Kikuo Takizawa

Effects of S and Mn content on the corrosion resistance of 18-8 stainless steel.

The effects of S and Mn content on the corrosion behavior of 18-8 stainless steels in the active region have been studied using mainly electrochemical means in sulfuric acid and L-ascorbic acid (C6 H8O6) solutions. The composition of sulfide inclusions (MnS) depended on the Mn/S ratio in the steels, and dissolution resistance of MnS inclusions was increased by decreases in the ratio. To the extent that MnS inclusions exist stably in the steel, they retard the cathodic reaction and the anodic dissolution reaction in the active region of the steel. When MnS inclusions were unstable and easily dissolved, however, the reactions are accelerated. Therefore, in a highly corrosive environment such as H2SO4 solution, in which the MnS inclusions are dissolved without difficulty, the corrosion resistance of the steel can be improved by decreasing the MnS content. On the other hand, in a corrosive environment such as C6H8O8 solution, in which MnS inclusions are dissolved with difficulty, corrosion resistance can be improved by decreasing the MnS contents or the Mn/S ratio.