AOD炉渣对MgO-C砖的侵蚀机理研究

不锈钢生产主要采用氩氧精炼(AOD)炉冶炼工艺,本文探究AOD炉渣对钢包内衬用MgO-C砖的侵蚀机理,为提高钢包内衬用MgO-C砖的使用性能和服役寿命提供理论支撑。结合FactSage6.2软件、X射线衍射(XRD)、场发射扫描电子显微镜(SEM)和能量色散光谱(EDS)等测试手段分析炉渣侵蚀后MgO-C砖的物相变化、显微结构和化学成分变化。结果表明,随着侵蚀反应的进行,方镁石逐渐被熔蚀,且逐步出现Ca₃MgSi₂O₈等低熔点物相,以及MgAl₂O₄等高熔点物相。AOD炉渣通过基质部分侵蚀渗透MgO-C砖,并与方镁石反应生成Ca₃MgSi₂O₈等低熔点物相,熔蚀方镁石;同时,方镁石边界处生成MgAl₂O₄,阻碍AOD炉渣对MgO-C砖的侵蚀渗透。     

A basic gunning material interfaces study

Corrosion mechanisms of various basic gunning materials were investigated using crucible tests. The low corrosion resistance of olivine-containing materials was shown to be related to melted phases formation which occurs, at the gunning material/slag interface, at high temperature. MgO-rich materials are more resistant to basic slag attack. Moreover, increasing the refractory material CaO content by means of dolomite addition rises the slag penetration resistance and lowers the bulk modification resulting from slag interaction. In these materials, the corrosion mechanism involves a slag reaction with the starting binder, (NaPO₃)_n, and dolomite initially contained in the gunning material. A dolomite-containing material was projected on slag-covered MgO-C bricks, using a laboratory test equipment. Investigations carried out at the gunned material/slag/bricks interface show that the suitable silicophosphate bond still forms, at interface, despite slag interaction.     

Properties of MgO–Fe–C refractories as linings of vanadium-extraction converter

For the purpose to extend the service life of MgO–C bricks used as linings of vanadium-extraction converters, MgO–Fe–C bricks with different carbon content were designed and the properties of this novel refractory were investigated by comparing to the traditional MgO–C bricks. The results showed that the poor service life of MgO–C bricks was due to the poor sinterability of the oxidized layer at 1400 °C, whereas the oxidized layer of MgO–Fe–C brick was well sintered due to the oxidation of Fe particles in the oxidized layer and formation of MgO–FeO_ss in air atmosphere. Excellent oxidation resistance and corrosion resistance against vanadium containing slag were also obtained due to the increase of compactness of oxidized layer and concentration of FeO in the oxidized layer compared to MgO–C bricks, and it is considered that MgO–Fe–C brick is a favorable substitute of MgO–C refractory to be used as linings of vanadium-extraction converters.     

Method of raw materials selection for production of the MgO-C bricks of comparable properties using PCA and K-medoids

MgO-C refractories are zonally installed in most of the key heat devices of steel and iron metallurgy with the exposure to various corrosive factors. One of the most significant factors is low-temperature decarburization resulting in the oxidation of carbon in MgO-C refractories and loss of its properties. Moreover MgO-C materials are exposed for direct attack of liquid slag or steel melt which easily infiltrate the porous, decarburized hot face of the bricks. Cost of MgO-C materials of high quality is important for refractories user. For this reason researches try to develop materials of high quality but with lower cost by substituting fused raw materials with sintered ones or with recycled MgO-C. In this article, method of selecting the raw materials for production of MgO-C bricks with comparable properties is shown. Twenty different variants of MgO-C materials were prepared with the use of various quality raw materials. Basic properties of the industrially produced MgO-C bricks were measured. To select recipes with similar quality principal components analysis method and K-medoids algorithm were applied. To verify the results corrosion resistance of selected MgO-C materials were tested with the use of induction furnace of medium frequency.     

