a ni — fe based super alloy having high strength and toughness at high temperatures even when used in high - temperature environments , and a process of producing the super alloy . a turbine disk using the super alloy , a process of producing the turbine disk , a turbine spacer using the super alloy , and a process of producing the turbine spacer , as well as a gas turbine are also provided . the ni — fe based super alloy contains not more than 0 . 03 % by weight of c , 14 - 18 % of cr , 15 - 45 % of fe , 0 . 5 - 2 . 0 % of al , not more than 0 . 05 % of n , 0 . 5 to 2 . 0 % of ti , 1 . 5 - 5 . 0 % of nb , and ni as a main ingredient .