A segmented quenching and cooling process for intensive hot coil continuous heat treatment

Abstract

The present invention discloses a segmented quenching cooling process for intensive hot coil continuous heat treatment, comprising: 1. dividing a cooling zone into a plurality of cooling zones by means of a pressure roller; along the traveling direction of the strip, each cooling zone is provided with spaced-apart mist cooling and high-pressure water spray cooling devices at upper and lower positions of the strip; 2. initial section: the strip enters the cooling zone, and the corresponding mist cooling and / or high-pressure water spray cooling devices are turned on, and a single mist, a single high-pressure water spray or a combination of the two cooling methods are selectively selected to cool the strip to a target intermediate temperature; 3. air cooling section: the strip enters the air cooling zone and travels according to a set air cooling time; each cooling device corresponding to the strip in the air cooling zone is in a closed state; 4. continuing cooling section: the strip that has completed air cooling travels to a new cooling zone, and by turning on the corresponding mist cooling and / or high-pressure water spray cooling devices, a single mist, a single high-pressure water spray or a combination of the two cooling methods are selectively selected to continue cooling the strip to a target final cooling temperature.

Description

Technical Field

[0001] The invention relates to a quenching process layout and method, which is a control technology applied to an intensive hot coil continuous heat treatment line; in particular, it relates to a segmented quenching cooling process for intensive hot coil continuous heat treatment. Background Art

[0002] For the quenching cooling of hot rolled strip heat treatment, the existing hot rolling heat treatment line is mainly for plate state heat treatment; the existing hot rolling heat treatment line cooling method generally adopts water cooling, such as water curtain, water nozzle and other methods or combinations; the existing hot rolling heat treatment line has flow distribution control for the cooling water edge, middle edge, upper and lower surfaces. However, for the intensive hot coil continuous heat treatment line, its equipment, products, specifications and process characteristics have undergone major changes, and a new quenching cooling mode and method that matches it must be adopted to better control the cooling uniformity and plate shape.

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

[0004] 1. Quenching and cooling technology

[0005] With the continuous improvement of product technology, especially the progress in equipment manufacturing, technology application and process control, cooling technology has become more and more important. In the existing technology, a variety of cooling technologies (including jet cooling, high-speed jet cooling, mist cooling, roller cooling technology and water quenching cooling, etc.) are used to deal with it in order to achieve a reasonable cooling effect. Mist cooling is one of the cooling methods. It uses the energy of compressed air to atomize water droplets and spray them onto the surface of the object at high speed. The mist cooling technology has the advantages of high surface heat transfer coefficient and uniform cooling. The heat transfer mechanism of mist cooling technology is complex. The cooling medium is a mixture of water and air, not a single medium. Different water pressure and air pressure settings will affect the heat exchange coefficient between the cooling medium and the strip. The purpose of atomization degree, cooling capacity and other purposes can be adjusted by controlling the air-water ratio and other methods.

[0006] Quenching of steel - a heat treatment process in which the steel is heated to a temperature above Ac3 or Ac1, maintained for a certain period of time, and then cooled at an appropriate rate to obtain martensite and / or bainite.

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

[0008] 2. Application of quenching

[0009] Gas mist cooling is widely used in production lines such as continuous casting and thin strip continuous casting. However, due to the quenching and cooling characteristics of hot rolled coils or plates (variety, specifications, etc.), gas mist quenching is rarely used in the field of quenching heat treatment of hot coils or hot rolled plates. At present, in the field of hot rolling, quenching still mainly uses water as the cooling medium, and water quenching is the main method.

