JPH07316631A - Deoxidizing and cleaning method of molten steel - Google Patents

Abstract

PURPOSE:To improve steel quality by suppressing formation of MgO inclusions in a steel making and refining process. CONSTITUTION:The compsn. of molten slag is regulated in the following manner in order to suppress the formation of the MgO inclusions: 5mass%<=Al2O3<=20 mass%, 5mass%<=MgO<=20mass%, slag basicity: by weight, CaO/SiO2<=2, 0.25<=MgO/Al2O3<=2. Further, preferably 0.4<=MgO/Al2O3<=1.2, 15<=Al2O3+ MgO<=30 are satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for deoxidizing molten steel in a steelmaking and refining process, a cleaning method, and in particular for suppressing the formation of non-ductile MgO-based inclusions in steel to improve the quality of molten steel. Deoxidizing and cleaning method.

[0002]

2. Description of the Related Art Conventionally, in the deoxidation of molten steel in the presence of molten slag, the formation of non-ductile inclusions, which are harmful to the quality of steel, particularly processing and surface properties, has been regarded as a problem. For example, when refining a steel cord material by Si-Mn deoxidation, a non-ductile Al ₂ O ₃ -based inclusion that occurs even though metal Al is not used as a deoxidizer.
(Here, generically, inclusions having 70 mass% or more of Al ₂ O ₃ and being solid at a steelmaking temperature or inclusions containing such crystallized substances) are harmful to the steel quality, particularly the ductile surface texture. In order to suppress the formation of such inclusions, it has been necessary to suppress the Al ₂ O ₃ concentration in the conventional steelmaking slag to be as low as less than 5 mass% for deoxidation refining.

However, it is controlled to be the incorporation of Al ₂ O ₃ to the slag below a few mass%, the refractory selection, along with the cost is increased selective like practically difficult auxiliary materials, Al ₂ A large amount of CaF ₂ has been unavoidably added to the slag from the viewpoint of improving deterioration of slagging property due to suppression of O ₃ concentration. And, such a large addition of CaF ₂ not only causes an increase in cost due to an increase in the amount of the slag forming agent,
It also led to an increase in refractory cost due to melting damage of refractory due to slag. Moreover, the elution of MgO from the refractory into the slag leads to an increase in the MgO concentration in the slag, which in turn leads to the non-ductile MgO-based inclusions (here, MgO-based inclusions are equivalent to 30 ma of MgO).
This causes a new problem of the formation of inclusions containing ss% or more, especially MgO-Al ₂ O ₃ -based spinel inclusions, or MgO periclase-based inclusions and inclusions containing these crystallized substances.

That is, in the conventional simple control of the Al ₂ O ₃ concentration in the slag, neither the formation of MgO-based inclusions nor the formation of Al ₂ O ₃ -based inclusions can be suppressed and the refining cost is increased. It can be said that he was holding.

The problem similar to this is not limited to the case of melting the steel cord material exemplified here, but widely, the generation of non-ductile inclusions is regarded as a problem and deoxidation is usually performed by suppressing the Al concentration in the molten steel. It commonly occurred in the melting of steel (including high carbon steel), stainless steel, special steel, and electronic materials (Fe-Ni alloys, Fe-Ni-Co alloys, etc.).

In Japanese Patent Publication No. 62-34801, CaO:
35 to 55% by weight, SiO ₂ : 34 to 53% by weight, MnO: 0.2 to 5% by weight, Al ₂ O ₃ : 8% by weight or less, MgO: 15% by weight or less, basicity: 0.85 to 1.25 and a slag composition. Although the specified method is disclosed, it is not sufficient to merely point out that the Al ₂ O ₃ concentration in the slag is reduced to suppress the formation of Al ₂ O ₃ -based inclusions. Further, regarding the suppression of the formation of MgO-based inclusions, it is not sufficient to similarly specify the upper limit of the MgO concentration in slag. In addition, considering the actual process, it is difficult to control the mixture of Al ₂ O _{3 in} the slag so that it is less than several mass%. However, this point is not particularly described in the above publication.

