回火温度对在线淬火Q690q桥梁钢显微组织和力学性能的影响

通过光学显微镜和扫描电镜观察了不同回火温度下在线淬火Q690q试验钢显微组织，并通过拉伸试验对其力学性能进行了测试.结果表明，在线淬火试验钢主要为板条贝氏体组织，在540~650℃回火，试验钢为回火索氏体组织(铁素体基体上分布着较多的碳化物颗粒).随着回火温度的升高，板条尺寸变大，碳化物颗粒析出数量增多，平均尺寸变大，大角度晶界数量增多.同时随着回火温度的升高，试验钢强度呈下降趋势，塑韧性呈上升趋势.620℃下试验钢的综合力学性能最佳，屈服和抗拉强度分别为878，992MPa，断后延伸率为20%，-40℃下冲击吸收功为143 J.

Effect of Tempering Temperature on Microstructure and Mechanical Properties of On-Line Quenched Q690 q Bridge Steel

The effects of tempering temperatures on microstructure and mechanical properties of the on-line quenched Q690q bridge steel were investigated through optical and scanning electron microscopes and tensile tests. The results show that the microstructure of the on-line quenched steel is primarily the lath bainite. After tempering at 540~650℃， the microstructure is the tempered sorbite. It is also found that with the increase of the tempering temperature， the lath width and the averaged grain size become larger， and the amounts of the carbide precipitations and large-angle grain boundaries increase. Meanwhile， with the tempering temperature increasing， the strength of the tested steel trends to be decreased， in contrast to the plasticity and toughness. At 620℃， the tested steels have the best mechanical properties， in which the yield and tensile strengths are 878 MPa and 992 MPa， the percentage elongation after fracture is 20%， and the impact absorption energy at -40℃ is 143 J.