Molded body

Abstract

The present invention provides a molded body having excellent impact resistance in a bent portion by means of a novel configuration. This molded body (1) has a bent section (2) formed from a steel plate, and is characterized in that the M value of the average Taylor factor of the inner surface layer (21) of the bent section (2) is 3.300 or less.

Description

Technical Field

[0001] The present invention relates to a shaped body having a bending section formed from a steel plate. Background Technology

[0002] For automotive running gear, the use of high-strength materials is being pursued to achieve lightweighting. However, this increased strength often leads to reduced formability. Therefore, there is a strong demand for materials that balance high strength and formability.

[0003] As such a material, for example, Patent Document 1 discloses a high-strength hot-rolled steel sheet with excellent bending workability as a steel sheet used in the manufacture of automotive running gears, etc. Specifically, Patent Document 1 discloses a hot-rolled steel sheet whose chemical composition contains C, Si, Mn, and sol.Al, and in the surface region, it is composed of {211} <111> ~{111} <112> The average polar density of the orientation group formed is similar to {110} <001> The sum of the extreme densities of the crystal orientations is greater than 0.5 and less than 6.0, and the tensile strength is greater than 780 MPa and less than 1370 MPa.

[0004] Similarly, Patent Document 2 discloses a high-strength steel sheet with excellent bending workability and fatigue properties, used in the manufacture of automotive running gear and the like. Specifically, Patent Document 2 discloses a high-strength hot-rolled steel sheet comprising a base and a surface portion. The average Vickers hardness of the surface portion is 50-80% of the average Vickers hardness at half the thickness of the high-strength hot-rolled steel sheet. The arithmetic mean surface roughness Ra of the surface portion is 3.0 μm or less, the effective grain size of the surface portion is 50.0 μm or less, and the Si content of the base portion is Si... B The Si content of the surface layer S The difference ΔSi=Si B -Si s The base metal microstructure, measured by area ratio, is 90% or more tempered martensite, with a mass content of 0.60% or more.

[0005] Patent document 3 discloses a high-strength steel sheet with excellent bending properties for use in manufacturing automotive running gear and the like. Specifically, Patent Document 3 discloses a high-strength steel plate whose composition contains C: 0.04~0.20%, Si: 0.6~1.5%, Mn: 1.0~3.0%, P: less than 0.10%, S: less than 0.030%, Al: less than 0.10%, N: less than 0.010%, and contains 0.01~1.0% of one or more of Ti, Nb, and V respectively. The remaining part consists of iron and unavoidable impurities. The microstructure has more than 50% bainite in terms of area ratio. The average grain size at a position 50 μm from the surface of the steel plate in the thickness direction is less than 2500 × [tensile strength TS (MPa)] - 0.85 μm. The amount of C in the precipitates with a grain size of less than 20 nm in the steel is more than 0.005% by mass. The arithmetic mean roughness Ra is less than 3.0 μm.

[0006] Furthermore, Patent Document 4 discloses a high-strength structural steel with excellent cold bending properties, used as a steel sheet in the manufacture of automotive running gear and the like. Specifically, Patent Document 4 discloses a high-strength structural steel that, by weight percent, consists of C: 0.02~0.1%, Si: 0.01~0.6%, Mn: 1.7~2.5%, Al: 0.005~0.5% or less, P: 0.02% or less, S: 0.01% or less, N: 0.0015~0.015%, with the remainder being Fe and other unavoidable impurities. Along the thickness direction, it is divided into an outer surface layer and an inner central layer with a fine microstructure. The surface layer contains tempered bainite as the matrix structure, and the central layer contains bainitic ferrite as the matrix structure.

[0007] Existing technical documents Patent documents Patent Document 1: International Publication No. 2020 / 110843 Patent Document 2: International Publication No. 2020 / 203934 Patent Document 3: Japanese Patent Application Publication No. 2017-150051 Patent Document 4: Japanese Patent Publication No. 2022-514018 Summary of the Invention

[0008] The problem that the invention aims to solve Generally, the running parts of an automobile have bent portions formed by stamping a material such as a steel plate into a specified shape corresponding to each purpose. Here, if the formability of the material is insufficient, the inner side of the bent portion is deformed in a way of being folded (the Japanese original text is: 織り込まれる) during the stamping process, and sometimes fine cracks are generated on the inner surface layer of the bent portion. Currently, even if such fine cracks are generated, there is no particular impact on the impact resistance of the component. However, in order to cope with the further weight reduction or further complication of future automobile components, it is desired to produce components with fewer such fine cracks and more excellent impact resistance.

[0009] Therefore, the object of the present invention is to provide a formed body with excellent impact resistance of the bent portion through a new structure.

[0010] Means for solving the problem The present invention includes the following aspects.

[0011] (Aspect 1) A formed body, characterized in that it is a formed body made of a steel plate and having a bent portion, wherein The M value of the average Taylor factor of the inner surface layer of the above-mentioned bent portion is 3.300 or less.

[0012] (Aspect 2) The formed body according to the above Aspect 1, characterized in that the Vickers hardness at the 1 / 4 plate thickness position of the above-mentioned steel plate is 250 HV or more.

[0013] (Aspect 3) The formed body according to the above Aspect 1 or 2, characterized in that the chemical composition of the above-mentioned steel plate is, by mass%: C: 0.02 - 0.30%, Si: 0.03 - 2.00%, Mn: 0.50 - 3.00%, Al: 0.01 - 1.00%, Ti: 0.06 - 0.20%, P: 0.100% or less, S: 0.010% or less, N: 0.0100% or less, Nb: 0 - 0.10%, Ca: 0 - 0.0060%, Mo: 0 - 1.00%, Cr: 0 - 1.00%, V: 0 - 0.40%, <000D074>Ni: 0 - 0.40%, B: 0~0.0020% Cu: 0~1.00% W: 0~1.00% Sn: 0~0.50% Zr: 0~0.050%, and The remainder consists of Fe and impurities.

[0014] Invention Effects According to the present invention, it is possible to provide a shaped article with excellent impact resistance in the bending process section. Attached Figure Description

[0015] Figure 1 This is an end view of a cross section parallel to the thickness direction TP of a formed body 1 including a bending processing portion 2 according to an embodiment of the present invention.

[0016] Figure 2 (a) is a cross-sectional SEM image of the inner surface of the bending section of the shaped body sample used as a comparison benchmark, and (b) is a cross-sectional SEM image of the inner surface of the bending section of the shaped body sample manufactured by changing the bending direction using the same steel plate as (a).

