Galvannealed steel sheet for hot stamping, hot stamped body, and methods for manufacturing the same

Abstract

To provide: a hot-stamped compact having high strength, suppressed in generation of scales after hot-stamped, and having excellent weldability and chemical convertibility; a galvanized steel sheet for hot-stamping enabling production of the hot-stamped compact; a production method for the hot-stamped compact; and a production method for the galvanized steel sheet.SOLUTION: A galvanized steel sheet for hot-stamp is provided, having: a steel sheet having a predetermined chemical composition; a galvanized zinc coating arranged on the steel sheet; a zinc oxide-containing coating arranged on the galvanized zinc coating; and a hot-stamped molded product obtained by hot stamping the galvanized steel sheet.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a galvannealed steel sheet for hot stamping, a hot-stamped product, and methods for producing the same. [Background technology]

[0002] In recent years, methods for increasing the strength of steel sheets and reducing their thickness have been investigated in order to reduce the weight of automobiles. As a technology for press-forming difficult-to-form materials such as high-strength steel sheets, hot forming methods such as hot stamping have been adopted, in which the steel sheet material to be formed is preheated before being formed.

[0003] This forming method allows for high-temperature forming with low deformation resistance and allows for simultaneous quenching, making it an excellent method for achieving both high strength and formability in components. However, this forming method requires heating the steel sheet material to temperatures above 700°C before forming, which can lead to the problem of oxidation of the steel sheet surface during heating before hot stamping. The iron oxide scale formed by this oxidation on the steel sheet surface can shed during hot stamping and adhere to the die, reducing productivity. It can also remain on the surface of the formed product after hot stamping, resulting in poor appearance. Furthermore, if this scale remains on the surface of the formed product, it can cause poor adhesion between the formed product and the coating when painted in the subsequent process, resulting in reduced corrosion resistance. Therefore, scale removal treatments such as shot blasting are required after hot stamping.

[0004] To solve these problems, it has been proposed to use, as a steel sheet material for hot forming, a zinc-plated or aluminum-plated steel sheet for the purpose of suppressing oxidation of the surface of the base steel sheet and / or improving the corrosion resistance of the press-formed product. Examples of the use of zinc-plated steel sheets for hot forming include the techniques described in Patent Documents 1 and 2.

[0005] Patent Document 3 proposes a zinc-coated steel sheet for hot forming that improves the adhesion of the oxide coating formed during hot forming to the steel sheet by controlling the C concentration, Si concentration, P concentration, and / or Ti concentration in the steel, and by controlling the Zn adhesion amount on the steel sheet surface and the Al concentration in the coating, thereby simplifying or eliminating the process of removing oxides from the surface of press-formed products. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-73774 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-353548 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-48254 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Documents 1 to 3, if an excessive zinc oxide layer is formed during hot stamping, the weldability may be poor after hot stamping. Automobile body parts are assembled by joining parts that have been hot stamped into various shapes together by resistance welding (particularly spot welding). In general, plated steel sheets have poorer weldability than cold-rolled steel sheets.

[0008] Furthermore, automobile body parts are required to have excellent chemical conversion treatability because they are subjected to a painting treatment consisting of chemical conversion treatment and electrodeposition after the above spot welding.

[0009] At the current technological level, in the formed products obtained by hot stamping galvannealed steel sheet, the heating time in the furnace (furnace time) must be approximately 4 minutes or more to improve weldability and phosphatability and to suppress liquid metal embrittlement (LME, Liquid Metal Embrittlement or LMC).As hot stamping is inferior to cold pressing in press productivity, there is a demand to shorten the furnace time.

[0010] The present invention has been made in view of the above-mentioned problems, and has an object to provide a hot-stamped product which has high strength, is inhibited from generating scale, and has excellent weldability and chemical conversion treatability, and a galvannealed steel sheet for hot stamping from which the hot-stamped product can be produced. Another object of the present invention is to provide a method for producing a galvannealed steel sheet for hot stamping, which can produce the above-mentioned galvannealed steel sheet for hot stamping. Another object of the present invention is to provide a method for producing a hot-stamped steel, which can produce the above-mentioned hot-stamped steel and can shorten the furnace time. [Means for solving the problem]

[0011] The gist of the present invention is as follows. (1) A galvannealed steel sheet for hot stamping according to one aspect of the present invention comprises a steel sheet, a galvannealed coating disposed on the steel sheet, and a zinc oxide-containing coating disposed on the galvannealed coating, The steel plate has a chemical composition in mass%: C: 0.02~0.58%, Mn: 0.10 to 3.00%, sol.Al: 0.001~1.000%, Si: 2.00% or less, P: 0.100% or less, S: 0.005% or less, N: 0.0100% or less, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0~1.00%, W: 0 to 1.00% Cr: 0~1.00%, Mo: 0-1.00%, Cu: 0-1.00% Ni: 0 to 1.00% B: 0~0.0100%, Ca: 0 to 0.05%, and REM: 0 to 0.05% and the balance being Fe and impurities, The galvannealed coating film is The Fe concentration is more than 8.0 mass%; Zn content: 15.0 to 40.0 g / m 2 and Al content: 400 to 1000 mg / m 2 and Ni content: 0 to 2000 mg / m 2 and The zinc oxide-containing coating is The amount of zinc oxide per side is 0.3 to 1.5 g / m2 in terms of metallic zinc. 2 is. (2) The galvannealed steel sheet for hot stamping according to the above (1) has a chemical composition, in mass%, of the steel sheet, Ti: 0.005 to 0.200%, Nb: 0.005 to 0.200%, V: 0.10~1.00%, W: 0.10~1.00%, Cr: 0.05 to 1.00%, Mo: 0.05 to 1.00%, Cu: 0.05 to 1.00%, Ni: 0.05 to 1.00%, B: 0.0010~0.0100%, Ca: 0.0005 to 0.05%, and REM: 0.0005 to 0.05% It may contain one or two selected from the group consisting of: (3) The galvannealed steel sheet for hot stamping according to (1) or (2) above has a Ni content of 50 to 2000 mg / m in the galvannealed coating. 2 may be. (4) A hot-stamped steel according to another aspect of the present invention includes a steel sheet, a plating film disposed on the steel sheet, and a zinc oxide-containing film disposed on the plating film, The steel plate has a chemical composition in mass%: C: 0.02~0.58%, Mn: 0.10 to 3.00%, sol.Al: 0.001~1.000%, Si: 2.00% or less, P: 0.100% or less, S: 0.005% or less, N: 0.0100% or less, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0~1.00%, W: 0 to 1.00% Cr: 0~1.00%, Mo: 0-1.00%, Cu: 0-1.00% Ni: 0 to 1.00% B: 0~0.0100%, Ca: 0 to 0.05%, and REM: 0 to 0.05% and the balance being Fe and impurities, The metal structure of the steel plate contains 80% by area or more of martensite, the plating film is composed only of an Fe-Zn solid solution phase and zinc oxide, Zn content: 15.0 to 40.0 g / m 2 and Al content: 400 to 1000 mg / m 2 and Ni content: 0 to 2000 mg / m 2 and the remainder being impurities, The zinc oxide-containing coating is The amount of zinc oxide per side is 0.3 to 1.5 g / m2 in terms of metallic zinc. 2 is. (5) In the hot stamped steel according to (4), the chemical composition of the steel sheet is, in mass%, Ti: 0.005 to 0.200%, Nb: 0.005 to 0.200%, V: 0.10~1.00%, W: 0.10~1.00%, Cr: 0.05 to 1.00%, Mo: 0.05 to 1.00%, Cu: 0.05 to 1.00%, Ni: 0.05 to 1.00%, B: 0.0010~0.0100%, Ca: 0.0005 to 0.05%, and REM: 0.0005 to 0.05% It may contain one or two selected from the group consisting of: (6) The hot-stamped product according to (4) or (5) above may have a chemical conversion coating on the zinc oxide-containing coating. (7) A method for producing a galvannealed steel sheet for hot stamping according to another aspect of the present invention is the method for producing a galvannealed steel sheet for hot stamping according to the above (1), A hot rolling process in which a slab having the chemical composition described in (1) is hot rolled to obtain a hot-rolled steel sheet; Optionally, a cold rolling step of cold rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet; Optionally, a Ni pre-plating step of obtaining a Ni pre-plated steel sheet by applying Ni pre-plating to the hot-rolled steel sheet or the cold-rolled steel sheet; an annealing step of holding the hot-rolled steel sheet, the cold-rolled steel sheet, or the Ni-preplated steel sheet in a reducing atmosphere at a temperature range of 460 to 850°C for 3 seconds or more to obtain an annealed steel sheet; a galvanizing step of immersing the annealed steel sheet in a molten zinc bath having an Al concentration of 0.190 to 0.400 mass% for 1.0 to 15.0 seconds to obtain a hot-dip galvanized steel sheet; an alloying step of performing alloying treatment on the hot-dip galvanized steel sheet; The amount of zinc oxide per side is 0.3 to 1.5 g / m2 in terms of metallic zinc. 2 and forming a zinc oxide-containing film, which is a zinc oxide-containing film comprising: (8) A method for producing a hot-stamped steel according to another aspect of the present invention is the method for producing a hot-stamped steel according to the above (4), A steel sheet, a galvannealed coating film disposed on the steel sheet, and a zinc oxide-containing coating film disposed on the galvannealed coating film, The steel plate has a chemical composition in mass%: C: 0.02~0.58%, Mn: 0.10 to 3.00%, sol.Al: 0.001~1.000%, Si: 2.00% or less, P: 0.100% or less, S: 0.005% or less, N: 0.0100% or less, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0~1.00%, W: 0 to 1.00% Cr: 0~1.00%, Mo: 0-1.00%, Cu: 0-1.00% Ni: 0 to 1.00% B: 0~0.0100%, Ca: 0 to 0.05%, and REM: 0 to 0.05% and the balance being Fe and impurities, The galvannealed coating film is The Fe concentration is more than 8.0 mass%; Zn content: 15.0 to 40.0 g / m 2 and Al content: 400 to 1000 mg / m 2 and Ni content: 0 to 2000 mg / m 2 and the remainder being impurities, The zinc oxide-containing coating is The amount of zinc oxide per side is 0.3 to 1.5 g / m2 in terms of metallic zinc. 2 The galvannealed steel sheet for hot stamping is heated, and the holding time in the temperature range of 100°C or higher is set to 150 seconds or less, the holding time in the temperature range of 850°C or higher is set to 30 seconds or less, and the hot stamped product is obtained by hot stamping in the temperature range of 782°C or higher. (9) The method for producing a hot-stamped steel according to (8) above, further comprising the steps of: Ti: 0.005 to 0.200%, Nb: 0.005 to 0.200%, V: 0.10~1.00%, W: 0.10~1.00%, Cr: 0.05 to 1.00%, Mo: 0.05 to 1.00%, Cu: 0.05 to 1.00%, Ni: 0.05 to 1.00%, B: 0.0010~0.0100%, Ca: 0.0005 to 0.05%, and REM: 0.0005 to 0.05% It may contain one or two selected from the group consisting of: (10) In the method for producing a hot-stamped product according to (8) or (9) above, a chemical conversion coating may be formed on the surface of the hot-stamped product. [Effects of the Invention]

