JP2000061588A - Twin roll continuous casting machine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To produce a thin plate having good mechanical strength by uniformly refining crystal grains, having good mechanical strength, reducing material variation, and having good surface roughness without skin roughness. Provided is a twin-roll continuous casting apparatus capable of reducing equipment costs. SOLUTION: After adjusting the temperature of a slab obtained by solidifying with a pair of water-cooled casting rolls to be within a temperature range in which an austenite structure exists in a matrix thereof,
Enclose the area from the kiss point of the water-cooled casting roll to the entry side of the in-line rolling mill with a degassing housing with an oxygen concentration of 5% or less. After solidification by the in-line rolling mill, at a temperature of 850 ° C or more and less than 1350 ° C, and 5% or more 50% in one pass. A twin-roll continuous process for producing slabs with a surface roughness of 20 μm or less and a crystal grain size of 30 μm or less and a variation of the total elongation of the steel material within 5% with a standard deviation by rolling down at the following rolling reduction Casting equipment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin roll type continuous casting apparatus for performing in-line rolling during conveyance of a thin sheet slab, and in particular, a thin sheet slab produced by a twin roll continuous casting method is used as a starting material. The present invention relates to a twin roll type continuous casting apparatus for producing thin plate casts which reduces surface variations of ordinary steel plates equivalent to hot rolled steel plates and variations in materials represented by elongation of steel products.

[0002]

2. Description of the Related Art Generally, a twin-roll type continuous casting apparatus is known as an apparatus to which the Bessemer type continuous casting method is applied, and a molten metal is injected between a pair of water-cooled casting rolls to solidify the metal. Manufactures thin plates. The thin plate production by the twin roll type continuous casting apparatus 11 of this type is performed as shown in FIG. As shown,
The molten metal is injected from above between a pair of casting rolls 12a, 12b arranged at a predetermined interval,
Rotate 12a and 12b inward while cooling with water. Then, the molten metal comes into contact with the casting rolls 12a, 12b to be cooled, and solidifies into an arc shape on the surface of each casting roll 12a, 12b as a solidification shell S. Each solidified shell S is a casting roll 12a,
As the 12b is rotated, it is approached and pressed at a minimum part of the roll interval (hereinafter, referred to as "roll kiss point") K to form a slab C having a predetermined thickness. The slab C is cast downward between the casting rolls 12a and 12b. It is taken out.

In this case, solidification of the solidification shell S starts at a point F at which the molten metal L comes into contact with the casting rolls 12a and 12b (hereinafter referred to as "solidification start point"). Each solidified shell S that has started to solidify from the solidification starting point F of each casting roll 12a, 12b continues to grow to the roll kiss point K, and each solidified shell S is pressed down at the roll kiss point K to obtain a cast piece C having a predetermined thickness. Becomes A related technique for winding and shipping the cast slab C thus cast onto a coiler as cast is disclosed in JP-A-58-359. In this method, a molten steel pool surrounded by a frame is formed between a pair of water-cooled rolls and a tundish, and a frame upper surface of the molten steel pool is closely adhered to a tundish bottom surface to form a pair of water-cooled roll surfaces. Continuous casting is performed on the solidified shell by applying an iron static pressure equivalent to the molten steel level in the tundish. According to this process, a thin strip with a thickness of the slab at the time of casting is about the same as that of the current rough-rolled and finish-rolled hot-rolled steel sheet can be obtained. Expected to be reduced. However, such a thin strip steel sheet has a problem in that it is inferior in terms of material compared to the current hot-rolled steel sheet.

That is, according to this method, since the produced slab is used as a product after being cast, it is impossible to obtain good mechanical strength such as coarse crystal grains and low elongation and workability. In the as-cast state, about 100
Since the scale of about μm is attached, the surface of the slab is rough. Therefore, in order to commercialize the cast slab C that has been cast, the scale of the cast slab C that has been cast is removed and the product is wound into a coiler to a predetermined thickness by hot rolling, and a method for casting after casting. There is a method in which the scale of the piece C is removed, a predetermined plate thickness is obtained by cold rolling, and the piece is further annealed and wound into a coiler to obtain a product.

A method for refining crystal grains is disclosed in Japanese Patent Laid-Open No.
It is disclosed in Japanese Patent Laid-Open No. 63-115654 and Japanese Patent Laid-Open No. 247049/1990. In the former, the cast metal sheet is
After cooling to a temperature below ₁ transformation point, heating or heating / holding again to a temperature above A ₃ transformation point, and then cooling again to a temperature below A ₁ transformation point is repeated inline two or more times. Is.

In the latter, the cast thin-walled slab is
After quenching at a temperature of 1250 to 1100 ° C at a cooling rate of 00 ° C / sec or more
Grain size is 50 μm by hot rolling at a reduction rate of 10-40%
The following austenitic stainless steels are manufactured. Further, Japanese Patent Application Laid-Open No. 60-83745 discloses a method of refining the structure by applying a plurality of rollings at a total reduction of 20% or more and hot to the slab. In addition, all of these measures aim to improve the material quality by making the metal structure fine by utilizing recrystallization or transformation. However, the reason why the material of the steel sheet as thin cast strip is inferior has not been clarified in detail about factors other than such a metal structure. In particular, when discussing the material of the thin casting strip, including the above-mentioned conventional techniques, no fluctuation of the material, that is, variation is mentioned at all.

