EP0015417B1 - Particulate slagging agent and process for the continuous casting of steel - Google Patents

Particulate slagging agent and process for the continuous casting of steel Download PDF

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Publication number
EP0015417B1
EP0015417B1 EP19800100749 EP80100749A EP0015417B1 EP 0015417 B1 EP0015417 B1 EP 0015417B1 EP 19800100749 EP19800100749 EP 19800100749 EP 80100749 A EP80100749 A EP 80100749A EP 0015417 B1 EP0015417 B1 EP 0015417B1
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EP
European Patent Office
Prior art keywords
slagging agent
ratio
value
finely
steel
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EP19800100749
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German (de)
French (fr)
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EP0015417A1 (en
Inventor
Joseph F. Uher
Jr. Charles M. Loane
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Bayer Corp
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Mobay Corp
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Priority claimed from US06/026,925 external-priority patent/US4235632A/en
Application filed by Mobay Corp filed Critical Mobay Corp
Priority to AT80100749T priority Critical patent/ATE3007T1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B22D11/111—Treating the molten metal by using protecting powders

Definitions

  • slagging agents also known as “mold powder”, “slag” or “flux”, have been proposed for the continuous casting of steel, a fairly new development in steelworks practice. These materials protect the molten metal from air oxidation, while they usually render and thereby remove certain contaminating oxides that are present in the molten steel. In addition, the lubrication of the mold can often be improved by using these materials. Generally, the material is sprinkled or poured onto the surface of the molten metal. Occasionally, this surface is also called the meniscus.
  • flux In engineering, the terms “flux”, “melting agent”, “slag” or “mold powder or powder” are used interchangeably for fried or predominantly fried materials to be used in continuous casting.
  • fine-particle slagging agent is used as a collective term for all types of materials used to protect and lubricate steel during continuous casting.
  • glazed is a completely glazed (fritted) material or mixture of fritted materials.
  • a “flux” is a vitrified material to which non-vitrified material has been added in less than about 30% of the total flux. A distinction must be made between both fluxes and glazed materials.
  • the particulate interlacing agents according to the invention are made without carbon by pulverizing the components and / or vitrified components and then mixing them if necessary.
  • some of the fluorine-providing material is mixed without frits with the rest of the fritters which are fritted. This is done to largely eliminate the furnace attack during the formation of the fritted part of the fine-particle slagging agent.
  • the steels that are cast on a large scale by continuous casting today include various steels quenched with aluminum, steels quenched with silicon and austenitic stainless steels.
  • the problems encountered in formulating a finely divided slagging agent for use in the continuous casting of steel have already been addressed in the specialist literature. Spe;: iell US Pat. Nos. 3,649,249, 3,704,744 and 3,899,324 describe some of the attempts made by other companies to maximize the properties and efficiency of the fine particulate slagging agents used.
  • the efficiency of the molten fine-particle slagging agent becomes so poor that the steel production of the pouring stand has to be throttled because the molten mass cannot dissipate the heat from the solidified strand shell or boundary layer that is formed quickly enough to make the strand shell sufficient to thicken.
  • the surface of the cast steel shows more and more inclusions because the molten slagging agent cannot absorb the contaminants, primarily aluminum oxide, from the molten steel quickly enough.
  • the exact optimal duration of the casting period is different for each individual continuous casting plant and for each steel type to be cast. The degree of protection that the molten steel receives from the air on its way to and through the caster affects the amount of alumina formed and later developed during casting.
  • the optimal length of a casting cycle can be as short as 45 minutes. This duration is even shorter than the time required to cast a single batch of steel. With some continuous casting machines with much better protection, the optimal duration of a casting period can be up to 8 or more hours. This means that several batches of steel can be cast without interruption.
  • the properties and the efficiency of the molten fine-particle slagging agent can deteriorate to such an extent that unacceptable surfaces on the steel to be cast result. Furthermore, the inclusion of more and more alumina in the slag can increase the viscosity of the molten agent to such a high value; that the lubrication of the mold is no longer required. The increase in viscosity can hinder the movement of the liquid slagging agent into the space between the mold wall and the solidified edge layer of the strand that forms. If the gap is no longer lubricated by the lack of liquid slag, the strand shell can eat at the mold wall and the resulting risk of breakthrough cannot be accepted.
  • the heat transfer value can become so low that a sufficiently thick solidified edge layer of the steel strand is not formed in the mold, which likewise presents the unacceptable risk of a breakthrough through a smaller hole. If one of these three phenomena or a combination of these phenomena occurs, the pouring stand must either be shut down immediately or the pouring cycle must be interrupted. These stoppages or interruptions occur despite the fact that unmelted fine particulate slag is continuously added to the molten mass of the fine-particle slagging agent covering the molten steel. The problem of alumina uptake is therefore not just a matter of adding additional slagging agent, which is of course costly in itself. The problem of the absorption of aluminum oxide practically leads to shorter, ineffective, costly casting runs or periods of the continuous caster.
  • the previous attempts to solve this problem have focused on the so-called "V” ratio.
  • the "V” ratio is generally defined as the ratio of lime to silicon dioxide.
  • U.S. Patent No. 3,788,840 prescribes a lime / silica ratio in the flux powder in the range of 0.7 to 1.0. This ratio is achieved by adding quartz powder.
  • an aluminum oxide content of the powder in the range of 2 to 12% by weight is also prescribed. Although this helps to improve the properties and the efficiency of the powdered flux during continuous casting, the flux powder cannot tolerate the addition of large amounts of aluminum oxide during a longer casting period and does not allow the casting process to be continued until the optimum duration.
  • the finely divided slagging agent according to the invention has the advantage of the increased ability to absorb larger amounts of aluminum oxide, so that an extension of the duration of the optimal continuous casting period is possible.
  • the invention relates to a finely divided slagging agent for the continuous casting of steel which tends to release alumina into the slagging agent during its use in the molten state during the continuous casting (e.g. US-A-3 788 840).
  • this slagging agent is no longer a start-up ADK value due to a fluidity of approximately 10.2 to 40.6 cm, a melting range which is at most not significantly above 1260 ° C (2300 ° F) as 500 seconds and further characterized by the following theoretical net analysis for oxides, the percentages being understood as percentages by weight and being chosen so that the sum is 100%.
  • Glass network builder
  • the ratio of the sum of the theoretical net analysis values for oxides for the components of the flux marked with an asterisk to the theoretical net oxide analysis value of Si0 2 (this ratio is referred to as the R 'ratio) is previously 1.5: 1 to 3: 1 set to achieve an operational ADK value that is at most not significantly above 750 seconds.
  • the invention comprises an improvement of the method for the continuous casting of steel, whereby a mass of molten steel is held in the upper end of a bottomless continuous casting mold.
  • the improvement is characterized in that a protective layer of the fine-particle slagging agent with the above-mentioned theoretical oxide analysis and the above-mentioned R 'ratio, possibly with a small proportion of elemental carbon, is formed and maintained on the top of the molten steel .
  • the slagging agent can be used as a glazed material or have a glazed portion. If the slagging agent is only partially glazed, preferably no more than 5% fluorine should be present in the glassy part and the rest should be in the form of unglazed parts of fluorine-containing material.
  • the glazed material or the glazed fraction of the flux according to the invention is manufactured in a conventional manner in a melting furnace or the like.
  • Molten glass from the melting furnace is fritted in a conventional manner by pouring a stream of the molten glass into water or then crushing it after it passes between chill rolls.
  • the frit obtained is used for continuous casting so that it passes through a sieve with a mesh size of 105 J.Lm (150 mesh Tyler Standard) or less.
  • Such a frit is basically made from glass network formers and fluxes for it.
  • Glass network formers include, for example, silicon dioxide, boron oxide and aluminum oxide, with silicon dioxide being the main one.
  • Phosphorus pentoxide is also suitable as a glass network former, but is less desirable for making steel liquid, especially with the fine-particle slagging agents according to the invention.
  • the main liquidizing oxides are Group 1A and 2A metal oxides, typically potassium oxide, sodium oxide, calcium oxide, magnesium oxide, strontium oxide, barium oxide, iron oxide (FeO), manganese oxide and lithium oxide.
  • Copper oxide, nickel oxide, phosphorus pentoxide and zinc oxide can also be effective as fluxes, but their use in finely divided slagging agents is unusual because these four oxides sometimes deteriorate and degrade the surface of the same metal types to be cast.
  • the proportions in which they can be used in the slagging agents according to the invention are the other oxides of metals of group IV of the periodic table with atomic numbers from 22 to 30, the oxides of titanium, cobalt, manganese, chromium, vanadium and zirconium as well Molybdenum oxide effective as a flux.
  • they are preferably viewed in part as glass-modifying agents, especially if they are used in a larger proportion.
  • Vanadium, phosphorus, and molybdenum oxides are not recommended for this use because they can pose serious problems with the water added at the end of the casting period.
  • Fluorine also causes alumina to dissolve and is also generally effective as a flux.
  • the glazed part of the flux according to the invention can consist of one or more frits.
  • the frits can be agglomerated, for example, by sintering.
  • mere mechanical mixing of the frits is sufficient and is preferred.
  • the raw batch of glass for the glazed portion of the flux, i.e. H. the vitrified material is usually in the form of minerals and chemicals with a purity satisfactory for glass manufacturing. This is a useful criterion.
  • the fluorine-providing material can consist of simple or complex fluoride salts, generally fluorspar, cryolite, alkali and alkaline earth fluorides and alkali fluorosilicates. For use with steel, synthetic or natural fluorspar is a preferred and particularly useful fluorine-providing raw material.
  • the invention is directed to a mold powder or powder which is produced by intimate mechanical mixing of the finely divided components of the raw batch mentioned above as frit components.
  • the particles of the components are no larger than about 149 microns (100 mesh Tyler sieve range).
  • the mixture can be heated to a certain extent, but not so much that the components melt together and begin to form a glazed material.
  • the mold powder if the mold powder is placed on the surface of the molten steel in the mold, it must melt without residue and thereby avoid the presence of by-products formed by fire, which cause surface defects on the cast steel body.
  • the very great advantage of a mold powder over a vitrified material or flux is the lower cost which is due to the fact that melting the raw batch components before use in continuous casting is no longer necessary.
  • 1 to 10% of finely divided carbon can also be added to the slagging agent.
  • Various properties of the fine-particle slagging agents according to the invention were determined by special tests.
  • the melting temperatures were determined using an optical pyrometer at the end of 14 minutes.
  • the fluidity was measured according to the method described in US Pat. No. 3,649,249.
  • the alumina dissolution kinetics (hereinafter referred to as ADK) and the melting ranges were determined by special tests, their methods to be explained later.
  • Various types of steel to be cast with the finely divided slagging agents according to the invention behaved better if the slagging agents had certain measured properties.
  • the melting range temperatures did not affect the casting process as long as the upper limits were below the lowest temperatures of the steel to be cast with the respective slagging agents.
  • a safety distance of at least a few hundred degrees Fahrenheit is preferred.
  • What is important when choosing the slagging agent with the correct values for the alumina dissolution kinetics and fluidity is the type of the calmed steel. In the case of steel calmed with aluminum, the fluidity value must be above 4 but not above 16.
  • the alumina dissolution kinetics (ADK) should initially be at the lower end of the values for the fine-particle slagging agent.
  • the initial ADK value is referred to below as the start-up ADK value, which characterizes the properties of a molten slagging agent at the beginning of a pouring period before a substantial amount of aluminum oxide has passed into the protective layer of slag.
  • the fluidity of the slagging agent can be less than 3 and its start-up ADC usually need not be as favorable.
  • the value of its "alumina dissolution rate" in seconds may be a higher number in such a case, but it does not exceed -500 seconds.
  • the operating ADK value is defined as the ADK value which, according to the ADK test method described later, for a sample of 225 parts by weight of a completely melted and vitrified slagging agent (excluding any added carbon), in which 25 parts by weight. Parts of additional aluminum oxide (Al 2 O 3 ) have been dissolved. In the case where the slagging agent tested in this way is volatile, e.g. B. releases carbon dioxide while it is being melted, these 225 parts by weight represent the non-volatile residue.
  • the special test procedure used to determine the melting ranges in the above examples required weighing a 3.00 g sample of the fine particulate slag.
  • the weighed sample was placed in a pellet form, the forms (12.7 mm) diameter in a cylindrical shape, a pellet from 1/2 inches.
  • the pellet formed from the sample material was placed in the center of a sheet of stainless steel, the mm a thickness of 12.7 (1/2 inch) and a size of 50.8 mm x 50.8 mm (2 inches x 2 inches ) would have.
  • the sheet with the pellet placed on it was then placed in an oven in which the sheet could be kept in a perfectly horizontal position (to prevent the molten material from running off the sheet).
  • the oven was also able to maintain predetermined temperatures between 816 ° C (1500 ° F) and 1260 ° C (2300 ° F).
  • the sample was kept in the oven for exactly 3.5 minutes.
  • the pellet was examined for signs of softening, mainly rounding off the edges. If there were such indications, the furnace temperature was taken as the lower temperature of the melting range. If there were no such signs, the oven temperature was increased by 27.8 ° C (50 ° F) and a new pellet was heated at the new temperature for exactly 3.5 minutes. After the lower melting range temperature was established, the furnace temperature was further increased by 50 ° F (27.8 ° C) until the upper melting range temperature was determined. The upper temperature was recognizable from the fact that the sample melted into a thin, i.e. H. a puddle or pool that had completely lost its cylindrical shape melted away.
  • the special test used to determine the alumina dissolution kinetics required the production of a graphite crucible without any drain holes.
  • the crucible was made by placing a 3.76 cm (1.5 inch) diameter and 12.7 cm (5 inch) deep hole in a pure graphite electrode of 7.62 cm (3 inch) diameter and 15.24 cm (6 inch) length was drilled.
  • An alumina tube having an outer diameter of 2.4 mm (3/32 inch) and an inner diameter of 0.92 mm (1/32-inch) was mixed with a surface coated with an abrasive cutting disc to a length of 1.89 cm (3/4 Inches).
  • a horizontal hole was 2.4 mm (3/32 inch) diameter 6.4 mm (1/4-inch) mm from the bottom of a rod of graphite electrode grade of 8 (0.31 inch ) Diameter and 205 mm (8.07 inches) long.
  • a 250 gram sample of the fine particulate slag was placed in the crucible.
  • the crucible was heated to a temperature of 1427 ° C (2600 ° F) with a 7.5 kW Lepel induction furnace. While the crucible was being heated, the graphite rod containing the alumina sample was over hung the crucible. This ensured an adequate warm-up period that reduced the possibility of the alumina tube tearing when immersed in the mass. However, the alumina was well above the melting agent to prevent premature dissolution of the alumina.
  • the alumina sample was immersed. Within 30 seconds or less, the graphite rod was pulled out to see if the alumina sample was cracked. Sharp irregular breaks, usually near the tip of the sample, would have indicated a break and the need to restart the test from the beginning. If no cracking was evident, the sample was immersed again. The rod was withdrawn every 15 seconds to determine if dissolution had occurred. Dissolution had occurred when there was no alumina left in the rod. The test was carried out three times on each sample so that an average value given as the test result could be calculated.
  • the ADK test is the most important for the purposes of the invention.
  • the invention is directed to controlling and regulating the properties regarding the absorption of aluminum oxide after the finely divided slagging agent has been used in a continuous caster for a very long period of time. Since the melt of the fine-particle slagging agent continuously absorbs more and more aluminum oxide, which is released from the steel to be cast, the properties of conventional slagging agents change. The most important change is perceived primarily as a change in the start-up ADK value to the operating ADK value. This change usually represents an increase, which means that the used slag no longer absorbs as much aluminum oxide as quickly as at the start of the casting period.
  • the counter of the “R” ratio in the context of the invention is the sum of the theoretical evaluable net oxides CaO, MgO, BaO, SrO, MnO and FeO.
  • Other divalent liquidifying and melting ions such as Ni, Cu, Zn are not included in the "R” ratio according to the invention, because these divalent liquidifying ions have an adverse effect on the surface of the steel to be cast and affect the ratios of the steel alloys if the Ions are reduced to elemental metal.
  • Zn would evaporate and pose health problems for workers near the foundry.
  • the total of the counter is obtained by adding the percentages of the theoretical net oxide analysis values for the two-part ions in the slagging agent.
  • the denominator of the "R” ratio remains the theoretical net oxide analysis value of silicon dioxide. This ratio is between 0.8: 1 and 2.5: 1.
  • the R 'ratio is defined by the numerator, which consists of the sum of the theoretical net oxide analysis values of the following components of the fine-particle slagging agent: CaO, MgO, BaO, SrO, MnO, FeO, B 2 0 3 and F, and the denominator , which consists of the theoretical net oxide analysis value of silicon dioxide.
  • This formula should not be expected to give accurate values of alumina dissolution kinetics, but merely an estimate of the quantitative impact on alumina dissolution kinetics for a given quantitative change in one of the components in the formula.
  • the first row was done with glazed materials or chill powder after formulation. The values obtained would represent the properties of the molten, fine-particle slagging agents when starting the continuous casting of steel.
  • the second set of experiments was conducted to determine an operational ADK for a sample made by adding additional alumina to the finely divided slag in an amount such that 10% of the increased weight of the slag that had received the additive in the molten state due to the addition of additional aluminum oxide. Since the increased weight is the slagging agent plus additive in the molten state, the person carrying out the test must compensate for any weight loss as a result of volatilization of components of the finely divided slagging agent by adding further slagging agent.
  • the fine-particle slagging agent For example, if 10% of the fine-particle slagging agent is lost due to volatilization during melting in the production of a sample for the operational ADK test with an increased weight of 250 g, 250 g would be used instead of 225 g. 25 g of aluminum oxide would be added to this amount of the fine-particle slagging agent of 250 g in order to obtain the final weight of 250 g of the molten slag with addition in the crucible.
  • the alumina of course, would have to be added to the cold vitrified material or powder as a cold raw material in order to subject it to the fluidity test.
  • the values obtained after the addition of aluminum oxide referred to as operating ADK values, would represent the properties of the molten, fine-particle slagging agent after prolonged optimal continuous casting of aluminum oxide-donating steel.
  • the five fine-particle slagging agents in this first group were all mold powder. These samples were made by intimately mechanically mixing the finely divided components of the raw batch, all of which were no larger than 149 1 1m (100 mesh Tyler). The mixtures were not heated.
  • the mold powders contained the following components of the raw slagging agent (in parts by weight):
  • the mold powders had the following theoretical net oxide analysis (in% by weight): Chill powder had the following R ratio:
  • the following six finely divided slagging agents were all mold powders made and tested in the manner described for Examples 1-5.
  • the slagging agents had the following raw composition (in parts by weight):
  • the samples had the following theoretical net oxide analysis (in% by weight):
  • All of these six samples are slagging agents or mold powder that would be suitable for use in a long casting period in the continuous casting of steel.
  • example 12 has the same analysis as example 6 etc. (ie 13 corresponds to 8; 14 corresponds to 9; 15 corresponds to 10 and 16 corresponds to 11).
  • the vitrified materials were made by usual dry mixing, melting and quenching (with water) raw batches of the following composition (in parts by weight):
  • the amount of fluorine actually remaining in the frit was 3.4% by weight.
  • the R ratios in all examples correspond to the previous examples in the same way as the theoretical net oxide analysis values.
  • the glazed materials had the following melting ranges:

