Model for diffusion coefficient estimation of calcium ions in CaO–Al2O3–SiO2 slags

Abstract

As a common component in metallurgical slag, CaO plays an important role in desulphurisation, dephosphorisation and absorption of non-metallic inclusions. In order to better understand the mechanism of the slag/metal reactions, the diffusion dynamics of calcium ions in CaO–Al₂O₃–SiO₂ slags were studied. It was found that there was almost a linear relation between the logarithms of pre-exponential factor and diffusion activation energy. By combining the relation between the diffusion activation energy and the optical basicity corrected in the CaO–Al₂O₃–SiO₂ slags, a simple model used to estimate the diffusion coefficient of calcium ion is proposed. The estimated values of the CaO–SiO₂ and CaO–Al₂O₃–SiO₂ systems agree well with the experiment data, with a mean deviation of 35·3 and 22·5% respectively.     

Practice of Hot Metal Full Pretreatment and Less-slag Steelmaking in ShouGangJingTang

The hot metal full pretreatment and less-slag steelmaking process constituted a platform to produce clean steel with low cost and rapid pace and also realized a professional production line. The w_[P] can be less than 0.030% at the end of De-P converter and 0.006% at the end of De-C converter. The w_[N] in steel can be less than 15×10⁻⁶ at the stirring station. This production line can make clean steel steadily used for auto sheet or pipeline, for example X65MS. The De-C slag was left in the converter for the next heat and recycled to De-P converter to reduce lime consumption, which has a great benefit for the cost saving.     

国内外超低碳IF钢炼钢工艺分析

介绍了国内外部分先进钢铁厂超低碳IF钢的化学成分及日本新日铁、JFE、德国蒂森克虏伯、美国内陆、我国宝钢和鞍钢IF钢的生产应用情况。分析了IF钢的铁水预处理、转炉冶炼、真空精炼和连铸工序的关键技术，提出了超低碳IF钢冶炼过程中必须严格控制化学成分、夹杂物含量及每道工序等。     

Thermal physical properties and dephosphorisation kinetics of rare earth oxides containing slags

ABSTRACT

The melting properties and viscosity of CaO–SiO₂–MnO–La₂O₃–CeO₂ slags, with mass ratios of 0.97 and 1.05 between CaO and SiO₂, were measured using the hot stage microscopy method and rotating cylinder method, respectively. In addition, the dephosphorisation kinetics of rare earth (RE) oxides containing slags was studied. For increasing mass contents of the RE oxides, La₂O₃ and CeO₂ (0, 3, 6, 9, and 12?wt.%), in the slag, the melting temperature initially decreases and then increases. Minimum values appeared for mass contents of 6?wt.%. RE oxide concentrations below 9?wt.% are beneficial to the decrease in viscosity, which increases significantly with the mass fraction of RE oxides in molten slags with a basicity of 1.05. In slags with a basicity of 0.97, the RE oxides favour the decrease in viscosity, which does not change noticeably as their mass fraction is increased above 6?wt.%. Finally, it was found that the rate-limiting step of the dephosphorisation process is the diffusion of phosphorus.     

Manganese Distribution between FeO‐MnO‐SiO2–CaO–MgO‐Al2O3 Slags and Molten Iron

Pretreatment of high manganese hot metal is suggested to produce hot metal suitable for further processing to steel in conventional LD converter and rich manganese slags satisfy the requirements for the production of silicomanganese alloys. Manganese distribution between slag and iron represents the efficiency of manganese oxidation from hot metal. The present study has been done to investigate the effect of temperature, slag basicity and composition of oxidizer mixture on the distribution coefficient of manganese between slag and iron. Ferrous oxide activity was determined in molten synthetic slag mixtures of FeO‐MnO‐SiO₂–CaO–MgO‐Al₂O₃. The investigated slags had chemical compositions similar to either oxidizer mixture or slags expected to result from the treatment of high manganese hot metal. The technique used to measure the ferrous oxide activity in the investigated slag systems was the well established one of gas‐slag‐metal equilibration in which molten slags contained in armco iron crucibles are exposed to a flowing gas mixture with a known oxygen potential until equilibrium has been attained. After equilibration, the final chemical analysis of the slags gave compositions having a particular ferrous oxide activity corresponding to the oxygen potential of the gas mixture. The determined values of ferrous oxide activity were used to calculate the equilibrium distribution of manganese between slag and iron. Higher manganese distribution between slag and iron was found to be obtained by using oxidizer containing high active iron oxide under acidic slag and relatively low temperature of about 1350°C.     