By the way, in the invention disclosed in Japanese Patent Laid-Open No. 63-115654, crystal grains are removed by cooling to the ferrite (α) region immediately after solidification and heating to the austenite (γ) region. Although it is miniaturized, there is a problem that equipment cost increases because the total length of the metal thin plate casting apparatus used for this becomes long. Incidentally, in order to commercialize the slab C by in-line rolling, in order to avoid an increase in the overall length of the apparatus,
It is preferable to employ hot rolling rather than cold rolling. In addition, when it is generally said that the material is inferior, in addition to the case where the characteristic value itself is low, there are cases where there are large variations in the characteristic value. In the latter case, the lower limit value must be adopted as the material property from the viewpoint of safety, so even though this material variation is an important issue in discussing the material of the steel material, it is produced by this process. There has not been sufficient examination of such thin casting strips.

Further, the technique described in the above-mentioned Japanese Patent Application Laid-Open No. 247049/1990 is directed to austenitic stainless steel, and since hot rolling is performed in the atmosphere, a thick scale layer is formed on the surface of the slab. As a result, there is a problem that hot rolling cannot be performed and a marked surface flaw is formed on the rolled steel sheet. Furthermore, in Japanese Utility Model Laid-Open No. 64-5472, a casting apparatus that prevents scale generation and slab cracking is provided on the downstream side of the cooling rolls by providing an oxygen-free atmosphere chamber including a rolling apparatus to maintain an oxygen-free atmosphere. It has been proposed, however, that no scale is produced in the anoxic state, or even if it is produced, the scale is very small, the surface of which the dimples of the casting roll are completely transferred and cannot be crushed by a small reduction amount. There is a problem that the steel sheet has a very large roughness and cannot be a product.

[0009]

DISCLOSURE OF THE INVENTION An object of the present invention is to reduce the material variation of a normal steel plate equivalent to a hot-rolled steel plate starting from a thin strip, which is said to be inferior in material quality to the current hot-rolled steel plate. It is to provide a method of reducing. Further, in view of the above problems, an object of the present invention is to produce a thin plate having a good mechanical strength by uniformly refining the crystal grains by in-line hot rolling and having a good surface roughness without rough skin. It is an object of the present invention to provide a twin-roll type continuous casting device that can be manufactured and can reduce the equipment cost.

[0010]

The gist of the present invention is as follows. (1) Injecting a melt of ordinary carbon steel having a C content of 0.005% by weight or more and 1% by weight or less between a pair of water-cooled casting rolls,
In a twin-roll type continuous casting apparatus equipped with an in-line rolling machine and a winder that rolls down the slab obtained by solidifying to a predetermined plate thickness, from the roll kiss point of the twin rolls to the entry side of the in-line rolling machine. A twin roll type continuous casting apparatus characterized in that a degassing housing having an oxygen concentration of 5% or less inside is provided to produce a slab having a surface roughness of 20 μm or less and excellent surface properties.

(2) A thermometer for measuring the temperature of the cast slab, a slab transport distance adjusting device for adjusting the transport distance of the cast slab, and the in-line rolling mill inside the deaeration housing. Heater and cooler installed in parallel just before the side,
The twin roll type continuous casting apparatus according to (1) above, further comprising a thermometer for measuring the temperature of the slab on the outlet side of the degassing housing.

(3) The sealing structure between the degassing housing and the casting roll under the casting roll has a structure in which a side end iron plate and a caul cloth are stuck together, and further, a caul between the side end iron plate and the casting roll. The twin roll type continuous casting apparatus according to (1) or (2) above, wherein the cloth has a slidable structure.

[0013]

According to the structure of the twin-roll type continuous casting method of the present invention, the temperature of the slab solidified by the pair of water-cooled casting rolls is adjusted, and then the slab is reduced to a predetermined plate thickness by an in-line rolling mill. That is, the rolling temperature of in-line rolling is adjusted within a temperature range in which the austenite structure exists in the matrix of the slab, and the rolling reduction is set to 5% or more and 50% or less.

The temperature range in which the austenite structure exists in the matrix of the slab is, specifically, 850 ° C. or higher and 1350 ° C.
The reason is as follows, and the reason why the temperature range is adjusted is to make the crystal grains of the slab uniform and fine with an appropriate rolling force. That is, if the rolling temperature is lower than 850 ° C., the rolling reaction force becomes large and the recrystallization time becomes long, so that the production line must be lengthened. Also, if the temperature is lower than 850 ° C, ferrite transformation may occur, and the final structure may become a worked structure, resulting in a marked decrease in elongation. On the other hand, when the rolling temperature exceeds 1350 ° C., the grain size adjusting effect is obtained, but since the temperature is high, the crystal grains grow after rolling, and the effect of refining is reduced. Further, a more preferable range of rolling temperature is 900 ° C. or higher and 1250 ° C. or lower in the present invention.

