This research was conducted aiming to find out the influence of heat treatment particularly quenching toward metals type FC 20. This research used some methods among others are observation and literature study by doing observation and information collection from various sources as well as information on heat treatment and things related to casting process. In the metal casting process, casting was taken for some metals such as return scrap, cast carbon, silicon, and used metals. The research results show that the composition test results in 3.18% for the carbon value so that the materials in this gear making are included in cast iron which basically has the properties of being resistant to heat and brittle. Hence, it is appropriate to be used as the gear making materials experiencing continuous force. The influence of Quenching oil heat treatment makes the materials become brittler. From the results of the research using Vickers hardness test, it is found that the heat treatment (Quenching) shows a significant changing score. It is shown by the highest score of the Vickers hardness test with Quenching oil materials reaching the score of 427.84 VHN. Meanwhile, in raw materials, the test shows the highest score 378.18 VHN.