| The focus of the presented research is the application of photothermal radiometry to hardness testing and case hardening monitoring of steel. 3-D frequency scan results along the end quenched Jominy bar AISI 8620 and 1018 are presented. The hardness profiles from mechanical hardness testing are compared with thermal diffusivity depth profiles, which are obtained by numerical fitting frequency responses, and the responses of several identical frequencies along the bar. 1-D frequency scans are performed on carbonitrided and quenched AISI 1018 samples. Radial line scan and 2-D lateral surface mapping are presented as techniques to select homogeneous samples. The comparisons of thermal diffusivity depth profiles with microhardness depth profiles show that there is a general anticorrelation between thermal diffusivity and hardness, but not perfect anticorrelation. The possibility of the industrial application of PTR case hardening testing and heat treatment monitoring without thermal diffusivity depth profile reconstruction is discussed. |
