JP2016125101A - Hot stamp molded body and manufacturing method of hot stamp molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot stamp molded body capable of manufacturing a molded body at high efficiency without generating metal mold attachment of plating when conducting hot stamp using a Zn-Ni plating steel sheet and securing coating adhesiveness without a post treatment such as a shot blast after hot stamp and a manufacturing method therefor.SOLUTION: There is provided a hot stamp molded body by hot stamping a steel sheet consisting of a predetermined component and conducted by a Zn-Ni plating with attached amount containing Ni of 3% mass to 20 mass% per a single surface and the balance Zn with inevitable impurities of 5 g/mor more and less than 100 g/m, where there are 1×10 to 1×10per 1 mm of a plating layer of particle material having an average diameter of 10 nm to 1 μm in a plating layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hot stamping body that is a part that is hardened simultaneously with molding by hot press molding, and that is mainly applied to a framework part, a reinforcing part, an undercarriage part, and the like of an automobile body, and a manufacturing method thereof.

  In recent years, efforts have been made to increase the strength of steel sheets and reduce the weight of steel sheets to be used for the purpose of reducing the weight that leads to improved fuel efficiency of automobiles. However, when the strength of the steel sheet used is increased, problems such as galling and breakage of the steel sheet occur during the forming process, and the shape of the molded article becomes unstable due to the springback phenomenon.

  As a technique for manufacturing a high-strength part, there is a method of increasing the strength after press forming rather than pressing a high-strength steel plate. An example of this is hot stamping. As described in Patent Documents 1 and 2, hot stamping is a method in which a steel sheet to be formed is preliminarily heated to be easily formed and then press-formed at a high temperature. In many cases, a hardenable steel type is selected as the molding material, and high strength is achieved by quenching during cooling after pressing. Thereby, the strength of the steel sheet can be increased simultaneously with the press forming without performing another heat treatment step for increasing the strength after the press forming.

  However, since hot stamping is a forming method for processing a heated steel sheet, formation of Fe scale due to surface oxidation of the steel sheet is inevitable. Even if the steel sheet is heated in a non-oxidizing atmosphere, an Fe scale is formed on the surface when exposed to the atmosphere when it is taken out from the heating furnace during press molding. Moreover, heating in such a non-oxidizing atmosphere is costly.

  If the Fe scale is formed on the surface of the steel sheet during heating, the Fe scale will drop off during pressing and adhere to the mold, impairing the productivity of press molding, or such Fe scale may be present in the product after pressing. There remains a problem that the appearance is poor. Moreover, if such an oxide film remains, the Fe scale on the surface of the molded product is inferior in adhesion, so if chemical conversion treatment and coating are performed on the molded product without removing this scale, there is a problem in coating adhesion. Occurs.

  Therefore, normally, as described in Patent Document 3, a sand blasting process or a shot blasting process is applied after hot stamping to remove the Fe scale, and then a chemical conversion process or coating is performed. However, such blasting is cumbersome and significantly reduces the productivity of hot stamps. Further, there is a risk of causing distortion in the molded product.

  On the other hand, Patent Documents 4 to 6 disclose techniques for performing hot stamping on a zinc-based plated steel sheet or an aluminum-plated steel sheet to suppress the generation of Fe scale. Other techniques for hot pressing on plated steel sheets are also disclosed in Patent Documents 7-9. Moreover, about the method of manufacturing a zinc-plated steel plate, it is disclosed by patent documents 10-12 grade | etc.,.

JP-A-7-116900 JP 2002-102980 A Japanese Patent Laid-Open No. 2003-2058 JP 2000-38640 A JP 2001-353548 A JP 2003-126921 A JP 2011-202205 A JP 2012-233249 A JP 2005-74464 A : JP-A-2003-126921 JP-A-4-191354 JP 2012-17495 A

  However, when aluminum-plated steel sheets, especially hot-dip aluminum-plated steel sheets, are hot stamped, mutual diffusion occurs between the plating layer and the steel base material when the steel sheets are heated, and between the Fe-Al and Fe-Al-Si metals at the plating interface. A compound is formed. In addition, an aluminum oxide film is formed on the surface of the plating layer. Although this aluminum oxide film is not as good as the iron oxide film, it still causes problems in paint adhesion and does not necessarily meet the severe paint adhesion required for automotive outer panels, leg parts, etc. . In addition, it is difficult to form a chemical conversion film widely used as a coating base treatment.

  Therefore, when hot stamping zinc-based plated steel sheets, especially hot-dip galvanized steel sheets, other than aluminum-plated steel sheets, Zn-Fe intermetallic compounds and Fe-Zn solid solutions are formed by mutual diffusion between the plating layer and the steel base material during heating. A phase is formed, and a Zn-based oxide film is formed on the outermost surface. These compounds, phases, and oxide films, unlike the above-described aluminum-based oxide films, do not impair coating adhesion and chemical conversion properties.

  However, when such a zinc-based steel sheet is hot stamped, a soft plating layer adheres to the mold at a high temperature, so it is necessary to frequently care for the mold, which impedes productivity. There was a problem.

  As a result of diligent studies to solve this problem, when a certain amount of Ni is contained in the plating layer, the melting point of the plating layer rises, and the hardness of the plating layer at high temperatures increases, thereby preventing adhesion of the plating mold. An inhibitory effect was obtained.

  On the other hand, the use of such a plated steel sheet as a hot stamp material may deteriorate the water-resistant adhesion of the coating film. This is considered to occur when the Fe scale is exposed on the surface during heating or pressing. When a Zn-Ni plated steel sheet is heated in the atmosphere, the Zn activity is high in the plating layer at the initial stage of heating, so that an oxide film mainly composed of a Zn-based oxide is formed as described above. The oxide film may peel off due to the thermal shock that occurs or sliding with the mold during pressing. Even after the oxide film is peeled off, if the activity of Zn on the outermost surface is sufficiently high, the oxide film mainly composed of Zn-based oxide is regenerated, but the alloying of the plating layer by heating proceeds, and the Fe activity on the surface is increased. When the amount is sufficiently high, Fe scale is formed, and it is considered that chemical conversion property and paint adhesion are deteriorated.

  The present invention overcomes the above-mentioned problems, and even when hot stamping a zinc alloy plated steel sheet containing Ni, it is possible to produce a molded body with high efficiency without causing plating adhesion, It is an object of the present invention to provide a hot stamped molded article that can ensure coating adhesion without post-processing such as shot blasting after stamping, and a method for producing the same.

