Resumo:
Piston rings are components of the internal combustion system of engines, and these are
mostly made of gray cast iron, which must have high tensile strength and hardness for
working in severe conditions. This work aimed to evaluate the influence of the addition of
inoculants on the occurrence of silicon inclusions in gray cast iron parts with thin cross
sections, such as piston rings. The presence of inclusions in metals generates a point of stress
concentration, which can result in the nucleation of fatigue cracks and lead the component to
failure during its operation. Understanding the influence of inoculants on the occurrence of
these inclusions will contribute to the reduction of parts rejected by foundries, in addition to
preventing an eventual failure of the component in the field. For this work, two castings were
designed to evaluate the behavior of the variables granulometry, amount of inoculant and
method (moment) of inoculation to meet the demand of the planned experiments. The results
obtained with the experiments were analyzed using statistical methods such as Chi-Square,
Regression Analysis, Design of Experiments (DOE) and Desirability. The cast samples that
presented silicon inclusions were analyzed according to the microstructure, chemical
composition and hardness specifications, and the inclusions were characterized through
microhardness tests, optical microscopy, and scanning electron microscopy. It was possible to
confirm that the occurrence of inclusions is associated with the addition of the inoculant, and
that the variables granulometry and amount of inoculant are strongly related to the occurrence
of the defect. Statistical methods confirmed that the greater the particle size and the amount of
inoculants added to the bath, the greater the probability of the occurrence of the silicon
inclusion defect in the piston ring.
