JP2007216298A - Method of manufacturing steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a steel sheet by which the amount of deformation caused by residual stress or the like in the steel sheet after cutting can be predicted or the amount of deformation can be controlled within a prescribed tolerance when cutting the steel sheet by using a laser beam, gas, etc. in customers. <P>SOLUTION: The temperature distribution on the surface of the steel sheet 8 which is hot-straightened with a hot-straightening apparatus 5 is measured with a thermometer 7. Next, the distribution of the residual stress or the like is calculated from the temperature distribution of the steel sheet 8 with a deformation predicting computer 18 or the like and a prescribed parameter is calculated from the distribution of residual stress or the like. Furthermore, allowable values which are set in accordance with the working conditions or the like of the customers are compared with the parameter. When the parameter is out of tolerance, by performing straightening process by using a straightening apparatus 10, a heat-treating furnace 9 or the like, the residual stress or the like is reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a steel sheet that is controlled so that characteristics such as a residual stress distribution are within a predetermined range.

  In a general steel plate manufacturing method, for example, a slab is heated to about 1000 to 1200 ° C., and hot rolling (rough rolling and finish rolling) is performed until a predetermined dimension is reached. Furthermore, in the case of TMCP (Thermo-Mechanical Control Process) steel plate, accelerated cooling or direct quenching is performed, and then the steel plate is flattened by hot straightening and cut to a predetermined size by gas cutting, plasma cutting, laser cutting or shear cutting. Is done.

  Due to variations in various manufacturing conditions in each of the above steps, non-uniform residual stress is generated in the steel sheet. For example, cooling during water cooling due to uneven temperature during heating (heating unevenness), poor flatness during rolling (waves and warpage), thickness deviation, and uneven surface scale properties (scale components and thickness) Uneven cooling, uneven cooling during accelerated cooling and descaling (especially around the steel plate), zero point deviation and roll deflection during hot correction, non-uniform cooling during air cooling, residual stress and structural changes due to thermal effects during thermal cutting Causes include hardening, cutting distortion during shear cutting, zero point deviation and roll deflection during cold correction, and differences in surface properties during heat treatment (presence of care and shot blasting).

  Conventionally, characteristics such as residual strain, residual stress, displacement of a steel sheet or parameters calculated from these are controlled according to processing information in a customer, for example, processing conditions, processing methods, processing shapes, processing tolerances, and allowable values of processing accuracy. There was no method for manufacturing steel sheets.

  Therefore, when a conventional steel sheet having the residual stress is cut by a customer, the residual stress is released by the cutting, and the steel sheet is stretched, contracted, bent, warped, and the like. When the deformation of the steel sheet due to the release of the residual stress is large, the shape and size of the cut steel sheet may deviate from the allowable error range. As a result, there has been a problem that productivity at the time of cutting and assembling the steel sheet in the customer is lowered. In addition, the steel sheet must be designed in consideration of the deformation of the steel sheet and the variation of the deformation, and there is a problem that the design restrictions are large.

  The present invention has been made to solve the above-described problems of the conventional example, and an object of the present invention is to provide a method of manufacturing a steel sheet in which characteristics such as residual stress are controlled.

  In order to achieve the above object, the steel sheet manufacturing method according to claim 1 is a steel sheet manufacturing method in a steel sheet manufacturing apparatus provided with a rolling device for rolling a heated slab and a straightening device for correcting the rolled steel plate. A residual stress calculating step for obtaining a residual stress distribution of the steel sheet after rolling using the size information, material information and rolling condition information of the steel sheet, and a deformation amount after the cutting of the steel sheet in the customer using the residual stress distribution. A parameter calculation step for obtaining a parameter value for predicting the value, and whether or not the parameter value is a value satisfying a deformation allowable amount or less which is an upper limit value of a required accuracy with respect to a deformation amount after cutting of a steel plate in a consumer A deformation amount determining step for determining whether or not the parameter value is not a value satisfying the deformation allowable amount or less in the deformation amount determining step. It is characterized by having a correction condition change step of setting or changing the correction conditions of the straightening device to the value of the data to be equal to or less than the allowable deformation amount.

  According to the above invention, in the residual stress calculation step, the residual stress distribution of the steel plate after rolling is obtained using the size information, material information and rolling condition information of the steel plate, and in the parameter calculation step, the residual stress distribution is used. A parameter value for predicting the amount of deformation after cutting of the steel sheet by the customer is obtained. And in the deformation amount determination step, it is determined whether or not the value of this parameter is a value that satisfies the deformation allowable amount or less that is the upper limit value of the required accuracy for the deformation amount after cutting of the steel sheet in the consumer. When it is determined in the deformation amount determination step that the parameter value is not a value that satisfies the deformation allowable amount or less, in the correction condition changing step, the correction condition of the correction device is set so that the parameter value is equal to or less than the deformation allowable amount. Be changed.

  Therefore, using the steel plate size information, material information and rolling condition information, the parameter value calculated from the residual stress of the steel plate is corrected so as to be within a predetermined allowable range. It becomes possible to manufacture a steel plate whose deformation is within a predetermined range.

  The steel sheet manufacturing method according to claim 2, wherein the steel sheet manufacturing apparatus includes a heat treatment furnace for performing heat treatment on the rolled steel sheet, and the value of the parameter satisfies the deformation allowable amount or less in the deformation amount determining step. If it is determined that the heat treatment condition is not equal to or less than the allowable amount of deformation, the heat treatment condition change step of changing the heat treatment condition of the heat treatment furnace is further included.

  According to the above invention, when it is determined in the deformation amount determination step that the parameter value is not a value satisfying the deformation allowable amount or less, in the heat treatment condition changing step, the heat treatment condition of the heat treatment furnace provided in the steel sheet manufacturing apparatus. Is set or changed.

  Therefore, since the heat treatment is performed so that the value of the parameter calculated from the residual stress of the steel sheet is within a predetermined allowable range, it is possible to manufacture a steel sheet that has the deformation after cutting by the customer within the predetermined range. It becomes possible.

  The steel sheet manufacturing method according to claim 3, wherein the steel sheet manufacturing apparatus includes an accelerated cooling device that rapidly cools the rolled steel sheet, and the residual stress calculation step uses cooling condition information of the accelerated cooling device. It is characterized by obtaining the residual stress distribution of the steel sheet after rolling.

  According to said invention, in a residual stress calculation process, the residual stress distribution of the steel plate after rolling is calculated | required using the cooling condition information of an acceleration cooling device. Therefore, even when a heated and cooled steel sheet (for example, a TMCP steel sheet) is manufactured, the residual stress distribution of the steel sheet after rolling is obtained using the cooling condition information of the accelerated cooling device in the residual stress calculation step. It becomes possible to manufacture a steel sheet that has a deformation after cutting at home within a predetermined range.

  The steel sheet manufacturing method according to claim 4, wherein the steel sheet manufacturing apparatus includes a thermometer that measures the temperature of the steel sheet after rolling, and the residual stress calculation step is performed after rolling using temperature information from the thermometer. It is characterized by obtaining the residual stress distribution of the steel plate.

  According to said invention, in a residual stress calculation process, the residual stress distribution of the steel plate after rolling is calculated | required using the temperature information by the thermometer arrange | positioned at the steel plate manufacturing apparatus. Therefore, since the residual stress distribution of the steel sheet is obtained using the actually measured temperature of the steel sheet by the thermometer, the residual stress distribution can be obtained more accurately.

  The method for manufacturing a steel sheet according to claim 5 is characterized in that the parameter calculating step obtains the value of the parameter using a cutting condition of the steel sheet in a consumer.

  According to said invention, in the parameter calculation process, the value of the parameter for predicting the amount of deformation after cutting of the steel sheet in the consumer is obtained using the cutting conditions of the steel sheet in the consumer. Therefore, the accuracy of predicting the amount of deformation after cutting of the steel sheet by the customer is improved.

  The steel sheet manufacturing method according to claim 6 is characterized in that the straightening device is a roller leveler, and the straightening condition is a roller leveler mesh.

  According to said invention, the setting or change of the inter mesh of the roller leveler arrange | positioned in the steel plate manufacturing apparatus in a correction condition change process is performed, and a steel plate is corrected by the correction device. On the other hand, the roller mesh level mesh can be easily changed (using electric or hydraulic cylinders), so even when the proper mesh size differs depending on the longitudinal position of the steel sheet, the proper mesh mesh setting is possible. It is possible to perform appropriate correction over the entire length of the steel sheet.

  The method for manufacturing a steel sheet according to claim 7 is characterized in that the straightening device is a cold roller leveler that performs straightening in the cold.

  According to the above invention, since the correction device is a cold roller leveler that corrects in the cold, it is accompanied by a change in the temperature of the steel sheet after correction compared to the hot roller leveler that corrects in the hot state. There is little change in residual stress, and more appropriate correction is possible.

  The method for manufacturing a steel sheet according to claim 8 is characterized in that the parameter is a stress parameter η defined by the following equation.

  However, the area of the entire steel sheet is S, the area of the minute region is s, the longitudinal direction residual stress value or the width direction residual stress value of the steel plate in the minute region is σ, and all the regions of the part to be cut by the customer of the steel plate are Ω.

  According to the above invention, the parameter for predicting the deformation amount after cutting the steel sheet is the stress parameter η defined by the equation (1), and therefore can be easily calculated and the deformation In the amount determination step, using the value of the stress parameter η, it is determined whether or not the value satisfies a deformation allowable amount that is an upper limit value of the required accuracy with respect to the deformation amount after cutting of the steel sheet in the customer. This determination is made accurately.

