Analýza vývoje mikrostruktury během válcování na hrubé profilové trati v Liberty Ostrava a.s.

Abstract

Master thesis deals with the analysis of the developement of the microstructure of S355J2 niobium microalloyed steel on the heavy rolling mill in Liberty Ostrava a.s. In the first part, the effect of reduced rolling temperature was verified before the 6th stand in the case of flat bars and before the 7th stand in the case of a round bar. Better values of impact toughness and ductility were obtained in almost all experiments. In the second part, based of the achieved results, a round bar O100 was selected to be analyzed in more detail by laboratory simulations. Carbonitrides dissolution temperature during heating was determined, which subsequently served as the heating temperature for further PSCT simulations of a real forming proces which consisted of 7 passes at different rolling temperatures, from which microstructural analysis were performed, including transmission electron microscopy (TEM). A microstructural model was then built for the given round bar, which showed very good accuracy after comparison with the microstructure results.