The precipitation diagram of [Ce]-[O]-[S] in liquid iron and its application

A space precipitation diagram of [Ce]-[O]-[S] in pure liquid iron has been constructed utilising recent experimental thermodynamic data gathered on allied equilibrium systems of RE-O, RE-S and RE-O-S. A quantitative correlation between the activities of oxygen, sulphur and the constitution of the formed RE inclusions has been found. This correlation was theoretically evaluated through thermodynamic calculation and verified by experimental data concerned with the activities of oxygen and sulphur in liquid iron and the composition of the formed RE inclusions.     

Thermodynamic behaviours of manganese and phosphorus between CaO‐MgOsat‐SiO2‐Al2O3‐FetO‐MnO‐P2O5 ladle slag and liquid iron

The thermodynamic equilibria of manganese and phosphorus between liquid iron and CaO‐MgO_Sat‐SiO₂‐Fe_tO‐MnO‐P₂O₅‐Al₂O₃ (0–33%) ladle slag have been investigated at 1873 K from the viewpoint of Mn and P yields for the production of high‐strength steels. The equilibrium distribution ratios of Mn and P were found to increase with increasing Fe_tO content; however, these ratios vary with basicity, but they do this the other way round. The addition of alumina into slag at a fixed basicity and Fe_tO content decreases both the equilibrium manganese and phosphorus distributions. The equilibrium distribution ratios were discussed in terms of the variation of activity coefficients of Fe_tO, MnO and PO_2.5, according to the slag basicity and Al₂O₃ content. The quantitative contributions of basicity and (%Fe_tO + %MnO) on L_Mn and L_P were empirically determined and their usefulness was discussed with the aid of plant data: To improve Mn and P yields in the practical RH operation, it is strongly recommended that Fe‐Mn and Fe‐P alloys be added after Al deoxidation treatment inducing relatively high Al₂O₃ in slag and maintaining low Fe_tO content. In addition, a ladle slag composition for the targeted Mn and P contents in liquid iron was substantially estimated using the empirical relationships.     

Aluminum deoxidation equilibrium in liquid Ni-Fe alloys equilibrated with CaO-Al2O3 slags

The deoxidation equilibrium for Al in Ni-Fe alloys was studied in the equilibrium experiments between CaO-Al₂O₃ slags and Fe-30, 50 and 70 % Ni alloys at 1873 K. By using the values for the first and second order interaction parameters between oxygen and nickel in liquid iron and those between oxygen and iron in liquid nickel, the effect of Ni on the activity coefficient of Al in liquid iron and that of Fe on the activity coefficient of Al in liquid nickel were determined in the whole composition range of Ni-Fe alloys. The oxygen contents in Ni-Fe alloys calculated by the iterative method based on pure iron were in good agreement with those based on pure nickel in the range of [% Al] < 0.03. From this fact, it was found that the Wagner's approximation relating to the multi-component solution was applicable to the deoxidation equilibrium in the whole composition range of Ni-Fe alloys in the restricted concentration of a deoxidizer.     

Ce/Mg处理对M50轴承钢洁净度的影响

采用真空感应熔炼工艺冶炼航空轴承钢M50,对比分析了Ce处理、Mg处理和Ce–Mg复合处理对氧、硫含量和夹杂物分布特征的影响,结合热力学计算,阐明了加入Ce、Mg元素对钢液洁净度的影响机理。研究发现,Ce具有很强的脱氧、脱硫能力,加入Ce会优先生成Ce₂O₂S夹杂物,随着钢液中氧含量的降低,Ce还会与As等有害杂质元素结合,起到净化钢液的效果。过量的Ce会加剧其与镁铝尖晶石材质耐火材料的反应,导致钢中夹杂物数量的增加,Ce的质量分数为0.018%时,钢中夹杂物的尺寸和数量最小;添加Mg不仅可以脱氧、脱硫,还可以抑制Ce与镁铝尖晶石耐材的反应,Ce–Mg复合处理可以显著降低钢中的夹杂物的尺寸和数量,将钢中的氧的质量分数降低至0.00075%。      

Composition Control of CaO‐MgO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel ‐ a Thermodynamic Analysis

The effect of oxide component content on the low melting point zone (LMP) in the CaO‐MgO‐Al₂O₃‐SiO₂ system has been analysed using FactSage software. The contents of dissolved elements [Si], [Mg], [O] and [Al] in liquid steel in equilibrium with the LMP inclusions in the CaO‐MgO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MgO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the MgO content is 10%. The LMP zone becomes wide with the increase in CaO content (within the range of 0~30 mass%) and the decrease in SiO₂ (from 25 to 5 mass%). To obtain the LMP (below 1400°C) inclusions, the [Mg], [Al] and [O] contents must be controlled within the range of 0.2~2 ppm, 1.0~2.0 ppm and 60~100 ppm, respectively.     

