JP6515336B2 - Cooling drum for twin-drum continuous casting apparatus, twin-drum continuous casting apparatus, and method of manufacturing thin-walled cast slab - Google Patents

Description

  The present invention is a twin-drum continuous casting apparatus used in a twin-drum continuous casting apparatus for producing thin-walled slabs by supplying molten metal to a molten metal reservoir formed by a pair of cooling drums and a pair of side ridges. The present invention relates to a cooling drum for a twin drum, a twin drum continuous casting apparatus equipped with a cooling drum for a twin drum continuous casting apparatus, and a method of manufacturing a thin-walled slab.

  For example, as shown in Patent Documents 1 to 7, as a method of manufacturing a thin-walled cast slab of metal, in a molten metal reservoir portion provided with a cooling drum having a water cooling structure inside and formed between a pair of rotating cooling drums. A molten metal is supplied, a solidified shell is formed and grown on the circumferential surface of the cooling drum, and the solidified shells respectively formed on the outer circumferential surfaces of the pair of cooling drums are joined at a drum kiss point and pressed down to a predetermined thickness. There is provided a twin-drum continuous casting method for producing thin-walled cast slabs. Such double-drum continuous casting method is applied to various metals.

In the above-described twin-drum continuous casting method, when the circumferential surface of the cooling drum is smooth, there is a problem that the solidified shell formed on the circumferential surface moves and cracks occur. In addition, there is a problem that the solidified shell and the cooling drum are in close contact with each other to cause strong cooling, and cracking occurs due to thermal strain.
Then, as shown to patent documents 1-7, while providing a gas gap with a solidification shell in a crevice by providing unevenness to a peripheral surface of a cooling drum, while attaining loose cooling and solidifying in a convex part A technique has been proposed for achieving uniform distribution of solidification contraction by constraining the shell and suppressing the occurrence of cracking during solidification.

In addition, in patent document 7, when an uneven part is formed in the surrounding surface of a cooling drum, the uneven part may be transcribe | transferred on the surface of a thin slab. It has been pointed out that, if the depression transferred to the thin cast slab is deep and steep, then a problem such as the formation of a scab (a sagging defect) in the subsequent rolling process.
Therefore, in Patent Document 7, the occurrence of the hesitation defect is prevented by defining the inclination angle of the convex portion formed on the cooling drum.

Japanese Patent Application Laid-Open No. 60-184449 Japanese Patent Application Laid-Open No. 62-254953 Japanese Patent Application Laid-Open No. 03-128149 Japanese Patent Publication No. 08-505811 Japanese Patent Application Publication No. 06-328204 Japanese Patent Application Publication No. 2002-522226 JP-A-11-010288

By the way, in order to suppress the occurrence of cracking of the thin-walled slab, it is necessary to uniformly restrain the solidified shell on the circumferential surface of the cooling drum and to achieve uniform gentle cooling. In the cooling drums described in Patent Documents 1 to 7, the shapes of the uneven portions are defined by various indexes, but with these provisions alone, uniform restraint and uniform gentle cooling of the solidified shell are sufficiently achieved. I could not.
In particular, when the casting speed in the twin-drum continuous casting apparatus is increased, there is a possibility that the occurrence of cracking can not be sufficiently suppressed.

  The present invention has been made in view of the above-described situation, and by defining the overall shape of the uneven portion formed on the circumferential surface of the cooling drum, the uniform restraint and uniform gentle cooling of the solidified shell can be reliably achieved. A cooling drum for a twin-drum type continuous casting device which can suppress the occurrence of cracking in the subsequent rolling process, and a twining drum equipped with this twin-drum type continuous casting device. An object of the present invention is to provide a drum-type continuous casting apparatus and a method for producing thin cast slabs.

In order to solve the above problems, as a result of intensive studies by the present inventors, by defining the arithmetic average roughness Ra of the concavo-convex part and the sharpness Ku of the concavo-convex part, uniform constraint and uniform looseness of the solidified shell are obtained. We have found that it is possible to achieve cooling.
Here, the sharpness Ku defines how far the bottom of the formed convex portion extends and the extent of the concave portion in a cross-sectional shape from the tip of the convex to the bottom of the concave portion Is an indicator that For this reason, by defining the sharpness Ku, when the solidified shell is restrained at the tip of the convex portion, the gas gap between the solidified shell and the cooling drum can be secured in the concave portion connected to the convex portion, It is possible to achieve uniform restraint and uniform gentle cooling of the shell.

