Manufacturing and Characterization of Plasma Gas Tungsten Arc-Welded Pipes Made of a Ni-Reduced Austenitic Stainless CrMnNi Steel

In this study, a Ni-reduced austenitic stainless TRIP/TWIP steel with < 5 vol.% δ-ferrite was investigated before and after plasma arc welding and gas tungsten arc welding. The 4-mm-thick hot-rolled sheet was produced as hot-rolled heavy plate on an industrial scale and manufactured as longitudinally welded pipes without filler metal. Microstructural characterization was done using light optical microscope and scanning electron microscope with electron backscatter diffraction (EBSD). The microstructure consisted of non-recrystallized austenite with a small amount of δ-ferrite. The welds exhibited skeletal and lacy δ-ferrite morphologies. ε-martensite and α´-martensite were found in the weld seam after pipe expansion. Further, the mechanical properties were evaluated using tensile test. The results showed a tensile strength of 823 MPa with a uniform elongation of 69% at room temperature. The change of hardness in the weld seam was studied for welded pipe, welded expanded pipe and welded, post-weld heat-treated (PWHT) pipe with Vickers hardness testing. The lowest hardness was achieved after PWHT. The corrosion resistance tests were conducted in chloride containing environment. The results showed that the susceptibility to pitting corrosion increased with the degree of deformation. Furthermore, the weld metal and heat-affected zone exhibited local attack whereas the base metal seemed unaffected.