A major challenge in automotive industry when producing heat treated engine parts is achievement of necessary material properties for a given component to withstand loads during its use. Critical properties involve correct microstructure and hardening depth which is essential to verify from manufacturing.

Today this is solely done by destructive testing where manufactured parts are sectioned to smaller pieces and the properties is verified relative the operational window of the process. For the case of camshafts this is necessary every time the production is reset from one type to another or other planned or un-planned interruptions. The verification process is very costly, since production stands still.

The need for non-destructive alternatives is therefore obvious and prior investigations has shown great potential in both the Barkhausen noise (BN) and Ultrasonic testing (UT) methods. Recent research has also advanced the analysing methodology of the response signal for sub-surface microstructural characterization and case depth measurements. BN is well known of its sensitivity to microstructure and UT is also known to be effective for material characterization. One major difference between the two technologies is the sensitivity range (analysing depth) under the surface of the material to be characterized. Traditional BN is only effective within few tenths of millimetres from the surface while UT is sensitive to both surface and sub-surface characteristics of the material depending on the configuration.

The major motive in this investigation has been to compare the two methods and to investigate if a combination of these methods could be used for assessment of the hardening depth of induction hardened steels for the depth interval 2-7 mm. This is a typical depth range when manufacturing induction hardened cam shafts within the heavy automotive industry.

In the present investigation cylindrical steel specimens of grade C45 was induction hardened to generate different hardness depths. The heat treatment was performed in an induction hardening equipment by alternating the scanning speed and power. The produced specimens had hardness depth in the range 2-7 mm and was evaluated with by BN and UT measurements, independently, followed by destructive verification of the material properties.

The results show a potential for both BN and UT to measure the hardening depth down to 4 mm. It was further shown that several BN parameters correlate with the hardening depth indicating that a combination of different parameters may be used for assessment using a triangulation approach.