Grain Refinement of P91 Steel Using Double Austenitization Treatment

TLDR: In this article, the effect of conventional normalizing and tempering (CNT) and double austenitization (DNT) heat treatments on the microstructure evolution and mechanical properties of creep strength-enhanced ferritic P91 steel were studied.

Abstract: The effect of conventional normalizing and tempering (CNT) and double austenitization–based normalizing and tempering (DNT) heat treatments on the microstructure evolution and mechanical properties of creep strength–enhanced ferritic P91 steel were studied. CNT treatment was performed at 1,050°C and air cooled for 1 h and also at 760°C and air cooled for 2 h. In double austenitization–based normalizing heat treatment, steel was austenitized at 1,050°C and air cooled for 1 h and then normalized in a temperature range of 950°C –1,150°C for 1 h followed by water quenching. After the double normalizing, tempering is performed at 760°C for 2 h. A DNT treatment resulted in homogeneous microstructure formation that led to improved mechanical properties as compared to CNT treatment. The incomplete dissolution of precipitates in single-stage tempering resulted in incomplete martensitic structure formation.