Structures and properties of Fe-(8-16)Mn-9Al-0.8C low density steel made by a centrifugal casting in near-rapid solidification

Abstract

Fe-Mn-Al-C low-density steel is a promising material in reducing the vehicle weight. Although a high Mn content (more than 18 wt%) could increase the austenite fraction to realize excellent ductility in the low-density steel, it would result in high material costs and challenges in production. A lower Mn content, on the other hand, could easily result in coarsened κ-carbides that tend to initiate cracking, especially in the steel with high Al content (more than 6 wt%). This work attempted to restrain the coarse and lamellar κ-carbides in steels with relatively low Mn (8, 12, 16 wt%) and high Al (9 wt%) contents by using a centrifugal casting method in near-rapid solidification. The coarse and lamellar κ-carbides have been completely restrained in the three strips prepared by this near-rapid solidification, and all strips presented a uniform dual-phase (austenite and ferrite) structure. Austenite was a dominant phase in these materials, which improved the properties of the strips. Transmission electron microscopy analysis showed that nanoscale κ-carbides were uniformly distributed in the austenite matrix in the as-cast trips. The 12 wt% Mn steel strips showed the highest yield strength due to the appearance of high-density planar substructures, possibly owing to the lowest stacking fault energy of this material. Moreover, occurrence of twin-induced plastic effect was found during deforming of 12 wt% Mn steel strip. 12Mn steel strip shows the highest yield stress, while the 16Mn steel shows the best integrated mechanical properties, whose ultimate tensile strength and total elongation reached to 923 MPa and 46.2%, respectively. The strength and elongation rate of all steel strips were improved by annealing at 550 °C for 3 h. This work showed that the near-rapid solidification could suppress the formation of coarse and lamellar κ-carbides in Fe-Mn-Al-C low-density steel with high Al content and relatively low Mn (below 18 wt%) content.