Automobile outer panel member, blank sheet, method for manufacturing blank sheet, and manufacturing apparatus for blank sheet

Abstract

The outer panel member for an automobile includes a steel sheet, and a rolling direction of the steel sheet extends in a left-right direction of a vehicle body in plan view.

Description

Technical Field

[0001] This invention relates to automotive exterior panel components, blank sheets, methods for manufacturing blank sheets, and equipment for manufacturing blank sheets. Background Technology

[0002] From an environmental protection perspective, there are demands for lighter vehicle bodies and improved crash safety. To meet these requirements, high-strength and thin-walled designs have been researched for panel components such as door panels. Unlike frame components, these panel components are visible to the naked eye and therefore require high aesthetic quality. Thus, even high-strength steel sheets previously used in frame components require high aesthetic quality when applied to panel components.

[0003] As a technology to improve appearance quality, for example, Patent Document 1 discloses a metal sheet with excellent surface properties. Its characteristic is that it is rolled using a roll that irradiates at least one side with a high-energy-density light beam, forming a large number of tiny raised and recessed patterns across the entire surface. The microstructure of the metal sheet surface consists of recesses formed by transferring the convex portions of the roll and relatively flat portions elsewhere, with a flat portion area ratio of 0.6 or more and a recess distribution density of 8 per mm. 2 Furthermore, the length ratio of the flat portion in any direction is 0.9 or less. The technology described in Patent Document 1 is a technology that makes the reflected image more distinct when an image is formed on the coated surface of a coated steel sheet.

[0004] Furthermore, panel components are generally manufactured by pressing blanks obtained from blanking rolled steel sheets. As a blanking method, for example, Patent Document 2 discloses a method that uses a hexagon, which is a resin-coated metal sheet formed by coating a resin film onto a long, rolled metal sheet, as the basic shape. The hexagon is formed into an arc shape by punching out blanks in a manner in which a pair of the two substantially parallel sides of the hexagon are at an angle of 80 to 100° with respect to the rolling direction of the resin-coated metal sheet.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2-30306

[0008] Patent Document 2: International Publication No. 98 / 055246

[0009] To improve appearance quality, suppressing the formation of ghost lines is one such issue. Ghost lines are microscopic, rib-like patterns on the surface, appearing as stripes on the order of 1 mm, caused by preferential deformation of the soft phase during the pressing of steel sheets containing hard and soft phases. Since ghost lines are unintentionally generated, they result in poor appearance quality in pressed products. Therefore, suppressing the formation of ghost lines is crucial for improving appearance quality.

[0010] However, the technology described in Patent Document 1 is a technique to make the reflected image clearer when the coated surface of the coated steel plate is imaged, but it does not take ghost lines into account. Therefore, there is room for improvement in the technology described in Patent Document 1. Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] The present invention was made in view of the above-mentioned actual situation. The object of the present invention is to provide an automotive outer panel component with reduced ghost lines, a blank sheet capable of reducing ghost lines generated by compression molding, a method for manufacturing the blank sheet, and equipment for manufacturing the blank sheet.

[0013] Methods for solving problems

[0014] The inventors of this invention conducted in-depth research on the influence of pressing forming on the presence or absence of ghost lines, and realized that the presence and degree of ghost lines vary depending on the deformation mode of the billet sheet during pressing forming. Specifically, the inventors of this invention have realized that the more intense the stretching deformation mode is in the width direction of the rolled steel sheet used as the billet sheet, the more likely ghost lines are to be generated, and the more likely ghost lines with large line widths are to be generated.

[0015] Based on the above understanding, the main idea of ​​the present invention is as follows.

[0016] [1] One aspect of the present invention is an automotive outer panel component comprising a steel plate, wherein, when viewed from above, the rolling direction of the steel plate extends along the left-right direction of the vehicle body.

[0017] [2] The automotive outer panel component described in [1] above can also reach a yield stress of 400 MPa or more.

[0018] [3] According to the automotive outer panel component described in [1] or [2] above, the chemical composition of the steel plate can also be expressed in mass % as follows:

[0019] C: 0.040~0.105%

[0020] Mn: 1.00~2.30%

[0021] Si: 0.005~1.500%

[0022] Al: 0.005~0.700%

[0023] P: below 0.100%

[0024] S: Below 0.0200%

[0025] N: below 0.0150%

[0026] O: Below 0.0100%

[0027] Cr: 0–0.80%

[0028] Mo: 0–0.16%

[0029] B: 0~0.0100%

[0030] Ti: 0~0.100%

[0031] Nb: 0~0.060%

[0032] V: 0~0.50%

[0033] Ni: 0~1.00%

[0034] Cu: 0–1.00%

[0035] W: 0~1.00%

[0036] Sn: 0~1.00%

[0037] Sb: 0~0.200%

[0038] Ca: 0~0.0100%

[0039] Mg: 0~0.0100%

[0040] Zr: 0~0.0100%

[0041] REM: 0–0.0100%, and

[0042] The remainder consists of Fe and impurities.

[0043] [4] In another aspect of the present invention, the blank sheet is a raw material for an automotive outer panel component, and is a blank sheet comprising a steel plate.

[0044] The rolling direction of the steel plate extends along the length of the billet sheet, and the thickness of the billet sheet is less than 0.6 mm.

[0045] [5] According to the blank sheet described in [4] above, the chemical composition of the steel plate can also be expressed in mass % as follows:

[0046] C: 0.040~0.105%

[0047] Mn: 1.00~2.30%

[0048] Si: 0.005~1.500%

[0049] Al: 0.005~0.700%

[0050] P: below 0.100%

[0051] S: Below 0.0200%

[0052] N: below 0.0150%

[0053] O: Below 0.0100%

[0054] Cr: 0–0.80%

[0055] Mo: 0–0.16%

[0056] B: 0~0.0100%

[0057] Ti: 0~0.100%

[0058] Nb: 0~0.060%

[0059] V: 0~0.50%

[0060] Ni: 0~1.00%

[0061] Cu: 0–1.00%

[0062] W: 0~1.00%

[0063] Sn: 0~1.00%

[0064] Sb: 0~0.200%

[0065] Ca: 0~0.0100%

[0066] Mg: 0~0.0100%

[0067] Zr: 0~0.0100%

[0068] REM: 0–0.0100%, and

[0069] The remainder consists of Fe and impurities.

[0070] [6] According to the blank sheet described in [4] or [5] above, the chemical composition of the steel plate can also be expressed in mass % as follows:

[0071] C: 0.040~0.100%

[0072] Mn: 1.00~2.00%

[0073] Si: 0.005~1.500%

[0074] P: below 0.100%

[0075] S: Below 0.0200%

[0076] Al: 0.005~0.700%

[0077] N: below 0.0150%

[0078] O: Below 0.0100%

[0079] Cr: 0–0.80%

[0080] Mo: 0–0.16%

[0081] B: 0~0.0100%

[0082] Ti: 0~0.100%

[0083] Nb: 0~0.060%

[0084] V: 0~0.50%

[0085] Ni: 0~1.00%

[0086] Cu: 0–1.00%

[0087] W: 0~1.00%

[0088] Sn: 0~1.00%

[0089] Sb: 0~0.200%

[0090] Ca: 0~0.0100%

[0091] Mg: 0~0.0100%

[0092] Zr: 0~0.0100%

[0093] REM: 0–0.0100%, and

[0094] Remaining components: Fe and impurities.

[0095] The arithmetic mean waviness Wa of the blank sheet is 0.10 to 0.30 μm.

[0096] [7] According to the blank sheet described in [4] or 5 above, the chemical composition of the steel plate can also be expressed in mass % as follows:

[0097] C: 0.040~0.105%

[0098] Mn: 1.00~2.30%

[0099] Si: 0.005~1.500%

[0100] Al: 0.005~0.700%

[0101] P: below 0.100%

[0102] S: Below 0.0200%

[0103] N: below 0.0150%

[0104] O: Below 0.0100%

[0105] Cr: 0–0.80%

[0106] Mo: 0–0.16%

[0107] Ti: 0~0.100%

[0108] B: 0~0.0100%

[0109] Nb: 0~0.060%

[0110] V: 0~0.50%

[0111] Ni: 0~1.00%

[0112] Cu: 0–1.00%

[0113] W: 0~1.00%

[0114] Sn: 0~1.00%

[0115] Sb: 0~0.200%

[0116] Ca: 0~0.0100%

[0117] Mg: 0~0.0100%

[0118] Zr: 0~0.0100%

[0119] REM: 0–0.0100%, and

[0120] Remaining components: Fe and impurities.

[0121] The C content at a depth of 20 μm from the surface, i.e., C 20 The C content at a depth of 60 μm from the above surface, i.e., C 60 The ΔC calculated by the following formula (1) is 0.20–0.90 mass% / mm.

[0122] The tensile strength of the blank sheet is above 500 MPa.

[0123] [8] Another aspect of the present invention is a method for manufacturing a blank sheet having a steel plate, which includes a cutting process in which the steel plate is cut in such a way that the rolling direction of the steel plate is extended along the length direction of the blank sheet.

[0124] [9] According to the blank sheet manufacturing method described in [8] above, the steel plates can also be cut alternately during the cutting process.

[0125]

[10] In another aspect of the invention, the blank sheet manufacturing equipment includes a cutting device having a shear for cutting the blank sheet from a steel plate or a die for punching the blank sheet from the steel plate.

[0126] The cutting device cuts the steel plate in such a way that the rolling direction of the steel plate extends along the length direction of the billet.

[0127] The effects of the invention

[0128] According to the present invention, it is possible to provide an automotive outer panel component with reduced ghost lines, a blank sheet capable of reducing ghost lines generated by compression molding, a method for manufacturing the blank sheet, and equipment for manufacturing the blank sheet. Attached Figure Description

[0129] Figure 1 It represents the strain e in the left-right direction of the vehicle body of the automobile hood panel manufactured by compression molding. x strain e in the longitudinal direction of the vehicle body y The ratio is the strain ratio e x / e y A graph showing the distribution of [something].

[0130] Figure 2 It is a diagram showing the cross-section of the blank sheet before pressing and the pressed product in the direction of the smallest curvature.

[0131] Figure 3 It is a diagram showing the cross-section of the blank sheet before pressing and the pressed product along the direction of the greatest curvature.

[0132] Figure 4 This is a diagram illustrating an example of the cutting orientation in a method for manufacturing a blank sheet according to an embodiment of the present invention.

[0133] Figure 5 This is a block diagram illustrating an example of a blank sheet manufacturing apparatus according to the above embodiments. Detailed Implementation

[0134] The following is for reference Figure 1 The automotive outer panel component of this embodiment will be described in detail. Figure 1 This represents the strain e in the left-right direction of the car body of the automobile engine hood manufactured by compression molding. x strain e in the longitudinal direction of the vehicle body y The ratio is the strain ratio e x / e y A graph showing the distribution of [something].

[0135] It should be noted that the present invention is not limited to the configuration disclosed in this embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0136] In this embodiment, when viewed from above, the rolling direction of the steel sheet extends along the left-right direction of the vehicle body. It should be noted that the term "automotive outer panel component" refers to a component that is centrally located in the left-right direction of the vehicle body and whose shape, when viewed from the vertical direction along the vehicle body, is approximately symmetrical about a straight line located at the center in the left-right direction. Specifically, this refers to the engine hood, back door panel, and trunk lid of an automobile.

[0137] The automotive outer panel component of this embodiment is manufactured by compression molding. The inventors of this invention conducted in-depth research on the influence of compression molding on the presence or absence of ghost lines, and as a result, realized that the presence and degree of ghost lines vary depending on the deformation mode of the blank during compression molding. Specifically, the inventors of this invention have realized that the more intense the stretching deformation in the width direction (the direction perpendicular to the rolling direction along the plate surface) of the rolled steel sheet used as the blank, the more likely ghost lines are to be generated, and the more likely large ghost lines are to be generated.

