Gas mist cooling device and method for intensive hot rolled coil continuous heat treatment

Abstract

The present invention discloses an aerosol cooling device and method for intensive hot-rolled coil continuous heat treatment, comprising a plurality of aerosol spraying beams, and the aerosol spraying beams are distributed on the upper and lower surface sides of the hot-rolled coil steel plate; each of the aerosol spraying beams is provided with a plurality of rows of aerosol spraying pipes; each row of the aerosol spraying pipes is provided with a plurality of aerosol nozzles on one side facing the hot-rolled coil steel plate, and a compressed air pipe and a water pipe on the other side. The present invention allows hot-rolled strip steel of different specifications to be quenched at different cooling rates, so that it meets the performance requirements while reducing the thermal stress and structural stress of the strip steel, reducing the surface temperature reversion phenomenon of the strip steel, avoiding the occurrence of self-tempering, and obtaining hot-rolled ultra-high strength steel with excellent performance uniformity, good surface quality, and no obvious wave shape.

Description

Technical Field

[0001] The present invention relates to the field of heat treatment technology, and more specifically to an aerosol cooling 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 heat treatment generally adopts offline heat treatment to produce thin-gauge ultra-high-strength steel. The general process is uncoiling, cutting, shot blasting, heating, quenching and tempering. The running speed of the strip can reach 75m / min. Water quenching is mainly adopted during quenching, and high-pressure slit injection and pressure injection are configured. The quenching plate shape is optimized by adjusting the upper and lower water ratio and the strip speed. By using slit injection or high-pressure water injection, water of different pressures is brought into contact with the surface of the hot steel plate to enhance the heat exchange effect and quickly cool the heated steel plate to room temperature without quenching temperature reversal phenomenon. However, slit injection has extremely high requirements on slit accuracy. It is difficult to make the slit size along the plate width direction the same, resulting in differences in heat exchange in different areas along the width direction of the steel plate; and although the high-pressure water nozzles are arranged in a staggered manner, there are still large direct impact areas and non-impact areas, resulting in large differences in heat exchange between the two areas. These factors directly lead to large structural stress and thermal stress in hot-rolled steel plates during quenching, poor plate shape, substandard surface quality and uneven performance. In addition, the steel plate moves at a high speed, the production line is long, and the floor space is large, and production in the form of a single plate results in low efficiency.

[0004] Intensive hot coil continuous heat treatment technology is to coil the hot rolled steel coil again after quenching and tempering. During the heating process, a rapid heating method is used to shorten the heating and soaking time, improve production efficiency, and shorten the length of the production line. In the intensive production line, the running speed of the strip is generally less than 10m / min, and the speed cannot be adjusted. If the traditional cooling method is used in the production process, the unevenness of the cooling of thin gauge steel plates will be more serious, and the plate shape will be difficult to control, which makes the selection of quenching equipment more difficult.

[0005] In existing patent applications, such as Chinese patent CN012492824A, a continuous heat treatment method for high-strength steel strips or steel plates is disclosed. The quenching device can realize mist cooling, water spray cooling or mist + water spray combined cooling. The device is used to cool the steel plate to 200-500°C. This method is mainly used for very thin cold-rolled strip steel with a specification of less than 2mm, mainly to obtain cold-rolled QP steel. For traditional hot-rolled engineering machinery steel, self-tempering or incomplete hardening occurs when quenching to this temperature range, affecting performance.

[0006] For example, Chinese patent CN016350640A discloses a method for continuous quenching of cold-rolled steel strip, including heating the cold-rolled steel strip to the ferrite-austenite phase transition temperature of 30-50°C, using mist cooling and jet cooling at a certain intermediate value between the martensite transformation start temperature and the end temperature, using mist cooling in the higher temperature area and jet cooling in the lower temperature area, the cooling rates are 100-200°C / s and 20-50°C / s, respectively, thereby reducing the deformation of the cold-rolled steel strip and reducing the production cost. However, the cooling rate in the lower area is too low, which is prone to martensite self-tempering, and the surface is oxidized due to the presence of water mist.

[0007] For example, Chinese patent CN203264989U discloses a rapid cooling aerosol nozzle, including an air-water mixing chamber and a nozzle, which mainly increases the number of injection holes by changing the basic structure of the nozzle to ensure that the cooling rate is increased without increasing the number of nozzles, and the maximum cooling rate can reach more than 100℃ / s. While increasing the number of injection holes, the water flow rate is increased, which will also aggravate the cooling unevenness, resulting in uneven performance.

