Produção de ferro fundido nodular e determinação de suas propriedades com e sem a presença de nióbio

Abstract

Cast irons are widely used in various industries due to their mechanical properties and cost-effectiveness. Among them, ductile iron stands out for its ductility and mechanical strength, properties attributed to its microstructure with nodular graphite. This study addresses the production of ductile iron and the determination of its properties with and without the addition of niobium. Additions of 0.18%, 0.25%, and 0.34% by mass of niobium in ductile iron were analyzed. The research focused on analyzing the resulting microstructures and their mechanical properties, such as tensile strength, yield strength, elongation, hardness, and impact energy absorption. Mechanical tests confirmed the significant effect of niobium addition on the properties of ductile iron. ANOVA, through the F-test with 95% confidence, revealed that in all tests, the addition of niobium significantly influences tensile strength, yield strength, Brinell hardness, elongation, and impact resistance. The Fisher test confirmed statistically significant differences between the evaluated concentrations, especially between 0% and 0.34%. For post-fracture elongation, the differences were significant in most comparisons, except between 0.25% and 0.34%. These results reinforce that niobium significantly improves the material's mechanical properties, particularly increasing mechanical strength and hardness. It was observed that increasing niobium concentrations within the studied range led to an increase in the pearlite fraction and a corresponding reduction in the ferrite fraction, positively impacting impact resistance up to the optimal concentration, beyond which a decline was observed. This behavior is due to niobium's ability to act as a carbide-forming element and influence pearlite stability, enhancing matrix strength. The results confirm that niobium, at specific concentrations, exerts a significant influence on the microstructure and mechanical properties of ductile iron. [resumo fornecido pelo autor]