Galvanized steel sheet for hot-stamp, hot-stamp compact and production methods thereof

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 studied in order to reduce the weight of automobiles. As a technique for press forming difficult-to-form materials such as high-strength steel sheets, hot forming methods such as hot stamping, in which the steel sheet material to be formed is heated in advance, are used.

[0003] Such a forming method is an excellent forming method that can achieve both high strength and formability of the member because it can be formed at a high temperature with low deformation resistance and can be quenched at the same time as forming. However, when this forming method is adopted, the steel plate material needs to be heated to a high temperature of 700°C or more before forming, which causes a problem that the steel plate surface is oxidized during heating before hot stamping. The scale made of iron oxide generated by the oxidation of the steel plate surface falls off during hot stamping and adheres to the die, reducing productivity, or remains on the surface of the formed product after hot stamping, causing poor appearance. Moreover, if such scale remains on the surface of the formed product, the adhesion between the formed product and the paint film is poor when painting is performed in the next process, causing a decrease in corrosion resistance. Therefore, after hot stamping, a scale removal process such as shot blasting is required.

[0004] In order to solve such problems, it has been proposed to use, as a steel sheet material for hot forming, a plated steel sheet coated with zinc plating or aluminum plating 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 using 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 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 the oxides on the surface of the press-formed product. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-73774 A [Patent Document 2] JP 2001-353548 A [Patent Document 3] JP 2005-48254 A Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Documents 1 to 3, when 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 hot stamped into various shapes by resistance welding (particularly spot welding). In general, plated steel sheets have poorer weldability than cold-rolled steel sheets.

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

[0009] At the current technological level, in order to improve weldability and chemical conversion treatability and to suppress liquid metal embrittlement (LME Liquid Metal Embrittlement or LMC Liquid Metal Cracking) in the formed body obtained by hot stamping alloyed hot-dip galvanized steel sheet, the heating time in the furnace (furnace time) needs to be about 4 minutes or more. Since 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 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 manufactured. 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 hot stamped steel and can shorten the in-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 embodiment of the present invention comprises 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 sheet has a chemical composition, in mass%, C: 0.02 to 0.58%, Mn: 0.10-3.00%, 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 to 1.00%, W: 0 to 1.00% Cr: 0-1.00%, Mo: 0-1.00%, Cu: 0-1.00%, Ni: 0-1.00%, B: 0~0.0100%, Ca: 0 to 0.05%, and REM: 0~0.05% with the remainder being Fe and impurities, The galvannealed coating film is The Fe concentration is more than 8.0 mass%; Zn content: 15.0-40.0g / m 2 and Al content is 400-1000mg / m 2 and Ni content: 0-2000mg / 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 It 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 to 1.00%, Cr: 0.05-1.00%, Mo: 0.05 to 1.00%, Cu: 0.05-1.00%, Ni: 0.05 to 1.00%, B: 0.0010~0.0100%, Ca: 0.0005 to 0.05%, and REM: 0.0005~0.05% It may contain one or two kinds selected from the group consisting of: (3) The galvannealed steel sheet for hot stamping according to the above (1) or (2) has a Ni content of 50 to 2000 mg / m 2 may be also possible. (4) A hot stamped steel according to another aspect of the present invention has a steel sheet, a plating film disposed on the steel sheet, and a zinc oxide-containing film disposed on the plating film, The steel sheet has a chemical composition, in mass%, C: 0.02 to 0.58%, Mn: 0.10-3.00%, 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 to 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: 0~0.05% with the remainder being Fe and impurities, The metal structure of the steel sheet contains 80% or more by area of ​​martensite, the plating film is composed only of an Fe-Zn solid solution phase and zinc oxide, Zn content: 15.0-40.0g / m 2 and Al content is 400-1000mg / m 2 and Ni content: 0-2000mg / 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 It is. (5) The hot stamped steel according to (4) above, wherein 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 to 1.00%, Cr: 0.05-1.00%, Mo: 0.05 to 1.00%, Cu: 0.05-1.00%, Ni: 0.05 to 1.00%, B: 0.0010~0.0100%, Ca: 0.0005 to 0.05%, and REM: 0.0005~0.05% It may contain one or two kinds selected from the group consisting of: (6) The hot stamped steel 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 a method for producing a galvannealed steel sheet for hot stamping according to the above (1), A hot rolling process for obtaining a hot-rolled steel sheet by hot rolling a slab having the chemical composition described in (1) above; 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 obtaining an annealed steel sheet by holding the hot-rolled steel sheet, the cold-rolled steel sheet, or the Ni pre-plated steel sheet in a reducing atmosphere at a temperature range of 460 to 850 ° C. for 3 seconds or more; 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 an 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, (8) A method for producing a hot stamped compact according to another aspect of the present invention is the method for producing a hot stamped compact 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 sheet has a chemical composition, in mass%, C: 0.02 to 0.58%, Mn: 0.10-3.00%, 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 to 1.00%, W: 0 to 1.00% Cr: 0-1.00%, Mo: 0-1.00%, Cu: 0-1.00%, Ni: 0-1.00%, B: 0~0.0100%, Ca: 0 to 0.05%, and REM: 0~0.05% with the remainder being Fe and impurities, The galvannealed coating film is The Fe concentration is more than 8.0 mass%; Zn content: 15.0-40.0g / m 2 and Al content is 400-1000mg / m 2 and Ni content: 0-2000mg / 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 hot-stamped steel sheet for hot stamping is heated to a temperature range of 100°C or higher for a holding time of 150 seconds or less, a temperature range of 850°C or higher for a holding time of 30 seconds or less, and hot stamped in a temperature range of 782°C or higher to obtain a hot-stamped body. (9) The method for producing a hot stamped steel according to the above (8) further comprises the steps of: Ti: 0.005 to 0.200%, Nb: 0.005 to 0.200%, V: 0.10~1.00%, W: 0.10 to 1.00%, Cr: 0.05-1.00%, Mo: 0.05 to 1.00%, Cu: 0.05-1.00%, Ni: 0.05 to 1.00%, B: 0.0010~0.0100%, Ca: 0.0005 to 0.05%, and REM: 0.0005~0.05% It may contain one or two kinds selected from the group consisting of: (10) In the method for producing a hot stamped steel according to (8) or (9) above, a chemical conversion coating may be formed on a surface of the hot stamped steel. Effect 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 is capable of producing the above-described hot stamped steel and shortening the in-furnace time. [Brief description of the drawings]

