Fe-based electroplated steel sheets, electrodeposited coated steel sheets, automotive parts, manufacturing methods of electrodeposited coated steel sheets, and manufacturing methods of Fe-based electroplated steel sheets.

Abstract

This invention provides an Fe-based electroplated steel sheet with excellent chemical processing properties, excellent corrosion resistance after coating as evaluated by saltwater immersion tests, and excellent resistance to resistance weld cracking characteristics in welded sections when the sheet assembly is made of galvanized steel sheet. The aforementioned Fe-based electroplated steel sheet comprises a Si-containing cold-rolled steel sheet containing 0.5% to 3.0% by mass of Si, and an adhesion amount of 15.0 g / m² formed on at least one side of the Si-containing cold-rolled steel sheet, with each side having an adhesion amount of 15.0 g / m². 2 The above are Fe-based electroplated layers.

Description

Technical Field

[0001] This invention relates to an Fe-based electroplated steel sheet, an electrodeposited coated steel sheet, automotive parts, and a method for manufacturing the electrodeposited coated steel sheet. More specifically, it relates to an Fe-based electroplated steel sheet with excellent chemical treatment properties, excellent corrosion resistance after coating as evaluated by salt-temperature water immersion tests, and excellent resistance to resistance weld cracking characteristics of the welded parts, as well as an electrodeposited coated steel sheet, automotive parts, and a method for manufacturing the electrodeposited coated steel sheet using the Fe-based electroplated steel sheet. Background Technology

[0002] In recent years, from the perspective of protecting the Earth's environment, there has been a strong demand for improved fuel efficiency in automobiles. Furthermore, from the perspective of ensuring occupant safety in the event of a collision, there has also been a strong demand for enhanced vehicle safety. To meet these demands, it is necessary to achieve both lightweight and high-strength vehicle bodies, leading to active efforts in thinning the walls of cold-rolled steel sheets used in automotive components to achieve high strength. However, since most automotive components are manufactured by forming steel sheets, in addition to requiring high strength, excellent formability is also essential.

[0003] Various methods exist to improve the strength of cold-rolled steel sheets, but solid solution strengthening based on Si addition is a method that can achieve high strength without significantly compromising the formability of cold-rolled steel sheets. However, it is known that when a large amount of Si, especially more than 0.5% by mass, is added to cold-rolled steel sheets, Si-containing oxides such as SiO2 and Si-Mn composite oxides are formed on the steel sheet surface during heating the slab, hot rolling, or annealing after cold rolling. Since these Si-containing oxides significantly reduce the formability of the steel sheet, most high-strength cold-rolled steel sheets containing Si have poor formability. Furthermore, high-strength cold-rolled steel sheets containing a large amount of Si exhibit coating peeling in salt-temperature water immersion tests after electrodeposition coating, compared to ordinary steel sheets, resulting in deteriorated corrosion resistance after coating.

[0004] Furthermore, in the manufacturing of automotive parts, pressure-formed components are mostly assembled using resistance welding (spot welding). When resistance-welded components contain high-strength galvanized steel sheets, residual stress is generated near the weld joint during resistance welding. This causes the zinc coating to melt and diffuse into the grain boundaries, leading to liquid metal embrittlement (LME), which may cause grain boundary cracks (LME cracks) in the steel sheet. Especially when welding is performed with the welding electrodes at an angle relative to the steel sheet, residual stress may increase, resulting in cracks. It is believed that as the strength of the steel sheet increases, residual stress increases, thus potentially leading to LME cracks. Even if the high-strength steel sheet is not galvanized, if the steel sheet to be welded is galvanized, its galvanized layer melts, thus causing LME cracks even in steel sheets without a galvanized coating.

[0005] Based on the above, we seek high-strength steel plates with excellent chemical treatment properties, corrosion resistance after coating, and resistance to resistance weld cracking characteristics of welded parts (hereinafter also referred to as "resistance weld cracking characteristics of welded parts") when the plate assembly is made of galvanized steel sheet.

[0006] Previously, improvement measures to address the aforementioned problems have been reported. For example, Patent Document 1 proposes a method for manufacturing high-strength cold-rolled steel sheets with excellent processing properties by heating the slab at a temperature of 1200°C or higher during hot rolling, removing oxide scale under high pressure, grinding the surface of the hot-rolled steel sheet with an abrasive nylon brush before pickling, and pickling twice in a 9% hydrochloric acid bath to reduce the Si concentration on the steel sheet surface. Patent Document 2 discloses a steel sheet having an internal oxide layer from the surface of the base material to a depth of 5.0 μm or more, where at least a portion of the grain boundaries are covered by oxides, and the grain boundary coverage of the oxides in the region from the surface of the base material to a depth of 5.0 μm is 60% or more. Furthermore, Patent Document 3 discloses a steel sheet in which cold-rolled steel sheets are annealed in a non-oxidizing atmosphere and then pickled to dissolve 0.5 g / m³ of the oxides. 2 Above, the adhesion amount is 1-5 g / m 2 Electroplating of Zn-Fe alloys.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent No. 3990349

[0010] Patent Document 2: Japanese Patent No. 6388099

[0011] Patent Document 3: Japanese Patent Application Publication No. 2015-89946 Summary of the Invention

[0012] However, in the high-strength cold-rolled steel sheet described in Patent Document 1, even if the Si concentration on the steel sheet surface is reduced before cold rolling, and Si-containing oxides are formed on the steel sheet surface by annealing after cold rolling, it is not expected to improve the corrosion resistance after coating. Furthermore, in the steel sheet described in Patent Document 2, the grain boundary adhesion is weak, and the corrosion resistance after coating evaluated by the salt-temperature water immersion test becomes insufficient. Moreover, in the steel sheet described in Patent Document 3, although the chemical treatment and corrosion resistance after coating are improved, no mention is made of the issue of resistance to resistance weld cracking characteristics.

[0013] Thus, in a large number of high-strength cold-rolled steel sheets containing Si (hereinafter also referred to as Si-containing cold-rolled steel sheets), it is difficult to consistently meet the high standards of chemical processing properties, corrosion resistance after coating, and resistance to resistance welding cracks in welded parts. In reality, steel sheets that consistently meet these properties at a high level have not yet been developed.

[0014] The present invention was made in view of the above-mentioned problems with Si-containing cold-rolled steel sheets, and its object is to provide a steel sheet with excellent chemical processing properties, excellent corrosion resistance after coating as evaluated by salt temperature water immersion test, and excellent resistance to resistance weld cracking characteristics of the welded parts.

[0015] To address the aforementioned issues, the inventors conducted repeated and in-depth research. Their findings revealed that, in order to consistently achieve high levels of performance in terms of chemical treatment properties, post-coating corrosion resistance, and resistance to resistance weld cracking in welded sections, it is crucial to apply an adhesion amount of 15.0 g / m² per single side to the surface of the continuously annealed Si-containing cold-rolled steel sheet after cold rolling. 2 The above process forms an Fe-based electroplating layer, producing an Fe-based electroplated steel sheet. By forming an Fe-based electroplating layer on the surface of the steel sheet, the Si-containing oxides formed on the surface of the steel sheet during annealing are completely coated, thereby improving the chemical processing properties and corrosion resistance after coating. Furthermore, the inventors discovered that by achieving an adhesion amount of 15.0 g / m² per single side of the Si-containing cold-rolled steel sheet... 2 The above forms a soft Fe-based electroplated layer, which alleviates the stress applied to the steel plate surface during welding. Furthermore, the Fe-based electroplated layer acts as a Si-deficient solid solution layer to suppress the reduction in toughness caused by Si solid solution, thereby improving the resistance to resistance welding cracks of the welded part, thus completing the present invention.

[0016] This invention was made based on the above circumstances. That is, the main components of this invention are as follows.

[0017] [1] An Fe-based electroplated steel sheet, comprising:

[0018] Si-containing cold-rolled steel sheet, containing 0.5% to 3.0% by mass of Si; and

[0019] An Fe-based electroplated layer is formed on at least one side of the aforementioned Si-containing cold-rolled steel sheet, with an adhesion amount of 15.0 g / m² on each side. 2 above.

[0020] [2] According to the Fe-based electroplated steel sheet described in [1] above, the proportion of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet to be integrated in terms of crystal orientation is less than 50% at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet.

[0021] [3] According to the Fe-based electroplated steel sheet described in [1] or [2] above, the adhesion amount of the Fe-based electroplated layer on each single side is 25 g / m. 2 above.

[0022] [4] The Fe-based electroplated steel sheet according to any one of [1] to [3] above, wherein the Si-containing cold-rolled steel sheet has the following composition: in addition to the Si above, it contains, by mass %, C: less than 0.8%, Mn: 1.0% to 12.0%, P: less than 0.1%, S: less than 0.03%, N: less than 0.010% and Al: less than 1.0%, and the remainder consists of Fe and unavoidable impurities.

[0023] [5] The Fe-based electroplated steel sheet according to [4] above, wherein the above composition further contains, by mass %, one or more of the following: B: less than 0.005%, Ti: less than 0.2%, Cr: less than 1.0%, Cu: less than 1.0%, Ni: less than 1.0%, Mo: less than 1.0%, Nb: less than 0.20%, V: less than 0.5%, Sb: less than 0.200%, Ta: less than 0.1%, W: less than 0.5%, Zr: less than 0.1%, Sn: less than 0.20%, Ca: less than 0.005%, Mg: less than 0.005%, and REM: less than 0.005%.

[0024] [6] The Fe-based electroplated steel sheet according to any one of [1] to [5] above, wherein the Fe-based electroplated layer has the following composition: containing one or more elements selected from B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V and Co in total of less than 10% by mass, and the remainder is composed of Fe and unavoidable impurities.

[0025] [7] An Fe-based electroplated steel sheet, comprising a cold-rolled steel sheet and an adhesion amount of 15.0 g / m² formed on at least one side of the cold-rolled steel sheet. 2 The above are Fe-based electroplated layers.

[0026] Here, the aforementioned cold-rolled steel sheet is the following: a test piece cut with the rolling right angle as the long side, measuring 50×150mm, and a hot-dip galvanized layer of the same size cut out on each side have an adhesion amount of 50g / m². 2 Hot-dip galvanized steel sheets are stacked to form a plate assembly.

