JPS6114057A - Continuous casting device for high-quality billet - Google Patents

Abstract

PURPOSE:To eliminate the center porosity, central segregation, internal crack, etc. of a steel ingot and to obtain the ingot having good quality by specifying the difference between the pitch of front stage rolls and the pitch of the succeeding rolls. CONSTITUTION:The ingot is drawn continuously by the pinch rolls of the rear stage while a molten steel is cooled and solidified in a mold and the secondary cooling zone provided right under the mold. The pitch Pn of the front stage rolls and the pitch Pn+1 of the succeeding rolls are specified at Pn-Pn+1=50mm.-15m and at least one set of such roll pitches are provided. The ingot having the extremely high internal quality is thus obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is capable of stably obtaining high quality slabs by eliminating defects such as center porosity-1 center segregation and internal cracks in continuously cast slabs. This invention relates to a continuous casting device that can be used for continuous casting.

(Prior Art) In recent years, continuous steel casting technology has made significant progress, and various types of continuous casting machines have been developed, some of which have been put into practical use. An outline of the continuous casting method for steel using a curved continuous casting machine, which is installed inside the continuous casting machine and has been widely put into practical use, will be described with reference to FIG.

In this curved type casting, the molten steel in the tundish l is injected into the mold 3 at a predetermined height by a single or multiple immersion nozzles 2 located at the center in the thickness direction of the mold 3. Supply so as to maintain the temperature. The molten steel in this mold 8 forms a solidified shell through primary cooling, and when this solidified shell grows to a thickness K that is strong enough to be pulled out from the mold 3, the guide roll 4 and pinch rolls (not shown) ff-
The solidified shell is further cooled by secondary cooling using five groups of nozzles while continuously drawing out the solidified shell to produce a slab 6. This continuous length slab 6 is cut into a predetermined length and supplied to the next process. This continuous steel casting process is the same regardless of the model or model.

In this way, in the continuous casting machine, the guide roll 4 is designed to have a slight reduction in order to correspond to the thickness dimension of the slab 6 to be manufactured, that is, to correspond to the solidification shrinkage of the slab 6. When the slab 6 solidifies, center porosity 1, center segregation, internal cracks, etc. are formed inside the slab. As a method for improving internal defects that occur during solidification of slabs, for example,
Methods such as those shown in Japanese Patent Publication No. 38899 and Japanese Patent Publication No. 46-41457 have also been proposed. These methods are
Both methods aim to eliminate center segregation, etc. by applying a considerable reduction; When the phase part reaches 5 to 30 mm, it is completely rolled down and the liquid phase part is terminated in front of the rolling roll, thereby eliminating center segregation, center porosity, etc.

However, even if these methods can eliminate process center segregation, center porosity, etc., if these methods are actually implemented, internal cracks will occur frequently. Further, it is impossible to perform the above-mentioned rolling reduction using ordinary guide rolls, and an investment in equipment is required.

(Problems to be Solved by the Invention) The present invention aims to solve the problems of internal cracking and large equipment investment, which are the disadvantages of the conventional method as described above. Between the pinch rolls provided after the complete solidification part, the preceding roll pitch P (n) and the succeeding roll pitch P (n+1) are P(
n)-P(n+1)=50 mm to 15 m I'ID%The object of the present invention is to provide a casting apparatus that can obtain slabs with extremely excellent internal quality.

(Means and effects for solving the problem) The present invention focuses on the fact that the conventional method of simply rolling down the vicinity of the crater tip does not sufficiently improve quality, and the present invention This was done based on the discovery of the most favorable role arrangement over the entire length from the cooling zone onwards.

That is, it has been found that in order to improve the internal quality of the slab without causing internal cracks, it is necessary to keep the relationship between the front and rear roll pitches and the subsequent roll pitch within a certain range.

In a general continuous casting machine, the thicker the solidified shell, the larger the roll pitch, and the larger the amount of reduction in the roll stroke to reduce the amount of solidification shrinkage. However, as the solidified shell becomes thicker, the amount of reduction possible by the rolls becomes smaller, and in the end, the amount of solidification shrinkage cannot be completely reduced. This results in worsening of center segregation and center porosity.
Problems such as the occurrence of However, in order to solve the above problem, if strong rolling is performed, internal cracks will occur.

Therefore, in the present invention, the roll pitch of the continuous casting apparatus is set to <P(n)-P(n+1)-50mm to 15m as described above.
The aim is to solve this problem and produce slabs free of center segregation, center porosity -1 internal cracks, etc. where P (n) - P (n +1) < 50
When the diameter is 10 mm, it becomes difficult to roll down as described above, and since it is necessary to perform strong rolling, internal cracks, etc. occur.

