1800MPa級フェールセーフ鋼の微視き裂発生のクライテリオン（微視組織制御からの破壊制御の構築）

• 井上 忠信

  物質・材料研究機構

• 木村 勇次

  物質・材料研究機構

書誌事項

タイトル別名

• Criterion of micro-crack initiation in 1800 MPa class fail-safe steel (Development of fracture control from microstructure design)

抄録

The criterion of micro-crack initiation on stronger, tougher steel, i.e., fail-safe steel, with an ultrafine elongated grain (UFEG) structure was studied through a combinations of numerical simulation and experimental observations and measurements. The test sample was machined from the rolled bar with 0° and 90° rotation along the rolling direction (RD). The static three-point bending test was conducted in a temperature range from 200 °C to -196 °C. The stresses near the initial notch were analyzed by three-dimensional finite element method. The conventionally quenched and tempered steel with a martensitic structure fractured brittlely with a peak bending loading. On the other hand, the developed steel did not fully fracture due to a lamella fracture even if load drops occurred during the bending test. The load drops are attributed to micro-cracks with normal to the loading direction (LD) or with an angle of 45° to the LD that occurred from near the initial notch root. When the crack orientation, i.e., LD is parallel to the RD, the developed steel showed a catastrophic fracture behavior. In the developed steel, the brittle fracture stress normal to the RD, σ_F⊥RD, was 3.2 GPa at temperature over -100 °C and 2.6 GPa at temperature below -170 °C. The σ_F of weak direction in the developed steel was 0.7 times lower than σ_F(QT) of the conventionally steel. When the effective grain size on fracture is assumed to be packet in the martensitic structure, the brittle fracture stress parallel to the RD, σ_F//RD, was estimated to be 6.2 GPa at temperature over -100 °C and 5.0 GPa at temperature below -170 °C. These values are 1.4 times as compared with the σ_F(QT), 1.9 times higher than the σ_F⊥RD regardless of the test temperatures. The anisotropic brittle fracture stress in the fail-safe steel is attributed to the microstructural features, and we would be able to control a fracture of the steel by designing microstructures.

収録刊行物

• 日本機械学会論文集

  日本機械学会論文集 82 (844), 16-00246-16-00246, 2016

  一般社団法人 日本機械学会

キーワード

• Iron and steel
• FEM
• Toughening
• Brittle fracture stress
• Crystal refinement
• Microstructural control

詳細情報

• CRID: 1390001205514488448
• NII論文ID: 130006943360
• DOI: 10.1299/transjsme.16-00246
• ISSN: 21879761
• Web Site: https://www.jstage.jst.go.jp/article/transjsme/82/844/82_16-00246/_pdf
• 本文言語コード: ja
• データソース種別:
  • JaLC
  • Crossref
  • CiNii Articles
  • KAKEN
• 抄録ライセンスフラグ: 使用不可