The present invention has been made based on the above-described findings, and the cooling drum for a twin-drum continuous casting apparatus according to the present invention is a molten metal pool formed by a pair of rotating cooling drums and a pair of side ridges. A cooling drum for a twin drum continuous casting apparatus used in a twin drum continuous casting apparatus for supplying a molten metal to a part and forming and growing a solidified shell on the circumferential surface of the cooling drum to produce a thin slab; An uneven portion that protrudes and retracts in a radial direction is formed on the circumferential surface on which the solidified shell is formed, and the arithmetic average roughness Ra is in a range of 10 μm to 100 μm, and the uneven portion The sharpness Ku is 0.2 or more and 1.0 or less, and the concavo-convex portion is characterized by having a convex portion and a spherical concave portion connected to the convex portion .

  According to the cooling drum for a twin-drum continuous casting apparatus having this configuration, a concavo-convex portion that protrudes and retracts in the radial direction is formed on the circumferential surface on which the solidified shell is formed, and the arithmetic mean roughness Ra is 10 μm or more. Because of this, it is possible to secure a space for forming a gas gap between the solidification shell and the cooling drum. Moreover, since arithmetic mean roughness Ra is 100 micrometers or less, it can suppress that a deep dent is formed in the surface of a thin slab, and it can suppress generation | occurrence | production of the hesitation defect in a rolling process.

  Furthermore, since the sharpness Ku of the concavo-convex portion is 0.2 or more, the solidified shell can be reliably restrained by the convex portion, and a gas gap can be secured in the concave portion connected to the convex portion. It is possible to prevent cracking due to local excessive cooling due to gas gap shortage. In addition, since the sharpness Ku of the uneven portion is 1.0 or less, it is possible to suppress the formation of a sharp recess on the surface of the thin cast slab, and to suppress the generation of a hesitation defect in the rolling process. Can.

  In the twin-drum continuous casting apparatus according to the present invention, molten metal is supplied to a molten metal reservoir formed by a pair of rotating cooling drums and a pair of side ridges, and a solidified shell is formed on the peripheral surface of the cooling drum. -A twin-drum continuous casting apparatus for growing thin-walled slabs, characterized in that the cooling drum includes the above-described twin-drum continuous casting apparatus cooling drum.

  According to the twin-drum continuous casting apparatus of this configuration, since the twin-drum continuous casting apparatus cooling drum of the above-described configuration is provided, it is possible to achieve uniform restraint and uniform gentle cooling of the solidified shell reliably. It is possible to suppress the occurrence of cracking. In addition, it is possible to suppress the occurrence of the hair defects in the rolling process.

  Further, according to the method of manufacturing a thin-walled slab of the present invention, molten metal is supplied to a molten metal reservoir formed by a pair of rotating cooling drums and a pair of side ridges, and a solidified shell is formed on the peripheral surface of the cooling drum. -A method for producing a thin-walled slab which is grown to produce a thin-walled slab, characterized in that the cooling drum for double-drum continuous casting apparatus described above is used as the cooling drum.

  According to the manufacturing method of thin-walled slab of this configuration, since the cooling drum for twin-drum type continuous casting apparatus of the above-mentioned configuration is used, it is possible to achieve uniform restraint and uniform gentle cooling of the solidified shell reliably. As a result, it is possible to obtain high quality thin slabs with few cracks. In addition, it is possible to obtain a thin cast slab capable of suppressing the occurrence of the sagging defect in the subsequent rolling process.

  As described above, according to the present invention, by defining the overall shape of the concavo-convex portion formed on the circumferential surface of the cooling drum, it is possible to reliably achieve uniform restraint and uniform gentle cooling of the solidified shell to achieve cracking. A cooling drum for a twin-drum continuous caster capable of suppressing the occurrence thereof and also suppressing the occurrence of a goug defect in a subsequent rolling process, a twin-drum continuous caster comprising the twin-drum continuous caster cooling drum, And, it is possible to provide a method for manufacturing thin cast slabs.

