The effect of silicon content on microstructure and mechanical properties of gray cast iron

Gray cast iron has a drawback, that is a very low ductility value so that when subjected to tensile forces a fracture plane will form because graphite resembling mica is very brittle. To get cast iron with high tensile strength, the value of Sc (eutectic degrees) must be smaller and also by adding a little calcium silicon or ferrous silicon to the molten iron just before pouring, that is to prevent the formation of white cast iron, thus the graphite produced is finely dispensed evenly on the pearlite matrix. This process is called inoculation. Silicon (Si) is an indispensable element in the manufacture of gray cast iron because Si is known as a graphite stabilizing element in cast iron. Silicon increases the formation of graphite in place of iron carbide. This study aims to analyze the effect of silicon content on the microstructure and mechanical properties of gray cast iron. In this study, the process of casting gray cast iron was carried out at PT. Mitra Rekatama Mandiri, Klaten. The silicon content studied were 1.7586 wt Si, 1.8282 wt Si, and 2.0065 wt Si. The testing process carried out is testing the chemical composition, observing the microstructure, testing the brinell hardness, and testing the tensile strength. The results showed that the increase in the silicon content in the sample led to an increase in the number of ferrite phases in gray cast iron. The increase in silicon content also influences the distribution and size of gray cast iron graphite. The highest hardness value is owned by Sample C, which is 282 BHN. While the lowest hardness value is owned by Sample B, which is 187.4 BHN. Sample B had the lowest tensile strength and percent elongation, namely 13.26 Kg/mm2 (130 MPa) and 1.88. Meanwhile, Sample C had the highest tensile strength and percent elongation, namely 19.13 Kg/mm2 (187.6 MPa) and 2.76.