Steel plate manufacturing equipment and manufacturing method

Abstract

The present invention provides a manufacturing device and a manufacturing method for a steel plate that can perform more uniform cooling during heat treatment of the steel plate and can manufacture a flat and homogeneous steel plate. One embodiment of the present invention relates to a manufacturing device (heat treatment device (1)) for a steel plate (2) that performs heat treatment on the steel plate (2), and is provided with a heating furnace (3) for heating the steel plate (2) below 100°C; a first shape straightening device (4) for straightening the heated steel plate (2) flatly; a quenching device (5) for quenching the straightened steel plate (2); and a second shape straightening device (6) for straightening the quenched steel plate (2) flatly.

Description

Technical Field

[0001] The invention relates to a manufacturing device and a manufacturing method for a steel plate. Background Art

[0002] In the manufacture of steel plates such as thick steel plates, cooling from high temperature is mostly implemented in order to adjust mechanical properties such as strength. Cooling is roughly divided into an online water cooling method and an offline water cooling method. In the online water cooling method, a water cooling device arranged online is used to water cool the steel plate after hot rolling. In the offline water cooling method, the rolled material is temporarily cooled to room temperature, and then heated and water-cooled again in a heat treatment furnace arranged offline. From the perspective of energy cost, the online water cooling method is very advantageous, but warping of the steel plate is likely to occur during rolling, so a cooling device cannot be arranged near the rolling mill. As a result, the temperature drops during the period from rolling to transportation to the cooling device, so there is a problem that water cooling cannot be performed at an appropriate temperature.

[0003] On the other hand, the off-line water cooling method is more advantageous in adjusting the mechanical properties because a cooling device is arranged on the outlet side of the heating furnace and quenching can be started from a temperature substantially equal to the heating temperature.

[0004] Generally speaking, hot-rolled steel plates are prone to temperature unevenness during cooling due to the differences in temperature distribution, shape or surface state of the steel plates after rolling. In addition, the temperature unevenness of the steel plates may also be caused by the performance of the cooling device. In addition, if the temperature unevenness of the steel plates occurs, deformation, residual stress, material deviation, etc. of the steel plates will occur after cooling. As a countermeasure, cooling devices capable of various uniform cooling have been developed. However, the methods that have been developed only improve the cooling devices, and in particular, they do not completely achieve the flattening of the steel plates after cooling. The poor shape of the steel plates after cooling is the cause of operational failures such as plate passing obstacles in the production line. In subsequent processes, pressurization and finishing treatment using a straightening device are required, so the cost also becomes high.

[0005] The causes of uneven temperature of steel plates include the design of the cooling nozzle and the shape of the steel plate during rolling. Depending on the design of the cooling nozzle, temperature deviations between the upper and lower surfaces and uneven temperature in the width direction occur. On the other hand, if the shape of the steel plate during rolling deteriorates, the cooling water flows unevenly on the steel plate, and the cooling capacity varies depending on the location, resulting in uneven temperature.

[0006] Here, there are many known technologies for suppressing temperature unevenness caused by cooling nozzles, such as temperature deviation of the upper and lower surfaces and uniformity in the width direction. On the other hand, there are almost no technologies for suppressing temperature unevenness that starts from shape defects generated during rolling. As a corresponding technology, there is a method of performing shape straightening before the accelerated cooling device to flatten the shape and ensure uniformity during cooling (Patent Documents 1 and 2). In Patent Documents 1 and 2, the purpose is to use the first shape straightening device to pass the shape straightening knife of the steel plate through the dewatering roller of the cooling device to fully remove water.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2002-11515

[0010] Patent Document 2: Japanese Patent Application Publication No. 2005-74480 Summary of the invention

[0011] However, in recent years, the number of production lines that actually use the technology of Patent Documents 1 and 2, which sets a linear straightening device before a cooling device, has gradually increased. However, in hot rolling, due to descaling during rolling, water cooling for temperature adjustment, etc., the temperature deviation is large in principle, and the temperature deviation generated in the plate surface becomes a difference in thermal shrinkage. Therefore, even if the shape is straightened by heating, there is a problem of deformation again when the temperature drops.

