0001]The present invention relates to high-strength one preferred hot stamping alloyed Al-plated steel sheet for hot stamping method is the molding method member is obtained and hot stamping member.
BACKGROUND
[0002]In the field of transportation machinery such as automobiles, efforts to that body mass reduction by the use of high strength materials has been actively conducted. That is, in recent years, there is a tendency that the vehicle body mass increases with the mounting of the crash safety and new functions. The body mass increased by offsetting of being advocated is possible to improve the fuel efficiency as much to reduce carbon dioxide emissions. For this reason, in the field of transportation machinery such as automobiles, the amount of high-strength steel sheet has been increasing steadily.
[0003]
　It has become in a stream of expanded use of such high-strength steel sheets a large obstacle is unavoidable when increasing the strength of the steel sheet, a manifestation of the phenomenon called "shape fixability deteriorates." This phenomenon is due to the high strength of the steel sheet, by the spring back amount in the product after the plastic working is increased, which is a general term for that is not easy to obtain the shape of the aim. To resolve this behavior, low strength material (shape fixability is excellent, or not problematic material) the additional unnecessary and a machining process (e.g., restriking) and go to, or change the product shape It is being carried out. However, a problem is forced to change from a cost and an increase in the desired design shape due to the increased number of steps have occurred in these solutions.
[0004]
　One way to solve these problems have led to hot forming method called hot stamping method is noted. Hot stamping method, the steel sheet (workpiece blank) after a predetermined temperature (generally a temperature at which the austenite phase) to lower the strength by heating (i.e., to facilitate molding), the workpiece a method of molding a mold of a low temperature (e.g., room temperature) compared to. By employing a hot stamping method, and at the same time easily impart shape to the product, it is possible to perform the quenching heat treatment using the temperature difference between the steel sheet and the mold (quenching) to ensure the strength of the product after molding . Such hot stamping method has recently led to its usefulness is widely recognized, and application also been increasing steadily.
[0005]
　On the other hand, due to the expanded use of hot stamping method, a weak point of the hot stamping method that has not been a problem to be low productivity This has come to be recognized as an issue that you want to by all means resolved. For example, when considering that one produce parts in one pressing step from a single blank (1 stroke), if the cold pressing method is a conventional method, a quite easy to press the one per second it is. Productivity for this example, 60 stroke per minute, are often referred to as short 60 spm.
[0006]
　On the other hand, in the hot stamping method, mainly by two factors: the productivity of the case, which was represented in the same notation there is a problem that at most only 2,3spm. One factor is that it takes time to heat the blank to a predetermined temperature. Another one of the factors, in order to ensure the cooling of the workpiece after forming (pressing) in a mold, is that often holds a predetermined time in the bottom dead center.
[0007]
　One means for improving the low productivity of such hot stamping method, there is a method of rapidly heating the blank. The method of low productivity caused the hot stamping method described above, is intended to improve the factors mentioned above the former. Although the rapid heating process of the blank there are various methods, electric heating methods Among them, the equipment has begun to be used by some producers because it does not become too big.
[0008]
　For example, Patent Document 1, fitted with two end portions each one point or more electrodes of the metal plate in a mold, by applying a current between the electrodes was heated metal plate to a predetermined processing temperature by Joule heat after hot press forming method and performing press molding is disclosed.
[0009]
　Incidentally, when the corrosion resistance is required for components after molding, the use of the Al-plated steel sheet as a blank can be mentioned as an option. When heating the Al-plated steel sheet by conduction heating method, it is necessary to contact the electrode for energizing the steel sheet. Electrode is generally is made of copper or copper alloy, and is water cooled during energization. Therefore, even when subjected to electrical heating, in a portion where the electrode is in contact of the Al-plated steel sheet, Al-plated layer is not heated to a temperature such that the Al-Fe alloy. Thus, the hot stamping method, so that this portion remains of the press-molded product of unalloyed state (hot stamping product) is produced.
　Unalloyed portion of the Al plating, there is a problem that poor spot weldability. That is, when the continuously performed spot welded to unalloyed portions of the Al plating, Al is deposited on the electrodes for welding, there is a problem called must frequently perform its removal. In other words, that there is unalloyed portions of the Al coating present in hot stamp products, (leading to a decrease in yield) that does not use the portion, to part design as it is not necessary to weld the portion (the degree of freedom in design there is limited), or inefficient welding step for receiving (productivity is lowered), and said selection there is a problem that is faced.
[0010]
　Against these problems, Patent Document 2, the Al plated steel sheet, and heat treatment using a box annealing furnace, the Al plating layer alloyed steel (hereinafter, referred to as alloyed Al-plated steel sheet) and after the hot stamping how to provide is disclosed. If this method, spot weldability problems unalloyed Al plating layer is also eliminated. However, there are concerns about the compatibility of fatigue properties and corrosion resistance for annealing is required over time it can not be expected the improvement of productivity.
CITATION
Patent Document
[0011]
Patent Document 1: Japanese Patent 2002-18531 JP
Patent Document 2: Japanese Patent 2011-137210 JP
Summary of the Invention
Problems that the Invention is to Solve
[0012]
　Alloyed Al-plated steel sheet in advance Al plating layer was alloyed, since it corresponds to the rapid heating of the hot stamping method is effective steel to enhance the productivity of the hot stamping method. In addition, application of alloyed Al-plated steel sheets in the field of transportation equipment and transportation vehicles such as automobiles, which tends to increase, the steel sheet comprising also other fatigue characteristics of the corrosion resistance is desired. That is, as long as the alloyed Al-plated steel sheet for hot stamping and excellent fatigue characteristics and corrosion resistance, applicable range is also wider.
　However far, in alloyed Al-plated steel sheet for hot stamping it has not been studied associated with alloyed plating layer and the corrosion resistance and fatigue properties. Therefore, development of a steel sheet for hot stamping has been desired which can both corrosion resistance and fatigue properties.
