cast iron

Engineering Metalurgy

1. CAST IRON FERROUS ALLOY It’s a eutectic alloy

2. COMPOSITION GREATER Than 2 % of carbon And also Small amounts of ALLOYING ELEMENTS (Silicon, Sulphur, Manganese and phosphorus). Cast irons are least expensive of all metals . Because of plenty of resource available. Molten cast iron can be cast in to any complex shapes and can be easily machined.

3. Composition of cast iron Carbon- 3.0 - 4.0% Silicon- 1.0% - 3.0% Manganese- 0.5% - 1.0% Sulphur and phosphorus- up to 1.0%

4. Cast iron Features Most widely used cheap metal Using casting methods we can produce complicated shapes .( Easy Castability) Easy to machine . Good mechanical rigidity Good strength in compression Example --- spheroidal graphite iron are strong , malleable cast irons are tough

5. Uses (VALVES)

6. Uses (Engine cylinder bore)

7. Effect of composition elements on Cast Iron 1. CARBON ( 3 – 4 %) Its present in the form of flakes of Graphite or cementite ( i.e. brittle iron carbide) Note When the cast iron having cementite Structure --- results poor mechanical property . so for application point of view its require to have carbon in the form of flakes of graphite .

8. 1.carbon If the iron having more cementite, it looks silvery white in the broken area . ( cementite is a silvery white component) We call it as white cast iron I f the iron having the presence of flakes of graphite the broken area looks grey colour --- this is called as grey cast iron

9. 2.Silicon This will some extent governs the form in which carbon is present in cast iron. Silicon causes cementite (unstable), so that it decomposes , thus releasing free graphite . Therefore high silicon iron tends to be a grey iron , whilst a low silicon iron tends to be a white iron.

10. 3.Sulphur Sulphur tends to stabilize cementite. Thus helps to produce white iron . It gives brittleness property to iron , so we have to keep this percentage as low.

11. 4.Manganese It gives toughness and strength to iron. It also control the harmful effect(Reactions ) of sulphur in metal

12. 5.Phosphorus It gives the property of fluidity (in melting ) for cast iron. It also give brittleness like sulphur . For that we have minimize the percentage level.

13. Factors affecting properties of cast iron Cooling rate Heat treatment Presence of elements

14. FACTOR -1------------COOLING RATE Slow cooling results grey cast iron Fast cooling results white cast iron

15. FACTOR -2----------Heat treatment Prolonged heating ( 700 degree celcius ) of white cast iron causes graphitization to occur. The cementite decomposes into ferrite and graphite during heating upto 700 degree celcius . This decomposed ferrite and cementite will occupy more space than the original cementite.

16. FACTOR -3 -------------ELEMENTS SILICON Highest percentage of silicon in iron results grey cast iron structure. Low percentage of silicon results white cast iron.

17. TYPES OF CAST IRON Alloy cast iron --- ( Special Purpose) Grey cast iron --- (General Purpose) White cast iron – ( Heat and wear resistant) Malleable cast iron-- ( Heat treated for ductility) Spheroidal Graphite cast iron – -(some ductility)

18. GREY CAST IRON Least Expensensive Most commonly used It is an alloy of carbon and silicon with iron . Composition: Carbon - 2.5 – 4 % Manganese – 0.4 – 1% Sulphur – 0.02 – 0.15% Silicon – 1 – 3 % Phosphorus – 0.15 – 1 % Remaining iron

19. Grey Cast iron Its Consists of graphite flakes ( like potato Chips) Graphite flakes are surrounded by alpha ferrite or pearlite matrix. Because of graphite it shows grey in colour These flakes not having much strength --- this lead to crack formation in edges and brittleness. The shape, size and distribution of flakes decide the property of grey cast iron.

20. Characteristics Good strength Excellent compressive strength Good torsional and shear strengths Good corrosion resistance Excellent fluidity Good wear resistance Excellent Machinability Good vibration damping capacity

21. Applications of Grey cast iron USED IN Machine tool bodies Engine blocks Engine cylinders Brake drums Crank shaft Pipe and pipe fittings Rolling mills Agriculture appliances

22. White cast iron White cast iron derives its names fact that fracture surface has a white or silvery appearance White iron combined with cementite . The broken cast iron area looks like silvery white . When the cooling is fast ----- Carbon content changes to cementite results white cast iron

23. composition Carbon --- 1.8 – 3 % Silicon ---- 0.5 – 1.9 % Manganese – 0.25 – 0.8 % Phosphorus – 0.05 – 0.2 % Sulphur ------- 0.1 – 0.3 % Remaining is a iron

24. Microstructure Cementite is caused by quick cooling of molten iron it produces White cast iron is very hard and brittle. RAPIDLY COOLED FROM THE CASTING TEMPERATURE The Cast iron is termed as “ CHILLED IRON”

25. Characteristics of white cast iron Very hard and brittle Very high resistance to abrasion High tensile strength and low compressive strength Cannot be machined because its hard.

26. Applications of white cast iron White cast iron is Used as a raw material in the production of malleable cast iron. Used in rolls, wear plates(brakes), pump linings, balls Used in outer surface for car wheels.

27. MALLEABLE CAST IRON and its MICROSTRUCTURE By heat treating the white cast iron we get malleable cast iron. For having malleable and ductile property . During heat treatment the cementite breaks into ferrite and graphite nodules. The graphite nodules called as tempered carbon-- it appears like popcorn. This rounded graphite permits a good combination of strength and ductility

28. Composition Carbon --- 2 – 3% Silicon ----- 0.6 – 1.3% Manganese --- 0.2 – 0.6% Sulphur ------ 0.1 % Phosphorus – 0.15% Remaining iron

29. Types of Malleable irons Ferritic malleable iron, Pearlitic malleable iron

30. 1. Ferritic Malleable cast iron Here the white iron is heated up to upper critical (815 ͦc to 1230 ͦc) temperature and hold it for prolonged time, so carbon in the cementite converts in to graphite. Subsequently the low cooling through the eutectoid reaction results in a ferritic matrix Finally the cast iron obtained is called ferritic malleable cast iron.

31. 2.Pearlitic Malleable cast iron The Rapid cooling of molten white cast iron in eutectoid transformation range results pearlitic matrix. This is due in fast cooling , the carbon in austenite will have not enough time to form additional graphite. So its retained in the pearlite matrix CHARACTERISTICS: It has higher strength and Lower ductility

32. CHARACTERISTICS OF MALLEABLE CAST IRON Good ductility and malleability than grey cast iron High yield and tensile strength Its not brittle as grey cast iron High young’s modulus and low co-efficient of expansion Excellent impact strength Good wear resistant Good vibration damping capacity Excellent machinability

33. Applications of Malleable cast iron USED IN Due to their Castability , machinability and shock resistance it Most widely used in automobile industries In brake shoe Wheel hub Axle housing Transmission gears Connecting rod Levers Pipe fittings Agriculture machineries and parts Switch gear equipments

34. SPHEROIDAL GRAPHITE OR NODULAR CAST IRON Its also called ductility cast iron In the grey cast iron they are adding magnesium or cerium This magnesium converts flakes graphite into perfect nodules. This perfect nodules improves the ductility of the cast iron. (nearly 20 % increased)

35. Characteristics of spheroidal graphite cast iron Excellent ductility Good toughness than grey cast iron Good fatigue strength Good impact strength Good hardness High modulus of elasticity Good wear resistance Good machinability Good oxidation resistant Excellent castability

36. Applications Used in Valves Pump bodies Crank shaft , Pinion and gears Rollers Rocker arm Flanges Power transmission equipments Earth moving machineries