Abstract
Press hardening steel (PHS) is the most popularly adopted one among car makers due to its economical operation process and good mechanical properties. During the austenitization step, PHS absorbs hydrogen through the coupled reactions: oxidation of metals (steel itself and coating) and reduction of moisture in the atmosphere. It is well known that tiny amount of diffusible hydrogen triggers the hydrogen embrittlement (HE) of advanced high strength steels with strength levels over 1000MPa. However, there is a challenge to confirm the HE susceptibility evaluation standard because complex factors affect the HE such as diffusible hydrogen content in the steel, deformation mode, application environment and so on. Conventional strain rate test, slow strain rate test and notched specimen tensile test were conducted to suggest a proper test methodology for the ultra-high strength PHS. The HE susceptibility of PHSs is also evaluated with respect to the Hydrogen Enhanced Localized Plasticity (HELP) to compare activation volume during the repeated stress relaxation tests of steel.