Effects of the aging treatment on the precipitates and the impact toughness of austenitic heat resistant steel

The Super304H was studied after aging treatment at 650°C. With the time extension of aging treatment, the matrix of austenitic heat-resistant steel was still austenitic, and the size of the austenitic grains had not changed significantly. The number of precipitates in the microstructure of austenitic heat-resistant steel was increased gradually, and the precipitated phases were coarsened, aggregated and grown. The aggregation and growth of precipitated phase M 23 C 6 and Nb (C, N) led to a decrease in the impact toughness. The ductile transgranular fracture was gradually turning into the brittle intergranular fracture, and the fracture morphology of large-sized dimples was gradually turning into the fracture morphology of the dissociative surfaces that were relatively flat.