Abstract: Carbides in new type Hf-Ta-containing nickel-based superalloy FGH98 Ⅰ powders prepared by plasma rotating electrode processing(PREP) before and after pre-heat treatment at different temperatures were studied.The results show that MC' type carbides in the initial powders can be divided into two groups.One is rich in Ti,Ta,Nb and the other contains the elements of Ta,Hf and Zr.The two types of carbides both contain a certain amount of non-carbide forming elements(Co,Ni) and medium carbide forming elements(Cr,Mo),and these carbides locate between interdendrites or cells and in block and granule shapes.Ti-Ta-Nb riched MC' type carbides in the powders can be transformed into MC type carbides and the total amount of Ti-Ta-Nb increases with increasing pre-heat treatment temperature.The Ta-Hf-Zr contained MC' type carbides can be decomposed and transformed into M₂₃C₆,M₆C and MC type carbides.It is also shown that the precipitate and dissolution temperatures of M₂₃C₆ type carbides are 950℃ and 1150℃ respectively,and the co-existing temperature of M₂₃C₆ and M₆C type carbide is within the range from 1000℃ to 1100℃.In addition,trance elements Hf and Ta in the powders take part in the reactions of carbides mainly in the form of carbides and γ' phases.