KR101560883B1 - Steel for hot press forming with excellent formability and weldability and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a steel sheet for hot press forming, more specifically, to a steel sheet for hot press forming which is excellent in workability and weldability applicable to automotive parts and the like, and a method of manufacturing the same.
According to the present invention, it is possible to provide a plated steel sheet excellent in corrosion resistance and spot weldability with little occurrence of liquefied brittle cracks and micro cracks after hot press forming, and such plated steel sheets can be suitably used as a steel sheet for hot press forming There are advantages.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet for hot press forming having excellent workability and weldability,

The present invention relates to a steel sheet for hot press forming, more specifically, to a steel sheet for hot press forming which is excellent in workability and weldability applicable to automotive parts and the like, 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, since springback phenomenon also occurs during processing, it is difficult to precisely dimension work, so that molding of a complicated product is 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 that the steel sheet is softened at high temperature and becomes highly ductile, 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. To prevent this, there are many plated steel materials having a zinc- Is used. In particular, a galvanized steel sheet having a zinc-based plated layer is a steel material improved in corrosion resistance by utilizing the self-sacrificing corrosion resistance of zinc.

As described above, Patent Document 1 discloses a hot-dip galvanized steel sheet as a steel sheet having corrosion resistance. This is because when the hot-rolled steel sheet is hot-rolled after hot-dip galvanizing, the steel sheet has an excellent corrosion resistance because an alloy phase having a zinc content of 70% or more is present on the surface of the steel sheet.

However, when a galvanized steel sheet such as a hot-dip galvanized steel sheet is heated in air at a high temperature, zinc oxide is formed on the surface of the galvanized steel sheet, and this zinc oxide acts as a resistance which interrupts current conduction in a welding process such as spot welding after molding Therefore, there is a problem that the weldability is heated.

In order to improve the spot weldability, there is a method of additionally performing a step of removing zinc oxide present on the surface of the steel sheet after molding, but this poses a problem that the manufacturing cost is increased.

Patent Document 2 discloses a steel sheet for hot press forming having a steel sheet coated with aluminum and having an Al coating layer as a method for preventing the formation of oxides on the steel sheet surface after hot press forming. This is because when the hot-press molding is performed after the molten aluminum plating having excellent heat resistance is performed, the oxide does not exist on the surface of the molded article after molding or is very small, thereby being excellent in spot weldability. However, aluminum has a much lower sacrificial capacity than zinc in preventing the corrosion of ferrous iron, and the corrosion resistance of ferric iron is drastically lowered when the ferric iron is exposed.

On the other hand, if the plated steel sheet is heated at a high temperature for press forming, the heating temperature becomes higher than the melting point of the plated layer, so that a part of the plated layer exists in a liquid state for a certain period of time. When such a plating layer existing in a liquid state remains on the surface of the steel sheet, a tensile stress is generated on the surface of the steel sheet during press working, and the liquid phase is wetted to the grain boundary of the steel sheet. There is a problem that cracks are easily generated under tensile stress.

This phenomenon is referred to as a "liquid metal embrittlement phenomenon", and cracking of the steel sheet due to liquefied brittleness occurs mainly at a site where bending occurs during press forming.

Such a liquefied brittle crack is more likely to occur in a zinc-based plated steel sheet than in an aluminum-based plated steel sheet because the liquefied brittle crack is more likely to occur as the melting point of the plated layer is lower.

In order to prevent this, it is possible to form all the solid phase in the press forming process by alloying the plating layer and the substrate iron by performing the heating process for a long time, but when the heating time is long, the productivity is lowered and thick oxide There is a possibility of being formed.

In addition, there is a high possibility that cracks are generated in the plating layer at the deep drawing portion where the surface friction is severe due to the direct contact between the mold and the plating layer during the press forming process after the high temperature heating. Thus, the cracks generated in the plating layer, There is a problem of micro-cracks in which fine cracks are generated to the surface of the steel sheet.

