JP2018158383A - Manufacturing method of differential plate material, tandem rolling mill, and rolling equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the manufacture of a higher-quality differential thickness plate material with reduced flatness failure.SOLUTION: A method for manufacturing a differential plate material is provided which includes a step of applying a caliber work roll using a caliber work roll having a diameter difference in the barrel length direction to a plate material made of a metal material to provide the plate material with plate thickness distribution in the plate width direction, and a step performed after the step of providing the thick-walled part of the plate material in the plate width direction and providing the thick-wall part of the plate material with elongation strains, and when the thickness of the thin-walled part of the plate material after the execution of caliber rolling is t1, and the plate width of the thin-walled part of the plate material after the execution of caliber rolling is W1, the thickness t1 of the thin-walled part and the width W1 in the thin-wall direction of the thin-walled part satisfy W1/t1≥15.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a manufacturing method of a differential thickness plate material, a tandem rolling mill, and a rolling facility for manufacturing a differential thickness plate material having a thickness distribution in the plate width direction.

  In recent years, weight reduction has been promoted in automobiles in order to improve fuel efficiency. As one method for reducing the weight, a method using a steel plate having a thickness distribution in a plane (differential thickness steel plate) has been studied. By using the differential thickness steel plate, the thickness of the part is increased only for a portion where the strength of the part is required, so that it is possible to reduce the weight of the part while ensuring the rigidity and safety at the time of collision.

  As a method of manufacturing the differential thickness steel plate, a method by rolling, a method of overlapping and joining a plurality of plate materials, or the like is considered. However, in the method of joining a plurality of plate materials, it is difficult to increase productivity because a number of steps such as a step of producing each of the plurality of plate materials and a step of bonding them are necessary, and manufacturing is difficult. Costs may increase. Moreover, in the board | plate material manufactured by the said method, when a great load is applied, the board | plate material will peel and the case where a high intensity | strength cannot be obtained may arise. Therefore, from the viewpoint of improving reliability, improving productivity, etc., as a method of manufacturing the differential thickness steel plate, a method of manufacturing the differential thickness steel plate as an integral member by rolling is drawing attention.

  Various methods have been proposed as a method for producing a differential thickness steel sheet by rolling. For example, Patent Document 1 discloses a method of manufacturing a differential steel sheet having a differential thickness in the longitudinal direction by rolling while changing the amount of reduction.

  However, in the method described in Patent Document 1, since it is difficult to frequently change the reduction position of the work roll at short time intervals, a thin part (thin part) and a thick part (thick part). It is difficult to shorten the length in the longitudinal direction by a predetermined length or more. In addition, since the steel plate is sent in the longitudinal direction even while the reduction position is changed, the thickness does not change steeply at the boundary between the thin portion and the thick portion, but at the boundary. Thus, a region having a predetermined length in which the plate thickness gradually changes is formed. As described above, in the method described in Patent Document 1, it is difficult to form the thin portion and the thick portion with a short pitch. Depending on the parts, there may be a need for a differential thickness steel plate in which a thin part and a thick part are provided at a short pitch. Therefore, the technique described in Patent Document 1 may not be able to handle various parts.

  Then, the method of patent document 2, 3 is proposed as another method of manufacturing a difference-thickness steel plate by rolling. Specifically, in Patent Documents 2 and 3, in the final stand of a hot tandem rolling mill, rolling is performed using a work roll having a diameter difference in the body length direction (hole work roll), thereby obtaining a plate width. A method for manufacturing a differential thickness steel sheet having a differential thickness in directions is disclosed. In addition, the difference thickness steel plate which has a difference thickness in a plate width direction is also called a vertical stripe steel plate. In addition, rolling using a hole work roll is also referred to as hole rolling.

JP-A-3-281010 Japanese Patent No. 5076707 JP 2014-180676 A

“Theory and practice of plate rolling (revised version)”, Japan Iron and Steel Institute, 2010, p. 96 " “Handbook of Iron and Steel (Volume 2) Rolling and Secondary Processing”, 5th edition, Japan Iron and Steel Institute, August 2014, p. 32 Shibahara et al., “Sheet width change behavior during hot tension rolling”, Proceedings of the Japan Society for Technology of Plasticity, 1984, 35th, p. 277

  Here, as a result of performing hole rolling in the same manner as the methods described in Patent Documents 2 and 3 and examining the manufactured differential thickness steel plate in detail, the present inventors, depending on the shape of the differential thickness steel plate. It has been found that undulation can occur in the thin-walled portion. However, Patent Documents 2 and 3 do not mention such poor flatness in the thin portion. That is, according to the methods described in Patent Documents 2 and 3, depending on the shape of the differential thickness steel plate, it may be difficult to manufacture a high quality differential thickness steel plate. Here, a steel plate has been described as an example, but the same problem arises when a plate made of another metal material is manufactured by hole-type rolling with a differential thickness plate having a plate thickness distribution in the plate width direction. obtain.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide a new and improved high-quality differential plate material with reduced flatness defects. Another object of the present invention is to provide a method for producing a differential thickness plate material, a tandem rolling mill, and rolling equipment.

  In order to solve the above problems, according to a certain aspect of the present invention, a plate material made of a metal material is subjected to hole rolling using a hole work roll having a diameter difference in the body length direction, and the plate material is subjected to plate rolling. Including a step of providing a plate thickness distribution in the width direction and a step of applying a plate thickness distribution in the plate width direction to the plate material, and applying an elongation strain to the thick part of the plate material, The thickness t1 of the thin portion when the thickness of the thin portion of the plate after the hole rolling is t1, the width t1 of the thin portion of the plate after the hole rolling is W1, and the thickness A method for manufacturing a differential thickness plate material is provided in which the width W1 of the thin portion in the plate width direction satisfies W1 / t1 ≧ 15.

  Moreover, in the manufacturing method of the said differential thickness board | plate material, the process of giving an elongation distortion to the said thick part may be performed by light reduction rolling.

  Further, in the manufacturing method of the differential thick plate material, in the hole-type rolling, the thickness reduction of the thick portion in the light rolling is added to the final desired thickness of the thick portion. The rolling conditions may be set so that the thick part after the hole-type rolling has a sufficient thickness.

  Moreover, in the manufacturing method of the said difference thickness board | plate material, in the said light rolling, the workpiece | work in which a roll profile is approximated by the function of 1st, 2nd, 3rd, or 4th, or the low order function equivalent to these. Rolling may be performed using a roll.

  Moreover, in the manufacturing method of the said differential thickness board | plate material, the process of giving an elongation distortion to the said thick part may be performed by leveler correction.

  Further, in the manufacturing method of the differential thickness plate material, the hole-type rolling is performed at any stand other than the final stand of the tandem rolling mill, and any one downstream of the stand performing the hole-shaped rolling of the tandem rolling mill The light rolling may be performed with a stand.

  Moreover, in the manufacturing method of the differential thick plate material, in the step of applying elongation strain to the thick portion, in the air cooling section of the plate material on the tandem rolling mill outlet side of the hot rolling line where the hole rolling is performed, A tension less than the yield stress may be applied to the plate material, and the thick portion may be stretched.

  Further, in the manufacturing method of the differential thick plate material, the tension includes the previously determined residual stress and creep characteristics of the thick wall portion, the outlet temperature of the tandem rolling mill, the plate passing speed of the plate material, and the air cooling section. It may be calculated from an air cooling distance that is a distance.

  Moreover, in the manufacturing method of the said difference thickness board | plate material, the process of giving an elongation distortion to the said thick part may be performed on the manufacturing line different from the said hole rolling.

  Further, in the manufacturing method of the differential thickness plate material, according to the steepness of the thin portion of the plate material after performing the hole rolling, which is predicted based on the rolling conditions of the hole rolling before the hole rolling is performed. The amount of elongation strain applied in the step of applying elongation strain to the thick portion may be set.

  Further, in the manufacturing method of the differential thickness plate material, an elongation strain is applied to the thick wall portion according to the steepness of the thin wall portion of the plate material after the hole rolling performed after the hole rolling is actually measured. The amount of elongation strain applied in the process may be set.

  In order to solve the above problem, according to another aspect of the present invention, the work roll of any one of the stands other than the final stand imparts a plate thickness distribution in the plate width direction to the plate made of a metal material. A hole-type work roll having a diameter difference in the body length direction for performing hole-type rolling, and the work roll of any one of the stands downstream from the stand on which the hole-type work roll is provided has a plate thickness distribution. Work roll whose roll profile is approximated by a first-order, second-order, third-order, or fourth-order function, or a lower-order function corresponding thereto, for lightly rolling the thick part of the applied plate material The thickness of the thin portion when the thickness of the thin portion of the plate after the hole rolling is t1 and the width in the plate width direction of the thin portion of the plate after the hole rolling is W1. t1, and the thin portion Width W1 in the width direction, so as to satisfy the W1 / t1 ≧ 15, the grooved work rolls are configured, tandem mill is provided.