[0013] [Figure 1] FIG. 13 is a diagram showing an example of a material temperature record in a gas furnace in an embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of the results of SEM observation of the presence or absence of LME cracks in an example. [Diagram 3] FIG. 2 is a diagram showing an example of the results of evaluating chemical conversion treatability by SEM in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A preferred embodiment of the present invention will be described in detail below. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications are possible without departing from the spirit of the present invention. The numerical ranges described below with "to" include the lower limit and the upper limit. The numerical values ​​indicated as "greater than" and "less than" are not included in 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 an embodiment 1. The galvannealed steel sheet for hot stamping according to the first embodiment has a steel sheet and a galvannealed coating film disposed on the steel sheet. Hereinafter, a description will be given of the steel sheet constituting the galvannealed steel sheet for hot stamping according to the first embodiment. Note that since the chemical composition of the steel sheet does not change before and after hot stamping, the chemical composition of the steel sheet constituting the galvannealed steel sheet for hot stamping according to the first embodiment is the same as the chemical composition of the steel sheet constituting 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: 0.02-0.58%, Mn: 0.10-3.00%, 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, 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 the steel sheet and obtaining the strength of the hot stamped body after hardening (hot stamping). C also lowers the Ac3 point and lowers the hardening treatment temperature. If the C content is less than 0.02%, the above effects cannot be obtained sufficiently. 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 portion and the hot stamped body after hot stamping is 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: 0.10-3.00% Mn is an important element for improving the hardenability of steel sheet and stably obtaining the strength of the hot stamped body after quenching. If the Mn content is less than 0.10%, the above effects cannot be obtained sufficiently. 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 become saturated 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. Incidentally, 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 If Si is contained in excess, it suppresses the transformation from ferrite to austenite during hot stamping heating 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, but an excessive reduction in the Si content causes an increase in refining costs, so the Si content may be set to 0.01% or more.

