JP3190319B2 - Twin roll continuous casting machine - Google Patents

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 while conveying a thin-plate slab, and particularly to a thin-plate slab manufactured by a twin-roll type continuous casting method as a starting material. TECHNICAL FIELD The present invention relates to a twin-roll continuous casting apparatus for producing a thin plate slab that reduces variations in the surface properties of a normal steel sheet equivalent to a hot-rolled steel sheet and the material typified by elongation of a steel material.

[0002]

2. Description of the Related Art In general, a twin-roll type continuous casting apparatus is known as an apparatus to which a Bessemer type continuous casting method is applied, and a molten metal is poured between a pair of water-cooled casting rolls to solidify the metal. We manufacture thin plates. Thin sheet production by this type of twin-roll continuous casting apparatus 11 is performed as shown in FIG. As shown,
A molten metal is injected from above the pair of casting rolls 12a and 12b arranged at a predetermined interval,
Rotate 12a and 12b inward and downward while cooling with water. Then, the molten metal comes into contact with the casting rolls 12a and 12b and is cooled, and solidifies as a solidified shell S on the surfaces of the casting rolls 12a and 12b in an arc shape. Each solidified shell S has a casting roll 12a,
The slab C is brought into close proximity with the rotation of the roll 12b and pressed by a minimum portion of a roll interval (hereinafter, referred to as a "roll kiss point") K to form a slab C having a predetermined thickness, and the slab C is lowered from between the casting rolls 12a and 12b. It is extracted.

In this case, the solidification of the solidified shell S starts at a point F where the molten metal L comes into contact with each of the casting rolls 12a and 12b (hereinafter, referred to as "solidification start point"). Each solidified shell S which has started to solidify from the solidification start point F of each of the casting rolls 12a and 12b continues to grow until it reaches the roll kiss point K. At the roll kiss point K, each solidified shell S is pressed down and the cast slab C having a predetermined thickness is formed. Becomes Japanese Patent Application Laid-Open No. 58-359 discloses a related technique when the slab C thus cast is wound around a coiler and shipped as it is. 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 top surface of the molten steel pool is brought into close contact with a bottom surface of the tundish, thereby being formed on a pair of water-cooled roll surfaces. Continuous casting is performed while applying a static iron pressure corresponding to the molten steel level in the tundish to the solidified shell. According to this process, a thin cast strip with a slab thickness at the time of casting that is approximately the same as that of a hot-rolled steel sheet that has undergone rough rolling and finish rolling can be obtained, so that the conventional hot-rolling process can be omitted and the production cost is drastically reduced. A significant reduction is expected. However, there is a problem that such a thin cast steel sheet is inferior in material quality as compared with the current hot-rolled steel sheet.

That is, according to this method, since the produced slab is used as a product as cast, it is not possible to obtain good mechanical strength such as coarse crystal grains and low elongation and workability. In addition, 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, there is a method of removing the scale of the cast slab C after casting, winding the cast slab C into a predetermined thickness by hot rolling to a coiler, and forming the cast slab C into a product. There is a method in which the scale of the piece C is removed, a predetermined thickness is obtained by cold rolling, and the material is further rolled up into a coiler by annealing.

[0005] A method for refining crystal grains is disclosed in
This is disclosed in JP-A-63-115654 and JP-A-2-247049. In the former, the cast sheet metal is A
After cooling to ₁ transformation point temperature, which is heated or heated and kept again A ₃ transformation point or above the temperature, repeated then A ₁ or 2 times to a heat treatment again transformation point temperature to cool at line It is.

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

In the invention disclosed in Japanese Patent Application Laid-Open No. 63-115654, crystal grains are cooled by cooling to a ferrite (α) region immediately after solidification and heating to an austenite (γ) region. Although it has been miniaturized, there has been a problem that the total cost of the sheet metal casting apparatus used for this purpose is long, so that the equipment cost is increased. 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 general, when it is said that the material is inferior, there is a case where the characteristic value itself is low and also a case where the characteristic value has a large variation. In the latter case, the lower limit has to be adopted as the material property from the safety point of view.Therefore, this material variation is an important issue in discussing the material of the steel material. Such thin cast strips have not been sufficiently studied.

