Experimental Research on Refining Slag Systems Containing BaO for Ultra-Low Sulphur Steel

The experimental research on refining slag systems for ultra-low sulphur steel was carried out in a 10 kg induction furnace.It was proved that sulphur element in molten steel can be removed to less than 5×10^(-6) by adding CaO-Al_2O_3-SiO_2-MgO-CaF_2 slag on the surface of molten steel and feeding CaO-BaO-CaF2 wire into molten steel.And L_s,which is the coefficient of sulphur between slag and molten steel,that is ω(s)/ω[s],increases by increasing I(I = ωBaO/ωCaO).When I=5/3,L_s can be up to its maximum of 633.The CaSi is effective for deep desulphurization,especially when it is added to the slag of wire feeding.

Dissolution behavior of Al_(2)O_(3)inclusions into CaO-MgO-SiO_(2)-Al_(2)O_(3)-TiO_(2)system ladle slags

To investigate the dissolution behaviors of Al_(2)O_(3)inclusions in CaO-5wt%MgO-SiO_(2)-30wt%Al_(2)O_(3)-TiO_(2)system ladle slags,confocal scanning laser microscopy was conducted on the slags with different TiO_(2)contents(0-10wt%),and scanning electron microscopy was performed to study the interfacial reaction between Al_(2)O_(3)and this slag system.The results disclose that the dissolution of Al_(2)O_(3)inclusions does not result in the formation of new phases at the boundary between the slag and the inclusions.In TiO_(2)-bearing and TiO_(2)-free ladle slags,there is no difference in the dissolution mechanism of Al_(2)O_(3)inclusions at steelmaking temperatures.Boundary layer diffusion is found as the controlling step of the dissolution of Al_(2)O_(3),and the diffusion coefficient is in the range of 4.18×10^(-10)to 2.18×10^(-9)m^(2)/s at 1450-1500℃.Compared with the solubility of Al_(2)O_(3)in the slags,slag viscosity and temperature play a more profound role in the dissolution of Al_(2)O_(3)inclusions.A lower viscosity and a lower melting point of the slags are beneficial for the dissolution.Suitable addition of TiO_(2)(e.g.,5wt%)in ladle slags can enhance the dissolution of Al_(2)O_(3)inclusions because of the low viscosity and melting point of the slags,while excessive addition of TiO_(2)(e.g.,10wt%)shows the opposite trend.

Boron removal in purifying metallurgical grade silicon by CaO-SiO_2 slag refining

Boron removal from metallurgical grade silicon （MG-Si） using a calcium silicate slag was studied. The results show that it is impossible basically to remove boron using a pure SiO2 refining. The oxidizing ability of CaO-SiO2 slag for boron removal was characterized by establishing the thermodynamic relationship between the distribution coefficient of boron （LB） and the activities of SiO2 and CaO. The experimental results show that the distribution coefficient and the removal efficiency of boron are greatly improved with the increase of CaO proportion in the slag. The maximal value of LB reaches 1.57 with a slag composition of 60%CaO-40%SiO2 （mass fraction）. The boron content in the refined silicon is reduced from 18×10^-6 to 1.8×10^-6 using slag refining at 1600 ℃ for 3 h with a CaO-SiO2/MG-Si ratio of 2.5, and the removal efficiency of boron reaches 90%.

Desulfurization Characteristics of CaO-SiO_2-BaO-CaF_2-Al_2O_3-MgO Refining Slag

The desulfurization characteristics of CaO-SiO2-BaO-CaF2-Al2O3-MgO refining slag were studied in laboratory with the methodology of orthogonal design. The influence of basicity, Al2O3, MgO, BaO and CaF2 contents in slag on the desulfurization rate was analyzed and the optimum composition of refining slag was determined.

Corrosion Resistance Mechanism of MgO-CaO Refractories to Refining Slag

Corrosion resistance and penetration resistance of MgO-CaO materials with different CaO contents （22%, 42%, 49%, 53%, in mass）to refining AOD slag or VOD slag were investigated using static crucible technique by visual observation, SEM and XRD. The corrosion resistance and penetration resistance of speci-mens decrease with the increase of CaO content. This may be caused by the formation of C3S and C2S during the reactions between specimens and the slag. The formed C3S and C2S can restrain the further penetration to the matrix. The higher the CaO content, the more the C2S or C3S formed, the lower the porosity of the speci-mens, and the lower the penetration depth and corrosion rate. The corrosion resistance to AOD slag is better than that to VOD slag, because the reaction between AOD slag and the matrix is slighter than that between VOD slag and the matrix.