[0021] P:0.100% or less Since P is contained in steel as an impurity and has the effect of embrittling steel, 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 excessive reduction in the P content causes an increase in 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 since it forms MnS and has the effect of embrittling steel, it is preferable that the S content is small. 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 excessive reduction of the S content causes an increase in 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 bodies, the lower the N content, the better. 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 excessive reduction in the N content causes an increase in 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 the 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 may not 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: 0.10~1.00% W: 0.10~1.00% Ti, Nb, V and W are elements that promote the mutual diffusion of Fe and Zn in the galvannealed coating and the steel sheet, and make it difficult to form a molten zinc alloy layer during hot stamping. If a molten zinc alloy layer is formed, cracks may occur during hot stamping, which is undesirable. Therefore, Ti, Nb, V and W may be contained in the steel sheet. In order to reliably obtain the above effects, it is preferable to contain one or more of Ti: 0.005% or more, Nb: 0.005% or more, V: 0.10% or more, and W: 0.10% or more. However, when the Ti content or Nb content exceeds 0.200%, or when the V content or W content exceeds 1.00%, the above effects are saturated 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: 0.05~1.00% Mo: 0.05 to 1.00% Cu: 0.05-1.00% 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 improve the strength of hot stamped body. Therefore, one or more of these elements may be contained. In order to reliably obtain the above effect, 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 effect is saturated and the alloy cost increases. Therefore, the Cr content, Mo content, Cu content and Ni content are each set to 1.00% or less, and the B content is set to 0.0100% or less. It is preferable that the B content is set to 0.0080% or less.

[0028] Ca: 0.0005~0.05% REM: 0.0005~0.05% 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. In order to reliably obtain the above effect, it is preferable to contain one or more 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 is saturated 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 content of REM refers to the total content of these elements. REM is often contained by misch metal, but in some cases, lanthanoid series elements are contained in combination in addition to La and Ce. Even in the case where lanthanoid series elements are contained in combination in addition to La and Ce, the hot stamped steel according to the first embodiment can exhibit its effects. In addition, even if metallic REM such as metallic La and Ce is contained, the hot stamped steel according to the first embodiment can exhibit its effects.

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

[0031] The galvannealed steel sheet for hot stamping according to the first embodiment has a galvannealed coating on a steel sheet. 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 150 mg / m 2 More than 400mg / m 2 The Ni content is 0 to 2000 mg / m 2 and the remainder consists of impurities. The details of the galvannealed coating will be described below.

[0032] Fe concentration in galvannealed coating: More than 8.0% by mass If the Fe concentration in the galvannealed coating is 8.0 mass% or less, the ηZn phase remains on the surface of the galvannealed coating, increasing the reflectance. 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 made to be more than 8.0 mass%. It is preferably 8.5 mass% or more, or 9.0 mass% or more.

[0033] There is no particular upper limit for the Fe concentration in the galvannealed coating. In order to form an Fe-Zn solid solution phase in a short furnace time, the higher the Fe concentration, the more preferable it is. However, 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, it is necessary to control the Fe concentration in the galvannealed coating so as not to be 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, it is not necessary to control the upper limit of the Fe concentration.

[0035] Zn content in galvannealed coating: 15.0-40.0g / 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 little plating due to unavoidable variations in the amount of plating applied. Furthermore, if the Zn content is made too small, the wiping nozzle must be brought closer to the steel sheet, depending on the capacity of the wiping device, increasing the risk of contact. For this reason, 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 amount of Zn in the galvannealed coating is more than 40.0 g / m, it takes a long time for the Fe-Zn solid solution to form, and the time in the furnace becomes long. 2 The thickness should be less than 35.0 g / m 2 The following is the result.

[0037] Amount of Al in galvannealed coating: 150mg / m 2 More than 400mg / m 2 less than The amount of Al in the galvannealed coating is 150mg / m 2If the Al content in the galvannealed coating is less than 150 mg / m, the amount of Al oxide generated on the surface of the galvannealed coating during heating before hot stamping is small. As a result, the oxidation of Zn is not suppressed, and Zn-based oxides are generated in excess, which causes sparks and / or deposition during spot welding, resulting in deterioration of weldability. Therefore, it is recommended to set the Al content in the galvannealed coating to 150 mg / m. 2 More preferably, it is 200 mg / m 2 That's all.

[0038] On the other hand, the Al content in the galvannealed coating is 400 mg / m 2 If the amount of Al in the galvannealed coating 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 to be within the above-mentioned range.

