JPH01317661A - Method and apparatus for continuously casting metal strip - Google Patents

Abstract

PURPOSE:To cast a metal strip having excellent surface characteristic by exhausting material vaporized from molten metal in pouring basin part to out of the system at upper part of the molten metal surface under isolating condition from circumference of cooling drums. CONSTITUTION:The vaporable metals of Mn, Cu, etc., are vaporized from the molten metal 5 in the pouring basin part 2. Exhaust draft 10 is set at upper part of the molten metal surface in the pouring basin part 2 and connected with an exhaust device through piping 11 for exhausting. The material vaporized with the exhaust draft 10 at the molten metal surface in the pouring basin part 2 is eliminated by sucking to prevent sticking to the surfaces of the cooling drums 1a, 1b. The method for isolating the material vaporized at the molten metal surface from the surfaces of the cooling drums can use coating body, partition wall having refractoriness, heat insulating plate having refractoriness, etc., besides the exhaust draft. By this method, contamination of the cooling drum is prevented and the metal strip having excellent surface characteristic can be cast.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for continuously casting thin metal sheets using a twin-drum method.

[Conventional technology]

A twin-drum method has been developed in which a pair of cooling drums are arranged parallel to each other, and the heat of molten metal injected into a pool formed between them is removed through the cooling drums to form a thin metal plate. When using this method, several ff1I11 to several tens of m
Because thin metal sheets with a thickness of .

In this twin-drum method, the surface of the molten metal injected into the sump is often oxidized, which gets caught up on the circumferential surface of the cooling drum, degrading the quality of the slab. Therefore, in Japanese Patent Application Laid-Open No. 60-170562, an inert gas is injected from the center of the pool toward the layer side to concentrate easily oxidizable impurities floating on the surface of the molten metal on the layer side.

Additionally, the surface of the molten metal is maintained in an inert atmosphere. The above-mentioned publication explains that this prevents oxidation of the molten metal surface and provides slabs with excellent surface properties.

[Problem to be solved by the invention]

However, even if such measures are taken, there are cases where the surface of the cast thin metal sheet becomes defective.

In the process of investigating and researching the cause of this, the present inventors discovered that deposits accumulate on the surface of the cooling drum as casting progresses. Due to the accumulation of this deposit, the surface quality of the cooling drum becomes non-uniform and the metallic luster is lost. As a result, heat flux from the molten metal to the cooling drum, wetting between the molten metal and the cooling drum, friction between the cooling drum and the solidified shell formed in contact with it, etc. become uneven, and the surface quality of the slab deteriorates. It is assumed that this will continue. therefore,
In order to stably produce sound slabs over a long period of time, it is necessary to maintain the surface quality of the cooling drum in a sound state.

According to research conducted by the present inventors, it has been found that the origin of deposits deposited on the circumferential surface of the cooling drum can be broadly classified into the following two types.

First, the first cause is that scum, oxide film, etc. generated on the surface of the hot water in the pool formed in contact with the circumferential surface of the cooling drum adhere to the circumferential surface of the cooling drum. The origin of this occurrence is easily predicted from experience with conventional casting methods. Countermeasures against this include reducing the amount of oxygen and inclusions contained in the molten metal poured into the molten metal by strengthening refining, etc., and using high-quality materials that do not wear or chip as cast refractories. use an injection nozzle with a structure that does not entrain scum, make the atmosphere in contact with the hot water surface in the pool non-oxidizing as shown in the above-mentioned publication, and brush the cooling drum. It may be kept clean by etc. These measures will significantly reduce deposits.

However, it was observed in tests with these measures that a small amount of deposits still accumulated unevenly on the circumferential surface of the cooling drum. At this time, it was found that the higher the manganese content of the molten metal being cast, the greater the amount of deposits accumulated.

Therefore, the present inventors thought that the origin of this kind of deposits was not due to scum, oxide film, etc., and after conducting a detailed investigation of the deposits using the following method, they found that We found that the origin was difficult to predict from the method.

