Development and prospects of molten steel deoxidation in steelmaking process

In the long traditional process of steelmaking,excess oxygen is blown into the converter,and alloying elements are used for deoxidation.This inevitably results in excessive deoxidation of products remaining within the steel liquid,affecting the cleanliness of the steel.With the increasing requirements for steel performance,reducing the oxygen content in the steel liquid and ensuring its high cleanliness is necessary.After more than a hundred years of development,the total oxygen content in steel has been reduced from approximately 100×10^(-6)to approximately 10×10^(-6),and it can be controlled below 5×10^(-6)in some steel grades.A relatively stable and mature deoxidation technology has been formed,but further reducing the oxygen content in steel is no longer significant for improving steel quality.Our research team developed a deoxidation technology for bearing steel by optimizing the entire conventional process.The technology combines silicon–manganese predeoxidation,ladle furnace diffusion deoxidation,and vacuum final deoxidation.We successfully conducted industrial experiments and produced interstitial-free steel with natural decarbonization predeoxidation.Non-aluminum deoxidation was found to control the oxygen content in bearing steel to between 4×10^(-6) and 8×10^(-6),altering the type of inclusions,eliminating large particle Ds-type inclusions,improving the flowability of the steel liquid,and deriving a higher fatigue life.The natural decarbonization predeoxidation of interstitial-free steel reduced aluminum consumption and production costs and significantly improved the quality of cast billets.

Ultrahigh cycle fatigue fracture mechanism of high-quality bearing steel obtained through different deoxidation methods

The mechanism of oxide inclusions in fatigue crack initiation in the very-high cycle fatigue(VHCF)regime was clarified by subjecting bearing steels deoxidized by Al(Al-deoxidized steel)and Si(Si-deoxidized steel)to ultrasonic tension-compression fatigue tests(stress ratio,R=−1)and analyzing the characteristics of the detected inclusions.Results show that the main types of inclusions in Si-and Al-deoxidized steels are silicate and calcium aluminate,respectively.The content of calcium aluminate inclusions larger than 15μm in Si-deoxidized steel is lower than that in Al-deoxidized steel,and the difference observed may be attributed to different inclusion generation processes during melting.Despite differences in their cleanliness and total oxygen contents,the Si-and Al-deoxidized steels show similar VHCF lives.The factors causing fatigue failure in these steels reveal distinct differences.Calcium aluminate inclusions are responsible for the cracks in Al-deoxidized steel.By comparison,most fatigue cracks in Si-deoxidized steel are triggered by the inhomogeneity of a steel matrix,which indicates that the damage mechanisms of the steel matrix can be a critical issue for this type of steel.A minor portion of the cracks in Si-deoxidized steel could be attributed to different types of inclusions.The mechanisms of fatigue fracture caused by calcium aluminate and silicate inclusions were further analyzed.Calcium aluminate inclusions first separate from the steel matrix and then trigger crack generation.Silicate inclusions and the steel matrix are closely combined in a fatigue process;thus,these inclusions have mild effects on the fatigue life of bearing steels.Si/Mn deoxidation is an effective method to produce high-quality bearing steel with a long fatigue life and good liquid steel fluidity.

Optimum Slag Basicity for Deoxidation DuringSecondary Refining Process

According to the coexistence theory of slag structures, the calculating model of the oxidizing capabilityfor CaO-MgO-FeO-Al2O3-SiO2 refining slag system has been deduced. Based on this model, the concept and thecalculating method of the optimum slag basicity are put forward. The results have proved that at this basicity,steel with lower oxygen content can be obtained and non-metallic indigenous globular inclusions can be avoidedmore effectively than at other basicity.

New steelmaking process based on clean deoxidation technology

After the converter steelmaking process,a considerable number of ferroalloys are needed to remove dissolved oxygen from the molten steel,but it also forms a lot of oxide inclusions that cannot be completely removed.At the same time,it increases the carbon emis-sions in the steel production process.After years of research,our team have developed a series of clean deoxidation technologies,includ-ing carbon deoxidation,hydrogen deoxidation,and waste plastic deoxidation of molten steel to address the aforementioned issues.In this study,thermodynamic calculations and laboratory experiments were employed to verify that carbon and hydrogen can reduce the total oxygen content in the molten steel melt to below 5×10^(-6) and 10×10^(-6),respectively.An analysis of the deoxidation mechanisms and ef-fects of polyethylene and polypropylene was also conducted.In addition,the applications of carbon deoxidation technology in different steels with the hot-state experiment and industrial production were discussed carefully.The carbon deoxidation experimental results of different steels were as follows:(1)the oxygen content of bearing steel was effectively controlled at 6.3×10^(-6) and the inclusion number density was lowered by 74.73%compared to aluminum deoxidized bearing steel;(2)the oxygen content in gear steel was reduced to 7.7×10^(-6) and a 54.49%reduction of inclusion number density was achieved with almost no inclusions larger than 5μm from the average level of industry gear steels;(3)a total oxygen content of M2 high-speed steel was as low as 3.7×10^(-6).In industrial production practice,car-bon deoxidation technique was applied in the final deoxidation stage for non-aluminum deoxidized bearing steel,and it yielded excellent results that the oxygen content was reduced to below 8×10^(-6) and the oxide inclusions in the steel mainly consist of silicates,along with small amounts of spinel and calcium aluminate.

