WO2018221991A1 - Steel sheet for hot press formed member having excellent plating adhesion, and method for manufacturing same - Google Patents

Abstract

The present invention relates to a steel sheet for a hot press formed member having excellent plating adhesion, and a method for manufacturing the same. A steel sheet for hot press forming according to one aspect of the present invention is an aluminum alloy plated steel sheet, wherein an average Fe content within a plated layer may be 40 wt% or more, and a concentration gradient of a section having a Fe content of 45-80% within the plated layer may be 7 wt%/μm or less in a result of GDS analysis in the thickness direction from a surface of the plated layer.

Description

Steel plate for hot press forming member with excellent plating adhesion and manufacturing method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet for hot press forming members having excellent plating adhesion and a method for manufacturing the same. (STEEL SHEET FOR HOT PRESS FORMED MEMBER HAVING EXCELLENT COATING ADHESION AND MANUFACTURING METHOD FOR THE SAME)

Recently, due to the depletion of petroleum energy resources and high interest in the environment, regulations on improving fuel economy of automobiles are becoming stronger.

In terms of materials, it is possible to reduce the thickness of the steel sheet used as one method for improving fuel efficiency of the automobile. However, reducing the thickness may cause a problem in the safety of the automobile. Should be.

For this reason, the demand for high strength steel sheets has been continuously generated, and various kinds of steel sheets have been developed. By the way, since these steel sheets have high strength in themselves, there is a problem that workability is poor. That is, since the product of strength and elongation for each grade of steel sheet tends to always have a constant value, when the strength of the steel sheet increases, there is a problem in that elongation, which is an index 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 quenching it at a low temperature to increase the strength of the final product. In this case, there is an advantage that the problem of workability can be minimized when manufacturing a member having a high strength.

However, in the hot press forming method, there is a problem in that the steel sheet surface is oxidized because the steel sheet needs to be heated to a high temperature, and thus a process of removing oxide from the steel sheet surface after the press molding has to be added.

In order to solve this problem, US Patent No. 6,296,805 has been proposed. In the above invention, the steel plate subjected to aluminum plating is used in a process of heating and quenching (hot post-heat treatment) after hot press molding or normal temperature molding. Since the aluminum plating layer is present on the steel sheet surface, the steel sheet is not oxidized at the time of heating.

By the way, in the hot press-formed member, two or more members may be used by adhering the member by an adhesive, in which case it is necessary to maintain sufficient adhesive strength. In order to check the bond strength, a test method is often used to determine whether the bond is easily maintained at high strength by applying tensile stress in a direction perpendicular to the bond surface.

At this time, the plating layer is often peeled off inside the plating layer or at an interface between the plating layer and the base steel sheet, in which case the two members are separated even at low stress.

According to one aspect of the present invention, there is provided a steel sheet for hot press forming, which can produce a hot press forming member having excellent plating adhesion, and one method for manufacturing the steel sheet.

The subject of this invention is not limited to what was mentioned above. Those skilled in the art will have no difficulty in solving the additional problems of the present invention from the general matters of the present specification.

The steel sheet for hot press forming according to one aspect of the present invention is an aluminum alloy plated steel sheet, and the average content of Fe in the plating layer is 40% by weight or more, and the Fe content in the plating layer is obtained by GDS analysis from the surface of the plating layer in the thickness direction. The concentration gradient in the range of 45 to 80% may be 7% by weight or less.

In one embodiment of the present invention, the concentration gradient may be 5% by weight or less.

In one embodiment of the present invention, the aluminum alloy plating layer may have an average content of Fe or more than 50% by weight.

In one embodiment of the present invention, the base steel sheet by weight% C: 0.04 ~ 0.5%, Si: 0.01 ~ 2%, Mn: 0.01 ~ 10%, Al: 0.001 ~ 1.0%, P: 0.05% or less, S It may have a composition comprising: 0.02% or less, N: 0.02% or less, residual Fe and other unavoidable impurities.

In one embodiment of the present invention, the composition of the steel sheet is weight percent, one or more sums selected from the group consisting of Cr, Mo and W: 0.01 to 4.0%, in the group consisting of Ti, Nb, Zr and V The sum of the species or more may further include at least one of 0.001 to 0.4%, Cu + Ni: 0.005 to 2.0%, Sb + Sn: 0.001 to 1.0%, and B: 0.0001 to 0.01%.

According to an aspect of the present invention, there is provided a method of manufacturing a steel sheet for a hot press-forming member, the method comprising: obtaining an aluminum plated steel sheet by aluminum plating and winding the surface of the steel sheet; Step an aluminum alloy plated steel sheet by annealing the aluminum plated steel sheet; And cooling the aluminum alloy plated steel sheet, wherein the aluminum plating amount is 30 to 200 g / m ² based on one side of the steel sheet, and a cooling rate of up to 250 ° C. after aluminum plating is obtained. Is less than or equal to 20 ℃ / second, the winding tension is 0.5 ~ 5kg / mm ² during winding, the annealing is carried out in a heating temperature range of 550 ~ 750 ℃ in an annealing furnace for 30 minutes to 50 hours, the annealing When heating from room temperature to the heating temperature, the average temperature increase rate is 20 ~ 100 ℃ / h, the average temperature increase rate of 400 ~ 500 ℃ section is 1 ~ 15 ℃ / h, the atmosphere temperature in the annealing furnace and the steel sheet The difference between temperatures can be 5-80 degreeC.

In one embodiment of the present invention, the base steel sheet by weight% C: 0.04 ~ 0.5%, Si: 0.01 ~ 2%, Mn: 0.01 ~ 10%, Al: 0.001 ~ 1.0%, P: 0.05% or less, S It may have a composition comprising: 0.02% or less, N: 0.02% or less, residual Fe and other unavoidable impurities.

