回火温度对55CrVNb弹簧钢组织与性能的影响

Effect of tempering temperature on microstructure and properties of 55CrVNb spring steel

采用扫描电镜、透射电镜、X射线衍射仪和万能拉伸试验机等研究了不同温度回火对55CrVNb弹簧钢组织演变与力学性能影响。结果表明:55CrVNb弹簧钢淬火后的组织主要是板条与针状马氏体;在250~550℃回火50 min时,随着回火温度的升高,马氏体板条模糊并逐渐消失,碳化物沿马氏体边界析出,数量增多尺寸也在增大,位错密度逐渐降低,固溶强化,位错强化、析出强化作用减弱,导致55CrVNb弹簧钢的强度降低,抗拉强度从2119.7 MPa下降至1228.0 MPa,屈服强度从1918.8 MPa下降至1188.9 MPa;随着回火温度升高,55CrVNb弹簧钢的伸长率呈现先升高后降低趋势,断裂类型由脆性断裂向韧性断裂转变;实验钢最佳的热处理工艺参数为:860℃奥氏体化30 min,450℃回火50 min。

Effect of different temperature tempering on microstructure evolution and mechanical properties of 55CrVNb spring steel was studied using scanning electron microscopy,transmission electron microscopy,X-ray diffractometer and universal tensile testing machine.The results show that the microstructure of the 55CrVNb spring steel after quenching is mainly lath and acicular martensite.When tempering at 250-550 ℃ for 50 min,with the increase of tempering temperature,the martensite lath is blurred and gradually disappears,the carbides precipitate along the martensite boundary,the number and size of carbides both increase,the dislocation density gradually decreases,and the solid solution strengthening,dislocation strengthening and precipitation strengthening weaken,resulting in the strength decreasing of the 55CrVNb spring steel,with the tensile strength decreasing from 2119.7 MPa to 1228.0 MPa,and the yield strength decreasing from 1918.8 MPa to 1188.9 MPa.As the tempering temperature increases,the elongation of the 55CrVNb spring steel shows a trend of first increasing and then decreasing,and the fracture type changes from brittle fracture to ductile fracture.The optimal heat treatment process parameters for the experimental steel are:austenitizing at 860 ℃ for 30 min and tempering at 450 ℃ for 50 min.