HEAT
RESISTANT ALLOY
WELDING
James Kelly
Director of Technology
November, 2002
Heat Resistant Alloy Welding
1
Carbon Steel versus Stainless
3
Surface Preparation
Shielding Gases
Cold Cracking versus Hot Cracking
Distortion
Penetration
Fabrication Time
3
4
5
6
8
8
Welding Austenitic Alloys
9
Alloys Under 20% Nickel
Alloys Over 20% Nickel
10
11
Age Hardening Alloys
17-4
718
12
12
14
Welding Processes
15
Gas Metal Arc Welding
Flux Cored Arc Welding
Shielded Metal Arc Welding
Gas Tungsten Arc Welding
Plasma Arc Welding
Submerged Arc Welding
Resistance Welding
16
18
19
20
22
22
24
Weld Fillers
Suggested Weld Fillers
Guidelines for Dissimilar Metal Joints
Dissimilar Metal Welds Involving Carbon Steel
Schaeffler—de Long diagram (from AvestaPolarit)
Heat Resistant Weld Filler Chemistries
Heat Resistant Alloy Specifications, Base Metal
Weld Filler Specifications & Tradenames, American vs. German
25
26
27
28
30
31
32
Bolts
33
Weld Filler Consumption
34
References
35
Bulletin 200
©2002 Rolled Alloys
James Kelly
Revised November 2002. Issued March 10, 2001
Heat Resistant Alloy Welding is based on Rolled Alloys’ experience and information from
suppliers such as AvestaPolarit Welding and Sandvik AB. For additional copies of this
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Disclaimer Clause: The information in this document represents Rolled Alloys experience
and opinions, and is believed to be reliable. However, this material is not intended as a
substitute for competent professional engineering assistance which is a requisite to any
specific application. Rolled Alloys makes no warranty and assumes no legal liability or
responsibility for results to be obtained in any particular situation, and shall not be liable
for any direct, special or consequential damages. This material is subject to revision
without prior notice.
James Kelly
Director of Technology
November 26, 2002
WELDING AUSTENITIC HEAT RESISTANT ALLOYS
Welding heat resistant alloys is touched on in our Bulletin No. 115, and covered
in more detail in Bulletin Numbers 201 & 207 for RA330®, 202 for RA 253 MA ®,
209 for RA 353 MA ®, 211 for RA alloy X, and Bulletin 120 for RA333® welding
products. Corrosion resistant alloy welding is discussed in Bulletins 203, for alloy
AL-6XN®, 205 for 20Cb-3® stainless and 1071 for RA2205 duplex stainless.
These alloys are all weldable but they do require more shop time, and a
DIFFERENT approach than stainless, or carbon steel.
A few important rules:
1. Make reinforced, stringer beads. Do not weave. Shallow fillet welds or
broad, flat weld beads tend to crack down the center as they solidify. Cover
or fill in craters, to prevent them from cracking.
2. Keep heat input low. Do not ever preheat, except to dry moisture off of the
metal. Keep the temperature of the metal between weld passes low, below
212°F (100°C).
3. For RA330 specifically, use RA330-04 or RA330-80-15 weld fillers. Do not
use AWS E330 weld wire, as it will be crack sensitive. Do not try to weld
RA330 with stainless rods such as E308, E309, or E310 as they are very
likely to crack. E312 electrodes are often sold under various tradenames for
general shop repair welding and dissimilar metal welds. Because of its very
high Ferrite Number, E312 may make a sound weld in RA330. However,
E312 weldments are not suited for high temperature service. They embrittle
severely with exposure above 600°F (1100°C). At red heat E312 welds are
very weak, as well as brittle. E312 should be reserved for weldments to be
used near room temperature—never for austenitic heat resistant alloy.
1
4. Make full penetration weld joints. Incompletely welded areas will open up
as cracks during normal heat treat thermal cycles. Incompletely penetrated
weld joints are the most common cause of weld failures in high temperature
service. Weld joints in fans, in particular, must be fully penetrated.
Let us back up a bit, and first describe some of the differences between welding
carbon steels, and welding either stainless or nickel alloys. Then, we will cover
the important differences between stainless (under 20% nickel) and the higher
nickel alloys.
CARBON STEEL
This book is written assuming the reader understands how to weld ASTM A 36
structural steel (plain low carbon steel). Welding higher strength carbon steel
requires a somewhat different procedure, to ensure that the weld does not crack.
Welding is essentially a heat treating operation, as far as the steel is concerned.
In order to keep the weldment from cracking, it is important that it not form
martensite on cooling, i.e., that it not harden. This is not an issue with A 36 steel.
If the steel near the weld bead hardens, it is subject to hydrogen induced
cracking, within a few hours after the weld cools. This is also called “underbead
cracking”, because of its usual location. If there is no source for hydrogen—such
as moisture in the flux coating, shielding gas or surface contamination—this
cracking will not occur. Even without hydrogen, a hard martensitic zone in the
weldment may be unable to withstand impact loading in service.
As the carbon content increases, along with manganese, and especially when
chromium and molybdenum are added, the potential for hardening during
welding increases. To prevent hardening, the steel may be pre-heated a few
hundred degrees. On cooling, this pre-heated steel now has time to transform to
some phase other than martensite by the time it reaches room temperature. This
reduces hardness and internal stresses. Steel in the range of 0.30—0.50%
carbon usually requires some preheat, along with low hydrogen welding practice.
2
Preheat and interpass temperatures in the 200—400°F range cover most
medium carbon steels. Alloy steels such as 4130 may require preheat in the
300—450°F range, and 4140 350—500°F. ASTM A 387 Grade 11 preheat may
range up to450°F, with a required post-weld heat treatment range of 1150—
1350°F, air cool. The higher preheats are suggested for thicker sections.
This subject is covered well in the AWS Welding Handbook, Eighth Edition,
Volume 4, Part 2. Some pre- and post-heats are given in the ANSI/AWS D1.1
Structural Welding Code. More detail, including required post-weld heat
treatments, is in the Welding Research Council bulletin 191, March 1978.
High sulphur free-machining steels, such as the AISI 11xx and 12xx series, may
also be subject to solidification cracking. This is usually a crack down the center
of the weld bead, or crater cracking. A higher manganese weld filler is suggested
in such cases.
CARBON STEEL VERSUS STAINLESS
Some important differences between welding the carbon or low alloy structural
steels and the austenitic stainless and nickel alloys include:
A. Surface
Preparation
B. Shielding Gases C. Cold cracking vs Hot Cracking D.
Distortion E. Penetration F. Fabrication Time.
A. Surface Preparation
When fabricating carbon steels it is common practice to weld right over scale, red
rust and even paint. A so-called “mill finish” is a layer of blue-black oxide, or
scale, on the metal surface. Carbon steel weld fillers normally contain sufficient
deoxidizing agents, such as manganese and silicon, to reduce these surface iron
oxides back to metallic iron. The resultant Mn-Si slag floats to the weld surface.
Iron oxide, or “scale”, melts at a lower temperature, 2500°F (1371°C)1, than
does the steel itself. One can see this in a steel mill when a large ingot is
removed from the soaking pit for forging—the molten scale literally drips off of the
white hot steel.
Stainless steel, by contrast, must be clean and free of any black scale from hot
rolling, forging or annealing operations. Of course, stainless normally comes
from the mill with a white or bright finish. A few users of heat resistant alloys,
though, do prefer “black plate”, that is, plate with the mill hot rolling scale intact.
This scale is thought to provide additional environmental protection at red heat.
3
Stainless steel melts at a lower temperature than does its chromium oxide scale,
and the stainless weld filler chemistry is not capable of reducing this scale back
to metallic chromium. As a result, with gas shielded processes it is difficult to get
the weld bead to even “wet”, or stick to, a scaled piece of stainless. With SMAW
a weld of sorts can be made, as the coating fluxes away most of the scale.
The need to clean or grind down to bright metal is more likely to cause trouble
when stainless is being joined to carbon steel. That is because in this dissimilar
metal joint it is necessary to grind that carbon steel to bright metal, on both sides
of the joint, free of all rust, mill scale, grease and paint. Incidentally, the best weld
fillers for this particular joint, to minimize the hard martensitic layer on the steel
side, are alloy 182 covered electrode, ENiCrFe-3, or alloy 82 bare wire,
ERNiCr-3. Alloy 62 bare wire, ERNiCrFe-5, and ENiCrFe-2 covered electrodes
are also appropriate. E309 electrodes are commonly used but may leave a hard
layer on the steel side, subject to cracking in service.
