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![Chapter 11 - 5
Fe-C True Equilibrium Diagram
Graphite formation
promoted by
• Si > 1 wt%
• slow cooling
Adapted from Fig. 11.2,
Callister & Rethwisch 8e.
[Fig. 11.2 adapted from
Binary Alloy Phase
Diagrams, 2nd ed.,
Vol. 1, T.B. Massalski (Ed.-
in-Chief), ASM International,
Materials Park, OH, 1990.]
1600
1400
1200
1000
800
600
400
0 1 2 3 4 90
L
γ +L
α + Graphite
Liquid +
Graphite
(Fe) C, wt% C
0.65
740ºC
T(ºC)
γ + Graphite
100
1153ºCγ
Austenite 4.2 wt% C
α + γ](https://image.slidesharecdn.com/lec05-150114115107-conversion-gate02/85/Lec-05-5-320.jpg)
Uploaded byRokonuzzaman Rony
Lec 05
This document discusses types of cast iron and their properties and applications. It covers gray iron, which contains graphite flakes and is strong in compression; ductile iron, which contains graphite nodules and has improved mechanical properties through heat treatment; white iron, which is very hard and brittle; and malleable iron, made by heat treating white iron to form graphite rosettes. Silicon promotes graphite formation while sulfur promotes cementite formation and brittleness. The next class will cover the relationship between structure and properties of cast irons.
Lec 05
- 1. Chapter 11 - MME-292 ArmanHussain Lecturer DGCE, BUET Metallic Materials Sessional Lecture 05 Cast Iron September 7, 2014
- 2. Chapter 11 -2 Chapter 11: Applications and Processing of Metal Alloys ISSUES TO ADDRESS... • How are Cast Iron classified and what are their common applications? • What are some of the common fabrication techniques for metals? • What heat treatment procedures are used to improve the mechanical properties of Cast Irons?
- 3. Chapter 11 -3 Adapted from Fig. 9.24, Callister & Rethwisch 8e. (Fig. 9.24 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.) Adapted from Fig. 11.1, Callister & Rethwisch 8e. Classification of Metal Alloys Metal Alloys Steels Ferrous Nonferrous Cast Irons <1.4wt%C 3-4.5wt%C Steels <1.4wt%C Cast IronsCast Irons 3-4.5wt%C3-4.5wt%C Fe3C cementite 1600 1400 1200 1000 800 600 400 0 1 2 3 4 5 6 6.7 L γ austenite γ+L γ+Fe3C α ferrite α+Fe3C α+γ L+Fe3C δ (Fe) Co , wt% C Eutectic: Eutectoid: 0.76 4.30 727ºC 1148ºC T(ºC) microstructure: ferrite/Pearlite graphite/cementite
- 4. Chapter 11 -4 Cast Irons • Ferrous alloys with > 2.1 wt% C – more commonly 3 - 4.5 wt% C • Low melting – relatively easy to cast, amenable to cast • Generally brittle→ casting is the most favorable process of fabrication • Cementite decomposes to ferrite + graphite Fe3C 3 Fe (α) + C (graphite) – generally a slow process
- 5. Chapter 11 -5 Fe-C True Equilibrium Diagram Graphite formation promoted by • Si > 1 wt% • slow cooling Adapted from Fig. 11.2, Callister & Rethwisch 8e. [Fig. 11.2 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.- in-Chief), ASM International, Materials Park, OH, 1990.] 1600 1400 1200 1000 800 600 400 0 1 2 3 4 90 L γ +L α + Graphite Liquid + Graphite (Fe) C, wt% C 0.65 740ºC T(ºC) γ + Graphite 100 1153ºCγ Austenite 4.2 wt% C α + γ
- 6. Chapter 11 - Typesof Cast Iron Gray iron Ductile iron White iron Malleable iron (Heat treated white iron) 6
- 7. Chapter 11 -7 Gray iron • C content: 2.5-4.0% • Si Content 1.0-3.0% • graphite flakes • Fracture surface is gray • weak & brittle in tension • stronger in compression • excellent vibrational dampening • wear resistant • Least expensive • Application: – Base of structure of machines and heavy equipments Adapted from Fig. 11.3(a) & (b), Callister & Rethwisch 8e.
- 8. Chapter 11 - Ductileiron • Add Mg and/or Ce • graphite as nodules not flakes • Greatly influence mechanical properties • Matrix: pearlite or ferrite depending on heat treatment • As-cast piece is pearlite • stronger but less ductile 8
- 9. Chapter 11 - Contd. •Heat treatment for several hours at about 7000 C will yield a ferrite matrix • Stronger and much more ductile • Applications: valves, pump bodies, crank- shaft, gears etc. 9
- 10. Chapter 11 -10 Whiteiron • < 1 wt% Si (low Si) • Rapid cooling rate • C remains as cementite instead of forming graphite • Fracture surface has a white apperance • Only suface layer is chilled, graphite flake is formed in the interior • pearlite + cementite • very hard and brittle thus unmachinable Application: hard and wear resisting surface without much ductility i.e. rollers in rolling machine, bearings etc. Adapted from Fig. 11.3(c) & (d), Callister & Rethwisch 8e.
- 11.
- 12. Chapter 11 - Malleableiron 12 • heat treat white iron at 800-900ºC for prolonged time in neutral atm. • Decomposition of cementite • graphite in rosettes surrounded by ferrite or pearlite matrix • reasonably strong and ductile Applications: Connecting rods, transmission gears, and differential cases for the automotive industry, and also flanges, pipe fittings, and valve parts for railroad, marine, and other heavy-duty services.
- 13.
- 14. Chapter 11 - Effectof Si 14 •• Si is a graphitizer • Favors solidification to the stable iron-graphite system • C is precipitated at the form of flake • Introducing Mg or Ce promote spheroidal graphite precipitation instead of flake
- 15. Chapter 11 - Effectof S in cast iron • Commercial gray irons contains: 0.06 to 0.12 % S • Effect of Si and S on the form of C are reversed • S content ↑ → Cementite formation ↑ → promote white iron formation • S reacts with Fe and form FeS → low M.P. compound → increase possibility of cracking • S↓ es fluidity → increases blow holes • Mn is used for desulphurization • MnS emains as dispersed inclusions 15
- 16. Chapter 11 - NextClass Structure properties relationship 16