The gist of the present invention is as follows.
(1) As a component of the steel sheet,
C: 0.10 to 0.35%,
Si: 0.01 to 3.00%,
Al: 0.01 to 3.00%,
Mn: 1.0 to 3.5%
P: 0.001 to 0.100%,
S: 0.001 to 0.010%,
N: 0.0005 to 0.0100%,
Ti: 0.000 to 0.200%,
Nb: 0.000 to 0.200%,
Mo: 0.00-1.00%,
Cr: 0.00 to 1.00%,
V: 0.000 to 1.000%
Ni: 0.00 to 3.00%
B: 0.0000 to 0.0050%,
Ca: 0.0000 to 0.0050%,
Mg: 0.0000-0.0050%
The balance is made of Fe and impurities, the Ni content is 3% by mass or more and 20% by mass or less per side, and the adhesion amount consisting of the residual Zn and unavoidable impurities is 5 g / m ² or more and less than 100 g / m ² This is a hot stamped molded body obtained by hot stamping a steel plate coated with Zn-Ni. In the plated layer of the hot stamped molded body, 1 × 10 granular materials having an average diameter of 10 nm to 1 μm per 1 mm of the plated layer length. ˜1 × 10 ⁴ hot stamped hot stamped molded articles,

(2) The steel sheet is mass%,
Ti: 0.001 to 0.200%,
Nb: 0.001 to 0.200%,
Mo: 0.01 to 1.00%,
Cr: 0.01 to 1.00%,
V: 0.001-1.000%,
Ni: 0.01 to 3.00%,
B: 0.0002 to 0.0050%,
Ca: 0.0002 to 0.0050%,
Mg: 0.0002 to 0.0050%
The hot stamping molded product according to (1), containing one or more of the above.

(3) The hot stamp according to (1) or (2), wherein the particulate material is one or more of oxides containing at least one of Si, Mn, Cr and Al. Molded body.

(4) As a component of steel in mass%,
C: 0.10 to 0.35%,
Si: 0.01 to 3.00%,
Al: 0.01 to 3.00%,
Mn: 1.0 to 3.5%
P: 0.001 to 0.100%,
S: 0.001 to 0.010%,
N: 0.0005 to 0.0100%,
Ti: 0.000 to 0.200%,
Nb: 0.000 to 0.200%,
Mo: 0.00-1.00%,
Cr: 0.00 to 1.00%,
V: 0.000 to 1.000%
Ni: 0.00 to 3.00%
B: 0.0000 to 0.0050%,
Ca: 0.0000 to 0.0050%,
Mg: 0.0000-0.0050%
And the balance of Fe and impurities is subjected to a hot rolling step, a pickling step, a cold rolling step, a continuous annealing step, a plating step, a temper rolling step, and a Zn-Ni After producing a plated steel sheet, a hot stamping process is performed on the plated steel sheet to produce a hot stamped body. In the continuous annealing process, 0.1% by volume to 30% by volume of hydrogen and dew point − In an atmospheric gas containing H ₂ O corresponding to 70 ° C. to −20 ° C., with the balance being nitrogen and impurities, while heating the steel plate, and within a range of the plate temperature of 350 ° C. to 700 ° C., with respect to the steel plate Repeated bending at a bending angle of 90 ° to 220 ° is performed four times or more. In the plating step, the steel sheet contains 3% by mass or more and 20% by mass or less of Ni per one side, and consists of residual Zn and inevitable impurities. Chakuryou is subjected to Zn-Ni plating than 5 g / m ² or more 100 g / m ^2, in the hot stamping process, the Zn-Ni-plated steel sheet was heated to a temperature range of 700 ° C. C. to 1100 ° C., the steel sheet A method of manufacturing a hot stamping molded body, which is hot stamped after reaching a predetermined temperature and cooled to room temperature.

(5) The steel is mass%,
Ti: 0.001 to 0.200%,
Nb: 0.001 to 0.200%,
Mo: 0.01 to 1.00%,
Cr: 0.01 to 1.00%,
V: 0.001-1.000%,
Ni: 0.01 to 3.00%,
B: 0.0002 to 0.0050%,
Ca: 0.0002 to 0.0050%,
Mg: 0.0002 to 0.0050%
The manufacturing method of the hot stamping molded object as described in (4) containing 1 type (s) or 2 or more types.

  According to the present invention, when hot stamping is performed using a Zn-Ni plated steel sheet, hot embrittlement can be ensured without suppressing hydrogen embrittlement of the steel and without post-treatment such as shot blasting after hot stamping. It is possible to provide a stamp molded body and a method for manufacturing the stamp molded body.

It is a figure showing the relationship between the formation amount of the oxide in a steel plate inside, and paint adhesion. It is a figure showing the relationship between the frequency | count of the bending process of 90 degrees at the time of heating, and the formation amount of the oxide in a steel plate, Comprising: It is a figure which shows the case where the frequency | count of a bending process is 0 times, once, twice, and three times. is there. It is a figure showing the relationship between the frequency | count of the bending process of 90 degrees at the time of a heating, and the formation amount of the oxide in a steel plate, Comprising: It is a figure which shows the case where the frequency | count of a bending process is 4, 5, and 7. It is a figure showing the relationship between the frequency | count of a 90 degree bending process at the time of a heating, and the formation amount of the oxide in a steel plate, Comprising: It is a figure which shows the case where the frequency | count of a bending process is 9 times. It is a figure showing the relationship between the angle of the bending added to a sample at the time of a heating, and the formation amount of the oxide in a steel plate inside. It is a figure showing the relationship between Ni mass% in a plating layer, and metal mold | die adhesion of plating.

  Details of the present invention will be described below. In the present specification, unless otherwise specified, a numerical range indicated using “to” indicates a range including numerical values before and after “to” as a lower limit value and an upper limit value, respectively.

  The inventor performed hot stamping under various heating conditions using a Zn-Ni plated steel sheet containing Ni in the plating layer produced under various conditions. As a result, when observing the cross-sectional structure of the steel sheet having good paint adhesion, a certain amount of fine granular material having an average diameter of 1 μm or less is present in the plating layer. It has been found that the oxide film mainly composed of is not peeled off and remains on the steel plate surface. Moreover, it has also confirmed that the coating adhesiveness of such a hot stamp molded object is superior to that when no particulate material is present.

