回火温度对Nb/Ti微合金化新型超低碳中锰钢的组织和力学性能的影响

Effect of tempering temperature on microstructure and mechanical properties of new ultra-low carbon medium manganese steel microalloyed by Nb and Ti

利用扫描电镜(SEM)、X射线衍射(XRD)、电子背散射衍射(EBSD)、透射电镜(TEM)以及Thermo-Calc软件等研究了回火温度对Nb/Ti微合金化超低碳中锰钢的显微组织和力学性能的影响。结果表明:随着回火温度的升高,试验钢先后获得了回火马氏体、逆转变奥氏体、ε-马氏体和α-马氏体等组织。经550℃回火后,试验钢中没有逆转变奥氏体形成,尽管其屈服强度和抗拉强度均超过800 MPa,但冲击吸收能量仅为13.7 J;经580℃回火后,逆转变奥氏体含量为4.2%,冲击吸收能量骤增至227 J,且强度无明显下降;随着回火温度升高至620℃,逆转变奥氏体的含量为12.3%,冲击吸收能量达到最高值为333.7 J,屈服强度下降至748 MPa,抗拉强度达到最低值为793.5 MPa;当回火温度升高至650℃或者更高时,逆转变奥氏体受其尺寸和成分因素的影响,稳定性明显下降,冲击吸收能量开始下降,而且屈服强度已低于520 MPa。ε-马氏体发生相变诱发塑性(TRIP)效应转变为α-马氏体吸收一定的能量,但是由于硬度较高,成为裂纹源及其快速传播的通道。

Effect of tempering temperature on microstructure and mechanical properties of a new ultra-low carbon medium manganese steel microalloyed by Nb and Ti was investigated by means of scanning electron microscopy(SEM),X-ray diffraction(XRD),electron backscatter diffraction(EBSD)technique,transmission electron microscopy(TEM)and Thermo-Calc software.The results show that with the increase of tempering temperature,the tempered martensite,reversed austenite,ε-martensite andα-martensite in the experimental steel are obtained successively.After tempering at 550℃,there is no reversed austenite in the experimental steel,and although the yield strength and tensile strength are both over 800 MPa,the impact absorbed energy is only 13.7 J.After tempering at 580℃,the content of reversed austenite is 4.2%,the impact absorbed energy increases to 227 J,and the strength does not decrease obviously.With the tempering temperature increasing to 620℃,the content of reversed austenite is 12.3%,the impact absorbed energy reaches the highest value of 333.7 J,the yield strength decreases to 748 MPa,and the tensile strength reaches the lowest value of 793.5 MPa.When the tempering temperature is increased to 650℃or higher,the stability of the austenite is obviously decreased due to the effect of its size and composition,the impact absorbed energy begins to decrease,and the yield strength is lower than 520 MPa.ε-martensite transformation toα-martensite will absorb some energy,but because of its high hardness,it will become the crack source and rapid crack propagation channel.