METALLIC-COATED STEEL SHEET FOR HOT STAMPING

Abstract

A hot-stamped, metallic-coated steel sheet comprising a base metal and a galvanized layer formed on a surface of the base metal, wherein the galvanized layer comprises a galvanized and annealed layer, a solidified zinc layer, and an oxide layer containing Al, in this order from the base metal, and a ratio of Zn content (g / m2) in the solidified zinc layer to Zn content (g / m2) in the galvanized layer is 10 to 95%.

Description

METALLIC-COATED STEEL SHEET FOR HOT STAMPING FIELD OF INVENTION

[0001] The present invention relates to a metal-coated steel sheet for hot stamping. STATE OF THE ART

[0002] Various automotive components that make up an automotive body are required to have different performance characteristics according to their uses. For automotive components such as an A-pillar reinforcement, a B-pillar reinforcement, a bumper reinforcement, a tunnel reinforcement, a side member reinforcement, a roof reinforcement, and a floor cross member, for example, only a specific region of each automotive component is required to have higher strength than the general strength of other regions. Therefore, a technique has been employed in which hot stamping is performed on an automotive component only in a portion corresponding to the specific region that needs to be reinforced to produce a hot-stamped member.

[0003] Currently, if a cold-rolled steel sheet that has not undergone surface treatment is used, iron oxide scale forms on the steel sheet surface during heating. These oxide scales not only flake off during forming, leading to wear on a press tool, but also cause surface defects on the steel sheet. Furthermore, if the oxide scales remain on the steel sheet surface after forming, they can result in poor welding or coating adhesion in subsequent welding processes.

[0004] Therefore, to prevent rust flaking, a zinc-based metal-coated steel sheet or similar, as described in Patent Document 1, may be used. By using a zinc-based metal-coated steel sheet, rusting of the iron is prevented by a small amount of zinc oxidizing before the iron, so that weldability and paintability can be significantly improved.

[0005] Furthermore, even these components have recently been required to have corrosion resistance; for example, in accordance with Patent Documents 2 to 5, techniques have been developed to improve corrosion resistance by increasing the weight per square meter of metallic coating adhered to a steel sheet before heating to make the metallic coating have a Zn content of approximately 70%, the remainder being mainly Fe, which remains on a surface of the metallic coating after heating. zccn Ln / zznz / E / YiAi LIST OF STATE OF THE ART DOCUMENTS PATENT DOCUMENTS

[0006] Patent Document 1: JP2003-126921A Patent Document 2: JP2005-240072A Patent Document 3: JP2006-022395A Patent Document 4: JP2007-182608A Patent Document 5: JP2011-117086A SUMMARY OF THE INVENTION TECHNICAL PROBLEM

[0007] In the case of forming a metallic coating layer along a continuous line, it is necessary that the metallic coating bath contains a small amount of Al to prevent the excessive Zn alloying in the metallic coating bath from reacting with the Fe in the base metal.

[0008] In particular, when using a zinc bath containing aluminum with a high weight of metallic coating per square meter, a cobweb-like surface defect can occur after heating and forming. This cobweb-like surface defect is a raised defect, which is undesirable from a quality standpoint, as it remains visible against the surface even after the coating has been applied to an automotive application.

[0009] Therefore, it is necessary to avoid the cobweb defect. However, no mechanism is known by which the cobweb defect occurs, nor is there a method to prevent it.

[0010] An objective of the present invention is to solve the problems described above and to provide a metal-coated steel sheet for hot stamping in which a cobweb-like surface defect can be avoided in a case where a Zn metal coating containing Al is used. SOLUTION TO THE PROBLEM

[0011] The present invention has been made to solve the problems described above, and the essence or basis of the present invention is the metal-coated steel sheet for hot stamping.

[0012] (1) A hot-stamped metallic-coated steel sheet comprising a base metal and a galvanized layer formed on a surface of the base metal, wherein the galvanized layer comprises a galvanized and annealed layer, a solidified zinc layer, and an oxide layer containing Al, in this order from the base metal, and zccn Ln / zznz / E / YiAi a ratio of a Zn content (g / m2) in the solidified zinc layer to a Zn content (g / m2) in the galvanized layer is from 10 to 95%.

