Microstructure evolution of 9Cr-1.7W-0.4Mo-Co ferritic heat-resistant steel during isothermal aging

The microstructure evolutions of 9Cr-1.7W-0.4Mo-Co ferritic heat-resistant steel during isothermal aging were investigated by optical microscope (OM), scanning electron microscope (SEM). In addition, the vicker's hardness of the steel and the distribution of alloying elements were analyzed, respectively. The occurance of recovery and recrystallization with the duration of isothermal aging can be found, and the width of martensitic plates increases. The density and particle size of precipitates (such as M23C6, MX) also increase sharply with the increase of aging time. Most of M23C6phase and MX phase are precipitated around ferritic grain and in the ferritic grain, respectively. The vicker's hardness firstly increases, and then decreases to a stable value during isothermal aging. © 2015, Editorial Office of Transactions of Materials and Heat Treatment. All right reserved.