Characterization of hardened cylindrical C1018 steel rods (0.14%-0.2% C, 0.6%-0.9% Mn) using photothermal radiometry.

Frequency-domain photothermal radiometry has been used for the evaluation of the hardened case depth and the measurement of the thermophysical properties (thermal conductivity and diffusivity) of cylindrical C1018 heat-treated steel rods. The measurement results of several steel cylinders nominally hardened identically during a common heat-treating process were consistent with each other and also with mechanical indentation hardness test results. The application of the two-layer composite cylinder thermal-wave theory yielded an effective case depth within the discrete two-layer thermal-wave approximation. This technique provides a relatively simple noncontact and nondestructive method for evaluating the thermophysical parameters of layered cylindrical samples. The good fit of the experimental frequency scans to the two-layer thermal-wave model was shown to constitute a reasonable method for calibrating actual continuously decreasing hardness depth profiles by means of abrupt two-layer-equivalent profiles.