[0013]
　The present invention has been devised in view of such circumstances, an excellent hot stamp member in corrosion resistance and fatigue characteristics, a suitable hot stamping alloyed Al-plated steel sheet in order to produce a hot stamping it is an object of the present invention to provide.
　Further, the present invention aims to provide an excellent hot stamp member in corrosion resistance and fatigue properties.
Means for Solving the Problems
[0014]
　The present inventors focused on the usefulness of alloyed Al-plated steel sheet as a hot stamp, were studied to provide a fatigue properties and excellent alloyed Al-plated steel sheet in corrosion resistance after hot stamping.
　The present inventors firstly, the alloyed Al-plated steel sheet fabricated in a number of alloying heat treatment conditions were subjected to hot stamping experiment. The individual properties of the obtained hot stamp after hot stamping member were examined in association with the phase structure of the Al-Fe alloy layer.
　As a result, the strength and ductility of the hot stamping member is not affected by the alloying conditions Al plating layer, namely the strength and ductility of the hot stamping member does not depend on the phase structure and morphology of the alloyed Al plating layer it was found. On the other hand, the fatigue characteristics and corrosion resistance of the hot stamping member has been found to be dependent on the phase structure and morphology of the alloyed Al plating layer alloyed Al-plated steel sheet before hot stamping.
　And further a result of extensive studies, revealed phase structure and morphology of excellent fatigue characteristics and corrosion resistance can be obtained alloyed Al plating layer. Further, newly found also alloying conditions for obtaining such a steel plate.
　The present invention was completed based on this new knowledge, its gist is as follows.
[0015]
(1) As the steel composition, by
mass%,
C: 0.18 ~
0.36%, Si: 0.02 ~ 0.5%, Mn: 1.2
~ 2.2%, P: 0.001 ~
%
0.03,
S: 0.0001 ~ 0.02%, Cr: 1.1 ~
2.1%, N: 0.001 ~ 0.01%, Ti: 0.01 ~
0.5%, Al :
0.01 ~ 0.1%, B: 0.0001 ~ 0.01%
containing the balance Fe, and a steel sheet of the impurity,
　the thickness of 15μm or more Al formed on the surface of the steel sheet comprising a -Fe alloy layer, and
　the Al-Fe alloy layer, Fe 45 to 85%, include Fe-Al-based alloy phase containing Si 4 ~ 13% perpendicular to the surface of the steel sheet the Fe-Al-based hot stamping alloyed Al plating alloy ratio phase length occupied 50% or less than 10% at a top surface of the cross section Plate.
(2) as the steel components, in mass%,
further, Nb: 0.01 ~ 1.0%
hot stamping alloyed Al-plated steel sheet according to contain (1).
(3) (1) or hot stamping steel sheet according to (2), after heating to a temperature at least part of the austenite phase, by a mold, the molding and quenching in the same step the resulting hot stamp member by performing.
(4) as the steel composition, by
mass%,
C: 0.18 ~
0.36%, Si: 0.02 ~ 0.5%, Mn: 1.2
~ 2.2%, P: 0.001 ~
%
0.03,
S: 0.0001 ~ 0.02%, Cr: 1.1 ~
2.1%, N: 0.001 ~ 0.01%, Ti: 0.01 ~ 0.5%,
Al :
0.01 ~ 0.1%, B: 0.0001 ~ 0.01%
containing the balance Fe, and a steel formed of impurity,
　the thickness of 15μm or more Al formed on the surface of the steel material comprising a -Fe alloy layer, and
　the Al-Fe alloy layer, Fe 45 to 85%, include Fe-Al-based alloy phase containing Si 4 ~ 13% perpendicular to the surface of the steel sheet hot stamping member ratio of the Fe-Al system alloy phase occupied length is 50% or less than 10% at a top surface of the cross section.
(5) as the steel components, in mass%,
further, Nb: 0.01 ~ 1.0%
hot stamp member according to contain (4).
The invention's effect
[0016]
　According to the present invention, the hot stamp member having excellent corrosion resistance and fatigue characteristics can provide a suitable hot stamping alloyed Al-plated steel sheet in order to produce by hot stamping.
　Further, the present invention can provide an excellent hot stamp member in corrosion resistance and fatigue properties.
　In particular, according to the hot stamping alloyed Al-plated steel sheet of the present invention, even when employing a rapid heating method such as electrical heating for heating for hot stamping, fatigue properties and corrosion resistance superior stamp products ( hot stamp member) can produce. Further, (those conducting the hot stamping) parts manufacturer is not a heating means using conventional annealing furnace, it is possible to use a rapid heating means such as electrical heating, it is possible to increase the stamp article productivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017]
[1] Hot stamping the steel sheet after alloying heat treatment of (alloyed Al-plated steel sheet), the surface and the cross section perpendicular, A phase in the uppermost surface of the Al-Fe alloy layer (Fe 45 to 85% of Si 4 the length of ~ 13% content to Fe-Al system alloy phase), which is a schematic view illustrating a length ratio of the a phase to the uppermost surface of the Al-Fe alloy layer.
FIG. 2 is a schematic diagram of the temperature history of the alloying heat treatment.
Is a diagram illustrating a FIG. 3 fatigue test piece. Unit of the values in the figure are in mm.
In [4] Example 1 is a graph showing the relationship between the value of the middle part of equation (1) when the Cr concentration and the A phase ratio in the steel became 50%.
Is a schematic perspective view of FIG. 5 hat hot stamping member. Unit of the values in the figure are in mm.
DESCRIPTION OF THE INVENTION
[0018]
　Alloyed Al-plated steel sheet for hot stamping according to the present invention comprises steel plates and, the Al-Fe alloy layer thickness 15μm or more formed on the surface of the steel sheet. Steel plate, as a steel component, in mass%, C: 0.18 ~ 0.36%, Si: 0.02 ~ 0.5%, Mn: 1.2 ~ 2.2%, P: 0.001 ~ 0.03%, S: 0.0001 ~ 0.02%, Cr: 1.1 ~ 2.1%, N: 0.001 ~ 0.01%, Ti: 0.01 ~ 0.5%, Al : 0.01 ~ 0.1%, B: contains 0.0001 to 0.01% or the balance Fe, and a steel sheet composed of impurities. Below, there is a case to say the steel sheet as a base material. In addition, the Al-Fe alloy layer, the Fe 45 ~ 85%, include Fe-Al-based alloy phase containing Si 4 ~ 13%. In the following description may be referred to as "Fe a 45 ~ 85%, Fe-Al-based alloy phase containing Si 4 ~ 13%" the A phase. Also, of the alloy phase or the metal phase included in the Al-Fe alloy layer, which may refer to phase other than A-phase and B-phase. A phase Al-Fe alloy layer, when viewed Al-Fe alloy layer on the surface and the cross section perpendicular of the steel sheet, the length ratio of the occupied by the A phase in the uppermost surface of the Al-Fe alloy layer, 10 % or more has become 50% or less.
[0019]
　It will be described in detail below hot stamping alloyed Al-plated steel sheet of the present invention. In the following description, the alloyed Al-plated steel sheet for hot stamping, sometimes also referred to as a hot stamping steel plate.
　First, the chemical components of the steel sheet as a base material of the hot stamping steel sheet will be described. Incidentally,% notation unless otherwise noted refers to mass%.
[0020]

