JP6566128B2 - Hot stamping body - Google Patents

Description

  The present invention relates to a hot stamping molded body.

Structural members (molded bodies) used in automobiles and the like are sometimes manufactured by hot stamping (hot pressing) in order to increase both strength and dimensional accuracy. When the molded body is manufactured by hot stamping, the steel material for hot stamping is heated to Ac ₃ or more, and the steel material for hot stamping is rapidly cooled while being pressed with a mold. That is, in the manufacturing, pressing and quenching are performed simultaneously. According to the hot stamp, it is possible to produce a molded article with high dimensional accuracy and high strength.

  On the other hand, since the molded body manufactured by hot stamping is processed at a high temperature, an iron scale is formed on the surface. For this reason, the technique which suppresses formation of an iron scale and improves the corrosion resistance of a molded object is proposed by using a plated steel plate as a hot stamping steel plate (refer patent documents 1 to 3). For example, Patent Document 1 discloses a hot-pressed plated steel sheet on which a Zn plating layer is formed, and Patent Document 2 discloses an automotive member plated steel sheet on which an Al plating layer is formed. Furthermore, Patent Literature 3 discloses a Zn-plated steel sheet for hot pressing in which various elements such as Mn are added to the plated layer of the Zn-plated steel sheet. However, these plated steel sheets have the following problems.

  In the technique of Patent Document 1, since Zn remains on the surface layer of the molded body after hot stamping, a high sacrificial anticorrosive action can be expected. However, in the technique of Patent Document 1, since the plated steel sheet is hot-pressed in a state where Zn is melted, the molten Zn enters the base material of the plated steel sheet during the hot press process, and cracks are generated inside the base material. May occur. This crack is called a liquid metal embrittlement crack (hereinafter sometimes referred to as “LME”). Due to LME, the fatigue characteristics of the molded body deteriorate.

  In addition, in order to avoid generation | occurrence | production of LME at present, it is necessary to control suitably the heating conditions at the time of processing of a plated steel plate. Specifically, a method of heating until all of the molten Zn diffuses into the base material of the plated steel sheet and becomes a Fe—Zn solid solution is employed. However, in order to carry out these methods, it is necessary to heat the plated steel plate for a long time, resulting in a problem that productivity is lowered.

  In the technique of Patent Document 2, since Al having a melting point higher than that of Zn is used as a component of the plating layer, the possibility that the molten metal enters the base material of the plated steel material as in Patent Document 1 is low. For this reason, according to the technique of Patent Document 2, it is expected that excellent LME resistance can be obtained, and as a result, a molded article having excellent fatigue characteristics after hot stamping can be obtained. However, the molded body on which the Al plating layer is formed has a problem that it is difficult to form a phosphate film at the time of the phosphate treatment performed before the coating of the automotive member. In other words, the molded article according to the technique of Patent Document 2 has a problem that the phosphate treatment property cannot be sufficiently obtained.

  In the technique of Patent Document 3, the outermost layer (oxide film) of the hot stamped molded body is modified to improve the weldability. However, even in the technique of Patent Document 3, there is a possibility that LME occurs and the fatigue characteristics of the hot stamped molded article cannot be sufficiently obtained. Moreover, in the technique of patent document 3, there exists a possibility that the element added to a plating layer may reduce phosphate processability.

Japanese Unexamined Patent Publication No. 2003-73774 Japanese Unexamined Patent Publication No. 2003-49256 Japanese Unexamined Patent Publication No. 2005-113233

  This invention is made | formed in view of the said situation, Comprising: It aims at providing the hot stamping molded object excellent in fatigue characteristics, phosphate processing property, coating-film adhesiveness, and weldability.

  The gist of the present invention is as follows.

(1) A hot stamping molded body according to an aspect of the present invention includes a base material; a plating layer, and the plating layer includes an interface layer and an intermediate layer in order from the base material side to the surface side. And the oxide layer, and the interface layer includes αFe, Fe ₃ Al, and FeAl having a total structure of 99% by area or more, and an average Al content is 8.0% by mass or more and 32.5% by mass. %, The average Zn content is limited to more than 5% by mass of Zn content of the base material, the remainder of the chemical component contains Fe and impurities, and the average film thickness is 1.0 μm or more And the intermediate layer contains Fe (Al, Zn) ₂ and Fe ₂ (Al, Zn) ₅ having a total structure of 99 area% or more, the average Al content is 30 to 50% by mass, and the average Zn content The amount is 10 to 40% by mass, and the remainder of the chemical component contains Fe and impurities. The average film thickness is 5.0 μm or more, and the oxide layer has an average film thickness of 0.1 to 3.0 μm.
(2) In the hot stamp molded article according to (1) above, the interface layer may have an average film thickness of 1.0 to 10.0 μm.
(3) In the hot stamped article according to (1) or (2) above, even if the total weight per unit area of Al and Zn in the plating layer is 20 g / m ² or more and 100 g / m ² or less. Good.
(4) In the hot stamping molded article according to any one of (1) to (3), the plating layer further includes an average of more than 0 mass% and 10.0 mass% or less of Si, and the intermediate layer In the above, 0 to 50 area% of the Fe (Al, Zn) ₂ and the Fe ₂ (Al, Zn) ₅ may be substituted with Fe (Al, Si).

  In the hot stamping molded body according to the present invention, the alloy form of the plating layer, the amount of Al and Zn in the specific layer in the plating layer, and the thickness of the oxide formed as the outermost layer of the plating layer are improved. Yes. As a result, according to the hot stamping molded product according to the present invention, the fatigue property improvement of the molded product based on the suppression of the occurrence of LME, the improvement of the phosphate treatment property of the molded product, and the improvement of the coating film adhesion thereby All of the improvement of the weldability of the molded body can be achieved.

It is an example of the cross-sectional SEM image which shows the process part of the molded object which carried out the hot V bending process immediately after heating Al-Zn type plated steel materials on the conditions of Example 1. FIG. It is an example of the cross-sectional SEM image which shows the process part of a molded object which carried out the hot V bending process immediately after heating Zn type plated steel materials on the conditions of Example 1. FIG. It is an example of the cross-sectional SEM image which shows the process part of the molded object which carried out the hot V bending process immediately after heating Al type plated steel materials on the conditions of Example 1. FIG. Immediately after heating the Al-Zn-based plated steel material under the conditions of Example 1, it is quenched while being processed with a flat plate mold equipped with a water-cooling jacket, and then the surface of the molded body is shown when subjected to phosphate treatment. It is an example of a SEM image (secondary electron image). An SEM image showing the surface of the molded product when the Zn-based plated steel material is quenched with a flat plate mold equipped with a water-cooling jacket immediately after being heated under the conditions of Example 1 and then subjected to phosphate treatment. It is an example of (secondary electron image). An SEM image showing the surface of the molded product when the Al-based plated steel material is rapidly cooled while being processed with a flat plate mold equipped with a water-cooling jacket immediately after being heated under the conditions of Example 1, and then subjected to phosphate treatment. It is an example of (secondary electron image). It is sectional drawing of the surface vicinity of the hot stamping molded object which concerns on this embodiment. It is a schematic diagram of Al concentration and Zn concentration near the surface of a hot stamping object concerning this embodiment.