  As a result of analyzing this particulate material, it was found that most of them were oxides containing oxidizable elements contained in steel, such as Si, Mn, Cr, and Al.

  In order to consider the excellent adhesion of the oxide film mainly composed of Zn-based oxides when these particulate materials (mainly oxides as described later) are present in a certain amount in the plating layer, The structure of the steel sheet that was cooled as it was without pressing the steel sheet heated under the same conditions as hot stamping was investigated. As a result, it was found that when the particulate material is present in a certain amount in the plating layer, moderate unevenness is generated at the interface between the oxide film mainly composed of Zn-based oxide and the plating layer. Generally, when the shape of the interface is complicated, it is thought that the wedge-fastening effect at the interface is exhibited and the paint adhesion is improved. It was speculated that the adhesion of the film was improved, the formation of Fe scale during heating was avoided, and the coating adhesion was improved.

The granular material that causes moderate unevenness on the interface was considered as follows.
From the components and generation amount, the particulate matter is presumed to be oxides mainly from the contained elements in the steel, not the impurity elements in the plating layer, and before hot stamping heating, the interface between the plating layer and the base iron, Or it may have existed inside the railway. Moreover, it is thought that these oxides were formed when the steel sheet after cold rolling was annealed in the steel sheet manufacturing process.

  In general, when an oxide is present at the interface between the plating layer and the ground iron, the oxide exhibits a barrier effect, thereby locally suppressing the Zn-Ni-Fe alloying reaction during hot stamping heating. I think that. However, since the effect of suppressing the Zn—Ni—Fe alloying reaction is small in the fine granular oxide having an average diameter of 1 μm or less, the influence of the interface oxide on the Zn—Ni—Fe alloying reaction is small. Conceivable.

  On the other hand, when the oxide is formed inside the base iron, the grain boundaries near the steel sheet surface are pinned during annealing, and the growth of crystal grains is suppressed. When the crystal grains on the surface of the steel sheet are small and there are many crystal grain boundaries, the Zn—Ni—Fe alloying reaction rate increases. That is, it is considered that the Zn—Ni—Fe alloying reaction is locally accelerated at the place where the internal oxide exists.

In addition, although the oxide said here is not specifically limited below, the oxide containing 1 type, or 2 or more types at least among Si, Mn, Cr, and Al is mentioned. Specific examples include single oxides of MnO, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , SiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ and single oxides of respective non-stoichiometric compositions; Composite oxides of FeSiO ₃ , Fe ₂ SiO ₄ , MnSiO ₃ , Mn ₂ SiO ₄ , AlMnO ₃ , FeCr ₂ O ₄ , Fe ₂ CrO ₄ , MnCr ₂ O ₄ , Mn ₂ CrO ₄ and respective non-stoichiometric compositions A composite structure thereof;

  In addition, since particles other than oxide can suppress the growth of crystal grains on the surface of the steel sheet during annealing due to the pinning effect, Fe exists as inclusions in the same region where the oxide is formed, Fe, A sulfide containing one or two of Mn and the like, and a nitride containing one or two or more of Al, Ti, Mn, Cr and the like can be particles having the same effect as the above oxide. However, since the amount of sulfide and nitride is very small with respect to the oxide (for example, about 0.1 per 1 mm of the plating layer length), there is little influence. In the present invention, it is sufficient to consider the oxide. I thought.

  When the pinning effect of suppressing the grain growth by the granular material made of the oxide or the like affects the grain boundary, the change in the progress of the Zn-Ni-Fe alloying reaction is caused by the following mechanism. It is considered that unevenness occurs at the interface.

  When the alloying rate of Zn—Ni—Fe alloy is locally different, when the alloying reaction is stopped in a certain period of time during heating, the portion where the plating becomes a solid Fe—Ni—Zn alloy phase in the vicinity of the surface layer of the plating And a molten Zn—Ni—Fe phase. The growth rate of the oxide film mainly composed of Zn-based oxide formed on the surface of the solid Fe-Ni-Zn alloy phase and the surface of the molten Zn phase is considered to be different. It was thought that irregularities occurred at the interface of the oxide film.

  Since the average diameter of the particulate material composed of oxides and the like present in a certain amount in the plating layer after hot stamping heating needs to have a certain size in order to influence the Zn-Ni-Fe alloying behavior, The lower limit is 0.01 μm (10 nm). In addition, if the average diameter of the granular material is too large, a region where one granular material affects the progress of the alloying reaction becomes large, and on the contrary, it becomes difficult to form irregularities, so the upper limit is set to 1 μm. The average diameter of the particulate material is preferably 50 nm to 500 nm.

As shown in FIG. 1, the density of the granular material suitable for improving the coating adhesion with the unevenness is 1 × 10 or more in the plating layer per 1 mm of the plating layer length when observing the cross section. is necessary. If the density is too small, the effect of giving unevenness to the interface cannot be obtained. Further, if it exists in excess of 1 × 10 ⁴ , most of the crystal grains on the surface of the steel sheet are refined due to the grain pinning effect by the granular material, and the local magnitude of the Zn—Ni—Fe alloying rate is reduced. Since it cannot be created, the upper limit is set to 1 × 10 ⁴ . Thus, when the number of granular materials is 1 × 10 to 1 × 10 ⁴ , it can be seen that the coating adhesion is excellent. In addition, the amount of the granular material was controlled by changing the annealing conditions at the time of manufacturing the steel plate as described above, and changing the number of granular materials (granular oxides) formed inside the steel plate. In addition, the observation surface of the particulate matter existing in the plating layer per 1 mm of the plating layer length may be any of the plate width direction, the longitudinal direction, and a direction at some angle from the plate layer length per 1 mm. I do not care.

  Here, the coating adhesion evaluation test was carried out by subjecting the hot stamped molded body to Palbond LA35 (Nihon Parker Rising Co., Ltd.), followed by chemical conversion treatment according to the manufacturer's prescription, and cationic electrocoating (Powernics 110: Nihon Paint Co., Ltd.) 20 μm was applied. This electrodeposited molded article was immersed in ion-exchanged water at 50 ° C. for 500 hours, and then a grid pattern was put on the coated surface by the method described in JISG3312 12.2.5 grid pattern test, and a tape peeling test was performed. . A case where the peeled area ratio (number of peeled cells out of 100 squares) is 2% or less is indicated by ○, a case where it is 1% or more is indicated by ◎, and a case where it exceeds 2% is indicated by ×.

