JPH0448851B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a method for water cooling a hot rolled high temperature steel plate from its upper and lower surfaces. This type of cooling method is technically difficult;
There are many themes to be solved, and various research and developments have been carried out from various fields in this industry, and some have been put into practical use. That is, since the cooling rate is not uniform in the thickness direction from the front surface to the center to the back surface, deformations such as buckling waves and warping are likely to occur. Because the board is wide, a large amount of water collects on the top surface,
Because of the outflow, the cooling uniformity in the upper and lower surfaces and in the width direction is likely to be disrupted, and deformations such as buckling waves and warping are likely to occur. Rolled steel plates are not uniform in temperature, size, shape (plate crown, etc.), and surface texture, and are prone to variations in cooling. There are many topics that need to be resolved. By the way, in online controlled cooling of high-temperature steel plates, the current state of the prior art will be explained with reference to Figures 1a and 1b. Figure 1a shows the case where cooling is performed without providing cooling water distribution in the width direction of the plate. As shown in the figure, the shape of the steel plate at room temperature is deformed at the edges. As a measure to prevent this cooling distortion, as shown in Fig. 1b, the cooling water distribution in the sheet width direction is made so that the distribution is smaller on the sheet edge side. Directional temperature distribution from about 800℃,
When cooling to the cooling stop temperature, that is, the temperature distribution in the width direction of the steel sheet after cooling, of approximately 550°C, no large cooling strain occurs. By the way, if the cooling stop temperature is lowered, cooling distortion becomes large as shown in FIG. 2, which not only results in a defective product but also causes operational troubles such as the inability to apply a hot leveler. On the other hand, from the material side, as shown in Figure 3,
There is a relationship between mechanical properties and cooling stop temperature. In other words, lowering the cooling stop temperature improves yield stress (YS) and tensile stress (TS).
In addition, for steel plates with the same strength level as conventional ones,
It is possible to lower Ceq, which leads to a reduction in additive components, which has great benefits such as improved weldability. That is, by lowering Ceq and lowering the cooling stop temperature, a material that satisfies mechanical properties can be manufactured. The ingredient list in FIG. 3 is as follows.

[Table] Although it is effective to lower the Ceq and the cooling stop temperature in this way, there is the problem of cooling distortion as mentioned above, and it is difficult to lower the cooling stop temperature to 550℃ or less. There is a limit. In other words, in a plate factory, if cooling is stopped at about 500°C and straightened with a hot leveler, steel plates with good flatness can be produced, but if cooling is stopped at a lower temperature than that, conventional technology In this case, manufacturing is impossible for the following reasons. For example, at 300℃, the steel plate is deformed in front of the hot leveler, requiring strong straightening, and even if straightening is possible, there is a large uneven temperature distribution in the steel plate. , when the steel plate is cooled to room temperature, it becomes defective in shape. When the steel sheet is cooled to near room temperature, the temperature distribution of the steel sheet is nearly uniform, but the deformation that occurs during the cooling process is large, and the strength of the steel sheet increases, so that it cannot be straightened sufficiently and the shape becomes defective. The conventional example will be explained once again with reference to FIGS. 4 and 5. In FIG. 4, A is the water volume distribution in the width direction, and the water injection distribution is such that the water volume is smaller on the edge side. B is the temperature distribution in the width direction, approximately
800°C → about 550°C → about 300°C → 100°C → room temperature, C indicates the shape of the steel plate, and D indicates the hot leveler. That is, in FIG. 4, in the width direction water amount distribution A,
By setting the cooling stop temperature from the cooling start temperature of about 800°C to about 550°C, the shape of the steel plate at room temperature will be normal if it is applied to the hot leveler D and air cooled as shown in Figure 4, but in this case, the cooling stop temperature is not that low, so it cannot be said that the mechanical properties and Cen are fully satisfied. Therefore, with the water flow distribution A in the width direction, the cooling start temperature is about 800℃, the cooling stop temperature is about 550℃, and the cooling temperature is about 300℃.
