Loading...
| Friend's email | |
| Your name | |
| Your email | |
| enter code | |
This page was sent successfuly
- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 40834 (07)
- University: Sharif University of Technology
- Department: Materials Science and Engineering
- Advisor(s): Kazeminezhad, Mohsen; Kokabi, Amirhossein
- Abstract:
- Considering that automobile weigth reduction in industry is important, improvement the strength of low carbon steel sheets is important. These sheets can be supported the service condition in lower thicknesses. Bulk nano-structured materials have been mostly attracted in materials science due to their unique physical and mechanical properties. Severe plastic deformation (SPD) is one of the most efficient methods to produce ultra fine grained or nano-structured materials. Materials produced by SPD are of great importance because of (1) non-porous structure, (2) great mechanical properties such as high strength and toughness and (3) proper dimension for mechanical and physical testing. Recently, several methods have been introduced for imposing the severe plastic deformation to the metals. In this study for the first time, costrained groove pressing (CGP) method is used for imposing the severe plastic deformation to the sheets of low carbon steel. In this research, strain magnitudes of 0 to 4.64 (each CGP pass imposes strain magnitude of 1.16) are imposed to the low carbon steel sheets containing 0.06wt% C to produce a high strength nano-structured sheet and in following, by using XRD, TEM, optical microscopy, tensile and hardness tests, characteristics of deformed sheets are investigated. Finally, in strain magnitude of 4.64, a deformed sheet with grain size of 230 nm and tensile strength of 400 MPa is obtained. Spot resistance welding is one of the most used joining processes in automobile industry, therefore welding of nano-structured sheets with this process is important. After producing of high strengthed nano-structured sheets with SPD method, these sheets are joined with spot resistance welding process. The results show that severe plastic deformation can effectively increase the electrical resistivity of steel sheets, therefore it can affect on microstructure and mechanical properties of spot welds. Microstructure and mechanical properties of fusion zone, heat affected zone (HAZ), recrystalized zone and base metal of SPDed sheets are investigated and the results are compared with characteristics of as-received specimen. The results show that with increasing the large pre-strain in sheets at constant welding parameters, fusion zone volume, electrode indentation, nugget diameter, and weld penetration are increased. Due to these subjects, peak load and hardness in fusion zone and HAZ are continuously increased with CGP pass number.
- Keywords:
- Severe Plastic Deformation ; Nanostructure ; Resistance Spot Welding ; Low Carbon Steel ; Grooved Dies
Digital Object List-
محتواي پايان نامه - view
Bookmark