JPH03204141A - Method for casting clean steel ingot - Google Patents

Abstract

PURPOSE:To produce a steel ingot having extremely high cleanliness without substantial macro-streak flaw by causing molten steel to flow into an ingot case under inert gas atmosphere and executing while shutting off the molten steel surface from the atmosphere. CONSTITUTION:Ar gas is introduced into a pouring tube 1 and a runner 3 from an Ar seal ring 2 arranged at top part of the molten metal pouring tube 1 to substitute the Ar gas for the air in the inner part thereof. Successively, by breaking a sheet-state material 5 (Al foil) for closing upper part of the pouring tube 1, molten steel 9 is poured into the pouring tube 1 and caused to flow into the case 4 by pushing up a valve 6 (metal foil, etc.) in a rising hole 31 of brick at bottom part of the ingot case 4 through the runner 3. The molten steel 9 flowing into the case 4 is brought into contact with powder 7 to be molten at early time and melted, and the molten steel surface is raised under condition of being covered with the molten material 7c of powder 7, and the molten steel is filled up into the case 4. Then, it is more desirable that the powder 8 is further put on upper part of the early molten powder 7 and the unmelting powder layer 8a, etc., exists on the molten steel layer. By this method, the development of non-metallic inclusion to cause macro-streak flow is prevented.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for casting steel ingots with extremely high cleanliness.

[Conventional technology]

When casting steel ingots, for example, when manufacturing bearing materials that have strict requirements for rolling fatigue strength, it is desirable to eliminate as much as possible the presence of nonmetallic inclusions that can cause ground scratches. Although efforts have been made to sufficiently remove nonmetallic inclusions in the melting and refining of steel, their presence in the ingot is unavoidable. This is because molten steel comes into contact with the atmosphere during ingot casting, and a new phenomenon of inclusion generation occurs in which, for example, AI is oxidized to become Al2O3. In order to prevent the formation of oxides, it is sufficient to perform casting in an atmosphere sealed with an inert gas such as Ar, and for this purpose, a gas jet nozzle is provided at the top of the molten steel injection pipe in bottom pour casting. Place the hollow ring and keep it almost airtight between it and the tap opening on the bottom of the ladle through the heat-resistant cushion material.
A method of performing a gas seal is adopted. However, even with this method, it is not possible to prevent molten steel from coming into contact with the air inside the injection pipe or runner and forming oxides. The fact that oxides are formed at the tip of the molten steel entering the runner is supported by the fact that there are many nonmetallic inclusions near the bottom of the ingot case of the steel ingot. If you try to perform casting under a completely inert gas atmosphere,
It would be possible to cover the ingot case and replace the inside with Ar gas, but this is not a realistic measure as it consumes a large amount of gas and takes a long time to replace.

[Problem to be solved by the invention]

The purpose of the present invention is to overcome the above-mentioned problems, maintain the entrance path of molten steel under an inert gas atmosphere without consuming an excessive amount of Ar gas during steel ingot casting, and keep the molten steel surface in the atmosphere. It is an object of the present invention to provide a casting method in which the formation of non-metallic inclusions that cause scratches on the ground is eliminated as much as possible by performing casting while being isolated from the ground.

[Means to solve the problem]

In the method of casting a clean steel ingot according to the present invention, when casting a steel ingot by the bottom pouring method, as shown in Fig. 1, an Ar seal ring (2) is installed at the top of the molten steel injection pipe (1). The upper part of the sheet-like material (5) is torn by falling molten steel.
At the same time, the brick opening (31) of the runner (3) that opens at the bottom of the inbot case (4) is closed with a closing material (6), and early melting powder (7) is placed directly above it. Then, by introducing Ar gas through the Ar seal ring (2), the air in the molten steel injection pipe (1) and the runner (3) is replaced with Ar, and then the molten steel starts flowing down, and the molten steel is placed in an Ar atmosphere. Injection pipe (1) and runner (3)
), it flows into the ingot case (4), where it immediately comes into contact with the early melting powder (7), and by melting this, the molten metal surface rises while being covered with the powder melt, filling the ingot case. It is characterized by being made to do. Aluminum foil is preferably used as the sheet material (5) for sealing the upper part of the molten steel injection pipe. On the other hand, it is possible to close the runner brick opening (31) simply by covering it with a closing material that slightly allows gas to pass through, but an example is shown in Fig. 2 A and B. It is effective to use a valve (6) made of metal foil, paper, or plastic that allows the gas to pass upwards as shown by the solid line, but prevents the gas from passing downwards as shown by the broken line. be. [Function] When the air in the molten steel injection pipe (1) and runner (3) is replaced with Ar and the molten steel is allowed to flow down, the sheet material (5) such as aluminum foil is torn and the molten steel flows into the injection pipe. to go into. The space between the bottom of the ladle containing molten steel and the injection pipe is kept airtight with a heat-resistant cushioning material such as Kao Wool. The molten steel that has entered the channel filled with Ar gas breaks through the above-mentioned paper valve-like closing material (6) at the runner brick opening (31) and enters the ingot case (4). ,
It immediately comes into contact with the early melting powder (7) and melts it, and the molten metal level rises while being covered with the molten material.
never comes into contact with air. In a preferred embodiment of the present invention, as shown in FIG.
is placed, and casting is carried out by allowing the hot water level to rise inside the ingot case while an unmelted powder layer exists on the hot metal surface. Early melting powder is a powder with a low melting point called ``front powder.'' When it comes into contact with molten steel, it quickly melts and coats the surface, cutting off contact between the atmosphere and the molten metal surface. However, as the hot water level rises, a film forms between the ingot case and the ingot and the metal is consumed. During this time, if the above-mentioned powder with a high melting point called "1 body powder" is brought into contact with the molten steel, the molten material will compensate for the lack of front powder, and a layer of unmelted powder will be formed to retain heat. Helpful. In this way, as shown in Figure 3, the ingot case (4) is melted in! ! Around and on top of (9) are melted front powder (7G), melted body powder (8G>, semi-melted material (8b), and unmelted material (8
a) In this state, the melt level will rise as the main body powder melts little by little, and casting will proceed in a state where it is kept warm while avoiding contact with air.

