JP2002248553A - Method for controlling secondary cooling of continuous- cast steel piece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling the secondary cooling of a continuous- cast steel piece, wherein the surface temperature of a cast steel piece at a position down the exit of the secondary cooling zone in the direction of casting is kept constant at a high target temperature, without deteriorating the quality of the surface and inside of the cast steel piece despite variations in the casting speed. SOLUTION: The target surface temperature of the cast steel piece at the exit of the secondary cooling zone is changed, based on the variations in the casting speed so that the surface temperature of the cast steel piece at a specific position down the exit of the secondary cooling zone in the direction of casting may become the predetermined target surface temperature of the cast steel piece. The volume of the secondary cooling water for the cast steel piece in the secondary cooling zone is controlled so that the new target temperature may be attained. Further, the target surface temperature of the cast steel piece at the exit of the secondary cooling zone is changed, based on the measured surface temperature of the cast steel piece between the exit of the secondary cooling zone and the specific position and the volume of the secondary cooling water for the cast steel piece is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for controlling secondary cooling of a continuously cast slab.

[0002]

2. Description of the Related Art The technique of controlling the surface temperature of a slab in a secondary cooling zone of a continuous casting machine is an important technique for obtaining a slab having good surface and internal quality. In particular, in continuous casting using a curved or vertical bending type continuous casting machine, cracks may occur on the surface or inside of the slab if the slab surface temperature is not within an appropriate range when straightening the slab. Cheap.

[0003] In order to prevent the occurrence of cracks on the surface or inside of these slabs, the surface temperature of the slabs at the straightening position of the slabs in the continuous casting machine, at the outlet of the secondary cooling zone, etc., is set to the value of the slabs specific to steel. The secondary cooling water amount of the slab in the secondary cooling zone is controlled so as to match the target surface temperature.

Japanese Patent Laid-Open Publication No. Sho 60-49850 discloses that the surface temperature of a slab is measured near the outlet of a secondary cooling zone so that the surface temperature at the slab correction position is a target constant temperature. There has been proposed a method of controlling a secondary cooling water amount of a slab in a secondary cooling zone so that a deviation between a measured temperature and a target surface temperature at that position is eliminated.

Japanese Patent Laid-Open Publication No. Hei 1-210158 discloses that even if the casting speed fluctuates, the secondary cooling water amount of the slab is adjusted so that the average temperature of the slab section at the outlet of the curved continuous casting machine becomes the target temperature. Control methods have been proposed. Specifically, the calculated value of the surface temperature of the slab in the curved portion is the target surface temperature, and the calculated value of the solidification thickness of the slab in the horizontal portion in the continuous casting machine is the target solidification thickness. This is a method of controlling the amount of secondary cooling water of the slab so as to be as follows.

In recent years, from the viewpoint of energy saving, continuous cast slabs are directly charged into a heating furnace of a hot rolling factory, which is the next step, or directly hot-rolled without reheating in a heating furnace. Is commonly done. At that time, it is desirable that the surface temperature of the slab at the time of arriving at the hot rolling factory in the next step is as high as possible. At a constant high temperature, energy saving can be achieved in addition to easy operation of the heating furnace.

[0007] By applying the method for controlling the amount of secondary cooling water of a slab proposed in Japanese Patent Application Laid-Open No. 60-49850 or Japanese Patent Application Laid-Open No. Hei 1-210158, even if the casting speed fluctuates, continuous operation is possible. The surface temperature of the slab at the outlet of the casting machine, that is, at the outlet of the secondary cooling zone, can be set as the target surface temperature. However, when the casting speed is reduced, the surface temperature of the slab may be significantly lowered downstream of the secondary cooling zone outlet in the casting direction, for example, at the slab cutting completion position. When the surface temperature of the slab at the cutting completion position of the slab decreases, the surface temperature of the slab arriving at the hot rolling mill in the next process further decreases, and it is necessary to reheat the slab for a longer time in the heating furnace And the effect of energy saving is reduced.

