KR20170138380A - Hot pressed part having excellent corrosion resistance and method for manufacturing same - Google Patents

Abstract

Disclosed is a hot press molded product, which is manufactured by means of hot press molding a Zn-Al-Mg plated steel material comprising base iron and a Zn-Al-Mg plating layer, and a method for manufacturing the same, the hot press molded product comprising an oxide layer formed on the surface thereof, wherein the content ratio of Al to Mg (Al/Mg) in the oxide layer is 0.8 or higher.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot press formed article having excellent corrosion resistance,

The present invention relates to a hot press formed article excellent in corrosion resistance and a method of manufacturing the same.

In recent years, the use of high-strength steels has been increasing to lighten automobiles, but such high-strength steels are easily worn or fractured at room temperature. In addition, due to springback phenomenon during machining, it is difficult to precisely dimension work, which makes molding of complex products difficult. Accordingly, Hot Press Forming (HPF) has been applied as a preferable method for machining high strength steel.

The hot press forming (HPF) is a method of processing a steel sheet into a complicated shape at a high temperature by using a property of softening and high ductility at a high temperature, more specifically, At the same time, quenching is performed to transform the structure of the steel sheet into martensite to form a product having high strength and precise shape.

However, when the steel material is heated to a high temperature, a phenomenon such as corrosion or decarburization may occur on the surface of the steel material. In order to prevent this, a zinc-based plated steel material having a zinc- In fact.

However, in general zinc-based plated steel materials, excessive oxidation of zinc occurs during heating for hot press forming, resulting in a decrease in the effective thickness of the plated layer and an excessive decrease in the content of zinc in the zinc-based plated layer, .

On the other hand, recently, a technique of adding magnesium in the plating layer for further improving the corrosion resistance of zinc-based plated steel has been proposed. When the magnesium in the plating layer is added, magnesium corrosion products are densely formed under the corrosive environment, so that the corrosion rate is reduced and the corrosion resistance improvement effect can be obtained. However, such magnesium is rapidly oxidized at a high temperature, thereby greatly damaging the plating layer. As a result, the addition of magnesium to zinc-based plated steel for hot press forming is limited.

One of the objects of the present invention is to provide a hot press molded article excellent in corrosion resistance and a method of manufacturing the same.

One aspect of the present invention is a hot press molded product produced by hot press forming a Zn-Al-Mg based plated steel material including a base steel and a Zn-Al-Mg based plating layer, wherein the hot press molded product has a (Al / Mg) of the content of Al to the content of Mg contained in the oxide layer is 0.8 or more.

In another aspect of the present invention, there is provided a method of manufacturing a Zn-Al-Mg-based plated steel sheet, comprising the steps of: dipping a base steel in a Zn-Al- Heating the cooled Zn-Al-Mg-based plated steel material to a heating temperature of 600 to 950 ° C in a heating furnace, and cooling the Zn-Al- Mg-based plated steel material with a mold and rapidly quenching, and the stay time indicating the time during which the Zn-Al-Mg-based plated steel material having reached the heating temperature stays in the heating furnace is 120 seconds or less The present invention also provides a method for producing a hot press molded article.

As one of the various effects of the present invention, the hot press formed product produced according to the present invention has an advantage of excellent corrosion resistance.

1 is a SEM (Scanning Electron Microscope) image obtained by observing a cross section of a hot press formed article according to Inventive Example 5, and Fig. 2 is a scanning electron microscope (SEM , Scanning Electron Microscope) images.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a hot press formed article having excellent corrosion resistance, which is one aspect of the present invention, will be described in detail.

The hot press-formed product of the present invention is produced by subjecting a Zn-Al-Mg based plated steel material containing bare iron and a Zn-Al-Mg based plating layer to hot press forming. At this time, the base steel may be a steel sheet or a steel wire.

In the present invention, there is no particular limitation on the composition of the above-mentioned ground iron. For example, it is preferable that the composition contains 0.15 to 0.35% of C, 0.5 to 8.0% of Si (excluding 0%), 0.5 to 8.0% 0.0020 to 0.0050%, the balance Fe and unavoidable impurities.

