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Adibi, Behnam | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44194 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. This study was conducted in order to investigate the effect of difference in electrical resistivity between low carbon steel and austenitic stainless steel on the physical and mechanical properties and fracture mode of dissimilar resistance spot welds of these alloys. For this purpose, plastic deformation using constrained groove pressing combined with rolling applied to low carbon steel in three levels of 40%, 156% and 272%. Microstructural characterization, micro-hardness measurements and shear-tension test were performed. It was shown that by increasing the pre-strain in low carbon steel its electrical resistivity increases from 13.08 μΩ.cm to 19.5 μΩ.cm and because of reduction of difference in electrical resistivity between low carbon steel and austenitic stainless steel, the symmetry of weld nugget is improved. Therefore, as a result of this effect, the peak load and energy absorption capability of the joints were increased. Failure behavior of the joints was investigated and two different fracture modes, i.e. Interfacial Failure (IF) and Partial Thickness-Partial Pullout Failure (PT-PP), were characterized. It was found that the spot weld strength in PT-PP fracture mode is controlled by the strength and fusion zone size (FZS) of carbon steel side. Considering the relation of FZS with peak load and energy absorption of the joints, it was concluded that the critical FZS of carbon steel side to insure PT-PP mode (that is, in this research, an indication of weld quality) is 5.8 mm. Moreover, depending on the dilution ratio of the base metals two different microstructures in FZ are achieved, consisting of austenite + ferrite + martensite to full martensite. In confirmation of these observations two different micro-hardness profiles were recorded
  9. Keywords:
  10. Electrical Resistivity ; Austenitic Stainless Steel ; Resistance Spot Welding ; Plastic Deformation ; Low Carbon Steel

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