Method for manufacturing cold-rolled steel sheet and manufacturing apparatus

Abstract

The present application relates to a method for manufacturing a cold-rolled steel sheet using a transverse full-width heating device and a cold-rolling mill, the transverse full-width heating device heating a steel sheet over the entire width of the steel sheet, the cold-rolling mill being disposed on the downstream side in the rolling direction relative to the transverse full-width heating device and rolling the steel sheet, wherein the method includes a step of heating the steel sheet using the transverse full-width heating device in such a manner that the temperature at the widthwise end of the steel sheet on the entry side of the cold-rolling mill is higher than the temperature at the widthwise center of the steel sheet.

Description

Technical Field

[0001] This invention relates to a method and equipment for manufacturing cold-rolled steel sheets. Background Technology

[0002] In the past, cold rolling has utilized single-stand reversible mills such as Sendzimir mills or tandem mills with multiple stands. However, regardless of the type, the temperature of the steel sheet at the mill feed side in the first pass is often room temperature. However, in the cold rolling of high-Si-content silicon steel sheets (electromagnetic steel sheets), brittle fracture is prone to occur at low sheet temperatures. The fracture can occur from the ends in the width direction or from the center in the width direction, but regardless of the cause, increasing the sheet temperature during cold rolling is an effective countermeasure. Against this backdrop, methods have been proposed to suppress fracture of silicon steel sheets by heating them before cold rolling. For example, Patent Document 1 describes a method of heating the ends in the width direction of the steel sheet at a specified target temperature at the mill feed side. Patent Document 2 describes a method of uniformly heating and rolling the entire steel sheet.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-148310

[0006] Patent Document 2: Japanese Patent Application Publication No. 2011-79025 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] As mentioned above, techniques for suppressing brittle fracture during cold rolling of silicon steel sheets with high Si content have been proposed. However, in techniques that heat only the ends of the steel sheet in the width direction, brittle fracture may occur in the central part of the width direction due to the low temperature near the center. Furthermore, in techniques that heat the entire width direction of the steel sheet uniformly, it is possible to consume more energy than necessary to heat the entire sheet, which warrants re-evaluation from the perspective of the SDGs (Sustainable Development Goals).

[0009] The present invention was made in view of the above-mentioned problems, and its object is to provide a method and equipment for manufacturing cold-rolled steel sheets with low environmental impact and capable of stably rolling silicon steel sheets.

[0010] Methods for solving problems

[0011] Through dedicated research aimed at achieving the aforementioned objectives, the inventors of this invention discovered that the fracture suppression temperature (the temperature of a steel plate with a high fracture suppression effect) is higher at the ends of the width direction than at the center. Therefore, the inventors found that appropriately controlling the output of a transverse full-width heating device that heats the entire width of the steel plate is highly effective in terms of fracture suppression and environmental impact, and conceived the following invention.

[0012] The present invention relates to a method for manufacturing cold-rolled steel sheets using a transverse full-width heating device and a cold rolling mill. The transverse full-width heating device heats the steel sheet throughout its width direction. The cold rolling mill is positioned downstream of the transverse full-width heating device in the rolling direction to roll the steel sheet. The manufacturing method includes the step of heating the steel sheet using the transverse full-width heating device in such a way that the temperature at the end of the steel sheet in the width direction on the feed side of the cold rolling mill is higher than the temperature at the center of the width direction.

[0013] Preferably, the temperature of the central portion and the ends of the steel plate in the width direction on the feed side of the cold rolling mill varies according to the Si content of the steel plate.

[0014] Preferably, the temperatures of the central portion and the ends of the steel plate on the feed side of the cold rolling mill in the width direction are temperatures calculated by the following mathematical formulas (1) and (2) as the Si content α varies.

[0015] T C ≥0.1α 4.5 +15…(1)

[0016] T E ≥0.1α 4.8 +15…(2)

[0017] in,

[0018] T C T represents the temperature [°C] of the steel plate at the center of the width direction on the feed side of the rolling mill. C ≤200℃,

[0019] T E T represents the temperature of the steel plate at the width end of the steel plate fed into the rolling mill, in the direction of its width [°C]. E ≤200℃,

[0020] α represents the Si content [%], where 0 < α ≤ 4.5.

[0021] The cold-rolled steel sheet manufacturing equipment of the present invention comprises: a transverse full-width heating device that heats the steel sheet throughout its width direction; and a cold rolling mill disposed downstream of the transverse full-width heating device in the rolling direction to roll the steel sheet, wherein the transverse full-width heating device heats the steel sheet such that the temperature at the end of the steel sheet in the width direction on the feed side of the cold rolling mill is higher than the temperature at the center of the width direction.

[0022] Preferably, the transverse full-width heating device causes temperature variations in the central portion and the ends of the steel plate on the feed side of the cold rolling mill according to the Si content of the steel plate.

[0023] Preferably, the transverse full-width heating device heats the temperature of the central portion and the end portion of the steel plate on the feed side of the cold rolling mill to a temperature that varies with the Si content α, calculated by the following mathematical formulas (1) and (2).

