Evaluation of effective case depth in heat treated steel products using photothermal radiometry

A quantitative calibrated methodology based on photothermal radiometric (PTR) depth-profilometry for non-contact, non-intrusive determination of effective case depth in heat treated case-hardened steel products was developed. Several types of heat-treated C1018 industrial steel screw products (with hexa- gonal, cylindrical and spherical heads) were statistically evaluated using the case-depth – induced interferometric thermal-wave phase minima. Calibration curves for each type of sample were established with the help of conventional destructive indenter measurements. It is shown that PTR thermal-wave interferometric phase minima can be used as a fast, on-line inspection methodology of industrial steel products for non-destructive quality control of heat treating processes