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Phases present 
                                    L
                                                             ferrit...
Steel is an interstitial solid solution of carbon in iron.

           Theoretically steel has a maximum of 2.11% carbon.
...
IRON-CARBON (Fe-C) PHASE DIAGRAM
    • 2 important                     T(°C)
                                1600
        ...
IRON-CARBON (Fe-C) PHASE DIAGRAM

     BCC crystal structure                 FCC crystal structure




Note:  phase is al...
ALLOYING STEEL WITH MORE ELEMENTS

              • Teutectoid changes:                • Ceutectoid changes:




          ...
Overview of cast iron
• Iron with 1.7 to 4.5% carbon and 0.5 to 3%
  silicon
• Lower melting point and more fluid than ste...
Production of cast iron

• Pig iron, scrap steel, limestone and
  carbon (coke)
• Cupola
• Electric arc furnace
• Electric...
Types of cast iron

• Grey cast iron - carbon as graphite
• White cast iron - carbides, often
  alloyed
• Ductile cast iro...
Effect of cooling rate
• Slow cooling favours the formation of graphite
  & low hardness
• Rapid cooling promotes carbides...
Effect of composition




• A CE over 4.3 (hypereutectic) leads to carbide
  or graphite solidifying first & promotes grey...
Grey cast iron

• Flake graphite in a matrix of
  pearlite, ferrite or martensite
• Wide range of applications
• Low ducti...
Typical properties
• Depend strongly on casting shape & thickness
• AS1830 & ASTM A48 specifies properties
• Low strength,...
Graphite form

       • Uniform
       • Rosette
       • Superimposed (Kish
         and normal)
       • Interdendritic ...
Matrix structure

• Pearlite or ferrite
• Transformation is to ferrite when
  – Cooling rate is slow
  – High silicon cont...
Properties of grey cast iron

• Machineability is excellent
• Ductility is low (0.6%), impact
  resistance low
• Damping c...
Applications

• Engines
    – Cylinder blocks, liners,
•   Brake drums, clutch plates
•   Pressure pipe fittings (AS2544)
...
Ductile iron

• Inoculation with Ce or Mg or both
  causes graphite to form as
  spherulites, rather than flakes
• Also kn...
Microstructure


        • Graphite spheres
          surrounded by ferrite
        • Usually some
          pearlite
    ...
Production

• Composition similar to grey cast
  iron except for higher purity.
• Melt is added to inoculant in ladle.
• M...
Properties

• Strength higher than grey cast iron
• Ductility up to 6% as cast or 20%
  annealed
• Low cost
  – Simple man...
Applications

• Automotive industry 55% of ductile
  iron in USA
  – Crankshafts, front wheel spindle
    supports, steeri...
Malleable iron

• Graphite in nodular form
• Produced by heat treatment of
  white cast iron
• Graphite nodules are irregu...
Microstructure




• Uniformly dispersed graphite
• Ferrite, pearlite or tempered martensite
  matrix
• Ferritic castings ...
Annealing treatments
• Ferritic malleable iron
   – Depends on C and Si
   – 1st stage 2 to 36 hours at 940˚C in a control...
Properties

•   Similar to ductile iron
•   Good shock resistance
•   Good ductility
•   Good machineability
Applications
•   Similar applications to ductile iron
•   Malleable iron is better for thinner castings
•   Ductile iron b...
Effects of alloy elements

• Promote graphite (Si, Ni)
• Promote carbides (Cr)
• Affect matrix microstructure
  – Ferrite,...
Increasing carbon

• Increases depth of chill in chilled
  iron
• Increases hardness
• Increases brittleness
• Promotes gr...
Increasing silicon

• Lowers carbon content of eutectic
• Promotes graphite on solidification
  – Reduces depth of chill
•...
Manganese and sulphur

• Each alone increases depth of chill
• Together reduces effect of other
  (MnS)
• Mn in excess sca...
Phosphorus

• Mild graphitiser
  – Reduces chill depth
  – Considered detrimental in alloy cast
    irons
Chromium

• Main uses:
  – Forms carbides
  – Gives corrosion resistance
  – High temperature stability
• Up to 3% - no ef...
Nickel

• Promotes graphite
• Increases strength of pearlite
• Increases hardenability
  – 2.5 to 4.5% Ni-Hard irons
• Sta...
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
Week13  Iron Carbon Phase Diagram @ Www.07 Met.Tk
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Week13 Iron Carbon Phase Diagram @ Www.07 Met.Tk

