JP4464343B2 - Aluminum killed steel manufacturing method - Google Patents

Description

  The present invention relates to a method for producing aluminum killed steel.

For example, in order to improve the rolling fatigue life and quietness of machine part steels such as rolling bearing steels, or the strength characteristics and workability of high-tensile steel sheets, non-representations such as those represented by the CaO-Al ₂ O ₃ system are used. It is important to reduce metal inclusions and oxygen concentration as much as possible (cleaning treatment).
Here, the CaO—Al ₂ O ₃ system is a CaO—Al ₂ O ₃ —MgO—SiO ₂ quaternary system conversion: CaO component is 5% or more, Al ₂ O ₃ component is 40% or more, MgO component And the SiO ₂ component is 20% or less.
The manufacturing process of such a high cleanliness steel generally includes the following four processes.
(A) Primary refining step in converter or electric furnace (B) Reductive refining step using gas stirring or electromagnetic stirring (C) Reflux-type vacuum degassing step such as RH (Rheinstahl-Heaus) (D) Continuous casting step or Ingot making process

  Of the above four processes, (B) and (C) as the secondary refining process are essentially adjustments to the final alloy components of the molten steel produced from the converter and gas components such as hydrogen until (D). This is done mainly for the purpose of removal. However, in recent years, in the processes (B) and (C), functions such as detoxification and high cleanliness by inclusion inclusion removal and inclusion composition control are also required.

Therefore, Patent Document 1 discloses the following refining method. That is, after tapping the completion of the molten steel was melted in a converter furnace, SiO ₂ in a weight ratio on ladle of molten steel: 10% or less, MgO: less than _{6~15%, Al 2 O 3:} 25~45%, The flux is added so that a top slag containing CaO: 35 to 60% is formed, and then the flux and the molten steel are mixed and stirred, and thereafter, the molten steel stirring process is performed by vacuum degassing.
Patent Document 2 discloses a thick steel plate satisfying a dissolved Al concentration: 0.01 to 0.07% and a dissolved Mg concentration: 0.00001 to 0.0001% by mass%. In addition, 0.00001 to 0.0001% is 0.1 to 1.0 ppm in terms of conversion.
Patent document 3 discloses the following amorphous refractory composition for molten steel ladle. That is, an alumina-based refractory composition comprising 55 to 85% by weight of a particle size having a particle size of 0.3 mm or less and 75 μm or less, and a magnesia content of 90%. 3 to 12% by weight of magnesia raw material with a weight percentage of 3% or more, 3 to 10% by weight of alumina cement with a calcia content of less than 20% by weight, and 0.3 to 1.5% by weight of ultrafine powder mainly composed of silica And containing.
Patent Document 4 discloses the following molten steel secondary refining treatment method. That is, in a secondary refining treatment method for molten steel in which molten steel is subjected to oxygen blown decarburization, vacuum decarburization, and killing treatment by the VOD method, and decarburization refining and cleaning treatment, MgO − having a C content of 5 to 15 wt% VOD treatment is performed using a ladle lined with slag lines with C refractories.
JP 2004-169147 A (Claim 3) JP 2003-213386 A (Claim 2) Japanese Patent Laying-Open No. 2002-234776 (Claim 1) JP-A-10-152720 (Claim 1)

However, Patent Document 1 does not describe a method for reducing CaO—Al ₂ O ₃ -based nonmetallic inclusions that greatly affects the rolling fatigue life. Also, the concentration of dissolved Mg in the molten steel and the refractory of the slag line portion of the ladle side wall (hereinafter sometimes referred to simply as slag line refractory), the side wall refractory other than the MgO component and slag line portion (hereinafter simply referred to as non-slag line refractory) (Also referred to as slag line side wall refractory.) Al ₂ O ₃ , MgO, SiO ₂ component is not described at all. Furthermore, it does not disclose arc heating for increasing the dissolved Mg concentration in a short time.
Moreover, although the said patent document 2 has prescription | regulation regarding the said dissolved Mg density | concentration, the said density | concentration is a value in a product stage, and also the said patent document 1, the MgO component of a slag line refractory and a non-slag line side wall refractory No mention is made of Al ₂ O ₃ , MgO and SiO ₂ components.
Moreover, the said patent document 3 is only prescribing | regulating regarding the composition in the side wall refractory of a ladle, and the said patent document 4 does not have description regarding dissolved Mg density | concentration.

