Isotropic Phase Transformation in Anisotropic Stainless Steel 301LN Sheets

The phase transformation due to mechanical loading in cold-rolled stainless steel 301LN sheets is investigated experimentally. A series of uniaxial tension experiments is performed to quantitatively investigate the effect of initial anisotropy on the martensitic transformation kinetics. Three methods are employed to measure the martensite content: (1) micrography, (2) global magnetic saturation, and (3) local magnetic induction. The first two methods require interrupted tests, while the third method allows for the in-situ detection of the evolution of the martensite volume ratio. All three methods are able to detect the increasing martensite content with plastic strain, and in addition they show that the rate of austenite-to-martensite transformation is not loading direction dependent. In particular, the local magnetic induction technique appears to be sufficiently sensitive to detect these relative differences. The results show that micrography has limited accuracy in quantifying the absolute martensite content due to material preparation. However, the global magnetic method is deemed to be an accurate method to quantify the absolute martensite content, and measurements using this method can be used to calibrate the local magnetic induction method for in-situ monitoring of martensite content evolution. In addition, it was determined that the martensite evolution in this textured material has no directional dependence.