JPH0120046Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a horizontal continuous casting mold that prevents wear and tear on the inner surface of the mold due to Zn in molten steel.

In a horizontal continuous caster (HCC), the mold is directly connected to the tundish through a refractory. FIG. 1 is a schematic vertical cross-sectional view showing a joint between such a mold and a tundish. 1st
In the figure, 1 is a horizontal continuous casting mold, and the mold 1 is connected to a tundish 4 via a refractory block 2 and a refractory block 3, and the molten steel 5 in the tundish 4 is transferred to the mold 1 without coming into contact with the atmosphere. Infiltrate the inside and remove the refractory block 2.
It begins to solidify at the point where it comes into contact with the solidified shell 6.
is formed to become the slab 7. The mold 1 is made of deoxidized copper or copper alloy, similar to the mold of a vertical continuous caster (VCC).

As mentioned above, in the horizontal continuous casting machine, the mold 1 is directly connected to the tundish 4, so in order to prevent the mold 1 from seizing, etc., the mold 1 is It is difficult to pull out the slab 7 while vibrating it. Therefore, in the horizontal continuous casting machine, the slab 7 is pulled out from the mold 1 in the horizontal direction by repeating a pattern of pulling and then stopping or pulling and then pushing back, thereby preventing the mold 1 from seizing or the like.

By the way, horizontal continuous casting machines can cast slabs of many steel types, from ordinary carbon steel to Ni-based alloy steel, but when casting molten steel with a high Zn content, There is a disadvantage that wear and tear occurs on the inner surface of 1.

FIG. 2 is a partial vertical sectional view of the mold showing locations where such wear occurs. The wear that occurs on the inner surface 1a of the mold 1 is limited to about 3 mm from the bent point where the inner surface 1a contacts the refractory block 2 and the molten steel 5 (hereinafter referred to as the triple point).
It covers the entire circumference of the inner surface 1a, and in the case of a mold for a square billet, it hardly occurs at the corners. This wear becomes deeper as the amount of casting increases. When the depth of this worn part is about 0.4 mm, this becomes a resistance when the slab 7 is pulled out, and it becomes almost impossible to pull out the slab 7 stably.

When the worn parts of the inner surface of the mold 1a are analyzed using an X-ray microanalyzer, it is observed that a Zn-enriched layer with a thickness of several tens of micrometers is formed on the surface layer of the worn parts. The wear was caused by the Zn in the molten steel diffusing into the mold and forming a Cu-Zn alloy layer, a low melting point alloy, on the inner surface layer of the mold, which made the inner surface layer brittle and easily damaged by melting. it is conceivable that.

This type of wear and tear on the inner surface of the mold due to Zn in molten steel is not a problem in the case of converter steel because the Zn content is small, but in the case of electric furnace steel, it is not a problem because scrap is used as a raw material. This becomes a problem because it generally contains a large amount of Zn. However, in the case of high-grade electric furnace steel, degassing treatment or gas bubbling treatment is performed after melting in the electric furnace, so Zn is almost completely removed from the molten steel and wear and tear on the inner surface of the mold occurs. It will never occur. However, in the case of general materials, since molten steel obtained in an electric furnace is directly cast, wear and tear occurs on the inner surface of the mold. Especially in the case where Zn-plated steel sheets are widely used and are being used more and more, as has been the case recently, the Zn content of electric furnace steel will gradually increase due to the use of scrap of Zn-plated steel sheets. Wear on the inner surface of the mold caused by Zn in molten steel is a problem that must be solved in order to achieve continuous horizontal casting of electric furnace steel, a common steel type.

As a countermeasure to this problem, conventionally, Cr was added to the inner surface of the mold.
Methods have been used to prevent the inner surface of the mold from coming into direct contact with molten steel, such as by plating with Ni or by thermally spraying a metal carbide material such as WC or CrC. However, since Zn penetrates these coating layers such as plating and diffuses into the mold, it has little effect. In horizontal continuous casting, the temperature of the inner surface of the mold is much higher than in vertical continuous casting, so the initial peeling of any of these coating layers, such as plating, is likely to occur, which is one of the reasons for the lack of effectiveness. It is.

On the other hand, as a fundamental countermeasure,
It is also possible that it is Zn. For example, Zn is removed by degassing treatment, molten steel stirring treatment using N ₂ or Ar gas in a ladle, or the like. However, although these methods have been confirmed to be extremely effective for removing Zn both theoretically and practically, they have problems in terms of economic efficiency. That is, in the case of degassing treatment, if there is existing treatment equipment, new treatment equipment must be installed, which is expensive. _N2 ,
In the case of molten steel stirring treatment using Ar gas, the required gas flow rate is estimated to be approximately ^1Nm3 per ton of molten steel, which is different from bubbling treatment, which is used to adjust the composition of molten steel and equalize its temperature. However, it has the disadvantage of requiring a large amount of gas. Furthermore, in order to flow a large amount of gas, it is necessary to use a suitable porous plug or change the shape of the ladle, which not only increases gas costs but also increases the burden on equipment. be. Therefore, the latter case also costs money.

