Generally, reasonable amounts of austenite are retained in steels and cast irons containing alloying elements during the hardening process. It is very important to estimate the amount of retained austenite (Vγ) in alloyed cast iron, because the retained austenite leads to fracture or deformation of cast iron products during servicing. In the case of alloyed white cast iron, since the carbides coexist in the matrix, it is difficult to measure the Vγ precisely. It is known that the permeability and conductivity of the cast iron decrease proportionately to the amount of retained austenite because the retained austenite is nonmagnetic. Therefore, it may be possible to estimate Vγ in the cast iron by measuring the change in electromagnetic properties of the cast iron using electromagnetic nondestructive inspection method.
  In this study, a small sensor which can nondestructively detect changes in magnetic properties of high chromium white cast iron was developed. Results of experiments conducted clarified that Vγ in the cast iron can be estimated by measuring the attenuation rate of magnetic flux density.

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