The present invention has been made in view of such various points, and its main purpose is in the secondary refining treatment step after primary refining (decarburization) in a converter or electric furnace, among non-metallic inclusions. In particular, an object of the present invention is to provide a highly clean aluminum killed steel manufacturing method that has a low content of CaO—Al ₂ O ₃ -based nonmetallic inclusions that lead to deterioration of rolling fatigue life and a low oxygen concentration.

Means and effects for solving the problems

  In order to achieve the above object, a method for producing aluminum killed steel according to the present invention is as follows.

The dissolved Mg concentration of the molten steel in the ladle after reduction refining (ladder refining) by arc heating and gas stirring or electromagnetic stirring is set to 0.1 ppm or more and 2.0 ppm or less.
Among the ladle refractories, the MgO component of the slag line refractory that comes into contact with the slag during the reduction smelting is 70% or more, and Al ₂ of the side wall refractory other than the slag line refractory (non-slag line side refractory). The O ₃ component is 80% or more, the MgO component is 10% or less, and the SiO ₂ component is 0.3% or more and 2.0% or less.
The SiO ₂ component of the slag after the reductive refining is 11% or less, the CaO component is 45% to 60%, the Al ₂ O ₃ component is 23% to 37%, and the MgO component is 4% to 12%. .
The percentage (%) in this specification means weight percent (W%).

  Thereby, the non-metallic inclusions of molten steel can be easily aggregated and floated and separated. Moreover, the oxygen concentration in molten steel can be made small. Therefore, it is possible to produce a highly clean aluminum killed steel that is particularly excellent in rolling fatigue life. Furthermore, the corrosion resistance and spalling resistance of the side wall refractory of the ladle can be made good.

Briefly speaking, the present invention appropriately treats the molten steel that has been subjected to primary refining (decarburization, etc.) in a converter or electric furnace and discharged into a ladle, so that CaO—Al ₂ O ₃ is contained in the molten steel. Non-metallic inclusions are prevented from being produced, while spinel is actively produced, so that non-metallic inclusions in the molten steel can be removed and the oxygen concentration in the molten steel is greatly reduced. (To be cleaned). Specifically, the present invention defines at least the dissolved Mg concentration of the molten steel after reduction refining, the component of the side wall refractory of the ladle, and the slag component.

Specifically, the dissolved Mg concentration of the molten steel in the ladle after reduction refining by arc heating and gas stirring or electromagnetic stirring is set to 0.1 ppm or more and 2.0 ppm or less.
Of the ladle refractory, the MgO component of the slag line refractory is 70% or more, the Al ₂ O ₃ component of the non-slag line side wall refractory is 80% or more, the MgO component is 10% or less, and the SiO ₂ component. Is 0.3% or more and 2.0% or less.
Furthermore, the SiO ₂ component of the slag after the reduction refining is 11% or less, the CaO component is 45% or more and 60% or less, the Al ₂ O ₃ component is 23% or more and 37% or less, and the MgO component is 4% or more and 12% or less. And

Hereinafter, the embodiment of the invention will be described together with the operation mainly on the reason for defining the above requirements. The steelmaking method described here is called a converter method, and includes the following steelmaking process. That is, hot metal preliminary treatment for removing phosphorus and sulfur from the hot metal discharged from the blast furnace, primary refining treatment for refining the hot metal into steel, and removing gases such as hydrogen and nitrogen remaining in the molten steel as necessary. And a secondary refining process in which an alloy is added for desulfurization and component adjustment.
FIG. 1A to FIG. 1G are schematic explanatory views of the production process of aluminum killed steel in the present embodiment. FIG. 2 (a) is a diagram showing the inclusion composition after reduction scouring, and FIG. 2 (b) is a diagram showing the inclusion composition after the reflux-type vacuum degassing step. In FIGS. 2A and 2B, the circles indicate the distribution of inclusions.

(Hot metal pretreatment)
As shown in FIG. 1 (a), the hot metal discharged from the blast furnace is subjected to dephosphorization / desulfurization treatment in a torpedo car that is a vehicle carrying the hot metal.

(Primary scouring)
Next, as shown in FIG. 1 (b), oxygen is blown into the hot metal at high speed and high pressure, and the hot metal in the converter is decarburized and heated so that the target carbon concentration and target temperature are obtained. Carry out blowing.