Such fine cracks are considered to act as a starting point for propagation of cracks in the base steel sheet, cause fatigue cracks, and have a high possibility of hindering the durability of parts.

Therefore, the characteristics required of the coated steel sheet for hot press forming with excellent workability as well as workability are that the lubrication brittle cracks and fine cracks do not occur during the molding process, and the surface oxides And at the same time, it should have a sacrificial property capable of sufficiently protecting the iron of the molded article.

Japanese Patent Application Laid-Open No. 2006-022395 U.S. Patent No. 6296805

One aspect of the present invention relates to a coated steel sheet for hot press forming, which is free from liquefaction brittle cracks and micro cracks and provides excellent workability and excellent spot weldability after molding, and a method for producing the same I would like to.

One aspect of the present invention includes a base steel sheet and a composite plating layer formed on the base steel sheet,

Wherein the composite plating layer comprises two or more multi-layer Mn plating layers and Al plating layers alternately, and the uppermost layer includes an Al plating layer, and the Mn plating layer contains 50% or less of the total thickness of the composite plating layer A steel sheet for hot press forming is provided.

According to another aspect of the present invention, there is provided a method of manufacturing a steel sheet, Forming a Mn plating layer on one surface of the upper base steel sheet by performing Mn plating; And forming an Al plating layer by performing Al plating on the Mn plating layer,

Wherein the step of forming the Mn plating layer and the Al plating layer is repeated once or twice or more to form a composite plating layer composed of two or more layers in a multilayered structure on one side of the base steel sheet, Of the present invention.

According to the present invention, it is possible to provide a plated steel sheet excellent in corrosion resistance and spot weldability with little occurrence of liquefied brittle cracks and micro cracks after hot press forming, and such plated steel sheets can be suitably used as a steel sheet for hot press forming There are advantages.

1 is a schematic cross-sectional view of a hot-rolled steel sheet according to an embodiment of the present invention
(B): a steel sheet having a composite plating layer of an Al plating layer / a Mn plating layer / an Al plating layer; (C) a Mn plating layer / an Al plating layer / an Mn plating layer / Al plating layer of a steel sheet having a composite plating layer.
Fig. 2 shows a schematic view of a molded product obtained by hot-pressing a plated steel sheet and a crack observation site.

The most suitable plated steel sheet for hot press forming (HPF) is required to have a solid plated layer in the press forming process after high temperature heating, and there is little occurrence of micro cracks after press forming, and the plated layer sufficiently protects The sacrificial system should be excellent.

The aluminum-plated steel sheet, which is well-known as a coated steel sheet, has a very thin oxide on the surface of the steel sheet after hot press forming due to heat resistance and is excellent in spot welding characteristics of the molded part, exists in solid phase during press molding at a high melting point of the Al- There is an advantage that brittle cracks are not caused and micro-cracks are not generated due to less friction with the die during molding.

However, such an aluminum-plated steel sheet is disadvantageous in that the alloy layer after the hot press forming has a galvanic corrosion resistance lower than that of the galvanized steel sheet because the electrochemical potential of the alloy layer is not sufficient to protect the steel sheet.

The inventors of the present invention have conducted intensive studies on a plated steel sheet which can satisfy all the properties required for a hot press forming steel sheet. As a result, the present inventors have found that, in the case where the thickness of the Mn plating layer is controlled in addition to the Al plating layer, There is no occurrence of liquefied brittle cracks and fine cracks after hot press forming, and a hot press forming part having excellent workability, excellent spot weldability due to few oxides formed on the surface of the plating layer, and excellent sacrificial corrosion resistance And the present invention has been accomplished.

Particularly, the present invention provides a steel sheet for hot press forming which has excellent physical properties after hot press forming as described above, and a method for producing the same.

Hereinafter, a steel sheet for hot press forming excellent in workability and weldability which is one aspect of the present invention will be described in detail.

