Analysis on Abnormity Erosion of Monolithic Stopper Slag Line

Monolithic stoppers play a very important role in continuous casting( short for CC). Sometimes,the stopper slag line is seriously eroded and broken,CC has to pause. The research shows that there are three main reasons which bring severe erosion of monolithic stopper slag line. Firstly,much Fe_2O_3 and MnO in slag react with carbon( C) in the stopper,C is gradually eroded and erosion resistance of the stopper greatly weakens. Secondly,F increase in tundish covering flux will quicken erosion of the stopper slag line. Thirdly, High LOI of tundish covering flux also makes erosion of the stopper slag line speed up. On one hand,CaCO_3 in tundish covering flux decomposes and brings CO_2; on the other hand,minerals with water in tundish covering flux decompose at high temperatures and bring water vapor.Then CO_2 and water vapor react with C in the stopper,C is gradually eroded,aggravating the erosion.     

Steelcasting and intermediate ladles for equipment for the continuous casting of steel

Conclusions The life of linings in large ladles depends on the grade of steel, the amount, chemical composition and consistency of the slag.The intermediate ladle made in the factory ensures reliable operation during the casting of metal by the continuous steel casting operation.Heating the intermediate ladle to 1100–1200°C by means of compact burners, working on coke gas, and new designs for cooled stoppers and stopper devices greatly reduces slab loss.In the process of evaluating the casting of transformer steel the loss due to nonmetallic inclusions was greatly reduced, but not completely eliminated.Further work must be done to explain the causes of the formation of slag inclusions and methods of handling the problem.     

Life of stopper heads in continuous steel casting

Conclusions Chamotte heads with 5, 10 and 15% graphite differ from conventional chamotte by high thermal endurance, thermal conductivity and wear resistance. The increased rigidity of stopper heads with a graphite content of 5 to 15% used in combination with magnesite sleeves enhances the formation of longitudinal cracks.Chamotte specimens fired at 1230° C are endowed with high wear-resistance. They differ from conventional chamotte refractories by higher thermal endurance and provide for good stopper service in reladling killed steel.High-alumina SP-9-type heads made at Chasov-Yar Combine wear less in intermediate ladles and are endowed with greater thermal strength than chamotte heads.The higher quality of the chamotte heads under conditions of Stalino Metallurgical Plant in comparison to that of Krasnoye Sormovo Plant is not only due to the quality of the refractory but also to such factors as the rate and degree of preheating intermediate ladles before filling with metal, careful placement of the stoppers, and use of graphite packing around the teeming head.Despite higher wear SP-12-type chamotte heads made at Chasov-Yar Combine allowed normal teeming of rimmed steel in 50 ton ladles.To ensure a steady service of the stoppers in continuous steel casting the preheating of intermediate ladles of 1300 and the use of precooled stoppers are recommended.     

Effect of argon blow through a monoblock stopper in continuous casting of steel on the service of the stopper and nonmetallic inclusions in the cast steel

Kinetic equations of the dependence of the wear of corundum-graphite monoblock stoppers in the slag line and the head on the temperature of the steel in the intermediate ladle in continuous casting are derived as a result of a full-scale experiment. The equations make it possible to calculate the casting time at any possible temperature of casting with the use of corundum-graphite monoblock stoppers of a standard composition (TU 14-8-371-81). In addition to increasing substantially the number of casting cycles in a batch, argon blow through monoblock stoppers with porous inserts improves the quality parameters of cast steel ShKh-15 with respect to segregation bands, globules, central porosity, carbide segregation, content of sulfides and oxides, and subshrinkage segregation.     

Increasing the resistance of stoppers in large steel-casting ladles

Conclusions The use in large ladles of stoppers with diameters of 205 mm, with a porosity of 17–20%, and stopper tubes with a porosity of 20–24% ensures normal operation of the stopper during the whole of the casting cycle.The dimensions of the socket brick GK-8 for the bigger stopper do not have to be altered.According to the experience of ChMZ and NTMK (Nizhne-Tagil'sk Metallurgical Combine) the temperature of initial deformation of stoppers without injury to their resistance can be reduced to 1320°C.The desirability of determining this property for stoppers should be established by the refractory institutes.Existing GOST 5500-50 was not fixed for the widely introduced semidry pressing of stopper equipment and changes in the technology of steel-casting.It is necessary to accelerate the incorporation of resolutions made at the All-Union Conference of Refractory workers in 1960 on re-examination of GOST 5500-50.     