[0012] In addition, Patent Documents 1 and 2 propose an online process of accelerating cooling after straightening by a first shape straightening device, and then performing final straightening by a second shape straightening device. However, no matter which technology is used alone, it is not possible to achieve a good effect on the temperature deviation of the upper and lower surfaces, the uniformity in the width direction, etc. caused by the cooling nozzle, and the cooling strain caused by it.

[0013] In the past, offline heat treatment equipment was configured in sequence according to a heating furnace, a quenching device, and a shape straightening device. The quenching device is cooled to below 100°C. Even if the cooling uniformity cannot be ensured, it can be cooled to a low temperature close to the water temperature of the cooling water, so the final cooling stop temperature of the steel plate is constant. Therefore, the uniformity of cooling is not taken into consideration. In recent years, from the perspective of improving quality, the demand for reducing the deviation of the cooling rate within the plate surface during quenching has been increasing, and it has become important to perform uniform cooling through offline heat treatment that can ensure the temperature uniformity before quenching. In addition, even if offline heat treatment is used, the cooling can be terminated at a temperature higher than room temperature, such as above 100°C. In this case, if the cooling is uneven, the temperature of the steel plate after the cooling is also deviated, so not only the specified quality cannot be ensured, but also the thermal expansion difference within the surface of the steel plate temperature causes strain in the steel plate.

[0014] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a steel plate manufacturing facility and a steel plate manufacturing method that can perform more uniform cooling during heat treatment of the steel plate and can manufacture a flat and homogeneous steel plate.

[0015] According to one embodiment of the present invention, there is provided a manufacturing device for a steel plate, which is a manufacturing device for a steel plate that performs heat treatment on the steel plate, and comprises: a heating furnace for heating the steel plate at a temperature below 100° C.; a first shape straightening device for straightening the heated steel plate to be flat; a quenching device for quenching the straightened steel plate; and a second shape straightening device for straightening the quenched steel plate to be flat.

[0016] According to one embodiment of the present invention, there is provided a method for manufacturing a steel plate, which is a method for manufacturing a steel plate that is subjected to heat treatment, and comprises: a heating step of heating the steel plate at a temperature below 100° C.; a first straightening step of straightening the steel plate to be flat after the heating step; a quenching step of quenching the steel plate after the first straightening step; and a second straightening step of straightening the steel plate to be flat after the quenching step.

[0017] According to one aspect of the present invention, there is provided a steel plate manufacturing facility and a steel plate manufacturing method that can perform more uniform cooling during heat treatment of the steel plate and can manufacture a flat and homogeneous steel plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic configuration diagram of a heat treatment facility of a steel plate manufacturing facility according to one embodiment of the present invention.

[0019] Figure 2 It is a perspective view showing the detailed structure of the first shape straightening device and the quenching device. DETAILED DESCRIPTION

[0020] Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments shown below illustrate the apparatus and method for realizing the technical idea of ​​the present invention. The technical idea of ​​the present invention does not limit the material, shape, structure, configuration, etc. of the constituent parts to the following embodiments. In addition, the accompanying drawings are schematic. Therefore, it should be noted that the relationship and ratio between the thickness and the plane size are different from the actual ones, and the drawings also include parts with different relationship and ratio of each other's size.

[0021] (Steel Plate Manufacturing Equipment)

[0022] Figure 1 The schematic structure of a heat treatment facility 1 for a thick steel plate 2 as a steel plate manufacturing facility according to one embodiment of the present invention is shown. Figure 2 The detailed structures of the first shape straightening device 4 and the quenching device 5 of this embodiment are shown respectively. In this embodiment, in order to ensure uniform temperature and shape, the mechanical properties of the material are adjusted by an offline heat treatment device that is not directly connected to the rolling line. The heat treatment device 1 is a device that performs heat treatment on a thick steel plate 2 as a steel plate, and the device includes a heating furnace 3, a first shape straightening device 4, a quenching device 5, and a second shape straightening device 6. In addition, as shown in FIG. Figure 1 As shown, in the heat treatment equipment 1, a heating furnace 3, a first shape straightening device 4, a quenching device 5, and a second shape straightening device 6 are arranged in order from the upstream side of the conveying direction of the thick steel plate 2. In addition, between each device of the heating furnace 3, the first shape straightening device 4, the quenching device 5, and the second shape straightening device 6, conveying rollers (not shown) for conveying the thick steel plate 2 are respectively provided.

