JP2005118802A - Method for producing base material of mold powder for continuous casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently and inexpensively mass-produce a premelt base material of mold powder used in such a manner that it is added inside a mold in continuous casting of steel, in particular a premelt base material in which nitrogen is allowed to enter into a solid solution. <P>SOLUTION: In the method for producing a base material of mold powder for continuous casting which consists essentially of two or more kinds selected from the group consisting of CaO, SiO<SB>2</SB>, Al<SB>2</SB>O<SB>3</SB>, MgO, MnO, B<SB>2</SB>O<SB>3</SB>and the oxides and fluorides of alkali metals, the raw materials including the main components are heated and melted, the base material in the melted state produced by the melting is crushed by water under the condition where its viscosity is ≤3.0 poise, and the crushed base material is dried and then pulverized to produce the premelt base material. A nitrogen-containing substance is added in heating the raw materials or to the produced base material in a melted state. Thus, nitrogen can efficiently be allowed to enter into a solid solution in the base material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a mold powder base material used by being added to a mold in continuous casting of steel, and more particularly to a method for manufacturing a base material manufactured by melting in an electric furnace or cupola. is there.

Mold powder used by adding into a mold in continuous casting of steel usually uses an oxide such as CaO, SiO ₂ , Al ₂ O ₃ , MgO, or MnO as a base material, and (1) As a physical property adjusting material for adjusting the physical properties of the base material, Na ₂ O, K ₂ O, CaF ₂ , MgF ₂ , Li ₂ CO ₃ , oxides of alkali metals or alkaline earth metals such as cryolite, fluorine a compound or carbonate, (2) optionally, a limestone or diatomaceous earth CaO, a component adjustment member of SiO ₂ is a main component of the base material, (3) a melting rate adjusting material carbon black, artificial graphite And a carbon substance such as are added. As the base material, blast furnace slag, glass powder, Portland cement, natural basalt or shirasu, calcium silicate produced by melting in an electric furnace or cupola, or the like is used.

  On the other hand, this mold powder is required to have the following characteristics. That is, (1) by covering the molten steel surface in the mold with a molten layer formed by melting the mold powder and an unmolten layer on the molten layer, the molten steel is prevented from being oxidized by air and at the same time (2) Since the molten mold powder flows between the mold and the solidified shell and functions as a lubricant, it must always be supplied in an appropriate amount. , Having a melting rate that matches the consumption rate and ensuring an appropriate thickness of the molten layer, (3) when the molten layer of mold powder absorbs non-metallic inclusions that float and separate from the molten steel, (4) The melted mold powder flows between the mold and the solidified shell to form a uniform powder film, and there is a lubricating action between them. Rukoto, (5) In order to prevent the entrainment into the molten steel of the mold powder, the molten mold powder is that, with a proper viscosity.

In the continuous casting operation that has increased the casting speed in recent years, in order to stably satisfy the characteristics of these various mold powders, a predetermined blending is performed with an electric furnace or cupola as a base material constituting the mold powder. A base material having a uniform composition (also referred to as “pre-melt base material”) in which a CaO source or a SiO ₂ source blended in a ratio is preheated and melted has been used (for example, see Patent Document 1). ). In this case, not only the above-described component adjusting material but also the physical property adjusting material are melted together to produce a base material having a composition very similar to the final composition of the mold powder.

  In addition, among these characteristics, the entrainment of mold powder in molten steel is often a problem during high-speed casting, and for steels with strict quality such as tinplate and thin steel plates for automobiles. In many cases, it becomes a problem even during medium-speed casting or low-speed casting.

  In order to prevent the entrainment of the mold powder, conventionally, increasing the viscosity of the mold powder has been performed (see, for example, Patent Document 2). However, when the viscosity is increased, the amount of mold powder flowing into the mold and the solidified shell decreases, causing poor lubrication, and the frequency of occurrence of so-called “restraint breakout” due to seizure between the mold and the solidified shell. Get higher. Therefore, there is a limit to increasing the viscosity of the mold powder, and recently, a method for changing the viscosity of the mold powder by incorporating nitrogen (N) in the mold powder has been proposed (for example, (See Patent Document 3). In this technique, by including nitrogen in the premelt base material of the mold powder, the part having a high shear rate acting on the mold powder, that is, the part near the mold, the viscosity of the mold powder is low, and the part having a low shear rate, This is a technique that prevents the entrainment of mold powder at the same time as ensuring the amount of mold powder flowing in by utilizing the fact that the viscosity is increased on the center side in the mold.