　C is the most important element in terms of strengthening the hot stamp member by a hot stamping method. To obtain a strength of about at least 1500MPa in hot stamp member, it is necessary to include C or above 0.18%. Preferably to contain C or above 0.2%. On the other hand, C weight can not be ensured weldability and toughness 0.36 percent. Therefore C amount is the upper limit 0.36%. Preferably, the 0.32% the upper limit of C content.
[0021]
Si adversely affects the Al plating resistance by forming an oxide film on the surface of the steel sheet during annealing of a steel sheet after cold rolling. However, its content is the effect equal to or less than 0.5% is acceptable. Preferably not more than 0.3%. Meanwhile, reducing the Si to less than 0.02% since overloading the steel making process, limited to 0.02% or more. Is preferably 0.05% or more.
[0022]
Mn is a very important element to ensure the hardenability of the hot stamp material at the time of hot stamp, the addition of more than 1.2% in order to obtain the effect is necessary. Preferably 1.4% or more. On the other hand, the upper limit of 2.2% because there is a possibility to degrade the mechanical properties due to solidification segregation and is contained by more than 2.2% of Mn. Preferably 2.0% or less.
[0023]

　P is an impurity, must be restricted to 0.03% or less because an adverse effect on hot workability. Preferably limited to 0.02% or less. On the other hand, it may be the lower limit 0.001% because reducing unnecessarily P multiplies a heavy load on the steel making process.
[0024]

　S is an impurity, hot workability and ductility, must be limited to 0.02% or less because an adverse effect on the mechanical properties such as toughness. Preferably limited to 0.01% or less. On the other hand, it may be the lower limit 0.0001% so reducing unnecessarily apply a heavy load to the steel making process.
[0025]
Cr has the effect of suppressing the nitridation reaction competing reactions of Al when Al-Fe alloying an Al plating layer (formation of AlN). Particularly it becomes clear that the effect by the addition of more than 1.1% of Cr, increases the adhesiveness of the base material and the plated layer. Therefore, Cr content is set to 1.1% or more. Preferably 1.2% or more. On the other hand, the even if added over 2.1% of Cr effect is saturated, the upper limit of 2.1% because only increases the production cost. Preferably 2.0% or less. The Cr has also been found possible to influence the phase structure and mode of forming an alloy layer also affects the diffusion behavior of Fe.
[0026]

　N, because having an action would reduce the contribution of combined with B to hardenability of B, it is desirable to reduce as much as possible. However performs addition of below-described Ti, and if the N content less than 0.01%, the effect of reducing the contribution to the hardenability is suppressed, the inclusion of N is allowed. More preferred N content is 0.005% or less. Meanwhile, reducing the N content more than necessary has a lower limit of a 0.0010% so apply a heavy load to the steel making process.
[0027]
Ti, by binding to N, has the effect of suppressing the effect of reducing the contribution to the hardenability of B by binding N and B. To obtain this effect stably it is necessary to add Ti 0.01% or more. Is preferably 0.02% or more. On the other hand, excessive addition of Ti, there is a risk degrading the productivity by suppressing the recrystallization of the steel sheet after cold rolling, Further, since Ti is likely to decrease the hardenability bonded to C, 0 the upper limit of .5%. Preferably not more than 0.3%.
[0028]
: of Al, but is used as a deoxidizing element, adversely affecting the plating property because it forms an oxide film. However, Al content is its adverse effect is acceptable as long as more than 0.1%. Preferably not more than 0.07%. Meanwhile, setting the Al content to less than 0.01% is the lower limit of 0.01% since applying a heavy load on the steel making process.
[0029]

　B emits an effect of enhancing the hardenability by the addition of 0.0001% or more. Therefore, in the present invention the amount B is 0.0001% or more, preferably 0.0005% or more. On the other hand, excessive addition of B is the upper limit 0.01% since lead to reduced hot workability occurs and ductility.
[0030]
　Components of the steel used for hot stamping steel sheet of the present invention, further Nb: may be added 0.01 to 1.0%.
[0031]

