Abstract
In this work we present a new method, based on the photothermal deflection technique, which permits the simultaneous determination of thermal conductivity and thermal diffusivity of steel undergoing a heat treatment (carburizing, nutriding, electroerosion, Jominy test). This method consists of the deposition of a thin graphite layer on the treated surface steel which will absorb the totality of the incident light and will play the role of a heat source. The local thermal properties of hardened steel are determined by drawing the experimental amplitude and phase curves of the photothermal signal versus square root modulation frequency and to compare them to the corresponding theoretical ones. The best coincidence between these curves is obtained for a unique and known thermal diffusivity and thermal conductivity. The main interest of this method is that such obtained thermal properties are correlated to hardness. In some cases, the thermal properties are related to hardness through an empiric mathematical law which permits us to deduce the hardness of steel without measuring it.