KR20160078852A - Steel having excellent corrosion resistance and forming part by using the same and manufacturing method thereof - Google Patents

Abstract

The present invention relates to structured steel for hot forming having excellent corrosion resistance, a member for hot forming having excellent corrosion resistance and crack propagation resistance and a manufacturing method thereof, which enable the member to have super high strength after the hot forming, to inhibit crack in a basic material in a portion where high shear stress is applied like a side part of the member and to ensure the corrosion resistance by forming an aluminum plating layer and a zinc plating layer sequentially on a substrate steel plate before the hot forming. The structured steel having excellent corrosion resistance according to an aspect of the present invention comprises: the substrate steel plate; the melted aluminum plating layer formed on the substrate steel plate; and the zinc plating layer formed on the melted aluminum plating layer. The member for hot forming having corrosion resistance and crack propagation resistance according to another aspect of the present invention comprises: the basic forming material; a zinc concentration layer formed on the basic material; an aluminum concentration layer formed on the zinc concentration layer; and an aluminum oxidation layer formed on the aluminum concentration layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-formed steel material excellent in corrosion resistance, a hot-formed member having excellent resistance to corrosion and crack propagation, and a method of manufacturing the same.

The present invention relates to a hot-formed steel material excellent in corrosion resistance, a hot-formed member excellent in corrosion resistance and crack propagation resistance, and a method of manufacturing the same.

The hot forming technology is known as a very superior technology for securing ultra high strength for light weight of vehicles and improvement of crashworthiness which are required in automobile companies. That is, the hot forming technique can solve the problem of moldability and shape dynamics in the cold forming according to the ultrahigh strength of the steel material.

In order to secure corrosion resistance of an automobile member, patents and techniques for aluminum or hot-dip galvanized steel have been developed, and Patent Document 1 discloses a technique for manufacturing an aluminum-plated steel material for hot forming.

In Patent Document 1, a steel material for HPF (Hot Press Forming) has a low strength before heat treatment. In the HPF process, high temperature heating (usually heating at 900 ° C. or higher and austenite at 100 ° C.) A hot-formed part having martensite as a main phase is produced, and Fe and an Al intermetallic compound are generated in the plating layer during heat treatment, so that heat resistance and corrosion resistance can be secured.

However, since Patent Document 1 relates to aluminum plating free from sacrificial corrosion resistance, physical corrosion resistance can be secured. However, since no sacrificial method can be expected instead of iron, a blank edge or a scratch or the like, There is a problem that desired corrosion resistance can not be secured.

In order to solve the corrosion resistance problem described above, a technique for hot-dip galvanized or electro-galvanized steel is proposed in Patent Document 2. However, Patent Document 2 has a problem that a crack penetrates through the iron core at a machining site where severe surface friction stress is applied to automobile parts. At this time, the depth of the crack penetrating the ferrite occurs from several um to several tens of um, which not only deteriorates the corrosion resistance of the component but also has a problem of drastically degrading the durability life.

Therefore, there is a demand for development of a steel material for hot forming excellent in corrosion resistance, a hot formed member excellent in corrosion resistance and crack propagation resistance, and a manufacturing method thereof.

Patent Document 1: United States Patent No. 6296805 Patent Document 2: Korean Patent Laid-Open Publication No. 2011-0076146

The present invention relates to a hot-formed steel material excellent in corrosion resistance that can be suitably used for automobile parts and the like, a hot-formed member excellent in corrosion resistance and crack propagation resistance, and a method of manufacturing the same.

According to an aspect of the present invention, A molten aluminum plating layer formed on the base steel sheet; And a zinc plated layer formed on the molten aluminum plated layer; Which is excellent in corrosion resistance.

According to another aspect of the present invention, A zinc enriched layer formed on the base material; An aluminum-enriched layer formed on the zinc enriched layer; And an aluminum oxide layer formed on the aluminum-enriched layer; Which is excellent in corrosion resistance and crack propagation resistance.