[0012] According to the above aspects of the present invention, it is possible to provide a hot-stamped product which has high strength, is inhibited from generating scale after hot stamping, and has excellent weldability and chemical conversion treatability, and a galvannealed steel sheet for hot stamping from which the hot-stamped product can be manufactured. Furthermore, according to the above-described another aspect of the present invention, it is possible to provide a method for producing a galvannealed steel sheet for hot stamping, which can produce the above-described galvannealed steel sheet for hot stamping. Furthermore, according to the above-described another aspect of the present invention, it is possible to provide a method for producing a hot-stamped steel, which can produce the above-described hot-stamped steel and can shorten the furnace time. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 10 is a diagram showing an example of a material temperature record in a gas furnace in an example. [Figure 2] FIG. 1 is a diagram showing an example of the results of SEM observation of the presence or absence of LME cracks in an example. [Figure 3] FIG. 2 is a diagram showing an example of the results of evaluating chemical conversion treatability by SEM in an example. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present invention will be described in detail below. However, the present invention is not limited to the configurations disclosed in the present embodiments, and various modifications are possible within the scope of the present invention. Numerical ranges indicated below with "to" include the lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" do not include the numerical range. Note that all "%" in chemical compositions indicates "mass %."

[0015] First, a description will be given of a galvannealed steel sheet for hot stamping according to Embodiment 1. The galvannealed steel sheet for hot stamping according to Embodiment 1 has a steel sheet and a galvannealed coating disposed on the steel sheet. The following describes the steel sheet that constitutes the galvannealed steel sheet for hot stamping according to the first embodiment. Note that the chemical composition of the steel sheet does not change before and after hot stamping, and therefore the chemical composition of the steel sheet that constitutes the galvannealed steel sheet for hot stamping according to the first embodiment is the same as the chemical composition of the steel sheet that constitutes the hot-stamped product obtained by hot stamping the galvannealed steel sheet for hot stamping according to the first embodiment.

[0016] The steel sheet constituting the galvannealed steel sheet for hot stamping according to the first embodiment has a chemical composition, in mass%, of C: 0.02 to 0.58%, Mn: 0.10 to 3.00%, sol. Al: 0.001 to 1.000%, Si: 2.00% or less, P: 0.100% or less, S: 0.005% or less, N: 0.0100% or less, and the balance: Fe and impurities. Each element will be described in detail below.

[0017] C: 0.02 to 0.58% C is an important element for improving the hardenability of steel sheet and obtaining the strength of the hot stamped body after quenching (hot stamping). C also lowers the Ac3 point and reduces the quenching temperature. If the C content is less than 0.02%, the above effects cannot be sufficiently obtained. Therefore, the C content is set to 0.02% or more. The C content is preferably 0.10% or more or 0.20% or more. On the other hand, if the C content exceeds 0.58%, the toughness of the welded joint and the hot stamped steel after hot stamping will be significantly deteriorated. Therefore, the C content is set to 0.58% or less. The C content is preferably 0.55% or less or 0.50% or less.

[0018] Mn: 0.10 to 3.00% Mn is an important element for improving the hardenability of steel sheet and for stably obtaining the strength of the hot stamped steel sheet after quenching. If the Mn content is less than 0.10%, the above effects cannot be sufficiently obtained. Therefore, the Mn content is set to 0.10% or more. The Mn content is preferably 0.20% or more, 0.30% or more, or 0.40% or more. On the other hand, if the Mn content is excessive, the above effects saturate and the alloy cost increases. Therefore, the Mn content is set to 3.00% or less. The Mn content is preferably 2.80% or less, 2.60% or less, or 2.40% or less.

[0019] sol.Al:0.001~1.000% Al has the effect of deoxidizing steel and improving the quality of the steel (suppressing the occurrence of defects such as blowholes in the steel). If the sol. Al content is less than 0.001%, the above effect cannot be obtained. Therefore, the sol. Al content is set to 0.001% or more. The sol. Al content is preferably 0.010% or more, 0.020% or more, or 0.030% or more. On the other hand, if the sol. Al content is excessive, the above effects saturate and the alloy cost increases. Therefore, the sol. Al content is set to 1.000% or less. The sol. Al content is preferably 0.800% or less, 0.100% or less, 0.075% or less, or 0.070% or less. The term "sol. Al" means acid-soluble Al, and indicates solute Al that is present in the steel in a solid solution state.

[0020] Si:2.00% or less Excessive Si content inhibits the transformation from ferrite to austenite during hot stamping and inhibits quench hardening by hot stamping. Therefore, the Si content is set to 2.00% or less. The Si content is preferably 1.00% or less, 0.70% or less, or 0.50% or less. A lower Si content is preferable, and there is no particular lower limit. However, excessively reducing the Si content increases refining costs, so the Si content may be set to 0.01% or more.

[0021] P:0.100% or less P is contained in steel as an impurity and has the effect of embrittling steel, so a low P content is preferable. Therefore, the P content is set to 0.100% or less. The P content is preferably 0.050% or less, 0.020% or less, or 0.015% or less. There is no particular lower limit for the P content, but since an excessively low P content increases refining costs, the P content may be set to 0.001% or more.

[0022] S: 0.005% or less S is an element contained as an impurity and forms MnS, which has the effect of embrittling steel, so a low S content is preferable. Therefore, the S content is set to 0.005% or less. Preferably, it is set to 0.004% or less, or 0.003% or less. There is no particular lower limit for the S content, but since an excessively low S content increases refining costs, the S content may be set to 0.0003% or more, or 0.001% or more.

[0023] N: 0.0100% or less Since N is contained as an impurity and forms inclusions in steel, which deteriorates the toughness of hot-stamped steel, a low N content is preferable. Therefore, the N content is set to 0.0100% or less. The N content is preferably 0.0080% or less, 0.0070% or less, 0.0050% or less, or 0.0045% or less. There is no particular lower limit for the N content, but an excessively low N content increases refining costs, so the N content may be set to 0.0005% or more.

[0024] The balance of the chemical composition of the steel sheet constituting the galvannealed steel sheet for hot stamping according to the first embodiment is Fe and impurities. Examples of impurities include elements that are inevitably mixed in from steel raw materials or scrap and / or during the steelmaking process, and elements that are permissible within a range that does not impair the properties of the hot-stamped steel according to the first embodiment.

[0025] The steel sheet constituting the galvannealed steel sheet for hot stamping according to the first embodiment may contain the following optional elements instead of the balance Fe. Note that the optional elements described below do not necessarily have to be contained, and when they are not contained, the content is 0%.

[0026] Ti: 0.005 to 0.200% Nb: 0.005 to 0.200% V: 0.10 to 1.00% W: 0.10~1.00% Ti, Nb, V, and W are elements that promote the interdiffusion of Fe and Zn between the galvannealed coating and the steel sheet, making it difficult for a molten zinc alloy layer to form during hot stamping. The formation of a molten zinc alloy layer is undesirable because it can cause cracks during hot stamping. Therefore, Ti, Nb, V, and W may be added to the steel sheet. To ensure the above effects, it is preferable to add at least one of Ti: 0.005% or more, Nb: 0.005% or more, V: 0.10% or more, and W: 0.10% or more. However, if the Ti content or Nb content exceeds 0.200%, or if the V content or W content exceeds 1.00%, the above effects saturate and the alloy cost increases. Therefore, the Ti content and Nb content are each set to 0.200% or less, and the V content and W content are each set to 1.00% or less. Preferably, the Ti content and Nb content are each set to 0.150% or less, and the V content and W content are each set to 0.50% or less.

