Stainless.
Weld and Steels Data:

 

OTC for optimum pulsed and best value.
Miller 350 P for best low price pulsed unit.

Welding Stainless or Duplex?

These are two of the best "cost effective" pulsed MIG
power sources available in North America.

 

E-mail. Question: Ed as we have a variety of weld process selections for stainless. What MIG and flux cored wires / processes should we consider when welding stainless in the gage to 25 mm range?

Answer: The following primary weld considerations will influence the weld process required.

[] Distortion potential.
[] Cleaning and oxidation concerns.
[] Part thickness.
[] Weld positions.

[] For stainless applications, it's been traditional and logical to use use TIG or the MIG short circuit process with an 0.035 (1mm) wire, when welding < 0.062 (<1.6mm) stainless.

[] A REAL WORLD PULSED MIG BENEFIT: In contrast to MIG short circuit, to increase weld speeds and provide superior weld surface, (more fluid) consider the pulsed MIG process. For pulsed use argon 2 - 5% CO2 and 0.045 wire. The pulsed choice is especially appropriate for stainless welds on applications in the range of 16 gage to 3/16.

[] For stainless / duplex applications > 6 mm for flat and horizontal welds, consider an 0.045 MIG wire. Use spray with argon 2 - 5 % CO2 for optimum welds, and consider pulsed with the same gas mix if heat, distortion or spatter issues. For these weld also consider the 0.062 (1.6 mm) gas shielded flux cored wire with argon 20 to 25% CO2.

[] For MIG welding in the vertical position. If parts are < 4 mm, try welding vert down. Use argon 2 - 5% CO2 and spray with 0.035 wires and pulsed MIG with 0.045 wires.

[] For MIG welding in the vertical position on stainless parts over 3/16 thick, (> 5mm) welding vertical up or overhead applications, consider an 0.045 gas shielded flux cored wire with argon 20- 25% CO2. Do not weld vertical down with the gas shielded flux cored wires.

 

 

Key Safety Weld Issue. Concerns anyone who welds stainless or other chrome alloys. OSHA held hearings on it's proposal to reduce the PEL for hexavelent chromium from 52 micrograms per cubic meter to 1 microgram per cubic meter as an 8 hour time weighted average. By court order OSHA is required to adopt a final rule by Jan 18 2006. Click

 

STAINLESS MIG GAS MIXES AND WELD REALITY: In the last three decades the biggest selling gas mix in North America for MIG, stainless gage applications, has been a tri-mix containing 90 helium - 7.5 argon and 2.5% CO2.

In contrast to the three part helium tri-mix, a less costly, two part mix, argon with 2 - 5% CO2 developed by Ed in the nineteen eighties, has always provided more weld benefits.

 

 

There are over 60 MIG gas mixes available for all MIG applications.
With these six mixes Ed has defined the world's best gas mixes.

Visit the MIG gas Section

 

WHAT IS STAINLESS STEEL?



STAINLESS COMES IN MANY FORMS IT CAN BE A LOW COST
METAL WITH A LITTLE CHROME A LOT OF IRON.

Austenitic, Martensenitic and Ferritic STAINLESS STEELS.

Austenitic Stainless Steels are the ones we are most familiar with. These chrome nickel steels, in contrast to the lower cost stainless have more alloys and are "non magnetic"
Exception, types 310 - 330

Austenitic steels. Grades 20-202-205-301-302-303-304-305-308-309-310-314-316-317-321-329-330-347-389-17 7PH- 17 4PH-PH15-7Mo-AM 350-AM 355 A 286.

Common Designations
304 (S30400) - 304L (S30403) 316 (S31600) - 316L (S31603) - 347 (S34700)

Austenitic Facts: Austenitic grades typically contain a minimum of 18% chrome - 8%nickel and are often called 18/8 steels.

Grades 301-302-304-305-308 usually welded with E308

18/8 grades used for machine parts exterior buildings and industrial parts.

18/8 not to exceed 800F 426C service temperature.

Manganese grades of stainless "200" series similar to 18/8 grades. Manganese in this series is used for "extra strength" Welding the manganese grades usually requires the use of the E308L filler.|

Martensitic and Ferritic Grades are common stainless grades that we don't want to weld and if we do, we weld with great caution.

Martensitic chrome steels. Weldability, limited. Preheating typical 250°C to 450°C. Postweld treatment: Slow cooling to 120°C (martensitic transformation) and annealing at 750°C or hardening (generally 1000°C / oil), tempering (generally 750°C). Watch for formation of chromium carbide between 500°C and 650°C!

Note: When welding these grades the weld procedure concerns and focus will be on HEAT treat requirements.

