直接淬火对EH690钢组织与性能的影响

Effect of direct quenching on microstructure and mechanical properties of EH690-grade steel

对比离线淬火(RQ)工艺,研究了在线直接淬火(DQ)对EH690钢组织与性能的影响。对经两种工艺淬火及回火后的试样,采用光学显微镜(OM)、扫描电镜(SEM)和电子背散射衍射(EBSD)分析其微观组织,采用X射线衍射法分析了织构,并测试了室温拉伸曲线和-40℃夏比冲击吸收能量。结果表明:直接淬火回火(DQT)后钢的屈服强度、抗拉强度和冲击吸收能量分别为1011 MPa、1073 MPa和52 J,而再加热淬火回火(RQT)后分别为883 MPa、921 MPa和108 J。DQT钢的位错密度更高,位错强化和微合金析出强化是强度的主要增量贡献。但DQT钢的冲击韧性低,这主要是其因为原始奥氏体晶粒尺寸(PAGS)粗大,导致相变后马氏体亚结构有效晶粒尺寸粗大。此外,DQT钢还存在对韧性不利的{001}<110>旋转立方织构,同时大角度晶界(HAGBs)比例也较低。

Compared with off-line reheating quenching(RQ)process,the effect of on-line direct quenching(DQ)on microstructure and properties of EH690-grade steel was studied.For the samples quenched by two processes and tempered,the microstructure was analyzed by optical microscope(OM),scanning electron microscopy(SEM)and electron backscatter diffraction(EBSD)technique,the texture was analyzed by X-ray diffraction,and the room temperature tensile curve and-40℃Charpy impact absorbed energy were measured.The results show that the yield strength,tensile strength and impact absorbed energy at-40℃of the steel after direct quenching and tempering(DQT)are 1011 MPa,1073 MPa and 52 J,respectively,while those after reheating quenching and tempering(RQT)are 883 MPa,921 MPa and 108 J,respectively.The dislocation density of the steel after DQT treatment is higher,and dislocation strengthening and micro alloying precipitation strengthening are the main incremental contributions to the strength.However,the impact toughness of the steel after DQT treatment is low,which is mainly due to the coarser prior austenite grain size(PAGS),resulting in the coarser effective grain size of martensite substructure after transformation.In addition,DQT steel also has{001}<110>rotating cubic texture which is unfavorable to toughness,and the proportion of high angle grain boundaries(HAGBs)is also low.