The dissolution behavior of complex inclusions in refining slag was studied using confocal laser scanning microscope.Based on the dissolution curve of complex inclusions,the main rate-limiting link of CaO-SiO_(2)-Al_(...The dissolution behavior of complex inclusions in refining slag was studied using confocal laser scanning microscope.Based on the dissolution curve of complex inclusions,the main rate-limiting link of CaO-SiO_(2)-Al_(2)O_(3)complex inclusions was the diffusion in the molten slag.The dissolution rate of CaO-SiO_(2)-Al_(2)O_(3)complex inclusions was affected by the composition and size of inclusion.The functional relationship between the dimensionless inclusion capacity(Zh)and the dimensionless dissolution rate(Ry)of CaO-SiO_(2)-Al_(2)O_(3)complex inclusions was calculated as Ry=2.10×10^(-6)Zh^(0.160),while it was Ry=2.10×10^(-6)Zh^(0.0087)for Al_(2)O_(3)-CaO complex inclusions.On this basis,the complete dissolution time and rate of the complex inclusions were calculated by using the function relation between the Zh and Ry numbers.展开更多
Slagging and calcium treatment are commonly used methods to control cleanliness and inclusions in steel.However,the inappropriate slagging and calcium treatment operations resulted in the generation of large-sized inc...Slagging and calcium treatment are commonly used methods to control cleanliness and inclusions in steel.However,the inappropriate slagging and calcium treatment operations resulted in the generation of large-sized inclusions and deterioration of steel cleanliness;meanwhile,changed inclusions from Al_(2)O_(3)–SiO_(2)–MnO type to Al_(2)O_(3)–SiO_(2)–CaO type after the calcium treatment during the production of an H-beam steel.Combining the thermodynamic analysis and industrial trials,measurements including reducing the basicity of refining slag to be less than 2.0 and the Al_(2)O_(3)content in slag to be less than 10 wt.%and the cancelation of calcium treatment under the total content less than 15×10^(−6)have been taken.After optimization,the content of total oxygen in tundish decreased by 24%;meanwhile,inclusions were changed from the Al_(2)O_(3)–SiO_(2)–CaO system to the Al_(2)O_(3)–SiO_(2)–MnO system with a low-melting point and a obvious decrease in the number density,area fraction,and maximum size of inclusions.It has achieved the improvement of steel cleanliness while reducing production costs.展开更多
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] ...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.展开更多
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...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%.展开更多
Non-metallic inclusions are a significant factor causing fractures during the manufacturing process of tire cord steel,and dissolution in the steel profoundly affects them.How the basicity and Al_(2)O_(3) content in S...Non-metallic inclusions are a significant factor causing fractures during the manufacturing process of tire cord steel,and dissolution in the steel profoundly affects them.How the basicity and Al_(2)O_(3) content in SiO_(2)-CaO-Al_(2)O_(3)-MgO refining slag affect non-metallic inclusions in tire cord steel at 1873 K was investigated.A quantitative relationship has been established between the slag basicity and the dissolved oxygen content in steel.The results demonstrate that non-metallic inclusions in steel transform along SiO_(2)-MnO-Al_(2)O_(3)→SiO_(2)-MnO system of inclusions.When the basicity is controlled within the range of 0.8-1.0,the corresponding dissolved oxygen content should be between 4×10^(−6) and 10×10^(−6).When Al_(2)O_(3) content in the refining slag is maintained at 5%,and the slag basicity is controlled between 0.8 and 1.0,or if the slag basicity is precisely 1.0 with Al_(2)O_(3) content kept below 11%,control over the plasticization of SiO_(2)-MnO-Al_(2)O_(3) system within the inclusions can be effectively achieved.Combined with thermodynamic calculation and measurement of the dissolved oxygen([O])activity in the steel,controlling SiO_(2)-MnO-Al_(2)O_(3)-like inclusions in the plastic region range can be achieved by adjusting the refining slag composition.展开更多
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...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.展开更多
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 yea...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.展开更多
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 te...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.展开更多
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)...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.展开更多
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 i...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.展开更多
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 ...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.展开更多
