Stainless vs. mild TIG

admin

I am planning on getting some stainless steel to make some small end tables . Given the high price, I was wondering if anyone has any stainless tips. I have concentrated mostly on mild steel TIG work since most of what I do is car restoration. I have a lincoln 185 machine and my setup for regular steel seems to be right on for stainless, 2% tungsten/DCEN/Argon. Since this stuff ain't cheap, like me, I am looking to cut down on what get thrown away.
Reply:Gavin,here is some info from previous post.http://weldingweb.com/vbb/showthread.php?t=3608
Reply:Gavin,   I am currently working on a large stainless piping job, on 1/2 & 3/4""SS sch10 pipe I run about 60 - 62 amps with a 1/16" tung. about 18cfm argon with 1/16" filler.  2" 68amps 3/32 tung. and filler  3" 72amps 3/32 tung. and filler  4" - 8" 80-85 amps 3/32 tung. and filler  10 - 14" 90-95amps 1/8 tung. and 3/32 - 1/8 filler  14 - 18" 100 - 105 amps 1/8 tung and 1/8" filler   We keep the argon around 18 for all the pipe sizes unless we are having wind problems, then you crank it up.  Most of the time your fit up determines the size of the fill rod.  All of our work is with gas drive welders (302G Trailblasers) with lift start tig.                                                             Finney
Reply:Assuming its 304(L), you can use 308(L) and everything else would be the same for mild steel, as you posted. Finney is right on with 18 for argon. You really won't need more than that. If you are running to high an amperage, just ease off the pedal. Make sure that the stainless is super clean, no oils, residue, or such. Use a stainless steel brush to clean the welding area, and make sure it's not the same brush you would use for aluminum.
Reply:18cfm?  I assume that's intended to be cfh and I wonder if that's for a standard collet or a gas lens?I've read that stainless is prone to carbide precipitation, which may necessitate a backpurge.  Someone with more experience in this regard might be able to elaborate.-Heath
Reply:halbritt, you are right it is cfh, my goof.As far as a back purge if you do not you will get a oxygen contamination on the back side, it depends on the application as to if we use one, if it is a food grade product or over 100psi we will use purge plugs. if not we do not.
Reply:Why would you use 3/32 and 1/8 tungsten at such low current?-Heath
Reply:As halbritt states, stainless steel is prone to carbide precipitation, however it is not really a function of poor shielding.Stainless steel, such as 304, is protected from corrosion by the chromium within the metal grains, and specifically it is the chromium oxide that forms on the metal surface that is the protective layer.  Chromium has a great affinity to combine with oxygen to form oxides, nitrogen to form nitrides, carbon to form carbides.  Carbide precipitation, also called sensitization, occurs in 300 series stainless steels when heated in the temperature range of 800 to 1500 deg. F.  With time at this temperature, chromium is depleted within the grains as chromium carbides are formed (precipitated) at the grain boundaries.  So for high temperature applications, such as engine exhaust systems, carbide precip is an issue.As it relates to welding, a portion of the heat affected zone (HAZ) next to the weld is heated within the sensitization temperature range, carbide precipitation occurs, and a narrow zone is now prone to corrosion.Carbide precip is minimized by limiting the time at temp by keeping weld heat input low, small beads, fast travel, using copper chills, and rapid cooling (300 stainless does not harden when quenched).Carbide precip is minimized by reducing the carbon content as in 304L, 308L, 316L.Carbide precip is minimized by adding titanium or niobium as in 321 and 347.  Ti and Nb have a stronger affinity for carbon than Cr, so Ti and Nb carbides are formed rather than Cr carbides.Carbide precip can be reversed by annealing.As for halbritt's mention of back purging, it does make sense that poor shielding will result in the formation of Cr nitrides which will reduce corrosion resistance.The following links are just a few I ran across that deal with this subject.http://www.burnsstainless.com/TechAr...s_article.htmlhttp://www.fergusonmetals.com/media/321-347.pdfhttp://www.msm.cam.ac.uk/phase-trans...stainless.html
Reply:Halbritt,    The reason we use this size tungsten is our welders uasually spend 6 -7hrs per day with the hood down. If you sharpen to a long point you will spend more time welding and less time adjusting or resharping your tungsten. It seems to carry the heat better for some reason.