The method for manufacturing a steel sheet according to claim 9, wherein the allowable deformation amount is 1.5 mm per 10,000 mm in length, and the straightening condition changing step includes an absolute value of the stress parameter η of 0.3 kg / The correction condition is set or changed so as to be equal to or less than mm ² .

According to the above invention, the absolute value of the stress parameter η is 0 in the straightening condition changing step for a steel sheet satisfying “1.5 mm per 10,000 mm length”, which is required as a deformation allowance from customers in recent years. It is possible to manufacture by setting or changing the correction condition so that it becomes ³ kg / mm ² or less.

  As described above, according to the steel sheet of the present invention, the characteristics of the steel sheet, for example, the residual strain of the steel sheet, the residual, depending on the processing information in the customer, for example, the processing conditions, the processing method, the processing shape, and the tolerance of the processing accuracy. Since the maximum value, minimum value, average value, sum, deviation, absolute value or distribution of stress, displacement or deformation amount, or the parameter value calculated from these values is controlled to be within a predetermined allowable range, It becomes possible to predict the deformation after the cutting process in the consumer.

(First embodiment)
1st Embodiment regarding the steel plate of this invention, a steel plate manufacturing apparatus, and a steel plate manufacturing method is described. In the first embodiment, the value of the stress parameter η is obtained by calculation from the residual stress distribution of the steel sheet, and control is performed so that the value of the stress parameter η is within a predetermined range.

  The structure of the steel plate manufacturing apparatus in 1st Embodiment is shown in FIG. First, the slab is heated to about 1000 to 1200 ° C. by the heating furnace 1 and rough rolling is performed by the first rolling device 2 until the plate thickness becomes the first predetermined dimension. Next, it is cooled by the cooling device 3 to, for example, about 800 to 1100 ° C. in the case of a 40 kg steel plate and about 700 to 1100 ° C. in the case of a TMCP steel plate, and finish-rolled until the plate thickness reaches the second predetermined dimension by the second rolling device 4. I do. Further, after rapid cooling to about 400 to 650 ° C. by the accelerated cooling device 5, the shape of the steel plate is flattened by the hot straightening device 6.

  On the upper part of the hot straightening device 6, a pulse generator (hereinafter referred to as PLG (Pulse Length Generator)) 11 that detects the tip of the steel plate being conveyed and generates a pulse signal at a constant interval is provided. . By counting the pulse signal from the PLG 11 and multiplying the counted number of pulses by a certain length (the amount of movement of the steel plate during the generation of one pulse), the current position from the tip of the steel plate can be determined.

  Further, a thermometer 7 such as a thermoviewer or a scanning type radiation thermometer is provided on the downstream side of the hot straightening device 6. By fixing the distance between the PLG 11 and the thermometer 7 and keeping the conveyance speed of the steel plate 8 constant, the temperature distribution on the surface of the hot-steeled steel plate 8 can be measured.

  The temperature measurement data by the thermometer 7 and the position information in the longitudinal direction of the steel sheet by the PLG 11 are transferred to the server computer 15 via the digital direct controller (hereinafter referred to as DDC) 12 and the process computer 13, respectively.

  On the other hand, information such as the rolling size, product size, product sampling position, strip cutting width, and steel plate grade of the steel plate 8 is input from the host computer 19 and transferred to the server computer 15 via the line computer 14 and the process computer 13. These pieces of information are transferred from the server computer 15 to a camber (lateral bending) prediction computer 16, a buckling prediction computer 17, and a deformation prediction computer 18.

  The camber prediction computer 16 calculates the residual stress distribution of the steel plate 8 by using the temperature measurement data and the position information, for example, by the calculation method described in Japanese Patent Publication No. 4-8128 by the present applicant. The calculated residual stress distribution data is transferred to the buckling prediction computer 17 and the deformation prediction computer 18 via the server computer 15. These computers 16 to 18 calculate the predicted camber value after buckling, the predicted buckling value, and the predicted deformation value at the time of cutting. The details of the calculation method of the camber prediction value and the buckling prediction value are described in, for example, Japanese Patent Laid-Open No. 10-56500 filed by the present applicant, and are omitted here.

  As an example of the deformation prediction value at the time of cutting, the characteristics of the steel sheet (residual stress distribution etc.) are calculated by the deformation prediction computer 18 based on the steel plate size, material, calculated value of residual stress distribution, cutting shape and cutting method at the customer, etc. ) Is calculated, and it is determined whether or not the parameter is within a predetermined allowable range.

  Examples of parameters in a broad sense include residual stress and residual strain of the steel sheet itself, and maximum values, minimum values, average values, sums, deviations, absolute values, distributions, and the like of displacement and deformation amounts when the steel sheet is cut. Further, as parameters in a narrow sense, a stress parameter η obtained by calculation from a residual stress distribution, a deformation parameter δ obtained by calculation from a displacement or a deformation amount, a strain parameter γ obtained by calculation from a residual strain distribution, and the like can be considered.

  In the first embodiment, a stress parameter η represented by the following equation (1) is calculated as a parameter. However, the area of the entire steel sheet is S, the area of the minute region is s, the longitudinal direction residual stress value or the width direction residual stress value in the minute region is σ, and the corrected total cutting region is Ω.

Between the stress parameter η and the allowable value η _c (q) determined by the customer's required accuracy q, the minimum allowable value is η _c ^min (q) and the maximum allowable value is η _c ^max (q), η _c ^min (q) ≦ η ≦ η _c ^max (q) holds.

  When the stress parameter η is calculated, the deformation prediction computer 18 compares the size with an upper limit value and a lower limit value of an allowable range determined in advance according to the customer and use transferred from the host computer 19. As a result of the comparison, when the stress parameter η is not within the allowable range, a straightening condition for reducing the residual stress of the steel plate 8 is set by the straightening device (roller leveler) 10 or the heat treatment furnace 9. Note that the residual stress reduction effect of correction by the roller leveler is described in, for example, Japanese Patent Application Laid-Open No. 9-57348 filed by the present applicant. The setting of correction conditions will be described later.

  Normally, correction (cold correction) is performed by adjusting the intermesh of the correction device (roller leveler) 10 according to the set correction conditions. Further, when the stress parameter η calculated from the residual stress distribution of the steel sheet when it is assumed that the correction is performed under the maximum correction condition determined from the ability of the correction device 10 exceeds the allowable value, the calculation is performed from the residual stress distribution after the heat treatment. The necessary minimum heat treatment conditions (heat treatment temperature and time) satisfying the allowable stress parameter η are set, the residual stress is reduced using the heat treatment furnace 9 as pretreatment for correction, and then the correction by the correction device 10 is performed. I do. The reduction of residual stress by heat treatment is described in, for example, Japanese Patent Application Laid-Open No. 9-78145 filed by the present applicant.

  Note that when setting the heat treatment conditions, the material such as strength and yield stress of the steel sheet changes due to the heat treatment, so it is necessary to determine in advance whether or not heat treatment is possible in consideration of the material change. In the steel plate manufacturing apparatus of the present embodiment, a table of creep coefficient and heat treatment availability according to the grade of the steel plate is provided in the memory or the like of the deformation prediction computer 18. The deformation prediction computer 18 assigns the following correction codes to the respective steel plates 8. For example, when the stress parameter η is equal to or less than a predetermined value, correction is not necessary, and therefore a correction code K = 0 indicating a pass is assigned. Further, in the case of light pressure correction by the correction device 10, the correction code K = 1 is given. Similarly, in the case of correction under medium pressure, the correction code K = 2 is given. In the case of correction under strong pressure, the correction code K = 3 is given. Further, when the heat treatment is performed, the correction code K = 4 is given. Further, when there is no possibility that the stress parameter η is less than or equal to a predetermined value even by correction or heat treatment, a correction code K = 5 indicating a defect is assigned.

  Calculation results and determination results (stress parameters, correction codes) by the deformation prediction computer 18 are transferred to the server computer 15 and stored. Furthermore, it is also transferred to the host process computer 13 and line computer 14. The line computer 14 determines the next process based on the correction code. For example, when the correction code K = 0, the product is shipped without correction and heat treatment. On the other hand, when the correction code K = 1 to 3, the steel plate 8 is conveyed to the correction device 10 and correction is performed according to the set correction code. Further, when the correction code K = 4, the steel plate 8 is first transported to the heat treatment furnace 9 and subjected to heat treatment, and then the steel plate 8 is further transported to the correction device 10 and correction is performed under high pressure. When the correction code K = 5, it is removed from the manufacturing process.

  In parallel with this, the line computer 14 transfers the correction and heat treatment conditions (the calculation correction condition and the calculation heat treatment condition) of the steel plate 8 to the correction device 10 and the heat treatment furnace 9, respectively. The straightening device 10 and the heat treatment furnace 9 perform straightening and heat treatment according to the conditions from the line computer 14, and transfer the executed straightening and heat treatment conditions (actual correction conditions and actual heat treatment conditions) to the line computer 14.

  The deformation prediction value (for example, the value of the stress parameter η), correction code, heat treatment code, calculation correction condition, calculation heat treatment condition, actual correction condition, actual heat treatment condition, flatness measurement result, etc. are transferred from the line computer 14 to the host computer 19. And stored in the quality analysis system. In this way, the residual stress distribution of the steel plate 8 is controlled within a certain range, and it is ensured that the deformation at the time of cutting by the customer is within the allowable range.

