tig welding stainless steel sheet metal

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Is tig welding stainless steel sheet metal about the same as tig welding mild steel sheet metal?
Reply:yes and no.  They flow about the same although the ss tends to be a bit harder to fuse weld.  You need to watch your heat input to get the colors right and you might need to back gas it but its not hard to do.  Don't try to rip across the material with alot of heat or you will get bad colors and you might get crystals on the back side of the weld.  If you want to mig it it is just like steel but you need to run a tri-mix gas or the weld will come out black.
Reply:Stainless Pulls much more than Mild Steel.    Trian with a Seasoned Tig Welder
Reply:Deejay,here is a generalized comparison of the physical properties of mild steel and 300 series stainless steel that helps explain why there are some differences in welding.1.  The thermal conductivity of 300 stainless steel is lower than mild steel.  This means that less amperage is needed to produce the same melted volume because the energy put into the weld is slower to be conducted away to the surrounding metal.  For this reason, the heat affected zone (HAZ) will also be smaller than that of steel for a given heat input.  Aluminum and copper are extreme examples of metals that require much higher amperage than stainless and steel, because of their high thermal conductivity.2.  The thermal expansion of 300 series stainless steel is higher than mild steel.  This means that stainless with distort more than mild steel for a given weld size/heat input.  Welding distortion occurs as the solidified, high temperature weld expands against the constraints of the surrounding base metal.  Generally, a sheet or plate will tend to restrict expansion along it's length and width, forcing the weld to expand in the thickness direction.  Upon cooling then, the weld contacts, creating residual tensile stress in the weld area, leading to distortion and cracking stresses.3.  Carbon steel, such as mild steel (low carbon content) is hardenable by heat treatment.  Rapid quenching of carbon steels, depending on its carbon and alloy content, can cause the steel to be hardened and strengthened, which when properly controlled can give desired properties, but when not controlled can result in brittle properties and cracking.  The 300 series stainless steel, however, are not hardenable by heat treatment.  You can quench these stainless steels immediately after welding without risk of hardening, although this may affect distortion of the weldment.4.  Stainless steel is corrosion resistant due to 12% or more chromium content that becomes distributed around the grains of iron in the steel, forming a protective layer of chromium oxide on the surface.  Extended heating of 300 series stainless, such as from excessive heat in welding and slow cooling, can allow the formation of chromium carbides and reduced corrosion resistance in the weld HAZ.  For critical applications, welding heat input must be controlled and rapid cooling may be needed.5.  Undesirable oxidation of stainless steel is very easily seen by the range of "heat tint" colors produced by welding heat and inadequate inert gas shielding.  The terms "sugaring" or "crystallization" are used by some to describe the severely oxidized stainless steel weld.  Ideally, the weld area, both front side and back side should be shielded from high temperature oxidation by inert gas such as argon.  A perfectly shielded weld, allowed to cool under the protection of inert gas, will show no discoloration at all.Hope this helps.
Reply:weldingman why do you think you need a try mix gas to mig stainless?im not trying to start anything but were ever you got that info it's wrongi've got hundreds of hours welding stainless with argon/c02 98/2and none of my welds ever came out black ?again im not trying to get you mad im just asking i've herd the same thing from other weldors and the only anser i got from them was you just do i think it just a way the gas companys get weldor to by it lolchuck
Reply:Tri-Mix is the standard recommendation for welding stainless using short-circuit transfer.  That is >90% helium with the balance of argon and CO2.  I suppose helium is preferred because it provides greater heat input and a nice appearance on a short-circuit bead.  I know of folks that have used 98/2 argon and oxygen for spray and also blends with a few percent CO2.  Reactive gas (O2 and CO2) is beneficial in that it provides good bead wetting properties, but it can't be used in any great quanitities when welding stainless as it will cause oxidation and carbide  precipitation which can at best affect bead appearance and at worst cause the joint to fail.  Interestingly, I've just read that one can use a little bit of H2 (1-2%) in combination with a little CO2 (1-2%) and the balance of argon to create a reducing atmosphere that provides excellent bead appearance on stainless.  One can also assume that it provides excellent corrosion resistance on the welded joint.-Heath
Reply:Probably dont want 02 for a shielding gass!!!!!!!!Also, we are talking TIG here not mig.  At least thats what the subject says.
Reply:My mistake.  Please ignore my advice as it is for MIG rather than TIG.-Heath
Reply:chopper,  I ment dont try to weld it with 75/25 or the weld will come out black with lots of spatter.  One of the guys on first shift forgot to change out the bottle and then welded the assembly and thats how it came out.  And the 98/2 I forgot about that one we used to use it but the company that we do stainless for called for the tri-mix gas.  Dont worry not offended
Reply:ok i needed to ask like i said i got hunded of hours welding that stuffany way some guys get bent wen you aks why you useing that wire or that gasi know there is more to learn than i know now but what i do know i have donefor years . glad to see you not madchuck