<p>Ferromanganese alloys, widely used in the steel industry, are produced through a horizontal casting process. This study investigates how different cooling methods influence crack formation in medium-carbon ferromanganese alloys during horizontal casting, with a focus on microstructural evolution and internal stress. Heat conduction and stress generation were numerically calculated, and experimental analyses of the microstructure were conducted. The probability of crack formation decreases when thermal stress and temperature gradients are reduced during the water-cooling stage. Initiating water cooling at a high temperature results in larger temperature gradients and thermal stresses near the alloy surface. This cooling condition leads to the formation of a mixed microstructure composed of acicular α-Mn and carbide phases in the upper region of the alloy. In contrast, when water cooling begins below the eutectoid temperature, thermal stress is reduced, and a gradual phase transformation occurs, producing a lamellar-shaped eutectoid structure. To minimize thermal stresses and suppress crack formation, implementing a slow cooling stage before reaching the eutectoid temperature is shown to be effective. This study elucidates the mechanisms of crack formation in ferromanganese under various cooling conditions by combining simulation with microstructural analysis and provides insights into optimizing the cooling process in horizontal casting of ferromanganese alloys.</p>