C: 0.15-0.35 wt%

Carbon is an austenite stabilizing element and is an element added for securing ingenuity and securing the strength of a molded product after hot press forming. If the carbon content is too low, there is a lack of incombustibility and it may be difficult to secure the target strength after hot pressing. Accordingly, in the present invention, the content is preferably 0.15% by weight or more, more preferably 0.18% by weight or more. However, if the carbon content is too high, the toughness and weldability may be deteriorated and the manufacturing process may be disadvantageous such as inhibiting the ducting in the annealing and plating process due to excessive increase in strength. Therefore, in the present invention, the content is preferably 0.35% by weight or less, more preferably 0.32% by weight or less.

Si: 0.5% by weight or less (excluding 0% by weight)

Silicon is a component that becomes blue for the purpose of deoxidation. If the content is excessively high, SiO ₂ oxide is generated on the surface of the steel during annealing, and unplated may occur. Accordingly, in the present invention, the content is preferably 0.5% by weight or less, more preferably 0.4% by weight or less.

Mn: 0.5 to 8.0 wt%

Manganese plays an important role in retarding the transformation from austenite to ferrite as well as contributing greatly to the strength increase as the solid solution strengthening element. If the manganese content is too low, the transformation temperature (Ae3) from austenite to ferrite is increased, and an excessively high heat treatment temperature is required for hot press working in the austenite single phase region. Therefore, in the present invention, it is preferably contained in an amount of 0.5 wt% or more, more preferably 1.0 wt% or more. On the other hand, if the content of manganese is excessively high, the weldability and hot rolling property may deteriorate. Therefore, in the present invention, the content is preferably 8.0 wt% or less, more preferably 7.8 wt% or less.

B: 0.0020 to 0.0050% by weight,

Boron serves to retard the transformation from austenite to ferrite. In order to obtain such an effect in the present invention, the content is preferably 0.0020% by weight or more, more preferably 0.0022% by weight or more. However, when the content is excessive, the effect is saturated and the hot workability can be deteriorated. Therefore, in the present invention, the content is preferably 0.0050 wt% or less, more preferably 0.0045 wt% or less.

The rest of the composition is 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 referred to in this specification, as they are known to one of ordinary skill in the art.

However, as typical examples of such impurities, Al, P and S can be mentioned. When the Al content in the substrate iron is increased, cracking of the steel may occur, so that the content thereof is preferably controlled to 0.2 wt% or less. As the content of S increases, the ductility may deteriorate. Therefore, it is preferable to control the content of S to 0.03 wt% or less and 0.001 wt% or less, respectively.

The Zn-Al-Mg based plating layer is formed on the surface of the base iron to prevent the corrosion of the base iron under the corrosive environment and contains 0.9 to 3.5% of Mg, 1.0 to 15% of Al, And other unavoidable impurities.

Mg is an indispensable element added to improve the corrosion resistance of a hot press molded product, and effectively forms a corrosion product on the surface of the plating layer under the corrosive environment, thereby effectively preventing corrosion of the hot pressed product. On the other hand, Mg in the Zn-Al-Mg-based plating layer is partially oxidized and disappears while hot pressing, and the Zn-Al-Mg-based plating layer is alloyed with Fe to decrease Mg content in the entire plating layer , A larger amount of Mg must be contained in order to secure the corrosion resistance equivalent to that of ordinary plated steel. In order to secure the desired corrosion resistance in the present invention, 0.9 wt% or more, and more preferably 0.95 wt% or more should be included. However, when the content is excessive, not only the oxidation of Mg on the surface of the plating bath becomes prominent to deteriorate the plating workability, but also the excessive MgO oxide is formed through the hot pressing process to promote oxidation and volatilization of Zn, It is possible to deteriorate the corrosion resistance. In order to prevent this, Mg should be contained in an amount of 3.5 wt% or less, and more preferably 3.3 wt% or less.

