JPH07188794A - Electroslag melting method - Google Patents

Abstract

PURPOSE:To provide an electroslag melting method capable of yielding an ingot free from blowhole defects. CONSTITUTION:This electroslag melting method comprises placing a start block 6 on a copper stool 5 pressed to the molded base of an electroslag melting device and introducing a consumable electrode 3 onto this start block 6. Melting is started in the presence of a flux 8 without contg. CaO and thereafter CaO powder 9 is added or a melting operation is continued in the presence of the CaO-contg. flux at the time of packing the flux and starting melting. CaF2-Al2O3 powder is usable as the flux 8 which does not contain the CaO.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electroslag melting method.

[0002]

2. Description of the Related Art Electroslag melting (hereinafter referred to as "ES
R ”. ), The consumable electrode immersed in the molten slag in the water-cooled mold is energized, the consumable electrode is melted by the Joule heat generated in the molten slag, and the resulting droplets perform refining action in the molten slag. It drops while receiving and is sequentially cast into a water-cooled mold. By the way, conventionally, when starting the melting, there are a hot start method using a slag that has been melted in advance and a cold start method using a start block made of the same material as the material of the consumable electrode, but the cold start method is usually adopted. That is, a copper stool is brought into contact with the mold bottom of the electroslag melting apparatus, a start block is placed on the copper stool, and then an ignition material is placed on the start block. After placing the consumable electrode on it, the consumable electrode is filled with a flux, a voltage is applied to the consumable electrode, and a current is passed between the consumable electrode and the start block.
As a result, an arc is generated between the consumable electrode and the start block, the flux is melted, and molten slag is formed. In this case, the flux may include CaO having a deoxidizing effect, for example, CaF ₂ -Al ₂ O ₃ -C.
aO and the like are used as preferred ones.

[0003]

By the way, when an ingot is melted by the cold start method, a blowhole defect may occur at the bottom of the ingot, that is, a portion formed at the initial stage of melting. Conventionally, such a blow hole generating portion has been cut and removed. Therefore, conventionally, it has been desired to reduce the number of blowholes generated as much as possible to improve the yield. According to the study of the present inventor, since CaO contained in the flux has a water absorbing property, it is considered that water is easily contained in the flux, and as a result, blowholes are formed during formation of the ingot. However, CaO is desired to be used because it has a deoxidizing effect. Therefore, the CaO-containing flux is dried and used, but even if it is dried, it absorbs moisture in a short time of about several minutes in the summer when the partial pressure of water vapor is high,
The desired result is not obtained. The present invention has been made for the purpose of satisfying the above requirements. That is, an object of the present invention is to provide an ESR melting method capable of obtaining an ingot without blowholes.

[0004]

As a result of the study, the inventors of the present invention found that it is preferable to use a flux having a low solubility of hydrogen first and a flux having a high solubility later due to the difference in the solubility of hydrogen in the flux. It was found that such results were obtained, and the present invention was completed. ES of the present invention
In the R melting method, a start block is placed on a copper stool that is in contact with the mold bottom of an electroslag melting device, a consumable electrode is introduced onto the start block, and flux is filled to start melting. After initiating dissolution in the presence of CaO-free flux, CaO
The melting operation is continued by adding powder or in the presence of CaO-containing flux.

The ESR dissolution method of the present invention will be described in detail below. FIG. 1 is a schematic configuration diagram of an ESR device for explaining the ESR melting method of the present invention. Reference numeral 1 denotes a water-cooled mold, which is configured to be cooled by the cooling water introduced into the cooling water jacket 2. 3 is a consumable electrode,
It is gripped by a clamp (not shown) that is vertically movable. The consumable electrode 3 has
A voltage is applied by the power source 4 so that a current flows between it and the copper stool 5.
A start block 6 is placed on the copper stool 5. In addition, 7 is an ignition material, 8 is a flux containing no CaO, and 9 is CaO powder.

When the melting is started by the cold start method in the above ESR apparatus, the copper stool 5 is brought into contact with the bottom of the water-cooled mold 1, and the start block 6 is placed thereon. After placing the ignition material 7 on the start block and introducing the consumable electrode onto the start mold, first, the CaO-free flux 8 is filled between the consumable electrode 3 and the water-cooled mold 1, and the CaO powder 9 is put thereon. Then, the state of starting to dissolve is obtained. When a voltage is applied to the consumable electrode in this state, an arc is generated between the consumable electrode and the start block, the flux is melted by the action of the ignition material, and the remelting of the consumable electrode is started. After the melting operation is completed, the formed ingot may be taken out from the water-cooled mold, and the portion of the bottom portion where deoxidation is not sufficient may be cut.

