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

The material used in this study was a commercial HAYNES (R) alloy 242 (TM) 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 degrees C and then water quenched. The ageing treatment is carried out at 650 degrees 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 degrees C for 4000 h. The enhanced diffusion resulted in the decomposition of the Ni-2(Mo,Cr) metastable phase into the stable Ni3Mo-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 degrees C temperatures.