JPH0833953A - Twin belt type continuous casting method - Google Patents

Abstract

PURPOSE:To increase the frequency of generation of nuclei in a short side at the initial solidifying time by forming many dimples on a solidified shell forming surface in a pair of shifting short side blocks forming the short sides of a mold. CONSTITUTION:This twin belt type continuous casting method uses the mold formed of a pair of belts 7a, 7b synchronously shifted with the speed of a cast slab 16 endlessly and a pair of shifting short side (copper) blocks 8a, 8b composed of plural blocks. The frequency of generation of nuclei in the short side at the initial solidifying time is increased by forming many dimples (dh) on each of the solidified shell developing surfaces of a pair of the shifting short side blocks 8a, 8b forming the short side of the mold, and the development of the longitudinal crack can be prevented by decreasing the nonuniformity of the initial solidification to stably cast the cast slab having good quality. Further, the frequency of the generation of nuclei in the short side at the initial solidifying time is increased by executing thermal-spraying of ZrO2 base refractory on the solidified shell forming surface of the shifting short side copper blocks 8a, 8b to form many dimples (projecting parts), and the development of the longitudinal crack is prevented by decreasing the nonuniformity of the initial solidification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin-belt steel continuous casting method used as a steel (carbon steel, stainless steel, etc.) continuous casting method in the field of iron and steel manufacturing.

[0002]

2. Description of the Related Art In recent years, in the field of continuous casting of iron and steel, there has been an increasing demand for reducing the thickness of cast slabs and increasing the speed of casting. To meet these demands, for example, a pair of endlessly moving molds is used. Development of a twin-belt continuous casting method using a belt and a pair of moving short-side blocks that move endlessly is in progress.

In this twin-belt type continuous casting machine, as shown in FIG. 6, for example, a molten steel s is supplied to a tundish d, and when a certain amount of the molten steel is accumulated in the tundish, the sliding is installed in the tundish. Nozzle c
And a pair of belts ba and bb which are wound between the two pulleys pa and pb and a tension adjusting pulley pc whose position is controlled by a tension control device via an injection nozzle e and which are endlessly rotationally moved. It is poured into a mold m formed by a pair of moving short-side blocks ca (cb) composed of a large number of copper blocks that move endlessly between both end portions of the pair of belts.

The belts ba and bb form the long side of the mold m, and the back surface of the position contacting the molten steel is formed by a plurality of fin rolls f arranged in a cooling box w through which cooling water flows. It is supported and cooled. In addition, a moving short side block ca composed of a large number of copper blocks
(Cb) forms the short side of the mold m, and is connected to a chain (not shown) that moves endlessly (not shown).
It is connected via a guide rail (not shown) and can be moved.

The molten steel s is cooled in the mold m, is deheated, is solidified, is sandwiched and pulled out by a support roll r disposed below the mold, and is carried out as a thin cast slab sc ( See, for example, Japanese Patent Laid-Open No. 1-254354). However, in the continuous casting method using the conventional twin-belt continuous casting machine in which the short side of the mold is formed by a moving short side block composed of a large number of copper blocks, the short side of the slab obtained by casting is laterally crossed. It is easy to crack. In the copper block, this lateral cracking is likely to cause non-uniform nucleation in the copper block because the cooling rate at the initial solidification is extremely high, and this non-uniform nucleation causes non-uniformity in the solidified shell ss thickness, resulting in a solidification delay portion. It is considered that this occurs due to the concentration of distortion.

However, conventionally, when the short side of the mold is formed by a moving short side block composed of a large number of copper blocks, sufficient measures have been taken to prevent such lateral cracking of the short side of the cast slab. It is hard to say. Actually, a lateral crack is generated on the short side of the slab obtained by this twin belt type continuous casting method, and in that sense, this twin belt type continuous casting method is more than fully completed. Hard to say.

