Analysis of Microstructure Evolution of GH2070P Alloy During High Temperature Creep-rupture Test

An investigation is conducted on the candidate material GH2070P alloy tube for the 650 ℃ ultra supercritical boiler service by performing the high-temperature creep rupture tests at 675 ℃ under various stress levels. The isothermal method is employed to predict the 100 000 h high-temperature creep strength. The microstructure evolution and the fracture characteristics at different durations of high-temperature creep are analyzed. It is revealed via the study that based on the existing data from the test the extrapolated 100 000 h creep strength of the GH2070P alloy tube at 675 ℃ is 141 MPa，meeting the design target requirements；along with the increase of the creep duration，the size of γ′ phase gradually coarsens，conforming to the LSW law；a great number of finely dispersed spherical γ′ phases have a strong pinning effect on the relative dislocations，providing the GH2070P alloy with good high-temperature strength and creep strength；the M₂₃C₆ carbides precipitated at the grain boundary in the GH2070P alloy form no network structure；the fracture surfaces of the GH2070P alloy after the high-temperature creep-rupture tests exhibit intergranular fractures as caused by the hi-temperature creep accompanied by micro-plastic deformation during the intergranular fracture of the specimens.