JPH0767599B2 - Continuous casting method - Google Patents

Description

The present invention relates to a continuous casting method of a type in which a tundish or a hot water supply nozzle and a mold are directly connected to each other, and more particularly to a continuous casting method capable of preventing surface defects caused by the directly connected portion. The present invention relates to a casting method.

(Prior art) In continuous casting of steel (hereinafter abbreviated as "continuous casting"), the horizontal type has a simple structure and a low height compared to the currently widely used vertical type, vertical bending type, curved type, etc. Therefore, the construction cost of the building and equipment is low, and there is a feature that a slab with excellent internal quality can be obtained without center segregation caused by molten steel static pressure and internal cracks caused by bending straightening.

However, on the other hand, as shown in Fig. 9, the tundish 1
Since it is necessary to connect the mold 2 to the mold 2, the in-mold lubrication using molten slag or oils is not performed, and the initial solidified shell 3 is formed in the molten steel 4 below the meniscus. A ceramic connecting refractory ring (hereinafter referred to as a "break ring") 7 is provided between the tundish nozzle 5 and the feed nozzle 6, and intermittent slab drawing from the fixed mold 2 is performed.

The connection method of the break ring 7 to the mold 2 in the horizontal continuous casting method of this type is shown in more detail.
FIG. 10 and FIG. 11.

That is, referring to FIG. 10 and FIG. 11, the feed nozzle pressing jig 8 is screwed to the water cooling jacket 11 of the mold 2 with the bolt 10 via the disc spring 9, for example.
The break ring 7 is pressed against the mold 2 via the. Note that FIG. 10 shows the outer peripheral surface of the break ring 7 with a taper, and FIG. 11 shows the one without a taper.

However, in any connection method shown in FIG. 10 and FIG. 11, the break ring 7 is
The formation of the solidified shell 3 and the inflow of new molten steel are repeated, resulting in a severe environment in which the heat load is very large. For this reason, BN and Si ₃ N ₄ system ceramics are generally used as the break ring 7, but these are not only expensive, but also have a short life and cannot endure long casting.

Therefore, since the drawing mark on the surface of the slab called cold shut by this method cannot withstand the subsequent rolling process and becomes defective, the following method has been conventionally proposed as a measure for reducing cold shut.

Japanese Patent Laid-Open No. 56-144849 uses a break ring having a hollow ring made of a high-melting-point metal material, and uses a heating means arranged in the ring or a cooling ring by blowing a cooling gas into the ring. There is disclosed a method capable of controlling the temperature of.

In Japanese Examined Patent Publication No. 60-1105, a molten metal is introduced into a horizontal water-cooled mold whose end is closed, and a horizontal continuous casting machine that moves the mold horizontally to cast the molten metal in a liquid phase of a semi-melting substance. , A method of sealing between the mold closing portion and the mold to promote lubrication between the cast piece and the mold.

The need for this break ring is not limited to horizontal continuous casting, but is also applicable to the vertical continuous casting method in which the tundish and the mold are directly connected. However, as a method of substituting the role of the break ring, the present applicant No. 61-216546, a feed nozzle 6 is provided between a tundish 1 and a mold 2 as shown in FIGS.
And a storage chamber 12 for the molten slag or the inert gas in the feed nozzle 6, and a ring formed by the lower end of the feed nozzle 6 and the inner peripheral wall of the mold 2. A layer 13 of molten slag or an inert gas supplied from the storage chamber 12 is formed in the gap between the tundish 1 and the mold 2 to prevent molten steel insertion (burr insertion) and to stabilize the solidified shell 3 Is proposed.

(Problems to be solved by the invention) However, with regard to, it is difficult to form an annulus in a small member called a break ring. It is very complicated in terms of mechanism. Further, if the unevenness and temperature control are not performed accurately, the initial solidified shell becomes non-uniform and stable casting becomes impossible.