[0040] Ni content in galvannealed coating: 0-2000mg / m 2 The amount of Ni in the galvannealed coating is 2000mg / 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, and production efficiency can be improved. In addition, the annealing temperature can be reduced, 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 2 More preferably, it is 80 mg / m or more. 2 More than 100mg / m 2 or 150 mg / m 2 That's all.

[0042] Remainder in galvannealed coating The balance of the galvannealed coating is made up of impurities, the content of which is 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 method. Only the galvannealed coating of the galvannealed steel sheet for hot stamping is dissolved and removed using a 5 volume % HCl aqueous solution containing an inhibitor.The Fe concentration, Zn amount, Al amount, and Ni amount in the obtained solution are analyzed by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) to obtain 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 measurements are 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 film disposed on the steel sheet, and a zinc oxide-containing coating film disposed on the galvannealed coating film. Hereinafter, the galvannealed steel sheet for hot stamping according to the second embodiment will be described.

[0045] Note that only the points different from the galvannealed steel sheet for hot stamping according to the above-mentioned first embodiment will be described, and a description of points overlapping 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 Since the galvannealed steel sheet for hot stamping according to the second embodiment has a zinc oxide-containing coating described later, it is possible to obtain excellent chemical conversion treatability in the hot stamped body even if the Al content in the galvannealed coating is high. Under normal manufacturing conditions, the Al content of the galvannealed coating is 1000mg / 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. Hereinafter, the zinc oxide-containing coating will be described in detail.

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

[0049] The zinc oxide-containing film may contain, in addition to zinc oxide, 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 film 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 zinc oxide in the zinc oxide-containing film is not particularly limited, but for example, the particle size is preferably 50 to 300 nm. 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. In general, secondary aggregation of fine powder occurs in the sol, so the particle size in the sol is larger than the particle size of the powder itself. When the particle size of the powder itself is less than 50 nm, not only is it difficult to knead, but secondary aggregation is also likely to occur, resulting in coarsening. Therefore, it may be difficult to make the particle size of zinc oxide in the sol less than 50 nm. In addition, when the particle size of zinc oxide in the sol is more than 300 nm, the particles are likely to settle, so unevenness may occur.

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

[0052] The amount of zinc oxide attached in the zinc oxide-containing coating can be obtained by immersing the film in an aqueous solution in which zinc oxide but not metallic 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 metallic zinc.

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

[0054] The hot stamped steel according to the present embodiment includes a steel sheet having the above-mentioned chemical composition, a plating layer disposed on the steel sheet, and a zinc oxide-containing coating disposed on the plating layer. The hot stamped steel according to the present embodiment may include a chemical conversion coating on the zinc oxide-containing coating.

[0055] In the hot stamped steel according to the present embodiment, the metal structure of the steel sheet contains 80 area % or more of martensite, the plating film is composed only of an Fe-Zn solid solution phase and zinc oxide, and the Zn amount is 15.0 to 40.0 g / m 2 The Al content is 400 to 1000 mg / m 2 The Ni content is 0 to 2000 mg / m 2 and the balance is impurities. 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 It is.

[0056] steel plate The chemical composition of the steel sheet constituting the hot stamped steel 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 ratio of martensite is less than 80%, the desired strength cannot be obtained. Therefore, the area ratio of martensite is set to 80% or more. It is preferably set to 85% or more. There is no particular upper limit for the area ratio 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 out from a position at least 50 mm away from the edge of the hot stamped product (if this position is not possible, a position that avoids 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 that avoids the weld and its vicinity.

[0060] The cross section of the above sample is etched with LePeller's reagent. The position of t / 4 (t is the plate thickness) of the cross section etched with LePeller's reagent is observed in 10 fields of view at a magnification of 500 times, and the obtained optical microscope photograph is subjected to image analysis 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 for a total of 10 observation fields to measure the area ratio of martensite, and the average value of these area ratios is calculated. The obtained average value is regarded as the area ratio of martensite. In this way, the area ratio of martensite is obtained. Moreover, the area ratio of the remaining structure is obtained by subtracting the area ratio of martensite from 100%.