Degradation mechanisms of magnesia-carbon refractories by high-alumina stainless steel slags under vacuum

The corrosion behaviour of a pitch-bonded magnesia-carbon refractory by an Al₂O₃ rich (∼15 wt.%) stainless steelmaking slag was investigated by rotating finger tests in a vacuum induction furnace at high temperature (>1650 °C) and low oxygen partial pressure (1.5–4.3 × 10⁻¹⁰ atm). This study confirms the poor slagline behaviour of MgO-C bricks industrially observed in VOD ladles. Higher temperatures and longer exposure times lead to more severe slag infiltration and direct MgO dissolution. The intrinsic MgO-C reaction is the major decarburisation mechanism, while extrinsic decarburisation by oxygen from the atmosphere and/or reducible slag components (CrO_x, FeO_x) was limited. Three kinds of metallic particles with different size, shape, location, composition and origin were observed in the refractory specimens. Concurrently, the thermodynamic conditions for the formation of a protective Mg(Al,Cr)₂O₄ spinel layer at the slag/refractory interface are investigated. The industrial relevance of this spinel layer formation is discussed with respect to the chosen Al₂O₃ level. Guidelines are proposed to minimise MgO refractory dissolution in VOD slaglines.     

镁硅质防粘渣涂料的防粘渣试验及其应用

为了验证以菱镁矿、石英、黏土、氧化铬微粉及磷酸盐为原料制成的镁硅质防粘渣涂料的防粘渣性能,采用静态坩埚法(1 600℃3 h,空气气氛)对比研究了转炉钢包渣线用普通镁碳砖和VOD钢包渣线用低碳镁碳砖在涂覆该涂料前后的防粘渣性能,分析了试验后涂料的显微结构,探讨了涂料的防粘渣机制,并在宝钢进行了实际使用试验。结果表明:防粘渣涂料在熔渣与镁碳砖之间形成了明显的隔离层,起到了较好的防粘渣作用。这是由于,防粘渣涂料在1 600℃的平衡物相为MgO、M2S及MA与MK的固溶体,无液相出现,隔离了镁碳砖与熔渣的接触,不易被钢渣溶解,也不与镁碳砖发生烧结反应,还在一定程度上保护炭素不被氧化,加之其较大的体积收缩和排气反应,使其容易与粘附在其表面的熔渣一起脱落,从而起到防粘渣的作用。实际使用表明,该涂料大大减轻了钢包的粘渣程度,并延长了渣线和包口镁碳砖的使用寿命,得到了钢厂的认可。     

Corrosion mechanism of magnesia-chrome refractory bricks with FetO-SiO2-Cr2O3 copper converter slag

The paper investigates the effect of Cr₂O₃ on the resistance of magnesia-chrome refractory bricks to copper converter slag. The static crucible method was employed to carry out the slag resistance experiment. The corrosion of magnesia-chrome refractory bricks under the action of Fe_tO-SiO₂-xCr₂O₃ (x = 0–5 wt%) slag at 1300 °C was discussed. The microstructure of the corroded sample was analyzed by XRD and SEM-EDS to elucidate the corrosion mechanisms of magnesia-chrome refractory bricks with Fe_tO-SiO₂-Cr₂O₃ slag. The results indicated that the permeability index of the slag-resistant samples gradually decreased with increasing Cr₂O₃ content in the Fe_tO-SiO₂-Cr₂O₃ slag. Combined with SEM and XRD characterization, the MgO in the refractory reacted with FeO and SiO₂ in the molten slag, leading to dissolution and reaction corrosion of the refractories. Meanwhile, forming a (Mg, Fe)O solid solution layer in corroded samples can prevent further chemical reactions and high-temperature dissolution between the Fe_tO-SiO₂-Cr₂O₃ slag and refractories. With the addition of Cr₂O₃ in the Fe_tO-SiO₂-Cr₂O₃ slag, the corrosion effect of slag on refractories was weakened, and the (Mg, Fe)O solid solution layer became thinner. The magnesia-chrome refractory bricks showed excellent slag resistance when the Cr₂O₃ content in the copper converter slag was 5 wt%.     

