CN113677811A

CN113677811A - Quenching device and method for manufacturing metal plate

Info

Publication number: CN113677811A
Application number: CN202080026372.5A
Authority: CN
Inventors: 桥向智弘; 吉本宗司
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2019-03-29
Filing date: 2020-03-17
Publication date: 2021-11-19
Also published as: WO2020203261A1; JP7314989B2; EP3943619A1; EP3943619B1; KR20210130208A; EP3943619A4; KR20240096738A; JPWO2020203261A1

Abstract

Provided are a quenching apparatus for a metal plate and a method for manufacturing a metal plate using the quenching apparatus for a metal plate, which can sufficiently ensure the cooling speed of the metal plate when the metal plate passes through a water jet device, and can prevent the occurrence of unevenness in the cooling speed depending on the position of the metal plate. The quenching apparatus according to the present invention is a quenching apparatus for cooling a high-temperature metal plate by immersing the metal plate in a liquid, the quenching apparatus including: an immersion tank containing a liquid to which the metal plate is immersed; a liquid ejecting apparatus provided so that at least a part thereof is positioned in the liquid contained in the immersion tank, the liquid ejecting apparatus including a plurality of nozzles that eject a cooling liquid from both surfaces of the metal plate toward the metal plate; and a pair of restraining rollers that restrain the metal plate respectively in front and rear of the liquid ejecting apparatus in a plate traveling direction.

Description

Quenching device and method for manufacturing metal plate

Technical Field

The present invention relates to a quenching apparatus for cooling a high-temperature metal plate by immersing the metal plate in a liquid, and a method for manufacturing the metal plate using the quenching apparatus.

Background

When manufacturing a metal plate such as a steel plate, the metal plate is cooled after heating in a continuous annealing facility to cause phase transformation or the like, thereby imparting material properties. In recent years, in the automobile industry, high-tensile steel sheets are being applied to achieve both weight reduction and collision safety of vehicle bodies, and rapid cooling (rapid cooling) techniques that are advantageous for the production of high-tensile steel sheets are becoming increasingly important to meet such a demand trend. As a water quenching method having the highest cooling rate, a method of immersing a heated high-temperature steel sheet in water and spraying cooling water to the steel sheet through a quenching nozzle provided in the water to rapidly cool the steel sheet is generally used. However, during this rapid cooling, the steel sheet suffers from out-of-plane deformation such as warpage or wave-like deformation, which causes a problem of shape defects.

In order to solve such a problem, patent document 1 proposes a method of suppressing out-of-plane deformation by arranging a pair of constraining rolls in a quenching apparatus and constraining metal sheets before and after a martensite transformation temperature range from both sides by the constraining rolls.

Patent document 2 discloses a technique for solving the problem of a decrease in the cooling rate of a metal sheet due to a pair of constraining rolls in a quenching apparatus as in patent document 1 by using a nozzle inclined from the horizontal plane.

Patent document 3 proposes a quenching apparatus that uses a roll provided with a groove through which cooling water can pass, thereby eliminating stagnation of cooling water near the roll and solving the problem of a decrease in cooling rate near the roll.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 6094722

Patent document 2: japanese laid-open patent publication No. 2017-119912

Patent document 3: japanese laid-open patent publication No. 2018-135552

Disclosure of Invention

Technical problem to be solved by the invention

However, if the quenching apparatus described in patent document 1 is used, although deformation of the metal sheet during quenching can be prevented, when the metal sheet passes through the restraining rolls provided inside the water jet apparatus, the cooling rate of the metal sheet is temporarily decreased, which causes a problem that the properties of the metal sheet are deteriorated. Specifically, since the cooling rate of the metal plate is low, a metal plate having desired material characteristics of the metal plate, for example, a desired tensile strength may not be obtained.

Further, in the method described in patent document 2, since the nozzles are arranged obliquely, it is necessary to set a large arrangement range of each nozzle in the board direction, and the number of nozzles arranged per unit length in the board direction is reduced, which causes a problem of a decrease in cooling speed. In this case, as in the above case, desired material characteristics of the metal plate may not be obtained.