[0017] Figure 3 (a) is a cross-sectional SEM image of the inner surface of the bent portion of the shaped body sample used as a comparison benchmark, and (c) is a cross-sectional SEM image of the inner surface of the bent portion of the shaped body sample manufactured using a different steel plate than (a) and with the same bending direction as (a). It should be noted that... Figure 3 The shaped sample of (a) and Figure 2 The shaped sample of (a) is the same.

[0018] Figure 4 This is a schematic diagram illustrating the method for measuring the average Taylor factor of the inner surface layer of a bent part.

[0019] Figure 5 This is a schematic diagram illustrating the relationship between the bending axis AB and the rolling direction DR when bending a blank material p cut from a hot-rolled steel sheet SP. Detailed Implementation

[0020] To achieve the above objectives, the inventors conducted a detailed study on the causes of crack formation on the inner surface layer of the bending section of the formed article and methods for suppressing it. As a result, the inventors discovered that the ease with which crack formation occurs on the inner surface layer of the bending section is influenced by the orientation of the crystals developed on the surface of the steel sheet in the bending section. Specifically, it was found that the higher the average Taylor factor (M value), which is determined by the relationship between the orientation of the crystals present on the surface of the steel sheet and the direction of strain, the more easily cracks develop on the inner surface layer of the bending section, and the more likely brittle fracture will occur. The mechanism is not necessarily clear, but it is believed that a larger M value, i.e., a greater ease of dislocation slip, leads to a greater likelihood of the development of shear bands on the surface layer that teach the relationship with crack formation.

[0021] This invention is based on the following insights and includes various embodiments.

[0022] Hereinafter, a preferred embodiment of the molded article of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the various numerical ranges in this specification refer to the ranges including their upper and lower limits.

[0023] <molded body> Figure 1 This is an end view of a cross section parallel to the thickness direction TP of a molded body 1 according to an embodiment of the present invention, including the bending processing portion 2. It should be noted that the molded body 1 of this embodiment is not particularly limited as long as it has the bending processing portion 2, and can be, for example, an upper arm, lower arm, torsion beam, stabilizer bar, or other automotive running parts.

[0024] Formed body 1 is formed by shaping a steel sheet into a specified shape, and has Figure 1 The diagram shows the specified bending section 2 and the plate-shaped section 3 connected to the bending section 2 but not subjected to bending. Furthermore, in... Figure 1 In the bending section 2, there are an inner surface layer 21 and an outer surface layer 22 facing each other in the thickness direction TP. The bending section 2 functions as a reinforcing rib to ensure the strength of the formed body 1, and is formed at stress-generating locations such as edges where stress easily concentrates from the outside. Furthermore, the bending section 2 can be formed not only at such stress-generating locations, but also at other locations. For example, the bending section 2 can be formed almost entirely over the outer periphery of the formed body 1. On the other hand, the plate-shaped portion 3 can be formed as a portion other than the bending section 2. The plate-shaped portion 3 can also have a flat structure like a steel plate that has not undergone bending or other processing. Alternatively, the plate-shaped portion 3 can be processed other than bending to have a certain degree of curvature, or have an uneven structure, or a structure with holes, etc. Furthermore, in Figure 1 In the middle, the symbol A BThis indicates the bending shaft of bending processing section 2. Bending shaft A B It is an imaginary axis used when bending steel plates. Figure 1 In the middle, the bending shaft A B As shown as an imaginary shaft extending in a direction perpendicular to the plane containing the end face of the bending section 2, the actual shaft components are not disposed inside the steel plate.

[0025] The location where the bending portion 2 is formed can be determined based on the component structure, shape, and application of the molded body 1. For example, if the molded body 1 is a lower arm of an automotive running gear, it is preferable that the location where the stress is most easily concentrated in the lower arm is the edge on the tire side along the length of the lower arm, and the bending portion 2 is formed at a location that includes at least such a location where the stress is most concentrated. Furthermore, such a location where the stress is most concentrated is also determined based on the overall structure, shape, and application of the molded body, such as the automotive running gear.

[0026] There are no particular limitations on the means of forming the bending part 2. The bending part 2 can be formed using general processing means and processing conditions such as stamping (especially cold stamping).

[0027] The average Taylor factor (M value) of the inner surface layer of the bending section is below 3.300. Furthermore, the molded body 1 of this embodiment has a characteristic configuration in which the average Taylor factor (M value) of the inner surface layer 21 of the bending section 2 is 3.300 or less. As a result, it is difficult for cracks to occur in the inner surface layer 21 of the bending section 2 when the steel sheet is stamped, resulting in a molded body with less cracking in the inner surface layer 21 of the bending section 2.

[0028] In this specification, the inner surface layer of the bending section refers to the area extending from the inner surface of the steel plate of the bending section to a depth of 1 / 8 of the plate thickness in the thickness direction. The same applies to the outer surface layer of the bending section. It should be noted that when the steel plate surface has been coated or plated, this refers to the area after the thickness of these coatings has been removed.

[0029] Here, a means for controlling the average Taylor factor M value of the inner surface layer 21 of the bending section 2 to be below 3.300 will be described. The inventors investigated the means for controlling this average Taylor factor M value and obtained the following insights: Specifically, the inventors found that if materials with high M values ​​before bending and materials with low M values ​​are deformed by the same bending process, the M values ​​of each material decrease compared to their values ​​before bending, but the relationship between the magnitudes of the M values ​​of the materials remains the same as before bending. Furthermore, the inventors found that if the relationship between the rolling direction of the steel sheet, which is a constituent material of the formed body, and the predetermined position for bending changes, the M value before bending also changes, and as a result, the bending performance and the M value after bending also change. Based on these insights, the inventors discovered that by adjusting the direction of cutting the blank material from the steel sheet (i.e., the blanking direction) in a way that makes the bending section have a certain low M value, the M value after bending can be controlled within a specified range.

[0030] Here, Figure 2 (a) is a cross-sectional SEM image of the inner surface of the bent portion of the shaped body sample used as a comparison benchmark, and (b) is a cross-sectional SEM image of the inner surface of the bent portion of the shaped body sample manufactured using the same steel plate as (a) but with a different bending direction. Additionally, in Figure 2 In the image, multiple arrows indicate the various cracks that have been created.

