Hot-stamped steel sheet and hot-stamped member

Abstract

A hot-stamped steel sheet having, on a surface, a portion having a surface treatment coating film, the portion having a radiation rate at a wavelength of 8.0 μm at 25°C of 60% or more, and a portion not having the surface treatment coating film, the surface treatment coating film containing: carbon black; and one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide, and the carbon black and the oxide being dispersed throughout the surface treatment coating film, the surface treatment coating film having a content of silicon dioxide of 0 to 0.3 g / m 2 The attachment amounts of the carbon black and the oxide are respectively set as X CB (g / m 2 ), X Oxide (g / m 2 ), and the following formula is satisfied. 118.9 ≤ 24280 / {6700 / (100+76×X CB + 18000 / (130+65×X Oxide )} ≤ 332.0.

Description

Technical Field

[0001] This invention relates to steel plates for hot stamping and hot stamped components. Background Technology

[0002] In recent years, the need to curb the consumption of chemical fuels in order to protect the environment and prevent global warming has become increasingly stringent, impacting various manufacturing industries. For example, automobiles, indispensable in daily life and activities as mobility devices, require improvements in fuel efficiency through measures such as lightweighting the vehicle body. However, simply achieving lightweighting in automobiles may lead to a decrease in safety, which is unacceptable from a product quality standpoint. Therefore, ensuring adequate safety is crucial when implementing vehicle body lightweighting.

[0003] Automobile structures are mostly made of iron, especially sheet steel, and reducing the weight of the steel sheets is crucial for lightweighting the car body. Furthermore, this requirement for steel sheets exists not only in the automotive industry but also in various other manufacturing sectors. If the goal were simply to reduce the weight of the steel sheets, one could consider making the sheets thinner. However, thinning the steel sheets would reduce the strength of the structure. Therefore, in recent years, research and development have focused on steel sheets that, even when thinner than previously used sheets, maintain or improve the mechanical strength of structures constructed from sheet steel by increasing their mechanical strength.

[0004] Generally, materials with high mechanical strength tend to exhibit reduced shape retention during forming processes such as bending. Therefore, processing complex shapes becomes difficult. One method to address this formability issue is the so-called "hot stamping method (also known as hot pressing, hot pressing, high-temperature stamping, or die-pressing hardening)." In this method, the material to be formed is heated to a high temperature, causing it to transform into a structure called austenite (austenitization). The softened steel sheet is then stamped to form the shape, followed by cooling. According to this hot stamping method, since the material is temporarily heated to a high temperature to soften it, it can be easily stamped. Furthermore, the quenching effect of cooling after forming improves the material's mechanical strength. Therefore, this hot stamping method can yield formed products with good shape retention and high mechanical strength.

[0005] On the other hand, depending on the component, sometimes it is required to have both high-strength and low-strength parts simultaneously. This is because, on the one hand, high strength is needed for personnel protection, and on the other hand, lower strength is needed to absorb the energy of a collision in the parts other than those that should be protected.

[0006] Based on the above viewpoints, for example, Patent Document 1 describes a component made by joining at least two Zn-based coated steel sheets with different steel compositions. Furthermore, Patent Document 2 describes a technique for separately manufacturing cooled microstructures based on differences in average cooling rate and cooling stop temperature according to the location of the steel sheets. Additionally, Patent Document 3 describes a technique for improving ductility by controlling the temperature of the mold and tempering localized areas after martensitic transformation.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2016 / 139953

[0010] Patent Document 2: Japanese Patent Application Publication No. 2014-161854

[0011] Patent Document 3: Japanese Patent Application Publication No. 2016-41440 Summary of the Invention

[0012] The problem the invention aims to solve

[0013] However, in order to manufacture the component described in the aforementioned Patent Document 1, it is necessary to manufacture steel plates of different strengths. Therefore, in addition to increasing the manufacturing load, a joining process is also required, which is uneconomical.

[0014] Furthermore, if the method described in Patent Document 2 is used, it is not preferred because it requires two types of cooling molds, which is economically disadvantageous or makes it difficult to ensure manufacturing robustness.

[0015] Furthermore, even when using the technology described in Patent Document 3, it is difficult to ensure manufacturing robustness, just like in Patent Document 2, and therefore it is not preferred.

[0016] Therefore, the current need is to find a technology that can perform hot stamping while suppressing cost increases and ensuring product robustness.

[0017] Therefore, the present invention was made in view of the above-mentioned problems, and the object of the present invention is to provide a hot-stamped steel sheet suitable for manufacturing parts having different strengths by hot stamping and a hot-stamped component having parts having different strengths.

[0018] Solution for solving the problem

[0019] In order to solve the above-mentioned problems and manufacture metal parts with different strengths, the inventors conducted in-depth research and came up with the idea of ​​increasing the temperature rise rate by applying a surface treatment coating with high emissivity to a part of the surface of the steel plate.

[0020] By applying a surface treatment coating that increases emissivity to a portion of the steel sheet, differences in heating rates during hot stamping can be established. In this hot stamping steel sheet, the coated portion is austenitized, while the remaining portion is not. It is then removed from the furnace in this state and rapidly cooled through a die. As a result, differences in hardenability occur between the coated portion and the remaining portion, enabling the manufacture of parts derived from steel sheets with varying strengths.

[0021] This invention is based on the above-mentioned insights obtained by the inventors, and the main points of this invention are as follows.

[0022] [1] A hot-stamping steel sheet, comprising on its surface: a portion having a surface-treatment coating, wherein the emissivity at a wavelength of 8.0 μm at 25°C is 60% or more; and a portion not having the surface-treatment coating, wherein the surface-treatment coating comprises: carbon black; and one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide, wherein the carbon black and the oxide are dispersed throughout the surface-treatment coating, and the silica content of the surface-treatment coating is 0 to 0.3 g / m 2 The amount of carbon black and oxide adhering is set as X, respectively. CB (g / m 2 ), X Oxide (g / m 2 When ), the following equation (1) is satisfied.

[0023] 118.9≤24280 / {6700 / (100+76×X CB )+18000 / (130+65×X Oxide )}≤332.0 Equation (1)

[0024] [2] The hot stamping steel sheet according to [1], wherein the surface treatment coating contains 5.0 to 40.0 vol% of the carbon black and 1.0 to 30.0 vol% of the oxide.

[0025] [3] According to the hot stamping steel sheet described in [1] or [2], wherein the amount of carbon black adhering is X CB (g / m 2 The amount of oxides attached to the oxide is X Oxide (g / m 2 The ratio XOxide / X CB It is above 0.20 and below 200.00.

[0026] [4] A hot-stamping steel sheet according to any one of [1] to [3], wherein the amount of carbon black adhering is X CB It is 0.030 g / m 2 The above refers to the amount of oxide attached, X. Oxide It is 0.030 g / m 2 above.

[0027] [5] The hot stamping steel sheet according to any one of [1] to [4], wherein the emissivity of the surface treatment coating at a wavelength of 8.0 μm at 700°C is 60% or more.

[0028] [6] A hot stamping steel sheet according to any one of [1] to [5], wherein a metal coating is provided between the substrate of the steel sheet and the surface treatment coating on one or both sides of the hot stamping steel sheet.

[0029] [7] A hot-stamped component having on the surface of a steel plate: a portion having a surface treatment coating; and a portion not having the surface treatment coating, wherein the surface treatment coating contains one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide, and the amount of the oxide adhering is X. Oxide It is 0.030 g / m 2 The silica content of the surface treatment coating is 0–0.3 g / m². 2 .

[0030] [8] According to the hot stamping component described in [7], when measuring the Vickers hardness specified in JIS Z 2244 (2009), there are locations that display the maximum hardness HVmax and locations that display the minimum hardness HVmin, and the hardness difference ΔHV between the maximum hardness HVmax and the minimum hardness HVmin is 150 or more.