If the cooling stop temperature is set at .degree. C., deformation will occur before being applied to the hot leveler, and even if this can be corrected, it will be deformed when air cooled, and it will not be possible to correct it at the hot level. The cause of this is the cooling of the cooling water poured into the steel plate,
When we calculate the cooling effect when water flows over the steel plate after cooling, the relationship shown in Figure 5 becomes clear, and
This result is because, as shown in FIG. 4, when cooling at temperatures below about 500° C., providing water injection distribution in the width direction will conversely lead to non-uniformity in the temperature distribution in the width direction. By the way, when considering the allowable temperature distribution in the width direction of the steel plate with reference to Fig. 14, the horizontal axis is the steel plate width, and the vertical axis is the temperature difference in the width direction (temperature difference between the center of the steel plate width and both ends of the steel plate). The relationship is shown; if the plate width is small, the flatness of the steel plate is good even if the temperature difference in the width direction is large, but if the plate width is large, buckling deformation occurs even if the temperature difference in the width direction is small. I understand that. In view of the above-mentioned phenomena and knowledge, the present invention is based on Ceq
It is an object of the present invention to provide a method for cooling a high-temperature steel sheet, which reduces the cooling strain and generates less cooling strain even when the cooling stop temperature is lowered. That is, in the present invention, in the method of water-cooling a hot-rolled high-temperature steel plate from its upper and lower surfaces, in the process of water-cooling the high-temperature steel plate, the range of the cooling start temperature and the cooling stop temperature is adjusted to a plurality of temperatures. divided into areas,
The feature is that cooling is performed while changing the cooling water injection pattern in the width direction of the steel sheet in accordance with the temperature range of each section. Hereinafter, the method for cooling a high temperature steel plate according to the present invention will be described in detail with reference to the drawings. FIG. 6 shows a schematic diagram of an embodiment of the present invention,
As is clear from FIG. 6, in this example, cooling is performed while changing the water injection pattern in the widthwise water amount distribution A to pattern, pattern, pattern. That is, the pattern is the same as the conventional example shown in FIG. 4, but when the temperature distribution in the width direction is from the cooling start temperature of about 550°C to the cooling stop temperature of about 300°C,
Unlike the pattern, the water amount distribution at the edge is slightly higher than the pattern, and the water amount distribution in the width direction is almost the same in the pattern. The outline of the cooling method of the present invention is as described above,
Although the control method will be described later, the apparatus used in the present invention will be explained with reference to FIGS. 7 to 10. In FIG. 7, reference numeral 1 denotes a steel plate to be cooled, which is cooled by water injection all at once during the process of passing the steel plate in the direction of the arrow. Table rollers 2 are arranged in rows at predetermined intervals in the sheet passing direction, and a lower cooling header 4 having a lower spray nozzle 7 is provided between the rollers 2. Reference numeral 3 denotes an upper cooling header, which has an upper hairpin nozzle 6 and injects cooling water into the upper surface of the steel plate 1 to be cooled, and is arranged in parallel in the width direction of the steel plate 1. 5 is an auxiliary header for upper cooling, and has a hairpin nozzle 8. That is, in the present invention, since the influence is large and important when water is injected from the upper surface of the steel plate, the lower cooling device has the same configuration as the conventional example, but the upper cooling device is configured as shown in Fig. 8. ing. That is, in FIG. 8, the upper cooling header 3 is fixedly installed on a pair of left and right upper header fixing bases 9 provided along the sheet passing direction, perpendicular to the sheet passing direction, using fasteners 10 such as U-bolts. An auxiliary header 5 is fixedly installed on an upper auxiliary header fixing base 11 between the upper cooling headers 3 using fasteners 12 such as U-bolts. That is, the upper cooling header 3 and the upper cooling auxiliary header 5, which are connected to the upper supply water pipe 14 shown in FIG. 10 through the flexible pipe 13, are installed alternately in the plate passing direction. As is clear from the water supply system diagram shown in Figure 10, the three-way switching valve 15,
16, 17, in particular the three-way switching valve 15, 1