  As described above, the amount of mold powder for continuous casting composed of a premelt base material is increasing. However, a premelt base material manufactured by melting in an electric furnace, cupola, or the like is made of blast furnace iron, glass powder, Portland cement. Compared to a base material that is simply blended and mixed to have a predetermined composition such as sand, basalt, shirasu, etc., the cost of melting treatment and subsequent preparation of particle size becomes much higher. Therefore, there has been a strong demand for a technique for stably mass-producing premelt base materials at low cost.

However, some proposals have been made on the technology of granulating blast furnace slag in the past (for example, see Non-Patent Document 1). However, the technology for producing a large amount of a mold powder premelt base material efficiently and inexpensively. Has not yet been made a valid proposal. Needless to say, a method for efficiently incorporating nitrogen into the premelt base material has not yet been proposed.
JP 59-27753 A JP-A-62-238053 JP 2001-347350 A Monna et al., Iron and Steel, Vol. 68 (1982), p. 81-89

  The present invention has been made in view of the above circumstances. The first object of the present invention is to efficiently and inexpensively use a mold powder pre-melt base material that is used by being added into a mold by continuous casting of steel. A second object is to provide a method for producing a large amount, and a second object is to improve the yield of nitrogen to be dissolved in the premelt substrate, and to inexpensively produce a premelt substrate for dissolving nitrogen. Is to provide.

  The present inventors have intensively studied and studied in order to solve the above problems. The results of the examination and research are explained below.

When producing a premelt base material, it is necessary to melt the raw material of the mold powder base material such as silica, limestone, and fluorite, and then solidify it. As the solidification method, high-pressure air is blown to the molten base material that has been generated and dispersed to cool and granulate (referred to as “wind crushing method”), or high-pressure water is sprayed and scattered to cool. A method of granulating together (referred to as a “water granulation method”), or a method of cooling a molten base material by flowing it over a high cooling capacity such as a thick steel plate and forced cooling with the thick steel plate and heat radiation to the air. However, it is easy to recover the solidified base material, obtain a particle size suitable for the next pulverization step, and do not produce a compound such as CaO-SiO ₂ system, and a homogeneous vitrified base material is obtained. The granulation method is optimal because of the advantages such as being obtained.

  Therefore, a total of 300 kg of raw materials such as silica, limestone, and fluorite blended so as to have a predetermined composition are charged into an electric furnace of 500 kVA, heated and melted by arc heating, and then melted. The base material in a state was solidified by a water granulation method at the time of unloading from the unloading port, and a test for manufacturing the substrate was performed. The test changes the temperature of the base material in the molten state before water granulation to four levels of 1200 ° C., 1300 ° C., 1400 ° C., and 1500 ° C., and affects the yield of the water-ground material and the ease of water granulation work. The effect of substrate temperature was investigated.

  As a result, in the test where the temperature of the molten substrate was 1400 ° C and 1500 ° C, it was possible to perform water granulation with a high yield without causing problems in the water granulation work, but the tests at 1200 ° C and 1300 ° C Then, the fluidity of the base material in the molten state deteriorated at the tap outlet portion of the electric furnace, and the trouble that solidified at the tap outlet portion and the water granulation treatment was impossible occurred. That is, it was found that if water granulation was performed at a temperature of 1400 ° C. or higher, water granulation could be performed stably.

  In order to investigate the relationship between the viscosity of the substrate and the temperature, the viscosity of the substrate was measured with a rotational viscometer at the test temperature. The measurement results are shown in FIG. As shown in FIG. 1, the viscosity of the base material is 3.0 poise (= 0.3 Pa · s) or lower in the temperature range of 1400 ° C. or higher. Therefore, the viscosity of the molten base material is 3.0 poise. When it exceeded, fluidity | liquidity deteriorated remarkably and it turned out that a water granulation becomes impossible. That is, in order to smoothly perform the water granulation treatment, it was found that it is necessary to perform water granulation in a temperature range where the viscosity of the molten base material is 3.0 poise or less.

In addition, nitrogen gas was blown into the molten base material and added, and a nitrogen compound such as silicon nitride (Si ₃ N ₄ ) was added to dissolve nitrogen in the molten base material. Although it is possible to dissolve nitrogen by either method from the test, it is more preferable to add a nitrogen compound from the point that it is possible to rapidly dissolve a high concentration of nitrogen. There was found.

