A quantitative alternative to the Vickers hardness test based on a correlation between thermal diffusivity and hardness—applications to laser-hardened carburized steel

A quantitative non-destructive test technique for characterizing heat treated steel based on a theoretical model was developed and verified by experiments using the optical beam deflection technique at metallic samples, heated by a Gaussian beam. The analytic solution of the heat equation with appropriate approximations provides a theoretical expression of the surface temperature, which is an important guide to optimize the experimental process. Measurements have been focused on determining both, mechanical parameters and thermal local properties, in order to find correlations. The theoretically described thermal diffusivity was experimentally measured by using the new developed photo-thermal deflexion inversion procedure. A simple correlation between the micro-hardness according to Vickers and the thermal diffusivity was found for laser-hardened specimens depending on their microstructure and individual chemical composition.