Study on long-term tempering on the microstructure of creep strength enhanced ferritic P92 steel

Present paper deal with the studies of effect of long term heating on the microstructure and mechanical properties of creep strength enhanced Cr-Mo P92 steel. Such steels are used in supercritical power plant boilers where continuous operating temperature and pressure can be as high as 650 0C and 300 bar respectively. The P92 specimens were thermally exposed at temperature of 650 0C for duration of varying from 1000 to 3000 hours. Tensile fracture and impact toughness fracture surfaces were studied by using scanning electron microscope. The fracture surface of P92 impact toughness specimen exhibited both inter lath-decohesion and ductile dimple tearing. The various phases that formed in the tempered P92 steel were analyzed by X-ray diffraction. In XRD analysis of tempered P92 it was observed that amount of precipitates increased as compared to untemperedcondition. After tempering time of 1440 h, some new precipitates such as NbC, NbCrN were also observed.