Vanadium Microalloyed Steel for Thin Slab Casting and Direct Rolling
Vanadium microalloyed steels with high yield strength (»600MPa), good toughness and ductility have been successfully produced in commercial thin slab casting plants employing direct rolling after casting. Because of the high solubility of VN and VC, most of the vanadium is likely to remain in solution during casting, equalisation and rolling. While some vanadium is precipitated in austenite as cuboids and pins the grain boundaries, a major fraction is available for dispersion strengthening of ferrite. Despite a coarse as-cast grain size, significant grain refinement can be achieved by repeated recrystallisation during hot rolling. Consequently, a fine and uniform ferrite grain structure is produced in the final strip. Increasing the V and N levels increases dispersion strengthening which occurs together with a finer ferrite grain size. The addition of titanium to a vanadium containing steel, decreases the yield strength due to the formation of V-Ti(N) particles in austenite during both casting and equalisation. These large particles reduced the amount of V and N available for subsequent precipitation of fine (~5nm) V rich dispersion strengthening particles in ferrite.
J.M. Rodriguez-Ibabe, I. Gutiérrez, B. López and A. Iza-Mendia
Y. Li and T.N. Baker, "Vanadium Microalloyed Steel for Thin Slab Casting and Direct Rolling", Materials Science Forum, Vols. 500-501, pp. 237-244, 2005