Coupling effect of microstructure and hydrogen absorbed during service on pitting corrosion of 321 austenitic stainless steel weld joints

• Published in: Corrosion science 2020-03, Vol.164, p.108339, Article 108339
• Main Authors: Cao, Ruohan, Xu, Lining, Jiang, Baolong, Gao, Mengjie, Qu, Dingrong, Shan, Guangbin, Xu, Shujian, Qiao, Lijie
• Format: Article
• Language: English
• Subjects: AFM; Austenite; Austenitic stainless steels; Boundaries; Corrosion effects; Ferrites; Heat affected zone; Hydrocracking; Hydrogen; Hydrogen enrichment; Immersion tests (corrosion); Microstructure; Pitting corrosion; Polarization; SIMS; Stainless steel; Weld metal; Welded joints
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2019.108339

(a) Optical morphology of fusion line for ToF-SIMS test, (b) corresponding negative ions ToF-SIMS mapping of red box in (a) after 10 min of sputtering, and (c) SEM high magnification images of pits on fusion line after the immersion test. [Display omitted] •Austenitic stainless steel weld joints served in a hydrocracking unit for 6 years•Hydrogen segregation occurred at the ferrite/austenite phase boundaries•Positions of the pit and hydrogen enrichment were microscopically consistent•Hydrogen enrichment conditions varied under different microstructures, which induced the difference in pitting susceptibility Pitting corrosion of austenitic stainless steel weld joints served in a hydrocracking unit for 6 years was examined. The microstructure of weld metal (WM) and fusion line (FL) was austenite and ferrite. After the immersion test, many pits were observed on the FL, whereas few pits were observed on the heat-affected zone (HAZ). Pits were microscopically initiated at ferrite/austenite boundaries. Hydrogen concentrations at FL and WM were higher than those of HAZ, and hydrogen segregation occurred at ferrite/austenite boundaries, which was consistent with the pit position. Hydrogen enrichment conditions varied under different microstructures, which induced the difference in pitting susceptibility.