[0010] 3. Problems with existing technologies

[0011] Compared with the traditional heat treatment line, the intensive hot coil continuous heat treatment line has a slower strip speed (strip running speed), thinner product specifications, and higher uniformity requirements. This is the biggest change in the quenching and cooling process. Based on the intensive hot coil continuous heat treatment line, the original technology has the following problems:

[0012] 1) Intensive hot coil continuous heat treatment line needs to realize the production of different varieties, some of which have requirements for the final cooling temperature, and must have precise control, and even realize segmented cooling (i.e. cooling to the intermediate temperature first, air cooling for a period of time, and then continuing to cool to the final cooling temperature). The existing quenching heat treatment process has only one stage and does not control the final cooling temperature, nor does it have precise control and segmented control functions, which cannot meet the requirements;

[0013] 2) In order to meet the development needs of steel grades with special performance requirements such as DP steel, segmented cooling is required. In traditional offline heat treatment production lines, there is no precedent for two-stage cooling, nor is there such capability.

[0014] 3) The existing hot-rolled plate and coil quenching heat treatment process is mainly for specifications with a thickness of more than 3mm. At the same time, the uniformity of specifications with a thickness of less than 4mm is difficult to control, and the plate shape problem is prominent. The intensive hot coil continuous heat treatment line covers a thinner specification range (thickness can reach 2mm, and the thickness is mainly 2-4mm). From the plate shape theory, we know that the thinner the strip specification, the smaller the flatness dead zone, and the smaller the ability to resist warping deformation under the same stress conditions. Therefore, it is more sensitive to cooling uniformity, and the existing heat treatment cooling method cannot meet the requirements;

[0015] 4) Cooling uniformity is directly related to the strip speed. The strip speed of the traditional heat treatment line can reach 75m / min, while the speed of the intensive hot coil continuous heat treatment line is lower (generally within 10m / min). The low speed will aggravate the unevenness of cooling, and the cooling uniformity requirements are higher. The existing heat treatment cooling method cannot meet the requirements. Summary of the invention

[0016] The technical problem to be solved by the present invention is to overcome the above-mentioned shortcomings of the prior art, and to provide a segmented quenching process for intensive hot coil continuous heat treatment that can accurately control the final cooling temperature and realize segmented quenching cooling through reasonable setting of cooling equipment and process parameters to meet the quenching needs of related products, so as to meet the intermediate temperature requirements, air cooling time requirements and final cooling requirements.

[0017] The technical problem to be solved can be implemented through the following technical solutions.

[0018] A segmented quenching and cooling process for intensive hot coil continuous heat treatment, characterized in that it comprises the following steps:

[0019] (1) The cooling zone is divided into several cooling zones by multiple sets of pressing rollers; along the traveling direction of the strip, an air mist cooling device and a high-pressure water spray cooling device are arranged at intervals above and below the strip in each cooling zone;

[0020] (2) Initial cooling stage

[0021] When the steel strip enters the cooling zone, the corresponding mist cooling device and / or high-pressure water spray cooling device are turned on, and the upper and lower surfaces of the steel strip passing through are cooled by selectively selecting a cooling method of single mist cooling, single high-pressure water spray cooling, or a combination of mist cooling and high-pressure water spray cooling; the steel strip is cooled to the set target intermediate temperature;

[0022] (3) Air cooling section

[0023] The strip enters the air cooling zone and proceeds according to the set air cooling time; the air mist cooling device and high-pressure water spray cooling device corresponding to the upper and lower surfaces of the strip in the air cooling zone are in a closed state;

[0024] (4) Continue cooling stage

[0025] After the air cooling is completed, the strip that has completed the air cooling task moves to a new cooling zone, and by turning on the corresponding mist cooling device and / or high-pressure water spray cooling device, selectively selecting a single mist cooling, a single high-pressure water spray cooling, or a combination of mist cooling and high-pressure water spray cooling to continue cooling the upper and lower surfaces of the strip that has passed through; cooling to the set target final cooling temperature.

[0026] As a further improvement of the technical solution, step (2) and step (4) select the same or different cooling methods. For example, step (2) selects mist cooling, and step (4) selects high-pressure water spray cooling.

[0027] As a further improvement of the present technical solution, the target intermediate temperature in step (2) is 500-800°C; the target final cooling temperature in step (4) is 0-500°C; and the air cooling time in step (3) is 0-25s.