[0007]

SUMMARY OF THE INVENTION The present invention provides a continuous casting method using a twin-belt type continuous casting machine, in which the solidification nuclei are forcibly generated on the surface of the moving short side block forming the short side of the mold to increase the nucleation frequency. (EN) A twin-belt continuous casting method in which unevenness during initial solidification on the short side is increased to prevent lateral cracking on the short side of a slab.

[0008]

The first invention of the present invention is as follows:
In the twin-belt continuous casting method using a pair of belts that move endlessly in synchronism with the speed of the slab and a pair of moving short-side blocks composed of a number of blocks, the short sides of the mold are formed. By forming a large number of dimples on the solidification shell generation surface of the pair of moving short side blocks, the nucleation frequency at the initial solidification on the short side is increased, the unevenness of the initial solidification is alleviated, and vertical cracking occurs. It is a twin belt type continuous casting method characterized by preventing, and the second invention, in the first invention, a large number of solidified shell generation surface of the copper block forming a pair of moving short side blocks. Twin-belt continuous casting characterized by increasing the frequency of nucleation during initial solidification on the short side by forming dimples (recesses), alleviating unevenness of initial solidification and preventing vertical cracking. By way . A third aspect of the present invention is the first aspect of the present invention, in which a large number of dimples (projections) are formed by spraying a ZrO ₂ -based refractory material on the solidified shell generation surface of the copper block forming the pair of moving short side blocks. Thus, the twin-belt continuous casting method is characterized in that the frequency of nucleation during initial solidification on the short side is increased, unevenness of initial solidification is alleviated, and vertical cracking is prevented.

[0009]

In the present invention, in the twin-belt type continuous casting method, a large number of dimples are formed on the solidification nucleation surface of the moving short side block forming the short side of the mold. It is possible to increase the frequency of nucleation, alleviate the unevenness of initial solidification and prevent the occurrence of vertical cracks, and stably cast a slab with good quality.

The present invention will be described below. The present inventors, in the belt-type continuous casting method, repeated experiments, analysis, lateral cracking of the short side of the slab, if the solidification shell generation surface of the copper block forming the short side of the mold is flat, abnormal quench structure It was found that this occurs due to the fact that the coagulation is generated and the coagulation becomes non-uniform. FIG. 1 schematically shows this abnormally quenched structure, and shows a state where solidification is nonuniform and lateral cracks occur at nonuniform boundaries.

It is considered that this lateral crack is caused by the concentration of strain in the solidification delay portion during solidification. Therefore,
The inventors of the present invention can prevent lateral cracking on the short side by preventing the abnormally quenched structure from being generated in the solidified shell on the solidified shell generation surface of the moving short side block forming the short side of the mold. After further consideration and further experiments and analyzes, the present invention has been completed.

In order to suppress the formation of an abnormally quenched structure of a slab, for example, in the twin drum type continuous casting method, there is an example in which a large number of dimples are formed on the surface of the cooling drum. Since there are many different conditions between the method and the twin belt type continuous casting method which is the object of the present invention, the suitability of the application of this dimple was examined. As a result, it was confirmed that the twin-belt continuous casting method is also effective for the moving short side block forming the short side of the mold.

FIG. 2 shows a conventional copper block bx having a flat solidified shell generation surface as shown in FIGS. 3 (a) and 3 (a1).
And a copper block by having a large number of dimples (recesses) dh formed on the solidified shell generation surface of the copper block as shown in FIGS. 3 (b) and 3 (b1), and FIGS. 3 (c) and 3 (c1). Such a copper block b in which a large number of sprayed dimples (projections) dp made of a ZrO ₂ refractory are formed on the solidified shell generation surface.
2 shows the frequency of occurrence of cracks on the short side of the slab when z is used as a moving short side block.

From this figure, when the copper blocks by and bz having the dimples dh and dp formed on the solidified shell producing surface are used, the conventional copper block b having a flat solidified shell producing surface is used.
Compared with the case where x is used, the frequency of lateral cracking can be significantly reduced, and in particular, a copper block having a large number of sprayed dimples (projections) dp formed by a ZrO ₂ refractory on the solidification nucleation surface. The effect of preventing lateral cracking is remarkable when bz is used.

