KR100216081B1 - Making method of steel making flux - Google Patents

Abstract

The present invention is for producing high purity steel, and more particularly, relates to a method for producing a flux (solvent) introduced into a molten metal to remove impurities contained in the metal.

In the conventional method of manufacturing steel fluxes, limestone and alumina raw materials are calcined and melted, and then a solid CaO-Al ₂ O ₃ system is prepared. The fluxes thus prepared must be pulverized in order to react quickly in a furnace. It uses the time spent in the sintering process, the consumption of calories, and the selected flux after grinding, but in reality, dust is generated in the workplace by injecting a flux of less than a certain thickness (injected with powder) into the molten steel. There was a problem.

In order to solve this problem, the present invention provides a limestone powder having a particle diameter of 0.1 mm or less, a CaO content of 52% or more, and an average particle diameter of 0.1 mm or less, and an Al ₂ O ₃ content of 84% (% or more). Is mixed so that the ratio of CaO and Al ₂ O ₃ content is (CaO: Al ₂ O ₃ ) 0.8-1.8: 1, and the organic binder is 7-18% (wt%) To make CaO-Al ₂ O ₃ flux by making granules, and to produce a large amount of CaO-Al ₂ O ₃ in granular form at low price and short time The object of the present invention is to provide a composition of flux and a method of preparing the flux, wherein the flux is melted in a short time at low temperature.

Description

[Name of invention]

Manufacturing method of steel flux

Detailed description of the invention

[Application field of the present invention]

The present invention is for producing high purity steel, and more specifically, it relates to a method for producing a flux that is injected into the molten metal to remove impurities contained in the iron.

[Private Technology]

Steels manufactured in converters and electric furnaces are deteriorated due to non-metal inclusions such as oxygen, sulfur, and phosphorus, and in particular, oxides or sulfides in non-metallic inclusions are materials that greatly degrade the stiffness of the steel. do.

Efforts have been made to reduce such impurities, and in order to remove oxide-based nonmetallic inclusions, it is necessary to select an appropriate deoxidation method, molten steel suppression, etc. to suppress the formation of the inclusions or to discharge the nonmetallic inclusions produced through proper stirring. do.

At this time, the slag that is pulled out of the converter has a limit to remove non-metallic inclusions in the molten steel unless the slag does not lower the harmfulness of the slag. Therefore, the purity of molten steel can be improved by reducing the oxidation degree of converter slag and forming slag advantageous for absorption of non-metallic inclusions, and at the same time, it is possible to produce steel with high purity.

For example, when the metal Al is added, the harmful components FeO, SiO _2, etc. in the converter slag layer are reduced by Al to generate Al ₂ O ₃ , so the slag of CaO-SiO ₂ -Fe ₂ O ₃ system is CaO-Al _2. O ₃ -SiO ₂ system composition is changed.

Similarly, the addition of metal Si reduces FeO and increases SiO ₂ to change to CaO-SiO ₂ -Al ₂ O ₃ -based composition.

The slag produced by this change has a relatively high melting point and high oxidizing property. Therefore, the appropriate flux must be added to the medium to induce the ladle slag into a composition having excellent inclusion capturing ability.

Conditions for slag with good ability to collect non-metallic inclusions.

1. Low melting point, good liquidity.

2. The oxygen potential is low.

3. Low activity of inclusions to be removed.

As described above, slag with SiO deoxidation steel has a CaO: SiO ₂ ratio of 1: 1 and Al ₂ O 3 content within 8%, while Al alone deoxidation steel has a CaO: SiO ₂ ratio of 4: 1 or more and 35 Slag containing Al ₂ O ₃ in% is effective.

Therefore, Si must replenish the deoxidation in the SiO ₂ and CaO components in the steel, Al deoxidized steel must replenish the CaO and Al ₂ O ₃ component, and Al-Si composite deoxidizing steel, the CaO and Al ₂ O ₃ component.