[0024] T C ≥0.1α 4.5 +15…(1)

[0025] T E ≥0.1α 4.8 +15…(2)

[0026] in,

[0027] T C T represents the temperature [°C] of the steel plate at the center of the width direction on the feed side of the rolling mill. C ≤200℃,

[0028] T E T represents the temperature of the steel plate at the width end of the steel plate fed into the rolling mill, in the direction of its width [°C]. E ≤200℃,

[0029] α represents the Si content [%], where 0 < α ≤ 4.5.

[0030] Preferably, the transverse full-width heating device is located within 10m of the feed side of the cold rolling mill.

[0031] Invention Effects

[0032] The cold-rolled steel sheet manufacturing method and equipment disclosed in this invention have low environmental impact and can stably roll silicon steel sheets. Attached Figure Description

[0033] Figure 1 This is a schematic diagram showing the structure of a cold-rolled steel sheet manufacturing apparatus as an embodiment of the present invention.

[0034] Figure 2This is a graph showing the results of evaluating the temperature dependence of the bending crack resistance of silicon steel sheets.

[0035] Figure 3 This is a graph showing the estimated temperature of the steel plate required to suppress brittle fracture, corresponding to the Si content of the steel plate.

[0036] Figure 4 This is a graph showing the results of evaluating the temperature dependence of the edge crack resistance of silicon steel sheets.

[0037] Figure 5 This is a graph showing the estimated steel plate temperature required to suppress edge cracking, corresponding to the Si content of the steel plate. Detailed Implementation

[0038] Hereinafter, with reference to the accompanying drawings, a method and apparatus for manufacturing cold-rolled steel sheet according to one embodiment of the present invention will be described. It should be noted that the constituent elements in the embodiments shown below include constituent elements that can be substituted and are easily substituted by those skilled in the art, or substantially the same constituent elements.

[0039] 〔structure〕

[0040] First, refer to Figure 1 The structure of the cold-rolled steel sheet manufacturing equipment, which is one embodiment of the present invention, will be described.

[0041] Figure 1 This is a schematic diagram showing the structure of a cold-rolled steel sheet manufacturing apparatus as one embodiment of the present invention. Figure 1 As shown, the cold-rolled steel sheet manufacturing equipment (hereinafter referred to as "manufacturing equipment") according to one embodiment of the present invention is a continuous tandem rolling line with multiple stands, comprising an unwinding coil 1, a joining device 2, a looper 3, a full-width heating device 4, a thermometer (plate temperature measuring device) 5, a tandem cold rolling mill 6, a cutting machine (cutting device) 7, and a tension coil 8.

[0042] The unwinding reel 1 is a device for unwinding the steel sheet S. The manufacturing equipment may also have multiple unwinding reels 1. In this case, the multiple unwinding reels unwind different steel sheets S respectively.

[0043] The joining device 2 is a device that joins the tail end of the steel plate first released from the unloading reel 1 (in the preceding material) and the top end of the steel plate released later from the unloading reel 1 (in the following material) to form a joined steel plate. A laser welding machine is suitable as the joining device 2.

[0044] The looper 3 is a device that stores steel plates S in a manner that enables the cold rolling of the tandem cold rolling mill 6 to continue until the steel plates are joined together by the joining device 2 (until the joining is completed).

[0045] The full-width heating device 4 is a device that heats the steel plate S throughout its width and rolling direction (length). The full-width heating device 4 is a transverse induction heating device capable of creating a temperature gradient along the width of the steel plate S, and ensuring that the temperature at the edge (end in the width direction) of the steel plate S is higher than the temperature at the center in the width direction. It should be noted that the full-width heating device 4 preferably ensures that the temperatures at the center and edge of the steel plate S on the feed side of the tandem cold rolling mill 6 are respectively the temperatures T corresponding to the Si content of the steel plate S, calculated using the following mathematical formulas (1) and (2). C and temperature T E The steel plate S is heated in a certain way. This effectively suppresses brittle fracture and edge cracking of the steel plate S.

[0046] T C ≥0.1α 4.5 +15…(1)

[0047] T E ≥0.1α 4.8 +15…(2)

[0048] in,

[0049] T C T represents the temperature [°C] of the steel plate at the center of the width direction on the feed side of the rolling mill. C ≤200℃,

[0050] T E T represents the temperature of the steel plate at the width end of the steel plate fed into the rolling mill, in the direction of its width [°C]. E ≤200℃,

[0051] α represents the Si content [%], where 0 < α ≤ 4.5.

[0052] Thermometer 5 is a device for measuring the surface temperature of steel plate S. Thermometer 5 is preferably located near the feed side of the tandem cold rolling mill 6. However, in practice, the steel plate temperature measured by thermometer 5 is not used as is, but rather a value that compensates for the drop in steel plate temperature between thermometer 5 and the feed side of the tandem cold rolling mill 6 is used for practical purposes.

