Effect of heat treatment process on Microstructure and properties of 4Cr13N corrosion resistant plastic die steel

Abstract

The effect of heat treatment process on microstructure and mechanical properties of 4Cr13N corrosion-resistant plastic die steel were investigated. The experimental results indicate that, with the increase of quenching temperature of 4Cr13N steel, the undissolved second phase gradually decreased, the martensitic lath gradually coarsened, and the hardness first rise up and then move down. The hardness of 4Cr13N steel reaches the highest at 1020 °C, at this time, the quenching microstructure is martensite + undissolved carbide + retained austenite, and the type of undissolved carbide is M23C6. The tempering hardness curve has an obvious secondary hardening peak, the peak temperature is 500 °C, and the peak hardness is 55 HRC. Below 500 °C , with the increase of tempering temperature, granular nitride Cr2N dispersion precipitation from matrix, resulted in second phase strengthening, hardness increased, impact toughness decreased, and the fracture mode is quasi-cleavage fracture; Above 500 °C, the structure gradually transformed to sorbite, the hardness decreased, and the toughness increased. Over all, to achieve a better match of strength and toughness, 4Cr13N plastic die steel should be tempered between 200 ~ 480 °C, impact energy are above 15 J, hardness above 50 HRC.