OS2102 オーステナイトステンレス鋼の700℃におけるフィッシュアイを伴う疲労破壊形態

Abstract

It has been clarified that fracture accompanying a fish-eye on its fracture surface occurred under long fatigue life regions in the stepwise S-N curve of an austenitic stainless steel obtained at 700℃. After a large fish-eye, which origin was located at the interior of the specimen, had reached the specimen surface, the fish-eye became a large surface crack and propagated as a Stage II crack. After a small fish-eye, which origin was located at the subsurface of the specimen, had reached the specimen surface, two types of fracture processes occurred. One type was that the fish-eye became a small surface crack and propagated as a Stage II crack. The other type was that fracture surface of the fish-eye was covered with oxides and the fish-eye became a non-propagating occluded crack. In the latter case, initiation of a new crack at the specimen surface was induced by the occluded crack and then fracture occurred. The depth of fish-eye origin from the specimen surface and stress intensity factor at the tip of fish-eye when it reached the specimen surface were pointed out as factors controlling which type of fracture processes occurred.