Manufacturing method for hot-dip galvanized steel sheets

Abstract

To provide a manufacturing method of a hot-dip galvanized steel sheet that can suppress variations in the oxide film thickness among coils.SOLUTION: There is provided a manufacturing method of a hot-dip galvanized steel sheet for forming an oxide film on the surface of the hot-dip galvanized steel sheet by applying acidic treatment liquid after subjecting the hot-dip galvanized steel sheet to temper rolling. On the basis of a levelling amount in a width direction of the temper rolling of a material to be rolled set on the basis of the actual oxide film thickness in a preceding part of the material to be rolled, levelling control is executed for the material to be rolled in the temper rolling.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a hot-dip galvanized steel sheet, which involves forming an oxide film on the surface of the steel sheet, and which can reduce variations in oxide film thickness between coils. [Background technology]

[0002] Hot-dip galvanized steel sheets, which have an oxide film formed on their surface, are manufactured by applying an acidic treatment solution to the surface of the steel sheet and leaving it for a predetermined time (film formation process). This process involves a chemical reaction between the hot-dip galvanized steel sheet and the acidic treatment solution, which forms the oxide film on the surface of the steel sheet. Conventionally, methods to reduce variations in oxide film thickness between coils have included increasing the temperature of the acidic treatment solution, extending the waiting time after application of the acidic treatment solution by reducing the line speed, and increasing the rolling load during temper rolling. By doing these things, variations have been reduced by increasing the thickness of the oxide film. It is known that the oxide film thickness also changes depending on the humidity of the film formation process, in addition to operating conditions, and methods such as humidity control in the film formation process also exist.

[0003] Patent Document 1 discloses that the oxide film thickness can be increased by raising the temperature of the acidic treatment solution or by extending the standing time after applying the acidic treatment solution.

[0004] Patent Document 2 discloses that increasing the temper rolling load increases the area of ​​the smooth portion of the plating layer, and that the amount of oxide film adhering to the smooth portion increases.

[0005] Patent Document 3 discloses that the oxide film thickness increases as the absolute humidity during the film formation process increases. Absolute humidity indicates the amount of water vapor contained in the atmosphere and is defined as the product of the saturated vapor pressure and relative humidity. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-203547 [Patent Document 2] Japanese Patent Publication No. 2005-256069 [Patent Document 3] Japanese Patent Publication No. 2009-108377 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, even when using the methods described in Patent Documents 1, 2, and 3, there were materials in which the variation in oxide film thickness between coils was not reduced, and the reason for this was unknown.

[0008] The present invention provides a method for manufacturing a hot-dip galvanized steel sheet that solves the above-mentioned problems and suppresses variations in oxide film thickness between coils. [Means for solving the problem]

[0009] The process leading to the completion of this invention will be explained below.

[0010] The inventors diligently investigated the cause of variations in oxide film thickness that still occurred even after controlling factors conventionally used as control factors for oxide film thickness on the surface of hot-dip galvanized steel sheets, such as the temperature of the acidic treatment solution, the standing time after application of the acidic treatment solution, the line speed, the rolling load in temper rolling, and the humidity in the film formation process. As a result, they found that the variation in oxide film thickness between coils is due to deviations in the width direction of the oxide film thickness. Furthermore, they found that deviations in the width direction of the oxide film thickness are caused by the properties of the material that forms the oxide film thickness, such as the plate shape, hardness distribution, and plate thickness distribution, which result from fluctuations in manufacturing conditions, as well as the mill conditions, such as the difference in the reduction load between the left and right sides. However, it is difficult to precisely control all of these items. Therefore, by adopting the leveling amount, which is the difference in the reduction load between the left and right sides of temper rolling, as a feedback control factor, and by adopting a method of controlling the leveling amount based on the actual value of the difference or deviation in the width direction of the oxide film thickness in the preceding area, the difference or deviation between the left and right sides can be significantly reduced, and as a result, the variation in oxide film thickness between coils can also be significantly suppressed.

