RELATIONSHIP BETWEEN CREEP PROPERTIES AND STRUCTURE OF STEEL 20Cr11MoVNbNB

Studies were made of the creep properties and structure change of steel 20Cr11MoVNbNB at 550—650℃. It is found that at 550℃ when creep stress 180MPa, there exists linear relation with two different slopes β_1 and β_2 between transitional creep strain e_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 as e_(11) = Aσ~nexp(-Q_c/RT), where, n=4.7, A exp(-Q_c/RT) = 5.37×10~(-16). Apparent creep active energy Q_c= 430kJ/mol at 550-650℃, which is much higher than the self-diffusion active energy of atoms for matrix Fe. In creep process, as creep stress and time increase, total weight of precipitated phases and relative weight of Cr, Mo and V increase, but those of Fe and Nb decrease in precipitated phases.