Effect of V/Mo ratio on the evolution of carbide precipitates and hydrogen embrittlement of tempered martensitic steel

[Display omitted] •V/Mo ratio affected hydrogen embrittlement (HE) resistance.•Steel containing V/Mo ratio of 3:1 (3V1Mo) had superior HE resistance to those of 1:6 (1V6Mo) and Base.•Undissolved V carbide in 3V1Mo refined the prior austenite grain (PAG) size.•Hydrogen trapping by V carbides and refinement of PAG improved HE resistance. Hydrogen embrittlement (HE) behavior of tempered martensitic steels subjected to V and Mo addition was investigated. V and Mo were added to a Base steel in two V/Mo wt.% ratios of 3:1 (3V1Mo) and 1:6 (1V6Mo). Addition of V and Mo improved the HE resistance, as a result of breakage of lamellar cementite and of hydrogen trapping by V/Mo carbides. The steel with high V/Mo ratio had better HE resistance than the steel with low V/Mo ratio, mainly because the high V content formed a large amount of V carbides, and that also refined prior austenite grains.