  Moreover, in order to solve the said subject, according to another viewpoint of this invention, it arrange | positions in the rolling direction downstream of the tandem rolling mill which performs finish rolling by hot rolling, and consists of a metal material. A cooling device for cooling the plate material, and a pair of pinch rolls disposed between the tandem rolling mill and the cooling device, and a work roll of a final stand of the tandem rolling mill is a plate with respect to the plate material It is a perforated work roll having a diameter difference in the body length direction for performing perforated rolling that gives a thickness distribution in the width direction, and the thickness of the thin portion of the sheet material after the perforated rolling is t1, When the width in the plate width direction of the thin portion of the plate material after the perforated rolling is W1, the thickness t1 of the thin portion and the width W1 of the thin portion in the plate width direction satisfy W1 / t1 ≧ 15. And the word of the final stand The rolls and said pair of pinch rolls, to impart tension to the sheet, rolling equipment is provided.

  As described above, according to the present invention, it is possible to manufacture a higher-quality differential thickness plate material with reduced flatness defects.

It is a figure for demonstrating the manufacturing method of the difference thickness steel plate by a hole rolling. It is a figure for demonstrating the parameter showing the shape of a difference thickness steel plate. It is a graph which shows the relationship between the flatness defect of a thin part, thin part thickness t1, and thin part width W1. It is a flowchart which shows an example of the procedure of the manufacturing method of the difference thickness steel plate which concerns on one Embodiment of this invention. It is the figure which showed an example of the rolling equipment for enforcing the manufacturing method of the differential thickness steel plate which performs the elongation strain provision by tension | tensile_strength provision. It is a graph which shows the relationship between the thin part width W1, the thin part, and the residual stress of a thick part of a difference thickness steel plate after perforation rolling. It is a flowchart which shows an example of the procedure of the manufacturing method of the difference thickness steel plate which provides tension | tensile_strength. It is a figure which shows the relationship between the thin part width W1 acquired in Example (1), and the steepness (lambda) of the thin part after a hole type rolling execution. It is a figure which shows the relationship between the steepness degree (lambda) before execution of light reduction rolling, the reduction ratio of light reduction rolling, and the steepness degree (lambda) after execution of light reduction rolling acquired in Example (1). It is a figure which shows the relationship between the steepness degree (lambda) before execution of tension | tensile_strength execution acquired in Example (2), provision tension | tensile_strength, and steepness degree (lambda) after execution of tension | tensile_strength provision. It is a figure which shows the relationship between the steepness degree (lambda) before execution of leveler correction, leveler elongation rate, and steepness degree (lambda) after execution of leveler correction acquired in Example (3).

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In addition, below, it demonstrates taking the case where the difference thickness board | plate material which is the object to manufacture is a steel plate as an example. However, the present invention is not limited to such an example, and the present invention can also be suitably applied to the manufacture of differential thickness plate materials of other metal materials.

(1. Background to the present invention)
Prior to describing one embodiment of the present invention in detail, the background that the inventors have conceived of the present invention will be described in order to clarify the present invention.

(1-1. Manufacturing method of differential thickness steel plate (vertical striped steel plate) by hole rolling)
As described above, as a manufacturing method of the differential thickness steel plate, a method of imparting a plate thickness difference in the plate width direction by performing hole rolling has been conventionally proposed. FIG. 1 is a diagram for explaining a method of manufacturing a differential thickness steel plate by hole rolling. As shown in FIG. 1, in the manufacturing method, when a steel plate 201 is rolled using a pair of work rolls 101 and 102 (upper work roll 101 and lower work roll 102), a perforated work is used as the upper work roll 101. A roll is used. As shown in the figure, the perforated work roll is a roll having a diameter difference in the body length direction. By rolling using such a perforated work roll, a plate thickness difference is given to the steel plate 201 in the plate width direction. That is, the differential thickness steel plate 201 in which the thick portion 203 and the thin portion 205 are distributed in the plate width direction can be formed.

  In the illustrated example, a hole work roll is used as the upper work roll 101, but the manufacturing method of the differential thickness steel plate is not limited to such an example. As a manufacturing method of the differential thickness steel plate, a hole work roll may be used as the lower work roll 102, and both the upper work roll 101 and the lower work roll 102 may be hole work rolls. Further, the hole rolling is usually performed by hot rolling, but may be cold rolling.

  Here, FIG. 2 is a diagram for explaining parameters representing the shape of the differential thickness steel plate 201. In FIG. 2, the shape of the cross section in the plate | board width direction of the difference thickness steel plate 201 is shown roughly. In this specification, as shown in FIG. 2, parameters representing the shape of the differential thickness steel plate 201 are defined as follows. Note that P = W1 + W2.

Thin portion thickness t1: Plate thickness of thin portion 205 Thick portion thickness t2: Plate thickness of thick portion 203 Difference thickness h: Difference thickness between plate thickness of thick portion 203 and thin portion 205 Thin portion width W1 : Length in the plate width direction of the thin portion 205 thick portion width W2: length in the plate width direction of the thick portion 203 thick portion pitch P: pitch of the thick portion 203 (in the plate width direction of the thick portion 203) The length from the center to the center in the plate width direction of the adjacent thick portion 203).
Plate thickness changing portion angle θ: angle with respect to the horizontal direction at the plate thickness changing portion (thin portion 205 and the boundary between thick portion 203 and thin portion 205).

(1-2. Examination of poor flatness in thin parts)
Here, for example, in the technique according to Patent Document 2, the purpose is to manufacture a differential thickness steel plate 201 for a steel column pipe for building materials, and the thin portion thickness t1 of the differential thickness steel plate 201 is about 9 mm to 22 mm, and the thick portion pitch. P is about 30 mm to 40 mm. On the other hand, in automotive parts, in order to achieve both high strength and light weight, for example, corners when a steel plate is bent into a hat shape, or ridge lines (corner portions when a square steel pipe is formed from a steel plate) ) Etc., it is thought that there is a demand to increase the thickness of the other parts and make the other parts thinner. When such a member is to be formed of the differential thickness steel plate 201, for example, the thin portion thickness t1 having a thin portion thickness t1 of about 0.8 mm to about 4.0 mm and a thick portion portion pitch P of about 50 mm or more. However, it is necessary to manufacture a differential thickness steel plate 201 that is thinner and has a longer thick part pitch P (hereinafter, also referred to as a differential thickness steel plate 201 with a thin and long pitch for convenience).

  Therefore, the present inventors tried to manufacture such a thin steel plate 201 having a thin and long pitch by using the above-described hole rolling. As a result, in the differential thickness steel plate 201 with a thin long pitch, it has been found that undulation (that is, poor flatness) may occur in the thin portion 205. Such flatness defects hardly occur in the differential thickness steel plate 201 having a relatively thin thickness t1 and a relatively short thickness P, which is the subject of the technique according to Patent Document 2, and this time. This is a phenomenon newly discovered by the present inventors. In the present specification, when simply described as “unsatisfactory flatness”, unless otherwise specified, it refers to a poorness in flatness of the thin portion in the differential thickness steel plate 201.

  The present inventors have analyzed the reason and conditions for the occurrence of such poor flatness using a finite element method (FEM). In the finite element method, a three-dimensional calculation model was used to analyze the deformation state of the steel sheet when the hole rolling was performed, and the stress and strain generated in the steel sheet when the hole rolling was performed. At this time, the steel plate was handled as an elasto-plastic body, and the hole work roll was handled as a rigid body. In addition, for hole rolling, calculation is performed using physical property values assumed in hot rolling (for example, material deformation resistance, flow stress and Young's modulus, and friction resistance between roll and material). Then, the perforated rolling was handled as hot rolling. The following facts were found as a result of repeated analysis while simulating hole rolling on different thickness steel plates of various shapes and changing the thickness of the steel plate and the shape of the hole work roll.

  In the hole rolling, the thin portion 205 has a large rolling reduction, so that a large elongation strain occurs in the longitudinal direction in the differential thickness steel plate 201 after rolling. On the other hand, since the rolling reduction of the thick portion 203 is small, the elongation strain in the longitudinal direction is small in the differential thickness steel plate 201 after rolling. Thus, in the difference thickness steel plate 201, the difference of the elongation strain of the thick part 203 and the thin part 205 of the longitudinal direction is large. Therefore, a large compressive stress is generated in the thin portion 205 in the longitudinal direction. For example, when the strength of the thin portion 205 is insufficient, such as when the thin portion thickness t1 is thin, the thin portion 205 is buckled and deformed. It is thought that poor flatness occurs.

