JP2009274116A - Continuous casting machine of vertical bending die type - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting machine of a vertical bending die type capable of easily manufacturing steel (a steel billet 5) free from any surface defect or internal crack. <P>SOLUTION: The continuous casting machine of the vertical bending die type casts the steel billet 5 having the chemical composition consisting of, by mass, 0.05-0.55% C, 0.10-2.00% Si, 0.30-1.90% Mn, 0.005-0.070% P, and 0.003-0.120% S and having the thickness of 280-350 mm at the casting rate of 0.7-1.1m/min and with the specific water amount of 0.15-0.40l/kg×steel, and adequately sets a vertical length, a bending length, a secondary cooling length, an arc length, and a straightening length. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In the present invention, for example, vertical bending is performed by casting a slab having a thickness of 280 mm to 350 mm at a casting speed of 0.7 to 1.1 m / min and a specific water amount of 0.15 to 0.40 l / kg · steel. The present invention relates to a mold continuous casting machine.

Conventionally, in a continuous casting machine, the molten steel produced from a converter, secondary refining equipment, etc. is transported to the tundish with a ladle, and the molten steel in the ladle is poured into the tundish, and then this tundish. The cast steel is continuously cast by supplying molten steel from the mold to the mold and pulling out while supporting the cast piece cast by the support roll disposed below the mold (Patent Documents 1 to 4). .
JP 2001-232451 A Japanese Patent Laid-Open No. 04-238660 JP 09-103856 A Japanese Patent Laid-Open No. 06-134558

Now, as one of the countermeasures against global warming in recent years, there is an increasing need for weight reduction / high strength of steel materials mainly by automobile manufacturers. For this reason, in the manufacture of steel materials, there is a demand for improvement in steel material quality that can withstand high strength. Along with the increase in strength, there has been a need for a high-strength steel material free from surface defects and internal cracks of the steel material.
In a continuous casting machine as shown in Patent Literature 1 to Patent Literature 4, a steel material free from surface defects and internal cracks of a steel material (slab) can be cast as usual, but a high-strength steel material that has been demanded in recent years. In order to manufacture (cast), such a conventional continuous casting machine is provided with ancillary equipment (for example, a heating device), or complicated control (for example, control for changing the cooling water according to the casting speed). ), And it is difficult to cast high-strength steel.

  Therefore, an object of the present invention is to provide a vertical bending type continuous casting machine capable of easily producing a steel material (slab) free from surface defects and internal cracks.

In order to achieve the above object, the present invention has taken the following measures.
That is, the chemical components were C: 0.05 to 0.55% by mass, Si: 0.10 to 2.00% by mass, Mn: 0.30 to 1.90% by mass, P: 0.005 to 0.005%. A slab of 070 mass%, S: 0.003 to 0.120 mass%, and a thickness of 280 mm to 350 mm, has a casting speed of 0.7 to 1.1 m / min and a specific water amount of 0.15. It is a vertical bending type continuous casting machine cast at ˜0.40 l / kg · steel, and the profile of the continuous casting machine is set to satisfy the formulas (1) to (5).

The inventor verified the continuous casting machine for easily producing a slab free from surface defects and internal cracks from various angles. First, the inventor verified the profile and casting conditions of a continuous casting machine for preventing surface cracks and internal cracks of the slab after presetting the components and thickness of the slab to be cast.
As a result, the chemical composition of the slab to be cast is C: 0.05 to 0.55% by mass, Si: 0.10 to 2.00% by mass, Mn: 0.30 to 1.90% by mass, P: 0.005 to 0.070 mass%, S: 0.003 to 0.120 mass%, the thickness of the slab is 280 mm to 350 mm, and the casting conditions for producing the slab are as follows. With a casting speed of 7 to 1.1 m / min and a specific water amount of 0.15 to 0.40 l / kg · steel, the vertical length satisfies Equation (1) and the bending length is Equation (2). So that the secondary cooling length satisfies Equation (3), the length from the vertical portion to the arc portion satisfies Equation (4), and the length from the vertical portion to the correction portion satisfies Equation (5). This makes it possible to easily produce slabs that are free from surface defects and internal cracks. It was heading.

