JPH0366459A - Method for continuously casting cast strip - Google Patents

Abstract

PURPOSE:To prevent the development of abnormal structure by supplying molten metal having the specific value or less overheat temp. to a rotary cooling drum under non-oxidizing gas atmosphere heated at the specific temp. or more. CONSTITUTION:The non-oxidizing atmospheric gas is preheated at >= 500 deg.C with a preheating device 11 and supplied. The molten metal in pouring basin part 7 is held to the condition just before solidifying at <= 10 deg.C overheat temp. As the atmospheric gas is preheated, transfer of heat into gas phase is restrained and the development of solidified film on the surface layer part of molten metal can be prevented. The solidified shell having uniform and high strength can be developed and the development of involving defect of solidified film can be prevented, and a product having excellent surface quality and material 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, technology has been developed to cast thin slabs close to the shape of the final product using a drum-type continuous casting machine equipped with an internal cooling mechanism, with the aim of reducing manufacturing costs and creating new materials. Various proposals have been made.

For example, JP-A-82-130749 describes a method of casting in an inert gas atmosphere in order to prevent the generation of scum (M compound) that deteriorates the surface quality of slabs due to entrainment during casting. There is.

[Problem to be solved by the invention]

However, when casting thin slabs under such atmosphere control, if you try to keep the superheating temperature of the molten metal as low as possible in order to prevent surface cracking of the slab, it is necessary to continuously cast thin slabs to control the atmosphere. As the introduced gas removes heat from the molten metal, an extremely thin coagulated film with a thickness of less than 100μ grows locally on the surface of the molten metal in the sump, especially on the meniscus near the cooling drum, and this film is used for cooling. Since the slab is discontinuously drawn into the drum, in the process of cooling and forming the slab, island-shaped abnormal structures with different solidification growth directions are generated on the slab surface. When a slab having this abnormal structure is cold-rolled, surface defects such as uneven gloss significantly impair the product surface quality, which poses a problem.

[Means to solve the problem]

The present invention solves the above-mentioned problems when casting thin slabs under controlled atmosphere.
It is characterized by performing low-temperature casting in which the molten metal is superheated at a temperature of 10°C or less while being heated to a temperature of 10°C or higher.

The present invention will be explained below based on a twin drum system.

[For production]

In FIG. 1, the molten metal 8 held in the tongue pusher 1
is supplied to the pool 7 under a non-oxidizing gas atmosphere through the pouring nozzle 2, and is rapidly cooled and solidified by a pair of cooling drums 3.4 that rotate opposite each other to form a slab 8-1.
is formatted. At this time, since the molten metal in the pool 7 is maintained at a superheated temperature of 10° C. or less and in a state immediately before solidification, the surface layer of the molten metal tends to solidify easily by cooling by the atmospheric gas. However, when the atmospheric gas is heated in advance by the gas preheating device 11 as in the present invention, the transfer of heat to the gas phase is suppressed, resulting in a solidified film like that seen when gas without preheating is introduced. occurrence is prevented. Figure 2 shows the gas preheating temperature (“C”) of the atmosphere in the water pool.
The relationship between the abnormal tissue area ratio (%) generated in the slab is plotted according to the type of non-oxidizing atmospheric gas.0 mark in the figure indicates Ar, Nz, Co, Cot gas,
・The mark is He.

From FIG. 2, which shows the case of N2 gas, it can be seen that no abnormal structure is generated when the atmospheric gas is preheated to a temperature of 500° C. or higher, regardless of the type of atmospheric gas. Also,
Although the upper limit of the preheating temperature is not particularly limited, it is not necessary to preheat to a temperature higher than the melting point of the molten metal used.

Therefore, in the present invention, the preheating temperature of the non-oxidizing atmospheric gas is set to 5.
The temperature range is 00°C or higher and lower than the melting point of the molten metal.

In addition, in Figure 2, the steel type used is 5US304.
It is made of austenitic stainless steel with molten steel, and the temperature of the molten metal in the pool is 1465°C, and the gas flow rate is 1001/min.

If a solidified film is not generated in the molten metal just before it starts solidifying by the method described above, a uniform and strong solidified shell can be generated by rapidly cooling the molten metal in a cooling drum, thereby preventing abnormal structures and cracks. It is possible to produce thin slabs with excellent surface quality.

In addition to the twin-drum type shown in FIG. 1, the present invention has the same effect on continuous casting machines such as a single-drum type and a drum-belt type. Furthermore, although not described in detail here, similar effects were confirmed with organic gases such as NHL.

〔Example〕

Example 1 Six pieces of SOS: 1104 were cast by a conventional method using a twin-drum continuous casting machine as shown in Fig. 1. A thin slab was cast at a casting speed of 80 m for 7 minutes. At this time, the temperature of the molten metal in the pool was kept constant at 1465° C. (superheating temperature 10° C.), the atmospheric gas in the pool was N2 gas, and this gas was heated to the following temperature for use.

(1) 750℃ (2) 500℃ (3) 400℃ (
4) 25"C Next, the area ratios of abnormal structures in slabs cast under the above ambient temperature were investigated, and the results were as follows.

(1) 0% (2>0% (3) 2% (4) 40%
In other words, since no abnormal tissue occurs when the atmospheric gas is above 500°C, the abnormal tissue is 2% at 400°C.
The surface of the product obtained by cold-rolling this slab in an actual machine had uneven gloss.

Example 2 A thin-walled slab was cast using N2 gas as the atmospheric gas in the sump, and other casting conditions were the same as in Example 1. The temperature of the atmospheric gas was as follows.

(1) 1000℃ (2) 500℃ (3) 400℃
(4) 200°C The abnormal tissue area ratios of the slabs at each of the above temperatures were as follows.

(1> 0% (2) 0% ku3) 4%
(4) When investigating the surface properties of products obtained by cold-rolling 20% or more of slabs, no surface abnormalities were observed in slabs with no abnormal structures, but those with abnormal structures did not. In the case of pieces, there are surface cracks and uneven gloss,
There were noticeable surface defects.

〔Effect of the invention〕

As explained above, the present invention can prevent the occurrence of abnormal structures (solidified film entrainment defects) that occur during low-temperature casting performed for the purpose of preventing slab cracking or improving solidification uniformity. We can produce products of high quality and materials.

[Brief explanation of drawings]

FIG. 1 is a schematic partial cross-sectional side view of a twin-drum continuous casting machine according to the present invention, and FIG. 2 is a graph showing the relationship between atmospheric gas preheating temperature and the amount of abnormal tissue generated. 1... Tongue push, 2... Pouring nozzle, 3.4
...Cooling drum, 5. Sealed chamber, 6. Side weir, 7. Pool, 8. Molten metal,
8-1... Slab, 9.10... Clean brush, 11... Atmosphere gas preheating device, 12... Atmosphere gas supply vibrator.

Claims (1)

[Claims] In a method of casting a thin slab using a rotating cooling drum equipped with an internal cooling mechanism in a non-oxidizing gas atmosphere,
In an atmosphere of the non-oxidizing gas heated to 0° C. or higher,
A continuous casting method for thin-walled slabs, characterized in that a molten metal having a superheated temperature of 10° C. or lower is supplied to the rotary cooling drum to cast slabs.