Ti-bearing lightweight steel with large high temperature ductility via thermally stable multi-phase microstructure

Abstract

The global demand for lightweight design is increasing to provide sustainable solutions to counteract climate change. We developed a novel Ti-bearing lightweight steel (8% lower mass density than general steels), which exhibits an excellent combination of strength (491 MPa ultimate tensile strength) and tensile ductility (31%) at elevated temperature (600 degrees C). The developed steel is suitable for parts subjected to high temperature at reduced dynamical load. The composition of the developed steel (Fe-20Mn-6Ti-3Al-0.06C-NbNi (wt%)) lends the alloy a multiphase structure with austenite matrix, partially ordered ferrite, Fe2Ti Laves phase, and fine MC carbides. At elevated temperature (600 degrees C), the ductility of the new material is at least 2.5 times higher than that of conventional lightweight steels based on the Fe-Mn-Al system, which become brittle at elevated temperatures due to the inter/intragranular precipitation of kappa-carbides. This is achieved by the high thermal stability of its microstructure and the avoidance of brittle kappa-carbides in this temperature range.