JPS63313633A - Horizontal type continuous casting method - Google Patents

Abstract

PURPOSE:To obtain a cast slab having shallow cold shut mark and good surface characteristic by casting while flowing as circling molten steel pouring in a mold from pouring hole vertically at width direction of center part of the mold. CONSTITUTION:By unevenly arranging a feed nozzle 8 of a tundish at near any side wall 6A in front or rear side from center of width direction at the upper face in the mold 6, the molten steel 2 develops the circular flow 2A toward the arrow direction. As in the center part of the mold 6, the new molten steel 2 is continuously supplied and flowed as circling, solidification in there is behind that at the other part and the solidified shell 12A at break point 16 is made to thin. In the solidified shell 12A shifted to right and left directions by drawing cast slab, as the thickness formed at initial stage is thin, interface with a secondary solidified shell formed on the initial solidified shell after cutting at the break point 16 is shallow and also the cold shut mark on the cast slab is shallow.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a horizontal continuous casting method, and in particular prevents surface defects in slabs called cold shut marks, and produces slabs with good surface quality. Regarding the horizontal continuous casting method that can be used to obtain the desired results, it is widely used in the field of continuous steel casting.

[Conventional technology]

In the field of continuous casting, instead of the conventional vertical or curved continuous casting method, a horizontal continuous casting method has been proposed in which a horizontally arranged continuous casting mold is used to pull out and cast slabs horizontally. Casting of slabs is carried out.

With these horizontal continuous casting methods, conventional vertical or curved continuous casting methods require large costs to construct buildings that reach heights of 30 to 40 meters and structures that support the associated large weight. On the other hand, it is attracting attention because of its advantages of being able to lower the height of the building and having relatively low equipment costs.

The horizontal continuous casting method also changed from the initial method of pulling the slab from one side of the mold to a method of pulling the slab from both ends of the mold in opposite directions, as disclosed in JP-A No. 58-138544, and production progressed. Capacity improvements have been achieved.

This method will be explained with reference to FIGS. 3(A) and 3(B).

Capacity V of ladle or tundish etc. that accommodates molten steel 2
Below iJ4, a mold 6 is horizontally arranged with its end directed in the horizontal direction. The container N4 and the mold 6 are communicated through a feed nozzle 8 so that there is no leakage of the molten TF42. The mold 6 and the container 4 are vibrated left and right by a vibrating device 10, and the slab 12 in which the molten steel 2 has solidified is pulled out left and right by pinch rolls 14.

However, in the horizontal continuous casting machine of both drawing types shown in FIG.
As a result, the thin initial solidified shell 12A formed approximately in the center of the mold 6 breaks every time the direction of vibration of the vibration device 10 changes, forming a break point 16 as shown in FIG. 4(A). It is pulled apart from side to side. On the surface of the water-cooled mold 6 between the left and right solidified shells 12A separated in this way, a new secondary solidified shell 12A grows again, as shown in FIG. 4(B).

Therefore, according to the conventional horizontal continuous casting method, the solidified shells 12A formed on the left and right sides go through the process shown in FIGS. 12, pull it out to the left and right as shown in FIG. 3(A).

However, due to the above-mentioned "tearing phenomenon" caused by the breakage that occurs during the formation of the solidified shell 12A and the secondary solidified shell that grows thereafter, surface defects called "cold shut marks" remain on the surface of the slab 12.

If this cold shut mark is shallow, it will be crimped during rolling, but if it is deep, it will remain on the product as a flaw even after rolling, so it is necessary to remove it by cutting the surface of the slab.

[Problem that the invention seeks to solve]

An object of the present invention is to provide an effective continuous casting method that can prevent the occurrence of "cold shut marks" on the surface of a slab according to the above-mentioned conventional technique in horizontal type continuous casting of a double-draw type.

[Means for solving problems]

The depth of the cold shut mark appearing as a surface defect on the slab is determined by the thickness of the solidified shell 12A itself when the initially solidified shell 12A is torn off at the break point 16. Therefore, in order to reduce the depth of the cold shut mark, it is necessary to keep the thickness of the solidified shell that initially solidifies in the mold 6 as thin as possible.

