Effect of Minor Carburizing on Microstructure and Mechanical Properties of M50 Bearing Steel

Abstract

Herein, by using scanning electron microscopy, transmission electron microscope, X‐ray diffraction, residual stress analyzer, and mechanical‐property tests, the effect of minor carburizing on the microstructure and mechanical properties of M50 steel is studied. It is shown in the results that after minor carburizing, the austenite content in the surface layer of the quenched M50 steel increases, while the martensite content and the hardness decrease. After tempering, the retained austenite in the surface layer is transformed into martensite, and a large amount of uniformly distributed carbides are precipitated. The hardness of the surface layer increases to exceed that of the core region in the steel. After the minor carburizing, there is a carbon concentration gradient between the surface layer and the core region of the M50 steel, which influences the phase transformation behavior and the residual stress state in the surface layer during the tempering process. Minor carburizing increases the rotational bending fatigue limit of the steel by 16.7% and improves the tensile strength, yield strength, and impact absorption energy of the steel.