A method for controlling quenching cooling uniformity of intensive hot coil continuous heat treatment

Abstract

This invention provides a method for controlling the uniformity of quenching cooling in intensive continuous heat treatment of hot coils, comprising the following steps: (1) using multiple sets of pressure rollers as dividing points, the cooling zone is divided into multiple segments, with the area between two adjacent sets of pressure rollers as one segment. After the strip enters the cooling zone, the tension of each segment of the cooling zone is controlled at 5-35 MPa; (2) spraying facilities for dispensing cooling medium are set at the upper and lower parts of the strip in each segment of the cooling zone; along the width direction of the strip, the surface of the strip is divided into 3-7 zones, with the middle zone as the central zone and the other zones as the edge zones. The air-to-water ratio of each zone is 2:6-6:2, and the flow rate ratio of the edge and central zones is 0.8:1-0.2:1.5; the flow rate ratio of the upper and lower surfaces of the strip provided by the corresponding spraying facilities is 1:2-2:1.

Description

Technical Field

[0001] This invention relates to quenching process layout and methods, and is a control technology applied to intensive hot coil continuous heat treatment lines. Specifically, it relates to a method for controlling the uniformity of quenching cooling in intensive hot coil continuous heat treatment. Background Technology

[0002] For the quenching and cooling of hot-rolled strip steel, existing hot continuous rolling heat treatment lines mainly perform heat treatment in the plate state. The cooling methods commonly used in existing hot rolling heat treatment lines are water cooling, such as water curtains, water nozzles, or combinations thereof. Existing hot rolling heat treatment lines have flow distribution control for the cooling water at the edge, center, and upper / lower surfaces. However, for intensive hot-rolled coil continuous heat treatment lines, the equipment, products, specifications, and process characteristics have all changed significantly, necessitating the adoption of new quenching and cooling modes and methods to better control cooling uniformity and strip shape.

[0003] The following is a further explanation of quenching in the prior art:

[0004] 1. Quenching and cooling technology

[0005] With continuous improvements in product processes, particularly in equipment manufacturing, technological applications, and process control, cooling technology has become increasingly important. Existing technologies employ various cooling methods (including jet cooling, high-speed jet cooling, aerosol cooling, roll cooling, and water quenching) to achieve optimal cooling effects. Aerosol cooling is one such method; it utilizes the energy of compressed air to atomize water droplets and spray them at high speed onto the surface of an object. Aerosol cooling technology offers advantages such as high surface heat transfer coefficients and uniform cooling. However, the heat transfer mechanism of aerosol cooling is complex. The cooling medium is a mixture of water and air, not a single medium, and different water and air pressure settings will affect the heat transfer coefficient between the cooling medium and the strip steel. The degree of atomization and cooling capacity can be adjusted by controlling the air-to-water ratio, among other things.

[0006] Steel quenching is a heat treatment process in which steel parts are heated to a temperature above Ac3 or Ac1, held for a certain time, and then cooled at an appropriate rate to obtain martensite and / or bainite.

[0007] Based on the characteristics of different cooling methods, a reasonable cooling method can be selected for quenching.

[0008] 2. Applications of quenching

[0009] Air mist cooling is widely used in continuous casting and thin strip continuous casting production lines. However, due to the quenching and cooling characteristics of hot-rolled coils or plates (variety, specifications, etc.), air mist quenching is less commonly used in the quenching and heat treatment process of hot coils or hot continuous rolled plates. Currently, in the field of hot continuous rolling, water is still the main cooling medium for quenching, with water quenching being the primary method.