[0007]

The problem to be solved by the present invention is to perform deoxidation and purification of molten steel in the process of steelmaking and refining during deoxidation and refining of molten steel in the presence of molten slag, especially MgO in steel. An object of the present invention is to provide a method for improving steel quality by suppressing the generation of system inclusions.

When deoxidizing molten steel in the presence of molten slag, not only the type of deoxidizing agent but also the slag composition is the deoxidizing level.
It is widely known that (oxygen potential and absorption of inclusions) and composition of inclusions generated by deoxidation are affected. This can be said to be generally recognized regardless of the type of molten steel, although the degree of influence varies depending on the molten steel composition, the type of deoxidizer, and the slag composition.

Conventionally, in such deoxidation of molten steel, the formation of inclusions harmful to the steel quality, especially the workability and surface properties, has been regarded as a problem. For example, when treating non-ductile inclusions as a problem when refining a steel cord material by Si-Mn deoxidation, metal Al is not used as a deoxidizer, but nevertheless the Al ₂ O ₃ -based There is a problem that non-ductile inclusions are generated.
Since such a non-ductile inclusion remains without changing its shape even during hot working, it may become a starting point of wire breakage during wire drawing to the steel filament. Further, in the austenitic stainless steel sheet, such non-ductile inclusions remain on the surface and may cause line defects, or in semiconductors and vacuum materials, may cause gas emission and particle emission. Sometimes. In addition, electronic materials (Fe-Ni
Alloys, Fe-Ni-Co alloys, etc.), non-ductile inclusions remaining on the surface without changing the morphology during hot working,
It is said to have an adverse effect on fine processing and aqueous solution treatment.

In order to suppress the formation of such Al ₂ O ₃ non-ductile inclusions that are harmful to steel quality, conventionally, for example, in the case of steel cord materials, Si-Mn deoxidation in secondary refining was used. In the process, it is necessary to suppress the Al ₂ O ₃ concentration in the steelmaking slag whose basic component is CaO-SiO ₂ -Al ₂ O ₃ -MgO-CaF ₂ system to 5 mass% or less as much as possible to perform deoxidation refining. It was

However, as described above, controlling the mixing of Al ₂ O ₃ into the slag to several mass% or less is practically difficult, such as refractory selection and auxiliary raw material selection, and leads to cost increase. There were problems, and it caused a new problem of the formation of non-ductile MgO-based inclusions.

[0012] Furthermore, since the MgO-based inclusions often have hydrophilicity, and if they remain on the surface of the steel material and come into contact with an aqueous solution or the like, they may become a starting point of corrosion. Such inclusions are also harmful.

That is, it can be said that the conventional simple suppression of the Al ₂ O ₃ concentration in the slag could not suppress the formation of MgO-based inclusions and Al ₂ O ₃ -based inclusions, resulting in an increase in the refining cost. .

The problem similar to this is not limited to the steel cord material shown here, but the above-mentioned ordinary steel, stainless steel, special steel, electronic materials (Fe-Ni alloy, Fe-Ni-Co alloy, etc.)
This is also a problem that can commonly occur in the melting of materials that have a problem of non-ductile inclusions in terms of steel quality.

[0015]

Therefore, as a result of various investigations to solve the above problems, the present inventor has found that the deoxidizing metal
Even when Al is not used, when Al ₂ O ₃ -based non-ductile inclusions are generated, the slag composition is strongly involved,
Furthermore, even when metal Mg is not used for deoxidation, MgO-based non-ductile inclusions are also formed when the concentration of Al ₂ O ₃ in the slag is reduced. I paid attention.

Here, as a result of many years of research and development, the present inventor has found that MgO-based inclusions in steel cause an increase in the MgO content in the inclusions due to the decomposition reaction of Mg from the slag, which is caused. Therefore, the present invention has been achieved by the knowledge that the above-mentioned formation of non-ductile inclusions can be suppressed by precisely controlling the slag composition.

