JP2002113556A - Casting roll and continuous casting method using this roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of a phenomenon that thermal stress cracking is caused in a short term on the surface of a casting roll and the surface crack of a cast slab by stably releasing the thermal load of the casting roll with molten metal at the initial contact stage. SOLUTION: In the casting roll 1 used for a twin-roll type continuous casting for iron base material containing a carbon steel and a stainless steel, plural projecting parts 9 formed as a mountain type having uniform height H on the roll surface 1a are formed, and the peaks of respective projecting parts 9 are disposed with the regular arrangement patterned so as to form any polygonal shape of triangular shape, quadrangular shape or combination of these angular shapes. Mutual peaks of respective projecting parts 9 are adjoined while having the interval S of 70-500 μm so as to form the flat part having >=1/2 of the width L of foot of the mountain formed with each projecting parts 9 on the respective projecting parts 9. With this way, the heat transfer at the initial stage of contacting of the casting roll 1 with the molten metal 6 is drastically lowered and the thermal load on the surface 1a of the casting roll 1 is drastically released.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting roll and a continuous casting method using the same.

[0002]

2. Description of the Related Art FIG. 7 shows an example of a general twin-roll type continuous casting machine in which a pair of water-cooled type casting rolls 1 are arranged horizontally and in parallel, and a gap 2 between the casting rolls 1 is formed. Side weirs 3 are arranged at both ends to form a mold surrounded by each side weir 3 and each of the casting rolls 1. A tundish 4 placed above the molds
From each casting roll 1 through a refractory pouring nozzle 5
The molten metal 6 is supplied to the gap 2 of the metal to form a pool 7, and the molten metal 6 in the pool 7 is cooled and solidified on the roll surface 1 a while rotating each of the casting rolls 1. Are continuously drawn downward from the gaps 2 of the respective casting rolls 1 to form cast slabs.

[0003] In such a twin-roll continuous caster,
If the surface of each casting roll 1 is excessively processed by a lathe or the like, the molten metal 6 comes into close contact with the roll surface 1a during casting, and the molten metal 6 (solidified shell 8) and the casting roll 1 The initial heat transfer coefficient becomes large, heat is rapidly removed from the molten metal 6, and the gradient of thermal strain between the surface side of the molten metal 6 in contact with the roll surface 1a and the inside becomes large, causing solidification. The molten metal 6 was being mixed with a tensile stress and a compressive stress, and the slab was likely to crack.

Therefore, in recent years, each casting roll 1
The surface of the roll 1a is made uneven by shot blasting or the like, so that the molten metal 6 is supported only by the projections of the roll surface 1a by surface tension, thereby alleviating sudden heat removal during solidification of the molten metal 6. It has been proposed that
It has already been confirmed that such a structure is effective in preventing a slab from cracking (for example, see Japanese Patent Application Laid-Open No. 2-1793).
No. 43).

[0005]

However, if the roll surface 1a of each of the casting rolls 1 is simply provided with an uneven shape by shot blasting or the like, thermal fatigue cracking occurs in a short time on the roll surface 1a of the casting roll 1. It is difficult to prevent the phenomenon from occurring, and the fact that the roll cost is increased due to the thermal fatigue cracking has not yet been solved.

In US Pat. No. 4,250,950, it is disclosed that regular irregularities are arranged on the roll surface 1a of the casting roll 1, but this is intended to discharge gas. However, merely arranging the regular asperities does not address the problem of thermal fatigue cracking of the casting roll 1.

In this regard, the molten metal 6 and the casting roll 1
It has been assumed that the heat transfer between the two is constant. However, the present inventors have not found a conventional method of measuring the temperature of the mold with a high-speed response (the conventional method of sandwiching a sheath thermocouple wire having a large heat transfer resistance,
A method of directly welding the copper-constantan wire to the inside near the mold surface) was developed and measured. As shown by the solid curve in FIG. Has a high heat load (heat flux) that is 6 times or more as compared with the average value of 20 MW / m ^2.
It has been found that this is a factor that causes thermal fatigue cracking in a short time on the roll surface 1a.