[0010] 3. Problems with existing technologies

[0011] Compared to traditional heat treatment lines, intensive continuous heat treatment lines for hot-rolled coils have slower strip speeds, thinner product dimensions, and higher uniformity requirements. These changes have the greatest impact on the quenching and cooling process. Based on intensive continuous heat treatment lines for hot-rolled coils, existing technologies have the following problems:

[0012] 1) Existing hot-rolled sheet and coil quenching heat treatment processes are mainly for specifications with a thickness of 3mm or more. For specifications with a thickness of less than 4mm, uniformity is already difficult to control, and sheet shape issues are prominent. However, intensive hot-rolled coil continuous heat treatment lines cover a wider range of thinner specifications (up to 2mm, primarily 2-4mm). From sheet shape theory, we know that the thinner the strip, the smaller the flatness dead zone, and under the same stress conditions, the lower its resistance to warping deformation. Therefore, it is more sensitive to cooling uniformity, and existing heat treatment cooling methods cannot meet the requirements.

[0013] 2) Cooling uniformity is directly related to strip speed. Traditional heat treatment lines can reach strip speeds of up to 75 m / min, while intensive hot coil continuous heat treatment lines have even lower speeds (generally less than 10 m / min). Low speeds exacerbate cooling unevenness, requiring higher cooling uniformity, which existing heat treatment cooling methods cannot meet.

[0014] 3) Cooling rate and uniformity are contradictory to some extent. It is necessary to achieve higher uniformity control while ensuring cooling rate. This requires control of cooling rate, which cannot be met by existing quenching heat treatment methods.

[0015] 4) Existing heat treatment methods mainly involve tension-free quenching, and the uniformity control methods are not suitable for controlling the quenching cooling uniformity of intensive hot coil continuous heat treatment.

[0016] The differences between continuous heat treatment lines and traditional heat treatment lines (specifications, speed, tension, process characteristics, etc.) place higher demands on uniformity control in continuous heat treatment. Therefore, existing cooling equipment, methods, and processes are inadequate for these new requirements, necessitating new and innovative methods and optimizations to meet the production quality requirements of continuous heat treatment lines. Summary of the Invention

[0017] The technical problem to be solved by the present invention is to provide a method for controlling the quenching uniformity of continuous heat treatment of hot-rolled coils, which can achieve temperature and performance uniformity adjustment and control across the entire surface of the hot-rolled coil and meet the quenching shape requirements of related products.

[0018] The technical problem it aims to solve can be addressed through the following technical solutions.

[0019] A method for controlling the uniformity of quenching and cooling in intensive continuous heat treatment of hot-rolled coils, characterized by the following steps:

[0020] (1) The cooling zone is divided into multiple sections by using multiple sets of pressure rollers as dividing points. The area between two adjacent sets of pressure rollers is one section. After the strip enters the cooling zone, the tension of each section of the cooling zone is controlled at 5 to 35 MPa.

[0021] (2) Spraying facilities for dispensing cooling medium are set up at the upper and lower parts of the strip in each cooling zone; the strip surface is divided into 3-7 zones along the width direction of the strip, with the middle zone as the central zone and the other zones as the edge zones. The air-water ratio of each zone is 2:6 to 6:2, and the flow ratio of the edge zone to the central zone (the flow ratio of a single edge zone to the central zone) is 0.8:1 to 0.2:1.5; the flow ratio of the upper and lower surfaces of the strip provided by the corresponding spraying facilities is 1:2 to 2:1.

[0022] As a further improvement to this technical solution, in step (2), when the strip thickness is <3mm, the flow rate ratio of the upper and lower surfaces of the strip is 1:0.5~1.2; when the strip thickness is 3~4mm, the flow rate ratio of the upper and lower surfaces of the strip is 1:1~1.5; when the strip thickness is >4mm, the flow rate ratio of the upper and lower surfaces of the strip is 1:1.2~1.8.

[0023] In a preferred embodiment of the present invention, the tension of the strip decreases in each cooling zone it passes through after entering the cooling zone.

[0024] As a further improvement to this technical solution, the crown of the tension roller is 0.01–3 mm. Preferably, the crown of the tension roller is 0.05–3 mm.

[0025] As a further improvement to this technical solution, in step (1), the tension of each cooling zone that the strip passes through after entering the cooling zone is controlled at 5 to 25 MPa.

[0026] Furthermore, after dividing the strip into sections along its width, the width of the central section is 10–1500 mm.