[0053] The tandem cold rolling mill 6 is an apparatus for cold rolling the steel sheet S, which has been heated by the full-width heating device 4, to achieve the target thickness. In this embodiment, the tandem cold rolling mill 6 has 5 stands, but the number of stands is not particularly limited. Furthermore, in this embodiment, the tandem cold rolling mill 6 adopts a 4Hi form with 4 rolls per stand, but it is not limited to this and other forms, such as 6Hi, can also be used.

[0054] The cutting machine 7 is a device for cutting the cold-rolled steel plate S.

[0055] The tension reel 8 is a device for winding up the steel sheet S cut by the cutting machine 7. The form of the tension reel 8 is not particularly limited; for example, it can be a rotary tension reel. Furthermore, the manufacturing equipment may also have multiple tension reels 8. In this case, multiple tension reels 8 continuously wind up multiple steel sheets S.

[0056] The equipment used in the manufacturing process is not limited to the aforementioned devices. The manufacturing equipment only requires that the full-width heating device 4 and the tandem cold rolling mill 6 be arranged sequentially (preferably adjacently) within 10m on their feed sides. Therefore, the rolling mill can be a tandem rolling mill or a reversible rolling mill. In this case, the full-width heating device 4 and the rolling mill are arranged sequentially in the first pass. Furthermore, it is possible to make the cold rolling process and the pickling process preceding it continuous, and a pickling device for pickling the steel plate S can be arranged between the looper 3 and the tandem cold rolling mill 6.

[0057] [Heating process]

[0058] Next, the features of the method for manufacturing cold-rolled steel sheet according to one embodiment of the present invention, namely the heating process of the steel sheet S by the full-width heating device 4, will be described. It should be noted that the full-width heating device 4 heats at least one of the upper surface and the lower surface of the steel sheet S, but more preferably heats both the upper surface and the lower surface.

[0059] In the heating process of the steel plate S in this embodiment, the full-width heating device 4 determines the target temperature of the full-width heating device 4 based on the temperature of the steel plate S measured by the thermometer 5, the target temperature of the steel plate S on the delivery side of the full-width heating device 4, the time it takes for the steel plate S to pass through the full-width heating device 4 (i.e., the heating time), and the thickness of the steel plate S. It should be noted that the target temperature of the steel plate S heated by the full-width heating device 4 needs to be set to take into account the distance between the thermometer 5 and the full-width heating device 4, and the distance between the thermometer 5 and the tandem cold rolling mill 6. For example, if the distance from the full-width heating device 4 to the tandem cold rolling mill 6 is very short, it is not a problem to use the target temperature of the steel plate S on the delivery side of the full-width heating device 4 as the target temperature of the steel plate S heated by the full-width heating device 4. On the other hand, if the distance between any of the full-width heating device 4, thermometer 5, and tandem cold rolling mill 6 is far, the target temperature of the steel plate S heated by the full-width heating device 4 needs to be set considering the temperature drop until the steel plate S reaches the feed side of the tandem cold rolling mill 6. However, from the viewpoint of environmental impact, the energy used in heating the steel plate should preferably be small, and the full-width heating device 4 and thermometer 5 should preferably be as close as possible to the tandem cold rolling mill 6.

[0060] Here, the inventors of this invention investigated the fracture rate of silicon steel sheets during cold rolling using a tandem rolling mill with five stands. The results showed that silicon steel sheets with high Si content had a higher fracture rate compared to those with low Si content. Furthermore, the investigation into the causes of fracture revealed that the causes differed between upstream fractures (e.g., #1std, #2std, etc.) and downstream fractures (e.g., #4std, #5std). Specifically, the upstream fractures, particularly those directly below #1std on the delivery side, were presumed to be caused by localized contractions in the sheet shape, such as central elongation and edge elongation, as well as bending deformation at the through rolls and shape detector. #1std generally had the highest reduction rate among all stands, suggesting it was prone to fracture due to rapid changes in the sheet shape. Furthermore, the investigation into upstream fractures revealed that the fracture rate (fracture occurrence rate) varied seasonally, with a higher fracture rate in winter compared to summer, presumably due to the influence of external air temperature (temperature within the rolling mill). On the other hand, regarding downstream fractures, it was confirmed that the fractures were caused by edge cracking propagated from the upstream stand. Therefore, although the location and cause of the fractures differed, it can be assumed that all fractures could be suppressed by increasing the temperature of the steel plate fed to #1std.

