| 1Cr10NiMoW2VNbN (10705AJ) is one of the modified 9~12Cr wt% ferritic / martenite steels, and it is mainly used as supercritical (ultra-supercritical) steam turbine blade steels and bolt steels at or below 600oC. For excelerating the use of this steel in the ultra-supercritical gas turbine power unit, it is urgent for us to master the performance and microstructure of this steel and to make it be used more safely.In this study, effect of heat-treatment technique on microstructure of the steel was investigated by OM and TEM. Short-term and long-term creep tests as well as stress relaxation tests have been carried out, and the high-temperature mechanical performance of the steel has been analyzed. Then, the microstructure evolution during creep testing was studied by OM, AFM, EBSD and TEM.Lath martensite with high-density dislocations is formed in steel 10705AJ after the steel is quenched between 1100 and 1140oC and microstructure of tempered martensite occurs after it is tempered between 600 and 700oC. The steels after heat-treatment are all meet the demands of the standard. The peak value of precipitation of carbides appears between 660 and 680oC. The carbides are mostly M23C6, and a small quantity of M6X and NbN are also observed. It is proved that it is better for steel 10705AJ to be quenched between 1100 and 1140oC and then to be tempered between 660 and 680oC.The first-stage creep curves of steel 10705AJ accord with the power characterization of the instantaneous creep, and the index value of them without monotone relationship is between 0.385 and 0.614. The activation energy for the first-stage creep related to the stress is 88~161.3 kJ/mol, which is far below the activation energy of self-diffusion of Fe inα-Fe (239 kJ/mol).There are two stages for the stress relaxation curves of steel 10705AJ. The stress relaxation rate of the first stage is much larger than that of the second one. Temperature is the primary factor to affect the behavior of stress relaxation. The higher the temperature is, the larger the stress relaxation rate is. The stress relaxation rate increases with increasing the initial stress. Extrapolation for residual stress of the steel at 25000h was achieved through double logarithm model and Jin-wei model. Both extrapolation results are near and represent lower errors. The former is appreciably smaller, and the latter is appreciably larger.The process of recrystallization is accelerated with creep time. Coarsening occurs in carbides, high temperature or low stress makes carbides agglomerate easily and inhomogeneously. The analysis of OIM and TEM displays that Sub-grain is formed during creep tests. Except for continued destroy of original large-angle grain boundaries, there exists the development of sub-grain boundaries transforming to large-angle boundaries. Occurrence of the ample dislocation sub-structure indicates that the deformation mechanism is dislocation creep. The precipitates act as the obstacles to block the movement of dislocations.
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