[0027] Cr: 0.05 to 1.00% Mo: 0.05 to 1.00% Cu: 0.05 to 1.00% Ni: 0.05 to 1.00% B: 0.0010~0.0100% Cr, Mo, Cu, Ni, and B are elements that improve the hardenability of steel sheet and the strength of hot-stamped steel sheets. Therefore, one or more of these elements may be contained. To ensure the above effects, it is preferable to contain one or more of Cr: 0.05% or more, Mo: 0.05% or more, Cu: 0.05% or more, Ni: 0.05% or more, and B: 0.0010% or more. However, if the Cr content, Mo content, Cu content, or Ni content exceeds 1.00%, or if the B content exceeds 0.0100%, the above effects saturate and alloy costs increase. Therefore, the Cr content, Mo content, Cu content, and Ni content are each limited to 1.00% or less, and the B content is limited to 0.0100% or less. The B content is preferably limited to 0.0080% or less.

[0028] Ca: 0.0005 to 0.05% REM: 0.0005 to 0.05% Ca and REM have the effect of refining inclusions in steel and preventing cracks caused by the inclusions during hot stamping. Therefore, one or more of these elements may be contained. To ensure the above effect, it is preferable to contain at least one of Ca: 0.0005% or more and REM: 0.0005% or more. However, if the Ca content or REM content exceeds 0.05%, the effect of refining inclusions in steel saturates and the alloy cost increases. Therefore, the Ca content and REM content are each set to 0.05% or less.

[0029] Here, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the REM content refers to the total content of these elements. REM is often contained in misch metal, but lanthanoid series elements in addition to La and Ce may also be contained in combination. Even when lanthanoid series elements in addition to La and Ce are contained in combination, the hot-stamped steel according to the first embodiment can still exhibit its effects. Furthermore, even when metallic REM such as metallic La or Ce is contained, the hot-stamped steel according to the first embodiment can still exhibit its effects.

[0030] The chemical composition of the above-mentioned steel sheet may be measured by a common analytical method. For example, it may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Sol-Al may be measured by ICP-AES using the filtrate obtained after thermal decomposition of a sample with acid. C and S may be measured using the combustion-infrared absorption method, and N may be measured using the inert gas fusion-thermal conductivity method. If the steel sheet has a galvannealed coating, plating coating, zinc oxide-containing coating, or chemical conversion coating on its surface, these may be removed by mechanical grinding before analyzing the chemical composition.

[0031] The galvannealed steel sheet for hot stamping according to the first embodiment has a galvannealed coating on a steel sheet. This galvannealed coating has an Fe concentration of more than 8.0 mass% and a Zn content of 15.0 to 40.0 g / m 2 and the Al content is 150 mg / m 2 More than 400mg / m 2 Ni content is 0 to 2000 mg / m 2 and the remainder consists of impurities. The galvannealed coating will be described in detail below.

[0032] Fe concentration in galvannealed coating: more than 8.0 mass% If the Fe concentration in the galvannealed coating is 8.0% by mass or less, the ηZn phase remains on the surface of the galvannealed coating, increasing the reflectivity. As a result, the heating rate in the heating furnace before hot stamping becomes slower, and the time in the furnace becomes longer. Therefore, the Fe concentration in the galvannealed coating is set to more than 8.0% by mass. Preferably, it is 8.5% by mass or more, or 9.0% by mass or more.

[0033] There is no particular upper limit to the Fe concentration in the galvannealed coating. To form an Fe-Zn solid solution in a short furnace time, a higher Fe concentration is preferable, but given the equipment capacity and heating time for normal alloying, 18.0 mass% is the practical upper limit.

[0034] In a typical galvannealed steel sheet, the Fe concentration in the galvannealed coating needs to be controlled so as not to become excessive in order to suppress the occurrence of powdering during cold pressing. However, in the present embodiment, since hot stamping is performed without cold pressing, there is no need to control the upper limit of the Fe concentration.

[0035] Zn content in galvannealed coating: 15.0 to 40.0 g / m 2 The amount of Zn in the galvannealed coating is 15.0 g / m 2 If the Zn content is less than 15.0 g / m, iron oxide scale may occur in areas with less coating due to unavoidable variations in coating weight. Furthermore, if the Zn content is too low, the wiping nozzle must be brought closer to the steel sheet, although this depends on the capacity of the wiping device, increasing the risk of contact. Therefore, the Zn content in the galvannealed coating is set to 15.0 g / m. 2 More preferably, 20.0 g / m 2 That's all.

[0036] On the other hand, the amount of Zn in the galvannealed coating was 40.0 g / m 2 If the Zn content in the galvannealed coating is more than 40.0 g / m, it takes time for the Fe-Zn solid solution to form, and the time in the furnace becomes long. 2 The thickness is preferably 35.0 g / m or less. 2 The following is the result.

[0037] Al content in galvannealed coating: 150 mg / m 2 More than 400mg / m 2 less than The Al content in the galvannealed coating is 150 mg / m 2If the Al content is less than 150 mg / m, the amount of Al oxides formed on the surface of the galvannealed coating during heating before hot stamping will be small. As a result, Zn oxidation will not be suppressed, and Zn-based oxides will be formed in excess, causing sparks and / or deposition during spot welding and deteriorating weldability. Therefore, it is recommended to set the Al content in the galvannealed coating to 150 mg / m. 2 Preferably, it is 200 mg / m or more. 2 That's all.

[0038] On the other hand, the Al content in the galvannealed coating was 400 mg / m 2 If the Al content is more than 400 mg / m, the chemical conversion treatability of the hot-stamped body is reduced. 2 Less than.

[0039] The Al content in the galvannealed coating of a galvannealed steel sheet for hot stamping is affected by the atmosphere during heating before annealing, the bath temperature, the temperature of the steel sheet when immersed in the molten zinc bath, the immersion time, the coating weight, the Al concentration in the bath, etc. Therefore, by empirically determining and controlling the relationship between these manufacturing conditions and the Al content in the galvannealed coating, the Al content in the galvannealed coating can be controlled within the above-mentioned range.

[0040] Ni content in galvannealed coating: 0 to 2000 mg / m 2 The amount of Ni in the galvannealed coating is 2000 mg / m 2 If the Ni content exceeds 2000 mg / m, the raw material and electricity costs for Ni plating will increase excessively. 2 The concentration should be less than 1500 mg / m 2 Below 1000mg / m 2 or less than 800 mg / m 2 The following is the result.

[0041] The amount of Ni in the galvannealed coating is 0 mg / m 2 The amount of Ni in the galvannealed coating may be 50 mg / m 2By setting the Ni content in the galvannealed coating to 50 mg / m or more, the temperature and time required for alloying can be reduced even if the Al concentration in the bath is relatively high, thereby improving production efficiency. In addition, the annealing temperature can be lowered, improving flatness and reducing the risk of contact between the wiping nozzle and the steel sheet. Therefore, the Ni content in the galvannealed coating is set to 50 mg / m or more. 2 More preferably, it is 80 mg / m or more. 2 More than 100mg / m 2 or more than 150 mg / m 2 That's all.

[0042] Remainder in galvannealed coating The balance of the galvannealed coating is made up of impurities, which are preferably 0.1 mass % or less.

[0043] The Fe concentration, Zn content, Al content and Ni content in the galvannealed coating are measured by the following methods. Only the galvannealed coating of a galvannealed steel sheet for hot stamping is dissolved and removed using a 5% by volume HCl aqueous solution containing an inhibitor.The Fe concentration, Zn amount, Al amount, and Ni amount in the galvannealed coating are determined by ICP analysis using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) to determine the Fe concentration, Zn amount, Al amount, and Ni amount in the galvannealed coating. When the galvannealed steel sheet for hot stamping has a zinc oxide-containing coating, the zinc oxide-containing coating is removed by shot blasting or mechanical grinding before the above-mentioned measurement is carried out.

[0044] Next, a galvannealed steel sheet for hot stamping according to a second embodiment will be described. The galvannealed steel sheet for hot stamping according to the second embodiment has a steel sheet, a galvannealed coating disposed on the steel sheet, and a zinc oxide-containing coating disposed on the galvannealed coating. Hereinafter, the galvannealed steel sheet for hot stamping according to the second embodiment will be described.

[0045] Only the differences from the galvannealed steel sheet for hot stamping according to the first embodiment described above will be described, and descriptions of the overlapping points with the galvannealed steel sheet for hot stamping according to the first embodiment will be omitted.

[0046] The galvannealed steel sheet for hot stamping according to the second embodiment has an Al content of 400 to 1000 mg / m 2 The galvannealed steel sheet for hot stamping according to the second embodiment has a zinc oxide-containing coating, which will be described later, and therefore, even if the galvannealed coating has a high Al content, excellent chemical conversion treatability can be obtained in the hot-stamped body. Under normal manufacturing conditions, the Al content of the galvannealed coating is 1000 mg / m 2 Therefore, the Al content of the galvannealed coating is unlikely to exceed 1000 mg / m 2 The following applies.

[0047] As described above, the galvannealed steel sheet for hot stamping according to the second embodiment has a zinc oxide-containing coating on the galvannealed coating. The zinc oxide-containing coating will be described in detail below.

[0048] The zinc oxide-containing coating has a zinc oxide content of 0.3 to 1.5 g / m2 per side, calculated as metallic zinc. 2 The amount of zinc oxide per side is 0.3 g / m2 in terms of metallic zinc. 2 By adjusting the above, it is possible to further improve the hot lubricity, corrosion resistance after painting, and chemical conversion treatability. In addition, the amount of zinc oxide per side is 1.5 g / m2 in terms of metallic zinc. 2 By setting the amount of zinc oxide per side to 1.5 g / m or less, the thickness of the zinc oxide-containing coating can be reduced, and the weldability of the hot stamped body can be further improved. 2 The following applies.

