Piston compression rings are made of cast iron.

Explanation:
- Cast iron is the most commonly used material for piston compression rings in internal combustion engines.
- Cast iron has several properties that make it suitable for this application:
- High strength: Cast iron has good tensile and compressive strength, which allows it to withstand the high pressures and forces experienced during engine operation.
- Wear resistance: Cast iron rings have excellent wear resistance, which is important for maintaining a proper seal between the piston and cylinder wall.
- Heat resistance: Cast iron can withstand the high temperatures generated during engine operation without deforming or losing its structural integrity.
- Self-lubricating: Cast iron rings have a self-lubricating property, which helps reduce friction between the ring and cylinder wall and minimizes wear.
- Cast iron rings are typically made through a process called casting. In this process, molten cast iron is poured into a mold and allowed to solidify into the desired shape. The rings are then machined to the required dimensions and surface finish.
- While cast iron is the most common material for piston compression rings, there are also other materials used in certain applications:
- Steel: Steel rings are sometimes used in high-performance engines where higher strength and reduced weight are desired. Steel rings can withstand higher temperatures and pressures than cast iron rings.
- PVD-coated rings: PVD (Physical Vapor Deposition) coatings can be applied to cast iron rings to improve their wear resistance and reduce friction.
- Overall, the choice of material for piston compression rings depends on various factors such as engine design, operating conditions, and performance requirements. Cast iron remains the most widely used material due to its excellent combination of strength, wear resistance, and heat resistance.