  Further, when the plastic strain in the thin portion 205 is analyzed in detail, the plastic strain in the plate width direction has a large plastic strain in the vicinity of the boundary with the thick portion 203 and moves away from the boundary in the plate width direction. It was found that the value of the plastic strain becomes smaller as the time elapses. Moreover, it turned out that the plastic strain of the longitudinal direction in the thin part 205 becomes large as it distances from the boundary with the thick part 203 to the board width direction. As a result, the difference in the plastic strain in the longitudinal direction between the thick portion 203 and the thin portion 205 also increases as the distance from the boundary increases in the plate width direction.

  A large plastic strain in the plate width direction in the vicinity of the boundary between the thin portion 205 and the thick portion 203 means that a metal flow from the thin portion 205 to the thick portion 203 is preferably generated in the vicinity of the boundary. doing. By filling the thick portion 203 with metal by such a metal flow, a difference thickness between the thick portion 203 and the thin portion 205 can be formed.

  On the other hand, the plastic strain in the plate width direction of the thin portion 205 decreases as the distance from the boundary increases in the plate width direction. The metal flow from the thin portion 205 to the thick portion 203 occurs as the distance from the boundary increases in the plate width direction. It means that it becomes difficult. For this reason, it is considered that the plastic strain in the longitudinal direction of the thin portion 205 also increases as the distance from the boundary in the plate width direction increases. That is, as the thin portion width W1 is larger, the possibility that there is a region where the plastic strain in the longitudinal direction is large in the thin portion 205 is increased.

  Further, as a result of the analysis by the present inventors, the range in which metal flow occurs from the thin portion 205 toward the thick portion 203 in the plate width direction of the thin portion 205 is almost determined by the thin portion thickness t1, and the thin portion It has been found that it is constant regardless of the width W1. When the thin portion thickness t1 is small, the range in which the metal flow occurs toward the thick portion 203 in the plate width direction of the thin portion 205 is small. That is, the thinner the thin portion thickness t1, the higher the possibility that there is a region where the plastic strain in the longitudinal direction is large in the thin portion 205.

  Thus, as the thin portion width W1 is larger and the thin portion thickness t1 is thinner, the metal flow to the thick portion 203 is less likely to occur in the thin portion 205, and the plastic strain in the longitudinal direction is large (that is, thick wall portion). Region where the difference in elongation strain between the portion 203 and the thin portion 205 in the longitudinal direction is large). Accordingly, it is considered that flatness defects are likely to occur in the differential thickness steel plate 201 with a thin long pitch.

  In summary, as a result of analysis by the present inventors, the cause of the occurrence of poor flatness in the thin portion 205 in the differential thickness steel plate 201 with a thin long pitch is the longitudinal length between the thick portion 203 and the thin portion 205 due to the difference in rolling reduction. It has been found that the thin-walled portion 205 causes buckling deformation due to the difference in elongation strain in the direction. When the thin-walled portion thickness t1 is small, the strength of the thin-walled portion 205 becomes small, and the metal flow from the thin-walled portion 205 to the thick-walled portion 203 hardly occurs, and the longitudinal direction between the thick-walled portion 203 and the thin-walled portion 205 For example, the difference in elongation strain between the two tends to be buckled and the flatness is likely to be poor. Further, when the thick part pitch P is large, for example, if the thin part width W1 and the thick part width W2 are approximately the same, the thin part width W1 also becomes large. Therefore, in the thin portion 205, there is an increased possibility that a region having a large difference in elongation strain in the longitudinal direction from the thick portion 203 is present in a portion away from the boundary with the thick portion 203, resulting in poor flatness. It becomes easy. Therefore, in the differential thickness steel plate 201 having a thin long pitch, it is considered that flatness defects are likely to occur in the thin portion 205.

  As described above, as a result of the analysis by the present inventors, the flatness failure of the thin portion 205 is caused when the thin portion thickness t1 is small and the thick portion pitch P is large (that is, when the thin portion width W1 is large). It was confirmed that this could occur significantly. Therefore, the present inventors arranged whether or not the flatness defect occurred, using the thin part thickness t1 and the thin part width W1 as parameters, and examined specific conditions for the flatness defect. The results are shown in FIG. FIG. 3 is a graph showing the relationship between the flatness failure of the thin portion 205 and the thin portion thickness t1 and thin portion width W1.

  In FIG. 3, a marker is plotted at a point corresponding to the shape of the differential thickness steel plate 201 on which the thin wall width W1 is taken on the horizontal axis, and the thin wall thickness t1 is taken on the vertical axis. A white marker indicates that no flatness failure has occurred, and a filled marker indicates that a flatness failure has occurred. The criterion for determining the occurrence of poor flatness (for example, the threshold value of the steepness λ) differs depending on the product, but here, when the steepness λ of the thin portion 205 is λ> 2%, the flatness failure occurs. It was judged that Note that all the data shown in FIG. 3 are the thickness ratio t2 / t1 = 2.0, and the difference thickness in which the thick portion 203 and the thin portion 205 are regularly arranged in the plate width direction when W1 = W2. It is the result of having performed FEM calculation about the steel plate 201. FIG.

  Referring to FIG. 3, it can be seen that a boundary indicating whether or not the flatness failure occurs is represented by a straight line T. When the slope of the straight line T was specifically calculated, W1 / t1 = about 15. Similarly, for the difference thickness steel plate 201 having a different thickness ratio t2 / t1, FEM calculation was performed while changing the thin part thickness t1 and the thin part width W1, and the boundary indicating whether or not the flatness defect occurred was considered. However, similar results were obtained.

  As described above, the present inventors have studied the conditions under which flatness defects occur, and as a result, in the differential thickness steel plate 201 in which at least the thick portion 203 and the thin portion 205 are regularly arranged at a predetermined pitch in the plate width direction. Obtained the knowledge that the flatness failure can be manifested in the thin portion 205 when W1 / t1 ≧ about 15. In the differential thickness steel plate 201, which is a vertically striped steel plate, the conditions under which flatness failure occurs have not been sufficiently studied so far, and the conditions under which flatness failure occurs are specifically defined by numerical values. This is what the present inventors have made anew this time.

  From the above conditions, in order not to cause flatness defects, the shape of the differential thickness steel plate 201 only needs to satisfy W1 / t1 <about 15. Therefore, for example, if the thin-walled portion thickness t1 is 2 mm, the maximum value of the thin-walled portion width W1 that can be rolled without causing poor flatness is about 30 mm. Thus, the freedom degree of manufacture of the difference thickness steel plate in a hole type rolling is small. In other words, if no measures are taken, it can be said that it is difficult to produce the above-described differential thickness steel plate 201 having a thin and long pitch without causing flatness defects by hole rolling.

(1-3. Countermeasures for poor flatness)
Therefore, the present inventors have examined a countermeasure that can improve the flatness defect with respect to the thin steel plate 201 having a thin and long pitch in which the flatness defect can be manifested so as to satisfy W1 / t1 ≧ about 15. .

  As described above, it is considered that the flatness failure in the thin portion 205 is caused by the difference in elongation strain between the thick portion 203 and the thin portion 205 in the longitudinal direction. Therefore, in order to suppress the occurrence of poor flatness, hole rolling may be performed so as to further reduce the difference in elongation strain in the longitudinal direction. For this purpose, it is effective to promote the metal flow from the thin portion 205 to the thick portion 203. If the metal flow from the thin wall portion 205 to the thick wall portion 203 is promoted, the plastic strain in the plate width direction in the thin wall portion 205 increases, so that the plastic strain in the longitudinal direction in the thin wall portion 205 decreases. In particular, the difference in elongation strain in the longitudinal direction can be further reduced.

  In order to promote the metal flow from the thin portion 205 to the thick portion 203, specifically, the diameter of the work roll is increased, and the contact length between the steel plate 201 and the work rolls 101 and 102 is increased. Increasing the coefficient of friction between the steel plate 201 and the work rolls 101 and 102 to restrain the elongation of the steel plate 201 is an effective means. However, when the diameter of the work rolls 101 and 102 is increased or the friction coefficient is increased, the rolling load increases. Therefore, there is a limit to the cost of improving the flatness failure in terms of equipment, and the above means cannot be a fundamental solution. Further, as described above, the metal flow from the thin portion 205 to the thick portion 203 is less likely to occur as the thin portion thickness t1 becomes thinner and the thin portion width W1 becomes longer. Therefore, it can be considered that there is a limit in the first place in the method of reducing the difference in elongation strain in the longitudinal direction by promoting metal flow.

  In addition, as another method for suppressing the occurrence of poor flatness, steel sheets are gradually formed under the condition that multi-pass hole rolling is performed with a hole work roll having the same or changed shape, and flatness defects are not manifested. A method of applying a rolling deformation to 201 can be considered. However, compared to a shape steel or rail that is also manufactured by multi-pass perforation rolling, a so-called thin plate such as a steel plate 201 is a thin object, and its thickness difference (difference thickness h) is small, and dimensional accuracy is also high. Strict. When manufacturing the differential thickness steel plate 201, which is a thin plate, by multi-pass perforation rolling, it is difficult to restrain the movement of the steel plate 201 in the width direction, the position shift in the plate width direction due to the meandering of the steel plate 201, Since the occurrence of biting is expected, it is considered difficult to ensure stable production and dimensional accuracy.

