JPH0663016B2 - Molten steel treating agent for absorbing and floating inclusions and molten steel treating method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a treatment agent for efficiently reducing inclusions in molten steel, and a molten steel treatment method using the treatment agent alone or in combination with other treatment agents. Regarding

[Conventional technology]

When manufacturing steel sheets for automobiles, steel sheets for can manufacturing, etc., the greatest challenge is to reduce oxide inclusions that cause defects such as flaws and cracks in products. Conventionally, in order to reduce the amount of these oxide-based inclusions, Si, Al, Ca or alloys thereof are added to the molten steel to combine these elements with oxygen in the molten steel to form oxides. The levitation method is adopted by using vacuum processing equipment such as RH and DH. However, when using this method,
It is not possible to sufficiently reduce the produced oxide to a level at which a product is satisfactory.

Therefore, as a means for further reducing the inclusions, for example, as described in JP-A-60-59011, slag on the bath surface is not substantially stirred or flowed, and the slag-forming property is good. At least 20% by weight, preferably 40%
A method of adding a treating agent containing CaF ₂ and the remaining component being CaO as a main component, and JP-A-58-34126 and JP-A-61-117209.
As described in Japanese Patent Publication No.
A method has been developed in which a calcined flux containing wt% CaF ₂ is added to molten metal maintained under vacuum conditions.

However, even with these methods, there are the following problems, and a sufficient effect of reducing inclusions cannot be obtained yet.

[Problems to be solved by the invention]

The method disclosed in JP-A-60-19011 was developed for the purpose of desulfurization.

As its potential effect, the treating agent used in this method is Al
_It is also effective for floating inclusions because it is aggregated with various inclusions in molten steel centered on ₂ O ₃ clusters to lower the melting point and then becomes spherical inclusions that are easy to float. Further, in this method, since the slag on the bath surface is not substantially stirred or flowed, there is an advantage that entrapment of ladle slag and the atmosphere can be suppressed. Therefore, for example, medium and high carbon Al-
For steel grades with relatively small amounts of inclusions such as Si-killed steel, the amount of inclusions can be reduced at the same time as desulfurization.

However, the amount of inclusions can be reduced for molten steel, such as ultra-low carbon steel, where the amount of inclusions is relatively large after deoxidation, compared to the case where this treatment method is not used. Can not be reduced to a satisfactory level.

Further, even when medium- or high-carbon Al-Si killed steel or the like is made to have an extremely bottom flow, the treatment agent blown into the bath is agglomerated with oxide inclusions such as Al ₂ O ₃ so that the treatment agent Since the desulfurization ability is reduced, when the amount of inclusions in the bath is large, the desulfurization effect, which is the original purpose, becomes small. Therefore, when melting ultra-low flow steel, the basic unit of processing agent with high CaF ₂ concentration, which has a low melting point, inevitably increases, so the amount of processing agent with high CaF ₂ concentration deposited on the bottom surface of ladle slag. , The melting point of the slag is significantly lowered, and the upper surface of the slag is melted. In such a case, the oxygen in the entire slag can easily move, so that the oxygen easily enters the deoxidized molten steel from the slag. In addition, such molten slag is likely to be entrapped in the bath by vortices generated by the injection flow into the mold or tundish in the subsequent casting stage, and may become a new inclusion. Therefore, in order to efficiently perform both desulfurization and inclusion reduction, it was necessary to develop a new method.

On the other hand, the method disclosed in JP-A-61-117209 is
This is a method of deoxidizing and desulfurizing while reducing the wear of the furnace refractory due to the treating agent. The definition of "deoxidizing" in this method corresponds to "low depletion of inclusions" in the present invention, but the following problems remain from the viewpoint of reducing inclusions.

That is, as a result of various studies by the present inventors,
Al contained in the treating agent having the composition disclosed in JP-A-61-117209
_In terms of ₂ O ₃ absorption capacity, Al ₂ O _{3 in} molten steel is not always required for steel types with essentially many inclusions such as ultra-low carbon steel.
It was found that inclusions such as system inclusions could not be reduced to such an extent that they would not cause any problems in product applications. Further, in order to enhance the effect of absorbing the inclusions of the treating agent, it is effective to blow the treating agent into the bath. At that time, the treating agent after absorbing the inclusions should also be quickly floated and removed. Is an important issue for ensuring the cleanliness of molten steel.

However, since JP-A-61-117209 does not disclose a method for promptly floating and removing the treating agent after absorbing the inclusions, it is essentially necessary to obtain molten steel with high cleanliness. I can't reach it.

