JPH0796146B2 - Method and apparatus for continuous casting of thin slab - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for producing a thin cast slab having excellent shape characteristics and surface properties by a twin roll method.

[Conventional technology]

In recent years, in the field of continuous casting of steel, the development of casting technology for thin-walled slabs has progressed, and various methods such as twin roll method, single roll method, twin belt method, single belt method, and roll-belt method are proposed. And some of them have reached the level of industrial production. However, it is hard to say that all of them have reached the stage of completion in terms of productivity, ensuring of slab quality, etc.

One of the things that has been frequently experimented for a long time in casting thin-walled slabs is, for example, a vertical or inclined twin-roll type continuous casting facility. In this case as well, there are problems in terms of the quality of the cast thin-walled slab, as well as the problems of equipment durability and operation. One of them is to prevent the inhomogeneity of the internal structure of the cast slab. Incidentally, when a thin cast slab with an inhomogeneous internal structure is rolled without sufficient heat treatment, the surface of the cold rolled product lacks smoothness, or defects such as cracking occur,
The workability is insufficient. As a result, the commercial value of the product is significantly impaired.

When manufacturing thin cast pieces with twin roll type continuous casting equipment, the time from the start of solidification to completion in the machine is relatively short, but the cast piece temperature immediately after completion of solidification is extremely high around 1400 ° C, so The homogenization of the internal structure tends to be unstable, and it is difficult to prevent the homogenization phenomenon of these structures by means such as spray cooling performed by a secondary cooling body in continuous casting such as slabs and billets.

As a means for preventing the occurrence of such a phenomenon, there is known a method of bringing a thin cast piece into contact with a cooling roll and rapidly cooling it. That is, the thin cast piece coming out from the kissing point is wound around the circumferential surface of one cooling roll for a certain length by the dynamic pressure of gas, the pulling force of the pinch roll, the pressure of the pressing roll, etc. The heat of the slab is rapidly removed by a cooling roll.

For example, in Japanese Examined Patent Publication No. 63-19258, a cooling gas is injected into a thin cast piece at a position close to the peripheral surface of a cooling roll on the downstream side of a kissing point, and a pinch arranged downstream of this injection position. Tension is applied to the thin-walled slab by the roll, and the thin-walled slab is continuously brought into close contact with the surface of the cooling roll in a predetermined range in the circumferential direction. As a result, it is said that the thin cast piece is rapidly cooled by contact heat transfer via the peripheral surface of the cooling roll, and a uniform and good quality product without a black oxide film is obtained.

Further, Japanese Patent Laid-Open No. 63-68248 discloses a roll-type continuous casting facility in which a large-diameter main roll and a small-diameter auxiliary roll are combined. Then, a water-cooled auxiliary roll having a small diameter is densely arranged on the outer periphery of the main roll on the downstream side of the kissing point with the same gap as the roll gap of the casting section. This improves the function of supporting the thin-walled slab after leaving the kissing point and the ability to cool the thin-walled slab. Therefore, it is said that the thin slab that is not completely solidified is prevented from breaking out after leaving the kissing point, and the continuous casting of the thin slab can be smoothly performed.

[Problems to be Solved by the Invention]

The proposal of Japanese Examined Patent Publication No. 63-19258 aims at producing an extremely thin plate material of about 100 μm, as described in the description of Examples. Therefore, even if a thin cast piece is wrapped around the peripheral surface of one of the cooling rolls and the substantial roll diameter increases, the increase in the roll diameter is small enough to be ignored, and both cooling rolls are the same. Even if it is driven at a rotational speed, the peripheral speed difference is very small, and there is not much concern about occurrence of lateral cracks.

However, when attempting to manufacture a relatively thin-walled slab of 1 mm or more with a pair of cooling rolls having the same diameter and constant velocity, the following problems arise due to the thickness of the thin-walled slab. That is, the one cooling roll around which the thin cast piece is wound has a roll diameter substantially increased by the thickness of the thin cast piece. Therefore, when both cooling rolls are driven at the same rotation speed, the peripheral speed of the cooling roll around which the thin cast piece is wound becomes higher than that of the other cooling roll. Due to this peripheral speed difference, a shearing force acts on the surface of the thin cast piece which has not yet exhibited sufficient strength, which causes defects such as lateral cracks.

