Effect of Hydrogen on Deformation Behavior of Carbon Steel S25C —Measurement of Time Evolution of Strain Distribution until Crack Initiation Using Digital Image Correlation Method

To explain hydrogen embrittlement, it is important to understand the effect of hydrogen on the plastic deformation of materials. In this study, we measured the plastic deformation process until crack initiation in hydrogen-charged and hydrogen-uncharged carbon steel S25C using the digital image correlation method. As a result, we found that the equivalent strain at crack initiation decreased at the stress-concentrated regions owing to the presence of hydrogen, whereas the size of regions with a high equivalent strain rate increased at an earlier stage. Comparing the equivalent strain rate in regions with roughly the same equivalent strain, we found that there is no significant difference between hydrogen-charged and hydrogen-uncharged specimens for small equivalent strain; however, the equivalent strain rate increased rapidly for large equivalent strain in hydrogen-charged specimens.