Method for manufacturing a workpiece

Abstract

To reduce residual tensile stress of a fractured surface of a worked material, in shearing a steel plate to manufacture the worked material and to suppress variation in property of a plurality of sheared end faces, even when the worked material has the plurality of sheared end faces.SOLUTION: A manufacturing method for a worked material is provided in which a steel plate is arranged between a first blade and a second blade and the first blade and the second blade are moved relatively to shear the steel plate. At a time point when the first blade and the second blade crack the steel plate, a plate thickness T(mm) of the steel plate and an inclination angle α of the steel plate satisfy the following formula (1), and the plate thickness T(mm) of the steel plate and a tilt angle β of the steel plate satisfy the following formula (2): 0°<α≤13.0° / T0.7 (1) and 0°≤β≤7.5° / T0.7 (2).SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] This application discloses a method for manufacturing a processed material.

Background Art

[0002] Patent Document 1 discloses a technique for obtaining a processed material by shearing a steel sheet using a punch and a die. In Patent Document 1, the tensile residual stress of the fracture surface of the processed material is reduced by pressing the fracture surface of the punched material punched by the punch against the fracture surface of the processed material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As disclosed in Patent Document 1, in a processed material obtained by shearing a steel sheet, the tensile residual stress of the fracture surface may increase. When obtaining a processed material by shearing a steel sheet, a new technique capable of reducing the tensile residual stress of the fracture surface of the processed material is required.

[0005] Further, when the processed material has a plurality of sheared end faces, it is also important to suppress variations in the properties of the plurality of sheared end faces. For example, as shown in FIG. 1, when shearing a steel sheet 5 to form a first sheared end face 1 and a second sheared end face 2, it is preferable to suppress variations in the properties of the first sheared end face 1 and the second sheared end face 2 and reduce the tensile residual stress of the fracture surface on both sheared end faces 1 and 2.

Means for Solving the Problems

[0006] As one means for solving the above problems, this application provides a method for manufacturing a processed material by shearing a steel sheet, Placing the steel plate between the first blade and the second blade, where the steel plate has a first surface and a second surface opposite to the first surface, the first surface being disposed on the first blade side and the second surface being disposed on the second blade side, and, Relatively moving the first blade and the second blade to shear the steel plate, including, When a crack is generated in the steel plate by the first blade and the second blade, the plate thickness T (mm) of the steel plate and the inclination angle α of the steel plate satisfy the relationship of the following formula (1), and the plate thickness T (mm) of the steel plate and the tilt angle β of the steel plate satisfy the relationship of the following formula (2), Manufacturing method of workpiece 0° < α ≤ 13.0° / T 0.7 ··· (1) 0° ≤ β ≤ 7.5° / T 0.7 ··· (2) is disclosed.

[0007] The manufacturing method of the present disclosure may include placing the steel plate between the first blade and the second blade and between the pressing member and the second blade, where the pressing member has a pressing surface that contacts the first surface.

[0008] The manufacturing method of the present disclosure may have a gap in at least one of the space between the pressing member and the steel plate and the space between the steel plate and the second blade when a crack is generated in the steel plate by the first blade and the second blade.

[0009] The manufacturing method of the present disclosure may have a gap larger than the plate thickness T between the pressing member and the second blade when a crack is generated in the steel plate by the first blade and the second blade.

[0010] The manufacturing method of the present disclosure may include arranging a support mechanism for providing a gap larger than the plate thickness T between the pressing member and the second blade.

[0011] In the manufacturing method of the present disclosure, when a crack is generated in the steel plate by the first blade and the second blade, the second blade and the pressing member may face each other with a gap therebetween. The gap may have a relatively small portion and a relatively large portion. When the relatively small portion of the gap is defined as the first portion, the gap may continuously or intermittently increase from the first portion toward the tip of the second blade.

[0012] The manufacturing method of the present disclosure may include disposing a spacer between at least one of the pressing member and the steel plate and between the steel plate and the second blade.

[0013] In the manufacturing method of the present disclosure, the pressing member may have a step at its tip for immersion.

[0014] In the manufacturing method of the present disclosure, the second blade may have a step at its tip for immersion.

[0015] In the manufacturing method of the present disclosure, the tensile strength of the steel plate may be 980 MPa or more.

[0016] In the manufacturing method of the present disclosure, the tensile strength of the steel plate may be 1470 MPa or more.

Advantages of the Invention

[0017] According to the manufacturing method of the present disclosure, when a steel plate is sheared to obtain a processed material, the tensile residual stress of the fracture surface of the processed material can be reduced. Further, even when the processed material has a plurality of sheared end faces, variations in the properties of the plurality of sheared end faces can be suppressed.

Brief Description of the Drawings

[0018]

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Embodiments for Carrying Out the Invention

[0019] 1. Problems and New Findings A processed material having a sheared end face can be obtained, for example, as follows. First, as shown in FIG. 1(A), a steel plate 5 is disposed between a first blade 21 and a second blade 22. Here, the steel plate 5 has a first surface 10a and a second surface 10b on the side opposite to the first surface 10a. The first blade 21 has a first bottom surface 21a, a first side surface 21b, and a first tip portion 21x (see FIG. 2(A)). The second blade 22 has a second bottom surface 22a, a second side surface 22b, and a second tip portion 22x (see FIG. 2(A)). As shown in FIGS. 1(A) and (B), the first bottom surface 21a is disposed on the first surface 10a side of the steel plate 5, and the second bottom surface 22a is disposed on the second surface 10b side of the steel plate 5. The first blade 21 may be a punch, and the second blade 22 may be a die. Subsequently, as shown in FIG. 1(B), the steel plate 5 is sheared by relatively moving the first blade 21 and the second blade 22. As a result, as shown in FIG. 1(C), a part of the steel plate 5 is sheared, and a processed material 10 is obtained. As shown in FIGS. 1(C) and (D), after separating the first blade 21 and the second blade 22, the steel plate 5 may be disposed between the first blade 21 and the second blade 22 again to shear the steel plate 5. By repeating FIGS. 1(A) to (D), a plurality of processed materials 10 having a first sheared end face 1 and a second sheared end face 2 may be obtained.

[0020] Figures 1(A) to 1(D) show a form in which no shear angle is provided between the first blade 21 and the second blade 22, but a shear angle may be provided between the first blade 21 and the second blade 22. Also, Figures 1(A) to 1(D) show a form in which the intersection line (the tip of the first blade 21) between the first bottom surface 21a and the first side surface 21b of the first blade 21 extends linearly in the longitudinal direction of the first blade 21, but the tip of the first blade 21 may extend in a curved shape in the longitudinal direction. That is, the shearing may be performed so that the shapes of the shearing end faces 1 and 2 in plan view are linear, or may be performed so that they are curved, or may be performed so that they are a combination of linear and curved. Also, Figures 1(A) to 1(D) show a form in which the workpiece 10 is punched out by the first blade 21, but by shearing the steel plate 5 with the first blade 21 and the second blade 22, a punched hole, a slit, or the like may be formed in a part of the steel plate 5. Also in this case, a workpiece 10 having shearing end faces 1 and 2 can be obtained.