[0049] In addition to zinc oxide, the zinc oxide-containing coating may contain, for example, zinc compounds such as zinc hydroxide, zinc sulfate, zinc nitrate, zinc phosphate, zinc acetate, zinc citrate, zinc oxalate, zinc oleate, zinc gluconate, etc. The zinc oxide-containing coating may contain only one of these zinc compounds in addition to zinc oxide, or may contain a mixture of multiple zinc compounds in addition to zinc oxide.

[0050] The size of the zinc oxide in the zinc oxide-containing coating is not particularly limited, but a particle size of 50 to 300 nm is preferred. There are two types of particle size of zinc oxide: the particle size of the powder itself and the particle size in the sol when the powder is made into a sol. In this embodiment, the particle size in the sol is preferably 50 to 300 nm. Generally, secondary aggregation of fine powder occurs in the sol, so the particle size in the sol becomes larger than the particle size of the powder itself. If the particle size of the powder itself is less than 50 nm, not only is kneading difficult, but secondary aggregation is also likely to occur, resulting in coarse particles. Therefore, it may be difficult to achieve a particle size of zinc oxide in the sol of less than 50 nm. Furthermore, if the particle size of zinc oxide in the sol exceeds 300 nm, the particles are likely to settle, which may result in unevenness.

[0051] The particle size of zinc oxide can be measured by known methods such as dynamic light scattering, stimulated diffraction grating, and laser diffraction / scattering.

[0052] The amount of zinc oxide deposited in the zinc oxide-containing coating can be obtained by immersing the film in an aqueous solution in which zinc oxide but not metal zinc is soluble, such as an aqueous solution of ammonium dichromate, measuring the zinc content, and calculating the amount of zinc oxide per area converted into metal zinc.

[0053] Next, a hot-stamped steel according to this embodiment will be described. The hot-stamped steel according to this embodiment can be obtained by hot stamping the galvannealed steel sheet for hot stamping according to the second embodiment described above. Hereinafter, the hot-stamped steel according to this embodiment will be described.

[0054] The hot-stamped steel according to this embodiment includes a steel sheet having the above-described chemical composition, a plating film disposed on the steel sheet, and a zinc oxide-containing coating disposed on the plating film. Note that the hot-stamped steel according to this embodiment may also include a chemical conversion coating on the zinc oxide-containing coating.

[0055] In the hot-stamped steel according to this embodiment, the metal structure of the steel sheet contains 80% by area or more of martensite, and the plating film is composed only of an Fe-Zn solid solution phase and zinc oxide, with the Zn content being 15.0 to 40.0 g / m 2 and the Al content is 400 to 1000 mg / m 2 and the Ni content is 0 to 2000 mg / m 2 and the balance is impurities, and the zinc oxide-containing coating has a zinc oxide amount per side of 0.3 to 1.5 g / m in terms of metallic zinc. 2 is.

[0056] steel plate The chemical composition of the steel sheet constituting the hot-stamped steel body is the same as the chemical composition of the above-mentioned galvannealed steel sheet for hot stamping, and therefore a description thereof will be omitted.

[0057] Metal structure: Area ratio of martensite is 80% or more If the area fraction of martensite is less than 80%, the desired strength cannot be obtained. Therefore, the area fraction of martensite is set to 80% or more, preferably 85% or more. There is no particular upper limit for the area fraction of martensite, but it may be set to 100% or less, or 95% or less.

[0058] The remaining structures other than martensite include ferrite, pearlite, retained austenite, and bainite. In relation to the area ratio of martensite, the area ratio of these remaining structures is preferably 20% or less.

[0059] The area fraction of martensite is obtained by the following method. A sample is cut from any position at least 50 mm away from the edge of the hot-stamped product (if sampling from this position is not possible, a position avoiding the edge) so that a cross section perpendicular to the surface (cross section through the plate thickness) can be observed. If the hot-stamped product contains a weld, the sample is taken from a position avoiding the weld and its vicinity.

[0060] The cross section of the sample is etched with LePeller's reagent. The t / 4 (t is the plate thickness) position of the cross section etched with LePeller's reagent is observed in 10 fields at a magnification of 500 times, and the obtained optical microscope photograph is analyzed using image analysis software "Photoshop CS5" manufactured by Adobe, to determine the area ratio of martensite. As an image analysis method, the maximum brightness value L max and the minimum brightness value L min and are obtained from the image, and the brightness is L max -0.3(L max -L min ) to L max The area with pixels up to L is the white area. min From L min +0.3(L max -L min ) are defined as black regions, and the other regions as gray regions, and the area ratio of martensite, which is the white region, is calculated. Image analysis is performed in the same manner as above to measure the area ratio of martensite for a total of 10 observation fields, and the average value of these area ratios is calculated. The obtained average value is considered to be the area ratio of martensite. This gives the area ratio of martensite. Moreover, the area ratio of the remaining structure is obtained by subtracting the area ratio of martensite from 100%.

[0061] plating film Consists of only Fe-Zn solid solution phase and zinc oxide The plating film according to this embodiment is composed only of an Fe-Zn solid solution phase and zinc oxide. By forming a plating film composed only of an Fe-Zn solid solution phase and zinc oxide, it is possible to suppress liquid metal embrittlement (LME) or liquid metal cracking (LMC) of the hot stamped body. The Fe-Zn solid solution phase is a phase formed by alloying zinc in a molten zinc bath with Fe in the steel sheet, and has a relatively high Fe concentration.

[0062] In the hot-stamped compact according to this embodiment, the only peaks detected by X-ray diffraction measurement using a Cu tube are those of the Fe-Zn solid solution phase and zinc oxide. The peak positions of zinc oxide are determined by referring to JCPDS card 00-036-1451 ZnO-Zincite. If an X-ray diffraction intensity peak appears at the angle listed, zinc oxide is deemed to be present. The peak positions of the Fe-Zn solid solution phase are listed in JCPDS card 00-006-0696 Iron. However, due to the presence of approximately 30% Zn in Fe, the crystal lattice expands, resulting in an actual X-ray diffraction intensity peak angle that is 1 to 3% smaller than the angle listed in the JCPDS card. Therefore, in this embodiment, if an X-ray diffraction intensity peak appears at an angle 1 to 3% smaller than the angle listed in the JCPDS card, the Fe-Zn solid solution phase is deemed to be present.

[0063] The plating film according to this embodiment contains Γ phase (Fe4Zn9, Fe3Zn 10 ), Γ1 phase (Fe 11 Zn 40 ), δ phase (FeZn8,Fe 13 Zn 126 ), and ζ phase (FeZn 13 ) is not included. If the alloying of the galvannealed coating does not progress and a liquid phase is present in the coating during furnace heating, the liquid phase will penetrate the grain boundaries of the steel sheet during hot stamping, causing LME, and the liquid phase will solidify as the Γ phase or δ phase.

[0064] Zn content in plating film: 15.0 to 40.0 g / m 2 The amount of Zn in the plating film is 15.0 g / m 2 If the Zn content is less than 15.0 g / m, iron oxide scale may form during heating in the furnace. 2 More preferably, 20.0 g / m 2 That's all. On the other hand, the amount of Zn in the plating film was 40.0 g / m 2 If the Zn content exceeds 40.0 g / m, the solid solution phase does not form during heating in the furnace, leaving a liquid phase, which may cause LME, or may require a longer time in the furnace, resulting in a decrease in production efficiency. 2 The thickness is preferably 35.0 g / m or less. 2 The following is the result.

[0065] Amount of Al in the plating film: 400 to 1000 mg / m 2 Since the hot stamped body according to this embodiment has a zinc oxide-containing coating, even if the Al content in the plating coating is high, the hot stamped body can have excellent chemical conversion treatability. Under normal manufacturing conditions, the Al content of the plating film is 1000 mg / m 2 Therefore, the Al content of the plating film is unlikely to exceed 1000 mg / m 2 The following applies.

[0066] Ni content in plating film: 0 to 2000 mg / m 2 The amount of Ni in the plating film is 0 mg / m 2 The amount of Ni in the plating film may be 50 mg / m 2 By setting the Ni content in the plating film to 50 mg / m or more, the temperature and time required for alloying can be reduced even if the Al concentration in the bath is relatively high, thereby improving production efficiency. In addition, the annealing temperature can be lowered, improving flatness and reducing the risk of contact between the wiping nozzle and the steel sheet. Therefore, the Ni content in the plating film is set to 50 mg / m or more. 2 More preferably, it is 80 mg / m or more. 2 More than 100mg / m 2 or more than 150 mg / m 2That's all.

[0067] The amount of Ni in the plating film is 2000 mg / m 2 If the Ni content exceeds 2000 mg / m, the raw material and electricity costs for Ni plating will increase excessively. 2 The concentration should be less than 1500 mg / m 2 Below 1000mg / m 2 or less than 800 mg / m 2 The following is the result.

[0068] Remainder in plating film The remainder of the plating film is made up of impurities, which are preferably 0.1 mass % or less.

[0069] The Fe concentration, Zn amount, Al amount and Ni amount in the plating film are measured by the following methods. The plating film on the hot-stamped body is dissolved and removed using a 5% by volume HCl aqueous solution containing an inhibitor. The Fe concentration, Zn content, Al content, and Ni content in the resulting solution are measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) to determine the Fe concentration, Zn content, Al content, and Ni content in the plating film. If the hot-stamped body has a zinc oxide-containing coating and / or a chemical conversion coating, these coatings are removed by shot blasting or mechanical grinding before the above measurements are carried out.