[0061] To verify the above hypothesis, the resistance to flexural fracture under flexural strain on steel plates was first evaluated on a laboratory scale. This is because the resistance to flexural fracture in this experiment can be considered to be related to the brittle fracture caused by bending deformation at the through roll and shape detector in the upstream frame. As test materials, four types of silicon steel plates with thicknesses of 2 mm and Si contents of 1.8 mass%, 2.8 mass%, 3.3 mass%, and 3.7 mass% (hereinafter, silicon steel plates with a Si content of M mass% are referred to as "M%Si steel") were annealed at 800°C (equivalent to hot-rolled plate annealing). Then, the annealed silicon steel plates were pickled, and test materials with a width of 24 mm and a length of 250 mm were cut using a shearing machine. Afterwards, the processing strain generated during shearing was removed by grinding each end face by 2 mm. This suppressed the occurrence of edge fracture. It should be noted that in actual continuous cold rolling lines, 1.8% Si steel and 2.8% Si steel are steel grades that are not prone to brittle fracture. On the other hand, 3.3% Si steel and 3.7% Si steel are steel grades that experience brittle fracture at a frequency of several percent, especially in the upstream stands. Typically, in cold rolling, the temperature of the steel sheet fed into the mill is kept at the same level as the temperature inside the mill, around 15°C in winter.

[0062] Therefore, the temperature dependence of silicon steel sheet in the range of 15℃ to 45℃ was investigated regarding the bending fracture resistance. In this experiment, a 1mm thick steel sheet was first produced by rolling a 2mm thick steel sheet with a reduction rate of 50%. This simulated #1std. Next, the bending deformation of the steel sheet at the pass roll and shape detector was simulated by passing the sheet through a roll straightener. Then, the bending fracture resistance was evaluated by subjecting the steel sheet to bending deformation. The roll straightener has 11 work rolls with a diameter of 50mm on both the upper and lower sides, with a roll spacing of 60mm. The bending stress on the surface of the steel sheet can be assigned any value by varying the indentation of the upper work roll. In this experiment, the fracture limit of the steel sheet was determined by varying the steel sheet temperature in 10℃ increments and the roll indentation in 0.5mm increments. The greater the indentation at fracture, the more difficult it is to fracture in the cold rolling line. Figure 2 The results obtained in this experiment are shown. It should be noted that, given the fracturing potential in actual continuous rolling mills, under the conditions of this experiment, if the plate can pass through without fracturing up to a pressing depth of 4.0 mm, it is considered that there will be no fracturing even in actual continuous rolling mills. The absence of fracturing at a pressing depth of 4.0 mm is taken as the target value of this experiment.

[0063] like Figure 2 As shown, comparing each Si content, in 1.8% Si steel, regardless of the steel plate temperature (15–45°C), no fracture occurred up to a pressing depth of 4.0 mm. In 2.8% Si steel, fracture occurred at a pressing depth of 3.5 mm at a steel plate temperature of 15°C, but above 25°C, no fracture occurred up to a pressing depth of 4.0 mm. In 3.3% Si steel, fracture occurred at a pressing depth of 1.5 mm at a steel plate temperature of 15°C, and at a pressing depth of 3.0 mm at a steel plate temperature of 25°C. However, at steel plate temperatures above 35°C, no fracture occurred up to a pressing depth of 4.0 mm. Furthermore, in 3.7% Si steel, fracture occurred at a sheet temperature of 15°C with an indentation depth of 1.0 mm, at 25°C with an indentation depth of 1.5 mm, and at 35°C with an indentation depth of 2.5 mm. If the sheet temperature was increased to 45°C, no fracture occurred up to an indentation depth of 4.0 mm. These experimental results confirm that Si content has a significant impact on the fracture resistance of the steel sheet; the higher the Si content, the easier the steel sheet is to fracture. This also matches the actual fracture conditions observed in continuous cold rolling mills. Especially in 3.3% Si and 3.7% Si steel, the results of experiments conducted while varying the sheet temperature showed that higher temperatures were more effective in suppressing brittle fracture.

[0064] Figure 3The results show the steel plate temperature required to suppress brittle fracture corresponding to the Si content of the steel plate, which was estimated based on the experimental results. The approximate curve in the figure can be represented by the following mathematical formula (3). In this experiment, for 1.8% Si steel, no brittle fracture occurred until the indentation was 4.0 mm even at a steel plate temperature of 15°C, so it was considered that steel plate heating with the full-width heating device 4 was not required. However, for 2.8% Si steel, fracture occurred at an indentation of 3.5 mm at a steel plate temperature of 15°C, so it was considered that steel plate heating with the full-width heating device 4 was required when the steel plate temperature was low. Therefore, it is best to assume that the value of Si content α [%] in mathematical formula (3) is practically α>2. In addition, the steel plate temperature T calculated according to mathematical formula (3) Cmin This is the minimum required temperature; from the perspective of fracture suppression, it should be above this temperature. However, if the steel plate temperature is too high, it will affect the shape and lubricity of the steel plate, so the steel plate temperature is kept below 200°C. In addition, the upper limit of the Si content α, 4.5%, is set based on the fact that the temperature of the edge of the steel plate is below 200°C, as described later.

[0065] T Cmin =0.1α 4.5 +15…(3)

[0066] in,

[0067] T Cmin The minimum required temperature [°C] for the central part of the steel plate in the width direction on the feed side of the rolling mill, where α is the Si content [%], and 0 < α ≤ 4.5.

