Materials Science & Engineering PDF

Materials Science & Engineering BITS Pilani Hyderabad Campus Details to be covered. Equilibrium and non equilibrium cooling. Formation Pearlite. Formation of Bainite. Formation of Martensite. TTT Diagram. BITS P...

Materials Science & Engineering BITS Pilani Hyderabad Campus Details to be covered. Equilibrium and non equilibrium cooling. Formation Pearlite. Formation of Bainite. Formation of Martensite. TTT Diagram. BITS Pilani, Hyderabad Campus Heat Treatment Process https://www.azom.com/ Isothermal Transformation Diagrams Fe-C system, Co = 0.76 wt% C Transformation at T = 675°C. % transformed 100 T = 675°C y, 50 0 1 10 2 10 4 time (s) T(°C) Austenite (stable) TE (727C) 700 Austenite (unstable) 600 Pearlite From Fig. 8.13 isothermal transformation at 675°C Callister’s Materials Science and Engineering, 500 Adapted Version (Fig. 8.13 adapted from H. Boyer (Ed.) 400 Atlas of Isothermal Transformation and Cooling Transformation Diagrams, time (s) American Society for Metals, 1977, p. 1 10 10 2 10 3 10 4 10 5 369.) Effect of Cooling History in Fe-C System Eutectoid composition, Co = 0.76 wt% C Begin at T > 727°C Rapidly cool to 625°C and hold isothermally. T(°C) Austenite (stable) TE (727C) 700 Austenite (unstable) From Fig. 8.14 600 Pearlite Callister’s Materials   Science and Engineering, Adapted Version.     (Fig. 8.14 adapted from H. Boyer (Ed.) Atlas of 500 Isothermal Transformation and Cooling Transformation Diagrams, American Society for 400 Metals, 1997, p. 28.) 1 10 10 2 10 3 10 4 10 5 time (s) Non-Equilibrium Transformation Products: Fe-C Bainite: -- lathes (strips) with long rods of Fe3C --diffusion controlled. Fe3C Isothermal Transf. Diagram (cementite)  (ferrite) 800 Austenite (stable) T(°C) A TE P 600 100% pearlite pearlite/bainite boundary 5 m From Fig. 8.17 100% bainite Callister’s Materials Science and Engineering, B Adapted Version. 400 A (Fig. 8.17 from Metals Handbook, 8th ed., Vol. 8, Metallography, Structures, and Phase Diagrams, American Society for Metals, Materials Park, OH, 1973.) 200 10-1 10 103 105 time (s) From Fig. 8.18, Callister’s Materials Science and Engineering, Adapted Version. (Fig. 8.18 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1997, p. 28.)  Martensite: Fe-C System Martensite: --(FCC) to Martensite (BCT) (involves single atom jumps) 60 m x Fe atom potential x x sites x x C atom sites From Fig. 8.20, Callister’s MSE, x Adapted Version. Isothermal Transf. Diagram 800 Austenite (stable) Martensite needles T(°C) TE Austenite A P From Fig. 8.21, Callister’s Materials Science and 600 Engineering, Adapted Version. (Fig. 8.21 courtesy United States Steel From Fig. Corporation.) 8.22 Callister’s 400 A B  to M transformation.. Materials Science and -- is rapid! Engineering, Adapted 200 M+A 0% -- % transf. depends on T only. 50% Version. M+A 90% M+A 10-1 10 103 105 time (s) Martensitic Formation slow  (FCC) cooling  (BCC) + Fe3C quench tempering M (BCT) M = martensite is body centered tetragonal (BCT) Diffusionless transformation BCT if C > 0.15 wt% BCT → few slip planes → hard, brittle Cooling Curve plot temp vs. time From Fig. 8.25, Callister’s Materials Science and Engineering, Adapted Version. 11 Thank You 12 BITS Pilani, Hyderabad Campus  Materials Science & Engineering BITS Pilani Hyderabad Campus Details to be covered. Heat treatment. Annealing. Normalising. Hardening. Tempering. BITS Pilani, Hyderabad Campus  T holding AT A Q T N time Annealing Furnace cooling RC 15 Normalizing Air cooling RC 30 Quenching Water cooling RC 65 Tempering Heating after quench RC 55 Austempering Quench to an inter- RC 45 mediate temp and hold BITS Pilani, Hyderabad Campus  Hardness Micro- Steel Rockwell C Wt% C structure Heat treatment Coarse A 15 0.8 Annealing pearlite fine B 30 0.8 normalizing pearlite C 45 0.8 bainite austempering Tempered D 55 0.8 tempering martensite E 65 0.8 martensite quenching BITS Pilani, Hyderabad Campus TTT diagram for eutectoid steel Stable austenite unstable austenite BITS Pilani, Hyderabad Campus TTT diagram for eutectoid steel Stable austenite Annealing: coarse pearlite Normalizing: fine pearlite unstable austenite BITS Pilani, Hyderabad Campus Thank You! BITS Pilani, Hyderabad Campus