Precipitation mechanism of dispersed carbide in a gear carburizing layer and its effect on properties

Abstract

AbstractHeat treatment is carried out on 20MnCr5 gear steel using a cycle carburizing process. The dispersed carbide precipitation mechanism in the carburized layer of 20MnCr5 gear steel is revealed, and the metallographic organization, microhardness, wear resistance, and fatigue properties are tested. The precipitation mechanism of two kinds of dispersed carbides at grain boundary and inside grain in carburized layer of gear steel was observed by experiment. The size of dispersed carbide particles is 0–5 μm, and 90% of the dispersed carbide is appropriately smaller than 1 μm. Compared to gears without dispersed carbide, gears with dispersed carbide have high microhardness within a 0.4 mm depth below the surface and a low friction coefficient. It has been verified by bench test that the presence of diffuse carbides dramatically improves the fatigue life of the gears after shot blasting and shot peening.