Further, the rolling reduction is set to 5% or more and 50% or less in order to obtain a strip having desired surface roughness, crystal grain size, and elongation, and having no roughened surface. That is, if the rolling reduction is less than 5%, the surface roughness and the crystal grain size are large, the elongation is low, and the processed surface becomes rough. This is because it is impossible to reduce That is, it is because minute defects such as plate thickness deviations and shrinkage cavities that the material has as-cast does not disappear, and material variations occur. On the other hand, when the rolling reduction exceeds 50%, the surface roughness becomes non-uniform due to heavy working, and in some cases, the plate thickness accuracy decreases.

Furthermore, if an inert gas atmosphere is provided from the casting roll to the inlet side of the in-line rolling mill, high temperature oxidation of the slab is prevented. In this case, the oxygen concentration is 5
%, The roughness of the scale adhering to the surface of the slab will be significantly reduced, so that a smooth strip having a small surface roughness after in-line rolling can be obtained. Further, a more preferable range of the oxygen concentration is an inert gas atmosphere having an oxygen concentration of 2% or less in the present invention.

FIG. 7 shows the relationship between the rolling reduction% and the slab surface roughness Rt. In this figure, C: 0.04%, in-line rolling temperature: 1100 ° C. Atmosphere is air (21% O ₂ )
Then, the surface roughness Rt increases as the rolling reduction increases, and is inferior to that before in-line rolling. However, when the atmosphere O ₂ is 5% or less, the effect of the rolling reduction is small, and if the rolling reduction is selected,
It can be seen that the surface roughness Rt can be about 1/2 or less before the in-line rolling, that is, the surface roughness 20 μm or less.

On the other hand, according to the structure of the twin roll type continuous casting apparatus, there is provided an in-line rolling machine for rolling down the slab solidified by the pair of water-cooled casting rolls to a predetermined plate thickness. In front of the entry side of this in-line rolling mill, a thermometer that measures the temperature of the slab immediately after solidification, and a temperature control that adjusts the slab to a temperature within the temperature range in which the austenite structure is present in the matrix based on the measured value. A heating device is provided. This temperature control is performed by adjusting the distance to the rolling mill, that is, by adjusting the residence time in the deaeration housing.

As another method, if the temperature of the cast piece immediately after solidification measured by a thermometer is lower than the temperature range in which the austenite structure exists in the matrix of the cast piece, the cast piece is heated by the above heater. The temperature may be adjusted within the temperature range by means of an in-line rolling mill. On the other hand, if the temperature is higher than the temperature range in which the austenite structure exists in the matrix of the slab, the slab may be cooled by a cooler to adjust the temperature within the temperature range, and then rolled by an in-line rolling mill. At that time, the reduction rate is 5% or more 50
%, The surface roughness is 20 .mu.m or less, the crystal grain size is 30 .mu.m or less, preferably 20 to 30 .mu.m, the elongation is 34% or more, and a strip having no roughened surface can be obtained.

If a degassing housing is formed between the casting roll and the entry side of the in-line rolling machine and the interior thereof is filled with an inert gas atmosphere, high temperature oxidation of the slab can be prevented. Further, it was found that the characteristic values of these materials are improved and the variation is remarkably reduced by adding only one pass after solidification by hot rolling, and the method for manufacturing a steel sheet by this process was established. is there. After rolling, it is desirable that the steel strip be water-cooled and wound at 500 to 700 ° C, as in the current hot rolling process. On the other hand, the next steps such as pickling and temper rolling may be performed according to those of the current hot-rolled steel sheet.

The material variation in the present invention is indicated by the standard deviation σ by statistically processing the variation in total elongation when performing the JIS No. 5 tensile test. The material requirement of the present invention is that the standard deviation of the total elongation is within 5%. In the present invention, the chemical components are not particularly limited, but the following findings have been obtained. C is the most important element that determines the strength of ordinary steel, and its addition amount may be appropriately selected according to the required strength.

Si is also appropriately added as a solution strengthening element in ordinary steel. However, if it exceeds 1.5%, the pickling property will be poor, so 1.5% or less is preferable. Similar to C and Si, Mn is also added to ordinary steel as a strengthening element, and from the viewpoint of preventing hot embrittlement due to S, it is usually preferable to add Mn at 5 times or more S%. However, from the viewpoint of weldability
2.0% or less is preferable.

Basically, it is desirable that the amounts of P and S are small, but unnecessary ultra-low phosphorus and ultra-low sulphide increase costs in the steelmaking process. Absent. The present invention does not particularly limit the other elements contained in the steel. For example, in order to improve mechanical properties such as strength and ductility of steel materials, Nb, Ti, V, B, etc. may be added in a trace amount in steel, but the present invention is not affected by these additions. is not. On the other hand, when scrap is used as the main raw material, Cu, Sn, Cr, Ni and the like may be mixed as unavoidable impurities, but the presence or absence of these elements does not hinder the present invention.

