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Effect of Alloying Elements and Heat Treatment on Microstructure and Mechanical Properties of Austempered Ductile Iron by Modulus above 2 Cm

Hamzehlou, Iman | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42463 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Varahram, Nasser; Ashuri, Hossein
  7. Abstract:
  8. Since its discovery in 1943, the use of ductile iron is increasing continuously, this is due to the combination of various excellent mechanical properties. Excessive amount of research has being carried out to improve the properties. Austempererd ductile iron is the most recent development in this field. The application of this material included to automobile, railway, military, agricultural, mining & construction industries. The newly developed austempered ductile iron is now replacing steel in many fields so it has become very important to various aspects of this material. In this thesis, the effect of alloying elements (copper & nickel) and the austempering process variables on the microstructure and mechanical properties of ADI by solidification modulus above 2 cm was studied. The main purpose of this study is investigation of replacement of cooper instead of nickel. After perusing of as-cast alloys, best alloy was selected for austempering process. Best composition was achieved by 1% Cu, 0.5% Ni, 0.3% Mn, 0.25% Mo, 3.5% C, 2.5% Si and 0.05% Mg (by weight). With increasing austenitizing temperature, the kinetic of austempering transformation and mechanical properties were decreased. With increasing austempering time, yield strength, tensile strength, elongation and impact energy are increasing but hardness is decreasing; after the first stage of transformation, this procedure was stopped or reversed. With increasing austempering temperature hardness and strength decreased but elongation and impact energy increased. According to the results, the best procedure for austempering is austenitizing in 900oC for 90 minutes then cooling in 375oC for 120 minutes. The mechanical properties results of this cycle are: impact energy 95J, elongation 9%, yield strength 700 MPa, tensile strength 930 MPa and hardness 310 BHN
  9. Keywords:
  10. Austempered Ductile Iron (ADI) ; Austemper ; Alloying Elements ; Mechanical Properties ; High Modulus

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