  Next, as shown in FIG.1 (c), the molten steel in which the appropriate process was performed as mentioned above is discharged from a converter to a ladle. In addition, the MgO component of the slag line refractory of the ladle is 70% or more (see also FIG. 1 (e)).

  Next, as shown in FIG. 1 (d), the oxidizing slag containing FeO or the like and adversely affecting the product quality is removed. Specifically, the ladle is inclined and the slag is scraped out by a separate removing machine.

(Secondary scouring)
Next, as shown in FIG. 1 (e), a flux containing CaO, Al ₂ O ₃ or the like as a main component is introduced in order to produce slag with a low basicity and low basicity, such as FeO and MnO. Reduction scouring is performed by arc heating and gas stirring (or electromagnetic stirring). Specifically, the reduction smelting includes deoxidation treatment of molten steel and component adjustment by reacting high basicity slag and molten steel by gas stirring.
At this time, Mg component is supplied to the molten steel from the slag as shown by the following formula.
(MgO) → [Mg] + [O]
(MgO): MgO component in slag
[Mg]: Dissolved Mg in molten steel
[O]: Dissolved O in molten steel
An arc electrode shown in the figure is used for arc heating, a gas stirring lance is used for gas stirring, and argon gas is used as an inert gas for stirring. The slag line refractory, as shown in the figure, refers to the slag line portion in contact with the slag in the ladle refractory, and the non-slag line side wall refractory, Of the refractory on the ladle side wall, it refers to a portion other than the slag line portion.

In addition, it prescribes | regulates as follows regarding the dissolved Mg density | concentration in molten steel. That is, the dissolved Mg concentration of the molten steel in the ladle after reduction refining is set to 0.1 ppm or more.
Thereby, the inclusions in the molten steel are stabilized not as CaO—Al ₂ O ₃ -based inclusions but as MgO · Al ₂ O ₃ (also called spinel). Both the CaO-Al ₂ O ₃ system, which is a liquid inclusion in the molten steel, and the spinel, which is a solid inclusion, are non-metallic inclusions, but the latter spinel is compared to the former CaO-Al ₂ O ₃ system. In the RH process, which will be described later, they tend to aggregate and coalesce with each other and can easily float and separate. Therefore, by setting the dissolved Mg concentration as described above, it is possible to remove almost all non-metallic inclusions in the molten steel in the RH process described later (see FIGS. 2A and 2B).
Note that the dissolved Mg concentration in the case of less than 0.1 ppm, inclusions, will be stabilized as CaO-Al ₂ O ₃ system, it can not be easily removed. In addition, non-metallic inclusions represented by the CaO-Al ₂ O ₃ system are important for rolling fatigue life and quietness of machine part steel such as rolling bearing steel, or strength characteristics and workability of high-strength steel sheets. It is supposed to have a negative effect.

Moreover, it defines as follows regarding the component of a ladle refractory. That is, the MgO component of the slag line refractory is set to 70% or more.
As described above, the dissolved Mg concentration in the molten steel must be 0.1 ppm or more, but the dissolved Mg in the molten steel is supplied from the MgO component of the slag. Moreover, the MgO component of the slag is supplied from the initial input flux or the MgO component of the slag line refractory. Therefore, it is important that the MgO component of the slag line refractory is 70% or more.
When the temperature of the slag is raised by arc heating, MgO is gradually eluted from the slag line refractory into the slag, so that the dissolved Mg concentration in the molten steel during the reduction refining is suitably maintained. After the refining, the dissolved Mg concentration becomes 0.1 ppm or more.

The dissolved Mg concentration is also defined as follows. That is, the dissolved Mg concentration of the molten steel in the ladle after reduction refining is set to 2.0 ppm or less.
If the dissolved Mg concentration exceeds 2.0 ppm, the Mg is stabilized not as spinel but as MgO alone, and aggregation / floating separation is unlikely to occur as in the CaO—Al ₂ O ₃ system. Therefore, it is important that the dissolved Mg concentration is 2.0 ppm or less.
Also, if the dissolved Mg concentration exceeds 2.0 ppm, it is not sufficient to increase the MgO component of the slag line refractory that supplies Mg into the molten steel, and the MgO concentration of the initial input flux to the slag is significantly increased. There is a need. However, if this is done, the solid phase rate of slag increases as the MgO concentration increases, causing problems in terms of the interaction between slag and molten steel and heat transfer. Therefore, also in this sense, it is important that the dissolved Mg concentration is 2.0 ppm or less.