Al is subjected to a hot pressing process to form a stable Al2O3 oxide layer on the surface thereof to suppress the oxidation and volatilization of Zn, thereby contributing to the improvement of the corrosion resistance of the hot press molded article. In order to obtain such an effect in the present invention, the content should be 1.0 wt% or more, and more preferably 1.1 wt% or more. However, if the content thereof is excessive, the heat resistance of the surface may be improved, but when melting is carried out, the melting temperature of the hot bath may become excessively high, which may make the operation difficult. In order to prevent this, Al should be contained in an amount of 15% by weight or less.

The hot-pressed product of the present invention includes an oxide layer formed on its surface, and the ratio of the content of Al to the content of Mg contained in the oxide layer (Al / Mg) is 0.8 or more. The more preferable range is 0.85 or more, and the more preferable range is 0.9 or more.

As a result of research conducted by the inventors of the present invention, the Mg-based oxide film is not physically stable and is easily broken to promote oxidation and volatilization of Zn in the plating layer. On the other hand, if the Al-based oxide film is stably formed on the surface of the Al-based oxide film, the oxidation and volatilization of Zn in the plating layer can be prevented, and the amount of the oxide itself can be minimized, The corrosion resistance of the hot press molded article can be greatly improved. In order to obtain such an effect in the present invention, it is necessary to control the ratio (Al / Mg) of Al to the content of Mg contained in the oxide layer to 0.8 or more.

In the present invention, the specific apparatus and method for measuring the content of Mg and Al contained in the oxide layer are not particularly limited, but can be measured using, for example, Glow Discharge Optical Emission Spectrometry (GDOES). At this time, it is preferable to analyze the analyte after calibrating the analytical equipment using the standard specimen.

According to one example, the total deposition amount of Zn, Al and Mg in the oxide layer may be 700 mg / m ² or less (excluding 0 mg / m ² ), more preferably 500 mg / m ² or less (excluding 0 mg / m ² ) And even more preferably not more than 100 mg / m ² (excluding 0 mg / m ² ).

The surface oxide increases the surface resistance of the specimen plate to cause weld spatter (spatter), which makes welding difficult or impossible. When the total deposition amount of oxides is suppressed to 700 mg / m ² or less as described above, can do. According to one example, when spot welding is performed according to the related procedures such as KS B ISO 15609, when the total deposition amount of the oxide is suppressed to 700 mg / m 2 or less, a welding current range of 0.5 KA or more is obtained, The weldable current range was 0.5 KA or less at the total adhesion amount or more.

According to one example, the oxide layer may include one or more selected from the group consisting of Mn, Si and Fe, and the sum of these contents may be 50% or less of the total metal content contained in the oxide layer, , More preferably not more than 30%, and even more preferably not more than 10%. The above elements may form physical and chemical defects in the oxide layer, which may hinder the effect of improving the high-temperature heat resistance due to the formation of the oxide layer. Therefore, it is preferable to suppress the content to the maximum.

According to one example, the ratio (Mg 2 _O / Mg _C ) of the total amount of Mg (Mg 2 _O ) contained in the oxide layer of the hot press formed product to the total amount of Mg (Mg _C ) contained in the plating layer of the hot press- Or less, more preferably 0.5 or less, and even more preferably 0.3 or less.

Mg contained in the plating layer contributes greatly to the improvement of the corrosion resistance of the hot press molded product. In order to secure excellent corrosion resistance, it is preferable to keep Mg in the plating layer as solid as possible by suppressing oxidation of Mg in the hot pressing process. When the total amount ratio (Mg _O / Mg _C ) is controlled to 1 or less as described above, the corrosion resistance of the hot press molded article can be further maximized.

According to one example, the Fe alloyed degree of the plated layer of the hot press formed product may be 20 to 70%, more preferably 25 to 65%, and still more preferably 30 to 60%. When the Fe content is in the above range, it is possible to effectively suppress the generation of an oxide film during the heating process, and it is advantageous that the corrosion resistance by the sacrificial system is excellent. If the Fe alloyed degree is less than 20%, a region in which a part of Zn in the plating layer is concentrated may exist as a liquid phase, which may cause liquid brittle cracking during processing. On the other hand, when the Fe alloying degree is more than 70%, the corrosion resistance may decrease.