Examples of Al deoxidized steel and Al-Si complex deoxidized steel include quicklime, fluorite (CaF ₂ ), and the like, and Al-dross and aluminum are used as Al ₂ O ₃ supplements.

At this time, CaO (melting point 2570 ℃) or Al ₂ O ₃ (melting point 2020 ℃) has a high melting point, it is difficult to change the slag properties in a short time, so a low melting point CaO-Al ₂ O ₃ compounds are used as the flux.

Particularly, in the pure CaO-Al ₂ O ₃ system, since CaO: Al ₂ O ₃ liquid phase starts to form at 1395 ° C in the range of 0.54-1.70: 1, the CaO-Al ₂ O ₃ -based flux (Ca ₃ Al ₂ O _6- Ca ₁₂ Al ₁₄ O ₃₃ -CaAl ₂ O ₄ based mixtures) should have a composition in this vicinity.

If a small amount of SiO ₂ is present, the melting point and fluidity of the flux are drastically reduced, and CaO: Al ₂ O ₃ is 1.14: 1 and SiO ₂ content is about 7%.

These CaO-Al ₂ O ₃ fluxes move the composition of the slag towards easy absorption of non-metallic inclusions and enhance the cleanliness of molten steel by easily dissolving Al ₂ O ₃ produced by quicklime and Al into slag. Will be done.

Conventionally, as CaO-Al ₂ O ₃ flux, CaO and Al ₂ O ₃ are reacted by sintering or electromelting, such as Ca ₃ Al ₂ O ₆ , Ca ₁₂ Al ₁₄ O ₃₃ , CaAl ₂ O ₄ , Ca ₂ SiO ₄ And a mineral composition such as Gehlenite (2CaOAl ₂ O ₃ SiO ₂ ) are used.

However, to produce fluxes that have already been low-melted by firing, electromelting, etc., energy consumption is high and complex processes of crushing, forming, drying, firing and cooling are required.

On the other hand, if CaO and Al ₂ O ₃ are added as a single compound rather than in a compound state, the reaction rate between CaO↔Al ₂ O ₃ is slow and solution generation is not easy, and CaO is rapidly extinguished upon contact with moisture. It is not easy to store because it becomes (Slaking) to Ca (OH) ₂ .

As described above, the method of manufacturing the flux for steelmaking in the prior art has prepared a CaO-Al ₂ O ₃ system in a solid state after calcining and melting limestone and alumina winch, so that the flux thus prepared can react quickly in the ladle. It must be pulverized, and it is difficult to manufacture and store such as time and calorie consumed during sintering process, and the pulverized flux has good affinity with moisture, and it uses the selected flux after pulverization. (Injected with powder, etc.) There was a problem in that dust was generated in the workplace by adding the flux to the molten steel.

[Purpose of invention]

The present invention produces a CaO-Al ₂ O ₃ -based flux without using a method such as calcination and melting, and produces a large amount of CaO-Al ₂ O ₃ -based granules at low prices and in a short time. It is an object of the present invention to provide a flux composition and a method for producing a flux which does not occur and thus is easy to use, and the manufactured flux is melted in a short time at a low temperature.

[Configuration of Invention]

In the present invention, the limestone powder having an average particle diameter of 0.1 mm or less and the CaO content of 52% (weight 96) or more and the alumina powder having an average particle diameter of 0.1 mm or less and 84% (weight%) of the Al ₂ O _{3 content} are CaO and Al _2. Mix the O ₃ content in the range of (CaO: Al ₂ O ₃ ) 0.8-1.8: 1, and add the organic binder so that the content of the organic binder is 7-18% (weight 96). Make it. As the alumina powder, any of alumina raw materials such as sintered alumina, electrolytic alumina, calcined alumina, sintered bauxite, calcined bauxite may be used, but in order to rapidly react with CaO to form a low melting solution, calcined bauxite Preference is given to using.

Bauxite is a natural mineral produced in the form of AlHO ₂ and Al (OH) ₃ , and when H ₂ O is removed by heating the mineral, it becomes Al ₂ O ₃ .