[0061] Plating film It 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 molten metal embrittlement (LME liquid metal embrittlement or LMC liquid metal cracking) 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 peaks detected by the X-ray diffraction measurement using a Cu tube are only those of the Fe-Zn solid solution phase and zinc oxide. The position of the zinc oxide peak is determined by referring to JCPDS card 00-036-1451 ZnO-Zincite, and if an X-ray diffraction intensity peak appears at the angle described, it is determined that zinc oxide is present. The original peak position of the Fe-Zn solid solution phase is described in JCPDS card 00-006-0696 Iron, but since about 30% of Zn is dissolved in Fe, the crystal lattice expands, and the angle at which the X-ray diffraction intensity peak actually appears is 1 to 3% smaller than that. Therefore, in this embodiment, if an X-ray diffraction intensity peak appears at an angle 1 to 3% smaller than the angle described in the JCPDS card, it is determined that the Fe-Zn solid solution phase is present.

[0063] In addition, the plating film according to this embodiment contains Γ phase (Fe4Zn9, Fe3Zn 10 ), Γ1 phase (Fe 11 Zinc 40 ), δ phase (FeZn8,Fe 13 Zinc 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 or δ phase.

[0064] Zn content in plating film: 15.0-40.0g / m 2 The amount of Zn in the plating film is 15.0 g / m 2 If the amount 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 is 40.0 g / m 2 If the amount of Zn in the plating film is more than 40.0 g / m, the formation of a solid solution phase does not progress during heating in the furnace, and a liquid phase remains, which may cause LME, or may require a longer time in the furnace, resulting in a decrease in production efficiency. 2 The thickness should be less than 35.0 g / m 2 The following is the result.

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

[0066] Amount of Ni 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 at 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, and production efficiency can be improved. In addition, the annealing temperature can be reduced, improving flatness and reducing the risk of contact between the wiping nozzle and the steel sheet. 2 More preferably, it is 80 mg / m or more. 2 More than 100mg / m 2 or 150 mg / m 2That's all.

[0067] The amount of Ni in the plating film is 2000mg / 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 is preferably 1500 mg / m or less. 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 method. Only the plating film of the hot stamped body is dissolved and removed using a 5 volume % HCl aqueous solution containing an inhibitor. The Fe concentration, Zn amount, Al amount, and Ni amount in the resulting solution are measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) to obtain the Fe concentration, Zn amount, Al amount, and Ni amount in the plating film. When the hot stamped article 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 a plating coating. The zinc oxide-containing film is the same as that in the galvannealed steel sheet for hot stamping according to the above-mentioned second embodiment, and therefore a description thereof will be omitted.

[0071] Chemical Coating The hot stamped steel according to this embodiment may have a chemical conversion coating on the zinc oxide-containing coating. By having the chemical conversion coating, it is possible to improve adhesion to a paint film and corrosion resistance after painting.

[0072] The amount of deposition 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 the chemical conversion treatment, the type, concentration, temperature, and treatment time of the chemical conversion treatment agent. For general automotive steel, chemical conversion treatment under specified conditions results in 2.0 to 3.0 g / m of chemical conversion crystals. 2 , 2.0-2.5g / m depending on conditions 2 What is formed is deemed to be proper.

[0073] The amount of the chemical conversion coating can be measured by a known analysis method such as fluorescent X-ray analysis. For example, a calibration curve showing the relationship between the amount of phosphorus attached and the fluorescent X-ray intensity is prepared in advance using a sample whose amount of phosphorus attached has already been measured by chemical analysis, and the amount 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 product 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 product 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. The upper limit of the tensile strength is not particularly limited, but may be 2500 MPa or less.

[0075] The tensile strength of the hot stamped compact 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 compact, 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 zinc oxide-containing film has an organic acid zinc content of 0.3 to 1.5 g / m2 per side in terms of metallic zinc. The organic acid zinc contained in the galvannealed film in the galvannealed steel sheet for hot stamping may be converted to zinc oxide by the heat treatment during hot stamping due to the combustion of organic components. Therefore, after hot stamping of the galvannealed steel sheet for hot stamping according to the first embodiment, a zinc oxide-containing film is formed on the plated film. The zinc oxide-containing film has an amount of zinc oxide 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 product 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 coating is high, so that the organic acid zinc contained in the galvannealed coating and the zinc oxide-containing coating is unlikely to change 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 coating 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-mentioned chemical composition to obtain a hot-rolled steel sheet, a cold rolling step of cold rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet, an 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 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 0.155 mass% or more and less than 0.190 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 heating temperature of the slab is preferably 1200°C or higher, and the holding time at 1200°C or higher is preferably 5 minutes or more. After hot rolling, pickling may be performed 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. The Ni pre-plating may or may not be performed. By performing Ni pre-plating, Ni can be contained in the alloyed hot-dip galvanized film. If the amount of Ni in the alloyed hot-dip galvanized film is preferably controlled, the temperature and time can be reduced in the alloying treatment described below. In addition, the temperature in the annealing process can be reduced, the flatness can be improved, and the risk of contact between the wiping nozzle and the steel sheet during wiping control of the coating weight can be reduced.