In situ studies of agglomeration between Al2O3–CaO inclusions at metal/gas,metal/slag interfaces and in slag

Abstract

Studies of inclusion behaviour at the metal/slag interface is of great importance for the steel industry in order to achieve better control of both the size and amount of the inclusions, as well as improving the steel quality and the casting process. In this work agglomeration of liquid Al₂O₃–CaO particles at both steel/argon gas and steel/slag interfaces was studied with a confocal scanning laser microscope. In addition, agglomeration of liquid Al₂O₃–CaO–SiO₂ inclusions present in the slag was investigated. The results showed that liquid inclusions more easily agglomerated to semiliquid inclusions than to liquid inclusions. Moreover, the agglomeration of liquid particles was found to be improved remarkably when the particles were present in the slag compared to when they were in the steel/slag interface.     

CAS-OB refining: slag modification with B2O3–CaO and CaF2–CaO

Abstract

Evaluation of CAS-OB refining slags showed that the melting temperature and viscosity were very high and could further increase during the CAS-OB refining process, causing excessive slag to stick to the snorkel with resulting operational problems. To avoid this, B₂O₃–CaO (mass ratio 1 : 1) and CaF₂–CaO (mass ratio 1 : 1) were employed as modifiers added to the slag. The fusibility (melting temperature and viscosity) and desulphurising capacity of modified slag were investigated. Both B₂O₃–CaO and CaF₂–CaO can effectively lower the melting temperature and viscosity of slag. The results of experiments on sulphur partition equilibrium between metal and slag indicate that the sulphur content of metal can be further decreased by the modified slag.     

转炉铁水预处理脱磷的影响因素

 基于炉外铁水深度预脱硫+转炉铁水预脱磷的铁水预处理工艺是当今低磷或超低磷钢冶炼的重要工艺平台,其中转炉铁水预处理脱磷是关键的技术环节。以国内“双联转炉炼钢法”预脱磷炉实践为出发点,在实验室高温炉上通过顶加脱磷剂、浸入吹氧进行了铁水模拟转炉预脱磷影响因素的试验研究,比较了铁水温度、铁水初始硅质量分数w(Si)_i、脱磷渣碱度、供氧制度、搅拌强度、萤石加入量对脱磷效率的影响。结果表明,各因素对脱磷率影响的顺序为铁水温度＞w(Si)_i＞供氧制度＞脱磷渣碱度、搅拌强度＞萤石加入量;适宜的工艺参数为铁水温度为1 300 ℃,w(Si)_i 为0.10%～0.26%或低于0.30%,脱磷渣碱度为2.9～3.0,供氧制度中气氧与固氧各占50%或固氧稍偏多,维持较高的搅拌强度;转炉内铁水预脱磷处理可不加萤石。     

Sulphur removal in ironmaking and oxygen steelmaking

Sulphur removal in the ironmaking and oxygen steelmaking process is reviewed. A sulphur balance is made for the steelmaking process of Tata Steel IJmuiden, the Netherlands. There are four stages where sulphur can be removed: in the blast furnace (BF), during hot metal (HM) pretreatment, in the converter and during the secondary metallurgy (SM) treatment. For sulphur removal a low oxygen activity and a basic slag are required. In the BF typically 90% of the sulphur is removed; still, the HM contains about 0.03% of sulphur. Different HM desulphurisation processes are used worldwide. With co-injection or the Kanbara reactor, sulphur concentrations below 0.001% are reached. Basic slag helps desulphurisation in the converter. However, sulphur increase is not uncommon in the converter due to high oxygen activity and sulphur input via scrap and additions. For low sulphur concentrations SM desulphurisation, with a decreased oxygen activity and a basic slag, is always required.     