[0068] Next, to suppress fractures caused by edge cracking of the steel sheet, the presence or absence of edge cracking was evaluated by rolling the steel sheet on a laboratory scale. This experiment focused on the fracture mode in which edge cracking originates on the upstream side of the rolling direction and gradually expands and breaks as it moves towards the downstream stand in the rolling direction. It was concluded that if edge cracking at the upstream stand can be completely suppressed, fractures caused by edge cracking of the steel sheet can be suppressed. As test materials, four types of silicon steel sheets with thicknesses of 2 mm and containing 1.8% Si, 2.8% Si, 3.3% Si, and 3.7% Si were cut into 20 mm wide and 250 mm long pieces and annealed at 800 °C (equivalent to hot-rolled sheet annealing). Then, the annealed silicon steel sheets were pickled. It can be considered that the state of the steel sheet edge at this time is similar to the state on the feed side of an actual continuous cold rolling mill.

[0069] It should be noted that in actual continuous cold rolling lines, 1.8% Si steel is a type of steel that is not prone to edge cracking. On the other hand, 3.3% Si steel and 3.7% Si steel are types of steel that experience edge cracking at a frequency of several percent. Typically, in cold rolling, the temperature of the steel sheet fed into the mill is similar to the temperature inside the mill, around 15°C in winter. Therefore, the temperature dependence of silicon steel sheet resistance to edge cracking was investigated within the range of 15°C to 65°C. In this experiment, simulation #1std was used to evaluate the resistance to edge cracking by counting the number of cracks (cracks larger than 1 mm) generated on both ends of the steel sheet (length direction) when rolling a test material of w20×L250mm at a reduction rate of 50%. It should be noted that the number of rolling passes was 5 for each Si content and temperature, and the number of edge cracks is the average of the 5 passes. Furthermore, the steel sheet temperature was set at 10°C intervals. Figure 4 The results obtained in this experiment are shown.

[0070] like Figure 4As shown, at a steel plate temperature of 15°C, comparing each Si content, in 1.8% Si steel, no edge cracks occurred on either end face. In 2.8% Si steel, a total of 7 edge cracks occurred on both end faces. In 3.3% Si steel, a total of 15 edge cracks occurred on both end faces, and in 3.7% Si steel, a total of 30 edge cracks occurred on both end faces. At a steel plate temperature of 25°C, except for 1.8% Si steel, the total number of edge cracks on both end faces in 2.8% Si steel also became 0. On the other hand, there were 11 edge cracks in 3.3% Si steel and 27 edge cracks in 3.7% Si steel. At a steel plate temperature of 35°C, the total number of edge cracks on both end faces in both 1.8% Si steel and 2.8% Si steel became 0. On the other hand, in 3.3% Si steel, a total of 5 edge fractures occurred on both ends, and in 3.7% Si steel, a total of 20 edge fractures occurred on both ends. At a steel plate temperature of 45°C, except for 1.8% Si and 2.8% Si steel, the total number of edge fractures on both ends of 3.3% Si steel became 0. On the other hand, 10 edge fractures occurred in 3.7% Si steel. At a steel plate temperature of 55°C, except for 1.8% Si and 2.8% Si steel, the total number of edge fractures on both ends of 3.3% Si steel also became 0. On the other hand, 3 edge fractures occurred in 3.7% Si steel. At a steel plate temperature of 65°C, except for 1.8% Si, 2.8% Si, and 3.3% Si steel, the total number of edge fractures on both ends of 3.7% Si steel also became 0. The experimental results confirmed that Si content has a significant impact on edge crack resistance; the higher the Si content, the easier it is for steel plates to crack at the edges. This is consistent with the actual state of edge cracking in steel plates during continuous cold rolling mills.

[0071] Figure 5 The results show the estimated temperature required to suppress edge cracking of the steel plate corresponding to the Si content of the steel plate, based on the experimental results. The approximate curve in the figure can be represented by the following mathematical formula (4). In this experiment, for 1.8% Si steel, no edge cracking occurred even at a steel plate temperature of 15°C, so it is considered that steel plate heating with the full-width heating device 4 is not required. However, for 2.8% Si steel, edge cracking occurred at a steel plate temperature of 15°C, so it is considered that steel plate heating with the full-width heating device 4 is required when the steel plate temperature is low. Therefore, it is best to assume that the Si content α [%] in mathematical formula (4) is practically α>2. In addition, the steel plate temperature T calculated according to mathematical formula (4) EminThis is the minimum required temperature; from the perspective of fracture suppression, it should be above this temperature. However, if the steel plate temperature is too high, it will affect the shape and lubricity of the steel plate, so the steel plate temperature is kept below 200°C. In addition, the upper limit of the Si content α, 4.5%, is set based on the range of the steel plate edge temperature being below 200°C calculated from mathematical formula (4). It should be noted that the heating range of the steel plate is set to be a range of 30 mm or more from the edge of the steel plate. This is because the wide range of influence during cold rolling that affects the cracking of the steel plate edge is said to be about 30 mm from the edge of the steel plate.