The steel sheet for hot press forming according to the present invention is a coated steel sheet comprising a base steel sheet and a composite plated layer formed on the base steel sheet, wherein the composite plated layer is composed of an Mn plating layer and an Al plating layer.

As the base steel sheet for the hot press forming steel sheet having the composite plated layer as described above, ordinary carbon steel can be used, and preferably 0.1 to 0.4% of carbon (C), 0.05 To 1.5%, manganese (Mn): 0.5 to 3.0%, Fe and other unavoidable impurities.

Hereinafter, the reasons for limiting the constituents of the above-mentioned base steel sheet will be described in detail.

C: 0.1 to 0.4%

Carbon (C) is the most effective element to increase the strength of the steel sheet, but it is an element that lowers the weldability and low temperature toughness when added in large amounts. When the content of C is less than 0.1%, it is difficult to secure a desired strength even if hot pressing is performed in a single phase of austenite, whereas when it exceeds 0.4%, weldability and low-temperature toughness deteriorate, which is not preferable , The strength becomes excessively high, which disadvantageously increases the manufacturing process such as inhibiting the ducting in the annealing and plating process.

Therefore, it is preferable that the carbon content is 0.1 to 0.4%.

Si: 0.05 to 1.5%

Silicon (Si) is used as a deoxidizer and is an element added for strength enhancement by solid solution strengthening. In order to exhibit such an effect in the present invention, it is preferable that the content is more than 0.05%. If the content is more than 1.5%, it is difficult to pick up the hot rolled sheet and scaly surface defects due to the hot rolled steel sheet, Lt; / RTI >

Mn: 0.5 to 3.0%

Manganese (Mn) is a solid solution strengthening element that not only contributes greatly to the strength increase but also is an effective element for delaying the transformation from austenite to ferrite. In order to exhibit such effects in the present invention, it is preferable that the content is 0.5% or more, but if the content exceeds 3.0%, the weldability, hot rolling property, and the like are deteriorated.

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.

However, the base steel sheet may contain 0.001 to 0.02% of nitrogen (N), 0.0001 to 0.01% of boron (B), 0.001 to 0.1% of titanium (Ti), 0.001 to 0.1% of niobium (Nb) , 0.001 to 0.01% of chromium (Cr), 0.001 to 1.0% of molybdenum (Mo), 0.001 to 0.1% of antimony (Sb) and 0.001 to 0.3% of tungsten (W) And may further include one or more selected ones.

N: 0.001 to 0.02%

Nitrogen (N) acts on aluminum during the coagulation process in austenite grains to precipitate fine nitrides to promote twinning, which improves the strength and ductility of the steel sheet. However, as the content of nitrogen increases, nitride is excessively precipitated It is preferable to control the content of N because the hot workability and the elongation are lowered. If the content of N is less than 0.001%, the manufacturing cost for controlling N in the steelmaking process is greatly increased. On the other hand, when the content of N exceeds 0.02%, excessive nitrides are precipitated to cause hot workability, elongation and cracking do.

B: 0.0001 to 0.01%

Boron (B) is an effective element to retard ferrite transformation in austenite. In order to achieve the above-mentioned effects, the steel of the present invention preferably contains 0.0001% or more, but when the content exceeds 0.01%, the hot workability is deteriorated.

Ti, Nb and V: 0.001 to 0.1%

Titanium (Ti), niobium (Nb), and vanadium (V) are effective elements for increasing the strength of the steel sheet, making the grain size finer, and improving the heat treatability. In order to achieve the above-described effects, the present invention preferably includes 0.001% or more of each element. When the content of each element is more than 0.1%, the manufacturing cost is increased and excessive amount of carbon and nitride are generated It is difficult to secure the desired strength and yield strength.

Cr and Mo: 0.001 to 1.0%

Chromium (Cr) and molybdenum (Mo) are effective elements for not only greatly improving the hardenability but also increasing the toughness of the steel sheet. Therefore, the effect is more remarkable when it is added to a steel sheet requiring a high impact energy characteristic. If the content is less than 0.001%, the above effects can not be sufficiently obtained. If the content exceeds 1.0%, the effect is saturated and the production cost is increased.

