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Hydrogen is known to degrade the performance of structural materials, a phenomenon commonly referred to as "hydrogen embrittlement". Hydrogen embrittlement is a well-known phenomenon in high strength materials and is responsible for subcritical crack growth in the material, fracture initiation and catastrophic failure with subsequent loss of mechanical properties such as ductility, toughness and strength. Recently, the effects of stress and plastic strain distributions on hydrogen embrittlement fracture of the U-bent martensitic steel sheet specimen in commercial JIS-SCM435 steel sheet were investigated [1]. They found that the fracture morphology mainly consisted of intergranular fracture inside the hydrogen-loaded U-bent specimen, and the elastic strain clearly depended on the depth of the material.
Although elastic stress is an important factor in hydrogen embrittlement, the direct relationship between elastic stress and hydrogen state is not well understood. Therefore, we have investigated the depth dependence of the muon state in the plate of the bolt-tightened U-bend steel at different temperatures to study the relationship between the hydrogen state and the elastic stress in the bolt-tightened U-bend SCM435. We observed only small differences between the muon spin relaxation spectra with different momentum or depth. These results may reflect the small elastic stress dependence of the hydrogen dynamics.
[1] Y. Shibayama et al, ISIJ International, Vol. 61 (2021), No. 4.
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