Studies were made of the creep properties and structure change of steet 20Cr11MoVNbNB at 550-650℃.It is found that at 550℃ when creep stress>180 MPa there exists linear rela- tion with two different slopes β_1 and β-2 between transitional creep strain ε_β and creep time t~(1/3),and β_1(in initiol period)>β_2(in later period).The Creep rate of stable stage at 550℃ can be expressed by =Aσ exp(-Q_ /RT),where,n=4.7.A exp(-Q_ /RT)= 5.37×10~(-16).Apparent creep activation energy Q_ =430 kJ/mol at 550-650℃,which is much higher than the self-diffusion activation energy of atoms for matrix Fe.In creep process,as the creep stress and time increase,the total weight of precipitated phases and rela- tive weight of Cr,Mo and V increase,but those of Fe and Nb decrease in precipitated phases,
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