Torsional Delayed Fracture Properties of Induction Heating Quenched and Tempered Spring Steel Wire

Abstract

High strength spring steel wire is intensely required for weight saving of coil spring. Induction hardening (quenching & tempering) gives higher strength and stable quality to the spring wire effectively. Generally, higher strength steel becomes more sensitive to hydrogen embrittlement. Relationship between austenite grain size and hydrogen embrittlement is not clear down to date. In this paper, a delayed fracture test under torsional load and a measurement of diffusible hydrogen were carried out using ITW^® Induction heating quenched and Tempered Wire with various austenite grain size and various tensile strength. It was revealed that delayed fracture properties were improved by refining of austenite grain size. Improvement was even recognized in super high strength ITW^® over 2160N/mm² grade.