In another aspect of the present invention, there is provided a ferritic stainless steel comprising 0.1 to 0.4% of C, 0.1 to 1.5% of Si, 0.5 to 3% of Mn, 0.03% or less of P (with 0% Of steel, 0.01 to 0.1% of Al, 0.001 to 0.1% of Cr, 0.01 to 1.0% of Cr, 0.0005 to 0.01% of B, 0.01 to 0.1% of Ti, and the balance Fe and other unavoidable impurities. Heating at 1000 to 1300 캜; A hot rolling step of hot-rolling the heated steel slab in a finishing rolling temperature range of Ar3 to 1000 占 폚 to obtain a hot-rolled steel sheet; Winding the hot-rolled steel sheet in a temperature range of 500 to 700 ° C; Plated hot-rolled steel sheet with molten aluminum; And galvanizing the molten aluminum plated steel sheet; And more particularly to a method of producing a steel material for hot forming having excellent corrosion resistance.

According to another aspect of the present invention, there is provided a method of manufacturing a steel sheet, comprising: a heat treatment step of raising the temperature of the steel material at a rate of 1 to 100 ° C / sec to austenite single phase inverse temperature of 850 to 1000 ° C and holding the steel material for 1 to 1000 seconds; And a step of hot-forming the heat-treated steel material and cooling the steel material at a cooling rate of 20 to 1000 ° C / sec. The present invention also relates to a method of manufacturing a hot-formed member excellent in resistance to corrosion and crack propagation.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof can be understood in more detail with reference to the following specific embodiments.

The present invention relates to a hot-formed steel material, a hot-formed member and a method of manufacturing the same, which are excellent in corrosion resistance, and an aluminum plating layer and a zinc plating layer are sequentially formed on a base steel sheet before hot forming, There is provided a hot-formed member excellent in corrosion resistance and crack propagation resistance to a base material, which can prevent cracking in a base material easily generated at a portion where a large amount of shear stress is applied, .

1 is a photograph showing a cross section of a member according to the present invention.
2 is a photograph showing a cross section of a steel material according to the present invention.
3 is a photograph of the inventive example A and the comparative example D in which the member crack length can be compared.

The inventors of the present invention found that, in hot-rolled aluminum-plated hot-formed members, there is no sacrificial corrosion resistance of aluminum plating itself, which makes it difficult to secure corrosion resistance. In galvanized hot-formed members, It is recognized that there is a problem that not only corrosion resistance but also member durability can be lowered by cracking of the base material.

As a result of intensive researches on steel plates and members for hot forming, which have excellent corrosion resistance and crack propagation resistance, and their manufacturing methods, it has been found that the hot plate forming process is performed by using the hot plate forming steel sheet comprising a multilayer of an aluminum plated layer and a zinc plated layer It is possible to obtain an ultra-high strength and resistance to corrosion resistance and crack propagation. In particular, it is found that the depth of the crack penetrating the ferrite is minimized at the side portion where the surface friction stress is most severe Thereby completing the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a steel for hot forming with excellent corrosion resistance according to one aspect of the present invention will be described in detail.

According to an aspect of the present invention, A molten aluminum plating layer formed on the base steel sheet; And a zinc plated layer formed on the molten aluminum plated layer; Which is excellent in corrosion resistance.

In hot-rolled aluminum-plated hot-formed members, there is no sacrificial corrosion resistance of aluminum plating itself, which makes it difficult to secure corrosion resistance. In galvanized hot-formed members, although sacrificial corrosion resistance can be ensured, There is a problem that not only the corrosion resistance but also the durability of the member may be deteriorated. However, when the member according to the present invention is manufactured through a hot forming process using a hot-forming steel sheet comprising a multilayer of an aluminum plated layer and a zinc plated layer, And the resistance to crack propagation can be obtained. In particular, the depth of the cracks penetrating the ferrite is minimized at the side portion where the surface friction stress is most severe.

At this time, the base steel sheet contains 0.1 to 0.4% of C, 0.1 to 1.5% of Si, 0.5 to 3% of Mn, 0.03% or less of P (not including 0%), 0.01% or less of S 0.001 to 0.1% of Cr, 0.01 to 1.0% of Cr, 0.0005 to 0.01% of B, 0.01 to 0.1% of Ti, and the balance of Fe and other unavoidable impurities.

Hereinafter, the reason why the alloy composition is controlled will be described (it is necessary to note that% is weight% unless otherwise specified).

