Study on the Thermomechanical Behaviour of Ultra High Strength Steels Treated Under Severe Cooling Rates

Abstract

Advanced High Strength Steels (AHSS) provide several important benefits such as low cost to manufacture, ability to reduce sheet weight, improve passenger safety, reduce carbon dioxide emissions to the atmosphere, and improve recyclability than conventional steels. Dual-Phase (DP) steels have the advantage of presenting unique mechanical properties, based on adequate control in the industrial manufacturing process (hot rolling), to generate a Dual-Phase ferrite martensite or ferrite-bainite structure. Since hot rolling is the manufacturing route, it is seen that there are two phenomena that act together: on the one hand, the system undergoes a plastic deformation, while on the other hand, there is the contribution of heat energy to promote the phase transformation phenomena in the solid state. For this reason, in this work emphasis will be placed on studying the correlation between the thermomechanical behavior of a Dual-Phase steel and the impact on the industrial processing variables. To achieve this aim, the dilatometry test for the study of phase transformations will be used as an experimental technique. This test was carried out on a Theta Dilatronics II equipment. The prepared samples consist of (5 x 5 x 50) mm square section prisms, which were tested at a heating rate of 0.17 ° C/s, up to a temperature of 1150 ° C. The cooling was carried out at various cooling rates, from 0.03 ° C/s to 100.00 ° C/s. Each specimen was tested in an air atmosphere. Likewise, all this information is correlated with structural studies, to determine the distribution and percentage of phases present for each thermal profile tested, as well as the determination of the mechanical resistance of each steel sample from the Vickers microhardness measurement.