[0138] The inventors of this invention speculate as follows: During the solidification process of steel in the manufacture of rolled steel sheets, which serve as raw materials for billets, elements such as Mn segregate. Rolling causes these segregated portions to extend in the rolling direction, forming bands. Near these segregated portions, the ferrite phase readily transforms into austenite during annealing. The austenite phase formed during annealing becomes hard martensite after annealing. Therefore, the annealed steel sheet contains bands of martensite extending in the rolling direction. Due to the presence of this hard martensite phase (hard phase) and other phases besides the soft martensite phase (soft phase), the unevenness of hardness (hardness difference) in the width direction of the steel sheet increases. It is speculated that if such a steel sheet is subjected to strong stretching in the width direction, the soft phase preferentially deforms, easily producing ghost lines.

[0139] Therefore, if the steel sheet is subjected to strong stretching in the rolling direction, preferential deformation of the soft phase is less likely to occur, thus reducing the generation of ghost lines. Therefore, for blanks subjected to press forming, if the rolling direction of the steel sheet is extended along the direction of large deformation during processing such as press forming, it is less likely to generate ghost lines in automotive outer panel components.

[0140] The inventors of this invention performed finite element analysis and found that: Figure 1 As shown, for automobile engine hoods manufactured by compression molding, the strain ratio e x / e y The proportion of elements exceeding 1.00 is high, and the area that produces greater deformation in the left-right direction of the vehicle body compared to the deformation in the longitudinal direction is dominant. Based on this deformation pattern in the pressing and forming of automotive outer panel components, and understanding the aforementioned ghost line generation mechanism, the inventors conducted research and achieved a technology that can reduce ghost lines in automotive outer panel components. Specifically, in the blank sheet used in automotive outer panel components manufactured by pressing and forming, by extending the rolling direction of the steel sheet along the left-right direction of the pressed and formed automotive outer panel component, the deformation in multiple areas where large deformation occurs during forming becomes along the rolling direction, the preferential deformation of the soft phase is suppressed, and therefore ghost lines become less likely to occur in the automotive outer panel component. It should be noted that the strain e in the left-right direction of the vehicle body... x strain e in the longitudinal direction of the vehicle body y The ratio is the strain ratio e x / e y The major areas are the dominant automotive exterior panel components, including the rear door panels and trunk lid, in addition to the engine hood.

[0141] It should be noted that for components (such as side doors) arranged in pairs on both sides of the vehicle body in the left-right direction, when viewed from above, that is, when viewed along the height direction of the vehicle body, the thickness direction of the steel plate extends along the left-right direction of the vehicle body. Therefore, components arranged in pairs on both sides of the vehicle body in the left-right direction are not included in the technical scope of the automotive outer panel component of this embodiment.

[0142] On the other hand, components arranged in pairs on both sides in the left-right direction of the automobile body are included in the technical scope of the following invention, which has the same technical concept as the automobile outer panel component of this embodiment. That is, components arranged in pairs on both sides in the left-right direction of the automobile body are included in the technical scope of the following invention: an automobile outer panel component in which the rolling direction of the steel sheet extends along the height direction of the automobile body when viewed from the side, in other words, when viewed along the left-right direction of the automobile body.

[0143] The automotive outer panel component of this embodiment and the automotive outer panel component of the above-described invention share the same technical feature: the rolling direction of the steel sheet extends along the direction that, when viewed along the direction normal to an imaginary reference plane corresponding to the component's arrangement, is the direction with the largest deformation amount (maximum displacement in the normal direction relative to the imaginary reference plane) resulting from the pressing process among the first and second mutually orthogonal directions of the imaginary reference plane. Specifically, when the automotive outer panel component is an engine hood, the front-rear direction corresponds to the first direction, and the left-right direction corresponds to the second direction; the left-right direction is the direction with the largest deformation amount from the pressed-formed flat plate. Furthermore, when the automotive outer panel component is a side door, the front-rear direction corresponds to the first direction, and the height direction corresponds to the second direction; the height direction is the direction with the largest deformation amount from the pressed-formed flat plate.

[0144] Here, refer to Figure 2 and Figure 3 For the strain ratio e in the car engine cover x / e y The reasons for the dominance of the large region are explained. Figure 2 It is a diagram showing the cross-section of the blank sheet before pressing and the pressed product (the blank sheet after pressing) in the direction of the smaller curvature. Figure 3 It is a diagram showing the cross-section of the blank sheet before pressing and the pressed product along the direction of the greatest curvature.

[0145] like Figure 2 and Figure 3As shown, in the section of the pressed product with low curvature, the lengths of its longitudinal walls at both ends are long, and the ratio of the linear length L1 of the section with low curvature in the pressed product to the linear length L0 of the blank sheet is large. On the other hand, in the section of the pressed product with high curvature, the lengths of the longitudinal walls of the pressed product are short, and the ratio of the linear length L1' of the section with high curvature in the pressed product to the linear length L0' of the blank sheet is small. In other words, in the direction of low curvature (in... Figure 2 and Figure 3 In the case of Figure 2 In terms of strain ratio e generated by compression molding x / e y Larger areas are dominant. In automotive press-molded parts such as car engine hoods, generally speaking, the curvature in the lateral direction of the vehicle body is smaller than the curvature in the longitudinal direction. Therefore, in car engine hoods, the strain is greater than e. x / e y The large area is dominant. Therefore, in the billet sheet, by extending the rolling direction of the steel sheet along the direction of the car body when it is made into an outer panel component for automobiles, the ghost line can be reduced.

[0146] The rolling direction of the steel sheet in automotive outer panel components can be determined through microstructure observation. Specifically, starting from the left-right direction of the vehicle body (defined as the 0° direction) towards the front of the vehicle body, the sheet is rotated counterclockwise by 15° each time until it reaches 90°, i.e., until the front-rear direction of the vehicle body. The resulting cross-section is then cut from the top-bottom direction of the vehicle body, and the resulting cross-section is used as a sample for microstructure observation. Therefore, multiple samples are obtained as microstructure observation samples, each cut from the 0° direction to the front-rear direction of the vehicle body (90° direction) at 15° intervals.

[0147] The microstructure of the cut section was observed, and the cutting direction of the sample with the greatest degree of segregation was taken as the rolling direction. The degree of segregation could be evaluated by optical microscopy of the cut section after nitric acid ethanol etching. The segregated area was observed to be blackened compared to the area without segregation. Therefore, the degree of segregation could be evaluated by the location of the black lines of segregation, based on the aforementioned differences in appearance. In the case of a non-rolling direction, the black lines indicating segregation were present near the center of the plate thickness, but were not observable if slightly deviated from the center. On the other hand, in the case of the rolling direction, the black lines were present not only at the center of the plate thickness but also at positions slightly away from the center. Therefore, the sample in which the black lines indicating segregation included the center of the plate thickness and were most widely distributed in the plate thickness direction could be identified as the rolling direction. In addition, if it was before coating, the rolling direction could also be determined by observing the transfer marks of the rolls on the surface.

[0148] It should be noted that, preferably, the rolling direction of the steel plate is consistent with the left-right direction of the vehicle body, but it does not have to be consistent. Within the range that can reduce ghost lines, the rolling direction of the steel plate can also have an angle with the left-right direction of the vehicle body. For example, the angle between the rolling direction of the steel plate and the left-right direction of the vehicle body is 15° or less. Therefore, the so-called rolling direction of the steel plate extending along the left-right direction of the vehicle body means that the angle between the rolling direction of the steel plate and the left-right direction of the vehicle body is 15° or less.

[0149] [Yield stress reached: above 400 MPa]

[0150] The automotive outer panel component of this embodiment preferably has a yield stress of 400 MPa or more at the point in time when it becomes an automotive product after vehicle assembly, painting, baking, etc. It should be noted that the yield stress at the point in time when it becomes an automotive product is sometimes referred to as the reached yield stress. The higher the strength of the steel sheet, the easier it is for ghost lines to form. If the blank sheet has a yield stress (reached yield stress) of 400 MPa or more at the point in time when it becomes an automotive product, the effect of reducing ghost lines is more significant. Furthermore, for the purpose of lightweighting the vehicle body, the pressed blank sheet for automobiles is preferably thinner, but the thinner the sheet, the more likely it is to have reduced dent resistance. Even with a thin sheet, excellent dent resistance can be obtained as long as the yield stress at the point in time when it becomes an automotive product is 400 MPa or more. Therefore, the reached yield stress of the automotive outer panel component is preferably 400 MPa or more. The yield stress at the point in time when it becomes an automotive product is more preferably 500 MPa or more. On the other hand, there is no particular upper limit to the yield stress at the point in time when it becomes an automotive product, but from a manufacturing point of view, it is, for example, 850 MPa.

[0151] The yield stress can be determined using the following method. Specifically, tensile test pieces (JIS 13B) are cut from five sample locations defined below, perpendicular to the left-right direction of the vehicle body. Tensile tests are performed according to JIS standards, and the yield stress (yield point or 0.2% yield stress) is calculated. The yield stress is then obtained by arithmetically averaging the yield stresses at these five locations. The sample locations are explained below. First, the x and y directions of the automotive exterior panel components are defined. For example, for the engine hood and trunk lid, the x direction is defined as the left-right direction of the vehicle body, and the y direction as the front-rear direction. For the rear door panel, the x direction is defined as the left-right direction of the vehicle body, and the y direction as the up-down direction. Then, for each component, the maximum value x in the x direction is defined. max Minimum value x min Calculate the median value x mid =(x max +x min ) / 2, x length x len =x max -xmin Similarly, find the maximum value y in the y-direction. max Minimum value y min Central value y mid =(y max +y min ) / 2, length y len =y max -y min The sample acquisition location is defined by these values ​​as follows. That is, the sample acquisition location is set to the following five points: (x, y) = (x... mid y mid ), (x mid +0.2×x len y mid +0.2×y len ), (x mid -0.2×x len y mid -0.2×y len ), (x mid +0.2×x len y mid -0.2×y len ), (x mid -0.2×x len y mid +0.2×y len ).

[0152] [Chemical Composition]

[0153] The chemical composition of the base steel sheet constituting the automotive outer panel component of this embodiment will be described. The values ​​enclosed in “~” below are within a range, including both the lower and upper limits. Values ​​expressed as “less than” or “more than” are not included in the numerical range. In the following description, “%” for chemical composition refers to “mass %” unless otherwise specified. It should be noted that the base steel sheet constituting the automotive outer panel component corresponds to the steel sheet included in the automotive outer panel component of this invention.

[0154] C: 0.040~0.105%

[0155] C is an element that improves strength. To obtain the desired strength, the C content is preferably 0.040% or more. To further improve strength, the C content can be 0.045% or more, 0.050% or more, 0.060% or more, or 0.070% or more.

[0156] On the other hand, the C content is preferably 0.105% or less. If the C content is 0.105% or less, the C content is reduced after decarburization annealing, which can suppress the excessive hardness difference in the decarburized layer formed near the surface. As a result, the formation of ghost lines in automotive exterior panel components can be further reduced. Furthermore, if the C content is 0.100% or less, the diffusion of Mn during solidification can be promoted, reducing the tendency for banded Mn segregation. As a result, ghost lines in automotive exterior panel components can be reduced. Therefore, the C content is more preferably 0.100% or less. From the viewpoint of reducing ghost lines, the C content can be 0.095% or less, or 0.090% or less. Additionally, from the viewpoint of suppressing the formation of hardness differences, the upper limit of the C content can be 0.085%, or 0.080% or less.

[0157] It should be noted that when the Mn content is below 1.40%, the C content is preferably above 0.075%. In this way, by strictly controlling the Mn and C contents, Mn diffusion in the steel can be promoted at high temperatures, and Mn segregation can be reduced.

[0158] Mn: 1.00~2.30%

[0159] Mn is an element that improves the hardenability of steel and contributes to increased strength. To obtain the desired strength, the Mn content is preferably 1.00% or more. The Mn content can be 1.05% or more, 1.10% or more, 1.20% or more, 1.30% or more, 1.40% or more, or 1.50% or more.