Therefore, for steel types that inherently have many inclusions, such as ultra-low carbon steel, the development of new treatment agents with excellent inclusion absorbency and the prompt rise of the treatment agent after inclusions absorption. Substantial effects do not occur without the combined use of new treatment methods that can be removed.

The CaO-CaF ₂ system powder introduced in the examples of JP-A-58-34126 has a CaF ₂ concentration of about 17% and the purpose is to reduce inclusions. Similarly, since the CaF ₂ concentration is high, a large effect of reducing inclusions cannot be expected. Further, the molten steel treatment using the powder with high CaF ₂ concentration is performed while stirring the molten steel and the slag by rotating the impeller on the molten steel surface, but there is a degassing effect, but the effect of floating inclusions is long after the impeller stirring is completed. Appears over time, but high
Since it is a CaF ₂ concentration powder, its effect is small and molten steel with sufficient cleanliness cannot be obtained.

INDUSTRIAL APPLICABILITY The present invention solves various problems in the above-described conventional inclusion reduction of molten steel, and uses the inclusions in the molten steel as a product application even for steel types having essentially many inclusions such as ultra-low carbon steel. To provide a molten steel treatment agent and a molten steel treatment method capable of quickly and economically and efficiently degrading to such an extent that no trouble occurs at all, and further a molten steel treatment method capable of performing desulfurization of molten steel at the same time quickly and efficiently. The purpose is to do.

[Means for solving problems]

In order to achieve the object, the molten steel treating agent for absorbing and floating inclusions of the present invention (hereinafter simply referred to as an inclusion reducing treatment agent) contains CaO and CaF ₂ as main components, and the balance consists of unavoidable components. And, the CaF ₂ concentration in the main component is 1 to 5% by weight.
Is characterized in that.

Further, in the molten steel treatment method of the present invention, the carrier gas blown into the bath floats in the bath and reaches the upper surface portion of the bath under reduced pressure or an inert gas atmosphere, and the slag is substantially present. An agent for reducing inclusions, wherein CaO and CaF ₂ are the main components, the balance is an unavoidable component, and the CaF ₂ concentration in the main components is 1 to 5% by weight, in an inert gas carrier gas. Is blown into the bath.

In this molten steel processing method, the upper surface portion of the blowing before and / or after the bath carrier gas forme blown into the bath to reach emerged through the bath into the bath of the CaO-CaF ₂ treatment agent Is maintained in a reduced pressure or an inert gas atmosphere, and in the bath in which slag is not substantially present, CaO and CaF ₂ are the main components and the balance consists of inevitable components, and the CaF ₂ concentration in the main components is A means for blowing the first desulfurization treating agent of 20% by weight or more into the above-mentioned bath by using an inert gas as a carrier gas may be added.

Further, when performing desulfurization treatment of molten steel in a reaction tank lined with a basic refractory containing MgO, the carrier gas blown into the bath floats in the bath and reaches the top surface of the bath to reduce the pressure or inactivate it. In the bath which is kept in a gas atmosphere and in which slag is not substantially present, an inert gas is used as a carrier gas and consists of CaO, CaF ₂ , MgO and inevitable components, and MgO is 10 to 60% by weight. The ratio of {CaF ₂ / (CaO + Ca
F ₂ )} × 100 = 20 to 80% by weight of the second desulfurizing treatment agent before and / or after the treatment is blown into the bath. It is one of the means of the invention.

Furthermore, the process of blowing the inert gas into the molten steel without substantially stirring or flowing the slag on the bath surface may be performed after any one of the above-mentioned processes.

[Action]

In the present invention, an inclusion reducing treatment agent containing CaO and CaF ₂ as main components and having a CaF ₂ concentration of 1 to 5 wt% in the main components is added to the molten steel. Thereby, the inclusions present in the bath can be absorbed into the treatment agent extremely efficiently.

The present inventors immerse an Al ₂ O ₃ rod having a diameter of 6 mm in various treatment agents held at 1550 to 1600 ° C., and reduce the weight of the Al ₂ O ₃ rod based on the treatment agent of CaO alone. A basic experiment was conducted to compare and measure the velocities, and the Al ₂ O ₃ absorption abilities of the treatment agents were compared and examined.