[0021] An example of the mechanism for forming the shear end faces 1 and 2 will be described. As shown in FIGS. 2(A) to (C), consider the case where the steel plate 5 is sheared by the first blade 21 and the second blade 22 to form the shear end faces 1 and 2. As shown in FIG. 2(A), when the first bottom surface 21a of the first blade 21 is pressed against the first surface 10a of the steel plate 5, a sag 1a is formed on the first surface 10a side of the steel plate 5. The sag 1a is formed in the process until the first tip portion 21x of the first blade 21 bites into the steel plate 5. After the sag 1a is formed, a shear surface 1e (see FIG. 14) may be formed in the process of the first tip portion 21x biting into the steel plate 5. As shown in FIG. 2(B), after the sag 1a and the shear surface 1e are formed, a first crack 1dx occurs from the first blade 21 side toward the second blade 22 side. On the other hand, similarly on the second blade 22 side, after the second tip portion 22x bites into the second surface 10b of the steel plate 5, a second crack 1dy occurs from the second blade 22 side toward the first blade 21 side. As shown in FIG. 2(C), when each of the first crack 1dx and the second crack 1dy progresses and meets each other, a fracture surface 1b is formed. Further, by moving the first blade 21 and the second blade 22 further, a part of the steel plate 5 is separated as a workpiece 10. At this time, as shown in FIG. 2(C), a burr 1c may be formed at the corner portion on the second blade 22 side of the shear end face 1. On the other hand, the second shear end face 2 is formed in the same flow as described above. As shown in FIG. 2(C), the second shear end face 2 has a sag 2a on the second surface 10b side and a burr 2c on the first surface 10a side, and may have a fracture surface 2b and an arbitrary shear surface therebetween. The fracture surface 2b is formed by the progress and meeting of the above-described first crack 1dx and second crack 1dy. As shown in FIGS. 2(A) to (C), the second shear end face 2 can be formed simultaneously with the first shear end face 1. Regardless of the presence or absence of the shear angle between the first blade 21 and the second blade 22 and the shape of the shear end face 1 in plan view (linear, curved, or a combination thereof, punched hole, slit, etc.), the shear end faces 1 and 2 can be formed by the mechanism as shown in FIGS. 2(A) to (C).

[0022] In the sheared end faces 1 and 2 formed as described above, compressive residual stress or tensile residual stress may be generated due to damage, distortion, etc. caused by shearing. If a large tensile residual stress exists in the sheared end faces 1 and 2, the hydrogen embrittlement resistance or fatigue strength, etc. of the sheared end faces 1 and 2 may decrease. In this regard, in order to obtain a high-performance processed material 10, how to reduce the tensile residual stress in the sheared end faces 1 and 2 can be an issue. In particular, as disclosed in Patent Document 1, it is preferable to be able to reduce the tensile residual stress in the fracture surfaces 1b and 2b among the sheared end faces 1 and 2.

[0023] As a result of repeatedly conducting numerous experiments and analyses on the relationship between the shearing conditions for the steel plate 5 and the properties of the sheared end faces 1 and 2 generated by the shearing, the present inventor obtained the following new findings.

[0024] As shown in FIGS. 3(A) to (C), a case where a part (first part) 11 of the steel plate 5 is punched out by the first blade 21 and another part (second part) 12 of the steel plate 5 is punched out by the second blade 22 will be described. In this case, as shown in FIG. 3(A), when a crack preferentially propagates from the first blade 21 side, the tensile residual stress in the sheared end face of the part 11 increases, while the tensile residual stress in the sheared end face of the other part 12 becomes extremely small. That is, while making the part 11 into scrap, the other part 12 can be suitably adopted as a product. Further, as shown in FIG. 3(B), when cracks propagate equally from both the first blade 21 side and the second blade 22 side, a small tensile residual stress of the same level can be generated in the sheared end faces of both the part 11 and the other part 12. That is, the variation in the properties between the part 11 and the other part 12 can be suppressed. In this regard, it can be said that it is suitable when both the part 11 and the other part 12 are adopted as products. Furthermore, as shown in FIG. 3(C), when a crack preferentially propagates from the second blade 22 side, the tensile residual stress in the sheared end face of the other part 12 increases, while the tensile residual stress in the sheared end face of the part 11 becomes extremely small. That is, while making the other part 12 into scrap, the part 11 can be suitably adopted as a product.

[0025] Based on the above findings, the present inventors have found the following (1) to (3). (1) The tensile residual stress generated in the fracture surfaces 1b and 2b of the shear end faces 1 and 2 changes depending on the propagation direction and length of the cracks 1dx and 1dy that form the fracture surface 1b. (2) At the fracture surfaces 1b and 2b, the more equal the lengths of the crack 1dx propagating from the sag 1a side (first blade side) and the crack 1dy propagating from the burr 1c side (second blade side), the more the variation in the properties of the shear end faces 1 and 2 is suppressed, and the tensile residual stress of the fracture surfaces 1b and 2b is reduced at both the shear end faces 1 and 2. (3) That is, when the area ratio of the portion derived from the first crack 1dx propagating from the sag 1a side (burr 2c side) and the area ratio of the portion derived from the second crack 1dy propagating from the burr 1c side (sag 2a side) are equal at the fracture surfaces 1b and 2b of the workpiece 10, the tensile residual stress of the fracture surfaces 1b and 2b can be reduced at both the first shear end face 1 and the second shear end face 2.

[0026] As a result of repeating numerous experiments and analyses regarding controlling the propagation direction and length of the cracks 1dx and 1dy during shearing of the steel plate 5, the present inventors have further obtained the following new findings.

[0027] As shown in FIGS. 4(A) and (B), the propagation direction and length of the cracks 1dx and 1dy change depending on the tilt angle β of the steel plate 5 generated during shearing. Specifically, when the steel plate 5 is greatly bent by the pushing-in of the blades 21 and 22 during shearing and the tilt angle β becomes large, as indicated by the white arrow in FIG. 4(A), the crack 1dx easily propagates from the first blade 21, and the variation in properties between the first shear end face 1 and the second shear end face 2 tends to be large. On the other hand, when the bending of the steel plate 5 due to the pushing-in of the blades 21 and 22 during shearing is small and the tilt angle β becomes small, as indicated by the white arrow in FIG. 4(B), the cracks 1dx and 1dy easily propagate from both the first blade 21 and the second blade 22, and it is easy to suppress the variation in properties between the first shear end face 1 and the second shear end face 2.

[0028] Based on the above findings, the inventor of the present invention repeatedly conducted numerous experiments and analyses on the relationship between the shearing conditions for the steel plate 5 and the tilting angle β of the steel plate 5 that occurs during shearing. As a result, it was found that by shearing the steel plate 5 in a tilted state (a state where the tilt angle α described below exceeds 0°), the tilting angle β can be easily reduced.

[0029] In addition, the inventor of the present invention found that the upper limit values of the tilt angle α and the tilting angle β that can suppress variations in the properties of the sheared end faces 1 and 2 of the processed material 10 after shearing vary depending on the plate thickness T of the steel plate 5. That is, the upper limit values of each of the tilt angle α and the tilting angle β of the steel plate 5 can be expressed as a function of the plate thickness T. By setting each of the tilt angle α and the tilting angle β to be equal to or less than the upper limit value expressed by the function, when the steel plate 5 is sheared, it becomes easier for cracks 1dx and 1dy to propagate from both the first blade 21 and the second blade 22, and it becomes easier to suppress variations in the properties between the first sheared end face 1 and the second sheared end face 2.