Next, the correction condition setting program by the deformation prediction computer 18 will be described with reference to the flowcharts shown in FIGS. When the setting of the correction condition is started, the camber prediction computer 16 calculates the residual stress of the steel sheet using the temperature measurement data and the position information (Step # 100). The calculated residual stress data is transferred to the deformation prediction computer 18, and the initial value η ₀ of the stress parameter η is calculated using this (step # 105). Further, the deformation prediction computer 18 determines whether or not the calculated stress parameter η ₀ is within a predetermined range (between η _min and η _max ) (step # 110).

When the stress parameter η ₀ is within a predetermined range (η _min ≦ η ₀ ≦ η _max : YES in step # 110), the steel sheet 8 has a sufficiently small residual stress and does not need to be corrected. Therefore, the deformation prediction computer 18 sets the correction code K = 0 and the stress parameter η = η ₀ (step # 115).

On the other hand, when the stress parameter η ₀ is not within the predetermined range (η ₀ <η _min or η _max <η ₀ : NO in step # 110), the steel sheet 8 has a large residual stress and requires a correction process. Therefore, the deformation prediction computer 18 calculates the residual stress when it is assumed that the correction is performed under the correction condition 1, that is, under the light pressure condition by the correction device 10 (step # 120). Further, the deformation prediction computer 18 calculates the stress parameter η ₁ using the corrected residual stress (step # 125), and the calculated stress parameter η ₁ is within a predetermined range (between η _min and η _max ). (Step # 130).

When the stress parameter η ₁ is within a predetermined range (η _min ≦ η ₁ ≦ η _max : YES in step # 130), the steel sheet 8 is reduced by the correction condition 1 to reduce the residual stress within the predetermined range. Is possible. Therefore, the deformation prediction computer 18 sets the correction code K = 1 and the stress parameter η = η ₁ (step # 135).

When the stress parameter η ₁ is not within the predetermined range (η ₁ <η _min or η _max <η ₁ : NO in step # 130), the steel sheet 8 still has a large residual stress even when corrected under the correction condition 1, It requires a more powerful correction process. Therefore, the deformation prediction computer 18 calculates the residual stress when it is assumed that correction is performed under the correction condition 2, that is, under the medium pressure condition by the correction device 10 (step # 140). Further, the deformation prediction computer 18 calculates the stress parameter η ₂ using the corrected residual stress (step # 145), and the calculated stress parameter η ₂ is within a predetermined range (between η _min and η _max ). Is determined (step # 150).

When the stress parameter η ₂ is within a predetermined range (η _min ≦ η ₂ ≦ η _max : YES at step # 150), the steel sheet 8 is reduced by the correction condition 2 to reduce the residual stress within the predetermined range. Is possible. Therefore, the deformation prediction computer 18 sets the correction code K = 2 and the stress parameter η = η ₂ (step # 155).

When the stress parameter η ₂ is not within the predetermined range (η ₂ <η _min or η _max <η ₂ : NO in step # 150), the steel sheet 8 still has a large residual stress even when corrected under the correction condition 2, It is necessary to perform the correction process by maximizing the ability of the correction apparatus 10. Therefore, the deformation prediction computer 18 calculates a residual stress when it is assumed that correction is performed under the correction condition 3, that is, under the condition of high pressure by the correction apparatus 10 (step # 160). Further, the deformation prediction computer 18 calculates the stress parameter η ₃ using the residual stress after correction (step # 165), and the calculated stress parameter η ₃ is within a predetermined range (between η _min and η _max ). Is determined (step # 170).

When the stress parameter η ₃ is within a predetermined range (η _min ≦ η ₃ ≦ η _max : YES at step # 170), the steel sheet 8 is reduced by the correction condition 3 to reduce the residual stress within the predetermined range. Is possible. Therefore, the deformation prediction computer 18 sets the correction code K = 3 and the stress parameter η = η ₃ (step # 175).

When the stress parameter η ₃ is not within the predetermined range (η ₃ <η _min or η _max <η ₃ : NO in step # 170), the residual stress of the steel plate 8 is large, and the ability of the straightening device 10 is maximized. Even the correction is inadequate.

  As described above, the possibility of heat treatment is determined in advance in consideration of the material change of the steel plate 8. Therefore, the deformation prediction computer 18 searches a table indicating whether the steel plate 8 is heat-treatable, and determines whether or not the steel plate 8 is heat-treatable (step # 180).

If the steel plate 8 cannot be heat treated (NO in step # 180), even if the steel plate 8 has the ability of the straightening device 10, the residual stress cannot be reduced within a predetermined range. Then, the correction code K = 5 representing the defective product and the stress parameter η = η ₃ are set (step # 185).

When the steel plate 8 can be heat-treated (YES in Step # 180), the deformation prediction computer 18 further performs the correction under the high pressure condition by the correction condition 3, that is, the correction device 10, after the heat treatment in the heat treatment furnace 9. The assumed residual stress is calculated (step # 190). Further, the deformation prediction computer 18 calculates the stress parameter η ₄ using the corrected residual stress (step # 195), and the calculated stress parameter η ₄ is within a predetermined range (between η _min and η _max ). Is determined (step # 200).

When the stress parameter η ₄ is not within the predetermined range (η ₄ <η _min or η _max <η ₄ : NO in step # 200), the residual stress of the steel plate 8 is large, heat treatment is performed in the heat treatment furnace 9, and Even if the ability of the correction device 10 is maximized, correction is insufficient. Therefore, the deformation prediction computer 18 sets a correction code K = 5 and a stress parameter η = η ₄ representing a defective product (step # 205).

When the stress parameter η ₄ is within a predetermined range (η _min ≦ η ₄ ≦ η _max : YES in step # 200), the steel sheet 8 is subjected to the correction under the correction condition 3 after the heat treatment, so that the residual stress is within the predetermined range. Can be reduced within. Therefore, the deformation prediction computer 18 sets a correction code K = 4 and a stress parameter η = η ₄ representing heat treatment (step # 210), and ends the correction condition setting program.

  Next, the evaluation method of the steel plate manufactured with the said steel plate manufacturing apparatus or the steel plate manufacturing method is demonstrated.

  In the steel plate manufactured by the conventional steel plate manufacturing method, the residual stress distribution is not controlled and is not measured. Therefore, when the steel sheet has a large residual stress, if the customer cuts the steel sheet, the steel sheet may extend beyond the allowable value, contract, lateral bending, or warp may occur.

Accordingly, the present inventors have conducted extensive research on the residual stress and residual strain of the steel sheet in order to develop a steel sheet with less deformation during the cutting process. In the process, it was found that the amount of deformation after cutting of the steel sheet can be predicted by controlling the value of the stress parameter η represented by the above formula (1). Results of finite element method (hereinafter referred to as FEM: Finite Element Method) analysis of various steel plate sizes, residual stress distributions, and cut shapes, and the relationship between the deformation of the steel plate after cutting and the stress parameter η Is shown in FIG. In FIG. 4, the horizontal axis represents the value of the stress parameter η (unit: kg / mm ² ), and the vertical axis represents the deformation amount (unit: mm / mm, that is, dimensionless) per predetermined length.

  Thus, if cutting information such as the cutting shape, cutting method, cutting size, cutting position in the entire steel sheet is given in advance, the residual stress distribution and cutting information of the steel sheet can be used for cutting without actually cutting the steel sheet. Can be predicted. Further, by controlling the stress parameter η, the deformation amount can be controlled within a target allowable value.

In recent years, a demand for deformation at the time of cutting a steel sheet has become stricter, and a steel sheet having a deformation such as contraction or extension of the steel sheet at the time of cutting of 1.5 mm or less per 10,000 mm is required. In order to satisfy this requirement, the absolute value of the stress parameter η is preferably controlled to 0.3 kg / mm ² or less from FIG.

  In addition, the correction | amendment cutting | disconnection area | region (omega | ohm) in said Formula (1) means all the area | regions of the site | part cut | disconnected. In addition, when the shape of the cutting region is T-shaped as shown in FIG. 5A, the material left around the vertical line portion of the T-shape does not contribute to bending and contraction (pull) after deformation. It can be considered that the shape of the cutting region shown in FIG.

  The residual stress value σ in the above formula (1) is an average value in the sheet thickness direction (an average value of values measured or analyzed at a plurality of positions in the sheet thickness direction). However, it is very complicated and difficult to actually measure or analyze the residual stress values at a plurality of positions in the thickness direction of the steel sheet. Therefore, if the residual stress value on the surface of the steel sheet can be measured and corrected to the average value in the thickness direction, the measurement or analysis of the residual stress value becomes simple and easy.

  In general, the residual stress value on the steel sheet surface does not necessarily match the average value in the sheet thickness direction, and varies greatly depending on the sheet thickness, grade, manufacturing method, and the like of the steel sheet. FIG. 6 shows the distribution of the longitudinal residual stress in the plate thickness direction for a steel plate having an average value of the longitudinal residual stress in the plate thickness direction of zero. Details of this steel sheet are shown in Table 1.

In FIG. 6, the horizontal axis represents the position of the measurement point in the plate thickness direction (ratio to the whole: the unit is dimensionless), and the vertical axis represents the longitudinal residual stress value (unit kg / mm ² ) of the steel plate at each measurement point. To express. As apparent from FIG. 6, the residual stress value is compression on the front and back surfaces of the steel sheet, and is greatly deviated from the average value. Further, in the vicinity of the central portion of the steel sheet in the thickness direction, the residual stress value is tensile and deviates greatly from the average value. On the other hand, in the vicinity of the position of ¼ of the plate thickness from the front or back surface in the plate thickness direction of the steel plate, the residual stress value is relatively close to the average value. That is, the residual stress value on the steel sheet surface does not coincide with the average value in the thickness direction. Therefore, it is preferable to perform conversion or correction according to the plate thickness, grade, or manufacturing method so that the residual stress on the surface of the steel plate is substantially equal to the average value in the plate thickness direction.

