JPH0734987B2 - Method for producing directionally solidified ingot by electroslag remelting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a directionally solidified ingot by remelting electroslag, and in particular, a molten steel is prepared by changing a drop position of a droplet formed at an electrode tip. The present invention relates to a method for producing an ingot having a solidified interface shape of a pool, which is more excellent in directional solidification.

[Conventional technology]

In the electroslag remelting method, the molten steel is constantly heated to the slag pool in the upper part even during solidification from the lower part,
The temperature gradient at the solidification interface is larger than that of other casting methods, and it can be said that this is an advantageous process for directional solidification. A conventional method for producing a directionally solidified ingot by remelting electroslag utilizing such characteristics is described in JP-A-51-50814 or JP-A-55-64957. The former is continuously drawn from the electroslag remelted ingot from the water-cooled mold, cooled in the cooling water tank immediately below the water-cooled mold, the latter by heating the molten steel pool by the electromagnetic induction heating coil installed on the outer periphery of the water-cooled mold, Flatten the solidification interface shape,
In addition, it is a method of increasing the temperature gradient to cause directional solidification.

[Problems to be solved by the invention]

The above-mentioned prior art does not mention the influence of the heat carried into the molten steel pool by the molten steel droplets formed at the consumable electrode tip during electroslag remelting on the solidification interface shape. There is a problem that directional solidification cannot be sufficiently performed.

That is, in electroslag remelting, the droplets formed at the tip of the consumable electrode are superheated to a temperature higher than the liquidus temperature in the slag pool and continuously fall into the molten steel pool. As a result, the temperature of the droplet drop portion becomes high, solidification is delayed, and the solidification interface shape of the molten steel pool becomes remarkably V-shaped. Since the crystal growth direction is almost perpendicular to the solidification interface, directional solidification cannot be performed when the solidification interface shape of the molten steel pool becomes V-shaped.

In the known example, the solidification interface shape is flattened by controlling the solidification by the cooling effect under the molten steel pool or the heating on the side of the molten steel pool, but it is impossible to eliminate the influence of the droplets.

The object of the present invention, in the method of producing a directional solidified ingot by electroslag remelting, in consideration of the influence of the drop of droplets formed at the consumable electrode tip during electroslag remelting on the solidification interface shape. It is another object of the present invention to provide a method capable of flattening the solidification interface shape to improve directional solidification.

[Means for solving problems]

The above objective is accomplished by imparting eccentric relative rotation to the consumable electrode and the ingot during electroslag remelting. This relative eccentric rotation causes the consumable electrode to be eccentric with respect to the axis of the water-cooled mold to impart rotation to the mold or to position a stub supporting the consumable electrode on the axis of the mold,
This can be done by eccentrically connecting the consumable electrode to the stub and applying rotation to the stub. Alternatively, both may be used together.

[Action]

Since the consumable electrode and the water-cooled mold are eccentrically rotated with respect to each other, the drop position of the liquid drop from the consumable electrode constantly changes in the horizontal direction in the water-cooled mold, and the liquid drops drop on average. Therefore, the temperature distribution in the horizontal direction of the molten steel pool is made uniform, and as a result, the solidification interface shape becomes flat and directional solidification is achieved.

〔Example〕

 One embodiment of the present invention will be described with reference to FIG.

The water-cooled mold 2 is placed on the water-cooled surface plate 1, and the consumable electrode 3 is eccentrically inserted therein. A plurality of current collecting brushes 4 are attached to the side surface of the water-cooled surface plate 1, and can be rotated in the circumferential direction by a motor 6 via a gear 5. As a result, the consumable electrode 3 and the ingot 7 are given eccentric relative rotation with respect to each other.

In the above state, electroslag remelting is started by hot start or cold start method. The consumable electrode 3 has its tip immersed in the slag pool 8 and the other end connected to a power source 10 via a cable 9. The tip of the consumable electrode 3 is melted by the Joule heat of the slag pool 8 and drops 11
Then, it falls to the bottom of the slag pool 8 and the molten steel pool 12
To form. The molten steel pool 12 is cooled by heat transfer to the water-cooled mold 2 and the ingot 7 that has already solidified, but since the water-cooled mold 2 is eccentrically rotated with respect to the consumable electrode 3,
The drop position of the droplet 11 is not fixed, and it constantly changes in the horizontal direction in the water-cooled mold 2 and drops on average. For this reason,
The horizontal temperature distribution of the molten steel pool 12 is made uniform, and as a result, the solidification interface shape becomes flat and directional solidification is achieved.

FIG. 1 shows an embodiment in which rotation is imparted to the mold, but as another embodiment, as shown in FIG. 2, the consumable electrode 3 is eccentrically connected to the stub 13, and the stub is connected.
By arranging 13 concentrically with the water-cooled mold and rotating the stub 13, the consumable electrode 3 and the ingot 7 can be eccentric to each other and relatively rotated. The other end of the stub 13 is connected to the power source 10 via the cable 9. The water-cooled mold is not shown in FIG.