[0013] (2) The hot stamping metal-coated steel sheet in accordance with (1), wherein a chemical composition of the oxide layer satisfies Formula (i) shown below. 3.0 < Zn / Al < 6.0 (i) where Zn and Al are the Zn and Al contents (g / m2) contained in the oxide layer, respectively.

[0014] (3) The hot-stamped metallic-coated steel sheet in accordance with either of points (1) or (2) above, wherein an average thickness of the oxide layer is LO pm or less.

[0015] (4) Hot stamping metallic-coated steel sheet in accordance with any of the above points (1) to (3), wherein the Zn content in the galvanized layer is 65 to 150 g / m2.

[0016] (5) Hot stamping metallic-coated steel sheet in accordance with any of points (1) to (4) above, wherein the Fe content in the galvanized layer is, by mass in %, less than 7%. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0017] In accordance with the present invention, it is possible to provide a metal-coated steel sheet for hot stamping in which a cobweb-like surface defect can be avoided in the case of using the Zn metal coating containing Al. DESCRIPTION OF THE MODALITIES

[0018] The current inventors investigated the cause of the cobweb-like surface defect and obtained the following results.

[0019] (a) In a case where Al is contained in a metallic coating bath, a thin oxide layer containing Al forms on a surface of a resulting metallic coating layer. In particular, in a case where the weight per square meter of the metallic coating is high, the metallic coating layer becomes a liquid phase and moves due to heating in hot stamping, and stress caused by the movement produces a fine crack in the oxide layer.

[0020] (b) In the metallic coating, Zn, Mn and the like flow into the gaps formed by cracking in the oxide layer and the gaps are filled with oxides of Zn, Mn and the like to form a cobweb-like pattern, resulting in a deterioration of the surface texture. zccn Ln / zznz / E / YiAi

[0021] The present inventors carried out intensive studies on how to prevent cracking in the oxide layer and further obtained the following results.

[0022] (c) It is possible to prevent the liquid phase of the metallic coating from moving by moderately alloying the metallic coating layer to form a galvanized and annealed layer to control a proportion of the solidified zinc layer formed in a layer over the galvanized and annealed layer.

[0023] (d) Furthermore, by reforming the oxide layer to relatively increase the Zn content with respect to the Al content in the oxide layer, the oxide layer is softened to further resist cracking.

[0024] (e) For oxide layer reformation, optimization of the sweep conditions is effective.

[0025] The present invention is based on the findings described above. The respective requirements of the present invention will be described in detail below.

[0026] (A) General configuration A hot-stamping, metallic-coated steel sheet according to one embodiment of the present invention includes a base metal and a galvanized layer formed on a surface of the base metal. One configuration of the galvanized layer will be described in detail.

[0027] (B) Galvanized coating In the present invention, the galvanized layer comprises a galvanized and annealed layer, a solidified zinc layer, and an oxide layer containing aluminum, in that order from the base metal. The coating weight per square meter of the galvanized layer is not limited to a specific weight per square meter but can be set between 30 and 180 g / m² depending on the zinc content. Corrosion resistance increases with increasing coating weight per square meter.

[0028] Furthermore, a cobweb-like surface defect is more likely to appear with an increase in the coating weight per square meter. Consequently, the advantageous effects of the present invention are most pronounced when the coating weight per square meter of the galvanized layer is 65 g / m² or higher in terms of Zn content. On the other hand, from the standpoint of preventing the cobweb-like surface defect, the coating weight per square meter of the galvanized layer is preferably 150 g / m² or lower in terms of Zn content.

[0029] To produce a normal galvanized and annealed steel sheet, the galvanized layer needs to be fully alloyed; therefore, the Fe content in the galvanized layer is 7% or more. In contrast, in the present invention, the galvanized layer is not fully alloyed, as will be described later. Consequently, the average Fe content throughout the galvanized layer is preferably, by mass %, less than 7%, more preferably 6% or less.