[0011] The present invention has the following configuration. [1] After hot-dip galvanized steel sheet is temper-rolled, an acidic treatment solution is applied, A method for manufacturing a hot-dip galvanized steel sheet, comprising forming an oxide film on the surface of the hot-dip galvanized steel sheet, In the temper rolling process, the setting is determined based on the actual oxide film thickness in the leading portion of the rolled material. A method for manufacturing a hot-dip galvanized steel sheet, characterized by controlling the leveling of the rolled material based on the amount of leveling in the width direction of the temper rolling of the rolled material. [2] The method for manufacturing a hot-dip galvanized steel sheet according to [1], characterized in that the amount of leveling in the width direction of temper rolling of the rolled material is set by the difference in the width direction of the actual oxide film thickness or by the deviation obtained by dividing the difference by the average of the actual oxide film thickness in the width direction. [3] A method for manufacturing a hot-dip galvanized steel sheet according to [1] or [2], characterized in that when leveling based on the leveling amount in the width direction of the temper rolling, the rolling load on one side in the width direction is made greater than the rolling load on the other side, thereby increasing the oxide film thickness. [4] The amount of leveling in the width direction of the temper rolling is The method is characterized by being calculated using a regression equation for obtaining a predetermined leveling amount, which is obtained based on information on the leveling amount corresponding to the difference in the width direction of the actual oxide film thickness or the deviation obtained by dividing the difference by the average value of the actual oxide film thickness. A method for manufacturing a hot-dip galvanized steel sheet as described in any of [1] to [3]. [5] Equation (1) comprising the difference, the lower limit target value of the difference, the upper limit target value of the difference, the actual value of the leveling amount in the width direction of the temper rolling, and the target value of the leveling amount in the width direction, or A method for manufacturing a hot-dip galvanized steel sheet according to [2] or [4], characterized by determining a target value for the leveling amount in the width direction and controlling the leveling using equation (2), which is composed of the aforementioned deviation, a lower limit target value for the deviation, an upper limit target value for the deviation, the actual value of the leveling amount in the width direction of the temper rolling, and a target value for the leveling amount in the width direction. α1×(Δs - Δsa1) ≤ (x - xa) ≤ α2×(Δs - Δsa2) ··· Equation (1) α1: Any constant, α2: Any constant, Δs: Difference, Δsa1: Upper limit target value of Δs, Δsa2: Lower limit target value of Δs, xa: Actual value of leveling amount (×10 mm), x: Target value of leveling amount (×10 -2 mm) α3×(Δt - Δta1) ≤ (x - xa) ≤ α4×(Δt - Δta2) ··· Equation (2) α3: Any constant, α4: Any constant, Δt: Deviation, Δta1: Upper limit target value of Δt, Δta2: Lower limit target value of Δt, xa: Actual value of leveling amount (×10 -2 mm), x: Target value of leveling amount (×10 -2 mm)

Advantages of the Invention

[0012] According to the present invention, in the temper rolling process of the hot-dip galvanized steel sheet, after subjecting the hot-dip galvanized steel sheet to temper rolling and then applying an acidic treatment solution to form an oxide film, it becomes possible to suppress the variation in the oxide film thickness between coils.

Brief Description of the Drawings

[0013] [Figure 1] It is a diagram showing an outline of a method for manufacturing a hot-dip galvanized steel sheet. [Figure 2(a)] It is a flowchart showing a control method of a temper rolling apparatus, and shows a flow of leveling control of a material to be rolled based on a preset leveling amount in the width direction based on a predetermined actual oxide film thickness. [Figure 2(b)] It is a flowchart showing a control method of a temper rolling apparatus, and shows a flow of leveling control of a material to be rolled based on a preset leveling amount in the width direction based on a difference or deviation in the width direction of a predetermined actual oxide film thickness. [Figure 3] It is a diagram for explaining the roll gap leveling amount of a temper rolling mill.

Embodiments for Carrying Out the Invention

[0014] The embodiments of the present invention will be described in detail below.

[0015] Figure 1 is a schematic diagram of the manufacturing method for hot-dip galvanized steel sheets, which is the subject of this invention. As shown in Figure 1, hot-dip galvanized steel sheets are manufactured by first performing temper rolling 1, then applying an acidic treatment solution to the surface of the steel sheet in a liquid contact step 2, and then leaving it for a predetermined time (film formation step 3), thereby forming an oxide film on the surface of the steel sheet through a chemical reaction between the hot-dip galvanized steel sheet and the acidic treatment solution. After this, a water washing process 4 is performed, and in the oxide film thickness evaluation process 5, the oxide film thickness described below is measured, and the difference or deviation of the oxide film thickness in the coil width direction is determined. Below, the actual oxide film thickness in the film formation process 3 and the variation of the actual oxide film thickness in the width direction are measured, and a method for controlling the leveling amount of temper rolling and suppressing variation in the actual oxide film thickness throughout the product is specifically explained, based on the difference in the width direction of the actual oxide film thickness (also called the difference) or the deviation (also called the deviation) obtained by dividing the difference by the average of the actual oxide film thickness in the width direction (also called the deviation) is used.