As a result, as shown in FIG. 1, 1 to 5% by weight of CaO,
It has been found that a treating agent containing a very small amount of CaF ₂ , preferably 2 to 4% by weight, dramatically improves the Al ₂ O ₃ absorbing ability of the treating agent. This is because when CaF ₂ is added to CaO, a part of CaO in the treating agent is melted and wets well with Al ₂ O ₃ , so that the Al ₂ O ₃ absorption reaction of the treating agent is promoted. it is conceivable that. On the contrary, in the range where the CaF ₂ concentration exceeds the weight%, the Al ₂ O ₃ absorption rate ratio is extremely lowered. It is presumed that this is because CaF ₂ inhibits the diffusion of Al ₂ O ₃ into the treatment agent, and the progress of the Al ₂ O ₃ absorption reaction is delayed.

In general, most of Al ₂ O ₃ -based inclusions in the bath have a high melting point and thus are in the form of clusters that are difficult to float, and exist in a non-spherical state in a static bath. However, when Al ₂ O ₃ -based inclusions are absorbed in the treatment agent due to the action of the treatment agent described above, the inclusions become a molten state in the bath, and it is easy to remove the levitation that is observed in a spherical shape in the stationary bath. It changes into inclusions.

As described above, the agent for reducing inclusions of the present invention is Al ₂ O 3.
_{It has} a great effect of absorbing and removing inclusions with respect to the reduction of ₃ inclusions. Further, the present treating agent effectively acts to remove inclusions other than the Al ₂ O ₃ system existing in the bath.

That, FeO present in molten steel before Al deoxidation, as in the FeO-MnO based inclusions and SiO ₂ -MnO-based inclusions, despite the a low-melting stationary bath is observed spherical, Even for inclusions that have a high specific gravity and are difficult to float, the specific gravity of the inclusions is reduced by aggregating with this treatment agent with a low specific gravity,
Elevation is encouraged.

When industrially producing the treatment agent of the present invention, Al ₂ O ₃ , SiO _{2 and the} like are mixed as usual inevitable impurities. It is desirable that the content of each of them be as small as possible.

The present invention also includes a method for maximizing the effects of the above-described inclusion reducing agent.

In this method, when the inclusion reducing agent is blown into the bath, the bath (molten steel) is stirred or flowed without substantially entraining the slag floating on the bath surface in the bath,
A decompression tank or an inert gas atmosphere tank is arranged in the circulation path as shown in FIGS. 2 and 3, and the slag is added to the upper surface portion of the bath where the blowing carrier gas or the levitation promoting gas floats in the bath and reaches it. Is present and a reduced pressure or inert gas atmosphere is formed. According to this method, the slag on the bath surface is not caught in the molten steel due to stirring, and the harmful effect of generating new inclusions can be prevented. In addition,
The apparatus shown in FIGS. 2 and 3 will be described in the section of Examples below.

The inclusion reducing agent thus blown in is present between the lower surface of the slag and the upper surface of the molten steel after absorbing the inclusions. As a result, the oxidizing slag layer on the bath surface
The interfacial reaction between slag and molten steel, which causes unnecessary oxidation of Al, Si, etc., is blocked. Due to this action, the supply of oxygen (oxygen invasion) from the slag on the bath surface is blocked by a low-intensity processing agent which has never been seen before. Further, the effect of absorbing the inclusions of the treating agent is further enhanced by eliminating the offsetting element found in the prior art.

Due to the above action, among the inclusions usually present in the bath,
There are very few clusters and non-spherical ones, and only spherical inclusions that easily float. Then, the spherical inclusions are reduced to a level at which the product is hardly hindered in the stage before casting.

Further, it prevents the decrease in desulfurization ability due to the aggregation of Al ₂ O ₃ -based inclusions in the desulfurization agent during desulfurization, which is seen in the case of the above-mentioned JP-A-60-59011, and also has a melting point. A treatment method was developed to prevent the cleanliness of molten steel from deteriorating when a large amount of desulfurization agent with a low CaF ₂ concentration of low temperature was injected and to efficiently desulfurize to obtain clean molten steel.

Hereinafter, the effects of both the case where the inclusion reducing treatment agent of the present invention is blown before the desulfurization treatment agent is blown and the case where the inclusion reduction treatment agent of the present invention is blown are described in detail.

Before adding the desulfurization agent, CaO with a CaF ₂ concentration of 1 to 5% by weight
-When a CaF ₂ -based high-melting point, low CaF ₂ concentration inclusion reducing agent is added, the effect of the inclusion reducing agent reduces the amount of inclusions in the bath before the desulfurization agent is injected. it can.
This removes obstacles to the desulfurization reaction and the like caused by absorption of inclusions such as Al ₂ O ₃ into the treatment agent that occurs when a desulfurization agent with a low melting point and a high CaF ₂ concentration is blown, and the desulfurization treatment agent is removed. The refining effect of is improved.

