Sung Jin Kim

Inappropriate selection of process parameters in plasma arc welding of 316L stainless steel can induce inhomogeneous microstructures and degraded mechanical properties. In addition, optimization of the pickling process to obtain a high-quality surface remains an industrial requirement. In this study, the influences of plasma arc welding current and speed on the microstructures and tensile properties of 316L stainless steel, as well as its acid pickling behaviors, were investigated. The microstructural evolution and mechanical behaviors of tubular specimens were examined in terms of welding current (200–300 A) and speed (20–30 cm/min). Dendrite arm spacing and δ-ferrite fraction exhibited clear trends with both welding current and speed. The combination of 250 A and 60 cm/min led to the finest microstructure with the lowest δ-ferrite content, resulting in the highest strength and ductility. Oxide layer analysis after post-weld heat treatment revealed that the weld developed thicker oxide scales than the base metal, necessitating extended pickling durations. The oxide layer was removed early during acid pickling, followed by intragranular corrosion and dissolution of Cr-depleted layer. The mass loss of the specimens increased parabolically with pickling time. An analytical model for estimating the pickling rate was then derived, providing a tool for predicting the service life of the pickling solution.