使用光学显微镜和扫描电镜研究了CAP1400蒸汽发生器压力边界焊接接头的显微组织，该压力边界焊接接头由SA508Gr.3Cl.2钢母材、热影响区、堆焊层和对接焊缝组成。结果表明：接头母材的显微组织为细小回火贝氏体，焊接热影响区的为粗大马氏体，不锈钢堆焊层的为柱状奥氏体和少量铁素体，镍基合金堆焊和对接焊缝的组织主要为柱状奥氏体；在多层多道焊接热循环作用下，不锈钢堆焊层和镍基合金对接焊缝中的奥氏体都发生了再结晶，奥氏体基体上有碳化物析出相。

Microstructures of the pressure boundary welded joint of CAP1400 steam generator were studied with optical microscope and scanning electron microscope. The pressure boundary joint is made up of SA508Gr.3Cl.2 steel base metal, heated affected zone, surfacing layer and butt weld. The results show that the base metal of the joint had a fine tempered bainite microstructure and the heat affected zone had a coarse martensite microstructure. The microstructure of the stainless steel surfacing layer was mainly composed of columnar austenite and little ferrite, and that of the nickel based alloy surfacing and butt weld mainly consisted of columnar austenite. Austenite recrystallization occurred both in the stainless steel surfacing layer and in the nickel based alloy butt weld because of the thermal cycling effect of the multi-layer and multi-pass welding. The carbides precipitated in the austenite matrix.