Lec 4 - ENGR ENGR 4250 Advanced Materials Engineering...

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ENGR 4250 ENGR 4250 – Advanced Materials Engineering Lecture 4 Introduction Introduction -4
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yper utectoid Steel Hyper eutectoid Steel 1600 1400 L δ T (°C) e- ntite) 1200 000 γ (austenite) γ + L L +Fe 3 C 1148°C (Fe C System) γ γ γ γ γ C (ceme n 1000 800 γ +Fe 3 C Adapted from Figs. 9.24 and 9.32, Callister 7e . (Fig. 9.24 adapted from Binary Alloy Phase Diagrams , 2nd ed., Vol. s r Fe 3 C γ γ γ γ γ Fe 3 600 400 0 123456 6 . 7 α +Fe 3 C e) t%C α 1, T.B. Massalski (Ed.-in- Chief), ASM International, Materials Park, OH, 1990.) 76 C o R S w Fe 3 C = r /( r + s ) w γ =(1- w Fe 3 C ) γ γ (Fe) C o , wt%C 0. 60 μ m Hypereutectoid teel w α = S /( R + S ) w Fe C =(1- w α ) w pearlite = w γ pearlite Adapted from Fig. 9.33, Callister 7e . proeutectoid Fe 3 C steel pearlite
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lloying Steel with More Elements Alloying Steel with More Elements T eutectoid changes: C eutectoid changes: C) oid (°C) Ti Mo Si W (wt% C Ni r T Eutect o Cr Mn eutect C Si Mn W Mo dapted from Fig 9 34 allister 7e (Fig 9 34 dapted from Fig 9 35 allister 7e (Fig 9 35 wt. % of alloying elements Ni wt. % of alloying elements Adapted from Fig. 9.34, Callister 7e . (Fig. 9.34 from Edgar C. Bain, Functions of the Alloying Elements in Steel , American Society for Metals, 1939, p. 127.) Adapted from Fig. 9.35, Callister 7e . (Fig. 9.35 from Edgar C. Bain, Functions of the Alloying Elements in Steel , American Society for Metals, 1939, p. 127.)
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ate of Phase Transformation Rate of Phase Transformation All out of material - done ormed, y Fixed T on transf o 0.5 maximum rate reached – now amount unconverted decreases so rate slows te increases as surface area increases log t Fracti Adapted from t 0.5 rate increases as surface area increases & nuclei grow Avrami rate equation => y = 1- exp (- k t n ) action me Fig. 10.10, Callister 7e. k & n fit for specific sample fraction transformed time By convention r = 1 / t 0.5
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ate of Phase Transformations Rate of Phase Transformations Adapted from Fig. 10.11, Callister 7e. (Fig. 10.11 adapted from B.F. Decker and 135 ° C 119 ° C 113 ° C 102 ° C 88 ° C 43 ° C D. Harker, "Recrystallization in Rolled Copper", Trans AIME , 188 , 1950, p. 888.) general rate increases as 11 0 1 0 2 10 4 In general, rate increases as T r = 1/ t 0.5 = A e - Q / RT gas constant R = gas constant T = temperature (K) A = preexponential factor = activation energy Arrhenius expression Q activation energy r often small: equilibrium not possible!
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ransformations & Undercooling Transformations & Undercooling Can make it occur at: ...727ºC (cool it slowly) Eutectoid transf. (Fe-C System): γ α + Fe 3 C 0.76 wt% C 0.022 wt% C 6.7 wt% C ...below 727ºC (“undercool” it!) 1600 T (°C) Adapted from Fig. te) 1400 1200 L γ ustenite) γ + L L +Fe 3 C δ 1148°C 9.24, Callister 7e . (Fig. 9.24 adapted from Binary Alloy Phase Diagrams , 2nd ed., Vol. 1, T.B. Massalski (Ed.- in-Chief), ASM International, aterials Park OH 1990 ) (cementi t 1000 800 (austenite) γ +Fe 3 C α ferrite Eutectoid: Equil. Cooling: T ansf = 727 º C Materials Park, OH, 1990.) Fe 3 C ( 600 00 α +Fe 3 C 727°C transf .
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Lec 4 - ENGR ENGR 4250 Advanced Materials Engineering...

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