[0030] 2. Manufacturing method of processed material The manufacturing method of the present disclosure is a method for manufacturing a processed material 10 by shearing a steel plate 5, placing the steel plate 5 between the first blade 21 and the second blade 22, where the steel plate 5 has a first surface 10a and a second surface 10b opposite to the first surface 10a, and the first surface 10a is disposed on the side of the first blade 21 and the second surface 10b is disposed on the side of the second blade 22 (FIG. 1(A)), and, relatively moving the first blade 21 and the second blade 22 to shear the steel plate 5 (FIG. 1(B)), is included. As shown in FIGS. 5(A) and 5(B), in the manufacturing method of the present disclosure, at the time when cracks are generated in the steel plate 5 by the first blade 21 and the second blade 22, it is important that the plate thickness T (mm) of the steel plate 5 and the tilt angle α of the steel plate 5 satisfy the relationship of the following formula (1), and the plate thickness T (mm) of the steel plate 5 and the tilting angle β of the steel plate 5 satisfy the relationship of the following formula (2). 0° < α ≤ 13.0° / T 0.7 ··· (1) 0° ≤ β ≤ 7.5° / T 0.7 ··· (2)

[0031] 2.1 First blade The first blade 21 may have a first bottom surface 21a, a first side surface 21b, and a first tip portion 21x. The first bottom surface 21a may have a surface that intersects the relative movement direction of the first blade 21, or may have a surface that is orthogonal to the movement direction. Further, the first side surface 21b may have a surface along the relative movement direction of the first blade 21, or may have a surface inclined with respect to the movement direction. The first tip portion 21x refers to a portion near the intersection line of the first bottom surface 21a and the first side surface 21b. For example, the first tip portion 21x may be a portion within a range of 2 mm in both the first bottom surface 21a side and the first side surface 21b side from the intersection line of the first bottom surface 21a and the first side surface 21b. When the tip of the first blade 21 is processed to have an R or is chamfered, assume the intersection line of the surface extended along the first bottom surface 21a and the surface extended along the first side surface 21b, and the portion included within a range of R + 2 mm in both the first bottom surface 21a side and the first side surface 21b side from the intersection line may be regarded as the first tip portion 21x.

[0032] The shape of the first bottom surface 21a can be determined according to the shape of the sheared end surfaces 1 and 2 of the target workpiece 10. The first bottom surface 21a may have a flat surface or a curved surface, and the flat surface or the curved surface may face the first surface 10a during shearing of the steel plate 5.

[0033] The shape of the first side surface 21b can be determined according to the shape of the sheared end surfaces 1 and 2 of the target workpiece 10. The first side surface 21b may have a flat surface or a curved surface.

[0034] The first tip portion 21x may extend linearly or curvilinearly in the longitudinal direction of the first blade 21 (the direction into the page in FIGS. 5(A) and 5(B)), and can be determined according to the shape of the sheared end surfaces 1 and 2 of the target workpiece 10. When providing a punched hole in the steel plate 5, the shape of the first tip portion 21x can be an annular shape along the edge of the punched hole.

[0035] In the standby state before the shearing operation, the first blade 21 may be disposed above the second blade 22. In this case, the first blade 21 may be a punch that punches a part of the steel plate 5 placed on the second bottom surface 22a of the second blade 22 from above downward.

[0036] The first blade 21 is made of a material that is common as a blade used for shearing. For example, the first blade 21 may be made of SKD11. Further, the first blade 21 may have a first coating on its surface.

[0037] 2.2 Second Blade The second blade 22 may have a second bottom surface 22a, a second side surface 22b, and a second tip portion 22x. The second bottom surface 22a may have a surface that intersects the relative movement direction of the second blade 22, or may have a surface that is orthogonal to the movement direction. Further, the second side surface 22b may have a surface along the relative movement direction of the second blade 22, or may have a surface inclined with respect to the movement direction. Further, the second tip portion 22x refers to a portion near the intersection line between the second bottom surface 22a and the second side surface 22b. For example, the second tip portion 22x may be a portion within a range of 2 mm from the intersection line between the second bottom surface 22a and the second side surface 22b toward both the second bottom surface 22a side and the second side surface 22b side. When the tip of the second blade 22 is processed to have an R or the tip is chamfered, an intersection line between a surface extended along the second bottom surface 22a and a surface extended along the second side surface 22b is assumed, and a portion included within a range of R + 2 mm from the intersection line toward both the second bottom surface 22a side and the second side surface 22b side may be regarded as the second tip portion 22x.

[0038] The shape of the second bottom surface 22a can be determined according to the shape of the sheared end faces 1 and 2 of the target workpiece 10. The second bottom surface 22a may have a flat surface or a curved surface, and the flat surface or the curved surface may face the second surface 10b during shearing of the steel plate 5.

[0039] The shape of the second side surface 22b can be determined according to the shape of the sheared end faces 1 and 2 of the target workpiece 10. The second side surface 22b may have a flat surface or a curved surface.

[0040] The second tip 22x may extend linearly or curvilinearly in the longitudinal direction of the second blade 22 (the direction into the page in FIGS. 5(A) and 5(B)), and can be determined according to the shapes of the sheared end faces 1 and 2 of the target workpiece 10. When providing a punched hole in the steel plate 5, the shape of the second tip 22x can be annular along the edge of the punched hole.

[0041] In the standby state before the shearing operation, the second blade 22 may be disposed below the first blade 21. In this case, the second blade 22 may be a die on which the steel plate 5 is placed.

[0042] The second blade 22 is made of a material common as a blade used for shearing. For example, the second blade 22 may be made of SKD11. Further, the second blade 22 may have a second coating on its surface.

[0043] 2.3 Steel Plate The plate thickness T of the steel plate 5 is not particularly limited and can be appropriately determined according to the use of the workpiece 10, etc. The plate thickness T of the steel plate 5 may be, for example, 0.5 mm or more, 0.8 mm or more, or 1.0 mm or more, and may also be 15 mm or less, 10 mm or less, 6.0 mm or less, or 3.0 mm or less. The steel plate 5 may be formed into some shape by bending or the like.

[0044] As shown in FIG. 5(A), the steel plate 5 includes a first surface 10a and a second surface 10b on the side opposite to the first surface 10a. The first surface 10a and the second surface 10b may be parallel to each other. Note that the "parallel" referred to in the present application is not limited to complete parallelism, and substantially parallel is sufficient. That is, even when the first surface 10a and the second surface 10b are not completely parallel, they are regarded as parallel if they are within the range of allowable error in industrial production. Specifically, when the angle formed by the first surface 10a and the second surface 10b is 0° ± 1°, the first surface 10a and the second surface 10b are regarded as parallel.

[0045] The steel sheet 5 may have a surface treatment layer. Examples of the surface treatment layer include a plating layer, a coating film, and the like. Further, the steel sheet 5 may include a plurality of layers having different steel grades. For example, it is also possible to adopt clad steel as the steel sheet 5.

[0046] The mechanical properties of the steel sheet 5 are not particularly limited and can be appropriately determined according to the use of the steel sheet 5. However, the problem of deterioration of hydrogen embrittlement resistance or fatigue strength due to tensile residual stress is particularly likely to occur in high-strength steel sheets. In this regard, the steel sheet 5 may have, for example, a tensile strength of 980 MPa or more, 1180 MPa or more, or 1470 MPa or more. The upper limit of the tensile strength of the steel sheet 5 is not particularly limited, but may be, for example, 2500 MPa or less, 2200 MPa or less, or 2000 MPa or less. Note that the "tensile strength" of the steel sheet referred to in the present application conforms to ISO 6892-1:2009.

