JPH07204811A - Continuous casting method - Google Patents

Abstract

PURPOSE:To provide a continuous casting method, by which a high carbon steel having high quality without surface and internal inclusion and surface and internal crack can be produced in high productivity and high product yield. CONSTITUTION:At the time of continuously casting the steel material containing >=0.03% carbon, the bending in the unsolidified condition of a cast slab 12 and the straightening at the unsolidified condition or after perfectly solidifying are executed by using a vertical bending type continuous caster 10. In the other way, further, >=40% of the total cooling water is jetted till completion of the bending in a secondary cooling zone 22 of the continuous caster 10 and the cooling water is also shut off at the end part of the cast slab at least at one zone in the secondary cooling zone 22. Further, divided rollers are used at the bending part and/or the straightening part of the secondary cooling zone 22 and the continuous casting is executed at >=0.8m/min casting velocity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to produce high carbon steel and special steel containing 0.30% or more of carbon with high yield and without producing surface cracks or internal cracks, and with high production capacity. The present invention relates to a continuous casting method capable of producing.

[0002]

2. Description of the Related Art High carbon steels and special steels with high carbon content are
It is known as a manufacturing problem that surface cracks and internal cracks of continuous cast pieces (hereinafter referred to as continuous cast pieces) are likely to occur during continuous casting. Therefore, when continuously casting such steel types, it is common to use a vertical type continuous casting machine (hereinafter referred to as a continuous casting machine) that does not structurally cause bending strain, straightening strain, etc. Target. For example, JP-A-59
No. 125251 discloses a sound continuous cast piece that does not crack by defining the relationship between the heat flux in the mold and the casting speed and the actual water injection density in the secondary cooling zone during low speed casting. A method of manufacturing has been proposed.

Since the vertical type continuous casting machine (or vertical solidification bending type continuous casting machine) performs continuous casting in a vertical state, inclusions caused by mold powder or the like float up before solidification of molten steel and solidified continuous casting. Does not mix in one piece. Therefore, it is possible to manufacture a high-quality continuous cast piece free from defects caused by inclusions and the like, and defects caused by inclusions in the vicinity of the surface generated at the stage of initial solidification of molten steel.

In addition to such characteristics of the vertical type continuous casting machine, by stirring molten steel in the mold and the secondary cooling zone, a continuous casting piece of high quality high carbon steel with few inclusions and segregation can be obtained. Various manufacturing methods have been proposed. For example, in JP-A-61-229450, by heating the molten steel in the tundish to a high temperature within 15 ° C. and stirring,
A method for obtaining a high carbon steel having an excellent internal quality is disclosed in JP-A-63-13.
Japanese Patent No. 650 discloses that the internal temperature of the tundish is kept higher than the liquidus by 10 to 20 ° C., and the unsolidified molten steel is stirred not only in the tundish but also in the mold and the secondary cooling zone. A method for obtaining high carbon steel is disclosed in Japanese Examined Patent Publication No. Sho 64-11387, in which medium and high carbon with small inclusions and surface segregation are defined by defining the relationship between the frequency of molten steel stirring in the mold and the magnetic flux density. Methods for producing killed steel are disclosed; respectively.

[0005]

As described above, the vertical continuous casting machine (or vertical solidification bending continuous casting machine) is suitable for the production of high carbon steel which is susceptible to cracking, and also includes inclusions and the like. It is possible to manufacture a high-quality continuous cast slab that is free from defects caused by the above and defects caused by inclusions in the vicinity of the surface generated at the stage of initial solidification of molten steel. However, the vertical continuous caster cannot increase the casting speed (casting speed) because of its configuration, and it is very difficult to realize a high production capacity.

That is, not only the vertical type continuous casting machine but also a continuous casting machine having a long machine length is required to increase the casting speed. However, unlike the curved type continuous casting machine and the like, in order to increase the length of the vertical type continuous casting machine, it is necessary to elevate the building or construct a large-scale underground structure. for that reason,
In order to realize a continuous casting machine capable of high-speed casting, there is a major architectural problem, and even if it is possible, it will be very expensive. Further, for the same reason, in the vertical continuous casting machine, it is very difficult to extend the length of the device once constructed, and it is virtually impossible to expand the production capacity.

On the other hand, a so-called curved type continuous casting machine can easily increase the machine length. However, because the curved continuous casting machine has a curved mold and the shape of the secondary cooling zone, it is difficult to float and separate inclusions in the molten steel unsolidified state, which is an advantage of the vertical continuous casting machine. Due to defects caused by inclusions or Ar bubbles in the vicinity of the surface of the continuous cast piece,
Problems of the internal and surface properties of the continuous cast piece are likely to occur. Further, as described above, the high carbon steel is apt to crack on the surface and inside thereof, and there is a problem also in this point in the continuous casting machine in which deformation such as bending and stretching of the continuous casting piece is essential.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to produce a high-quality high-carbon steel free from the inclusion of inclusions near the surface and internal inclusions as well as surface and internal cracks with high production capacity. Another object of the present invention is to provide a continuous casting method that can be manufactured with a high product yield.

[0009]

In order to achieve the above object, the first aspect of the present invention is to provide a vertical bending type continuous casting machine when continuously casting a steel material containing 0.30% or more of carbon. The present invention provides a continuous casting method, which comprises bending a cast piece in an unsolidified state, and straightening the cast piece in the unsolidified state or straightening after complete solidification.

In the second aspect of the present invention, the carbon content is 0.
When continuously casting a steel material containing 30% or more, use a vertical bending type continuous casting machine to bend the cast piece in the unsolidified state, and straighten the cast piece in the unsolidified state or straighten it after complete solidification. And, while injecting 40% or more of the total cooling water amount by the end of bending in the secondary cooling zone of the continuous casting machine, shut off the cooling water at the end of the slab in at least one zone of the secondary cooling zone, Further, the present invention provides a continuous casting method characterized by performing continuous casting at a casting speed of 0.8 m / min or more by using a dividing roller in the bending portion and / or the straightening portion of the secondary cooling zone.

Here, bending means deformation of the cast piece due to change from vertical casting to constant curvature, while straightening means deformation of the cast piece from constant curvature to straight line.

The continuous casting method of the present invention will be described in detail below. The continuous casting method of the present invention uses 0.30 carbon.
The present invention relates to a continuous casting method for high carbon steel or special steel containing at least 0.1%. In the present invention, all of various steel materials containing 0.30% or more of carbon can be targeted, but specifically, high carbon steel is S30 referred to in JIS standard.
C to S58C, etc., while special steel means SK7 to S
K1, SCM430, SNCM240, etc. are shown. In addition,
In the following description, these steel materials are collectively referred to as high carbon steel.

1 and 2 are conceptual diagrams of a continuous casting machine (hereinafter referred to as a continuous casting machine) for carrying out the continuous casting method according to the first and second aspects of the present invention. Here, FIG.
Shows an example of straightening a continuous cast piece in a non-solidified state, and FIG. 2 shows an example of straightening a continuous cast piece after completely solidified. In addition, in the continuous casting method of the present invention (hereinafter, referred to as a continuous casting method), the examples shown in FIGS. 1 and 2 are the cooling rate and the casting rate (that is, the state inside the slab particularly in the straightening portion described later). Since the continuous casting machine has basically the same configuration except that the same is different, the same members are denoted by the same reference numerals and will be described in the same manner.

As shown in FIGS. 1 and 2, the continuous casting machine 10 used in the present invention vertically pulls out a continuous cast piece (hereinafter referred to as a continuous cast piece) 12 and then continuously casts it. The piece is bent in a non-solidified state, and after that, the continuous cast piece is unsolidified or completely solidified, and then the continuous cast piece is linearly extended (that is, straightened) to cast the continuous cast piece 12. It is a continuous casting machine. The continuous cast piece 12 manufactured by such a continuous caster 10 is cut by the torch 14 or the like and then conveyed to the next step such as hot rolling.

In the illustrated example, the molten steel from the tundish 16 is poured into the mold 20 by the immersion nozzle 18 or the like. The molten steel injected into the mold 20 is cooled, starts solidification (forms a so-called shell), and is drawn out to the secondary cooling zone 22. Here, in the mold 20, the molten steel (continuous cast piece 12) is cooled by cooling the mold 20 with water or the like.

The secondary cooling zone 22 of the illustrated continuous casting machine 10 is
As with a normal continuous casting machine, a large number of transport rollers 24, 24, 2
4 ... or a spray nozzle or the like arranged in the gap between the transport rollers 24, and as an example, the first zone 22a,
Second zone 22b, third zone 22c, fourth zone 22
d and the fifth zone 22e, a total of five zones are provided, and the continuous cast piece 12 is pulled out in the vertical direction.
Bending 2 and then straightening it straight while transporting it while spraying water or mist (spray mixture)
The continuous cast piece 12 is cooled by. In the continuous casting method of the present invention, the secondary cooling zone 22 is not limited to being composed of 5 zones, but may be further divided into smaller zones or 5 zones.
Of course, it may be composed of less than zones.

In the illustrated example, the first zone 22a is a vertical portion, and the continuous cast piece 12 is pulled out from the mold 20 in the vertical direction. A second zone 22b arranged next to the first zone 22a is a bent portion, and the continuous cast piece 12 is conveyed and cooled while being curved to have a predetermined curvature here, and the third zone 22b.
In c, the sheet is cooled while being conveyed with a predetermined curvature. The fourth zone 22d to be arranged next is a straightening part, and the curved continuous cast piece 12 is straightened and cooled here, and is further conveyed and cooled in the fifth zone 22e while being straightened, and is then moved by the torch 14. It is cut to a predetermined length and conveyed to the next step such as surface care and hot rolling.

In the continuous casting method of the present invention, such a vertical bending type continuous casting machine 10 is used to bend the continuous casting piece 12 in a state where the inside of the continuous casting piece 12 is not solidified (hatched portion in the figure). Correction 1
The continuous cast piece 12 is not solidified (hereinafter simply referred to as unsolidified) as shown in FIG. 2, or the continuous cast piece 12 is completely solidified (hereinafter simply referred to as solidified as shown in FIG. 2). Correct). By carrying out continuous casting of high carbon steel in this way, it is possible to increase production efficiency and manufacture high quality high carbon steel with no defects due to inclusions, and also surface and internal cracks at high yield. is there.

FIG. 3 shows the relationship between the surface cracking index and the carbon content of the continuous cast piece when the high carbon steel slab is manufactured by the vertical bending type continuous casting machine. This graph is an example of using a split roll described later from the meniscus (solidification start point in the mold) to 15 m in the secondary cooling zone at a casting speed of 0.7 m / min. The surface cracking index is a value expressed by converting the cracks generated on the surface of the slab per unit area, and the higher the index, the easier the cracking occurs.

As shown in FIG. 3, the crack initiation index of the continuous cast piece is concentrated in the high carbon region with a carbon content of around 0.3% as a boundary. It is considered that this is because as the carbon concentration increases, the difference between the liquidus temperature and the solidus temperature opens, and the strength appearance temperature decreases. Further, the high carbon steel contains components such as Si, Mn, Cr, Ni, and Mo which increase the crack susceptibility as a result, but even in that case, this tendency does not change significantly.

As a result of further study, 0.3% of carbon was added.
In the high carbon steels contained above, the cracking susceptibility becomes very high when the surface temperature is lowered to 850 ° C or lower. Such a tendency is not a big problem in the vertical continuous casting machine. However, although high-speed casting is possible, this poses a serious problem in a vertical bending type continuous casting machine in which the upper bending portion and the lower straightening portion are indispensable to be deformed twice. That is, in the vertical bending type continuous casting machine, it is extremely important to secure the surface temperature of the continuous casting piece at the bending portion and the straightening portion.

The present invention solves the above problems by bending the continuous cast piece 12 in the unsolidified state by using the continuous bender 12 of the above-mentioned configuration, that is, the vertical bending type.

That is, the vertical casting type continuous casting machine is used to bend the continuous casting pieces in an unsolidified state, so that the machine length can be easily increased, continuous casting can be performed at high speed, and bending (correction) can be performed.
The surface temperature of the continuous cast piece 12 at that time can be secured, and the surface and internal cracks of the continuous cast piece 12 can be significantly reduced. Further, since the primary cooling (mold 20) and a part of the secondary cooling zone 22 (first zone 22a) are vertical, inclusions and the like can be floated at this part, and there is no defect in the inside or surface properties. Therefore, a high quality continuous cast piece 12 can be manufactured.

Continuous casting machine 10 used in the continuous casting method of the present invention
In the above, there is no particular limitation on the length of the vertical portion, and it may be appropriately determined depending on the ease of removing inclusions according to the stainless steel type, but according to the study by the present inventors, most removal is possible. Even if it is difficult, if there is a vertical portion within 5 m, almost all the inclusions can be removed. Therefore, in order to reduce the height of the continuous casting machine, it is preferable that the height of the vertical portion be within 5 m. Further, the curvature of the continuous cast piece 22 when curved is not particularly limited, and may be appropriately determined depending on the length of the continuous caster, the type of stainless steel, etc. within a range in which cracking due to an increase in surface strain can be prevented.

Further, in the second aspect of the present invention,
At least in the secondary cooling zone 22 of the continuous casting machine 12 in continuous casting of high carbon steel in order to prevent cracking of the continuous cast piece 12 more appropriately and to realize production of higher quality continuous cast piece 12. The total amount of cooling water until the end of bending of the continuous cast piece 12 and the end of bending of the continuous cast piece 12 in one zone is 40%.
% Or more injection, use of split rollers in the bending and / or straightening section, that is, the second zone 22b and / or the fourth zone 22d, and further continuous casting speed 0.8 m / m
Continuous casting is performed under the condition of in or more.

In the secondary cooling zone 22 of the continuous casting machine 10,
A large number of spray nozzles (mist nozzles) arranged in the width direction of the continuous cast piece 12 (a direction substantially orthogonal to the conveying direction) is arranged between the conveying rollers of the continuous cast piece 12, and water spray or mist spray is performed from the spray nozzles. By injecting
Secondary cooling of the continuous cast piece 12 is performed.

Here, in the continuous casting machine 10, the operation of the spray nozzles arranged in the width direction is controlled according to the width of the continuous casting piece 12 to be manufactured, and cooling is performed without waste. . That is, as shown in FIG.
, Where spray nozzles a, b, c ... Are arranged, and the width of the continuous cast piece 12 is w ₁ , a, b, c ...
... When the spray is sprayed from all spray nozzles and the width of the continuous cast piece 12 is w ₂ , the spray injection from the spray nozzles a and b is stopped according to the width, and the inside from the spray nozzle c is stopped. The continuous casting piece is cooled by the spray nozzle of (as well as the opposite end portion).

In the continuous casting method of the second aspect of the present invention, in at least one zone of the secondary cooling zone 22, the spray corresponding to the end of the continuous cast piece 12 stops the cooling water and continuously casts. Secondary cooling of piece 12 is performed (however, continuous cast piece 12
Unless the width of the spray band is wider than the width of the spray band and it is not necessary to stop the cooling water at the end).

As described above, the vertical bending type continuous casting machine 10 used in the present invention can realize a long machine length while having the advantages of the continuous casting machine having the vertical portion. However, in the vertical bending type continuous casting machine 10, it is inevitable that the continuous casting piece 12 is deformed twice in the upper bending portion and the lower straightening portion. The distortion of the continuous cast slab 12 due to this deformed portion is caused by the temperature of the continuous cast slab in a specific region, particularly 850 described above.
If it is in a supercooled state such as ℃ or less, it will cause cracks at the corners of the continuous cast piece 12.

On the other hand, in the second aspect of the present invention, in at least one zone of the secondary cooling zone 22, the cooling water by spraying corresponding to the end of the continuous cast piece 12 is stopped (hereinafter referred to as width). Cut it). That is, in the example shown in FIG. 4, when the width of the continuous cast piece 12 is w ₁ , the spray nozzle a corresponding to the corner portion of the continuous cast piece 12 is stopped so that the inside from the spray nozzle b is stopped. The continuous spray slab is cooled by the spray nozzle of (also at the opposite end),
When the width of the continuous cast piece 12 is w ₂ , in addition to the spray nozzles a and b according to the width, the spray nozzle c corresponding to the corner portion of the continuous cast piece 12 is also stopped, and The continuous cast piece is cooled by a spray nozzle.

With such a structure, it is possible to prevent overcooling of the continuous cast piece 12, particularly overcooling of the corners, and to prevent continuous cooling of the continuous cast piece 12 due to distortion in the bending and straightening sections of the continuous caster 10.
It is possible to preferably prevent cracks in the corners of the product and further improve the product yield.

In particular, when cooling is performed with a mist spray, by stopping only the water of the spray corresponding to the corner and spraying the air spray, the water sprayed from other sprays by this air spray is stopped. Can be prevented from cooling to the corners or end faces of the continuous cast slab 12 and cooling this part more reliably, preventing cracks in the corners of the continuous cast slab 12 and realizing a higher product yield. You can

In the continuous casting method according to the second aspect of the present invention,
There is no particular limitation on the zone in which the width cutting is performed, and there is no limitation to perform the width cutting in all the spray nozzles in the zone in which the width cutting is performed.

In order to surely prevent cracks at the corners of the continuous cast piece 12, it is preferable that the width cutting be performed at least at the bent portions. In this region, strong cooling is necessary to suppress bulging (bulging caused by the pressure of unsolidified molten steel), but the corners are supercooled by this strong cooling, and the continuous cast pieces 12 are bent and straightened. Will cause cracks. Therefore, width cutting in this region is very effective in preventing cracks at the corners of the continuous cast piece 12. Further, ensuring the surface temperature of the continuous cast piece 12 in the straightening portion, particularly the surface temperature of the corner portion, has a great effect on preventing cracking. Therefore, if possible, it is preferable to perform the width cutting also in the correction unit.

Here, the intensity of the secondary cooling is greatly influenced by the water amount distribution (in the case of mist spray, it is further the air / water ratio). Since the air-water ratio of the mist spray varies depending on the high temperature strength of the continuous cast piece 12 and the method of performing secondary cooling, it is difficult to uniquely determine the limit. On the other hand, although the water amount distribution will be described in detail later in Examples, according to the study by the present inventors, when continuously casting high carbon steel by the vertical bending type continuous casting machine 10, continuous casting is performed. By injecting (injecting) 40% or more of the total amount of cooling water by the end of bending of the piece 12 (the second zone 22b in the illustrated example), it is possible to significantly reduce the occurrence of internal cracks and surface cracks in the continuous cast piece 12. You can

According to a study by the present inventors, in order to produce a sound continuous cast piece of high carbon steel in a vertical bending type continuous caster, strong cooling to the extent that bulging does not occur is required, Moreover, it is effective to inject a large amount of cooling water in the initial stage until the end of bending. That is, by strongly cooling the continuous casting piece 12 in the upper part of the continuous casting machine 10, a shell that is relatively strong at the initial stage of solidification is formed, and bulging is suppressed.
In addition, the continuous casting speed can be secured while preventing internal cracking of the continuous cast piece 12.

The amount of cooling water to be poured by the time the bending of the continuous cast piece 12 is completed is preferably about 50 to 65% of the total amount of cooling water. By setting the amount of cooling water in this range, it is possible to more preferably prevent the continuous cast piece 12 from cracking.

Further, in the second aspect of the present invention, the bending portion and / or the straightening portion of the secondary cooling zone 22 of the continuous casting machine 10, that is, the second zone 22b and / or the fourth zone 22d is divided. Use a roller.

The transport roller 24 constituting the secondary cooling zone 22 of the continuous casting machine 10 holds (holds) the continuous casting piece 12 with a strong force in order to prevent bulging of the continuous casting piece 12. In particular,
In the bending part and / or the straightening part of the continuous casting machine 10,
Since the continuous cast piece 12 is forcibly curved or deformed into a linear shape, a very large force is applied to the conveying roller 24 in this portion. Moreover, in the continuous casting method of the present invention, since the continuous cast piece 22 is bent in a non-solidified state, and in some cases straightening is performed in the unsolidified state, a large pressure of unsolidified molten steel is applied to the shell of the continuous cast piece 12. Barbs (especially bending and straightening)
Easy to cause bulging. Therefore, the conveying rollers 24 of the bending portion and the straightening portion in particular bend without sustaining the force, which causes deformation such as bulging or distortion of the continuous cast piece 10 or cracks of the continuous cast piece 10, It becomes impossible to manufacture high quality products.

On the other hand, in the second aspect of the present invention, the dividing roller is used in the bending portion and / or the straightening portion so that the distortion of the conveying roller 24 can be minimized. The dividing roller is a roller divided into a plurality (two in the illustrated example) in the width direction W of the continuous cast piece 12 as shown in FIG.