[0015] Here, ZrO ₂ quality refractory used for the thermal spraying dimple formation has a moderate thermal conductivity, refractory properties stable at high temperatures, a weldability also good to copper block, ZrO ₂ In addition to the simple substance, for improving the thermal spraying property, a mixture of less than 10% Y ₂ O ₃ is preferable.

From such a point of view, in the twin belt type continuous casting method of the present invention, the solidified shell forming surfaces as the moving short side blocks ca and cb are solidified as shown in FIGS. 3 (b) and 3 (b1), for example. A copper block by having a large number of dimples (recesses) dh formed on the shell generation surface, and FIG.
As shown in (c1), a copper block bz having a large number of sprayed dimples (projections) dp of ZrO ₂ refractory on the solidified shell generation surface is used to prevent lateral cracking on the short side of the slab. It is characterized by

[0017]

【Example】

Example 1 An example of the present invention will be described below. FIG.
(A)-(d) shows the outline of the twin belt type continuous casting machine which implemented this invention. In this twin belt type continuous casting machine,
Tundish 1 is supplied with molten steel 2
When the molten steel 2 has accumulated to some extent, the sliding nozzle 3 installed in the tundish 1 is operated to remove the molten steel 2
Via the injection nozzle 4, two pulleys 5a, 5b and a tension adjusting pulley 5c whose position is controlled by a tension control device 6.
A pair of belts 7a, 7 wound between and rotating endlessly
b and a pair of moving short-side blocks 8a composed of a large number of blocks which move endlessly between both side ends of the pair of belts,
It is poured into the mold 9 formed in 8b.

The belts 7a and 7b form the long sides of the mold 9, and the back surface at the position in contact with the molten steel is constructed to be cooled by the cooling water 11 flowing in the cooling box 10, and , A large number of moving short side blocks 8a, 8b
Is for forming the short side of the mold 9, and this moving short side block is a copper block in which a large number of dimples (recesses) dh are formed on the solidified shell generation surface as shown in FIGS. 4 (c) and 4 (d). It is formed by and is connected to a chain 12 that moves endlessly through a connecting link (not shown) and moves along a guide rail 13 and is cooled by a cooling device 14 that is arranged along the moving path during the moving process. And is configured to contact molten steel. The molten steel 2 is cooled in the cooled mold 9 and is heat-removed to be solidified, and is sandwiched and pulled out by a support roll 15 arranged below the mold 9.
The thin cast piece 16 is carried out.

Using the twin-belt type continuous casting machine configured as described above, continuous casting of thin cast pieces of low carbon steel was carried out. Operating conditions Steel type: Carbon steel {Ingredient composition (% by weight) is shown in Table 1} Casting temperature: 1530 to 1570 ° C Casting speed: 5 to 10 m / min Slab size: thickness 75 mm x width 1300 mm Belt material: carbon steel Size: Thickness 1mm x Width 1500mm Moving short side block Material: Copper Dimensions: 75mm x 100mm x 100mm Cooling condition: Coolant sprayed from outside

[0020]

[Table 1]

In this embodiment, C shown in Table 1 is 0.0
In the twin-belt type continuous casting machine, three kinds of carbon steels containing 2,0.05,0.15 wt% of the short side of the mold are shown in FIG.
As shown in FIGS. (C) to (d), the movable short side block 8a (8b) is formed by a copper block by having a large number of cylindrical dimples (recesses) dh, and continuous casting is performed. Regarding the obtained slab, the occurrence of lateral cracks on the short side was examined. In this case, the solidification structure of the slab obtained in the present invention at this time is schematically shown in FIG. The results are shown in Table 2.

[0022]

[Table 2]

As shown in FIG. 5, the solidification structure of the short side of the cast piece obtained by the present invention is fairly uniform, and as shown in Table 2, the occurrence of lateral cracks which leads to deterioration in quality is almost recognized. There wasn't. On the other hand, in the case of using a moving short side block made of a copper block having no conventional dimple, regardless of the steel type, obvious lateral cracking occurs on the short side of the slab, and a slab with good quality is obtained. I couldn't do it.