[0070] Zinc oxide-containing coating The hot-stamped product according to this embodiment has a zinc oxide-containing coating on the plating coating. The zinc oxide-containing coating is the same as that of the galvannealed steel sheet for hot stamping according to the second embodiment described above, and therefore a description thereof will be omitted.

[0071] Chemical conversion coating The hot-stamped steel according to this embodiment may have a chemical conversion coating on the zinc oxide-containing coating. The presence of the chemical conversion coating can improve adhesion to a paint film and corrosion resistance after painting.

[0072] The coating weight of a chemical conversion coating is governed by the amount of zinc oxide in the zinc oxide-containing coating and the amount of zinc oxide resulting from the oxidation of Zn in the plating coating during heat treatment. It is also affected by the pretreatment conditions for chemical conversion treatment, the type, concentration, temperature, and treatment time of chemical conversion treatment agents. For general automotive steel, chemical conversion treatment under specified conditions results in a chemical crystallization of 2.0 to 3.0 g / m 2 , 2.0 to 2.5 g / m depending on conditions 2 What is formed is considered appropriate.

[0073] The deposition weight of the chemical conversion coating can be measured by known analytical methods such as fluorescent X-ray analysis. For example, a calibration curve showing the relationship between fluorescent X-ray intensity and deposition weight can be prepared in advance using a sample whose phosphorus deposition amount has already been measured by chemical analysis, and the deposition weight of the chemical conversion coating can be determined from the measurement results of the fluorescent X-ray intensity using this calibration curve.

[0074] The hot stamped steel according to this embodiment preferably has a tensile strength of 1000 MPa or more. By setting the tensile strength to 1000 MPa or more, the steel can be suitably applied to automobile parts. The tensile strength is preferably 1400 MPa or more, 1500 MPa or more, or 1800 MPa or more. There is no particular upper limit to the tensile strength, but it may be 2500 MPa or less.

[0075] The tensile strength of the hot-stamped body is measured by taking a JIS No. 5 test piece from a position excluding a region within 10 mm from the edge of the hot-stamped body and conducting a tensile test in accordance with JIS Z 2241:2011.

[0076] The hot-stamped body obtained by hot stamping the galvannealed steel sheet for hot stamping according to the second embodiment has been described above, but the hot-stamped body may also be obtained by hot stamping the galvannealed steel sheet for hot stamping according to the first embodiment. This hot-stamped body has a steel sheet having the above-mentioned chemical composition and a plating film disposed on the steel sheet, and the plating film has an Al content of 150 mg / m 2 More than 400mg / m 2 The organic acid zinc contained in the galvannealed coating film of the galvannealed steel sheet for hot stamping may be converted to zinc oxide due to the combustion of organic components by the heat treatment during hot stamping. Therefore, after hot stamping of the galvannealed steel sheet for hot stamping according to the first embodiment, a zinc oxide-containing coating is formed on the coating film. This zinc oxide-containing coating has a zinc oxide amount per side of 0.3 to 1.5 g / m2 in terms of metallic zinc. 2 and has the same characteristics as those of the hot-stamped steel obtained by hot stamping the galvannealed steel sheet for hot stamping according to the second embodiment. Other points are the same as those of the hot-stamped steel obtained by hot stamping the galvannealed steel sheet for hot stamping according to the second embodiment.

[0077] In the galvannealed steel sheet for hot stamping according to the second embodiment, the Al content in the galvannealed film is high, so the organic acid zinc contained in the galvannealed film and the zinc oxide-containing film is unlikely to convert to zinc oxide. Therefore, in the galvannealed steel sheet for hot stamping according to the second embodiment, the amount of zinc oxide in the zinc oxide-containing film does not change significantly before and after hot stamping.

[0078] Next, a method for producing a galvannealed steel sheet for hot stamping according to the present embodiment will be described. First, a method for producing a galvannealed steel sheet for hot stamping according to a first embodiment will be described.

[0079] Manufacturing method of galvannealed steel sheet for hot stamping The method for producing a galvannealed steel sheet for hot stamping according to the first embodiment includes a hot rolling step of hot rolling a slab having the above-described chemical composition to obtain a hot-rolled steel sheet, optionally a cold rolling step of cold rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet, optionally a Ni pre-plating step of Ni pre-plating the hot-rolled steel sheet or the cold-rolled steel sheet to obtain a Ni pre-plated steel sheet, an annealing step of holding the hot-rolled steel sheet, the cold-rolled steel sheet, or the Ni pre-plated steel sheet in a reducing atmosphere in a temperature range of 460 to 850°C for 3 seconds or more to obtain an annealed steel sheet, a galvanizing step of immersing the annealed steel sheet in a molten zinc bath having an Al concentration of 0.155% by mass or more and less than 0.190% by mass for 1.0 to 15.0 seconds to obtain a galvannealed steel sheet, and an alloying step of performing an alloying treatment on the galvannealed steel sheet to obtain a galvannealed steel sheet for hot stamping. Each step will be described in detail below.

[0080] Hot rolling process A hot-rolled steel sheet is obtained by hot-rolling a slab having the above-mentioned chemical composition. The slab is preferably heated to a temperature of 1200°C or higher and held at 1200°C or higher for 5 minutes or longer. After hot-rolling, the slab may be pickled to remove scale.

[0081] Cold rolling process A cold-rolled steel sheet is obtained by cold-rolling the hot-rolled steel sheet. Note that cold rolling may or may not be performed. When cold rolling is performed, the cumulative reduction rate in cold rolling is preferably 30 to 80%. The cumulative rolling reduction can be expressed as {(t0-t1) / t0}×100(%), where t0 is the thickness of the hot-rolled steel sheet before cold rolling and t1 is the thickness of the cold-rolled steel sheet after cold rolling.

[0082] Ni pre-plating process The hot-rolled steel sheet or the cold-rolled steel sheet is subjected to Ni pre-plating to obtain a Ni pre-plated steel sheet. Ni pre-plating may or may not be performed. Ni pre-plating allows Ni to be contained in the galvannealed coating. By appropriately controlling the Ni content in the galvannealed coating, the temperature and time in the alloying treatment described below can be reduced. Furthermore, the temperature in the annealing process can be reduced, improving flatness and reducing the risk of contact between the wiping nozzle and the steel sheet during wiping control of the coating weight.

[0083] Ni pre-plating has a coating weight of 0.05 to 2000 mg / m per side after the alloying process. 2 In addition, the amount of Ni deposited on one side after the Ni pre-plating step is preferably 0.3 to 2.0 mg / m 2 Approximately half or more of the amount of Ni pre-plated is dissolved during hot dip galvanizing.

[0084] The method of Ni pre-plating is not particularly limited, and examples include electroplating, electroless plating, vapor deposition, etc. In electroplating, for example, a hot-rolled steel sheet or cold-rolled steel sheet is electrolytically degreased, immersed in 10% hydrochloric acid for 10 seconds for pickling activation, and then current is passed through a general Ni electroplating bath (Watts bath or Wood's bath).

[0085] Annealing process The hot-rolled steel sheet, cold-rolled steel sheet, or Ni-preplated steel sheet is held in a reducing atmosphere at a temperature range of 460 to 850°C for at least 3 seconds to obtain an annealed steel sheet. The reducing atmosphere is a mixed gas consisting mainly of reducing gases composed of inert gases such as nitrogen and argon and hydrogen, with the concentration of oxidizing gases such as oxygen being limited to unavoidable impurities. The dew point may be -50 to -10°C.

[0086] Typical annealing conditions are hydrogen: 10% by volume or less, oxygen: 100 ppm by volume or less, and the remainder: nitrogen. Typical plated steel sheets are annealed in a reducing atmosphere to recrystallize the steel sheet to obtain desired mechanical properties and to reduce iron oxide on the surface to ensure reactivity with the zinc plating. In this embodiment, it is not necessary to recrystallize the steel sheet to obtain desired mechanical properties. Therefore, annealing is performed to reduce iron oxide on the surface to ensure reactivity with the zinc plating.

[0087] If the holding temperature in the annealing step is less than 460°C, the temperature of the steel sheet when immersed in the molten zinc bath will inevitably be less than 460°C, and heat will be lost from the molten zinc bath as the sheet passes, making it difficult to maintain the bath temperature. Therefore, the holding temperature is set to 460°C or higher, preferably 500°C or higher. On the other hand, if the holding temperature exceeds 850°C, the reduction effect and the effect of improving mechanical properties will saturate, and wear of the furnace body and fuel consumption will be promoted. Therefore, the holding temperature is set to 850°C or less, and preferably 800°C or less.

[0088] When annealing Ni-plated steel sheets, the wettability with the zinc plating is ensured by the Ni in the Ni pre-plating, so there is no need to reduce the iron oxide on the surface. Therefore, the holding temperature in the annealing process can be within a range that allows the bath temperature to be maintained. Furthermore, from the viewpoint of flatness, since the cause of deterioration in flatness is non-uniform recrystallization in the steel sheet, the holding temperature is preferably set to the Ac1 point or lower. That is, when annealing a Ni pre-plated steel sheet, the holding temperature is preferably set to 460°C or higher and the Ac1 point or lower.

[0089] Furthermore, when Ni pre-plating is not performed, i.e., when annealing hot-rolled or cold-rolled steel sheets, the holding temperature is preferably set within a temperature range where iron oxide can be reduced to ensure plateability. For normal hydrogen and water vapor concentrations, the holding temperature is preferably set above the Ac1 point. That is, when annealing hot-rolled or cold-rolled steel sheets, the holding temperature is preferably set above the Ac1 point. More precisely, based on the free energy of formation equation for water vapor and FeO, it is preferable to select a temperature such that "17895 - 9.79 × T + R × T × ln(PH2O / PH2) < 0" is satisfied depending on the hydrogen and water vapor concentrations. Here, T is the absolute temperature, R is the gas constant 8.31 J / mol K, PH2O is the partial pressure of water vapor, and PH2 is the partial pressure of hydrogen.