Sb: 0.001 to 0.1%

Antimony (Sb) is an element that plays a role in suppressing selective oxidation of grain boundaries during hot rolling, thereby making the scale uniform and improving the pickling resistance of the hot rolled material. In order to exhibit the above-mentioned effects, the present invention preferably includes 0.001% or more. However, when the content is more than 0.1%, not only the effect is saturated but also the production cost is increased and brittleness is caused in hot working.

W: 0.001 to 0.3%

Tungsten (W) is an element that improves the heat-curing ability of a steel sheet, and tungsten-containing precipitates are elements that act to secure strength. In order to achieve the above-mentioned effects, the present invention preferably includes 0.001% or more. However, when the content exceeds 0.3%, the effect is saturated and the manufacturing cost is increased.

In order to apply the above-described base steel sheet as a steel sheet for hot press forming, it is preferable to have a plating layer on the base steel sheet, wherein the plating layer is a composite plating layer, and the composite plating layer is preferably composed of an Mn plating layer and an Al plating layer Do.

In the present invention, the addition of the Mn plating layer in addition to the Al plating layer is intended to improve the low sacrificial corrosion resistance of the plated steel sheet having only the conventional Al plating layer. In addition, since the present invention further includes the Mn plating layer, have.

However, in forming the Mn plating layer, it is preferable that the Mn plating layer is formed to be 50% or less of the total thickness of the composite plating layer.

Mn and Al-Mn-Fe based alloys having a high melting point are produced when Mn and Al are alloyed when the base steel sheet having the composite coating layer composed of the Mn plating layer and the Al plating layer is heated for hot press forming, The plating layer is present in a solid phase. At this time, as the proportion of the Mn plating layer is increased, an alloy phase having a higher melting point is formed, so that the liquefaction phenomenon of the plating layer can be effectively suppressed.

However, Mn is an element whose electrochemical potential is lower than Fe. The alloy phase formed by alloying Mn with Al and Fe has a lower electrochemical potential than Al alone or Al-Fe alloy phase. Therefore, as the ratio of the Mn plating layer in the composite plating layer increases, the potential of the alloy layer after the hot pressing is lowered, so that the sacrificial resistance to the iron is increased. However, if the Mn plating layer exceeds 50% Is diffused to the surface layer of the plating layer, and a part thereof is formed of Mn oxide. As described above, since the Mn oxide formed on the surface of the plating layer has a large electrical resistance as compared with the metal, it causes a deterioration in the weldability in spot welding.

Therefore, in the present invention, it is preferable that the Mn plating layer is formed to be 50% or less of the total thickness of the composite plating layer.

The composite plating layer of the present invention may include two layers of Mn plating layer and Al plating layer, one layer each, or alternatively three or more layers in total. However, it is preferable that the uppermost layer of the above-mentioned composite plating layer includes an Al plating layer.

For example, as shown in Fig. 1, when the composite plating layer of the present invention is composed of two layers, it is preferable to include Mn plating layer / Al plating layer in this order. When the composite plating layer is composed of three layers, the Al plating layer / / Al plating layer in the order of Mn plating layer / Al plating layer / Mn plating layer / Al plating layer in the order of Mn plating layer / Al plating layer / Mn plating layer / Al plating layer.

As described above, it is preferable that the composite plating layer of the present invention, which can contain Mn plating layer and Al plating layer in multiple layers, has a thickness of 5 to 30 占 퐉.

When the thickness of the composite plating layer is less than 5 mu m, the corrosion resistance can not be sufficiently secured. On the other hand, when the thickness exceeds 30 mu m, corrosion resistance can be sufficiently secured, but production cost is increased. At this time, the thickness of the plating layer is based on one side.