  The average diameter and the number of the granular materials are quantitatively measured by the following method, for example. A sample is cut out from an arbitrary place of the hot stamping body. The cross section of the cut sample is exposed with a cross section polisher and then used with an FE-SEM (Field Emission-Scanning Electron Microscope), or the cross section of the cut sample is exposed with a FIB (Focused Ion Beam) and then a TEM ( Using a Transmission Electron Microscope), one field of view is 20 μm (plate thickness direction: steel plate thickness direction) × 100 μm (plate width direction: direction perpendicular to the steel plate thickness direction) at a magnification of 10,000 to 100,000 times. As a region, observe at least 10 fields of view. An image is taken within the observation field of view, and a binarized image is created by extracting a portion having a luminance corresponding to a granular material by image analysis. After performing noise removal processing on the created binarized image, the equivalent circle diameter for each granular material is measured. The measurement of the equivalent circle diameter is carried out for each observation of 10 visual fields, and the average value of the equivalent circle diameters of all the granular materials detected in each observation visual field is set as the average diameter value of the granular materials.

  On the other hand, after the noise reduction process is performed on the created binarized image, the number of granular substances existing on an arbitrary 1 mm line is measured. The direction of 1 mm is arbitrary as described above, and it may be anywhere as long as the distance of the plating layer length of 1 mm can be ensured on the cross section of the steel plate on which the granular material is observed. In addition, the sampling position for measurement is arbitrary, but in consideration of operational variations, the center is preferably in the width direction of the steel plate or about 100 mm inside from both edges, and the middle is in the longitudinal direction of the steel plate. It is preferable that the inside of the part, or the inside or the like about 100 m from the front or rear end. This number is measured every 10 observations, and the average value of the number of granular substances measured in each observation field is the value of the number of granular substances present in the plating layer per 1 mm of plating layer length. To do.

  In addition, the said granular material includes what exists in a plating layer and the interface of a plating layer and a ground iron, and the interface of a plating layer and a Zn-type oxide film. Regarding the identification of these interfaces, when cross-sectional observation is performed, the distribution of Zn, Fe, Ni, O is investigated using EDS (Energy Dispersive X-ray Spectroscopy) or EPMA (Electron Probe MicroAnalyser), and the SEM observation image It can be specified by comparing with. When SEM observation is performed using reflected electrons, it is easier to identify the interface. The particle diameter of the oxide is evaluated by the equivalent circle diameter by image analysis. The composition of the compound is identified using energy dispersive X-ray spectroscopy (EDS) attached to FE-SEM or TEM.

  Next, the component of the steel plate used as a plating original plate is described. In order to maintain a predetermined strength after hot stamping, the steel sheet is premised on the following component elements and their ranges.

  The steel sheet is in mass%, C: 0.10 to 0.35%, Si: 0.01 to 3.00%, Al: 0.01 to 3.00%, Mn: 1.0 to 3.5% , P: 0.001 to 0.100%, S: 0.001 to 0.010%, N: 0.0005 to 0.0100%, Ti: 0.000 to 0.200%, Nb: 0.000 To 0.200%, Mo: 0.00 to 1.00%, Cr: 0.00 to 1.00%, V: 0.000 to 1.000%, Ni: 0.00 to 3.00%, B: 0.0000 to 0.0050%, Ca: 0.0000 to 0.0050%, Mg: 0.0000 to 0.0050%, with the balance being Fe and impurities.

  The steel sheet is in mass%, C: 0.10 to 0.35%, Si: 0.01 to 3.00%, Al: 0.01 to 3.00%, Mn: 1.0 to 3.5% , P: 0.001 to 0.100%, S: 0.001 to 0.010%, N: 0.0005 to 0.0100%, Ti: 0.001 to 0.200%, Nb: 0 0.001 to 0.200%, Mo: 0.01 to 1.00%, Cr: 0.01 to 1.00%, V: 0.001 to 1.000%, Ni: 0.01 to 3.00 %, B: 0.0002 to 0.0050%, Ca: 0.0002 to 0.0050%, Mg: 0.0002 to 0.0050%, or two or more of them may be contained.

In the components of the steel plate, Ti, Nb, Mo, Cr, V, Ni, B, Ca, and Mg are components arbitrarily included in the steel plate. That is, these component elements may not be contained in the steel sheet, and the lower limit of the content thereof includes zero.
The reasons for limiting the content of each component element will be described below.

  The content of C is 0.10 to 0.35%. If the C content is 0.10% or more, sufficient strength cannot be secured if it is less than 0.10%. On the other hand, the C content is set to 0.35% or less because, at a carbon concentration exceeding 0.35%, the cementite that is the starting point of crack generation at the time of punching is increased and delayed fracture is likely to occur. Was the upper limit. The content of C is preferably 0.11 to 0.28%.

  The Si content is 0.01 to 3.00%. Since Si is effective for increasing the strength as a solid solution strengthening element, the tensile strength increases as the content increases. However, if the Si content exceeds 3.00%, the steel sheet becomes extremely brittle and it becomes difficult to produce the steel sheet. This is the upper limit. When Si is used for deoxidation or the like, it is inevitably mixed. Therefore, 0.01% was made the lower limit. The Si content is preferably 0.01 to 2.00%.

  The Al content is 0.01 to 3.00%. When Al content exceeds 3.00%, the steel sheet becomes extremely brittle and it becomes difficult to manufacture the steel sheet, so this is the upper limit. When Al is used for deoxidation, it may be inevitably mixed. Since it is unavoidable, 0.01% was made the lower limit. The content of Al is preferably 0.05 to 1.10%.

  The Mn content is 1.0 to 3.5%. The reason why the Mn content is set to 1.0% or more is to ensure the hardenability during hot stamping (hot pressing). On the other hand, when the Mn content exceeds 3.5%, Mn segregation occurs. This is the upper limit because it is easy to crack during hot rolling.

  The content of P is 0.001 to 0.100%. P acts as a solid solution strengthening element and increases the strength of the steel sheet. However, if its content is increased, the workability and weldability of the steel sheet are deteriorated, which is not preferable. In particular, when the P content exceeds 0.100%, the workability and weldability of the steel sheet are significantly deteriorated. Therefore, the P content is preferably limited to 0.100% or less. Although the lower limit is not particularly defined, it is preferably 0.001% or more in consideration of dephosphorization time and cost.