Next, FIG. 7 shows the relationship between the plate thickness and the longitudinal residual stress on the surface of the steel plate with respect to the steel plate having an average value in the plate thickness direction of the longitudinal direction residual stress (40 kg / mm ² steel plate as rolled). In FIG. 7, the horizontal axis represents the plate thickness (unit: mm) of each steel plate as a sample, and the vertical axis represents the residual stress value (unit: kg / mm ² ) on the surface of the steel plate. As is apparent from FIG. 7, as the plate thickness increases, the absolute value of the residual stress on the steel plate surface increases. Therefore, the average value in the plate thickness direction can be corrected by subtracting the value obtained from FIG. 7 according to the plate thickness from the measured value of the residual stress on the steel plate surface.

Further, FIG. 8 shows the relationship between the correction value of the surface residual stress according to the plate thickness, the manufacturing method, and the grade of the steel plate. In FIG. 8, the horizontal axis represents the thickness (unit: mm) of each steel plate as a sample, and the vertical axis represents the correction value (unit: kg / mm ² ) of the residual stress on the surface of the steel plate. In the figure, “▲” represents the value of the rolled steel sheet, “●” represents the value of the accelerated cooling steel sheet, and “♦” represents the value of the heat treated and / or straightened steel sheet. As is clear from FIG. 8, the high-grade steel plate subjected to heat treatment and straightening has a smaller change in the residual stress in the plate thickness direction than the rolled steel plate and the accelerated cooled steel plate, and the correction value due to the plate thickness is The change is small. Further, the change in the residual stress in the thickness direction varies depending on the manufacturing method, such as a rolled steel plate and an accelerated cooled steel plate. Therefore, it is preferable to perform correction from the surface residual stress measurement value to the average value in the plate thickness direction using different correction values depending on conditions such as the manufacturing method and grade of the steel plates.

  Next, the measurement time point of the temperature distribution on the surface of the steel sheet will be examined. In the steel plate manufacturing apparatus shown in FIG. 1, the temperature distribution on the surface of the steel plate 8 is measured by the thermometer 7 after the hot straightening by the hot straightening device 6, but is not limited to this. The measurement may be performed after rolling by the second rolling device 4 or after accelerated cooling by the accelerated cooling device 5, but considering the necessity of correction of the measured value, measurement after hot correction is desirable.

  Longitudinal residual after cooling by FEM analysis on steel plate (product length is 20 m) with temperature distribution (temperature distribution in the longitudinal direction is uniform) near the edge in the width direction The stress was calculated, and the change in the residual stress distribution was analyzed when test pieces of various sizes (for example, 3 m and 8 m in length) were cut from the steel plate. The details of the steel sheet are shown in Table 2. Moreover, the longitudinal direction residual stress distribution measured in the vicinity of the center position in the longitudinal direction of the test piece and at a plurality of positions in the width direction is shown in FIG.

In FIG. 9, the horizontal axis represents the position of the measurement point in the width direction of the steel sheet (position relative to the width of 3000 mm: unit mm), and the vertical axis represents the value of the residual stress in the longitudinal direction of the steel sheet at each measurement point (unit kg / mm). ² ). As is clear from FIG. 9, it can be seen that the restraint state of the steel sheet differs depending on the test piece length, and the distribution of the residual stress in the longitudinal direction changes. That is, when attention is paid to a test piece having a length of 3 m, the residual stress in the longitudinal direction of the cut test piece changes even though the residual stress distribution is the same before cutting. In addition, the value of the residual stress increases near the side of the steel plate, and the value of the residual stress decreases near the center of the steel plate. On the other hand, in the case of a test piece having a length of 8 m, the longitudinal residual stress distribution almost coincides with that of the product before cutting (length: 20 mm). Therefore, when the length of the test piece is short, it is necessary to calculate the stress parameter η by correcting the measured residual stress value to the length processed by the customer. On the contrary, it can be seen that by cutting the test piece to be at least 8 m long, it is not affected by the length of the test piece.

  From the above, when the test piece is short, it is necessary to correct the measured residual stress. The relationship between the specimen length and the residual stress correction coefficient is shown in FIG. 10, the horizontal axis represents the length (unit m) of a test piece obtained by cutting a steel plate (for example, a product having a length of 20 m), and the vertical axis represents a correction coefficient. In addition, “▲” represents a correction coefficient (unitless dimension) of the residual stress in the vicinity of the central portion in the width direction of the steel plate, and “●” represents a correction value of the residual stress in the vicinity of the end portion in the width direction of the steel plate. . The correction coefficient is the ratio (ratio) of the residual stress value at the same position in the width direction of the test piece after cutting to the residual stress value at a predetermined position from the center and end in the width direction of the steel sheet before cutting. It is. As is apparent from FIGS. 9 and 10, when the test piece length is short, correction is required at any position near the end in the width direction and near the center in the width direction, and the correction amount is different. Therefore, it is preferable to correct the residual stress by multiplying the reciprocal of the correction coefficient obtained from FIG. 10 according to the length of the test piece.

  As is well known, a steel sheet may be deformed by a cutting method at the time of cutting. For example, in thermal cutting such as gas cutting, plasma cutting, and laser cutting, the deformation amount of the steel sheet varies depending on heat input during cutting. FIG. 11 shows the result of analysis by thermoelastic-plastic FEM of the difference in deformation amount depending on the cutting method when a steel plate having a thickness of 16 mm is cut. In FIG. 11, the horizontal axis represents the cutting method, and the vertical axis represents the amount of contraction (unit: mm) during cutting. Note that FIG. 11 also shows the case of shear cutting.

As is clear from FIG. 11, the amount of heat input by cutting differs depending on the cutting method, and the amount of deformation after cutting differs, so that the stress parameter of the steel sheet depends on the cutting method and the cutting heat input so that the amount of deformation falls within the allowable range. It is preferable to correct η. The correction value of the stress parameter η is shown in FIG. In FIG. 12, the horizontal axis represents the cutting method, and the vertical axis represents the correction value (unit kg / mm ² ) of the stress parameter η. Specifically, the correction value obtained from FIG. 12 is subtracted from the value of the stress parameter η according to the cutting method for correction. Note that this correction value is a value when the steel plate is cut into the shape shown in FIG. 13, for example, but the correction value varies depending on the cutting shape and thickness, so several levels are prepared according to the cutting shape and thickness. It is preferable to keep it.

  As described above, according to the first embodiment, the amount of deformation due to the residual stress after processing is set to a predetermined allowable value according to the processing information in the customer, for example, the processing condition, the processing method, the processing shape, or the allowable value of processing accuracy. A steel sheet in which the residual stress distribution in the unprocessed state is controlled so as to be less than or equal to the value is obtained.

  Further, the residual stress value or residual stress distribution on the surface of the steel sheet is calculated from the temperature distribution on the surface of the steel sheet, the value of the stress parameter η is calculated from the residual stress, and whether or not the value of the stress parameter η is within a predetermined range. By judging, it is possible to predict the deformation amount of the steel sheet after the cutting process without actually cutting the steel sheet.

  Further, by converting or correcting the value of the residual stress obtained by measuring the surface of the steel plate to the average value in the thickness direction, the measurement or analysis of the residual stress becomes easy. Furthermore, by correcting according to the plate thickness, grade, and manufacturing method of the steel plate, it is possible to more accurately determine the average value in the plate thickness direction converted or corrected from the residual stress on the surface of the steel plate. Furthermore, by correcting the residual stress value according to the measurement position in the width direction of the steel sheet, it becomes possible to determine the average value of the residual stress in the sheet thickness direction more accurately even when the measurement data is small. . Furthermore, by correcting the value of the residual stress according to the size of the test piece cut from the steel plate (product), it is possible to obtain the average value of the residual stress in the plate thickness direction more accurately even from a small test piece. It becomes. Alternatively, by setting the test piece to a certain size or more (for example, a length of 8 m or more), it is possible to eliminate the change in the residual stress value due to the size of the test piece and the measurement position, and correction is unnecessary.

(Second Embodiment)
Next, 2nd Embodiment regarding the steel plate of this invention, a steel plate manufacturing method, and a steel plate manufacturing apparatus is described. The second embodiment is basically the same as the case of the first embodiment, and is controlled so that the residual stress value is within a predetermined range instead of the stress parameter η.

Between the residual stress value σ and the allowable value σ _c (q) determined by the customer's required accuracy q, the maximum value of the residual stress is σ ^max , the minimum value of the residual stress is σ ^min , and the upper limit of the allowable value is sigma _c ^max, the lower limit of the sigma _c ^min tolerances, the tolerance of the plate in the deviation of the residual stress value as ^{_{σ c dev, σ c min (}} q) ≦ σ ≦ σ c max (q) and sigma ^max - [sigma] ^min ≦ σ _c ^dev (q) At least one of the relationships is established.

  The deformation prediction computer 18 in FIG. 1 performs control so that the maximum value, minimum value, average value, sum, deviation, absolute value, or distribution of residual stress is within a predetermined range. Other parts not specifically described are the same as those in the first embodiment.

