Pre-strain effects on critical stress and hydrogen content for hydrogen-induced quasi-cleavage fracture in a TRIP-aided bainitic ferrite steel: Martensitic transformation, matrix damage, and strain aging

• Published in: International journal of hydrogen energy 2020-10, Vol.45 (51), p.27920-27928
• Main Authors: Kumai, Bakuya, Hojo, Tomohiko, Koyama, Motomichi, Akiyama, Eiji, Waki, Hiroyuki, Nagasaka, Akihiko
• Format: Article
• Language: English
• Subjects: High-strength steel; Hydrogen embrittlement; Pre-straining; Retained austenite; Transformation-induced plasticity
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2020.07.036

In this study, we characterized the details of the pre-strain effects on the microstructure, deformation/fracture behavior, and hydrogen content, with respect to the true fracture strength in the TRIP-aided bainitic ferrite steel. Three types of hydrogen embrittlement behavior were distinguished, based on pre-strain and hydrogen content. Pre-strain reduces the fraction of retained austenite, which in turn decreases the hydrogen embrittlement susceptibility when the hydrogen content is low. However, further pre-straining increases dislocation density, which has three main effects: an increase in hydrogen content, work hardening, and strain-age hardening. The increase in the hydrogen content that exceeds 4 mass ppm has been found to decrease the true fracture strength from approximately 1.5 to 1.2 GPa. The work hardening and strain-age hardening were found to increase until the critical fracture stress was achieved with respect to the strain; this led to a reduction in the elongation, particularly when the hydrogen content was high. [Display omitted] •Pre-strain effects on fracture behavior and hydrogen content are characterized.•Effect of pre-strain is only advantageous when hydrogen content is low.•Local accumulation of dislocations increases probability of quasi-cleavage fracture.•Critical stress for quasi-cleavage fracture decreases when hydrogen content is high.