6, the water injection pattern can be changed into patterns in this example as shown in FIG. In Fig. 9, a indicates the upper header center, b indicates the upper auxiliary header center, ○ mark indicates the upper hairpin nozzle position, △ mark indicates the upper auxiliary hairpin nozzle position, and black ○ mark indicates that the upper hairpin nozzle is not used. There is. That is, as shown in FIG. 11, when the steel plate 1 to be cooled is cooled by passing it through a cooling device 17 that injects water all at once from the upper and lower surfaces thereof, the range of the cooling start temperature and the cooling stop temperature is set to a plurality of temperature ranges. How to cool the steel sheet by dividing it into sections and changing the cooling water injection pattern in the width direction of the steel sheet according to the temperature range of each section will be explained based on the functional outline diagram shown in FIG. 11 and the flowchart shown in FIG. 12. Thermometers 18 and 19 are provided on the inlet and outlet sides of the cooling device 17, respectively, and a steel plate tracking sensor 20 is provided on the inlet side, and a steel plate tracking function 21, water injection amount calculation, and cooling time calculation function 22, A water injection command and a water injection stop command 23 are given to the cooling device 17, and furthermore, a water injection amount distribution change function 24, a temperature actual value estimation 25, etc. are possible. A flowchart from the start of cooling to the end of cooling will be explained with reference to FIG. In Fig. 12, block A is the actual cooling start temperature _TscT , _the target cooling stop temperature _TFCTO , the plate thickness t,
This is a block of expected data such as board width and board length. B is a block for calculating the target cooling rate CR _T , which is set experimentally and empirically according to the steel type, plate thickness, etc. C is a calculation block for the cooling time _τt , which is obtained by the following calculation. τ _t =Tsc _T −T _F c _T o/CR _T D is a calculation block for the required water density w, and this w is calculated by the following formula. w=[CR _T /A·f(T)] ^1/n where CR _T [°C/s], w [m ³ /min.m ² ], and A·n are coefficients, respectively. E is a calculation block for calculating the required total amount of water w _T and the threading speed V, and w _T is calculated by the following formula. w _T = w×lw×ll×η lw; Cooling zone width, ll; Cooling zone length, η;
Correction value that takes into account water injection distribution in the upper part, etc. Further, V is calculated using the following formula. V=l _l +lc _T +lc _B -l/τ _t lc _T ; Amount of protrusion of the top of the steel plate (leading edge), lc _B ; Amount of protrusion of the bottom (rear end) of the steel plate l; Length of the steel plate From the above, the water injection timing block with code F is commanded. When the water injection timing is YES, a command to open the three-way switching valves 15 and 17 of the upper and lower main headers shown in Fig. 10 is issued to block G, and when the water injection timing is NO, it is delayed. Then, the water injection pattern is created as described above, but when there is a water injection pattern change command as in symbol H, the time until the water injection pattern change in I is given.
A block for calculating T ₁ , a block for integrating the water injection time for J, a block for determining whether or not it is time to change the water injection pattern for K, a block for commanding the opening of the upper auxiliary header three-way valve for L, a block for determining whether or not cooling has ended, and N for determining whether or not cooling has ended. The process ends after a command block for closing the three-way valves of the upper and lower main headers and the upper auxiliary header, a command block for transporting the steel plate O to the outside of the cooling device, and a block for capturing the actual temperature value of the steel plate after cooling P. Therefore, τ ₁ is calculated using the following formula. τ ₁ = Tsc _T −Tchi／CR _T chi Note that the steel plate temperature when changing the water injection pattern is Tchi
If the average cooling rate so far is CR _T chi, then CR _T chi = CR _T of (Tchi). However, the above I may be performed after E. Further, in this example, a three-way valve is used for L, but since the amount of water injected from the auxiliary header is small, an ON-OFF type butterfly valve or the like may be used. 7 to 11 illustrate an example in which an auxiliary header is attached as an upper cooling device, but as shown in FIG. There may be two types of water injection patterns in the width direction for the lower stage, the cooling temperature range is divided by the above-mentioned Tchi, and the upper and lower headers can be used differently. In the control flowchart in this case, G in Fig. 12 is the three-way valve opening command for the upper and lower pattern I, L is the pattern header three-way valve opening command and pattern header three-way valve opening command, and N is the upper and lower three-way valve closing command. The rest is the same as the example illustrated in FIG. In addition, Fig. 15 and Fig. 16 show examples of changes in the injection pattern of steel plate cooling water, and both show the cooling start temperature.
This is an example of dividing the cooling stop temperature into two ranges from 800°C to 300°C. Figure 15 shows the case where the water density at the center of the board width is constant, and the water density at both ends of the board width is varied between patterns. Figure 16 shows three examples of patterns and patterns when the water density at the center of the board width is changed.
An example is shown. Note that although the pattern in the figure shows an example in which the water volume density is increased, the pattern may also be used to decrease it. Then, as shown in Fig. 17, the cooling start temperature is 800.
