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Microstructural study of a High Bainite Dual Phase (HBDP) steel austempered at different temperatures

Bakhtiari, R ; Sharif University of Technology | 2010

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  1. Type of Document: Article
  2. DOI: 10.4028/www.scientific.net/DDF.297-301.62
  3. Publisher: Trans Tech Publications Ltd , 2010
  4. Abstract:
  5. 4340 steel bars were austenitized at 850°C for 1 hour followed by heating at 700°C (ferrite and austenite region) for 90 min and quenching into a salt bath with different temperatures of 300, 350, 400 and 450°C. The steel bars were held for 1 hour at these temperatures before air cooling to room temperature. Various ferrite-bainite microstructures with 34% volume fraction of ferrite and different bainite morphologies were obtained. The results of SEM studies showed that by increasing the austempering temperature, the morphology of bainite varies from lower to upper bainite. According to the T-T-T diagram of the studied steel, the bainite transformation will not complete for the holding time of 1 hour at 400 and 450°C austempering temperatures and there can be 9 and 23Vol% of martensite at these temperatures respectively. Microstructural studies of specimens austempered at these temperatures showed complex microstructures of ferrite, bainite and martensite. Mechanical testing results showed reduction in yield and ultimate tensile strengths, hardness, uniform and total elongations and impact energy with increase of the austempering temperature from 300 to 400°C. But for dual phase steel austempered at 450°C, the yield and tensilestrengths and hardness increased and a severe reduction in total elongation and impact energy was obtained. This brittle behaviour was related to martensite formation during cooling from this austempering temperature. © (2010) Trans Tech Publications
  6. Keywords:
  7. Austempering temperature ; Ferrite ; Lower bainite ; Upper bainite ; Bainite ; Bars (metal) ; Electric field effects ; Fatigue crack propagation ; Ferrite ; Hardness ; Hardness testing ; Martensite ; Martensitic steel ; Microstructure ; Morphology ; Steel testing ; Tensile strength ; Tensile testing ; Diffusion in solids ; Heat transfer ; Mass transfer ; Mechanical testing ; Air cooling ; Austempering temperature ; Bainite transformations ; Complex microstructures ; Dual phase ; Dual-phase steel ; Holding time ; Impact energy ; Lower bainite ; Martensite Formation ; Micro-structural ; Room temperature ; Salt bath ; SEM study ; Steel bars ; Total elongations ; Ultimate tensile strength ; Upper bainite ; Ferrite-bainite microstructures ; Yield and tensile strength ; Bainitic transformations
  8. Source: Defect and Diffusion Forum ; Volume 297-301 , 2010 , Pages 62-67 ; 10120386 (ISSN); 3908451809 (ISBN); 9783908451808 (ISBN)
  9. URL: https://www.scientific.net/DDF.297-301.62