チオ硫酸イオンを含む塩化物水溶液中における SUS316L 鋼の応力腐食割れ感受性電位域

概要

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Susceptible potential region for stress corrosion cracking, SCC, of SUS316L stainless steel has been investigated in 20 mass% NaCl aqueous solution containing 10^<-2> kmol・m^<-3> thiosulfate ion by using a slow strain rate technique, SSRT. Potential from -400 to -340 mV_<Ag/AgCl> was controlled either chemically by changing the concentration of dissolved oxygen, DO, in the solution or electrochemically by using a potentiostat. In both cases, cracks always generated at pits. In case of controlling DO, free corrosion potential raised and a shape of pit and crack changed with increase in the concentration of DO. Strain at the maximum stress, e_<SCC>, was, however, independent of the concentration of DO, and depended on the number of cracks in the fracture surface. In case of applying potential, localized corrosion was found to generate beyond a critical potential of -370mV_<Ag/AgCl> ; cracks were observed from -370 to -340 mV_<Ag/AgCl> and pit size increased with increase in applied potential. e_<SCC> was found not to be sensitive to the applied potential, but to be mainly decided by the strain at which pit generated. The crack growth rate which was estimated by the analysis of the stress-strain curves was found to be almost constant in the potential range between -370 and -340mV_<Ag/AgCl>.
1992-02-01