The range and variance analysis of orthogonal experiment were used to analyze the experimental results. Through the comprehensive balance method, the optimal conditions were selected under the four indexes of the sample thickness, surface hardness, effective hardened layer depth and comprehensive friction and wear properties. The optimal scheme was obtained as follows: 580 ℃ × 4 h, NH3: CO2 = 0 4: Then, the surface hardness and microhardness of the samples were tested and the results were analyzed.

The surface hardness of lzqt600-3 ductile iron profile was tested under the optimal scheme after slightly grinding the sample surface. It can be seen from the table that the surface hardness values of the edge, 1 / 2R and core of the nitrocarburizing process increase gradually, and the surface hardness of the core reaches the highest value. This is due to the fact that the cooling rate at the edge is the largest and the cooling rate at the core is the smallest in the process of profile production. Therefore, the time of austenite transformation to pearlite is different, which leads to the increase of pearlite content from the edge to the core, and the pearlite content in the core is the most. Therefore, after nitrocarburizing, the surface hardness of the profile core is the largest, which is significantly higher than that of as cast lzqt600-3 ductile iron profile.