Both those stainless and high nickel alloys which are designed for corrosion
resistance are produced to very low carbon contents, less than 0.03% and
sometimes less than 0.01% carbon. Any higher carbon will reduce the metal’s
corrosion resistance if welded. For this reason it is necessary to clean these
alloys thoroughly of all traces of grease and oil before welding. Also the very
high nickel alloys, such as 400 alloy (Monel® , UNS N04400), or commercially
pure nickel 200/201, are sensitive to weld cracking from the sulphur in grease.
Metallic zinc paint is a common way to protect structural steel from corrosion.
Even a small amount of that zinc paint overspray on stainless or nickel alloy will
cause the metal to crack badly when welded. Consider completing all stainless
welding before painting the structural steel in the area.
Keep inorganic zinc paint away from any austenitic alloy!
B. Shielding Gases
For gas metal arc welding (a.k.a. MIG) carbon steel the shielding gases are
usually 95% argon 5% oxygen, 75% argon 25% CO2 (carbon dioxide) or 100%
CO2. These are suitable with carbon or low alloy steel welding wire but far, far
too oxidizing for use with stainless or nickel alloys. It is not unknown to hear the
complaint “. . . clouds of red smoke are coming off when I weld your 310. . .
heavy spatter. . .” and then learn that the shielding gas used was 75%Ar
25%CO2. A fine gas for carbon steel but absolutely not for stainless.
One exception to this high CO2 prohibition is when using flux cored wire,
either stainless or nickel alloy. Some of these cored wires are specifically
formulated to run best with 75%Ar 25%CO2.
4
Stainless and nickel alloys have been GMAW spray-arc welded with 100%
argon. Weldability may be greatly improved by adding from 10 to 20% helium.
75% argon 25% helium is used, although it will not give a true spray-arc. At this
lower level of argon, arc transfer somewhat resembles globular transfer.
The weldability of stainless steel is impaired by the stable oxide film which exists
on the metal. A helium addition provides a little hotter arc, which helps to burn
away that oxide. A very small amount of CO2, about 1% or less, tends to stabilize
the arc (prevents arc wander). Two proprietary gases from Air Liquide, ArcalTM
121 and BlueShield TM 20, are designed specifically for stainless and nickel alloy
GMAW.
The heat resisting alloy RA 602 CATM requires a nitrogen addition to the shielding
gas to avoid hot cracking. The recommended gas is CRONIGON® HT, a
patented gas available from AGA and HOLOX in the USA, and from Linde Gas
AG in Europe. This is an argon-based gas with significant nitrogen, and small
additions of active gases. Strictly speaking, it is for “MAG” welding, Metal Active
Gas, in European terminology. CRONIGON HT may also be used for other highly
alloyed heat resistant grades. It is required for gas metal arc welding RA 602 CA.
Short-circuiting arc welding generally requires the 75%Ar 25%He mix, but a
90%He 7 1/2%Ar 2 1/2%CO2 “tri-mix” is commonly used. Carbon dioxide helps
reduce “arc wander”, by increasing emissivity of electrons from the work surface.
The potential for carbon pick-up from the CO2 is not an issue when welding heat
resistant alloys. Short-circuiting arc welding is used for sheet gages. With plate it
may be necessary to grind starts and stops to minimize lack of fusion defects.
C. Cold Cracking versus Hot Cracking
Carbon steel weldments may harden, and crack, as they cool from welding. High
hardness, and the resulting cracking, are more likely when the steel contains
over 0.25% carbon. Alloying elements which increase hardenability, such as
manganese, chromium, molybdenum, etc., can make steels of lower carbon
content also harden. Hydrogen pickup from moisture in the air causes underbead
cracking in steels that harden as they cool from welding. To prevent such
cracking the steel is usually preheated before welding, to retard the cooling rate
of the weld and avoid martensite formation. Postweld heat treatment, or stress
relief, is also applied to some steels, or for certain applications .
Austenitic stainless and nickel alloys do NOT harden no matter how fast they
cool from welding. So, it is not necessary to preheat stainless, nor to post weld
heat treat it. As a matter of fact preheating stainless, beyond what may be
necessary to dry it, can be positively harmful. Stress relief 1100-1200°F (600650°C) as applied to carbon steel is only partially effective with stainless or nickel
alloys, and may be damaging to the aqueous corrosion resistance.
5
Stainless steel welds generally do not crack unless contaminated. This may be
from a surface smear of zinc or copper, less commonly by aluminum.
High nickel alloys are susceptible to cracking in restrained joints, or heavy
sections. This is a hot tearing (solidification cracking), not a cold crack. That is,
the weld bead tears rather than stretching, as the weld bead contracts upon
solidifying. This hot tearing/hot cracking has nothing to do with hardness. The
faster a nickel alloy weld freezes solid, the less time it spends in the temperature
range where it can tear. For this reason preheating, which slows down the
cooling rate, is actually harmful, as it permits more opportunity for hot tearing to
occur.
D. Distortion2,3
Stainless steel has poor thermal conductivity, only about one fourth that of plain
carbon steel, such as A 36 structural steel. This means the welding heat tends to
remain concentrated, rather than spread out. Stainless also expands with heat
about half again as much as does carbon steel. The combination of these two
factors means that stainless or nickel alloy fabrications distort significantly more
than similar designs in carbon steel.
Among other things, tack welds need to be more closely spaced in stainless or
nickel alloy welds. Welds should be sequenced about the ne utral axis of the
fabrication to balance welding stresses, hence minimize distortion. Back step
welding is also helpful.
Tacks should be done in sequence, as well
1
6
4
7
3
8
6
5
9
2
If the tacks are simply done in order from one end, the plate edges close up
1
2
3
4
5
Weld runs should be done symmetrically about the joint's center of gravity to balance
stresses
12
10
8
5
4
2
1
3
6
7
11
9
Double V - joint
1
3
4
2
Flange to cylinder
7
Back step welding helps reduce distortion
3
2
1
E. Penetration
The arc will not penetrate a stainless nearly as deeply as it will carbon steel.
Penetration is even less in high nickel alloys. Inc reasing welding current will not
solve the problem! Stainless, and especially nickel alloy, joints must be more
open, single or double beveled, with a root gap, so that the weld metal may be
placed in the joint. Lack of weld penetration is the single most important reason
why austenitic alloy weldments fail in high temperature service.
F. Fabrication Time
Cleanliness, distortion control measures, maintaining low interpass temperatures
and even machining add up to more time spent fabricating stainless than carbon
steel. A shop experienced with stainless may require 1.6 times as long to
complete the same fabrication in stainless, as in carbon steel. A good carbon
steel shop encountering stainless or nickel alloys for the first time can easily
spend twice as long, maybe even three times as long, to do the stainless
fabrication, as it would the same job in carbon steel.
8
WELDING AUSTENITIC ALLOYS
The fundamental problem to be overcome in welding austenitic nickel bearing
alloys is the tendency of the weld to hot tear upon solidification. This matter is
readily handled in alloys under about 15% or so nickel. In these stainless grades
the weld metal composition is adjusted, usually by slightly higher chromium and
reduced nickel, to form a small amount of ferrite upon solidification.
The amount of ferrite in the weld may be measured magnetically, and is reported
as a Ferrite Number, FN. This ferrite acts to nullify the effects of the elements
responsible for hot cracking in the Ni-Cr-Fe austenitics. These elements are
chiefly phosphorus, sulphur, silicon and boron.
In higher nickel grades, over about 20% nickel, it is metallurgically impossible to
form any measurable amount of ferrite. Therefore other means of minimizing hot
cracking must be used. Foremost among these is to use high purity raw
materials in the manufacture of weld fillers. Phosphorus cannot be removed from
stainless steel by current refining methods. Whatever phosphorus comes from
the raw materials, mostly from the iron, will end up in the weld wire. Low silicon,
when feasible, is desirable. Sulphur is easily removed by the AOD refining
process.