The case (conventional surface) of the solid line curve in FIG. 8 is the roll surface 1a of the casting roll 1.
Each of the projections has a height of about 30 μm when the projections and depressions are formed by shot blasting or the like, and the projections have narrow valleys with no valley width. The case of the dashed curve is
This relates to an embodiment of the present invention described later.

[0009] Further, the present inventors have conducted repeated studies,
When the roll surface 1a of each casting roll 1 is made uneven by shot blasting or the like as in the prior art, the protrusions are formed at a high density, and the reproducibility is poor. When the molten metal 6 is supported on the tops of these projections, the molten metal 6
As a result, the total area of the apex portion of each convex portion contacting with the molten metal 6 is increased, and a large portion of the air gap formed between the molten metal 6 is formed, and a large heat transfer is performed through a thin air layer. It was also found that a large heat load was applied when the molten metal 6 first came into contact with each projection on the roll surface 1a.

That is, regarding the occurrence of thermal fatigue cracking on the roll surface 1a of the casting roll 1, it is considered that the effect of the local high heat load due to the convex portions having irregular heights also has an adverse effect.

Incidentally, the surface of the molten metal 6 warps immediately after solidification starts after the initial contact with the casting roll 1 and the adhesion of the molten metal 6 to the top of each projection is impaired. Therefore, it is considered that the heat load rapidly sinks in a short time.

The present invention has been made in view of the above-mentioned circumstances, and alleviates the thermal load in the initial stage of contact between a molten metal and a casting roll to cause thermal fatigue cracking on the casting roll surface in a short period of time. And at the same time, prevent the productivity from being impaired by reducing the average heat removal.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a casting roll for use in twin-roll continuous casting of an iron-based material including carbon steel and stainless steel. Convex portions are formed, and the vertices of each convex portion are arranged in a regular array that is patterned so as to form any one of a triangular shape, a quadrangular shape, and a polygonal shape formed by a combination thereof. The vertices of the part are 70 μm to 5
A flat portion that is adjacent to each other with a spacing of 00 μm and that is equal to or more than 裾 of the width of the crest formed by each convex portion is formed between each convex portion.

Thus, the distance between the vertices of the adjacent convex portions is set to 70 μm or more, and a flat portion having a width of 以上 or more of the crest formed by each convex portion is formed between the convex portions. If it is formed, the top portion of each convex portion forming a contact portion when the molten metal comes into contact with the casting roll and the small portion of the air gap formed therearound are reduced, The heat transfer in the initial stage of contact between the molten metal and the casting roll is greatly reduced, and the maximum heat load on the roll surface of the casting roll is greatly reduced.

The distance between the vertices of adjacent convex portions is 50.
If the thickness exceeds 0 μm, it becomes difficult to support the molten metal at each convex portion due to surface tension, and the molten metal easily enters a valley between the convex portions. Therefore, the upper limit of the distance between the vertexes of adjacent convex portions. Needs to be set to 500 μm. In addition, the reason why the distance between the vertices of the adjacent convex portions is set to 70 μm or less is that irregularities in the order of minute μm of the height of the convex portions affect the presence or absence of contact with the molten steel, and a phenomenon in which the contact portion flies occurs. Is known.

Further, in the present invention, in order to reduce a small portion of the air gap formed around the apex of the convex portion, each convex portion is formed so that the apex angle of the mountain formed by the convex portion is 120 ° or less. Preferably, a portion is formed. Further, a hemispherical surface or a flat surface may be formed at the top of each convex portion smoothly continuing to the mountain skirt.