  According to the present invention, a steel material (slab) free from surface defects and internal cracks can be reliably produced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an overall side view of a continuous casting machine for casting a slab (for example, bloom) having a thickness of 280 mm to 350 mm.
The continuous casting machine 1 is a vertical bending type continuous casting machine, a tundish 3 for temporarily storing molten steel 2, a rectangular mold 4 to which the molten steel 2 from the tundish 3 is supplied, The slab 5 formed by the mold 4 is pulled out, and a plurality of support rolls 6 for supporting the slab 5 and a cooling means (for example, a cooling nozzle) 7 for cooling the slab 5 are provided.

The tundish 3 has a bottomed box shape as a whole, and an immersion nozzle 8 is provided at the bottom of the tundish 3. The immersion nozzle 8 can be opened and closed by a slide valve, and the injection of the molten steel 2 into the mold 4 is stopped or restarted by opening and closing the slide valve.
The support roll 6 is disposed downstream from the bottom of the mold 5 in order. Here, looking at the profile (roll profile) of the continuous casting machine 1, the continuous casting machine 1 arranges the support roll 6 in the vertical direction from the mold 4 toward the downstream side, and A bent portion 11 formed by arranging the support roll 6 while being bent gradually inward from the terminal end (downstream end portion) of the vertical portion 10 and the support roll 6. An arc portion 12 configured by arranging the support rolls 6 horizontally from the end of the arc portion 12 and an arcuate portion 12 configured by arranging the support rolls 6 horizontally from the end of the arc portion 12. It has become with.

Hereinafter, the vertical bending type continuous casting machine of the present invention will be described in detail.
In this continuous casting machine 1, the chemical components are C: 0.05 to 0.55 mass%, Si: 0.10 to 2.00 mass%, Mn: 0.30 to 1.90 mass%, P: 0 0.005 to 0.070 mass% and S: 0.003 to 0.120 mass% for casting the slab 5, and the continuous casting machine 1 has the characteristics of the slab 5 of these chemical components This is a configuration that takes into account.
In this continuous casting machine 1, it is formed so that Formula (1)-Formula (5) may be satisfy | filled. That is, the profile of the continuous casting machine 1 satisfies the expressions (1) to (5). In the continuous casting machine 1, the radius of the arc portion 12, that is, the arc radius (constant arc radius) R is 10 m or more from the viewpoint of reducing internal strain of the slab 4 and high speed casting.

[Vertical length]
The vertical length V _L shown in Expression (1) is the vertical length of the vertical portion 10, in other words, the length from the upper end of the mold 4 to the most downstream support roll 6 a that vertically supports the slab 5. is there.
FIG. 2 shows the relationship between the length in which the slab 5 is vertical in the continuous casting machine 1 and the inclusions remaining inside the slab 5, according to ISIJ international, vol34 (1994), No6. It is disclosed. Fk in FIG. 2 is a value obtained by dividing the inclusion supplement rate of the bending continuous casting machine (bending die continuous casting machine) by the inclusion supplement rate of the vertical bending continuous casting machine (vertical bending die continuous casting machine). The smaller this value, the more effective the floating separation of inclusions by the vertical bending type continuous casting machine.

As shown in FIG. 2, in a vertical bending type continuous casting machine, by increasing the length V _L of the vertical portion 10 than 2.5 m, light alumina than molten steel (specific gravity = 7g / cm ³⁾ And the like (specific gravity = ³ to 4 g / cm ³ ) can be sufficiently levitated in the vertical portion 10, and the effect of levitation of inclusions in the vertical portion of the vertical bending type continuous casting machine is sufficiently exhibited. be able to.
[Bending length]
The bending length _BL shown in the formula (2) is the length of the bending portion 11, in other words, the length from the support roll 6 a at the start of the bending portion 11 to the support roll 6 b at the end of the bending portion 11. .

As shown in FIG. 3, in the bending portion 11 that bends the slab 5, a large static pressure of molten steel is applied and the load of the support roll 6 is large, and the support roll 6 has high rigidity to bend the slab 5. Therefore, the roll diameter of the support roll 6 is 200 mm or more.
Further, in the vertical portion 10 and the bending portion 11 at the lower end of the mold 4, a large bending strain is applied to the slab 5, so that the bulging distortion is reduced between the support rolls 6 of the vertical portion 10 and the bending portion 11. Is provided with a cooling nozzle 7.

