Steel plates and parts containing them

Abstract

The present invention provides a steel sheet containing Ni, Cu, and Sn, which has excellent paint film adhesion, and a part including the steel sheet. The steel sheet and parts including the steel sheet of the present invention have a chemical composition containing, in mass%, Ni: 0.010 to 1.000%, Cu: 0.010 to 1.000%, and Sn: 0.003 to 1.000%, and are characterized in that, in the X-ray diffraction pattern of the steel sheet surface, the peak half-width of the (310) plane of the ferrite phase is 0.5° or more.

Description

[Technical Field]

[0001] The present invention relates to a steel sheet and a part including the same. [Background technology]

[0002] In order to improve the paint film adhesion to steel sheets, it is effective to enhance the chemical conversion treatability of the steel sheet surface and to form a uniform chemical conversion coating on the steel sheet surface.

[0003] In this regard, for example, Patent Document 1 discloses that when a high-strength cold-rolled steel sheet is continuously annealed in a continuous annealing furnace or a cold-rolled steel sheet / hot-dip galvanized steel sheet dual-purpose facility having a continuous annealing furnace, the cooling method of which in a cooling zone including a part or all of the steel sheet temperature range of 600 to 250°C following heating for recrystallization is one or more of gas cooling, diffusion cooling, and cooling pipe cooling, the steel sheet surface is exposed to an atmosphere in which iron oxidizes within the above-mentioned steel sheet temperature range, pickled at the outlet side of the annealing furnace, and then iron or Ni plating is applied to the steel sheet in an amount of 1 to 50 mg / m 2 Furthermore, Patent Document 1 teaches that, while oxidation of a steel sheet is usually prevented by an extremely low concentration of oxygen and / or an inert gas atmosphere with an extremely low dew point around the steel sheet, the steel sheet is actively exposed to an oxidizing atmosphere to oxidize not only Si and Mn but also the iron in the steel sheet, and that by pickling after leaving an annealing furnace, the oxide films of Si, Mn, etc. are removed together with the oxide film on the iron in the steel sheet, thereby obtaining a high-strength cold-rolled steel sheet that is free from "bleaching" and has good chemical treatability, even if the contents of Si, Mn, etc. are high.

[0004] Patent Document 2 also describes a method for manufacturing a steel sheet containing copper (Cu) at a concentration of 0.10 mass % or more and 0.50 mass % or less, in which the number of residual scales on the surface is 160,000 pieces / mm 2Patent Document 2 further teaches that the above-mentioned configuration makes it possible to provide a steel sheet with excellent chemical conversion treatability, since the particle size of the copper compound particles exposed on the steel sheet surface, which serves as the cathode point in chemical conversion treatment, is 2 μm or less and the residual scale is reduced to a predetermined amount or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-190030 [Patent Document 2] Japanese Patent Publication No. 2020-084238 Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned Patent Document 2 teaches that elements such as nickel (Ni) and tin (Sn) in addition to copper (Cu) reduce the mechanical properties required for automotive steel sheets, such as strength and formability, as well as chemical stability such as corrosion resistance, and that copper compounds present on the surface of the steel sheet in particular reduce the chemical conversion treatability required for improving corrosion resistance. Generally, when chemical conversion treatability is reduced, areas where a chemical conversion coating is not formed, known as "whiteout," may occur, which may result in reduced paint film adhesion.

[0007] Therefore, an object of the present invention is to provide a steel sheet containing Ni, Cu, and Sn, which has excellent paint film adhesion, and a part including the steel sheet. [Means for solving the problem]

[0008] The present invention includes at least the following aspects.

[0009] (Aspect 1) A steel plate, The steel plate is, in mass%, Ni: 0.010 to 1.000%, Cu: 0.010 to 1.000%, and Sn: chemical composition including 0.003 to 1.000% A steel sheet characterized in that, in an X-ray diffraction pattern of the surface of the steel sheet, the peak half-width of the (310) plane of the ferrite phase is 0.5° or more.

[0010] (Aspect 2) The steel sheet according to the above-mentioned aspect 1, wherein the peak half width is 1.0° or more.

[0011] (Aspect 3) The steel sheet according to the above-mentioned aspect 1, wherein the peak half width is 1.3° or more.

[0012] (Aspect 4) In the element distribution image of the cross section of the steel plate taken by an electron microprobe analyzer, The steel sheet according to any one of Aspects 1 to 3, characterized in that a specific element-containing portion containing at least one of Ni, Cu, and Sn in a solid solution state is present in a region from the surface of the steel sheet to a depth of 5 μm.

[0013] (Aspect 5) the chemical composition further comprises Si; 5. The steel sheet according to any one of the above aspects 1 to 4, wherein the thickness of silicon oxide is 10 nm or less when measured on the surface of the steel sheet by X-ray photoelectron spectroscopy.

[0014] (Aspect 6) A part comprising the steel sheet according to any one of the above aspects 1 to 5. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a steel sheet containing Ni, Cu, and Sn and having excellent paint film adhesion, and a part including the steel sheet. DETAILED DESCRIPTION OF THE INVENTION

[0016] As mentioned above, generally, when chemical conversion treatability is reduced, areas where the chemical conversion coating is not formed, known as "skid zones," may appear, resulting in reduced paint adhesion. For example, when elements such as Ni, Cu, and Sn are present in a solid solution in steel sheet, the potential of the steel sheet becomes more noble than when these elements are not present in a solid solution, which can reduce the etching ability of Fe during chemical conversion treatment. In such cases, the chemical conversion treatability of the steel sheet may be reduced, resulting in reduced paint adhesion. Therefore, when steel sheet simultaneously contains the three elements Ni, Cu, and Sn, this reduced paint adhesion is particularly problematic.

[0017] Two commonly known methods for producing steel include, for example, a method in which molten iron is obtained in a blast furnace using iron ore, a natural resource, as the main raw material, and then refined in a converter or other furnace to produce molten steel; and a method in which molten steel is produced in an electric furnace using scrap material, a recycled resource, as the main raw material. Steel produced by the former method, i.e., blast furnace steel, may contain elements such as Ni, Cu, and Sn as additive elements. Therefore, if these elements are present, the above-mentioned problems must be addressed appropriately. On the other hand, steel produced by the latter method, i.e., electric furnace steel, uses scrap material as the main raw material, as described above, and therefore contains relatively large amounts of scrap-derived elements such as Ni, Cu, and Sn (so-called tramp elements). Furthermore, it is likely that the three elements Ni, Cu, and Sn are simultaneously present. Therefore, the above-mentioned problems are particularly pronounced in electric furnace steel.

