ANALYSIS OF SOFTENING PROCESSES BY ISOTHERMAL INTERRUPTED TESTS FOR VANADIUM MICROALLOYED STEEL

Successful application of progressive technologies of controlled rolling and cooling of various types of steels is closely associated with getting to know mutual links between the chemical composition and microstructure and complex of own unique metallurgical products, i.e. strength properties, ductility, formability etc., for whose achievement it is not necessary to perform secondary operations after rolling, especially the heat treatment operations. According to the experience of many authors the most efficient means of increasing mechanical properties of steel during rolling is the refinement of grain and use of disperse steel hardening by means of small addition of elements forming carbides, nitrides, and borides, modification of hot rolling process and controlled cooling from the finishing temperature. Within the optimization of the controlled rolling it is therefore necessary to consider also the progress of hardening and recovering processes (precipitation, recrystallization, recovery or interaction of these processes), all that with the differentiation to static, dynamic, post-dynamic processes and mostly with considering of the deformation history. The aim of this research was to analyze the softening processes on the basis of isothermal interrupted tests that were performed on the plastometer SETARAM in the Metallurgy and Material Research Company in Ostrava, in steel micro-alloyed by vanadium, or resp. softening of material during forming, which according to theoretical suppositions has essential influence on the resulting strength properties of steel. The realized study consisted on the basis of performed tests especially in the specification of softening degree X, its dependence on time and mathematical description. The realized evaluation also included the calculation of activation energy SRX.