Properties of Induction Heat-treated High Strength Spring Wire

Abstract

Induction heat-treatment technique has been applied to develop a new high strength Si-Cr steel (SAE 9254) spring wire. The features of this technique are : (1) uniform heating (by rapid heating and holding) and (2) short heating time.
The induction-heating, quenched and tempered wires (ITW) with diameter of 12 mm show fine micro structure, fine austenite grains and less decarburization. The ITW have very high tensile strength from 1 770 to 2 060 MPa, and also show high ductility and toughness. These properties are attributed to their fine microstructure and non-equilibrium tempering effect with short induction heating time for tempering, and provide excellent cold formability.
Coil springs cold-coiled from the ITW possess sufficient sag resistance and fatigue life. As no decrease in fatigue life is observed even at such high strengths, advantage can be taken of the fact that sag resistance rises with the increase in tensile strength. Since maximum stress of coil spring can be raised by using the ITW, considerable weight saving becomes possible.