Vanadium microalloying additions are common in medium carbon ferrite-pearlite steel shafts. The increased load capacity provided by vanadium carbonitride precipitation is beneficial in many applications. Induction hardening can further increase the surface strength of a component; however, the implications of the vanadium carbonitride precipitates on microstructural evolution during induction hardening are unclear. Evidence that vanadium microalloying influences the microstructural evolution of the induction hardened case as well as the case/core transition regions are presented in the current study. Vanadium increases the amount of non-martensitic transformation products in the case while decreasing austenite formation kinetics in the case/core transition region. Observations in induction-hardened shafts were supported by Gleeble physical simulations of computer simulated thermal profiles. Characterization was conducted using scanning electron microscopy, dilatometry, and microhardness testing.

Microalloying of medium carbon bar steels is a common practice for a number of traditional components; however, use of vanadium microalloyed steels is expanding into applications beyond their original designed use as controlled cooled forged and hot rolled products and into heat treated components. As a result, there is uncertainty regarding the influence of vanadium on the properties of heat treated components, specifically the effect of rapid heat treating such as induction hardening. In the current study, the torsional fatigue behavior of hot rolled and scan induction hardened 1045 and 10V45 bars are examined and evaluated at effective case depths of 25, 32, and 44% of the radius. Torsional fatigue tests were conducted at a stress ratio of 0.1 and shear stress amplitudes of 550, 600, and 650 MPa. Cycles to failure are compared to an empirical model, which accounts for case depth as well as carbon content.