1995 Volume 44 Issue 10 Pages 550-556
The quantitative evaluation of tarnish (stain and rust) of type 304 stainless steel was carried out using Computer Image Analysis. The shapes and degree of tarnish could be evaluated by several parameters such as total area of tarnish, ratio of red rust to stain one, and average size of rust particles. Effect of wet and dry test condition after salt spray at cyclic corrosion test on tarnish has been studied by these parameters, and main results are as follows. Total area of tarnish and average size of rust particles depend mainly on the relative humidity (RH) in the constant humidity process after salt spray, and they indicate maximum value at 70% RH. Ratio of red rust to stain one increases with the duration time in wet cycles. Red rust and stain one are also FeO(OH) in structure, and Fe-Cr-Ni ratio is nearly same as the stainless steel. To control the condition, cyclic corrosion tests were able to simulate tarnish (area and ratio of red rust) of one year seaside exposure tests.