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Effect of Martensite Volume Fraction on Fatigue Properties of Ferrite- Bainite- Martensite Triple Phase Steel

Goudarzi, Ahmad | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42331 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ekrami, Ali Akbar
  7. Abstract:
  8. The introduction of multi phase steels in recent years resulted in a considerable increase in development of some industries such as automobiles. By inducing soft and hard phases together, these steels could bring better mechanical properties than classical ones. Recent studies on 4340 ferritic- bainitic and ferritic- martensitic dual phase steels, indicate that 34 volume percent ferrite with hard phase, has the best combination of strength, toughness and fatigue properties. In present research, by proper heat treatment on a 4340 steel, it is tried to prepare specimens ferritic- bainitic- martensitic triple phase steels with 34 volume percent of ferrite and different percents of martensite. Thereafter, through fatigue test in room temperature, the process of their fatigue limit is studied. In addition, specimens with tempered martensite microstructure are prepared to be compared with above microstructures. Also the results of the mechanical properties of the former microstructures are compared to those of the steel with ferrite- bainite dual phase with the same composition. Finally it is found that the fatigue limit of triple phase steels are greater than dual phase steel but lower than steel with tempered martensite. Moreover, it is showed that the more martensite volume percent, the greater fatigue limit. Lastly, the characteristics of fatigue fracture surfaces are studied by scanning electron microscope
  9. Keywords:
  10. Triple Phase Steel ; Microstructure ; Mechanical Properties ; Fatigue

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