JP2022030694A - Surface-treated steel sheet and method for manufacturing processed material - Google Patents

Abstract

[Problem] A surface-treated steel sheet is disclosed that can provide a processed material with reduced tensile residual stress on the fracture surface when sheared. [Solution] The surface-treated steel sheet has a steel plate and a surface treatment layer, and at least one of the front and back surfaces is constituted by the surface treatment layer, the friction coefficient of the front surface is 1.4 times or more the friction coefficient of the back surface, and the difference between the friction coefficient of the front surface and the friction coefficient of the back surface is 0.10 or more. [Selected Figure] Figure 4

Description

The present application discloses a method for manufacturing a surface-treated steel sheet and a processed material.

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 against the fracture surface of the processed material.

Patent Document 2 discloses a technique for cutting a zinc-based plated steel sheet having a predetermined Zn basis weight and plate thickness. In Patent Document 2, the rust resistance of the cut end face is improved by cutting a galvanized steel sheet using a punch and a die having a predetermined shape and having a predetermined clearance.

International Publication No. 2016/136909 Japanese Unexamined Patent Publication No. 2009-287082

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 become large. This also applies to a surface-treated steel sheet provided with plating or the like. From this point of view, when a surface-treated steel sheet is sheared to obtain a processed material, a new technique capable of reducing the tensile residual stress of the fracture surface of the processed material is required.

The present application is one of the means for solving the above problems.
A surface-treated steel sheet having a steel sheet and a surface-treated layer,
At least one of the front surface and the back surface is composed of the surface treatment layer.
The coefficient of friction on the front surface is 1.4 times or more the coefficient of friction on the back surface.
The difference between the friction coefficient of the front surface and the friction coefficient of the back surface is 0.10 or more.
Disclose a surface-treated steel sheet.

In the surface-treated steel sheet of the present disclosure, the front surface and the back surface may be composed of the surface-treated layer, and the type of the surface-treated layer constituting the front surface and the type of the surface-treated layer constituting the back surface may be used. It may be the same or different.

The surface-treated steel sheet of the present disclosure may have a sheared end face.
The sheared end face has sagging, fracture surface and burrs.
The sagging may be present on the front surface side, and the burr may be present on the back surface side.

In the surface-treated steel sheet of the present disclosure, the thickness of the surface-treated layer may be 1 μm or more and 50 μm or less.

In the surface-treated steel sheet of the present disclosure, the surface-treated layer may contain plating.

In the surface-treated steel sheet of the present disclosure, the surface-treated layer may contain a coating film.

In the surface-treated steel sheet of the present disclosure, the tensile strength of the steel sheet may be 980 MPa or more.

In the surface-treated steel sheet of the present disclosure, the tensile strength of the steel sheet may be 1470 MPa or more.

The present application is one of the means for solving the above problems.
The surface-treated steel sheet of the present disclosure is arranged between the first blade and the second blade, where the surface of the surface-treated steel sheet is arranged on the first blade side and the back surface of the surface-treated steel sheet is arranged. Arranged on the second blade side,
Shearing the surface-treated steel sheet by relatively moving the first blade and the second blade.
including,
Disclose the manufacturing method of the processed material.

When the surface-treated steel sheet of the present disclosure is sheared, it is easy to obtain a processed material in which the tensile residual stress of the fracture surface is reduced.

It is a schematic diagram for demonstrating an example of the flow of shearing of a surface-treated steel sheet. (A) shows a state in which the surface-treated steel plate is arranged between the first blade and the second blade, and (B) shows the state where the first blade and the second blade are relatively moved and brought close to each other. The state where the bottom surface of the first blade is in contact with the surface of the surface-treated steel plate and the bottom surface of the second blade is in contact with the back surface of the surface-treated steel plate is shown, and (C) shows a part of the surface-treated steel plate by the first blade. The punched state is shown, and (D) shows the state where the first blade and the second blade are separated and returned to the position of (A). It is a schematic diagram for demonstrating an example of the formation mechanism of a sheared end face at the time of shearing a surface-treated steel sheet. It is a cross section along the relative moving direction of the first blade and the second blade, and shows the form of the cross section including the first blade, the second blade and the surface-treated steel plate. (A) shows a state in which sagging is formed on the surface-treated steel sheet by pressing the first blade and the second blade against the surface-treated steel sheet, and (B) shows the state in which sagging is formed on the surface-treated steel sheet, and then the first blade and the first blade are formed on the surface-treated steel sheet. By further pressing the two blades, a state in which a crack is generated in the surface-treated steel sheet is shown, and after the crack is formed in (C), the first blade and the second blade are further pressed against the surface-treated steel sheet to further press the surface-treated steel sheet. It shows the state where a part of is punched out. It is a schematic diagram for demonstrating the new knowledge by this inventor. When (A) develops a crack from the first blade, (B) develops a crack from both the first blade and the second blade, and (C) develops a crack from the second blade. Is. “◯” means that the tensile residual stress is small, “Δ” means that the tensile residual stress is medium, and “×” means that the tensile residual stress is large. It is sectional drawing to explain an example of the structure of the surface-treated steel sheet. When (A) has a surface treatment layer on the back surface (second surface), when (B) has a surface treatment layer on the front surface (first surface), (C) has a surface treatment layer on both the front surface and the back surface. If you have. It is sectional drawing to explain an example of the structure of the surface-treated steel plate (processed material) which has a sheared end face. It is a schematic diagram for demonstrating an example of the structure of a sheared end face. The state where the shear end face is seen from the front is shown. It is a schematic diagram for demonstrating the method of discriminating the 1st part and the 2nd part in a fracture surface. (A) schematically shows the direction of hydrogen embrittlement cracks generated in the fracture surface, and (B) indicates an arbitrary position X between the burr side and the sagging side in the fracture surface and the direction of hydrogen embrittlement cracks (B). The relationship with the angle θ) is schematically shown. It is a schematic diagram for demonstrating an example of the flow of the manufacturing method of a processed material. It is a schematic diagram for demonstrating a shear angle.

1. 1. Issues and new findings For example, the flow when shearing a surface-treated steel sheet to obtain a processed material is as follows. First, as shown in FIG. 1A, the surface-treated steel plate 5 is arranged between the first blade 21 and the second blade 22. Here, the surface-treated steel plate 5 has a front surface (first surface) 10a and a back surface (second surface) 10b, and the first blade 21 has a first bottom surface 21a, a first side surface 21b, and a first tip portion 21x (FIG. The second blade 22 has a second bottom surface 22a, a second side surface 22b, and a second tip portion 22x (see FIG. 2). As shown in FIG. 1B, the first bottom surface 21a is in contact with the surface 10a of the surface-treated steel sheet 5, and the second bottom surface 22a is in contact with the back surface 10b of the surface-treated steel sheet 5. The first blade 21 may be a punch and the second blade 22 may be a die. Subsequently, as shown in FIGS. 1B and 1C, the surface-treated steel sheet 5 is sheared by relatively moving the first blade 21 and the second blade 22. As a result, as shown in FIGS. 1C and 1D, a part of the surface-treated steel sheet 5 is punched out as scrap 15 by the first blade 21, and the remaining part of the surface-treated steel sheet 5 has a sheared end face 1. It can be a processed material 10 to have. The scrap 15 may be used for some products.

