High hardness and toughness of white cast iron: The proposal of a novel process

Based on the microstructure desired, a novel process is proposed to treat white cast iron balls, that is, destabilizing heat treatment following the multicycle quenching and sub-critical treatment (De-MQ-Sct) process, and the complex process is simply performed by alternate water quenching and air cooling. During the De-MQ-Sct process the precipitation of M7C3 secondary carbides promotes the martensitic transformation, meanwhile, the formation of martensite also accelerates the precipitation of M7C3 secondary carbides in austenite, and such an interaction effectively shortens the process time. Fe-2.4C-12Cr (mass%) cast balls were treated by the De-MQ-Sct process, and 60 HRC hardness and 12.6 J/cm2 impact toughness as average values were obtained, which are much higher than those of the counterpart treated by the conventional normalization (NOR) process. Characterization of microstructures reveals that excellent mechanical properties are attributed to the mixture of martensite matrix and considerable secondary carbides as well as retained austenite, and they replace the majority of pearlite matrix in NOR balls. The advantages of the De-MQ-Sct process are clarified by comparison with popular destabilizing heat treatment or sub-critical one.