[0016] Figures 2(a) and 2(b) are flowcharts illustrating the control method of a temper rolling mill. The process of controlling the leveling of the rolled material based on a predetermined widthwise leveling amount based on a predetermined actual oxide film thickness (Figure 2(a)), and the process of controlling the leveling of the rolled material based on a predetermined widthwise leveling amount based on a predetermined widthwise difference or deviation of the actual oxide film thickness (Figure 2(b)), are carried out in the following sequence: In S1, the actual oxide film thickness is measured in the leading portion of the rolled material to be temper-rolled. In S2, the actual oxide film thickness measured in S1 and the corresponding widthwise leveling amount for temper rolling are calculated and set. In S3, based on the widthwise leveling amount for temper rolling corresponding to the actual oxide film thickness set in S2, leveling is controlled by a widthwise leveling amount that yields a predetermined oxide film thickness. Temper rolling is continuously performed by repeating this series of S1 to S3 steps. As steps S1 to S3 are repeated, data on the actual oxide film thickness and the corresponding leveling amount in the width direction of temper rolling are accumulated (S4). Based on this data, the relationship between the actual oxide film thickness and the leveling amount can be referenced in S2 as a pre-stored relational expression. Furthermore, in S5, the actual oxide film thickness is measured in the leading portion of the rolled material to be temper-rolled. In S6, the difference or deviation of the actual oxide film thickness in the width direction measured in S5 is calculated. In S7, the difference or deviation set in S6 and the corresponding leveling amount in the width direction of temper rolling are calculated and set. In S8, based on the leveling amount in the width direction of temper rolling corresponding to the difference or deviation of the actual oxide film thickness set in S7, leveling is controlled by a leveling amount in the width direction that yields a predetermined difference or deviation. Temper rolling is continuously performed by repeating this series of steps S5 to S8. By repeating steps S5 to S8, data on the difference or deviation of the actual oxide film thickness and the corresponding leveling amount in the width direction of temper rolling are accumulated (S9). Based on this data, the regression equation between the difference or deviation of the actual oxide film thickness and the leveling amount can be referenced in S6 as a pre-stored regression equation. By limiting the control method for temper rolling shown in Figure 2 to the more preferable method described below, the variation in actual oxide film thickness between coils from the same manufacturing lot can be further reduced.

[0017] [Measurement of actual oxide film thickness in the width direction, evaluation of difference or deviation] First, we will explain the method for measuring the actual oxide film thickness. It is preferable to take samples from two or more different locations in the coil width direction and measure the actual oxide film thickness. The actual oxide film thickness can be measured, for example, using an X-ray fluorescence analyzer under the following measurement conditions. The measurement conditions are as follows: Ten samples with known oxide film thicknesses are irradiated with X-rays in a vacuum with a measurement diameter of 30 mm, and the X-ray fluorescence intensity of O (oxygen) is measured. A calibration curve is set by fitting a linear function with an intercept to the plot of the obtained X-ray fluorescence intensity and the known oxide film thickness. Similarly, samples with unknown oxide film thicknesses are irradiated with X-rays in a vacuum with a measurement diameter of 30 mm, and the X-ray fluorescence intensity of O (oxygen) is measured, allowing the actual oxide film thickness to be determined from the set calibration curve.

[0018] The sampling locations for widthwise samples should preferably be at a distance sufficient to distinguish the difference in actual oxide film thickness in the widthwise direction. For example, from the viewpoint of accurately measuring the difference or deviation in the widthwise direction, it is preferable to sample within 300 mm from the outermost edge on the Op (Operator) side toward the center of the coil width, and within 300 mm from the outermost edge on the Dr (Drive) side toward the center of the coil width. From the viewpoint of accurately measuring the difference or deviation in the widthwise direction, it is even more preferable to sample within 50 to 150 mm from the outermost edge on the Op side toward the center of the coil width, and within 50 to 150 mm from the outermost edge on the Dr side toward the center of the coil width. Note that the Op side of the coil width refers to the side where the control device or operator is located, and the Dr side refers to the opposite side that is opposite to the Op side. If it is difficult to distinguish between Op and Dr, the right side of the upper surface of the steel plate in the direction of steel plate travel is considered the Op side, and the left side is considered the Dr side. Furthermore, it is preferable to supplement the data in between as appropriate (data between 300 mm from the outermost edge on the Op side toward the center of the coil width and 300 mm from the outermost edge on the Dr side toward the center of the coil width) and measure at three or more points in the width direction.