In patent document 3, the problem of the coolant staying near the constraining rollers, which is caused by the provision of the constraining rollers as described in patent document 1, can be solved by providing the constraining rollers with grooves. However, in the method disclosed in patent document 3, the cooling water flows preferentially to the groove portions, and the flow of the cooling water is blocked in portions other than the groove portions, so that variation in the cooling rate of the metal plate occurs at the same period as the groove intervals in the plate width direction. Thus, variations in the material of the metal plate, such as tensile strength, occur with the same period as the groove interval. Various problems arise when the metal plate is subjected to processing such as punching or bending due to variations in material. For example, there are problems that dimensional accuracy is lowered due to uneven deformation of the metal plate during machining, or a striped pattern is generated on the surface of the metal plate depending on the machining method.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a quenching apparatus for a metal sheet and a method for manufacturing a metal sheet using the quenching apparatus for a metal sheet, which can sufficiently ensure a cooling rate of a metal sheet when the metal sheet passes through a water jet apparatus, and can prevent variation in the cooling rate depending on the position of the metal sheet.

Technical solution for solving technical problem

The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and finally have obtained the following findings. In the production of steel sheets, in the rapid cooling of high-temperature steel sheets by immersion in water and spraying of cooling water, the microstructure control for causing martensitic transformation of the steel sheets may be used. At this time, if martensite transformation occurs, the structure rapidly expands in volume, and the steel sheet has a complicated and uneven shape. In a high-tensile steel sheet having a martensite structure (high-strength steel sheet), during quenching, a maximum stress acts on the steel sheet from an Ms point where transformation expansion occurs during thermal contraction to a vicinity of an Mf point, and deformation occurs. Here, the Ms point refers to the start temperature of the martensitic transformation, and the Mf point refers to the finish temperature of the martensitic transformation.

It is also understood that, if variation in cooling rate occurs in the width direction or the thickness direction, the stress generated in the portion where the martensitic transformation occurs is released in the portion where the transformation has not been completed, and a very large out-of-plane deformation occurs. The reason for the uneven cooling rate is that the position of the metal plate in the out-of-plane direction is displaced during cooling. Specifically, the metal plate is pressed in an out-of-plane direction (a direction perpendicular to the surface of the metal plate) by the sprayed cooling water, and the position of the passing line of the metal plate is shifted. Although it is desirable that the metal plate passes through the center portion in the out-of-plane direction at an equal distance from the front-side nozzle and the front-side nozzle, the passing line of the metal plate may be shifted from the center portion in the out-of-plane direction to the out-of-plane direction by the cooling water. In particular, in the case where the restraining roller is not provided inside the water jet device for the purpose of preventing the cooling rate in the vicinity of the roller from decreasing as described above, the tension of the metal plate inside the water jet device is insufficient, and the position of the passing line of the metal plate is likely to be displaced.

The distance from the nozzle to the metal plate becomes uneven depending on the front and back sides of the metal plate or the position in the plate width direction due to the positional deviation of the passing line of the metal plate, and unevenness in the cooling speed occurs. The inventors of the present invention have found that the cooling rate can be made uniform by holding the pass line of the metal plate at the center portion in the out-of-plane direction, and that it is effective for suppressing the deformation of the metal plate.

The technical scheme of the invention is as follows:

[1] a quenching apparatus for cooling a high-temperature metal plate by immersing the metal plate in a liquid, comprising: an immersion tank containing a liquid to which the metal plate is immersed; a liquid ejecting apparatus provided so that at least a part thereof is positioned in the liquid contained in the immersion tank, the liquid ejecting apparatus including a plurality of nozzles that eject a cooling liquid from both surfaces of the metal plate toward the metal plate; and a pair of restraining rollers that restrain the metal plate respectively in front and rear of the liquid ejecting apparatus in a plate traveling direction.