Service of refractories in the continuous casting of 100 ton converter heats

Conclusions Refractories for steel-casting ladles used at present in the converter shop of the Novolipetsk Factory can be used for casting 100-ton heats. However, it is necessary to increase the resistance of the ladle linings.Ladle bricks, stopper tubes, and zircon nozzles provide reliable casting of 3–4 heats in series without replacing the intermediate ladle.To provide reliable covering of the jets where necessary it is recommended that use be made of highalumina plugs for intermediate ladle stoppers.Translated from Ogneupory, No. 7, pp. 37–41, July, 1968.     

Wear of magnesia spinel refractories in portion vacuum-processing steel plant

Conclusions The processes of wear in the lining of vacuum chambers of outdoor-furnace vacuum-treatment plants (UPVS) are due to the simultaneous action of high temperatures, deep vacuum, gaseous medium, molten metal, and slag. The corrosion and erosion of aggressive melts of slag and metal are the decisive forms of wear.Laboratory investigations established the relationship between slag resistance in vacuum and the ratio of corrosive and erosive constituents in the wear of different magnesia-spinel refractories and their phase composition, structure, and properties.Refractories obtained from fused periclase-chromite material with a low content of fusible silicates showed that in laboratory vacuum equipment and during service in the linings of the vaccum chamber of industrial plant they have higher slag resistance and lower wear than refractories based on sintered magnesite, spinel, and chromite ores.Translated from Ogneupory, No. 3, pp. 14–21, March, 1980.     

Al2O3-C质整体塞棒在浇铸钙处理钢中的应用

分析了Al2O3-C质整体塞棒在钙处理钢浇铸过程中的侵蚀机制和其他一些重要影响因素,针对Al2O3-C质整体塞棒的特性,从炼钢的工艺改进、设备保障、优化过程控制和耐火材料材质优化等方面采取了相应措施,并提出了改进意见,使Al2O3-C质整体塞棒在钙处理钢的使用寿命不断提升,达到了比较满意的效果。     

The service of refractories in stream treatment of metal with continuous casting of the steel

Conclusions The service of monoblock stoppers, controlling nozzles, and submerged nozzles with stream blowing of the metal with gas was studied. The desirability of use of a monoblock stopper with a hole in the lower portion and a thread in the upper for treatment of the metal with gas in the intermediate ladle was concluded.The service of straight-through submerged nozzles under conditions of blowing was studied and means of increasing their life were noted.Translated from Ogneupory, No. 2, pp. 47–50, February, 1984.     

连铸用复合式整体塞棒

整体塞棒的棒体部位以特级高铝熟料、电熔刚玉和鳞片状石墨为主原料；塞头部位以电熔刚玉、特级高铝熟料和鳞片状石墨、碳化硅为主原料。选用液体树脂为结合剂并加入适量的添加剂。该制品在８ｔ连铸中间包使用，可连浇８炉。     

Service of zircon nozzles for continuous casting of converter steel

Conclusions In the continuous casting of converter steel without replacing the intermediate ladle between heats there is an increase in the resistance of the zircon nozzles. Wear somewhat increases with an increase in the number of heats from one to two, after which there is practically no change up to four heats.It became clear that an increase in the density of the zircon nozzles reduces their erosion.The nature of the erosion of zircon nozzles during continuous casting of converter steel does not alter, compared with the previously known character.With the use of zircon nozzles in the Red Army Silica Factory for rates 0.7 m/min, it is possible to cast without braking the jet of steel with the stopper.S. Z. Afonin, E. I. Ermolaeva, V. V. Parfenteva, V. D. Ryazantsev, and T. K. Chirkina took part in the work.Translated from Ogneupory, No. 1, pp. 20–23, January, 1968.     