FIGS. 1 (A) to 1 (D) show a form in which a shear angle is not provided between the first blade 21 and the second blade 22, but there is a gap between the first blade 21 and the second blade 22. A shear angle may be provided. Further, in FIGS. 1A to 1D, the line of intersection (the tip of the first blade 21) between the first bottom surface 21a of the first blade 21 and the first side surface 21b is in the longitudinal direction of the first blade 21. Although the form of extending linearly toward the blade is shown, the tip of the first blade 21 may extend linearly in the longitudinal direction. That is, the shape of the sheared end surface 1 in a plan view may be sheared so as to be linear, may be sheared so as to be curved, or may be sheared so as to be a combination of linear and curved. You may. Further, FIGS. 1A to 1D show a form in which the end portion of the surface-treated steel sheet 5 is sheared and removed by the first blade 21 and the second blade 22, but the first blade 21 and the second blade 21 are shown. By shearing the surface-treated steel plate 5 with the two blades 22, punch holes, slits, and the like may be formed in a part of the surface-treated steel plate 5. In this case as well, the processed material 10 having the sheared end face 1 can be obtained.

An example of the formation mechanism of the shear end face 1 will be described. As shown in FIGS. 2A to 2C, a case where a processed material 10 having a sheared end face 1 is obtained by shearing a surface-treated steel sheet 5 with a first blade 21 and a second blade 22 will be considered. As shown in FIG. 2A, the first bottom surface 21a of the first blade 21 is pressed against the surface 10a of the surface-treated steel sheet 5, so that the sagging 1a is formed on the surface 10a side of the surface-treated steel sheet 5. The sagging 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 sagging 1a is formed, the sheared surface 1e (see FIG. 5) may be formed in the process of the first tip portion 21x biting into the surface-treated steel sheet 5. As shown in FIG. 2B, after the sagging 1a and the sheared surface 1e are formed, a first crack 1dx is generated from the first blade 21 side toward the second blade 22 side. On the other hand, also on the second blade 22 side, similarly, after the second tip portion 22x bites into the back surface 10b of the surface-treated steel plate 5, the second crack is made from the second blade 22 side toward the first blade 21 side. 1dy is generated. As shown in FIG. 2C, the fracture surface 1b is formed by each of the first crack 1dx and the second crack 1dy extending and joining each other. Further, by further moving the first blade 21 and the second blade 22, the surface-treated steel plate 5 is separated into the scrap 15 and the target processed material 10. At this time, as shown in FIG. 2C, a burr 1c may be formed at a corner portion on the second blade 22 side of the sheared end surface 1 of the processed material 10. FIG. 2 regardless of the presence or absence of a shear angle between the first blade 21 and the second blade 22 and the shape of the shear end surface 1 in a plan view (straight, curved or a combination thereof, punch holes, slits, etc.). The shear end face 1 can be formed by a mechanism such as (A) to (C).

In the shear end face 1 formed as described above, compressive residual stress or tensile residual stress may occur due to damage or strain due to shearing. If a large tensile residual stress is present in the shear end face 1, the hydrogen embrittlement resistance or fatigue strength of the shear end face 1 may decrease. In this respect, in order to obtain the processed material 10 having high performance, how to reduce the tensile residual stress in the sheared end face 1 can be one of the problems. In particular, as disclosed in Patent Document 1, it is preferable that the tensile residual stress in the fracture surface 1b of the sheared end face 1 can be reduced.

The present inventor has obtained the following new findings as a result of repeating a number of experiments and analyzes on the relationship between the shearing conditions for the surface-treated steel sheet 5 and the properties of the sheared end face 1 generated by the shearing.

As shown in FIGS. 3A to 3C, a case where a part 11 of the surface-treated steel sheet 5 is punched out by the first blade 21 and the other part 12 of the surface-treated steel sheet 5 is punched out by the second blade 22 will be described. do. In this case, as shown in FIG. 3A, when the crack grows preferentially from the first blade 21 side, the tensile residual stress at the shear end face of the part 11 increases, while the tensile residual stress at the other part 12 increases. The tensile residual stress on the sheared end face of the is reduced. That is, while a part 11 is used as scrap 15, the other part 12 can be suitably used as a product (processed material 10). Further, as shown in FIG. 3B, when cracks grow equally from both the first blade 21 side and the second blade 22 side, they are equivalent to the shear end faces of both the partial 11 and the other portion 12. Tensile residual stress can occur. That is, the variation in the characteristics between the part 11 and the other part 12 can be suppressed. In this respect, it can be said that it is suitable when both the part 11 and the other part 12 are adopted as products. Further, as shown in FIG. 3C, when the crack grows preferentially from the second blade 22 side, the tensile residual stress at the shear end face of the other portion 12 increases, while the shear of a part 11 The tensile residual stress on the end face becomes smaller. That is, while the other part 12 is used as scrap 15, a part 11 can be suitably used as a product (processed material 10).

Based on the above findings, the present inventor has found the following (1) to (4).
(1) The tensile residual stress generated in the fracture surface 1b of the shear end surface 1 changes depending on the growth direction and length of the cracks 1dx and 1dy forming the fracture surface 1b.
(2) In the fracture surface 1b, the longer the crack 1dx extending from the sagging 1a side, the smaller the tensile residual stress of the fracture surface 1b of the work material 10, and the larger the tensile residual stress of the fracture surface of the scrap 15.
(3) That is, in the fracture surface 1b of the processed material 10, the area ratio of the portion derived from the first crack 1dx extending from the sagging 1a side is the portion derived from the second crack 1dy extending from the burr 1c side. When it is larger than the area ratio, the area ratio of the part derived from the first crack 1dx extending from the sagging 1a side is smaller than the area ratio of the part derived from the second crack 1dy extending from the burr 1c side. Also, the tensile residual stress of the fracture surface 1b can be relatively reduced.

The present inventor has obtained the following new findings as a result of repeating a number of experiments and analyzes on controlling the growth direction and length of cracks 1dx and 1dy when the surface-treated steel sheet 5 is sheared. ..
(4) When the friction coefficient of the front surface 10a of the surface-treated steel sheet 5 is made larger than the friction coefficient of the back surface 10b to a certain level or more so that the first blade 21 is brought into contact with the front surface 10a during shearing of the surface-treated steel sheet 5. It becomes easy for stress concentration to occur in the surface, and it becomes easy for the first crack 1dx to be preferentially generated / propagated from the surface 10a side. As a result, the tensile residual stress of the sheared end face 1 (particularly the fracture surface 1b) can be reduced.

The surface-treated steel sheet of the present disclosure has been completed based on the above findings.