In contrast to the fixed mold-intermittent drawing method, which is the mainstream of the current horizontal continuous casting method, the continuous casting is a type in which a water-cooled mold with closed ends is used and the mold is moved horizontally to produce a slab. Limited to the law. Further, although the semi-melting substance is used for the seal between the closed part of the mold and the mold, in the example of horizontal continuous casting described, the density of the semi-melting substance is higher than the density of the molten metal. Since it is small, the semi-melting substance below floats, which makes it difficult to carry out the intended sealing.

As for, the same disadvantages as those not used for horizontal continuous casting are the same. Further, in the method limited to the vertical type, as in the case of the continuous casting method using the conventional oscillation mold, the slag is consumed due to the lubricating action between the mold and the slab, so that the forced replenishment is required. However, partial sintering occurs in the process of forming molten slag, the supply from the narrow slit is not stable, and the static pressure of molten steel in the tundish is not balanced, so the intended purpose is not achieved and cold is not achieved.・ Shuts. Further, in the case of pressurization with an inert gas, the inert gas easily floats and separates from the end portion of the tundish refractory or the hot water supply nozzle refractory connected to the mold, so that equilibrium with the molten steel static pressure becomes more difficult. Therefore, since the solidified shell is not formed at a stable position, there is a problem that the refractory is scraped off, the surface of the slab is disturbed, and cold shut is formed.

The present invention provides a continuous casting method capable of producing a slab without surface defects by preventing burr insertion and cold shut at the connection portion in continuous casting in which a tundish or a hot water supply nozzle is directly connected to a mold. It is a thing.

(Means for Solving the Problem) First, the concept for completing the present invention will be described.

When molten steel is filled in the boundary between the tundish or the contact portion of the hot water supply nozzle and the mold, which is a connecting portion, so-called burr insertion occurs.

Even if a break ring is used at the boundary of the direct connection part that is the connection part, a small amount of solidified shell is formed on the break ring side, so new molten steel flows in by drawing of the slab, and a so-called cold shut surface due to the step of solidification Defect marks occur.

This surface defect occurs regardless of whether the continuous casting method is horizontal type or vertical type, or whether the mold is fixed or oscillated.

On the other hand, a method of controlling the flow of molten steel using electromagnetic force is widely used.

For example, when vertically casting Al, Cu or its alloy,
A method of maintaining the shape near the molten metal surface by electromagnetic force without using a mold and then solidifying and cooling by water cooling has already been used.

The present invention, in order to prevent the above-mentioned burr insertion and surface defects due to the start of solidification at the direct part boundary which is the connection part, suppress molten steel contact to the direct connection part boundary which is the connection part by using electromagnetic force, Prevents seizure between the mold and cast by supplying the lubricant (oil) to the solidification start position closer to the casting drawing piece from the boundary of the direct connecting part, and the space created by this It is something that is done.

That is, the present invention is a method for casting molten steel using a continuous casting apparatus in which a mold is directly connected to a tundish or a hot water supply nozzle, and a tundish in the vicinity of an end face on the mold inlet side which is a boundary between the tundish or the hot water supply nozzle and the mold. Alternatively, a current-carrying pipe is arranged in the hot-water supply nozzle, a high-frequency current is supplied to the current-carrying pipe to generate an electromagnetic force, and casting is performed while maintaining the molten steel surface of the molten steel in the mold in a non-contact state with the direct connection boundary. Further, the electromagnetic force generating current-carrying tube is arranged so that at least the inner peripheral surface thereof projects inward from the inner wall of the mold,
An anti-seizure agent is supplied to the molten steel so that it does not come into contact with the boundary of the directly connected portion by electromagnetic travel generated by the high-frequency current supplied to the current-carrying tube, or a portion where the molten steel does not come into contact.

(Operations and Examples) Hereinafter, the principle of maintaining the surface shape of molten steel by electromagnetic force will be described, and then the examples of the method of the present invention to which this principle is applied will be described.

