The application of water-air spray cooling in the process of induction surface hardening according to the simultaneous dual-frequency technology represents a hitherto unexploited and equivalent alternative to conventionally employed polymer solutions. The reason for this is that the selection of the optimum parameters is associated with a high experimental outlay and analytical effort for performing the tests and evaluating the results, respectively, and the parameters must be selected for a specific application. In order to reduce this effort, a numerical model was developed to formulate the coupled thermal, microstructural, and mechanical processes during quenching by means of water-air spray cooling of induction heated spur gearwheels made from 42CrMo4 hardening and tempering steel. The model was implemented in the commercial simulation software ANSYS Workbench 13.0 and verified using simulation results for temperature development, hardness distribution, residual stresses, and distortion. A comparison of the simulated and experimental results show that the model introduced here is suitable for predicting the hardening results during quenching using spray cooling subsequent to induction heating.

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Application of products with properties locally adapted for specific loads and requirements has become widespread in recent decades. In the present study, an innovative approach to manufacture tubes with tailored properties in the longitudinal direction from a boron-alloyed steel 22MnB5 was developed. Due to advanced heating and cooling strategies, a wide spectrum of possible steel phase compositions can be obtained in tubes manufactured in a conventional tube forming line. A heat-treatment station placed after the forming line is composed of an inductive heating and an adapted water-air cooling spray system. These short-action processes allow fast austenitizing and subsequent austenite decomposition within several seconds. To describe the effect of high inductive heating rates on austenite formation, dilatometric investigations were performed in a heating rate range from 500 K s-1 to 2500 K s-1. A completed austenitizing was observed for the whole range of the investigated heating rates. The austenitizing was described using Johnson-Mehl-Avrami model. Furthermore, series of experiments on heating and cooling with different cooling rates in the developed technology line was carried out. Complex microstructures were obtained for the cooling in still as well as with compressed air, while the water-air cooling at different pressures resulted in quenched martensitic microstructures. Nondestructive testing of the mechanical properties and the phase composition was realized by means of magnetization measurements. Logarithmic models to predict the phase composition and hardness values from the magnetic properties were obtained. Subsequently, a simulation model allowing virtual design of tubes in the FE-software ANSYS was developed on basis of experimental data. The model is suited to predict microstructural and mechanical properties under consideration of the actual process parameters.

The choice of embedding-media for metallographic specimen preparation, where subsequent scanning electron microscopy will be performed, is highly important since the quality of the analytical results in the specimen's near-surface region is limited by the properties of the embedding-material. Due to their high electrical conductivity and only slight tendency to form gaps between near the sample surface, warm curing embedding-media are usually best suited. Hot embedding-presses use relatively high pressures at elevated temperatures that can be detrimental for sensitive materials or coatings. Cold embedding with conventional embedding-media, which does not require high pressure mounting, requires compromising for a material with a lower electric conductivity, a higher amount of pores in the material, and inferior interfacial connectivity to the specimen. For this reason, the development of alternative electrically conductive and cold hardening embedding-media is of great interest for metallographic sample preparation of electron microscopy specimens. In the present study, various embedding-media were evaluated with respect to their suitability for scanning electron microscopy and a novel conductive mounting compound has been identified and qualified.