Distance from water-cooled mold wall to consumable electrode is at least 10 mm
It is desirable to set the above. If this distance is less than 10 mm, the solubility and fluidity of the slag powder added during the melting of the elector slag will be impaired, and the ingot casting surface will be likely to deteriorate.

The relationship between the diameter D of the water-cooled mold and the diameter d of the consumable electrode is d / D =
It is preferably in the range of 0.6 to 0.2. When the value of d / D is small, it becomes difficult to flatten the solidification interface and productivity is deteriorated. From this point, d / D is preferably 0.2 or more. As d / D becomes larger, the solidification slows down and the solidification interface tends to be dented, and the liquid drops fall into the center of the ingot, increasing the delay of solidification and making the solidification interface flat. From this, d /
The value of D is preferably 0.6 or less.

The rotation speeds of the mold and the consumable electrode are determined by the size of the ingot and the consumable electrode, and the melting conditions such as current and voltage.

Specific examples of the present invention will be described below.

Example 1 JI with a diameter of 50 mm was placed inside a water-cooled mold having a diameter of 120 mm and a height of 350 mm.
Electroslag remelting was performed using a consumable electrode of S standard SK3 and using calcium fluoride 40% -calcium oxide 30% -alumina 30% as slag. Voltage is 40V, current is 1
It was set to 800A. The consumable electrode was eccentric to the center axis of the mold by 25 mm, and the rotation speed of the mold and the ingot was 10 rpm. As a result of longitudinally examining the steel ingot, columnar dendrites were formed up to the center of the ingot. Further, FIG. 3 ((a) in the figure) shows the result of measuring the crystal growth angle (dendritic growth angle) with respect to the horizontal surface of the ingot. Compared with the result of Comparative Example 1 (FIG. 3 (b)) described below in which the consumable electrode and the mold were not eccentrically rotated, melting was performed under the same conditions as in this Example. It is clear that it is superior to.

Comparative Example 1 Example 1 except that the consumable electrode and the mold were not eccentrically rotated.
Electr slag was redissolved under exactly the same conditions as above. The dendrite growth angle is shown in (b) of FIG. As a result of macroscopic observation, equiaxed dendrite with no directionality was recognized in the central part of the ingot.

Example 2 Using the same mold as in Example 1, a consumable electrode made of a heat-resistant Ni alloy having a composition shown in Table 1 and having a diameter of 50 mm was inserted into the mold, and titanium oxide was slightly added to the slag having the same composition as in Example 1. Using the added slag, electroslag remelting was performed while flowing argon gas into the water-cooled mold. The other conditions were the same as in Example 1. When the obtained ingot was forged, the ingot by the conventional method cracked along the crystal grain boundaries, but did not occur in the ingot obtained in this example, the heat of the directionally solidified ingot. It was revealed that the inter-workability was remarkably improved.

EFFECTS OF THE INVENTION As is clear from the above description, according to the present invention, the eccentric rotation is imparted to the consumable electrode and the mold during the remelting of the electroslag, and the drop of the droplet formed at the electrode tip is dropped. By changing the position, the solidification interface shape of the molten steel pool can be flattened and the directional solidification of the ingot can be enhanced. This makes it possible to obtain an ingot having excellent mechanical properties and physical properties in a specific direction.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an electroslag remelting apparatus according to an embodiment of the present invention, FIG. 2 is a view showing a connection between a stub and a consumable electrode according to another embodiment of the present invention, and FIG. It is a comparison figure of the solidification characteristic of the implemented ingot and the conventional electroslag remelting ingot. 1 ... Water-cooled surface plate, 2 ... Water-cooled mold 3 ... Consumable electrode, 4 ... Current collecting brush 5 ... Gear, 6 ... Motor, 7 ... Ingot, 8 ... Slug pool, 9 ... Cable, 10 ...... Power supply 11 …… Droplet, 12 …… Molten steel pool 13 …… Stub.

Claims (5)

[Claims] 1. A method for producing a directionally solidified ingot by remelting a consumable electrode in a molten slag pool in a water-cooled mold to produce a directionally solidified ingot, wherein the consumable electrode and the solidified ingot are exchanged during the electroslag remelting. A method for producing a directionally solidified ingot by electroslag remelting, characterized in that eccentric relative rotation is applied to. 2. The consumable electrode is displaced from the axis of the water-cooled mold,
And, the rotation of the water-cooled mold is applied to the mold.
A method for producing a directionally solidified ingot by remelting electroslag according to the item. 3. A stub that supports the consumable electrode is positioned on the axis of the water-cooled mold, the consumable electrode is eccentrically connected to the stub, and the stub is rotated about the axis. 2. A method for producing a directionally solidified ingot by remelting electroslag according to claim 1. 4. The directional solidification casting by remelting electroslag according to claim 1, 2 or 3, wherein the distance from the wall surface of the water-cooled mold to the consumable electrode during eccentric rotation is at least 10 mm or more. Method of manufacturing lumps. 5. The diameter D of the water-cooled mold and the diameter d of the consumable electrode are
The method for producing a directionally solidified ingot by remelting electroslag according to claim 4, wherein d / D = 0.6 to 0.2.