Abstract: A superalloy disk to be utilized for a rotating body of an aircraft or turbine engine is manufactured by a casting mold provided with a cavity having an inner shape for forming a disk. A molten bath of superalloy melted under a vacuum or an inert gas atmosphere is poured into the casting mold under a vacuum or an inert gas atmosphere and the casting mold with the molten bath is stirred so as to prepare a rough casting of fine crystal grains by applying an external force such as an eccentric centrifugal force. The thus produced disk material may be heated thereafter. The rough casting is formed of crystal grains less than 100 .mu.m in diameter, and a rate of strain during the rotational forging is less than 10.sup.0 /sec. amd more than 10.sup.-2 /sec.