08. iron-carbon phase diagrams

Equilibrium crystallisation of Iron-Equilibrium crystallisation of Iron-Carbon alloysCarbon alloys

Metallography - Lecture 8.

2012/2013. Academic Year

2013.

Metallography of Iron-Carbon alloysMetallography of Iron-Carbon alloys

Definition of Iron-Carbon alloys – the base metal is iron (Fe);– it is always a multi-component alloy having several

elements inevitably from the manufacturing processes, but it may be regarded as binary Fe-C alloy until the following conditions are fulfilleda Si < 0,5 %, Mn < 0,7 %, S+P < 0,035 %

– in these cases their equilibrium crystallisation can be studied in the iron-carbon binary phase diagram

– the iron-carbon binary phase diagram – or Heyn-Charpy

Characteristic features of Heyn-Charpy Characteristic features of Heyn-Charpy dual phase diagram dual phase diagram

Dual phase diagram since it contains

– the Fe-Fe3C metastable phase diagram (the carbon is chemically bonded in iron-carbide)

– the Fe-C stable phase diagram (the carbon is present in the form of free graphite)

Hein-Charpy dual phase diagramHein-Charpy dual phase diagram

AB

C

D

E F

G

H

I

K

L

M

N

P S

Q

(austenite)

liquid + Fe3C(liquid + graphite)

+Fe 3C

+ graphite)

liquid

+

723 oC

Fe 1 2 3 4 5 6

700

900

1000

1100

1200

1300

1400

1600

769 oC

C'

D'

E'

S'

F'

20

738 oCA1

A cm

A3 O

K'

6.687

800

1500

1147 oC

1153 oC

Weight percent, % C

Temperature oC

Figure 8.1

+ liquid

+Fe 3C

(+ graphite)

+ liquid

Characteristic points of Hein-Charpy dual phase

diagram

Table 8.1.

Point Temperature

T (oC)

Carbon-content

C (%)

A 1536 0,000

B 1493 0,510

C 1147 4,300

C' 1153 4,260

D 1250 6,687

D' * 100,000

E 1147 2,060

E' 1153 2,030

F 1147 6,687

F' 1153 100,000

G 911 0,000

H 1493 0,100

I 1493 0,160

K 723 6,687

K' 738 100,000

L 20 6,687

L' 20 100,000

M 769 0,000

N 1392 0,000

O 769 0,512

P 723 0,025

P' 738 0,020

Q 20 0,006

S 723 0,800

S' 738 0,690

Characteristic features of Heyn-Charpy Characteristic features of Heyn-Charpy dual phase diagramdual phase diagram

Unlimited liquid solubility

– 3 liquidus section 3 primary crystals

-solid solution (along AB-liquidus)

-solid solution (along BC-liquidus)

Fe3C primary cementite ( graphite in the stable system)


three solid solution zone

-solid solution (below the GP-curve)

-solid solution (below the IE-solidus curve)

-solid solution (below the AH-solidus curve)


Three chemical compounds

– along the DC-curve: I. Fe3C primary cementite

( primary graphite)

– along the ES-curve: II.Fe3C secondary cementite

( secondary graphite)

– along the PQ-curve: III.Fe3C tertiary cementite

( tertiary graphite)


In solid state limited solubility

– along the ES-curve: II.Fe3C secondary cementite

( secondary graphite)

– along the PQ-curve: III.Fe3C tertiary cementite

( tertiary graphite)


three non-variant reaction

– peritectic reaction at the T=THIB line

H + liquidB I

– eutectic reaction at the T=TECF line

liquidC E + Fe3C (ledeburite)

– eutectoid reaction at the T=TPSK line

S P + Fe3C (perlite)

Analyis of crystallisation of alloysAnalyis of crystallisation of alloys

A

B

C

D

E F

G

H

I

K

L

M

N

P S

Q

(austenite)

+ olv.