One way to reduce the initial thickness of the solidified shell is to increase the degree of superheating of the molten steel.In general, the growth rate of the solidified shell is influenced by the degree of superheating of the molten steel if the water cooling conditions of the mold are constant; The higher the degree of superheating, the slower the growth rate of the solidified shell. However, increasing the degree of superheating causes another problem, such as a reduction in the thickness of the solidified shell produced in the mold, which necessitates lower casting speeds.

In addition to the above-mentioned degree of superheating of WI steel, the present inventors realized that when the molten steel flow rate is high, the growth rate of the solidified shell becomes slow. As a result of repeated experiments, we were able to complete the present invention.

The gist of the present invention is as follows.

That is, in a horizontal continuous casting method in which molten steel is injected into a mold through an injection hole in the center of a horizontally arranged mold and slabs are pulled out from both ends of the mold in opposite directions, the molten steel is injected into the mold through the injection hole. This is a horizontal continuous casting method characterized by casting molten steel while swirling it up and down in the width direction of the center of the mold.

As mentioned above, the thickness of the initial solidification tube 12A is reduced (
In order to do this, the injected molten steel is cast while being swirled up and down in a region at right angles to the mold length direction, that is, in the mold width direction, at the center of the mold 6. As specific methods for creating swirling flow, the following two methods are most effective.

(A) The feed nozzle 8 of the tundish 4, which is usually provided at the center of the widthwise center of the mold, is shown in Fig. 1(A).
As shown in CB), place it unevenly near either the front or rear side wall.

(b) As shown in FIG. 2, the feed nozzle 8 of the tundish 4 is tilted to cause the supplied molten steel 2 to collide with the side wall of the mold 6.

The above two aspects will be explained below.

(a) As shown in FIGS. 1(A) and 1(B), the feed nozzle 8 is unevenly located in the vicinity of the side wall 6A on either the front or back side of the upper surface of the mold 6 in the width direction. The molten steel 2 produced by this process produces a swirling flow 2A in the direction of the arrow.

However, the center part of the mold 6 where the swirling flow 2A is generated is continuously supplied with new molten steel 2, and since the swirling flow is occurring, solidification is delayed compared to other parts, as shown in FIG. 4(A). The solidified shell 12A at the break point 16 as well as other solidified shells generated near the center of the mold 6 become thinner. As a result, the solidified shell 12A that separates and moves to the left and right as the slab 12 is pulled out has a solidified layer that gradually becomes thicker, but the solidified shell 12A that was formed initially
Since the thickness of A is small, the interface with the secondary solidified shell formed on the initial solidified shell after breaking off at the break point 16 is shallow, and therefore the cold shut mark remaining on the slab is also extremely shallow.

(b) As shown in FIG. 2, even when the feed nozzle 8 is tilted, the injection W! The Iw4 flow 2A collides with the side wall surface 6A and generates a swirling flow at the center of the mold 6 as shown by the arrow, making it possible to reduce the thickness of the initial solidified shell 12A and, in turn, to reduce the thickness of the cold shut mark. The depth could be made extremely small.

Note that the inclination angle of the feed nozzle 8 in this case is
Of course, it is necessary to collide with either the front or rear side walls of the central part of the mold in a limited area in the width direction of the central part of the mold, and to avoid tilting in the longitudinal direction of the mold.

〔Example〕

A horizontal continuous casting mold with a cross-sectional area of 150 m@ For the case where 45 parts are unevenly distributed perpendicularly to the length direction of the mold from the center, the top surface, bottom surface, side surface No. of the manufactured slab with other casting conditions being the same,
1. The depth of the cold shut mark was measured on the side surface Na2, and the effects of the conventional method and the present invention shown in FIGS. 1(A) and 1(B) were compared. The results were as shown in Table 1.

Table 1 As is clear from Table 1, there is a clear difference in the depth of the cold shut mark between the method of the present invention and the conventional method, and the depth of the cold shut mark of the slab according to the present invention is , was found to be reduced to about 1/10 of the conventional value.

