Abstract
The fracture surfaces of ferritic-perlitic steel caused by hydrogen induced cracking (HIC) and sulfide stress cracking (SSC) under the wet H2S environment were investigated by a scanning electron microscope. It was clarified that HIC and SSC were caused by hydrogen embrittlement. The cracks of HIC initiated around the nonmetallic inclusions (MnS) and they grew in a step-wise manner by connecting each other. On the other hand, the process of SSC took place as follows; the separated small cracks of HIC were connected by the cracks perpendicular to the stress axis. The fracture due to hydrogen embrittlement exhibited some characteristic fracture patterns, such as a river like pattern, flat pattern and so on. It was supposed that these fracture patterns were formed depending on the crystallographic orientation of grains. The striation type pattern was observed on the river like pattern as well as on the flat pattern. This striation type pattern seemed to correspond to the discontinuous propagation of hydrogen embrittlement cracking. In order to determine the sharp of the river like pattern, the stereo-matching technique was applied and it was found that this pattern could be classified into three types.
