18Ni マルエージ鋼の低温時効組織における遅れ破壊亀裂と破壊靱性値

概要

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In the previous paper, the authors reported about the peculiar phenomena with regard to an 18Ni maraging steel with low temperature aged structure, that K_<IC> was strongly dependent upon the prior γ grain size and the delayed failure crack was observed in front of the fatigue precrack. This study has been made in order to investigate these phenomena in more details and to discuss the mechanism by which K_<IC> is increased. It is made clear that an increment in K_<IC> is completely associated with slow crack growth of delayed failure which precedes the unstable fracture. However, its increment is not an increment in true K_<IC> as a material constant but an increment in apparent K_<IC>. This may be due to the blunting at crack front caused by the microbranching of the delayed failure crack, the degree of which also depends upon the prior γ grain size. Tensile ductility also markedly decreases under the same condition in which an apparent K_<IC> increases. This is attributed to the occurence of the delayed failure crack at the specimen surface adjacent to or in the necking region. Thus, the 18Ni margaing steel with low temperature aged structure shows the complicated behavior on toughness and ductility because of the high sensitivity to delayed failure.
社団法人日本鉄鋼協会の論文
1974-10-01