<![CDATA[AISI 1045 steel is a medium-carbon steel widely used for machine components due to its favorable combination of strength, toughness, and machinability. Its mechanical properties can be enhanced through heat treatment, specifically quenching using various cooling media. This study aims to analyze the effect of different cooling media on the microstructural changes of AISI 1045 steel following the quenching process. An experimental method was employed using three cooling media variations: 25% NaCl solution, SAE 10W-30 oil, and distilled water. Specimens were heated to an austenitizing temperature of 850°C with a 60-minute holding time, followed by quenching for 5 minutes in each respective medium. Microstructural characterization involved metallographic preparation comprising grinding, polishing, and etching with 5% nital solution followed by observation under a metallographic microscope at 200× and 400× magnifications. Observations revealed that the raw material was dominated by ferrite and pearlite structures. After quenching, a martensitic structure formed, with the quantity and distribution varying according to the cooling medium used. The 25% NaCl solution produced the most dominant and relatively uniform martensitic structure, followed by distilled water, whereas SAE 10W-30 oil resulted in a lower proportion of martensite, with ferrite and pearlite remaining dominant. These differences indicate that the cooling rate characteristics of the quenching media influence phase transformation and the resulting microstructure of AISI 1045 steel. Based on the observations, the 25% NaCl solution provided the most intensive cooling effect compared to distilled water and SAE 10W-30 oil.]]>
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