[0031] [9] According to the hot-stamped component of [8], both the portion showing the maximum hardness HVmax and the portion showing the minimum hardness HVmin exist in a region composed of a common raw material.

[0032] The effects of the invention

[0033] According to the present invention described above, it is possible to provide a hot-stamped steel sheet suitable for manufacturing parts having different strengths, and a hot-stamped component having parts having different strengths. Attached Figure Description

[0034] Figure 1The diagram illustrates the start / finish time of austenitization in the coated and uncoated areas during hot stamping heating.

[0035] Figure 2 The diagram schematically shows the coated portion and its center (P1) and the uncoated portion and its center (P2) on the surface of the hot-stamped steel sheet. Detailed Implementation

[0036] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0037] (Hot stamping steel plate)

[0038] The hot-stamping steel sheet described below is suitable for manufacturing components having portions with varying strengths. This hot-stamping steel sheet has on its surface: portions having a surface-treatment coating, wherein the emissivity at 8.0 μm at 25°C is 60% or more; and portions not having the surface-treatment coating. In this embodiment, as described above, by applying a surface-treatment coating to a portion of the steel sheet, the emissivity at 8.0 μm at 25°C can be increased to 60% or more.

[0039] In the hot-stamping steel sheet described in this embodiment, the type of steel sheet used as the base material (base steel sheet) is not particularly limited. Examples of such steel sheets include various hot-rolled steel sheets, cold-rolled steel sheets, and galvanized steel sheets. Galvanized steel sheets include, for example, steel sheets subjected to hot-dip aluminizing, hot-dip galvanizing, alloyed hot-dip galvanizing, electro-galvanizing, etc., but are not limited to these galvanized steel sheets as long as they are suitable for hot stamping.

[0040] Previously, steel sheets used for automotive frame components were mostly hot-rolled or cold-rolled steel sheets, or coated steel sheets with aluminum or zinc plating. These steel sheets have low emissivity, so their heating rate is relatively slow compared to radiant heating with a wavelength of about 8.0 μm.

[0041] In this embodiment, such as Figure 1 As illustrated, by applying a specific surface treatment coating only to a portion of the steel sheet surface, the heating rate of the coated portion during hot stamping is increased. After the coated portion reaches a temperature above Ac3 and the uncoated portion reaches a temperature below Ac3, hot stamping of the steel sheet allows for the localized formation of a quenched structure (martensitic structure) in the coated portion.

[0042] In this embodiment, a surface treatment coating with high emissivity is applied to a portion of the steel plate surface. Specific methods for applying the surface treatment coating include coating / lamination, but are not limited to these methods. The surface treatment coating may be applied to only one side of the steel plate or to both sides. On the surface of the steel plate, the emissivity at a wavelength of 8.0 μm at 25°C in the area where the surface treatment coating is applied is 60% or more. Preferably, the emissivity at a wavelength of 8.0 μm at 25°C in the area where the surface treatment coating is applied is 70% or more, and more preferably 80% or more.

[0043] It should be noted that the method for measuring emissivity can be performed as described in Japanese Industrial Standard JIS R 1801 (2002). In this method, the sample is placed in a Fourier transform infrared spectrometer, and the radiation intensity at a wavelength of 8.0 μm at 25°C is measured to calculate the emissivity.

[0044] Alternatively, a radiation thermometer with the measurement wavelength set to 8.0 μm can be used to measure the radiation intensity of the area of ​​interest at 25°C, and the emissivity can be calculated based on the ratio of the radiation intensity to that of a blackbody.

[0045] When applying a surface treatment coating to only a portion of the steel sheet surface via coating, for example, an organic or inorganic treatment solution containing carbon black and metal oxides can be applied to a portion of the steel sheet surface using a roller coater or curtain coater, and then the volatile components in the treatment solution can be dried to apply the surface treatment coating. Alternatively, by covering a portion of the steel sheet with polyester tape or other raw materials before applying it to a coating process using the aforementioned treatment solution, a coating can be applied to any part of the steel sheet surface.

[0046] Especially in inkjet coating, not only can the treatment liquid be applied with high precision at any position, but the film thickness can also be continuously changed.

[0047] <Surface Treatment Coating>

[0048] In the hot-stamping steel sheet according to this embodiment, the emissivity at 8.0 μm wavelength at 25°C of the portion with the surface treatment coating is 60% or more. When the emissivity at 8.0 μm wavelength at 25°C is less than 60%, the difference in heating rate between the portion and the portion without the surface treatment coating becomes smaller. This makes it difficult to ensure the hardness difference after heating / cooling during hot stamping, or reduces the freedom of timing when removing the steel sheet from the furnace used for ensuring this, placing a burden on manufacturing and making it difficult to achieve both lightweight and safety performance for automotive parts. The emissivity at 8.0 μm wavelength at 25°C is preferably 80% or more. With an emissivity of 80% or more at 25°C, it is easier to ensure the aforementioned hardness difference, or to further reduce the burden on manufacturing. It should be noted that the higher the emissivity at 8.0 μm wavelength at 25°C of the portion with the surface treatment coating, the better; however, no upper limit is specified, and it can be 100%.

[0049] To achieve an emissivity of 60% or higher at a wavelength of 8.0 μm at 25°C, the surface treatment coating of this embodiment contains carbon black and specific metal oxides as detailed below. Furthermore, the surface treatment coating of this embodiment may, as needed, contain binder components, various additives, etc. Moreover, the surface treatment coating of this embodiment may be silica-free or may contain silica within a certain range. By adjusting the content of carbon black and metal oxides, the film thickness of the surface treatment coating, etc., the desired emissivity can be achieved.

[0050] More specifically, the surface treatment coating according to this embodiment contains: carbon black; and one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide, wherein the carbon black and the aforementioned oxides are dispersed throughout the surface treatment coating. Furthermore, when the amount of carbon black attached is expressed as X... CB (g / m 2 The amount of oxides attached is expressed as X. Oxide (g / m 2 When ), the surface treatment coating involved in this embodiment satisfies the relationship shown in the following formula (1).

[0051] 118.9≤24280 / {6700 / (100+76×X CB )+18000 / (130+65×X Oxide )}≤332.0

[0052] Equation (1)

[0053] Equation 1 above defines the relationship between the rate of increase (%) of heating rate (°C / s) and the amount of carbon black and oxides attached. More specifically, the rate of increase of heating rate is formulated for the case where carbon black functions as an endothermic material up to 700°C, and Zr oxide, Zn oxide, and Ti oxide that remain in the temperature range above 700°C also function as endothermic materials.

[0054] As briefly mentioned earlier, the surface treatment coating according to this embodiment can be formed by applying a treatment liquid containing carbon black and a specific oxide to a desired area of ​​a steel sheet. As a result, in the surface treatment coating according to this embodiment, carbon black and oxides are dispersed throughout the entire surface treatment coating. Because carbon black and oxides are dispersed throughout the entire surface treatment coating, the emissivity of the surface treatment coating at a wavelength of 8.0 μm at 25°C is uniform throughout the entire coating. Consequently, when the area to which the surface treatment coating according to this embodiment is applied is hot-stamped, the entire surface treatment coating can be heated uniformly.

[0055] The distribution of carbon black and oxides can be confirmed by using an electron probe microanalyzer (EPMA) to perform surface analysis on the surface-treated coating, identifying elements (e.g., C) from the carbon black or elements (i.e., Zr, Zn, Ti) from the oxides.

[0056] It should be noted that when processing solutions containing carbon black and oxides are prepared separately, and these solutions are applied separately to form a laminated film, the carbon black and oxides will not be dispersed throughout the entire film. Furthermore, if multiple processing solutions are used to form the film, a second film must be formed after the first, thus increasing the size of the manufacturing equipment and manufacturing costs.

