Quenching production line, and plate shape control method in steel plate quenching

Abstract

A quenching production line, comprising a shot blasting machine (4), a heating furnace (3), and a quenching machine (1) which are sequentially arranged along a quenching center line. A slotted nozzle cooling section (1.1), a circular high-pressure nozzle cooling section (1.2), and a high-pressure spraying pipe cooling section (1.3) are sequentially arranged in the quenching machine (1) along the running direction of a steel plate (2); the slotted nozzle cooling section (1.1) and the circular high-pressure nozzle cooling section (1.2) each are divided into a plurality of cooling control areas along the width direction of the steel plate (2) and the upper and lower surfaces of the steel plate (2); and the flow of cooling water in the cooling control areas is independently adjustable. The quenching machine (1) having the plurality of cooling control areas in which the flow of the cooling water is independently adjustable is used, and on the basis of water flow characteristics of the upper and lower surfaces of the steel plate (2) in the cooling process and stress problems caused by thermal stress and tissue phase change borne by the steel plate (2) in different cooling areas, parameters of different cooling control areas are set, thereby effectively controlling the plate shape in the quenching process, so that the plate shape of the steel plate (2) can be improved.

Description

A quenching production line and a method for controlling the shape of a steel plate during quenching Technical Field

[0001] The present invention relates to the technical field of metallurgical manufacturing, and in particular to a quenching production line and a method for controlling the shape of a quenched steel plate. Background Art

[0002] Ultra-high strength and lightweighting are inevitable choices for the machinery manufacturing industry to achieve green development. Therefore, thin-gauge ultra-high-strength steel is widely used in crane booms, aerial platforms, and other fields. Users not only require thin-gauge, high-strength steel to reduce weight, but also require integrated molding to minimize weld lengths. As a result, demand for ultra-thin and ultra-wide steel plates (also known as high-width-to-thickness-ratio ultra-high-strength steel plates, with a width-to-length ratio exceeding 300 and a thickness of 6mm or less) is gradually increasing.

[0003] Offline quenching heat treatment of rolled steel plates is currently the main production method for ultra-high strength steel (Rel ≥ 960MPa) in the world. The hot-rolled raw materials are cut into fixed lengths and then reheated to 30 to 50°C above the austenitizing temperature. After heat preservation and homogenization, they are taken out of the furnace and water-cooled quenched to obtain martensitic structure, which is the key process for obtaining ultra-high strength for such products. However, the quenching process is difficult to achieve precise and synchronous control due to the thermal stress and phase transformation process of different parts of the steel plate. As a result, the shape of the quenched steel plate is very easy to warp, the shape is poor, and the shape control is extremely difficult.

[0004] Summary of the Invention

[0005] The purpose of the present invention is to provide a quenching production line and a method for controlling the shape of quenched steel plates in order to improve the quality of the steel plates, in view of the deficiencies in the prior art.

[0006] The technical solution adopted by the present invention is: a quenching production line, comprising a shot blasting machine, a heating furnace and a quenching machine arranged in sequence along the quenching center line, wherein the quenching machine is provided with a slot nozzle cooling section, a circular high-pressure nozzle cooling section and a high-pressure nozzle cooling section in sequence along the running direction of the steel plate;

[0007] The slit nozzle cooling section and the circular high-pressure nozzle cooling section are respectively divided into a first edge upper cooling control zone, a first edge lower cooling control zone, a middle upper cooling control zone, a middle lower cooling control zone, a second edge upper cooling control zone and a second edge lower cooling control zone along the width direction of the steel plate and the upper and lower surfaces of the steel plate, wherein the first edge upper cooling control zone and the first edge lower cooling control zone, the second edge upper cooling control zone and the second edge lower cooling control zone constitute the edge cooling control zone, and the middle upper cooling control zone and the middle lower cooling control zone constitute the middle cooling control zone;

[0008] The high-pressure nozzle cooling section is divided into a high-pressure nozzle upper cooling control area and a high-pressure nozzle lower cooling control area along the upper and lower surfaces of the steel plate;

[0009] The cooling water flow in each cooling control zone can be adjusted individually.