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Description

Verschiedene feinteilige Verschlackungsmittel, auch als »Kokillenpulver«, »Schlacken« oder »Flußmittel« bezeichnet, wurden für das Stranggießen von Stahl, eine ziemlich neue Entwicklung in der Stahlwerkspraxis, vorgeschlagen. Diese Materialien schützen das geschmolzene Metall gegen Luftoxidation, während sie gewöhnlich gewisse verunreinigende Oxide, die in der Stahlschmelze vorhanden sind, flüssig oder löslich machen und hierdurch entfernen. Darüber hinaus kann häufig die Schmierung der Kokille durch Verwendung dieser Materialien verbessert werden. Im allgemeinen wird das Material auf die Oberfläche des geschmolzenen Metalls gestreut oder gegossen. Gelegentlich wird diese Oberfläche auch als Meniskus bezeichnet.Various finely divided slagging agents, also known as “mold powder”, “slag” or “flux”, have been proposed for the continuous casting of steel, a fairly new development in steelworks practice. These materials protect the molten metal from air oxidation, while they usually render and thereby remove certain contaminating oxides that are present in the molten steel. In addition, the lubrication of the mold can often be improved by using these materials. Generally, the material is sprinkled or poured onto the surface of the molten metal. Occasionally, this surface is also called the meniscus.