STAINLESS INTERNATIONAL WIRE SPECS


US AWS A5.9 / UK BS2901 / Japan JIS Z3321/ ISO 3581/ Germany DIN 8555 - 8556

UNS International filler metal numbers start with WXXXXX

 

From Avesta: Stainless steel evaporators at Smurfit Kappa Kraftliner, Piteå.

 

 

TYPICAL STAINLESS FILLER METALS

 

 

SMUT AFTER PICKLING ON STAINLESS:

 

From Avesta:

Stainless smut is a common problem that results after pickling. Smut is an undesired discoloration that deposits on stainless steel surfaces after pickling, it appears as a dark sticky film. Its difficult to pinpoint why the smut has formed. There are a large number of possible causes and factors. The most frequent of these are:

• Contaminated surfaces (dirt and or glue residues from plastic film).
• Uneven pickling.
• Inadequate rinsing.
• Poor water quality.
• Substandard circulation/stirring in the pickling bath.
• Old, contaminated pickling bath.
• Poor steel quality.
• Nitrate-free pickling solutions.

Research has shown that smut is more likely to occur when metal dissolution by the pickling acid increases Fe2+ levels to the point where the redox potential of the pickling solution falls below a certain value (Fe + 2Fe3+=> 3Fe2+).Under these conditions, a passive chromium layer is not formed. This leaves the steel surface vulnerable.Loose oxide particles and other elements in the pickling acid may then easily attach themselves to the surface. Low alloy-stainless steels are more sensitive to smut formation than are their high-alloy counterparts. This may be due to the high pickling rates
that, particularly with high acid levels, are characteristic of low-alloy steel grades. Reducing smut with FinishOne™ Besides excellent NOx reduction and passivating power, FinishOne™ has also demonstrated that it is a real “smut killer”. Sprayed onto a still wet steel surface, it promotes Fe2+ to Fe3+ oxidation and thus prevents smut formation (Fe2+ + FinishOne => Fe3+ + H2O). Smut caused by silicone residues on the surface Smut and NOx reduction using FinishOne™. Smut caused by a film of oil on the surface When Fe3+ is the dominant ion, the resultant passivation protects steel
surfaces from both corrosion and adhesion.A final rinse with FinishOne™ ensures a passivated surface that is free from water stains.

If they do not receive proper post-weld treatment, stainless steels soon lose their stainless property. Thus, correct pickling, passivation, et cetera are all vital. This is especially true in the pulp and paper industry, where highly aggressive media are used at high temperatures. Avesta Finishing Chemicals has the products, expertise and support to meet the stainless steel finishing requirements of the pulp and paper industry worldwide.

 

[] Austenitic stainless steels are prone to hot cracking and so attention is required to cleaning before welding and welding using low to medium weld parameters. Concern for formation of chromium carbide at grain interface especially if the carbon content is higher then 0.04%. No preheat is usually required.

Filler metal: % C = max. 0.04%

In welding carbon steels to stainless, the austenitic / nickel filler metals offer unique features that can reduce weld crack potential in both the welds and weld heat affected zone (HAZ). Carbon to stainless welds require that the stainless weld metal have sufficient ferrite to resist cracking. When welding carbon steel to stainless and a 309L wire is used, the resulting ferrite is approximately 14-16FN.

If the steel is a high carbon steel, a 309L, first weld pass on the carbon to stainless will likely end up with "insufficient ferrite". The carbon from the high carbon steel when mixed with the stainless weld will suppress the ferrite formation. Instead of the 309L for this application, a 312 electrode may be recommended.

The 312 filler metal, (70 to 90 FN in the weld metal) produces much higher ferrite levels than the 309L. This is the prime reason the 312 is recommended for applications sensitive to weld cracks. Filler metals such as 307 - 308 Mo and 310 can resist cracking with the aid of alloys and without the aid of ferrite.

HOW AUSTENITIC & NICKEL WELD ELECTRODES CAN HELP HIGH STRENGTH CARBON STEELS.

High carbon, high strength steels welded to each are subject to hydrogen assisted cracking.

[1] High hardness,
[2] a source of hydrogen and
[3] high stresses, these are the three fundamental requirements for hydrogen assisted cracking.

With the high carbon steels, high hardness is typical in the HAZ unless very high, (often not practical) preheat and interpass temperatures are utilized for the welds.

The stresses that can influence HAZ cracking typically result from weld residual stresses caused by weld shrinkage, these stresses can be further exaggerated by weld joint restrictions as found in certain fixtures.

As we are all aware, hydrogen in the weld can be derived from many sources.

