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Effect of Warm Rolling on The Microstructure and Tensile Properties of Severely Deformed Low Carbon Steel in Grooved Die

Ahmadi Chadegani, Amir Hoseein | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56178 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kazeminejad, Mohsen
  7. Abstract:
  8. In recent years, various research has been done on the severe deformation of low carbon steel sheets. One of the methods used is the pressing in the grooved die, only two passes of the pressing process in the grooved mold have been successful when applied to these sheets, but on the other hand, these two passes also lessen the sheet's ductility while increasing its strength. Due to the fact that the sheet surface produced by the pressing in the grooved die is not entirely smooth, the attempt in this project was to improve the ductility to some extent using warm rolling in addition to the smoothness of the surface using higher temperature while improving the strength or maintain it. To account for that, the samples in this study undergo a severe deformation pass and subsequent hot rolling with a reduction of 30, 50, and 70% at temperatures of 300, 400, and 500° C. In order to determine the effect of CGP on the hot-rolled sample mechanical characteristics, hot-rolled CGPed samples a have been compared to raw hot-rolled samples. The results of this research have been evaluated by tensile test, microstructure examination with optical microscope and secondary electron microscope. The findings indicate that raising the temperature has enhanced the material's tensile strength and raised fracture strain under constant rolling strain. The tensile strength rose, but the failure strain reduced when the rolling strain increased at a constant temperature. It has been demonstrated that the CGP process improved its strength compared to the hot-rolled raw sample under constant rolling strain and temperature due to the rise in the density of dislocations. The grains were crushed by the CGP process as a result of grain fragmentation, as shown in the optical microscope images. Due to dynamic recrystallization, the sample grains get finer as the subsequent hot rolling's temperature rises. On the other hand, the sample's grains lengthen and take on a pancake-like form at constant temperature as the percentage of reduction in cross-sectional area increases. The optimum sample is the 50% deformed sample at 500°C. This sample has a fine-grained structure with ductile fracture, shown in the photos from the optical and electron microscopes. Tensile test results revealed a yield of 500 MPa and a tensile strength of 680 MPa, which were better than the sample of a severely deformed for one pass. Additionally, it is noted that the recrystallization temperature of low carbon steel in this research is closer to 400°C than the typical value of 600°C
  9. Keywords:
  10. Severe Plastic Deformation ; Low Carbon Steel ; Warm Rolling ; Microstructure ; Tensile Properties ; Dynamic Recrystallization ; Grooved Dies

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