A Sound Pressure Field during the Quenching of a Steel Specimen in Different Water Solutions

The production of machine parts usually ends with some kind of a heat treatment. A proper heat treatment, like quenching, provides increased surface hardness, which improves wear resistance. The quenching process must be fast to achieve the required hardness, but not too fast to prevent surface damage. Monitoring of the quenching process in real time, and an appropriate control can improve the quality of the production. During the quenching process different stages of heat transfer occur (Figure 1). The appearance of the individual stage depends on the process parameters and on the properties of the work-piece. The quenching of a steel work-piece always starts from temperatures over 800 °C (austenitizing temperature). At the beginning of the immersion, the cooling liquid is vaporized and a stable film of vapour is formed around the work-piece, keeping its surface dry, (the film boiling or vapour blanket stage). The vapour film collapses chaotically and causes an uneven heat removal from the surface, 1 . A nucleate boiling occurs where the surface cools down below the Leidenfrost temperature and the cooling liquid wets the surface. The convective heat transfer stage is followed by the nucleate boiling stage, 1, 2 . All three stages can coexist simultaneously on different surfaces of the work-piece, and even on different areas of the same surface. A distribution of these three cooling stages determines the heat transfer from the work-piece into the