Inclusion variations of die steel H13, including changes of species, morphologies, compositions, amounts and sizes, in the production of EAF-LF--VD-ingot casting-electro slag refining （ESR） procedure, were investi- ...Inclusion variations of die steel H13, including changes of species, morphologies, compositions, amounts and sizes, in the production of EAF-LF--VD-ingot casting-electro slag refining （ESR） procedure, were investi- gated by systematic sampling, and analyzed with scanning electron microscope （SEM）, energy dispersive spectrum （EDS） , and metallographic microscope. The variation mechanism was studied by comprehensive analysis of total oxygen, nitrogen, and acid soluble aluminum as well as chemical test of refining slag. Based on the investigations, technical measures for cleanness improvement were discussed. The resuhs show that oxide inclusions in H13 steel change from irregular Al2O3- near globular CaO-MgO-Al2O3 and CaO-Al2O3-SiO2 complex inclusions-finer CaO- Al2O3-SiO2 inclusions with higher CaO content-CaO-Al2O3-SiO2 inclusions with higher Al2O3 content and irregular MgO-AI203 inclusions--fine irregular MgO-Al2O3-CaS inclusions in various steps of the production; the variations are related with changes of acid soluble aluminum content, reactions between slag and steel, re-oxidation of liquid steel during casting, and refining of ESR. It is also found that Al2O3 inclusions are modified by refining slag in LF and VD refining~ and ESR plays a good role in inclusion removal, especially in controlling the large linear VC-CrC- MoC inclusions distributed in grain boundaries. It is suggested that casting protection should be improved, and the basicity of refining slag and acid soluble aluminum content in steel should be raised.展开更多
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 ...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.展开更多
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 sl...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.展开更多
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 e...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.展开更多
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 laborato...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.展开更多
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 vis...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.展开更多
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 r...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.展开更多
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...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.展开更多
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 e...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.展开更多
基金support from the National Key R&D Program(No.2023YFB3709900)the National Natural Science Foundation of China(Grant No.U22A20171)+1 种基金the High Steel Center at the North China University of Technologythe University of Science and Technology Beijing,China.
文摘The dissolution behavior of complex inclusions in refining slag was studied using confocal laser scanning microscope.Based on the dissolution curve of complex inclusions,the main rate-limiting link of CaO-SiO_(2)-Al_(2)O_(3)complex inclusions was the diffusion in the molten slag.The dissolution rate of CaO-SiO_(2)-Al_(2)O_(3)complex inclusions was affected by the composition and size of inclusion.The functional relationship between the dimensionless inclusion capacity(Zh)and the dimensionless dissolution rate(Ry)of CaO-SiO_(2)-Al_(2)O_(3)complex inclusions was calculated as Ry=2.10×10^(-6)Zh^(0.160),while it was Ry=2.10×10^(-6)Zh^(0.0087)for Al_(2)O_(3)-CaO complex inclusions.On this basis,the complete dissolution time and rate of the complex inclusions were calculated by using the function relation between the Zh and Ry numbers.
基金support from the National Key R&D Program(Nos.2023YFB3506802 and 2023YFB3709900)the National Natural Science Foundation of China(Grant Nos.52174293 and U22A20171)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.FRF-BD-20-04A)the High Steel Center(HSC)at North China University of Technology.
文摘Slagging and calcium treatment are commonly used methods to control cleanliness and inclusions in steel.However,the inappropriate slagging and calcium treatment operations resulted in the generation of large-sized inclusions and deterioration of steel cleanliness;meanwhile,changed inclusions from Al_(2)O_(3)–SiO_(2)–MnO type to Al_(2)O_(3)–SiO_(2)–CaO type after the calcium treatment during the production of an H-beam steel.Combining the thermodynamic analysis and industrial trials,measurements including reducing the basicity of refining slag to be less than 2.0 and the Al_(2)O_(3)content in slag to be less than 10 wt.%and the cancelation of calcium treatment under the total content less than 15×10^(−6)have been taken.After optimization,the content of total oxygen in tundish decreased by 24%;meanwhile,inclusions were changed from the Al_(2)O_(3)–SiO_(2)–CaO system to the Al_(2)O_(3)–SiO_(2)–MnO system with a low-melting point and a obvious decrease in the number density,area fraction,and maximum size of inclusions.It has achieved the improvement of steel cleanliness while reducing production costs.
文摘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.
基金Projects (51104080,u1137601) supported by the National Natural Science Foundation of ChinaProject (14118557) supported by the Personnel Training Foundation of Kunming University of Science and Technology in China
文摘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%.
基金supported by the National Natural Science Foundation of China(Nos.52274337,52174317 and U1960203)2023 Liaoning Province Department of Education Fundamental Research Project Achievements(No.JYTMS20230928).