Here, the gist of the present invention is to add a deoxidizing agent to molten steel in the presence of molten slag whose basic component is CaO--SiO ₂ --Al ₂ O ₃ --MgO--CaF ₂ system to remove deoxidized steel. Acid, deoxidation of molten steel to be cleaned, cleaning method, wherein the composition of the molten slag is 5
mass% ≤ Al ₂ O ₃ ≤ 20 mass%, and 5 mass% ≤ MgO ≤ 20
It is regulated to be mass%, the slag basicity is CaO / SiO ₂ ≤2 by weight, and the MgO / Al ₂ O ₃ ratio is by weight.
This is a deoxidizing and cleaning method for molten steel, which is characterized by suppressing the formation of MgO-based inclusions by controlling 0.25 ≦ MgO / Al ₂ O ₃ ≦ 2.

According to another aspect of the present invention, in controlling the composition of the molten slag, 0.4 ≦ MgO / Al ₂ O ₃ ≦ 1.
2 and by limiting 15 ≦ Al ₂ O ₃ + MgO ≦ 30, it is possible to more effectively suppress the formation of MgO 3 -based inclusions.

[0019]

The function of the present invention will be described below. The type of deoxidizer in the present invention is not particularly limited,
It is most effective to use a weak deoxidizer such as Si-Mn deoxidizer, Al-Si-Mn deoxidizer, and Al semikilled deoxidizer.

For example, the use of a strong deoxidizing agent such as Al deoxidizing, Ca deoxidizing, or deoxidizing by REM (rare earth metal element) is an oxide of the deoxidizing element because it uses an element having a strong affinity with oxygen. (Mostly non-ductile or hydrophilic) is generated mainly, and since this stable inclusion remains as it is, it is not easily affected by slag, so the effect of slag control based on the present invention Is small.

However, when only the formation of MgO-based inclusions is suppressed even with Al deoxidation, or when the Ca treatment is performed after Al deoxidation to lower the melting point of the inclusions, the formation of MgO-based inclusions is suppressed. When suppressing, the present invention is very effective. Further, in weak deoxidation such as Si deoxidation or C deoxidation, the formation of non-ductile inclusions due to slag is unlikely to occur, so the effect according to the present invention is small.

The basic composition of the slag, and generally _{CaO-SiO 2 -Al 2 O 3} -MgO -CaF 2 system used in steelmaking slag,
A slag having unavoidable impurities such as MnO, FeO, and Cr ₂ O ₃ was selected. The reason for this is that it is common to make steel using a large amount of slag and to carry out refining in consideration of cost.

Here, since MnO, FeO, and Cr ₂ O ₃ cause reoxidation and cause deterioration of slag slag-forming property, it is desirable to suppress it to a minimum value by preliminary deoxidation in advance. . Preferably, the total amount is limited to 3% or less.

FIG. 1 is a graph illustrating the slag composition regulated in the present invention with respect to MgO and Al ₂ O ₃ mass%. In the slag according to the present invention, the Al ₂ O ₃ concentration and Mg
The reason for limiting the O 2 concentration in this way is described.

First, the Al ₂ O ₃ concentration in the slag is 20 from the viewpoint of suppressing the formation of Al ₂ O ₃ -based inclusions in deoxidation of Si-Mn or the like.
It is desirable to set it to mass% or less. However, as will be described later, according to the present invention, the Al ₂ O ₃ concentration in the slag does not need to be less than 5% in order to suppress the formation of Al ₂ O ₃ -based inclusions as in the prior art, but rather, From the viewpoint of suppressing the formation of MgO-based inclusions and ensuring the slagification property, the Al ₂ O ₃ concentration in the slag must be 5% or more. Further, if the Al ₂ O ₃ concentration in the slag is set to 5% or more, the restrictions on refractories and auxiliary materials are eased, which is relatively easy and has good controllability. Considering these points, the Al ₂ O ₃ concentration in the slag is preferably 8 to 15%.