[0024]

EXAMPLE 1 Hereinafter, an example of a twin roll type continuous casting method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic side view showing an embodiment of a twin roll type continuous casting apparatus according to the present invention. As shown in the figure, the twin roll type continuous casting apparatus 1 of the present embodiment includes:
A pair of casting rolls 2a and 2b having a water cooling function are arranged at a predetermined interval. Side weirs 3 are provided at both ends of the casting rolls 2a, 2b, and a pool 4 for pooling the molten metal L is formed in a portion defined by these side dams 3.

When the molten metal L is poured into the molten metal pool 4 from above and the casting rolls 2a and 2b are rotated inward while being cooled with water, the molten metal L is cast into the casting rolls 2a and 2b.
To be cooled and solidified in an arc shape on the surface of each casting roll 2a, 2b as a solidification shell S. The solidified shells S are brought close to each other as the casting rolls 2a and 2b rotate, and are pressed at roll kiss points K to form a slab C having a predetermined thickness, which is extracted downward from between the casting rolls 2a and 2b.

Further, an in-line rolling mill 5 is provided downstream of the casting rolls 2a and 2b for rolling the solidified slab C into a predetermined plate thickness by hot rolling. A commonly used roll type rolling mill is used as the in-line rolling mill 5, but since a rolling reduction of 5% or more and 50% or less with respect to the plate thickness of the cast slab C is adopted, a rolling mill having such a rolling reduction force should be used. use.

Further, in front of the entry side of the in-line rolling mill 5, a thermometer 6 for measuring the temperature of the slab C immediately after solidification, and the slab C in the matrix based on the measured value. A temperature adjusting device 7 for adjusting the temperature is sequentially provided in a temperature range in which the austenite structure (γ) exists. The thermometer 6 includes, for example, platinum-platinum rhodium (Pt-Rh)
In addition to thermocouples such as the above, an instrument that can measure temperatures of approximately 700 ° C to 1500 ° C will be used. Further, as the temperature control device 7, a heater 7a such as a high frequency induction heater or a cooler 7b such as a heat retainer and / or a water cooler is adopted. In addition, as a heat retainer,
As a heater, a gas burner or the like, and as a cooler, a movable roll or a steam cooler for the purpose of cooling adjustment by increasing the transportation time, etc. It is suitable. However, the present invention is not limited to these.

Specifically, the slab C immediately after solidification by the thermometer 6
When the measured value is out of the temperature range in which the austenite structure (γ) exists in the matrix of the cast slab C, the slab C is heated or cooled by the temperature control device 7 to control the rolling temperature. adjust. That is, if the temperature of the cast slab C is lower than 850 ° C, the cast slab C is heated by the heater 7a.
After adjusting the temperature within a temperature range of 850 ° C. or higher and 1350 ° C. or lower, it is rolled down by an in-line rolling mill 5. On the other hand, if the temperature of the slab C is higher than 1350 ° C, the slab is cooled by the cooler 7b to adjust the temperature within the temperature range of 850 ° C or higher and 1350 ° C or lower, and then is reduced by the in-line rolling mill 5. is there.

The thin plate cast pieces C rolled by the inline rolling mill 5 are successively wound by the coiler 8 installed on the downstream side of the inline rolling mill 5. Further, between the casting rolls 2a and 2b and the entry side of the in-line rolling mill 5, a deaeration housing 9 is provided so as to surround the carrier line for the slab C. The degassing housing 9 has an exhaust device (not shown) for exhausting the inside thereof and a gas supply device (not shown) for supplying an inert gas such as argon (Ar) or nitrogen (N ₂ ) to the inside thereof. (Not shown) is connected.

A loop detector 19, a pinch roll 14, a cooling zone 15 and a transport roll 1 are placed in the air-deadening housing 9.
6 is provided. Also, on the outlet side of the deaeration housing 9,
One is a movable roll 17 to adjust the transport distance,
The other is provided with a transport roll which is a fixed roll 18.
Further, the slab temperature is measured by the thermometer 20, and the data is passed through the converter 21 to control the flow rate adjusting valve 22 of the cooling water W.

FIG. 5 (a) shows the deaeration housing 23 under the casting roll, FIG. 5 (b) is an enlarged view of part A of FIG. 5 (a), and FIG. 6 is a front view. In these drawings, the deaeration housing 9 is covered from the roll kiss point, and the caul cloth 25 is attached to the side end iron plate 24 to secure the airtightness. Further, the caul cloth is slid between the iron plate 24 and the casting roll to ensure the airtightness.

