The phase transformation model is coupled with the inverse heat conduction problem (IHCP) to estimate the steel/quenchant interfacial heat flux. Cylindrical steel probes having section thicknesses 25 and 50mm, respectively, and lengths 30mm were made from medium and high carbon steels (AISI 1045 and 52100). The probes were quenched in mineral, neem, and sunflower oils. The cooling curves at the centre and near the surface of steel probes were recorded. The near-surface cooling curve was used as a reference temperature data in the IHCP algorithm for the estimation of surface heat flux, whereas the cooling curve at the centre was used as the boundary condition of the axisymmetric model of the probe. The effect of phase transformation on the metal/quenchant interfacial heat flux was indicated by a kink and rise of heat flux. The increase in the section thickness of the probe from 25 to 50mm decreased the magnitude of the heat flux. Increasing section thickness increases the phase transformation, increasing the resistance to heat flow at the metal/quenchant interface.

The cooling behavior of neem and mineral oil was obtained using instrumented ISO 9950 Inconel probe. Flash, fire points and the viscosity of quenching media were measured. These oils were used to quench harden AISI 1045 and AISI 1090 grade steel probes of section diameters 25 and 50 mm. (The top and bottom faces of steel probes were coated with insulating paste to minimize end effects of heat transfer during quenching.) The measured temperature data in steel probes were used to estimate spatiotemporal heat flux by solving inverse heat conduction problem at the interface of the probe/quenching medium. The estimated heat flux transients, microstructure, and hardness measurements were found to be similar for both oils indicating the potential application of neem oil as quenchant for heat treatment of steels.