JPH0815642B2 - Continuous casting method for thin slabs - Google Patents

Description

TECHNICAL FIELD The present invention relates to a continuous casting method for directly producing a thin cast piece of an aluminum killed steel, an alloy steel or the like having a high oxygen level from a molten metal.

[Conventional technology]

Recently, attention has been focused on a method for directly producing a thin cast piece having a wall thickness of several mm to several tens of mm close to the final shape from a molten metal such as molten steel. According to this continuous casting method, there is no need for a multi-step hot rolling process as in the prior art, and the rolling to the final shape can be light, and the process and equipment can be simplified.

As a continuous casting method of this kind, a twin drum system in which a pool is formed between a pair of cooling drums rotating in opposite directions, a drum-belt system in which a pool is formed between a cooling drum and a belt, There are a single drum system in which a pool is formed on a part of the peripheral surface of one cooling drum, and a twin belt system in which a pool is formed between a pair of belts running in opposite directions. In all of these methods, the molten metal is rapidly cooled and solidified at the portion in contact with the surface of the cooling drum or the belt to form a solidified shell.
Therefore, when the molten metal injected into the molten metal pool is oxidized by oxygen in the atmosphere, the produced oxide is easily entrained in the solidified shell, accompanying the rotation of the cooling drum or the running of the belt. As a result, the thin cast piece that was cast has rough skin,
Defects such as cracks are likely to occur.

Therefore, in Japanese Patent Laid-Open No. 62-130749, a twin drum system in which the space above the molten metal pool formed between the cooling drums is covered with a sealing body and an inert gas is blown therein to prevent the oxidation of the molten metal The continuous casting method has been proposed.

[Problems to be Solved by the Invention]

These new continuous casting methods have made it possible to prevent the oxidation of molten metal. However, when a thin cast piece is produced from molten steel or the like containing elements such as aluminum, manganese, and calcium that easily evaporate, the yield deteriorates due to evaporation in the basin and the evaporated elements are Non-uniformly adheres to and reoxidizes. Since this oxide causes cracks in the slab, it is necessary to suppress evaporation of aluminum, manganese, calcium, etc. in the molten metal pool.

Further, the molten metal in the new continuous casting method has its components adjusted before being poured into the pool. Therefore, when manufacturing a steel material containing a large amount of easily oxidizable elements, it is difficult to control the components and strict atmosphere control is required. As a result, the equipment configuration becomes complicated and the processing operation becomes troublesome.

In particular, when manufacturing a steel material having a high oxygen level, oxygen in the molten steel and carbon react with each other to generate CO gas. This CO gas causes wrinkles and the like. In this respect, CO
It is necessary to prevent the generation of gas.

Therefore, the present invention, the molten metal is poured into the basin part maintained in a non-oxidizing atmosphere at atmospheric pressure or higher, and an intermediate container or the like is held by adding a metal or alloy that is easily evaporated and easily oxidized. The purpose of the present invention is to alleviate the restrictions on the atmosphere to be used, increase the efficiency of addition of additional elements, and manufacture a steel material in which the additional elements are uniformly dispersed with simple equipment. In particular,
The present invention is intended to suppress the boiling of CO gas generated when manufacturing a steel product having a high oxygen level, and to manufacture a steel product having a high oxygen level without defects such as wrinkles.

[Means for solving the problem]

In order to achieve the object, the continuous casting method of the present invention injects a molten metal into a molten metal pool section defined by a running cooling drum and / or belt, and cools and solidifies the molten metal to continuously produce a thin cast piece. At the time of casting, the space above the basin is maintained in an inert gas atmosphere of 1.3 atm or more and 2 atm or less, and molten metal having a high oxygen content is injected under the atmosphere. As a result, it is possible to manufacture a thin cast piece free from defects such as wrinkles while suppressing CO gas boiling that tends to occur at that time. Further, in the present invention, addition of easily oxidizable metal or alloy is also performed under the atmosphere.

[Action]

The present invention includes a twin drum system, a drum-belt system,
The present invention can be applied to any continuous casting method such as a single drum method and a twin belt method, but in the following description, the case of applying the twin drum method will be described.

In the twin-drum type continuous casting apparatus, as shown in FIG. 1, a pair of cooling drums 1a and 1b are arranged so as to rotate in mutually opposite directions. And this cooling drum 1a, 1
A basin 2 is formed between b. A pouring nozzle 4 extending from an intermediate container 3 such as a tundish is immersed in the basin 2, and molten metal 5 in the intermediate container 3 is poured into the basin 2. At this time, the space above the basin 2 is covered with the casing 6, and an inert gas such as argon or helium is blown from the gas introduction pipe 7 opened in the casing 6.