[2] According to the quenching apparatus described in [1], the pair of constraining rollers are disposed so that the positions of the central axes of the rollers in the traveling direction are different. A pair of

[3] The quenching apparatus according to [1] or [2], wherein the constraining rollers are provided at positions 0m to 1.2m from a nozzle cooling start point and a nozzle cooling end point of the liquid ejecting apparatus, respectively.

[4] A method for manufacturing a metal sheet, which is performed by quenching using a quenching apparatus after annealing the metal sheet by a continuous annealing furnace, the quenching apparatus comprising: an immersion tank containing a liquid to which the metal plate is immersed; a liquid ejecting apparatus provided so that at least a part thereof is positioned in the liquid contained in the immersion tank, the liquid ejecting apparatus including a plurality of nozzles that eject a cooling liquid from both surfaces of the metal plate toward the metal plate; a pair of constraining rollers disposed respectively in front of and behind a traveling direction of the liquid ejecting apparatus; the metal plate is restrained by the pair of restraining rollers in such a manner that a pass line of the metal plate is held at a center portion in an out-of-plane direction while the metal plate passes through the liquid ejecting apparatus. A pair of

[5] According to the method of manufacturing a metal plate recited in item [4], the pair of restraining rollers are disposed so that positions of central axes of the rollers in the plate traveling direction are different. A pair of

[6] The method of manufacturing a metal plate according to [4] or [5], wherein the constraining rollers are provided at positions 0m to 1.2m from a nozzle cooling start point and a nozzle cooling end point of the liquid ejecting apparatus, respectively.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention can prevent the cooling rate of the metal plate from being lowered when the metal plate passes through the water jet device, and can prevent the cooling rate of the metal plate from being uneven depending on the position, thereby manufacturing the metal plate uniformly having desired material characteristics.

Drawings

FIG. 1 is a schematic view showing an example of a quenching apparatus according to the present invention.

Fig. 2 is an enlarged view showing the vicinity of the water jet device of the quenching apparatus of fig. 1.

FIG. 3 is a schematic view showing another example of the quenching apparatus of the present invention.

Detailed Description

An example of the quenching apparatus of the present invention will be described with reference to fig. 1 to 2. Fig. 1 is a schematic diagram showing a quenching apparatus 10. Fig. 2 is an enlarged view showing the vicinity of the water jet device 14 of the quenching apparatus 10 of fig. 1. The quenching apparatus is suitable for a cooling device provided on the exit side of a soaking zone of a continuous annealing furnace. Hereinafter, the description will be made using the steel sheet 11 as a specific example of the metal sheet, using the water 12 as an example of the liquid (coolant), using the water tank 13 as an example of the immersion tank, and using the water jet device 14 as an example of the liquid jet device, but the present invention is not limited to these examples.

In the quenching apparatus 10 of fig. 1, water 12 is contained in a water tank 13 in such a manner that at least a part of the water spray device 14 is located in the water 12. The high-temperature steel sheet 11 sent out from the soaking zone of the continuous annealing furnace that performs a series of annealing treatments of heating, soaking, cooling, and reheating is transported from above the water tank 13 to the water 12. Then, cooling water is sprayed from the nozzles 16 of the water spray device 14 to both surfaces of the steel sheet 11, thereby quenching the steel sheet 11. The steel sheet 11 is rapidly cooled to, for example, the temperature of the cooling water by immersion in the water 12 and spraying of the cooling water, and then is sent out from the outlet 19 of the water tank 13 and conveyed to the next step.

As shown in fig. 1, the quenching apparatus 10 includes: a water tank (immersion tank) 13 that contains water 12 to be used for immersing the steel sheet (steel strip) 11; and a water jet device 14 for jetting cooling water to the steel sheet 11. The quenching apparatus 10 is disposed so as to be positioned in water 12 stored in a water tank 13, and includes a sink roll 15 that changes the conveying direction (traveling direction) of the steel sheet 11.

