We have shown that samples with a seemingly normal case depth can have mechanical (and therefore magnetic) properties that will lead to inaccurate NDE measurements. One of the underlying problems here is in the rather loose definition of case depth. If one is to tie NDE results in with the properties of the case-hardened steel being measured then, as a bare minimum, we require values for the surface hardness, substrate hardness and parameters describing the functional form at any point in between. By parameterizing the hardness profile it is possible to tie up certain measurements with individual hardness parameters. For example, the RMS Barkhausen signal is strongly related to surface hardness. Once we have measurements that can be used to predict the true mechanical properties of a steel sample it should be a simple matter to then calculate case-depth according to the standard definitions.
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