In a normal continuous casting operation, the casting speed may fluctuate. Therefore, even if the casting speed fluctuates, even at a position downstream of the secondary cooling zone outlet in the casting direction, for example, at a cutting completion position of the slab. There is a demand for a method capable of setting the surface temperature of a slab to a constant and high target surface temperature of a slab specific to steel.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to a method of manufacturing a steel sheet, which does not deteriorate the quality of the surface and the inside of a slab even if the casting speed fluctuates.
For example, an object of the present invention is to provide a method for controlling the secondary cooling of a slab, which can set the surface temperature of the slab at the cutting completion position of the slab to a constant and high target slab surface temperature specific to steel. And

[0010]

The gist of the present invention resides in the following methods (1) to (3). (1) The secondary cooling is performed on the basis of the variation in the casting speed so that the surface temperature of the slab at a specific position downstream of the secondary cooling zone of the continuous casting machine in the casting direction becomes a predetermined temperature. Secondary cooling of the continuous cast slab which changes the surface temperature of the target slab at the zone outlet and controls the amount of secondary cooling water of the slab in the secondary cooling zone so as to obtain this new target slab temperature Control method. (2) Between the secondary cooling zone outlet and the specific position such that the surface temperature of the slab at a specific position downstream from the secondary cooling zone outlet of the continuous casting machine in the casting direction becomes a predetermined temperature. The slab in the secondary cooling zone is changed based on the measured value of the surface temperature of the slab at the outlet of the secondary cooling zone based on the measured value of the surface temperature of the slab in order to obtain the new target slab temperature. For controlling secondary cooling of continuous cast slabs by controlling the amount of secondary cooling water. (3) The target slab surface temperature at the outlet of the secondary cooling zone is changed based on the measured value of the slab surface temperature at the specific position, so that the new target slab temperature is obtained. The method for controlling secondary cooling of a continuously cast slab according to the above (2), wherein the secondary cooling water amount of the slab in the secondary cooling zone is controlled.

[0011] The surface temperature of the slab is, for example, a surface temperature that can be measured by a radiation thermometer. Also,
The surface temperature of the slab can also be obtained by calculation by solidification heat transfer analysis. That is, when the chemical composition of the steel, the size of the slab, the casting speed, the conditions for the secondary cooling of the slab, and the like are determined, the surface temperature of the slab according to the distance from the molten steel meniscus can be calculated. By properly selecting the surface heat transfer coefficient, the surface temperature of the slab obtained by this calculation can be made to match well with the measured surface temperature.

The “measured value of the surface temperature of the slab between the secondary cooling zone outlet and the specific position” defined in the present invention is measured at an arbitrary position from the secondary cooling zone outlet to the specific position. Means the surface temperature of the cast slab.

Further, the “specific position on the downstream side in the casting direction from the outlet of the secondary cooling zone of the continuous casting machine” defined in the present invention is:
It means a position in a region within the continuous casting machine after the outlet of the secondary cooling zone and in which the moving speed of the slab is limited by the casting speed. Specifically, it means a position within a region from the outlet of the secondary cooling zone to the cutting completion position of the slab on the downstream side in the casting direction. In that region, since the slab is continuously connected from the mold outlet, the moving speed of the slab in the casting direction is the same as the casting speed itself until the slab is cut and separated from the slab body. Become. In the following description, the specific position will be described as the cutting completion position of the slab.

Normally, even when the casting speed fluctuates, the secondary cooling water amount of the slab in the secondary cooling zone is controlled so that the surface temperature of the slab at the outlet of the secondary cooling zone becomes the target surface temperature. I have. However, in the conventional method for controlling the amount of secondary cooling water of a slab, when the casting speed fluctuates, the surface temperature of the slab fluctuates downstream of the outlet of the secondary cooling zone of the slab, for example, at the cutting completion position of the slab. I do. Specifically, when the casting speed is reduced, the surface temperature of the slab at the cutting completion position of the slab decreases even if the surface temperature of the slab at the outlet of the secondary cooling zone is the target surface temperature.