In addition, a treatment agent for reducing inclusions with a low CaF ₂ concentration, which has a high melting point,
By interposing in advance between the lower surface of the slag and the upper surface of the molten steel, even if the desulfurization agent having a low CaF ₂ concentration and having a low melting point is deposited on the lower surface of the slag on the bath surface during the desulfurization treatment performed subsequently, the melting point of the slag The decrease can be prevented as much as possible. By this action, even when a large amount of desulfurization agent having a high CaF ₂ concentration with a low melting point is blown in, oxygen can be prevented from entering the molten steel from the slag.

On the other hand, after adding the desulfurizing agent, the CaF ₂ concentration of 1 to 5% by weight
When a CaO-CaF ₂ system high melting point, low CaF ₂ concentration inclusion reducing agent is added, the Al ₂ O ₃ system in the bath cannot be completely absorbed by a desulfurization agent with a low melting point and high CaF ₂ concentration. As shown in FIG. 1, the inclusions can be almost eliminated. Further, the melting point is lowered by the desulfurization treatment agent, and the inclusion reduction treatment agent having a high melting point and low CaF ₂ concentration can be interposed on the lower surface of the bath-melted slag. This can prevent the inclusion of slag due to the vortex of the injection flow in the casting stage that occurs when only the desulfurization treatment agent is added, and suppress the generation of new inclusions.

As the desulfurization treatment agent and the desulfurization treatment method used at this time, the desulfurization treatment method disclosed in JP-A-60-59011 or the desulfurization treatment proposed in JP-A-60-41018 is used. Any of the treating agents can be used. Particularly, when the treatment is carried out in a reaction tank lined with a basic refractory containing MgO which is usually used for molten steel treatment, Japanese Patent Application No. 60-4
By using the desulfurization treatment agent proposed in Japanese Patent No. 1018, it is possible to prevent melting damage of the refractory during the desulfurization treatment.

Due to the operation described above, the present invention brings about an excellent effect of reducing inclusions, whereby the desulfurization obstacles that have been caused by inclusions in the related art can be removed and desulfurization can be efficiently performed.

As described above, the CaF ₂ concentration of the present invention is 1 to 5% by weight.
The effect of the O-CaF ₂ high melting point, low CaF ₂ concentration inclusion reducing agent is that the inclusions that are difficult to float and separate are spheroidized or have a low density that makes them difficult to wet with molten steel. It is to promote levitation separation. This action works even more effectively by blowing only an inert gas into the molten steel after carrying out the previous treatment.

That is, as a result of repeated studies by the present inventors, when an inert gas is blown into the molten steel under the condition that slag does not substantially exist on the bath surface, the inclusions, particularly spherical inclusions, are reduced. I found that the effect was remarkable. This is because the strong agitation of the molten steel caused by the blowing of the inert gas promotes the agglomeration of spherical inclusions and the inclusion of gas bubbles blown on the surface and inside of the low-melting spherical inclusions. This is because the floating of the spherical inclusions is promoted by the action of reducing the apparent density of the objects. The effect of this inert gas injection is small for Al ₂ O ₃ clusters. Therefore, in order to reduce all the inclusions such as spheres and Al ₂ O ₃ clusters, only the CaO-CaF ₂ inclusion reducing agent with a CaF ₂ concentration of 1 to 5% by weight is blown, or the inclusions are reduced. It is necessary to blow the treatment agent before and / or after the desulfurization treatment agent, and after absorbing the Al ₂ O ₃ clusters in the treatment agent to make the inclusions spherical, then blow only the inert gas. Is.

The effect of reducing the spherical inclusions due to the blowing of the inert gas is obtained by floating the inert gas at a position where there is substantially no slag on the bath surface. For example, FIG. 6 shows a conventional ladle refining apparatus. In this case, an inert gas is blown into the molten steel 5 contained in the ladle 1 from a blowing pipe 3.

In such a reaction vessel, the slag 4 on the bath surface is caught in the molten steel 5 and, conversely, the amount of inclusions in the bath increases. Therefore, it is difficult to obtain the effects of the present invention. The reference numeral 18 in FIG. 6 is a lid provided on the ladle 1.

Further, the molten steel circulation path in the present invention is formed in a decompression tank or an inert gas atmosphere tank. This makes it possible to prevent oxygen from entering the molten steel from the atmosphere where slag does not substantially exist on the bath surface, so that inclusions are effectively reduced. In addition, the circulation path that blocks the invasion of oxygen simultaneously advances the degassing and decarburization reactions, and is therefore preferable in reducing the concentrations of nitrogen, hydrogen, carbon and the like.