The gas stirring time (or electromagnetic stirring time) is preferably 20 minutes or longer and 90 minutes or shorter.
The reason for setting the gas stirring time to 20 minutes or more is as follows. That is, it is for sufficiently carrying out slag heating and component adjustment, slag hatching (dissolution), supply of MgO from the slag line refractory to the slag, and the like.
On the other hand, the reason for setting it to 90 minutes or less is as follows. That is, the supply of MgO from the slag line refractory to the slag becomes excessive, and the slag line refractory is prevented from being significantly melted.

Moreover, it prescribes | regulates as follows regarding a non-slag line side wall refractory. That is, the Al ₂ O ₃ component of the non-slag line side wall refractory is 80% or more and the MgO component is 10% or less.
Thereby, the spalling resistance in the non-slag line side wall refractory can be improved. Note that the spalling is a phenomenon in which a side wall refractory or the like is cracked or cracked due to thermal shock or temperature gradient, and the surface peels off.

In order to produce a high cleanliness steel, it is necessary to keep the oxygen concentration in the molten steel low in thermodynamic equilibrium in reductive refining. For that purpose, a high basicity (basicity: CaO / SiO ₂₎ is required. ) Slag is used.
However, when the SiO ₂ contained in the non-slag line sidewall refractories are eluted into the molten steel by melting, by the SiO ₂ eluted by the difference in specific gravity floats to the molten steel, is absorbed in the slag, The basicity of the slag may be lowered.
Therefore, by suppressing the SiO ₂ component of the non-slag line side wall refractory to 2.0% or less, elution into the molten steel is suppressed, and an increase in slag basicity can be suppressed. The above oxygen concentration is a rough indicator of the amount of inclusions in the molten steel.
On the other hand, if the SiO ₂ component of the non-slag line side wall refractory is too small, the side wall refractory is liable to melt, and as a result, the number of times the ladle can be used is extremely limited. Therefore, in order to ensure the corrosion resistance of the side wall refractory, the SiO ₂ component is set to 0.3% or more as described above.

Moreover, the slag component after reductive scouring is defined as follows. That is, the SiO ₂ component of the slag after refining is 11% or less, and the CaO component is 45% or more and 60% or less. Thereby, reduction scouring with slag having a high basicity can be performed, so that the oxygen concentration in the molten steel can be kept low in terms of thermodynamic equilibrium.
In addition, the Al ₂ O ₃ component of the slag after reduction refining is 23% or more and 37% or less. Thereby, since the fluidity | liquidity of the said slag is ensured moderately, the stirring reaction and heat transfer between slag-molten steel will be performed efficiently.
Further, the MgO component of the slag after refining is 4% or more and 12% or less. By setting the MgO component to 4% or more in this way, it is possible to ensure a dissolved Mg concentration of 0.1 ppm or more in combination with the elution from the slag line refractory.
Moreover, since the solid-phase rate of slag is suppressed by setting it as 12% or less, the stirring reaction and heat transfer between slag and molten steel will be performed efficiently.

After the reductive scouring (LF), vacuum degassing (RH) using a reflux type vacuum degassing apparatus is performed (see FIG. 1 (f): arrows indicate molten steel reflux).
Specifically, argon gas is blown into the molten steel from one of the two tubes (snorkel) immersed in the molten steel in the ladle, and the molten steel in the tube is raised into the vacuum chamber by the action of an air lift pump. Let The molten steel is exposed to vacuum in the RH tank, and then returns to the ladle through another one (downcomer pipe). In this step, the spinel, which is an inclusion generated in the reduction scouring (LF) step, is aggregated and coalesced and removed by floating separation (see also FIGS. 2A and 2B). ).
As described above, the CaO—Al ₂ O ₃ -based non-metallic inclusions are inclusions that hardly aggregate and coalesce with each other and are difficult to float and separate in this step.

  The molten steel after final component adjustment is cast by a continuous casting facility (see FIG. 1 (g)) or an agglomeration facility in an air-breaking environment. Then, it is processed into machine part steel such as rolling bearing steel or high-tensile steel plate.

