JPH0312126B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for efficiently reducing inclusions in molten steel. Conventional technology In the fields of steel sheets for automobiles, steel sheets for can manufacturing, etc.
Reducing oxide inclusions that cause defects and cracks in products has become the biggest challenge. Conventionally, in order to reduce oxygen (hereinafter referred to as O) in steel, Si,
By adding Al, Ca or their alloys to molten steel, these elements are combined with oxygen in the steel bath,
A method is adopted in which the generated oxide is floated using vacuum processing equipment such as RH and DH. However, in this method, it is not possible to reduce the generated oxides to a level that is satisfactory as a product. Therefore, as a means to further reduce inclusions,
For example, a treatment method in which a treatment agent is added under vacuum to promote the floating of the generated oxide
13767), a deoxidizing treatment method in which a CaO-based treatment agent is injected into molten steel in a ladle together with a carrier gas (Special Publication No. 1983-
22765), ladle slag during in-die extraction treatment,
Treatment method that can suppress atmospheric entrainment (patent application 1983)
-166079) etc. were developed. However, these methods have the following problems, and it has not yet been possible to obtain a sufficient effect of reducing inclusions. Problems to be Solved by the Invention () The method shown in Japanese Patent Publication No. 56-13767 places the treatment agent used to absorb inclusions on the molten steel, so that sufficient contact with the inclusions in the molten steel can be achieved. absorption rate is low. In addition, Al ₂ O ₃ in the CaO-Al ₂ O _3- based slag forming agent used as one of the processing agents is
It interferes with the absorption of cluster-like and non-spherical Al ₂ O ₃ -based inclusions, which are the main inclusions in molten steel. () Oxidizing slag generated during oxygen blowing is substantially present on the received molten steel in the ladle. This oxidizing slag generates new inclusions by supplying oxygen to the molten steel and entraining the slag itself into the molten steel, which adversely affects the inclusion reduction effect of the treatment agent. Therefore, as shown in Japanese Patent Publication No. 56-13767, when a treatment agent is added to the upper surface of molten steel, the effect of the treatment agent is inhibited by the ladle slag. For this reason, methods have been devised to remove the oxidizing slag before treatment, but these methods lack economic efficiency due to equipment costs and the need to compensate for the drop in molten steel temperature due to heat dissipation after slag removal. () The method shown in Japanese Patent Publication No. 59-22765 uses the turbulence of the molten steel surface caused by strong stirring of an inert gas injected as a carrier gas to remove gas components from the atmosphere to the molten steel, especially oxygen and nitrogen (hereinafter referred to as Since the absorption of N (referred to as N) and the entrainment of slag into the steel bath are unavoidable, new inclusions are generated, and this method cannot be used for refining low-nitrogen steel or low-hydrogen steel. () The method shown in Japanese Patent Application No. 58-166079 was developed for the purpose of desulfurization. As a potential effect, the treatment agent of this method aggregates and coalesces with various inclusions in the molten steel, mainly Al ₂ O ₃ clusters,
Since the spherical inclusions are formed into spherical inclusions that are easy to float after lowering the melting point, it is also effective in floating inclusions. Furthermore, since this method does not substantially stir or flow the slag on the bath surface, it has the advantage of suppressing the entrainment of ladle slag and the atmosphere. Therefore, for example, medium- and high-carbon Al-Si with a relatively small amount of inclusions
For killed steel, etc., inclusion reduction can be expected in the same way as desulfurization. However, in the case of molten steel, such as ultra-low carbon steel, which has a relatively large number of inclusions after deoxidation, although the amount of inclusions is reduced compared to when this treatment method is not used, it does not satisfy the inclusion defects of the steel plate. However, it has not been possible to reduce it to the extent that it could be. The present invention solves the above-mentioned conventional problems in reducing inclusions in molten steel, and even for steel types that inherently have many inclusions, such as ultra-low carbon steel, inclusions in molten steel can be used in products. The aim is to quickly, economically and efficiently reduce the amount of water used to reduce the amount of water used in the production process, to the extent that no problems occur at all. Means for Solving the Problems The present invention provides (1) to substantially remove the processing agent that has absorbed slag or inclusions onto the upper surface of the bath where the carrier gas blown into the bath floats within the bath and reaches the bath; CaF ₂ and CaO are the main components and the remainder is unavoidable components, and the above-mentioned CaF ₂ and CaO
