Effects of Electropulsing at Different Solidification Stages on the Pitting Corrosion Behavior of SUS303 Stainless Steel

SUS303 austenitic stainless steel has excellent machinability owing to its relatively high sulfur content, but MnS inclusions also promote localized corrosion. In this study, electropulsing was applied at three characteristic stages, namely the high-temperature molten stage, the initial precipitation stage of MnS, and the subsequent solidification stage, to investigate its effect on the pitting corrosion behavior of SUS303 stainless steel. Samples treated at current densities of 0–127.39 A·cm−2 were evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy, and corrosion microscopy. Within each treatment group, increasing current density generally shifted the pitting potential (Epit) to more positive values, increased the fitted charge-transfer resistance (Rct), and reduced the characteristic pit size. In the 1450 °C group, Epit increased from 0.284 to 0.410 VSCE, while Rct increased from 296.4 to 440.5 kΩ·cm2. Similar within-group trends were observed for the other treatment endpoints. SEM observations showed refinement of coarse Type I MnS under electropulsing. Representative corrosion morphology indicated localized dissolution associated with coarse sulfide inclusions. The electrochemical and microstructural trends suggest that refinement of Type I MnS may contribute to improved pitting resistance.