Synergetic Effects of Complex Additions of Mo and Ni on the Phase Transformation Behavior and Mechanical Properties of Austenitic Lightweight Steels

Abstract

Fe-30Mn-10.5Al-1.1C alloys with different Mo and Ni contents are prepared to investigate the phase transformation behavior and mechanical properties of austenitic lightweight steels. Solution-treated samples have microstructures consisting of an austenite matrix and ordered kappa-carbides, and the size of the kappa-carbides decreases with the addition of Mo or Ni. In addition, the ordered body-centered cubic (BCC) phases of B2 and DO3 also form when 3wt%Mo and 3wt%Ni are complexly added, resulting in a large decrease of the austenite grain size. Nanoindentation experiments show that the intrinsic strength of the austenite matrix changes depending on the precipitation behavior of the kappa-carbide; i.e., the addition of 3wt%Mo or 3wt%Ni decreases the intrinsic strength of the austenite by suppressing kappa-carbide precipitation, while complex additions of 3wt%Mo and 3wt%Ni increase them again. The results of tensile tests show that the alloy containing both 3wt%Mo and 3wt%Ni exhibits the highest yield (1102 MPa) and tensile strength (1155 MPa) with large tensile ductility (33%) due to the effects of grain refinement of the austenite grains and formation of secondary hard phases of DO3 and B2, as well as kappa-carbides. Finally, the changes in the precipitation behavior of the kappa-carbide are investigated via transmission electron microscopy and atom probe tomography analyses. © 2022 Wiley-VCH GmbH.