[0010] The present invention also provides a method for controlling the flatness of a steel plate after quenching based on the production line described above, the method comprising:

[0011] S1. providing the production line;

[0012] S2, the steel plate is put on line and centered after shot blasting by shot blasting machine;

[0013] S3. The steel plate is placed in a nitrogen-protected radiant tube heating furnace and heated to 30-50°C above the austenitizing temperature, and kept warm;

[0014] S4, after accelerating the steel plate to the set quenching speed, it leaves the heating furnace and enters the quenching machine for water quenching treatment;

[0015] S5. Dry the surface moisture of the steel plate after quenching;

[0016] S6. Stacking of quenched steel plates.

[0017] According to the above scheme, in S4, in the slot nozzle cooling section of the quenching machine, the total amount of cooling water in the slot nozzle cooling section is 800~1040m 3 / h, the ratio of the total cooling water volume of the edge cooling control zone to the total cooling water volume of the middle cooling control zone is 0.20~0.35; the ratio of the cooling water volume of the upper edge cooling control zone to its corresponding lower edge cooling control zone is 0.70~0.75, and the ratio of the cooling water volume of the upper middle cooling control zone to the lower middle cooling control zone is 0.72~0.78.

[0018] According to the above scheme, in S4, in the circular high-pressure nozzle cooling section of the quenching machine, the total amount of cooling water in the circular high-pressure nozzle cooling section is 380~500m 3 / h; in the circular high-pressure nozzle cooling section, the ratio of the total cooling water volume of the edge cooling control zone to the total cooling water volume of the middle cooling control zone is 0.40~0.45; the ratio of the cooling water volume of the upper edge cooling control zone to its corresponding lower edge cooling control zone is 0.93~1.03, and the ratio of the cooling water volume of the upper middle cooling control zone to the lower middle cooling control zone is 0.82~0.85.

[0019] According to the above scheme, the total amount of cooling water in the high-pressure nozzle cooling section is 300-400m 3 / h; the ratio of cooling water volume in the upper cooling control area of ​​the high-pressure nozzle to the lower cooling control area of ​​the high-pressure nozzle is 0.75~0.85.

[0020] According to the above scheme, in S4, the pressure of the cooling water is 0.8±0.05MPa, and the temperature of the cooling water is ≤23.5℃.

[0021] According to the above scheme, the quenching speed is 20 to 30 m / min.

[0022] According to the above scheme, the cooling rate of the steel plate during the quenching process is 30 to 40°C / s.

[0023] According to the above scheme, in S3, the oxygen content [O] in the heating furnace is ≤500ppm.

[0024] According to the above solution, the quenching machine is a roller quenching machine.

[0025] The beneficial effects of the present invention are:

[0026] The present invention adopts a quenching machine with multiple cooling control zones with individually controllable cooling water flow rates. According to the water flow characteristics on the upper and lower surfaces of the steel plate during the cooling process and the stress problems caused by the thermal stress and structural phase change of the steel plates in different cooling zones, the parameters of different cooling control zones are set, including the cooling water flow rate and water ratio on the upper and lower surfaces of the steel plate, as well as the water volume and water ratio between the edge zone and the middle zone, so as to achieve effective control of the plate shape during the quenching process and improve the plate shape of the steel plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a schematic diagram showing the layout of the quenching production line of the present invention.

[0028] FIG2 is a schematic diagram of the transverse partition arrangement of the slot-type nozzle cooling section of the present invention; it is also a schematic diagram of the transverse partition arrangement of the circular high-pressure nozzle cooling section.

[0029] Among them: 1. Quenching machine; 1.1. Slit nozzle cooling section; 1.2. Circular high-pressure nozzle cooling section; 1.3. High-pressure nozzle cooling section; 1.4. First side upper cooling control zone; 1.5. First side lower cooling control zone; 1.6. Middle upper cooling control zone; 1.7. Middle lower cooling control zone; 1.8. Second side upper cooling control zone; 1.9. Second side lower cooling control zone; 2. Steel plate; 3. Heating furnace; 4. Shot blasting machine. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are described. The described embodiments are part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without making any innovative efforts shall fall within the scope of protection of the present invention.

