It is significant to evaluate the corrosion resistance of a new stainless steel, SUS443J1, in atmospheric environment. In this study, the growth behavior of pits on the surface of a 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, it was obtained that the pit growth rate values, n, were 0.2 for both 2B and HL surfaces of SUS443J1 and SUS304. It could be predicted that the pit growth behavior of SUS443J1 and SUS304 were equivalent to each other.
The pitting potential values, V’c10, of SUS443J1 and SUS304 were almost equivalent to each other, and the repassivation potential showed the same tendency. Pitting potential was reduced with increasing 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 would represent a degree of pit growth. It was suggested that a deep pit would expand with larger growth rate than that of a shallow pit because a pit could growth easily and repassivation would hardly occur within a deep pit.