FIG. 1 is a diagram showing a change in the surface temperature of the slab at the outlet of the secondary cooling zone when the casting speed changes. FIG. 2 is a diagram illustrating a change in the surface temperature of the slab at the cutting completion position of the slab when the casting speed is changed. Machine length is 43m, using a vertical bending type continuous casting machine in which the distance from the secondary cooling zone outlet to the cutting completion position of the slab is 11m, a low-carbon steel slab having a thickness of 270mm and a width of 1000 to 1600mm, The target surface temperature of the slab at the outlet of the secondary cooling zone is 860 ° C, and the specific water volume of the secondary cooling is 1.7 liter / k.
g-steel, an example in which casting is performed under the target casting speed of 2 m / min, and both examples are examples in which casting is performed by a conventional method of controlling secondary cooling of a slab.

FIG. 1 shows that even when the casting speed is lower than the target speed, the surface temperature of the slab at the outlet of the secondary cooling zone is the target surface temperature. Further, FIG. 2 shows that when the casting speed is reduced, the surface temperature of the slab at the cutting completion position of the slab is lower than the target surface temperature.

As described above, according to the conventional method for controlling the secondary cooling of the cast slab, when the casting speed is reduced, the surface temperature of the cast slab at the outlet of the secondary cooling zone becomes the target surface temperature, The reason why the surface temperature of the cast piece at the cutting completion position of the piece decreases is as follows. That is, the slab cutting device is usually arranged at a fixed position on the downstream side of the secondary cooling zone outlet, and is a device that moves in the casting direction at the same moving speed as the slab. The time from the start of cutting the slab in the width direction to the completion of the cutting is proportional to the width of the slab, but is almost constant, so that the slab is cut after leaving the secondary cooling zone outlet. The time depends on the casting speed. That is, when the casting speed is reduced, the time from when the slab exits the secondary cooling zone outlet to when it is cut is increased. During that time, the amount of heat radiated from the slab surface to the atmosphere increases, and the surface temperature of the slab decreases. Further, as described above, the cutting completion position depends on the width of the slab, but is almost constant, and the position where the cutting is to be completed is determined in view of the equipment arrangement.

In the method of the present invention, the variation of the surface temperature of the slab at a specific position downstream of the outlet of the secondary cooling zone is calculated and obtained based on the information on the variation of the casting speed. The surface temperature of the target slab at the outlet of the secondary cooling zone is changed so that the deviation between the obtained surface temperature and the preset target temperature is eliminated. The secondary cooling water amount of the slab in the secondary cooling zone is varied such that the surface temperature of the slab at the secondary cooling zone outlet becomes the target temperature at the new secondary cooling zone outlet. Thereby, even if the casting speed fluctuates,
The surface temperature of the slab at a specific position can be set to a preset target temperature.

In another method of the present invention, the target surface temperature of the slab at the outlet of the secondary cooling zone is determined based on the measured value of the surface temperature of the slab between the secondary cooling zone outlet and a specific position. And the secondary cooling water amount of the slab in the secondary cooling zone is controlled so as to obtain the new target slab temperature.

If the position where the surface temperature of the slab is measured is close to the outlet of the secondary cooling zone, the influence of the casting speed fluctuation on the surface temperature of the slab at a specific position can be quickly grasped. Also,
If the position where the surface temperature of the slab is measured is close to the specific position, the influence of the casting speed fluctuation on the surface temperature of the slab at the specific position can be correctly grasped as a quantity. The measurement position is preferably selected according to the continuous casting machine and the facilities and operation policies of the next step, the hot rolling mill. Hereinafter, a case where the position where the surface temperature of the slab is measured is near the intermediate position between the secondary cooling zone outlet and the specific position will be described.

Here, "near the intermediate position between the secondary cooling zone outlet and the specific position" means two positions before and after the intermediate position between the secondary cooling zone outlet and the specific position (position equidistant from both).
Means a position within a range of up to 3 m.

