Simulação computacional do início da precipitação induzida por deformação durante o processamento termomecânico de um aço microligado ao nióbio em resfriamento contínuo

Abstract

Improving the steel processing is a major focus of the metallurgical industry because the need of materials and products with lower weight and more strength, in addition to increasingly stringent specifications imposed by customers. The production of high strength low alloy steel, especially the higher cost ones, has only become possible with the understanding of the physical metallurgy of industrial processing. The knowledge and kinetic control of the phenomena that occur during hot processing such as recrystallization, precipitation and grain growth are mandatory for the grain size refinement, which is one parameter that determines the properties of semi-finished products. Over the years, several ways have been followed to investigate the industrial processing. One can cite as examples the use of pilot plants, physical simulations, and numerical simulations. The study of hot forming assisted by computer simulation is well spread nowadays. The development of materials models trustful enough to reduce cost with prototypes and virtually explore an infinitude of possibilities and thermomechanical loads is of interest of the metallurgical industry. The objective of this study was, therefore, to model the microstructural evolution and thermomechanical behavior of a niobium microalloyed steel during hot forming process, enabling the analysis of how the process parameters such as temperature, strain, strain rate influence the evolution of softening, precipitation and grain size mechanism during processing, using the commercial software DEFORMTM3D developed for forming processes analysis with the aid of subroutines in FORTRAN. The main results of this thesis were not only determining and understanding the plastic and microstructural gradients generated by thermomechanical processing, but also the construction of finite element model that might be useful to others researchers on the investigation of the thermomechanical behavior of new microalloyed steels in the processing products with complex geometry.