Measuring of the quenching effect of liquid hardening agents on the basis of synthetics

Abstract

To judge liquids for steel hardening, normally special test specimens are quenched by means of immersion. Characteristics are taken from temperature-time curves, which are picked up in the sample center. These characteristics (i.e. temperature of transition from filmboiling to nucleate boiling – LEIDENFROST-Temperature – and cooling rates) serve as criterions for the judgement of quenching effect. The effect of sample characteristics (geometry and material) upon characteristic values of the cooling curve was determined. Hence a proposal to design a test specimen was derived. This specimen (Chromenickel-steel-cylinder, diameter 15 mm, length 45 mm, rounded edges) presents of all examined configurations a very good possibility to a precise judgement of quenching media as well as chances to estimate the quenching process in case of steel hardening. As common quenching tests (with a single – central – hot junction) do not allow to draw conclusions referring to steel hardening, an additional method was developed to calculate the surface-temperature dependent heatflux density (respectively heattransfer coefficient) from three temperature-time-curves, measured on different radii of the sample cylinder. The reliability of this method was proved (differential method according to Binder-Schmidt).