Abstract
Recently, for reinforcing the regulation of CO2 emission and growing environmental concern in the automobile industry, uses of ultra-high strength steels (UHSSs) above 1GPa grades are gradually increasing as the means of car-body weight reduction for automobiles. However, it is well-known that a little limitation presents due to concerned issue on hydrogen embrittlement (HE) for usage in case of the UHSSs. In this study, fracture trajectory analysis was performed to quantitatively assess the role of the pre-existing hydrogen with respect to the overall deformation modes. It is reasonable to assume that the effects of hydrogen with various level on ductile fractures would be more pronounced under triaxial stress conditions generated by introducing as a given specimens, as Notched tensile (NT), Plane strain (PS), Central hole (CH), and Shear (SH) specimens. The 4 type of specimens were tested under differential hydrogen concentration using slow strain rate tensile test (SSRT), in a similar manner, to quantitatively evaluate effect of triaxial stress conditions corresponding to fracture strain estimated using digital image correlation (DIC).