After blowing a processing agent whose main components have _{a CaF 2 concentration} of 20% by weight or less into the bath using an inert gas as a carrier gas, and a method for reducing inclusions in molten steel, characterized in that a treatment agent having a CaF ₂ concentration of more than 20% by weight in the main components consisting of CaF ₂ and CaO is blown into the bath using an inert gas as a carrier gas. (2) In the first step, CaF ₂ and CaO are the main components, and the remainder is unavoidable components, and the above CaF ₂
After blowing a treatment agent having a CaF ₂ concentration of more than 20% by weight in the main components consisting of The above-mentioned CaF ₂ and CaO are the main components, with the remainder being unavoidable components, and the treatment agent that has absorbed slag or inclusions is not substantially present on the upper surface of the bath that floats through the bath and reaches the upper surface of the bath. ₂ and CaO
A method for reducing inclusions in molten steel, characterized in that a treatment agent having a concentration of CaF ₂ in the main component consisting of 20% by weight or less is blown into the bath using an inert gas as a carrier gas. (3) The carrier gas blown into the bath floats in the bath and reaches the upper surface of the bath, where the treatment agent that has absorbed slag or inclusions is not substantially present, and mainly CaF ₂ and CaO are removed. component and the remainder consists of unavoidable components, and the above CaF ₂ and CaO
After blowing into the bath a treatment agent having _{a CaF 2 concentration} of 20% by weight or less in the main components, using an inert gas as a carrier gas, , and a treatment agent having a CaF ₂ concentration of more than 20% by weight in the main components consisting of CaF ₂ and CaO is blown into the bath using an inert gas as a carrier gas, and then the slag on the bath surface is substantially stirred. Or, a method for reducing inclusions in molten steel, characterized by stirring the molten steel with an inert gas without causing it to flow. (4) In the first step, the main components are CaF ₂ and CaO, and the remainder is unavoidable components, and the above CaF ₂
After blowing a processing agent having a CaF ₂ concentration of more than 20% by weight in the main components consisting of The above-mentioned CaF ₂ and CaO are the main components, with the remainder being unavoidable components, and the treatment agent that has absorbed slag or inclusions is not substantially present on the upper surface of the bath that floats up and reaches the bath. ₂ and CaO
A treatment agent having a concentration of CaF ₂ in the main component consisting of 20% by weight or less is blown into the bath using an inert gas as a carrier gas, and then without substantially stirring or fluidizing the slag on the bath surface, This is a method for reducing inclusions in molten steel, characterized by stirring the molten steel with an inert gas. Function The present invention uses a composition containing CaO-CaF ₂ as a main component as a treatment agent to be blown into molten steel to reduce inclusions, and CaF ₂ is expressed as (%CaF ₂ )/{( %CaO) + (%CaF ₂ )}≦0.2. This increases the amount of Al ₂ O ₃ inclusions absorbed into the treatment agent particles blown into the molten steel, as shown in the example of Al ₂ O ₃ inclusions in FIG. In this way, once the inclusions are absorbed by the treatment agent, the high-melting-point Al ₂ O ₃ inclusions, which are difficult to float in the form of clusters and non-spherical even in the static bath, become molten and In this case, the particles change into spherical inclusions that float easily and float to the surface. Furthermore, FeO present in molten steel before Al deoxidation,
Even for FeO-MnO inclusions and SiO ₂ -MnO inclusions, which have a low melting point and are observed as spherical in a static bath, they have a high specific gravity and are difficult to float. It aggregates with small processing agents, reduces the specific gravity of inclusions, and promotes flotation. In addition, impurities that are usually unavoidably contained in the processing agent used in the present invention include Al ₂ O ₃ ,
There are SiO ₂ , MgO, etc., and their total content is 5% or less in weight concentration. In the present invention, when the above-mentioned treatment agent is blown into the bath, the bath (molten steel) is stirred or fluidized so that the slag on the bath surface is not substantially involved in the bath. As shown in the figure, an RH degassing tank is used to form a state in which slag does not exist on the upper surface of the bath where the carrier gas or floatation promoting gas floats through the bath and reaches it, and is blown into the molten steel. By doing so, it is possible to prevent the harmful effect of stirring the slag 8 on the bath surface of the ladle 1 and generating new inclusions. Further, the injected treatment agent is interposed between the lower surface of the slag and the upper surface of the molten steel after the inclusions are absorbed. By doing this, the oxidizing slag layer on the bath surface is absorbed by the molten steel.