[0023] The heating furnace 3 heats the thick steel plate 2 having a temperature of 100° C. or less after hot rolling to an austenite temperature region. The thick steel plate 2 is a steel plate having a plate thickness of 4.0 mm or more.

[0024] The first shape straightening device 4 is a device for straightening the thick steel plate 2 heated by the heating furnace 3 to be flat, and is provided between the heating furnace 3 and the quenching device 5. The first shape straightening device 4 can use a skin-pass straightening device of a reduction type or a roller straightening device of a repeated bending type. In addition, for the reasons described later, it is preferred that the first shape straightening device 4 use a roller straightening device. And, for the reasons described later, when a roller straightening device is used, it is more preferred to further provide a pressurizing type straightening mechanism that can correct the warping of the front and rear ends of the thick steel plate 2.

[0025] Here, the temperature of the thick steel plate 2 drops from the time when the thick steel plate 2 is taken out of the heating furnace 3 to the time when it reaches the first shape straightening device 4. If the temperature drop is smaller, the increase in the deformation resistance of the thick steel plate 2 becomes smaller, and shape straightening can be performed with a small straightening force. Therefore, the distance from the heating furnace 3 to the time when it enters the first shape straightening device 4 is preferably less than 4m. In addition, in order to shorten the transportation time from the heating furnace 3 to the quenching device 5, the first shape straightening device 4 is preferably a small device with a small space. In addition, in order to straighten the thick steel plate 2 with relatively low deformation resistance during heating, the first shape straightening device 4 preferably uses a shape straightening device with a lower load-bearing capacity than the second shape straightening device 6. The first shape straightening device 4 has a load-bearing capacity of at least 500 tons, preferably about 3,000 tons. It should be noted that in this embodiment, tons represent metric tons.

[0026] The quenching device 5 is a device for quenching the thick steel plate 2 that has been straightened by the first straightening device 4 by water cooling. Figure 2 As shown, the quenching device 5 is a device for rapidly cooling the thick steel plate 2 after shape straightening, and has an upper cooling nozzle 51 and a lower cooling nozzle 52. The upper cooling nozzle 51 and the lower cooling nozzle 52 are respectively arranged in a plurality in the width direction of the thick steel plate 2 in the vertical direction relative to the conveying line, and a plurality of locations are arranged in parallel at a predetermined interval along the conveying direction of the thick steel plate 2. Cooling water 53 is sprayed toward the thick steel plate 2 from each of the upper cooling nozzle 51 and the lower cooling nozzle 52. In addition, in the quenching device 5, restraining rollers 50 can be respectively arranged before and after the upper cooling nozzle 51 and the lower cooling nozzle 52. By providing the restraining rollers 50, even if deformation strain is generated in the thick steel plate 2 due to uneven cooling, the thick steel plate 2 can be restrained to a certain extent, thereby preventing out-of-plane deformation.

[0027] The second shape straightening device 6 is a device for straightening the thick steel plate 2 quenched by the quenching device 5 in a flat manner, and is arranged on the outlet side of the quenching device 5 (the downstream side of the conveying direction of the thick steel plate 2). The second shape straightening device 6 can use a skin-pass straightening device of a reduction type, a roller straightening machine straightening device of a repeated bending type, or a pressurized straightening device. In addition, for the same reasons as the first shape straightening device 4, it is preferred that the second shape straightening device 6 use a roller straightening machine straightening device. And, for the same reasons as the first shape straightening device 4, when using a roller straightening machine straightening device, it is more preferred to further provide a pressurized straightening mechanism that can correct the warping of the front and rear ends of the thick steel plate 2. In addition, from the perspective of implementing shape straightening of the thick steel plate 2 near room temperature, the second shape straightening device 6 preferably has a high straightening reaction force, and preferably has a load-bearing capacity of at least 2000 tons or more.

[0028] (Method for manufacturing thick steel plate)

[0029] In the method for manufacturing a thick steel plate according to the present embodiment, first, a cast sheet or the like is used as a material and hot rolled in a hot rolling line (not shown) different from the heat treatment equipment 1 to manufacture a thick steel plate 2 of a predetermined thickness (e.g., 30 mm) and width (e.g., 2000 mm). Next, the hot-rolled thick steel plate 2 is cooled to room temperature and then descaled by a surface descaling device (not shown).

[0030] Then, the descaled thick steel plate 2 is placed in a heating furnace 3 and heated to an austenite temperature region (eg, about 910° C.) (heating step).

