Cast iron is made by smelting iron-carbon alloys with a carbon content of more than 2%. The metal is poured into a mold after it has been smelted. Cast iron’s excellent castability is due to a combination of high carbon content and the presence of silicon. Cast irons consist of 4 types: white cast iron, gray cast iron, ductile iron, and malleable cast iron. They are manufactured using various heat treatment and processing techniques.
White Cast Iron
- Composition: 1,75-2,3% C; 0,05-1,2% Si; 0,1-0,4% Mn; 0,12-0,35% S; 0,05-0,2% P.
- Microstructure consists of pearlite and cementite, cementite makes up the matrix
- The fracture surface is white
- Very hard, brittle, and difficult to machine
- Resistant to wear and corrosion
- Hardness: 350-650 BHN and almost no elongation
- Has a specific gravity of 7.25 kg/dm3 and a melting point of 1150-1250°C.
Applications
The chilling process used to produce white cast iron produces a brittle material that is highly resistant to wear and abrasion. As a result, it is used in the manufacture of mill linings, railroad brake shoes, shot-blasting nozzles, rolling mill rolls, slurry pump housings, and crushers.
Ni-Hard Iron is primarily used for mixer paddles, ball mill liner plates, augers and dies, coal chutes, and wire guides for drawing wires.
Gray Cast Iron
- Composition: 2,5-3,75% C; 1-2,5% Si; 0,4-1% Mn; 0,05-0,1% S; 0,1-1% P
- The microstructure is composed of ferrite + pearlite + C (graphite in the form of “flakes,” and the matrix is composed of ferrite or pearlite.
- The fracture surface is gray.
- Has poor mechanical properties and is brittle when subjected to tensile loads but strong and ductile when subjected to compressive loads.
- At casting temperatures, it has high fluidity/flowability, and gray cast iron shrinks slowly.
- Capable of dampening high vibrations, storing heat, and not wearing out easily.
Applications
Gray cast iron is used to make engine blocks and cylinder heads, manhole covers, gratings, garden benches, and outdoor furniture.
Ductile Iron
- Also known as nodular cast iron
- Composition: 3,2-4,2% C; 1-4 % Si; 0,5-1% Mn; 0,1-1% Mg; 0-3,5% Ni
- Microstructure: pearlite + graphite (if moderately cooling); ferrite + graphite (if slow cooling)
- It has mechanical properties similar to steel and is stronger and more ductile than gray cast iron.
Applications
Ductile cast iron is used to make steering knuckles, crankshafts, heavy-duty gears, hydraulic components, and heavy-duty drainage covers (manhole covers and gratings).
Malleable Cast Iron
- Microstructure: pearlite + graphite (if fast cooling); ferrite + graphite (if slow cooling)
- Graphite shape: “cluster or rosset”
- High strength, ductility, and malleability.
Applications
Malleable cast iron is used for heavy-duty bearing surfaces, sprockets, chains, connecting rods, railroad rolling stock, drive train and axle components, and farm and construction machinery.