The crevice corrosion repassivation potential of austenitic S30400 and S31600 stainless steels (SSs) was determined in 0.1 and 1 mol/L NaCl solutions and in 5 mol/L CaCl2 solution at temperatures between 0 and 90°C. The repassivation potential of S30400 SS decreased with increasing chloride concentrations and temperatures in the range from 0 to 60°C, reaching a constant value in the range from 60 to 90°C. The repassivation potential of S31600 SS showed a decrease with increasing chloride concentrations and temperatures. Crevice-corroded spots showed crystalline attack plus pitting corrosion. Crystalline attack prevailed in S31600 SS and pitting corrosion prevailed in S30400 SS. A solution of 0.5 mol/L HCl was used to simulate the crevice-like environment. The effect of the 2.5% Mo addition in S31600 SS compared to S30400 SS on the crevice corrosion resistance was analyzed in the context of the Galvele’s localized acidification model. The molybdenum addition produced a 30 mV increase in the corrosion potential in the crevice-like solution and a significant increase of the ohmic potential drop, especially for dilute chloride solutions. The polarization needed to sustain the critical crevice chemistry was not significantly affected by the alloying with molybdenum under the tested conditions.

Subject
Pits, Scanning electron microscopy, Materials, Repassivation potentials, Chloride solutions, Crevices, Corrosion attacks, Crevice corrosion, Pitting, Corrosion resistance, Stainless steel, Chlorides, Corrosion potential
Keywords:
S30400, S31600, temperature, chloride, localized corrosion, Galvele
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2016
Association for Materials Protection and Performance (AMPP)
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