In situ observation of the dissolution kinetics of Al_(2)O_(3) particles in CaO–Al_(2)O_(3)–SiO_(2) slags using laser confocal scanning microscopy

The dissolution kinetics of Al_(2)O_(3) in CaO-Al_(2)O_(3) SiOslags was studied using a high-temperature confocal scanning laser microscope at 1773 to 1873 K.The results show that the controlling step during the Al_(2)O_(3) dissolution was the diffusionin molten slag.It was found that the dissolution curves of Al_(2)O_(3) particles were hardly agreed with the traditional boundary layer diffusion model with the increase of the CaO/Al_(2)O_(3) ratio of slag.A modified diffusion equation considering slag viscosity was developed to study the dissolution mechanism of Al_(2)O_(3) in slag.Diffusion coefficients of Al_(2)O_(3) in slag were calculated as 2.8×10to 4.1×10m~2/s at the temperature of 1773-1873 K.The dissolution rate of Al_(2)O_(3) increased with higher temperature,CaO/Al_(2)O_(3),and particle size.A new model was shown to be v_(Al_(2)O_(3))=0.16×r_(0)^(1.58)×x^(3.52)×(T-T_(mp))^(1.11)to predict the dissolution rate and the total dissolution time of Al_(2)O_(3) inclusions with various sizes,where vAl_(2)O_(3) is the dissolution rate of Al_(2)O_(3) in volume,μm^(3)/s;x is the value of CaO/Al_(2)O_(3) mass ratio;R_(0) is the initial radius of Al_(2)O_(3),μm;T is the temperature,K;T_(mp) is the melting point of slag,K.

Oxidizing Capability of Refining Slags Containing BaO

According to the coexistence theory of slag structure melts, the oxidizing capability of the refining slag CaO-MgO-FeO- A12O3SiO2 is studied and the relationship between the mass action concentration of FeO (NFeO) and the activity of FetO (αFetO) for this slag is found to be as NFeo=0.656 1 αFetO. Furthermore, the calculating model of oxidizing capability of the refining slag BaO-CaO-MgO- FeOA12O3-SiO2 is established. A satisfactory result is obtained when using the above oxidizing capability relationship to calculate the desulphurizing capability of such refining BaO-slags.

Experimental Study on Composition Optimization for Refining Slag Containing BaO

Laboratory study; was carried out on deep desulfurization of molten steel by CaO-Al2O3 based refining slag containing BaO at 1873K to achieve lower sulphur level in steel. A mathematical model of desulfurization was established with the methodology of quadratic orthogohal regression. According to the modle, the influence of AlO3/CaO, MgO, CaF2, BaO in slag on desulfurization rate was analyzed. The results showed that the desulfurization rate almost linearly decreased with the increase of Al2O3/CaO and it increased firstly then decreased when MgO and BaO content increased respectixely, yet the trend is on the contrary as CaF2 content increased. Based on the comprehensive analysis, the optimum composition of the refining slag was achieved under the experimental conditions.

EAF steelmaking process with increasing hot metal charging ratio and improving slagging regime

A new electric arc furnace （EAF） steelmaking process with increasing hot metal charging ratio and improving slagging regime simultaneously was developed and applied in a 50 t electric arc furnace for more than a year at No. 1 Steelmaking Plant of Shanxi Taigang Stainless Corporation Limited. The essential fact of the new EAF steelmaking process was to charge hot metal in two portions or steps： firstly, 35wt%-40wt% hot metal was pretreated by blowing oxygen in a specially designed reactor for decar burization and improving hot metal temperature and melting premelted slag; secondly, 30wt% hot metal was charged into EAF with high basicity refining slags from ladle furnace （LF）-vacuum degassing furnace （VD） refining process. The results show that the hot metal charging ratio can reach to about 65wt%-70wt% for the new EAF steelrnaking process; meanwhile, the tap-to-tap time of a 50 t EAF can shorten by 5-10 min, the electricity consumption can decrease by 35-50 kW·h/t, the lime consumption can reduce by 10.5 kg/t of molten steel, and the content of harmful heavy metals in molten steel can be easily controlled to less than the upper limits of aimed steel specification or grade compared with the traditional EAF steelmaking process. In addition, the dephosphorization ability shows a slight strengthening, however, a small degree of lessening for desulphurization ability is observed for the new EAF steelmaking process, but the weakness of desulphurization ability cannot become an obstacle to its further application since a stronger desulphurization ability can be achieved during secondary refining of LF coupled with VD after EAF steelmaking process.