[0083] The 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 Ni pre-plating amount dissolves 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 method is considered in which a hot-rolled steel sheet or a 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, the cold-rolled steel sheet, or the Ni pre-plated steel sheet is held in a reducing atmosphere at a temperature range of 460 to 850°C for 3 seconds or more to obtain an annealed steel sheet. The reducing atmosphere refers to a mixed gas that is mainly composed of reducing gases composed of inert gases such as nitrogen and argon and hydrogen, and has a concentration of oxidizing gases such as oxygen at the level of unavoidable impurities. The dew point may be -50 to -10°C.

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

[0087] If the holding temperature in the annealing process is less than 460°C, the temperature of the steel sheet when entering 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 the 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 pre-plated steel sheet, 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 the range where the bath temperature can be maintained. From the viewpoint of flatness, since the cause of deterioration of flatness is non-uniform recrystallization in the steel sheet, the holding temperature is preferably set to Ac1 point or lower. That is, when annealing is performed on a Ni pre-plated steel sheet, the holding temperature is preferably set to 460° C. or higher and Ac1 point or lower.

[0089] In addition, when Ni pre-plating is not performed, that is, when annealing is performed on hot-rolled steel sheets or cold-rolled steel sheets, the holding temperature is preferably set to a temperature range where iron oxide can be reduced in order to ensure plating properties. For normal hydrogen and water vapor concentrations, the holding temperature is preferably set to Ac1 point or higher. In other words, when annealing is performed on hot-rolled steel sheets or cold-rolled steel sheets, the holding temperature is preferably set to Ac1 point or higher. More precisely, it is preferable to select a temperature that satisfies the free energy equation of formation of water vapor and FeO according to the hydrogen concentration and water vapor concentration, such that "17895-9.79×T+R×T×ln(PH2O / PH2)<0". Note that 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 symbol in the above formula indicates 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 keep up and 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. In addition, 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 deteriorates. Therefore, the Al concentration in the molten zinc bath is set to 0.155 mass% or more, and preferably 0.160 mass% or more. On the other hand, if the Al concentration of the molten zinc bath is 0.190 mass% or more, a large amount of Al oxide is generated on the surface during furnace heating, which deteriorates the chemical conversion treatability of the hot stamped body. Therefore, the Al concentration of the molten zinc bath is set to less than 0.190 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] By the manufacturing method described above, the galvannealed steel sheet for hot stamping according to the first embodiment can be manufactured. Next, a method for producing a galvannealed steel sheet for hot stamping according to a second embodiment will be described. In the following, only the points different from the method for producing a galvannealed steel sheet for hot stamping according to the first embodiment will be described, and the description of the overlapping points will be omitted.

[0096] Zinc plating process In the manufacturing method of the 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 manufacturing method of the galvannealed steel sheet for hot stamping according to the second embodiment, a zinc oxide-containing film is formed on the galvannealed film, so that 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, and even if Ni pre-plating is performed, the temperature and time required for alloying increase, and the electricity cost and fuel cost for heating increase, resulting in a decrease in productivity. Therefore, the Al concentration in the molten zinc bath is set to 0.400 mass% or less. It is preferably 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 higher the temperature and time required for alloying. However, Ni pre-plating has the effect of reducing the temperature and time required for alloying, so 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 amount per one side is 0.3 to 1.5 g / m in terms of metallic zinc on the surface (surface of the galvannealed coating film). 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 a method 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 a method of applying the mixture by 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] By the manufacturing method described above, the galvannealed steel sheet for hot stamping according to the second embodiment can be manufactured.