[0031] Thereafter, the thick steel plate 2 is taken out of the heating furnace 3, conveyed to the first shape straightening device 4 by a plurality of table rollers (not shown) provided at the exit side of the heating furnace 3, and is straightened (flattened) by the first shape straightening device 4 (first straightening step).

[0032] Here, the reason for setting the first shape straightening device 4 before the quenching device 5 (on the upstream side in the conveying direction of the thick steel plate 2) is described below. The thick steel plate 2 is pre-hot-rolled to a predetermined thickness and width using a hot rolling line different from the heat treatment equipment 1 as described above. At this time, if the thick steel plate 2 during rolling has a temperature deviation, the degree of thermal shrinkage during the cooling to room temperature varies depending on the part of the thick steel plate 2, so that a shape defect occurs after cooling. In the heat treatment equipment 1, the thick steel plate 2 is inserted into the heating furnace 3 in a state where a shape defect occurs, so even if it is uniformly heated by the heating furnace 3, a shape defect remains. Even if such a thick steel plate 2 is taken out of the heating furnace 3 and heat-treated by the quenching device 5, the shape defect is not eliminated, but the treatment of the cooling water is uneven, thereby promoting temperature unevenness. Therefore, by flattening the thick steel plate 2 by the first shape straightening device 4 after heating by the heating furnace 3 that ensures uniform heating, and cooling by the quenching device 5, a thick steel plate 2 with high flatness can be manufactured. That is, in order to obtain the effects of the present invention, the shape (initial shape) of the thick steel plate 2 before entering the quenching device 5 needs to be flattened.

[0033] In addition, when warping occurs at the front end of the thick steel plate 2, there is a risk that the nozzle of the quenching device 5 and the like will collide with the thick steel plate 2. Therefore, compared with the skin-pass straightening device that has a low ability to straighten the warping in the long-side direction generated at the front and rear ends of the thick steel plate 2, the first shape straightening device 4 is preferably a roller straightening machine straightening device that can perform repeated bending processing. The roller straightening machine straightening device is a straightening machine that uses multiple rollers (for example, 4 rollers on the top and 3 rollers on the bottom) to perform repeated bending, and the straightening effect is low at the distance of the spacing between the rollers. Therefore, when using a roller straightening machine straightening device, it is more preferable to further provide a pressurized straightening mechanism that can correct the warping of the front and rear ends of the thick steel plate 2.

[0034] Furthermore, the temperature of the thick steel plate 2 during shape straightening by the first shape straightening device 4 is preferably within the range of ±150° C. from the temperature Ar3 at which the thick steel plate 2 transforms from austenite to ferrite. By setting the temperature to such a range, the yield stress of the thick steel plate 2 can be sufficiently reduced, and the reaction force during shape straightening can be reduced.

[0035] After the first straightening step, the thick steel plate 2 is quenched by the quenching device 5 (quenching step).

[0036] After the quenching process, the thick steel plate 2 is straightened by the second shape straightening device 6 (second straightening process). For the quenching (cooling) performed by the quenching device 5, it is not easy to manage the flow rate in the width direction of the cooling water 53 sprayed from the upper cooling nozzle 51 and the lower cooling nozzle 52 to be completely consistent. Therefore, due to the uneven temperature during quenching, a slight warp may occur, and the thick steel plate 2 needs to be further straightened by the second shape straightening device 6. In addition, when straightening by the second shape straightening device 6, it is preferred that the temperature of the thick steel plate 2 is below 100°C.

[0037] <Modification>

[0038] The present invention has been described above with reference to specific embodiments, but the invention is not limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention including the disclosed embodiments and various variations are also obvious to those skilled in the art. Therefore, it should be understood that the embodiments of the invention described in the patent claims include the embodiments including these variations described in this specification alone or in combination.

[0039] For example, in the above embodiment, although the steel plate has a thick steel plate 2 with a plate thickness of 4.0 mm or more, the present invention is not limited to the above example. The plate thickness of the steel plate may also be less than 4.0 mm. It should be noted that the present invention is suitable for steel plates with a plate thickness of 4.0 mm or more, and more suitable for steel plates with a plate thickness of 6.0 mm or more.