In der Technik werden die Ausdrücke »Flußmittel«, »Schmelzmittel«, »Schlacke« oder »Kokillenpulver oder -puder« austauchbar für gefrittete oder überwiegend gefrittete Materialien verwendet, die beim Stranggießen zu verwenden sind. Der Einfachheit halber wird der Ausdruck »feinteiliges Verschlackungsmittel« als Sammelbegriff für alle Arten von Materialien gebraucht, die zum Schutz und zur Schmierung des Stahls während des Stranggießens verwendet werden. Als »verglast« wird für den vorliegenden Zweck ein vollkommen verglastes (gefrittetes) Material oder Gemisch von gefritteten Materialien bezeichnet. Ein »Flußmittel« ist ein verglastes Material, dem nicht verglastes Material in einem geringen Anteil von weniger als etwa 30% des gesamten Flußmittels zugesetzt worden ist. Zu unterscheiden sowohl von Flußmitteln als auch verglasten Materialien sind die »Kokillenpuder oder -pulver«, die im wesentlichen als Rohmaterialien, die nicht in nennenswertem Maße verglast worden sind, definiert werden. Typischerweise werden die feinteiligen Verschlakkungsmittel gemäß der Erfindung ohne Kohlenstoff hergestellt, indem die Komponenten und/oder verglasten Komponenten pulverisiert und dann, falls erforderlich, gemischt werden. Beispielsweise ist bei den in US-PS 3926246 und 4092159 beschriebenen glasigen Flußmitteln ein Teil des fluorliefernden Materials ungefrittet mit dem Rest der Glasbildner, die gefrittet sind, gemischt. Dies geschieht, um den Schmelzofenang.riff während der Bildung des gefritteten Teils des feinteiligen Verschlackungsmittels weitgehend auszuschalten. Gewöhnlich werden 1 bis 10%, vorzugsweise 1 bis 5 Gew.-% pulverförmiger Graphit zur Herstellung des endgültigen feinteiligen Verschlackungsmittels für den Strangguß zugesetzt. Dieser Graphit dient dem Zweck, Wärmeverluste von der Oberfläche des geschmolzenen Metalls so gering wie möglich zu halten.In engineering, the terms "flux", "melting agent", "slag" or "mold powder or powder" are used interchangeably for fried or predominantly fried materials to be used in continuous casting. For the sake of simplicity, the term "fine-particle slagging agent" is used as a collective term for all types of materials used to protect and lubricate steel during continuous casting. For the present purpose, "glazed" is a completely glazed (fritted) material or mixture of fritted materials. A "flux" is a vitrified material to which non-vitrified material has been added in less than about 30% of the total flux. A distinction must be made between both fluxes and glazed materials. These are called “mold powder or powder”, which are essentially defined as raw materials that have not been glazed to any significant extent. Typically, the particulate interlacing agents according to the invention are made without carbon by pulverizing the components and / or vitrified components and then mixing them if necessary. For example, in the glassy fluxes described in U.S. Patent Nos. 3,926,246 and 4,092,159, some of the fluorine-providing material is mixed without frits with the rest of the fritters which are fritted. This is done to largely eliminate the furnace attack during the formation of the fritted part of the fine-particle slagging agent. Usually 1 to 10%, preferably 1 to 5% by weight of powdered graphite is added to produce the final fine-particle slagging agent for continuous casting. This graphite serves the purpose of keeping heat losses from the surface of the molten metal as low as possible.

Zu den Stählen, die heute großtechnisch durch Stranggießen vergossen werden, gehören verschiedene mit Aluminium beruhigte Stähle, mit Silicium beruhigte Stähle und austenitische nichtrostende Stähle. Die Probleme, die bei der Formulierung eines feinteiligen Verschlackungsmittels für die Verwendung beim Stranggießen von Stahl auftreten, sind bereits in der Fachliteratur angesprochen worden. Spe;:iell die US-PS 3 649 249, 3 704 744 und 3 899 324 beschreiben einige der von anderen Firmen gemachten Versuche, die Eigenschaften und den Wirkungsgrad der verwendeten feinteiligen Verschlackungsmittel zu maximieren.The steels that are cast on a large scale by continuous casting today include various steels quenched with aluminum, steels quenched with silicon and austenitic stainless steels. The problems encountered in formulating a finely divided slagging agent for use in the continuous casting of steel have already been addressed in the specialist literature. Spe;: iell US Pat. Nos. 3,649,249, 3,704,744 and 3,899,324 describe some of the attempts made by other companies to maximize the properties and efficiency of the fine particulate slagging agents used.

In der Fachliteratur ist auch ein Problem, das die Absorption von Aluminiumoxid in das geschmolzene Verschlackungsmittel während des Stranggießens betrifft, erkannt und angesprochen worden. Das Aluminiumoxid stammt aus dem Stahl, der vergossen wird. Das Problem ist äußerst ernst, wenn mit Aluminium beruhigter Stahl vergossen wird. Natürlich ist mit Aluminium beruhigter Stahl der überwiegende Stahityp, der in Stranggießanlagen hergestellt wird. Die Absorption von Aluminiumoxid in das feinteilige Verschlackungsmittel führt schließlich zu einer Verschlechterung der Eigenschaften und des Wirkungsgrades. Mit länger werdender Dauer der Gießperiode beim Stranggießen nimmt.das geschmolzene feinteilige Verschlackungsmittel immer mehr Aluminiumoxid auf. Nach einer bestimmten optimalen Länge der Gießperiode wird der Wirkungsgrad des geschmolzenen feinteiligen Verschlackungsmittels so schlecht, daß die Stahlproduktion des Gießstandes gedrosselt werden muß, weil die geschmolzene Masse die Wärme von der sich bildenden erstarrten Strangschale oder Randschicht nicht schnell genug abführen kann, um die Strangschale genügend zu verdicken. Ferner zeigt die Oberfläche des vergossenen Stahls immer mehr Einschlüsse, weil das geschmolzene Verschlackungsmittel die Verunreinigungen, in erster Linie Aluminiumoxid, aus dem geschmolzenen Stahl nicht schnell genug aufnehmen kann. Die genaue optimale Dauer der Gießperiode ist für jede einzelne Stranggußanlage und für jeden zu vergießenden Stahltyp verschieden. Der Grad des Schutzes, den der geschmolzene Stahl aus der Luft auf seinem Weg zum und durch den Gießstand erhält, beeinflußt die gebildete und später während des Gießens entwickelte Aluminiumoxidmenge. Bei einigen Stranggießeinrichtungen können bereits 45 Minuten die optimale Länge eines Gießganges sein. Diese Dauer ist noch kürzer als die zum Abguß einer einzelnen Stahlcharge erforderliche Zeit. Bei einigen Stranggießeinrichtungen mit viel besserem Schutz kann die optimale Dauer einer Gießperiode bis zu 8 oder mehr Stunden betragen. Dies bedeutet, daß mehrere Stahlchargen ohne Unterbrechung vergossen werden können.A problem related to the absorption of alumina into the molten slag during continuous casting has also been recognized and addressed in the literature. The aluminum oxide comes from the steel that is cast. The problem is extremely serious when potting aluminum-calmed steel. Of course, steel that has been calmed with aluminum is the predominant type of steel that is produced in continuous casting plants. The absorption of aluminum oxide in the fine-particle slagging agent ultimately leads to a deterioration in the properties and the efficiency. As the casting period for continuous casting increases, the molten, fine-particle slagging agent absorbs more and more aluminum oxide. After a certain optimal length of the pouring period, the efficiency of the molten fine-particle slagging agent becomes so poor that the steel production of the pouring stand has to be throttled because the molten mass cannot dissipate the heat from the solidified strand shell or boundary layer that is formed quickly enough to make the strand shell sufficient to thicken. Furthermore, the surface of the cast steel shows more and more inclusions because the molten slagging agent cannot absorb the contaminants, primarily aluminum oxide, from the molten steel quickly enough. The exact optimal duration of the casting period is different for each individual continuous casting plant and for each steel type to be cast. The degree of protection that the molten steel receives from the air on its way to and through the caster affects the amount of alumina formed and later developed during casting. With some continuous casting machines, the optimal length of a casting cycle can be as short as 45 minutes. This duration is even shorter than the time required to cast a single batch of steel. With some continuous casting machines with much better protection, the optimal duration of a casting period can be up to 8 or more hours. This means that several batches of steel can be cast without interruption.

Die Eigenschaften und der Wirkungsgrad des geschmolzenen feinteiligen Verschlackungsmittels können sich in einem solchen Maße verschlechtern, daß unannehmbare Oberflächen auf dem zu vergießenden Stahl die Folge sind. Ferner kann durch die Aufnahme von immer mehr Aluminiumoxid in die Schlacke die Viskosität des geschmolzenen Mittels auf einen so hohen Wert steigen; daß die notwendige Schmierung der Kokille nicht mehr gegeben ist. Der Viskositätsanstieg kann die Bewegung des flüssigen Verschlackungsmittels in den Raum zwischen Kokillenwand und der sich bildenden erstarrten Randschicht des Strangs behindern. Wenn der Spalt durch fehlende flüssige Schlacke nicht mehr geschmiert wird, kann die Strangschale an der Kokillenwand fressen, und die sich hieraus ergebende Gefahr eines Durchbruchs kann nicht in Kauf genommen werden. Schließlich kann der Wärmeübergangswert so gering werden, daß keine genügend dicke erstarrte Randschicht des Stahlstrangs in der Kokille ausgebildet wird, wobei ebenfalls die nicht in Kauf zu nehmende Gefahr eines Durchbruchs durch ein kleineres Loch entsteht. Wenn eine dieser drei Erscheinungen oder eine Kombination dieser Erscheinungen eintritt, muß der Gießstand entweder sofort stillgelegt oder der Gießgang unterbrochen werden. Diese Stillstände oder Unterbrechungen treten trotz der Tatsache auf, daß der geschmolzenen Masse des den geschmolzenen Stahl bedeckenden feinteiligen Verschlackungsmittels kontinuierlich ungeschmolzenes feinteiliges Verschlackungsmittel zugesetzt wird. Das Problem der Aufnahme von Aluminiumoxid ist somit nicht nur eine Angelegenheit der Zugabe von zusätzlichem Verschlackungsmittel, die natürlich an sich kostspielig ist. Das Problem der Absorption von Aluminiumoxid führt praktisch zu kürzeren, unwirksamen, kostspieligen Gießgängen oder -perioden des Stranggießstandes.The properties and the efficiency of the molten fine-particle slagging agent can deteriorate to such an extent that unacceptable surfaces on the steel to be cast result. Furthermore, the inclusion of more and more alumina in the slag can increase the viscosity of the molten agent to such a high value; that the lubrication of the mold is no longer required. The increase in viscosity can hinder the movement of the liquid slagging agent into the space between the mold wall and the solidified edge layer of the strand that forms. If the gap is no longer lubricated by the lack of liquid slag, the strand shell can eat at the mold wall and the resulting risk of breakthrough cannot be accepted. Finally, the heat transfer value can become so low that a sufficiently thick solidified edge layer of the steel strand is not formed in the mold, which likewise presents the unacceptable risk of a breakthrough through a smaller hole. If one of these three phenomena or a combination of these phenomena occurs, the pouring stand must either be shut down immediately or the pouring cycle must be interrupted. These stoppages or interruptions occur despite the fact that unmelted fine particulate slag is continuously added to the molten mass of the fine-particle slagging agent covering the molten steel. The problem of alumina uptake is therefore not just a matter of adding additional slagging agent, which is of course costly in itself. The problem of the absorption of aluminum oxide practically leads to shorter, ineffective, costly casting runs or periods of the continuous caster.

