PY2M20PY2M20Material Properties and Phase DiagramsL t 6Lecture 6

P. Stamenov, PhDS h l f Ph i TCDSchool of Physics, TCD

PY2M20-6

Microstructures i E t ti S t Iin Eutectic Systems: I

• Co < 2 wt% Sn• Result:

T(°C)400

L: Co wt% Sn

• Result:- at extreme ends

polycrystal of grains300 L

L

- polycrystal of grainsi.e., only one solid phase. L+

200 (Pb-Sn

100

TE(Pb SnSystem)

: Co wt% Sn

100 +

0Co, wt% Sn

10

2

20Co

30

(room T solubility limit)(room T solubility limit)

Microstructures i E t ti S t IIin Eutectic Systems: II

• 2 wt% Sn < Co < 18.3 wt% Sn• Result:

T(°C)400

L: Co wt% Sn

• Result: Initially liquid + then alone 300

LL then alone

finally two phases polycrystal

L +

200

: Co wt% Sn

polycrystal fine -phase inclusions

200TE

Pb-Snsystem

100+

y

Co , wt% Sn10

18 3

200Co

302

(sol limit at T ) 18.3(sol. limit at TE)

(sol. limit at Troom)

Microstructures i E t ti S t III• Co = CE

in Eutectic Systems: III Co CE

• Result: Eutectic microstructure (lamellar structure)- alternating layers (lamellae) of and crystals.g y ( ) y

Micrograph of Pb-Sn eutectic

i t t

T(°C)L: C wt% Sn microstructure

Pb-Snt

300 LL+

L: Co wt% Sn

systemL200

L 183°C

TE

Adapted from Fig 9 14 Callister 7e160m

100: 97.8 wt% Sn

Adapted from Fig. 9.14, Callister 7e.

20 60 80 1000 40

: 18.3 wt%Sn

C, wt% Sn0 60 80 000 0

18.3 97.8CE61.9

Lamellar Eutectic Structure

← Other possible eutectic structures are: rod-like, globular

and acicular.

Microstructures i E t ti S t IV

% S C % S

in Eutectic Systems: IV• 18.3 wt% Sn < Co < 61.9 wt% Sn• Result: crystals and an eutectic microstructure

C = 18.3 wt% Sn• Just above TE :T(°C) L: Co wt% Sn L

LCL = 61.9 wt% Sn

SR + S

W= = 50 wt%Pb-Snsystem

300 LL+

SR

SR

WL = (1- W) = 50 wt%R + S

• Just below TE :

systemL+200

TE

primary

Just below TE :C = 18.3 wt% SnC = 97.8 wt% Sn

100 +

18 3 61 9 97 8

eutectic eutectic

C 97.8 wt% SnS

R + SW= = 73 wt%

W 27 t%20 60 80 1000 40

18.3 61.9 97.8 W = 27 wt%Co, wt% Sn

Hypoeutectic & Hypereutectic

300 LL+

L+200

L

TE

(Pb-Sn S t )

T(°C)

+ 100

System)

Co, wt% Sn20 60 80 1000 40

hypereutectic: (illustration only)hypoeutectic: C = 50 wt% Sn 61 9eutectic

hypereutectic: (illustration only)

hypoeutectic: Co 50 wt% Sn 61.9

eutectic: Co =61.9wt% Sn

160 meutectic micro constituent

175 m

eutectic micro-constituent

Intermetallic Compounds

Mg PbMg2Pb

Note: intermetallic compound forms a line - not an area -Note: intermetallic compound forms a line not an area because the stoichiometry (i.e. composition) is exact.

Eutectic

Eutectic - liquid in equilibrium with two solids

L + coolL heat

Example: Eutectoid & Peritectic

Cu-Zn Phase diagramPeritectic transition + L

Cu-Zn Phase diagram

Eutectoid transition + Peritectoid – solid state PeritecticEutectoid transition + Peritectoid – solid state Peritectic

Eutectoid & Peritectic

E t t id lid h i ilib i Eutectoid - solid phase in equilibrium with two solid phaseswith two solid phasesS2 S1+S3 intermetallic compound

+ Fe3C (727ºC)

intermetallic compound - cementite

cool 3 ( )heat

Peritectic - liquid + solid 1 solid 2S + L SS1 + L S2

+ L (1493ºC)coolheat

περιτεκτικός → περι - included

Iron-Carbon Phase Diagram Extract

• 2 important 1600

T(°C)points

-Eutectic (A):

1600

1400 L

-Eutectoid (B):L +Fe3C

e)

1200 (austenite)

+LL+Fe3C1148°C

ASR

+Fe3C

emen

tit1000

800

+Fe3C

SR

e 3C

(ce800

600 +Fe C

727°C = Teutectoid

R SB

Fe

4000 1 2 3 4 5 6 6.7

+Fe3C

(Fe) C wt% C4.300 76α – bcc (FM)β bcc (NM) obs (Fe) Co, wt% C4.300.76

tect

oid Fe3C (cementite-hard)

(ferrite-soft)

β – bcc (NM) obs.γ – fcc (NM)δ bcc (NM)