[0040] <Effects of implementation>

[0041] (1) A manufacturing device (heat treatment device 1) for a steel plate (e.g., a thick steel plate 2) according to one embodiment of the present invention is a manufacturing device for a steel plate that performs heat treatment on the steel plate, and the device comprises: a heating furnace 3 for heating the steel plate at a temperature below 100°C; a first shape straightening device 4 for straightening the heated steel plate to be flat; a quenching device 5 for quenching the straightened steel plate; and a second shape straightening device 6 for straightening the quenched steel plate to be flat.

[0042] According to the configuration of (1) above, by flattening the steel plate using the first shape straightening device 4, the cooling during quenching can be made uniform. Therefore, the steel plate can be made flat and homogeneous. In addition, by flattening the steel plate using the second shape straightening device 6 after quenching, even if the cooling of the quenching device 5 is uneven, the finally manufactured steel plate can be made flat.

[0043] (2) In the configuration of (1) above, the load-bearing capacity of the first shape-straightening device 4 is lower than the load-bearing capacity of the second shape-straightening device 6 .

[0044] According to the configuration of (2) above, the load capacity can be optimized according to the difference in deformation resistance caused by the temperature unevenness of the steel plate. Since the first shape straightening device 4 does not use a straightening device with a high load capacity, the initial equipment introduction cost is low.

[0045] (3) In the configuration of (1) or (2) above, when straightening is performed by the first straightening device 4, the temperature of the steel sheet is in the range of the Ar3 temperature ±150°C.

[0046] According to the configuration of (3) above, the yield stress of the steel sheet is sufficiently low, and the reaction force during shape straightening can be reduced.

[0047] (4) In any one of the above configurations (1) to (3), the temperature of the steel sheet is 100° C. or less when straightening is performed by the second straightening device 6 .

[0048] According to the configuration of (4) above, the straightening temperature is almost room temperature, and no re-deformation due to thermal contraction caused by a further temperature drop after straightening occurs, so a good shape can be obtained.

[0049] (5) In any one of the above configurations (1) to (4), the first profile-straightening device 4 and the second profile-straightening device 6 are roller-type straightening devices.

[0050] According to the configuration of (5) above, the warping of the front and rear ends of the steel plate can be straightened. Therefore, not only can the warping of the steel plate itself be suppressed, but also contact with the cooling nozzle and other equipment constituting the quenching device 5 during quenching can be prevented.

[0051] (6) In any one of the above structures (1) to (5), the quenching device quenches the steel plate by water cooling.

[0052] (7) A method for manufacturing a steel plate according to one embodiment of the present invention is a method for manufacturing a steel plate by heat treating the steel plate, the method comprising: a heating step for heating a steel plate 2 at a temperature below 100° C.; a first straightening step for straightening the steel plate to be flat after the heating step; a quenching step for quenching the steel plate after the first straightening step; and a second straightening step for straightening the steel plate to be flat after the quenching step.

[0053] (8) In the configuration of (7) above, in the first straightening step, the temperature of the steel sheet during straightening is in the range of ±150°C of the Ar3 temperature.

[0054] (9) In the configuration of (7) or (8) above, in the second straightening step, the temperature of the steel sheet is 100° C. or less.

[0055] According to the above-mentioned structures (7) to (9), the same effects as those of the above-mentioned structures (1), (3) and (4) can be obtained.

[0056] Example

[0057] The following describes the embodiments implemented by the present inventors. Figure 1 In the heat treatment equipment 1 shown, a thick steel plate 2 (plate thickness 6mm, 12mm, 25mm, 40mm×plate width 3500mm×plate length 7m) at room temperature, from which oxide scale has been removed in advance by sandblasting, is heated to 900°C in a nitrogen atmosphere by a heating furnace 3. Next, the heated thick steel plate 2 is taken out, and the thick steel plate 2 is straightened by a first shape straightening device 4 (roller straightening machine type), and quenched to below 100°C by a quenching device 5. Then, the quenched thick steel plate 2 is shape-straightened again by a second shape straightening device 6. The quenching device 5 uses a spray nozzle as a cooling nozzle 51, 52. It should be noted that the Ar3 temperature of the material is 800°C, and the temperature of the thick steel plate 2 when taken out from the heating furnace 3 and straightened by the first shape straightening device 4 is about 860°C.

