Static recrystallisation of steels produced by direct strip casting – the effect of carbon and vanadium concentration

Six steel alloys containing a range of carbon and vanadium concentrations have been prepared by simulated strip casting. The alloys were cold rolled and annealed to examine the recrystallisation behaviour. The annealing treatment resulted in three processes occurring concurrently: recrystallisation; spheroidisation of cementite, and precipitation of vanadium-enriched nano-precipitates. These nano-precipitates had a much higher concentration of Fe than would be expected from traditional processing methods, and this increased their maximum attainable volume fraction. In the two alloys that did not contain second phase particles, recrystallisation showed typical reaction kinetics, and the recrystallised grain size continued to increase with increasing time at temperature. However, in those alloys with second phase particles the recrystallised grains showed unusual behaviour, rapidly reaching an upper limit to their size. Continued time at temperature was not accompanied by an increase in the grain size. This growth limit has been attributed to Zener pinning, with the limiting grain size being proportional to the Zener pinning pressure. It has been proposed that the delayed recrystallisation that is typically observed in strip cast steels is likely to be the result of nano-scale precipitation which is unique to rapidly cooled materials, such as those produced by strip casting.