Zn-plated hot stamped products

Abstract

The Zn-plated hot-stamped product of the present invention is a Zn-plated hot-stamped product comprising a steel material, a Zn-plated layer, and an oxide layer. The surface area of ​​the Zn-plated layer, i.e., the upper layer, is a two-phase structure of a Γ phase and an Fe-Zn solid solution. The area of ​​the Zn-plated layer other than the upper layer, i.e., the lower layer, is a single-phase structure of an Fe-Zn solid solution. The thickness of the upper layer and the thickness of the lower layer satisfy the following formula: the ratio of the maximum value Max.Mn to the minimum value Min.Mn of the Mn content on the surface of the Zn-plated hot-stamped product, i.e., the Mn content ratio, is 10.0 or less, and the average value Ave.Mn is 0.5 to 7.5% by mass. 0.20≤upper layer thickness / (upper layer thickness+lower layer thickness)≤0.80

Description

Technical Field

[0001] The present invention relates to a Zn-plated hot stamped product. Background Art

[0002] In the field of automotive components, the demand for higher strength is increasing to improve fuel efficiency and crash safety, and as a solution, the application of hot stamping technology is expanding. Hot stamping is a technology that produces high-strength pressed products with high shape freezeability by simultaneously hot forming a billet heated to a temperature above the austenite single-phase region (Ac3 point), for example, around 900°C, and then rapidly cooling (quenching) the mold to remove heat.

[0003] Furthermore, since scale such as iron oxide is generated during heating for hot stamping, it is necessary to remove the scale by shot blasting or the like after hot stamping. However, as described in Patent Document 1, the generation of scale can be suppressed by using plated steel sheets, and the scale removal step can be omitted, thereby expanding the application of Zn-based plated steel sheets for hot stamping.

[0004] When Zn-plated steel sheets are used, Zn components remain in the surface layer of the steel sheet after hot stamping, resulting in improved corrosion resistance compared to hot stamped materials made from non-plated steel sheets. In recent years, there has been a demand for hot stamped materials for components requiring high rust resistance, and further improvements in the corrosion resistance of hot stamped products are desired.

[0005] Furthermore, hot stamping materials have been primarily used as reinforcements for skeletal components in locations not visible from the outside after assembly into a vehicle. However, improving the appearance of hot stamping materials is expected to expand their use in visible locations. However, when hot-dip galvanized steel sheets are used for hot stamping, a pattern resembling a tortoise's shell or a spider's nest (so-called tortoise shell pattern) has traditionally developed on the surface, leading to a need to suppress this pattern.

[0006] However, in Zn-based hot stamped products having a Γ phase and an Fe-Zn solid solution, the Γ phase is approximately 70-85 mass% Zn and 15-30 mass% Fe, and the Fe-Zn solid solution is 10-40 mass% Zn and 60-90 mass% Fe.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent No. 3582511 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] Neither the Γ phase nor the Fe-Zn solid solution is excellent in both corrosion resistance and coating adhesion. In addition, a structure that combines corrosion resistance and adhesion with steel sheets as steel materials is unknown.

[0012] The present invention has been made in view of the above, and an object of the present invention is to provide a Zn-based plated hot stamped product that can ensure plating adhesion to steel materials and corrosion resistance and has excellent appearance.

[0013] Means for solving problems

[0014] The inventors discovered that the tortoise shell pattern is formed by localized oxidation of Mn, and gained the insight that controlling the formation state of the oxide film formed in the outermost layer during hot stamping heating, as well as the volume change and flow caused by the plating phase transition beneath the oxide, is crucial. Furthermore, the inventors discovered that by controlling the thickness ratio of the upper layer to the lower layer of the plating layer (where the upper layer consists of a Γ phase and an Fe-Zn solid solution and the lower layer consists of an Fe-Zn solid solution) within a specific range, both excellent post-painting corrosion resistance and excellent plating adhesion can be achieved.

[0015] The present invention has been made by further research based on the above findings, and the gist of the present invention is as follows.

[0016] (1) A Zn-plated hot-stamped product according to one embodiment of the present invention is a Zn-plated hot-stamped product comprising a steel material, a Zn-plated layer containing Zn formed on the surface of the steel material, and an oxide layer containing Zn and Mn formed on the surface of the Zn-plated layer, wherein the region on the surface side of the Zn-plated layer, i.e., the upper layer, is a two-phase structure of a Γ phase and an Fe-Zn solid solution, and the region other than the upper layer, i.e., the lower layer, is a single-phase structure of an Fe-Zn solid solution, and the thickness of the upper layer and the thickness of the lower layer satisfy the following formula (1), and the maximum value Max.Mn, the minimum value Min.Mn, and the average value Ave.M of the Mn content on the surface of the Zn-plated hot-stamped product satisfy the following formulas (2) and (3) in terms of mass %.

[0017] 0.20≤Upper layer thickness / (Upper layer thickness+Lower layer thickness)≤0.80 (1)

[0018] Ave.Mn=0.5~7.5 (2)

[0019] Max.Mn / Min.Mn≤10.0 (3)

[0020] (2) According to the Zn-based plated hot stamped product described in (1), the ratio of the Γ phase in the upper layer to the Γ phase in the dual-phase structure of the Fe-Zn solid solution may be 20% to 80%.

[0021] (3) In the Zn-plated hot stamped article according to (1) or (2), the Zn content of the Zn-plated layer may be 30.0% or more in terms of mass%.

[0022] (4) The Zn-based plated hot stamped product according to any one of (1) to (3) above, wherein the plate thickness may be 1.0 mm to 3.2 mm.

[0023] Effects of the Invention

[0024] According to the above aspect of the present invention, it is possible to provide a Zn-based plated hot stamped product that can ensure plating adhesion to steel materials and corrosion resistance and has excellent appearance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic cross-sectional view of the Zn-based plated hot stamped product according to the present embodiment.

[0026] Figure 2 These are reflected electron images ((a) and (b), where the contrast is changed between (a) and (b)) and a secondary electron image (c) of the Zn-plated hot-stamped product according to this embodiment.

[0027] Figure 3 This figure shows the boundary between the upper layer and the lower layer in the cross-sectional SEM image of the Zn-based plated hot stamped product according to the present embodiment as a dotted line.

