Abstract In this study, aiming to optimize the acoustic properties of ultrasonic horns, the effects of various heat treatment processes on two alloy steels, 36CrNiMo4 and 42CrMo4, were investigated. These two steels are chemically very similar, with the primary difference being the presence of nickel in 36CrNiMo4. The applied heat treatment methods included annealing, normalizing, oil quenching, and water quenching. Parameters such as Rockwell C hardness, damping ratio, sound velocity, natural frequency, and thermal behavior under operational conditions were eva‎luated. The results revealed that the highest hardness was observed in the water-quenched sample, while the annealed specimen exhibited the lowest hardness. Additionally, oil quenching at 840 °C for 100 minutes led to the lowest damping ratio (0.1698) and the highest sound velocity (5097 m/s). Under these conditions, 42CrMo4 demonstrated superior performance compared to 36CrNiMo4 and was identified as the most suitable material for ultrasonic horn manufacturing. In contrast, the annealed 36CrNiMo4 sample, with the highest damping ratio (0.9606) and the lowest sound velocity (1442 m/s), showed the weakest acoustic performance. The one-hour thermal test results also indicated that the lowest temperature rise occurred in the oil-quenched samples, while the highest was observed in the annealed ones. Microstructural analysis revealed a significant presence of ferrite and pearlite in the annealed specimens, contributing to increased vibration absorption and reduced sound velocity. Conversely, the oil-quenched samples predominantly exhibited needle-like martensitic structures along with small amounts of retained austenite, which provide favorable dynamic and acoustic properties, along with adequate hardness and low brittleness—making them well-suited for ultrasonic horn applications.

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عليرضا مومني , ابوالحسن عسگر شمسي