The present invention has been made on the basis of the above examination results, and the method for producing a base material of a mold powder for continuous casting according to the first invention includes CaO, SiO ₂ , Al ₂ O ₃ , MgO, MnO, B _A method for producing a base material of a mold powder for continuous casting, comprising 2 or more of ₂ O ₃ , an alkali metal oxide, and a fluoride as a main component, wherein the raw material containing the main component is heated. Molten, melted and formed into a molten base material under a condition that the viscosity is 3.0 poise or less, the base material is water-ground, the water-ground base material is dried, and then pulverized It is what.

  According to a second aspect of the present invention, there is provided a method for producing a base material for a mold powder for continuous casting according to the first aspect, wherein a nitrogen-containing material is added to the molten base material when the raw material is heated or generated. This is characterized in that nitrogen is dissolved in the solid.

  According to a third aspect of the present invention, there is provided a method for producing a base material for a mold powder for continuous casting according to the second aspect, wherein the nitrogen-containing material is a solid nitrogen compound.

  According to a fourth aspect of the present invention, there is provided a method for producing a base material for a mold powder for continuous casting in the second aspect, wherein the nitrogen-containing material is a gas containing nitrogen, and the gas is blown into the molten base material. It is characterized by being added in step (b).

  According to the present invention, since the molten base material is granulated under a condition where the viscosity of the base material is 3.0 poise or less, the mold powder pre-melt base material can be efficiently and inexpensively and stably manufactured in a large amount with a high yield. Can be manufactured. Also, a premelt base material in which nitrogen is dissolved can be stably produced in large quantities at a cost equivalent to that of a premelt base material not containing nitrogen. As a result, even in a continuous casting operation with a recent increase in casting speed, it is possible to stably cast high-quality slabs without causing operational troubles, resulting in industrially beneficial effects. .

  Hereinafter, the present invention will be specifically described. The base material of the mold powder for continuous casting according to the present invention is manufactured by heating and melting the raw material of the base material such as silica or limestone using a melting furnace such as an electric furnace or cupola.

Since the base material is mainly composed of at least two components of CaO, SiO ₂ , Al ₂ O ₃ , MgO, MnO, B ₂ O ₃ , alkali metal oxide, and fluoride, The raw materials are blended according to the composition of the base material to be subjected to. The raw material of CaO is limestone, slaked lime, quick lime, etc., the raw material of SiO ₂ is silica, quartz, etc. The raw material of Al ₂ O ₃ is bauxite, the raw material of MgO is magnesia clinker, etc. Manganese ore, B ₂ O _{3 as} a raw material, boric acid, etc., alkali metal oxide as a raw material, sodium carbonate, lithium carbonate, potassium carbonate, etc., fluoride raw material as fluorite . Blast furnace slag, converter slag, and the like can be used as raw materials for both CaO and SiO ₂ . Of course, glass powder, Portland cement, basalt, shirasu, and the like can also be used depending on the composition of the substrate.

The composition of the mold powder used in continuous casting of steel is, for example, CaO: 20 to 50% by mass, SiO ₂ : 20 to 50% by mass, Al ₂ O ₃ : 0.5 to 10% by mass, MgO: 0 to 20 wt%, MnO: 0 to 15 wt%, B ₂ O _3: 0~15 wt%, Na ₂ O: 1~20 wt%, Li ₂ O: 0~5 wt%, K ₂ O: 0~10 Since the mass% and F are in the range of 1 to 20 mass%, it is preferable that the composition of the premelt base material to be produced is the same composition as that of the mold powder with respect to these components. Mold powder made from a pre-melt base material with a composition equivalent to that of the mold powder is homogeneously dissolved because there is no variation in the components, so it has uniform melting characteristics and high-speed casting that requires strict melting characteristics. This is because it is most suitable as a mold powder for use in the process.

  If the base material is melted, it is discharged from the melting furnace outlet while maintaining the temperature of the base material in the temperature range where the viscosity of the base material is 3.0 poise or less. Use water granulation. By this water granulation treatment, a glassy base material having a particle size of about 5 mm or less (referred to as “water granulated base material”) can be obtained. As described above, in the present invention, since the temperature of the molten base material is maintained in a temperature range in which the viscosity of the base material is 3.0 poise or less, solidification of the base material at the spout is prevented. The water granulation treatment can be performed smoothly.