[0028] Figure 4 This figure shows a state in which the upper layer in a cross-sectional SEM image of the Zn-based plated hot stamped product according to the present embodiment is divided into blocks with a pitch of 1 μm×1 μm. DETAILED DESCRIPTION

[0029] The inventors believe that the presence of the Γ phase is important for improving corrosion resistance after painting because the Zn concentration is high and the substitutional corrosion protection performance is high. However, since the Γ phase is an intermetallic compound, it is hard and brittle. In contrast, the Fe-Zn solid solution is considered to have high plastic deformation ability because it is a metal in which Zn is solid-dissolved in ferrite. Therefore, from the perspective of plating adhesion, the presence of the Fe-Zn solid solution is considered to be important. Based on this idea, the inventors conducted in-depth research on the reduction of the tortoise shell pattern and found that the tortoise shell pattern is formed by the local oxidation of Mn that diffuses from the base steel to the surface of the hot stamped product during hot stamping. It was found that it is important to control the formation state of the oxide film generated in the outermost layer during hot stamping heating and the volume change and flow caused by the plating phase change under the oxide.

[0030] Specifically, it was found that during the initial stage of hot stamping heating, the Al contained in the coating is oxidized as the coating melts, and an Al oxide layer with a thickness of tens of nanometers is mainly formed in the outermost layer, followed by the generation of Zn oxide and Mn oxide. However, due to the local generation of Mn oxide at the site of the Al oxide layer fracture, a tortoise shell pattern is visible. Based on the above situation, in-depth research was conducted on the method of suppressing the tortoise shell pattern. As a result, it was found that if the ratio of the maximum value Max.Mn to the minimum value Min.Mn of the Mn content on the surface of the Zn-plated hot stamped molded product, that is, the Mn content ratio (Max.Mn / Min.Mn), is below a specific value, and the average value Ave.Mn of the Mn content of the molded product is within a specific range, the formation of the oxide layer and the reaction of the coating can be uniformly promoted, the generation of the tortoise shell pattern can be suppressed, and a good appearance can be obtained.

[0031] Furthermore, the present inventors have discovered that by controlling the ratio of the thickness of the upper layer to the thickness of the lower layer of the plating layer, in which the upper layer is a Γ phase and an Fe-Zn solid solution and the lower layer is an Fe-Zn solid solution, within a specific range, both excellent post-coating corrosion resistance and excellent plating adhesion can be achieved. The present invention has been completed based on the above findings.

[0032] Reference Figure 1 , the Zn-based plated hot stamped product 100 of the present embodiment is described. The Zn-based plated hot stamped product 100 of the present embodiment includes a steel material 1, a Zn-based plating 2 and an oxide layer 3. The Zn-based plating 2 includes a lower layer 21 and an upper layer 22. The upper layer 22, which is the region on the surface side of the Zn-based plating 2, is a two-phase structure in which Fe-Zn solid solution 15 is distributed in an island shape in the Γ phase (capital gamma phase) 14. The lower layer 21, which is the region on the steel material side of the Zn-based plating 2, is a single-phase structure of Fe-Zn solid solution. The following describes each structure. It should be noted that the thickness of the Zn-based plating 2 is about several to several tens of μm. On the other hand, the thickness of the oxide layer 3 is mostly about several hundred nm to several μm, which is smaller than the thickness of the Zn-based plating 2. However, for the convenience of illustration, Figure 1 The thickness of the oxide layer 3 is magnified in this figure.

[0033] (Steel)

[0034] Steel material 1 will be described. The chemical composition of steel material 1 is not particularly limited, but an example of a chemical composition for an automotive steel sheet includes, by mass%, C: 0.05% to 0.45%, Si: 0.50% or less, Mn: 0.50% to 2.50%, P: 0.030% or less, S: 0.015% or less, Al: 0.100% or less, N: 0.010% or less, Cu: 0-1.00%, Ni: 0-1.00%, Cr: 0-0.50%, Mo: 0-0.50%, Nb: 0-0.10%, V: 0-0.10%, Ti: 0-0.10%, B: 0-0.0050%, Ca: 0-0.0100%, REM: 0-0.0100%, and the remainder being iron and impurities. The chemical composition of these elements will be described below.

[0035] C: 0.05% to 0.45%

[0036] Carbon (C) is an element that increases the strength of Zn-plated hot stamped products after hot stamping. If the C content in the steel 1 is too low, the above-mentioned effect cannot be obtained. Therefore, the lower limit of the C content in the steel 1 is preferably set to 0.05%. The preferred lower limit of the C content is 0.10% or 0.15%. On the other hand, if the C content in the steel 1 is too high, the toughness of the steel plate decreases. Therefore, the upper limit of the C content is preferably set to 0.45%. The preferred upper limit of the C content is 0.40% or 0.35%.

[0037] "Si: 0.50% or less"

[0038] Silicon (Si) is an element inevitably contained in the steel 1. In addition, Si has the effect of deoxidizing the steel 1. However, if the Si content in the steel 1 is too high, the Si in the steel 1 diffuses during the heating in hot stamping, and oxides are formed on the surface of the steel 1. The oxides reduce the phosphate treatability. Si also has the effect of increasing the Ac3 point of the steel 1. If the Ac3 point increases, the heating temperature during hot stamping sometimes exceeds the evaporation temperature of Zn. When the Si content in the steel 1 exceeds 0.50%, the above-mentioned problem becomes significant, so the upper limit of the Si content is preferably set to 0.50%. The more preferred upper limit of the Si content is 0.40% or 0.30%. There is no need to specifically specify the lower limit of the Si content, but for sufficient deoxidation, the lower limit can also be set to 0.05%.

[0039] Mn: 0.50% to 2.50%

[0040] Manganese (Mn) is an element that improves the hardenability of the steel 1 and the strength of the Zn-coated hot stamped product 100. If the Mn content is too low, the effect cannot be obtained. In order to obtain this effect, the lower limit of the Mn content of the steel 1 is preferably set to 0.50%. The preferred lower limit of the Mn content of the steel 1 is 0.60% or 0.80%. On the other hand, if the Mn content is too high, the effect is saturated. Therefore, the upper limit of the Mn content of the steel 1 is preferably set to 2.50%. The preferred upper limit of the Mn content of the steel 1 is 2.30% or 2.00%.

[0041] "P: 0.030% or less"

[0042] Phosphorus (P) is an impurity contained in Steel Material 1. P segregates at the grain boundaries of Steel Material 1, reducing the toughness of the steel and lowering its delayed fracture resistance. Therefore, the P content of Steel Material 1 is preferably as low as possible. However, if the P content exceeds 0.030%, its effects become significant. Therefore, the upper limit of the P content in Steel Material 1 may be set at 0.030%. The lower limit of the P content is 0%.

[0043] "S: 0.015% or less"

[0044] Sulfur (S) is an impurity contained in Steel 1. Sulfur forms sulfides, which lowers the toughness of the steel and reduces its delayed fracture resistance. Therefore, the upper limit of the S content is 0.015%. The S content is preferably as low as possible. The lower limit of the S content is 0%.

