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Graduate Seminar I

Graduate Seminar I. Compositionally Graded High Manganese Steels by Morteza Ghasri Supervisor: Prof. McDermid Nov. 18, 2011. Presentation Outline. Introduction Literature Review Project Objectives Experimental Method Preliminary Results Plan for Future Work. Introduction.

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Graduate Seminar I

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  1. Graduate Seminar I Compositionally Graded High Manganese Steels by MortezaGhasri Supervisor: Prof. McDermid Nov. 18, 2011

  2. Presentation Outline • Introduction • Literature Review • Project Objectives • Experimental Method • Preliminary Results • Plan for Future Work

  3. Introduction • Typical mechanical properties of several classes of steels • W. Bleck: International Conference on TRIP-Aided High Strength Ferrous Alloys, Ghent, Belgium 2002, p. 13-23

  4. History of high Mn steels • Hadfield steels were invented in 1882. They had 13 wt. % Mn and 1.2 wt. % C. • New class of modern high Mn steels contain 18-30 wt. % Mn, 0-0.7 wt. % C, and up to 1-2 wt. % (Al, Si) Sir Robert Hadfield 1858-1940

  5. Literature Review • High Mn steels can be divided into: • Twinning Induced Plasticity (TWIP) • Transformation Induced Plasticity (TRIP)

  6. Stacking Fault Energy Stacking fault formation 1. Dissociation of a perfect dislocation 2. Equilibrium between two partial dislocations d: the equilibrium separation between partials μ: shear modulus b: the magnitude of the Burger’s vector γ: stacking fault energy

  7. SFE dependence of deformation products Deformation structures of Fe-20Mn-4Cr-0.5C as a function of both temperature and SFE L. Remy et al., Materials science and Engineering, Vol. 28, pp. 99-107, 1977 Deformation structures of different alloys observed near room temperature as a function of SFE L. Remy et al., Materials Science and Engineering, Vol. 26, pp. 123-132, 1976

  8. SFE dependence of deformation products (cont’d) The calculated iso-SFE lines in the carbon/manganese (wt.%) map at 300K S. Allain et al., Materials Science and Engineering A, Vol. 387-389, pp. 158-162, 2004

  9. SFE dependence of deformation products (cont’d) The calculated iso-SFE contours in Fe-Mn-C system at 298 K with martensite boundaries J. Nakano et al., CALPHAD, Vol. 34, pp. 167-175, 2010.

  10. Fe-30Mn-0C alloy • Minor ε-martensite for εT<0.3 Evolution of ε-martensite phase volume fraction with plastic strain in Fe-30Mn-0C alloy Xin Liang, Master’s thesis, McMaster University, 2008.

  11. Fe-30Mn-0C alloy • Dislocation cell structure with no significant transformation products • Indicates that dislocation glide is the dominant deformation mechanism at 298 K BF image of well-developed cell structures in one grain Xin Liang, Master’s thesis, McMaster University, 2008.

  12. Fe-22Mn-C alloys • Eileen Yang decarburized an Fe-22Mn-0.6C alloy to obtain homogenous 0.2 C and 0.4 C alloy. • Mechanical properties varied significantly with alloy carbon content. Tensile behavior of Fe-22Mn alloys with different carbon content. Eileen Yang, Master’s thesis, McMaster University, 2010

  13. Fe-22Mn-C alloys • 0.6 C alloy………TWIP • 0.2 C alloy……….TRIP Evolution of ε-martensite phase volume fraction with plastic strain for all alloys Eileen Yang, Master’s thesis, McMaster University, 2010

  14. Strain Hardening • Isotropic Strain Hardening • The mechanical response is symmetric after a change of strain path from pure tension to pure compression and vice versa. • The Kocks-Mecking model considers only this type of strain hardening. • Kinematic Strain Hardening • The mechanical behaviour becomes asymmetric after a change of strain path from pure tension to pure compression. • This occurs in addition to isotropic strain hardening. • Kinematic strain hardening has a significant contribution to overall hardening in high Mn steels.