The amount of change in the surface temperature of the slab in the vicinity of the intermediate position between the secondary cooling zone outlet and the specific position when the casting speed fluctuates is determined in advance, and the intermediate temperature measured when the casting speed fluctuates is measured. The target surface temperature of the slab at the outlet of the secondary cooling zone is changed such that the deviation between the surface temperature of the slab near the position and the surface temperature of the slab obtained in advance is eliminated. The secondary cooling water amount of the slab in the secondary cooling zone is varied such that the surface temperature of the slab at the secondary cooling zone outlet becomes the target temperature at the new secondary cooling zone outlet.

More specifically, a difference in the surface temperature of the slab when the casting speed fluctuates between the vicinity of the intermediate position and the specific position is determined in advance, so that when the casting speed fluctuates, the slab at the specific position is determined. The surface temperature of the slab in the vicinity of the intermediate position such that the surface temperature becomes the target surface temperature can be determined in advance. A new target temperature at the outlet of the secondary cooling zone is determined such that the surface temperature of the slab near such an intermediate position is obtained, and the surface temperature of the slab at the outlet of the secondary cooling zone is set to the new target slab temperature. The secondary cooling water amount of the slab in the secondary cooling zone is controlled so that Thereby, even if the casting speed fluctuates, the surface temperature of the slab at a specific position can be set to a preset target temperature.

Since the casting speed is not usually higher than the target speed from the viewpoint of ensuring the quality of the slab, the method of the present invention is applied particularly when the casting speed is lower than the target speed. Is effective.

[0025] Even if the casting speed is lower than the target speed and the surface temperature of the target slab at the outlet of the secondary cooling zone is increased, the quality of the surface and the inside of the slab can be kept good. The reason is as follows.

That is, as will be described later, when increasing the target of the surface temperature of the slab at the outlet of the secondary cooling zone, the temperature range to be raised is up to about 100 ° C. At this time, by setting the surface temperature at the time of straightening the slab to a temperature higher than the embrittlement temperature of steel, the occurrence of surface cracks in the slab can be prevented.

Further, the final solidification position inside the slab temporarily moves to the upstream side in the casting direction when the casting speed decreases. Thereafter, when the target surface temperature of the slab at the outlet of the secondary cooling zone is increased within a range of about 100 ° C., the final solidification position returns to the downstream side again. At this time, by preventing the final solidification position from being located downstream of the outlet of the secondary cooling zone, it is possible to prevent the occurrence of internal defects such as internal cracks in the slab. This is because the thickness of the solidified shell when straightening the slab can be set to an appropriate range. It is also possible to prevent the slab from bulging downstream of the outlet of the secondary cooling zone.

[0028]

FIG. 3 is a schematic view showing an example of a continuous casting machine when the method of the present invention is carried out, and shows an example of a vertical bending type continuous casting machine. The slab 5 having the solidified shell 2 immediately after being pulled out from the mold 1 is sprayed with water or the like by a spray nozzle 4 or the like, and is secondarily cooled.
It is pulled out by the pinch roll 6 while being supported by the guide roll pair 3. The slab having the increased thickness of the solidified shell is straightened with a pinch roll at the position of the straightening point. The slab drawn from the secondary cooling zone outlet 7 is cut by a slab cutting device 8. The cut slab is carried out of the continuous casting machine by a transfer device (not shown).

In the following description, the specific position will be described as the cutting completion position of the slab cutting device. In the example of FIG. 3, the surface temperature of the slab is near the secondary cooling zone outlet, the cutting completion position of the slab cutting device that is the specific position, and the intermediate position between the secondary cooling zone outlet and the specific position. Measuring devices 9, 10 and 11 are arranged respectively.

The surface temperature of the slab can be measured by, for example, a radiation thermometer. Further, the casting speed can be measured based on a calculation based on the rotation speed of a normal pinch roll, or a method in which a roll is brought into contact with a slab and obtained from the rotation speed.

