JPH08176643A - Deoxidation and refining of molten steel - Google Patents

Abstract

PURPOSE: To provide an oxidation and refining method capable of effectively removing a deoxidation product, and easily manufacturing a clean steel in a large amount. CONSTITUTION: In the reaction when CaCO3 and Al are simultaneously added to a non-oxidated molten steel to generate the deoxidation product, the molten steel is preliminarily fluidized to the local part to be reacted. When simultaneously adding, CaCO3 powder may be coated on the surface of the core of the Al grain, or CaCO3 powder may be mixed with Al powder. CaCO3 added in the molten steel is dissociated into CaO and CO2 by the heat of the molten steel, and CO2 generates a small and rapid stirring flow in the molten steel to promote the enlargement of the sizes of the impurities, and efficiently adsorb Al2 O3 in which CaO becomes inclusions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for deoxidizing and refining molten steel.

[0002]

2. Description of the Related Art Conventionally, as a method of deoxidizing and refining molten steel, a method of adding a deoxidizing agent such as Al to undeoxidized molten steel has been a well-known technique. It is known that a large amount of inclusions such as alumina clusters are generated as acid products, which remain in the steel and become internal defects, thereby deteriorating the quality of the steel material.

Therefore, when adding a deoxidizing agent, the molten steel is forcibly stirred by using an inert gas blowing stirrer, an electromagnetic induction stirrer, or the like, to coagulate and fuse alumina and the like suspended in the molten steel. Treatment, and further, CaO, CaO-Al
Clean steel is manufactured by injecting reducing slag such as ₂ O ₃ into molten steel, adsorbing and removing alumina and the like suspended in the molten steel, and floating inclusions. .

[0004]

However, according to the prior art, when performing stirring by injecting an inert gas or electromagnetic induction, deoxidation using a reducing slag which reacts relatively slowly is performed. In such a case, for example, LF method or A
A dedicated smelting vessel as used in the SEA-SKF method was required. For this reason, a huge amount of capital investment is required, and a special out-of-pile smelting facility must be added to the normal steelmaking equipment line. Due to restrictions, it could not always be easily introduced.

Further, even when the inert gas is blown or the stirring is performed by electromagnetic induction, it is not easy to sufficiently remove the alumina and the like suspended in the molten steel. Unless agitated, the steel material may be defective. On the other hand, if the agitation is performed over a long period of time, the steelmaking process may be prevented from proceeding sequentially.

Accordingly, an object of the present invention is to provide a deoxidizing and refining method capable of removing deoxidized products more effectively than in the past and enabling easy and large-scale production of clean steel. .

[0007]

In order to achieve the above-mentioned object, a method for deoxidizing and refining molten steel according to the present invention is characterized in that a gas-releasing substance for releasing gas in molten steel is provided. , A deoxidizing substance that binds to oxygen in the molten steel, and simultaneously added to the undeoxidized molten steel, and during the reaction to produce a deoxidized product,
It is characterized in that a flow of molten steel is given in advance to a local part to be subjected to the reaction.

According to the method for deoxidizing and refining molten steel of the present invention,
When the gas releasing substance and the deoxidizing substance are simultaneously added to the molten steel, the gas is released from the gas releasing substance. Due to the rapid expansion of the gas, a minute and sharp Generates an irregular stirring flow,
The chances of collision between the deoxidized substance and oxygen, between deoxidized products, and between other substances as inclusions greatly increase.
That is, in the conventional stirring device, only a relatively large circulating flow is generated in the molten steel, and the deoxidizing agent is moved along with the flow of the molten steel while maintaining a state of being unevenly distributed. In many cases, the gas is left in the steel in a minute state without collision, whereas in the present invention, a small, abrupt and irregular stirring flow accompanying the generation of gas causes a local participant in the reaction. The flow of the molten steel is given to the local part in advance, and the deoxidized products often collide with each other, and the deoxidized products are likely to become large. As a result, the deoxidized product is very easy to float, the cleaning of the molten steel is promoted, and the floating deoxidized product can be easily removed from the system of the molten steel.

