Invention name: Hot stamp molded article
Technical field
[0001]
　The present invention relates to a hot stamp molded article.
Background technology
[0002]
　Structural members (molded bodies) used in automobiles and the like may be manufactured by hot stamping (hot pressing) in order to improve both strength and dimensional accuracy. When the molded product is manufactured by hot stamping, the steel plate is heated to 3 or more points of Ac and rapidly cooled while being pressed with a die. That is, in the production, press working and quenching are performed at the same time. According to the hot stamp, it is possible to produce a molded product having high dimensional accuracy and high strength.
[0003]
　On the other hand, since the molded product produced by hot stamping is processed at a high temperature, scale is formed on the surface. Patent Documents 1 to 5 propose techniques for suppressing scale formation and improving corrosion resistance by using a plated steel sheet as a hot stamping steel sheet.
[0004]
　For example, Japanese Patent Application Laid-Open No. 2000-38640 (Patent Document 1) discloses a steel sheet for hot pressing using Al plating. Japanese Unexamined Patent Publication No. 2003-49256 (Patent Document 2) discloses an aluminum-plated steel sheet for high-strength automobile members on which an Al-plated layer is formed. Japanese Unexamined Patent Publication No. 2003-73774 (Patent Document 3) discloses a steel sheet for hot pressing on which a Zn-plated layer is formed. Further, Japanese Patent Application Laid-Open No. 2005-11233 (Patent Document 4) discloses a Zn-based plated steel material for hot pressing in which various elements such as Mn are added to the plating layer of a Zn-plated steel sheet. Japanese Unexamined Patent Publication No. 2012-112010 (Patent Document 5) discloses a plated steel material using Al—Zn-based alloy plating.
Prior art literature
Patent documents
[0005]
Patent Document 1: Japanese Patent Application Laid-Open No. 2000-38640
Patent Document 2: Japanese Patent Application Laid-Open No. 2003-49256
Patent Document 3: Japanese Patent Application Laid-Open No. 2003-73774
Patent Document 4: Japanese Patent Application Laid-Open No. 2005-11233
Patent Document 5: Japanese Patent Application Laid-Open No. 2012-112010
Outline of the invention
Problems to be solved by the invention
[0006]
　According to the technique of Patent Document 1, scale generation during hot stamping, decarburization, etc. are suppressed. However, since such a hot stamped molded body is mainly composed of Al plating, it tends to be inferior in sacrificial corrosion resistance to a plated steel sheet mainly composed of Zn, which is insufficient from the viewpoint of rust prevention. Patent Document 2 relating to a plated steel sheet mainly composed of Al plating has the same problems as described above.
[0007]
　In the techniques of Patent Document 3 and Patent Document 4, Zn remains on the surface layer of the steel material after hot stamping, so that a high sacrificial anticorrosion effect can be expected. However, these Zn-based plated steel materials have a problem that red rust is generated at an early stage because a large amount of Fe elements are diffused from the base iron in the plating layer. Further, since the steel sheet is processed in a state where Zn is melted, the molten Zn may invade the steel sheet and crack may occur inside the steel material. This crack is called a liquid metal embrittlement (hereinafter, also referred to as "LME"). Then, due to the LME, the fatigue characteristics of the steel sheet deteriorate.
[0008]
　When the plated steel sheet of Patent Document 5 is subjected to hot stamping, liquid phase Zn is generated even in the Al—Zn-based alloy plated steel sheet to generate LME. Further, in the Al—Zn-based alloy plated steel sheet, the plating layer is alloyed, and a large amount of Fe element is diffused from the base iron in the plating layer, so that red rust may occur.
[0009]
　Since the hot stamp molded body is mainly used as an automobile structural member, spot welding is performed after molding. Generally, in order to improve the corrosion resistance, it is effective to set the plating thickness thick, but Al and Zn contained in the plating layer react with Cu of the spot electrode, and the plating layer is thick. In that case, the continuous spotting property of spot welding is significantly reduced. Therefore, it has been difficult to achieve both sufficient corrosion resistance and spot weldability in a hot stamped molded product of a plated steel sheet.
[0010]
　The present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved molded product having improved fatigue characteristics, corrosion resistance, and spot weldability.
Means to solve problems
[0011]
　In order to achieve the above object, the present inventors have conducted intensive research on a plated steel sheet having a Zn—Al—Mg-based plating layer. As a result, the present inventors obtained the following findings.
[0012]
　FIG. 1 is a plated steel sheet 10a manufactured under normal conditions. The steel material 10a has a plating layer 13a on the surface of the base material 11a, and between the base material 11a and the plating layer 13a, there is a diffusion layer 12a in which Fe of the base iron is diffused into the plating layer.
[0013]
　FIG. 2 is a normal hot stamp molded body 20a. The hot stamp molded body 20a has a surface layer portion 2a having a constant thickness on the surface of the base material 1a. The surface layer portion 2a has a layered structure including an interface layer 21a and a metal layer 21b in the order closer to the base material 1a, and an oxide layer 4a on the outermost layer.
[0014]
　When the plated steel sheet 10a manufactured under normal conditions is hot stamped under normal conditions, it becomes like a hot stamp molded body 20a. The interface layer 21a of the hot stamped body 20a is a portion derived from the diffusion layer 12a of the plated steel sheet 10a manufactured under normal conditions. The interface layer 21a includes a portion where Fe of the base iron is diffused into the plating layer 13a at the time of hot stamping. The chemical composition of the interface layer 21a differs depending on the chemical composition of the base material 11a and the plating layer 13a. For example, in the case of the plating layer 13a containing Al, Mg and the like and mainly containing Zn, Fe 2 (Al, Zn) 5 , The Fe—Al phase such as Fe (Al, Zn) 3 and the plating layer 13a containing a large amount of Si are composed of the Fe—Al—Si phase such as Fe 3 (Al, Si) and Fe (Al, Si). It becomes a layer. Further, the oxide layer 4a is an oxide layer mainly composed of Zn.
[0015]
　Since the diffusion layer 12a of the plating layer of the plated steel sheet 10a manufactured under normal conditions is thick, it causes various problems during hot stamping. Specifically, Zn in the plating layer 13a becomes a liquid phase state when the hot stamp is heated and evaporates, so that the amount of Zn in the metal layer 21b decreases. Further, since Zn in the plating layer 13a reacts with the interface layer 21a during hot stamping, the amount of Zn in the metal layer 21b is reduced. Therefore, when the plated steel sheet 10a manufactured under normal conditions is hot-stamped, the plating layer (in the metal layer 21b of the hot-stamped molded body 20a) has a Zn sacrificial anticorrosion action but does not easily remain, so that the corrosion resistance is significantly reduced. There is. Further, the evaporation of Zn increases the thickness of the oxide layer 4a, which causes a decrease in spot weldability.
[0016]
　As a result of examining the relationship between the plated steel sheet 10a manufactured under normal conditions and the hot stamped molded body 20a in order to solve the above problems, the present inventors have determined the thickness of the diffusion layer 12a of the plated steel sheet 10a. We found the manufacturing conditions to make it thinner.
[0017]
　Usually, the plating bath temperature is set in the range of about + 50 ° C. to 100 ° C., which is the melting temperature of the plating, in order to form the homogeneous plating layer 13a. This is because when the temperature of the plating bath approaches the melting temperature, a part of the plating bath solidifies and becomes dross during manufacturing, which tends to deteriorate the surface cleanliness of the plating layer.
[0018]
　Then, in order to sufficiently promote the diffusion of Fe into the plating layer 13a, the immersion time in the plating bath is usually set to 5 seconds or more. Further, the temperature of the steel sheet (penetration plate temperature) before being immersed in the plating bath is usually maintained at the plating bath temperature + 0 to −15 ° C. The reason is that it is easy to raise the temperature of the plating bath, but it is difficult to lower the temperature of the plating bath, and when the penetrating plate temperature is high, it is necessary to cool the plating bath. In this regard, for example, in Patent Document 5, the penetration plate temperature is set to a temperature of the plating bath temperature (° C.) to the plating bath temperature −10 (° C.) in all the examples.
[0019]
　However, it was manufactured under such normal plating conditions (plating bath temperature is plating melt temperature + 50 to 100 ° C., immersion time is 5 seconds or more, steel plate penetration plate temperature is plating bath temperature + 0 to -15 ° C., etc.). The plated steel sheet 10a is dominated by the plating bath temperature and the immersion time, and Fe is easily diffused to the plating side. Then, in the plated steel plate 10a manufactured under normal conditions, with reference to FIG. 1, Fe 2 (Al, Zn) 5 , Fe (Al, Zn) 3 and plating are Si on the surface layer of the base material (base iron). When a large amount of the above is contained , the diffusion layer 12a composed of Fe 3 (Al, Si), Fe (Al, Si) and the like grows thickly (1 μm or more) between the base iron and the plating layer.
[0020]
　Therefore, the present inventors manufacture the plated steel sheet under the conditions of the plating bath temperature, the immersion time, and the penetration plate temperature of the steel sheet, which are different from the normal plating conditions, so that the thickness of the diffusion layer 12a is made thicker than before. I succeeded in making it thinner.