  Hereinafter, embodiments of a hot stamping molded body according to the present invention will be described in detail. The unit “%” relating to the chemical components of the hot stamped article according to the present embodiment means “% by mass” unless otherwise specified. Moreover, in this embodiment, a hot stamping molded body means what is obtained by performing hot stamping (hot pressing) on a plated steel material for hot stamping. Hereinafter, the hot stamped molded body may be simply referred to as “formed body”, and the hot stamped plated steel material may be simply referred to as “steel material” or “plated steel material”.

The present inventors examined the fatigue properties (LME resistance) and phosphate treatment properties of hot stamped bodies (Al-Zn-based plated steel materials, Zn-based plated steel materials, and Al-based plated steel materials). As a result, the inventors of the present invention have, in order from the base material side to the surface side, the plating layer of the hot stamp molded body includes an interface layer, an intermediate layer, and an oxide layer. Includes a total of 99 area% or more of αFe, Fe ₃ Al, and FeAl, and the Al content is in the range of 8.0 mass% to 32.5 mass% and decreases as the base material is approached. The Zn content is limited to 5% by mass or less, the remainder of the chemical component contains Fe and impurities, the average film thickness is 1.0 μm or more, and the intermediate layer has Fe ( Al, Zn) ₂ and Fe ₂ (Al, Zn) ₅ , the average Al content is 30 to 50% by mass, the average Zn content is 10 to 40% by mass, and the balance of the chemical components is Fe And an impurity, and the average film thickness is 5.0 μm or more Ri, the oxide layer, when the average film thickness is 0.1μm or more 3.0μm or less, to obtain a knowledge of the fatigue properties and phosphating of hot stamping member are both good, and. In the present specification, the average film thickness means an average value of the maximum film thickness and the minimum film thickness of a target layer (film).

<Hot stamp molding>
Below, the hot stamping molded object which concerns on this embodiment is demonstrated. As shown in FIG. 7, the hot stamp molded body 1 according to this embodiment includes a base material 10 and a plating layer 20.

[Ingredients of base material]
Below, the preferable component of the preform | base_material of the hot stamping molded object which concerns on this embodiment is demonstrated. The improvement of the LME resistance and the phosphate treatment property, which is a problem of the hot stamped article according to the present embodiment, is realized by the configuration of the plating layer. Therefore, the base material of the hot stamp molded body according to the present embodiment is not particularly limited. However, when the component of the base material is within the range described below, in addition to LME resistance and phosphate treatment property, a molded body having suitable mechanical properties can be obtained. Hereinafter, the unit “%” of the content of alloy elements contained in the base material means “mass%”.

(C: preferably 0.05 to 0.40%)
When 0.05% or more of carbon (C) is contained in the base material, the strength of the hot stamped molded body is increased. On the other hand, when the C content of the base material exceeds 0.40%, the toughness of the base material of the molded body may be insufficient. Therefore, the C content of the base material may be 0.05 to 0.40%. A more preferable lower limit of the C content of the base material is 0.10%, and a still more preferable lower limit is 0.13%. A more preferable upper limit of the C content of the base material is 0.35%.

(Si: preferably 0.5% or less)
Silicon (Si) has the effect of deoxidizing steel. However, when the Si content increases, the wettability of the steel material with respect to plating decreases, and there is a possibility that the plating process cannot be performed normally. Therefore, the Si content of the base material may be 0.5% or less. Further, the upper limit value of the Si content of the base material is preferably 0.3%, and the upper limit value of the Si content of the base material is more preferably 0.2%. A more preferable lower limit value of the Si content of the base material can be determined according to a required deoxidation level, for example, 0.05%.

(Mn: preferably 0.5 to 2.5%)
When manganese (Mn) exceeding 0.5% is contained in the base material, the hardenability of the base material of the steel material before hot stamping is improved, and the strength of the base material of the formed body after hot stamping is increased. On the other hand, when the Mn content of the base material exceeds 2.5%, this effect is saturated. Therefore, the Mn content of the base material may be 0.5 to 2.5%. A more preferable lower limit value of the Mn content of the base material is 0.6%, and a more preferable lower limit value is 0.7%. A more preferable upper limit value of the Mn content of the base material is 2.4%, and an even more preferable lower limit value is 2.3%.

(P: preferably 0.03% or less)
Phosphorus (P) is an impurity contained in steel. The P contained in the base material may segregate at the crystal grain boundaries of the base material to reduce the toughness of the base material of the molded body, and may reduce the delayed fracture resistance of the base material. Therefore, the P content of the base material may be 0.03% or less. It is preferable to reduce the P content of the base material as much as possible.

(S: preferably 0.01% or less)
Sulfur (S) is an impurity contained in steel. S contained in the base material may form sulfides, thereby reducing the toughness of the base material of the molded body and reducing the delayed fracture resistance of the base material. Therefore, the S content of the base material may be 0.01% or less. It is preferable to reduce the S content of the base material as much as possible.

(Sol.Al: preferably 0.10% or less)
When the term “Al content” is used with respect to the base material of the molded body according to the present embodiment, this term means sol. It means the content of Al (acid-soluble Al). Aluminum (Al) is generally used for the purpose of deoxidizing steel. However, when the Al content is high, the Ac ₃ point of the steel material before hot stamping rises, and the heating temperature necessary for quenching of the steel rises during hot stamping, which is not desirable for hot stamping production. Therefore, the Al content of the base material may be 0.10% or less. A more preferable upper limit value of the Al content of the base material is 0.05%. A more preferable lower limit of the Al content of the base material is 0.01%.

(N: preferably 0.01% or less)
Nitrogen (N) is an impurity contained in the steel. N contained in the base material may form nitrides and reduce the toughness of the base material of the molded body. Further, N contained in the base material is combined with B to reduce the amount of solid solution B when B is contained in the base material in order to improve the hardenability of the steel material before hot stamping, and the hardenability of B. The improvement effect may be reduced. Therefore, the N content of the base material may be 0.01% or less. It is preferable to reduce the N content of the base material as much as possible.

  The base material of the hot stamped molded body of the present embodiment can further contain one or more selected from the group consisting of B and Ti.

(B: preferably 0 to 0.0050%)
Since B has a function of improving the hardenability of steel, it increases the strength of the base material of the molded body after hot stamping. However, this effect is saturated if the B content of the base material is too high. Therefore, the B content of the base material may be 0 to 0.0050%. A more preferable lower limit of the B content of the base material is 0.0001%.

(Ti: preferably 0 to 0.10%)
Ti contained in the base material combines with N contained in the base material to form a nitride. When Ti and N are bonded in this way, the bonding between B of the base material and N of the base material is suppressed, and a decrease in the hardenability of the base material due to BN formation can be suppressed. Furthermore, Ti contained in the base material has an effect of making the austenite grain size finer when heated in a hot stamp due to its pinning effect, thereby increasing the toughness of the molded body. However, if the Ti content of the base material is too large, the above effects are saturated, and further, Ti nitride may be excessively precipitated to reduce the toughness of the base material of the molded body. Therefore, the Ti content of the base material may be 0 to 0.10%. A preferable lower limit of the Ti content of the base material is 0.01%.

