Effect of Cryogenic Treatment on the Microstructure and Wear Resistance of X45Cr9Si3 and X53Cr22Mn9Ni4N Valve Steels

Abstract

The effect of cryogenic treatment on the microstructure and wear resistance of X45Cr9Si3 and X53Cr22Mn9Ni4N valve steels is investigated by conducting an optical and scanning electron microscopy (SEM) study and reciprocating wear test (ASTM standard G-133). The materials are subjected to shallow (193 K) and deep cryogenic treatment (85 K), and the microstructure and wear resistance are compared with those of conventional heat treatment. The wear test data show that for a maximum load of 30 N and 5 Hz frequency, the wear resistance of the X45Cr9Si3 and X53Cr22Mn9Ni4N improved by 15.2 and 10.3%, respectively, due to shallow cryogenic treatment (SCT) and 42.39 and 22.08%, respectively, due to deep cryogenic treatment (DCT) compared to that of the conventional heat treatment. The enhancement in the wear resistance of the X45Cr9Si3 and X53Cr22Mn9Ni4N valve steels observed through the optimized DCT was 46.51 and 27.8%, respectively, compared to the samples without cryogenic treatment. The microstructural study clearly proves that the full elimination of the retained austenite was not achieved in the SCT and DCT specimens. However, there was a reduction in the amount of retained austenite when compared to conventional heat treatment (CHT) specimens. After studying the metallurgy of the cryogenically processed valve steels, it was concluded that the formation of fine carbides dispersed in the tempered martensite structure was the main reason for the enhancement of wear resistance along with the retained austenite transformation.