[0031] Figure 2 The shaped sample shown in (a) and Figure 2 Although the shaped samples shown in (b) use the same steel plate as material, the blanking direction of the steel plate, i.e., the direction from which the blank is punched, is different. As a result, the M value before bending is different. Specifically, Figure 2 The formed sample shown in (a) is a bending axis A during the bending process of the blank material when it is punched from a steel sheet. B A shaped sample is obtained by punching a blank material in a manner that intersects with the rolling direction of the steel plate and then forming the blank material. Figure 2 The formed sample shown in (b) is formed when the blank is punched from a steel sheet, so that the bending axis A is used to bend the blank. B A sample is obtained by punching a blank material in a manner that does not intersect the rolling direction of the steel sheet, and then forming the sample using the blank material. It should be noted that, in the description of the manufacturing method of the formed body described later, the bending axis A during the bending process of the blank material punched from the steel sheet... B The relationship with the rolling direction is explained in detail.

[0032] Figure 2The M-value of the shaped sample shown in (a) before bending is 3.285, and the M-value after bending is 3.268. On the other hand, Figure 2 The M value of the shaped sample shown in (b) before bending is 3.337, and the M value after bending is 3.312. Figure 2 The M values ​​of either of the shaped samples in (a) and (b) after bending are lower than those before bending, but their magnitude relationship remains the same as before bending.

[0033] Moreover, according to Figure 2 It can be seen that, compared with the molded body sample with an M value of a certain value below a certain value after bending (b), the molded body sample with an M value of a certain value after bending (a) has more cracks on the inner surface of the bending part.

[0034] in addition, Figure 3 (a) is a cross-sectional SEM image of the inner surface of the bent portion of the formed body sample used as a comparison benchmark, and (c) is a cross-sectional SEM image of the inner surface of the bent portion of the formed body sample manufactured using a blank material punched from a different steel plate than (a) in the same blanking direction as (a). Furthermore, in Figure 3 In the image, multiple arrows indicate the various cracks that have been created.

[0035] Figure 3 The shaped sample shown in (a) is similar to Figure 3 The steel plates of the shaped samples shown in (c) have the same blanking direction, but the chemical composition of the steel plates used as materials is different, resulting in different M values ​​before bending. It should be noted that... Figure 3 The shaped sample of (a) and Figure 2 The molded sample of (a) is the same, therefore Figure 3 The shaped body samples shown in (a) and (c) are both shaped body samples of the following type: when blanking a steel sheet, the bending axis A is used to bend the blank during the bending process. B A blank material is punched in a manner that intersects with the rolling direction of the steel plate, and a shaped sample is obtained by forming the blank material.

[0036] Figure 3 As described above, the shaped sample shown in (a) has an M value of 3.285 before bending and an M value of 3.268 after bending. On the other hand, Figure 3 The M value of the shaped sample shown in (c) before bending is 3.311, and the M value after bending is 3.309. Figure 3 The M values ​​of either (a) or (c) after bending are lower than those before bending, but their magnitude relationship remains the same as before bending.

[0037] Moreover, according to Figure 3 It can be seen that, compared with the molded sample (a) whose M value after bending is smaller than that of (c), the molded sample (c) has more cracks on the inner surface layer of the bent portion. However, Figure 3 The molded sample shown in (c) is similar to Figure 2 Compared to the shaped sample shown in (b), the M value after bending is smaller, indicating that the cracking ratio of the inner surface layer of the bent portion is lower. Figure 2 The number of molded samples shown in (b) is small.

[0038] according to Figure 2 and Figure 3 A comparison of the formed samples shown in (a) to (c) reveals that the average Taylor factor M value of the inner surface layer of the bending section is related to the blanking direction of the steel plate, i.e., the bending axis A when bending the blank material from the steel plate. B The rolling direction of the steel sheet has the greatest impact, followed by the type of steel sheet, i.e., its chemical composition. Therefore, the bending axis A during the bending process of blank material cut from steel sheet is crucial. B By adjusting the rolling direction at angles of 45 to 135 degrees, the average Taylor factor (M value) of the inner surface layer of the bent section can be controlled within the aforementioned specified range, thus reducing cracking of the inner surface layer of the bent section. Furthermore, by adjusting the texture of the steel sheet, i.e., adjusting the chemical composition of the steel sheet, the M value of the steel sheet before bending can be more reliably reduced to below a certain level. Therefore, it is easier to control the average Taylor factor (M value) of the inner surface layer of the bent section after bending within the aforementioned specified range. As a result, cracking of the inner surface layer of the bent section can be further reduced.

[0039] It should be noted that, as a means to more easily control the average Taylor factor M value of the inner surface layer of the bending part within the range specified above, for example, the following methods can be listed: softening the surface layer of the material such as steel plate at least the part corresponding to the bending part, thereby concentrating the strain on the surface layer and reducing the M value after bending; and ensuring the formability of the material such as steel plate to a higher degree, thereby imparting a large strain during bending and reducing the M value after bending.

[0040] In this embodiment, if the average Taylor factor (M) of the inner surface layer of the bending section is greater than 3.300, multiple cracks are easily generated in the bending section. Therefore, to obtain the effects of the present invention, the M value needs to be controlled below 3.300. The M value can be below 3.200, below 3.100, or below 3.000. Furthermore, there is no particular limitation on the lower limit of the M value; the lower the M value, the better the effects of the present invention can be obtained. However, the M value is by definition not less than 2.000. The M value can be above 2.100, above 2.400, or above 2.700.

[0041] (Method for determining the average Taylor factor M value of the inner surface layer of the bending section) The average Taylor factor M value of the inner surface layer of the bent section can be calculated by measuring a section perpendicular to the bending axis, including the overall thickness of the sample being measured, using EBSD. Figure 4 This is a schematic diagram illustrating the method for measuring the average Taylor factor of the inner surface layer of the bending section 2.

[0042] When determining the average Taylor factor of the inner surface layer of the bent section, firstly, as... Figure 4 As shown, crystal orientation is determined by MR in a rectangular measurement region centered at the apex of the inner surface of the bent section 2, within a cross-section perpendicular to the bending axis that includes the overall thickness of the sample being measured. The surface of the sample including the measurement region MR is finished by electrolytic polishing after mirror polishing. In the measurement, an EBSD analysis apparatus is used, consisting of a thermal field emission scanning electron microscope (e.g., JEOL JSM-7200F) and an EBSD detector (e.g., an EDAX Velocity (registered trademark) ultra-high-speed action EBSD detector). The vacuum level within the apparatus is set to 9.6 × 10⁻⁶. -5 Below Pa, the accelerating voltage is set to 25kV, the irradiation current level is set to 15~18, and the working distance (WD) is set to 15mm. For example... Figure 4 As shown, the measurement region MR is set as follows: a rectangular area with a thickness length (less than 1 / 8 of the plate thickness) that is confined to the surface region as the short side and a 750 μm long side orthogonal to this thickness length as the long side. For example, when the thickness of the sample being measured is 3 mm, the measurement region MR can be set as a rectangular area with a short side of 300 μm in the thickness direction and a long side orthogonal to this thickness direction of 750 μm. In this case, the measurement step size is set to 2 μm.