  The base material constituting the hot stamp molded body of this embodiment can further contain one or more selected from the group consisting of Cr and Mo.

(Cr: preferably 0 to 0.5%)
Cr contained in the base material improves the hardenability of the base material of the steel before hot stamping. However, if the base material has too much Cr content, Cr carbide is formed. This Cr carbide is difficult to dissolve during the heating of the hot stamp, may hinder the progress of austenitization, and may reduce the hardenability. Therefore, the Cr content of the base material may be 0 to 0.5%. A more preferable lower limit of the Cr content of the base material is 0.1%.

(Mo: preferably 0 to 0.50%)
Mo contained in the base material enhances the hardenability of the base material of the steel material before hot stamping. However, if the Mo content of the base material is too large, the above effect is saturated. Therefore, the Mo content of the base material may be 0 to 0.50%. A more preferable lower limit of the Mo content of the base material is 0.05%.

  The base material constituting the hot stamp molded body of the present embodiment may further contain one or more selected from the group consisting of Nb and Ni.

(Nb: preferably 0 to 0.10%)
Nb contained in the base material forms carbides, refines the crystal grains of the base material during hot stamping, and increases the toughness of the molded body. However, if the base material has too much Nb content, the above effect is saturated. Furthermore, if the Nb content of the base material is too large, the hardenability of the base material may deteriorate. Therefore, the Nb content may be 0 to 0.10%. A more preferable lower limit of the Nb content of the base material is 0.02%.

(Ni: preferably 0 to 1.0%)
Ni contained in the base material increases the toughness of the base material of the molded body. The base material Ni further suppresses embrittlement due to the presence of molten Zn during heating with a hot stamp. However, if the Ni content of the base material is too high, these effects are saturated. Therefore, the Ni content of the base material may be 0 to 1.0%. A more preferable lower limit of the Ni content of the base material is 0.1%.

  The balance of the chemical composition of the base material constituting the hot stamping molded body of this embodiment is composed of Fe and impurities. In this specification, an impurity means what may be contained in the ore or scrap as a raw material when manufacturing a molded object industrially, or the thing which may be mixed due to a manufacturing environment etc.

[Plating layer]
Next, the plating layer 20 of the hot stamp molded body 1 according to this embodiment will be described. As shown in FIG. 7, the plated layer 20 of the molded body 1 includes an interface layer 21, an intermediate layer 22, and an oxide layer 23 from the base material 10 side of the molded body 1 toward the surface side of the molded body 1. And sequentially.

[Interface layer]
The interface layer is formed adjacent to the base material. Most of the structure of the interface layer is composed of αFe, Fe ₃ Al, and FeAl. That is, the interface layer of the hot stamping molded body according to the present embodiment is mainly composed of an Fe—Al alloy phase with a low Al content. There may be a slight inclusion in the interface layer due to impurities mixed during plating formation. However, the inventors, when observing the interface layer in the cross section of the plated layer of the hot stamping molded body, if the structure contains αFe, Fe ₃ Al, and FeAl in a total of 99 area% or more, as described above It was confirmed that the influence of inclusions can be ignored. In order to control the structure of the interface layer as described above, the average Al content of the interface layer needs to be 8.0 mass% or more and 32.5 mass% or less. As will be described later, the Al content in the interface layer is not uniform, and the Al content in the interface layer decreases as it approaches the base material.

  In the interface layer, Zn is present in a solid solution state in the Fe-Al alloy phase. However, the inventors have found that Zn hardly dissolves in the interface layer of the molded body according to the present embodiment, and the average Zn content of the interface layer is 5% by mass or less. Due to the presence of the interface layer, liquid metal embrittlement cracking (LME) can be suppressed. In addition, although Zn content of an interface layer may not be uniform, since LME will be suppressed as long as the average Zn content of an interface layer is 5 mass% or less, an interface layer is more than 5 mass% Zn. It may include a region containing. The Zn content in the interface layer is minimized at the interface between the interface layer and the base material. Therefore, the minimum value of the Zn content in the interface layer exceeds the Zn content of the base material.

The configuration of the interface layer is schematically shown in FIG. As described above, the Al content in the interface layer 21 is not uniform. The Al content at the interface between the base material 10 and the interface layer 21 is the same as the Al content of the base material 10. As the distance from the interface between the base material 10 and the interface layer 21 increases, the Al content increases, and the structure is the αFe phase with the smallest Al content, the Fe ₃ Al phase with the second smallest Al content, and the Al content third. It changes in the order of few FeAl phases. The Zn content at the interface between the base material 10 and the interface layer 21 is the same as the Zn content of the base material 10. The Zn content also increases as the distance from the interface between the base material 10 and the interface layer 21 increases. However, the amount is kept low, and the average Zn content in the entire interface layer 21 does not exceed 5 mass%. .

  When the average film thickness of the interface layer is less than 1.0 μm, the LME suppressing effect cannot be sufficiently obtained. Therefore, the average film thickness of the interface layer needs to be 1.0 μm or more. When the average film thickness of the interface layer is set to 2.0 μm or more, the above effect is exhibited at a higher level. The lower limit value of the average film thickness of the interface layer is more preferably 5.0 μm, 6.0 μm, or 7.0 μm. Although it is not necessary to specify the upper limit of the average film thickness of the interface layer, an interface layer having an average film thickness exceeding 15.0 μm is not preferable because it may deteriorate the performance such as corrosion resistance. Therefore, the upper limit value of the average film thickness of the interface layer is preferably 15.0 μm, more preferably 10.0 μm, 9.0 μm, or 8.0 μm.

[Middle layer]
The intermediate layer 22 is a layer containing Fe, Al, and Zn, and is formed on the interface layer 21. Most of the structure of the intermediate layer is composed of Fe (Al, Zn) ₂ and Fe ₂ (Al, Zn) ₅ . Fe (Al, Zn) ₂ is a phase in which part of Al in FeAl _2, which is a kind of Fe—Al intermetallic compound, is substituted with Zn, and Fe ₂ (Al, Zn) ₅ A part of Al in Fe ₂ Al _5, which is a kind of Fe—Al intermetallic compound, is a phase substituted with Zn. In some cases, inclusions caused by impurities mixed during the formation of the plating are slightly included in the intermediate layer. However, the inventors, when observing the intermediate layer in the cross section of the plated layer of the hot stamped molded body, contains Fe (Al, Zn) ₂ and Fe ₂ (Al, Zn) ₅ having a total structure of 99 area% or more. In other words, it was confirmed that the influence of the inclusions as described above can be ignored.

  In the intermediate layer, the contents of Al and Zn are substantially uniform. The chemical component of the intermediate layer includes, by unit mass%, Al having an average of 30% to 50% and Zn having an average of 10% to 40%. Moreover, the average Al content of the intermediate layer exceeds the average Al content of the interface layer.