[0018] Therefore, the present inventors conducted research, focusing particularly on the surface condition of the steel sheet, in order to provide a steel sheet that has excellent paint adhesion even when the steel sheet simultaneously contains the three elements Ni, Cu, and Sn. As a result, the present inventors discovered that by creating a specific strain state on the surface of a steel sheet containing Ni, Cu, and Sn, the steel sheet surface can be easily phosphatably treated, resulting in excellent paint adhesion. Specifically, the present inventors discovered that by creating a specific strain state on the surface of a steel sheet containing Ni, Cu, and Sn, such that the full width at half maximum of the peak of the (310) plane of the ferrite phase in an X-ray diffraction pattern is 0.5° or more, the steel sheet surface can be easily phosphatably treated, and paint adhesion can be significantly improved. Here, in this specification, the term "steel sheet surface" refers to the surface of the steel sheet itself. Therefore, for example, in the case of a plated steel sheet in which a plating layer is formed on the surface of a base steel sheet, the term "steel sheet surface" refers to the surface of the base steel sheet, not the surface of the plated steel sheet.

[0019] The present invention has been completed based on the above findings, and includes the following embodiments.

[0020] Hereinafter, preferred embodiments of the steel sheet of the present invention will be described in detail.

[0021] <Steel plate> A steel sheet according to one embodiment of the present invention has a chemical composition containing, in mass %, Ni: 0.010 to 1.000%, Cu: 0.010 to 1.000%, and Sn: 0.003 to 1.000%. The steel sheet of this embodiment has a characteristic configuration in which the peak full width at half maximum of the (310) plane of the ferrite phase is 0.5° or more in the X-ray diffraction pattern of the steel sheet surface. That is, the steel sheet of this embodiment has a specific strain state in the steel sheet surface in which a certain amount or more of various types of strain are introduced in a dispersed state with different degrees, such that the peak full width at half maximum of the (310) plane of the ferrite phase is 0.5° or more.

[0022] Strain, in other words, dislocations and subgrain boundaries, are relatively weak defects known as planar or line defects, making them susceptible to corrosion. Therefore, if such strain is introduced into the steel sheet surface, it can promote the anodic dissolution (i.e., etching) of Fe in the chemical conversion treatment solution during chemical treatment. In chemical conversion treatment, electrons are generally generated by the anodic dissolution (etching) of Fe, and at the cathode site, the electrons generated by the anodic dissolution of Fe cause a cathodic reaction (2H + +2e - →H2, 10H + +NO3 - +8e - →NH4 + As a result, the pH of the chemical conversion treatment solution near the steel sheet surface rises, and as a result, compounds such as zinc phosphate crystals that make up the chemical conversion treatment film are precipitated on the steel sheet surface.

[0023] As described above, the steel sheet of this embodiment has a specific strain state on the surface of the steel sheet, in which the peak full width at half maximum of the (310) plane of the ferrite phase is 0.5° or more, and therefore the steel sheet surface can be uniformly and finely etched during chemical conversion treatment, thereby exhibiting good chemical conversion treatability. As a result, the steel sheet of this embodiment can significantly improve paint adhesion.

[0024] The steel sheet of this embodiment includes not only electric furnace steel, which inevitably contains Ni, Cu, and Sn as tramp elements, but also blast furnace steel, which contains Ni, Cu, and Sn as essential elements or optional added elements. Furthermore, the steel sheet of this embodiment can exhibit superior paint adhesion and, in turn, superior corrosion resistance compared to conventional steel sheets that simultaneously contain the three elements Ni, Cu, and Sn. Therefore, the steel sheet of this embodiment is particularly useful in the automotive field, where excellent paint adhesion and / or corrosion resistance are required.

[0025] Hereinafter, each component of the steel sheet of this embodiment will be described in detail.

[0026] [Ferrite phase (310) plane peak half-width: 0.5° or more] The steel sheet of this embodiment has a characteristic configuration in which the peak half width of the (310) plane of the ferrite phase is 0.5° or more in the X-ray diffraction pattern of the steel sheet surface. The half-width of the peak in the diffraction pattern obtained by X-ray diffraction (XRD) is one of the evaluation parameters for the density of crystal lattice defects in metallographic structures, etc., and can be used to quantitatively evaluate the strain state on the steel sheet surface. When the amount of strain is large, the inter-crystalline lattice distance expands or contracts from its original length, and this behavior is reflected in the half-width of the peak obtained by XRD. In other words, the greater the amount of strain, the greater the number of inter-crystalline lattice distances that are longer or shorter than their original length, and therefore the larger the half-width of the peak. In this embodiment, the crystal lattice defect density, which serves as an index of the strain state for obtaining good chemical conversion treatability, is defined using the peak half-width of the (310) plane of the ferrite phase in the diffraction pattern obtained by XRD. That is, in this embodiment, by limiting the strain state to a specific state in which the peak half-width of the (310) plane of the ferrite phase is 0.5° or more, the steel sheet surface can be uniformly and finely etched during chemical conversion treatment, and good chemical conversion treatability can be achieved.

[0027] The peak half-width of the (310) plane of the ferrite phase in the diffraction pattern obtained by the above-mentioned XRD may be 0.5° or more on at least one of the front and back surfaces of the steel sheet.

[0028] Peaks such as those of the (110) plane could be considered as peaks to be used as indicators of the strain state on the steel sheet surface, but as the amount of strain increases, the measured peak half-width saturates, and this may not be an appropriate indicator of the strain state on the steel sheet surface.On the other hand, the (310) plane is an appropriate indicator of the strain state on the steel sheet surface because the plane index of the peak half-width itself is high, there is little measurement error, and the peak half-width increases as the amount of strain increases.

[0029] The peak of the (310) plane of the ferrite phase is a peak whose center is located at 2θ = 116.4 ± 0.5. The peak half width of the (310) plane of the ferrite phase means the width at half the peak height of the (310) plane.

[0030] In this embodiment, the peak half width of the (310) plane of the ferrite phase is preferably 1.0° or more, and more preferably 1.3° or more, in order to obtain better chemical conversion treatability.

[0031] The peak half-width of the (310) plane of the ferrite phase in the X-ray diffraction pattern was measured using an X-ray diffractometer (Rigaku Corporation, "Ultima III") with a Cu-K X-ray source. α After obtaining an X-ray diffraction pattern by XRD using 1.6 kW X-ray source load power (tube voltage / tube current = 40 kV / 40 mA) and 1.54 Å X-rays (wavelength λ = 1.54 Å), the width at half the peak height of the (310) plane of the ferrite phase is measured from the X-ray diffraction pattern. The specific method and conditions for measuring the peak half width of the (310) plane of the ferrite phase will be described later.

[0032] The means for bringing the steel sheet surface into the above-mentioned specific strain state is not particularly limited, but it is preferable to use, for example, a shot blasting treatment. Specific means and conditions for bringing the steel sheet surface into the above-mentioned specific strain state will be described later.