On the other hand, the method described in Japanese Patent Laid-Open No. 63-68248 aims at preventing breakout of thin cast pieces. However, in this method, there is no specific description about the peripheral speeds of the main roll and the auxiliary roll, and there is no mention of prevention of lateral cracking due to the peripheral speed difference between the main roll and the auxiliary roll. Is hard to say.

Therefore, the present invention eliminates the substantial peripheral speed difference between the pair of cooling rolls immediately after the completion of solidification, without causing lateral cracking in the surface layer portion of the thin cast piece immediately after completion of solidification coming out from the kissing point, Further, the present invention provides a casting method and apparatus for a thin cast slab capable of homogenizing the internal structure.

[Means for Solving the Problems]

The continuous casting method of the present invention, in order to achieve the purpose,
When molten metal is poured into a pool of water formed between a pair of cooling rolls with adjustable peripheral speed ratio, the molten metal is rapidly cooled and solidified to cast a thin slab, the thin wall immediately after being sent out from the kissing point. In a casting method of a thin cast piece, which is designed to be cooled by making the cast piece contact with the peripheral surface of one of the cooling rolls, the peripheral speed of one or both of the cooling rolls is adjusted according to the thickness of the thin cast piece. The peripheral speed of the outer surface of the thin slab in contact with the one cooling roll and the peripheral speed of the outer peripheral surface of the other cooling roll in contact with the outer surface of the thin slab are matched.

Further, the continuous casting apparatus of the present invention, a pair of cooling rolls that form the pool, and a pressing roll that runs while pressing the thin cast piece fed from the kissing point of the cooling roll against the peripheral surface of one cooling roll. And a driving device for rotating and driving each of the cooling rolls independently of each other according to the thickness of the thin cast piece, so that the peripheral speeds of the contact surfaces of the thin cast piece and the cooling roll are matched. It is characterized in that the peripheral speed of the cooling roll is controlled.

Here, a pressing means for pressing the thin cast piece can be added to the peripheral surface of one of the cooling rolls from the kissing point to the pressing roll so as to face the peripheral surface. As the pressing means, a plurality of auxiliary pressing rolls having a large pressing force against the cooling roll on the kissing point side, a nozzle for injecting the liquid refrigerant onto the surface of the thin cast piece, and the like are used.

As the pressing roll, one having a cooling means inside or outside is used. Further, the cooling roll on the side that comes into contact with the thin cast piece sent out from the kissing point may have a larger diameter than the other cooling roll.

[Action]

In the present invention, the thin cast piece immediately after leaving the kissing point is pressed against the peripheral surface of one of the cooling rolls by the pressing roll. The thin cast piece is rapidly cooled by contact heat transfer through the peripheral surface of the cooling roll. This suppresses the inhomogeneity of the slab structure after solidification is completed. At this time, the cooling roll on the side where the thin cast piece is pressed has a roll diameter substantially increased by the thickness of the thin cast piece.

When both cooling rolls are rotated at the same rotation speed in this state, the stress due to the peripheral speed difference is generated in the thin cast piece as described above. Therefore, the number of rotations of the cooling roll on the side on which the thin cast piece is wound is reduced according to the thickness of the thin cast piece, and the peripheral speed of the cooling roll is made equal to the peripheral speed of the other cooling roll.

At this time, when the roll diameter of the cooling roll on the side on which the thin cast piece with the wall thickness t is wound is d ₁ , the rotation speed is v _1, and the roll diameter of the other cooling roll is d ₂ and the rotation speed is v _2. , It is necessary to maintain the relationship of v ₁ / v ₂ = d ₂ / (d ₁ + 2t) (1) between the rotational speeds v ₁ and v ₂ . In the case of using a cooling roll having the same roll diameter d maintains the rotational speed ratio, the _{v 1 / v 2 = 1-2t /} (d + 2t) ...... (2).