Further, the present invention relates to a continuous casting method in which a casting roll adopting the above-described structure is rotated and used as a moving wall of a mold. It is possible to perform continuous casting while effectively suppressing the heat transfer at the initial stage of contact between the casting roll and the casting roll. , The frequency of exchanging the casting rolls can be reduced, the operating efficiency of the continuous casting machine can be increased, and there is also a good effect of preventing the surface cracks of the slab.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 6 show an embodiment of the present invention, and the portions denoted by the same reference numerals as those in FIG. 7 represent the same components.

In this embodiment, as shown in FIGS. 1 and 2, a casting roll 1 used in a twin-roll type continuous casting machine as shown in FIG. The plurality of projections 9 to be formed are formed by machining, and the vertices of adjacent projections 9 are 70 μm to 500 μm.
m, and each protrusion 9 is arranged so as to have an interval S of m. In addition, the width L of the foot of the mountain formed by each protrusion 9 between the protrusions 9
Is formed so as to form a flat portion with an interval P of at least 1/2 or more of the above.

Here, for example, the width L of the foot of the mountain formed by each projection 9
Is about 60 μm, in order to form a flat portion with an interval P of Ｌ L or more between the vertices of the adjacent convex portions 9,
Although it is necessary to set the interval S to about 90 μm or more, in practice, it is sufficient to select an interval S of about 100 to 400 μm, and in the present embodiment, the interval S is set to about 300 μm.

In the example shown in FIG. 2, the vertices of the projections 9 on the roll surface 1a are arranged in a regular array patterned so as to form a square grid like a grid. However, squares other than squares (rectangular, rhombic, parallelogram, trapezoidal) are repeatedly arranged in the same pattern, and triangles other than equilateral triangles (right-angled triangles, isosceles triangles , Three-sided triangles) in the same pattern.
It is also possible to arrange them in a regular array patterned so as to form a polygonal shape by a combination of these triangular shapes and quadrangular shapes.

Furthermore, in the figure, the pyramid is formed as a quadrangular pyramid-shaped mountain, but each convex portion 9 is formed as a polygonal pyramid or a conical mountain except a square. A hemispherical surface 9a may be formed at the top of each projection 9 as shown in FIG. 1 and may be smoothly continuous with the skirt, or a flat surface 9b may be formed as shown in FIG. Is also good.

Further, as shown in FIG.
A flat portion is formed so as not to be in contact with the molten metal 6, and this flat portion may be a surface having an uneven surface sufficiently lower than the convex portion 9 (not particularly shown). It is preferable that the height H of each projection 9 is included in the range of 5 to 100 μm.

As shown in FIG. 5, each convex portion 9 is preferably formed such that the peak angle θ of the mountain shape formed by the convex portions 9 is 120 ° or less, preferably 90 ° or less.

It should be noted that the peak angle θ of the peak formed by the convex portion 9 as defined in the present invention is defined as the slope of the mountainside which forms the main gradient from the top of the convex portion 9 to the foot of the mountain. The extended slope line extends upward, and refers to an angle formed by the extended slope lines at a point where the extended slope lines intersect upward, regardless of the presence or absence of the hemispherical surface 9 a or the flat surface 9 b at the top of each convex portion 9. Can be specified.

The width L of the foot of the mountain is defined by the same gradient line extending to the bottom of the valley between the projections 9 and the point of intersection with the line along the surface of the valley is used as the base point for measurement. It refers to a mountain-shaped width dimension formed by the portion 9.

When continuous casting is performed by a twin-roll type continuous casting machine using such a casting roll 1, as shown in FIG. In the supported state, the air gap 10 is formed between the convex portions 9 without contacting the flat portions and the uneven portions between them.
The distance S between the vertices of the adjacent convex portions 9 is set to 70 μm or more, and a flat portion having a half or more of the width L of the crest formed by each convex portion 9 is formed between the convex portions 9. The reason is that the top portion of each convex portion 9 forming a contact portion when the molten metal 6 comes into contact with the casting roll 1 and the small portion of the air gap 10 formed therearound are reduced. Heat transfer in the initial stage of contact between the molten metal 6 and the casting roll 1 is greatly reduced, and the roll surface 1a of the casting roll 1 is reduced.
Is greatly reduced.