Mg~(2+)-CO_3~(2-)-Nta~(3-)-H_2O体系热力学平衡分析

以氨三乙酸盐为配体浸出次生氧化矿杂质镁的常见形态碳酸镁,建立了Mg~(2+)-CO_3~(2-)-Nta~(3-)-H_2O体系的配合平衡热力学,并在氨三乙酸根(Nta~(3-))总浓度0~2.5mol/L和pH 5~14范围内绘制了其热力学平衡图,考察了Nta~(3-)配体对镁的选择性。结果表明,碳酸镁在酸性条件下的浸出主要是H+的作用,在碱性条件下的浸出主要是Nta~(3-)和Mg~(2+)的配合作用,但是其配合能力较弱,导致其在碱性条件下溶出量有限。因此,碱性氨三乙酸盐体系对矿物中镁具有较高的选择性。     

Thermodynamic assessment of the Al deoxidation reaction in liquid iron

The deoxidation reaction of aluminum in liquid iron has been investigated thermodynamically using Al₂O₃ crucible at 1873 K under Ar atmosphere as a fundamental study for the accurate control of inclusions in the ladle refining process. In addition to the equilibrium constant log K_A1 for the aluminum deoxidation reaction, the first-order and second-order interaction parameters between aluminum and oxygen were experimentally determined in the concentration range of aluminum up to 1 %. The temperature dependence of the equilibrium constant and the first-order interaction parameter e^A1 was also obtained: log K_A1 = 12.32 - 47400/T, e^A1 = 15.57 - 36500/T. The equilibrium relation between aluminum and oxygen contents in the aluminum deoxidized iron by applying interaction parameters and the equilibrium constant determined in this work satisfies fairly well the equilibrium data over the whole concentration range of aluminum considered.     

150 t BOF-LF-VD-CC流程无铝脱氧工艺高速轨钢冶炼过程的夹杂物行为

时速350 km高速钢轨要求钢中全氧含量T[O]≤20×10^-6,非金属夹杂物B、C、D类≤1.0级。国内在重轨钢冶炼中,通常采用无铝脱氧工艺,即采用SiCaBa合金强化脱氧,形成了低熔点的Mn-Al-Si-Ba-Ca多元型氧化物夹杂,该类夹杂物在精炼中全部排出钢液。研究了铁水预处理脱硫-150 t顶底复吹转炉-LF-VD-280 mm ×380 mm连铸流程冶炼钢轨钢U71MnG时的夹杂物行为,包括无铝脱氧工艺钢轨钢中氧化物夹杂的组成及特征,转炉终点[C]对钢水氧活度的影响以及LF精炼渣碱度和VD后期软吹氩搅拌对钢氧含量和夹杂物的影响。结果得出,钢轨头部的≤20μm氧化物夹杂为精炼时二次脱氧产物,通过控制转炉终点[C]＞0.15%,控制精炼渣碱度(CaO)/(SiO₂)=2.5~3,∑(FeO+MnO)≤1.0%可有效降低钢轨钢中氧化物的数量和尺寸。     

