In situ monitoring of the martensitic transformation induced by plasticity in a stainless steel

Background: The current understanding of strain-induced martensitic transformation in AISI 304L stainless steel lacks comprehensive non-destructive testing (NDT) for effective monitoring, limiting the ability to assess phase trans- formation in industrial applications. Objective: This study aims to develop and evaluate NDT methods for monitoring strain-induced martensitic transformation in AISI 304L stainless steel. Methods: The research employs direct micro- scopic analyses, including optical microscopy and electron backscatter diffraction (EBSD), alongside indirect NDT techniques such as microhardness testing, magnetic permeability measurements, and eddy current (EC) sensor inductance evaluations. Novel aspects include the integration of these methods to correlate phase transformation with measurable properties. Results: The study finds that the martensitic phase fraction increases significantly beyond 25 % strain, with inductance and permeability showing strong correlations with phase transformation. Tensile and equibiaxial tests indicate that inductance measurement is a promising tool for monitoring transformations in complex geometries, while microhardness reflects material hardening but lacks direct correlation with phase transformation. Conclusions: The findings support EC sensor measurements as a robust method for NDT applications in assessing strain-induced transformations in stainless steel from lab specimens to complex components.