Residual Stress Evolution during Manufacture of Aerospace Forgings

Abstract

The residual stresses present through the quenching, ageing, and machining processes in sub-scale forgings of RR1000 have been measured experimentally using neutron diffraction, and the contour method. The forgings, 88.9mm in diameter, and 25.450.8mm thickness, were of small enough geometry to allow neutron strain measurement in 3 directions throughout most of the bulk. The contour method was employed successfully to generate a full 2D map of the hoop stress in the as-aged and machined samples. The two experimental data sets have been shown to agree very well. Finite element modelling predictions based on an experimentally derived heat transfer coefficient (HTC) curve allowed further comparison and generated additional data. Agreement between the experimental and simulated data was found to be reasonable with some discrepancy visible in the axial direction. The water quenching process was found to generate peak stresses up to 1400MPa in the hoop and radial direction, which were relaxed by as much as 700MPa through ageing. Material removal by machining had a less significant impact in most cases, relaxing residual stress by 100-200MPa.