[0027] Next, using a servo motor-driven single-phase AC (50Hz) resistance welding machine, with the plate assembly tilted at 5° relative to the electrode (6mm front diameter) of the welding machine, the plate assembly was subjected to a pressure of 3.5kN, a holding time of 0.1 seconds, and the thickness of the cold-rolled steel sheet was set to t, with the weld nugget diameter being [missing information]. Plate assemblies with welded sections are produced by resistance welding under specific welding current and welding time conditions.

[0028] Next, the aforementioned plate assembly with the welded portion was cut in half, including the welded portion. When the cross-section of the welded portion was observed using an optical microscope (200x), a crack with a length of more than 0.1 mm was observed.

[0029] [8] An electrodeposited coated steel sheet, wherein the Fe-based electroplated steel sheet described in any one of [1] to [7] above further has a chemical formation film formed in contact with the Fe-based electroplated layer and an electrodeposited coating film formed on the chemical formation film.

[0030] [9] An automotive component is made of at least a portion of the electrodeposited coated steel sheet described above [8].

[0031]

[10] A method for manufacturing an electrodeposited coated steel sheet, comprising the following steps:

[0032] The chemical forming process involves performing a chemical forming process on the Fe-based electroplated steel sheet described in any one of [1] to [7] above without performing any additional plating process, thereby obtaining a chemically formed steel sheet having a chemically formed coating in contact with the Fe-based electroplated layer; and

[0033] In the electrodeposition coating process, the above-mentioned chemically treated steel sheet is subjected to electrodeposition coating treatment to obtain an electrodeposition coated steel sheet with an electrodeposition coating film formed on the above-mentioned chemically treated film.

[0034]

[11] A method for manufacturing Fe-based electroplated steel sheet, wherein a Si-containing cold-rolled steel sheet containing 0.5% to 3.0% by mass of Si is annealed to produce a Si-containing cold-rolled steel sheet.

[0035] Next, the aforementioned Si-containing cold-rolled steel sheet was subjected to Fe-based electroplating to obtain a coating with an adhesion amount of 15.0 g / m² on at least one side. 2 The above refers to Fe-based electroplated steel sheets with Fe-based electroplating layers.

[0036]

[12] A method for manufacturing Fe-based electroplated steel sheet, wherein a cold-rolled steel sheet is annealed before annealing to produce a cold-rolled steel sheet.

[0037] Next, the above-mentioned cold-rolled steel sheet was subjected to Fe-based electroplating to obtain a coating with an adhesion amount of 15.0 g / m² on at least one side. 2 The above refers to Fe-based electroplated steel sheets with Fe-based electroplating layers.

[0038] Here, the aforementioned cold-rolled steel sheet is the following: a test piece cut with the rolling right angle as the long side, measuring 50×150mm, and a hot-dip galvanized layer of the same size cut out on each side have an adhesion amount of 50g / m². 2 Hot-dip galvanized steel sheets are stacked to form a plate assembly.

[0039] Next, using a servo motor-driven single-phase AC (50Hz) resistance welding machine, with the plate assembly tilted at 5° relative to the electrode (6mm front diameter) of the welding machine, the plate assembly was subjected to a pressure of 3.5kN, a holding time of 0.1 seconds, and the thickness of the cold-rolled steel sheet was set to t, with the weld nugget diameter being [missing value]. Plate assemblies with welded sections are produced by resistance welding under specific welding current and welding time conditions.

[0040] Next, the plate assembly with the welded part was cut in half, including the welded part. When the cross-section of the welded part was observed using an optical microscope (200x), cracks with a length of more than 0.1 mm were observed.

[0041]

[13] The method for manufacturing Fe-based electroplated steel sheet according to

[11] or

[12] above, wherein the Fe-based electroplating is carried out using an Fe-based electroplating bath, wherein the Fe-based electroplating bath contains one or more elements selected from B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V and Co in such a way that the total content of the following elements is less than 10% by mass.

[0042] According to the present invention, a Si-containing cold-rolled steel sheet with excellent chemical processing properties, excellent corrosion resistance after coating as evaluated by salt temperature water immersion test, and excellent resistance to resistance weld cracking characteristics of the welded part when the sheet assembly object is galvanized steel sheet, and an automotive part using the Si-containing cold-rolled steel sheet, can be provided. Attached Figure Description

[0043] Figure 1 This is a diagram showing a general outline of the cross-section of an Fe-based electroplated steel sheet.

[0044] Figure 2 This is an image showing an observation of the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet in Invention Example No. 43.

[0045] Figure 3 This is an image showing an observation of the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet of Invention Example No. 46.

[0046] Figure 4 These are (a) a perspective view and (b) an A-A cross-sectional view of an observation sample used to determine the proportion of crystal orientation integration.

[0047] Figure 5 The figures are used to illustrate the evaluation method for the proportion of crystal orientation integration. (a) is a figure in which the boundary line is drawn at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet in the SIM image. (b) is a figure in which the boundary line and the decision region are drawn in the binarized image. (c) is an enlarged view of the part enclosed by the box in (b).

[0048] Figure 6 The image shown in Invention Example No. 43 illustrates the drawing of the boundary line and determination region after binarization processing of the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet.

[0049] Figure 7 The image shown in Invention Example No. 46 illustrates the drawing of the boundary line and determination region after binarization processing of the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet.

[0050] Figure 8 (a) is a diagram illustrating the evaluation method for the resistance to cracking characteristics of welded parts. In (b), the upper diagram is a top view of the welded plate assembly for the evaluation, and the lower diagram is a B-B sectional view of the upper diagram. Detailed Implementation

[0051] The aforementioned LME cracks can be broadly classified into "cracks generated on the surface in contact with the electrode (hereinafter, surface cracks)" and "cracks generated near the ductile metal ring region between steel plates (hereinafter, internal cracks)." It is known that surface cracks are easily generated in resistance welding with a high current range that produces sputtering; however, surface cracks can be suppressed by setting the current to an appropriate range that does not produce sputtering. On the other hand, internal cracks can still occur even when the current during resistance welding is within an appropriate range that does not produce sputtering. Furthermore, surface cracks are easily detected by visual inspection during the manufacturing process, while internal cracks are difficult to detect by visual inspection. For these reasons, internal cracks are a particularly significant problem in LME cracking. If resistance welding is performed with the welding electrode at an angle relative to the steel plate, residual stress may increase, leading to internal cracks. It is believed that residual stress increases with the increase in the strength of the steel plate, and therefore, internal cracks may occur with the increase in the strength of the steel plate. In this disclosure, it is possible to improve resistance welding crack resistance characteristics, and in particular, to improve the characteristics of preventing such internal cracks.

[0052] The embodiments of the present invention will be described below.

[0053] Furthermore, in the following description, the content of each element in the composition of Si-containing cold-rolled steel sheet and the content of each element in the coating composition are all expressed in "mass%" unless otherwise specified. Additionally, in this specification, the numerical range indicated by "~" refers to the values ​​listed before and after "~" as the lower and upper limits. Furthermore, in this specification, "high strength" steel sheet means that the tensile strength TS of the steel sheet measured according to JIS Z 2241 (2011) is 590 MPa or higher.

[0054] [Implementation Method 1]

[0055] Figure 1 This section shows a summary of the cross-section of the Fe-based electroplated steel sheet 1 according to this embodiment. (As shown...) Figure 1 As shown, the Fe-based electroplated steel sheet 1 has an Fe-based electroplated layer 3 on at least one side of the Si-containing cold-rolled steel sheet 2. First, the composition of the Si-containing cold-rolled steel sheet will be explained.

[0056] Si: 0.5%–3.0%

[0057] Si (Si) has a significant effect on increasing the strength of steel through solid solution without significantly impairing processability (solution strengthening energy), making it an effective element for achieving high strength in steel sheets. On the other hand, Si negatively impacts chemical treatment properties, post-coating corrosion resistance, and resistance to resistance weld cracking in welded sections. When adding Si to achieve high strength in steel sheets, an addition of 0.5% or more is required. Furthermore, if Si is less than 0.5%, it does not particularly cause problems with chemical treatment properties and resistance to resistance weld cracking in welded sections, and the present invention is not necessary. On the other hand, if the Si content exceeds 3.0%, hot-rolling and cold-rolling properties are significantly reduced, adversely affecting productivity or leading to a decrease in the ductility of the steel sheet itself. Therefore, Si is added in the range of 0.5% to 3.0%. The Si content is preferably 0.7% or more, more preferably 0.9% or more. Furthermore, the Si content is preferably 2.5% or less, more preferably 2.0% or less, and even more preferably 1.7% or less.

[0058] The Si-containing cold-rolled steel sheet involved in this embodiment requires that it contain Si within the above-mentioned range. Other components are permissible as long as they are within the composition range of ordinary cold-rolled steel sheets, and are not particularly limited. Among them, when the Si-containing cold-rolled steel sheet of this embodiment has a high strength of 590 MPa or more tensile strength (TS), the following composition is preferred.

[0059] C: Below 0.8% (excluding 0%)

[0060] C improves workability by forming martensite and other structures within the steel. Good weldability is achieved when C is present; therefore, the C content is preferably 0.8% or less, more preferably 0.30% or less. There is no particular limitation on the lower limit of C, but to obtain good workability, the C content is preferably more than 0%, more preferably 0.03% or more, and even more preferably 0.05% or more.

[0061] Mn: 1.0%~12.0%

[0062] Mn is an element that enhances the strength of steel through solid solution strengthening, improves hardenability, and promotes the formation of retained austenite, bainite, and martensite. This effect is achieved by adding 1.0% or more of Mn. Conversely, if the Mn content is 12.0% or less, the aforementioned effects are obtained without increasing costs. Therefore, the Mn content is preferably 1.0% or more, more preferably 12.0% or less. The Mn content is more preferably 1.3% or more, further preferably 1.5% or more, and most preferably 1.8% or more. Furthermore, the Mn content is more preferably 3.5% or less, more preferably 3.3% or less.