By lowering the rotation speed of the cooling roll on the side on which the thin cast piece is wound in this manner, the peripheral speed on the surface side of the thin cast piece is made to match the peripheral speed of the other cooling roll in contact with the surface. As a result, no stress is generated between the surface of the thin slab and the peripheral surface of the other cooling roll, and the occurrence of defects such as lateral cracks is prevented, and particularly continuous casting of thin slabs with an intermediate thickness of 1 to 9 mm It has a remarkable effect when applied to. In addition, the obtained thin-walled slab has a homogenized structure by quenching and has excellent surface properties, and is particularly suitable for the production of stainless thin-walled slabs, and surface property defects such as gloss unevenness in the rolling process that is a post-process. It is possible to obtain a product that is free from internal defects and has excellent workability.

〔Example〕

Hereinafter, the features of the present invention will be specifically described by way of examples with reference to the drawings.

The outline of the continuous casting equipment used in this example is shown in FIG. In this embodiment, the pair of cooling rolls 1a and 1b are arranged in parallel with each other, and both end portions in the roll axial direction of the peripheral surface are partitioned by side dams (not shown) to partition the hot water pool 2.
Molten steel was poured into the pool 2 from an intermediate container such as a tundish via a pouring nozzle. The injected molten steel is
Cooling and solidification by heat removal via the cooling rolls 1a, 1b,
It grows as a solidified shell on the peripheral surface of each cooling roll 1a, 1b.

The solidified shell is conveyed toward the kissing point 3 as the cooling rolls 1a and 1b rotate, and is bonded in the vicinity of the kissing point 3 to form a single thin cast piece 4. The thin cast slab 4 after coming out of the kissing point 3 travels while being pressed against the peripheral surface of one cooling roll 1a by a pressing roll 5 having a water cooling mechanism inside. At this time, since the thin cast slab 4 is in close contact with the peripheral surface of the cooling roll 1a, the heat retained therein is removed through the cooling roll 1a. As a result, the thin cast piece 4 is rapidly cooled, and the nonuniformity of the structure is suppressed.

In this way, when the thin cast piece 4 is closely attached to the cooling roll 1a and is sent out from the kissing point 3,
This means that the substantial roll diameter of 1a is increased by the thickness of the thin cast piece 4. Therefore, in order to cancel the peripheral speed difference based on the substantial fluctuation of the roll diameter, the cooling rolls 1a and 1b are driven by separate driving devices 6a and 6b, respectively, and the surface of the thin cast piece 4 wound around the cooling roll 1a is driven. The individual drive devices 6a and 6b are controlled so that the peripheral speed of the same is the same as the peripheral speed of the cooling roll 1b facing each other at the kissing point 3. Therefore, no circumferential stress is generated in the thin-walled slab 4 at the kissing point 3, and lateral cracks are generated in the thin-walled slab 4 even when the relatively thick-walled slab 4 is manufactured. Without using the pressing roll 5, the thin cast piece 4 can be rapidly cooled.

The peripheral speed control of the cooling rolls 1a and 1b by the drive devices 6a and 6b is performed by presetting the thickness of the thin cast piece 4 and cooling rolls 1a and 1b.
It is performed by inputting the roll gap detection value and the like. Further, the diameter of the pressing roll 5 is determined in consideration of the allowable strain when the thin cast piece 4 is sufficiently cooled and separated from the cooling roll 1a. The thin cast piece 4 separated from the cooling roll 1a is conveyed to a post process such as rolling via the pinch roll 7.

In order to improve the contact state between the thin cast piece 4 and the cooling roll 1a while the thin cast piece 4 travels from the kissing point 3 to the pressing roll 5, various means are adopted as shown in FIG. be able to.

In FIG. 2A, a plurality of auxiliary pressing rolls 8a and 8b are arranged between the kissing point 3 and the pressing roll 5 along the peripheral surface of the cooling roll 1a. These auxiliary pressing rolls 8a, 8b improve the contact state of the thin cast piece 4 with the peripheral surface of the cooling roll 1a. At this time, it is preferable that the pressing force of the auxiliary pressing roll 8a at the uppermost stage is made larger than the pressing force of the auxiliary pressing roll 8b on the downstream side. As a result, the tensile force resulting from the thermal contraction of the thin cast piece 4 is greatly reduced from being applied to the brittle thin cast piece 4 in the kissing point 3 region.

