Fusion zone and heat affected zone cracking susceptibility of stabilised austenitic stainless steels

Abstract

Fusion zone (FZ) and heat affected zone (HAZ) cracking behaviour of three stabilised stainless steels were studied using the Varestraint hot cracking test. Materials ranged in solidification mode from fully austenitic D9 to primary austenitic 347 and primary ferritic 321. The materials exhibited high cracking susceptibility in the FZ and base metal HAZ. In the weld metal HAZ, type 347 was highly susceptible, while alloy D9 and type 321 were resistant to cracking. The FZ cracking behaviour could be related to the stabilisation ratio (Nb, Ti)/C rather than the P + S content and Creq/Nieq ratio, as in unstabilised stainless steels. In fact, analysis of cracking data using the Creq/Nieq ν. P + S content diagram did not reveal any systematic trend in cracking susceptibility. In the base metal HAZ, the high cracking in type 347 as well as in type 321 was found to be caused by the high impurity levels in conjunction with the presence of niobium and titanium. Cracking occurred much less in alloy D9.