Abstract: Grain structures of nickel-base superalloy IN 738LC are invesitated under various casting conditions. It is found that grain size of y matrix and dimension of MC carbides reduce obviously by lowering the temperature of melt homogeneous treatment.The mechanism of grain refinement can be the existence of a number of unmeIted MC particles that serve as the substrata of nonspontaneous nucleation of y matrix during freezing.By comparing meIt pouring tempera-ture,mold preheating temperature with melt homogeneous treatment temperature,it can be con cluded that the last one plays a more predominant role on the grain structures than the first two。Therefore,one of the effective methods of refining grain structures is via controlling the melt homogeneous temperature.

Key words: heat resistant alloys, grain size, carbides