[0057] Furthermore, the surface treatment coating involved in this embodiment is determined by the amount of carbon black adhered X. CB The amount of oxides attached X OxideSatisfying the relationship shown in Equation (1) above, the emissivity at a wavelength of 8.0 μm at 25°C becomes 60% or more, and the difference in heating rate between the area and the area without surface treatment coating becomes significant. When the value specified in the intermediate term of Equation (1) above is less than 118.9, the amount of carbon black and oxides adhering is insufficient, and the emissivity described above cannot be achieved. The value specified in the intermediate term of Equation (1) above is preferably 119.0 or more, more preferably 170.0 or more, and even more preferably 220.0 or more. On the other hand, when the value specified in the intermediate term of Equation (1) above exceeds 332.0, the adhesion of the coating decreases, which is therefore undesirable. The value specified in the intermediate term of Equation (1) above is preferably 330.0 or less, more preferably 310.0 or less, and even more preferably 300.0 or less.

[0058] Here, the amount of carbon black adhering to the surface treatment coating, X, is... CB The surface-treated coating can be measured using cross-sectional analysis with a transmission electron microscope (TEM), as follows: A cross-sectional analysis of the area represented by film thickness × 5 μm is performed using TEM-EDS to determine the film thickness and the area fraction occupied by particles with a carbon content of 70% by mass or higher. When the film thickness is set as d (μm) and the area fraction as a (%), the value represented by d × a becomes the carbon black adhesion amount × CB (g / m 2 ).

[0059] In addition, the amount of oxide of at least one of Zr, Zn, and Ti in the surface treatment coating is X. Oxide This refers to the average amount of Zr oxides, Zn oxides, and Ti oxides (i.e., ZrO2, ZnO, TiO2) adhered per unit area, calculated as metallic Zr, metallic Zn, and metallic Ti, respectively. The amount of these oxides adhered is X. Oxide Elemental analysis of the surface of the surface-treated coating can be performed using an X-ray fluorescence analyzer (RIGAKU Corporation, ZSX Primus) to quantitatively determine the metals Zr, Zn, and Ti.

[0060] The hot-stamping steel sheet according to this embodiment, having the characteristics described above, can achieve an emissivity of 60% or more at a wavelength of 8.0 μm at 700°C. Hereinafter, the substances contained in the characteristic surface treatment coating used to achieve the emissivity described above will be described in more detail.

[0061] Carbon Black

[0062] In areas where a surface treatment coating is applied to the surface of a steel plate, the amount of carbon black adhering to the surface treatment coating is X.CB The preferred value is 0.030 g / m 2 That's all. By adjusting the adhesion amount X CB Set to 0.030 g / m 2 The above methods reliably increase the heating rate in the region up to 700°C. Adhesion amount X CB More preferably 0.100 g / m 2 That's all. On the other hand, the amount of adhesion X CB The upper limit value is determined by the above formula (1). Adhesion amount X CB The preferred value is 0.800 g / m 2 The preferred value is 0.600 g / m³. 2 the following.

[0063] Furthermore, the surface treatment coating more preferably contains 5.0 to 40.0% by volume of carbon black. Carbon black has a particularly strong effect of increasing the heating rate in the temperature range up to 700°C. Due to factors such as the roughness and waviness of the steel sheet, or the difference in the rate of evaporation of volatile components such as water in the treatment solution during coating formation, the thickness of the surface treatment coating may vary locally. In such cases, by having a carbon black content of 5.0% by volume or more, the difference between the areas that appear black due to the carbon black and the rest can be suppressed, maintaining the appearance design, which is preferable from an aesthetic point of view. On the other hand, by having a carbon black content of 40.0% by volume or less in the surface treatment coating, the decrease in the adhesion of the coating after hot stamping can be suppressed. Although the mechanism is unclear, it is speculated that by suppressing the residue of compounds from residual carbon black or carbon black oxides, the obstacle to the bonding between the coating and the substrate is suppressed.

[0064] Furthermore, carbon black's main components are carbon, hydrogen, and oxygen; therefore, carbon black is destroyed when heated to high temperatures. Thus, by including carbon black in the surface treatment coating, it is possible to maintain properties such as adhesion after hot stamping.

[0065] With a carbon black content of 5.0% by volume or more, oxidation of the steel plate or coating beneath the surface-treated film is suppressed, thus ensuring strong adhesion during coating (treatment agent) application and maintaining coating adhesion. Furthermore, emissivity is increased, and the heating rate is accelerated. The carbon black content in the surface-treated film is further preferably 8.0% by volume or more. Setting the carbon black content in the surface-treated film to 8.0% by volume or more further increases the heating rate. On the other hand, by setting the carbon black content in the surface-treated film to 40.0% by volume or less, the effect of increasing emissivity is sufficiently achieved, and the increase in coating cost is suppressed. The carbon black content in the surface-treated film is further preferably 30.0% by volume or less. Setting the carbon black content in the surface-treated film to 30.0% by volume or less further suppresses coating cost.

[0066] Metal Oxides

[0067] In areas where a surface treatment coating is applied to the surface of a steel plate, the total amount of Zr oxide, Zn oxide, and Ti oxide adhered to the surface treatment coating is X. Oxide The preferred value is 0.030 g / m 2 That's all. By adjusting the adhesion amount X Oxide Set to 0.03g / m 2 The above methods can reliably increase the heating rate in areas above 700°C. Adhesion amount X Oxide More preferably, it is 0.060 g / m 2 That's all. On the other hand, the amount of adhesion X Oxide The upper limit value is determined by the above formula (1). Adhesion amount X Oxide The preferred value is 0.500 g / m 2 The following is more preferably 0.300 g / m 2 the following.

[0068] Furthermore, the surface treatment coating more preferably contains a total of 1.0 to 30.0 vol% Zr oxide, Zn oxide, and Ti oxide. These oxides (i.e., metal oxides of Zr, Zn, and Ti) remain in the surface treatment coating even when heated to temperatures above 700°C, where the effect of carbon black diminishes. As a result, in the area where the surface treatment coating is applied, since these metal oxides have a higher emissivity than the steel plate surface or the plated surface at temperatures above 700°C, the heat input due to radiative heat from the heating atmosphere is greater. Therefore, the effect of increasing the heating rate can be maintained even at temperatures above 700°C. By having a content of 1.0 vol% or more of these metal oxides, the effect of increasing the heating rate can be sufficiently obtained. The content of these metal oxides is further preferably 3.0 vol% or more. On the other hand, by having a content of 30 vol% or less of these metal oxides, the coating cost can be suppressed, which is economically preferable. The content of these metal oxides is further preferably 25.0 vol% or less.

[0069] It should be noted that the content (volume %) of various compounds such as carbon black and metal oxides in the surface treatment coating can be calculated based on their area percentage by observing the cross-section using a scanning electron microscope (SEM) after the sample is embedded in the resin. Alternatively, the compounds can be estimated through quantitative analysis using the EDX function provided with the SEM.

[0070] In the surface treatment coating according to this embodiment, the amount of carbon black adhering to X CB (g / m 2 The amount of oxides attached to the surface.Oxide (g / m 2 The ratio X Oxide / X CB Preferably, the value is 0.20 or higher and 200.00 or lower. Through ratio X Oxide / X CB Within the aforementioned range, it is possible to apply more appropriate heating to the areas where surface treatment coatings have been applied. Ratio X Oxide / X CB More preferably, it is 0.40 to 10.00, and even more preferably, it is 0.60 to 5.00.

[0071] In addition, the surface treatment coating involved in this embodiment may contain various binder components and additives, in addition to the carbon black and metal oxides mentioned above.