Phosphorus, in particular, must be kept below 0.015% in the weld wire itself.
Certain alloy additions such as manganese, columbium (niobium), molybdenum
and carbon serve in one way or another to reduce the austenitic propensity for
weld hot cracking. Manganese ranges from about 2% in AWS E310-15 covered
electrodes to 5% in RA330-04 wire & electrodes and 8% in alloy 182 (ENiCrFe-3)
covered electrodes.
A low level of columbium, such as the 0.5% in 347 stainless, is harmful, whereas
2 to 4% columbium is quite beneficial in many nickel base weld fillers.
Molybdenum isn’t necessarily added specifically for weldability but it does
enhance the properties of RA333-70-16 covered electrodes. High molybdenum
may be responsible for the popularity of the various “C type” electrodes (15Cr
15Mo balance Ni) in repair welding. 2% Mo contributes to 316 as being the most
weldable of the stainless steels.
Carbon is slightly elevated in 310 weld fillers, to about 1/10%. The one welding
electrode specifically using high carbon to promote sound welds is the heat
resistant grade RA330-80-15 (UNS W88338). A weld deposit chemistry of some
0.85% carbon permits this electrode to make sound welds in both wrought and
cast 35% Ni high silicon heat resistant alloys.
9
The distinction between the lower nickel stainless grades, which depend upon
ferrite to ensure weldability, and the high nickel alloys, which require high purity
weld fillers, is an important one to remember. Most ferrite containing (stainless)
weld fillers are useless with nickel alloy base metal, as dilution of the weld bead
with nickel from the base metal eliminates this ferrite. Likewise a high purity
nickel alloy weld filler, such as ER320LR, may be not quite so crack resistant
when contaminated by phosphorus from use on cast alloy 20 (CN-7M), 316L or
carbon steel base metal.
With respect to welding there are some distinctions between those alloys
intended for use above 1000°F (540°C), and those meant for aqueous corrosion
service. One difference is in carbon content. Corrosion resistant grades are
generally limited to 0.03% carbon maximum, and typically much lower. They may
have small additions of columbium or titanium. Restriction of carbon, or tying it up
with a stabilizing element (Cb or Ti) is necessary to prevent heat affected zone
(HAZ) intergranular corrosion and polythionic acid stress corrosion cracking
(PASCC) due to carbide precipitation.
Heat resistant alloys by contrast typically require 0.04 - 0.010% carbon for good
hot strength. RA 602 CA is even higher, near 0.2%, while RA330HC belt pin
stock and the cast heat resista nt alloys have a nominal 0.4% carbon. In the
absence of a wet corrosive environment a little intergranular carbide precipitation
is not particularly harmful.
In both classes of material, incompletely penetrated welds and open crevices
must be avoided in fabrication design. Serious aqueous corrosion can begin in
crevices. In high temperature carburizing service, crevices are where carbon
(soot) can deposit, grow, and pry the joint apart like tree roots in rock.
For either heat or corrosion resistant alloys, weldability alone is not the entire
issue. The weld filler must also have the mechanical and environmental
resistance required for its intended service. Usually this point is addressed in
fabricating corrosion resistant alloys, where a higher alloy weld filler is often
used. It is sometimes overlooked in heat resistant alloy fabrication. It is even
less often considered in repair of high temperature alloy fixturing.
ALLOYS UNDER 20% NICKEL
Most austenitic grades containing less than 20% nickel are joined with weld fillers
that utilize perhaps 4-12 FN (Ferrite Number) to ensure weldability. Wrought
heat resistant alloys with 20% or less nickel include 304H, 321, RA 253 MA,
RA309, RA310. All save RA310 depend upon some level of ferrite in the weld
bead to prevent solidification defects.
10
Ferrite does a good job of ensuring sound weldments. The covered electrodes
used to weld stainless steel are almost invariably AC/DC titania coated,
designated either –16 or –17. Such electrodes have good welder appeal, and
run exceptionally well when direct current is used.
RA310 stands in an odd position between the stainless and the nickel alloys.
RA310 welds contain no ferrite—see page 28. Neither do they contain any
particular alloy addition for weldability. Not surprisingly, 310 welds have a
reputation for fissuring. The current AWS specification for ER310 weld wire
permits 0.030% phosphorus maximum. This is too high. For ER310 welding wire
to be of practical use the phosphorus must be kept under 0.015% maximum.
Because 310 is a difficult alloy to weld, the preferred choice in E310 covered
electrodes are the DC lime-type electrodes, usable only with direct current. The
lime coating tends to ameliorate the effects of impurities such as phosphorous.
Not so with a titania coating. An E310-16 AC/DC electrode is a poor choice for
welding 310 base metal.
In the past it was possible for 310S (UNS N031008) base metal to contain as
much as 1.50% silicon in the ASTM/ASME specifications. Heats on the high side
of silicon and phosphorus were a problem to weld (Rolled Alloys had traditionally
limited silicon in RA310 to 0.75% max).
With the advent of 310H (UNS S31009), ASTM limited silicon to 0.75% maximum
as well. In practice all 310 varieties now melted in North America have less than
0.75% Si, which is of some benefit to weldability.
ALLOYS OVER 20% NICKEL
Heat resistant alloys in this category include RA800H/AT, RA330®, RA 353 MA ®,
803, alloy X (UNS N06002), RA333®, 617, Haynes alloys HR-120, 230 and 214,
601, RA 602 CATM, 600, and Nimonic® 75. The cobalt alloys N155, 556, 188,
L605, and HR-160 may be treated in similar fashion with appropriate weld fillers.
Many nickel alloys are joined with matching composition weld fillers, modified
only by restrictions on phosphorus, sulphur, silicon and boron. Titanium may be
added for deoxidation. Other nickel weld fillers contain manganese, high carbon,
columbium or molybdenum to improve resistance to fissuring and hot cracking.
Such chemistry modifications are rarely as effective as is the use of ferrite in the
lower nickel stainless weld fillers. Welding technique and attention to cleanliness,
then, become increasingly important to ensure the soundness of fully austenitic
welds. Techniques include reinforced, convex stringer beads and low interpass
temperature. Cleanliness includes NOT using oxygen additions to the GMAW
shielding gases for nickel alloys.
11
It is worth repeating here that high nickel alloys cannot be reliably welded using
stainless steel weld fillers. Stainless steel (308, 309, etc.) depends upon a small
amount of deposited ferrite to ensure a sound weld. When a stainless rod is
deposited on a high nickel base metal, the resultant weld bead will include some
nickel from the base metal. It may be possible for that additional nickel to make
the weld bead fully austenitic, with no ferrite at all. Without ferrite, the stainless
weld bead, already typically a little high in phosphorus, may crack down the
center. See the diagram on page 28, to calculate ferrite number.
While stainless steel welding electrodes are usually AC/DC titania, nickel alloy
covered electrodes are often produced with a lime-type DC coating. Shops
accustomed to stainless welding need to remember to switch to direct current,
and to pay attention to polarity. Normally one uses Reverse Polarity, that is,
electrode positive, workpiece negative.
RA333-70-16 is an exception among the high nickel electrodes, having an
AC/DC titania coating. For this reason it runs well, and tends to be readily
accepted by welders.
AGE HARDENING ALLOYS
The two age hardening (also called precipitation hardening) alloys to be covered
here are 17-4PH® stainless, and the nickel alloy 718.
17-4PH metallurgy and welding
17-4PH is a low-carbon martensitic stainless steel. It is strengthened by a four
hour aging (precipitation hardening) treatment. 17-4PH is normally sold in the
annealed condition. Usually we think of “annealed” as meaning soft and ductile.
Annealed 17-4PH isn’t especially hard, typically about Rockwell C30. But since
“annealed” 17-4PH is really untempered martensite, it has very low ductility and
notch impact strength.
Light gage 17-4PH may be welded in the annealed condition. This is followed by
a post-weld precipitation hardening treatment of 4 hours. Temperature should be
in the range of 950 to 1150°F.
When making welds in heavy cross-sections, it is generally best to first age the
metal to condition H-1100 or H-1150. This makes the base metal more ductile,
and less likely to crack from welding stresses. The heat of welding will leave
some zone of the base metal in the annealed condition. Likewise, any matching
17-4PH filler metal will be in the annealed condition. So after welding, the
fabrication should again be aged for 4 hours, to regain strength and ductility in
the weld area. For heavy sections, treatments in the 950 to 1025°F range are
often used.