Incidentally, CaO: 47 to 50 wt%, SiO _2: 42~45 wt%, Al ₂ O _3: 2.5~3.5 wt%, MgO: 0.4 to 1.0 wt%, Na ₂ O: In the case of a substrate having a composition range of 0.5 to 1.5% by mass and F: 3 to 4% by mass, the temperature at which the viscosity of the molten substrate becomes 3.0 poise or less is 1400 ° C. or higher. When producing a substrate having this composition range, the temperature of the melted substrate may be maintained at 1400 ° C. or higher for water granulation. When the composition of the substrate is out of this composition range, the relationship between the viscosity and the temperature may be measured in advance and adjusted to a temperature range in which the viscosity is 3.0 poise or less. Recently, a highly accurate estimation formula of slag viscosity has been reported (Sakai Hidenori, Osaka University Doctoral Dissertation, November 2000), which may be used.

  Thereafter, the granulated base material is dried using a rotary dryer or the like, and after drying, pulverized with a vibro mill or the like to prepare a predetermined particle size. After mixing a physical property adjusting material such as lithium carbonate and fluorite as necessary, the carbon material such as carbon black and artificial graphite is further mixed as a melting rate adjusting material to the base material prepared to a predetermined particle size. A mold powder for continuous casting of the desired steel is produced.

  In the case where nitrogen is dissolved in the substrate, there are a case where nitrogen is added as a gas and a case where nitrogen is added as a solid. First, the case where nitrogen is added as a gas will be described.

  The gas to be used is a nitrogen-containing gas such as nitrogen gas or ammonia gas, but it is preferable to use nitrogen gas because it is less expensive than other nitrogen-containing gases. Although air also contains nitrogen gas, it is unsuitable as a gas for dissolving nitrogen in the substrate. When adding the nitrogen-containing gas, since the addition yield is high, after the raw material is dissolved and a molten base material is formed, the tip of the blowing lance is immersed in the molten base material, and the nitrogen-containing gas is supplied to the base material. It is preferable to blow in and add. The nitrogen content in the substrate can be adjusted by obtaining the nitrogen addition yield in advance and adjusting the blowing amount based on the obtained yield. However, when added using a nitrogen-containing gas, the nitrogen concentration in the base material is about 0.1% by mass at the maximum. Therefore, when the concentration is higher than this, it is added as a solid described below. The method is preferably used.

  Since the temperature of the melted base material is lowered by blowing the nitrogen-containing gas, it is necessary to further carefully adjust the temperature range so that the viscosity of the base material is 3.0 poise or less.

  When added as a solid, the nitrogen source used may be sodium nitride, aluminum nitride, silicon nitride, etc., but the mold powder often contains a large amount of silicon as a main component, and is mixed by the addition of the nitrogen source. Even so, it is preferable to use silicon nitride because the components of the substrate can be adjusted relatively easily. These nitrogen sources can be charged into a melting furnace simultaneously with raw materials such as silica and limestone, heated and melted, or added to the molten base after the molten base is formed. Either way.

  Silicon nitride is a high-grade ceramic and inherently does not react with molten slag at low temperatures, and therefore, it reacts more easily as the temperature is raised. FIG. 2 shows the result of investigating the yield of nitrogen and the change over time of the nitrogen concentration in the molten substrate by adding a certain amount of silicon nitride to the molten substrate maintained at 1300 ° C., 1400 ° C., and 1500 ° C. It is. As the temperature of the molten base material is increased, dissolution of silicon nitride is promoted. However, as shown in FIG. 2, if the temperature is increased too much, the yield of nitrogen decreases, and therefore, the upper limit is adjusted to about 1500 ° C. Is preferred. Further, if the molten base material is held after the silicon nitride is melted, nitrogen in the base material is released into the atmosphere and the nitrogen concentration is lowered. Therefore, 50 minutes after the silicon nitride is melted It is preferable to be water-crushed within. In this case as well, it is necessary to adjust the temperature range so that the viscosity of the substrate is 3.0 poise or less.

Using an electric furnace having an electric capacity of 500 kVA, a total of about 350 kg of raw materials mainly composed of silica, limestone and fluorite are melted by arc heat, CaO: 48 mass%, SiO ₂ : 43 mass%, Al ₂ O ₃ : 3% by mass, F: 4% by mass, Na ₂ O: 1% by mass, and MgO: 0.5% by mass were obtained in the molten state. After melting, the temperature of the molten base material generated by adjusting the input power is adjusted to 1420 ° C., and while maintaining this state, the water is granulated with a water amount of 48 tons / hr, and the size of the granulated water is 5 mm or less. A substrate was obtained.