The hot-pressed product of the present invention described above can be produced by various methods, and the production method thereof is not particularly limited. However, it can be produced by the following method as one embodiment thereof.

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

First, base steel is immersed in a Zn-Al-Mg-based plating bath and plated to obtain a Zn-Al-Mg-based plated steel. In the present invention, a concrete method of obtaining the plated steel material is not particularly limited, but the following method may be used to further maximize the effect of the present invention.

(a) Control of kind and surface roughness of base iron

According to the results of research conducted by the present inventors, the surface roughness of the pre-plating iron influences the activity of Al in the plating layer, and in particular, the lower the surface roughness of the base iron, the higher the activity of Al, Which is advantageous for stably forming Al ₂ O ₃ on the surface. In order to obtain such an effect in the present invention, it is preferable to use a cold-rolled steel sheet whose surface roughness (Ra) is controlled to 2.0 μm or less as a base steel. On the other hand, lower surface roughness is advantageous for increasing the activity of Al, so that the lower limit of the present invention is not particularly limited. However, if the surface roughness of the base steel is too low, the steel slips during rolling, Therefore, from the viewpoint of preventing this, the lower limit can be limited to 0.3 μm.

(b) Control of plating bath composition

According to the study results of the present inventors, when Al and Mg are added in the plating bath, the content ratio of Al and Mg also affects the activity of Al, and in particular, the higher the Al / Mg ratio, So as to stably form Al ₂ O ₃ on the surface of the hot press-molded article. In order to obtain such effects in the present invention, it is preferable to control the Al / Mg ratio in the plating bath to 0.8 or more. On the other hand, as the Al / Mg ratio is higher, it is advantageous to increase the activity of Al, so that the lower limit of the present invention is not particularly limited.

(c) Formation of pre-plating layer and control of annealing condition

According to the results of research conducted by the present inventors, when iron oxide contains a large amount of a phosphorus-containing element such as Mn, the proliferation of the phosphorus-containing element prominently occurs in the plating layer. Thus, the phosphorylation element diffused into the plating layer lowers the activity of Al ₂ > O < ₃ >

In order to prevent this, according to one example, it is possible to perform plating on the surface of a ferrous material obtained by annealing at least one metal selected from the group consisting of Fe, Ni, Cu, Sn, and Sb on the surface thereof have. On the other hand, in the present invention, there is no particular limitation on the method of preliminarily plating, and for example, it can be formed by an electroplating method.

At this time, the thickness of the pre-plating layer is preferably 5 to 100 nm. If the thickness is less than 5 nm, diffusion of the chiefly oxidized element into the plating layer is difficult to effectively suppress. On the other hand, if the thickness exceeds 100 nm, it may be effective to suppress surface oxide, but it is difficult to secure economical efficiency.

On the other hand, the annealing treatment is carried out in order to recover the recrystallized iron structure, and the annealing treatment can be performed at a temperature of 750 to 850 캜, which is sufficient to recover the recrystallized iron structure.

According to one example, the annealing treatment can be performed in an atmosphere of 1 to 15% by volume of hydrogen gas and the balance of nitrogen gas. If the amount of the hydrogen gas is less than 1% by volume, it may be difficult to effectively suppress the surface oxide. On the other hand, when the amount of the hydrogen gas exceeds 20% by volume, not only the cost due to the increase of the hydrogen content is increased, .

Next, the Zn-Al-Mg-based plated steel material is heated to a predetermined heating temperature in a heating furnace.

At this time, it is preferable that the stay time indicating the time during which the Zn-Al-Mg-based plated steel material having reached the heating temperature stays in the heating furnace is controlled to 120 seconds or less.

