Phase diagrams (cont.) and the Fe-C system - cribMEcribme.com/uta/data/Engineering/Material Science...

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

Transcript of Phase diagrams (cont.) and the Fe-C system - cribMEcribme.com/uta/data/Engineering/Material Science...

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

Solidification: Pro-eutectic vs

Eutectic

Ideal liquid, uniform distribution

Solid Pb(Sn) (α) nucleates

Solubility limit leads toSn

rich area just outside α

Sn

easily redistributes in L

Pro-eutectic solidification

Process continues untileutectic temperature is reached

Eutectic solidification

18

L + α200

T(°C)

Co, wt% Sn

20 400

300

100

L

α

60

L: Cowt%Sn

α + β

TE

α: 18.3wt%Sn

β

080 100

L + β

CE18.3 97.861.9

183°C

β: 97.8wt%Sn

Co

= CE•

Eutectic microstructure--alternating layers of α

and β

crystals.

Adapted from Fig. 9.12, Callister 6e. (Fig. 9.12 from Metals Handbook, Vol. 9, 9th ed., Metallography and Microstructures, American Society for Metals, Materials Park, OH, 1985.)

MICROSTRUCTURES IN EUTECTIC SYSTEMS

Phases at P1?

Microconstituents

at P1?

How much of each phase?

P1

20

T(°C)

(Pb-Sn System)

L + α200

Co, wt% Sn20 400

300

100

L

α

60

α + β

TE β

080 100

L + β

18.361.9

97.8

Cohypoeutectic

Cohypereutectic

eutectic

hypereutectic: (illustration only)

160μm

eutectic: Co=61.9wt%Sn

175μm

β

ββ

ββ

β

α

α

α

αα

α

hypoeutectic: Co=50wt%Sn

eutectic micro-constituent

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.)

(Figs. 9.12 and 9.15 from Metals Handbook, 9th ed.,Vol. 9, Metallography and Microstructures, American Society for Metals, Materials Park, OH, 1985.)

HYPOEUTECTIC & HYPEREUTECTIC

L + α200

T(°C)

Co, wt% Sn

20 400

300

100

L

α

60

L: Cowt%Sn

α + β

TEβ

080 100

L + β

Co18.3 61.9

primary α

97.8

S

S

RR

eutectic αeutectic β

19

Example: Pb-Sn

system

18.3wt%Sn < Co

< 61.9wt%Sn

Adapted from Fig. 9.14, Callister 6e.

MICROSTRUCTURES IN EUTECTIC SYSTEMS

Phases? Composition?

How much of each?

Just Above TE

Microconstituents?How much of each?

L + α200

T(°C)

Co, wt% Sn

20 400

300

100

L

α

60

L: Cowt%Sn

α + β

TEβ

080 100

L + β

Co18.3 61.9

primary α

97.8

S

S

RR

eutectic αeutectic β

19

Example: Pb-Sn

system

18.3wt%Sn < Co

< 61.9wt%Sn

Adapted from Fig. 9.14, Callister 6e.

MICROSTRUCTURES IN EUTECTIC SYSTEMS

Phases? Composition?

How much of each?

Just Below TE

Microconstituents?How much of each?

Systems with intermediate compounds or solid solutions

Cu, Zn

Iron -

Carbon system: Consider only Fe to Fe3

C portion

AXES:Cementite: Fe3

C(Compound)

PURE IronFerrite (α): BCCAustenite(γ): FCCFerrite (δ): BCC

Solid solutionsα,δ,γ, interstitial CDifferent solubilities

Peritectic

and Eutectic Example: Iron -

Carbon system

Eutectiod: all solidsOne solid phase separates into two different solid phases upon coolingHere: γ → α + Fe3

C

Peritectic: Liquid + solid phase at given composition converts to one different

solid phase upon coolingHere: L + δ → γ

Phases?

Alloy Classifications in the Iron Carbon system

Hypo Eutectoid

Steel0.008 –

0.76

Hyper Eutectoid Steel0.76 –

2.14Cast Iron

2.14 –

6.7% C

Iron0 –

0.008

Numbers in %

21

(Adapted from Fig. 9.24, Callister 6e. (Fig. 9.24 from Metals Handbook, 9th ed., Vol. 9, Metallography and Microstructures, American Society for Metals, Materials Park, OH, 1985.)

Result: Pearlite = alternating layers of α and Fe3C phases.