　In the present invention, the content of Nb is optional. Nb combines with N as with Ti, with the effect of inhibiting reducing the contribution to hardenability of B by binding N and B. Because the effect is to be clearly the addition of more than 0.01%, Nb content is preferably 0.01% or more. More preferably, 0.02% or more. On the other hand, even if added over 1.0% of Nb this effect is saturated. Further, if adding over 1.0% of Nb, there is a risk that damage the productivity by suppressing the recrystallization after cold rolling, further, there is a possibility of reducing the hardenability in combination with C. Therefore Nb content is preferably up to 1.0%. More preferably 0.5% or less.
[0032]
　Incidentally, other than the above components in a hot stamping steel sheet of the present invention (the balance) is a Fe, impurities mixed from such raw material for melting or refractory, such as scrap is acceptable. Also, other elements within the range that does not impair the effects of the present invention may be added a small amount.
[0033]
　Will now be described, wherein the Al-Fe alloy layer on the surface of the hot stamping steel sheet of the present invention.
[0034]
　Hot stamping steel sheet according to the present invention, the A-phase on the surface (Fe a 45 ~ 85%, Fe-Al-based alloy phase containing Si 4 ~ 13%) steel (an alloy having Al-Fe alloy layer containing it is of Al-plated steel sheet). First the inventors have, and this alloyed Al-plated steel sheet was investigated compares it to each of the alloy layer of the hot stamping the hot stamp member.
　As a result, the heating of the steel sheet during hot stamping, when performing a short time adopts the rapid heating method heating rate 50 ° C. / sec or more, such as current methods, alloying Al-plated steel sheet alloy and the layer, between the alloy layer of the hot stamping member after hot stamp was found that almost no difference. That is, the configuration of the alloy layer of the hot stamping before the steel sheet, properties were found to be inherited by hot stamping member after hot stamping. This is a hot stamping method, since the time Al-Fe alloy layer is in the high temperature is short, the phase structure of Al-Fe alloys in the solid phase diffusion of elements occurs accompanying the component changes and it it is supposed to be due almost unchanged. Therefore, we studied to to have a high alloy layer of alloying Al-plated steel sheet before hot stamping fatigue properties and corrosion resistance.
[0035]
　Per the study was examined first alloying process of the Al coating layer in detail.
　Alloying the Al plating layer, since a step of diffusing the Fe from the steel sheet side Al plating layer, in the early stages of alloying, high alloy phase of Al concentration in the Al plating layer outermost surface, for example FeAl 3 , Fe 2 Al 5 , etc. are formed. The roughness along with the formation of the Al concentration of high alloy phase Al plating layer surface was found to be elevated. The roughness variation, Fe 2 Al 5 is considered that it is the result of reflecting the crystal growth and crystalline form, such as. When the diffusion of Fe proceeds further with the progress of alloying, it was also found to turn to decrease the surface roughness of the above. This high Fe concentration than high alloy phase of Al concentration of the phases (A phase (Fe a 45 ~ 85%, Fe-Al-based alloy phase containing Si 4 ~ 13%)) is Al plating layer top since we are also formed in the surface, the crystal form is reflected, it is estimated that overall roughness was reduced. A phase of Fe 45 ~ 85%, a FeAl alloy phase containing Si 4 ~ 13%, FeAl 2 , Fe 2 Al 5 , at least one alloy phase estimated mainly of FeAlSi compound to.
[0036]
　From this change in surface roughness, the enhanced fatigue characteristics promote the diffusion of Fe, a high Fe concentration phase (A phase (Fe a 45 ~ 85%, Fe-Al-based alloy containing Si 4 ~ 13% phase)) it was found that it is better to increase the percentage of the outermost surface of the alloy layer. On the other hand, since the Fe concentration is known to be inferior in corrosion resistance higher phase, high Al concentration so as not to impair the corrosion resistance which is the original purpose of using Al plated steel sheet phase (B phase) need to be be left it was found that there is.
[0037]
　So it was examined phase structure having excellent fatigue properties and excellent corrosion resistance can both alloy layers, total length occupied by the A phase in the uppermost surface of the surface perpendicular to Al-Fe alloy layer section of the steel sheet, measuring length it became clear that the case is less than 10% to 50% of the.
[0038]
　The Al-Fe ratio of the total length occupied by the A phase to the entire top surface of the alloy layer (A phase ratio) is less than 10% can not be obtained excellent fatigue characteristics. To enhance the fatigue characteristics, the A-phase ratio preferably 25% or more. On the other hand, A phase ratio can not be obtained an excellent corrosion resistance at 50 percent. To enhance the corrosion resistance, it is preferably not more than 35% phase A ratio.
[0039]
　In addition, the Al-Fe alloy layer, including A phase (Fe a 45 ~ 85%, Fe-Al system alloy phase containing Si 4 ~ 13%) B phase as other phases. B phase, Fe 2 Al 5 phase, FeAl 2 and a phase mainly phase, in addition to these, the left three-phase (FeAl 2 , Fe 2 Al 5 chemical component close to one of, FeAlSi compound alloy phase composed mainly of) and it has a. Chemical composition close to the one of the left three-phase, since the deviation from the stoichiometric ratio, considered identification can not material.
[0040]
　Al-Fe alloy layer according to the present invention, since it is intended to Fe in the steel sheet of the base material is formed by diffusing into the Al plating layer, high Fe concentration in the steel plate side of the Al-Fe alloy layer, Al Fe concentration towards the surface side of the -Fe alloy layer has a Fe concentration distribution decreases. Fe content of Al-Fe alloy layer is preferably the entire 40 to 80 mass%. If the average value of the Al-Fe alloy layer Fe content in is less than 40%, low melting point, such as partial burn during heating of the hot stamp undesirably may occur. On the other hand, the corrosion resistance when the average value of the Fe content exceeds 80% undesirably becomes inferior.
[0041]
　Further, Si is contained in the Al-Fe alloy layer. Si is added to the molten Al plating bath in order to suppress excessive alloying between Al and Fe in molten Al plating, it will be included in the Al-Fe alloy layer. Average content of Si in Al-Fe alloy layer is in the range of 3 to 15% by weight relative to the total amount of Al and Si. The A phase, characterized in the present invention, Si is contained 4-13%.
[0042]
