<![CDATA[The purpose of this study was to determine how the chemical composition and microstructure formed in medium carbon steel hardened with banana tree sap fluid compared to oil and water. The process of carbon steel hardening is being heated to the austenite area (850oC ) then held for 10 minutes after which it is cooled quickly (quenching). During the cooling process, it is also measured the cooling rate of the three cooling media. Hardening process material is carried out by microstructure observation using an optical microscope with 400x magnification and also chemical composition testing with SEM-EDX. The results for measuring the cooling rate of banana fluid have a fast cooling rate of 36.9oC/s while water is 16.6oC/s and oil is 7.0oC/s. In observing the microstructure of water it has an unstable micro structure that is still the structure of pearlite, this is because the temperature of the cooling media is too high during quenching. And for oil microstructure and banana fluid get a homogeneous structure, namely martensite and bainite. From the results of testing the chemical composition, it was seen that there was an increase in carbon content in steel after hardening and quenching with the three cooling media. Conclusion The hardening process by quenching oil and banana fluids has a homogeneous micro structure compared to water. Water cooling process has the highest carbon content increase of 1.53 %C from before 0.52 %C.]]>
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