Microstructure And Creep Character Of 403Nb Heat Resisting Steel

403Nb steel is used to manufacturing turbine blade, and working chronically in higher temperature, it is very significant to investigate elevated creep properties and microstructure of 403Nb steel. Hot continuous rolled 403Nb steel is mainly talked about in this paper, through a lot of heat treatment experiments and creep property tests, microstructures before and after creep, creep property and deformation mechanism of hot continuous rolled 403Nb steel before and after heat treatment have been investigated by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD).Results show that: dynamic re-crystallization of 403Nb steel occurs and fine equiaxed grain forms during hot continuous rolling, the microstructure of the steel consists ofα-Fe, Cr₂₃C₆ and NbC phases. Thereinto, Cr₂₃C₆ particles are mostly distributed in the regions of the grain boundaries, and NbC particles are mainly distributed within the grains. Under the condition of the applied stress and the applied temperature, creep resistance of hot continuous rolled 403Nb steel before heat treatment is lower, The activation energy of the steel during steady state creep is measured to be Q1=287.5 kJ/mol, and stress index is measured to be n1 = 8.5. Microstructure of hot continuous rolled 403Nb steel by quenching treatment is lath martensite, with the increase of quenching temperature, the grain size of steel increases, when the temperature comes to 1150℃, a lot of delta ferrites appears along the grain boundary, this microstructure decreases creep properties. Creep property of hot continuous rolled 403Nb steel by quenching and tempering treatment is improved obviously, especially, creep prorerty of steel by quenched at 1100℃and tempered at 650℃is the best; it is main reason why the creep property of hot continuous rolled 403Nb steel by quenching and tempering is improved that high dispersed nano-sized Cr₂₃C₆ carbides precipitate in the prior martensite lath or between the martensite.Under the condition of the applied stress and the applied temperature, the activation energy of the 403Nb steel by this heat treatment is measured to be Q2=463 kJ/mol, and stress index is measured to be n2 = 14. Creep deformation mechanism of hot continuous rolled 403Nb steel before and after quenching at 1100℃and tempering at 650℃is deformation dislocation concentration and dynamic re-crystallization during creep. Creep fracture mechanism of 403Nb steel by this heat treatment is crack initiation and extension in the grain boundary along the direction of perpendicular to stress axis in the later creep stage.