Research status and development prospect of Fe–Mn–C–Al system low-density steels

The rapid development of automotive industry results in a series of increasingly serious problems such as energy consumption and environmental pollution, so that developing the automotive steels with high-strength and low-density is of great significance for energy conservation and emission reduction. Recently, Fe–Mn–C–Al system steel is favored by numerous researchers because of its low density and excellent combination of strength and ductility. However, too much Al addition inevitably triggers various changes of microstructure, deformation mechanism, and mechanical properties. In this paper, the composition design, production process, strengthening and strain hardening mechanism, and microstructure evolution are systematically expounded. The discussion mainly focuses on various strengthening (solid solution strengthening, grain refinement strengthening and precipitation strengthening) and strain hardening mechanisms (phase transformation-induced-plasticity (TRIP), twinning-induced-plasticity (TWIP), microband-induced-plasticity (MBIP), shear-band-induced-plasticity (SIP) and dynamic slip band refinement (DSBR), etc.). Also, the existing problems and future challenges in Fe–Mn–Al–C low-density steels are pointed out via analyzing the service performance (cryogenic performance, impact toughness, fatigue performance, hydrogen embrittlement, wear performance, and tensile properties). Finally, we look forward to the future development direction of Fe–Mn–Al–C low-density steels and provide the valuable ideas.