughness
• Less Distortion
Soaking Times
• With inserted thermocouples soak time shall be 30 minutes after Ts-Tc < 25°F
(15°C), or 90 minutes maximum after Ts=1885°F (1030°C), whichever
occurs first.
Good heating practice means that soaking is more effective. Soaking is performed
partly to equalize tool temperature but principally to dissolve carbides and
increase effective alloy content of the matrix. This does not start until close to
austenitizing temperatures. Too long a soak time increases the risk of sagging and
can cause grain growth. A more common fault is too little soaking.
Austenitizing: Equipment, Precautions
The heating and cooling rates, load capacity, and uniformity should be established for individual equipment by
instrumented tests before used on actual tools.
Additional thermocouples attached to the work will assist control, reduce risk and increase efficiency.
Vacuum
Furnaces
Characteristics
Precautions
• Good support – work is not moved during
whole heating and quenching cycle.
• Loading pattern is important. Do not charge very
large parts along with very small.
• Heating is by convection and radiation.
• Must control load size to assure that the minimum
quench rate can be achieved.
• Furnace has low thermal mass. Work is
charged into cold furnace, heating is rapid
and must be controlled.
• Good control over oxidation and
decarburization is typical
• Use thermocouples attached to tools, (Ts and Tc)
to measure actual tool temperature.
• Vacuum of 50 to 100 microns with leak rate below 5 microns per hr. Very low pressure may
cause loss of alloys from surface.
• Austenitizing temperatures usually chosen
towards top of recommended range.
Equipment
Class 1 Special Quality Die Steels Premium —
• Vacuum furnace with a minimum 2 bar backfill capability and a programmable furnace controller
linked to multiple load thermocouples.
• Sufficient cooling capability to cool die surface from 1885° F (1030 °C) at a minimum rate
of50°F/min. (28°C/min.).
• Furnace must be capable of isothermal hold during quench based on input from surface and core
thermocouples where interrupted quench is required.
Class 2 Special Quality Die Steels Superior —
• ‡ Vacuum furnace with a minimum 5 bar backfill capability and a programmable furnace controller
linked to multiple load thermocouples.
• Sufficient cooling capability to cool die surface from 1885°F (1030°C) at a minimum rate of
50°F/min. (28°C/min.).
• Furnace must be capable of isothermal hold during quench based on input from surface and core
thermocouples where interrupted quench is required.
‡ Modifications from NADCA Premium Quality for Superior Quality
Quenching: Practical Techniques
H13 has high hardenability so that pressurized gas quenching is satisfactory if properly controlled. A
minimum quench rate of 50°F (28°C) per minute is recommended.
Practical quenching techniques are described below but the heat treater must take into account equipment capability as well as size and geometry of the tool.
EQUIPMENT:
Vacuum Furnaces
Minimum 2 bar (premium
quality) or 5 bar (superior
quality) backfill capability
with a programmable
controller linked to multiple
load thermocouples.
Sufficient cooling
capability to cool die
surface (Ts) from 1885°F
(1030°C) to 1000°F
(540°C) at a rate of 50°F
(28°C) per minute.
Ts should reach 1000°F
(540°C) in less than 18
minutes.
DETAILS:
TECHNICAL
INFORMATION:
Single StepPressure gas quench until coreTc < 300°F
(150°C) – air cool until die surface Ts less
than 120°F (50°C). Temper immediately.
Quench rate is not solely a
function of quench pressure (2
bar, 5 bar etc.).
Quench rate depends on block
size, gas quenchant, velocity
and pressure, heat exchanger
efficiency and the furnace load.
In dies with ruling size greater
than 12” (300mm), it may not
be possible to achieve the
recommended quench rate with
all equipment.
Quenching: Toughness, Isothermal Quenching
Selection of a quenching rate is a “trade off”; faster quench rates give better metallurgical structure,
but increase distortion and the risk of cracking.
Isothermal or step quenching techniques can be used to optimize metallurgical properties while
reducing distortion and the risk of cracking.
Quenching Rate vs. Structure
Four quenching rates are shown: 1-fastest...4-slowest
1. Structure martensite. Ideal structure; quench rate is too fast to be practical.
2. Structure martensite plus grain boundary carbides. Achievable with small
tools.
3. Structure is martensite plus bainite plus grain boundary carbides. Practical
structure for medium to large tools. Curve shown is slowest recommended
and is achievable by pressurized gas quench.
4. Structure contains pearlite which reduces toughness and heat checking
resistance even though tempered hardness maybe correct.
Effect On Toughness
Effect of cooling rate versus toughness is shown for quench rates 2, 3 and 4
above. Faster quench rates result in increased toughness.
The cooling rate is a function of the size of the tool and the quenching power
of the equipment used. This relationship should be established before the heat
treatment begins.
Causes of Distortion
The surface cools faster than the core.
Above the martensite transformation temperature, the surface and corners contract faster than the
core, causing stresses which lead to distortion of large blocks.
At lower temperatures, the surface transforms to martensite or bainite and expands. The core is above
the transformation temperature and is still contracting. Stresses develop between these regions which
may distort or crack the tool.
