Effect of chloride ion content on pitting corrosion of dispersion-strengthened-high-strength steel

Chloride ion is an important corrosion factor in marine environment. Chloride ion has a small radius and strong permeability, which can destroy the oxide film on the surface of marine structural steel. The uneven adsorption of chloride ion on the metal surface will cause pitting corrosion. The effect of chloride ion content on pitting corrosion of the as-cast and heat-treated Dispersion-Strengthened-High-Strength (DSHS) steel was studied by electrochemical test, composition analysis and surface analysis. The results showed that high content of chloride ion reduced the content of dissolved oxygen in the solution, and the corrosion rate of DSHS steel was the slowest in 5.0 wt.% NaCl solution. In high content chloride ion solution, the formation of α-FeOOH was inhibited and the protection of corrosion products was weakened. Pitting corrosion of DSHS steel before and after heat treatment was the most serious in 2.0 wt.% NaCl solution. After heat treatment, grain size of DSHS steel decreased, and more dense and stable protective corrosion products were produced. Therefore, the induction and development of pitting corrosion of heat-treated DSHS steel were inhibited.