120μm

• 2 important points

-Eutectic (A):

-Eutectoid (B): L ⇒ γ + Fe3C

γ ⇒ α +Fe3C

Fe

3C

(c

em

en

tite

)

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

γ (austenite)

γ+L

γ+Fe3C

α+Fe3C

α+γ

L+Fe3C

δ

(Fe) Co, wt% C0.77 4.30

727°C = Teutectoid

1148°C

T(°C)

A

B

SR

R S

γ γγγ

Fe3C (cementite-hard)α (ferrite-soft)

αC

eu

tec

toid

IRON-CARBON (Fe-C) PHASE DIAGRAM

Eutectoid: 0.76% C Pearlite

formation

Solid transformation•

γ →

α

+ Fe3C

0.76%

0.02%

6.7%

Similar to Eutectic transformation-

but now, diffusion occurs within solid

Hypo eutectoid microstructure at Room T

Proeutectoid

Ferrite + Pearlite

γ → α + γ•

Ferrite phase increases as T decreases

At T(eutectoid)γ

+ α → Pearlite

+ α

Remaining austenite transforms to pearlite

22

Adapted from Figs. 9.21 and 9.26,Callister 6e. (Fig. 9.21 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)

Adapted fromFig. 9.27,Callister6e. (Fig. 9.27 courtesy Republic Steel Corporation.)

HYPOEUTECTOID STEEL

(Fe-C System)

Co

Fe

3C

(c

em

en

tite

)

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

γ (austenite)

γ+L

γ+Fe3C

α+Fe3C

L+Fe3C

δ

Co, wt% C0.7

7

727°C

1148°C

T(°C)

R S

γ γγγ

α

γγγ γ

γγ γ

γ r s

wα =s/(r+s)wγ =(1-wα)

wα =S/(R+S)wFe3C =(1-wα)

wpearlite = wγ

α

αα

αα

α pearlite

100μm Hypoeutectoid steel

(Fe-C System)

Co

Fe

3C

(c

em

en

tite

)

1600

1400

1200

1000

800

600

4000 1 2 3 4 5 6 6.7

L

γ (austenite)

γ+L

γ+Fe3C

α+Fe3C

L+Fe3C

δ

Co, wt% C0.7

71148°C

T(°C)

R S

γ γγγ

αs

wFe3C =r/(r+s)wγ =(1-wFe3C)

wα =S/(R+S)wFe3C =(1-wα)

wpearlite = wγpearlite

60μm Hypereutectoid steel

rγγ

γ γ

γγγ γ

Fe3C

23

Adapted from Figs. 9.21 and 9.29,Callister 6e. (Fig. 9.21 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.)

Adapted fromFig. 9.30,Callister6e. (Fig. 9.30copyright 1971 by United States Steel Corporation.)

HYPEREUTECTOID STEEL

Hyper eutectoid microstructure at Room T

Proeutectoid

Cementite

+ Pearlite

γ → cementite

+ γ•

cementite

phase

increasesAt T(eutectoid)•

γ

+ Fe3C → Fe3C

+

Pearlite–

Remaining austenite transforms to pearlite

TE

ute

cto

id (

°C)

wt. % of alloying elements

Ti

Ni600

800

1000

1200

0 4 8 12

Mo SiW

Cr

Mn

wt. % of alloying elements

Ce

ute

cto

id (

wt%

C)

Ni

Ti

0 4 8 120

0.2

0.4

0.6

0.8

Cr

SiMnW

Mo

24

Change in Teutectoid

(727 oC): •

Change in Ceutectoid

(0.76% C):

Adapted from Fig. 9.31,Callister 6e. (Fig. 9.31 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. 9.32 from Edgar C. Bain, Functions of the Alloying Elements in Steel, American Society for Metals, 1939, p. 127.)

ALLOYING STEEL WITH MORE ELEMENTS

12

Effect of solid solution strengthening on:

--Tensile strength (TS) --Ductility (%EL,%AR)

--Peak as a function of Co --Min. as a function of Co

MECHANICAL PROPERTIES:

Cu-Ni System

Elo

ng

ati

on

(%

EL

)Composition, wt%Ni

Cu Ni0 20 40 60 80 10020

30

40

50

60

%EL for pure Ni

%EL for pure Cu

Te

nsi

le S

tre

ng

th (

MP

a)

Composition, wt%NiCu Ni0 20 40 60 80 100

200

300

400

TS for pure Ni

TS for pure Cu