Hot Working Behavior in Multiphase Steel with Ti and V

This study investigated the effect of hot working conditions on changes in yield stress and the softening degree in the newly developed multiphase steel with Ti and V microadditions. The research was performed on the GLEEBLE 3800 thermomechanical simulator. In order to determine the sigma-epsilon curves, continuous compression tests were carried out. The samples were plastically deformed at temperatures from 900 degrees C to 1100 degrees C at the rate of 0.1 s(-1), 1 s(-1) and 10 s(-1). The activation energy of the plastic deformation was 375 kJ center dot mol(-1). The analysis of the shape and course of the curves indicated that the decrease in strain hardening was mainly the result of the continuous dynamic recrystallization process. Two-stage compression with isothermal holding of the samples was also carried out between the two stages of deformation lasting from 1 s to 50 s. The structure of primary austenite was generated using the ARPGE software. The different size of austenite grain is the result of various thermally activated processes-when increasing the strain rate from 0.1 s(-1) to 10 s(-1), the average grain size of the primary austenite decreases from approx. 16 mu m to approx. 6 mu m. The time t(0.5) needed to form 50% of the austenite fraction recrystallized at 1100 degrees C is approx. 4 s and extends to approx. 10 s with the reduction in the plastic deformation temperature to 900 degrees C. The time of complete austenite recrystallization t(R), which varies from approx. 50 s to approx. 90 s in the tested temperature range, lengthens even more. The obtained results make it possible to develop thermomechanical treatment technology for the production of forgings from the tested multiphase steel.