[0160] Furthermore, the Mn content is preferably 2.30% or less. If the Mn content is 2.30% or less, the tendency for hardness differences to form can be suppressed. As a result, the formation of ghost lines in automotive exterior panel components can be further reduced. The Mn content can also be 2.10% or less. Furthermore, if the Mn content is 2.00% or less, banded Mn segregation during solidification of the steel constituting the automotive exterior panel components can be reduced. As a result, the tendency for hardness differences to form in the steel constituting the automotive exterior panel components is further reduced, and ghost lines in the automotive exterior panel components can be further reduced. The Mn content can be 1.95% or less, 1.90% or less, 1.85% or less, 1.80% or less, 1.75% or less, or 1.70% or less.

[0161] Si: 0.005~1.500%

[0162] Si is an element that forms coarse Si oxides, which act as the starting point for crack formation. By keeping the Si content at 1.500% or less, the formation of Si oxides can be reduced, making it less prone to cracking. As a result, the embrittlement of the steel constituting the outer panel components of automobiles can be further suppressed. Therefore, the Si content is preferably 1.500% or less. The Si content is more preferably 1.300% or less or 1.000% or less, and even more preferably 0.800%, 0.600%, or 0.500% or less.

[0163] The lower limit of Si content can also be 0%, but in order to improve the strength-formability balance, the Si content can also be 0.005% or more, 0.010% or more, or 0.020% or more.

[0164] Al: 0.005~0.700%

[0165] Al is an element that functions as a deoxidizing material. However, Al is also an element that forms coarse oxides, which become the starting point for damage, and embrittles the steel constituting automotive exterior components. If the Al content is 0.700% or less, the formation of coarse oxides, which act as the starting point for damage, can be further reduced, and the slab's susceptibility to cracking can be further suppressed. Therefore, the Al content is preferably 0.700% or less. The Al content is preferably 0.650% or less, 0.600% or less, 0.400% or less, 0.200% or less, or 0.100%, and more preferably 0.085% or less, 0.070% or less, 0.065% or less, or 0.060% or less.

[0166] The lower limit of the Al content can also be 0%, but in order to fully obtain the deoxygenation effect brought by Al, the Al content can also be 0.005% or more. In addition, the Al content is preferably 0.010% or more, 0.020% or more, 0.025% or more, 0.030% or more, or 0.040% or more.

[0167] P: below 0.100%

[0168] Phosphorus (P) is an element that causes steel to become embrittled. If the P content is 0.100% or less, it can suppress the embrittlement of steel sheets, preventing them from becoming prone to cracking during the production of billet sheets or automotive exterior parts. Therefore, the P content is preferably 0.100% or less. From a productivity point of view, the P content is more preferably 0.050% or less, and even more preferably 0.030% or less or 0.020% or less.

[0169] The lower limit of P content can also be 0%, but by making the P content above 0.001%, manufacturing costs can be further reduced. Therefore, the P content can also be above 0.001%.

[0170] S: below 0.0200%

[0171] Sulfur (S) is an element that forms Mn sulfides and deteriorates the formability of steel sheets, including ductility, porosity, tensile flange properties, and bending properties. If the S content is 0.0200% or less, a significant decrease in the formability of the steel sheet can be suppressed. Therefore, the S content is preferably 0.0200% or less. More preferably, the S content is 0.0100% or less or 0.0080% or less, and even more preferably 0.0060% or less or 0.0040% or less.

[0172] The lower limit of sulfur content can also be 0%, but by making the sulfur content above 0.0001%, manufacturing costs can be further reduced. Therefore, the sulfur content can also be above 0.0001%.

[0173] N: below 0.0150%

[0174] Nitrogen (N) is an element that forms nitrides and deteriorates the formability of steel sheets, including ductility, porosity, tensile flange properties, and bending properties. If the N content is 0.0150% or less, the reduction in formability of the steel sheet can be suppressed. Therefore, the N content is preferably 0.0150% or less. Furthermore, N is also an element that causes welding defects during welding, thus hindering productivity. Therefore, the N content is more preferably 0.0120% or less or 0.0100% or less, and even more preferably 0.0080% or less or 0.0060% or less.

[0175] The lower limit for nitrogen content can also be 0%, but by making the nitrogen content above 0.0005%, manufacturing costs can be further reduced. Therefore, the nitrogen content can also be above 0.0005%.

[0176] O: Below 0.0100%

[0177] O is an element that forms oxides and hinders the formability of steel sheets, such as ductility, hole expansion, tensile flange formation, and bending. If the O content is 0.0100% or less, it can suppress a significant decrease in the formability of the steel sheet. Therefore, the O content is preferably 0.0100% or less. More preferably, the O content is 0.0080% or less or 0.0050% or less, and even more preferably 0.0030% or less or 0.0020% or less.

[0178] The lower limit for the O content can also be 0%, but by making the O content above 0.0001%, manufacturing costs can be further reduced. Therefore, the O content can also be above 0.0001%.

[0179] The remaining portion of the chemical composition of the base steel sheet constituting the automotive outer panel component of this embodiment may also be Fe and impurities. Examples of impurities include elements that are unavoidably mixed in from steel raw materials or scrap, elements that are unavoidably mixed in during the steelmaking process, or elements that are permissible within a range that does not impair the characteristics of the billet sheet and pressed product of this embodiment. Examples of impurities include, for instance, H, 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, and Po. The total amount of impurities may also be 0.100% or less.

[0180] The base steel sheet constituting the automotive outer panel component of this embodiment may also contain the following elements as optional elements to replace a portion of Fe. The lower limit of the content of the following optional elements is 0%.

[0181] Cr: 0–0.80%

[0182] Cr is an element that improves the hardenability of steel and contributes to increased strength. Cr may or may not be present, therefore the lower limit of Cr content can be 0%. To fully obtain the strength improvement effect brought by Cr, the Cr content is preferably 0.01% or more, or 0.20% or more, and more preferably 0.30% or more.

[0183] Furthermore, if the Cr content is 0.80% or less, the formation of coarse Cr carbides that can become the starting point for damage can be reduced. Therefore, the Cr content is preferably 0.80% or less. In order to reduce the cost of the alloy, the Cr content can also be 0.60% or less, 0.40% or less, 0.20% or less, 0.10% or less, 0.06% or less, or 0.05% or less, as needed.

[0184] Mo: 0–0.16%

[0185] Mo is an element that suppresses phase transitions at high temperatures and contributes to increased strength. Mo may not necessarily be present, therefore the lower limit for Mo content can be 0%. To fully obtain the strength-enhancing effect brought about by Mo, the Mo content is preferably 0.05% or more, more preferably 0.10% or more.

[0186] Furthermore, if the Mo content is 0.16% or less, the reduction in hot workability and consequently, the decrease in productivity can be suppressed. Therefore, the Mo content is preferably 0.16% or less. To reduce alloy costs, the Mo content can also be 0.12% or less, 0.10% or less, 0.08% or less, 0.06% or less, 0.04% or less, or 0.02% or less, depending on the requirements.

[0187] It should be noted that by including 0.01–0.80% Cr and 0.01–0.16% Mo, the strength of the steel plate can be improved more reliably. Therefore, it is preferable to include 0.01–0.80% Cr and 0.01–0.16% Mo.

[0188] Ti: 0~0.100%

[0189] Ti is an element that reduces the content of S, N, and O, which contribute to the formation of coarse inclusions that act as initiators of damage. Furthermore, Ti has the effect of refining the microstructure and improving the strength-formability balance of the steel sheet. Ti may not necessarily be present, therefore the lower limit of Ti content can be 0%. To fully obtain the above effects, the Ti content is preferably 0.001% or more, more preferably 0.010% or more.

[0190] Furthermore, if the Ti content is 0.100% or less, the formation of coarse Ti sulfides, Ti nitrides, and Ti oxides can be reduced, ensuring the formability of the steel sheet. As a result, formability is ensured. Therefore, the Ti content is preferably 0.100% or less. The Ti content is preferably set to 0.080% or less, 0.075% or less, or 0.060% or less, and more preferably 0.040% or less or 0.020% or less. To reduce alloy costs, the Ti content can also be set to 0.040% or less, 0.020% or less, 0.010% or less, or 0.005% or less, as needed.

[0191] Nb: 0~0.060%

[0192] Nitrogen (Nb) is an element that contributes to the strength improvement of steel sheets through strengthening by precipitates, grain refinement strengthening by inhibiting ferrite grain growth, and dislocation strengthening by inhibiting recrystallization. Nib may or may not be present, therefore the lower limit of Nib content can be 0%. To fully obtain the above effects, the Nib content is preferably 0.001% or more, more preferably 0.005% or more, and even more preferably 0.010% or more.

[0193] Furthermore, if the Nb content is 0.060% or less, recrystallization can be promoted while suppressing the retention of unrecrystallized ferrite, thus ensuring the formability of the steel sheet. As a result, formability is ensured. Therefore, the Nb content is preferably 0.060% or less. More preferably, the Nb content is 0.050% or less, and even more preferably 0.040% or less. To reduce alloy costs, the Nb content can also be 0.030% or less, 0.020% or less, 0.015% or less, 0.010% or less, or 0.005% or less, depending on the requirements.

[0194] V: 0~0.50%

[0195] V is an element that contributes to strength improvement through strengthening by precipitates, grain refinement strengthening by inhibiting ferrite grain growth, and dislocation strengthening by inhibiting recrystallization. V may not necessarily be present, so the lower limit of V content can be 0%. To fully obtain the strength improvement effect brought about by V, the V content is preferably 0.01% or more, and more preferably 0.03% or more.

[0196] Furthermore, if the V content is 0.50% or less, the excessive precipitation of carbonitrides, which would reduce the formability of the steel sheet, can be further suppressed. As a result, the reduction in formability can be suppressed. Therefore, the V content is preferably 0.50% or less. To reduce alloy costs, the V content can also be 0.30% or less, 0.20% or less, 0.10% or less, 0.08% or less, 0.06% or less, 0.05% or less, 0.03% or less, or 0.02% or less, depending on the requirements.

[0197] Ni: 0~1.00%

[0198] Ni is an element that suppresses phase transitions at high temperatures and contributes to increased strength. Ni may not necessarily be present, so the lower limit of Ni content can be 0%. In order to fully obtain the strength improvement effect brought by Ni, the Ni content is preferably 0.01% or more, more preferably 0.05% or more, and even more preferably 0.20% or more.

[0199] Furthermore, if the Ni content is 1.00% or less, the reduction in weldability of the steel sheet can be suppressed. Therefore, the Ni content is preferably 1.00% or less. To reduce alloy costs, the Ni content can also be 0.70%, 0.60%, 0.50%, 0.40%, 0.30%, 0.20%, 0.15%, 0.10%, 0.08%, or 0.03% or less, depending on the requirements.

[0200] Cu: 0~1.00%

[0201] Cu is an element that exists in steel in the form of fine particles and contributes to increased strength. Cu may not necessarily be present, so the lower limit of Cu content can be 0%. In order to fully obtain the strength improvement effect brought by Cu, the Cu content is preferably 0.01% or more, more preferably 0.05% or more, and even more preferably 0.15% or more.

[0202] Furthermore, if the Cu content is 1.00% or less, the reduction in weldability of the steel sheet can be further suppressed. Therefore, the Cu content is preferably 1.00% or less. To reduce alloy costs, the Cu content can also be 0.70%, 0.60%, 0.50%, 0.40%, 0.30%, 0.20%, 0.15%, 0.10%, 0.08%, or 0.03% or less, depending on the requirements.

[0203] W: 0~1.00%

[0204] W is an element that suppresses phase transitions at high temperatures and contributes to increased strength. W may not necessarily be present, therefore the lower limit for W content can be 0%. To fully obtain the strength-enhancing effect brought about by W, the W content is preferably 0.01% or more, more preferably 0.03% or more, and even more preferably 0.10% or more.

[0205] Furthermore, if the W content is 1.00% or less, it can suppress the decrease in hot workability and thus the decrease in productivity. Therefore, the W content is preferably 1.00% or less. In order to reduce the cost of the alloy, the W content can also be 0.70% or less, 0.50% or less, 0.30% or less, 0.20% or less, 0.15% or less, 0.10% or less, 0.08% or less, 0.05% or less, or 0.02% or less, as needed.

