Solidification behavior and cracking susceptibility of pulsed-laser welds in austenitic stainless steels

The solidification cracking susceptibility of several commercial heats of Types 304L, 316L and 321Mo stainless steels was evaluated under pulsed-laser welding conditions. Both the Suutala weldability diagram and the WRC constitution diagram predicted that all the heats tested in this investigation would be resistant to weld solidification cracking based on the individual values of their Cr[sub eq]/Ni[sub eq] ratio. Under the rapid solidification conditions imposed by pulsed-laser welding, however, a number of these resistant heats were found to be extremely susceptible to weld solidification cracking. As a result, a modified weldability diagram is proposed for austenitic stainless steels welded under conditions producing rapid solidification. The variation from predicted cracking susceptibility resulted from a shift in solidification behavior under rapid solidification growth conditions. Alloys susceptible to cracking exhibited a primary austenite solidification mode with a fully austenitic microstructure. Crack-resistant alloys were also fully austenitic, but this microstructure resulted from a massive transformation to austenite following primary solidification as ferrite. Several alloys exhibited mixed solidification modes, resulting in variable cracking susceptibility. The solidification conditions under which this shift in the primary solidifying phase occurs is reviewed in the context of the current results and previous observations.