Atmospheric Corrosion Resistance of High-Cr Stainless Steels for Building uses and their Estimation Methods
Yoshihiro Yazawa, Takumi Ujiro, Susumu Satoh, Keiich Yoshioka
Recently high-Cr ferritic stainless steels have been adopted as exterior parts of buildings especially at waterfronts. In this study, atmospheric corrosion resistance of various kinds of stainless steels was evaluated in various environments. Correlation between the atmospheric corrosion resistance and laboratory corrosion tests and a method for evaluating atmospheric corrosion resistance were investigated. Results are as follows. 1) Atmospheric corrosion resistance of stainless steels was improved by increasing pitting index (P. I.; ferritic stainless steel: Cr+3.3Mo, austenitic and dual phase stainless steels; Cr+ 3.3Mo+16N). 2) Ferritic stainless steel that have the same P.I. value as austenitic and duplex stainless steels showed better corrosion resistance than the austenitic and duplex stainless steels. The pitting index of the steels is useful for estimating corrosion resistance for each type of steel. 3) Corrosion resistance in atmospheric exposure tests had a good correlation with pitting potential. If pitting potentials of stainless steels were more than critical pitting potentials (Vcrit) which correspond to each exposure site, the steels did not have rust. The Vcrit values can be used as one of the criteria for selecting steels to site a service environment. 4) In a severe corrosive environment such as a coastal area, Mo-bearing high-Cr ferritic stainless steels are required.
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