JPH06586A - Method for continuously forging beam blank - Google Patents

Abstract

PURPOSE:To uniformly cool a beam blank and to reduce the generation of flaws by dividing a control system for mold cooling water at the center part of a web of the beam blank into two systems of equal halves in the right and the left sides and independently controlling each flow rate. CONSTITUTION:At the time of continuously casting the beam blank, the cooling water system for mold is bisected in the right and the left sides by making the center part of a web part 12 as a boundary and the flow rates in the cooling water systems at the divided right half part and the left half part in the mold are independently controlled respectively. By this method, the heating amount of the molten steel at the right and the left sides are balanced and the solidified shell thicknesses (a), (b) of a flanges at the right and the left sides are almost the same. The flaws of longitudinal crack and breakout are drastically reduced. This effect is obtd. not only in the case of unsymmetrical single nozzle, but also in the case symmetrical plural nozzles and opening nozzle in an immersion nozzle 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of continuously casting a beam blank, and particularly, the rate of occurrence of vertical cracks in a beam blank slab is small, and each portion forms a solidified shell having a uniform thickness.
The present invention relates to a continuous casting method for a beam blank with extremely few breakouts.

[0002]

2. Description of the Related Art A beam blank is mainly an H-shaped steel material, and therefore has a complicated cross-sectional shape as shown in FIG. 1 or 3. Therefore, when continuously casting the beam blank, the immersion nozzle is clogged during casting. In such cases, uneven flow occurs due to flow fluctuation between each nozzle, it is difficult to perform uniform heating of each part of the beam blank, and therefore it is extremely difficult to solidify the solidified shell of each part while maintaining a uniform thickness, As a result, vertical crack defects may occur in the beam blank slab due to internal stress during solidification, or the beam blank may cause a breakout accident. In response to this, various countermeasures have been disclosed in the past, and an outline of a typical conventional technique will be described.

[JP-A-52-13428] The present invention provides an initial continuous beam blank casting method by the same applicant as the present invention, and the gist thereof will be described with reference to FIG. And as follows. That is,
"In a continuous casting method of a beam blank using a water-cooled mold that can be divided into two parts in the mold part corresponding to the flange central part 12b of the beam blank 10, the gap between the joint parts of the left and right split molds is maintained at 1 mm or less, The amount of cooling water of the mold portion corresponding to the fillet portion 13 is determined by the flange portion 1
2 and the average amount of cooling water in the mold portion corresponding to the web portion 11 excluding the fillet portion is 1.3 to 3 times,
In the mold spray zone provided between the subsequent cooling zones, the average cooling water amount to the web portion 11 excluding the fillet portion is at least larger than or equal to or less than 3 times, and the average amount supplied to the entire flange portion 12 of the beam blank. Of the cooling water amount, the cooling water supply amount to the flange 12b is at least larger than or equal to or less than 3 times the supply water amount supplied to the other flange portions, and the solidified shell is generated at a uniform speed. Continuous casting method. It is. Although the present invention attempts to achieve uniform cooling by increasing the amount of cooling water in the thick portion such as the flange portion to 3 times or less that in the thin portion such as the web portion, there is a problem in controlling the amount of cooling water.

[JP-A-58-224050] The gist of the present invention is as follows. That is, "One immersion nozzle having a plurality of asymmetrical discharge holes attached to the bottom wall of the tundish is arranged on one side in the mold, and the molten metal is injected into the mold through the plurality of asymmetrical discharge holes of the immersion nozzle. The method of continuously casting a beam blank is characterized in that According to the present invention, the provision of two symmetrical immersion dips as shown in FIG. 3 means that when the distance between the two immersion nozzles is short, there is no room in the space for installing the stopper, and the opening of the stopper is too small to control. Alternatively, since a nozzle clogging occurs, a single-hole asymmetrical immersion nozzle is used, which is a typical method of the prior art.

[JP-A-62-3852] The gist of the present invention is as follows. That is, "1. In continuous casting of a beam blank by a curved continuous casting machine, a pair of pinch rolls are supported horizontally and roll roll cylinders of the roller apron that reach the pinch rolls are formed.
A continuous casting mold is installed in a direction in which the flange surface of the beam blank is in contact, and a single immersion nozzle is arranged in the mold only at a position corresponding to the center of the flange on one side of the beam blank to inject molten steel from the tundish. A method for continuously casting a beam blank, which comprises: 2. The method according to claim 1, wherein the position of the immersion nozzle in the mold is a position corresponding to the center of the beam blank located opposite to the drawing side. It is. This invention also uses an asymmetrical single-hole immersion nozzle, and attempts to avoid deformation of the beam blank during casting and melting damage of the nozzle.