[0090] The Ac1 point can be expressed by the following formula. Ac1(℃)=723-10.7×Mn+29.1×Si-16.9×Ni+16.9×Cr+6.38×W Here, the element symbols in the above formulas indicate the content of the element in mass %. If the element is not contained, 0 is substituted.

[0091] If the holding time in the annealing process is less than 3 seconds, the sheet temperature may not follow the target temperature and may not reach the target temperature. Therefore, the holding time is set to 3 seconds or more. There is no particular upper limit to the holding time, but it may be set to 100 seconds or less. When Ni pre-plating is not performed, that is, when annealing is performed on a hot-rolled steel sheet or a cold-rolled steel sheet, the holding time is preferably 30 seconds or more to ensure time for the reduction reaction of iron oxide to proceed.

[0092] Zinc plating process The annealed steel sheet is immersed for 1.0 to 15.0 seconds in a molten zinc bath having an Al concentration of 0.155 mass % or more and less than 0.190 mass %, thereby obtaining a hot-dip galvanized steel sheet. The Al content of the galvannealed coating can be adjusted by controlling the composition of the molten zinc bath, the bath temperature, and the immersion time in the molten zinc bath.

[0093] If the Al concentration in the molten zinc bath is less than 0.155 mass %, the weldability will deteriorate. Therefore, the Al concentration in the molten zinc bath is set to 0.155 mass % or more, preferably 0.160 mass % or more. On the other hand, if the Al concentration of the molten zinc bath is 0.190% by mass or more, a large amount of Al oxide is generated on the surface during furnace heating, which deteriorates the chemical treatability of the hot-stamped body. Therefore, the Al concentration of the molten zinc bath is set to less than 0.190% by mass.

[0094] Alloying process The hot-dip galvanized steel sheet is subjected to an alloying treatment to obtain a hot-dip galvanized steel sheet for hot stamping. In the alloying treatment, the steel sheet is preferably held in a temperature range of 500 to 600°C for 5 to 30 seconds.

[0095] The manufacturing method described above can manufacture the galvannealed steel sheet for hot stamping according to the first embodiment. Next, a description will be given of a method for manufacturing a galvannealed steel sheet for hot stamping according to a second embodiment. Hereinafter, only differences from the method for manufacturing a galvannealed steel sheet for hot stamping according to the first embodiment will be described, and a description of overlapping points will be omitted.

[0096] Zinc plating process In the method for producing a galvannealed steel sheet for hot stamping according to the second embodiment, the Al concentration in the molten zinc bath is set to 0.190 to 0.400 mass% in the galvanizing step. In the method for producing a galvannealed steel sheet for hot stamping according to the second embodiment, a zinc oxide-containing coating is formed on the galvannealed coating, so the Al concentration in the molten zinc bath can be increased. However, if the Al concentration in the molten zinc bath exceeds 0.400 mass%, the Al amount becomes excessive. Even if Ni pre-plating is performed, the temperature and time required for alloying increase, and the electricity and fuel costs for heating increase, resulting in reduced productivity. Therefore, the Al concentration in the molten zinc bath is set to 0.400 mass% or less. Preferably, it is 0.300 mass% or less.

[0097] The higher the Al concentration in the molten zinc bath and the higher the Al concentration in the galvannealed coating, the longer the temperature and time required for alloying. However, since Ni pre-plating has the effect of reducing the temperature and time required for alloying, from the viewpoint of productivity, it is preferable to apply Ni pre-plating when the Al concentration in the molten zinc bath is high.

[0098] Zinc oxide-containing film formation process In the method for producing a galvannealed steel sheet for hot stamping according to the second embodiment, after the alloying step, a zinc oxide layer is formed on the surface (surface of the galvannealed coating) so that the amount of zinc oxide per side is 0.3 to 1.5 g / m in terms of metallic zinc. 2 A zinc oxide-containing coating is formed.

[0099] The zinc oxide-containing coating can be formed, for example, by applying a paint containing zinc oxide, followed by a curing treatment by baking and drying. Examples of methods for applying the paint containing zinc oxide include a method in which a sol containing zinc oxide is mixed with an organic binder and applied to the surface of a galvannealed steel sheet for hot stamping, and an application method using powder coating.

[0100] Examples of the organic binder include polyurethane resins, polyester resins, acrylic resins, silane coupling agents, etc. These organic binders are preferably water-soluble so that they can be dissolved in the sol containing zinc oxide.

[0101] The manufacturing method described above can manufacture the galvannealed steel sheet for hot stamping according to the second embodiment.

[0102] Method for manufacturing hot-stamped body The method for producing a hot-stamped product according to this embodiment involves heating a galvannealed steel sheet for hot stamping, which has a steel sheet having the above-described chemical composition, a galvannealed coating film disposed on the steel sheet, and a zinc oxide-containing coating disposed on the galvannealed coating film, and hot stamping the steel sheet in a temperature range of 782°C or higher with a holding time of 150 seconds or less in a temperature range of 100°C or higher and a holding time of 30 seconds or less in a temperature range of 850°C or higher. The method for producing a hot-stamped steel will be described in detail below.

[0103] The galvannealed steel sheet for hot stamping to be subjected to hot stamping is the galvannealed steel sheet for hot stamping according to the second embodiment described above. Therefore, the galvannealed coating has an Fe concentration of more than 8.0 mass% and a Zn content of 15.0 to 40.0 g / m 2 and the Al content is 400 to 1000 mg / m 2 and the Ni content is 0 to 2000 mg / m 2 The zinc oxide-containing coating has a zinc oxide content of 0.3 to 1.5 g / m2 per side in terms of metallic zinc. 2 is.

[0104] In the method for producing a hot-stamped steel according to this embodiment, productivity can be improved by shortening the time in the furnace compared to conventional techniques. If the holding time in the temperature range of 100°C or higher exceeds 150 seconds, productivity decreases. Therefore, in the heating before hot stamping, the holding time in the temperature range of 100°C or higher is set to 150 seconds or less, preferably 130 seconds or less. There is no particular lower limit to the holding time in the temperature range of 100°C or higher.

[0105] If the holding time in the temperature range of 850°C or higher exceeds 30 seconds, productivity decreases. Therefore, in the heating before hot stamping, the holding time in the temperature range of 850°C or higher is set to 30 seconds or less, preferably 25 seconds or less, or 20 seconds or less. The lower limit of the holding time in the temperature range of 850° C. or higher is not particularly limited, but it may be 3 seconds or more.

[0106] Examples of a method for heating the galvannealed steel sheet for hot stamping include, but are not particularly limited to, heating in an electric furnace or gas furnace, flame heating, electrical heating, high-frequency heating, and induction heating.

[0107] Next, hot stamping is performed in a temperature range of 782°C or higher. 782°C is the temperature at which the coating melt in the molten zinc bath solidifies into the Γ phase. To avoid LME, it is necessary to advance the formation of a Zn-Fe solid solution phase to eliminate the liquid phase, or to solidify the liquid phase in a temperature range of 782°C or lower. To achieve quench hardening using the latter method, it is necessary to add alloying elements to the steel to lower the Ac1 point to 782°C or lower, which increases alloy costs. In this embodiment, hot stamping is performed in a temperature range of 782°C or higher to advance the formation of a Zn-Fe solid solution phase to eliminate the liquid phase. This makes it possible to reduce alloy costs and improve productivity.

[0108] After hot stamping, it is preferable to cool the steel at an average cooling rate of 20°C / s or more to a temperature range of 250°C or less. By cooling the steel at an average cooling rate of 20°C / s or more to a temperature range of 250°C or less, a desired amount of martensite can be obtained in the hot stamped steel. As a cooling method after hot stamping, for example, a method in which hot stamping is performed using a die through which a water-cooled pipe is passed, and the material is rapidly cooled by contact with the die during the hot stamping, can be mentioned.

[0109] In this embodiment, after the above-described cooling, a chemical conversion coating may be formed on the surface of the hot-stamped body (the surface of the zinc oxide-containing coating). The chemical conversion coating may be formed by immersing the hot-stamped body in a known chemical conversion treatment solution containing a phosphate. By immersing in the chemical conversion treatment solution, zinc in the zinc oxide-containing coating containing zinc oxide reacts with the phosphate contained in the chemical conversion treatment solution, and a chemical conversion coating is formed on the zinc oxide-containing coating.

[0110] Although the method for manufacturing a hot-stamped product using a galvannealed steel sheet for hot stamping according to the second embodiment has been described above, hot stamping may also be performed using a galvannealed steel sheet for hot stamping according to the first embodiment. This method for manufacturing a hot-stamped product includes a steel sheet and a galvannealed coating disposed on the steel sheet, and the coating has an Al content of 150 mg / m 2 More than 400mg / m 2 The method for producing a hot-stamped product using a galvannealed steel sheet for hot stamping having a hardness of less than 1000 kJ / cm is similar to the method for producing a hot-stamped product using a galvannealed steel sheet for hot stamping according to the second embodiment in other respects. [Example]

[0111] Next, examples of the present invention will be described, but the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0112] A slab having the chemical composition shown in Table 1 was hot rolled, pickled, and cold rolled to produce a 1.6 mm thick full hard sheet (a cold rolled, unannealed sheet, i.e., a cold rolled steel sheet that had not been annealed). In the hot rolling, the slab was heated to a temperature of 1200°C or higher, and the holding time in the temperature range of 1200°C or higher was 5 minutes or longer. In the cold rolling, the cumulative reduction was 30 to 80%.