[0021]
　The first is the temperature and immersion time of the plating bath. If the temperature of the plating bath is too high, the diffusion layer 12a such as Fe 2 (Al, Zn) 5 in the plated steel sheet grows to 1 μm or more, forming a thick interface layer on the hot stamped compact, and forming a layered metal layer. Formation cannot be avoided. Further, even if the temperature of the plating bath is reduced, the same problem occurs when the immersion time is too long. Therefore, the plating bath temperature was lowered as much as possible, specifically, the plating melt temperature was limited to +5 to 20 ° C., and the immersion time was limited to 1 to 3 seconds. The diffusion layer 12 that grows between the base metal (base iron) 11 and the plating layer 13 under such conditions becomes a thin layer mainly composed of Fe 2 (Al, Zn) , with reference to FIG . The plated steel sheet 10 having such a diffusion layer 12 does not grow an interface layer composed of Fe 2 (Al, Zn) 5 or the like even if hot stamping is performed thereafter .
[0022]
　Second, the temperature at which the steel sheet penetrated into the plating bath was examined. In the present invention, if the temperature of the plating bath is lowered and the immersion time is shortened, the growth of the diffusion layer 12 such as Fe 2 (Al, Zn) 5 , which will become a thick interface layer in the future, can be suppressed. However, if the penetration plate temperature is lower than the plating bath temperature, there is a concern that the plating bath will solidify and the cleanliness of the plating layer 13 will be impaired. On the other hand, if the penetration temperature is too high, there is a problem that the cooling rate is lowered and the diffusion layer 12 such as Fe 2 (Al, Zn) 5 grows thick. In consideration of these problems, the penetration plate temperature was set to the plating bath temperature + 5 to 20 ° C.
[0023]
　In addition to the above-mentioned production conditions, the present inventors have further devised to contain 7.0% or more of Mg in the plating layer 13. Mg is combined with Zn in the plating layer 13 to form MgZn two- phase 32a. Therefore, it is possible to prevent the deterioration of spot weldability caused by LME and molten Zn, which are caused by molten Zn invading into the steel material during hot stamping and causing cracks inside the steel material. Then, by including Mg in the plating layer 13, Fe of the base material can be suppressed from penetrating the thinned diffusion layer 12 and diffusing into the plating layer 13 at the time of hot stamping. Then, the excessive reaction between Zn, Al of Fe or a mixture of Zn and Al and the base iron can be suppressed, and the growth of the diffusion layer 12 can also be suppressed. Further, a small amount of Fe contained in the plating layer 13 reacts with Al to form an island-shaped FeAl two- phase 32b.
[0024]
　Also, surprisingly, the present inventors have found that the FeAl 2- phase 32b of the hot stamped product is island-shaped. Since this island-shaped FeAl 2- phase 32b is an intermetallic compound having a high melting point, it is considered that it has an effect of improving continuous spotting property at the time of spot welding and suppressing LME.
[0025]
　FIG. 3 is a schematic view of a plated steel sheet manufactured under the conditions found by the present inventors as described above. FIG. 4 is a schematic view of a hot stamped molded product manufactured by hot stamping a plated steel sheet manufactured under the conditions found by the present inventors as described above. As shown in FIG. 4, in the hot stamp molded body 20 manufactured under the conditions found by the present inventors, the interface layer 31 is thin, and the main layer 32 in a state where MgZn 2- phase 32a and island-shaped FeAl 2- phase 32b are mixed. To be equipped. Since the island-shaped FeAl 2- phase 32b is an intermetallic compound having a high melting point, it has an effect of improving continuous spot welding during spot welding and suppressing LME.
[0026]
　The present invention has been made based on the above findings, and the gist thereof is as follows.
　(1) A
　hot stamp molded body including a steel base material and a metal layer formed on the surface of the steel base material,
　wherein the metal layer is by mass%, Al: 30.0 to 36.0%. The interface layer is 100 nm to 5 μm in thickness, and the interface layer located at the interface with the steel base material is a mixture of MgZn 2 phase and island-shaped FeAl 2 phase, and the thickness is 3 μm to 40 μm. The
　metal layer is provided with a main layer located above, and the average composition of the metal layer is, in terms of mass%,
Al: 20.0 to 45.0%,
Fe: 10.0 to 45.0%,
Mg: 2.0. ~ 10.0%,
Sb: 0 to 0.5%,
Pb: 0 to 0.5%,
Cu: 0 to 1.0%,
Sn: 0 to 1.0%,
Ti: 0 to 1.0% ,
Ca: 0 to 3.0%,
Sr: 0 to 0.5%,
Cr: 0 to 1.0%,
Ni: 0 to 1.0%,
Mn: 0 to 1.0%,
Si: 0 to 1.0%,
The balance is 12.0 to 45.0% Zn and impurities, and in the
　main layer, the MgZn 2 phase is, by mass%,
Mg: 13.0 to 20.0%,
Zn: 70.0 to 87. It contains 0.0 %,
Al: 0 to 8.0%,
Fe: 0 to 5.0%, and in the
　main layer, the FeAl 2 phase is mass% and
Al: 40.0 to 55.0%. ,
Fe: 40.0 to 55.0%,
Zn: 0 to 15.0%, a
hot stamp molded product.
[0027]
　(2) in said main layer,
　the FeAl 2 volume fraction of the phases is the 50.0 to 80.0%,
　the MgZn 2 volume fraction of phase is 20.0 to 50.0%,
the ( 1) Hot stamp molded body.
[0028]
　(3) In the main layer,
　the FeAl 2 volume fraction of the phases is the 60.0 to 75.0%,
　the MgZn 2 volume fraction of phase is 25.0 to 45.0%,
the ( The hot stamped body of 1) or (2).
The invention's effect
[0029]
　According to the present invention, it is possible to provide a hot stamp molded product having excellent fatigue characteristics, spot weldability, and corrosion resistance after painting.
A brief description of the drawing
[0030]
[Fig. 1] Fig. 1 is a schematic view showing a plated steel sheet manufactured in a normal plating process.
FIG. 2 is a schematic view showing a hot stamped molded product obtained from a plated steel sheet manufactured in a normal plating process.
FIG. 3 is a schematic view showing a plated steel sheet manufactured under the conditions found by the present inventors.
FIG. 4 is a schematic view showing a hot stamped molded product obtained from a plated steel sheet manufactured under the conditions found by the present inventors.
FIG. 5 is a reflected electron image of a cross section of a metal layer of a hot stamped molded product according to an embodiment of the present invention.
FIG. 6 is a schematic view showing the definition of an island-shaped FeAl two- phase of a hot stamped article according to an embodiment of the present invention .
Mode for carrying out the invention
[0031]
　Hereinafter, a hot stamped molded product according to an embodiment of the present invention, a plated steel sheet for obtaining the hot stamped molded product, and a method for manufacturing the hot stamped molded product will be described. The "%" of the content shall mean "mass%" unless otherwise specified.
[0032]
　1. 1.
　The outline of the hot stamped molded product 20 according to the present embodiment will be described with reference to FIGS. 4 and 5 with respect to the hot stamped molded product 20. With reference to FIGS. 4 and 5, the hot stamp molded body 20 according to the present embodiment includes a steel base material (hereinafter, also simply referred to as “base material”) 1 and a metal layer 3, and the metal layer 3 Is provided with an interface layer 31 and a main layer 32 at the interface with the base metal 1, and the main layer 32 is in a state where MgZn 2- phase 32a and island-shaped FeAl 2- phase 32b are mixed. In some cases, the oxide layer 4 is present on the outer surface of the metal layer 3. However, due to the chemical composition of the plating layer 13, particularly the Zn and Mg components, it is difficult to form layered oxides in the plating cross section over the entire surface of the plated steel sheet. Therefore, even if the oxide layer 4 is observed, a small amount of oxides such as Zn, Mg, and Ca components are partially adhered to the oxide layer 4. Further, the oxide layer 4 may be removed by an alkali treatment during a process such as chemical conversion treatment and may not remain on the surface of the final product.
[0033]
　1-1. Regarding the
　base material 1, the base material 1 is not particularly limited as long as it has characteristics according to the use of the hot stamp molded body 20 according to the present embodiment. For the base material 1, for example, steel having the following chemical composition can be used.
[0034]
　C: 0.05% to 0.40%
　carbon (C) is an element effective for increasing the strength of the hot stamped product, but if the C content is too large, the toughness of the hot stamped product is lowered. Let me. Therefore, the C content is set to 0.05% to 0.40%. The lower limit of the preferable C content is 0.10%, and the lower limit of the more preferable C content is 0.13%. The upper limit of the preferable C content is 0.35%.
[0035]
　Si: 0.5% or less
　Silicon (Si) is an effective element for deoxidizing steel. However, if the Si content is too high, Si in the steel diffuses during the heating of the hot stamp to form oxides on the surface of the steel sheet, resulting in reduced efficiency of the phosphate treatment. Si is an element that raises the Ac 3 points of steel . Therefore, the excessive content of Si raises the Ac 3 points of the steel sheet and raises the heating temperature of the hot stamp, so that the evaporation of Zn in the plating layer is unavoidable. Therefore, the Si content is set to 0.5% or less. The upper limit of the preferable Si content is 0.3%, and the more preferable upper limit of the Si content is 0.2%. The lower limit of the preferred Si content varies depending on the desired deoxidation level, but is usually 0.05%.
