WO2023121241A1 - Plated steel sheet having excellent plating adhesion and corrosion resistance after hot press forming, preparation method for plated steel sheet, and hot pressed forming member - Google Patents

Abstract

The present invention relates to: a plated steel sheet for hot press forming, having excellent plating adhesion and corrosion resistance after hot press forming; a preparation method for the plated steel sheet; and a hot pressed forming member. The plated steel sheet according to an aspect of the present invention comprises a base steel sheet and a plating layer consisting of Al-Fe alloy formed on the base steel sheet, wherein the total amount of Al and Fe in the plating layer is 80 % or more by weight, the average amount of Fe in the plating layer is 20 % or more by weight, and the product of Ra and RPC of the surface of the plating layer may be 60-150 μm/cm. Here, Ra represents arithmetic mean roughness and the unit thereof is μm, and RPc represents the number of peaks per unit length and the unit thereof is /cm.

Description

Plated steel sheet showing excellent paint adhesion and corrosion resistance after hot press forming, manufacturing method of coated steel sheet, and hot press formed member

The present invention relates to a coated steel sheet for hot press forming, a method for manufacturing the coated steel sheet, and a hot press formed member.

Recently, due to the depletion of petroleum energy resources and high interest in the environment, regulations for improving fuel efficiency of automobiles are becoming stronger day by day. In terms of materials, one way to improve the fuel efficiency of a car is to reduce the thickness of the steel sheet used. However, if the thickness is reduced, problems may arise in the safety of the car, so improvement in the strength of the steel sheet must be supported. It should be.

For this reason, demand for high-strength steel sheets has been continuously generated, and various types of steel sheets have been developed. However, since these steel sheets themselves have high strength, there is a problem in that workability is poor. That is, since the product of strength and elongation always tends to have a constant value for each grade of steel sheet, when the strength of the steel sheet increases, the elongation rate, which is an indicator of workability, decreases.

In order to solve this problem, a hot press molding method has been proposed. The hot press forming method is a method of forming a low-temperature structure such as martensite in a steel sheet by processing the steel sheet at a high temperature suitable for processing and then rapidly cooling it to a low temperature to increase the strength of the final product. In this case, there is an advantage in that workability problems can be minimized when manufacturing a member having high strength.

However, in the case of the hot press forming method, since the steel sheet is heated to a high temperature, the surface of the steel sheet is oxidized, so there is a problem that a process of removing oxides from the surface of the steel sheet must be added after press forming. Patent Document 1 has been proposed as a method for solving this problem. In Patent Document 1, a steel sheet subjected to aluminum plating is used in a process of heating and rapidly cooling after hot press forming or room temperature forming (briefly, 'post heat treatment'), and since the aluminum plating layer exists on the surface of the steel sheet, the steel sheet is oxidized during heating. It doesn't work.

(Patent Document 1) US Patent Publication No. 6,296,805

According to one aspect of the present invention, there is provided a coated steel sheet for hot press forming capable of improving coating adhesion of a hot press formed member and ensuring corrosion resistance, and a method of manufacturing the coated steel sheet.

According to another aspect of the present invention, a hot press-formed member excellent in paint adhesion and corrosion resistance is provided.

The object of the present invention is not limited to the above range. Anyone skilled in the art to which the present invention pertains will have no difficulty in understanding the additional problems of the present invention from the overall details described in this specification.

A plated steel sheet according to one aspect of the present invention includes a base steel plate and a plating layer made of an Al-Fe alloy formed on the base steel plate, and the total content of Al and Fe in the plated layer is 80% or more by weight, wherein the The average content of Fe in the plating layer may be 20% or more by weight, and the product of Ra and RPc of the surface of the plating layer may be 60 to 150 μm/cm.

However, Ra means arithmetic average roughness and its unit is μm, and RPc means the number of peaks per unit length and its unit is /cm.

A coated steel sheet according to another aspect of the present invention includes a base steel sheet and a plating layer made of an Al-Fe alloy formed on the base steel sheet, wherein the total content of Al and Fe in the plating layer is 80% or more by weight, The average content of Fe in the plating layer is 20% or more by weight, and the number of cracks existing in each region obtained by dividing the surface of the plating layer into 10 equal parts horizontally and vertically when observing the surface of the plating layer at a magnification of 100 times with a scanning electron microscope. is 10 to 200 per 1 mm ² , and the ratio of the area occupied by the indentation portion on the surface of the plating layer may be 5 to 50%.

Here, the indentation means a region having a brightness of 70% or more compared to the highest brightness measured in an area observed at a magnification of 100 times with an optical microscope.

A method for manufacturing a plated steel sheet according to another aspect of the present invention includes obtaining an Al-Fe alloy plated steel sheet having a plating layer made of an alloy of Al and Fe formed on a base steel sheet; and performing skin pass rolling on the Al-Fe alloy coated steel sheet under the condition that the SPMI expressed by the following relational expression 1 is 5000 to 8500.

[Relationship 1]

Here, P is the rolling force during skin pass rolling (unit: ton), the Ra _roll is the arithmetic average roughness of the surface of the skin pass rolling roll (unit: μm), and the RPc _roll is the number of peaks per unit length of the skin pass rolling roll (unit: /cm). In addition, the unit of the SPMI is √Ton·㎛/cm.

A hot press-formed member according to another aspect of the present invention includes a base steel plate and a plating layer made of an Al-Fe alloy formed on the base steel plate, and the total content of Al and Fe in the plated layer is 70% by weight. In the above, the content of Fe in the plating layer may be 30% or more by weight, and the product of Ra and RPc of the surface of the plating layer may be 60 to 150 μm/cm.

However, Ra means arithmetic average roughness and its unit is μm, and RPc means the number of peaks per unit length and its unit is /cm.

A hot press-formed member according to another aspect of the present invention includes a base steel plate and a plating layer made of an Al-Fe alloy formed on the base steel plate, and the total content of Al and Fe in the plated layer is 70% by weight. Above, the average content of Fe in the plating layer is 30% or more by weight, and present in each region obtained by dividing the field of view obtained when the surface of the plating layer is observed at a magnification of 100 times with a scanning electron microscope into 10 horizontally and vertically. The number of cracks may be 15 to 220 per 1 mm ² , and the ratio of the area occupied by the indentation portion on the surface of the plating layer may be 5 to 50%.

Here, the indentation means a region having a brightness of 70% or more compared to the highest brightness measured in an area observed at a magnification of 100 times with an optical microscope.

As described above, since the Ra and RPc of the surface of the coated steel sheet of the present invention are controlled to appropriate levels, it is possible to secure sufficient paint adhesion of the member even if a large increase in roughness does not occur during the hot press forming process.

1 is a photograph of the surfaces of aluminum-iron-based coated steel sheets prepared by Comparative Example 1 (a) and Inventive Example 2 (b) observed with a scanning electron microscope (SEM).

Figure 2 is a photograph of the image processing result of observing the surface of the aluminum-iron-based coated steel sheet prepared by Comparative Example 1 (a) and Inventive Example 2 (b) with an optical microscope.