The greater the temperature difference between the surface
and the core the greater the risk.
Isothermal Treatments
The initial cooling rate must be fast enough to minimize grain boundary
precipitation and to suppress the formation of pearlite.
Once below 1000° F (540° C), pearlite will not be produced. The tool may be
held at a constant temperature between 750°F - 850° F (400°C - 455°C) to allow
the surface and core to equalize before quenching further. Although the surface
still cools faster, the temperature difference is reduced so the stress is reduced.
Prolonged isothermal holds should be avoided to minimize the formation of
bainite.
Tempering - Practical
Directly after quenching, H13 is hard, brittle and highly stressed. It is vulnerable to cracking
spontaneously and must be tempered while still warm.
Further tempering will reduce the stress level and hardness but increase toughness and resistance to
cracking in service.
The final hardness level chosen depends on the application and is normally in the range of 42-50
Rockwell C.
This is achieved by careful control of temperature and time of tempering. A minimum of two tempers
is required to give dimensional stability and the correct metallurgical structure.
Hardness is not a good indicator of how a tool will perform. Tool life is more dependent on the
metallurgical structure of the steel.
Preparation:
Cool to surface temperature ≤ 120°F (50°C)
Select final hardness range and plan tempering
schedule.
Do not allow tool to cool below 90°F (33°C). Keep it away
from drafts, avoid rapid cooling.
Use data in Tempering – Technical section to help plan the
schedule. Use steel manufacturer’s data if available.
First Temper — Mandatory
Place tool in furnace at 800°F (425°C)maximum.
Hold at 1050°F (565°C) minimum for two hours
after core reaches setpoint. Allow 60 min. per in.
of thickness to reach heat.
Air cool to ambient temperature.
Furnaces may be vacuum, electric or gas, with temperature
control to give accuracy and uniformity of ± 10° F (±5°C)
maximum.
Some surface discoloration will occur but decarburization or
other metallurgical damage is not caused at these low
temperatures.
The tool is now safe to cool to room temperature and the
hardness should be measured.
Second Temper — Mandatory
Place in furnace at 800°F (425°C) maximum.
Hold for specified time - two hours minimum,
Minimum temperature 1025°F (550°C).
Air cool to Ambient temperature.
From the hardness value, determine which tempering curve to
use. See next page.
Select the temperature and time to give the required hardness.
Aim low; tempering can be repeated to reduce hardness, but if
the tool is softened too low it may have to be rehardened.
Check hardness in specified position.
Third Temper (If necessary)
Hardness still too high: Adjust tempering parameters and retemper.
A third temper may be required to “fine tune” the hardness
level.
Hardness correct: Tool can be finished and stress
tempered.
Even if hardness is correct, a stress temper after finishing has
the following advantages:
Note: May be combined with surface treatmentsoxiding, nitriding, nitrocarburizing, etc.
• It leaves an oxide coating to reduce soldering.
• Elevated temperature surface treatments can be used as the
stress temper.
Tempering: Technical
Tempering relieves internal quenching stresses and changes the metallurgical structure. A secondary
hardness peak occurs at around 950° F (510° C) caused by elimination of retained austenite and
formation of complex carbides. At higher temperatures, hardness drops and toughness increases.
The shape and position of the tempering curve is affected by composition, hardening temperature,
soak time and quench rate. Longer soak times are preferred over higher tempering temperatures to
promote better hardness uniformity.
Selection of Final Hardness
Final hardness is at the die caster’s discretion and should be selected
based upon steel grade, size, and die design. Do not temper below
1000° F (540° C). Lower hardness is specified for larger tools to
give better toughness.
High hardness (up to 52 HRC): Increased wear resistance and better
resistance to heat checking.
Low hardness (42 HRC): Greater resistance to gross cracking, but
less resistance to heat checking.
Tempering Curves
Curves shown are typical. Use steel manufacturer’s information when
available.
Response to tempering can vary with the steel composition and the
hardening schedule. Choose the curve which most closely fits the
hardness obtained after the first temper.
Example: As quenched, the tool was 56 HRC. After first (1000° F
[540°C]) temper, hardness dropped to 54 HRC. The center curve
should be used. To achieve 46 HRC, the second temper should be
1080° F (580° C).
Master Tempering Parameter
The Master Tempering Parameter is a useful way of judging the effect of time (although temperature is the
major factor). Time of tempering also affects the process. The Master Tempering Parameter permits one to
calculate the effect.
For example, to achieve 46 HRC, a small tool may be tempered at 1080° F (580°C) for four hours.
A large tool may have to soaked for 24 hours to attain uniformity. In this case, the temperature must
be reduced to 1025° F (550° C).
In both cases, the Master Tempering Parameter is 31727 and the final hardness is 46 HRC.
This graph gives the tempering parameter. This value may be used to calculate many combinations of
time and temperature.
Stress Tempering of Hardened Tools
This is a low temperature treatment that will not soften the body of a hardened and tempered tool but imparts useful
benefits e.g.:
It will reduce stress levels and temper rehardened layers in tools which have been welded or electrical discharge
machined (EDM).
