Suitability of different micromagnetic measurement methods for the detection of thermo-mechanical surface damages from grinding

Grinding of hardened components always bears the risk of detrimental thermo-mechanical modifications in the surface/sub-surface region. For the non-destructive detection of these damages also known as grinding burns, micromagnetic methods have found increasing interest. Existing studies on the detectability of grinding burn by Barkhausen noise evaluation point out the need for a combination of different characteristic values to distinguish between damage-free surfaces and different pronounced damages. Besides Barkhausen noise, the 3MA-II-method offers three additional measurement techniques that were also investigated in this study. Results show the potential of a combination of Incremental permeability and Harmonic analysis for the detection and distinction of different classes of grinding damages. On the other hand, no clear definition exists to categorize different levels of damages. The classification provided by the observed grey-scale after nital etching is often used, which is rather subjective and cannot be quantitatively described in terms of surface-near properties. Therefore, the present study gives a new attempt to define a parameter that describes quantitatively the existing surface state and its level of damage based on X-ray diffraction analysis. It describes the surface state characterized by the peak width, related to hardness and residual stresses in one single parameter. The investigations show that this approach could be validated for different workpieces and heat treatment conditions, and could allow a quantitative classification of damages thus making non-destructive analysis easier to apply.