[0019] The method for evaluating the difference and deviation in the width direction of the actual oxide film thickness is as follows.

[0020] If measurements are taken at two locations, the difference between the actual oxide film thicknesses measured at the two locations is defined as the difference in actual oxide film thickness, and the deviation of the actual oxide film thickness is calculated by dividing this difference by the average of the actual oxide film thicknesses measured at the two locations. If measurements are taken at three or more locations, the difference between the maximum and minimum values ​​in the actual oxide film thickness data from the three or more locations is defined as the difference in actual oxide film thickness, and the deviation of the actual oxide film thickness is calculated by dividing this difference by the average of the actual oxide film thickness data from the three or more locations.

[0021] Furthermore, a threshold can be set for either the difference in actual oxide film thickness or the deviation obtained by dividing the difference by the average of the actual oxide film thickness, thereby pre-setting a predetermined leveling amount. In particular, setting a threshold for the above-mentioned deviation is preferable because it allows for more accurate and appropriate setting of the leveling amount, thereby reducing variations in oxide film thickness. This is because the effect of leveling adjustment is more pronounced as the absolute value of the oxide film thickness increases.

[0022] The oxide film thickness is measured on a steel sheet manufactured on the temper rolling line before temper rolling of the rolled material undergoing widthwise leveling during temper rolling. In other words, it is measured on a coil manufactured prior to the rolled material or in a portion of the rolled material that precedes the rolled material during temper rolling. Therefore, the preceding portion of the rolled material refers to a portion of the rolled material that precedes the rolled material or a separate coil manufactured prior to the rolled material. Since temperature variations in the widthwise direction in the preceding processes (hot rolling, annealing, liquid contact process 2, and film formation process 3) and the amount of crown formation in the hot rolling and cold rolling processes often occur in similar conditions in the coil preceding the rolled material, the measurement site for the oxide film thickness does not necessarily have to be the preceding portion of the rolled material; it may be a separate coil that precedes it. In short, the preceding portion of the rolled material mentioned above refers to information from the preceding portion of the same coil or a separate coil that precedes it.

[0023] When using information from a preceding coil, it is desirable that the preceding coil was manufactured in the same production lot in one or more of the following processes: hot rolling, cold rolling, annealing, temper rolling process 1, liquid contact process 2, and film deposition process 3. In the case of the same production lot, the deviation in the width direction of the actual oxide film thickness due to the processing temperature of each process and the amount of crown formation mentioned above are almost the same, so the deviation in the width direction of the actual oxide film thickness tends to show a similar trend. In particular, it is desirable that the preceding coil was manufactured in the same production lot in one or more of the following processes: cold rolling, temper rolling process 1, liquid contact process 2, and film deposition process 3. This is because the manufacturing conditions in the cold rolling process, temper rolling process 1, liquid contact process 2, and film deposition process 3 tend to have a particularly strong influence on the deviation in the width direction of the actual oxide film thickness. Furthermore, since typically about 20 coils are produced in a single manufacturing lot, it is preferable that the preceding coils are within 20 coils before or after the coil that undergoes leveling adjustment in the cold rolling process, and that in any of the temper rolling process 1, liquid contact process 2, or film formation process 3, they are within 1 to 20 coils before the coil that undergoes leveling adjustment.