[0030] (C) Galvanized and annealed layer zccn Ln / zznz / E / YiAi The galvanized and annealed layer is formed from intermetallic compounds produced by a reaction between the zinc in the metallic coating bath and the iron in the base metal. Forming a moderate amount of this galvanized and annealed layer allows for control of the proportion of solidified zinc layer described below, preventing a liquid phase of the metallic coating from being displaced during hot stamping.

[0031] (D) Solidified zinc layer The solidified zinc layer is a layer in which a hot-dip galvanizing bath solidifies and is normally called the η layer. In the present invention, the proportion of a Zn content (g / m2) in the solidified zinc layer is established between 10 and 95% with respect to a Zn content (g / m2) in the galvanized layer.

[0032] In the case of a normal, galvanized, non-alloyed steel sheet produced on a continuous line, the aluminum (Al) in the coating bath prevents the reaction between the zinc (Zn) in the coating bath and the iron (Fe) in the base metal. As a result, most of the galvanized layer consists of the solidified zinc layer; for example, the proportion of zinc in the solidified zinc layer may exceed 95%.

[0033] As described above, if the coating weight per square meter is high, the solidified zinc layer becomes a liquid phase and moves due to heating during hot stamping. Therefore, in the present invention, the proportion of the solidified zinc layer is moderately reduced. Specifically, the movement of the liquid phase can be prevented by setting the Zn content in the solidified zinc layer to 95% or less relative to the Zn content in the galvanized layer. To prevent the movement of the liquid phase of the metallic coating, the Zn content in the solidified zinc layer is preferably 85% or less, or 75% or less, and more preferably 65% ​​or less, or 55% or less.

[0034] Conversely, in the case of a normal galvanized and annealed steel sheet, its galvanized layer is completely alloyed within a galvanized and annealed layer. That is, the proportion of Zn content in the solidified zinc layer of the galvanized and annealed steel sheet is almost 0%. However, such a low proportion of the solidified zinc layer leads to a degradation of corrosion resistance. Therefore, it is necessary in the present invention to establish the proportion of Zn content in the solidified zinc layer at 10% or more relative to the Zn content in the entire galvanized layer. To avoid degrading the corrosion resistance of the galvanized layer, the proportion of Zn content in the solidified zinc layer is preferably 20% or more, and more preferably 30% or more.

[0035] (E) Zccn oxide layer Ln / zznz / E / YiAi An oxide layer containing aluminum forms on the surface of the galvanized coating. This aluminum oxide layer is relatively hard, and therefore, if the solidified zinc layer becomes liquid and moves during heating, there is a risk of cracking.

[0036] As described above, decreasing the proportion of solidified zinc layer prevents the liquid phase of the metallic coating from moving, thus avoiding cracking. Furthermore, softening the oxide layer can more effectively prevent cracking. This is achieved by relatively concentrating the Zn in the oxide layer to bring the Zn / Al ratio to 3.0 or higher. Additionally, reducing the Zn / Al ratio to 6.0 or lower prevents the proportion of Zn-based oxides from becoming excessively high, resulting in excellent paint adhesion when applying automotive or similar paint after hot stamping. Therefore, it is preferable for the oxide layer's chemical composition to satisfy Formula (i) shown below. 3.0 < Zn / Al < 6.0 (i) where Zn and Al are the Zn and Al contents (g / m2) in the oxide layer, respectively.

[0037] Furthermore, the average thickness of the oxide layer is preferably 1.0 pm or less. By setting the average thickness at 1.0 pm or less, the rigidity of the oxides is low, so that the oxides are finely pulverized, preventing large, clear cracks even if movement of the metallic coating bath occurs; thus, a distinct cobweb-like defect can be avoided. The average thickness of the oxide layer is more preferably 0.8 pm or less, and even more preferably 0.6 pm or less.

[0038] It is not necessary to set a lower limit on the average thickness of the oxide layer because it is desirable that the average thickness be as small as possible. However, in a case where Al is contained in the metallic coating bath, the formation of the oxide layer is inevitable as described above, and therefore the average thickness of the oxide layer is practically greater than 0 pm.