[0036]
　Mn: 0.5% to 2.5%
　manganese (Mn) enhances hardenability and enhances the strength of the hot stamped product. On the other hand, even if Mn is excessively contained, the effect is saturated. Therefore, the Mn content is set to 0.5% to 2.5%. The lower limit of the preferable Mn content is 0.6%, and the lower limit of the more preferable Mn content is 0.7%. The upper limit of the preferable Mn content is 2.4%, and the lower limit of the more preferable Mn content is 2.3%.
[0037]
　P: 0.03% or less
　Phosphorus (P) is an impurity contained in steel. P segregates at the grain boundaries to reduce the toughness of the steel and lower the delayed fracture resistance. Therefore, the P content is 0.03% or less. The P content is preferably as low as possible, preferably 0.02% or less. An excessive reduction in P content leads to an increase in cost, so a preferable lower limit is 0.01%.
[0038]
　S: 0.01% or less
　Sulfur (S) is an impurity contained in steel. S forms sulfide to reduce the toughness of the steel and reduce the delayed fracture resistance. Therefore, the S content is 0.01% or less. The S content is preferably as low as possible, preferably 0.005% or less. An excessive reduction in the S content causes an increase in cost, so the preferable lower limit is 0.0001%.
[0039]
　sol. Al: 0.1% or less
　Aluminum (Al) is effective for deoxidizing steel. However, the excessive content of Al raises the Ac 3 points of the steel sheet and raises the heating temperature of the hot stamp, so that the evaporation of Zn in the plating layer is unavoidable. There is a possibility that the three Ac points of the steel will rise and the heating temperature during hot stamping will exceed the evaporation temperature of Zn in the plating layer. Therefore, the Al content is 0.1% or less. The upper limit of the preferable Al content is 0.05%, and the lower limit of the more preferable Al content is 0.01%. In this specification, the Al content is referred to as sol. It means the content of Al (acid-soluble Al).
[0040]
　N: 0.01% or less
　Nitrogen (N) is an impurity inevitably contained in steel. N forms a nitride and reduces the toughness of the steel. When boron (B) is further contained in the steel, N reduces the amount of solid solution B by combining with B and lowers hardenability. Therefore, the N content is 0.01% or less. The N content is preferably as low as possible, preferably 0.005% or less. An excessive reduction in N content leads to an increase in cost, so the preferable lower limit is 0.0001%.
[0041]
　B: 0 to 0.005%
　boron (B) enhances the hardenability of the steel and enhances the strength of the steel sheet after hot stamping, and may be contained in the base material. However, even if B is excessively contained, the effect is saturated. Therefore, the B content is set to 0 to 0.005%. The lower limit of the preferable B content is 0.0001%.
[0042]
　Ti: 0 to 0.1%
　titanium (Ti) can be combined with nitrogen (N) to form a nitride, and a decrease in hardenability due to BN formation can be suppressed. Further, Ti can improve the toughness of the steel sheet by making the austenite particle size finer when the hot stamp is heated due to the pinning effect. Therefore, Ti may be contained in the base material. However, even if Ti is excessively contained, the above effect is saturated, and if Ti nitride is excessively precipitated, the toughness of the steel is lowered. Therefore, the Ti content is set to 0 to 0.1%. The lower limit of the preferred Ti content is 0.01%.
[0043]
　Cr: 0 to 0.5%
　chromium (Cr) is effective in enhancing the hardenability of steel and increasing the strength of the hot stamped product, and may be contained in the base material. However, if the Cr content is excessive and a large amount of Cr carbides that are difficult to dissolve during hot stamping are formed, austeniticization of the steel is difficult to proceed, and conversely, the hardenability is lowered. Therefore, the Cr content is set to 0 to 0.5%. Further, the lower limit of the preferable Cr content is 0.1%.
[0044]
　Mo: 0 to 0.5%
　molybdenum (Mo) enhances the hardenability of steel and may be contained in the base material. However, even if Mo is excessively contained, the above effect is saturated. Therefore, the Mo content is set to 0 to 0.5%. The lower limit of the preferable Mo content is 0.05%.
[0045]
　Nb: 0 to 0.1%
　niobium (Nb) is an element that forms carbides to refine crystal grains during hot stamping and enhance the toughness of steel, and may be contained in the base material. However, if Nb is excessively contained, the above effect is saturated and the hardenability is further lowered. Therefore, the Nb content is set to 0 to 0.1%. The lower limit of the preferable Nb content is 0.02%.
[0046]
　Ni: 0 to 1.0%
　nickel (Ni) may be contained in the base material because embrittlement caused by molten Zn can be suppressed during heating of the hot stamp. However, even if Ni is excessively contained, the above effect is saturated. Therefore, the Ni content is set to 0 to 1.0%. The lower limit of the preferable Ni content is 0.1%.
[0047]
　The balance of the chemical composition of the base material constituting the hot stamp molded product according to the present embodiment is Fe and impurities. In the present specification, the impurity is a component that can be contained in ore or scrap as a raw material when a steel material is industrially manufactured, or a component that can be mixed due to a manufacturing environment or the like, and is a component of the present invention. It is an acceptable ingredient as long as it does not interfere with the effect. The optional additive element may be contained in the base material as the above-mentioned impurities.
[0048]
　1-3. About the metal layer 3
　(a) About the
　interface layer 31 The interface layer 31 is a layer in which the Al component in the plating layer is diffused to the base material (base iron) by heating of hot stamping and is bonded to Fe. It is composed of an intermetallic compound mainly composed of -Al (hereinafter, also simply referred to as "Fe-Al").
[0049]
　Fe—Al is an intermetallic compound having a fixed atomic ratio. The elemental composition ratio (mass%) of Fe—Al is Al: about 33% and Fe: about 67%. According to TEM (Transmission Electron Microscope) observation, the Al 3 Fe phase having a high Al concentration is formed on the polar surface layer of the interface layer 31 as microdepositions that do not form a layer, and the Fe 3 Al phase and the like are formed in the vicinity of the base metal. , May be formed as microprecipitates that do not form a layer. Then, when the layer is quantitatively analyzed at a magnification of about 5000 times using SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy) or the like, the Al content is 30.0 to 36.0%. It fluctuates in the range. Therefore, the Al content of the interface layer is in the range of 30.0 to 36.0%.
[0050]
　Depending on the chemical composition of the base material of the plated steel plate and the plating layer, a small amount of Zn, Mn, Ni, etc. may be dissolved in Fe—Al and contained in the intermetallic compound mainly composed of Fe—Al. Therefore, it can be said that the Fe-Al-based intermetallic compound contains Al: 30.0 to 36.0%, and the balance is substantially Fe. Here, "substantially" means allowing the inclusion of less than 3% of other components (eg, Zn, Mn, Si, and Ni).
[0051]
　Here, the interface layer serves as a barrier film of the base material and has a certain degree of corrosion resistance. Therefore, the interface layer prevents the elution of the ground iron during corrosion under the coating film, and the flow red rust generated from the cut scratches in the corrosion test or the like (specifically, the red rust that forms a drooping streak pattern from the cut scratches). ) Can be suppressed. In order to obtain such an effect, the thickness of the interface layer is set to 100 nm or more. However, if the interface layer is too thick, red rust formed from Fe—Al itself flows and becomes red rust, so the thickness of the interface layer is set to 5 μm or less. Therefore, the thickness of the interface layer is 100 nm or more and 5 μm or less. The lower limit of the thickness of the interface layer is preferably 500 nm, and the upper limit is preferably 2 μm in order to confirm a clear rust suppressing effect. The upper limit is more preferably 1 μm.
[0052]
(B) Regarding the main layer 32 With reference to
　FIGS. 4 and 5, the main layer 32 is a layer in which MgZn 2- phase 32a and island-shaped FeAl 2- phase 32b are mixed. The main layer 32 has an effect of suppressing the generation of scale during hot stamping, and is responsible for the corrosion resistance of the hot stamped molded product 20. The corrosion resistance of the hot stamp molded body 20 is the action of preventing red rust from being generated on the base material (base iron) by sacrificial corrosion protection of the main layer 32, and the adhesion between the main layer 32 and the coating film (not shown) of the upper layer. It is exerted by the action of ensuring the property and not expanding the rust range.
[0053]
　The state in which the MgZn 2- phase 32a and the island-shaped FeAl 2- phase 32b are mixed means that the island-shaped FeAl 2- phase 32b is dispersed (scattered) in the entire main layer 32. The specific state of the island-shaped FeAl two- phase 32b is shown in FIG. The island-shaped FeAl 2- phase 32b includes not only the island-shaped FeAl 2- phase 32b present alone but also a plurality of adjacent island-shaped FeAl 2- phase 32b aggregated.
[0054]
　The FeAl two- phase 32b of the present invention is characterized by having an island shape. The length obtained by projecting the FeAl 2- phase 32b onto the interface between the metal layer 3 and the base material 1 is 2d ( see 2d 1 , 2d 2 , 2d 3 , 2d 4 in FIG. 6 ), and the peripheral length of the FeAl 2- phase 32b. The relative peripheral length R was calculated from the measured 2d and L using the following equation, and the FeAl 2 phase having an R of 2 or more was regarded as an island shape.