Effect of components on desulfurization of an Al_2O_3-CaO base pre-molten slag containing SrO

The desulfurization experiment of an Al2O3-CaO base pre-molten refining slag containing SrO was carried out. Experimental samples were made from industrial materials. In order to predict the slag's desulfurization ability, sulphur capacity was calculated by means of optical basicity, and there is consistency between calculated results and experimental data. A mathematical model between components and sulphur partition ratio was established with the experimental data. Based on the regression equation, the effects of single and interactive components on sulphur partition ratio were discussed. The results show that the sulphur capacity and distribution ratio decrease with the increment of Al2O3/CaO. SrO and MgO can increase the sulphur partition ratio. The best content of SrO in the slag should not be more than 10%, and the MgO content should be about 8%. The effect of CaF2 on sulphur partition ratio is not obvious, therefore the addition should be limited for environmental protection.

Purifying Fe-based amorphous alloys to enhance glass-forming ability by designing a novel refining slag

Designing low melting point and low basicity refining slag suitable for Fe-based amorphous alloys and understanding the inclusions’formation,removal,influencing mechanisms are quite vital in the fields of metallurgy and materials.In this study,a novel 13%SiO_(2)-32%CaO-30%Al_(2)O_(3)-25%B_(2)O_(3)(wt.%)refining slag was designed after careful calculations of the liquid phase region,slag-metal equilibrium,surface tension,viscosity,deoxidation capability and sulfur distribution ratio.After refining with our designed slag,the content of impurities and the number density of inclusions in a representative Fe_(83)Si_(2)B_(15)(at.%)amor-phous alloy were significantly reduced.Moreover,the glass-forming ability(GFA)of the alloy was also enhanced,enabling the preparation of amorphous ribbons with a lower cooling rate.Based on the impu-rities in Fe-based amorphous alloys as well as the calculated oxide and sulfide free energy diagrams,CaO,SiO_(2),Al_(2)O_(3) oxides and CaS,TiS,MnS sulfides will form in the master alloy.The high melting point in-clusions in the melt are generally removed via a floatation-separation-absorption process and the Mn,Ti,S impurities are removed via slag-metal interface reactions during refining.As for the detrimental effect of inclusions on glass formation,the small lattice disregistry between Ti,Mn-containing inclusions and primaryα-Fe gains reveal that these inclusions are effective in promoting the heterogeneous nucleation,and therefore greatly deteriorate the GFA.These findings are important and provide an ideal solution to purifying the Fe-based amorphous alloys by refining and enhancing the GFA for industrial production.

Industrial Application of Desulfurization Using Low Basicity Refining Slag in Tire Cord Steel

Desulfurization performance with low binary basicity refining slag in 72 grade tire cord steel was calculated using FactSage and it is found that sulfur content in steel decreases with the increase of basicity of slag, MgO content in slag and slag/steel ratio while sulfur partition ratio between slag and steel increases gradually with the increase of basicity of slag as well as MgO content. Experiments were carried out and the results are of great agreements with theoretical calculation. Then industrial application tests were performed in a domestic plant and good results were achieved. Sulfur content in steel decreases gradually during refining process, as a result, sulfur content in the billets is controlled in the range of 0.007 1%-0.008 1%. Sulfur content in steel refined with slag basicity of 1.21 is lower than that of 1.02, while the plasticity of oxide compound inclusions is a little better controlled in low basicity heats. Using refining slag with basicity of 1.0-1.2 and MgO content of 5%-10% and reducing the slag takeover of LD are favorable for improving the desulfurization performance and the plasticity of inclusions during the industrial production.

Effect of B_2O_3 on Melting Temperature of CaO-Based Ladle Refining Slag

B2O3 is selected as fluxing agent of CaO-based ladle refining slag to decrease the melting temperature as well as to improve the speed of slag forming and the refining efficiency. The effects of B2O3 on the melting temperature of two series of refining slags including the low basicity slags （the mass ratio of CaO/SiO2 is 3--4） and the high basicity slags （the mass ratio of CaO/SiO2 is 5--8.75） were investigated. The slag melting temperature was meas- ured using the hemisphere method. The results indicate that the fluxing action of B2O3 is better than that of CaF2 and A1203. For the CaO-based refining slag with low basicity, the melting temperature is decreased effectively when B2O3 is used to substitute for equal mass of CaF2, Al2O3 and SiO2, respectively. For the CaO-based refining slag with high basicity, when CaF2 is substituted by B2 03, the melting temperature can be decreased remarkably. Espe- cially, when the mass ratios of CaO/Al2O3 and CaO/SiO2 are in the range of 1.1--4.0 and 5.25--8. 0, respectively, the slag melting temperature is lower than 1 300 ℃. Therefore, the 132 03-containing refining slags with high ratios of CaO/Al2O3 and CaO/SiO2 have ultra low melting temperature.

