Quenching device and method for producing metal strip

Abstract

To provide a quenching device capable of reducing the number of waves in the width direction of a metal strip due to wavy deformation while suppressing shape defects occurring in the metal strip during rapid cooling and quenching.SOLUTION: A quenching device that cools a metal strip by immersing the metal strip in liquid includes a water tank that contains the liquid in which the metal strip is immersed, a liquid ejection device that is at least partially provided in the liquid in the water tank and has a plurality of nozzles that eject the liquid onto a front surface and a back surface of the metal strip, a pair of restraining rolls that are provided between an inlet-side end portion and an outlet-side end portion of the metal strip in the liquid ejection device and restrain the metal strip, and an adjustment device that adjusts a position of each of the pair of restraining rolls.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a metal strip quenching device that can suppress an increase in the wave number in the width direction of a metal strip due to shape defects and wavy deformation that occur in the metal strip during rapid quenching in continuous annealing equipment that anneals the metal strip while continuously passing it through, and a metal strip manufacturing method that uses the quenching device. [Background technology]

[0002] In the manufacture of steel and other metal sheets, the metal sheet is heated and then cooled in a continuous annealing facility, where a phase transformation occurs to refine the material's properties. In recent years, the automotive industry has seen an increase in demand for thin, high-tensile steel sheets (hereafter, high-tensile steel sheets will be referred to as "hi-ten") in order to achieve both lightweight car bodies and crashworthiness. While one method of increasing the strength of steel sheets is to adjust the steel sheet composition, such as by adding Si to enhance solid solution strength, another method is to transform the internal structure of the steel sheet into a high-strength structure by rapid cooling. In the method of transforming into a high-strength structure by rapid cooling, the technology to rapidly cool the steel sheet is important.

[0003] Water quenching is known as one of the techniques that can cool steel plates with the fastest speed. In this method, heated steel plates are immersed in water and simultaneously quenched by spraying cooling water onto the steel plate from a quench nozzle installed in the water. However, quenching steel plates can cause defects in shape due to out-of-plane deformation such as warping and wavy deformation.

[0004] As a technique for preventing shape defects during quenching of steel sheets, Patent Document 1 discloses a technique for suppressing wavy deformation of metal sheets that occurs during quenching in a continuous annealing furnace. According to Patent Document 1, wavy deformation of metal sheets that occurs during quenching can be suppressed by providing bridle rolls before and after the quenching process to change the tension of the steel sheet.

[0005] Patent Document 2 discloses a technique for suppressing out-of-plane deformation by restraining a metal sheet from both sides in an area where compressive stress in the sheet width direction occurs due to cooling or in an area nearby the area. Furthermore, Patent Document 3 discloses a technique for suppressing out-of-plane deformation of a metal sheet by arranging a pair of restraint rolls in a rapid cooling and quenching apparatus and restraining the metal sheet from both sides with the restraint rolls. Patent Document 3 states that by arranging the pair of restraint rolls between the position where martensitic transformation of the metal sheet starts and the position where martensitic transformation ends, it is possible to suppress out-of-plane deformation of the metal sheet that occurs during rapid cooling and quenching. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-184773 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-277833 [Patent Document 3] International Publication No. 2016 / 084283 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology disclosed in Patent Document 1 applies a large tension to a high-temperature metal sheet, which may cause the metal sheet to break. Furthermore, the bridle roll provided before the quenching section comes into contact with the high-temperature metal sheet, causing a large thermal crown on the bridle roll. This thermal crown causes uneven contact between the bridle roll and the metal sheet in the width direction, which can lead to buckling and surface defects in the metal sheet, making it difficult to improve the steel sheet shape.

[0008] As a result of examining the technology disclosed in Patent Document 2, it was found that there is a problem in that the shape correction effect of the metal plate is small even when the metal plate is restrained from both sides in the region where compressive stress occurs or in the region nearby. While the technology disclosed in Patent Document 3 can prevent deformation of the metal plate during rapid cooling and quenching, there is a problem in that the wave number in the width direction increases due to the wave-like deformation. When the wave number of the wave-like deformation increases, twisting and springback are more likely to occur during press forming at automotive parts manufacturers, which can result in a problem in that the dimensional accuracy after press forming may deteriorate.