Similar to the stress parameter η, the residual stress value itself affects the deformation during cutting. FIG. 14 shows the result of the elastic analysis of the relationship between the residual stress value of the steel sheet and the deformation at the time of cutting. In FIG. 14, the horizontal axis represents the absolute value (unit kg / mm ² ) of the residual stress value in the longitudinal direction of the steel sheet, and the vertical axis represents the absolute value (unit mm / mm) of the deformation after cutting the steel sheet of a predetermined length. That is, dimensionless).

  The residual stress value here is an average value of the residual stress in the longitudinal direction in a substantially square region of 100 mm × 100 mm. The cutting conditions were analyzed assuming that the absolute value of the deformation at the time of cutting the steel sheet was maximized. When the absolute value of the residual stress value increases, the absolute value of deformation when the steel sheet is cut also increases, so it is necessary to control the residual stress value so that the amount of deformation becomes the target value.

As is apparent from FIG. 14, generally, the absolute value of the residual stress value may be about 4 kg / mm ² or less. In particular, when the absolute value of deformation after cutting is 1.5 mm or less per 10,000 mm in length, the absolute value of the residual stress value is preferably 3.14 kg / mm ² or less.

FIG. 15 shows the relationship between the residual stress deviation (maximum value-minimum value) in an arbitrary 100 mm × 100 mm square region and the deformation after cutting for steel sheets having various sizes and residual stress distributions. In consideration of the average value in the plate thickness direction, the deviation of the residual stress value in the plate surface is preferably regulated to 11 kg / mm ² or less, more preferably 10.5 kg / mm ² or less.

Further, as in the first embodiment, the absolute value, the maximum value, the minimum value, the average value, the deviation, etc. of the residual stress value can be corrected according to the plate thickness, grade, cutting method, etc. of the steel plate. preferable. FIG. 16 shows a correction value of the residual stress value according to the cutting method. In FIG. 16, the horizontal axis represents the cutting method, and the vertical axis represents the correction value (unit kg / mm ² ) of the residual stress value. Specifically, the correction is performed by subtracting the correction value obtained from FIG. 12 according to the cutting method from the residual stress value. This correction value is also a value when the steel plate is cut into the shape shown in FIG. 13, for example, and it is preferable to prepare several levels according to the cutting shape.

(Third embodiment)
Next, 3rd Embodiment regarding the steel plate of this invention, a steel plate manufacturing method, and a steel plate manufacturing apparatus is described. The third embodiment is basically the same as the case of the first or second embodiment described above, and instead of the stress parameter η, the shape of the cut portion of the steel plate and the longitudinal displacement or longitudinal deformation amount of the steel plate. Is controlled so that the value of the deformation parameter δ obtained from the above is within a predetermined range. The deformation prediction computer 18 in FIG. 1 performs control so that the value of the deformation parameter δ represented by the following equation (2) falls within a predetermined range. Other parts not specifically described are the same as those in the first or second embodiment.

  However, the area of the entire steel sheet is S, the longitudinal displacement in the minute region, the longitudinal deformation, the lateral displacement or the lateral deformation is Δ, and the corrected total cutting region is Ω.

Between the deformation parameter δ and the allowable value δ _c (q) determined by the required accuracy q of the customer, the minimum allowable value is δ _c ^min (q) and the maximum allowable value is δ _c ^max (q), The relationship of δ _c ^min (q) ≦ δ ≦ δ _c ^max (q) is established.

  As in the case of the first embodiment, FEM analysis is performed on steel plates having various steel plate sizes, residual stress distributions, and cut shapes, and the relationship between the deformation amount of the steel plate after cutting and the deformation parameter δ is calculated. 17 shows. In FIG. 17, the horizontal axis represents the value of the deformation parameter δ (unit dimensionless), and the vertical axis represents the deformation amount per unit length (unit mm / mm, ie dimensionless). By controlling the value of the deformation parameter δ, the amount of deformation after cutting the steel sheet can be predicted.

  As is clear from FIG. 17, since the deformation amount such as shrinkage and elongation of the steel sheet during cutting satisfies the requirement of 1.5 mm or less per 10,000 mm length, the absolute value of the deformation parameter δ is set to 1.6. It is preferable to control to the following.

  As a method of actually obtaining the deformation parameter δ, as in the case of the first embodiment, the longitudinal residual stress is calculated from the steel plate surface temperature distribution after accelerated cooling, and the processing information and the residual stress at the consumer are used. The deformation parameter δ is calculated.

  In the steel plate manufacturing apparatus shown in FIG. 1, the PLG 11 or the like is used to inspect all the steel plates being manufactured. In the present embodiment, the manufactured steel plates are extracted, and the test pieces are cut and inspected. Regarding the measurement of the amount of deformation of the cut part at the time of cutting, it is necessary to have a measurement accuracy of 0.1 mm unit displacement or deformation amount Δ for a steel plate having a length of 10,000 mm, and advanced technology is required for the measurement It is. Therefore, in this embodiment, a jig was attached to the back surface of the steel plate with a magnet, and the relative displacement was measured by an eddy current meter attached to the table. In addition, three CCD cameras (replaceable with a digital camera or a video camera) were prepared, the steel plate longitudinal method top, middle and bottom targets were measured, and the displacement was calculated by image processing. In addition, the displacement or deformation amount may be measured using a laser distance meter, an encoder, or the like.

  FIG. 18 shows a correction value of the deformation parameter δ for correcting the difference in deformation amount depending on the cutting method. In FIG. 18, the horizontal axis represents the cutting method, and the vertical axis represents the correction value (unitless dimension) of the deformation parameter δ. Specifically, the correction value obtained from FIG. 18 is subtracted from the value of the deformation parameter δ in accordance with the cutting method for correction. In addition, although this correction value is a value when cutting a steel plate into the shape shown in FIG. 13, for example, since the correction value differs depending on the cutting shape, it is preferable to prepare several levels according to the cutting shape.

(Fourth embodiment)
Next, a fourth embodiment relating to a steel plate, a steel plate manufacturing method, and a steel plate manufacturing apparatus according to the present invention will be described. The fourth embodiment is basically the same as the first to third embodiments, and is controlled so that the deformation strain value is within a predetermined range instead of the deformation parameter δ. The deformation prediction computer 18 in FIG. 1 performs control so that the maximum value, minimum value, average value, sum, deviation, absolute value, or distribution of deformation distortion falls within a predetermined range. Other parts not specifically described are the same as those in the first to third embodiments.

Between the distortion value Δε of the cutting site and the allowable value Δ _c ε (q) determined by the customer's required accuracy q, the minimum allowable value is Δ _c ε ^-min (q), and the maximum allowable value is Δ _c As ε ^−max (q), the relationship Δ _c ε ^−min (q) ≦ Δε ≦ Δ _c ε ^−max (q) holds.

  In the present embodiment, a plurality of smaller test pieces (500 mm × 500 mm substantially square test pieces) were cut from a steel plate (preferably a length of 8 m or longer), and the longitudinal displacement of the cut portion was measured. As shown in FIG. 19, the sampling positions of the test pieces are the central portion in the longitudinal direction of the steel sheet, and there are three locations in the vicinity of both ends and the central portion in the width direction. The details of the steel sheet are shown in Table 3.

  FIG. 20 shows the relationship between the longitudinal strain (horizontal axis) and the maximum displacement (vertical axis) of the cut portion when the test piece (test pieces A and B) is cut from the vicinity of the end in the width direction of the steel sheet. . Further, FIG. 21 shows the relationship between the longitudinal strain (horizontal axis) and the maximum displacement (vertical axis) of the cut portion when the test piece (test piece C) is cut from the vicinity of the center in the width direction of the steel sheet. . Here, the maximum value of the displacement in the longitudinal direction is the amount of deformation when cutting is performed under the condition that the absolute value of deformation at the time of cutting is maximized. Further, the strain ε of the cut site is defined by ε = (L′−L) / L. However, L is the length of the longitudinal direction before the cutting | disconnection in the center part of the width direction of the cutting site | part of a 500 mm x 500 mm test piece, L 'is the length of the longitudinal direction after the cutting.

  20 and 21, the horizontal axis represents the distortion (unit: mm / mm, that is, dimensionless) of the cut portion, and the vertical axis represents the maximum value (unit: mm / mm, that is, dimensionless) of the longitudinal displacement. As is apparent from FIG. 20, when the test piece is cut from the vicinity of the center portion in the longitudinal direction of the steel sheet and from the vicinity of the end portion in the width direction, the deformation strain of the cut portion is within the range of −0.005 or more and 0.005 or less. It is preferable that Further, as apparent from FIG. 21, when the test piece was cut from the position in the vicinity of the central portion in the longitudinal direction of the steel sheet and in the vicinity of the central portion in the width direction, the deformation strain at the cut portion was −0.0007 or more and 0.0007. It is preferable to be within the following range.

  In addition, when cutting a test piece from the edge part vicinity of the width direction of a steel plate, as shown in FIG. 19, the test pieces A and B are each cut | disconnected from the both ends of the width direction in the same position of a longitudinal direction. At that time, the strain and displacement (deformation amount) of the cut portion are the average values of the two test pieces A and B. The reason for this is that if the test piece A or B is cut only from the vicinity of one end in the width direction, the steel plate may bend laterally and the distortion and displacement of the cut portion may not be accurately measured. .

