At the IFW a micromagnetic system is used to characterize the surface integrity state of casehardened workpieces after external grinding. The grinding process is performed with corundum grinding wheels of different specification by using varying cutting speeds and material removal rates. This variation results in faultless workpieces as well as workpieces with increasing damage. The respective surface integrity state is documented by laboratory measurements such as X-ray diffraction and metallographical inspection.

The micromagnetic measurement is done withe a sensor prototype using two independent receivers, a coil to detect the Barkhausen noise and a Hall-element to measure the tangential magnetization field. With two quantities deduced from these receivers, the enclosed area A_MH and the distortion factor K, a characterization of the surface integrity state is possible even under variation of the retained austenite content of the case-hardened workpieces due to different heat treatment. A classification in three ranges is achieved. Besides faultless workpieces and definitely damaged parts a transition area can be found. A decision whether parts with this result can be accepted or have to be rejected depends on the later use.

The developed classification system can be adapted to varying case-hardening depths without changing the thresholds of the different ranges. The correlation of the micromagnetic result to the X-Ray calculated residual stress state is possible within a few seconds and thus this technology can be installed in the production line as a very fast quality control test after grinding.