The inclusion reduction treatment agent and the desulfurization treatment agent used in the present invention can be used in any form of a mixture of CaO, CaF ₂ and / or MgO, a fired body, and a premelted body.

Further, when the molten steel is treated while the supply amount of the treatment agent is largely changed with time in this manner, it is necessary to switch the supply of the treatment agent quickly and appropriately. Therefore, the present inventor has developed that the cutting of each processing agent hopper is independently performed based on the information of the processed molten steel.
As a result, appropriate treatment can be performed moment by moment without being affected by the state of molten steel in the previous stage. For example, without being dragged by the CaF ₂ concentration in the desulfurization process,
A low CaF ₂ concentration can be maintained in the inclusion reduction treatment step. Therefore, molten steel is processed with high efficiency in each process.

〔Example〕

Next, each embodiment of the present invention is shown in Tables 1 to 6 and 2 to 5.
A detailed description will be given with reference to the drawings.

Here, the first embodiment is the claims 1 and 2 of the present invention, the second embodiment is the fourth and sixth claims, and the third embodiment is the third.
It corresponds to the terms, the fifth term, and the seventh term, respectively. Also the fourth
The description relating to the figures corresponds to an exemplary device for carrying out the method of the invention.

Example 1 In this example, an apparatus equipped with a ladle 1, a reaction vessel 2 and a blowing tube 3 as shown in FIG. 2 was used. here,
The reaction tank 2 is a vacuum degassing tank. Also, the slag 4 floats only on the surface of the molten steel 5 in the ladle 1, and the reaction tank 2
Is substantially absent on the molten steel surface inside. Then, the treating agent is blown from the blowing pipe 3 using Ar gas as a carrier gas,
A low carbon Al killed steel, which is a material for tinplate, was manufactured.

The following Table 1 shows the composition of the treating agent used in Experimental Examples A and B of Example 1.

CaF ₂ was contained in the treating agents of Experimental Examples A and B in an amount of 2% by weight and 4.5% by weight, respectively, and the main components CaO and CaF ₂
In addition, inevitable components are Al ₂ O ₃ , SiO ₂ and MgO in total of 2
It was contained by weight%. The unit consumption of the treating agent was 1.1 kg / ton-molten steel.

As a comparative example, the equipment shown in FIG. 2, the treating agent blowing conditions, and the treating agent basic unit were the same as in the experiment examples A and B, and only the composition of the treating agent was changed. And
Then, in the same manner as in Example 1, a low carbon Al killed steel as a material for tin plate was manufactured. The compositions of the treating agents used in Experimental Examples L, M and N are also shown in Table 1 in comparison with Example 1. That is, in the treatment agents used in Comparative Examples L, M and N
The CaF ₂ concentrations are 0, 10, and 40% by weight, respectively, which is different from Experimental Examples A and B. In addition, also in the comparative example, Al ₂ O ₃ and SiO ₂ were contained in total of 2% by weight as unavoidable components. The amount of treated molten steel is 340 tons in both the example and the comparative example.

Inclusions present in molten steel after being treated with Experimental Examples A, B, L, M, N were classified into spherical with a detection frequency of inclusions of 1 μm or more, non-floating non-spherical, and Al ₂ O ₃ clusters. It is shown in FIG. The inclusion detection frequency in this case is the ratio of the number of inclusions electrolytically extracted from the quenched sample collected from the treated molten steel, and is a relative value when the total number of inclusions in Comparative Example L is 10.

As is apparent from FIG. 5, in Experimental Examples A and B in which the inclusion reducing treatment agent of the present invention was blown, the treatment agent basic unit was 1 kg / t.
Although it is a small amount with molten steel, it is non-spherical after processing, Al ₂ O
_{The number of 3} clusters is significantly reduced as compared with the experimental examples L, M, and N. In particular, in Example A in which the CaF ₂ concentration in the treating agent was 2% by weight, Al ₂ O ₃ clusters were eliminated.
In addition, in the case of Experimental Examples A and B, the total number of inclusions is slightly reduced as compared with Experimental Examples L, M, and N.

Further, an experiment was conducted using a device having a structure shown in FIG. 3 instead of the device shown in FIG. This device is ladle 1
The inside is divided into a main body 1a and a circulation chamber 1b, and a lower passage 6a is provided between them.
And the upper passage 6b. Then, the opening of the blowing pipe 3 is desired near the lower passage 6a, and the treating agent is blown together with the carrier gas. As a result, a circulating flow is generated in the molten steel 5 as shown by the arrow, and the main suspension 1a and the circulation chamber are
Cycles to and from 1b. A bolus brick 7 is arranged at a position corresponding to the bath surface of the molten steel 5a in the circulation chamber 1b,
The carrier gas blown from the blow pipe 3 is discharged from the exhaust system 8 through the porous brick 7 to the outside of the system. On the other hand, the slag 4 floats on the bath surface of the molten steel 5 in the main body 1a. The treated molten steel 5 is discharged from the tap hole 9 provided on the bottom wall of the main body 1a.