On the other hand, the MgO concentration in the slag is set to 20% or less from the viewpoint of suppressing the formation of MgO-based inclusions and ensuring the slagification property. The reason for this is that if it exceeds 20%, the probability of formation of MgO-based inclusions increases, and at the same time, the slagification property deteriorates as the liquidus temperature rises. On the other hand, the reason for setting the MgO concentration in the slag to 5% or more is to suppress the formation of Al ₂ O ₃ -based inclusions and to protect the slag line refractory. Preferably 7-
15%.

Further, considering the formation and slagging property of non-ductile inclusions, the total amount of Al ₂ O ₃ and MgO in the slag is preferably in the range of 15% ≦ (MgO + Al ₂ O ₃ ) ≦ 30%. . Slag basicity is generally used as an index showing the physicochemical characteristics of slag. In the present invention, the slag basicity is limited to 2 or less.

The reason for defining the slag basicity is as follows.
Since slag basicity is a factor that determines the oxidation potential of the slag-metal reaction, Al ₂ O ₃ -based inclusions and Mg
From the viewpoint of suppressing the generation of O 2 -based inclusions, the basicity is a high oxygen potential slag having a weight ratio of 2 or less. However,
The optimum basicity varies slightly depending on the deoxidation method, such as Si-
In the case of Mn complex deoxidation, the basicity of 0.8 to 1.5 is optimal. The reason for defining the lower limit is that the high oxygen potential slag causes reoxidation of molten steel. Also, Al
In the -Si-Mn complex deoxidation, even higher 1.2 to 1.8 can be said to be the optimum value of basicity from the viewpoint of preventing reoxidation by the high oxygen potential slag.

Next, the reasons for limiting the MgO / Al ₂ O ₃ ratio in the slag will be described. Al ₂ O ₃ concentration and MgO concentration in slag are Al ₂ O ₃
As described above, it is a factor that causes the formation of system inclusions and MgO system inclusions. It is also generally known that MgO in the molten oxide has basicity and Al ₂ O ₃ has neutrality or acidity. Further, in particular, MgO and Al ₂ O ₃ have high affinity, and in fact, it is known that a binary MgO-Al ₂ O ₃ system forms a stable complex oxide having a spinel structure.

From such a consideration, as in the case of molten slag,
Even in molten oxide, these MgO and Al₂O ₃ Strong interaction between
That there is a₂O₃ Formation of system inclusions and MgO system
I found that the formation of inclusions is closely related to each other
And MgO / Al₂O₃ I got to get the index.

Here, the reason why the MgO / Al ₂ O ₃ content is set to 2 or less is that if it exceeds this value, the formation of MgO-based inclusions and deterioration of slag slag formation occur, while if it is less than 0.25, Al in the slag is reduced. _{This is because the 2} O ₃ activity increases and Al ₂ O ₃ type inclusions are generated. Considering slag formation, it is preferably 0.
About 4 to 1.2 is good for suppressing the formation of MgO-based inclusions and Al ₂ O ₃ -based inclusions. In addition, for CaO, SiO ₂ , and CaF ₂ ,
Preferably, CaO: 26 to 48 mass%, SiO ₂ : 22 to 47 mass%
Restricted to. In particular, CaF ₂ ≦ 10 mass%.

The amount of these molten slags is not particularly limited as long as it is used in ordinary steelmaking and refining, and may be, for example, several kg / t to several tens kg / t, and the optimum amount under other steelmaking conditions. Can be selected. However, in order to obtain the effect of the present invention well, 10 to 50 kg / t is preferable.

Regarding the operating temperature, especially the ordinary steelmaking temperature
The temperature may be in the vicinity of 1600 to 1700 ° C, but if the slag formation is good, it is desirable to carry out deoxidation with the molten slag according to the present invention at 1650 ° C or less in consideration of refractory melting loss. Further, as a secondary effect of the present invention, improvement of slag-forming property,
It is the reduction of slag line refractory melting loss and the reduction of added CaF ₂ .