The actual measurement example indicated by the broken line in FIG. 8 is based on the present invention. The vertexes of the adjacent projections 9 are set at an interval S of 300 μm, the height of the pyramid is 30 μm, and the length of each side is 120 μm. The case where the interval between them is 180 μm and the width of the flat portion at the bottom of the valley is sufficiently large is shown. As can be seen from the figure, the large thermal load at the initial stage of the contact is significantly reduced by about half compared with the conventional type.

The graph of FIG. 6 shows the result of the theoretical analysis by the present inventors, and shows that the angle of the pyramid is made sharper than in the example of FIG. 8 to further reduce the thermal load at the initial stage of contact. Shows the case when aiming. The horizontal axis in the graph indicates the interval S between the vertices of each protrusion 9, and the vertical axis indicates the molten metal 6.
Shows the heat flux (the amount of heat moving across a unit area per unit time per unit time) at the time of initial contact between the casting roll 1 and the casting roll 1. In this case, the length L of one side is about 60 μm and the height H Is a pyramid-shaped convex part 9 having a hemispherical surface 9a formed on the top of which is 30 μm.

According to the results shown by the curves in the graph of FIG. 6, in the dense state where the protrusions 9 are so close to each other that the interval S is about 60 μm, the protrusions per unit area are large. Due to the high density of the protrusions 9, the total area of the tops of the protrusions 9 that come into contact with the molten metal 6 increases, and the hills of the adjacent protrusions 9 overlap with each other, so that the hills of the protrusions 9 Since the air gap 10 is not formed, the heat flux at the time of initial contact between the molten metal 6 and the casting roll 1 shows an extremely high value, while the interval S is 10 μm.
A significant decrease in heat flux is observed only when the distance is increased to about 70 μm. In particular, when the interval S is increased to 300 μm, the density of the projections 9 per unit area is significantly reduced, and each of the projections 9 Air gap 1 large enough around
0 is formed, and the value of the heat flux is reduced to about 14 MW / m ² which is the average value of the heat flux at the initial stage of contact between the molten metal 6 and the casting roll 1 (so that the heat is removed with a substantially constant heat flux). ) Was confirmed.

Incidentally, this increase in the interval S of 300 μm or more shows only a gradual decrease in the heat flux. In particular, when the interval S is increased beyond 500 μm, the molten metal 6 is caused to have its respective convex portions formed by surface tension. 9 becomes difficult to support, and each projection 9
It is considered that the upper limit of the distance S between the vertices of the adjacent convex portions 9 is about 500 μm because the molten metal 6 easily enters the valley portions between them.

In the description of the present embodiment described above in detail, a hemispherical surface 9a (see FIGS. 1, 4 and 5) and a flat surface 9b (see FIG. 3) are provided on the top of each convex portion 9. The reason for the formation is that the molten metal 6 is properly supported by the tops of the projections 9. If the tops of the projections 9 are too sharply sharp, the molten metal 6 Since the tip of each projection 9 is pierced into the inside and cannot be favorably supported, it is necessary to form the projection as necessary to avoid this.

On the other hand, the peak angle .theta.
The reason why the angle is set to 0 ° or less is to suppress the spread of each convex portion 9 from the hillside to the foot of the mountain and to easily form a sufficiently large air gap 10 around each convex portion 9. The significance of forming the above-mentioned hemispherical surface 9a (see FIGS. 1, 4 and 5) and flat surface 9b (see FIG. 3) as the peak angle .theta. And the hemispherical surface 9a and the flat surface 9a
If b is formed, the apex angle θ is preferably set to 90 ° or less.

Therefore, according to the above embodiment, the molten metal 6
The heat transfer in the initial stage of contact between the casting roll 1 and the casting roll 1 can be significantly suppressed, and the heat load applied to the roll surface 1a of the casting roll 1 can be greatly reduced. The phenomenon of thermal fatigue cracking can be prevented, the life of the casting roll 1 can be extended, and the cost of the roll can be significantly reduced.
The operation efficiency of the continuous casting machine can be significantly increased by reducing the frequency of replacing the casting roll 1.

