2018 Volume 104 Issue 1 Pages 27-35
There are risks of hydrogen embrittlement in ultra-high strength steels. We need to clarify the mechanism of hydrogen embrittlement and to develop steels which have superior hydrogen embrittlement resistance. Hydrogen is trapped at various trapping sites in steels. The influence of hydrogen on hydrogen embrittlement depends on the hydrogen trapping sites. 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 in ultra-high strength steel sheets. 1180 MPa grade dual-phase steel was used. Various strain were applied to the samples by rolling, which was followed by cathodic electrolytic hydrogen charging. Hydrogen desorption rate was measured from –50 ºC using a Thermal Desorption Analysis device (TDA), which enables evaluation of each hydrogen trapping site. The TDA results were analyzed with using Gaussian function to identify each hydrogen trapping site. Four types of hydrogen trapping sites were identified in the DP steel. Hydrogen desorption peak appeared at 35°C was assigned to dislocations, peak appeared at 54°C was assigned to carbide in the martensite structure of the DP steel, Peak at 75°C was assigned to various boundaries in martensite and ferrite-martensite interface in the DP steel, and Peak at 110°C was assigned to a vacancy cluster.