2015 Volume 55 Issue 5 Pages 1091-1099
Evaluation of the corrosion resistance of a new stainless steel, SUS443J1, in atmospheric environments is a significant issue. In this study, the growth behavior of pits on the surface of the ferritic stainless steel, SUS443J1, and an austenitic stainless steel, SUS304, were compared by field exposure tests and electrochemical measurements.
It is known that the pit growth rate can be approximated as X = atn, where X is pit depth, t is time, a and n are constants. As a result of field exposure tests, pit growth rate values of approximately n = 0.2 were obtained for both 2B and HL surfaces of SUS443J1 and SUS304. From this, it could be predicted that the pit growth behaviors of SUS443J1 and SUS304 were mutually equivalent.
The pitting potential values V’c10 of SUS443J1 and SUS304 were almost equivalent, and the repassivation potential showed the same tendency. The pitting potential decreased with increasing the maximum valley depth Rv of the surface. The repassivation potential was affected by the turning current density, where the sweep of potential was reversed. The turning current density represents the degree of pit growth. It was suggested that a deep pit would expand at a larger growth rate than that of a shallow pit because the deep pit grows easily and repassivation is difficult in deep pits.