On the other hand, when P(n) −P(n,+1)>15m,
The machine length of the continuous casting machine becomes long, and the rolling effect cannot be expected because it becomes close to complete solidification. In addition, P(n)−P(n+1)
-250 mm to 10 m is most preferable from the above-mentioned internal quality improvement effect due to rolling reduction.

Furthermore, in order to carry out the present invention effectively, it is necessary that the coagulation rate is 20
Add bulging to the slab at %~75cm.

Here, when the solidification rate is 20% or less, it is difficult to provide bulging due to the solidification of the mold, so a solidification rate of 75 cm from just below the mold is the most preferable range determined through experiments.

This bulging is caused by the roll pitch of the previous stage P (n) K
Therefore, it is applied to the slab, and the roll pitch P(n)
In the case of a curved type continuous casting machine, it is equivalent to the bend straightening part, and in the case of a vertical type, it is about 15 m, and it was found that the length is the same for the curved type and the vertical type. Note that the roll pitch P (n) increases or decreases depending on the required amount of bulging of the slab, and the amount of bulging can be increased by increasing the roll pitch 'f' (n).

Next K P (n) K corresponding subsequent roll pitch P(
By reducing n+1) by the roll pitch of the previous stage, the bulging portion can be compressed and the internal quality can be improved. In addition, since this crimping still includes an unsolidified part, a center porosity is formed inside the slab again near the final solidified part due to the contraction of the remaining unsolidified part, so the subsequent roll pitch P(n) −
When P(n+1)=50 nm to 15 m, and one slab is further rolled down one after another, there are few unsolidified parts and there is almost no effect of internal solidification shrinkage, and internal defects can be effectively eliminated.

In addition, when improving the internal quality of slabs by rolling down without adding bulging, the roll pitch is set to P(n).
By successively rolling down the slab with -P(n+1)=50 mm to 15 m, it is also possible to produce a slab free of center porosity -1 center segregation and internal cracks.

The present invention provides a set of P(n)-P('n+1) = 50 between the pinch rolls directly below the mold and after the fully solidified part.
Casting is performed by providing rolls with a pitch of mm to 15 m, or by providing multiple sets of the above-mentioned roll pitches,
Also, P (n)th and P(n+1.)th ('P (
n) −P(n+1)), the P(n+2)th
(n+1)-P (n+2) = within 50 mm to 15 m, and the roll pitch of the previous stage is also small, and multiple sets are provided to perform slab O reduction in sequence, effectively eliminating internal defects in slabs. Naturally, this roll arrangement is included in the present invention.

(Example) Next, an example in which a roll pitch according to the present invention is provided will be described.

In Fig. 2, 4 is a guide roll, 7 is an unsolidified part, 6 is a slab, p(n) is a roll pitch of 2000 mm, and P
(n+1) is a roll pitch of 500 mm.

Here P (n) - P (n+1) = 1500m
It is m.

Using the roll pitch according to the present invention in Table 1, kA-8
A comparison is shown between when steel is cast using an i- and when it is cast using a conventional roll pitch ch. It is clear from this table that the present invention is effective for center segregation and center porosity.
1. It can be seen that it is superior in terms of internal cracking.

(Effects of the Invention) As described above, according to the present invention, high quality internal quality is achieved without causing frequent internal cracks and without requiring excessive capital investment, that is, without center segregation or center porosity. It is an extremely excellent continuous casting device that can cast continuous slabs.

[Brief explanation of drawings]

FIG. 1 is a schematic view of a continuous steel casting method using a curved continuous casting machine, and FIG. 2 is an enlarged view of the vicinity of a crater to which the present invention is applied. Explanation of symbols 1...Tandish 2...Immersion nozzle 3...
Mold 4...Guide roll 5...Nozzle group 6...Slab 7...Unsolidified portion Pn...Previous roll pitch Pn+1...Subsequent roll pitch Fig. 1 Fig. 2

Claims (1)

[Claims] In a continuous casting machine, molten steel is cooled and solidified in a mold and a secondary cooling zone provided directly below the mold, and the slab is continuously pulled out by pinch rolls in the subsequent stage. support, or the roll pitch P(n) of the front roll and the roll pitch P(n+1) of the following roll are P(n)-P(n+1)
= 50 mm to 15 m, and at least one set of the above-mentioned roll pitches is provided.