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.

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.

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.

Calculation of phase diagram of Ti-Ni-O system and application to deoxidation of TiNi alloy

The Ti-Ni-O ternary system was assessed by means of Calphad method using ternary experimental data in previous study.Isothermal sections at 1 173 and 1 273 K were calculated.The result shows that the present calculated results are in good agreement with most of the experimental results.The consistent model parameter set determined in this work may provide theoretical guidance for the deoxidation of TiNi alloy.

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.

Deoxidation Behavior of Alloys Bearing Barium in Molten Steel

The deoxidation behaviors of alloys bearing barium in pipe steel were researched with MgO crucible under argon atmosphere in MoSi2 furnace at 1 873 K.The total oxygen contents of molten steel,the distribution,size and morphology of deoxidation products in the steel were surveyed.The metamorphic mechanism for deoxidation products of alloy bearing barium was also discussed.The results show that applying alloy bearing barium to the pipe steel,very low total oxygen contents can be obtained,and deoxidation products,which easily float up from molten steel,can be changed into globular shape and uniformly distributed in steel.The equilibrium time of total oxygen is about 25 min,and the terminal total oxygen contents range from 0.002 0%to 0.002 2% after treating with SiCa wire.The best deoxidizers are SiAlBaCa and SiAlBaCaSr.

Al Preparation from Solid Al_2O_3 by Direct Electrochemical Deoxidation in Molten CaCl_2-NaCl at 550℃

Al was prepared by a new method in molten salt at low temperature. Sintered alumina pellets were used as cathode; graphite rod was employed as anode; and the molten CaCl2-NaCl was the electrolyte. A constant 3.2 V voltage was applied in this experiment, and oxygen in solid alumina cathode was reduced by direct electrochemical deoxidation at 550℃. In this process, the current gradually decreased with increasing time and the alumina pellets became grey and porous. The metallic particles were obtained and characterized by XRD （X-ray diffraction） and SEM （scanning electron microscopy）.

Deoxidation of H13 tool steel with CaF_(2)-MgO-CaO-Al_(2)O_(3)-SiO_(2) slags at 1873 K

Laboratory-scale experiments were performed to investigate the deoxidation of H13 tool steel with CaF_(2)-MgO-Al_(2)O_(3)-CaO-SiO_(2) slags at 1873 K.The calculation of thermodynamics and kinetics was also verified through the experimental results.The results show that[Si]-[O]reaction is the control reaction,and with the increase of basicity of slag,the limitation of deoxidation was decreased.The limitation of deoxidation is the lowest for the slag with basicity of 2.0.Under the conditions of the basicity of 2.0 and the content of CaF_(2) more than 50%,the limitation of deoxidation is less than 10×10^(−6),and it does not depend on the contents of Al_(2)O_(3) and CaF_(2) in slags.The mass transport of oxygen in the metal phase is the rate-controlling step,and the slag composition has no effect on the equilibrium time of deoxidation.Based on this finding,the optimized slag composition is designed and it contains the following components:51.5%CaF_(2),20.3%MgO,16.2%Al_(2)O_(3),8.2%CaO and 3.8%SiO_(2).In the case of the optimized deoxidizing slag,the total oxygen content in H13 steel can be reduced from 25×10^(−6) to 6×10^(−6).

Preparation of low-oxygen Ti powder from TiO_(2) through combining self-propagating high temperature synthesis and electrodeoxidation

An effective method was reported to prepare low-oxygen Ti powder,which included two experimental steps:the fast conversion of TiO_(2) to TiO_(x<1) powder by self-propagating high-temperature synthesis(SHS)process and the generation of low-oxygen Ti powder by electrodeoxidizing TiO_(x<1) powder at the cathode in molten CaCl_(2).The key intermediate steps were analyzed by XRD,SEM and electrochemical testing techniques.The results demonstrated that TiO_(x<1) powder(TiO_(0.325) and TiO_(0.97))was generated after acid leaching MgO in SHS products with TiO_(2)/Mg molar ratio of 1:2,and the TiO_(x<1) powder with 16.3 wt.%oxygen could be transformed into pure titanium powder with 0.121 wt.%oxygen by electrodeoxidation at a constant potential of−3.3 V for 10 h.The electrodeoxidation of TiO_(x<1) powder in CaCl_(2) molten salt follows the step-by-step deoxidation mode,and the lattice of TiO_(x<1) powder after electrodeoxidation shrinks.

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.

Effect of Zr-Ti combined deoxidation on impact toughness of coarse-grained heat-affected zone with high heat input welding

In this study, the effects of Zr-Ti combined deoxidation and AI deoxidation on the impact toughness of coarse- grained heat-affected zone in high-strength low-alloy steels were investigated. More fine oxides were formed in the Zr-Ti-killed steel than in Al-killed steel. It was also found that more acicular ferrite grains were formed in the coarse-grained heat-affected zone in the Zr-Ti-killed steel than in Al-killed steel. The impact toughness of coarse-grained heat-affected zone of Zr-Ti-kiUed steel was higher than that of Al-killed steel. The good impact toughness was attributable to the pinning effect of fine oxides and the formation of acicular ferrite grains on fine oxides.

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.