  When the configuration of the interface layer is controlled as described above, thereby suppressing LME in the interface layer and imparting excellent fatigue characteristics to the molded body, the average Al content of the intermediate layer is 30% by mass or more. In addition, when the oxide layer is mainly composed of Zn oxide, the average Al content of the intermediate layer is 50% by mass or less when imparting excellent phosphate processing properties to the molded body. That is, when the average Al content of the intermediate layer is outside the range of 30 to 50% by mass, there is a very high possibility that the configuration of the interface layer or the oxide layer will be inappropriate. The lower limit value of the average Al content of the interface layer is preferably 32% by mass or 35% by mass. In this case, the LME suppressing effect of the interface layer can be expressed more reliably. Moreover, the preferable upper limit of the average Al content of the interface layer is 50% by mass or 45% by mass, and in this case, the phosphate treatment property of the oxide layer can be further improved.

  When the oxide layer of the molded body is mainly composed of Zn oxide and imparts excellent phosphate processability to the molded body, the average Zn content of the intermediate layer is 10% by mass or more. Moreover, when LME is suppressed in the interface layer and excellent fatigue properties are imparted to the molded body, the average Zn content in the intermediate layer is 30% by mass or less. That is, when the average Zn content in the intermediate layer is outside the range of 10 to 40% by mass, there is a very high possibility that the configuration of the interface layer or the oxide layer will be inappropriate. A preferable lower limit of the average Zn content in the intermediate layer is 12% by mass or 13% by mass, and in this case, the phosphate treatment property of the oxide layer can be further improved. A preferable upper limit of the average Zn content of the intermediate layer is 28% by mass or 25% by mass, and in this case, the LME suppressing effect of the interface layer can be more reliably exhibited.

  The film thickness of the intermediate layer does not directly affect the phosphatability and LME resistance of the molded body. However, when the thickness of the intermediate layer is small, the corrosion resistance performance of the molded body is lowered. Therefore, the thickness of the intermediate layer is preferably 5.0 μm or more. Moreover, when the film thickness of an intermediate | middle layer becomes large too much, there exists a possibility that manufacturing cost may become high and also HS heating time may become long. Therefore, the film thickness of the intermediate layer is desirably 30.0 μm or less.

[Oxide layer]
Further, an oxide layer 23 mainly composed of Zn oxide is formed as the outermost surface layer of the molded body on the surface side of the molded body of the intermediate layer. The oxide layer 23 is formed by oxidizing the plating of the hot stamping plated steel material in the heating process when manufacturing the hot stamping molded body. This oxide layer improves the phosphatability of the hot stamping body. In order to obtain the effect of improving the phosphate treatment property and the coating film adhesion, the average film thickness of the oxide layer needs to be 0.1 μm or more. However, if the oxide layer is too thick, it adversely affects the corrosion resistance and weldability of the compact, so the average thickness of the oxide layer is 3.0 μm or less. In addition, when the average film thickness of an oxide layer shall be 2.0 micrometers or less, since performance, such as a corrosion resistance of a molded object and weldability, is exhibited at a high level, it is preferable.

The states of the interface layer, the intermediate layer, and the oxide layer can be specified by the following means.
The Al content of the interface layer is obtained by cutting the molded body perpendicularly to the surface, polishing the cross section, and analyzing the Al content distribution in the region including the interface layer in this cross section with an analyzer such as EPMA. . The average Zn content of the interface layer, the average Al content and average Zn content of the intermediate layer, and the average Si content of the plating layer are obtained based on the concentration distribution obtained by the above method.
The metal structures of the interface layer and the intermediate layer can be obtained by crystal structure analysis using TEM or the like.
The thicknesses of the interface layer, the intermediate layer, and the oxide layer can be obtained by taking an enlarged photograph of the above-mentioned cross section with an electron microscope and performing image analysis on the enlarged photograph.
In addition, the structure of the plating layer of the molded object which concerns on this embodiment is not substantially uniform along the direction parallel to the surface of a molded object. In particular, the thicknesses of the interface layer, the intermediate layer, and the oxide layer often differ between the processed region and the unprocessed region. Therefore, the analysis described above must be performed in an unprocessed area of the green body. A molded body in which the state of the plating layer in the unprocessed region is within the above-described range is regarded as the molded body according to the present embodiment.

  In the hot stamping molded body according to the present embodiment having the above-described configuration, the alloy form of the interface layer and the intermediate layer constituting the plating layer, the Al content and the Zn content in the interface layer and the intermediate layer, and the interface layer The film thicknesses of the intermediate layer and the oxide layer are improved. As a result, according to the hot stamping molded body according to the present embodiment, it is possible to achieve both improvement in fatigue characteristics of the molded body based on suppression of LME generation and improvement in phosphate processability.

  Although the present embodiment has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the invention.

For example, the plating layer is preferably formed so that the total amount of Al and Zn in the plating layer is 20 g / m ² or more and 100 g / m ² or less. By making the total amount of Al and Zn in the plating layer 20 g / m ² or more, the effects (fatigue properties and phosphate treatment properties) of the interface layer, intermediate layer, and oxide layer described above can be further enhanced. it can. On the other hand, when the total amount is 100 g / m ² or less, the raw material cost of the molded body can be suppressed, the manufacturing cost can be reduced, and the weldability of the hot stamped molded body can be further improved. In addition, the more preferable lower limit of the total amount of Al and Zn in the plating layer is 30 g / m ² . A more preferable upper limit of the total amount of Al and Zn in the plating layer is 90 g / m ² .

  The total amount of Al and Zn contained in the plating layer can be measured by dissolving the hot stamped article with hydrochloric acid and subjecting the solution to inductively coupled plasma emission spectroscopy (ICP analysis). By using this method, the amounts of Al and Zn can be obtained individually. When dissolving a plated steel material before hot stamping, it is common to add an inhibitor that suppresses dissolution of Fe as a base material to hydrochloric acid in order to dissolve only the plating layer. However, since the plating layer of the hot stamp molded body contains Fe, the plating layer of the hot stamp molded body is not sufficiently dissolved by the above method, or the dissolution rate is extremely slow. Therefore, when determining the amounts of Al and Zn during plating of the molded body by ICP analysis, a method of dissolving the plating layer at a liquid temperature of 40 to 50 ° C. using hydrochloric acid without an inhibitor is suitable. In addition, it is desirable to analyze the composition of the surface of the hot stamped article after dissolution by EPMA in order to confirm whether there is any remaining undissolved plating component such as Al or Zn after dissolution. The analysis described above must be performed in an unprocessed area of the green body.

  Furthermore, the plating layer preferably contains an average of more than 0 mass% and 10.0 mass% of Si. By setting the average Si content in the plating layer to more than 0% by mass, the adhesion between the base material and the plating layer can be improved. On the other hand, by setting the average Si content to 10.0% by mass or less, it is possible to prevent deterioration in performance such as corrosion resistance and weldability of the hot stamped molded body. The more preferable lower limit of the average Si content of the plating layer is 0.1% by mass or 0.3% by mass. A more preferable upper limit of the average Si content of the plating layer is 8.0% by mass. However, even if the plating layer does not contain Si, the hot stamped article according to the present embodiment has excellent characteristics, and therefore the lower limit value of the average Si content of the plating layer is 0% by mass.