In the conventional example in which the steel plate is cooled in one pattern to the cooling stop temperature of 300°C, as mentioned above, the average amount of deformation of the steel plate becomes significantly large when the cooling stop temperature is around 500° to 550°C. , In the case of A-1 in Fig. 15, the occurrence of cooling strain is significantly reduced even when the cooling stop temperature is as low as 200°C or less. This can be said to be a cooling method for high-temperature steel sheets that prevents cooling distortion even though it satisfies the mechanical properties. In addition, in the case of the above example, the cooling start temperature is
The example was given as a case where the cooling start temperature is divided into two categories from around 800℃ to the cooling stop temperature of around 300℃, but if the cooling start temperature is around 800℃ and the cooling stop temperature is around 100℃, for example, it is divided into three categories, and each category is divided into two categories. The cooling water injection pattern in the width direction of the steel plate may be changed depending on the temperature range. Further, the cooling start temperature is not limited to around 800°C, but generally needs to be around the Ar ₃ transformation point or higher, and the cooling stop temperature may also be around 550°C or lower. That is, in the above example, the pattern is the same as the conventional example, but even in the range from the cooling start temperature of around 800°C to the cooling stop temperature of 500°C to 550°C, it is divided into multiple temperature ranges, and each The cooling water injection pattern in the width direction of the steel plate may be changed depending on the classification, and this is particularly effective for steel plates with a thickness of 50 mm or more. Next, an embodiment of the present invention will be described in comparison with a conventional example. <Conventional example> Steel plate size (mm)...11.8 x 3190 x 14.800 Cooling start temperature (°C)...750 Cooling stop temperature (°C)...350 Cooling water amount ( ^m3 /min・^m2 )...0.26 <Implementation of the present invention Example> Steel plate size (mm)…10.3×3210×14.800 Cooling start temperature (°C)…770 Pattern change temperature (°C)…520 Cooling stop temperature (°C)…330 Cooling water amount…0.26m ³ /min・m ^2As mentioned above The cooling stop temperature distributions of the conventional example and the embodiment of the present invention are as shown in Fig. 18a and b, and in the conventional example, the temperature distribution is uneven in the width direction of the plate as shown in Fig. 18a. On the other hand, in the embodiment of the present invention, the temperature distribution in the width direction of the plate becomes uniform as shown in FIG. 18b. Therefore, as shown in Reference Photo 1, in the conventional example, the edges of the steel plate are deformed into a corrugated plate shape in actual operation, whereas in the embodiment of the present invention, the steel plate is deformed in actual operation. It can be seen that cooling has been performed, indicating good flatness. In summary, in the present invention, in the process of cooling a high-temperature steel plate with water,
The range of cooling start temperature and cooling stop temperature is divided into multiple temperature ranges, and cooling is performed while changing the cooling water injection pattern in the width direction of the steel sheet corresponding to each temperature range. Even if the cooling temperature is lowered, the occurrence of cooling strain can be reduced, and lowering the cooling stop temperature has the advantage of lowering Ceq and improving weldability by reducing additive components, as well as reducing yield stress, tensile stress, etc. Mechanical properties can be significantly improved.

[Brief explanation of the drawing]

Figures 1a and 1b are diagrams explaining the current state of the prior art;
Figure 2 is a diagram showing the relationship between cooling stop temperature and cooling strain of a steel plate, Figure 3 is a diagram to explain the effect of cooling stop temperature on material quality, Figure 4 is a schematic diagram of a conventional example, and Figure 5 is an explanatory diagram of a conventional example showing steel plate temperature and secondary cooling/direct cooling, FIG. 6 is a schematic diagram showing an embodiment of the present invention, FIG. 7 is a side view of an example of a cooling device used in the present invention, and FIG. The figure is a plan view of the upper cooling device in FIG. 7, FIG. 9 is an explanatory diagram of an example of using an upper hairpin nozzle in the present invention and an example of using an auxiliary nozzle for pattern change, and FIG. 10 is a cooling device used in the present invention. FIG. 11 is a functional overview diagram of the cooling method of the present invention, FIG. 12 is an explanatory diagram of an example of a flowchart of an embodiment of the present invention, and FIG. 13 is an upper cooling device in a second embodiment of the present invention. cross-sectional view, 1st
Fig. 4 is an explanatory diagram showing an example of the temperature distribution tolerance in the width direction of the steel plate, and Fig. 15 is an explanatory diagram showing three examples of water injection patterns of the steel plate cooling water of the present invention when the water flow density at the center of the plate width is constant. FIG. 16 is an explanatory diagram showing three examples of injection patterns of the steel sheet cooling water of the present invention when the water flow density at the center of the sheet width is changed, and FIG. 17 is a graph diagram showing the results of pattern A-1 in FIG. 15. 18th
Figures a and b show the cooling stop temperature distributions of the conventional example and the embodiment of the present invention, where a is the conventional example and b is the embodiment of the present invention. 1... Steel plate to be cooled, 3... Upper cooling header,
4... Lower cooling header, 5... Upper cooling auxiliary header, 6... Upper hairpin nozzle, 7... Lower spray nozzle, 8... Upper auxiliary hairpin nozzle.

Claims (1)

[Claims] 1. In a method of water-cooling a hot-rolled high-temperature steel plate from its upper and lower surfaces, in the process of water-cooling the high-temperature steel plate, the range of cooling start temperature and cooling stop temperature is divided into multiple temperature ranges. divided,
A method for cooling a high-temperature steel plate, characterized by cooling the steel plate while changing a cooling water injection pattern in the width direction of the steel plate in accordance with the temperature range of each classification.