That is, the Al ₂ O ₃ concentration or the MgO concentration in the slag is not unnecessarily suppressed, but by selecting the optimum slag composition as in the present invention, the slag forms a multi-component slag to lower the melting point and form slag. It is possible to secure the sex. Ensuring slag formability not only facilitates handling of slag during operation, but also can be expected to absorb and remove floating inclusions. Further, since an appropriate MgO concentration is always required for the slag, it leads to suppression of melting loss of MgO-based refractory materials such as MgO-C bricks commonly used for slag lines. Further, since the slaging property is improved, the amount of CaF ₂ added can be reduced, and the decrease in the CaF ₂ concentration in the slag leads to a reduction in the basic unit of flux, suppression of refractory melting loss, and further improvement of the slag processability.

[0035]

EXAMPLES In order to demonstrate the effect of the present invention, the following experiment was conducted to investigate the influence of the slag composition on the inclusion composition during deoxidation of molten steel. Figure 2 shows 2t molten steel
It is a schematic explanatory drawing of the vacuum refining furnace 1 by the high frequency induction heating system which can melt | dissolve. The upper lid 2 of the vacuum refining furnace 1 is equipped with an auxiliary raw material addition device 3 capable of charging slag (not shown) into the molten steel 10 and a sampling device 4 capable of sampling at a proper time. The molten steel 10 is held by the refractory material 5 whose main component is MgO.

In this example, the experiment was carried out in an atmosphere of Ar 100 torr, but in this vacuum refining furnace 1, the molten steel was held by the steam ejector pump (not shown) through the exhaust hole 6, and the vacuum degree was set to a predetermined pressure up to 1 torr. It is possible to maintain the atmosphere. Further, the furnace bottom has a porous brick tuyere 7 for stirring the molten steel 10, and it is possible to promote the slag-metal reaction by performing stirring by blowing Ar gas.

Here, the reason why the Ar atmosphere is adopted is to prevent reoxidation of the molten steel in the atmosphere and to facilitate the control of the inclusion composition morphology by the slag. Similarly, the reason why the pressure is reduced is that stirring by blowing Ar gas is performed more effectively and efficiently.

(Example 1) The molten steel used as Example 1 is
Carbon: 0.8%, Si: 0.3%, Mn: 0.6%, P: 0.008
%, S: 0.007%, molten steel 2t corresponding to a tire cord material having a steel composition (mass%) consisting of balance iron and unavoidable impurities. Using the vacuum refining furnace shown in Fig. 2, Ar
After melting and holding at 1580 ℃ in 100torr atmosphere, 45% CaO-30
80kg of slag having various compositions with the basic composition of% SiO ₂ -10% Al ₂ O ₃ -10% MgO -5% CaF ₂ and containing inevitable impurities such as FeO and MnO. Then
Next, Si and Mn were added as deoxidizing agents so as to have the above-mentioned steel composition, and then high frequency stirring and Ar gas stirring were used together to secure the slag-metal reaction. 30 minutes to 60 after input
A metal sample and a slag sample were collected in minutes, and the molten steel composition and the composition morphology of inclusions were investigated.

FIG. 3 shows the effect of the Al ₂ O ₃ concentration in the slag on the number of non-ductile inclusions. Al ₂ O ₃ concentration in slag
If it exceeds 20%, the number of Al ₂ O ₃ -based inclusions increases, while 5
It can be seen that the number of MgO-based inclusions increases when the ratio falls below%.

FIG. 4 shows the effect of the MgO concentration in the slag on the number of non-ductile inclusions. It can be seen that when the MgO concentration in the slag exceeds 20%, the number of MgO-based inclusions increases, while when it falls below 5%, the number of Al ₂ O ₃ -based inclusions increases.

FIG. 5 shows the effect of slag basicity on the total oxygen concentration. The higher the slag basicity, the lower the total oxygen concentration. This means a reduction in the number of inclusions. When the basicity is less than 0.8, the total oxygen concentration rises sharply, which is considered to indicate the deterioration of cleanliness.

FIG. 6 shows the effect of slag basicity on the number of non-ductile inclusions. It can be seen that when the slag basicity exceeds 2, the number of non-ductile inclusions increases rapidly. Figure 7
The effect of (% MgO) / (% Al ₂ O ₃ ) on the number of non-ductile inclusions is shown. It can be seen that if this index exceeds 2, the number of MgO-based non-ductile inclusions increases sharply, and if it falls below 0.2, the number of Al ₂ O ₃ -based inclusions increases.

