Modelling High Integrity Steel Forgings for Turbine Applications in the Power Generation Industry

Abstract:

The continuous drive toward higher operating efficiency, greater reliability and longer life of steam turbines has introduced a need for higher integrity components to operate at higher temperatures and pressures. This poses several material and processing challenges to ensure that the components have metallurgical stability and the required mechanical properties in the high temperature environment. Modelling the open-die press forging process, used to manufacture steam turbine discs from cast ingots, is complex due to the variation of strain, strain rate and temperature within the ingot. These variations mean that recrystallisation and grain growth do not occur uniformly throughout the ingot. Severe plastic deformation is used to promote recrystallisation in order to refine the grain size and improve strength and toughness properties. A major part of the modelling described in this paper involves prediction and validation of strain, strain rate and temperature distributions during open-die forging. A sensitivity study has confirmed the requirement for accurate thermal and physical data such as Interfacial Heat Transfer Coefficient (IHTC), work-piece emissivity, specific heat and friction coefficient. In this paper experimental determination of these data for the grade of heat resistant steel being modelled, over process parameter ranges appropriate to open-die forging operations, is described. Incorporation of these data into a finite element-based model for strain variation within an ingot is reported with consideration and measurement of dead zone for thermo-mechanical simulation trials.

• Periodical: Advanced Materials Research (Volume 922)
• Pages: 795-800
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.922.795
• Online since: May 2014
• Authors: Christopher J. Watson*, Trevor A. Dean, Martin Strangwood, Claire L. Davis
• Keywords: Hot Open-Die Forging, Modeling, Parametric Sensitivity Analysis, Power Generation Steel, Simulation, Steam Turbine Discs

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