Rewetting Behaviour During Immersion Quenching

Th. Lübben, F. Frerichs, F. Hoffmann, H.-W. Zoch:
New challenges in heat treatment and surface engineering – conference in honour of prof. Božidar Liščić (09 – 12 June 2009, Dubrovnik – Cavtat, Croatia)

Immersion quenching is a widely used technique in heat treatment, because this technique provides higher heat transfer coefficients than the most alternative gas quenching techniques.
The disadvantage of immersion quenching in evaporating fluids is the complex heat transfer mechanism which consists of three phases, namely film boiling, nucleate boiling and convective cooling. Especially the transition from film to nucleate boiling – the rewetting of the sample surface – is a complicated process which leads to an extreme local dependence of the heat transfer coefficient. Therefore immersion quenching is very difficult to control and often leads to distortion of the quenched workpieces. During our experiments the rewetting behaviour was investigated by means of hollow and solid cylinders.
These workpieces offer the possibility to investigate different distributions of surface temperatures of samples with the same outer geometry/curvature. The observation of the rewetting process was done by means of video films. Additionally, the cooling curves at two positions near to the surface were measured. From these data, the heat transfer for the quenching simulation by Finite Element Method were estimated and rewetting curves were calculated.

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