[0063] P: Less than 0.1% (excluding 0%)

[0064] By suppressing the content of phosphorus (P), the decrease in weldability can be prevented. Furthermore, it prevents P segregation at grain boundaries, thus preventing deterioration in ductility, flexibility, and toughness.

[0065] Furthermore, adding a large amount of phosphorus (P) promotes the ferrite phase transformation, thereby increasing the crystal grain size. Therefore, the P content is preferably below 0.1%. There is no particular lower limit for the P content; due to limitations in production technology, it can exceed 0% and can be above 0.001%.

[0066] S: Less than 0.03% (excluding 0%)

[0067] The sulfur content is preferably 0.03% or less, more preferably 0.02% or less. By suppressing the sulfur content, it is possible to prevent a decrease in weldability and a decrease in ductility at heat, suppress hot cracking, and significantly improve surface properties. Furthermore, by suppressing the sulfur content, coarse sulfides are formed as impurity elements, which can prevent a decrease in the ductility, bendability, and tensile flangeability of the steel sheet. These problems are significant when the sulfur content exceeds 0.03%, and it is preferable to minimize the sulfur content as much as possible. There is no particular lower limit for the sulfur content; due to limitations in production technology, it can exceed 0% and can be 0.0001% or more.

[0068] N: Less than 0.010% (excluding 0%)

[0069] The nitrogen (N) content is preferably 0.010% or less. By setting the N content to 0.010% or less, N forms coarse nitrides with Ti, Nb, and V at high temperatures, preventing damage to the high strength effect of the steel sheet resulting from the addition of Ti, Nb, and V. Furthermore, setting the N content to 0.010% or less also prevents a decrease in toughness. Moreover, setting the N content to 0.010% or less prevents slab cracks and surface defects during hot rolling. The N content is preferably 0.005% or less, more preferably 0.003% or less, and even more preferably 0.002% or less. There is no particular limitation on the lower limit of the N content; due to limitations in production technology, it can exceed 0% and can be 0.0005% or more.

[0070] A1: Less than 1.0% (excluding 0%)

[0071] Al is thermodynamically the most readily oxidized material, thus oxidizing before Si and Mn. This inhibits oxidation of the outermost layer of Si and Mn steel sheets while promoting oxidation within the Si and Mn steel sheets. This effect is achieved when the Al content is 0.01% or higher. On the other hand, if the Al content exceeds 1.0%, the cost increases. Therefore, when added, the Al content is preferably 1.0% or less. More preferably, it is 0.1% or less. The lower limit for Al is not particularly limited; it can exceed 0% and can be 0.001% or more.

[0072] The composition may further contain one or more of the following: B: less than 0.005%, Ti: less than 0.2%, Cr: less than 1.0%, Cu: less than 1.0%, Ni: less than 1.0%, Mo: less than 1.0%, Nb: less than 0.20%, V: less than 0.5%, Sb: less than 0.200%, Ta: less than 0.1%, W: less than 0.5%, Zr: less than 0.1%, Sn: less than 0.20%, Ca: less than 0.005%, Mg: less than 0.005%, and REM: less than 0.005%.

[0073] B: Below 0.005%

[0074] Boron (B) is an effective element for improving the hardenability of steel. To improve hardenability, the amount of B is preferably 0.0003% or more, more preferably 0.0005% or more. However, if B is added excessively, the formability decreases, so the amount of B is preferably 0.005% or less.

[0075] Ti: below 0.2%

[0076] Ti is effective for precipitation strengthening of steel. There is no particular limit to the lower limit of Ti, but it is preferable to be 0.005% or more in order to achieve the effect of strength adjustment. However, if Ti is added excessively, the hard phase becomes too large and the formability decreases. Therefore, when Ti is added, the amount of Ti is preferably 0.2% or less, and more preferably 0.05% or less.

[0077] Cr: less than 1.0%

[0078] The Cr content is preferably 0.005% or more. By setting the Cr content to 0.005% or more, hardenability can be improved, and the balance between strength and ductility can be enhanced. When added, from the viewpoint of preventing increased costs, the Cr content is preferably 1.0% or less.

[0079] Cu: below 1.0%

[0080] The Cu content is preferably 0.005% or more. By setting the Cu content to 0.005% or more, the formation of the residual γ phase can be promoted. In addition, from the viewpoint of preventing cost increases, the Cu content is preferably 1.0% or less when adding Cu.

[0081] Ni: below 1.0%

[0082] The Ni content is preferably 0.005% or more. By setting the Ni content to 0.005% or more, the formation of the residual γ phase can be promoted. In addition, when Ni is added, from the viewpoint of preventing cost increases, the Ni content is preferably 1.0% or less.

[0083] Mo: 1.0% or less

[0084] The Mo content is preferably 0.005% or more. By setting the Mo content to 0.005% or more, the strength adjustment effect can be obtained. In addition, when adding Mo, from the viewpoint of preventing cost increase, the Mo content is preferably 1.0% or less.

[0085] Nb: below 0.20%

[0086] The strength is improved by containing 0.005% or more of Nb. Furthermore, when Nb is present, from the viewpoint of preventing cost increases, the Nb content is preferably 0.20% or less.

[0087] V: Below 0.5%

[0088] The strength is improved by containing 0.005% or more of V. Furthermore, from the viewpoint of preventing cost increases, the amount of V is preferably 0.5% or less when V is present.

[0089] Sb: below 0.200%

[0090] Sb can be included from the viewpoint of suppressing nitriding, oxidation, or decarburization in the tens of micrometers of the steel plate surface caused by oxidation. By suppressing nitriding and oxidation on the steel plate surface, Sb prevents a decrease in the amount of martensite formed on the steel plate surface, thereby improving the fatigue properties and surface quality of the steel plate. To achieve this effect, the Sb content is preferably 0.001% or more. On the other hand, to obtain good toughness, the Sb content is preferably 0.200% or less.

[0091] Ta: below 0.1%

[0092] Ta increases strength by containing 0.001% or more. Furthermore, when Ta is present, from the viewpoint of preventing increased costs, the amount of Ta is preferably 0.1% or less.

[0093] W: below 0.5%

[0094] W increases strength by containing 0.005% or more. Furthermore, when W is present, from the viewpoint of preventing cost increases, the amount of W is preferably 0.5% or less.

[0095] Zr: below 0.1%

[0096] Zr content of 0.0005% or more results in increased strength. Furthermore, when Zr is present, from the viewpoint of preventing increased costs, the Zr content is preferably 0.1% or less.

[0097] Sn: below 0.20%

[0098] Sn is an effective element for inhibiting denitrification, deboration, and other processes that reduce the strength of steel. To achieve this effect, the Sn content is preferably 0.002% or more. On the other hand, to obtain good impact resistance, the Sn content is preferably 0.20% or less.

[0099] Ca: below 0.005%

[0100] Ca, by containing 0.0005% or more, suppresses the morphology of sulfides, thereby improving ductility and toughness. Furthermore, from the viewpoint of achieving good ductility, the Ca content is preferably 0.005% or less.

[0101] Mg: less than 0.005%

[0102] By containing 0.0005% or more of Mg, the morphology of sulfides can be suppressed, thereby improving ductility and toughness. Furthermore, from the viewpoint of preventing cost increases, the amount of Mg is preferably 0.005% or less when Mg is present.

[0103] REM: below 0.005%

[0104] REM, by containing 0.0005% or more, can control the morphology of sulfides and improve ductility and toughness. Furthermore, from the viewpoint of obtaining good toughness, the amount of REM is preferably 0.005% or less when it contains REM.

[0105] In the Si-containing cold-rolled steel sheet of this embodiment, the remaining components other than those mentioned above are Fe and unavoidable impurities.

[0106] Next, the Fe-based electroplating layer formed on at least one side of the Si-containing cold-rolled steel sheet described above will be explained.

[0107] Fe-based electroplating layer: 15.0 g / m 2 above

[0108] With an adhesion amount of 15.0 g / m² per single side. 2 The above-mentioned Fe-based electroplating layer can cover the Si-containing oxide layer formed on the steel plate surface during annealing, thereby improving the chemical treatment properties and corrosion resistance after coating. Furthermore, the Fe-based electroplating layer is considered soft, thus mitigating the stress applied to the steel plate surface during welding, reducing residual stress in the resistance weld, and improving the resistance weld crack resistance characteristics of the weld, particularly enhancing the prevention of internal cracks (stress mitigation effect). Moreover, the Fe-based electroplating layer acts as a Si-deficient layer, thus suppressing the reduction in weld toughness caused by Si solid solution, resulting in a steel plate with excellent resistance weld crack resistance characteristics. The coating thickness is 15.0 g / m² per single side. 2The mechanism by which Fe-based electroplating improves the resistance to resistance weld cracking in welded sections is not yet clear. However, it is believed that when the amount of dissolved Si on the steel plate surface is high, the toughness of the welded section decreases, and the resistance to resistance weld cracking in the welded section deteriorates. Conversely, it is believed that when there is a certain amount of Fe-based electroplating on the steel plate surface, this Fe-based electroplating acts as a Si-deficient layer, reducing the amount of Si dissolved in the welded section. Therefore, the reduction in toughness of the welded section is suppressed, and the resistance to resistance weld cracking in the welded section, especially the ability to prevent internal cracks, is improved (toughness reduction suppression effect). In addition, by applying the Fe-based electroplating after annealing, the proportion of the Fe-based electroplating and the Si-containing cold-rolled steel plate becoming integrated at the interface can be reduced. Therefore, it is believed that the ability to prevent dissolved zinc plating from penetrating into the grain boundaries of the Si-containing cold-rolled steel plate via the grain boundaries of the Fe-based electroplated steel plate can be improved, particularly the ability to prevent internal cracks (zinc grain boundary intrusion suppression effect). The contributions of these Fe-based electroplating layers to stress mitigation, toughness reduction inhibition, and zinc grain boundary intrusion inhibition in resistance weld crack resistance are complex and quantitatively unclear, but they are believed to improve resistance weld crack resistance through a composite effect. If the adhesion amount of the Fe-based electroplating layer per single side is 3 g / m... 2 The above results in excellent chemical treatment properties and corrosion resistance after coating. However, to improve the resistance to resistance welding cracking characteristics of the welded parts, the adhesion amount of the Fe-based electroplating layer per single side needs to be set to 15.0 g / m². 2 The above. There is no particular upper limit to the amount of Fe-based electroplated coating adhering to each single side. From a cost perspective, it is preferable to set the amount of Fe-based electroplated coating adhering to each single side to 60 g / m². 2 The following applies: the preferred adhesion amount of the Fe-based electroplated layer is greater than 15 g / m². 2 More preferably 17g / m 2 The above is further preferred to be 20g / m 2 The optimal value is 25g / m³. 2 Above, or 30g / m 2 The above describes the preferred method for Fe-based electroplated steel sheets, which involves having Fe-based electroplating layers on both the front and back sides of a Si-containing cold-rolled steel sheet. The Fe-based electroplating layer is set to an adhesion amount of 25 g / m². 2 The welded parts exhibit particularly good resistance to resistance welding cracks, especially in preventing internal cracks.