[0024] [Calculation of the leveling amount in the width direction of temper rolling and control of the leveling amount of temper rolling] Next, a method for calculating and controlling the leveling amount in the width direction of temper rolling of the rolled material will be described based on the difference or deviation in the width direction of the actual oxide film thickness obtained. As shown in Figure 3, the leveling amount 10 in the width direction is defined as the difference in the amount of reduction at both ends of the roll axis direction 14 of the upper roll 12 and lower roll 13 that roll the rolled material 11. The leveling amount 10 in the width direction is affected by various conditions such as the material's crown and physical properties, the amount of meandering, the annealing temperature, the treatment and removal conditions of the chemical solution, and the sheet feeding speed, and therefore cannot be determined by the conditions of the rolling mill alone. Therefore, for example, by measuring the oxide film thickness at a predetermined width position in the leading portion of the rolled material and adjusting the leveling amount based on the measurement results, variations in oxide film thickness can be suppressed. The leveling amount is adjusted by first determining the relationship between the oxide film thickness on the width position where the oxide film thickness is measured and the leveling amount on the same side, that is, the change in oxide film thickness with respect to the leveling amount. Using this relationship, a leveling correction amount corresponding to the oxide film thickness correction amount is calculated, and this correction amount is added to the actual leveling amount of the leading portion to set the leveling amount of the rolled material 11. The rolled material 11 is then controlled to level with this leveling amount. Since fluctuations in oxide film thickness in the width direction are one of the factors causing variations in oxide film thickness, this type of control can further reduce variations in oxide film thickness that could not be suppressed by conventional oxide film thickness control guidelines. It is also possible to control the width position where the oxide film thickness is measured and the leveling control on different sides. In that case, the relationship between the leveling amount and the change in oxide film thickness is reversed in sign from the above, but the relationship between the two is determined in the same way, and the correction amount for the leveling amount corresponding to the correction amount for the oxide film thickness is calculated, and the leveling amount of the rolled material 11 is set by adding this correction amount to the actual leveling amount of the preceding part. Furthermore, for example, it is particularly preferable from the viewpoint of reducing variations in oxide film thickness to know in advance the change amount of the difference or deviation in the width direction of the actual oxide film thickness corresponding to the leveling amount 10 in the width direction, and to calculate the leveling amount by adding the leveling correction amount corresponding to the correction amount for the oxide film thickness using that change amount, thereby controlling the leveling.

[0025] In this process, the information source (accumulated data) is the difference in actual oxide film thickness obtained from already manufactured coils, or the deviation obtained by dividing the difference by the average of the actual oxide film thickness, and the corresponding leveling amount. For example, if three or more points can be identified (by performing machine learning), a regression equation can be obtained based on that data. In other words, the above regression equation can be created based on the information accumulated from this data, and the target leveling amount can be calculated. In order to operate without reducing manufacturability, it is preferable to have an oxide film thickness difference of -8nm to 8nm, and it is preferable that the value obtained by dividing the difference in oxide film thickness in the width direction by the average of the oxide film thickness in the width direction be -0.2 to 0.2.

[0026] As a preferable example, taking the deviation in the width direction of the actual oxidized film thickness obtained from two or more different positions as Δt, and taking the target deviations Δt as Δta1 and Δta2, and further taking the leveling amount (×10 -2 mm) of the skin pass rolling as xa and the target leveling amount as x, x is determined by Equation (2), and by controlling the leveling amount within the above range, it becomes possible to suppress the variation in the oxidized film thickness between coils. α3×(Δt - Δta1) ≦ (x - xa) ≦ α4×(Δt - Δta2) ··· Equation (2) α3: Arbitrary constant, α4: Arbitrary constant, Δt: Deviation, Δta1: Upper limit target value of Δt, Δta2: Lower limit target value of Δt, xa: Actual value of the leveling amount (×10 -2 mm), x: Target value of the leveling amount (×10 -2 mm) Also, taking the difference in the width direction of the actual oxidized film thickness obtained from two or more different positions as Δs, and taking the target differences Δs as Δsa1 and Δsa2, and further taking the leveling amount (×10 -2 mm) of the skin pass rolling as xa and the target leveling amount as x, x is determined by Equation (1), and by controlling the leveling amount within the above range, it is also possible to suppress the variation in the oxidized film thickness between coils. α1×(Δs - Δsa1) ≦ (x - xa) ≦ α2×(Δs - Δsa2) ··· Equation (1) α1: Arbitrary constant, α2: Arbitrary constant, Δs: Difference, Δsa1: Upper limit target value of Δs, Δsa2: Lower limit target value of Δs, xa: Actual value of the leveling amount (×10 -2 mm), x: Target value of the leveling amount (×10 -2 mm) Although α1, α2, α3, and α4 are arbitrary constants, in order to obtain a predetermined deviation, it is preferable that α1 and α2 are 2 to 5, and α3 and α4 are 100 to 300.

[0027] In Equations (1) and (2), the difference in the oxidized film thickness is the value obtained by subtracting the measured value on the Dr side from the measured value on the Op side, and the leveling amount is a value that becomes larger on the negative side when the pushing amount on the Op side becomes larger.

[0028] Furthermore, when leveling based on the leveling amount in the width direction of the temper rolling, the oxide film thickness can be increased by increasing the load in the width direction. Therefore, the oxide film thickness in the width direction can be controlled while controlling the load in the width direction. In other words, when areas with low oxide film thickness occur in the width direction, it is possible to increase the oxide film thickness by making the rolling load on one side in the width direction greater than the rolling load on the other side.