At this time, the reactivity of the produced Al ₂ O ₃ varies depending on the heating temperature. When firing at a temperature of about 1300 ° C. or higher, the sintering of Al ₂ O ₃ proceeds to obtain a state with a dense crystal structure and a high volume specific gravity. Because it does not react well with CaO etc., it is mainly used as a raw material for amorphous dialogs.

In addition, bauxite is rapidly dehydrated at 450 ° C. and is changed from 650-700 ° C. to alumina crystal. However, sintering is not progressed to about 1300 ° C., so the reactivity is excellent.

This process of removing water or carbon dioxide is called calcination, but in the present invention, it is preferable to use calcined bauxite heat-treated at 1300 ° C. or lower as the alumina powder raw material.

Bauxite is also advantageous for producing low melting fluxes, including the appropriate amount of impurities (SiO ₂ , TiO _2, etc.).

Alumina powder and limestone powder should be used with an average particle diameter of 0.1mm or less. If the grain size is larger than this, CaO and Al ₂ O ₃ react to form a liquid phase.

In the present invention, alumina powder and limestone powder to have a AlO ₃ and CaO win a certain level are used as (源) Al ₂ O ₃ and CaO purity in the CaO-Al ₂ O3 based flux is Al ₂ O ₃ content in alumina powder It is ideal to use more than 84% (wt%) of limestone powder and more than 52% (wt%) of CaO content.

If the purity is lower than this, it is difficult to supply a sufficient Al ₂ O ₃ composition and CaO composition, and SiO ₂ , Fe ₂ O _3, etc. present in the impurities reduce the accuracy of molten steel.

In the flux of the present invention, the ratio of the total CaO content and the Al ₂ O ₃ content (CaO: Al ₂ O ₃ ) should be 0.8-1.8: 1, and preferably the range of 0.9-1.3: 1 is preferably 0.8-. In the range of 1.8: 1, the entire liquid phase is present at a temperature of 1450 ° C or lower. Especially, in the range of 0.9-1.3: 1, the rate of change to the liquid phase is high, so that the effect of the flux can be exerted to the maximum.

In addition, when the ratio of CaO and Al ₂ O ₃ is 0.8: 1 or less, it is difficult to make the slag composition excellent in inclusion absorption ability.

In the present invention, the powder having the composition described above is granulated by using an organic binder, so that the powder can be quickly melted when introduced into the slag layer. Starch, wheat flour, etc. are used as the organic binder.

The organic binder should be used 7-8% (wt%), but less than 7% (wt%) is difficult to granulate, and low dry strength generates a lot of dust when entering the slag layer, CaO and Al ₂ O ₃ When the adhesion decreases, rapid melting does not occur, and when it exceeds 18% (wt%), the voids after the oxidation loss of organic bonds are so large that the adhesion between CaO and Al ₂ O ₃ is low and the volume specific gravity is low, thereby obtaining the same effect. Too much flux has to be added for this purpose, so some of the flux does not come into contact with the molten slag, resulting in slow melting.

The present invention is also prepared by mixing the limestone powder, alumina powder, organic binder in the same range as the above basis and uniformly mixed by spraying water on the tilting plate to form the mixture into granules by centrifugal force and rolling force and then dried Provided is a steel manufacturing flux.

If the particle size of steelmaking flux is too small, it may cause deterioration of working conditions due to dust generation, and if the particle size is too large, it takes much time for drying and melting, so that the particle size is supplied in granules with a diameter of 2mm-30mm. desirable.

Existing fluxes produced by sintering, melting, etc. are produced in the form of agglomerates (liquid-solidified form), so they are pulverized to a desired particle size, but in this case, the pulverized particles may be uneven and the powder produced during the pulverization process may be Although the present invention is used as a raw material of the fine powder alumina and limestone to make it into a granular state.

