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Effect of Nickel and Manganese on Weld Microstructure and Mechanical Properties in Shielded Metal arc Welded HSLA-X80

Sheykh Jaberi, Fariba | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40110 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein; Maddah Hosseini, Hamid Reza
  7. Abstract:
  8. Microstructure and mechanical properties developments of X80 weld metal by addition of different amounts of alloying elements such as: Nickel and Manganese in coated electrodes were investigated. For this reason samples were welded by electrodes that Ni value has been changed between 0.8%- 3.2% in tow critical amounts of Mn: 0.7 and 1.6. The weld quality was evaluated using nondestructive testing methods (NDT), such as visual inspection and radiography. Tensile test, Charpy impact test and microhardness results indicated the suitable range of Ni and Mn for achieving acceptable mechanical properties. In addition, optical microscopy and scanning electron microscopy (SEM) were applied to link the microstructure with mechanical properties. It was shown that amount of M-A as a microphase plays a remarkable role in impact toughness of weld metal. A well-balanced mixture of acicular ferrite with lower bainite was found to give optimum strength and impact toughness. Acicular ferrite has a very fine grain size and high concentration of dislocations that are responsible for its toughness and ductility. The hardness of weld metals were found to increase linearly by Mn and Ni, which was attributed mainly to solid solution strengthening and in part to formation of hard phases. Based on toughness and mechanical properties, the optimum levels of Ni were suggested to be 3.2% at low level of Mn and 0.8% at high level of Mn
  9. Keywords:
  10. Alloying Elements ; Toughness ; High Strength Steels ; Pipeline Steel ; Acicular Ferrite

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