[0033] [Chemical composition] In this embodiment, the steel sheet has a chemical composition containing, in mass %, Ni: 0.010 to 1.000%, Cu: 0.010 to 1.000%, and Sn: 0.003 to 1.000%. As described above, an object of the present invention is to provide a steel sheet containing Ni, Cu, and Sn, which has excellent paint adhesion, and this object is achieved by having the steel sheet surface in the above-mentioned specific strain state, i.e., a specific strain state in which the peak half-width of the (310) plane of the ferrite phase is 0.5° or more. Therefore, the chemical composition of the steel sheet is not particularly limited except that it contains, in mass%, Ni: 0.010 to 1.000%, Cu: 0.010 to 1.000%, and Sn: 0.003 to 1.000%. It is clear that elements other than Ni, Cu, and Sn are not essential technical features for achieving the object of the present invention.

[0034] The chemical composition of the steel plate according to one embodiment of the present invention may contain, in addition to Ni, Cu, and Sn, any alloying elements that are commonly added in the technical field of the present invention in appropriate amounts.

[0035] Hereinafter, the chemical compositions that can be employed in the steel sheet of this embodiment will be described in detail. However, these descriptions are intended to merely exemplify preferred chemical compositions of steel sheets for application in automotive steel sheets and the like, and are not intended to limit the present invention to steel sheets having such specific chemical compositions.

[0036] For example, the steel plate of this embodiment has, in mass%, C: 0.001 to 0.500%, Si: 0 to 3.00% Mn: 0.10 to 3.00%, Al: 0.001 to 2.000%, Ni: 0.010 to 1.000%, Cu: 0.010 to 1.000%, Sn: 0.003 to 1.000%, P: 0.100% or less, S: 0.100% or less, N: 0.0150% or less, O: 0.0100% or less, Ti: 0 to 0.150% Nb: 0 to 0.150%, B: 0~0.0100%, Mo: 0 to 1.000%, Cr: 0 to 1.000%, V: 0~0.150%, W: 0 to 1.000%, Hf: 0 to 0.050%, Mg: 0 to 0.050% Zr: 0 to 0.500%, Ca: 0 to 0.050%, REM: 0~0.010%, As: 0~0.100%, Ir: 0 to 1.000%, Zn: 0 to 1.000%, and Remainder: Fe and impurities It may have a chemical composition consisting of: Each of these elements will be described in more detail below.

[0037] [C: 0.001~0.500%] C is an element that inexpensively increases strength and is an important element for controlling the strength of steel. To fully obtain this effect, the C content is preferably 0.001% or more. The C content may be 0.005% or more, 0.010% or more, 0.030% or more, 0.040% or more, 0.070% or more, 0.100% or more, 0.150% or more, or 0.200% or more. On the other hand, excessive C content may result in reduced elongation. For this reason, the C content is preferably 0.500% or less. The C content may be 0.450% or less, 0.400% or less, 0.350% or less, 0.300% or less, or 0.250% or less.

[0038] [Si: 0-3.00%] Si is an element that is effective in increasing strength as a solid solution strengthening element. The Si content may be 0%, but to obtain this effect, the Si content is preferably 0.01% or more. The Si content may be 0.05% or more, 0.10% or more, 0.30% or more, 0.50% or more, 0.80% or more, or 1.00% or more. On the other hand, excessive Si content may increase the steel strength but decrease the elongation. For this reason, the Si content is preferably 3.00% or less. The Si content may be 2.50% or less, 2.00% or less, 1.50% or less, or 1.20% or less.

[0039] [Mn: 0.10~3.00%] Mn is an element that improves the hardenability of steel and is effective in increasing strength. To fully obtain this effect, the Mn content is preferably 0.10% or more. The Mn content may be 0.50% or more, 1.00% or more, 1.30% or more, 1.50% or more, or 1.80% or more. On the other hand, excessive Mn content may increase the steel strength but decrease the elongation. For this reason, the Mn content is preferably 3.00% or less. The Mn content may be 2.80% or less, 2.50% or less, or 2.00% or less.

[0040] [Al: 0.001 to 2.000%] Al acts as a deoxidizer for steel and improves the quality of the steel. To fully achieve this effect, the Al content is preferably 0.001% or more. The Al content may be 0.005% or more, 0.010% or more, 0.020% or more, or 0.030% or more. On the other hand, excessive Al content may generate coarse Al oxides, reducing the elongation of the steel sheet. For this reason, the Al content is preferably 2.000% or less. The Al content may be 1.500% or less, 1.000% or less, 0.500% or less, 0.100% or less, or 0.050% or less.

[0041] [Ni: 0.010~1.000%] [Cu: 0.010~1.000%] Ni and Cu are elements that contribute to improving strength through precipitation strengthening or solid solution strengthening. To fully achieve these effects, the contents of these elements are preferably 0.010% or more, and may be 0.020% or more, 0.030% or more, 0.040% or more, 0.050% or more, 0.080% or more, 0.100% or more, 0.150% or more, or 0.200% or more. On the other hand, excessive inclusion of these elements may promote the formation of oxides, particularly Si-based surface oxides and iron oxides, on the steel sheet surface. Therefore, the Ni and Cu contents are preferably 1.000% or less, and may be 0.800% or less, 0.600% or less, 0.400% or less, or 0.300% or less.

[0042] [Sn: 0.003~1.000%] Sn is an element effective in improving corrosion resistance. To fully obtain this effect, the Sn content is preferably 0.003% or more. The Sn content may be 0.004% or more, 0.008% or more, 0.010% or more, 0.020% or more, 0.030% or more, 0.040% or more, 0.050% or more, 0.080% or more, or 0.100% or more. On the other hand, excessive Sn content may promote the formation of oxides, particularly Si-based surface oxides and iron oxides, on the steel sheet surface. Therefore, the Sn content is preferably 1.000% or less. The Sn content may be 0.800% or less, 0.600% or less, 0.400% or less, 0.300% or less, or 0.200% or less.

[0043] [P:0.100% or less] P is an element that segregates at grain boundaries and promotes embrittlement of steel. The lower the P content, the better, and ideally it is 0%. However, excessive reduction in the P content may result in a significant increase in costs. For this reason, the P content may be 0.0001% or more, or may be 0.001% or more, or 0.005% or more. On the other hand, excessive P content may result in embrittlement of steel due to grain boundary segregation, as described above. Therefore, the P content is preferably 0.100% or less. The P content may be 0.050% or less, 0.030% or less, 0.020% or less, or 0.010% or less.

[0044] [S:0.100% or less] S is an element that generates nonmetallic inclusions such as MnS in steel, reducing the ductility of steel parts. Since a lower S content is preferable, ideally 0%. However, excessive reduction in the S content can result in a significant increase in costs. For this reason, the S content may be 0.0001% or more, or may be 0.0005% or more, 0.001% or more, or 0.002% or more. On the other hand, excessive S content can cause cracks to occur originating from nonmetallic inclusions during cold forming. Therefore, the S content is preferably 0.100% or less. The S content may be 0.050% or less, 0.020% or less, or 0.010% or less.