12
From the strict metallurgical viewpoint, it would be preferable to give the welded
fabrication a 1900°F solution anneal. Then cool to room temperature, and age
harden. However that 1900°F treatment becomes quite impractical with a large
fabrication. In practice, most 17-4PH fabrications are simply age hardened only,
after welding.
For dissimilar welds involving 17-4PH stainless fillers such as 309 have been
used. The preferred fillers are alloy 82 (ENiCrMo-3) bare wire or the covered
electrodes 182 (ERNiCrFe-3) and INCO-WELD® A (ENiCrFe-2). These high
nickel fillers have thermal expansion coefficients more closely matching those of
the 17-4PH. Their lower strength and good ductility reduce the welding strains on
the base metal, as the weldment cools and contracts.
Heat treatments for 17-4PH and their designations
Designation
Processing
Condition A*
Heated at 1900°F ± 25F for 12 hour, air cooled or oil
quenched to below 90F. This is the anneal, or solution
treatment, normally performed by the steel mill.
H 925, H 1025,
H 1075, H 1100
Condition A material which has been heated at the
specified temperature for 4 hours and air cooled.
H 1150-M
Condition A material heated at 1400 ± 25°F for 2 hours, air
cooled, then heated at 1150 ± 15°F for 4 hours and air
cooled. This heat treatment is used for maximum toughness,
and for cryogenic applications to –320°F.
* For most applications, 17-4PH should not be used in Condition A. This is true even though the
desired tensile strength may be provided by that condition. While the alloy is relatively soft in
Condition A, the structure is untempered martensite that has low fracture toughness and ductility,
with poor resistance to stress-corrosion cracking. Superior service performance is assured by
using 17-4PH in the age hardened condition.
Weld Fillers for 17-4PH
17-4PH is welded with fillers similar, but not identical, to the base metal. The
specifications for matching covered electrodes are AWS A5.4 E630, UNS
W37410, AMS 5827. Bare welding wire is in AWS A5.9 ER630, UNS S17480,
AMS 5826
13
718 Metallurgy and Welding
718 is a fully austenitic nickel alloy. It is strengthened by a precipitation
hardening (a.k.a. age hardening) reaction involving columbium. A commonly
used heat treatment is to anneal 1700-1850°F, rapid air cool or quench. This is
the condition in which 718 normally is provided by the mill or by Rolled Alloys.
Strength is achieved by aging at 1325°F for 8 hours, furnace cool to 1150°F, hold
at 1150°F for a total time of 18 hours in the furnace, then air cool.
Cleanliness of both the base metal and the weld wire affect welding this grade.
Freshly cleaned 718 may be covered with plastic wrap to maintain cleanliness
before welding. E-Grade 718 weld wire GTAW wire with thoroughly mechanically
cleaned surface is available from stock for critical welding applications.
Heat input and interpass temperature should be low. Do not preheat. Make small
stringer beads, and remove all oxide film before depositing the next bead.
718 may be welded either in the annealed, or in the precipitation hardened
condition. For many non-aerospace applications the only heat treatment required
after welding is the 1325/1150°F aging, to strengthen the weld bead and base
metal near the fusion line. This does leave a zone near the weld in an over-aged,
relatively low strength, condition. To maximize the properties of the weldment it is
necessary to re-anneal sheet gauges 1700-1850°F, followed by 1325/1150°F
age.
For highly restrained joints where some reduction in weldment strength is
permitted, fillers such as 625 (ERNiCrMo-3) or Hastelloy W (ERNiMo-3) are
sometimes used. 625 offers more strength than alloy W.
GTAW shielding is commonly argon torch and back-up gas, for material up to
1/4” thick. Helium torch and back-up gas is preferred for heavier sections.
Weldments in 718 are sub ject to formation of a brittle Laves phase during
solidification. This reduces the strength and toughness of weldments. The effect
is more pronounced in plate gauges (over 3/16”) than in sheet. Solution
annealing 1900-1950°F should re-dissolve the Laves phase and increase the
tensile ductility of the weldment. Following this higher temperature solution
anneal the normal aging treatment is 1400°F 10hours, furnace cool to 1200°F,
hold at 1200°F for a total aging time in the furnace of 18 hours, air cool.
For highly restrained joints where some reduction in weldment strength is
permitted, fillers such as 625 (ERNiCrMo-3) or Hastelloy W (ERNiMo-3) are
sometimes used. 625 offers more strength than alloy W.
14
GTAW shielding is commonly argon torch and back-up gas, for material up to
1/4” thick. Helium torch and back-up gas is preferred for heavier sections.
Weldments in 718 are subject to formation of a brittle Laves phase during
solidification. This reduces the strength and toughness of weldments. The effect
is more pronounced in plate gauges (over 3/16”) than in sheet. Solution
annealing 1900-1950°F should re-dissolve the Laves phase and increase the
tensile ductility of the weldment. Following this higher temperature solution
anneal the normal aging treatment is 1400°F 10hours, furnace cool to 1200°F,
hold at 1200°F for a total aging time in the furnace of 18 hours, air cool.
WELDING PROCESSES
Five different arc welding processes are generally used with heat resisting alloys.
The most common, in North America, is Gas Metal Arc Welding (GMAW),
formerly known as MIG (Metal Inert Gas), using spooled bare wire filler. Next in
popularity is Shielded Metal Arc Welding (SMAW), or just plain “stick” welding,
with covered electrodes. The least volume of work is done by Gas Tungsten Arc
Welding (GTAW), formerly called TIG (Tungsten Inert Gas) and originally trade
named Heliarc®. Two other methods are Plasma Arc Welding (PAW) and
Submerged Arc Welding (SAW). In addition resistance welding, particularly
cross wire resistance welding, is often used in heat resistant alloy fabrication.
There are two basic types of welding machines, Constant Current, and Constant
Potential. A constant current machine is used for GTAW (TIG) and SMAW (stick)
welding. Practically speaking it won’t work for GMAW (MIG) welding.
The dial on a Constant Current machine reads in amperes, and the current is
regulated by this dial. Constant Potential (voltage) machines are used for GMAW
(MIG) welding. They don’t work well with covered electrodes (SMAW). The dial
regulates voltage, and is marked with numbers in the 20-40 range.
15
Gas Metal Arc Welding
In this process, the weld filler metal is bare wire. The most common size is
0.045” (1.14 mm), though 0.035” (0.89 mm) and 0.0625” (1.59 mm) are also
stocked, typically on 25-30 pound (11-14 kg) spools.
Wire is fed continuously through a hollow cable to the welding gun, where it
makes electrical contact. The arc between weld wire and workpiece melts the
metal. Molten weld filler transfers as either a spray of fine drops, or as larger
globs. The metal is protected from oxidation by a continuous flow of shielding
gas, usually argon, through the weld torch and around the wire. Current is
always Electrode Positive (DCRP, direct current reverse polarity).
The GMAW process is fast and well suited to high volume work. It can be
automated, as for welding long tubes. Welding with relatively high current, about
190-220 amperes for 0.045” (1.14 mm) wire, and argon shielding is used for the
spray-arc transfer mode. In this mode, molten weld metal crosses the arc to the
work as a fine spray. At lower current, roughly 100 amperes for 0.035” (0.89
mm) wire, with 75% argon 25% helium shielding, the molten weld metal
transfers as large, individual drops. This is known as short-arc, or short-circuiting
arc, welding, characterized by a noisy arc, spatter, and low heat input.
Choice of shielding gas is important. First, do not use oxygen additions to the gas
when welding nickel alloys and NEVER use 75% argon 25% carbon dioxide for
GMAW welding either stainless or nickel alloys. Oxygen above 2% starts burning
out major alloying elements. CO2 above 5% adds carbon to the low carbon
stainless grades. Although very small amounts of CO2 may be used in argon, at
above 15% CO2 in argon the arc transfer mode is no longer spray, but rather a
hot globular transfer with a great deal of spatter.