[0109] It should be noted that the thickness of the Fe-based electroplated layer was measured as follows. A 10×15mm sample was taken from the Fe-based electroplated steel sheet and embedded in resin to create a cross-section of the embedded sample. Using a scanning electron microscope (SEM), observations were made at three arbitrary locations on this cross-section at an accelerating voltage of 15kV and magnifications ranging from 2000 to 10000 times, depending on the thickness of the Fe-based electroplated layer. The average thickness at the three fields of view was multiplied by the specific gravity of iron to calculate the amount of Fe-based electroplated layer deposited per side.

[0110] As Fe-based electroplating layers, in addition to pure Fe, alloy plating layers such as Fe-B alloys, Fe-C alloys, Fe-P alloys, Fe-N alloys, Fe-O alloys, Fe-Ni alloys, Fe-Mn alloys, Fe-Mo alloys, and Fe-W alloys can be used. The composition of Fe-based electroplating layers is not particularly limited, but it typically consists of one or more elements selected from B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co, totaling no more than 10% by mass, with the remainder being Fe and unavoidable impurities. By setting the amount of elements other than Fe to a total of no more than 10% by mass, it is possible to prevent a decrease in electrolysis efficiency and form Fe-based electroplating layers at low cost. In the case of Fe-C alloys, the C content is preferably 0.08% by mass or less.

[0111] Furthermore, the Fe-based electroplated steel sheet involved in this embodiment preferably does not have any coating other than Fe-based electroplating on its surface. By ensuring that the Fe-based electroplated steel sheet does not have any coating other than Fe-based electroplating on its surface, it is possible to provide components that do not require excessive rust prevention from galvanized steel sheets at a low cost, or components that can be used in environments with mild corrosion and where excessive rust prevention is not required.

[0112] At the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet, the proportion of crystal orientation integration between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet is not particularly limited and can be 50% or less. In this embodiment, the Si-containing cold-rolled steel sheet is annealed before Fe-based electroplating, and no further annealing is performed. Therefore, the proportion of crystal orientation integration between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet is low. Therefore, it is expected that the molten galvanized steel sheet can be prevented from penetrating the grain boundaries of the Si-containing cold-rolled steel sheet via the grain boundaries of the Fe-based electroplated steel sheet, and it is even expected that the resistance to resistance weld cracking characteristics of the welded part, especially the characteristics of preventing internal cracks, can be further improved. In this embodiment, the proportion of crystal orientation integration between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet at the interface can be 30% or less, or 25% or less.

[0113] Here, at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet, the proportion of crystal orientation integration between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet was determined as follows. A 10×10mm sample was taken from the Fe-based electroplated steel sheet. The sample was processed at any one location using a focused ion beam (FIB) device to form a 45° cross-section at one location. This cross-section had a width of 30μm in the rolling direction (parallel to the right angle direction of the steel sheet's rolling and perpendicular to the steel sheet surface), and a length of 50μm in the 45° direction relative to the T-section. This cross-section was used for observation. Figure 4 A summary of the sample used for this observation is shown. Figure 4 (a) is a three-dimensional view of the sample used for observation. Figure 4 (b) is Figure 4 A-A cross-sectional view of the sample for observation is shown in (a). Next, the central part of the 45° section of the sample for observation was observed at 5000x magnification using a Scanning Ion Microscope (SIM), and an 8-bit SIM image with a width of 1024 × height of 943 pixels was captured. Based on the SIM images taken at each of the three locations, the proportion of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet at the interface was determined according to the following formula (1). In addition, the decimal places were rounded to the nearest whole number.

[0114] (The proportion of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet at the interface where the crystal orientation of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet are integrated) = (The length of the part where the crystal orientation of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet are integrated at the interface) ÷ (The length of the interface in the field of view) × 100……(1)

[0115] Furthermore, at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet, whether the crystal orientations of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet are integrated is determined through image processing. Figure 5 The evaluation method for the proportion of crystal orientation integration is explained. First, as... Figure 5As shown in (a), a boundary line B was drawn at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet in the aforementioned SIM image using a scanning electron microscope (SIM). Next, the SIM image and the image with the drawn boundary line were processed separately to create an image. Specifically, firstly, the grain boundaries were emphasized in the 8-bit SIM image (1024 pixels wide × 943 pixels high) using a Sobel filter. Then, the image with emphasized grain boundaries was smoothed using a Gaussian filter (radius (R): 10 pixels). Next, the smoothed image was binarized (threshold: 17). Then, the boundary line B of the image with the drawn interface was transferred to the binarized image. Subsequently, as... Figure 5 As shown in (b), in the binarized image, along the decision region with a width of 40 pixels centered on the boundary line B ( Figure 5 The boundary line B on the binarized image (the region enclosed by L1 and L2 in (b)) is drawn. The total length of boundary line B, representing the length of the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet (the white and black boundary in the binarized image) where no Fe-based electroplated layer exists within the determination region, is considered as the length of the crystal orientation integration. Here, the total length of the boundary line representing the length of the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet where no Fe-based electroplated layer exists within the determination region is calculated as follows. For illustration, Figure 5 (c) shows the result of Figure 5 A magnified view of the area enclosed by the box in (b). First, as... Figure 5 As shown in (c), the two normal lines passing through boundary line B (in) Figure 5 In (c), l1 and l2, and l3 and l4), searching the entire decision region can divide the decision region into approximately rectangular areas that contain only parts of either white or black. Next, the maximum distances between the intersections of the boundary line of this part and the two normals in the entire decision region are summed, and this summation is taken as the length of the boundary line, which includes the length of the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet that does not exist within the decision region.

[0116] Figure 2 A SIM image of the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet in Invention Example No. 43, which is described later, is shown in Figure 6. The image after binarization of the SIM image as described above is shown in Figure 6. In Invention Example No. 43, at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet, the proportion of crystal orientation integration between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet is 6%. Furthermore, Figure 3The image shown is a SIM image of the interface between an Fe-based electroplated layer and a Si-containing cold-rolled steel sheet, according to Invention Example No. 46 of the embodiments described later. The image after binarization of the SIM image as described above is shown below. Figure 7 In Invention Example No. 46, at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet, the proportion of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated in terms of crystal orientation is 10%.

[0117] <Manufacturing Method of Fe-based Electroplated Steel Sheet>

[0118] Next, the manufacturing method of Fe-based electroplated steel sheets will be explained.

[0119] One embodiment relates to a method for manufacturing Fe-based electroplated steel sheets, which involves annealing a Si-containing cold-rolled steel sheet containing 0.5% to 3.0% by mass of Si before annealing to produce a Si-containing cold-rolled steel sheet.

[0120] Next, the aforementioned Si-containing cold-rolled steel sheet was subjected to Fe-based electroplating to obtain a coating with an adhesion amount of 15.0 g / m² on at least one side. 2 The above refers to Fe-based electroplated steel sheets with Fe-based electroplating layers.

[0121] First, a Si-containing pre-annealing cold-rolled steel sheet containing 0.5% to 3.0% by mass of Si is manufactured. The manufacturing method for the Si-containing pre-annealing cold-rolled steel sheet can follow the usual method for manufacturing cold-rolled steel sheets. In one example, the Si-containing pre-annealing cold-rolled steel sheet is manufactured by hot-rolling a steel billet having the above-mentioned composition to produce a hot-rolled sheet, then pickling the hot-rolled sheet, and finally cold-rolling the hot-rolled sheet to produce the Si-containing pre-annealing cold-rolled steel sheet.

[0122] Next, before performing Fe-based electroplating, the Si-containing cold-rolled steel sheet is annealed to obtain a Si-containing cold-rolled steel sheet. The annealing conditions are not particularly limited; in one example, an annealing process is performed in a reducing atmosphere with a dew point below 30°C and a hydrogen concentration of 1.0 vol% to 30.0 vol%, held at a temperature range of 650°C to 900°C for 30 to 600 seconds, followed by cooling, to obtain the Si-containing cold-rolled steel sheet. The annealing process is performed to increase the strength of the steel sheet by removing the strain caused by the rolling process and allowing the microstructure to recrystallize.

[0123] Hydrogen concentration: 1.0 vol% to 30.0 vol%

[0124] In one example, the annealing process can be carried out in a reducing atmosphere with a hydrogen concentration of 1.0 vol% to 30.0 vol%. Hydrogen is necessary to activate the steel sheet surface and suppress the oxidation of Fe on the surface of the cold-rolled steel sheet before Si-containing annealing. If the hydrogen concentration is 1.0 vol% or higher, the Fe on the steel sheet surface will oxidize, thereby preventing the deterioration of the adhesion of the Fe-based electroplating layer. Therefore, the annealing process is preferably carried out in a reducing atmosphere with a hydrogen concentration of 1.0 vol% or higher, more preferably in a reducing atmosphere with a hydrogen concentration of 2.0 vol% or higher. There is no particular upper limit to the hydrogen concentration in the annealing process, but from a cost point of view, the hydrogen concentration is preferably 30.0 vol% or less, more preferably 20.0 vol% or less. The remainder of the annealing atmosphere other than hydrogen is preferably nitrogen.