[0206] B: 0~0.0100%

[0207] B is an element that suppresses phase transitions at high temperatures and contributes to increased strength. B may not necessarily be present, therefore the lower limit for B content can be 0%. To fully obtain the strength-enhancing effect brought about by B, the B content is preferably 0.0001% or more, more preferably 0.0005% or more, and even more preferably 0.0010% or more.

[0208] Furthermore, if the B content is 0.0100% or less, the formation of B precipitates can be suppressed, thus reducing the suppression strength. Therefore, the B content is preferably 0.0100% or less. To reduce alloy costs, the B content can also be 0.0050% or less, 0.0030% or less, 0.0020% or less, 0.0010% or less, or 0.0005% or less, depending on the requirements.

[0209] Sn: 0~1.00%

[0210] Sn is an element that inhibits grain coarsening and helps improve strength. Sn may not necessarily be present, so the lower limit of Sn content can be 0%. To fully obtain the effects brought by Sn, the Sn content is preferably 0.01% or more.

[0211] Furthermore, if the Sn content is 1.00% or less, it can suppress the embrittlement of the steel plate and prevent fracture during rolling. Therefore, the Sn content is preferably 1.00% or less. To reduce the cost of the alloy, the Sn content can also be 0.50% or less, 0.20% or less, 0.10% or less, 0.05% or less, or 0.02% or less, depending on the requirements.

[0212] Sb: 0~0.200%

[0213] Sb is an element that inhibits grain coarsening and contributes to increased strength. Sb may not necessarily be present, therefore the lower limit of Sb content can be 0%. To fully achieve the above effects, the Sb content is preferably 0.001% or more, more preferably 0.005% or more.

[0214] Furthermore, if the Sb content is 0.200% or less, it can suppress the embrittlement of the steel plate and prevent fracture during rolling. Therefore, the Sb content is preferably 0.200% or less. To reduce the cost of the alloy, the Sb content can also be 0.100% or less, 0.070% or less, 0.040% or less, 0.010% or less, or 0.005% or less, depending on the requirements.

[0215] Ca: 0~0.0100%

[0216] Mg: 0~0.0100%

[0217] Zr: 0~0.0100%

[0218] REM: 0~0.0100%

[0219] Ca, Mg, Zr, and REM are elements that contribute to improving the formability of steel sheets. Ca, Mg, Zr, and REM may not necessarily be present; therefore, the lower limit for the total content of these elements includes 0%. To fully obtain the effect of improving formability, the content of each of these elements is preferably 0.0001% or more, more preferably 0.0010% or more. To fully obtain the above effect, it is not necessary to contain all of the above elements; it is sufficient if the content of any one of them is 0.0001% or more.

[0220] Furthermore, if the contents of Ca, Mg, Zr, and REM are each 0.0100% or less, the reduction in the ductility of the steel sheet can be suppressed. Therefore, the contents of these elements are each set to 0.0100% or less, preferably 0.0050% or less. To reduce alloy costs, the contents of Ca, Mg, Zr, and REM can also be set to 0.0030% or less, 0.0020% or less, 0.0010% or less, or 0.0003% or less, depending on the requirements.

[0221] REM (Rare Earth Metals) refers to a total of 17 elements including Sc, Y, and the lanthanides. The content of REM refers to the total content of these elements.

[0222] The chemical composition of the base steel sheet constituting the automotive outer panel components can be determined using general analytical methods. For example, ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) can be used. It should be noted that C and S can be determined using the combustion-infrared absorption method, N can be determined using the inert gas melting-thermal conductivity method, and O can be determined using the inert gas melting-non-dispersive infrared absorption method.

[0223] Taking into account the effects of the above elements, the preferred embodiment of the automotive outer panel component is that the chemical composition of the base steel sheet constituting the automotive outer panel component, expressed in mass percent, is:

[0224] C: 0.040~0.105%

[0225] Mn: 1.00~2.30%

[0226] Si: 0.005~1.500%

[0227] Al: 0.005~0.700%

[0228] P: below 0.100%

[0229] S: Below 0.0200%

[0230] N: below 0.0150%

[0231] O: Below 0.0100%

[0232] Cr: 0–0.80%

[0233] Mo: 0–0.16%

[0234] B: 0~0.0100%

[0235] Ti: 0~0.100%

[0236] Nb: 0~0.060%

[0237] V: 0~0.50%

[0238] Ni: 0~1.00%

[0239] Cu: 0–1.00%

[0240] W: 0~1.00%

[0241] Sn: 0~1.00%

[0242] Sb: 0~0.200%

[0243] Ca: 0~0.0100%

[0244] Mg: 0~0.0100%

[0245] Zr: 0~0.0100%

[0246] REM: 0–0.0100%, and

[0247] The remainder consists of Fe and impurities.

[0248] If the chemical composition of the base steel sheet constituting the automotive outer panel component of this embodiment is within the above-mentioned range, it becomes a high-strength blank with reduced segregation. As a result, the automotive outer panel component obtained by pressing such a blank further reduces ghost lines, and the appearance quality becomes even better.

[0249] The automotive outer panel component of this embodiment may also have a coating on at least one surface of the base steel sheet constituting the automotive outer panel component. Examples of coatings include zinc coatings, zinc alloy coatings, and alloyed zinc coatings and alloyed zinc alloy coatings on which they have undergone alloying treatment.

[0250] Zinc coatings and zinc alloy coatings may also contain one or more of the following elements, within a range that does not impair the corrosion resistance and formability of automotive exterior panel components: Al, Ag, B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Ge, Hf, Zr, I, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb, Rb, Sb, Si, Sn, Sr, Ta, Ti, V, W, Zr, and REM. In particular, Ni, Al, and Mg are effective in improving corrosion resistance.

[0251] If the Al content of the zinc coating is less than 0.5% by mass, the adhesion between the steel plate surface and the zinc coating can be fully ensured. Therefore, the Al content of the zinc coating is preferably less than 0.5% by mass.

[0252] Zinc coatings and zinc alloy coatings are formed by hot-dip galvanizing, electroplating, or vapor deposition.

[0253] When the zinc coating is a hot-dip galvanized layer formed by hot-dip galvanizing, in order to improve the adhesion between the steel plate surface and the hot-dip galvanized layer, the Fe content of the hot-dip galvanized layer is preferably 3.0% by mass or less.

[0254] When the zinc coating is an electroplated zinc layer formed by electroplating, from the viewpoint of improving corrosion resistance, the Fe content of the electroplated zinc layer is preferably 0.5% by mass or less.

[0255] When the coating is an alloyed zinc coating or an alloyed zinc alloy coating that has undergone alloying treatment on a hot-dip galvanized layer or a hot-dip galvanized alloy layer, from the viewpoint of improving the adhesion between the steel sheet surface and the alloyed zinc coating or the alloyed zinc alloy coating, the Fe content of the alloyed zinc coating or the alloyed zinc alloy coating is preferably 7.0 to 13.0% by mass. By performing alloying treatment on the steel sheet having a hot-dip galvanized layer or a hot-dip galvanized alloy layer, Fe is introduced into the coating, increasing the Fe content. Therefore, the Fe content can be made to be 7.0% by mass or more. That is, a zinc coating with an Fe content of 7.0% by mass or more is an alloyed zinc coating or an alloyed zinc alloy coating.

[0256] The Al and Fe content in the coating can be obtained using the following method: The coating is dissolved and removed using a 5% (v / v) aqueous solution containing an inhibitor. The Fe content (mass %) in the coating is then determined by measuring the Fe content in the resulting solution using ICP-AES.

[0257] When automotive exterior panel components have a coating, the chemical composition of the base steel sheet can be determined simply by removing the coating through mechanical grinding and then analyzing its chemical composition.

[0258] Regarding the thickness of the base steel sheet constituting the outer panel component of an automobile, considering versatility and manufacturability, a thickness of 0.2 to 5.0 mm is preferred. It should be noted that when the base steel sheet constituting the outer panel component of the automobile has a coating, the thickness of the coating is included. The thickness of the base steel sheet constituting the outer panel component of the automobile depends on the thickness of the steel sheet to be cut. Steel sheets with a thickness of 0.2 mm or more are easier to maintain a flat shape, improving dimensional and shape accuracy during cutting. Therefore, base steel sheets constituting the outer panel component of the automobile with a thickness of 0.2 mm or more have high dimensional and shape accuracy. Therefore, the thickness of the base steel sheet constituting the outer panel component of the automobile is preferably 0.2 mm or more. The thickness of the base steel sheet constituting the outer panel component of the automobile is more preferably 0.4 mm or more.

[0259] On the other hand, if the thickness of the steel sheet to be cut is 5.0 mm or less, it becomes easier to apply appropriate strain and control the temperature during the manufacturing process, resulting in a homogeneous microstructure. Therefore, the microstructure of the base steel sheet constituting the outer panel component of the automobile becomes more homogeneous when the thickness is 5.0 mm or less. Thus, the thickness of the base steel sheet constituting the outer panel component of the automobile is preferably 5.0 mm or less. More preferably, the thickness of the base steel sheet constituting the outer panel component of the automobile is 4.5 mm or less. From the viewpoint of lightweight automobiles, the thickness of the base steel sheet constituting the outer panel component of the automobile is even more preferably 0.7 mm or less, even more preferably 0.6 mm or less, and may also be 0.5 mm or less.

[0260] This concludes the description of the automotive outer panel component according to this embodiment.

[0261] There are no particular limitations on the blank sheet that can be used as the raw material for the automotive outer panel component of this embodiment, but the blank sheet described later is preferred. Hereinafter, an example of a blank sheet that can be used as the raw material for the automotive outer panel component of this embodiment will be described.

[0262] The blank sheet in this embodiment is a raw material for automotive outer panel components manufactured by pressing. It is a blank sheet comprising a steel sheet, the rolling direction of which extends along the length direction of the blank sheet, and the thickness of the blank sheet is 0.6 mm or less. The blank sheet of this embodiment can be used for the aforementioned automotive outer panel components.

[0263] The blank sheet in this embodiment preferably has the same chemical composition as the steel sheet constituting the outer panel component of the automobile described above. In addition, the above-described coating may be provided on at least one surface.

[0264] [Arithmetic mean ripple Wa: 0.10~0.30μm]

[0265] Generally, it is considered that the smaller the arithmetic mean waviness Wa of the blank sheet, the more preferable it is from the viewpoint of appearance quality. This is because excessive surface roughness results in poor appearance quality. However, the inventors of this invention have recognized that in order to reduce the generation of ghost lines in automotive exterior panel components, the generation of ghost lines can be further reduced by moderately roughening the surface of the blank sheet without compromising appearance quality. Therefore, the arithmetic mean waviness Wa of the blank sheet in this embodiment is preferably 0.10 μm or more. The arithmetic mean waviness Wa of the blank sheet in this embodiment is more preferably 0.13 μm or more.

[0266] Furthermore, the inventors of this invention have discovered that if the arithmetic mean waviness Wa is 0.30 μm or less, superior appearance quality can be obtained for both the blank sheet and automotive outer panel components. Therefore, the arithmetic mean waviness Wa is preferably 0.30 μm or less. In this embodiment, the arithmetic mean waviness Wa of the blank sheet is more preferably 0.25 μm or less.

[0267] It should be noted that the arithmetic mean waviness Wa refers to the arithmetic mean waviness of the steel plate when the billet does not have a coating, and to the arithmetic mean waviness of the coating when the billet has a coating on its surface.

[0268] In this embodiment, the arithmetic mean ripple degree Wa is obtained using the following method.

[0269] A 50mm × 50mm test piece was cut from a position at least 10mm away from the end face of the billet. Next, using a laser displacement measuring device (KEYANCE VK-X1000), three profiles were measured along a direction perpendicular to the rolling direction. Based on the results, according to JIS B 0601:2013, a waviness curve was obtained by sequentially applying profile curve filters with cutoff values ​​λc and λf to the cross-sectional curves. Specifically, based on the measured results, components with wavelengths λc below 0.8mm and wavelengths λf above 2.5mm were removed to obtain the waviness curve. Based on the obtained waviness curve, the arithmetic mean waviness was calculated according to JIS B 0601:2013, and the average value of the three calculated values ​​was calculated. The arithmetic mean of the three calculated values ​​was taken as the arithmetic mean waviness Wa of the steel plate.