[0045] [N: 0.0150% or less] N is an element that forms coarse nitrides in steel sheets and reduces the workability of the steel sheets. Since a lower N content is preferable, ideally it is 0%. However, excessive reduction in the N content may result in a significant increase in manufacturing costs. For this reason, the N content may be 0.0001% or more, 0.0005% or more, or 0.0010% or more. On the other hand, excessive N content may form coarse nitrides as described above, reducing the workability of the steel sheets. Therefore, the N content is preferably 0.0150% or less. The N content may be 0.0100% or less, 0.0080% or less, 0.0050% or less, or 0.0030% or less.

[0046] [O:0.0100% or less] O is an impurity that is mixed in during the manufacturing process. O is an element that forms coarse inclusions and reduces the workability of steel sheets. While O can be considered to be included in the impurities, the O content will be described in more detail below. Since a lower O content is preferable, the ideal O content is 0%. However, excessive reduction of the O content may result in a significant increase in manufacturing costs. Therefore, the O content may be 0.0001% or more. The O content may be 0.0005% or more or 0.0010% or more. On the other hand, excessive O content may form coarse inclusions, as described above, and reduce the workability of steel sheets. Therefore, the O content is preferably 0.0100% or less. The O content may be 0.0080% or less, 0.0060% or less, or 0.0040% or less.

[0047] The preferred basic chemical composition of the steel sheet is as described above. Furthermore, the steel sheet may contain at least one of the following elements in place of a portion of the remaining Fe, as required.

[0048] [Ti: 0~0.150%] [Nb: 0~0.150%] [V: 0~0.150%] Ti, Nb, and V form carbonitrides in steel, improving the strength of the steel sheet through precipitation strengthening. The Ti, Nb, and V contents may be 0%, but to achieve this effect, the Ti, Nb, and V contents are preferably 0.001% or more, and may be 0.002% or more, 0.005% or more, or 0.010% or more. However, even if these elements are contained in excess, the effect saturates, and excessive inclusion of these elements in steel increases manufacturing costs. Therefore, the Ti, Nb, and V contents are preferably 0.150% or less, and may be 0.120% or less, 0.100% or less, 0.080% or less, 0.050% or less, 0.020% or less, or 0.015% or less.

[0049] [B: 0~0.0100%] B segregates at grain boundaries to increase grain boundary strength, thereby improving low-temperature toughness. The B content may be 0%, but to obtain this effect, the B content is preferably 0.0001% or more. The B content may be 0.0002% or more, 0.0005% or more, or 0.0010% or more. On the other hand, if B is contained excessively, the effect saturates and there is a risk of increasing manufacturing costs. Therefore, the B content is preferably 0.0100% or less. The B content may be 0.0050% or less, 0.0030% or less, 0.0020% or less, or 0.0015% or less.

[0050] [Mo: 0-1.000%] [Cr:0~1.000%] [W: 0~1.000%] Mo, Cr, and W are elements that improve the hardenability of steel and contribute to improving its strength. The Mo, Cr, and W contents may be 0%, but to achieve these effects, the Mo, Cr, and W contents are preferably 0.001% or more, and may be 0.010% or more, 0.020% or more, or 0.030% or more. However, even if these elements are contained in excess, the effects saturate, and adding more than necessary to steel increases manufacturing costs. Therefore, the Mo, Cr, and W contents are preferably 1.000% or less, and may be 0.500% or less, 0.100% or less, 0.050% or less, or 0.040% or less.

[0051] [Hf:0~0.050%] [Mg: 0~0.050%] [Zr: 0~0.500%] [Ca: 0~0.050%] [REM:0~0.010%] Hf, Mg, Zr, Ca, and REM are elements that can control the morphology of nonmetallic inclusions. The contents of Hf, Mg, Zr, Ca, and REM may be 0%, but to obtain these effects, the contents of these elements are preferably 0.0001% or more, and may be 0.0005% or more, or 0.001% or more. However, even if these elements are contained in excess, the effects saturate, and adding more than necessary to the steel sheet increases production costs. Therefore, the contents of Hf, Mg, and Ca are preferably 0.050% or less, and may be 0.010% or less, 0.005% or less, or 0.003% or less. Similarly, the Zr content is preferably 0.500% or less, and may be 0.100% or less, 0.050% or less, or 0.010% or less. Furthermore, the REM content is preferably 0.010% or less, and may be 0.005% or less, or 0.003% or less. REM is a collective term for 17 elements: scandium (Sc), atomic number 21; yttrium (Y), atomic number 39; and the lanthanides, lanthanum (La), atomic number 57, through lutetium (Lu), atomic number 71. The REM content is the total content of these elements.

[0052] [As:0~0.100%] As is an element effective in improving corrosion resistance. The As content may be 0%, but to obtain this effect, the As content is preferably 0.001% or more. The As content may be 0.002% or more, or 0.003% or more. On the other hand, even if an excessive amount of As is contained, the effect saturates, and adding more As than necessary to the steel sheet increases the manufacturing cost. Therefore, the As content is preferably 0.100% or less. The As content may be 0.050% or less, 0.010% or less, 0.008% or less, or 0.005% or less.

[0053] [Ir: 0~1.000%] Ir is an element that segregates at prior austenite grain boundaries to increase the strength of the grain boundaries. The Ir content may be 0%, but to obtain this effect, the Ir content is preferably 0.001% or more. The Ir content may be 0.003% or more, 0.005% or more, or 0.010% or more. On the other hand, even if an excessive amount of Ir is added, the effect saturates, and adding more Ir than necessary to the steel increases the manufacturing cost. Therefore, the Ir content is preferably 1.000% or less. The Ir content may be 0.500% or less, 0.100% or less, 0.030% or less, or 0.015% or less.

[0054] [Zn: 0-1.000%] Zn is an element effective in controlling the shape of inclusions. The Zn content may be 0%, but to obtain this effect, the Zn content is preferably 0.001% or more. The Zn content may be 0.003% or more, 0.005% or more, or 0.010% or more. On the other hand, even if Zn is contained in an excessive amount, the effect saturates, and adding more Zn than necessary to the steel material increases the manufacturing cost. Therefore, the Zn content is preferably 1.000% or less. The Zn content may be 0.500% or less, 0.100% or less, 0.030% or less, or 0.015% or less.

[0055] The remainder of the steel sheet other than the above elements consists of Fe and impurities. The impurities in the steel sheet are components that are mixed in due to various factors in the manufacturing process, including raw materials such as ore and scrap, when the steel sheet is industrially manufactured.

[0056] The chemical composition of steel sheets can be measured using common analytical methods. For example, the chemical composition of steel sheets can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) of chips in accordance with JIS G 1201:2014. Specifically, for example, a 35 mm square test piece is obtained from the 1 / 4 position of the steel sheet thickness, and the test piece is measured using a Shimadzu ICPS-8100 (measuring device) or similar under conditions based on a pre-prepared calibration curve. C and S, which cannot be measured by ICP-AES, can be measured using a combustion-infrared absorption method, and N can be measured using an inert gas fusion-thermal conductivity method.

