Microstructure variation tendency of T91-steel based on quantitative analysis

Carbide size,substructure and dislocation density of T91-steel in different service stage were investigated quantitatively by scanning electron microscopy(SEM),electron backscattered diffraction microscope(EBSD)and X-ray diffraction(XRD).The results show that the quantity of the carbide particle precipitates increases obviously with the microstructure deterioration of T91 steel at early service stage,however,the carbide particles grows obviously by aggregation at later service stage.During early service stage,the density of dislocation reduces distinctively and the substructure merges due to the movement of dislocation.The movement of dislocation also induces substructure coarsening.During the later service stage,the density of dislocation keeps stability approximately while the substructure merges quickly which causes the density of sub-grain boundary decreases notablely.