[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, the galvannealed steel sheet having the above-mentioned 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 above-mentioned second embodiment. Therefore, the galvannealed coating has an Fe concentration of more than 8.0 mass% and a Zn amount of 15.0 to 40.0 g / m 2 The Al content is 400 to 1000 mg / m 2 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 It is.

[0104] In the method for producing a hot stamped product according to the present embodiment, the time in the furnace is shortened compared to the conventional technology, thereby improving productivity. If the holding time in the temperature range of 100°C or higher exceeds 150 seconds, the 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, the 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 may be 3 seconds or more.

[0106] Examples of a method for heating the galvannealed steel sheet for hot stamping include, but are not limited to, heating in an electric furnace or a 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. In order to avoid LME, it is necessary to advance the 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. In order to harden the steel by the latter, it is necessary to make the Ac1 point 782°C or lower by including alloy elements in the steel, which increases the alloy cost. In this embodiment, hot stamping is performed in a temperature range of 782°C or higher to advance the 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, there is a method in which hot stamping is performed using a die through which a water-cooled pipe passes, and in that case, quenching is performed by contact with the die.

[0109] In this embodiment, after the above-mentioned 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 the body 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, forming a chemical conversion coating on the zinc oxide-containing coating.

[0110] Although the method for producing a hot-stamped product using the galvannealed steel sheet for hot stamping according to the second embodiment has been described above, the hot-stamped product may be hot-stamped using the galvannealed steel sheet for hot stamping according to the first embodiment. This method for producing a hot-stamped product includes a steel sheet and a galvannealed coating film disposed on the steel sheet, the coating film having an Al content of 150 mg / m 2 More than 400mg / m 2 The other points are the same as those in the method for producing a hot-stamped product using the galvannealed steel sheet for hot stamping according to the second embodiment. EXAMPLES

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

[0112] A slab having the chemical composition shown in Table 1 was subjected to hot rolling, pickling, and cold rolling to produce a fully hardened sheet (cold-rolled unannealed sheet, i.e., cold-rolled steel sheet that was not annealed) having a thickness of 1.6 mm. In the hot rolling, the heating temperature of the slab was set to 1200°C or higher, and the holding time in the temperature range of 1200°C or higher was set to 5 minutes or more. In the cold rolling, the cumulative reduction rate was set to 30 to 80%.

[0113] Under the conditions shown in Table 2, some of the examples were subjected to a Ni plating process, and all of the examples were subjected to an annealing process and a zinc plating process. In addition, a zinc oxide-containing coating was formed in some of the examples. 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 calculated as metallic zinc is 0.0 g / m 2 The example in (2) is an example in which no zinc oxide-containing film is 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 a current for 3.2 seconds, Ni pre-plating was applied at 0.3 g / m per side. 2 The Ni pre-plating was applied at 1.0 g / m per side. 2 When applying the material, the current application time was increased in proportion to the amount of material applied.

[0115] Next, an annealing process was carried out. In the annealing process, the specimen was 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 an example where the holding time was 800°C, and 3 seconds in an example where the holding time was 500°C.

[0116] Next, a galvanizing process was carried out. The bath 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. Then, an alloying process was carried out by placing the material in an electric furnace at 500 to 600° C. and holding the material in the temperature range of 500 to 600° C. for 5 to 30 seconds.

[0117] A zinc oxide-containing film forming step was carried out for some of the examples. 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-mentioned method, a galvannealed steel sheet for hot stamping was obtained.

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

[0119] The composition of the galvannealed coating was determined by immersing a galvannealed steel sheet for hot stamping cut to a specified size in 5 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 solution.

[0120] Hot stamping was performed using the obtained galvannealed steel sheet for hot stamping, and a die and a flat die for LME evaluation described later. First, a test piece of a predetermined size was taken from the galvannealed steel sheet for hot stamping. In 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 with 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 so that the hot stamping conditions were the same. By the above method, a hot stamped body was obtained.

[0121] From the temperature records obtained by the 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 (die with 90 degree bend radius = 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 of 50 μm or more in depth were observed, as shown in Figure 2 below, it was deemed that LME cracking had occurred and the sample was judged as failing, and this was recorded as NG in the table. On the other hand, if cracks of 50 μm or more in depth were not observed, it was deemed that LME cracking had not occurred and the sample was judged as passing, and this was recorded 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 bodies, if the metal structure of the steel plate contains 80% or more by area of ​​martensite, the hardened structure in the table is marked as OK, and if it does not contain 80% or more by area of ​​martensite, the hardened structure in the table is marked as NG.