An alternative to a high carbon, high strength filler metals, in which the carbon dilution from the base metal will result in a hard weld, subjecting the weld to transverse cracking, is to use an austenitic or a specific nickel based filler metal (ENiCrFe-2).

The austenitic or nickel filler metals greatly reduces the weld transverse cracking potential. Also these filler metals greatly reduce, slow down or trap the weld hydrogen that can diffuse from the weld into the HAZ, this greatly reduces HAZ hydrogen cracking potential.

The diffusion of hydrogen though austenitic and nickel filler metal welds and steel can be approximately 80 - 110 times slower than through carbon steels and welds. The use of the austenitic and nickel filler metals can greatly reduce cracking however these filler metals can still absorb hydrogen so these electrodes should be treated with the same respect and rules that apply to any low hydrogen filler metals.

Note: MIG welding. Use Eds uniquee Stainless. Duplex MIG gas mix to reduce any types of weld cracking. With any stainless flux cored wires use the argon CO2 mixes recommended for carbon steel flux cored wires.

When to use a 308L, 309L
or 316L filler metal.

 

[] 308L and 308LSi is predominately used on austenitic stainless steels, such as types 301, 302, 304, 305 and cast alloys CF-8 and CF-3.

[] For high temperature applications such as in the power industry, higher carbon 308H electrodes will provide superior creep resistance than does 308L .

[] Use 309L and 309LSi when joining 309 or mild steels / low alloy steels to stainless steels. Use 309 when joining dissimilar stainless steels such as 409 to itself or to 304L stainless. CG-12 is the cast equivalent of 309.

 

[] Some 308L applications may be substituted with 309L filler metal, but 316L or 316 applications generally require molybdenum. Note, 309L contains no molybdenum.

[] 316L and 316LSi should be used with 316L and 316 base metals. CF-8M and CF-3M are the cast equivalents of 316 and 316L, respectively.

[] Type 347 stainless steel filler metal is used for 347 and 321 base materials because it matches these stabilized grades. CF-8C is the cast equivalent of 347. Type 347 filler metal is also suitable most 308L filler metal applications.

 

Excellent stainless gas shielded flux cored wires are
available from Alloy Rods and Kobleco.

Around the Globe Sanvik and Avesta set
the standard for MIG Stainless wires.

 

ELIMINATE STAINLESS WELD POROSITY:

Weld porosity, a cavity discontinuity that forms from a gas reaction. The porosity can be trapped in the weld or at the weld surface. The porosity is typically round in shape but can also be elongated. In contrast to argon oxygen mixes, Ed's Stainless. Duplex gas mix was developed for less oxide reaction, less porosity potential.


ROBOTS AND MIG POROSITY. When you find the robot weld porosity is always at the same location and the weld porosity is not at the weld starts or ends, examine the robot movement and see if the robot arm is causing a restriction of the gas flow line. Also it's common with robot cells to see a severe gas flow restiction due to the narrow orrifice found in gas line connections. In a robot cell its critical to measure gas flow as it exits the gun. If the porosity is at the weld start or stop increase the gas pre flow and post flow times.

Weld porosity, a cavity or discontinuity that forms in the weld from a gas reaction in molten metal.

The weld porosity can be trapped in the weld or evident at the weld surface. Weld porosity is typically round in shape, but can also be elongated.

Weld porosity is caused by the absorption of oxygen, nitrogen and hydrogen into the molten weld pool. The gases are then released on solidification and may become trapped in the weld metal.

Nitrogen and oxygen absorption in the weld pool usually originates from inadequate or contaminated gas shielding, leaks in the MIG gas line, excess gas flow rates, draughts and plate contamination.

Hydrogen can originate from a number of sources including moisture from the electrodes,moisture on the parts, contaminates on the workpiece surface. (Use dry pre-heat > 100F , oxy fuel > 250 F)

CLUSTER WELD POROSITY. A localized group of pores with random distribution. Causes. Arc blow, insufficient, inconsistent or excessive weld gas flow, material or weld wire contamination, (low) weld parameters or poor technique.

PIPING, WORM HOLE, WAGGON TRACKS POROSITY. Sometimes called "waggon tracks". Typically found in the center of the weld, parallel to weld axis. Classic porosity when moisture is evident in gas shielded flux cored wires, (the cheaper the product the more prone to waggon tracks).

Increasing the flux cored wire stick out and increasing the wire feed rate helps by adding energy to the wire. Baking flux cored wires and storing the wires in a dry environment also reduces potential. Slow weld speeds, make welds larger, avoid weaves. All recommendations are intended to increase the weld arc energy and decrease the weld cooling rate.

Worm holes are elongated gas pores producing a herring bone appearance on a radiograph. Worm hole porosity is common in gas shielded flux cored welds when the electrodes have too much moisture in the wire flux.

