Specific Methods for Welding Stainless Steel

    The type of stainless steel that you are likely to encounter varies by what the specific application is. There are three grades of stainless steel, and although there is naturally some overlap of function, each grade is used far more commonly for some purposes than others. When trying to determine which grade of steel you are dealing with, look first at what kind of object you are about to weld – this is often all the clue that you need to determine grade and, thus, procedure.

   The three stainless steel grades or varieties are:

1)    Austenitic stainless steel has a huge chromium content – up to 18% -- a large nickel content – up to 8% -- and is practically carbon free. Heat does not harden this kind of stainless steel, so be especially careful for warping or distortion. This steel melts at 200° F less than mild steel does due to the high chromium and nickel content. Its purposes include structural and nautical construction, as well as food-safe equipment and medical machinery. It can be readily welded and gives an excellent, strong weld.

2)    Ferritic stainless steel is the 400 series in alloy numbers, having around 11% chromium, and only a scanty trace of carbon, if any. It is used in light industrial applications such as cookware, building trim, folding chair frames, and the like. It can be welded.

3)    Martensitic stainless steel is another 400 series group of steels, as well as having alloy numbers in the 500 series. It has at least 1% carbon and is very hard, but has limited applications, mostly for the blades of knives and various tool steels. Some alloys can’t be welded, while others are magnetic and have a mirrored finish.

How to successfully weld stainless steel

    This technique applies primarily to the 300 series of stainless steels, which are the alloys you are most likely to be welding, anyway; after all, how often do you weld the blade of a broken hunting knife back together? Since the 300 series are the steels used for machinery, construction, and marine structures, these are likely to comprise 90% -- or 100% -- of your stainless welding.

    The two secrets to successfully welding stainless steel – which distorts easily and violently in excessive heat, and which needs to cool very quickly to prevent the chromium from precipitating out – consist of using low welding amperage, and welding quickly and without dawdling. Lower the amperage below what you would use for mild steel and tack the two pieces together before making a continuous weld bead along the seam.

    When making the actual weld, move the arc quickly, which will keep the heat low and allow the weld bead to cool fast, once the arc is away from it. Feed the filler metal into the welding pool as rapidly as you can, because the supply of new, cool metal will cool the entire welding pool a crucial few degrees. Preheating of the metal is absolutely proscribed. Having gas blowing on the reverse side of the welded joint will help to keep carbon at a minimum, too.