The technique described in the above-mentioned Japanese Patent Application Laid-Open No. 2-247049 discloses a technique in which a target is austenitic stainless steel and hot rolling is performed in the atmosphere, so that a thick scale layer is formed on the slab surface. Therefore, there is a problem that hot rolling cannot be performed or a remarkable surface flaw is formed on the rolled steel sheet. Further, in Japanese Utility Model Application Laid-Open No. 64-5472, there is provided a casting apparatus in which an oxygen-free atmosphere chamber including a rolling device is provided downstream of a cooling roll so as to maintain an oxygen-free atmosphere to prevent scale generation and slab cracking. It has been proposed that no or no scale is produced in anoxic conditions, so that the dimples of the casting roll are transferred to the surface and cannot be crushed by a small amount of rolling. There is a problem that the steel plate has a very large roughness and is not a product.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the material variation of a normal steel sheet equivalent to a hot-rolled steel sheet starting from a thin cast strip, which is said to be inferior in material quality as compared with existing hot-rolled steel sheets. An object is to provide a method for reducing this. Further, in view of the above problems, an object of the present invention is to produce a thin sheet having good mechanical strength by uniformly miniaturizing crystal grains by in-line hot rolling and having good surface roughness without roughening. An object of the present invention is to provide a twin-roll continuous casting apparatus capable of reducing the equipment cost.

[0010]

The gist of the present invention is as follows. (1) Between a pair of water-cooled casting rolls, a molten carbon of ordinary carbon steel consisting of 0.005% by weight or more and 1% by weight or less is injected,
In a twin-roll continuous casting apparatus equipped with an in-line rolling mill and a winder for rolling down a cast slab obtained by solidification to a predetermined plate thickness, between a roll kiss point of a twin roll and an entry side of the in-line rolling mill. A twin-roll continuous casting apparatus characterized by producing an insulated housing having an oxygen concentration of 5% or less inside, thereby producing a slab having excellent surface properties with a surface roughness of 20 μm or less.

(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 an inlet for the in-line rolling mill. Heater and cooler provided in parallel just before the side,
The twin-roll continuous casting apparatus according to the above (1), further comprising a thermometer for measuring a slab temperature on the outlet side of the degassing housing.

(3) A 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 kaor cloth are bonded to each other. The twin-roll continuous casting apparatus according to the above (1) or (2), wherein the cloth is slidable.

[0013]

According to the construction of the twin-roll continuous casting method of the present invention, a slab solidified by a pair of water-cooled casting rolls is temperature-adjusted and then reduced to a predetermined thickness by an inline rolling mill. That is, the rolling temperature of the in-line rolling is adjusted within the temperature range where 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 austenitic structure exists in the matrix of the slab is specifically 850 ° C. or higher and 1350 ° C.
The reason why the temperature is adjusted to such a temperature range is to uniformly refine the crystal grains of the slab with an appropriate rolling force. That is, if the rolling temperature is lower than 850 ° C., the rolling reaction force increases and the recrystallization time increases, so that the production line must be lengthened. If the temperature is lower than 850 ° C., ferrite transformation may occur, and the final structure may become a processed structure, and elongation may be significantly reduced. On the other hand, when the rolling temperature exceeds 1350 ° C., although there is a grain sizing effect, since the temperature is high, crystal grains grow after rolling, and the effect of refining is reduced. Further, a more preferable range of the rolling temperature is 900 ° C. or more and 1250 ° C. or less in the present invention.

The reason for setting the rolling reduction to 5% or more and 50% or less is to obtain a strip having a desired surface roughness, crystal grain size, elongation and 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 alleviate this. That is, internal defects such as minute plate thickness deviations and shrinkage cavities of the as-cast material do not disappear and variations in the material occur. On the other hand, when the rolling reduction exceeds 50%, the surface roughness becomes non-uniform due to the heavy working, and in some cases, the thickness accuracy decreases.

[0016] Further, when an inert gas atmosphere is provided from the casting roll to the entry side of the in-line rolling mill, high-temperature oxidation of the slab is prevented. In this case, oxygen concentration 5
% Or less, the roughness of the scale adhering to the surface of the slab is extremely 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, the results are as follows: C: 0.04%, in-line rolling temperature: 1100 ° C. Atmosphere is air (21% O ₂ )
In this case, 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 influence of the rolling reduction is small, and if the rolling reduction is selected,
It can be seen that the surface roughness Rt can be reduced to about 以下 or less before the in-line rolling, that is, the surface roughness is 20 μm or less.

