Microstructure and mechanical properties of TIG welded 20G/316L clad pipe joint

Tensile strength, bending strength, impact toughness and non-destructive inspection tests of TIG welded 20G/316L clad pipe joint were carried out.The microstructure and the diffusion of the major alloying elements were analysed using optical microscopy, SEM and chemical analysis.The results showed that the weld can be divided into four layers including carbon steel layer, diffusion layer, transition layer and stainless steel layer.The microstructure in diffusion layer was characterized by the martensite and retained austenite.The transition layer only contained austenite, and the stainless steel layer included afterbirth-like crystal.The defect-free joint was produced and performed well under the experimental parameters.The concentration of nickel and chromium element in weld root did not decrease compared with the corresponding welding materials, which proved that the employment of transition welding wire could maintain the concentration of the major alloying elements in welding root.