Precipitation in vanadium bearing ultralow carbon strip steels

Two novel ultralow carbon (ULC) steels were investigated, one based on combined vanadium and titanium additions and the second based on titanium only additions. Grain size and mechanical property measurements have been performed on continuously annealed specimens previously subjected to 80% cold rolling reduction on both strip steel grades. The recrystallisation and grain coarsening characteristics of annealed ULC strips have been studied. The amount of precipitated species, under equilibrium conditions, at various annealing temperatures has also been calculated using MT-DATA thermodynamic modelling software. Transmission electron microscopy characterisation coupled with EDX study of the precipitation sequences on continuous annealing strips was also performed. Precipitate studies of the novel ULC steels confirmed the major role of TiC precipitates in retarding the recrystallisation behaviour of ULC strip steels. The role of vanadium addition in ULC steel grades in reducing the recrystallisation temperature of ULC strip steels was also identified.