3 is a graph showing the relationship between the number of cracks generated on the surface of an aluminum-iron-based coated steel sheet according to skin pass rolling conditions.

The terminology used herein is intended only to refer to specific embodiments and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite.

As used herein, the meaning of "comprising" specifies specific characteristics, regions, integers, steps, operations, elements, and/or components, and other specific characteristics, regions, integers, steps, operations, elements, elements, and/or groups. does not exclude the presence or addition of

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having meanings consistent with related technical literature and currently disclosed content, and are not interpreted in ideal or very formal meanings unless defined.

Further, in the present invention, the steel sheet refers to a coil or sheet state before being processed into a specific shape, and a member refers to a steel sheet processed into a non-plate shape by a molding process. In addition, the plating layer referred to in the present invention means a layer of metal, alloy or intermetallic compound formed in contact with the base steel sheet.

It should be noted that in the present invention, when the content of each element is expressed, it is based on weight unless otherwise specified. In addition, the ratio of crystals or structures is based on area unless otherwise specified, and the content of gas is based on volume unless otherwise specified.

Hereinafter, the present invention will be described in detail.

As described above, when the aluminum-coated steel sheet is heated for hot press forming, problems such as melting of the aluminum plating layer depending on the heating rate and contaminating equipment may occur. In addition, in the case of a high-strength member, there may be a case where hydrogen trapped in the base steel sheet is accumulated and a problem of so-called hydrogen delayed fracture that leads to the destruction of the part may occur.

As one way to solve this problem, there may be a method of heating an aluminum-coated steel sheet before heating to form an aluminum-iron alloy layer on the steel sheet, and then using the steel sheet having the aluminum-iron alloy plating layer formed thereon for hot press forming. That is, if the plating layer is alloyed in a relatively low temperature range before heating for hot press forming, even if it is heated at a relatively high speed, since aluminum is already alloyed, even if it is heated to a temperature higher than the melting point of aluminum, the melting of aluminum problems can be avoided. In addition, in the case of a pre-alloyed plated steel sheet, it may have an alloy layer having a structure in which hydrogen is easily discharged on the surface, thereby reducing the possibility of hydrogen delayed fracture.

On the other hand, when painting is performed on a general plated steel sheet, there is no anchor capable of fixing the painting (paint) layer, which may cause insufficient adhesion between the painting and the surface of the steel sheet. Therefore, in order to solve this problem, phosphate treatment is usually performed, and the roughness of the surface of the steel sheet after phosphate treatment increases, thereby increasing the adhesion between the steel sheet and the paint.

However, there is a problem that it is difficult to increase the surface roughness of the member any longer when hot press forming the plated steel sheet having the aluminum-iron plating layer formed on the surface thereof. The plating layer formed on the surface of the hot press-formed member is formed by an alloying reaction between aluminum and iron and is relatively chemically stable. As such, since the surface of the hot press-formed member is chemically stable, it is difficult to improve the roughness any longer even with phosphate treatment. However, in the case of hot press forming by heating a conventional aluminum-coated steel sheet, since the surface roughness increases in the process of heating the aluminum-coated steel sheet, sufficient roughness can be secured without phosphate treatment, so there may be no major problem in paint adhesion.

On the other hand, in the case of an aluminum-iron alloy coated steel sheet in which an aluminum-iron alloy layer is formed by prior alloying treatment, the increase in roughness is not large during subsequent heating for hot press forming. Therefore, although the roughness is partially increased in the pre-alloying heat treatment process, the increase in roughness in the subsequent hot press forming process is not large, so the surface roughness of the member obtained by hot press forming the aluminum-iron alloy coated steel sheet is obtained by alloying the aluminum coated steel sheet. Compared to the surface roughness of a member obtained by direct hot press molding without heat treatment, there may be a problem that the paint adhesion is not sufficient.

In addition, since the aluminum alloy plating layer is not superior in sacrificial corrosion protection performance compared to the zinc-based plating layer, there is a problem in that corrosion occurs along with blisters when the steel sheet is exposed due to cracks or the like.

In general, when the surface roughness (Ra) is increased, it is common that the coating adhesion is improved, and thus the corrosion resistance after coating is also improved. However, according to the present inventors, not only the surface roughness is simply increased, but also the As a result of the study, it was confirmed that increasing the value of the product of roughness (Ra) (Ra×RPc) is effective in improving paint adhesion and corrosion resistance.

In addition, while the inventors of the present invention grasped the paintability of a hot press formed member manufactured using a so-called aluminum-iron alloy plated steel sheet already alloyed before hot press forming, as described above, in the case of an alloy plated steel sheet, a considerable amount has already been obtained. Since iron was diffused into the plating layer, the increase in surface roughness (Ra) and number of peaks per unit length (RPc) due to additional iron diffusion was not large. It has been found that increasing the number (RPc) and consequently increasing the Ra x RPc value is effective in increasing the Ra x RPc value of the hot press formed part.

Therefore, in one embodiment of the present invention, in consideration of the surface Ra × RPc of the member obtained by hot press molding in order to secure high paint adhesion, Ra × RPc of the surface of the plated layer of the coated steel sheet may be 60 μm / cm or more. In the formula, Ra is the arithmetic mean roughness and has a unit of μm, and RPc is the peak count (Peak Count) and has a unit of the reciprocal of cm (/cm). When the Ra×RPc is not sufficient, it may be difficult to expect sufficient paint adhesion, so the lower limit of the Ra×RPc may be set at 60 μm/cm. In some cases, the lower limit of Ra×RPc may be set to 70 μm/cm. In order to improve the coating adhesion, the higher the value of Ra × RPc, the better. However, if the value is too high, excessive cracks may be introduced to the surface of the plating layer during the processing process to increase Ra and RPc, and corrosion resistance may be lowered. Therefore, the present invention In one implementation example, the upper limit of the RaХRPc may be set to 150 μm/cm, and in some cases, the upper limit of the Ra×RPc may be set to 140 μm/cm.

In addition, in the coated steel sheet according to another embodiment of the present invention, by appropriately adjusting the ratio of the number of cracks formed on the surface and the area ratio of the indentation portion, the coating adhesion and corrosion resistance of the member obtained by the subsequent hot press forming process can be improved. . To this end, the plated steel sheet according to one embodiment of the present invention may have 10 to 200 cracks per 1 mm ² of the surface area of the plated layer, and the ratio of the area occupied by the indentation portion on the surface of the plated layer may be 5 to 50%.

