Hydrogen Embrittlement and Hydrogen-Enhanced Strain-Induced Vacancies in α-Iron

Clarifying the states of hydrogen present in iron and steel is important in order to understand hydrogen embrittlement mechanisms and develop materials with high resistance to hydrogen embrittlement. Although it is widely recognized that the fracture strain of iron and steel decreases with increasing amounts of absorbed hydrogen, it is not yet well understood whether hydrogen directly decreases the fracture strain. Therefore, the objective of this study is to clarify the atomic-scale changes in strained alpha-iron specimens containing hydrogen. Low temperature thermal desorption spectroscopy (L-TDS), which can heat samples from lower temperatures than conventional TDS, was used to identify the peak temperatures and hydrogen states corresponding to various lattice defects in alpha-iron. The results indicate that new hydrogen trap sites in strained alpha-iron specimens containing hydrogen are enhanced compared to those without hydrogen. These sites are not dislocations, but hydrogen-enhanced strain-induced vacancies, because they are removed during aging at 30 degrees C.