[0057] [Area containing specific elements within a depth of 5 μm from the steel plate surface] Furthermore, the steel sheet of this embodiment may have a specific element-containing portion containing at least one of Ni, Cu, and Sn in a solid solution state in a region from the steel sheet surface to a depth of 5 μm in an element distribution image of the steel sheet cross section obtained by an electron probe microprobe analyzer (EPMA). Here, "containing at least one specific element of Ni, Cu, and Sn in a solid solution state" means that the specific element is contained in the steel sheet at a concentration of 0.3 mass% or more when the distribution of elements in the steel sheet cross section is analyzed by area analysis using an element distribution image obtained by EPMA.

[0058] The specific element-containing portion is a region also referred to as an enriched portion, and refers to an enriched region in which the concentration of at least one element selected from Ni, Cu, and Sn is 0.3 mass% or more when the distribution of elements in the region from the surface of the steel sheet to a depth of 5 μm is analyzed using an EPMA element distribution image. For example, when the region is analyzed using an EPMA element distribution image, the Ni concentration is 0.3 mass% or more, i.e., the Ni-enriched region (also referred to as a Ni-enriched portion) is the specific element-containing portion.

[0059] (Method for measuring the concentration of specific elements in the area from the steel plate surface to a depth of 5 μm using EPMA) When performing area analysis of an element distribution image of a steel sheet cross section using an EPMA, first, a region of the steel sheet cross section cut in the thickness direction from the steel sheet surface to a depth of 5 μm is photographed using an EPMA (e.g., JXA-8500 manufactured by JEOL Ltd.) at a magnification of 1000 times under conditions of an acceleration voltage of 15 kV and an irradiation current of 5 × 10 A to obtain a mapping image. Next, the obtained element distribution image is binarized (min = 0, max = 255) using the image analysis software "ImageJ" and area analysis is performed with pixels of 0.25 μm × 0.25 μm. Quantitative analysis of Ni, Cu, and Sn can be performed to determine the concentrations of these specific elements in the above region.

[0060] As described above, when Ni, Cu, and Sn are present in the form of solid solution in a steel sheet, the potential of the steel sheet becomes more noble than when these elements are not present in the steel sheet, which reduces the etching ability of Fe during chemical conversion treatment and, as a result, may result in a decrease in the chemical conversion treatability of the steel sheet.

[0061] However, the steel sheet of this embodiment has a specific strain state on the surface of the steel sheet, in which the peak full width at half maximum of the (310) plane of the ferrite phase is 0.5° or more. Therefore, even if the steel sheet has a specific element-containing portion containing at least one of Ni, Cu, and Sn in a solid solution state in a region up to a depth of 5 μm from the surface of the steel sheet, the steel sheet can exhibit good chemical conversion treatability and, as a result, excellent paint film adhesion.

[0062] [Thickness of silicon oxide (SiO2) on the steel sheet surface: 10 nm or less] Furthermore, the steel sheet of this embodiment may contain Si in its chemical composition. In this case, the steel sheet of this embodiment preferably has a silicon oxide (SiO2) thickness of 10 nm or less when measured by X-ray photoelectron spectroscopy (XPS) on the steel sheet surface. When the chemical composition of the steel sheet contains Si, silicon oxide may be formed on the steel sheet surface. Silicon oxide is a surface oxide that particularly reduces chemical conversion treatability, so reducing this silicon oxide to a certain amount or less can more reliably achieve good chemical conversion treatability. As a result, the steel sheet of this embodiment can more reliably exhibit excellent paint adhesion.

[0063] The thickness of silicon oxide measured on the steel sheet surface by XPS measurement is preferably 9 nm or less, 8 nm or less, or 7 nm or less, in order to more reliably obtain good chemical conversion treatability. The lower limit of the thickness of silicon oxide measured on the steel sheet surface by XPS measurement is not particularly limited, and may be 0 nm, i.e., no silicon oxide is present, or may be more than 0 nm, or may be 1 nm or more.

[0064] The XPS measurement is carried out as follows. First, an evaluation material for specifying the thickness of silicon oxide, which is a surface oxide, and a reference base material are prepared.

[0065] Here, the evaluation material is a steel plate for which the thickness of silicon oxide is to be specified, cut out from a target product or the like. The evaluation material is one from which oil and dirt have been removed from the surface without changing the thickness of silicon oxide. Specifically, if oil has been applied to the surface of the steel plate to be evaluated, the evaluation material is obtained after removing the oil by an appropriate method that does not cause surface oxidation of the steel plate. Note that an example of an appropriate method that does not cause surface oxidation of the steel plate is a method of removing the oil using a solvent.

[0066] On the other hand, the base material is prepared by grinding and / or polishing a steel sheet to a depth of about 100 to 500 μm from the surface of the steel sheet, and adjusting the arithmetic mean roughness Ra of the surface to 0.8 μm or less. The grinding and polishing method for the base material is not particularly limited, but care must be taken to prevent surface oxidation during grinding and / or polishing. In other words, grinding and polishing methods that result in high temperatures must be avoided. Furthermore, when finish polishing is performed, it is preferable to perform the finish polishing using a wet method using distilled water or ethanol.

[0067] For each of the test material and base material prepared as described above, the maximum strength of the steel sheet surface is measured within a bond energy range of 532.9±0.4 eV. If the ratio of the maximum strength of the test material to the maximum strength of the base material is 1.2 or greater, it is determined that silicon oxide, a surface oxide, is present on the surface of the test material. Next, the test material is subjected to XPS measurement at 1 nm intervals in the thickness direction by sputtering. The thickness at which the ratio of the maximum strength of the test material to the maximum strength of the base material is less than 1.2 is determined to be the thickness of silicon oxide.

[0068] The XPS measurement conditions for determining the thickness of silicon oxide are as follows: X-ray source: mono-Al Kα (1486.6eV) X-ray diameter: 50 to 200 μm Measurement area: 100~700μm×100~700μm Vacuum degree: 1×10 -10 ~1×10 -11 torr (1 torr = 133.32 Pa) Acceleration voltage: 1 to 10 kV

[0069] When the above-mentioned XPS measurement is performed using a sample obtained from an automobile, the coating film and chemical conversion coating film are removed from the sample according to the following coating film and chemical conversion coating film removal method before the XPS measurement.

[0070] (Method for removing paint films and chemical conversion coatings) In order to remove the paint film and chemical conversion coating from the sample obtained from the automobile, the following (1) paint film removal step and (2) chemical conversion coating removal step are carried out in this order.