Since the cracks can serve as a fixing part in which the coating layer is anchored on the surface of the hot press-formed member, in one embodiment of the present invention, 10 or more cracks per unit area of 1 mm ² of the plating layer, in some cases There may be more than 15 cracks. The number of cracks is measured by converting the number of cracks observed in 100 areas obtained by dividing the field of view of a microscope (magnification: 100 times) into 10 equal parts horizontally and vertically, respectively, to those observed in an observation area of 1 mm ² . In one embodiment of the present invention, the microscope may be a ZEISS SUPRA 55VP model scanning electron microscope. In this case, even if there is one crack, if there are a plurality of observed regions, the number of cracks may be equal to the number of regions where the cracks are observed. Of course, if a plurality of cracks are observed in one area, the number of cracks is equal to that number. This is a concept considering the total length of cracks within the observation area, and this is because the total length of cracks affects the fixing effect of the coating layer. However, since the aluminum-based coated steel sheet does not have a sacrificial corrosion protection function unlike the zinc-based coated steel sheet, corrosion may occur through the crack when a crack exists. Therefore, since an excessive number of cracks may impair the corrosion resistance of the steel sheet, the upper limit of the number of cracks per 1 mm ² calculated in the above-described manner may be limited to 200, and in some cases may be limited to 180.

In addition, in one embodiment of the present invention, a large number of indentations may be formed on the surface of the coating layer to increase the contact area of the coating layer. When the indentation portion exists, Ra and RPc of the surface of the plating layer may increase. To this end, in one embodiment of the present invention, the ratio of the indentation portion on the surface of the plating layer may be 5% or more, and in some cases may be 8% or more. In one embodiment of the present invention, the indentation may mean an area having a brightness of 70% or more compared to the highest brightness measured in an area observed at a magnification of 100 times with an optical microscope. In addition, although not necessarily limited to this, in one embodiment of the present invention, the result of observing the surface image at 100 times magnification with a Leica DM6000M model optical microscope was divided into 256 color brightness using Clemex Vision PE software. After that, the area ratio can be obtained by specifying a portion having a brightness equal to or higher than 70% of the highest brightness value as the indentation portion. If the ratio of the indentation part is too high, the load applied to the steel sheet to form the indentation part is excessive and surface cracks may increase, so the upper limit of the ratio of the indentation part may be set to 50% or 45%. . In one embodiment of the present invention, the indentation portion may be formed by skin pass rolling, but is not necessarily limited thereto.

In addition, since the object of the present invention is an alloy plated steel sheet of aluminum and iron, the total content of Al and Fe needs to be 80% or more by weight. The upper limit of the sum of the contents of these elements does not need to be particularly determined, and a plating layer made of only 100% Al and Fe may also correspond.

In addition, in one embodiment of the present invention, since the target is a sufficiently alloyed plated steel sheet, the average content of Fe has a value of 20% or more based on weight. If the content of Fe in the plating layer is less than 20%, it may not be very helpful in solving problems such as melting of the aluminum plating layer or hydrogen embrittlement during heating, so in the present invention, Al-Fe containing 20% or more of Fe by weight Applies to alloy coated steel sheets. In some cases, the Fe content may be 30% or more, and may be 40% or more.

The upper limit of the Fe content is not particularly limited, but when considering the Fe content in a conventional alloy coated steel sheet, the upper limit of the Fe content may be set to 90%, and in some cases may be set to 80% or less. Here, the average content of Fe means the average of the Fe content in the entire plating layer, and there may be various measurement methods. After integrating the Fe content curve according to the depth (thickness) that appears when the interface is analyzed, it can be used as a value divided by the thickness of the plating layer (ie, the distance from the surface to the interface of the steel sheet). There may be various standards for determining the interface between the coating layer and the steel sheet, but in this embodiment, the point where the Al and Fe content curves intersect, that is, the content of the two elements is equal, is defined as the interface between the coating layer and the steel sheet from the GDS results. can

According to one embodiment of the present invention, the plating layer may further include general elements included in the plating layer in addition to the above-described Al and Fe. Examples of these elements include one or two or more selected from among Mg, Zn, Mn, Cr, Mo, Si, and Ti, and they may be included in the plating layer up to 20% by weight or less in total.

In addition, according to one embodiment of the present invention, the Fe content in the surface portion of the aluminum iron alloy plated steel sheet for hot press forming may be 50% or more compared to the average content of Fe in the plating layer. That is, by setting the Fe content on the surface to 50% or more of the average Fe content in the plating layer, a plated steel sheet sufficiently alloyed to the surface of the plating layer can be obtained. In one embodiment of the present invention, the Fe content on the surface may be 15% or more by weight. In one embodiment of the present invention, the surface portion may mean a point having a depth of 1 μm from the outermost surface. In addition, in one embodiment of the present invention, the Fe content of the surface portion can be measured through EDS surface analysis at a site magnified 100 times with a scanning electron microscope.

The steel sheet of the present invention is a steel sheet for hot press forming, and the composition is not particularly limited as long as it is used for hot press forming. However, in accordance with one aspect of the present invention, by weight% (hereinafter, it is necessary to note that the composition of the steel sheet and the plating layer of the present invention is based on weight unless otherwise specifically expressed), C: 0.01 to 0.5%, Si: 2.0% or less (excluding 0%), Mn: 0.1 to 4.0%, P: 0.05% or less, S: 0.02% or less, Al: 0.001 to 1%, Cr: 5.0% or less (excluding 0%), N: 0.02% or less, Ti: 0.1% or less (excluding 0%), B: 0.0001 to 0.01%, the balance may have a composition including Fe and unavoidable impurities.

C: 0.01 to 0.5%

C is an essential element to increase the strength of the heat treated member and may be added in an appropriate amount. That is, in order to sufficiently secure the strength of the heat treated member, the C may be added in an amount of 0.01% or more. In one embodiment, the lower limit of the C content may be 0.05%. However, if the content is too high, the strength of the hot-rolled material is too high when the hot-rolled material is cold-rolled in the case of producing cold-rolled material, so that not only the cold-rollability is greatly inferior, but also the spot weldability is greatly reduced. It may be added in an amount of 0.5% or less to secure weldability. In addition, the C content may be limited to 0.45% or less and 0.4% or less.

Si: 2.0% or less (excluding 0%)

Si not only needs to be added as a deoxidizer in steelmaking, but also suppresses the formation of carbides, which have the greatest effect on the strength of hot-press-formed parts, and also converts to martensite lath grain boundaries after martensite is formed in hot-press forming. It can be added in steel to enrich the carbon to obtain retained austenite. However, the upper limit of the Si content may be set at 2% (excluding 0%) in order to secure sufficient plating properties when aluminum plating is performed on the steel sheet. In one embodiment of the present invention, the Si content may be limited to 1.5% or less. In addition, in another embodiment of the present invention, the lower limit of the Si content may be set to 0.01%.

Mn: 0.1 to 4.0%

The Mn may be added in an amount of 0.1% or more to secure a solid solution strengthening effect and to lower a critical cooling rate for securing martensite in a hot press molded member. In addition, the Mn content may be 4% or less in terms of securing workability in the hot press forming process by properly maintaining the strength of the steel sheet, reducing manufacturing cost, and improving spot weldability, and one embodiment of the present invention In , it can be 3.5% or less, or 2.5% or less.

