不同开轧温度对薄规格500 MPa级桥梁钢组织和性能的影响

Effects of finish-rolling temperature on microstructure and properties of 500 MPa-grade thin bridge steel plate

利用光学显微镜、扫描电子显微镜(SEM)、显微硬度计、拉伸和冲击试验机,研究了不同开轧温度对以铁素体和贝氏体为基体组织的薄规格500 MPa级桥梁钢组织性能的影响。结果表明:在终轧温度不变的条件下,开轧温度由960℃降低至900℃,钢中铁素体含量由60%增加至70%,并且其显微硬度由190±7 HV25g提高至241±18 HV25g,贝氏体组织逐渐由尺寸较大的粒状贝氏体向上贝氏体和板条贝氏体转变,拉伸曲线由吕德斯带不连续屈服型向连续屈服型转变。当开轧温度为900℃,钢的屈强比为0.79,−40℃夏比冲击功达147 J,满足低屈a强比500 MPa级桥梁钢的力学性能要求。

Effects of finish-rolling temperature on microstructure and properties of Q500qE thin bridge steel plate with ferrite and bainite matrix are studied by using optical microscope,scanning electron microscope,micro-hardness tester,tensile tester and impact tester.When the finish-rolling temperature is reduced from 960℃ to 900℃,fraction of ferrite in the steel increases from 60% to 70%,and its micro-hardness increases from 190±7 HV25g to 241±18 HV25g.At the same time,the bainitic structure in the steel is gradually transitioned from coarse granular bainite to upper bainite and lath bainite.Tensile curves of the steel change from Lüders bands-typed discontinuous yielding to continuous yielding shape.When the finish-rolling temperature is 900℃,yield ratio of the steel is 0.79,and its Charpy impact energy at-40℃ reaches 147 J,meeting the requirements of Q500qE with low yield ratio.