Mist water mixed quenching device and method for intensive hot rolled coil continuous heat treatment

Abstract

The present invention discloses a mist-water mixed quenching device and method for intensive hot-rolled coil continuous heat treatment, comprising a plurality of alternately arranged mist spray beams and water spray beams, and the mist spray beams and the water spray beams are distributed on the upper and lower surface sides of the hot-rolled coil steel plate; the mist spray beam is provided with a mist nozzle on one end facing the hot-rolled coil steel plate, and a compressed air pipe 1 and a water pipe on the other end; the water spray beam is provided with a water nozzle on one end facing the hot-rolled coil steel plate, and a compressed air pipe 2 on the other end; the water nozzle is arranged obliquely and forms an angle with the moving direction of the hot-rolled coil steel plate. The present invention controls the cooling speed of the strip by changing the cooling method and pressure, and realizes the quenching of steel plates with different thickness specifications.

Description

Technical Field

[0001] The present invention relates to the field of heat treatment technology, and more specifically to a mist water mixing quenching device and method for intensive hot rolled coil continuous heat treatment. Background Art

[0002] With the development of industrial technology, the market demand for hot-rolled high-strength steel and ultra-high-strength steel is growing. The demand for medium and high-strength steel in the steel field in industries such as engineering machinery, dump trucks, heavy trucks, and armored trucks is increasing year by year. The heat treatment technology of hot-rolled strip steel is very important. Quenching, as the core technology of heat treatment of hot-rolled strip steel, has become a top priority.

[0003] At present, hot-rolled strip is generally cut into plates of a certain length during heat treatment, and then quenching and tempering and other heat treatment processes are carried out. During quenching, the quenching machine structure is mainly slit injection + high-pressure water + water mist. Slit injection and high-pressure water are used in the high-temperature zone to quickly cool the steel plate to below the Ms point. Water mist cooling is used in the low-temperature zone to reduce the cooling rate and complete the martensitic phase transformation. However, if the cooling rate in the high-temperature zone is too fast, the thermal stress will cause serious plate shape problems, and the slit injection has extremely high requirements on the slit accuracy. It is difficult to ensure that the slit size is the same, causing uneven heat exchange; the cooling rate in the low-temperature zone is too slow, resulting in self-tempering of martensite, affecting the quenching performance. In fact, after the thin-gauge hot-rolled plate is injected by slit injection or high-pressure water injection, it has been cooled to room temperature, and water mist cooling has no effect, and the plate shape is poor.

[0004] In existing patent applications, such as Chinese patent CN102268517A, an alternating quenching cooling system of air, air-water mist, water spray, and water immersion is disclosed. For heat treatment of rods with Ms in the range of 300-400°C, normalizing of rods with a diameter of Φ>100mm is performed by water spray or spray; quenching of rods with a diameter of Φ<100mm is performed by cooling with water spray, water spray agent or spray. The cooling system is limited to placing the rods in a water tank and cooling them with a cooling medium of water or a water-based polymer, in order to eliminate quenching pollution and save space. The quenching layout is very different from that of intensive hot coil continuous heat treatment, the cooling rate is difficult to control, and the cooling system cannot be used for hot coil quenching.

[0005] For example, Chinese patent CN102747213A discloses a cooling method for continuous heat treatment of high-strength steel, in which the heated strip surface is slowly cooled by blowing air, and then the steel plate is cooled by aerosol, laminar water column or water knife, and finally the steel surface is dried to complete the quenching process. The high-pressure water of the laminar water column in the cooling method is at an acute angle or right angle to the strip surface, and first passes through a slow cooling section before quenching, so as to avoid problems such as uneven cooling, uneven performance and poor plate shape caused by the high water temperature of the strip. However, ferrite will also appear due to the low initial cooling temperature, affecting the performance. In addition, this method is only applicable to steel plates with a thickness of less than 2 mm, and is used for quenching of cold-rolled continuous annealing. For hot-rolled strips with a thickness of 2-6 mm, this method is no longer applicable.