For spray-arc welding the most common gas has been 100% argon. To improve
bead contour and reduce arc wander, respectively, from 10 to 20% helium and a
small amount of CO2 may be added to the argon. One such gas from Air Liquide,
their BlueShield TM 20 is a nominal 81% argon 18% helium and 1% carbon
dioxide. A mix of 75%Ar 25%He is also used, although the transfer mode will
then not quite be a true spray-arc. For short-circuiting arc transfer 75% Ar 25%
He is used, as is the commonly available 90% He 7 1/2% Ar 2 1/2% CO2 .
Because the welding wire must be pushed through a cable, ranging from 10 to 15
feet (3 to 4 1/2m) long, there may be feeding problems. The result can be a
tangle of wire known, appropriately, as a “bird’s nest”. This shuts down the
operation until the welder clears it. The care with which the filler metal is wound
on the spool does affect how smoothly the wire feeds. The manufacturer, then,
is often blamed for feeding problems. However, more often than not, proper
attention to machine set up will ensure freedom from “bird’s nests”.
16
Smooth feeding depends on the cast and helix of the spooled wire. Both AWS
A5.9 for stainless, and A5.14 for nickel alloy wire require cast and helix of wire on
12 inch (300mm) spools to be4 “such that a specimen long enough to produce a
single loop, when cut from the spool and laid unrestrained on a flat surface, will
do the following:
1. Form a circle not less than 15 in. (380mm) in diameter and not more than 50
in. (1300mm) in diameter
2. Rise above the flat surface no more than 1 in. (25mm) at any location” Our
RA 253 MA wire, for example, typically has 36 to 42 inch (915 to 1070mm)
cast and 1/2 inch (12.7mm) helix.
The following discussion is based on information from Ron Stahura, Avesta
Welding Products, Inc.: Many heat and corrosion resistant alloy weld wires are
much higher in strength than stainless wire (e.g., ER308, ER316L), and therefore
require more care to feed smoothly. When tangling, or bird’s nest, occurs the
first thing we suggest is to examine machine set-up. Does this problem occur on
more than one machine? How long is the cable—the longer the cable, the more
tension in the feed rolls. Are the feed rolls, inlet guide and outlet guide all clean?
Incidentally, V groove rolls are used with solid stainless/nickel alloy wire, U
groove for copper or aluminum, and serrated rolls for flux cored wire.
Use minimal pressure on the feed rolls—more is not better. A rule of thumb is to
hold the wire between the fingers as it enters the feed rolls. If you can hold it
back, there is not enough pressure. Adjust the pressure until you just can not
hold the wire, then give it another half turn beyond that.
For 0.045 inch (1.14mm) wire, consider using a 1/16 inch (1.6mm) conduit,
instead of a 0.045”/1.14mm conduit. The oversize conduit won’t hurt, and will
give more room for the wire to flex.
A heavy duty contact tip is preferred instead of a standard contact tip. When
spray-arc welding the tip runs hot, and the wire may swell into the tip and jam it.
The heavy duty tip simply has more copper, and can handle more heat.
17
Gas Metal Arc Welding GMAW, a.k.a. “MIG”)
Flux Cored Arc Welding
FCAW is similar to GMAW except that the wire used is tubular, with flux and
metal alloy powders inside. Because this wire contains its own flux, gas
shielding may be 75% Argon 25% CO2, even with nickel alloys!
The advantage of flux cored wire is greater overall productivity than when solid
wire is used, and the arc is “softer”. Flux cored wire is sensitive to moisture pickup, and should be left in its sealed plastic bag until ready to use.
Flux Cored Arc Welding (FCAW)
18
Shielded Metal Arc Welding
Covered welding electrodes consist of an alloy core wire and a flux coating. The
core wire is usually, but not always, similar to the base metal in composition.
Often, however, various alloy additions are made in the coating, so that the weld
bead chemistry will not be the same as the chemistry of the core wire itself.
In the case of RA330-80-15 or -16, and most RA330-04-15 covered electrodes, a
35%Ni 15%Cr AWS E330 core wire is used. The additional carbon, manganese
and chromium required in the weld deposit are added to the flux coating. During
welding, these additions melt in and adjust the chemistry of the weld bead to the
specified composition. RA333-70-16 electrodes do use RA333 core wire. The
electrode coating does four basic jobs:
1.
Provides a gas that shields the metal crossing the arc from oxidation
2.
Produces a molten slag which further protects the molten weld bead from
oxidation, affects out-of-position weldability, and controls the bead shape
3.
Adds more alloying elements, such as manganese, carbon or chromium
4.
Promotes electrical conductivity across the arc and helps to stabilize the
arc, important when alternating current (AC) is used
There are three types of coatings used on Rolled Alloys electrodes. Coating type
is designated by a “-15”, a “-16”, or, more recently, a “-17”.
DC lime-type coatings are designated -15. RA330-04-15 and RA330-80-15 both
have DC (Direct Current) lime coatings. This means that these electrodes can
ONLY be used with direct current. Normally the current is reverse polarity
(DCRP, or Electrode Positive). That is, the electrode is the positive, and the
workpiece is negative electrical pole of the circuit. Electrons are emitted from the
work and go toward the electrode.
If the welder attempts to use a DC electrode with an AC (alternating current)
setting on the welding machine, the electrode simply won’t run. He will not be
able to keep the arc going. This would seem to be very basic knowledge, but
every couple of years someone complains that RA330-04-15 “won’t run”. Well, it
will indeed run on DC current, but not on AC. That is, not unless that AC current
is turned up so high that the whole electrode glows red and the coating spalls off.
The AC/DC titania coated electrodes are designated -16. RA333-70-16 and
RA330-80-16 both have AC/DC coatings. These electrodes may be used with
19
alternating current (AC). They ha ve compounds of potassium and titanium in the
coating which stabilize the arc. This means it will not extinguish itself as the
current reverses direction (and goes to zero) 60 times a second on normal 60
cycle current (50 cycle in Europe).
AC/DC electrodes may also be used with direct current, DC. In fact, they run the
best when using DC. Weld repair with RA333-70-16 covered electrodes is best
accomplished using direct current, reverse polarity (DCRP).
The newer coating designation is -17, which also operates on alternating
current, as well as on direct current. At this writing RA 253 MA-17 is the only
electrode we stock with this coating.
Remove all slag or flux after welding!
If there is any residual weld flux on the fabrication, that flux will continue to do its
job when put into high temperature service. The result will be one form or another
of hot corrosion, dependent upon the atmosphere. Fluoride containing fluxes are
wonderful getters for sulphur. Residual flux may lead to local sulphidation attack
even though the sulphur level is quite low in the surrounding atmosphere. This
has been well illustrated in work published by the former Huntington Alloy
Products Division, now Special Metals. In carburizing environments, Rolled
Alloys’ experience has been that the flux will promote rapid carburization, hence
embrittlement. In carbon and sulphur free oxidizing environments that flux will
increase local oxidation rates.
Gas Tungsten Arc Welding
In GTAW, the arc is struck between the workpiece and a tungsten electrode,
which remains unmelted. The argon shielding gas, which protects both the hot
tungsten electrode and the molten weld puddle, is brought in through a nozzle or
gas cup which surrounds the electrode. This process used to be called TIG
(Tungsten Inert Gas), and was originally patented as Heliarc ®, a name still used
occasionally.
For both stainless and nickel alloys the current used is DCSP, direct current
straight polarity. The work is electrically positive and the tungsten electrode is
the negative electrical pole. The electrode is usually thoriated tungsten, that is,
tungsten metal with 1 or 2% thorium oxide added to improve the emissivity of
electrons. Rare earth oxides are also used. For welding aluminum the electrode
is pure tungsten, used with AC (alternating current).
20
Shielding gas is normally pure argon or helium. Argon is used for manual
welding. A helium addition may be used for automated welding, where a hotter
arc is preferred. No oxygen or carbon dioxide can be tolerated or the tungsten
electrode would literally burn up. For the new heat resistant nickel alloy
RA 602 CA, it is necessary to add 2.5% nitrogen to the argon. In this particular
alloy, nitrogen reduces hot cracking susceptibility.
The arc between the tungsten electrode and the work is what melts the
workpiece. The weld filler metal is fed by hand into the molten puddle. GTAW
weld wire for heat or corrosion resistant alloys is sold as 36” (914 mm) straight
lengths of bare wire, in 10 pound (4 1/2 kg) tubes.