  The S content is 0.001 to 0.010%. If the S content is too large, the stretch flangeability deteriorates, and further, cracking occurs during hot rolling. Therefore, S is preferably reduced as much as possible. In particular, in order to prevent cracking during hot rolling and improve workability, it is preferable to limit the S content to 0.010% or less. Although the lower limit is not particularly defined, it is preferably 0.001% or more in consideration of the desulfurization time and cost.

  The N content is 0.0005 to 0.0100%. N lowers the absorbed energy of the steel sheet, and is preferably as small as possible. Therefore, the upper limit is made 0.0100% or less. The lower limit is not particularly defined, but is preferably 0.0005% or more in consideration of denitrification time and cost.

The Ti content is 0.000 to 0.200%, preferably 0.001 to 0.200%. The Nb content is 0.000 to 0.200%, preferably 0.001 to 0.200%.
Ti and Nb have the effect of reducing the crystal grain size. When Ti and Nb exceed 0.200%, the hot deformation resistance at the time of manufacturing the steel sheet is excessively increased, making it difficult to manufacture the steel sheet. Moreover, since the effect is not exhibited if it is less than 0.001%, it is preferable to make this into a minimum.

The Mo content is 0.00 to 1.00%, preferably 0.01 to 1.00%.
Mo is an element that improves hardenability. If the Mo content exceeds 1.00%, the effect is saturated, so this is the upper limit. Moreover, since the effect is not exhibited if it is less than 0.01%, it is preferable to make this into a lower limit.

The content of Cr is 0.00 to 1.00%, preferably 0.01 to 1.00%.
Cr is an element that improves hardenability. If the Cr content exceeds 1.00%, Cr deteriorates the zinc-based plating property, so this is the upper limit. Further, if it is less than 0.01%, the quenching effect is not exhibited, so this is preferably made the lower limit.

The V content is 0.000 to 1.000%, preferably 0.001 to 1.000%.
V has the effect of reducing the crystal grain size. If the content is increased, V causes a slab crack during continuous casting and makes production difficult, so 1.000% is made the upper limit. Moreover, since the effect is not exhibited if it is less than 0.001%, it is preferable to make this into a minimum.

The content of Ni is 0.00 to 3.00%, preferably 0.01 to 3.00%.
Ni is an element that significantly lowers the transformation point. If Ni content exceeds 3.00%, the alloy cost becomes very high, so this was made the upper limit. Moreover, since the effect is not exhibited if it is less than 0.01%, it is preferable to make this into a lower limit. The Ni content is more preferably 0.02 to 1.0%.

The B content is 0.0000 to 0.0050%, preferably 0.0002 to 0.0050%.
B is an element that improves hardenability. For this reason, it is preferable to contain B 0.0002% or more. Moreover, since the effect will be saturated if it exceeds 0.0050%, this is made the upper limit.

The Ca content is 0.0000 to 0.0050%, preferably 0.0002 to 0.0050%.
The content of Mg is 0.0000 to 0.0050%, preferably 0.0002 to 0.0050%.
Ca and Mg are elements for controlling inclusions. For Ca and Mg, if the content is less than 0.0002%, the effect is not sufficiently obtained, so this is preferably made the lower limit. If it exceeds 0.0050%, the alloy cost becomes very high, so this is the upper limit.

  In addition, an impurity refers to the component contained in a raw material, or the component mixed in in the process of manufacture, and was not intentionally contained in the steel plate.

Next, the manufacturing method of the hot stamping molded object of this invention is demonstrated.
The manufacturing method of the hot stamping molded body of the present invention includes a hot rolling process, a pickling process, a cold rolling process, a continuous annealing process, a temper rolling process, and a plating process for the steel containing the above-described component elements. This is a method for producing a hot stamped body by performing a hot stamping step on the plated steel sheet after performing a Zn-Ni plated steel sheet.

  Specifically, for example, the steel containing the above-described component elements is converted into a predetermined hot-rolled steel sheet in a hot-rolling process according to a conventional method, scale removal before cold rolling is performed in a pickling process, and cold rolling is performed. Roll to a predetermined plate thickness in the process. Thereafter, the cold-rolled sheet is annealed in a continuous annealing process and rolled at an elongation of about 0.4% to 3.0% in a temper rolling process. Next, in the plating step, the obtained steel sheet is plated with a predetermined plating adhesion amount by, for example, electroplating to obtain a Zn-Ni plated steel sheet. And the said plated steel plate is shape | molded in a predetermined | prescribed shape at a hot stamp formation process. Through this process, a hot stamping body is manufactured.

The continuous annealing process will be described.
In the continuous annealing step, recrystallization and annealing for obtaining a predetermined material are performed. It is in this continuous annealing step that oxides or the like that become the basis of the particulate matter that is subsequently formed in the plating layer are formed at the interface between the plating and the base iron or inside the base iron.

In general, in the continuous annealing process, the steel sheet is heated in a mixed gas containing N ₂ and H ₂ as main components in order to avoid oxidation of Fe on the surface. However, since the easily oxidizable elements added to the steel sheet have a low element / oxide equilibrium oxygen potential, a part of the vicinity of the surface is selectively oxidized even in such an atmosphere. The oxides of these elements are present on the surface and inside the steel plate.

  Regarding the method of forming oxides in the steel plate appropriately, the inventors focused on the continuous annealing process formed by the oxide, and heating the steel plate until reaching a soaking plate temperature for securing recrystallization and material. Inside and within a temperature range of 350 ° C. to 700 ° C., when the steel plate is subjected to strain caused by repeated bending at least four times or more, an oxide is formed inside the steel plate in an appropriate amount and shape. I found out. This is because the inward diffusion of oxygen into the steel is promoted by imparting strain due to repeated bending to the steel sheet surface as the oxidation of the easily oxidizable element proceeds, and part of the oxide is formed in the steel. it is conceivable that.

The atmospheric gas condition in the furnace is a commonly used atmospheric gas, specifically, 0.1% by volume to 30% by volume of hydrogen and H ₂ O (corresponding to a dew point of −70 ° C. to −20 ° C. Atmosphere gas containing the water vapor and the balance being nitrogen and impurities. The impurity in the atmospheric gas refers to a component contained in the raw material or a component mixed in the manufacturing process and not intentionally included in the atmospheric gas.