【Example】

A casting apparatus having the structure shown in FIG. 1 was assembled. The upper part of the molten steel injection pipe was sealed with aluminum foil, the runner brick opening was closed with a valve made of Japanese paper and shown in Figure 2, and Ar gas was injected from the Ar seal ring at a rate of 5001)/min. injected for minutes. The valve of the closing material moves and the air is
I was watching the dormitory being replaced by r. The ingot case is for 4.6 tons, and Al5I43 is used.
20 steel was cast into 18 ingots from one ladle charge. A front powder and a main body powder having the following composition and physical properties were used at the positions shown in FIG. 1 in amounts of 1.5 ffff and 5 Ky, respectively. Main body powder 40% by weight 6 8 Front powder 5102 33% by weight A, fl 2 o311 Fe203 4 CaO35 Na20 5 仝C5,5 6 Softening point 1140'C1190°C The obtained ingot was rolled to a diameter of 160 m, and the surface layer depth was 5m
The area of ~50m was examined every 5m and the number of ground scratches was counted. The results are as follows when compared with the conventional case where only the molten steel flow from the ladle was sealed and cast. Comparative Examples 1-5 1-5 16-30 Present Invention
OOO Assuming that the air inside the ingot case is also replaced with Ar gas, the volume of the space to be replaced is 10 times the volume of the injection pipe and runner alone, so 10 times the amount of Ar gas is required, and the replacement operation is It takes a long time and is not practical. [Effects of the Invention] According to the casting method of the present invention, it is possible to replace the casting equipment with inert gas while consuming the necessary minimum amount of Ar gas, and it is possible to obtain a clean ingot with substantially no ground scratches. can.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a casting apparatus showing a molten steel injection pipe, one ingot case, and its runner, for explaining the casting method of the present invention. 2A and 2B show the structure of a valve used as a closing member for the runner brick opening in the casting apparatus of FIG. 1, with A being a plan view and B being a sectional view. FIG. 3 shows, in a preferred embodiment of the casting method of the present invention,
FIG. 3 is a cross-sectional view showing how the hot water level rising inside the ingot case is coated with powder. 1... Molten steel injection pipe 2... Ar seal ring 3... 3 runners... Runway brick opening 4... Ingot case 5... Sheet material 6... Valve (closed) Material) 7... Early melting (front) powder 8... (Main body) powder 8a... Unmelted material 8b... Semi-melted material 8C...
・Melted material 9... Molten steel

Claims (1)

[Claims] (1) When casting a steel ingot by the bottom pouring method, an Ar seal ring is installed at the top of the molten steel injection pipe, and the upper part is sealed with a sheet material that can be torn by the flow of molten steel. , the runner brick riser opening at the bottom of the ingot case is closed with a closing material, the early molten powder is placed directly above it, and the air in the molten steel injection pipe and runner is introduced by introducing Ar gas through the Ar seal ring. After the molten steel is replaced with Ar, the molten steel starts flowing down, advances through the injection pipe and runner in an Ar atmosphere, flows into the ingot case, where it immediately comes into contact with the early molten powder, and melts it. A method of casting a clean steel ingot, characterized in that the ingot case is filled with the ingot by rising while the surface is covered with powder melt. (2) Seal the top of the molten steel injection pipe using aluminum foil, and close the runner brick opening with a valve made of metal foil, paper, or plastic that allows gas to pass upward but downward. 2. A method as claimed in claim 1, wherein passage through is effected by an obstructing closure. (3) The manufacturing method according to claim 1, wherein the powder is placed above the early melting powder, and the melt level is raised in the ingot case in a state where an unmelted powder layer exists on the melt surface. .