| In this article aging heat treatments are carried out on T91/P91 matrix and tubular joints of manual arc welding at the temperature of 650℃, 750℃and 850℃, and standard tubular tensile test specimens are made to be tested at room temperature . Hardness distributions of welded joints are tested on the Vickers Hardness Tester. The electron scanning microscopy is used to analyze specimens at various stages, in order to measure the second-phase particle size and distribution, and the use of IMAGE-J software for statistical analysis. Using EDX spectrometer measures the distribution of alloying elements. the study shows that: T91/P91 steel initial state at room temperature has good mechanical performance ; tensile strength and yield strength reached 647MPa and 219MPa, after the 150h long time aging strength decreased, especially after 850℃50h aging stage tensile strength and yield strength reach 453MPa and 153MPa, a decrease of about 30% respectively, but the fractured elongations increase sharply, up to about 64% .Hardness distribution of weld joints: the hardness of weld metal is greater than that of matrix metal, weld center hardness is about 500HV before aging, and the matrix metal hardness is about 300HV, there is also a HAZ softening zone. With the aging experiments, the hardness of weld metal shows a downward trend, declining by about 200HV. Hardness of matrix metal increases at the first time, after 850℃50h aging, the hardness decreased, but hardness values change marginally.Scanning electron microscopy analysis find that: after 650℃aging, a large number of second-phase particles precipitated , the number changes from the previous stage of about 210 to about 330 , but after 750℃aging, the number decreases with apparent particle coarsening, the average particle area change from previous stage of 0.057 to 0.084μm2.Based on Ostwald ripening life formula, life analysis formula is derived, and the name radius value of the second phase particles is use in formula respectively to figure out constants so as to obtain the relationship between the name radius R and time t, temperature T, which can provide a certain reference value to life prediction. |
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