Microstructural Modulation through Process Control Leading to Ultrastrong Ductile Fe–10Al–15Mn–0.8C–5Ni wt% Low‐Density Steel

The article involves synthesis, characterization, and mechanical property studies of Fe–10Al–15Mn–0.8C–5Ni wt% steel, prepared by hot rolling, cold rolling (CR), and annealing treatment. A partial substitution of iron (density, 7.8 g/cc) with a lighter element like Al (density, 2.7 g/cc) is strategic to fabricate the low density steel, following a thumb rule that 1 wt% Al additions in steel lead to the density reduction of roughly 1.2%. However, the sample processing imposes challenges, based on the microstructure that an excessive use of Al in the alloy chemistry results in ≈27% δ‐ferrite during solidification‐casting. The hot and CR transforms the δ into B2 stringer bands, that is, an Fe‐Al‐based intermetallic phase. A bamboo‐like morphology of the B2‐stringer after heat treatment causes a premature failure of the austenitic steel. With proper process control, the article finds a way to circumvent the issue. The outcome results in nearly 1 GPa yield strength, 28% total elongation, and over 1.7 kJ mol −1 (or 238.4 J cm −3 ) toughness, tantamount to the development of crack‐resistant ultrahigh strength steel for the automotive body in white. The current article also analyzes intra‐ and intergranular precipitation of the B2 second‐phase, tailoring the mechanical properties.