C: 0.1 to 0.4%

The C is an essential element for securing the strength of the martensite. When the C content is less than 0.1%, it is difficult to obtain sufficient strength. When the C content is more than 0.4%, the impact resistance of the slab is decreased, and the weldability of the hot-formed member is deteriorated. Therefore, the C content is preferably 0.1 to 0.4%.

Si: 0.1 to 1.5%

When the Si content is less than 0.1%, sufficient deoxidation may not be achieved. When the Si content is more than 1.5%, it is difficult to secure a good plating surface quality due to Si oxide which may be formed on the surface of the steel material. Therefore, the Si content is preferably 0.1 to 1.5%.

 Mn: 0.5 to 3.0%

The Mn is added to suppress unwanted ferrite or bainite transformation during hot forming. When the Mn content is less than 0.5%, it is difficult to sufficiently secure the above effect. On the other hand, if the Mn content exceeds 3.0%, the steel plate production cost may increase. Therefore, the Mn content is preferably 0.5 to 3.0%.

P: 0.03% or less (0% is not included)

Since P is a grain boundary segregation element, it is preferably added as little as possible, since it is an element that hinders the characteristics in a steel for heat treatment. Therefore, it is important to manage the upper limit. If the P content is added in excess of 0.03%, the bending property, the impact property, the weldability, and the like of the member are heated, so that the upper limit is preferably controlled to 0.03%.

S: 0.03% or less (0% is not included)

The S is an impurity inevitably contained in the steel. It is present as a sulfide such as MnS and inhibits the bendability and weldability of the member. Therefore, the S is preferably added as little as possible. Therefore, it is important to manage the upper limit, and when the S content exceeds 0.03%, the upper limit is preferably controlled to 0.03% because the bending property and the weldability of the member are heated.

Al: 0.01 to 0.1%

The above Al is an element that deoxidizes like S. It is preferable that 0.01% or more of Al is added for sufficient deoxidation. On the other hand, when the Al content exceeds 0.1%, the effect is not only saturated but also the austenite single-phase reversed temperature is raised to weaken the surface characteristics of the heat treatment member and the surface quality of the plating material. Therefore, the Al content is preferably 0.01 to 0.1%.

Cr: 0.01 to 1.0%

The Cr is an element added to secure the hardenability of the steel. When the Cr content is less than 0.01%, it is difficult to secure sufficient curing ability. On the other hand, when the content exceeds 1.0%, the characteristics are saturated and the manufacturing cost of steel is increased. Therefore, the Cr content is preferably 0.01 to 1.0%.

B: 0.0005 to 0.01%

And B is an element added to suppress ferrite formation in the hot-formed member. In order to achieve the above object, it is required to be added in an amount of 0.0005% or more. When the content exceeds 0.01%, the effect is saturated and the B content is 0.0005 to 0.01% because it is segregated in the slab grain boundary and the hot- desirable.

Ti: 0.01 to 0.1%

The Ti is added to precipitate nitrogen existing in the steel as nitride to maximize the B effect in the steel. If the Ti content is less than 0.01%, the effect is not sufficiently expected. If the Ti content exceeds 0.1%, the characteristics become saturated and the cost of steel production increases. Therefore, the Ti content is preferably 0.01 to 0.1%.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

Hereinafter, a hot-formed member having excellent corrosion resistance and crack propagation resistance to a base material, which is another aspect of the present invention, will be described in detail.

According to another aspect of the present invention, A zinc enriched layer formed on the base material; An aluminum-enriched layer formed on the zinc enriched layer; And an aluminum oxide layer formed on the aluminum-enriched layer; Which is excellent in corrosion resistance and crack propagation resistance.

As shown in Fig. 1, the plated layer of the hot-formed member is largely divided into an upper layer in which aluminum is concentrated and a lower layer in which zinc is concentrated. Aluminum oxide is also present at the top, and an Fe-Al diffusion layer may exist between the aluminum-rich layer and the zinc-rich layer.

The aluminum oxide in the extreme surface layer can play a role of uniformly dispersing the shear stress in the region where friction is strong in the hot-formed member, and cracks that can be generated by the shear stress are uniformly cracked in the aluminum- The effect of suppressing the concentration of shear stress on a specific crack can be obtained.

