In this doctoral thesis a comparative research were conducted on niobium microalloyed steel which has fine niobium precipitates, steel with same base chemical composition but without the addition of niobium and on niobium microalloyed steel with large precipitates of niobium. With the tensile testing, at the same time the methods of thermography and digital image correlation were applied, which enables the continuous measurement of temperature changes and strain. By using software packages IRBIS 3 Professional and MatchID 2D is enabled a quantitative and qualitative analysis of measured changes in temperature and strain. Research results have shown that microalloyed niobium steel has a significantly different behavior upon deformation in relation to the steel of the same base composition without niobium. Effect of the fine precipitates of niobium is especially pronounced at the beginning of plastic flow of material. After yielding the niobium microalloyed steel has rheological complex behavior. Research has shown that this behavior is associated with the occurrence of Lüders bands. Lüders band is formed in such way that plastic deformation starts at the one end of sample, in doing so the strain of 0,004 mm/mm is carried out. After that Lüders band propagates at the angle of 45°. It was found that on the Lüders band front there is increase in temperature of about 4.5 to 6 °C, which is associated with increases in stress. Behind the Lüders front the strain of 0.05 mm/mm is achieved, Lüders deformation. After that, in the formed deformation zone, further plastic deformation continues and stresses are concentrated in the centre of the deformation zone, as in the low-carbon steel. Proposed mathematical model links measured stress and deformation with the measured temperature changes, with which is possible from the measured values of deformation and temperature changes determine the amount of stress in the observed points of deformation zone. By comparing the results of the research and the results obtained by the developed model, it was shown that the values match up to the speed of 30 mm / min, where is shown a significant discrepancies.