Thermo-graphic investigations were carried out on niobium microalloyed steel. During tensile testing temperature changes of samples, due to elastic and plastic deformation, were measured using infrared camera. The results of temperature measurements indicate that the specimen’s temperature is lowered during the elastic deformation. This temperature drop is in other studies associated with so-called thermo-elastic effect which occurs in the metals during elastic deformation. Parallel with the infrared camera, surface of samples was recorded with digital imaging camera. Analysis of recorded images was analyzed using digital image correlation method. This is used to determine the deformation that occurs during stretching. The results show that during elastic deformation of samples the volume of samples is slightly increased. The volume change of samples and temperature drop, due to thermo-elastic effect, are compared for all samples. The analysis of experimental results explains that the thermo-elastic effect is directly related to the change of specimen volume during the elastic deformation of steel.