合金钢稀土渗氮层的硬度增强机理

Hardness enhancement mechanism of rare earth nitrided layer on alloy steels

为研究合金钢稀土渗氮层硬度增强机理,采用扫描电镜、透射电镜和显微硬度计等测试方法,对3种常用合金钢的常规渗氮和稀土渗氮的显微组织和渗层硬度进行分析。结果表明:稀土原子的渗入导致钢表层晶粒缺陷密度增加,在缺陷处生成气团,使晶粒内氮原子偏聚区增多,晶粒亚结构细化,导致硬度提高;同时稀土原子沿晶界渗入和扩散,会诱导晶界迁移,使晶界表面突壁和扭折密度发生变化,可以使常规渗氮中容易析出的网状ε氮化物减少,降低了沿晶界断裂的可能性,强化了晶界。这些作用的叠加,提高了渗氮层的硬度和材料的力学性能。

Microstructure and nitrided layer hardness of three kinds of commonly used alloy steels after conventional nitriding and rare earth nitriding were analyzed by means of scanning electron microscopy, transmission electron microscopy and microhardness tester, and the hardness enhancement mechanism was investigated. The result shows that the infiltration of rare earth atom leads to the surface crystal defect density proliferation of the steels and promotes to generate Cottrell atmosphere in the defect, makes the nitrogen atom segregation region increase and the substructure refine, and all these lead to the increase of hardness. Infiltration and diffusion of the rare earth atoms along the grain boundary will induce migration of the grain boundary, and make the density of extruded wall and kink on the grain boundary surface change, it will reduce the reticular ε nitrides forming along the grain boundary, cut down the possibility of intergranular fracture and strengthen the grain boundary. Cooperation of all these factors enhances the hardness of nitride layer and increases mechanical properties.