In addition, since the agitated flow can be generated without using a conventional agitating device, large-scale dedicated equipment is not necessarily required, and it can be easily implemented with ordinary steel making equipment. Of course, even when a stirring device is provided, the deoxidizing treatment can be performed more efficiently by using the deoxidizing and refining method of the present invention in combination.

Here, in the present invention, the gas releasing substance
Is a substance that is decomposed by the heat of molten steel and releases gas.
The substance contained in the part may be a substance that evaporates and releases gas.
No. More specifically, as an example of the former, CaCO_Three,
MgCO_Three, Na_TwoCO_ThreeSuch as carbonates
As an example of the latter, SiO 2_TwoSystem of hydrated minerals
Can be mentioned. However, the amount of gas generated per addition amount is
Many points, inert CO_TwoWhere slag occurs
Considering that the higher the value, the better the cleaning effect
Is more desirable, and among carbonates, CaCO 2_ThreeIs particularly desirable
New That is, CaCO_ThreeIn the case of_TwoAt the same time
Because CaO is produced, it fuses with the deoxidized product
It becomes a large slag, and the deoxidized product easily floats.
MgCO_ThreeA similar reaction occurs in the case of_Two
MgO generated at the same time as the generation of
Dispersibility in CaO is not as good as CaO,
CO _ThreeWithout using CaCO_ThreeIt is better to mix them.

The deoxidizing substances include Al, Si, M
n, Mg, etc., which may be used alone, in the form of a composite composition of two or more kinds, or in an alloy containing Fe or the like. It is Al that has an effect. As the Al, a new lump Al is melted, and in the case of dissolving particulate metal Al, metal aluminum or an aluminum alloy obtained by an atomizing method, aluminum dross generated on the surface of the molten metal is pulverized and processed to have an aluminum pure content of 20%.
Granules containing the above, Al chips generated by machining, and the like can be used. That is, not only pure Al, but A
The composition may be any composition having a pure content of 20% or more. As the shape, a shape that can be easily dissolved in molten steel, such as a particle or a powder, is preferable.

Further, in the present invention, simultaneous addition means that the gas-releasing substance and the deoxidizing substance are charged into molten steel in a state of contact with the gas-releasing substance. A method of adding a suitable binder to the mixture and adding a mixture thereof, and using one of a gas releasing substance and a deoxidizing substance as a nucleus, and using the surface of the other as a core. Any method such as adding a substance coated with a substance may be used. In particular, not only the gas-releasing substance and the deoxidizing substance are simply mixed, but also the one that is integrally processed, the deoxidizing substance is actively dispersed in the molten steel by the force of the gas rapidly generated from the gas-releasing substance. Therefore, it is more desirable in that the chance of collision with oxygen and deoxidation products increases.

[0013] In addition, the deoxidizing and refining method of the present invention is not only applied to molten steel that has not been subjected to any deoxidizing treatment, but is also subjected to a deoxidizing treatment in advance, and fine deoxidized products are suspended. It also has the effect of removing deoxidized products from molten steel in a turbid state.Undeoxidized molten steel in the present invention includes molten steel in which minute deoxidized products are suspended. It is.

As is clear from the above description, in the present invention, as described in claim 2, calcium carbonate as the gas releasing substance and aluminum as the deoxidizing substance are replaced by undeoxidized aluminum. It is desirable to simultaneously add the molten steel to the molten steel, and further, as described in claim 3, the composite deoxidizing and refining agent formed into a particulate form with the calcium carbonate and the aluminum as main components is added to the undeoxidized molten steel. More desirable.

That is, calcium carbonate and aluminum
When added simultaneously, first, CO 2 _TwoOccurs,
The steel is rapidly stirred and Al and oxygen, Al_TwoO_ThreeEach other
Or Al_TwoO_ThreeAnd collision of CaO are promoted.
The generated CaO-Al_TwoO_ThreeSystem low melting point reducing slur
Is present as a single substance_TwoO_ThreeEtc. are adsorbed and become larger
Third, it is easy to float, and thirdly, Al is removed by deoxidation._TwoO
_ThreeThe reaction that produces CaO and the reaction that produces CaO are extremely
Since they occur simultaneously in the vicinity, Al_TwoO_ThreeMiss
Effectively without CaO-Al_TwoO_ThreeSystem low melting point reducing slur
Fourth, CaCO_ThreeRaw by dissociation of
What is the case where the separately prepared CaO is added
No, it absorbs extra things like moisture
Is active, etc.
As deoxidation progresses as a result, inclusions remaining in the steel
It is significantly reduced. In particular, calcium carbonate and aluminum
And adding it as a main component into particles,
Generated in CO_TwoAl is actively dispersed by the force of
If the uneven distribution of Al is prevented and there is a further cleaning effect
Conceivable.

