A continuous quenching process for strip steel

Abstract

This invention provides a continuous quenching process for steel strip, belonging to the field of steel strip heat treatment technology. The invention involves passing the steel strip through at least three quenching zones in a quenching equipment according to the steel strip conveying direction on the production line. In each quenching zone, a cooling medium is sprayed onto the steel strip and tension is applied to sequentially achieve the three stages of austenite transformation, austenite-to-martensite transformation, and martensite transformation, thus completing the quenching treatment. The tension applied to the steel strip in each quenching zone increases sequentially according to the steel strip conveying direction on the production line. This invention helps to avoid deformation of the steel strip during the phase transformation process and improves the yield rate of the quenched steel strip.

Description

Technical Field

[0001] This invention relates to the field of strip heat treatment technology, and in particular to a continuous quenching process for strip steel. Background Technology

[0002] To improve the strength of high-strength hot-rolled strip steel, quenching treatment is commonly used.

[0003] The strip steel thickness ranges from 2 to 8 mm, compared to the 2 to 350 mm thickness of steel plates, making continuous production line quenching a viable option. However, due to the relatively thin strip steel, uneven cooling during quenching easily leads to inconsistent temperatures across different parts of the strip, resulting in asynchronous austenite-to-martensite transformation. This phase transformation process not only causes a dramatic increase in strength but also an increase in volume, resulting in different actual volumes in different parts of the strip. Furthermore, it generates significant phase transformation stress within the strip, leading to poor strip shape and a low strip heat treatment pass rate.

[0004] Therefore, a new technical solution is needed to solve the above-mentioned technical problems. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a continuous quenching process for strip steel to solve the problem of low yield caused by deformation during the quenching process of strip steel in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a continuous quenching process for strip steel, specifically configured as follows: the strip steel passes through at least three quenching zones in the strip steel conveying direction of the production line in the quenching equipment. In each quenching zone, the strip steel is sprayed with cooling medium and tension is applied to achieve the three stages of transformation: austenite, austenite-to-martensite transformation, and martensite transformation in sequence, thereby completing the quenching treatment. The tension applied to the strip steel in the quenching zones increases sequentially according to the strip steel conveying direction of the production line.

[0007] Optionally, the amount of cooling medium sprayed onto the strip in each quenching zone is determined based on the temperature difference between the strip inlet end and the strip outlet end in each quenching zone.

[0008] Optionally, the temperature at the inlet end of the austenitic stage strip is set to 880℃~950℃, the temperature at the outlet end of the austenitic stage strip is set to 390℃~460℃, the temperature at the outlet end of the austenitic-to-martensite transformation stage strip is set to 230℃~260℃, and the temperature at the outlet end of the martensite stage strip is set to 20℃~40℃.

[0009] Optionally, the tension of the austenitic stage on the strip is set to 65% to 85% of the austenitic yield strength, the tension of the austenitic to martensitic transformation stage on the strip is set to 75% to 90% of the martensite yield strength generated during the austenitic to martensitic transformation stage, and the tension of the martensitic stage on the strip is set to 85% to 95% of the martensitic yield strength of the martensitic stage.

[0010] Optionally, the conveying direction of the strip in each of the quenching zones is inclined downward at an angle of 5° to 45° along the horizontal direction.

[0011] Optionally, the quenching equipment includes a tension roller, and the wrap angle of the strip on the tension roller is set to 10° to 120°.

[0012] Optionally, the quenching equipment includes a slit nozzle, wherein the pressure of the cooling medium injected by the slit nozzle is set to 0.05-0.1 MPa, and the width of the slit nozzle for injecting the cooling medium is set to 0.2-0.5 mm.

[0013] Optionally, the slit nozzles are arranged opposite to each other on the upper and lower sides of the strip, and the slit nozzles are arranged linearly along the conveying direction of the strip.

[0014] Optionally, the quenching equipment includes a squeeze roller and a temperature detector, the squeeze roller being used to squeeze out the cooling medium on the strip, and the temperature detector being used to detect the current temperature of the strip.

[0015] Optionally, the austenitic stage, the austenitic-to-martenitic transformation stage, or the martensite stage includes at least one of the quenched regions.

