JPS6027445A - Production of monolithic steel ingot by electroslag refining - Google Patents

Abstract

PURPOSE:To improve the melt stickability between a material to be melted and a molten metal with a titled process for producing a steel ingot having different sectional areas in an axial direction by rotating circumferentially a slag bath and the molten metal in the stage of melt sticking. CONSTITUTION:A partial ingot 2 is fixed perpendicularly on a water-cooled surface plate 7 connecting to a power source 10 through a current collector 9 by penetrating the central hole in the bottom of an auxiliary water-cooled casting mold 14 in such a way that at least the top end thereof is housed into a water-cooled casting mold 3. A slag bath 4 is formed into the space consisting of the mold 14 and the ingot 2 and the tip of a consumable electrode 1 to be electroslag-refined is dipped therein and is conducted with electricity, by which said electrode is successively melted. A molten metal bath 6 is formed in the lower part of the bath 4 and is solidified to fill gradually the space in the mold 14. The mold 3 and the ingot 2 are rotated via gears 12, 13 and the plate 7 by a speed-reducing motor 11 and therefore the baths 4, 6 rotate circumferentially. Then the quantity of the heat transmitted from the bath 6 to the ingot 2 is increased, by which the current density for melting is uniformly distributed and the steel ingot 2 is uniformly melted.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for producing a monolithic steel ingot by electroslag remelting, and particularly to a method for producing a monolithic steel ingot having different axial cross-sectional areas. Regarding preferred methods. The present invention can be applied to rolling rolls, rotor shafts, and other various types of shafts.

[Background of the invention]

By welding the material to be melted, which consists of a separately prepared partial steel ingot and the remainder of the consumable electrode, with the molten metal produced by electroslag remelting of the consumable electrode, an irregularly shaped integral body with different axial cross-sectional areas is formed. A method of manufacturing a steel ingot has been proposed. For example, it is described in Japanese Patent Publication No. 46-17426.

First, the above-mentioned conventional method will be explained based on the case of manufacturing a rolling roll having journal portions at both ends of the main body portion shown in FIG. 1.

The consumable electrode 1 to be electroslag remelted is a metal rod having the necessary geometry and chemical composition to form the roll body and one journal part (upper journal part) to be manufactured. The partial steel ingot 2 is a separately prepared metal rod, and is attached to the other journal part (lower journal part) of the roll.
It has the necessary geometry and chemical composition to form. This partial steel ingot 2 protrudes into a central hole provided at the bottom of the water-cooled mold 3 and is fixed vertically.

Electricity is applied between the consumable electrode 1 and the partial steel ingot 2 via the slag bath 4. The slag bath 4 is formed by either a cold start method or a hot start method. Consumable electrode 1
The melting current flowing from the to the partial steel ingot 2 heats the slag bath 4 and melts the -F end of the consumable electrode 1 as well as the upper end of the partial steel ingot 2 protruding above the bottom surface of the water-cooled mold 3, and finally both is welded and solidified. The roll body 5 is then formed by an electroslag remelting process, and after the required height of the roll body is obtained, the electroslag remelting process is completed and the remaining part of the consumable electrode 1 is placed in the molten metal bath 6. The upper journal part is formed by welding the casting.

According to the above method, advantages such as being able to manufacture a composite roll in which the roll body and journal are made of different materials, shortening electroslag remelting time, and reducing forging work can be expected, but the welding process is extremely slow. The disadvantage is that the melting current density is unavoidable during the remelting of the electroslag during the welding process of the molten metal generated by remelting the electroslag and the partial steel ingot. Due to uneven distribution, the amount of heat transferred from the slag bath to the partial steel ingots is uneven, and a large amount of heat generated in the slag bath when electricity is applied is transferred to the partial steel ingots and the water-cooled mold. In extreme cases, it is difficult to obtain uniform welding strength over the entire upper end of the partial steel ingot due to insufficient heat required to melt and weld the upper end of the partial steel ingot. This may lead to non-adhesion with molten metal.
It can no longer be used as a product.