2. 2. Surface-treated steel sheet As shown in FIGS. 4A to 4C, the surface-treated steel sheet 5 of the present disclosure has a steel sheet 5x and a surface-treated layer 5y, and at least one of the front surface 10a and the back surface 10b is surface-treated. It is composed of layers 5y. In the surface-treated steel plate 5, the friction coefficient of the front surface 10a is 1.4 times or more the friction coefficient of the back surface 10b, and the difference between the friction coefficient of the front surface 10a and the friction coefficient of the back surface 10b is 0.10 or more.

The specific values of the friction coefficient of the front surface 10a and the friction coefficient of the back surface 10b of the surface-treated steel plate 5 are not particularly limited as long as the above friction coefficient ratio is satisfied. For example, the coefficient of friction of the front surface 10a and the back surface 10b may be in the range of 0.01 or more and 3.00 or less.

As shown in FIGS. 4A and 4B, in the surface-treated steel sheet 5 of the present disclosure, either one of the front surface 10a and the back surface 10b may be composed of the surface-treated layer 5y. Alternatively, as shown in FIG. 4C, in the surface-treated steel sheet 5 of the present disclosure, the front surface 10a and the back surface 10b may be composed of the surface-treated layers 5y and 5y, and in this case, the surface constituting the surface 10a. The type of the treated layer 5y and the type of the surface treated layer 5y constituting the back surface 10b may be the same or different.

2.1 Steel plate The steel plate 5x may be in the form of a plate that can be sheared, and its thickness can be determined according to the application. The plate thickness of the steel plate 5x may be, for example, 0.8 mm or more, 1.2 mm or more, 3.0 mm or less, or 1.8 mm or less. When the thickness of the steel sheet 5x is thin, the effect of the technique of the present disclosure on hydrogen embrittlement resistance is small, but it is considered that the effect on fatigue strength is exhibited. On the other hand, if the thickness of the steel sheet 5x is too thick, although the effect of the technique of the present disclosure is exhibited, cracks may develop from an unintended side during shearing. The steel plate 5x may be formed into any shape by bending or the like.

The steel plate 5x may include a front surface 5xa and a back surface 5xb. The front surface 5xa and the back surface 5xb of the steel plate 5x may be parallel to each other. The term "parallel" as used in the present application is not limited to perfect parallelism, but may be substantially parallel. That is, even if the front surface 5xa and the back surface 5xb are not completely parallel, they are regarded as parallel as long as they are within the margin of error allowed in industrial production. Specifically, when the angle between the front surface 5xa and the back surface 5xb is 0 ° ± 1 °, it is considered that the front surface 5xa and the back surface 5xb are parallel.

The mechanical properties of the steel sheet 5x are not particularly limited, and may be appropriately determined depending on the use of the steel sheet 5x. However, problems such as a decrease in hydrogen embrittlement resistance due to tensile residual stress are particularly likely to occur in high-strength steel sheets. In this respect, the tensile strength of the steel sheet 5x may be, for example, 980 MPa or more, 1180 MPa or more, or 1470 MPa or more. The upper limit of the tensile strength of the steel sheet 5x is not particularly limited, but may be, for example, 2500 MPa or less, 2200 MPa or less, or 2000 MPa or less. The "tensile strength" of the steel sheet referred to in the present application is in accordance with ISO 6892-1: 2009.

The chemical composition and metallographic structure of the steel sheet 5x are not particularly limited, and can be appropriately determined depending on the use of the surface-treated steel sheet 5. According to the technique of the present disclosure, it is possible to reduce the tensile residual stress in the fracture surface 1b regardless of the chemical composition and the metallographic structure of the steel sheet 5x. As an example of the chemical composition, the steel plate 5x has a mass% of 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. It may have a chemical composition consisting of 050%, La: 0 to 0.050%, Ce: 0 to 0.050%, and the balance: Fe and impurities. Further, in the above chemical composition of the steel material 5, Cr, Mo, B, Ti, Nb, V, Cu, Ni, O, W, Ta, Co, Sn, Sb, As, Mg, which are elements arbitrarily added, The lower limit of the content of Ca, Y, Zr, La, and Ce may be 0.0001% or 0.001%.

2.2 Surface treatment layer The surface treatment layer 5y may be a layer provided on at least one of the front surface 5xa and the back surface 5xb of the steel sheet 5x, and the type thereof is not particularly limited. For example, the surface treatment layer 5y may contain plating. Examples of the plating include metal plating and alloy plating containing at least one metal selected from the group consisting of zinc, tin, chromium, nickel, magnesium, aluminum, copper and iron, and these are appropriately used depending on the application. You can use it properly. Plating can be provided on the surface of the steel sheet 5x by a known method. The plating may be hot-dip plating or electrolytic plating.

The surface treatment layer 5y may contain a coating film. Further, the surface treatment layer 5y may contain a film other than plating such as diamond-like carbon (DLC) or a coating film. The coating film may be, for example, a form in which a resin film is attached to the surface of the steel sheet 5x, or a form in which a resin paint is applied to the surface of the steel sheet 5x. Examples of the resin that can form a coating film include polyester resin, melamine resin, isocyanate resin, silicone acrylic resin, and the like, and two or more of these may be combined.

The surface treatment layer 5y may be composed of one layer or may be composed of a plurality of layers. Further, the surface-treated layer 5y may be formed on the surface treated with chemical conversion. For example, when a coating film is formed on the surface of the steel sheet 5x, the adhesion between the steel sheet 5x and the coating film may be improved by subjecting the surface of the steel sheet 5x to a chemical conversion treatment. The same applies to the case where a coating film is formed on the surface of the plating after plating the steel sheet 5x, and even if the surface of the plating is subjected to chemical conversion treatment to improve the adhesion between the plating and the coating film, etc. good. Examples of the chemical conversion treatment include a chemical conversion containing at least one chemical component selected from the group consisting of a phosphoric acid-based, a zircon-based, a sulfide-based, and an oxide-based compound, and a chemical conversion consisting of a plurality of chemical components, which are appropriately used depending on the intended use. You can use it properly. Further, oil may be appropriately applied on the chemical conversion treatment by utilizing the surface unevenness of the chemical conversion treatment.

The thickness of the surface treatment layer 5y is not particularly limited, and may be appropriately determined according to the purpose. For example, the thickness of the surface-treated layer 5y (in the case of a plurality of layers, the total thickness of the plurality of layers) may be 1 μm or more, 5 μm or more, or 10 μm or more. It may be 80 μm or less, 60 μm or less, or 40 μm or less.

The surface-treated steel sheet 5 may be any as long as it includes the above-mentioned steel sheet 5x and the surface-treated layer 5y. Here, the surface-treated steel plate 5 may be coated with a lubricant, metal soap, soap, or the like. When a lubricant or the like is applied, it is considered that the front and back surfaces of the steel plate 5x and the surface treatment layer 5y are formed including the presence of the lubricant or the like. For example, when the lubricant is applied to the surface-treated layer 5y, the surface of the lubricant is the "surface of the surface-treated steel plate 5".