FIG. 2 (b) shows a thin-walled slab on the peripheral surface of the cooling roll 1a in order to make up for the lack of cooling capacity when contact cooling the thin-walled slab 4 with the cooling roll 1a and prevent the occurrence of uneven cooling. Four
The state in which the liquid refrigerant is sprayed on is shown. By spraying this liquid refrigerant, more uniform cooling can be achieved especially when casting a thick thin cast piece 4. However, it is necessary to select the nozzle tip 9 so that the liquid refrigerant does not hit the kissing point 3 directly. Therefore, a plurality of louvers 10 are attached to the side of the nozzle tip 9 where the nozzle holes are opened, and the liquid refrigerant jetted from the nozzle holes is guided by the louvers 10 to the surface of the thin cast piece 4.

In FIG. 2C, the pressing roll 5 is of an external cooling type. That is, the cooling water nozzle 11 faces the peripheral surface of the pressing roll 5, and the peripheral surface of the pressing roll 5 is cooled by the cooling water sprayed from the cooling water nozzle 11. With this method, the pressing roll 5 can be downsized, and the cooling roll 1a can be prevented from being adversely affected by vibration or the like.

In FIG. 2 (d), the cooling roll 1a used for contact cooling of the thin cast piece 4 of both cooling rolls 1a, 1b has a larger roll diameter than the other cooling roll 1b.
In this case, it is easy to increase the length of the thin cast slab 4 to be contact-cooled, and it becomes easy to attach and maintain the roll for pressing the slab and the liquid refrigerant nozzle.

In any of FIGS. 2 (a) to 2 (d) described above, the cooling rolls 1a and 1b are connected to separate drive devices 6a and 6b as shown in FIG. , Drive 6
By controlling a and 6b, the peripheral speed on the surface of the thin cast piece 4 is made to match the peripheral speed of the other cooling roll 1b.

In this way, the method of casting the thin-walled slab 4 while rotating the cooling rolls 1a and 1b at different peripheral speeds is such that the thickness t of the thin-walled slab 4 exceeds 1/500 of the roll diameter d. When it does, it exerts a remarkable effect. That is, t / d is 1/500
In the following, even if 2t / (d + 2t) ≈0 in the equation (2) described above, no problem occurs in actual operation. However, when t / d exceeds 1/500, this correction term is incorporated and the cooling roll is
It is necessary to match the actual peripheral speeds of 1a and 1b.

Further, the present invention is capable of rapid cooling, and is applied to casting of a stainless thin cast piece of 1 to 9 mm, which has a high risk of lateral cracking due to a peripheral speed difference between cooling rolls, and exerts a remarkable effect. is there.

Next, concrete operation data are shown.

Molten stainless steel having a SUS 304 composition and a temperature of 1500 ° C. was poured into the pool 2 and a thin cast piece 4 having a thickness of 2 mm and a plate width of 800 mm was cast at a casting speed of 90 m / min. Cooling rolls used 1a, 1b
Both had a roll diameter of 1200 mm. Then, the thin cast piece 4 coming out from the kissing point 3 was made to travel 450 mm along the peripheral surface of the cooling roll 1a, then separated from the peripheral surface and conveyed to the subsequent step.

At this time, the rotation speed of the cooling roll 1a was maintained at 24.0 rpm, and the rotation speed of the cooling roll 1b was maintained at 24.1 rpm. As a result, at the interface between the surface of the thin cast piece 4 and the peripheral surface of the cooling roll 1b, the peripheral speeds of the surface of the thin cast piece 4 and the cooling roll 1b were both 24 m / min. The thin cast piece 4 obtained in this state had no surface defects such as lateral cracks and had a homogeneous internal structure. When this thin cast piece 4 was rolled, an excellent product without surface defects such as uneven gloss and internal defects could be obtained.