[0072] T Emin =0.1α 4.8 +15…(2)

[0073] in,

[0074] T Emin The minimum required temperature [°C] at the width end of the steel plate fed into the rolling mill.

[0075] α represents the Si content [%], where 0 < α ≤ 4.5.

[0076] The two experiments described above show that the heating temperatures required to suppress fractures originating from the center of the steel sheet in the width direction are different from those required to suppress fractures originating from the edge. For example, in the case of 3.7% Si steel, the temperature required to suppress fractures originating from the center in the width direction is 45°C or higher, while the temperature required to suppress fractures at the edge is 65°C or higher. Thus, it is clear that in order to suppress fractures in silicon steel sheets, in addition to setting a heating amount corresponding to the Si content, it is also necessary to create a temperature gradient in the width direction of the steel sheet, such as making the temperature at the edge higher than that at the center in the width direction, within the same steel grade. This invention was conceived. It should be noted that when multiple steel sheets with different Si contents are transported using the same equipment, the full-width heating device 4 can obtain information indicating the Si content of the preceding and following materials and adjust and determine the target temperature based on this information. Furthermore, in this embodiment, silicon steel sheets are used as the material to be rolled, but the type of steel sheet is not limited. Examples of steel sheets suitable for applying the technology of this invention, other than silicon steel sheets, include high-strength steel sheets and high-alloy steel sheets.

[0077] As explained above, according to the cold-rolled steel strip manufacturing equipment and method according to one embodiment of the present invention, a full-width heating device 4 capable of imparting a temperature gradient in the width direction of the steel sheet S is used to appropriately control the temperature required to suppress fracture from the center portion in the width direction and edge fracture, thereby suppressing steel sheet fracture. Therefore, according to the cold-rolled steel strip manufacturing equipment and method according to one embodiment of the present invention, when cold-rolling silicon steel sheet, steel sheet fracture can be suppressed with the minimum required energy, thus enabling stable cold rolling of silicon steel sheet with minimal environmental load.

[0078] Example

[0079] An embodiment demonstrating the effects of the present invention will be described. In this embodiment, a full-width heating device 4 is provided on the feed side of the cold rolling mill, allowing the temperature of the steel plate on the feed side to be set to an arbitrary temperature. Furthermore, a tandem cold rolling mill with five stands is used to finish the plate to a specified thickness. All steel used in this embodiment is silicon steel plate, divided into three groups based on Si content. Specifically, these are groups with Si content of 1.0 mass% to 2.0 mass%, 2.0 mass% to 3.0 mass%, and 3.0 mass% to 3.5 mass%. In all groups, the plate thickness before rolling is 1.8 mm to 2.4 mm, and the plate thickness after rolling is 0.3 mm to 0.5 mm. To investigate the fracture rate caused by different Si contents, care was taken to ensure that the plate thickness was not uneven due to group differences. The fracture rate of 200 coils was investigated in each group. It should be noted that the external air temperature (temperature inside the factory) was approximately 15°C. The surveyed coils and conditions are shown in Table 1. The steel plate temperature was measured using a thermometer located on the feed side of the rolling mill.

[0080] [Table 1]

[0081]

[0082] [Reference Example]

[0083] This example illustrates a case where the steel plate is heated without using a full-width heating device, meaning the temperature of the steel plate on the mill feed side is approximately 15°C. The breakage rate of the 200mm coil with a Si content of 1.0 to 2.0 mass% is 0%. On the other hand, the breakage rate of the 200mm coil with a Si content of 2.0 to 3.0 mass% is 1%, and the breakage rate of the 200mm coil with a Si content of 3.0 to 3.5 mass% is 3%.

[0084] [Example 1 of the invention]

[0085] An example is shown where the steel sheet temperature at the feed side of the tandem cold rolling mill, corresponding to the Si content of the silicon steel sheet, was calculated according to the above mathematical formulas (1) and (2), and the steel sheet was heated using a full-width heating device. The distance between the tandem cold rolling mill and the full-width heating device is 10 m. In this example, the temperature at the edge is higher than the temperature at the center in the width direction. The breakage rate of 200 coils with a Si content of 1.0 mass% to 2.0 mass% (17°C at the center and 18°C ​​at the edge) is 0%. In addition, the breakage rate of 200 coils with a Si content of 2.0 mass% to 3.0 mass% (30°C at the center and 35°C at the edge) is also 0%, and the breakage rate of 200 coils with a Si content of 3.0 mass% to 3.5 mass% (45°C at the center and 60°C at the edge) is also 0%. Based on this invention, it is confirmed that by heating the silicon steel sheet, the breakage of the steel sheet can be significantly reduced.