[0039] (F) Measurement Method In the present invention, the chemical compositions, thicknesses, and the like of the entire galvanized layer and of each layer of the galvanized layer are to be measured by the following procedure.

[0040] First, only the oxide layer is dissolved by immersing the metallic-coated steel sheet in a 10% aqueous solution of chromic acid. Then, ICP atomic emission spectroscopy is performed on the resulting solution to measure the Al and Zn contents, which are taken to be the Al and Zn contents in the oxide layer.

[0041] Next, the metal-coated steel sheet is subjected to constant-current electrolysis in an aqueous solution of 150 g / L ammonium chloride at 4 mA / cm². A silver chloride electrode is used as the reference electrode. Then, ICP atomic emission spectroscopy is performed on a solution of the dissolved metal-coated steel sheet at -0.95 V or less to measure the Zn content in the solidified zinc layer.

[0042] Subsequently, the residual metallic coating layer is subjected to constant current electrolysis until the potential becomes constant near -0.5 V, which is the potential of a base metal steel sheet. ICP atomic emission spectroscopy is then performed on the solution obtained from the constant current electrolysis to measure the Zn content, which is taken as the Zn content in the galvanized and annealed layer.

[0043] In addition, a galvanized layer from another piece cut from the metal-coated steel sheet in a position adjacent to the sample is fully dissolved in an aqueous solution of 10% hydrochloric acid with an inhibitor such as IBIT 700BK from Asahi Chemical Co., Ltd. ICP atomic emission spectroscopy is performed on the resulting solution to measure the contents of Zn, Al, and Fe, whereby the Fe content in the entire galvanized layer is determined.

[0044] In addition, another adjacent piece of the metallic-coated steel sheet is subjected to light discharge optical emission spectrometry (GDS) for component analysis. Cathodic deposition is performed in a depth direction from its surface, yielding an Al density profile. The oxide layer thickness is then defined as half the depth at which the Al density, determined from the surface, first falls below 0.1% by mass. One such measuring device is the Rigaku Corporation GDA-750, and the measurement conditions are 900 V - 20 mA and a measuring diameter of 4 mm. The measurement is performed at any 10 points for a given material, and the average of the measurements at these 10 points is taken as the material's measurement value.If oil or dirt adheres to a surface of the material, the measurement is made after degreasing the oil or dirt with an organic solvent.

[0045] (G) Production Method. The steps for producing the metal-coated steel sheet for hot stamping in the present embodiment include a base metal production step and a galvanizing layer formation step on a surface of the base metal. The steps will be described in detail below.

[0046] [Base Material Production Step] In a base material production step, a base metal is produced from hot-rolled steel sheet with a metallic coating. For example, molten steel with a predetermined chemical composition is produced, and this molten steel is used to produce a plate through a casting process or an ingot through an ingot-making process. The plate or ingot then undergoes a hot-rolling process, which yields the base metal (hot-rolled sheet). zccn Ln / zznz / E / YiAi

[0047] Hot-rolled sheet may undergo a pickling process, the pickled hot-rolled sheet is then cold-rolled, and the resulting cold-rolled sheet can be used as base metal. In addition, the pickled hot-rolled sheet or the pickled cold-rolled sheet may be annealed, and the resulting hot-rolled annealed steel sheet or the cold-rolled annealed steel sheet can be used as base metal.

[0048] [Metal Coating Step] In a metal coating step, a metallic coating layer is formed on a base metal surface, producing the metal-coated steel sheet for hot stamping. The galvanized layer can be formed, for example, by a hot-dip galvanizing process.

[0049] For example, an example of the formation of the galvanized layer by the hot-dip galvanizing process is as follows. The base metal is immersed in a hot-dip galvanizing bath containing Zn, Al, and impurities, whereupon the galvanized layer adheres to the surface of the base metal. The chemical composition of the hot-dip galvanizing bath consists primarily of Zn. Specifically, the Zn content in the hot-dip galvanizing bath is 90% by mass or more. The Al content in the hot-dip galvanizing bath is preferably 0.05 to 1.00%, more preferably 0.10 to 0.50%, and even more preferably 0.12 to 0.30%. The hot-dip galvanizing bath may additionally contain Mg, Pb, Si, and similar elements, the total content of which is, however, preferably 10% by mass or less.