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Transcript of "Week13 Iron Carbon Phase Diagram @ Www.07 Met.Tk"

  1. 1. Phases present  L  ferrite  Bcc structure Bcc structure Ferromagnetic Paramagnetic Fairly ductile  austenite Fe3C cementite Fcc structure Orthorhombic Non­magnetic Hard Reactions ductile brittle Peritectic L +  =  Max. solubility of C in ferrite=0.022% Eutectic L = + Fe3C Max. solubility of C in austenite=2.11% Eutectoid  =  + Fe3C
  2. 2. Steel is an interstitial solid solution of carbon in iron. Theoretically steel has a maximum of 2.11% carbon. In practice, the amount of carbon rarely exceeds 0.8% Classification/Nomenclature Low carbon steels up to 0.2%C AISI 1020:  Last two numbers indicate Medium carbon steels 0.2­0.4%C Amount of carbon :0.2%C 10 indicates plain carbon steel High carbon steels >0.4% C AISI 4340: 0.4%C 43 indicates alloy steel
  3. 3. IRON-CARBON (Fe-C) PHASE DIAGRAM • 2 important T(°C) 1600 points δ -Eutectic (A): 1400 L L ⇒ γ + Fe3C γ+L γ A 1200 1148°C L+Fe3C Fe3C (cementite) -Eutectoid (B): (austenite) R S γ ⇒ α + Fe3C 1000 γ γ γ γ γ+Fe C 3 α+ 800 α γ B 727°C = T eutectoid R S 600 α+Fe C 3 400 0 1 2 3 4 5 6 6.7 (Fe) 0.77 4.30 C , wt% C 120µm o C eutectoid Result: Pearlite = Fe3C (cementite-hard) alternating layers of α and Fe C phases. α (ferrite-soft) 3 (Adapted from Fig. 9.24, Callister 6e. Adapted from Fig. 9.21,Callister 6e. (Fig. 9.21 (Fig. 9.24 from Metals Handbook, 9th adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 9, Metallography and ed., Microstructures, American Society for Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM Metals, Materials Park, OH, 1985.) International, Materials Park, OH, 1990.)
  4. 4. IRON-CARBON (Fe-C) PHASE DIAGRAM BCC crystal structure FCC crystal structure Note:  phase is also called  ferrite and is a BCC phase 1
  5. 5. ALLOYING STEEL WITH MORE ELEMENTS • Teutectoid changes: • Ceutectoid changes: C eutectoid (wt%C) 0.8 T Eutectoid (°C) 1200 Ti Si Mo W 0.6 Ni 1000 Cr Cr 0.4 Si 800 Mn Mn 0.2 W Ti Mo 600 Ni 0 0 4 8 12 0 4 8 12 wt. % of alloying elements wt. % of alloying elements
  6. 6. Overview of cast iron • Iron with 1.7 to 4.5% carbon and 0.5 to 3% silicon • Lower melting point and more fluid than steel (better castability) • Low cost material usually produced by sand casting • A wide range of properties, depending on composition & cooling rate – Strength – Hardness – Ductility – Thermal conductivity
  7. 7. Production of cast iron • Pig iron, scrap steel, limestone and carbon (coke) • Cupola • Electric arc furnace • Electric induction furnace • Usually sand cast, but can be gravity die cast in reusable graphite moulds • Not formed, finished by machining
  8. 8. Types of cast iron • Grey cast iron - carbon as graphite • White cast iron - carbides, often alloyed • Ductile cast iron – nodular, spheroidal graphite • Malleable cast iron
  9. 9. Effect of cooling rate • Slow cooling favours the formation of graphite & low hardness • Rapid cooling promotes carbides with high hardness • Thick sections cool slowly, while thin sections cool quickly • Sand moulds cool slowly, but metal chills can be used to increase cooling rate & promote white iron
  10. 10. Effect of composition • A CE over 4.3 (hypereutectic) leads to carbide or graphite solidifying first & promotes grey cast iron • A CE less than 4.3 (hypoeutectic) leads to austenite solidifying first & promotes white iron
  11. 11. Grey cast iron • Flake graphite in a matrix of pearlite, ferrite or martensite • Wide range of applications • Low ductility - elongation 0.6% • Grey cast iron forms when – Cooling is slow, as in heavy sections – High silicon or carbon
  12. 12. Typical properties • Depend strongly on casting shape & thickness • AS1830 & ASTM A48 specifies properties • Low strength, A48 Class 20, Rm 120 MPa – High carbon, 3.6 to 3.8% – Kish graphite (hypereutectic) – High conductivity, high damping • High strength, A48 Class 60, Rm 410 MPa – Low carbon, (eutectic composition)
  13. 13. Graphite form • Uniform • Rosette • Superimposed (Kish and normal) • Interdendritic random • Interdendritic preferred orientation
