抄録
In regard to the austenitic stainless steels, the interrelations among the corrosion resistance, pickling and nonmetallic inclusions such as MnS have been investigated metallographically in solution of L-ascorbic acid (C6H8O6) as a food additive by an electrochemical method. In case of SUS 304 and SUS 316 stainless steels containing just a small quantity of MnS, the corrosion potential, Ecorr, and the critical current density for passivation, icrit, of each specimen were resulted in further noble value and smaller than those of the steels of the same kind containing a large quantity of MnS by pickling in the solution of 12%HNO3+1%NH4F, respectively. That is to say, the pickling inhibits the anodic dissolution reaction in the active region. On the other hand, as for SUS 303 and SUS 304 containing a large quantity of MnS, MnSe or Ca, Ecorr and icrit were resulted in the value of the most noble and smaller by pickling in 12%HNO3 solution, respectively. In all of the specimens pickled in the solution of 12%HNO3 or 12%HNO3+1%NH4F, the pitting potentials, Vc′100, came to further noble value than those of the specimens pickled in 30%HNO3 solution, because the surface inclusions such as MnS that act as the starting point of pitting were dissolved by the pickling in the solutions of the two varieties of the former.