[0270] If the blank sheet has a coating on its surface, the above-mentioned line analysis can be performed on the surface of the coating.

[0271] Taking into account the effects of the aforementioned elements and the arithmetic mean waviness Wa, the preferred form of the billet sheet in this embodiment is that the chemical composition of the base steel plate constituting the billet sheet, expressed as a percentage by mass, is:

[0272] C: Above 0.075% and below 0.100%

[0273] Mn: 1.00~1.40%

[0274] Si: 0.005~1.500%

[0275] P: below 0.100%

[0276] S: Below 0.0200%

[0277] Al: 0.005~0.700%

[0278] N: below 0.0150%

[0279] O: Below 0.0100%

[0280] Cr: 0–0.80%

[0281] Mo: 0–0.16%

[0282] B: 0~0.0100%

[0283] Ti: 0~0.100%

[0284] Nb: 0~0.060%

[0285] V: 0~0.50%

[0286] Ni: 0~1.00%

[0287] Cu: 0–1.00%

[0288] W: 0~1.00%

[0289] Sn: 0~1.00%

[0290] Sb: 0~0.200%

[0291] Ca: 0~0.0100%

[0292] Mg: 0~0.0100%

[0293] Zr: 0~0.0100%

[0294] REM: 0–0.0100%, and

[0295] Remaining components: Fe and impurities.

[0296] The arithmetic mean waviness Wa of the blank sheet is 0.10 to 0.30 μm.

[0297] If the chemical composition of the base steel sheet constituting the billet is within the aforementioned range, banded Mn segregation can be reduced. This suppresses the formation of martensite due to annealing and inhibits the increase in hardness difference. For billets with suppressed hardness difference, the generation of ghost lines during pressing can be further reduced. Furthermore, if the arithmetic mean waviness Wa is 0.10–0.30 μm, even better appearance quality can be obtained.

[0298] Furthermore, similarly to the above, considering the effects of the aforementioned elements and the arithmetic mean waviness Wa, the preferred embodiment of the billet sheet in this embodiment has the following chemical composition (by mass%) of the base steel plate constituting the billet sheet:

[0299] C: 0.040~0.075%

[0300] Mn: 1.00~2.00%

[0301] Si: 0.005~1.500%

[0302] P: below 0.100%

[0303] S: Below 0.0200%

[0304] Al: 0.005~0.700%

[0305] N: below 0.0150%

[0306] O: Below 0.0100%

[0307] Cr: 0–0.80%

[0308] Mo: 0–0.16%

[0309] B: 0~0.0100%

[0310] Ti: 0~0.100%

[0311] Nb: 0~0.060%

[0312] V: 0~0.50%

[0313] Ni: 0~1.00%

[0314] Cu: 0–1.00%

[0315] W: 0~1.00%

[0316] Sn: 0~1.00%

[0317] Sb: 0~0.200%

[0318] Ca: 0~0.0100%

[0319] Mg: 0~0.0100%

[0320] Zr: 0~0.0100%

[0321] REM: 0–0.0100%, and

[0322] Remaining components: Fe and impurities.

[0323] The arithmetic mean waviness Wa of the blank sheet is 0.10 to 0.30 μm.

[0324] When the chemical composition of the base steel sheet constituting the billet is within the aforementioned range, banded Mn segregation is reduced, suppressing the increase in hardness difference. For billets with suppressed hardness difference, the generation of ghost lines during pressing is reduced. Furthermore, if the arithmetic mean waviness Wa is 0.10–0.30 μm, even better appearance quality can be obtained.

[0325] [The C content at a depth of 20 μm from the surface, i.e., C] 20 The C content at a depth of 60 μm from the above surface, i.e., C 60 ΔC calculated using the following formula (1): 0.20~0.90 mass% / mm

[0326] ΔC=(C 60 -C 20 ) / (0.04) (1)]

[0327] ΔC represents the carbon concentration gradient in the region from a depth of 20 μm to a depth of 60 μm from the surface. By setting ΔC to 0.20–0.90 wt% / mm, a sharp increase in the carbon concentration gradient in the decarburized layer can be suppressed. As a result, ghost lines can be suppressed after pressing.

[0328] In the base steel sheet having the chemical composition of this embodiment, a ΔC value below 0.20 wt% / mm indicates insufficient decarburization or excessive decarburization from the steel sheet surface to very deep locations. Insufficient decarburization can lead to significant unevenness in the hardness of the base steel sheet, making it difficult to suppress ghost lines. Conversely, excessive decarburization can result in softening, failing to achieve the desired steel sheet strength. Therefore, ΔC is preferably 0.20 wt% / mm or higher. Furthermore, if ΔC exceeds 0.90 wt% / mm, significant hardness differences within the decarburized layer can occur, making it difficult to suppress ghost lines. ΔC is more preferably set to 0.30 wt% / mm or higher, 0.35 wt% / mm or higher, 0.40 wt% / mm or higher, or 0.45 wt% / mm or higher. Additionally, ΔC is preferably set to 0.80 wt% / mm or lower, or 0.75 wt% / mm or lower.

[0329] It should be noted that when the base steel plate has a coating on its surface, the "surface" in "position at a depth of 20 μm from the surface" and "position at a depth of 60 μm from the surface" refers to the interface between the coating and the base material. It should also be noted that when performing GDS analysis using the method described later to determine the Fe content from the surface, the depth position where the Fe content is 95% by mass or higher is considered the interface between the coating and the base material.

[0330] In addition, the ΔC is specified for depths greater than 20 μm from the surface because C concentrations below 20 μm from the surface do not affect ghost lines.

[0331] ΔC is obtained using the following method.

[0332] For any three locations on the steel plate, glow discharge optical emission spectrometry (GDS analysis) was used to measure the carbon content (mass%) from the surface of the steel plate along the depth direction (thickness direction) up to 100 μm. The carbon content (C) at a depth of 20 μm from the surface was also measured. 20 ), C content at a depth of 60 μm from the surface (C 60 ) and the above formula (1), calculate ΔC (mass% / mm). ΔC is obtained by calculating the average value of ΔC at 3 locations.

[0333] For the determination, a Marcus-type high-frequency glow discharge luminescent surface analyzer (GD-Profiler) manufactured by Horiba Corporation was used.

[0334] Taking into account the effects of the aforementioned elements and the influence of the C concentration gradient, the preferred form of the billet sheet in this embodiment is that the chemical composition of the base steel plate constituting the billet sheet, expressed as a percentage by mass, is:

[0335] C: 0.040~0.105%

[0336] Mn: 1.00~2.30%

[0337] Si: 0.005~1.500%

[0338] Al: 0.005~0.700%

[0339] P: below 0.100%

[0340] S: Below 0.0200%

[0341] N: below 0.0150%

[0342] O: Below 0.0100%

[0343] Cr: 0–0.80%

[0344] Mo: 0–0.16%

[0345] Ti: 0~0.100%

[0346] B: 0~0.0100%

[0347] Nb: 0~0.060%

[0348] V: 0~0.50%

[0349] Ni: 0~1.00%

[0350] Cu: 0–1.00%

[0351] W: 0~1.00%

[0352] Sn: 0~1.00%

[0353] Sb: 0~0.200%

[0354] Ca: 0~0.0100%

[0355] Mg: 0~0.0100%

[0356] Zr: 0~0.0100%

[0357] REM: 0–0.0100%, and

[0358] Remaining components: Fe and impurities.

[0359] The C content at a depth of 20 μm from the surface, i.e., C 20 The C content at a depth of 60 μm from the above surface, i.e., C 60 The ΔC calculated by the following formula (1) is 0.20 to 0.90 mass% / mm.

[0360] If the chemical composition of the base steel sheet constituting the blank sheet in this embodiment is within the above-mentioned range, and ΔC is 0.20 to 0.90 wt% / mm, the hardness difference within the decarburized layer can be reduced. As a result, automotive outer panel components obtained by pressing such blank sheets can further reduce ghost lines and achieve superior appearance quality.

[0361] It should be noted that, from the perspective of appearance quality, the blank sheet in this embodiment can also have the following characteristics: an arithmetic mean waviness Wa of 0.10 to 0.30 μm and a ΔC of 0.20 to 0.90 wt% / mm.

[0362] The yield stress of the blank sheet may change during automobile manufacturing processes such as vehicle assembly and painting / baking. However, if it is above 240 MPa, the yield stress will reach approximately 400 MPa or higher. Therefore, the yield stress of the blank sheet is preferably 240 MPa or higher. More preferably, the yield stress of the blank sheet is 300 MPa or higher. There is no particular upper limit to the yield stress of the blank sheet; for example, it could be 350 MPa or 450 MPa.

[0363] The higher the tensile strength of the steel plate, the more prone it is to ghost lines. Therefore, the tensile strength of the billet sheet is preferably 440 MPa or higher. More preferably, the tensile strength of the billet sheet is 500 MPa or higher, and even more preferably, 550 MPa or higher or 600 MPa or higher.

[0364] Furthermore, by ensuring the tensile strength is 750 MPa or less, the deterioration of the appearance after compression molding can be suppressed. Therefore, the tensile strength of the blank sheet is preferably 750 MPa or less. More preferably, the tensile strength of the blank sheet is 700 MPa or less.

[0365] The tensile strength of the billet was evaluated according to JIS Z 2241:2011. The test piece was set as test piece No. 5 of JIS Z 2241:2011. The sampling position of the tensile test piece was set at 1 / 4 of the distance from the end in the width direction (the direction perpendicular to the rolling direction on the surface of the billet), and the direction perpendicular to the rolling direction was taken as the length direction.

[0366] Tensile strength was evaluated according to JIS Z 2241:2011. The test piece was set as test piece No. 5 of JIS Z 2241:2011. The tensile test piece was collected at a distance of 1 / 4 from the end in the width direction of the plate, and the direction perpendicular to the rolling direction was taken as the length direction.

[0367] In this embodiment, the thickness of the blank sheet is 0.6 mm or less. From the viewpoint of lightweighting automobiles, the thickness of the blank sheet is more preferably 0.5 mm or less. There is no particular limitation on the lower limit of the blank sheet thickness; for example, the thickness of the blank sheet can be set to 0.2 mm or more. From the viewpoint of ensuring strength, the thickness of the blank sheet is preferably 0.4 mm or more.

[0368] It should be noted that, generally speaking, the thickness of the steel sheet used in automotive frame components such as chassis beams is 1.0 mm or more from the viewpoint of ensuring strength. The blank sheet in this embodiment is used for automotive outer panel components, and its thickness differs from that of the steel sheet used for automotive frame components.

[0369] The blank sheet in this embodiment has a generally linearly symmetrical shape, such as a trapezoid, rectangle, hexagon, or other polygon. In this embodiment, the direction perpendicular to the axis of symmetry is along the rolling direction. This direction corresponds to the length direction of the blank sheet. Preferably, the direction perpendicular to the axis of symmetry coincides with the rolling direction, but it may not. Within the range that reduces ghost lines during pressing, the direction perpendicular to the axis of symmetry and the rolling direction may have an angle. For example, the angle between the direction perpendicular to the axis of symmetry and the rolling direction is 15° or less.

[0370] Next, refer to Figure 4The method for manufacturing the blank sheet according to this embodiment will be described. Figure 4 This is a diagram showing an example of the cutting orientation in the blank sheet manufacturing method according to this embodiment.

[0371] The billet manufacturing method of this embodiment is a method for manufacturing billets containing steel plates, which includes a cutting process in which the steel plate is cut in a manner that extends the rolling direction of the steel plate along the length direction of the billet. The cutting mentioned here refers to the cutting of the billet, which has become a raw material, using a die or the like, and using a shearing machine.

[0372] First, an example of a method for manufacturing rolled steel sheet, which serves as the raw material for billet sheets, will be explained. It should be noted that the method for manufacturing rolled steel sheet, which serves as the raw material for billet sheets, described below is merely an example and is not limited to the method described below.

[0373] [First Manufacturing Method]

[0374] By using steel having the above-described chemical composition, for example by controlling the following conditions (I) to (IV) in a combined and inseparable manner, it is possible to stably manufacture steel sheets with preferably controlled arithmetic mean waviness Wa. The conditions will be explained below.

