Materials Science & Engineering (PDF) - BITS Pilani

Materials Science & Engineering BITS Pilani Dr. Piyush Chandra Verma Department of Mechanical Engineering Pilani Campus ( Iron Carbon system and Heat Treatment of steel). BITS Pilani, Hyderabad Campus Allo...

Materials Science & Engineering BITS Pilani Dr. Piyush Chandra Verma Department of Mechanical Engineering Pilani Campus ( Iron Carbon system and Heat Treatment of steel). BITS Pilani, Hyderabad Campus Allotropy / Polymorphism What do they have in common?.. Polymorphism is a physical phenomenon, where a material have two or more crystal structure BITS Pilani, Hyderabad Campus Allotropy / Polymorphism Poly means MANY and morph means SHAPES. When a substance exists more than in one crystalline form , the phenomenon is known as polymorphism. BITS Pilani, Hyderabad Campus Allotropy / Polymorphism BITS Pilani, Hyderabad Campus Types of Steel and Applications Low Carbon Mild Steel Medium Carbon High Carbon Applications Applications Applications: Applications -Car body panels -Automotive parts -Hammers -High speed -Filing cabinets -Brackets -Chisels tooling Properties: Properties: Properties: Properties: -Malleable -Low hardness -Medium -Hard -Very ductile -Medium tensile hardness -Brittle -Soft strength -Good tensile -Low ductility -Good ductility strength -Medium ductility BITS Pilani, Hyderabad Campus Two or more distinct crystal structures for the same material (allotropy/polymorphism) iron system liquid titanium , -Ti 1538ºC BCC -Fe carbon 1394ºC diamond, graphite FCC -Fe 912ºC BCC -Fe BITS Pilani, Hyderabad Campus f24_07_pg208 BITS Pilani, Hyderabad Campus 9 Iron-Carbide equilibrium phase diagram BITS Pilani, Hyderabad Campus Iron-Carbon (Fe-C) Phase Diagram 2 important T(°C) 1600 points  -Eutectic (A): 1400 L L   + Fe3C   +L 1200 A L+Fe3C 1148°C -Eutectoid (B): (austenite) Fe3C (cementite) R S    + Fe3C 1000    +Fe3C    800 B 727°C = Teutectoid R S 600 +Fe3C 400 0 1 2 3 4 5 6 6.7 (Fe) 0.76 4.30 Co, wt% C 120 m C eutectoid Result: Pearlite = Fe3C (cementite-hard) alternating layers of  (ferrite-soft)  and Fe3C phases (From Fig. 7.27, Callister Adapted Version.) From Fig. 7.24, Callister Adapted Version. BITS Pilani, Hyderabad Campus Hypoeutectoid Steel T(°C) 1600  1400 L   (Fe-C   +L   1200 1148°C L+Fe3C System) Fe3C (cementite) (austenite)   1000    + Fe3C From Figs. 7.24 and 7.29 Callister’s Materials  Science and Engineering,   800 r s 727°C Adapted Version.    RS (Fig. 7.24 adapted from Binary Alloy Phase w  =s/(r +s) 600 w  =(1- w )  + Fe3C Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in- Chief), ASM International,  400 Materials Park, OH, 0 1 2 3 4 5 6 6.7 (Fe) Co , wt% C 1990.) 0.76 C0 pearlite w pearlite = w  Hypoeutectoid w  =S/(R+S) 100 m steel w Fe3 =(1-w  ) C pearlite proeutectoid ferrite From Fig. 7.30 Callister’s Materials Science and Engineering, Adapted Version. BITS Pilani, Hyderabad Campus Hypereutectoid Steel T(°C) 1600  1400 L (Fe-C   +L System)     1200 1148°C L+Fe3C Fe3C (cementite) (austenite)   1000    +Fe3C From Figs. 7.24 and 7.32, Callister’s Materials Fe3C   Science and Engineering, 800 r s Adapted Version.    (Fig. 7.24 adapted from R S Binary Alloy Phase w Fe3C =r/(r +s) 600  +Fe3C Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in- w  =(1-w Fe3C ) Chief), ASM International, 400 Materials Park, OH, 0 1 Co 2 3 4 5 6 6.7 0.76 (Fe) Co , wt%C 1990.) pearlite w pearlite = w  w  =S/(R+S) w Fe3C =(1-w  ) 60 mHypereutectoid steel pearlite proeutectoid Fe3C From Fig. 7.33, Callister’s Materials Science and Engineering, Adapted Version. BITS Pilani, Hyderabad Campus f27_07_pg212 BITS Pilani, Hyderabad Campus f26_07_pg211 BITS Pilani, Hyderabad Campus f28_07_pg213 BITS Pilani, Hyderabad Campus f29_07_pg213 BITS Pilani, Hyderabad Campus f30_07_pg214 BITS Pilani, Hyderabad Campus f32_07_pg216 BITS Pilani, Hyderabad Campus f33_07_pg217 BITS Pilani, Hyderabad Campus  Materials Science & Engineering BITS Pilani Dr. Piyush Chandra Verma Department of Mechanical Engineering Pilani Campus  BITS Pilani Pilani Campus Cast Irons. Fe-C True Equilibrium Diagram T(°C) 1600 Graphite formation 1400 L Liquid + promoted by  +L Graphite 1200  1153°C Si > 1 wt% Austenite 4.2 wt% C 1000 Slow cooling +  + Graphite 800 740°C 0.65 600  + Graphite 400 0 1 2 3 4 90 100 (Fe) Co , wt% C BITS Pilani, Hyderabad Campus  Types of Cast Iron Gray Iron: Graphite flakes Weak & brittle under tension Stronger under compression Excellent vibrational dampening Wear resistant Ductile iron Add mg or ce Graphite in nodules not flakes Matrix often pearlite - better ductility BITS Pilani, Hyderabad Campus  Types of Cast Iron White iron