Blocks the slag-molten steel interface reaction that contributes to unnecessary oxidation of Al, Si, etc. Through this action, blocking of oxygen supply (oxygen intrusion) from the slag on the bath surface is achieved using a treatment agent with an unprecedentedly low unit consumption, and there is no countervailing factor for the inclusion absorption effect of the treatment agent described above. It increases further. Due to the above-mentioned effects, the amount of clusters and non-spherical inclusions that normally exist in the bath becomes extremely small, and the proportion of easily floating spherical inclusions increases. These spherical inclusions will be reduced to a level where they will hardly cause any trouble to the product by the time of casting, but after blowing in the treatment agent, inert gas When injected into molten steel, it promotes agglomeration and coalescence of spherical inclusions and makes it easier for the inclusions to float, resulting in a further effect of reducing inclusions. Furthermore, if a reduced pressure tank or an inert gas atmosphere tank is used as a circulation path for molten steel in the present invention, it is possible to prevent oxygen from entering the molten steel from the atmosphere, which is effective in reducing inclusions. Further, since the degassing reaction proceeds at the same time, the temperature of nitrogen, hydrogen, etc. is also reduced, which is preferable. In addition, CaO− containing _CaF2 with a weight concentration of 20% or more
The method shown in Japanese Patent Application No. 166,079/1982 in which CaF ₂ is added cannot achieve the great effect of reducing inclusions seen in the present invention for the following reasons. (i) As shown in FIG. 1, the inclusion absorption effect of the treatment agent decreases when the weight concentration exceeds 20%. (ii) When a treatment agent with a high concentration of CaF ₂ is deposited on the lower surface of the slag on the bath surface, the melting point of the slag decreases significantly, and the upper surface of the slag is melted. This action facilitates the movement of oxygen in all the slag,
Oxygen easily enters the molten steel from the slag. However, in the method of the present invention, the CaF ₂ concentration
(i) above by performing a desulfurization treatment by adding a CaO-CaF ₂ -based processing agent with a CaF ₂ concentration of 20% by weight or more after treatment with a CaO-CaF ₂ -based processing agent of 20% by weight or less,
Problem (ii) is solved and an excellent inclusion reduction effect can be achieved. Examples The apparatus shown in FIG. 3 was used in the examples of the first to fourth aspects of the present invention. As shown in Table 1, processing was performed in which processing agents of different compositions were continuously blown into the bath. That is, in Examples V and W of the present invention, after the fourth step of the present invention is carried out as a treatment, the subsequent second step is performed.
The process uses a CaO-CaF _{2 -} based treatment agent ((%CaF ₂ )/{(%CaO) + {%CaF ₂ )}=0.45, 0.51) containing 45 and 50% by weight of CaF 2 for the purpose of desulfurization. Blowing The treatment according to the first invention was carried out. Further, in Examples X and Y of the second invention of the present invention, CaO-CaF ₂ -based processing agents containing 45 and 50% by weight of CaF ₂ ((%CaF ₂ )/{(%CaO + (%CaF ₂ )}=0.45, 51) was blown into the desulfurization treatment, and inclusion removal treatment was then carried out in the subsequent treatment.Furthermore, in Examples W and Y of the present invention, after the completion of the treatment, the inclusions were removed. Flow rate from pipe 3
3rd and 4th by blowing Ar gas at 1800Nl/min for 5 minutes.
Two treatments were carried out for the invention. Also, as a comparative example, using the equipment shown in Figure 3.
Treatment was performed using a CaO-CaF ₂ -based treatment agent containing 45% by weight of CaF ₂ ((%CaF ₂ )/{(%CaO) + {%CaF ₂ )}=0.45). Table 1 shows the processing conditions for the inventive examples and comparative examples.
