Measurement of the strain induced α'-martensite content by eddy current method in the presence of elastic stresses of austenitic stainless steels

Abstract

The effect of elastic and plastic deformation on the added voltage of eddy current probe under step loading of austenitic steel AISI 321 is investigated. The effect of mechanical stress on the added voltage significantly depends on the amount of residual plastic deformation is shown. This is due to an increase in the volume fraction of the strain induced α'-martensite content. The added voltage decreases at loading in the elastic region. At loading beyond the yield point, the added voltage of eddy current probe increases sharply. Under measuring the strain induced α'-martensite content by eddy current method it is necessary to take into account the influence of mechanical stresses is shown. An algorithm is proposed to reduce the measurement error of the magnetic phase fraction by taking into account the stress-strain state of the material.