Investigation On The Effect Of High Temperature Creep And High Energy Ion Irradiation On The Evolution Behaviors Of Precipitate Phases In Ferritic/Martensitic Steels

9-12%Cr ferritic martensitic steel has good mechanical properties,heat transfer efficiency,stress corrosion cracking resistance,creep resistance and radiation resistance,which make it a candidate material for the 4^th generation nuclear reactors and fusion reactors.During the heat treatment process or service life of 9-12%Cr ferritic/martensitic steel,metal atoms in supersaturated solid solution can form precipitates through aggregation or dispersion in the matrix.The precipitates can pin dislocations and slow down the recovery or recrystallization of dislocations to realize the thermal strengthening of the material.The type,size distribution,thermal stability and irradiation stability of precipitates play an important role in the safety of the material used in nuclear power plants.At present,researches on precipitate identification,precipitation mechanism and effect of precipitates on the properties of11%Cr ferrite/martensite steel(which is one of the candidate structural materials for the 4^th generation fission reactor)under high-temperature creep are still rare.In addition,the evolution mechanism of precipitates in CLAM steel（which is one of the candidate cladding materials for future fusion reactor）under high-temperature irradiation also needs to be further studied.Based on this,this paper conducts experimental investigations on the microstructure evolution and precipitation behavior of 11%Cr ferritic/martensitic steel under short-time high temperature creep and CLAM steel under heavy ion irradiatio,by means of transmission electron microscope,energy dispersive spectrometer and X-ray diffractometer for characterization.The key research contents and results are shown as follows.The precipitates in 11%Cr ferritic/martensitic steel were identified after 1100-h short-time high-temperature creep at 600℃/180 MPa and 600℃/150 MPa.The effect of short-time high-temperature creep on the microstructure and the influence of precipitates on the creep resistance performance of the material were analyzed.The results show that,there are eight precipitates in 11%Cr ferritic/martensitic steel after creeping at 600℃/180 MPa:Fe-W-Cr-rich M₆C carbide,Cr-rich M₇C₃ carbide,Fe-W-rich Laves phase,Cr-rich M₂₃C₆ phase,Nb-rich MC phase,Ta-rich MC phase,V-rich MC carbide and sigma phase（σ-Fe Cr phase andσ-Fe Cr W phase）.After creeping at600℃/150 MPa,there are four precipitates in 11%Cr ferritic/martensitic steel:Nb-rich MX phase based on Nb C,Fe-W-Cr-rich MC carbide based on Fe₃W₃C,Fe-W-laves-rich phase based on Fe₂W and M₂₃C₆ phase based on Cr₂₃C₆.The composition,characteristics and size of the precipitates in 11%Cr ferrite/martensite steel before and after creep and under different creep stresses were compared.The evolution law of precipitates after short-term high-temperature creep was also explored.The results show that,compared with the 11%Cr ferritic/martensitic steel in normalized-tempered state,the composition of M₂₃C₆ carbide in the material after high-temperature creep changes insignificantly.Also,the content of Nb and Ta/Cr in Nb-rich MC carbides slightly increases and decreases,respectively,after high-temperature creep.The size of precipitated MC carbide significantly decreases,while the size of precipitated M₂₃C₆ carbide remains unchanged.In addition,the formation of M₆C carbide in 11%Cr ferrite/martensite steel during short-term high-temperature creep is resulted from the dissolution of originalδ-ferrite in the steel.The existence ofδ-ferrite in high Cr ferrite/martensite steel may lead to the premature formation of large-size M₆C carbides during high-temperature creep.The microstructure of CLAM steel under standard heat treatment conditions was observed.The morphology,distribution,size,quantity,chemical composition and type of precipitated phase particles were completely analyzed.The results show that there are eight precipitates in normalized-tempered CLAM steel:Ta-rich MX phase,Ta-rich M₃X₂ phase（discovered for the first time）,Ta-rich MSi2 phase（discovered for the first time）,V-rich MX phase,V-rich M₂C phase,Cr-rich M₂₃C₆ phase,Cr-Ta-rich M₇C₃phase and Cr-rich M₆C phase（discovered for the first time）.M₂₃C₆ and MX phases are the main precipitates of the material.The evolution behaviors of precipitates in CLAM steel under room temperature/10h,400℃/2 h and 700℃/2 h Fe¹³⁺ion irradiation conditions were studied.The effects of irradiation temperature on the precipitates of CLAM steel were discussed.The results show that,there are mainly two types of precipitates in normalized-tempered CLAM steel:Cr-rich M₂₃C₆ precipitate represented by a lumpy large-size precipitate and Ta-rich MX precipitate represented by a spherical small-size precipitate.The average size of both precipitates is slightly reduced after a 10 h-Fe¹³⁺irradiation at room temperature.However,the average size of both precipitates increases due to element segregation at a 400℃short-time（2 h）irradiation.When the irradiation temperature increases up to700℃,the average size of these two precipitates decreases under the effect of high-temperature recovery.The number density of small spherical precipitates increases with the increase of irradiation temperature.