After that, the crack penetrates through the zinc enriched layer and diffuses into the base material. At this time, the zinc enriched layer does not greatly affect the crack propagation inhibition, but the effect of improving the corrosion resistance of the hot- . In addition, the aluminum-enriched layer does not chemically contribute to the improvement of corrosion resistance, but it produces hydroxides in physically generated cracks, thereby preventing cracks, thereby ensuring better corrosion resistance.

According to another aspect of the present invention, an Fe-Al diffusion layer may exist between the aluminum-rich layer and the zinc-rich layer.

Since the Fe-Al diffusion layer has a relatively dense and flexible structure, it can suppress crack propagation more effectively. However, it is not essential to achieve the object of the present invention.

Hereinafter, a method for producing a steel material for hot forming having excellent corrosion resistance, which is another aspect of the present invention, will be described in detail.

In another aspect of the present invention, there is provided a ferritic stainless steel comprising 0.1 to 0.4% of C, 0.1 to 1.5% of Si, 0.5 to 3% of Mn, 0.03% or less of P (with 0% Of steel, 0.01 to 0.1% of Al, 0.001 to 0.1% of Cr, 0.01 to 1.0% of Cr, 0.0005 to 0.01% of B, 0.01 to 0.1% of Ti, and the balance Fe and other unavoidable impurities. Heating at 1000 to 1300 캜; A hot rolling step of hot-rolling the heated steel slab in a finishing rolling temperature range of Ar3 to 1000 占 폚 to obtain a hot-rolled steel sheet; Winding the hot-rolled steel sheet in a temperature range of 500 to 700 ° C; Plated hot-rolled steel sheet with molten aluminum; And galvanizing the molten aluminum plated steel sheet; And more particularly to a method of producing a steel material for hot forming having excellent corrosion resistance.

Heating step

The steel slab satisfying the above-mentioned composition is heated at 1000 to 1300 캜.

Hot-rolled  step

The heated steel slab is hot-rolled to obtain a hot-rolled steel sheet.

The hot rolling finishing temperature is not limited in the present invention as long as it does not hinder the cold rolling property and the like, but it is preferably carried out at a temperature of Ar3 transformation point to 1000 deg. If the hot-rolling finishing temperature is lower than the Ar3 temperature, the hot-rolling property can be inhibited. If the hot-rolling finish temperature is above 1000 DEG C, an excessive scale can be generated and the thermal-

Winding  step

The coiling temperature is not limited in the present invention as long as it does not hinder the cold rolling property, but it is preferable that the coiling is carried out at a temperature of 500 to 7000 캜. If the coiling temperature is less than 500 캜, the thermal expansion coefficient of the material in the width direction becomes large and the cold rolling property may be deteriorated. If the coiling temperature exceeds 700 캜, the pickling property may be deteriorated in the cold rolling process.

Step of molten aluminum plating

The wound hot-rolled steel sheet may be hot-melted without cold rolling after pickling, or it may be hot-rolled and then subjected to hot-dip aluminum plating to obtain a more accurate steel sheet thickness.

First, the aluminum-plated steel is subjected to a predetermined annealing process and then secured by aluminum plating. At this time, the annealing and plating conditions are not particularly limited, but they can be usually plated using a plating bath containing 7 to 12 mass% of Si and the remaining Al and other unavoidable impurities.

The plating amount is not particularly limited, but plating can be performed so as to be 20 to 100 g / m ^{2 on one} side basis.

When the plating amount is less than 20 g / m ² , it is difficult to exhibit sufficient corrosion resistance. When the plating amount exceeds 100 g / m ² , there is a problem in that the cost is increased compared to the effect.

Step for galvanizing

The molten aluminum-plated steel material produced as described above can be subjected to hot-dip galvanizing or electroplating to secure a desired plating structure as shown in Fig.

At this time, the hot-dip galvanizing can be plated through a usual plating process, but it is preferable to perform annealing at 660 ° C or lower and then plated to prevent melting of aluminum.

Further, although the method of electroplating is not limited to a great extent, the plating can be performed so that the amount of plating on the hot-dip zinc and electroplated zinc plating is 20 to 80 g / m ^{2 on a one-} side basis.

When the plating amount is less than 20 g / m ² , it is difficult to exhibit sufficient corrosion resistance through the sacrificial plating method. When the plating amount exceeds 80 g / m ² , there is a problem that the cost is increased.

Hereinafter, a method of manufacturing a hot-formed member having excellent corrosion resistance and crack propagation resistance, which is another aspect of the present invention, will be described in detail.

