2019 Volume 59 Issue 10 Pages 1828-1837
In view of the heightened risk of hydrogen embrittlement in ultra-high strength steels, it is necessary to clarify the mechanism of hydrogen embrittlement and develop steels with superior hydrogen embrittlement resistance. Hydrogen is trapped at various types of trapping sites in steels, and the influence of hydrogen on hydrogen embrittlement depends on the trapping site. Therefore, it is important to identify the kinds of hydrogen trapping sites in steels. The purpose of this study is to identify the hydrogen trapping sites that exist in ultra-high strength steel sheets. In this study, 1180 MPa grade dual-phase steel was used. Various levels of strain were applied to the samples by rolling, which was followed by cathodic electrolytic hydrogen charging. The hydrogen desorption rate was measured from −50°C by using a Thermal Desorption Analysis (TDA) device which enables evaluation of each hydrogen trapping site. The TDA results were analyzed with a Gaussian function to identify each hydrogen trapping site. Four types of hydrogen trapping sites were identified in the DP steel. The analysis showed that the type of hydrogen trapping site detected as a peak at 35°C was dislocations, the type at 54°C was carbides in the martensite structure of the DP steel, that at 75°C was various interfaces in the martensite and the ferrite-martensite interface in the DP steel, and that at 110°C was vacancy clusters.