Die bisherigen Versuche zur Lösung dieses Problems konzentrierten sich auf das sog. »V«-Verhältnis. Das »V«-Verhältnis wird allgemein als Verhältnis von Kalk zu Siliciumdioxid definiert. In der US-PS 3 788 840 wird ein Kalk/Siliciumdioxid-Verhältnis im Flußmittelpulver im Bereich von 0,7 bis 1,0 vorgeschrieben. Dieses Verhältnis wird durch Zusatz von Quarzpulver erreicht. In der genannten Patentschrift wird ferner ein Aluminiumoxidgehalt des Pulvers im Bereich von 2 bis 12 Gew.-% vorgeschrieben. Dies trägt zwar dazu bei, die Eigenschaften und den Wirkungsgrad des pulverförmigen Flußmittels beim Stranggießen zu verbessern, jedoch verträgt das Flußmittelpulver nicht den Zusatz großer Aluminiumoxidmengen während einer längeren Gießperiode und gestattet nicht die Fortsetzung des Gießganges bis zur optimalen Dauer. Das feinteilige Verschlackungsmittel gemäß der Erfindung hat den Vorteil der verstärkten Fähigkeit zur Aufnahme größerer Aluminiumoxidmengen, so daß eine Verlängerung der Dauer der optimalen Stranggießperiode möglich ist.The previous attempts to solve this problem have focused on the so-called "V" ratio. The "V" ratio is generally defined as the ratio of lime to silicon dioxide. U.S. Patent No. 3,788,840 prescribes a lime / silica ratio in the flux powder in the range of 0.7 to 1.0. This ratio is achieved by adding quartz powder. In the patent specification mentioned, an aluminum oxide content of the powder in the range of 2 to 12% by weight is also prescribed. Although this helps to improve the properties and the efficiency of the powdered flux during continuous casting, the flux powder cannot tolerate the addition of large amounts of aluminum oxide during a longer casting period and does not allow the casting process to be continued until the optimum duration. The finely divided slagging agent according to the invention has the advantage of the increased ability to absorb larger amounts of aluminum oxide, so that an extension of the duration of the optimal continuous casting period is possible.

Gemäß dem Oberbegriff des Patentanspruches 1 betrifft die Erfindung ein feinteiliges Verschlackungsmittel für das Stranggießen von Stahl, der zur Abgabe von Aluminiumoxid in das Verschlackungsmittel während seines Gebrauchs im geschmolzenen Zustand beim Stranggießen (z. B. US-A-3 788 840) neigt. Nach dem Kennzeichen des Anspruchs 1 ist dieses Verschlackungsmittel durch eine Fluidität von etwa 10,2 bis 40,6 cm, einen Schmelzbereich, der höchstens nicht wesentlich über 1260° C (2300° F) liegt, einen Anfahr-ADK-Wert von nicht mehr als 500 Sekunden und ferner durch die folgende theoretische Netto-Analyse nach Oxiden gekennzeichnet, wobei die Prozentsätze als Gewichts-Prozentsätze zu verstehen und so gewählt sind, daß die Summe 100% beträgt.

Figure imgb0001
Glasnetzwerkbildner
Figure imgb0002
 According to the preamble of claim 1, the invention relates to a finely divided slagging agent for the continuous casting of steel which tends to release alumina into the slagging agent during its use in the molten state during the continuous casting (e.g. US-A-3 788 840). According to the characterizing part of claim 1, this slagging agent is no longer a start-up ADK value due to a fluidity of approximately 10.2 to 40.6 cm, a melting range which is at most not significantly above 1260 ° C (2300 ° F) as 500 seconds and further characterized by the following theoretical net analysis for oxides, the percentages being understood as percentages by weight and being chosen so that the sum is 100%.
Figure imgb0001
 Glass network builder
Figure imgb0002

Das Verhältnis der Summe der theoretischen Netto-Analysenwerte nach Oxiden für die mit Stern gekennzeichneten Bestandteile des Flußmittels zum theoretischen Netto-Oxidanalysenwert von Si02 (dieses Verhältnis wird als R'-Verhältnis bezeichnet) wird vorher auf 1,5 : 1 bis 3 : 1 festgelegt, um einen Betriebs-ADK-Wert zu erreichen, der höchstens nicht wesentlich über 750 Sekunden liegt.The ratio of the sum of the theoretical net analysis values for oxides for the components of the flux marked with an asterisk to the theoretical net oxide analysis value of Si0 2 (this ratio is referred to as the R 'ratio) is previously 1.5: 1 to 3: 1 set to achieve an operational ADK value that is at most not significantly above 750 seconds.

Nach einem weiteren Merkmal umfaßt die Erfindung eine Verbesserung des Verfahrens zum Stranggießen von Stahl, wobei eine Masse von geschmolzenem Stahl im oberen Ende einer bodenlosen Stranggießkokille gehalten wird. Die Verbesserung ist dadurch gekennzeichnet, daß man auf der Oberseite des geschmolzenen Stahls eine Schutzschicht aus dem feinteiligen Verschlackungsmittel mit der vorstehend genannten theoretischen Oxid-Nettoanaiyse und dem vorstehend genannten R'-Verhältnis, gegebenenfalls mit einem geringen Anteil an elementarem Kohlenstoff, bildet und aufrecht erhält.According to a further feature, the invention comprises an improvement of the method for the continuous casting of steel, whereby a mass of molten steel is held in the upper end of a bottomless continuous casting mold. The improvement is characterized in that a protective layer of the fine-particle slagging agent with the above-mentioned theoretical oxide analysis and the above-mentioned R 'ratio, possibly with a small proportion of elemental carbon, is formed and maintained on the top of the molten steel .

Das Verschlackungsmittel kann als verglastes Material eingesetzt werden oder einen verglasten Anteil besitzen. Wenn das Verschlackungsmittel nur teilweise verglast ist, soll vorzugsweise nicht mehr als 5% Fluor im glasigen Teil vorhanden sein und der Rest in Form von unverglasten Teilen von fluorhaltigem Material vorliegen.The slagging agent can be used as a glazed material or have a glazed portion. If the slagging agent is only partially glazed, preferably no more than 5% fluorine should be present in the glassy part and the rest should be in the form of unglazed parts of fluorine-containing material.

Das verglaste Material oder die verglaste Fraktion des Flußmittels gemäß der Erfindung wird in üblicher Weise in einem Schmelzofen od. dgl. hergestellt. Geschmolzenes Glas aus dem Schmelzofen wird in üblicher Weise gefrittet, indem ein Strom des geschmolzenen Glases in Wasser gegossen oder anschließend nach seinem Durchgang zwischen Kühlwalzen zerkleinert wird. Häufig wird die erhaltene Fritte für die Verwendung beim Stranggießen so gemahlen, daß sie ein Sieb einer Maschenweite von 105 J.Lm (150 mesh Tyler Standard) oder weniger passiert.The glazed material or the glazed fraction of the flux according to the invention is manufactured in a conventional manner in a melting furnace or the like. Molten glass from the melting furnace is fritted in a conventional manner by pouring a stream of the molten glass into water or then crushing it after it passes between chill rolls. Often, the frit obtained is used for continuous casting so that it passes through a sieve with a mesh size of 105 J.Lm (150 mesh Tyler Standard) or less.

Eine solche Fritte wird grundsätzlich aus Glasnetzwerkbildnern und Flußmitteln dafür hergestellt. Zu den Glasnetzwerkbildnern gehören beispielsweise Siliciumdioxid, Boroxid und Aluminiumoxid, wobei Siliciumdioxid der hauptsächliche ist. Phosphorpentoxid ist ebenfalls als Glasnetzwerkbildner geeignet, jedoch für das Flüssigmachen von Stahl, insbesondere mit den feinteiligen Verschlackungsmitteln gemäß der Erfindung, weniger erwünscht. Die hauptsächlichen flüssigmachenden Oxide sind die Oxide von Metallen der Gruppe 1A und 2A, typischerweise Kaliumoxid, Natriu-moxid, Calciumoxid, Magnesiumoxid, Strontiumoxid, Bariumoxid, Eisenoxid (FeO), Manganoxid und Lithiumoxid. Kupferoxid, Nickeloxid, Phosphorpentoxid und Zinkoxid können ebenfalls als Flußmittel wirksam sein, jedoch ist ihre Verwendung in feinteiligen Verschlackungsmitteln ungewöhnlich, weil diese vier Oxide zuweilen die Oberfläche der gleichen zu vergießenden Metalltypen verschlechtern und abbauen. In den Mengenanteilen, in denen sie in den Verschlackungsmitteln gemäß der Erfindung verwendet werden können, sind die anderen Oxide von Metallen der Gruppe IV des Periodensystems mit Ordnungszahlen von 22 bis 30, die Oxide von Titan, Kobalt, Mangan, Chrom, Vanadium und Zirkonium sowie Molybdänoxid als Flußmittel wirksam. In der Technik werden sie zum Teil vorzugsweise als glasmodifizierende Mittel angesehen, besonders wenn sie in einem größeren Anteil verwendet werden. Vanadium-, Phosphor- und Molybdänoxide sind nicht für diese Verwendung zu empfehlen, da sie mit dem zur Beendigung der Gießperiode zugesetzten Wasser ernste Probleme aufwerfen können. Fluor bewirkt ferner Auflösung von Aluminiumoxid und ist auch als Flußmittel allgemein wirksam.Such a frit is basically made from glass network formers and fluxes for it. Glass network formers include, for example, silicon dioxide, boron oxide and aluminum oxide, with silicon dioxide being the main one. Phosphorus pentoxide is also suitable as a glass network former, but is less desirable for making steel liquid, especially with the fine-particle slagging agents according to the invention. The main liquidizing oxides are Group 1A and 2A metal oxides, typically potassium oxide, sodium oxide, calcium oxide, magnesium oxide, strontium oxide, barium oxide, iron oxide (FeO), manganese oxide and lithium oxide. Copper oxide, nickel oxide, phosphorus pentoxide and zinc oxide can also be effective as fluxes, but their use in finely divided slagging agents is unusual because these four oxides sometimes deteriorate and degrade the surface of the same metal types to be cast. In the proportions in which they can be used in the slagging agents according to the invention are the other oxides of metals of group IV of the periodic table with atomic numbers from 22 to 30, the oxides of titanium, cobalt, manganese, chromium, vanadium and zirconium as well Molybdenum oxide effective as a flux. In the art, they are preferably viewed in part as glass-modifying agents, especially if they are used in a larger proportion. Vanadium, phosphorus, and molybdenum oxides are not recommended for this use because they can pose serious problems with the water added at the end of the casting period. Fluorine also causes alumina to dissolve and is also generally effective as a flux.