[0072] Adhesive Composition

[0073] The binder component that may be contained in the surface treatment coating according to this embodiment is preferably a water-dispersible or water-soluble resin. The content of the binder component selected from water-dispersible or water-soluble resin is preferably 40% by volume or more relative to the total volume of the surface treatment coating.

[0074] As a binder component selected from water-dispersible or water-soluble resins, various known resins exhibiting water dispersibility or water solubility can be used. Examples of such water-dispersible or water-soluble resins include polyurethane resins, polyester resins, acrylic resins, epoxy resins, fluoropolymers, polyamide resins, polyolefin resins, and polymer compounds obtained by hydrolysis / condensation of a silane coupling agent. More preferably, the binder component is selected from one or more of the group consisting of polyester resins, polyurethane resins, polyolefin resins, acrylic resins, epoxy resins, fluoropolymers, and polyamide resins. It should be noted that when multiple resins are used as binder components, the total content of the various resins used is treated as the content of the binder component.

[0075] It should be noted that when using polyurethane resin as a binder component, polyether-based polyurethane resin is preferred. This is because, compared to polyester-based polyurethane resin, polyether-based polyurethane resin can prevent hydrolysis caused by acids and alkalis, and compared to polycarbonate-based polyurethane resin, it can inhibit the formation of a hard and brittle coating, thereby ensuring the tightness of the seal during processing and the corrosion resistance of the processed part.

[0076] Whether a substance contains polyurethane resin can be determined by observing whether a 3330 cm⁻¹ region is observed in the infrared absorption spectrum obtained using infrared spectroscopy. -1 (NH stretching), 1730cm -1 (C=O expansion / contraction), 1530cm-1 (CN), 1250cm -1 The characteristic absorption of (CO) can be used to determine the content. Alternatively, the content of polyurethane resin can be determined by creating a standard curve showing the relationship between content and the intensity of characteristic absorption using samples with known content, and then using the intensity of the obtained characteristic absorption.

[0077] In addition, for resins other than the polyurethane resins mentioned above, the presence and content can also be determined by focusing on the characteristic absorption of the functional groups unique to each resin, just like with the polyurethane resins mentioned above.

[0078] "additive"

[0079] In the surface treatment coating involved in this embodiment, without impairing the effect of the present invention, the additives used in the preparation of the treatment liquid before coating formation may also contain various additives such as leveling agents, water-soluble solvents, metal stabilizers, and etching inhibitors.

[0080] As leveling agents, and as nonionic or cationic surfactants, examples include polyethylene oxide or polypropylene oxide adducts, or alkynyl diol compounds.

[0081] Examples of water-soluble solvents include alcohols such as ethanol, isopropanol, tert-butanol, and propylene glycol; cellosols such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether; esters such as ethyl acetate and butyl acetate; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0082] Examples of metal stabilizers include chelating compounds such as EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid).

[0083] Examples of etching inhibitors include amine compounds such as ethylenediamine, triethylenepentamine, guanidine, and pyrimidine.

[0084] It should be noted that the contents of the above-mentioned binder components and additives can also be determined in the same way as those of carbon black and metal oxides.

[0085] Silicon Dioxide

[0086] As mentioned before, the surface treatment coating involved in this embodiment may be silica-free or contain silica within a certain range. More specifically, in the surface treatment coating involved in this embodiment, the silica content is 0–0.3 g / m³. 2 When it contains more than 0.3g / m 2When using silica, a temperature increase is not expected, and the cost increases, making it less economically viable. Furthermore, since silica is a material with low electrical conductivity, a content exceeding 0.3 g / m³ is problematic. 2 When silica is present, it is not preferable in terms of weldability after hot stamping. The lower the silica content of the surface treatment coating, the better. More preferably, the silica content of the surface treatment coating is 0.10 g / m³. 2 The following is a further preferred value: 0.05 g / m 2 the following.

[0087] Film Thickness in Surface Treatment Coatings

[0088] The thickness of the surface-treated coating containing the above-mentioned components is preferably set to, for example, 0.5 to 5.0 μm. By setting the thickness of the surface-treated coating within the above range, the emissivity at a wavelength of 8.0 μm at 25°C can be more reliably set to 60% or more. The thickness of the surface-treated coating is more preferably 1.0 to 3.0 μm.

[0089] <Metallic Coating>

[0090] The hot-stamping steel sheet of this embodiment has a metal coating on one or both sides, preferably on at least a portion between the base steel sheet and the surface treatment coating. The metal coating further improves the corrosion resistance after hot stamping and coating. Furthermore, the presence of the metal coating prevents the formation of iron oxide scale during hot stamping. Iron oxide scale can contaminate the heating furnace or adhere to the conveying rollers, thus becoming a manufacturing burden. Therefore, in the event of iron oxide scale formation, processes such as shot peening are required to remove it, which is not economically preferable.

[0091] There are no particular limitations on the type of metal coating. Examples of metal coatings that constitute this metal coating include aluminum plating, Al-Si plating, zinc plating, alloyed zinc plating, Zn-Ni plating, Zn-Al-Mg plating, and Zn-Al-Mg-Si plating.

[0092] In addition, methods for forming metal coatings include hot-dip plating, electroplating, physical vapor deposition, and chemical vapor deposition, but there are no particular limitations.

[0093] <Base Material Steel Plate>

[0094] Next, there are no particular limitations on the base steel sheet used for the hot-stamping steel sheet according to this embodiment, as long as it is a steel sheet suitable for hot stamping. Examples of steel sheets applicable to the hot-stamping steel sheet according to this embodiment include, for example, a steel sheet with the following chemical composition (by mass%): C: 0.10–0.40%, Si: 0.01–0.60%, Mn: 0.50–3.00%, P: 0.05% or less, S: 0.020% or less, Al: 0.10% or less, Ti: 0.01–0.10%, B: 0.0001–0.0100%, N: 0.010% or less, with the balance being Fe and impurities. Furthermore, examples of the form of the base steel sheet include, for example, hot-rolled steel sheets and cold-rolled steel sheets. The chemical composition of the base steel sheet will be described in detail below. It should be noted that in the following description of the chemical composition of the base steel plate, unless otherwise specified, the expression "%" means "mass %".

[0095] [C: 0.10~0.40%]

[0096] Carbon (C) is included to ensure the target mechanical strength. A sufficient increase in mechanical strength can be achieved by having a C content of 0.10% or more, thus fully realizing the benefits of C. Therefore, a C content of 0.10% or more is preferred. A C content of 0.20% or more is more preferred. On the other hand, a C content of 0.40% or less can harden and improve the strength of the steel sheet, while suppressing the decrease in elongation and reduction of section. Therefore, a C content of 0.40% or less is preferred. A C content of 0.35% or less is more preferred.

[0097] [Si: 0.01~0.60%]

[0098] Si is one of the strength-enhancing elements that improve mechanical strength, and like C, it is included to ensure the target mechanical strength. With a Si content of 0.01% or more, the strength-enhancing effect can be fully utilized, resulting in a sufficient increase in mechanical strength. Therefore, a Si content of 0.01% or more is preferred. A Si content of 0.10% or more is even more preferred. On the other hand, Si is also an easily oxidized element. Therefore, with a Si content of 0.60% or less, the decrease in wettability during hot-dip Al plating caused by the influence of Si oxides formed on the surface of the steel sheet is suppressed, and the formation of uncoated areas can be prevented. Therefore, a Si content of 0.60% or less is preferred. A Si content of 0.40% or less is even more preferred.