According to another aspect of the present invention, there is provided a method of manufacturing a steel sheet, comprising: a heat treatment step of raising the temperature of the steel material at a rate of 1 to 100 ° C / sec to austenite single phase inverse temperature of 850 to 1000 ° C and holding the steel material for 1 to 1000 seconds; And a step of hot-forming the heat-treated steel material and cooling the steel material at a cooling rate of 20 to 1000 ° C / sec. The present invention also relates to a method of manufacturing a hot-formed member excellent in resistance to corrosion and crack propagation.

Heat treatment step

It is preferable to raise the temperature of the steel material according to the present invention to austenite single phase inverse temperature of 850 to 1000 占 폚 at a rate of 1 to 100 占 폚 / sec and maintain the steel material for 1 to 1000 seconds.

Although the rate of temperature rise is not limited to a large degree, a sufficient productivity can not be ensured at less than 1 ° C / sec., And an excessive facility cost is required at a temperature increase rate exceeding 100 ° C / sec. When the austenite single-phase reverse temperature is lower than 850 DEG C, ferrite may be formed on the base material, so that sufficient strength can not be ensured. When the temperature exceeds 1000 DEG C, austenite grows excessively to lower the impact characteristics, There is a problem.

Cooling step

Thereafter, the heat-treated steel material is hot-formed into a mold and cooled at a cooling rate of 20 to 1000 ° C / sec.

When the cooling rate is less than 20 ° C, undesirable bainite is generated and it is difficult to secure an ultra-high strength. In order to obtain a cooling rate exceeding 1000 ° C / second, excessive facility investment costs may be incurred.

As described above, the hot-formed member having the plating layer structure as shown in Fig. 1 and having excellent resistance to corrosion and crack propagation can be manufactured through the heating, holding and cooling steps.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example)

The steel slab formed as shown in the following Table 1 was vacuum-melted and heated at a reheating temperature of 1200 占 폚 for 1 hour and then subjected to hot rolling. The hot rolling finish temperature was 880 占 폚 and the coiling temperature was 600 占 폚. . The hot-rolled steel sheet was pickled and cold-rolled to a final thickness of 1.5 mm at a cold rolling reduction of 50%, followed by annealing to produce a cold-rolled steel sheet.

The cold-rolled steel sheet was annealed at 780 占 폚. Thereafter, molten aluminum plating was carried out using a plating bath containing aluminum as a main component and containing Si: 8.5% by weight, Fe: 2% by weight and other unavoidable impurities in the amount of Al plating shown in Table 2 below. However, in the case of Comparative Example D, no Al plating was performed.

The aluminum-plated steel sheet thus prepared was subjected to electro-galvanizing by the Zn plating amount shown in Table 2 to prepare an aluminum-zinc multi-layered coated steel sheet, and heat treatment was performed to simulate hot forming. In Comparative Example C, however, zinc plating was not performed.

The coated steel sheet was heat-treated for 5 minutes in a heating furnace heated to 900 ° C, transferred to a mold having a HAT shape, hot-formed and quenched to produce a member.

The tensile strength, crack length and corrosion depth of the member were measured and are shown in Table 2 below.

Mechanical properties of the member were measured using the tensile test specimen of JIS Z 2201 5 from the above member. The crack length was obtained by taking a sample from the side surface of the HAT member and measuring the length of the cracked layer propagated to the base member and the plating layer structure, .

In addition, the corrosion depth was measured 57 times by CCT (salt cyclone corrosion test) using salt spray, and the corrosion depth was measured at 3 mm intervals at 2 mm intervals.

Chemical composition (% by weight) C Si Mn P S Al Ti Cr B 0.23 0.2 1.1 0.016 0.004 0.04 0.03 0.15 0.0025

Manufacturing conditions Plating condition Absence characteristic Remarks Al plating amount
(g / m ² ) Zn plating amount
(g / m ² ) TS
(MPa) Crack length
(um) Corrosion depth
(mm) A 50 60 1502 4 0.02 Honor B 70 30 1497 3 0.01 Honor C 80 - 1525 - 0.12 Comparative Example D - 70 1548 27 0.16 Comparative Example

In the case of the inventive inventions A and C according to the present invention, the length of the crack penetrating the base material is not only less than 5 탆, but also the corrosion depth is less than 0.1 mm, which shows excellent corrosion resistance and crack resistance.

