Effect of cooling rate on microstructure and hardness in gray cast iron casting process

Casting is conducted by melting and solidifying the metal and forming it according to the desired shape in the mold. Due to environmental issues, there were considerations to choose permanent molds instead of sand molds. This study aims to investigate the thermal conditions of the molds, changes in microstructure and hardness of casting products using sand mold and permanent mold. The use of sand mold and permanent mold results in different cooling rates. Thermal analysis was performed using a thermocouple to obtain a temperature versus time curve. Metallographic observations were carried out using a Scanning Electron Microscope equipped with Energy-Dispersive X-ray Spectroscopy. The Vickers hardness test was carried out in three areas with different thicknesses. The results showed a constant temperature at 691 °C where the eutectoid phase reaction occurred. Testing with sand mold showed that cast iron with flake graphite was finer and spreader than graphite in cast iron produced by permanent mold. Meanwhile, gray cast iron from a casting process with a permanent mold has a higher hardness than gray cast iron from a casting process using a sand mold.