Optimal Batching Plan of Deoxidation Alloying based on Principal Component Analysis and Linear Programming

As the market competition of steel mills is severe,deoxidization alloying is an important link in the metallurgical process.To solve this problem,principal component regression analysis is adopted to reduce the dimension of influencing factors,and a reasonable and reliable prediction model of element yield is established.Based on the constraint conditions such as target cost function constraint,yield constraint and non-negative constraint,linear programming is adopted to design the lowest cost batting scheme that meets the national standards and production requirements.The research results provide a reliable optimization model for the deoxidization and alloying process of steel mills,which is of positive significance for improving the market competitiveness of steel mills,reducing waste discharge and protecting the environment.

A deoxidation thermodynamic model for 304 stainless steel considering multiple-components coupled reactions

A thermodynamic model for predicting the equilibrium oxygens of 304 stainless steel was developed based on the theory of slag-steel equilibrium,the law of mass conservation,and the ion and molecule coexistence theory.In the developed model,the Fe-Cr-Mn-Si-Al-S-O-melts reaction system and CaO-MgO-CaF_(2)-FeO-MnO-Al_(2)O_(3)-SiO_(2)-Cr2O_(3)slags were considered.The oxygen contents calculated by the model are in good agreement with experimental results and reference data.The equilibrium oxygen contents in 304 stainless steel mainly decrease with increasing binary basicity(w(CaO)/w(SiO_(2)),where w(i)is the mass percentage of component i)and decreasing temperature.Controlling binary basicity at 2.0 while maintaining temperatures lower than 1823 K will keep the oxygen contents in the 304 stainless steel lower than 15×10^(-6).The equilibrium oxygen contents may also be decreased with increasing content of MgO in slags,which is more significant at lower binary basicity.Besides,a small amount of FeO,MnO,and Al_(2)O_(3)(about 0-2.5 wt.%)in slags has little effect on equilibrium oxygen contents.Furthermore,it is found that the[C]-[O]reaction may occur during refining process but will not significantly affect the equilibrium oxygen contents.

Research status of inclusions in bearing steel and discussion on non-alloy deoxidation process

Non-metallic inclusion in steel is a very key factor affecting the fatigue life and quality stability of high-quality bearing steel.Inclusions mainly affect the fatigue life and toughness of the material by affecting the continuity of the steel matrix,thereby endangering the safety and stability of the equipment.The research progress of inclusion formation,removal and modification was discussed.Based on the current research status of Al deoxidation or Si deoxidation process,the feasibility of non-alloy deoxidation process for high-quality bearing steel was proposed and discussed.C or H_(2) is used as non-alloy deoxidizer,and the deoxidation products are CO and H_(2)O gases,which are easy to be removed from the molten steel.There are few studies on the non-alloy deoxidation process,especially the research and application of C or H_(2) deoxidation for high-quality bearing steel.However,the non-alloy deoxidation process is of great significance for reducing oxygen content and improving cleanliness of high-quality bearing steel.Therefore,it is necessary to study the mechanism and kinetics of C and H_(2) deoxidation and analyze the factors affecting deoxidation effect systematically,so as to provide a solid theoretical basis for the practice of non-alloy deoxidation process for high-quality bearing steel.

Thermodynamic model for deoxidation of liquid steel considering strong metal-oxygen interaction in the quasichemical model framework

Herein,a thermodynamic model aimed at describing deoxidation equilibria in liquid steel was developed.The model provides explicit forms of the activity coefficient of solutes in liquid steel,eliminating the need for the minimization of internal Gibbs energy preliminarily when solving deoxidation equilibria.The elimination of internal Gibbs energy minimization is particularly advantageous during the coupling of deoxidation equilibrium calculations with computationally intensive approaches,such as computational fluid dynamics.The model enables efficient calculations through direct embedment of the explicit forms of activity coefficient in the computing code.The proposed thermodynamic model was developed using a quasichemical approach with two key approximations:random mixing of metallic elements(Fe and oxidizing metal) and strong nonrandom pairing of metal and oxygen as nearest neighbors.Through these approximations,the quasichemical approach yielded the activity coefficients of solutes as explicit functions of composition and temperature without requiring the minimization of internal Gibbs energy or the coupling of separate programs.The model was successfully applied in the calculation of deoxidation equilibria of various elements(Al,B,C,Ca,Ce,Cr,La,Mg,Mn,Nb,Si,Ti,V,and Zr).The limitations of the model arising from these assumptions were also discussed.