2.3 Friction coefficient As shown in FIGS. 4A to 4C, the surface-treated steel sheet 5 has a front surface 10a and a back surface 10b. Here, in the surface-treated steel plate 5, the friction coefficient of the front surface 10a is 1.4 times or more the friction coefficient of the back surface 10b, and the difference between the friction coefficient of the front surface 10a and the friction coefficient of the back surface 10b is 0.10 or more. Is. The coefficient of friction ratio is 1.6 times or more, 1.8 times or more, 2.0 times or more, 2.5 times or more, 3.0 times or more. However, it may be 4.0 times or more, or 5.0 times or more. Further, the coefficient of friction difference may be 0.20 or more or 0.40 or more. The upper limit of the friction coefficient ratio and the friction coefficient difference is not particularly limited. By increasing the dynamic friction coefficient of the surface 10a of the surface-treated steel sheet 5 (making the slip worse), the side surface of the blade bites when the surface-treated steel sheet 5 is deformed at the initial stage of shearing, and stress concentration is likely to occur on the surface 10a. As a result, cracks are likely to occur in the surface-treated steel sheet 5. As a result, in the sheared end face 1 after shearing, the area ratio of the portion derived from the first crack 1dx extending from the sagging 1a side is higher than the area ratio of the portion derived from the second crack 1dy extending from the burr 1c side. Also tends to increase, and it becomes easy to reduce the tensile residual stress of the fracture surface 1b.

The friction coefficient of the front surface 10a and the friction coefficient of the back surface 10b of the surface-treated steel plate 5 are measured by a pin-on disk as follows. The pin material of the pin-on disc is SKD11 (equivalent to HRC58-60), and the pin diameter is φ0.71 cm (0.357 x 0.357 x π = 0.4 cm ² (0.9 MPa at 29.4 kN)). do. The load is 29.4 kN. The measurement condition is linear motion (pins are always moved so as to slide the new surface), and the pins on the front surface or the back surface of the surface-treated steel sheet are scanned at a speed of 30 mm / sec. The scanning time is 7 seconds (moving distance 30 mm / sec × 7 seconds). The average value of the measured values excluding the first 1 second and the last 1 second is obtained, and this is used as the dynamic friction coefficient. The coefficient of dynamic friction is measured at three different points on the front surface and the back surface of the surface-treated steel sheet, and the average value is taken as the "friction coefficient on the front surface" and the "friction coefficient on the back surface" of the surface-treated steel sheet.

In the surface-treated steel sheet 5, various methods can be considered as a method for setting the friction coefficient of the front surface 10a to 1.4 times or more the friction coefficient of the back surface 10b. For example, a surface treatment layer 5y having a relatively large coefficient of friction may be provided on the surface 10a. Alternatively, a surface treatment layer 5y having a relatively small coefficient of friction may be provided on the back surface 10b. Alternatively, the type and supply amount of the lubricant applied on the front surface 10a and the back surface 10b may be changed.

When a surface-treated layer 5y having a relatively large coefficient of friction is provided on the surface 10a of the surface-treated steel sheet 5, specific examples of such a surface-treated layer 5y include metal plating of at least one selected from aluminum, nickel and zinc. Examples thereof include alloy plating or a coating film of the resin as described above.

When a surface-treated layer 5y having a relatively small coefficient of friction is provided on the back surface 10b of the surface-treated steel sheet 5, specific examples of such a surface-treated layer 5y include a combination of phosphorylation treatment and anointing, MoS. , MoS ₂ or a combination of these with a anointing, or composite plating of Ni-P and PTFE. Alternatively, regardless of the type of the surface treatment layer 5y, it is possible to reduce the friction coefficient by applying the lubricating oil or soap only to the back surface 10b side.

2.4 Example of sheared end face The surface-treated steel plate 5 may be sheared. For example, as shown in FIGS. 5 and 6, the surface-treated steel sheet 5 may have a sheared end face 1, the sheared end face 1 having a sagging 1a, a fracture surface 1b, and a burr 1c, and sagging on the surface 10a side. 1a may be present, and burrs 1c may be present on the back surface 10b side. As described above, in the sheared end surface 1 having the sagging 1a on the surface 10a side, the tensile residual stress of the fracture surface 1b is likely to be reduced as described above.

As shown in FIGS. 5 and 6, the shear end face 1 includes a sag 1a, a fracture surface 1b, and a burr 1c. Further, the sheared end surface 1 may include a sheared surface 1e. Of the sheared end faces 1, the sagging 1a, the burrs 1c, and the sheared surface 1e can take any form. The sagging 1a, the burr 1c, and the sheared surface 1e may have the same form as the conventional one.

As shown in FIGS. 5 and 6, the fracture surface 1b may include a first portion 1bx and a second portion 1by. The first portion 1bx may be formed by the first crack 1dx extending from the sagging 1a side to the burr 1c side, and the second portion 1by may be formed by the second crack extending from the burr 1c side to the sagging 1a side. It may be formed by 1 dy.

The growth direction of the first crack 1dx may be any direction from the sagging 1a side to the burr 1c side. The growth direction of the first crack 1dx may be a direction along the plate thickness direction of the surface-treated steel plate 5 (direction orthogonal to the front surface 10a and the back surface 10b), or may be inclined with respect to the plate thickness direction. It may be in the direction. Further, the growth direction of the second crack 1dy may be any direction from the burr 1c side to the sagging 1a side. The growth direction of the second crack 1dy may be a direction along the plate thickness direction of the surface-treated steel plate 5 (a direction orthogonal to the front surface 10a and the back surface 10b), or may be inclined with respect to the plate thickness direction. It may be in the direction. For example, when a clearance C (see FIG. 8) is provided between the first blade 21 and the second blade 22 when the surface-treated steel sheet 5 is sheared, the growth of the first crack 1dx and the second crack 1dy The direction can be a direction inclined with respect to the plate thickness direction, and the larger the clearance, the larger the inclination can be.

The first crack 1dx may be one that extends from the sagging 1a side to the burr 1c side and is combined with the second crack 1dy on the burr 1c side, and is not necessarily the first from the sagging 1a side to the burr 1c side. It is not necessary to travel in the shortest path toward 2 cracks 1 dy. For example, the first crack 1dx propagates in the plate width direction, the plate length direction, etc. (the direction toward the back of the paper surface in FIG. 2B, etc.) while advancing from the sagging 1a side to the burr 1c side. May be good. The same applies to the second crack 1dy.

In the sheared end face 1, the area ratio of the first portion 1bx in the fracture surface 1b may be larger than the area ratio of the second portion 1by in the fracture surface 1b. In other words, on the sheared end face 1, the average length of the first crack 1dx extending from the sagging 1a side toward the burr 1c side is the average of the second crack 1dy extending from the burr 1c side toward the sagging 1a side. It may be longer than the length. As described above, when the area ratio of the portion of the fracture surface 1b derived from the crack 1dx extending from the sagging 1a side is larger than the area ratio of the portion derived from the crack 1dx extending from the burr 1c side, the fracture occurs. It is easy to relatively reduce the tensile residual stress of the cross section 1b.