On the other hand, according to the configuration of the twin-roll continuous casting apparatus, there is provided an in-line rolling mill for rolling down a slab solidified by a pair of water-cooled casting rolls to a predetermined thickness. Before entering this in-line rolling mill, there is a thermometer for measuring the temperature of the slab immediately after solidification, and a control for adjusting the temperature of the slab to a temperature range in which austenite structure exists in the matrix based on the measured value. And a heating device. This temperature adjustment is performed by adjusting the distance to the rolling mill, that is, by adjusting the residence time in the deaerated housing.

Another method is to heat the slab by the heater if the temperature of the slab immediately after solidification measured by a thermometer is lower than the temperature range in which the austenite structure exists in the matrix of the slab. After adjusting the temperature within the temperature range, the temperature may be reduced by an inline 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 reduced by an inline rolling mill. At that time, reduce the draft by 5% or more to 50%.
%, A strip having a surface roughness of 20 μm or less, a crystal grain size of 30 μm or less, preferably 20 to 30 μm, an elongation of 34% or more, and no roughened surface can be obtained.

Further, if a degassing housing is formed between the casting roll and the entry side of the in-line rolling mill and the inside thereof is made to have an inert gas atmosphere, high-temperature oxidation of the slab is prevented. In addition, it was found that the property value of these materials was improved and the variation was remarkably reduced only by adding one pass after the solidification of hot rolling, and a method of 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 in accordance with those of the current hot-rolled steel sheet.

The material variation in the present invention was obtained by statistically processing the variation of the total elongation when a JIS No. 5 tensile test was performed, and indicated by a standard deviation σ. The material requirement of the present invention is that the standard deviation of the total elongation is within 5%. Now, in the present invention, although the chemical components are not particularly limited, 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 solid solution strengthening element in ordinary steel. However, if it exceeds 1.5%, the pickling property is inferior, so that 1.5% or less is preferable. Mn is also added to ordinary steel as a strengthening element similarly to C and Si. From the viewpoint of preventing hot embrittlement due to S, it is preferable that Mn is usually added at least 5 times S%. However, from the viewpoint of weldability,
2.0% or less is preferable.

Basically, it is desirable that P and S are small. However, unnecessary ultra-low phosphorization and ultra-low sulfuration increase costs in the steel making process. Absent. The present invention does not particularly limit other elements contained in the steel. For example, in order to improve mechanical properties such as strength and ductility of steel materials, a small amount of Nb, Ti, V, B, etc. may be added to steel, but the present invention is not affected at all by these additions. is not. On the other hand, when scrap is used as a 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 disturb the present invention.

[0024]

<Embodiment 1> An embodiment of a twin-roll continuous casting method and apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic side view showing one embodiment of a twin-roll continuous casting apparatus according to the present invention. As shown in the figure, the twin-roll 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 dams 3 are provided at both ends of the casting rolls 2a and 2b, and a pool section 4 for storing the molten metal L is formed in a section defined by these.

The molten metal L is poured into the pool 4 from above, and when the casting rolls 2a, 2b are rotated inward and downward while cooling with water, the molten metal L is cast into the casting rolls 2a, 2b.
, And is cooled as a solidified shell S on the surface of each of the casting rolls 2a and 2b in an arc shape. Each of the solidified shells S is brought close together with the rotation of the casting rolls 2a and 2b, pressed at a roll kiss point K to form a slab C having a predetermined thickness, and is drawn downward from between the casting rolls 2a and 2b.

An in-line rolling mill 5 for reducing the solidified slab C to a predetermined thickness by hot rolling is provided downstream of the casting rolls 2a and 2b. A roll mill generally used is used for the in-line rolling mill 5. Since a rolling reduction of 5% or more and 50% or less with respect to the thickness of the slab C is adopted, a rolling mill having such a rolling force is used. use.

Further, before entering the in-line rolling mill 5, a thermometer 6 for measuring the temperature of the slab C immediately after solidification, and the slab C based on the measured value are put in the matrix. And a temperature control device 7 for adjusting the temperature within a temperature range in which the austenite structure (γ) exists. The thermometer 6 includes, for example, platinum-platinum rhodium (Pt-Rh).
In addition to the thermocouple, etc., an instrument capable of measuring a temperature of about 700 to 1500 ° C is adopted. Further, the temperature control device 7 employs a heater 7a such as a high-frequency induction heater or a cooler 7b such as a heat retainer and / or a water cooler. In addition, as a heat insulator,
As a heater, a gas burner, etc., as a heater, and as a cooler, a movable roll, a steam-water cooler, etc. for the purpose of cooling adjustment by increasing transport 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 is used.
When the measured value is out of the temperature range where the austenitic structure (γ) exists in the matrix of the slab C, the slab C is heated or cooled by the temperature control device 7 to reduce the rolling temperature. adjust. That is, if the temperature of the slab C is lower than 850 ° C., the slab C is heated by the heater 7a.
After the temperature is adjusted within a temperature range of 850 ° C. or more and 1350 ° C. or less, the in-line rolling mill 5 reduces the temperature. 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 a temperature range of 850 ° C. to 1350 ° C., and then reduced by the in-line rolling mill 5. is there.

