Correlation between intergranular corrosion and impurities of extra high purity austenitic stainless steels

An intergranular corrosion is a main degradation mechanism of austenitic stainless steels for use in a nuclear fuel reprocessing plant. The intergranular corrosion is caused by the segregation of impurities to grain boundaries and the resultant formation of active sites. Extra High Purity (EHP) austenitic stainless steel was developed with conducting the new multiple refined melting in order to suppress the total harmful impurities less than 100ppm. The intergranular corrosion behavior of EHP austenitic stainless steels added various impurities was examined in boiling HNO3 solution with highly oxidizing ions to find a correlation between the intergranular corrosion and the impurities of EHP-SSs. The corrosion rate of EHP austenitic stainless steels supported with the degree of intergranular corrosion relatively well. The relationships between the corrosion rate and the impurities content for EHP-SSs was determined using a multiple regression analysis. The influence on corrosion rate became small in order of B, P, Si, C, S and Mn. There is little effect of Mn on corrosion rate of EHP-SSs in case of 10000appm or less. It was important to control B and P in intergranular corrosion behavior of EHP-SSs. (author)