[0099] [Mn: 0.50~3.00%]

[0100] Mn is one of the strengthening elements for steel and also one of the elements that improve hardenability. Mn is also an element that effectively prevents hot brittleness caused by sulfur (S), which is an impurity. These effects can be fully obtained when the Mn content is 0.50% or more. Therefore, to reliably exhibit the above effects, the Mn content is preferably 0.50% or more. More preferably, the Mn content is 0.80% or more. On the other hand, Mn is an austenite-forming element; therefore, when the Mn content is 3.00% or less, the retained austenite phase does not become excessive, and the reduction in strength is suppressed. Therefore, the Mn content is preferably 3.00% or less. More preferably, the Mn content is 1.50% or less.

[0101] [P: below 0.05%]

[0102] P is an impurity contained in steel. By keeping the P content below 0.05%, it is possible to suppress the segregation of P from the steel sheet to the grain boundaries, which would reduce the toughness of the base material of the hot-stamped form and also suppress the reduction in the steel sheet's resistance to delayed fracture. Therefore, the P content is preferably below 0.05%, and the P content is preferably as low as possible.

[0103] [S: below 0.020%]

[0104] Sulfur (S) is an impurity contained in steel. By keeping the S content below 0.020%, the formation of sulfides from sulfur in the steel plate can be suppressed, thus preventing a decrease in the toughness of the steel plate and a reduction in its resistance to delayed fracture. Therefore, the S content is preferably below 0.020%, and the S content is preferably as low as possible.

[0105] [Al: below 0.10%]

[0106] Al is typically used for deoxidation of steel. On the other hand, by having an Al content of 0.10% or less, the rise of the Ac3 point of the steel sheet is suppressed, thus reducing the heating temperature required to ensure the hardenability of the steel during hot stamping, which is desirable in hot stamping manufacturing. Therefore, the Al content of the steel sheet is preferably 0.10% or less, more preferably 0.05% or less, and even more preferably 0.01% or less.

[0107] [Ti: 0.01~0.10%]

[0108] Ti is one of the strength-enhancing elements. With a Ti content of 0.01% or more, both strength and oxidation resistance can be adequately improved. Therefore, to reliably exhibit these effects, a Ti content of 0.01% or more is preferred. A Ti content of 0.03% or more is even more preferred. On the other hand, with a Ti content of 0.10% or less, the formation of carbides and nitrides is suppressed, thereby preventing the softening of the steel and achieving the target mechanical strength. Therefore, a Ti content of 0.10% or less is preferred. A Ti content of 0.08% or less is even more preferred.

[0109] [B: 0.0001~0.0100%]

[0110] Boron (B) has the effect of increasing strength during quenching. This strength-enhancing effect can be sufficiently obtained when the B content is 0.0001% or less. Therefore, the B content is preferably 0.0001% or more. The B content is more preferably 0.0010% or more. On the other hand, when the B content is 0.0100% or less, the formation of inclusions is reduced and the embrittlement of the steel plate is suppressed, which can suppress the decrease in fatigue strength. Therefore, the B content is preferably 0.0100% or less. The B content is more preferably 0.0040% or less.

[0111] [N: below 0.010%]

[0112] Nitrogen (N) is an impurity contained in steel. By keeping the N content below 0.010%, the formation of nitrides caused by N in the steel sheet is suppressed, thus preventing a decrease in the toughness of the steel sheet. Furthermore, when the steel sheet contains boron (B), the combination of N and B in the steel sheet can be suppressed, reducing the amount of dissolved B and preventing a decrease in the hardenability-enhancing effect of B. Therefore, the N content is preferably below 0.010%, and more preferably as low as possible.

[0113] In addition, the base steel plate for hot stamping steel plates involved in this embodiment may contain elements such as Cr, Mo, Ni, Co, Cu, Mo, V, Nb, Sn, W, Ca, REM, O, and Sb as optional additives.

[0114] [Cr: 0~1.00%]

[0115] Cr is an element that improves the hardenability of steel plates. To fully achieve this effect, the Cr content is preferably set to 0.01% or more. On the other hand, by setting the Cr content to 1.00% or less, this effect can be fully achieved, and cost increases can be suppressed. Therefore, the Cr content when present is 1.00% or less.

[0116] [Ni: 0~2.00%]

[0117] [Co: 0-2.00%]

[0118] Ni and Co are elements that improve the hardenability of steel and ensure the stable strength of quenched steel plate components. To fully realize this effect, the Ni content is preferably 0.10% or more, and the Co content is preferably 0.10% or more. On the other hand, by keeping the Ni and Co contents at 2.00% or less, the above-mentioned effects can be fully obtained, and economic efficiency is improved. Therefore, the Ni content and Co content are preferably 2.00% or less.

[0119] [Cu: 0~1.000%]

[0120] Cu is an element that improves the hardenability of steel and ensures the stable strength of quenched steel plate components. Furthermore, Cu improves resistance to pitting corrosion in corrosive environments. To fully realize this effect, the Cu content is preferably set to 0.100% or more. On the other hand, by setting the Cu content to 1.000% or less, the above-mentioned effects can be fully obtained, and economic efficiency is improved. Therefore, the Cu content when present is preferably set to 1.000% or less.

[0121] [Mo: 0~1.00%]

[0122] Mo is an element that improves the hardenability of steel and can stably ensure the strength of quenched steel plate components. To fully realize this effect, the Mo content is preferably set to 0.10% or more. On the other hand, the above-mentioned effect can be fully obtained by setting the Mo content to 1.00% or less, and the economy is improved. Therefore, the Mo content when present is preferably set to 1.00% or less.

[0123] [V: 0~1.00%]

[0124] V is an element that improves the hardenability of steel and can stably ensure the strength of quenched steel plate components. To fully realize this effect, the V content is preferably set to 0.10% or more. On the other hand, the above-mentioned effect can be fully obtained by setting the V content to 1.00% or less, and the economy is improved. Therefore, the V content when present is preferably set to 1.00% or less.

[0125] [Nb: 0~1.00%]

[0126] Nitrogen (Nb) is an element that improves the hardenability of steel and ensures the stable strength of quenched steel plate components. To fully realize this effect, the Nb content is preferably set to 0.01% or more. On the other hand, the above-mentioned effect can be fully obtained by setting the Nb content to 1.00% or less, and the economy is improved. Therefore, the Nb content when present is preferably set to 1.00% or less.

[0127] [Sn: 0~1.00%]

[0128] Sn is an element that improves resistance to pitting corrosion in corrosive environments. To fully realize this effect, the Sn content is preferably set to 0.01% or more. On the other hand, by keeping the Sn content at 1.00% or less, the decrease in grain boundary strength is suppressed, which can suppress the decrease in toughness. Therefore, when present, the Sn content is preferably set to 1.00% or less.

[0129] [W: 0~1.00%]

[0130] W is an element that improves the hardenability of steel and can stably ensure the strength of steel plate components after quenching. In addition, W improves resistance to pitting corrosion in corrosive environments. To fully realize this effect, the W content is preferably set to 0.01% or more. On the other hand, by setting the W content to 1.00% or less, the above-mentioned effects can be fully obtained, and economic efficiency is improved. Therefore, the W content when present is preferably set to 1.00% or less.

[0131] [Ca: 0~0.010%]

[0132] Ca is an element that refines inclusions in steel and improves toughness and ductility after quenching. To fully realize this effect, the Ca content is preferably 0.001% or more, more preferably 0.002% or more. On the other hand, by keeping the Ca content below 0.010%, this effect can be fully obtained while controlling costs. Therefore, the Ca content when present is preferably 0.010% or less, more preferably 0.004% or less.

[0133] [REM: 0~0.30%]

[0134] REM, like Ca, is an element that refines inclusions in steel and improves toughness and ductility after quenching. To fully realize this effect, the REM content is preferably 0.001% or more, more preferably 0.002% or more. On the other hand, this effect can be fully achieved with a REM content of 0.30% or less, while also controlling costs. Therefore, the REM content when present is preferably 0.30% or less, more preferably 0.20% or less.

