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Investigation of Effect of Hot rolling Parameters on Mechanical and Physical Properties of a Fe-Ni-Co Alloy

Yazdani, Mohammad | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39840 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali; abbasi, mehdi
  7. Abstract:
  8. Fe-29Ni-17Co alloy with commercial name “Kovar” is an alloy with low expansion coefficient. The main specification of this alloy is to maintain this property at the high temperatures that is used in sealing of glass-metal. Achieving to desirable physical properties associated with suitable mechanical properties is the purpose of related industries. However the effect of cold work and heat treatment was studied on the physical properties of this alloy, there is no report about the effect of the hot work. Thus, in this investigation, the effect of the hot work on the physical and mechanical properties of Kovar was studied. At first, slabs of Kovar alloy were cast and remelted. Then, homogeneity of structure of these slabs was improved by homogenizing treatment and initial hot rolling. Hot tensile test was utilized to determine the optimum temperature of hot working followed by hot compression test for accurate expression of the alloy’s behavior. For this purpose, constitutive equations also were used. Next, parameters of hot rolling such as temperature, strain and number of passes were changed and the effect of these parameters on microstructure, physical and mechanical properties of the alloy was analyzed by means of suitable tests. The results of tensile test showed that in range of 1100 to 1200ºC, highest workability of this alloy was achieved. Hot compression test results at 1000 and 1100ºC showed homogeneous microstructure and finer grains. Activation energy of hot work was 389kj/mol for Sinh constitutive equation. Based on the observations, a different dynamic recrystallization mechanism was suggested. Rolling at 1100 ºC with maximum strain in every pass was determined as the optimized conditions of the rolling. It means that hot rolling with high total strain should be done in the minimum number of passes. Also, the results showed that hot work doesn’t have significant effect on the physical properties of Kovar such as thermal expansion and electrical resistivity.

  9. Keywords:
  10. Hot Rolling ; Dynamic Recrystallization ; Physical Properties ; Mechanical Properties ; Cobalt-Nickel-Ferrum Alloy ; Hot Compression ; Hot Torsion

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