Effect of Rare Earth La on the Precipitation Characteristics of Carbides in 42CrMo Steel and the Mechanism of Enhanced Tribological Properties

Rare earth 42CrMo steel was prepared by vacuum melting technology. The microstructure, tensile fracture, wear surface and subsurface of the material were characterized by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The improvement of carbide precipitation characteristics and enhancement mechanism of tribological properties in 42CrMo steel by La were studied. The results showed that La could make 42CrMo steel have smaller austenite grains and carbides by increasing nucleation points and reducing grain boundary tension, interface energy and carbide nucleation barrier. The prior austenite and carbide sizes of rare earth steel were reduced by about 46.5% and 19.4%, respectively. After adding La, 42CrMo steel had better mechanical and tribological properties. Compared with normal steel, the yield strength, tensile strength and elongation after fracture were increased by 9.29%, 9.48% and 25.01%, and the wear rate was reduced by 36.71%. The enhancement of the strength and plasticity of rare-earth steel is attributed to improving the interface flexibility between carbide and matrix and the refinement of grain and carbide. The tribological properties improve due to the flexible interface between the carbide and the matrix that coordinates the deformation during the friction and wear. It reduces the formation of microcracks and peeled carbides, making the self-lubricating film formed on the friction surface denser, more complete and less prone to damage. In addition, La also improves the plasticity and tribological properties of rare earth steel by reducing inclusions.