[0045] "Al: 0.100% or less"

[0046] Aluminum (Al) is an element that is effective for deoxidation of steel. There is no need to specify a lower limit for the Al content, and the lower limit is 0%. However, for deoxidation purposes, the Al content of the steel material 1 may be set to 0.005% or more or 0.010% or more. On the other hand, if the Al content is too high, the Ac3 point of the steel sheet may rise, and the necessary heating temperature during hot stamping may exceed the evaporation temperature of the Zn-based coating 2. Therefore, the upper limit of the Al content of the steel material 1 is preferably set to 0.100%. The more preferred upper limit of the Al content of the steel material 1 is 0.070% or 0.050%. The Al content in this specification refers to the so-called total Al (T-Al) content.

[0047] "N: 0.010% or less"

[0048] Nitrogen (N) is an impurity inevitably contained in the steel 1. N is an element that forms nitrides and reduces the toughness of the steel 1. When B is contained, N combines with B to reduce the amount of solid-solution B. The reduction in the amount of solid-solution B reduces the hardenability. Therefore, the N content of the steel 1 is preferably as low as possible. When the N content of the steel 1 exceeds 0.010%, its influence becomes significant, so the upper limit of the N content of the steel 1 can also be set to 0.010%. There is no need to specifically specify the lower limit of the N content, and the lower limit of the N content is 0%.

[0049] The chemical composition of the steel material 1 of this embodiment may also have, for example, a chemical composition comprising the aforementioned elements and the remainder consisting of Fe and impurities. As used herein, impurities are elements that are mixed into or intentionally added from raw materials such as ore, scrap, or the manufacturing environment during industrial production of steel materials. Examples of such elements include those that are tolerated within a range that does not impair the properties of the Zn-based plated hot stamped product 100 of this embodiment.

[0050] The steel material 1 constituting the Zn-plated hot-stamped product 100 of this embodiment contains one or more optional elements selected from Cu, Ni, Cr, Mo, Nb, V, Ti, B, Ca, and REM as a partial Fe replacement. The following elements are optional elements. The lower limit of their content is 0%.

[0051] [Cu: 0-1.00%]

[0052] Cu is an element that dissolves in steel and can improve strength without compromising toughness. However, excessive Cu content can sometimes cause microscopic cracks on the surface during rolling. Therefore, the Cu content is preferably 1.00% or less or 0.60% or less, more preferably 0.40% or less or 0.25% or less. To fully achieve the above-mentioned effects, the Cu content is preferably 0.01% or more, more preferably 0.05% or more.

[0053] "Ni: 0% to 1.00%"

[0054] Nickel (Ni) improves the toughness of the steel 1. Furthermore, Ni suppresses embrittlement caused by liquid Zn during heating during hot stamping. To achieve these effects, the preferred lower limit of the Ni content in the steel 1 is 0.10%. However, if the Ni content in the steel 1 is too high, these effects saturate. Therefore, the upper limit of the Ni content is preferably set to 1.00%.

[0055] "Cr: 0% to 0.50%"

[0056] Chromium (Cr) is an element that improves the hardenability of steel. To achieve this effect, the preferred lower limit of the Cr content in Steel 1 is 0.10%. However, if the Cr content in Steel 1 is too high, Cr carbides will form, which become difficult to dissolve during hot stamping. This makes austenitization of Steel 1 difficult, reducing hardenability. Therefore, the upper limit of the Cr content in Steel 1 is preferably set to 0.50%.

[0057] Mo: 0% to 0.50%

[0058] Molybdenum (Mo) is an element that improves the hardenability of steel 1. To achieve this effect, the preferred lower limit of the Mo content in steel 1 is 0.05%. However, if the Mo content in steel 1 is too high, this effect is saturated. Therefore, the upper limit of the Mo content in steel 1 is preferably set to 0.50%.

[0059] [Nb: 0~0.10%, V: 0~0.10%, Ti: 0~0.10%]

[0060] Nb, V, and Ti contribute to the improvement of steel plate strength through carbide precipitation. Therefore, they may be contained singly or in combination, as needed. However, if any one element is contained in excess, a large amount of carbides will form, reducing the toughness of the steel plate. Therefore, the content of these elements may be set to 0.10% or less. Alternatively, the content of these elements may be set to 0.08%, 0.05%, or 0.03%, respectively, as needed.

[0061] "B: 0% to 0.0050%"

[0062] Boron (B) is an element that improves the hardenability of steel and increases the strength of the Zn-plated hot-stamped product 100. To achieve this effect, the preferred lower limit of the B content in the steel material 1 is 0.0001%. However, if the B content in the steel material 1 is too high, the effect is saturated. Therefore, the upper limit of the B content in the steel material 1 is preferably set to 0.0050%.

[0063] [Ca: 0~0.0100%, REM: 0~0.0100%]

[0064] Ca and REM are elements that control the morphology of non-metallic inclusions that become the starting point of fracture and cause deterioration of workability, and improve workability, so they can be contained as needed. However, if the content of these elements is excessive, the effect is saturated and the raw material cost increases. Therefore, the Ca content and REM content are preferably set to 0.0100% or less, respectively. As needed, the content of these elements can also be set to 0.0060% or less, 0.0040% or less, or 0.0030% or less, respectively. REM is a general term for a total of 17 elements including Sc, Y and lanthanides, and the REM content refers to the total amount of the above elements.

[0065] The chemical composition of the steel material 1 can be measured using common analytical methods. For example, ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) can be used. It should be noted that C and S can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas dissolution-thermal conductivity method. The surface coating can be removed by mechanical polishing before chemical composition analysis.

[0066] (Zn-based coating)

[0067] The Zn-plated hot stamped product 100 of the present embodiment has a Zn-plated layer 21 and an upper layer 22. The surface area of ​​the Zn-plated layer 2, i.e., the upper layer 22, is a two-phase structure in which Fe-Zn solid solution 15 is distributed in the capital gamma phase (Γ phase) 14 in an island shape. The steel side of the Zn-plated layer 2, i.e., the lower layer 21, is a single-phase structure of Fe-Zn solid solution. The crystal structure of Fe-Zn solid solution is the same as that of α-Fe. Fe-Zn solid solution contains Fe and Zn dissolved in Fe. Γ phase 14 is a metal compound of Fe and Zn, i.e., Fe3Zn 10 By forming the upper layer 22 on the surface side into a two-phase structure of the Γ phase 14 and the Fe-Zn solid solution 15, the corrosion resistance after painting is improved.