  15. Project Objectives 1. Producing compositionally graded high manganese steels. 2. Microstructural evolution and mechanical properties of produced alloys. 3. Modeling of mechanical properties The rule-of-mixture approximations Continuum finite element formulation of the constitutive phases

  16. Experimental alloys Fe-30Mn-0.6C 1. Fe-30Mn-0C alloy will be carburized to obtain carbon gradient from 0 wt. % at the core to 0.6 wt. % at the surface. 2. Fe-30Mn-0.6C alloy will be decarburized to obtain carbon gradient from 0 wt. % at the surface to 0.6 wt. % at the core. Fe-30Mn-0C Fe-30Mn-0.6C Fe-30Mn-0C Fe-30Mn-0.6C Fe-30Mn-0C

  17. Experimental Alloys (cont’d) Fe-22Mn-0C 3. Fe-22Mn-0.6C alloy will be decarburized to obtain carbon gradient from 0 wt. % at the surface to 0.6 wt. % at the core. Fe-22Mn-0.6C Fe-22Mn-0C

  18. Experimental Method • Carburizing and Decarburizing Heat Treatment • A gas mixture of CO/CO2 was used for carburizing the Fe-30Mn-0C alloy. The gas mixture was then replaced by CH4/H2. • Fe-22Mn-0.6C alloy was decarburized by CO/CO2. • The experiments were carried out at 1000 and 1100 °C. • Mico-Hardness Measurements • To evaluate the distribution of carbon within the cross section of carburized and decarburized samples.

  19. Experimental Method (cont’d) • Characterization Techniques • Carbon and sulfur combustion analysis • Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS) • Electron BackScattered Diffraction (EBSD) • X-Ray Diffraction (XRD) • Transmission Electron Microscopy (TEM)

  20. Preliminary Results 1. Carburization of Fe-30Mn-0C alloy Illustration of micro-hardness profile after carburizing at 1100°C under a CO/CO2 ratio of 30 for 4 and 7 hours. The calculated CO/CO2 ratio required for carburization was 16. Significant increase in hardness was only observed at 50 µm or less from the surface.

  21. Fe Mn O EDS map of cross section of Fe-30Mn-0C alloy after carburizing for 7 h at 1100 °C.

  22. XRD pattern of 7 h-carburized sample.

  23. Thermodynamic Aspects The oxygen partial pressure in the furnace is calculated to be 4.24×10-16 atm when T=1373 K and CO/CO2 =30. The oxygen partial pressure required for manganese oxidation of Fe-30Mn-0C is calculated to be 3.34×10-21 atm.

  24. 2. Carburization of Fe-30Mn-0C alloy using CH4/H2 CO/CO2 gas mixture was replaced by CH4/H2 mixture to prevent MnO formation. Methane decomposition leads to carburization Oxygen as impurity in methane leads to MnO formation. Ti wire was used to lower the oxygen potential.

  25. 3. Decarburization of Fe-22Mn-0.6C alloy Illustration of micro-hardness profile after decarburizing at 1000°C under CO/CO2 ratios of 6 and 1 for 4 hours. The high amount of hardness at 50 μm below the surface is attributed to MnO formation. The carbon content of decarburized samples decreased from 0.40 wt. % to 0.20 wt. % when the CO/CO2 decreased from 6 to 1.

  26. Thermodynamic Aspects The oxygen partial pressure in the furnace is calculated to be 2.17×10-16 atm when T=1273 K and CO/CO2 = 6. The oxygen partial pressure required for manganese oxidation of Fe-22Mn-0.6C is calculated to be 2.36×10-23 atm.

  27. Plan for Future Work

  28. Conclusion • MnO layer on high Mn steels prevents carbon diffusion into the sample, but it has no significant effect on decarburization.

  29. Acknowledgement • Prof. McDermid • Dr. Zurob • Doug Culley • Chris Butcher • Tom Zhou • Research Group Fellows

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