炉渣氧化性对粘渣层与镁碳砖之间结合的影响

以镁碳砖为试样 ,采用不同氧化性的炉渣进行了粘渣实验 ,并且对粘渣层的结合状态进行了显微镜观察。结果发现 ,粘渣层与镁碳砖的结合状态受炉渣氧化性或炉渣熔点、粘度及其与镁碳砖反应活性的影响 :炉渣氧化性低 ,粘渣层与镁碳砖之间结合紧密 ,粘渣层厚 ;炉渣氧化性高 ,粘渣层与镁碳砖之间含有较大的气泡 ,粘渣层薄而不连续 ;采用含碳镁质材料调整炉渣氧化性后 ,粘渣层与镁碳砖之间结合状态得到改善。     

几种钢包用含碳耐火材料对IF钢增碳的比较

通过感应炉试验分析了钢包渣线用3种碳含量不同的镁碳砖(C的质量分数分别为8.3%、15.5%和17.9%),钢包底用蜡石-碳化硅砖(C的质量分数为3.71%)以及实验室开发的MgO-Al2O3-SiC质钢包渣线浇注料(C的质量分数为4.07%)对IF钢增碳的影响,并对其增碳的机理进行了初步分析讨论。试验结果表明:渣线镁碳砖的碳含量越高,对IF钢造成的增碳量越大;包底蜡石-碳化硅砖对IF钢水的增碳量达到渣线镁碳砖的7.73倍;MgO-Al2O3-SiC质浇注料也对IF钢产生明显的增碳效果,不宜用作冶炼超低碳钢的钢包渣线材料。     

Thermodynamic investigation of vanadium oxide in CaO–SiO2–VOx system at 1873 K

Owing to the complexity of the multivalence states of vanadium oxides in slag systems and experimental difficulties, thermodynamic properties of vanadium oxides have not been established yet. In the present study, the mixed-valence states and activities of the vanadium oxides in CaO–SiO₂–VO_x slag were investigated experimentally at 1873 K and oxygen partial pressures of 3.2 × 10^–9 and 3.1 × 10^–7 atm. After the CaO–SiO₂–VO_x slag had equilibrated with a platinum strip, the mixed-valence states of the vanadium oxides in the slag were estimated by performing X-ray photoelectron spectroscopy, and the activities of the vanadium oxides in the slag were calculated using the activity of vanadium in the platinum strip at equilibrium using thermodynamic equations. At an oxygen partial pressure of 3.2 × 10^–9 atm, V³⁺ was the dominant ion and V⁴⁺ was the second most abundant ion. With increasing VO_x content or basicity (CaO/SiO₂ ratio), the fraction of V³⁺ decreased, whereas that of V⁴⁺ increased. The activity of VO_1.5 was greater than those of the other vanadium oxides. On the other hand, when the oxygen partial pressure increased to 3.1 × 10^–7 atm, V⁴⁺ became the dominant ion. As the slag basicity increased, the fraction of V⁴⁺ increased further, whereas that of V³⁺ decreased to less than that of V⁵⁺. The activity of VO_1.5 was greater than those of the other vanadium oxides, limiting the effect of the slag basicity. Consequently, the valence state of vanadium oxide was affected by the slag basicity at a low oxygen partial pressure by acting as a network modifier. In contrast, at a higher oxygen partial pressure, the activity of vanadium oxide increased further but was not affected by the slag basicity because of its contribution to the network structure formation. The present findings can be applied to optimize the slag composition in steel refining or vanadium pentoxide production processes to increase the yield rate of vanadium.     

Properties,Performance and Quality Control of Recycled MgO-C Bricks

Properties, section structure and service results of recycled MgO-C bricks and new MgO-C bricks for ladle slag line of Baosteel were analyzed and compared, and the measures of improving stability and quality of recycled MgO-C bricks were summarized. The results show that: (1) High quality recycled MgO-C materials can be produced by scientific, meticulous and strict management for every process such as dismantling furnace, selection, removing impurity and slag, stacking and homogenization; (2) Using high qua...     

Kinetics of the formation of protective slag layers on MgO–MgAl2O4–C ladle bricks determined in laboratory

Carbon-bonded magnesia and magnesia-alumina bricks are the state of the art lining materials of the sidewalls and the bottom of steel ladles. Industrial trial tests revealed, that a new generation of MgO–MgAl₂O₄–C bricks, where pre-reacted spinel is added in form of a new calcium magnesium aluminate (CMA) raw material, exhibit a longer service life caused by an enhanced corrosion resistance due to the formation of a protective slag layer. In terms of this work, laboratory corrosion tests have been performed in order to mimic the protective slag layer formation and to study the kinetics of the formation. It has been found that the formation highly depends on the amount of iron present in the melt, which leads to the precipitation of the brownmillerite-phase. Furthermore, the study was extended to force the formation of protective slag layers of different composition which are reliable at higher temperatures and wider temperature ranges by targeted adaption of the brick composition. Cup tests showed that there is a potential to manipulate the composition of a protective slag layer by targeted adaption of the brick composition. Especially MgO, Al₂O₃, Fe_xO_y, and SiO₂ from the brick or slag enrich at the slag/refractory-interface.     