[0135] Here, REM refers to a total of 17 elements, including Sc, Y, and the lanthanides. The REM content mentioned above refers to the total content of these elements. REM is, for example, added to molten steel using an Fe-Si-REM alloy, which may contain, for example, Ce, La, Nd, and Pr.

[0136] [O: below 0.0070%]

[0137] O is not an essential element and may be present in steel as an impurity. O is an element that forms oxides, becoming a fracture initiation point and contributing to the deterioration of steel sheet properties. Furthermore, oxides present near the surface of the steel sheet can sometimes cause surface defects, degrading appearance quality. Therefore, the lower the O content, the better. In particular, by setting the O content to 0.0070% or less, property deterioration can be suppressed; therefore, an O content of 0.0070% or less is preferred. While there is no particular limitation on the lower limit of O content, which can be 0%, in practice, the practical lower limit of O content under refining conditions is 0.0005%.

[0138] [Sb: below 0.100%]

[0139] There is no particular limitation on the lower limit of Sb content, which can be 0%. Sb is an element that effectively improves the wettability and adhesion of the plating. To achieve this effect, the Sb content is preferably 0.001% or more. On the other hand, by setting the Sb content to 0.100% or less, defects generated during manufacturing can be suppressed, and the reduction in toughness can be prevented. Therefore, the Sb content is preferably 0.100% or less.

[0140] The balance other than the above-mentioned components consists of Fe and impurities. In addition, the base steel sheet may contain impurities introduced during the manufacturing process. Examples of such impurities include Zn (zinc).

[0141] The above provides a detailed description of an example of the chemical composition of the base steel sheet for hot stamping steel sheets according to this embodiment.

[0142] The areas of steel sheets with the aforementioned chemical composition that have been coated with a surface treatment film can be used to produce hot-stamped components with a tensile strength of approximately 1000 MPa or more by heating / quenching using a hot stamping method. Furthermore, in the hot stamping method, since pressing can be performed while the material is softened at high temperatures, it can be easily formed.

[0143] The hot-stamping steel sheet described in this embodiment, compared to the method of hot-stamping by welding different types of steel sheets and controlling the cooling rate according to the part by controlling the temperature of the die, does not require the use of multiple steel sheets, nor does it require pre-welding equipment / processes. Furthermore, it eliminates the need for equipment for changing the die temperature and its associated operating costs. Therefore, it is economically preferable.

[0144] <Manufacturing of hot-stamped components with varying strengths>

[0145] In automotive frame components, sometimes the strength of one part is increased, while the strength of other parts is reduced for the purpose of absorbing energy during a collision. Components with such different strengths can be manufactured using hot-stamped steel sheets, as described above, with a surface-treated coating applied to a portion of the surface.

[0146] First, a surface treatment coating is applied to a portion of the surface of a metal raw material, such as a rolled steel sheet, to pre-form areas with different emissivity. Then, various processing methods, such as cutting and stamping, are performed to obtain the hot-stamping steel sheet according to this embodiment. Alternatively, the hot-stamping steel sheet according to this embodiment can also be obtained by applying a surface treatment coating to a steel sheet that has been cut, pressed, or stamped. Furthermore, by changing the thickness of the surface treatment coating, the emissivity can be continuously varied.

[0147] For example, a hot-stamping steel sheet with a surface-treatment coating applied as described above is subjected to hot stamping. As a heating device, examples include electric heating furnaces, gas heating furnaces, far-infrared furnaces, and conventional heating devices equipped with infrared heaters. Figure 1 As shown, the emissivity of the area with the surface-treated coating (coated area) is increased, resulting in a greater heat transfer effect due to radiation and a faster heating rate. However, the heating rate of other areas (uncoated areas) is slower. The coated area, after rapid heating, reaches a temperature above the Ac3 point, where the metallographic structure transforms into austenite. On the other hand, the uncoated area, due to its slower heating rate, can remain at a temperature below the Ac3 point even if the coated area reaches a temperature above the Ac3 point, as the metallographic structure has not completely transformed into a single austenite phase. In this embodiment, to achieve the above-described state, the heating device used can be appropriately controlled.

[0148] Next, the heated steel sheet is formed and cooled. Regions heated to above the Ac3 temperature (where the metallographic structure transforms into austenite) are quenched, resulting in increased strength. Conversely, regions heated below the Ac3 temperature and failing to complete the austenite single-phase transformation have relatively lower strength. As a result, components with varying strengths (i.e., hot-stamped parts) can be obtained, and the strength difference between these regions can be expressed as 150 Hv or higher in terms of Vickers hardness (load F: 50 kgf, approximately 9.8 N / 1 kgf) as specified in JIS Z 2244 (2009).

[0149] As described above, by changing the thickness of the surface treatment coating, the heating rate can be continuously varied, and thus the hardness can also be continuously varied. In areas with a thicker surface treatment coating, the austenitization is more pronounced due to the higher heating rate, resulting in higher strength during quenching due to martensite formation. Conversely, in areas with a thinner coating, the austenite fraction during heating is lower, and compared to thicker areas, less martensite is formed, thus lower strength. Furthermore, in areas without a coating, the austenite fraction during heating is further reduced, the amount of martensite formed is further decreased, and the strength is further reduced.

[0150] Thus, in the hot stamping steel sheet according to this embodiment, by appropriately controlling the location and thickness of the surface treatment coating, when using the hot stamping steel sheet to manufacture hot stamping components, it is possible to arbitrarily separate and manufacture parts with different strengths.

[0151] <Hot-stamped components>

[0152] The hot-stamped component obtained as described above has on the surface of the steel sheet: a portion having a surface-treated coating; and a portion not having a surface-treated coating. The surface-treated coating contains one or more oxides selected from the group consisting of Zr oxides, Zn oxides, and Ti oxides, and the amount of oxide adhered is X. Oxide It is 0.030 g / m 2 That's all. Additionally, the silica content of this surface-treated coating is 0–0.3 g / m³. 2 The carbon black present in the surface treatment coating of the hot-stamping steel sheet used as raw material for hot-stamping components disappears after the hot-stamping process, leaving behind the aforementioned metal oxides. The amount of oxides adhering to the surface treatment coating of the hot-stamping component is X. Oxide The amount of oxides adhering to the surface treatment coating of the hot-stamped steel sheet used as raw material depends on the amount of oxides in the coating, but its upper limit is approximately 0.600 g / m². 2 .

[0153] Preferably, when measuring the Vickers hardness (load F: 50 kgf, 1 kgf is approximately 9.8 N) as specified in JIS Z 2244 (2009), there are locations showing the maximum hardness HVmax and the minimum hardness HVmin, and the hardness difference ΔHV between the maximum hardness HVmax and the minimum hardness HVmin is 150 or more.

[0154] As can be clearly seen from the above description, both the region exhibiting the maximum hardness HVmax and the region exhibiting the minimum hardness HVmin exist within a region composed of a common raw material (i.e., the hot-stamping steel sheet according to this embodiment). Here, "common component" refers to a situation where the ratio (ratio between components) of a specific element (e.g., C, Si, Mn, P, S, Al, Ti, B, N) in a 0.05 mm field of view near the center of the sheet thickness is in the range of 0.80 to 1.2 times everywhere. For example, components with the same composition when checked at the center of the sheet thickness and manufactured through the same manufacturing process are referred to here as "common components". It should be noted that this common raw material can be composed of a single steel sheet, or it can be a raw material obtained by joining multiple identical steel sheets (i.e., the hot-stamping steel sheet according to this embodiment) by some method.

[0155] Example

[0156] The following describes embodiments of the present invention. The conditions described in the embodiments are merely examples used to confirm the feasibility and effectiveness of the present invention, and the present invention is not limited to these single examples. Various conditions can be used as long as they do not depart from the spirit of the present invention and achieve the purpose of the present invention.

