Measurement of hardening depth using ultrasonic backscattering

Induction hardening is a well established technique to improve the resistance of components against loading, and to protect the surface against wear. At the moment, a quality assurance of the hardening process can only be ascertained by random testing, using destructive measures which are time consuming and costly. The using of the ultrasonic backscattering offers a powerful tool for the non-destructive determination of hardening depth in induction hardened components. It allows one to measure the depth of the heat affected zone which in many cases directly corresponds to the hardening depth as measured destructively. The technique can be applied to hardening depths in the range >_1mm, the typical measuring accuracy +-0,2 mm, no special presentation of the results is performed in realtime by means of a PC. In the article, the principles of the technique and the set-up of the system are described.