Preparation And Properties Of 9Cr-ODS Steel With Bimodal Grain Size Distribution

ODS steel has become an important candidate structural material for the first wall/cladding of conversions reactor due to its excellent radiation resistance and high temperature resistance.Taking 9Cr-ODS steel as the research object,this paper tries to prepare 9Cr-ODS steel with bimodal grain size distribution,Uses mechanical alloying method to prepare alloy powder with different ball grinding degree by controlling time,and then adds coarse powder with volume fraction of 35%into the fine crystal powder and mixes it evenly.Hot isostatic sintering(HIP)was carried out at 1000?and 135MPa,and the microstructure evolution,oxide dispersion particle formation dynamics and fracture behavior of 9Cr-ODS steel with bimodal grain size distribution were systematically studied.In this paper,the microstructure of ODS steel was characterized by means of TEM,SEM and OM,and the tensile properties under different conditions were measured.The microstructure and mechanical properties of 9Cr-ODS ferrite steel with double grain size distribution were analyzed.In the process of preparation,it was found that in the process of mechanical ball grinding,with the extension of ball grinding time,the greater the degree of ball grinding of powder,the smaller the grain size of powder,and the second phase particles were distributed in the matrix lattice in the form of nanocrystals after ball grinding.In the process of hot isostatic pressing sintering,recrystallization nucleation occurs first in the fine crystal area because the ball is grinded into larger size and the deformation energy stored in the alloy powder is higher.When the deformation energy is used up,the second phase particles less than 80nm will nail the grain boundary and inhibit the grain growth.bimodal of grain size distribution of the preparation of 9Cr-ODS steel distribution in dispersion in the matrix has a very high density of nano-sized oxide dispersion strengthened phase at the same time,the grain structure of nanocrystalline materials and micro crystal double scales,including nanoscale oxide dispersion strengthened phase for the excellent performance of high temperature creep and irradiation resistance to provide guarantee,the nanocrystals with micro crystal to balance under the function of strength and plasticity of the materials.When the fracture behavior was investigated,it was found that 9Cr-ODS steel with bimodal grain size distribution had good mechanical properties,and its tensile strength reached 1100MPa.When the fracture morphology was analyzed,it was found that brittle fracture occurred in the fine grain area,and ductile fracture occurred in the coarse grain area to form dimples.It was observed that the crack originated from the fine crystal region and extended to the coarse crystal region.The fracture mechanism will not change from room temperature to 700?,but the introduction of mixed crystals will complicate the fracture mechanism,so that the dimple fracture,cleavage fracture and quasi-cleavage fracture exist in 9Cr-ODS steel with bimodal grain size distribution at the same time.In the analysis of the kinetic process of precipitation of Y₂O₃,it is found that the growth mechanism of second-phase particles is diffusion control.The apparent activation energy of the second phase particles was calculated to be 308KJ/mol,which can well explain why the second phase particles are difficult to grow up.At the same time,it was found that the precipitation rate of the second phase particles did not change significantly when the heating rate was between5K/min and 25K/min.