[0125] Dew point: below 30℃

[0126] In one example, the annealing process can be performed at a dew point of 30°C or lower in the annealing atmosphere. By setting the dew point of the annealing atmosphere to below 30°C during the annealing process, oxidation of the surface of the cold-rolled steel sheet containing Si before annealing can be prevented, and the adhesion of the Fe-based electroplating layer can be further improved. Therefore, the dew point of the annealing atmosphere is preferably below 30°C. More preferably, the dew point of the annealing atmosphere is below 20°C. There is no particular limitation on the lower limit of the dew point of the annealing atmosphere; however, temperatures below -80°C are difficult to achieve industrially, so temperatures above -80°C are preferred. The dew point of the annealing atmosphere is preferably above -55°C.

[0127] Holding time in the temperature range of 650℃ to 900℃: 30 seconds to 600 seconds

[0128] In the annealing process, it is preferable to set the holding time in the temperature range of 650°C to 900°C to 30 seconds to 600 seconds or less. By setting the holding time in this temperature range to 30 seconds or more, the natural oxide film of Fe formed on the surface of the Si-containing cold-rolled steel sheet before annealing can be appropriately removed, preventing the formation of an oxide film directly beneath the subsequently formed Fe-based electroplated layer, and improving the adhesion of the Fe-based electroplated layer. Therefore, the holding time in this temperature range is preferably 30 seconds or more. There is no particular upper limit to the holding time in this temperature range, but from a productivity point of view, the holding time in this temperature range is preferably 600 seconds or less.

[0129] Maximum reach temperature of cold-rolled steel sheet before Si annealing: 650℃~900℃

[0130] The maximum reaching temperature of the cold-rolled steel sheet before Si annealing is not particularly limited, but is preferably 650°C to 900°C. By setting the maximum reaching temperature of the cold-rolled steel sheet before Si annealing to 650°C or higher, the recrystallization of the steel sheet structure can proceed appropriately, resulting in preferred strength. Furthermore, the natural oxide film of Fe formed on the surface of the steel sheet is appropriately reduced, further improving the adhesion of the Fe-based electroplating layer. Additionally, if the maximum reaching temperature of the cold-rolled steel sheet before Si annealing is 900°C or lower, the diffusion rate of Si and Mn in the steel can be prevented from increasing excessively, and the diffusion of Si and Mn to the surface of the steel sheet can be prevented, thus further improving the adhesion of the Fe-based electroplating layer. Furthermore, if the maximum reaching temperature is 900°C or lower, damage to the heat treatment furnace can be prevented, and costs can be reduced. Therefore, the maximum reaching temperature of the cold-rolled steel sheet before Si annealing is preferably 900°C or lower. The above-mentioned maximum reaching temperature is based on the temperature measured on the surface of the cold-rolled steel sheet before Si annealing.

[0131] Next, the surface of the Si-containing cold-rolled steel sheet is subjected to Fe-based electroplating treatment. There are no particular limitations on the Fe-based electroplating treatment method. For example, sulfuric acid bath, hydrochloric acid bath, or a mixture of both can be used as the Fe-based electroplating bath.

[0132] The Fe ion content in the Fe-based electroplating bath before energization is determined by Fe. 2+ The preferred concentration is 0.5 mol / L or higher. If the Fe ion content in the Fe-based electroplating bath is... 2+ A concentration of 0.5 mol / L or higher is sufficient to achieve adequate Fe adhesion. Furthermore, to obtain sufficient Fe adhesion, the Fe ion content in the Fe-based electroplating bath before energization is preferably 2.0 mol / L or lower.

[0133] Furthermore, the Fe-based electroplating bath may contain elements selected from Fe ions and at least one element selected from B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co. The total content of these elements in the Fe-based electroplating bath is preferably 10% by mass or less in the Fe-based electroplated layer. Additionally, metallic elements may be contained as metallic ions, and non-metallic elements may be contained as part of boric acid, phosphoric acid, nitric acid, organic acids, etc. Furthermore, the ferric sulfate plating solution may contain conductive additives such as sodium sulfate and potassium sulfate, chelating agents, and pH buffers. Furthermore, after performing the Fe-based electroplating treatment, it is preferable not to perform additional annealing on the Fe-based electroplated steel sheet.

[0134] There are no particular limitations on other conditions for the Fe-based electroplating bath. Considering temperature stability, the temperature of the Fe-based electroplating bath is preferably 30°C or higher, and more preferably 85°C or lower. The pH of the Fe-based electroplating bath is not particularly specified, but from the viewpoint of preventing a decrease in current efficiency due to hydrogen generation, it is preferably 1.0 or higher, and considering the conductivity of the Fe-based electroplating bath, it is preferably 3.0 or lower. From a productivity perspective, the current density is preferably 10 A / dm³. 2 From the perspective of easily controlling the adhesion amount of Fe-based electroplated layers, the preferred value is 150 A / dm. 2 The following applies. From a productivity point of view, the plate speed is preferably 5 mpm or more, and from the point of view of stable control of the amount of adhesion, it is preferably 150 mpm or less.

[0135] In addition, as a pretreatment before Fe-based electroplating, degreasing and rinsing can be performed to clean the surface of the Si-containing cold-rolled steel sheet, followed by pickling and rinsing to activate the surface of the Si-containing cold-rolled steel sheet. After these pretreatments, Fe-based electroplating is performed. The methods for degreasing and rinsing are not particularly limited and conventional methods can be used. In the pickling process, various acids such as sulfuric acid, hydrochloric acid, nitric acid, and mixtures thereof can be used. Sulfuric acid, hydrochloric acid, or mixtures thereof are preferred. The concentration of the acid is not particularly specified, but considering the ability to remove the oxide film and to prevent excessive pickling leading to surface roughness (surface defects), it is preferably around 1 to 20 mass%. Furthermore, the pickling solution may contain defoamers, pickling accelerators, pickling inhibitors, etc.

[0136] <Electrodeposition Coated Steel Sheet>

[0137] Furthermore, according to this embodiment, an electrodeposited coated steel sheet can also be provided, wherein the aforementioned Fe-based electroplated steel sheet further comprises a formation treatment film formed in contact with the aforementioned Fe-based electroplated layer and an electrodeposited coating film formed on the formation treatment film. The Fe-based electroplated steel sheet according to this embodiment exhibits excellent formation treatment properties, post-coating corrosion resistance, and resistance to resistance weld cracking characteristics in welded parts; therefore, the electrodeposited coated steel sheet formed using this Fe-based electroplated steel sheet is particularly suitable for automotive parts. The electrodeposited coated steel sheet according to this embodiment preferably has a formation treatment film formed directly on the Fe-based electroplated layer. In other words, the electrodeposited coated steel sheet according to this embodiment preferably does not have any additional coating layers besides the Fe-based electroplated layer. The types of formation treatment film and electrodeposited coating film are not particularly limited, and can be known formation treatment films and electrodeposited coating films. As a formation treatment film, zinc phosphate film, zirconium film, etc., can be used. As a electrodeposited coating film, there is no particular limitation as long as it is an electrodeposited film for automotive use. Depending on the application, the thickness of the electrodeposited film is preferably around 10 μm to 30 μm when dry. Additionally, according to this embodiment, an Fe-based electroplated steel sheet for electrodeposition coating can also be provided.

[0138] <Manufacturing Method of Electrodeposited Coated Steel Sheets>

[0139] Next, the manufacturing method of the above-mentioned electrodeposited coated steel sheet will be described. The above-mentioned electrodeposited coated steel sheet can be manufactured according to the following manufacturing method, which includes the following steps: a chemical formation process, in which an Fe-based electroplated steel sheet is subjected to a chemical formation process without additional plating, resulting in a chemically formed steel sheet having a chemically formed coating in contact with the Fe-based electroplated layer; and an electrodeposition coating process, in which the chemically formed steel sheet is subjected to an electrodeposition coating process, resulting in an electrodeposited coated steel sheet having an electrodeposited coating coating formed on the chemically formed coating. The chemical formation process and the electrodeposition coating process can be performed using known methods. Furthermore, as a pretreatment before the chemical formation process, degreasing, washing, and surface conditioning treatments for cleaning the surface of the Fe-based electroplated steel sheet can be performed. After these pretreatments, the chemical formation process is performed. The methods for degreasing and washing are not particularly limited, and conventional methods can be used. In surface conditioning, surface conditioning agents containing Ti colloid or zinc phosphate colloid can be used. No special procedures are required when applying these surface conditioning agents; conventional methods can be followed. For example, the desired surface conditioning agent is dissolved in a specified amount of deionized water, stirred thoroughly, and a treatment solution is prepared at a specified temperature (usually room temperature, 25–30°C). The steel sheet is then immersed in this treatment solution for a specified time (20–30 seconds). The steel sheet is then immersed in the treatment solution without drying before proceeding to the next step, chemical treatment. In chemical treatment, conventional methods are followed. For example, the desired chemical treatment agent is dissolved in a specified amount of deionized water, stirred thoroughly, and a treatment solution is prepared at a specified temperature (usually 35–45°C). The steel sheet is then immersed in this treatment solution for a specified time (60–120 seconds). Examples of chemical treatment agents include zinc phosphate treatment agents for steel, zinc phosphate treatment agents for steel and aluminum, and zirconium treatment agents. The next step, electrodeposition coating, is then performed. Electrodeposition coating can be performed using conventional methods. After pretreatment such as water washing as required, the steel sheet is impregnated in a thoroughly stirred electrodeposition coating, and an electrodeposition coating of the desired thickness is obtained through electrodeposition. In addition to cationic electrodeposition coatings, anionic electrodeposition coatings can also be used. Furthermore, depending on the application, a topcoat can be applied after the electrodeposition coating.

[0140] <Automotive Parts>

[0141] Furthermore, according to this embodiment, an automotive component made at least partially of the aforementioned electrodeposited coated steel sheet can be provided. The Fe-based electroplated steel sheet involved in this embodiment has excellent chemical treatment properties, post-coating corrosion resistance, and resistance to resistance weld cracking in the welded portion; therefore, the electrodeposited coated steel sheet using this Fe-based electroplated steel sheet is particularly suitable for use in automotive components. The automotive component made using the electrodeposited coated steel sheet may include steel sheets other than those involved in this embodiment as materials. Because the electrodeposited coated steel sheet involved in this embodiment has excellent resistance to resistance weld cracking in the welded portion, secondary cracking in the welded portion can be appropriately prevented even when the automotive component made using this Fe-based electroplated steel sheet includes high-strength galvanized steel sheet as the welding object. The type of automotive component made at least partially of the electrodeposited coated steel sheet is not particularly limited; for example, it may be a side beam component, a pillar component, or a body.