[0009] The present invention has been made in view of the above circumstances, and has an object to provide a quenching device and a method for manufacturing a metal strip, which are capable of reducing the number of waves in the width direction of the metal strip caused by wavy deformation while suppressing shape defects that occur in the metal strip during rapid quenching, in continuous annealing equipment that anneals the metal strip while continuously passing it through. [Means for solving the problem]

[0010] The means for solving the above problems are as follows. [1] A quenching device that cools a metal strip by immersing it in a liquid, comprising: a water tank that contains the liquid in which the metal strip is immersed; a liquid spraying device that is at least partially disposed in the liquid in the water tank and has a plurality of nozzles that spray liquid onto the front and back surfaces of the metal strip; a pair of restraint rolls that are disposed between the inlet end and outlet end of the metal strip in the liquid spraying device and that restrain the metal strip; and an adjustment device that adjusts the positions of each of the pair of restraint rolls. [2] The quenching device according to [1], wherein the adjustment device adjusts the roll gap between the pair of restraint rolls within a range of 1 mm or more and 30 mm or less. [3] A method for manufacturing a metal strip, which comprises cooling the metal strip with the quenching device described in [1] or [2], wherein the metal strip cooled with the quenching device contains a martensitic structure. [Effects of the Invention]

[0011] The quenching apparatus according to the present invention includes an adjustment device for adjusting the positions of the pair of constraining rolls, and therefore the roll gap between the pair of constraining rolls can be adjusted. By adjusting the roll gap between the constraining rolls with this adjustment device, it is possible to reduce the wave number in the width direction of the metal strip due to wavy deformation while suppressing shape defects that occur in the metal strip during quenching. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a quenching device according to this embodiment. [Figure 2] FIG. 2 is an enlarged schematic view of the region where the restraining rolls are provided. [Figure 3] FIG. 3 is a schematic diagram illustrating the definition of the amount of warpage of a metal strip. [Figure 4] FIG. 4 shows the surface profile of a rapidly quenched metal strip. [Figure 5] FIG. 5 is a graph showing the relationship between the roll gap of the restraining rolls and the average amount of warpage of the metal strip and the wave number in the width direction of the metal strip. DETAILED DESCRIPTION OF THE INVENTION

[0013] This technique uses microstructural control to induce martensitic transformation by immersing the metal strip in water and rapidly cooling it by injecting cooling water. Martensitic transformation causes rapid volume expansion of the structure, which can result in complex, uneven, irregular shapes in the metal strip. Furthermore, when high-tensile steel sheets with martensitic structures are rapidly quenched, the greatest stress acts on the steel sheet near the Ms point to Mf point, where transformation expansion occurs during thermal contraction, resulting in shape defects. The Ms point is the temperature at which martensitic transformation begins, and the Mf point is the temperature at which martensitic transformation ends.

[0014] The inventors have confirmed that when the metal strip is restrained from both sides by constraining rolls to suppress deformation of the metal strip during rapid cooling and quenching, the uneven out-of-plane deformation that occurs in the martensitic transformation region is transformed into a small wave shape in the width direction, thereby mitigating buckling and suppressing shape defects. In addition, the inventors have discovered that by adjusting the roll gap of the constraining rolls, the magnitude of the buckling that results in the small wave shape can be adjusted, and thereby the wave number (number of concaves and convexes) of the small wave shape in the strip width direction can be controlled.

[0015] Regarding this phenomenon, although large deformation due to martensitic transformation can be suppressed by narrowing the gap between the constraining rolls, there is a point at which two shape defects occur: deformation due to stress generated by suppressing deformation after passing through the constraining rolls. The inventors discovered that by optimizing the gap between the constraining rolls, it is possible to suppress in a balanced manner two shape defects: stress due to martensitic transformation and deformation (small wave shape) due to stress released after passing through the constraining rolls, and thus completed the present invention. Hereinafter, the present invention will be specifically described through embodiments of the present invention. The following embodiments show preferred examples of the present invention, and the present invention is not limited to these embodiments in any way.

[0016] Fig. 1 is a cross-sectional schematic view showing an example of a quenching device 50 according to this embodiment. Fig. 2 is an enlarged schematic view of an area where a restraint roll 20 is provided. The quenching device 50 according to this embodiment will be described with reference to Figs. 1 and 2.

[0017] The quenching device 50 is used in cooling equipment installed at the outlet of the soaking zone of a continuous annealing furnace to cool a high-temperature metal strip 40. Here, "high temperature" means a temperature where the surface temperature of the metal strip 40 exceeds the Ms point. The quenching device 50 includes a water tank 10 containing water 12, a pair of left and right liquid sprayers 14 that spray cooling water onto the metal strip 40, a sink roll 18 that changes the threading direction of the metal strip 40, a pair of left and right restraint rolls 20 that restrain the metal strip 40 to suppress deformation, and an adjustment device 22. Note that water is an example of the liquid, and an aqueous solution of a water-soluble polymer may also be used as the liquid. Reference numeral 30 denotes a pair of seal rolls installed at the outlet of the soaking zone of the continuous annealing furnace.