The method of the present invention will be specifically described below. FIG. 4 is a diagram showing a control block in an example of the apparatus for controlling the amount of secondary cooling water of a slab used when carrying out the method of the present invention. When carrying out the method of the present invention, a secondary cooling water control device 12 and a secondary cooling water controller 13 having at least the following functions are arranged.

The secondary cooling water amount controller 12 comprises a slab temperature setting section 14 and a slab temperature calculating section 15.
By the switching mechanism, the slab temperature setting unit 14 or the slab temperature calculating unit 15 sends a new target slab at the outlet of the secondary cooling zone changed to the secondary cooling water controller 13 based on the variation of the casting speed. Is input. The secondary cooling water controller 13 sends a signal for varying the amount of secondary cooling water of the slab in the secondary cooling zone based on the target surface temperature of the slab at the outlet of the new secondary cooling zone. Input to a device (not shown).

In the method of the present invention, the target surface temperature of the slab at the outlet of the secondary cooling zone is determined based on the variation of the casting speed so that the surface temperature of the slab at a specific position becomes a predetermined temperature. And the secondary cooling water amount of the slab in the secondary cooling zone is controlled so as to obtain the new target slab temperature. This will be described with reference to FIG.

The slab temperature setting section 14 receives a preset target value of the slab surface temperature at a specific position downstream of the secondary cooling zone outlet and a measured casting speed. The slab temperature setting unit 14 calculates and obtains the variation of the surface temperature of the slab at this specific position based on the information on the input variation of the casting speed, and obtains the surface temperature obtained by the calculation. And the target surface temperature of the target slab at the outlet of the secondary cooling zone is changed so that the deviation between the target temperature and the preset target temperature is eliminated. The target surface temperature of the slab at the outlet of the changed new secondary cooling zone is input to the secondary cooling water controller 13. In the secondary cooling water controller 13, the secondary cooling water amount of the slab in the secondary cooling zone is adjusted so that the surface temperature of the slab at the secondary cooling zone outlet becomes the target temperature at the new secondary cooling zone outlet. A signal to be varied is input to a secondary cooling water amount adjusting device (not shown). In this way, even if the casting speed fluctuates, the surface temperature of the slab at this specific position can be set to a preset target temperature. This can be expressed as follows.

Deviation = T (specific) _O− T (specific) _S (a) T (exit) _F = T (exit) _O + Ka × (Vs−Vc) + Kb (b) where T (specified) _O : Surface temperature of target cast piece at specific position (° C) T (specified) _S : Calculated surface temperature of cast piece at specific position (° C) T (outlet) _O : outlet of secondary cooling zone T (outlet) _F : New target surface temperature of cast slab at outlet of secondary cooling zone (° C) Vs: Reference pouring speed (m / min) Vc: Measured casting speed (m / min) Ka: Influence ratio of casting speed on surface temperature of cast slab (° C
/ M / min) Kb: constant (° C.) That is, a new target casting at the outlet of the secondary cooling zone is performed so that the deviation of the surface temperature of the slab at the specific position defined by the above equation (a) becomes zero. Piece surface temperature T (outlet) _F
Is the temperature defined by the above equation (b). The coefficients Ka and Kb in the equation (b) are coefficients to be changed depending on continuous casting equipment, steel, secondary cooling conditions, and the like, and are determined in advance by experiments. The amount of the secondary cooling water is changed so that the surface temperature of the new target slab at the outlet of the secondary cooling zone becomes this T (outlet) _F.

According to another method of the present invention, the surface temperature of the slab between the outlet of the secondary cooling zone and the specific position is adjusted so that the surface temperature of the slab at the specific position becomes a predetermined temperature. Based on the measured values, the surface temperature of the target slab at the outlet of the secondary cooling zone is changed, and the secondary cooling water amount of the slab in the secondary cooling zone is changed so as to obtain this new target slab temperature. Control.

At this time, the measurement of the surface temperature of the slab between the secondary cooling zone outlet and the above-mentioned specific position is performed by determining the intermediate temperature between the secondary cooling zone outlet and the cutting completion position of the slab cutting device at the specific position. It can be near the position. Therefore, in the following description, FIG. 4 shows a case where the position where the surface temperature of the slab is measured is near the intermediate position between the secondary cooling zone outlet and the cutting completion position of the slab cutting device which is the specific position. It will be described using FIG.

