JPH0366454A - Method for continuously casting cast strip - Google Patents

Abstract

PURPOSE:To improve wettability in addition to slow cooling effect between molten metal and cooling drum by cleaning the drum surface with cleaning brush arranged to the cooling drum and applying drum coating agent with coating brush to form thin film. CONSTITUTION:The surfaces of cooling drums 3, 4 are cleaned with the cleaning brushes 9, 10 and successively, the thin film having <= about 5mum is uniformly formed on the surface with the coating brushes 11, 12. If the film thickness is made thick, uneven coating is easily developed and solidified uniformity comes to rather worse. As the drum coating agent improving the wettability, e.g., oxide of CeO, etc., nitride of BN, etc., fluoride of CaF, etc., carbide of WC, etc., is used. The wettability in addition to slow cooling effect between the molten metal and the cooling drum is drastically improved, and the development of solidified shell is uniformized and the cast strip having surface characteristic without any crack, molten metal fold, etc., and excellent quality can be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to twin-drum type, single-drum type, drum-type
This invention relates to a method for producing thin slabs with excellent surface properties and quality using a continuous casting machine such as a belt type casting machine.

[Conventional technology]

In recent years, in the field of continuous metal casting, various techniques have been proposed for casting thin slabs close to the shape of the final product, with the aim of reducing production costs through energy conservation and manufacturing thin sheets of difficult-to-roll materials.

For example, there is a technology in which thin-walled slabs are cast by rapidly cooling molten metal using a drum-type continuous casting machine equipped with an internal cooling mechanism, but these casting methods do not allow for stable surface properties and quality of slabs. It is important to maintain high standards.

In other words, unlike the case of slabs manufactured by conventional continuous casting equipment, these continuous casting methods were developed with the aim of obtaining thin slabs that can reduce the degree of rolling in subsequent processes. It is something that Therefore, if there is a thickness variation or surface crack in a thin slab, this will become a defect on the product surface, and there is a high risk of significantly reducing the commercial value. (The so-called non-uniform solidification) is the main cause, and in order to alleviate this, a technique has been disclosed in the past in which a heat insulating layer is formed on the surface of the cooling drum to provide a warming and cooling effect (see JP-A No. 60-24249). 〉.

[Problem to be solved by the invention]

However, it has been found that simply forming a heat insulating layer on the surface of the cooling drum does not provide sufficient and stable effects regarding the surface properties of thin slabs.

For example, it is extremely difficult with the current technology to stably and uniformly form a heat insulating layer on the surface of a cooling drum that rotates at high speed. Although it was certainly possible to obtain slabs with excellent surface properties, if casting was carried out for a long time, the heat insulating layer formed on the surface of the cooling drum would actually promote non-uniform solidification, causing wrinkles and cracks. It was found that slabs with poor surface properties were prone to frequent cracks, etc.Furthermore, as a new finding, in order to reduce non-uniform solidification, in addition to slow cooling, wetting of the molten metal and cooling drum (particularly It has become clear that the homogenization of 〉 at the initial solidification part of the meniscus is an extremely important factor.

Therefore, the present invention aims to improve the method of forming a heat insulating layer applied to the surface of the cooling drum, to make the wettability of the molten metal and the cooling drum uniform, and to produce thin slabs with excellent surface properties and shape characteristics. purpose.

[Means to solve the problem]

In order to achieve the above object, the present invention first uses a cleaning brush provided on a rotating cooling drum to remove dirt that adheres unevenly to the surface of the cooling drum (for example, when casting austenitic stainless steel, Fe, Si, ,M
After cleaning the drum surface and homogenizing it to a certain extent, oxides, nitrides, etc. for the purpose of slow cooling and wettability are applied to the surface of the cooling drum. A thin film is formed uniformly using a soft brush to which a drum coating agent such as fluoride or carbide is applied in advance. Thereafter, the thin film is brought into contact with the molten metal in the sump and cast.

[For production]

In FIG. 1, the molten metal 7 held in the tongue pusher 1 is passed through the pouring nozzle 2 to the cooling drum 3°4 and the side weir 5.
The molten metal is supplied to a sump 6 consisting of molten metal, and is rapidly cooled and solidified by a pair of cooling drums 3 and 4 that rotate opposite each other to form a slab 8. Cleaning brush 9.1
0 is placed on each of the cooling drums 3.4, and removes and cleans dirt attached to the surface of the cooling drum due to casting.

However, dirt is not evenly removed from the surface of the cooling drum that has passed through the cleaning brush, and the surface condition is non-uniform.

Therefore, in the direction of rotation of the cooling drum, coating brushes ii and 12 to which a drum coating agent is attached are arranged between the cleaning brush 9 and 10 and the water reservoir 6, and the coating brushes coat the surface of the cooling roll with a thickness of about 5 μm or less. Forms an extremely thin film uniformly. This reduces nonuniform wettability between the surface of the cooling drum and the molten metal. It should be noted that if the film thickness exceeds 5 μm, uneven coating tends to occur, and the uniformity of solidification becomes worse.

