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.
Alloying elements that help stabilize the austenitic phase reduce the tendency of the austenitic stainless steels to work harden. Nickel additions have been used traditionally to do this, but nitrogen also has a profound affect on stability of the austenite phase.
Austenitic stainless steels are generally non-magnetic with magnetic permeabilities of around 1.0. Permeabilities above 1.0 are associated with the amount of either ferrite or martensite phases present in the 'austenitic' steel and so depend on: