渗碳齿轮钢18CrNiMo7-6的疲劳性能及其影响因素

以18CrNiMo7-6齿轮钢为研究用基础钢，在传统真空脱气冶炼方式基础上，采用Nb微合金化和电渣重熔冶炼相结合获得一种对比试验钢，通过旋转弯曲疲劳试验表征了两种试验钢的疲劳性能，并利用显微组织、硬度分布、疲劳断口表征以及夹杂物分析等手段，探究了两种试验齿轮钢疲劳性能的影响因素。结果表明，采用电渣重熔方法冶炼并Nb微合金化的试验钢的疲劳极限较基础钢提高90 MPa,且相同载荷下寿命显著提高，渗碳层晶粒度由基础钢的7.5级细化至9级，而残留奥氏体含量的增加导致其表面硬度降低。通过Aspex夹杂物表征发现试验钢中夹杂物数量较基础钢大幅度降低，且硬质氧化物夹杂较少，与断口表征结果相一致。综合分析可知，晶粒细化和非金属夹杂物水平下降是提升试验钢疲劳性能的主要因素。

Fatigue properties and influencing factors of carburized gear steel 18CrNiMo7-6

Taking 18CrNiMo7-6 gear steel as base steel, a tested 18CrNiMo7-6 gear steel was prepared by traditional vacuum degassing smelting + Nb microalloying + electroslag remelting smelting, then the fatigue properties and influencing factors of both steels were comparatively studied by rotary bending fatigue test combined with analyses and characterization of microstructure, hardness distribution, inclusions and fatigue fracture. The results show that the fatigue limit of the tested steel smelted by electroslag remelting and Nb microalloyed is 90 MPa higher than that of the base steel, the service life under the same load is significantly increased, the grain size of the carburized layer of the tested steel is refined from grade 7.5 of the base steel to grade 9, but the surface hardness is decreased due to the increase of retained austenite content. The Aspex inclusion characterization shows that the number of inclusions in the tested steel is significantly lower than that in the base steel, and there are fewer hard oxide inclusions, which is consistent with the fracture characterization results. The comprehensive analysis shows that the grain refinement and decrease of non-metallic inclusion level are the main influencing factors to improve the fatigue properties of the tested steel.