On Physico‐Chemical and Technical Limits in Clean Steel Production

Great progresses in steel cleanliness have been attained during the last decades. In the measures of oxygen the lowest levels are approaching 5 ppm in O_tot i.e. close to the thermodynamic limit of Al deoxidation. As the thermodynamics of the reaction system is firmly anchored to the steel chemistry and thus to the properties of steel and the final product, it is useful to examine the thermodynamic constraints for selected steels in the refining and casting processes. In most steels Al‐O equilibrium determines the limit of deoxidation. Calculations by applying thermodynamic software showed that in selected “common” steels the equilibrium oxygen content varied from below 5 ppm up to 30 ppm or higher depending on the aluminium content, interaction effect of other alloying elements and temperature. For lower oxygen content there are several possibilities. The first one is to use stronger deoxidizing additions like Ca, Zr, Ce etc. However, they can be problematic as substitutes as they produce inclusions which influence steel properties. The second way is to intensify the deoxidizing power of certain elements e.g. Si by bringing the steel in intimate contact with a proper slag with low SiO₂ activity in ladle treatment with violent stirring. In the calculation example it was possible to decrease oxygen content from 30 ppm to the level below 10 ppm in C/Mn/Si steel at very low Al level. The third potential but unused process is vacuum deoxidation especially for medium and high carbon steels. Equilibrium oxygen contents below 1 ppm are thermodynamically easily attainable. But in practice the vacuum treatment should be designed to intensify the carbon‐oxygen reaction on the top surface of the stirred steel liquid. Also the eventual reactions with refractory materials should be suppressed.     

A thermodynamic model for deoxidation equilibria in steel

For relattively dilute solutions of oxygen and a deoxidizer M (M=Al, Cr, Ca, Mg, ...) in molten Fe, a thermodynamic model is proposed wherein the dissolved species are M*O associates as well as unassociated M and O atoms. At higher metal concentrations, a small amount of M ₂*O associates also form. Experimental deoxidation equilibria for 15 deoxidizers M are quantitatively reproduced at all temperatures, with only a constant, temperature-independent and composition-independent empirical parameter for the Gibbs energy of formation of each associate. The deoxidation behavior of Mg, Ca, and Ba is elucidated for the first time. The parameters are stored in a database, which can be used to predict complex deoxidation equilibria in multicomponent steels.     

Thermodynamics of Composition Control of CaO‐MnO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel

The effect of oxide component content on the low melting point zone (simplified as LMP) in the CaO‐MnO‐Al₂O₃‐SiO₂ system has been analysed by FactSage. The contents of [Si], [Mn], [O] and [Al] in liquid steel which are in equilibrium with the LMP inclusions in the CaO‐MnO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MnO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the CaO content is 15%, and that the LMP zone becomes wider with increase in SiO₂ and MnO contents (within the range of 0~25%). To obtain LMP inclusions (below 1400°C), [Si] and [Mn] can be controlled within a wide range, but [Al] and [O] must be controlled within the range of 0.5~5 ppm and 50~120 ppm, respectively.     

石油套管钢LF精炼过程T[O]和夹杂物的控制

通过对100 t LF精炼37Mn5套管钢时1 540～1580℃钢水中稳定氧化物夹杂含量与T[O]的关系以及钢-渣平衡时渣碱度对钢中活性氧含量影响的分析,提出降低钢中T[O]和夹杂物含量的改进工艺措施。热力学计算和试验结果表明,当[Al]s为0.03%～0.04%,精炼渣碱度为3,(CaO)/(Al₂O₃)=3～3.5时,37Mn5钢中的氧含量降到10×10^-6,管材基本消除了粗系夹杂,细系夹杂A+B+C+D≤5.0级,达到使用要求。     

Modification of Inclusions in Liquid Iron by Mg Treatment

Effect of Mg addition on the compositions of inclusions were studied. The results show that Mg can minimize the inclusions of steel obviously. Under the present condition, Mg deoxidation products of low-S content experimental steel would be changed in the order of Al₂O₃→MgAl₂O₄→Mg→Al–O–S→Mg–O–S. Mg deoxidation products of high-S content experimental steel generate Mg–S(–O)+MnS type inclusions, except for usual oxysulfide. And it is consistent with the results of thermodynamics calculation. Mg is preferred to react with oxide, compared with sulfide. The reaction reaches the equilibrium after 1 min or 5 min. It shows that the number and diameter of inclusions in all experimental steel samples are well under control, helping to improve the properties of steel.     

