Quasi in-situ analysis of geometrically necessary dislocation density in alpha-fibre and gamma-fibre during static recrystallization in cold-rolled low-carbon Ti-V bearing microalloyed steel

摘要

In the present study, cold-rolled low-carbon steel is annealed at three different conditions: 700 degrees C for 0 s, 800 degrees C for 0 s and 800 degrees C for 2 min at the heating rate of similar to 10 C/s. Recrystallization behaviour on sample surface is studied using a heated stage Scanning Electron Microscopy and Electron Backscattered Diffraction. For the lower annealing temperature of 700 degrees C with no dwell, almost no recrystallization is observed and microstructure resembles the as-received deformed material with the exception of occasional sub-micron sized nuclei. For the annealing conditions of 800 degrees C 0 s and 800 degrees C 2 min, onset and evolution of recrystallization is observed in-situ as a function of the initial as-cold rolled texture. Slower recovery rate of alpha fibre than gamma fibre is observed and confirmed by lower drop in average geometrically necessary dislocation (GND) density for un-recrystallized alpha fibres (1.1E + 14 M-2 for 700 degrees C 0 s, 1.4E +14 m(-2) for 800 degrees C 0 s and 4.5E +14 M-2 for 800 degrees C 2 min) than for un-recrystallized gamma fibre grains (3.0E + 14 M-2 for 700 degrees C 0s, 6.2E +14 m(-2) for 800 degrees C Os and 9.8E + 14 M-2 for 800 degrees C 2 min) during annealing. Strong gamma texture in recrystallized matrix is found for annealing conditions of 800 degrees C 0 s and 800 degrees C 2 min. From TEM characterisation it was shown that sub-grain boundaries are decorated with fine precipitates (diameter d 15 nm) of titanium-vanadium carbides (Ti,V)C for the annealing condition of 700 degrees C 0 s, which suggests that these precipitates play a major overall role in retardation of the recrystallization kinetics.