ANS:B - cast iron

Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. It is characterized by its relatively low melting point, good fluidity when molten, excellent castability, and high damping capacity. Here are some key points about cast iron:

1. Composition: Cast iron typically contains 2% to 4% carbon, along with silicon, manganese, sulfur, and phosphorus. The presence of carbon in the form of graphite flakes or nodules gives cast iron its distinctive properties.
2. Types: There are several types of cast iron, including gray cast iron, white cast iron, ductile cast iron (also known as nodular cast iron), and malleable cast iron. Each type has unique properties and applications.
3. Properties:
   • Gray Cast Iron: Contains graphite flakes, which provide good machinability, damping capacity, and thermal conductivity. It is commonly used for engine blocks, cylinder heads, and machine tool structures.
   • White Cast Iron: Contains cementite (iron carbide), which makes it hard and brittle. It is used for applications requiring wear resistance, such as grinding balls and mill liners.
   • Ductile Cast Iron: Contains nodular graphite, which improves ductility and toughness compared to gray iron. It has applications in automotive components, pipes, and gears.
   • Malleable Cast Iron: Heat-treated white cast iron that has been annealed to convert cementite into graphite nodules. It combines good ductility with moderate strength and is used for fittings and small parts.
4. Applications: Cast iron is used in a wide range of applications due to its versatility and cost-effectiveness. Common applications include automotive parts (engine blocks, brake discs), pipes and fittings, machinery components (pulleys, gears), cookware, and architectural elements (railings, ornamental castings).
5. Processing: Cast iron is typically produced by melting scrap iron and steel in a furnace and then pouring the molten metal into molds. The cooling rate and alloy composition determine the microstructure and properties of the final casting.