碳化硅的冶金性能及其在钢铁工业中的应用

在分析SiC的脱氧性质、溶解特性等冶金性能的基础上,结合部分钢铁企业应用SiC脱氧剂的实例,分析了SiC脱氧剂在钢铁冶炼过程中脱氧合金化、精炼脱氧及钢水提温的冶金性能及机理。SiC在脱氧合金化过程中,脱氧反应迅速,能使钢液增Si、增C,净化钢液,提高钢水流动性,并且能提高合金收得率,降低炼钢成本。     

Equilibria between cerium or neodymium and oxygen in molten iron

Autoradiographs show that there is an obvious reaction between Ce and Nd in liquid iron and the MgO/CaO crucible wall. For reaching the Ce-O, Nd-O equilibrium, a long melting period and the addition of rare earth elements (RE’s) in several batches were needed to ensure the full reaction between the RE’s in the melt and crucible wall. The dissolved Ce or Nd content in iron was measured by means of radioactive isotopes¹⁴¹Ce or¹⁴⁷Nd and electrolysis in the organic electrolyte. The oxygen activity was measured by solid electrolyte sensors made of ZrO₂(MgO) tube. The relationships between the equilibrium constants and the temperatures for reactions Ce₂O₃ (s) = 2[Ce] + 3[O], CeO₂ (s) = [Ce] + 2[O], and Nd₂O₃ (s) = 2[Nd] + 3[O], as well as the corresponding thermodynamic parameters, have been determined. Formerly Graduate Student at the University of Science and Technology Beijing     

Mathematical Modelling of Non‐equilibrium Decarburization Process during Vacuum Circulation Refining of Molten Steel: Application of the Model and Results (II) ‐ Non‐equilibrium Factors and their Influences on the Decarburization Process

The results, which were obtained by applying the novel three‐dimensional mathematical model proposed and developed earlier [1] to model and analyse the decarburization process of molten steel during the RH and RH‐KTB refining in a 90‐t multifunction RH degasser, showed that under the conditions of the present work, the contributions of the flow, mass diffusion and chemical reactions and other non‐equilibrium processes to the Raleigh‐Onsager dissipation function are not large throughout vacuum circulation refining of molten steel. Thus, it is held everywhere in the whole flow field of the system that the value of the non‐linear dissipation factor is approximately equal to one. The entropy generation and energy dissipation in the system rapidly decrease with increasing refining time. Compared to the work done by the drag force while the bubbles passing through the liquid phase as well as by the viscous and turbulent flow and diffusion processes, the carbon‐oxygen reaction itself plays a more governing role to the entropy production and energy dissipation in the system. The RH refining process of low and ultra‐low carbon steels seems to be close to the linear zone of the non‐equilibrium state. The influences of the viscous and turbulent flow dissipation as well as diffusion processes on the non‐equilibrium activity coefficients of the carbon and oxygen in the molten steel may almost be neglected. Except in the regions where the chemical C‐O reaction takes place (the up‐snorkel zone and the bath in the vacuum vessel), the non‐equilibrium components of the non‐equilibrium activity coefficients of the carbon and oxygen in the molten steel at the other places in the degasser are all tending towards one. The non‐equilibrium effects (mainly, the C‐O reaction itself) give a restraining role on the decarburization of liquid steel in the RH refining process. This model is able to model more reasonably and precisely the non‐equilibrium decarburization process during the vacuum circulation refining of molten steel in comparison to a model without considering the non‐equilibrium effects.     

The thermochemistry of magnesium in nickel-base alloys: Part II. activity of magnesium

The experimental method described in Part I^[49] of this article was applied to the liquid nickel-magnesium system for the determination of magnesium activity. From a practical point of view, knowledge of the thermodynamic properties of magnesium is becomming increasingly important as the control of processing parameters tightens. Magnesium is added to nickel-base alloys for improved ductility, at levels typically less than 100 parts per million (ppm). Thus, experimental results presented are applicable to levels of less than 100 ppm Mg. The following parameters were determined: the equilibrium constant for the formation of spinel, the magnesium-oxygen and aluminum-oxygen interaction coefficients, the equilibrium constant for solution of magnesium in liquid nickel, and the Raultian activity coefficient of magnesium in an infinitely dilute solution. Formerly Graduate Student, University of British Columbia     

120 t BOF-LF-VD-CC流程冶炼的20CrMnTi齿轮钢氧含量和夹杂物特性

采用全流程系统取样的方式,对120 t BOF-LF-VD-CC工艺生产20CrMnTi齿轮钢中氧含量和夹杂物特性的演变规律进行系统的分析和研究。实验结果表明,采用铝脱氧和高碱度[（CaO）/（SiO₂）=3.8～7]还原渣工艺,能使铸坯中T[O]低于20×10^-6;中间包钢水中平均T[O]增加6×10^-6;齿轮钢冶炼过程中,夹杂物完成了Al₂O₃→Al₂O₃-MgO→Al₂O₃-CaO-MgO的转变。