Grain growth model of IN718 during holding period after hot deformation

After hot deformation, a practical forging is unavoidably held at a high te mperature for some time. The microstructure and mechanical properties of th e forging will change during the holding period. In order to obtain a deter minate final microstructure and good mechanical properties in an IN718 forg ing, it is necessary to understand the microstructure variation behavior an d to be able to predict the grain size of superalloy IN718 during a holding period after hot deformation. In the present work, isothermal constant spe ed compression tests were conducted using a computer-controlled MTS machine at temperatures of 980 and 1020 degrees C, with initial strain rates rangi ng from 0.001 to 1.0 s(-1). The specimens were compressed to an engineering strain of 0.1, 0.4, or 0.7 (corresponding to 10, 40, and 70% reduction in height) and then were held at the deformation temperature for 0, 10, 30, or 60 min. The microstructure variation behavior of superalloy IN718 during t he holding period after hot deformation was studied. The effect of hot defo rmation and holding parameters on the grain growth was analyzed and a model was developed to express the relationship of the grain size with both hot deformation and fielding parameters. (C) 2000 Published by Elsevier Science S.A. All rights reserved.