[0068] In the Zn-based plated hot stamped product 100 , the thickness of the upper layer 22 and the thickness of the lower layer 21 of the Zn-based plated layer 2 satisfy the following formula (1).

[0069] 0.20≤Upper layer thickness / (Upper layer thickness+Lower layer thickness)≤0.80(1)

[0070] When the upper layer 22 and the lower layer 21 of the Zn-based plating layer 2 satisfy the above-mentioned formula, the corrosion resistance of the Zn-based plated hot stamped product 100 and the plating adhesion to the steel material can be ensured.

[0071] If "upper layer thickness / (upper layer thickness + lower layer thickness)" is less than 0.20, the ratio of the Γ phase 14 in the Zn-based plating layer 2 may decrease, and sufficient corrosion resistance may not be obtained. In addition, if "upper layer thickness / (upper layer thickness + lower layer thickness)" is greater than 0.80, the adhesion between the lower layer 21 and the steel material 3 may be reduced, and sufficient plating adhesion may not be obtained.

[0072] The ratio of the Γ phase 14 in the two-phase structure of the Γ phase 14 and the Fe-Zn solid solution 15 in the upper layer 22 of the Zn-based plating layer 2 (the ratio of the Γ phase relative to the Γ phase 14 and the Fe-Zn solid solution 15 in the upper layer 22) is preferably set to 20% or more and 80% or less. By setting the ratio of the Γ phase relative to the Γ phase 14 and the Fe-Zn solid solution 15 in the upper layer 22 to 20% or more and 80% or less, the plating adhesion between the lower layer 21 and the upper layer 22 (durability against fracture in the Zn-based plating layer 2) can be improved. If the ratio of the Γ phase relative to the Γ phase 14 and the Fe-Zn solid solution 15 in the upper layer 22 is less than 20%, the corrosion resistance after coating is sometimes reduced. In addition, if the ratio of the Γ phase relative to the Γ phase 14 and the Fe-Zn solid solution 15 in the upper layer 22 exceeds 80%, the ratio of the hard and brittle Γ phase increases, thereby reducing the workability of the upper layer 22. As a result, the adhesion between the upper layer 22 and the lower layer 21 is sometimes reduced, and the plating adhesion is reduced. As needed, the lower limit of "upper layer thickness / (upper layer thickness+lower layer thickness)" can be set to 25%, 30% or 35%, and the upper limit can be set to 75%, 70% or 65%.

[0073] Regarding the ratio of the Γ phase 14 inside the upper layer 22, it is sufficient to take the SEM image when measuring the thickness of the upper layer 22, as shown in FIG. Figure 4 In this way, the blocks are divided into three types: Γ phase only, Fe-Zn solid solution only, and both Γ phase and Fe-Zn solid solution. The number of blocks of Γ phase and Fe-Zn solid solution is counted, and the Γ phase ratio is calculated from the ratio of these blocks. It should be noted that for the blocks containing both Γ phase and Fe-Zn solid solution, the 1μm×1μm blocks can be further subdivided to more accurately measure their area fractions, or 0.5 blocks can be added for each of Γ phase and Fe-Zn solid solution.

[0074] It should be noted that in the present embodiment, the Zn content of the Zn-based plating layer 2 is 30.0% or more in terms of mass %. As needed, the lower limit of the Zn content may be set to 35.0%, 40.0%, or 50.0%. The upper limit of the Zn content is preferably set to 80.0%. As needed, the upper limit of the Zn content may also be set to 78.0% or 75.0%. It is not necessary to specifically specify the content of elements other than Zn, but the chemical composition of the Zn-based plating layer 2 (excluding Zn) is preferably set to, for example, Fe: 20.0-70.0%, Al: 0-1.0%, Si: 0-1.0%, Mg: 0-1.0%, Mn: 0-1.0%, Ni: 0-1.0%, Sb: 0-1.0%, and the remainder: impurities in terms of mass %.

[0075] The so-called Zn-based plating 2 of this embodiment has an Fe content set to a range of less than 95.0%, and the analysis position of the chemical composition of the Zn-based plating 2 is set to the center of the thickness of the Zn-based plating 2 (the center of the film thickness). The above-mentioned chemical composition analysis method is set as follows. From the surface of the Zn-based plated hot stamped product 100, the Fe content is measured along the thickness direction of the Zn-based plated hot stamped product 100 (that is, from the surface of the Zn-based plated hot stamped product 100 toward the center of the plate thickness) by GDS (glow discharge luminescence analysis), and the range from the surface of the Zn-based plated hot stamped product 100 to the point where the Fe content exceeds 95.0% is specified. Afterwards, the content of each element at the center of the distance from the position where the initial Fe content becomes 95.0% to the surface (this range is the Zn-based plating 2) (that is, the center of the thickness of the Zn-based plating 2) is analyzed by GDS, and its analysis value is set as the chemical composition of the Zn-based plating 2. Since an oxide layer exists further on the surface side of the Zn-plated hot-stamped product 100, the position where the Zn content reaches 80.0% (if there are multiple layers, the position closest to the surface) is considered to be the surface position of the Zn-plated layer 2. It should be noted that even when the Zn content of the Zn-plated layer 2 is approximately 30%, since Zn is concentrated in the oxide layer, the position where the Zn content reaches 80% is set as the boundary between the Zn-plated layer 2 and the oxide layer 3.

[0076] However, if there is no region with a Zn content exceeding 80.0% in the outermost layer of the hot stamped product, the outermost layer is regarded as the surface position of the Zn-based plating layer 2 and the center of the thickness of the Zn-based plating layer 2 (the center of the film thickness) is determined.

[0077] The observation of the Γ phase 14 and the Fe-Zn solid solution 12, 15 can be carried out as follows. In such a way that the Zn-based coating 2 can be observed from a cross section, a sample cut into about 20 mm square is embedded in a resin and then mechanically polished to a mirror surface. The resin-embedded sample is observed using a scanning electron microscope (SEM) using a backscattered electron (BSE) image and a secondary electron (Secandary Electron) image magnified to 2000 times. In this SEM-BSE observation, since elements with large atomic weights are observed to have a bright contrast (whiter), the Γ phase, Fe-Zn solid solution and steel can be identified separately by the difference in contrast. Specifically, the Γ phase containing a lot of Zn with an atomic weight larger than Fe is observed to be white, the Fe-Zn solid solution is black, and the steel is observed to be even blacker. As shown by Figure 2 As can be judged from the reflected electron images with changed contrast in (a) and (b), the Γ phase 14, the Fe-Zn solid solution 12, 15, and the steel material 1 can be easily distinguished by the difference in contrast of the reflected electron images. In addition, when observing the difference in contrast of the Γ phase 14, the Fe-Zn solid solution 12, 15, and the steel material 1 by SEM-BSE observation (i.e., reflected electron image) as described above, the oxide containing many light elements turns black and cannot be distinguished from the surrounding resin. Therefore, by performing SEM-SE observation on the same field of view as the SEM-BSE observation (i.e., as Figure 2 By observing the secondary electron image as shown in (c), the oxide layer formed on the surface side of the plating layer can be observed.

