Microstructure of welding zone of super-Ni laminated composite and 18-8 steel TIG joint

Super-Ni laminated composite(with 0.3 mm-thick cover layer) and 18-8 stainless steel were welded with filler alloy by tungsten inert gas welding(TIG) .The microstructure,microhardness and element distributions in the welding zone were analyzed.The results show that a valid connection forms between the laminated composite and the weld metal,the microhardness(190 HM) near the fusion zone of Super-Ni cover layer side increases.The microhardness of the welding seam region on 18-8 steel side is lower than that of the base metal,and the highest microhardness(290 HM) appears in the heat-affected zone(HAZ) of 18-8 steel.δferrite and carbide phase form on the HAZ of 18-8 steel side.The transition of Fe and Ni elements obviously occurs between the base metal and the weld,with 80-85μm-wide transition zone near the laminated composite side and about 20μm-wide transition zone near the 18-8 steel side.In the welding process,the welding tungsten arc should be controlled towards the 18-8 steel side to avoid excessive melting loss of the Ni cover layer.