[0375] (I) Set the winding temperature to 550°C or higher.

[0376] (II) The pickling time should be more than 50 seconds.

[0377] (III) The surface roughness Ra of the roll surface in the final pass of cold rolling is 0.2 to 0.7 μm.

[0378] (IV) The reduction rate of the quenching and tempering rolling is 0.3 to 0.7%, and the surface roughness Ra of the rolls is 1.5 to 3.5 μm.

[0379] (I) Winding temperature: 550℃ or above

[0380] By setting the coiling temperature after hot rolling to a high temperature range of 550°C or higher, it becomes easier for oxide scale to form on the surface of the steel sheet. As a result, it becomes easier for unevenness to form on the surface of the pickled steel sheet. The coiling temperature is more preferably 600°C or higher, and even more preferably 650°C or higher.

[0381] (II) Pickling time: 50 seconds or more

[0382] In the pickling process after coiling and before cold rolling, it becomes easier to create unevenness on the surface of the steel sheet by setting the pickling time to 50 seconds or more. A pickling time of 70 seconds or more is more preferable.

[0383] (III) Arithmetic mean surface roughness Ra of the rolls in the final cold rolling pass: 0.2–0.7 μm

[0384] After pickling, by making the surface roughness Ra of the rolls in the final pass of cold rolling 0.2 to 0.7 μm, a suitable unevenness can be formed on the surface of the steel sheet during cold rolling. More preferably, the arithmetic mean roughness Ra of the rolls is 0.3 μm or more. It should be noted that the arithmetic mean roughness Ra is the arithmetic mean roughness.

[0385] Since the arithmetic mean roughness Ra described above is not present in ordinary rolling mill rolls, the steel sheet of this embodiment cannot be manufactured. To manufacture the steel sheet of this embodiment, it is preferable to use special rolling mill rolls in the final pass of cold rolling.

[0386] (IV) Reduction rate for quenching and tempering rolling: 0.3–0.7%; arithmetic mean surface roughness Ra of the rolls: 1.5–3.5 μm

[0387] In the quenching and tempering rolling after annealing (or after plating if it is a plated material), by making the reduction rate 0.3 to 0.7%, the arithmetic mean roughness Ra of the roll surface is made to be 1.5 to 3.5 μm, thereby forming an uneven surface on the steel sheet. More preferably, the reduction rate during quenching and tempering rolling is 0.5% or more, and more preferably, the surface roughness Ra of the roll surface is 2.3 μm or more.

[0388] There are no particular limitations beyond the conditions described above. For example, the slab used as raw material for steel plate may be heated for 30 minutes in a temperature range of 1100°C to 1200°C. After heating, the slab is hot-rolled. After hot rolling, it is coiled and then pickled. After pickling, it is cold-rolled. The cumulative reduction rate during cold rolling is preferably set to 30% to 90%. After cold rolling, it is annealed. Then, as needed, the above-described coating is formed. Furthermore, it is preferable to perform quenching and tempering rolling thereafter.

[0389] Furthermore, in the manufacture of rolled steel sheets, which serve as raw materials for billets, decarburization annealing can also be performed on cold-rolled steel sheets obtained using the above method. In this case, for example, by setting the dew point (average dew point in the annealing furnace) during decarburization annealing to above -20°C, and by holding the steel sheet at temperatures above 700°C for 50 to 400 seconds, stable decarburization of the steel sheet surface can be achieved. There is no particular upper limit to the dew point, but it is generally around 10°C. If the dew point is too low or the aforementioned holding time is too short, decarburization will not be sufficient. Conversely, if the aforementioned holding time is too long, sufficient tensile strength may not be obtained. It should be noted that the annealing temperature is, for example, around 750 to 850°C.

[0390] Using the first manufacturing method described above, it is possible to manufacture steel plates with an arithmetic mean waviness Wa of 0.10 to 0.30 μm.

[0391] [Second Manufacturing Method]

[0392] Using steel with the above-mentioned chemical composition, by annealing it under the following conditions after hot rolling and cold rolling, it is possible to stably manufacture steel sheets with preferably controlled ΔC (C concentration gradient).

[0393] (Annealing after hot rolling)

[0394] First, a hot-rolled steel sheet is obtained by hot rolling a slab with the above-mentioned chemical composition under normal conditions. The obtained hot-rolled steel sheet is then subjected to a single annealing at a high temperature in an atmospheric atmosphere. This single annealing is performed at an annealing temperature of 550–700°C and an annealing time of 2 hours or more. By annealing at a high temperature after hot rolling, internal oxides of Si and Mn are formed on the surface of the steel sheet. As a result, surface concentration of Si and Mn is suppressed during annealing after cold rolling, and decarburization is promoted. Therefore, ΔC can be preferably controlled.

[0395] If the annealing temperature is below 550°C or the annealing time is less than 2 hours, it may be impossible to optimally control the ΔC of the steel plate.

[0396] After the aforementioned annealing, a steel sheet or strip of the desired thickness is manufactured by pickling followed by cold rolling with a cumulative reduction of 70% or more. By achieving a cumulative reduction of 70% or more during cold rolling, austenite recrystallization is promoted during post-cold rolling annealing, while suppressing an increase in the austenite fraction. As a result, the fraction of ferrite with a high carbon diffusion coefficient increases during post-cold rolling annealing, promoting decarburization.

[0397] It should be noted that the cumulative reduction rate mentioned here is expressed as {1-(thickness of plate after cold rolling / thickness of plate before cold rolling)}×100(%).

[0398] After cold rolling, a secondary annealing process is performed to obtain a steel sheet with the desired mechanical properties. At this time, for example, by setting the dew point (average dew point in the annealing furnace) during secondary annealing to above -10°C and the residence time of the steel sheet in a temperature range above 700°C to 50–400 seconds, stable decarburization of the steel sheet surface can be achieved. There is no particular upper limit to the dew point, but it is generally around 10°C. If the dew point is too low or the residence time is too short, decarburization will not be sufficient, and ΔC cannot be optimally controlled. Furthermore, if the residence time is too long, sufficient tensile strength may not be obtained. It should be noted that the annealing temperature is, for example, around 750–850°C.

[0399] There are no particular limitations beyond the conditions described above. For example, hot rolling can also be performed after heating the slab, which is the raw material for steel plate, to a temperature range of 1100°C or higher. The coating described above can also be formed as needed.

[0400] Using the second manufacturing method described above, steel plates with a ΔC of 0.20 to 0.90 wt% / mm can be manufactured.

[0401] For example, the rolled steel sheet, which is the raw material for the blank sheet, manufactured using the above method, is cut in the following manner: the rolling direction of the steel sheet extends along the direction that forms the left and right sides of the vehicle body for the outer panel component of the automobile. Figure 4 The example shown is, for instance, using a cutting and pressing device to punch a blank sheet 2 from a rolled steel sheet 1, which is the raw material, as a blank sheet. Figure 4 In this process, the blank sheet 2 is roughly trapezoidal, and is punched in a manner that extends the rolling direction of the rolled steel plate 1, which is the raw material for the blank sheet, along two roughly parallel edges that form the roughly trapezoidal shape. In this case, the direction in which the two roughly parallel edges extend is the left-right direction of the car body. When using a cutting and pressing device, such as... Figure 4 As shown, blank sheet 2 is punched at arbitrary intervals.

[0402] In addition, when a shearing machine (so-called a rotary shearing machine) with a mechanism for cutting material at any angle is used, the billet sheet 2 is cut out from the rolled steel plate 1, which is the raw material for the billet sheet, in a manner that the amount of end material is reduced without gaps.

[0403] For example, the technology described in Patent Document 2 is a technique for improving yield when manufacturing cylindrical containers using long metal sheets as raw materials, and it cannot be applied to the manufacturing of automotive exterior panel parts. In general automotive exterior panel part manufacturing technology, considering yield, the sheet is cut in a manner that aligns the direction of the vehicle body's front-to-back direction during pressing with the rolling direction of the steel sheet. However, in the blank sheet manufacturing method of this embodiment, unlike the above, the rolled steel sheet used as the raw material for the blank sheet is cut in a manner that extends the rolling direction of the steel sheet along the direction of the automotive exterior panel part that aligns with the left-to-right direction of the vehicle body. Therefore, in the blank sheet manufacturing method of this embodiment, the yield may decrease. However, by staggering the cutting directions, the decrease in yield can be suppressed. Therefore, in the blank sheet manufacturing method of this embodiment, it is preferable to... Figure 4 As shown, the cutting directions of the blank sheet 2 are staggered.

[0404] As described above, it is preferable that the cutting orientations of the blank sheet 2 are staggered, but the cutting orientations can also be such that the blank sheets 2 are in the same orientation. For example, if the blank sheet 2 is approximately trapezoidal, it can also be cut in such a way that the shorter side of one of the two approximately parallel sides is positioned on one end side of the rolled steel sheet that is the raw material for the blank sheet.

[0405] Alternatively, the cutting can be done in a way that makes the shape of the blank sheet 2 approximately linearly symmetrical, such as a rectangle.

[0406] Next, refer to Figure 5 The equipment for manufacturing the blank sheet according to this embodiment will be described. Figure 5 This is a block diagram illustrating an example of a blank sheet manufacturing apparatus according to one embodiment of the present invention.

[0407] The blank manufacturing equipment of this embodiment includes a feeding device 10, a cutting device 20, and a receiving device 30.

[0408] The feeding device 10 is a device that feeds the rolled steel sheet, which serves as the raw material for the billet, into the cutting device 20. The feeding device 10 is not particularly limited and can be any feeding device found in known cutting equipment. The feeding device 10 may also include at least one of an uncoiling device for uncoiling the coil, a leveling device for flattening the uncoiled coil, and a cutting device for cutting the flattened steel strip into a specified size. The rolled steel sheet, which serves as the raw material for the billet, inserted into the feeding device 10 can be a leveled steel strip or a long steel sheet (strip) cut from the steel strip into a specified length. This rolled steel sheet, which serves as the raw material for the billet, is processed by the cutting device 20.

[0409] The cutting device 20 is a device that cuts the steel sheet in a manner that extends the rolling direction of the steel sheet along the length direction of the blank. The cutting device 20 is, for example, a cutting shearing machine having a shearing machine that cuts blanks from the steel sheet as raw material, or a cutting press having dies that punch blanks from the steel sheet. The cutting device 20 cuts the steel sheet in a manner that extends the rolling direction of the steel sheet along the direction that forms the left-right direction of the automotive outer panel component. When the cutting device 20 is a cutting shearing machine, a turning shearing machine is preferred in order to cut blanks from the rolled steel sheet in an alternating manner. Furthermore, when the cutting device 20 is a cutting press, two dies are preferably arranged in an alternating manner to punch blanks from the rolled steel sheet.

[0410] The receiving device 30 is a device for loading blank sheets. The receiving device 30 is not particularly limited and can be a receiving device found in known cutting equipment. For example, the receiving device 30 may have a transfer mechanism for transferring blank sheets obtained in the cutting device 20 and a receiving section for loading and storing blank sheets.

[0411] This concludes the description of the blank manufacturing equipment of this embodiment. However, the configuration of the blank manufacturing equipment of this embodiment is not limited to the above configuration, and may be further equipped with known configurations as needed.

[0412] Next, the manufacturing method of the automotive outer panel component according to this embodiment will be described. The manufacturing method of the automotive outer panel component according to this embodiment simply involves pressing the steel sheet in the blank along a direction that becomes the left-right direction of the vehicle body. As a pressing forming method, for example, it can be performed by pressing the blank sheet with a cutting bracket and a die, then pressing a punch to apply strain to the steel sheet, thereby stretching it. It should be noted that such forming is called deep drawing or stretch forming.

[0413] Example

[0414] The inventors of this invention have verified the effect of reducing ghost lines caused by the chemical composition of the blank sheet, the arithmetic mean waviness Wa, and the aforementioned ΔC. The conditions in the embodiments are one example adopted to confirm the feasibility and effectiveness of the invention. The invention is not limited to this single example. Various conditions can be used to achieve the purpose of the invention as long as they do not depart from its spirit and intent.