高硅铁水转炉提钒对钒渣质量的影响及对策

铁水[Si]对转炉提钒钒渣质量影响较大,铁水[Si]抑制钒渣的氧化,钒渣渣态稀,导致钒渣品位下降、产渣率下降、半钢余钒偏高。通过采用提钒复吹工艺、在提钒终点加入碳质还原剂浓缩钒渣、预脱硅技术、优化提钒冷却剂、供氧时间和氧枪枪位等措施,钒渣品位由原来的15.2%提高到目前的16.2%。     

Post-mortem analysis of alumina-magnesia-carbon refractory bricks used in steelmaking ladles

Post-mortem studies in secondary steelmaking ladles are an important way to determine the factors related to Alumina-Magnesia-Carbon (AMC) refractory corrosion. AMC refractory bricks installed in the impact zone of a steelmaking ladle bottom were analyzed after 100 castings. X-ray diffraction, X-ray fluorescence chemical analysis, reflected optical light microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, density and porosity measurements, and mercury porosimetry were used to analyze the chemical and physical characteristics of the slag, the unused refractory and the slag+steel attacked bricks. The corrosion process produced a specific microstructure characterized by: i) a thick discontinuous slag layer composed by secondary spinel+steel+liquid; ii) a thick dense, cracked, and continuous layer consisting of calcium aluminates+steel+liquid at the slag/refractory interface; iii) next to this layer, a wide densified layer with a uniform microstructure in which corundum aggregates and spinel crystals were linked together by elongated CaAl₁₂O₁₉ crystals.The formation of these reaction layers constituted a barrier that effectively suppressed the massive slag penetration and surely reduced the wear rate. Thermodynamic calculations based on simplified and complex condensed phase equilibrium diagrams, were used to further understanding of the corrosion mechanism.     

加废钢条件下铁水包的异常侵蚀与用材问题探讨

对铁水包的异常侵蚀进行了调研,对铁水包用砖的性能、组成与结构进行分析.结果表明:1)铁水包包壁采用的铝碳化硅碳砖与包底用铝碳化硅碳砖不同,含较多的叶蜡石,Al2O3含量只有36.32％(w);体积密度、显气孔率、耐压强度均低于行业标准的要求;其抗氧化性差,使用过程中氧化形成多孔层,造成砖衬结构疏松,引起断砖、局部磨损及...     

Corrosion of Disposing Urban Domestic Wastes on Refractories for Cement Rotary Kilns

Corrosion of burning urban domestic wastes to alkali-resistant bricks and spalling-resistant high alumina bricks was researched by static crucible method and SEM in order to choose refractories for cement rotary kilns for collaboratively disposing wastes. The result indicates that the main corrosion mechanism is slag permeation and corrosion; the emitted high temperature gases containing alkali,sulfur and chlorine during burning the wastes react with refractories forming low melting point sulfate,chloride and compound salts,which metamorphose the refractories,and the loose metamorphic layer is easy to spall under thermal stress. So,corrosion resistance and spalling resistance shall be taken into account when choosing refractories for cement rotary kilns for collaboratively disposing wastes. It is suggested that decomposition furnaces should adopt spalling resistant high alumina bricks and anti-coating Si C castables,and preheating equipment should adopt high strength alkali-resistant bricks and castables.     

Enhanced performance of ultra-low carbon MgO–C bricks by the addition of special C/MgAl2O4 composite powders