[0043] Based on the multiple crystal orientation information obtained in this way, the average Taylor factor was calculated using EBSD analysis software. The analysis software used was TSL's "OIM Analysis" (registered trademark) Ver. 7.3.1.

[0044] Furthermore, the bending process subjectes strain, which can sometimes reduce measurement accuracy. Therefore, only points with a CI value (accuracy index) of at least 0.05 are used. Additionally, to ensure the accuracy of the average Taylor factor, at least 2000 measurement points with a CI value of 0.05 or higher are required. For this purpose, the detector exposure time is set sufficiently long, or the SEM magnification is significantly increased. If the MR of the measurement area is not captured in a single image due to increased SEM magnification, the MR of the measurement area can be divided into multiple regions for measurement.

[0045] When calculating the Taylor factor, the slip system is assumed to be {110}, which is the principal slip system of the BCC. <111> The calculations are performed using these 12 methods. Furthermore, the deformation of the inner surface layer of the bent section is calculated using a tensor assuming compressive deformation under plane strain conditions. That is, it is assumed that, relative to the compression caused by bending deformation, the expansion used to maintain a constant volume only occurs in the thickness direction of the plate. For example, when the x-axis is parallel to the bending axis, the z-axis is in the thickness direction, and the y-axis is perpendicular to both the bending axis and the thickness direction, the diagonal components of the provided tensor for x, y, and z are 0, -1, and 1, respectively, and the off-diagonal components are all 0.

[0046] (Minimum radius of curvature r of the bending section) In the molded body 1 of this embodiment, there is no particular limitation on the minimum radius of curvature r of the inner side of the bending processing section 2. From the viewpoint of effectively utilizing the limited design space, the minimum radius of curvature r can be 8.0 mm or less, 5.0 mm or less, or 3.0 mm or less. In addition, from the viewpoint of suppressing wrinkles and cracks that may be generated on the surface during bending processing, the minimum radius of curvature r can be 0.8 mm or more, 1.2 mm or more, 1.6 mm or more, or 2.0 mm or more.

[0047] In this embodiment, the steel plate used in the molded body is not particularly limited in terms of other requirements, as long as the average Taylor factor M value of the inner surface layer of the bending section of the molded body can be adjusted to the range specified above. For example, the strength and thickness of the steel plate can be the specified strength and thickness required for the component using the molded body.

[0048] The Vickers hardness at 1 / 4 of the steel plate's thickness is above 250 HV. For example, a tensile strength of 780 MPa or higher can be cited as a suitable strength for the steel sheet used in this invention. The Vickers hardness at a position one-quarter of the sheet thickness of such a high-strength steel sheet is greater than 250 HV. Typically, with increased strength, such steel sheets are more prone to cracking on the inner surface of the bent portion after bending. However, even when using a steel sheet with a Vickers hardness of 250 HV or higher at one-quarter of the sheet thickness, the formed body 1 of this embodiment can reduce cracking on the inner surface of the bent portion by keeping the average Taylor factor M value of the inner surface of the bent portion below 3.300.

[0049] In addition, the so-called 1 / 4 position of the steel plate thickness means the position in the thickness direction of the steel plate, starting from the surface of the steel plate, which is 1 / 4 of the total thickness.

[0050] From the perspective of the impact resistance of the formed body, the Vickers hardness at one-quarter of the steel plate thickness can be above 252 HV, 255 HV, 258 HV, or 260 HV. There is no specific upper limit to the Vickers hardness at one-quarter of the steel plate thickness. The Vickers hardness at one-quarter of the steel plate thickness can be below 450 HV, 400 HV, 350 HV, or 300 HV.

[0051] Furthermore, this invention is also applicable to steel plates with a Vickers hardness of less than 250 HV. Such steel plates, due to their low tensile strength, inherently possess excellent bending workability; therefore, by applying this invention, the formation of cracks can be more reliably suppressed.

[0052] (Method for determining Vickers hardness at 1 / 4 of the plate thickness) The Vickers hardness at the 1 / 4 mark of the steel plate thickness can be determined according to JIS Z 2244:2009. For the Vickers hardness at the 1 / 4 mark of the steel plate thickness, 10 measurements can be performed at the 1 / 4 mark of the plate thickness (excluding the bending section) under a load of 1 kgf (approximately 9.80 N), and the average of these 10 measurements is obtained. In this case, the interval between measurement locations should ensure a distance of at least three times the indentation depth.

[0053] In addition, regarding the thickness of steel plates, for example, thicknesses of 1.5 mm and above can be listed. Steel plate thicknesses can be 1.8 mm and above, 2.0 mm and above, or 2.2 mm and above. There is no particular upper limit to the thickness of steel plates; from the viewpoint of ensuring good bending workability, steel plate thicknesses can be 6.0 mm or less, 5.5 mm or less, 5.0 mm or less, 4.5 mm or less, or 4.0 mm or less.

[0054] It should be noted that the thickness of the steel sheet is measured using a micrometer at a relatively smooth location on the component (formed body). Furthermore, portions of the sheet thickness that are locally reduced due to thickness reduction caused by pressing processes are not included in the measurement.

[0055] (Chemical composition) In this embodiment, the steel plate used for the formed body 1 preferably has the following specific chemical composition: C: 0.03~0.30% Si: 0.03~2.00% Mn: 0.50~3.00% Al: 0.01~1.00% Ti: 0.06~0.20% P: Below 0.100% S: Below 0.010% N: below 0.0100% Nb: 0~0.10%, Ca: 0~0.0060% Mo: 0~1.00% Cr: 0~1.00% V: 0~0.40%, Ni: 0~0.40% B: 0~0.0020% Cu: 0~1.00% W: 0~1.00% Sn: 0~0.50% Zr: 0~0.050%, and The remainder consists of Fe and impurities.

[0056] The following is a more detailed explanation of the chemical composition of the steel plate. It should be noted that, unless otherwise specified, the "%" used to indicate the content of each element refers to "mass %".

