Welding stainless steels is not necessarily difficult if you follow a few basic guidelines. Tig or Gas Tungsten Arc Welding is often used for joining stainless, especially if the weld must be of extremely high quality. If you're just getting started or are looking to improve your stainless steel Tig welds, here are a few basics that will help you along the way:
1. Know your base metal! There are many different stainless alloys with various mechanical & chemical properties. If you know your base metal type or grade it will be much easier to select the proper filler metal for your application.
2. Use a sharpened, 2% ceriated or lanthanated tungsten electrode. These are excellent all-around electrodes that work well with AC or DC & they aren't radioactive like 2% Thorium. Avoid pure & zirconium tungsten because they are known as "ball formers" that are more desirable when welding materials like aluminum using AC current. Don't forget to use a tungsten rated for your welding range. There is no one-size-fits-all electrode ... As each diameter has a specified operating range. However, I find a 3/32" diameter works for most jobs.
3. Use 100% argon shielding gas for almost every application. Flow rates should be between 15-20 cubic feet per hour, perhaps more if your welding near a draft or outside. If your weld or tungsten show signs of oxidation - by turning gray or black - you may need to increase your flow rate or block any drafts.
4. Clean your material using only dedicated tools to prevent cross continamination with other alloys or impurities like rust. It's a good idea to keep a stainless steel wire brush on hand. I also have a dedicated angle grinder setup with cutoff wheels, sanding discs & buffing pads that are only used on stainless.
5. Use Direct Current Electrode Negative (DCEN) or "straight" polarity. This concentrates the arc on the base metal & minimizes any tungsten erosion that might occur.
6. Consider pulsing to minimize your heat input & control distortion. Pulse at a low rate to slow things down & produce a distinct ripple pattern in the weld ... And use higher pulse frequencies to focus & concentrate your arc.
7. Tack it, tack it & when you think you've tacked it enough, tack it some more! Stainless is a relatively poor conductor of heat, so it has a tendency to heat & cool unevenly - causing it to warp & distort severely. If the material is very thin, use a back-step technique ... Or weld the end section first, back step to weld the middle, then weld the beginning. Remember that distortion happens "in the direction of travel" & is directly proportional to the average weld width ... So keep your weld as narrow as possible.
8. Keep the heat input low. Contrary to popular belief, you won't "burn out the chrome" but you could cause serious damage to the corrosive properties of the alloy if you overheat it. Figure that you'll need about 1 amp for every 0.001" of metal thickness ... And you'll want to get up to that amperage relatively quickly so you can form a puddle & get moving. Ramping up too slowly allows for excess heat to build in the metal & widen your heat-affected zone.
9. Use accessories if you've got 'em ... Like a gas lens to improve your shielding & allow for greater tungsten stick-out. A remote control is also nice for adjusting your welding amperage on the fly to control things like weld width & heat input.
10. Turn the post flow ON ... To protect your weld & electrode as they cool to room temperature. You need a minimum of five (5) seconds in general & a good rule of thumb is 1 second for every 10 amps.
If you follow these guidelines for your Tig setup you should be off to a good start for some quality weld results. However, keep in mind these pointers are just the basics and your application may require significantly more effort depending on the alloy or grade, service conditions and quality requirements. It's not uncommon to purge the backside of the weld with argon or use a heat-syncing fixture to pull heat away.