Next, the twin roll type continuous casting apparatus 1 described above
The twin roll type continuous casting method of this embodiment performed by using The casting rolls 2a and 2b of the twin roll type continuous casting apparatus 1 used in the present embodiment are formed into dimensions of roll width: 350 mm and roll diameter: 400 mmφ, and are Cu rolls of internal water cooling system. The casting conditions are casting speed: 30 m / min,
Cast plate thickness: It is set to 3.0mm. Further, the inside of the degassing housing 9 is set to an inert gas atmosphere: 1% O ₂ . Furthermore, the in-line rolling mill 5 has 2
HI, 1 step, work roll diameter: 300 mmφ. And the casting material is low carbon aluminum killed steel (0.
04% C) was adopted. The slab was water-cooled and wound at 650 ° C.

Under the above-mentioned conditions, the twin roll type continuous casting method of the present embodiment uses the in-line rolling mill 5 at a rolling temperature of 11
At 00 ℃, rolling reduction: 0%, 2%, 5%, 10%, 20%, 30
%, 40%, 50%, 60%, 70%, surface roughness (μ
m), crystal grain size (μm), strength (kgf / mm ² ), elongation (%)
And an experiment was conducted to confirm the condition of roughened skin. The experimental results are shown in Table 1 below. The result is determined by the surface roughness:
20μm or less, crystal grain size: 20-30μm, strength: 36kgf / mm
² or more, elongation: 34% or more, roughened surface: no streaking due to ridging was taken as a pass standard. For the strength and elongation of the steel sheet, 35 JIS No. 5 tensile test pieces were prepared from each of the obtained steel sheets, subjected to a tensile test, and the obtained total elongation was statistically processed to obtain an average value and a standard deviation.

[0034]

[Table 1]

As shown in Table 1, the surface roughness is
The rolling reduction ratio was 5% or more and 50% or less, and a pass value (20 μm or less) was obtained. Regarding the crystal grain size, a pass value (20 to 30 μm) was obtained at a rolling reduction of 5% or more and 70% or less. The growth is
Reduction rate: Pass value (34% or more) in the range of 5% to 70%
was gotten. Regarding the roughened skin, a pass value (none) was obtained at a rolling reduction of 5% or more and 70% or less.

That is, in the manufacturing method using the twin roll type continuous casting apparatus of this embodiment, the ingot rolling machine 5 of the cast slab C of the low carbon aluminum killed steel (0.04% C) at the rolling temperature of 1100 ° C. With a reduction rate of 5% or more and 50% or less, it has a desired surface roughness (20 μm or less), a crystal grain size (20 to 30 μm), an elongation (34% or more), and has a roughened surface. It was confirmed that no strip was obtained.

Example 2 In this example, the casting material used in Example 1 was changed. Specifically, as a casting material, medium carbon aluminum killed steel (0.13% C)
Is adopted, and the other conditions are the same as those in the first embodiment. Under the conditions as described above, the twin-roll continuous casting method according to the present embodiment is performed at a rolling temperature of the in-line rolling mill 5 of 1100 ° C.
Reduction ratio: 0%, 2%, 5%, 10%, 20%, 30%, 40%,
For 50%, 60% and 70%, an experiment was conducted to confirm the conditions of surface roughness (μm), crystal grain size (μm), strength (kgf / mm ² ), elongation (%) and roughened surface.

The experimental results are shown in Table 2 below. In addition, the result judgment was the same acceptance criteria as in Example 1 except that the strength was 40 kgf / mm ² or more.

[0039]

[Table 2]

As shown in Table 2, the surface roughness is
The rolling reduction ratio was 5% or more and 50% or less, and a pass value (20 μm or less) was obtained. The crystal grain size is a pass ratio (30 μm or less, preferably 20 to 30 μ) when the rolling reduction is 10% or more and 50% or less.
m) was obtained. Regarding the elongation, a pass value (34% or more) was obtained when the rolling reduction was 10% or more and 70% or less. The roughened skin is
A reduction value: A pass value (none) was obtained in the range of 5% to 70%.

That is, in the manufacturing method using the twin roll type continuous casting apparatus of this embodiment, the ingot rolling machine 5 of the ingot C of medium carbon aluminum killed steel (0.13% C) at the rolling temperature of 1100 ° C. is used. With a reduction rate of 10% or more and 50% or less, it has a desired surface roughness (20 μm or less), crystal grain size (20 to 30 μm), elongation (34% or more), and has a roughened surface. It was confirmed that no strip was obtained.

<Embodiment 3> In this embodiment, the rolling temperature of the in-line rolling mill 5 in Embodiment 1 is changed, and the other conditions are the same as those in Embodiment 1. Specifically, the twin roll type continuous casting apparatus of the present embodiment has a rolling temperature of the in-line rolling machine 5 of 850 ° C. and a reduction ratio of 0%.
2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70
%, An experiment was performed to confirm the surface roughness (μm), crystal grain size (μm), strength (kgf / mm ² ), elongation (%) and roughened surface.

The experimental results are shown in Table 3 below. The result judgment was based on the same acceptance criteria as in Example 1.

