Influence of thermomechanical sequences on the mechanical properties of DP 800 steel

The influence of thermomechanical processing sequences on the microstructure and mechanical properties of Advanced High-Strength Steels (AHSS) DP800 steel was studied. Initially, the phase transformation domains were identified by dilatometry. Based on the identification of these domains, some thermomechanical sequences were produced. In all sequences, the steel was austenitized at 900 ° C for 20 minutes, followed by a 10% deformation (rolling) and then quenched. After tempering, the material was reheated to decompose under different conditions of time and temperature. For the decomposition, temperatures of 380 °, 480 °, 580 ° and 680 deg C were used, in times of 15 and 30 minutes. After treatments, samples were prepared by metallography for microstructural characterization by scanning electron microscopy (SEM). The phases present in the microstructures produced by the different treatment sequences could be identified. The mechanical properties were determined by uniaxial tensile test on a servo-hydraulic machine. Some of the tested thermomechanical sequences showed better values than those required by the standard. The sequence that showed the best results was performed at 680 °C in 15 minutes. In which, an increase of 8% in the yield strength, 12.25% in the ultimate tensile strength and 97.3% in the elongation was observed. (author)