[0078] It should be noted that the coating of this embodiment has a two-layer structure, wherein the lower layer 21 in contact with the steel material 1 is a single-phase structure of the Fe-Zn solid solution 12, and the upper layer 22 is a two-phase structure of the Γ phase 14 and the Fe-Zn solid solution 15. The method of distinguishing the upper layer 22 from the lower layer 21 is described below, taking as an example the case where the upper layer 22 is a two-phase structure of the Γ phase 14 and the Fe-Zn solid solution 15.

[0079] like Figure 3As shown in FIG, an imaginary line drawn perpendicular to the thickness direction of the steel material 1 (i.e., parallel to the surface) from the portion of the relatively white Γ phase 14 observed to be closest to the steel material 1 in the thickness direction is set as the boundary line between the upper layer 22 and the lower layer 21. The thickness of the upper layer 22 is set to the shortest distance from the outermost portion of the upper layer 22 (i.e., the portion of the Zn-based coating 2 that is farthest from the steel material 1 in the thickness direction) to the above-mentioned boundary line. The thickness of the lower layer 21 is set to the shortest distance from the above-mentioned boundary line to the portion of the interface between the Zn-based coating 2 and the steel material 1 that is closest to the center of the steel material (i.e., the portion of the Zn-based coating 2 that is farthest from the surface in the thickness direction). This operation is performed in any five viewing fields, and the thickness of the upper layer and the thickness of the lower layer are measured, and the average value is set as the upper layer thickness and the lower layer thickness.

[0080] (Oxide layer)

[0081] The Zn-plated hot stamped product 100 of the present embodiment has an oxide layer 3 containing Zn and Mn. The average value Ave.Mn of the Mn content on the surface of the oxide layer 3 (the surface of the hot stamped product 100) is 0.5 to 7.5% in mass%. That is, Ave.Mn satisfies the following formula (2) in mass%. A more preferred Ave.Mn of the oxide layer 3 is 1.0% or more. The Mn in the oxide layer 3 is Mn diffused from the steel material 1 to the surface of the oxide layer 3 during hot stamping. The Ave.Mn of the oxide layer 3 is preferably 7.0% or less. The Ave.Mn of the oxide layer 3 is further preferably 6.5% or less. If the Ave.Mn of the oxide layer 3 is 0.5% or more and 7.0% or less, the generation of a tortoise shell pattern can be suppressed.

[0082] Ave.Mn=0.5~7.5 (2)

[0083] The ratio of the maximum value Max.Mn to the minimum value Min.Mn of the Mn content on the surface of the Zn-coated hot stamped product 100 (the surface of the oxide layer 3), Max.Mn / Min.Mn, that is, the Mn content ratio is 10.0 or less. That is, Max.Mn / Min.Mn satisfies the following formula (3). If the Mn content ratio is 10.0 or less, the tortoise shell pattern after hot stamping can be reduced, and an excellent appearance quality can be obtained. The Mn content ratio is more preferably 8.0 or less. The Mn content ratio is further preferably 5.0 or less. The lower limit of the Mn content ratio is 1.0. As needed, the lower limit can also be set to 1.2, 1.3 or 1.5.

[0084] Max.Mn / Min.Mn≤10.0 (3)

[0085] The Mn content of the oxide layer in the Zn-plated hot stamped product 100 can be measured by the following method. Use an electron beam microanalyzer (e.g., EPMA-1720H manufactured by Shimadzu Corporation) to observe the surface of the Zn-plated hot stamped product 100. At this time, the acceleration voltage is set to 15kV, the beam current is set to 100nA, and the beam diameter is set to the minimum conditions of the device (wherein, it is set to 1 to 4μm). On the surface of the Zn-plated hot stamped product 100, the Mn content is measured under the conditions of a measurement length of 40mm, a measurement spacing of 20μm (2000 point measurement), and a measurement time of 1.0sec / point. In order to eliminate the influence caused by the roughness of the surface layer, etc., each adjacent 10 points (200μm points = 0.2mm points) in the measurement range are set as one area and averaged, and set as the Mn content of the area. The maximum value of the measured Mn content (Mn content in the 200 region) is set as Max.Mn, the minimum value is set as Min.Mn, and the Mn content ratio (Max.Mn / Min.Mn) is calculated. The average value of the measured Mn content is set as Ave.Mn.

[0086] It should be noted that when hot stamped parts are coated with a resin or other coating, the coating is removed by dissolving it with a stripper, and then the Mn content of the oxide is measured using the above method. In this case, stripping conditions must be selected based on the type and thickness of the coating to minimize coating residue and avoid removing surface oxides.

[0087] It should be noted that in this embodiment, an oxide layer 3 containing Zn and Mn exists on the surface of the Zn-based plated hot stamped product 100. Figure 2 As shown in (c), the presence of the oxide layer 3 can be confirmed by using a secondary electron image obtained by SEM-SE observation. Confirming the types of oxides contained in the oxide layer 3 is very complicated and technically difficult, so it is not necessary to confirm. It is assumed that the oxide layer 3 is present by confirming that the Mn content (Max.Mn, Min.Mn and Ave.Mn) on the surface of the hot stamped product 100 as described above satisfies equations (2) and (3).

[0088] (plate thickness)

[0089] The thickness of the hot stamped product 100 used in automobile components is often 1.0 to 3.2 mm. Therefore, the thickness of the hot stamped product 100 is preferably set to 1.0 to 3.2 mm. Alternatively, the thickness may be set to 1.0 to 2.6 mm as needed.

[0090] (Manufacturing Method)

[0091] Next, a description will be given of a method for manufacturing the Zn-based plated hot stamped product 100. The method for manufacturing the Zn-based plated hot stamped product 100 of this embodiment is not limited to the method described below.

[0092] (Slab heating temperature: 1100~1300℃)

[0093] First, steel is prepared. For example, molten steel having a chemical composition within the preferred range described above is produced. Slabs are produced using this molten steel through a casting method such as continuous casting. The slab heating temperature is preferably set to 1100°C or higher. There is no specific upper limit for slab heating. Heating the slab to temperatures exceeding 1300°C requires a significant amount of energy, resulting in a significant increase in manufacturing costs. Therefore, the slab heating temperature is preferably set to 1300°C or lower.