[0006] Another example is Chinese patent CN102747205A, which discloses a water quenching system for producing cold-rolled phase-change strengthened high-strength strip steel. The system includes a sealing device, a pair of water knives and two sets of nozzle cooling devices arranged in sequence along the strip steel travel method. It can realize three-stage cooling of water knife cooling, nozzle cooling, sub-liquid nozzle cooling + water quenching tank immersion cooling. This method can improve the cooling rate and cooling uniformity. The use of water quenching tank immersion cooling will cause uneven heat exchange during cooling, resulting in poor plate shape problems. This method can only be limited to cold-rolled high-strength steel or ultra-high-strength steel below 2mm, and cannot meet the heat treatment conditions of hot-rolled strip steel.

[0007] In summary, for cold-rolled high-strength steel or ultra-high-strength steel, quenching is mostly carried out by jet, spray, water jet or laminar water column. By adjusting different cooling methods, the cooling rate and plate shape are guaranteed, but the cooling rate cannot be accurately controlled. For the heat treatment of hot-rolled strip, slit spray or high-pressure water + water mist is often used. Although the cooling rate can be guaranteed, the cooling rate cannot be controlled, and the plate shape is very poor. There are few reports on quenching devices for intensive hot coil continuous heat treatment. This patent adopts a mist water mixed quenching device. By changing the cooling method and pressure, the cooling rate of the strip is controlled to achieve quenching of steel plates of different thicknesses. The cooling rate control range is large. Mist cooling is used for thin-gauge hot-rolled strip, and pressure oblique spray is used for thick-gauge hot-rolled strip. In addition, the use of mist water mixture makes the entire area of ​​the strip under the impact zone, reducing the temperature reversion phenomenon and ensuring performance. Summary of the invention

[0008] In view of the above-mentioned defects existing in the prior art, the purpose of the present invention is to provide a mist water mixed quenching device and method for intensive hot-rolled coil continuous heat treatment, which can control the cooling rate of the strip by changing the cooling mode and pressure to achieve quenching of steel plates with different thickness specifications.

[0009] To achieve the above object, the present invention adopts the following technical solution:

[0010] On the one hand, a mist-water mixed quenching device for intensive hot-rolled coil continuous heat treatment comprises a plurality of alternately arranged mist spraying beams and water spraying beams, and the mist spraying beams and the water spraying beams are distributed on the upper and lower surface sides of the hot-rolled coil steel plate;

[0011] The aerosol spraying beam is provided with an aerosol nozzle on one end facing the hot-rolled steel coil, and a compressed air pipe and a water pipe on the other end;

[0012] The water spray beam is provided with a water nozzle on one end facing the hot-rolled steel coil, and a compressed air pipe 2 on the other end;

[0013] The water nozzle is arranged obliquely and forms an angle with the moving direction of the hot-rolled steel coil.

[0014] Preferably, the water spraying beam is inclined toward one end of the hot-rolled steel coil.

[0015] Preferably, two water nozzles are provided, both of which are arranged at the lower end of one end of the water spraying beam which is inclined.

[0016] Preferably, the water jet beam is provided with a water inlet pipe, one end of the water inlet pipe is connected to an external water source, and the other end is connected to the water jet beam;

[0017] Two water nozzle inlet pipes are also arranged in the water spraying beam, which are respectively connected with the corresponding water nozzles.

[0018] Preferably, the other end of the water inlet pipe is connected to the water jetting beam through a guide pipe.

[0019] Preferably, the water nozzle is a fan-shaped water nozzle, and the angle between the jet flow and the moving direction of the hot-rolled steel coil is 20° to 50°.

[0020] On the other hand, a mist water mixed quenching method for intensive continuous heat treatment of hot rolled coils is provided, wherein the mist water mixed quenching device for intensive continuous heat treatment of hot rolled coils is arranged on the upper and lower surface sides of the hot rolled coil steel plate, and according to the thickness of the hot rolled coil steel plate, the hot rolled coil steel plate is cooled by either aerosol cooling or a pressure oblique spraying method.

[0021] Preferably, the thickness of the hot rolled coil is 2 mm to 6 mm.

[0022] Preferably, when the thickness of the hot-rolled steel coil is 2 mm to 4 mm, the aerosol cooling method is adopted, that is, the aerosol nozzle is turned on, the water nozzle is closed, the movement speed of the hot-rolled steel coil is 7 to 15 m / min, the compressed air pressure is 2 to 6 bar, and the cooling rate is 40 to 200°C / s.

