Mechanistic interpretation on acidic stress-corrosion cracking of NiCrMoV steam turbine steel

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2021-01, Vol.802, p.140433, Article 140433
• Main Authors: De Seranno, T., Lambrechts, E., Verliefde, A.R.D., Depover, T., Verbeken, K.
• Format: Article
• Language: English
• Subjects: A. electron microscopy; A. stress/strain measurements; Acetic acid; Anodic dissolution; B. iron alloys; Corrosion; Corrosion rate; D. plasticity; Dissolution; Ductility tests; Hydrogen embrittlement; Hydrogen reduction; Nickel chromium molybdenum steels; Steam turbines; Stress corrosion cracking
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2020.140433

The present work evaluates the acidic stress-corrosion cracking (SCC) of NiCrMoV steam turbine steel. Between a pH of 4.2 and 7, iron oxidises to Fe2O3, whereas iron dissolution (Fe2+) and hydrogen proton (H+) reduction are favoured at lower pH. The corrosion rate increases with the H+ concentration via a linear relationship as well as by a temperature increase. During in-situ constant extension rate testing, both the ductility and strength losses, caused by anodic dissolution and hydrogen embrittlement, increase with a higher acetic acid concentration. Hydrogen embrittlement causes larger embrittled zones with higher acetic acid concentrations as well as stress-corrosion cracking. •Acidic SCC of NiCrMoV steam turbine steel assessed by in-situ CERT and SEM.•Both anodic dissolution and hydrogen formation took place at a pH lower than 4.2•Linear increase of corrosion rate with hydrogen proton concentration.•Ductility and strength drop increased with higher acetic acid concentrations.•Embrittled zones and stress-corrosion cracks due to hydrogen embrittlement.