First, FIG. 7 shows the principle of holding the surface shape of molten steel by electromagnetic force.

When a high-frequency current 16: J _{0 is} passed through a current-carrying tube 15 that is buried near the inner wall of a refractory material 14 that holds the molten steel 4, an alternating magnetic field H (17 is a magnetic flux line) is generated, and at the same time, the current-carrying tube 15 is An eddy current 18: J having a phase opposite to that of the high frequency current 16 flows in the nearby molten steel 4. This eddy current 18 causes an electromagnetic force 19: F based on Fleming's left-hand rule to act toward the center of the molten steel 4 due to the interaction with the magnetic field H, and holds the molten steel 4 from the side surface apart from the refractory wall. This retained area as shown in FIG.
By forming 20 around the boundary between the tundish or the contact part of the hot water supply nozzle and the direct connection part, which is the contact part of the mold, and letting solidification start from the position in contact with the inner wall of the water-cooled mold, casting without surface defects such as the burr insertion and cold shut. It should be possible to cast the piece stably.

The holding area 20 is the size of the conducting tube 15, the strength of the current, the frequency,
In addition to the molten steel static pressure, it is determined by the positional relationship between the current-carrying pipe 15, the water-cooled copper mold, and the molten steel, so a casting experiment was conducted under the following conditions for confirmation.

[Experimental conditions]

Casting dimension: Vertical continuous casting method Casting method: φ180mm Casting speed: 1.2m / min Molten steel: 0.2wt% C-0.4wt% Practical carbon steel whose main component is Mn Casting temperature: 1520 ℃ in tundish Pipe size: 30 mm x 100 mm (1 turn, water cooling) Current: 2 x 10 ⁴ A Frequency: 1.1 x 10 ³ Hz Molten steel surface position: 50 mm above the top of the water-cooled copper mold The positional relationship is shown in Figs. 1 to 3. As shown in FIGS. 1 to 3, the results of the three cases (Cases 1 to 3) changed as shown are that the solidified portion is a refractory material because the contact portion with the mold on the molten metal surface is above the upper end of the mold 2. It starts above the boundary of the direct connection, which is the connection between 14 and the mold.
It was found that stable casting for a long time is difficult due to surface defects caused by the formation of shuts and wear of the contact hot water supply nozzle.

As shown in FIGS. 4 and 5, the inner peripheral surface of the energizing tube 15 is further increased.
As a result of the examination with the arrangement in which 15a is projected to the inner side of the inner wall 2a of the mold 2 (cases 4 and 5), it was determined that the copper mold 2 below the boundary A of the direct connection part which is the connection part can be solidified.

Therefore, in the tundish 2 in order to separate the molten steel 4 from the boundary of the directly connected portion which is the connection portion in the directly connected mold of the tundish 2 in a state where the free surface 21 of the molten steel 4 wets the refractory material 14, With the position of the molten steel surface 100 mm above the top of the water-cooled copper mold, the current pipe being flat, and the inner peripheral surface of which was 40 mm overhanging the inner wall of the mold, the current pipe cooling was strengthened to double the current (4 × 10 ⁴ A) Run experiments were carried out. The result was successful, and a slab having no surface defects such as burrs and cold shut was obtained. It is thought that it was as shown in Fig. 6 to infer the situation during the casting, and the intended purpose was sufficiently achieved.

When the method of the present invention is employed in vertical type continuous casting, it is particularly effective in the case of a slab having a small cross section. For example, when casting a round cast piece of φ180 mm as a material for producing a seamless steel pipe, from the viewpoint of ensuring productivity, the refractory immersion nozzle is, for example, considerably thick with an outer diameter of φ120 mm, between the mold inner wall and the nozzle outer surface. The average gap is only 30 mm. Even if powder was added here as a lubricant, sufficient heat could not be obtained, and the powder was trapped on the surface of the solidified shell of the slab with insufficient slag (melting), resulting in dent defects on the slab. May occur. As a preventive measure, in the method of the present invention in which the tundish and the mold are directly connected to each other, since the tundish has a large diameter and casting can be performed without powder addition, there is no possibility of causing such defects.