[0027] Preferably, the air-to-water ratio in each zone along the width of the strip is 3:5 to 5:3.

[0028] As a preferred embodiment of the present invention, the strip is divided into 7 sections along the width direction, the width of the middle section is 1000mm, and the flow rate ratio of the side and middle sections is 0.8:1.

[0029] The quenching and cooling uniformity control method of the intensive hot coil continuous heat treatment using the above technical solution, when applied to the intensive hot coil continuous heat treatment line, has the characteristics of rapid heating, full continuity, automation, and intensification. It has the advantages of high production efficiency, low production cost, and good working environment, and is particularly suitable for the production of thin-gauge (below 4mm) ultra-high strength steel strip with high plate shape quality requirements. Attached Figure Description

[0030] Figure 1 This is a layout diagram of the quenching zone equipment of the present invention;

[0031] In the diagram: 1—Soaking furnace, 2—Strip steel, 3—Water mist baffle;

[0032] 4 – Group 1 pressure rollers, 41 – Group 2 pressure rollers, 42 – Group 3 pressure rollers, 43 – Group 4 pressure rollers;

[0033] 5—Aerosol cooling beam, 5.1—Aerosol nozzle, 5.2—Water inlet pipe, 5.3—Compressed air pipe, 6—Angled spray box, 6.1—(High-pressure dense) water nozzle. Detailed Implementation

[0034] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0035] The quenching process layout and method involved in this invention is a method for controlling the uniformity of quenching cooling in an intensive continuous heat treatment line for hot coils. By adjusting the flow rate at the edges, the ratio of upper and lower flow rates, tensioned quenching, using differential speed pressure rollers to increase tension in the quenching zone, and optimizing the roller shape to control the lateral tension distribution, the uniformity of cooling in both the transverse and thickness directions is improved.

[0036] Reference Figure 1 The quenching zone equipment layout shown indicates that after the strip steel 3 comes out of the soaking furnace 1, it passes through the first group of pressure rollers 4, the second group of pressure rollers 41, the third group of pressure rollers 42 and the fourth group of pressure rollers 43 in sequence.

[0037] The following control methods are specifically adopted:

[0038] 1. Edge-to-edge flow control:

[0039] In the quenching process section, each row of nozzles in the upper and lower tables adopts edge-center-edge partitioning; corresponding edge-center-edge partitioning and flow control are set for different widths; the partitioning principle in the width direction is shown in Table 1 below;

[0040] Table 1: Edge-in-Edge Partition Settings

[0041]

[0042]

[0043] 2. Upper and lower table flow control:

[0044] For different thickness specifications, set corresponding upper and lower flow control. The upper and lower flow ratio (set flow rate, not real-time instantaneous flow rate) process parameter configuration is shown in Table 2 below.

[0045] Table 2: Flow Control of Upper and Lower Tables

[0046]

[0047] 3. Segmented tension control:

[0048] Tension quenching is employed, with tension control used on the first and second groups of pressure rollers and the third and fourth groups of pressure rollers. Differential speed pressure rollers are used to increase the tension in the quenching zone. Simultaneously, the lateral tension distribution is controlled through the roller shape (roller crown) design. Specific tension and roller shape process parameters are configured as shown in Table 2.

[0049] like Figure 1 As shown, the cooling zone between the first group of pressure rollers 4 and the second group of pressure rollers 41 is the first cooling zone, the cooling zone between the second group of pressure rollers 41 and the third group of pressure rollers 42 is the second cooling zone, and the cooling zone between the third group of pressure rollers 42 and the fourth group of pressure rollers 43 is the third cooling zone. Corresponding cooling facilities are installed on the upper and lower surfaces of the strip in each cooling zone. The air mist cooling beam 5 in the figure is equipped with air mist nozzles 5.1, a water inlet pipe 5.2, and a compressed air pipe 5.3; as well as an inclined spray box 6 and (high-pressure densely packed) water nozzles installed on the inclined spray box. Label 3 in the figure represents a water mist baffle.

