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

Abstract

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.

Effect of Pre-Stretching on Residual Stresses and Microstructures of Inconel 718 Superalloy

“…During quenching, due to the surface layer of the specimen being in direct contact with the quenching medium, the cooling rate of the outer surface is faster than that of the core, which results in a gradient of tensile and compressive residual stress. Staron et al [13] and Dye et al [14] characterized the compressive residual stress on the surface of IN718 alloy after quenching by the neutron diffraction method and a finite element model at around 440-500 MPa. It was found that the size and shape have little effect on the distribution of residual stress on the specimen surface.…”