[0008] For example, Chinese patent CN101293229A discloses a dual-purpose cooling device for jet and spray, which can achieve a wide range of cooling rates by changing the nozzle position, nozzle angle and cooling medium. However, in terms of nozzle angle adjustment, it is the nozzle spray angle. When the cooling nozzle is fixed, as the angle increases, the horizontal and vertical impact areas have almost no obvious changes, and the cooling rate can only be increased by changing the water volume by the narrow slit width of the nozzle.

[0009] For example, Chinese patent CN105793446A discloses a continuous heat treatment method and equipment for steel strips, which uses a cooling method including spraying liquid, a synthetic fluid of gas and liquid, or a mist-type composition, so that the cooling rate is above 200℃ / s, followed by hot dip coating on the surface of the steel plate. This method is used for cold-rolled steel plates with a thickness of less than 2mm, and its applicability to hot-rolled strip steel with a specification of 2-6mm is unclear.

[0010] Another example is the Chinese patent CN110168117A, which discloses a rapid cooling method and part of a continuous production line for metal strip processing. By arranging different types of aerosol nozzles, quenching cooling is achieved with a cooling rate of 400-1200°C / s. The nozzle inclination angle is 5-15°, so that the cooling rate of a 2mm strip is increased to 1000°C / s when cooling in the range of 800-500°C. If the cooling rate is too fast at 800-500°C, thermal stress cannot be released, which will cause plate shape problems.

[0011] In summary, mist or gas cooling is used for cold-rolled steel strip with a thickness of less than 2mm to ensure the cooling rate while having good uniformity and surface quality; currently, water quenching technology is mostly used for quenching technology of hot-rolled steel strip with a thickness of 2-6mm. The cooling rate cannot meet the requirements by using conventional mist cooling method, and mist cooling is rarely used to quench hot-rolled steel strip. In order to obtain hot-rolled ultra-high strength steel with high strength, high uniformity, low structural stress and thermal stress, good plate shape and good surface quality, this patent adopts a mist cooling device, and changes the nozzle rotation angle and the layout of the mist spray beam according to different types and thicknesses of hot-rolled steel strip, so as to obtain hot-rolled ultra-high strength steel with excellent performance and good quality. In the aerosol cooling device of this patent, an external mixing nozzle is used, so that there is no mutual interference when adjusting the air pressure and water pressure, which is convenient for control and adjustment. Summary of the invention

[0012] In view of the above-mentioned defects existing in the prior art, the purpose of the present invention is to provide an aerosol cooling device and method for intensive continuous heat treatment of hot-rolled coils, so that hot-rolled strips of different specifications can be quenched at different cooling rates, so that they can meet the performance requirements while reducing the thermal stress and structural stress of the strips, reducing the surface temperature regeneration phenomenon of the strips, avoiding self-tempering, and obtaining hot-rolled ultra-high strength steel with excellent performance uniformity, good surface quality and no obvious wave shape.

[0013] To achieve the above object, the present invention adopts the following technical solution:

[0014] In one aspect, an aerosol cooling device for intensive hot rolled coil continuous heat treatment comprises a plurality of aerosol spraying beams, and the aerosol spraying beams are distributed on the upper and lower surface sides of the hot rolled coil steel plate;

[0015] Each of the aerosol spraying beams is provided with a plurality of aerosol spraying pipes;

[0016] Each row of the aerosol spray pipes is provided with a plurality of aerosol nozzles on one side facing the hot-rolled steel coil, and a compressed air pipe and a water pipe on the other side.

[0017] Preferably, the aerosol nozzle is an external mix nozzle.

[0018] Preferably, the distance between the aerosol nozzle and the hot-rolled steel coil is 50 to 300 mm.

[0019] Preferably, the distance between two adjacent aerosol nozzles on the same row of aerosol spray pipes is 30 to 150 mm.

[0020] Preferably, the spacing between two adjacent rows of the aerosol spraying tubes is 30 to 200 mm.

[0021] Preferably, the angle between the jet flow of the aerosol nozzle and the aerosol spray pipe is 7-75°.

[0022] Preferably, the distance between two adjacent aerosol spraying beams is 40 to 400 mm.