[0071] (1) Paint film removal process A paint remover (Neo River #160, manufactured by Sansai Kako Co., Ltd.) is applied to the surface of a sample cut from an automobile body at room temperature and allowed to stand for 5 minutes. The coated sample surface is then rubbed with a hard sponge (e.g., Kanefiel, manufactured by Aion Co., Ltd.) to remove the paint film from the sample surface. The sample surface after the paint film removal is then washed with water and dried. The remaining paint film is then confirmed by SEM-EPMA measurement of the sample surface (100 μm square, 5 fields of view) after washing and drying. In the element distribution image obtained by EPMA, regions with a carbon concentration of 10% by mass or more are identified, and if the area ratio of these regions is 5% or more, it is determined that the paint film has not been sufficiently removed. To measure the area ratio of regions with a carbon concentration of 10% by mass or more, first obtain an element distribution image of carbon using an EPMA with a carbon concentration range of 10 to 30%. The obtained element distribution image of carbon is then image-processed to measure the area ratio. Image analysis software "ImageJ" is used for image processing. Specifically, after loading the above C element distribution image into ImageJ, "Make Binary" in "Binary" under "Process" is used to binarize the image so that areas with a C concentration of 10% by mass or more are displayed in black and areas with a C concentration of less than 10% by mass are displayed in white. After binarization, "Measure" under "Analyze" is used to read the "Area fraction" value in "Results." This value is determined as the area fraction of areas with a C concentration of 10% by mass or more. If the coating film is not sufficiently removed, coating film removal is repeated until the area fraction of areas with a C concentration of 10% by mass or more is reduced to less than 5%.

[0072] (2) Chemical conversion coating removal process The chemical conversion coating is removed from the surface of a sample cut from an automobile body by a method conforming to JIS K 3151:1996. Specifically, the chemical conversion coating is removed from the surface of the sample by immersing the removed sample in a 5% chromic acid solution heated to 75°C for 15 minutes. The surface of the sample after the chemical conversion coating removal is then washed with water and dried. The remaining state of chemical conversion crystals is confirmed by SEM-EPMA measurement of the washed and dried sample surface (100 μm square, 5 fields of view). In the element distribution image obtained by EPMA, regions with a P concentration of 5% by mass or more are identified, and if the area ratio of these regions is 5% or more, it is determined that the chemical conversion coating has not been sufficiently removed. To measure the area ratio of regions with a P concentration of 5% by mass or more, first obtain an element distribution image of P using an EPMA with a P concentration range of 5 to 10%. The obtained element distribution image of P is then image-processed to measure the area ratio. Image analysis software "ImageJ" is used for image processing. Specifically, the above P element distribution image is loaded into ImageJ, and then binarized using "Make Binary" under "Binary" in "Process" so that areas with a P concentration of 5% by mass or more are displayed in black and areas with a P concentration of less than 5% by mass are displayed in white. After binarization, "Measure" under "Analyze" is used to read the value for "Area fraction" in "Results." This value is determined to be the area fraction of areas with a P concentration of 5% by mass or more. If the chemical conversion coating is not sufficiently removed, removal of the chemical conversion coating is repeated until the area fraction of areas with a P concentration of 5% by mass or more is reduced to less than 5%.

[0073] The above-described method for removing paint films and chemical conversion coatings is not limited to XPS measurements, and can also be applied when performing various measurements and analyses using samples obtained from automobiles. For example, when performing the above-described XRD or EPMA measurements or analyzing the chemical composition of a steel sheet using a sample obtained from an automobile, the paint film and chemical conversion coating can be removed from the sample according to the above-described method for removing paint films and chemical conversion coatings, and then the XRD or EPMA measurement or chemical composition analysis can be performed.

[0074] The means for reducing the amount of silicon oxide on the steel sheet surface to a certain level or less is not particularly limited, but examples thereof include a means for rinsing the steel sheet with a rinsing solution having low electrical conductivity when rinsing the steel sheet after shot blasting the surface of the steel sheet in the manufacturing process of the steel sheet, and a means for controlling the coiling temperature, which will be described later.

[0075] (Thickness of steel plate) The thickness of the steel plate is not particularly limited, but is generally 0.2 to 8.0 mm. For example, the thickness may be 0.3 mm or more, 0.6 mm or more, 1.0 mm or more, 1.6 mm or more, or 2.0 mm or more. Similarly, the thickness of the steel plate may be, for example, 7.0 mm or less, 6.0 mm or less, 5.0 mm or less, or 4.0 mm or less.

[0076] (mechanical properties) In this embodiment, the strength of the steel plate is not particularly limited, but for example, the steel plate may have a Vickers hardness of 90 HV or more. The Vickers hardness of the steel plate may be 150 HV or more, 190 HV or more, 200 HV or more, 250 HV or more, 300 HV or more, 350 HV or more, 400 HV or more, or 450 HV or more. The upper limit of the Vickers hardness is not particularly limited, but for example, the Vickers hardness of the steel plate may be 650 HV or less, 600 HV or less, 550 HV or less, or 500 HV or less.

[0077] The Vickers hardness is determined in accordance with JIS Z 2244-1:2024 as follows. First, a test specimen is cut from any position on the steel plate, excluding the edge, so that a cross section perpendicular to the surface (thickness cross section) can be observed. The cut-out thickness cross section of the test specimen is polished using #600 to #1500 silicon carbide paper. Next, the thickness cross section of the test specimen is polished to a mirror finish using a diluted solution such as alcohol or a liquid in which diamond powder with a particle size of 1 to 6 μm is dispersed in pure water, and this thickness cross section is used as the measurement surface. Next, the Vickers hardness of the test specimen is measured using a micro Vickers hardness tester at a load of 1 kgf and at intervals of at least three times the indentation. Specifically, a total of 20 measurements are taken randomly at 1 / 4 of the test specimen's thickness, and the arithmetic average of these measurements is determined as the Vickers hardness of the steel plate.

[0078] <Parts> As described above, the steel sheet according to the embodiment of the present invention can achieve superior paint adhesion and, in turn, superior corrosion resistance compared to conventional steel sheets that simultaneously contain the three elements Ni, Cu, and Sn. Therefore, the steel sheet according to the embodiment of the present invention is useful for use in parts in technical fields that require superior paint adhesion and / or corrosion resistance. In particular, the steel sheet according to the embodiment of the present invention is useful for use in parts in the automotive field.

[0079] In a preferred embodiment, an automobile part including a steel sheet according to an embodiment of the present invention is provided. Examples of automobile parts include frame parts, bumpers, and other structural and reinforcing parts that require strength. Further, other examples of automobile parts include exterior panel parts such as roofs, hoods, fenders, and doors that require high designability. At least a portion of these parts may include a steel sheet according to an embodiment of the present invention. Therefore, at least a portion of these parts satisfies the characteristics of the steel sheet according to the embodiment described above. In a portion of the steel sheet that does not come into direct contact with a mold during forming such as press forming, or that comes into direct contact with the mold but is processed to a relatively low degree, the characteristics of the steel sheet do not change particularly before and after forming.