Argon oxygen decarburization (AOD) refining as one type of secondary refining plays an important role in the steel industry. MgO–CaO and MgO–C bricks are widely used in AOD refining, and MgO–CaO bricks are easily hydrated. MgO–C bricks containing carbon easily pollute molten steel and have lower mechanical strength. In this study, ultra-low carbon MgO–C bricks containing C/MgAl₂O₄ composite powders used in AOD refining were explored. MgAlON as the strength phase was in situ generated in the composites (M3) containing 2 wt% C/MgAl₂O₄ composite powders. The samples were further compared with commercial MgO–CaO bricks (M1), which are currently used in the slag line of the AOD furnace, and the sample (M2) without the addition of C/MgAl₂O₄ composite powders. The hot modulus of rupture (HMOR) of M3 was the highest at 27.3 MPa, which increased 44% compared with that of M2 and increased 158% compared with that of M1. The number of thermal shock test cycles of M3 was 1.6 times that of M2. HMOR and cold crush strength (CCS) of samples after thermal shock resistance test were measured. The HMOR of M3 after 3 cycles of the thermal shock test was 2.1 times greater than that of M1. After 20 thermal shock cycles, the residual CCS ratio of M3 was highest, up to 94.6%. Improvement in the thermal shock resistance of the composites can be achieved by the addition of C/MgAl₂O₄ composite powders, which promote the generation of MgAlON. It was also found that the slag corrosion depth of M3 was the lowest at 64.7% of that of M2 and was 13% of that of M1. The internal micromorphologies researched by XRD and SEM and the corrosion mechanism revealed by thermodynamic calculations show that MgAlON was formed in situ after the corrosion test and endowed the composites with excellent properties.     

Effect of in situ formation of Ti(C,N) on the properties of Al2O3–ZrO2–C slide plate material

Al₂O₃–ZrO₂–C slide plate was ordinarily used in sliding nozzle system because of its excellent mechanical properties and slag corrosion resistance. This study improved the slag corrosion resistance of the slide plate by the carbothermic reduction of TiO₂ and aluminothermic reduction of TiO₂ under high temperature in coke bed to generate Ti(C,N) phase in situ. The result revealed that TiC of the high melting point phase could enter into anorthite (CaAl₂Si₂O₈) of the low melting point phase, forming eutectic phase CaAl₂Si₂O₈–TiC, and improve the viscosity of the slag. Furthermore, TiC and CaAl₂Si₂O₈ captured FeO and MnO from the slag, resulting in the increase of the slag viscosity, inhibiting the penetration corrosion of the slag, and improving the slag corrosion resistance of the materials. In general, compared with the material without TiO₂ powder, the slag corrosion resistance of the material introduced 2 wt.% TiO₂ powder was increased by 24%. Meanwhile, the cold crushing strength of fired specimen at room temperature was increased by 35.6%.     

Synthesis of Al2O3-SiC powder from electroceramics waste and its application in low-carbon MgO-C refractories

Composite additives are an efficient means to improve the high-temperature stability and slag resistance of low-carbon MgO-C refractories. In this work, Al₂O₃-SiC powder was firstly synthesized from electroceramics waste by carbon embedded method at 1500°C, 1550°C, and 1600°C for 4 h, and then the as-synthesized Al₂O₃-SiC powder was used as an additive to low-carbon MgO-C refractories. The effects of its addition amounts of 0, 2.5 wt.%, 5.0 wt.%, and 7.5 wt.% on the properties of the refractories were investigated in detail. It was found that increasing the heat treatment temperature is beneficial to the phase conversion of mullite and quartz to alumina and silicon carbide in the electroceramics waste. Furthermore, the addition of Al₂O₃-SiC powder effectively improves the performance of low-carbon MgO-C samples, and the formation of spinel dense layer and high-viscosity isolation layer is the internal reason for the improvement of the oxidation resistance and slag resistance of low-carbon MgO-C samples. This work provides ideas for the reuse of electroceramics waste and presents an alternative strategy for the performance optimization of low-carbon MgO-C refractories.     

Improvement of low carbon MgO-C refractories by MA-CA2 additives fabricated from metallurgical waste

In the present work, MA-CA₂ material was fabricated by adding industrial alumina into industrial waste residue, and its effect on the physical properties, oxidation resistance, slag resistance, and thermal shock resistance when it was added to the composition of a low carbon MgO-C refractory was discussed in detail. Although the introduction of MA-CA₂ material led to a slight inferior slag corrosion resistance, the volume stability and oxidation resistance of refractories were improved. Moreover, the samples containing MA-CA₂ addition showed significantly lower thermal expansion coefficients and increased thermal shock resistance performance. However, owing to the dissolution of SiO₂ impurity into the MA-CA₂ material, an excessive addition of MA-CA₂ material would increase the liquid phase amount in the sample during the heat treatment and slag attack, resulting in a performance degradation. In this study, the best comprehensive performance of the MgO-C refractory was obtained with 6 wt% MA-CA₂ addition.