According to the results of research conducted by the present inventors, the higher the temperature of the material, the more active the production of MgO. Particularly, Mg is an element which is easier to oxidize than other elements. When the temperature of the material increases at high temperature, The oxide by the element is reduced and the ratio of Mg in the oxide layer is increased. In this case, the formation of a physically unstable oxide layer promotes the volatilization and oxidation of Zn, and as a result, the corrosion resistance of the hot-press molded article is deteriorated. Thus, the present invention manages the stay time to 120 seconds or less.

On the other hand, according to further research results of the present inventors, the heating temperature and the heating rate also affect the formation of the desired oxide layer.

As a result of research conducted by the inventors of the present invention, when heating for hot press forming, the Al ₂ O ₃ film is stably formed at the initial stage of heating, and when the temperature of the material becomes higher as the heating progresses, MgO is generated and Al ₂ O ₃ Is reduced. Therefore, in order to prevent the generation of MgO and the reduction of Al ₂ O ₃ , it is necessary to control the heating rate to 10 ° C / sec or faster.

On the other hand, in the general hot press forming, the heating temperature of the material is 600 to 950 ° C. If the heating temperature is 800 ° C. or more and 950 ° C. or less, the temperature raising rate is controlled to 20 ° C./sec or more more quickly, It is desirable to manage the time shorter than 60 seconds. As described above, the heating rate is faster and the staying time is shorter because MgO is excessively produced in the high temperature region. At this time, the staying time is preferably controlled to be 40 seconds or less, more preferably 20 seconds or less, and most preferably 15 seconds or less.

The heating rate is considerably faster than that in the case of using an ordinary furnace such as an electric furnace. According to one example, the heating may be performed by any one of radiant heating, high frequency induction heating, and energization heating have.

Although the above heating can be performed in the air, heating can be performed in an inert gas atmosphere (e.g., nitrogen, argon, etc.) in order to suppress surface oxidation by impurities and promote the production of Al ₂ O ₃ oxides.

Next, the hot-pressed product can be obtained by molding the Zn-Al-Mg-based plated steel material which has reached the heating temperature by the die and quenching it.

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 and specify the present invention and not to limit the scope of the present invention. And the scope of the present invention is determined by the matters described in the claims and the matters reasonably deduced therefrom.

( Example )

A steel material having the composition (% by weight) shown in the following Table 1 was prepared, and then the steel material was processed into a cold-rolled steel sheet having a thickness of 1.5 mm. Thereafter, annealing was performed for 40 seconds at a temperature of 780 占 폚 at the maximum in a nitrogen gas atmosphere containing 5 vol% of hydrogen, and the substrate was immersed in a zinc-based plating bath having the composition shown in Table 2 to obtain a plated steel material. At this time, the temperature of the zinc plating bath was kept constant at 450 캜.

Thereafter, each of the plated steel materials was heated under the conditions shown in Table 3 below, molded by a die, and quenched to manufacture a molded article.

Then, the tensile strength of each molded product was measured, and corrosion resistance and weldability were evaluated. The results are shown in Table 3 below. The corrosion resistance was measured by the salt spray test specified in KS R 1127, and the maximum corrosion depth of the substrate was measured after 1200 hours of corrosion after surface corrosion. In addition, weldability evaluation was performed by spot welding according to KS B ISO 15609, and the welding current range was measured.

Steel grade (% By weight) C Si Mn P S Al B River 1 0.18 0.25 1.3 0.01 0.001 0.02 0.0025 River 2 0.2 0.3 7.5 0.02 0.003 0.1 0.0040 River 3 0.31 0.3 2.2 0.01 0.003 0.05 0.0025

