Lecture10.Phase Diagram Fe-Fe3C
Transcript of Lecture10.Phase Diagram Fe-Fe3C
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METALLURGY I(RM-1420)
Dosen:Fahmi Mubarok, ST., MSc.Metallurgy LaboratoryMechanical EngineeringITS- Surabaya2008
Crystal Structures of Iron
Fe – Fe3C Phase Diagram
Steels
Cast Iron
http://www.its.ac.id/personal/material.php?id=fahmi
LECTURE XLECTURE X
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Fahmi Mubarok
X 2Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Review (Concept of solubility)
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
(a) The three forms of water – gas, liquid, and solid – are each a phase.
(b) Water and alcohol have unlimited solubility.
(c) Salt and water have limited solubility.
(d) Oil and water have virtually no solubility.
Illustration of phases and solubility:
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Fahmi Mubarok
X 3Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Crystal Structures of ironCrystal Structures of iron
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Fahmi Mubarok
X 4Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Fe - FeFe - Fe33C C Phase Phase DiagramDiagram
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Fahmi Mubarok
X 5Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Fe-Fe3C Phase Diagram
• Region– Pure Iron < 0.008% wt C– Steel 0.008 < % wt C < 2.14– Cast Isron 2.14 < %wt C < 6.70
• Phases:– α-Ferrite (α)– Austenite ()– δ-Ferrite (δ)– Cemenite (Fe3C)
• Critical temperature:
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Fahmi Mubarok
X 6Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Four Solid Phases
• α-Ferrite (α)– Solid solution of a carbon in α-Iron– BCC structure– Carbon only slightly soluble in matrix
• Maximum solubility of 0.022 % wt C at 727oC to about 0.008 wt% C in room temperature
• Austenite ()– Solid solution of a carbon in δ-Iron– FCC structure can accomodate more carbon than ferrite
• Maximum solubility of 2.14 % wt C at 1147oC, then decreased to 0.8 wt% C at 727oC.
• The difference in C solid solubility between and α is the basis of hardening in many steel.
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Fahmi Mubarok
X 7Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Four Solid Phases
• δ-Ferrite (δ)– Solid solution of a carbon in δ-Iron– BCC structure– NO technological importance cause only stable at high
temperature.• Maximum solubility of ferrite being 0.09 % wt C at 1493oC
• Cementite (Fe3C)– Intermetallic Fe-C compound– Fe3C : 6.7 wt% C + 93.3 wt% Fe– Forms when solubility limit of carbon in α-ferrite is exceeded
below 727oC– Orthorombic crystal structure : very hard and brittle.
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Fahmi Mubarok
X 8Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Three Invariant ReactionsThree Invariant Reactions
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Fahmi Mubarok
X 9Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Eutectoid steel (Pearlitic steel)
• Microstructure: pearlite- Lamellar eutectoid product
alternates plates of α + Fe3C- Two phases grow simultaneously
• Lever rule
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Fahmi Mubarok
X 10Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Formation of Pearlite
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Fahmi Mubarok
X 11Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypoeutectoid steel
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Fahmi Mubarok
X 12Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypoeutectoid steel ->Lever Rule
3
αt(total ferrite)
Fe C (Cementite)
6.70 0.38 100%6.70 0.022
= 95%1 95% 5%
W x
W
(proeutectoid ferrite)
γ(that will form pearlite)
0.76 0.38 100%(0.76 0.022)
52%1 52% 48%
W x
W
1
2
3a
3b Example: Calculating composition of steel with 0.38 wt%CT = 730oC T=725oC3b3a
The fraction of eutectoid ferrite thus are:
αe ααt 95% 52% 43%
W W W
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Fahmi Mubarok
X 13Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypoeutectoid steel composition (0.38 wt% C)
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Fahmi Mubarok
X 14Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypereutectoid steel
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Fahmi Mubarok
X 15Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypereutectoid steel -> lever rule
Exercise 10a. Determine the following composition of 1.4 wt%C at a temperature near eutectoid line :
a. The fraction of pealite and proeutectoid cementiteb. The fraction of total ferrite and cementite phasesc. The fraction of eutectoid cementite
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Fahmi Mubarok
X 16Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypereutectoid steel composition (1.4 wt% C)
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Fahmi Mubarok
X 17Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Plain Carbon Steels
1. Satisfactory where strength and other requirement are not too severe
2. Used successfully at room temperatures and in atmospheres that are not highly corrosive
3. Can be produced in a great range of strengths at a relatively low costLimitation