The water jet device 14 is provided so that at least a part thereof is positioned in the water 12 stored in the water tank 13, and is provided with a predetermined gap in fig. 1 between both sides of a steel plate running line through which the steel plate 11 passes. The water jet device 14 has a plurality of nozzles 16 extending in the plate width direction of the steel plate 11 and jetting cooling water to the steel plate 11 from both sides of the steel plate 11. Eight nozzles 16 are disposed on both sides of a pass line through which the steel sheet 11 passes, with a predetermined gap therebetween in the conveyance direction of the steel sheet 11, in fig. 1. In fig. 1, the nozzles 16 are all provided in the water 12 contained in the water tank 13.

The steel sheet 11 is rapidly cooled and thermally contracted by cooling water sprayed from the nozzles 16 of the water spray device 14 in the water 12 contained in the water tank 13, that is, at a position below the water surface of the water tank 13. In particular, when the steel sheet 11 is made of a material that causes martensite transformation, rapid thermal contraction and transformation expansion occur simultaneously in the steel sheet 11 when the temperature of the steel sheet 11 reaches the Mf point, which is the temperature at which the martensite transformation ends, from the Ms point, which is the temperature at which the martensite transformation starts, and the stress acting on the steel sheet 11 becomes maximum, and the steel sheet 11 is deformed. At this time, if the pass line of the steel sheet 11 deviates from the center in the out-of-plane direction, the distance from the nozzle to the steel sheet becomes uneven in the width direction and the front and back sides, and the cooling rate in the width direction or the thickness direction becomes uneven, and very significant out-of-plane deformation occurs.

In the quenching apparatus 10 of the present invention, a pair of restraining rollers 20 are provided in front of and behind the water jet device 14 in the traveling direction. The constraining rolls 20 maintain the steel sheet 11 flat when passing through the water jet device 14, and maintain the pass line of the steel sheet 11. More specifically, two pairs of pinch rolls are arranged at predetermined plate-traveling direction positions before and after the water jet device 14, and the steel sheet 11 deformed by rolling or annealing is restrained from both sides by the pinch rolls, whereby the steel sheet 11 is held flat inside the water jet device 14, and the pass line of the steel sheet 11 is held at the center portion in the out-of-plane direction. By holding the steel plate 11 flat, it is possible to prevent a positional deviation in the out-of-plane direction of the steel plate 11, stabilize the pass line, and prevent cooling unevenness inside the water jet system 14 due to the positional deviation of the steel plate 11. Therefore, in the method for manufacturing a metal plate (steel plate), by using the quenching apparatus of the present invention, a steel plate 11 having desired material properties uniformly can be manufactured. The diameter of the constraining rolls 20 is not particularly limited, but is preferably 100mm to 200mm in diameter from the viewpoint of applying a sufficient constraining force to the steel sheet 11.

The "out-of-plane direction" indicates a direction orthogonal to the front and back of the steel sheet 11. The deviation in the out-of-plane direction means that the steel sheet 11 is positionally deviated in a direction (in the left-right direction in fig. 1) perpendicular to the front and back surfaces through a pass line in an ideal state. In the ideal pass line, as seen in a side view of the steel sheet 11 in the sheet width direction as shown in fig. 1, the center portion in the sheet thickness direction of the steel sheet 11 passes through the center portion in the out-of-plane direction of the straight line connecting the midpoints at equal distances from the opposing

nozzles

16 and 16. As long as the effects of the present invention can be obtained, a slight deviation of the pass line of the metal plate (steel plate) from the center portion in the out-of-plane direction is allowed. Specifically, as seen in a side view of fig. 1, the offset amount of the center portion in the thickness direction of the steel sheet from the center portion in the out-of-plane direction can be set to a value within 8% with respect to the distance between the nozzle and the surface of the steel sheet.

In the present invention, it is not necessary to provide a separate roller inside the water jet device 14, more specifically, between the pass line of the steel sheet 11 and the nozzle 16. Therefore, in the present invention, when the steel sheet 11 passes through the vicinity of the pass line and the roller of the steel sheet 11, the cooling rate of the steel sheet 11 does not temporarily decrease, and the problem of the property deterioration of the steel sheet 11 can be solved.

