Synergistic effect of temperature and HCl concentration on the degradation of AISI 410 stainless steel

- Corrosion domains are established for 410 SS as a function of [HCl] and temperature.
- Synergistic effect of hydrogen and chloride ions is found for passive film breakdown.
- Permanent uniform degradation of passive film occurs above critical temperature.
- Metastable pitting initiates from non-metallic inclusions below critical temperature.
- Sigma phase particles are identified in 410 SS by TEM/SAED and remain uncorroded.

The corrosion behavior of AISI 410 stainless steel was investigated in relatively dilute HCl solutions with different concentrations and temperature levels. General corrosion occurred at pH < 1.5 while pitting occurred at 2.25 ≤ pH ≤ 4.25. Important pitting parameters were evaluated as a function of both temperature and HCl concentration. Critical temperature (Tcrit) increased linearly with pH. Below Tcrit, passive film remained largely intact and sporadic metastable pitting initiated from non-metallic inclusions. Above Tcrit, passivity was completely destroyed and black film consisting of oxy-hydroxide and hydrated oxide formed. Sigma-phase particles were found in this steel and remained un-corroded.