Corrosion degradation of chromium coatings on steel in NaCl concentrated solution

Corrosion-electrochemical behavior of chromium coatings at steel substrates (40X, 20X13, and 12X18H10T) in concentrated (318 g/l) NaCl solution at elevated temperatures is studied, in particular, under conditions of friction against rubber (thus modeling the mine screw-driller rotor operation conditions). By and large, the chromium coatings in the studied solution have fairly good corrosion stability. However, when through pores occur in the coatings, chromium-steel galvanic couples are formed, in which chromium is the anode, and steel, the cathode. This causes intense corrosion damage to the coating in close proximity to the pores. Steel undergoes no corrosion here. It is the Cr-coating porosity that gives rise to its accelerated degradation under the friction, although friction as such does not accelerate the corrosion catastrophically.