Evalution of Micro-Fracture Mechanisms and Fracture Toughness of Cryogenic Structural Steels and Weldment

Keita Ohnishi, Tetsuo Shoji, Hideaki Takahashi

Research output: Contribution to journalArticlepeer-review


In order to evaluate the fracture toughness of structural steels for superconducting magnets of fusion reactor, elastic-plastic fracture toughness testing was performed at 4.2 K on AISI 310S base metal, weld metal and 20 Mn steel. Fracture toughnesses were evaluated by a single specimen technique using the Key Curve reported previously. Elastic-plastic fracture toughness J1C and tearing modulus Tmat of weld metal were significantly lower than those of base metal. As the result of AE measurement, microfracturing was detected at the early stage of loading, and pop-in cracking was observed at the later stage. Fractographic and metallographic examination of fracture surfaces and fracture paths revealed a difference in dimple sizes between the weld metal and the base metal, and also micro void formation ahead of a growing crack tip, which resulted in smaller crack opening angle of the weld metal than the base metal. Finally, the significance of crack growth analysis of the weld metal was emphasized to ensure the structural integrity of superconducting magnet.

Original languageEnglish
Pages (from-to)170-173
Number of pages4
JournalTransactions of the Japan Society of Mechanical Engineers Series A
Issue number473
Publication statusPublished - 1986 Jan 1


  • Acoustic Emission
  • Elastic-Plastic Fracture Toughness
  • Fracture
  • J-Integral
  • Key Curve Method
  • Structure Steels. Cryogenic Temperature
  • Superconducting Magnet
  • Weld Metal

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering


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