Pulsed eddy currents (PEC) method can be easily applied to ADI materials in a differential mode using a reference specimen. In the case of Austempered Ductile Iron (ADI), the study has been conducted on bars with different heat treatment conditions. The magnitude of the resulting differential signal appears as the most significant parameter, which is clearly sensitive to heat treatment conditions. This parameter is not unique for various combinations of austenitisation temperature, austempering temperature and time. However, for a given composition PEC may be used to sort real parts, provided a reference specimen representative of the required microstructure state is available. The resulting differential signal would then be a good indicator of wrong treatment conditions. Especially, the results show that this parameter is expected to increase markedly for too long austempering times.
Previously, Pulsed Eddy Currents had been used mostly for flaw detection. This work shows that the PEC response is sensitive enough to ADI microstructure state to be used as a non-destructive characterisation tool. However, it should be noted that, in contrast to Barkhausen noise, PEC provide global information, i.e. averaged over the various constituents of ADI. So the exploitable result arising from the project consists of a potential application of PEC differential measurements for ADI characterisation. However, considering the appropriate equipment well adapted for a practical application in industrial conditions (especially, a hand held probe is required), complementary studies remain to be carried out.