The slab temperature calculating section 15 includes a preset target value of the slab surface temperature near the intermediate position between the secondary cooling zone outlet and a specific position of the slab cutting completion position and the measured slab surface temperature. The surface temperature of the piece is entered and the casting speed is also entered. In the slab temperature calculating section 15, based on the input information on the fluctuation amount of the casting speed, a preset target value of the slab surface temperature in the vicinity of the intermediate position between the secondary cooling zone outlet and the specific position is set. The target surface temperature of the slab at the outlet of the secondary cooling zone is changed so that the deviation from the measured surface temperature of the slab is eliminated. The surface temperature of the target slab at the outlet of the changed secondary cooling zone is changed by the secondary cooling water controller 1.
Enter 3 In the secondary cooling water controller 13, the secondary cooling water amount of the slab in the secondary cooling zone is adjusted so that the surface temperature of the slab at the secondary cooling zone outlet becomes the target temperature at the new secondary cooling zone outlet. A signal to be varied is input to a secondary cooling water amount adjusting device (not shown).

As described above, the difference in the surface temperature of the slab near the intermediate position and at a specific position when the casting speed fluctuates, and the difference between the casting temperature at the outlet of the secondary cooling zone and near the intermediate position when the casting speed fluctuates. If the difference between the surface temperatures of the slabs is obtained in advance, if the secondary cooling water amount is controlled so that the deviation between the surface temperature of the slab near the intermediate position and its target value is eliminated, the surface of the slab at a specific position is obtained. The temperature can be the target surface temperature. This can be expressed as follows.

Deviation = T (intermediate) _O− T (intermediate) _A (C) T (intermediate) _F = T (exit) _O + Ka × (Vs−Vc) + Kb (d) T (exit) ) _F = T (exit) _O + {T (intermediate) _F- T (intermediate) _A } (e) where T (intermediate) _O : surface temperature of the initially target slab near the intermediate position ( ° C) T (intermediate) _A : Surface temperature of slab measured near intermediate position (° C) T (intermediate) _F : Surface temperature of new target slab near intermediate position (° C) T (exit) _O : Initial target surface temperature of slab at outlet of secondary cooling zone (° C.) T (outlet) _F : Surface temperature of new target slab at outlet of secondary cooling zone (° C.) Vs: Reference casting speed ( m / min) Vc: measured pouring speed (m / min) Ka: ratio of influence of casting speed on surface temperature of cast slab (° C.
/ M / min) Kb: constant (° C.) That is, a new target slab near the intermediate position is set so that the deviation of the surface temperature of the slab near the intermediate position defined by the above formula (c) becomes zero. Surface temperature T (intermediate) _F
Is the temperature defined by the above equation (d). The coefficients Ka and Kb in the equation (d) are coefficients to be changed depending on continuous casting equipment, steel, secondary cooling conditions, and the like, and are obtained in advance by experiments. T (intermediate) calculated from equation (d)
_{Using F} , a new target surface temperature T (outlet) _F of the slab at the outlet of the secondary cooling zone defined by the above equation (e) is obtained. The amount of the secondary cooling water is changed so that the surface temperature of the new target slab at the outlet of the secondary cooling zone becomes this T (outlet) _F.

In the method of the present invention, when the casting speed is decreased and the target of the surface temperature of the slab at the outlet of the secondary cooling zone is increased, it is desirable that the temperature range to be increased is up to 100 ° C.

Usually, the secondary cooling condition of the slab is determined so that the final solidification position inside the slab does not fall on the downstream side of the secondary cooling zone outlet, and the secondary cooling condition is set within the range of the secondary cooling condition. The target surface temperature of the slab at the outlet of the next cooling zone is set high.

