Spring steel is a low-alloy, medium- or high-carbon steel with an incredibly high yield strength. This allows it to be flexed or bent and return to its original shape.
Spring steel is, as its name implies, perfect for springs. Because springs are made to be pushed and flexed, a metal with lower yield strength loses shape and ceases to function as a spring. Spring steel is also commonly used for prop swords, lockpicks and aircraft landing gear. The most widely used spring steel incorporates nickel as a part of the alloy and is used as music wire for pianos, guitars and other instruments.