Study on LF Refining Slag and Slagging Regime of High-Aluminium Steel

During secondary refining of molten steel, reaction of steel-slag has great influence on the quality of steel. Taking high aluminium steel ([Al]≥0.8%) for instance, reaction control of 4[Al]+3(SiO2) = 2(Al2O3)+3[Si] was discussed by both thermodynamics calculation and industrial experiments. The results show that content of silicon increased sharply when content of SiO2 in slag exceeded 10%. In order to prevent the increment of silicon content and reoxidation for high aluminium steel, reasonable component range of LF refining slag is: %CaO/%Al2O3=1.6-1.9, %SiO2 【10. Results of the industrial experiments indicate that the CaO-Al2O3 based refining slag has strong ability of desulfurization and inclusion absorption. Average desulfurization rate is 80%, and T[O] reduces above 50% after refining, with the average sulfur content and T[O] about 0.0025% and 11×10-6,respectively, which can meet the requirements of secondary refining and obtain good castability of steel in continuous casting process.

Effect of CaF2 content in refining slag on formation behavior of spinel inclusion in Ni-Cr-V-alloyed special steel

The influence of CaF2 content on the formation behavior of spinel inclusions in the Ni-Cr-V-alloyed special steel was presented. The spinel was not formed at CaF2 content lower than 10 wt%. However, it was formed at early stage when the CaF2 content was greater than 30 wt%, followed by a modification to the aluminosilicate-type inclusions. Because the slag was saturated by MgO, the activity of MgO was unity irrespective of CaF2 content in the slag. Thus, Mg was transferred from slag to metal phase. Mg transferred to molten steel reacted with Al2O3-rich inclusions to form MgO.Al2O3 spinel. However, the spinel inclusion was modified to aluminosilicate-type inclusions by the reaction with Si and Ca transferred from slag to molten steel about 2-3 h later.

Improving cleanliness of 30Cr2Ni4MoV low-pressure rotor steel by CaO-SiO_(2)-MgO-Al_(2)O_(3) slag refining

The optimal composition of a CaO-SiO_(2)-Al_(2)O_(3)-MgO slag in the ladle furnace refining process was investigated to precisely control the contents of[0]and[Si]and improve the cleanliness of 30Cr2Ni4MoV steel.The iso-[O]lines and iso-[Si] lines of the equilibrium between the CaO-SiO_(2)-Al_(2)O_(3)-MgO refining slag and 30Cr2Ni4MoV steel at 1873 K were calculated by the thermodynamic software FactSage 7.3,and the activities of SiO_(2),Al_(2)O_(3)and CaO in the refining slag were discussed to achieve the optimal composition range of the refining slag.Finally,combined with high-temperature"slag-steel"equilibrium experiments,the effects of different refining slags on the oxygen contents,chemical composi-tions,quantities and sizes of inclusions in steels were studied,and then the thermody namic formation mechanism of MgAl_(2)O_(4) inclusions in 30Cr2Ni4MoV steel was discussed.The results showed that the contents of dissolved[O]nd[Si]in steel can be controlled below 10 × 10^(-6)and 0.05%.respectively;when the slag basicity is above 7.the CaO/Al_(2)O_(3)ratio is above I.and the mass fraction of SiO_(2)in the slag docs not cxcced 7%.The chemical composition of the slag has a great influence on the removal and composition of inclusions.The assessed stability phase diagrams of MgO.Al_(2)O_(3)and MgOAl_(2)O_(3) inclusion formation in the Fe-Al-Mg-O system calculated by FactSage 7.3 show good agreement with the experimental results.