[0018] The water tank 10 contains water 12 for cooling the metal strip 40. The liquid jetting device 14 is partially submerged in the water tank 10 and is disposed on the front and back surfaces of the metal strip 40 with a predetermined gap therebetween. The liquid jetting device 14 has a plurality of nozzles 16 extending in the width direction of the metal strip 40, and achieves rapid cooling of the metal strip 40 by jetting cooling water onto the metal strip 40 through the plurality of nozzles 16. Note that the liquid jetting device 14 is disposed so that a portion of it is submerged in the water tank 10, but it may also be disposed so that the entirety of it is submerged. In other words, it is sufficient that at least a portion of the liquid jetting device 14 is disposed submerged in the water tank 10.

[0019] The constraint rolls 20 are provided underwater in the water tank 10, between the inlet end and the outlet end of the liquid jetting device. The constraint rolls 20 are a pair of left and right rolls arranged facing each other on the front and back surfaces of the metal strip 40. The constraint rolls 20 are preferably arranged with their central axes offset in the running direction of the metal strip 40. By arranging the constraint rolls 20 with their central axes offset in the running direction of the metal strip 40, the constraint force of the constraint rolls 20 on the metal strip 40 is increased, and the effect of correcting defective shapes can be improved.

[0020] The adjustment device 22 adjusts the position of the constraint roll 20 in the thickness direction of the metal strip 40. The adjustment device 22 has a shaft portion 24, a fixed portion 26, and a bearing portion 28. The bearing portion 28 supports the rotation shaft of the constraint roll 20 from both sides. The bearing portion 28 is joined to the shaft portion 24, and the shaft portion 24 is screwed into the fixed portion 26. The fixed portion 26 is fixed to the water tank 10, for example.

[0021] In this configuration, by rotating the shaft portion 24, the bearing portion 28 moves in the thickness direction of the metal strip 40. In this way, the adjustment device 22 adjusts the position of the constraint roll 20 in the thickness direction of the metal strip 40. By adjusting the positions of the pair of constraint rolls 20 in the thickness direction of the metal strip 40, the roll spacing of the constraint rolls 20 is adjusted.

[0022] By adjusting the roll gap of the constraint rolls 20, it becomes possible to control the warpage shape of the metal strip 40 and the wave number in the width direction of the metal strip 40. It is preferable that the roll gap of the constraint rolls 20 can be adjusted within a range of 1 mm or more and 30 mm or less.

[0023] It is preferable to provide a pair of constraining rolls 20 at positions where the temperature of the metal strip 40 is within a range from the Ms point at which martensitic transformation starts to the Mf point at which the transformation ends, and to constrain the metal strip 40 with the constraining rolls 20. This makes it possible to constrain the metal strip 40 at a position where a large stress is applied by the martensitic transformation, thereby enhancing the shape straightening effect due to the constraining.

[0024] As described above, the quenching apparatus 50 according to this embodiment can suppress shape defects due to martensitic transformation during quenching of the metal strip 40 and can reduce the wave number in the width direction of the metal strip 40. Therefore, the quenching apparatus 50 according to this embodiment is preferably used to manufacture high-tensile steel that contains a martensitic structure after quenching and quenching. There is no particular upper limit on the tensile strength of the high-tensile steel, but it is preferably used to manufacture high-tensile steel having a tensile strength of 580 MPa or more and 2000 MPa or less. The tensile strength is a value measured according to the tensile testing method for metallic materials specified in JIS Z 2241:2022. [Example]

[0025] Next, an example will be described in which the relationship between the roll gap of the restraint rolls 20, the average warpage of the metal strip 40, and the wave number in the width direction of the metal strip 40 was confirmed. Using the quenching apparatus 50 shown in Figure 1, a high-tensile steel sheet having a thickness of 1.0 mm and a width of 120 mm and a tensile strength of 1310 MPa was passed through at a passing speed of 1.5 m / s to perform rapid quenching. The surface temperature of the metal strip before the start of cooling was 740°C, and the surface temperature of the metal strip after cooling was 30°C.

[0026] In the examples, the roll gap of the restraint rolls 20 was changed to 2 mm, 6 mm, 10 mm, and 30 mm while the metal strip was being passed through, and the average amount of warpage and the wave number in the width direction of the metal strip after quenching were measured under each condition. FIG. 3 is a schematic diagram illustrating the definition of the amount of warpage of a metal strip. As shown in FIG. 3, in this example, the amount of warpage of the metal strip was defined as the height of the highest position in the width direction of the metal strip when the metal strip after quenching was placed on a horizontal surface. The amount of warpage was measured at multiple different positions in the longitudinal direction of the metal strip, and the amount of warpage of the metal strip after quenching was evaluated using the average value of these measurements, i.e., the average amount of warpage.