[0023] On the other hand, a mist cooling method for intensive continuous heat treatment of hot rolled coils is provided, wherein the mist cooling 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 by changing the angle between the mist nozzle and the mist injection pipe and the spacing arrangement between the mist injection beams, the hot rolled coil steel plates of different thickness specifications are quenched at different cooling rates.

[0024] Preferably, the thickness of the hot-rolled steel coil is 2 to 6 mm;

[0025] The hot rolled steel coil is quenched at different cooling rates: the cooling rate is 30-100°C / s above the martensitic transformation start temperature, and the cooling rate is 50-200°C / s below the martensitic transformation start temperature.

[0026] Preferably, the air pressure of the aerosol nozzle is 3-6 bar, and the water pressure is 2-5 bar.

[0027] The present invention provides a mist cooling device and method for intensive hot rolled coil continuous heat treatment, which has the following beneficial effects:

[0028] 1) The aerosol cooling device of the present invention can adjust the rotation angle of the aerosol nozzle and the layout of the aerosol spray beam, control the spray flow area, control the heat exchange during the cooling process, and use different cooling parameters for different thickness specifications, so that the aerosol jet can cover the entire width direction, so that the temperature and performance uniformity during the quenching of the hot-rolled strip are better;

[0029] 2) The aerosol cooling device of the present invention adjusts the rotation of the aerosol nozzle and the layout of the aerosol spray beam, which can effectively increase the impact area, extend the heat exchange time, and increase the cooling rate of the hot-rolled strip aerosol quenching;

[0030] 3) The aerosol nozzle in the aerosol cooling device of the present invention adopts an external mixing type, and there is no mutual interference when the air pressure and water pressure are adjusted, which is convenient for control and adjustment;

[0031] 4) In the aerosol cooling method of the present invention, the cooling rate above the martensitic phase transformation temperature is 30-100°C / s, which avoids the transformation of ferrite, pearlite and bainite in the higher temperature zone. At the same time, the cooling rate is low, which can significantly reduce the thermal stress, thereby reducing the poor plate shape caused by thermal stress; the cooling rate below the martensitic phase transformation start temperature is 50-200°C / s, which reduces the tissue stress while obtaining martensite, and does not cause self-tempering, thereby reducing the poor plate shape caused by tissue stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the structure of the aerosol cooling device of the present invention;

[0033] Figure 2 It is a schematic diagram of the layout of the aerosol spray pipe and the aerosol nozzle in the aerosol cooling device of the present invention;

[0034] Figure 3 is a schematic diagram of the cooling curve of a hot-rolled ultra-high strength steel in Examples 1-3 of the gas mist quenching method of the present invention,

[0035] Figure 4 It is a schematic diagram of the gas mist quenching metallographic structure of a hot-rolled ultra-high strength steel in Example 3 of the gas mist quenching method of the present invention. DETAILED DESCRIPTION

[0036] 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.

[0037] Combination Figure 1 and Figure 2 As shown, the present invention provides an aerosol cooling device for intensive hot rolled coil continuous heat treatment, comprising a plurality of parallel aerosol spraying beams 1, and the aerosol spraying beams 1 are distributed on the upper and lower surface sides of the hot rolled coil steel plate 6.

[0038] Each aerosol spraying beam 1 is provided with a plurality of parallel rows of aerosol spraying pipes 2 .

[0039] Each mist injection pipe 2 is provided with a plurality of mist nozzles 3 on one side facing the hot-rolled steel coil, and a compressed air pipe 4 and a water pipe 5 on the other side.

[0040] The aerosol nozzle 3 is an external mixing nozzle, and there is no mutual interference when the air pressure and the water pressure are adjusted, which is convenient for control and adjustment.

[0041] The aerosol cooling device of the present invention adjusts the rotation angle of the aerosol nozzle 3 and the layout of the aerosol spray beam 1, such as the setting height of the aerosol nozzle 4, the lateral spacing between two adjacent aerosol nozzles 4 on a single row of aerosol spray pipes 2, the longitudinal spacing between two adjacent rows of aerosol spray pipes 2, and the longitudinal spacing between two adjacent aerosol spray beams 1, and controls various parameters to adjust the fan-shaped spray flow area and control the cooling process. The specific settings are as follows:

[0042] The air pressure of the aerosol nozzle 4 is 3 to 6 bar, and the water pressure is 2 to 5 bar.