That is, a sponge impregnated with hydrochloric acid is pressed against the circumferential surface of the cooling drum after casting, and the deposits are dissolved and collected by the acid.
The composition of the deposit was investigated by quantifying the content of each element in this recovered solution using atomic absorption spectrometry. In addition, in the following tests, molten steel was used as the molten metal.

Table 1 shows the composition of the deposits investigated in this manner in relation to the molten steel injected into the pool. In addition, in order to eliminate the effects of scum, oxide films, etc., as countermeasures against the first source mentioned above, we have reduced the oxygen content in the injected molten steel by strengthening refining, using alumina-based refractories, and increasing the upward direction of molten steel discharge. This includes using injection nozzles, supplying argon air to the atmosphere in contact with the hot water surface in the pool, and brushing the cooling drum.

(Hereinafter, the margin of this page) Table 1 Comparison of composition of injected molten steel and deposits As is clear from Table 1, compared to molten steel injected into the pool, more deposits accumulate on the circumferential surface of the cooling drum. The Mn content of the deposits is significantly high. Furthermore, it can be seen that Cu is also significantly concentrated in the deposits. On the other hand, Fe, Cr, Ni, etc., which are contained in large amounts in molten steel, do not have to be so high in deposits.

The magnitude relationship of the content of each element in such deposits attached to the circumferential surface of the cooling drum has a certain relationship with the magnitude relationship of each element's bond to oxygen (the magnitude relationship of the standard formation energy of each oxide). Furthermore, the composition is significantly different from the oxidized scale of the slab and the composition of the air oxidation products or deoxidation products of the injected molten steel. Rather, Mn and Cu, which are known as volatile elements, are concentrated.

Generally, it is known that the evaporation rate (JX) of each element (X) that evaporates from the surface of molten steel is expressed by the following equation.

However, α is the evaporation coefficient (habo 1), γ is the activity coefficient of element X in molten steel + pH is the vapor pressure of pure element X, 1M7. is the atomic weight of Fe, (X%) is the concentration of element X in molten steel, ρ is the density of molten steel 1M is the atomic weight of element X, R is the gas constant, and T is the absolute temperature.

That is, under conditions where the temperature T and density ρ of molten steel are constant,
Elements with large γ・P0/( are more likely to evaporate and become concentrated in evaporated matter.

Table 2 shows the concentration ratio of each element in Table 1, and clearly represents this tendency.

Table 2: a reduction degree of each element, and Figure 5 shows the enrichment degree of each element defined by the following formula and γ・
It shows the relationship with Po/'j-.

As is clear from Figure 5, the concentration of each element and γ・po
A highly correlated proportional relationship is established between /−/−■. However, regarding N1, N1 plating is applied to the circumferential surface of the cooling drum, and a portion of the N+ plating is dissolved and mixed in when collecting deposits with hydrochloric acid, resulting in a deviation from the proportional relationship. In view of these results, the substances adhering to the circumferential surface of the cooling drum are M evaporated from the surface of the molten steel.
It is thought that n, Cu, etc. were deposited during casting.

Therefore, an object of the present invention is to prevent the evaporated elements from coming into contact with the circumferential surface of the cooling drum, keep the circumferential surface of the cooling drum clean, and produce a thin metal plate with good surface quality. do.

[Means to solve the problem]

Examples of the molten metal surface where elements evaporate include the surface of the pool formed in contact with the cooling drum, the surface of the molten metal during pouring, and the surface of air bubbles present in the molten metal in the pool. It will be done. However, the evaporated elements generated from the bubble surface eventually reach the circumferential surface of the cooling drum via the hot water surface of the hot water pool and are deposited thereon. Therefore, in order to prevent the deposition of vaporized elements on the circumferential surface of the cooling drum, H2. N2. Ar, C
To reduce the gas components such as o and the area of the pool as much as possible, to prevent the evaporated elements generated from the pool from being absorbed on the surface of the hot water and reaching the circumferential surface of the cooling drum, and to prevent the molten metal from reaching the circumferential surface of the cooling drum. Possible measures include isolating the peripheral surface of the cooling drum that is not in contact with the evaporated elements from the cloud surrounding the surface of the hot water containing the evaporated elements.

