Ultrasonic horns are critical components in high-power acoustic systems, where effective wave transmission depends strongly on the material’s microstructural and mechanical characteristics. This review investigates how hot forging—typically performed at 1050–1150 ℃ with strain rates of 0.1–10 s−1—modifies the grain structure, hardness, and ultrasonic attenuation of horn materials such as C45 and H13 steels. Controlled thermomechanical processing leads to refined equiaxed grains (5–20 µm), increased hardness (>45 HRC), and reduced internal scattering. Experimental studies report up to 30% improvement in wave amplitude and a decrease in attenuation coefficient by 15–25% compared to as-cast or annealed conditions. Modeling techniques, including finite element analysis (FEA) and cellular automata (CA), are also discussed for predicting microstructural evolution and wave behavior. This work consolidates recent findings to inform the design of forging strategies that optimize both structural integrity and acoustic efficiency in ultrasonic horn applications.