[0080] When taking samples from automobile parts for various measurements and analyses, the following points (i) to (iv) shall be avoided. (i) Welds: Within 20 mm of the toe of spot welds and within 20 mm of the toe of arc / laser welds. (ii) Processed part: A processed part with a curvature radius of less than 15 mm, and a location within 5 mm of the processed part. (iii) Edge: The edge within 5 mm of the cut end face of the part. (iv) Red rust: Areas within 5 mm of areas where red rust is visible.

[0081] <Steel sheet manufacturing method> Next, a preferred method for manufacturing a steel plate according to an embodiment of the present invention will be described. The following description is intended to exemplify a characteristic method for manufacturing a steel plate according to an embodiment of the present invention, but is not intended to limit the steel plate to one manufactured by the manufacturing method described below.

[0082] A steel sheet according to one embodiment of the present invention can be manufactured by a manufacturing method including, for example, a casting step of casting molten steel having an adjusted chemical composition to form a steel billet, a hot rolling step of hot rolling the steel billet to obtain a hot-rolled steel sheet, a shot blasting step of performing shot blasting to impart strain to the steel sheet surface of the hot-rolled steel sheet, and a pickling step of pickling the hot-rolled steel sheet.

[0083] Preferred conditions for these steps will be described in detail below.

[0084] [Casting process] In the method for producing a steel sheet according to this embodiment, the casting step is a step of casting molten steel having an adjusted chemical composition to form a steel slab. The conditions for the casting step are not particularly limited. For example, the casting step may involve melting in a blast furnace, an electric furnace, or the like, followed by various secondary smelting processes, and then casting by a method such as ordinary continuous casting or ingot casting.

[0085] [Hot rolling process] In the method for producing a steel sheet according to this embodiment, the hot rolling step is a step of hot-rolling a steel slab to obtain a hot-rolled steel sheet. The hot rolling step is carried out by hot-rolling a cast steel slab, either directly or after cooling, followed by reheating. When reheating is carried out, the heating temperature of the steel slab may be, for example, 1100 to 1250°C. In the hot rolling step, rough rolling and finish rolling are usually carried out. The temperature and reduction ratio of each rolling step can be appropriately determined depending on the desired metal structure and plate thickness. For example, the end temperature of finish rolling may be 900 to 1050°C, and the reduction ratio of finish rolling may be 10 to 50%.

[0086] The hot-rolled steel sheet after finish rolling is coiled at a predetermined coiling temperature and then subjected to the subsequent shot blasting process. In the steel sheet manufacturing method of this embodiment, the hot-rolled steel sheet is coiled at a coiling temperature of 520°C or higher. By controlling the coiling temperature to 520°C or higher, a surface oxide is formed on the outside (surface) of the steel sheet, and an internal oxide is also formed in the inside (surface layer) of the steel sheet. In general, in the case of a steel sheet containing Si, the internal oxide is mainly composed of Si-based oxides. Therefore, a Si-depleted layer is formed directly below the internal oxide formed in the surface layer of the steel sheet, due to the consumption of Si in the steel due to the formation of the internal oxide.

[0087] In particular, by controlling the coiling temperature to 520°C or higher, the thickness of the Si-depleted layer can be controlled to 0.3 μm or more. The above-mentioned surface oxides and internal oxides are removed in the shot blasting process and pickling process after coiling, so that a Si-depleted layer having a thickness of 0.3 μm or more remains on the surface of the hot-rolled steel sheet after these processes. By forming the surface of the hot-rolled steel sheet with a Si-depleted layer having a thickness of 0.3 μm or more, the steel sheet surface is depleted in Si, and therefore the formation of Si-based surface oxides on the steel sheet surface can be sufficiently suppressed. As a result, better paint film adhesion can be achieved.

[0088] From the viewpoint of further improving the coating adhesion, it is preferable to control the coiling temperature to 550°C or higher. By controlling the coiling temperature to 550°C or higher, it is possible to further promote the formation of internal oxides, which in turn makes it possible to make the Si-depleted layer thicker. As a result, it is possible to more significantly suppress the formation of Si-based surface oxides. There is no particular upper limit to the coiling temperature, but the coiling temperature may be, for example, 600°C or lower.

[0089] [Shot blasting process] In the steel sheet manufacturing method of this embodiment, the shot blasting step is a step of performing shot blasting to impart strain to the surface of the hot-rolled steel sheet. The treatment conditions in the shot blasting step are not particularly limited as long as they can bring the steel sheet surface into the above-mentioned specific strain state, i.e., the specific strain state in which the peak half-width of the (310) plane of the ferrite phase in the X-ray diffraction pattern is 0.5° or more. For example, the shot blasting may be performed using a shot material with an average particle size of 0.1 to 5.0 mm (for example, "TSH30" manufactured by IKK Shot Co., Ltd.) at a speed of 5 kg / m 2 The shot blasting treatment may be carried out with a shot amount of 50 kg / m or more. 2 It is preferable that the saturation is 100 kg / m or more. 2 More preferably, it is 200 kg / m or more. 2 The upper limit of the projection amount is not particularly limited, but it is, for example, 800 kg / m 2 The projection speed of the projection material is not particularly limited, but may be, for example, 10 to 150 m / sec. It should be noted that the blasting amount required for the purpose of removing scale (for example, the blasting amount used in the comparative examples of the present invention in the examples described below) cannot put the steel sheet surface into the above-mentioned specific strain state.

[0090] Furthermore, in this embodiment, a water-rinsing step may be carried out after the shot blasting treatment, in which the steel sheet surface is rinsed with water. For example, in this embodiment, a pickling step may be carried out after the shot blasting treatment, and then a water-rinsing step may be carried out. In the water-rinsing step, the steel sheet surface is preferably rinsed with water having an electrical conductivity of 80 mS / m or less. If such water having an electrical conductivity of 80 mS / m or less is used when rinsing the steel sheet surface, oxidation-reduction reactions are less likely to occur on the steel sheet surface during rinsing, and the generation of surface oxides that cause a decrease in chemical conversion treatability can be significantly suppressed. It is more preferable that the electrical conductivity of the water used to rinse the steel sheet surface is 60 mS / m or less.

[0091] [Pickling process] In the steel sheet manufacturing method of this embodiment, the pickling step is a step of pickling the hot-rolled steel sheet before or after the shot blasting step to remove surface oxides and internal oxides. The conditions for the pickling step are not particularly limited, and the pickling step may be carried out using a commonly used pickling solution under conditions appropriate for removing the surface oxides and internal oxides. The pickling may be carried out once, or may be carried out multiple times to ensure that the surface oxides and internal oxides are removed.

[0092] The basic steps of the manufacturing method of the steel sheet of this embodiment are as described above. The steel sheet of this embodiment, manufactured by the manufacturing method including the above steps, has a surface in the specific strain state described above, particularly due to the shot blasting step described above, i.e., a specific strain state in which the peak half-width of the (310) plane of the ferrite phase in the X-ray diffraction pattern is 0.5° or more. Therefore, during chemical conversion treatment, the steel sheet surface can be uniformly and finely etched, and good chemical conversion treatability can be achieved. As a result, the steel sheet of this embodiment can exhibit significantly improved paint adhesion.

