1996 Volume 45 Issue 5 Pages 292-297
AC impedance method has been applied to the study of degradation of coated SUS 304 stainless steels with a macroscopic line defect. The 304 stainless steels having different surface treatments, i.e. 304 stainless steels of bright annealed (BA), hair line finished (HL) and chromate coated (TR), were coated with epoxy type paint and employed as specimens. A corrosion test was conducted by 5 days exposure in 0.5kmol/m3 NaCl solution containing 5vol% H2O2. After the corrosion test, the impedance was measured in NaCl solution and the delamination area due to the corrosion was estimated by the double layer capacitance. Also, the impedance was measured for specimens covered the macroscopic defective part with epoxy resin after the corrosion test and the degradation of coatings was evaluated by a breakpoint frequency method. The results from both the evaluation methods well agreed with the result of a conventional delamination test with adhesive tape. It was found that the corrosion resistance increased in the order of 304HL<304BA<304TR.