Grain growth model of IN718 during holding period after hot deformation

After hot deformation, a practical forging is unavoidably held at a high temperature for some time. The microstructure and mechanical properties of the forging will change during the holding period. In order to obtain a determinate final microstructure and good mechanical properties in an IN718 forging, it is necessary to understand the microstructure variation behavior and to be able to predict the grain size of superalloy IN718 during a holding period after hot deformation. In the present work, isothermal constant speed compression tests were conducted using a computer-controlled MTS machine at temperatures of 980 and 1020°C, with initial strain rates ranging 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 the holding period after hot deformation was studied. The effect of hot deformation 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 holding parameters.