Der verglaste Teil des Flußmittels gemäß der Erfindung kann aus einer oder mehreren Fritten bestehen. Im letzteren Fall können die Fritten beispielsweise durch Sintern agglomeriert werden. Bloßes mechanisches Mischen der Fritten ist jedoch ausreichend und wird bevorzugt. Das rohe Glasgemenge für den verglasten Teil des Flußmittels, d. h. das verglaste Material, liegt gewöhnlich in Form von Mineralien und Chemikalien mit einer für die Glasherstellung befriedigenden Reinheit vor. Dies ist ein zweckmäßiges Kriterium. Das fluorliefernde Material kann aus einfachen oder komplexen Fluoridsalzen, im allgemeinen Flußspat, Kryolith, Alkali- und Erdalkalifluoriden und Alkalifluosilicaten bestehen. Für die Verwendung mit Stahl ist synthetischer oder natürlicher Flußspat ein bevorzugtes und besonders zweckmäßiges fluorlieferndes Rohmaterial.The glazed part of the flux according to the invention can consist of one or more frits. In the latter case, the frits can be agglomerated, for example, by sintering. However, mere mechanical mixing of the frits is sufficient and is preferred. The raw batch of glass for the glazed portion of the flux, i.e. H. the vitrified material is usually in the form of minerals and chemicals with a purity satisfactory for glass manufacturing. This is a useful criterion. The fluorine-providing material can consist of simple or complex fluoride salts, generally fluorspar, cryolite, alkali and alkaline earth fluorides and alkali fluorosilicates. For use with steel, synthetic or natural fluorspar is a preferred and particularly useful fluorine-providing raw material.

Gemäß einem weiteren Merkmal ist die Erfindung auf ein Kokillenpulver oder -puder gerichtet, das durch inniges mechanisches Mischen der vorstehend als Frittenbestandteile genannten feinteiligen Komponenten der rohen Charge hergestellt wird. Die Teilchen der Komponenten sind nicht größer als etwa 149 µm (100 mesh Tyler-Siebreihe). Das Gemisch kann in einem gewissen Maße erhitzt werden, aber nicht so stark, daß die Komponenten zusammenzuschmelzen und ein verglastes Material zu bilden beginnen. Wenn jedoch das Kokillenpulver auf die Oberfläche der Stahlschmelze in der Kokille gegeben wird, muß es ohne Rückstand schmelzen und hierdurch die Anwesenheit von durch Feuer gebildeten Nebenprodukten vermeiden, die Oberflächenfehler auf dem Stahlgußkörper verursachen. Der sehr große Vorteil eines Kokillenpulvers gegenüber einem verglasten Material oder Flußmittel sind die niedrigeren Kosten, die darauf zurückzuführen sind, daß das Schmelzen der Komponenten der rohen Charge vor dem Gebrauch beim Stranggießen nicht mehr erforderlich ist.According to a further feature, the invention is directed to a mold powder or powder which is produced by intimate mechanical mixing of the finely divided components of the raw batch mentioned above as frit components. The particles of the components are no larger than about 149 microns (100 mesh Tyler sieve range). The mixture can be heated to a certain extent, but not so much that the components melt together and begin to form a glazed material. However, if the mold powder is placed on the surface of the molten steel in the mold, it must melt without residue and thereby avoid the presence of by-products formed by fire, which cause surface defects on the cast steel body. The very great advantage of a mold powder over a vitrified material or flux is the lower cost which is due to the fact that melting the raw batch components before use in continuous casting is no longer necessary.

Dem Verschlackungsmittel kann ferner 1 bis 10% feinteiliger Kohlenstoff zugemischt werden.1 to 10% of finely divided carbon can also be added to the slagging agent.

Verschiedene Eigenschaften der feinteiligen Verschlackungsmittel gemäß der Erfindung wurden durch spezielle Tests ermittelt. Die Schmelztemperaturen wurden mit Hilfe eines optischen Pyrometers ermittelt, und zwar am Ende von 14 Minuten. Die Fluidität (flowidity) wurde nach der in der US-PS 3 649 249 beschriebenen Methode gemessen. Die Aluminiumoxid-Auflösungskinetik (nachstehend als ADK bezeichnet) und die Schmelzbereiche wurden durch Spezialtests, deren Methoden später erläutert werden, gemessen.Various properties of the fine-particle slagging agents according to the invention were determined by special tests. The melting temperatures were determined using an optical pyrometer at the end of 14 minutes. The fluidity was measured according to the method described in US Pat. No. 3,649,249. The alumina dissolution kinetics (hereinafter referred to as ADK) and the melting ranges were determined by special tests, their methods to be explained later.

Verschiedene Stahltypen, die mit den feinteiligen Verschlackungsmitteln gemäß der Erfindung zu vergießen waren, verhielten sich besser, wenn die Verschlackungsmittel bestimmte gemessene Eigenschaften aufwiesen. Die Schmelzbereichstemperaturen beeinträchtigten den Gießprozeß nicht, so lange die oberen Grenzen unter den untersten Temperaturen des mit den jeweiligen Verschlackungsmitteln zu vergießenden Stahls lagen. Bevorzugt wird ein Sicherheitsabstand von wenigstens einigen Hundert Grad Fahrenheit. Wichtig bei der Wahl des Verschlackungsmittels mit den richtigen Werten für die Aluminiumoxid-Auflösungskinetik und Fluidität ist jedoch der Typ des beruhigten Stahls. Im Fall von mit Aluminium beruhigtem Stahl muß der Fluiditätswert über 4, darf jedoch nicht über 16 liegen. Die Aluminiumoxid-Auflösungskinetik (ADK) sollte zu Beginn am unteren Ende der Werte für das feinteilige Verschlackungsmittel liegen. Der Anfangs-ADK-Wert wird nachstehend als Anfahr-ADK-Wert bezeichnet, der die Eigenschaften eines geschmolzenen Verschlackungsmittels zu Beginn einer Gießperiode kennzeichnet, bevor eine wesentliche Menge Aluminiumoxid in die Schutzschicht aus Schlacke übergegangen ist. Bei austenitischen nichtrostenden Stählen und mit Silicium beruhigten Stählen können die Fluiditätswerte des Verschlackungsmittels unter 3 liegen, und sein Anfahr-ADK-Wert braucht gewöhnlich nicht so günstig zu sein. Beispielsweise kann der Wert seiner »Aluminiumoxid-Auflösungskinetik« in Sekunden in einem solchen Fall eine höhere Zahl sein, die jedoch -500 Sekunden nicht überschreitet. Nachdem genügend Aluminiumoxid aus dem zu vergießenden Stahl aufgenommen worden ist, um die aufgenommene Aluminiumoxidmenge auf 10% des geschmolzenen Mittels zu bringen, sollte der ADK-Wert 750 Sekunden nicht überschreiten. Dieser zweite ADK-Wert wird nachstehend als Betriebs-ADK-Wert bezeichnet. Der Betriebs-ADK-Wert wird als der ADK-Wert definiert, der nach der später beschriebenen ADK-Testmethode für eine Probe von 225 Gew.-Teilen eines vollständig geschmolzenen und verglasten Verschlackungsmittels (ausschließlich von etwaigem zugesetztem Kohlenstoff), in der 25 Gew.-Teile zusätzliches Aluminiumoxid (Al2O3) gelöst worden sind, ermittelt worden ist. In dem Fall, in dem das in dieser Weise getestete Verschlackungsmittel flüchtige Stoffe, z. B. Kohlendioxid, abgibt, während es geschmolzen wird, stellen diese 225 Gew.-Teile den nicht-flüchtigen Rückstand dar.Various types of steel to be cast with the finely divided slagging agents according to the invention behaved better if the slagging agents had certain measured properties. The melting range temperatures did not affect the casting process as long as the upper limits were below the lowest temperatures of the steel to be cast with the respective slagging agents. A safety distance of at least a few hundred degrees Fahrenheit is preferred. What is important when choosing the slagging agent with the correct values for the alumina dissolution kinetics and fluidity is the type of the calmed steel. In the case of steel calmed with aluminum, the fluidity value must be above 4 but not above 16. The alumina dissolution kinetics (ADK) should initially be at the lower end of the values for the fine-particle slagging agent. The initial ADK value is referred to below as the start-up ADK value, which characterizes the properties of a molten slagging agent at the beginning of a pouring period before a substantial amount of aluminum oxide has passed into the protective layer of slag. For austenitic stainless steels and silicon-quenched steels, the fluidity of the slagging agent can be less than 3 and its start-up ADC usually need not be as favorable. For example, the value of its "alumina dissolution rate" in seconds may be a higher number in such a case, but it does not exceed -500 seconds. After enough alumina has been taken up from the steel to be cast to bring the amount of alumina taken up to 10% of the molten agent, the ADC value should not exceed 750 seconds. This second ADK value is referred to below as the operational ADK value. The operating ADK value is defined as the ADK value which, according to the ADK test method described later, for a sample of 225 parts by weight of a completely melted and vitrified slagging agent (excluding any added carbon), in which 25 parts by weight. Parts of additional aluminum oxide (Al 2 O 3 ) have been dissolved. In the case where the slagging agent tested in this way is volatile, e.g. B. releases carbon dioxide while it is being melted, these 225 parts by weight represent the non-volatile residue.

