The aim of the present study is to investigate the effect of stress-induced martensite phase on the nucleation of a main crack in SUS304 steel under Stress Corrosion Cracking （SCC） conditions. First, stress-induced martensite phase was produced on sensitized SUS304 steel by applying the pre-strain in liquid nitrogen. Then, the microstructure of martensite/austenite dual phase SUS304 steel specimens was investigated by means of the Electron Back Scatter Diffraction （EBSD） method. Second, an in-house SCC machine that can perform 3-point bending tests on specimens under corrosive conditions （0.1mass％K₂S₄O₆, ph＝2.0） at slow strain rates was developed. Then, a slow strain rate SCC test was conducted on the martensite/austenite dual phase SUS304 steel specimens. From the experimental results using EBSD analysis, microstructure and deformation behavior under slow strain rate SCC test, the effect of the stress-induced martensite phase on the nucleation of a main crack in SUS304 steel under SCC condition was discussed.

The pitting potentials of various metals in different solutions of modified actual mother liquor, which were assumed to be possible compositions in a salt production process, were measured. The target metals of test pieces were UNS S31600, S31254, S32053, N08354, and N06022, from which evaporators are fabricated. Experimental conditions in the study for austenitic stainless steels（S31600, S31254, S32053, and N08354） were divided into two categories: situations where pitting corrosion occurred on surface of test pieces and situations where pitting corrosion did not occur but instead water decomposition reaction（oxygen evolution reaction） occurred mainly, thus suggesting that the potential for oxygen evolution couldnʼt be influenced by concentrations and temperatures of mother liquor and metals but pitting potential could be influenced. Therefore, prediction equations were developed using the acquired data, with pitting potential and limit concentration of pitting corrosion as response variables, and concentrations and temperatures of mother liquor and pitting index of metals as explanatory variables. However, in the study, pitting corrosion did not occur but instead transpassive dissolution occurred on the surfaces of test piece for nickel alloy（N06022）, suggesting that the transpassive dissolution potential could also be influenced by concentrations and temperatures of the mother liquor. Consequently, a prediction equation was developed using the acquired data, with transpassive dissolution potential as the response variable, and concentrations and temperatures of the mother liquor as explanatory variables. These prediction equations should allow for estimating pitting potential and limit concentration of pitting corrosion in the mother liquor of salt production by ion exchange membrane, which may contribute to selecting metal materials used for evaporators.