Effect of Electrochemical Potential on Stress Corrosion Cracking Susceptibility of EN 1.4301 (AISI 304) Austenitic Stainless Steels in Simulated Hot Black Liquor

Stress corrosion cracking (SCC) susceptibility of austenitic EN 1.4301 (AISI 304, UNS S30400) stainless steel was studied as a function of electrode potential at T = 190°C in 15 g/kg NaOH + 150 g/kg Na₂S containing caustic environment simulating heavy black liquors (HBL) of the pulp industry. Severe cracking was detected at the corrosion potential and at the cathodic potential of −0.11 V_Mo/MoS2 reference electrode. On the other hand, at anodic potentials of 0.03 V_Mo/MoS2 to 0.3 V _Mo/MoS2 no cracking was observed. Thus, SCC of EN 1.4301 steel can potentially be mitigated in HBL environment by applying anodic protection. At the corrosion potential, selective dissolution of Fe and slight localized enrichment of Ni and Cr, as well as Na, S, and O, was observed. At anodic potentials, Fe was selectively dissolved and marked enrichment of both Ni and Cr, as well as Na, S, and O, took place in the corrosion product. The simultaneous enrichment of Ni and Cr in the corrosion product film was concluded to be the precondition to prevent SCC.