[0028] Preferably, the target intermediate temperature in step (2) is 600-800° C.; the target final cooling temperature in step (4) is 150-400° C.; and the air cooling time in step (3) is 0-15 s.

[0029] Also as a further improvement of the technical solution, the air-water ratio of the mist cooling is 1:6 to 6:1.

[0030] Furthermore, when the strip thickness is ≤3mm, the air-water ratio of the gas mist cooling is 3-6:2-5; when the strip thickness is greater than 3 and less than or equal to 4mm, the air-water ratio of the gas mist cooling is 3-6:3-6; when the strip thickness is greater than 4mm, the air-water ratio of the gas mist cooling is 2-5:3-6.

[0031] Preferably, the air-water ratio of the mist cooling is 2:5 to 5:2.

[0032] Similarly, when the strip thickness is ≤3mm, select single mist cooling; when the strip thickness is greater than 3mm and less than or equal to 5mm, select a combined cooling method of mist cooling and high-pressure water spray cooling; when the strip thickness is greater than 5mm, select single high-pressure water spray cooling.

[0033] As a further improvement of the technical solution, the air flow rate during cooling is 0-20m 3 / h, water flow rate is 0~0.5m 3 / h.

[0034] Preferably, the air flow rate during cooling is 0 to 15 m 3 / h, water flow rate is 0~0.3m 3 / h.

[0035] As a preferred embodiment of the present invention, the aerosol cooling device is an aerosol spraying beam, and each aerosol spraying beam is provided with a double row of nozzles.

[0036] It is also preferred that the pressure of the high-pressure water sprayed by the high-pressure water spray cooling device is 5 to 15 bar.

[0037] The segmented quenching and cooling process for intensive continuous heat treatment of hot coils using the above technical solution, through the reasonable layout and use of mist water spray beams in several cooling zones separated by pressure rollers, performs water cooling, mist cooling and air cooling in different cooling zones, reasonably sets the air cooling section and intermediate temperature, realizes segmented quenching and cooling, and meets the quenching needs of related products. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of conventional cooling and two-stage cooling of the present invention;

[0039] Figure 2 This is the equipment layout diagram of the quenching zone of the present invention;

[0040] In the figure: 1 - soaking furnace, 2 - strip steel, 3 - water mist baffle;

[0041] 4, 41, 42, 43 – pressure rollers;

[0042] 5——aerosol cooling beam, 5.1——aerosol nozzle, 5.2——water inlet pipe, 5.3——compressed air pipe, 6——oblique spray box, 6.1——(high pressure dense drainage) water nozzle. DETAILED DESCRIPTION

[0043] The specific implementation modes of the present invention will be further described in detail below with reference to the accompanying drawings.

[0044] refer to Figure 2 The layout of the quenching equipment shown in the figure is as follows: 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; there is a cooling zone between every two pressure rollers, and the entire cooling device can be provided with 1 to 4 cooling zones.

[0045] Corresponding cooling facilities are arranged at the upper and lower positions corresponding to the upper and lower surfaces of the strip in each cooling zone. An aerosol cooling nozzle (i.e., the aerosol cooling beam 5 in the figure) is installed on the spray beam of each cooling zone (i.e., the aerosol cooling beam 5 in the figure), and each spray beam is installed with double exhaust aerosol cooling nozzles; the figure also illustrates a water inlet pipe 5.2 and a compressed air pipe 5.3.

[0046] After coming out of the soaking furnace, the steel strip 2 passes through the water mist baffle 3 and then passes through each cooling section in sequence. 1 to 4 spray beams are placed in each cooling zone; a row of high-pressure water spray cooling is installed between every two spray beams.

[0047] Aerosol quenching and high-pressure water quenching are arranged at intervals, that is, a group of high-pressure water spray boxes are arranged between two aerosol spray beams, namely the inclined spray box 6 in the figure, and the inclined spray box 6 is provided with (high-pressure densely packed) water nozzles 6.1 to achieve flexible selection of different cooling modes; since thick-gauge strip steel (>5mm) has a slower cooling speed than thin-gauge strip steel and is not prone to plate shape problems, high-pressure water cooling can be selected, and aerosol cooling can be selected for thin-gauge strip steel (≤3mm).

