Influence of Material State on Austenitic Transformation in HSLA-Type Steel

The paper presents the results of research on the influence of the material condition – HSLA steel with Ti and Nb microadditions – on the course of the austenitic transformation. In order to determine the kinetics of phase transformations occur in steel during individual stages of the austenitic transformation, tests were carried out using a Bähr 805 A/D dilatometer. In order to determine the influence of hot plastic deformation on the course of the austenitic transformation, plastometric tests were carried out using the Gleeble 3800 thermomechanical simulator. For detailed microstructural analysis, microscopic examinations were carried out using the light microscope and the scanning electron microscope. The obtained results were compared with hardness measurements. The tests carried out showed significant differences in the course of the austenitic transformation and the values of critical temperatures for steel before and after using the plastic deformation. The Ac1 temperature for steel in the as-cast state is 850°C and the Ac3 temperature is 950°C. As the annealing temperature increases, the hardness increases from 210 HV100 for a temperature of 700°C to 260 HV100 for a temperature of 920°C. Knowledge about the phase transformations of supercooled austenite is extremely important, especially for newly developed steels, hence the aim of the work is to analyze the atypical course of the austenitic transformation of HSLA steels and to determine the influence of deformation on the austenitic transformation during heating.