Analysis of process parameters of hypoeutectoid steel ultrasonic horns with different heat treatment processes

An ultrasonic horn operated at 28 kHz was simulated by finite element analysis. The horns and samples were formed from hypoeutectoid steel containing 0.178 wt% C and 1.3 wt% Cr. They were austenized at 875 degrees C with a soaking time of 33 min, then quickly water-quenched and oil-quenched. Tempering was performed at different temperatures (200 degrees C-500 degrees C) and soaking times (120-240 min). Over the cross-section, the hardness was consistently lower at the center position than at other positions. The maximum (minimum) hardness was achieved after water and oil quenching, tempering at low (high) temperature, and soaking for a short (long) time. Heat treatment decreased the anti-resonance frequency of the ultrasonic horns but increased the mechanical quality factor and the impedance at the anti-resonance frequency. The mechanical quality factor was proportional to both tempering temperature and soaking time. As shown in microstructural images, high mechanical quality was also related to small grain size.