[0031] A quenching production line includes a shot blasting machine 4, a heating furnace 3, and a quenching machine 1 arranged in sequence along a quenching centerline, as shown in FIG1 ; wherein, within the quenching machine 1, a slot nozzle cooling section 1.1, a circular high-pressure nozzle cooling section 1.2, and a high-pressure nozzle cooling section 1.3 are sequentially arranged along the running direction of the steel plate 2;

[0032] The slit nozzle cooling section 1.1 and the circular high-pressure nozzle cooling section 1.2 are respectively divided into a first edge upper cooling control zone 1.4, a first edge lower cooling control zone 1.5, a middle upper cooling control zone 1.6, a middle lower cooling control zone 1.7, a second edge upper cooling control zone 1.8 and a second edge lower cooling control zone 1.9 along the width direction of the steel plate 2 and the upper and lower surfaces of the steel plate 2, wherein the first edge upper cooling control zone 1.4, the first edge lower cooling control zone 1.5, the second edge upper cooling control zone 1.8 and the second edge lower cooling control zone 1.9 constitute the edge cooling control zone, and the middle upper cooling control zone 1.6 .6 and the middle lower cooling control zone 1.7 form a middle cooling control zone, as shown in Figure 2; the first side upper cooling control zone 1.4 and the first side lower cooling control zone 1.5 form a side cooling control zone; the second side upper cooling control zone 1.8 and the second side lower cooling control zone 1.9 form another side cooling control zone; that is, the first side upper cooling control zone 1.4 and the first side lower cooling control zone 1.5, the second side upper cooling control zone 1.8 and the second side lower cooling control zone 1.9 respectively form two side cooling control zones; these two side cooling control zones are respectively located on both sides of the middle cooling control zone;

[0033] The high-pressure nozzle cooling section 1.3 is divided into a high-pressure nozzle upper cooling control area and a high-pressure nozzle lower cooling control area along the upper and lower surfaces of the steel plate 2;

[0034] The cooling water flow in each cooling control zone can be adjusted individually.

[0035] In this embodiment, the first edge upper cooling control zone 1.4 and the first edge lower cooling control zone 1.5 are symmetrically arranged on the upper and lower sides of the steel plate 2; the second edge upper cooling control zone 1.8 and the second edge lower cooling control zone 1.9 are symmetrically arranged on the upper and lower sides of the steel plate 2; the middle upper cooling control zone 1.6 and the middle lower cooling control zone 1.7 are symmetrically arranged on the upper and lower sides of the steel plate 2; the middle upper cooling control zone 1.6 is located between the first edge upper cooling control zone 1.4 and the second edge upper cooling control zone 1.8, and the middle lower cooling control zone 1.7 is located between the first edge lower cooling control zone 1.5 and the second edge lower cooling control zone 1.9.

[0036] In the present invention, the quenching machine 1 is a roller quenching machine 1, the slit nozzle cooling section 1.1 is provided with a slit nozzle, the circular high-pressure nozzle cooling section 1.2 is provided with a circular high-pressure nozzle, and the high-pressure nozzle cooling section 1.3 is provided with a high-pressure nozzle. This is the existing configuration; the total length of the edge cooling control zone is 820 mm, with 410 mm on each side; the length of the middle cooling control zone is 1380 mm.

[0037] In the present invention, the heating furnace 3 is a nitrogen-protected radiation tube heating furnace 3 .

[0038] A method for controlling the flatness of a quenched steel plate based on the production line described above, specifically a method for controlling the flatness of a quenched thin steel plate with a large width ratio (i.e., a steel plate with a width / length ratio exceeding 300 and a thickness ≤ 6 mm), is provided. The method comprises:

[0039] S1. Provide the production line as described above;

[0040] S2, steel plate 2 is put on line, shot blasted by shot blasting machine 4 and then aligned;

[0041] S3, the steel plate 2 enters the nitrogen-protected radiation tube heating furnace 3 and is heated to 30-50°C above the austenitizing temperature and kept at this temperature for 10-15 minutes;

[0042] S4, the steel plate 2 is accelerated to the set quenching speed and then exits the heating furnace 3, and then enters the quenching machine 1 for water quenching treatment (i.e., quenching treatment using cooling water);

[0043] S5. After quenching, the steel plate 2 is blown dry with compressed air from the outlet of the quenching machine 1 to remove any remaining moisture on the surface.

[0044] S6. The quenched steel plate 2 is transported by a roller conveyor to a stacker for stacking.