It is an explanatory view showing a double drum type continuous casting device which is an embodiment of the present invention. It is an expansion explanatory view of a peripheral surface of a cooling drum for a double drum type continuous casting apparatus which is an embodiment of the present invention. It is explanatory drawing which shows the sharpness of an uneven part.

Hereinafter, a cooling drum for a dual drum continuous casting apparatus and a dual drum continuous casting apparatus according to an embodiment of the present invention will be described with reference to the attached drawings. The present invention is not limited to the following embodiments.
In the present embodiment, molten steel is used as the molten metal, and the thin cast slab 1 made of steel material is to be manufactured. In addition, as a steel type, for example, 0.001 to 0.01% C extremely low carbon steel, 0.02 to 0.05% C low carbon steel, 0.06 to 0.4% C medium carbon steel, 0.5 ~ 1.2% C high carbon steel, SUS 304 steel, SUS 430 steel, 3.0 to 3.5% Si directional electromagnetic steel, 0.1 to 6.5% Si non-directional electromagnetic steel etc. (Note that% is , Mass%).

As shown in FIG. 1, the twin-drum continuous casting apparatus 10 according to the present embodiment supports a pair of cooling drums 11 and 11, bender rolls 12 and 12 for bending the thin slab 1, and the thin slab 1. Molten steel reservoirs defined by pinch rolls 13 and 13, side ridges 15 disposed at the widthwise end of the pair of cooling drums 11 and 11, and the pair of cooling drums 11 and 11 and the side ridges 15 The tundish 18 and the immersion nozzle 19 which supply the molten steel 3 to 16 are provided.
In this double-drum continuous casting apparatus 10, the solidified shells 5 and 5 grow on the circumferential surfaces of the cooling drums 11 and 11 by cooling the molten steel 3 in contact with the rotating cooling drums 11 and 11. The thin-walled slab 1 having a predetermined thickness is cast by pressing the solidified shells 5, 5 respectively formed on the pair of cooling drums 11, 11 at a drum kiss point.

Here, as the above-mentioned cooling drum 11, the cooling drum for a twin drum continuous casting apparatus according to the present embodiment is used.
In this cooling drum 11, as shown in FIG. 2, the uneven part 20 (concave part 21 and convex part 22) is formed in the surrounding surface by shot processing mentioned later.

In the present embodiment, the arithmetic average roughness Ra (JIS B 0601: 2013) on the circumferential surface of the cooling drum 11 is set in the range of 10 μm to 100 μm.
The arithmetic mean roughness Ra is calculated by the following equation. Here, Z: uneven portion height direction displacement, x: mold surface displacement, l: measurement length.
In the present embodiment, the displacement in the height direction of the uneven portion 20 was measured in the axial direction of the cooling drum 11. In addition, in the case where a thinning defect or a crack occurs in the thin-walled slab 1, the measurement length l is set to 5 cm or more because the distance between these defects at the occurrence location is within 5 cm.

And in this embodiment, the sharpness Ku (JIS B 0601: 2013) of the uneven part 20 is made into the range of 0.2 or more and 1.0 or less.
The sharpness Ku is calculated by the following equation. Here, Z: displacement in uneven portion height direction, x: mold surface displacement, l: measured length, σ: uneven portion height standard deviation. Also in the measurement of the sharpness Ku, the measurement length l is set to 5 cm or more for the above-mentioned reason.

  Here, the sharpness Ku will be described with reference to FIG. The degree of sharpness Ku defines how and how the skirt extends relative to the formed protrusion 22, and the recess has a cross-sectional shape from the tip of the protrusion 22 toward the bottom of the recess 21. It is an indicator that shows the spread of 21. Here, in the present embodiment, as shown in FIG. 3, the height distribution is obtained with the bottom of the uneven portion 20 (the bottom of the recess 21) as a reference position, and the hem of the protrusion 22 is obtained by this sharpness Ku. The shape of the portion (the rising portion of the recess) is defined.

