Effect of B2 Precipitation on Hot Ductility of Fe-22Mn-9Al-0.6C Low-Density Steel

Fe-Mn-Al-C low-density steels are regarded as promising materials applied in the automotive industry to achieve the minimization of vehicular emissions and fuel consumption. This study investigates the high-temperature strength and hot ductility of Fe-22Mn-9Al-0.6C low-density steel through high-temperature tensile tests at 800-950 degrees C. The high-temperature strength decreases with an increasing deformation temperature. This indicates that the precipitation of B2 reduces the hot ductility during the hot deformation of steel, where the results are consistent with those during the solid-solution treatment at 800-950 degrees C with a holding time of 0.5 h. Furthermore, at 800 degrees C the gamma transforms into a mixture of alpha + DO3 and kappa-carbide precipitates. A transformation of kappa + DO3 -> B2 occurs in the temperature range of 850-900 degrees C, and at this point the kappa-carbide dissolves into the matrix and B2 is generated, resulting in a significant decrease in hot ductility. As the temperature increases up to 950 degrees C, B2 emerges and transforms into the delta phase, and the kappa-carbide precipitates along the gamma/gamma grain boundaries. The precipitation of B2 during high-temperature treatments in Fe-Mn-Al-C low-density steels is the critical factor affecting hot ductility, leading to crack generation; therefore, it is extremely essential to prevent the temperature interval of B2 precipitation during hot deformation processes.