Influence of Heat Treatment Process on Corrosion Resistance of SUS420J2 Plastic Die Steel

The phase composition, microstructure and corrosion resistance of SUS420J2 plastic die steel after quenching + tempering treatment were studied by means of X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and electrochemical workstation. The results show that the existence of M₂₃C₆ in SUS420J2 plastic die steel was closely related to the quenching and tempering temperature, some M₂₃C₆ carbide remained in the samples after quenching at lower temperature (980 ℃ and 1 030 ℃), while a large amount of M₂₃C₆ carbide with small size precipitated the sample after high temperature tempering at 650 ℃. When quenching temperature was 1 030 ℃, M₂₃C₆ carbides (particle size less than 0.1 μm) could be seen in the sample tempered at 300 ℃, and undissolved M₂₃C₆ carbides (particle size was about 0.5 μm) could be seen in the sample tempered at 650 ℃. Compared with the sample tempered at 500 ℃, the passivation film on surface of the sample tempered at 300 ℃ and 650 ℃ had better protection performance to the substrate and the corrosion resistance of the sample was better. The pitting corrosion resistance of the sample tempered at 300 ℃ was better than that of the sample tempered at 650 ℃, and the pitting corrosion resistance of the sample tempered at 500 ℃ was worse, which was mainly due to the size and existence form of Cr-rich M₂₃C₆ carbide during heat treatment.