Substituição de coque calcinado de petróleo por grafite sintético na fabricação de ferro fundido cinzento.

Abstract

Currently, with the development of foundry industry technology, materials focused on the production of parts for the automotive industry, such as cast iron, have stimulated significant research activities. Cast irons have a carbon percentage greater than 2.1% by mass and are a ternary alloy of Fe-C-Si (Iron-Carbon-Silicon), with a silicon percentage greater than 1% by mass. Gray cast iron is a highly selected material in this industry for a multitude of internal parts of combustion engines due to its high tensile strength and hardness under severe conditions. This increase in carbon in the matrix is achieved through the extra addition of carbon (carburization) with calcined petroleum coke, among other methods. To improve the cast iron manufacturing process by increasing carbon concentration more effectively and contributing to less waste of this raw material, synthetic graphite was chosen in this work because, in addition to dissolving the carburizer faster and more uniformly, it has a crystalline structure. Thus, this work aimed to evaluate the substitution of calcined petroleum coke with synthetic graphite in the manufacture of internal parts of gray cast iron combustion engines in the PIM industry. Thermal analysis, spectrometry for chemical composition analysis of metals, tensile mechanical testing, hardness testing, metallography, and optical microscopy techniques were used. According to initial tests, synthetic graphite is a potential substitute fuel for calcined petroleum coke, since using the same quantity of standard coke (17 + 3 kg) the adequate mechanical properties of the factory specifications for gray cast iron (FC250) were achieved, i.e., gray cast iron with a ferritic matrix and “type A” carbon > 70%. Tests with smaller quantities, 16 and 14 kg, are ongoing for mechanical properties; however, the carbon composition was achieved in both tests with values higher than coke and with greater homogeneity. For 16 kg charge of synthetic graphite, an 8.2% higher composition was obtained. While for the lowest charge, a 5.5% higher yield was obtained compared to calcined petroleum coke. Thus, synthetic graphite can be a substitute for calcined carbon coke as a fuel for the manufacture of gray cast iron.