WELD ROOT POROSITY.
Weld root porosity frequently occurs when MIG welding using "argon oxygen" (oxidizing) mixes on parts >6 mm. With these gas mixes the resulting root is typically narrow, finger shaped. The root finger area solidifies rapidly trapping porosity. To reduce the stainless root weld porosity, change to an argon 2 - 4 CO2 gas mix. Increase the weld parameters, slow the weld speed and avoid weld weaves.

ALIGNED WELD POROSITY. Linear porosity, an array of small round pores typically found in a line. Often caused from the base metal lubricants or metal surface contaminate. Add weld energy (increase wire feed), increase push angle allowing the arc to break up surface oxides ahead of weld.


SCATTERED WELD POROSITY. Weld porosity scattered randomly throughout the weld or welds. If the MIG weld surface is gray and looks oxidized, the porosity is typically a result of insufficient gas flow. If the weld surface looks clean with scattered porosity the porosity is usually caused by the base metal part or electrode contamination, or perhaps the weld data used causes the weld to freeze too rapidly.


LARGE PORE WELD POROSITY. If weld surface is clean and does not look oxidized, the large pore MIG / FCAW porosity could be a result of excessive gas flow. Gas turbulence is caused with gas flow greater than 40 cuft/hr. Optimum MIG and flux cored gas flow for carbon steels is 25 to 35 cuft/hr, the gas flow should be measured as it exits the gun nozzle. If the weld surface is dirty (oxidized) the cause of larger pore porosity is ofen a result of insufficient gas flow, less than 20 cuft /hr.

 

 

Jan 2004. Sandvik Announces New Ultrahigh- Strength Stainless Steel "NANOFLEX":

Sandvik Materials Technology recently developed a new stainless steel called Sandvik Nanoflex that features ultra high strength and good formability, corrosion resistance, and surface finish. According to the company, the steel is well suited for mechanical applications requiring lightweight, rigid designs such as medical equipment and for replacement of hard-chromed, low-alloy steels in the automotive industry.

Examples of the strength properties of Sandvik Nanoflex are 1700 MPa tensile strength, 1500 MPa yield strength, 8% elongation, 45-58 HRC hardness, and a Charpy V impact strength of a minimum of 27 J at -20°C. Exact strength values depend on the product form and the manufacturing route.

Despite its high hardness, the company claims it is easy to perform cold forming operations such as bending, cutting, turning, and grinding. After reaching the desired shape, a simple low-temperature heat treatment gives the material its high strength without distorting the workpiece.

This material also displays good welding properties. It is available in tube, strip, wire, and bar forms.

 

 

