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