P: 0.05% or less

The P exists as an impurity in steel, and the smaller the content, the more advantageous it is. Accordingly, in one embodiment of the present invention, P may be included in an amount of 0.05% or less. In another embodiment of the present invention, P may be limited to 0.03% or less. Since P is an impurity element that is advantageous the smaller it is, there is no need to specifically set an upper limit on its content. However, in order to excessively lower the P content, there is a concern that the manufacturing cost will increase. In this case, the lower limit may be set to 0.001%.

S: 0.02% or less

S is an impurity in steel, and since it is an element that impairs the ductility, impact properties and weldability of members, the maximum content is set to 0.02% (preferably 0.01% or less). In addition, since the manufacturing cost may increase if the minimum content is less than 0.0001%, in one embodiment of the present invention, the lower limit of the content may be 0.0001%.

Al: 0.001~1%

The Al, together with Si, can be added in an amount of 0.001% or more because it can increase the cleanliness of the steel by deoxidizing in steelmaking. In addition, the Al content may be 1% or less in order to prevent the temperature of Ac3 from becoming too high so that the heating required during hot press molding can be performed in an appropriate temperature range.

Cr: 5.0% or less (excluding 0%)

Since the Cr serves to improve the strength of the hot press formed part by improving the hardenability of the steel, it is necessary to add Cr. In some cases, the lower limit of the Cr content may be set to 0.001%. However, if the content exceeds 5.0%, it is difficult to expect a further increase in effect and costs may increase, so the upper limit of the Cr content may be set at 5.0%.

N: 0.02% or less

N is an element included as an impurity in steel, and the lower the content is, the more advantageous it is to reduce the sensitivity to crack generation during continuous casting of slabs and secure impact characteristics, and therefore may be included at 0.02% or less. Although it is necessary to specifically set the lower limit, the N content may be set to 0.001% or more in one embodiment in consideration of the increase in manufacturing cost.

Ti: 0.1% or less (excluding 0%)

By reacting with nitrogen, the Ti may contribute to improving hardenability by B. In addition, since fine precipitates are formed to improve the strength of the hot press molded member and refine crystal grains, it is effective in improving impact toughness, so it may be added in an amount of 0.1% or less (excluding 0%). In order to obtain the above-mentioned effect more reliably, in one embodiment of the present invention, the lower limit of the Ti content may be set to 0.0005%.

B: 0.0001 to 0.01%

B is an element capable of improving hardenability even with a small amount of addition and suppressing brittleness of hot press formed parts due to segregation of grain boundaries of P and/or S by being segregated at old austenite grain boundaries. Accordingly, B may be added in an amount of 0.0001% or more. However, if it exceeds 0.01%, the effect is not only saturated, but also causes brittleness in hot rolling, so the upper limit may be 0.01%, and in one embodiment, the B content may be 0.005% or less.

In one embodiment of the present invention, one or two or more elements selected from Nb: 0.1% or less, Mo: 0.5% or less, Ni: 1% or less, Cu: 1% or less, and V: 0.5% or less, if necessary. can include more.

Nb: 0.1% or less

Since Nb is effective in improving the steel sheet of heat treated members by forming fine precipitates, stabilizing retained austenite and improving impact toughness by refining crystal grains, it can be added to steel. However, if the added amount exceeds 0.1%, the effect is saturated and the cost may increase due to the excessive addition of ferroalloy. In one embodiment of the present invention, 0.001% or more of Nb may be added.

Mo: 0.5% or less

Mo is an element capable of securing strength and crystal grain refinement through enhancement of hardenability and precipitation strengthening effect. However, when added excessively, weldability may be deteriorated, so it may be added in an amount of 0.5% or less in consideration of this. In one embodiment of the present invention, when the Mo is added, the lower limit of the amount added may be set to 0.001%.

Ni: 1% or less

The Ni is an element that improves strength by forming fine precipitates. However, if the value exceeds 1.0%, excessive cost increases, so the upper limit is set at 1%. In one embodiment of the present invention, the addition amount of Ni may be 0.005% or more in order to surely obtain the above-mentioned effect.

Cu: 1% or less

Like Ni, Cu is an element that improves strength by forming fine precipitates. However, if the value exceeds 1.0%, excessive cost increases, so the upper limit is set at 1%. In order to reliably obtain the above-mentioned effect, the addition amount of Cu may be 0.005% or more.

V: 0.5% or less

The V may be added to steel because it is effective in improving the steel sheet of the heat treated member by forming fine precipitates, stabilizing retained austenite and improving impact toughness by refining crystal grains. However, if the added amount exceeds 0.5%, the effect is saturated and the cost may increase due to excessive addition of ferroalloy. In one embodiment of the present invention, 0.001% or more of V may be added in order to ensure the effect of adding V described above.

Iron and unavoidable impurities may be mentioned as the remainder other than the above-mentioned components, and any component that can be included in the steel sheet for hot forming is not particularly limited.

Hereinafter, one example of a method for manufacturing a steel sheet for hot press forming according to an aspect of the present invention is described below. However, the manufacturing method of the steel sheet for hot press forming described below is an example, and the steel sheet for hot press forming of the present invention does not necessarily have to be manufactured by the present manufacturing method, and any manufacturing method is a method that satisfies the scope of the present invention. It should be noted that if it is, there is no problem in using it to implement each implementation example of the present invention.

According to one embodiment of the present invention, the steel sheet is obtained by obtaining an aluminum-iron (Al-Fe) alloy plated steel sheet having an aluminum-iron alloy plating layer formed on the steel sheet; And it can be manufactured by performing skin pass rolling with respect to the aluminum-iron (Al-Fe) alloy plated steel sheet.

In one embodiment of the present invention, the aluminum-iron alloy-coated steel sheet is obtained by obtaining an aluminum-coated steel sheet coated with aluminum or an aluminum alloy; And it can be obtained by a process comprising the step of alloying by heating the aluminum-coated steel sheet.

At this time, any aluminum-coated steel sheet may be used as long as it is industrially referred to as aluminum-based, and in one embodiment of the present invention, one having an Al content of 70% or more by weight may be used. As the remaining elements other than Al in the plating layer, one or more components selected from Si, Mg, Zn, Mn, Cr, Mo, Ti, Fe, and/or other impurity elements that may be normally added to the aluminum-based plating layer are selected. can be heard Among them, Si may be included in an amount of 0.01 to 20%. In order to control the Si content below 0.01%, high purity raw materials are required, so the manufacturing cost rises too much. hard to get Therefore, in the present invention, the Si content included in the plating bath may be limited to 0.01 to 20%. One or two or more elements selected from Mg, Zn, Mn, Cr, Mo, and Ti may be included in the plating layer by 20% by weight or less in total.

The above-described aluminum-based plating layer may be formed by a hot-dip aluminum plating method in which a hot-rolled or cold-rolled and annealed steel sheet is immersed in a molten aluminum plating bath.