Summarizing the above effects, it is as follows.
As shown in FIG. 2 (a), inclusions in molten steel are stabilized not as CaO—Al ₂ O ₃ inclusions but as spinel (MgO · Al ₂ O ₃ ) during reduction refining (LF) or RH treatment. Thus, by appropriately defining the dissolved Mg concentration in the molten steel, the nonmetallic inclusions in the molten steel can be easily put into a state of being easily agglomerated and separated. In other words, the nonmetallic inclusions contained in the molten steel can be made removable by using, for example, a reflux vacuum degassing apparatus (RH) as shown in FIG.
Further, since the SiO ₂ component in the slag is kept low, it is possible to reduce the oxygen concentration in the molten steel.
Therefore, it is possible to produce a highly clean aluminum killed steel that is particularly excellent in rolling fatigue life.
Furthermore, the corrosion resistance and spalling resistance of the side wall refractory of the ladle can be made good.

〔Example〕
Hereinafter, the present embodiment will be described more specifically with reference to examples. FIG. 3 shows test conditions and results of an aluminum killed steel manufacturing test.

In this production test (sometimes simply referred to as this test), a 240-ton scale converter was used. After the primary scouring in the converter, as the LF treatment in the ladle, the alloy adjustment of the molten steel was performed to near the target component. At the same time, the slag was hatched and heated.
Thereafter, vacuum degassing (RH) was performed using a reflux type vacuum degassing apparatus.

Each item in FIG. 3 is as follows in detail.
[Arc heating implementation] indicates whether or not the slag was heated and hatched by arc heating during ladle scouring.
[Processing time] indicates the time at which the reduction scouring was performed.
[Dissolved Mg concentration] indicates the dissolved Mg concentration of the molten steel in the ladle after the reduction refining.
[Slag line refractory] is as described above. FIG. 3 shows the MgO component of the slag line refractory.
[Non-slag line side wall refractory] is also as described above. FIG. 3 shows the Al ₂ O ₃ component, MgO component, and SiO ₂ component of the non-slag line side wall refractory.
[Slag component] indicates each component of slag after reduction scouring. FIG. 3 shows the SiO ₂ component, CaO component, Al ₂ O ₃ component, MgO component of the slag, and CaO / SiO ₂ as the basicity described above.

[The number of CaO—Al ₂ O ₃ inclusions] was measured as follows. That is, the composition and number of inclusions were measured on the speculum surface (measurement plane subjected to polishing treatment) of the billet sample manufactured under each test condition. At this time, an EMPA analyzer (manufactured by JEOL Ltd .: JXA-8000 series) and an energy dispersive X-ray analyzer (EDS detector) were used as the metal sample analyzer.
In the measurement, the acceleration voltage was 20 kV, the X-ray type was K-ray, and the beam diameter was 2 to 3 μm. Among the inclusions observed by this EMPA analysis method, the following were used as objects to be measured in the number measurement. That is, the diameter is 20 μm or more, and the CaO—Al ₂ O ₃ —SiO ₂ —MgO quaternary conversion is 5% or more of CaO component, 40% or more of Al ₂ O ₃ component, and 20 of MgO and SiO ₂ . % Or less contained in the measurement object. Moreover, in order to ensure the representativeness in the said measurement, at least 3000 mm < ² > or more was observed among the said microscopic surfaces.
[T. O] is an abbreviation for total oxygen (indicating oxygen concentration), and the billet sample under each test condition was analyzed and measured by the combustion-infrared absorption method.
[Law damage status of ladle refractories] indicates the melt damage status of each ladle refractory under each test condition. Specifically, [corrosion resistance] and [spalling resistance] were evaluated.
[Corrosion resistance (erosion depth)] was evaluated by carrying out a rotary erosion test and measuring the erosion dimension of the ladle refractory.
[Spalling resistance] is that the temperature of the ladle refractory is heated to 1650 ° C., the state is continued for 30 minutes, and then air-cooled to room temperature, and this heating and cooling is repeated 6 times in total. The state of cracking of the refractory was visually observed.
[Evaluation] is the above-mentioned [Number of inclusions in the CaO-Al ₂ O ₃ -based inclusion] · [T. O], [corrosion resistance (erosion depth)], and [spoling resistance].

Hereinafter, the test results shown in FIG. 3 will be considered.
[Test No. 1 and 2] Evaluation ×
In the first place, the concentration of dissolved Mg is extremely low (less than 0.1 ppm) unless arc heating type reduction scouring is performed. As a result, CaO—Al ₂ O ₃ inclusions were measured at 40 pieces / cm ² or more. This represents that the inclusions in the molten steel were stabilized as CaO—Al ₂ O ₃ inclusions.