[0057] [C: 0.02~0.30%] Carbon (C) is an element that increases the strength of steel sheets. To achieve this effect, the C content is preferably 0.02% or more. The C content can be 0.03% or more, 0.04% or more, or 0.05% or more. On the other hand, from the viewpoint of ensuring good bending workability during forming, especially during cold stamping, the C content is preferably 0.30% or less. The C content can be 0.25% or less, 0.20% or less, or 0.15% or less.

[0058] [Si: 0.03~2.00%] Si is a deoxidizing element in steel and an effective solid solution strengthening element for increasing strength without compromising the ductility of the steel sheet. To fully achieve this effect, the Si content is preferably 0.03% or more. The Si content can be 0.05% or more, 0.08% or more, or 0.10% or more. On the other hand, from the viewpoint of suppressing ferrite formation to ensure the specified strength, or from the viewpoint of ensuring good bending workability, the Si content is preferably 2.00% or less. The Si content can be 1.80% or less, 1.60% or less, or 1.40% or less.

[0059] [Mn: 0.50~3.00%] Mn is an element that improves the hardenability of steel and contributes to increased strength. To fully achieve this effect, the Mn content is preferably 0.50% or more. The Mn content can be 0.60% or more, 0.80% or more, or 1.00% or more. On the other hand, from the viewpoint of ensuring good bending workability by suppressing the inhomogeneity of the microstructure caused by the microsegregation of Mn, the Mn content is preferably 3.00% or less. The Mn content can be 2.80% or less, 2.60% or less, or 2.40% or less.

[0060] [Al: 0.01~1.00%] Al acts as a deoxidizer and is an effective solid solution strengthening element for improving the strength of steel. Furthermore, Al also inhibits carbide formation and readily forms retained austenite. To fully obtain these effects, the Al content is preferably 0.01% or more. The Al content can be 0.05% or more, 0.10% or more, or 0.15% or more. On the other hand, from the viewpoint of ensuring good bending workability by suppressing the formation of coarse precipitates at the grain boundaries of the original austenite grains, the Al content is preferably 1.00% or less. The Al content can be 0.80% or less, 0.60% or less, or 0.40% or less.

[0061] [Ti: 0.06~0.20%] Ti is an element that controls the morphology of carbides and increases the strength of ferrite. To fully achieve this effect, the Ti content is preferably 0.06% or more. The Ti content can be 0.08% or more or 0.10% or more. On the other hand, from the viewpoint of suppressing the formation of coarse Ti oxides or TiN to ensure good bending workability, the Ti content is preferably 0.20% or less. The Ti content can be 0.18% or less, 0.16% or less, or 0.14% or less.

[0062] [P: below 0.100%] Phosphorus (P) is an element introduced during the manufacturing process and is considered an impurity. Furthermore, P segregates at the original austenite grain boundaries, sometimes causing grain boundary embrittlement and reducing the formability of the steel sheet. Therefore, a lower P content is better. The P content can also be 0%. However, from the viewpoint of shortening refining time and ensuring good productivity, the P content can be 0.0001% or more, 0.0005% or more, or 0.001% or more. On the other hand, from the viewpoint of suppressing the reduction in the toughness of the steel sheet and ensuring good bending workability, the P content can also be 0.100% or less. The P content can be 0.080% or less, 0.060% or less, or 0.040% or less.

[0063] [S: below 0.010%] Sulfur (S) is an element introduced during the manufacturing process and is considered an impurity. Furthermore, S forms non-metallic inclusions such as MnS in steel, sometimes leading to increased hardness and decreased ductility in the steel sheet. Therefore, the lower the S content, the better. The S content can also be 0%. However, from the viewpoint of shortening refining time while ensuring good productivity, the S content can be 0.0001% or more, 0.0005% or more, or 0.0010% or more. On the other hand, from the viewpoint of ensuring good bending workability, the S content can be 0.010% or less. The S content can also be 0.008% or less, 0.006% or less, or 0.004% or less.

[0064] [N: below 0.0100%] Nitrogen (N) is an element introduced during the manufacturing process. Like carbon (C), N is effective for increasing the strength of steel, but it also affects the occurrence of cross-slip dislocations during forming, especially cold stamping. If the N content is high, strain concentration cannot be suppressed during steel sheet forming, leading to porosity and reduced formability. From the viewpoint of ensuring good formability, the lower the N content, the better. The N content can also be 0%. However, from the viewpoint of shortening refining time and ensuring good productivity, the N content can be 0.0001% or higher, 0.0005% or higher, or 0.0010% or higher. On the other hand, from the viewpoint of ensuring good bending workability, the N content can be 0.0100% or lower. The N content can be 0.0080% or lower, 0.0060% or lower, or 0.0050% or lower.

[0065] In this embodiment, the preferred basic chemical composition of the steel sheet used for the formed body 1 is as described above. Furthermore, in this embodiment, the steel sheet may, as needed, contain one or more of the following optional elements to replace a portion of the remaining Fe. These optional elements will be described in detail below.

[0066] [Nb: 0~0.10%] Nitrogen (Nb) is an effective element for controlling the morphology of carbides, and it is also effective in refining grains and improving the toughness and bending workability of steel sheets. The Nb content can be 0%, but to fully obtain these effects, the Nb content can be 0.001% or more. The Nb content can be 0.005% or more, 0.007% or more, or 0.010% or more. On the other hand, from the viewpoint of suppressing excessive strengthening, the Nb content can be 0.10% or less. From an economic point of view, the Nb content can be 0.08% or less, 0.06% or less, or 0.04% or less.

[0067] [Ca: 0~0.0060%] Ca is an element that helps to finely disperse inclusions and improves toughness. In other words, Ca helps to improve the formability of steel sheets. The Ca content can be 0%, but to achieve this effect, the Ca content can be 0.0001% or more. The Ca content can be 0.0005% or more, 0.0010% or more, or 0.0015% or more. On the other hand, from the viewpoint of ensuring good bending workability, the Ca content is preferably 0.0060% or less. The Ca content can be 0.0050% or less, 0.0040% or less, or 0.0030% or less.

[0068] [Mo: 0~1.00%] Mo is an element that suppresses phase transformation at high temperatures and contributes to increasing the strength of steel sheets. The Mo content can be 0%, but to achieve this effect, the Mo content can be 0.001% or more. The Mo content can be 0.01% or more, 0.05% or more, or 0.10% or more. On the other hand, from the viewpoint of suppressing the reduction in bending workability caused by the formation of coarse Mo carbides, the Mo content can be 1.00% or less. The Mo content can be 0.80% or less, 0.60% or less, or 0.40% or less.