As in the present invention, when the plating layer is composed of the Mn plating layer and the Al plating layer, it is possible to satisfy not only the properties required as the coated steel sheet for hot press forming, but also the weldability But it is worth noting that it can be secured.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a preferred method for producing a steel sheet for hot press forming according to the present invention will be described in detail as one embodiment.

The method for producing a steel sheet for hot press forming according to the present invention may comprise a step of forming a composite plated layer by subjecting a base steel sheet to Mn plating and Al plating.

At this time, the composite plating layer forming step may be repeated one or more times, thereby forming a composite plating layer composed of two or more double-layered layers on one side of the base steel sheet.

In addition, a composite plating layer comprising an Al plating layer / a Mn plating layer / an Al plating layer may be formed by sequentially performing Al plating / Mn plating / Al plating on one surface of the above-mentioned base steel sheet.

The Mn plating and Al plating may be performed by one of the methods selected from electroplating, hot dip galvanizing, electroless plating, vapor deposition plating, sputtering, ion plating and spray coating.

At this time, it is preferable to use the deposition plating method which facilitates the plating operation, the plating efficiency and the deposition amount adjustment, and the Al plating is a plating method which is advantageous in terms of convenience of plating operation, plating efficiency and plating cost desirable.

In the meantime, in order to improve the adhesion between the base steel sheet and the plating layer, the surface of the base steel sheet may be pre-plated before the plating process, wherein the pre-plating is performed in a range of 0.02 to 2 g / m ² And at least one of Fe, Ni, Co, Cu, Zn, Sn, Bi, Cr, Mg, Si, P, Ti and Mo may be mixed.

Further, the steel sheet for hot press forming having the composite plating layer as described above can be heated at a high temperature for subsequent press forming, and at this time, the steel sheet is heated to a temperature range of Ac ₃ transformation point to 1000 ° C, .

Heating by an electric furnace, gas or the like, flame heating, energization heating, high frequency heating, induction heating, and the like may be carried out during the heating, but the present invention is not limited thereto.

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 from them.

( Example )

A cold-rolled steel sheet having a thickness of 1.5 mm was prepared from a base steel sheet, and then pretreated under normal conditions to remove surface foreign substances from the cold-rolled steel sheet. Then, a first plating layer was formed by depositing Mn on the upper side of the base steel sheet so as to have a plating thickness as shown in Table 1 below, and Al was vapor-deposited thereon to form a second plating layer.

For comparison, a plated steel sheet plated with Al, Mn or Zn alone was prepared on a base steel sheet.

Table 1 shows the total thickness of the plated layer obtained by dissolving the plated layers of each of the prepared plated steel sheets and analyzing the amount of deposited plated layers.

division
Plated layer
Configuration The first plating layer The second plated layer Plated layer
Overall Thickness
(One side, 탆) Plated layer
Thickness ratio
(%) Plating species Plating Thickness
(One side, 탆) Plating species Plating Thickness
(One side, 탆) Inventive Steel 1 Second floor Mn 1.1 Al 8.9 10 11 Invention river 2 Second floor Mn 3.2 Al 8.9 12.1 26.4 Invention steel 3 Second floor Mn 3.3 Al 13.9 17.2 19.2 Inventive Steel 4 Second floor Mn 5.5 Al 15.4 20.9 26.3 Invention steel 5 Second floor Mn 2.5 Al 10.1 12.6 19.8 Invention steel 6 Second floor Mn 9.0 Al 10.1 19.9 45.2 Invention steel 7 Second floor Mn 5.2 Al 11.1 16.3 31.9 Inventive Steel 8 Second floor Mn 2.8 Al 19.8 22.6 12.4 Comparative River 1 fault Al 15 - - 15 100 Comparative River 2 fault Mn 13.8 - - 13.8 100 Comparative Steel 3 fault Zn 9.5 - - 9.5 100 Comparative Steel 4 Second floor Mn 13.6 Al 1.4 15 90.7 Comparative Steel 5 Second floor Al 13.5 Mn 2.4 15.9 84.7

(In Table 1, the plating layer thickness ratio is calculated as {(first plating layer thickness / total plating layer thickness) x 100}.

