JP3544110B2 - Slag for remelting electroslag and method for producing high cleanliness material using the slag - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a slag for remelting electroslag used for manufacturing a high-cleanliness material suitable for a retaining ring for a turbine, a turbine rotor shaft, and the like, and a method for manufacturing a high-cleanliness material using the slag. .
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electroslag remelting method (hereinafter, referred to as an ESR method) is known as a method for producing a material requiring a high cleanliness. The ESR method is a method in which an electrode is melted by resistance heat of a molten slag, and this molten metal is sequentially solidified in a water-cooled mold to produce a clean ingot. In the ESR method, it is necessary to use a slag having an appropriate specific resistance, viscosity, melting point, and the like, and generally, a ternary slag of CaF ₂ —CaO—Al ₂ O ₃ is used. By the way, in recent years, the characteristics required for materials for improving the reliability of products in various applications have become increasingly severe, and the demand for cleanliness for ESR ingots has also increased.
However, when the slag containing Al ₂ O ₃ is used during the ESR as described above, it is inevitable that non-metallic inclusions mainly composed of Al ₂ O ₃ are generated in the ingot, and as a result, the ESR There is a problem that the cleanness of the ingot deteriorates.
In contrast, in JP-A 7-238344, JP-slag-free (hereinafter _Al 2 _{O 3} - free slag) an _Al 2 _{O 3} is a method for producing high cleanliness steel is disclosed by using, Al _{2 O} 3 _- the use of free slag inclusions large decreases (by Senshokusagu scratch method) PT number of defects is also significantly reduced.
[0003]
[Problems to be solved by the invention]
However, Al ₂ O ₃ is a component for making the slag sufficiently function as a heat source by increasing the specific resistivity of the slag. When a slag containing no Al ₂ O ₃ is used, sufficient heat is generated for melting. It becomes difficult to secure from slag, and a sufficient dissolution rate cannot be obtained. Therefore, in order to obtain a sufficient dissolution rate, a method is required in which the electrode is immersed deeply in the slag to increase the contact area with the slag to compensate for the dissolution rate. However, when the contact area between the electrode and the slag is increased, the ESR voltage becomes unstable (the fluctuation is about 10% in the past, but when this method is employed, the fluctuation exceeds 100%). In addition, the dissolution rate becomes unstable, and the surface of the ingot surface is significantly deteriorated.
[0004]
The present invention has been made in view of the above circumstances, and one of its objects is to provide an electroslag remelting slag capable of producing an ESR ingot having high cleanliness and good surface texture. Another object is to provide a method for manufacturing a high-cleanliness material that can efficiently obtain a high-cleanliness material having high cleanliness using the slag.
[0005]
[Means for Solving the Problems]
To solve the above problems, electroslag remelting for slag of the present invention, in _{weight%, CaF 2: 50~85%,} CaO: 10~30%, BaO: 5~20%, MgO: 10% or less It is characterized by becoming .
[0006]
Further, a method for producing a high cleanliness material of the present invention is characterized in that an electrode of a component corresponding to a target component is redissolved in the slag of the present invention to obtain an ingot of the target component.
[0007]
The slag of the present invention aims at achieving an increase in specific resistance (decrease in specific conductivity) and a reduction in oxygen by adding BaO without adding Al ₂ O _{3 in} order to ensure cleanliness. is there.
The increase in specific resistance enhances the function as a heat source required for melting, and as a result, stable melting of the ESR electrode becomes possible. Thereby, it is not necessary to immerse the electrode deeply in the slag, so that a good casting surface can be obtained without deterioration of the surface of the ingot.
In addition, BaO has a property of high basicity, and has an effect of reducing the amount of residual oxygen in the ESR ingot to make it possible to reduce oxygen by adding to slag, thereby further reducing oxides.
Hereinafter, the action of each component and the reason for determining the content thereof will be described.
[0008]
CaF _2: 50~85%
CaF ₂ is a basic component of slag, and is contained in order to obtain appropriate slag fluidity, necessary melting point, conductivity, and the like. In the present invention, since the viscosity is increased by adding BaO and Al ₂ O ₃ which lowers the melting point is not added, it is necessary to increase the fluidity and lower the melting point more than before, so that CaF ₂ Is set to 50%. On the other hand, if the content of CaF ₂ is large, the specific resistance of the slag is reduced to make the slag difficult to dissolve, and the casting surface is deteriorated. Therefore, the content of CaF ₂ is specified to be 50 to 85%.
For the same reason, it is desirable to set the lower limit to 60% and the upper limit to 80%.
[0009]
CaO: 10 to 30%
CaO has the effect of increasing the basicity of the slag and improving the refining ability. In order to obtain this effect, it is necessary to contain 10% or more. On the other hand, if the content is too large, the viscosity is increased and the melting point is promoted, so the CaO content is set to 10 to 30%.
[0010]
BaO: 5-20%
BaO is effective in lowering the melting point and increasing the specific resistance, and has the effect of reducing oxides in the ingot. However, when the BaO content exceeds 20%, slag boiling becomes severe, and a change in slag composition becomes a problem. Also, when the BaO content increases, the solubility of C in slag increases, and C pickup of ESR occurs. For these reasons, the BaO content is set to 20% or less. Note that the lower limit is set to 5% in order to sufficiently obtain the above operation . For the same reason as above, it is desirable to set the upper limit to 15%. Further, it is more desirable to set the lower limit to 10% for the same reason as described above.