Using this device, the treatment agent is introduced from the blow pipe 3 into the circulation chamber 1b.
The same result as when the apparatus shown in FIG. 1 was used was also obtained when it was fed into the molten steel 5a.

Example 2 In order to produce a material for API × 70 class sour-resistant line pipe, 340 tons of medium carbon Al-Si killed steel was used in accordance with the treatment pattern shown in Table 2 to reduce inclusions. The treatment agent and the first desulfurization treatment agent or the second desulfurization treatment agent were continuously blown using argon gas as a gas carrier gas for 25 charges each.

In this case, the inclusion reducing agent is mainly composed of CaO and CaF ₂ , and the concentration of CaF ₂ is 2% by weight. The first desulfurizing agent is mainly composed of CaO and CaF _{2. 2} concentration is 4
0% by weight is used, and the first desulfurization treatment agent is C
The main components are aO, CaF ₂ , and MgO, and the weight ratio is {CaF ₂ / (CaO + Ca
F ₂ )} × 100-40% and containing MgO at 10 wt% was used. Each of these treatment agents contained Al ₂ O ₃ and SiO ₂ as an inevitable component in a total amount of 2% by weight.

The equipment shown in Fig. 4 is the same as the treatment equipment shown in Fig. _{2 but with} a hopper for CaF ₂ .
10, a hopper 11 for CaO, a hopper 12 for MgO, a molten steel sampling analyzer 13, a processing pattern setting device 14, and processing agent cutting feeders 15a, 15b, 15c. Also,
The signal A from the molten steel sampling analyzer 13 is input to the processing pattern setter 14, and the setting processing pattern of the processing pattern setter 14 which is input as the setting signal B in advance is compared with the operation command device 16 every moment. This makes Ca
F _2, CaO, and calculates the addition timing and the required mixing ratio of MgO. And, to this, blow pipe 3 from hopper 10,11,12
Treating agent by subtracting the conveying time of the treating agent cutout feeders 15a, 15b, a cut command C _1, C _2, C ₃ to 15c emit. Furthermore, the lining of the reaction tank 2 maintained in a reduced pressure atmosphere by the pressure reducing device 17 contains 74% by weight of MgO.
Using gO-Cr ₂ O ₃ based basic refractory.

Further, as a comparative example, as in this example, the equipment shown in FIG. 4 was used to perform a treatment in which only the first or second desulfurizing treatment agent was blown, and this was designated as Experimental Examples O and P. Then, we conducted an experiment with 25 charges each. In this case, as the first and second desulfurizing treatment agents, those having the same composition as in this example were used. In addition, the target steel type of the comparative example is also the same as the present example API × 70 class medium carbon Al for sour line pipe
-Si killed steel.

The basic unit of each treating agent in Examples and Comparative Examples is shown in Table 2. Table 3 shows an example of typical molten steel [S] levels before and after the treatment in Examples C to H and Comparative Examples O and P, and an example of the inclusion detection frequency after the treatment is spherical and non-spherical. , Al ₂ O ₃ clusters are shown in FIG.

As is apparent from FIG. 5, C to C in the example in which the inclusion reducing agent blowing, the first desulfurizing agent blowing, and the second desulfurizing agent blowing were combined in various ways. It can be seen that in the case of H, the total number of inclusions, the non-spherical shape, and the Al ₂ O ₃ cluster are significantly reduced, as compared with Comparative Examples O and P in which only the desulfurizing treatment agent is blown. In particular, in Experimental Examples E and H in which the inclusion reduction treatment agent was blown before and after the desulfurization treatment agent, the inclusion reduction effect was large.

Further, as is clear from Table 3, in Experimental Examples C, E, F, and H in which the inclusion reducing treatment agent was blown in before the addition of the first desulfurization treatment agent or the second desulfurization treatment agent. As a result, the level of molten steel [S] after the treatment is also reduced as compared with the comparative example.