　The A phase is contained between 4 and 13% of Si. If Si content in the A phase is less than 4%, since the alloying of Fe-Al alloy phase is not sufficiently proceed, it can not be obtained the distribution ratio of the A-phase at the surface of interest in the present invention. If the ratio of B phase is high it is the same. Further, when the Si content in the A phase exceeds 13%, undesirably lowering the corrosion resistance.
[0043]
　Al-Fe alloy layer Fe, but balance other than Si is Al and impurities, corrosion resistance, in view of the fatigue properties, Mg, may be appropriately added Zn and the like.
[0044]
　The thickness of the Al-Fe alloy layer is not less than 15 [mu] m. In less than 15μm thickness of Al-Fe alloy layer, the corrosion resistance total length occupied by the A phase in the alloy layer outermost surface (A phase ratio) is excellent even 50% or less of the total alloy layer uppermost surface This is because not be obtained.
　On the other hand, the thickness of the upper limit of the Al-Fe alloy layer may not be provided otherwise from the viewpoint of corrosion resistance, there is a possibility that a crack occurs in too thick alloy layer during hot stamping. Therefore, preferably 100μm or less in thickness, more preferably 70μm or less.
　The thickness of the Al-Fe alloy layer is measured as follows. That is, a scanning electron microscope equipped with energy dispersive X-ray elemental analyzer (EDS) (SEM), Al in the cross section by performing elemental analysis while observing the cross-section of the steel sheet surface and perpendicular Al-Fe alloy layer identify the existence region, the presence region of Al is qualified as Al-Fe alloy layer, by measuring the thickness of the Al-Fe alloy layer, measuring the thickness of the Al-Fe alloy layer.
[0045]
　Al-Fe alloy layer outermost surface in the length of the A-phase, their total, and A phase ratio can be determined by the method shown schematically in Figure 1.
　That is, by observing the cross section of the steel sheet surface and perpendicular Al-Fe alloy layer with an optical microscope (OM), and parallel to both ends of the thickness center line of the phase A are emerge on top of Al-Fe alloy layer projected onto the straight line, the distance between the intersection length of the a phase and (L). The total length of the A-phase (L total), as shown in FIG. 1, sequentially measuring the length of the A-phase (L1, L2, · · · Ln), the sum as the following equation (2) found by. Further, A-phase ratio is obtained as the following equation (3). Note that the equation (3) "Measurement Length" in, as shown in FIG. 1, in the cross section of the Al-Fe alloy layer, was projected at both ends of the outermost surface in a straight line parallel with the steel sheet thickness center line is the distance between the intersections of the time.
L Sum L1 + L2 = + · · · + Ln · · · (2)
A phase ratio (%) = (L Total / measuring length) × 100 ··· (3)
[0046]
　Identification of the A phase is performed scan EDS (energy dispersive spectroscopy) of electron microscopic (SEM) analysis and light together. Further, the "measurement length" examined in multiple field-of-view so as to 500μm or more in total. Distinction between A and B phases is performed by comparing the both components obtained by the SEM-EDS analysis. A phase 45 to by 85% Fe, and contains Si 4 ~ 13%, with respect to the balance of a high phase of Fe concentration of Al and impurities, B phase Al concentration is higher Si than the A-phase 4 a Fe-Al alloy phase of less than%.
[0047]
　In the present invention, "excellent fatigue characteristics" means, 1 × 10 plane bending fatigue test 7 fatigue limit ratio obtained for times the number of repetitions of (sigma W / sigma B , sigma W is the fatigue limit, sigma B is a tensile strength) refers to the case of 0.4 or more.
　The term "excellent corrosion resistance" in the present invention, the number of cycles until rust in the corrosion test, refers to equal to or more than the hot-dip Zn plated steel sheet of the same plating thickness ones. It described in detail in the examples to be described later corrosion test methods.
[0048]
　Next a method for manufacturing the hot stamping steel sheet according to the present invention.
[0049]
　First, casting a billet having a predetermined chemical components described above. Continuous casting from the viewpoint of productivity is desirable. The cast slab thus obtained was hot rolled, followed by pickling. Furthermore, when the cold-rolled steel sheets, cold rolled, performing annealing. They, i.e., pickled hot-rolled steel sheets or Al plating against annealed cold-rolled steel sheet, and performing heat treatment for Al-Fe alloy of the Al plating layer (alloying heat treatment).
[0050]
　Hot rolling, pickling, cold rolling, annealing, and Al plating may be suitably performed depending on the equipment owned by the manufacturer, not particularly limited conditions. One example of a hot rolling, a slab was reheated to 1100 ~ 1300 ° C., performing hot rolling of 80% or higher reduction ratio finish temperature of 850 ~ 950 ° C.. Coiling temperature can be exemplified 600 ~ 750 ° C.. Pickling the generated scale to allow efficient removal, type of acid, concentration, and temperature may be selected. Cold rolling rate is preferably a reduction ratio of 40% or more in order to ensure the flatness. The annealing temperature can be exemplified 700 ~ 780 ° C..
　Moreover, not particularly limited in how the Al plating, electroplating method including the hot-dip plating method, a vacuum deposition method is susceptible clad method or the like, the molten plating is preferable. Al bath for Al plating, for example, bath temperature 670 ° C., but will use those containing 3 to 15 wt% of Si as a subcomponent, and more preferably contains around 10% Si. Also, the Al plating bath, Fe or the like eluted from steel as an impurity is mixed. As other additive elements, particularly effective element for improving corrosion resistance and fatigue properties (e.g., Mg, and Zn, etc.) can also be added in small portions.
　Incidentally, Al plating thickness is adjusted to be above 15 [mu] m.
[0051]
(Alloying heat treatment)
　then allowed to warm to Al-plated steel sheet Al-plated to a predetermined temperature, a heat treatment is performed for the Al-Fe alloy of the Al plating layer. At this time, the uppermost surface of the surface perpendicular to the cross section of steel sheet Al-Fe alloy layer, the length ratio of the A-phase occupied is controlled to be 10% to 50%.
[0052]
　Specifically, the heat treatment conditions, at room temperature to a 600 average heating rate of ° C. 51 ° C. / s or higher, a maximum heating temperature of 600 ° C. or higher 700 ° C. or less, the time at which the steel becomes 600 ° C. 0 (s) , steel plate and steel plate temperature after t (s) T (° C.) from the time became 600 ° C., the time that the steel sheet is in the above 600 ° C. as th (s), heated so as to satisfy the following formula (1) . Furthermore the cooling rate from the maximum heating temperature to 350 ° C. and cooled as 10 ° C. / s or higher. Such heat treatment Al-Fe alloy layer can be realized according to the present invention by undergoing.
[0053]
[Equation 1]