[0069] [Cr: 0~1.00%] Cr is an element that improves the hardenability of steel and contributes to the strength of steel plates. The Cr content can be 0%, but to achieve this effect, the Cr content can be 0.001% or more. The Cr content can be 0.01% or more, 0.10% or more, 0.20% or more, or 0.30% or more. On the other hand, from the viewpoint of suppressing the reduction in bending workability caused by the formation of coarse Cr carbides, the Cr content can be 1.00% or less. The Cr content can be 0.80% or less, 0.60% or less, or 0.50% or less.

[0070] [V: 0~0.40%] V is an effective element for controlling the morphology of carbides, and it is also effective in refining grains and improving the toughness and bending workability of steel sheets. The V content can be 0%, but to achieve this effect, the V content can be 0.001% or more. The V content can be 0.005% or more, 0.01% or more, or 0.02% or more. On the other hand, from the viewpoint of suppressing the reduction in the formability of steel sheets caused by excessive precipitation of carbonitrides, the V content can be 0.40% or less. The V content can be 0.30% or less, 0.20% or less, or 0.10% or less.

[0071] [Ni: 0~0.40%] Ni is an element that suppresses phase transformation at high temperatures and contributes to increasing the strength of steel sheets. The Ni content can be 0%, but to achieve this effect, the Ni content can be 0.001% or more. The Ni content can be 0.01% or more, 0.03% or more, or 0.05% or more. On the other hand, from the viewpoint of suppressing the reduction in the ductility of the steel sheet and ensuring good bending workability, the Ni content can be 0.40% or less. The Ni content can be 0.30% or less, 0.25% or less, or 0.20% or less.

[0072] [B: 0~0.0020%] Boron (B) is an element that suppresses phase transformation at high temperatures and contributes to increasing the strength of steel sheets. The B content can be 0%, but to achieve this effect, the B content can be 0.0001% or more. The B content can be 0.0005% or more, 0.0010% or more, or 0.0015% or more. On the other hand, from the viewpoint of suppressing the reduction in bending workability caused by the formation of coarse B oxides that become the starting point for porosity during steel sheet forming, the B content can be 0.0020% or less. The B content can be 0.0018% or less, 0.0016% or less, or 0.0015% or less.

[0073] [Cu: 0~1.00%] Cu is an element that exists in steel in the form of fine particles and helps to improve the strength of steel sheets. The Cu content can be 0%, but to achieve this effect, the Cu content can be 0.001% or more. The Cu content can be 0.01% or more, 0.03% or more, or 0.05% or more. On the other hand, from the viewpoint of suppressing the reduction in the bending workability of steel sheets caused by the large precipitation of coarse precipitates and inclusions, the Cu content can also be 1.00% or less. The Cu content can be 0.80% or less, 0.60% or less, or 0.40% or less.

[0074] [W: 0~1.00%] W is an element that suppresses phase transformation at high temperatures and contributes to increasing the strength of steel sheets. The W content can be 0%, but to achieve this effect, the W content can be 0.001% or more, or 0.005% or more. On the other hand, from the viewpoint of preventing a decrease in productivity due to reduced bending workability, the W content is 1.00% or less. The W content can be 0.08% or less.

[0075] [Sn: 0~0.50%] Sn is an element that inhibits grain coarsening and contributes to improving the strength of steel sheets. The Sn content can be 0%, but to achieve this effect, the Sn content can be 0.001% or more. The Sn content can be 0.01% or more, 0.05% or more, or 0.08% or more. On the other hand, from the viewpoint of suppressing the decrease in the bending workability of steel sheets caused by the increase of coarse precipitates and inclusions, the Sn content can be 0.50% or less. The Sn content can be 0.40% or less, 0.30% or less, or 0.20% or less.

[0076] [Zr: 0~0.050%] Zr is an element that helps improve the formability of steel sheets. The Zr content can be 0%, but to achieve this effect, the Zr content can be 0.0001% or more. The Zr content can be 0.0005% or more, 0.0010% or more, or 0.0015% or more. On the other hand, from the viewpoint of suppressing the reduction of ductility in steel sheets and ensuring good bending workability, the Zr content can be 0.050% or less. The Zr content can be 0.040% or less, 0.030% or less, or 0.020% or less.

[0077] [Remaining components: Fe and impurities] In this embodiment, the remaining portion of the steel plate, excluding the aforementioned elements, consists of Fe and impurities. Here, "impurities" refers to components introduced during the industrial manufacturing of steel plates, typically from raw materials such as ores and scrap iron, due to various reasons in the manufacturing process. Examples of impurities include, for instance, H, O, Na, Cl, Co, Zn, Ga, Ge, As, Se, Y, Tc, Ru, Rh, Pd, Ag, Cd, In, Te, Cs, Ta, Re, Os, Ir, Pt, Au, Pb, Bi, Sb, and Po. Impurities may be present in amounts totaling 0.100% or less.

[0078] Here, the chemical composition of the steel plate can be determined using general analytical methods. For example, the chemical composition of the steel plate can be determined using inductively coupled plasma-atomic emission spectrometry (ICP-AES). C and S can be determined using the combustion-infrared absorption method, N can be determined using the inactive gas melting-thermal conductivity method, and O can be determined using the inactive gas melting-non-dispersive infrared absorption method.

[0079] As described above, the molded body 1 of this embodiment exhibits fewer cracks on the inner surface layer of the bending section. Therefore, the molded body of this embodiment can be applied to various automotive running gear components requiring high impact resistance, such as upper arms, lower arms, torsion beams, and stabilizer bars.

[0080] <Manufacturing Method of Molded Body> Next, a preferred manufacturing method for the molded body 1 according to one embodiment of the present invention will be described. It should be noted that the following description is intended to illustrate a characteristic method for manufacturing the molded body 1 as an embodiment of the present invention, and is not intended to limit the molded body 1 to the molded body manufactured by the manufacturing method described below.

[0081] When manufacturing the molded body 1 of this embodiment, a steel plate is first manufactured.

[0082] (Methods for manufacturing steel plates) In this embodiment, the method for manufacturing the steel plate is not particularly limited, but a method that can produce a steel plate with the specific chemical composition described above is preferred. Examples of such a method include a casting process that casts a slab having the specific chemical composition described above, and a hot rolling process that hot-rolls the cast slab.

[0083] The following section explains the optimal conditions for these processes.