[0050] This method has the following beneficial effects:

[0051] 1. Based on the variety, specifications and related requirements, the flow rate ratio of the middle and upper surfaces is reasonably set to meet the requirements of cooling uniformity.

[0052] 2. By segmenting tension and designing the roller profile, the tension distribution in the width direction is reasonably controlled to meet the requirements of uniformity and plate shape control.

[0053] The following are more specific examples.

[0054] Example 1:

[0055] The quenching cooling uniformity control method of the present invention was tested and implemented on a certain integrated hot coil continuous heat treatment production line, and applied to a steel grade 1 with a thickness of 4×1600mm. The process parameters are set as shown in Table 3 below:

[0056] Table 3:

[0057]

[0058] Ideally, the tension in the third cooling zone should also be maintained at 10 MPa.

[0059] After implementing these parameter settings, the process control requirements can be met.

[0060] Example 2:

[0061] The quenching cooling uniformity control method of the present invention was tested and implemented on a certain integrated hot coil continuous heat treatment production line, and applied to a certain steel grade 2 with a thickness of 3×1300mm. The process parameters are set as shown in Table 4 below.

[0062] Table 4:

[0063]

[0064] After implementing these parameter settings, the process control requirements can be met.

Claims

1. A method of quench cooling uniformity control for an intensive coil-to-coil continuous heat treatment, characterized by, It comprises the following steps: (1) Divide the cooling zone into several sections with the set groups of pressure rollers as the dividing points, and take the area between two adjacent groups of pressure rollers as one section. The tension of each section of the cooling zone through which the strip steel passes is controlled at 5-35 MPa after the strip steel enters the cooling zone; Wherein, when the section tension is controlled, the quenching zone tension is increased by differential speed pressure rollers, and the transverse tension distribution is controlled by the roller crown; (2) The upper and lower positions of the strip steel in each section of the cooling zone are provided with spraying facilities for applying cooling medium. The strip steel surface is divided into 3-7 sub-zones along the width direction of the strip steel, with the middle one of the sub-zones as the middle zone and the others as the edge zones. The air-water ratio of each sub-zone is 2:6-6:2, and the edge-to-middle sub-zone flow ratio is 0.8:1-0.2:1.

5. The upper-to-lower surface flow ratio provided by the corresponding spraying facilities is 1:2-2:

1.

2. The method of quench cooling uniformity control for an intensive coil-to-coil continuous heat treatment according to claim 1, characterized in that, In step (2), when the thickness of the strip steel is <3 mm, the upper-to-lower surface flow ratio of the strip steel is 1:0.5-1.2; when the thickness of the strip steel is 3-4 mm, the upper-to-lower surface flow ratio of the strip steel is 1:1-1.5; and when the thickness of the strip steel is >4 mm, the upper-to-lower surface flow ratio of the strip steel is 1:1.2-1.

8.

3. The method of quench cooling uniformity control for an intensive coil-to-coil continuous heat treatment according to claim 1, characterized in that, The tension of each section of the cooling zone through which the strip steel passes decreases.

4. The method of quench cooling uniformity control for an intensive coil-to-coil continuous heat treatment according to claim 1, characterized in that, The crown of the tension roller is 0.01-3 mm.

5. The method of quench cooling uniformity control for an intensive coil-to-coil continuous heat treatment according to claim 1, characterized in that, The crown of the tension roller is 0.05-3 mm.

6. The method of quench cooling uniformity control for an intensive coil-to-coil continuous heat treatment according to claim 1, characterized in that, After the division along the width direction of the strip steel, the width of the middle zone is 10-1500 mm.

7. The method of quench cooling uniformity control for an intensive coil-to-coil continuous heat treatment according to claim 1, characterized in that, The air-water ratio of each sub-zone along the width direction of the strip steel is 3:5-5:

3.

8. The method of quench cooling uniformity control for an intensive coil-to-coil continuous heat treatment according to claim 1, characterized in that, The width of the middle zone is 1000 mm when the strip steel is divided into 7 sub-zones along the width direction, and the edge-to-middle sub-zone flow ratio is 0.8:1.

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