[0029] Furthermore, differences or deviations in the width direction of the actual oxide film thickness may occur even within the same coil. By applying the present method to each part in the longitudinal direction of the same coil, it is possible to reduce variations in the oxide film thickness within the same coil. [Examples]

[0030] Cold-rolled steel sheets of various dimensions, with a thickness of 0.6 to 1.6 mm and a width of 800 to 1880 mm, were charged into a continuous hot-dip galvanizing line, annealed, galvanized, and after adjusting the plating amount, the plating layer was heated to form an Fe-Zn alloy. After cooling, temper rolling was performed in a temper rolling mill, and then a Zn-based oxide film with a target oxide thickness of 30 nm was formed in an electrolytic treatment facility.

[0031] The following treatment solution was used as the reference bath for the electrolytic treatment. Electrolytic treatment solution: CH3COONa·3H2O: 20~40g / l Fe 2+ : 0.0~1.0g / l FeSO4·7H2O: 0.0~1.0g / l Zn 2+ :15g / l or less Fe(OH)3: 3g / l or less Liquid temperature: 30-50℃ pH: 1.0~2.0 at 35℃ The lead coil and the coil under evaluation were manufactured in the same manufacturing lot, undergoing the annealing, liquid contact, and film formation processes. One lead coil and ten coils under evaluation were produced in that order, and each was manufactured in four different manufacturing lots. In other words, a total of four lead coils and 40 coils under evaluation were produced for each condition. In the comparative example, there was no lead coil. After the film forming treatment for each charged coil, the oxide film thickness of the alloyed hot-dip galvanized steel sheet was measured using an X-ray fluorescence analyzer. The measurement conditions are as shown in the embodiment. The manufacturing conditions were six different, No. 1 to 6, as shown in Table 1.

[0032] Examples No. 1 and No. 2 are examples where the leveling amount was fixed and the entire product was manufactured. Example No. 1 was manufactured at a low speed with the coil transport speed in the chemical contact process set to 100 mpm, while example No. 2 was manufactured at a high speed with the coil transport speed in the chemical contact process set to 130 mpm. For No. 3, the actual oxide film thickness was measured at two locations in the width direction (200 mm from the Op edge and 200 mm from the Dr edge) on a preceding coil of the same manufacturing lot. The difference between these measurements was divided by the average of the actual oxide film thicknesses to determine the deviation of the oxide film thickness. Based on this deviation of the actual oxide film thickness, the leveling amount was calculated based on a predetermined appropriate leveling amount (the change in the leveling amount relative to the leveling amount of the coil used to measure the actual oxide film thickness). This leveling amount was then reflected in the manufacturing conditions for leveling, and manufacturing was carried out. The actual oxide film thickness was measured for each coil, and the reflection of the measurement in the leveling conditions was applied to the latter half of the measured coil or to the next coil to be manufactured. Furthermore, the evaluation was conducted on the coil or a portion of the coil that reflected the leveling conditions.

[0033] Here, the appropriate leveling amount, which was predetermined based on the deviation of the actual oxide film thickness, was grouped according to the range of the deviation of the actual oxide film thickness (the difference divided by the mean value), as shown in Table 2, and an appropriate value was set for each group. (Table 2 is a supplementary explanation to item 1) described in Table 1.) In Examples 1, Nos. 3 and 4, as shown in Table 2, the groups consisted of four groups where the deviation of the actual oxide film thickness was A: less than -0.20, B: -0.20 to less than 0, C: 0 to less than +0.20, and D: +0.20 or more. From the correlation diagram between the deviation of the actual oxide film thickness and the leveling amount obtained in advance, the leveling amount for each group was set as A: -45 (×10 -2 (mm), B:-17 (×10 -2 mm), C: +17 (×10 -2 (mm), D: +45 (×10 -2 The leveling was set to (mm). The correction amounts for the deviation of the actual oxide film thickness due to each leveling (estimated values ​​from the prior correlation diagram) are A: +0.28, B: +0.10, C: -0.10, and D: -0.28. These values ​​were set so that the deviation of the actual oxide film thickness becomes zero after leveling for materials near the center of the oxide film thickness in each group. In Examples No. 3 and 4, the leveling amounts shown in Table 2 were selected based on the measurement results of the actual oxide film thickness and reflected in the leveling conditions. Example No. 4 is an example in which the coil transport speed was increased to 130 mpm.