[0084] (Casting process) In the steel plate manufacturing method of this embodiment, the casting process is a process of casting a slab having the specific chemical composition described above. The casting process uses a continuous casting machine equipped with a plurality of adjacent pressure rolls in the slab conveying direction and the distance between adjacent pressure rolls being 290 mm or less.

[0085] (Hot rolling process) Hot rolling is the process of hot rolling a cast slab. In hot rolling, it is preferable to heat the slab to above 1200°C before hot rolling. By setting the heating temperature above 1200°C, the rolling reaction force during hot rolling will not become excessive, making it easier to achieve the target thickness. There is no particular upper limit to the heating temperature; from an economic point of view, it is preferable to set the heating temperature below 1300°C.

[0086] In the hot rolling process, the heated slab is subjected to rough rolling and finish rolling. Here, by appropriately selecting various conditions for rough rolling and finish rolling, the steel plate can be made to have the preferred and unique Vickers hardness as described above, and the average Taylor factor M value of the inner surface layer of the bent portion 2 formed after bending can be easily controlled within the specific range mentioned above.

[0087] In the hot rolling process, the starting temperature of rough rolling is, for example, below 1150°C. If the starting temperature of rough rolling is below 1150°C, the heat dissipation effect from the rolls can be reduced, resulting in uniform rolling of the steel sheet surface and back. On the other hand, the starting temperature of rough rolling is, for example, above 1050°C. If the starting temperature of rough rolling is above 1050°C, it can be controlled in a way that the rolling reaction force does not become excessive.

[0088] In the hot rolling process, the finishing temperature is, for example, 800°C or higher. If the finishing temperature is 800°C or higher, the average grain size of the hot-rolled steel sheet and the final product can be reduced, thus ensuring sufficient yield strength. On the other hand, there is no particular upper limit to the finishing temperature; from an economic point of view, the finishing temperature is, for example, 980°C or lower.

[0089] Furthermore, the diameter of the rolls used in the hot rolling process is, for example, 100 mm or more. If the roll diameter is 100 mm or more, strain is less likely to concentrate on the surface in contact with the roll, allowing for uniform rolling of the steel sheet's surface and back. On the other hand, there is no particular upper limit to the roll diameter; from an economic point of view, it is, for example, 700 mm or less. It should be noted that the rolls used in the hot rolling process can be preheated. Preheating the rolls can suppress heat loss from the steel sheet caused by the rolls, reducing uneven heat loss from the steel sheet.

[0090] Hot-rolled steel sheets obtained in the hot rolling process are coiled at a coiling temperature of, for example, 450 to 600°C. By setting the coiling temperature above 450°C, the strength of the hot-rolled steel sheet does not become excessively high, and the reduction in bending workability can be suppressed. On the other hand, by setting the coiling temperature below 600°C, coarse ferrite and pearlite are less likely to form in the microstructure of the hot-rolled steel sheet, and bainite is more easily obtained in the microstructure of the hot-rolled steel sheet, which can improve the strength of the steel sheet.

[0091] It should be noted that the coiling temperature of hot-rolled steel sheets can be, for example, below 450°C. By setting the coiling temperature below 450°C, a large amount of bainite and martensite will form, making it easy to ensure the desired strength even with the addition of fewer alloying elements. The coiling temperature can also be, for example, below 200°C. By setting it below 200°C, a large amount of martensite will form, which can improve the strength of the steel sheet even with a small amount of alloying elements.

[0092] (Temperature and heat treatment rolling process) Hot-rolled steel sheets obtained through the hot rolling process can undergo temper rolling for the purpose of correcting their shape. Furthermore, temper rolling is not included in cold rolling; therefore, steel sheets obtained through temper rolling are also hot-rolled steel sheets.

[0093] Hot-rolled steel sheets or steel sheets obtained by quenching and tempering rolling (hereinafter collectively referred to as "hot-rolled steel sheets") can be supplied to any processing process such as plating as needed.

[0094] Then, the hot-rolled steel sheet obtained by the above manufacturing method is supplied to the subsequent forming process. That is, from the viewpoint of easily and reliably obtaining the effects of the present invention, the steel sheet used in the formed body of this embodiment is preferably a hot-rolled steel sheet.

[0095] (Forming process) The forming process includes: a stamping process for punching steel plates into a specified shape; and a bending process for bending the blank material that has been punched into a specified shape.

[0096] The blanking process is a process of blanking a billet material with a top view shape that corresponds to the shape of the formed body 1 before bending processing from the rolled steel plate, i.e., the hot-rolled steel plate.

[0097] Here, Figure 5 This is a bending shaft A used to describe the bending process when blank material p is cut from hot-rolled steel sheet SP. B A schematic diagram showing the relationship with the rolling direction DR. (e.g.) Figure 5 As shown, in the blanking process, when blanking the billet p from the hot-rolled steel sheet SP after the rolling process, the bending axis A is used to bend the billet p. B The blanking direction (i.e., the blanking direction of the sheet) of the billet p is adjusted by intersecting the rolling direction DR of the hot-rolled steel sheet SP. Specifically, the bending axis A is used as the guide. B The blanking direction of the sheet metal is adjusted at angles θ relative to the rolling direction DR, ranging from 45 degrees to 135 degrees. That is, the bending axis A of the hot-rolled steel sheet SP, which becomes the bending section 2, is used as the guide. B The hot-rolled steel sheet SP undergoes punching and bending processes at an angle of 45 to 135 degrees to the rolling direction DR of the hot-rolled steel sheet SP.

[0098] In addition, Figure 5 In the diagram, for convenience, the blank material p is shown in a rectangular top view shape, but it actually has a top view shape corresponding to the formed body 1 before bending.

[0099] As described above, the bending shaft A, which is part of the bending process section 2 in the hot-rolled steel sheet SP, is used. B By performing the punching and bending processes of the hot-rolled steel sheet SP in a manner that intersects with the rolling direction DR of the hot-rolled steel sheet SP, the average Taylor factor M value of the inner surface layer of the bending section can be controlled within the range specified above.

[0100] In this embodiment, the blank material p is cut in the following direction, specifically the bending axis A. B The angle θ between the rolling direction DR and the rolling direction is not particularly limited as long as it is between 45 degrees and 135 degrees. From the point of view of impact resistance, it can be in the range of 60 degrees and 120 degrees, 85 degrees and 95 degrees, or 90 degrees.