When the plating layer contains an average of more than 0% by mass and 10.0% by mass of Si, the phase configuration of the intermediate layer changes. As described above, when the plating layer does not contain Si, the intermediate layer contains a total of 99 area% or more of Fe (Al, Zn) ₂ and Fe ₂ (Al, Zn) ₅ , but the plating layer has an average of 0 mass. In the case of containing more than 10.0% by mass of Si, part of Fe (Al, Zn) ₂ and Fe ₂ (Al, Zn) ₅ is replaced with Fe (Al, Si). Fe (Al, Si) is a phase in which a part of Al in FeAl is replaced by Si. When the hot stamping molded product according to this embodiment is manufactured so that the average Si content of the plating layer is 10.0% by mass, the amount of Fe (Al, Si) in the intermediate layer is about 50 area%. Therefore, when the plating layer contains an average of more than 0 mass% and 10.0 mass% of Si, the intermediate layer has a total of 99 area% or more of Fe (Al, Zn) ₂ , Fe ₂ (Al, Zn) ₅ and Fe (Al , Si), and the content of Fe (Al, Si) is 0 to 50% by area.

When the amount of Si is very small, Si is dissolved in Fe (Al, Zn) ₂ and Fe ₂ (Al, Zn) _5, and the configuration of the intermediate layer does not change. According to the investigation by the present inventors, when the average Si content of the plating layer is 0 to 0.1% by mass, it is estimated that Fe (Al, Si) is not generated in the intermediate layer. Further, according to the investigation by the present inventors, it is presumed that the phase configuration of the interface layer does not change even when the plating layer contains an average of more than 0 mass% and 10.0 mass% of Si. Therefore, even if the plating layer contains an average of more than 0% by mass and 10.0% by mass of Si, the interface layer contains a total of 99 area% or more of αFe, Fe ₃ Al, and FeAl.

<Method of manufacturing a hot stamping body>
Next, a method for manufacturing a hot stamping molded body according to this embodiment will be described. The manufacturing method of the hot stamping molded body of this embodiment includes a step of manufacturing a hot stamped plated steel material and a step of hot stamping the hot stamped plated steel material. The process of manufacturing the hot stamping plated steel includes a process of manufacturing a base metal of the hot stamping plated steel, and a process of forming an Al—Zn plating layer on the base metal of the hot stamping plated steel. The manufacturing method of the hot stamping molded object which concerns on this embodiment includes a rust prevention oil film formation process and a blanking process as needed. Hereinafter, each process is explained in full detail.

[Base material manufacturing process]
A plated steel material that is a material of the hot stamping molded body includes a base material and a plating layer. In the base material manufacturing process, a base material for hot stamped steel is manufactured. For example, a molten steel having the same chemical composition as that of the base material of the hot stamping molded body according to this embodiment exemplified above is manufactured, and a slab is manufactured by a casting method using this molten steel. Or you may manufacture an ingot by the ingot-making method using the molten steel manufactured as mentioned above. Subsequently, the base material (hot rolled sheet) of the hot stamped plated steel material is obtained by hot rolling the slab or the ingot. If necessary, the hot-rolled sheet is subjected to pickling treatment, and the cold-rolled sheet obtained by performing cold rolling on the hot-rolled sheet after pickling treatment is used as a base for the hot stamped plated steel material. It is good also as a material.

[Plating process]
In the plating treatment step, an Al—Zn plating layer is formed on the base material of the hot stamping plated steel material to produce a hot stamping plated steel material.

  In the plating treatment step, the Al content in the plating bath is 40 to 70% by mass, and the Zn content is 30 to 60% by mass. By using the plating bath having such a composition to form the plated steel material for hot stamping and hot stamping the plated steel material for hot stamping under the conditions described later, the configuration of the plating layer of the hot stamped molded body is described above. Can be.

  Note that the Al content (concentration) and Zn content (concentration) of the plating bath are substantially the same as the Al content (concentration) and Zn content (concentration) of the plating layer of the hot stamping plated steel material. However, the average Al content (concentration) and the average Zn content (concentration) of the plating layer of the hot stamping body are lower than the Al content (concentration) and Zn content (concentration) of the plating bath. This is because the Fe concentration in the plating layer increases due to alloying that occurs between Al and Zn of the plating layer and Fe of the base material during hot stamping.

  Hereinafter, the plated layer of the hot stamped plated steel material may be referred to as an unalloyed plated layer. The average Al content and the average Zn content in the unalloyed plating layer are analyzed by inductively coupled plasma emission spectroscopy after dissolving the unalloyed plating layer in hydrochloric acid containing an acid corrosion inhibitor (inhibitor). It is measurable by doing. Further, in order to improve the adhesion between the base metal of the hot stamping plated steel material and the unalloyed plating layer, 0.1-15.0 mass% Si is added to the unalloyed plating layer of the hot stamping plated steel material. Furthermore, it is preferable to contain. The Si content of the unalloyed plating layer decreases because Fe diffuses into the plating layer during alloying of the base material and plating. Therefore, when the Si content of the unalloyed plating layer is 0 to 15% by mass, the Si content of the alloyed plating layer is 0 to 10% by mass.

  The formation method of the unalloyed plating layer may be a hot dipping process, spray coating process, vapor deposition, as long as the average Al content and average Zn content in the unalloyed plating layer are controlled as follows: Any other treatment such as plating treatment may be used. For example, when an unalloyed plating layer is formed by a hot dipping process, the plating process includes immersing the base material of the hot stamped plated steel in a hot dipping bath containing Al, Zn, impurities, and optionally Si. And a step of pulling up the base material of the hot stamping plated steel material to which the plating metal has adhered from the plating bath. When the unalloyed plating layer is formed by other treatment, the plating treatment may be performed according to a conventional method so that the chemical composition of the obtained unalloyed plating layer is in the range described above.

In addition, as described above, in the hot stamping molded body, the plating layer is formed with a total weight per unit area of Al and Zn in the plating layer of 20 g / m ² or more and 100 g / m ² or less with respect to the base material. It is preferable that In order to secure the total weight per unit area, in this step, the total weight per unit area of Al and Zn in the plating layer when the base material of the hot stamped plated steel material is pulled up from the plating bath is 20 g. It is important to set it to / g ² or more and 100 g / m ² or less. Note that the total weight per unit area of Al and Zn contained in the plating layer is slightly reduced during alloying due to oxidation and evaporation. Moreover, in this process, ensuring of the said total amount is realizable by adjusting suitably the pulling-up speed of the steel materials from a plating bath, and the flow volume of the gas of wiping.

  The hot stamped plated steel produced by the above-described method includes a base material and an unalloyed plated layer, and the unalloyed plated layer comprises 40.0 to 70.0% by mass of Al and 30.0 to 60.0 mass% Zn and 0-15.0 mass% Si are included. When hot stamping is performed on the plated steel material for hot stamping under the conditions described later, the hot stamping molded body according to the present embodiment is obtained. Hereinafter, the hot stamp condition will be described in detail.

