Abstract
This paper deals with the hydrogen embrittlement (HE) of a CrMoV steel where more than 0.2% vanadium is alloyed to CrMo steel. The standard CrMo steel (JIS SCM435) is prone to HE in SSRT (slow strain rate tension test), exhibiting inter-granular (IG) fracture. The vanadium addition makes the steel resisting to HE by suppressing IG fracture. With more hydrogen absorption, not being referred ordinarily, the steel undergoes ductile fracture and the fracture strength falls into smaller value. This fracture initiates as IG fracture, and spreads with dimple-like ductile fracture on PAGB (prior austenitic grain boundary), which has been yielded through the accumulation of vacancy type lattice defects during SSRT. Both IG fracture and dimple-like ductile fracture are derived from the refined grain size with vanadium addition. The vanadium addition also acts to reduce the film-like cementite along PAGB to avoid IG fracture. The CrMoV steel may fracture in CLT (constant load tension test) just like the case of SSRT; the fracture strength may become somewhat higher than that of SSRT with more hydrogen absorption. The steel can be applicable to various usage like bolt, spring or hydrogen gas vessel, and it works in diverse ways for preventing HE.
