Correlation between grain size, mechanical properties and deformed microstructure of Fe–20Mn–6Al–0.6C–0.15Si low-density steel

The effects of austenite grain size on the deformed microstructure and mechanical properties of an Fe–20Mn–6Al–0.6C–0.15Si (wt.%) low-density steel were investigated. The microstructure of the experimental steel after solution treatment was single austenitic phase. The austenite grain size increased with solution temperature and time. A model was established to show the relationship between temperature, time and austenite grain size for the experimental steel. In addition, as the solution temperature increased, the strength decreased, while the elongation first increased and then decreased. This decrease in elongation after solution treatment at 1100 °C for 90 min is contributed to the over-coarse austenite grains. However, after solution treatment at 900 °C for 90 min, the strength–elongation product reached the highest value of 44.4 GPa%. As the austenite grain size increased, the intensity of <111>//tensile direction fiber decreased. This was accompanied by a decrease in dislocation density, resulting in a lower fraction of low-angle grain boundaries and a lower work hardening rate. Therefore, the austenite grain size has a critical influence on the mechanical properties of the low-density steels. Coarser grains lead to a lower yield strength due to the Hall–Petch effect and a lower tensile strength because of lower dislocation strengthening.