Identification of lattice defects beneath fracture surfaces of cold-drawn pearlitic steel fractured in elastic/plastic regions in the presence of hydrogen

摘要

The kinds of lattice defects formed beneath fracture surfaces were analyzed using thermal desorption analysis (TDA) for cold-drawn pearlitic steel that was fractured in the elastic/plastic regions in the presence of hydrogen. A sample thickness of 0.3 mm made it possible to obtain two separate peaks: a low temperature peak and a high temperature peak. Tensile tests apd constant load tests were conducted under various hydrogen charging conditions to prepare samples with different elongations and fracture times. Samples of 0.3 mm in thickness beneath fracture surfaces were charged with hydrogen to determine the kinds of lattice defects and hydrogen desorption profdes were obtained using TDA. For samples that were fractured in the plastic region, a broad hydrogen desorption profile continuing to around 180 °C was obtained compared to samples without hydrogen charging and straining. Since this broad desorption profile was disappeared by aging at 200 °C, it probably corresponded to desorption from vacancies. In contrast, for samples that were fractured in the elastic region, this broad desorption profile was not obtained. These findings indicate that one of the factors causing hydrogen embrittlement in the plastic region is probably vacancies, whereas other factors cause it in the elastic region.