Stainless Steel Welding

Stainless Steel Welding

Stainless Steel Welding may not be as difficult as welding aluminum, the metal does have its specific properties that vary from your more common steels.

To make a steel "stainless" it needs to contain a minimum of 12% Chromium (Cr). The Cr oxidises in the atmosphere forming a passive layer on the surface. This layer, unlike coated steels, is self repairing should it be scratched.

The problem with 12% Cr is that it is fairly brittle and only provides the minimum corrosion resistance. Increasing the Chromium content to 17% improves corrosion resistance but increases brittleness. Adding 8% Nickel makes the steel ductile again. Thus 18/8 stainless was born (304). 316 / 316L has additional Molybdenum and higher Nickel which provides greater corrosion resistance.

With stainless when you see two numbers they always refer to the Chromium and Nickel content - 18/8 is 18%Cr and 8%Ni. If you see 3 numbers like 19/12/3 they refer to the Chromium, Nickel and Molybdenum content. 316L is 19%Cr, 12%Ni and 3%Mo.

The usual choice for the filler when welding stainless to mild is 309L. 309 is over alloyed stainless steel (19/10) so when diluted by the mild steel gives a deposit approximately like 308L / 304L.

There are other fillers that give a crack free weld, 312, 308MoL, 307 and 310 will all work but these are less widely available than 309L.