Further, the surface temperature of the slab at the outlet of the secondary cooling zone downstream from the rectification position is determined so as to avoid the above-mentioned embrittlement temperature at the position where the slab is corrected. ing. Although the temperature range varies depending on the chemical composition of the steel, the slab is easily embrittled in a temperature range of about 700 to 850 ° C., and when the slab is straightened, cracks are easily generated on the surface or inside of the slab. It is.

Therefore, when raising the target of the surface temperature of the slab at the outlet of the secondary cooling zone, there is no particular problem with the surface crack of the slab. Since the temperature may be downstream from the band outlet, the temperature range to be raised is preferably up to 100 ° C.

The method of using the measured value of the surface temperature of the slab between the outlet of the secondary cooling zone and the specific position has been described in detail above when the measurement position is near the intermediate position. Before or after the vicinity of the intermediate position, and even when the measurement position is set to the specific position, the vicinity of the intermediate position described above is replaced by a position before, after, or a specific position near the intermediate position, so that the vicinity of the intermediate position is obtained. Similarly, based on the surface temperature of the slab measured at those positions, the surface temperature of the target slab at the secondary cooling zone outlet is changed, and the secondary slab temperature is changed so as to obtain this new target slab temperature. The secondary cooling water amount of the slab in the cooling zone can be controlled.

[0046]

EXAMPLE A vertical bending type continuous casting machine having a length of 43 m and a distance of 11 m from the outlet of the secondary cooling zone to the position where the slab was cut was used. The thickness was 270 mm and the width was 1600 to 1000.
mm of low carbon steel was cast.

The reason why the slab width is 1600 to 1000 mm is that the width was changed during casting. The target casting speed is 2 m / min, the specific water volume of the secondary cooling at that time is 1.7 liters / kg-steel, and the surface temperature of the target slab at the outlet of the secondary cooling zone is 860 ° C. .

The specific position on the downstream side in the casting direction from the outlet of the secondary cooling zone defined in the present invention is a slab cutting completion position, and the target surface temperature of the slab at the specific position is 94%.
0 ° C. In each test, casting was performed by appropriately reducing the casting speed to a speed between 2.0 m / min and 1.5 m / min.

Test No. of the present invention example In FIG. 4, FIG.
The test was performed using the secondary cooling water amount control device and the secondary cooling water controller having the configuration shown in FIG. At that time, from the measured casting speed, the amount of variation of the surface temperature of the slab at a specific position is calculated and obtained, so that the deviation between the calculated surface temperature and the preset target temperature is eliminated. Tests were performed using the method of the present invention to change the target slab surface temperature at the outlet of the secondary cooling zone.

Test No. of the present invention example In No. 2, a test was performed by another method of the present invention using a measured value of the surface temperature of the slab between the outlet of the secondary cooling zone and a specific position.
The measured value of the surface temperature of the slab was in the vicinity of an intermediate position between the secondary cooling zone outlet and the specific position. Test No. Like 1,
The test was performed using a secondary cooling water amount controller and a secondary cooling water controller. At that time, when the casting speed fluctuates, the surface temperature of the slab near the measured intermediate position and the surface temperature of the slab at a specific position when the casting speed fluctuates are set in advance so that the target surface temperature. The target surface temperature of the slab at the outlet of the secondary cooling zone was changed so that the deviation from the surface temperature of the slab near the set intermediate position was eliminated.

Test No. of Comparative Example In No. 3, the method of the present invention is not applied, and the conventional method of controlling the secondary cooling which is usually used, that is, when the casting speed fluctuates, the surface temperature of the slab at the outlet of the secondary cooling zone is kept constant. The test was conducted by controlling the target temperature.

Test No. of Comparative Example In 3, when the casting speed is reduced to a speed between 2.0 m / min and 1.5 m / min, the surface temperature of the slab at the outlet of the secondary cooling zone becomes 860 ° C., which is the target temperature at that position. Although it could be almost maintained, the surface temperature of the slab at the specific position was the result shown in FIG. 2, and the casting speed was 0.5 m higher than the target of 2.0 m / min.
At 1.5 m / min, the surface temperature of the slab at the specific position was about 50 ° C. lower than the target.

