Q1: Lead is poured into the joint between two __________ pipes.

ANS:C - cast iron

Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. It is a versatile and widely used material known for its excellent castability, good machinability, and relatively low cost. Cast iron typically contains other elements such as silicon, manganese, sulfur, and phosphorus, which contribute to its properties. There are several types of cast iron, including:

1. Gray Cast Iron: This is the most common type of cast iron, characterized by its gray color and graphite flakes distributed throughout the matrix. The presence of graphite flakes provides good machinability but reduces its strength and ductility. Gray cast iron is often used in applications where strength and impact resistance are not critical, such as engine blocks, cylinder heads, and machinery parts.
2. White Cast Iron: White cast iron has a white, crystalline fracture surface due to the absence of graphite. It contains mostly cementite (iron carbide) in its microstructure, making it extremely hard and brittle. White cast iron is used in applications requiring wear resistance, such as grinding balls, rolls for crushing grains, and certain types of wear-resistant parts.
3. Ductile Cast Iron (Nodular Cast Iron): Ductile cast iron contains spherical graphite nodules instead of flakes, which improve its ductility and toughness compared to gray cast iron. It offers a good balance of strength, toughness, and wear resistance, making it suitable for a wide range of applications, including automotive components, gears, and pipes.
4. Malleable Cast Iron: Malleable cast iron is produced by heat treating white cast iron, causing the carbon to form irregular-shaped graphite nodules. This process imparts improved ductility and toughness to the material, allowing it to be bent, stretched, or formed without fracturing. Malleable cast iron is used in applications where some deformation is required, such as pipe fittings, agricultural equipment, and hand tools.

Cast iron is valued for its ability to be cast into complex shapes and its excellent damping capacity, which makes it suitable for applications where vibration absorption is necessary. However, its relatively high brittleness and susceptibility to cracking under tensile loading limit its use in structural applications where high strength and toughness are required.