Effect of P Addition on the Corrosion Resistance of Steels Before and After Rust Formation

Abstract

This paper presents the effect of P addition on the corrosion resistance of steels before and after rust formation. Electrochemical measurements and surface analysis of P-containing steels (Fe-0.5 mass% P, Fe-1.0 mass% P, and Fe-1.5 mass% P) were conducted to analyze the contribution of P to their initial corrosion resistance before rust formation. The results showed that the initial corrosion resistance of the steel was worse with higher P content. According to the surface analysis conducted by SEM/EDS, more P-segregations at grain boundaries existed with higher P content. Based on the results of polarization measurements, it was considered that these P-segregation became the initiation sites of localized corrosion, resulting in the decrease in the initial corrosion resistance.

Although the initial corrosion resistance was worse with higher P content, the long-term corrosion resistance was better with higher P content. According to the results of atmospheric exposure tests at Miyakojima and the surface analysis of rust layers, P was incorporated into the rust layer, and it promoted the protective ability against corrosion.