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

In the deaerated housing 9, a loop detector 19, a pinch roll 14, a cooling zone 15, and a transport roll 1 are provided.
6 are provided. Also, on the exit side of the degassing housing 9,
One is a movable roll 17 to adjust the transport distance,
The other is provided with a transport roll that is a fixed roll 18.
The slab temperature is measured by a thermometer 20, and the data is passed through a converter 21 to control a flow control valve 22 for the cooling water W.

FIG. 5A shows the degassing housing 23 under the casting roll, FIG. 5B is an enlarged view of a portion A in FIG. 5A, and FIG. 6 is a front view. In these figures, the degassing housing 9 is covered from the roll kiss point, and a caul cloth 25 is adhered to the side end iron plate 24 to secure the airtightness. The airtightness is ensured between the iron plate 24 and the casting roll by sliding the kaoru cloth.

Next, the twin-roll continuous casting apparatus 1 described above
The twin-roll continuous casting method according to the present embodiment, which is performed using the method described above, will be described. The casting rolls 2a and 2b of the twin-roll continuous casting apparatus 1 used in the present embodiment are formed with dimensions of a roll width: 350 mm and a roll diameter: 400 mmφ, and are Cu rolls of an internal water cooling system. The casting conditions were: casting speed: 30 m / min,
Cast plate thickness: Set to 3.0mm. The inside of the degassing housing 9 is set to an inert gas atmosphere: 1% O ₂ . Further, the in-line rolling mill 5 includes two
HI, 1 stage, work roll diameter: 300 mmφ. In addition, low carbon aluminum killed steel (0.
04% C). The slab was water-cooled and wound at 650 ° C.

Under the above conditions, the twin-roll continuous casting method of the present embodiment employs a rolling temperature of the in-line rolling mill 5 of 11:
At 00 ° C., rolling reduction: 0%, 2%, 5%, 10%, 20%, 30%
%, 40%, 50%, 60%, 70%
m), grain size (μm), strength (kgf / mm ² ), elongation (%)
An experiment was conducted to confirm the condition of the roughened surface. The experimental results are shown in Table 1 below. In addition, the result is determined by the surface roughness:
20 μm or less, crystal grain size: 20-30 μm, strength: 36 kgf / mm
Acceptance criteria: ² or more, elongation: 34% or more, roughened surface: no streaking due to ridging The strength and elongation of the steel sheet were determined by preparing 35 JIS No. 5 tensile test pieces from the obtained steel sheet, subjecting them to a tensile test, and statistically processing the obtained total elongation to obtain an average value and a standard deviation.

[0034]

[Table 1]

As shown in Table 1, the surface roughness is
An acceptable value (20 μm or less) was obtained at a rolling reduction of 5% or more and 50% or less. Regarding the crystal grain size, acceptable values (20 to 30 μm) were obtained when the rolling reduction was 5% or more and 70% or less. The growth is
Reduction rate: Acceptable value from 5% to 70% (34% or more)
was gotten. Regarding the roughness of the processed surface, an acceptable value (none) was obtained at a draft of 5% or more and 70% or less.

That is, in the manufacturing method using the twin-roll type continuous casting apparatus of the present embodiment, a slab C of low carbon aluminum killed steel (0.04% C) is rolled at an in-line rolling mill 5 at a rolling temperature of 1100 ° C. By reducing at a rolling reduction of 5% or more and 50% or less, a desired surface roughness (20 μm or less), a crystal grain size (20 to 30 μm), an elongation (34% or more) and a roughened surface are obtained. It was confirmed that no strip could be obtained.