Example 2 The molten steel used in Example 2 was Cr:
18%, Ni: 9%, Mn: 1.2%, Si: 0.6%, Al: ≤0.00
Steel composition consisting of 2%, balance iron and inevitable impurities (ma
ss%) austenitic molten stainless steel 1.8t
Met. Ar 100torr using this vacuum refining furnace
After melting and holding in an atmosphere of 1590 ° C., 70 kg of slag having various compositions was added as in Example 1, and then as a deoxidizing agent.
Si and Mn were added so as to have the above steel composition, and then high frequency stirring and Ar gas stirring were used together to secure the slag-metal reaction. A metal sample was taken 30 to 60 minutes after the introduction, and the composition of molten steel and the composition morphology of inclusions were investigated.

[0044] FIG. 8 is a slag concentration of Al ₂ O _3, and organized in the MgO concentration _{(MgO) / (Al 2 O} 3) ratio, _{(MgO) / (Al 2 O} 3) is in steel non ductile interposed The effect on the number of objects is shown. The Al ₂ O ₃ concentration and the MgO concentration in the slag at this time were adjusted so that (MgO + Al ₂ O ₃ ) = 20%. Also, the basicity (CaO) / (SiO ₂ ) was adjusted to 1.3. As shown in the figure, when (MgO) / (Al ₂ O ₃ ) is less than 0.25, more clearly less than 0.4, the number of Al ₂ O ₃ -based inclusions is more than 2, more clearly more than 1.2. It can be seen that the present invention is effective in suppressing the formation of non-ductile inclusions.

(Example 3) The molten steel used in Example 3 was C:
1.0%, Cr: 1.5%, Mn: 0.4%, Si: 0.3%, Al: 0.
Steel composition consisting of 02%, balance iron and inevitable impurities (ma
It was 2t of molten steel corresponding to bearing steel having ss%). This was melted and held in an Ar 100 torr atmosphere at 1570 ° C. using a vacuum refining furnace shown in FIG.
Mn was added so as to have the above steel composition, and then high frequency stirring and Ar gas stirring were used together to secure the slag-metal reaction. A metal sample was taken 30 to 60 minutes after the slag was charged, and the molten steel composition and the composition morphology of inclusions were investigated. The basicity was adjusted to (CaO) / (SiO ₂ ) = 1.6, and the Al ₂ O ₃ concentration and MgO concentration in the slag were adjusted to (MgO + Al ₂ O ₃ ) = 25%.

FIG. 9 shows the effect of (MgO) / (Al ₂ O ₃ ) on the number of non-ductile inclusions in the steel. From the results shown in the figure, in this example, since Al is basically deoxidized, the inclusions are Al ₂ O.
_Although there are many _3- type inclusions, when (MgO) / (Al ₂ O ₃ ) is less than 0.25, the Al ₂ O ₃ -type inclusions increase, and when it exceeds 2, the MgO inclusions increase, so the present invention is not It can be seen that it is effective in suppressing the formation of ductile inclusions.

Example 4 The molten steel used in Example 4 was Ni:
41.5%, C: 0.002%, Mn: 0.5%, Si: 0.13%, Al:
It was 1.5 t of high Ni alloy molten steel having a steel composition (mass%) consisting of ≤ 0.001%, balance iron and unavoidable impurities. Using a vacuum refining furnace as shown in Fig. 2, Ar 100 torr atmosphere 1600 ℃
After melting and holding at 80 kg, 80 kg of slag having various compositions is added as in Example 1, and then Si and Mn are added as deoxidizing agents so as to have the above steel composition, and then high frequency stirring and Ar gas stirring are used together. Then, the slag-metal reaction was secured. A metal sample was taken 30 to 60 minutes after the slag was charged, and the molten steel composition and the composition morphology of inclusions were investigated. Basicity is (CaO) / (SiO ₂ ) = 1.2, Al ₂ O ₃ concentration in slag and
The MgO concentration was adjusted so that (MgO + Al ₂ O ₃ ) = 18%.

