真空分级淬火对8Cr4Mo4V钢组织和性能的影响

在真空条件下对航空轴承用8Cr4Mo4V钢进行不同温度的分级淬火并采用扫描电镜观察其微观组织、用XRD谱进行相分析并测试洛氏硬度、冲击性能和旋转弯曲疲劳性能,研究了真空分级淬火对其微观组织和力学性能的影响。结果表明,真空分级淬火后的8Cr4Mo4V钢其微观组织由下贝氏体、马氏体/残余奥氏体和碳化物组成；随着分级淬火温度的提高,淬火和回火态钢中析出碳化物的数量增加,残余奥氏体的含量降低。分级淬火温度为580℃时淬火态钢中贝氏体的含量最高(达到13.87%),残余奥氏体的含量为28.59%。回火后析出碳化物的含量和洛氏硬度均为所有分级温度中的最大值,分别为4.37%和62.38HRC。真空分级淬火能提高8Cr4Mo4V钢的综合力学性能。与未分级真空淬火相比,进行580℃×10 min真空分级淬火的8Cr4Mo4V钢的冲击韧性提高了23.3%,旋转弯曲疲劳极限提高了110 MPa。

Effect of Vacuum Graded Quenching on Microstructure and Mechanical Properties of 8Cr4Mo4V Steel

The 8Cr4Mo4V steel for aviation bearing manufacturing was subjected to graded quenching at different temperatures after being vacuum heat-treated. The effect of vacuum graded quenching on microstructure and mechanical properties of 8Cr4Mo4V steel were investigated by scanning electron microscope, XRD, Rockwell hardness tester, impact tester and rotational bending fatigue tester. Results show that the graded quenching 8Cr4Mo4V steel presents a microstructure of lower bainite, martensite/retained austenite and carbides. With the increase of graded quenching temperature, the number of precipitated carbides in the quenched and tempered steel increases, while the amount of retained austenite decreases. When the graded quenching temperature is 580℃, the bainite volume fraction of the quenched steel reaches a maximum of 13.87%, and the residual austenite volume fraction is 28.59%, and then after tempering, the precipitated carbides volume fraction and the Rockwell hardness reach the maximum namely 4.37% and 62.38 HRC respectively, in comparison to other desired graded quenching temperatures. The vacuum graded quenching can improve the comprehensive mechanical properties of 8Cr4Mo4V steel. In other word, the 580℃×10 min vacuum graded quenching treated 8Cr4Mo4V steel presents impact toughness and fatigue limit of rotational bending 23.3% and 110 MPa respectively higher than those of the traditional vacuum quenching treated ones.