Metallographic, structural and mechanical characterization of low-density austenitic Fe-Mn-Al-C steels microalloyed with Ti/B and Ce/La in hot-rolling condition

Abstract

Low-density austenitic Fe-Mn-Al-C steels have high strength, high ductility and a significant weight reduction respect to other alloyed steels. However, this complex system exhibits second-phase precipitation, particularly κ-carbide. It is well-known that the microalloying elements addition to steel generates precipitation hardening, as well as grain refinement effect. It is worth noting that low-density steels can cause cracking during hot-rolling due to high Mn, Al and C contents and segregation in grain boundaries. Hot-rolling conditions play an important role in the dynamic recrystallization mechanisms, and therefore in the austenitic grain size. The main objective of this research work is the metallographic, structural and mechanical characterization of low-density steels microalloyed with Ti/B and Ce/La in hot-rolling condition. For this purpose Fe-(27-30)Mn-(7-8)Al-(1.2-1.8)C (wt.%) low density steels microalloyed with Ti/B and Ce/La were hot-rolled at 1200 °C in two stages. Metallographic, structural and mechanical characterization was carried out by optical (LOM) and scanning electron (SEM) microscopies, electron backscatter diffraction (EBSD) through quality images, inverse pole figures (IPF) and orientation distribution functions (ODF) maps, X-ray diffraction (XRD) and microhardness Vickers (HV) testing. In general, the first stage of hot-rolling exhibits a strongly bimodal microstructure of dynamically recrystallized austenitic grains, while the second stage shows more uniform recrystallized grain size. In the first stage of hot-rolling the austenite is the predominant phase, while in the second stage the α-ferrite phase is barely visible. Low-density steel microalloyed with Ti/B presented better grain size and microhardness values compared to steel microalloyed with Ce/La. Preferred crystallographic orientations were not found.