Quantitative non-destructive single-frequency thermal-wave-radar imaging of case depths in hardened steels.

Single-frequency thermal-wave radar (SF-TWR) imaging was used to produce dynamic images of effective case depths from phase image frequency scans in AISI 9310 and Pyrowear 53 steels. SF-TWR, as a fast non-destructive testing technique, was also compared with conventional photothermal radiometry measurements in these two types of steel samples using a three-layer theoretical thermal-wave model. In this paper, a novel approach of SF-TWR imaging, combining a three-distinct-layer thermal-wave model and radial phase profiles to image mean value case depths and their lateral non-uniform distributions, yielded quantitative images of case depths in the two hardened steels and exhibited very good correlation with standard Vickers measurements. The SF-TWR images further revealed strong inhomogeneities in the case depth thickness profiles to be used as important feedback to the heat treating manufacturing industry toward the optimization of their case depth hardening process. [ABSTRACT FROM AUTHOR]