[0023] Preferably, when the thickness of the hot-rolled steel coil is 4 mm to 6 mm, the pressure oblique spraying method is adopted, that is, the water nozzle is opened and the aerosol nozzle is closed, the movement speed of the hot-rolled steel coil is 3 to 7 m / min, the compressed air pressure is 3 to 8 bar, and the cooling rate is 60 to 500°C / s.

[0024] The mist water mixing quenching device and method for intensive hot rolled coil continuous heat treatment provided by the present invention have the following beneficial effects:

[0025] 1) The mist water mixed quenching device of the present invention has a wider cooling rate control range by changing the cooling mode and pressure, thereby meeting the quenching requirements of hot-rolled strip steels of different specifications;

[0026] 2) The mist water mixing quenching device of the present invention optimizes the internal structure of the pressure oblique spray water nozzle to achieve rapid opening and closing, thereby avoiding the uneven cooling phenomenon caused by residual water droplets falling on the surface of the hot strip;

[0027] 3) The mist water mixing quenching device of the present invention transforms the water nozzle of the pressure oblique spray and adopts a fan-shaped nozzle, which reduces the impact force without affecting the cooling rate, and has better cooling uniformity, which is beneficial to the plate shape;

[0028] 4) The use of mixed mist water in the mist water mixed quenching method of the present invention is beneficial for the steel strip to be always in the impact zone, reduce the temperature recovery phenomenon of the hot steel plate, and achieve uniform cooling and better performance uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the mist water mixing quenching device of the present invention;

[0030] Figure 2 It is a schematic diagram of the internal structure of the water spraying beam in the mist water mixing quenching device of the present invention;

[0031] Figure 3 It is a schematic diagram of the gas mist quenching metallographic structure of a hot-rolled high-strength steel in Example 1 of the mist water mixed quenching method of the present invention;

[0032] Figure 4 It is a schematic diagram of the metallographic structure of a hot-rolled high-strength steel subjected to pressure oblique spray quenching in Example 3 of the mist water mixed quenching method of the present invention. DETAILED DESCRIPTION

[0033] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0034] Combination Figure 1As shown, the mist-water mixed quenching device for intensive continuous heat treatment of hot-rolled coils provided by the present invention comprises a plurality of alternately arranged mist spray beams 1 and water spray beams 2, and the mist spray beams 1 and water spray beams 2 are distributed on the upper and lower surface sides of the hot-rolled coil steel plate 8.

[0035] Two aerosol nozzles 3 are arranged on one end of the aerosol spraying beam 1 facing the hot-rolled steel coil 8, and a compressed air pipe 5 and a water pipe 6 are arranged on the other end.

[0036] Two water nozzles 4 are arranged on one end of the water spraying beam 2 facing the hot rolled steel coil 8, and a compressed air pipe 7 is arranged on the other end.

[0037] The jet flow of the water nozzle 4 is an inclined jet and forms an angle of 20° to 50° with the moving direction of the hot-rolled steel coil 8 .

[0038] The water nozzle 4 adopts a fan-shaped water nozzle (the jet flow is fan-shaped), which reduces the impact force without affecting the cooling rate, and has better cooling uniformity, which is beneficial to the plate shape.

[0039] Combination Figure 2 As shown, the water spraying beam 2 is tilted toward one end of the hot-rolled steel coil 8 so that there is a height difference in the water flow inside it, which can achieve rapid opening and closing.

[0040] The two water nozzles 4 are both arranged at the lower end of one end of the water spraying beam 2 which is inclined.

[0041] A water inlet pipe 23 is also provided on the water spraying beam 2 . The upper end of the water inlet pipe 23 is connected to an external water source, and the lower end of the water inlet pipe 23 is connected to the water spraying beam 2 through a guide pipe 24 .

[0042] Two water nozzle inlet pipes 22 are also provided in the water spraying beam 2 and are connected to the corresponding water nozzles 4 respectively.

[0043] After the valve is opened, the pressurized water enters the guide pipe 24 from the water inlet pipe 23, and then enters the interior of the water jet beam 2. As the water continues to flow in, the water level in the water jet beam 2 continues to rise. When the water level is higher than the top of the water nozzle water inlet pipe 22, it begins to enter the water nozzle water inlet pipe 22, and then the pressurized water flows out of the water nozzle 4, achieving rapid opening. After the valve is closed, the pressurized water no longer flows into the water inlet pipe 23, the water level inside the water jet beam 2 immediately drops, the pressurized water no longer flows into the water nozzle water inlet pipe 22, and the pressurized water in the water nozzle 4 no longer flows out, achieving rapid closing.