R = L / 2d ≧ 2
[0055]
　The island-shaped FeAl 2- phase 32b does not grow in layers from the base iron side to the plating layer at the interface between the plating layer and the base iron, but nucleates and grows spherically in the plating layer. When observing the actual cross-sectional structure, the spherical phases are observed in contact with each other and fixed. Since the island-shaped FeAl 2- phase 32b grows in a spherical shape three-dimensionally, MgZn 2 inside the main layer is compared with the layered FeAl 2- phase at the interface between the plating layer / base iron formed by a normal manufacturing method. The contact area with the phase is large.
[0056]
　The details of the mechanism by which the island-shaped FeAl two- phase 32b is formed are not clear, but the following hypothesis is conceivable. The diffusion layer 12 (Fe 2 (Al, Zn) 5, etc.) of the plated steel sheet 10 before hot stamping of the present invention has a thin thickness of less than 1 μm and a small amount of Si solid dissolved in the diffusion layer 12. Therefore, the chemical bond is not very strong. Therefore, when the plated steel sheet 10 is manufactured, a small amount of Fe is dispersed in the plated layer 13 through the diffusion layer 12. Further, even during the heating of the hot stamp, Fe in the base metal passes through the diffusion layer 12 and diffuses into the plating layer 13 in the molten state. It is presumed that the trace amount of dispersed Fe in the plating layer binds to Al atoms and Zn atoms as nucleation sites during hot stamping and grows in an island shape.
[0057]
When the island-shaped FeAl 2 phase is formed, 0.05 to 0.5% of Fe is detected when the solution dissolved in the plating layer 13 before heating with fuming nitric acid is analyzed. On the other hand, in the case of the plated steel sheet 10a manufactured under normal conditions, the diffusion of Fe in the base metal does not reach the plated layer 13a in the molten state, and as a result, the interface layer 21a such as Fe 2 (Al, Zn) 5 It is considered that the obtained hot stamped molded product 20a will have a layered structure.
[0058]
　Since MgZn 2- phase 32a is an intermetallic compound, the component concentration is substantially constant from the atomic ratio, the Mg concentration is about 16.0%, and the Zn concentration is about 84.0%. However, in the MgZn 2 phase, Al may be dissolved in the range of 0 to 8.0% and Fe may be dissolved in the range of 0 to 5.0%, so that the Mg concentration is 13.0 to. It is defined in the range of 20.0% and the Zn concentration is defined in the range of 70.0-87.0%. The rest other than these components are impurities. Examples of impurities include 0 to 0.01% Ni and 0 to 0.01% Si.
[0059]
　Since the island-shaped FeAl 2- phase 32b is an intermetallic compound, the component concentration is substantially constant from the atomic ratio, and both the Al concentration and the Fe concentration are about 50.0%. However, since Zn may dissolve in the FeAl 2 phase in the range of 0 to 15.0%, the Al concentration is defined in the range of 40.0 to 55.0%, and the Fe concentration is defined as. It is defined in the range of 40.0 to 55.0%. The rest other than these components are impurities. Examples of impurities include 0 to 0.01% Ni and 0 to 0.01% Si.
[0060]
　By changing the FeAl 2- phase 32b from a layered state to an island-like state, the Al component in the MgZn 2- phase 32a in the metal layer is reduced, so that the continuous spotting property during spot welding is improved. This is because the Al component present in the MgZn two- phase 32a reacts with the Cu electrode of spot welding and significantly reduces the continuous dot property. Further, since the FeAl 2 phase is not layered but island-shaped, the invasion of molten Zn generated during hot stamping into the base material is suppressed, which has the effect of suppressing LME. However, if the amount of FeAl 2- phase 32b is simply increased, the corrosion resistance may be deteriorated, so the balance between the amount and morphology of FeAl 2- phase is important.
[0061]
The size of the 　island-shaped FeAl two- phase 32b is not particularly limited, but if it is too large, it may be unevenly distributed in the main layer 32. If the island-shaped FeAl two- phase 32b is unevenly distributed, it may adversely affect the corrosion resistance and chipping resistance. Therefore, it is preferable that the size of the island-shaped FeAl two- phase 32b is as small as possible, and that it is not unevenly distributed.
[0062]
　By containing MgZn two- phase 32a in the main layer 32, it is possible to suppress the occurrence of red rust in the hot stamp molded product. Generally, as the amount of MgZn two- phase increases, the corrosion resistance improves. Further, the MgZn two- phase 32a prevents the solid solution of Zn in the main phase layer and suppresses the generation of the liquid phase Zn during the heating of the hot stamp. The liquid phase Zn is also generated during spot welding and reacts with the Cu electrode to reduce the continuous spotting property. By allowing MgZn 2- phase 32a to exist in the main layer 32, it is possible to suppress the generation of liquid-phase Zn and also suppress the deterioration of continuous dotability. However, MgZn 2 if the amount of phase is too large, at the time of hot stamping, or plating layer is deposited on the mold, MgZn 2 is a possibility that the LME by region Zn concentration is high in the intra-phase is generated or generated is there.
[0063]
　Therefore, in the main layer 32, the volume fraction of FeAl 2- phase 32b is preferably 50.0 to 80.0%, and the volume fraction of MgZn 2- phase 32a is preferably 20.0 to 50.0%. Within this range, excellent corrosion resistance, spot weldability, LME property, and mold weldability can be easily obtained. The volume fraction of FeAl 2- phase 32b is preferably 60.0 to 75.0%, and the volume fraction of MgZn 2- phase 32a is preferably 25.0 to 40.0%.
[0064]
　If the thickness of the main layer 32 is less than 3 μm, the base metal (base iron) cannot be sufficiently protected during corrosion, so the thickness of the main layer 32 is set to 3 μm or more. When the thickness of the main layer 32 increases, the corrosion resistance tends to improve, but if it is too thick, the spot weldability is adversely affected, so the thickness of the main layer 32 is set to 40 μm or less. The lower limit of the thickness of the main layer 32 is preferably 6 μm, more preferably 10 μm. The upper limit of the thickness of the main layer 32 is preferably 30 μm, more preferably 25 μm.
[0065]
　(C) About the average composition of the
　metal layer 3 The metal layer 3 has the following average composition.
[0066]
　Al: 20.0 to 45.0%
　Al forms an interface layer 31 near the interface between the base material 1 and the metal layer 3 by heating during hot stamping, and forms FeAl 2- phase 32b in the main layer 32. This is an essential element for suppressing excessive diffusion of Fe from the base material 1 into the main layer 32. If the Al content in the metal layer 3 is too small, the thickness of the interface layer 31 becomes thin, Fe tends to diffuse from the base material 1 to the main layer 32, and the Fe content dissolved in the MgZn 2- phase 32a becomes high. It gets higher. It also reduces FeAl 2- phase 32b in the main layer 32 . As a result, spot weldability is deteriorated, LME is generated, and welding is generated during hot stamping. Therefore, the lower limit of the Al content in the metal layer 3 is set to 20.0%.
[0067]
　On the other hand, if the Al content in the metal layer 3 is too large, the concentration of Al that dissolves in the MgZn 2- phase 32a in the metal layer 3 becomes high, the sacrificial anticorrosion action is weakened, and the corrosion resistance under the coating film is lowered. There is a problem that the time until red rust occurs deteriorates. Therefore, the upper limit of the Al content in the metal layer 3 is 45.0%. The preferable lower limit of the Al content is 25.0%, and the more preferable lower limit is 29.0%. The preferred upper limit of the Al content is 44.0%, and the more preferable upper limit is 38.0%.
[0068]
　Fe:
　When the plated steel sheet is heated during hot stamping of 10.0 to 45.0% , Fe diffuses from the base material 1 to the metal layer 3, so that the metal layer 3 of the hot stamping compact 20 always contains Fe. .. Fe combines with Al in the metal layer 3 to form the FeAl two- phase 32b in the interface layer 31 and the main layer 32 . The Fe concentration in the metal layer 3 increases as the thickness of the interface layer 31 increases and the amount of FeAl 2- phase 32b in the main layer 32 increases. When the Fe concentration is low, the amount of FeAl two- phase 32b also decreases, so that the structure of the main layer 32 tends to collapse. Specifically, when the Fe concentration is less than 10.0%, the amount of MgZn 2- phase 32a in the main layer 32 tends to increase relatively, and the spot weldability and weldability tend to deteriorate. The lower limit of the Fe content of the metal layer 3 is 10.0%. On the other hand, when the Fe concentration is too high, the amount of FeAl 2- phase 32b increases and the MgZn 2- phase 32b in the main layer 32 decreases relatively, so that the structure of the main layer 32 collapses and the corrosion resistance tends to deteriorate. Therefore, the upper limit of the Fe content of the metal layer 3 is 45.0%. The lower limit of the Fe content of the metal layer 3 is preferably 20.0%, more preferably 27.0%, and even more preferably 32.5%. The upper limit of the Fe content of the metal layer 3 is preferably 42.0%, preferably 36.5%.