文摘Non-metallic inclusions are a significant factor causing fractures during the manufacturing process of tire cord steel,and dissolution in the steel profoundly affects them.How the basicity and Al_(2)O_(3) content in SiO_(2)-CaO-Al_(2)O_(3)-MgO refining slag affect non-metallic inclusions in tire cord steel at 1873 K was investigated.A quantitative relationship has been established between the slag basicity and the dissolved oxygen content in steel.The results demonstrate that non-metallic inclusions in steel transform along SiO_(2)-MnO-Al_(2)O_(3)→SiO_(2)-MnO system of inclusions.When the basicity is controlled within the range of 0.8-1.0,the corresponding dissolved oxygen content should be between 4×10^(−6) and 10×10^(−6).When Al_(2)O_(3) content in the refining slag is maintained at 5%,and the slag basicity is controlled between 0.8 and 1.0,or if the slag basicity is precisely 1.0 with Al_(2)O_(3) content kept below 11%,control over the plasticization of SiO_(2)-MnO-Al_(2)O_(3) system within the inclusions can be effectively achieved.Combined with thermodynamic calculation and measurement of the dissolved oxygen([O])activity in the steel,controlling SiO_(2)-MnO-Al_(2)O_(3)-like inclusions in the plastic region range can be achieved by adjusting the refining slag composition.
基金Item Sponsored by National Key Basic Research and Development Program of China(2010CB30806)Central South University Postdoctoral Funded Project of China(120961)
文摘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.
文摘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.
基金Item Sponsored by National High Technology Research and Development Program(863 Program)of China(2007AA03Z548)Natural Science Foundation of Jiangsu Province of China(BK2010355)
文摘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.
基金Item Sponsored by National Key Fundamental Research Development Project of China(G1998061500)
文摘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.
基金supported by the National Natural ScienceFoundation of China(Grant Nos.51774217,52074198 and51604201).
文摘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.
基金supported by the National Natural Science Foun-dation of China (No.52174217)China Postdoctoral Science Foundation (No.2020M682495).
文摘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.
基金Item Sponsored by National Science and Technology Support Plan of China(2009AA04Z163)
文摘Inclusion variations of die steel H13, including changes of species, morphologies, compositions, amounts and sizes, in the production of EAF-LF--VD-ingot casting-electro slag refining （ESR） procedure, were investi- gated by systematic sampling, and analyzed with scanning electron microscope （SEM）, energy dispersive spectrum （EDS） , and metallographic microscope. The variation mechanism was studied by comprehensive analysis of total oxygen, nitrogen, and acid soluble aluminum as well as chemical test of refining slag. Based on the investigations, technical measures for cleanness improvement were discussed. The resuhs show that oxide inclusions in H13 steel change from irregular Al2O3- near globular CaO-MgO-Al2O3 and CaO-Al2O3-SiO2 complex inclusions-finer CaO- Al2O3-SiO2 inclusions with higher CaO content-CaO-Al2O3-SiO2 inclusions with higher Al2O3 content and irregular MgO-AI203 inclusions--fine irregular MgO-Al2O3-CaS inclusions in various steps of the production; the variations are related with changes of acid soluble aluminum content, reactions between slag and steel, re-oxidation of liquid steel during casting, and refining of ESR. It is also found that Al2O3 inclusions are modified by refining slag in LF and VD refining~ and ESR plays a good role in inclusion removal, especially in controlling the large linear VC-CrC- MoC inclusions distributed in grain boundaries. It is suggested that casting protection should be improved, and the basicity of refining slag and acid soluble aluminum content in steel should be raised.
基金Item Sponsored by National Basic Research Program of China(2010CB630806)National Natural Science Foundation of CHina(51404020)State Key Laboratory of Advanced Metallurgy(USTB)of China(41603015)
文摘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.
文摘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.
文摘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.
基金support of the funds by the National Key Research and Development Program of China(No.2017YFB0304001)
文摘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.
文摘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.
基金Items Sponsored by the National Natural Science Foundation of China(51104080,u1137601)the Natural Science Foundation of Yunnan Province(2009CD027)the Educational Science Foundation of Yunnan Province(2010Z010)
文摘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.
基金The authors thank for the instrUction of Prof. Jian Zhang of the University of Science and Technology Beliing and the financia
文摘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.
文摘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.
