To check long term degradation behavior of hydraulic forged superalloy 718 during exposure at high temperature, an Alloy 718 ingot with a diameter of 400mm was manufactured by the vacuum melting process, VIM followed by VAR. The ingot was broken down for uniform microstructure and mechanical properties by a controlled cogging process using a hydraulic press. To investigate long term degradation behavior of impact properties and hardness, the specimens were exposed to 600oC, 650oC and 700oC for holding times up to 12,112 hours. Impact energy absorption tests were performed at room temperature. The fractured area and the microstructure of the impact specimens were observed by OEM and SEM and Brinell hardness tests were also performed. The changes of impact energy and hardness are remarkably different for each temperature condition. The results suggest that the impact properties and hardness of Ni based superalloy 718 is strongly related to temperature and time during high temperature exposure.