[0045] In S4, in the slot nozzle cooling section 1.1 of the quenching machine 1, the total amount of cooling water in the slot nozzle cooling section 1.1 is 800 to 1040 m 3 / h, the ratio of the total amount of cooling water in the edge cooling control zone (referring to a single edge cooling control zone, the same below) to the total amount of cooling water in the middle cooling control zone is 0.20-0.35; the ratio of the cooling water volume of the upper edge cooling control zone to its corresponding lower edge cooling control zone is 0.70-0.75, and the ratio of the cooling water volume of the upper middle cooling control zone 1.6 to the lower middle cooling control zone 1.7 is 0.72-0.78. Among them, the edge cooling control zone refers to the edge cooling control zone on one side, and the meaning is the same as here below; similarly, the upper edge cooling control zone also refers to the upper edge cooling control zone on one side, that is, the first upper edge cooling control zone 1.4, or the second upper edge cooling control zone 1.8; the lower edge cooling control zone also refers to the lower edge cooling control zone on one side, that is, the first lower edge cooling control zone 1.5, or the second lower edge cooling control zone 1.9.

[0046] In S4, in the circular high-pressure nozzle cooling section 1.2 of the quenching machine 1, the total amount of cooling water in the circular high-pressure nozzle cooling section 1.2 is 380 to 500m 3 / h; in the circular high-pressure nozzle cooling section 1.2, the ratio of the total amount of cooling water in the edge cooling control zone to the total amount of cooling water in the middle cooling control zone is 0.40-0.45, that is, the edge-to-middle water ratio; the ratio of the cooling water volume of the upper edge cooling control zone to its corresponding lower edge cooling control zone (that is, the upper and lower water ratio of the edge area) is 0.93-1.03, and the ratio of the cooling water volume of the upper middle cooling control zone 1.6 to the lower middle cooling control zone 1.7 (that is, the upper and lower water ratio of the middle area) is 0.82-0.85.

[0047] In S4, the total amount of cooling water in the high-pressure nozzle cooling section 1.3 is 300 to 400 m 3 / h; the ratio of cooling water volume in the upper cooling control area of ​​the high-pressure nozzle to the lower cooling control area of ​​the high-pressure nozzle is 0.75~0.85.

[0048] In the present invention, the cooling water volume in the upper cooling control zone is the water volume on the upper surface of the steel plate, and the cooling water volume in the lower cooling control zone is the water volume on the lower surface of the steel plate; the cooling water volume is the flow rate.

[0049] In S4, the roll gap setting value of the quenching machine 1 is 0.25 to 0.50 mm smaller than the actual thickness of the steel plate 2; the pressure of the quenching cooling water is 0.8 ± 0.05 MPa, and the water temperature of the cooling water is ≤ 23.5 ° C; the quenching speed (that is, the running speed of the steel plate 2 in the quenching machine 1) is 20 to 30 m / min; the cooling rate of the steel plate 2 during the quenching process is 30 to 40 ° C / s.

[0050] In the present invention, the design of cooling water temperature, quenching speed and cooling speed is mainly to obtain the necessary microstructure and properties of steel plate 2, and to achieve the ideal microstructure and properties through the optimal combination of parameters such as water volume, flow speed, water temperature, etc., while avoiding the generation of excessive internal stress on the surface and core caused by excessive cooling speed.

[0051] In S2, the roughness of the steel plate 2 after shot blasting is Ra≤2.5.

[0052] In S3, the oxygen content [O] in the heating furnace 3 is ≤500ppm. For the quenching production of thin-gauge steel plates 2 with a large width-to-thickness ratio, even slight unevenness in the cooling process can cause major problems with the plate shape. Therefore, the uniformity of cooling during the quenching process must be controlled throughout the entire process. After shot blasting, the steel plate 2 enters the nitrogen-protected heating furnace 3 for heating. If the oxygen content is higher than 500ppm, uneven iron oxide scale will form on the surface of the steel plate 2. Due to the large difference in heat transfer efficiency between the iron oxide scale and the steel substrate and water, uneven cooling of the surface of the steel plate 2 will occur. However, an oxygen content [O] ≤500ppm in the heating furnace 3 can effectively improve the plate shape of thin-gauge steel plates 2 with a large width-to-thickness ratio.