[0048] Table 1 below shows the relevant device parameter settings.

[0049] Table 1: Equipment layout

[0050]

[0051] The following are the specific process parameter setting requirements:

[0052] Each row of nozzles in each spray beam can adjust the air-water ratio to achieve fine control of the atomization degree, that is, control the "particle size" (droplet size).

[0053] Through air-water ratio control, the cooling capacity of a single row of nozzles can be adjusted, that is, the temperature drop of a single row of nozzles can be controlled; according to the cooling capacity requirements, single mist cooling, single high-pressure water spray cooling, and a combination of mist cooling + high-pressure water spray cooling can be selected; according to the needs, the control requirements of different intermediate temperatures, air cooling time and final cooling temperature can be realized to achieve segmented quenching cooling.

[0054] Combination Figure 1 As shown in the schematic diagram of conventional cooling and two-stage cooling of the present invention, after passing through the cooling zone, the steel strip passes through each cooling zone in turn, and is cooled to the set intermediate temperature according to the selected cooling method. After air cooling for a certain period of time, it is cooled again to the set final cooling temperature. In the whole process, the steel strip moves forward all the time, and the position of the steel strip after each stage is not limited by the cooling zone. For example, after cooling to the intermediate temperature, the steel strip may just stop at the end of the first cooling zone, or stop in the middle of the second cooling zone. The overall quenching is divided into two stages (referring to the two stages before and after air cooling), which is different from Figure 1 The difference between one-stage cooling and conventional cooling is obvious.

[0055] Conventional cooling directly cools to room temperature without the need to control intermediate temperatures or air cooling time.

[0056] The specific process parameter configuration is shown in Table 2.

[0057] Table 2: Process parameters

[0058]

[0059]

[0060] The present invention provides a step-wise quenching and cooling process for continuous heat treatment of hot coils, which has the following beneficial effects:

[0061] 1. According to the variety, specifications and related needs, the cooling capacity and uniformity requirements can be met by selecting single mist cooling, single high-pressure water spray cooling, and combined mist cooling + high-pressure water spray cooling modes;

[0062] 2. Through air-water ratio control, the temperature drop and atomization degree of a single spray beam or a single row of nozzles can be controlled to achieve cooling capacity and uniformity requirements;

[0063] 3. Through the air-water ratio control, the temperature drop and atomization degree of a single spray beam or a single row of nozzles can be controlled to achieve different target temperatures and air cooling time requirements, and realize segmented quenching cooling.

[0064] The following are more specific examples.

[0065] Embodiment 1:

[0066] The segmented quenching and cooling process method for economical hot coil continuous heat treatment of the present invention was tested and implemented on a certain intensive hot coil continuous heat treatment production line, and was applied to steel type 1 with a thickness of 3 mm. Its process parameters are shown in Table 3 below.

[0067] Table 3:

[0068]

[0069] The parameter settings of this embodiment can meet the process control requirements after implementation.

[0070] Embodiment 2:

[0071] The segmented quenching and cooling process method for economical hot coil continuous heat treatment of the present invention was tested and implemented on a certain intensive hot coil continuous heat treatment production line, and was applied to steel type 2 with a thickness of 6 mm. Its process parameters are shown in Table 4 below.

[0072] Table 4:

[0073]

[0074] The parameter settings of this embodiment can meet the process control requirements after implementation.