[0101] Furthermore, depending on the type of component to which the formed body is applied, the direction of extension of the bending axis in the formed body is sometimes not constant. Specifically, there may be cases where the bending axis is curved, or there may be multiple bending axes. In such cases, considering the direction of stress envisioned in the usage environment of the component to which the formed body is applied, and the dimensions of the bending section, the blanking direction (i.e., the sheet metal cutting direction) of the blank material can be set as long as it matches the part where cracking is most desired to be reduced. In addition, when there are multiple bending axes, the bending axes may be parallel to each other or intersect at an angle other than perpendicular.

[0102] The bending process is a process of bending a blank material that has been punched into a specified shape. There are no particular limitations on the means by which the blank material is bent in the bending process; for example, stamping can be used. Furthermore, the bending process can be performed only once, or it can be performed in multiple stages.

[0103] Furthermore, in the above-described embodiments, the bending process involves bending the blank material that has been punched into a specified shape by the blanking process, but this is not limited to this method. The bending process can be performed simultaneously by punching the blank material and bending a specified portion of the blank material. That is, the blanking process and the bending process can be performed in parallel, or the bending process can be performed after the blanking process as described above.

[0104] The molded body obtained through the above molding process can undergo painting treatment and other surface treatment processes for the purpose of improving appearance and design.

[0105] Furthermore, the present invention is not limited to the above-described embodiments and the following examples. Without departing from the purpose and spirit of the present invention, appropriate combinations, substitutions, and modifications can be made.

[0106] The present invention will be described in more detail below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0107] Example In the following embodiments, a molded body, as an embodiment of the present invention, was manufactured under various conditions, and the impact resistance characteristics of the bending portion of the obtained molded body were investigated.

[0108] (Steel plate manufacturing) A slab with the chemical composition shown in Table 1 below is cast by using a continuous casting machine equipped with multiple pressure rolls arranged with a roll spacing of less than 290 mm.

[0109] Next, the obtained slab undergoes a hot rolling process. Specifically, the slab is heated to 1250°C and subjected to rough rolling and finish rolling. The starting temperature for rough rolling is 1050°C, and the ending temperature for finish rolling is 940°C to 980°C. Furthermore, the coiling temperature of the resulting hot-rolled steel sheet is set to 450°C to 480°C. This yields a hot-rolled steel sheet with a thickness of 3 mm.

[0110] It should be noted that the chemical composition of the samples collected from the obtained hot-rolled steel sheet was analyzed, and the results confirmed that the chemical composition of the slab remained unchanged. The chemical compositions of the obtained hot-rolled steel sheet are shown in Table 1 below as steel grades A to H. Furthermore, the underlines for various numerical values ​​in Table 1 indicate conditions that are not preferred when manufacturing the molded articles of the present invention.

[0111] (Manufacturing of the molded body) So that the bending axis A, which forms the predetermined position in the direction of sheet material cutting, i.e., the bending section, is formed. B The hot-rolled steel sheet is punched into long strips with a width of 30 mm and a length of 100 mm, with the angle θ between the strip and the rolling direction DR being 0 degrees, 15 degrees, 30 degrees, 45 degrees, or 90 degrees. It should be noted that two strips are punched from each adjacent position; one strip is used to determine the average Taylor factor (M value) of the inner surface layer of the bending section. The other strip is used for the fabrication of the formed body and the evaluation of its impact resistance.

[0112] The obtained elongated blank material is then stamped according to JIS Z2248:2006 "6.3 V-block method" to manufacture a formed body. The bending angle of the punch used in this stamping process is 90 degrees. In this way, the formed bodies No.1 to 8 shown in Table 2 are obtained.

[0113] For the molded bodies No. 1 to 8 obtained above, the average Taylor factor M value of the inner surface layer of the bent portion was measured according to the "Method for Determining the Average Taylor Factor M Value of the Inner Surface Layer of the Bending Section" described above. Furthermore, the Vickers hardness was measured according to the "Method for Determining the Vickers Hardness at 1 / 4 Position of the Steel Plate Thickness" described above. Then, the impact resistance test described below was performed on the molded bodies No. 1 to 8 to evaluate the impact resistance of the bent portion of these molded bodies. These measurement results and evaluation results are shown in Table 2 below.

[0114] (Impact resistance test) First, the molded body used as the test subject was cooled to -40°C. Next, the cooled molded body was placed on a horizontal test bench with the outer surface of the bent portion facing upwards. Then, a cone weighing approximately 120 kg, positioned 0.18 m above the surface of the test bench, was allowed to fall freely, colliding with the outer surface of the bent portion of the molded body. Furthermore, the cone was positioned with its bottom surface facing downwards before the free fall. Additionally, a cone with a bottom surface area sufficient to cover the entire bent portion of the component was used.

[0115] Then, observe the state of the formed body after the cone collides with the bending part of the formed body. If the bending part does not break, it is judged as "excellent impact resistance"; if the bending part breaks, it is judged as "poor impact resistance".

[0116] It should be noted that in Table 2, "〇" indicates a judgment of "excellent impact resistance" and "×" indicates a judgment of "poor impact resistance". Furthermore, the underlines for various numerical values ​​in Table 2 indicate that the invention is outside the scope of this invention or that manufacturing conditions under which the molded article of this invention could not be obtained.

[0117] As shown in Table 2, it can be seen that the molded body of the present invention exhibits excellent impact resistance in the bending process. On the other hand, it can be seen that the molded body of the comparative example has poor impact resistance in the bending process.

[0118] Explanation of reference numerals in the attached figures 1 formed body 2 Bending Processing Section 21 Inner surface layer 22 Outer surface layer

Claims

1. A shaped body, characterized by, It is a formed body having a bending processed portion formed of a steel sheet, wherein An M value of an average Taylor factor of an inner side skin layer of the bending processed portion is 3.300 or less.

2. The shaped body of claim 1, wherein, A Vickers hardness at a 1 / 4 position of the steel sheet is 250 HV or more.

3. The shaped body according to claim 1 or 2, characterized in that A chemical composition of the steel sheet is, in mass%: C：0.02~0.30%、 Si: 0.03 to 2.00%, Mn: 0.50 to 3.00%, Al：0.01~1.00%、 Ti: 0.06 to 0.20%, P: 0.100% or less, S: 0.010% or less, N: 0.0100% or less, Nb: 0 to 0.10%, Ca: 0 to 0.0060%, Mo: 0 to 1.00%, Cr：0~1.00%、 V：0~0.40%、 Ni: 0 to 0.40%, B：0~0.0020%、 Cu: 0 to 1.00%, W：0~1.00%、 Sn: 0 to 0.50%, Zr: 0 to 0.050%, and a remainder: Fe and impurities.

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