渗碳硬化层性态的综合分析

A SYNTHETLCAL INVESTIGATION ON THE CHARACTERLSTICS OF CARBURIZED HARDENING LAYER

通过对20CrMnMo钢渗碳硬化层的组织结构、层内残余应力和硬度的分布以及渗碳硬化试棒的扭转性能进行系统的分析研究,经综合分析总结出20CrMnMo钢的渗碳硬化层具有下列几个特点,即:(1)渗碳层中基体组织的主体是枣核马氏体.枣核马氏体基体由表及里一直可延伸到含碳量为0.5%的层深部位(即有效层深,HV550处).(2)表面碳势为1.1%C的渗碳硬化层内,临近外表面部位的枣核马氏体中会出现显微裂纹.(3)残余奥氏体呈小块状(角状),它们被细小的枣核马氏体晶体分割.位于不同地点的残余奥氏体发生马氏体转变时,将对渗碳硬化层的性能起着不同的影响.(4)在心部组织相同的条件下,表面碳势及渗层深度与渗碳件的扭转塑变抗力无关,但马氏体内的显微裂纹和残余压应力的分布方式将直接影响渗碳硬化层的扭转断裂塑性.

The microstructure, residual stress, hardness and torsional properties of carburized hardening layer for 20CrMnMo steel were analysed systematically in this paper. Experiment results have shown that: (1) The matrix of hardened layer is mainly constituted by jujube-stonelike martensites. (2)When carburized under high carbon potential (1. 1% C), microcracks tend to appear on the martensitic matrix near the outer surface of the layer. (3)Retained austenites are separated by jujube-stone martensites and they will transform to martensites in service. The transformation of retained austenites can influence the mechanical properties of carburizing layer. (4)The distributive curve of carbon content is similar to the distributive curve of HV hardness. The position at the effective depth of carburizing layer is corresponding to the position at which the HV hardness number and the carbon content are equal to 550 and 0.5% respectively. (5)The torsional deformation resistance is independent of carbon potential and carburizing depth, but the microcracks in martensitic matrix can influence the torsional fracture plasticity directly.