Hydrogen embrittlement of Type 4340 steel has been investigated by straining round-notched specimens in 10(5) Pa hydrogen atmosphere at a constent cross-head spead of 1.4x10(-4) mm/s. The circumferentially notched spe...Hydrogen embrittlement of Type 4340 steel has been investigated by straining round-notched specimens in 10(5) Pa hydrogen atmosphere at a constent cross-head spead of 1.4x10(-4) mm/s. The circumferentially notched specimens exhibited a significant embrittlement when their mechanical behaviour in hydrogen was compared with that in air. Although the effect of notch depth on fracture strength in air is negligible, an increase in the depth of notch increase susceptibility to embrittlement when testing in gaseous hydrogen. However, analysis of the effects is complicated by the facts that (i) the specimens show some degree of notch severity even when strained in air and (ii) the behaviour is complicated by the localised plastic deformation that may occur for relatively shallow notches. Such effects are eliminated at high stress concentration factors, so there is a systematic loss in fracture stress in hydrogen as the notch sensitivity increases from K-t=2.6 to 5.7 (where a 87% reduction of fracture stress occurs) but a relatively stable value is then reached even for very severe notching by fatigue pre-cracking. Whether or not the effect is due to increasing concentration of hydrogen in the triaxial stress region ahead of the notch, there is no doubt that increasing the stress concentration makes hydrogen more effective as an embrittlement agent.展开更多
文摘Hydrogen embrittlement of Type 4340 steel has been investigated by straining round-notched specimens in 10(5) Pa hydrogen atmosphere at a constent cross-head spead of 1.4x10(-4) mm/s. The circumferentially notched specimens exhibited a significant embrittlement when their mechanical behaviour in hydrogen was compared with that in air. Although the effect of notch depth on fracture strength in air is negligible, an increase in the depth of notch increase susceptibility to embrittlement when testing in gaseous hydrogen. However, analysis of the effects is complicated by the facts that (i) the specimens show some degree of notch severity even when strained in air and (ii) the behaviour is complicated by the localised plastic deformation that may occur for relatively shallow notches. Such effects are eliminated at high stress concentration factors, so there is a systematic loss in fracture stress in hydrogen as the notch sensitivity increases from K-t=2.6 to 5.7 (where a 87% reduction of fracture stress occurs) but a relatively stable value is then reached even for very severe notching by fatigue pre-cracking. Whether or not the effect is due to increasing concentration of hydrogen in the triaxial stress region ahead of the notch, there is no doubt that increasing the stress concentration makes hydrogen more effective as an embrittlement agent.