Stainless Filler Metal Selection
Stainless Type	FILLER METAL SELECTION AWS A5-9. Use first choice. Confirm choice with wire manufacturer
AUSTENITIC CHROME NICKEL NONE MAGNETIC Stainless 201 to austenitic 200-300 series use 201 used for low temp cryo applications to -320F	308 for 330 use 312
Stainless 202 to austenitic 200-300 series use	308 for 330 use 312
Stainless 201-202-301 303 to mild steel use	312
Stainless 210 - 202 -301 to mild steel. Stainless type 201 requires special consideration required to avoid hot cracking as ferrite extremely low	312 can reduce cracking as it provides much higher ferrite than 309.
Stainless 301 to austenitic 200-300 series use	308 for 330 use 312
Stainless 302 to austenitic 200-300 series use	308 for 330 use 312
Stainless 302 - 302b 304 to mild steel use	310
Stainless 302 - 302B -304 to mild steel use	310
Stainless 303 to austenitic 200-300 series use	308 for 330 use 312
Stainless 303 to 310-314-330- use	312
Stainless 303 to mild steel use	312
Stainless 304 to austenitic 200-300 series use	308 for 330 use 312
Stainless 305 308 to mild steel use	312
Stainless 305 to austenitic 200-300 series use	308 for 330 use 312
Stainless 305 - 308 to mild steel use	312
Stainless 308 to austenitic 200-300 series use	308 for 330 use 312
Stainless 309 to 309 - 310 - 314 -316 - 317 use	309
Stainless 309 to 330 use	312
Stainless 309 to 347 use	308 - 347
Stainless 310 to 310-3140	310
Stainless 310 to 316 use	316
Stainless 310 to 317 use	317
Stainless 310 to 321 use	308
Stainless 310 to 330 use	312
Stainless 310 to 347 use	308
Stainles 310 to mild steel use	310
Stainless 314 to 314 use	310
Stainless 314 to 316 use	316
Stainless 314 to 317 use	317
Stainless 314 to 321	308
Stainless 314 to 330 use	312
Stainless 314 to 347 use	308
Stainless 314 to mild steel use	310
Stainless 316 to 316 - 317 use	316
Stainless 316 to 321 - 347 use	308
Stainless 316 to 330	312 - 309
Stainless 316L to mild steel use	309
Stainless 316LN a nitrogen addition to a low carbon stainless Incesase both corrosion resistance and strength as compared to 316L	316L or 317L 317L typical for corrosion 316L for toughness (cryogenic type applications
Stainless 317 to 317	317
Stainless 317 to 321	308
Stainless 317 to 330 use	312
Stainless 317 to 347 use	308L
Stainless 317 - 321 - 348 403 - 405 410 414 416 to mild steel use	309
Stainless 321 to 321 - 347	347
Stainless 321 to 330 use	312 - 309
Stainless 330 to 330 use	330
Stainless330 to 347 use	312 - 309
Stainless 348	347
Stainless 384	309
Stainless AM 350	AM 350
Stainless 410 Condition A ASTM 276 12% Chrome, chrominum / martensitic steel	to itself or carbon 309L
Stainless 501 502 430 431 442 448 to mild steel use	310
17-7PH use	W17-7PH
PH15-7Mo use	WPH 15-7Mo
17-4PH use	17-4PH
A286	A286
Sanicro 28 27 Cr - 31 Ni -Mo 3.5 -Cu 1 Tensile 73 ksi Yield 31 ksi	Sanvik 27.31.4.LCu ER028L
Duplex Ferritic Austenitic SAF 2304 UNS 32304 DIN X2CrNiN 24-4 23 Cr - 4 Ni - N 0.1 Tensile 87 ksi - Yield 58 ksi	308 MoL
Duplex Ferritic Austenitic SAF 2205 UNS S31803 22 Cr - 5.5 Ni -Mo 3 - N Tensile 990 ksi - Yield 65 ksi Weld Note: For MIG use argon with 2% CO2. When welding 2205 or 2304 to dissimilar butter first with ER309MoL then weld with 308MoL No concern for interpass temp, high amps can be use	2209
Duplex 3RE60 18.5 Cr - 4.9 Ni - 2.7 Mo	weld same as 2205
254 SMO alloy	Electrode Avesta p12 Sanvik Sanicro 60 ENiCrMo3
Stainless to carbon	309 or 312 which has higher ferrite reduces cracking
MARTENSITIC STEELS 403 - 410 - 414 416- 420- 422 -431- 440 Preheat and interpass temp 500F 260C Post heat 1350F 732C> Control cool 50F / hr to 1100F> Control cool to 1100F 600C then air cool. Treat the 500 series the same as the Martensitic series
Stainless 403 to 400 series use	410 ASTM 276
Stainless 403 to 501 use	502
Stainless 403 to 505 use	505
Stainless 405 to 505 use	505
Stainless 405 to 501 use	502
Stainless 405 to 430 use	430 - 309
Stainless 405 to 400 series use	410
Stainless 410 to carbon steel	309L
Stainless 410 - 414 WELD same as 405
Stainless 416 - 440 butter with 312 or 309 first
Stainless 416 to 505 -502-501 -446 - 440 -430 -420 use	309
Stainless 416 to 431-420-416 use	410
Stainless 420 to 505	505
Stainless 420 to 501-502 use	502
Stainless 420 to 446 use	430
Stainless 420 to 440 -420 use	420
Stainless 420 to 431 -430 use	410
Stainless 430 to 505 use	505
Stainless 430 to 501 - 502 use	502
Stainless 430 to 446 - 440 - 431 - 430 use	430
Stainless 430F to 400 series use	309
Stainless 431 to 505 use	505
Stainless 431 to 501 -502 use	502
Stainless 431 to 446-440 use	309
Stainless 440 weld same as 431
Stainless 446 to 505 use	505
Stainless 446 to 501 - 502 use	502
Stainless 446 to 446 use	309
Stainless 505 to 505 use	505
Stainless 501 to 505 - 502 - 501 use	502
Stainless 502 to 505 - 502 use	502
Ferritic steels 405 - 409 - 429 - 430 -434 - 436 - 442 -444 - 446
444 to 444 or to other metal use	316L or 309MoL
Ferritic magnetic avoid prolong heat in the range of 750F -1700F (400-925C
Feritic preheat at 350F 176C To improve ductility
Ferritic steels most frequent electrodes	309 - 310 - 312
Ferritic steel if post heat required use Austenitic filler

A summary of Stainless Welds and Sensitization.

Metallurgist could write a book on this subject. I will try to keep it short and I hope its easy to understand.

