Hardening mechanism and thermal-solid coupling model of laminar plasma surface hardening of 65 Mn steel

In present work, the laminar plasma surface hardening method is employed to enhance the service life of metal components fabricated from 65 Mn steel. The mechanical and wear behaviors of the laminar plasma surface hardened 65 Mn steel were analyzed. The martensite transition temperature of the laminar plasma hardened 65 ferrites Mn steel was determined by a thermal-solid coupling model. Based on the orthogonal experimental results, the optimal hardening parameters were confirmed. The scanning velocity, quenching distance and arc current are 130 mm/min, 50 mm and 120 A, respectively. The pearlites and ferrites are transformed to martensites in the hardened zone, while the ratio of martensite in the heat-affected zone decreases with the increase of the hardening depth. Compared with the untreated 65 Mn steel, the average hardness increases from 220 HV0.2 to 920 HV0.2 in the hardened zone and the corresponding absorbed power increases from 118.7 J to 175.5 J, while the average coefficient of friction (COF) decreases from 0.763 to 0.546, and the wear rate decreases from 5.39×10-6 mm3/(N.m) to 2.95×10-6 mm3/(N.m), indicating that the wear resistance of 65 Mn steel could be improved much by using laminar surface hardening. With the same hardening parameters, the depth and width of the hardened zone predicted by the thermal-solid coupling model are 1.85 mm and 11.20 mm, respectively, which are in accordance with the experimental results: depth is 1.83 mm and width 11.15 mm. Besides, the predicted hardness distributions of the simulation model are also in accordance with the experimental results. These results indicate that the simulation model could predict the microstructure characteristics of 65 Mn steel effectively.