Effect of inclusion and microstructure transformation on corrosion resistance of 316L stainless steel after isothermal heat treatment

The transformation mechanism of the inclusions and microstructure in 316L stainless steel after post-isothermal heat treatment (IHT) was revealed, along with the pitting behavior of the inclusions in a chloride environment before and after the transformation. The effect of the inclusion transformation on the pitting corrosion behavior of 316L stainless steel and its intrinsic mechanism was also revealed. Results revealed a gradual transformation of MnO–SiO₂ inclusions into MnO–Cr₂O₃ within the temperature range of 1373 to 1573 K. MnO–Cr₂O₃ inclusions exhibited minimal dissolution in chloride ion corrosion environments, while MnO–SiO₂ oxides demonstrated higher electrochemical activity and were more prone to dissolve and form pits. Meanwhile, IHT significantly reduced the dislocation density of stainless steel, rendering it more stable in corrosive environments. X-ray photoelectron spectroscopy peak distributions of the passive films demonstrated that IHT increased the proportion of Cr and Fe oxides and hydroxides in the passive film which improved the stability and corrosion resistance of the steel.