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The mechanical strength for spring applications is obtained by cold working the austenitic and ferritic steel types, as they are not hardenable by conventional heat treatments.
The austenitics are a better choice for higher strengths as they respond more to cold work than ferritics. The austenitic 1.4310 will respond more to cold work than grade 1.4301, due to its lower nickel content.
The martensitic and precipitation hardening steels are heat treated to obtain their spring properties. After forming, the heat treatment processes are similar to those for other product types made from these steels.
BS EN 10151 provides an excellent review of the features of the various grades in Table A.1. Additional information on hardness ranges, elongation minima at the various tensile strength levels and moduli of elasticity are given in the standard.
BEN 10270-3 shows elastic and calculated shear (torsional) moduli in both delivery and heat-treated conditions for the three grades in the standard.
Both standards show heat treatments for all grade types to enhance their proof and tensile strengths. This includes the austenitics, which can be ‘tempered’ in the range of 250 / 425ºC, 30 minutes to 4 hours for wire and 250/450ºC, 30 minutes to 24 hours for strip.
BS EN 10151 has graphs showing the increase in tensile strength range, depending on the initial strip cold rolled strength in Figures A.1, A.2 and A.3. BS EN 10270-3 shows the increase in tensile strength range for each wire grade as a function of wire diameter.
The expert body on spring materials is the Institute of Spring Technology,