The welder has the most control when using gas tungsten arc, and this process
makes the best quality weld, but it is relatively slow. It may be automated for
volume production. In automatic GTAW the wire is fed into the joint from a spool
of wire, just like GMAW wire. For faster welding speed helium is added to the
argon shielding gas, making the arc hotter. GTAW is often used to make the root
pass in pipes or whenever the joint can only be made from one side. The rest of
the weld may be built up with either GMAW or SMAW, both of which are faster.
Remember—the core wire of RA330-04-15 covered electrodes is AWS ER330,
and not RA330-04 chemistry. Welders sometimes knock the coating off an
electrode and use the core wire as GTAW filler. Do not do this with RA330-04-15
or the RA330-80 electrodes. This AWS ER330 will make a crack-sensitive weld,
without the benefit of the alloying elements which were in the coating.
Atmospheric contamination, as from strong winds or too long an arc length, is a
potential cause of porosity. Look at work to tip distance, shielding gas flow rates,
cup size and consider the use of a gas lens. When using a 2—4% nitrogen
addition for welding RA 602CA or some of the corrosion resistant alloys, the
shielding gas will be just that much more sensitive to atmospheric contamination.
Minimize the arc length, no more than 1/4 to 3/8 inch (6-9.5mm). The longer the
arc length, the greater the opportunity to entrain air into the shielding gas. Gas
cup size depends upon what diameter tungsten electrode is being used. A 3/32”
(2.4mm) electrode should use anywhere from a No. 6 to No. 8 cup (9.5-12.7mm
cup dia), No. 7 (11mm) being about right. An 1/8 inch (3.2mm) electrode
requires a No. 8 (12.7mm) cup. Consider using a gas lens, a wire screen which
serves to reduce turbulence of the shielding gas flow. It is this turbulence which
causes air to get mixed in with the argon shielding gas.
21
Gas Tungsten Arc Welding (GTAW, a.k.a. TIG)
Plasma Arc Welding
The plasma arc torch is roughly analogous to a GTAW torch. It generates
intense heat in a very narrow zone, and has been used to weld RA330 without
added filler (with GTAW this would be extremely difficult). PAW is an excellent
welding process for heat resisting alloys.
®
For the corrosion resistant alloy AL-6XN , plasma welding is less desirable. This 6%
molybdenum grade requires the use of an over-alloyed weld filler, typically ERNiCrMo -3, to
maintain corrosion resistance in the weld bead. With plasma arc welding so little filler is used that
the weld bead is heavily diluted with base metal and has reduced corrosion resistance due to
molybdenum micro segregation. A full 2150ºF (1177ºC) anneal is necessary to restore full
corrosion resistance in plasma welds of AL-6XN.
Submerged Arc Welding
Submerged arc uses a spool of weld wire, much like GMAW. Instead of
shielding gas, a hopper feeds granulated flux into the arc to shield the arc and
molten weld puddle. While it is possible to use 0.045” (1.14 mm) dia. wire, larger
sizes such as 1/16 or 3/32” (1.6 or 2.4 mm) are generally preferred. For nickel
alloys such as RA330 a strongly basic flux must be used, such as Avesta Flux
805 or Böhler-Thyssen’s RECORD NiCrW. Absolutely do not use acid fluxes or
any flux meant for stainless steel. Heat input must be as low as possible, and for
this reason 1/8” (3.2 mm) wire is not suggested with nickel heat resistant alloys.
22
SAW is process naturally inclined to high heat input, but this heat must be kept to
a minimum to avoid centerbead cracking in fully austenitic alloys. It is for this
reason that 3/32” (2.4mm), rather than 1/8” (3.2mm), wire is suggested for use
with nickel heat resistant alloys.
23
Resistance Welding3
Spot and seam welding parameters for heat resistant alloys will differ from those
used with stainlesses such as 304L or 316L, and markedly from those used for
carbon steel. Heat resistance alloys may have twice the yield strength of
stainless and considerably higher electrical resistivity. Electrode force, welding
current and time, and electrode tip contours may all need to be modified
accordingly.
A restricted-dome electrode is suggested for spot welding. Average dome radius
may be 3 inch (76 mm) for material up to 11 gage (3mm). For a larger nugget
size in material 16 to 11 gage (1.6 to 3mm) a 5 to 8 inch (127 to 203mm) radius
dome is sometimes preferred.
In seam welding heat time should be adjusted to ensure that the wheel maintains
pressure until the weld nugget has solidified, to avoid porosity and cracking.
Likewise cool time should be sufficient that welded areas are not remelted. The
metal must be clean and free of all grease, or a sound weld cannot be made.
24
Suggested Weld Filler Selections
Base Metal
Preferred
bare wire
covered electrodes
Alternates
RA330®
RA330-04
--
RA330-04-15
RA330-80-15
RA333® , RA82
RA333-70-16
RA333®
RA333
RA333-70-16
ERNiCrWMo-1
RA 602 CATM
S 6025
6225 Al
(SG-, EL- NiCr25FeAlY)
RA601
S 6025
RA333
6225 Al
RA600
82
182
RA 353 MA ®
RA 353 MA
RA 353 MA
RA 253 MA ®
RA 253 MA
RA 253 MA-17
RA333, RA333-70-16
RA800H/AT
RA333
556
RA333-70-16
--
ERNiCrCoMo-1
RA330-04
82, ENiCrFe-2
RA309
ER309
E309-16
RA 253 MA-17
RA310
ER310
E310-15
RA330-04*
RA446
ER309
ER310
E309-16
E310-15
E312-16
HK, HT, HU
RA330-80-15 DC lime is the preferred 35% nickel rod for cast
heat resistant alloys. Alternates RA333-70-16, RA330-04-15
617
(2.4627,
ERNiCrCoMo-1)
--
RA330-04
--
General: Do choose the weld filler for its performance under the expected service
conditions, as well as for weldability issues.
*Where sulphidation is an issue, do not use weld fillers with more than 20% nickel
Do not use—any stainless weld filler on nickel alloys (e.g., on RA330, RA333, RA600,
RA601, RA 353 MA, RA 602 CA). The welds will crack. We suggest not using alloy X
(ERNiCrMo-2, ENiCrMo-2) weld fillers on RA333 base metal. The X weld bead may be
subject to catastrophic oxidation at the higher service temperatures where RA333 is
commonly used. Alloy 617 (ERNiCrCoMo-1) welds are strong, but they significantly lack
oxidation resistance compared with RA 602 CA for extreme temperature service.
25
Dissimilar Metal Joints, Suggested Weld Filler Guidelines
Considerations in selecting a filler metal for a dissimilar metal weld joint include the
expected service conditions at the joint, relative thermal expansion coefficients of the
three metals involved, and freedom from weld metal hot cracking. The final selection
should be approved by the end user and weld procedures qualified by the fabricator.
These suggestions are from experience and general metallurgical knowledge. 602 CA is
a new alloy, data incomplete
Base
Metals
Carbon
Steel
Stainless
(304,316)
RA 253 MA
RA 602 CA Cast Alloys
HK, HT, HP
RA330®
RA800H/AT
182
RA330-04
RA330-04
RA333
617A
RA330-04
RA330-80-15
RA333®
182
RA333
RA330-04
RA333
RA333
RA330-04
617A
RA333-70-16
RA 353 MA®
182
RA 353 MA
RA 353 MA
RA 353 MA
-RA 353 MA
RA330-80-15
RA 602 CATM 182
82
182
82
617A
S 6025
6225 Al
617A
RA 253 MA®
E309-16
RA 253 MA
RA 253 MA
RA333
617A
RA333-70-16
RA330-80-15
RA600
82
182
82
182
RA333
RA333-70-16
82
182
RA333-70-16
RA330-80-15
RA601
82
182
82
182
RA333
RA333-70-16
S 6025
6225 Al
RA333-70-16
RA330-80-15
RA309
E309-16
182
E309-16
ER309
E309-16
RA 253 MA
82B
182B
RA330-80-15
RA310
E309-16
182
E309-16
E310-15
RA 253 MA
--
82B
182B
RA330-80-15
RA333-70-16
RA446
E309-16
E310-15
E309-16
E310-15
E309-16
RA 253 MA-17
82B
182B
RA333-70-16
--
Note: The carbon steel joint must be ground to bright metal. A “mill finish” is not
acceptable. All rust, blue-black hot rolling scale and paint must be removed before
welding with any stainless or nickel alloy weld wires. Nickel alloy weld wire lacks the
deoxidation characteristics of carbon steel weld wires.