[0044]

[Table 3]

As shown in Table 3, the surface roughness is
The rolling reduction ratio was 5% or more and 50% or less, and a pass value (20 μm or less) was obtained. The crystal grain size is a pass value (30 μm or less, preferably 20 to 30 μ) when the rolling reduction is 20% or more and 70% or less.
m) was obtained. Regarding the elongation, a pass value (34% or more) was obtained when the rolling reduction was 10% or more and 70% or less. The roughened skin is
A reduction value: A pass value (none) was obtained in the range of 5% to 70%.

That is, in the manufacturing method using the twin roll type continuous casting apparatus of the present embodiment, the ingot C of the low carbon aluminum killed steel (0.04% C) is rolled at the rolling temperature of 850 ° C. and the in-line rolling mill 5 is used. With a reduction rate of 20% or more and 50% or less, it has a desired surface roughness (20 μm or less), crystal grain size (20 to 30 μm), elongation (34% or more), and has a roughened surface. It was confirmed that no strip was obtained.

<Embodiment 4> In this embodiment, the rolling temperature of the in-line rolling mill 5 in Embodiment 1 is changed, and the other conditions are the same as those in Embodiment 1. Specifically, the twin roll type continuous casting apparatus of the present embodiment has a rolling temperature of the in-line rolling machine 5 of 1300 ° C. and a rolling reduction of 0%.
2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70
%, An experiment was performed to confirm the surface roughness (μm), crystal grain size (μm), strength (kgf / mm ² ), elongation (%) and roughened surface.

The experimental results are shown in Table 4 below. The result judgment was based on the same acceptance criteria as in Example 1.

[0049]

[Table 4]

As shown in Table 4, the surface roughness is
The rolling reduction ratio was 5% or more and 50% or less, and a pass value (20 μm or less) was obtained. Regarding the crystal grain size, a pass value (20 to 30 μm) was obtained at a rolling reduction of 5% or more and 70% or less. The growth is
Reduction rate: Pass value (34% or more) in the range of 5% to 70%
was gotten. Regarding the roughened skin, a pass value (none) was obtained at a rolling reduction of 5% or more and 70% or less.

That is, in the manufacturing method using the twin roll type continuous casting apparatus of Example 4, the ingot rolling machine 5 of the cast slab C of low carbon aluminum killed steel (0.04% C) at the rolling temperature of 1300 ° C. With a reduction rate of 5% or more and 50% or less, it has a desired surface roughness (20 μm or less), a crystal grain size (20 to 30 μm), an elongation (34% or more), and has a roughened surface. It was confirmed that no strip was obtained.

<Comparative Example 1> A comparative example 1 will be described which was carried out in order to confirm the operation and effect of the twin roll type continuous casting apparatus of Examples 1 to 4. In this comparative example, the rolling temperature in Example 1 was changed. Specifically, rolling temperature: 750 ° C, reduction ratio: 0%, 2%, 5%, 10%, 20
%, 30%, 40%, 50%, 60%, 70%, surface roughness (μm), crystal grain size (μm), strength (kgf / mm ² ), elongation (%) and roughened surface A comparative experiment was performed to confirm.

The experimental results are shown in Table 5 below. The result judgment was based on the same acceptance criteria as in Example 1.

[0054]

[Table 5]

As shown in Table 5, at all rolling reductions, the crystal grain size exceeded 30 μm, the elongation (%) was lower than 34%, and the processed surface was rough, and the judgment criteria were satisfied. I didn't. That is, in this comparative example, even if the ingot C of the low carbon aluminum killed steel (0.04% C) is rolled down by the in-line rolling mill 5 at a rolling reduction rate of 0% to 70%, at the rolling temperature of 750 ° C. Couldn't get a healthy strip.

Comparative Example 2 In this comparative example, the rolling temperature of the in-line rolling mill in Example 1 was changed. Specifically, the rolling temperature is 1350 ° C and the rolling reduction is:
0%, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60
%, 70%, surface roughness (μm), crystal grain size (μ
m), strength (kgf / mm ² ), elongation (%), and a comparative experiment for confirming the condition of roughened skin.

The experimental results are shown in Table 6 below. The result judgment was based on the same acceptance criteria as in Example 1.

[0058]

[Table 6]

As shown in Table 6, at all reduction rates, the crystal grain size exceeded 30 μm and the reduction rate was 0% or more.
At 50% or less, the elongation was lower than 34%, and the processed surface was rough, and the criterion was not satisfied. That is, in this comparative example, even if the cast slab C of low carbon aluminum killed steel (0.04% C) is rolled down by the in-line rolling mill 5 at a rolling reduction rate of 0% to 70%, at the rolling temperature of 1350 ° C. Couldn't get a healthy strip.

As described above, comparing the twin roll type continuous casting apparatus of Examples 1 to 4 with Comparative Examples 1 and 2,
Carbon steel slab C at a rolling temperature of 850 ° C or higher and lower than 1350 ° C,
By the reduction with a reduction rate of 5% or more and 50% or less by the inline rolling mill 5, a desired surface roughness (20 μm or less),
It has been found that a strip having a crystal grain size (20 to 30 μm), an elongation (34% or more) and having no roughened surface can be produced. As described above, in the twin roll type continuous casting apparatus according to the present invention, a product thin plate can be manufactured by directly performing hot rolling during the transportation of the slab C without performing cold rolling. Therefore, the facility cost and the manufacturing cost can be significantly reduced.