In view of the above-mentioned current situation, this idea was developed to reduce the amount of Zn in molten steel.
This invention provides a horizontal continuous casting mold that prevents wear and tear on the inner surface of the mold caused by contact with molten steel on the inner surface of the mold, in a horizontal continuous casting mold that is horizontally connected to a tundish through a refractory block. A groove is provided on at least one of the surface or the contact surface with the refractory block, which extends to the end of the contact surface in the casting direction, including the point where the two contact surfaces intersect, and is open to the outside air at the end. It has particular characteristics.

Hereinafter, embodiments of this invention will be described in detail based on the drawings.

First, the wear mechanism of the inner surface of the mold due to Zn in molten steel will be explained. As a result of investigating the wear mechanism of the inner surface of the mold, it was found that the following occurs near the triple point 8 where the inner surface of the mold 1a is bent, where the contact surface of the inner surface of the mold 1a with the refractory block 2 and the contact surface with the molten steel 5 intersect. It was found that the following phenomenon occurs. FIG. 3 shows an enlarged view of the vicinity of triple point 8. When the molten steel 5 enters the mold 1 from the tundish and begins to solidify at the point where it comes into contact with the refractory block 2 and forms the shell 6, most of the Zn in the molten steel 5 is Due to its extremely high concentration, it is released as Zn vapor. At the triple point 8, by cooling the refractory block 2 and the mold 1 from two directions, the molten steel 5 becomes a shell 6 and solidifies and shrinks, and the shell 6 further shrinks due to heat, so that the solidified shell 6 and A gap 9 is formed between the refractory block 2 and the mold 1. Zn vapor released during solidification is accumulated in this void 9,
From there, it diffuses into the mold 1, and a low melting point Cu-Zn alloy is produced on the surface layer of the mold inner surface 1a. As a result, the mold inner surface 1a within a range of approximately 3 mm from the triple point 8 of the mold 1 becomes an extremely brittle material and is easily damaged by melting, resulting in wear and tear.

Therefore, if the Zn vapor accumulated in the void 9 at the triple point 8 of the mold 1 is released outside the mold 1 or brought into contact with the atmosphere to cause the reaction Zn+1/2O ₂ →ZnO, Zn is no longer diffused into the mold 1, and wear and tear on the inner surface 1a of the mold 1 caused by Zn can be prevented. That is, gaps are provided between the inner surface 1a of the mold 1 and the slab 7, and between the inner surface 1a and the refractory block, in order to release the Zn vapor accumulated in the void 9 of the triple point 8 to the atmosphere or to remove it by contacting the atmosphere. It may be provided between 2 and 2.

Therefore, in this invention, the inner surface 1a of the mold 1
A groove communicating with the outside air is provided in the mold 1 to remove Zn vapor that accumulates in the void 9 inside the mold 1.

FIG. 4a is a vertical cross-sectional view of the square billet mold of this invention, FIG. 4b is a view taken along line A--A in FIG. 4a, and FIG. 4c is a view taken along line B-- This is a view taken along the line B. In the drawings, reference numeral 10 denotes grooves provided on the four inner surfaces 11a of the mold 11. Ten grooves are continuously provided in parallel.The grooves 10 are
The outer ends of the contact surfaces 11a' and 11a'' are open to the atmosphere. The groove 10 has a width of 50 μm and a depth of 500 μm.
It is formed with a rectangular cross-sectional shape.

According to such a mold 11, when a slab is cast from molten steel, it is released from the molten steel as it solidifies, and is released from the molten steel near the triple point on the mold inner surface 11a, which is the junction between the contact surfaces 11a' and 11a''. accumulated in voids
Zn vapor can be removed from the voids because it can be vented to the atmosphere through the grooves 10 or brought into contact with the atmosphere in the grooves 10 and oxidized.

In the above example, the groove 10 has a width of 50 μm and a depth of 500 μm.
Although 10 pieces are provided on both the contact surfaces 11a' and 11a'' in the case of M, they can also be provided on only one of the contact surfaces 11a' or 11a''. Further, the width, depth, cross-sectional shape, number, direction, etc. of the grooves 10 are not limited to the numerical values in the above example. The width and depth of the groove 10, or whether the groove 10 is provided on the entire inner surface 11a or the contact surface 1
Whether to provide it on one of the grooves 1a' or 11a'' is determined as appropriate in consideration of the Zn vapor removal effect of the grooves 10 and the prevention of a decrease in the strength of the mold 11.