[Test No. 1, 3, 4] Evaluation ×
Since the MgO component of the slag line refractory is 70% or less, the dissolved Mg concentration was extremely low as described above, and the same result was obtained. This means that even if arc heating was performed (test numbers 3 and 4), the supply of MgO into the slag due to the slag line refractory elution was not sufficient.

[Test No. 5] Evaluation ×
When the SiO ₂ component of the non-slag line side wall refractory is less than 0.3% (0.1%), the corrosion resistance is extremely poor. This represents that the side wall refractory was easily melted because the SiO ₂ component was too small.

[Test No. 6] Evaluation ×
When the SiO ₂ component of the non-slag line side wall refractory was more than 2.0% (4.2%), the corrosion resistance deteriorated similarly to the result of Test No. 5. In addition, as a result of the low basicity in the slag, the T.O. O (oxygen concentration) was significantly deteriorated.

[Test No. 7] Evaluation ×
When the Al ₂ O ₃ component of the non-slag line side wall refractory is less than 80% (79.1%) and the MgO component is more than 10% (17.4%), the corrosion resistance is good, but the anti-spalling property Was significantly worse.

[Test numbers 8 to 10] Evaluation ○
On the other hand, the dissolved Mg concentration of the molten steel in the ladle after reduction refining by arc heating and gas stirring is 0.1 ppm to 2.0 ppm, the MgO component of the slag line refractory is 70% or more, and the non-slag line side wall The Al ₂ O ₃ component of the refractory is 80% or more, the MgO component is 10% or less, and the SiO ₂ component is 0.3% or more and 2.0% or less. In addition, the SiO ₂ component of the slag after the reduction refining is 11% or less, the CaO component is 45% or more and 60% or less, the Al ₂ O ₃ component is 23% or more and 37% or less, and the MgO component is 4% or more and 12% or less. Then, it became as follows.
That is, the number of CaO—Al ₂ O ₃ inclusions and oxygen concentration (T.O) were simultaneously very good. That is, the number of CaO—Al ₂ O ₃ inclusions is extremely small, and the oxygen concentration is extremely low at less than 5 ppm.
In addition, there was no particular problem in the erosion resistance and spalling resistance melting confirmation test of the ladle refractories.

As described above, the following effects can be achieved by suitably defining the dissolved Mg concentration of the molten steel after reductive refining, the component of the side wall refractory of the ladle, the slag component, and the like.
That is, high cleanliness steel having an oxygen concentration of 5 ppm or less can be produced industrially and stably. In addition, since the number of non-metallic inclusions such as CaO-Al ₂ O ₃ is significantly reduced, it has excellent rolling fatigue life and quietness as machine part steel such as rolling bearing steel. It becomes possible to manufacture a very high quality and high cleanliness steel that can sufficiently suppress surface flaws caused by objects. In addition, the fact that the ladle refractory has a good erosion status (corrosion resistance and spalling resistance) is also a great advantage of this production method.

  Although the present invention has been described in the preferred embodiments above, the present invention is not so limited. It will be understood that various other embodiments may be made without departing from the spirit and scope of the invention. Furthermore, in this embodiment, although the effect by the structure of this invention is described, these effect is an example and does not limit this invention.

The schematic explanatory drawing of the manufacturing process of aluminum killed steel. Inclusion composition diagram. The figure which shows the test conditions and result of a manufacturing test of aluminum killed steel.

Claims (1)

The dissolved Mg concentration of the molten steel in the ladle after reduction refining by arc heating and gas stirring or electromagnetic stirring is 0.1 ppm to 2.0 ppm,
Of the ladle refractory, the MgO component of the slag line refractory in contact with the slag during the reduction smelting is 70% or more, and the side wall refractory Al ₂ O ₃ component other than the slag line refractory is 80% or more, MgO component is 10% or less, SiO ₂ component is 0.3% or more and 2.0% or less,
The SiO ₂ component of the slag after the reductive refining is 11% or less, the CaO component is 45% to 60%, the Al ₂ O ₃ component is 23% to 37%, and the MgO component is 4% to 12%. The manufacturing method of the aluminum killed steel characterized by the above-mentioned.

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