Rolling temperature: The temperature range of 850 ° C. or higher and lower than 1350 ° C. is the temperature range in which the austenite structure (γ) exists in the matrix of the cast slab C, and specifically, the ferrite structure (α) and the austenite structure. It is a coexisting region with (γ) or a one-phase region of an austenite structure (γ). Also,
As described above, the preferable condition of the reduction ratio with respect to the plate thickness of the cast slab C is slightly different depending on the rolling temperature and the steel type of each example.
Reduction ratio: A desired strip can be reliably obtained in the range of 20% or more and 50% or less. The twin roll type continuous casting apparatus according to the present invention has a carbon content of 0.0005% C to 1.0% C.
The target is carbon steel.

Particularly noteworthy in the present invention is 20 μm.
The point is that a product thin plate having the following surface roughness and a crystal grain size of 20 to 30 μm can be obtained. Here, FIG. 2 is a graph showing the relationship between the average grain size and the grain size number.
As shown in the figure, carbon steel with a grain size number of 5 or more is generally called fine grain steel (see Iron and Steel Institute of Japan, New Edition Steel Technology Course, Volume 3 Properties and Testing of Steel Materials, pp. 414-419),
When the crystal grain size is 30 μm or less, it is understood that the grain size is 7.5 or more.

That is, according to the twin roll type continuous casting apparatus according to the present invention, the ferrite grain size of the cast slab C as cast is obtained by performing the light rolling of 5% or more and 50% or less during the transportation of the slab C. By increasing the grain size to 7.5 or more, it is possible to manufacture a thin plate slab having a uniform fine grain structure in the width direction and the longitudinal direction from the surface of the slab. <Embodiment 5> In the present embodiment, the internal atmosphere of the degassing housing 9 in Embodiment 1 is changed.
Specifically, the main part of the degassing housing 9 is set to an inert gas atmosphere: 2% O ₂ , and the other conditions are the same as in the first embodiment.

Under the conditions as described above, the twin-roll type continuous casting apparatus of this embodiment has a rolling temperature of the in-line rolling machine 5:
At 1100 ℃, rolling reduction: 0%, 2%, 5%, 10%, 20%, 30
%, 40%, 50%, 60%, 70%, surface roughness (μ
m), crystal grain size (μm), strength (kgf / mm ² ), elongation (%)
And an experiment was conducted to confirm the condition of roughened skin. The experimental results are shown in Table 7 below. The result judgment was based on the same acceptance criteria as in Example 1.

[0065]

[Table 7]

As shown in Table 7, the surface roughness is
The rolling reduction ratio was 5% or more and 50% or less, and a pass value (20 μm or less) was obtained. Regarding the crystal grain size, a pass value (20 to 30 μm) was obtained at a rolling reduction of 5% or more and 70% or less. Strength is
Acceptable values (36 kgf / mm ² or more) were obtained at all rolling reductions. Regarding the elongation, a pass value (34% or more) was obtained at a rolling reduction of 5% or more and 70% or less. The roughened skin has a reduction rate of 5
A pass value (none) was obtained in the range of 70% to 70%.

That is, in the twin roll type continuous casting apparatus of this embodiment, the inert gas atmosphere in the degassing housing is 2
% O ₂ , the ingot C of low carbon aluminum killed steel (0.04% C) was rolled at a rolling temperature of 1100 ° C. with an in-line rolling mill 5 at a rolling reduction of 5% or more and 50% or less to obtain a desired surface roughness. Degree (20 μm or less), crystal grain size (20 to 30 μm
m), elongation (34% or more), and it was confirmed that a strip having no roughened surface could be obtained.

<Comparative Example 3> On the other hand, Comparative Example 3 will be described which was carried out in order to confirm the function and effect of the twin roll type continuous casting apparatus of this example. In this comparative example, the internal atmosphere of the degassing housing 9 in Example 5 was changed. Specifically, the inside of the degassing housing 9 is set to an inert gas atmosphere: 3% O ₂ , at a rolling temperature: 1100 ° C.,
Reduction ratio: 0%, 2%, 5%, 10%, 20%, 30%, 40%,
For 50%, 60% and 70%, comparative experiments were conducted to confirm the conditions of surface roughness (μm), crystal grain size (μm), strength (kgf / mm ² ), elongation (%) and roughened surface.

The experimental results are shown in Table 8 below. The result judgment was based on the same acceptance criteria as in Example 1.

[0070]

[Table 8]

As shown in Table 8, the surface roughness exceeded 20 μm and did not satisfy the criteria for all reductions. That is, in this comparative example, even if the cast slab C of low carbon aluminum killed steel (0.04% C) is rolled at a rolling temperature of 1100 ° C. and a rolling reduction of 5% or more and 50% or less by the in-line rolling mill 5. In an inert gas atmosphere: 3% O ₂ , the surface roughness increased and a sound strip could not be obtained.

