Nb元素对汽车渗碳齿轮用20CrMnTi钢热处理过程中晶粒粗化的影响

Effect of Nb element on grain coarsening of automobile carburized gear steel 20CrMnTi during heat treatment

分析了工业生产的两种汽车渗碳齿轮钢在相同伪渗碳工艺下的晶粒长大和析出颗粒分布情况,阐明了Nb元素在汽车渗碳齿轮钢中的作用。结果表明,添加0.02wt%Nb元素,可以减少0.02wt%Mo和0.02wt%Ti的添加量,但在960℃高温渗碳4 h后,Nb-Ti-Mo钢奥氏体晶粒尺寸略小于Ti-Mo钢,且混晶程度得到降低。此外,添加0.02wt%Nb元素,在960℃高温渗碳4 h后,Nb-Ti-Mo钢中析出颗粒体积分数略小于Ti-Mo钢,但是析出颗粒平均尺寸小于Ti-Mo钢,提供较好的钉扎作用,细化晶粒。添加0.02wt%Nb元素改善了析出颗粒的热稳定性,能够提供更优异的析出强化效果,析出强化贡献量为87.54 MPa。

Grain growth and precipitation particle distribution of two kinds of industrial carburized gear steels under the same pseudo⁃carburizing process were analyzed.Besides,the role of Nb element in automobile gear carburized steel was clarified.The results show that the addition of 0.02%wt Nb reduces the addition of 0.02%wt Mo and 0.02%wt Ti,and the austenite grain size of the Nb⁃Ti⁃Mo steel is slightly smaller than that of the Ti⁃Mo steel after carburizing at 960℃for 4 h.Furthermore,the degree of mixed crystal is reduced in the Nb⁃Ti⁃Mo steel.In addition,with the addition of the Nb,the volume fraction of precipitated particles in Nb⁃Ti⁃Mo steel after carburizing at 960℃for 4 h is slightly less than that of the Ti⁃Mo steel,but the average size of precipitated particles is smaller than that of the Ti⁃Mo steel,providing better pinning effect and grain refinement.The addition of the mass fraction of 0.02wt%Nb improves the thermal stability of precipitated particles and provides better precipitation strengthening effect,and the contribution of precipitation strengthening is 87.54 MPa.