Falls eine gewisse Menge solcher flüchtigen Komponenten bei diesem Test zu erwarten ist, sollte dies durch Erhöhen des Anfangsgewichts des ungeschmolzenen Verschlackungsmittels berücksichtigt werden. Bei diesem Test ist es üblich, das feinteilige Verschlackungsmittel für den Test vor dem Schmelzen mit zusätzlichem pulverförmigem Al2O3 zu mischen.If a certain amount of such volatile components is expected in this test, this should be taken into account by increasing the initial weight of the unmelted slagging agent. In this test, it is customary to mix the finely divided slagging agent for the test with additional powdered Al 2 O 3 before melting.

Das spezielle Testverfahren, das zur Bestimmung der Schmelzbereiche bei den vorstehenden Beispielen angewandt wird, erforderte das Auswiegen einer Probe von 3,00 g des feinteiligen Verschlackungsmittels. Die ausgewogene Probe wurde in eine Pelletform gegeben, die ein Pellet von 1/2 Zoll (12,7 mm) Durchmesser in Zylinderform bildet. Die Form wurde dann in eine hydraulische Presse gestellt und einem Druck von 5000 psi (350 kg/cM 2=34,3 N/mm2) unterworfen. Das aus dem Probenmaterial gebildete Pellet wurde in die Mitte eines Blechs aus nichtrostendem Stahl gelegt, das eine Dicke von 12,7 mm (1/2 Zoll) und eine Größe von 50,8 mm x 50,8 mm (2 Zoll x 2 Zoll) hatte. Das Blech mit dem darauf gelegten Pellet wurde dann in einen Ofen gelegt, in dem das Blech in genau waagerechter Lage gehalten werden konnte (um zu vermeiden, daß das geschmolzene Material vom Blech abläuft). Der Ofen konnte ferner vorbestimmte Temperaturen zwischen 816° C (1500° F) und 1260° C (2300° F) aufrecht erhalten. Die Probe wurde genau 3,5 Minuten im Ofen gehalten.The special test procedure used to determine the melting ranges in the above examples required weighing a 3.00 g sample of the fine particulate slag. The weighed sample was placed in a pellet form, the forms (12.7 mm) diameter in a cylindrical shape, a pellet from 1/2 inches. The mold was then placed in a hydraulic press and subjected to a pressure of 5000 psi (350 kg / c M 2 = 34.3 N / mm 2 ). The pellet formed from the sample material was placed in the center of a sheet of stainless steel, the mm a thickness of 12.7 (1/2 inch) and a size of 50.8 mm x 50.8 mm (2 inches x 2 inches ) would have. The sheet with the pellet placed on it was then placed in an oven in which the sheet could be kept in a perfectly horizontal position (to prevent the molten material from running off the sheet). The oven was also able to maintain predetermined temperatures between 816 ° C (1500 ° F) and 1260 ° C (2300 ° F). The sample was kept in the oven for exactly 3.5 minutes.

Nach Herausnahme aus dem Ofen wurde das Pellet auf Anzeichen von Erweichung, hauptsächlich Abrundung der Kanten, untersucht. Wenn solche Anzeichen vorhanden waren, wurde die Ofentemperatur als untere Temperatur des Schmelzbereichs genommen. Wenn solche Anzeichen nicht vorlagen, wurde die Ofentemperatur um 27,8°C (50°F) erhöht und ein neues Pellet genau 3,5 Minuten bei der neuen Temperatur erhitzt. Nach der Festlegung der unteren Temperatur des Schmelzbereichs wurde die Ofentemperatur weiterhin um jeweils 27,8° C (50° F) erhöht, bis die obere Temperatur des Schmelzbereichs bestimmt war. Die obere Temperatur war daran erkennbar, daß die Probe zu einer dünnen Schmelze, d. h. einer Pfütze oder Lache, die die zylindrische Form vollständig verloren hatte, zerfloß.After removal from the oven, the pellet was examined for signs of softening, mainly rounding off the edges. If there were such indications, the furnace temperature was taken as the lower temperature of the melting range. If there were no such signs, the oven temperature was increased by 27.8 ° C (50 ° F) and a new pellet was heated at the new temperature for exactly 3.5 minutes. After the lower melting range temperature was established, the furnace temperature was further increased by 50 ° F (27.8 ° C) until the upper melting range temperature was determined. The upper temperature was recognizable from the fact that the sample melted into a thin, i.e. H. a puddle or pool that had completely lost its cylindrical shape melted away.

Für den zur Bestimmung der Aluminiumoxid-Auflösungskinetik angewandten speziellen Test war die Herstellung eines Graphittiegels ohne jegliche Abflußlöcher erforderlich. Der Tiegel wurde hergestellt, indem ein Loch von 3,76 cm (1,5 Zoll) Durchmesser und 12,7 cm (5 Zoll) Tiefe in eine Elektrode aus reinem Graphit von 7,62 cm (3 Zoll) Durchmesser und 15,24 cm (6 Zoll) Länge gebohrt wurde. Ein Aluminiumoxidrohr mit einem Außendurchmesser von 2,4 mm (3/32 Zoll) und einem Innendurchmesser von 0,92 mm (1/32 Zoll) wurde mit einer mit einem Schleifmittel beschichteten Schneidscheibe auf eine Länge von 1,89 cm (3/4 Zoll) zugeschnitten. Um das Rohrstück aus Aluminiumoxid zu halten, wurde ein waagerechtes Loch von 2,4 mm (3/32 Zoll) Durchmesser 6,4 mm (1/4 Zoll) vom Boden eines Stabes aus Graphit von Elektrodenqualität von 8 mm (0,31 Zoll) Durchmesser und 205 mm (8,07 Zoll) Länge gebohrt.The special test used to determine the alumina dissolution kinetics required the production of a graphite crucible without any drain holes. The crucible was made by placing a 3.76 cm (1.5 inch) diameter and 12.7 cm (5 inch) deep hole in a pure graphite electrode of 7.62 cm (3 inch) diameter and 15.24 cm (6 inch) length was drilled. An alumina tube having an outer diameter of 2.4 mm (3/32 inch) and an inner diameter of 0.92 mm (1/32-inch) was mixed with a surface coated with an abrasive cutting disc to a length of 1.89 cm (3/4 Inches). In order to keep the piece of pipe made of alumina, a horizontal hole was 2.4 mm (3/32 inch) diameter 6.4 mm (1/4-inch) mm from the bottom of a rod of graphite electrode grade of 8 (0.31 inch ) Diameter and 205 mm (8.07 inches) long.

Eine Probe von 250 g des feinteiligen Verschlackungsmittels wurde in den Tiegel gegeben. Der Tiegel wurde mit einem 7,5-kW-Lepel-Induktionsofen auf eine Temperatur von 1427° C (2600° F) erhitzt. Während der Tiegel erhitzt wurde, wurde der die Aluminiumoxidprobe enthaltende Graphitstab über den Tiegel gehängt. Hierdurch wurde eine angemessene Aufwärmperiode sichergestellt, die die Möglichkeit, daß das Aluminiumoxidrohr beim Eintauchen in die Masse riß, verringerte. Das Aluminiumoxid befand sich jedoch genügend weit über dem schmelzenden Mittel, um vorzeitige Auflösung des Aluminiumoxids zu verhindern.A 250 gram sample of the fine particulate slag was placed in the crucible. The crucible was heated to a temperature of 1427 ° C (2600 ° F) with a 7.5 kW Lepel induction furnace. While the crucible was being heated, the graphite rod containing the alumina sample was over hung the crucible. This ensured an adequate warm-up period that reduced the possibility of the alumina tube tearing when immersed in the mass. However, the alumina was well above the melting agent to prevent premature dissolution of the alumina.

Wenn der Tiegel eine von einem optischen Pyrometer angezeigte Temperatur von 1427° C (2600° F) erreicht hatte, wurde die Aluminiumoxidprobe eingetaucht. Innerhalb von 30 Sekunden oder weniger wurde der Graphitstab herausgezogen, um festzustellen, ob die Aluminiumoxidprobe gerissen war. Scharfe unregelmäßige Brüche gewöhnlich in der Nähe der Probenspitze würden einen Bruch und die Notwendigkeit angezeigt haben, den Test von Anfang an erneut zu beginnen. Wenn keine Rißbildung erkennbar war, wurde die Probe erneut eingetaucht. In Abständen von 15 Sekunden wurde der Stab herausgezogen, um festzustellen, ob Auflösung stattgefunden hatte. Auflösung hatte stattgefunden, wenn kein Aluminiumoxid mehr im Stab blieb. Der Test wurde mit jeder Probe dreimal durchgeführt, so daß ein als Prüfergebnis angegebener Durchschnittswert berechnet werden konnte.When the crucible had reached a temperature indicated by an optical pyrometer of 1427 ° C (2600 ° F), the alumina sample was immersed. Within 30 seconds or less, the graphite rod was pulled out to see if the alumina sample was cracked. Sharp irregular breaks, usually near the tip of the sample, would have indicated a break and the need to restart the test from the beginning. If no cracking was evident, the sample was immersed again. The rod was withdrawn every 15 seconds to determine if dissolution had occurred. Dissolution had occurred when there was no alumina left in the rod. The test was carried out three times on each sample so that an average value given as the test result could be calculated.