olv. + Fe3C

+ Fe3C

+ Fe3C

liquid

723 oC

Fe 1 2 3 4 5 6

700

900

1000

1100

1200

1300

1400

1600

20

A1

A cm

A3O

6,687

1147 oC

1 2 4 53

800

1500

Weight percent, % C

Tem

pera

ture

, o C

Crystallisation of alloy-1 in the metastable Crystallisation of alloy-1 in the metastable system (carbon content C=0,12 %)system (carbon content C=0,12 %)

olvB

T > T

T = T - T

T = THIB + T

T = 20 oC

T = THIB - T

T = TGOS + T

T = TPSK + T

T = TNI - T

T = TPSK - T

olv0,12

0,12

0,12

P S

P P

Fe3C

T = 20 oC

Q III. Fe3C Q

Fe3C

H + olvB I

perliteferrite

Eutectoid

S P + Fe3C

0,12

nuclei

liquid

reaction

tertiarycementite

perlite

ferrite

Peritecticreaction

liquid0,12

tertiarycementite

Crystallisation of alloy-1 in the metastable Crystallisation of alloy-1 in the metastable system (carbon content system (carbon content C=0,12 %)C=0,12 %)

Calculation of quantity of phases

before reaction after reaction

phases participating in the peritectic reaction

.%505,0110,051,0

10,012,0

%,9595,0110,051,0

12,051,0

kgolv

kg

B

H

%.3333,0110,016,0

10,012,0

%,6767,0110,016,0

12,016,0

kg

kg

I

H

IBH kgolvkgkg 33,005,028,0


T > T

T = T - T

T = TSol. - T

T = TPSK + T

olv0,8

T = 20 oC

0,8

0,8

P

Fe3C

perliteQ Fe3C)

T = TPSK - T

perlite

0,8

nuclei

liquid liquid


perlite

nuclei

T > T

T = T - T

T = Ts - T

T = TES + T

olv1,2

T = 20 oC

1,2

1,2

S II. Fe3C

Q Fe3C)

T = TPSK + T

T = TPSK - T II. Fe3CP Fe3C+

II. Fe3C

II. Fe3C

0,8

II. Fe3C

liquid1,2liquid1,2

perlite

Quantity of microstructural elements in Quantity of microstructural elements in alloy with C=1,2 %alloy with C=1,2 %

Calculations concerning the quantity of secondary cementite

analysis of microstructure

6,687 1,2% 100% 93,2%

6,687 0,8perlite

%8,6%1008,0687,6

8,02,1%. 3

CFeII


E

olv2,5

olvC

T > Tl

T = Tl - T

T = TECF + T

T = TECF - T

T = TPSK + T

T = TPSK - T

olv2,5

T = 20 oC

Eutectic reaction

olvc E + Fe3C

II. Fe3C

II. Fe3C

II. Fe3CQ

Fe3C

+

S

PFe3C+

E Fe3C+

(S Fe3C)+

(p Fe3C)+

(Q Fe3C)+

ledeburite

perlite

ledeburite

ledeburite

ledeburite

ledeburite perlite


Determination of quantity of microstructural elements at room temperature (3 microstructures - perlite+secondary cementite+ledeburite) therefore we have to find what are they originated from

– II. Fe3C is originated from E : the quantity of E

should be determined at the temperature of eutectic reaction 4,3 2,5

% 100% 80,4%,4,3 2,06

2,5 2,06% 100% 19,6%.

4,3 2,06

E

ledeburit


The maximum quantity of II. Fe3C (if the composition of the alloys should correspond to point E)

The real quantity of II. Fe3C

the third microstructural element is the perlite

%4,21%1008,0687,6

8,006,2).( max3

CFeII

3 3 max( . ) ( . ) 0,804 21,3% 17,2%real EII Fe C II Fe C

3% % ( . ) % 80,4 17,2 63,2%E realperlit II Fe C

Micro-Micro-structure-structure-

diagram for diagram for Fe-FeFe-Fe33C C

alloysalloys

Figure 8.8. Figure 8.8.