　where, [Cr] in the formula (1) is the concentration of Cr in the steel plate was expressed by mass%.
[0054]
　Be in the form as stacked in parallel for each phase is the surface of the steel sheet constituting the alloy layer at room temperature ~ 600 ° C. The average heating rate of less than 51 ° C. / s of, in phase A of the other phases in the alloy phase outermost layer is not formed forms partially emerges to. This is because the average heating rate is less than 51 ° C. / s at room temperature ~ 600 ° C., the diffusion behavior of Fe, have speculated that not because a uniform look plate plane from the surface. Although not particularly limited upper limit of the average heating rate from room temperature ~ 600 ° C., may be appropriately determined from the balance of the equipment, for example, a 100 ° C. / s or less.
[0055]
　The maximum heating temperature is set to 600 ° C. or higher 700 ° C. or less. The maximum heating temperature is less than 600 ° C. takes a long time to alloying, it detract from productivity. On the one hand, the maximum heating temperature of 700 ° C. greater, there is a fear that Al is adhered to the heat treatment in the facility occur melted Al prior to alloying. Further, when the maximum heating temperature to 700 ° C. greater, are steel plates hardened by passing through the subsequent cooling, the hardness is significantly increased hot stamping alloyed Al-plated steel sheet, which may hinder the hot stamping occurs. Therefore the maximum heating temperature is set to 600 ° C. or higher 700 ° C. or less.
[0056]
　In the course of the steel sheet is cooled through a maximum heating temperature after reaching 600 ° C., A time located above 600 ° C. with integration values of the temperature (middle side in the above equation (1)) to emerge on the top surface to determine the ratio of the phase. The value of the medium sides 3.90 × 10 in the above formula (1) 4 does not become 10% or more ratio of the A phase is less than. On the other hand, the value of the middle side in the formula (1) × 10 2.00 6 -3.90 × 10 5 Ratio of × exceed [Cr] When the A phase exceeds 50%. Therefore, the ratio of the A phase is less than 50% more than 10%, in order to achieve both corrosion resistance and fatigue characteristics, it is important to satisfy the above equation (1).
　Time th steel sheet is in the above 600 ° C. It is preferably less than 3600 sec. When the steel sheet is excessively long time located above 600 ° C., which may deteriorate the high becomes corrosion resistance Fe concentration average of Al-Fe alloy layer. Preferably, the time th of the steel sheet is in the above 600 ° C. and less than 2600Sec.
[0057]
　Although Cr concentration of the steel sheet mechanisms involved in construction of the A-phase is not necessarily clear, since Cr has a tendency to concentrated in the surface layer or near the surface of the steel sheet, the effect on the diffusion of the plating layer of Fe somehow It is presumed to be had.
[0058]
　The method of manufacturing a hot stamping alloyed Al-plated steel sheet of the present embodiment, the cooling after heating is important in achieving a balance between the fatigue properties and corrosion resistance by controlling the form of Al-Fe alloy layer. Alloying heat treatment of the Al plating layer is a step of diffusing the Fe from the steel sheet side Al plating layer, in the early stages of alloying, high alloy phase of Al concentration in the Al plating layer outermost surface (e.g. FeAl 3 , Fe 2 Al 5 , etc.) is formed, the roughness of the Al plating layer surface is increased. The roughness variation, FeAl 3 , Fe 2 Al 5 guess the result of reflecting the crystal growth and crystalline form, such as. The surface roughness of the above with To A phase formation proceeds diffusion of Fe further with the progress of alloying starts to decrease. By cooling in by sure to allow the A-phase is formed 10 ° C. / s or more cooling rate, fixing the metal structure of Fe-Al alloy layer in a state in which the surface roughness of the Fe-Al alloy layer is reduced it can be, thereby making it possible to achieve both the fatigue properties and corrosion resistance. Incidentally, the alloyed Al-plated steel sheet in a state where Al plating layer is alloyed by heat treatment, when directly subjected to hot stamping step without the cooling step, hot stamping without being immobilized metal structure of Fe-Al alloy layer it is the result in, undesirable fatigue strength and corrosion resistance may be lowered.
[0059]
　To obtain the effects of cooling after heat treatment, it is cooled from the maximum heating temperature to 350 ° C. at an average rate of 10 ° C. / s or higher. The ratio between the average cooling rate is slower than 10 ° C. / s of the A-phase is to exceed 50%. Incidentally cooling rate in controlling the configuration form of Al-Fe alloy layer may even faster, because there is a possibility that flatness of the steel sheet is impaired by unevenness occurs in the cooling situation too fast, 350 from the maximum heating temperature the average cooling rate to ° C. is preferable not more than 30 ° C. / s.
　The cooling of the low-temperature side of 350 ° C. may be selected preferred conditions on equipment specifications, mildly, may be any of quenching. Cooling end temperature is preferably 50 ° C. or less, more preferably room temperature.
[0060]
　In still present invention, the atmosphere of the alloying heat treatment is not particularly limited, the atmosphere (air), but such can be applied hydrogen gas atmosphere, the atmosphere is preferred. Moreover, alloying heat treatment may be subjected to heat treatment in a coil state by using a box annealing furnace may be a continuous annealing furnace.
[0061]
　Against above process produced through the alloyed Al-plated steel sheet (strip), as appropriate, may be given a skin-pass rolling or leveler processing. Note that case, the strain is imparted is preferably 5% or less.
[0062]
　Hot stamping steel sheet of the present invention produced in this way (alloyed Al-plated steel sheet) is a hot stamping method, is a high strength member performs shaping and quenching in the same step. Specifically, the stamp heated mold the steel sheet was cut into a predetermined size (blank) as needed. As the heating method blank, conduction heating method in order to obtain a high productivity is desirable. The heating temperature is a generally be set to a temperature at which the entire blank and austenite phase, in order to give characteristics to the member, a method of heating only a part to austenite phase may be selected.
Cooling by the mold, it is common that the heated portion to the austenite phase is carried out at a cooling rate of transformation to the martensite phase. However, in order to have a feature in member, a method for the part of the cooling rate of the heated portion in the austenite phase and martensite transformation does not such gradual cooling rate can be selected.
[0063]
　For example, as a more specific hot stamping conditions, and heated to 700 ~ 1000 ° C. at a heating rate of 5 ~ 500 ° C. / sec, performing hot stamping after holding of 1 to 120 seconds time. Subsequently, for example, can be exemplified conditions is cooled to a cooling rate 1 ~ 1000 ° C. / sec at room temperature over 300 ° C. or less.
[0064]
　Hot stamping steel sheet of the present embodiment as a blank, a hot stamp material produced by combination with hot stamp method energization heating method includes an Al-Fe alloy layer on the surface of the steel material. Al-Fe alloy layer of the hot stamping material, the same composition as the Al-Fe alloy layer of the hot stamping steel sheet, also has the same metal structure, furthermore, the ratio of length A phase occupied is 10% or more and 50% or less. This is because, as mentioned earlier, for rapidly heating the blank by energization heating method, because the hot pressing is completed before the like the composition of Al-Fe alloy layer is changed. Thus, hot stamp material manufactured, as well as the steel sheet for hot stamping, becomes excellent in fatigue properties and corrosion resistance. The chemical composition of the steel of the hot stamping material is the same composition as the chemical components in steel of the hot stamping steel plate, steel metal structure, unlike the steel sheet hot stamping steel plate becomes hardened tissue .
Example
[0065]
　Hereinafter will be described by showing Examples The present invention. The conditions in the embodiment shown below is an example of conditions adopted for confirming the workability and effects of the present invention, the present invention is not limited to this single example of conditions. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various conditions.
[0066]