Next, using a mold having a cross-sectional area of 150 + m The 173 points at the height of the side wall were oriented from the bottom end of the side wall in a plane perpendicular to the longitudinal direction, and continuous casting was performed under the same casting conditions. The depth was measured. When the results were compared with the conventional method shown in Table 1, it was found that approximately 171
It was observed that the depth had decreased to about 0. Furthermore, regarding the method of the present invention, there is almost no difference in effectiveness between the mode shown in Figure 1 in which the feed nozzles are unevenly distributed and the mode shown in Figure 2 in which the feed nozzles are tilted and the molten steel collides with the side wall. 17% compared to the conventional method.
1O, the depth of the cold shut mark could be significantly reduced, and the surface quality of the steel material after rolling was extremely good.

〔Effect of the invention〕

In the case of the conventional horizontal continuous casting method, this occurs when a secondary solidified shell is generated after the initial solidified shell is separated to the left and right in the vicinity of the center of the mold. In order to solve the problem of deep so-called cold shut marks, which remain as surface defects on steel products after rolling, in the present invention, when pouring molten steel into a mold, molten steel is poured vertically in a limited area in the mold width direction at the center of the mold. This problem was solved by generating a swirling flow and thereby reducing the thickness of the initially formed solidified shell, and the following effects were achieved.

(b) Generate swirling flow of the molten metal.Specific methods include placing the feed nozzle unevenly near the side wall, and tilting the feed nozzle to direct the molten steel injection direction toward the bottom of the side wall. Compared to the method in which molten steel was injected vertically downward from the center in the width direction, the depth of the cold shut mark formed on the manufactured slab was reduced to approximately 171 mm, resulting in extremely good surface quality. We were able to produce slabs.

(b) With (a), the conventional work such as cutting the slab before rolling becomes unnecessary, making it possible to reduce labor costs and improve yield.

(c) The manufacturing cost or modification cost of the molding apparatus according to the present invention is small, and is more than compensated for by the effects of the present invention.

[Brief explanation of the drawing]

FIG. 1(A) is a cross-sectional view showing the swirling flow of molten steel in the center of the mold in which the feed nozzle is unevenly located near the side wall in a horizontal continuous casting apparatus according to the present invention, and FIG. 1(B)
is a vertical sectional view of the same part, and Fig. 2 is a cross-sectional view showing the swirling flow state of molten steel in the center of the mold when the feed nozzle is tilted and the molten steel injection direction is directed toward the lower part of the side wall, which is another embodiment of the method of the present invention. 3(A) and 3(B) show a conventional horizontal continuous casting apparatus, (A) is a vertical cross-sectional view showing the state of injection of molten steel and the state of solidified shell formation in the center of the mold, and (Bl is The cross-sectional views at the center of the mold, FIGS. 4(A) and 4(B), show the solidified shell formation near the break point at the center of the mold in a conventional horizontal continuous casting device, and (A) shows the initial solidified shell, (B) is 2 after breaking at the break point.
FIG. 3 is a schematic cross-sectional view in the longitudinal direction of the mold, illustrating how the next solidified shell is formed. 2... Molten steel 2A... Molten steel swirl flow 4...
・Tandish 6... Mold 8... Feed nozzle 12... Slab 12A... Solidified shell 16
...Break point arrow Figure 1 (A) CB) No. 32 (A)

Claims (3)

[Claims] (1) In a horizontal continuous casting method in which molten steel is injected into the mold from an injection hole in the center of a horizontally arranged mold and slabs are pulled out from both ends of the mold in opposite directions, the molten steel is injected into the mold from the injection hole. 1. A horizontal continuous casting method, characterized in that the molten steel is cast while swirling up and down in the width direction of the center of the mold. (2) The swirling flow of molten steel in the center of the mold is caused by unevenly distributing the feed nozzle forming the injection hole in the vicinity of either front or rear side wall from the widthwise center of the upper surface of the mold. Horizontal continuous casting method described in . (3) The swirling flow of the molten steel in the center of the mold is caused by tilting the feed nozzle forming the injection hole and causing the flow of the injected molten steel to collide with either the front or rear side wall of the mold. Horizontal continuous casting method described in Section.