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Effect of Variations in Flux Composition on Mechanical Properties and Microstructure of Weld Metal of Self-shielded Flux-cored arc Welding

Khazaee, Moein | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48810 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein
  7. Abstract:
  8. Flux-cored arc welding has become prevalent in the recent decades worldwide. One of the variants of this welding method is self-shielded welding which requires no external shielding, neither with mineral flux nor with shielding gases. In this study, the variation of microstructure and mechanical properties of flux-cored self-shielded welds was investigated and optimization of this properties was also carried out. For this purpose, a basic combination of powders was chosen from the literature to fabricate the flux-cored wire. These powders contain fluorine, calcium carbonate, aluminum, magnesium and iron. Then, same amount of alloying elements such as molybdenum and nickel was added to this combination. To investigate the properties of weld metal under external protection, the wire with the basic combination of powder was also welded with the protection of mineral flux used in SAW. To survey mechanical properties, tensile and impact test and also hardness measurements were carried out. Microstructure and fracture surface of impact test samples were analyzed with optical microscope and SEM. Ultimate tensile strength and total extension of the weld metal welded with basic combination of powders and no external shielding is alternatively 470 MPa (68.2 ksi) and 19.7% which are acceptable for structural steel welding. However, impact energy of this weld metal is not a high value. Adding alloying elements to this combination improved some of the mechanical properties and degraded some others while still being acceptable. Also, applying external shielding improves mechanical properties, as ultimate tensile strength and total extension of weld metal with external shielding have alternatively increased 18.3 and 157 percent in comparison with the weld metal with no external shielding. The reason of this improvement can be summarized in microstructure, non-metallic inclusions, residual elements and grain size
  9. Keywords:
  10. Mechanical Properties ; Microstructure ; Nitrogen ; Flux Cord Arc Welding (FCAW) ; Self-Shielded Flux Cored Arc Welding ; Non-Metallic Inclusions

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