[0050] Next, the base metal with the adhered galvanized layer is removed from the coating bath. After removal from the coating bath, the steel sheet undergoes gas flushing, in which gas is blown onto the surface of the coated steel sheet, thereby controlling the thickness of the galvanized layer.

[0051] At this point, the gas blowing causes a new surface to appear on the surface of the galvanized layer, and from this point on, oxidation of the metallic coating surface begins, forming a new oxide layer. After the gas blowing, the alloy heat treatment described below is carried out; in this respect, the present inventors found that optimizing the cooling and heating conditions from the gas blowing to the alloy heat treatment is effective in controlling the oxide layer on the metallic coating surface and, by extension, in preventing a cobweb-like pattern from appearing after the subsequent hot stamping.More specifically, the present inventors discovered that it is important to optimize a temperature and gas flow rate in the sweep in order to avoid causing the solidification of the metallic coating during a period that ranges from the extraction of the metallic coating bath until the performance of the alloy heat treatment. zccn Ln / zznz / E / YiAi

[0052] In general, the temperature of the hot-dip galvanizing bath is usually 450 to 470 °C. The metallic coating layer of a steel sheet, immediately after coating, is at almost the same temperature as the coating bath and is in a molten state. The metallic coating layer then cools gradually; in particular, when the blown gas is at a lower temperature and a higher flow rate, the temperature of the metallic coating layer drops rapidly. The solidification temperature of the zinc coating is approximately 419 °C; therefore, when the temperature of the metallic coating layer becomes equal to or lower than the solidification temperature, the coating solidifies rapidly.

[0053] It is clarified that, when the metallic coating is in a molten state, the oxide layer formed on the surface of the galvanized layer is relatively soft, whereas when the metallic coating solidifies, the oxide layer on the surface of the galvanized layer becomes highly solid, and the Zn / Al density becomes low, which tends to cause the appearance of a cobweb-like pattern in the hot stamping performed subsequently.

[0054] Accordingly, the temperature and flow rate of the gas in the purge are adjusted as appropriate so that the surface temperature of the galvanized layer does not fall to 419 °C or less during the period from the removal of the metallic coating bath until the completion of the alloy heat treatment.

[0055] After gas sweeping, the oxide layer on the metallic coating surface grows momentarily, and therefore the oxide layer forms solidly if the time from gas sweeping until a maximum temperature is reached in the alloy heat treatment is greater than 30 s; therefore, the time is desirablely adjusted to 30 s less, more desirablely 20 s less, still more desirablely 15 s less.

[0056] Although air, nitrogen, or similar gases are used for gas purging, it is desirable to use a gas in which the oxygen density is reduced as much as possible from the standpoint of preventing oxidation. Even when air is used as the gas for gas purging, oxidation can be minimized in some cases, depending on the heating pattern from the gas purge to the subsequent heating; however, it is effective to use nitrogen gas or air with a high partial pressure of nitrogen in which the partial pressure of oxygen is controlled to ideally 15% or less, and more ideally 10% or less.

[0057] Next, the alloy is heat-treated to form the galvanized and annealed layer. The conditions for the alloy heat-treating are not limited to any particular conditions; however, a heating temperature is preferably set to 440 to 600 °C or 460 to 550 °C, and a heating time is adjusted accordingly to the heating temperature, preferably to 1 to 30 s, 1 to 15 s, 1 to 10 s, or 1 to 5 s. zccn Ln / zznz / E / YiAi

[0058] The present invention will be described below more specifically with reference to examples, but the present invention is not limited to these examples. EXAMPLE

[0059] A cold-rolled steel sheet having a thickness of 1.0 mm and a chemical composition including, in % by mass, C: 0.21%, Si: 0.2%, Mn: 2.0%, P: 0.01%, S: 0.007%, Cr: 0.2%, Ti: 0.02%, and B: 0.003%, the remainder being Fe and impurities, was annealed through a continuous galvanizing line and subsequently metal-coated under the conditions indicated in Table 1. The cold-rolled steel sheet was then subjected to alloy heat treatment under the conditions indicated in Table 1 to produce a metal-coated steel sheet.

