Spring Steel Review

Engineering Materials

Spring Steel Review and Specifications

Spring steel is generally classified as a low alloy, medium carbon steel or high carbon steel with a very high yield strength. This allows the shaped materialto return to their original shape despite significant bending or twisting.

For small springs, steel is often supplied to spring manufacturers in a form that requires no heat treatment except perhaps a low-temperature anneal to relieve forming strains. Types of previously treated steel wire for small helical springs are music wire which has been given a special heat treatment called patenting and then cold-drawn to develop a high yield strength, hard-drawn wire which is of lower quality than music wire since it is usually made of lower-grade material and is seldom patented, and oil-tempered wire which has been quenched and tempered.

The wire usually has a Brinell hardness between 352 and 415, although this will depend on the application of the spring and the severity of the forming operation. Steel for small flat springs has either been coldrolled or quenched and tempered to a similar hardness.

Steel for both helical and flat springs which is hardened and tempered after forming is usually supplied in an annealed condition. Plain carbon steel is satisfactory for small springs; for large springs it is necessary to use alloy steels such as chrome-vanadium or silicon-manganese steel in order to obtain a uniform structure throughout the cross section. Note that it is especially important for springs that the surface of the steel be free from all defects and decarburization, which lowers fatigue strength.

Common Spring Steel Grades

SAE grade (ASTM grade)	Composition	Yield Strength	Hardness (HRC)	Max. Hardness (HRC)
1074/1075	-	-	44–50	50
1095 (A684)	-	60-75 ksi (413-517MPa)	48-51	59
5160 (A689)	-	-	-	63
9255	-	-	-	-
301 (A666) Spring Tempered Stainless Steel	-	147 ksi (1014 MPa)	-	42