中合金铬钼渗氮轴承钢旋转弯曲疲劳性能研究

Rotating bending fatigue properties of medium alloy Cr and Mo nitriding bearing steel

为了研究化学热处理对大型轴承疲劳性能的影响规律,对中合金铬钼轴承钢进行离子渗氮处理和旋转弯曲疲劳(RBF)试验。以双真空熔炼(VIM+VAR)的中合金铬钼轴承钢作为实验材料,分析经调质处理(930℃+550℃)后的组织和经离子渗氮后的相组成,分析经过旋转弯曲疲劳试验后断口形貌及裂纹萌生机理,构建表面缺陷与疲劳断裂机理之间的关系。实验结果表明:实验钢经过调质处理后组织为回火索氏体,主要析出M2C型和M3C型碳化物;渗氮后渗氮层中化合物层主要由CrN和Fe4N(γ′相)组成,厚度约为16μm,其不利于基体的疲劳性能提升;实验钢渗氮后的RBF极限为947MPa,较未渗氮试样旋转弯曲疲劳极限提升19.4%;渗氮层中化合物层始裂及非金属夹杂物始裂为主要的两种起裂方式,化合物层和表层粗糙度对渗氮后实验钢的疲劳寿命影响较大。研究结果可为提高中合金铬钼轴承钢的疲劳性能提供实验及理论依据。

In order to study the influence of chemical heat treatment on the fatigue performance of large bearings,plasma nitriding and rotating bending fatigue test are conducted for the medium alloy Cr and Mo nitriding bearing steel.The middle alloy Cr and Mo bearing steel with double vacuum melting is used as the experimental material to analysis the microstructure after hardening and tempering(930℃+550℃)and the phase after plasma nitriding.The fatigue morphology and the mechanismroom of crack initiation after the test are analyzed.The relationship between surface defects and fatigue fracture mechanism is established.The results of experimentalshow that the microstructure of the test steel after hardening and tempering is tempered sorbite,M2 C and M3 C is the mainly precipitations.After nitriding,the compound layers in the nitriding layers are mainly composed ofγ′phase(Fe4 N)and CrN and the thickness is about 16μm,which is not conducive to improve the performance ofmatrix fatigue.The RBF limit of the experimental steel after nitriding is 947 MPa,which is 19.4%higher than the RBF limit of the non-nitriding sample.The cracking of compound layer in the nitrided layer and the cracking of non-metallic inclusions are the two main ways of cracking.The compound layer and surface roughness have great influence on the fatigue life of test steel after nitriding.The results provide experimental and theoretical basis for improving the fatigue performance of medium alloy Cr and Mo nitriding bearing steel.