[0016] As described above, the continuous quenching process for strip steel of the present invention has the following beneficial effects:

[0017] By passing the strip steel entering the quenching equipment through more than three quenching zones along the strip steel conveying direction of the production line, precise control of the strip steel in each quenching zone can be achieved. Cooling media is sprayed onto the strip steel in each quenching zone to rapidly cool the strip steel, causing the strip steel to undergo three stages of phase transformation: austenite, austenite-to-martensite, and martensite. That is, different parts of the strip steel can undergo different stages of phase transformation simultaneously. At the same time, tension is applied to the strip steel in each quenching zone, and the magnitude of the tension applied to the strip steel in the quenching zone increases sequentially according to the strip steel conveying direction of the production line. This prevents the strip steel from deforming during the phase transformation process and helps to improve the pass rate of the strip steel after quenching treatment. Attached Figure Description

[0018] Figure 1 The diagram shown is a structural schematic of a quenching device according to an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached figures

[0020] 1-Strip steel;

[0021] 2-Slit nozzle;

[0022] 3-Tension roller;

[0023] 4-Squeeze roller. Detailed Implementation

[0024] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show components relevant to the present invention and are not drawn according to the actual number, shape, and size of components in implementation. In actual implementation, the shape, quantity, and proportion of each component can be arbitrarily changed, and the component layout may be more complex. The structures, proportions, and sizes shown in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of the present invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effects and objectives of the present invention, should still fall within the scope of the technical content disclosed in the present invention. Furthermore, terms such as "upper," "lower," "left," "right," "middle," and "one" used in this specification are only for clarity of description and are not intended to limit the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0026] Figure 1 The diagram shown is a structural schematic of the quenching equipment. Please refer to [link / reference]. Figure 1This invention provides a continuous quenching process for steel strip. The steel strip 1 passes through at least three quenching zones in the quenching equipment according to the production line's steel strip conveying direction, allowing for precise control of the steel strip 1 in each quenching zone. The number of quenching zones can be three, four, five, etc., depending on actual needs. Cooling medium is sprayed onto the steel strip 1 in each quenching zone to rapidly cool it, causing the steel strip 1 to undergo three phase transformations: austenite, austenite-to-martensite, and martensite. That is, different parts of the steel strip 1 can undergo different stages of phase transformation simultaneously. Simultaneously, tension is applied to the steel strip 1 in each quenching zone, with the tension increasing sequentially according to the production line's steel strip conveying direction. This prevents deformation of the steel strip 1 during the phase transformation process, which helps improve the yield rate of the heat-treated steel strip 1.

[0027] It should be noted that the quenching equipment includes slit nozzles 2 that spray cooling medium onto the strip 1. Slit nozzles 2 are arranged opposite each other on the upper and lower sides of the strip 1 to cool both sides simultaneously, preventing uneven cooling and deformation. Furthermore, the slit nozzles 2 in each quenching zone are linearly arranged along the conveying direction of the strip 1.

[0028] In some embodiments, the amount of cooling medium sprayed by the slit nozzle 2 of each quenching zone onto the strip 1 is determined based on the temperature difference between the inlet end and the outlet end of the strip 1 in each quenching zone, thereby precisely controlling the cooling rate of the strip 1 so that the strip 1 undergoes a preset phase change in each quenching zone.

[0029] It should be noted that the austenitic stage, the austenitic-to-martensite transformation stage, or the martensite stage includes at least one quenched region. That is, the austenitic stage may include one quenched region, or it may include two or three quenched regions; the austenitic-to-martensite transformation stage may include one quenched region, or it may include two or three quenched regions; the martensite stage may include one quenched region, or it may include two or three quenched regions, depending on the actual needs.

[0030] In some embodiments, according to the phase transformation requirements of strip 1 at each stage, the temperature at the inlet end of strip 1 in the austenitic stage is set to 880°C to 950°C, the temperature at the outlet end of strip 1 in the austenitic stage is set to 390°C to 460°C, the temperature at the outlet end of strip 1 in the austenitic to martensite transformation stage is set to 230°C to 260°C, and the temperature at the outlet end of strip 1 in the martensite stage is set to 20°C to 40°C, thereby controlling the cooling rate of strip 1 in each quenching stage.

