Spring steel is a low alloy, medium carbon steel with a very high yield strength. This allows objects made of spring steel to return to their original shape despite significant bending or twisting.

Silicon is the key component to most spring steel alloys. An example of a spring steel used for cars would be AISI 9255 (DIN and UNI: 55Si7, AFNOR 55S7), containing 1.50%-1.80% silicon, 0.70%-1.00% manganese and 0.52%-0.60% carbon.

Most spring steels (as used in cars) are hardened and then tempered to about 45 on the Rockwell C-Scale.