[0094] Hot rolling after heating the slab, cooling after hot rolling, and coiling may be performed by a general method and are not particularly limited.

[0095] After coiling, the steel is annealed as needed. After coiling or annealing, the hot-rolled steel sheet is pickled as is. After pickling, cold rolling may be performed as needed. This can be done using known methods based on the properties required for the intended component.

[0096] (Zn-based plating)

[0097] The hot-rolled steel sheet or cold-rolled steel sheet is subjected to Zn plating to form a Zn plating layer on the surface of the steel sheet, thereby obtaining a hot stamping steel material. The Zn plating layer is formed by any method, but hot-dip galvanizing is preferred.

[0098] The coating weight of the Zn-based plating layer of the hot stamping steel material is preferably set to 80 g / m 2 Above and 150g / m 2 If the coating weight of the Zn-based plating layer is 80 g / m 2 Above 150 g / m² can improve the corrosion resistance of hot stamped products, so it is preferred. 2 Below, good appearance can be obtained after plating treatment, so it is preferred (if with 150g / m 2Compared to increasing the amount of coating adhesion, when hot-dip galvanizing is performed, the coating sometimes sags and the appearance deteriorates, and the appearance of the hot-stamped product also deteriorates). It should be noted that the Zn-based coating of the steel material for hot stamping is a hot-dip galvanized steel sheet (GI) in which the amount of oxides in the formed product during hot stamping is small. Alloyed hot-dip galvanizing (GA) is not suitable as the Zn-based coating of the present invention because the amount of oxides generated in the formed product during hot stamping is large and the appearance deteriorates. Therefore, as the raw material of the hot stamping formed product 100, that is, the steel material for hot stamping, alloyed hot-dip galvanized steel sheet (GA) is not preferred, and hot-dip galvanized steel sheet (GI) is preferably set. Even if the alloyed hot-dip galvanized steel sheet (GA) is used to manufacture the hot stamped formed product 100, Ave.Mn=0.5~7.5 cannot be satisfied, and as a result, the goal of obtaining an excellent appearance cannot be met.

[0099] The coating weight of the Zn-based plating on hot-stamping steel can be determined by immersing the steel in a 5% aqueous HCl solution containing 0.02% of a corrosion inhibitor (Ibit700A, Asahi Chemical Co., Ltd.) to inhibit the dissolution of Fe in the hot-rolled or cold-rolled steel sheet at room temperature for 10 minutes to dissolve the entire Zn-based plating layer, and then calculating the weight change before and after dissolution. However, the completion of Zn-based plating dissolution is determined by the completion of foaming caused by hydrogen generation during dissolution.

[0100] The chemical composition of the Zn-based plating layer of a hot stamping steel material can be, for example, set to, by mass%, Al: 0.1% to 1.0%, Fe: 0.1% to 20.0%, Si: 0% to 0.5%, Mg: 0% to 0.5%, Mn: 0% to 0.5%, Pb: 0% to 0.5%, Sb: 0% to 0.5%, and the remainder: Zn and impurities. The Zn content of the remainder is preferably set to 80% or more.

[0101] After forming the Zn-based coating, it is preferred to adjust the surface roughness Ra (μm) of the hot stamping steel material and the plate thickness t (mm) of the hot stamping steel material by temper rolling so that the surface roughness Ra (μm) and the plate thickness t (mm) of the hot stamping steel material satisfy the following equation (4). A person skilled in the art can adjust Ra / t to the range of the following equation (4) by controlling the surface roughness Ra (μm) and elongation of the tempering roller. For example, by tempering rolling with an elongation of approximately 1.5% using a tempering roller with Ra ≤ 2.5 μm, Ra / t can be adjusted to the range of the following equation (4).

[0102] 0.05≤Ra / t≤0.25 (4)

[0103] If the value of Ra / t exceeds 0.25, the appearance quality may be degraded due to the formation of a tortoise shell pattern. Furthermore, if the value of Ra / t is less than 0.05, the thickness of the Fe-Zn solid solution 15 in the lower layer 21 may increase, and the thickness ratio of the upper layer 22 to the lower layer 21 may not be achieved. It should be noted that Ra is more preferably 0.3 μm or less.

[0104] (Hot stamping process)

[0105] Hot stamping is performed on the above-mentioned hot stamping steel material provided with the Zn-based coating. Detailed description will be given below.

[0106] In order to set the ratio of the thickness of the lower layer 21 to the thickness of the upper layer 22 of the Zn-based plating layer 2, the hot stamping steel is heated in the hot stamping process so that the Fe-Zn solid solution parameter P defined by the following formula (5) satisfies 0.5≤P≤2.5.

[0107] P=[(T-782)×{(t2-t1) / 2+(t-t2)}]÷W 2 (5)

[0108] Where T is the furnace temperature setting temperature (heating temperature) (°C), t is the time from inserting the steel plate into the heating furnace to unloading it (heating time) (seconds), t1 is the time for the steel plate temperature to reach 782°C (seconds), t2 is the time to reach the heating temperature (T) - 10°C (T-10°C reaching time) (seconds), W is the coating adhesion (g / m 2 ).

[0109] When the P value is less than 0.5, the lower layer 21 containing the Fe—Zn solid solution may not cover the interface on the steel material side of the Zn-based plating layer 2, and the plating adhesion may be reduced. To avoid such a state, the P value is 0.5 or more.

[0110] When the P value exceeds 2.5, the ratio of the Fe-Zn solid solution in the Zn-based plating layer 2 increases, and the corrosion resistance after coating decreases. Therefore, the P value is 2.5 or less.

[0111] If the heating temperature T is lower than Ac3, quenching is impossible. Therefore, the heating temperature is preferably above the Ac3 point. When the heating temperature is above 950°C, the surface oxidation (formation of Zn oxide) of the Zn-plated hot stamped product 100 progresses excessively, and the Mn content ratio exceeds 10.0. Therefore, the heating temperature T is preferably lower than 950°C. It should be noted that the Ac3 point (°C) is expressed by the following formula (6).

[0112] Ac3=912-230.5×C+31.6×Si-20.4×Mn-14.8×Cr-18.1×Ni+16.8×Mo-39.8×Cu (6)

[0114] In addition, the element symbol in the above formula represents the content of the element in mass %, and 0 is substituted when the element is not contained.

[0115] If the heating time is less than 240 seconds, quenching may not be possible. Therefore, the heating time is preferably 240 seconds or more. If the heating time exceeds 600 seconds, surface oxidation (formation of Zn oxide) of the Zn-plated hot stamped product 100 may progress excessively. Therefore, the heating time is preferably 600 seconds or less.