Thermodynamic Analysis of Desulfurization and Its Connection With Deoxidation and Temperature for SPHC in JISC During LF Refining Process

The thermodynamic characteristics of desulfurization reaction (CaO)+[S]=(CaS)+[O] is analyzed based on the detailed composition of liquid steel and slag of Steel Plate Hot Commercial (SPHC) in Jiuquan Iron & Steel Corporation(JISC), where the activities of CaO, CaS and Al2O3 in molten slag are calculated by thermodynamic software FactSage for a more accurate result. The critical values of [O%]/[S%] for desulfurization at different temperature is are obtained, typically 0.09 at 1873K, which shows directly that it should deoxidize adequately for obtaining a favorable desulfurization condition. In addition, the thermodynamic analysis indicates that the actual dissolved O is much higher than that of equilibrium calculation which shows Al-O reaction in LF is far away from equilibrium, but it is perfect agreement with the computing results when taking the activity of Al2O3 as 1 that due to the inclusion component in LF is mainly Al2O3. Besides, with the temperature rise, the sulfur partition ratio increases softly meanwhile the reaction between Al and O is limited to a great degree resulting in the increase a dissolved oxygen in liquid steel that decreases the sulfur partition ratio seriously. As a result, the sulfur partition ratio appears to decrease with temperature increase in Al killed steel.

Thermodynamic Modeling of Deoxidation Products and Inclusion Chemistry in Mn/Si Killed Tire-Cord Steel

The present work deals with thermodynamic modeling of oxide systems, in the context of slags and inclusions in steelmaking. The work has emphasis on oxides encountered during the production of tire – cord steel. Control of inclusion chemistry and variation in eutectic temperature and eutectic composition of MnO-Al2O3-SiO2 slag system have been studied, using Thermo-CalcR software. Relatively low liquidus temperatures are obtained for ratio of MnO / SiO2 = 0.5 - 1.5 and Al2O3 content from 10 - 20 mass%. It has been observed that the addition of Alumina leads to further increase in the liquidus temperature. The stability of inclusions is analyzed in terms of free energy values of related slag systems; and an appropriate minimum of Gibbs free energy value of slag phase observed at around 50 ppm of Oxygen. The observations could not be verified using thermodynamic experiments, but have been compared with findings in the open literature.

A novel approach to synthesize porous graphene by the transformation and deoxidation of oxygen-containing functional groups

In this study,impurity-free porous graphene(PG) with intrinsic pore structure was synthesized through a facile acid-alkali etching-assisted sonication approach.The pore structure appears on the surface of graphene sheets due to intrinsic defects of graphene.The PG possessed an extremely high specific surface area of 2184 m^2/g,the size of^5 μm and layer numbers of 3-8.Additionally,PG contained micropores and mesopores simultaneously,with an average pore diameter of approximately 3 nm.The effects of acid,alkali,and ultrasound treatment on PG preparation were elucidated by transmission electron microscopy and fourier transform infrared spectroscopy.First,in an acidic solution,oxygen-containing functional groups(hydroxyls,carboxyl,and epoxides) were formed due to the hydrolysis of sulfate and continuous transformations of these functional groups on graphene oxide.Second,under the synergistic effects of alkali and ultrasound treatment,PG was obtained due to the loss of carboxyl and epoxide groups.A new route for preparing PG was provided by the proposed method.

Controlling oxygen content in electro-slag remelting steel by optimizing slag-steel reaction process

The thermodynamic equilibrium of deoxidation reactions between molten slag and steel was calculated using a slag-steel coupling thermodynamic model and the mass conservation model based on the ion-molecular coexistence theory.The study focused on the effects of slag composition and deoxidizer type on the oxygen content of low alloy steel during the electroslag remelting(ESR)process.The measured and predicted values of the oxygen content in remelted ingots,and the contents of FeO and MnO in slags were compared and analyzed.Results show that the measured content of total oxygen has a certain correlation with the trend of dissolved oxygen predicted by the model when using Ca-Si alloys as deoxidizer,but it is not correlated with the trend of dissolved oxygen predicted by the model when using Al as deoxidizer.The deoxidation mechanisms of Ca-Si and Al are different.Ca-Si alloy directly reacts with FeO and MnO in slag to reduce the oxygen potential of slag,hence it can inhibit the transfer of oxygen from the slag to molten steel.While,when Al deoxidizer is used,the oxygen content in steel is mainly reduced through floating up the alumina inclusions.Compared to Al,utilizing Ca-Si alloy as a deoxidizer is more effective in reducing the oxygen content and the amount of inclusions in ESR ingot.