[0060] Note that, after removing the steel sheet from the metal coating bath, the gas purging conditions were optimized to prevent solidification of the coating layer. For the gas purging conditions shown in Table 1, a case where solidification of the coating layer did not occur was designated O, and a case where solidification occurred was designated x. In all examples, the time elapsed from gas purging until the maximum temperature in the alloy heating process was reached was set at 10 s, and the oxygen content of the gas for gas purging was 15%, with the remainder being nitrogen. Furthermore, the composition of the metal coating bath was such that Al was 0.13% by mass, with the remainder being Zn, and the temperature of the metal coating bath was set at 460 °C.

[0061] zccn Ln / zznz / E / YiAi Table 1 Test No. Proportion of solidified zinc layer (%) Iron content (mass) Zn / Al oxide layer Oxide layer thickness (pm) Weight per square meter of metallic coating (g / m2) Gas sweeping conditions Heating temperature (°C) Heating time (S) Cobweb defect Corrosion resistance 1 98 0.2 2.3 1.6 90 O - 0 FA Comparative example 2 95 0.4 2.5 1.2 90 o 480 5 CA Invention example 3 94 0.5 3.4 0.9 90 o 500 3 BA Invention example 4 95 0.4 4.1 0.7 90 o 520 2 BA Invention example 5 93 0.6 5.3 0.3 90 0 540 1 BA Invention example 6 91 0.7 2.7 0.8 90 0 480 7 CA Example of invention 7 90 0.8 3.7 0.6 90 0 500 5 BA Example of invention 8 89 0.9 4.0 0.2 90 0 520 3 BA Example of invention 9 81 1.5 3.7 0.6 90 0 500 9 BA Example of invention 10 70 2.4 3.8 0.5 90 0 500 13 BA Example of invention 11 61 3.1 3.9 0.4 90 or 500 17 BA Example of invention 12 49 4.0 2.8 0.7 90 or 480 25 CA Example of invention 13 50 3.9 3.9 0.4 90 or 500 20 BA Example of invention 14 51 3.8 4.4 0.2 90 or 520 15 BA Example of invention 15 50 3.9 4.9 0.1 90 0 540 10 AA Example of invention 16 52 3.7 6.4 0.2 60 or 500 10 AB Example of invention 17 49 4.0 4.2 0.3 70 0 500 15 BA Example of invention 18 50 3.9 3.3 0.5 140 0 500 30 BA Example of invention 19 48 4.0 2.7 0.6 160 or 500 40 CA Example of invention 20 50 3.9 2.5 1.3 90 X 500 10 CA Example of invention 21 40 4.6 3.9 0.4 90 or 500 22 BA Example of invention 22 30 5.4 3.9 0.3 90 or 500 25 BA Example of invention 23 21 6.0 3.8 0.3 90 or 500 27 BA Example of invention 24 12 6.7 2.9 0.4 90 0 480 40 CA Example of invention 25 10 6.8 3.8 0.3 90 0 500 30 BA Example of invention 26 11 6.7 4.5 0.3 90 0 520 22 BA Example of invention 27 10 6.8 5.3 0.2 90 0 540 15 AA Example of invention 28 4 7.2 6.5 0.2 90 0 480 50 BF Comparative Example 29 5 7.2 6.9 0.2 90 0 500 40 AF Comparative Example 30 4 7.2 7.2 0.2 90 O 520 30 AF Comparative Example 31 5 7.2 7.4 0.1 90 or 540 20 AF Comparative example 32 0 8.2 6.6 0.2 90 or 480 70 AF Comparative example 33 0 8.0 6.9 0.1 90 or 500 60 AF Comparative example 34 0 8.5 7.0 0.1 90 0 520 50 AF Comparative example 35 0 9.0 7.5 0.1 90 0 540 40 AF Comparative example.