[0415] [Example 1]

[0416] Steel with the chemical composition shown in Table 1 was smelted and continuously cast to produce slabs with a thickness of 240–300 mm. Using the obtained slabs, cold-rolled steel sheets and clad steel sheets were manufactured under conditions (I) to (VI) described later. It should be noted that in Table 2, "OK" is marked in the condition column when the conditions are met, and "NG" is marked in the condition column when the conditions are not met. Furthermore, the thickness of the obtained steel sheets and clad steel sheets ranged from 0.2 to 2.0 mm.

[0417] In addition, annealing was performed after cold rolling.

[0418] The manufacturing conditions, excluding conditions (I) to (VI), are as follows. The slab is heated to a temperature range of 1100°C or higher and then hot-rolled. After hot rolling, it is coiled and then pickled. After pickling, it is cold-rolled with a cumulative reduction of 30% to 90%. After cold rolling, annealing is performed to form an alloyed hot-dip galvanized layer (GA), a hot-dip galvanized layer (GI), or an electroplated layer (EG), as needed. Then, temper rolling is performed.

[0419] Conditions (I) to (VI) in the table are as follows.

[0420] (I) Set the winding temperature to 550°C or higher.

[0421] (II) The pickling time should be more than 50 seconds.

[0422] (III) The arithmetic mean roughness Ra of the roll surface of the final cold rolling pass is 0.2 to 0.7 μm.

[0423] (IV) The reduction rate of the quenching and tempering rolling is 0.3 to 0.7%, and the arithmetic mean roughness Ra of the rolls is 1.5 to 3.5 μm.

[0424] (V) Heat the slab to a temperature range of 1200°C or higher and maintain it in that temperature range for more than 5 hours.

[0425] (VI) Annealing is performed on steel plates in a temperature range of -20°C or higher and 700°C or higher, with a residence time of 50 to 400 seconds.

[0426] Next, using the manufactured steel sheet and clad steel sheet (blank sheet), a roughly semi-cylindrical simulated component (press-formed article) simulating the outer panel of a door was manufactured by press forming. During the press forming of this simulated component, material (steel sheet or clad steel sheet) was actively fed into the mold, ensuring that at any point on the surface of the simulated component, the ratio of strain along any direction on the surface of the simulated component to strain in a direction perpendicular to that direction was approximately 1. That is, press forming was performed in an anisotropic manner, where no strain was generated at any point on the surface of the simulated component. Therefore, in this embodiment, the generation of ghost lines in the simulated component is independent of the orientation of the blank sheet.

[0427] For the obtained steel plates and coated steel plates, the arithmetic mean waviness Wa and tensile strength were calculated using the above method.

[0428] If the obtained tensile strength is 500 MPa or higher, it is judged as high strength and is deemed acceptable. On the other hand, if the obtained tensile strength is lower than 500 MPa, it is judged as poor strength and is deemed unacceptable.

[0429] In addition, the average value μ and standard deviation σ of Mn concentration were obtained using the following method.

[0430] After mirror grinding of the thick section of the base steel plate, the Mn concentration was measured at 600 points at 1 μm intervals along the rolling direction of the base steel plate at a specified depth. The average Mn concentration (mass%) at the specified depth position was obtained by calculating the average value of the obtained Mn concentrations. This operation was performed in the thickness direction from a position on the base steel plate at a distance of 1 / 8 of the thickness from the surface in the thickness direction to a position at a distance of 3 / 8 of the thickness from the aforementioned surface in the thickness direction. The average value μ of the total Mn concentration was obtained by calculating the average value (arithmetic mean) of all obtained Mn concentrations. Furthermore, the standard deviation σ of the Mn concentration was obtained by calculating the standard deviation from all obtained Mn concentrations.

[0431] The apparatus used was an electron probe microanalyzer (EPMA), and the measurement conditions were an accelerating voltage of 15 kV.

[0432] If (3σ / μ)×100 is below 7.0, then Mn segregation in the base steel plate is significantly reduced.

[0433] In addition, the thickness of the decarburized layer was determined using the following method.

[0434] For any three locations on the base steel plate, the carbon concentration in the region extending from the surface to a position half the thickness of the plate in the depth direction (thickness direction) is measured at 1 μm depths. The region with a carbon concentration less than half the thickness of the plate at the position half the thickness of the plate from the surface is considered the decarburized layer, and its thickness is calculated, thus obtaining the thickness of the decarburized layer.

[0435] For the determination, a Markus-type high-frequency glow discharge luminescent surface analyzer (GD-Profiler) manufactured by Horiba Manufacturing Co., Ltd. was used.

[0436] In addition, the appearance quality of the simulated parts was evaluated using the following method.

[0437] Appearance quality is evaluated based on the degree of ghost lines generated on the surface of the molded simulated part. The pressed surface is polished with a mold, and stripes spaced several millimeters apart are identified as ghost lines. These ghost lines are scored from 1 to 5 based on the degree of rib-like patterns. A 100mm x 100mm area is visually inspected. A case where no rib-like patterns are observed is designated as "1"; a case where the maximum length of the rib-like patterns is less than 20mm is designated as "2"; a case where the maximum length of the rib-like patterns exceeds 20mm but is less than 50mm is designated as "3"; a case where the maximum length of the rib-like patterns exceeds 50mm but is less than 70mm is designated as "4"; and a case where the maximum length of the rib-like patterns exceeds 70mm is designated as "5". A score of "3" or lower is considered excellent and deemed acceptable. Conversely, a score of "4" or higher is considered poor and deemed unacceptable.

[0438] Furthermore, the appearance quality was evaluated more rigorously based on the formula Wz, which is the sum of the maximum peak height Zp and the maximum valley height Zv of the waviness curve. Using the same method as when calculating the arithmetic mean waviness Wa, the waviness curve of the pressed molded part (simulated component) was obtained according to JIS B 0601:2013. From this waviness curve, the maximum peak height Zp and the maximum valley height Zv were calculated, and Wz was obtained by summing them. When the obtained Wz is below 0.40 μm, the appearance quality is considered superior.

[0439] [Table 1]

[0440]

[0441] [Table 2]

[0442]

[0443] Table 2 shows that the pressed products obtained using the following blanks exhibit high strength and excellent appearance. The chemical composition (by mass%) of the base steel plate of these blanks is as follows: C: 0.040–0.100%, Mn: 1.00–2.00%, Si: 0.005–1.500%, P: less than 0.100%, S: less than 0.0200%, Al: 0.005–0.700%, N: less than 0.0150%, O: less than 0.0100%, Cr: 0–0.80%, Mo: 0–0.16%, B: 0.040–0.100%, Mo: 0.0200%, B: 0.040–0.100%, Mo: 0.0200%, Mo: 0.040–0.100%, Mo: 0.040–0.100%, Mo: 0.040–0.100%, Mo: 0.040–0.04 ... The composition of the blank sheet is as follows: 0–0.0100% Ti, 0–0.100% Nb, 0–0.060% V, 0–0.50% Ni, 0–1.00% Cu, 0–1.00% W, 0–1.00% Sn, 0–1.00% Sb, 0–0.200% Ca, 0–0.0100% Mg, 0–0.0100% Zr, 0–0.0100% REM, and the remainder being Fe and impurities. The arithmetic mean waviness Wa of this blank sheet is 0.10–0.30 μm. Furthermore, it is known that the above blank sheet has high strength, and using this blank sheet, pressed molded articles with excellent appearance quality can be manufactured.

[0444] [Example 2]

[0445] Steel with the chemical composition shown in Table 3 was smelted and continuously cast to produce slabs with a thickness of 240–300 mm. The resulting slabs were then hot-rolled after being heated to a temperature range above 1100°C. After hot rolling, the slabs were coiled, annealed once under the conditions shown in Table 4, and then pickled. The finishing temperature of the hot rolling was set above 900°C, and the coiling temperature was set below 650°C. After pickling, cold rolling was performed with a cumulative reduction of 70–90%. After cold rolling, a second annealing was performed under the conditions shown in Table 4, resulting in alloyed hot-dip galvanized (GA), hot-dip galvanized (GI), or electro-galvanized (EG) coatings, as needed. Using the above method, the steel sheets and clad steel sheets shown in Table 2 were obtained. It should be noted that the thickness of the obtained steel sheets and clad steel sheets is 0.2–2.0 mm.

[0446] After annealing following cold rolling, a simulated part was manufactured by pressing using steel sheet and clad steel sheet (blank sheet). In the pressing process of this embodiment, the material (steel sheet or clad steel sheet) was actively fed into the die, and pressing was performed in an anisotropic manner so that no strain was generated at any location on the surface of the simulated part. Therefore, in this embodiment, the generation of ghost lines in the simulated part is also independent of the orientation of the blank sheet.

[0447] The method described above was used to calculate ΔC for the obtained steel sheet, coated steel sheet, and simulated part (pressed product). It should be noted that since the ΔC values ​​for the steel sheet and coated steel sheet are the same as those for the simulated part, the ΔC value for the simulated part is not recorded in the table.

[0448] In addition, the tensile strength of the steel plate and the appearance quality of the simulated component were evaluated using the following methods. It should be noted that since there was no significant difference between the tensile strength of the steel plate and the tensile strength of the simulated component (pressed part), the evaluation of whether the steel plate possessed the expected tensile strength for a door outer panel was conducted at a specific time point.

[0449] In addition, tensile strength and appearance quality were evaluated using the same method as in Example 1.

[0450] [Table 3]

[0451]

[0452] [Table 4]

[0453]

[0454] Table 4 shows that the pressed products obtained using the following blanks exhibit high strength and excellent appearance. The chemical composition (by mass%) of the base steel plate of these blanks is as follows: C: 0.040–0.105%, Mn: 1.00–2.30%, Si: 0.005–1.500%, Al: 0.005–0.700%, P: less than 0.100%, S: less than 0.0200%, N: less than 0.0150%, O: less than 0.0100%, Cr: 0–0.80%, Mo: 0–0.16%, T i: 0–0.100%, B: 0–0.0100%, Nb: 0–0.060%, V: 0–0.50%, Ni: 0–1.00%, Cu: 0–1.00%, W: 0–1.00%, Sn: 0–1.00%, Sb: 0–0.200%, Ca: 0–0.0100%, Mg: 0–0.0100%, Zr: 0–0.0100%, REM: 0–0.0100%, and the remainder: Fe and impurities, determined by the C content at a depth of 20 μm from the surface of the base metal steel plate. 20 The carbon content at a depth of 60 μm from the surface of the base steel plate, i.e., C 60 The ΔC calculated by the following formula (1) is 0.20 to 0.90 wt% / mm, and the tensile strength of the blank sheet is 500 MPa or more. In addition, it can be seen that the above blank sheet can be used to manufacture high-strength, high-quality pressed products with excellent appearance.

[0455] Industrial availability

[0456] According to the above-described solution of the present invention, it is possible to provide an automotive outer panel component with reduced ghost lines, a blank sheet capable of reducing ghost lines generated by compression molding, a method for manufacturing the blank sheet, and equipment for manufacturing the blank sheet.

[0457] Explanation of symbols

[0458] 10 Feeding device

[0459] 20 Cutting device

[0460] 30 Containment Devices

Claims

1. An automotive outer panel component comprising a steel plate, The aforementioned automotive outer panel component refers to a component that is centrally located in the left-right direction of the vehicle body, and whose shape, when viewed from the vertical direction along the vehicle body, is approximately symmetrical about a straight line located at the center in the left-right direction. Viewed from above, the rolling direction of the steel plate extends along the left-right direction of the vehicle body. The chemical composition of the steel plate, expressed as a percentage by mass, is as follows: C：0.040～0.100%、 Mn: 1.00~2.00% Si: 0.005~1.500%, P: Below 0.100% S: Below 0.0200% Al：0.005～0.700%、 N: below 0.0150% O: Below 0.0100% Cr：0～0.80%、 Mo: 0–0.16% B：0～0.0100%、 Ti: 0~0.100%, Nb: 0~0.060%, V：0～0.50%、 Ni: 0~1.00%, Cu: 0~1.00%, W：0～1.00%、 Sn: 0~1.00% Sb: 0~0.200%, Ca: 0~0.0100% Mg: 0~0.0100%, Zr：0～0.0100%、 REM: 0–0.0100%, and Remaining components: Fe and impurities. The arithmetic mean ripple Wa is 0.10–0.30 μm.

