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The main objective of Vacuum Arc Remelting is to control solidification conditions in order to obtain a columnar dendritic structure throughout the whole ingot. The change in primary dendrites' growth direction, determined by the pool shape, leads to non-isotropic material properties in terms of plastic flow. As the correct prediction of flow behavior is crucial for the further analysis of forming processes (as for example in the application of damage criteria), this specific feature of remelted material has to be accounted for in the modeling of ingot breakdown. Using Barlat's formulation for the plastic flow, the structural constitution of alloy 718 VAR ingots could be linked to the alloy's plastic flow behavior by modeling the inhomogeneity of properties determined by remelting experiments and simulations. Hence, the influence of different remelting process conditions on hot workability could be examined. Compared to the commonly used von Mises approach some differences could be revealed. 65

Abstract. The main objective of remelting processes commonly used in the production of superalloys is to obtain a columnar dendritic solidification structure throughout the whole ingot. Besides reduced microsegregation, this cast structure features a preferred orientation, which is depending on the primary dendrites' growth direction and therefore closely related to the ingot's pool shape. As a result, non-isotropic material behaviour can be observed during initial forging operations. Since the correct prediction of material flow is a prerequisite for the further analysis of forging processes by means of numerical simulation, the solidification texture's influence on plastic flow was accounted for by the application of an anisotropic material model. The model according to Barlat was used to scale the flow stress with respect to the crystal orientations observed in the examination of vacuum arc remelted alloy 718, thereby considering the flow stress' dependency on strain, strain rate and temperature. The parameters defining the material's anisotropy could be determined by the upsetting of cylindrical specimen from a remelted ingot.

This paper focuses on metallurgical issues and manufacturing of impellers for an integrally geared 2-stage expander for a corrosive hot-gas application. The design employs the largest single piece forging in Alloy 718 material for use in the low pressure stage impeller. Alloy 718 was chosen due to the combination of best corrosion resistance and mechanical properties. With this single piece forging it is possible to manufacture very large impellers in a "non-welddesign". Information about development of the disc production, the manufacturing process and mechanical properties are presented.

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