  As described above, it can be said that a suitable manufacturing method has not been established so far for the differential thickness steel plate 201 having a thin and long pitch that satisfies the W1 / t1 ≧ about 15 and can cause poor flatness. . The inventors of the present invention have come up with the present invention as a result of earnestly studying a manufacturing method capable of further reducing the flatness failure in the thin steel plate 201 having such a thin and long pitch. According to the present invention, it is possible to manufacture a high-quality differential thickness steel plate 201 with reduced flatness defects even in the differential thickness steel plate 201 with a thin and long pitch that satisfies W1 / t1 ≧ about 15. Hereinafter, a preferred embodiment of the present invention conceived by the present inventors will be described in detail.

(2. Manufacturing method of differential thickness steel plate)
The manufacturing method of the differential thickness steel plate 201 which concerns on one Embodiment of this invention is demonstrated. Note that the manufacturing method according to the present embodiment relates to a method of manufacturing the differential thickness steel plate 201 that satisfies W1 / t1 ≧ about 15 and in which flatness defects can be manifested. The thin portion thickness t1 of the differential thickness steel plate 201 that is the subject of the present embodiment is, for example, about 0.8 mm to about 4.0 mm.

  As described above, it is considered that the flatness failure in the thin portion 205 is caused by the difference in elongation strain between the thick portion 203 and the thin portion 205 in the longitudinal direction. Therefore, in order to reduce the occurrence of poor flatness, the difference in elongation strain in the longitudinal direction may be made smaller. Therefore, the inventors of the present invention, after performing the step of forming the differential thickness steel plate 201 by hole rolling, the step of applying a longitudinal elongation strain to the thick portion 203 of the formed differential thickness steel plate 201 I came up with a way to do more.

  At the stage where the hole rolling has been completed, the elongation strain in the longitudinal direction of the thick wall portion 203 is small, and the elongation strain in the longitudinal direction of the thin wall portion 205 is large. The flatness defect occurs in the portion 205. In this state, by applying an elongation strain in the longitudinal direction to the thick portion 203, the difference in the elongation strain in the longitudinal direction between the thick portion 203 and the thin portion 205 is reduced, and the flatness of the thin portion 205 is poor. Will be corrected.

  Examples of a method for imparting longitudinal strain to the thick wall portion 203 include a method of performing light reduction rolling on a differential thickness steel plate after the completion of hole rolling and a method of imparting tension. . Hereinafter, a method of applying an elongation strain in the longitudinal direction to these thick portions 203 will be described.

(2-1. Elongation strain imparted by light rolling)
First, a method for imparting an elongation strain in the longitudinal direction to the thick wall portion 203 by light rolling will be described. For example, the differential thickness steel plate 201 is lightly reduced with a work roll having a straight roll profile (a roll profile approximated by a linear function). By performing such light rolling, it is possible to selectively perform rolling only on the thick wall portion 203 having a small elongation strain after the perforated rolling is performed, and it is possible to give the elongation strain. It is possible to efficiently reduce the difference in elongation strain between the portion 205 and the longitudinal direction.

  Here, when the flatness failure occurs after the hole rolling, the elongation strain difference between the thick portion 203 and the thin portion 205 is Δε and the steepness of the thin portion 205 is λ. It is known that there is a relationship represented by the following mathematical formula (1) between the difference Δε and the steepness λ (refer to Non-Patent Document 1 for details).

  Note that the elongation strain difference Δε is the length in the longitudinal direction of the thin portion 205 when the wavy shape is generated, and the length in the longitudinal direction of the thin portion 205 when the corrugated shape is corrected to a flat shape. When it is assumed that l + Δl, Δε = Δl / l. Further, the steepness λ is a ratio between the wave height δ and the wave pitch L when the outer shape of the thin portion 205 in a state where the wavy shape is generated is viewed as a waveform. It is obtained by λ = δ / L. If an elongation strain corresponding to the elongation strain difference Δε is applied to the thick portion 203, the flatness defect in the thin portion 205 can be corrected.

  From the above formula (1), for example, when λ = 5 (%), Δε = about 0.006, and when λ = 10 (%), Δε = about 0.025, and λ = 15. In the case of (%), Δε = about 0.056. Assuming that the plate thickness strain (rolling strain) applied to the thick wall portion 203 is all converted into elongation strain, the steepness λ (5%, Elongation strain equivalent to the elongation strain difference Δε corresponding to 10% and 15%) is obtained. That is, in the above method, the rolling reduction of the light rolling that can correct the flatness failure of the thin portion 205 is about several percent at the maximum. Even if light rolling is performed at a rolling reduction of about several percent, the change in the plate thickness is small, and the cross-sectional shape of the differential thickness steel plate 201 after punch rolling does not change significantly. That is, according to the above method, even after light rolling, the cross-sectional shape of the differential thickness steel plate 201 after the hole rolling can be substantially maintained, so that the differential thickness steel plate 201 having a desired shape can be obtained. is there.

  Moreover, in light rolling, it is possible to use a work roll with a straight roll profile as described above. Therefore, in the light rolling, there is no need to consider the position in the plate width direction according to the shape of the differential thickness steel plate 201. Therefore, there is no inconvenience due to the positional deviation in the sheet width direction of the differential thickness steel plate 201 as in the case where rolling is performed in a plurality of passes and the difference in sheet thickness is given in stages.

  Hereinafter, the specific procedure of the manufacturing method of the differential thickness steel plate 201 which gives the elongation strain by light rolling will be described in detail.

  FIG. 4 is a flowchart showing an example of the procedure of the manufacturing method of the differential thickness steel plate 201 that performs elongation strain application by light rolling. Referring to FIG. 4, in the manufacturing method of the differential thickness steel plate 201 that performs elongation strain application by light rolling, first, after performing the hole rolling, before performing the hole rolling, based on the rolling conditions of the hole rolling. The steepness λ of the thin wall portion 205 is predicted (step S101). Here, the rolling conditions of the hole rolling include the entry side plate thickness t0, the shape of the differential thickness steel plate 201 as the target value after the hole rolling is performed (thin wall thickness t1, thick wall thickness t2, thin wall width W1, Thick part pitch P (if the thin part width W1 and thick part pitch P are determined, the thick part width W2 is also determined as a result), the plate thickness changing part angle θ, etc.), and the hole type A work roll diameter or the like of the work roll may be included. The rolling conditions are determined in advance according to the shape of the desired differential thickness steel plate 201 that is finally desired to be manufactured. Specifically, for example, the plate thickness changing portion angle θ may be about 30 ° ≦ θ <90 °. In the example shown in FIG. 1 described above, the corner portion of the plate thickness changing portion formed by perforation rolling is configured by a straight line, but in this embodiment, in order to avoid stress concentration, the corner portion is You may comprise by a curve.

  In step S101, for example, the steepness λ is obtained by obtaining the shape change of the differential thickness steel plate 201 by FEM calculation when the die rolling is performed according to the rolling conditions. At this time, the steepness λ may be obtained by executing FEM calculation every time the hole rolling is executed. Alternatively, a database on the relationship between the rolling conditions and the steepness λ of the thin portion 205 is executed in advance by performing FEM calculation corresponding to a plurality of rolling conditions of the hole rolling corresponding to the shapes of various differential thickness steel plates 201 that can be assumed. Then, the steepness λ according to the rolling conditions of the hole rolling to be performed from now on may be obtained using the database. As described above, since the steepness λ (that is, flatness) of the thin portion 205 is correlated with the thin portion thickness t1 and the thin portion width W1, in the database, for example, these parameters and the steepness of the thin portion 205 are steep. The relationship with degree λ can be preserved.

  However, the present embodiment is not limited to such an example, and various methods may be used as a method for predicting the steepness λ of the thin portion 205. For example, the database regarding the relationship between the rolling conditions described above and the steepness λ of the thin-walled portion 205 may be created based on the operation result data when the hole-type rolling has been executed in the past.

  Next, based on the predicted steepness λ of the thin portion 205, a rolling reduction ratio of light reduction that can correct the flatness failure of the thin portion 205 is calculated (step S103). In step S103, for example, the shape change of the differential thickness steel plate 201 when light rolling is performed on the differential thickness steel plate 201 in which the undulation is generated in the thin portion 205 after the hole rolling is performed by FEM calculation. By obtaining, the reduction ratio can be calculated. At this time, similarly to the FEM calculation performed in step S101, the FEM calculation may be performed every time the light reduction rolling is executed, and the reduction ratio may be calculated. Alternatively, FEM calculation corresponding to various possible steepness λ is executed in advance, steepness λ before the light reduction rolling, reduction ratio of the light reduction rolling, and steepness λ after the light reduction rolling execution. (That is, the degree of improvement of the steepness λ of the thin-walled portion 205 by light rolling) and a difference thickness steel plate that is a target of light rolling to be performed from now on using the database. A rolling reduction rate that can correct the flatness failure according to the steepness λ 201 of 201 may be obtained. Note that the FEM calculation for obtaining the rolling reduction can be executed continuously following the FEM calculation for obtaining the steepness λ that can be performed in step S101.