The amount of the inert gas blown from the gas introduction pipe 7 is set so that the pressure in the casing 6 is 1.3 atmospheric pressure or more. A sliding portion 8 that comes into contact with the peripheral surfaces of the cooling drums 1a and 1b is provided at the lower end of the casing 6 to prevent the inert gas from escaping from the inside of the casing 6 to the outside. However, since this escape cannot be completely suppressed, the inert gas is supplied in a blowing amount that anticipates the amount of escape.

In this way, by keeping the space above the basin 2 at 1.3 atm or more and casting a thin steel piece with a high oxygen level, it is possible to suppress boiling due to CO gas.
This makes it possible to sufficiently manufacture a steel material having a high oxygen level without adding a deoxidizing element from the charging pipe.

Further, in the space above the pool 2 which is maintained in an inert atmosphere of 1.3 atm or more, an additive 9 such as an easily oxidizable element such as aluminum or calcium, or an easily oxidizable element thereof, or an alloy thereof.
Is added from a charging pipe 10 opened in the casing 6. The added additive 9 dissolves in the molten metal in the pool 2 and diffuses. At this time, since the inside of the casing 6 is maintained in the inert atmosphere, the additive 9 is not oxidized in the stage until the dissolution. Therefore, the addition efficiency of the additive 9 becomes high. Moreover, the inside of the casing 6 is 1.3
Since the atmosphere is higher than atmospheric pressure, the loss due to evaporation is also suppressed. Further, as the additive 9, not only a wire shape but also a powder shape as shown in the drawing can be used.

In this way, the boiling of CO gas generated from the molten metal is suppressed to prevent the formation of wrinkles and the like on the slab,
Furthermore, in order to suppress the oxidation and evaporation of the additive 9, the atmospheric pressure in the casing 6 is maintained at 1.3 to 2 atmospheres. If the atmospheric pressure is less than 1.3 atm, wrinkles and the like are likely to occur on the obtained steel slab, and the effect of suppressing oxidation or evaporation by the inert gas is insufficient. On the contrary, when the atmospheric pressure exceeds 2 atm, not only a large amount of inert gas is consumed, but also the pressure in the casing 6 overcomes the static pressure of molten steel, which hinders the smooth fall of the molten metal 5 from the intermediate container 3. .

When the additive 9 is added in powder form, an inert gas is used as a carrier gas. This inert gas also helps maintain an inert atmosphere within the casing 6. Further, the additive 9 may be mixed with the inert gas blown from the gas introduction pipe 7 without providing the dedicated injection pipe 10.

In this way, since the easily oxidizable additive 9 that is easily evaporated in a non-oxidizing atmosphere of 1.3 atm or more and 2 atm or less is added, the efficiency of addition of the easily oxidizable element is improved, and aluminum-killed steel or a large amount of It is also possible to cast steel materials containing aluminum, calcium, etc. As the additive 9 exhibiting the effect according to the present invention, there are manganese and the like in addition to aluminum and calcium.

The additive 9 added to the basin 2 is taken into the rapidly cooled and solidified molten metal or solidified shell, and uniformly dispersed inside the slab. As a general tendency of this type of casting method, solidification progresses rapidly, so that the effect of floating inclusions in the pool is not obtained, and if large inclusions are present, serious defects will occur in the slab. easy. In this respect,
In the present invention, the addition of the additive 9 to the basin 2 prevents the inclusions from gathering and growing large. Therefore, the inclusions are finely dispersed in the slab and do not cause defects.

〔Example〕

Example 1 Molten steel having a common steel composition at a temperature of 1545 ° C. was poured into the pool 2 at a rate of 800 kg / min to cast a thin cast piece having a wall thickness of 3 mm and a plate width of 800 mm. At this time, the atmospheric pressure in the casing 6 is
The pressure was changed from 1 atm to 2 atm by blowing helium gas. FIG. 3 is a graph showing the relationship between the atmospheric pressure and the wrinkle generation state due to CO gas boiling. In addition,
The wrinkle generation index is represented by the wrinkle length (m) per 1 m ^{2 of} thin cast piece. In the figure, the one marked with ○ is a wrinkle occurrence index of 0 m / m ² , and the one marked with △ is a wrinkle occurrence index of 1.0 m / m ^2.
Less than, those marked with x are those with a wrinkle generation index of 1.0 m / m ² or more.

