Stainless Steel Welding

    A very common type of steel in the modern world, stainless steel is used for a wide range of tools and utensils because of its ability to shun rust. Most people encounter it as silverware or the screwdrivers, hammers, and needlenose pliers in their toolboxes. However, it is used in many other applications, too, and you never known when you might be called upon to weld it.

    Furniture frames are made out of stainless steel, as well as many parts in industrial machinery. Medical equipment of various kinds uses stainless steel so that fluids in contact with the metal will not become contaminated with rust. Storage tanks for liquids are made of stainless steel for the same reason, and are usually constructed and repaired with welding. There are also many construction and aerospace applications that make use of stainless steel.

    The techniques for welding stainless steel are a bit different from those used in welding ordinary carbon steel. This is because stainless steel contains a high amount of chromium. It is a deposit of chromium oxide on the steel’s exterior that keeps it from rusting, and it is necessary to weld in such a way that this deposit – and the chromium in the steel – is not lost. The fact that stainless steel contains up to 18% chromium as well as some nickel changes the way it responds to heat, also.

Special considerations with stainless steel

    Welding stainless steel requires a stainless steel filler metal as well, which sometimes is labeled as an “L” alloy. The electrode also needs to be of an “L” alloy – the L standing for “low carbon”. Introducing too much carbon into the stainless steel while welding it will precipitate the chromium out into chromium carbide. This, in turn, will weaken or entirely disperse the protective layer of chromium oxide and leave the formerly stainless steel vulnerable to rust.

    You need to be conservative while applying heat as well, lest you distort the stainless steel hideously. Thanks to its alloyed metals, stainless steel expands at 150% of the rate – half again as fast – as carbon steel. Therefore, even a small overheating of this metal can result in a major deformation of the finished piece, possibly ruining it entirely.

Heating and cooling stainless steel

    Weld color is a good guide to whether or not stainless steel has been overheated. A properly executed weld, which is cool enough to leave the chromium intact but hot enough to produce a vigorous bond, is either copper or straw colored. If the weld looks blue, it has been moderately overheated and the chromium protection along the weld line has been weakened. Black steel, or grey steel, along the weld line is a sign of disaster – the chromium has been baked out, and the weld is now vulnerable to rust.

    Stainless steel needs to be cooled as rapidly as possible after welding. Slow cooling gives the chromium time to bond with introduced carbon, so cool your welds fast for best results.