  However, the method of calculating the rolling reduction of light rolling is not limited to this example, and various methods may be used. For example, the database on the relationship between the steepness λ before the light rolling described above, the rolling reduction ratio of the light rolling, and the steepness λ after the light rolling is performed when the light rolling is performed in the past. It may be created based on the operation performance data.

  Next, hole rolling is performed in accordance with the rolling conditions corresponding to the desired shape of the differential thickness steel plate 201 (that is, the rolling conditions corresponding to the steepness λ calculated in step S101) (step S105). Here, the hole-type rolling is performed by hot rolling. However, the application of elongation strain by light rolling can also be performed outside the hot rolling step, and the hole rolling may be performed by cold rolling as long as the processing is possible.

  And light reduction rolling is performed with respect to the thick part 203 of the difference thickness steel plate 201 after piercing rolling by the reduction rate calculated by step S103 (step S107). In step S107, light rolling is performed using a work roll having a straight roll profile. As a result, only the thick portion 203 is lightly reduced, and an elongation strain is applied to the thick portion 203. At this time, as described above, since the reduction ratio of the light rolling can be very small, the shape of the differential thickness steel plate 201 is not greatly deformed by the light rolling. Further, by using a work roll having a straight roll profile, it is not necessary to perform alignment in the sheet width direction between the hole rolling and the light rolling to maintain the shape accuracy of the differential thickness steel plate 201.

  Note that the hole rolling in step S105 and the light reduction rolling in step S107 may be performed on separate production lines by two different rolling mills, or may be continuously performed by using a tandem rolling mill. . When using a tandem rolling mill, for example, hole rolling using a hole work roll is performed in any one of the stands other than the final stand, and any of the stands downstream from the stand that performs the hole rolling (for example, In the final stand, light rolling can be performed using a work roll having a straight roll profile. In addition, when using a tandem rolling mill, since the difference thickness steel plate 201 will be cooled after the flatness defect of the thin part 205 is corrected, the effect which suppresses generation | occurrence | production of a cooling nonuniformity can also be anticipated.

  In the above, the manufacturing method of the differential thickness steel plate 201 which gives the elongation strain by light rolling is demonstrated. In such a method, light rolling is performed on the thick portion 203 after performing the hole rolling. At the stage where the hole-type rolling is completed, flatness failure may have occurred in the thin-walled portion 205 of the differential thickness steel plate 201. However, by performing light reduction rolling on the thick-walled portion 203 after the hole-rolling, the thickness is reduced. A difference in elongation strain in the longitudinal direction between the meat portion 203 and the thin portion 205 is reduced, and the flatness defect of the thin portion 205 can be corrected. In this way, even in the differential thickness steel plate 201 that satisfies W1 / t1 ≧ about 15 and in which the flatness failure can be manifested in the thin portion 205, the high quality differential thickness steel plate 201 in which the flatness failure is reduced is obtained. It can be manufactured.

  In the procedure described above, the processes in steps S101 and S103 can be executed by an information processing apparatus such as a PC (Personal Computer). The processing in step S101 and step S103 can be executed by the processor of the information processing apparatus executing arithmetic processing according to a predetermined program.

  Further, it is possible to create a computer program for causing the information processing apparatus to execute the processing in step S101 and step S103. In addition, a computer-readable recording medium storing such a computer program can be provided. The recording medium is, for example, a magnetic disk, an optical disk, a magneto-optical disk, a flash memory, or the like. Further, the above computer program may be distributed via a network, for example, without using a recording medium.

  In the above description, a work roll having a straight roll profile was used in the light rolling, but in the light rolling, it is only necessary to give elongation strain to the thick portion 203, and the shape of the work roll is as follows. It may be arbitrary. For example, light rolling may be performed using a work roll whose roll profile can be approximated by a quadratic to quartic function or a low-order function corresponding to these functions.

  Further, in the above description, in step S101, the rolling conditions for the perforated rolling may be determined in consideration of the reduced thickness of the thick portion 203 in the light rolling performed after the perforated rolling. In other words, since the thick part 203 is lightly reduced by light rolling, the thick part thickness t2 decreases although it is very small, so that the desired thick part thickness t2 of the desired differential thickness steel plate 201 is finally obtained. On the other hand, the thick part thickness t2 that is increased by the decrease in the light rolling may be adopted as the rolling condition of the hole rolling in step S101. At this time, the thick part thickness t2 that is increased by the decrease in the light rolling may be reflected in the design of the hole work roll prior to the hole rolling. Thereby, since the desired thick part thickness t2 can be obtained with higher accuracy after light rolling, the shape accuracy of the differential thickness steel plate 201 can be further improved.

  Further, in the above description, the steepness λ of the thin portion 205 after the hole rolling is predicted in advance, and the reduction ratio of the light reduction rolling is calculated based on the prediction result. However, the reduction ratio of the light reduction rolling is calculated. The method is not limited to such an example. For example, after performing the hole-type rolling, the steepness λ of the thin portion 205 may be measured, and the reduction ratio of the light reduction rolling may be calculated based on the actual measurement result. In this case, in the procedure shown in FIG. 4, the order in which the process in step S103 and the process in step S105 are performed is reversed.

(2-2. Elongation strain applied by applying tension)
Next, a method for applying an elongation strain in the longitudinal direction to the thick wall portion 203 by applying tension will be described.

(2-2-1. Equipment configuration)
First, with reference to FIG. 5, the equipment configuration for carrying out the manufacturing method of the differential thickness steel plate 201 that performs elongation strain application by tension application will be described. FIG. 5 is a diagram showing an example of a rolling facility for carrying out the method of manufacturing the differential thickness steel plate 201 that applies elongation strain by applying tension. The rolling equipment 1 is equipment for a hot rolling process and includes a tandem rolling mill 100, a cooling device 120, and a winding device 140.

  The tandem rolling mill 100 is a rolling mill that performs hot finish rolling including a plurality of stands. Each stand of the tandem rolling mill 100 is, for example, a quadruple rolling mill, and includes a pair of work rolls and a pair of backup rolls that support the work rolls. In the rolling equipment 1 that produces the differential thickness steel plate 201 by applying elongation strain by applying tension, a hole work roll is used for at least one of the upper work roll 101a and the lower work roll 102a of the final stand of the tandem rolling mill 100. It is done. In the following description, an example in which a perforated work roll is used as the upper work roll 101a of the final stand of the tandem rolling mill 100 will be described.

  The cooling device 120 is disposed on the downstream side in the rolling direction of the tandem rolling mill 100 and cools the differential thickness steel plate 201 after hole rolling. The cooling device 120 cools the differential thickness steel plate 201 by, for example, injecting cooling water onto the differential thickness steel plate 201.

  A pinch roll 110 including an upper pinch roll 111 and a lower pinch roll 112 is installed between the tandem rolling mill 100 and the cooling device 120. The pinch roll 110 is installed to apply tension to the differential thickness steel plate 201 between the hole-type work rolls 101 a and 102 a that are the work rolls of the final stand of the tandem rolling mill 100 and the pinch roll 110. The tension can be detected by converting the motor current value of the motor that drives the pinch roll 110 into torque. Note that the differential thickness steel plate 201 that has been hole-rolled at the final stand of the tandem rolling mill 100 is air-cooled until it reaches the cooling device 120 from the exit side of the tandem rolling mill 100.

  A deflector roll 130 and a winding device 140 are provided downstream of the cooling device 120 in the rolling direction. The winding device 140 is disposed downstream of the cooling device 120 in the rolling direction, and winds the differential thickness steel plate 201 conveyed through the deflector roll 130 in a coil shape.

(2-2-2. Elimination of flatness defects in thin parts due to tensile tension)
In such a rolling equipment 1, the differential thickness steel plate 201 formed by hole rolling in the tandem rolling mill 100 includes a thick portion 203 and a thin portion 205 as shown in FIG. 1. At this time, in the differential thickness steel plate 201 in which the thick portion 203 and the thin portion 205 are regularly arranged at a predetermined pitch in the plate width direction, the thin portion width W1 and the thin portion thickness t1 satisfy W1 / t1 ≧ about 15. In this case, a flatness defect may be manifested in the thin portion 205.

