PY2N20 Mteril Properties nd Phse Digrms ecture 6 P. Stmenov, PhD School of Physics, TCD PY2N20-6
Microstructures in Eutectic Systems: I C o < 2 wt% Sn Result: - t extreme ends - polycrystl of grins i.e., only one solid phse. T( C) 400 300 200 T E : C o wt% Sn : C o wt% Sn + (Pb-Sn System) 100 + b 0 C o 10 20 2 (room T solubility limit) 30 C o, wt% Sn
Microstructures in Eutectic Systems: II 2 wt% Sn < C o < 18.3 wt% Sn Result: Initilly liquid + then lone finlly two phses polycrystl fine b-phse inclusions 400 300 200 100 T( C) T E + + b : C o wt% Sn : C o wt% Sn b Pb-Sn system 0 10 20 2 C o (sol. limit t T room ) 18.3 (sol. limit t T E ) 30 C o, wt% Sn
Microstructures in Eutectic Systems: III C o = C E Result: Eutectic microstructure (lmellr structure) - lternting lyers (lmelle) of nd b crystls. 300 Pb-Sn system 200 T E T( C) + 183 C : C o wt% Sn b b Microgrph of Pb-Sn eutectic microstructure 100 b b: 97.8 wt% Sn : 18.3 wt%sn 160 m Adpted from Fig. 9.14, Cllister 7e. 0 20 40 60 80 100 18.3 C E 97.8 61.9 C, wt% Sn
mellr Eutectic Structure Other possible eutectic structures re: rod-like, globulr nd ciculr.
Microstructures in Eutectic Systems: IV 18.3 wt% Sn < C o < 61.9 wt% Sn Result: crystls nd n eutectic microstructure Just bove T E : T( C) 300 Pb-Sn system 200 T E 100 0 + R R + b : C o wt% Sn S 20 40 60 80 100 18.3 61.9 97.8 S + b C o, wt% Sn b primry eutectic eutectic b C = 18.3 wt% Sn C = 61.9 wt% Sn S W = = 50 wt% R + S W = (1- W ) = 50 wt% Just below T E : C = 18.3 wt% Sn C b = 97.8 wt% Sn W S = = 73 wt% R + S W b = 27 wt%
Hypoeutectic & Hypereutectic 300 T( C) 200 T E 100 + + b + b b (Pb-Sn System) C o, wt% Sn 0 20 40 60 80 100 eutectic hypoeutectic: C o = 50 wt% Sn 61.9 hypereutectic: (illustrtion only) eutectic: C o = 61.9 wt% Sn b b b b b b 175 m 160 m eutectic micro-constituent
Intermetllic Compounds Mg 2 Pb Note: intermetllic compound forms line - not n re - becuse the stoichiometry (i.e. composition) is exct.
Eutectic Eutectic - liquid in equilibrium with two solids cool het + b
Exmple: Eutectoid & Peritectic Cu-Zn Phse digrm Peritectic trnsition + Eutectoid trnsition + Peritectoid solid stte Peritectic
Eutectoid & Peritectic Eutectoid - solid phse in equilibrium with two solid phses S 2 S 1 +S 3 intermetllic compound - cementite cool + Fe 3 C (727ºC) het Peritectic - liquid + solid 1 solid 2 S 1 + S 2 cool + (1493ºC) het περιτεκτικός περι - included
Iron-Crbon Phse Digrm Extrct Fe 3 C (cementite) 2 importnt points -Eutectic (A): + Fe 3 C -Eutectoid (B): + Fe 3 C 1600 1400 1200 1000 800 600 α bcc (FM) β bcc (NM) obs. γ fcc (NM) δ bcc (NM) ε hcp (p >13 GP) T( C) + (ustenite) 400 0 1 2 3 4 5 6 6.7 (Fe) R 0.76 C eutectoid B 1148 C R S A +Fe 3 C 727 C = T eutectoid +Fe 3 C +Fe 3 C S 4.30 C o, wt% C Fe 3 C (cementite-hrd) (ferrite-soft)