[0157] As the base steel sheet, it is preferable to use a steel sheet with high mechanical strength (referring to various properties related to mechanical deformation and fracture, such as tensile strength, yield point, elongation, reduction of area, hardness, impact value, and fatigue strength). Table 1 below shows the chemical composition of the base steel sheet used in the hot-stamping steel sheets shown in the following examples before plating.

[0158] [Table 1]

[0159]

[0160] A surface treatment coating was applied to the base steel sheets (steel No. S1 to S18) having the chemical composition shown in Table 1. More specifically, as... Figure 2 As shown, in a steel plate with a width of 100mm × length of 200mm and a thickness of 1.2mm, the upper 100mm of the 200mm length is designated as the coated area by applying a surface treatment coating to one or both sides, while the remaining 100mm is designated as the uncoated area by not applying a surface treatment coating.

[0161] An industrial inkjet printer is used to apply a water-based treatment solution to a portion of the base steel plate, followed by drying to apply a surface treatment coating. The water-based treatment solution, in addition to a water-based acrylic resin as a binder, also contains commercially available carbon black and at least one compound such as TiO2, ZrO2, ZnO, Fe2O3, Fe3O4, CuO, SiO2, TiC, TiN, SiC, and SiN. Furthermore, a portion of the water-based treatment solution also contains silica in addition to the above components. The thickness of the surface treatment coating is set to be in the range of 1.0–2.5 μm, and when applied to both sides, the same type of coating is applied to both sides.

[0162] Then, in Figure 2 Thermocouples are connected to the center of the area with the surface treatment coating (coated area) (P1) and the center of the area without the coating (uncoated area) (P2), respectively, to allow temperature measurement at each location. The steel sheet is then heated in an electric furnace at a set temperature of 900°C. When the coated area reaches 880°C, the steel sheet is removed from the furnace. The steel sheet is then rapidly cooled using a metal die to obtain a hot-stamped component. It should be noted that the coated area exhibits the maximum hardness (HVmax) when measuring the Vickers hardness of the manufactured hot-stamped component, while the uncoated area exhibits the minimum hardness (HVmin) when measuring the Vickers hardness of the manufactured hot-stamped component.

[0163] Using a radiation thermometer, the radiation intensity at the center P1 of the area with the surface-treated coating at a wavelength of 8.0 μm at 25 °C was measured, and the emissivity (%) was calculated based on the ratio of the radiation intensity to that of a blackbody.

[0164] It should be noted that for some base steel plates, the above-mentioned surface treatment coating is applied after hot-dip galvanizing with Al-10% by mass Si, Zn, or Al, or after electroplating with Zn-3% by mass Ni. In the case of hot-dip galvanizing, after immersing the base steel plate in the plating bath, the adhesion amount is adjusted to an average of 70 g / m² on one side using a gas wiping method. 2 In the case of electroplating, the single-sided adhesion amount is adjusted to 20 g / m². 2 .

[0165] The composition of the coating on the surface-treated area and the difference in Vickers hardness between P1 and P2 of the resulting hot-stamped component were investigated. In some embodiments, appearance, coating adhesion and corrosion resistance after coating were also investigated.

[0166] The evaluation methods for each evaluation item are as follows.

[0167] (1) Strength characteristics

[0168] (score)

[0169] Using the method described in Japanese Industrial Standard JIS Z 2244 (2009), the Vickers hardness was measured at the center P1 of the part with the surface treatment coating and the center P2 of the part without the surface treatment coating from the cross section of the steel plate (load F: 50 kgf). The strength characteristics were evaluated based on the hardness difference between P1 and P2. If the hardness difference was Hv150 or higher, the component was considered to have excellent strength characteristics and different strengths.

[0170] 3: The difference in Vickers hardness ΔHV is above Hv200.

[0171] 2: The difference in Vickers hardness ΔHV is greater than or equal to Hv150 and less than 200.

[0172] 1: The difference in Vickers hardness ΔHV is less than Hv150.

[0173] (2) Appearance

[0174] (score)

[0175] Five CIE 1976 L*a*b* color spaces were measured using the method described in Japanese Industrial Standard JIS Z 8781-4 (2013), and the ratio of L* values ​​when comparing any two spaces was evaluated (RL* = L* value 1 / L* value 2).

[0176] 2:0.5~2.0

[0177] 1: Less than 0.5 or greater than 2.0

[0178] (3) Coating adhesion

[0179] The samples underwent phosphoric acid chemical conversion treatment and a 15 μm thick electrodeposition coating, followed by calcination at 170 °C for 20 minutes to apply the coating. Then, after immersion in deionized water at 60 °C for 200 hours, 100 checkerboard patterns with 1 mm intervals were cut using a cutter. The number of peeled portions in the checkerboard pattern was visually measured, and the area ratio of the peeled portions was calculated. A score was then awarded based on the calculated area ratio.

[0180] (score)

[0181] 3: The peeled area is more than 0% and less than 10%.

[0182] 2: The peeled area is more than 10% but less than 70%.

[0183] 1: The peeling area is more than 70% and less than 100%.

[0184] (4) Corrosion resistance after coating

[0185] For coatings subjected to the same conditions as in (3), a cutter was used to create scratches, using the method specified in JASO M609 established by the Automotive Technology Association. The width (maximum value on one side) of the coating expansion from the cut scratches was measured after 180 cycles of corrosion testing.

[0186] (score)

[0187] 3: Expansion width ≥ 0mm and < 1.5mm

[0188] 2: Expansion width ≥ 1.5mm and < 3mm

[0189] 1: Expansion width 3mm or more

[0190] The evaluation results obtained from Examples 1 to 4 implemented based on the above are shown in Tables 2, 3, 4, and 5, respectively.

[0191] <Example 1>

[0192] In Table 2 shown below, A1 to 21 are examples, and a1 to a3 are comparative examples.

[0193] In Example 1, when preparing the aqueous treatment solution, at least any one of carbon black, titanium nitride, titanium carbide, titanium oxide, iron oxide, copper oxide, zirconium oxide, silicon nitride, cobalt oxide, and tin oxide was used as compounds other than the binder component. The total content of the compounds other than the binder component in the aqueous treatment solution was in the range of 2 to 50% by volume relative to the total volume of the solid components. The solid component concentration of the aqueous treatment solution was set to 10 to 40% by mass, and after coating on a steel plate with a liquid film thickness of 3 μm to 25 μm, it was dried to obtain a coating. The drying atmosphere was set to atmospheric or nitrogen atmosphere, and the temperature was set to 100 to 300°C. The total content of the compounds in the aqueous treatment solution was the same as the total content of the compounds in the surface-treated coating obtained after drying. In this example, the emissivity at a wavelength of 8.0 μm was adjusted by adjusting the content of the compounds and the amount of the surface-treated coating.

[0194] [Table 2]

[0195]

[0196] In comparative examples a1 to a3, the emissivity at 8.0 μm at 25°C for the coated portion P1 was as low as 58%, 56%, and 58%, respectively. The hardness difference between the coated portion P1 and the uncoated portion P2 of the hot-stamped component, measured by Vickers hardness, was less than ΔHV150 (score 1). The emissivity at 8.0 μm at 25°C for the coatings in a1 to a3 was less than 60%. Therefore, it can be inferred that there would not be a significant difference in the heating rate between the coated portion P1 and the uncoated portion P2, and there would not be a difference in Vickers hardness greater than ΔHV150 in the microstructure of the hot-stamped component.

[0197] On the other hand, in Invention Examples A1 to A21, the emissivity at a wavelength of 8.0 μm at 25°C is 60% or more. As a result, the hardness difference between the coated and uncoated parts of the hot-stamped component is HV150 or more and less than 200 (score 2) on a Vickers hardness scale.