  Here, FIG. 6 shows the result of analyzing the relationship between the thin portion width W1 and the residual stress of the thin portion and the thick portion with respect to the differential thickness steel plate 201 after die rolling. In FIG. 6, the rolling direction stress indicating the residual stress is indicated by a negative value when it is a compressive stress, and is indicated by a positive value when it is a tensile stress. Referring to FIG. 6, it can be seen that compressive stress in the rolling direction remains in the thin portion 205 of the differential thickness steel plate 201 after the hole rolling. On the other hand, tensile stress remains in the thick portion 203. This is because as the steepness increases, the compressive stress of the thin portion increases, and correspondingly, the tensile stress increases in the thick portion due to the balance in the plate width direction in the steel plate. In FIG. 6, it can be seen that the thin portion tends to saturate the compression stress due to buckling deformation when the thin portion width W1 is 40 mm or more.

  As described above, since the tensile residual stress in the rolling direction is generated in the thick portion 203, the thick portion 203 can be stretched and deformed by applying a relatively low tension to the differential thickness steel plate 201. On the other hand, since compressive stress remains in the thin-walled portion 205, even if tension is applied to the differential thickness steel plate 201, tensile strength sufficient to deform the thin-walled portion 205 is not obtained. Stretched.

  Therefore, by applying tensile tension to the differential thickness steel plate 201, the thick portion 203 can be stretched and the flatness failure of the thin portion 205 can be eliminated. Here, the timing for extending the thick portion 203 will be described.

  The differential thickness steel plate 201 after hot rolling has a thick portion 203 and a thin portion 205. The temperature difference of the differential thickness steel plate 201 heated by hot rolling is lowered in a later process. In the thick wall portion 203 and the thin wall portion 205, the temperature of the thin wall portion 205 decreases more quickly and is easily cooled. Thereby, the thick part 203 is more easily affected by the tensile tension than the thin part 205. Therefore, the thick part 203 can be preferentially extended | stretched by providing tension | tensile_strength after the hole-type rolling by hot rolling is performed with respect to the difference thickness steel plate 201. FIG.

  For example, in the rolling equipment 1 described in FIG. 5, tension may be applied to the differential thickness steel plate 201 after being pierced at the final stand of the tandem rolling mill 100. The differential thickness steel plate 201 is air-cooled and then transported to the cooling device 120 where water cooling is performed. Before the temperature is lowered by the cooling device 120, the thick wall portion 203 can be preferentially stretched. Therefore, tension may be applied in the air cooling section from the final stand of the tandem rolling mill 100 to the cooling device 120.

(How to apply tension)
As shown in FIG. 5, the differential thickness steel plate 201 formed by hole rolling at the final stand of the tandem rolling mill 100 is coiled by a winding device 140 after air cooling by a runout table and water cooling by a cooling device 120. Rolled up. At this time, in order to eliminate the flatness failure of the thin portion 205 of the differential thickness steel plate 201 based on the above-described viewpoint, the rolling equipment 1 is downstream in the rolling direction by a predetermined distance from the final stand provided with the perforated work roll. A pinch roll 110 is installed at a position distant to the side. Thereby, tension can be applied to the differential thickness steel plate 201 between the final stand and the pinch roll 110. As will be described later, the pinch roll 110 is preferably provided upstream of the cooling device 120 in the rolling direction in order to suppress the elongation of the material caused by the creep characteristics.

  The tension σ necessary for eliminating the flatness failure of the thin portion 205 is calculated from the tensile residual stress of the thick portion 203 and the creep characteristics of the material. It is known that in the tandem rolling mill, which performs finish rolling in the hot rolling process, between the stands or the run-out table, the steel sheet shrinks due to the action of the rolling direction tension below the yield stress (for details, see (See Patent Document 2). This phenomenon is also called a creep phenomenon. The width shrinkage due to the tension can be formulated by the time change of the elongation strain of the steel sheet under a constant tension condition, and the amount of the elongation strain depends on the absolute value of the tension and the temperature.

  Specifically, the tension σ necessary for eliminating the flatness failure of the differential thickness steel plate 201 takes into consideration the time-dependent characteristics of stress and elongation strain, for example, the strain rate dependency represented by the following formula (2). Based on the yield stress equation, it can be calculated from the temperature, the air cooling time, and the target elongation strain (see Non-Patent Document 3 for details). Here, an example of obtaining the elongation strain amount ε necessary for eliminating the flat defect using the formula (2) will be described, but the method for calculating the elongation strain amount ε necessary for eliminating the flat defect is as follows. It is not restricted to Formula (2).

  The coefficients A, n, and m are derived from the results of a tensile test at a low strain rate. Here, the coefficient A is a function of the carbon content of the differential thickness steel plate 201 and the temperature. Since ε is the amount of elongation strain necessary for eliminating the flatness failure, εdot is the strain rate, and the strain rate εdot can be approximately expressed by the amount of elongation strain per unit time (ε / Δt). Can be further expressed by the following mathematical formula (3).

  In Equation (3), the amount of elongation strain ε required for eliminating the flat defect can be obtained from Equation (1) using the predicted steepness λ. The unit time Δt represents a time during which the tension σ can be applied. For example, in the rolling equipment 1 shown in FIG. 5, it can be obtained from the air cooling distance l from the final stand of the tandem rolling mill 100 to the pinch roll 110 and the sheet passing speed of the differential thickness steel plate 201. That is, the tension σ necessary for eliminating the flatness failure of the differential thickness steel plate 201 can be calculated by using the outlet temperature of the tandem rolling mill 100, the sheet passing speed of the differential thickness steel plate 201, and the air cooling distance l. .

  Moreover, the residual stress of the thick part 203 and the thin part 205 can be predicted from the width of the thin part 205 after the punch rolling using a database storing past experimental data and the like. For example, with reference to FIG. 6, the value of the residual stress of the thick portion 203 is acquired from the width of the thin portion 205 after the hole rolling. And the value which remove | eliminated the residual stress of this thick part from tension | tensile_strength (sigma) required for cancellation of the flatness defect of a thin part calculated using the said Numerical formula (3) is the final stand of the tandem rolling mill 100, and the pinch roll 110. It is the value of the applied tension to be applied between.

(2-2-3. Manufacturing Flow of Differential Thickness Steel Sheet for Applying Tension)
FIG. 7 shows the processing in the rolling equipment 1 until the applied tension is obtained in this way and the tension is applied to the differential thickness steel plate 201. FIG. 7 is a flowchart showing an example of a procedure of a manufacturing method of the differential thickness steel sheet for applying tension.

  Referring to FIG. 7, in the manufacturing method of the differential thickness steel plate 201 for applying tension, first, before performing the hole rolling, as in the manufacturing method of the differential thickness steel plate 201 in the case of performing the light rolling shown in FIG. Based on the rolling conditions of the hole rolling, the steepness λ of the thin portion 205 after the hole rolling is performed is predicted (step S201). The prediction of the steepness λ is the same as that in step S101 in FIG.

  Next, based on the predicted steepness λ of the thin-walled portion 205, the amount of elongation strain necessary for eliminating the flatness failure of the thin-walled portion 205 is calculated (step S203). In step S203, for example, the necessary amount of elongation strain is calculated using Equation (1). It should be noted that the amount of elongation strain necessary for eliminating the flatness failure in the simulation was larger than the amount of elongation strain converted from the steepness of equation (1). From this result, the amount of elongation strain necessary for eliminating the flatness defect is set larger than the amount of elongation strain converted from the steepness of equation (1) in order to reliably eliminate the flatness failure of the steel sheet. Further, when calculating the elongation strain amount Δε required for eliminating the flatness failure, the correlation between the steepness λ calculated by the FEM calculation when obtaining the elongation strain amount and the steepness λ generated in actual rolling. Is obtained in advance, and the target value of the final steepness λ after applying the tension and the elongation strain amount Δε that can achieve the target value may be set from the correlation.

  Further, the flatness of the thin portion is eliminated from the relationship between the elongation strain amount calculated in step S203, the elongation strain due to the exit temperature of the tandem rolling mill and the creep characteristics of the material, and the time for applying the tension. Necessary tension is calculated (step S205). The tension necessary for eliminating the flatness failure of the thin portion can be calculated using, for example, the above mathematical formula (3).

  Further, the residual stress of the thick portion 203 is predicted from the width W1 of the thin portion 205 of the differential thickness steel plate 201 (step S207). The residual stress of the thick portion 203 may be predicted based on, for example, the relationship shown in FIG. 6 obtained from a database or the like in which past experimental data is accumulated in advance.

  Then, the value obtained by removing the residual stress of the thick portion 203 predicted in step S207 from the tension necessary for eliminating the flatness failure of the thin portion calculated in step S205 is set as the applied tension (step S209). . For example, in the rolling equipment 1 shown in FIG. 5, the applied tension can be applied between the perforated work rolls 101 a and 102 a installed on the final stand of the tandem rolling mill 100 and the pinch roll 110.

  Thereafter, the motor that rotates and drives the pinch rolls 111 and 112 is controlled so that the applied tension calculated in step S209 is applied, and tension is applied to the differential thickness steel plate 201 (step S211).

