Abstract
This study was performed to investigate the application of the Friction Stir Welding process in the dissimilar joining of cladded plates for the oil and gas industry. Samples of 4 mm thick ASTM 572 steel plate cladded with 3 mm thick nickel-based alloy 625 were used. In order to limit mixing between the dissimilar materials, a two-steps welding procedure was defined. The first step consist welding the 4 mm steel side and the second step the 3 mm Inconel ® 625 layer. Different parameters were tested for each step and all samples were analyzed and compared to define the best welding parameters. The specimens were evaluated by light microscopy to identify defects in the weld and by mechanical tests such as microhardness, bending and tensile. Defect free joints have been obtained with a well defined interfacial region between both materials. Preliminary results have shown that in both joints (steel pipe and the Inconel®625) the hardness values in the stirred zone are higher than those measured in the base material (overmatching). This is due to diffusionless phase transformations in the steel microstructure and Hall-Petch effect coupled with precipitation of carbon nitrides in the Inconel®625. The mixing zone formed in the interface between both materials is currently being analysed.
