高强韧桥梁钢Q690q的单轴拉伸性能与低周疲劳性能

Uniaxial tensile and low cycle fatigue properties of high strength and toughness bridge steel Q690q

针对热机械轧制(TMCP)+回火(T)和调质(QT)两种工艺处理的Q690q桥梁钢板,进行了表面和心部的单轴拉伸和低周疲劳试验,同时利用光学显微镜和扫描电镜对表面和心部的微观组织及原始奥氏体晶粒尺寸进行了观察,并分析了其对拉伸性能和低周疲劳性能的影响。结果表明,TMCP+T工艺钢板的微观组织主要由板条贝氏体(LB)、粒状贝氏体(GB)和少量马奥岛(M/A)组成,表面的LB占大多数,且比心部的组织更加细小,同时原始奥氏体晶粒尺寸较均匀;与心部相比,表面的屈服强度、抗拉强度、屈强比及伸长率均增大,低周疲劳寿命明显提高。而QT工艺钢板的微观组织以回火索氏体(TS)和GB为主,心部的GB占比增加,但比表面的组织反而细小些,同时原始奥氏体晶粒也更为细小均匀;与表面相比,心部的屈服强度、抗拉强度、屈强比及伸长率均减小,但低周疲劳寿命反而提高。两种工艺相比,无论是表面还是心部,TMCP+T工艺钢板的屈服强度较低,抗拉强度较高,屈强比较低,同时伸长率较低。而两种工艺钢板的低周疲劳寿命变化范围极为接近,处理工艺对试验钢的低周疲劳性能影响不大。同时对拉伸性能与低周疲劳性能之间的相关性进行分析,表明疲劳强度系数与抗拉强度呈线性相关,疲劳延性系数与伸长率呈线性相关。

For the Q690q bridge steel plates produced by two processes of thermo⁃mechanical control process+tempering(TMCP+T)and quenching and tempering(QT),the uniaxial tensile and low cycle fatigue(LCF)tests were conducted on the surface and core of the plates.The microstructure and the prior austenite grain sizes(PAGS)of the surface and core were observed and measured by means of optical microscope(OM)and scanning electron microscope(SEM),and their influences on the tensile properties and LCF properties were analyzed.The results show that the microstructure of the TMCP+T⁃processed steel mainly consists of lath bainite(LB),granular bainite(GB),and a small amount of martensite⁃austenite islands(M/A).The LB is the majority on the surface and is finer than that of the core,and the surface PAGS is also more uniform.Compared with that of the core,the yield strength,tensile strength,yield ratio,and elongation of the surface are all increased,and the LCF life is significantly improved.The microstructure of the QT⁃processed steel is mainly tempered sorbite(TS)and GB.The proportion of GB in the core is increased,but it is finer than that of the surface,and the PAGS is also finer and more uniform.Compared with that of the surface,the yield strength,tensile strength,elongation,and yield ratio of the core are all decreased,but the LCF life is increased.Comparison between the two processes,whether being the surface or the core,the TMCP+T⁃processed steel has lower yield strength,higher tensile strength,lower yield ratio,and lower elongation.However,the LCF life change ranges of the tested steel obtained by the two processes are very similar,implying that on which the process difference has a little effect.In addition,the correlation between the tensile properties and the LCF test data shows that the fatigue strength coefficient is linearly correlated to the tensile strength,and the fatigue ductility coefficient is linearly correlated to the elongation.