The significance of inclusion morphology and composition in governing hydrogen transportation and trapping in steels

• Published in: International journal of hydrogen energy 2021-08, Vol.46 (56), p.28811-28822
• Main Authors: Peng, Zhixian, Liu, Jing, Huang, Feng, Zhang, Shiqi, Hu, Qian, Wang, Zhen, Wang, Yicong
• Format: Article
• Language: English
• Subjects: Hydrogen induced cracking; Hydrogen trapping; Inclusions; Pipeline steel
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2021.06.096

In this paper, two steels with different morphology of inclusions are studied. Scanning electron microscopy, finite element calculations, and electrochemical hydrogen permeation tests were conducted. Furthermore, in-situ observations of hydrogen de-trapping from the surface of steels were achieved using a hydrogen charging device and optical microscope. Results show that stripe-shaped complex inclusions exhibit a higher level of residual stress, especially at the boundary of oxide components. The hydrogen molecule is also prone to emerge at the oxide composition and intensifies the risks of cracking. In contrast, the residual stress levels around spherical inclusions are comparatively lower due to discrete sites of stress concentration. Thus, the effect of dispersed tiny dioxide sphere inclusions can help relieve the local hydrogen pressure and promote the resistance against hydrogen-induced cracking. An in-situ optical hydrogen escaping observation device (a) and bubble forming and detection mechanism (b). [Display omitted] •Provide an in-situ method for observing the hydrogen molecules formation around inclusion.•Specified the actual sites of hydrogen trapping and diffusion around inclusions.•The compounded spheric inclusions can help homogenize the hydrogen distribution and hind the hydrogen diffusion.•The stripe-shaped inclusions can accelerate hydrogen diffusion and promote hydrogen aggregation.•The oxide parts of compounded inclusions may cause a larger stress field other than the tip sites.