[0031] It should be noted that the temperature at the exit end of the austenitic stage strip 1 is the temperature at the inlet end of the austenitic-to-martensite transformation stage strip 1, that is, the temperature at the inlet end of the austenitic-to-martensite transformation stage strip 1 is set to 390℃~460℃. The temperature at the exit end of the austenitic-to-martensite transformation stage strip 1 is the temperature at the inlet end of the martensite stage strip 1, that is, the temperature at the inlet end of the martensite stage strip 1 is set to 230℃~260℃.

[0032] In some embodiments, the quenching equipment includes a temperature detector for detecting the current temperature of the strip 1, so as to monitor the temperature of the strip 1 in each quenching zone in real time, provide strip 1 temperature data support for the amount of cooling medium sprayed by the slit nozzle 2, and then implement closed-loop control of the temperature of the strip 1.

[0033] It should be noted that temperature detectors are installed at both the inlet and outlet ends of each quenching zone. These detectors are used to verify whether the cooling medium has cooled the strip 1 to the preset temperature, allowing for real-time adjustment of the cooling medium injection rate. The cooling medium injection rate can be controlled by adjusting the valve on the slit nozzle 2, which is located at the inlet end where the cooling medium enters the slit nozzle 2.

[0034] In some embodiments, the conveying direction of the strip 1 in each quenching zone is tilted downward at an angle of 5° to 45° along the horizontal direction, so that the cooling medium sprayed by the slit nozzle 2 onto the strip 1 can move along the conveying direction of the strip 1, avoiding the cooling medium from lingering at the same position on the strip 1, thereby reducing the probability of a vapor film forming on the surface of the strip 1.

[0035] In some embodiments, the width of the slit nozzle 2 for spraying the cooling medium is set to 0.2–0.5 mm to precisely control the spray volume of a single slit nozzle 2. The pressure of the cooling medium sprayed by the slit nozzle 2 is set to 0.05–0.1 MPa, resulting in a small spray volume per slit nozzle 2. This ensures that by the time the strip 1 moves from the spray area of ​​the previous slit nozzle 2 to the spray area of ​​the next slit nozzle 2, the cooling medium sprayed by the previous slit nozzle 2 has completely evaporated, thus preventing the formation of a vapor film on the surface of the strip 1 within the spray area. Simultaneously, this also helps prevent splashing of the cooling medium after impacting the strip 1, ensuring that the cooling medium slowly covers the surface of the strip 1 in the form of a water curtain, facilitating sufficient heat exchange with the strip 1.

[0036] In this embodiment, the austenite stage, the austenite-to-martensite transformation stage, and the martensite stage all include a quenching region.

[0037] When strip 1 is in the austenitic stage, the heat released by strip 1 during cooling in the austenitic stage is Q. AB It can be calculated using the following formula:

[0038] Q AB =m AB (C A t A -C B t B );

[0039] Where, m AB This indicates the mass of austenitic strip 1 passing through per hour, in kg / h; C A Represents 0-t A The average specific heat capacity of strip 1 between the two, in kJ / kg·℃; t A This indicates the temperature at which strip 1 enters the austenite stage, i.e., the temperature at the inlet end of the austenite stage of strip 1, in °C; C B Represents 0-t B The average specific heat capacity of strip 1 between the two, in kJ / kg·℃; t B This indicates the temperature at which strip 1 begins to transform from austenite to martensite, i.e., the temperature at the exit end of the austenite stage of strip 1, in °C.

[0040] The heat Q' absorbed by the cooling medium injected by the slit nozzle 2 during the austenite stage AB It can be calculated using the following formula:

[0041]

[0042] Among them, Q' AB1 This represents the amount of heat absorbed by the cooling medium as it rises from room temperature to 100°C during the austenitic stage; Q' AB2 This represents the heat absorbed by the cooling medium as it evaporates into vapor during the austenitic stage; m' AB The amount of cooling medium injected during the austenitic stage is expressed in kg; C1 represents the average specific heat capacity of the cooling medium between 0-100℃, expressed in kJ / kg·℃; t0 represents the temperature of the cooling medium at room temperature, typically 20℃; and r1 represents the heat of vaporization of the cooling medium, expressed in kJ / kg.

[0043] Due to Q' AB =Q AB The injection rate m' of the cooling medium in the austenitic stage can be determined using the above formula. AB .