That is, as shown in FIG. 3B, in the case where the degree of sharpness Ku is large, the bottom of the convex portion 22 is narrow and the bottom of the concave portion 21 is wide. On the other hand, as shown in FIG. 3C, in the case where the degree of sharpness Ku is small, the skirt portion of the convex portion 22 is wide and the bottom portion of the concave portion 21 is narrow. Thus, by defining the sharpness Ku, it is possible to specify the overall shape of the concavo-convex portion 20 (concave portion 21 and convex portion 22).
In addition, when the height distribution of the concavo-convex portion 20 is a normal distribution, the above-described sharpness Ku is zero.

Next, a method of forming the above-described uneven portion 20 in the cooling drum 11 according to the present embodiment will be described. In the present embodiment, the circumferential surface of the cooling drum 11 has a structure in which a Cr—Ni plated film is formed on the surface of a steel material.
In the present embodiment, the uneven portion 20 is formed by performing a shot process on the peripheral surface of the cooling drum 11. As shot grains, bearing steel balls are used.

Here, in the present embodiment, in order to obtain the above-described arithmetic average roughness Ra and sharpness Ku, the heat treatment conditions of the cooling drum, the particle diameter of the shot particles, and the shot injection pressure are adjusted.
Specifically, the Vickers hardness of the surface of the cooling drum is set to 450 Hv or less by heating the peripheral surface of the cooling drum using an infrared ceramic heater or the like.
Moreover, the shot particle size is set in the range of 1.0 mm or more and 2.0 mm or less.
Furthermore, the shot injection pressure is set in the range of 0.5 MPa or more and 1.0 MPa or less.
The shot processing is performed a plurality of times, and the above-described sharpness Ku can be obtained by breaking a shot mark (spherical concave portion) formed in one shot processing.

  Next, a method of manufacturing a thin cast slab according to this embodiment using the above-described double-drum continuous casting apparatus 10 will be described.

  The molten steel 3 is supplied from the tundish 18 through the immersion nozzle 19 to the molten steel reservoir 16 formed by the pair of cooling drums 11 and 11 and the side weir 15, and the pair of cooling drums 11 and 11 in the rotational direction R The respective cooling drums 11 are rotated so that the area in which the pair of cooling drums 11 and 11 approach each other is directed in the drawing direction of the thin slab 1 (downward in FIG. 1).

Then, the solidified shell 5 is formed on the circumferential surface of the cooling drum 11. Here, in the present embodiment, as shown in FIG. 2, since the concavo-convex portion 20 is formed on the peripheral surface of the cooling drum 11, the solidified shell 5 is restrained by the tip of the convex portion 22, and Thus, a gas gap G is formed between the cooling drum 11 and the solidification shell 5.
Here, in the present embodiment, since the arithmetic average roughness Ra and the sharpness Ku are set as described later, the coagulating shell 5 is familiar with the circumferential surface of the cooling drum 11, and accordingly, the coagulating shell 5 is Since the manner of contact between the cooling drum 11 and the cooling drum 11 is uniform at each convex portion 22, the solidified shell 5 is uniformly restrained by the convex portion 22, and between the cooling drum 11 and the solidified shell 5 uniformly by the concave portion 21. A gas gap G is to be formed.

  Then, the solidified shell 5 is grown on the circumferential surface of the cooling drum 11, and the solidified shells 5 and 5 formed on the pair of cooling drums 11 and 11 are pressure-bonded at a drum kiss point to obtain a thin wall having a predetermined thickness. The slab 1 is cast.

According to the dual drum continuous casting apparatus 10 and the cooling drum 11 (cooling drum for dual drum continuous casting apparatus) according to the present embodiment configured as described above, the uneven portion on the circumferential surface of the cooling drum 11 Since 20 is formed and the arithmetic mean roughness Ra is 10 μm or more, a space for forming the gas gap G between the solidified shell 5 and the cooling drum 11 can be secured. Moreover, since arithmetic mean roughness Ra is 100 micrometers or less, it can suppress that a deep dent is formed in the surface of thin cast slab 1, and can suppress generation | occurrence | production of the hesitation defect in a subsequent rolling process. .
In order to secure the space of the gas gap G reliably, the lower limit of the arithmetic average roughness Ra of the circumferential surface of the cooling drum 11 is preferably 35 μm or more, and more preferably 40 μm or more. On the other hand, in order to reliably suppress the formation of a deep recess on the surface of the thin cast slab 1, the upper limit of the arithmetic average roughness Ra of the circumferential surface of the cooling drum 11 is preferably 90 μm or less, preferably 70 μm or less It is further preferred that

