Study On Microstructure And Properties Of 10CrMoWVNbN Steel

In recent years, many high-performance modified 9~12Cr wt% steels have been imported in order to meet the needs of ultra super critical gas turbine power set, and 10CrMoWVNbN(10705AJ)is one of them. For excelerating the use of this steel in the ultra super critical gas turbine power set and breaking the technological wall by foreign companies, it is needed for us to master the performance and microstructure of this steel.In this thesis, two main facets about the microstructure and performance of this steel are studied: one of them is changes of microstructures by different heat treatment systems; the other is the change of microstructures in high-temperature mechanical behavior and process of creeping.For better studying the roles of quenching temperature and annealing temperature on the microstructure of specimen, OM, EBSD and TEM have been carried out on specimen with different heat treatment systems. Further study has been made by extracting experiments, in order to make sure the percentage of carbide in specimen. Result shows that: for the Luhe specimen, the best heat treatment system is queching at 1140℃for one hour and then annealing at 680℃for two hours; for the Shangwu specimen, the best is quenching the specimen at 1100℃for one hour and then annealing it at 660℃for two hours. In the studying of carbide extracting, separated carbide of Luhe specimen is more than that of shangwu. But further study is needed in order to evaluate the influence of amount of separated carbon; In the process of annealing, in-situ recrystallization has been found, and Martensite has been broken and new grains observed. And dislocation jungles have been found in the annealed grain. Carbides separate from the matrix on the grain boundary.In the study of high-temperature mechanical performance, short-period creeping and long-period creeping have been separatedly carried out. Analysis of creep datas has been carried out on the first stage of creeping. The activation energy of the first stage of creeping is 45.7 ~ 119.7 kJ/mol, which is far below the activation energy of self-diffusion of Fe inα-Fe andγ-Fe(280 kJ/mol). And further studys show that activation energy of creeping goes up with the growth of stress, which implies that energy gurgitation by temperature is small in high stress. In the studying of relationship of stress and temperature in the smallest creeping speed, the stress index of 10705AJ is comparatively small, about 2. The mechanism of deformation is under the control of dislocation sliding, and separated grains on the blocking of dislocation. And in the studying of temperature and the smallest creeping speed, it is concluded that energy activations are mainly belong to two points, and with two separate deformation mechanism.In the long-period creeping ,the study of steady creep rate to stress shows that stress index is not consistent to short-period creeping's.One reason is the improvement of short-period creeping tests,the other is material's bugs.The development of microstructure in creep is studied by AFM,EBSD and TEM.In short-peirod creeping, appropriate stress is useful to urge fine precipitation depositing in grain boundary and improve creep properties.But in high temperature,low stress make carbides agglomerate easily and inhomogeneously.The analysis of EBSD and TEM display that in creeping sub-grain is formed in grain.Large-angle grain boundaries are destroyed in creeping,meanwhile,sub-grain boundaries transform to large-angle boundaries.In temper tests and creepng,situ-recrystallization and dynamic recrystallization are rivals.But high temperature urges dynamic recrystallization,high stress urges situ-recrystallization.