On the other hand, during the welding process between the molten metal and the remaining part of the consumable electrode, the temperature of the consumable electrode is not necessarily uniform, so even if you try to melt and weld the lower end of the consumable electrode, welding will not be uniform. It won't happen. In addition, although the electrode has a large heat capacity, only a portion of the heat of the molten metal and slag bath can be used, making it impossible to obtain a large welding strength. If the heat shortage is extreme, casting defects such as slag entrainment and voids will occur at the welding boundary.

[Purpose of the invention]

An object of the present invention is to improve the weldability between a material to be melted consisting of a separately prepared partial steel ingot and the remaining part of a consumable electrode and molten metal produced by electroslag remelting of the consumable electrode. An object of the present invention is to provide a method for manufacturing an integral steel ingot by electroslag remelting.

[Summary of the invention]

In the present invention, in order to improve the weldability between the material to be melted and the molten metal, the slag bath and the molten metal are rotated in the circumferential direction during the welding process.

In order to completely weld the material to be melted and the molten metal, it is necessary to raise the temperature sufficiently so that the surface of the material to be melted melts. The amount of heat that enters the material to be melted from the slag bath is calculated using the following formula.

Q=H(T g −T o ) Here, Q is heat input, t (Cat/y? ・s), H
is the heat transfer coefficient (cat/c-·S·C), T8 is the slag bath temperature (c), and To is the temperature of the material to be melted (1?). Based on this equation, it can be seen that in order to increase the amount of heat input to the material to be melted, it is necessary to (1) increase the slag bath temperature Tg, and (2) increase the heat transfer coefficient H.

As a result of extensive experiments on how to increase the slag bath temperature near the material to be melted without increasing the input (current, voltage), we found that
A method of rotating the slag bath in the circumferential direction by imparting rotation in the circumferential direction to the water-cooled mold and the material to be melted, an external magnetic field is obtained in the slag bath, and the slag is removed by the magnetic field excited by the melting current and the external magnetic field. A method of rotating the bath circumferentially was found to be effective. In other words, when no rotation or electromagnetic stirring is applied, the slag bath temperature distribution in the radial direction is
As shown in Figure (a), when rotation or electromagnetic stirring is applied, the cold, heavy slag is pushed toward the mold wall by centrifugal force, while the hot, light slag moves toward the center. As a result, the slag bath temperature distribution in the radial direction was as shown in (b), and it was confirmed that the slag bath temperature near the material to be melted increased.

On the other hand, it is known that the value of the heat transfer coefficient increases by imparting a relative velocity to the slag bath and the material to be melted. Examples of this method include rotating a water-cooled mold, rotating a steel ingot, and rotating a slag bath in the circumferential direction by electromagnetic stirring. The same applies to heat transfer between the molten metal and the material to be melted.

[Embodiments of the invention]

A water-cooled mold 3 is fixed via a mold support frame 8 on a water-cooled surface plate 7 having an 11-rotation mechanism, which will be described below with reference to FIG. The water-cooled surface plate 7 is connected to a power source 10 via a plurality of collectors 9 in contact with its side surface, and is connected to a gear 12.1 by a reduction motor 11.
It is designed to be rotated through 3. The bottom surface of the water-cooled mold 3 has holes necessary to accommodate the partial steel ingot 2, and is connected to an auxiliary water-cooled mold 14, which has a smaller cross-section than the water-cooled mold 3 and a larger cross-section than the partial steel ingot. Auxiliary water cooling mold 14
has a hole in the bottom surface capable of accommodating the partial steel ingot 2 and a length necessary to obtain the desired welding strength.

A pipe-shaped or plural rod-shaped auxiliary electrode 15 is arranged above the water-cooled mold 3 so as to surround the consumable electrode 1, and is connected to a power source 1o via a changeover switch 16. Auxiliary electrode 1
5 is neither expendable nor non-expendable. Although not shown, when performing electromagnetic stirring, an electromagnetic coil is arranged around the auxiliary water-cooled mold 14 and the water-cooled mold 3.

