Abstract
Anodic polarization and immersion tests in 3% NaCl solution and other chloride solutions at 35°C have been carried out using mild steels, alloy steels and aluminum alloy in order to investigate the relation between number of pits per unit area and pit diameter, shape of pit and the difference between the pit occurring by anodic polarization and that occurring by immersion.
The results obtained are summarized as follows:
(1) In the case of the immersion test, growth of pit is closely related to pH of the solution. Pits grow more easily in low pH solution than in high pH solution.
(2) In the case of anodic polarization test, number of pits per unit area and their morphology depend greatly on the potential applied. The morphology of pits occurring in SUS316 by the anodic polarization test less than 0.3 VSCE is nearly same as that of naturally occured one.
(3) It was observed that pits occured at triple points of grain boundary and at nonmetallic inclusions.
(4) Grain boundaries, micro-pits and crystallographic morphology were observed at the bottom of pit in SUS316 after immersion in FeCl3 solution.