  If the hydrogen concentration is less than 0.1% by volume, the Fe-based oxide film present on the surface of the steel sheet cannot be sufficiently reduced, and plating wettability cannot be ensured. Therefore, the hydrogen concentration in the reduction annealing atmosphere is set to 0.1% by volume or more. On the other hand, if the hydrogen concentration exceeds 30% by volume, the oxygen potential in the atmospheric gas becomes small, and it becomes difficult to form a certain amount of oxide of an easily oxidizable element. Therefore, the hydrogen concentration in the reduction annealing atmosphere is set to 30% by volume or less.

A dew point shall be -70 degreeC--20 degreeC. When the temperature is lower than -70 ° C, it becomes difficult to secure an oxygen potential necessary for internal oxidation of easily oxidizable elements such as Si and Mn in steel. On the other hand, when it exceeds -20 degreeC, a Fe type oxide film cannot fully be reduced and plating wettability cannot be secured.
The hydrogen concentration and dew point in the atmosphere are measured by constantly monitoring the atmospheric gas in the annealing furnace using a hydrogen concentration meter or dew point meter.

  When annealing a steel plate in the said atmospheric gas, the temperature range which should give a bending repeatedly with respect to a steel plate is 350 to 700 degreeC. Since the oxidation of the easily oxidizable element in the steel plate proceeds remarkably at a high temperature of 350 ° C. or higher, there is no effect on oxidation even if bending is repeatedly performed in a temperature region below 350 ° C. It is considered that the inward diffusion of oxygen into the steel sheet is promoted by the formation of oxides in the steel sheet by imparting strain due to repeated bending to the steel sheet surface in a temperature range where this oxidation phenomenon occurs remarkably.

  Moreover, when a steel plate is heated until it exceeds 700 degreeC, the recrystallization and grain growth of the structure of a steel plate will advance. Therefore, in order to make the structure of the steel sheet surface fine by forming an oxide inside the steel sheet, it is necessary to repeatedly bend the steel sheet in a temperature range of 350 ° C. to 700 ° C. to impart strain.

2A to 2C, C: 0.20%. The amount of oxide formed inside the steel sheet was examined when a 90 ° bending process was applied a predetermined number of times while a steel sheet containing Si: 0.15% and Mn: 2.0% was heated to a constant temperature. Results are shown. The atmosphere in the furnace during heating was a mixed atmosphere of 5% H ₂ and N ₂ , and the dew point was controlled at −40 ° C. The holding time was 3 minutes. It can be seen that when the number of bendings is set to 4 times or more when heated at 350 ° C. or higher, the amount of oxide formed in the steel sheet increases.

  Confirmation and control of whether or not the number of repeated bends is a predetermined number within a predetermined temperature range is to measure the temperature of the steel sheet in the annealing furnace by introducing a radiation thermometer or contact thermometer into the furnace. Is preferred. However, the installation is limited in terms of equipment, and implementation is difficult, although not impossible. Therefore, when it is impossible to directly measure the temperature of the steel sheet, the structure in the furnace, the input heat amount, the flow of the gas in the furnace, the size of the steel sheet to pass through, the line speed, the temperature in the furnace, the entrance / exit side of the furnace And / or use the measured or target value of the plate temperature. Based on these conditions, using a heat transfer simulation by computer or simple heat transfer calculation, it is possible to repeatedly bend the plate temperature within the range of 350 ° C to 700 ° C from the online prediction result or the offline calculation result. Check the number of times. If necessary, it is preferable to control and adjust the input heat amount, line speed, and the like. It should be noted that the heat transfer simulation and the simple heat transfer calculation may be a method commonly used by those skilled in the art, for example, a simple heat transfer equation or a computer simulation as long as the heat transfer theory is followed.

  Since the effect is hardly obtained when the number of repeated bending is 3 or less, it is necessary to be at least 4 times. From FIG. 2A to FIG. 2C, the upper limit of the number of repeated bendings is 4 times or more, although there are some variations up to 10 times, but the effect is almost the same, so there is no particular upper limit. Since the equipment may be considerably larger and longer than usual, the upper limit is preferably 10 times due to equipment restrictions. However, if there are no restrictions on the furnace equipment, it may be 10 times or more.

  The angle of repeated bending described here is 90 ° to 220 ° from FIG. If it is less than 90 °, the effect of bending cannot be sufficiently obtained. Although the upper limit is not particularly specified, it is difficult to make it over 220 ° from the arrangement of rolls and pass lines in the furnace, so 220 ° is the upper limit. Here, the bending angle is an angle formed by the longitudinal direction of the steel plate before bending and the longitudinal direction of the steel plate after bending. Although it does not prescribe | regulate in particular about the method of bending a steel plate, in a continuous-type annealing line, bending can be provided to the longitudinal direction of a steel plate using an in-furnace hearth roll. The bending angle in this case corresponds to the contact angle with the hearth roll.

  In addition, the number of times of repeated bending of the steel plate is counted as one bend on both sides of the steel plate. In addition, the number of repeated bendings is counted when the bending of the steel sheet is continued twice or more in the same direction, and this two or more bendings are counted as one time. Furthermore, when the bending of a steel sheet having a bending angle of less than 90 ° C. is continued twice or more in the same direction, and the total bending angle is 90 ° to 220 °, this two or more consecutive bendings is counted as one. To do.

In FIG. 3, C: 0.20%. Si: 0.15%, Mn: 2.0%,
While the steel sheet containing P: 0.01%, S: 0.005%, Al: 0.05%, and N: 0.002% is heated to a constant temperature, bending with different bending angles is added four times. It was the result of investigating the amount of oxide formation inside the steel sheet at the time of heating, and the atmosphere in the furnace during heating was a mixed atmosphere of 5% H2 and N2, and the dew point was controlled at -40 ° C. . The holding time was 3 minutes.

Next, the plating process will be described.
In the plating step, Zn—Ni containing 3% by mass or more and 20% by mass or less of Ni per side of the steel sheet, and having an adhesion amount composed of the remaining Zn and inevitable impurities of 5 g / m ² or more and less than 100 g / m ^2. Apply plating. The plating adhesion amount is required to be 5 g / m ² or more from the viewpoint of suppressing iron scale at the time of hot stamping heating, so this is the lower limit. On the other hand, if it exceeds 100 g / m ² , the effect is saturated and the cost is increased, so 100 g / m ² is the upper limit.