Characteristics and Metallurgical Effects of Medium Basicity Refining Slag on Low Melting Temperature Inclusions

Recently, large sized CaO-Alz 03 inclusions with low melting temperature have been the main reason for lowering mechanical properties of high strength low alloy （HSLA） steel plates. New philosophy, i.e. refining by top slag with relatively low basicity and Al2O3 content, was proposed to control such kind of inclusions. Firstly, the characteristics of refining slag, such as component activities and sulphide capacity （Cs） of CaO-Al2O3-SiO2-MgO slag, were studied through thermodynamic calculation. Then, slag-metal equilibrium experiments were carried out in laboratory to investigate the exact chemical composition of refining slag together with thermodynamic analysis. Finally, industrial trials were done to verify the desulphurization ability and inclusions control in steel refined by the new slag. Thermodynamic calculations indicated that the slags with basicity of 3.5 and Al2O3 content of 200/oo and basicity of 5.0 and Al2O3 content of 20 % or 25 % have high values of CaO activity, sulphide capacity and ratio of MgO activity to Al2O3 activity. Laboratory equilibrium experiments showed that the slag with basicity of about 4.5 and A12 03 content of about 20% is helpful for increasing the melting temperature of inclusions in steel. After introducing such kind of refining slag in industrial trials, the sulphur content in eight heats of steel is below 20 ×l0-6 , which meets the requirement of HSLA steel, and most inclusions distribute in relatively high melting zone （≥1773 K） of CaO- Al2O3-MgO（-SiO2） quasi-ternary diagram. New philosophy of top refining slag is feasible to control low melting point inclusions of CaO-Al2O3 system in HSLA steel.

Inclusion evolution in 50CrVA spring steel by optimization of refining slag

In order to control the CaO-Al;O;-SiO;-MgO system inclusions in 50 CrVA spring steel in a lower melting temperature region,high temperature equilibrium experiments between steel and slag were performed in the laboratory,under the conditions of the initial slag basicity within 3-7and the content of Al;O;between 18-35mass%,to investigate the formation and evolution of this type of inclusion.The results indicate that the total oxygen content in the steel decreases with the increase of slag basicity and the decrease of Al;O;content in slags,and CaO-Al;O;-SiO2-MgO inclusions tend to deviate from the low melting point region with the increase of Al;O;content in slags.The most favorable composition for the refining slag is composed of 51-56mass% CaO,9-13mass% SiO;,20-25mass% Al;O;and 6mass% MgO.In this case,the inclusions in 50 CrVA spring steel are mostly in the low melting point regions,in which their plasticities are expected to improve during steel rolling.The MgO-based inclusions were observed in the steel matrix and the formation mechanism was theoretically and schematically revealed.It is also found that adding around 11mass% of MgO into the refining slags is beneficial to reducing the refractory corrosion.Further work should be carried out focusing on the evolution rates of MgO-based inclusions.

Refractories for RH Degassers and Ways of Improving Their Lining Life

This paper attempts to clarify the systematic works of the refractories for the RH degassers and the ways of improving their lining life. It includes ： （ 1 ） types of RH degassers ; （2） the operating conditions of refining and the severely damaged areas in RH degassers ; （3） the reasons why side wall and bottom of lower vessel, throat and snorkels become the severe wear areas are analyzed, such as erosion and abrasion caused by the high circula- tion rate of treated molten steel, thermal and structural spalling by the violent temperature change, high corrosion by the Fe-oxides containing siliceous slag and CaF：riched desulfurization powders attack, degradation of texture by the vaporization of refractory components in vacuum and in oxygen blowing; besides the above men- tioned factors, what other reasons to make the snorkels become the most quick wear elements are also explained; （4） the studies of resistance to refining slags attack and slag penetration and its prevention ; the evaluation of va- rious refractory materials to withstand the attack of slags is based on the experimental results of rotating cylinder method, rotary drum test and induction furnace test, and the phase diagrams analyses; the measures to reduce the slag penetration are discussed, for example the deep of slag penetration can be decreased by reducing the size of brick pores ; （5） suitable refractory materials selection and recent developments for the different severe wear areas in RH, and lining maintenance; （6） refractories for RH to refine silicon steel; （7） the ways of improving RH lining life.

Boron Removal From Metallurgical Grade Silicon by Molten Slag Refining in Induction Furnace

The impurities Al,Ca,Ti,B,P etc in metallurgical grade silicon(MG-Si)can be effectively removed by refining using molten slag based CaO-SiO_2,and it is especially effective for boron removal.The experiments of boron removal were studied using CaO-SiO_2 binary slag in induction furnace.The results showed that the distribution coefficient of boron(L_B)between slag and silicon increased with more proportion of CaO/SiO_2(mass%).It was advantaged to boron removal for higher basicity of slag,so the boron in MG-Si was reduced from 18ppmw to 1.4ppmw with the addition of Li_2O and K_2O to CaO-SiO_2 slag.The proportion of SiO_2 in slag affected the oxidizing capacity of slag,which reduced the efficiency of boron removal.