In order to specify the area ratio of each of the first portion 1bx and the second portion 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 is determined. It shall not be considered. For example, as shown in FIG. 6, when the sheared end surface 1 is viewed from the front, the position that is the starting point of the first crack 1dx is P1, the position that is the starting point of the second crack 1dy is P2, and the first one. When the position where the crack 1dx and the second crack 1dy meet is P3, the area ratio of the first portion 1bx in the fracture surface 1b when the distance between P1 and P3 is larger than the distance between P2 and P3. However, it can be determined that the area ratio of the second portion 1by in the fracture surface 1b is larger than the area ratio.

According to the findings of the present inventor, the larger the area ratio of the first portion 1bx in the fracture surface 1b, the smaller the tensile residual stress of the fracture surface 1b. For example, the area ratio of the first portion 1bx in the fracture surface 1b may be 1.2 times or more or 1.5 times or more the area ratio of the second portion 1by in the fracture surface 1b. It may be 1.7 times or more, 2.0 times or more, 2.2 times or more, or 2.5 times or more.

The burr 1c may have a size that cannot be visually confirmed. Regarding which of the front surface 10a and the back surface 10b of the surface-treated steel sheet 5 is the surface on the sagging 1a side and which is the surface on the burr 1c side, observe the shape of the surface-treated steel sheet 5 even if the burr 1c cannot be confirmed. It can be easily identified by doing so.

In the sheared end surface 1, the properties of the sheared surface 1e and the fracture surface 1b are different. For example, the shear surface 1e and the fracture surface 1b have different roughness (glossiness). In this respect, the sheared surface 1e and the fracture surface 1b can be easily distinguished only by observing the appearance.

In the fracture surface 1b, the boundary between the first portion 1bx and the second portion 1by (the position where the first crack 1dx and the second crack 1dy meet) is formed by, for example, introducing a large amount of hydrogen into the shear end surface 1. It can be discriminated. As mentioned above, the stress generated during crack growth depends on the crack growth direction. That is, as shown in FIGS. 7A and 7B, it can be said that the residual stress suddenly changes at the position where the first crack 1dx and the second crack 1dy meet. Therefore, the direction of hydrogen embrittlement cracks caused by the intrusion of hydrogen also suddenly changes 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 suddenly changes can be regarded as the position where the first crack 1dx and the second crack 1dy meet.

3. 3. Manufacturing Method of Processed Material As shown in FIG. 8A, in the manufacturing method of the processed material 10, first, the surface-treated steel plate 5 of the present disclosure is arranged between the first blade 21 and the second blade 22. do. Here, the front surface 10a of the surface-treated steel plate 5 is arranged on the first blade 21 side, and the back surface 10b of the surface-treated steel plate 5 is arranged on the second blade 22 side. Next, as shown in FIG. 8B, the first blade 21 and the second blade 22 are relatively moved to shear the surface-treated steel sheet 5.

3.1 First blade The first blade 21 has 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 moving direction of the first blade 21, or may have a surface inclined with respect to the moving direction. Further, the first tip portion 21x refers to a portion near the line of intersection between the first bottom surface 21a and the first side surface 21b. For example, it may be a portion within a range of 2 mm from the line of intersection between the first bottom surface 21a and the first side surface 21b toward both the first bottom surface 21a side and the first side surface 21b side. When the tip of the first blade 21 is processed to have R or the tip is chamfered, a surface extended along the first bottom surface 21a and a surface extended along the first side surface 21b. Assuming the line of intersection, the portion included within the range of R + 2 mm from the line of intersection toward both the first bottom surface 21a side and the first side surface 21b side may be regarded as the first tip portion 21x.

The shape of the first bottom surface 21a can be determined according to the shape of the sheared end face 1 of the target processed material 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 surface 10a when the surface-treated steel plate 5 is sheared.

The shape of the first side surface 21b can be determined according to the shape of the sheared end face 1 of the target processed material 10. The first side surface 21b may be a flat surface, a curved surface, or a combination of a flat surface and a curved surface.

The first tip portion 21x may extend linearly in the longitudinal direction of the first blade 21 (direction toward the back of the paper surface in FIG. 8) or may extend in a curved shape, and may be a target processed material. It can be determined according to the shape of the sheared end face 1 of 10. When the surface-treated steel sheet 5 is provided with a punch hole, the shape of the first tip portion 21x may be an annular shape along the edge of the punch hole.

In the standby state before the shearing operation, the first blade 21 may be arranged above the second blade 22. In this case, the first blade 21 may be a punch that punches a part of the surface-treated steel plate 5 placed on the second bottom surface 22a of the second blade 22 from top to bottom.

The first blade 21 is made of a material that is generally used 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.

3.2 Second blade The second blade 22 has 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 moving direction of the second blade 22, or may have a surface inclined with respect to the moving direction. The second tip portion 22x refers to a portion near the line of intersection between the second bottom surface 22a and the second side surface 22b. For example, it may be a portion within a range of 2 mm from the line of intersection 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 R or the tip is chamfered, the second tip 22x can be specified as in the case of the first tip 21x described above. That is, assuming an intersection line of a surface extending along the second bottom surface 22a and a surface extending along the second side surface 22b, from the intersection line to both the second bottom surface 22a side and the second side surface 22b side. The portion included in the range of R + 2 mm may be regarded as the second tip portion 22x.

The shape of the second bottom surface 22a can be determined according to the shape of the sheared end face 1 of the target processed material 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 back surface 10b when the surface-treated steel plate 5 is sheared.

The shape of the second side surface 22b can be determined according to the shape of the sheared end face 1 of the target processed material 10. The second side surface 22b may be a flat surface, a curved surface, or a combination of a flat surface and a curved surface.

The second tip portion 22x may extend linearly or curvedly in the longitudinal direction of the second blade 22 (direction toward the back of the paper surface in FIG. 8), and may be a target processed material. It can be determined according to the shape of the sheared end face 1 of 10. When the surface-treated steel sheet 5 is provided with a punch hole, the shape of the second tip portion 22x may be an annular shape along the edge of the punch hole.

In the standby state before the shearing operation, the second blade 22 may be arranged below the first blade 21. In this case, the second blade 22 may be a die on which the surface-treated steel plate 5 is placed.

The second blade 22 is made of a material that is common as a blade used for shearing. For example, the second blade 22 may be made of SKD11. The material of the second blade 22 may be the same as or different from the material of the first blade 21. Further, the second blade 22 may have a second coating on its surface.

