35CrMoA钢激光淬火-渗氮复合改性层微观组织及脆性

研究了气体渗氮层和激光淬火-渗氮层的相组成、微观结构、显微硬度及脆性。结果表明, 激光淬火-渗氮白亮层中ε-Fe₃N含量由14.74%增至69.45%, 而脆硬的ξ-Fe₂N含量由79.95%降至25.03%。表层的N含量降低, 渗氮层N浓度曲线降低趋势平缓, N的总扩散通量增加, 渗氮层厚度增加。激光淬火-渗氮层组织晶粒细小致密, 渗碳体分布在条状下贝氏体组织中, 硬度高的Cr₂N颗粒数目增加, 白亮层显微硬度值显著提高, 渗氮层脆断的临界压力由气体渗氮层的3 N提高到激光淬火-渗氮层的6 N。 

Microstructure and brittle of 35CrMoA steel in laser quenching-nitriding compound modified layer

The phase composition, microstructure, micro-hardness and brittleness of gas nitriding layer and laser quenching-nitriding layer have been studied. The results show that the content of ε-Fe₃N in bright layer of laser quenching-nitriding layer increases from 14.74% to 69.45%, while the content of crisp and hard ξ-Fe₂N drops from 79.95% to 25.03%. The curve of nitrogen concentration in nitriding layer decreases gently with the decrease of the nitrogen content in the surface layer. The total diffusion flux of nitrogen and the thickness of nitriding layer increase. After laser quenching-nitriding, the crystal grain is tiny with cementite distributing in strip lower bainite. The number of high hardness Cr₂N particles enchances, which obviously improves the micro-hardness of bright layer. Brittle fracture critical pressure of nitriding layer increases from 3 N of gas nitriding layer to 6 N of laser quenching-nitriding layer.