高強度鋼の遅れ破壊強さに及ぼす変動荷重及び動ひずみ時効の影響

概要

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Delayed failure tests of notched specimens of 18Ni-maraging steel, precipitation hardening stainless steel (JIS : SUS630) and Cr-Mo low alloyed steel (JIS : SCM435), which were aged or tempered to high strength levels, were carried out in 3% NaCl aqueous solution under static and superposed repeating load. Moreover, the effects of static and dynamic strain aging at 573 K or 673 K on the delayed failure strength were investigated on the Cr-Mo steel. The superposition of repeating load drastically decreases the delayed failure strength and the lower limit values of apparent stress intensity factor, under which no crack initiation occurs within 360 ks, for every steel. For Cr-Mo steel, the dynamic strain aging at 673 K is effective to increase the delayed failure strength not only under static load but also under repeating load, while the static strain aging at 673 K and the dynamic strain aging at 573 K has no improving effect.