Steel ladle well block post mortem analysis

Spinel-containing castables are widely used as steel ladle refractory lining, due to their outstanding basic slag (calcium aluminate based) corrosion resistance. In order to understand their corrosion mechanism, a post mortem evaluation of a steel ladle well-block castable was carried out. The interaction among the refractory castable, slag and molten steel was mainly evaluated by light optical and scanning electron microscopy using SEM multielement mapping. The results indicated that an equilibrium state was attained, leading to the formation of a densified barrier that protected the original castable from corrosion located at the deepest regions, regarding the metal flow. Each one of these layers was evaluated, underscoring the damage that the refractory is liable to during application and also the possibilities of steel contamination, due to castable wear, and reoxidation. The experimental results were compatible with the literature, pointing out how corrosion takes place and the possibilities to reduce its negative effect.     

The impact of pre-formed and in situ spinel formation on the physical properties of cement-bonded high alumina refractory castables

Alumina–magnesia and alumina–spinel castables present some unique characteristics. Whereas the in situ spinel (MgAl₂O₄) formation provides an enhanced corrosion and thermal-shock resistance to the castable, the composition with pre-formed grains shows higher volumetric stability and do not have the inherent MgO hydration problems. As these distinct ways of spinel incorporation result in particular properties to the refractory material, a castable containing both in situ and pre-formed spinel might present balanced properties and a suitable performance in steel ladle applications. Considering these aspects, cement-bonded high alumina castables containing both pre-formed and in situ spinel were developed and evaluated by means of assisted sintering tests, microstructural analyses, thermodynamics simulation and mechanical and thermal-mechanical properties evaluation. The CA₆ formation presented different features according to the content of in situ spinel generation in the matrix, which affected the castable properties. Additionally, compositions containing both in situ and pre-formed spinel seemed to be a feasible way of attaining a designed linear dimensional change without affecting the spinel and CA₆ contents.     

Insulating Permanent Lining of Calcium Hexaluminate Based Castable for 300t Ladle in Baosteel

Minimizing of heat loss of liquid steel through the ladle lining led to the integration of increasing insulation function of the permanent lining and high-quality insulating layer between the permanent lining and the ladle steel shell.In this paper,a study was made on physical and thermomechanical properties and corrosion resistance of calcium hexaluminate based castables.The chemical and physical properties of CA6 based castables fabricated in this work can fulfill general requirements of the permanent lining in ladle.The permanent linings of CA6 based castables offer superb thermal insulation and corrosion resistance,compared to conventional refractory systems of 300t ladle in Baosteel.Both functions of insulation and safety work effectively in whole process of ladle operation.     

The development of a thermodynamic model for Al2O3–MgO refractory castable corrosion by secondary metallurgy steel ladle slags

Alumina magnesia in situ spinel castables are used as ladle refractory lining in the steel industry. In contact with slag, they suffer degradations which limits their performance. The purpose of this article is to predict the thermochemical attack of a slag on alumina magnesia refractory using Factsage^® thermodynamic modeling. To evaluate the reliability of the thermodynamic results, a validation step was carried out, which supported that the database was well adapted to the alumina magnesia spinel system. The corrosion phenomenon was then computed for a simple to a complete system to understand the mechanism and the influence of specific oxides. The model was also compared to corroded microstructures from a steel ladle to evaluate the contribution of each constituent in the castable. The aggregates of alumina react with slag to produce monomineral layers of lime aluminates (CA6 and CA2), while complex spinels (Mg, Fe, Mn)O (Fe₂, Al₂)O₃ are formed from the reaction of the slag with the matrix of the castable. Several oxides (MnO, FeO, Fe₂O₃) from the slag contribute to the formation of the spinel structures. The microstructures of refractories used in steel ladles confirm the main conclusions and the thermodynamic approach.     

Effect of Microsilica Addition on Properties of CMA72 Bonded Al_2O_3-MgO Castables

CMA72 bonded Al_2O_3-MgO castable is promising for application of steel ladle wall,because of unique combination of thermo-mechanical properties,slag corrosion resistance and cost benefit. In these castables,microsilica can be introduced to counterbalance the expansion generated by spinel formation. In this paper,the effect of microsilica dosage on properties of castables was evaluated. Expansion,expressed by the permanent linear change( PLC),is highly dependent on the dosage of microsilica. Unexpected expansion occurs when the dosage of microsilica is too low due to dominant effect of spinel and CA_6 formation. Too high dosage results in sintering shrinkage,which is related to amount of liquid phase generated by microsilica addition. In addition,HMOR declines dramatically with increasing microsilica dosage. Considering the balance between expansion control and hot property retention,1. 0 mass% of microsilica is recommended for the castable containing 4 mass%of magnesia.     

