Microstructural Evolution during Induction Hardening Heat Treatment of a Vanadium Microalloyed Steel

Abstract

The microstructural evolution during induction heat treatment applied to a forged 0.1 wt. % V microalloyed steel has been investigated. The study examined both as-forged and forged plus normalized starting microstructures. The core of the as-forged steel was comprised of ferrite and pearlite. The prior austenite grain size was about 150 μm and only a faint indication of banding was observed. After normalizing the ferrite/pearlite microstructure was refined. The prior austenite grain size was reduced to 10 μm and banding became more evident. During induction heating, the banded appearance persisted in all but the extreme outer portion of the surface layer that underwent austenitization. Banding was more apparent in the as-forged steel after induction hardening. The austenite average grain sizes developed in both the as-forged and forged and normalized steels after induction hardening were less than 20 μm. High levels of compressive residual stresses were measured in the hardened outer surface layer using an x-ray diffraction technique. Residual stress relaxation due to the application of cycling loading will be discussed.