  In the above, the manufacturing method of the difference thickness steel plate in the case of giving tension | tensile_strength was demonstrated. In the above description, tension is applied to the differential thickness steel plate 201 between the hole work roll of the final stand of the tandem rolling mill 100 and the pinch roll 110, but a method of applying tension to the differential thickness steel plate 201. Is not limited to such an example.

  For example, in the rolling equipment 1 shown in FIG. 5, tension is applied to the differential thickness steel plate 201 between the hole-type work roll and the winding device 140 using the force of winding the steel plate by the winding device 140. May be. Also in this case, according to the distance (air cooling distance) from the perforated work rolls 101a, 102a to the cooling device 120 entry side and the plate passing speed, the applied tension calculated from the above formula (3) is used as the perforated work roll 101a. , 101b and the winding device 140 may be applied. In the differential thickness steel plate 201, the elongation of the steel plate due to the tensile creep property is less likely to occur as the temperature decreases. Therefore, the tension calculated by the formula (3) may be applied to the differential thickness steel plate 201 cooled by the cooling device 120 on the assumption that no elongation due to the applied tension occurs.

  Up to this point, as a method for imparting elongation strain to the thick portion 203 of the differential thickness steel plate 201, explanation has been given regarding light rolling under pressure or tension application between a perforated work roll and a pinch roll. The method of giving elongation strain to the thick part 203 of the differential thickness steel plate 201 is not limited to such an example. The method for imparting elongation strain to the thick wall portion 203 is not limited to light rolling or tension application between a perforated work roll and a pinch roll, and may be another method. For example, leveler correction using a leveler device such as a tension leveler may be performed instead of light rolling or applying tension between a perforated work roll and a pinch roll. In this case, the leveler correction is performed after the hole rolling is performed.

  An example in which the manufacturing method according to the present embodiment described above is executed on a computer will be described. In the embodiment, as a method for eliminating the flatness of the differential thickness steel plate 201, the embodiment (1) describes a case where light rolling is performed after punch rolling, and the embodiment (2) describes a case where tension is applied. . In Example (3), a case where leveler correction is performed will be described.

(Example (1))
In this example, FEM calculation simulating hole rolling and light rolling was performed in this order on the computer, and the results were confirmed. In addition, the rolling conditions of the hole rolling are as shown in Table 1 below.

  First, the result of FEM calculation for the hole rolling will be described. In this example, not only the rolling conditions shown in Table 1 above, but also for the case where only the thin wall width W1 was changed variously from the conditions shown in Table 1 above for reference, FEM calculation was performed, respectively, The relationship between the width W1 and the steepness λ of the thin portion 205 after the hole rolling was acquired.

  FIG. 8 is a diagram showing the relationship between the thin part width W1 and the steepness λ of the thin part 205 after the hole rolling, obtained in the present example. As shown in FIG. 8, between the thin portion width W1 and the steepness λ of the thin portion 205 after the hole rolling, the steepness λ increases linearly as the thin portion width W1 increases. It can be seen that a relationship exists. This result supports the inventors' consideration that the flatness defect in the thin portion 205 is more likely to become obvious as the thin portion width W1 is increased.

  In the case where the differential thickness steel plate 201 is actually manufactured by the procedure shown in FIG. 4, in step S101, for example, only the conditions corresponding to the thin part width W1 = 40 (mm) which is the condition of the current die rolling are FEM. Calculation may be performed to calculate the steepness λ. Alternatively, in step S101, when using a database about the relationship between the rolling conditions and the steepness λ of the thin portion 205 after the hole rolling, parameters included in the rolling conditions as shown in FIG. The relationship between the steepness λ of the thin wall portion 205 after the hole rolling is stored in a database, and the steepness λ may be obtained using such a database.

  From the results shown in FIG. 8, the steepness λ of the thin portion 205 after the hole rolling is performed in the case of the thin portion width W1 = 40 (mm), which is the condition of the present hole rolling, λ = about 8.7. (%)Met.

  Next, the results of FEM calculation for light rolling will be described. From the results of the FEM calculation for the above-described hole rolling, in this example, the FEM calculation related to the light rolling was performed with the steepness λ of the thin portion 205 before the light rolling as 8.7%.

  The results are shown in FIG. FIG. 9 is a diagram illustrating the relationship between the steepness λ before execution of the light reduction rolling, the reduction ratio of the light reduction rolling, and the steepness λ after execution of the light reduction rolling, acquired in this example. In the example shown in FIG. 9, the relationship is a graph in which the horizontal axis represents the rolling reduction ratio r (set value) of the light rolling, and the vertical axis represents the value of the steepness λ of the thin portion 205 after the light rolling. It is represented by a diagram. The steepness λ corresponding to the point where the rolling reduction ratio r on the horizontal axis is zero corresponds to the steepness λ when the light rolling is not performed, that is, the steepness λ before the light rolling is performed. The rolling reduction r shown on the horizontal axis in FIG. 9 is a rolling reduction calculated according to the following formula (4) from the thick part thickness t2 that is the entry side plate thickness and the roll gap g of the light rolling.

  From the results shown in FIG. 9, it can be confirmed that the steepness λ of the thin portion 205 is surely reduced by performing light rolling on the thick portion 203 of the differential thickness steel plate 201 after die rolling. . It can also be seen that the larger the reduction ratio r, the greater the reduction allowance. This result supports the inventors' consideration that the flatness defect of the thin portion 205 can be corrected by applying an elongation strain to the thick portion 203.

  In the case of actually manufacturing the differential thickness steel plate 201 by the procedure shown in FIG. 4, in step S103, for example, data as shown in FIG. 9 is obtained by FEM calculation, and based on the result, after light rolling. What is necessary is just to obtain | require the preferable rolling reduction r which can reduce the steepness (lambda) to the range which does not have a problem as a product. Alternatively, in step S103, when using a database on the relationship between the steepness λ before the light reduction rolling, the reduction ratio of the light reduction rolling, and the steepness λ after the light reduction rolling, FIG. The relationship as shown may be stored in a database, and a preferable reduction ratio r may be obtained using such a database.

  In the FEM calculation used in this example, it is known that the steepness λ tends to be calculated to be large due to the characteristics of the FEM calculation. That is, the value of the steepness λ shown in FIGS. 8 and 9 is larger than the steepness λ generated when the rolling is actually performed under the corresponding conditions. Therefore, in practice, the correlation between the steepness λ calculated by the FEM calculation and the steepness λ generated in the actual rolling is acquired in advance, and from this correlation, the target value of the final steepness λ after correction, And the reduction ratio r that can achieve the target value may be set. For example, it can be seen from the correlation that if the steepness λ in the FEM calculation is 2% or less, the steepness λ can be reduced to a level where there is no problem as a product when the rolling is actually performed. If so, from the relationship shown in FIG. 9, the reduction ratio r of the light rolling may be set to 5% for the purpose of setting the steepness λ after the light rolling to 2% or less.

(Example (2))
In this example, the above-described mathematical expression (3) was used to confirm the effect of reducing strain on the differential thickness steel sheet. The coefficients A, n, and m in Equation (3) are derived from the results of a low strain rate tensile test. In this example, the carbon content is 0.04%, the outlet temperature of the tandem rolling mill is 900 ° C., and the tandem The sheet passing speed on the outlet side of the rolling mill was 240 m / min (4 m / s), and the distance from the hole work roll to the pinch roll placed on the final stand of the tandem rolling mill was 10 m. At this time, the time Δt during which a tension equivalent to the air cooling time can be applied was 2.5 seconds.

  In this example, FEM calculation was performed on the assumption that the same hole-type work roll as in Example (1) was used. From the results shown in FIG. 8, the steepness λ of the thin portion 205 after the hole rolling is performed in the case of the thin portion width W1 = 40 (mm), which is the condition of the hole rolling, is λ = about 8.7 (% )Met. The results are shown in FIG. FIG. 10 is a diagram illustrating the relationship between the steepness λ before execution of tension application, the applied tension, and the steepness λ after execution of tension application acquired in the present embodiment.

When converted into an elongation strain difference Δε, Δε = (π / 2 × λ) ² was 1.9%. However, in order to eliminate the flatness failure, it is necessary to apply a larger elongation strain to the steel sheet. As a result, since it was found that an elongation strain of 3% was required for Δε, the required elongation strain amount Δε was set to 3%.

  From the results of the low strain rate tensile test, the coefficient A was 149 MPa, n = 0.153, and m = 0.101. At this time, the tension required for eliminating the flatness failure of the thin-walled portion calculated by Equation (3) was 55.6 MPa.

  Here, from the relationship between the thin portion width and the residual stress shown in FIG. 6, when the thin portion width is 40 mm, the residual stress in the thick portion is 24.5 MPa. From this, the applied tension was 31.1 MPa by removing the residual stress of the thick part from the necessary tension.

