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Developement of Bimodal Grain Size Microstructure in a Stainless Steel using Thermal-Mechanical Treatment

Hojati, Zahra Sadat | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51188 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. Thermomechanical processing during hot rolling and subsequent annealing of rolled sheets are one of the procedures for improving the tensile and formability properties of metals and alloys. In this regard temperature and reduction in area are the most important variables governing the behavior of 304 L austenitic stainless steel during the hot rolling process. The aim of this research was to investigate the effect of rolling temperature and subsequent annealing on 304L steel in order to achieve a microstructure with favorable mechanical properties and bimodal grain size. For this purpose, the rolling process at temperatures of -50, 25, 200, 400, 600, 800 and 900 °C using different thickness reduction of 35 to 80% was carried out and subsequently the rolled samples annealed at 700°C for 5 hours. To further investigate the effects of annealing treatment, samples of 80% thickness reduction were annealed at different temperatures and times. The microstructural examination by scanning electron microscopy (SEM) and tensile and hardness tests were performed on the samples. The results indicated that increasing rolling temperature reduces the yield and tensile strength. Rolling of the steel at 800°C with thickness reduction of 80% and then annealing at 900°C develop a bimodal microstructure. This microstructure presented a yield strength of 322 MPa and ductility of 79%. Also in the samples rolled at 400°C, the bimodal microstructure is obtained with different levels after annealing at different temperatures. The optimum sample presented a yield strength of 378 MPa and fracture strain of 71%
  9. Keywords:
  10. Thermomechanical Processing ; 304 Austenitic Stainless Steel ; Thermomechanical Treatment ; Microstructure ; Grain Size ; Bimodal Grain Size

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