Hydrogen embrittlement resistances of alloying elements adding ultrahigh-strength low-alloy TRIP-aided steels

To develop ultra high strength steels for automotive impact safety parts, effects of alloying elements on hydrogen embrittlement resistance of ultra high strength low alloy TRIP-aided steels with martensitic matrix (TM steel) were investigated. Hydrogen embrittlement susceptibilities of TRIP-aided steels were decreased by addition of alloying elements although tensile strength and diffusible hydrogen concentration of alloying elements adding TM steels were increased compared with base steel. Particularly, when 1.0 mass% chromium was added to the TM steels, TM steel indicated low hydrogen embrittlement susceptibility. It is considered that uniform and refined lath matrix and retained austenite/matrix interface absorbed a large amount of diffusible hydrogen in order to suppress hydrogen trapping to the grain boundaries and the lath boundaries and strain induced transformation of stable retained austenite suppressed initiation and growth of voids and initiation and propagation of cracks effectively.