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Production of Alloying Bonded Flux and Sdudy of Weld Metal Peroperties in Submerged Arc Welding

Mohammad Mirzaei, Mahdi | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50129 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein
  7. Abstract:
  8. The effect of alloying elements such as Chrome, Molybdenum and Chrome-Molybdenum on microstructure and mechanical properties of submerged-arc weld of structural St37 and 4135 Chromoly Steel was investigated. Addition of alloying elements was done through flux and slag-weld metal reactions. Bonded flux was used to achieve this purpose. Mechanical properties were studied by means of Longitudinal Tensile, Hardness and Charpy V-notch tests. Microstructure was studied by means of Optical and Scanning Electron Microscope. The results show that chromium increase Ultimate Tensile Strength (UTS) and impairs Impact Toughness (IT), although it increases the percentage of acicular ferrite (AF). In the meanwhile, further increasing of Cr Content was changed the microstructure of a mixture of AF and Grain-boundary ferrite (GBF) to a mixture of AF and brittle ferrite with second aligned phases (FSA). The increase of Mo content created an acicular ferrite-predominant weld metal microstructure, Subsequently Bainite and FSA are formed. Mo addition of 0.4 wt.% in the WM significantly Increases volume fraction of AF. The combined presence of Mo and Cr in the WM increase the volume fraction of AF. The best combination of microstructure and impact properties was obtained in 0.35% Mo and 0.28%Cr. In this specimen the UTS was increased about 20% (100 Mpa) and Impact toughness was decreased about 15% (20 j). The UTS and IT of quenched tempered Chromoly WM that welded by this Flux and S2 increased about 200 Mpa and 10 j respectively
  9. Keywords:
  10. Submerged Arc Welding (SAW) ; Inclusion ; Acicular Ferrite ; Alloying Elements ; Impact Energy ; Bonded Flux

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