[0034] In Nos. 5 and 6, the actual oxide film thickness of the lead coil was measured at three locations: Op150mm, center, and Dr150mm. The difference between the maximum and minimum values ​​was calculated, and this difference was divided by the average value of these actual oxide film thicknesses to obtain the deviation of the actual oxide film thickness. The relationship between the deviation of the actual oxide film thickness and the leveling amount in the width direction was investigated in advance, and a prediction formula representing the relationship of this data was obtained using machine learning. Based on this prediction formula, the coefficients in equation (2) were determined. The upper limit of the target oxide film thickness deviation in equation (2) was set so that the deviation of the actual oxide film thickness was +0.05 relative to the obtained prediction formula, and the lower limit of the target oxide film thickness deviation was set so that the deviation of the actual oxide film thickness was -0.05 relative to the obtained prediction formula. Based on the measurement results of the actual oxide film thickness of the lead coil, the leveling conditions for each coil were adjusted so that the leveling amount fell within this range. No. 6 is an example in which the coil transport speed was increased to 130 mpm.

[0035] Table 1 shows the presence or absence of leveling control implemented under each condition and the method used, the range of deviation in actual oxide film thickness for the preceding coil (minimum to maximum value), the coil transport speed, the number of coils manufactured (total of 4 manufacturing lots), the range of deviation in actual oxide film thickness for the manufactured coils (minimum to maximum value), and the defect rate, which is the ratio of coils whose actual oxide film thickness fell outside the target range (coil length outside the target range / total coil length). When the target oxide film thickness was 30 μm, the acceptable range for actual oxide film thickness was defined as follows: coils with an actual oxide film thickness in the range of 20 to 60 nm were accepted, and those outside this range were rejected. Actual oxide film thickness of the manufactured coils was measured at five locations along the length of the coil: the tip, 1 / 4 position, middle, 3 / 4 position, and tail end. The measurement width position for actual oxide film thickness was set at Op200 mm. The coil was divided into sections from tip to 1 / 4 position, 1 / 4 position to middle, middle to 3 / 4 position, and 3 / 4 position to tail end, and any section where at least one measurement result of the actual oxide film thickness at both ends fell below the acceptable value was rejected. The defect rate is the ratio of the length of the defective portion to the total length of the coil.

[0036] Table 1 shows that in the comparative example, a defect rate of 4% occurred even at a low conveying speed of 100 mpm, and the defect rate increased significantly when the conveying speed was increased to 130 mpm. This is because increasing the conveying speed makes it easier for thin film thicknesses to occur in certain areas.

[0037] In contrast, under the conditions of No. 3 and No. 4, which were manufactured using the present invention and based on the actual oxide film thickness deviation of the preceding coil, an appropriate leveling amount was set from the relationship between the actual oxide film thickness deviation and the leveling amount that was set in advance, and the deviation of the actual oxide film thickness (actual value) was reduced, and as a result, the defect rate of the coil was kept to 3% or less. In particular, in No. 4, even when the coil transport speed was increased to 130 mpm, the deviation of the actual oxide film thickness was kept small, and the defect rate was significantly reduced compared to the comparative example with a high transport speed.

[0038] Furthermore, by using machine learning to determine the relationship between the actual oxide film thickness deviation and the leveling amount, and by expressing the control range of leveling as a mathematical formula, the deviation in oxide film thickness (actual value) was further reduced in No. 5 and 6, and the defect rate was reduced to less than 2%.

[0039] Thus, by adopting the present invention, in addition to suppressing fluctuations in the longitudinal direction of the coil, which has been the conventional method, it is possible to suppress fluctuations in the width direction of the coil, and thus contribute to suppressing variations in oxide film thickness between coils.

[0040] Furthermore, it was confirmed that the above-mentioned defect rate can be reduced by calculating the predetermined leveling amount using data on the difference in the width direction of the actual oxide film thickness and controlling it to that predetermined leveling amount.

