I am looking for data on initial permeability of some common steels(e.g. AISI 420, UNI 100Cr6 equiv to AISI 52100)

By initial permeability (the term was new to me), I mean the low field limit of the relative (dimensionless) magnetic permeability, not the max DC permeability.  The initial permeability of the material is that which is probed by eddy current testing and metal detection (in low kHz to MHz freq range).

I would assume that for the materials above, the value is of the order 100.  I would like to know how the initial permeabilities for these two materials differ and what % variation from nominal could be expected between batches of balls of these steels.