In one embodiment of the present invention, the plating amount during the aluminum plating may be 10 to 100 g / m 2 on a single side basis. If the plating amount is less than 10 g/m 2 , corrosion resistance is reduced, whereas if the plating amount exceeds 100 g/m 2 , a problem of deteriorating weldability occurs. Therefore, in the present invention, it is preferable to limit the coating amount to 10 to 100 g / m 2 on a single side basis during aluminum plating. On the other hand, in another embodiment of the present invention, the plating amount during the aluminum plating may be 20 to 90 g / m 2 on a single side basis.

In addition, in one embodiment of the present invention, the step of heating and alloying the aluminum-coated steel sheet is directly connected to a line for plating the steel sheet with aluminum or aluminum alloy, and is performed by online heating in which the coated steel sheet is heated while running. can In one embodiment of the present invention, the heating temperature range during the alloying may be 670 to 900 ° C, and the holding time may be 1 to 20 seconds. In addition, in another embodiment of the present invention, the heating temperature range may be 680 to 880 ° C, and the holding time may be 1 to 10 seconds.

In another embodiment of the present invention, the step of heating and alloying the aluminum-coated steel sheet may be performed by upper annealing of heating the coiled coated steel sheet in a box-shaped annealing furnace. At this time, the coil cooled to room temperature after aluminum plating may be heated for 0.1 to 100 hours at a temperature in the range of 600 to 800 ° C in an upper annealing furnace in a hydrogen or hydrogen and nitrogen atmosphere having a dew point temperature of less than -10 ° C (the present invention In the above temperature range, the highest temperature at which the furnace atmosphere temperature reaches is set as the heating temperature).

In each embodiment, the holding time means the time from when the ambient temperature reaches the target temperature until cooling is initiated.

In one embodiment of the present invention, the skin pass rolling may be performed under the condition that the SPMI represented by the following relational expression 1 is 5000 to 8500.

[Relationship 1]

Here, P is the rolling force during skin pass rolling (unit: ton), the Ra _roll is the arithmetic average roughness of the surface of the skin pass rolling roll (unit: μm), and the RPc _roll is the number of peaks per unit length of the skin pass rolling roll (unit: /cm). In addition, the unit of the SPMI is √Ton·㎛/cm.

That is, the SPMI is a condition that can control the surface state of the steel sheet devised by the present inventors, and the Ra and RPc of the steel sheet surface are affected not only by the Ra and RPc of the roll surface but also by the rolling force applied by the roll, and their influence As a result of quantitatively analyzing the figure, it was found as a result of the study that the relationship represented by the above relational expression 1 was shown. In order for the product of Ra and RPc of the surface of the steel sheet to have a sufficient value, the SPMI value needs to be 5000 or more, and in some cases, the SPMI value may be limited to 5500 or more. However, if the SPMI value is too high, the corrosion resistance of the member obtained after hot press molding may be deteriorated, so the value may be limited to 8500 or less, and in some cases may be limited to 8000 or less.

Hereinafter, a hot press-formed member according to one aspect of the present invention will be described. However, the method for manufacturing a hot press-formed member is not particularly limited in the present invention because it consists of a process of heating and maintaining a steel sheet at a temperature equal to or higher than the austenitizing temperature, followed by rapid cooling and forming at the same time as is well known in the prior art.

A hot press-formed member according to one aspect of the present invention includes a base steel plate and a plating layer made of an Al-Fe alloy formed on the base steel plate, and the product of Ra and RPc of the surface of the plated layer is controlled to combine paint adhesion and corrosion resistance. can

In one embodiment of the present invention, Ra×RPc of the surface of the plating layer of the member obtained by hot press molding may be 60 μm/cm or more in order to secure high paint adhesion. In the formula, Ra is the arithmetic mean roughness and has a unit of μm, and RPc is the peak count (Peak Count) and has a unit of the reciprocal of cm (/cm). When the Ra×RPc is not sufficient, it may be difficult to expect sufficient paint adhesion, so the lower limit of the Ra×RPc may be set at 60 μm/cm. In some cases, the lower limit of Ra×RPc may be set to 70 μm/cm. In order to improve paint adhesion, the higher the value of Ra × RPc, the better, but if the value is too high, according to one embodiment of the present invention, in the process of processing the plated steel sheet to increase the Ra and RPc of the member, the surface of the plated layer is excessively Since cracks may be introduced and corrosion resistance may be deteriorated, in one embodiment of the present invention, the upper limit of Ra×RPc may be set to 150 μm/cm, and in some cases, the upper limit of RaХRPc may be set to 140 μm/cm. there is.

In addition, in the hot press formed member according to another embodiment of the present invention, the number of cracks formed on the surface of the Al-Fe alloy plating layer and the area ratio of the indentation portion are appropriately adjusted to paint the member obtained by the subsequent hot press forming process. Adhesion and corrosion resistance can be improved. To this end, the plated steel sheet according to one embodiment of the present invention may have 15 to 220 cracks per 1 mm ² of the surface area of the plated layer, and the ratio of the area occupied by the indentation portion on the surface of the plated layer may be 5 to 50%.

Since the cracks can serve as a fixing part in which the coating layer is anchored on the surface of the hot press-formed member, in one embodiment of the present invention, 15 or more cracks per unit area of 1 mm ² of the plating layer, in some cases More than 20 cracks may be present. The number of cracks is measured by converting the number of cracks observed in 100 areas obtained by dividing the field of view of a microscope (magnification 100 times) into 10 equal parts horizontally and vertically, respectively, to those observed in an observation area of 1 mm ² . In one embodiment of the present invention, the microscope may be a ZEISS SUPRA 55VP model scanning electron microscope. In this case, even if there is one crack, if there are a plurality of areas to be observed, the number of cracks may be equal to the number of areas in which the cracks are observed. Of course, if a plurality of cracks are observed in one area, the number of cracks is equal to that number. This is a concept considering the total length of cracks within the observation area, and this is because the total length of cracks affects the fixing effect of the coating layer. However, since the aluminum-based coated steel sheet (member) does not have a sacrificial corrosion protection function unlike the zinc-based coated steel sheet, corrosion may occur through the crack when a crack exists. Therefore, since an excessive number of cracks may impair the corrosion resistance of the member, the upper limit of the number of cracks per 1 mm ² may be limited to 220, and in some cases may be limited to 200.

In addition, in one embodiment of the present invention, a large number of indentations may be formed on the surface of the coating layer of the steel sheet in order to increase the contact area of the coating layer, and these indentations may remain on the member to improve paint adhesion. When the indentation portion exists, Ra and RPc of the surface of the plating layer may increase. To this end, in one embodiment of the present invention, the ratio of the indentation portion on the surface of the plating layer may be 5% or more, and in some cases may be 8% or more. Although not necessarily limited to this, in one embodiment of the present invention, the result of observing the surface image at 100 times magnification with a Leica DM6000M model optical microscope is the highest after classifying the color brightness into 256 using Clemex Vision PE software. A portion of the brightness value corresponding to 70% of the brightness value or more was specified as the indentation portion, and the area ratio thereof was obtained. If the ratio of the indentation part is too high, the load applied to the plating layer to form the indentation part is excessive and surface cracks may increase. Therefore, the upper limit of the ratio of the indentation part may be set to 50% or 45%.