The ESR device of FIG. 1 is a fixed type in which a copper stool is fixed to a hydrogenation mold.
It can also be applied to an ESR device of a type in which a copper stool is moved downward to pull out an ingot.
In this case, in the ESR device, the ingot formed in the water-cooled mold is continuously pulled down by moving the copper stool downward, and is pulled up and taken out after the completion of the melting operation.

In the present invention, the flux is C
_{aF 2, Al 2 O 3,} TiO 2, MgO, but one or more combinations selected from SiO ₂ and CaO can be used, at the time of dissolution starts, it is necessary to use a flux containing no CaO. CaO may be filled on top of the CaO-free flux at the start of melting, or may be filled at an appropriate time after the start of melting. Further, instead of CaO, CaO-containing flux may be filled.

[0009]

In the present invention, since the melting operation is carried out in the presence of the flux containing no CaO at the beginning of melting, the water content in the flux at the beginning of melting is reduced. Since the water content in the flux reaches an equilibrium state as the temperature rises, the presence of the CaO-containing flux at that stage eliminates the effect of water absorption by CaO. Therefore, according to the present invention, the influence of moisture at the beginning of ingot formation is reduced, and thus an ingot without blowhole defects can be obtained.

[0010]

【Example】

Example 1 ESR dissolution was performed using the ESR apparatus shown in FIG. E
The conditions for SR dissolution were as follows. As a consumable electrode,
A φ175 mm high carbon steel (SKH9) was used, and a copper mold having a size of φ240 mm × length 2000 mm was used as the water-cooled mold. The copper stool on which the start block was placed was brought into contact with the bottom of the copper mold, an ignition material was placed on the start block, and then a consumable electrode was introduced. Between the consumable electrode and the copper stool,
As a flux, 12 kg of a powder having a composition (wt%) of 80CaF ₂ -20Al ₂ O ₃ was filled, and 3 kg of CaO was charged thereon, and in that state, a current of 50 V and 7 kA was flowed to start the melting, A 1400 mm thick ingot was obtained. No blowholes were generated at the bottom of the formed ingot, but deoxidation was not sufficient within the range of 30 mm from the lower end, so 50 mm from the lower end was cut and removed. Comparative Example 1 At the start of melting, as a flux, 60CaF ₂
-20Al ₂ O ₃ powder 15 having the composition -20CaO
A length of 1 was obtained under the same conditions as in Example 1 except that 1 kg was filled.
A 400 mm ingot was prepared. Since a blow hole was generated in the range of 150 mm from the lower end on the bottom of the formed ingot, 200 mm was cut from the lower end and removed.

Example 2 ESR dissolution was performed using the ESR apparatus shown in FIG. E
The conditions for SR dissolution were as follows. As a consumable electrode,
A φ380 mm steel material (SUS440C) was used, and a copper mold having a size of φ520 mm × length 2000 mm was used as a water-cooled mold. The copper stool on which the start block was placed was brought into contact with the bottom of the copper mold, an ignition material was placed on the start block, and then a consumable electrode was introduced. Between the consumable electrode and the copper stool,
As a flux, 64 kg of a powder having a composition (wt%) of 75CaF ₂ -25Al ₂ O ₃ was filled, and 16 kg of CaO was put on the powder, and in that state, 45 V, 11 kA
The current was applied to start melting, and an ingot having a length of 1200 mm was obtained. No blowholes were generated at the bottom of the formed ingot, but deoxidation was not sufficient within the range of 50 mm from the lower end, so 70 mm from the lower end was cut and removed. Comparative Example 2 At the start of melting, as a flux, 60CaF ₂
Powder having a composition of -20Al ₂ O ₃ -20CaO 80
A length of 1 was obtained under the same conditions as in Example 2 except that 1 kg was filled.
A 200 mm ingot was prepared. Since a blow hole was generated in the range of 150 mm from the lower end on the bottom of the formed ingot, 200 mm was cut from the lower end and removed.

[0012]

As described above, the present invention is
Since the ingot is formed in the presence of the CaO-free flux, the influence of water at the beginning of ingot formation can be eliminated, and an ingot without blowhole defects can be obtained, thus improving the yield.

[Brief description of drawings]

FIG. 1E for explaining the ESR dissolution method of the present invention
It is a schematic block diagram of an example of an SR dissolution apparatus.

[Explanation of symbols]

1 ... Water cooling mold, 2 ... Cooling water jacket, 3 ... Consumable electrode, 4
… Power supply, 5… Copper stool, 6… Start block, 7
... Ignition material, 8 ... CaO-free flux, 9 ... C
aO powder.

Claims (1)

[Claims] 1. When a start block is placed on a copper stool that is in contact with the bottom of a mold of an electroslag melting apparatus, a consumable electrode is introduced onto the start block, and flux is filled to start melting. After initiating dissolution in the presence of CaO-free flux, CaO
An electroslag melting method, characterized in that the melting operation is continued by adding powder or in the presence of CaO-containing Lux.