[0069]
　Mg: 2.0 to 10.0%
　Mg is an element effective for improving the corrosion resistance of the metal layer 3 and improving the swelling width under the coating film in the corrosion test. Further, Mg has an effect of suppressing LME cracking because it binds to the Zn component in the metal layer 3 to prevent the generation of liquid phase Zn during hot stamp heating. If the Mg concentration in the metal layer 3 is excessively low, the MgZn 2 phase is not formed and the solid solution Zn remains in the main layer 32, so that the possibility of LME occurring increases. Therefore, the Mg content is set to 2.0% or more. On the other hand, if the Mg content in the metal layer 3 is too large, sacrificial anticorrosion works excessively, and in the corrosion test, the coating film swelling width and the flow rust tend to increase rapidly. Therefore, the upper limit of the Mg content is 10.0%. The Mg content is preferably 3.0% or more, more preferably 3.5% or more.
[0070]
　Sb: 0 to 0.5%
　Pb: 0 to 0.5%
　Cu: 0 to 1.0%
　Sn: 0 to 1.0%
　Ti: 0 to 1.0%
　Sb, Pb, Cu, Sn and Ti , It is replaced with Zn in the metal layer 3 and forms a solid solution in the MgZn 2 phase, but if it is within a predetermined content range, it does not adversely affect the hot stamped molded product 20. Therefore, these elements may be contained in the metal layer 3. However, when the content of each element is excessive, oxides of these elements are precipitated when the hot stamp is heated, the surface properties of the hot stamp molded product 20 are deteriorated, and the phosphorylation treatment becomes poor. Corrosion resistance tends to deteriorate after painting. In addition, the time until red rust occurs in the corrosion test is shortened. Further, when the contents of Pb and Sn are excessive, the weldability and LME property are deteriorated. The content of Sb and Pb is 0.5% or less, and the content of Cu, Sn and Ti is 1.0% or less. The content of Sb and Pb is preferably 0.2% or less, and the content of Cu, Sn and Ti is preferably 0.8% or less, more preferably 0.5% or less.
[0071]
　Ca: 0 to 3.0%
　Sr: 0 to 0.5%
　Ca and Sr can suppress the formation of top dross formed on the plating bath during production. Further, since Ca and Sr tend to suppress atmospheric oxidation during the heat treatment of hot stamping, it is possible to suppress the color change of the plated steel sheet after the heat treatment. Since Sr is stronger than Ca, these effects are more effective with a small amount of Sr. In addition, if the content of these elements is excessive, the swelling width of the coating film and the flow rust are adversely affected in the corrosion test. Therefore, one or more selected from Ca and Sr may be contained in the metal layer 3 in the range of Ca content of 3.0% or less and Sr content of 0.5% or less. The Ca content is preferably 2.0% or less, more preferably 1.5% or less. The Sr content is preferably 0.3% or less, and more preferably 0.1% or less. In order to obtain the above effects, the Ca content is preferably 0.1% or more, and the Sr content is preferably 0.05% or more.
[0072]
　Cr: 0 to 1.0%
　Ni: 0 to 1.0%
　Mn: 0 to 1.0% In
　a plated steel sheet, Cr, Ni and Mn are concentrated near the interface between the plating layer and the base material and plated. It has the effect of eliminating spangles on the layer surface. These elements are replaced with Fe in the metal layer 3 of the hot stamped compact 20 and are contained in the interface layer 31 or form a solid solution in the FeAl 2 phase 32b in the main layer 32 . Therefore, one or more selected from Cr, Ni and Mn may be contained in the metal layer 3. However, when the content of these elements is excessive, the swelling width of the coating film and the flow rust increase, and the corrosion resistance tends to deteriorate. Therefore, the contents of Cr, Ni and Mn are set to 1.0% or less, respectively. The content of Cr, Ni and Mn is preferably 0.5%, more preferably 0.1% or less. The lower limit of the contents of Cr, Ni and Mn is preferably 0.01%.
[0073]
　Si: 0 to 1.0%
　Si is an element that greatly reduces the activity of Zn and Al in the molten state and greatly affects the diffusion of Fe and the elements constituting the metal layer 3 at the time of hot stamping. Therefore, Si may significantly disrupt the dispersed structure of FeAl 2- phase 32b , and therefore needs to be limited to an appropriate content. When the Si content in the metal layer 3 is excessive, the MgZn 2 phase 32a in the metal layer 3 decreases, and the Mg 2 Si phase is formed starting from the interface between the base metal and the metal layer, and the corrosion resistance is greatly deteriorated. To do. Further, due to the decrease of the MgZn two phase, the free Zn forms the Zn phase, so that LME may occur. Further, Si suppresses the diffusion of Fe into the metal layer 3 and inhibits the growth of the interface layer 31 and the growth of FeAl 2 phase 32b. Therefore, the Si content is preferably reduced as much as possible, and is 1.0% or less. The Si content is preferably 0.2% or less, more preferably 0%.
[0074]
　Remaining part: 12.0 to 45.0% of Zn and impurity
　metal layer 3 contains Zn from the viewpoint of rust prevention. Most of the Zn components contained in the metal layer 3 exist as MgZn two- phase 32a. On the other hand, since the Zn atom can be replaced with the Al atom, Zn can be dissolved in FeAl 2- phase 32b in a small amount . Therefore, when the amount of MgZn 2- phase 32a contained in the metal layer increases, the Zn concentration in the metal layer 3 also increases.
[0075]
　Here, high Zn content in the metal layer 3, Zn is MgZn 2 are present as a phase 32a, hot stamping body 20, when subjected to corrosion test, MgZn 2 white rust by elution phase 32a appear. On the other hand, the hot stamped compact having a low Zn content in the metal layer 3 and almost no Fe-free intermetallic compound such as MgZn 2 phase contains Fe in the metal layer when subjected to a corrosion test. The intermetallic compound corrodes, causing red rust. That is, whether white rust or red rust is generated during corrosion is closely related to the Zn content in the metal layer 3 and the presence of MgZn 2- phase 32a in the main layer 32 .
[0076]
　Specifically, when the Zn content in the metal layer 3 is 12.0% or more, white rust occurs in the corrosion test from the coating film cross-cut scratches, but the Zn content in the metal layer 3 is 12. If it is less than 0.0%, red rust will occur immediately. Therefore, the Zn content in the metal layer 3 is set to 12.0% or more. On the other hand, if the Zn content is too high, a Zn phase that does not react with Mg is precipitated in the metal layer 3. Precipitation of the Zn phase can cause LME, and as a result, can worsen the fatigue strength of the hot stamped article. Therefore, the Zn content is set to 45.0% or less. The preferable lower limit of the Zn content is 16.5%, and the more preferable lower limit is 18.5%. The preferable upper limit of the Zn content is 40.0%, and the more preferable upper limit is 32.0%.
[0077]
　As described above, the balance of the metal layer 3 is 12.0 to 45.0% Zn and impurities. As an impurity, any element other than the above may be contained within a range that does not interfere with the effects of the present invention.
[0078]
　1-4. Oxide layer 4 The
　oxide layer 4 may be formed on the outermost surface layer of the hot stamp molded product 20 according to the present embodiment by oxidation of a plating component. The oxide layer 4 is preferably thin because it may deteriorate the phosphorylation processability and electrodeposition coating property provided after hot stamping. If the thickness is 1.0 μm or less, the main performance of the metal layer 3 is not affected.
[0079]
　2. 2. About the plated steel sheet 10 The plated steel sheet 10
　used to obtain the hot stamped compact 20 according to the present embodiment will be described. With reference to FIG. 3, the plated steel sheet 10 used to obtain the hot stamped molded body 20 according to the present embodiment includes a diffusion layer 12 between the base material (base iron) 11 and the plating layer 13. Since the chemical composition of the base material 11 is the same as the chemical composition of the base material 1 of the hot stamp molded body 20 according to the present embodiment, the description thereof will be omitted. The diffusion layer 12 is a thin layer mainly composed of Fe 2 (Al, Zn). The plating layer 13 is a Zn—Al—Mg-based plating layer, and is not particularly limited as long as it forms the metal layer 3 having the above-mentioned chemical composition after hot stamping. As the plating layer 13, for example, a plating layer 13 having the following chemical composition can be used.
[0080]
　Zn: 17.0% or more
　Zn is an essential element for forming MgZn two- phase 32a in the main layer 32 of the hot stamping compact 20 according to the present embodiment , and its content is 17.0% or more. Is recommended.
[0081]
　Al: 10.0 to 70.0%
　Al is an essential element for forming an island-shaped FeAl two- phase 32b on the main layer 32 of the hot stamping compact 20 according to the present embodiment , and its content is It is recommended to set it to 10.0 to 70.0%.
[0082]
　Mg: 7.0 to 20.0%
　Mg is an essential element for forming MgZn 2- phase 32a in the main layer 32 of the hot stamping compact 20 according to the present embodiment , and its content is 7. It is recommended to set it to 0 to 20.0%. Mg in this range suppresses an excessive reaction between Zn, Al in a molten state or a mixture of Zn and Al and the base iron.
[0083]
　Fe: 0.05 to 2.0%
　Fe is recommended to have a content of 0.05% or more in order to precipitate island-shaped FeAl 2 phases during heating of the hot stamp . On the other hand, in order to suppress an excessive alloying reaction during hot stamping, the Fe content is preferably 2.0% or less. The Fe in the plating layer includes not only those contained in the plating bath but also those derived from the base material.