Testing ladle brick made by various factories

Conclusions The resistance of linings in steel-casting ladles depends on the working conditions and the construction of the lining, the quality of the brick laying during repairs of the working layer, and the resistance of the ladle brick. The greatest effect on the wear of the lining in ladles is exerted by the following working conditions: chemical composition of the slag, temperature of the metal being cast, the dwell time of metal and slag in the ladle during one casting, the height of the slag layer in the ladle, the thickness of the lining in each belt of the structure. The quality of the structure in the ladles is mainly determined by the size of the joints, the care with which they are filled with mortar, uniformity of drying and warming-up of the ladles before filling them with metal.The resistance of the ladle brick depends mainly on the apparent porosity and nature of the pores and the concentration of fluxes and mullite in the brick.The highest resistance in service was shown by Zaporozh'e ladle brick made from Polozhe kaolin and having the lowest apparent porosity. The concentration of iron oxides in the brick was moderate, and on average equalled 1.39%.In terms of falling resistance the ladle brick of the remaining concerns can be placed in the following order: Chasov-Yar, Semiluks, Bogdanovich, Magnitogorsk, and Borovich.In order to increase the resistance of steel casting ladle linings it is necessary to increase the resistance of the ladle brick by reducing the apparent porosity, using raw materials with low concentrations of fluxes and improving the firing in order to obtain the maximum conditions of the ladle, reducing to a minimum the quantity of slag and reducing the casting time; to use a more rational thickness for laying the ladles over the courses, taking into account better use of their capacity.Translated from Ogneupory, No.5, pp. 27–32, May, 1970.     

Nozzles for equipment for semicontinuous casting of stainless steels under synthetic slag

Summary The most aggressive influence is exerted by synthetic slag on aluminosilicate refractories, and the least — on zirconia and graphite-containing refractories.During the casting of steel under synthetic slag, high-alumina, zircon, and zirconia nozzles were cracked in the first minutes of operation and did not insulate the jet of metal from slag.Alumina-graphite, alumina-silicon carbide and alumina-graphite nozzles during the casting of steel did not crack, were only slightly eroded with slag and metal and provided normal working of the continuous casting plant.Alumina-graphite or alumina-graphite elongated nozzles are recommended for a unit used for the semicontinuous casting of titanium-containing steels involving synthetic slag.     

Destructive mechanism for periclase-spinel and magnesite-chromite refractories in oxygen converter linings

Conclusions The greatest wear of magnesite-chrome and periclase-spinel linings was observed in the cylindrical part of the converter in the places showing intense movement of metal and slag and maximum heat load. In these sections of the structure we get a predominant erosion by fusion, but the share of the erosion due to scaling is substantial.In the throat, wear of the lining occurs mainly due to scaling as a result of frequent changes in temperature and air.The wear of the lining of the bottom is slight compared with sections located above and takes place mainly as a result of erosion developed during intensive movement of the metal in the blow period.PS refractories are more resistant in the linings of the converter than MC refractories, which is explained by the difference in the mechanism of their wear.To increase the resistance of refractories PS against the action of converter slags it is necessary to make them from enriched chromitic ores and magnesite with the use of high-temperature firing, which will ensure better development of the direct bond of the grains of periclase with the chrome-spinel and more complete mineral formation (with maximum yield of secondary spinel).Translated from Ogneupory, No. 1, pp.32–38, January, 1967.     

ZrO2-C质耐火材料抗侵蚀性的研究现状

由于ZrO2-C质耐火材料具有优异的抗侵蚀性,因此它被广泛应用于连铸用浸入式水口渣线部位以及塞棒的棒头部位。本文介绍了ZrO2-C质耐火材料的主要原料,阐述了ZrO2-C质耐火材料的蚀损机理以及改进抗侵蚀性的措施。     

