Effect of heat treatment on the microstructure of a Ni–Fe based superalloy for advanced ultra-supercritical power plant applications

Abstract

The effect of heat treatment on the microstructure and microhardness of a Ni–Fe based superalloy for 700 °C advanced ultra-supercritical coal-fired power plants was investigated. Results showed that the main phases in the alloy were γ, γ′, MC and M23C6, and no harmful phase was observed in the alloy. M23C6-type carbides discretely distributed nearby grain boundaries as the alloy was aged at above 840 °C. The microhardness decreased with increasing aging temperature. The coarsening of γ′ led to the increment of microhardness at 780 °C and 810 °C for a short aging time, and a significant decrease in microhardness after aging at 840 °C. The aging temperature had more significant role on the microstructure than holding time. Therefore, to obtain optimum strengthening effect for this alloy, the aging temperature should not exceed 810 °C.