[0084]
　Si: 0 to 1.0% If
　the content of Si is too large, it reacts with Mg during hot stamping to form Mg 2 Si phase, and the corrosion resistance is greatly deteriorated. Therefore, the content is preferably 1.0% or less.
[0085]
　The plating layer 13 may further contain the following elements. The content of these elements hardly changes before and after hot stamping. Further, the range of the content of each element is the same as the description in the metal layer 3, and is therefore omitted.
　Sb: 0 to 0.5%
　Pb: 0 to 0.5%
　Cu: 0 to 1.0%
　Sn: 0 to 1.0%
　Ti: 0 to 1.0%
　Ca: 0 to 3.0%
　Sr: 0 to 0.5%
　Cr: 0 to 1.0%
　Ni: 0 to 1.0%
　Mn: 0 to 1.0%
[0086]
　The plating layer 13 may contain any element other than the above as an impurity as long as it does not interfere with the effects of the present invention.
[0087]
　The thickness of the plating layer 13 may be, for example, 3 to 50 μm. Further, the plating layer 13 may be provided on both sides of the steel sheet, or may be provided on only one side of the steel sheet.
[0088]
　3. 3. Method for Manufacturing Hot Stamp Mold 20
　Next, a method for manufacturing the hot stamp molded body 20 according to the present embodiment will be described. The method for producing a hot stamped body according to the present embodiment includes a step of preparing a base material (base material preparation step) and a step of forming a Zn—Al—Mg plating layer on the base material to prepare a plated steel plate (plating). A treatment step) and a step of hot stamping the plated steel plate (hot pressing step), and if necessary, a rust preventive oil film forming step and a blanking processing step are included. Hereinafter, each step will be described in detail.
[0089]
　[Base material preparation step]
　This step is a step of preparing the base material. For example, a molten steel having the above-mentioned chemical composition is produced, and the produced molten steel is used to produce a slab by a casting method. Alternatively, the ingot may be produced by the ingot method using the produced molten steel. Further, the base metal (hot rolled plate) is manufactured by hot rolling the manufactured slab or ingot. If necessary, the hot-rolled plate may be pickled and then cold-rolled, and the cold-rolled plate may be used as a base material.
[0090]
　[Plating process]
　This step is a step of forming a Zn—Al—Mg plating layer on the base material. In this step, a Zn—Al—Mg plating layer having the above-mentioned composition is formed on both surfaces of the base material. The amount of the plating layer adhered is preferably 170.0 g / m 2 or less per side . In this step, it is possible to perform various pre-plating such as Ni pre-plating and Sn pre-plating as an aid to plating adhesion, but since various pre-plating changes the alloying reaction, pre-plating The amount of adhesion is preferably 2.0 g / m 2 or less per side .
[0091]
　However, in order to prevent the diffusion layer 12a composed of Fe 2 (Al, Zn) 5 and the like from growing on the plated steel sheet, it is recommended to perform the plating treatment under the following conditions.
[0092]
　If the temperature of the plating bath is too high, the diffusion layer 12a such as Fe 2 (Al, Zn) 5 in the plated steel sheet grows to 1 μm or more, forming a thick interface layer on the hot stamped compact, and forming a layered metal layer. Formation cannot be avoided. Further, even if the temperature of the plating bath is reduced, the same problem occurs when the immersion time is too long. Therefore, it is preferable to reduce the plating bath temperature as much as possible, specifically, to limit the plating melt temperature to +5 to 20 ° C. and to limit the immersion time to 1 to 3 seconds. The diffusion layer 12 that grows between the base metal (base iron) 11 and the plating layer 13 under such conditions becomes a thin layer mainly composed of Fe 2 (Al, Zn) , with reference to FIG . The plated steel sheet 10 having such a diffusion layer 12 does not grow an interface layer composed of Fe 2 (Al, Zn) 5 or the like even if hot stamping is performed thereafter .
[0093]
　As described above, if the temperature of the plating bath is lowered and the immersion time is shortened, the growth of the diffusion layer 12 such as Fe 2 (Al, Zn) 5 , which will become a thick interface layer in the future, can be suppressed. However, if the penetration plate temperature is lower than the plating bath temperature, there is a concern that the plating bath will solidify and the cleanliness of the plating layer 13 will be impaired. On the other hand, if the penetration temperature is too high, there is a problem that the cooling rate is lowered and the diffusion layer 12 such as Fe 2 (Al, Zn) 5 grows thick. Considering these problems, the penetration plate temperature is preferably the plating bath temperature + 5 to + 20 ° C.
[0094]
　[Hot Pressing Step]
　This step is a step of slowly heating the above-mentioned plated steel sheet and then performing hot stamping. In this step, the plated steel sheet is heated mainly by energization heating (Joule heat) or radiant heat.
[0095]
　In the hot stamping process, first, the plated steel sheet is inserted into a heating furnace , the plated steel sheet is homogenized at 900 ° C., which is a temperature of 3 points or more of Ac of the steel sheet , then the plated steel sheet is taken out from the furnace, and the water-cooled jacket is immediately put on. By sandwiching it with the provided flat plate mold, it cools at the same time as press working. It takes about 5 seconds to take out the heated plated steel sheet from the furnace and start cooling, and the cooling is started when the temperature of the plated steel sheet is about 800 ° C. The cooling is performed so that the cooling rate up to the martensitic transformation start point (410 ° C.) is 50 ° C./sec or more even in the portion where the cooling rate of the plated steel sheet is slow.
[0096]
　Optimal conditions exist for the hot stamp heating process and retention time. The heating rate in the heating process is preferably 10 ° C./sec or higher, more preferably 30 ° C./sec or higher. By setting the rate of temperature rise to the above value or higher, it is possible to prevent excessive Fe from being supplied from the base iron into the plating layer. Further, for the same reason, the holding time for soaking heat is preferably 60 seconds or less at 900 ° C., more preferably 30 seconds or less.
[0097]
　By the above hot stamping step, a hot stamped compact can be obtained from the plated steel sheet. In the hot stamping process, the plated steel sheet is exposed to a high temperature, but the plating layer suppresses the oxidation of the base iron, so that scale formation can be suppressed. It is possible to change the shape of the hot stamped molded product by using various shapes such as a rectangular shape and a circular shape for the cooling mold.
[0098]
　In the above, the method for producing the hot stamped molded product according to the present embodiment has been described from the preparation of the base material of the plated steel sheet, but the present invention is not limited to the above description. For example, the hot stamped molded product according to the present embodiment can also be manufactured by hot stamping a plated steel sheet having a desired plating layer purchased from the market. In the following, the steps that can be arbitrarily selected in the manufacturing method are also described.
[0099]
　[Rust-preventive oil film forming step]
　This step is a step of applying rust-preventive oil to the surface of the plated steel plate for hot stamping to form a rust-preventive oil film after the plating treatment step and before the hot stamping step. If a long period of time has passed from the manufacture of the plated steel sheet for hot stamping to the hot stamping, the surface of the plated steel sheet may be oxidized. However, the surface of the plated steel sheet on which the rust-preventive oil film is formed by this step is difficult to oxidize, which suppresses the formation of scale. As a method for forming the rust preventive oil film, a known technique can be appropriately used.
[0100]
　[Blanking process] In
　this process, at least one of shearing and punching is performed on the hot stamped steel sheet after the rust preventive oil film forming process and before the hot stamping process to obtain the plated steel sheet. This is the process of processing into a specific shape. The sheared surface of the plated steel sheet after blanking is easily oxidized, but if a rust-preventive oil film is formed on the surface of the plated steel sheet in advance by the above-mentioned rust-preventive oil film forming step, the sheared surface of the plated steel sheet is also rust-proof. By spreading the oil to some extent, it is possible to suppress the oxidation of the plated steel sheet after the blanking process.
[0101]
　Although the hot stamp molded product according to the embodiment of the present invention has been described above, the above-described embodiment is merely an example of the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the design can be appropriately changed within a range not deviating from the gist thereof.
[0102]
　4. About the analysis method of the hot stamp compact 20
　Next, the analysis method of the metal layer in the hot stamp compact according to this embodiment will be described.
[0103]
　The thickness of each of the metal layer 3, the interface layer 31 and the main layer 32 of the hot stamped molded product 20 according to the present embodiment is obtained by cutting out a test piece from the hot stamped molded product 20, embedding it in a resin or the like, and then polishing the cross section. , It can be judged by measuring the length of the SEM observation image. Further, if the observation is carried out with a reflected electron image in the SEM, the contrast at the time of observation differs depending on the metal component, so that it is possible to identify each layer and confirm the thickness of each layer. If the interface between the interface layer 31 and the main layer 32 is difficult to understand and the thickness of the interface layer 31 is difficult to specify, line analysis is performed and the interface is located where the Al concentration is 30.0 to 36.0%. It may be specified as the interface between the layer 31 and the main layer 32. The same tissue structure is observed in three or more different visual fields, the average thickness in each visual field is calculated, and this is used as the thickness of each of the metal layer 3, the interface layer 31, and the main layer 32.
