S含量对18CrNiMo7-6齿轮钢中夹杂物和疲劳性能的影响

Influence of Sulfur Content on Inclusion and Fatigue Properties of 18CrNiMo7-6 Gear Steels

以w[S]为0.002%(低S含量)和0.022%(高S含量)的两种18CrNiMo7-6齿轮钢为研究对象,参照齿轮热处理工艺获得伪渗碳试样,并对其力学性能、显微组织、疲劳性能和夹杂物分布进行了分析表征。结果表明,两种齿轮钢的强度基本相当,而高S含量试验钢具有更好的塑性和低温冲击韧性,并且其疲劳极限、疲劳寿命均优于低S含量试验钢,疲强比由0.445提高到0.479。S含量显著影响钢中的夹杂物分布情况:低S含量试验钢中夹杂物以MnS-Oxide为主,数量较少,同时尺寸更大;而高S含量试验钢夹杂物以CaS-MnS-Oxide复合型夹杂物为主,数量提高1倍以上,但尺寸更为细小。高S含量试验钢采用Ca处理工艺对夹杂物进行改性,夹杂物尺寸明显细化,有利于钢的塑韧性提升,并改善疲劳性能。

In this paper,two kinds of 18CrNiMo7-6 gear steels with sulfur content of 0.002%(low sulfur content)and 0.022%(high sulfur content)were studied.Pseudo-carburizing samples were obtained by reference to gear heat treatment process,and the effects of sulfur content on mechanical properties,microstructure,fatigue properties and inclusion distribution of the steels were investigated.The results show that the strength of the two steels is basically similar,while the steel with high sulfur content has better plasticity and low temperature impact toughness.Meanwhile,its fatigue limit and fatigue life are better than those of the low sulfur content steel,the fatigue ratio increases from 0.445 to 0.479.Sulfur content significantly affects the distribution of inclusions in steel,the inclusions in low sulfur content steel are mainly composed of MnS and oxides with less quantity but larger size,while the inclusions in the high sulfur content steel are mainly complex inclusions composed of Cas,MnS and oxides with more than doubled quantity but smaller size.By employing Ca treatment technique,the inclusion size of high sulfur content steel is obviously refined,which favors better mechanical properties and fatigue performance of steel.