[0116] In hot stamping, a hot stamping steel material is typically pressed using a die through which a cooling medium (e.g., water) circulates. During the pressing process, the hot stamping steel material is quenched by heat removal from the die. Through the above steps, a Zn-plated hot stamped part 100 is manufactured.

[0117] To achieve an upper layer composed of a dual-phase structure of Γ phase and Fe-Zn solid solution, a lower layer composed of a single phase of Fe-Zn solid solution, and a Zn-based plating layer 2 with a ratio of "upper layer thickness / (upper layer thickness + lower layer thickness)" of 0.20 to 0.80, the temperature at which the hot stamping steel material is started (the quenching start temperature) is set to a temperature below the lower limit (approximately 750°C) at which the liquid Zn contained in the Zn-based plating layer completely solidifies, but above the upper limit of the temperature range that forms a single layer of Γ phase. The specific temperature range that achieves the aforementioned structure can be easily determined through, for example, preliminary testing. Simply starting quenching from the temperature range thus determined allows the hot stamping process to commence.

[0118] If the average cooling rate from the rapid cooling start temperature to 450°C is lower than 20°C / second, sufficient strength cannot be obtained. Therefore, the average cooling rate from the rapid cooling start temperature to 450°C is set to 20°C / second or higher.

[0119] Furthermore, the average cooling rate from 450° C. to 200° C. is preferably 15° C. / second or more.

[0120] Example

[0121] Next, the embodiments of the present invention will be described. However, the conditions in the embodiments are merely examples of conditions employed to confirm the feasibility and effectiveness of the present invention, and the present invention is not limited to these examples. Various conditions may be employed in the present invention as long as they do not deviate from the spirit of the present invention and achieve the purpose of the present invention.

[0122] A slab cast from molten steel having a chemical composition of C: 0.20%, Si: 0.19%, Mn: 1.31%, P: 0.010%, S: 0.005%, Cu: 0.01%, Ni: 0.01%, Cr: 0.20%, Mo: 0.01%, Ti: 0.01%, B: 0.0002%, N: 0.002%, Ca: 0.0002%, REM: 0.0002%, Al: 0.020%, with the remainder being iron and impurities (Ac3: 842°C) is heated, hot-rolled, and then coiled. The resulting steel is then pickled to produce a hot-rolled steel.

[0123] The hot-rolled steel sheets were cold-rolled to the thicknesses listed in Table 1, annealed, and Zn-plated (hot-dip galvanized) under the conditions listed in Table 1. Some of the hot-dip galvanized steel sheets (Nos. 17 and 18) were alloyed to obtain plated steel sheets.

[0124] The obtained plated steel sheets were temper-rolled to obtain Ra values ​​shown in Table 1, thereby obtaining steel materials for hot stamping.

[0125] The hot stamping steel material obtained by the above method was hot stamped under the conditions shown in Table 1 to obtain a Zn-plated hot stamped product. Table 1 shows the P value for each condition.

[0126] (Zn-based plating adhesion amount)

[0127] The coating adhesion of the Zn-based coating on hot stamping steel is determined as follows. A sample (30 mm × 30 mm) cut from the hot stamping steel obtained above is covered with masking tape on the surface opposite to the evaluation surface. The sample is then immersed in a 5% HCl aqueous solution containing 0.02% of a corrosion inhibitor (Ibit700A, Asahi Chemical Industry Co., Ltd.) that inhibits the dissolution of Fe in the hot-rolled steel sheet at room temperature for 10 minutes to dissolve the entire Zn-based coating. The weight change before and after dissolution is calculated. Whether the dissolution of the entire coating is completed is determined based on the completion of foaming caused by the generation of hydrogen during dissolution. The results obtained are shown in Table 1.

[0128] (Upper layer thickness and lower layer thickness)

[0129] A sample that has been ground after being embedded in a resin in a manner that allows the observation of a Zn-coated hot stamped product is used, and the Zn-coated cross section is observed at a magnification of 2000 times. An imaginary line drawn perpendicularly to the thickness direction of the steel at the position closest to the steel in the region containing the Γ phase observed in white is set as the boundary between the upper layer and the lower layer. The thickness of the upper layer is set to the shortest distance from the outermost layer of the upper layer to the imaginary line. The thickness of the lower layer is set to the shortest distance from the boundary between the upper layer and the lower layer, from the position on the most steel side of the interface between the Zn-coated layer and the steel to the imaginary line. Five visual fields are arbitrarily observed for each sample, and the thickness of the upper layer and the thickness of the lower layer are measured and their average value is set as the thickness of the upper layer and the thickness of the lower layer. The results are shown in Table 2.

[0130] (Γ phase ratio)

[0131] Regarding the Γ phase ratio within the upper layer of the Zn-plated hot-stamped Zn-plated product, the SEM image taken when measuring the thickness of the upper layer was divided into 1μm×1μm blocks, each containing only the Γ phase, only the Fe-Zn solid solution, and both the Γ phase and the Fe-Zn solid solution. The number of blocks containing the Γ phase and the Fe-Zn solid solution was counted, and the Γ phase ratio was calculated from the ratio of these blocks. Note that for blocks containing both the Γ phase and the Fe-Zn solid solution, 0.5 blocks of both the Γ phase and the Fe-Zn solid solution were added. The results are shown in Table 2.

[0132] (Mn content)

[0133] Using an electron beam microanalyzer (EPMA-1720H manufactured by Shimadzu Corporation), the surface of the Zn-plated hot stamped product was measured under the conditions of an acceleration voltage of 15kV, a beam current of 100nA, a beam diameter of 4μm, a measurement length of 40mm, a measurement spacing of 20μm (2000 point measurement), and a measurement time of 1.0sec / point. In order to eliminate the influence of the roughness of the surface layer, the adjacent 10 points (200μm points = 0.2mm points) of the measurement range were set as one area and averaged, and the Mn content of the area was set. The maximum value of the measured value of the Mn content (each Mn content in the area of ​​200) was set as Max.Mn, the minimum value was set as Min.Mn, the Mn content ratio (Max.Mn / Min.Mn) was calculated, and the average value of the measured value of the Mn content was set as Ave.Mn. The obtained results are shown in Table 2.

[0134] It should be noted that the chemical composition of the Zn-based plating 2 was analyzed by the above-mentioned GDS method, and the results showed that the chemical composition of the Zn-based plating 2 was all in the range of Zn: 30-80%, Fe: 20.0-70.0%, Al: 0-1.0%, Si: 0-1.0%, Mg: 0-1.0%, Mn: 0-1.0%, Ni: 0-1.0%, and Sb: 0-1.0% in mass%.