1. Cannot be strengthened beyond about 100.000 psi without significant loss in toughness (impact resistance) and ductility
2. Large section cannot be made with a martensitic structure throughout
3. Rapid quench rates are necessary for full hardening in medium-carbon plain carbon steels to produce a martensitic structure. This rapid quenching leads to shape distortion and cracking of heat-treated steel
4. Show a marked softening with increasing tempering temperature5. Poor impact resistance at low temperatures6. Poor corrosion resistance for many engineering environments7. Oxidezed readily at elevated temperatures
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Fahmi Mubarok
X 18Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Elements in Plain Carbon Steels1.Sulfur (<0.05 %)
• Sulfur combines with iron to form iron sulfide (FeS), which usually occurs as a grain boundary precipitation
• FeS is hard and has a low melting point, it can cause cracking during hot working of steel (hot-short)
2.Manganese (0.03 % -1.0 %)• The fuction of manganese in counteracting the negative effects
of sulfur• Manganese combines with the sulfur persent in the steels to
produce manganese sulfide (MnS), thus no FeS will form.3.Phosphorus (< 0.04 %)
• This small quantity tends to dissolve in ferrite, increasing the strength and hardness slightly
• In large quantities, phosphorus reduces ductility, thereby increasing the tendency of the steel to crack when cold worked (cold-short)
4.Silicon (from 0.05%-0.30%)• Silicon dissolves in ferrite, increasing the strength of the steel
without greatly decreasing the ductility• Silicon is used as a deoxidizer, and forms SiO2 or silicate
inclusions
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Fahmi Mubarok
X 19Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Alloying SteelsPlain Carbon Steels
Plain-carbon steels properties are not always adequate for all engineering
applications of steel
Alloy Steels1. Alloy steels have been developed which, although they cost more, are
more economical for many uses2. In some applications, alloy steels are the only materials that are able to
meet engineering requirements3. The principal element that are added to make alloy steels are nickel,
chromium, molybdenum, manganese, silicon, and vanadium4. Other elements sometimes added are cobalt, cooper, and lead
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Fahmi Mubarok
X 20Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Effect of carbon content
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Fahmi Mubarok
X 21Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hardness and Strength
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Fahmi Mubarok
X 22Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Toughness and Ductility
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Fahmi Mubarok
X 23Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Cast Iron
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Fahmi Mubarok
X 24Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
White Cast Iron
• Chemical composition:– Carbon 1.8-3.6 %– Silicon 0.5-1.9 %– Manganese 0.25-0.80 %– Sulfur 0.06-0.20 %– Phosphorus 0.06-0.18 %
• Solidification rate fast enough• Carbon combined with iron cementite (hard, brittle)• Microstructure pearlite in a white interdendritic network of
cementite• Shows a “white” crystalline fractured surface
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Fahmi Mubarok
X 25Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
White Cast Iron
• High compressive strength and excellent wear resistance but extremely brittle and difficult to machine
• Used where:– resistance to wear is most important– The service does not require ductility
• White cast iron Malleable cast iron (malleabilization)• Mechanical properties:
– Hardness brinell 375 – 600 BHN– Tensile strength 20.000 – 70.000 psi– Compressive strength 200.000 – 250.000 psi– Modulus of elasticity 24 – 28 milion psi
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Fahmi Mubarok
X 26Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
White Cast Iron
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Fahmi Mubarok
X 27Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Summary
• ! Pearlite• ! Peritectic reaction• ! Phase• ! Phase diagram• ! Phase equilibrium• ! Primary phase• ! Proeutectoid cementite• ! Proeutectoid ferrite• ! Solidus line• ! Solubility limit• ! Solvus line• ! System• ! Terminal solid solution• ! Tie line• ! Liquidus line• ! Metastable
• ! Austenite• ! Cementite• ! Component• ! Congruent transformation• ! Equilibrium• ! Eutectic phase• ! Eutectic reaction• ! Eutectic structure• ! Eutectoid reaction• ! Ferrite• ! Hypereutectoid alloy• ! Hypoeutectoid alloy• ! Intermediate solid solution• ! Intermetallic compound• ! Invariant point• ! Isomorphous• ! Lever rule
Make sure you understand language and concepts:
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METALLURGY I(RM-1420)
Dosen:Fahmi Mubarok, ST., MSc.Metallurgy LaboratoryMechanical EngineeringITS- Surabaya2008
MINGGU XI-XIIIMINGGU XI-XIII
NON EQUILIBRIUMTRANSFORMATION
-Isothermal transformation diagram- Coling tranformation diagram
- Formation of martensite