Effect of cathodic protection on the corrosion-fatigue strength of steels of various hardness in sea water

Abstract

1. Steels 20, 40 and 45KhNMFA of widely different hardnesses were shown to have a qualitatively similar dependence of their corrosion-fatigue strength in a 3% NaCl solution (simulating sea water) on the cathodic current density: the effectiveness of cathodic protection increases as the current density increases to a certain critical value, and beyond it decreases. 2. Under optimum cathodic polarization conditions, the corrosion-fatigue limit of steel 20 practically reaches, and that of steel 40 exceeds, the corresponding fatigue limits in air. The maximum corrosion-fatigue limit of steel 45KhNMFA at the optimum cathodic current density is 20% lower than the fatigue limit in air. 3. A reduction in effectiveness of cathodic protection at current densities higher than the optimum is observed for all steels, but is particularly large for hard steels. 4. The character of the dependence of corrosion-fatigue strength on cathodic current density is explained as being a result of the interaction of two factors producing opposite effects. The “positive” factor is the protective action of cathodic polarization and the “negative,” the reduction in fatigue strength by absorbed hydrogen.