The case where a roll is manufactured using such an apparatus will be explained with reference to FIGS. 3 and 4.

The electroslag remelted consumable electrode 1 has the necessary geometries and chemical composition to form the roll body and one journal part (upper journal part) to be manufactured. The partial steel ingot 2 is separately produced by electroslag remelting or metal casting, and has the necessary dimensions and chemical composition to form the other journal part (lower journal part) of the roll. In order to facilitate melting of the tip of the partial steel ingot 2, it is desirable that the cross section be made step-like or conical so that the cross section becomes smaller as it goes upward. This partial steel ingot 2 is fixed vertically on the water-cooled surface plate by passing through the center hole at the bottom of the auxiliary water-cooled part W14 so that at least the tip thereof is accommodated in the water-cooled mold 3. At the tip of the consumable electrode 1, a pipe-shaped or a plurality of rod-shaped electrodes are fixed by welding or the like, surrounding the partial steel ingot 2, and are used to fill the inside of the auxiliary water-cooled mold.

First, a suitable amount of molten slag is added to the space formed by the auxiliary water-cooled mold 14 and the partial steel ingot 2 to form a slag bath 4, and the pipe-shaped or rod-shaped electrode at the tip of the consumable electrode 1 is immersed in the slag bath 4. Then, apply electricity to dissolve it. A molten metal bath 6 is formed below the slag bath 4, solidifies and gradually fills the space inside the auxiliary water-cooled mold.

At this stage, since the water-cooled mold 3 and the partial steel ingot 2 are rotated in the circumferential direction, the slag bath 4 and the molten metal bath 6 rotate in the circumferential direction. In this case, the temperature of the slag bath near the partial steel ingot increases due to the action of centrifugal force, so the amount of heat transferred from the slag bath to the partial steel ingot increases, and the weldability between the molten metal and the partial steel ingot 2 improves. do. Further, by rotating, the non-uniform portion of the dissolution current density distribution is not fixed at a specific position, but is uniformly applied. As a result, the slag bath temperature is averaged, so that the partial steel ingots 2 penetrate uniformly and the welding strength becomes uniform.

When the upper surface of the slag bath 4 reaches the upper end of the auxiliary water-cooled mold 14, an appropriate amount of molten slag is added. Solid slag powder may be added.

Melting of the pipe-shaped or rod-shaped electrode continues until the upper end surface of the partial steel ingot 2 is melted and welded to the molten metal. At this stage, the partial steel ingot 2 has been sufficiently preheated, so that the upper end surface of the partial ingot 2 is well welded to the molten metal.

Subsequently, the consumable electrode 1 is remelted with electroslag to form the roll body 5. At the stage of forming the roll body 5, the rotation of the water-cooled mold 3 and the partial steel ingot 2 may be stopped.

After the roll body 5 reaches the required height, the electroslag remelting step is completed and the remaining tip of the consumable electrode 1 is immersed in the slag bath 4. Then, the pipe-shaped or plural rod-shaped auxiliary electrodes 15 arranged around the consumable electrode 1 are immersed in the slag bath 4, and the power supply 10 is connected to the
The slag bath 4 is heated by connecting it to the slag bath 4 and applying electricity. At the same time, rotation is applied to the water-cooled mold 3 and the partial steel ingot 2. In this way, a relative velocity is generated between the remaining part of the consumable electrode 1 and the slag bath 4, and as a result, heat transfer is promoted and the remaining part of the consumable electrode 1 is easily melted, and the remaining part of the consumable electrode 1 is easily melted and is highly welded to the molten metal. You will be able to do this. It goes without saying that similar effects can be obtained by electromagnetically stirring the slag bath 4 and the molten metal bath 6.

When the remaining portion of the consumable electrode 1 is plunged into the molten metal bath 6 and cast, the two are welded together to form an upper journal portion and an integral roll is manufactured.

The rotation direction of the slag bath 4 and the molten metal bath 6 may be arbitrary as long as it is in the circumferential direction. You can also do this.

In the embodiment, a roll in which the journal portion and the body portion are made of the same material has been described, but it goes without saying that a so-called composite roll made of different materials can be manufactured.

