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Investigation of Work Hardening of Triple Phase Ferrite-martensite-bainite
Steels

Rezaei Ghalehtaki, Behzad | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46889 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ekrami, Ali Akbar
  7. Abstract:
  8. St52 was heated at 745°C for 70 minutes and then quenched into a salt bath at 400°C. To obtain different volume fraction of bainite and martensite with constant volume fraction of ferrite (67%), samples were quenched into water after different times. Presence of three phases of ferrite, bainite and martensite was proved by optical microscope and hardness test. Different volume fractions were measured by image analysis. Optical microscope results showed that with increasing of martensite up to 9.4%, morphology of martensite is a uniform distribution of small and sphere particles. These samples then were cold worked at various degrees. Tensile test and hardness test show that increasing the volume fraction of martensite up to 9.4% causes an increase in yield stress, ultimate tensile stress and hardness but total and uniform elongation decreases. Cold work results showed that increasing the cold work degree causes an increase in Hollomon’s parameters (n & k) in both steps and these parameters increase with increasing of martensite content. Investigation of fracture surface with help of images of OM, scanning electron microscopy and stereo microscopy showed that flexibility of samples decrease with increasing of martensite content and cold work. Reduction of flexibility with incasing of martensite content and cold work is related to dislocations created from deformation in phase boundaries and adjacent areas in ferrite grains
  9. Keywords:
  10. Triple Phase Steel ; Work Hardening ; Tensile Properties ; Rolling Process

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