<![CDATA[Carbon steel is one of the most widely used engineering materials in the manufacturing and construction industries due to its favorable mechanical properties, ease of fabrication, and relatively low production cost. One of the most important parameters in evaluating carbon steel quality is hardness, which reflects the material's resistance to plastic deformation. This study aims to characterize the mechanical properties of carbon steel through Rockwell hardness testing using the Jominy End Quench method, determine the hardness distribution along the specimen, and analyze the relationship between the testing position and hardness value. The research employed ST 37 carbon steel specimens with a diameter of 25 mm and a length of 100 mm. The specimens were heated to 763°C, held for 5 minutes, cooled using the Jominy End Quench method, and subsequently tested using the Rockwell hardness method at ten measurement points. The results indicate that the hardness decreased from 78.6 HRB at a distance of 4 mm to 72.1 HRB at 40 mm, reflecting the reduction in cooling rate along the specimen. The average hardness value obtained was 67.205 HRB, with a measurement accuracy of 99.91%. Regression analysis produced the equation Y = 73.255 − 0.3025X, indicating that every 1 mm increase in testing distance resulted in a hardness reduction of approximately 0.3025 HRB. The correlation coefficient of −0.886 demonstrates a very strong negative relationship between testing position and hardness, while the coefficient of determination of 78.53% indicates that most of the hardness variation is influenced by the testing position or cooling rate. The findings confirm that the combination of the Jominy End Quench method and Rockwell hardness testing is effective for evaluating the hardenability and hardness distribution of carbon steel.]]>
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