Handbook-Welding Ferrous Metals

Welding Technique. As noted above, you need a suitable filler metal and a flux specifically formulated for

stainless steel welding. The flux should be mixed with water to form a thin paste, and then painted on the surfaces to be welded. Because stainless steel has much lower heat conductivity than ordinary carbon steel, the welding tip selected should be one or two sizes smaller than the size you would use with carbon steel of the same thickness. Adjust the welding flame to have a slight excess of acetylene. (A truly neutral flame will be satisfactory, but any excess of oxygen will cause trouble; a slight visible excess of acetylene is suggested to guard against the possibility of excess oxygen.) Since the austenitic stainless steels have a much higher coefficient of expansion than mild steel, particular attention must be paid to the expansion/contraction problem. For sheet metal, careful jigging, with chill plates designed to conduct heat out of the metal at a point close to the weld zone, is strongly recommended. In material thicker than 2 mm (16-gauge) sheet, when a weld longer that 30 cm (1 ft.) must be made, it’s a good idea to tack- weld both ends in normal fashion, but then keep a wedge in the joint, 15-20 cm ahead of the weld puddle, and move the wedge periodically as the weld progresses. While welding, try to avoid moving the filler rod any more than is absolutely necessary. Keep the weld puddle as quiet as possible, trying to melt both rod and base metal almost simultaneously. This will minimize the chance of excessive oxidation of the molten metal, with resultant loss of chromium. While the standard forehand welding technique is preferred for welding sheet, the backhand method is probably better for heavy material, since that technique makes it easier to melt both rod and base metal together.