As is clear from Fig. 3, thin wall slabs without wrinkles were obtained from molten steel with a high oxygen level as the atmospheric pressure increased. By increasing the atmospheric pressure to 1.3 atmospheric pressure or higher, CO gas It can be seen that boiling is suppressed.

Example 2 Molten steel having a normal steel composition at a temperature of 1545 ° C. was poured into the pool 2 at a rate of 800 kg / min to cast a thin cast piece having a wall thickness of 3.0 mm and a plate width of 800 mm. At this time, the powdered aluminum additive 9 (A-99
%) Was added to the pool 2 in a predetermined amount. Table 1 shows the yield of the additive 9 at that time. The inside pressure of the casing 6 was set to 1.4 atm by blowing an inert gas at a flow rate of 250 Nm ³ / min. Also,
The addition amount of the additive 9 is represented by a value converted into aluminum.

As is clear from Table 1, the additive 9 was added at an extremely high yield, and it was possible to produce a slab having a high aluminum content. On the other hand, for example, the intermediate container 3
When adjusting the molten steel containing 0.15% aluminum at the stage, it is necessary to maintain the atmosphere of the intermediate container 3 in a vacuum or an inert atmosphere, and the equipment becomes complicated accordingly.

Further, FIG. 2 is a graph showing the influence of the atmospheric pressure on the addition efficiency. As shown in FIG. 2, the yield of the additive 9 is improved with the increase of the atmospheric pressure because the loss of the additive 9 added to the basin 2 is caused not only by oxidation but also by evaporation. It is thought that this is due to the fact that That is, when the atmospheric pressure is increased to 1.3 atm or higher, the evaporation of the additive 9 is suppressed and the addition efficiency is improved. This tendency is remarkable especially when an element having a high vapor pressure such as calcium is used as the additive 9.

〔The invention's effect〕

As described above, in the present invention, the basin is
Since it maintains the pressure above atmospheric pressure and injects molten metal into it, CO gas boiling in the pool can be suppressed, and steel with high oxygen level can be manufactured without defects such as wrinkles. Becomes

Further, in the present invention, an easily oxidizable element can be efficiently contained in the cast slab by adding an additive to the pool portion maintained in an inert atmosphere of 1.3 atm or more and 2 atm or less, and aluminum-killed steel It is possible to manufacture steel and alloy steel. Moreover, since an easily oxidizable element is added immediately before solidification, it is not necessary to maintain an intermediate container such as a tundish in an inert atmosphere, and thin-walled slabs having a predetermined composition can be manufactured with simple equipment. It

[Brief description of drawings]

FIG. 1 shows the equipment structure when the present invention is applied to a twin drum type continuous casting method, FIG. 2 is a graph showing the relationship between the inert atmosphere pressure and the yield of additives, and FIG. It is a graph showing the relationship between the active atmosphere pressure and the generation of wrinkles. 1a, 1b: Cooling drum, 2: Hot water pool part 3: Intermediate container, 4: Pouring nozzle 5: Molten metal, 6: Casing 7: Gas introduction pipe, 8: Sliding part 9: Additive, 10: Input pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kunimasa Sasaki 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Research Institute (72) Keiichi Yamamoto 4-chome, Kannon Shinmachi, Nishi-ku, Hiroshima Prefecture 6-22 No. 22 Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd. (56) Reference JP-A-51-71827 (JP, A) JP-A-61-180653 (JP, A)

Claims (2)

[Claims] 1. A pool of molten metal when a molten metal is poured into a pool of water defined by a running cooling drum and / or belt, and the molten metal is cooled and solidified to continuously cast a thin cast piece having a high oxygen level. A continuous casting method for thin cast slabs, characterized in that the space above the part is maintained in an inert gas atmosphere of 1.3 atm or more and 2 atm or less, and molten metal is injected into the molten metal pool under the atmosphere. 2. A molten metal is poured into a molten metal pool defined by a running cooling drum and / or belt, and the molten metal is cooled and solidified to continuously cast a thin cast piece having a high oxygen level. The space above the part is maintained in an inert gas atmosphere of 1.3 atm or more and 2 atm or less, and a molten metal is injected under the atmosphere to add an easily oxidizable metal or alloy to the pool. Continuous casting method for thin-walled slabs.