Therefore, in the present invention, as a result of testing various deposition prevention methods from this viewpoint, it has been found that the following method can reduce the deposition on the circumferential surface of the cooling drum.

The first means, as shown in FIG. 1, is a method in which evaporated substances evaporated from molten metal are removed by suction by an exhaust draft.

In this twin drum system, a pair of cooling drums la,
Molten metal 5 is poured from an intermediate holding container 3 such as a tundish through an injection nozzle 4 into a pool 2 formed between lbs.
is injected. The molten metal 5 is transferred to cooling drums la, lb
It is cooled and solidified by heat removal through the cooling drum la.
, a solidified shell 5a formed on the circumferential surface of each of the lbs.
, 5b. These solidified shells 5a, 5b are
They are integrated at the drum gap 7 and sent out as a thin metal plate 8 by a drawing roll 9.

At this time, Mn,
Evaporable metals such as Cu evaporate. Therefore, the hot water pool part 2
An exhaust draft 10 is arranged above the hot water level, and the exhaust draft 10 is connected to an exhaust device (not shown) via an exhaust pipe 11. The exhaust draft 10 sucks and removes substances evaporated from the hot water surface of the hot water reservoir 2, and prevents them from depositing on the surfaces of the cooling drums la, lb.

The exhaust draft 10 preferably has a slit-shaped fireproof suction port extending in the width direction of the water reservoir 2. In addition, the tip of the suction port of the exhaust draft 10 is placed close to the boundary where the hot water reservoir 2 contacts the cooling drums la and lb in order to perform uniform and efficient suction and exhaust in the width direction. It is preferable.

As shown in FIG. 2, the second means is to cover the surface portions of the cooling drums la, lb located above the hot water level of the water reservoir 2 with a covering 12 that covers the periphery of the cooling drums la, ], b. cooling drums la, l as needed.
A non-oxidizing gas 13 is placed in the gap between the peripheral surface of b and the covering 12.
Introduce and ventilate. Note that the reference numeral 14 is a ventilation pipe through which the non-oxidizing gas 13 is sent. This non-oxidizing gas 13 prevents the substances evaporated from the water reservoir 2 from going around the circumferential surfaces of the cooling drums la, lb.

In the third means, as shown in FIG. 3, a fire-resistant partition wall 15 is installed to separate the surface portions of the cooling drums la and lb located above the hot water pool 2 from the cloud surrounding air above the hot water pool 2. It is placed. This refractory partition 15 prevents substances evaporated from the water reservoir 2 from depositing on the circumferential surfaces of the cooling drums la, lb.

In the fourth method, as shown in FIG. 4, the hot water surface of the hot water pool 2 is covered with a fireproof heat insulating board 16, thereby greatly reducing the exposed area of the hot water surface. This reduces the amount of evaporated substances generated from the hot water surface. The refractory heat insulating board 16 can be placed on the surface of the hot water either by floating it in the pool 2 or by fitting it into the injection nozzle 4.

Of course, the effects of each of the above means can be improved by combining them. However, on the other hand, the combination lacks economic efficiency and may impede operability. Therefore, it is preferable that each means independently exhibit sufficient effects.

Which of these means to adopt is determined depending on the operating method, casting equipment type, etc. Furthermore, the above-mentioned means are not limited to twin-drum continuous casting.
The present invention can be similarly applied to a casting method in which a slab is manufactured by bringing injected molten metal into direct contact with a cooling body without using a casting auxiliary material such as casting powder.

〔Example〕

Mn1.0%, Cr18%, Ni8.5%, Cu0.2
Molten steel at a temperature of 1500°C containing 0%
Using each of the apparatuses shown in the figure, a thin metal plate with a thickness of 2 cylinders and a width of 800 mm was cast. The amount of molten steel injected is 960k.
g/min, and the casting speed was 80 m/min.

