Characterization of Residual Stresses in 718 Turbine Discs by Neutron Diffraction and Finite Element Modelling

Abstract

The results of our investigations on residual stresses in commercially produced forged IN 718 compressor discs are reviewed. The residual stresses in the discs with a diameter of 320 mm and a thickness of up to 25 mm were studied using neutron diffraction to verify the predictions of a finite element simulation, which was used to model forging and cooling of the discs. In addition to the disc, a thin plate of the same material was also studied for testing the influence of specimen geometry on the model predictions. While the model results for the disc were not strongly influenced by the heat transfer coefficient, the stress distributions in the thin plate could only be predicted satisfactorily by using a temperature-dependent heat transfer coefficient that was derived from temperature measurements during quenching. Eventually, this led to an improvement of the FE simulation used for optimizing the production process.