Plating bath type Plating bath component (% by weight) Mg Al Plating Bath 1 0.97 1.1 Plating Bath 2 1.41 1.43 Plating Bath 3 1.45 15 Plating Bath 4 3.12 2.54 Plating Bath 5 0 0.2

division Steel grade Plating bath type Surface roughness (Ra) Lead gold Lead gold deposition amount
(mg / m ² ) Plating layer thickness
(탆) Heating rate
(° C / sec) Heating temperature
(° C) Stay time
(second) Press start temperature
(° C) The ratio of Al / Mg in the oxide layer Mg _O / Mg _C Total deposition amount of Zn, Mg, and Al
(mg / m ² ) The tensile strength
(MPa) Welding current range
(KA) Maximum corrosion depth
(Mm) Inventory 1 River 1 Plating Bath 1 0.3 Fe 150 6 15 880 10 750 1.0 0.8 450 1480 1.0 0.5 Inventory 2 River 1 Plating Bath 2 0.9 - - 8 20 900 10 750 0.9 0.7 540 1510 1.0 0.4 Inventory 3 River 1 Plating Bath 3 0.9 - - 8 120 950 10 500 1.5 0.8 290 1530 1.1 0.4 Honorable 4 River 1 Plating Bath 4 0.9 - - 8 15 870 10 750 1.2 0.5 250 1490 1.2 0.5 Inventory 5 River 2 Plating Bath 4 2.0 - - 4 4 610 120 500 1.3 0.3 90 1310 1.4 0.5 Inventory 6 River 3 Plating Bath 4 1.5 Fe-Ni 300 5 4 780 10 500 1.0 0.9 600 1510 0.6 0.3 Honorable 7 River 2 Plating Bath 3 1.2 - - 8 4 700 10 500 1.3 0.2 70 1490 1.5 0.4 Honors 8 River 2 Plating Bath 4 1.2 - - 8 30 770 10 500 1.1 0.4 60 1510 1.8 0.5 Proposition 9 River 3 Plating Bath 3 1.5 - - 8 30 770 10 500 1.0 0.3 90 1480 1.0 0.3 Inventory 10 River 3 Plating Bath 4 1.5 - - 8 4 770 20 550 0.7 0.6 250 1530 0.9 0.4 Exhibit 11 River 3 Plating Bath 4 1.5 Ni 250 8 4 770 20 550 0.9 0.4 100 1530 1.2 0.3 Comparative Example 1 River 1 Plating Bath 1 0.9 - - 8 4 900 180 750 0.3 220 1700 1550 0 0.7 Comparative Example 2 River 1 Plating Bath 2 0.9 - - 8 4 900 300 750 0.4 345 2300 1520 0 - Comparative Example 3 River 1 Plating Bath 3 0.9 - - 8 4 900 300 750 0.4 1.5 900 1490 0.2 - Comparative Example 4 River 1 Plating Bath 5 0.9 - - 8 4 930 300 750 0.5 300 2500 1480 0 - Comparative Example 5 River 2 Plating Bath 4 1.2 - - 8 4 800 300 500 0.7 1.1 800 1520 0.2 0.8 Comparative Example 6 River 3 Plating Bath 5 1.5 - - 8 4 770 300 500 - - 1700 1510 0 0.7

In Examples 1 to 11 which satisfied all of the conditions proposed in the present invention, the Al / Mg content ratio in the oxide layer was all 0.8 or more, and thus, the 1,200 hours of brine water specified in KS R 1127 It can be confirmed that the maximum corrosion depth of the base member after the spray test is 0.5 mm or less, indicating excellent corrosion resistance. In addition, it can be confirmed that the weldable current range is 0.5 kA or more, indicating excellent weldability.

In Table 3, or the absence of Mg in the plating bath, as there is no Mg _O / Mg _C is described a plating bath 5, a case where the iron of the substrate does not remain Mg is depleted. In addition, the maximum depth of corrosion is the case where penetration corrosion occurs due to the specimen thickness and corrosion depth can not be measured.

1 is an SEM (Scanning Electron Microscope) image of a cross-section of a hot press molded article according to Inventive Example 5, and Fig. 2 is a scanning electron microscope (SEM) image obtained by scanning electron microscopy (SEM, Scanning Electron Microscope) image.

