DEVELOPMENT OF S500MC GRADE MICROALLOYED STEEL IN HBIS SERBIA HOT STRIP MILL

The object of this paper is development of hot rolled coils of microalloyed S500MC grade steel in 6.00x1500 mm and 12.00x1500 mm dimensions in HBIS Serbia hot strip mill, according to European Standard EN 10149-2:2013. The basis for this development was present experience in production of grade S460MC. First step was design of chemical composition. This modification required the increase of the content of microalloying elements. Second step included modification of parameters of rolling technology (transfer bar thickness, reheating temperature/time etc.). Finally, after cooling and coiling, hot rolled strips were tested by means of tensile testing and Charpy impact toughness. Results show that in all cases yield strength, ultimate tensile strength, elongation and Charpy impact toughness satisfy requirements from EN 10149-2:2013. Also, due to difference in cooling rate for thin (6,00mm) and thick (12.00mm) hot strips, a driving force for nucleation of ferrite grains will be different. Therefore, chemical compositions for the same grade, but different thickness have to be different in order to compensate the lower driving force for ferrite nucleation in 12.0 mm strip. Slightly increased content of Nb and V in 12.00mm hot strip provided good mechanical properties.