Method of imparting the plating layer, if the amount of plating deposition is than ² less than the plating layer 5 g / m ² or more per side 100 g / m can be secured, hot dipping, electroplating, vapor deposition plating, etc., may be any. The method of incorporating Ni in the plating layer differs depending on the plating technique. In the case of hot dipping, the steel sheet is immersed in a molten metal containing Zn and Ni at a predetermined ratio to form a Zn—Ni alloy plating layer. Further, heat treatment may be performed after plating, and the alloy plating layer and the ground iron may be reacted to form Zn—Fe—Ni alloy plating. In the case of electroplating or vapor deposition, Zn and Ni are electrodeposited and vapor-deposited on the steel sheet at a predetermined ratio to form a Zn-Ni alloy plating layer.

  In order to increase the strength of the plating layer at a high temperature and suppress the adhesion of the plating mold, it is necessary to set the Ni concentration in the plating per side to 3% by mass or more. On the other hand, if the Ni adhesion amount per side exceeds 20% by mass, the effect is saturated and the cost is increased, so this is the upper limit. FIG. 4 shows the relationship between the Ni concentration in the plating layer and the degree of plating adhesion to the mold. A Zn—Ni plated steel sheet with an adjusted Ni concentration during plating was prepared. These were heated to 850 ° C., cooled to 680 ° C., and hot stamped. The relationship between the Ni concentration in the plating layer and the adhesion of the mold after hot stamping was determined. As for the degree of adhesion of the mold, ◎: No need to care for the mold (plating mold adherence is very slight), ○: The deposit can be treated by wiping with a waste cloth (adhesion of plating mold is slight) , X: Evaluation was divided to indicate that polishing of the mold was necessary (plating mold adhesion was large), and ◎ and ○ were determined to be acceptable. As shown in FIG. 4, it can be seen that when the Ni concentration during plating is less than 3%, the degree of plating die adhesion increases.

  In addition, Ni does not necessarily have to be dissolved in Zn in the plating layer or exist as a Zn-Ni intermetallic compound in the production of the plated steel sheet. Even if the plating layer containing a large amount of Ni is formed on the interface or the surface of the plating layer containing a large amount of Zn, the sum of the components in the plating layers may be a predetermined one. .

  The composition of the plating layer is not particularly limited. If Ni is contained in an amount of 3% by mass or more and 20% by mass or less and zinc is 70% or more by mass%, the aforementioned components such as Fe, Cr, Co, etc. A zinc alloy plating layer containing the above alloy elements inevitable impurities or depending on the purpose may be used. In addition, Al, Mn, Mg, Sn, Pb, Be, B, Si, P, S, Ti, V, W, Mo, Sb, Cd, Nb, Cr, which may be inevitably mixed from raw materials, etc. Some of Sr and the like may be contained. Some of these overlap with the alloying elements in the case of electrozinc alloy plating, but if less than 0.1%, they are treated as impurities.

  In the hot stamping process, the Zn-Ni plated steel sheet is heated up to a temperature range of usually 700 ° C to 1100 ° C, and after the steel sheet reaches a predetermined temperature within the range shown on the left, the hot stamping is performed after holding for a certain period of time. Cool to room temperature.

The heating method of the steel sheet may be any of energization heating, induction heating, radiant heating using infrared rays, an electric heater, a radiant tube, etc., or direct fire heating using a burner, or a combination thereof.
For example, specifically, the Zn—Ni plated steel sheet is heated to a temperature range of usually 700 ° C. to 1100 ° C. by energization heating or induction heating. After the steel sheet reaches a predetermined temperature, the steel sheet is held for 0 second to 120 seconds and then allowed to cool, and hot stamping is performed within a temperature range of 600 ° C to 800 ° C. If the heating temperature is less than 700 ° C., the required strength cannot be obtained, and if it exceeds 1100 ° C., the plating layer is diffused and evaporated more than necessary, such being undesirable. If the temperature at which hot stamping is performed is less than 600 ° C., the necessary strength cannot be obtained. On the other hand, if the temperature at which hot stamping is performed exceeds 800 ° C., there is a possibility that liquid embrittlement cracking of zinc may occur, which is not preferable. In addition, it is preferable to secure a heating rate of 50 ° C./s or higher by high-speed heating means such as energization heating, if necessary, because high productivity and unnecessary diffusion and evaporation of the plating layer can be avoided.

By carrying out the hot stamping process of the above conditions on the plated steel sheet that has been subjected to the Zn-Ni plating through the continuous annealing process and the plating process, a granular material having an average diameter of 10 nm to 1 μm is plated in the plating layer. It can be generated at 1 × 10 to 1 × 10 ⁴ per 1 mm of layer length. In addition, according to the conditions such as heating of a hot stamp normally assumed, 0 g / m ^{2 to} 80 g / m ² of a Zn—Ni—Fe intermetallic compound and the balance are Fe—Ni in the plating layer of the hot stamping molded body. -Zn solid solution phase is generated.

Examples of the present invention are shown below.
First, the steel of the component shown in Table 1 was hot-rolled, pickled, and cold-rolled by a conventional method to obtain steel plates (original plates) of steel types A to T. Next, the obtained steel plate was continuously annealed. The continuous annealing was performed under conditions of 800 ° C. × 100 seconds in an atmosphere gas containing 10% by weight of hydrogen, water vapor corresponding to a dew point of −40 ° C., and the balance being nitrogen and impurities. In continuous annealing, repeated bending of a steel sheet with a roll was performed the number of times shown in Table 2 during heating and within a range of 350 ° C to 700 ° C. The repeated bending of the steel sheet was performed alternately at different bending angles shown in Tables 2 to 3 in different directions of the plate surface. In addition, all the repeated bending to the steel plate was implemented at the bending angles shown in Tables 2 to 3. Thereafter, the continuously annealed steel sheet was cooled to room temperature and then temper-rolled at an elongation of 1.0%.

  Next, electroplating was performed on the steel plates that had been subjected to continuous annealing and temper rolling with the plating type and the plating adhesion amount per one side shown in Tables 2 to 3 to obtain Zn-Ni plated steel plates. The components of the plated layer of the steel sheet, the coating adhesion amount, and the Zn amount and Ni amount in the plating layer were investigated by ICP emission analysis of a solution obtained by dissolving the plating layer with 10% HCl containing an inhibitor.