Test No. of the present invention example In the case of 1, the coefficient Ka in the above equation (b) is set to 150 ° C./m/min,
Was controlled as 0 ° C. The surface temperature of the slab at the specific position was a result shown in FIG. 5 below. FIG. 5 is a diagram showing the relationship between the surface temperature of the slab at a specific position and the casting speed. The casting speed is 0.5 m / min.
Even at 1.5 m / min, the surface temperature of the slab at the specific position almost reached the target surface temperature, and the variation of the surface temperature was as good as about 10 ° C.

In the test No. of the present invention, In No. 2, the coefficient Ka in the above equation (d) is set to 56 ° C./m/min, Kb
Was controlled at 85 ° C. The surface temperature of the slab at the specific position was a result shown in FIG. 6 below. FIG. 6 is a diagram illustrating the relationship between the surface temperature of the slab at a specific position and the casting speed. Casting speed 0.5m from target 2.0m / min
Even at 1.5 m / min, the surface temperature of the cast slab at the specific position almost reached the target surface temperature, and the variation in the surface temperature was about 7 ° C. The result was even better than 1.

[0055]

According to the method of the present invention, even if the casting speed fluctuates, the quality of the surface and the inside of the slab is not deteriorated, and the downstream of the secondary cooling zone outlet in the casting direction is not deteriorated.
For example, the surface temperature of the slab at the cutting completion position of the slab can be a constant and high target slab surface temperature specific to steel, and the slab having a higher surface temperature is the next step. Can be sent to hot rolling mill.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in a surface temperature of a slab at an outlet of a secondary cooling zone when a casting speed is changed.

FIG. 2 is a diagram illustrating a change in the surface temperature of a slab at a cutting completion position of the slab when the casting speed is changed.

FIG. 3 is a schematic view showing an example of a continuous casting machine when performing the method of the present invention.

FIG. 4 is a diagram showing a control block in an example of a device for controlling a secondary cooling water amount of a slab used when carrying out the method of the present invention.

FIG. 5 is a diagram showing a relationship between a surface temperature of a slab at a specific position and a casting speed.

FIG. 6 is a diagram showing a relationship between a surface temperature of a slab at a specific position and a casting speed.

[Explanation of symbols]

1: Mold 2: Solidified shell
3: Guide roll pair 4: Spray nozzle 5: Cast piece 6: Pinch roll 7: Secondary cooling zone outlet 8: Cutting device 9-11: Surface temperature measuring device 12: Secondary cooling water amount control device 13: Secondary cooling Water controller 14: Slab temperature setting unit 15: Slab temperature calculation unit

Claims (3)

[Claims] 1. The method according to claim 1, wherein the surface temperature of the slab at a specific position downstream from the secondary cooling zone outlet of the continuous casting machine in the casting direction is a predetermined temperature.
The surface temperature of the target slab at the outlet of the secondary cooling zone is changed, and the secondary cooling water amount of the slab in the secondary cooling zone is controlled so that the new target slab temperature is obtained. Control method of secondary cooling of continuous cast slab. 2. The secondary cooling zone outlet and the specific position are arranged such that the surface temperature of the slab at a specific position downstream in the casting direction from the secondary cooling zone outlet of the continuous casting machine becomes a predetermined temperature. Based on the measured value of the surface temperature of the slab during, change the surface temperature of the target slab at the outlet of the secondary cooling zone,
A method for controlling secondary cooling of a continuous cast slab, wherein the secondary cooling water amount of the slab in the secondary cooling zone is controlled so as to obtain the new target slab temperature. 3. The method according to claim 1, further comprising: changing a surface temperature of the target slab at the outlet of the secondary cooling zone based on the measured value of the surface temperature of the slab at the specific position so as to obtain the new target slab temperature. The method for controlling secondary cooling of a continuously cast slab according to claim 2, wherein the secondary cooling water amount of the slab in the secondary cooling zone is controlled.