Further, the maximum melting loss of the refractory per treatment, which was measured at a position near the bath surface in the reaction vessel, was measured after continuously treating 25 treatments of each of C to H in this example. Indicated.
From Table 4, in the case of Experimental Examples F, G, and H in which the second desulfurization treating agent containing MgO was injected as the desulfurization treating agent,
It can be seen that the melting loss of the refractory material in the reaction layer could be reduced as compared with C, D, and H that were desulfurized by the first desulfurization treatment agent.

Example 3 As in the case of Example 2, using the equipment shown in FIG. 4, according to the treatment pattern shown in Table 5, the inclusion reducing treatment agent, the first desulfurization treatment agent, and the second desulfurization treatment agent were used. After the argon gas was blown into the bath as a carrier gas, only the argon gas was blown from the blowing tube 3 at a flow rate of 2000 Nl / min for 5 minutes.

In this case, the composition of the inclusion reduction treatment agent, the first desulfurization treatment agent, and the second desulfurization treatment agent was the same as in Example 2, and the molten steel amount was 340 tons. Further, the target steel type of Experimental Example I is a low carbon Al killed steel of a tin material similar to that of Examples A and B, and the target steel type of Experimental Examples J and K is API × 7 as in C to H of the Examples.
It is a medium carbon Al-Si killed steel used as a material for class 0 sour line resistant pipes.

Inclusion detection frequencies after treatment in Experimental Examples I to K are classified into spherical, non-spherical, and Al ₂ O ₃ clusters and shown in FIG. As is clear from FIG. 5, in Experimental Examples I to K, not only spherical and Al ₂ O ₃ clusters but also the number of spherical inclusions was significantly reduced, and steel with extremely high cleanliness was produced. I was able to.

Table 6 shows [S] of the molten steel before and after the treatment in Experimental Examples J and K.
It shows the level. As you can see in this table,
The [S] level after the treatment was 1 PPm in each case, and it was possible to produce an extremely low sulfur and high cleanliness steel.

[Effects of the Invention] As described above, the agent for reducing inclusions of the present invention is
Consists of CaO and CaF ₂ and other inevitable components, and
_{Since the} concentration of ₂ is 1 to 5% by weight, the inclusions in molten steel centered on Al ₂ O ₃ clusters are treated even for steel types such as ultra-low carbon steels that have many inclusions. It can be rapidly, accurately and economically reduced to such an extent that it is absorbed in the agent and does not cause any trouble in product use.

Further, in the molten steel treatment method for absorption / floating separation of inclusions of the present invention, the slag existing on the molten steel surface is not caught in the bath, and further, in order to avoid the molten steel and the slag interfacial reaction, With substantially no slag present in the molten steel upper surface where the blown carrier gas or the floatation promoting gas reaches,
Since the above-mentioned treatment agent for reducing inclusions is blown into the bath, interruption of the oxygen supply from the slag floating on the bath surface can be achieved with a treatment unit of a low basic unit which has never been seen before. Therefore, without being offset by oxygen intrusion,
The effect of absorbing the inclusions of the above-mentioned treatment agent can be exerted.

Further, according to the present invention, since the above treatment method is carried out before and / or after the desulfurization treatment agent is blown, an extremely low copper sulfide having excellent cleanability can be obtained quickly and economically.

In addition, reduction of temperature drop of molten steel caused by side, reduction of treatment time, reduction of treatment cost as a result of process omission due to process integration when using a degassing tank such as RH or DH as reaction environment Is planned. As described above, the industrial effect of the present invention is great.

Then, by using a device that can control the cutting feeder provided in each processing agent hopper, each process can be accurately performed under desired conditions without being affected by the preceding process. became.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the CaF ₂ concentration in the treating agent and the Al ₂ O ₃ absorption rate of the treating agent obtained in the basic experiment, and FIG. 2 shows the equipment used in the first embodiment of the present invention. , FIG. 3 shows the first of the present invention.
The other type of equipment used in the examples is shown, FIG. 4 shows the equipment used in the second example of the present invention, and FIG. 5 is the inclusions after treatment in the examples and comparative examples of the present invention. Fig. 6 is a diagram showing the detection frequency classified into spherical inclusions, non-spherical particles that are difficult to float, and Al ₂ O ₃ clusters. Fig. 6 shows the treatment by stirring the slag on the bath surface that has been widely used in the past. It is a side sectional view of a ladle refining device for performing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Nagata 1 Nishinosu, Oita City, Oita Prefecture Shin-Nippon Steel Co., Ltd. Oita Steel Works (56) Reference JP-A-58-34126 (JP, A)

Claims (7)