[JP-A-55-126355] The gist of the present invention is as follows. That is, "1. Using a pair of immersion nozzles symmetrically arranged apart from each other along the long side of the water-cooled mold for continuous casting, the pouring flow rate from each immersion nozzle is measured on both short sides of the water-cooled mold. The nozzle side-by-side continuous casting method consists of controlling the temperature range of the cooling water used for cooling so as to reduce it. " The present invention uses a pair of symmetrical immersion nozzles as shown in FIG. 3, where the imbalance in the pouring flow rate from the two immersion nozzles is
From the knowledge that the temperature difference of the cooling water used for cooling the both short sides of the water-cooled mold was found to be advantageous and suitable, and based on this finding, the symmetrical installation was performed so as to reduce the temperature difference of the cooling water on both the short sides. This is an attempt to balance the pouring flow rates from the two immersion nozzles that have been formed, and thus to uniformly form the solidified shell of the slab, which is also one of the representatives of the prior art.

As described above, in the conventional continuous casting of beam blanks, the asymmetric single-hole immersion nozzle shown in FIGS. 1 and 2 or two symmetrical immersion nozzles shown in FIG. Molten steel stored 3
Is injected into the mold 6 through the immersion nozzle 4,
It is important that each part of the molten steel 3 is uniformly heated so that a uniform solidified shell is formed in each part and is withdrawn. However, even in the case of symmetrical casting, the left and right molten steel supply amounts are different,
Even within the same mold, the cooling capacity of the mold is different with respect to the amount of molten steel supplied, the thickness of the solidified shell becomes uneven, which may cause vertical cracking as shown in Fig. 4, and further, a serious cause of breakout. . As a result, in the case of symmetrical casting and asymmetrical casting, use dedicated molds respectively, or when performing symmetrical casting and asymmetrical casting in the same mold, slow the casting speed only in asymmetrical casting and operate. It is the current situation.

[0008]

However, if the casting speed is slowed down, the productivity is naturally lowered. Also, in the case of a slab with a complicated cross-sectional shape such as a beam blank, the joint between the flange and the web is the final solidification region, so especially when the casting speed is high, the internals caused by solidification shrinkage in that region There is a problem that cracks and surface cracks are likely to occur. If there is such a crack defect, the inside of the beam blank is oxidized in the heating furnace furnace, or an oxide film is generated on the surface of the crack, so if such a beam blank is rolled, it is generated in the heating furnace furnace. The oxide film remains on the product H-section steel and becomes a serious defect.

It is an object of the present invention that the cooling rate of molten steel during continuous casting of beam blanks is uniform in all parts,
Therefore, even when a solidified shell having a uniform thickness is formed and the immersion nozzles are asymmetrical as shown in FIG. 1, the two immersion nozzles are symmetrical as shown in FIG. 3, and even in the case of open casting without connection to the tundish nozzle, Similarly, it is an object of the present invention to provide an effective continuous casting method capable of performing stable continuous casting operation and thus obtaining a sound beam blank slab without crack defects and deformation during drawing.

The gist of the present invention is as follows. That is, in continuous casting of the beam blank, the control system of the mold cooling water is divided at the central portion of the web of the beam blank, and the flow rate is controlled independently for each of the right half and the left half of the mold. This is a continuous casting method of a beam blank.

[Examples] The details of the present invention will be described with reference to the following two examples. Example 1 100 mm from the meniscus for the case of performing the asymmetrical single hole immersion nozzle casting as shown in FIG. 1 and the case of the open nozzle where the upper part is not connected to the tundish nozzle.
The thickness of the solidified shell formed at the distances of 00 mm, 300 mm, and 400 mm was measured at the center of the left and right flanges as shown in FIG. 1, and the ratio a / b was taken as the vertical axis, and the ratio a / b was taken as the vertical axis from the meniscus. The result of plotting the distance on the horizontal axis is shown in FIG. That is, in this case, as shown in FIGS. 1 and 2, since the one-side immersion nozzle casting is used, the thickness ratio a / b in the central portion of the left and right flanges of the solidified shell is remarkably different as shown by the curve B in FIG. However, in the case of the open nozzle, the amounts of heat of molten steel in the left and right halves of the mold with the center of the web as the boundary were almost the same, so as shown by the curve A in FIG. It was found that the ratio a / b of the thickness of the solidified shells measured in step 1 was about 1 and the left and right solidified shells were uniform. Therefore, if the cooling water amount is independently controlled so that the left half and the right half have the same amount of molten steel heat by positively dividing at the center of the web of the mold, a beam blank with uniform left and right solidified shell thickness can be obtained. It turned out that it can be formed.

Example 2 The present inventors conducted the following experiment in order to confirm the findings of the present invention obtained in Example 1. That is, FIG. 1 and FIG.
As shown in Table 1, in the casting apparatus having a single-hole immersion nozzle on the right side, the cooling water series is divided into two series at the central part of the web, and the right and left halves are each provided with an apparatus capable of independently controlling the flow rate. As described above, when the flow rate in the cooling water system in the right half is 1, the ratio of the flow rate in the cooling water system in the left half is changed to 1: 1, 1: 1.3, and 1: 1.8, respectively.

