| Abstract Scope |
LC steel features low-carbon (≤0.1 wt%) and ultra-fine grained (≤10μm) bainite/martensite microstructure, through controlled rolling, offline quenching and tempering processes, resulting in a yield strength of 965 MPa and Charpy impact energy up to 220 J at -40℃. Grain refinement significantly changed the fracture mode of LC steel, which led to a significant increase in impact toughness. The findings indicate that the incorporation the micro-alloy content for the same rolling process is able to regulate the recrystallization temperature of the steel and induce a large number of transformation nuclei by introducing more deformation bands in the steel by increasing the proportion of rolling in the non-crystallization zone. In addition, high density of Nb and Ti co-precipitated in large amounts in LC steel. Nano-scale Ti-Nb co-precipitates in LC steel promote adequate Zener drag for a given rolling reduction, ensuring fine grains are formed after offline heat treatment. |