According to one embodiment of the present invention, the aluminum-iron (Al-Fe) alloy plating layer may include a total of 70% or more of Al and Fe by weight. Since the plating layer may be made of only these elements, there is no need to specifically set an upper limit on the sum of the contents, and the sum of the contents of these elements may be 100%.

Since Fe in the plating layer may diffuse into the plating layer during hot press molding, Fe may be included in an amount of 30% or more by weight. If the content of Fe in the plating layer is less than 30%, it may not be very helpful in solving problems such as hydrogen embrittlement during storage. In some cases, the Fe content may be 35% or more, and may be 40% or more.

There is no particular limitation on the upper limit of the Fe content, but when considering the Fe content in the plating layer of a conventional hot press-formed member, the upper limit of the Fe content may be set to 90%, and in some cases set to 80% or less. Here, the average content of Fe means the average of the Fe content in the entire plating layer, and there may be various measurement methods. After integrating the Fe content curve according to the depth (thickness) that appears when the interface of is analyzed, it can be used as a value divided by the thickness of the plating layer. There may be various criteria for determining the interface between the coating layer and the steel sheet, but in this implementation example, the point where the Al and Fe content curves intersect, that is, the content of the two elements becomes equal in the GDS results, is defined as the interface between the coating layer and the steel sheet. can

According to one embodiment of the present invention, the plating layer of the hot press-formed member may further include common elements included in the plating layer in addition to the above-described Al and Fe. Examples of these elements include one or two or more selected from among Mg, Zn, Mn, Cr, Mo, Si, and Ti, and they may be included in the plating layer up to 20% by weight or less in total.

The holding steel sheet of the hot press-formed member of the present invention may have various structures for each strength. If the tensile strength is 400 to 800 MPa, it may have a microstructure consisting of one or two or more phases selected from 5 to 50% of martensite and the remaining ferrite, pearlite, bainite, and austenite based on area, and tensile strength When is 800 to 1300 MPa, it may have a microstructure consisting of 90% or more of martensite and one or more phases selected from the remaining ferrite, pearlite, bainite and austenite based on area, and the tensile strength is 1300 MPa or more may have a microstructure consisting of one or more phases selected from 95% or more of martensite and the remaining ferrite, pearlite, bainite, and austenite on an area basis.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are only for exemplifying and specifying the present invention, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

(Example)

A cold-rolled steel sheet for hot press forming having a composition shown in Table 1 was prepared as a base steel sheet. After annealing heat treatment of the base steel sheet in a conventional manner, molten aluminum plating was performed. The plating bath was set to have a composition substantially consisting of 9.5% Si and balance Al by weight%, and the plating bath temperature was set to 660°C. After plating, the coating weight was adjusted to 40 g/m ² based on one side using an air knife.

Thereafter, alloying was performed by on-line or phase annealing for each invention example and comparative example to obtain an Al-Fe alloy plated steel sheet. Online alloying was performed by reheating the steel sheet to 720 ° C, holding it for 5 seconds and cooling it to room temperature, and alloying by normal annealing was performed by maintaining the coil in an ordinary annealing furnace at 650 ° C for 10 hours.

After alloying, the coated steel sheet was skin-pass rolled with a rolling force shown in Table 2 using a roll having surface roughness (Ra) and peak number (RPc) shown in Table 2, thereby adjusting the surface state of the alloyed plating layer of the steel sheet.

In all inventive examples and comparative examples, the sum of the contents of Al and Fe in the alloy plating layer obtained by each alloying method and skin pass rolling and the Fe content were 90% and 43%, respectively, and there was no particular difference between examples. In addition, in all inventive examples and comparative examples, the Fe content on the surface of the plating layer was 77% of the average Fe content in the plating layer, and did not show a large difference. At this time, the surface of the plating layer means a point having a depth of 1 μm from the outermost surface of the plating layer.

The skin pass-rolled plated steel sheet was heated at 930° C. for 6 minutes in an air atmosphere, and hot press forming and rapid cooling were performed to obtain a hot press formed part. It was confirmed that the internal structure of the obtained hot-press-formed part consisted of substantially 100% martensite, and that the strength was 1500 MPa. However, the structure and strength of the steel material can be changed as needed, and a person skilled in the art will have no difficulty in manufacturing a member having a target structure and strength by changing the manufacturing conditions including the composition of the steel material or cooling conditions. .

In addition, in the hot press formed members obtained by all the inventive examples and the comparative examples, the sum of Al and Fe contents in the alloy plating layer and the Fe content were 83% and 44%, respectively, and no particular difference was confirmed for each example.

The surface roughness (Ra), the number of peaks (RPc), the number of cracks per unit area, and the ratio of indentations were measured for the skin pass-rolled plated steel sheet and the hot press formed member. The surface roughness and number of peaks were obtained by measuring five areas according to the JIS B 0601 (2013) standard and averaging the values. The number of cracks was measured by converting the total number of cracks observed in each of 100 areas obtained by dividing the field of view of a microscope (magnification: 100 times) into 10 equal parts horizontally and vertically, respectively, to those observed in an observation area of 1 mm ² . A ZEISS SUPRA 55VP model scanning electron microscope was used for the measurement, and the average value of the measurements for five sites was obtained and used for analysis. In addition, the ratio of the indentation was 70% of the highest brightness value after observing the surface image at 100 times magnification with a Leica DM6000M model optical microscope and classifying the color brightness into 256 using Clemex Vision PE software. A portion having a brightness corresponding to or greater than that was specified as the indentation portion, and the area ratio thereof was obtained. The area ratio was also set as the average value of the results of observing five locations. Among the above measurement results, those for coated steel sheets are shown in Table 3, and those for hot press formed parts are shown in Table 4.

In addition, the coating adhesion and corrosion resistance of the obtained hot press-formed parts were evaluated by the following methods, and the results are shown in Table 4.

First, the coating adhesion rating was determined by coating the member obtained according to the GMW14829 method, forming grid scratches at 1 mm intervals, and evaluating the peeling of the tape. If the rating is 1 or less, it can be regarded as good.

