核电机组不锈钢锻管窄间隙焊接头组织与性能研究

Microstructure and Performance Investigation of Narrow Gap Welded Joint for Stainless Steel Forged Pipe of Nuclear Power Plant

针对三代机组HPR1000不锈钢大壁厚锻造主管道,采用自主开发的窄间隙全位置焊接系统制备窄间隙焊接接头,检测分析了接头焊缝及熔合区组织特征、凝固模式,及焊缝金属力学性能随焊接热输入量的变化。结果表明:焊接接头全壁厚组织分布均匀,无超标缺陷,力学性能满足要求;熔合区靠焊缝侧组织由胞状晶和亚晶界枝晶组成,焊缝组织为奥氏体基体+骨架状枝晶铁素体,由焊缝边缘向焊缝中心,Creq/Nieq逐渐增大,凝固组织呈现奥氏体+共晶铁素体(AF凝固模式)→奥氏体+骨架状铁素体(FA凝固模式)的变化规律;随着焊接热输入量增大,不锈钢焊缝金属的强度和硬度逐渐减小。

In view of HPR1000 stainless steel forging main pipe with large wall thickness of the third generation units,narrow gap welded joint was made by all-position narrow gap welding system which was self-developed.The microstructure and solidification mode of the weld and fusion zone of the welded joint,and the change of mechanical properties of weld metal with welding input were detected and analyzed.The results show that the microstructure of the welded joint in wall thickness is uniform,there is no defects beyond the standard and the mechanical properties meet the requirement.The microstructure of the fusion zone near the weld seam is cellular and subboundary dendrites,and the microstructure of weld seam is austenitic matrix and skeletal ferrites.Creq/Nieqincreases gradually from the edge of the weld to the center of the weld and the solidification structure changes from austenitic matrix+eutectic ferrite(AF solidification mode)to austenitic matrix+skeletal ferrite(FA solidification mode).In addition,the strength and hardness of weld metal reduce with increase of welding input.