<Embodiment 2> In this embodiment, the casting material in Embodiment 1 is changed. Specifically, medium carbon aluminum killed steel (0.13% C)
The other conditions are the same as in the first embodiment. Under the above conditions, the twin-roll type continuous casting method of the present embodiment is performed at a rolling temperature of the in-line rolling mill 5 of 1100 ° C.
Reduction rate: 0%, 2%, 5%, 10%, 20%, 30%, 40%,
For 50%, 60%, and 70%, experiments were conducted to confirm the surface roughness (μm), crystal grain size (μm), strength (kgf / mm ² ), elongation (%), and roughness of the processed surface.

The results of the experiment are shown in Table 2 below. The results were evaluated based on the same pass 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
An acceptable value (20 μm or less) was obtained at a rolling reduction of 5% or more and 50% or less. The crystal grain size is determined to be a pass value at a rolling reduction: 10% or more and 50% or less (30 μm or less, preferably 20 to 30 μm).
m) was obtained. As for elongation, a pass value (34% or more) was obtained when the draft was 10% or more and 70% or less. The rough surface is
An acceptable value (none) was obtained when the rolling reduction was 5% or more and 70% or less.

That is, in the manufacturing method using the twin-roll continuous casting apparatus of the present embodiment, a slab C of medium-carbon aluminum killed steel (0.13% C) was rolled at an in-line rolling mill 5 at a rolling temperature of 1100 ° C. The desired surface roughness (20 μm or less), crystal grain size (20 to 30 μm) and elongation (34% or more) are obtained by rolling down at a rolling reduction of 10% or more and 50% or less. It was confirmed that no strip could be obtained.

<Embodiment 3> In this embodiment, the rolling temperature of the in-line rolling mill 5 in Embodiment 1 is changed, and other conditions are the same as those in Embodiment 1. Specifically, the twin-roll continuous casting apparatus of the present embodiment has a rolling temperature of the in-line rolling mill 5 of 850 ° C., a rolling reduction of 0%,
2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70
%, An experiment was conducted 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 was determined based on the same acceptance criteria as in Example 1.

[0044]

[Table 3]

As shown in Table 3, the surface roughness is
An acceptable value (20 μm or less) was obtained at a rolling reduction of 5% or more and 50% or less. The crystal grain size is a passing value at a rolling reduction: 20% or more and 70% or less (30 μm or less, preferably 20 to 30 μm).
m) was obtained. As for elongation, a pass value (34% or more) was obtained when the draft was 10% or more and 70% or less. The rough surface is
An acceptable value (none) was obtained when the rolling reduction was 5% or more and 70% or less.

That is, in the manufacturing method using the twin-roll continuous casting apparatus of the present embodiment, a slab C of low carbon aluminum killed steel (0.04% C) was rolled at an 850 ° C. rolling temperature at an in-line rolling mill 5. The desired surface roughness (20 μm or less), crystal grain size (20 to 30 μm), elongation (34% or more) are obtained by rolling down at a rolling reduction of 20% or more and 50% or less. It was confirmed that no strip could be obtained.

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

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

[0049]

[Table 4]

As shown in Table 4, the surface roughness is
An acceptable value (20 μm or less) was obtained at a rolling reduction of 5% or more and 50% or less. Regarding the crystal grain size, acceptable values (20 to 30 μm) were obtained when the rolling reduction was 5% or more and 70% or less. The growth is
Reduction rate: Acceptable value from 5% to 70% (34% or more)
was gotten. Regarding the roughness of the processed surface, an acceptable value (none) was obtained at a draft of 5% or more and 70% or less.

That is, in the manufacturing method using the twin-roll continuous casting apparatus of Example 4, a slab C of low carbon aluminum killed steel (0.04% C) was rolled at a rolling temperature of 1300 ° C. in an in-line rolling mill 5. By reducing at a rolling reduction of 5% or more and 50% or less, a desired surface roughness (20 μm or less), a crystal grain size (20 to 30 μm), an elongation (34% or more) and a roughened surface are obtained. It was confirmed that no strip could be obtained.

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

The results of the experiment are shown in Table 5 below. The result was determined 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 (%) fell below 34%, and the processed surface was rough. I didn't. That is, in this comparative example, even if the slab C of the low carbon aluminum killed steel (0.04% C) was reduced by the in-line rolling mill 5 at a reduction ratio of 0% to 70%, even if the rolling temperature was 750 ° C. Did not 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), grain size (μm)
m), strength (kgf / mm ² ), elongation (%), and a comparative experiment for confirming the condition of the roughened surface.

