Phase diagrams (cont.) and the Fe-C system

Transcription

1 Phase diagrams (cont.) and the Fe-C system

2 Solidification: Pro-eutectic vs Eutectic Pro-eutectic solidification Ideal liquid, uniform distribution Solid Pb(Sn) () nucleates Solubility limit leads to Sn rich area just outside Sn easily redistributes in Process continues until eutectic temperature is reached Eutectic solidification

3 TE 100 T( C) 0 0 MICROSTRUCTURES IN EUTECTIC SYSTEMS C o = C E Eutectic microstructure --alternating layers of and crystals C + P1 : Cowt%Sn + : 97.8wt%Sn : 18.3wt%Sn CE Co, wt% Sn Phases at P1? Microconstituents at P1? How much of each phase? Adapted from Fig. 9.12, Callister 6e. (Fig from Metals Handbook, Vol. 9, 9th ed., Metallography and Microstructures, American Society for Metals, Materials Park, OH, 1985.) 18

4 HYPOEUTECTIC & HYPEREUTECTIC T( C) 300 Adapted from Fig. 9.7, Callister 6e. (Fig. 9.7 adapted from Binary Phase Diagrams, 2nd ed., Vol. 3, T.B. Massalski (Editor-in-Chief), ASM International, Materials Park, OH, 1990.) 200 TE (Pb-Sn System) (Figs and 9.15 from Metals Handbook, 9th ed., Vol. 9, Metallography and Microstructures, American Society for Metals, Materials Park, OH, 1985.) 0 0 Co Co hypoeutectic hypereutectic hypoeutectic: Co=50wt%Sn 175μm 60 eutectic eutectic: Co=61.9wt%Sn 160μm eutectic micro-constituent Co, wt% Sn hypereutectic: (illustration only) 20

5 300 MICROSTRUCTURES IN EUTECTIC SYSTEMS 18.3wt%Sn < C o < 61.9wt%Sn T( C) Example: Pb-Sn system : Cowt%Sn Just Above T E Phases? Composition? How much of each? 200 TE + R R S S Co 61.9 Co, wt% Sn primary eutectic eutectic Microconstituents? How much of each? Adapted from Fig. 9.14, Callister 6e. 19

6 300 MICROSTRUCTURES IN EUTECTIC SYSTEMS 18.3wt%Sn < C o < 61.9wt%Sn T( C) Example: Pb-Sn system : Cowt%Sn Just Below T E Phases? Composition? How much of each? 200 TE + R R S S Co 61.9 Co, wt% Sn primary eutectic eutectic Microconstituents? How much of each? Adapted from Fig. 9.14, Callister 6e. 19

7 Systems with intermediate compounds or solid solutions Cu, Zn

8 Iron - Carbon system: Consider only Fe to Fe 3 C portion AXES: Cementite: Fe 3 C (Compound) PURE Iron Ferrite (): BCC Austenite(): FCC Ferrite (δ): BCC Solid solutions,δ,, interstitial C Different solubilities

9 Peritectic and Eutectic Example: Iron - Carbon system Phases? Peritectic: iquid + solid phase at given composition converts to one different solid phase upon cooling Here: + δ Eutectiod: all solids One solid phase separates into two different solid phases upon cooling Here: + Fe 3 C

10 Alloy Classifications in the Iron Carbon system Numbers in % Iron Hypo Eutectoid Steel Hyper Eutectoid Steel Cast Iron % C

11 IRON-CARBON (Fe-C) PHASE DIAGRAM 2 important points -Eutectic (A): + Fe 3 C -Eutectoid (B): +Fe 3 C 1600 δ T( C) + (austenite) + R B 1148 C R 727 C = Teutectoid A +Fe3C S +Fe3C +Fe3C S Fe3C (cementite) 120μm Result: Pearlite = alternating layers of and Fe3C phases. (Adapted from Fig. 9.24, Callister 6e. (Fig from Metals Handbook, 9th ed., Vol. 9, Metallography and Microstructures, American Society for Metals, Materials Park, OH, 1985.) (Fe) Co, wt% C Fe3C (cementite-hard) (ferrite-soft) Ceutectoid 21

12 Eutectoid: 0.76% C Pearlite formation Solid transformation + Fe3C 0.76% 0.02% 6.7% Similar to Eutectic transformation - but now, diffusion occurs within solid

13 Hypo eutectoid microstructure at Room T Proeutectoid Ferrite + Pearlite + Ferrite phase increases as T decreases At T(eutectoid) + Pearlite + Remaining austenite transforms to pearlite

14 w =s/(r+s) w =(1-w) 1600 δ w =S/(R+S) w Fe3C =(1-w) T( C) 600 Co HYPOEUTECTOID STEE + (austenite) r s R S pearlite w pearlite = w 727 C 1148 C +Fe3C +Fe3C +Fe3C Fe3C (cementite) Co, wt% C 100μm (Fe-C System) Hypoeutectoid steel Adapted from Figs and 9.26,Callister 6e. (Fig adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.) Adapted from Fig. 9.27,Callister 6e. (Fig courtesy Republic Steel Corporation.) 22

15 Fe3C 1600 δ T( C) + (austenite) R w Fe3C =r/(r+s) 600 w =(1-w Fe3C ) +Fe3C w =S/(R+S) w Fe3C =(1-w) 0.77 pearlite w pearlite = w HYPEREUTECTOID STEE r Co s S 1148 C +Fe3C +Fe3C Fe3C (cementite) Co, wt% C (Fe-C System) 60μm Hypereutectoid steel Adapted from Figs and 9.29,Callister 6e. (Fig adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.) Adapted from Fig. 9.30,Callister 6e. (Fig copyright 1971 by United States Steel Corporation.) 23

16 Hyper eutectoid microstructure at Room T Proeutectoid Cementite + Pearlite cementite + cementite phase increases At T(eutectoid) + Fe3C Fe3C + Pearlite Remaining austenite transforms to pearlite

17 AOYING STEE WITH MORE EEMENTS Change in T eutectoid (727 o C): Change in C eutectoid (0.76% C): TEutectoid ( C) 1200 Ti Mo Ni Si W Cr Mn wt. % of alloying elements Ceutectoid (wt%c) Ni Cr 0.4 Si Mn 0.2 W Ti Mo wt. % of alloying elements Adapted from Fig. 9.31,Callister 6e. (Fig from Edgar C. Bain, Functions of the Alloying Elements in Steel, American Society for Metals, 1939, p. 127.) Adapted from Fig. 9.32,Callister 6e. (Fig from Edgar C. Bain, Functions of the Alloying Elements in Steel, American Society for Metals, 1939, p. 127.) 24

18 MECHANICA PROPERTIES: Cu-Ni System Effect of solid solution strengthening on: --Tensile strength (TS) --Ductility (%E,%AR) Tensile Strength (MPa) TS for pure Cu Cu Ni TS for pure Ni Composition, wt%ni Elongation (%E) %E for pure Cu Cu Ni %E for pure Ni Composition, wt%ni --Peak as a function of Co --Min. as a function of Co 12