Among these, the width of the groove 10 is important because it greatly influences the Zn vapor removal effect. That is, if the width of the groove 10 is too large, molten steel will enter the groove 10 and
Since it solidifies following the shape of Zn, it is no longer effective as a gap for communicating Zn vapor with the atmosphere. Therefore, the optimal width l of the groove is determined by the formula: lP ≧
It is determined by 2γcosθ (where θ is the contact angle). For example, the height of the molten steel in the tundish is
In the case of 0.7 m, if the width l is 40 μm or less, molten steel will not enter into the groove 10 and the groove 10 will be maintained as a gap. Grooving of this width can be easily formed without any problem with current processing technology. The number of grooves 10 depends on the directionality, but for example, if they are provided parallel to the casting direction, it is possible to improve the removal effect of Zn vapor and reduce stress concentration on the grooves 10, so it is preferable to use a plurality of grooves 10. It is preferable that there be. It is appropriate that the depth of the groove 10 is 2 mm or less, especially from the viewpoint of the influence on the strength and cooling effect of the mold 11 and the ease of processing.

Next, we will discuss the results of casting a 115 mm square billet from ordinary carbon steel with a Zn content of 50 to 80 ppm using the mold of this invention. The mold used was mold 11 (hereinafter referred to as the No. 1 mold of the present invention) in which ten grooves each having a width of 50 μm and a depth of 500 μm were provided throughout the inner surface 11a shown in FIGS. 4 a to c.
and only on the contact surface 11a' of the inner surface 11a with the molten steel,
The present invention is applied only to the contact surface 11a'' between the mold (hereinafter referred to as the No. 2 mold of the invention) and the refractory block of the inner surface 11a, which is provided with the same groove as the contact surface 11a' of the mold of the invention No. 1. No.1 mold contact surface
There are three types of molds (hereinafter referred to as the No. 3 mold of the present invention) in which grooves are provided in the same manner as 11a''.

As a result, the relationship between the number of casting heats and the depth of wear near the triple point on the inner surface of the mold was as shown in FIG. For comparison, the results for a conventional mold in which no grooves were provided on the inner surface of the mold are also shown in FIG.

As is clear from Fig. 5, in all of the molds No. 1 to 3 of the present invention, even when the number of casting heats increases, the wear around the triple point on the inner surface of the mold does not increase significantly, and the wear is drastically reduced compared to the conventional mold. I know what you're doing. In particular, in the No. 1 mold of the present invention, the depth of the wear was only 0.02 mm even after 57 casting heats, and it was found that the mold was extremely effective against wear caused by Zn in molten steel.

In addition, only linear traces were observed on the surface of the slab, and no casting problems such as surface flaws occurred by using these molds Nos. 1 to 3. As the casting process continued, the grooves became clogged with ZnO and scales that had peeled off from the slab surface, but this could be removed by occasionally wiping with an extremely low concentration acid aqueous solution. .
Furthermore, since the contact surface with the refractory block on the inner surface of the mold is joined to the refractory block with mortar in between, in the case of the No. 3 mold of the present invention, the groove provided on the contact surface is filled with mortar. Although there was some concern, although such a phenomenon occurred in some cases, it did not cause any major problems, and as shown in FIG. 5, excellent results were obtained.

In the above embodiment, a mold for a square billet was explained, but the invention is not limited to this.
It is equally applicable to molds for slabs with non-square cross-sections, such as round billets, and large slabs.

Since the horizontal continuous casting mold of this invention is constructed as described above, wear and tear on the inner surface of the mold due to Zn in molten steel is prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view showing the joint between the horizontal continuous casting mold and the tundish, and FIG.
FIG. 3 is an enlarged longitudinal sectional view showing the mold shown in FIG. 1 and a refractory block, and FIG. 4a shows an embodiment of the mold of this invention. The vertical sectional view shown in FIG. 4b is a view taken along the line A-A in FIG. 4a, and FIG.
-B line arrow view, FIG. 5 is a graph showing the relationship between the number of casting heats and the depth of wear on the inner surface of the mold caused by Zn when casting using the mold of this invention and the conventional mold. In the drawings, 1, 11...mold, 2, 3... refractory block, 4... tundish, 5... molten steel, 6...
Shell, 7... Slab, 8... Triple point, 9... Gap, 10... Groove, 1a, 11a... Inner surface, 11
a′, 11a″…Contact surface.

Claims (1)

[Scope of utility model registration request] In a horizontal continuous casting mold that is horizontally connected to a tundish through a refractory block, at least one of the contact surface with the molten steel on the inner surface of the mold or the contact surface with the refractory block has the two contact surfaces. A mold for horizontal continuous casting, characterized in that a groove is provided that extends to the end of the contact surface in the casting direction, including the intersection, and is open to the outside air at the end.