Next, the Zn-Ni plated steel sheet was hot stamped under the conditions shown in Tables 2 to 3. Specifically, the steel sheet was heated by dielectric heating at an average temperature increase rate shown in Tables 2-3. After the steel plate reached the heating ultimate temperature shown in Tables 2 to 3, the steel sheet was held until the holding times shown in Tables 2 to 3 passed. Then, it cooled at 20 degreeC / s and hot stamped at 680 degreeC.
Through the above process, hot stamped articles having different structures and structures of plating layers after hot stamping were manufactured.

Moreover, the cross section of this sample was observed, and the average diameter of the granular material in the plating layer and the number of the granular materials per 1 mm of the plating layer were determined by the above-described method. The cross section of the sample was observed at a magnification of 50000 times using FE-SEM / EDS. Incidentally, the granular particles present in the plating layer in tests performed this _{time, MnO,} Mn 2 SiO 4, was (Mn, _Cr) of 3 _{O 4} particles.

  In addition, after hot press molding, randomly select 10 locations from the press surface of the press die, attach the die deposit to the cellophane tape, and use SEM / EDS, Zn-Ni-Fe intermetallic compound It was investigated whether or not was attached to the mold.

  Furthermore, the above-mentioned coating adhesion test was performed on the obtained hot press molded product. A case where the peeled area ratio (number of peeled cells out of 100 squares) was 2% or less was marked as ◯, a value above 1% was marked as ◎, and a value exceeding 2% was marked as ×.

Those satisfying the requirements of the present invention have no adhesion of plating to the mold, formation of Fe scale, and excellent coating adhesion.
The details of the examples and the evaluation results are listed in Tables 1 to 3 below. Table 3 is a continuation of Table 2.

  The preferred embodiments and examples of the present invention have been described above. However, these embodiments and examples are merely examples within the scope of the present invention and do not depart from the spirit of the present invention. Thus, addition, omission, replacement, and other changes of the configuration are possible. That is, the present invention is not limited by the above description, is limited only by the scope of the appended claims, and can be appropriately changed within the scope.

Claims (5)

As a component of the steel sheet,
C: 0.10 to 0.35%,
Si: 0.01 to 3.00%,
Al: 0.01 to 3.00%,
Mn: 1.0 to 3.5%
P: 0.001 to 0.100%,
S: 0.001 to 0.010%,
N: 0.0005 to 0.0100%,
Ti: 0.000 to 0.200%,
Nb: 0.000 to 0.200%,
Mo: 0.00-1.00%,
Cr: 0.00 to 1.00%,
V: 0.000 to 1.000%
Ni: 0.00 to 3.00%
B: 0.0000 to 0.0050%,
Ca: 0.0000 to 0.0050%,
Mg: 0.0000-0.0050%
The balance is made of Fe and impurities, the Ni content is 3% by mass or more and 20% by mass or less per side, and the adhesion amount of the remaining Zn and unavoidable impurities is 5 g / m ² or more and less than 100 g / m ² This is a hot stamped molded body obtained by hot stamping a steel plate coated with Zn-Ni. In the plated layer of the hot stamped molded body, 1 × 10 granular materials having an average diameter of 10 nm to 1 μm per 1 mm of the plated layer length. ˜1 × 10 ⁴ hot stamp molded articles, The steel sheet is in mass%,
Ti: 0.001 to 0.200%,
Nb: 0.001 to 0.200%,
Mo: 0.01 to 1.00%,
Cr: 0.01 to 1.00%,
V: 0.001-1.000%,
Ni: 0.01 to 3.00%,
B: 0.0002 to 0.0050%,
Ca: 0.0002 to 0.0050%,
Mg: 0.0002 to 0.0050%
The hot stamping molded product according to claim 1, comprising one or more of the following.   The hot stamping body according to claim 1 or 2, wherein the particulate material is one or more oxides containing at least one of Si, Mn, Cr and Al. As a component of steel,
C: 0.10 to 0.35%,
Si: 0.01 to 3.00%,
Al: 0.01 to 3.00%,
Mn: 1.0 to 3.5%
P: 0.001 to 0.100%,
S: 0.001 to 0.010%,
N: 0.0005 to 0.0100%,
Ti: 0.000 to 0.200%,
Nb: 0.000 to 0.200%,
Mo: 0.00-1.00%,
Cr: 0.00 to 1.00%,
V: 0.000 to 1.000%
Ni: 0.00 to 3.00%
B: 0.0000 to 0.0050%,
Ca: 0.0000 to 0.0050%,
Mg: 0.0000-0.0050%
And the balance of Fe and impurities is subjected to a hot rolling step, a pickling step, a cold rolling step, a continuous annealing step, a plating step, a temper rolling step, and a Zn-Ni After producing a plated steel sheet, a hot stamping process is performed on the plated steel sheet to produce a hot stamped body. In the continuous annealing process, 0.1% by volume to 30% by volume of hydrogen and dew point − In an atmospheric gas containing H ₂ O corresponding to 70 ° C. to −20 ° C., with the balance being nitrogen and impurities, while heating the steel plate, and within a range of the plate temperature of 350 ° C. to 700 ° C., with respect to the steel plate Repeated bending at a bending angle of 90 ° to 220 ° is performed four or more times. In the plating step, the steel sheet contains 3% by mass to 20% by mass of Ni per side, and consists of residual Zn and inevitable impurities. Chakuryou is subjected to Zn-Ni plated of less than 5 g / m ² or more 100 g / m ^2, in the hot stamping process, the Zn-Ni plated steel sheet was heated to a temperature range of 700 ° C. C. to 1100 ° C., the steel sheet A method of manufacturing a hot stamping molded body, which is hot stamped after reaching a predetermined temperature and cooled to room temperature. The steel is in% by mass,
Ti: 0.001 to 0.200%,
Nb: 0.001 to 0.200%,
Mo: 0.01 to 1.00%,
Cr: 0.01 to 1.00%,
V: 0.001-1.000%,
Ni: 0.01 to 3.00%,
B: 0.0002 to 0.0050%,
Ca: 0.0002 to 0.0050%,
Mg: 0.0002 to 0.0050%
The manufacturing method of the hot stamping molded object of Claim 4 containing 1 type, or 2 or more types of these.