On tools welded with maraging, stainless steel, or other welding rods, always follow the welding rod manufacturer’s
recommendations. If the welding was done using maraging rod, stress tempering can age harden the welds to
approximately that of the die. Used at regular intervals on production tools, stress relieving will reduce the rate of
heat checking and increase die life.
Use On
• Electrical discharge machined tools (EDM)
• Tools welded with H13 rods
• Tools welded with maraging, stainless or other welding rods
• Tools taken out of service
Heating Temperature
Holding (Soak)
Close temperature control is essential. Use vacuum, electric or gas furnace.
Cooling
Simple shapes: Take out and cool in still air.
Complex shapes: e.g. where section thickness varies by more than 3”(75mm)
Furnace cool to 800°F (430°C) maximum, to reduce cooling stress, take out and
Cleaning
air cool.
In both cases, cool as uniformly as possible in still air away from drafts to
prevent re-introduction of thermal stresses.
Do not remove the oxide layer since this will help prevent soldering in service.
Appendix 3:
Welding Die Casting Die Materials
Introduction
Die casting dies are welded for two primary reasons. The first is corrections or changes to dies before
they go into service. The second is for repair.
Welding of die casting dies involves risks such as cracking. The following general guidelines and
information are designed to help reduced potential defects. Note: A welded die will never be as good
as an unwelded one and a decrease in life expectancy may occur.
The Weld Zone
Heat Affected Zone
The weld area will be composed primarily of weld rod material. The structure will
consist of as-cast, quenched, and un-tempered material. The heat affected zone will
be composed of base material exposed to high heat from the welding process. This
zone will typically be softer than the base material.
Die Preparation for Welding
1. Remove Cracks: Remove all cracks completely by grinding or machining. The groove
shape should be in a “U” configuration. Avoid shapes with
sharp corners such as “V” shapes.
2. Clean Die: Clean the die by removing oxide, dirt’ and discolorations. Dry material
thoroughly.
3. Examine Die: Examine the die for residual cracks using crack detection
techniques
such as die penetrant, or magnetic particle inspec tion. If cracks are
found, follow step 1. above. Clean die after penetrant or magnetic
particle inspection.
Welding Procedure
1. Weld Materials: Weld materials should be chosen based on the material being
welded, the amount of weld required, and the desired properties of
the weld. When in doubt, contact the material supplier for details.
2. Preheat Die Block: Pre-heat die blocks to the recommended temperature for that
particular grade. Rules of thumb: Annealed material: 1000°F
Hardened material: 75% of the tempering temperature maintain
heat during welding.
3. Deposit Weld Bead: Deposit weld bead using equipment designed to produce good
clean welds.
Avoid welding with un-shielded electrodes
Maintain pre-heat temperatures during welding
4. Examine Weld:
5. Post-heat Die Block: Check the weld for undercuts or imperfections. Allow the
finished weld to cool slowly. Quenching the tool or
allowing the tool to sit un-tempered for a long period of
time may cause cracking.
Annealed dies: Re-anneal completely or temper at appropriate tempering temperature.
Hardened dies: Temper at 25 degrees F below the previous tempering temperature for
two hours minimum.
Pre-heat Guidelines
Pre-heating before welding will minimize the risk of cracking a die during welding. Pre-heating
allows the base material and weld to cool slowly from the welding temperature, minimizing thermal
shock.
Pre-heat temperatures for specific materials can be obtained from the material supplier or from the
weld material supplier.
A good rule of thumb for pre-heating hardened materials is to use a temperature roughly equal to
75% of the tempering temperature used during heat treatment of the tool.
Post-heat Guidelines
Welded tools should be post-heat treated by either fully annealing or tempering the entire weld zone.
The postheat treatment relieves stresses caused from the microstructural and thermal changes that
happen during the welding process.
The post-heat treatment should be done immediately following the welding process to minimize the
risk of stresses cracking the die.
NOTE: These processes are necessary to insure a quality weld. They should not be considered optional.
Charpy full size test impact specimen per ASTM A370, Fig. 11a.
Charpy full size test impact specimen per ASTM A370, Fig. 11a.
Figure 1b
Figure 1a
One or more metallograpic specimens for rating the annealed microstructure, microcleanliness, and microbanding on a longitdiual, short-transverse face.
Figure 2b
Figure 2a
Fig. 2a- Photo showing test coupon attached to the surface of an insert in preparation for hardening.
Fig. 2b- Sketch showing location and orientation of CVN and microstructure specimens to be removed from test
coupon after hardening.
Figure 3a
Figure 3b
Figure 4c
Figure 4d
Figure 4a
Figure 4b
To welding rod manufacturer’s recommendations.
50°F below highest tempering temperature (if known)
OR
1000°F (540°C)
Welding rod manufacturer’s instructions. (if available)
Soak 1/2 hr. per inch of maximum section with a minimum of two hours, after furnace reaches temperature.
OR
Until center of tool reaches specified temperature, by a thermocouple in the center of the tool.