[] With a stainless welds on specific alloys, sensitization occurs in the weld's heat affected zone (HAZ) when this zone is between approx. 900 and 1600F.

[] Sensitization occurs when the carbon content is sufficient to produce precipitation of chromium rich carbides along the HAZ grain boundaries.

[] The formation the chromium carbides results in a chrome depleted area around the grain boundaries. This location will be in the weld's HAZ at the furthest point from the weld.

[] If the weld's HAZ depleted chromium carbide area is subject to a corrosive medium the grains can rapidly corrode and cause separation from the weld.

[] A 304L metal will contain a maximum of 0.03% carbon. In contrast a 304 base metal can contain twice the carbon level of the 304L.

[] Welding and subjecting a 304 base to 900F to 1600F will cause sensitization in HAZ.

Solution to Stainless Sensitization.

[1] Use a low carbon ( L grade) stainless. The typical 0.03 max carbon content is not sufficient for carbide precipitation.

[2] Consider a stabilized stainless steel such as 347 or 321. These steels are stabilized against chrome depletion with alloy elements that have a greter affinity to form carbides.

[3] Type 347 which is similar to 304 has niobium (columbium) for carbide formation. Let the niobium do its job and the chrome has no carbides to attach to, thus we prevent carbide precipitation.

[4] Type 321 is also similar to 304. Type 321 contains titanium and the titanium does the same job as the niobium. Keep in mind both the 321 and 347 are typically much more costly than the 304L.

[5] What about those common multi-pass "316 or 308 welds"? Of course the multi-pass welds are subject to the 900F to 1600F, however the weld metal in contrast to the stainless base metal will contain a small amount of ferrite in the austenitic structure. Chrome diffuses in ferrite approx. 100 times faster than it will in the austenite. The ferrite has more chrome than the austenitic matrix. The ferrite area will be rich in chrome so this area can supply an area subject to sensitization.

 

 

Avesta: A typical Pulp and Paper Mill Layout

Typical Pulp and Paper Mill Weld Consumables from Avesta

 

AVESTA 308L/MVR
Avesta 308L is excellent for the welding of evaporators,
storage tanks, etc. made from 304L (EN 1.4307, Outokumpu
4307), a general purpose steel.

AVESTA 316L/SKR
For welding 316L (EN 1.4404/1.4436, Outokumpu 4404/4436),
a well-proven austenitic grade that is used extensively in the
pulp and paper industry.

AVESTA P12
Avesta P12 was specially designed for welding fully austenitic
6 Mo steels, e.g. Outokumpu 254 SMO (EN 1.4547). Owing
to their good resistance to corrosion (stress, pitting and
crevice), these steels are used in, amongst other things, filter
washers and wash presses in modern ECF bleaching plants.

AVESTA P54
Avesta P54 is an iron-based filler metal that was specially
developed for welding fully austenitic 6 and 7 Mo steels (e.g.
Outokumpu 254 SMO) in applications where conventional
nickel-based alloys are vulnerable to transpassive corrosion.
D stage filters in the ClO2 bleaching of pulp are just one
example.

AVESTA P5
A molybdenum-alloyed filer of the 309MoL type, commonly used in the pulp and paper industry for dissimilar welding.

Stainless and Nitrogen Purge Gas Question.

Ed as you are aware Nitrogen is a lot cheaper than argon when utilized as a purge gas for stainless. My question, When MIG welding stainless tanks edge or corner welds, tube or pipe open root welds, can nitrogen react with the stainless and have a negative impact?

Answer: Nitrogen has a diatomic, "two atoms" per molecule. Nitrogen in the diatomic form is usually insoluble in molten stainless. However if the nitrogen gets into the weld arc, the plasma arc energy can seperate the diatomic molecules and create monatomic molecules.

The monatomic molecules are soluble in the weld. The nitrogen, monatomic (seperated molecules) become an alloying element and can reduce the ferrite in a stainless weld. A reduction in ferrite in some alloys can cause the weld to be more austenitic and sensitive to hot cracking. If nitrogen enters a weld or the welding arc, it can have a negative and sometimes a positive influence. Thats the reason one of my gas mixes for duplex has the addition of nitrogen, and the other gas mix does not.

There are stainless alloys which do not need ferrite like 320 / 310. With these alloys nitrogen has no negative impact on these alloys. Also if the stainless alloys have high ferrite levels they typically can afford to loose a little of the ferrite to the nitrogen.

With closed root, austenitic stainless welds, as found in tanks, corner, edge welds, or thin gage, partial penetration tube welds, nitrogen is the logical, economical, purge gas choice for all austenitic, duplex, martensitic and precipitation hardening stainless steel applications. The only concern would be a few specific, ferritic alloys in which nitrogen could cause severe weld mechanical issues.