The cooling nozzle 7 is disposed between the support rolls 6 so as not to come into contact with the support roll 6. For example, the tip 7 a is slightly radially outward from the upper and lower center lines C of the support roll 6. It is located at a position as close as possible to the slab 5 in consideration of the sprayed state of the cooling water on the slab 5. The gap D (one-side nozzle gap D1) between the tip 7a of the cooling nozzle 7 and the support roll 6 is at least 10 mm.
Table 1 summarizes the spraying state of the cooling nozzle 7 and the surface defects of the slab 5 when casting was performed with the bending length B _L (the length of the bending portion 11) set to 3.0 m. Is.

As shown in Table 1, the roll diameter of the support roll 6 was 0.20 m, the number of bending points (the number of support rolls of the bending part 11) was 12, and the roll pitch of the support roll 6 was set to 0.25 m. In the experiment, casting was performed for a long period (1 week to 6 months) by changing the diameter (size) of the tip 7a of the cooling nozzle 7.
In addition, the gap column of the nozzle gap in Table 1 indicates the total (unit: mm) of the gap D1 from the tip 7a of the cooling nozzle 7 to the upper and lower support rolls 6, and the column on one side of the nozzle gap is the cooling column. It shows the value (unit: mm) of the gap D1 between one (upper or lower) support roll 6 from the tip 7a of the nozzle 7.

  In the evaluation of the nozzle spraying conditions in Table 1, after the cooling nozzle 7 is installed as set, it is cooled after 1 week (after 1 W), after 2 weeks (after 2 W), after 4 weeks (after 4 W), and after 6 months. The water spray status was confirmed. And in the said evaluation, the state in which there is no abnormality in spraying and the cooling water is applied to the slab 5 as prescribed (those that can be regarded as the same as the initial installation state) is “good”, the tip of the cooling nozzle 7 If the scale or the like is deformed due to the volume of the part 7a or the nozzle is deformed, or if a part of the cooling nozzle 7 is in contact with the roll of the support roll 6 due to the accumulation of scale, the cooling nozzle 7 is defective. The state where the bent or the slab 5 was not exposed to the cooling water was defined as the poorest “x”.

Moreover, in the surface defect evaluation of Table 1, the sample of the slab 5 was sampled after 1 W, 2 W, 4 W, and 6 months, and the magnetic particle flaw detection test for the sample in the same manner as the nozzle spray situation (JIS G0565) was performed. According to the provisions of the test, a case where the surface of the slab 5 is regarded as having no defect was determined as “good”, and a case where it was recognized as a defect was determined as “bad”. After the slab 5 was cast, it was subjected to block rolling (heating → rolling → hot scarf → rolling), and after cooling the steel slab and removing the surface scale, a magnetic particle inspection test was performed.
As shown in Table 1, as shown in Experiment No. 1 to Experiment No. 3, when the bending length _BL is set so as to satisfy the formula (2), after 1W, 2W, 4W and 6 months later After any progress, the nozzle spraying condition was good and the surface defect was evaluated well.

On the other hand, as shown in Experiment No. 4 to Experiment No. 7, if the bending length _BL is set so as not to satisfy Expression (2), after 1W, 2W, 4W and 6 months later After any progress, the nozzle spraying condition became defective and the evaluation of the surface defect was also determined to be poor.
That is, as shown in Table 1 and FIG. 4, the gap D between the cooling nozzle 7 and the support roll 6 is small (nozzle gap D1 is 10 mm or less), and the bending length _BL does not satisfy the formula (2). When the casting is performed over a long period of time, the scale deposited on the tip 7 a of the cooling nozzle 7 comes into contact with the support roll 6. As a result, the cooling nozzle 7 is bent or deformed, and due to this influence, the cooling water is not sprayed uniformly on the slab 5, which causes a defective nozzle spraying condition or a surface defect. In particular, as shown in Table 1, when the bending length _BL is very close to the value of the formula (2), there is a result that each evaluation is good after about 2 W from the start of casting. When B _L deviated greatly from the value of the formula (2), each evaluation immediately resulted in a failure even after 1 W from the start of casting.

