The weldability and welding characteristics of duplex stainless steels are better than those of ferritic stainless steels, but generally not as good as austenitic materials. Modern duplex steels with significant nitrogen contents are readily weldable. However, weldment properties are strongly affected by welding, so correct welding procedures, such as the heat input range, should be followed to obtain a correct weldment structure. The typical level of heat input used for duplex steels is 0.5-2.5 kJ/mm. For lean duplex and superduplex steels the levels is however somewhat lower and more narrow (0.2-1.5 kJ/mm). Duplex stainless steels commonly solidify with a fully ferritic structure with austenite nucleation and growth during cooling. Rapid cooling from high temperatures may still result in high ferrite levels in the weld metal and adjacent base metal. Therefore filler metals are specially designed with higher nickel contents to produce a phase balance similar to that of the base material. Of the same reason, autogenous welding (without filler) is generally not recommended for duplex steels. Even if duplex steels are not fully resistant to solidification and hydrogen cracking, this is a less significant issue than for some other stainless steels.

The duplex microstructure is more sensitive to the effect of subsequent passes compared to e.g. standard austenitic grades. To reduce this effect on microstructure from previous passes, the interpass temperature should be maximized to 150°C for standard/lean duplex and 100°C for superduplex steels.

Duplex weldment. Weld metal (left), HAZ (right).