With an open root "MIG stainless weld" the nitrogen purge gas has little opportunity to get into the weld arc as the gas flow rate / pressure of the welding gas should be higher than that of the purging gas . However nitrogen could still be picked up by the weld. .

With duplex stainless there should be no concerns for open root nitrogen issues. The majority of the common, open root stainless alloys will not be adversely affected by nitrogen purge gas. However in the world of product liability, here is the welding bottom line. If your weld job is large enough to produce a substantial cost reduction from using nitrogen gas, then it's logical to "pre qualify the nitrogen purge welds" and have the weld chemistry, ferrite and mechanicals tested.

 

 

 

 

Failed Stainless Pipe Weld Tests.

Question: Ed we weld austenitic stainless and carbon steel pipes. For cost reduction, in our stainless weld tests we only utilize "carbon steel pipes" and 309L SMAW or flux cored, electrodes. We frequently have root cracking issues, or during the bend test the weld sample breaks. What is strange is that we visually examine all the roots and we wont let them be mechanically tested unless the welds look OK. Why the inconsistency? why do some tests welds pass and other good looking welds fail?

Ed's Answer: The bottom line the 309L electrode is designed to weld "carbon steel to stainless" this electrode was not designed to weld carbon steel to carbon steel thats why we have carbon steel electrodes.

Use the 309L electrode on two carbon steel pipes and weld dilution becomes a concern in the weld root area. If the weld parameters and edge prep is such that the resulting weld dilution is minimal, the resulting 309L weld should be austenite with a little ferrite. It's the austenite / ferrite combination that provides weld ductility.

If while welding the carbon steel pipe root, the welder uses higher current, slower weld speeds or a wider weld weave, the 309L weld can end up with more weld dilution with the carbon steels, reducing the weld ferrite level and making the weld more austenitic. A reduction or loss of ferrite can make the weld subject to "hot centerline cracking" (hot cracking, the weld cracks during the weld or soon after).

A hot weld crack surface in a bend test can be identified by a blue or gray color. Even if the root pass does not crack the high austenite composition can turn to martensite when cooling. The brittle martensite can readily fracture during the bend test. (a silver color or bright fracture surface).


The bottom line if you look at the costs involved in the stainless to carbon steel pipe weld test, it makes little sense to use two carbon steel pipes. Ensure for your weld test that one of the test pipes is at least stainless.

 

FAILED 308 L FLUX CORED
WELDS SUBJECT TO HIGH TEMP:

Gas shielded stainless flux cored wires have an Achilles Heel: As pointed out by Kotecki in the QA section, March Weld Journal, it would appear that there is a problem with the use of specific stainless flux cored wires on pressure vessel applications subject to high temperatures or post heat treatment. In the stainless application reviewed, the weld shop applied a stress relief of 1475F for 12 hours to a 304L pressure vessel welded with gas shielded 308L flux cored wires. After the heat treatment many cracks were found in the 308L flux cored welds. These welds had no cracks before the post heat treat.

It would appear the flux cored wire manufactures add specific alloys and compounds for easy slag removal. One compound contains bismuth.

Note from Ed: The bottom line for the 308L gas shielded flux cored weld cracking issues or part / weld premature creep failures at elevated temperatures is the stainless gas shielded flux cored wires utilized contain a compound containing "bismuth" This compound assists in easy slag removal. It's been reported that with levels of bismuth at 200 ppm. (200 ppm is a typical bismuth level) weld cracks have occurred at a reheat temp of 1050F.

What should you do if your stainless pressure vessel is to be used in a high temp application or the vessel requires post heat treat.

[] POST HEAT TREAT: To avoid major issues on an application subject to high temp post heat treat, its logical that a weld qualification procedure should encompass the required post heat treatment. This way you can check the welds in the real world welded condition.

[] CONTROL THE BISMUTH LEVELS: For high temp applications gas shielded stainless flux cored wires are available with bismuth levels < 20 ppm. These products are supposed not to exhibit reheat cracks or premature creep failure. Talk to your weld wire supplier about your concerns for the high temp.

[] REPUTABLE WIRE MANUFACTURERS: Don't purchase weld consumables that fell of the back of a truck on their way from China. Deal with reputable flux cored wire companies like Sanvik, Avesta and ESAB.

[] PROCESS ALTERNATIVES. Consider SAW or MIG.

Its important to note, that the majority of stainless are put into service at tempertures below < 500F and these applications have not been subject to the issues discussed. However there are also 300 series that undergo annealing and stress relief or are subject to high temp > 900F applications in the power industry.