[Hot stamp process]
In the hot stamping process, hot stamping is performed on the hot stamping plated steel material. The normal hot stamping is performed by heating a steel material to a hot stamping temperature range (hot working temperature range), then hot working the steel material, and further cooling the steel material. According to a normal hot stamping technique, it is preferable to increase the heating rate of the steel material as much as possible in order to shorten the manufacturing time. Further, since the alloying of the plating layer proceeds sufficiently if the steel material is heated to the hot stamp temperature range, the normal hot stamp technology does not place importance on the control of the heating condition of the steel material. However, in the hot stamping process for manufacturing the hot stamp member according to the present embodiment, (1) the hot stamping plated steel is heated to the alloying temperature range, and (2) the temperature of the hot stamping plated steel is changed to the alloying temperature. (3) The hot stamping plated steel is heated to the hot stamping temperature range, and (4) the hot stamping plated steel is hot worked and cooled. It has been described above that the present inventors have substantially stopped the temperature rise of the steel material within the alloying temperature range and then resumed the temperature rise when raising the temperature of the hot stamped plated steel material to the hot stamp temperature range. It was found to be essential for obtaining a plating layer having a structure.

  In the hot stamping process, first, the hot stamping plated steel material is charged into a heating furnace (gas furnace, electric furnace, infrared furnace, etc.). In the heating furnace, the hot stamped plated steel material is heated to a temperature range of 500 to 750 ° C. (alloying temperature range) and held within this temperature range for 10 to 450 seconds. By maintaining the temperature, the base material Fe diffuses into the plating layer, and alloying proceeds. By this alloying, the non-alloyed plating layer changes from the base material side to the surface side of the formed body, including an interface layer, an intermediate layer, and an oxide layer. In addition, the above-mentioned holding time is the time when the temperature of the hot stamped plated steel material is within the alloying temperature range. As long as the above holding time condition is satisfied, the temperature of the hot stamped plated steel material may vary within the alloying temperature range during the temperature holding.

  When the temperature of the plated steel material for hot stamping is maintained below the alloying temperature range (that is, less than 500 ° C.), the rate at which the plated layer is alloyed is extremely small, and the heating time is extremely extended. Is not preferable. When the temperature of the hot stamped plated steel is maintained above the alloying temperature range, that is, above 750 ° C., the oxide growth on the surface of the plated layer is excessively promoted during this holding process, and is obtained after HS. The weldability of the molded product is reduced.

  When the time for keeping the temperature of the hot stamping plated steel within the alloying temperature range is less than 10 seconds, alloying of the plating layer is not completed, so the plating having the above-described interface layer, intermediate layer, and oxide layer No layer is obtained. When the time for maintaining the temperature of the hot stamped plated steel within the alloying temperature range is longer than 450 seconds, the amount of oxide growth becomes excessive and the productivity is lowered.

  The heating conditions for heating the hot stamped plated steel material to the above-mentioned alloying temperature range are not particularly limited. However, from the viewpoint of productivity, it is desirable that the heating time is short.

In the hot stamp included in the manufacturing method of the hot stamping molded body according to the present embodiment, the temperature of the hot stamped plated steel material is maintained within the alloying temperature range as described above, and then the temperature is from Ac _{3 to} 950 ° C. The hot stamped plated steel is heated and then hot worked. At this time, it is necessary to limit the time during which the temperature of the hot stamped plated steel material is within the temperature range of Ac _{3 to} 950 ° C. (oxidation temperature range) to 60 seconds or less. If the hot stamping plated steel material temperature is within the oxidation temperature range, an oxide layer on the surface of the plating layer grows. When the time for which the temperature of the hot stamped plated steel material is within the oxidation temperature range is longer than 60 seconds, the oxide film grows too much, and there is a concern that the weldability of the formed body may deteriorate. On the other hand, since the oxide film formation rate is very fast, the lower limit of the time during which the hot stamped plated steel material temperature is within the oxidation temperature range is more than 0 seconds. However, when the hot stamping plated steel material is heated in a non-oxidizing atmosphere such as a 100% nitrogen atmosphere, an oxidized layer is not formed, so the hot stamping plated steel material must be heated in an oxidizing atmosphere such as an air atmosphere. There is.

  As long as the time during which the temperature of the hot stamped steel material is within the oxidation temperature range is 60 seconds or less, the conditions such as the heating rate and the maximum heating temperature are not particularly specified, and various conditions that allow hot stamping are selected. Can do.

  Next, the hot stamped plated steel material taken out from the heating furnace is press-molded using a mold. In this step, the steel material is quenched by a mold simultaneously with the press molding. A cooling medium (for example, water) circulates in the mold, and the mold promotes heat removal from the hot stamping plated steel material and quenching is performed. A hot stamping body can be manufactured by the above process.

  In the above description, the hot stamped plated steel material was heated using a heating furnace. However, the plated steel material for hot stamping may be heated by energization heating. Even in this case, the steel material is heated for a predetermined time by energization heating, and the steel material is press-molded using a mold.

  The above is an indispensable process in the manufacturing method of the hot stamping molded body of the present embodiment, but the optional process in the manufacturing method will be described below.

[Rust prevention oil film formation process]
The rust-preventing oil film forming process is to form a rust-preventing oil film by applying rust-preventing oil to the surface of the hot stamping plated steel after the plating process and before the hot stamping process. May be included. When the time from when the hot stamped plated steel material is manufactured to when the hot stamping is performed is long, the surface of the hot stamped plated steel material may be oxidized. However, since the surface of the hot stamped plated steel material on which the rust-preventing oil film is formed by the rust-preventing oil film forming step is difficult to oxidize, the rust-preventing oil film forming step can suppress the formation of the scale of the molded body. Note that any known technique can be used as a method of forming the rust-preventing oil film.

[Blanking process]
This step is a step of forming the steel material into a specific shape by performing a shearing process and / or a punching process on the plated steel material for hot stamping after the antirust oil film forming step and before the hot stamping step. . The sheared surface of the steel material after blanking is easily oxidized. However, if a rust-preventing oil film is formed in advance on the steel material surface, the rust-preventing oil spreads to some extent on the shear surface. Thereby, the oxidation of the steel material after blanking can be suppressed.

  As mentioned above, although embodiment of this invention was described, embodiment mentioned above is only the illustration of this invention. Therefore, the present invention is not limited to the above-described embodiment, and can be appropriately changed in design without departing from the spirit of the present invention.

  Hereinafter, the effects of the present invention will be specifically described with reference to invention examples. The present invention is not limited to the conditions used in the following invention examples.

  The inventors formed an Al—Zn plating layer, a Zn plating layer, and an Al plating layer on the base material 10, respectively. The Al—Zn-based plating layer includes 55.0% by mass of Al and 45.0% by mass of Zn, the Zn-based plating layer is substantially composed only of Zn, and the Al-based plating layer is substantially In particular, it was made only of Al.

