HEAT-AFFECTED ZONE LIQUATION CRACKING IN AUSTENITIC AND DUPLEX STAINLESS-STEELS

The heat-affected zone (HAZ) liquation cracking susceptibility of several commercial austenitic and duplex stainless steels was evaluated using the spot Varestraint test. Test results revealed that among the austenitic stainless steels, the susceptibility to cracking was a strong function of ferrite potential (FP), a measure of the tendency for ferrite formation along HAZ grain boundaries adjacent to the fusion line derived from a calculated ferrite number (FN). Low FP heats (FP 0-1) of Type 304L were found to be more susceptible to cracking than a Type 304 alloy with FP 8. The HAZ liquation cracking susceptibility of the duplex stainless steels, Ferralium 255 and Alloy 2205, was roughly equivalent to that of the low-FP austenitic stainless steels. Metallographic and fractographic examination of the spot Varestraint samples revealed that cracking was characteristically intergranular in all the alloys, but that the amount of grain boundary liquid associated with the HAZ cracks varied considerably. Essentially no grain boundary liquid films could be detected in the duplex stainless steels or the high-FP austenitic stainless steel. Segregation-based grain boundary liquation models are reviewed and discussed in the context of the observed cracking susceptibility.