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Effect of Rapid Annealing on Microstructure and Mechanical Properties of Severely Deformed Low Carbon Steel

Ghiabakloo, Hadi | 21013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45570 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science Engineering
  6. Advisor(s): Kazeminezhad, Mohsen
  7. Abstract:
  8. A low-carbon steel, containing 0.05 C, 0.203 Mn and 0.0229 Si (all in wt%) rapidly annealed in temperature range 300 ºC - 900 ºC, after severe plastic deformation (SPD) by constrained groove pressing (CGP). Microstructure evolution was investigated by Scanning Electron and Optical Microscopy. Mechanical properties were evaluated by hardness measurements and Shear Punch Testing (SPT). The result showed a thermal stability at 300 ºC and 400 ºC, which recrystallization did not occurred in these temperatures up to 2 h holding time. By annealing at 500 ºC and 600 ºC, the onset of recrystallization observed after holding times of 10 min and 20 s, respectively. Predicting the kinetic of recrystallization at 600 ºC showed a bi-linear JMAK plot indicating two different stages of recrystallization rate. In the first and second stages, progress of recrystallization showed a JMAK exponent of 1.6 and 0.6, respectively. At annealing temperatures higher than 700 ºC, a competition between recrystallizations and phase transformation observed, in which, the onset of phase transformation hindered recrystallization. This competition intensified by increasing in annealing temperature. A non-equilibrium austenite formation observed in the initial stages of annealing at 700 ºC that by increasing holding time, the amount of this austenite decreased. By increasing deformation, up to 3 passes of CGP, the competition between recrystallization and phase transformation at 800 ºC became weaker, because of more driving force for recrystallization before phase transformation. The hardenability of austenite, formed in the inter-critical region, showed a decreasing trend by increasing the annealing temperature. Water quenching after rapid annealing at 800 ºC, showed a better combination of strength and ductility, compared to those of 400 ºC and 600 ºC
  9. Keywords:
  10. Low Carbon Steel ; Nanostructure ; Severe Plastic Deformation ; Mechanical Properties ; Rapid Annealing

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