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The relevance of &precipitates for controlling the grain size in Nickel-base alloys during the forging process is well known. However, a high volume fraction of &-phase causes a lower Nbcontent of the matrix, followed by a reduced fraction of y"-precipitates and, thus, less favourable mechanical properties. Considering these facts, the possibility of calculating the dissolution kinetics of &precipitates as a function of time, temperature, chemical composition and size is of high importance for modelling the microstructure development during a forging process. In computer simulations of diffusional phase transformations (e.g, with software DICTRA) the high number of relevant alloying elements in INCONEL718 leads to massive problems with the numerical stability. Therefore, a multi-component precipitation model included in the thermo-kinetic computer program MatCalc was used to calculate the &phase dissolution at various temperatures. Interrupted annealing experiments were performed and the fraction, size distribution and morphology of the &precipitates were determined by means of quantitative optical microscopy. When comparing the experimental data with the calculations, very good agreement was found.

S C I X L ~'press forging experiments on industrial equipment are carried out in order to evaluate the potential of this process for the production of jet engine disks from the direct aged nickel base alloy IN718. Metallography, electron microscopy and elevated temperature tensile tests are pel-l'ormed to analyse and quantify the strength improvements due to direct aging. The results of these analyses clearly demonstrate that the production of direct aged IN718 turbine disks is possible on ; I screw press.