端部激光熔覆复合管焊接接头组织与性能分析

Microstructures and properties of welded joints of bimetal composite pipe with laser cladding at the end

分别采用激光熔覆和GTAW对L415/316L复合管管端进行堆焊,使复合管端部由机械结合转变为冶金结合,然后采用GTAW焊打底,手工电弧焊填充盖面进行对接焊,对比分析两种管端处理工艺对接头组织和性能的影响。采用光学显微镜、扫描电镜和电子探针对焊接接头的微观组织和化学成分进行分析,并对焊接接头进行力学和耐蚀性能测试。结果表明:管端激光熔覆和GTAW堆焊两种焊接接头的力学性能和耐腐蚀性能均满足要求;L415/焊缝界面出现明显的脱碳层和增碳层,脱碳层位于L415一侧,而增碳层位于焊缝一侧,两者之间存在碳迁移过渡层。相对GTAW堆焊,L415/熔覆层界面元素扩散梯度较大,扩散区较窄,L415稀释率低;激光熔覆工艺更能保证双金属复合管管端的耐蚀性能。

The laser cladding and Tungsten inert gas(GTAW)surfacing were used to the beading weld,in order to realize the metallurgical combination of the ends of bimetal mechanical lined pipe L415/316L.Then the butt welding of L415/316L was performed by the GTAW welding for the root welding and shielded metal arc welding(SMAW)for the filler and capping welding.The effects of two kinds of pipe end treatments on the microstructure and properties of welded joints were analyzed.The microstructures and chemical composition of the welded joints were analyzed by using the optical microscopy(OM),scanning electron microscopy(SEM)and electron probe microscope analysis(EPMA).In addition,the mechanical and corrosion properties were measured.The results show that the mechanical and corrosion properties of the two weld joints can both meet the requirements.There is a decarburized layer and a recarburized layer on the L415/weld interface,and a carbon migration transition layer is located between the two layers.The decarburized layer is located on the L415 side,while the recarburized layer is located on the weld side.Compared with the GTAW surfacing,the element diffusion gradient on the L415/cladding coating interface is bigger,the diffusion area is narrower,and the dilution rate of L415 is lower.This shows the laser cladding process can better ensure the corrosion resistance of the bimetal composite pipe end.