[0041] [Table 1]

[0042] [Table 2] [Explanation of symbols]

[0043] 1. Temper rolling 2 liquid contact process 3 Film formation process 4 Washing process 5. Oxide film thickness evaluation process 10 Leveling amount 11 Rolled material 12 Upper roll material 13 Lower roll material 14 Roll axis direction

Claims

1. After hot-dip galvanized steel sheet is temper-rolled, an acidic treatment solution is applied, A method for manufacturing a hot-dip galvanized steel sheet, comprising forming an oxide film on the surface of the hot-dip galvanized steel sheet, In the aforementioned temper rolling, Based on the amount of leveling in the width direction of temper rolling of the rolled material, which is set based on the actual oxide film thickness in the leading portion of the rolled material, the rolled material is leveled. The aforementioned leveling amount in the width direction is determined by first determining the change in oxide film thickness with respect to the leveling amount, calculating a leveling correction amount corresponding to the oxide film thickness correction amount using the relationship between the leveling amount and the change in oxide film thickness, and adding this correction amount to the actual leveling amount of the preceding portion. When leveling based on the leveling amount in the width direction of the temper rolling, the oxide film thickness is increased by making the rolling load on one side in the width direction greater than the rolling load on the other side. A method for manufacturing a hot-dip galvanized steel sheet, characterized in that the preceding portion of the rolled material is a preceding portion of the rolled material or a separate coil manufactured prior to the rolled material, and the separate coil is a coil manufactured in the same manufacturing lot in one or more of the cold rolling process, temper rolling process, liquid contact process, and film formation process.

2. A method for manufacturing a hot-dip galvanized steel sheet according to claim 1, characterized in that the amount of leveling in the width direction of temper rolling of the rolled material is set by the difference in the width direction of the actual oxide film thickness or by the deviation obtained by dividing the difference by the average of the actual oxide film thickness in the width direction.

3. The amount of leveling in the width direction of the temper rolling is, A method for manufacturing a hot-dip galvanized steel sheet according to claim 1 or 2, characterized in that it is calculated using a regression equation for obtaining a predetermined leveling amount, which is obtained based on information on the difference in the width direction of the actual oxide film thickness or the deviation obtained by dividing the difference by the average value of the actual oxide film thickness.

4. Equation (1) is composed of the difference, the lower limit target value of the difference, the upper limit target value of the difference, the actual value of the leveling amount in the width direction of the temper rolling, and the target value of the leveling amount in the width direction, or A method for manufacturing a hot-dip galvanized steel sheet according to claim 2, characterized in that a target value for the leveling amount in the width direction is determined and leveling is controlled using formula (2), which is composed of the aforementioned deviation, a lower limit target value for the deviation, an upper limit target value for the deviation, the actual value of the leveling amount in the width direction of the temper rolling, and a target value for the leveling amount in the width direction. α1×(Δs-Δsa1)≦(x-xa)≦α2×(Δs-Δsa2) ...Formula (1) α1: arbitrary constant, α2: arbitrary constant, Δs: difference, Δsa1: upper limit target value of Δs, Δsa2: lower limit target value of Δs, xa: actual value of leveling amount (×10) －２ mm), x: leveling amount (×10 －２ Target value (mm) α3×(Δt-Δta1)≦(x-xa)≦α4×(Δt-Δta2) ​​...Formula (2) α3: arbitrary constant, α4: arbitrary constant, Δt: deviation, Δta1: upper limit target value of Δt, Δta2: lower limit target value of Δt, xa: actual value of leveling amount (×10) －２ mm), x: leveling amount (×10 －２ Target value (mm)

5. Equation (1) comprising the difference, the lower limit target value of the difference, the upper limit target value of the difference, the actual value of the leveling amount in the width direction of the temper rolling, and the target value of the leveling amount in the width direction, or A method for manufacturing a hot-dip galvanized steel sheet according to claim 3, characterized in that a target value for the leveling amount in the width direction is determined and leveling is controlled using formula (2), which is composed of the aforementioned deviation, a lower limit target value for the deviation, an upper limit target value for the deviation, the actual value of the leveling amount in the width direction of the temper rolling, and a target value for the leveling amount in the width direction. α1×(Δs-Δsa1)≦(x-xa)≦α2×(Δs-Δsa2) ...Formula (1) α1: arbitrary constant, α2: arbitrary constant, Δs: difference, Δsa1: upper limit target value of Δs, Δsa2: lower limit target value of Δs, xa: actual leveling amount (×10⁻² mm), x: target value of leveling amount (×10⁻² mm) α3×(Δt-Δta1)≦(x-xa)≦α4×(Δt-Δta2) ​​...Formula (2) α3: arbitrary constant, α4: arbitrary constant, Δt: deviation, Δta1: upper limit target value of Δt, Δta2: lower limit target value of Δt, xa: actual leveling amount (×10⁻² mm), x: target value of leveling amount (×10⁻² mm)

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