As described above, in the vertical bending type continuous casting machine, by satisfying the expression (2) for the bending length _BL , there is no abnormality in spraying by the cooling nozzle 7 even if casting is performed for a long period of time. It was able to be maintained satisfactorily, and could be maintained satisfactorily without causing surface defects in the cast slab 5.
[Minimum secondary cooling length]
Secondary cooling length W _L shown in equation (3), those represented by the range of the cooling nozzle 7 from the lower mold 4 is disposed toward the casting direction, the left-hand side of equation (3), the secondary cooling The minimum value of the length W _L (installation range of the cooling nozzle 7) is shown. The left-hand side of equation (3), the value established range obtained by subtracting the length M _L of the mold 4 to the length obtained by adding the length B _L of the bending portion 11 and the length V _L of the vertical portion 10 of the cooling nozzle 7 It is shown above. In other words, the left side of the expression (3) indicates that the cooling nozzle 7 is disposed in the bent portion 11 through the vertical portion 10 from below the mold 4. In the left side of the formula (3), it is assumed that the length M _L of the mold 4 is shorter than the length V _L of the vertical portion 10 (M _L <V _L ). In the description of the secondary cooling length, it is assumed that the specific water amount (water amount of cooling water) is in the range of 0.15 to 0.40 l / kg · steel so that the cooling condition is within a predetermined range. .

  FIG. 5 shows changes in various strains when casting is performed on a steel type (S55C) in which internal cracking is likely to occur while the casting speed Vc is 1.1 m / min and the amount of cooling water is relatively small. ing. Specifically, FIG. 5A shows changes in various strains when secondary cooling is performed at the bending portion 11, and FIG. 5B shows a case where secondary cooling is not performed at the bending portion 11. This shows changes in various distortions. The bulging strain, the bending strain, the correction strain, and the total solidification interface total strain shown in FIG. The constant A in Equation (6) was calculated by measuring strain by experiment. This equation (6) is general and is described in R & D Kobe Steel Engineering Reports vol.56 No3 (Dec.2006) P12.

As shown in FIGS. 5A and 5B, when the meniscus distance (m) is viewed, around 5.0 m corresponds to the bending portion 11, and bending strain is caused by the support roll 6 at the bending portion 11. It has occurred. Comparing FIG. 5A and FIG. 5B, when the secondary cooling is not performed at the bending portion 11, the bulging strain and the solidification interface strain are about 0. 0 compared with the case where the secondary cooling is performed. It is increased by about 05%, and it can be seen that internal cracks of the slab 5 are likely to occur.
Table 2, the water discharge of the cooling nozzle 7 partially changing the secondary cooling length W _L by stopping summarizes the internal cracks when performing the casting. As in the case of FIG. 5, the casting conditions were set at a casting speed Vc = 1.1 m / min, and a steel type (S55C) in which internal cracks are likely to occur was cast.

In the evaluation of internal cracks in Table 2, the cast slab 5 was cooled to room temperature, cut in the horizontal and vertical directions, and pickled for each sample, and then visually checked for internal cracks. Those having a crack length of 2.0 mm or more were defined as internal cracks. FIG. 6A shows a cross macro obtained by cutting the sample in the horizontal direction (width direction), and FIG. 6B shows a vertical macro obtained by cutting the sample in the vertical direction (longitudinal direction).
Table 2 Experiment No. 8 Experiment No. 9, the secondary cooling length W _L is because they meet the value of the left-hand side of equation (3), inner cracks were good without generating (Table 2, Internal crack evaluation "○").

