Tuning The Microstructure Of The 9Cr2WVTa Reduced Activation Steels And Its Effect On Properties

Reduced activation ferritic/martensitic (RAFM) steels are the leading candidates for the first wall structural materials of breading blankets, as they have higher resistance to void swelling, higher thermal conductivity and lower thermal expansion. However, high-energy neutron irradiation causes changes in organizational structure and properties, especially the mechanical properties of the reduced activation steels. This paper is based on the theory of grain boundary engineering, through cold rolling deformation and subsequent high temperature annealing as a method to improve the grain boundary character distribution of materials, the effect of grain boundary character distribution on the properties was studied comparing the corrosion resistance, tensile and creep properties of the material. From this work, the following conclusions were drawn:(1) The solution treatment had a significantly effect on the microstructure and tensile property of the 9Cr2WVTa reduced activation steels, the sample tempered at 760℃ for 90min after annealed at 1050℃ for 30min had the best static toughness on the promise of good ductility. The stress exponent of 9Cr2WVTa reduced activation steels under the optimized heat treatment was about 27, indicating the creep was controlled by dislocation. By using the extrapolation, the creep limit was estimated to be 209MPa when the minimum creep rate was 10-/%/s at 550℃, which was comparable to other RAFM steels.(2) Thermomechanical treatment could improve the density of subgrain boundary and the formation of special boundaries. The optimum thermomechanical treatment processes was annealled at 1050℃ for 30min after 5% cold-rolling.(3) Tensile results show grain boundary design and control increased the yield strength by 40MPa, tensile strength by 50MPa and elongation by 10% respectively. Grain boundary design and control could greatly enhance the high temperature creep property of 9Cr2WVTa reduced activation steels. Under 550℃ and 275MPa condition, matreial’s creep life was increased by about one time and the average creep strain rate reduced by about one order of magnitude, this is because that the lower diffusivity of these special CSL and the low angle boundaries reduced the coarsening of the precipitates, which inhibited the nucleation and expanded along grain boundaries of corrosion and crack.