In the present invention, the nozzles 16 may be provided in the horizontal direction, more specifically, substantially parallel to the out-of-plane direction of the steel sheet 11. Therefore, the installation range in the board direction of each nozzle can be suppressed, and the number of nozzles installed per unit length in the board direction can be increased, thereby achieving high cooling performance.

Although the constraining rollers are provided so that the positions of the central axes of the two rollers in the plate traveling direction are the same in the example of fig. 1 and 2, the effect of the present invention can be obtained by another embodiment if the steel plate 11 can be held at the center in the out-of-plane direction of the water jet device 14. For example, as shown in fig. 3, the pair of constraining rollers may be provided so as to be offset in the traveling direction from the positions of the central axes of the rollers in the traveling direction, in other words, so as to be offset in the traveling direction.

As shown in fig. 3, the pair of constraining rollers is provided offset in the traveling direction, whereby the effect of holding the steel sheet 11 flat can be enhanced. More specifically, this effect can be enhanced by positioning the roller of the pair of restraining rollers 20 on the far side from the water jet device 14 in the direction of sandwiching the steel plate 11. When the contact state between the pair of restraining rollers 20 and the steel plate 11 (the contact state between the steel plate 11 and the pair of restraining rollers 20 and the state where the winding of the steel plate 11 in the restraining rollers 20 is 0 °) is 0mm, it is preferable to move the roller on the far side from the water jet device 14 by about 1mm to 5mm toward the steel plate 11 side.

As the distance between the front and rear constraining

rolls

20, 20 of the water jet device 14 increases, the effect of holding the steel sheet 11 flat becomes small, and the ability to hold the pass line of the steel sheet 11 at the center portion in the out-of-plane direction deteriorates. Therefore, the smaller the distance between the front and rear constraining rollers 20, the better. On the other hand, if the restraining rolls are provided at the interference positions with the nozzles 16 of the water jet device 14 as in the quenching apparatuses disclosed in patent documents 1 to 3, there is a problem that sufficient cooling performance cannot be secured or the flow of cooling water in the vicinity of the restraining rolls is hindered. Therefore, in the present invention, it is preferable to shorten the distance between the front and rear constraining rollers as much as possible within a range not interfering with the flow of the cooling water of the nozzle 16.

Specifically, the constraining rolls 20 are preferably disposed within 0 to 1.2m from the nozzle cooling start point and the nozzle cooling end point of the water jet device 14, respectively. Within this range, the flow of cooling water may not be disturbed, and the steel sheet can be held sufficiently flat. The nozzle cooling start point is a contact position between the upper end of the water stream ejected from the nozzle closest to the entrance side and the front surface (or the back surface) of the steel plate 11, and the nozzle cooling end point is a contact position between the lower end of the water stream ejected from the nozzle closest to the exit side and the front surface (or the back surface) of the steel plate 11. When the distance from the nozzle cooling start point or the nozzle cooling end point to the restraining roll 20 is measured, the upper end portion or the lower end portion of the roll closer to the water jet device 14 side may be used as a starting point.

The present invention is preferably applied to a steel sheet manufacturing apparatus having a tensile strength of 590MPa or more.

Examples

The following examples are given for further understanding of the present invention, but are not intended to identify the contents of the present invention.

A high-tensile cold-rolled steel sheet having a thickness of 1.0mm, a width of 1m and a tensile strength of 1470MPa was produced at a running speed of 100mpm by using the quenching apparatus 10 shown in FIG. 1. The quenching start temperature (the dipping start temperature in the water tank 13) of the steel sheet 11 was 750 ℃, and the steel sheet was cooled to a water temperature of 30 ℃. Restraining rolls 20 (example 1) each composed of two pairs of pinch rolls were provided at positions 20mm apart from the nozzle cooling start point and the nozzle cooling end point, respectively, before and after the water jet device 14 in the traveling direction. The diameter of the constraining roller 20 is 150 mm. On the other hand, in comparative example 1, as shown in patent document 1, the same experiment was performed in the case where a pair of restraining rollers are provided inside the water jet device. Comparative example 2 as shown in patent document 3, the same experiment was performed in the case where a pair of constraining rolls having grooves are provided inside the water jet device.

