JPH0622745B2 - High quality ingot manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a high-quality steel ingot, and more particularly to a method for producing a high-quality steel ingot having a beautiful surface and a sound internal quality.

[Conventional technology]

In order to prevent defects in the steel ingot due to solidification shrinkage, a riser is generally attached to the head of the ingot, and various methods have been devised for keeping the riser warm. Above all, the molten slag is charged on the molten steel surface in the riser, the electrode is immersed in the molten slag and an electric current is passed between the electrode and the molten steel, or between a plurality of electrodes, and the resistance heat generation of the slag is used. The method of heating the molten steel in the riser is already known, and is called the electroslag hot-top method (hereinafter referred to as ESHT method).

The BEST method, which is regarded as a representative technique of the ESHT method, is developed by Austrian VEW company and disclosed in Japanese Patent Publication No. 47-39817. The outline is as shown in FIG.
A mold 4 is placed on top of which a feeder frame 6 cooled by a liquid is placed. A part of the molten steel 8 forms a solidified shell 10, a molten slag 12 is charged in the feeder frame 6, and the outside thereof is a solidified slag 14. Molten slag 12
A consumable electrode 16 is immersed in the battery and connected to a power supply 18. Further, the auxiliary electrode 20 is provided when a special metallurgical reaction is added by superimposing a direct current.

According to the above apparatus, the amount of feeder to be cut off can be minimized and the generation of shrinkage holes in the steel ingot can be avoided, and the negative segregation of the bottom of the steel ingot, the positive segregation of the head, and the improvement of inclusions can be achieved. It is possible.

However, in this method, as the solidification of the molten steel 8 progresses, a void is created between the solidified shell 10 and the mold 4, and as the solidified shell 10 near the molten slag 12 is redissolved in this void, the molten slag 12 and the molten steel 8 are separated. In addition to the problem that the amount of molten slag becomes insufficient, it is liable to cause a problem that the ingot casting surface is damaged and a part of the electrode material flows out into the voids to reduce the yield.
A part of the amount of heat obtained by the electrode 16 is part of the water-cooled feeder frame 6
There is a lot of loss of energy removed by.

As a method for solving the problem that molten steel, molten slag, and the like enter the voids formed between the mold and the solidified shell described above,
Japanese Unexamined Patent Publication No. 53-73425 shown in FIG. 5 has been proposed.
In the contact area between the edge of the molten steel 8 and the cooling inner wall of the feeder frame 6 in FIG. 3, the points A to B are strongly cooled.
When the molten steel solidified shell contracts, the cooled molten steel solidified shell between AB moves to A′B ′. Although the slag enters the annular gap formed by this contraction, it is solidified at the inlet of the gap and forms a seal plug 22 for the slag that is about to further enter. Since the height of the slag bath is not affected by the formation of this seal plug 22, the electric heating state for forming Joule heat does not change. Therefore, not only the required energy supply, but also the metallurgical effects that depend on it, remain constant over time.

Next, FIG. 4 shows an embodiment in which the molten steel 8 is not poured above the mold 4, and the conical surface 26 has an angle α with respect to a vertical line so that the protrusion 24 does not prevent the molten steel solidified shell from contracting. However, at the time of solidification contraction, the slag seal plug 22 is formed between AC and A′C ′ as described above. Further, FIG. 5 shows a method in which a feeder frame in which a refractory material 30 is attached to the metal structure 28 is used, and the metal structure 28 is cooled by absorbing heat to perform the same operation.

However, these methods cool the upper part of the molten steel to form a solidified shell and prevent the slag and the molten steel from flowing into the gap between the mold and the solidified shell, which is a lossy method in terms of energy efficiency. is there.

[Problems to be solved by the invention]

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing a high quality steel ingot capable of preventing molten slag and molten steel from flowing into a gap between a mold and a solidified shell without energy loss. Especially.

[Means and Actions for Solving Problems]

The gist of the present invention is as follows. That is, molten steel is injected into the mold and the feeder frame, molten slag is charged on the molten steel surface in the feeder frame, and energy is supplied to the molten slag to heat and heat the molten steel in the feeder frame. In the method for producing a high-quality steel ingot, a slag frame whose lower end is immersed in the molten steel at least 80 mm or more is arranged in the feeder frame, and the molten slag is held on the molten steel surface in the slag frame. , Filling the gap between the feeder frame and the slag frame with a heat insulating material, and keeping the molten steel in contact with the inner and lower ends of the slag frame in a fluidized state for most of the casting time, the molten steel and the molten slag are It is a method for producing a high-quality steel ingot, which prevents flowing into a gap formed between a solidified shell in contact with a mold.

The details of the present invention will be described with reference to FIG. The description of the conventional example shown in FIG. 2 will be omitted because it overlaps, but the slag frame 32 whose lower end is immersed in the molten steel 8 in the feeder frame 6
Is provided. The slag frame 32 has a suitable depth of molten steel 8
Since it is immersed inside, it can be moved up and down by floating float type or slide type movable type. The minimum value H of the immersion depth in the molten steel of the slag frame 32 is the molten slag thickness: 200 m
If m, molten steel specific gravity: 7.0, and molten slag specific gravity: 2.5, it can be calculated by the following formula.

