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There is an ever-growing demand for lightweighting of steel for structural applications, particularly for automobile and transportation applications. It is mainly to improve the fuel efficiency, reduce the CO2 emissions and cater the increased passenger safety. Hence, the main focus is to reduce the density of the steel structure without affecting other properties. This can be achieved by down-gauging of the conventional steel by replacing the steel with higher strength, however, it is limited by dent resistance and stiffness. So, the novel idea is to reduce the density of the steel itself. It is well-known that addition of Al to steel reduces the density of the steel. About 1wt% of Al addition to steel can reduce the density by 1.3%, decreases the elastic modulus by 2% and it improves the strength by about 40 MPa. There is a new class of low-density/lightweight steel with addition of about 6–9 wt% Al to steel. Addition of higher than 9 wt% of Al in steel leads to embrittlement issues due to ordering and environmental effect. These disordered Fe–Al lightweight steels have raised considerable interest due to their low-density, high ductility, cost-effectiveness and feasibility for bulk production. The low-density steels are envisaged in the development of an advanced lightweight ground transportation system, huge structures and also for certain defence applications and in thermal power plants.