For corrosion resistance, after phosphate treatment and painting were performed on the member according to GMW14872 standard, a cyclic corrosion test was performed 52 times in a saline atmosphere after crosscutting, and then the blister width was measured. In this embodiment, it was judged that the width was 2 mm or less as good.

element	C	Si	Mn	P	S	Al	Cr	N	Ti	B
Content (% by weight)	0.21	0.25	1.1	0.011	0.003	0.025	0.2	0.005	0.025	0.0025

division	alloying method	Ra(μm)	RPc(/cm)	Pressing force (ton)	SPMI
Comparative Example 1	online	One	200	400	4000
Comparative Example 2	upper annealing	One	200	500	4472
Comparative Example 3	online	One	200	600	4899
Invention Example 1	upper annealing	4	90	200	5091
Invention example 2	upper annealing	4	90	300	6235
Inventive example 3	online	4	90	400	7200
Inventive Example 4	upper annealing	4	90	500	8050
Inventive Example 5	online	8	50	200	5657
Inventive example 6	online	8	50	300	6928
Inventive Example 7	upper annealing	8	50	400	8000
Comparative Example 4	upper annealing	8	50	500	8944
Comparative Example 5	online	8	50	600	9798
Comparative Example 6	upper annealing	8	50	700	10583

division	Ra(μm)	RPc(/cm)	Ra×RPc (μm/cm)	Number of cracks (pcs/mm 2 )	Percentage of indentation (area %)
Comparative Example 1	0.22	175	38.5	6.1	One
Comparative Example 2	0.25	164	41.0	7.3	2
Comparative Example 3	0.27	165	44.6	9.4	4
Invention example 1	0.8	76	60.8	15.8	6
Invention example 2	1.2	88	105.6	89.5	20
Inventive example 3	1.6	75	120.0	93.6	33
Inventive example 4	1.9	70	133.0	145.4	45
Inventive Example 5	2.4	41	98.4	62.3	16
Inventive Example 6	3.1	43	133.3	120.4	32
Inventive Example 7	3.5	40	140.0	181.2	48
Comparative Example 4	3.7	49	181.3	215.9	53
Comparative Example 5	3.8	48	182.4	257.6	61
Comparative Example 6	4	47	188.0	274.1	69

division	Ra(μm)	RPc(/cm)	Ra×RPc (μm/cm)	Number of cracks (pcs/mm 2 )	Percentage of indentation (area %)	Paint Adhesion Grade	Blister width (mm)
Comparative Example 1	0.25	172	43.0	7.5	One	2	4.1
Comparative Example 2	0.26	160	41.6	9.4	3	3	4.3
Comparative Example 3	0.28	163	45.6	12.6	4	2	4.2
Invention Example 1	0.82	75	61.5	16.2	7	0	0.8
Invention example 2	1.3	84	109.2	93.4	21	0	0.7
Inventive example 3	1.7	73	124.1	98.4	32	0	0.6
Inventive Example 4	2	68	136.0	155.1	46	0	0.5
Inventive Example 5	2.5	40	100.0	70.4	17	0	0.7
Inventive example 6	3.2	42	134.4	148.3	33	0	0.5
Inventive Example 7	3.6	38	136.8	218.1	47	0	1.2
Comparative Example 4	3.8	46	174.8	235	54	0	4.5
Comparative Example 5	3.9	45	175.5	271.5	60	0	4.7
Comparative Example 6	4.2	45	189.0	278.1	68	0	4.9

In Comparative Examples 1 to 3, the SPMI was less than 5000 during skin pass rolling, and as a result, Ra × RPc on the surface of the alloyed plated steel sheet was not sufficiently secured or the indentation ratio and the number of cracks were not sufficiently formed. The hot press formed part obtained by hot press forming such a steel sheet also had a sufficiently low Ra x RPc, or had an insufficient number of cracks or an insufficient indentation ratio. In this case, it may be difficult for the paint layer to firmly bind to the surface of the member due to the lack of anchoring effect, and as a result, it was confirmed that all paint adhesion grades were not good at 2 or higher. On the other hand, in Comparative Examples 4 to 6, the SPMI values if this is too high. In this case, the Ra × RPc of the plating layer, the indentation ratio, and the number of cracks may be sufficient to secure the paint adhesion of the member, but the corrosion resistance of the member deteriorates as shown in Table 4 as damage occurs to the plating layer. was That is, if the plating layer is damaged, corrosion may occur due to exposure of the base steel sheet through the damaged gap in the aluminum alloy-based plating layer that does not provide the anticorrosive performance of the sacrificial anode method. can be bigger

On the other hand, in Inventive Examples 1 to 7 satisfying the conditions of the present invention, skin pass rolling conditions were appropriately controlled to secure the surface characteristics of the plated steel sheet, and as a result, paint adhesion and corrosion resistance of the finally obtained member could be secured at the same time.

1 shows a coated steel sheet (a) manufactured by Comparative Example 1 and a coated steel sheet (b) manufactured by Inventive Example 2. As can be seen in the figure, the plated steel sheet manufactured by Comparative Example 1 does not have sufficient surface irregularities, whereas the plated steel sheet manufactured according to Inventive Example 2 has sufficiently formed irregularities on the surface, followed by hot press forming. The surface of the member produced by this can be made suitable for fixing the paint layer.

In FIG. 2, the surface of the steel sheet manufactured by Comparative Example 1 and Inventive Example 2 was observed with a microscope (DM6000M) at 100 magnification, processed using Clemex Vision PE software, and then the area (indentation part) of 70% or more of the highest brightness was white. The results indicated by . As can be seen from the figure, in the case of Inventive Example 2, in which skin pass rolling was performed by controlling the SPMI to an appropriate range according to the present invention, a much higher indentation was formed than in Comparative Example 1, in which skin pass rolling was performed under low SPMI conditions.

The graph of FIG. 3 shows the relationship between the SPMI value and the number of cracks. From the figure, it can be seen that when the SPMI value has a value between 5000 and 8000 √Ton·μm/cm, the number of cracks can be maintained within an appropriate range.

Thus, the advantageous effects of the present invention could be confirmed.

Claims (23)

1. base steel plate and

   A plating layer made of an Al-Fe alloy formed on the base steel sheet,

   The total content of Al and Fe in the plating layer is 80% or more by weight,

   The average content of Fe in the plating layer is 20% or more by weight,

   The product of Ra and RPc of the surface of the plating layer is 60 to 150 μm / cm

   Plated steel sheet for hot press forming.

   However, Ra means arithmetic average roughness and its unit is μm, and RPc means the number of peaks per unit length and its unit is /cm.
2. base steel plate and

   A plating layer made of an Al-Fe alloy formed on the base steel sheet,

   The total content of Al and Fe in the plating layer is 80% or more by weight,

   The average content of Fe in the plating layer is 20% or more by weight,

   The number of cracks present in each region obtained by dividing the field of view obtained when the surface of the plating layer is observed at a magnification of 100 times with a scanning electron microscope into 10 horizontally and vertically is 10 to 200 per 1mm ² ,

   The ratio of the area occupied by the indentation on the surface of the plating layer is 5 to 50%

   Coated steel sheet for hot press forming.

   Here, the indentation means a region having a brightness of 70% or more compared to the highest brightness measured in an area observed at a magnification of 100 times with an optical microscope.
3. According to claim 1,

   The coated steel sheet for hot press forming, wherein the Fe content of the surface portion of the plating layer is 50% or more relative to the average Fe content in the plating layer.

   Here, the Fe content of the surface portion is a value measured through EDS surface analysis at a site magnified 100 times with a scanning electron microscope (SEM), and the average Fe content is the depth at which Fe and Al content intersect from the surface layer obtained through GDS analysis. It means the value obtained by integrating the Fe content curve up to and dividing it by the distance from the surface layer to the depth where the Fe and Al content intersect.
4. According to claim 3,

   A coated steel sheet for hot press forming wherein the Fe content of the surface portion of the plating layer is 15% or more by weight.
5. According to claim 2,

   A coated steel sheet for hot forming, wherein the Fe content of the surface portion of the plating layer is 50% or more compared to the average Fe content in the plating layer.

