Abstract: Relationship between the size of γ′ phase,hardness and variation of overheated temperature was studied in overheated condition by using replica technique and film technique. It is found that with increasing temperature,the carbide in grain boundary reduces from 800 ℃ to 950 ℃,the size and quantity of γ′ phase also decrease obviously,and so does the hardness. According to analyzing the size of γ′ phase in replica specimen and film specimen,it is shown that the size of γ′ phase can be gained from using replica technique.