Abstract
Stainless steel is often used in atmospheric environment without anticorrosive treatment, and there have been many researches on atmospheric corrosion of stainless steel. However, the correlation between corrosion behavior of stainless steel in the atmospheric environment and environmental factors has not been sufficiently clarified. Therefore, in this study, the exposure test of 11 kinds of stainless steel was carried out at 7 exposure test sites in Japan, Vietnam, and Indonesia, and the correlation between corrosion behavior and environmental factors was investigated. As a result, it was clarified that there exists a critical pitting index in which pitting corrosion does not initiate in each environment. The effect of deposited SO2 on the critical pitting index was small, and the effect of airborne sea salt was dominant. The critical pitting index C.P.I. in the atmospheric environment could be approximated by C.P.I.＝9.4 log （S）＋26.7 （where S is amount of airborne sea salt, mdd）. This result suggests that the increase in pitting index requires the formation of more droplets on the surface of stainless steel for pitting initiation.