  If the relationship between the longitudinal strain and the maximum value of displacement for each cutting site as shown in FIG. 20 or FIG. 21 is obtained, a 500 mm × 500 mm approximately square test piece is cut from any steel plate, By measuring the deformation strain, it becomes possible to predict the deformation of the steel sheet after cutting. The deformation of the steel plate here assumes the case of cutting under the condition that the absolute value of the deformation is greatest at the time of cutting, but as shown in FIG. 22, the level of deformation in advance according to the cutting shape of the customer. You may prepare several types. Similarly, in FIG. 22, the horizontal axis represents the distortion (unit: mm / mm, ie, dimensionless) of the cut site, and the vertical axis represents the maximum value (unit: mm / mm, ie, dimensionless) of the longitudinal displacement.

  Note that the amount of deformation of the test piece in the case of cutting the test piece from the steel plate differs depending on the test piece collection position. For example, using a steel plate shown in Table 2 in which the distribution in the width direction of the longitudinal residual stress is uniform in the length direction, an approximately square test of 500 mm × 500 mm from each of the center in the width direction and a plurality of positions in the length direction. The piece was cut, and the amount of deformation at the cut site was calculated by elastic-plastic FEM analysis.

  FIG. 23 shows the relationship between the specimen collection position and the amount of deformation of the cut site. In FIG. 23, the horizontal axis represents the distance (unit m) from the tip of the specimen collection position in the longitudinal direction, and the vertical axis represents the maximum value (unit: mm / mm, ie, dimensionless) of the longitudinal displacement. As can be seen from FIG. 23, the amount of deformation at the cut site differs depending on the specimen collection position even for the same steel plate. Therefore, correction is required depending on the sampling position of the test piece.

  FIG. 24 shows the relationship between the specimen collection position in the longitudinal direction of the specimen and the correction coefficient for the deformation of the cut site. In FIG. 24, the horizontal axis represents the distance (unit m) from the tip of the test piece sampling position in the longitudinal direction, and the vertical axis represents the correction coefficient (unit dimensionless). In addition, “●” represents data from a test piece collected from the vicinity of the end in the width direction of the steel sheet, and “▲” represents data from a test piece collected from the vicinity of the center in the width direction. As is clear from FIG. 24, the amount of deformation differs depending on the sampling position in the width direction of the steel sheet, and a correction coefficient corresponding to the test specimen sampling position is required. Specifically, it is preferable to correct the deformation of the cut site by multiplying the reciprocal of the correction coefficient obtained from FIG.

  Further, as is apparent from FIG. 23, even when the test piece is collected from the vicinity of the central portion in the longitudinal direction of the steel plate, correction is necessary if the length of the steel plate is short. In addition, when the specimen collection position is 4 m or more away from the longitudinal tip of the steel plate, the amount of deformation at the cutting site is almost constant, so a steel plate having a length of at least 8 m or more is required in the length direction. If the test piece is cut at a position 4 m or more away from the tip, the influence of the length of the steel plate is almost eliminated.

  Furthermore, as is clear from FIG. 24, when the specimen collection position is 4 m or more away from the front end in the longitudinal direction of the steel sheet, even when the specimen is collected from the vicinity of the end in the width direction of the steel sheet, It can be seen that even when the test piece is collected from the vicinity of the center, the correction coefficient value, that is, the amount of deformation of the cut portion is almost the same. That is, if a test piece is cut at a position at least 4 m away from the tip in the length direction of a steel plate having a length of at least 8 m, the length of the steel plate is independent of the sampling position of the test piece in the width direction of the steel plate. The effect of is almost gone.

  Furthermore, when correcting the deformation amount of the cut site due to the difference in the cutting method, it is preferable to correct the deformation strain value of the steel sheet according to the cutting method. FIG. 25 shows correction values for deformation distortion in the longitudinal direction of the steel sheet. In FIG. 25, the horizontal axis represents the cutting method, and the vertical axis represents the deformation distortion correction value (unit: mm / mm, ie, dimensionless). Specifically, the correction value obtained from FIG. 25 is subtracted from the deformation distortion value in accordance with the cutting method for correction. In addition, although this correction value is a value when cutting a steel plate into the shape shown in FIG. 13, for example, since the correction value differs depending on the cutting shape, it is preferable to prepare several levels according to the cutting shape.

  Thus, according to the fourth embodiment, the test piece is cut from the steel plate, the deformation strain is measured from the test piece, and it is determined whether the value of the deformation strain is within a predetermined range. The part from which the piece is collected is wasted, but the amount of deformation of the steel sheet after cutting can be predicted.

(Fifth embodiment)
Next, a fifth embodiment relating to a steel plate, a steel plate manufacturing method, and a steel plate manufacturing apparatus according to the present invention will be described. The fifth embodiment is basically the same as the fourth embodiment, and is controlled so that the deformation amount is within a predetermined range instead of deformation distortion. The deformation prediction computer 18 in FIG. 1 performs control so that the maximum value, minimum value, average value, sum, deviation, absolute value, or distribution of the deformation amount is within a predetermined range. Other parts not particularly described are the same as those in the first to fourth embodiments.

Between the amount of deformation Δ ^d of the cut part and the allowable value Δ _c ^d (q) determined by the required accuracy q of the customer, the minimum allowable value is Δ _c ^d-min (q) and the maximum allowable value is Δ _{As c} ^d-max (q), a relationship of Δ _c ^d-min (q) ≦ Δ ^d ≦ Δ _c ^d-max (q) is established.

  Similar to the fourth embodiment, also in this embodiment, a plurality of smaller test pieces (500 mm × 500 mm substantially square test pieces) are cut from a steel plate (preferably a length of 8 m or more), The amount of deformation in the longitudinal direction was measured. As shown in FIG. 19, the sampling positions of the test pieces are the central portion in the longitudinal direction of the steel sheet, and there are three locations in the vicinity of both ends and the central portion in the width direction. The details of the steel plate are the same as those shown in Table 3.

  FIG. 26 shows the relationship between the amount of deformation in the longitudinal direction (horizontal axis) and the maximum value of the displacement (vertical axis) when the test piece (test pieces A and B) is cut from the vicinity of the end in the width direction of the steel sheet. Shown in Further, FIG. 27 shows the relationship between the longitudinal deformation amount (horizontal axis) and the maximum displacement (vertical axis) of the cut portion when the test piece (test piece C) is cut from the vicinity of the center in the width direction of the steel sheet. Shown in Here, the maximum value of the displacement in the longitudinal direction is the amount of deformation when cutting is performed under the condition that the absolute value of deformation at the time of cutting is maximized. Further, the deformation amount Δ of the cut site is defined by Δ = L′−L. However, L is the length of the longitudinal direction before the cutting | disconnection in the center part of the width direction of the cutting site | part of a 500 mm x 500 mm test piece, L 'is the length of the longitudinal direction after the cutting.

  In FIGS. 26 and 27, the horizontal axis represents the distortion (unit: mm / mm, ie, dimensionless) of the cut portion, and the vertical axis represents the maximum displacement (unit: mm / mm, ie, dimensionless) in the longitudinal direction. As is clear from FIG. 26, when the test piece is cut from the vicinity of the central portion in the longitudinal direction of the steel sheet and from the vicinity of the end portion in the width direction, the deformation amount Δ of the cut portion is in the range of −2.0 mm to 2.0 mm. It is preferable to be within. As is clear from FIG. 27, when the test piece is cut from the vicinity of the central portion in the longitudinal direction of the steel sheet and from the vicinity of the central portion in the width direction, the deformation amount Δ of the cut portion is −0.4 mm or more and 0.4 mm or less. It is preferable to be within the range.

  If the relationship between the amount of deformation in the longitudinal direction and the maximum value of displacement for each cutting site as shown in FIG. 26 or FIG. 27 is determined, a 500 mm × 500 mm approximately square test piece is cut from any steel plate and cut. By measuring the deformation amount of the part, it becomes possible to predict the deformation of the steel sheet after cutting. The deformation of the steel plate here assumes a case where the cutting is performed under the condition that the absolute value of the deformation is greatest at the time of cutting, but according to the cutting shape of the customer as in the case of the fourth embodiment. Several kinds of deformation levels may be prepared in advance. Further, the correction by the test piece cutting position and the correction by the cutting method are the same as in the case of the fourth embodiment.

(Sixth embodiment)
Next, a sixth embodiment relating to a steel plate, a steel plate manufacturing method, and a steel plate manufacturing apparatus according to the present invention will be described. The sixth embodiment is basically the same as the case of the first or third embodiment, and instead of the stress parameter η and the deformation parameter δ, the shape of the cut portion of the steel plate and the longitudinal residual strain of the steel plate The value of the distortion parameter γ determined from the distribution is controlled so as to be within a predetermined range. The deformation prediction computer 18 in FIG. 1 performs control so that the value of the distortion parameter γ represented by the following equation (3) falls within a predetermined range. Other parts not specifically described are the same as those in the first or third embodiment.

  However, the area of the entire steel sheet is S, the area of the minute region is s, the longitudinal residual strain value or the width direction residual strain value in the minute region is ε, and the corrected total cutting region is Ω.

Between the distortion parameter γ and the allowable value γ _c (q) determined by the customer's required accuracy q, the minimum allowable value is γ _c ^min (q) and the maximum allowable value is γ _c ^max (q).
The relationship of γ _c ^min (q) ≦ γ ≦ γ _c ^max (q) is established.

  As in the case of the first or third embodiment, FEM analysis was performed on steel plates having various steel plate sizes, residual stress distributions, and cut shapes, and the relationship between the deformation amount of the steel plate after cutting and the strain parameter γ was obtained. The results are shown in FIG. By changing the value of the strain parameter γ, the amount of deformation after cutting of the steel sheet can be controlled.

