The microstructural variations in different sub-regions of the Fe-1.2Mn-0.3Cr-1.4Ni-0.4Mo-C steel welded joint were investigated by means of optical microscope and scanning electron microscope equipped with electron backscattered diffraction. This study focused on the correlation between microstructural characteristics and mechanical properties of the welded joint which was carried out by gas metal arc welding. The microhardness of the fusion line (FL) and fine-grained heat affected zone was inferior to other locations of welded joint due to the diffusion of alloy elements and granular bainite phase transformation, respectively. The tensile strength of the welded joint was about 980 MPa, which reached the required strength of the 1000 MPa grade steel plate for hydropower station. The final fracture was located at the weld metal (WM) because that the crack easily nucleated and propagated in proeutectoid ferrite. The impact toughness at −60 °C of various sampling locations for welded joint was higher than 47 J. The low temperature impact toughness improved gradually as the distance between the V-notch and weld center line increased. The inclusions in the WM and non-uniformity of microstructure and composition near the FL could increase the deterioration on impact toughness at −60 °C.

利用光学显微镜和配备电子背散射衍射的扫描电子显微镜，研究了Fe-1.2Mn-0.3Cr-1.4Ni-0.4Mo-C钢焊接接头不同区域的组织变化。这项研究的重点是通过气体保护金属电弧焊进行的焊接接头的显微组织特征与力学性能之间的关系。由于合金元素的扩散和颗粒贝氏体相变，熔合线（FL）和细晶粒热影响区的显微硬度均次于焊接接头的其他位置。焊接接头的抗拉强度约为980 MPa，达到了水电站1000 MPa级钢板所需的强度。最终的裂纹位于焊缝金属（WM）处，因为裂纹易于成核并在共析铁素体中扩展。焊接接头的各个采样位置在-60°C时的冲击韧性均高于47J。随着V型缺口和焊缝中心线之间的距离增加，低温冲击韧性逐渐提高。WM中的夹杂物以及FL附近的微观结构和成分的不均匀性可能会增加-60°C下冲击韧性的恶化。