JPH04187346A - Method for continuously casting thin cast strip - Google Patents

Abstract

PURPOSE:To avoid uneven cooling and to produce a cast strip having good surface property by supplying the specific content or more of absorbable gas on the surface of molten metal between cooling roll pair. CONSTITUTION:A closed lid 5 for converting the upper side of the cooling rolls 1a, 1b and pouring basin part 3a air-tightly, is provided and atmospheric containing >=60vol% absorbable gas, is supplied from a supplying pipe 6. The injection at the flow rate of 10l/m<2> of surface area of the strip is preferable. This gas is absorbed in molten metal 3 and solidified shell accompanied with the rolling surface of the cooling roll 1a and is not interposed in between the roll surface and the molten metal. Therefore, the solidification speed in the roll surface can be uniformized and the development of crack on the cast strip can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a continuous casting method for thin cast slabs, and is particularly directed to producing thin cast slabs with good surface properties by a twin roll method.

[Conventional technology]

In recent years, 1) rotating molten metal in opposite directions to each other
The so-called direct casting method of thin strips was developed, in which the thin strips are fed between a pair of cooling rolls and rapidly solidified into thin strips.This method has attracted attention because it can save process steps, improve yields, and reduce initial capital investment. ing.

In order to realize this method of direct thin strip casting, there are issues such as pouring technology, casting technology, winding and conveying technology, quality improvement, post-process technology, and expansion of steel types. There is a strong demand for

That is, it is important that the surface of the slab obtained be free of cracks, fine cracks, or uneven unevenness.

In order to obtain slabs with good surface properties, for example,
-199152, 60-170562 and 6
2-130749, it is effective to prevent the formation of oxides by creating an inert gas atmosphere on the surface of the pool of molten metal between the cooling rolls and shielding it from the atmosphere. It is a means. This is because when oxides are generated on the surface of the molten metal, these oxides are entrained on the roll surface and become entangled, intervening between the roll and the molten metal, causing uneven cooling and deteriorating the surface quality of the slab. It is from.

[Problem to be solved by the invention]

Casting in an inert gas atmosphere is effective in suppressing the formation of oxides, but on the other hand, this inert gas is entrained in the molten metal as the rolls rotate, causing It is still not possible to obtain slabs with good surface quality because they are interposed between the metal and the molten metal and cause uneven cooling.

Therefore, an object of the present invention is to propose a method for avoiding the uneven cooling caused by the above-mentioned inert gas, without hindering the blocking of the molten metal from the atmosphere.

[Means to solve the problem]

This invention provides a method for producing a thin slab by supplying molten metal to a pool between a pair of cooling rolls that rotate oppositely and continuously quenching and solidifying it on the surface of the cooling roll. This continuous casting method for thin slabs is characterized in that an atmospheric gas having an absorbent gas content of 5Q vol% or more is supplied to the surface of the molten metal supplied between the pair of rolls and these rolls.

Now, Fig. 1 shows a twin-roll direct continuous ribbon casting apparatus used directly in the method of the present invention.
is a hollow cylindrical cooling roll whose inside is water-cooled, and molten metal 3 is supplied from a supply nozzle toward the cooling roll l a , 1 b ra'lΦ roll kissing part to form a pool part 3 a between the rolls. Then, the thin slab 4 is produced by forcing rapid cooling and solidification on the roll surface.

In addition, the upper side of the cooling rolls la and lb and the sump portion 3
A hermetically sealed lid 5 is installed to airtightly cover the container a, and atmospheric gas is introduced into the hermetically sealed lid 5 from a supply pipe 6 to replace the atmosphere. During casting, atmospheric gas is supplied from a plurality of nozzles 7a to 7d arranged toward the cooling rolls la, lb and the sump 3a. The nozzles 78 to 7d are formed by forming slits 8b arranged in a row on the circumferential surface of a vibrator 8a as shown in FIG. 2, and are arranged so that the axial direction thereof is parallel to the axial direction of the cooling roll.

Further, FIG. 3 shows an example in which the vertical continuous casting machine of FIG. 1 is changed to a horizontal type, and in this case as well, the same casting as shown in FIG. 1 can be performed.