[0104]
　If the structure of the metal layer 3 has a spread, the thickness of each layer can be accurately grasped by using a mapping image or the like by EPMA (Electron Probe MicroAnalyzer). In addition, using an alloy whose components have been determined in advance, a calibration curve for quantitative analysis is created with a high-frequency glow discharge emission spectrometer (GDS), and the element intensity distribution in the depth direction of the target layer is grasped. By doing so, the thickness of each layer can also be determined. For example, in a GDS analysis of φ5 mm, the component in the place where the component strength in the depth direction becomes almost flat may be grasped, and the thickness of each layer may be determined by adopting the average value from the measurement results of 5 or more places. ..
[0105]
　The chemical composition of the entire metal layer 3 is as follows: The metal layer 3 is dissolved in an acid solution containing an inhibitor that suppresses corrosion of the base iron, and the exfoliation solution of the metal layer 3 is subjected to ICP (inductively coupled plasma) emission spectroscopy. It can be confirmed by measuring. In this case, what is measured is the total average component value of the interface layer 31 and the main layer 32. The average composition of the plating layer before heating can be confirmed by dissolving the plating layer with fuming nitric acid and measuring the stripping solution by ICP emission spectrometry. Here, the reason why fuming nitric acid is used is that if fuming nitric acid is used, the influence of the Fe—Al intermetallic compound remains without being dissolved, and the Fe concentration contained only in the plating layer can be measured. Because.
[0106]
The component values 　of MgZn 2- phase 32a and FeAl 2- phase 32b in the main layer 32 are preferably quantitatively analyzed by SEM-EDX, EPMA observation, or the like. In this case, it is preferable to carry out the quantitative analysis at a plurality of places having similar tissue structures and adopt the average value of these as the component value. In determining the components of each phase, it is preferable to adopt an average value of at least 10 points or more.
[0107]
The volume fraction 　of MgZn 2- phase 32a and FeAl 2- phase 32b in the main layer 32 can be calculated by performing computer image processing from the reflected electron image of the SEM of the main layer 32 in an arbitrary cross section. Usually, MgZn 2- phase 32a and FeAl 2- phase 32b have structures having significantly different contrasts in the reflected electron image, so that the area ratio of each phase may be simply measured by binarization. Specifically, MgZn 2 phase 32a and FeAl 2 volume fraction of phase 32b is at least 5 cross-section (5 fields) more MgZn from the reflected electron image of SEM 2 phases 32a and FeAl 2 measuring the area ratio of the phase 32b , The average of the measured area ratios is defined as the volume fraction of each phase in the main layer 32 as it is.
[0108]
　It is most preferable to evaluate the corrosion resistance of the metal layer 3 by using an exposure test that can obtain data suitable for the actual environment. However, since it takes time to evaluate high corrosion resistance plating, the corrosion resistance is evaluated by a corrosion acceleration test. You may. For example, the corrosion resistance can be evaluated by performing a salt spray test or a composite cycle corrosion test to determine the white rust generation status or the red rust generation status. Since the hot stamped molded product is often used by painting, the hot stamped molded product may be pre-painted for automobiles, and if necessary, the surface of the hot stamped molded product may be scratched. May be good.
[0109]
　Spot weldability is evaluated by performing a weld lobe test on a plated steel sheet that has been heat-treated equivalent to hot stamping using a spot welder to measure the appropriate current value, and then performing a continuous dot test. be able to. For example, the spot weldability can be evaluated by setting the nugget diameter at the start to 6 mm and measuring the number of hit points until the nugget diameter falls below 4√t (t is the thickness of the steel plate).
[0110]
　The occurrence of LME can be confirmed by observing the cracked portion from the metal layer 3 on the test piece subjected to the bending test after hot stamping. Specifically, the hot stamped molded product is immediately subjected to a V-bending test or the like, the test piece subjected to the V-bending test is embedded in a resin or the like, the surface is polished, and the cracked portion from the metal layer 3 is observed for confirmation. Can be done. At the same time, by observing the mold used in the bending test, it is possible to determine whether or not the plating layer is welded during hot stamping.
[0111]
It was determined that the 　FeAl 2 phase was island-shaped by the following procedure .
(1) as described above, FeAl 2 in the same manner as in the measurement of the area ratio of phase, all the contour FeAl recognizable in the main layer 32 in 2 recognizes the phase 32b from the reflected electron image of SEM. At this time, the measurement target was one having a circle-equivalent diameter of 100 nm or more calculated from the area of the FeAl two- phase. FeAl 2 phases less than 100 nm have no substantial effect on performance and are ignored.
(2) The length 2d obtained by projecting the FeAl 2- phase 32b onto the interface between the metal layer and the base material, and the contour line (peripheral length) L of the FeAl 2- phase were measured. When a plurality of adjacent island-shaped FeAl 2 phases were aggregated , 2d and L of the respective FeAl 2 phases constituting the aggregate were measured.
(3) Then, the measured 2d and L were applied to the equation R = L / 2d to calculate the R value.
(4) As described above, as in the measurement of the area ratio of FeAl 2- phase 32, from the reflected electron images of SEM having at least 5 cross sections (5 fields of view), 5 or more per cross section, for a total of 50 or more FeAl 2.The R value of phase 32b was measured. Then, the average of the measured R values ​​was taken as the R value of FeAl 2- phase 32 in the main layer 32.
(5) When R = 2.0 or more, FeAl 2- phase 32b was considered to be island-shaped. On the other hand, when FeAl 2- phase 32b is less than 2.0, FeAl 2- phase 32b is considered to be layered. When the FeAl 2- phase 32b was less than 2.0, the FeAl 2- phase 32b was in almost the same state as the conventional hot stamped body, and the FeAl 2- phase 32b that could be used for measuring the R value was very small.
Example
[0112]
　Hereinafter, the present invention will be specifically described with reference to Examples. The present invention is not limited to the following examples.
[0113]
　First, a base material constituting the hot stamp molded body was prepared. That is, a slab was produced by a continuous casting method using molten iron containing the chemical composition shown in Table 1 and having the balance of Fe and impurities. Next, the slab was hot-rolled to produce a hot-rolled steel sheet, the hot-rolled steel sheet was further pickled, and then cold-rolled to produce a cold-rolled steel sheet. The manufactured cold-rolled steel sheet was used as a base material (thickness: 1.4 mm or 0.8 mm) of a plated steel sheet used for hot stamping.
[0114]
[table 1]

[0115]
　Next, using the manufactured base material, using a batch hot-dip galvanizing apparatus manufactured by Resca, and using a plating bath containing the components shown in Tables 2 and 3, under the conditions shown in Tables 4 and 5. A plated steel sheet was manufactured. In addition, No. Comparative examples of 45 and 46 are an Al alloy plated steel sheet and an alloyed galvanized steel sheet, which are conventionally used as plated steel sheets for hot stamping, respectively. Specifically, No. A comparative example of No. 45 is an Al-10% Si alloy plated steel sheet, No. 45. A comparative example of 46 is a Zn-11% Fe alloyed galvanized steel sheet.
[0116]
　For hot stamping, the furnace temperature of the heating furnace is set to 900 ° C., which is the temperature of three or more points of Ac of the steel sheet , the plated steel sheet is charged into the heating furnace, heated at 900 ° C. It was carried out by pressing with. Two types of hot stamping were carried out by changing the heat treatment conditions.
[0117]
　In the heat treatment A, the heating method of the hot stamp is energization heating, both ends of the steel sheet are sandwiched between electrodes, the temperature is raised from room temperature to 900 ° C. at 50 ° C./sec, held for 30 seconds, and then the steel sheet is removed from the heating furnace. A hot stamped molded body was manufactured by taking it out and immediately sandwiching the steel plate in a flat plate mold equipped with a water-cooled jacket and hot stamping. At this time, the oxygen concentration in the furnace was controlled to less than 18% by carrying out a nitrogen flow in the heating furnace.
[0118]
　In the heat treatment B, the heating method of the hot stamp is radiant heat heating in an open-air furnace, the temperature is raised from room temperature to 900 ° C. in 120 seconds at 5 to 10 ° C./sec, held for 60 seconds, and then from the heating furnace. A hot stamped molded body was manufactured by taking out the steel plate and immediately sandwiching the steel plate in a flat plate mold equipped with a water-cooled jacket and hot stamping.
[0119]
　The cooling conditions are the same for both heat treatments A and B, and quenching is controlled so that the cooling rate is 50 ° C./sec or more up to the martensitic transformation start point (410 ° C.) even in the part where the cooling rate is slow. did. Further, if necessary, a sample was cut out from the hot stamp molded product.
[0120]
[Table 2]

[0121]
[Table 3]

[0122]
[Table 4]

[0123]
[Table 5]

[0124]
　A cut plate sample was cut out from the produced hot stamped product, plated and peeled off, and the chemical composition of the metal layer of the hot stamped product was measured. In addition, the thickness of the interface layer and main layer is measured by embedding the cutting plate with resin and quantitative analysis is performed by SEM-EDX or EPMA analysis , and the components of Al 2 Fe phase and Mg Zn 2 phase are quantified. analyzed. The results are shown in Tables 6-9.
[0125]
[Table 6]

[0126]
[Table 7]

[0127]
[Table 8]

[0128]
[Table 9]

[0129]
　The performance of the hot stamp molded product is shown in Tables 10 and 11. The test method for each performance is as follows.
