Classifications

• • 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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• 1980
  • 1980-02-14 DE DE8080100749T patent/DE3062658D1/de not_active Expired
  • 1980-02-14 EP EP19800100749 patent/EP0015417B1/de not_active Expired
  • 1980-02-22 ES ES488867A patent/ES488867A0/es active Granted
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