硫酸-塩化ナトリウム溶液中における溶体化オーステナイトステンレス鋼type 304の応力腐食割れ

塩化ナトリウム濃度とクロメイトの影響

抄録

Stress corrosion cracking (SCC) of austenitic stainless steel type 304 has been investigated as functions of chromate concentration and test temperature in 0.82kmol/m³ H₂SO₄-NaCl solution under a constant applied load by using a constant load method. The linear relationship between the logarithms of time to failure and steady state elongation rate was obtained under a constant applied stress of 388MPa (or 392MPa) irrespective of NaCl concentration, chromate concentration and test temperatures as follows: logl_ss=-logt_f+C. Under the present experimental conditions, the steady state elongation rate was was found to be a useful parameter both for predicting time to failure and for the assessment of SCC susceptibility. The critical chromate concentration (C^cri_Na2CrO4) and critical test temperature (T^cri) were estimated under a constant nominal stress of 388MPa and were obtained below, respectively;
logC^cri_Na2CrO4=0.70·logC_NaCl-0.73
10³/T^cri=-0.64logC_Na2CrO4+2.11
The results obtained were discussed in terms of ion selectivity of film formed, corrosion current density at crack tips and the length of crack propagation.