Quantitative analysis of microstructural and mechanical behavior for Fe–0.1C–(V, Nb) steels as a function of the final rolling temperature

The microstructure, tensile property and impact toughness of Fe–0.1C steel were investigated as a function of the final rolling temperature (FRT: 950 or 860 °C) and microalloying contents: Fe–V steel, Fe–V–Nb steel, and Fe–Nb steel. Microstructural features (ferrite volume fraction and grain size) were correlated with mechanical properties (hardness, tensile strength, and impact toughness). Specifically, the mixed grain size of ferrite was quantitatively and statistically analyzed to explain the level of toughness. For FRT 860 °C, the impact toughness of Fe–Nb steel deteriorated due to the inhomogeneity of ferrite grain size, although its ferrite grain size was mostly the same or slightly smaller than the Fe–V steel. However, Fe–V–Nb steel showed the smallest average and the narrowest distribution of ferrite grain size, which produced comparable impact toughness with Fe–V steel with a minimum loss of the tensile property.