[0142] [Implementation Method 2]

[0143] Next, the Fe-based electroplated steel sheet according to Embodiment 2 of the present invention will be described.

[0144] The Fe-based electroplated steel sheet involved in this embodiment is a cold-rolled steel sheet, with the coating formed on at least one side of the cold-rolled steel sheet, and the coating amount on each side being 15.0 g / m. 2 The above refers to Fe-based electroplated steel sheets with Fe-based electroplating layers.

[0145] Here, the aforementioned cold-rolled steel sheet is the following: a test piece cut with the rolling right angle as the long side, measuring 50×150mm, and a hot-dip galvanized layer of the same size cut out on each side have an adhesion amount of 50g / m². 2 The hot-dip galvanized steel sheets are stacked to form a plate assembly.

[0146] Next, using a servo motor-driven single-phase AC (50Hz) resistance welding machine, with the aforementioned plate assembly tilted at 5° relative to the electrode (6mm diameter at the front end) of the welding machine, the plate assembly was subjected to a pressure of 3.5kN, a holding time of 0.1 seconds, and the thickness of the cold-rolled steel plate was t while the weld nugget diameter was [missing information]. Resistance welding is performed under controlled welding current and welding time conditions to produce plate assemblies with welded sections.

[0147] Next, the plate assembly with the welded part was cut in half, including the welded part. When the cross-section of the welded part was observed using an optical microscope (200x), cracks with a length of more than 0.1 mm were observed.

[0148] The cold-rolled steel sheet involved in this embodiment is not particularly limited in that, if the sheet assembly is galvanized steel sheet and the weld portion exhibits poor resistance to resistance weld cracking characteristics, then the cold-rolled steel sheet is not particularly limited in composition. The inventors have observed that if the cold-rolled steel sheet has a Si content of 0.5% by mass or more, the weld portion exhibits poor resistance to resistance weld cracking characteristics as evaluated in the following tests. Furthermore, after forming an Fe-based electroplating layer, when evaluating the resistance to resistance weld cracking characteristics of the weld portion in the case where the sheet assembly is galvanized steel sheet according to the tests described later, a cold-rolled steel sheet with the same Si content but without an Fe-based electroplating layer can be prepared, and the following tests can be performed. If the Si content is the same, the same evaluation results are obtained for the resistance to resistance weld cracking characteristics of the weld portion in the case where the sheet assembly is galvanized steel sheet. Therefore, if a cold-rolled steel sheet with the same Si content but without an Fe-based electroplating layer is used, the resistance to resistance weld cracking characteristics of the weld portion of the cold-rolled steel sheet used in the Fe-based electroplated steel sheet can be indirectly evaluated.

[0149] <Characteristics of resistance weld crack resistance in welded sections when the plate assembly is made of galvanized steel>

[0150] use Figure 8 The evaluation method for the resistance to cracking characteristics of welded parts is explained. A test piece 6, cut with the rolling right-angle direction (TD) as the long side, measuring 50×150mm, and a piece of the same size with a hot-dip galvanized coating adhesion of 50g / m² per single side are compared. 2 Hot-dip galvanized steel sheets 5 are stacked to form a plate assembly. The evaluation surface (Fe-based electroplating layer) of the plate assembly 6 is aligned with the galvanized layer of the alloyed hot-dip galvanized steel sheet 5 used for testing. The plate assembly is fixed to a mounting platform 8 via a 2.0mm thick spacer 7. The spacer 7 is a pair of steel plates, each 50mm long x 45mm short x 2.0mm thick. Figure 8 As shown in (a), the long side end faces of a pair of steel plates are aligned with the short side end faces of the plate assembly. Therefore, the distance between the pair of steel plates is 60 mm. The fixing platform 8 is a plate with a hole in its center.

[0151] Next, using a servo motor-driven single-phase AC (50Hz) resistance welding machine, while applying pressure to the plate assembly using a pair of electrodes 9 (front diameter: 6mm) and stacking the plate assembly, the plate assembly was subjected to a pressure of 3.5kN, a holding time of 0.02 seconds or 0.1 seconds, and a weld nugget diameter of [missing value] based on the thickness t of the aforementioned cold-rolled steel sheet. Resistance welding is performed under the conditions of welding current and welding time to obtain a plate assembly with a welded portion. At this time, a pair of electrodes 9 apply pressure to the plate assembly from vertically upwards and downwards, and the lower electrode applies pressure to the test piece 6 through the hole in the fixing table 8. During pressure application, the lower electrode of the pair of electrodes 9 is fixed to the fixing table 8 by contacting a plane extending from the surface of the separator 7 that contacts the fixing table 8, allowing the upper electrode to move. In addition, the upper electrode is in contact with the central portion of the test alloyed hot-dip galvanized steel plate 5. Furthermore, the plate assembly is positioned on a vertical plane relative to the line connecting the central axes of the electrode pairs of the resistance welding machine ( Figure 8 In (a) where the direction is horizontal, welding is performed with the aforementioned plate assembly tilted at 5° towards its long side. Through the aforementioned separator, a gap of 60mm in the long side direction and 2.0mm in the thickness direction of the plate assembly is formed between the lower electrode and the test piece 6. Furthermore, the holding time here refers to the time from the end of the welding current flow until the electrode is released. Here, refer to... Figure 8 In Figure (b) below, the weld nugget diameter *r* refers to the distance between the ends of the weld nuggets 10 along the long side of the plate assembly. It should be noted that when the thickness of the cold-rolled steel sheet is set to *t* (mm), the weld nugget diameter *r* satisfies... In certain situations, there is a particular tendency for internal cracks to develop.

[0152] Next, the plate assembly with the welded portion is cut in half along the center of the welded portion including the weld nugget 10. The cross-section of the welded portion is observed using an optical microscope (200x magnification), and the resistance to resistance weld cracking characteristics of the welded portion are evaluated according to the following criteria. Furthermore, if the value is ○ or △, the resistance to resistance weld cracking characteristics of the welded portion are judged to be excellent. If the value is ×, the resistance to resistance weld cracking characteristics of the welded portion are judged to be poor.

[0153] ○: No cracks longer than 0.1 mm were observed during a holding time of 0.02 seconds.

[0154] △: Cracks longer than 0.1 mm were observed when the holding time was 0.02 seconds, but no cracks longer than 0.1 mm were observed when the holding time was 0.1 seconds.

[0155] ×: Cracks longer than 0.1 mm were observed when the holding time was 0.1 seconds.

[0156] It should be noted that, in Figure 8 Figure (b) below schematically illustrates an example of a crack produced in test piece 6, indicated by symbol 11.

[0157] The Fe-based electroplating layer of the Fe-based electroplated steel sheet involved in this embodiment is the same as in Embodiment 1 described above, so the description is omitted here. Furthermore, at the interface between the Fe-based electroplating layer and the cold-rolled steel sheet, the proportion of crystal orientation integration between the Fe-based electroplating layer and the cold-rolled steel sheet is not particularly limited, and can be 50% or less, similar to Embodiment 1 described above. The detailed information regarding the proportion of crystal orientation integration between the Fe-based electroplating layer and the cold-rolled steel sheet at the interface is the same as in Embodiment 1 described above, so the description is omitted here.

[0158] Next, the manufacturing method of the Fe-based electroplated steel sheet according to Embodiment 2 will be described.

[0159] One embodiment of the method for manufacturing Fe-based electroplated steel sheet may be as follows: annealing a cold-rolled steel sheet before annealing to produce a cold-rolled steel sheet.

[0160] Next, the above-mentioned cold-rolled steel sheet was subjected to Fe-based electroplating to obtain a coating with an adhesion amount of 15.0 g / m² on at least one side. 2 The above refers to Fe-based electroplated steel sheets with Fe-based electroplating layers.

[0161] Here, the aforementioned cold-rolled steel sheet is a test piece cut from a 50×150mm sheet with the rolling right-angle direction as the long side, and a hot-dip galvanized layer of the same size is cut from the test piece with an adhesion amount of 50g / m² on each single side. 2 Hot-dip galvanized steel sheets are stacked to form a plate assembly.

[0162] Next, using a servo motor-driven single-phase AC (50Hz) resistance welding machine, with the aforementioned plate assembly tilted at 5° relative to the electrode (6mm front diameter) of the welding machine, the plate assembly was subjected to a pressure of 3.5kN, a holding time of 0.1 seconds, and the thickness of the cold-rolled steel plate was t while the weld nugget diameter was [missing information]. Plate assemblies with welded sections are produced by resistance welding under specific welding current and welding time conditions.

[0163] Next, the plate assembly with the welded part was cut in half, including the welded part. When the cross-section of the welded part was observed using an optical microscope (200x), cracks with a length of more than 0.1 mm were observed.

[0164] First, cold-rolled steel sheets are manufactured before annealing. The manufacturing method for cold-rolled steel sheets before annealing can follow the usual method for manufacturing cold-rolled steel sheets. In one example, a steel billet is hot-rolled to produce a hot-rolled sheet, which is then pickled and subsequently cold-rolled to produce a cold-rolled steel sheet before annealing.

[0165] Next, before performing Fe-based electroplating, the cold-rolled steel sheet is subjected to an annealing process to obtain the cold-rolled steel sheet. The conditions for the annealing process are not particularly limited; for example, it can be an annealing process held in a reducing atmosphere with a dew point below 30°C and a hydrogen concentration of 1.0 vol% to 30.0 vol% for 30 to 600 seconds in a temperature range of 650°C to 900°C, followed by cooling. The details of the annealing process have already been described above, so they are omitted here.

[0166] Next, the surface of the annealed cold-rolled steel sheet is subjected to Fe-based electroplating treatment to obtain Fe-based electroplated steel sheet. The details of the Fe-based electroplating treatment have been described above, so they are omitted here.