Claims

1. A segmented quenching and cooling process for intensive hot coil continuous heat treatment, wherein the line speed of the intensive hot coil continuous heat treatment is within 10 m / min, and the strip thickness is 2 to 6 mm, characterized in that: The steps include: (1) The cooling zone is divided into several cooling zones by multiple sets of pressure rollers; along the running direction of the strip, an air mist cooling device and a high-pressure water spray cooling device are arranged at intervals above and below the strip in each cooling zone; (2) Initial cooling stage When the steel strip enters the cooling zone, the corresponding mist cooling device and / or high-pressure water spray cooling device are turned on, and the upper and lower surfaces of the steel strip passing through are cooled by selectively selecting a cooling method of single mist cooling, single high-pressure water spray cooling, or a combination of mist cooling and high-pressure water spray cooling; the steel strip is cooled to the set target intermediate temperature; (3) Air cooling section The strip enters the air cooling zone and proceeds according to the set air cooling time; the gas mist cooling device and high-pressure water spray cooling device corresponding to the upper and lower surfaces of the strip in the air cooling zone are in a closed state; (4) Continue cooling After the air cooling is completed, the strip that has completed the air cooling task moves to a new cooling zone, and by turning on the corresponding mist cooling device and / or high-pressure water spray cooling device, selectively selecting a single mist cooling, a single high-pressure water spray cooling, or a combination of mist cooling and high-pressure water spray cooling to continue cooling the upper and lower surfaces of the strip that has passed through; cooling to the set target final cooling temperature.

2. The segmented quenching and cooling process for intensive hot coil continuous heat treatment according to claim 1 is characterized in that: Step (2) and step (4) select the same or different cooling methods.

3. The segmented quenching and cooling process for intensive hot coil continuous heat treatment according to claim 1 is characterized in that: The target intermediate temperature in step (2) is 500 to 800° C.; the target final cooling temperature in step (4) is 0 to 500° C.; and the air cooling time in step (3) is 0 to 25 seconds.

4. The segmented quenching and cooling process for intensive hot coil continuous heat treatment according to claim 3 is characterized in that: The target intermediate temperature in step (2) is 600-800°C; the target final cooling temperature in step (4) is 150-400°C; and the air cooling time in step (3) is 0-15s.

5. The segmented quenching and cooling process for intensive hot coil continuous heat treatment according to claim 1 is characterized in that: The air-water ratio of mist cooling is 1:6 to 6:

1.

6. The segmented quenching and cooling process for intensive hot coil continuous heat treatment according to claim 5 is characterized in that: When the strip thickness is ≤3mm, the air-water ratio of the gas mist cooling is 3~6:2~5; when the strip thickness is greater than 3 and less than or equal to 4mm, the air-water ratio of the gas mist cooling is 3~6: 3~6; when the strip thickness is greater than 4mm, the air-water ratio of the gas mist cooling is 2~5: 3~6.

7. The segmented quenching and cooling process for intensive hot coil continuous heat treatment according to claim 5 is characterized in that: The air-water ratio of mist cooling is 2:5 to 5:

2.

8. The stepwise quenching and cooling process for intensive hot coil continuous heat treatment according to claim 1 is characterized in that: When the strip thickness is ≤3mm, select single gas mist cooling; when the strip thickness is greater than 3mm and less than or equal to 5mm, select a combined cooling method of gas mist cooling and high-pressure water spray cooling; when the strip thickness is greater than 5mm, select single high-pressure water spray cooling.

9. The stepwise quenching and cooling process for intensive hot coil continuous heat treatment according to claim 1, characterized in that: The air flow rate during cooling is 0~20m 3 / h, water flow rate is 0~0.5m 3 / h.

10. The stepwise quenching and cooling process for intensive hot coil continuous heat treatment according to claim 9, characterized in that: The air flow rate during cooling is 0~15m 3 / h, water flow rate is 0~0.3m 3 / h.

11. The stepwise quenching and cooling process for intensive hot coil continuous heat treatment according to claim 1, characterized in that: The aerosol cooling device is an aerosol spraying beam, and each aerosol spraying beam is provided with a double row of nozzles.

12. The stepwise quenching and cooling process for intensive hot coil continuous heat treatment according to claim 1, characterized in that: The high-pressure water sprayed by the high-pressure water spray cooling device has a pressure of 5 to 15 bar.

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