The coating brushes 11 and 12 according to the present invention are coated with drum coating agents that improve wettability, such as oxides such as CeO, BH
It is manufactured by dissolving or dispersing nitrides such as nitrides such as CaF, fluorides such as CaF, and carbides such as CaF in a solution, and then immersing a brush in this solution and drying it. The material of the brush is preferably soft and dense, such as synthetic resin or animal hair.

The surface of the cooling drum with improved wettability comes into contact with the molten metal in the sump 6. Since the wettability of the drum surface is improved, the contact between the molten metal and the cooling drum becomes uniform and good, resulting in uniform solidification. The properties of the cast slab were significantly improved, and excellent effects were obtained on the surface and shape characteristics of the slab.

The surface texture effect of the pressed slab according to the present invention will be explained based on FIGS. 2 and 3.

Figures 2 and 3 show that austenitic stainless steel with a 5OS304 rating is manufactured using the twin-drum continuous casting machine shown in Figure 1, and the surface cracks and roughness of the slab are measured by the thickness of the coating film on the cooling drum. It is plotted in relation to In the example of the present invention, the drum coating brushes 11 and 12 are made of synthetic resin flocks with four types of coating agents, CeO, BN, CaF, and WC, and the brushes have an IQALm of 0.5 to IQALm.
A thin film of was formed on the surface of the cooling drum. - On the other hand, the comparative example used a cooling drum that did not form such a thin film.

As is clear from each figure, CeO, BN, CaF
When WC is applied, cracks on the surface of the slab will not occur if the coating thickness is 5 μm or less, and the surface roughness of the slab is 9 μm or less and the surface quality of the slab is extremely good.

In addition, in the case of CeO, there is no surface cracking at a coating thickness of 0.5 μm.
．． 02vA/-, and the surface roughness is about 14μm.Also, CaF has a coating thickness of 0.5μm and the surface roughness is 10μm, so the lower limit of the coating film is set to more than 0.5μm. It is preferable to do so. In the comparative example, the amount of surface cracking was 0.3
The surface roughness of the slab was 5 stories/m'' and the surface roughness was 37 μ-, and the surface quality of the slab was poor.

〔Example〕

Using a twin-drum continuous caster shown in Figure 1, thin-walled slabs with a plate width of 800 mm and a plate thickness of 21 mm were cast using S[JS304 Kumikai 9 austenitic stainless steel produced by a conventional method. Casting was performed at 80 m/min.

Drum application brushes 11 and 12 are made of resin flocked with Ce.
O, BN, CaF, and WC are used to form a thin film (Category A) with a thickness (μ11) shown in the coating below on the surface of the cooling drum that has been cleaned with cleaning brush 9.10. The amount of surface cracking (m/m''> (Category B) and surface roughness (μ scale) (Category C) in each thin film was investigated.

As shown in the above figure, slabs cast using a cooling drum having a coating thickness within the range of the present invention have improved both the amount of surface cracking and surface roughness, and as a result of actual machine cold rolling tests, the slabs have an extremely good surface. A quality product was obtained.

(Effects of the Invention) As explained above, in the present invention, by applying a drum coating agent to the surface of the cooling drum during casting using a coating brush, in addition to the slow cooling effect, the molten metal and the cooling drum are Significantly improved wettability.

As a result, the growth of the solidified shell becomes uniform, making it possible to produce thin slabs with excellent surface quality and quality without cracks or creases.

[Brief explanation of drawings]

Fig. 1 is a partial cross-sectional side view of a twin drum continuous casting machine according to the present invention, Fig. 2 is a graph showing the relationship between the coating film thickness of the coating agent and the amount of surface cracks generated, and Fig. 3 is a graph showing the relationship between the coating film thickness of the coating agent and the amount of surface cracking. It is a graph showing the relationship between the coating film thickness of the agent and the surface roughness. 1... Tandesche, 2... Pouring nozzle, 3
．． 4...Cooling drum, 5...Side weir, 6...
7. Molten metal, 8. Slab, 9.10. Cleaning brush, 11, 12. Drum coating brush.

Claims (1)

[Claims] 1. In a method for continuously producing thin slabs by supplying molten metal to the pool of a rotating cooling drum equipped with an internal cooling mechanism, the surface of the drum is cleaned by a cleaning brush provided on the cooling drum. Then, a drum coating agent is applied to the surface of the cooling drum using a coating brush to form a thin film, and then the thin film surface is brought into contact with molten metal in a sump to perform casting. Continuous casting method for slabs. 2. The method according to claim 1, wherein a thin film of 2.5 μm or less is uniformly formed.