 

Rust on Stainless Welds

 

Recently our company fabricated 316L gage pipe. The finished weld products have been out doors at the site for approximately 2 weeks and now about 15% of the welds are showing rust at the weld seams. Our procedure for weld cleanup was to use a stainless wire brush followed with a citric acid passivation. We really are at a loss as to why this happened.

From Brad Hass. This very interesting for me, we had a similar problem on 304L structures for a blast freezer. It turned out to be from the use of a 302ss powered brushing operation. We had a company come in, to apply pickling gel to the damaged areas. It works! The reason I don't believe you had a carbon steel brush in use, is citric acid treatments will remove that, and will not remove contamination from 302 and 304 powered brushing. Nitric/Hydroflouric and brush electropolishing is the only thing we have found to remove this. I have confirmed all the above with salt spray testing 24 hr 5% solution. One other thing the larger the bristle diameter the worse the contamination. I recommend in the future 316L brushes or Scotch-brite type abrasives for your clean up, this works.

From Ed.I have seen this situation twice.

[1] Robot welded stainless parts and the steel fixtures. The carbon steel fixtures were designed not only to hold the parts but were in very close proximity to the weld joints to act as a heat sink. The stainless welds ended up picking carbon and resulted in rust in the weld HAZ.

[2] When I look at the pipe seam and circumferential welds, it's notable that only a small percentage of the welds were contaminated. Therefore it's logical to assume there was no consistency in the cleaning method used. I would put my money on the fact that in some areas the correct stainless brushes were utilized and at other times the welders picked up carbon steel brushes.

 

 

Stainless Weld Data.

 

 

When MIG Welding stainless you can use the optimum MIG wire feed data recommended at this site for carbon steels. The only change that will be required is weld voltage. As stainless will use a low reactive gas mix, less weld volts will be required. For MIG stainless welds typically 2 - 3 lower volts are required than that recommended for carbon steels.

Keep stainless clean, only use stainless wire brushes.

Manganese grades usually weld with a 308L

Welding XXXL ensure filler is low carbon as designated XXXL




With fixtures avoid carbon steels in close proximity to stainless welds, as carbon pick up possible, the weld area will rust. There are many ways to introduce carbon to stainless welds.

For stainless vert up welds on parts 3 to 6 mm, consider pulsed,

For stainless all position welds on parts > 6 mm, first logical choice will be always be stainless gas shielded flux cored wires.

Minimize the drive roll tension applied to stainless flux cored wires.

For stainless flux cored weld data, use the carbon steel flux cored wire data found in my flux cored book.

For stainless flux cored use an argon mix with 15 - 25 CO2.

STAINLESS & CARBIDE PRECIPITATION (chrome depletion):

Use weld data to avoid Carbide Precipitation. (CP)

For stainless corrosive environments control of CP is critical.

CP occurs with 300 series in the temperature range of 800F - 1600F, 430-870C.

CP typically occurs within 3 mm of either side of a weld HAZ

In the temperature range of 800-1600F the chrome will move to join carbon, this results in "chrome depletion" leaving an area with less chrome.

A chrome depleted area may not resist the corrosive environment. To combat CP use (L) low carbon base and filler metals. Ensure the C02 gas composition has less than 5 % CO2.

Stainless and stabilized electrodes.

You can combat CP with stabilized fillers which provide alloys that grab the carbon before it can affect the chrome. Alloys like E347 which work at reducing chrome depletion.

Stabilized fillers are typically used in high strength high temp service. However if base metal is not an L grade CP will occur.

Rapid cooling of stainless through the 800 - 1600F range reduces Carbide Precipitation.

 

 

TIG welding and the influence of "sulfur"
in austenitic stainless applications. When the parts to be welded have normal sulfur content (greater than 0.005%) an interesting event can occur. With increasing weld temperature the surface tension of the weld pool also increases. The result is the hottest part of the fluid weld surface is attracted to the middle of the weld pool causing deep narrow weld penetration.

With lower sulfur in the weld, the weld surface tension is less. The resulting weld is wider with less fusion. When two parts welded together have different levels of sulfur tension the weld may pull towards the lower tension, lower sulfur part, resulting in inconsistent weld fusion or penetration favoring one side of the weld joint. This occurrence is especially notable when automated TIG welding Dissimilar parts such as cast parts to sheet or pipe. The following weld solutions may assist the sulfur issues.
[1] Pulse the application.
[2] Use a weave.
[3] Weld twice.
[4] Use heat sink back up bars in close proximity to weld.

General Stainless (P-8) 300 Series Pipe Weld Procedure Data.
Max interpass Temp 350F