[0043] The installation height of the gas mist nozzle 4, that is, the distance h between the gas mist nozzle 4 and the hot-rolled steel coil 6, is 50 to 300 mm.

[0044] The lateral spacing 32 between two adjacent gas mist nozzles 4 on the same exhaust mist injection pipe 2 is 30 to 150 mm.

[0045] The distance 33 between two adjacent rows of mist spraying beams 1 is 30-200 mm.

[0046] The angle 34 between the jet 31 of the aerosol nozzle 4 and the aerosol spraying pipe 2 is 7 to 75 degrees.

[0047] The distance w between two adjacent aerosol spraying beams 1 is 40-400 mm.

[0048] Before cooling, the parameters such as the angle 34 of the aerosol nozzle 4, the lateral spacing 32 between two adjacent aerosol nozzles 4 and the spacing 33 between two rows of aerosol spray beams 1 are set in advance, and the aerosol nozzle 4 is arranged to achieve uniform quenching. The aerosol nozzle 4 can be arranged in a staggered layout or aligned in the movement direction of the hot-rolled coil steel plate 6.

[0049] The present invention also provides an aerosol cooling method for intensive continuous heat treatment of hot-rolled coils. The aerosol cooling 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 coil steel plate 6. By changing the angle between the aerosol nozzle 4 and the aerosol spray pipe 2 and the spacing arrangement between the aerosol spray beams 1, hot-rolled coil steel plates 6 of different specifications can be quenched at different cooling rates.

[0050] The hot-rolled coil steel plate 6 is quenched at different cooling rates: the cooling rate is 30-100°C / s above the martensitic phase transformation start temperature to avoid ferrite, pearlite and bainite transformation in the higher temperature zone. At the same time, the cooling rate is low, which can significantly reduce the thermal stress, thereby reducing the poor plate shape caused by thermal stress; the cooling rate is 50-200°C / s below the martensitic phase transformation start temperature. While obtaining martensite, the tissue stress is reduced, and the self-tempering phenomenon will not occur, thereby reducing the poor plate shape caused by tissue stress.

[0051] The present invention uses three embodiments to test a hot-rolled ultra-high strength steel, with a critical cooling rate of 50°C / s. Each test is performed with a couple embedded in the same position for temperature measurement.

[0052] Example 1

[0053] A certain hot-rolled ultra-high strength steel is cooled by aerosol after heating. The aerosol spray pipe 2 is arranged in a row, the rotation angle of the aerosol nozzle 4 is 15°, the height of the aerosol nozzle 4 from the hot-rolled coil steel plate 6 is 200mm, the lateral spacing 32 between the aerosol nozzles 4 is 120mm, the spacing 33 between the aerosol spray pipes 4 is 350mm, the air pressure is 4bar, and the water pressure is 3bar. The cooling rate of the 2mm hot-rolled ultra-high strength steel above the martensitic phase transformation start temperature point under the aerosol cooling device is 95℃ / s, and the cooling rate below the martensitic phase transformation start temperature point is 185℃ / s. The organization after aerosol quenching is quenched martensitic organization.

[0054] Example 2

[0055] A certain hot-rolled ultra-high strength steel is cooled by aerosol after heating. The aerosol spray pipe 2 is arranged in two rows, the rotation angle of the aerosol nozzle 4 is 45°, the height of the aerosol nozzle 4 from the hot-rolled coil steel plate 6 is 150mm, the lateral spacing 32 between the aerosol nozzles 4 is 100mm, the spacing 33 between the aerosol spray pipes 2 is 100mm, the spacing w between the aerosol spray beams 1 is 300mm, the air pressure is 5bar, and the water pressure is 4bar. The cooling rate of the 4mm hot-rolled ultra-high strength steel above the martensitic phase transformation start temperature point under the aerosol cooling device is 78℃ / s, and the cooling rate below the martensitic phase transformation start temperature point is 147℃ / s. The structure after aerosol quenching is quenched martensitic structure.

