Effects of the aging treatment on the precipitates and the tensile strength of austenitic heat-resistant steel

The Super304H was studied after aging treatment at 650 °C. With the time extension of aging treatment, the austenitic grains have not changed significantly. The number of the precipitates in the microstructure of austenitic heat-resistant steel was increased gradually. The tensile strength was gradually increased for precipitation strengthening of carbide precipitates, Cr 23 C 6 , the tensile strength reached its maximum and then dropped down after 600 h of aging treatment. The aggregation and growth of precipitated phase M 23 C 6 and Nb(C, N) led to a decrease in the tensile strength. The fractography of the tensile specimens changed from ductile to brittle fracture, and the fracture morphology changed from dimples to relatively flat cleavage planes.