In the example of the present invention, changes in the composition of the processing agent between treatments were accepted in a separate hopper.
CaF ₂ and CaO were cut out from each hopper in accordance with the required blending ratio that changed as the process changed over time, and the blending ratio of CaO and CaF ₂ was continuously changed. Or, in the treatment agent, the inevitable components are Al ₂ O ₃ 0.42% by weight, SiO ₂ 3.04% by weight, and
It contained 0.43% by weight of MgO. In addition, in both the present invention example and the comparative example,
After deoxidizing with Al and Si, each treatment was started. The composition of the molten steel used was [C]: 0.08~
0.1% by weight, [Si]: 0.15-0.23% by weight, [Mn]:
0.92 to 1.28% by weight, [Al]: 0.02 to 0.06% by weight, and the molten steel components remained within these ranges both before and after treatment. Further, the ultimate vacuum degree in the circulation path 2 of the equipment shown in FIG. 3 was 1.0 to 1.2 Torr. Table 2 also shows the molten steel [S] concentration and total oxygen amount before and after treatment for the inventive examples and comparative examples. In addition, the detection frequency of inclusions after treatment was determined by spherical, non-spherical, and
It is classified into Al ₂ O ₃ clusters and shown in Figure 2. As is clear from Table 2, in the examples V, W, X, and Y of the present invention, the molten steel [S] concentration after treatment was reduced to 1 to 3 ppm, and the total oxygen amount was reduced to 9 to 13 ppm. In addition, as shown in FIG. 2, the frequency of detection of non-spherical and Al ₂ O ₃ clusters was also small. In particular, W, which was subjected to Ar injection after adding the processing agent,
In and Y, spherical inclusions were also reduced, the total inclusion detection frequency became 2 or less, and extremely low sulfur high cleanliness steel was obtained. Further, as shown in Examples V and W of the first invention of the present invention, when the treatment is performed subsequent to the treatment, V and W significantly reduce Al ₂ O ₃ type inclusions in the bath due to the treatment. Because of the reduction, the desulfurization consumption rate has improved. In addition, since inclusion flotation treatment is performed for X and Y after the desulfurization treatment, oxidized inclusions generated by the oxygen brought in by the desulfurization flux also float, and the total amount of oxygen in the molten steel after treatment reaches a low level of 9 ppm or less. did. On the other hand, in the comparative example Z, as is clear from Table 2 and Figure 2, the molten steel [S] concentration after treatment was
Although the total oxygen content was 3 ppm, the total oxygen content and inclusion detection frequency were high, and an ultra-low sulfur steel with few inclusions like the example of the present invention could not be obtained. In addition, the apparatus shown in FIG. 3 includes, in addition to the circulation path 2, the blowing pipe 3, the container 1, and the pressure reducing device 40, a CaF ₂ hopper 50,
Inputting the signals from the CaO hopper 51, the molten steel sampling analyzer 52, the processing pattern setting device 53, the processing agent cutting feeders 54, 55, and the sampling analyzer 52, and comparing them with the processing pattern set by the setting device 53 from time to time, Calculate the required blending ratio and addition timing of CaF ₂ and CaO, and add Hopper 5 to this.
It consists of an arithmetic command device 56 which issues a cutting command to the feeders 54 and 55 by subtracting the processing agent conveyance time to the blowing pipe 3 from 0.51.