At step 22, the nozzle 7a is introduced into the sealing lid 5 and during casting.
It is important that the atmospheric gas supplied from 7d to 7d contains 60 to 1% or more of absorbing gas. The absorbent gas must be reactive with the molten steel and must not cause the generation of oxides, and the molten steel must have an absorption capacity of 0.1 cm"/g or more for the absorbable gas. It must have CO, H!,
HCI, SOx, Nz, Nz+Ib.

C1□, H, S, etc. are advantageously suitable, and the remaining gas in the case of forming a mixed gas may be any gas that does not contain oxygen in order to prevent oxidation of the molten steel.

In addition, the atmospheric gas is 101 per 1 m1z of the surface area of the plate.
It is preferable that the gas be sprayed at a flow rate of 100 ml, and furthermore, it is necessary to arrange a gas pipe along the roll surface in order to cause the gas to be adsorbed onto the roll surface.

[For production]

When continuous casting of thin slabs is performed in an inert gas atmosphere such as Ar gas, as shown in Fig. 4, the inert gas G supplied near the surface of the molten metal 3 hits the rotating surface of the cooling roll 1a. The inert gas G that is entrained in the molten metal 3 and attached to the roll surface is interposed between the roll surface and the molten metal 3 and its solidified shell 3b. Then, on the roll surface, a part A that comes into direct contact with the molten metal 3 and a part B that comes into indirect contact with the molten metal 3 are formed, and the solidification rate on the roll surface becomes non-uniform. Therefore, solidification of the roll surface progresses preferentially in the direct contact area A, but progresses later in the indirect contact area B, so stress is concentrated in this area B, and cracks occur in the resulting slab.

On the other hand, the method according to the present invention uses an atmospheric gas mainly consisting of an absorbing gas, so as shown in FIG. The gas F is absorbed by the molten metal 3 and its solidified shell 3b, and is not present between the roll surface and the molten metal 3.

Therefore, the solidification rate on the roll surface can be made uniform, and cracks can be prevented from occurring in the slab.

〔Example〕

As shown in Figure 1, the thickness is 2 mm and the diameter is 600 w.
In order to continuously cast thin slabs of m in thickness from various types of molten steel shown in Table 1, after filling the airtight lid 5 with an atmospheric gas having the composition shown in Table 1, the slabs 1 are further cast from nozzles 7a to 7d.
Atmospheric gas was supplied at a flow rate of 1ON or more per 1I2. Table 1 shows the results of investigating the surface properties of the obtained slabs.

For comparison, the surface properties of the slabs obtained were also investigated when similar continuous casting was performed under an inert gas atmosphere. The results are also listed in Table 1.

Table 1 [Effects of the Invention] According to the present invention, a thin slab with excellent surface quality is free from surface defects such as cracks, cracks, and non-uniform irregularities that are inevitable in conventional twin-roll continuous casting. It is possible to produce thin slabs that are comparable to hot-rolled materials obtained from conventional slabs through hot rolling.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a twin-roll continuous casting machine used in the present invention, Fig. 2 is a perspective view showing a nozzle for supplying atmospheric gas, and Fig. 3 is another twin-roll continuous casting machine. FIGS. 4 and 5 are schematic diagrams showing the behavior of atmospheric gas during casting. la, lb... cooling roll, 2... supply nozzle, 3... molten metal, 3a... sump, 3b...
Solidified shell, 4... Thin slab, 5... Airtight lid, 6...
- Supply pipe, 7a to 7d... nozzle, 8a... pipe, 8b... slit. Figure 1 Figure 5 Figure 4

Claims (1)

[Claims] 1. In manufacturing a thin slab by supplying molten metal to a pool between a pair of cooling rolls that rotate opposite each other and continuously rapidly solidifying it on the surface of the cooling roll. , the absorbent gas content is 60 vol with respect to the surface of the cooling roll pair and the molten metal supplied between these rolls.
A continuous casting method for thin slabs, characterized by supplying an atmospheric gas of % or more.