二次回火对50CrNi9MoV钢组织和力学性能的影响

Effect of second tempering on microstructure and mechanical properties of 50CrNi9MoV steel

利用SEM、TEM、XRD、MTS等仪器,研究了在相同的温度下一次回火与二次回火后50Cr Ni9Mo V试验钢组织与力学性能的变化。结果表明,50Cr Ni9Mo V钢在相同的温度下二次回火后的硬度、规定塑性延伸强度R（p0.2）、伸长率A、断面收缩率Z、冲击性能、断裂韧性K（IC）比一次回火后的高,而抗拉强度的变化则相反。50Cr Ni9Mo V钢在550℃一次回火后的残留奥氏体含量为6.21%,经550℃两次回火后的残留奥氏体含量为4.18%;在550℃一次回火后的Rm为1918 MPa,R（p0.2）为1013 MPa,屈强比为0.53;在550℃两次回火后的Rm为1710 MPa,R（p0.2）为1177 MPa,屈强比为0.69。可知,50Cr Ni9Mo V钢经二次回火能够降低残留奥氏体的含量,提高材料的屈强比,保证了材料在服役时的安全性。

Through SEM,TEM,XRD,MTS instrument,the microstructure and mechanical properties of the tested 50Cr Ni9Mo V steel were studied by first tempering and second tempering treatment at the same temperature.The results show that the hardness,proof strength R（p0.2）,elongation A percentage reduction of area Z,impact toughness and fracture toughness K（IC）of the 50Cr Ni9Mo V steel after the second tempering at the same temperature are higher than those after the first tempering,and the change of tensile strength Rmis opposite.The retained austenite content in the 50Cr Ni9Mo V steel after the first tempering at 550℃is 6.21%,and the retained austenite content after the second tempering at 550℃is 4.18%.After the first tempering of the 50Cr Ni9Mo V steel at 550℃,the Rmis 1918 MPa,the Rmis 1013 MPa,and the yield ratio is 0.53.After the second tempering of the 50Cr Ni9Mo V steel at 550℃,the Rmis 1710 MPa,the R（p0.2）is 1177 MPa,and the yield ratio is 0.69.It is seen that after the second tempering,the retained austenite content in the 50Cr Ni9Mo V steel is decreased,the yield ratio is enhanced,and the safety of the material in service is ensured.