Lecture 4 - ENGR 4250 Advanced Materials Engineering...

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ENGR 4250 – Advanced Materials Engineering Lecture 4 Introduction - 4 Dr. A. Keshavarz - ENGR 4250U
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Hyper eutectoid Steel Fe 3 C (cementite) 1600 1400 1200 1000 800 600 400 0 1 2 3 4 5 6 6.7 L γ (austenite) γ + L γ +Fe 3 C α +Fe 3 C L +Fe 3 C δ (Fe) C o , wt%C 1148°C T (°C) α Adapted from Figs. 9.24 and 9.32, Callister 7e . (Fig. 9.24 adapted from Binary Alloy Phase Diagrams , 2nd ed., Vol. 1, T.B. Massalski (Ed.-in- Chief), ASM International, Materials Park, OH, 1990.) (Fe-C System) 0.76 C o Adapted from Fig. 9.33, Callister 7e . proeutectoid Fe 3 C 60 µ m Hypereutectoid steel pearlite R S w α = S /( R + S ) w Fe 3 C =(1- w α ) w pearlite = w γ pearlite s r w Fe 3 C = r /( r + s ) w γ =(1- w Fe 3 C ) Fe 3 C γ γ γ γ γ γ γ γ γ γ γ γ Dr. A. Keshavarz - ENGR 4250U
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Alloying Steel with More Elements T eutectoid changes: C eutectoid changes: 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.) T Eutectoid (°C) wt. % of alloying elements Ti Ni Mo Si W Cr Mn wt. % of alloying elements C eutectoid (wt%C) Ni Cr Si Mn W Mo Dr. A. Keshavarz - ENGR 4250U
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Dr. A. Keshavarz - ENGR 4250U
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Rate of Phase Transformation Avrami rate equation => y = 1- exp (- k t n ) k & n fit for specific sample All out of material - done log t Fraction transformed, y Fixed T fraction transformed time 0.5 By convention r = 1 / t 0.5 Adapted from Fig. 10.10, Callister 7e. maximum rate reached – now amount unconverted decreases so rate slows t 0.5 rate increases as surface area increases & nuclei grow Dr. A. Keshavarz - ENGR 4250U
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Rate of Phase Transformations In general, rate increases as T r = 1/ t 0.5 = A e - Q / RT R = gas constant T = temperature (K) A = preexponential factor Q = activation energy Arrhenius expression r often small: equilibrium not possible! Adapted from Fig. 10.11, Callister 7e. (Fig. 10.11 adapted from B.F. Decker and D. Harker, "Recrystallization in Rolled Copper", Trans AIME , 188 , 1950, p. 888.) 135 ° C 119 ° C 113 ° C 102 ° C 88 ° C 43 ° C 1 10 10 2 10 4 Dr. A. Keshavarz - ENGR 4250U
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Transformations & Undercooling Can make it occur at: ...727ºC (cool it slowly) ...below 727ºC (“undercool” it!) Eutectoid transf. (Fe-C System): γ α + Fe 3 C 0.76 wt% C 0.022 wt% C 6.7 wt% C Fe 3 C (cementite) 1600 1400 1200 1000 800 600 400 0 1 2 3 4 5 6 6.7 L γ (austenite) γ + L γ +Fe 3 C α +Fe 3 C L +Fe 3 C δ (Fe) C o , wt%C 1148°C T (°C) α ferrite 727°C Eutectoid: Equil. Cooling: T transf . = 727 º C T Undercooling by T transf. < 727 ° C 0.76 0.022 Adapted from Fig. 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, Materials Park, OH, 1990.) Dr. A. Keshavarz - ENGR 4250U
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Dr. A. Keshavarz - ENGR 4250U
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Eutectoid Transformation Rate Course pearlite formed at higher T - softer Fine pearlite formed at low T - harder Diffusive flow of C needed α α γ γ α Growth of pearlite from austenite: Adapted from Fig. 9.15, Callister 7e .
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This note was uploaded on 06/02/2011 for the course ECONMICS ECN204 taught by Professor Brenan during the Spring '08 term at Ryerson.

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Lecture 4 - ENGR 4250 Advanced Materials Engineering...

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