  14. 14. Matrix structure • Pearlite or ferrite • Transformation is to ferrite when – Cooling rate is slow – High silicon content – High carbon equivalence – Presence of fine undercooled graphite
  15. 15. Properties of grey cast iron • Machineability is excellent • Ductility is low (0.6%), impact resistance low • Damping capacity high • Thermal conductivity high • Dry and normal wear properties excellent
  16. 16. Applications • Engines – Cylinder blocks, liners, • Brake drums, clutch plates • Pressure pipe fittings (AS2544) • Machinery beds • Furnace parts, ingot and glass moulds
  17. 17. Ductile iron • Inoculation with Ce or Mg or both causes graphite to form as spherulites, rather than flakes • Also known as spheroidal graphite (SG), and nodular graphite iron • Far better ductility than grey cast iron
  18. 18. Microstructure • Graphite spheres surrounded by ferrite • Usually some pearlite • May be some cementite • Can be hardened to martensite by heat
  19. 19. Production • Composition similar to grey cast iron except for higher purity. • Melt is added to inoculant in ladle. • Magnesium as wire, ingots or pellets is added to ladle before adding hot iron. • Mg vapour rises through melt, removing sulphur.
  20. 20. Properties • Strength higher than grey cast iron • Ductility up to 6% as cast or 20% annealed • Low cost – Simple manufacturing process makes complex shapes • Machineability better than steel
  21. 21. Applications • Automotive industry 55% of ductile iron in USA – Crankshafts, front wheel spindle supports, steering knuckles, disc brake callipers • Pipe and pipe fittings (joined by welding)
  22. 22. Malleable iron • Graphite in nodular form • Produced by heat treatment of white cast iron • Graphite nodules are irregular clusters • Similar properties to ductile iron • See AS1832
  23. 23. Microstructure • Uniformly dispersed graphite • Ferrite, pearlite or tempered martensite matrix • Ferritic castings require 2 stage anneal. • Pearlitic castings - 1st stage only
  24. 24. Annealing treatments • Ferritic malleable iron – Depends on C and Si – 1st stage 2 to 36 hours at 940˚C in a controlled atmosphere – Cool rapidly to 750˚C & hold for 1 to 6 hours • For pearlitic malleable iron – Similar 1st stage above (2 - 36 h at 940˚C) – Cool to 870˚C slowly, then air cool & temper to specification • Harden and temper pearlitic iron for martensitic castings
  25. 25. Properties • Similar to ductile iron • Good shock resistance • Good ductility • Good machineability
  26. 26. Applications • Similar applications to ductile iron • Malleable iron is better for thinner castings • Ductile iron better for thicker castings >40mm • Vehicle components – Power trains, frames, suspensions and wheels – Steering components, transmission and differential parts, connecting rods • Railway components • Pipe fittings AS3673
  27. 27. Effects of alloy elements • Promote graphite (Si, Ni) • Promote carbides (Cr) • Affect matrix microstructure – Ferrite, pearlite, martensite or austenite • Corrosion resistance (Cr)
  28. 28. Increasing carbon • Increases depth of chill in chilled iron • Increases hardness • Increases brittleness • Promotes graphite during solidification
  29. 29. Increasing silicon • Lowers carbon content of eutectic • Promotes graphite on solidification – Reduces depth of chill • Negative effect on hardenability – Promotes pearlite over martensite • Raises Ms if martensite forms • Can improve resistance to scaling at high temperature
  30. 30. Manganese and sulphur • Each alone increases depth of chill • Together reduces effect of other (MnS) • Mn in excess scavenges S and stabilises austenite • Solid solution strengthener of ferrite / pearlite • Sulphur lowers abrasion resistance
  31. 31. Phosphorus • Mild graphitiser – Reduces chill depth – Considered detrimental in alloy cast irons
  32. 32. Chromium • Main uses: – Forms carbides – Gives corrosion resistance – High temperature stability • Up to 3% - no effect on hardenability • More than 10% - M7C3 carbides stronger and tougher than M3C
  33. 33. Nickel • Promotes graphite • Increases strength of pearlite • Increases hardenability – 2.5 to 4.5% Ni-Hard irons • Stabilises austenite – Over 6.5%

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