Hot Ductility Behavior and Repair Weldability of Service-Aged, Heat-Resistant Stainless Steel Castings

The loss of repair weldability after service exposure in heat-resistant alloys has been related to the loss of ductility due to the formation of carbides and other compounds, such as nickel silicide. The hot ductility behavior of three service-aged, heat-resistant stainless steel castings, HP-45Nb, HP-50Nb, and 20-32Nb, were studied using the Gleeble® thermomechanical simulator. Results from hot ductility testing are presented and detailed fractographic analysis of samples tested at 900° and 1100°C is described. During the simulated cooling cycle, the HP-Nb modified alloy demonstrated significantly higher ductility as compared to the 20-32Nb alloy. The differences in high-temperature stability of the preexisting embrittling constituents in these alloys resulted in different microstructure evolution that influenced their hot ductility behavior. Based on the results, the service-exposed HP-Nb modified alloy is considered to have acceptable repair weldability. In contrast, the service-exposed 20-32Nb alloys showed severe susceptibility to liquation cracking and significant loss in on-cooling ductility, and are considered difficult to repair unless a high-temperature solution annealing heat treatment is performed.