Meanwhile, in Experiment No. 10 to Run No. 12 in Table 2, since the secondary cooling length W _L does not satisfy the left side value of the expression (3), as shown in FIG. 6 (a), of the slab 5 As shown in FIG. 6B, an internal crack caused by bulging (bulging) occurs in the vicinity of the corner portion 17, and as shown in FIG. 6B, an internal crack caused by pressing of the support roll 6 inside the slab 5 (bending inside of the slab 5). (Table 2, internal crack evaluation “×”).
[Maximum secondary cooling length]
The right side of Expression (3) indicates the maximum value of the secondary cooling length W _L (installation range of the cooling nozzle 7). Right side of equation (3) is the length of installation range is the sum of the length C _L of the length B _L and the arcuate portions 12 of the bending portion 11 and the length V _L of the vertical portion 10 of the cooling nozzle 7, a mold It indicates that this is the fourth length M _L and recuperation area from after cooling ends to enter the correction unit 13 (the distance required for recuperation) R _L obtained by subtracting. In other words, the right side of the expression (3) indicates that the cooling nozzle 7 is disposed in the arc portion 12 from the lower portion of the mold 4 through the vertical portion 10 to the bent portion 11 and in the region within the arc portion 12, the slab 5. This indicates that the arrangement of the cooling nozzle 7 is completed before the end of the arc portion 12 in consideration of the recuperation.

FIG. 7 shows the relationship between the aperture value and the surface temperature for a steel type (SCM420) that is susceptible to surface cracking. As shown in FIG. 7, in the steel type of SCM420, there is a tendency that the drawing value (deformability) decreases with a decrease in the surface temperature, and the drawing value becomes minimum especially between the A3 and A1 transformation points. In SCM420 which is easy to break, it becomes an embrittlement region at a 780 ° C. to 830 ° C. where the aperture value is less than 40%, and the surface crack is most likely to occur. This is also disclosed in, for example, the Iron and Steel Institute (1982), Outline of the 104th Discussion Session A165.
Thus, in the state where the surface temperature of the SCM 420 is 780 ° C. to 830 ° C., if the slab 5 is corrected from the bent state to the horizontal state by the correction unit 13, the surface slab 5 is actually caused. When located on the correction part 13, the surface temperature needs to be 830 ° C. or higher.

FIG. 8 shows changes in the surface temperature when the SCM 420 is cast in a state where the casting speed Vc = 0.7 m / min and the amount of cooling water for the slab 5 is large (a state where the cooling water is easily applied).
As shown in FIG. 8, when the cooling nozzle 7 is arranged in the correction part 13 (the most downstream cooling nozzle 7 is arranged at the point P1), the surface temperature of the slab 5 in the correction part 13 as shown by the dotted line. Becomes 830 ° C. or less, and surface cracks occur. On the other hand, when the most downstream cooling nozzle 7 is located at least 1.0 m before the correction unit 13 (the most downstream cooling nozzle 7 is disposed at the point P2), as shown by the solid line, when the cooling is completed, the slab 5 The surface temperature of slab 5 is 830 ° C., but the surface temperature of the slab 5 becomes 830 ° C. or higher due to recuperation before entering the correction portion 13.

Therefore, the most downstream cooling nozzle 7 needs to be arranged in front of the correction portion 13 by the recuperation distance R _L in consideration of the distance required for the recuperation of the slab 5, and the secondary cooling length In other words, it is necessary to make the maximum value smaller than the value on the right side of Equation (3).
Table 3, the water discharge of the cooling nozzle 7 partially changing the secondary cooling length W _L by stopping summarizes the internal cracks when performing the casting. As in the case of FIG. 8, the casting condition was set at a casting speed Vc = 0.7 m / min, and a steel type (SCM420) that easily causes surface cracking was cast.

Table 3 Experiment No. 13 Experiment No. 14, the secondary cooling length W _L because they meet the value of the right side of equation (3), surface cracks were good without generating (Table 3, Surface defect evaluation “○”). Meanwhile, in Experiment No. 15 Experiment No. 16 in Table 3, since the secondary cooling length W _L does not satisfy the value of the right side of equation (3), surface cracking occurred (Table 3, the surface defect evaluation "× ").
[Length from vertical part to arc part, length from vertical part to correction part]
Equation (4) is the length from the vertical portion 10 to the arc portion 12, and shows the total length of the vertical portion 10, the bent portion 11, and the arc portion 12.