[0047] The chemical composition and metallographic structure of the steel plate 5 are not particularly limited and can be appropriately determined according to the use of the processed material 10. According to the technology of the present disclosure, regardless of the chemical composition and metallographic structure of the steel plate 5, the tensile residual stress at the fracture surfaces 1b and 2b can be reduced. As an example of the chemical composition, the steel plate 5 contains, by mass%, C: 0.050 to 0.800%, Si: 0.01 to 3.00%, Mn: 0.01 to 10.00%, Al: 0.001 to 0.500%, P: 0.100% or less, S: 0.050% or less, N: 0.010% or less, Cr: 0 to 3.000%, Mo: 0 to 1.000%, B: 0 to 0.0100%, Ti: 0 to 0.500%, Nb: 0 to 0.500%, V: 0 to 0.500%, Cu: 0 to 0.50%, Ni: 0 to 0.50%, O: 0 to 0.020%, W: 0 to 0.100%, Ta: 0 to 0.10%, Co: 0 to 0.50%, Sn: 0 to 0.050%, Sb: 0 to 0.050%, As: 0 to 0.050%, Mg: 0 to 0.050%, Ca: 0 to 0.050%, Y: 0 to 0.050%, Zr: 0 to 0.050%, La: 0 to 0.050%, Ce: 0 to 0.050%, and the balance: Fe and impurities. In addition, in the above chemical composition of the steel plate 5, the lower limit of the content of Cr, Mo, B, Ti, Nb, V, Cu, Ni, O, W, Ta, Co, Sn, Sb, As, Mg, Ca, Y, Zr, La, and Ce, which are optionally added elements, may be 0.0001% or 0.001%.

[0048] 2.4 Arrangement of the steel plate In the manufacturing method of the present disclosure, the steel plate 5 is arranged between the first blade 21 and the second blade 22 as described above. Here, as shown in FIG. 1(A), the first surface 10a of the steel plate 5 is arranged on the first blade 21 side, and the second surface 10b is arranged on the second blade 22 side. There is no particular limitation on the arrangement of the steel plate 5 between the first blade 21 and the second blade 22, and it may be arranged so that the steel plate 5 can be appropriately sheared. For example, as shown in FIG. 1(A), while the first blade 21 is arranged above the steel plate 5, the steel plate 5 may be placed on the bottom surface 22a of the second blade 22.

[0049] 2.5 Operations and relationships of the first blade and the second blade during shearing In the manufacturing method of the present disclosure, after arranging the steel plate 5 between the first blade 21 and the second blade 22, the steel plate 5 is sheared by relatively moving the first blade 21 and the second blade 22. The relative movement of the first blade 21 and the second blade 22 may be performed by a moving device (not shown). Alternatively, at least one of the first blade 21 and the second blade 22 may be manually moved.

[0050] 2.5.1 Clearance As shown in FIG. 6(A), a clearance C may be provided between the first blade 21 and the second blade 22 during shearing. The clearance C can be appropriately determined according to the material and shape of the steel plate 5, etc. For example, when the steel plate 5 is plate-shaped, the clearance C may be 5% or more of the thickness of the steel plate 5 and may be 30% or less of the thickness of the steel plate 5. Further, according to the new findings of the present inventor, when the clearance C is 5% or more and 15% or less of the thickness of the steel plate 5, it is easy for the first crack 1dx and the second crack 1dy to progress equally with respect to the steel plate 5. Note that the "clearance" referred to in this application conforms to ISO 16630:2009.

[0051] 2.5.2 Shear Angle As shown in FIG. 6(B), a shear angle θs may be provided between the first blade 21 and the second blade 22 during shearing. The shear angle θs can be appropriately determined according to the material and shape of the steel plate 5, etc. For example, the shear angle θs may be 0° or more and may be 5° or less. Further, according to the new findings of the present inventor, when the shear angle θs is 1° or more and 2° or less, it is easy for the first crack 1dx and the second crack 1dy to progress equally with respect to the steel plate 5.

[0052] 2.6 Inclination Angle and Tilt Angle As shown in FIGS. 5(A) and (B), in the manufacturing method of the present disclosure, when a crack is generated in the steel plate 5 by the first blade 21 and the second blade 22, it is important that the plate thickness T (mm) of the steel plate 5 and the inclination angle α of the steel plate 5 satisfy the following formula (1), and the plate thickness T (mm) of the steel plate 5 and the tilt angle β of the steel plate 5 satisfy the following formula (2). 0° < α ≦ 13.0° / T 0.7··· (1) 0° ≦ β ≦ 7.5° / T 0.7 ··· (2).

[0053] In the present application, the "tilt angle α" and the "tilt angle β" can be specified, for example, as follows, based on the traveling direction of the first blade 21 and the second blade. First, as shown in FIGS. 5(A) and 5(B), in a cross section including the first blade 21, the second blade 22, and the steel plate 5, in a cross section orthogonal to the extending direction of the tip portions 21x and 22x, the relative moving direction of the first blade 21 and the second blade 22 is defined as the Y direction, and the direction orthogonal to the Y direction is defined as the X direction. Also, the portion of the steel plate 5 pressed by the first blade 21 (when the first blade 21 is a punch, the portion punched by the punch) is defined as the first portion 11, and the portion of the steel plate 5 pressed by the second blade 22 (when the second blade 22 is a die, the portion remaining on the die) is defined as the second portion 12. Further, when a crack is generated in the steel plate 5 by the first blade 21 and the second blade 22, it is assumed that the first portion 11 pressed by the first blade 21 falls in the moving direction of the first blade 21, and a bend occurs in the steel plate 5 at the boundary between the first portion 11 and the second portion 12. In such a state, as shown in FIGS. 5(A) and 5(B), in the above cross section, the angle formed by the line L1 along the X direction and the line L2 along the extending direction of the second portion 12 is defined as the "tilt angle α". Also, the angle formed by the line L2 along the extending direction of the second portion 12 and the line L3 along the extending direction of the first portion 11 is defined as the "tilt angle β" (the angle obtained by subtracting the tilt angle α from the angle formed by the line L1 along the X direction and the line L3 along the extending direction of the first portion 11 is defined as the "tilt angle β"). When the first portion 11 and the second portion 12 extend in a curved shape in the above cross section due to the bending of the steel plate 5 or a pressing member (not shown), as shown in FIG. 5(B), when specifying L2 and L3, the "tangent line" related to the extending direction of each of the portions 11 and 12 at the boundary between the first portion 11 and the second portion 12 may be adopted. Incidentally, as shown in FIGS. 5(A) and 5(B), in the above cross section, the straight line connecting the centers in the thickness direction (the centroid in the thickness direction) of the steel plate 5 is regarded as the "extending direction" of the steel plate 5.

[0054] Alternatively, in the present application, the "tilt angle α" and the "fall angle β" can be specified, for example, as follows, based on the shape of the sheared end face after shearing. Figures 7(A) and (B) show an example of a method for specifying the tilt angle α and the fall angle β based on the shape of the sheared end face. Figure 7(A) shows the case where the clearance is small, and Figure 7(B) shows the case where the clearance is large. As shown in Figures 7(A) and (B), the angle γ formed by the first surface 10a of the first portion 11 and the sheared surface of the sheared end face 2 is specified. Further, the angle α (which coincides with the "tilt angle α") formed by the second surface 10b of the second portion 12 and the shape of the second surface 10b in the vicinity of the burr of the sheared end face 1, which is the shape of the surface extending from the burr toward the second portion 12 side (the shape of the surface pressed by the second bottom surface of the second blade) is specified. In this case, the "fall angle β" can be specified as β = 90° - α - γ.