In FIG. 28, the horizontal axis represents the value of the distortion parameter γ (unit dimensionless), and the vertical axis represents the deformation amount per unit length (unit mm / mm, ie dimensionless). As is clear from FIG. 28, in order to satisfy the requirement that the amount of deformation such as shrinkage and elongation of the steel sheet during cutting satisfies 1.5 mm or less per 10,000 mm length, the absolute value of the strain parameter γ is 1.5. It is preferable to control to ^x10-12 or less.

  Further, FIG. 29 shows the relationship between the correction value of the residual strain on the surface according to the plate thickness, the manufacturing method, and the grade of the steel plate. In FIG. 29, the horizontal axis represents the thickness (unit: mm) of each steel plate as a sample, and the vertical axis represents the correction value (unitless dimension) of the residual strain on the surface of the steel plate. In the figure, “▲” represents the value of the rolled steel sheet, “●” represents the value of the accelerated cooling steel sheet, and “♦” represents the value of the heat treated and / or straightened steel sheet. As is clear from FIG. 29, the high-grade steel plate subjected to heat treatment and correction has a smaller change in residual strain in the plate thickness direction than the rolled steel plate and the accelerated cooled steel plate, and the correction value due to the plate thickness. The change is small. Also, the change in residual strain in the thickness direction differs depending on the manufacturing method, such as a rolled steel plate and an accelerated cooled steel plate. Therefore, it is preferable to perform correction from the surface residual strain measurement value to the average value in the plate thickness direction using different correction values depending on conditions such as the manufacturing method and grade of the steel plates.

  When the test piece is short, it is necessary to correct the measured or analyzed residual strain. FIG. 30 shows the relationship between the test piece length and the residual distortion correction coefficient. In FIG. 30, the horizontal axis represents the length (unit m) of a test piece obtained by cutting a steel plate (for example, a product having a length of 20 m), and the vertical axis represents a correction coefficient. In addition, “▲” represents the residual strain correction count (unitless dimension) in the vicinity of the center in the width direction of the steel sheet, and “●” represents the correction value of the residual strain in the vicinity of the end in the width direction of the steel sheet. . The correction coefficient is the ratio (ratio) of the residual strain value at the same position in the width direction of the test piece after cutting to the residual strain value at a predetermined position from the center portion and the end portion in the width direction of the steel plate before cutting. It is. As is clear from FIGS. 29 and 30, when the test piece length is short, correction is required at any position near the end in the width direction and near the center in the width direction, and the correction amount is different. Therefore, it is preferable to correct the residual distortion by multiplying the reciprocal of the correction coefficient obtained from FIG. 30 according to the length of the test piece.

  FIG. 31 shows a correction value of the distortion parameter γ for correcting the difference in residual distortion depending on the cutting method. In FIG. 31, the horizontal axis represents the cutting method, and the vertical axis represents the distortion parameter correction amount (unitless dimension) at the time of cutting. Specifically, the correction value obtained from FIG. 31 is subtracted from the value of the distortion parameter γ according to the cutting method for correction. In addition, although this correction value is a value when cutting a steel plate into the shape shown in FIG. 13, for example, since the correction value differs depending on the cutting shape, it is preferable to prepare several levels according to the cutting shape.

  As for the measurement of residual strain, the residual strain can be obtained from the temperature distribution on the surface of the steel sheet, as in the case of measurement of residual stress. Further, a drilling method, a method using X-rays, a method using neutron diffraction, or the like may be used. In the case of the drilling method, the residual strain of the steel sheet varies depending on the restraint state such as the specimen size and the steel sheet size. Ideally, the strain parameter is determined by measuring the residual strain from a steel sheet of a size processed by the customer. It is desirable to calculate γ.

(Seventh embodiment)
Next, a seventh embodiment relating to a steel plate, a steel plate manufacturing method, and a steel plate manufacturing apparatus according to the present invention will be described. The seventh embodiment is basically the same as the sixth embodiment, and is controlled so that the residual strain value is within a predetermined range instead of the strain parameter γ. The deformation prediction computer 18 in FIG. 1 performs control so that the maximum value, minimum value, average value, sum, deviation, absolute value, or distribution of residual strain is within a predetermined range. Other parts not particularly described are the same as those in the first to sixth embodiments.

Between the residual strain ε and the allowable value ε _c (q) determined by the customer's required accuracy q, the maximum value of the residual strain is ε ^max , the minimum value of the residual strain is ε ^min , and the upper limit of the allowable value is ε _c ^max , ε _c ^{min as} the lower limit of the allowable value, ε _c ^dev as the allowable value of the residual strain deviation in the plate,
A relationship of at least one of ε _c ^min (q) ≦ ε ≦ ε _c ^max (q) and ε ^max −ε ^min ≦ ε _c ^dev (q) is established.

  Similar to the strain parameter γ, the residual strain itself affects the deformation during cutting. FIG. 32 shows the result of obtaining the relationship between the residual strain of the steel sheet and the deformation at the time of cutting by elastic analysis. In FIG. 32, the horizontal axis represents the absolute value (unit dimensionless) of the residual strain in the longitudinal direction of the steel sheet, and the vertical axis represents the absolute value (unit mm / mm, that is, dimensionless) of the deformation amount after cutting the steel sheet. The residual strain value here is an average value of the residual strain values in the longitudinal direction in a substantially square area of 100 mm × 100 mm. The cutting conditions were analyzed assuming that the absolute value of deformation at the time of cutting was maximized. When the absolute value of the residual strain value increases, the absolute value of deformation at the time of cutting also increases. Therefore, it is necessary to control the residual strain value so that the deformation amount becomes the target value.

As is apparent from FIG. 32, generally, the absolute value of the residual strain value may be about 2.0 × 10 ⁻⁴ or less. In particular, when the absolute value of deformation after cutting is 1.5 mm or less per 10,000 mm in length, the absolute value of the residual strain value is preferably 1.5 × 10 ⁻⁴ or less.

FIG. 33 shows the relationship between the residual strain deviation (maximum value−minimum value) in an arbitrary square area of 100 mm × 100 mm and the amount of deformation after cutting for steel sheets having various sizes and residual strain distributions. The residual strain deviation in the plate surface is preferably regulated to 5.0 × 10 ⁻⁴ or less.

  Also, it is preferable to add corrections according to the thickness, grade, cutting method, etc. of the steel sheet for the absolute value, maximum value, minimum value, average value, deviation, etc. of the residual strain value. FIG. 34 shows the correction value of the residual strain value corresponding to the cutting method. In FIG. 34, the horizontal axis represents the cutting method, and the vertical axis represents the residual strain value correction value (unitless dimension). Specifically, the correction value obtained from FIG. 34 is subtracted from the residual strain value in accordance with the cutting method for correction. In addition, although this correction value is a value when cutting a steel plate into the shape shown in FIG. 13, for example, since the correction value differs depending on the cutting shape, it is preferable to prepare several levels according to the cutting shape.

(Other embodiments)
In each of the above-described embodiments, the calculation is performed so as to calculate the deformation prediction value in consideration of the cutting method and cutting means for each consumer. However, the present invention is not limited to this, and the data transfer amount is reduced and the processing speed is improved. From this point of view, the cutting conditions and the cutting method may be fixed to the strictest conditions. Here, the strictest cutting conditions are the largest of the possible slit shapes at the time of cutting. Also, the most severe cutting method is the case of gas cutting, which has a large influence by cutting heat input on the contraction of the steel sheet, and is set assuming a cutting method that has no influence by cutting heat input on the expanding steel sheet. do it. Furthermore, the allowable deformation value may be fixed to the strictest conditions.

  Further, as a method for controlling the stress parameter η, in the above-described embodiment, after cutting the steel sheet, a mechanical method for directly controlling the residual stress by the straightening device (roller leveler) 10 and, if necessary, heat treatment by the heat treatment furnace 9 Although the thermal method that directly controls the residual stress is used, the present invention is not limited to this, and the stress parameter η can also be controlled by an indirect method that strictly manages processes such as heating, rolling, and accelerated cooling. Is possible.

  Furthermore, in each of the above embodiments, the residual stress or residual strain in the longitudinal direction of the steel sheet was measured at a plurality of positions in the width direction of the steel sheet, but the present invention is not limited to this, and a plurality of longitudinal stresses in the steel sheet are not limited thereto. The same effect can be obtained by measuring the residual stress or residual strain in the width direction of the steel plate at the position. That is, it may be considered that the longitudinal direction and the width direction of the steel plate are replaced. Furthermore, you may measure or analyze the thickness direction residual stress, thickness direction residual strain, etc. of a steel plate.

(Experimental example)
Next, an experiment was performed in which a steel plate manufactured by the above steel plate manufacturing method and a steel plate manufactured by a conventional method were actually cut and their deformation amounts were compared. The details of the experimental materials are shown in Table 4.

The original rolling size was 16 ^t x2600 ^W x22,000 ^L (unit mm), from which a product of 16 ^t x2500 ^W x10,000 ^L (unit mm) was cut. The heating temperature in the heating furnace 1 was 1200 ° C., and the temperature at the completion of rolling was 780 ° C. The shape after rolling was flat.

  The accelerated cooling conditions by the accelerated cooling device 5 were a pre-cooling temperature of 760 ° C., a post-cooling temperature of 550 ° C., and a cooling rate of 7 ° C./s. Further, the correction conditions by the hot straightening device 6 were that the set amount of reduction was 12.0 mm on the input side and 15.0 mm on the output side. The correction temperature was 540 ° C. The flatness after hot correction was also flat. The flatness determination method performed the flatness measurement with the stretcher on a roller table and a square bar.