Perlite Fe 3 C (cementite-hrd) (ferrite-soft) 120 m Result: Perlite = lternting lyers of nd Fe 3 C phses
Hypoeutectoid Steel 0.76 Fe 3 C (cementite) w = s /( r + s ) w = (1- w ) 1600 1400 1200 1000 800 600 T( C) + (ustenite) r s 727 C 1148 C + Fe 3 C + Fe 3 C +Fe 3 C (Fe-C System) w = S /( R + S ) w Fe3 C = (1- w ) 400 0 1 2 3 4 5 6 6.7 (Fe) C 0 perlite w perlite = w C o, wt% C
Hypoeutectoid Steel perlite w perlite = w 100 m w = S /( R + S ) w Fe3 C = (1- w ) perlite Proeutectoid ferrite proeutectoid phse the first phse tht forms upon cooling the solid
0.76 Fe 3 C (cementite) Hypereutectoid Steel Fe 3 C w Fe3 C = r /( r + s ) w =(1- w Fe3 C ) w = S /( R + S ) w Fe3 C = (1- w ) 1600 1400 1200 1000 800 600 T( C) C o + (ustenite) R 400 0 1 2 3 4 5 6 6.7 perlite (Fe) w perlite = w r s S 1148 C +Fe 3 C +Fe 3 C (Fe-C System) +Fe 3 C C o, wt%c
Hypereutectoid Steel w = S /( R + S ) w Fe3 C = (1- w ) perlite w perlite = w 60 m perlite proeutectoid Fe 3 C
Exmple For 99.6 wt% Fe-0.40 wt% C t temperture just below the eutectoid, determine the following ) the mount of perlite nd proeutectoid ferrite () per 100 g of steel b) composition of Fe 3 C nd ferrite () c) the mount of crbide (cementite) in grms tht forms per 100 g of steel
Fe C (cementite) Solution. the mount of perlite nd proeutectoid ferrite () note: mount of perlite = mount of just bove T E C o = 0.40 wt% C C = 0.022 wt% C C perlite = C = 0.76 wt% C C o C C C x 100 51.2 g T( C) 1600 1400 1200 1000 + (ustenite) 1148 C + Fe 3 C +Fe 3 C perlite = 51.2 g proeutectoid = 48.8 g 800 600 R S 727 C + Fe 3 C 400 0 1 2 3 4 5 6 6.7 C C C o, wt% C C O
Fe C (cementite) Fe Solution - continued Fe3C Fe C 3 3 b) composition of Fe 3 C nd ferrite () c) the mount of crbide (cementite) in grms tht forms per 100 g of steel 0.4 6.7 C 5.7 g 94.3 g C C o Fe 3 C C C x100 0.022 x 100 5.7g 0.022 T( C) 1600 1400 1200 1000 800 600 + (ustenite) C O = 0.40 wt% C C = 0.022 wt% C C Fe C = 6.70 wt% C 3 400 0 1 2 3 4 5 6 6.7 C o, wt% C C R C O 727 C 1148 C + Fe 3 C S + Fe 3 C +Fe 3 C C Fe C 3
T Eutectoid ( C) C eutectoid (wt%c) Alloying Steel with More Elements T eutectoid chnges: C eutectoid chnges: Ti Mo Si W Ni Cr Ni Cr Mn Ti Si Mo W Mn wt. % of lloying elements wt. % of lloying elements
Txonomy of Metls Metl Alloys Ferrous Nonferrous Steels <1.4 wt% C Cst Irons 3-4.5 wt% C Cu Al Mg Ti 1600 1400 T( C) microstructure: ferrite, grphite cementite 1200 1000 ustenite + 1148 C 4.30 +Fe 3 C Eutectic: ferrite 800 600 727 C Eutectoid: 0.76 +Fe 3 C +Fe 3 C Fe 3 C cementite 400 0 1 2 3 4 5 6 6.7 (Fe) C o, wt% C
Steels incresing strength, cost, decresing ductility
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