[0086] [Example 2 of the invention]

[0087] An example is shown where the steel sheet temperature at the feed side of the tandem cold rolling mill, corresponding to the Si content of the silicon steel sheet, was calculated based on the aforementioned mathematical formulas (1) and (2), and the steel sheet was heated using a full-width heating device. The distance between the tandem cold rolling mill and the full-width heating device is 1 m. That is, compared to Example 1 of the Invention, the distance between the tandem cold rolling mill and the full-width heating device is shorter. Other conditions are the same as in Example 1 of the Invention. In this example of the Invention, the breakage rate of 200 coils (17°C at the center and 18°C ​​at the edge) with a Si content of 1.0 mass% to 2.0 mass% is 0%. In addition, the breakage rate of 200 coils (30°C at the center and 35°C at the edge) with a Si content of 2.0 mass% to 3.0 mass% is also 0%, and the breakage rate of 200 coils (45°C at the center and 60°C at the edge) with a Si content of 3.0 mass% to 3.5 mass% is also 0%. If only the fracture rate is considered, fracture is suppressed until the Si content reaches 3.5 mass%, the same as in Invention Example 1, but the energy consumption is significantly reduced compared to Invention Example 1, confirming the superiority of Invention Example 2. Therefore, it is confirmed that from the viewpoint of reducing energy consumption (environmental resistance), the closer the distance between the tandem cold rolling mill and the full-width heating device, the better.

[0088] [Comparative Example 1]

[0089] An example is shown where the mill feed temperature corresponding to the Si content of the silicon steel sheet was calculated according to the above mathematical formulas (1) and (2), and the steel sheet was heated using a full-width heating device. The distance between the tandem cold rolling mill and the full-width heating device is 20m. That is, it is an example where the distance between the tandem cold rolling mill and the full-width heating device in the conditions of Invention Example 1 is extended. Because the distance between the tandem cold rolling mill and the full-width heating device is long, even if the upper limit of the capacity of the full-width heating device is used, the mill feed temperature calculated according to mathematical formulas (1) and (2) cannot be achieved. The breakage rate of 200 coils (15°C at the center and 15°C at the edge) with a Si content of 1.0mass% to 2.0mass% is 0%, and the breakage rate of 200 coils (25°C at the center and 30°C at the edge) with a Si content of 2.0mass% to 3.0mass% is also 0%. On the other hand, the breakage rate of 200 coils (40°C in the center and 50°C at the edges) with a Si content of 3.0mass% to 3.5mass% was 1%. It was confirmed that the distance between the tandem cold rolling mill and the full-width heating device is preferably short. When the distance is set such that even if the upper limit of the capacity of the full-width heating device is used, the steel plate temperature calculated according to the above mathematical formulas (1) and (2) cannot be guaranteed, the higher the Si steel is, the more likely it is to break.

[0090] [Comparative Example 2]

[0091] An example is shown where the steel sheet is heated using a full-width heating device at a temperature approximately 30% lower than the temperature of the steel sheet on the mill feed side corresponding to the Si content of the silicon steel sheet calculated according to the above mathematical formulas (1) and (2). Other conditions are the same as in Invention Example 1. The fracture rate of 200 coils (15°C at the center and 15°C at the edges) with a Si content of 1.0mass% to 2.0mass% is 0%, and the fracture rate of 200 coils (20°C at the center and 25°C at the edges) with a Si content of 2.0mass% to 3.0mass% is also 0%. On the other hand, the fracture rate of 200 coils (30°C at the center and 40°C at the edges) with a Si content of 3.0mass% to 3.5mass% is 1.5%. It is confirmed that when the temperature is lower than the steel sheet temperature calculated according to the above mathematical formulas (1) and (2), the higher the Si content of the steel, the easier it is to fracture.

[0092] [Comparative Example 3]

[0093] An example of using a solenoid-type full-width heating device is shown. In a solenoid-type full-width heating device, it is impossible to impart a temperature gradient in the width direction of the steel plate. The temperature of the steel plate heated using the solenoid-type full-width heating device is calculated according to mathematical formula (1). That is, it is impossible to ensure the temperature required to suppress edge cracking, and the temperature of the steel plate at the edge tends to drop more easily than that at the center in the width direction, so the temperature at the edge is lower than that at the center in the width direction. The breakage rate of 200 coils with a Si content of 1.0mass% to 2.0mass% (17°C at the center of the width, 16°C at the edge) is 0%. On the other hand, the breakage rate of 200 coils with a Si content of 2.0mass% to 3.0mass% (30°C at the center of the width, 25°C at the edge) is 0.5%, and the breakage rate of 200 coils with a Si content of 3.0mass% to 3.5mass% (45°C at the center of the width, 35°C at the edge) is 2%. The fracture patterns of the broken roll material were investigated. Although fractures originating from the center in the width direction were suppressed, fractures caused by edge breakage were not suppressed.