[0167] The cold-rolled steel sheet involved in this embodiment is not particularly limited to those with poor resistance weld crack resistance characteristics in the welded portion when evaluated through the above-mentioned tests, especially if the sheet assembly is made of galvanized steel sheet, provided that the sheet is annealed before the formation of the Fe-based electroplating layer. The composition of the cold-rolled steel sheet is also not particularly limited; however, if the cold-rolled steel sheet has a Si content of 0.5% by mass or more, the resistance weld crack resistance characteristics of the welded portion are poor, as evaluated through the following tests. Furthermore, when evaluating the resistance weld crack resistance characteristics of the welded portion in the case of galvanized steel sheet after the formation of the Fe-based electroplating layer, if a separate cold-rolled steel sheet with the same Si content but without the Fe-based electroplating layer is prepared and the following tests are performed, the resistance weld crack resistance characteristics of the welded portion of the cold-rolled steel sheet used in the Fe-based electroplated steel sheet can be indirectly evaluated.

[0168] In this embodiment, similar to Embodiment 1 described above, an electrodeposited coated steel sheet can also be provided. The Fe-based electroplated steel sheet according to this embodiment further includes a formation treatment film formed in contact with the aforementioned Fe-based electroplating layer and an electrodeposited coating film formed on the formation film. Additionally, an Fe-based electroplated steel sheet for electrodeposited coating can also be provided. The details of the electrodeposited coated steel sheet and its manufacturing method are the same as in Embodiment 1 described above, and therefore, descriptions are omitted here.

[0169] Furthermore, in this embodiment, a car component can also be provided in the same manner as in Embodiment 1 described above. The details of the car component have already been described above, and therefore will not be repeated here.

[0170] The present invention will now be described in detail based on specific embodiments.

[0171] Example

[0172] The steel sheets with the chemical composition shown in Table 1 are produced by hot rolling, pickling and cold rolling to form cold-rolled steel sheets with a thickness of 1.4 mm.

[0173] [Table 1]

[0174] Table 1

[0175] steel markings C Si Mn P S N Al B Ti Nb Mo Cu Ni A 0.18 <![CDATA[ 0.41 ]]> 1.55 0.02 0.002 0.004 0.039 0.001 0.01 - - - - Reference steel B 0.15 0.91 2.16 0.02 0.002 0.004 0.036 - - - - - - Suitable for steel C 0.18 1.02 3.08 0.02 0.002 0.006 0.038 0.001 0.01 0.018 - - - Suitable for steel D 0.12 1.20 1.85 0.01 0.001 0.004 0.032 0.001 0.01 - - - - Suitable for steel E 0.24 1.41 1.33 0.01 0.001 0.003 0.034 0.001 0.01 - - - Suitable for steel F 0.13 1.39 1.94 0.01 0.001 0.007 0.033 0.001 0.01 - - - - Suitable for steel G 0.08 1.49 1.52 0.01 0.001 0.003 0.035 0.001 0.01 - - - - Suitable for steel H 0.17 1.53 2.31 0.01 0.001 0.004 0.037 - - - 0.11 - - Suitable for steel I 0.19 1.51 2.72 0.01 0.001 0.004 0.034 0.001 0.01 - - 0.12 - Suitable for steel J 0.15 1.65 1.33 0.02 0.002 0.005 0.036 0.001 0.01 - - - 0.14 Suitable for steel K 0.17 1.68 2.51 0.02 0.002 0.004 0.036 0.001 0.01 - - - - Suitable for steel

[0176] The underlined part indicates that the invention is outside its suitable scope.

[0177] "-" indicates the level of unavoidable impurities.

[0178] Next, the cold-rolled steel sheet was subjected to reduction annealing under conditions of 15% H2-N2, a soaking temperature of 800°C, and a dew point of -40°C. The reduction annealing was performed for 100 seconds. Following this, the steel sheet was degreased using an alkali, and then electrolyzed using the steel sheet as the cathode under the conditions shown below, without further annealing, to produce an Fe-based electroplated steel sheet. The amount of Fe-based electroplated coating was controlled by the energizing time.

[0179] [Electrolysis conditions]

[0180] Bath temperature: 50℃

[0181] pH: 2.0

[0182] Current density: 45A / dm 2

[0183] Fe-based electroplating bath: containing 1.5 mol / L Fe 2+ ion

[0184] Electrode (anode): Iridium oxide electrode

[0185] Based on the Fe-based electroplated steel sheet manufactured as described above, the adhesion amount of the Fe-based electroplated layer on each side and the proportion of the crystal orientation integration between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet at the interface of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet are determined according to the above method.

[0186] For the Fe-based electroplated steel sheets obtained above, the chemical treatment properties, corrosion resistance after coating, and resistance to resistance weld cracking characteristics of the welded parts were investigated. The measurement and evaluation methods are shown below.

[0187] Chemical treatment properties and corrosion resistance after coating

[0188] (1) Chemical treatment

[0189] Degreasing, surface conditioning, and chemical forming treatments were performed on test pieces taken from the aforementioned Fe-based electroplated steel sheets to produce chemically formed test pieces with chemically formed coatings on both the front and back sides. First, the test pieces taken from the aforementioned Fe-based electroplated steel sheets were immersed in a degreasing agent, and degreasing treatment was performed under the following standard conditions.

[0190] [Defatting treatment]

[0191] • Degreasing agent: FC-E2011 (manufactured by Nippon Parkerizing)

[0192] Processing temperature: 43℃

[0193] Processing time: 120 seconds

[0194] Next, the degreased test pieces were sprayed with a surface conditioner and surface conditioning was performed under the following standard conditions.

[0195] [Surface Conditioning Treatment]

[0196] • Surface conditioning agent: Preparen X (PL-X: manufactured by Nippon Parkerizing)

[0197] pH: 9.5

[0198] • Processing temperature: room temperature

[0199] Processing time: 20 seconds

[0200] Next, the surface-modified test piece is immersed in a formation agent and the formation process is carried out under the following standard conditions.

[0201] [Chemicalization treatment]

[0202] • Chemical treatment agent: Palbond PB-SX35 (manufactured by Nippon Parkerizing)

[0203] • Temperature of the chemical formation treatment solution: 35℃

[0204] Processing time: 90 seconds

[0205] Using the formation-treated test piece manufactured as described above, the formation-treated properties described below were determined.

[0206] (2) Electrodeposition coating treatment

[0207] The surface of the above-mentioned chemically treated test pieces was coated with an electrodeposition coating of Kansai Paint Co., Ltd., GT-100, with a film thickness of 15 μm, to prepare electrodeposition coated test pieces. These electrodeposition coated test pieces were then subjected to the saltwater immersion test described later.

[0208] <Chemical Processing>

[0209] The surface of the above-mentioned chemically treated test pieces (n=1) was observed by SEM at a magnification of 1000x, and evaluated according to the following criteria. Furthermore, if the result is ◎ or ○, it is considered to have excellent chemical treatment properties.

[0210] ◎: The particle size of the crystals formed is less than 5 μm and no unprecipitated parts were observed.

[0211] ○: The particle size of the crystals formed is greater than 5 μm, but no unprecipitated portion was observed.

[0212] ×: The particle size of the crystals formed is greater than 5 μm and no precipitates are observed.

[0213] <Salt Water Immersion Test>

[0214] After making a 45mm long cross-shaped cut on the surface of the electrodeposited coating test piece (n=1) with a knife, the test piece was immersed in a 5 mass% NaCl solution (60°C) for 360 hours, followed by washing with water and drying. Next, an adhesive tape was applied to the cross-shaped cut area of ​​the test piece, and a peel test was performed to measure the maximum total peel width of the electrodeposited coating film on both sides of the cross-shaped cut area. The maximum total peel width of the electrodeposited coating film was evaluated according to the following criteria. Furthermore, if it is ◎ or ○, it is judged to have excellent corrosion resistance after coating.

[0215] The following evaluation will be conducted:

[0216] ◎: Maximum total peel width is less than 3.0mm

[0217] ○: Maximum total peel width is less than 5.0 mm

[0218] ×: The maximum total peel width exceeds 5.0 mm.

[0219] <Characteristics of resistance weld crack resistance in welded sections when the plate assembly is made of galvanized steel>

[0220] For Fe-based electroplated steel sheets, based on the above method, the evaluation of the sheet group was conducted at a tensile strength of 980 MPa and an adhesion weight of 50 g / m² per single side. 2 Resistance weld crack resistance characteristics of welded sections were investigated using alloyed hot-dip galvanized steel sheets (1.4 mm thick). The welding time was 18 cycles (50 Hz). The weld nugget diameter was measured by varying the welding current, corresponding to Example No. , and an evaluation was conducted with a weld nugget diameter of 5.3 mm.

[0221] The results of the above experiments are shown in Table 2. The results indicate that in the Fe-based electroplated steel sheet of the inventive example, which forms an Fe-based electroplating layer under conditions suitable for this invention after continuous annealing, all characteristics—chemical treatment properties, post-coating corrosion resistance, and resistance to resistance weld cracking in the welded portion—are excellent. Furthermore, for Reference Examples 1 and 2, Si is less than 0.5%, therefore there are no particular problems with chemical treatment properties or resistance to resistance weld cracking in the welded portion. The Fe-based electroplating layer adhesion amount was set to 25 g / m². 2 In the above-mentioned invention examples, even under the condition of a holding time of 0.02 seconds, no cracks with a length of more than 0.1 mm were observed, and the resistance welding crack resistance characteristics of the welded part were particularly good.

[0222] [Table 2]

[0223] Table 2

[0224]

[0225] The underlined part indicates industrial applicability outside the suitable scope of the invention.

[0226] The Fe-based electroplated steel sheet manufactured using this invention has excellent chemical processing properties, corrosion resistance after coating, and resistance to resistance welding cracks, especially internal crack prevention, in the case of galvanized steel sheets. It also has high strength and excellent processability. Therefore, it can be used not only as a material for automotive parts, but also preferably as a material for applications requiring the same properties in the fields of home appliances and building components.