3.3 Arrangement of surface-treated steel sheet In the manufacturing method of the present disclosure, the surface-treated steel sheet 5 is arranged between the first blade 21 and the second blade 22 as described above. There is no particular limitation on the arrangement of the surface-treated steel plate 5 between the first blade 21 and the second blade 22, and the first bottom surface 21a is brought into contact with the front surface 10a and the second bottom surface 22a is brought into contact with the back surface 10b. The surface-treated steel plate 5 may be arranged so that it can be appropriately sheared. For example, as shown in FIG. 8A, the surface-treated steel plate 5 is placed on the second bottom surface 22a of the second blade 22 while the first blade 21 is arranged above the surface-treated steel plate 5. You may place it. Further, in the manufacturing method of the present disclosure, in order to facilitate shearing of the surface-treated steel sheet 5, when the surface-treated steel sheet 5 is arranged between the first blade 21 and the second blade 22, a holding member (not shown) is provided. The surface-treated steel plate 5 may be pressed against the first bottom surface 21a or the second bottom surface 22a by the (holder). The form of the pressing member is not particularly limited, and a general pressing member may be adopted.

3.4 Operation and relationship between the first blade and the second blade during shearing In the manufacturing method of the present disclosure, after arranging the surface-treated steel plate 5 between the first blade 21 and the second blade 22, the first blade is used. The surface-treated steel plate 5 is sheared by relatively moving the 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.

3.4.1 Clearance As shown in FIGS. 8A and 8B, 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 depending on the material, thickness, and the like of the surface-treated steel sheet 5. For example, the clearance C may be 5% or more of the plate thickness of the surface-treated steel plate 5, or 25% or less of the plate thickness. The "clearance" referred to in the present application is in accordance with ISO 16630: 2009.

3.4.2 Shear angle As shown in FIG. 9, a shear angle α may be provided between the first blade 21 and the second blade 22 during shearing. The shear angle α can be appropriately determined depending on the material, shape, and the like of the surface-treated steel sheet 5. For example, the shear angle α may be 0 ° or more, or 10 ° or less. Further, according to a new finding of the present inventor, when the shear angle is 0 ° or more and 1 ° or less, the first crack 1dx is advanced to the surface-treated steel sheet 5 before the second crack 1dy. Easy to make.

4. Processed Material According to the manufacturing method of the present disclosure, it is easy to obtain a processed material 10 having a reduced tensile residual stress in the fracture surface 1b, among the sheared end faces 1. The processed material 10 may be the same as the surface-treated steel sheet 5 having the sheared end face 1. That is, as shown in FIGS. 5 and 6, the sheared end surface 1 of the processed material 10 includes a sagging 1a, a fracture surface 1b, and a burr 1c. The fracture surface 1b may include a first portion 1bx and a second portion 1by. The first portion 1bx is formed by the first crack 1dx extending from the sagging 1a side to the burr 1c side, and the second portion 1by is formed by the second crack 1dy extending from the burr 1c side to the sagging 1a side. Will be done. The area ratio of the first portion 1bx in the fracture surface 1b may be larger than the area ratio of the second portion 1by in the fracture surface 1b. By further shearing the surface-treated steel sheet 5 having the sheared end face 1, the processed material 10 having a plurality of sheared end faces 1 may be obtained.

The processed material 10 may have a sheared end face 1, and the configuration other than the sheared end face is not particularly limited. The shape of the processed material 10 corresponds to the shape of the surface-treated steel plate 5 described above. That is, the processed material 10 may have a plate shape as described above. Further, the processed material 10 may have a front surface 10a and a back surface 10b on the opposite side of the front surface 10a as surfaces other than the sheared end surface 1, and the front surface 10a and the back surface 10b are interposed via the sheared end surface 1. May be linked. The front surface 10a and the back surface 10b may be parallel to each other. Further, the processed material 0 may be formed by bending or the like. The mechanical properties, chemical composition, and the like of the steel sheet 5x constituting the processed material 10 are also as described above.

5. Action / Effect As described above, by shearing the surface-treated steel sheet 5 of the present disclosure, it is easy to obtain a processed material 10 in which the tensile residual stress in the fracture surface 1b is reduced. By reducing the tensile residual stress of the fracture surface 1b, for example, hydrogen embrittlement resistance or fatigue strength of the sheared end face 1 can be improved.

1. 1. Steel plate As a steel plate constituting the surface-treated steel plate which is the work material, a steel plate a having a tensile strength of 1470 MPa (plate thickness: about 1.8 mm) and a steel plate b having a tensile strength of 1180 MPa class (plate thickness: about 1.8 mm). , A steel plate c (plate thickness: about 1.8 mm) having a tensile strength of 980 MPa was prepared. The front and back surfaces of each steel sheet were subjected to surface treatment described later to obtain surface-treated steel sheets A to C for evaluation.

2. 2. Surface treatment layer 2.1 Example 1
A Zn—Fe alloy layer (GA) having a thickness of 8 μm was provided on both the front surface and the back surface of the steel sheet. Then, the back surface was subjected to chemical conversion treatment (thickness 1 μm) with manganese phosphate, and further, lubricating oil was applied so as to have a coating thickness of 1 μm to obtain a surface-treated steel sheet according to Example 1.

2.2 Example 2
A Zn—Fe alloy layer (GA) having a thickness of 8 μm was provided on both the front surface and the back surface of the steel sheet. Then, a chemical conversion treatment (thickness 0.009 μm) with manganese phosphate was applied to the back surface, and further, metal soap (thickness 1 μm) and sodium stearate soap (thickness 1 μm) were applied to the front surface according to Example 2. A treated steel sheet was obtained.

2.3 Example 3
A Zn—Fe alloy layer (GA) having a thickness of 8 μm was provided on both the front surface and the back surface of the steel sheet. Then, a chemical conversion treatment (thickness 1 μm) with a phosphate (iron) was applied to the back surface, and further, a metal soap (thickness 1 μm) and a sodium stearate soap (thickness 2 μm) were applied, and according to Example 3. A surface-treated steel sheet was obtained.

2.4 Example 4
A Zn—Fe alloy layer (GA) having a thickness of 8 μm was provided on both the front surface and the back surface of the steel sheet. Then, the back surface is subjected to chemical conversion treatment (thickness 2 μm) with zinc phosphate, and further coated with metal soap (thickness 1 μm) and sodium stearate soap (thickness 2 μm), and the surface-treated steel sheet according to Example 4 is applied. Got

2.5 Example 5
A Zn plating layer having a thickness of 12 μm was provided on the front surface of the steel sheet, and a Zn plating layer having a predetermined thickness was provided on the back surface. Then, a coating film (thickness 40 μm) made of a melamine resin and a polyester resin was provided on the front surface, and MoS ₂ was sprayed on the back surface to provide a MoS ₂ layer to obtain a surface-treated steel sheet according to Example 5. On the back surface of the surface-treated steel sheet according to Example 5, the MoS ₂ layer and the Zn-plated layer are alloyed, and the MoS ₂ -Zn layer (thickness 4 μm) and MoS ₂ are placed on the Zn-plated layer (thickness 10 μm). A layer (thickness 2 μm) was formed.