[0016]

Next, embodiments of the present invention will be described. (1) Preparation of composite deoxidizing refining agent Al particles containing 99.7% of metal Al (particle size: 0.5 to 1.0 m)
m) To 700 g, 50 g of a 5% aqueous sodium silicate solution as a binder was added, and mixed with a rotary mixer until the whole was wetted. Next, 300 g of calcium carbonate fine powder having an average particle size of 5 to 6 μm, a CaO content of 53% or more, a SiO ₂ content of less than 2.0%, and a loss on ignition of 41 to 44% is added and mixed, and taken out of the mixer. Let dry. As a result, a target product in which the surface of the Al particles was coated with the fine calcium carbonate powder was obtained. (2) Production of Clean Steel [Part 1] In a graphite crucible having an inner diameter of 145 mm set in a high-frequency induction furnace, 10 kg of a commercially available S25C steel bar was melted. After 5 minutes from the meltdown, the fused silica tube (inner diameter 8
mm × 12 mm in outer diameter), and 20 g of the above-mentioned composite deoxidizing and refining agent was injected together with N ₂ gas. This is 1570
After holding at 10 ° C. for 10 minutes, a cast steel mold (inner diameter 50 mm
× height 100 mm) (sample 1).

Similarly, 10 kg of S25C steel bar was melted in a graphite crucible, 3 minutes after melting, and 5 minutes after melting.
After one minute, 20 g of the above-mentioned complex deoxidizing and refining agent was added by an overhead method, and the mixture was stirred with a silica tube. This was kept at 1570 ° C. for 10 minutes, and then cast into the same cast steel mold as above (Sample 2).

Further, for comparison, 10 kg of S25C steel bar was melted in a graphite crucible, kept at 1570 ° C. for 10 minutes without adding the composite deoxidizing refining agent, and then cast into the same cast steel as above. (Sample 3). (3) Measurement / comparison test of inclusions [Part 1] For each of the three types of samples obtained by the above-described method, three vertical and vertical positions on the axis were measured using ASTM-E4.
Inclusions were measured and compared by five methods. Table 1 shows the test results. Note that the test results are the average of the results of preparing two samples and measuring them.

[0019]

[Table 1]

As is clear from the above results, by adding the above-mentioned complex deoxidizing refining agent, it is possible to reduce B-based inclusions, which are oxide-based inclusions represented by alumina. In particular, when the composite deoxidizing refining agent is blown into molten steel by an injection method, an excellent cleaning effect is exhibited. (4) Production of Clean Steel [Part 2] Next, the case where the above-mentioned composite deoxidizing refining agent is blown by the injection method in which a particularly excellent cleaning effect is recognized,
For comparison with the case where a deoxidizer made of ordinary metal Al was blown, clean steel was manufactured by the following two methods.

First, 10 kg of molten steel equivalent to S45C melted in a high-frequency melting furnace was discharged into a ladle lined with zircon brick, and immediately, 20 g of the above composite deoxidizing and refining agent was injected together with N ₂ gas. This at 1650 ° C for 10
After holding for 1 minute, molten steel was drawn out and cast into a cast steel mold (inner diameter 35 mm × height 100 mm) (sample 4).

For comparison, 10 kg of molten steel similarly melted in a high-frequency melting furnace was discharged into a ladle, and immediately 20 g of a deoxidizing agent composed of metal Al particles was injected together with N ₂ gas. After holding this at 1650 ° C. for 10 minutes, molten steel was drawn out and cast into the same mold as above (Sample 5). (5) Inclusion measurement / comparison test [Part 2] For each of the two types of samples obtained by the above-described method, three vertical and axial lower and upper positions were determined by ASTM-E4.
Inclusions were measured and compared by five methods. Table 2 shows the test results. The test result is an average of the results of preparing five samples and measuring them.

