The main properties of a spring steel are those of bearing an intermittent load, accumulating energy and measuring forces.
It must have an elastic deformation without plastic alteration, so the yielding unit load shall be elevated and this is achieved after an adequate quenching and tempering.
Spring steels must have an elevated hardenability, verified with the Jominy hardenability that allows to calculate martensite at heart that you can obtain, which has to be at least 80%.
In order to get a better elasticity and a high elastic limit, spring steels must have a fine grain to be less sensible to overheating.
They must have an elevated tensile strength and fatigue strength, combined with plastic reserve, consequently toughness is diminished.
Inclusions and superficial defects have to remain within restricted limits. Steels with SI, CR and NI have an elevated elastic limit and a great hardenability. They are employed for springs and twist bars.
Spring steels (UNI 3545)
|52SiCrNi5 spheroidal annealed