Abstract
The effect of SSRT (slow strain rate testing) in the presence of hydrogen (in-situ SSRT test) was investigated for CrMo and CrMoV steels and compared with that of hydrogen addition after pre-straining (pre-SSRT test). The amount of hydrogen trapped by dislocations (A1 hydrogen content) has a same linear relationship with the amount of strain as in the pre-SSRT test. The A1 hydrogen content is proportional to the amount of hydrogen trapped by cementite (A0), grain boundary (A2), and two types of vanadium carbides (V1 and V2). The proportionality coefficients are the same as in the pre-SSRT test. However, the ratio of A2 to A1 is virtually large in the in-situ SSRT test. The amount of hydrogen trapped in vacancies (B), vacancy clusters (C) or microvoids (D) is the same as in the pre-SSRT test when plastic strain at fracture is used. For high-strength materials sensitive to hydrogen content, owing to the increased amount of A2 hydrogen though in-situ SSRT, brittle IG fracture occurs at stresses near the yield point. If the material is low in strength and insensitive to IG fracture due to hydrogen, work hardening proceeds beyond yield point and the dislocation density increases. This results in the formation of B, C, and D sites, and ductile fracture at decreasing load.