Spinel-containing alumina-based refractory castables

Due to their high corrosion resistance to basic slags, either pre-formed or in situ spinel (MgAl₂O₄) containing refractory castables are nowadays widely used as steel ladle linings. Nevertheless, whereas the pre-formed spinel castables present high volumetric stability and a well-known processing technology, the in situ spinel castables still require further understanding due to the challenges related to magnesia hydration and their expansive behaviour at high temperatures. Therefore, the objective of this paper is to review the knowledge already available for high-alumina spinel-containing castables (preformed and in situ) in order to provide a support for novel technological developments in the area. The main variables considered are the spinel content and grain size, the effect of calcium aluminate cement and hydratable alumina on the general castables’ properties, the influence of different alumina and magnesia sources and the silica fume content. Nowadays research subjects, including the use of mineralising compounds, the addition of nano-scaled particles and the evaluation of the effect of expansion under constraint will also be addressed, pointing out alternatives for the design of high-performance alumina-magnesia refractory castables.     

The impact of bonite aggregate on the properties of lightweight cement-bonded bonite–alumina–spinel refractory castables

The lightweight bonite–alumina–spinel (CA₆–Al₂O₃–MA) refractory castables with bonite aggregate and different spinel sources (pre-formed and in situ formation) were prepared in this study. The phase composition, microstructural features, and mechanical and thermo-mechanical properties of CA₆–Al₂O₃–MA castables treated at various temperatures were investigated by techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), three-point bending method, and thermal shock test. The results indicated that the incorporation of bonite aggregate had a positive influence on the strength, thermal shock resistance and slag corrosion resistance. It especially decreased the thermal conductivity and had a slightly negative influence on the refractory under load and slag penetration resistance of the castables. For the in situ spinel-containing castable, the formation of in situ spinel with finer particle sizes and acicular CA₆ grains led to higher overall volume expansion, resulting in higher thermal expansion (∆L/L₀), linear change and the apparent porosity of castables. Also, the heat insulation, thermal shock and slag penetration resistance of castables with in situ spinel improved, while the strength, displacement, refractory under load and slag corrosion resistance decreased sharply.     

多孔球形莫来石基浇注料的制备及性能研究

为制备保温性能及机械性能均较优异的高温窑炉用隔热耐火材料,以多孔球形莫来石、矾土细粉、α-Al₂O₃微粉、硅微粉和Secar71水泥为主要原料,制备了多孔球形莫来石基浇注料,研究了矾土细粉掺量对多孔球形莫来石基浇注料机械性能、导热系数、抗侵蚀性能及热震稳定性的影响。结果表明,改变矾土细粉的掺量,可使多孔球形莫来石基浇注料在保持较高机械性能的基础上提高保温性、热震稳定性和抗侵蚀性能。随着矾土细粉掺量的增加,多孔球形莫来石基浇注料的机械性能变化不大,但导热系数小幅降低,抗侵蚀性能出现较大差异,热震稳定性先提高后降低。当矾土细粉掺量为28%(质量分数)时,多孔球形莫来石基浇注料的机械性能、热震稳定性及抗侵蚀性能良好,在1 000 ℃时导热系数为0.905 W·m^-1·K^-1。多孔球形莫来石基浇注料的导热系数低于中间包和钢包永久层用高铝浇注料,可替代中间包、钢包永久层用高铝浇注料以减少热损失。     