[0062] The chemical composition of the galvanized layer of the resulting metal-coated steel sheet was measured using the method described above. In addition, the thickness of the oxide layer of the resulting metal-coated sheet was measured using the GDS. The results of these measurements are shown together in Table 1. As shown in Table 1, in test number 1, the proportion of its solidified zinc layer was 98%, which is equivalent to a normal, non-alloyed galvanized steel sheet. In tests number 32 to 35, their galvanized layers were so fully alloyed that the proportions of the solidified zinc layers were 0%, which is equivalent to a normal, annealed galvanized steel sheet.

[0063] Next, a sheet of metal-coated steel in each of the test specimens was cut into 100 mm square pieces, which were heated to 900 °C in an electric furnace with an air atmosphere for 3 minutes, removed, and immediately placed in a flat press machine with built-in water-cooling tubes for rapid cooling, thereby obtaining a high-strength, hot-stamped material. The surface of the material was observed to assess whether or not there was a cobweb-like defect.As an evaluation criterion, a case in which a cobweb-like defect was very clearly visible on the surface of the material was graded F, a case in which a cobweb-like defect was slightly visible and was still visible even after chemical conversion and electrodeposition was graded C, a case in which a cobweb-like defect was slightly visible but not visible after chemical conversion and electrodeposition was graded B, and a case in which no cobweb-like defect was visible even before chemical conversion and electrodeposition was graded A.

[0064] In addition, corrosion resistance was evaluated by a coating adhesion test by immersion in hot salt water. A sample material, after hot stamping heating, was subjected to zinc phosphate treatment with PBL-3080 from NIHON PERKERIZING Co.The sample was treated under normal chemical treatment conditions and then subjected to electroplating with GT-10 electroplating paint from KANSAI PAINT CO., LTD. by energizing at a voltage of 200 V, and subjected to a baking finish at a baking temperature of 150 °C for 20 minutes. The coating thickness was 20 µm. The resulting sample was immersed in a 5% aqueous NaCl solution at 50 °C for 500 hours, and then a coating peel test was performed using adhesive tape on the coating; a case in which 5% or more coating peel occurred was graded F, a case in which 1% or more to less than 5% coating peel occurred was graded B, and a case in which less than 1% peel occurred was graded A.

[0065] The evaluation results are shown together in Table 1. As can be seen from the results shown in Table 1, in cases where the specifications of the present invention were met, cobweb defect was avoided and corrosion resistance was excellent. In particular, in examples where the Zn / Al values ​​in the oxide layer were from 3.0 to 6.0, cobweb defect was not observed, or almost none. zccn Ln / zznz / E / YiAi INDUSTRIAL APPLICABILITY

[0066] In accordance with the present invention, it is possible to provide a metal-coated steel sheet for hot stamping in which a cobweb-like surface defect can be avoided in the case of using a Zn metal coating containing Al.

Claims

1. A hot-stamped, metallic-coated steel sheet comprising a base metal and a galvanized layer formed on a surface of the base metal, wherein the galvanized layer includes a galvanized and annealed layer, a solidified zinc layer, and an oxide layer containing Al, in this order from the base metal, and a ratio of a Zn content (g / m2) in the solidified zinc layer to a Zn content (g / m2) in the galvanized layer is from 10 to 95%.

2. The hot-stamping metal-coated steel sheet according to claim 1, wherein a chemical composition of the oxide layer satisfies Formula (i) shown below. 3.0 < Zn / Al < 6.0 (i) where Zn and Al are the Zn and Al contents (g / m2) contained in the oxide layer, respectively.

3. The hot-stamping metal-coated steel sheet according to claim 1 or claim 2, wherein the average thickness of the oxide layer is 1.0 μιη or less.

4. The hot-stamped, metallic-coated steel sheet according to any of claims 1 to 3, wherein the Zn content in the galvanized layer is 65 to 150 g / m2.

5. The hot-stamped metal-coated steel sheet according to any one of claims 1 to 4, wherein the Fe content in the galvanized layer is, by mass, less than 7%.