[0227] Symbol Explanation

[0228] 1Fe series electroplated steel sheet

[0229] 2: Si-containing cold-rolled steel sheet

[0230] 3: Fe-based electroplating layer

[0231] 5: Experimental alloyed hot-dip galvanized steel sheet

[0232] 6: Test piece

[0233] 7: Isolation material

[0234] 8: Fixed platform

[0235] 9: Electrode

[0236] 10 Melting Core

[0237] 11 Cracks

Claims

1. An Fe-based electroplated steel sheet having: a Si-containing cold-rolled steel sheet containing 0.5 to 3.0 mass% of Si; and an Fe-based electroplated layer on a surface of the Si-containing cold-rolled steel sheet, wherein the Fe-based electroplated layer does not have a plated layer other than the Fe-based electroplated layer on the surface, wherein at an interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet, a proportion of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated in crystal orientation is 50% or less, wherein the proportion of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated in crystal orientation is determined as follows, wherein a sample of 10 x 10 mm is taken from the Fe-based electroplated steel sheet, and an arbitrary one position of the sample is processed using a focused ion beam device to form a 45° cross section of 30 μm width in a rolling right angle direction and 50 μm length in a 45° direction with respect to a T cross section direction at the one position, thereby preparing an observation sample, the T cross section being a cross section parallel to the rolling right angle direction of the steel sheet and perpendicular to a surface of the steel sheet, wherein next, a central portion of the 45° cross section of the observation sample is observed at a magnification of 5000 times using a scanning ion microscope, and a SIM image of 1024 x 943 pixels in width x height, 8 bits is captured, and based on the following formula (1), the proportion of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated in crystal orientation at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet is calculated from the SIM image captured for each of the 45° cross sections prepared at three portions; (a proportion of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated in crystal orientation at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet) = (a length of a portion of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated in crystal orientation at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet) ÷ (a length of the interface of an observation field of view) x 100... (1). the Si-containing cold-rolled steel sheet has a component composition containing, in mass%, C: 0.8% or less, Mn: 1.0 to 12.0%, P: 0.1% or less, S: 0.03% or less, N: 0.010% or less, and Al: 1.0% or less, in addition to the Si, and the remainder composed of Fe and inevitable impurities. the component composition further contains, in mass%, one or two or more selected from the group consisting of B: 0.005% or less, Ti: 0.2% or less, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0% or less, Mo: 1.0% or less, Nb: 0.20% or less, V: 0.5% or less, Sb: 0.200% or less, Ta: 0.1% or less, W: 0.5% or less, Zr: 0.1% or less, Sn: 0.20% or less, Ca: 0.005% or less, Mg: 0.005% or less, and REM: 0.005% or less. Fe-based plating layer formed on at least one side of the Si-containing cold-rolled steel sheet, the adhesion amount of each side being 17 g / m 2 The above, ​ ​ ​ ​ ​ ​ 2. The Fe-based electroplated steel sheet according to claim 1, wherein The Fe-based plating layer has an adhesion amount of 25 g / m2per single side 2 The above.

3. The Fe-based electrogalvanized steel sheet according to claim 1 or 2, wherein, ​ 4. The Fe-based electroplated steel sheet according to claim 3, wherein ​ 5. The Fe-based electrogalvanized steel sheet according to claim 1 or 2, wherein, The Fe-based electroplated layer has a composition containing 10 mass% or less of one or two or more elements selected from B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co, and the remainder of Fe and inevitable impurities.

6. A Fe-based electroplated steel sheet having a Si-containing cold-rolled steel sheet, and an Fe-based electroplated layer formed on at least one side of the Si-containing cold-rolled steel sheet, the Fe-based electroplated layer having an adhesion amount of 17 g / m2 per side 2 the above Fe-based electroplated layer, The Fe-based electroplated steel sheet has no plating layer other than the Fe-based electroplated layer on the surface, The proportion of the crystal orientation of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet is 50% or less, Here, the Si-containing cold-rolled steel sheet is a sheet group made by overlapping a test piece cut in a rolling diagonal direction to be a long side in a size of 50 x 150 mm and a hot-dip galvanized steel sheet in which the attached amount of a hot-dip galvanizing layer per single side is 50 g / m 2 2. The method according to claim 1, wherein the Si-containing cold-rolled steel sheet is a sheet group made by overlapping a test piece cut in a rolling diagonal direction to be a long side in a size of 50 x 150 mm and a hot-dip galvanized steel sheet in which the attached amount of a hot-dip galvanizing layer per single side is 50 g / m Next, using a servo motor pressurized 50 Hz single-phase resistance welder, in a state where the plate set is inclined at 5° with respect to a 6 mm diameter electrode of the front end of the resistance welder, resistance welding is performed on the plate set under conditions of a pressurizing force of 3.5 kN, a holding time of 0.1 seconds, and a welding current and a welding time of 2.5 kA and 0.1 seconds, respectively, for a plate thickness of the Si-containing cold-rolled steel sheet of t, to obtain a plate set with a welded portion. Next, using a servo motor pressurized 50 Hz single-phase resistance welder, in a state where the plate set is inclined at 5° with respect to a 6 mm diameter electrode of the front end of the resistance welder, resistance welding is performed on the plate set under conditions of a pressurizing force of 3.5 kN, a holding time of 0.1 seconds, and a welding current and a welding time of 2.5 kA and 0.1 seconds, respectively, for a plate thickness of the Si-containing cold-rolled steel sheet of t, to obtain a plate set with a welded portion. Next, the plate set with the weld portion is cut in half in a manner including the weld portion, and when the cross section of the weld portion is observed at 200 times using an optical microscope, a crack of 0.1 mm or more in length is observed, The proportion of the crystal orientation of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated is determined as follows, A sample of 10 x 10 mm in size is taken from the Fe-based electroplated steel sheet, and using a focused ion beam device, an arbitrary one position of the sample is processed, a 45° cross section of 30 μm in width in the rolling right angle direction and 50 μm in length in the 45° direction with respect to the T cross section direction is formed at an angle of 45° with respect to the T cross section direction at one position, and an observation sample is prepared, the T cross section being a cross section parallel to the rolling right angle direction of the steel sheet and perpendicular to the surface of the steel sheet; Next, the central portion of the 45° cross section of the observation sample is observed at a magnification of 5000 times using a scanning ion microscope, and a SIM image of 1024 x 943 pixels in width x height, 8 bits is captured, and based on the following formula (1), the proportion of the crystal orientation of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet is calculated from the SIM image captured from each of the 45° cross sections prepared at three positions; (The proportion of the crystal orientation of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet being integrated at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet) = (the length of the portion where the crystal orientation of the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet is integrated at the interface between the Fe-based electroplated layer and the Si-containing cold-rolled steel sheet) ÷ (the length of the interface of the observation field of view) x 100 …… (1).

7. An electrodeposited coated steel sheet further having a chemical conversion coating formed in contact with the Fe-based electroplated layer and an electrodeposited coating film formed on the chemical conversion coating on the Fe-based electroplated steel sheet according to claim 1 or 2.

8. An automobile component made at least in part using the electrodeposited coated steel sheet according to claim 7.

9. A method for manufacturing an electrodeposited coated steel sheet, comprising the following steps: a chemical conversion step of subjecting the Fe-based electroplated steel sheet according to claim 1 or 2 to chemical conversion without subjecting to additional plating treatment, to obtain a chemical conversion steel sheet having a chemical conversion coating formed in contact with the Fe-based electroplated layer; and a plating step of subjecting the chemical conversion steel sheet to plating treatment to form an electrodeposited coating film on the chemical conversion coating. An electrodeposition coating process is performed on the chemical conversion treated steel sheet to obtain an electrodeposition coated steel sheet having an electrodeposition coating film formed on the chemical conversion film.

10. A method for producing an Fe-based electrogalvanized steel sheet, which is a method for producing the Fe-based electrogalvanized steel sheet according to any one of claims 1 to 6, wherein an Si-containing annealed cold-rolled steel sheet containing 0.5 to 3.0 mass% of Si is annealed to produce an Si-containing cold-rolled steel sheet. Next, Fe-based plating is performed on the Si-containing cold-rolled steel sheet to obtain an Fe-based plated steel sheet having an Fe-based plated layer formed on at least one side thereof, the Fe-based plated layer having an adhesion amount of 17 g / m2per side 2 Fe-based plated steel sheet having the above Fe-based plated layer.

11. A method for producing an Fe-based electrogalvanized steel sheet, which is a method for producing the Fe-based electrogalvanized steel sheet according to any one of claims 1 to 6, wherein an annealed cold-rolled steel sheet is annealed to produce a cold-rolled steel sheet. Next, Fe-based plating is performed on the cold-rolled steel sheet to form an Fe-based plated layer having an adhesion amount of 17 g / m2per one side at least on one side of the cold-rolled steel sheet 2 Fe-based plated steel sheet having the above Fe-based plated layer, Here, the cold-rolled steel sheet is a cold-rolled steel sheet in which a test piece of 50 x 150 mm cut in a rolling diagonal direction is overlapped with a hot-dip galvanized steel sheet of which the attached amount of a hot-dip galvanizing layer per single side is 50 g / m 2 cut in the same size is overlapped to make a sheet group. Next, a resistance welder of 50 Hz single-phase AC using a servo motor was used to perform resistance welding on the set of plates in a state in which the set of plates was inclined at 5° with respect to a 6 mm diameter electrode of the resistance welder, under conditions of a pressing force of 3.5 kN, a holding time of 0.1 seconds, and a welding current and a welding time of 2.5 kA and 0.1 seconds, respectively, for a cold-rolled steel plate having a plate thickness of t and a nugget diameter of 2.5 t. a set of plates with a weld portion was produced. Next, the plate group with the weld portion is cut in half in a manner that the weld portion is included, and when the cross section of the weld portion is observed using an optical microscope at 200 times, a crack of 0.1 mm or more in length is observed.

12. The method of producing a Fe-based electrogalvanized steel sheet according to claim 10 or 11, wherein The Fe-based plating is performed using an Fe-based plating bath containing one or two or more elements selected from B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co in a manner that the total content of these elements is 10 mass% or less in the Fe-based plated layer. The Fe-based plating is performed using an Fe-based plating bath containing one or two or more elements selected from B, C, P, N, O, Ni, Mn, Mo, Zn, W, Pb, Sn, Cr, V, and Co in a manner that the total content of these elements is 10 mass% or less in the Fe-based plated layer.

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