Precipitation behavior and kinetics in Nb-V-bearing low-carbon steel

The chemical composition and lattice parameter of the nanometer-sized carbides in ferrite of Nb-V bearing low-carbon steel were studied by high resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The results indicate that the average size of the carbides increased with increase in isothermal holding time. V was found to be gradually incorporated into NbC lattice to form a complex (Nb_xV_1-x)C particle during precipitation and the atomic ratio of V/Nb gradually increased during coarsening, which leads to a decrease in the lattice parameter of carbide and reduces the misfit strain between the carbide and ferrite matrix, resulting in acceleration of precipitation kinetics.