Next, a steel material (plated steel material composed of a base material and a plating layer) on which each plating layer is formed is charged into a first heating furnace, heated to 700 ° C., and held for 120 seconds within this temperature range. did. Thereafter, the plated steel material is immediately charged in a second heating furnace and heated to 900 ° C., and then the plated steel material is adjusted so that the time during which the steel material temperature is in the range of Ac _{3 to} 950 ° C. is 30 seconds. 2 was removed from the furnace. Immediately after the plated steel material was taken out of the second heating furnace, a hot V bending test was performed on the plated steel material using a hand press machine. The time from the removal of the steel material from the furnace to the start of processing on the steel material was about 5 seconds, and the bending was performed at a steel material temperature of about 800 ° C. The V-bending was performed so that the outer diameter of the portion to be bent increased by about 15% from before the V-bending. Thereafter, the steel material was quenched to quench the steel material. The cooling was performed so that the cooling rate from about 800 ° C. to the martensitic transformation start point (about 410 ° C.) was 50 ° C./second or more. Finally, an SEM image of the bent outer side of the processed part of the molded body after cooling was taken, and the fatigue characteristics (LME resistance) of the molded body were evaluated based on whether or not LME was generated.

  FIG. 1 to FIG. 3 are cross-sectional photographs of a processed part of a molded body manufactured from an Al—Zn-based plated steel material, a Zn-based plated steel material, and an Al-based plated steel material. 1, the alloyed Al—Zn-based plating layer 30 is formed on the base material 1, and in the molded body of FIG. 2, the alloyed Zn-based plating layer 40 is formed on the base material 1, and the molding shown in FIG. In the body, the alloyed Al-based plating layer 50 was formed on the base material 1. Note that the observed processed part of the molded body is a part where the tensile process is performed, and is an outer part of the V-bend processed part where the occurrence of LME is concerned with respect to the bending center.

  According to FIGS. 1 to 3, the molded body having the alloyed Zn-based plating layer 40 has cracks extending to the inside of the base material 10, whereas the molding having the alloyed Al—Zn-based plating layer 30. It can be seen that in the molded body having the body and the alloyed Al-based plating layer 50, no cracks extend inside the base material 10.

  Furthermore, after the steel material heated and maintained at the temperature as described above is taken out of the furnace and formed using a flat plate mold equipped with a water-cooled jacket, the martensitic transformation start point (about 410 ° C.) Until the cooling rate was 50 ° C./second or more. Thereafter, the surface of the molded body was adjusted, and the molded body was subjected to phosphate treatment. Finally, an SEM image of the surface of the molded body was taken, and the phosphate processability was evaluated based on the degree of formation of the phosphate coating.

  4 to 6 show that the Al—Zn plated steel material, the Zn based plated steel material, and the Al based plated steel material taken out from the second heating furnace are rapidly cooled while being processed with a flat plate mold equipped with a water cooling jacket. It is an example of the SEM image (secondary electron image) which shows the surface of these molded objects at the time of performing an acid salt process.

  According to FIGS. 4 to 6, for Al—Zn-based plating and Zn-based plating, chemical conversion crystal 60 (phosphate coating) is formed on the entire surface, whereas for Al-based plating, the surface of It can be seen that there is a region where a chemical conversion crystal is not formed in part, so-called transparent region 70.

First, slabs were manufactured by continuous casting using molten steel having the chemical composition shown in Table 1. Next, the slab was hot-rolled to produce a hot-rolled steel material. The hot-rolled steel material was further pickled, and then cold-rolled to produce a cold-rolled steel material. And this cold-rolled steel material was made into the base material (plate thickness 1.4mm) used for manufacture of a hot stamping molded object. The Ac ₃ point of the base material was approximately 810 ° C.

Next, plating was formed on the base material thus manufactured using a plating bath having the composition shown in Table 2 to obtain a steel material for hot stamping. The adhesion amount of plating was controlled so that the total weight of Al and Zn was a value shown in Table 2. This steel was heated to the alloying temperature shown in Table 2, and the temperature was maintained for the alloying time shown in Table 2. Thereafter, the steel material was charged into a heating furnace and heated to a temperature range of Ac ₃ points to 950 ° C., and then the time during which the temperature of the steel material was within this temperature range became the holding time shown in Table 2, Was removed from the furnace.

  Next, in order to perform a hot V bending test, the following steps were performed. The steel material taken out from the heating furnace was immediately subjected to hot V bending using a hand press. The time from the start of taking out the steel material from the heating furnace to the start of the processing of the steel material was set to 5 seconds. Further, the shape of the mold was such that the outer portion of the bending radius by the V bending process was extended by about 15% at the end of the bending process.

  Moreover, in order to perform a phosphate processability evaluation test and a coating-film adhesiveness evaluation test, the following processes were implemented. The steel material taken out from the heating furnace was immediately hot stamped using a flat plate mold equipped with a water cooling jacket, and then accelerated cooled. The cooling rate was set to a cooling rate of 50 ° C./second or more up to the martensite transformation start point (410 ° C.). Furthermore, the surface adjustment was performed for 20 seconds at room temperature using the surface adjustment processing agent (brand name: Preparen X) by Nippon Parkerizing Co., Ltd. for each hot stamping molded object. Subsequently, each hot stamping molded body was subjected to phosphate treatment using a zinc phosphate treatment solution (trade name: Palbond 3020) manufactured by Nippon Parkerizing Co., Ltd. In the phosphate treatment, the temperature of the treatment liquid was 43 ° C., and the hot stamping molded body was immersed in the treatment liquid for 120 seconds. After carrying out the above-mentioned phosphating treatment, each hot stamping body was electrodeposited with a cationic electrodeposition paint manufactured by Nippon Paint Co., Ltd. by applying a slope of 160V, and further 20 at a baking temperature of 170 ° C. Baked for a minute. The average film thickness of the paint after electrodeposition coating was 10 μm in all the inventive examples and comparative examples.

  The configurations of Invention Examples and Comparative Examples obtained by the above-described means were confirmed by the following method.

  The states of the interface layer, the intermediate layer, and the oxide layer of the inventive examples and comparative examples were specified by the following means. The average Al content and average Zn content of the interface layer, the average Al content and average Zn content of the intermediate layer, and the average Si content of the plating layer are obtained by cutting the molded body perpendicularly to the surface of the molded body, It was obtained by polishing the cross section and analyzing the cross section with an analyzer such as EPMA. The metal structures of the interface layer and the intermediate layer were obtained by crystal structure analysis using TEM or the like. An example in which the metal structure satisfies the provisions of the present invention was described as “OK”, and an example in which the metal structure did not satisfy was described as “NG”. The thicknesses of the interface layer, the intermediate layer, and the oxide layer were obtained by taking an enlarged photograph of the above-described cross section with an electron microscope and performing image analysis on the enlarged photograph. The analysis described above was performed in an unprocessed area of the molded body.

  The total weight of Al and Zn in the plating layers of the inventive examples and the comparative examples was measured by high frequency inductively coupled plasma optical emission spectrometry (ICP-OES). That is, a sample was taken from an unprocessed portion (a portion that was not bent) of each invention example and comparative example, and the plating layer was dissolved with a 10% HCl aqueous solution and analyzed. Each element was identified and surveyed by applying plasma energy to each solution, exciting the constituent elements, and measuring the position and intensity of the emitted light lines (spectral lines).