Phosphorous Enrichment in Molten Adjusted Converter Slag： Part I Effect of Adjusting Technological Conditions

 The effects of adjusting technological conditions on the phosphorous enrichment of adjusted converter slag were investigated. The results showed that the phosphorus could be effectively enriched to 2CaO·SiO2 and 2CaO·SiO2-3CaO·P2O5 solid solution (SS, namely phosphorus-rich phase) to be formed with the decreasing of basicity and cooling rate. Moreover, the morphology of the phosphorus-rich phase changed from granular for the original converter slag with higher basicity to the coexistence of granular shape and rod-like for the adjusted slag with lower basicity. P2O5 content in phosphorus-rich phase exceeded 30% while the basicity was 13 at the cooling rate of 10 ℃/min.     

Study on refining slags targeting high cleanliness and lower melting temperature inclusions in Al killed steel

Abstract

Three high basicity slags (A, B and C) were used in laboratory to refine Al killed steel to target high oxide cleanliness and low melting temperature inclusions. Inclusions were of CaO–MgO–Al₂O₃–SiO₂ system after 90 min reaction, parts of which were MgO based. Total oxygen were in the range of 0·0007–0·0010 and 0·0005–0·0010% respectively when slag A (CaO/SiO₂, 6–8; Al₂O₃, ～40%) and slag B (CaO/SiO₂, 6–8; Al₂O₃, ～30%) were applied, with inclusions all in spherical shape and mainly <5 μm. Inclusion composition concentrated in or around the lower melting point region (<1500°C) under slag A, while it became more scattered under slag B. Total oxygen varied between 0·0008 and 0·0011% under slag C (CaO/SiO₂, 3–4; Al₂O₃, about 20–25%). Many of the inclusions were in larger size, irregular morphology and located far away from the lower melting point region. Formation of MgO based inclusions closely related to solubility behaviour of MgO in the slag.     

A review of phosphorus partition relations for use in basic oxygen steelmaking

Phosphorus removal in basic oxygen steelmaking is a significant problem for integrated steelmakers. Phosphorus removal is required due to its deleterious effect on the mechanical properties of steel. However, this is progressively becoming more difficult due to the increasing phosphorus content of many iron ores. Many studies have investigated dephosphorisation and published empirical phosphorus partition (L_P) equations for a range of conditions. The structure of these equations has been used to develop a new partition relation that allows the effect of minor slag constituents such as TiO₂, Al₂O₃ and V₂O₅ on steel dephosphorisation to be tested. Al₂O₃ was found to have a weak negative effect on the measured L_P, except at the lower oxygen potential range tested, where a positive correlation was observed. Increasing TiO₂ and V₂O₅ contents were found to decrease the measured L_P; however, these correlations became less prevalent at the higher oxygen potential ranges tested.     

攀钢半钢炼钢技术进步及效果

介绍了攀钢在半钢炼钢工艺的技术进步及其效果，通过采用铁水预处理，使用活性石灰造渣，改进造渣工艺和终点控制制度，实施溅渣护炉等措施，有效地控制了终点钢、渣氧化性，缩短了冶炼周期，提高了生产率，提高了炉龄，提高了钢质量。     

Reaction Kinetics of FeO Containing Molten Slags

The kinetic study of FeO‐containing slag is valuable if we consider slag‐gas and slag‐metal reactions in steelmaking process. In the present work, the reduction rate of Fe_tO‐SiO₂–TiO₂–MO_x (MO_x = CaO, MgO, AlO_1.5, PO_2.5) melts in equilibrium with solid iron by CO gas was measured using the thermobalance system at 1673 K. A rate equation was developed based on the results obtained. The mechanisms of the reaction and the effect of P₂0₅ as a surfactant were discussed. Solid CaO was reacted with FeO‐containing slag at 1573 to 1673 K. The CaO–slag interface was analyzed by SEM and EDX, and the reacted layers were identified. The rate of solid CaO dissolution into a stagnant FeO‐containing slag at hot‐metal temperatures was explained by the FeO diffusion in slag phase.     