　Table steel slabs having the chemical compositions shown in 1, and heated to 1200 ° C., hot rolled as finishing temperature 880 ~ 900 ° C., wound at coiling temperature 630 ~ 700 ° C., a thickness of 2. 4 mm, or a plurality prepared hot-rolled steel sheet of 2.8 mm. After pickling them, 2.4 mm material intact, 2.8 mm material was cold-rolled steel sheet 1.4 mm.
[0067]
　Then, it was carried out continuously annealing and Al plated using the laboratory melt plating apparatus. Annealing conditions is for holding for 1.5 minutes 740 ° C., the plating thickness was adjusted to 10 ~ 70 [mu] m per side. Plating bath conditions were a bath temperature of 670 ° C., the bath composition, and the Al-10% Si (containing impurities).
[0068]
　Then, with respect to hot-rolled steel sheet and cold-rolled steel sheet thus obtained was heat treated to Al-Fe alloying an Al plating layer.
　As shown schematically in Figure 2, was performed in three steps of Atsushi Nobori from room temperature (A → B → C), held at the maximum heating temperature (C → D), cooled to room temperature (D → F → G). The horizontal axis of the graph shown in FIG. 2, the time at which the temperature of the steel sheet became 600 ° C. was expressed time (s) as 0 (s).
　Table 2 shows a list of the heat treatment pattern (H01 ~ H14). Incidentally, Table "C" in 2 and "time" in the "D" respectively, show the "elapsed time point B (0 s) ~ C point", "elapsed time point B (0 s) ~ D point" cage, also "th" in "E" indicates the "elapsed time of point B (0s) ~ E point".
[0069]
　And observing the surface and cross-section perpendicular of the steel sheet. A combination of OM and EDS were determined by the length ratio of occupied by the A phase in Al-Fe alloy layer uppermost surface (A phase ratio) the manner already described (see Fig. 1). That is, the identification of the A-phase was performed against the scanning electron EDS microscope (SEM) (energy dispersive spectroscopy) analysis results. Further, the "measurement length", was examined in multiple field-of-view so as to 500μm or more in total. Identification of A phase, was carried out by comparing the both components obtained by the SEM-EDS analysis. The Fe 45 ~ 85%, contains Si 4 ~ 13%, the balance was Phase A phase is Al and impurities.
[0070]
　Then, it was subjected to hot stamp experiment in a laboratory of press testing machine.
　Using electric heating method is to heat the steel sheet was heated to 910 ° C. at a heating rate of 100 ° C. / s, it is conveyed between the dies within 5s, to obtain a pressed member with a flat plate that is a pair of upper and lower water-cooled (hereinafter, referred to as a hot stamp material).
[0071]
　From the obtained hot stamp material, JIS 5 No. type tensile specimens, (3) fatigue test piece, and were taken corrosion resistance evaluation test piece. Tensile test pieces and the fatigue test piece, their longitudinal direction, taken in the direction perpendicular to the rolling direction. Corrosion resistance evaluation test piece is a rectangular 75 mm × 150 mm, 4 sides (the cut surface) was obtained by coating with a resin.
[0072]
　A tensile strength JIS5 test piece No. (sigma B a) was examined.
　Also performs plane bending fatigue test using a fatigue test piece, 10 7 fatigue limit for times (sigma W a) determining, fatigue ratio sigma W / sigma B was determined. Fatigue test, a stress ratio -1 was performed with repetition rate in the 5 Hz.
[0073]
　Corrosion resistance evaluation test is repeated the following 3 steps as one cycle.
Step 1: Salt Spray (5% NaCl aqueous solution, 35 ° C., 4 h)
Step 2: Dry (relative humidity 50%, 60 ℃, 2 hours)
Step 3: humid environmental protection (relative humidity 95%, 50 ℃, 2 time)
　as an evaluation method, a single heat treatment pattern five specimens for each placed in a test chamber, the number of cycles earliest rusting among the five was rusting number of cycles of the thermal treatment pattern.
　In order to evaluate the corrosion resistance, using a hot-dip Zn plated steel sheet with a plating thickness same as comparative materials, the molten Zn-plated steel sheet rusting cycle number (in Table 3 () described in) equivalent or an what results were obtained was evaluated as good.
　Table 3 shows the evaluation test results.
[0074]
　H01 to heat treatment pattern, and, using the H02 No. 1, and, No. 2 A phase is not observed on the outermost surface of the Al-Fe alloy layer, fatigue ratio sigma W / sigma B fatigue properties were found to be inferior below the 0.40. Perhaps, No. 1, No. 2 together, because less and a slow 50 ° C. / s average heating rate from room temperature ~ 600 ° C. in the heat treatment step of alloying, a form in which each phase constituting the Al-Fe alloy layer is stacked parallel to the surface of the steel sheet and to estimate because I.
　Using the H03 to a heat treatment pattern No. In 4, the value of the middle side is 3.90 × 10 in the above formula (1) 4 due to the low percentage of the A phase in the outermost surface of less than Al-Fe alloy layer, also the fatigue characteristics were inferior.
[0075]
　The plating thickness was 10μm No. In 8, rusting cycle number is small, it was found to be inferior in corrosion resistance compared to the molten Zn-plated steel sheet of the same thickness (comparison material).
　The plating thickness was 15μm No. 3, and, No. In 4, rusting cycle number, since it is above the melting Zn-plated steel sheet of the same thickness, in the present invention, was 15μm and the lower limit of the plating thickness.
[0076]
　No. 5, 6, 7, 9, and 10, the plating thickness is 25 ~ 70 [mu] m, A phase ratio is 10 to 32% indicates that the fatigue characteristics excellent after hot stamping, excellent corrosion resistance are both It has been.
[0077]
　For steel A, it was alloyed by a heat treatment pattern H10 No. A ratio of 50% of the 11, A-phase, the fatigue characteristics excellent after hot stamping, while the excellent corrosion resistance is compatible, allowed to alloying heat treatment pattern H11 No. In 13, the above formula the value of the middle side is 2.00 × 10 in (1) 6 -3.90 × 10 5 next FeAl phase ratio of 52% exceeds the × [Cr], the corrosion resistance after hot stamping is inferior It became.
[0078]
　Similarly, for steel B, No. 12 and No. 14, the steel C, No. 15 and No. 16, the steel D, No. 17 and No. 18, and for steel E is, No. 19 and No. By comparing the 20, if the 50% ratio of A-phase, the fatigue characteristics excellent after hot stamping, while the can both have excellent corrosion resistance, that does not show the excellent corrosion resistance is 50 percent It became clear.
[0079]
　Cr amount is about 2.1% of the steel F, were alloyed by a heat treatment pattern H04 No. And 21, were alloyed by a heat treatment pattern H10 No. 22 and are both in the range A phase ratio of 10-50%, were all shown to corrosion resistance and excellent excellent fatigue properties after hot stamping is compatible.
[0080]
　From the results of Example 1 above, the value of the middle side in the above formula ratio of the A phase is 50% (1) is graphed since appeared to have some correlation between the Cr concentration of the steel Tokoro Figure 4 were obtained. From FIG. 4, six Cr concentration [Cr] ratio of the A phase for all (mass%) of 50%, the equation (1) was side values at 2.00 × 10 = 6 -3.90 10 × 5 × led the [Cr].
Therefore, the upper limit of the middle side of the value 2.00 × 10 in the above formula (1) in the present invention 6 -3.90 × 10 5 is limited and × [Cr].
[0081]
　In any embodiment, before and after hot stamping, is Al-Fe percentage of the A phase in the alloy layer, the thickness of the Al-Fe alloy layer, observed as (or almost no change was not for component ).
[0082]
[Table 1]