"In-situ Recycling" :Monolithic Ladle Repair with Shotcreting

The service life of refractories in ladle walls is limited by corrosion,abrasion,thermal shock and structural spalling mechanisms. When the ladle is lined with bricks they typically need to be completely removed after a certain number of heats to be replaced by new bricks of the same size as the original bricks. Not so for monolithic ladle linings. At the end of their service life the remains of the castable can almost completely be recycled as they can in fact stay in place. Only the worn-out part of the lining has to be replaced by a new castable. 20%-50% of the initial ladle lining can be recycled "insitu". The installation can efficiently be done by shotcreting technics. But it requires a castable that resists slag penetration very well. Castables based on a calcium magnesium aluminate bond provide the required penetration resistance. Pumping and shotcreting is very well adapted for repairs of blast furnace shafts,torpedo cars,hot metal and steel ladle linings[1]. However,very little is published about how a good pumping and shotcreting performance can be achieved when the installation has to be done under extreme weather conditions. At high ambient temperature the challenge is to ensure a good pumping result without early castable stiffening. Blockage of the pump would be the consequence. At low ambient temperature the difficulty is to de-activate the highly efficient deflocculant fast enough with a gelling agent added intothe wet mix at the nozzle to prevent the gunned material slipping off the wall. This paper studies strategies how to achieve good installed properties even at extreme ambient temperatures. The interactions between deflocculants,retarders,gelling agents,and calcium magnesium aluminate binder as a function of temperature are studied for an alumina- spinel ladle castable. Beside a new gelling agent for this castable type also a special stabilizer to reduce the temperature sensitivity has been investigated. It will be highlighted how the use of the new calcium magnesium aluminate binder in ladle castables and shotcretes maximises their service life and minimises material consumption.     

Basic slag attack of spinel-containing refractory castables

The better performance of spinel-containing refractory castables when in contact with basic slag is mainly associated with their higher corrosion resistance. Although the literature has shown various studies related to this subject, only few of them evaluated the overall microstructural effect on the corrosion resistance. Considering this aspect, four different compositions were produced, in order to evaluate the binder source influence (calcium aluminate cement or hydratable alumina), the silica fume addition and spinel incorporation method (in situ or pre-formed) effects. Based on the physical properties (apparent porosity, linear thermal expansion and pore size diameter distribution) and also on the phases generated (detected by SEM, before and after corrosion), a basic slag corrosion mechanism, for the set conditions, is proposed. The results pointed out that lower penetration can be attained by reducing the pore size diameters, whereas chemical corrosion resistance is a consequence of higher content of fine alumina, lower amount of calcium aluminates and the lack of liquid phase in the castable matrix. This study stresses that the castable formulation design and the proper raw material selection are of utmost importance to understand and master the performance of this class of refractory castables.     

Use of alumina dispersant in alumina-spinel castable: Comparison between in situ and preformed spinels

The role of alumina dispersant as a flow modifier, completely replacing fume silica, on the properties of preformed and in situ spinel-containing low cement high alumina castables was investigated with variations in spinel content and granulometry. Both 10 and 20 wt.% spinel-containing compositions were prepared using preformed spinel or magnesia in alumina castable compositions with vibratable and self-flowing consistency. The castables underwent conventional processing methods and accessed for various refractory-related parameters post-heat treatments. No glassy phase was observed in the castables upon firing. The presence of self-flowing consistency led to improved characteristics. Preformed spinel-containing compositions showed improved density, strength, hot strength, and thermal shock resistance properties, whereas slag corrosion and penetration resistances were found to be higher for in situ spinel-containing castable.     

Effect of spinel content on slag attack resistance of high alumina refractory castables

High alumina refractory castables based on the Al₂O₃-MgO-CaO diagram ternary system were prepared using tabular alumina, white electrofused corundum, calcined alumina, synthetic spinel, dead-burned magnesia, dolomite, and calcium aluminate cement as starting raw materials. Two kinds of slags with 9.02 and 4.14 CaO/SiO₂ ratios were studied for slag resistance by means of crucible tests. The corrosion thickness increases with increase in magnesia content in all the designed compositions. The slag penetration decreases with increases in spinel content. Taking into account these results a refractory castable composition for its positioning into a steelmaking ladle was chosen.

Microstructural studies by SEM of samples taken from the slag line and wall in a steelmaking ladle were carried out. The correct amount of spinel required for practical applications was determined by the Al₂O₃-MgO-CaO-SiO₂ diagram quaternary system. A detailed model of the attack mechanisms is proposed.     

Spinel Castables for Steel Ladle Lining:In-Situ Versus Preformed

The paper discusses the difference in the formulation concepts of alumina-spinel (spinel containing) and alumina-magnesia (spinel forming) castables and the influence on their physical properties. The individual property profile is discussed with respect to the requirements of refractory lining materials for the different zones of a steel ladle.     

