A quasi in-situ study on the deformation mechanism in a 2.2Cr heat resistant steel

We elucidate here the micromechanism of deformation at elevated temperatures in a newly designed 2.2Cr–bainitic high strength and heat resistant steel using a quasi in–situ approach, which enabled us to describe the evolution of microstructure and corresponding mechanisms concerning plastic deformation at elevated temperatures. A new mechanism referred as dynamic precipitation (M₇C₃)−assisted continuous dynamic recrystallization process is proposed that illustrates the underlying reason for the ultrahigh strength (>400 MPa at 650 °C) of newly designed heat resistant steel. The study revealed the interactions between grain boundary sliding, dynamic recrystallization and shearing process, and the critical stress required for transition to corresponding deformation mechanisms are discussed quantitatively. It is proposed that the newly defined mechanism can enhance strain–hardening ability at high temperature, which is mainly attributed to dynamic precipitation at triple junctions of (sub)-grain boundaries. The study provides a new pathway to stretch the limits of high–temperature strength of heat–resistant steels.