Shear-mode Crack Initiation Behavior in the Martensitic and Bainitic Microstructures

Kentaro Wada, Soma Yoshimura, Tomoko Yamamoto, Yoshihiro Ohkomori, Hisao Matsunaga

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1 Citation (Scopus)


Fully reversed torsional fatigue tests were conducted to elucidate the behaviour of shear-mode crack initiation and propagation in one martensitic and two bainitic steels. The relationship between the crack initiation site and microstructure was investigated by means of an electron backscatter diffraction (EBSD) technique. From the S-N diagram, two notable results were obtained: (i) the shear-mode crack was initiated on the prior austenitic grain boundary in martensitic steel, while in bainitic steels, the crack was initiated along the {110} plane; one of the slip planes of bcc metals, and (ii) the torsional fatigue limit of lower bainitic steel with finer grains was 60 MPa higher than that of upper bainitic steel with coarser grains even though the hardnesses were nearly equivalent. The mechanism determining the torsional fatigue strength in these steels is discussed from the viewpoint of microstructure morphology.

Original languageEnglish
Article number04009
JournalMATEC Web of Conferences
Publication statusPublished - May 25 2018
Event12th International Fatigue Congress, FATIGUE 2018 - Poitiers Futuroscope, France
Duration: May 27 2018Jun 1 2018

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Science(all)
  • Engineering(all)


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