[0055] Thus, in the manufacturing method of the present disclosure, when shearing the steel sheet 5, by providing a predetermined tilt angle α to the steel sheet 5, the fall angle β can be reduced, and it is easy for the cracks 1dx and 1dy to propagate from both the first blade 21 and the second blade 22. As a result, variations in the properties of the sheared end faces 1 and 2 are suppressed, and the tensile residual stress in the fracture surfaces 1b and 2b of the sheared end faces 1 and 2 is reduced. In the manufacturing method of the present disclosure, the tilt angle α and the fall angle β only need to be within a range that satisfies the above formulas (1) and (2), and can be appropriately determined according to the plate thickness. The tilt angle α may be more than 0°, 1° or more, 2° or more, 3° or more, or 4° or more, and may be 15° or less, 12° or less, or 10° or less. Further, the fall angle β may be 10° or less, 8° or less, or 6° or less, and may be 0° or more, more than 0°, 2° or more, or 4° or more.

[0056] 2.7 Control Modes of Tilt Angle and Fall Angle When shearing the steel plate 5, various methods can be considered as a method for controlling the inclination angle α and the tilt angle β within the above ranges. For example, as shown in Fig. 5(A), when shearing the steel plate 5, a form in which a part of the second surface 10b of the steel plate 5 is floated with respect to the second bottom surface 22a can be mentioned. Also, a specific pressing member described later may be adopted, a specific shape may be provided on the second blade 22, or other members may be arranged. Hereinafter, an example of a method capable of controlling the inclination angle α and the tilt angle β within a specific range will be described.

[0057] 2.7.1 Pressing Member As shown in Fig. 8, the manufacturing method of the present disclosure may include arranging the steel plate 5 between the first blade 21 and the second blade 22 and between the pressing member 31 and the second blade 22, where the pressing member 31 has a pressing surface 31a that contacts the first surface 10a. The pressing member 31 only needs to be able to appropriately press a part of the first surface 10a of the steel plate 5, and the specific shape, size, etc. are not particularly limited. The pressing surface 31a may be a flat surface, a curved surface, or a combination of a flat surface and a curved surface. The pressing member 31 may be connected to a known moving device or the like and be relatively movable with respect to the second bottom surface 22a of the second blade 22. That is, by moving the pressing member 31 relatively closer to the second bottom surface 22a, the steel plate 5 can be pressed against the second bottom surface 22a.

[0058] 2.7.2 Distance and Gap between the Pressing Member and the Second Blade When using the pressing member 31, as shown in Fig. 9(A), at the time when a crack is generated in the steel plate 5 by the first blade 21 and the second blade 22, there may be gaps G1 and G2 in at least one of the space between the pressing member 31 and the steel plate 5 and the space between the steel plate 5 and the second blade 22. Alternatively, as shown in Fig. 9(B), at the time when a crack is generated in the steel plate 5 by the first blade 21 and the second blade 22, there may be an interval I larger than the plate thickness T (the distance between the first surface 10a and the second surface 10b) between the pressing member 31 and the second blade 22. Thus, at the time when a crack is generated in the steel plate 5 by the first blade 21 and the second blade 22, the presence of predetermined gaps G1, G2 or interval I between the pressing member 31 and the second blade 22 makes it easier to control the inclination angle α and the tilt angle β within the above ranges.

[0059] 2.7.3 Support mechanism Also, when using the pressing member 31, as shown in Fig. 10, the manufacturing method of the present disclosure may include arranging a support mechanism 41 for providing an interval I larger than the plate thickness T (the distance between the first surface 10a and the second surface 10b) between the pressing member 31 and the second blade 22. The support mechanism 41 may have a shape, rigidity, etc. such that it can hold the pressing member 31 and the second blade 22 at a predetermined interval I. Thus, even when a predetermined support mechanism 41 is arranged between the pressing member 31 and the second blade 22, it is easier to control the inclination angle α and the tilt angle β within the above ranges.

[0060] 2.7.4 Shapes of the tips of the pressing member and the second blade Also, when using the pressing member 31, as shown in Figs. 11(A) and (B), at the time when a crack is generated in the steel plate 5 by the first blade 21 and the second blade 22, the second blade 22 and the pressing member 31 face each other with an interval I, and the interval I has a relatively small part and a relatively large part. When the relatively small part of the interval I is defined as the first part (narrow part) F, the interval I may increase continuously or intermittently from the first part F toward the tip of the second blade 22. Thus, even when the interval I is increased at the tip of the second blade 22, it is easier to control the inclination angle α and the tilt angle β within the above ranges.

[0061] 2.7.5 Spacer Further, when using the pressing member 31, as shown in FIGS. 12(A) and 12(B), the manufacturing method of the present disclosure may include arranging spacers 51 and 52 between at least one of the pressing member 31 and the steel plate 5 and between the steel plate 5 and the second blade 22. The size and shape of the spacers 51 and 52 are not particularly limited, and any shape may be used as long as it can provide a desired gap between the pressing member 31 and the steel plate 5 or between the steel plate 5 and the second blade 22. Thus, even when the spacers 51 and 52 are arranged at a predetermined position between the pressing member 31 and the second blade 22, it is easy to control the inclination angle α and the tilting angle β within the above ranges.

[0062] 2.7.6 Step Further, as shown in FIG. 13(A), the pressing member 31 may have a step 35 that is recessed at its tip. The position, depth, and size (the range where the step 35 is provided) of the step 35 are not particularly limited and may be appropriately determined according to the shape of the steel plate 5 and the like. Thus, by providing the step 35 by recessing the tip of the pressing member 31, even when the distance I between the pressing member 31 and the second blade 22 is increased at the tip, it is easy to control the inclination angle α and the tilting angle β within the above ranges.

[0063] Further, as shown in FIG. 13(B), the second blade 22 may have a step 25 that is recessed at its tip. The position, depth, and size (the range where the step 25 is provided) of the step 25 are not particularly limited and may be appropriately determined according to the shape of the steel plate 5 and the like. Even in such a case, the inclination angle α and the tilting angle β can be within the above ranges. Although the pressing member 31 is shown in FIG. 13(B), when the step 25 is provided at the tip of the second blade 22, even if the pressing member 31 does not exist, it is easy to control the inclination angle α and the tilting angle β within the above ranges.

[0064] 3. An Example of the Properties of the Workpiece According to the manufacturing method of the present disclosure, the variation in the properties between the first shear end face 1 and the second shear end face 2 can be reduced, and the tensile residual stress can be reduced at the fracture surfaces 1b and 2b of both the shear end faces 1 and 2. The first shear end face 1 and the second shear end face 2 can have a similar configuration. Hereinafter, an example of the configuration of the first shear end face 1 of the workpiece 10 will be described, but the form of the workpiece obtained by the manufacturing method of the present disclosure is not limited to the following form. As shown in FIGS. 14 and 15, the first shear end face 1 of the workpiece 10 includes a sag 1a, a fracture surface 1b, and a burr 1c. The fracture surface 1b includes a first fracture part 1bx and a second fracture part 1by. The first fracture part 1bx is formed by a first crack 1dx that progresses from the sag 1a side to the burr 1c side, and the second fracture part 1by is formed by a second crack 1dy that progresses from the burr 1c side to the sag 1a side. As described above, according to the manufacturing method of the present disclosure, by setting the inclination angle α and the tilt angle β within the above ranges, the lengths of the first crack 1dx and the second crack 1dy are likely to be equal.

[0065] As shown in FIGS. 14 and 15, the first shear end face 1 includes a sag 1a, a fracture surface 1b, and a burr 1c. Further, the first shear end face 1 may include a shear surface 1e. Among the first shear end face 1, the sag 1a, the burr 1c, and the shear surface 1e can take any form according to the form of the workpiece 10. The sag 1a, the burr 1c, and the shear surface 1e may have the same form as in the prior art.