[0126] The scale evaluation was carried out by the following method. The surface of the hot stamped body was visually observed, and if iron oxide scale was formed or scale peeling was observed, it was judged as failing and the table recorded "scale present." If iron oxide scale was not formed and scale peeling was not observed, it was judged as passing and the table recorded "scale absent."

[0127] Weldability was evaluated by welding resistance. One side of a sample taken from the hot stamped body was ground to expose the base material (steel plate). A welding electrode with a diameter of 6 mm and 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 been applied for 4 seconds. The welding resistance of the currently mass-produced GA steel plate processed under the current hot stamp mass-production conditions was 0.57 mΩ. Examples where the welding resistance exceeded 0.86 mΩ, which is 1.5 times the welding resistance of the current material, were judged to have poor weldability and to have failed. On the other hand, examples where the welding resistance was 0.86 mΩ or less were judged to have excellent weldability and to have passed.

[0128] The chemical conversion treatability was evaluated by the following method. Samples taken from the hot stamped compact were washed with water to degrease them, and then immersed in surface conditioning liquid PL-X. Next, they were immersed in chemical conversion treatment liquid SX35 to perform zinc phosphate chemical conversion treatment. The samples after zinc phosphate chemical conversion treatment were observed with a SEM for secondary electron images, and 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 passed, and this is indicated as OK in the table. The examples judged to pass had a chemical conversion coating on the surface of the hot stamped compact. On the other hand, as shown in Figure 3 (Production No. 5) below, the surface is not covered with phosphate crystals. 2 When the above-mentioned regions were observed, the sample was judged as having poor chemical conversion treatability and was therefore judged as failing the test. In addition, weldability and chemical conversion treatability 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 records in a 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 the 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 falls below 0.155 mass%, the Al content in the galvannealed coating is 155 mg / m 2 It can be seen that the welding resistance of the hot stamp formed body increases and the weldability is poor. In addition, in the case of Production Nos. 1 and 2, the Zn content in the galvannealed coating was 40.0 g / m 2 Above this value, 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] From 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 It can be seen that, even if a zinc oxide-containing coating is not formed, the chemical conversion treatability of the hot stamped body is poor.

[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 product. 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°C, 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 heating rate in the furnace becomes slow, and the temperature cannot be raised sufficiently in a short furnace time, 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] From 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 It can be seen that even if a zinc oxide-containing coating is formed, chemical conversion treatability is ensured and desired characteristics are satisfied. Moreover, it can be seen from Production No. 11 that the same results as 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 inferior.

[0141] From Production Nos. 4, 13, 16 to 27, 30, 32 and 33, it is seen that preferable characteristics 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 Si content was excessive, which caused the Ac3 point to rise, the martensite to be less than 80% by area, and the tensile strength to deteriorate. It can be seen from Production No. 29 that the Mn content was insufficient, which caused the Ac3 point to rise, the martensite to be less than 80% by area, and the tensile strength to deteriorate. 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 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, as well as 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 sheet 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% with the remainder 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 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 sheet 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% with the remainder being Fe and impurities, The metal structure of the steel sheet contains 80% or more by area 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: 0.0010-0.0100%, 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. A method for producing a galvannealed steel sheet for hot stamping according to claim 1, A hot rolling process for obtaining a hot rolled steel sheet by hot rolling a slab having the chemical composition according to claim 1; 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 obtaining an annealed steel sheet by holding the hot-rolled steel sheet, the cold-rolled steel sheet, or the Ni pre-plated steel sheet in a reducing atmosphere at a temperature range of 460 to 850 ° C. for 3 seconds or more; 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 an 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, The present invention relates to a method for producing a galvannealed steel sheet for hot stamping.

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 sheet 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% with the remainder being Fe and impurities, The alloyed hot-dip galvanized 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 hot-stamped steel sheet is heated to a temperature range of 100° C. or higher for a holding time of 150 seconds or less, a temperature range of 850° C. or higher for a holding time of 30 seconds or less, and hot stamped in a temperature range of 782° C. or higher to obtain a hot-stamped product. The present invention relates to a method for producing a hot stamped product.

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: 0.0010-0.0100%, 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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