Further, if lubrication is required, a method of providing a narrow-mouthed supply pipe 22 at the boundary of the direct connection portion as a connection portion as shown in FIG. 6 and allowing oils (eg, rapeseed oil, mineral oil) to exude from this is adopted. Is possible.

In this case, by ensuring the space 20 of the holding portion for the stroke of the upper and lower oscillations of the mold 2, the slab can be continuously withdrawn by tundish-mold oscillation instead of intermittent withdrawal, which stabilizes the operation and quality. .

Although the vertical type embodiment has been described above, the method of the present invention also exhibits the same effect in the horizontal continuous casting. That is, it is possible to solve the problems of burr insertion, cold shut, and poor lubrication all at once.

(Effects of the Invention) As described above, the present invention is the boundary between the tundish or the hot water supply nozzle and the mold, in the molten steel casting method using the continuous casting apparatus in which the tundish or the hot water supply nozzle and the mold are directly connected. An energizing pipe is placed in the tundish or hot water supply nozzle near the end face of the mold, and a high-frequency current is supplied to this energizing pipe to generate electromagnetic force, so that the molten steel surface in the mold does not come into contact with the direct connection boundary. What is cast while maintaining the state, and the energizing tube for electromagnetic force generation is arranged so that at least its inner peripheral surface projects inward from the inner wall of the mold, and the electromagnetic force generated by the high-frequency current supplied to this energizing tube. The anti-seizure agent is supplied to the part where the molten steel is not in contact with the boundary of the direct connection part, or the part where the molten steel is not in contact, by the effect listed below. Have fruit.

Regardless of whether it is a vertical type or a horizontal type, the tundish or hot water supply nozzle can be connected to the mold to perform casting with or without a break ring.

A slab with no surface defects such as burrs and cold shut can be obtained.

The mold (both tundish) can be oscillated and the lubricant can be supplied to the connection voids, so the friction between the mold and the slab is reduced, the solidified shell does not break out, and the casting is stable for a long time. Can be done.

[Brief description of drawings]

1 to 3 are drawings showing the influence of the position of the coil and the mold on the molten steel surface shape during the casting experiment, FIGS. 4 and 5 are drawings showing the examination results of the molten steel surface shape, and FIG. 6 is Drawing which shows one Example of the method of this invention, FIG. 7 is a principle explanatory drawing of molten steel holding by electromagnetic force, FIG. 8 is explanatory drawing of the molten steel holding state at the time of casting, FIG. 9 is a schematic explanation of horizontal continuous casting method. FIG. 10, FIG. 10 and FIG. 11 are explanatory views of the boundary of a direct connection part which is a connection part between a tundish and a mold, and FIG. 12 is a schematic view of a vertical type contact hot water supply method,
FIG. 13 is an explanatory diagram of a method replacing the break ring. 2 is a mold, 3 is a solidified shell, 4 is molten steel, and 15 is a current tube.

Claims (3)

[Claims] 1. A method for casting molten steel using a continuous casting apparatus in which a tundish or a hot water supply nozzle and a mold are directly connected to each other, and a tundish near a mold inlet side end surface which is a boundary between the tundish or the hot water supply nozzle and the mold. Alternatively, an energizing pipe is arranged in the hot water supply nozzle, a high frequency current is supplied to this energizing pipe to generate an electromagnetic force, and casting is performed while maintaining the molten metal surface in the mold in a non-contact state with the direct connection boundary. Characteristic continuous casting method. 2. The continuous casting method according to claim 1, wherein the electromagnetic force generating current-carrying tube is arranged such that at least the inner peripheral surface thereof projects inward from the inner wall of the mold. 3. The continuous casting method according to claim 1 or 2, wherein an anti-seizure agent is supplied to a portion where the molten steel is not in contact.