Dilatometric study on phase transformations in non-deformed and plastically deformed medium-Mn multiphase steels with increased Al and Si additions

In this work, two novel alloys containing 4 and 5 mass.% Mn were subjected to theoretical calculations using JMatPro software and experimental studies using dilatometry in order to determine their critical temperatures and ranges of phase transformations of supercooled austenite in undeformed and deformed states. The differences in the kinetics of phase transformations and final microstructures were observed using a light microscope and compared for both investigated alloys. The Mn addition had a strong effect on reducing the A_c3 and M_s temperatures. The plastic deformation applied prior cooling affected the M_s temperature of investigated alloys and kinetics of phase transformations. Both investigated alloys showed high hardenability in the deformed and non-deformed states; and therefore, they can be used as good candidates for products obtained via the Quenching and Partitioning process. Investigated alloys can be used both for sheets and plates of increased thickness because the homogeneous martensitic microstructure can be obtained in a wide range of cooling rates during quenching. The obtained results show a wide technological window for the investigated alloys in producing sheets and plates via the Quenching and Partitioning process.