Analysis of the Possibility of Plastic Deformation Characterisation in X2CrNi18-9 Steel Using Measurements of Electromagnetic Parameters

An analysis was conducted on the possibility of making an assessment of the degree of plastic deformation epsilon in X2CrNi18-9 steel by measuring three electromagnetic diagnostic signals: the Barkhausen noise features, the impedance components in in-series LCR circuits, and the residual magnetic field components. The impact of epsilon on a series of different extracted features of diagnostic signals was investigated. The occurrence of two regions of sensitivity was found for all the features of the analysed signals. The two regions were separated by the following critical deformation value: epsilon similar to 10% for the components of the residual magnetic field and epsilon similar to 15% for the normalised components of impedance. As for the Barkhausen noise signal, the values were as follows: epsilon similar to 20% for the mean value, epsilon similar to 20% for the peak value of the signal envelope, and epsilon similar to 5% for the total number of the signal events. Metallographic tests were performed, which revealed essential changes in the microstructure of the tested material for the established critical values. The martensite transformation occurring during the plastic deformation process of X2CrNi18-9 austenitic steel process generated a magnetic phase. This magnetic phase was strong enough to relate the strain state to the values of diagnostic signals. The changes in the material electromagnetic properties due to martensitic transformation (gamma -> alpha') began much earlier than indicated by the metallographic testing results.