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

[0058]

[Table 6]

As shown in Table 6, at all rolling reductions, the crystal grain size exceeded 30 μm, and the rolling reduction was 0% or more.
At 50% or less, the elongation was reduced to less than 34%, and the processed surface was rough, and did not satisfy the criteria. That is, in this comparative example, even if the slab C of low-carbon aluminum killed steel (0.04% C) was reduced by the in-line rolling mill 5 at a reduction ratio of 0% to 70%, the rolling temperature of 1350 ° C Did not get a healthy strip.

As described above, when the twin-roll continuous casting apparatus of Examples 1 to 4 is compared with Comparative Examples 1 and 2,
At a rolling temperature of 850 ° C or higher and lower than 1350 ° C,
The desired surface roughness (20 μm or less) can be obtained by reducing the in-line rolling mill 5 at a reduction ratio of 5% or more and 50% or less.
It has been found that a strip having a crystal grain size (20 to 30 μm) and elongation (34% or more) and having no roughened surface can be manufactured. As described above, in the twin-roll continuous casting apparatus according to the present invention, a product thin plate can be manufactured by directly performing hot rolling during conveyance of the slab C without performing cold rolling. Therefore, equipment costs and manufacturing costs can be significantly reduced.

The above-mentioned rolling temperature: a temperature range of 850 ° C. or more and less than 1350 ° C. is a temperature range in which an austenite structure (γ) exists in the matrix of the slab C, and specifically, a ferrite structure (α) and an austenite structure. (Γ) or one phase region of the austenitic structure (γ). Also,
As described above, the preferable conditions of the rolling reduction with respect to the plate thickness of the slab C are slightly different depending on the rolling temperature and the steel type of each embodiment.
When the rolling reduction is in the range of 20% or more and 50% or less, a desired strip can be reliably obtained. The twin-roll continuous casting apparatus according to the present invention has a carbon content of 0.0005% C to 1.0% C.
Of carbon steel.

It should be particularly noted in the present invention that 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 having a grain size number of 5 or more is generally referred to as fine-grained steel (see the Iron and Steel Institute of Japan, New Edition Steel Technology Course, Vol. 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 steel is a fine grain steel having a grain size number of 7.5 or more.

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

Under the above conditions, the twin-roll type continuous casting apparatus of the present embodiment uses the rolling temperature of the in-line rolling mill 5 as follows:
At 1100 ° C, rolling reduction: 0%, 2%, 5%, 10%, 20%, 30%
%, 40%, 50%, 60%, 70%
m), grain size (μm), strength (kgf / mm ² ), elongation (%)
An experiment was conducted to confirm the condition of the roughened surface. The results of the experiment are shown in Table 7 below. The result was determined based on the same acceptance criteria as in Example 1.

[0065]

[Table 7]

As shown in Table 7, the surface roughness is
An acceptable value (20 μm or less) was obtained at a rolling reduction of 5% or more and 50% or less. Regarding the crystal grain size, acceptable values (20 to 30 μm) were obtained when the rolling reduction was 5% or more and 70% or less. The strength is
Acceptable values (36 kgf / mm ² or more) were obtained at all rolling reductions. As for elongation, a pass value (34% or more) was obtained at a draft of 5% or more and 70% or less. Roughness of processed surface, reduction ratio: 5
A pass value (none) was obtained in the range of 70% to 70%.

That is, in the twin-roll continuous casting apparatus of the present embodiment, the inert gas atmosphere in the degassing housing: 2
% O ₂ , a low carbon aluminum killed steel (0.04% C) slab C is 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 (20μm or less), crystal grain size (20-30μ)
m), it was confirmed that a strip having elongation (34% or more) and having no roughened surface could be obtained.

<Comparative Example 3> On the other hand, a description will be given of Comparative Example 3, which was conducted to confirm the operation and effect of the twin-roll continuous casting apparatus of the present embodiment. 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 , and a rolling temperature: 1100 ° C.
Reduction rate: 0%, 2%, 5%, 10%, 20%, 30%, 40%,
For 50%, 60%, and 70%, comparative experiments were performed to confirm the surface roughness (μm), crystal grain size (μm), strength (kgf / mm ² ), elongation (%), and roughened surface.

