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

Key words:  bimetal composite pipe L415/316L  laser cladding  welded joints  microstructures  properties

Abstract:

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.