[0066] The workpiece 10 has a characteristic in the configuration of the fracture surface 1b of the first shear end face 1. As shown in FIGS. 14 and 15, the fracture surface 1b includes a first fracture part 1bx and a second fracture part 1by. The first fracture part 1bx is formed by a first crack 1dx that progresses from the sag 1a side to the burr 1c side, and the second fracture part 1by is formed by a second crack 1dy that progresses from the burr 1c side to the sag 1a side.

[0067] The advancing direction of the first crack 1dx may be any direction from the sag 1a side toward the burr 1c side. When the workpiece 10 is plate-shaped, the advancing direction of the first crack 1dx may be a direction along the thickness direction of the workpiece 10 (a direction perpendicular to the first surface 10a and the second surface 10b), or may be a direction inclined with respect to the thickness direction. Also, the advancing direction of the second crack 1dy may be any direction from the burr 1c side toward the sag 1a side. When the workpiece 10 is plate-shaped, the advancing direction of the second crack 1dy may be a direction along the thickness direction of the workpiece 10 (a direction perpendicular to the first surface 10a and the second surface 10b), or may be a direction inclined with respect to the thickness direction. For example, when shearing the steel plate 5 and a clearance C is provided between the first blade 21 and the second blade 22, the advancing directions of the first crack 1dx and the second crack 1dy may be inclined with respect to the thickness direction, and the greater the clearance, the greater the inclination may be.

[0068] The first crack 1dx only needs to start from the sag 1a side and advance toward the burr 1c side and merge with the second crack 1dy on the burr 1c side, and does not necessarily have to advance along the shortest path from the sag 1a side toward the second crack 1dy on the burr 1c side. For example, the first crack 1dx may advance in the direction of the back of the paper in Fig. 2(B) (when the workpiece 10 is plate-shaped, for example, the plate width direction) while advancing from the sag 1a side toward the burr 1c side. The same applies to the second crack 1dy.

[0069] On the first shear end face 1, the area ratio X1 of the first fracture part 1bx in the fracture face 1b may be equal to the area ratio X2 of the second fracture part 1by in the fracture face 1b. In other words, on the first shear end face 1, the average length of the first crack 1dx advancing from the sag 1a side toward the burr 1c side may be equal to the average length of the second crack 1dy advancing from the burr 1c side toward the sag 1a side. As described above, when the area ratio X1 and the area ratio X2 are equal, the variation in the properties of the shear end faces 1 and 2 can be suppressed, and the tensile residual stress of the fracture face 1b can be reduced.

[0070] When specifying the area ratio of each of the first fracture part 1bx and the second fracture part 1by and the length of each of the first crack 1dx and the second crack 1dy in the fracture surface 1b, the unevenness of the surface of the fracture surface 1b shall not be considered. For example, as shown in FIG. 15, when the first shear end face 1 is viewed from the front, if the position where the first crack 1dx starts is P1, the position where the second crack 1dy starts is P2, and the position where the first crack 1dx and the second crack 1dy meet is P3, the ratio of the interval between P1 and P3 to the interval between P1 and P2 can be regarded as the area ratio X1 of the first fracture part 1bx, and the ratio of the interval between P2 and P3 to the interval between P1 and P2 can be regarded as the area ratio X2 of the second fracture part 1by.

[0071] According to the findings of the present inventors, the more the area ratio X1 of the first fracture part 1bx in the fracture surface 1b is equal to the area ratio X2 of the second fracture part 1by in the fracture surface 1b, the more the variation in the properties of the shear end faces 1 and 2 can be suppressed.

[0072] In addition, the burr 1c may have a size that cannot be visually confirmed. Regarding which of the first surface 10a and the second surface 10b of the workpiece 10 is the surface on the sag 1a side and which is the surface on the burr 1c side, even if the burr 1c cannot be confirmed, it can be easily determined by observing the shape of the workpiece 10.

[0073] In the first shear end face 1, the shear surface 1e and the fracture surface 1b have different properties. For example, the shear surface 1e and the fracture surface 1b have different roughness (glossiness). In this regard, even by simply observing the appearance, the shear surface 1e and the fracture surface 1b can be easily distinguished.

[0074] At the fracture surface 1b, the boundary between the first fracture part 1bx and the second fracture part 1by (the position where the first crack 1dx and the second crack 1dy meet) can be determined, for example, by introducing a large amount of hydrogen into the first shear end face 1. As described above, the stress generated during the crack propagation depends on the crack propagation direction. That is, as shown in FIGS. 16(A) and (B), it can be said that the residual stress changes abruptly at the position where the first crack 1dx and the second crack 1dy meet. Therefore, the direction of the hydrogen embrittlement crack caused by the intrusion of hydrogen also changes abruptly at the position where the first crack 1dx and the second crack 1dy meet. Considering this, the position where the direction of the hydrogen embrittlement crack changes abruptly can be regarded as the position where the first crack 1dx and the second crack 1dy meet.

[0075] The workpiece 10 only needs to have the first shear end face 1, and the configuration other than the first shear end face 1 is not particularly limited. As described above, the workpiece 10 may have an end face other than the first shear end face 1 (for example, the second shear end face 2). The shape of the workpiece 10 corresponds to the shape of the steel plate 5 described above. That is, the workpiece 10 may have a plate-like portion as described above. Further, the workpiece 10 may include a first surface 10a and a second surface 10b on the side opposite to the first surface 10a as surfaces other than the shear end faces 1 and 2, and the first surface 10a and the second surface 10b may be connected via the shear end faces 1 and 2. The first surface 10a and the second surface 10b may be parallel to each other. Further, the workpiece 10 may have a surface treatment layer as described above. Further, the workpiece 10 may include a plurality of layers having different steel grades. An example of the mechanical properties and chemical composition of the workpiece 10 is also as described above.

Example

[0076] As steel plates, a steel plate A with a tensile strength of 1470 MPa, a steel plate B with a tensile strength of 1310 MPa, a steel plate C with a tensile strength of 1180 MPa, and a steel plate D with a tensile strength of 980 MPa were prepared.

[0077] Using a punch as the upper blade (first blade) and a die as the lower blade (second blade), a part of the steel plate was sheared while maintaining the distance between the punch and the die at 10% of the plate thickness to obtain a processed material. After shearing, the tensile residual stress was measured for each of the sheared end face on the steel plate side (first sheared end face 1, see Fig. 1) and the sheared end face on the processed material side (second sheared end face 2, see Fig. 1).

[0078] Incidentally, the tensile residual stress was measured as follows. Fig. 17 shows the method for measuring the tensile residual stress. As shown in Fig. 17, at the center position in the plate thickness direction, residual stress measurement by X-ray was carried out with a spot diameter of φ500 μm (at three different positions in the plate width direction). The measurement directions of the residual stress were three directions: the plate thickness direction, the plate width direction, and the direction 45 degrees from the plate thickness direction. For calculating the residual stress, the 2 sinψ method was used. Assuming that the residual stress in the end face normal direction is zero, the maximum principal stress was calculated from the residual stresses in the three calculated directions. The values of the maximum principal stress calculated at the three positions were averaged.

[0079] 1. First form 1.1 Example 1 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 4.0° and the tilt angle β was set to 4.5°. The inclination angle α and the tilt angle β were adjusted by providing a gap of 0.5 times the plate thickness between the plate presser (pressing member) and the lower blade (die) as shown in Fig. 9 during shearing of the steel plate. Table 1 below shows the measurement results of the tensile residual stress.

