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

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.