Solid particle erosion on coatings employed to protect die casting molds

In this study, the performance of coatings that were subjected to solid particle erosion tests was evaluated. These coatings can be used to protect die casting molds. The main interest of this research project was to find possible alternatives to increase the wear resistance of these mechanical components. Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity, which is machined into two hardened tool steel or coated dies. Most die castings are made from non-ferrous metals, such as aluminium, copper, magnesium, lead, zinc, tin based alloys but also they can be protected by specific coatings that have high wear resistance. The erosive wear damage in die casting molds is caused due to the molten metal is blown into the mold by high pressure dry air. Filling the mold cavities during the blown step, molten metal and sand particles impact the internal surface producing erosive wear damage. Coatings such as chromium nitride (CrN) and titanium aluminium nitride (TiAlN) that exhibit low wear damage in these types of applications due to high abrasion and erosion resistance were tested. In addition, uncoated 4140 steel and 6061 aluminium were also tested. An erosion test rig similar to that shown in ASTM G76-95 standard was designed and built to perform the tests. The abrasive particle used was angular silicon carbide (SiC) with a particle size of 420–450 μm. Tests were carried out using different impact angles (30°, 45°, 60° and 90°) with a particle velocity of 24 ± 2 m/s and an abrasive flow rate of 0.7 ± 0.5 g/min. The particle velocity and the abrasive flow rate were low in all of the tests to reduce the interaction between the incident particles and the rebounding particles in the system. The surfaces were examined with a scanning electron microscope (SEM) to characterize the erosive damage. The wear mechanisms identified were pitting and ploughing action at low impact angles (α ≤ 45°) due to sliding component commonly observed at these incident angles whereas bigger craters, radial cracks and a more roughened surfaces were seen at angles near or at 90°.In addition, it was observed that the damaged area was extended in all of the cases at 30° and 45° reducing considerably at 60° and 90°. The wear scars were characterized by an elliptical shape at 30° and 45°, which is a characteristic feature when the specimens are impacted at low-incident angles (α ≤ 45°) whereas a roughly circular was seen at 60° and 90°.     

旋风炉SiC质炉衬损毁机理研究

热电厂旋风炉ＳｉＣ炉衬，由于受液态渣的侵蚀，在短期内损毁。本文研究了液态渣的物相、渣村的相互关系，认为ＳｉＣ炉衬的侵蚀机理：一方面由于增钙，液态渣变稀，渣中多钙、铝而少硅，对炉衬的渗透力强，能夺取ＳｉＣ中的硅，造成化学侵蚀；另一方面是由于旋风燃烧的作用，液态渣对炉衬的机械侵蚀。该研究结果为研制新炉衬提供了依据。     

Comparison of Values of Independent Random Variables in a Bayesian Setting

Abstract

An optimal stopping problem for independent observations in a Bayesian setting is considered. One optimal stopper knows only the prior distributions of the independent X _i 's, while the other stopper knows the conditional distributions of the X _i 's. We show that the extremal relationship of the returns to the two different optimal stoppers is the same as the relationship between an optimal stopper and a “prophet” in a usual corresponding optimal stopping setting.     

Damage Mechanism and Countermeasures of Carbon Bonded Refractories for Continuous Casting

The long nozzle,stopper,and submerged entry nozzle play an important role in continuous casting. They are of the similar composition and are mainly damaged by liquid steel thermal shock which leads to immediate cracks or fracture in their combined area because of the thermal mechanical properties mismatch,or damaged by corrosion on their interface. The failure mechanisms are the thermal shock damage and continuous reaction corrosion. High efficiency and long life of the long nozzle,stopper,and submerged entry nozzle can be realized by optimizing the thermal mechanical properties,the key erosion step,and the combination match.     

Effect of some properties on the life of steel discharge blocks in converters

Conclusions Investigations in service and with the regression-correlation analytical method showed that the resistance of experimental blocks, in steel discharge apertures of converters within the limits investigated, is determined mainly by structural characteristics including strength, resistance to abrasion and erosion, pore sizes, and gas permeability.The least wear (0.19 mm per heat) was exhibited by magnesite-chromite refractories made from sinter-active and fine-grained bodies.The wear of the steel discharge blocks is determined mainly by mechanical (abrasion and erosive) action of currents of liquid slag and metal.Translated from Ogneupory, No. 2, pp. 38–44, February, 1973.