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Some aspects of deformation, precipitation, and recrystallization behavior in medium carbon V-microalloyed and low carbon Nb/Ti-microalloyed steels are presented in the paper. Changes in microstructure are explained together with methods of quantification. The temperature of No-recrystallization (Tnr) is defined as a milestone to show the onset of retardation of recrystallization while the apparent activation energy for hot working shows the extent of this retardation. In the case of high cooling rates, this method is not sufficiently sensitive and Trl (recrystallization limit temperature) and Trs (recrystallization stop temperature) must be evaluated from softening data. Paper presented the possibility to estimate Tnr temperature on six stands finishing train at Hot Strip Mill in HBIS Iron and Steel Serbia, Smederevo as well as the activation energy for static recrystallization, QSRX, derived from Tnr temperatures.

The aim of this work was to determine TTT diagram of medium carbon V-N micro-alloyed steel with emphasis on the development of intragranular ferrite morphologies. The isothermal treatment was carried out at 350, 400, 450, 500, 550 and 600?C. These treatments were interrupted at different times in order to analyze the evolution of the microstructure. Metallographic evaluation was done using optical and scanning electron microscopy (SEM). The results show that at high temperatures (? 500?C) polygonal intragranulary nucleated ferrite idiomorphs, combined with grain boundary ferrite and pearlite were produced and followed by an incomplete transformation phenomenon. At intermediate temperatures (450, 500?C) an interloced acicular ferrite (AF) microstructure is produced, and at low temperatures (400, 350?C) the sheave of parallel acicular ferrite plates, similar to bainitic sheaves but intragranularly nucleated were observed. In addition to sheaf type acicular ferrite, the grain boundary nucleated bainitic sheaves are observed. [Projekat Ministartsva nauke Republike Srbije, br. OI174004]