转炉留渣双渣操作生产实践

介绍了福建三安炼钢厂的转炉留渣双渣操作,以及留渣操作中安全问题的解决措施,分析了应用留渣双渣操作工艺的石灰消耗、钢铁料耗、转炉炉龄、氧耗、冶炼周期、脱磷等效果。通过优化顶底复吹转炉留渣双渣工艺制度,提高转炉前期脱磷效果,在无铁水预处理的设备条件下可以冶炼高铬铁水,满足了对钢的洁净度要求。     

Control of Sulfur Content in the Production of Clean Steel in Panzhihua Steel

This article mainly introduced the process of clean steel with different ways in Panzhihua Steel based on high sulfur content hot metal. With the development and application of sulfur control technologies in hot metal pretreatment, converter steel-making and refining processes, Panzhihua Steel had achieved the production of clean steel such as 350km/h steel for high speed railway, electric steel, etc.     

Control of Non‐metallic Inclusions by Slag‐metal Reactions for High Strength Alloying Steels

A laboratory study was carried out to investigate non‐metallic inclusions in high strength alloying steel refined by high basicity slag. The results indicated that the inclusions were mainly of the CaO? MgO? Al₂O₃ system, Al₂O₃? MgO and MgO‐based inclusions. The steel/slag reaction time and Al₂O₃ content in slag had a great effect on inclusions characteristics. With the reaction time increasing from 30 to 180 minutes, inclusions experienced a transformation process: from mainly Al₂O₃? MgO system and MgO‐based inclusions to spherical CaO? MgO? Al₂O₃ system inclusions surrounded by a lower melting temperature surface layer of CaO? Al₂O₃. Formation and transformation mechanisms of the inclusions were given based on the results. It was also found that with Al₂O₃ content in slag reduced from 40% to 30%, [Mg] contents in steel melts were increased and MgO in slag reached saturation, which contributed to the formation of more MgO‐based inclusions and a more scattered inclusion composition distribution after 90 min reaction.     

Application and analysis of slag holdup model in BF deadman

The operation of blast furnace is considerably influenced by slag performance, particularly in BF hearth. Slag holdup in deadman has negative effects on hearth, such as sharp peripheral flow of hot metal and carbon brick erosion. Therefore, it is urgent to monitor the slag holdup. In this paper, a slag holdup model was proposed to give a transient snapshot of the internal state of BF. Based on the analysis of practical example of Jingtang (Hebei, China) No. 1 blast furnace, three typical models and the slag holdup model were compared. Furthermore, the effects of slag basicity(CaO/SiO₂), MgO/Al₂O₃ ratio, temperature of hot metal, diameter of coke, shape factor of coke and voidage of deadman on slag holdup were investigated. The results show that current slag holdup model can timely predict the general trend of the permeability of the deadman and internal state of hearth. In addition, the influence extent of the six factors which affect the slag holdup is in the following order (from large to small effect): the voidage of deadman, shape factor of coke, diameter of coke, basicity(CaO/SiO₂), MgO/Al₂O₃ ratio, temperature of hot metal. The weighting ratio of these factors is 1:0.92:0.69:0.69:0.38:0.23.     

Reduction of synthetic stainless steel slags by aluminium

One of the most efficient ways to eliminate the harm of chromium oxide in stainless steel slag is to reduce chromium oxide in stainless steel slag using aluminium. In the present work, the Al reduction of synthetic CaO–SiO₂–Al₂O₃–MgO–Fe₂O₃–Cr₂O₃ stainless steelmaking slags at different conditions, including temperature, slag basicity and Al amount was investigated to get optimal conditions for the reduction and the metal–slag separation. It was found that the agglomeration of metal droplets and metal–slag separations were improved by increasing temperature. The reduction degrees of SiO₂, Fe₂O₃ and Cr₂O₃ were enhanced with increasing basicity of slag. The addition of CaF₂ in slag leads to better agglomerations of metal droplets and metal–slag separations. The highest reduction degree of chromium could reach 99% in slag with basicity of 2 at 1873 K.