[0044] The present invention also provides a mist water mixed quenching method for intensive continuous heat treatment of hot-rolled coils, and the mist water mixed quenching device for intensive continuous heat treatment of hot-rolled coils of the present invention is arranged on the upper and lower surface sides of the hot-rolled steel plate 8, and according to the thickness of the hot-rolled steel plate 8, the hot-rolled steel plate is cooled by a mist cooling method or a pressure oblique spray method.

[0045] The hot-rolled coil steel plate 8 is a hot-rolled coil with a thickness of 2 mm to 6 mm.

[0046] When the thickness of the hot rolled steel coil 8 is 2 mm to 4 mm, the mist cooling method is adopted, that is, the mist nozzle 3 is turned on, the water nozzle 4 is turned off, the movement speed of the hot rolled steel coil 8 is 7 to 15 m / min, the compressed air pressure is 2 to 6 bar, and the cooling speed is 40 to 200°C / s. The mist cooling method is adopted to accurately control the cooling speed, which is conducive to the shape control of the hot rolled steel coil 8.

[0047] When the thickness of the hot rolled steel coil 8 is 4mm to 6mm, the pressure oblique spraying method is adopted, that is, the water nozzle 4 is opened, the mist nozzle 3 is closed, the movement speed of the hot rolled steel coil 8 is 3 to 7m / min, the compressed air pressure is 3 to 8bar, and the cooling rate is 60 to 500℃ / s. The pressure oblique spraying method (fan-shaped water nozzle 4 pressure oblique spraying) is adopted to reduce the surface temperature reversal phenomenon of the hot rolled steel coil 8, increase the cooling rate, and facilitate the control of the thicker hot rolled plate shape.

[0048] The present invention tests a hot-rolled high-strength steel of different thicknesses through three embodiments, with a target strength of 1150 MPa, a target elongation after fracture of 13%, a target plate shape of 5 mm / m, and a critical cooling rate of 50°C / s. The temperature is measured by embedding a couple at the same position in each test.

[0049] Example 1

[0050] A hot-rolled high-strength steel with a thickness of 2 mm is cooled by mist after heating. The mist nozzle 3 is turned on and the water nozzle 4 is turned off. The movement speed of the hot-rolled steel coil 8 is 15 m / min and the pressure is 3 Bar. The cooling rate of the 2 mm hot-rolled high-strength steel above the martensitic transformation start temperature under the mist water mixing device is 105 ° C / s, and the cooling rate below the martensitic transformation start temperature is 174 ° C / s. The organization after mist quenching is the quenched martensitic structure (see Figure 3 As shown in the figure, the original austenite grain size is about 10μm, the gas mist quenching cooling rate is higher than 100℃ / s, which is greater than the critical cooling rate of 50℃ / s, and finally the quenched martensite structure is obtained without carbide precipitation. The quenching strength is 1210MPa, the elongation after fracture is 14.5%, and the plate shape is 4.6mm / m.

[0051] Example 2

[0052] A hot-rolled high-strength steel with a thickness of 4mm is cooled by mist after heating. The mist nozzle 3 is turned on and the water nozzle 4 is turned off. The movement speed of the hot-rolled coil 8 is 8m / min and the pressure is 6Bar. The cooling rate of the 4mm hot-rolled high-strength steel above the martensitic phase transformation start temperature point under the mist water mixing device is 85℃ / s, and the cooling rate below the martensitic phase transformation start temperature point is 130℃ / s. The structure after mist quenching is quenched martensitic structure. The quenching strength is 1195MPa, the elongation after fracture is 15%, and the plate shape is 4mm / m.