【table】

[Table] Effects of the Invention As described above, the present invention provides a carrier gas blown into the bath in order to prevent slag present on the surface of the molten steel from being drawn into the bath and furthermore to avoid an interfacial reaction between the molten steel and the slag. Or, at a weight concentration with good inclusion absorption without substantially slag being present on the upper surface of the bath where the floatation-promoting gas reaches (%CaF ₂ )/{(%CaO + (%CaF ₂ )}≦0.2 Since desulfurization is performed in the pre- or post-process by injecting a CaO-CaF ₂ treatment agent, it is possible to eliminate inclusions in molten steel, even for steel types such as ultra-low carbon steel that has a high desulfurization rate and inherently has many inclusions. It is possible to quickly, accurately, and economically reduce the amount of molten steel to the extent that it does not cause any problems in the product application.In addition, by reducing the secondary temperature drop of molten steel and shortening processing time, it saves resources and energy. In addition, in the above treatment method, as a reaction environment,
By using a vacuum degassing tank such as RH or DH, or an inert gas atmosphere tank, it is possible to reduce inclusions and degas at the same time. This makes it possible to omit processes through integration and combination, and as a result, the present invention brings great benefits to industry, such as a significant reduction in manufacturing costs and an improvement in manufacturing yield.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the CaF ₂ concentration of the CaO-CaF ₂ treatment agent and the amount of Al ₂ O ₃ inclusions absorbed into the treatment agent in the present invention, and Figure 2 is the detection of inclusions after treatment in the example. The frequency of spherical inclusions and non-spherical ones that are difficult to float,
Figure 3, a diagram showing Al ₂ O ₃ clusters, is
FIG. 1 is a configuration explanatory diagram of an apparatus implementing an example of the present invention in an embodiment. 1... Container, 2... Circulation path, 3... Blowing pipe, 7
... Molten steel, 8 ... Slag, 9 ... Pressure reduction device, 5
0,51...Hopper, 52...Analyzer, 53
...Processing pattern setter, 54, 55...Feeder, 56...Calculation/instruction device, 57...Setting signal.

Claims (1)

[Scope of Claims] 1. CaF ₂ is removed without substantially having a processing agent that has absorbed slag or inclusions on the upper surface of the bath where the carrier gas blown into the bath floats up and reaches the bath. A processing agent containing CaO as a main component and the remainder being unavoidable components, and in which the concentration of CaF ₂ in the main components consisting of CaF ₂ and CaO is 20% by weight or less, is added to the bath using an inert gas as a carrier gas. After injecting, the main components are CaF ₂ and CaO with the remainder being unavoidable components, and the above CaF ₂ and
A method for reducing inclusions in molten steel, characterized in that a treatment agent having a CaF ₂ concentration of more than 20% by weight in the main component consisting of CaO is blown into the bath using an inert gas as a carrier gas. 2 As the first step, the main components are CaF ₂ and CaO, the remainder is unavoidable components, and the CaF ₂ concentration in the main components consisting of CaF ₂ and CaO is 20% by weight.
In the second step, after blowing a processing agent such as ultraviolet chloride into the bath using an inert gas as a carrier gas, slag or CaF ₂
and CaO as the main components, with the remainder being unavoidable components, and among the main components consisting of CaF ₂ and CaO,
A method for reducing inclusions in molten steel, comprising blowing a treatment agent having a CaF ₂ concentration of 20% by weight or less into the bath using an inert gas as a carrier gas. 3. The carrier gas blown into the bath floats in the bath and reaches the top surface of the bath, without substantially having a treatment agent that has absorbed slag or inclusions, and which contains CaF ₂ and CaO as the main components. After blowing into the bath using an inert gas as a carrier gas a treatment agent in which the remainder consists of unavoidable components and the CaF ₂ concentration in the main components consisting of CaF ₂ and CaO is 20% by weight or less, the CaF ₂ and CaO as the main components, and the remainder consists of inevitable components, and the above-mentioned CaF ₂ and
A treatment agent having a concentration of CaF ₂ in the main component consisting of CaO of more than 20% by weight is blown into the bath using an inert gas as a carrier gas, and then without substantially stirring or flowing the slag on the bath surface, A method for reducing inclusions in molten steel, characterized by stirring the molten steel with an inert gas. 4 As the first step, the main components are CaF ₂ and CaO, the remainder is unavoidable components, and the CaF ₂ concentration in the main components consisting of CaF ₂ and CaO is 20% by weight.
In the second step, after blowing a processing agent such as ultraviolet chloride into the bath using an inert gas as a carrier gas, slag or CaF ₂
and CaO as the main components, with the remainder being unavoidable components, and among the main components consisting of CaF ₂ and CaO,
A treatment agent having a _CaF2 concentration of 20% by weight or less is blown into the bath using an inert gas as a carrier gas,
A method for reducing inclusions in molten steel, which comprises stirring the molten steel with an inert gas without substantially stirring or fluidizing the slag on the bath surface.