[0080] 1.2 Example 2 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 5.0° and the tilt angle β was set to 3.5°. The inclination angle α and the tilt angle β were adjusted by providing a gap of 1.0 times the plate thickness between the plate presser (pressing member) and the lower blade (die) as shown in Fig. 9 during shearing of the steel plate. Table 1 below shows the measurement results of the tensile residual stress.

[0081] 1.3 Comparative Example 1 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 0°, and the tilt angle β was set to 5.5°. The inclination angle α and the tilt angle β were adjusted to be in the form as shown in Fig. 4(A) using tools (punch, die, and pressing member) as shown in Fig. 8 during shearing of the steel plate. That is, when the steel plate was sheared with the punch while holding the steel plate with the die and the pressing member, the tilt angle β naturally became 5.5°. In addition, when the plate thicknesses of the steel plates were the same, it was also confirmed that substantially the same tilt angle β was obtained regardless of the strength of the steel plate. Table 1 below shows the measurement results of the tensile residual stress.

[0082] 1.4 Reference Example When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 0°, and the tilt angle β was set to 0°. The inclination angle α and the tilt angle β were adjusted to be in the form as shown in Fig. 4(B) by installing a reverse plate presser at the position where the upper blade (punch) and the steel plate were sandwiched in addition to the tools (punch, die, and pressing member) as shown in Fig. 8 during shearing of the steel plate. Table 1 below shows the measurement results of the tensile residual stress.

[0083]

Table 1

[0084] 2. Second Form 2.1 Example 3 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 1.5°, and the tilt angle β was set to 4.5°. The inclination angle α and the tilt angle β were adjusted by installing a step with a height of 0.1 mm at a position 10 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. Table 2 below shows the measurement results of the tensile residual stress.

[0085] 2.2 Example 4 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 2.2° and the tilt angle β was set to 4.3°. The inclination angle α and the tilt angle β were adjusted by providing a step of 0.2 mm in height at a position 10 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. Table 2 below shows the measurement results of the tensile residual stress.

[0086] 2.3 Example 5 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 4.5° and the tilt angle β was set to 4.0°. The inclination angle α and the tilt angle β were adjusted by providing a step of 0.5 mm in height at a position 10 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. Table 2 below shows the measurement results of the tensile residual stress.

[0087] 2.4 Example 6 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 9.0° and the tilt angle β was set to 2.5°. The inclination angle α and the tilt angle β were adjusted by providing a step of 2.0 mm in height at a position 20 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. Table 2 below shows the measurement results of the tensile residual stress.

[0088] 2.5 Example 7 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 7.0° and the tilt angle β was set to 3.0°. The inclination angle α and the tilt angle β were adjusted by providing a step of 2.0 mm in height at a position 30 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. Table 2 below shows the measurement results of the tensile residual stress.

[0089] 2.6 Comparative Example 2 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 14.0° and the tilt angle β was set to 2.0°. The inclination angle α and the tilt angle β were adjusted by providing a step of 2.0 mm in height at a position 10 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. Table 2 below shows the measurement results of the tensile residual stress.

[0090]

Table 2

[0091] 3. Third form 3.1 Example 8 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 1.0° and the tilt angle β was set to 5.0°. The inclination angle α and the tilt angle β were adjusted by providing a step of 2.0 mm in height at a position 20 mm from the tip of the plate clamp (clamping member) as shown in Fig. 12(A) or Fig. 13(A) during shearing of the steel plate. Table 3 below shows the measurement results of the tensile residual stress.

[0092] 3.2 Example 9 When a crack was generated in a steel plate (plate thickness: 1.6 mm) by a punch and a die, the inclination angle α of the steel plate was set to 6.0° and the tilt angle β was set to 3.0°. The inclination angle α and the tilt angle β were adjusted by providing a step of 2.0 mm in height at a position 40 mm from the tip of the plate clamp (clamping member) as shown in Fig. 12(A) or Fig. 13(A) during shearing of the steel plate. Table 3 below shows the measurement results of the tensile residual stress.

[0093]

Table 3

[0094] 4. Fourth form 4.1 Example 10 When a crack was generated in a steel plate (plate thickness: 0.8 mm) by a punch and a die, the inclination angle α of the steel plate was set to 2.5°, and the tilt angle β was set to 8.0°. The inclination angle α and the tilt angle β were adjusted by installing a step with a height of 0.1 mm at a position 10 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. The measurement results of the tensile residual stress are shown in Table 4 below.

[0095] 4.2 Example 11 When a crack was generated in a steel plate (plate thickness: 0.8 mm) by a punch and a die, the inclination angle α of the steel plate was set to 3.5°, and the tilt angle β was set to 7.5°. The inclination angle α and the tilt angle β were adjusted by installing a step with a height of 0.2 mm at a position 10 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. The measurement results of the tensile residual stress are shown in Table 4 below.

[0096] 4.3 Example 12 When a crack was generated in a steel plate (plate thickness: 0.8 mm) by a punch and a die, the inclination angle α of the steel plate was set to 7.5°, and the tilt angle β was set to 6.5°. The inclination angle α and the tilt angle β were adjusted by installing a step with a height of 0.5 mm at a position 10 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. The measurement results of the tensile residual stress are shown in Table 4 below.

[0097] 4.4 Example 13 When a crack was generated in a steel plate (plate thickness: 0.8 mm) by a punch and a die, the inclination angle α of the steel plate was set to 15.0°, and the tilt angle β was set to 4.0°. The inclination angle α and the tilt angle β were adjusted by installing a step with a height of 2.0 mm at a position 20 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel plate. The measurement results of the tensile residual stress are shown in Table 4 below.

[0098] 4.5 Example 14 When a crack was generated in a steel sheet (sheet thickness: 0.8 mm) by a punch and a die, the inclination angle α of the steel sheet was set to 11.5° and the tilt angle β was set to 5.0°. The inclination angle α and the tilt angle β were adjusted by providing a step of 2.0 mm in height at a position 30 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel sheet. Table 4 below shows the measurement results of the tensile residual stress.

[0099] 4.6 Comparative Example 3 When a crack was generated in a steel sheet (sheet thickness: 0.8 mm) by a punch and a die, the inclination angle α of the steel sheet was set to 0° and the tilt angle β was set to 9.0°. The inclination angle α and the tilt angle β were adjusted to be in the form as shown in Fig. 4(A) using tools (punch, die and pressing member) as shown in Fig. 8 during shearing of the steel sheet. That is, when the steel sheet was sheared with a punch while holding the steel sheet with a die and a pressing member, the tilt angle β naturally became 9.0°. Table 4 below shows the measurement results of the tensile residual stress.

[0100] 4.7 Comparative Example 4 When a crack was generated in a steel sheet (sheet thickness: 0.8 mm) by a punch and a die, the inclination angle α of the steel sheet was set to 23.0° and the tilt angle β was set to 3.5°. The inclination angle α and the tilt angle β were adjusted by providing a step of 2.0 mm in height at a position 10 mm from the tip of the lower blade (die) as shown in Fig. 12(B) or Fig. 13(B) during shearing of the steel sheet. Table 4 below shows the measurement results of the tensile residual stress.