On the other hand, in the case where only aluminum plating was applied as in Comparative Example C, cracks were hardly observed and crack resistance was excellent, but corrosion resistance was found to be 0.12 mm in corrosion depth.

Further, in the case of zinc plating alone as in Comparative Example D, since the crack length passing through the base material is as large as 27 um, not only the durability is lowered but also the corrosion depth is 0.16 mm in spite of the sacrificial corrosion resistance of zinc, It can be seen that it is greatly opened.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (12)

Base steel sheet;
A molten aluminum plating layer formed on the base steel sheet; And
A zinc plated layer formed on the molten aluminum plated layer;
Wherein the steel sheet has excellent corrosion resistance.
The method according to claim 1,
Wherein said base steel sheet comprises 0.1 to 0.4% of C, 0.1 to 1.5% of Si, 0.5 to 3% of Mn, 0.03% or less of P, 0% or less of S, And a balance of Fe and other unavoidable impurities, characterized in that it contains 0.001 to 0.1% of Al, 0.01 to 1.0% of Cr, 0.0005 to 0.01% of B, 0.01 to 0.1% of Ti, Steel for hot forming.
Forming base material;
A zinc enriched layer formed on the base material;
An aluminum-enriched layer formed on the zinc enriched layer; And
An aluminum oxide layer formed on the aluminum-enriched layer;
A thermoforming member having excellent corrosion resistance and crack propagation resistance.
The method of claim 3,
And a Fe-Al diffusion layer is present between the zinc-enriched layer and the aluminum-enriched layer. The hot-formed member is excellent in corrosion resistance and crack propagation resistance.
The method according to claim 3 or 4,
Wherein said base steel sheet comprises 0.1 to 0.4% of C, 0.1 to 1.5% of Si, 0.5 to 3% of Mn, 0.03% or less of P, 0% or less of S, And the balance of Fe and other unavoidable impurities, characterized in that it contains 0.001 to 0.1% of Al, 0.01 to 1.0% of Cr, 0.0005 to 0.01% of B, 0.01 to 0.1% of Ti, A hot-formed member excellent in propagation resistance.
0.1 to 0.4% of C, 0.1 to 1.5% of Si, 0.5 to 3% of Mn, 0.03% or less of P (0% is not included), S is 0.01% Heating a steel slab containing 1000 to 1300 占 폚 containing 0.001 to 0.1% of Al, 0.01 to 1.0% of Cr, 0.0005 to 0.01% of B, 0.01 to 0.1% of Ti and the balance of Fe and other unavoidable impurities; ;
A hot rolling step of hot-rolling the heated steel slab in a finishing rolling temperature range of Ar3 to 1000 占 폚 to obtain a hot-rolled steel sheet;
Winding the hot-rolled steel sheet in a temperature range of 500 to 700 ° C;
Plated hot-rolled steel sheet with molten aluminum; And
Galvanizing the molten aluminum plated steel sheet;
Wherein the hot-rolled steel sheet has an excellent corrosion resistance.
The method according to claim 6,
Further comprising a step of cold-rolling the wound hot-rolled steel sheet between the winding step and the step of hot-dipping aluminum.
The method according to claim 6,
Wherein the step of performing the hot-dip aluminum plating is performed so that the plating amount is 20 to 100 g / m ^{2 on one} side basis using a plating bath containing 7 to 12% by weight of Si, the remaining Al and unavoidable impurities. Wherein
The method according to claim 6,
Wherein the step of zinc plating is performed by hot dip galvanizing after annealing at 660 占 폚 or lower.
The method according to claim 6,
Wherein the step of zinc plating is performed by an electroplating method.
The method according to claim 6,
Wherein the zinc plating step is carried out so that the amount of plating is 20 to 80 g / m ^{2 on a one-} side basis.
A heat treatment step of raising the temperature of the steel material of claim 1 or 2 up to austenite single phase inverse temperature of 850 to 1000 ° C at a rate of 1 to 100 ° C / sec and holding the steel material for 1 to 1000 seconds; And
Wherein the heat-treated steel material is hot-formed and cooled at a cooling rate of 20 to 1000 ° C / sec.

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