Brown lowland soil collected from 20 sites was prepared, and the corrosion rate of buried carbon steel was measured by AC impedance method. In this study, soil corrosiveness was defined as the progress of corrosion in one dry/wet cycle, and its relationship with the soil particle size distribution was evaluated. The soil corrosiveness was different depending on particle size distribution. It is considered that the wet area of the steel surface and the diffusion distance of dissolved oxygen were different by the inter-particle spacing.
To evaluate the effect of oxidants, which are formed by radiolysis of water under gamma ray irradiation, on the corrosion of a carbon steel in humid environment, ozone was introduced as a model oxidant in to humidity-controlled air at 50℃ in a thermo-hygrostat chamber. Corrosion monitoring was performed by using an Atmospheric Corrosion Monitor-type （ACM） sensor consisting of a carbon steel anode and an Ag cathode. The output current of the ACM sensor was increased with the increase in relative humidity and it was obviously increased with the increase in the introduced ozone concentration at each relative humidity. The results indicate that ozone accelerates the corrosion of the carbon steel. The effect of ozone on the corrosion acceleration is attributed to the fast reduction reaction and fast dissolution reaction in to water compared to that of oxygen.
Author discusses a relationship between grain boundary characteristics and acoustic emission （AE） activity in the intergranular stress corrosion cracking （IG-SCC） of Type-304 and Type-316 austenitic stainless steels in chloride and acidic tetra-thionic solutions. The author also discusses source mechanism of the AE signals emitted during crack opening operation of the IG-SCC, based on the coincidence site lattice （CSL） data of the both steels. He found that the Type-316 steel showed a high resistance against both the chloride and acidic tetra-thionic IG-SCC and a much emission of AEs, while the Type-304 steel showed lower resistance and lower AE emission rate. He observed many projections on the fracture surface of the sensitized Type-316 steel, but quiet few projection for the Type-304 steel. The authors demonstrates that the projections are produced by mechanical fracture of the coincident grain boundaries which possess higher resistance against anodic dissolution and that this portion corresponds to the short edges of twin bands. The mechanical fracture of the short edges produces much AE signals, and then the higher emission rate of AE signals designates a higher resistance against the IG-SCC.