[0130]
　[Hot V-bending test] In
　order to examine the LME property, a plated steel sheet (50 mm × 50 mm × 1.4 mm) before hot stamping was placed in a heating furnace and heated to 900 ° C. The furnace temperature of the heating furnace was set to 900 ° C., which is the temperature of three or more points of Ac of the steel plate .
[0131]
　Next, the steel sheet was taken out from the heating furnace, and immediately hot V-bending was performed using a large press. The time from the start of taking out the steel sheet from the heating furnace to the start of processing the steel sheet was set to 5 seconds. After processing, the mixture was quenched to a martensitic transformation start point (410 ° C.) at a cooling rate of 50 ° C./sec or higher. The shape of the mold is such that the outer portion of the bending radius due to the V bending process is extended by about 15% at the end of the bending process.
[0132]
　The presence or absence of liquid metal embrittlement cracking (LME) was confirmed by observing the cross section of the V-bent portion in the thickness direction of the steel sheet using an SEM and a reflected electron detector and confirming the reflected electron image.
[0133]
　The cross section of the V-bent processed portion was observed and evaluated as follows. Those in which no cracks have occurred and those in which cracks have occurred but whose termination is in the main layer are defined as "AAA" (best). When the end of the crack is in the interface layer, it is defined as "A" (good). Those in which cracks reach the base material are designated as "B" (defective). Then, the evaluation "A" or higher was passed. The results are shown in Tables 10 and 11.
[0134]
　At the same time, the same V-bending test was repeated 100 times. After each test, the plating adhesion (welding) to the mold used in the hot V-bending test was confirmed, and if even a slight welding was confirmed on the mold, it was judged to be welded. A case where the occurrence rate of welding is 0% is evaluated as "AAA" (best), and a case where the occurrence rate of welding is 0 to 5% is evaluated as "A" (good), and the occurrence rate of welding is 5. When it was% or more, it was evaluated as "B" (defective). Then, the evaluation "A" or higher was passed. The results are shown in Tables 10 and 11.
[0135]
　[Corrosion test]
　Next, the surface of the hot stamped molded product (plate-shaped 100 x 50 mm) is adjusted at room temperature for 20 seconds using a surface adjusting agent (trade name: Preparen X) manufactured by Nihon Parkerizing Co., Ltd. It was. Next, the surface-adjusted hot stamped body was subjected to phosphate treatment using a zinc phosphate treatment solution (trade name: Palbond 3020) manufactured by Nihon Parkerizing Co., Ltd. Specifically, the temperature of the treatment liquid was set to 43 ° C., and the hot stamp molded product was immersed in the treatment liquid for 120 seconds. As a result, a phosphate film was formed on the surface of the steel plate of the hot stamp molded product.
[0136]
　After performing the above-mentioned phosphate treatment, a cationic electrodeposition paint manufactured by Nippon Paint Co., Ltd. was electrodeposited on the plate-shaped hot stamp molded body of each test number by energizing a slope with a voltage of 160 V. Further, baking was performed at a baking temperature of 170 ° C. for 20 minutes. The average film thickness of the paint after electrodeposition coating was 15 μm for all the samples.
[0137]
　The red rust resistance was evaluated by making a cross cut in the hot stamped molded product after coating until it reached the steel material and performing a composite cycle corrosion test (JASO M609-91). As a specific evaluation method, evaluation was made based on the time until red rust occurred. Those with red rust at 30 cycles of the above composite cycle corrosion test are evaluated as "B" (defective), those with red rust at 60 cycles are evaluated as "A" (slightly good), and 90 cycles. Those with red rust at that time were evaluated as "AA" (good), and those without red rust even after 150 cycles were evaluated as "AAA" (best). Then, the evaluation "A" or higher was passed. The results are shown in Tables 10 and 11.
[0138]
　Further, at 120 cycles of the above composite cycle corrosion test, the maximum swelling width of the coating film from the cut scratch was calculated by averaging 8 points around the cross cut, and the swelling property of the coating film was evaluated. Those having a coating film swelling width of 3 mm or more at 120 cycles are evaluated as "B" (defective), and those having a coating film swelling width of 2 mm to 3 mm are evaluated as "A" (good), and the coating film swelling width is evaluated. Those with a value of less than 2 mm were evaluated as "AAA" (best). Then, the evaluation "A" or higher was passed. The results are shown in Tables 10 and 11.
[0139]
　In addition, at the 120th cycle of the above composite cycle corrosion test, the flow rust (rust dripping width) from the tip of the coating film swelling part to the tip of the rust adhesion part is calculated by averaging 8 points around the cross cut, and the flow rust width is measured. did. Those with a flow rust width of 5 mm or more at 120 cycles are evaluated as "B" (defective), those with a flow rust width of 3 mm to 5 mm are evaluated as "A" (good), and the flow rust width is less than 3 mm. Was evaluated as "AAA" (best). Then, the evaluation "A" or higher was passed. The results are shown in Tables 10 and 11.
[0140]
　[Spot Welding]
　Next, in order to confirm the continuous spotting property of the hot stamped compact, a sample (0.8 mm plate) having a main layer thickness of 25 μm was prepared in the hot stamped compact.
[0141]
　Welding conditions were 1860 N pressing force, 30 cycles of squeeze time, 3 cycles of upslope, 7 cycles of energization time, 25 cycles of hold time, electrodes used: Obara DHOM type, and 20 pre-strike points. The nugget diameter was measured by peel peeling, and the button diameter was evaluated as the nugget diameter. In the case of different diameters, the average value of the major and minor diameters was taken as the nugget diameter. For the current value of continuous striking points, a weld lobe test was carried out in advance under the same welding conditions, and a current value having a nugget diameter of 6 mm was adopted. Under the above conditions, continuous hitting was performed until the hitting point where the average nugget diameter was 3.8 mm or less.
[0142]
　Those with less than 100 points in a row are evaluated as "B" (defective), those with a number of points in a row of 100 to 200 are evaluated as "A" (slightly good), and those with a number of points in a row of 200 or more. Those with 1000 points or more were evaluated as "AA" (good), and those with 1000 points or more in continuous hits were evaluated as "AAA" (best). Then, the evaluation "A" or higher was passed. The results are shown in Tables 10 and 11.
[0143]
[Table 10]

[0144]
[Table 11]

[0145]
　With reference to Tables 2 to 11, it can be seen that the hot stamp molded article of the invention example is excellent in fatigue characteristics, spot weldability, and corrosion resistance.
[0146]
　On the other hand, the hot stamp molded product of the comparative example includes a "B" (defective) evaluation in the evaluation items of fatigue characteristics, spot weldability, and corrosion resistance, and is any of fatigue characteristics, spot weldability, and corrosion resistance. One or more results were unsatisfactory.
Description of the sign
[0147]
10 Plated steel plate
11 Base material
12a Diffusion layer
13a Plating layer　
20 Hot stamp molded body according to this embodiment
1 Steel base material (base material)
3 Metal layer
31 Interface layer
32 Main layer
32a MgZn 2 phase
32b FeAl 2 phase
4 Oxide Layer
10a Plated steel plate manufactured under normal conditions
11a Base material
12a Diffusion layer
13a Plating layer　
20a Normal hot stamping molded body
1a Base material
2a Surface layer
21a Interface layer
21b Metal layer
4a Oxide layer
The scope of the claims
[Claim 1]
　A
　hot stamped body comprising a steel base material and a metal layer formed on the surface of the steel base material,
　wherein the metal layer contains Al: 30.0 to 36.0% in mass%. The thickness is 100 nm to 5 μm, the interface layer located at the interface with the steel base material, the MgZn 2 phase and the island-shaped FeAl 2 phase are mixed, and the thickness is 3 μm to 40 μm, and the thickness is on the interface layer. The
　metal layer is provided with a located main layer, and the average composition of the metal layer is, in
terms of mass%, Al: 20.0 to 45.0%,
Fe: 10.0 to 45.0%,
Mg: 2.0 to 10. 0%,
Sb: 0 to 0.5%,
Pb: 0 to 0.5%,
Cu: 0 to 1.0%,
Sn: 0 to 1.0%,
Ti: 0 to 1.0%,
Ca: 0 to 3.0%,
Sr: 0 to 0.5%,
Cr: 0 to 1.0%,
Ni: 0 to 1.0%,
Mn: 0 to 1.0%,
Si: 0 to 1.0 %,
Remaining: 12.0 to 45.0% Zn and impurities, and in the
　main layer, the MgZn 2The phase contains
Mg: 13.0 to 20.0%,
Zn: 70.0 to 87.0%,
Al: 0 to 8.0%,
Fe: 0 to 5.0% in mass% .
　In the main layer, the FeAl 2 phase is hot , containing
Al: 40.0 to 55.0%,
Fe: 40.0 to 55.0%, and
Zn: 0 to 15.0% in mass%.
Stamp molded body.
[Claim 2]
　In the main layer,
　the FeAl 2 volume fraction of the phases is the 50.0 to 80.0%,
　the MgZn 2 volume fraction of phase is 20.0 to 50.0%,
according to claim 1 Hot stamp molded body.
[Claim 3]
Claim 1 or 2 in which the volume fraction of the
　FeAl 2 phase is 60.0 to 75.0% and the volume fraction of the
　MgZn 2 phase is 25.0 to 45.0% in the 　main layer.
The hot stamp molded body described in.