As described above, when the twin roll type continuous casting apparatus of Example 5 is compared with Comparative Example 3, when an inert gas atmosphere having an oxygen concentration of 2% or less is used, the scale of the scale attached to the surface of the cast slab C is reduced. The roughness is remarkably reduced, and a hot-rolled strip can be obtained without roughening of the processed surface. <Embodiment 6> Next, a twin roll type casting apparatus of Embodiment 6 will be described. Steel type is low carbon aluminum killed steel (0.04% C), rolling temperature is 1100 ℃, rolling reduction is 0%, 2%, 5%, 10
% And 20%. After rolling, the slab was water-cooled and wound at 650 ° C. The results are shown in Table 9. From this table, the rolling reduction is 0%,
That is, the standard deviation exceeds 7% in the as-cast material and under 2% pressure. In particular, the as-cast material has a very large variation in material quality, so the average value is low. On the other hand, when the rolling reduction is 5% or more, the standard deviation is within 5%, and it can be seen that the average value is almost stable regardless of the rolling reduction.

[0073]

[Table 9]

<Embodiment 7> Next, a twin roll type continuous casting apparatus of Embodiment 7 will be described. Table 10 shows steels with various components.
Continuous casting was performed at various casting thicknesses shown in Fig. 11, rolling was performed at various rolling temperatures and reduction ratios, then water cooling, and winding at 550 to 670 ° C. The mechanical test and the arrangement of mechanical properties are the same as in Example 6. The test results are also shown in the right column of Table 11. According to this, all of the conditions 1 to 6 of the present invention have the standard deviation of the total elongation within 5%, but the as-cast 7 and the rolling reduction of 3% are 8%.
Has a standard deviation of more than 5% and a large material variation.

Further, in the case of rolling temperature 9 which is remarkably low at 750 ° C., the value of elongation itself is low.

[0076]

[Table 10]

[0077]

[Table 11]

[0078]

As described above, according to the twin roll type continuous casting apparatus according to the present invention, the crystal grains are uniformly refined to have good mechanical strength, and the surface roughness is not rough. It has an excellent effect that it is possible to manufacture a thin plate having the above and can reduce the equipment cost. In addition to the total elongation as a requirement of the present invention, it is expected that the material variations similarly exist for various processing modes such as overhanging property. It is considered to contribute to the improvement of mechanical properties. On the other hand, the present invention basically relates to a method for producing a hot rolled steel sheet equivalent material from a thin strip, but the present cold rolled steel sheet and its plated steel sheet are produced from hot rolled steel sheet as a raw material. Considering the above, the steel sheet produced by the present invention can also be a cold rolled material.

[Brief description of drawings]

FIG. 1 is a schematic side view showing an embodiment of a twin roll type continuous casting apparatus according to the present invention.

FIG. 2 is a graph showing the relationship between the average crystal grain size and the crystal grain size number.

FIG. 3 is a side view of an essential part showing an example of a conventional twin roll type continuous casting apparatus.

FIG. 4 is a diagram showing an example of a deaeration housing.

FIG. 5 (a) is a side view of a degassing housing in the vicinity of a casting roll. FIG. 5B is a detailed view of part A of FIG.

FIG. 6 is a front view of a degassing housing near a casting roll.

FIG. 7 is a diagram showing the relationship between the rolling reduction and the surface roughness.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shiomi Kiyo             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Yoshiyuki Uejima             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Toshiaki Mizoguchi             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Satoshi Akamatsu             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Shigeru Ogawa             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Kazuo Koyama             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division

Claims (3)

[Claims] 1. C is 0.005 between a pair of water-cooled casting rolls.
Twin-roll continuous casting equipped with an in-line rolling machine and a winder for pouring a molten metal of ordinary carbon steel containing 1% by weight or more and solidifying it to reduce it to a predetermined thickness. In the apparatus, a degassing housing having an oxygen concentration of 5% or less inside was provided between the roll kiss point of the twin rolls and the inlet side of the in-line rolling machine, so that excellent surface properties with a surface roughness of 20 μm or less were obtained. A twin-roll type continuous casting apparatus, which is characterized by producing a slab. 2. A thermometer for measuring a temperature of a cast slab, a slab transport distance adjusting device for adjusting a transport distance of the cast slab, and an inlet side of the in-line rolling mill in the deaeration housing. The twin roll type continuous casting apparatus according to claim 1, further comprising a heater and a cooler which are provided in parallel immediately before each other, and a thermometer for measuring the temperature of the slab on the outlet side of the deaeration housing. 3. The sealing structure between the deaeration housing and the casting roll under a casting roll is a structure in which a side end iron plate and a caul cloth are bonded together, and further, a caul cloth is provided between the side end iron plate and the casting roll. The twin-roll type continuous casting apparatus according to claim 1 or 2, wherein the structure is slidable.