焊接热输入对Q890钢焊缝金属组织及韧性的影响

Effect of heat input on microstructure and toughness of weld metal for Q890 steel

采用熔化极气体保护焊对Q890钢进行不同热输入的对接焊试验。利用金相显微镜、扫描电子显微镜、透射电镜和电子背散射衍射技术研究热输入对焊缝组织及冲击性能的影响。结果表明,3种热输入焊缝金属组织主要由板条马氏体和板条贝氏体及少量的粒状贝氏体和残留奥氏体组成。随着热输入的增加,焊缝组织中板条粗化,而粒状贝氏体逐渐增多,部分板条内析出细小针状碳化物;随着热输入的增加,焊缝分析区域内残留奥氏体量逐渐减少分别为1.2%、0.53%、0.41%。焊缝金属冲击断口形貌从韧脆混合型断裂特征向脆性断裂特征的变化,与焊缝金属冲击吸收能量变化趋势一致。

A series of measurements were carried out by means of optical microscopy,scanning electron microscopy,transmission electron microscopy and electron back-scattered diffraction on specimens of GMAW plates of Q890 quenched and tempered steel to determine effect of heat input on microstructure and impact toughness of weld metal. The results reveal that microstructure of weld metal mainly consists of lathmartensite / bainite,as well as a small amount of granular bainite and retained austenite for three kinds of heat input. With the increasing of heat input,the lath structure is coarsened,while the number of granular bainite increases,and fine carbides precipitate inside lath,and the volume fractions of retained austenite decrease in weld metal those are 1. 2%,0. 53% and 0. 41%,respectively. The fractograph of weld with different heat inputs shows that radiation tendency from ductile / brittle mixed fracture characteristics to brittle fracture one which is consistent with the variation tendency of Charpy impact values of welded metals.