Influence of plastic deformation and prolonged ageing time on microstructure of a Haynes 242 alloy

Summary The material used in this study was a commercial HAYNES® alloy 242™ with a nominal composition of Ni‐25% Mo‐8% Cr (in wt.%). In the standard heat treatment, the 242 alloy is annealed at a temperature between 1065 and 1095 °C and then water quenched. The ageing treatment is carried out at 650 °C for 24 h in order to develop the long‐range‐order strengthening. The alloy in the conventionally aged condition was additionally cold rolled to 50% reduction in thickness and subsequently subjected to prolonged ageing at 650 °C for 4000 h. The enhanced diffusion resulted in the decomposition of the Ni 2 (Mo,Cr) metastable phase into the stable Ni 3 Mo‐based phase. The presence of the new stable phase increased the yield and tensile strengths but deteriorated the ductility of the alloy at both room and 650 °C temperatures.