Effects of pack chromizing on the microstructure and anticorrosion properties of 316L stainless steel.

Abstract To extend the applications of 316L stainless steel in corrosive environments and correlate the corrosion resistance with composition and microstructure, homogeneous Cr-rich layer with the thickness of 75 μm was fabricated on 316L stainless steel by pack chromizing and post heat treatment. The chromizing layer was mainly composed of Fe Cr solid solution. Post heat treatment eliminated the precipitates and Cr-depletion in the chromizing layer. The corrosion behaviors were studied by electrochemical measurements and corrosion morphology observation. The pitting corrosion in Cl− containing solutions was avoided after chromizing treatment, which was ascribed to the reduced sensitivity of Cr-rich surface to Cl− ions. The higher Cr concentration in the modified layer also improved the long-term stability of corrosion resistance. After immersion in NaCl solution for 24 days, the charge transfer resistance of chromizing sample was higher than that of 316L by a factor of 8.19. In addition, the free corrosion potential shifted to the positive direction after post heat treatment, and the corrosion current density was also reduced to 0.066 μA/cm2. The further improvement on anticorrosion performance was attributed to the homogeneous microstructure. Graphical abstract Unlabelled Image Highlights • The Cr-rich layer was fabricated by high-temperature pack chromizing treatment. • The chromizing layer provided enhanced pitting corrosion resistance for 316L SS. • The correlation between corrosion resistance and composition/microstructure was studied. • Post heat treatment homogenized the microstructure and further improved the performance. [ABSTRACT FROM AUTHOR]