Alloy 718 is a widely used alloy in SNECMA's engines for applications in forged rotating parts. The most important mechanical property, low cycle fatigue, depends strongly on grain size, which results directly from the forging process. Metallurgical data have been coupled with FORGE2R metal flow numerical results to give a prediction of grain size in recrystallized and dead zones. After calibration, using measurements on forged parts, this approach proved to be an efficient metallurgical forge modelling.