Surface Structuring as a Method to Influence on Rewetting during Liquid Quenching

Quenching is an important process in the heat treatment of metallic components. This is usually performed as immersion quenching in vaporizing liquids, such as water. Quenching in water is characterized by relatively small effort and high average quenching rate. Disadvantage of this method is the occurrence of the Leidenfrost effect. The Leidenfrost effect manifests itself in the fact that a thin vapor film is formed on the hot component surface, which greatly reduces the heat flow between the component and the quenching medium. Depending on the component geometry and quenching conditions the vapor film collapses unevenly at different time and location. This causes component distortion, residual stresses and unevenness of metal structure. Many studies on the Leidenfrost effect are dealing with influences of quenching medium and quenching conditions. In this work, the influence of component surface structure on the quenching kinetic has been investigated as a novel approach in the surface engineering. The focus of the work is on the investigation of surface structures, which can be produced during the turning process of cylindrical components without much additional effort. The investigation was made with water as a quenching medium by means of aluminium and steel components with defined groove surface structures. Geometry of the surface structures was varied. The evaluation was based on time-temperature measurements, and rewetting front observations. It was found that the purposefully structured surface can affect quenching kinetic considerably. The possibility to control and homogenize the quenching process by surface structuring adapted to component geometry was confirmed. This indicates a high potential for homogenizing of immersion quenching in vaporizing liquids and therefore reduction of asymmetrical residual stresses and avoidance of distortion in the quenched components. The integration of the surface structuring in a manufacturing process of components is relatively easy, because in most cases it only requires an adaptation of turning parameters.