The hot working behavior especially dynamic recrystallization of low-carbon and medium-carbon vanadium microalloy steels has been studied by performing isothermally compression tests and Avrami analysis.The Avrami plots of the two experiment steels have been constructed based on flow stress curves following a new approach (Jonas,et al.Acta Mater.,2009,57(2):2748-2756;Wu et al,Acta Metall.Sin.,2010,46(7):838-843).It is experimentally found that the carbon effect on dynamic recrystallization is opposite to each other in lower and higher strain ranges:Carbon causes a softening effect at low strain rates (0.01,0.1,and 1.0 s-1),and a hardening effect at high strain rates (10.0 and 30.0 s-1).Correspondingly,carbon promotes the dynamic recrystallization at low strain rates and retards the dynamic recrystallization at high strain rates in the experimental steels.The phenomenon is then tentatively explained based on the possible mechanisms of dynamic process at different strain rates. The hot working behavior especially dynamic recrystallization of low-carbon and medium-carbon vanadium microalloy steels has been studied by performing isothermally compression tests and Avrami analysis. The Avrami plots of the two experiment steels have been constructed based on flow stress curves following a new approach (Jonas, et al. Acta Mater., 2009, 57 (2): 2748-2756; Wu et al, Acta Metall. Sin. 2010,46 (7): 838-843). It is experimentally found that the carbon effect on dynamic recrystallization is opposite to each other in lower and higher strain ranges: Carbon causes a softening effect at low strain rates (0.01,0.1, and 1.0 s-1), and a hardening effect at high strain rates (10.0 and 30.0 s -1) .Correspondingly, carbon promotes the dynamic recrystallization at low strain rates and retards the dynamic recrystallization at high strain rates in the experimental steels.The phenomenon is then tentatively explained based on the possible mechanisms of dynamic process at different strain rates.