Numerical Interpretation of Hydrogen Thermal Desorption Spectra for Iron with Hydrogen-Enhanced Strain-Induced Vacancies
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TRODUCTION
HYDROGEN embrittlement (HE) is known as one cause of delayed fracture of high-strength steels and cold cracking of weld alloys.[1–4] As is widely known, in HE, H atoms gather at the location of stress concentration resulting from tensile stress or residual stress and lead to toughness degradation in materials by promoting the production of defects and/or by weakening the strength of atomic bonds, and then the toughness degradation causes cracks or fractures.[5,6]
KEN-ICHI EBIHARA is with the Center for Computational Science & e-Systems, Japan Atomic Energy Agency (JAEA), Tokaimura, Naka-gun, Ibaraki, 319-1195, Japan. Contact e-mail: [email protected] YURI SUGIYAMA is with the Graduate School of Science and Technology, Sophia University, Chiyoda-ku, Tokyo, 102-8554, Japan. RYOSUKE MATSUMOTO is with the Faculty of Engineering, Kyoto University of Advanced Science, 18, Yamanouchi-Gotandacho, Ukyo-ku, Kyoto, 615-8577, Japan. KENICHI TAKAI is with the Department of Engineering and Applied Sciences, Sophia University, Chiyoda-ku, Tokyo, 102-8554, Japan. TOMOAKI SUZUDO is with the Center for Computational Science & e-Systems, Japan Atomic Energy Agency (JAEA), and also with the Institute for Materials Research, Tohoku University, Oaraimachi, Higashiibaraki-gun, Ibaraki, 313-1313, Japan. Manuscript submitted July 6, 2020; accepted October 17, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
In recent years, it has been reported that defects are formed in tempered martensitic steels to which elastic stress is applied during charging with H atoms (H charging); this is referred to as H-enhanced lattice defect formation[7]. From the measurement of the positron annihilation lifetime (PAL), it is reported that the formed defects are considered as vacancies. The report[8] also mentions the effect of H atoms on the vacancy formation in deformed steel based on PAL measurement. Similar vacancy formation is also observed in tempered martensitic steels prestressed cyclically during H charging[9], in Inconel 625, iron[10], and nickel alloys[11], which are deformed and H charged concurrently. In the report[11], PAL is also used for estimating vacancy formation. Because ductility loss is observed in a tensile test of the steels and of the alloys even after H atoms charged for the vacancy formation are removed, as shown in Figure 1, it is implied that the vacancies themselves bring about HE, and it is mentioned that the phenomenon may support the H-enhanced strain-induced vacancy (HESIV) model that is proposed as a mechanism of HE[12–14]. However, how many vacancies bring about HE is still unclear, and the amount and size of vacancy clusters that can be generated by vacancy agglomeration relating to HE are also unknown.
Fig. 1—Example of ductility loss by vacancies. [H + stress(96 h)] is the tensile test result of the steel specimen in which H atoms used for the vacancy formation are fully degassed and vacancies still remain. [H + stress(96 h)+200 C] is the result after removing vacancies by annealing at 473 K from
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