Thermodynamics of Ti in liquid steels and slags

Thermodynamics of Ti in liquid steels and slags was studied in order to establish a data base for the prediction of TiOx and TiN formation in liquid steels.The interaction parameters between Ti and i（i = Cr,Ti,Al, Si,Ni,Mo,Nb,N,O） in liquid iron and the equilibrium constants for the formation of TiN and TiOx in liquid iron were determined as a function of temperature.In view of high Ti yield during ladle treatment,thermodynamics of titanium oxides in ladle slags was studied as well.Activity coefficient and redox equilibrium of TiOx in MgO saturated CaO-Al2O3 slag are also discussed by measuring the distribution ratio of Ti between slag and iron melts and the Ti3+/Ti4+ ratio in slag at 1 873 K.

Preparation of ultrafine Ti (C, N)-based cermet using oxygen-rich powders

The availability using oxygen-rich powders to prepare ultrafine Ti(C,N)-based cermets was investigated. The deoxidation process, denitrification phenomenon and the effect of deoxidation on microstructure and mechanical properties of sintered samples were discussed, respectively. The results show that oxygen in the samples prepared even with high oxygen contained in starting powders can be almost completely cleaned away through suitable sintering process. The ultrafine oxygen-rich powders have a significant effect on microstructure, which promotes the formation of white core phase. A ultrafine Ti(C,N)-based cermet with mean particle size of 0. 30 μm, uniform microstructure and excellent mechanical properties is successfully prepared. It is also found that there exists severe denitrification phenomenon in the preparation process of ultrafine Ti(C,N)-based cermet.

Deoxidization of CuCr25 alloys prepared by vacuum induction melting

The influence of crucible and vacuum on oxygen content of CuCr25 prepared by vacuum induction melting (VIM) has been investigated. The experimental results show that the selection of crucible is very important. Alkaline oxide MgO crucible can result in increment of oxygen content and segregation of Cr in the CuCr25 alloys prepared. Neutral oxide Al 2O 3 crucible has no contribution to oxygen in CuCr25. The results also indicate that some kinds of deoxidant, such as Al, are further beneficial to deoxidization of the alloys. [

Modification of Inclusions in ESR Bearing Steel

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Experimental Study on Deoxidization of Bariumand Barium Alloy

Based on the review of latest papers related to the application of barium alloy, the deoxidizationeffects of barium and barium alloy, and the dynamic characteristics of molten bath have beensystematically studied by means of the convection free bath, natural convection bath, air andvacuum induction melting experiments. It was found that both the total oxygen content andsoluble oxygen content in molten bath decreased rapidly. The results obtained provided practicaland theoretical basis for further synthetic applications of barium alloy in metallurgical industry.

Design, Selection and Application of High Efficient Complex Alloys

The design, selection and application principles of complex alloys according to the requirements of making low-alloy steels are discussed. The designed complex alloys containing calcium, barium, magnesium, strontium, rare earth elements, etc. should not only be able to deoxidize, desulphurize and refine liquid steel, but also alloy it. The application principles of alloys are as follows: using Si- Mn or Si-Mn-Al alloys for pre-deoxidizing, Si-Al-Ba or Si-Al-Ca-Ba alloys for final deoxidizing and Si-CaBa-Mg(Sr) alloys for refi- ning.

EQUILIBRIA OF Sr,Ba AND O,S IN LIQUID Fe

The equilibrium constants between Sr-O,Ba-O and Sr-S,Ba-S in liquid iron at 1570℃ andthe interaction coefficients concerning these elements have been determined as follows:KSro=1.897×10-7,eOSr=-43.8KBaO=8.204×10-8,eOBa=-98.0KSrS=8.356×10-7,eSSr=-3.9KBaS=4.083×10-7,eSBa=-3.

Effect of Rare Earths on Fe-Based High Chromium Alloy Powder During Mechanical Milling

The effect of adding rare earths and its oxides into Fe based high chromium alloy powder system during mechanical milling on the powder was studied. The results show that the amount of removed active oxygen achieves the maximum value when the addition of element cerium amounts to 0 4%～0 6%. Part of the rare earth oxides added are favorable to the deoxidization. Thermodynamic analysis indicates that rare earths can deoxidize the majority amount of oxygen and preserve carbon in the powder system.