Study on the friction and wear properties of 40Cr steel by selective laser transformation

To solve the surface wear problem of 40Cr steel parts, incorporated with the theory of surface texture, laser phase transformation hardening technology was applied to preparate various shapes (spot and striation) of hard-soft coupling surfaces with regular distribution. Scanning electron microscopy, X-ray diffraction, friction and wear machine and ultra-depth of field microscopy were adopted to analyze the microstructure, physical phase, anti-wear performance, and wear surface morphology of the phase transformation zone. the results show that the cross-section hardness of the spot phase transformation zone is higher than the striation, with the average of (720±3) HV_0.1, and the hardening layer is deeper. Martensite, Cr₇C₃, and Fe₇C₃ are generated after phase transformation. By comparing the friction coefficient between the untreated surface and the hard-soft coupling surface of 40Cr steel, the friction coefficient of the hard-soft coupling surface is inferior to 0.5 and its fluctuation is smaller which demonstrates great friction stability. In addition, the wear surface damage of the hard-soft coupling surface is small, and the reason of this is that the hard phase could resist the deformation while the soft phase could release the stress concentration and the accumulation of plastic deformations. The soft phase field is mainly pear peeling and adhesion damage, and the hard phase area is mainly small pitting pits. The 900W spot soft-hard coupling surface with the first-rate anti-wear performance. Above all, the conclusion is that the hardening phase with great plastic toughness and a certain proportion (50%) of inerratic surface distribution can markedly increase and promote the anti-wear performance of the material working surface, improve the contact surface of the fraction pair as well as stabilize the friction coefficient, this study can provide a reference for improving the surface wear of 40Cr parts.