2.6 Example 6
A Zn plating layer having a thickness of 3 μm was provided on the front surface of the steel sheet, and a Zn plating layer having a predetermined thickness was provided on the back surface. Then, MoS ₂ was sprayed on the back surface to provide a MoS ₂ layer, and a lubricating oil was further applied so that the coating thickness was 1 μm to obtain a surface-treated steel sheet according to Example 6. On the back surface of the surface-treated steel sheet according to Example 6, the MoS ₂ layer and the Zn-plated layer are alloyed, and the MoS ₂ -Zn layer (thickness 3 μm) and MoS ₂ are placed on the Zn-plated layer (thickness 5 μm). A layer (thickness 2 μm) was formed.

2.7 Example 7
A Ni plating layer having a thickness of 4 μm was provided on the front surface of the steel sheet, and a Ni plating layer having a thickness of 8 μm was provided on the back surface. Then, MoS ₂ was sprayed on the back surface to provide a MoS ₂ layer (thickness 2 μm) to obtain a surface-treated steel sheet according to Example 7.

2.8 Example 8
An Al—Si plating layer having a thickness of 30 μm was provided on the front surface of the steel sheet, and an Al—Si plating layer having a predetermined thickness was provided on the back surface. Then, MoS ₂ was sprayed on the back surface to provide a MoS ₂ layer to obtain a surface-treated steel sheet according to Example 8. On the back surface of the surface-treated steel sheet according to Example 8, the MoS ₂ layer and the Al—Si plated layer are alloyed, and the MoS ₂ -Al—Si layer (thickness) is placed on the Al—Si plated layer (thickness 27 μm). 3 μm) and _two MoS layers (3 μm thick) were formed.

2.9 Example 9
A Zn—Al—Mg plating layer having a thickness of 40 μm was provided on both the front surface and the back surface of the steel sheet. Then, the back surface is subjected to chemical conversion treatment (thickness 0.01 μm) with manganese phosphate, and further coated with metal soap (thickness 1 μm) and sodium stearate soap (thickness 1 μm), and the front surface according to Example 9. A treated steel sheet was obtained.

2.10 Example 10
A Ni—W (P) plating layer having a thickness of 3 μm was provided on the front surface of the steel sheet, and a Ni—W (P) plating layer having a thickness of 6 μm was provided on the back surface. Then, a DLC film (thickness 1 μm) was provided on the back surface to obtain a surface-treated steel sheet according to Example 10.

2.11 Example 11
A Cr plating layer having a thickness of 1 μm was provided on the front surface of the steel sheet, and a Cr plating layer having a thickness of 5 μm was provided on the back surface. Then, a DLC film (thickness 0.5 μm) was provided on the back surface to obtain a surface-treated steel sheet according to Example 11.

2.12 Example 12
A Ni plating layer having a thickness of 3 μm was provided on the front surface of the steel sheet, and a composite plating layer of Ni-P and PTFE having a thickness of 10 μm was provided on the back surface. After that, a coating film (thickness 40 μm) made of an isocyanate resin and a polyester resin was provided on the front surface, and a lubricating oil was applied to the back surface so that the coating thickness was 1 μm to obtain a surface-treated steel sheet according to Example 12. ..

2.13 Example 13
A Ni plating layer having a thickness of 2 μm was provided on the front surface of the steel sheet, and a Ni plating layer having a thickness of 5 μm was provided on the back surface. Then, a PTFE layer (thickness 10 μm) was provided on the back surface to obtain a surface-treated steel sheet according to Example 13.

2.14 Example 14
An Fe plating layer having a thickness of 10 μm was provided on the surface of the steel sheet. On the other hand, the back surface is subjected to chemical conversion treatment (thickness 0.007 μm) with phosphate (iron), and further coated with metal soap (thickness 0.5 μm) and sodium stearate soap (thickness 1 μm). A surface-treated steel sheet according to Example 14 was obtained.

2.15 Example 15
A Sn plating layer having a thickness of 10 μm was provided on the front surface of the steel sheet, and a Ni plating layer having a thickness of 8 μm was provided on the back surface. After that, a coating film containing a polyester resin (thickness 50 μm) is provided on the front surface, MoS ₂ is sprayed on the back surface to provide a MoS ₂ layer (thickness 3 μm), and a lubricating oil is applied so that the coating thickness becomes 1 μm. To obtain a surface-treated steel sheet according to Example 15.

2.16 Example 16
A Zn plating layer having a thickness of 20 μm was provided on both the front surface and the back surface of the steel sheet. After that, the surface is subjected to chemical conversion treatment with zinc phosphate (thickness 0.008 μm), a coating film made of silicone acrylic resin (thickness 30 μm) is further provided, and the back surface is subjected to chemical conversion treatment with zinc phosphate (thickness). 0.008 μm) was applied, and a lubricating oil was further applied so that the coating thickness was 1 μm to obtain a surface-treated steel sheet according to Example 16.

2.17 Example 17
An Fe plating layer having a thickness of 10 μm was provided on the front surface of the steel sheet, and a Ni plating layer having a thickness of 5 μm was provided on the back surface. Then, a PTFE layer (thickness 10 μm) was provided on the back surface to obtain a surface-treated steel sheet according to Example 17.

2.18 Example 18
The surface of the steel sheet was polished without a surface treatment layer to adjust the surface roughness Ra to 5 μm, and then an Fe plating layer with a thickness of 2 μm was provided, while the back surface was polished. After adjusting the surface roughness Ra to 0.5 μm, a Zn-plated layer having a thickness of 5 μm was provided to obtain a surface-treated steel sheet according to Example 18.

2.19 Example 19
A Ni-plated layer having a thickness of 5 μm was provided on the surface of the steel sheet, and a PTFE layer having a thickness of 10 μm was further provided. On the other hand, the back surface is subjected to chemical conversion treatment (thickness 0.007 μm) with phosphate (iron), and further coated with metal soap (thickness 0.5 μm) and sodium stearate soap (thickness 1 μm). A surface-treated steel sheet according to Example 19 was obtained.

2.20 Comparative Example 1
No surface treatment was applied to either the front surface or the back surface of the steel sheet.

2.21 Comparative Example 2
A Zn—Fe alloy layer (GA) having a thickness of 8 μm is provided on both the front surface and the back surface of the steel sheet, subjected to chemical conversion treatment (thickness 1 μm) with manganese phosphate, and further coated with lubricating oil so that the thickness becomes 1 μm. The coating was applied to obtain a surface-treated steel sheet according to Comparative Example 2.

2.22 Comparative Example 3
The surface of the steel sheet was plated with Ni with a thickness of 5 μm, and the back surface was plated with Zn with a thickness of 5 μm to obtain a surface-treated steel sheet according to Comparative Example 3.

