Void Consolidation during Open-Die Forging for Ultralarge Rotor Shafts : 3rd Report, Satisfaction of Criterion for Void Consolidation by Precooling Ingot Forging Method

A hydrostatic stress ratio of greater than 0.9 was proposed as one of the most significant criterion for void consolidation after closing during open die forging, on the basis of some physical modeling tests on 3.5NiCrMoV-rotor steel billet with a hole at the centerline and numerical simulation using the three-dimensional rigid-plastic finite-element method. To satisfy the criterion for void consolidation in a forging process of large rotor shafts, it was found that the use of a precooling ingot forging method for a rectangular cross-section-ingot is highly effective since the hydrostatic stress ratio at the center of the ingot remarkably increases with the increase of aspect ratio in the cross section from 1.0 to 1.8. The enlargement of width in the rectangular cross section enabled the development of the optimum maufacturing process of an ultralarge low-pressure turbine rotor shaft with 2800 mm and over diameter.