Ceu

t ( )δ – bcc (NM)ε – hcp (p >13 GPa)

Pearlite

Fe3C (cementite-hard)

(ferrite-soft)

Result: Pearlite = 120 m

alternating layers of and Fe3C phases3 p

Hypoeutectoid Steel

1600

T(°C)

1400 L

+L

(Fe-C System)

entit

e)

1200

1000

(austenite)

+ Fe C

L+Fe3C1148°C

C (c

eme

800

+ Fe3C

727°Cr s

Fe3C600

400

+ Fe3C

w =s/(r+s)w =(1- w)

4000 1 2 3 4 5 6 6.7(Fe) Co, wt% CC0

0.76

pearlite

w =S/(R+S)wF C =(1-w)

wpearlite = wpearlite

wFe3C (1 w)

Hypoeutectoid Steel

100

lit 100 mw =S/(R+S)w C = (1 w)

wpearlite = wpearlite

wFe3C = (1-w)

Proeutectoidferrite

pearlite

proeutectoid phase – the first phase that forms upon cooling the solid

Hypereutectoid Steel

T(°C)1600

1400 L

T( C)(Fe-C System)

te)

1400

1200 (austenite)

+LL+Fe3C1148°C

emen

tit

1000

( )

+Fe3CFe3C

Fe3C

(ce800

600 +Fe C R S

sr

wF C =r/(r+s)

Fe3C

F

4000 1 2 3 4 5 6 6.7

+Fe3C

(Fe) C wt%C.76

Co

pearlite

wFe3C =r/(r+s)w =(1-w Fe3C)

(Fe) Co, wt%C0.

w =S/(R+S)w =(1 w )

wpearlite = wpearlite

wFe3C =(1-w)

Hypereutectoid Steel

pearlite

w =S/(R+S)wFe C =(1-w)

wpearlite = wp

Fe3C ( )

60 m60 m

proeutectoid Fe3Cpearlite

Example

For a 99 6 wt% Fe-0 40 wt% C at aFor a 99.6 wt% Fe-0.40 wt% C at a temperature just below the eutectoid, determine the following

a) the amount of pearlite anda) the amount of pearlite and proeutectoid ferrite () per 100 g of steel

b) composition of Fe C and ferrite ()b) composition of Fe3C and ferrite ()c) the amount of carbide (cementite) in ) ( )

grams that forms per 100 g of steel

Solutiona. the amount of pearlite and proeutectoid ferrite ()

t t f lit t f j t b Tnote: amount of pearlite = amount of just above TE

Co = 0.40 wt% CCo 0.40 wt% CC = 0.022 wt% CCpearlite = C = 0.76 wt% C 1600

Co C x 100 51.2 g e)

1400

1200

L

+LL+Fe3C1148°C

T(°C)

C Cx 100 51.2 g

emen

tit

1200

1000

(austenite)

+ Fe3C

L+Fe3C1148 C

pearlite = 51 2 g e 3C

(ce

800

600 + Fe C

727°CR S

pearlite 51.2 gproeutectoid = 48.8 g

F600

4000 1 2 3 4 5 6 6.7

+ Fe3C

C wt% CCOCC Co, wt% CCO

Solution - continuedb) composition of Fe3C and ferrite ()c) the amount of carbide

(cementite) in grams that CO = 0.40 wt% CC = 0.022 wt% CC 6 70 t% Cforms per 100 g of steel CFe C = 6.70 wt% C

31600

100xCFe

CFe

CFe3

3

3

CC

CCo

e)

1400

1200

L

+LL+Fe3C1148°C

T(°C)

g7.5100 022.07.6022.04.0

3

x

emen

tit

1200

1000

(austenite)

+ Fe3C

L+Fe3C1148 C

g 5.7 CFe3 e 3C

(ce

800

600 + Fe C

727°CR S

g 3.943

F600

4000 1 2 3 4 5 6 6.7

+ Fe3C

C wt% CCO CFe CC Co, wt% CCO CFe C3C

Alloying Steel with More Elements

• Teutectoid changes: • Ceutectoid changes:

) TiMo

Si

C)

d(°

C Mo W

(wt%

C NiCr

utec

toid Cr

M toid Si

MnW

TE

u

NiMn

Ceu

tect

TiW

Mo

wt. % of alloying elements wt. % of alloying elements

C

Taxonomy of MetalsMetal Alloys

Ferrous Nonferrous

Cu Al Mg TiSteels<1.4wt%C

Cast Irons3-4.5wt%C

1600

T(°C) microstructure:ferrite, graphite cementite

1400

1200

L

+L

L+Fe3C

1148°C

cementite

Fe3C

1000

800

austenite

+Fe3C

Eutectic:4.30

727°C Fe3C cementite

800

600

ferrite

+Fe3CEutectoid:

0.76

727°C

4000 1 2 3 4 5 6 6.7

(Fe) Co , wt% C

Steels

increasing strength, cost, decreasing ductility

St lSteelTTypes

( for your(…for your information

only…Not requiredNot required

for thefor the examination!)