2.23 Comparative Example 4
A Zn plating layer having a thickness of 20 μm was provided on the front surface of the steel sheet, and a Zn plating layer having a predetermined thickness was provided on the back surface. After that, the surface is subjected to chemical conversion treatment (thickness 0.008 μm) with zinc phosphate, and lubricating oil is applied so that the coating thickness is 1 μm, while MoS ₂ is sprayed on the back surface to form a MoS ₂ layer. Further, a lubricating oil was applied so that the coating thickness was 1 μm, and a surface-treated steel sheet according to Comparative Example 4 was obtained. On the back surface of the surface-treated steel sheet according to Comparative Example 4, the MoS ₂ layer and the Zn-plated layer are alloyed, and the MoS ₂ -Zn layer (thickness 3 μm) and MoS ₂ are placed on the Zn-plated layer (thickness 5 μm). A layer (thickness 2 μm) was formed.

2.24 Comparative Example 5
A Zn-plated layer having a thickness of 3 μm was provided on the front surface of the steel sheet, and a Zn—Fe alloy layer (GA) having a thickness of 8 μm was provided on the back surface to obtain a surface-treated steel sheet according to Comparative Example 5.

The details of the surface treatment layer are summarized in Tables 1 and 2 below.

3. 3. Evaluation conditions Each surface-treated steel sheet was placed between the punch and the die, and by moving the punch and the die relatively, a part was punched out with the punch to obtain a processed material having a sheared end face on the die. .. When arranging the surface-treated steel sheet, the front surface of the steel sheet was the punch side and the back surface was the die side. The coefficient of friction on the front and back of the surface-treated steel sheet before shearing was measured as follows, and the properties of the sheared end face of the processed material after shearing were evaluated as follows.

3.1 Measurement of friction coefficient For each surface-treated steel plate, the friction coefficient of the punch side surface and the friction coefficient of the die side surface were measured by a pin-on disk. If the lubricant was present, the coefficient of friction was measured in the presence of the lubricant. The details of the measurement method have already been described.

3.2 Properties of the sheared end face The residual stress of the sheared end face was measured for each processed material as follows. That is, at the center position in the plate thickness direction, the residual stress was measured by X-ray with a spot diameter of φ500 μm (three points different in the plate width direction). The residual stress was measured in three directions: the plate thickness direction, the plate width direction, and the 45 degree direction from the plate thickness direction, and the sin ² ψ method was used to calculate the residual stress. Assuming that the residual stress in the normal direction of the end face is zero, the maximum principal stress was calculated from the calculated residual stress in the three directions. The values of the maximum principal stress calculated at three points were averaged.

In the case of surface-treated steel sheet A1 (1470 MPa class), "A" is when the residual stress value is less than 600 MPa, "B" is when it is 600 MPa or more and less than 1000 MPa, and "C" is when it is 1000 MPa or more and less than 1400 MPa. The case of 1400 MPa or more and less than 1800 MPa was evaluated as "D", and the case of 1800 MPa or more was evaluated as "E".
In the case of surface-treated steel sheet B1 (1180 MPa class), "A" is when the residual stress value is less than 450 MPa, "B" is when it is 450 MPa or more and less than 800 MPa, and "C" is when it is 800 MPa or more and less than 1150 MPa. The case of 1150 MPa or more and less than 1450 MPa was evaluated as "D", and the case of 1450 MPa or more was evaluated as "E".
In the case of surface-treated steel sheet C1 (980 MPa class), "A" is when the residual stress value is less than 400 MPa, "B" is when it is 400 MPa or more and less than 650 MPa, and "C" is when it is 650 MPa or more and less than 950 MPa. The case of 950 MPa or more and less than 1200 MPa was evaluated as "D", and the case of 1200 MPa or more was evaluated as "E".
When the evaluation results were A to D, it was determined to be acceptable, and when it was E, it was determined to be unacceptable.

4. Evaluation Results The evaluation results are shown in Table 3 below.

As shown in Table 3, by changing the type of the surface-treated layer on the front and back of the surface-treated steel plate, the friction coefficient of the front surface (punch side surface) of the surface-treated steel plate is higher than the friction coefficient of the back surface (die side surface). When the surface-treated steel plate is sheared in a state where the friction coefficient difference is larger than a predetermined value and the friction coefficient difference is a predetermined value or more, the tensile residual stress of the fracture surface is remarkably reduced on the sheared end face of the processed material obtained after the shearing. I know I can do it. It is probable that the area ratio of the first portion derived from the first crack extending from the punch side could be increased in the fracture surface of the processed material. From various experiments by the present inventor, the above effect is similarly recognized regardless of the thickness and strength of the steel sheet.

The surface-treated steel sheet material of the present disclosure can be used as a constituent material of, for example, automobiles, home appliances, building structures, ships, bridges, construction machinery, various plants, pen stocks and the like.

1 Shear end face 1a Dripping 1b Fracture surface 1b x 1st part 1by 2nd part 1c Burr 1dx 1st crack 1dy 2nd crack 1e Shear surface 5x Steel plate 5y Surface treatment layer 5 Surface treatment steel plate 10 Processed material 10a Surface 10b Back surface 11 Steel plate 12 Other part of steel plate 15 Scrap 21 1st blade 21a 1st bottom surface 21b 1st side surface 21x 1st tip part 22 2nd blade 22a 2nd bottom surface 22b 2nd side surface 22x 2nd tip part

Claims (9)

A surface-treated steel sheet having a steel sheet and a surface-treated layer,
At least one of the front surface and the back surface is composed of the surface treatment layer.
The coefficient of friction on the front surface is 1.4 times or more the coefficient of friction on the back surface.
The difference between the friction coefficient of the front surface and the friction coefficient of the back surface is 0.10 or more.
Surface-treated steel sheet. The front surface and the back surface are composed of the surface treatment layer.
The type of the surface treatment layer constituting the front surface and the type of the surface treatment layer constituting the back surface are the same or different.
The surface-treated steel sheet according to claim 1. Has a sheared end face and
The sheared end face has sagging, fracture surface and burrs.
The sagging is present on the front surface side, and the burr is present on the back surface side.
The surface-treated steel sheet according to claim 1 or 2. The thickness of the surface treatment layer is 1 μm or more and 50 μm or less.
The surface-treated steel sheet according to any one of claims 1 to 3. The surface treatment layer contains plating,
The surface-treated steel sheet according to any one of claims 1 to 4. The surface treatment layer contains a coating film,
The surface-treated steel sheet according to any one of claims 1 to 5. The tensile strength of the steel sheet is 980 MPa or more.
The surface-treated steel sheet according to any one of claims 1 to 6. The tensile strength of the steel sheet is 1470 MPa or more.
The surface-treated steel sheet according to claim 7. The surface-treated steel sheet according to any one of claims 1 to 8 is arranged between the first blade and the second blade, where the surface of the surface-treated steel sheet is arranged on the first blade side. , The back surface of the surface-treated steel sheet is arranged on the second blade side.
Shearing the surface-treated steel sheet by relatively moving the first blade and the second blade.
including,
Manufacturing method of processed materials.

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