Produção e caracterização física e mecânica de ferros fundidos nodulares e ferros fundidos nodulares austemperados com adição de nióbio

Abstract

The production of ductile cast iron and austempered ductile cast iron - ADI- usually involves an inoculation 0.03-0.06% Magnesium and the presence of Chromium, Nickel, Copper and Molybdenum. The addition of Niobium is not common. Reports in theliterature show that Niobium leads to improved mechanical properties of the ductile cast iron and recent findings indicate that the 0.5% Niobium increases its strength andimpact strength, but decreases its hardness in relation to a ductile iron without Niobium. The process of production of cast iron with Niobium is difficult, according to the literature, due to the presence of carbon at higher levels, which are typical of this alloy. This study presents a methodology for the production of cast iron with Niobium and analyzes the effects of the addition of 0.23%, 0.47%, 0.67% and 0.85% Niobium to a ductile cast iron in their microstructures, tensile strength, yield strength and elongation, impact resistance, wear and fatigue properties. The study showed that the volume fraction of perlite increases and the number of spheroidal graphite decreases as the content of Niobium is increased, leading to an increase in tensile strength and hardness of these materials. These is also an increase in the tensile ductility, impact resistance and elongation for an addition of 0.23% Niobium. For austempered ductile cast iron with niobium, the results indicate a preponderance of the influence of the matrix compared to the influence of the addition of Niobium.