  Then, it dried with the rotary dryer and grind | pulverized the dried granulated base material with a vibro mill. As a result, a base material having a particle size of 74% by mass and having a particle size of 45 μm or less was obtained, and a base material for the mold powder for continuous casting of steel could be obtained.

Using an electric furnace having an electric capacity of 500 kVA, a total of about 350 kg of raw materials mainly composed of silica, limestone and fluorite are melted by arc heat, CaO: 48 mass%, SiO ₂ : 43 mass%, Al ₂ O ₃ : 3% by mass, F: 4% by mass, Na ₂ O: 1% by mass, and MgO: 0.5% by mass were obtained in the molten state. After melting, the temperature of the molten substrate produced by adjusting the input power is adjusted to 1420 ° C., and the tip of a carbon lance with a diameter of 50 mm is immersed in the molten substrate while maintaining the state. Nitrogen gas was blown from this lance at 10 Nl / min for 15 minutes. Then, while maintaining the temperature of the molten base material at 1420 ° C., water granulation was performed with an amount of water of 48 tons / hr to obtain a granulated base material having a size of 5 mm or less.

  From the nitrogen analysis of the water-crushed base material, the nitrogen concentration of the base material before blowing nitrogen gas was 0.019% by mass, whereas the nitrogen concentration increased to 0.068% by mass, that is, nitrogen. It was confirmed that it was possible to dissolve the solid solution.

  Then, it dried with the rotary dryer and grind | pulverized the dried granulated base material with a vibro mill. As a result, a base material having a particle size of 76% by mass and having a particle size of 45 μm or less was obtained, and a base material having no hindrance was obtained as a base material for mold powder for continuous casting of steel.

Using an electric furnace with an electric capacity of 500 kVA, a total of about 250 kg of raw materials mainly composed of silica, limestone, and fluorite were melted by arc heat at the same mixing ratio as in Example 1, and these raw materials were completely After melting, 3.8 kg of silicon nitride was added as a nitrogen source, and 2.5 kg of quicklime was added to adjust the basicity, and the mixture was melted. During this time, the temperature of the molten substrate produced by adjusting the input power was adjusted to 1450 ° C. After confirming that the added silicon nitride and quicklime were melted, with the temperature maintained at 1450 ° C., the water was crushed in an amount of 48 ton / hr for about 13 minutes, CaO: 48 mass%, SiO ₂ : 43 5% or less in size of 5% by mass, Al ₂ O ₃ : 3% by mass, F: 4% by mass, Na ₂ O: 1% by mass, MgO: 0.5% by mass, and N: 0.38% by mass. A granulated substrate was obtained.

  The nitrogen content calculated from the amount of silicon nitride added was 0.59% by mass. Therefore, it was found that nitrogen could be dissolved in a high yield of about 64%. Further, it was confirmed that 0.1 mass% or more of nitrogen, which could not be realized by blowing nitrogen gas, could be dissolved, and it was found that a substrate containing a high concentration of nitrogen could be stably produced.

  Then, it dried with the rotary dryer and grind | pulverized the dried granulated base material with a vibro mill. As a result, a base material having a particle size of 75% by mass with a mass ratio of 45 μm or less was obtained, and a base material having no hindrance was obtained as a base material for mold powder for continuous casting of steel.

It is a figure which shows the investigation result of the relationship between the viscosity of a base material, and temperature. It is the result of investigating the yield of nitrogen and the change over time of the nitrogen concentration in the molten base material.

Claims (4)

Process for producing a base material of a mold powder for continuous casting, comprising mainly two or more of CaO, SiO ₂ , Al ₂ O ₃ , MgO, MnO, B ₂ O ₃ , alkali metal oxides and fluorides The raw material containing the main component is heated and melted, and the base material in a molten state produced by melting is hydrolyzed under conditions where the viscosity of the base material is 3.0 poise or less. A method for producing a base material for continuous casting mold powder, characterized in that the ground base material is dried and then ground.   The base of the mold powder for continuous casting according to claim 1, wherein a nitrogen-containing material is added to the base material in a molten state produced during heating of the raw material, and nitrogen is dissolved in the base material. A method of manufacturing the material.   The method for producing a base material for a mold powder for continuous casting according to claim 2, wherein the nitrogen-containing material is a solid nitrogen compound.   The said nitrogen-containing material is a gas containing nitrogen, and the gas is blown into a molten base material and added, and the base material for continuous casting mold powder according to claim 2, Method.

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