Each of the plated steel sheets was subjected to hot press forming under the conditions shown in Table 2 below to produce molded articles, and the properties of the molded articles thus produced were evaluated.

At this time, whether or not the liquefied brittle cracks and fine cracks of the molded article were observed was determined by observing the cross section of the portion shown in Fig. 2 with an optical microscope 100 times and then measuring the maximum depth in the depth direction from the base steel surface of the largest crack size, Table 2 shows the results.

In order to evaluate the spot weldability of the molded product, the contact resistance was measured. For the corrosion resistance evaluation, the salt corrosion test (SST) was carried out for 1200 hours, and the maximum corrosion depth of the substrate iron was measured and shown in Table 2 below .

division Hot press heating conditions Evaluation of physical properties of molded products Heating temperature
(° C) Average
Heating rate
(° C / s) Retention time
(sec) Liquefied brittle crack depth
(탆) Fine crack depth
(탆) spot
Weldability
(mΩ) Corrosion resistance
(mm) Inventory 1 900 6 150 &Lt; 0.1 &Lt; 0.1 <0.5 0.19 Inventory 2 880 6 150 &Lt; 0.1 &Lt; 0.1 <0.5 &Lt; 0.1 Inventory 3 880 100 150 &Lt; 0.1 &Lt; 0.1 <0.5 &Lt; 0.1 Honorable 4 930 7.4 30 &Lt; 0.1 &Lt; 0.1 <0.5 &Lt; 0.1 Inventory 5 900 15 200 &Lt; 0.1 &Lt; 0.1 <0.5 &Lt; 0.1 Inventory 6 900 4.2 100 &Lt; 0.1 &Lt; 0.1 <0.5 &Lt; 0.1 Honorable 7 900 6 150 &Lt; 0.1 &Lt; 0.1 <0.5 &Lt; 0.1 Honors 8 900 6 150 &Lt; 0.1 &Lt; 0.1 <0.5 &Lt; 0.1 Comparative Example 1 900 6 150 <0.5 &Lt; 0.1 <0.5 0.45 Comparative Example 2 900 6 120 &Lt; 0.1 &Lt; 0.1 7.8 0.25 Comparative Example 3 900 6 150 25 18.5 5.6 0.29 Comparative Example 4 900 6 150 &Lt; 0.1 &Lt; 0.1 2.2 0.21 Comparative Example 5 900 6 150 &Lt; 0.1 &Lt; 0.1 4.2 0.41

As shown in Tables 1 and 2, Inventive Examples 1 to 8 show the steel sheets for hot press forming (invention steels 1 to 8) produced according to the present invention at a heating rate of 4.2 to 100 DEG C per second to a temperature of 880 to 930 DEG C The steel plate was formed by heating and holding at the temperature for 30 to 200 seconds and then cooled and formed. The depth of the liquefied brittle cracks and fine cracks was less than 0.1 mu m and the contact resistance of the molded product was as small as 0.5 m? The corrosion depth was 0.19mm or less and the corrosion resistance was excellent.

On the other hand, in Comparative Example 1, when Al was plated to a thickness of 15 탆, the liquefaction brittle crack was less than 0.5 탆, the fine crack depth was less than 0.1 탆, and the contact resistance of the molded article was as small as 0.5 m? As a result of the sacrificial corrosion resistance, it was confirmed that the corrosion depth of the substrate iron after the salt spray test was deep as 0.45 mm.

Comparative Example 2 was a case where Mn was plated to a thickness of 13.8 占 퐉 and the melting point of Mn was high and liquefied embrittlement cracks were excellent at less than 0.1 占 퐉 and surface friction characteristics were excellent and the fine crack depth was measured at less than 0.1 占 퐉, The contact resistance of the molded product was very high as 7.8 m? As the surface Mn was oxidized to form a thick oxide and the corrosion resistance was not excellent due to the formation of the Fe-Mn alloy phase.

