Cast Iron
- 1. Prepared By: PALLAV RADIA Asst prof. AITS, RAJKOT.
- 2. 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 Damping capacity
- 3. Advantages and disadvantages of cast irons (in comparison with steels): Advantages : • good castability • good machinability • antivibration properties • low stress concentration Disadvantages : • high brittleness • non machinable (white cast iron, chilled cast iron) • cold brittleness
- 4. White cast iron - carbides, often alloyed Grey cast iron - carbon as graphite Malleable cast iron S.G (Spheroidal graphite ) cast iron Nodular cast iron Alloy of cast iron 4
- 5. 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 5
- 6. Characteristics: White cast iron derives its name from the fact that its freshly broken surface shows bright white fracture. When iron of proper composition cool fast enough the free carbon will go in the combined form and give rise to white iron casting. The result is a material with lots of iron carbide , Fe3C. Iron carbide is a Extremely hard and brittle. Thus, white cast iron possesses excellent abrasive wear resistance. White cast iron under normal circumstances is brittle and Not easily machined
- 7. White iron casting can be made in sand moulds. The solidification range of white iron is 2550 – 2065 f Shrinkage is 1/8 inch per foot White cast iron is first step in the production of malleable iron casting Also made on surface of grey iron casing provide the material in special composition The white iron contains 1.8 – 3.6 % C 0.5 – 2.0 % Si 0.2 – 0.8 % Mn 0.18 % P 0.10 % s
- 8. Application: 1. For producing malleable iron casting. 2. For manufacturing those component part which required a hard and abrasion resistant material.
- 9. White cast iron showing Massive carbide areas (white) in fine pearlite(dark) areas
- 10. 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 10
- 11. Mechanical properties 1. High Compressive strength 2. Low tensile strength 3. High rigidity 4. High stability Casting properties 1. High fluidity and ability to make sound casting 2. Relative low melting temperature 1130 – 1250 C 11
- 12. Machine ability 1. Easily machined to a good finish. 2. Forms a discontinuous chip. Special properties 1. Self damping does not vibrate 12
- 13. Characteristics: Gray iron basically is an alloy of silicon and carbon with iron. It readily cast into desired shape in a sand mould. The white iron contains 2.5 – 3.8 % C 1.1 – 2.8 % Si 0.4 – 1.0 % Mn 0.15 % P 0.10 % s It posses machinability better than steel It has high resistance to wear.
- 14. it marked by the precence of flake on grephite in a matrix of ferrite. Graphite flakes occupy about 10 % of metal volume Length of flake vary from 0.05 to 0.1 mm. It posses machinability better than steel It possesses high vibration damping capacity It has low ductility and low impact strength as compare to steel. Grey cast iron solidification range 2400 -2000 f
- 15. It has shrinkage 1/8 inch per foot It has possesses excellent casing qualities for pro- ductile simple and complex shape
- 16. machine tool structure(bed, frame and details) Gas or water pipe for underground purpose Manhole cover Cylinder blocks and head for I.C engine Brake drums, clutch plates Furnace parts, ingot and glass moulds Piston ring 16
- 17. Tunnel segment Rolling mill House hold application 17
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- 19. Inoculation with Ce or Mg or both causes graphite to form as spherulites, rather than flakes Also known as Ductile or nodular graphite iron Far better ductility than grey cast iron See AS1831 19
- 20. Characteristics: Unlike long flakes as in gray cast, graphite appears as rounded particles, or nodule or spheroids in nodular cast iron. Ductile cast iron possesses very good machinabilty. S.G cat iron contain 3.2 – 4.2 % C 1.1 – 3.5 % Si 0.3 – 0.8 % Mn 0.08 % P 0.2 % S Soft annealed grades of nodular cast iron can be turnes at very high feeds and speed.
- 21. Characteristics: The spheroidizing element when added to melt element sul-phur and oxygen which change solidification characteristics and possibility account for the nodulization. It possesses damping capacity intermediate between cast iron and steel. It possesses excellent cast ability and wear resistance The properties of S.G cast iron depend upon the metal composition and cooling rate
- 22. Paper industry machinery. Internal combustion engine. Power transmission equipment. Farm implements and tractor. Valve and fitting. Steel mill rolls and roll equipment. Pipes. Pumps and compressor. Construction machinary. 22
- 23. Nodular cast iron showing grephite nodule surrounded by ferrite 23
- 24. 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. 24
- 25. 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 25
- 26. Graphite in nodular form Produced by heat treatment of white cast iron Graphite nodules are irregular clusters Similar properties to ductile iron 26
- 27. Malleable cast iron is one which can be rolled and hammered to obtain different shapes. Produced by heat treatment of hard and brittle white cast iron. Malleable cast iron possesses high yield strength. It has solidification range 2550 – 2065 f. Malleable cast iron contain 2 – 3 % C 0.15 % P 0.6 – 1.3 % Si 0.10 % S 0.2 – 0.6 % Mn 27
- 28. It has low to moderate cost. It has shrinkage of 3/16 inch per foot. It possesses good wear resistance. It possesses good vibration damping capacity. It has low Coefficient thermal expansion. 28
- 29. Similar to ductile iron Good shock resistance Good ductility Good machineability 29
- 30. 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, crank shaft Steering components, transmission and differential parts, connecting rods Railway components Electrical line hardware Conveyor chain links Agricultural implements Pipe fittings AS3673 30
- 31. Malleable cast iron showing ferrite matrix and temper carbon only 31
- 32. Alloying elements improve the mechanical properties of an iron, by: • Refining the grain size. • Stabilising hard carbides. • Producing cast irons with a martensitic or austenitic structure. 1 Nickel: Graphitizing effect on cementite (tends to grey iron). Refines grains for heavy sections – improving toughness. 2 Chromium: Forms chromium carbide (harder than cementite). Wear resistance. Less susceptible to cementite 'growth‘. 3 Molybdenum: Increases hardness and toughness of thick sections. 4 Vanadium: Increases strength and hardness. Better heat-resistance by stabilising carbides so that they do not decompose on heating. 5 Copper: Not much solubility but resists rusting 32
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