[Table 1] In this case, the ratio a / b of the thickness of the solidified shell due to the difference in the distance (mm) from the meniscus is as shown in FIG. That is, when the amount of cooling water in the right half of the mold is used as a reference, and the amount of cooling water in the left half shown by the C curve is set to 1.8, the amount of molten heat in the left and right halves is almost balanced. It was found that the thickness ratio a / b of the left and right solidified shells became almost 1 as shown in FIG. As a result, the vertical crack occurrence rate of the beam blank slab in each of the A curve, B curve, and C curve is as shown in FIG. 7, and in the example indicated by the C curve, the vertical crack occurrence rate is 1/2 that of the conventional case. Diminished.

[0013]

In the continuous casting of beam blanks,
Conventionally, it was extremely difficult to obtain a solidified shell having a uniform thickness due to the complicated shape of the beam blank, but in the present invention, the cooling water series of the mold is set to 2 with the center of the mold web as a boundary.
Since the cooling water series of the divided right and left mold halves was independently controlled, the following effects could be obtained. (A) Since the heat quantities of molten steel in the left and right parts of the beam blank at the center of the web are almost balanced, the ratio of the thickness of the solidified shell in the left and right flanges of the beam blank in the solidification process is a / b≈1, that is, each part is cooled uniformly. This makes it possible to reduce the number of accidents such as breakouts to 1/3 that of the past.
The vertical cracking defect of the beam blank slab is reduced to 1
It decreased to / 2. (B) The present invention is effective not only when the immersion nozzle is an asymmetric single nozzle, but also when the immersion nozzle is a symmetrical multiple nozzle and an open nozzle. (C) The continuous casting operation of the beam blank is stable, the production capacity can be improved, and the cost is reduced.

[Brief description of drawings]

FIG. 1 is a horizontal cross-sectional view showing a solidified shell at the initial stage of casting by an asymmetric single-hole immersion nozzle in continuous casting of a beam blank and solidified shell thicknesses a and b in the left and right flanges.

FIG. 2 is a front sectional view showing a tundish, an immersion nozzle and a beam blank mold in the case of FIG.

FIG. 3 is a schematic horizontal sectional view showing the arrangement of symmetrical multiple immersion nozzles and solidified shells in the initial stage of casting in continuous casting of beam blanks.

FIG. 4 is a perspective view showing vertical cracks occurring in a beam blank slab.

FIG. 5 shows a case of an open immersion nozzle in Example 1 (curve A) and a case of a single-hole asymmetrical immersion nozzle (curve B).
FIG. 6 is a diagram comparing the solidified shell thickness ratio a / b in the left and right flange portions with the distance (mm) from the meniscus.

FIG. 6 shows the distance (mm) from the meniscus and the thickness a / of the solidified shell of the left and right flanges when the cooling water amount ratios in the left half and the right half of the mold in Example 2 are different as shown in Table 1.
It is a diagram which shows the relationship with b.

FIG. 7 is a diagram showing vertical crack occurrence rates occurring in beam blank slabs when the mold cooling water amount ratios in Example 2 were 1.0, 1.3 and 1.8, respectively.

[Explanation of symbols]

 2 Tundish 3 Molten steel 4 Immersion nozzle 6 Beam blank mold 8 Solidified shell 10 Flange portion 12 Web portion 14 Vertical crack

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[Procedure amendment]

[Submission date] February 19, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a horizontal cross-sectional view showing a solidified shell at the initial stage of casting by an asymmetric single-hole immersion nozzle in continuous casting of beam blanks and solidified shell thicknesses a and b in the left and right flanges.

FIG. 2 is a front sectional view showing a tundish, a dipping nozzle and a beam blank mold in the case of FIG.

FIG. 3 is a schematic horizontal cross-sectional view showing the arrangement of symmetrical multiple immersion nozzles and solidified shells at the initial stage of casting in continuous casting of beam blanks.

FIG. 4 is a perspective view showing vertical cracks generated in a beam blank slab.

FIG. 5 is a case of an open immersion nozzle in Example 1 (A curve) and a case of a single-hole asymmetrical immersion nozzle (B curve).
FIG. 6 is a diagram comparing the solidified shell thickness ratio a / b in the left and right flange portions according to the distance (mm) from the meniscus of FIG.

FIG. 6 shows the distance (mm) from the meniscus and the thickness a of the solidified shells of the left and right flanges when the cooling water amount ratios in the left half and the right half of the mold in Example 2 are different as shown in Table 1.
It is a diagram which shows the relationship with / b.

FIG. 7 is a diagram showing vertical crack occurrence rates occurring in beam blank slabs when the mold cooling water amount ratios in Example 2 were 1.0, 1.3, and 1.8, respectively.

FIG. 8: Beer according to the prior art JP-A-52-13428
It is a perspective view which shows the end surface of the beam blank explaining the continuous casting method of a beam blank.

[Explanation of symbols] 2 Tundish 3 Molten steel 4 Immersion nozzle 6 Beam blank mold 8 Solidification shell 10 Flange portion 12 Web portion 13 Filet portion 14 Vertical cracking

Claims (1)

[Claims] 1. In continuous casting of a beam blank, the control system of the mold cooling water is divided at the center of the web of the beam blank, and the flow rate is controlled independently for each of the right half and the left half of the mold. A method for continuously casting a beam blank, the method comprising: