JP3218361B2 - Continuous casting of steel and continuous casting and rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a continuous casting method for steel materials,
And a method of performing continuous casting and hot rolling in combination,
In particular, we have developed a continuous casting method that can dramatically increase the casting efficiency and improve the quality of cast slabs.In addition, by combining this continuous casting method with hot rolling, it is possible to continuously integrate hot-rolled steel from continuous casting. It relates to a continuous casting / rolling method that can be produced.

In order to drastically reduce the production cost of hot-rolled steel, a method of directly connecting a continuous casting process and a hot-rolling process has been proposed. There is a need for a method of making a continuous casting method, which is regarded as a net shape process, closer to a net shape. They are not contradictory, have a common purpose and a common technical task, and their fusion will be the most desirable production system. Although some low-grade steel sheets have already reached the level of actual production, medium-grade steel and higher and other steel sheets are difficult. The following are two representative technical issues related to direct connection and near net shaping.

[0003] 1. The upper and lower processes have almost the same production efficiency. In the conventional continuous casting method, the casting efficiency per strand is about a fraction of the subsequent rolling efficiency, and it is extremely inefficient if the upstream continuous casting process and the downstream rolling process are only directly mechanically connected. . Alternatively, if the hot slab is directly fed and rolled from continuous casting of multiple strands, the efficiency is balanced but the direct coupling effect is greatly reduced. On the other hand, large sections and large machine lengths of slabs are being used to improve continuous casting efficiency.However, in the former case, a break-down process is indispensable and direct connection is naturally impossible, and in addition, near net shape Would go against the flow to In the latter case, the efficiency has been considerably improved in slabs and blooms, but the rolling efficiency is two to three times higher than the continuous casting efficiency, and there is basically no direct connection possible. From the above, to dramatically improve continuous casting efficiency,
There is also a long-awaited need for relatively small-to-medium-scale rolling equipment at a cost. Recently, this problem has been solved for steel sheets by continuous thin slab casting and strip casting, but is limited to low-grade steel sheets due to quality problems described below.

[0004] 2. To have the same level of quality as before. In the current production systems are operated independently with the continuous casting, rolling both steps, because it is their own quality control, quality that is appropriate to the purpose the product is reliably ensured. In addition, by performing intermediate processes such as breaking down, slab refining, and reheating, both surface quality and internal quality have been improved. Therefore, if the small-section continuous casting is directly connected to rolling as it is, the quality naturally deteriorates.

[Prior art]

[0005] Continuous thin slab casting: CSP process Reference (1) "SEAISI, Jan. 1990, P.3"
As shown in FIG. 8 ", the method comprises continuous casting of a thin slab of about 50 mm thickness and continuous rolling to a steel sheet of about 3 mm thickness directly connected to the slab. In this method, the space in the short width direction of the mold section is about 50 mm. Is extremely narrow because of the operation
There are many difficulties in quality. For example, in a mold, an immersion nozzle + powder casting method, which is naturally required for quality maintenance, is applied. In this method, only a immersion part called a funnel type having a space for setting an immersion nozzle is wide. Requires a specially shaped template. In this case, there is a problem that an excessive force acts on the thin solidified shell, which is disadvantageous in generating vertical cracks and horizontal cracks, and that the slab width is too thin to make smooth powder casting difficult. As described further, the thin cast slab during solidification has a very large temperature gradient from the slab surface to the center, which is advantageous for refining grains and reducing segregation, but it has surface cracks and internal cracks. Has a common drawback that the thin wall is likely to occur. In addition, the solidification end point, which is inevitable in the casting process, is formed,
Center segregation is necessarily present. Therefore, products are limited to relatively low-grade products.

[0006] Thin slab continuous casting: ISP process Literature (2) "SEAISI. Jan. 1990. P. 2"
As shown in 3 ", the present method is to provide a continuous casting of a thin slab having a thickness of 50 to 100 mm with a roll reduction device to reduce the unsolidified slab or the slab after the solidification is completed to a thinner slab. The immersion nozzle + powder casting method is applied similarly to the reference (1) .In this method, the problem of the mold described in the preceding paragraph has been solved by using a rectangular cross-section mold and a flat nozzle, but the above-mentioned method is common to thin-walled slabs. There are all the weak points, and the reduction of the unsolidified slab increases the risk of cracking, and the risk of specific segregation accompanying cracking increases, making quality control difficult.

[0007] Strip continuous casting method A method of casting a steel sheet or a steel sheet material having a thickness of several mm directly from molten steel. The mechanism is to cast molten steel between rotating twin rolls to instantaneously adhere the solidified surfaces to each other. Several mm
It forms slabs of thickness x (1000-2000) mm width. The production line is extremely compact and lightweight, and many heating furnaces and expensive rolling equipment are omitted.
The effect of reducing equipment costs is extremely large. In addition, the operating costs are of course greatly improved. However, in this method, the cast steel sheet is instantaneously solidified and formed.
Surface defects such as thermal stress cracking and running out of hot water are easy to occur. In addition, subtle fluctuations in the heat flow velocity to the cooling wall immediately affect the solidified shell thickness and internal stress, causing internal defects and other extremely difficult quality problems. It is unlikely to be applicable to high-quality steel sheets due to its high content and lack of forging ratio, etc.It is being developed for low-grade products or stainless steel sheets, and has been put to practical use in only a part. It's just

Hollow slab pressure welding method Japanese Patent Application Laid-Open No. 57-97842 proposes a continuous casting method without center segregation and a method of directly connecting it to hot rolling. In the present method, a curved slab trajectory is guided higher than the casting surface, and an unsolidified portion inside the slab is left to form a vacuum cavity, and the hollow slab is rolled to form a solid slab. Can be As a result, eliminating center segregation, control of slab thickness,
Although effects such as production of thin slabs are described, defects such as semi-macro segregation, porosity, and V segregation which are usually widely distributed around the core in terms of quality cannot be solved. On the production side, there is no mention as to whether the casting efficiency is reduced by the reduction of the substantial cross section or, on the contrary, is improved by any means or means. From these two sides, the validity of the combination of continuous casting and rolling and the near net shaping is unclear.

[0009]

SUMMARY OF THE INVENTION As described above, the direct connection between continuous casting and rolling represented by the thin slab continuous casting method,
The net shape method has many problems. However, if these problems can be solved and applied to not only thin plates but also thick steel plates, as well as thick or small diameter bars, flat bars, wire rods, etc., the effect is extremely large. For this purpose, the casting efficiency should be dramatically improved without increasing the cross section of the slab in continuous casting, the casting defect in the central part, the inside or the surface should be eliminated, and the cross section of the slab should be as small as possible. It is a specific issue to simplify the rolling equipment by making it near-net-shaped and to improve the equipment cost to performance ratio.

The present invention has been made in view of such circumstances, and its main object is to dramatically improve casting efficiency by improving a normal curved continuous casting method, and to achieve good surface quality. To provide a continuous casting method that can exhibit the effects of obtaining a homogeneous internal structure, eliminating core defects, and easily obtaining cast pieces having an arbitrary thickness and shape. Things. The horizontal continuous casting method can be improved by using the principle of the present invention. Another one
One of the objectives is to efficiently connect the improved continuous casting method described above and the subsequent hot rolling to integrate hot rolling products such as steel plates, steel bars, flat bars, shaped steel bars, and wire rods from casting. And to provide a method of producing.

[0011]

Next, the configuration of the present invention which can solve the above-mentioned problems will be described. (1) First, the improvement of the continuous casting method will be described as follows. The basic configuration of the continuous casting method of the present invention is as follows. The liquid core inside the slab is kept at a specific point Q on the slab withdrawal locus.
The main point is that an air core is formed inside the slab downstream of the point and the air core portion is pressed into contact with a roll to be drawn as a solid slab. Particularly, in a typical embodiment of the present invention, the cross-sectional shape of the mold is rectangular, and the invention is disclosed in Japanese Patent Application No. 5-3210.
In the same manner as shown in 96, at least immediately after the slab drawing locus is discharged from the mold, a curved die continuous casting of a steel material which performs bending drawing is performed, and the curved length in the slab drawing locus is set to の of the circumference. As described above, the slab is pulled out to a position higher than the casting surface, and a position higher than the casting surface by the height of the static molten steel head corresponding to the atmospheric pressure head is defined as a specific point Q, and the solidification shell thickness ratio α at the point Q is α (= 2 d / A) is 0.2
The gist should be 5 to 0.85. In the formula, d: slab solidification shell thickness (m) A: short width dimension of the mold cross section (m)

In such a continuous casting method, by setting the casting temperature to a range higher by 20 to 60 ° C. than the liquidus temperature of the steel type, the inside of the chill crystal having a thickness of several mm of the cast slab is substantially reduced. The inside of the chill crystal with a thickness of several mm of the slab skin is substantially formed by using a solid slab such as a columnar crystal or a range higher by 0 to 15 ° C. and applying electromagnetic stirring to molten steel in the mold. A solid cast slab having a granular structure can be obtained.

In order to concretely carry out the method described in the paragraphs 0011 and 0012, it is preferable to set equipment specifications and casting conditions according to the following equations (1) to (5). Pn = 4k ² ρ · Ln · [(1 / α) + (β / α) -1] ··· (1) V = Ln · (2k / αA) ² ··· (2) R = (Ln-1.4) / π (3) d = k (Ln / V) ^0.5 (4) A ′ = 2 (1−p) · d (5) where Pn: casting efficiency (kg / min) ) Ρ: Steel material density (7600 kg / m ³ ) Ln: Machine length (length between casting surface and specific point Q: m) k: Solidification constant 0.023 to 0.031 (m / min)
^0.5 ) R: radius of the curved portion in the slab drawing locus (m) B: mold cross-sectional length (m) α: solidified shell thickness ratio 0.25 ≦ α ≦ 0.85 β: rectangular ratio β = B / A A ': Short width thickness (m) of cross section of solid cast slab p: Substantial reduction ratio by pressing roll = (2d-A') /
2d = 0.05 to 0.40

Advantageous conditions for manufacturing a high-grade steel sheet from a thin slab or a thick slab are described as follows.
In addition to the method described in Section 12, the short width dimension A of the mold cross section is set to 0.100 to 0.300 m, and the thickness d of the slab solidified shell immediately before pressure welding is set to 0.025 to 0.120 m. The entire width of the strip is pressed in the short width direction to obtain a short width thickness A ′ of the solid cast piece.
Is set to 0.035 to 0.200 m.

[0015] In producing a beam blank, a near-net-shaping method is used. As a pressure welding method for adhering the air core inside the slab by pressure welding, a hole rolling method or a universal mill is used. It is recommended that the cross-sectional shape of the solid slab be changed to an I-shape, H-shape or the like by pressing and rolling by a four-side simultaneous rolling method.

As a means for reducing the thickness of the solidified shell, as a means for shortening the machine length, the curved length in the slab withdrawal trajectory is set to a half or more of the circumference and the slab is raised to a position higher than the casting surface. The method is not limited to the method of drawing, and the lowermost point of the arc is defined as the specific point Q with the curved length in the slab drawing locus exceeding 1/4 of the circumference, and the slab is drawn to a position higher than the Q point. It is also possible to adopt a method in which the liquid core inside the slab is kept in the vicinity of the point Q near the point Q, and the inside of the slab downstream of the point Q is filled with an inert gas under pressure to form an air core. it can. It is desired that the solidified shell thickness ratio due to the formation of the air core is controlled to 0.05 to 0.5.

Advantageous conditions for producing a general steel sheet are as follows: In section 0016 , the short width dimension A of the mold cross section is set to 0.100 to 0.140 m, and the slab solidification shell thickness d at point Q is set. Is set to 0.010 to 0.020 m, the shell thickness d is set according to the equation (6) so that the solid cast slab short width thickness A 'is set to 0.012 to 0.03 m, and the actual reduction by the pressing roll is performed. The ratio p is set to 0.05 to 0.4. d = k · (πR ′ / 2V) ^0.5 (6) R ′: radius of bending portion (m) in slab drawing locus

Particularly preferred for a thinner solidified shell thickness is that the mold 3 surface is formed by a rectangular groove formed along the outer periphery of a water-cooled wheel rotating in a vertical plane, and the endless mold is formed.
This is a method in which a mold in which a belt is brought into close contact with the groove so as to close the solidification progressing section and the remaining one surface is formed is driven in synchronization with the drawing of the slab.

(2) Next, the invention in which the rolling method is directly connected to the continuous casting method will be described as follows. First, most basically, the solid red slab produced by the above continuous casting method is 1) cut once to form a steel slab.
Or 2) as a continuous cast slab, a) after soaking through a soaking furnace or b) directly to a single-strand rolling line without passing through a soaking furnace, to supply a steel sheet, a shaped steel, a flat steel,
The method of rolling into bar steel, wire rod, etc. is shown. Further, between the rough rolling and the finish rolling, the rolled material can be cut into two or more strips in the rolling direction and supplied to different or identical finish rolling lines to perform product rolling. In these, especially when a wire is manufactured, the unit weight of the wire coil is 3 to 20 tons.

[0020]

The structure, operation and effect of the present invention will be described below in detail with reference to the accompanying drawings. In the present invention, Japanese Patent Application No.
As shown in -321096, an ordinary curved continuous casting facility is used as a prototype, and a facility having an overall structure as shown in FIG. 1 is used. FIG. 2 is an enlarged explanatory view of a main part of FIG.
The molten steel Me supplied from the ladle 1 to the mold 3 via the tundish 2 is cooled by the mold 3 to form a solidified shell, and becomes a slab 6, which is drawn out by a pinch roll 10 and a guide roll 9. . At this time, the drawing trajectory of the slab 6 is set to an arc shape with a radius R and at least 1/2 of the circumference, and a position higher than the casting surface L of the molten steel Me (that is, the molten steel surface level in the mold). Then, as shown in the enlarged explanatory view of FIG. 2, the slab 6 is pulled out, and as shown in the enlarged explanatory view of FIG. Then, the liquid core Lq exists up to the position Q in the slab 6, and a vacuum air core Cv is formed downstream thereof. The air core portion S is pressed down from the outer surface by a press roll 8 to press it into a solid slab, and subsequently sent to a tandem type rough rolling row 15 via guide rolls 9 and shears 13 to finish rolling row. Winding machine 19 through 18
Is wound as a hot-rolled product by the concentrator 20 to form a coil. During this time the billet 6 is continuously rolled without cutting, but that the divided during focusing in accordance with the unit weight of the products most desirable.

In the above, in the continuous casting of steel, at the specific point Q of the slab drawing locus, the liquid core in the slab is discharged to the upstream side to form an air core portion on the downstream side, and the air core portion is pressed and rolled. Various methods are conceivable as described later in a specific embodiment of a continuous casting method characterized by being drawn out as a solid slab.

In such a continuous casting method, there are various effects and actions in addition to the following three essential effects. 1) Improvement of casting efficiency 2) Elimination of core defects 3) Production of thin-walled cast pieces Examination of casting efficiency: The theoretical casting efficiency Po is obtained by equation (7) when one piece has a square cross section of A (m). . Po = ρ × A ² × V (7) [ρ: steel density kg / m, V: drawing speed m / min] The progress of solidification is represented by the well-known solidification approximation formula (8). It is. d = k × t ^0.5 (8) [d: solidified shell thickness m, k: solidified constant m / min ^0.5 ,
t: time min] The machine length L, that is, the length of the solidification section, is expressed by equation (9). L = V × to (9) [to: solidification completion time min] Since d = A / 2 at t = to, (8), (9)
From the formula, A ² V = 4k ² L (10) When this is substituted into the formula (7), Po = 4ρk ² L (11) Theoretical casting efficiency when the slab section is rectangular. Po 'is (1
2) Po ′ = 4ρk ² βL (12) [β: rectangle ratio = long piece size / rectangular piece size] That is, the casting efficiency is independent of the cast piece size and is proportional to only k and the machine length L that depend on the cooling strength. . In actual operation, due to quality and work restrictions, the casting efficiency is at most 60 to 8 theoretical values.
At 0%, the required number of strands is determined based on this substantial efficiency. If L is further increased to improve efficiency, problems such as quality, work, and equipment cost are further amplified due to an increase in the drawing speed V.

On the other hand, in the present invention, in the case of a rectangular cross section, the theoretical casting efficiency Pn is expressed by equation (13) with the solidified shell thickness ratio α (= 2d / A) as a parameter. Pn = 4ρk ² Ln (1 / α + β / α-1) (13) The machine length Ln in the present invention is from the casting surface to the point Q.
When the conventional method and the present invention are compared under the same machine length (that is, Ln = L), Expressions (12) and (13) are combined into Expression (14). Pn = Po '(1 / α + β / α-1) / β (14)

Next, each basic characteristic of the casting machine and the casting conditions will be described. By the same calculation as above, the casting efficiency P
n, drawing speed V, bending radius R, shell thickness d, and solid slab thickness A ′ are (1), (2), (3), (4),
It is easily related by equation (5). For example, drawing speed V
Equation (2) can be easily obtained from the following equation: V = Ln / tn, dn = k · tn ^0.5 = αA / 2. [Tn:
Time to reach specific point Q (min), shell thickness at dn: Q (m)] The solidified shell thickness ratio α is 0.2 in order to correspond to steel materials of various thicknesses.
5 to 0.85 is desirable. The actual reduction ratio p is used as it is because 0.05 to 0.40 is employed in normal pressure rolling. In carrying out the present invention, it is an important requirement that continuous casting conditions be set so as to satisfy the relations of equations (1) to (5). As described above, the first effect of the present invention is that the casting efficiency is dramatically improved. Improvements in casting efficiency necessarily lead to an increase in drawing speed. Increasing the drawing speed causes quality deterioration such as core defects and internal cracks, and work accidents such as breakout. Such a problem is solved by the following second effect.

Next, a description will be given of a second effect and improvement of quality such as elimination of a core defect. In the casting of steel, the solidification structure is rapidly cooled from the surface to the center of the skin (usually about several mm) to form a dense and uniform chill crystal, and several mm to several tens of mm inside the steel itself are homogeneous. Columnar crystals, and the inside is composed of granular crystals. In the vicinity of the core, casting defects such as semi- and macro-segregation and macro- and micro-shrinkage pores occur between the granular crystals. In the center, the distribution of solutes in the solid and liquid phases in addition to the center shrinkage holes Inevitably, center segregation occurs. In the conventional continuous casting method for these internal defects, measures such as dispersing defects by granular crystallization and miniaturization by low-temperature casting or electromagnetic stirring, and removing segregation by liquid core pressure have been taken. Both are insufficient, and in particular, semi-macro-segregation around the core and porosity are not improved. To obtain a particularly homogeneous solidification structure, use the unidirectional solidification steel ingot method instead of continuous casting.
P. 304 "and ESR (Electroslag Remelting). In the present invention, in continuous casting, ESR
A homogeneous tissue comparable to the method can be obtained. In other words, the structure of the slab obtained by the present invention essentially forms chill crystals, columnar crystals, and granular crystals inside thereof, as in conventional continuous casting, but the solidification shell thickness ratio is appropriately set. Therefore, semi-macro segregation, macro-
The liquid core is separated before reaching a state where microscopic shrinkage or the like is generated, and the solidification front surface is pressed against the liquid core. In addition, setting the optimum casting temperature further increases the effect of eliminating internal defects according to the present invention. That is, when the casting temperature is set to a higher value corresponding to the slab size, even granular crystals are not generated at all, and a dense and homogeneous structure of substantially only chill crystals and columnar crystals is formed, similar to the unidirectionally solidified steel ingot. become. Even in general slab continuous casting, if the casting temperature is raised, it is relatively easy to make columnar crystals up to the center,
In this case, the center of segregation is inevitably formed by the aggregation of the concentrated molten steel existing at the solid-liquid interface due to the abutment of solidification from both the front and back surfaces, so that a simple columnar crystal structure does not provide a homogeneous steel material. On the other hand, the growth properties of columnar crystals become more pronounced as the slab cross-sectional dimension increases, but they mainly depend on the casting temperature and cannot be determined deterministically due to other factors. For example, "No. 69,7
0th Nishiyama Memorial Lecture (Iron and Steel Institute of Japan) (1980) P171:
FIG. 3 according to the present invention is obtained by rearranging FIGS. 31 and 32 shown in “Shield” and shows the effect of casting temperature (degree of superheat) on the growth of columnar crystals. According to FIG. 3, when the degree of superheat changes from 20 ° C. to 50 ° C., the columnar crystal length becomes about 0.0
It can be seen that it increases from 80 m to about 0.150 m. However, when electromagnetic stirring is applied to this, the columnar crystal length becomes shorter. Therefore, in the present invention, in the case of a small-section slab, the lower limit of the degree of superheat is set to 20 ° C. in order to obtain a columnar crystal length of at least 0.060 m.
In order to obtain 60 m, the upper limit of the degree of superheat was set to 60 ° C. However, as the degree of superheat increases, internal cracks and surface cracks due to thermal stress are more likely to occur. Therefore, it is preferable to set the temperature in the above range as low as possible. As described above, according to the second effect of the present invention, it is possible to obtain a homogeneous solidified structure having no core defect,
In some cases, it can be replaced by a directionally solidified ingot method or an ESR method.
In addition, even when the hot forging ratio is insufficient in the near net shaping, the homogeneous solidified structure obtained by the present invention can make up for it.

In some products, such as stainless steel, the growth of columnar crystals is disturbed and a structure with many granular crystals may be preferred. In such a case, low temperature casting (superheat degree 0
15 ° C.) and electromagnetic stirring of the molten steel in the mold. However, when applying this means to the present invention, if the value of the solidified shell thickness ratio α is appropriately taken, semi-fluidity around the core, which has been inevitable in the past, can be avoided. The occurrence of macro segregation, macro and micro shrinkage pores and V segregation can be eliminated.

The effect of the present invention on the increase in defects associated with high-speed casting will be described in relation to quality problems. A major drawback of high speed casting is that bulging tends to occur. This can cause internal cracking and breakout. In particular, if the cross section is large, it is very difficult to prevent it. In the present invention, the machine height is reduced to a fraction of the conventional height by the principle that the machine length is extremely small and that the machine is pulled upward. Therefore, the molten steel static pressure acting on the solidified shell is reduced by that amount, and bulging is less likely to occur.

Next, a third effect, that the near net shape process can be easily performed, will be described. In the present invention, the slab cross-sectional shape and dimensions are made the same as in normal slab continuous casting, the machine length, that is, the slab trajectory arc radius is made as small as possible, and the drawing speed is made as large as possible. And thin. That is, a thin slab can be easily manufactured simply by changing the drawing direction of the conventional continuous slab casting. Naturally established techniques such as immersion nozzle + powder-cast method and electromagnetic stirring which have a great effect on the surface quality can be used as they are. This is the reason why the slab cross-sectional short width dimension is limited to 0.100 to 0.300 m. Solidifying shell thickness minimum value reason for the 25mm of d is based on the smaller of course economical, but a practical minimum of R 2m, the maximum value 5 to 6 m / min and V,
If the minimum value of k is set to 23 mm / min ^0.5 , d becomes about 0.025 m.
Similarly, for A ', the maximum of the actual rolling reduction p by the pressing roll was 0.3, and the lower limit of A' was 0.035 m.
The thin slab obtained as described above has excellent surface quality equivalent to that of a conventional slab. A hot-rolled thin plate can be easily produced in the process.

To cast a beam blank, see FIG.
(A), a thin square tubular hollow core cast piece 22 as shown in FIG.
When it was pressed and pulled out as a solid slab,
The four faces simultaneous reduction by universal mill 34 shown in caliber rolling mill 32 and FIG. 4 (c) shown in (b), if the cross-sectional shape of the solid slab or the like type I 31, H-type 33, the conventional Near-net /
Become a shape. In addition, excellent quality in both surface and internal quality can be easily obtained without encountering quality problems due to peculiar shapes such as surface cracks, internal cracks, and segregation unlike conventional beam blank continuous casting.

If it is desired to manufacture a thinner slab than the one described above, a new device is required to implement the present invention. It will be described next. In order to reduce the wall thickness, it is necessary to minimize the solidification time by minimizing the machine length and maximizing the drawing speed as shown in equation (4). For this purpose, it is recommended to use a gas pressure to place the specific point Q at the lowest point of the slab drawing arc. The outline is shown in FIG. In this case, the shell thickness d is calculated by equation (6). The reason for limiting the solidified shell thickness ratio to 0.05 to 0.5 is that the shell thickness is naturally reduced in a region smaller than 0.05, and is actually 10 mm or less. This thickness is usually formed in the mold, but the progress of solidification in the mold tends to be unexpectedly uneven depending on the position and time, and various inconveniences are likely to occur due to uneven strain in pressure rolling. On the other hand, if it is 0.5 or more, the shell thickness becomes too large and is not suitable for its intended purpose.

The method of FIG. 5, that is, a specific method of producing a gas-filled air-core slab downstream of point Q, is shown in FIG.
A description will be given along (b) and (c). FIG. 7 (a) shows the situation at the start of casting, where the lower opening of the mold is a dummy bar 1
At the end of the dummy bar, a gas blowing nozzle 27 of a steel pipe or a ceramic pipe is attached, and casting is started while blowing an inert gas through the nozzle 27, and the dummy bar is pulled out. At this time, a bubbling phenomenon occurs, but there is no particular problem in operation. FIG.
As shown in (b), when the amount of blowing gas is increased to some extent at the time when the nozzle exceeds the lowest point of the slab trajectory, an air core is formed inside the slab and excess gas is reduced to the lowest point Q.
From the molten steel, flows back through the molten steel, and floats as bubbles in the molten steel. At the same time, the liquid level m of the liquid core is maintained on the upper solidification front of the slab at the lowest point. Solidification does not naturally proceed downstream of the molten metal surface m. As shown in FIG. 7 (c), when the nozzle reaches the pressure roll, the nozzle is pressed down and the gas blowing stops, but the tip of the slab is completely closed and the gas in the air core remains as it is. Since the inert gas is used, the enclosed gas does not react with the molten steel or solidified shell, and therefore the gas pressure is maintained. It is in a casting state. When the arc radius R is reduced, the bending strain acting on the inner surface of the slab which is still in the brittle temperature range when the hollow core slab is pulled out increases, and internal cracks may occur. Even in such a case, there is no problem because the concentrated molten steel does not enter the cracks as in the liquid core reduction method. This is one of the effects of the present invention.

Next, a specific method of maximizing the drawing speed will be described. In this case, it is possible to propose the application of a synchronous vertical rotating mold instead of a general reciprocating vibration type curved mold. The reason is that the slab drawing radius R (=
This is because if the curved mold radius is designed to be extremely small, it will be close to the practical size of the synchronous rotary mold and replacement will be easy. In this case, the maximum effect of the synchronous system, that is, the speeding up of casting is facilitated. Specifically, in FIG. 6, reference numeral 21 denotes a rotating mold composed of water-cooled wheels, 23 denotes a rectangular groove, and 24 denotes an endless belt for covering the same. Molten steel Me is cast. Then, the slab 6 is pulled out while the peripheral speed of the wheel is matched with the traveling speed of the belt. In the synchronous mold, a drawing speed of about 10 m / min has already been put to practical use. Accordingly, also in the present invention, the solidification shell thickness can be further reduced by sequentially increasing the speed from 5 m / min.

As described above, the third aspect of the present invention based on air core pressure
Although the near net shape process, which eliminates core defects and facilitates homogenization, has been described, the biggest application of these features is continuous casting and rolling for various hot rolled products. The reason is to combine them rationally.
As described above, by the three effects of the present invention, this problem can be implemented very easily, rationally and economically. In addition to directly connecting the upper and lower processes, as well as reducing the number of expensive rolling mills by reducing the casting cross section as far as quality permits, it is possible to obtain both the process direct connection effect and the near net shape effect Can also. Regarding the method of combining continuous casting and rolling, a solid slab is cut once to form a steel slab, and is subjected to rolling in a batch system or to a continuous system without cutting. Prior to rolling, the steel sheet is passed through a heat equalizing furnace so as to be uniformly heated or directly subjected to rolling. An appropriate choice should be made in consideration of the product and production circumstances.

By continuously rolling the solid slab, it is possible to easily manufacture a large unit weight wire coil, which has been conventionally difficult to manufacture. In the conventional method, large single billet,
It requires a large heating furnace, etc., and is economically burdensome, with a maximum of 3 tons at the practical limit. In this method, since only the wire coil unloading equipment needs to be large, a 3 to 20 ton coil can be manufactured easily and at low cost. This is an extremely effective means for rationalizing the secondary processing of the wire rod.

In the production of small-diameter wire rods and small-diameter steel bars, the bottleneck of production efficiency lies in the finish rolling speed. For this reason, multi-rolling was once used as a method of enhancing production capacity, but recently, the so-called slit rolling method in which a rolled material is divided into two or more strips in the rolling direction before finish rolling and each is sent to separate or identical finish rolling. May be adopted. The present invention is based on the principle that a single strand is continuously processed from a continuous casting to a product. Therefore, this slit rolling method is applied as required in FIG. 8 and FIG. Thereby, the effect of the present invention is successfully exhibited.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Table 1 summarizes the basic specifications of a continuous casting facility when the present invention is applied to the production of various hot rolled steel products. Casting efficiency and the middle group Dzu fluff actual slab dimensions in the table, those skilled in the art readily且can be designed rationally subsequent rolling equipment.

[0037]

According to the present invention, according to the present invention, in a curved type continuous casting, a cast slab is drawn upward in a state where an unsolidified portion is left to form an air-core slab, which is pressed and rolled into a solid slab. The following many effects can be obtained by appropriately setting the thickness of the solidified shell and setting the casting temperature appropriately before pulling out, or by adopting an integrated continuous system that immediately sends it to the rolling process. Can be. Since the casting efficiency is dramatically improved, it is possible to directly connect the continuous casting and the rolling, thereby greatly reducing equipment costs and operating costs. This is extremely advantageous in the field of high-grade steel since no segregation phenomenon occurs and the inside consists only of homogeneous columnar crystals. One effect is that the hot forging ratio can be reduced. This results in significant reductions in equipment costs and costs. Similarly, in place of a special casting method such as the one-way solidified steel ingot method or the ESR method, a homogeneous slab can be produced by continuous casting at low cost and high productivity. When applied to low-grade mass-produced ordinary steel, there is no segregation, so that impurity management can be relaxed within the standard. This results in lower scrap and refining costs.
When applied to slabs, compared to conventional slab continuous casting, the surface quality is the same, the internal quality is greatly improved, and a thin slab can be easily formed. In addition, an extremely thin slab can be obtained depending on the setting conditions. This will be a new near net shape process for steel sheets. When applied to large section steels, thin, high quality beam blanks can be easily manufactured. When applied to a wire, a super heavy wire coil can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic side view illustrating a continuous casting / continuous rolling facility used in the present invention.

FIG. 2 is a schematic diagram of the core of the present invention under air core slab pressure reduction.

FIG. 3 is an example showing the effect of casting temperature on columnar crystal length.

FIG. 4 shows an example of manufacturing a beam blank by rolling down an air core slab.

FIG. 5 is an example showing the production of a gas-filled hollow core slab.

FIG. 6 shows an example in which the present invention is applied to a rotary casting method.

FIG. 7 illustrates a method of forming a gas-filled air core.

FIG. 8 is an example showing a direct connection between continuous casting and rolling used in the present invention.

[Explanation of symbols]

1: Ladle 2: Tundish 3: Mold
4: Electromagnetic stirrer 5: Immersion nozzle 6: Slab
7: Secondary cooling device 8: Press roll 9: Guide
Roll 10: Pinch roll 11: Dummy bar 12: Solid slab 13: Shear 14: Soaking furnace 15: Tandem type rough rolling row 16 : Intermediate rolling row 17: Split roll 18: Finish rolling row 19:
Winding machine 20: Bundle machine 21: Rotating mold 22: Air-core slab 23: Rectangular groove 24: Endless belt
25: Belt guide 26: Tapered block
27: Gas blowing nozzle 31: I-beam blank 32: Hole roll 33: H-beam blank 34: Universal roll Q: Specific point
Lq: Liquid core Me: Molten steel Cv: Vacuum air core S:
Air core L: Casting surface level Cg: Gas-filled air core
m: Gas core side hot surface

[Table 1]

──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application No. 6-150697 (32) Priority date May 26, 1994 (May 26, 1994) (33) Priority claim country Japan (JP) The patentee is prepared to transfer or license. (58) Field surveyed (Int.Cl. ⁷ , DB name) B22D 11/128 350 B22D 11/128 B22D 11/115 B22D 11/12 B22D 11/20

Claims (7)

(57) [Claims] 1. In continuous casting of steel, by keeping a liquid core inside a slab at a specific point Q of a slab drawing locus,
An air core is formed inside the slab downstream from the point Q, and the air core is pressed by a roll to draw a solid slab. At least immediately after being discharged from the casting mold, perform curved die continuous casting to perform drawing such that it is curved, and set the curved length in the slab withdrawal trajectory to 周 or more of the circumference and move the slab to a position higher than the casting surface. At the same time as pulling out, the position higher than the casting surface by the height of the static molten steel
And a solidified shell thickness ratio α (= 2d / A) determined at the point Q by the following equation is 0.25 to 0.85. In the formula, d: thickness of slab solidified shell at point Q (m) A: short width of mold cross section (m) 2. In continuous casting of steel, by keeping the liquid core inside the slab at a specific point Q of the slab drawing locus,
An air core was formed inside the slab downstream of the point Q, and the air core portion was pressed by a roll so that at the time of drawing as a solid slab, at least the slab drawing locus was discharged from the mold.
Immediately afterwards, curved continuous casting is performed to draw in a curved shape.
The bending length in the slab drawing locus should be less than half the circumference.
Pull out the slab to a position higher than the casting surface as the top,
Static steel head equivalent to an atmospheric pressure head rather than the casting surface
By setting the position higher by the height as the specific point Q and setting the casting temperature in the range of 20 to 60 ° C. higher than the liquidus temperature of the steel type, the inside of the chill crystal of the slab skin is made substantially columnar. A continuous casting method wherein the inside of the chill crystal of the slab slab is made substantially granular by applying electromagnetic stirring to the molten steel in the mold at a temperature higher by 0 to 15 ° C. The 3. A casting temperature by a 20 to 60 ° C. range above liquidus temperature of the steel species, or you substantially columnar crystals inside the chill crystals of the slab skin, or 0
The continuous casting method according to claim 1, wherein the inside of the chill crystal of the slab slab is made into a substantially granular crystal by applying electromagnetic stirring to molten steel in a mold by setting the temperature to a range higher by about 15 ° C. 4. The continuous casting method according to claim 1, wherein the equipment specifications and casting conditions are set according to the following equations (1) to (5). Pn = 4ρk ² · Ln · [(1 / α) + (β / α) -1] (1) V = Ln · (2k / αA) ² ··· (2) R = (Ln-1.4) / π (3) d = k (Ln / V) ^0.5 (4) A ′ = 2 (1−p) · d (5) where Pn: casting efficiency (kg / min) ) Ρ: Steel material density (7600 kg / m ³ ) Ln: Machine length (length between casting surface and specific point Q: m) k: Solidification constant 0.023 to 0.031 (m / min)
^0.5 ) R: radius of the curved portion in the slab drawing locus (m) B: mold cross-sectional length (m) α: solidified shell thickness ratio 0.25 ≦ α ≦ 0.85 β: rectangular ratio β = B / A A ': Short width thickness (m) of cross section of solid cast slab p: Substantial reduction ratio by pressing roll = (2d-A') /
2d = 0.05 to 0.40 5. The solid cast slab according to claim 1, wherein said solid slab is H-shape or I- shape by press-contacting by means of a groove rolling method or a simultaneous four-side pressing method using a universal mill. continuous casting method characterized by the. 6. In continuous casting of steel, by keeping the liquid core inside the slab at a specific point Q of the slab drawing locus,
By forming an air core inside the slab downstream from the point Q and pressing the air core with a roll, when drawing as a solid slab, at least immediately after the slab drawing locus is discharged from the mold, Perform curved type continuous casting to perform bending drawing, set the curved length in the slab drawing locus to be more than 1/4 of the circumference, set the lowest point of the arc as the specific point Q, and cast to a position higher than the Q point. While pulling out the slab, the liquid core inside the slab remains at the foremost point near point Q, and the inside of the slab downstream from point Q is filled with an inert gas under pressure to form an air core and solidify. A continuous casting method in which the shell thickness ratio α is set to 0.05 to 0.5. 7. The method according to claim 4 or 6, wherein the solid slab of red heat is cut 1) once as a steel slab, or 2) as a continuous slab, a) through a soaking furnace. after soaking, or b) the steel sheet is supplied to the rolling line of the direct single-strand without going through the soaking furnace, section steel, flat steel, steel bars, continuous casting, characterized in that the rolling in either wire Rolling method.