[0044] When strip 1 is in the austenite-to-martensite transformation stage, the heat released by strip 1 during cooling in the austenite-to-martensite transformation stage is Q. BC It can be calculated using the following formula:

[0045] Q BC =m BC r BC ;

[0046] Where, m BC This represents the mass of strip 1 passing through during the austenite-to-martensite transformation stage per hour, in kg / h; r BC The value represents the phase transformation heat of strip 1 from austenite to martensite, expressed in kJ / kg.

[0047] The heat Q' absorbed by the cooling medium injected by the slit nozzle 2 during the austenite-to-martensite transformation stage. BC It can be calculated using the following formula:

[0048]

[0049] Among them, Q' BC1 This represents the amount of heat absorbed by the cooling medium as it rises from room temperature to 100°C during the austenite-to-martensite transformation stage; Q' BC2 This represents the heat absorbed by the cooling medium as it evaporates into vapor during the austenite-martensite transformation process; m' BC The amount of cooling medium injected during the austenite-to-martensite transformation stage is expressed in kg; C1 represents the average specific heat capacity of the cooling medium between 0-100℃, expressed in kJ / kg·℃; t0 represents the temperature of the cooling medium at room temperature, typically 20℃; and r1 represents the heat of vaporization of the cooling medium, expressed in kJ / kg.

[0050] Due to Q' BC =Q BC The injection rate m′ of the cooling medium during the austenite-to-martensite transformation stage can be determined using the above formula. BC .

[0051] When strip 1 is in the martensitic stage, the heat released by strip 1 during cooling in the martensitic stage is Q. CD It can be calculated using the following formula:

[0052] Q CD =m CD (C C t C -C D t D );

[0053] Where, m CD This indicates the mass of strip 1 passing through the martensitic stage per hour, in kg / h; C C Represents 0-t C The average specific heat capacity of strip 1 between the two, in kJ / kg·℃; t C This indicates the temperature at which strip 1 enters the martensitic stage, i.e., the temperature at the inlet of the martensitic stage of strip 1, in °C; C D Represents 0-t DThe average specific heat capacity of strip 1 between the two, in kJ / kg·℃; t D This indicates the temperature at which strip 1 leaves the martensitic stage, i.e., the temperature at the exit end of the martensitic stage of strip 1, in °C.

[0054] The heat Q' absorbed by the cooling medium injected by the slit nozzle 2 during the martensitic stage CD It can be calculated using the following formula:

[0055]

[0056] Among them, Q' CD1 This represents the amount of heat absorbed by the cooling medium as it rises from room temperature to 100°C during the martensitic stage; Q' CD2 This represents the heat absorbed by the cooling medium as it evaporates into vapor during the martensitic stage; m' CD The amount of cooling medium injected during the martensitic stage is expressed in kg; C1 represents the average specific heat capacity of the cooling medium between 0-100℃, expressed in kJ / kg·℃; t0 represents the temperature of the cooling medium at room temperature, typically 20℃; and r1 represents the heat of vaporization of the cooling medium, expressed in kJ / kg.

[0057] Due to Q' CD =Q CD The injection rate m' of the cooling medium in the martensitic stage can be determined using the above formula. CD .

[0058] Among them, the mass (m) of strip steel 1 in each quenching stage AB m BC m CD The following formula can be used to calculate it:

[0059] (m AB m BC m CD =60vhb;

[0060] Where v represents the speed at which strip 1 moves, in m / min; h represents the thickness of strip 1, in m; and b represents the width of strip 1, in m.

[0061] It should be noted that the lengths of each quenching zone can be the same or different, depending on the actual needs.

[0062] For example, the cooling medium can be set as pure water, deionized water or tap water with scale inhibitor, which helps to prevent the cooling medium from clogging the slit nozzle 2.

[0063] In some embodiments, to prevent strip 1 from deforming during phase transformation, the tension on strip 1 during the austenite stage is set to 65% to 85% of the austenite yield strength, the tension on strip 1 during the austenite-to-martensite transformation stage is set to 75% to 90% of the yield strength of the martensite generated during the austenite-to-martensite transformation stage, and the tension on strip 1 during the martensite stage is set to 85% to 95% of the yield strength of the martensite in the martensite stage.

[0064] In some embodiments, the quenching equipment includes a tension roller 3, on which the strip 1 is wound and tension is provided. The wrap angle of the strip 1 on the tension roller 3 is set to 10° to 120°.