[0101]

Table 4

[0102] From the results shown in Tables 1 to 4, the following can be understood. (I) From the results of the reference examples shown in Tables 1 to 3, when shearing the steel plate, the steel plate is pressed against the die using a plate holder, and the steel plate is pressed against the punch using a reverse plate holder, so that the tilting angle β does not occur in the steel plate, thereby suppressing the variation in the tensile residual stress between the first shearing end face and the second shearing end face. As shown in Fig. 4(B), it is considered that during the shearing of the steel plate, cracks propagated equally from both the punch side and the die side. (II) From the comparison between Examples 1 to 9 and Comparative Example 1 shown in Tables 1 to 3, the following can be said regarding the shearing of a 1.6-mm-thick steel plate. That is, when shearing the steel plate, when the steel plate is tilted (when the tilting angle α exceeds 0°), the tilting angle β becomes smaller than when the steel plate is not tilted, and the variation in the tensile residual stress between the first shearing end face and the second shearing end face is suppressed. (III) From the comparison between Examples 10 to 14 and Comparative Example 3 shown in Table 4, the following can be said regarding the shearing of a 0.8-mm-thick steel plate. That is, when shearing the steel plate, when the steel plate is tilted (when the tilting angle α exceeds 0°), the tilting angle β becomes smaller than when the steel plate is not tilted, and the variation in the tensile residual stress between the first shearing end face and the second shearing end face is suppressed. (IV) From the comparison between Examples 1 to 9 and Comparative Examples 1 and 2 shown in Tables 1 to 3, the following can be said regarding the shearing of a 1.6-mm-thick steel plate. That is, when shearing the steel plate, when the tilting angle α of the steel plate becomes larger than 14°, although the tilting angle β can be made smaller, the variation in the tensile residual stress between the first shearing end face and the second shearing end face rather becomes larger. (V) From the comparison between Examples 10 to 14 and Comparative Examples 3 and 4 shown in Table 4, the following can be said regarding the shearing of a 0.8-mm-thick steel plate. That is, when shearing the steel plate, when the tilting angle α of the steel plate becomes larger than 23°, although the tilting angle β can be made smaller, the variation in the tensile residual stress between the first shearing end face and the second shearing end face rather becomes larger. (VI) From the comparison between Examples 1 to 9 and Comparative Examples 1 and 2 shown in Tables 1 to 3, and Examples 10 to 14 and Comparative Examples 3 and 4 shown in Table 4, the following can be said. As described above, when shearing the steel plate, if the inclination angle α of the steel plate is too large, although the falling angle β can be made small, the variation between the tensile residual stress of the first shear end face and the tensile residual stress of the second shear end face rather becomes large. The upper limit value of the inclination angle α that can suppress such variation changes depending on the thickness of the steel plate. Specifically, when the steel plate is thick, the upper limit value of α becomes small, and when the steel plate is thin, the upper limit value of α becomes large. As will be described later, the upper limit value of the inclination angle α can be expressed as a function of the thickness T of the steel plate. (VII) From the comparison between Comparative Example 1 shown in Tables 1 to 3 and Comparative Example 3 shown in Table 4, the following can be said. That is, when the steel plate on the die is pressed with a plate presser to make the inclination angle α 0°, and the steel plate is sheared by a punch, the thinner the steel plate thickness, the larger the falling angle β. In other words, the upper limit value of the falling angle β can also change depending on the thickness of the steel plate. As will be described later, the upper limit value of the falling angle β can be expressed as a function of the thickness T of the steel plate.

[0103] In relation to the above findings (VI) and (VII), the present inventor confirmed the relationship between the inclination angle α and the falling angle β at the time of steel plate shearing, and the tensile residual stress generated on the shear end face, for steel plates of various thicknesses. As a result, it was found that the upper limit values of each of the inclination angle α and the falling angle β can be organized as a function of the thickness T of the steel plate. Specifically, when shearing the steel plate, when the inclination angle α of the steel plate satisfies the relationship of the following formula (1) and the falling angle β satisfies the relationship of the following formula (2), it was found that the variation in the tensile residual stress between the first shear end face and the second shear end face can be suppressed. 0° < α ≦ 13.0° / T 0.7 ··· (1) 0° ≦ β ≦ 7.5° / T 0.7 ··· (2) For example, when the thickness of the steel plate is 0.8 mm, the upper limit of the inclination angle α is 13.0° ÷ 0.8 0.7 = 15.2°, and the upper limit of the inclination angle β is 7.5° ÷ 0.8 0.7=8.8°. Also, when the thickness of the steel plate is 1.6 mm, the upper limit of the inclination angle α is 13.0°÷1.6 0.7 =9.4°, and the upper limit of the inclination angle β is 7.5°÷1.6 0.7 =5.4°.

Industrial Applicability

[0104] The processed material manufactured by the method of the present disclosure can be used as a constituent material for, for example, automobiles, home appliances, building structures, ships, bridges, construction machinery, various plants, penstocks, etc.

Explanation of Signs

[0105] 1 First shear end face 1a Sag 1b Fracture surface 1bx First fracture part 1by Second fracture part 1c Burr 1dx First crack 1dy Second crack 1e Shear surface 2 Second shear end face 2a Sag 2b Fracture surface 2c Burr 10 Processed material 5 Steel plate 10a First surface 10b Second surface 11 Part of the steel plate (first part) 12 Other part of the steel plate (second part) 21 First blade 21a First bottom surface 21b First side surface 21x First tip 22 Second blade 22a Second bottom surface 22b Second side surface 22x Second tip 25 Step 31 Pressing member 31a Pressing surface 35 Step 41 Support mechanism 51 Spacer 52 spacers

Claims

1. A method for manufacturing a processed material by shearing a steel plate, comprising: placing the steel plate between a first blade and a second blade and between a pressing member and the second blade, wherein the steel plate has a first surface and a second surface opposite to the first surface, the first surface is disposed on the first blade side, the second surface is disposed on the second blade side, and the pressing member has a pressing surface facing the first surface; and relatively moving the first blade and the second blade to shear the steel plate. The method includes: when the pressing member has a stepped portion that sinks at its tip, at the time when a crack is generated in the steel plate by the first blade and the second blade, the plate thickness T (mm) of the steel plate and the inclination angle α of the steel plate satisfy the following formula (1), and the plate thickness T (mm) of the steel plate and the tilting angle β of the steel plate satisfy the following formula (2): A method for manufacturing a processed material. 0° < α ≤ 13.0° / T ０．７ ... (1) 0° ≤ β ≤ 7.5° / T ０．７ ... (2)

2. A method for manufacturing a processed material by shearing a steel plate, comprising: placing the steel plate between a first blade and a second blade and between a pressing member and the second blade, wherein the steel plate has a first surface and a second surface opposite to the first surface, the first surface is disposed on the first blade side, the second surface is disposed on the second blade side, and the pressing member has a pressing surface facing the first surface; placing a spacer between at least one of the pressing member and the steel plate and between the steel plate and the second blade; and relatively moving the first blade and the second blade to shear the steel plate. The method includes: when shearing the steel plate with the spacer disposed between at least one of the pressing member and the steel plate and between the steel plate and the second blade, at the time when a crack is generated in the steel plate by the first blade and the second blade, the plate thickness T (mm) of the steel plate and the inclination angle α of the steel plate satisfy the following formula (1), and the plate thickness T (mm) of the steel plate and the tilting angle β of the steel plate satisfy the following formula (2): A method for manufacturing a processed material. 0° < α ≤ 13.0° / T ０．７ ... (1) 0° ≤ β ≤ 7.5° / T ０．７ ・・・ (2)

3. The manufacturing method according to claim 1 or 2, wherein the tensile strength of the steel plate is 980 MPa or more.

4. The manufacturing method according to claim 3, wherein the tensile strength of the steel plate is 1470 MPa or more. ​ ​

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