[0023]

[Table 2]

As is apparent from the above results, the injection of the above-mentioned complex deoxidizing refining agent gives the metal A
Inclusions can be reduced as compared with the case where 1 is injected. In particular, it has been found that, of course, B-based inclusions caused by the addition of Al can be reduced, but also A-, C-, and D-based inclusions can be reduced. This is because CO ₂ is released from calcium carbonate, expands rapidly and becomes a foamed state, and in the very vicinity of the substance serving as inclusions, a small, rapid and irregular stirring flow is generated in the molten steel, and It is considered that the chance of collision significantly increased, and the large inclusions floated up and were separated from the molten steel.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modes can be adopted without departing from the gist of the present invention. For example, in the embodiment, CaCO ₃ was used as a gas releasing substance,
carbonates such as gCO ₃ and Na ₂ CO ₃ , SiO ₂
Gases can be generated even from hydrated minerals of the system, and the effect of stirring molten steel can be expected. However, carbonate is more preferable in consideration of the fact that a large amount of gas is generated per added amount, that inert CO ₂ is generated, and that the higher the basicity of slag, the higher the cleaning effect, and the like. In the case of CaCO ₃ , CO
_Since CaO is generated at the same time as the generation of ₂ , CaO is particularly desirable because it fuses with the deoxidized product to form a large slag, and the deoxidized product easily floats.

In the embodiment, Al is used as the deoxidizing substance. However, Si, Mn, Mg or the like may be used as the deoxidizing agent. These may be used alone, in combination of two or more, or in an alloy containing Fe or the like. Further, as for Al, a new lump Al is melted, and in the case of dissolving particulate metal Al, metal aluminum or an aluminum alloy obtained by the atomizing method, aluminum dross generated on the surface of the molten metal is pulverized and processed to have an Al pure content of 20% or more And Al chips generated by machining can be used.

In addition, in the embodiment, the surface of the Al particles
Although a composite deoxidizing refining agent coated with CO ₃ was used,
A method of adding a mixture of Al powder and CaCO ₃ powder,
For example, a method of adding a binder to the mixture and adding a molded product may be used. In the embodiment, the aqueous solution of sodium silicate is used as the binder. However, the binder may be simply wetted with water and hardened. Especially when using a binder,
Substances that emit less smoke during combustion, such as sodium silicate and polyethylene oxide, are more preferable.

[0028]

As described above, according to the method for deoxidizing and refining molten steel of the present invention, it is possible to produce clean steel having extremely high cleanliness without using special out-of-pile refining equipment. And it is easy to produce clean steel in large quantities.

[0029] In particular, the deoxidizing method according to claim 2 or 3
According to the refining method, stirring by CO _{2 and A} by CaO
Since l ₂ O ₃ adsorption proceeds simultaneously, the cleaning effect is extremely high. Further, according to the deoxidizing and refining method of the third aspect, the dispersing effect of Al is extremely high, so that there is a further cleaning effect.

Claims (3)

[Claims] 1. A reaction for producing a deoxidized product by simultaneously adding a gas releasing substance releasing gas in molten steel and a deoxidizing substance combined with oxygen in the molten steel into undeoxidized molten steel. A method for deoxidizing and refining molten steel, wherein a flow of molten steel is given in advance to a local part subjected to a reaction. 2. The method for deoxidizing and refining molten steel according to claim 1, wherein calcium gas is used as the gas releasing substance.
A method for deoxidizing and refining molten steel, comprising simultaneously adding aluminum as the deoxidizing substance to undeoxidized molten steel. 3. The method for deoxidizing and refining molten steel according to claim 2, wherein the composite deoxidizing and refining agent formed into a particulate form mainly comprising the calcium carbonate and the aluminum is introduced into the undeoxidized molten steel. A method for deoxidizing and refining molten steel, characterized by being added.