| Nanostructured ODS steels are the leading cladding candidate materials for fast neutron reactor application due to their high-density nano-scale precipitates,ultrafine grain size,excellent radiation resistance and high temperature mechanical properties.The traditional manufacture process of nanostructured ODS steels has low efficiency,restricting the industrial production and the application of nanostructured ODS steels.A new manufracture process of nanostructured 15Cr-ODS steel by hot rolling of alloying powders was studied to improve production efficiency and capacity of 15Cr-ODS steel.And the effects of hot rolling on the structure and properties of nanostructured 15Cr-ODS steel prepared by conventional method were studied in order to optimize the alloy structure and improve the mechanical properties of the material.1#,2#and 3#samples were prepared by different hot rolling forming processes.The 1#sample was hot-rolled at 900? and 1000? using super-saturated atomized powders.The 2#sample was hot-rolled at 1000? using supersaturated atomized powder ball milled for 8 hours.The 3#sample increased the rolling deformation on the basis of the 2#sample.The grain,precipitate,hardness,tensile properties of the three samples were analyzed.Type of precipitates and the tensile properties at different temperatures of the 3#sample were studied.The difference in tensile properties between 3#and HIPed 15Cr-ODS samqples was compared.The following conclusions were obtained:(1)Among the three samples manufactured by different hot rolling forming processes,the average grain sizes of 1#,2#and 3#samples are 6.16 ?m,1.66 ?m and 1.26 ?m,respectively.The nuiber densities of precapitates of three samples are?2×1020m-3,1.64×1021m-3,6.96x1021ni-3,respectively.The hardness value of three samples is 267 HV,322 HV,370 HV,respectively.Among them,the grain size of the 3#sample is the smallest,the density of precipitate is the highest,the hardness value is the largest,and the preparation process is the best.(2)Y-Zr-O,Y-Ti-O,Y-Al-O,and Al-O precipitates are observed in the 3#Sample.The Y-Zr-O phase is mainly Y4Zr3O12 and the size is less than 15 nm.Y-Ti-O phase is mainly Y2TiO5,and the size is in the range of about 10-20 nm.Y-Al-O phase consists mainly of Y4Al2O9 and YAlO3 with the size of from 15 nm to 35 nm Al-O phase is mainly Al2O3,and the size is larger than 35 nm(3)The tensile strength of the 3#samples at 25?,400?,500?,600? and 700? is 1123 MPa,910 MPa,678 MPa,452 MPa and 229 MPa,respectively.The tensile strength decreases gradually with the temperature from 25? to 700?,and the decrease is significantly obvous from 400? to 700?.The total elongation of the 3#sample at 25?,400?,500?,600? and 700? is 22.8%,26.8%,30.8%,45%and 41.6%respectively.The total elongation increases with the increasing temperature from 25? to 600? and decreases with the temperature from 600? to 700?.The fracture mode which is dominated by transgranular fracture evolves into the fracture mode which is partly intergranular fracture with the temperature from 600? to 700?.(4)The 3#sample prepared by supersaturated solid solution atomized alloy powders,short-time ball milling and hot rolling forming process has the same tensile strength as 15Cr-ODS steels prepared by HIP,but the total elongation is superior than 15Cr-HIP sample.So it is expected to be a new process for the preparation of nanostructured ODS steel.In the hot rolling treating proces,30%HR,50%HR and 70%HR samples were prepared by hot rolling of 15Cr-HIP samples at different reduction rates,then the grain,precipitate and hardness of the three samples were analyzed.The micro structure and mechanical properties of 70%HR sample before and after annealing were compared.The following conclusions were obtained:(1)With the increase of hot rolling reduction,the average grain size of the sample decreases and the hardness value of the sample increases,but the density and size distribution of the precipitates are no t changed obviously.The average grain sizes of 30%HR,50%HR and 70%HR samples are 1.98?m,1.63?m and 1.21pm,respectively.The hardness value of three samples is 548 HV,559 HV,584 HV,respectively.The density of precipitates of three samples are 1.29×1022 m-3,1.3×1022 m-3,1.27×1022 m-3,respectively.(2)After hot rolling,the anisotropy of 30%HR,50%HR and 70%HR samples is obvious,and the anisotropy of the samples increases with the increase of rolling reduction No obvious fiber texture is observed in the 30%HR sample.The 50%HR sample shows obvious ? fiber texture(<100>//ND)and y fiber texture(<111>//ND).And 70%HR sample does not change the type of fiber texture,but the texture strength increases.(3)After annealed at 1150? for 2h,the average grain size of the 70%HR specimen increases,the hardness value decreases and the anisotropy of the material is significantly weakened,which provides a feasible process for weakening the anisotropy of the nanostructured 15Cr-ODS steel... |
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