Uncovering the origin of critical hydrogen concentration for initiation of hydrogen-induced cracking and its relation to inclusion type and size

This paper presents a theoretical criterion and approach for determining the relationship between the critical hydrogen concentration for hydrogen-induced cracking (HIC) initiation and the type and size of non-metallic inclusions. We used plate-like MnS and sphere-like Al2O3 as representative inclusions for in-depth analyses. Our results indicate that decreasing inclusion size increases the hydrogen concentration required for HIC initiation, particularly in the range of small inclusion sizes. Al2O3 exhibits a higher susceptibility to HIC than MnS. Each type of inclusion has a specific hydrogen concentration below which crack initiation cannot begin. The critical concentration for HIC initiation in the entire steel corresponds to the lowest value among these concentrations. This study provides a quantitative and comprehensive solution to this issue.