  Table 3 shows configurations of invention examples and comparative examples confirmed by the above-described means. The balance of the average composition of the interface layer and the intermediate layer shown in Table 3 was Fe and impurities.

  Furthermore, the fatigue characteristics (LME resistance), phosphate processability, coating film adhesion, and weldability of the inventive examples and comparative examples obtained by the above-described means were confirmed by the following methods.

  The fatigue properties of the examples and comparative examples were evaluated by the following means. By observing the backscattered electron image using a scanning electron microscope (SEM) and a backscattered electron detector in the cross section of the steel material in the thickness direction of the V-bending portion of the examples and comparative examples, liquid metal embrittlement cracking ( The presence or absence of occurrence of LME) was observed. And the sample in which the crack did not generate | occur | produce and the sample which the crack generate | occur | produced, but terminated in the plating layer were evaluated as favorable (GOOD) about a fatigue characteristic. On the other hand, a sample in which cracks extend beyond the plating layer to the base material was evaluated as defective (BAD) in terms of fatigue characteristics.

The phosphate treatment properties of the examples and comparative examples were evaluated by the following means. The phosphate coating formed on each phosphate-treated sample was dissolved and removed using an ammonium dichromate solution, and the difference in weight of the steel before and after removal of the coating was measured. It was regarded as the amount of coating. And the sample whose adhesion amount is 2.0 g / m < ² > or more was evaluated as favorable (GOOD) about phosphate processability. On the other hand, a sample having an adhesion amount of less than 2.0 g / m ² was evaluated as being poor (BAD) in terms of phosphate processability.

The coating film adhesion of Examples and Comparative Examples was evaluated by the following means. Each electrodeposited sample was immersed in a 5% NaCl aqueous solution having a temperature of 50 ° C. for 500 hours. After immersion, a polyester tape was applied to the entire test area of 60 mm × 120 mm, and then peeled off. The area of the area where the coating film was peeled off by peeling the tape was determined, and the coating film peeling rate (%) was determined based on the following formula.
Coating film peeling rate = (A2 / A1) × 100
A1 is the area of the test area (60 mm × 120 mm = 7200 mm ² ), and A2 is the area (mm ² ) of the area where the coating film is peeled off. A sample having a coating film peeling rate of less than 5.0% was evaluated as good (GOOD) for coating film adhesion. On the other hand, a sample having a coating film peeling rate of 5.0% or more was evaluated as defective (BAD) in coating film adhesion.

  The weldability of the examples and comparative examples was evaluated by the surface resistance value. The surface resistance value of the sample was calculated from the voltage value when a current 2A was passed through the sample at a pressure of 250 kgf using a pressurized DC inverter power supply. A sample having a surface resistance value of 20 mΩ or less was evaluated as good for weldability (GOOD).

  Table 4 shows the fatigue characteristics (LME resistance), phosphate processability, coating film adhesion, and weldability of the invention examples and comparative examples confirmed by the above-described means.

[Evaluation results]
As shown in Table 3, with respect to the hot stamping body of the invention example, which is improving the alloy form and composition of the plating layer and improving the film thickness of the oxide formed as the outermost layer of the plating layer In both cases, it can be seen that both the improvement of the fatigue characteristics of the molded body based on the suppression of the occurrence of LME and the improvement of the phosphatability of the molded body were achieved.

  On the other hand, for the hot stamped molded body of the comparative example, which is not improved with respect to the alloy form or composition of the plating layer, any of fatigue characteristics, phosphate treatment, and weldability, It turns out that it has not improved enough.

Since Comparative Example 101 was produced using a plating bath with insufficient Al content, LME could not be prevented. For this reason, the fatigue characteristics of Comparative Example 101 were poor.
Since the comparative example 102 was manufactured using the plating bath with insufficient Zn content, the structure of the intermediate layer became inappropriate due to insufficient Zn. For this reason, in the comparative example 102, the phosphate processability was impaired and the coating film adhesion was poor.
In Comparative Example 103, since the alloying temperature at the time of hot stamping was too high, the thickness of the oxide layer was excessive, and the weldability was poor.
In Comparative Example 104, since the alloying temperature at the time of hot stamping was too low, alloying of the plating layer became insufficient, a Zn-rich phase was generated, and LME could not be prevented. For this reason, the fatigue characteristics of Comparative Example 104 were poor.
In Comparative Example 105, the alloying time at the time of hot stamping was too long, so the thickness of the oxide layer was excessive and the weldability was poor.
In Comparative Example 106, the alloying time at the time of hot stamping was too short, so heating for alloying was insufficient. For this reason, in the comparative example 106, LME generate | occur | produced and the fatigue characteristic fell. Further, in Comparative Example 106, since the heating was insufficient, the amount of oxide was small, and phosphate treatment property and coating film adhesion were insufficient.
In Comparative Example 107, since the alloying temperature and the holding time at the time of hot stamping were excessive, the thickness of the oxide layer was excessive and the weldability was poor.

  According to the present invention, both the fatigue characteristics and the phosphate treatment property are sufficiently exhibited for the hot stamped molded body in which the plating layer is formed on the surface of the base material. Therefore, the present invention is particularly promising in the field of structural members used in automobiles and the like.

DESCRIPTION OF SYMBOLS 1 Hot stamp molded object 10 Base material 20 Plating layer 21 Interface layer 22 Intermediate layer 23 Oxide layer 30 Al-Zn type plating layer 40 Zn type plating layer 50 Al type plating layer 60 Chemical conversion crystal 70 Transparent region

Claims (4)

With the base material;
A plating layer;
A hot stamping body comprising:
The plating layer includes, in order from the base material side to the surface side, an interface layer, an intermediate layer, and an oxide layer,
The interface layer includes αFe, Fe ₃ Al, and FeAl having a total structure of 99 area% or more, and an average Al content is in the range of 8.0 mass% to 32.5 mass%. Zn content is limited to more than 5% by mass Zn content of the base material, the remainder of the chemical component contains Fe and impurities, and the average film thickness is 1.0 μm or more,
The intermediate layer includes Fe (Al, Zn) ₂ and Fe ₂ (Al, Zn) ₅ having a total structure of 99 area% or more, an average Al content is 30 to 50% by mass, and an average Zn content is 10 to 40% by mass, the remainder of the chemical component contains Fe and impurities, and the average film thickness is 5.0 μm or more,
The oxide layer has an average film thickness of 0.1 to 3.0 μm. 2. The hot stamping article according to claim 1, wherein the interface layer has an average film thickness of 1.0 to 10.0 μm. 3. The hot stamped article according to claim 1, wherein the total weight per unit area of Al and Zn in the plating layer is 20 g / m ² or more and 100 g / m ² or less. The plating layer further includes an average of more than 0 mass% and 10.0 mass% or less of Si,
In the intermediate layer, 0 to 50 area% of the Fe (Al, Zn) ₂ and the Fe ₂ (Al, Zn) ₅ is substituted with Fe (Al, Si). The hot stamping molded product according to any one of 1 to 3.