Von den beiden vorstehend beschriebenen Testmethoden ist der ADK-Test für die Zwecke der Erfindung der wichtigste. Die Erfindung ist darauf gerichtet, die Eigenschaften bezüglich der Aufnahme von Aluminiumoxid zu steuern und zu regeln, nachdem das feinteilige Verschlackungsmittel während eines sehr langen Zeitraums in einer Stranggießanlage gebraucht worden ist. Da die Schmelze des feinteiligen Verschlackungsmittels ständig mehr und mehr Aluminiumoxid aufnimmt, das von dem zu vergießenden Stahl abgegeben wird, ändern sich die Eigenschaften üblicher Verschlackungsmittel. Die wichtigste Veränderung wird in erster Linie als Änderung des Anfahr-ADK-Werts zum Betriebs-ADK-Wert wahrgenommen. Diese Änderung stellt gewöhnlich einen Anstieg dar, der bedeutet, daß die gebrauchte Schlacke nicht mehr soviel Aluminiumoxid so schnell wie beim Beginn der Gießperiode aufnimmt. In der technischen Praxis galt bisher, daß, wenn das »V«-Verhältnis (CaO/Si02) des feinteiligen Verschlackungsmittels ungefähr 1,2 überschritt, die Löslichkeit von Al2O3 im geschmoizenen Verschlackungsmittel abzunehmen pflegte. Von der Anmelderin wurde jedoch gefunden, daß, wenn der Zähler des »V«-Verhältnisses so erweitert wird, daß neben CaO auch andere zweiwertige flüssigmachende Ionen einbezogen werden, eine Erhöhung dieses Verhältnisses in Wechselbeziehung zu einer erhöhten Fähigkeit der Schlacke steht, Aluminiumoxid während einer langen optimalen Stranggießperiode aufzunehmen und zu absorbieren. Dieses neue Verhältnis mit einem erweiterten Zähler wird hier als »R«-Verhältnis bezeichnet. Genauer gesagt, der Zähler des »R«-Verhältnisses im Rahmen der Erfindung ist die Summe der theoretischen bewertbaren Netto-Oxide CaO, MgO, BaO, SrO, MnO und FeO. Andere zweiwertige flüssigmachende und schmelzende Ionen wie Ni, Cu, Zn werden nicht in das »R«-Verhältnis gemäß der Erfindung einbezogen, weil diese zweiwertigen flüssigmachenden Ionen nachteilige Auswirkungen auf die Oberfläche des zu vergießenden Stahls haben sowie die Verhältnisse der Stahllegierungen beeinträchtigen, wenn die Ionen zu elementarem Metall reduziert werden. Darüber hinaus würde Zn abgedampft werden und Gesundheitsprobleme für die Arbeiter in der Nähe des Gießstandes aufwerfen. Die Summe des Zählers ergibt sich durch Addition der Prozentsätze der theoretischen Nettooxid-Analysenwerte für die zweiertigen lonen im Verschlackungsmittel. Der Nenner des »R«-Verhältnisses bleibt der theoretische Netto-Oxid-Analysenwert von Siliciumdioxid. Dieses Verhältnis liegt zwischen 0,8 : 1 und 2,5 : 1.Of the two test methods described above, the ADK test is the most important for the purposes of the invention. The invention is directed to controlling and regulating the properties regarding the absorption of aluminum oxide after the finely divided slagging agent has been used in a continuous caster for a very long period of time. Since the melt of the fine-particle slagging agent continuously absorbs more and more aluminum oxide, which is released from the steel to be cast, the properties of conventional slagging agents change. The most important change is perceived primarily as a change in the start-up ADK value to the operating ADK value. This change usually represents an increase, which means that the used slag no longer absorbs as much aluminum oxide as quickly as at the start of the casting period. In technical practice it was previously the case that when the "V" ratio (CaO / Si0 2 ) of the fine-particle slagging agent exceeded approximately 1.2, the solubility of Al 2 O 3 in the slagged slagging agent tended to decrease. However, it has been found by the applicant that if the counter of the "V" ratio is expanded to include other divalent liquid ionizing ions besides CaO, an increase in this ratio correlates with an increased ability of the slag to remove alumina during one long optimal continuous casting period to absorb and absorb. This new ratio with an extended counter is referred to here as the “R” ratio. More precisely, the counter of the “R” ratio in the context of the invention is the sum of the theoretical evaluable net oxides CaO, MgO, BaO, SrO, MnO and FeO. Other divalent liquidifying and melting ions such as Ni, Cu, Zn are not included in the "R" ratio according to the invention, because these divalent liquidifying ions have an adverse effect on the surface of the steel to be cast and affect the ratios of the steel alloys if the Ions are reduced to elemental metal. In addition, Zn would evaporate and pose health problems for workers near the foundry. The total of the counter is obtained by adding the percentages of the theoretical net oxide analysis values for the two-part ions in the slagging agent. The denominator of the "R" ratio remains the theoretical net oxide analysis value of silicon dioxide. This ratio is between 0.8: 1 and 2.5: 1.

Ein verfeinertes Verhältnis zur Voraussage der Wirkung einer Veränderung der Prozentwerte der Netto-Oxyd-Analyse ist das R'-Verhältnis. Das R'-Verhältnis wird definiert durch den Zähler, der aus der Summe der theoretischen Nettooxid-Analysenwerte der folgenden Komponenten des feinteiligen Verschlackungsmittels besteht: CaO, MgO, BaO, SrO, MnO, FeO, B203 und F, und den Nenner, der aus dem theoretischen Netto-Oxid-Analysenwert von Siliciumdioxid besteht.A more refined ratio to predict the effect of a change in the percentages of the net oxide analysis is the R 'ratio. The R 'ratio is defined by the numerator, which consists of the sum of the theoretical net oxide analysis values of the following components of the fine-particle slagging agent: CaO, MgO, BaO, SrO, MnO, FeO, B 2 0 3 and F, and the denominator , which consists of the theoretical net oxide analysis value of silicon dioxide.

Schließlich wurde die nachstehende Formel empirisch aufgestellt, um die Wirkung einiger Komponenten, die zur Bildung des feinteiligen Verschlackungsmittels verwendet werden, auf den Wert der Anfahr-Aluminiumoxid-Auflösungskinetik vorauszusagen. Ein negativer Koeffizient neben dem Wert für den theoretischen Netto-Oxid-Analysenwert der Komponente in den rohen Bestandteilen würde einem niedrigeren Wert der Aluminiumoxid-Auflösungskinetik entsprechen. Dieser niedrigere Wert würde einer kürzeren Zeit der Aluminium-Auflösungskinetik entsprechen, der ein Zeichen für ein geschmolzenes feinteiliges Verschlackungsmittel ist, das leichter Aluminiumoxid aus dem zu vergießenden Stahl aufnehmen und absorbieren könnte. Die Formel lautet:

Figure imgb0003
wobei X20 die Summe der prozentualen theoretischen Netto-Oxidanalysenwerte von Na20 und K20 ist und wobei das Verhältnis von K20 zu Na20 bei 1 : 8 gehalten wird.Finally, the following formula was empirically established to predict the effect of some components used to form the fine particulate slagging agent on the value of the start-up alumina dissolution kinetics. A negative coefficient in addition to the value for the theoretical net oxide analysis value of the component in the raw components would correspond to a lower value of the alumina dissolution kinetics. This lower value would correspond to a shorter time of aluminum dissolution kinetics, which is a sign of a molten, fine-particle slagging agent that could easily absorb and absorb aluminum oxide from the steel to be cast. The formula is:
Figure imgb0003
 where X 2 0 is the sum of the percentage theoretical net oxide analysis values of Na 2 0 and K 2 0 and the ratio of K 2 0 to Na 2 0 is kept at 1: 8.

Bevorzugt sind solche Verschlackungsmittel, deren so berechneter ADK-Wert möglichst niedrig ist.Preference is given to slagging agents whose ADK value calculated in this way is as low as possible.

Man sollte nicht erwarten, daß diese Formel genaue Werte der Aluminiumoxid-Auflösungskinetik angibt, sondern lediglich eine Schätzung des quantitativen Einflusses auf die Aluminiumoxid-Auflösungskinetik für eine gegebene quantitative Änderung einer der Bestandteile in der Formel gibt.This formula should not be expected to give accurate values of alumina dissolution kinetics, but merely an estimate of the quantitative impact on alumina dissolution kinetics for a given quantitative change in one of the components in the formula.

Die folgenden Beispiele veranschaulichen Ausführungsformen der Erfindung, die nicht als Begrenzung der Erfindung anzusehen sind. In diesen Beispielen beziehen sich alle Mengenangaben in Teilen und Prozentsätzen auf das Gewicht, falls nicht anders angegeben. Alle Teilchengrößen entsprechen derTyler-Standardsiebreihe.The following examples illustrate embodiments of the invention, which should not be construed as limiting the invention. In these examples, all parts and percentages are by weight unless otherwise stated. All particle sizes correspond to the Tyler standard sieve series.

Bei allen Beispielen wurden zwei Versuchsreihen durchgeführt. Die erste Reihe wurde mit verglasten Materialien oder Kokillenpulvern nach der Formulierung durchgeführt. Die erhaltenen Werte würden die Eigenschaften der geschmolzenen feinteiligen Verschlackungsmittel beim Anfahren des Stranggießens von Stahl darstellen. Die zweite Versuchsreihe wurde durchgeführt, um einen Betriebs-ADK-Wert für eine Probe zu bestimmen, die durch Zugabe von zusätzlichem Aluminiumoxid zum feinteiligen Verschlackungsmittel in einer solchen Menge hergestellt wurde, daß 10% des erhöhten Gewichts des Entschlackungsmittels, das den Zusatz erhalten hatte, im geschmolzenen Zustand auf die Zugabe von zusätzlichem Aluminiumoxid zurückzuführen waren. Da es sich bei dem erhöhten Gewicht um das im geschmolzenen Zustand vorliegende Verschlackungsmittel plus Zusatz handelt, muß der den Test Durchführende einen etwaigen Gewichtsverlust als Folge der Verflüchtigung von Komponenten des feinteiligen Verschlackungsmittels durch Zusatz von weiterem Verschlackungsmittel ausgleichen. Wenn beispielsweise bei der Herstellung einer Probe für den Betriebs-ADK-Test mit einem erhöhten Gewicht von 250 g 10% des feinteiligen Verschlackungsmittels durch Verflüchtigung beim Schmelzen verloren gehen, würden nicht 225 g, sondern 250 g verwendet. Dieser Menge des feinteiligen Verschlackungsmittels von 250 g würden 25 g Aluminiumoxid zugesetzt, um das Endgewicht von 250 g der geschmolzenen Schlacke mit Zusatz im Tiegel zu erhalten. Das Aluminiumoxid müßte natürlich als kaltes Rohmaterial dem kalten verglasten Material oder Pulver zugesetzt werden, um es dem Fluiditätstest zu unterwerfen. Die nach der Zugabe von Aluminiumoxid erhaltenen, als Betriebs-ADK-Werte bezeichneten Werte würden die Eigenschaften des geschmolzenen feinteiligen Verschlackungsmittels nach längerem optimalem Stranggießen von Aluminiumoxid abgebendem Stahl darstellen.Two series of experiments were carried out in all examples. The first row was done with glazed materials or chill powder after formulation. The values obtained would represent the properties of the molten, fine-particle slagging agents when starting the continuous casting of steel. The second set of experiments was conducted to determine an operational ADK for a sample made by adding additional alumina to the finely divided slag in an amount such that 10% of the increased weight of the slag that had received the additive in the molten state due to the addition of additional aluminum oxide. Since the increased weight is the slagging agent plus additive in the molten state, the person carrying out the test must compensate for any weight loss as a result of volatilization of components of the finely divided slagging agent by adding further slagging agent. For example, if 10% of the fine-particle slagging agent is lost due to volatilization during melting in the production of a sample for the operational ADK test with an increased weight of 250 g, 250 g would be used instead of 225 g. 25 g of aluminum oxide would be added to this amount of the fine-particle slagging agent of 250 g in order to obtain the final weight of 250 g of the molten slag with addition in the crucible. The alumina, of course, would have to be added to the cold vitrified material or powder as a cold raw material in order to subject it to the fluidity test. The values obtained after the addition of aluminum oxide, referred to as operating ADK values, would represent the properties of the molten, fine-particle slagging agent after prolonged optimal continuous casting of aluminum oxide-donating steel.