[0093] The method for manufacturing a steel sheet according to this embodiment may further include, in addition to the above-described steps, any processing steps that are generally carried out in methods for manufacturing a steel sheet.

[0094] The present invention is not limited to the above-described embodiments or the following examples, and appropriate combinations, substitutions, modifications, etc. are possible within the scope that does not deviate from the object and intent of the present invention.

[0095] The present invention will be described in more detail below with reference to examples. However, the following examples are merely examples of the present invention, and the present invention is not limited to these examples in any way. [Example]

[0096] In the following examples, steel sheets according to the embodiments of the present invention were produced under various conditions, and the properties of the resulting steel sheets were investigated.

[0097] First, molten steel was cast by continuous casting to form a billet having the chemical composition shown in Table 1. The billet was cooled once, then reheated to 1200°C and hot rolled. The hot rolling was performed by rough rolling and finish rolling, with the finish rolling end temperature being 900 to 1050°C, the coiling temperature being 520°C or higher, and the finish rolling reduction being 30%. Next, the obtained hot-rolled steel sheets were subjected to a shot blasting treatment using TSH30 manufactured by IKK Shot Co., Ltd. as a shot material at a shot amount shown in Table 2. The steel sheets after the shot blasting treatment were pickled and then washed with wash water having an electrical conductivity shown in Table 2, thereby obtaining various steel sheets as examples or comparative examples.

[0098] [Table 1]

[0099] [Table 2]

[0100] [Table 3]

[0101] The various steel sheets obtained as described above were subjected to various measurements including Vickers hardness, XRD, EPMA, and XPS. The XRD measurements were performed under the conditions shown in Table 3. Furthermore, the paint adhesion of the various steel sheets was evaluated according to the following evaluation method. The results of these measurements and evaluations are shown in Tables 1 and 2. Note that the underlines next to various values ​​in Table 2 indicate values ​​outside the range of the present invention. Furthermore, the "-" next to the SiO2 thickness in the XPS measurement in Table 2 indicates that no SiO2 was detected.

[0102] [Evaluation of coating adhesion] The paint adhesion of the steel sheet was evaluated as follows. First, a 50 mm×50 mm sample of the steel plate produced as described above was subjected to zinc phosphate treatment as a chemical conversion treatment under the following conditions. Degreasing: The sample was immersed in a degreasing agent (Fine Cleaner E2083) at 40°C for 2 minutes, and then rinsed with water. Surface conditioning: The sample was immersed in a surface conditioning agent (Preparen Z) at room temperature for 30 seconds. Chemical conversion treatment: The steel was immersed in a zinc phosphate treatment agent (Palbond L3020) at 40°C for 2 minutes, then rinsed with water and dried.

[0103] Chemically treated steel samples were electrocoated (Powernics Excel 1200, manufactured by Nippon Paint Industrial Coating Co., Ltd.) at 30°C to a coating thickness of 16 μm. The coated samples were then baked at 170°C for 30 minutes. The electrocoated samples were then subjected to a saltwater immersion test (SDT). Specifically, the coated samples were immersed in a 5% NaCl solution at 55°C for 1000 hours. After the SDT test, the samples were removed and dried. A tape peel test was then performed on one side of the sample. The peeled tape was scanned, and the area ratio of the coating peeled was calculated by binarization using the image analysis software "ImageJ." The coating adhesion was evaluated as follows: AAAA: Peeling area rate less than 3% AAA: Peeling area rate less than 3-5% AA: Peeling area rate: 5 to less than 10% A: Peeling area rate 10-15% B: Peeling area rate over 15%

[0104] Steel sheets with paint film adhesion ratings of AAA, AA and A were evaluated as containing Ni, Cu and Sn and having excellent paint film adhesion.

[0105] As shown in Table 2, the steel sheets of Comparative Examples 30 to 34, in which the shot blasting amount was small and the peak half-width of the (310) plane of the ferrite phase in the X-ray diffraction pattern was less than 0.5°, did not have the above-mentioned specific strain state and therefore had poor paint film adhesion. On the other hand, the steel sheets of Examples 1 to 29 of the present invention, which had a large shot blasting amount and in which the peak half-width of the (310) plane of the ferrite phase in the X-ray diffraction pattern was 0.5° or more, had the above-mentioned specific strain state and therefore had excellent paint film adhesion.

[0106] Furthermore, as shown in Table 2, the comparison results of the steel sheets of Examples 1 to 29 of the present invention reveal that as the shot blasting amount increases, the half-value width of the peak of the (310) plane of the ferrite phase in the X-ray diffraction pattern also increases, and even better paint film adhesion can be achieved.

[0107] In addition, in Examples 16 and 22, in which the thickness of the silicon oxide was very thin, no peeling of the coating occurred, indicating that suppressing the amount of silicon oxide generated can provide even better coating adhesion.

Claims

1. A steel plate, The steel plate comprises, in mass%, C: 0.001 to 0.500%, Si: 0-3.00%, Mn: 0.10-3.00%, Al: 0.001-2.000%, Ni: 0.010 to 1.000%, Cu: 0.010-1.000%, Sn: 0.003-1.000%, P: 0.100% or less, S: 0.100% or less, N: 0.0150% or less, O: 0.0100% or less, Ti: 0 to 0.150%, Nb: 0 to 0.150%, B: 0 to 0.0100%, Mo: 0-1.000%, Cr: 0-1.000%, V: 0 to 0.150%, W: 0-1.000%, Hf: 0 to 0.050%, Mg: 0 to 0.050%, Zr: 0 to 0.500%, Ca: 0-0.050%, REM: 0-0.010%, As: 0 to 0.100%, Ir: 0-1.000%, Zn: 0 to 1.000%, and Remainder: Fe and impurities and a chemical composition consisting of A steel sheet characterized in that, in an X-ray diffraction pattern of the surface of the steel sheet, the peak half width of the (310) plane of the ferrite phase is 0.5° or more.

2. The steel sheet according to claim 1, wherein the peak half width is 1.0° or more.

3. The steel sheet according to claim 1, wherein the peak half width is 1.3° or more.

4. In the element distribution image of the cross section of the steel plate taken by an electron microprobe analyzer, The steel sheet according to any one of claims 1 to 3, characterized in that a specific element-containing portion containing at least one of the Ni, the Cu, and the Sn in a solid solution state is present in a region from the steel sheet surface to a depth position of 5 µm.

5. the chemical composition further comprises Si; The steel sheet according to any one of claims 1 to 3, characterized in that, in X-ray photoelectron spectroscopy measurement of the steel sheet surface, the thickness of silicon oxide is 10 nm or less.

6. A part, characterized in that it comprises the steel sheet according to any one of claims 1 to 3.

7. A component comprising the steel sheet according to claim 4.

8. A component comprising the steel sheet according to claim 5.

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