[0053] In the present invention, the quenching machine 1 has three cooling sections: a slit nozzle cooling section 1.1, a circular high-pressure nozzle cooling section 1.2, and a circular high-pressure nozzle section. Furthermore, the main cooling areas (slit nozzle cooling section 1.1 and circular high-pressure nozzle cooling section 1.2) are divided into three sections along the width of the steel plate 2 (i.e., an edge cooling control section, a middle cooling control section, and an edge cooling control section). Furthermore, the cooling control sections are divided along the upper and lower surfaces of the steel plate 2 into an upper cooling control zone and a lower cooling control zone, each capable of independently controlling the amount of cooling water. In other words, each of the two cooling sections (slit nozzle cooling section 1.1 and circular high-pressure nozzle cooling section 1.2) has six cooling control zones. The parameters of each cooling control zone are set based on the uneven cooling characteristics of thin-gauge steel with a large width-to-thickness ratio during quenching, ensuring uniformity in the cooling process and improving the shape of the steel plate 2. According to the cooling characteristics of the steel plate 2 during the quenching process, the edge and middle water volume and water ratio of different cooling sections, and the water volume and water ratio of the upper and lower surfaces of the steel plate 2 are set differently. For example, in the slit nozzle cooling section 1.1, the factor affecting the plate shape of the steel plate 2 is the coupling result of thermal stress and phase change stress, and the two factors have opposite effects on the plate shape. Therefore, the upper and lower water ratios in this cooling control area are set between 0.70 and 0.78, and the edge and middle water ratios are also set to be smaller; for the high-pressure nozzle cooling section, the reason for the change in plate shape of this cooling section is the influence of temperature changes. Therefore, the middle and edge parts are a whole and restrict each other. Therefore, the water ratio for the edge is set to 0.93~1.03, and the middle part is 0.82~0.85, which is significantly different from the water ratio setting in the slit nozzle area.

[0054] In the present invention, the chemical composition of the steel plate 2 includes a C content of 0.15-0.25% wt, a Mn content of 1.25-1.85% wt, a Mo content of 0.25-0.50% wt, a Cr content of 0.15-0.50% wt, a B content of 0.0010-0.0050% wt, and the remainder is iron and unavoidable impurities; the carbon equivalent Ceq of the steel plate 2 is ≥0.38.

[0055] Example

[0056] The method described in the present invention was used to quench different steel grades. The specific process parameters are shown in Table 1, the relevant control parameters are shown in Table 2, and the shape parameters of each steel plate 2 after quenching are shown in Table 3. Table 3 shows that, using the technical solution described in the present invention, the transverse unevenness of the steel plates 2 after quenching is ≤3 / 1000, and the longitudinal unevenness is ≤5 / 1000. The steel plates 2 have uniform hardness across the entire surface, low internal stress, and a hardness difference across the width of the plate within 10HV10, and a cross-sectional hardness difference along the thickness within 5HV10. The steel plates 2 obtained using the method described in the present invention have a good shape.

[0057] Table 1 Process parameter value list

[0058] Table 2 Control parameter values

[0059] In Table 2, the upper surface water volume, lower surface water volume, edge upper and lower surface water ratio, middle upper and lower surface water ratio, upper and lower surface water ratio, and edge to middle water ratio respectively represent the upper surface cooling water volume of the steel plate in the corresponding cooling section (i.e., the total amount of cooling water in each cooling control zone located above the steel plate in this cooling section), the lower surface cooling water volume of the steel plate (i.e., the total amount of cooling water in each cooling control zone located below the steel plate in this cooling section), the ratio of the upper surface cooling water volume to the total amount of cooling water in the edge cooling control zone on one side, the ratio of the upper surface cooling water volume to the lower surface cooling water volume in the middle cooling control zone, the ratio of the upper and lower surface cooling water volume of the steel plate, and the ratio of the cooling water volume in the edge cooling control zone on one side to the cooling water volume in the middle cooling control zone. In addition, the sum of the upper surface water volume and the lower surface water volume is the total amount of cooling water in the corresponding cooling section; the two edge cooling control zones are configured identically.

[0060] Table 3 Shape parameters of steel plates after quenching

[0061] In Table 3, the transverse and longitudinal detection of steel plate unevenness refers to standard GT / 709-2019; the hardness of steel plate refers to GB T4340.1-2009.