The steel sheets produced in examples and comparative examples were evaluated for tensile strength, change in tensile strength, and shape of the steel sheet. The evaluation results are shown in table 1. Tensile strength was determined by conducting a tensile test according to the provisions of JIS Z2241 using a tensile test piece JIS5 with the tensile direction being the rolling direction, and the tensile strength was evaluated as X when the tensile strength was less than 1470MPa and as O when the tensile strength was 1470MPa or more. The tensile strength test was performed on test pieces sampled at intervals of 40mm in the sheet width direction of the steel sheet, and the rate of change in tensile strength was determined as the ratio of the average value to the maximum value minus the minimum value of the change in sheet width, and evaluated as o if the rate of change was less than 4% and x if it was 4% or more. Further, the determination of the shape of the steel sheet was evaluated as "o" when the warpage of the steel sheet was 10mm or less, and as "x" when the warpage of the steel sheet exceeded 10 mm. The height of the highest position in the case of placing the steel sheet on a horizontal plane is taken as the warp of the steel sheet.

In example 1 in which there was no roll that hindered the flow of cooling water inside the water jet system 14, it was confirmed that the shape of the steel sheet was good, the tensile strength was high, and the strength change in the sheet width direction did not occur. On the other hand, in comparative example 1 in which the grooved constraining rolls were used inside the water jet device 14, the shape of the steel sheet was good, but the tensile strength did not reach the predetermined value because the cooling rate was decreased compared to those in example 1 and comparative example 2. In comparative example 2 in which a pair of constraining rolls having grooves were provided inside the water jet device 14, the steel sheet had a good shape and the tensile strength was equal to or higher than a predetermined value, but the difference in cooling rate between the grooves and the cooling rate outside the grooves was large, and therefore the change in tensile strength was also large.

[ Table 1]

Description of the reference numerals

10 quenching device;

11 steel plate;

12, water;

13 water tank;

14 a water jet device;

15 sinking the roller;

16 nozzles;

19 an outlet;

the rollers are constrained 20.

Claims

1. A quenching apparatus for cooling a high-temperature metal plate by immersing the metal plate in a liquid, comprising:

an immersion tank containing a liquid to which the metal plate is immersed;

a liquid ejecting apparatus provided so that at least a part thereof is positioned in the liquid contained in the immersion tank, the liquid ejecting apparatus including a plurality of nozzles that eject a cooling liquid from both surfaces of the metal plate toward the metal plate;

and a pair of restraining rollers that restrain the metal plate respectively in front and rear of the liquid ejecting apparatus in a plate traveling direction.

2. The quenching apparatus as set forth in claim 1,

the pair of constraining rollers are disposed so that the positions of the central axes of the rollers in the running direction are different.

3. The quenching apparatus according to claim 1 or 2,

the constraining rollers are disposed at positions 0m to 1.2m from a nozzle cooling start point and a nozzle cooling end point of the liquid ejecting apparatus, respectively.

4. A method for manufacturing a metal sheet, which comprises annealing the metal sheet in a continuous annealing furnace and then quenching the metal sheet in a quenching apparatus,

the quenching apparatus comprises: an immersion tank containing a liquid to which the metal plate is immersed; a liquid ejecting apparatus provided so that at least a part thereof is positioned in the liquid contained in the immersion tank, the liquid ejecting apparatus including a plurality of nozzles that eject a cooling liquid from both surfaces of the metal plate toward the metal plate; a pair of constraining rollers disposed respectively in front of and behind a traveling direction of the liquid ejecting apparatus;

the metal plate is restrained by the pair of restraining rollers in such a manner that a pass line of the metal plate is held at a center portion in an out-of-plane direction while the metal plate passes through the liquid ejecting apparatus.

5. The method of manufacturing a metal plate according to claim 4,

6. The manufacturing method of a metal plate according to claim 4 or 5,