Piano wire (carbon wire) is a high-strength, high-elasticity wire material manufactured from high-carbon steel through a cold drawing process. Possessing excellent tensile strength and fatigue resistance, it exhibits high spring characteristics and is therefore widely used in applications requiring precise elasticity. Its main applications are diverse, including valve springs and seat springs in automotive parts, compression, tension, and torsion springs in various industrial machinery, wire ropes, PC steel wire, and piano strings for musical instruments. Processing methods include wire diameter adjustment and strength improvement through cold drawing, coil forming using spring forming machines, and, as needed, heat treatment for stress relief and surface treatment for rust prevention. Due to its characteristics, it is an indispensable material for products requiring high reliability and durability.