[0135] (Corrosion resistance after painting)

[0136] The corrosion resistance evaluation after painting was carried out by the following method. For Zn-plated hot stamped products (plate-shaped), surface conditioning treatment agent (trade name: Preparen X) manufactured by Nihon Parkerizing Co., Ltd. was used to perform surface conditioning at room temperature for 20 seconds. Next, phosphate treatment was performed using zinc phosphate treatment solution (trade name: Palbond 3020) manufactured by Nihon Parkerizing Co., Ltd. Specifically, the temperature of the treatment solution was set to 43°C, and the Zn-plated hot stamped products were immersed in the treatment solution for 120 seconds. Thus, a phosphate film was formed on the surface of the steel.

[0137] After the phosphate treatment, the hot-stamped steel sheets (molded products) of each test number were electroplated with a cationic electrodeposition coating manufactured by Nippon Paint Co., Ltd. by applying a 160V ramp. The coating was then baked at 170°C for 20 minutes. The coating film thickness after the electrodeposition coating was controlled to achieve a thickness of 15 μm on the plated steel sheets before hot stamping.

[0138] For the steel plate (molded product) after electroplating coating, a cross cut is formed in a manner until it reaches the steel material of the substrate, and a composite corrosion test (neutral salt water spray cycle test specified in JIS H 8502 (1999)) is implemented. Specifically, a corrosion evaluation test is carried out with salt water spray (35°C, 2 hours), drying (60°C, 25% RH, 4 hours), and wetting (50°C, 98% RH, 2 hours) as one cycle. It should be noted that 5% salt water was used in the salt water spray. The corrosion resistance is evaluated by the width of the coating bulge. After 180 cycles of the composite corrosion test, the steel plate with a coating bulge width of less than 3 mm is evaluated as "OK", and the steel plate with a coating bulge width greater than 3 mm is evaluated as "NG". The results are shown in Table 2.

[0139] (Plating Adhesion)

[0140] The chipping resistance evaluation (plating adhesion evaluation) was performed by the following method. The steel sheet was cut into 70 mm x 150 mm pieces and subjected to automotive degreasing, chemical conversion, and three-layer coating. The three-layer coating was set as electrodeposition coating, mid-coat coating, and top-coat coating from the steel sheet side. The steel sheet was cooled and maintained at -20°C with an air pressure of 2 kgf / cm 2 Irradiate gravel (0.3-0.5 g) vertically. Irradiate 10 gravels for each sample. Observe the cracks and evaluate the position of the peeling interface. The steel plate with a peeling interface above the coating (the interface between the coating and the chemical conversion film or the interface between the electroplating coating and the intermediate coating) is evaluated as "OK", and the steel plate with peeling inside the coating and the steel plate with only one peeling interface between the coating and the base metal is evaluated as "NG". The results are shown in Table 2.

[0141] (Appearance and taste)

[0142] Tortoise shell pattern evaluation (appearance quality evaluation) was performed using the following method. For hot stamped materials produced in a 100 mm x 100 mm area, steel sheets with no visually observed linear surface unevenness were rated "OK," while those with even a single linear surface unevenness were rated "NG." The results are shown in Table 2.

[0143]

[0144]

[0145] Nos. 2 to 7, 10, and 13 to 16, which satisfy the conditions of the present invention, are excellent in corrosion resistance after painting, plating adhesion, and appearance quality.

[0146] The Zn-plated hot stamped product No. 1 did not satisfy the conditions for the ratio of the upper layer to the lower layer, and therefore had poor plating adhesion.

[0147] The Zn-plated hot stamped products of No. 8 and 9 did not satisfy the upper layer / lower layer ratio and the Mn content ratio, and therefore had inferior corrosion resistance and appearance quality after painting.

[0148] The Zn-plated hot stamped product No. 11 did not satisfy the Mn content ratio, and therefore had a poor appearance.

[0149] The Zn-plated hot stamped product No. 12 did not satisfy the ratio of the upper layer to the lower layer, and therefore had poor corrosion resistance after painting.

[0150] The Zn-plated hot stamped product No. 17 had low corrosion resistance after painting because the ratio of the upper layer to the lower layer was not satisfactory. In addition, the appearance quality was poor due to the use of alloyed hot-dip galvannealing (GA).

[0151] The Zn-plated hot stamped product No. 18 has a poor appearance quality because it uses alloyed hot-dip galvannealing (GA).

[0152] Industrial applicability

[0153] The Zn-based plated hot stamped product of the present invention has excellent corrosion resistance after painting, plated adhesion, and appearance, and therefore has high industrial applicability.

[0154] Explanation of symbols

[0155] 1 Steel

[0156] 2 Zn coating

[0157] 3 Oxide layer

[0158] 14 Γ phase

[0159] 12, 15Fe-Zn solid solution

[0160] 21 Lower Level

[0161] 22 Upper

[0162] 100 Hot stamping products

Claims

1. A Zn-plated hot stamped product, comprising: Steel, A Zn-containing Zn-based plating layer formed on the surface of the steel material, and An oxide layer containing Zn and Mn formed on the surface of the Zn-based plating layer, The surface side region of the Zn-based plating layer, i.e., the upper layer, is a two-phase structure of the Γ phase and the Fe-Zn solid solution, and the region other than the upper layer, i.e., the lower layer, is a single-phase structure of the Fe-Zn solid solution. The thickness of the upper layer and the thickness of the lower layer satisfy the following formula (1): The maximum value Max.Mn, the minimum value Min.Mn and the average value Ave.Mn of the Mn content on the surface of the Zn-based plated hot stamped product satisfy the following formulas (2) and (3) in terms of mass %. 0.20≤Upper layer thickness / (Upper layer thickness+Lower layer thickness)≤0.80(1) Ave.Mn=0.5~7.5 (2) Max.Mn / Min.Mn≤10.0 (3).

2. The Zn-plated hot stamped product according to claim 1, wherein: The ratio of the Γ phase in the upper layer to the Γ phase in the dual-phase structure of the Fe-Zn solid solution is 20 to 80%.

3. The Zn-plated hot stamped product according to claim 1 or 2, characterized in that: The Zn content of the Zn-based plating layer is 30.0% or more by mass.

4. The Zn-based plated hot stamped product according to claim 1 or 2, wherein: The plate thickness is 1.0~3.2mm.

5. The Zn-based plated hot stamped product according to claim 1 or 2, wherein: The upper layer thickness / (upper layer thickness+lower layer thickness) is greater than 0.25.

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