Prediction of Distortions in Hot Forged Martensitic Stainless Steel Turbine Blades by Numerical Simulation

Hot forged parts characterized by thin sections may suffer geometric distortions during the cooling phase that force the process designers to work with significant machining allowances. The correct identification of the such defects during the process design might allow the proper set of the process parameters for their compensation and, therefore, the reduction of the allowances and the machining steps. The early computation of such distortions can be fulfilled by using thermal-mechanical-metallurgical models of both the forging and cooling phases, which must be calibrated through extensive experimental campaigns, involving both laboratory experiments and on-field measurements during industrial production.The paper presents a coupled experimental and numerical approach to predict the geometrical distortions of turbine blades in martensitic stainless steel. The presented approach comprises both the development of the numerical models of the forging and cooling phases and their calibration using accurate material data. In order to validate the numerical models, the numerically predicted geometries are compared to those measured during cooling by using a newly developed laser scanning system devoted to high temperature measurements of complex-shaped parts just after the forging step and during all the cooling phases.