If the distance between the centers of the adjacent dimples (recesses) exceeds 2/5 mm, sufficient nucleation frequency of the solidified shell cannot be obtained, resulting in uneven solidification, resulting in cracking. To do. Further, when the depth of the dimples (recesses) exceeds 3.0 mm, the molten steel penetrates into the dimples too deeply, so that a remarkable restraining force is generated, which rather promotes cracking. If the depth of the dimples (recesses) is less than 0.1 mm or the diameter is less than 0.2 mm, the dimples are too small, forcible nucleation of the solidified shell does not occur, and lateral cracking occurs.

From the above, in the present invention, the dimples (recesses) formed on the surface of the copper block of the moving short side block forming the short side of the mold have a diameter of 0.2 mm or more and a depth of 0.1 to 2. A cylindrical type with a diameter of 0.5 mm or a similar shape, and the distance between the centers of adjacent dimples is 0.3 to
It is preferably 3.0 mm. The dimples do not necessarily have to have the same size, and the arrangement may be regular or irregular.

[Embodiment 2] Under the conditions of Embodiment 1, the moving short side blocks 8a and 8b are replaced with a conventional copper block bx having a flat solidification nucleation surface on a large number of dimples (concave portions) dh. Instead, as shown in FIGS. 3 (c) and 3 (c1), a low carbon steel using a copper block bz in which a large number of dimples (projections) dp are formed by spraying a ZrO ₂ refractory material on the solidified shell formation surface. Was continuously cast. Component composition of thermal spray dimples: ZrO ₂ refractory material (component composition (% by weight) is shown in Table 3).

[0027]

[Table 3]

The solidification structure of the short side of the slab obtained in this example is shown in FIG. 5 (b), and the state of lateral cracking on the short side of the slab is shown in Table 4 together with the case of the comparative example outside the scope of the present invention. Show.

[0029]

[Table 4]

As shown schematically in FIG. 5 (b), the solidification structure of the short side of the slab obtained by the present invention is a uniform solidification structure free from abnormal rapid cooling solidification structure. As shown, the occurrence of lateral cracks, which would lead to deterioration in quality, was not observed at all. On the other hand, in the case of using the moving short side block made of the conventional copper block having no dimple,
Clear lateral cracking occurred on the short side of the slab, and a slab with good quality could not be obtained.

In this example, Z is formed on the surface of the copper block.
The rO ₂ -based refractory was sprayed to form dimples (projections), but the dimples (recesses) were formed as in Example 1.
Even if the ZrO ₂ refractory is sprayed thereon, the same effect can be obtained in terms of homogenizing the solidification structure. However, in this case, since a large amount of expensive ZrO ₂ is required, the cost becomes high. Therefore, it is advantageous in terms of cost to form only the dimples (projections) from the ZrO ₂ refractory.

The height (thickness) of the dimples (projections) is preferably about 0.1 to 2.0 mm.
If it is less than 0.1 mm, a sufficient effect cannot be obtained as a starting point for nucleation of the solidified shell, and if it exceeds 2.0 mm, a large restraining force is generated, which promotes cracking. The diameter of the dimples (projections) is preferably 0.2 to 2.0 mm, and the distance between the centers of adjacent dimples is preferably 0.2 to 2.5 mm. If it is less than 0.2 mm, the dimples (projections) are too small, and a sufficient effect cannot be obtained as a starting point for nucleation of the solidified shell.

From the above, in the present invention, the dimples (projections) formed on the surface of the copper block of the moving short side block forming the short side of the mold have a diameter of 0.2 to 2.0 mm and a depth of 0. 1 to 2.5 mm frusto-conical or a similar shape, and the distance between the centers of adjacent dimples is 0.2 to 2.5.
It is preferable to set it to mm. The dimples do not necessarily have to have the same size, and the arrangement may be regular or irregular.

