Microstructure and mechanical properties of cold rolled, annealed HSLA strip steels

A large testing programme of a strip steel grade, microalloyed by vanadium, titanium and niobium, was conducted. The experiment was based on combination of cold rolling, recrystallization annealing, mechanical testing, metallographic examinations, SEM and TEM analyses. Samples in the form of stripes with dimensions of 3.9×25×500 mm were rolled in several passes with the total height reduction of 5 to 75 %. Particular partial strains were realized at room temperature in the housingless, hydraulically prestressed laboratory mill. Afterwards the laboratory mill products were annealed in the vacuum furnace with the protective gas atmosphere consisting of N2+H2. The annealed samples underwent the tensile test at the room temperature and the Brinell hardness test. The gained results – hardness, yield stress, tensile strength and their ratio, as well as elongation A80, were summarized in dependence on cold deformation before annealing.