Examples of Fractured Steel Parts during Actual Usage due to Hydrogen Embrittlement and Consideration Regarding the Behavior of Hydrogen at the Prior Austenite Grain Boundary

Abstract

Steel parts fractured during actual use were investigated, and the mechanism of fracture for some of them was attributed to hydrogen embrittlement. This article describes a summary of the observation results fractured by hydrogen embrittlement. Fracture occurred under tensile stress within the elastic limit including residual stress. Most of the parts had a martensitic microstructure, and intergranular fracture surfaces were always observed in martensitic steels at least on part of the fracture surface. This observation indicates the importance of the role of hydrogen on the prior austenite grain boundary in hydrogen embrittlement.

In a significant number of the fractured parts due to hydrogen embrittlement, the origin of hydrogen was traced back to the production process. Apart from the well-known plating process, hydrogen can also be absorbed during heat treatment.

The literature was reviewed to explore the importance of the behavior of hydrogen on the prior austenite grain boundary. It is suggested that immediately after hydrogen charging, the amount of hydrogen on the prior austenite grain boundary is small and increases with increasing holding time due to diffusion from less dangerous sites such as dislocations.