Furthermore, since the sharpness Ku of the concavo-convex part 20 is 0.2 or more, the solidified shell 5 can be reliably restrained by the convex part 22 and the gas gap G in the concave part 21 connected to the convex part 22 Can be secured. In addition, since the sharpness Ku of the concavo-convex portion 20 is set to 1.0 or less, it is possible to suppress the formation of a dent having a steep slope on the surface of the thin cast slab 1, and Occurrence can be suppressed.
The lower limit of the sharpness Ku of the concavo-convex portion 20 is preferably 0.3 or more in order to reliably restrain the solidified shell 5 by the convex portion 22 and secure the gas gap G in the concave portion 21. More preferably, it should be .5 or more. On the other hand, it is preferable to set the upper limit of the sharpness Ku of the concavo-convex portion 20 to 0.9 or less, in order to reliably suppress the formation of a concave having a steep slope on the surface of the thin cast slab 1. More preferably, it is 8 or less.

  Further, in the present embodiment, the circumferential surface of the cooling drum 11 is heat-treated to set the Vickers hardness to 450 Hv or less, the shot particle diameter within a range of 1.0 mm to 2.0 mm, and the shot injection pressure to 0.5 MPa or more Since shot processing is repeated and performed within the range of 1.0 MPa or less, it is possible to reliably form the uneven portion 20 having the above-described arithmetic average roughness Ra and sharpness Ku.

  As described above, according to this embodiment, it is possible to reliably achieve uniform restraint and uniform gentle cooling of the solidified shell, and to suppress the occurrence of cracking. Moreover, the depth and inclination of the depression transferred to the surface of the thin cast slab 1 can be suppressed, and the generation of the hesitation defect in the subsequent rolling process can be suppressed.

As described above, although the cooling drum for the twin-drum continuous casting apparatus, the twin-drum continuous casting apparatus, and the method for producing a thin cast slab according to the embodiment of the present invention have been specifically described, the present invention is not limited thereto However, it can be suitably changed in the range which does not deviate from the technical idea of the invention.
For example, although the thin-walled steel slab has been described in the present embodiment, the present invention is not limited to this, and thin-walled steel slabs of aluminum or other metals may be used.
Moreover, although this embodiment demonstrated by having arrange | positioned the vendor roll and the pinch roll, arrangement | positioning of these rolls etc. is not limited, You may change a design suitably.

Below, the experimental result implemented in order to confirm the effect of this invention is demonstrated.
In the twin-drum continuous casting apparatus shown in FIG. 1, the uneven portion was formed on the peripheral surface of the cooling drum by shot processing. At this time, the arithmetic mean roughness Ra of the peripheral surface and the sharpness Ku of the uneven portion were adjusted as shown in Table 1 by changing the shot processing conditions and the like. A cooling drum having a size of 1200 mm in diameter and 800 mm in width was prepared, and a Cr—Ni alloy plated film was formed on the peripheral surface.

  The arithmetic mean roughness Ra of the circumferential surface of the cooling drum and the sharpness Ku of the uneven portion replica-transfer the surface of the cooling drum, and the height of the uneven portion in the axial direction of the cooling drum by a two-dimensional roughness meter. The longitudinal displacement Z was measured and calculated. The measurement length l was 5 cm.

Then, a thin slab made of 0.05% C steel and having a thickness of 3.5 mm is cast at a casting speed of 55 m / min, and the obtained thin slab is cold rolled to produce a product plate having a thickness of 0.4 mm. did.
It confirmed visually about the crack of the obtained product board, and a baldness defect. The number of cracks per unit area and the number of hage defects are shown in Table 1.