[0094] [Comparative Example 4]

[0095] An example of using a solenoid-type full-width heating device is shown. The temperature of the steel sheet heated using the solenoid-type full-width heating device is calculated according to mathematical formula (2). That is, the steel sheet is heated throughout the width direction in such a way that the temperature of the edge is the temperature considered necessary to suppress edge cracking. The fracture rate of 200 coils with a Si content of 1.0mass% to 2.0mass% (20°C at the center of the width, 18°C ​​at the edge) is 0%, the fracture rate of 200 coils with a Si content of 2.0mass% to 3.0mass% (40°C at the center of the width, 35°C at the edge) is also 0%, and the fracture rate of 200 coils with a Si content of 3.0mass% to 3.5mass% (70°C at the center of the width, 60°C at the edge) is also 0%. However, the center of the steel sheet in the width direction is heated beyond what is necessary from the viewpoint of fracture suppression, and it is best to reduce the energy input when considering the environmental load.

[0096] [Comparative Example 5]

[0097] An example is shown where an edge heating device is used instead of a full-width heating device, but only heating the two ends of the steel plate in the width direction. The temperatures at the two ends of the steel plate in the width direction heated by the edge heating device are calculated according to mathematical formula (2). The fracture rate of 200 coils with a Si content of 1.0mass% to 2.0mass% (15°C at the center of the width, 35°C at the edge) is 0%. On the other hand, the fracture rate of 200 coils with a Si content of 2.0mass% to 3.0mass% (15°C at the center of the width, 35°C at the edge) is 0.5%, and the fracture rate of 200 coils with a Si content of 3.0mass% to 3.5mass% (15°C at the center of the width, 60°C at the edge) is 2%. The fracture mode of the fractured coils was investigated. Although fracture caused by edge cracking was suppressed, fracture from the center of the width direction was not suppressed.

[0098] As shown above, it has been confirmed that heating the steel sheet on the feed side of a tandem cold rolling mill using the present invention can suppress steel sheet breakage. In particular, in the case of silicon steel sheets with a Si content of 3 mass% or more, heating the steel sheet to a suitable temperature can significantly reduce steel sheet breakage, thereby achieving improved productivity and yield.

[0099] The above description of the manufacturing equipment and method for cold-rolled steel strip according to the present invention has been specifically provided through embodiments and methods for carrying out the invention. However, the scope of the invention is not limited to these descriptions and must be interpreted broadly based on the claims. Furthermore, it goes without saying that various modifications and alterations based on these descriptions are also included in the scope of the invention.

[0100] Industrial availability

[0101] According to the present invention, a method and equipment for manufacturing cold-rolled steel sheets that have low environmental impact and can stably roll silicon steel sheets are provided.

[0102] Explanation of reference numerals in the attached figures

[0103] 1. Release the reel

[0104] 2. Connecting device

[0105] 3 Loops

[0106] 4 Full-width heating device

[0107] 5 thermometers

[0108] 6-tank cold rolling mill

[0109] 7 Cutting Machine

[0110] 8-Tension Reel

[0111] S-shaped steel plate.

Claims

1. A method for manufacturing cold-rolled steel sheet, comprising a method for manufacturing cold-rolled steel sheet using a transverse full-width heating device and a cold rolling mill, wherein the transverse full-width heating device heats the steel sheet throughout its width direction, and the cold rolling mill is disposed downstream of the transverse full-width heating device in the rolling direction to roll the steel sheet, wherein... The manufacturing method includes the step of heating the steel plate using the transverse full-width heating device in such a way that the temperature at the end of the steel plate on the feed side of the cold rolling mill in the width direction is higher than the temperature at the center in the width direction. The temperatures of the steel plate at its center and ends in the width direction on the feed side of the cold rolling mill are calculated using the following mathematical formulas (1) and (2), which vary depending on the Si content α. T C ≥0.1α 4.5 +15 …（1） T E ≥0.1α 4.8 +15 …（2） in, T C T represents the temperature [°C] of the steel plate at the center of the width direction on the feed side of the rolling mill. C ≤200℃, T E T represents the temperature of the steel plate at the width end of the steel plate fed into the rolling mill, in the direction of its width [°C]. E ≤200℃, α represents the Si content [%], where 0 < α ≤ 4.

5.

2. A cold-rolled steel sheet manufacturing equipment, comprising: A transverse full-width heating device heats the steel plate across its entire width; and A cold rolling mill, positioned downstream of the transverse full-width heating device, rolls the steel plate. The transverse full-width heating device heats the steel plate in such a way that the temperature at the end of the steel plate on the feed side of the cold rolling mill is higher than the temperature at the center of the steel plate in the width direction. The transverse full-width heating device heats the steel plate fed into the cold rolling mill to the temperature at the center and ends of the plate in the width direction, which varies with the Si content α, and is calculated by the following mathematical formulas (1) and (2). T C ≥0.1α 4.5 +15 …（1） T E ≥0.1α 4.8 +15 …（2） in, T C T represents the temperature [°C] of the steel plate at the center of the width direction on the feed side of the rolling mill. C ≤200℃, T E T represents the temperature of the steel plate at the width end of the steel plate fed into the rolling mill, in the direction of its width [°C]. E ≤200℃, α represents the Si content [%], where 0 < α ≤ 4.

5.

3. The equipment for manufacturing cold-rolled steel sheets according to claim 2, The transverse full-width heating device is located within 10m of the feed side of the cold rolling mill.

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