2. An automotive outer panel component comprising a steel plate, The aforementioned automotive outer panel component refers to a component that is centrally located in the left-right direction of the vehicle body, and whose shape, when viewed from the vertical direction along the vehicle body, is approximately symmetrical about a straight line located at the center in the left-right direction. Viewed from above, the rolling direction of the steel plate extends along the left-right direction of the vehicle body. The chemical composition of the steel plate, expressed as a percentage by mass, is as follows: C：0.040～0.105%、 Mn: 1.00~2.30%, Si: 0.005~1.500%, Al：0.005～0.700%、 P: Below 0.100% S: Below 0.0200% N: below 0.0150% O: Below 0.0100% Cr：0～0.80%、 Mo: 0–0.16% B：0～0.0100%、 Ti: 0~0.100%, Nb: 0~0.060%, V：0～0.50%、 Ni: 0~1.00%, Cu: 0~1.00%, W：0～1.00%、 Sn: 0~1.00% Sb: 0~0.200%, Ca: 0~0.0100%, Mg: 0~0.0100%, Zr：0～0.0100%、 REM: 0–0.0100%, and Remaining components: Fe and impurities. The C content at a depth of 20 μm from the surface, i.e., C 20 The C content at a depth of 60 μm from the surface, i.e., C 60 The ΔC calculated by the following formula (1) is 0.20~0.90 mass% / mm. ΔC=(C 60 -C 20 ) / (0.04) (1)。 3. The automotive outer panel component according to claim 1 or 2, wherein the yield stress reaches 400 MPa or more.

4. A blank sheet, which is a raw material for automotive outer panel components, is a blank sheet containing steel plates. The aforementioned automotive outer panel component refers to a component that is centrally located in the left-right direction of the vehicle body, and whose shape, when viewed from the vertical direction along the vehicle body, is approximately symmetrical about a straight line located at the center in the left-right direction. The rolling direction of the steel plate extends along the length of the billet sheet, and the thickness of the billet sheet is less than 0.6 mm. The chemical composition of the steel plate, expressed as a percentage by mass, is: C：0.040～0.100%、 Mn: 1.00~2.00% Si: 0.005~1.500%, P: Below 0.100% S: Below 0.0200% Al：0.005～0.700%、 N: below 0.0150% O: Below 0.0100% Cr：0～0.80%、 Mo: 0–0.16% B：0～0.0100%、 Ti: 0~0.100%, Nb: 0~0.060%, V：0～0.50%、 Ni: 0~1.00%, Cu: 0~1.00%, W：0～1.00%、 Sn: 0~1.00% Sb: 0~0.200%, Ca: 0~0.0100%, Mg: 0~0.0100%, Zr：0～0.0100%、 REM: 0–0.0100%, and Remaining components: Fe and impurities. The arithmetic mean ripple Wa is 0.10–0.30 μm.

5. A blank sheet, which is a raw material for automotive outer panel components, is a blank sheet containing steel plates. The aforementioned automotive outer panel component refers to a component that is centrally located in the left-right direction of the vehicle body, and whose shape, when viewed from the vertical direction along the vehicle body, is approximately symmetrical about a straight line located at the center in the left-right direction. The rolling direction of the steel plate extends along the length of the billet sheet, and the thickness of the billet sheet is less than 0.6 mm. The chemical composition of the steel plate, expressed as a percentage by mass, is: C：0.040～0.105%、 Mn: 1.00~2.30%, Si: 0.005~1.500%, Al：0.005～0.700%、 P: Below 0.100% S: Below 0.0200% N: below 0.0150% O: Below 0.0100% Cr：0～0.80%、 Mo: 0–0.16% B：0～0.0100%、 Ti: 0~0.100%, Nb: 0~0.060%, V：0～0.50%、 Ni: 0~1.00%, Cu: 0~1.00%, W：0～1.00%、 Sn: 0~1.00% Sb: 0~0.200%, Ca: 0~0.0100%, Mg: 0~0.0100%, Zr：0～0.0100%、 REM: 0–0.0100%, and Remaining components: Fe and impurities. The C content at a depth of 20 μm from the surface, i.e., C 20 The C content at a depth of 60 μm from the surface, i.e., C 60 The ΔC calculated by the following formula (1) is 0.20~0.90 mass% / mm. ΔC=(C 60 -C 20 ) / (0.04) (1)。 6. The blank sheet according to claim 5, wherein, The tensile strength of the blank sheet is above 500 MPa.

7. A method for manufacturing a blank sheet, which is a raw material for automotive outer panel components and a method for manufacturing a blank sheet comprising a steel plate. The aforementioned automotive outer panel component refers to a component that is centrally located in the left-right direction of the vehicle body, and whose shape, when viewed from the vertical direction along the vehicle body, is approximately symmetrical about a straight line located at the center in the left-right direction. It has the following processes: The coiling process involves coiling the hot-rolled steel sheet at a coiling temperature of 550°C or higher. The chemical composition of the steel sheet, in mass percent, is as follows: C: 0.040–0.100%, Mn: 1.00–2.00%, Si: 0.005–1.500%, P: below 0.100%, S: below 0.0200%, Al: 0.005–0.700%, N: below 0.0150%, O: below 0.0100%, Cr: 0–0.80%, Mo: 0–0. 0.16%, B: 0-0.0100%, Ti: 0-0.100%, Nb: 0-0.060%, V: 0-0.50%, Ni: 0-1.00%, Cu: 0-1.00%, W: 0-1.00%, Sn: 0-1.00%, Sb: 0-0.200%, Ca: 0-0.0100%, Mg: 0-0.0100%, Zr: 0-0.0100%, REM: 0-0.0100%, and the remainder: Fe and impurities; The pickling process involves pickling the coiled steel plate for a pickling time of more than 50 seconds. The cold rolling process involves cold rolling the pickled steel sheet and using rolls with an arithmetic mean roughness Ra of 0.2 to 0.7 μm to perform the final pass of the cold rolling. The quenching and tempering rolling process uses rolls with an arithmetic mean roughness Ra of 1.5–3.5 μm and performs quenching and tempering rolling with a reduction rate of 0.3–0.7%; and The cutting process involves cutting the steel plate in a manner that extends the rolling direction of the steel plate along the length direction of the billet.

8. A method for manufacturing a blank sheet, which is a raw material for automotive outer panel components and a method for manufacturing a blank sheet comprising a steel plate. The aforementioned automotive outer panel component refers to a component that is centrally located in the left-right direction of the vehicle body, and whose shape, when viewed from the vertical direction along the vehicle body, is approximately symmetrical about a straight line located at the center in the left-right direction. It has the following processes: The first annealing process involves annealing the hot-rolled steel plate in an atmospheric atmosphere at an annealing temperature of 550–700°C for at least 2 hours. The chemical composition of the steel plate, in mass percent, is as follows: C: 0.040–0.105%, Mn: 1.00–2.30%, Si: 0.005–1.500%, Al: 0.005–0.700%, P: less than 0.100%, S: less than 0.0200%, N: less than 0.0150%, O: less than 0.0100%, Cr:

0. ~0.80%, Mo: 0~0.16%, Ti: 0~0.100%, B: 0~0.0100%, Nb: 0~0.060%, V: 0~0.50%, Ni: 0~1.00%, Cu: 0~1.00%, W: 0~1.00%, Sn: 0~1.00%, Sb: 0~0.200%, Ca: 0~0.0100%, Mg: 0~0.0100%, Zr: 0~0.0100%, REM: 0~0.0100%, and the remainder: Fe and impurities; The pickling process involves pickling the steel plate after the first annealing process. The cold rolling process involves cold rolling the steel sheet after the pickling process with a cumulative reduction rate of 70% or more. A secondary annealing process is performed on the steel sheet after the cold rolling process, wherein the dew point is above -10°C and the residence time in the temperature range of above 700°C is 50 to 400 seconds; and the steel sheet is subjected to secondary annealing after the cold rolling process. The cutting process involves cutting the steel plate in a manner that extends the rolling direction of the steel plate along the length direction of the billet.

9. The method for manufacturing a blank sheet according to claim 7 or 8, wherein in the cutting process, the steel plates are cut in an alternating manner.

10. A blank sheet manufacturing apparatus, which is a raw material for automotive outer panel components and comprises a steel sheet blank sheet. The aforementioned automotive outer panel component refers to a component that is centrally located in the left-right direction of the vehicle body, and whose shape, when viewed from the vertical direction along the vehicle body, is approximately symmetrical about a straight line located at the center in the left-right direction. It includes the following devices: A coiling device coils hot-rolled steel sheets at a coiling temperature of 550°C or higher. The chemical composition of the steel sheets, in mass percent, is: C: 0.040–0.100%, Mn: 1.00–2.00%, Si: 0.005–1.500%, P: less than 0.100%, S: less than 0.0200%, Al: 0.005–0.700%, N: less than 0.0150%, O: less than 0.0100%, Cr: 0–0.80%, Mo: 0–0. 0.16%, B: 0-0.0100%, Ti: 0-0.100%, Nb: 0-0.060%, V: 0-0.50%, Ni: 0-1.00%, Cu: 0-1.00%, W: 0-1.00%, Sn: 0-1.00%, Sb: 0-0.200%, Ca: 0-0.0100%, Mg: 0-0.0100%, Zr: 0-0.0100%, REM: 0-0.0100%, and the remainder: Fe and impurities; A pickling treatment device that pickles the coiled steel plate for a pickling time of more than 50 seconds. A cold rolling unit that cold rolls the pickled steel sheet and uses rolls with an arithmetic mean roughness Ra of 0.2 to 0.7 μm to perform the final pass of the cold rolling; A tempering rolling apparatus that uses rolls with an arithmetic mean surface roughness Ra of 1.5–3.5 μm and performs tempering rolling at a reduction rate of 0.3–0.7%; and A cutting device comprising a shear for cutting blanks from a steel plate or a die for punching the blanks from the steel plate. The cutting device cuts the steel plate in such a way that the rolling direction of the steel plate extends along the length direction of the billet.

11. A blank sheet manufacturing apparatus, which is a raw material for automotive outer panel components and comprises a steel sheet blank sheet. The aforementioned automotive outer panel component refers to a component that is centrally located in the left-right direction of the vehicle body, and whose shape, when viewed from the vertical direction along the vehicle body, is approximately symmetrical about a straight line located at the center in the left-right direction. It includes the following devices: A primary annealing apparatus is used to anneal hot-rolled steel plates under atmospheric conditions, an annealing temperature of 550–700°C, and an annealing time of at least 2 hours. The chemical composition of the steel plate, in mass percent, is as follows: C: 0.040–0.105%, Mn: 1.00–2.30%, Si: 0.005–1.500%, Al: 0.005–0.700%, P: less than 0.100%, S: less than 0.0200%, N: less than 0.0150%, O: less than 0.0100%, Cr:

0. ~0.80%, Mo: 0~0.16%, Ti: 0~0.100%, B: 0~0.0100%, Nb: 0~0.060%, V: 0~0.50%, Ni: 0~1.00%, Cu: 0~1.00%, W: 0~1.00%, Sn: 0~1.00%, Sb: 0~0.200%, Ca: 0~0.0100%, Mg: 0~0.0100%, Zr: 0~0.0100%, REM: 0~0.0100%, and the remainder: Fe and impurities; A pickling treatment device, which pickles the steel plate after the first annealing process. A cold rolling unit that performs cold rolling on the steel sheet after the pickling process with a cumulative reduction rate of 70% or more; A secondary annealing apparatus, which sets the dew point to above -10°C and the residence time of the steel sheet in a temperature range above 700°C to 50-400 seconds, performs secondary annealing on the steel sheet after the cold rolling process; and A cutting device comprising a shear for cutting blanks from a steel plate or a die for punching the blanks from the steel plate. The cutting device cuts the steel plate in such a way that the rolling direction of the steel plate extends along the length direction of the billet.

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