Split roller 24A shown in FIG. 5 (a)
Has two rollers 24A-1 and 24A-2, and each roller has an independent rotating shaft 26-1.
And 26-2. Further, the rotary shaft 26-1 is rotatably supported at its ends by bearings 28 and 30, while the rotary shaft 2
The end portion 6-2 is rotatably supported by bearings 32 and 34, and each roller is rotatably supported.

Further, FIG. 5B shows another type of split roller 24B. In this example, the two rollers 24B-1 and 24B-2 are supported by one rotating shaft 36 with a slight gap in the middle in the width direction. Both ends of the rotary shaft 36 are pivotally supported by bearings 38 and 40, and the intermediate portion is pivotally supported by a bearing 42.

In such a split roller, since the rotary shaft is supported by bearings not only at both ends of the rotary shaft but also between the rollers, a large force is exerted at the bending portion and the straightening portion of the continuous cast piece 12. Even if it is applied, the distortion of the roller is extremely small.
Therefore, continuous cast piece 1 such as bending strain, correction strain, and bulging strain
It is possible to minimize the strain and deformation that occur in No. 2 and prevent the occurrence of cracks, and it is possible to stably manufacture high-quality products with a high yield.

In the continuous casting method of the present invention, the dividing roller to be used is not limited to the two-divided roller shown in the figure, and three or more divided rollers may be used. The continuous cast piece 12 is not supported between the divided rollers, and bulging is likely to occur. Therefore, it is preferable to make the distance between the rollers as small as possible, such as downsizing the bearing. . Further, it is not necessary to use all of the conveying rollers of the bending portion and / or the straightening portion (the second zone 22b and / or the fourth zone 22d) as the dividing rollers, and even if the dividing rollers are used only in the places where the force is particularly applied. Good. Further, if necessary, split rollers may be used in addition to the bending portion and the straightening portion.

Further, in the second aspect of the present invention,
Continuous casting is performed at a speed of 0.8 m / min or more. As mentioned above, in order to perform efficient continuous casting, it is essential to improve the casting speed. Here, according to the study of the present inventors, by setting the casting speed to 0.8 m / min or more, high production efficiency can be realized, and high-efficiency production of high-carbon steel can be realized. it can.

Further, as described above, in the vertical bending type continuous casting machine 10, in order to prevent the continuous casting piece 12 from cracking, it is very important to secure the temperature of the continuous casting piece 12 during bending and straightening. Therefore, the improvement of the casting speed is also important for that. Moreover, as will be described later in detail in Examples, when the casting speed is less than 0.8 m / min, surface cracks of the continuous cast pieces 12 are likely to occur, resulting in a decrease in product yield.

Preferably, the casting speed is 1.0 to 1.2 m /
By setting it to about min, more preferable results are obtained in terms of energy efficiency, prevention of cracks in the corners of the continuous cast piece, and the like.

Although the continuous casting method of the present invention has been described above in detail, the present invention is not limited to this and various modifications and improvements may be made without departing from the scope of the present invention. Is.

[0049]

EXAMPLES The present invention will be described in more detail with reference to specific examples of the present invention.

The carbon content was 0.3-1 ..% by the processes of hot metal pretreatment, electric furnace conversion, and secondary refining.
Various 2% high carbon steels were melted. Using this molten steel,
In the vertical bending type continuous casting machine with a machine length of 30 m (5 m until the end of bending) shown in Fig. 5, various thicknesses of the continuous casting conditions are changed to a thickness of 0.18 m to 0.3 m, a width of 0.8 m to 1.65 m, and a long length. Various continuous cast pieces having a length of 5.0 to 9.0 m were manufactured. The following various characteristics were investigated for these continuous castings.

FIG. 6 shows the end of the continuous cast piece in the secondary cooling zone up to a distance of 5 m from the meniscus in the above various continuous castings of various high carbon steels having a carbon content of 0.8 to 1.2%. The cracking occurrence rates of the continuous cast piece corners when the cooling water by spraying corresponding to (1) is stopped (width cutting) and when the width cutting is not performed are shown. The continuous casting speed is 0.8 m /
It was set to min.

As shown in FIG. 6, by performing the width cutting, the occurrence of cracks at the corners of the continuous cast piece can be significantly reduced, and the product yield can be greatly improved. On the other hand, when the width cutting was not carried out under the above conditions, the 60% continuous cast piece cracked at the corners.