[0062] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0063] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent replacements for some of the technical features therein. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A quenching production line, characterized in that: It includes a shot blasting machine, a heating furnace and a quenching machine which are sequentially arranged along the quenching center line, wherein a slot nozzle cooling section, a circular high-pressure nozzle cooling section and a high-pressure nozzle cooling section are sequentially arranged in the quenching machine along the running direction of the steel plate; The slit nozzle cooling section and the circular high-pressure nozzle cooling section are respectively divided into a first edge upper cooling control zone, a first edge lower cooling control zone, a middle upper cooling control zone, a middle lower cooling control zone, a second edge upper cooling control zone and a second edge lower cooling control zone along the width direction of the steel plate and the upper and lower surfaces of the steel plate, wherein the first edge upper cooling control zone and the first edge lower cooling control zone, the second edge upper cooling control zone and the second edge lower cooling control zone constitute the edge cooling control zone, and the middle upper cooling control zone and the middle lower cooling control zone constitute the middle cooling control zone; The high-pressure nozzle cooling section is divided into a high-pressure nozzle upper cooling control area and a high-pressure nozzle lower cooling control area along the upper and lower surfaces of the steel plate; The cooling water flow rate in each cooling control zone is individually adjustable.

2. A method for controlling the shape of a steel plate after quenching based on the production line according to claim 1, characterized in that: The method is: S1, providing the production line; S2, the steel plate is put on line and centered after shot blasting by shot blasting machine; S3, the steel plate enters a nitrogen-protected radiation tube heating furnace and is heated to 30-50°C above the austenitizing temperature and kept warm; S4, accelerate the steel plate to the set quenching speed, then leave the heating furnace, and then enter the quenching machine for water quenching treatment; S5. Dry the surface moisture of the steel plate after quenching; S6. Stacking of steel plates after quenching.

3. The method for controlling the shape of a steel plate after quenching according to claim 2, characterized in that: In S4, in the slot nozzle cooling section of the quenching machine, the total amount of cooling water in the slot nozzle cooling section is 800-1040m 3 / h, the ratio of the total cooling water volume of the edge cooling control zone to the total cooling water volume of the middle cooling control zone is 0.20-0.35; the ratio of the cooling water volume of the upper edge cooling control zone to its corresponding lower edge cooling control zone is 0.70-0.75, and the ratio of the cooling water volume of the upper middle cooling control zone to the lower middle cooling control zone is 0.72-0.

78.

4. The method for controlling the shape of a steel plate after quenching according to claim 2, characterized in that: In S4, in the circular high-pressure nozzle cooling section of the quenching machine, the total amount of cooling water in the circular high-pressure nozzle cooling section is 380 to 500 m 3 / h; in the cooling section of the circular high-pressure nozzle, the ratio of the total amount of cooling water in the edge cooling control zone to the total amount of cooling water in the middle cooling control zone is 0.40-0.45; the ratio of the cooling water volume of the upper edge cooling control zone to its corresponding lower edge cooling control zone is 0.93-1.03, and the ratio of the cooling water volume of the upper middle cooling control zone to the lower middle cooling control zone is 0.82-0.

85.

5. The method for controlling the shape of a steel plate after quenching according to claim 2, characterized in that: The total amount of cooling water in the high-pressure nozzle cooling section is 300-400m 3 / h; the ratio of cooling water volume in the upper cooling control area of ​​the high-pressure nozzle to that in the lower cooling control area of ​​the high-pressure nozzle is 0.75-0.

85.

6. The method for controlling the shape of a quenched steel plate according to claim 3 or 4, characterized in that: In S4, the pressure of cooling water is 0.8±0.05MPa, and the temperature of cooling water is ≤23.5℃.

7. The method for controlling the shape of a quenched steel plate according to claim 2, characterized in that: The quenching speed is 20-30m / min.

8. The method for controlling the shape of a steel plate after quenching according to claim 2, characterized in that: The cooling rate of the steel plate during quenching is 30-40°C / s.

9. The method for controlling the shape of a steel plate after quenching according to claim 2, characterized in that: In S3, the oxygen content [O] in the heating furnace is ≤500ppm.

10. The method for controlling the shape of a quenched steel plate according to claim 2, characterized in that: The quenching machine is a roller quenching machine.

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