Table 3 shows the amount of substances attached to the circumferential surface of the cooling drum and the surface properties of the obtained slabs. Note that the amount of deposits on the cooling drum is measured when no measures are taken to prevent evaporated substances.
, lb is expressed as a ratio to the reference flow. In addition, the fireproof insulation board 16
When using a hot water tank, 70% of the hot water surface of the hot water pool 2 was covered with a fireproof heat insulating board 16.

Table 3: Effects of Each Means As is clear from Table 3, when measures are adopted to prevent substances evaporated from the surface of the hot water in the pool 2 from coming into contact with the circumferential surfaces of the cooling drums la and lb, is the cooling drum la
, the amount of material adhering to the periphery of the lb is significantly reduced. As a result, the solidified shells 5a and 5b formed on the circumferential surfaces of the cooling drums la and lb were smoothed, and a thin metal plate 8 with excellent surface quality was manufactured.

〔Effect of the invention〕

As explained above, in the present invention, by isolating the surface of the cooling drum from substances that evaporate from the molten metal injected into the pool, contamination of the cooling drum surface is prevented, and metal with excellent surface quality is Casting thin plates. Also,
Exhaust drafts, coverings, fire-resistant bulkheads, fire-resistant heat insulating plates, etc. as means of isolation can be easily added to conventional twin-drum continuous casting equipment without changing the basic structure. It is. In this way, according to the present invention, it is possible to stably produce a thin metal plate with excellent surface properties over a long period of time.

[Brief explanation of the drawings] Figure 1 shows a continuous casting device that uses an exhaust draft.
Figure 2 shows a continuous casting machine that uses a covering, Figure 3 shows a continuous casting machine that uses a fire-resistant partition wall, Figure 4 shows a continuous casting machine that uses a fire-resistant heat insulating plate, and Figure 5 shows a continuous casting machine that uses a fire-resistant heat insulating plate. The figure is a graph that explains the origin of deposits formed on the surface of the cooling drum. Ia, lb: Cooling drum 2: Reservoir 3: Intermediate holding container 4: Injection nozzle 5: Molten metal 6a
, 6b: Solidified shell 7: Drum gap portion 8: Metal thin plate 9, drawing roll 10: Exhaust draft 11, exhaust piping 12: Coating 13: Non-oxidizing gas
14: Ventilation piping 15: Fire-resistant bulkhead 16: Fire-resistant heat insulating board Patent applicant: Nippon Steel Corporation Representative
Masu Kobori (2 idiots) Figure 1 Figure 2

Claims (1)

[Claims] 1. When producing a thin metal plate by cooling and solidifying molten metal poured into a pool formed between a pair of cooling drums, evaporated water from the surface of the pool A continuous casting method for thin metal sheets characterized by exhausting substances outside the system in a state where they are isolated from the circumferential surface of a cooling drum above the surface of the molten metal. 2. It is characterized by comprising a pair of cooling drums forming a hot water pool, an exhaust draft arranged above the hot water surface of the hot water pool, and an exhaust pipe connecting the exhaust draft to an exhaust device. Continuous casting equipment for thin metal sheets. 3. A pair of cooling drums forming a water pool, a covering that covers the surface of the cooling drum located above the hot water surface of the water pool, and a gap between the surface of the cooling drum and the covering. 1. A continuous casting apparatus for thin metal sheets, characterized in that it is equipped with ventilation piping for feeding non-oxidizing gas into the metal sheet. 4. A pair of cooling drums forming a hot water pool, and a fire-resistant partition wall that blocks the surface of the cooling drum located above the hot water surface of the hot water pool from the space above the hot water pool. A continuous casting device for thin metal sheets, characterized by: 5. A continuous casting apparatus for thin metal sheets, comprising: a pair of cooling drums forming a molten metal pool; and a fire-resistant heat insulating plate that covers most of the surface of the molten metal in the molten metal pool.