[0065] For example, the tension of each quenching zone on strip 1 can be calculated using the following formula:

[0066] F 出 =F 入 ·e μα

[0067] Where μ represents the coefficient of friction between strip 1 and tension roll 3; α represents the wrap angle of strip 1 on tension roll 3; F 入 F1 represents the tension of strip 1 at the inlet of tension roller 3; F2 represents the tension of strip 1 at the outlet of tension roller 3.

[0068] The wrap angle of the strip 1 in each quenching zone on the tension roller 3 can be determined according to the above formula.

[0069] In some embodiments, the quenching equipment includes a squeeze roller 4, which works in conjunction with a tension roller 3 to squeeze out the cooling medium on the strip 1, effectively preventing the cooling medium from the previous quenching zone from entering the next quenching zone and thus affecting the cooling of the strip 1 by the cooling medium in the next quenching zone.

[0070] In summary, the continuous quenching process for strip steel provided by this invention involves passing the strip steel entering the quenching equipment through more than three quenching zones along the strip steel conveying direction of the production line, thereby enabling precise control of the strip steel in each quenching zone. Cooling media is sprayed onto the strip steel in each quenching zone to rapidly cool it, causing the strip steel to undergo three phase transformations: austenite, austenite-to-martensite, and martensite. This means that different phase transformations can occur simultaneously in different parts of the strip steel. Simultaneously, tension is applied to the strip steel in each quenching zone, with the tension increasing sequentially along the strip steel conveying direction of the production line. This prevents deformation of the strip steel during the phase transformation process and helps improve the yield rate of the quenched strip steel.

[0071] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A continuous quenching process for strip steel, characterized in that: In the quenching equipment, the strip steel passes through at least three quenching zones in the strip steel conveying direction of the production line. In each quenching zone, the strip steel is sprayed with cooling medium and tension is applied to achieve the three stages of transformation in sequence: austenite, austenite to martensite transformation and martensite transformation, thus completing the quenching process. In this process, the tension applied to the strip in the quenching area increases sequentially according to the strip conveying direction of the production line; and the strip conveying direction in each quenching area is inclined downward at an angle of 5° to 45° along the horizontal direction.

2. The continuous strip quenching process according to claim 1, characterized in that: The amount of cooling medium sprayed onto the strip in each quenching zone is determined based on the temperature difference between the strip inlet and outlet ends of each quenching zone.

3. The continuous strip quenching process according to claim 1 or 2, characterized in that: The temperature at the inlet end of the austenitic stage strip is set to 880℃~950℃, the temperature at the outlet end of the austenitic stage strip is set to 390℃~460℃, the temperature at the outlet end of the austenitic-to-martensite transformation stage strip is set to 230℃~260℃, and the temperature at the outlet end of the martensite stage strip is set to 20℃~40℃.

4. The continuous strip quenching process according to claim 3, characterized in that: The tension on the strip during the austenitic stage is set to 65% to 85% of the austenitic yield strength; the tension on the strip during the austenitic to martensitic transformation stage is set to 75% to 90% of the martensitic yield strength generated during the austenitic to martensitic transformation stage; and the tension on the strip during the martensitic stage is set to 85% to 95% of the martensitic yield strength of the martensitic stage.

5. The continuous strip quenching process according to claim 1, characterized in that: The quenching equipment includes a tension roller, and the wrap angle of the strip on the tension roller is set to 10°~120°.

6. The continuous strip quenching process according to claim 1, characterized in that: The quenching equipment includes a slit nozzle, wherein the pressure of the cooling medium injected by the slit nozzle is set to 0.05~0.1 MPa, and the width of the slit nozzle for injecting the cooling medium is set to 0.2~0.5 mm.

7. The continuous strip quenching process according to claim 6, characterized in that: The slit nozzles are arranged opposite each other on the upper and lower sides of the strip, and the slit nozzles are arranged linearly along the conveying direction of the strip.

8. The continuous strip quenching process according to claim 1, characterized in that: The quenching equipment includes a squeeze roller and a temperature detector. The squeeze roller is used to squeeze out the cooling medium on the strip, and the temperature detector is used to detect the current temperature of the strip.

9. The continuous quenching process for strip steel according to claim 1, characterized in that: The austenitic stage, the austenitic-to-martenitic transformation stage, or the martenitic stage includes at least one of the quenched regions.

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