It should be noted that the casting roll and the continuous casting method using the same according to the present invention are not limited to the above-described embodiment, and that various changes can be made without departing from the gist of the present invention. Of course.

[0037]

According to the casting roll of the present invention and the continuous casting method using the same, the heat transfer in the initial stage of the contact between the molten metal and the casting roll is significantly suppressed, and the heat load applied to the roll surface of the casting roll is reduced. Can significantly reduce the occurrence of thermal fatigue cracks on the roll surface of the casting roll in a short period of time, prolonging the life of the casting roll and greatly reducing the roll cost. In addition to reducing the frequency of exchanging casting rolls, the operating efficiency of the continuous casting machine can be significantly increased.
Since a large thermal strain on the slab surface can be stably alleviated, an excellent effect that it is also effective in preventing the slab from cracking can be obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged perspective view showing a main part of an example of an embodiment of the present invention.

FIG. 2 is a plan view showing an arrangement state of convex portions in FIG.

FIG. 3 is a perspective view showing an example in which a flat surface is formed on the top of each convex portion in FIG.

FIG. 4 is a cross-sectional view schematically showing a contact state between the casting roll of FIG. 1 and a molten metal.

FIG. 5 is an explanatory diagram of a mountain-shaped apex angle formed by the protrusions of FIG. 1;

FIG. 6 is a graph showing a relationship between an interval between vertexes of adjacent convex portions and a heat flux.

FIG. 7 is a schematic view showing an example of a conventional general twin-roll type continuous casting machine.

FIG. 8 is a graph showing a temporal transition of a heat flux due to contact between a molten metal and a casting roll.

[Explanation of symbols]

 Reference Signs List 1 casting roll 1a roll surface 6 molten metal 9 convex portion 9a hemispherical surface 9b flat surface 10 air gap H height S interval θ apex angle

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jun Hirata 1st Shin-Nakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa Ishikawashima-Harima Heavy Industries Co., Ltd. Machinery & Plant Development Center (72) Inventor Akihiro Nomura Isogo-ku, Yokohama-shi, Kanagawa No. 1 Shin-Nakahara-cho Ishi Kawashima-Harima Heavy Industries Co., Ltd. Machinery & Plant Development Center (72) Inventor Hiroyuki Otsuka No. 1 Shin-Nakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Ishi Kawashima-Harima Heavy Industries Co., Ltd. Machinery & Plant Development Center (72) Inventor Shiro Nagata 1 Shinnakaharacho, Isogo-ku, Yokohama-shi, Kanagawa Ishikawashima Harima Heavy Industries, Ltd. Yokohama Engineering Center F-term (reference) 4E004 DA13 NA05 NB07 NC02 NC04 QA01

Claims (4)

[Claims] 1. A casting roll used for twin-roll continuous casting of an iron-based material including carbon steel and stainless steel, wherein a plurality of convex portions forming a mountain shape having a uniform height are formed on the roll surface. The vertices of the protrusions are arranged in a regular array patterned so as to form any one of a triangular shape, a square shape, and a polygonal shape by a combination thereof, and the vertices of each protrusion are 70 μm to 500 μm. A casting roll, characterized in that a flat portion having a width equal to or more than half the width of a mountain skirt formed by each of the convex portions is formed between adjacent convex portions with an interval of. 2. The casting roll according to claim 1, wherein each convex portion is formed such that the apex angle of a mountain formed by the convex portion is 120 ° or less. 3. The casting roll according to claim 1, wherein a hemispherical surface or a flat surface is formed at the top of each convex portion and is gently continuous with the skirt. 4. A continuous casting method, wherein the casting roll according to claim 1, 2 or 3 is rotated and used as a moving wall of a mold.