FIG. 9 shows changes in the surface temperature of the slab 5 when three types of slabs 5 (SCM420) having thicknesses of 280 mm, 300 mm, and 350 mm are cast at a slow casting speed Vc = 0.7 m / min. It is.
As shown in FIG. 9, even if the thickness of the slab 5 is different, in any case, when correction is started at 9.0 m or more, the surface temperature of the slab 5 can be corrected at 830 ° C. or more, The surface crack of the slab 5 can be prevented. That is, if the total length of the vertical portion 10, the bent portion 11, and the arc portion 12 is 9.0 m or more so as to satisfy the formula (4), the slab 5 is corrected without surface cracks in the correcting portion 13. be able to. On the other hand, even if correction is performed by the correction unit 13, the surface temperature of the slab 5 becomes less than 830 ° C. unless correction is completed within 21.0 m. Therefore, if the total length of the vertical portion 10, the bent portion 11, the arc portion 12, and the correction portion 13 is 21.0 m or less so as to satisfy Equation (5), the slab 5 is corrected without surface cracks. can do.

FIG. 10 shows changes in the surface temperature of the slab 5 when the casting speed Vc is changed. As shown in FIG. 10, when the casting speed Vc is 1.0 m / min and 1.1 m / min and is larger than 0.7 m / min, the surface temperature of the slab 5 is 830 ° C. or less. There was no entry into the embrittlement region.
Table 4 summarizes the results of casting a plurality of steel types by changing the casting speed in the continuous casting machine 1 of the present invention satisfying the expressions (1) to (5).

In this continuous casting machine 1, M _L = 0.9 m, V _L = 3.0 m, B _L = 3.3 m, W _L = 6.5 m, C _L = 11.6 m, arc radius R = 10 m, steel Evaluation with a piece UT, evaluation with a steel bar UT, evaluation with a steel piece automatic MT, evaluation with a steel bar ROTO, and evaluation with a steel bar macro test were performed. Various evaluation tests were performed under the conditions shown in Table 5.

As shown in Table 4, as long as the casting speed Vc is in the range of 0.7 m / min to 1.1 m / min, there is no inclusion in any steel type, and no surface defects or internal cracks are confirmed. (Table 4, evaluation column “◯”).
In Experiment Nos. 28, 34, and 40, when the casting speed Vc was 1.2 m / min, defects of internal cracks were confirmed in the steel types S45C, S45CS1, and S55S (Table 4, evaluation column “×”). In Experiment No. 41, when the casting speed Vc = 0.6 m / min, a surface crack defect was confirmed in the steel type of SCM420 (Table 4, evaluation column “×”).

  The present invention is not limited to the above embodiment.

It is a whole side view of a continuous casting machine. It is a related figure of the length with which the slab in the continuous casting machine is vertical, and the inclusion inside a slab. It is an arrangement plan of a support roll and a cooling nozzle. It is a figure where the cooling nozzle is contacting the support roll. This shows bulging distortion, bending distortion, straightening distortion, and total solidification interface distortion. (A) When secondary cooling was performed at the bending section, (b) did not perform secondary cooling at the bending section. It is the figure which showed the case. (A) is the cross-sectional macro view which cut | disconnected the sample to the horizontal direction (width direction), (b) is the vertical macro view which cut | disconnected the sample to the vertical direction (longitudinal direction). It is a related figure of an aperture value and surface temperature about a steel type (SCM420). It is a change figure of the surface temperature at the time of casting of SCM420 in casting speed Vc = 0.7m / min state. It is a change figure of surface temperature at the time of casting three types of slabs (SCM420) at casting speed Vc = 0.7m / min. It is a change figure of the surface temperature of a slab when changing casting speed Vc.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vertical bending type continuous casting machine 5 Mold 6 Support roll 10 Vertical part 11 Bending part 12 Arc part 13 Straightening part

Claims (1)

Chemical components are C: 0.05 to 0.55 mass%, Si: 0.10 to 2.00 mass%, Mn: 0.30 to 1.90 mass%, P: 0.005 to 0.070 mass% %, S: 0.003 to 0.120% by mass, and a slab having a thickness of 280 to 350 mm, a casting speed of 0.7 to 1.1 m / min and a specific water amount of 0.15 to 0 A vertical bending type continuous casting machine for casting at 40 l / kg · steel,
A vertical bending type continuous casting machine, wherein the profile of the continuous casting machine is set to satisfy the formulas (1) to (5).

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