On the other hand, when the cooling rolls 1a and 1b were driven at the same rotation speed and the thin-walled slab 4 was cast under the same conditions other than that, considerable lateral cracking occurred on the surface of the obtained thin-walled slab 4. Since the lateral cracks cause a plate breakage or the like when the thin cast piece 4 is rolled, they are not used for rolling and are scrapped.

〔The invention's effect〕

As described above, in the present invention, the thin cast piece that has come out from the kissing point is brought into contact with the peripheral surface of one of the cooling rolls, and the retained heat of the thin cast piece is removed via the cooling roll. At this time, by adjusting the rotation speed of the cooling roll, it is possible to prevent the thin cast piece from being subjected to stress due to the peripheral speed difference. As a result, the thin cast piece is not subjected to shearing force or the like, and a product having excellent shape characteristics can be obtained. Further, the manufactured thin cast piece is rapidly cooled to homogenize its structure, and when rolled in a subsequent step, surface defects such as gloss unevenness and internal defects such as cracks can be prevented.

[Brief description of drawings]

FIG. 1 shows an outline of the equipment structure used in the embodiment of the present invention, and FIG. 2 shows some examples of means for improving the pressing state of the thin cast piece against one cooling roll. 1a, 1b: Cooling roll, 2: Hot water pool part 3: Kissing point, 4: Thin cast piece 5: Pressing roll, 6a, 6b: Drive device 7: Pinch roll, 8a, 8b: Auxiliary pressing roll 9: Nozzle tip, 10: Louver 11: Cooling water nozzle

(72) Inventor Go Yamane 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (72) Inoue Kunimasa 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima Prefecture Mitsubishi Heavy Industries Hiroshima Works Co., Ltd.

Claims (7)

[Claims] 1. A molten metal is poured into a molten metal pool formed between a pair of cooling rolls whose circumferential speed ratio can be adjusted, and when the molten metal is rapidly cooled and solidified to cast a thin slab, the molten metal is fed from a kissing point. In the casting method of the thin-walled slab, which was cooled by moving the thin-walled slab immediately after being brought into contact with the peripheral surface of one of the cooling rolls, one or both of the cooling rolls depending on the wall thickness of the thin-walled slab. Adjusting the peripheral speed to adjust the peripheral speed of the outer surface of the thin slab in contact with the one cooling roll and the peripheral speed of the outer peripheral surface of the other cooling roll in contact with the outer surface of the thin slab to match. Continuous casting method of slab. 2. A pair of cooling rolls forming a basin,
A pressing roll that runs while pressing the thin cast piece sent from the kissing point of the cooling roll against the peripheral surface of one cooling roll, and each of the cooling rolls is controlled independently of each other according to the thickness of the thin cast piece. A continuous casting device for thin-walled slabs, comprising: a driving device for rotationally driving the slab, wherein the peripheral speed of the cooling roll is controlled so that the peripheral speeds of the contact surfaces of the thin-walled slab and the cooling roll coincide with each other. 3. The one of the cooling rolls from the kissing point to the pressing roll according to claim 2, facing the peripheral surface of the cooling roll,
A continuous casting device for thin cast pieces, characterized in that pressing means for pressing the thin cast pieces is added to the peripheral surface. 4. A continuous casting apparatus for thin cast slabs according to claim 3, wherein the pressing means is a plurality of auxiliary pressing rolls, and the pressing force of the auxiliary pressing rolls on the kissing point side against the cooling roll is increased. . 5. A continuous casting apparatus for thin cast pieces, wherein the pressing means according to claim 3 is a nozzle for injecting a liquid refrigerant onto the surface of the thin cast pieces. 6. A continuous casting device for a thin cast piece, wherein the pressing roll according to claim 2 is provided with a cooling means inside or outside. 7. The cooling roll according to claim 2, wherein the diameter of the cooling roll on the same side as the pressing roll for pressing the thin cast piece fed from the kissing point is smaller than that of the other cooling roll. A continuous casting device for thin-walled slabs, which has a large diameter for the thickness.