Therefore, in order to prevent the molten slag from flowing out in consideration of the kinetic energy at the time of pouring, the immersion depth of the slag frame 32 in the molten steel 8 needs to be 80 mm or more. The slag frame 32 has a diameter smaller than that of the feeder frame 6 and has a sufficient internal volume for accommodating the molten slag 12, and the material of the slag frame 32 is a refractory material or a composite material such as water-cooled metal. 8,
It is necessary to sufficiently withstand heat shock and melting damage from the molten slag 12.

A heat insulating material 34 is filled in the gap between the feeder frame 6 and the slag frame 32. The chemical composition of the heat insulating material 34 is Si by weight.
_{O 2: 8~15%, Al 2} O 3: 25~35%, metal Al: nineteen to two
_{3%, Fe 2 O 3 +} FeO: 12~16%, total carbon: 6-10%
Etc. are preferred.

The slag frame 32 of the present invention moves up and down in accordance with the positional change of the molten steel surface accompanying the solidification volume contraction of the steel ingot or the positional change of the molten steel surface caused by the melting of the electrode 16, and the molten steel 8 and the molten slag 12 are cast into the mold. 4 and the solidified shell 10 are prevented from flowing into a gap 36 formed between the solidified shell 10 and the slag frame 3
By keeping the molten steel 8 in contact with the inner and lower ends of 2 in a fluidized state during most of the casting time, the occurrence of internal defects in the steel ingot can be prevented.

Example An 81t steel ingot was produced by the method of the present invention using the apparatus shown in FIG. The composition of molten steel and electrode before ESHT treatment
Shown in the table.

75t mother molten steel was cast into a mold with an average diameter of 2369mm, molten slag at 1490 ° C was added to the thickness of 200mm in the slag frame, and the power was applied by a 6t electrode having a cross-sectional area of 295mm x 420mm. ESHT processing was performed at 300 to 1200 KW.

The slag frame used in this example has a divided structure and is lined with a refractory material using a steel metal frame in a key portion, and is constructed in consideration of buoyancy so that the immersion depth in the molten steel of the slag frame is 120 mm. Four guides are provided on the circumference to prevent the positional relationship between the slag frame and the feeder frame from fluctuating due to level fluctuations and molten slag flow, and the distance between the slag frame and the feeder frame is 100mm. The slag frame was held so that it could move up and down. The surface of the molten steel on the outer peripheral portion of the slag frame was coated with a heat insulating material to a thickness of 200 mm.

During the ESHT process, the action of the slag frame keeps the molten steel in contact with the inner and lower ends of the slag frame in the fluidized state for most of the casting time, and prevents the molten steel and the molten slag from flowing into the gap between the mold and the solidified shell. I was able to prevent it.

After the ESHT treatment was completed, the power application was stopped and the immersion depth in the molten steel of the slag frame was set to 80 mm.

After solidifying the molten steel and the molten slag, the slag frame was collected together with the solidified slag. Since the slag frame has a four-divided structure in the circumferential direction, it is possible to easily collect disc-shaped slag with a thickness of 200 mm.
After collection, it was crushed and reused. In the slag frame used in this example, the refractory was worn at a speed of 1 mm / Hr in the portion in contact with the slag, but it could be repaired and reused.

The steel ingot after die cutting had a depth of 80 where the slag frame was immersed in the head.
The ring-shaped recess of mm remained, but the others were flat and beautiful with no molten slag or molten steel flowing into the surface. When the steel ingot was cut and the internal shape was confirmed, it was found that the pitting defect, V
There was no segregation or reverse V segregation, and it was sound.

〔The invention's effect〕

As is apparent from the above-described embodiment, the present invention provides the following effects by providing a rising slag frame whose lower end is immersed in molten steel in the feeder frame and supplying energy to the molten slag in the slag frame. I was able to name it.

(B) The molten steel in the feeder frame was kept in a fluidized state for most of the casting time, and it was possible to obtain a sound steel ingot by preventing the variation of components in the solidification process of the ingot and the occurrence of solidification shrinkage holes.

(B) It was possible to prevent molten steel and molten slag from flowing into the gap between the mold and the solidified shell and obtain a steel ingot with an excellent surface shape.

(C) In preventing the inflow of molten steel and molten slag into the gap of (b), the energy loss was smaller than that of the conventional method using a cooled solidified shell.

[Brief description of drawings]

FIG. 1 is a sectional view of a manufacturing apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view of a manufacturing apparatus showing a conventional BEST method, FIG. 3, and FIG.
Both FIG. And FIG. 5 are sectional views of a manufacturing apparatus showing a conventional feeder method. 4 ... Mold, 6 ... Feeder frame 8 ... Molten steel, 10 ... Solidified shell 12 ... Molten slag, 32 ... Slag frame 34 ... Heat insulating material, 36 ... Gap

Claims (1)

[Claims] 1. Molten steel is poured into a mold and a feeder frame, molten slag is charged on the molten steel surface in the feeder frame, and energy is supplied to the molten slag to supply molten steel in the feeder frame. In a method for producing a high-quality steel ingot to heat and retain the molten slag, the lower end of the slag frame is immersed in the molten steel at least 80 mm or more in the feeder frame, and the molten slag is melted on the molten steel surface in the slag frame. Holding, filling the gap between the feeder frame and the slag frame with a heat insulating material, while keeping the molten steel in contact with the inner and lower ends of the slag frame in a fluidized state for most of the casting time, the molten steel and the molten slag are A method for producing a high-quality steel ingot, characterized by preventing the inflow into a gap formed between the mold and a solidified shell in contact with the mold.