FIG. 10 shows the effect of (MgO) / (Al ₂ O ₃ ) on the number of non-ductile inclusions in the steel. From the figure, in this embodiment,
Since it is basically Si-Mn deoxidization, most of the inclusions are ductile inclusions of manganese silicate type, but (MgO) / (Al ₂ O ₃ ) is 0.
When it is less than 25, the amount of Al ₂ O ₃ -based inclusions increases, and when it exceeds 2, the amount of MgO ₃ inclusions increases, so that it is clear that the present invention is effective in suppressing the formation of non-ductile inclusions.

[0049]

As described above, according to the present invention, it is possible to suppress the formation of non-ductile MgO-based inclusions and process various steel materials such as ordinary steel, stainless steel, special steel, electronic materials, etc. The properties and surface properties can be improved.

[Brief description of drawings]

FIG. 1 MgO mass% and Al of molten slag regulated by the present invention
₂ is a graph showing the relationship with ₂ O ₃ mass%.

FIG. 2 is a schematic diagram of a refining furnace by a high-frequency induction heating method capable of melting 2t of molten steel.

FIG. 3 is a diagram showing the effect of Al ₂ O ₃ concentration in slag on the number of non-ductile inclusions.

FIG. 4 is a diagram showing the effect of MgO concentration in slag on the number of non-ductile inclusions.

FIG. 5 is a diagram showing the influence of slag basicity on the total oxygen concentration.

FIG. 6 is a diagram showing the influence of slag basicity on non-ductile inclusions.

FIG. 7 is a diagram showing the influence of (MgO) / (Al ₂ O ₃ ) in slag on the number of non-ductile inclusions.

FIG. 8 is a diagram showing the influence of (MgO) / (Al ₂ O ₃ ) in slag during melting of austenitic stainless steel on the number of non-ductile inclusions in the steel.

FIG. 9 is a diagram showing the effect of (MgO) / (Al ₂ O ₃ ) in slag during production of bearing steel on the number of non-ductile inclusions in steel.

FIG. 10: (MgO) / (Al ₂ O ₃ ) in slag when melted with Fe-Ni alloy
It is a figure which shows the influence which has on the number of non-ductile inclusions in steel.

Claims (2)

[Claims] 1. A deoxidizer is added to molten steel in the presence of molten slag whose basic component is CaO—SiO ₂ —Al ₂ O ₃ —MgO—CaF ₂ system to deoxidize,
A method for deoxidizing and purifying molten steel to be cleaned, wherein the composition of the molten slag is 5 mass% ≦ Al ₂ O ₃ ≦ 20 mass%, and 5
It is regulated so that mass% ≦ MgO ≦ 20 mass%, and the slag basicity is CaO / SiO ₂ ≦ 2 by weight ratio, and MgO /
A method for deoxidizing and cleaning molten steel characterized by suppressing the formation of MgO-based inclusions by controlling the Al ₂ O ₃ ratio by weight to be 0.25 ≦ MgO / Al ₂ O ₃ ≦ 2. . 2. A deoxidizing agent is added to molten steel in the presence of molten slag whose basic component is CaO—SiO ₂ —Al ₂ O ₃ —MgO—CaF ₂ system to deoxidize,
A method for deoxidizing and purifying molten steel to be cleaned, wherein the composition of the molten slag is 5 mass% ≦ Al ₂ O ₃ ≦ 20 mass%, and 5
It is regulated so that mass% ≦ MgO ≦ 20 mass%, and the slag basicity is CaO / SiO ₂ ≦ 2 and MgO / Al ₂ O _{3 in} weight ratio.
The ratio by weight is 0.4 ≤ MgO / Al ₂ O ₃ ≤ 1.2, and 15 ≤ Al ₂ O
_A method for deoxidizing and cleaning molten steel, which is characterized by suppressing the formation of MgO-based inclusions by controlling ₃ + MgO ≤ 30.