A
617 (ERNiCrCoMo-1) lacks the oxidation resistance of RA 602 CA
B
These high nickel fillers are quite unsuitable for sulphur bearing environments
26
Dissimilar Metal Weldments Involving Carbon Steel
There are two fundamental concerns when joining stainless or nickel alloys to
carbon steel. 1. that the weld bead remain austenitic and not form martensite.
2. if this joint is to operate at any elevated temperature, say 600°F for
discussion, it is important to minimize the thermal expansion mismatch between
the stainless/nickel alloy and the carbon steel.
How particular one becomes over these concerns are depends upon the
expected life of the equipment. For heat treating equipment, where life is
measured in years, it is almost unheard of to have any failures of alloy
components to carbon steel. Both RA330-05-15 DC lime type electrodes, and
RA333-70-16 AC/DC electrodes have been used quite successfully to join
radiant tubes, muffles and salt pots to carbon steel flanges.
In utility boilers life is measured in decades. Failure is extremely costly. Here
standard practice is to use alloy 182 (ENiCrFe-3) covered electrodes to join tube
supports and spacers to the chrome-moly steel boiler tubes.
The first matter is to ensure that the weld bead remains austenitic, and does not
harden (form martensite). A ny weld bead is an alloy of the weld metal, mixed with
both base metals. On the carbon steel side of the joint the bead will be diluted by
iron. If enough iron is added to a stainless weld, some portion of that weld bead
may become an air-hardening martensitic steel. Regardless of any reasonable
pre- or post-heat, a zone of hard martensite remains in the weld. This may be
subject to brittle failure under impact, or to one or the other type of stress
corrosion cracking. Where it is most important that this does not happen, the use
of a high nickel weld filler is suggested. Commonly that would be alloy 82 bare
wire (ERNiCr-3), and the covered electrodes 182 or Inco-Weld A® (ENiCrFe-3,
ENiCrFe-2). With these 65—72% nickel fillers a very high amount of iron dilution
may be tolerated without martensite formation on cooling. One would also expect
the corrosion resistant weld fillers such as alloy C-276 (ERNiCrMo-5 wire,
ENiCrMo-5 covered electrodes) or Inco-Weld 686 CPT (ERNiCrMo-14) to
tolerate high iron dilution.
It should be noted that tons of alloy steel, including armor plate, have been
successfully welded with stainless fillers. Whether any martensite formed, the
structures performed well, including in battle. The use of high nickel fillers is
suggested here as a precaution, especially for field welding where conditions and
joint configurations may be less than ideal.
In order to predict the possibility of martensite in the weld, one may use a
diagram such as the one below, taken from AvestaPolarit’s web site,
www.avestapolarit.com/template/page_2389.asp-16x
27
28
Dissimilar Metal Weldments Involving Carbon Steel, continued
Thermal expansion is the second issue. The thermal expansion coefficient of
stainless is roughly 50% greater than that of carbon or alloy steel. At 600°F, for
example, the coefficient of expansion of 304 stainless is 9.9x10-6 inch/inch°F,
that of A 387 Cr-Mo steel 7.4x10-6.
When the dissimilar metal joint operates at some elevated temperature, that
means a continual thermal strain in the region of the joint. Eventually that causes
shear failure on the carbon steel side of the joint. With a stainless filler such as
E308 or E309, carbon will diffuse from the steel into the stainless weld bead. This
leaves a thin layer of weak ferrite on the steel side, and a brittle carbide rich zone
in the stainless.
The state of the art in minimizing these problems is to use alloy 182 (ENiCrFe-3)
covered electrodes. With a nominal 65% nickel the expansion coefficient of 182
is relatively low, approaching that of carbon steel. This minimizes the thermal
strain, and averages out the relative expansion coefficients of the two metals to
be joined. In addition, the solubility of carbon in 65% nickel is low, reducing the
possibility of diffusing carbon away from the Cr-Mo steel. The use of ENiCrFe-3
is the best current practice, not an absolute solution to the matter.
There is a third matter, worth repeating. That is, stainless/nickel alloy weld wire
cannot be used successfully to weld over the hot rolling scale and rust normally
present on carbon steel. These weld fillers do not contain the deoxidizing
additions present in carbon or alloy steel weld fillers. The carbon steel must be
ground to bright metal on both sides of the joint. Otherwise the weld bead will not
fuse completely to the base metal. With covered electrodes a rather sloppy weld
to hot rolled carbon steel may be possible. This is because the electrode coating
will flux away much of the steel scale and rust. Possible, but not
recommended—grind off all that scale and rust from carbon steel before welding
to it with stainless or nickel alloy.
29
Heat Resistant Alloy Weld Filler Metals
Grade
UNS
RA330-04
N08334
RA330-04-15 W88334
RA330-80-15 W88338
RA330-80-16 W88338
RA333®
N06333
RA333-70-16 W86333
RA 253 MA ® S30815
RA 253 MA-17 W30816
RA 353 MA ® - RA 353 MA-15 - 309-16
W30910
310-15
W31010
S 6025
N06025
6225 Al
-230-W
N06231
617
N06617
82
N06082
182
W86182
AWS
Cr
Ni
Mo
Co
W
Si
Mn
C
Fe
----------E309-16
E310-15
ERNiCrFe-12
ENiCrFe-12
ERNiCrWMo-1
ERNiCrCoMo-1
ERNiCr-3
ENiCrFe-3
19
17.5
17.5
17.5
25
25
21
21
28
28
23
26
25
25
22
22
19
16
35
33.5
33.5
33.5
45
45
10
11
34
35
13
20
63
62
59
52
72
65
----3
3
--------2
9
---
----3
3
---------12.5
---
----3
3
--------14
----
0.8
0.8
0.8
0.8
1
1
1.6
1.7
0.7
0.5
0.5
0.4
0.03
0.5
0.5
0.5
0.2
0.6
5.2
5.2
2.2
1.7
3
2.5
0.6
0.7
1.7
1.5
1.9
1.8
0.05
0.1
0.6
0.5
3
7.8
0.25
0.22
0.85
0.85
0.05
0.05
0.07
0.06
0.03
0.08
0.10
0.10
0.18
0.2
0.1
0.1
0.02
0.04
39
43
45
45
17
18
66
65
35
34
61
51
9
10
1.5
1.5
2
7.5
30
Heat Resistant Alloy Specifications
alloy
UNS
RA333®
N06333 Plate, sheet, strip
Bar
Smlss pipe & tube
Welded pipe
Welded tube
N08330 Plate, sheet, strip
Bars & shapes
Billets & bars
Smlss pipe & tube
Welded pipe
Welded tube
Fusion weld pipe
N06025 Plate, sheet
Rod, bar,wire
S30815 Plate, sheet, strip
Bars and shapes
Pipe
Welded tube
RA330®
RA 602 CATM
RA 253 MA ®
RA 353 MA ®
S35315
RA800H/AT
N08811
(N08810)
RA309
S30908
RA310
S31008
RA446
RA600
S44600
N06600
RA601
N06601
Product Form
Plate, sheet, strip
Bars and shapes
Pipe
Plate, sheet, strip
Rod and bar
Smlss pipe & tube
Plate, sheet, strip
Bars and shapes
Pipe
Plate, sheet, strip
Bars and shapes
Pipe
Plate, sheet, strip
Plate, sheet, strip
Rod, bar, wire
Smlss pipe & tube
Plate,sheet, strip
Rod, bar, wire
Bar, forgings,rings
Smlss pipe & tube
ASME
ASTM AMS W.Nr, EN
-B 718 5593 2.4608
-B 719 5717
-B 722
-B 723
-B 726
SB-536 B 536 5592 1.4886
SB-511 B 511 5716
-B 512
SB-535 B 535
SB-710 B 710
-B 739
-B 546
-B 168 - 2.4633
-B 166
SA-240 A 240 - 1.4893
SA-479 A 479
1.4835
SA-312 A 312
SA-249 A 249
ASME Code Case 2033-1
SA-240 A 240 - 1.4854
SA-479 A 479
SA-312 A 312
SB-409 B 409 - -SB-408 B 408 - (1.4876)
SB-407 B 407
SA-240 A 240 - 1.4833
SA-479 A 479
1.4833
SA-312 A 312
SA-240 A 240 5521 1.4845
SA-479 A 479 5651 1.4845
SA-312 A 312
-A 176 - 1.4763
SB-168 B 168 - 2.4816
SB-166 B 166 5665
SB-167 B 167
SB-168 B 168 5870 2.4851
SB-166 B 166
--5715
SB-167 B 167
31
Weld Filler Specifications & Tradenames, American versus German
Grade
UNS No.