[0011]
MgO: 10% or less MgO decreases the melting point by a small amount of additives, than the specific resistance increases, it is added. However, if added in excess of 10%, the viscosity of the slag increases and the casting surface deteriorates, so the MgO content is set to 10% or less, preferably 5% or less.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The slag of the present invention can be used for the production of 18Mn-18Cr steel, Ni-based and Ni-Fe-based superalloys, etc., but the present invention is not limited to these types of application, and It is required to have a high degree of cleanliness, and is particularly suitable for producing a material in which the presence of alumina inclusions is to be avoided. Therefore, in producing the high cleanliness material of the present invention, the target component of the ingot that is required also depends on the applied material. At the time of ESR, the electrode component does not form a cast ingot, but is subject to component fluctuation. Therefore, it is necessary to provide a component corresponding to the target component in the electrode in consideration of this. In addition, since the degree of the component variation also differs depending on the slag composition and the ESR operating conditions, the components of the electrode are appropriately determined by combining these.
[0014]
In addition, the slag of the present invention is prepared in the above-described component range, and the slag can be manufactured by a conventional method by a conventional method.
In the ESR using the slag of the present invention, the operating conditions are not particularly limited, and the ESR can be performed using an electrode having an appropriate component as described above. In particular, the slag of the present invention has appropriate specific resistivity, fluidity, and melting point similarly to the conventional slag, and can perform ESR in a stable state.
The ESR ingot obtained by using the slag has a good surface texture and a higher cleanness than before. Therefore, in the production of a highly clean material, a material having a high degree of cleanliness can be produced with a high yield by using the ESR ingot.
[0015]
【Example】
As a slag, a conventional material (containing Al ₂ O ₃ ) containing CaF ₂ : 50%, CaO: 20%, and Al ₂ O ₃ : 30%, and CaF ₂ : 80%, CaO: 15%, MgO: 5% Comparative material (Al ₂ O ₃ free) containing, and an inventive material containing 70% of CaF ₂ , 15% of CaO, 10% of BaO, and 5% of MgO are prepared, and the specific conductivity of each slag is prepared. Was measured at a temperature simulating an ESR run. The result is as shown in FIG. 1, and the conventional material and the invention material have the same specific conductivity. On the other hand, in the comparative material in which Al ₂ O _{3 is} free, the specific conductivity is large, that is, the specific resistance is small. For this reason, it has been clarified that the comparative material cannot obtain a sufficient amount of heat generated during ESR. On the other hand, it has been clarified that the invented material can obtain the same calorific value as the conventional material.
[0016]
Next, an alloy containing 18% Cr-18% Mn-0.7% N-remaining Fe as a target component was melted by a conventional method to produce an ESR electrode having a diameter of 550 mm. Using this electrode, ESR was performed using a slag having the above composition. In the operation of ESR, the ESR current, the ESR voltage, and the immersion depth of the electrode were adjusted so that almost the same dissolution rate was obtained when each slag was used.
The obtained ESR ingot having a diameter of 750 mm has a target component, its surface skin is visually observed, and oxide inclusions in each ESR ingot are measured. FIG. 2 shows the relationship.
[0017]
As a result, when the ESR ingot is manufactured using the slag of the material of the present invention and the conventional material, the surface skin is good, while the comparative material is clearly inferior to the surface skin.
Next, looking at oxide inclusions, in the ESR ingot using the comparative material, the number of oxides is smaller and the size is smaller than that using the conventional material. In those used, the number of oxides was further reduced and the size was also reduced, and in particular, the reduction of large oxides was remarkable.
In addition, in the ingot manufactured from the slag of the comparative material, it was necessary to cut the surface to a depth of 10 mm due to poor surface texture.
[0018]
【The invention's effect】
As described above, according to the electroslag remelting slag of the present invention, CaF ₂ : 50 to 85%, CaO: 10 to 30%, BaO: 5 to 20%, MgO: 10% or less by weight% since consisting without alumina inclusions are produced in the ESR ingot, also without the ingot skin it is deteriorated due to no addition of Al2O3, obtained ingot highly clean with good casting surface Can be Further, the oxygen reduction has the effect of further reducing oxygen inclusions.
[0019]
In addition, if a high-cleanliness material is manufactured using the slag, a high-cleanliness material can be obtained with good yield from an ingot having good surface texture, and the manufacturing cost can be reduced. Moreover, since the obtained material has very few inclusions and has an excellent structure, a highly reliable product can be manufactured at low cost by using this highly clean material as a material.
[Brief description of the drawings]
FIG. 1 is a graph showing the specific conductivity of slag of a material of the present invention, a conventional material and a comparative material at each temperature.
FIG. 2 is a graph showing the size and number of oxides in the obtained ESR ingot.

Claims (2)

An electroslag remelting slag composed of 50 to 85% by weight of CaF ₂ , 10 to 30% of CaO, 5 to 20% of BaO, and 10% or less of MgO by weight%. A method for producing a high-cleanliness material, comprising remelting an electrode of a component corresponding to a target component in a slag according to claim 1 to obtain an ingot of the target component.

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