Synergistic Effects of a Sulfate-Reducing Bacteria and an Applied Stress on the Corrosion Behavior of 17-4 PH Stainless Steel After Different Heat Treatments

The individual and synergistic effects of sulfate-reducing bacteria (SRB) and an applied stress on the corrosion behavior of 17-4 precipitation-hardened (PH) stainless steel in sterile and SRB-inoculated solutions were investigated by electrochemical impedance spectroscopy and fractographic observation. Different heat treatments were applied to the 17-4 PH stainless steel, including single-stage aging, double-stage aging, and an intermediate treatment. The microstructures of the 17-4 PH stainless steels were mainly composed of lath martensite. However, the samples subjected to an intermediate treatment showed improved toughness as a result of the uniform and fine lath martensite. Among the samples considered in this study, the double-stage aged samples exhibited the highest yield strength and maximum stress corrosion cracking (SCC) susceptibility (I-scc) of 43.2% in the sterile solution. In the SRB-inoculated solution, the impedance values of all samples were reduced, and the production of harmful metabolites, such as FeS and H2S, occurred, indicating that SRB promoted corrosion of the stainless steel. The double-stage aged samples were the most sensitive to the SRB among the samples considered herein, where the I-scc was 52.8%. The SCC mechanism for single-stage aged and intermediate-treated samples was anodic dissolution (AD), and that for the double-stage aged samples was hydrogen induced cracking (HIC).