In order to investigate the influence of residual stress due to surface-treatments on the hydrogen sensitivity and delayed fracture strength, static bending tests and cantilever bending delayed fracture tests were performed on Cr-Mo high strength steel. The methods of paper polish, sandblast and shotblast were adopted in this experiments and the results of these specimens were compared with those without surface-treatment. The residual stress in the surface layer was measured by X-ray diffraction technique.
The conclusions obtained were summarized as follows;
The sensitivity of hydrogen embrittlement for the blasted specimens decreased by the presence of compressive residual stress in comparison with that for the specimens without surface-treatment. It was found that there was a good correlation for the surface-treated specimens between the variation of maximum stress in static bending tests and that of residual stress corresponding to the change in hydrogen charged time.
The delayed fracture life for the surface-treated materials also depended on the residual stress distribution near the surface, and the crack initiation time in delayed fracture tests was largely prolonged in the case that high compressive residual stress was created from the surface to the inner part such as the case of shotblasted specimen.
Therefore, it was considered that the application of blast-treatment to the material surface was much effective for the improvement of not only the adhesion of coating but also delayed fracture strength.
