对890 MPa级以上的高强焊接接头采用钨极氩弧焊（Tungsten inert gas，TIG）多层多道焊接工艺。应用光学显微镜、扫描电镜和透射电镜等手段对高强焊接接头焊缝的末道组织、焊缝的再热组织以及不同焊道下的冲击断口的形貌进行观察，分析钨极氩弧焊工艺下不同的焊道组织对焊缝韧性的影响。结果表明，焊缝末道组织由板条马氏体和联合贝氏体组成。联合贝氏体对冲击韧性是不利的。多层多道焊的再热作用有利于改善和细化组织，使柱状晶消失，同时使原来方向一致的板条马氏体组织变为回火马氏体组织，粗大的联合贝氏体组织消失，这也是焊缝韧性提高的主要原因。此外，多层多道焊接工艺还会使焊缝中残余奥氏体形态发生改变，由薄膜态转变为块状残余奥氏体，但由于块状残余奥氏体尺寸较小且含量较少，所以其对韧性影响较小。
High strength weld metal with strength over 890 MPa are made using tungsten inert gas arc welding(TIG) with multi-layer and multi-pass process. The microstructure of the as-weld metals and reheated metals and charpy impact fracture surface is characterized with optical microscope(OM), scanning electron microscope(SEM), transmission electron microscope(TEM),and the influence of microstructure on weld metal toughness is analysed. The result shows that the as-weld metals are mainly composed of martensite and coalesced bainite, which is harmful to impact toughness. The reheated metals are mainly composed of finer temper martensite with column and coalesced bainite disappearing, which improves the weld toughness. The morphology of retained austenite turned from films into block due to the effect of reheat, with little contribution to the toughness.
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