Corrosion Evaluation of Various Stainless Steels in Environments that Simulate Automotive Salt Damage

Corrosion properties of stainless steels were evaluated by the corrosion test developed to simulate automotive salt damage environment in our previous work. In addition, corrosion resistance of the stainless steels in the field was estimated from comparison of test results and measurement of wet/dry condition of the engine compartment in typical salt damage regions. As a result of the corrosion test, the stainless steels with large pitting index had small corrosion depth both inside and outside of crevice. In case where the pitting index was equal between ferritic and austenitic stainless steels, corrosion depth of ferritic stainless steels tended to be deeper than that of austenitic stainless steels especially in low-humidity test condition. Electrochemical measurements under the same condition as the corrosion test indicated that the pitting potential of ferritic stainless steels was easier to lower with increase of chloride concentration in solution than that of austenitic stainless steels. Thus, the reason for the difference of corrosion depth in low-humidity test condition was thought to be the increase of chloride concentration in the surface water film. Comparing these results, the relative corrosion resistance of stainless steels in automotive salt damage environment was estimated on the basis of SUS304. The corrosion resistance of SUS316L was 1.5 to 1.8 times that of SUS304, and that of SUS444 was 1.0 to 1.3 times that of SUS304.