[0027] Figure 4 shows the surface profile of a metal strip that was quenched and quenched. Figure 4(a) is the surface profile of a metal strip that was quenched and quenched at a roll gap of 2 mm. Figure 4(b) is the surface profile of a metal strip that was quenched and quenched at a roll gap of 6 mm. Figure 4(c) is the surface profile of a metal strip that was quenched and quenched at a roll gap of 10 mm. The wave number in the width direction of the metal strip was confirmed by creating a surface profile of the metal strip as shown in Figure 4.

[0028] Fig. 5 is a graph showing the relationship between the roll gap of the restraint rolls 20, the average amount of warpage of the metal strip, and the wave number in the width direction of the metal strip 40. The circle plot in Fig. 5 indicates the average amount of warpage (mm), and the bar graph in Fig. 5 indicates the wave number.

[0029] As shown in Figure 5, even when the roll gap of the constraining rolls 20 was widened, the average amount of warpage did not increase up to a roll gap of 10 mm. However, when the roll gap of the constraining rolls 20 was widened from 10 mm to 30 mm, it was confirmed that the average amount of warpage of the metal strip after quenching increased significantly, and the shape defects of the metal strip worsened significantly.

[0030] Similarly, even when the roll gap of the constraining rolls 20 was widened, the wave number in the width direction of the metal strip did not change up to a roll gap of 6 mm. However, when the roll gap of the constraining rolls 20 was widened from 6 mm to 10 mm, the wave number in the width direction decreased by one, and a tendency for the wave number to decrease was confirmed.

[0031] From the results of the average warpage of the metal strip after quenching and the wave number in the width direction of the metal strip shown in Figure 5, it can be seen that by adjusting the roll gap of the constraining rolls 20 to 6 mm, it is possible to reduce the wave number in the width direction of the metal strip while suppressing warpage of the metal strip. Furthermore, the roll gap of the constraining rolls 20 that can reduce the wave number in the width direction of the metal strip while suppressing warpage of the metal strip was in the range of 1 mm to 30 mm. From these results, it can be seen that it is preferable to be able to adjust the roll gap of the constraining rolls 20 in the range of 1 mm to 30 mm.

[0032] The quenching apparatus 50 according to this embodiment has an adjustment device for adjusting the positions of the pair of constraining rolls, and therefore the roll gap between the pair of constraining rolls can be adjusted. This makes it possible to confirm the average amount of warpage and the wave number in the width direction of the metal strip after quenching under conditions where the roll gap between the constraining rolls 20 is changed, and to adjust the roll gap between the constraining rolls 20 so that the wave number in the width direction of the metal strip can be reduced while suppressing warpage of the metal strip. As a result, it can be seen that in a cooling facility provided on the outlet side of the soaking zone of a continuous annealing furnace, it is possible to suppress shape defects in the metal strip after quenching and to produce a metal strip after quenching with a small wave number in the width direction of the metal strip.

[0033] In the quenching apparatus 50 according to this embodiment, an example has been shown in which the adjustment device 22 adjusts the position of the constraining rolls 20 in the thickness direction of the metal strip 40, but this is not limiting. The adjustment device 22 may be able to adjust the position of the constraining rolls 20 not only in the thickness direction of the metal strip 40 but also in the conveyance direction of the metal strip 40. If the position of the metal strip 40 in the conveyance direction can be adjusted, the adjustment device 22 can freely adjust the position of the constraining rolls 20, and it can also adjust the distance (offset amount) in the sheet passing direction between the center axes of the pair of constraining rolls 20. [Explanation of symbols]

[0034] 10. Aquarium 12 water 14 Liquid ejection device 16 nozzles 18 Sink Roll 20 Confinement Roll 22 Adjustment device 24 shaft section 26 Fixed part 28 Bearing 30 sticker rolls 40 Metal Strip 50 Quenching equipment

Claims

1. A quenching device that cools a metal strip by immersing it in a liquid, a water tank containing a liquid in which the metal strip is immersed; a liquid jetting device at least partly disposed in the liquid in the water tank and having a plurality of nozzles for jetting liquid onto the front and back surfaces of the metal strip; a pair of restraint rolls provided between an inlet end and an outlet end of the metal strip in the liquid jetting device, the restraint rolls restraining the metal strip; an adjustment device for adjusting the respective positions of the pair of restraint rolls; A quenching device having:

2. 2. The quenching device according to claim 1, wherein the adjustment device adjusts the roll gap between the pair of constraint rolls within a range of 1 mm to 30 mm.

3. A method for manufacturing a metal strip, in which the metal strip is cooled by the quenching apparatus according to claim 1 or 2, The method for manufacturing a metal strip, wherein the metal strip cooled in the quenching device contains a martensite structure.

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