[0113] Under the conditions shown in Table 2, some examples were subjected to a Ni plating process, and all examples were subjected to an annealing process and a zinc plating process. In addition, some examples were formed with a zinc oxide-containing coating. In Table 2, the Ni amount in the Ni pre-plating process was 0.0 g / m 2 The example shown is one in which the Ni pre-plating process was not performed, and the amount of zinc oxide in terms of metallic zinc is 0.0 g / m 2 In the example of (2), no zinc oxide-containing coating was formed.

[0114] For Ni pre-plating, the cold-rolled unannealed sheet was electrolytically degreased and then immersed in 10% by volume hydrochloric acid for 10 seconds for pickling activation. Next, the sheet was immersed in a Watts bath (Ni sulfate: 240 g / L, Ni chloride: 45 g / L, boric acid: 35 g / L, pH: not adjusted, actual pH: 4.0 to 4.3, bath temperature: 50°C) at a current density of 4 A / dm 2 By applying current for 3.2 seconds, Ni pre-plating was achieved at 0.3 g / m per side. 2 Ni pre-plating was applied at 1.0 g / m per side. 2 When applying the coating, the energization time was increased in proportion to the amount of coating.

[0115] Next, an annealing process was carried out. In the annealing process, the specimens were heated at an average heating rate of 10°C / s to the holding temperature shown in Table 2 in an atmosphere of N2-10%H2 with a dew point of -40°C and an oxygen concentration of 100 ppm or less. The holding time was 30 seconds in the case of a holding time of 800°C, and 3 seconds in the case of a holding time of 500°C.

[0116] Next, a galvanizing process was carried out. The temperature of the molten zinc bath was kept constant at 460°C, and the composition was Zn-(0.130 to 0.205) mass% Al, with 0.04 mass% Fe added. Thereafter, an alloying step was carried out, in which the material was placed in an electric furnace at 500 to 600°C, and the holding time in the temperature range of 500 to 600°C was set to 5 to 30 seconds.

[0117] In some examples, a zinc oxide-containing film forming step was carried out. The zinc oxide-containing film was formed by applying a coating material containing a ZnO-containing liquid and an organic binder with a bar coater and drying it in a hot air oven. By the above method, a galvannealed steel sheet for hot stamping was obtained.

[0118] For zinc oxide-containing coatings, the amount of zinc oxide converted to metallic zinc was calculated by measuring the ratio of ZnO to the organic binder components in the ZnO-containing solution in advance, measuring the weight difference of the steel sheet before and after the application and drying of the ZnO-containing solution, and assuming that the coating composition is equal to the solid components of the solution. In addition, the amount of zinc oxide was calculated in terms of metallic zinc by immersing the steel sheet in an ammonium dichromate solution to dissolve only the zinc oxide and measuring the zinc content in the solution with ICP. This amount of zinc oxide agreed with the amount calculated from the weight difference of the steel sheet before and after application of the ZnO-containing solution and drying.

[0119] The composition of the galvannealed coating was determined by immersing a galvannealed steel sheet for hot stamping cut to a predetermined size in 5% by volume hydrochloric acid containing an inhibitor to dissolve and remove only the galvannealed coating, and then performing ICP analysis of the Fe concentration, Zn amount, Al amount, and Ni amount in the resulting solution.

[0120] Hot stamping was performed using the obtained galvannealed steel sheet for hot stamping, as well as the die and flat die for LME evaluation described below. First, test pieces of a predetermined size were taken from the galvannealed steel sheet for hot stamping. For hot stamping, a gas furnace was maintained at a furnace temperature of 910°C with an air-fuel ratio of 1.1. A thermocouple was welded to the test piece, and the test piece was placed in the furnace. When the temperature of the test piece reached 900°C, it was removed from the gas furnace and immediately hot stamped using a die. After hot stamping, the test piece was cooled to a temperature range of 250°C or less at an average cooling rate of 20°C / s or more. For the same production number, hot stamping was performed using the die for LME evaluation and the flat die under the same conditions. By the above method, a hot stamped body was obtained.

[0121] From the temperature records obtained using a thermocouple, the holding time in the temperature range above 100°C, the holding time in the temperature range above 850°C, and the forming start temperature were read. These hot stamping conditions are shown in Tables 3A and 3B.

[0122] LME cracking was evaluated from hot-stamped compacts obtained using a die for LME evaluation (a die with a 90-degree bend radius of 0). Bent samples for LME evaluation were taken from the hot-stamped compacts, embedded in resin so that the cross section of the bent sample could be observed, and LME cracking was observed using an SEM. If cracks 50 μm or deeper were observed, as shown in Figure 2 below, the sample was deemed to have had LME cracking and was judged to have failed, and this was indicated as NG in the table. On the other hand, if cracks 50 μm or deeper were not observed, the sample was deemed to have had no LME cracking and was judged to have passed, and this was indicated as OK in the table.

[0123] Samples were taken from the hot stamped body obtained using a flat die, and the metal structure of the steel sheet, the composition of the plating film, the amount of zinc oxide in terms of metallic zinc in the zinc oxide-containing film, tensile strength, weldability, and chemical conversion treatability were evaluated.

[0124] When the tensile strength was less than 1000 MPa, the specimen was judged to have poor strength and to have failed, whereas when the tensile strength was 1000 MPa or more, the specimen was judged to have excellent strength and to have passed.

[0125] In the case of hot stamped steel sheets, if the metal structure of the steel sheet contained 80% or more by area of ​​martensite, the hardened structure in the table was marked as OK, and if it did not contain 80% or more by area of ​​martensite, the hardened structure in the table was marked as NG.

[0126] The scale evaluation was carried out by the following method. The surface of the hot stamped body was visually inspected, and if iron oxide scale was formed or scale peeling was observed, the body was judged as failing and recorded as "scale present" in the table. If no iron oxide scale was formed and no scale peeling was observed, the body was judged as passing and recorded as "scale absent" in the table.

[0127] Weldability was evaluated by welding resistance. One side of a sample taken from the hot-stamped compact was ground to expose the base material (steel plate). A welding electrode with a diameter of 6 mm and a radius of 40 mm was applied to the surface of the base material with a pressure of 250 kgf, and the electrical resistance (mΩ) was measured from the voltage after a current of 2 A had passed for 4 seconds. The welding resistance of a currently mass-produced GA steel plate processed under the current hot-stamping mass-production conditions was 0.57 mΩ. Samples with a welding resistance exceeding 0.86 mΩ, which is 1.5 times the welding resistance of this currently-produced material, were deemed to have poor weldability and were therefore deemed to have failed. On the other hand, samples with a welding resistance of 0.86 mΩ or less were deemed to have excellent weldability and were deemed to have passed.

[0128] Chemical conversion treatability was evaluated using the following method. Samples taken from the hot-stamped compact were washed with water, degreased, and immersed in surface conditioning solution PL-X. Next, they were immersed in chemical conversion treatment solution SX35 to perform a zinc phosphate conversion treatment. Secondary electron images of the samples after zinc phosphate conversion treatment were observed using an SEM. If the surface was densely covered with phosphate crystals, as in Production Nos. 1, 2, and 3 in Figure 3 described below, the sample was judged to have excellent chemical conversion treatability and was deemed to have passed, and this was marked as OK in the table. Examples judged to have passed had a chemical conversion coating on the surface of the hot-stamped compact. On the other hand, as shown in Production No. 5 in Figure 3 below, the surface is not covered with phosphate crystals, and the 5 μm 2 When the above-mentioned regions were observed, the surface was judged to be poor in chemical conversion treatability and to have failed. In addition, weldability and phosphatability were not evaluated for some of the examples in which scaling occurred, LME cracking occurred, and the hardened structure was inappropriate.

[0129] Figure 1 shows some of the material temperature results inside the gas furnace. Figure 2 shows some of the results of SEM observations of the presence or absence of LME cracks. Figure 3 shows some of the results of evaluating phosphatability using an SEM.

[0130] [Table 1]

[0131] [Table 2]

[0132] [Table 3A]

[0133] [Table 3B]

[0134] [Table 4]

[0135] From Production Nos. 2 and 3, when the Al concentration in the molten zinc bath was below 0.155 mass%, the Al content in the galvannealed coating was 155 mg / m 2 It can be seen that the welding resistance of the hot stamped body increases and the weldability is poor. In addition, in Production Nos. 1 and 2, the Zn content in the galvannealed coating was 40.0 g / m 2 When this value is exceeded, it can be seen that LME cracking occurs when the residence time in the temperature range of 850°C or higher is 30 seconds or less.

[0136] In Production No. 5, the Al concentration in the molten zinc bath was 0.190 mass% to 0.400 mass%, and the Al content in the galvannealed coating was 400 to 1000 mg / m 2 Even if the zinc oxide-containing coating is not formed, it is clear that the hot stamped body has poor chemical conversion treatability.

[0137] From production No. 6, the amount of Zn in the plating film was 15.0 g / m 2 It can be seen that when the temperature is lower than this, iron scale is formed in the hot stamped body. From production No. 7, the amount of Zn in the plating film was 40.0 g / m 2 It can be seen that when this temperature exceeds 1000 K, LME cracking occurs in the hot stamped compact.

