Pitting Initiated by MnO·Cr₂O₃–MnS and MnS Inclusions in a Si‐/Mn‐Killed Stainless Steel

Two types of inclusions in the stainless steels are detected: MnO·Cr 2 O 3 –MnS dual‐phase ones and pure MnS ones. The increase of sulfur content can inhibit the formation of MnO–Cr 2 O 3 –MnS inclusions and reduce the harm of MnO·Cr 2 O 3 –MnS inclusions on the pitting corrosion of stainless steels. When the sulfur content increases from 26 to 70 ppm, the average pitting potential increases from 0.34 to 0.4 V SCE due to the decrease in the number density of MnO–Cr 2 O 3 –MnS inclusions. A Cr‐depletion zone exists in the steel matrix around MnO–Cr 2 O 3 –MnS inclusions. The size of pits induced by MnO·Cr 2 O 3 –MnS inclusions is larger, which poses a more serious threat to the pitting resistance of stainless steels.