抄録
The influence of hydrogen-supply and hydrogen-diffusion on the crack growth of a high-strength steel (SNCM 439) was investigated under repetitional stresses and under a sustained-load by changing hydrogen-diffusion conditions (ie, Pre-Charge, Bulk-Diffusion and Tip-Diffusion conditions). Under the Pre-Charge condition, hydrogen was fully charged into metal from all the surfaces of the specimen before and during the test, so that hydrogen could be supplied from the crack tip as well as from the bulk metal. Under the Bulk-Diffusion condition, hydrogen was supplied not from the crack tip but only from the bulk metal. Under the Tip-Diffusion condition, hydrogen was supplied only from the crack tips. The summary of the results obtained is as follows:
(1) Under the Pre-Charge condition, the crack-growth-rate was highly accelerated.
(2) In the case of KFSCC≤Kmax<KISCC cyclic SCC crack growth was much more accelerated by the hydrogen supply of Tip-Diffusion than by that of Bulk-Diffusion. In the case of Kmax≥KISCC the acceleration of crack growth depended on the cooperative effect of Tip- and Bulk-Diffusions.
(3) The acceleration of crack growth promoted by hydrogen diffusion was observed under repetitional stresses. The greater the cycle frequency was, the more remarkable the acceleration became. The promotion of hydrogen diffusion by cyclic stresses was also supported by the fractographical observation.
