Microstructure evolution and mechanical properties of X12CrMoWVNbN10-1-1 steel during quenching and tempering process

The effect of heat treatments was investigated on the microstructure evolution and mechanical properties of X12CrMoWVNbN10-1-1 steel. The as-received steel was austenitized at 1080 °C for 16 h and cooled in furnace, following tempered in two steps, i.e. at 570 °C for 18 h and then at 690 °C for 24 h. The austenitized sample had a typical lath martensite structure with some retained austenite and no delta ferrite was observed after austenitization . After the first tempering at 570 °C, there was no retained austenite remained but it resulted in the forming of precipitates, such as Cr-rich M 7 C 3 , Cr-rich M 23 C 6 , Cr-rich M 2 N, Nb-rich MN, and the subgrain , as well as the reduction in dislocation density . However, microstructure observation after secondary tempering proved the further arrangement of dislocation, subgrain growth and the coarsening of precipitates. Hardness and impact tests were carried out for establishing a correlation between microstructure and mechanical properties. Finally, a careful fractographic analysis of impact samples had been done using SEM and EDS .