발간논문

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Vol.30, No.2, 236 ~ 244, 1992
Title
The effect of Strain Induced Martensite in Austenite on the Relation between Fatigue Crack Initiation and ∇Ｋth
조윤성Y . S . Jo, 권숙인S . I . Kwun
Abstract
The fatigue crack initiation behavior of SUTS304 austenitic stainless steel with different strain induced martensite morphologies resulted from 3 different heat treatments was investigated. The speciment, without Cr-carbide precipitate showed that primary crack initiations sites were twin boundaries with preferred strain induced martensitic transformation in this region. On the other hand, the sensitized specimen showing Cr-carbide precipitation and consequent strain induced martensitic transformation along grain boudaries showed the enhanced intergranular crack initiation accompanied by shorter crack initiation life than that with no Cr-carbide. The sensitization in STS304 austenitic stainless steel gives contrasting effects on crack initiation and near-threshold fatigue crack propagation behaviors. The heat treatment which resulted in not only coarsened Cr-carbides on grain boundarlies but also Cr-carbide precipitation on twin boundaries inside the grains showed the shortest crack initiation life and the lowest ΔK_(1h) value among 3 conditions. It was considered that in this condition the crack initiation was due to strain induced martensite transformed at. Cr-carbides and these crack initiation sensitive regions were distributed more continuously along crack path showing little extrinsic toughening, resulting in the same detrimental effects on both crack initiation and near-threshold fatigue crack propagation behavior.
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