[Claims] 1. A main component of CaO and CaF ₂ , the balance being an unavoidable component, and a CaF ₂ concentration in the main component of 1 to 5
A molten steel treatment agent for absorbing and floating separation of inclusions, characterized by being in a weight percentage. 2. The above-mentioned bath in which the carrier gas blown into the bath floats in the bath and reaches the upper surface of the bath under reduced pressure or an inert gas atmosphere, and in which slag is not substantially present. In addition, CaO and CaF ₂ with an inert gas as a carrier gas
And a balance of unavoidable components, and the CaF ₂ concentration in the main component is 1 to 5% by weight. A molten steel treatment agent for absorbing and floating inclusions is blown into the molten steel treatment method. 3. A carrier gas in which the carrier gas blown into the bath floats in the bath and reaches the upper surface of the bath under reduced pressure or an inert gas atmosphere, and slag is not substantially present in the bath. In addition, CaO and CaF ₂ with an inert gas as a carrier gas
Of the slag on the bath surface after injecting a molten steel treating agent for absorbing and floating separation of inclusions having a CaF ₂ concentration of 1 to 5 wt% in the main component A method for treating molten steel, characterized in that an inert gas is blown into the molten steel without substantially stirring or flowing. 4. A carrier gas blown into the bath floats in the bath and reaches the upper surface of the bath under reduced pressure or an inert gas atmosphere, and without causing slag to substantially exist, CaO and CaF ₂ as a main component, and the balance of inevitable ingredients, and CaF ₂ in the main component consisting of the CaO and CaF ₂
Before and / or after blowing the desulfurization treatment agent having a concentration of 20% by weight or more into the bath with an inert gas as a carrier gas, CaO and CaF ₂ as the main components with the inert gas as a carrier gas, and the balance Consists of unavoidable components,
A method for treating molten steel, characterized in that a molten steel treating agent for absorbing and floating inclusions having a CaF ₂ concentration of 1 to 5% by weight is blown. 5. The carrier gas blown into the bath floats up in the bath and reaches the upper surface of the bath under reduced pressure or an inert gas atmosphere, and without causing slag to substantially exist. and CaF ₂ as a main component, and the balance of inevitable ingredients, and CaF ₂ in the main component consisting of the CaO and CaF ₂
Before and / or after blowing the desulfurization treatment agent having a concentration of 20% by weight or more into the bath with an inert gas as a carrier gas, CaO and CaF ₂ as the main components with the inert gas as a carrier gas, and the balance Is an unavoidable component, and after injecting a molten steel treating agent for inclusion absorption / floating separation with CaF ₂ concentration of 1 to 5 wt% in the main component, the slag on the bath surface is substantially stirred. Alternatively, a method for treating molten steel, characterized in that an inert gas is blown into the molten steel without flowing. 6. When performing a desulfurization treatment of molten steel in a reaction tank lined with a basic refractory containing MgO, the carrier gas blown into the bath floats in the bath and reaches a reduced pressure on the upper surface of the bath. Alternatively, it is kept in an inert gas atmosphere, and without causing slag to substantially exist, it is composed of CaO, CaF ₂ , MgO and an unavoidable component with an inert gas as a carrier gas, and MgO is 10 to 60% by weight. The ratio of {CaF ₂ / (CaO + Ca
F ₂ )} × 100 = 20 to 80% by weight of a desulfurization treatment agent before and / or after the treatment is blown into the bath, with CaO and CaF ₂ as the main components using an inert gas as a carrier gas and the balance being unavoidable. A molten steel treatment method comprising the steps of: injecting a molten steel treating agent for absorbing and floating inclusions, which is composed of the components and has a CaF ₂ concentration of 1 to 5% by weight. 7. When performing a desulfurization treatment of molten steel in a reaction tank lined with a basic refractory containing MgO, the carrier gas blown into the bath floats in the bath and reaches the upper surface of the bath to reduce the pressure. Alternatively, it is kept in an inert gas atmosphere, and without causing slag to substantially exist, it is composed of CaO, CaF ₂ , MgO and an unavoidable component with an inert gas as a carrier gas, and MgO is 10 to 60% by weight. The ratio of {CaF ₂ / (CaO + Ca
F ₂ )} × 100 = 20 to 80% by weight of a desulfurization treatment agent before and / or after the treatment is blown into the bath, with CaO and CaF ₂ as the main components using an inert gas as a carrier gas and the balance being unavoidable. Bubbling a molten steel treating agent for absorbing and floating inclusions, which is composed of the above components and has a CaF ₂ concentration of 1 to 5% by weight, and further without substantially stirring or flowing the slag on the bath surface. ,
A method for treating molten steel, characterized in that an inert gas is blown into the molten steel.