0 2 4,3

Ferrite

Perlite

Secondary cementite

Ledeburite

Primary cementite

6,687 %C

Tertiary cementite

100

%

AB

C

D

E F

G

H

I

KL

M

N

P SQ

(austenite)

+ liquid

liquid + Fe3C

+ Fe3C

+ Fe3C

liquid

+ liquid

+

723 oC

Fe 1 2 3 4 5 6

700

900

1000

1100

1200

1300

1400

1600

20

A cm

A3

O

6,687

1147 oC

Temperature oC

Weight percent, % Ca) Fe-Fe3C phase diagram

A1

b) Microstructure diagram (T = 20oC)

Phases Phases in the in the

Fe-FeFe-Fe33C C

systemsystem

Figure Figure 8.8. 8.8.

AB

C

D

E F

G

H

I

KL

M

N

P SQ

(austenite)

+ liquid

liquid + Fe3C

+ Fe3C

+ Fe3C

liquid

+ liquid

+

723 oC

Fe 1 2 3 4 5 6

700

900

1000

1100

1200

1300

1400

1600

20

A cm

A3

O

6,687

1147 oC

Temperature oC

Weight percent, % Ca) Fe-Fe3C phase diagram

A1

0

- Ferrite

6,687 %C

Fe3C - Cementite

c) Diagram of phases (T = 20 oC)

100

%

Analysis of crystallisation in the Fe-C Analysis of crystallisation in the Fe-C stable systemstable system

The dotted lines in the Hein-Charpy dual phase diagram relate for the stable system

the basic difference between the stable and metastable system can be found in the form of carbon

– in the metastable system: carbon is present in chemically bonded form of Fe3C (iron-carbide),

– in the stable system: carbon is present in the form of free C (i.e. graphite),

Summary of differences between the Summary of differences between the stable and metastable systemstable and metastable system

metastable stable

Fe3C C (primary, secondary, tertiary)

perlite graphite eutectoid ( + C)

ledeburite graphite eutectic (graphite eutectoid + C)

Analysis of crystallisation of alloy with Analysis of crystallisation of alloy with carbon content C=2,5 %carbon content C=2,5 %

liquid 2,5

T > Tl

T = Tl - T

T = TE'C'F' + T

T = TE'C'F' - T

olv2,5

' Eutectic reaction

'E' Cgr liquidC' E' Cgr

T = 20 oC II.Cgr Q' Cgr)

T = TP'S'K' - T P' Cgr P' Cgr)II.Cgr

T = TP'S'K' + T S' II.CgrS' Cgr)

C'liquid

Grafiteeutectic

Grafiteeutectic

Grafiteeutectic

Grafiteeutectoid

ClassiClassi--fication fication of iron-of iron-carbon carbon alloys alloys on the on the

basis of basis of phase phase

diagramdiagram

H y p o - H y p er-

e u tec to id

P ig iro n

H y p o -H y p er

-e u tec tic

AB

C

D

E F

G

H

I

K

L

M

N

P SQ

(a u sten ite )

+ o lv .

o lv . + F e 3C

+ F e 3C

+ F e 3C

liq u id

+ liq u .

+

7 2 3 oC

F e 1 2 3 4 5 6

7 0 0

9 0 0

1 0 0 0

1 1 0 0

1 2 0 0

1 3 0 0

1 4 0 0

1 6 0 0

2 0

A 1

A cm

A3

O

6 ,6 8 7

11 4 7 oC

S te e ls

8 0 0

1 5 0 0

T em p era tu re , oC

w eig h t % C

Figure 8.2.

08. iron-carbon phase diagrams

Documents

fe3c secondary

fe3c primary

fe3c tertiary

characteristic

secondary

solid solution

tertiary graphite

carbon alloys