Stress Corrosion Cracking of Solution Annealed Austenitic Stainless Steel Type 304 in Sulfuric Acid-Sodium Chloride Solution

Effects of NaCl Concentration and Chromate

Abstract

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.