Characterization of hardened cylindrical samples using photothermal radiometry

The evaluation of the hardness case depth and the measurement of the thermophysical properties of cylindrical C1018 heat-treated steel rods has been demonstrated. By using a cylindrical two-layer model and a multi-parameter fitting algorithm, the effective case depth and the corresponding thermal conductivity and thermal diffusivity of the hardened layer are obtained for a nominal 0.04′′ case depth hardening. The measurement results from different samples in the same batch of heat treated cylinders are consistent with each other and are also consistent with mechanical indentater test results in the sense of yielding an effective case depth within the discrete two-layer thermal-wave approximation.