The corrosion resistance of microsilica-containing Al2O3–MgO and Al2O3–spinel castables

Microsilica addition in Al₂O₃–MgO and Al₂O₃–spinel castables helps to improve their flowability and partially accommodate their residual expansion after firing. Nevertheless, there is a lack of conclusive statements in the literature regarding the effects of microsilica on one of the main requisites for steel ladle refractories: corrosion resistance. In the present work, the performance of alumina–magnesia and alumina–spinel with or without microsilica when in contact with a steel ladle slag was evaluated based on three aspects: the material's physical properties, its chemical composition and the microstructural features before the slag attack. According to the attained results, microsilica induced liquid formation and pore growth during sintering, favoring the physical slag infiltration. Moreover, due to this liquid, CA₆ was formed in the matrix, mainly for the Al₂O₃–spinel composition, which also favored the castable dissolution into the molten slag.     

How effective is the addition of nanoscaled particles to alumina–magnesia refractory castables?

The addition of nanoscaled alumina and magnesia particles to the matrix of alumina–magnesia refractory castables drastically reduces the residual expansion related to the in situ spinel formation. Nonetheless, as their benefits on other relevant properties have not been reported so far, the effectiveness of such nanoengineering design for castables applied in steel ladles is still uncertain. In the present work, not only the expansion level, but also the corrosion resistance, the hot modulus of rupture and the creep deformation of different nanoparticle-containing castables were evaluated and compared with the results attained by refractory materials designed only by micrometric-scaled Al₂O₃ and MgO. Although the addition of a nanoalumina and nanomagnesia mixture ensured the best results regarding to the expansive behavior, thermo-mechanical and thermo-chemical properties, its performance was only slightly superior to the castable containing micrometric alumina and magnesia particles. Therefore, as the cost–benefit ratio is one of the main requirements for the end users, the nanotechnology use in the refractory production must be previously carefully analyzed.     

Preparation and Application of Bauxite-based Sintered Mullite Homogenized Grog in Ladle Castable

Preparation of bauxite-based sintered mullite homogenized grog was introduced and its application in ladle castable was studied.Two kinds of bauxite-based sintered mullite homogenized grogs were used,named as GA and GB,respectively.The results show that bauxitebased sintered homogenized grog with uniform components,stable microstructure and mullite as main crystal phase can be prepared using joint process of three-step homogenization,automatic component batching,wet cogrinding,high-temperature calcinations.It also indicates that carbon steel ladle castables with GA or composite aggregate of GA and GB as main materials have the same excellent general performance indicators,great erosion resistance,anti-strip performance and longer service life in field applications,and compared with castables with single aggregate of GA,the castables with aggregate of GA and GB as main materials had higher cost performance because of lower bulk density of GB.     

Improvement of Mullite and Magnesia‐Based Refractory Castables Through Addition of Nano‐Spinel Powder

Two different commercial refractory castables based on mullite or magnesia aggregates have been improved through addition of 0–25 wt.% nano‐magnesium aluminate spinel (MA) powder. Physico‐mechanical and refractory properties were tested at different firing temperatures. The phase composition, thermal analysis, and microstructure of these refractory castables were detected using X‐ray diffraction (XRD), differential thermal analysis (DTA), as well as scanning electron microscope (SEM) attached with energy dispersive X‐ray unit, respectively. The castable sample mix containing 10 wt.% nano‐MA spinel powder was chosen as an optimum composition according to its good sintering, mechanical as well as refractory properties.     

In situ spinel bonded refractory castable in relation to co-precipitation and sol–gel derived spinel forming agents

This paper deals with the preparation and characterization of two types of in situ spinel bonded low cement high alumina based castable refractories. Semidried magnesium aluminate mass was prepared from cheaper precursors via coprecipitation and sol–gel routes for application in a refractory castable composition in different concentrations. The pH, average particle size, solid content, DTG analysis and XRD patterns of those two additives were observed. After being fired at elevated temperatures those two kinds of in situ spinel bonded castables were characterized and compared in terms of bulk density, apparent porosity, cold crushing strength, flexural strength, volume shrinkage, spalling resistance, and XRD phase analysis. Scanning electron microscopy of some selected fired samples was done to analyse the mode of interaction of in situ spinel bonds in castable microstructure. The corrosion resistance of the castables was estimated by heating with blast furnace and converter slags.     

钢包铝镁尖晶石浇注料的改进试验及应用

针对高铝矾土原料质量下降导致钢包铝镁浇注料使用寿命下降情况,对配方进行调整实验,结果表明：（1）适当增加了镁点,解决产品的高温收缩。（2）引入刚玉原料优化浇注料的基质组成,既降低了施工加水量,又减少了收缩,提高产品的耐高温性,使铝镁尖晶石浇注料具有优良的抗渣性和抗剥落性能。