真空油淬马氏体不锈钢表面白亮层的形成原因

Formation causes of white bright layer on surface of vacuum oil quenched martensitic stainless steel

马氏体不锈钢螺母的表面在空气环境中易出现棕黄色锈迹,利用光学显微镜、扫描电镜和化学元素检测等方法对马氏体不锈钢表面锈蚀进行分析。结果表明,马氏体不锈钢在真空固溶+油液淬火后表面形成一层均匀的白亮层组织,白亮层组织耐蚀性较正常的马氏体组织差,白亮层组织在空气中易锈蚀,锈蚀通常不穿透白亮层。通过碳含量测定及机理分析,认为白亮层产生的必要条件为真空加热、油液冷却。真空加热引起不锈钢表层合金元素Cr贫化、冷却时油液中的碳渗入导致表层增碳,导致淬火时不锈钢表层未发生马氏体转变,形成耐蚀性较差的白亮层组织。

Surface of martensitic stainless steel nut was prone to brown yellow rust in the air environment. The surface rust of martensitic stainless steel was analyzed by means of optical microscope, scanning electron microscopy and chemical element detection. The results show that a uniform white bright layer structure is formed on surface of the martensitic stainless steel after vacuum quenched in oil. The corrosion resistance of the white bright layer is worse than that of normal martensite. The white bright layer is easy to rust in the air, and the rust does not penetrate the white bright layer. Through the measurement of carbon content and mechanism analysis, it is considered that the necessary conditions for the formation of white bright layer are vacuum heating and oil cooling. Vacuum heating causes the depletion of alloy element Cr on the surface of stainless steel, and carbon infiltration due to the oil decomposition leads to the carburization of the surface, which leads to no martensitic transformation on the surface of stainless steel during quenching, forming a white bright layer structure with poor corrosion resistance.