OVERLOAD EFFECTS IN ENVIRONMENTAL HYDROGEN-INDUCED FRACTURE

A study has been made of the effect of short periods of overloading on the environmental hydrogen induced fracture (HIF) life of 0.42% C, 0. 87% Cr, 0.2% Mo steel tested in a 0.5 mol/L H2SO4 solution under conti nuously hydrogen charging conditions. Experimental results showed that when the overloading was applied during the early or middle stage of the test, the HIF life was longer than that obtained at constant stres s; however, if the overloading was applied during the later stages, a shortened HIF life was obtained. It is important to note that the proc esses of HIF (including hydrogen absorption, transportation and accumu lation, crack initiation and propagation) depend not only on the elect rochemical condition, but also on both stress-strain state and stress history. In view of the above considerations, effects of plasticity in duced closure, residual compression stress, dislocation shielding and overload damage, which control HIF life, are discussed.