Beispiele 1 bis 5Examples 1 to 5

Die fünf feinteiligen Verschlackungsmittel dieser ersten Gruppe waren sämtlich Kokillenpulver. Diese Proben wurden durch inniges mechanisches Mischen der feinteiligen Komponenten der rohen Charge, die sämtlich eine Größe von nicht mehr als 149 11m (100 mesh Tyler) hatten, hergestellt. Die Gemische wurden nicht erhitzt. Die Kokillenpulver enthielten die folgenden Bestandteile des rohen Verschlackungsmittels (in Gew.-Teilen):

Figure imgb0004
The five fine-particle slagging agents in this first group were all mold powder. These samples were made by intimately mechanically mixing the finely divided components of the raw batch, all of which were no larger than 149 1 1m (100 mesh Tyler). The mixtures were not heated. The mold powders contained the following components of the raw slagging agent (in parts by weight):
Figure imgb0004

Die Kokillenpulver hatten die folgende theoretische Netto-Oxidanalyse (in Gew.-%):

Figure imgb0005
Kokillenpulver hatten das folgende R-Verhältnis:
Figure imgb0006
 The mold powders had the following theoretical net oxide analysis (in% by weight):
Figure imgb0005
 Chill powder had the following R ratio:
Figure imgb0006

Diese fünf Beispiele veranschaulichen, daß ein hohes R-Verhältnis zu kleinen Änderungen der Herty-Fluidität und ADK-Zeiten auch nach Zugabe von zusätzlichem Aluminiumoxid führt, während ein niedriges R-Verhältnis wie in Beispiel 3 zu großen Veränderungen führt.These five examples illustrate that a high R ratio leads to small changes in Herty fluidity and ADK times even after the addition of additional alumina, while a low R ratio leads to large changes as in Example 3.

Beispiele 6 bis 11Examples 6 to 11

Die folgenden sechs feinteiligen Verschlackungsmittel waren sämtlich Kokillenpulver, die auf die für die Beispiele 1 bis 5 beschriebene Weise hergestellt und getestet wurden. Die Verschlackungsmittel hatten die folgende rohe Zusammensetzung (in Gewichtsteilen):

Figure imgb0007
The following six finely divided slagging agents were all mold powders made and tested in the manner described for Examples 1-5. The slagging agents had the following raw composition (in parts by weight):
Figure imgb0007

Die Proben hatten die folgende theoretische Netto-Oxidanalyse (in Gew.-%):

Figure imgb0008
The samples had the following theoretical net oxide analysis (in% by weight):
Figure imgb0008

Alle Kokillenpulver hatten ein R-Verhältnis von 1,25All mold powders had an R ratio of 1.25

Sie hatte die folgenden Schmelzbereiche:

Figure imgb0009
It had the following melting ranges:
Figure imgb0009

Alle diese sechs Proben stellen Verschlackungsmittel bzw. Kokillenpulver dar, die für die Verwendung in einer langen Gießperiode beim Stranggießen von Stahl geeignet sein würden.All of these six samples are slagging agents or mold powder that would be suitable for use in a long casting period in the continuous casting of steel.

Beispiele 12 bis 16Examples 12 to 16

Die folgenden fünf Proben waren sämtlich verglaste Materialien, die so formuliert wurden, daß die gleiche theoretische Netto-Oxidanalyse wie bei den vorhergehenden Beispielen mit Ausnahme von Beispiel 7 erhalten wurde. Entsprechend der zahlenmäßigen Reihenfolge hat Beispiel 12 die gleiche Analyse wie Beispiel 6 usw. (d. h. 13 entspricht 8; 14 entspricht 9; 15 entspricht 10 und 16 entspricht 11). Die verglasten Materialien wurden durch übliches Trockenmischen, Schmelzen und Abschrecken (mit Wasser) von rohen Chargen derfolgenden Zusammensetzung (in Gew.-Teilen) hergestellt:

Figure imgb0010
The following five samples were all vitrified materials formulated to provide the same theoretical net oxide analysis as in the previous examples except for example 7. According to the numerical order, example 12 has the same analysis as example 6 etc. (ie 13 corresponds to 8; 14 corresponds to 9; 15 corresponds to 10 and 16 corresponds to 11). The vitrified materials were made by usual dry mixing, melting and quenching (with water) raw batches of the following composition (in parts by weight):
Figure imgb0010

Die tatsächlich in der Fritte verbleibende Fluormenge betrug 3,4 Gew.-%. Die R-Verhältnisse bei allen Beispielen entsprechen den vorherigen Beispielen in der gleichen Weise wie die theoretischen Netto-Oxidanalysenwerte.The amount of fluorine actually remaining in the frit was 3.4% by weight. The R ratios in all examples correspond to the previous examples in the same way as the theoretical net oxide analysis values.

Die verglasten Materialien hatten die folgenden Schmelzbereiche:

Figure imgb0011
The glazed materials had the following melting ranges:
Figure imgb0011

Diese fünf Beispiele veranschaulichen, daß ein hohes R-Verhältnis selbst nach Zugabe von 10% Aluminiumoxid zu kleinen Veränderungen der Herty-Fluidität und der ADK-Zeiten führt.These five examples illustrate that a high R ratio results in small changes in Herty fluidity and ADK times even after adding 10% alumina.

Claims (10)

1. Finely-divided slagging agent for the continuous casting of steel which tends to release aluminium oxide into the slagging agent during its use in the molten state, characterised in that it has a fluidity of about 10.2 to 40.6 cm (4 to 16 inches), a melting range which, at most, is not substantially above 1,260° C (2,300° F) and a start-up ADK value of not more than 500 seconds, and is further characterised by the following theoretical net oxide analysis values in the ranges mentioned below, the percentages being understood as percentages by weight and being chosen so that the sum is 100%:
Figure imgb0015
Glass network former
Figure imgb0016
and the ratio of the sum of the theoretical net oxide analysis values of the fluxing-agent constituents marked with an asterisk to the theoretical net oxide analysis value of SiO2 (this ratio is designated as the R' ratio) is fixed beforehand at 1.5.: 1 to 3 : 1 in order to reach an operational ADK value which is not substantially above 750 seconds at most.
2. Finely-divided slagging agent according to Claim 1, characterised in that the ratio of the sum of the theoretical net oxide analysis values of the alkaline earth metal oxides plus FeO and MnO to the theoretical net oxide analysis value of silicon dioxide (this ratio being designated as the »R« ratio) is between 0.8 : 1 and 2.5 : 1.
3. Slagging agent according to Claim 1 or 2, characterised in that the theoretical net oxide analysis values are evaluated by solving the equation below, the sum of the Na20 and K20 oxide analysis values being represented, in the equation, by X2O and the ratio of the oxide analysis values of K2O to Na2O being set at 1 : 8, and the oxide analysis values for F, B203, CaO, X20 and Si02 being so determined that the start-up ADK value according to the equation is as low as possible:
Figure imgb0017
4. Finely-divided slagging agent according to one of Claims 1 to 3, in the form of a vitrified material.
5. Finely-divided slagging agent according to one of Claims 1 to 3, characterised in that it is partially glassy.
6. Slagging agent according to Claim 5, characterised in that it contains fluorine, not more than about 5% of fluorine being present in the glassy part of the slagging agent, and the rest being present in the form of non-vitrified particles of fluorine-donating material.
7. Finely-divided slagging agent according to one of Claims 1 to 3, characterised in that it has been mixed intimately, but not vitrified, in order to form an ingotmould powder.
8. Finely-divided slagging agent according to one of Claims 1 to 7, modified by having had about 1 to 10% of finely divided carbon admixed to it.
9. Finely-divided slagging agent according to one of Claims 1 to 8, characterised in that when additional aluminium oxide is dissolved in the slagging agent the fluidity value increases and the operational ADK value is lower than the start-up ADK value.
10. Process for the continuous casting of steel, a steel melt being kept in the upper end of a continuous casting mould which has no bottom, characterised in that a protective layer comprising the finely divided slagging agent according to one of Claims 1 to 9 is formed and maintained on the top side of the steel melt.
EP19800100749 1979-02-23 1980-02-14 Particulate slagging agent and process for the continuous casting of steel Expired EP0015417B1 (en)

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AT80100749T ATE3007T1 (en) 1979-02-23 1980-02-14 FINE PARTICULATE SLAGING AGENT AND METHOD FOR CONTINUOUS STEEL CASTING.

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US1464979A 1979-02-23 1979-02-23
US06/026,925 US4235632A (en) 1979-04-04 1979-04-04 Particulate slagging composition for the extended optimum continuous casting of steel
US26925 1998-02-20
US14649 2001-12-11

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CN107530769A (en) * 2015-05-04 2018-01-02 株式会社Posco Crystallizer protecting residue and use its continuous cast method, and using its manufacture slab
CN107824754A (en) * 2017-11-30 2018-03-23 攀钢集团西昌钢钒有限公司 A kind of covering slag for chamfer crystallizer and the steel strand method using chamfer crystallizer
CN108213366A (en) * 2018-02-27 2018-06-29 首钢京唐钢铁联合有限责任公司 Covering slag in continuous casting production and application thereof

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CN105436447A (en) * 2016-01-26 2016-03-30 中南大学 Tundish covering agent for continuous casting of low-carbon steel containing Al and Ti and application thereof
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CN107530769A (en) * 2015-05-04 2018-01-02 株式会社Posco Crystallizer protecting residue and use its continuous cast method, and using its manufacture slab
CN107530769B (en) * 2015-05-04 2021-05-11 株式会社Posco Continuous casting method using mold flux, and slab manufactured using the same
CN107824754A (en) * 2017-11-30 2018-03-23 攀钢集团西昌钢钒有限公司 A kind of covering slag for chamfer crystallizer and the steel strand method using chamfer crystallizer
CN108213366A (en) * 2018-02-27 2018-06-29 首钢京唐钢铁联合有限责任公司 Covering slag in continuous casting production and application thereof

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ES488867A0 (en) 1980-12-16

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