[0058] In the examples, the shape of the steel plate when the heat treatment of the thick steel plate 2 is performed by the above-mentioned equipment configuration is investigated. In the investigation, the thick steel plate 2 is placed on the platen, and the amount obtained by subtracting the plate thickness from the maximum height of the thick steel plate 2 based on the platen surface is measured (called the warpage amount), and the results are shown in Examples 1 to 4 of Table 1. It should be noted that the allowable value of the warpage of the thick steel plate 2 is 5 mm or less. For the thick steel plates 2 with a plate thickness of 6 mm, 12 mm, 25 mm, and 40 mm, all the warpage amounts are achieved to be less than 5 mm, which is a good shape (evaluation: ○).

[0059] As comparative examples, heat treatment was performed under the conditions where neither the first shape straightening device 4 nor the second shape straightening device 6 was used (Comparative Examples 1 to 4), the conditions where the first shape straightening device 4 was not used and only the second shape straightening device 6 was used for straightening (Comparative Examples 5 to 8), and the conditions where only the first shape straightening device 4 was used for straightening without using the second shape straightening device 6 (Comparative Examples 9 to 12). Then, the shape of the thick steel plate 2 that had been heat treated was investigated in the same manner as in the example. It should be noted that, in addition to the above-mentioned conditions, heat treatment was also performed under the same conditions as in the example. As shown in Table 1, in Comparative Examples 1 to 12, the warpage was greater than 5 mm under any condition, and sufficient flatness could not be obtained as a product (evaluation: ×).

[0060] [Table 1]

[0061]

[0062] Explanation of symbols

[0063] 1 Heat treatment equipment

[0064] 2 Thick steel plate

[0065] 3 Heating furnace

[0066] 4. First shape straightening device

[0067] 5 Quenching device

[0068] 50 Constraint Roller

[0069] 51 Cooling nozzles on the upper side

[0070] 52 Cooling nozzles on the bottom

[0071] 53 Cooling water

[0072] 6 Second shape straightening device

Claims

1. A steel plate manufacturing equipment is a steel plate manufacturing equipment for heat treating a steel plate, and has the following devices: A heating furnace for heating the steel plate at a temperature below 100° C. a first shape straightening device for straightening the heated steel plate to be flat, wherein the distance from the heating furnace to the first shape straightening device is less than 4 m; A quenching device for quenching the straightened steel plate; as well as a second shape straightening device, which straightens the quenched steel plate flatly; When the first shape straightening device is used for straightening, the temperature of the steel sheet is within the range of ±150° C. of the Ar3 temperature.

2. The steel plate manufacturing equipment according to claim 1, wherein: The load-bearing capacity of the first shape straightening device is lower than the load-bearing capacity of the second shape straightening device.

3. The steel plate manufacturing equipment according to claim 1 or 2, wherein: When the second shape straightening device is used for straightening, the temperature of the steel plate is 100° C. or less.

4. The steel plate manufacturing equipment according to claim 1 or 2, wherein: The first shape straightening device and the second shape straightening device are roller straightener straightening devices.

5. The steel plate manufacturing equipment according to claim 3, wherein: The first shape straightening device and the second shape straightening device are roller straightener straightening devices.

6. The steel plate manufacturing equipment according to claim 1 or 2, wherein: The quenching device quenches the steel plate by water cooling.

7. The steel plate manufacturing equipment according to claim 3, wherein: The quenching device quenches the steel plate by water cooling.

8. The steel plate manufacturing equipment according to claim 4, wherein: The quenching device quenches the steel plate by water cooling.

9. The steel plate manufacturing equipment according to claim 5, wherein: The quenching device quenches the steel plate by water cooling.

10. A method for manufacturing a steel plate, comprising heat treating the steel plate, comprising the following steps: A heating step of heating the steel plate at a temperature below 100° C. in a heating furnace; a first straightening step, after the heating step, straightening the steel plate flatly by using a first shape straightening device, wherein the distance from the heating furnace to the first shape straightening device is less than 4 m; A quenching process, after the first straightening process, quenching the steel plate using a quenching device; as well as a second straightening step, after the quenching step, using a second shape straightening device to straighten the steel plate flatly; In the first straightening step, the temperature of the steel sheet during straightening is within the range of ±150° C. of the Ar3 temperature.

11. The method for manufacturing a steel plate according to claim 10, wherein: In the second straightening step, the temperature of the steel sheet is 100° C. or lower.

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