〔Effect of the invention〕

As described above, according to the present invention, the welding of the molten metal produced by electroslag remelting of the consumable electrode and the material to be melted, which is made up of a separately prepared partial steel ingot and the remaining part of the consumable electrode, is carried out to a high degree. It can be done quickly and firmly.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the state of roll manufacturing according to the prior art, FIG. 2 is a radial slag bath temperature distribution diagram, and FIG. 3 is a sectional view of the electroslag remelting device used in the present invention.
FIG. 4 is a sectional view showing a state in which roll manufacturing is also carried out. DESCRIPTION OF SYMBOLS 1... Consumable electrode, 2... Partial steel ingot, 3... Water cooling mold, 4... Slag bath, 5... Roll body, 6...
- Molten metal bath, 7... Water-cooled surface plate, 8... Mold support frame, 9... Current collector, 10... Electric 4I7. ．． 11...
Reduction motor, 12.13... Gear, 14... Auxiliary water cooling mold, 15... Auxiliary electrode, 1-6... Changeover switch. Agent Patent Attorney Akio Takahashi's Illustrated Book, Uncovered

Claims (1)

[Claims] 1. At least a part of a separately prepared partial steel ingot is placed in the bottom space of a water-cooled mold, and a consumable electrode inserted into the water-cooled mold is remelted with electroslag to form a main steel ingot. , after welding the main steel ingot and the partial steel ingot and completing the electroslag remelting process, weld the remaining part of the consumable electrode into the molten metal bath of the main steel ingot to form an integral steel ingot. The manufacturing method is characterized in that the partial steel ingot and the main steel ingot, and the main steel ingot and the remaining portion of the consumable electrode are welded while applying circumferential rotation to a slag bath and molten metal. A method for producing an integral steel ingot by electroslag remelting. 2. Integration by electroslag remelting according to claim 1, characterized in that the rotation of the slag bath and the molten metal is performed by rotating the water-cooled mold and the partial steel ingot in a circumferential direction. Method of manufacturing steel ingots. 3. In claim 1, an external magnetic field is applied to the slag bath and the molten metal, and the slag bath and the molten metal are rotated in a circumferential direction by the magnetic field excited by the melting current and the external magnetic field. A method for producing an integral steel ingot by electroslag remelting. 4. In claim 1, a pipe-shaped electrode or a plurality of rod-shaped electrodes that cover the maximum cross section of the partial steel ingot disposed in the bottom space of the water-cooled mold are attached to the tip of the consumable electrode, and at least the An integrated steel ingot by electroslag remelting, characterized in that electroslag remelting is started in a state where the pipe-shaped electrode or the rod-shaped electrode and the partial steel ingot face each other, and the consumable electrode is electroslag-melted continuously. manufacturing method. 5.% - The method for manufacturing an integral steel ingot by electroslag remelting according to claim 1, wherein the cross section of the partial steel ingot becomes smaller toward the top or has an equal cross section. . 6. In claim 1, the rotation of the slag bath and the molten metal is performed by rotating the water-cooled mold and the partial steel ingot in the circumferential direction; A method for producing an integral steel ingot by electroslag remelting, characterized in that the process is carried out by applying an external magnetic field and using a melting current in combination with a magnetic field excited by the external magnetic field. 7. According to claim 2 or 3, while heating the slag bath by passing a melting current through a pipe-shaped or plural rod-shaped auxiliary electrodes disposed around the consumable electrode, the remaining portion of the consumable electrode is heated. and the main steel ingot are welded together. 8. Claim 4, wherein an auxiliary water-cooled mold having a smaller cross section than the water-cooled mold is fixed to the bottom surface of the water-cooled mold having holes necessary for accommodating the partial steel ingot, and the auxiliary water-cooled mold is Integration by electroslag remelting, characterized in that the space formed by the and the partial steel ingot is filled by electroslag remelting of the pipe-shaped or rod-shaped electrode attached to the tip of the consumable electrode. Method of manufacturing steel ingots.