Atomic Force Microscopy of Tempered Martensitic Steels with Different Delayed Fracture Properties

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  • Hayakawa Masao
    National Institute for Materials Science
  • Matsuoka Saburo
    Department of Advanced Energy Engineering Science, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University
  • Hanada Hitoshi
    National Institute for Materials Science
  • Nakashima Hidehiko
    National Institute for Materials Science
  • Sugisaki Masayasu
    Department of Advanced Energy Engineering Science, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University | National Institute for Materials Science

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Other Title
  • 遅れ破壊特性の異なる高強度マルテンサイト鋼のAFM組織解析
  • オクレ ハカイ トクセイ ノ コトナル コウキョウド マルテンサイト コウ ノ AFM ソシキ カイセキ

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Tempered martensitic microstructures were quantitatively evaluated by AFM and delayed fracture properties were obtained for an induction-heating-quenched and induction-heating-tempered (IHT) specimen and an induction-heating-quenched and furnace-heating-tempered (FHT) specimen of prestressed steel (mass% of 0.36 C, 1.63 Si and 0.72 Mn). The strength levels of both specimens were controlled so that the tensile strength was 1470 MPa. The critical diffusible hydrogen content for delayed fracture was 0.4 and 0.1 mass ppm for the IHT and FHT specimens, respectively. Cementite particles were smaller in the IHT specimen than in the FHT specimen, particularly on prior austenite ($gamma$) grain boundaries. These results demonstrate that delayed fracture property is correlated with cementite particle size on prior $gamma$ grain boundaries.

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