[0138] From Production No. 8, it can be seen that when the Fe concentration in the galvannealed coating falls below 8 mass%, the temperature rise rate in the furnace becomes slow and the temperature cannot be raised sufficiently in a short time in the furnace, resulting in poor tensile strength. From Production No. 9, it can be seen that even if the galvannealed coating does not contain Ni, the properties after hot stamping are satisfactory as long as the Zn amount, Al amount and Fe concentration are within the desired ranges.

[0139] In Production No. 10, the Al concentration in the molten zinc bath was 0.190 to 0.400%, and the Al content in the galvannealed coating was 400 to 1000 mg / m 2 Even if a zinc oxide-containing coating is formed, chemical conversion treatment properties are ensured and desired properties are satisfied. Furthermore, it can be seen from Production No. 11 that results similar to those of Production No. 10 can be obtained even if Ni is not contained in the galvannealed coating.

[0140] It can be seen from Production No. 12 that the Al concentration in the molten zinc bath was below 0.155 mass%, and therefore the Al content in the galvannealed coating was below the lower limit, resulting in increased welding resistance in the hot-stamped body. From Production No. 14, it can be seen that although the Al concentration in the molten zinc bath was 0.205 mass %, a zinc oxide-containing coating was not formed, and therefore the chemical conversion treatability of the hot stamped body was poor. From Production No. 15, it can be seen that the Fe concentration in the galvannealed coating was below 8 mass%, just like Production No. 8, so the temperature could not be raised sufficiently in the short time in the furnace, and as a result, the tensile strength was found to be inferior.

[0141] From Production Nos. 4, 13, 16 to 27, 30, 32 and 33, it is clear that desirable properties can be obtained if the chemical composition, production conditions, etc. are within the ranges of the present invention.

[0142] It can be seen from Production No. 28 that the excessive Si content caused the Ac3 point to rise, martensite to be less than 80% by area, and the tensile strength to deteriorate. It can be seen from Production No. 29 that the Ac3 point rose due to an insufficient Mn content, martensite was less than 80% by area, and the tensile strength was poor. It can be seen from Production No. 31 that the amount of zinc oxide in the zinc oxide-containing coating was excessive, which caused the welding resistance to increase. [Industrial Applicability]

[0143] According to the above aspects of the present invention, it is possible to provide a hot-stamped product that has high strength, is inhibited from generating scale after hot stamping, and has excellent weldability and chemical conversion treatability, a galvannealed steel sheet for hot stamping from which the hot-stamped product can be manufactured, and methods for manufacturing the same.

Claims

1. A galvannealed steel sheet for hot stamping, comprising: a steel sheet; a galvannealed coating film disposed on the steel sheet; and a zinc oxide-containing coating film disposed on the galvannealed coating film, The steel plate has a chemical composition, in mass%, C: 0.02-0.58%, Mn: 0.10-3.00%, sol. Al: 0.001 to 1.000%, Si: 2.00% or less, P: 0.100% or less, S: 0.005% or less, N: 0.0100% or less, Ti: 0-0.200%, Nb: 0 to 0.200%, V: 0 to 1.00%, W: 0 to 1.00% Cr: 0-1.00%, Mo: 0-1.00%, Cu: 0 to 1.00%, Ni: 0 to 1.00%, B: 0 to 0.0100%, Ca: 0 to 0.05%, and REM: 0~0.05% and the balance being Fe and impurities, The galvannealed coating film is The Fe concentration is more than 8.0% by mass, Zn content: 15.0 to 40.0 g / m ２ and Al content: 400 to 1000 mg / m ２ and Ni content: 0 to 2000 mg / m ２ and The zinc oxide-containing coating is The amount of zinc oxide per side is 0.3 to 1.5 g / m2 in terms of metallic zinc. ２ is 1. A galvannealed steel sheet for hot stamping, comprising:

2. The chemical composition of the steel plate is, in mass%, Ti: 0.005-0.200%, Nb: 0.005-0.200%, V: 0.10-1.00%, W: 0.10-1.00%, Cr: 0.05-1.00%, Mo: 0.05-1.00%, Cu: 0.05-1.00%, Ni: 0.05-1.00%, B: 0.0010 to 0.0100%, Ca: 0.0005 to 0.05%, and REM: 0.0005-0.05% Contains one or two selected from the group consisting of The galvannealed steel sheet for hot stamping according to claim 1.

3. The amount of Ni in the galvannealed coating is 50 to 2000 mg / m ２ is The galvannealed steel sheet for hot stamping according to claim 1 or 2.

4. A hot-stamped product having a steel sheet, a plating film disposed on the steel sheet, and a zinc oxide-containing film disposed on the plating film, The steel plate has a chemical composition, in mass%, C: 0.02-0.58%, Mn: 0.10-3.00%, sol. Al: 0.001 to 1.000%, Si: 2.00% or less, P: 0.100% or less, S: 0.005% or less, N: 0.0100% or less, Ti: 0-0.200%, Nb: 0 to 0.200%, V: 0 to 1.00%, W: 0 to 1.00% Cr: 0-1.00%, Mo: 0-1.00%, Cu: 0 to 1.00%, Ni: 0 to 1.00%, B: 0 to 0.0100%, Ca: 0 to 0.05%, and REM: 0~0.05% and the balance being Fe and impurities, The metal structure of the steel plate contains 80% by area or more of martensite, the plating film is composed only of an Fe-Zn solid solution phase and zinc oxide, Zn content: 15.0 to 40.0 g / m ２ and Al content: 400 to 1000 mg / m ２ and Ni content: 0 to 2000 mg / m ２ and the remainder being impurities, The zinc oxide-containing coating is The amount of zinc oxide per side is 0.3 to 1.5 g / m2 in terms of metallic zinc. ２ is A hot stamped product characterized by:

5. The chemical composition of the steel plate is, in mass%, Ti: 0.005-0.200%, Nb: 0.005-0.200%, V: 0.10-1.00%, W: 0.10-1.00%, Cr: 0.05-1.00%, Mo: 0.05-1.00%, Cu: 0.05-1.00%, Ni: 0.05-1.00%, B: 0.0010 to 0.0100%, Ca: 0.0005 to 0.05%, and REM: 0.0005-0.05% Contains one or two selected from the group consisting of The hot stamped product according to claim 4 .

6. The hot-stamped product according to claim 4 or 5, further comprising a chemical conversion coating on the zinc oxide-containing coating.

7. The method for producing a galvannealed steel sheet for hot stamping according to claim 1, A hot rolling process in which a slab having the chemical composition according to claim 1 is hot rolled to obtain a hot rolled steel sheet; Optionally, a cold rolling step of cold rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet; Optionally, a Ni pre-plating step of obtaining a Ni pre-plated steel sheet by applying Ni pre-plating to the hot-rolled steel sheet or the cold-rolled steel sheet; an annealing step of holding the hot-rolled steel sheet, the cold-rolled steel sheet, or the Ni-preplated steel sheet in a reducing atmosphere at a temperature range of 460 to 850°C for 3 seconds or more to obtain an annealed steel sheet; a galvanizing step of immersing the annealed steel sheet in a molten zinc bath having an Al concentration of 0.190 to 0.400 mass% for 1.0 to 15.0 seconds to obtain a hot-dip galvanized steel sheet; an alloying step of performing alloying treatment on the hot-dip galvanized steel sheet; The amount of zinc oxide per side is 0.3 to 1.5 g / m2 in terms of metallic zinc. ２ and a zinc oxide-containing film forming step of forming a zinc oxide-containing film comprising 1. A method for producing a galvannealed steel sheet for hot stamping, comprising:

8. The method for producing a hot-stamped product according to claim 4, A steel sheet, a galvannealed coating film disposed on the steel sheet, and a zinc oxide-containing coating film disposed on the galvannealed coating film, The steel plate has a chemical composition, in mass%, C: 0.02-0.58%, Mn: 0.10-3.00%, sol. Al: 0.001 to 1.000%, Si: 2.00% or less, P: 0.100% or less, S: 0.005% or less, N: 0.0100% or less, Ti: 0-0.200%, Nb: 0 to 0.200%, V: 0 to 1.00%, W: 0 to 1.00% Cr: 0-1.00%, Mo: 0-1.00%, Cu: 0 to 1.00%, Ni: 0 to 1.00%, B: 0 to 0.0100%, Ca: 0 to 0.05%, and REM: 0~0.05% and the balance being Fe and impurities, The galvannealed coating film is The Fe concentration is more than 8.0% by mass, Zn content: 15.0 to 40.0 g / m ２ and Al content: 400 to 1000 mg / m ２ and Ni content: 0 to 2000 mg / m ２ and the remainder being impurities, The zinc oxide-containing coating is The amount of zinc oxide per side is 0.3 to 1.5 g / m2 in terms of metallic zinc. ２ The galvannealed steel sheet for hot stamping is heated, and the holding time in the temperature range of 100°C or higher is set to 150 seconds or less, the holding time in the temperature range of 850°C or higher is set to 30 seconds or less, and the hot stamping is performed in the temperature range of 782°C or higher to obtain a hot stamped body. A method for producing a hot stamped body, comprising:

9. The chemical composition of the steel plate is, in mass%, Ti: 0.005-0.200%, Nb: 0.005-0.200%, V: 0.10-1.00%, W: 0.10-1.00%, Cr: 0.05-1.00%, Mo: 0.05-1.00%, Cu: 0.05-1.00%, Ni: 0.05-1.00%, B: 0.0010 to 0.0100%, Ca: 0.0005 to 0.05%, and REM: 0.0005-0.05% Contains one or two selected from the group consisting of The method for producing a hot-stamped product according to claim 8 .

10. A chemical conversion coating is formed on the surface of the hot stamped body. The method for producing a hot-stamped product according to claim 8 or 9.

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