Effect of slag composition on kinetic behavior of deep deoxidation of 5 wt.% Si high-silicon austenitic stainless steel

Based on a thermodynamic study of 5 wt.%Si high-silicon austenitic stainless steel(SS-5Si)smelting using CaF_(2)-CaO-Al_(2)0_(3)-Mg-Si0_(2) slag to obtain a low oxygen content of less than 10×10^(-4) wt.%,a kinetic mass transfer model for deep deoxidation was established through laboratory studies,and the effects of slag components and temperature on deoxidation during the slag-steel reaction process of sS-5Si were systematically studied.The experimental data verified the accuracy of the model predictions.The results showed that the final oxygen content in the steel at 1873 K was mainly controlled by the oxygen content derived from the activity of SiO_(2) regulated by the[Si]-[O]equilibrium reaction in the slag system;in particular,when the slag basicity R(R=w(CaO)/w(SiO2),where w(CaO)and w(SiO_(2))are the contents of CaO and SiO_(2) in the slag,respectively)is 3,the Al2O3 content in the slag needs to be less than 2.7%.The mass transfer rate equation for the kinetics of the deoxidation reaction revealed that the mass transfer of oxygen in the liquid metal is the rate-controlling step under different slag conditions at 1873 K,and the oxygen transfer coefficient ko.m increases with increasing the slag basicity from 4.0×10^(-6)m s^(-1)(R=1)to 4.3×10^(-5) m s^(-1)(R=3).ko.m values at R=2 and R=3 are almost the same,indicating that high slag basicity has little effect.The integral of the mass transfer rate equation for the deoxidation reaction of SS-5Si under different slag conditions is obtained.The total oxygen content of the molten steel decreases with increasing basicity from an initial content of 22×10^(-4) to 3.2×10^(-4) wt.%(R=3),consistent with the change in ko.m with slag basicity.At R=2,the slag-steel reaction takes 15 min to reach equilibrium(w[O]=5.5×10^(-4) wt.%),whereas at R=3,the slag-steel reaction takes 30 min to reach equilibrium(w[0]=3.2×10^(-4) wt.%).Considering the depth of deoxidation and reaction time of SS-5Si smelting,it is recommended the slag basicity be controlled at approximately 2.Similarly,the effect of temperature on the deep deoxidation of SS-5Si was studied.

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.

Effect of Basicity on Deoxidation Capability of Refining Slag

Mass action concentration （activity） calculation model was used to analyze the variation rule of mass action concentrations of slag compositions with basicity changing, and the effect of basicity on deoxidation capability and control of spinel and globular inclusions was investigated theoretically. From the calculation and experimental results, it was found that with the increase of basicity, the mass action concentration of Al2O3 and SiO2 decreases, while the mass action concentration of FeO and MgO increases at first and then decreases.Slag basicity below 3 to 4 would help to control spinel inclusions formation, and higher basicity improves formation of globular inclusions. Slag with basicity under 2 can effectively control the formation of globular inclusions. Deoxidation capability of slag increases with the increase of basicity, and slag with basicity about 4 could almost reach the maximum deoxidation capability. In order to smelt low oxygen steel with globular inclusions controlled, refining slag basicity should be controlled at about 4.

Deoxidation of Molten Steel by Aluminum

The deoxidation equilibrium of liquid steel was investigated from a new perspective. Dissolved associate MmOn was used to describe the interaction between dissolved M and dissolved oxygen instead of the interaction parameter of Wagner. The concentration of unassociated oxygen could be considered as the activity of oxygen. Or, the percentage of unassociated oxygen in the total dissolved oxygen was the activity coefficient of oxygen. When the content of deoxidizer was low, the dissolved oxygen was mainly composed of the unassociated oxygen, while more and more MxO formed with gradually increasing M content. The present model gave a good description to the aluminum deoxidation equilibrium after considering AlO and Al2O. Furthermore, the higher the con- tent of A1 was, the higher the content of Al2O relative to the content of AlO would be.

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.

Characteristics of Deoxidation and Desulfurization during LF Refining Al-killed Steel by Highly Basic and Low Oxidizing Slag

Steel and slag samples were taken at the start and the end of LF refining for steel plate cold common （SPCC）, in the compact strip production （CSP） process, and at the same time, the temperature and oxygen activity a[o] were measured by using an oxygen sensor. Furthermore, inclusions in steel samples were monitored by scanning electron microscopy （SEM） combined with energy dispersive spectroscopy （EDS）. It was confirmed that a [o] in liq- uid steel was in equilibrium with inclusion rather than with top slag during LF refining. Desulfurization was related to deoxidation since a[o] at slag-steel interface was clarified to be very close to that in liquid steel under the specific con- dition in LF with intense stirring by argon blowing and refined by highly basic low oxidizing slag for Al-killed steel. Sulfur partition ratio （Ls） was very sensitive to a[o]. Since a[o] increased rapidly with temperature rise, it not only offset promotion to desulfurization reaction with temperature rise but decreased Ls. For Al-killed steel, the.modifica- tion of Al2O3 for lowering the activity of Al2O3 in inclusion was believed to be favorable for both deoxidation and desulfurization during LF refining.

Laboratory study on the formation of Al2O3 inclusions at the on-set of deoxidation and during reoxidation

The formation of Al2O3 inclusions in liquid iron has been investigated in a resistance heated tube furnace to obtain deoxidation and reoxidation related data. The formation of inclusions during the early stages of deoxidation was simulated by bringing a piece of AI in contact for a short time with liquid Fe containing different dissolved oxygen levels. Reoxidation was studied by exposing AI containing Fe melts to a CO/CO2 atmosphere, Through modeling, an estimate of the local and time-dependent growth conditions for the inclusions can be made and linked to the inclusion characteristics.