  The cut shape is shown in FIG. The cutting method is slit cutting by one-stroke writing using a laser as shown in FIG. In addition, the amount of deformation was measured by measuring the amount of displacement of the reference point before and after cutting.

  The steel plate according to the conventional example had a flat shape on the table roller after cooling and product cutting. On the other hand, in the steel sheet according to the present invention, the stress parameter η according to the above embodiment was 0.35, and the correction code was 3.

  The details of the straightening device (roller leveler) 10 are a maximum straightening load of 5000 tons, a straightening roll diameter of 360 mm × body length of 4800 mm, the number of straightening rolls is four each on the top and bottom, and one below is a straightening roll diameter of 300 mm × body length of 4800 mm. It was. The correction conditions were that the amount of intermesh was 9.0 mm for the first pass, 7.0 mm for the second pass, 5.0 mm for the third pass, and the correction speed was 20 rpm. Moreover, the shape on the table roller after correction was flat.

  The result of the cutting experiment is shown in FIG. In FIG. 36, the horizontal axis represents the distance (unit: mm) from the tip in the longitudinal direction of the steel sheet, and the vertical axis represents the deformation (unit: mm / mm, ie, dimensionless) at each measurement point in the longitudinal direction of the steel sheet. . As apparent from FIG. 36, the steel plate according to the present invention hardly deformed after cutting, whereas the conventional steel plate greatly deformed.

It is a figure which shows the structure of the steel plate manufacturing apparatus in one Embodiment of this invention. It is a flowchart which shows the correction condition setting program in the said steel plate manufacturing apparatus. It is a continuation of the flowchart of FIG. It is a figure which shows the result of having calculated | required the relationship between the deformation amount of the steel plate after a cutting | disconnection, and the stress parameter (eta). (A) is a figure which shows the case where the shape of a cutting area | region is T shape, (b) is a figure which shows the case where the shape of a cutting area | region is a rectangle. It is a figure which shows distribution of the thickness direction of a longitudinal direction residual stress about the steel plate whose average value of the thickness direction of a longitudinal direction stress is zero. It is a figure which shows the relationship between plate | board thickness and the longitudinal direction residual stress of the steel plate surface about the steel plate whose average value of the plate | board thickness direction of a longitudinal direction residual stress is zero. It is a figure which shows the relationship between the correction value of the residual stress of the surface according to plate | board thickness, a manufacturing method, and the grade of a steel plate. It is a figure which shows the longitudinal direction residual stress distribution measured in the center position vicinity in the longitudinal direction of a test piece, and the several position in the width direction. It is a figure which shows the relationship between the test piece length and the correction coefficient of residual stress. It is a figure which shows the result of having analyzed the difference in the deformation amount by the cutting method by thermoelastic-plastic FEM. It is a figure which shows the correction value for the stress parameter η according to the cutting method. It is a figure which shows an example of the cutting shape of a steel plate. It is a figure which shows the result of having calculated | required the relationship between the residual stress value of a steel plate, and the deformation | transformation at the time of a cutting process by an elastic analysis. It is a figure which shows the relationship between the residual stress deviation (maximum value-minimum value) of a steel plate, and the deformation amount after a cutting | disconnection. It is a figure which shows the correction value of the residual stress value according to the cutting method. It is a figure which shows the result of having calculated | required the relationship between the deformation amount of the steel plate after a cutting | disconnection, and deformation parameter (delta). It is a figure which shows the correction value of deformation | transformation parameter (delta) according to the cutting method. It is a figure which shows the sampling position of a test piece. It is a figure which shows the relationship between the longitudinal direction residual strain of the cutting | disconnection site | part at the time of cut | disconnecting a test piece from the edge part vicinity in the width direction of a steel plate, and the maximum value of displacement. It is a figure which shows the relationship between the longitudinal direction residual strain of the cutting | disconnection site | part at the time of cut | disconnecting a test piece from the center part vicinity in the width direction of a steel plate, and the maximum value of displacement. It is a figure which shows the several level of the relationship between the longitudinal direction residual strain for every cutting site | part according to a customer's cutting shape, and the maximum value of a displacement. It is a figure which shows the relationship between a test piece collection position and the deformation amount of a cutting | disconnection site | part. It is a figure which shows the relationship of the correction coefficient of the test piece collection position in the longitudinal direction of a test piece, and the deformation | transformation of a cutting | disconnection site | part. It is a figure which shows the correction value of a deformation | transformation residual distortion according to the cutting method. It is a figure which shows the relationship between the longitudinal direction deformation | transformation amount of the cutting site | part at the time of cut | disconnecting a test piece from the edge part vicinity in the width direction of a steel plate, and the maximum value of a displacement. It is a figure which shows the relationship between the longitudinal direction deformation | transformation amount of the cutting site | part at the time of cut | disconnecting a test piece from the center part vicinity in the width direction of a steel plate, and the maximum value of a displacement. It is a figure which shows the result of having calculated | required the relationship between the deformation amount of the steel plate after a cutting | disconnection, and the distortion parameter (gamma). It is a figure which shows the relationship between the correction value of the residual stress of the surface according to plate | board thickness, a manufacturing method, and the grade of a steel plate. It is a figure which shows the relationship between the test piece length and the correction coefficient of residual distortion. It is a figure which shows the correction value of distortion parameter (gamma) according to the cutting method. It is a figure which shows the result of having calculated | required the relationship between the residual distortion of a steel plate, and the deformation | transformation at the time of cutting by elastic analysis. It is a figure which shows the relationship between the residual distortion deviation (maximum value-minimum value) of a steel plate, and the deformation amount after a cutting | disconnection. It is a figure which shows the correction value of the residual distortion value according to the cutting method. It is a figure which shows the cutting shape of the steel plate at the time of comparing the steel plate by this invention with the conventional steel plate. It is a figure which shows the result of the said cutting experiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 1st rolling device 3 Cooling device 4 2nd rolling device 5 Accelerated cooling device 6 Hot straightening device 7 Thermometer 8 Steel plate 9 Heat treatment furnace 10 Straightening device (roller leveler)
11 Pulse generator (PLG)
12 Digital Direct Controller (DDC)
13 process computer 14 line computer 15 server computer 16 camber prediction computer 17 buckling prediction computer 18 deformation prediction computer

Claims (9)

A method for producing a steel sheet in a steel sheet production apparatus comprising a rolling device for rolling a heated slab and a straightening device for straightening the rolled steel sheet,
A residual stress calculation step for obtaining a residual stress distribution of the steel plate after rolling using the size information, material information and rolling condition information of the steel plate;
A parameter calculation step for obtaining a value of a parameter for predicting a deformation amount after cutting the steel plate in a consumer using the residual stress distribution;
A deformation amount determination step for determining whether or not the value of the parameter is a value satisfying a deformation allowable amount or less that is an upper limit value of the required accuracy for the deformation amount after cutting the steel sheet in a consumer,
When it is determined in the deformation amount determination step that the value of the parameter is not a value that satisfies the deformation allowance or less, a correction condition of the correction device is set so that the parameter value is equal to or less than the deformation allowance or The manufacturing method of the steel plate characterized by having the correction condition change process to change.   The steel sheet manufacturing apparatus includes a heat treatment furnace that performs heat treatment on the rolled steel sheet, and when it is determined in the deformation amount determination step that the value of the parameter does not satisfy the deformation allowable amount or less, The method for manufacturing a steel sheet according to claim 1, further comprising a heat treatment condition changing step for setting or changing a heat treatment condition of the heat treatment furnace so that a value is equal to or less than the allowable deformation amount. The steel plate manufacturing apparatus includes an accelerated cooling device that rapidly cools the rolled steel plate,
The said residual stress calculation process calculates | requires the residual stress distribution of the steel plate after rolling using the cooling condition information of the said accelerated cooling apparatus, The manufacturing method of the steel plate of Claim 1 or 2 characterized by the above-mentioned. The steel plate manufacturing apparatus includes a thermometer for measuring the temperature of the steel plate after rolling,
The said residual stress calculation process calculates | requires the residual stress distribution of the steel plate after rolling using the temperature information by the said thermometer, The manufacturing method of the steel plate in any one of Claims 1-3 characterized by the above-mentioned.   The said parameter calculation process calculates | requires the value of the said parameter using the cutting conditions of the steel plate in a consumer, The manufacturing method of the steel plate in any one of Claims 1-4 characterized by the above-mentioned. The straightening device is a roller leveler,
The method for producing a steel sheet according to any one of claims 1 to 5, wherein the correction condition is an intermesh of a roller leveler.   The steel sheet manufacturing method according to claim 6, wherein the straightening device is a cold roller leveler that performs straightening in the cold. The said parameter is stress parameter (eta) defined by the following formula | equation, The manufacturing method of the steel plate of Claims 1-7 characterized by the above-mentioned.

However, the area of the entire steel sheet is S, the area of the minute region is s, the longitudinal direction residual stress value or the width direction residual stress value of the steel plate in the minute region is σ, and all the regions of the part to be cut by the customer of the steel plate are Ω. The deformation tolerance is 1.5 mm per 10,000 mm length,
The steel sheet manufacturing method according to claim 8, wherein the straightening condition changing step sets or changes the straightening condition so that the absolute value of the stress parameter η is 0.3 kg / mm ² or less.

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