2021 年 107 巻 12 号 p. 1036-1046
Mass gain rates of various steels during atmospheric corrosion under cyclic conditions of dry and controlled-humidity air were investigated. Fe, SBHS500 carbon steel and SMA490AW weathering steel were selected for the test materials. A droplet of MgCl2 solution was set on the plate steel specimen. The specimen was exposed in the humidity-controlled air for about 82.8 ks and in the dry air for 3.6 ks. After the process, an area as well as a volume of the corroded part, surface appearance and a mass of the specimen were recorded. The process was repeated over 5000 ks of an accumulated wet time. Selected values of relative humidity were 75, 43 and 33%. For the Fe specimen, the condition of RH75% induced Region(i), (ii) and (iii), where Region(i) is the period in which a corroded area was independent of time and a mass of the specimen linearly increased with time, Region(ii) is the period in which an area and a mass increased more rapidly, and Region(iii) is the period in which increments of an area and a mass relatively decrease. The conditions of RH43% induced only the Region(i) and RH33% provided Region(ii) in addition to (i). A mass gain rate in Region(i) was larger under RH75% than those under RH43 and 33%. For the condition of RH75%, any of the three specimens showed the three regions, and a mass gain rate in Region(i) was a maximum for SBHS500 steel and a minimum for Fe.
