Effects of Quenching & Partitioning Heat Treatment on Microstructure and Corrosion Resistance of Die Steel 30Cr13

The phase composition and microstructure evolution of die steel 30Cr13 after quenching and partitioning (Q&P) heat treatment were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). And the corrosion behavior of the die steel treated in different heat treatment processes was analyzed in 3.5% (mass) NaCl solution by method of dynamic potential polarization. The results show that residual austenite content in 220Q sample quenched in salt bath and 220P sample treated by one-step Q&P heat treatment were smaller than 3% (volume). When the partitioning temperature in two-step Q&P process rose from 300℃ to 500℃, the content of residual austenite in the die steel increased first and then decreased, and got the maximum value when the partition temperature was 400℃. The microstructure of 220Q and 220P samples was composed of lath martensite. The microstructure of samples after Q&P heat treatment was also composed of lath martensite, and there were white bright bar or granular M₃C carbides between martensite laths. The difference between uniform corrosion resistance of the die steels treated in different Q&P processes was little. The two-step Q&P treated die steel samples had higher pitting potential than salt bath quenched sample and one-step Q&P treated sample.