Comparative Example 3 was a case of a hot-dip galvanized steel sheet in which, after heating, the presence of liquid zinc in the plated layer resulted in a very large liquefied brittleness crack of 25 mu m and a poor cracking property of zinc at high temperature, resulting in a fine crack depth of 18.5 mu m Respectively. In addition, it was confirmed that the contact resistance of the molded product was as large as 5.6 m? As the zinc was oxidized at a high temperature and a comparatively thick oxide was formed on the surface, and the corrosion resistance was improved by the depth of the substrate iron corrosion depth of 0.29 mm.

Comparative Example 4 is a case where Mn plating and Al plating are sequentially performed according to the present invention, but when the ratio of the thickness of the Mn plating layer among the entire plating layers exceeds 50%, the liquefied embrittlement cracks and micro crack depths are less than 0.1 mu m However, the contact resistance of the molded product was as high as 2.2mΩ and the corrosion depth was 0.21mm as the part of Mn in the Mn plating layer was diffused into the surface layer to form oxides.

Comparative Example 5 was a case in which Al plating and Mn plating were performed sequentially and the liquefaction brittle cracks and fine cracks had depths of less than 0.1 mu m but Mn in the surface layer formed oxides in the surface during high temperature heating , The contact resistance of the molded product was as high as 4.2 mΩ or less and the spot weldability was poor, and the base iron corrosion depth was 0.41 mm, indicating that the corrosion resistance was also improved.

Claims (10)

A base steel sheet, and a composite plating layer formed on the base steel sheet,
Wherein the composite plating layer comprises two or more multi-layer Mn plating layers and Al plating layers alternately, and the uppermost layer includes an Al plating layer, and the Mn plating layer contains 50% or less of the total thickness of the composite plating layer Steel sheet for hot press forming.
delete The method according to claim 1,
Wherein the composite plating layer has a thickness of 5 to 30 占 퐉. The steel sheet for hot press forming has excellent processability and weldability.
The method according to claim 1,
Wherein said base steel sheet comprises 0.1 to 0.4% carbon (C), 0.05 to 1.5% silicon (Si), 0.5 to 3.0% manganese (Mn), Fe and other unavoidable impurities, A steel sheet for hot press forming excellent in weldability.
5. The method of claim 4,
Wherein the base steel sheet comprises 0.001 to 0.02% of nitrogen (N), 0.0001 to 0.01% of boron (B), 0.001 to 0.1% of titanium (Ti), 0.001 to 0.1% of niobium (Nb) (Sb): 0.001 to 0.1%, and tungsten (W): 0.001 to 0.3%, and the molybdenum (Mo) Wherein the steel sheet further contains two or more kinds of steel sheet.
A step of preparing a base steel sheet and a step of forming an Mn plating layer and an Al plating layer on one surface of the base steel sheet are repeated one or more times to form a composite plating layer comprising two or more layers and an Al plating layer Lt; / RTI &gt;
The step of forming the Mn plating layer and the Al plating layer includes the steps of forming an Mn plating layer by performing Mn plating, forming an Al plating layer by performing Al plating on the Mn plating layer, or forming an Al plating layer by performing Al plating And forming a Mn plating layer by performing Mn plating on the Al plating layer,
Wherein the Mn plating layer is formed to a thickness of 50% or less of the total thickness of the composite plating layer.
The method according to claim 6,
Wherein the forming of the composite plating layer comprises sequentially performing Al plating / Mn plating / Al plating on one surface of the base steel sheet, wherein the processability and weldability are excellent.
delete The method according to claim 6,
Wherein the composite plated layer is formed to have a thickness of 5 to 30 占 퐉.
The method according to claim 6,
The Mn plating and Al plating are carried out by one of the methods selected from electroplating, hot dip galvanizing, electroless plating, vapor deposition plating, sputtering, ion plating and spray coating. &Lt; / RTI &gt;

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