Creep Behavior and Microstructure Evolution of P92 Steel during Creep Test at 873 K

In this paper, the creep behavior of P92 steel has been analyzed by creep strain and creep rate variations after the creep tests were stopped at the steady-state creep stage. The microstructure evolution of the P92 steel at the steady-state stage during creep test at 873 K under different load stresses of 125-160 MPa were studied by using a scanning electron microscopy (SEM) and a transmission electron microscopy (TEM). The grain boundary characteristics in the P92 steels during creep test were investigated by an electron backscattered diffraction (EBSD) technique. Experimental results showed that with increasing load stresses from 125 MPa to 160 MPa, creep rates of the P92 steels increased in Norton's power law relation and creep times to the steady-state creep stage decreased. With decreasing load stresses and increasing creep times, martensite lath microstructure occurred recovery and the dislocation densities in ferritic matrix decreased. M23C6 particles located in prior austenite grain, sub-grain and lath boundaries showed slight coarsening. Some Laves phase particles precipitated in the grain boundaries for the P92 specimens after creep test under a load stress of 125 MPa. Comparing to as-tempered P92 steel, the volume fractions of LAGBs are lower and the volume fraction of HAGBs are higher with decreasing load stresses and increasing creep times. It is considered that understanding on creep behavior and microstructual evolution of the P92 steels during creep test will effectively support life design and assessment of the high temperature metal parts in fossil-fired power plant.