Metallurgical Properties And Microstructure Evolution Of Iron-containing Burdens Under Hydrogen-rich Conditions

In order to reduce CO₂ emissions in the steel industry,metallurgical workers at home and abroad have proposed ideas for hydrogen-rich smelting,and have achieved certain achievements,such as Japan's new process of blowing natural gas and waste plastics into blast furnaces,and domestic all-oxygen blast blowing coal.Powder and natural gas process,Sweden's ULCORED new reduction process.Although there have been many studies on blast furnace hydrogen-rich conditions,there are few related researches on the product evolution law and reduction mechanism of iron-containing burdens materials under hydrogen-rich conditions at medium and high temperatures.Based on this,this paper systematically studies the metallurgical properties and microstructure of iron-containing burdens materials under hydrogen-rich conditions,analyzes their reaction mechanism and microscopic evolution rules,and obtains the following conclusions:Theoretical analysis of thermodynamics and kinetics found that the reduction reaction at T<1100 K is mainly dominated by CO,doped with H₂ reduction and carbon precipitation reaction.When T>1100 K,the reduction reaction is mainly dominated by H₂,and it is mixed with water gas reaction;Fitting and comparison,it was found that the hydrogen-rich hydrogen-rich reaction process followed the Random Pore Model,and three different reduction modes of CO-like reduction,H₂-reduction and H₂ reduction occurred.The pulverization experiment found that under the condition of H₂+CO₂+N₂,the pulverization effect of lump O,pellet P and sinter S improved obviously;under H₂+CO₂+N₂+CO conditions,lump O,pellet P and The optimum H₂ addition amount of sinter S is 10%,20%,20%,and its RDI+3.15 is increased by 11.08%,6.13%,and 30.23%,respectively.Combined with the RDI+6.3 index,it can be seen that hydrogen-rich reduction can effectively improve The powdering properties of the burden.Through the reduction experiments of iron-containing burden materials,it was found that the optimal reduction hydrogen enrichment of pellets P and sintered ore S was 25% and the optimal reduction of lump O was maintained under the condition that the content of CO in the reducing gas phase was kept unchanged and the content of H₂ was changed.The hydrogen-rich content was 10%,and the degree of reduction was increased by 10.16%,6.65%,and 6.00%,respectively.Hematite in the pellet P is largely transformed into magnetite and iron phases,and the dendrites are well connected;after sinter ore S is reduced,it presents a variety of iron-containing phases including magnetite phases;after reduction of lump ore The internal metal iron phase generation amount increases.When the composition of the reducing gas phase is?CO+H₂?:N₂ = 30%:70%,the reduction degree of the pellet P increases at 10% hydrogen,and the "hematite-magnetite-iron phase" nests inside.Lump O and sintered ore S have excellent reduction degree at 20% hydrogen content.Lump ore O shows a good slag phase and iron phase,and a good "acicular calcium ferrite phase-magnetite appears inside the sintered ore S.Phase-iron phase " layering phenomenon.The high temperature soft melt dripping experiment found that the softening and melting properties of the burden under the CO+H₂+N₂=30%+30%+70% atmosphere were effectively improved.And the slag contains Mg O lower,but Al₂O₃ is higher,forming a large number of low melting point compounds,reducing the melting temperature of the slag.From the microstructure of the sintered ore,it can be seen that after hydrogenation reduction,a large amount of hexagonal crystal hematite oxide is rapidly reduced to an equiaxed crystal magnetite,which contains the fascia and iron phases;magnetite and flux occur The reaction generates SFCA phase,and the SFCA phase changes to SFCA-? phase with the increase of the amount of hydrogen.