Continuous cooling transformation behaviour of V-Bearing 0.2C-0.5Si-0.08P-Mn TRIP steel

The continuous cooling transformation (CCT) behaviour was investigated for the 0.2C-0.5Si-0.08P-Mn TRIP steel with 0.19% vanadium on a thermo-simulator. The results revealed that the starting transformation temperature of ferrite (Ar3) is increased by 42~58°C during subsequently continuous cooling after the deformation rate has been up to 50% in the zone where the austenite has not been recrystallized. At the same cooling rate especially it is lower than 20°C/s, the deformation of austenite stimulates the formation of ferrite with the bainitic nucleation rate reduced. The vanadium nitrides and vanadium carbides both disperse and precipitate within ferritic grains or at grain boundaries, and most of the precipitated particle sizes are in the range from 2 to 5 nm at the cooling rate 0.5°C/s, regardless of whether the austenite is deformed or undeformed. It was found in specimens that only a few precipitate particle sizes are about 20 nm.