[0053] Example 3

[0054] A hot-rolled high-strength steel with a thickness of 6 mm is cooled by pressure spray after heating. The water nozzle 4 is turned on and the mist nozzle 3 is turned off. The movement speed of the hot-rolled coil steel plate 8 is 6 m / min, the angle between the jet flow and the movement direction of the steel plate is 25°, and the pressure is 5 Bar. The cooling rate of the 6 mm hot-rolled high-strength steel above the martensitic phase transformation start temperature point under the mist water mixing device is 190 ° C / s, and the cooling rate below the martensitic phase transformation start temperature point is 268 ° C / s. The organization after aerosol quenching is quenched martensitic structure (see Figure 4 As shown in the figure, the original austenite grain is about 10μm, the gas mist quenching cooling rate is higher than 190℃ / s, which is greater than the critical cooling rate of 50℃ / s, and finally the quenched martensite structure is obtained without carbide precipitation. The quenching strength is 1292MPa, the elongation after fracture is 14.5%, and the plate shape is 4.8mm / m.

[0055] Combining the statistical table formed by the cooling rate, performance and plate shape of the above three embodiments (see Table 1 below), it can be seen from the results that by adopting the method of the present invention, after quenching 2-6 mm hot-rolled high-strength steel to room temperature, complete quenched martensite is obtained, the cooling rate is above the critical cooling rate, the strength is above 1150 MPa, the elongation is greater than 13%, and the plate shape is below 5 mm / m, which meets the target requirements.

[0056] Table 1

[0057]

[0058] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A mist water mixing quenching device for intensive hot rolled coil continuous heat treatment, characterized in that: It comprises a plurality of alternately arranged mist spray beams and water spray beams, and the mist spray beams and the water spray beams are distributed on the upper and lower surface sides of the hot-rolled steel coil; The aerosol spraying beam is provided with an aerosol nozzle on one end facing the hot-rolled steel coil, and a compressed air pipe and a water pipe on the other end; The water spray beam is provided with a water nozzle on one end facing the hot-rolled steel coil, and a compressed air pipe 2 on the other end; The water nozzle is tilted and forms an angle with the moving direction of the hot rolled steel coil. The water jet beam is tilted toward one end of the hot-rolled steel plate so that there is a height difference in the water flow inside the beam, thereby realizing rapid opening and closing. There are two water nozzles, both of which are arranged at the lower end of one end of the water spraying beam that is inclined.

2. The mist water mixing quenching device for intensive hot rolled coil continuous heat treatment according to claim 1, characterized in that: The water jet beam is provided with a water inlet pipe, one end of which is connected to an external water source, and the other end of which is connected to the water jet beam; Two water nozzle inlet pipes are also arranged in the water spraying beam, which are respectively connected with the corresponding water nozzles.

3. The mist water mixing quenching device for intensive hot rolled coil continuous heat treatment according to claim 2, characterized in that: The other end of the water inlet pipe is communicated with the water jetting beam through a guide pipe.

4. The mist water mixing quenching device for intensive hot rolled coil continuous heat treatment according to claim 2, characterized in that: The water nozzle is a fan-shaped water nozzle, and the angle between the jet flow and the moving direction of the hot-rolled steel coil is 20° to 50°.

5. A mist water mixed quenching method for intensive hot rolled coil continuous heat treatment, characterized in that: A mist water mixed quenching device for intensive hot rolled coil continuous heat treatment as described in any one of claims 1 to 4 is arranged on the upper and lower surface sides of the hot rolled steel plate, and according to the thickness of the hot rolled steel plate, the hot rolled steel plate is cooled by gas mist cooling or pressure oblique spraying.

6. The mist water mixed quenching method for intensive hot rolled coil continuous heat treatment according to claim 5, characterized in that: The thickness of the hot-rolled steel coil is 2 mm to 6 mm.

7. The mist water mixed quenching method for intensive hot rolled coil continuous heat treatment according to claim 6, characterized in that: When the thickness of the hot-rolled steel coil is 2 mm to 4 mm, the aerosol cooling method is adopted, that is, the aerosol nozzle is opened, the water nozzle is closed, the moving speed of the hot-rolled steel coil is 7 to 15 m / min, the compressed air pressure is 2 to 6 bar, and the cooling speed is 40 to 200°C / s.

8. The mist water mixed quenching method for intensive hot rolled coil continuous heat treatment according to claim 6, characterized in that: When the thickness of the hot-rolled steel coil is 4 mm to 6 mm, the pressure oblique spraying method is adopted, that is, the water nozzle is opened and the aerosol nozzle is closed, the moving speed of the hot-rolled steel coil is 3 to 7 m / min, the compressed air pressure is 3 to 8 bar, and the cooling speed is 60 to 500°C / s.

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