The arithmetic average roughness Ra of the circumferential surface is smaller than the range of the present invention, and the sharpness Ku of the uneven portion is smaller than the range of the present invention. In No. 7, the number of cracks on the product surface was very large. It is inferred that the constraint of the solidified shell is insufficient and the gas gap can not be secured, and uneven cooling occurs and thermal distortion occurs.
In addition, No. 1 in which the calculated average roughness Ra of the circumferential surface is smaller than the range of the present invention and the sharpness Ku of the uneven portion is within the range of the present invention. In No. 8, the number of cracks on the product surface was large. It is presumed that the gas gap can not be secured and the thermal distortion occurs due to uneven cooling.
Furthermore, the calculated average roughness Ra of the circumferential surface is in the range of the present invention, and the sharpness Ku of the uneven portion is smaller than the range of the present invention. In 9, 10 and 11, the number of cracks on the product surface was large. It is inferred that the constraint of the solidified shell was insufficient, and uneven cooling resulted in thermal distortion.

The arithmetic mean roughness Ra of the circumferential surface is larger than the range of the present invention, and the sharpness Ku of the uneven portion is larger than the range of the present invention. In the case of No. 12, the number of hesitation defects was very large. It is presumed that the depth of the recess formed by the transfer of the uneven portion on the surface of the thin cast slab is deep and the inclination is steep.
In addition, the calculated average roughness Ra of the circumferential surface is larger than the range of the present invention, and the sharpness Ku of the uneven portion is within the range of the present invention. In No. 13, the number of hesitation defects was large. It is presumed that the depth of the recess formed by the transfer of the uneven portion to the surface of the thin cast slab has become deeper.
Furthermore, the calculated average roughness Ra of the circumferential surface is within the range of the present invention, and the sharpness Ku of the uneven portion is larger than the range of the present invention. In 14 and 15, the number of hage defects was large. It is presumed that the slope of the depression formed by transferring the uneven portion on the surface of the thin cast slab is steep.

On the other hand, the arithmetic average roughness Ra of the peripheral surface and the sharpness Ku of the concavo-convex portion were within the range of the present invention. In the case of 1-6, it was possible to suppress the occurrence of the crack defect of the product and the hesitation defect. It is surmised that the convex portion sufficiently restrains the solidified shell, and the concave portion secures the gas gap, thereby achieving uniform cooling.
As described above, according to the present invention, it is possible to suppress the occurrence of cracking by achieving uniform restraint and uniform gentle cooling of the solidified shell, and it is possible to prevent the formation of hesitation defects in the subsequent rolling process. It has been confirmed that the occurrence can be suppressed.

1 Thin-walled slab 3 Molten steel (molten metal)
DESCRIPTION OF SYMBOLS 5 Solidification shell 10 Double drum type continuous casting apparatus 11 Cooling drum 20 Irregularities 21 Concaves 22 Convex

Claims (3)

A twin-drum type that supplies molten metal to a molten metal reservoir formed by a pair of rotating cooling drums and a pair of side ridges, and forms and grows a solidified shell on the peripheral surface of the cooling drum to produce a thin slab A cooling drum for a twin drum continuous casting apparatus used in a continuous casting apparatus, comprising:
The peripheral surface on which the solidified shell is formed is formed with a concavo-convex portion that appears in the radial direction, and the arithmetic average roughness Ra is in the range of 10 μm to 100 μm, and the pointed portion of the concavo-convex portion Degree Ku is 0.2 or more and 1.0 or less ,
The said uneven | corrugated | grooved part has a convex part and the spherical recessed part connected with this convex part, The cooling drum for twin drum type continuous casting apparatuses characterized by the above-mentioned. A twin-drum type that supplies molten metal to a molten metal reservoir formed by a pair of rotating cooling drums and a pair of side ridges, and forms and grows a solidified shell on the peripheral surface of the cooling drum to produce a thin slab A continuous casting device,
A dual drum continuous casting apparatus comprising the dual drum continuous casting apparatus cooling drum according to claim 1 as the cooling drum. A thin-walled slab for supplying molten metal to a molten metal reservoir formed by a pair of rotating cooling drums and a pair of side ridges, and forming and growing a solidified shell on the peripheral surface of the cooling drum to produce thin slab Manufacturing method of
A method for producing a thin-walled cast slab characterized by using the cooling drum for a twin-drum continuous casting apparatus according to claim 1 as the cooling drum.

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