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Influence of Ti on microstructure of high boron steel structure

Author: JiangJun
Tutor: ZhaoPing
School: West China University
Course: Materials Processing Engineering
Keywords: shielding material boron-added steels microstructure smelting technique heat treatment
CLC: TG156
Type: Master's thesis
Year: 2009
Downloads: 169
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Abstract


The research and development of shielding materials have been marching into a new stage, driven by the growing advancement on the technology of harnessing nuclear energy and expanding on the quantity and scale of nuclear plants, new shielding materials are continuously produced. But so far in the world countries, including US, Japan, England etc. 304 stainless steel with the addition of boron, which has promising mechanical and neutron absorption properties,is still the predominant shielding material. However, its industrialization is somewhat confined by its high cost. So it’s inevitable to tap some new shielding materials. Our research is carried out under such situation.One new way is put forward to develop boron-added steel as shielding m aterial, which is to add boron and titanium into the low alloyed steels. The steels are produced according to the component planned. The boron content is 1. 5% and 1%. A comprehensive study is carried out, which includes microscopic analysis, component analysis, SEM and so on. The result of experiment reveals that high-boron steel can be smelted by oxidation with aluminum and manganese and denitridation with titanium. It is helpful to introduce electromagnetic agitation into the process of smelting in the vacuum induction furnace, which makes boron evenly distribute without macrosegregation. The recovery rate of boron exceeds 80%.The amount of boron atom reacted with iron is decreased due to the reaction of boron and titanium, and as a result lessen the quantity of boride precipitated at grain boundary. In the boron-added steel without titanium, boride completely precipitate at boundary and form net microstructure. But when titanium is added, the net boundary is partly broken. It’s beneficial both to steel’s mechanical and neutron absorption properties. A study reveals that the grain size is directly related to the content of boron and titanium. The higher their content, the smaller the grain size.The research on heat treatment shows normalization alone can’t e-liminate the boron phases precipitated at the boundary. The high-boron steel’s strength, as well as its plasticity and toughness, can be remarkably improved by the combination of large deforming and rapid cooling, which refines austenite grain and seriously breaks net boundary and makes boron more homogeneously distributed, and the result shows the best heat treatment is 950℃×120min(annealing) +1050℃×45min (quenching) .

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Heat treatment > Heat treatment process
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