炭素鋼S25Cの引張試験におけるボイド発生に及ぼす水素の影響

抄録

To investigate the effects of hydrogen on void initiation in tensile tests of a carbon steel S25C, tensile tests were conducted using hydrogen charged and uncharged specimens which were introduced pre-strain (0%, 5% and 10 %). Hydrogen content of hydrogen charted specimens increased in increasing pre-strain. The tensile strength and the yield stress of hydrogen specimens was approximately equal to those of uncharged. However, the reduction of area of hydrogen charged specimens was smaller than that of uncharged. In particular, the reduction of area of 10% pre-strained hydrogen charged specimen was smallest because of the largest hydrogen content. After tensile tests, the fracture surface and longitudinal section near necking section was observed. On fracture surface of uncharged specimen, only typical dimples were observed. However, on that of hydrogen charged specimen, typical dimples and flat fracture were observed. On the other hand, many voids were observed near the center of specimens and a few voids near specimen surface on longitudinal section of uncharged specimen. However, many voids were observed over the cross section on longitudinal section of hydrogen charged specimen. From these observation, hydrogen might make void easy to initiate. In hydrogen charged specimen, many voids initiate over the cross section and the specimen breaks before necking progress substantially. In uncharged specimen, fewer voids initiate compared with hydrogen charged. And the uncharged specimen breaks after the reduction of area becomes larger sufficiently.