Stainless steel is often used because it is very resistant to both rust and corrosion, thanks to the high levels of chromium contained in it. Being able to weld stainless steel is a great skill for any welder to have because not only does it make a welder very valuable, but some jobs are designed just for welders capable of welding stainless steel. It isn't the easiest metal to weld. Stick and wire feed welders can both be used when you want to weld stainless steel, but if you use a MIG welder, or wire feed, you have to use gas. This is because you won't find stainless steel in a flux-cored form.
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There are some things that you can do to make it easier when you are welding stainless steel. For example, make sure that you thoroughly clean the steel before you weld it. You have to clean the stainless steel because of the high chromium content and if you use a wire brush on the surface it should be clean. This will remove any chromium buildup, grease, oils, paint, and dirt. You have to make sure that stainless steel is completely free of any debris before you will be able to properly weld it.
You should always use low heat when you weld stainless steel. Most of the time stainless steel is in very thin sheets, and if you do not use low heat to weld it, you can warp it. Start with cool settings and then add heat slowly if you need to for stronger welds and better penetration. Sheets of stainless steel need to tack welded like car body panels. Tack weld them in several places then fill in later. This will reduce the chance of warping and you can easily make sure that everything is properly aligned. Another way to avoid warping the steel is to weld in short bursts of three to four seconds, stop and allow the steel to cool off, then weld again.
If you use a stick welder to work on stainless steel, use only stainless rods. If the rod's suffix ends with "-16" then use it with AC welders and if it ends with "-15" then it's for direct current reverse polarity use. Your strongest results will come from the "-15" rod but both will work very well. If you are planning to use a regular MIG or flux cored rods or wire for stainless steel welding, you need to remember that any portions that are welded will rust. Add primer or clear paint to help prevent corrosion.