Spring steels feature the unique characteristic of being able to withstand considerable twisting or bending forces without any distortion. Products made from these steels can be bent, compressed, extended, or twisted continuously, and they will return to their original shape without suffering any deformation. This characteristic is defined as high yield strength and is the result of the specific composition and hardening of the steel alloy.
Achieving a high yield strength can be achieved through either hardening by heat treatment or through work hardening.
Hardening and Tempering
Most spring steels are manufactured by heat treatment from medium to high carbon steels, and alloyed carbon steels. A minimum percentage of carbon is required to facilitate this process and whilst grades with upwards 0.25% carbon will respond to heat treatment, carbon springs steels more typically start with 0.50% carbon through to 1.25%. Additional elements including silicon, manganese and chromium also have an impact on a steels response to heat treatment. Whilst basically hardening the steel is achieved by heating and quenching, this process does cause the steel to become brittle and a key part of the overall process is tempering, which is performed after quenching and used to relieve stresses and to achieve more controlled tensile strengths. Spring steel in the hardened and tempered condition is used mainly for the production of flat springs, blades and saws, and is it very difficult to form.
Work hardening is mainly used with the austenitic stainless grades, mainly 1.4310 (301), or to a lesser degree with 304. The hardening is achieved by rolling and reducing the thickness. This increases the tensile strength of the material. Greater reductions result is higher tensile strengths. If the tensile strength is pushed too high then the material becomes brittle and prone to breaking. Typically the best range is achieved between 1200 and 1500 n/mm² although higher tensile strengths are used in some applications.
One great benefit of stainless spring steels is that they can be used to form components without the need to heat treat afterwards, which enables manufacturers without heat treatment facilities to produce in house.
BSS stock 301 spring temper stainless in a wide range of thicknesses, with sheets available for same day despatch, or slit from coil.
Carbon spring steels are also available in the annealed condition. Annealing is a process that is undertaken after the rolling of steel to soften the steel and make it more malleable to facilitate forming.