Wear evaluation and microstructure analysis of cryogenically treated AISI 440C bearing steel

Abstract

In this study, two types of cryogenic treatment [deep cryogenic treatment (−196 °C) and shallow cryogenic treatment (−80 °C)] were used to increase wear resistance in AISI 440C bearing steel. Out focus was to find a way to increase wear resistance via deep microstructural analyses, and also to correlate the microstructure with the wear characteristics of specimens subjected to deep cryogenic treatment, conventional heat treatment, or shallow cryogenic treatment. Microstructural examinations of the specimens were performed using scanning electron microscopy, energy dispersive analysis of X-rays, and X-ray diffraction to study the wear characteristics of AISI 440C bearing steel. The results show that the specimens subjected to deep cryogenic treatment have greater wear resistance than the specimens subjected to shallow cryogenic or conventional heat treatment. The wear mechanisms included the formation and delamination of white layers. The microstructure of the steel was altered by the heat treatment process: the precipitation characteristics of the secondary carbides were modified and the levels of retained austenite were reduced, which correlated with the wear characteristics, and were identified as the potential mechanisms behind the increased wear resistance of the bearing steels due to the deep cryogenic treatment.