Basic Research On The Preparation Of Low-Oxygen And Low-Aluminum Ferrotitanium By Multi-Stage And Depth Reduction

Ferrotitanium is mainly used as deoxidizer,degassing agent and carbon sulfur stabilizer in steel production,and it is also used as electrode flux and hydrogen storage material.At present,its preparing methods mainly include aluminothermic reduction method,remelting method,carbothermal reduction and molten salt electrolysis.Aluminothermic method is a simple way to produce ferrotitanium with a low production cost.However,ferrotitanium prepared by this method normally has a high Al and O contents,especially in high-titanium content ferrotitanium.Therefore,a novel method of the multi-stage and deep reduction to prepare the low-oxygen and low-aluminum ferrotitanium is put forward in this study.Specifically,at first,a high temperature melt is obtained by the aluminothermic reduction with an insufficient amount of Al powders.Then,the pre-melted CaO-Al2O3 slag,which aims to improve the basicity of the slag,is added into the melt to improve the slag-metal separation.Finally,Ca is used for a deep reduction,producing the ferrotitanium with a low-oxygen and low-aluminum content.In this paper,the aluminothermic reduction,the strengthened melt separation and the deep reduction by Ca in the multi-stage and depth reductionprocess are systematically studied.Thermodynamics of the aluminothermic reduction,the strengthened melt separation and the deep reduction by Ca were calculated.The results show that,in the aluminothermic reduction process,the reaction heat per unit mass of the system obviously increases with an increased ratio of KClO3.However,it decreases with the increased ratio of CaO and the decreased ratio of the reduction agent Al.The thermodynamics model of the molten metal indicates that,the reduction of TiO by Al is the control step in the step-by-step reaction processes of TiO2.With an increased Al content,the deoxidization limit of this reaction in the Ti-Al-O melt decreases,which is beneficial for the deoxygenation of titanium oxides as well as the decrease of O content in the melt.When a new component Fe is introduced into this melt,the melt turns into a new system,namely Ti-Al-Fe-O melt.The deoxidization limit of the TiO reduction in the Ti-Al-Fe-O melt further decreases,which promotes the deoxygenation of titanium oxides,and its effect is more obvious with a larger Fe content.In the strengthened melt separation,the increase of CaO in the pre-melted slag contributes to the removal of Al2O3 inclusion and the desulfurization in the alloy.It is feasible to have a deep reduction using Ca as the reduction agent for the deoxygenation and desulfurization,but a high temperature is unfavorable.In the aluminothermic reduction,the effects of the reaction heat per unit mass(q),the ratio of the reduction agent Al(RAl)and the ratio of CaO(RC/A)on the burn rate of ingredients,the slag-metal separation and the alloy recovery were studied.The results show that both the burn rate of ingredients and the recovery of alloys increase with the increased reaction heat per unit mass.With the decreased ratio of the reduction agent Al,the burn rate of ingredients firstly decreases and then increases,and the recovery of alloys gradually reduces.With the increased ratio of CaO,the burn rate of ingredients decreases,the recovery of alloys firstly increases and then decreases.When the reaction heat per unit mass and the ratio of CaO increase,Al2O3 inclusions in the alloy decrease indicating an improved slag-metal separation.When the ratio of the reduction agent Al decreases,Al2O3 inclusions in the alloy rapidly increases,indicating a bad slag-metal separation.Sulfur capacity of the slag and the ratio of sulfur distribution(Ls)in slag both increase with an increased ratio of CaO,while the S content in the alloy decreases.In the strengthened melt separation,the effects of melt temperature,separation time and the composition of pre-melted slags on the slag-metal separation,the removal of Al2O3 inclusions and the desulfurization were studied.The results show that,O content of the alloy after a strengthened melt separation slightly decreases with an increased temperature ranging from 1873 K to 2023 K.Al and O contents greatly decrease with the increase of the melt separation time.The effect of slag-metal separation can be greatly strengthened by adding pre-melted slag to improve the basicity of the slag and extending the melt separation time.The removal of Al2O3 inclusions is a separation process that particles float,gather,regrow,enter into the slag-metal interface and then are absorbed by the slag.After the direct melt separation,the mass fractions of A1 and O residuals are reduced from 10.38%and 9.36%to 6.52%and 4.54%,respectively.However,after the melt separation with the pre-melted slag,they are dramatically reduced to 3.31%and 0.98%,respectively.The contents of Al,O and S residuals all decrease with the increase of CaO content in the pre-melted slag.When the mass fraction of CaO in the pre-melted slag is 66.67%,the mass fraction of Al,O and S residuals are reduced to 3.31%,0.98%and 0.182%,and its removal rates are 53.51%,80.44%and 54.84%,respectively.In the deep reduction,the effect of the Ca addition on the deoxygenation,desulfurization and the microstructure of the alloy were studied.The results show that,after the depth reduction by Ca,sub-oxides,such as Fe4Ti2O,in the alloy are deeply deoxidized,and long-strip,Si-rich phase and Ti3Al phase disappear because of the atomic migration,but AlFe3 and elemental Ti phase arises.With the increased addition of Ca,the size of elemental Ti phase becomes smaller,and the O,S residual content in the alloy gradually decreases.The mass fraction of Al,O and S residuals in the alloy prepared by aluminothermic reduction are 7.48%,8.72%and 0.386%,respectively.They are reduced to 3.31%,2.71%and 0.175%,respectively,after a strengthened melt separation and they are further reduced to 2.12%,0.67%and 0.031%,respectively,by the deep reduction with the 12%of Ca addition.In the depth reduction,the removal rates of Al,O and S are 35.95%,75.28%and 77.97%,respectively,and they are 71.66%,92.32%and 92.08%,respectively,during the multi-stage and depth reduction.High ferrotitanium can be produced by the multi-stage and depth reduction,and its mass fractions of Ti,Al,Si,O and S are respectively 72.13%,2.57%,1.79%,0.67%and 0.031%,which meets the national standard of the high ferrotitanium.