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

[0070]

[Table 8]

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

As described above, when the twin-roll continuous casting apparatus of Example 5 is compared with that of Comparative Example 3, the inert gas atmosphere having an oxygen concentration of 2% or less can reduce the scale adhered to the surface of the slab C. Roughness is extremely reduced, and a strip having no roughened surface can be obtained by hot rolling. Embodiment 6 Next, a twin roll type casting apparatus according to Embodiment 6 will be described. The steel type is low carbon aluminum killed steel (0.04% C), rolling temperature is 1100 ℃, rolling reduction is 0%, 2%, 5%, 10%
% And 20%. The slab was rolled at 650 ° C. after cooling with water. Table 9 shows the results. From this table, the reduction rate is 0%,
That is, the standard deviation exceeds 7% for the as-cast material and 2% reduction. Particularly, the as-cast material has a very low average value because the material variation is extremely large. 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 continuous casting apparatus of Embodiment 7 will be described. Table 10 shows the steel compositions of various components.
Continuous casting was performed at various casting thicknesses shown in FIG. 11, rolled at various rolling temperatures and rolling reductions, then cooled with water and wound at 550 to 670 ° C. The mechanical test and the arrangement of the mechanical characteristics are the same as in the sixth embodiment. The test results are shown in the right column of Table 11. According to this, all of the conditions 1 to 6 of the present invention have a standard deviation of the total elongation of 5% or less.
Has a large standard deviation exceeding 5% and a large material variation.

Further, when the rolling temperature is extremely 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 continuous casting apparatus of the present invention, the crystal grains are uniformly refined to have good mechanical strength and good surface roughness without roughening. , And an excellent effect of reducing equipment costs can be exhibited. In addition, in addition to the total elongation as a requirement of the present invention, it is expected that the material variation similarly exists for various processing modes such as overhanging property, so that the effect of the present invention is more practical. It is thought 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 cast strip, and the current cold-rolled steel sheet and its plated steel sheet are manufactured using the hot-rolled steel sheet as a material. In consideration of the above, the steel sheet manufactured according to the present invention can also be a cold-rolled material.

[Brief description of the drawings]

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

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

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

FIG. 4 is a view showing an example of a degassing housing.

FIG. 5 (a) is a side view of a deaerated housing near a casting roll. FIG. 5B is a detailed view of a portion A in FIG.

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

FIG. 7 is a diagram showing a relationship between a draft and a surface roughness.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B22D 11/22 B22D 11/22 B (72) Inventor Yoshiyuki Uejima 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Inside the Development Division (72) Inventor Toshiaki Mizoguchi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Inside the Technology Development Division (72) Inventor Satoshi Akamatsu 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation (72) Inventor Shigeru Ogawa 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Company (72) Inventor Kazuo Koyama 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation (56) References JP-A-2-247049 (JP, A) JP-A-65-20008 (JP, A) JP-A-3-60848 (JP, A) JP-A-7- 195103 (JP, A) 62-161442 (JP, A) JP-A-62-29753 (JP, A) JP-A-62-29752 (JP, A) JP-A-6-397552 (JP, A) JP-A-1-166864 (JP, A) A) JP-A-63-30159 (JP, A) JP-A-63-30158 (JP, A) JP-A-63-26240 (JP, A) Fully open Showa 64-5742 (JP, U) Really open Showa 63 -76308 (JP, U) WO 95/26242 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/06 330 B22D 11/12 B22D 11/16 104 B22D 11 / twenty two

Claims (3)

(57) [Claims] (1) C is 0.005 between a pair of water-cooled casting rolls.
Twin-roll continuous casting equipped with an in-line rolling mill and a winder for injecting and solidifying a melt of ordinary carbon steel consisting of not less than 1% by weight and not more than 1% by weight. In the apparatus, between the roll kiss point of the twin rolls and the entry side of the in-line rolling mill, by providing an aerated housing having an oxygen concentration of 5% or less inside, an excellent surface property with a surface roughness of 20 μm or less is provided. A twin-roll continuous casting apparatus for producing cast slabs. 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 of the in-line rolling mill. 2. The twin-roll continuous casting apparatus according to claim 1, further comprising a heater and a cooler provided immediately before and in parallel with each other, and a thermometer for measuring a slab temperature on the outlet side of the degassing housing. 3. A sealing structure between the degassing housing and the casting roll under a casting roll has a structure in which a side end iron plate and a kaor cloth are bonded to each other, and further, a gap between the side end iron plate and the casting roll is a kaor cloth. 3. The twin-roll continuous casting apparatus according to claim 1, wherein the apparatus has a slidable structure.