FIG. 7 shows the index of internal crack generation when the amount of cooling water until the end of bending of the continuous cast piece (that is, the second zone) was changed in the various types of continuous casting described above. The casting speed was 1 m / min. Further, this index is an index obtained by quantifying the length of the internal crack generated per unit cross-sectional area of the continuous cast piece and calculating this value by the ratio.

As described above, in order to produce a sound continuous cast piece of high carbon steel in a vertical bending type continuous caster, strong cooling to the extent that bulging does not occur is required, as shown in FIG. As described above, by injecting 40% or more of the total amount of cooling water until the end of bending, the occurrence of internal cracks can be significantly reduced.

FIG. 8 shows the surface crack occurrence rate when the continuous casting speed was changed in the same continuous casting in the vertical bending type continuous casting machine.

As shown in FIG. 8, in continuous casting of high carbon steel by unsolidified bending using a vertical bending type continuous casting machine, cracking occurred by setting the casting speed to 0.8 m / min or more. Can be prevented, and in this respect also, it is important to increase the continuous casting speed to some extent.

Among the various examples above, various casting conditions and internal and surface crack generation indexes in continuous casting of high carbon steel having a carbon content of 0.8% are summarized in Table 1 below. .

[0058]

[Table 1]

The above example corresponds to the first and second aspects of the present invention shown in FIG. 1 in which bending and straightening are performed in a state where a part of the cast piece is not solidified. But,
Similar results were obtained in the second aspect of the present invention in which the correction is performed in the completely solidified state.

[0060]

As described above in detail, by utilizing the continuous casting method of the present invention, the carbon content of 0.3
% High-carbon steel and special steel with excellent production efficiency, and with high product yield with very few defects due to surface and internal cracks and inclusions, it is possible to manufacture stable, high-quality products. it can.

[Brief description of drawings]

FIG. 1 is a view conceptually showing a continuous casting machine for carrying out the continuous casting method according to the first and second aspects of the present invention.

FIG. 2 is a view conceptually showing a continuous casting machine for carrying out another example of the continuous casting method according to the first and second aspects of the present invention.

FIG. 3 is a graph showing the relationship between the carbon content of high carbon steel and the surface crack initiation index.

FIG. 4 is a schematic diagram for explaining width cutting of cooling water according to a second aspect of the present invention.

FIG. 5 is a conceptual diagram showing an example of a split roller used in the second aspect of the present invention.

FIG. 6 is a graph showing the occurrence rate of cracks at the corners of continuous cast pieces in the case where width cutting is performed in the secondary cooling zone in continuous casting of high carbon steel and in the case where width cutting is not performed.

FIG. 7 is a graph showing the relationship between the amount of cooling water until the end of bending and the index of occurrence of internal cracks in continuous casting of high carbon steel.

FIG. 8 is a graph showing the relationship between the casting speed and the continuous cracking surface crack occurrence rate in continuous casting of high carbon steel.

[Explanation of symbols]

 10 Continuous Casting Machine (Continuous Casting Machine) 12 Continuous Casting Piece (Continuous Casting Piece) 14 Torch 16 Tundish 18 Immersion Nozzle 20 Mold 22 Secondary Cooling Zone 24 Conveying Roller 26, 36 Spindle 28, 30, 32, 34, 38 , 40, 42 bearings

Claims (2)

[Claims] 1. When continuously casting a steel material containing 0.30% or more of carbon, a vertical bending type continuous casting machine is used to bend a cast piece in a non-solidified state and to cast a non-solidified piece. A continuous casting method characterized by straightening in a state or straightening after complete solidification. 2. When continuously casting a steel material containing 0.30% or more of carbon, a continuous bending machine of a vertical bending type is used to bend the cast piece in an unsolidified state, and the unsolidified state of the cast piece. Straightening or straightening after complete solidification, and in the secondary cooling zone of the continuous casting machine, 40% or more of the total cooling water amount is injected by the end of bending, and casting is performed in at least one zone of the secondary cooling zone. The present invention is characterized in that cooling water at one end is shut off, and a dividing roller is used in a bending portion and / or a straightening portion of the secondary cooling zone to perform continuous casting at a casting speed of 0.8 m / min or more. Continuous casting method.