Study On Precipitation Behaviors Of Carbonitride Of Vanadium In HRB400 Reinforced Steel Bars

In order to make full use of vanadium's effect (refine grain and precipitation), the performace of carbonitride precipitating in austenite of HRB400 reinforced steel bars microalloyed with vanadium was investigated by the stress relaxation on Gleeble ther- -mal simulator in this paper. At last the curves of precipitation-temperature-time (PTT) were plotted according to the curves of stress relaxation at different temperature but at the same deformation amount. The precipitates formed in the sample during stress relaxation at different temperatures were observed under transmission electron microscope(TEM) .The results of the experiments show that the precipitation start time is relative to temperature, deformation. At the same degree of deformation, the shape of precipitation-temperature -time (PTT) is typical of C curve, and there exist a fastst precipitation point. When compression deformationε=0.05(e=-0.05), the fastest precipitation point at 850℃and corresponding beginning time of precipitation is 6 second. When compression deformationε=0.20(e=-0.22), the fastest precipitation point at 870℃and corresponding beginning time of precipitation is 0.7 second. When compression deformationε=0.50(e=-0.05), the fastest precipitation point at 870℃and corresponding beginning time of precipitation is 1.2 second. The precipitation start time is accelerated by the increasing degree of deformation when the temperature is constant. The precipitates of foil samples experienced stress-relaxation were observed under TEM, we find that the precipitation is not only in the intragranular but also around the dislocation. At last the results were matched with the outcome caculated by thermaldynamic theory and principle of dynamics.