Aiming at finding out the relationship between microstructural evolution and degradation of creep rupture strength,the microstructural evolution of the weld joint metal 12%Cr martensite steel used for superheater header after 45 000hours service at 600℃ has been investigated,by means of carbon replica extraction method,transmission electron microscopy(TEM)and energy dispersive spectroscopy(EDS).The results show that,the microstructure of weld joint metal 12%Cr martensite steel after 45 000hours service at h...