Stability of Inclusions Extracted from 18-8 Stainless Steel and the Effect of Inclusions on the Corrosion Resistance of the Steel

Abstract

Attempts have been made to clarify the chemical and electrochemical properties of inclusions in 18-8 stainless steel. To investigate the electrochemical property of inclusions, a method has been developed for measuring the polarization curve of a few mg weight of inclusions extracted from 18-8 stainless steel. The solubilities in water and 3% NaCl solutions and polarization curves in a 3% NaCl solution of the extracted α-MnS and MnSe containing a few percent of Fe and Cr were investigated.
The sulfides dissolved greatly in aerated hot water and 3% NaCl solutions (pH≤4) while the selenides did not dissolve in aerated boiling water and 3% NaCl solution at pH 2. The polarization curves showed that the decomposition potential of the selenides was nobler than that of the sulfides. These results show that the selenides are more stable than the sulfides.
Microscopic observations of 18-8 stainless steels containing sulfides or selenides in a 3% NaCl solution at pH 3 showed that the corrosion resistance of the steel containing stable selenides was superior to that of the steel containing less stable sulfides.