[0034]

According to the present invention, in the twin belt type continuous casting method, since a large number of dimples are formed on the solidified shell producing surface of the moving short side block forming the short side of the mold, the initial solidification on the short side is achieved. It is possible to increase the frequency of nucleation, to alleviate the unevenness of initial solidification and prevent the occurrence of vertical cracks, and to stably cast a slab of good quality.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing an abnormally quenched structure that causes lateral cracking on a short side of a slab in twin belt type continuous casting.

FIG. 2 is an explanatory diagram showing the relationship between the shape of the solidified shell generation surface of the moving short side block and the occurrence frequency of lateral short cracks of the slab in twin belt type continuous casting.

3 is an explanatory view showing an example of the shape of a solidification nucleation surface of the moving short side block in FIG. 2, FIG. 3 (a) is a schematic side sectional view in the case of a conventional flat copper block, and FIG. ,
(A) is a schematic front view of the copper block seen from the solidified shell side, (b) is a schematic side sectional view of a copper block having dimples (recesses), and (b1) is a schematic view (b). The schematic front view of the copper block in the figure as seen from the solidification shell side, (c) is the schematic cross-sectional side view of the copper block with sprayed dimples (projections), and (c1) is the (c) diagram. Front schematic explanatory view of the copper block of FIG.

FIG. 4 is an explanatory view showing an example of a twin belt type continuous casting machine in an embodiment of the present invention, FIG.
(B) is a schematic cross-sectional view taken along the line Aa-Ab in (a),
FIG. 6C is a schematic explanatory view of a cross-section taken along the arrow Aa-Ab of the copper block for forming dimples (recesses), and FIG. 6D is a schematic front view of the copper block of FIG. Fig.

FIG. 5 is a schematic diagram of a solidification structure of a short side of a slab obtained in an example of the present invention, in which (a) is the case of Example 1 and (b) is
The case of Example 2 is shown.

FIG. 6 is a side sectional schematic explanatory view showing an example of a conventionally known twin belt type continuous casting machine.

[Explanation of symbols]

1 Tundish 2 Molten Steel 3 Sliding Nozzle 4 Immersion Nozzle 5a, 4b Pulley 5c Tension Adjusting Pulley 6 Tension Control Device 7a, 7b Belt 8a, 8b Moving Short Side Block 9 Mold 10 Cooling Box 11 Cooling Water 12 Chain 13 Guide Rail 14 Cooling Device 15 support roll 16 thin cast s molten steel sc cast ss solidified shell ba, bb belt ca moving short side block bx flat copper block by dimple (concave) forming copper block bz thermal spray dimple (convex) forming copper block dh dimple (concave) ) Dp Thermal spray dimples (projections)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyuki Misumi No. 1 Nishinosu, Oita City, Oita Prefecture New Nippon Steel Co., Ltd. Oita Works

Claims (3)

[Claims] 1. A twin-belt continuous casting method using a mold formed of a pair of belts that move endlessly in synchronization with the speed of a cast piece and a pair of moving short-side blocks composed of a plurality of blocks, By forming a large number of dimples on the solidification shell generation surface of a pair of moving short side blocks that form the short side of the mold, the frequency of nucleation during initial solidification on the short side is increased and unevenness of initial solidification is mitigated. The twin-belt continuous casting method is characterized by preventing vertical cracks from occurring. 2. The nucleation frequency during initial solidification on the short side according to claim 1, wherein a large number of dimples (recesses) are formed on the solidified shell formation surface of the copper block forming the pair of moving short side blocks. The twin-belt continuous casting method is characterized in that the unevenness of the initial solidification is increased to prevent the occurrence of vertical cracks. 3. The ZrO film according to claim 1, which is formed on the solidified shell forming surface of the copper block forming the pair of moving short side blocks.
By forming a large number of dimples (projections) by spraying a _two- grade refractory, the frequency of nucleation during initial solidification on the short side is increased, unevenness of initial solidification is alleviated, and vertical cracking is prevented. A twin-belt continuous casting method characterized by: