Abstract: 50CrNiMoVNb steel belts after annealing were cold rolled by using cold rolling mill, and the cold rolled specimens were annealed in high temperature muffle furnace. The effects of cold rolling reduction rate, annealing temperature and annealing time on recrystallization were studied by means of metallographic microscope and microhardness tester. The results show that the growth rate of recrystallized grains is increased with the increase of cold rolling reduction rate, and the greater the reduction rate, the finer and more uniform recrystallized grains. The average grain size of the steel annealed at 800 ℃ for 1 h is reduced from 8.0 μm at reduction rate of 0% to 5.6 μm at reduction rate of 50%. At the same cold rolling reduction rate, when the steel is air cooled after annealing, the hardness decreases first and then increases with the increase of annealing temperature. The degree of recrystallization completion is improved with annealing temperature increasing and holding time prolonging. The completion time of recrystallization is 70 min for the steel with the reduction rate of 30% at the annealing temperature of 800 ℃. The relationships between the volume fraction x, the recrystallization time t_R, grain size d and the nucleation rate N, linear growth rate v, holding time t are x(t)≈Nv³t⁴,$t_{\mathrm{R}}=\sqrt[4]{\frac{3}{\pi N v^{3}}}$,$d=2 \sqrt[4]{\frac{3 v}{\pi N}}$, respectively.

Key words: cold rolling reduction rate, annealing temperature, holding time, alloy steel 50CrNiMoVNb, recrystallization