The present invention uses an organic binder to produce a limestone powder and alumina powder in a granular form, and the organic binder is sufficiently mixed with CMC (carboxy methyl celluiose), polyvinyl alcohol, pulp waste, petroleum by-products and then pressurized. Method of drying after molding, method of using resin-based binding system, method of adding hydrate such as portland cement or alumina cement, and molding together with water, then drying, molding and drying with viscous inorganic material such as clay In the present invention, the mixed powder of limestone and alumina is formed into a granular state by using an organic binder which has viscosity when mixed with moisture, such as starch and flour, and which can express dry strength after drying.

In particular, the present invention uses a tilting rotating disk for mass production, and when the disk is inclined at a certain angle, and the mixture of limestone, alumina, and organic binder is supplied on the rotating plate, the limestone and alumina powder are formed by the rolling force and centrifugal force on the disk. The organic binder is agglomerated as a medium, and the agglomerated powders grow gradually (the size may vary depending on necessity, but the granular diameter is generally within the range of 2-30 mm). When the size of the particles grows to a size (diameter 2mm-30mm) that can achieve the object of the present invention, the heavy granular particles are moved to the edge by centrifugal force (moving to the outer circumferential surface of the tilting plate) and the tilting plate is inclined so that the particles are sufficiently As it becomes larger (usually 10mm-20mm in diameter), the weight is naturally heavy, and the particles are rotated on the outer circumferential surface of the tilt wheel, and then discharged downward from the lower part of the tilt tilt wheel.

The granules discharged from the tilting plate are transferred to the drying apparatus and put into the drying furnace to be dried. At this time, the granules are hardened by the binding force of the organic binder to express dry strength.

Effects of the Invention

In the present invention, the flux is composed of CaCO ₃ + Al ₂ O ₃ + organic binder + impurities, and when the full flux is added to the ladle or totish, the organic binder is oxidized and lost by the molten steel and then CO ₂ in CaCO ₃ is converted into a gas. Become novel. At this time, CaO ₂ remaining after the novel CaO ₂ remains in a very reactive state in a short time. (The quicklime used in the steelmaking process is sintered, so the reactivity is not very good.)

As a result, CaO reacts rapidly with the surrounding Al ₂ O ₃ to change into a liquid phase with a eutectic point (melting point of eutectic mixture), and the liquid phase is capable of absorbing (absorbing or absorbing) existing slag flow and nonmetallic inclusions. Will increase.

In this case, the use of a highly reactive calcined bocoxide as the Al ₂ O ₃ source can reduce the liquid phase generation time.

At this time, a portion of the high-flow liquid phase of the eutectic point composition initially generated freely moves to the non-liquefaction site to promote the liquefaction of the residual solid phase.

Due to this effect, the present invention can be slag into a highly fluid liquid phase in a short time rather than the conventional dense flux that is already low melting point by sintering, melting and the like.

EXAMPLE

Using limestone powder, alumina powder and flour as shown in Table 1, mix them as shown in Table 2, and then mix powder and water together on a rotating plate with a diameter of 3m rotation speed of 50rpm and a tilt angle of 30 °. It was molded into granules and dried at 200 ° C. for 30 minutes to prepare a flux specimen having a water content of 0.1% or less.

The specimen was placed in an electric furnace maintained at 1450 ° C. and time was measured until the height of the sample became 5 mm or less.

Dissolved oxygen [O _f ] concentration in the magnesia crucible is dissolved in 40kg of steel with a concentration of around 500ppm and a carbon concentration of about 0.2%, maintained at 1680 ° C, 80g of converter slag, 200g of quicklime, 40g of fluorite, 80g of aluminum, and prepared in Table 2 After 10 minutes of 80 g of flux, molten steel was collected and the total oxygen concentration was measured.

The converter slag used at this time has a composition of T.Fe 21.9%, CaO 42.0%, SiO ₂ 8.1%, Al ₂ O ₃ 2.2%, MgO 8.0%.

The total oxygen concentration (T [0]) of the molten steel recovered 10 minutes after the administration of only slag, quicklime, formation, and aluminum without any flux was 50 ppm.

[In table 2]

In the present invention, A-1, A-2, A-5, and A-7 are very excellent in meltability and non-metallic individual absorption ability as compared with the conventional example.

