Avaliação do percentual de deformação a quente na microestrutura e propriedades mecânicas do aço AHSS DP 800 submetidos a tratamentos termomecânicos

Abstract

This work studied the influence of the variation of hot deformation in a thermomechanical treatment on the microstructure and mechanical properties of an AHSS DP 800 steel. isothermal. From previous studies of phase transformation of DP 800 steel by dilatometry, a temperature of 900 °C was determined for austenitization for 30 minutes, after which the material was rolled at 0%, 15%, 20% and 25% and immediately cooled in water at room temperature, then the specimens were subjected to isothermal treatment in a lead bath at 380 °C for 30 minutes. Separately, a route with 25% strain, which was not subjected to isothermal treatment, was performed to compare routes with and without isothermal decomposition. The treated specimens underwent tensile testing to verify the mechanical properties of resistance limit, yield limit and elongation, in addition to metallographic preparation and scanning electron microscopy (SEM) to verify the corresponding microstructure. In this way, it was determined that the variation of the percentage of hot deformation does not affect the resistance limit when it is associated with an isothermal decomposition, where route 1 (without deformation) presented the best results, improving the properties of resistance limit and limit yield without much reduction in ductility. In addition, the results suggested that the isothermal treatment can nullify the effects of lamination on the strength limit and reduces the effect of work hardening on the yield strength.