Claims (19)

A hot press formed product produced by hot press forming a Zn-Al-Mg based plated steel material including a base steel and a Zn-Al-Mg based plating layer,
Wherein the hot press-molded article includes an oxide layer formed on a surface thereof,
(Al / Mg) of the content of Al to the content of Mg contained in the oxide layer is 0.8 or more.
The method according to claim 1,
(Al / Mg) of the content of Al to the content of Mg contained in the oxide layer is 0.9 or more.
The method according to claim 1,
Wherein the total deposition amount of Zn, Al and Mg in the oxide layer is not more than 700 mg / m ² (excluding 0 mg / m ² ).
The method according to claim 1,
Wherein the oxide layer includes at least one selected from the group consisting of Mn, Si, and Fe, and the sum of the contents of Mn, Si, and Fe contained in the oxide layer is a ratio of the total metal content 50% or less.
The method according to claim 1,
Wherein the ratio of the total amount of Mg (Mg 2 _O ) contained in the oxide layer of the hot press formed article to the total amount (Mg _C ) of Mg contained in the plating layer of the hot press formed article is 1 or less.
The method according to claim 1,
The hot-rolled formed article having a plated layer of the hot-pressed product has an Fe alloyed degree of 20 to 70%.
The method according to claim 1,
Wherein the Zn-Al-Mg-based plating layer contains 0.9 to 3.5% of Mg, 1.0 to 15% of Al, and the balance of Zn and other unavoidable impurities in weight percent.
The method according to claim 1,
The above-mentioned ground iron is preferably a hot press comprising 0.15 to 0.35% of C, 0.5% or less of Si (excluding 0%), 0.5 to 8.0% of Mn, 0.0020 to 0.0050% of B, and the balance Fe and unavoidable impurities Shaped article.
The method according to claim 1,
A hot pressed product having a maximum corrosion depth of not more than 0.5 mm after a 1200 hour salt spray test as specified in KS R 1127.
The method according to claim 1,
A hot-pressed product having a tensile strength of 1300 MPa or more.
Immersing the substrate iron in a Zn-Al-Mg plating bath and performing plating to obtain a Zn-Al-Mg-based plating steel;
Heating the Zn-Al-Mg-based plated steel material to a heating temperature of 600 to 950 ° C at a rate of 10 ° C / sec or more in a heating furnace; And
Molding the Zn-Al-Mg-based plated steel material having reached the heating temperature by a mold and quenching it,
Wherein the stay time indicating the time during which the Zn-Al-Mg-based plated steel material which has reached the heating temperature stays in the heating furnace is 120 seconds or less.
12. The method of claim 11,
Wherein the heating temperature is 800 ° C or higher and 950 ° C or lower, the average heating rate to the heating temperature is 20 ° C / sec or higher, and the staying time is 60 seconds or lower.
12. The method of claim 11,
Wherein the heating is performed by any one of radiant heating, high frequency induction heating and energized heating.
12. The method of claim 11,
Wherein the heating is performed in an inert gas atmosphere.
12. The method of claim 11,
Wherein the ratio (Al / Mg) of the content of Al to the content of Mg contained in the Zn-Al-Mg system plating bath is 0.8 or more.
12. The method of claim 11,
Wherein the base steel is a cold-rolled steel sheet, and the surface roughness (Ra) before plating of the cold-rolled steel sheet is 2.0 占 퐉 or less.
12. The method of claim 11,
The above-mentioned ground iron is contained in an amount of 0.15 to 0.35% by weight, 0.5 to less than 0% (excluding 0%), 0.5 to 8.0% of Mn, 0.0020 to 0.0050% of B, and Fe and unavoidable impurities Wherein the hot press molded product is produced by a method comprising the steps of:
18. The method of claim 17,
Before obtaining the plated steel material,
Introducing at least one metal selected from the group consisting of Fe, Ni, Cu, Sn, and Sb to an average thickness of 5 to 100 nm; And
Annealing the preliminarily fired iron;
Further comprising the steps of:
19. The method of claim 18,
Wherein the annealing is performed in an atmosphere of 1 to 15% by volume of hydrogen gas and the balance of nitrogen gas.

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