  FIG. 10 shows the relationship between the applied tension and the steepness λ improved by the applied tension. From this correlation, it is known that if the steepness λ in the FEM calculation is 2% or less, the steepness λ can be reduced to a level that does not cause a problem when the product is actually rolled. From the relationship shown in FIG. 10, a tension of 31.1 MPa was applied to the steel plate between the hole work roll and the pinch roll for the purpose of setting the steepness λ after applying the tension to 2% or less. It was confirmed that it should be given.

(Example (3))
In this example, the strain reduction effect of the tension leveler on the differential thickness steel plate was confirmed. In this example, the results of FEM calculation when leveler correction by a tension leveler is performed on a differential thickness steel plate after die rolling will be described. In this example, when the same hole type work roll as in Examples (1) and (2) was used, FEM calculation was performed in the same manner to obtain the steepness λ. From the results shown in FIG. 8, the steepness λ of the thin portion 205 after performing the hole rolling in the case of the thin portion width W1 = 40 (mm), which is the condition of the hole rolling, is the other embodiment described above. Similarly, λ = about 8.7 (%). The result of the FEM calculation is shown in FIG. FIG. 11 is a diagram illustrating the relationship between the steepness λ before execution of leveler correction, the leveler elongation, and the steepness λ after execution of leveler correction obtained in the present embodiment.

  In the tension leveler in a present Example, by giving elongation rate, bending and tension | tensile_strength are provided to a steel plate and the shape correction of a steel plate is performed. In this way, by applying bending and tension to the differential thickness steel sheet with the tension leveler, by applying an elongation strain to the thick part, the flatness defect of the thin part is corrected. Referring to FIG. 11, it can be seen that the steepness λ decreases as the leveler elongation increases. From this correlation, it is known that if the steepness λ in the FEM calculation is 2% or less, the steepness λ can be reduced to a level that does not cause a problem when the product is actually rolled. 11 shows that the steepness λ after leveler correction can be reduced to 2% or less if the leveler elongation is 3% or more for the purpose of reducing the steepness λ after leveler correction to 2% or less. did.

(4. Supplement)
The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, in the above-described embodiment, the condition that the flatness failure becomes obvious in the differential thickness steel plate 201 is “W1 / T1 ≧ 15”. However, the condition is that when the steepness λ in the thin portion 205 is λ> 2%. This is a condition obtained when it is determined that a flatness failure has occurred. Since the threshold value of the steepness λ for determining that the flatness defect has occurred differs depending on the product, the threshold value may be changed according to the product to which the present invention can be applied. The above conditions can also be changed. Alternatively, the occurrence of flatness failure may be determined based on an index other than the steepness λ, and the above condition may be obtained according to the result.

  Moreover, in the said embodiment, although the case where the difference thickness board | plate material which is the object to manufacture was a steel plate was demonstrated as an example, this invention is not limited to this example. The principle that flatness failure may occur in the thin wall portion due to the difference in the elongation strain in the longitudinal direction between the thick wall portion and the thin wall portion is the same in a metal material other than steel. It can apply suitably also to manufacture of the difference thickness board material which becomes. However, “W1 / T1 ≧ 15”, which is a condition that causes a flatness failure in the above-described embodiment, is a condition that holds in steel and a metal material having a longitudinal elastic modulus (Young's modulus) equivalent to that of steel. In other metal materials having different rates, the conditions under which flatness defects are manifested are different. As is clear from the relationship of σ = Eε (σ: stress, ε: strain, E: Young's modulus), even if the difference in longitudinal strain between the thick and thin portions is the same, This is because the stress in the longitudinal direction varies depending on the Young's modulus, and the conditions under which buckling (that is, poor flatness) in the thin portion becomes obvious are also different. Specifically, in general metal materials (for example, aluminum, titanium, magnesium, nickel, copper, etc.), the Young's modulus is lower than that of steel, so flatness defects are more likely to occur. The threshold value of W1 / T1 at which the defect becomes apparent is expected to be smaller than “15” in the above embodiment. When the present invention is applied to steel and a differential thickness plate made of a metal material other than a metal material having a Young's modulus equivalent to that of steel, the flatness failure becomes obvious in consideration of the Young's modulus in the metal material. What is necessary is just to determine the conditions to perform suitably.

DESCRIPTION OF SYMBOLS 100 Tandem rolling mill 101a Upper work roll 102a Lower work roll 110 Pinch roll 120 Cooling device 130 Deflector roll 140 Winding device 201 Differential thickness steel plate (steel plate)
203 Thick part 205 Thin part

Claims (13)

Performing hole rolling using a hole work roll having a diameter difference in the body length direction with respect to a plate material made of a metal material, and providing a plate thickness distribution in the plate width direction to the plate material;
Performed after the step of imparting a plate thickness distribution to the plate material in the plate width direction, a step of imparting elongation strain to the thick part of the plate material, and
Including
When the thickness of the thin portion of the plate after the hole rolling is t1, and the width of the thin portion of the plate after the hole rolling is W1, the thickness t1 of the thin portion, and The width W1 in the plate width direction of the thin portion satisfies W1 / t1 ≧ 15.
A manufacturing method of the differential thickness plate material. The step of applying elongation strain to the thick part is performed by light rolling.
The manufacturing method of the difference thickness board | plate material of Claim 1. In the hole-type rolling, a thickness obtained by adding the thickness reduction of the thick-walled portion in the light rolling to the final desired thickness of the thick-walled portion is the thickness after the hole-rolling is performed. The rolling conditions are set so that the thick part has,
The manufacturing method of the difference thickness board | plate material of Claim 2. In the light rolling, rolling is performed using a work roll whose roll profile is approximated by a first, second, third, or fourth order function, or a lower order function corresponding thereto.
The manufacturing method of the difference thickness board | plate material of Claim 2 or 3. The step of applying elongation strain to the thick part is performed by leveler correction.
The manufacturing method of the difference thickness board | plate material of Claim 1. Perform the above-mentioned roll rolling at any stand other than the final stand of the tandem rolling mill,
Performing the light reduction rolling at any one of the downstream of the stand performing the hole rolling of the tandem rolling mill,
The manufacturing method of the difference thickness board | plate material of any one of Claims 2-4. In the step of applying elongation strain to the thick part, in the air cooling section of the plate material on the tandem rolling mill output side of the hot rolling line where the hole rolling is performed, the plate material is given a tension less than the yield stress, Extending the thick part,
The manufacturing method of the difference thickness board | plate material of Claim 1. The tension is calculated from the residual stress and creep characteristics of the thick part obtained in advance, the outlet temperature of the tandem rolling mill, the sheet passing speed, the air cooling distance which is the distance of the air cooling section,
The manufacturing method of the difference thickness board | plate material of Claim 7. The step of imparting elongation strain to the thick part is performed on a production line different from the hole rolling,
The manufacturing method of the difference thickness board | plate material of any one of Claims 1-5. According to the steepness of the thin portion of the plate material after execution of the hole rolling, which is predicted based on the rolling conditions of the hole rolling before the hole rolling is performed, an elongation strain is applied to the thick portion. The amount of elongation strain applied in the process is set,
The manufacturing method of the difference thickness board | plate material of any one of Claims 1-9. In accordance with the steepness of the thin portion of the plate after the hole rolling that is actually measured after the hole rolling, the amount of elongation strain to be applied in the step of applying elongation strain to the thick portion is set.
The manufacturing method of the difference thickness board | plate material of any one of Claims 1-9. A perforated workpiece having a diameter difference in the body length direction for performing a perforated rolling in which the work roll of any one of the stands other than the final stand imparts a plate thickness distribution in the plate width direction to a plate material made of a metal material. Role,
The work profile of any of the stands downstream from the stand on which the hole-type work roll is provided has a primary roll profile for lightly rolling the thick part of the plate material to which the plate thickness distribution has been imparted. A work roll approximated by a second, third, or fourth order function, or a lower order function corresponding thereto,
When the thickness of the thin portion of the plate after the hole rolling is t1, and the width of the thin portion of the plate after the hole rolling is W1, the thickness t1 of the thin portion, and The perforated work roll is configured so that the width W1 of the thin portion in the plate width direction satisfies W1 / t1 ≧ 15.
Tandem rolling mill. A tandem rolling mill that performs finish rolling by hot rolling;
A cooling device that is disposed on the downstream side in the rolling direction of the tandem rolling mill and cools a plate material made of a metal material;
A pair of pinch rolls disposed between the tandem rolling mill and the cooling device;
With
The work roll of the final stand of the tandem rolling mill is a perforated work roll having a diameter difference in the body length direction for performing perforated rolling that gives a plate thickness distribution in the plate width direction to the plate material,
When the thickness of the thin portion of the plate after the hole rolling is t1, and the width of the thin portion of the plate after the hole rolling is W1, the thickness t1 of the thin portion, and The width W1 of the thin portion in the plate width direction satisfies W1 / t1 ≧ 15,
Rolling equipment that applies tension to the plate by the work roll and the pair of pinch rolls of the final stand.

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