Optimization of Process Conditions for Ultralightweight Steel with More Than 13wt% of Al and 5wt% of Cr

An ultralightweight Fe–30Mn–13.2Al–1.6C–5Cr steel, which contains more than 13 wt% of Al and thereby reduces the density by 20%, is developed. The ultralightweight steel, which is very brittle due to high Al content, is fabricated by optimizing hot rolling and heat treatment conditions. Hot rolling is conducted after soaking at the temperature range of 1100–1200 °C for 2 h. The ultralightweight steel is hot‐rolled successfully after soaking at 1100 °C, whereas specimens soaked at 1150 and 1200 °C are intergranularly cracked after hot rolling, resulting from coarse grain and a large fraction and size of ferrite, which is transformed to ordered DO3 phase during cooling, at the grain boundaries. In homogenization heat treatment, water quenching and air cooling are performed, respectively, after holding at 1050 °C for 2 h. The air‐cooled steel has inferior tensile property due to the formation of brittle ordered DO3 phase at grain boundaries. Meanwhile, the water‐quenched steel shows an excellent tensile property, which is attributed to a uniform microstructure comprising austenite, fine κ‐carbide in austenite, and a very small fraction of the ordered DO3 phase.