[0198] <Example 2>

[0199] In Table 3, in Invention Example B1, carbon black (CB) was set at 2.7 vol% of the surface treatment coating, and TiO2 was set at 0.6 vol%. As a result, the emissivity at 8.0 μm at 25°C in the coated area was 86%, and the hardness difference between the coated and uncoated areas of the hot-stamped component was Vickers hardness HV150 or higher and less than 200 (score 2). Although the coating adhesion was rated 3, the appearance was rated 1. Furthermore, in Invention Example B2, where carbon black was set at 4.0 vol% of the surface treatment coating and TiO2 was set at 1.0 vol%, the emissivity at 8.0 μm at 25°C in the coated area was 80%, and the hardness difference between the coated and uncoated areas of the hot-stamped component was Vickers hardness HV150 or higher and less than 200 (score 2). In Invention Example B5, where carbon black constitutes 58.3 vol% of the surface treatment coating and ZnO constitutes 1.2 vol% of the surface treatment coating, and in Invention Example B6, where carbon black constitutes 47.3 vol% of the surface treatment coating and ZnO constitutes 1.0 vol%, the emissivity at 8.0 μm at 25°C at the coated area is 88% and 90%, respectively, and the appearance is rated 2. Furthermore, the coating adhesion is rated 2.

[0200] On the other hand, in Invention Examples B3 to B4, where carbon black is set as 5.0% to 40.0% of the surface treatment coating, the emissivity at 8.0 μm at 25°C in the coated area is 82% and 86%, respectively. The hardness difference between the coated and uncoated areas of the hot-stamped component is Vickers hardness HV200 or higher (rating 3), and the appearance is rated 2, while the coating adhesion is rated 3.

[0201] Based on the above results, as in Invention Examples B3 to B4, by including 5.0 vol% to 40.0 vol% carbon black, a molded article with excellent strength properties, appearance, and coating adhesion can be obtained.

[0202] [Table 3]

[0203]

[0204] <Example 3>

[0205] In Table 4, compared with Invention Example C1 (where the Zn oxide content in the surface treatment coating is set to 0.2 vol%), Invention Example C2 (where the Ti oxide content in the surface treatment coating is set to 0.3 vol%), and Invention Example C6 (where the Ti oxide content in the surface treatment coating is set to 37.5 vol%), as in Invention Examples C3 to C5, by setting the Ti oxide and Zr oxide content in the surface treatment coating to 1.0 to 30.0 vol%, the hardness difference between the coated and uncoated parts of the hot-stamped component is further increased (score 3). The main reason for the increased hardness difference can be attributed to the fact that the emissivity of oxides is greater than that of compounds on the steel plate surface, and that the presence of the interface between the steel plate surface and oxide particles hinders the reflection of infrared rays, thereby increasing the heat input to the sample and thus increasing the difference in heating rate between the coated and uncoated parts.

[0206] [Table 4]

[0207]

[0208] <Example 4>

[0209] In Table 5, in Invention Example D1, the emissivity at 8.0 μm at 700°C in the coated area is 56%, and the hardness difference between the coated and uncoated areas of the hot-stamped component is a Vickers hardness of HV150 or higher and less than 200 (score 2). On the other hand, in Invention Examples D2 to D6, where the emissivity at 8.0 μm at 700°C in the coated area is 60% or higher, the hardness difference between the coated and uncoated areas of the hot-stamped component is a Vickers hardness of HV200 or higher (score 3).

[0210] [Table 5]

[0211]

[0212] <Example 5>

[0213] In Table 6, comparing Invention Examples E1 to E5 with E6, it can be seen that in Invention Example E6 without plating, the corrosion resistance after coating is "1", while in Invention Examples E1 to E5 with Al-10 mass%Si or Zn-3 mass%Ni plating, the corrosion resistance after coating is improved to "2" or "3".

[0214] [Table 6]

[0215]

[0216] As described above, according to the present invention, by applying a surface treatment coating to the desired portion of the steel plate and performing hot stamping, it is possible to form portions with different strengths in the resulting hot-stamped component.

[0217] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to these examples. Obviously, anyone skilled in the art to which this invention pertains will be able to conceive of various modifications or alterations within the scope of the technical concept described in the claims, and these are also understood to fall within the protection scope of this invention.

[0218] Industrial availability

[0219] According to the present invention, in a region with a surface-treated coating that increases the emissivity at a wavelength of 8.0 μm at 25°C, rapid heating is achieved by increasing heat transfer through radiation. By applying differences in hardenability, portions with varying strengths can be formed in a hot-stamped component from a single sheet of steel. Therefore, it has high industrial applicability.

Claims

1. A hot-stamping steel sheet, the steel sheet comprising, on at least one side of a surface: a portion having a surface-treatment coating, the portion having an emissivity of 60% or more at a wavelength of 8.0 μm at 25°C; and a portion not having the surface-treatment coating. The surface-treated coating comprises: carbon black; and one or more oxides selected from the group consisting of Zr oxides, Zn oxides, and Ti oxides, wherein the carbon black and the oxides are dispersed throughout the surface-treated coating. The silica content of the surface treatment coating is 0~0.3 g / m. 2 , The amount of carbon black and oxide adhering is set as X respectively. CB (g / m 2 ), X Oxide (g / m 2 When ), the following equation (1) is satisfied. 118.9≤24280 / {6700 / (100+76×X) CB ) + 18000 / (130 + 65 × X) Oxide )}≤332.0 Equation (1).

2. The hot-stamping steel plate according to claim 1, wherein, The surface treatment coating contains 5.0 to 40.0 vol% of the carbon black and 1.0 to 30.0 vol% of the oxide.

3. The hot-stamping steel plate according to claim 1 or 2, wherein, The amount of carbon black adhering X CB (g / m 2 The amount of X adhering to the oxide Oxide (g / m 2 The ratio X Oxide / X CB It is above 0.20 and below 200.

00.

4. The hot-stamping steel sheet according to any one of claims 1 to 3, wherein, The amount of carbon black adhering X CB It is 0.030 g / m 2 The above refers to the amount of oxide attached, X. Oxide It is 0.030 g / m 2 above.

5. The hot-stamping steel sheet according to any one of claims 1 to 4, wherein, The emissivity of the surface treatment coating at 700°C and a wavelength of 8.0 μm is greater than 60%.

6. The hot-stamping steel sheet according to any one of claims 1 to 5, wherein, On one or both sides of the hot-stamping steel sheet, there is a metal coating between the substrate of the steel sheet and the surface treatment coating.

7. The hot-stamping steel sheet according to any one of claims 1 to 6, wherein, The amount of oxide attached X Oxide 0.300g / m 2 the following.

8. A hot-stamped component having on the surface of a steel plate: a portion having a surface-treatment coating; and a portion not having the surface-treatment coating, the hot-stamped component having portions of different strengths formed from a single steel plate. The surface treatment coating contains one or more oxides selected from the group consisting of Zr oxides, Zn oxides, and Ti oxides, and the amount of the oxides attached is X. Oxide It is 0.030 g / m 2 above, The silica content of the surface treatment coating is 0~0.3 g / m. 2 .

9. The hot-stamped component according to claim 8, wherein, When measuring the Vickers hardness as specified in JIS Z 2244 (2009), there are regions that display the maximum hardness HVmax and regions that display the minimum hardness HVmin, and the hardness difference ΔHV between the maximum hardness HVmax and the minimum hardness HVmin is 150 or more.

10. The hot-stamped component according to claim 9, wherein, Both the region displaying the maximum hardness HVmax and the region displaying the minimum hardness HVmin exist within a region composed of a common raw material.

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