AWS
RA330-04
RA330-04-15
RA333
RA333-70-16
Alloy X
601
S 6025
6225 Al
617
Inco-Weld ® A
62
82
182
80-20
N08334
W88334
N06333
W86333
N06002
N06601
--N06617
W86113
N06062
N06082
W86182
N06076
----A5.14
“
“
A5.11
A5.14
A5.11
A5.14
“
A5.11
“
Classification ASME
F No.
--------ERNiCrMo-2
ERNiCrFe-11
-ERNiCrFe-12
-ENiCrFe-12
-ERNiCrCoMo-1
ENiCrFe-2
ERNiCrFe-5
ERNiCr-3
43
ENiCrFe-3
43
ERNiCr-6
32
W. Nr.
DIN Designation
--2.4608
-2.4613
-2.4649
-2.4627
--NiCr26MoW
-SG-NiCr21Fe18Mo
-SG-NiCr25FeAlY
EL-NiCr25FeAlY
SG-NiCr22Co12Mo
-2.4806
2.4620
2.4951
-SG-NiCr20Nb
EL-NiCr16FeMn
NiCr 20Ti
Bolts—another means of joining heat resistant alloys
Bolts are commonly used at elevated temperature to withstand a shear load. For example,
RA330® alloy threaded rod, nuts and washers are used to assemble high temperature
equipment where loose joints are desired to accommodate thermal expansion & contraction
during thermal cycling.
A good discussion of fasteners in the chemical process industry has been presented by Robert
Smallwood6.
At high temperatures relaxation is the primary limitation to the use of threaded fasteners to
maintain a clamping load. The most common alloy choice for applications up to 1150°F (620°C)
is RA718, an age hardening nickel base alloy. ASME bolting design stresses are published
though this temperature. A-286, a less expensive age hardening stainless, is sometimes
suggested but its temperature capability may be limited to about 1000F (540C). A-286 is not so
readily available as is 718, in various bar sizes. Above 1150F (620C), to about 1400-1500°F
(760-816°C) the choices narrow down to René 41® or WASPALOYTM. More of this high
temperature bolting experience has been with WASPALOY.
In addition to selecting a strong bolt material it is important to look at the relative expansion
coefficients of the alloy to be clamped, and the alloy from which the bolt is made. If the metal to
be clamped expands faster than the bolt, that expansion will add to the tensile load in the bolt
and may stretch it, so that the assembly is loose once it comes back down to room temperature.
What appear to us as insufficiently conservative alloy selection suggestions are offered by the
Industrial Fasteners Institute as7: Below 450°F (230°C), low alloy steel. 450 to 900°F (230 to
480°C), one of the grades in ASTM A 193. From 900 to 1200°F (480 to 650°C), A286 and 718 .
Above 1200°F up to 1600°F (650 to 870°C), Rene 41 or WASPALOY.
Some cautions. Never, NEVER use anti-seize compounds containing copper anywhere near
high temperature equipment. If some of tha t copper gets carried into an area where the metal is
operating above 1981°F (1083°C) it will melt. Molten copper alloys will embrittle or eat holes
through any austenitic alloy they touch. Zinc or galvanized coatings embrittle austenitics and
can also embrittle steel bolts at moderately elevated temperatures, even without melting the zinc
(melting point 787°F/419°C).
Bolted connections are often difficult or impossible to disassemble after high temperature
exposure. One of the reasons is that a chromium oxide scale forms on the alloy. This oxide
tends to bond male and female threads together. There are ways to minimize the strength of this
bond. One is to coat both parts with magnesium hydroxide, commonly available from the local
drug store as Phillips® Milk of Magnesia. This will calcine to magnesium oxide, quite inert and
harmless to heat resistant alloys. The magnesia simply acts as a parting compound. Another
approach is to use a braze stop-off, such as one of those available from Wall Colmonoy
Corporation, www.colmonoy.com.
33
Weld Filler Consumption
Filler metal requirements range from about 2-1/2 to 5 percent of the weight of plate involved
in a fabrication. Estimated weight of covered electrodes and spooled wire for various joint
configurations is given below.
APPROXIMATE WEIGHT, IN POUNDS, OF
PLATE
THICKNESS,
inch
WELD METAL
DEPOSITED PER
LINEAL FOOT
WITH
REINFORCEMENT
COVERED
ELECTRODES
REQUIRED,
PER FOOT (A)
GMAW,
GTAW
WIRE
REQUIRED
(B)
SINGLE FILLET
1/8
3/16
1/4
3/8
1/2
5/8
0.032
0.072
0.13
0.29
0.52
0.80
0.064
0.144
0.26
0.58
1.03
1.61
0.038
0.085
0.15
0.34
0.60
0.94
"V" GROOVE
1/4
3/8
1/2
0.37
0.62
0.85
0.73
1.23
1.7
0.43
0.73
1.00
DOUBLE "V"
GROOVE
1/2
5/8
3/4
1
0.77
0.95
1.32
1.83
1.53
1.90
2.63
3.65
0.90
1.12
1.55
2.16
JOINT DESIGN
(A) Assumes 50% deposition efficiency
(B) Assumes 85% deposition efficiency
34
References
1. Thaddeus B. Massalski, Editor-in-Chief, Binary Alloy Phase Diagrams, Volume 1,
ISBN 0-87170-262 American Society for Metals, Metals Park, Ohio, U.S.A., 1986
2. Avesta handbook for the welding of stainless steel, Inf. 8901, Avesta Welding AB, S-74401
Avesta, Sweden 1989
3. Berthold Lundqvist, SANDVIK Welding Handbook, Sandvik publication 0,34 E, Sandvik AB,
Sandviken, Sweden June, 1977
4. Specification for Nickel and Nickel-Alloy Bare Welding Electrodes and Rods, ANSI/AWS
A5.14/A5.14M-97, ISBN 0 -87171-543-0, American Welding Society, Miami, Florida, U.S.A.
5. Welding Dissimilar Metals, ed. N. Bailey, The Welding Institute, 1986
6. T.G. Gooch, Solidification Cracking of Austenitic Stainless Steel, pp31-40, Weldability of
Materials, ed. R.A. Patterson & K.W. Mahin, ISBN: 0-87170-401-3 ASM International 1990
7. E.F. Nippes & D.J. Ball, Copper-Contamination Cracking: Cracking Mechanism & Crack
Inhibitors, pp75-s to 81-s, Welding Research Supplement, March 1982 AWS
8. Resistance Welding Manual, 4th Edition, ISBN 0-9624382-0-0, Resistance Welder
Manufacturers’ Association, 1900 Arch Street, Philadelphia, Pennsylvania 19103 USA, 1989
9. R.E. Smallwood, Fastener Problems in the Process Industry, Corrosion 91
Paper No. 161, NACE, Houston, Texas
10. Fastener Standards, 6th Edition, available from: Industrial Fasteners Institute,
1505 East Ohio Building, 1717 East Ninth Street, Cleveland, Ohio 44114 U.S.A.
The best general reference we know for welding this class of materials is: R. J. Castro & J.J. de
Cadenet, Welding Metallurgy of Stainless and Heat-resisting Steels, ISBN 0 521 20431 3,
Cambridge University Press, 1975. First published, in French, as: Métallurgie du soudage des
aciers inoxydables et résistant à chaud, by Dunod, Paris, 1968.
Trademarks
353 MA and 253 MA area registered trademarks of AvestaPolarit
602 CA is a trademark of ThyssenKrupp VDM
INCO-WELD is a registered trademark of Special Metals, Inc.
35
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