   Here, the Fe content of the surface portion is a value measured through EDS surface analysis at a site magnified 100 times with a scanning electron microscope (SEM), and the average content of Fe is the depth at which Fe and Al content intersect from the surface layer obtained through GDS analysis. It means the value obtained by integrating the Fe content curve up to and dividing it by the distance from the surface layer to the depth where the Fe and Al content intersect.
6. According to claim 5,

   A coated steel sheet for hot press forming wherein the Fe content of the surface portion of the plating layer is 15% or more by weight.
7. The coated steel sheet for hot press forming according to any one of claims 1 to 6, wherein the average content of Fe in the plating layer is 90% or less.
8. According to any one of claims 1 to 6,

   The plating layer is a coated steel sheet for hot press forming containing one or more elements selected from Mg, Zn, Mn, Cr, Mo, Si, and Ti in a total amount of 20% by weight or less.
9. According to any one of claims 1 to 6,

   The base steel sheet contains, by weight, C: 0.01 to 0.5%, Si: 2.0% or less (excluding 0%), Mn: 0.1 to 4.0%, P: 0.05% or less, S: 0.02% or less, Al: 0.001 to 1 %, Cr: 5.0% (excluding 0%), N: 0.02% or less, Ti: 0.1% or less (excluding 0%), B: 0.0001 to 0.01%, balance for hot press molding with a composition containing Fe and unavoidable impurities plated steel.
10. 10. The method of claim 9, wherein the base steel sheet further contains one or more elements selected from Nb: 0.1% or less, Mo: 0.5% or less, Ni: 1% or less, Cu: 1% or less, and V: 0.5% or less. Plated steel sheet for hot press forming comprising.
11. Obtaining an Al-Fe alloy-coated steel sheet having a plating layer made of an alloy of Al and Fe formed on the base steel sheet; and

    Skin pass rolling of the Al-Fe alloy coated steel sheet under the condition that the SPMI expressed by the following relational expression 1 is 5000 to 8500

    Method for manufacturing a coated steel sheet for hot press forming comprising a.

    [Relationship 1]

    

    Here, P is the rolling force during skin pass rolling (unit: ton), the Ra _roll is the arithmetic average roughness of the surface of the skin pass rolling roll (unit: μm), and the RPc _roll is the number of peaks per unit length of the skin pass rolling roll (unit: /cm). In addition, the unit of the SPMI is √Ton·㎛/cm.
12. The method of claim 11, wherein the Al-Fe alloy plated steel sheet

    Obtaining an aluminum-coated steel sheet coated with aluminum or aluminum alloy; and

    A method of manufacturing a coated steel sheet for hot press forming obtained by a process comprising the step of heating and alloying the aluminum-coated steel sheet.
13. 13. The method of claim 12, wherein the step of heating and alloying the aluminum-coated steel sheet is performed by online heating, which is directly connected to a line for plating the steel sheet with aluminum or an aluminum alloy, and the coated steel sheet is heated in a running state. Manufacturing method of galvanized steel sheet for molding.
14. [Claim 13] The method of claim 12, wherein the step of heating and alloying the aluminum-coated steel sheet is performed by upper annealing by heating the rolled-up coated steel sheet in a box-shaped annealing furnace.
15. According to any one of claims 11 to 14,

    The base steel sheet contains, by weight, C: 0.01 to 0.5%, Si: 2.0% or less (excluding 0%), Mn: 0.1 to 4.0%, P: 0.05% or less, S: 0.02% or less, Al: 0.001 to 1 %, Cr: 5.0% or less (excluding 0%), N: 0.02% or less, Ti: 0.1% or less (excluding 0%), B: 0.0001 to 0.01%, the balance being hot press molding having a composition containing Fe and unavoidable impurities Manufacturing method of galvanized steel sheet.
16. The method of claim 15, wherein the base steel sheet further contains one or two or more elements selected from Nb: 0.1% or less, Mo: 0.5% or less, Ni: 1% or less, Cu: 1% or less, and V: 0.5% or less. Method for manufacturing a plated steel sheet for hot press forming comprising.
17. base steel plate and

    A plating layer made of an Al-Fe alloy formed on the base steel sheet,

    The total content of Al and Fe in the plating layer is 70% or more by weight,

    The content of Fe in the plating layer is 30% or more by weight,

    The product of Ra and RPc of the surface of the plating layer is 60 to 150 μm / cm

    Hot press forming part.

    However, Ra means arithmetic average roughness and its unit is μm, and RPc means the number of peaks per unit length and its unit is /cm.
18. base steel plate and

    A plating layer made of an Al-Fe alloy formed on the base steel sheet,

    The total content of Al and Fe in the plating layer is 70% or more by weight,

    The average content of Fe in the plating layer is 30% or more by weight,

    The number of cracks present in each region obtained by dividing the field of view obtained when the surface of the plating layer is observed at a magnification of 100 times with a scanning electron microscope into 10 horizontally and vertically is 15 to 220 per 1mm ² ,

    The ratio of the area occupied by the indentation on the surface of the plating layer is 5 to 50%

    Hot press forming part.

    Here, the indentation means a region having a brightness of 70% or more compared to the highest brightness measured in an area observed at a magnification of 100 times with an optical microscope.
19. According to claim 17 or 18,

    The base steel sheet contains, by weight, C: 0.01 to 0.5%, Si: 2.0% or less (excluding 0%), Mn: 0.1 to 4.0%, P: 0.05% or less, S: 0.02% or less, Al: 0.001 to 1 %, Cr: 5.0% or less (excluding 0%), N: 0.02% or less, Ti: 0.1% or less (excluding 0%), B: 0.0001 to 0.01%, the balance being hot press molding having a composition containing Fe and unavoidable impurities absence.
20. The method of claim 19, wherein the base steel sheet further contains one or more elements selected from Nb: 0.1% or less, Mo: 0.5% or less, Ni: 1% or less, Cu: 1% or less, and V: 0.5% or less. A hot press-formed member comprising:
21. The method of claim 17 or 18, wherein the base steel sheet has a microstructure composed of 5 to 50% of martensite and one or more phases selected from ferrite, pearlite, bainite, and austenite on the basis of area, A hot press-formed member with a tensile strength of 400 to 800 MPa.
22. The method of claim 17 or 18, wherein the base steel sheet has a microstructure consisting of 90% or more of martensite and the remaining one or two or more phases selected from ferrite, pearlite, bainite and austenite based on area, and tensile A hot press-formed member with a strength of 800 to 1300 MPa.
23. The method of claim 17 or 18, wherein the base steel sheet has a microstructure consisting of 95% or more of martensite and the remaining one or two or more phases selected from ferrite, pearlite, bainite and austenite on an area basis, and tensile A hot press-formed member having a strength of 1300 MPa or more.

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