[0056] Example 3

[0057] A certain hot-rolled ultra-high strength steel is cooled by aerosol after heating. The aerosol spray pipes 2 are arranged in four rows, the rotation angle of the aerosol nozzles 4 is 60°, the height of the aerosol nozzles 4 from the hot-rolled coil steel plate 6 is 100mm, the lateral spacing 32 between the aerosol nozzles 4 is 80mm, the spacing 33 between the aerosol spray pipes 2 is 150mm, the spacing w between the aerosol spray beams 1 is 200mm, the air pressure is 6bar, and the water pressure is 5bar. The cooling rate of the 6mm hot-rolled ultra-high strength steel above the martensitic phase transformation start temperature point under the aerosol cooling device is 58℃ / s, and the cooling rate below the martensitic phase transformation start temperature point is 103℃ / s. The microstructure after aerosol quenching (such as quenched martensitic microstructure) is quenched martensitic microstructure. Figure 4 As shown in the figure, the original austenite grain is about 10μm, the gas mist quenching cooling rate is higher than 58℃ / s, which is greater than the critical cooling rate of 50℃ / s, and finally the quenched martensite structure is obtained without carbide precipitation.

[0058] Figure 3The cooling curves of the three embodiments show that the cooling rates of hot-rolled ultra-high strength steels of different thicknesses are different above and below the martensitic transformation start temperature, and the cooling rate above the martensitic transformation start temperature is lower than the cooling rate below the martensitic transformation start temperature. During the gas mist quenching process, the cooling rates above and below the martensitic transformation start temperature of the 2mm hot-rolled ultra-high strength steel are 95℃ / s and 185℃ / s, respectively; those of the 4mm hot-rolled ultra-high strength steel are 78℃ / s and 147℃ / s, respectively; and those of the 6mm hot-rolled ultra-high strength steel are 58℃ / s and 103℃ / s, respectively.

[0059] Table 1 below is a cooling rate statistical table of three embodiments. From the results, it can be seen that by adopting the method of the present invention, after quenching 2-6 mm hot-rolled ultra-high strength steel to room temperature, complete quenched martensite is obtained, the cooling rate is above the critical cooling rate, and the cooling rate above the martensitic phase transformation start temperature point is not high, and the thermal stress is small; the cooling rate below the martensitic phase transformation start temperature point is relatively high, ensuring that the tempering quenching martensite will not occur while the self-tempering phenomenon.

[0060] Table 1

[0061]

[0062] 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 cooling device for intensive hot rolled coil continuous heat treatment, characterized in that: It comprises a plurality of aerosol spraying beams, and the aerosol spraying beams are distributed on the upper and lower surface sides of the hot-rolled steel coil; Each of the aerosol spraying beams is provided with a plurality of aerosol spraying pipes; Each row of the aerosol spray pipes is provided with a plurality of aerosol nozzles on one side facing the hot-rolled steel coil, and a compressed air pipe and a water pipe on the other side. The distance between the aerosol nozzle and the hot-rolled steel plate is 50 to 300 mm. The distance between two adjacent aerosol nozzles on the same row of aerosol spray pipes is 30 to 150 mm. The distance between two adjacent rows of aerosol spray pipes is 30 to 200 mm. The angle between the jet of the aerosol nozzle and the aerosol spray pipe is 7 to 75 degrees. The distance between two adjacent aerosol spraying beams is 40 to 400 mm. By changing the angle between the aerosol nozzle and the aerosol spraying pipe and the spacing arrangement between the aerosol spraying beams, the hot-rolled steel coils with different thickness specifications can be quenched at different cooling rates.

2. The gas mist cooling device for intensive hot rolled coil continuous heat treatment according to claim 1, characterized in that: The aerosol nozzle is an external mixing nozzle.

3. A mist cooling method for intensive hot rolled coil continuous heat treatment, characterized in that: An aerosol cooling device for intensive hot-rolled coil continuous heat treatment as described in any one of claims 1 to 2 is arranged on the upper and lower surface sides of the hot-rolled steel coil, and the hot-rolled steel coils of different thickness specifications are quenched at different cooling rates by changing the angle between the aerosol nozzle and the aerosol spray pipe and the spacing between the aerosol spray beams.

4. The mist cooling method for intensive hot rolled coil continuous heat treatment according to claim 3, characterized in that: The thickness of the hot-rolled steel coil is 2 to 6 mm; The hot rolled steel coil is quenched at different cooling rates: the cooling rate is 30-100°C / s above the martensitic transformation start temperature, and the cooling rate is 50-200°C / s below the martensitic transformation start temperature.

5. The mist cooling method for intensive hot rolled coil continuous heat treatment according to claim 3, characterized in that: The air pressure of the aerosol nozzle is 3-6 bar, and the water pressure is 2-5 bar.

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