Basic Research On Hydrogen-Rich Reduction Behavior Of Fluxed Pellets And Microscopic Reconstruction Mechanism Of Minerals

As a blast furnace burden,fluxed pellets have the advantages of good metallurgical properties and less pollution in the production process compared with sinter.Therefore,increasing the proportion of pellets into the furnace and improving the metallurgical properties of pellets can reduce pollution emissions in the raw material preparation process and smelting process.At the same time,under the guidance of the“double carbon”policy,hydrogen metallurgy is regarded as the main goal of the current research on green metallurgical technology.Domestic scholars have previously mainly studied the reduction kinetics of pellets,but there are few studies on the reduction behavior of fluxed pellets under microscopic conditions in the case of hydrogen-rich smelting.Therefore,in this thesis,the reduction behavior and microstructure evolution of fluxed pellets under hydrogen-rich conditions will be studied.The main conclusions are as follows:（1）In the preparation process of flux-oxidized pellets,when the basicity of flux-oxidized pellets is 1.0,w（MgO）%=2.2%,roasting time is 30 min,and oxidation roasting temperature is 1250°C,the compressive strength of green pellets,drop times and compressive strength of cooked pellets are the best.During the roasting process of fluxed pellets,when w（MgO）%increases,the melting point of slag phase increases and the mineral phase structure is stable.Excessive w（MgO）%leads to the lack of liquid phase in the pellet,the recrystallization of Fe₂O₃ is reduced,and the strength of the pellet is reduced.With the increase of alkalinity,the liquid phase of low melting point calcium ferrite increases,which enhances the connection between Fe₂O₃ grains and makes the pellet structure more stable.（2）In the preparation process of fluxed pellets,the formation of monocalcium ferrite and semi-calcium ferrite gradually increased with the increase of basicity,and the iron silicate phase gradually transformed into calcium-based olivine phase.The recrystallization of Fe₂O₃ was enhanced,and the appropriate basicity could effectively increase the metallurgical properties of the pellets.However,when the basicity exceeded 0.9,the liquid phase of calcium ferrite was generated in large quantities,the recrystallization of Fe₂O₃ was reduced,and the basicity was too high,which inhibited the metallurgical properties of the pellets.With the increase of w（MgO）%,the production of Fe₃O₄ and magnesium ferrite increased significantly,and some MgO and Fe₃O₄ were mutually soluble to form magnesium-containing magnetite.The production of calcium ferrite,half calcium ferrite and Fe₂O₃ decreased gradually,and the liquid phase production decreased,which stabilized the mineral phase structure.Appropriate w（MgO）%can improve the metallurgical properties of pellets.（3）When the H₂ content in the reducing atmosphere is 30%,the RDI_+3.15 of fluxed pellets is 95.56%,and the reduction expansion rate is 11.18%.In the reducing atmosphere of 20%CO+10%CO₂+2%H₂+68%N₂,when the basicity of fluxed pellets is 1.0,w（MgO）%=2.2%,RDI_+3.15 is 80.9%,and the reduction expansion rate is18.53%.（4）When the H₂content in the reducing atmosphere is 30%,the increase of w w（MgO）%in the fluxed pellets can accelerate the reduction reaction.When w（MgO）%is higher than 2.2%,the iron whiskers decrease,and when the basicity is higher than1.0,the growth of iron whiskers is delayed.Appropriate w（MgO）%and basicity provide more growth sites for metallic iron and promote the formation of metallic iron.Excessive w（MgO）%and basicity will hinder the growth of iron whiskers in pellets and inhibit their structural changes.