[0083]
[Table 2]

[0084]
[table 3]

[0085]

　steel slabs having the chemical components shown in Table 4 (steel code G, H), and heated to 1200 ° C., hot rolled as finishing temperature 880 ~ 910 ° C., at a coiling temperature 600 ~ 640 ° C. winding, and the hot-rolled steel plate having a thickness of 3.0mm and more prepared. After pickling them, it was a cold-rolled steel sheet of 1.5mm.
[0086]
　Then, it was carried out continuously annealing and Al plated using the laboratory melt plating apparatus. Annealing conditions are those that retain one minute 740 ° C., the plating thickness was adjusted to 30μm per side. Plating bath conditions were a bath temperature of 670 ° C., the bath composition, and the Al-10% Si (containing impurities).
[0087]
　Then, for some of the resulting cold-rolled steel sheet, to obtain a heat-alloyed Al-plated steel sheet to Al-Fe alloying an Al plating layer. Alloying conditions were heat treatment pattern H08 in Table 2 (Example 1).
[0088]
　Alloyed Al-plated steel sheet described above to hot stamp an Al-plated steel sheet did not alloyed.
　Heating the steel sheet, for Al-plated steel sheet that has not been alloyed performed in a furnace heating method and inserted into a furnace maintained at 910 ° C., the temperature of the steel sheet was immediately stamp taken out after 5 minutes after reaching 900 ° C. .
　On the other hand, the alloying Al-plated steel sheet, and the furnace heating method, performed in both the conduction heating method, electric heating is heated to 910 ° C. at a heating rate of 100 ° C. / s, between the mold within 5s It was pressed to convey.
　Molded shape was a hat-schematically shown in Figure 5. Units of the numerical values which indicate the respective dimensions are both mm.
[0089]
　Hot stamp material molded into a hat-type (referred to as HS member) was observed in detail.
　As a result, there is one separation of the very small plating a shoulder 41 for any steel type in HS member of the steel plate G (Display only one side) is observed. Perhaps the Cr concentration of the steel plate G is estimated that the adhesion between the base material is weakened to outside the scope of the present invention.
　After molding dimensions were exactly the same for any steel type of any of the steel.
[0090]
　For HS member of the steel sheet H (No.1 ~ No.3 in Table 5), it was measured Vickers hardness of the cross section (thickness center) along the dotted line shown in FIG. Central point of the hat Atamahen P1, 10mm from the dotted line on the P1, and 20mm distant point, aspects end point P2 of the shoulder, 10mm from the dotted line on P2, 20mm, and 30mm distant point, the dotted line on 10mm from the end P3 of the bottom side It was measured for the points away.
　The results are shown in Table 5.
　Vickers hardness of the cross section, Atamahen the bottom at 480-488 to be stamped at a higher cooling rate, the vertical wall portion at 459 to 468 that the cooling rate is slightly slower was obtained as compared with the former. These can be judged with the same regardless of the type or method of heating the steel plate.
[0091]
　For these reasons, by hot stamping by steel energization heating method of the present invention, it was shown that can produce a high-strength member having both corrosion resistance and excellent excellent fatigue properties at high productivity. And they have also been shown to no different when hot stamping of Al-plated steel sheet in a furnace heating method.
[0092]
[Table 4]

[0093]
[table 5]

Industrial Applicability
[0094]
　According to the hot stamping alloyed Al-plated steel sheet of the present invention, even when employing a rapid heating method such as electrical heating for heating for hot stamping, fatigue properties and corrosion resistance superior stamp products (hot stamping member) can produce. Further, (those conducting the hot stamping) parts manufacturer is not a heating means using conventional annealing furnace, it is possible to use a rapid heating means such as electrical heating, it is possible to increase the stamp article productivity. Therefore, the industrial applicability is provided with enough.
DESCRIPTION OF SYMBOLS
[0095]
41 shoulder

WE CLAIM

As the steel ingredients, by
mass%,
C:
0.18 ~ 0.36%, Si: 0.02 ~ 0.5%,
Mn: 1.2 ~ 2.2%, P: 0.001 ~ 0.03
%,
S:
0.0001 ~ 0.02%, Cr: 1.1 ~
2.1%, N: 0.001 ~ 0.01%, Ti: 0.01 ~
0.5%, Al: 0.
~ 0.1% 01, B: 0.0001 ~ 0.01%
containing the balance Fe, and a steel sheet of the impurity,
　Al-Fe alloy having a thickness of 15μm or more formed on the surface of the steel sheet comprising a layer, a
　said Al-Fe alloy layer 45 to by 85% Fe is included Fe-Al system alloy phase containing Si 4 ~ 13%, the top surface of the surface perpendicular to the cross section of the steel sheet the Fe-Al alloy of Al-plated steel sheet for hot stamping is length ratio of the alloy phase occupied 50% 10% or more in.
[Requested item 2]
　As the steel components, in mass%,
further, Nb: 0.01 ~ 1.0%
hot stamping alloyed Al-plated steel sheet according to claim 1 containing.
[Requested item 3]
Hot stamping alloyed Al-plated steel sheet according to claim 1 or claim 2, after heating to a temperature at least part of the austenite phase, by a mold, the same process of molding and quenching hot stamping member obtained by performing at.
[Requested item 4]
　As the steel ingredients, by
mass%,
C:
0.18 ~ 0.36%, Si: 0.02 ~ 0.5%,
Mn: 1.2 ~ 2.2%, P: 0.001 ~ 0.03
%,
S:
0.0001 ~ 0.02%, Cr: 1.1 ~
2.1%, N: 0.001 ~ 0.01%, Ti: 0.01 ~
0.5%, Al: 0.
~ 0.1% 01, B: 0.0001 ~ 0.01%
containing the balance Fe, and a steel formed of impurity,
　Al-Fe alloy having a thickness of 15μm or more formed on the surface of the steel material comprising a layer, a
　said Al-Fe alloy layer 45 to by 85% Fe is included Fe-Al system alloy phase containing Si 4 ~ 13%, the top surface of the surface perpendicular to the cross section of the steel sheet hot stamping member ratio of the Fe-Al system alloy phase occupied length is 50% or less than 10% at a.
[Requested item 5]
　As the steel components, in mass%,
further, Nb: 0.01 ~ 1.0%
hot stamp member according to claim 4 containing.