What Is Stainless Steel?
Duplex Stainless Steel
Duplex stainless steels have a two-phase structure of almost equal proportions of austenite and ferrite. The composition of the most common duplex steels lies within the range 22-26% Cr, 4-7% Ni, and 0-3% Mo, normally with a small amount of nitrogen (0.1-0.3%) to stabilize the austenite. Modern duplex steels are readily weldable, but the procedure, especially maintaining the heat input range, must be strictly followed to obtain the correct weld metal structure.
Avoiding weld imperfections – Although most welding processes can be used, low heat input welding procedures are usually avoided. Preheat is not normally required, and the maximum interpass temperature must be controlled. Choice of filler is important as it is designed to produce a weld metal structure with a ferrite-austenite balance to match the parent metal. To compensate for nitrogen loss, the filler may be overalloyed with nitrogen or the shielding gas itself may contain a small amount of nitrogen.