The present invention A-3 and A-4 A-6 have the same or somewhat inferior absorption ability of meltability and nonmetallic inclusions as compared with the prior art.

The present inventions B-1 to B-4 are fluxes that are poor in meltability and meltability of nonmetallic inclusions.

In particular, the present invention examples B-1, B-2 have a long time to the melting time, and the ability to absorb non-metallic agents is somewhat lower.

Inventive Example B-3 uses sintered alumina as an alumina raw material, and the reaction time with CaO is long, so that the melting time is long, and thus the nonmetallic substance absorbing ability is rather low in a short time.

Inventive Example B-4 uses sintered bauxite calcined in silver at 1300 ° C or higher as an alumina raw material, and has a low melting time compared to Inventive Example A, and thus has a low ability to absorb nonmetallic substances in a short time.

In Comparative Example 1 and Comparative Example 3, the particle size of the limestone raw material and the alumina raw material is larger than the size of the particle size shown in the detailed description of the present invention, and the time to melting time is long, and the inclusion absorption ability is low.

In Comparative Example 2, a limestone raw material and an alumina winch used a lower purity than that described in the detailed description of the present invention, and the melting time was fast, but the slag composition was not properly controlled, so that the absorption of the substance was low.

Comparative Example 5 and Comparative Example 6, the CaO: Al ₂ O ₃ ratio is beyond the ratio shown in the detailed description of the present invention does not melt the whole amount at 1450 ℃ and very low absorption effect of the substance.

Comparative Example 7 was less than the amount of the organic binder used in the detailed description of the present invention could not determine the effect due to dust generation when administered on the molten steel.

In Comparative Example 8, the amount of the organic binder used is greater than that of the detailed description of the present invention, and the adhesion time between CaO and Al ₂ O ₃ is low, so that the melting time is long, and even when the molten steel is administered, the total amount does not dissolve in a short time (10 minutes). The effect is very low.

As described above, the ratio of limestone powder, alumina powder and organic binder is mixed in the range of 40-70%: 25-40%: 7-20% (weight 96), respectively, to prepare granules. The flux of the finished product prepared by is 28-38% (weight 96) of CaO, 20-30% (weight%) of Al ₂ O ₃ , and 1-8% (weight% of other impurities (iron oxide, SiO _2, etc.)). ), The loss of ignition (usually novel at 1,000 ℃, organic bond bonding, Co _2, etc.) should be within 35-45% (wt%), so that the rate of change to the reactive and liquid phase is faster. The effect can be obtained.

Conventional Example is a conventional sintering flux as in the prior art Example 1 is a CaO content of 54.9%, Al ₂ O ₃ content 35.3%, Conventional Example 2 is a CaO content of 50.9%, Al ₂ O ₃ content of 43.8%, melting rate And the absorbent ability to absorb the substance is good compared to the practice of the present invention, the manufacturing method is complicated, the energy consumption during the production, there is a fear of dust generation when used.

TABLE 1

TABLE 2

[Effects of the Invention]

As in the above embodiment, the present invention has a simple manufacturing process by granulating pulverized limestone powder, alumina powder, and organic binder in comparison with the conventional method of pulverization-molding-drying-firing-engraving-milling, so that the production process is simple and mass production in a short time. In addition, the manufacturing cost is low, and there is no fear of dust generation when used in a granular form, and it is effective in melting and non-metallic inclusions.

Claims (1)

40 to 70% (wt%) of limestone powder with CaO content of 52% (wt%), 25 to 40% (wt%) of alumina powder with 84% (wt%) of Al ₂ O ₃ and organic binders. % (% By weight), respectively, the average particle diameter of the limestone powder and alumina powder is 0.1mm or less, and the ratio of CaO content in the limestone powder and Al ₂ O ₃ content in the alumina powder (CaO: Al ₂ O ₃ ) is 0.8 The manufacturing method of the steelmaking flux manufactured from granular form which is -1.8: 1.