In one embodiment of the present invention, the composition of the steel sheet is weight percent, one or more sums selected from the group consisting of Cr, Mo and W: 0.01 to 4.0%, in the group consisting of Ti, Nb, Zr and V The sum of the species or more may further include at least one of 0.001 to 0.4%, Cu + Ni: 0.005 to 2.0%, Sb + Sn: 0.001 to 1.0%, and B: 0.0001 to 0.01%.

According to one aspect of the present invention, the steel sheet for hot press forming is plated with an Al-Fe-based plating layer, thereby reducing the possibility of voids occurring in the plating layer in a subsequent hot press forming process, thereby adhering the two members with an adhesive. Even in one case, there is a possibility that the inside of the plating layer is peeled off by the pores, and the adhesive layer can have a high adhesive strength.

1 is a photograph observing a plated layer cross section of a hot press-formed member in which plated layer peeling has occurred.

2 is a component profile obtained by analyzing a plated layer of a steel sheet manufactured according to Inventive Example 1 by using a GDS analyzer.

3 is a component profile obtained by analyzing a plated layer of a steel sheet manufactured according to Inventive Example 2 with a GDS analyzer.

4 is a component profile obtained by analyzing a plated layer of the steel sheet manufactured by Comparative Example 1 with a GDS analyzer.

5 is a component profile obtained by analyzing a plated layer of a steel sheet manufactured by Comparative Example 2 with a GDS analyzer.

6 is a component profile obtained by analyzing a plated layer of the steel sheet manufactured by Comparative Example 3 with a GDS analyzer.

Hereinafter, the present invention will be described in detail.

In the present invention, the member refers to a part or a part material manufactured by hot press molding. In addition, a steel plate means the thing before hot press molding, and this steel plate may be wound up during a manufacturing process, and may have a coil form, and this time is also called a coil.

The present inventors have conducted research in various fields in order to investigate the cause of the plating layer peeling which causes a decrease in adhesive strength. As a result, as shown in FIG. 1, fine voids existed in the lower part of the cross section of the plating layer of the hot press-formed member, and it turned out that the fall of adhesive strength occurs in this case.

That is, the fine pores existing in the lower part of the plated layer cross section of the hot press-molded member (depending on the thickness of the plated layer, but in the normal plating amount up to 15 μm from the interface between the plated layer and the base iron) cause the bonding strength of the plated layer to decrease. In this case, cracks are generated and propagated in the plating layer starting from the pores, and thus, the plating layer is finally separated.

As a result of the researches of the present inventors, it has been found that the generation of voids can be suppressed or encouraged depending on how the shape of the plating layer of the hot press forming steel sheet is controlled, and in the present invention, the steel sheet having the plating layer such that the voids are not generated. To provide.

Although it is not certain, as a mechanism for generating voids, the voids in the hot press forming member may be caused by an imbalance between the diffusion rates of Fe in the base iron and Al in the plating layer, which occurs during the heating of the hot press forming process, which is heated at a relatively high speed. . In other words, Fe diffuses at a relatively slow speed while Al diffuses relatively fast. As a result, it seems that the voids are generated because Fe is not filled in the sites where Al is diffused and removed.

In this invention, in order to prevent such a problem, the composition of the plating layer of a steel plate is controlled. By spreading a large amount of Fe in the plated layer of the steel sheet before hot press molding, the diffusion amount of Fe and Al is not large when heating for hot press molding so as to reduce the size of the imbalance of the diffusion amount.

Therefore, the hot press-formed steel sheet of the present invention is an aluminum alloy plated steel sheet having an average content of Fe in the plating layer of 40% by weight or more, preferably 50% by weight or more, and the result of GDS analysis in the thickness direction from the surface of the plating layer. In the Fe content in the 45 to 80% of the concentration gradient is characterized in that less than 7% by weight / ㎛.

If the average content of Fe is low, there is still room for voids because of the large amount of Al and Fe diffused during the hot press forming process. Therefore, the content of Fe in the plating layer needs to be limited to the above-mentioned range. Although the upper limit of the average content of Fe does not need to be specifically determined, considering the efficiency of alloying etc., it may also be set to 80 weight% or less. Here, the average content of Fe refers to the average content of Fe in the entire plating layer, but there may be various measurement methods. However, in the present embodiment, the surface of the plating layer from the surface of the plating layer by Glow Discharge Spectrometry (GDS) method. Integrating the content curve of Fe according to the depth (thickness) appearing when analyzed to the interface of can be used as the value divided by the plating layer thickness. There may be various criteria for determining the interface between the plated layer and the steel sheet, but in this embodiment, the point where the Fe content is 92% of the base Fe content from the GDS results may be defined as the interface between the plated layer and the steel sheet.

In addition, the present inventors have found that in order to reduce the formation of the vacancy, in addition to controlling the average content of Fe in the plating layer, the concentration gradient of Fe at the position where the vacancy mainly occurs is gentle.

Therefore, the hot press-formed steel sheet of the present invention is an aluminum alloy plated steel sheet and has a concentration gradient of 7% by weight or less in a section in which the Fe content is 45 to 80% in the plating layer from the GDS analysis results. That is, when the Fe content is a value obtained by dividing the difference (weight%) of the Fe content at the start point and the end point of the section by the length (μm) of the section, the weight of 7 wt% / µm or less, Al and Al in the additional heating process for hot press forming The spread of Fe is not so rapid that it can suppress the generation of public. In addition, there may be a section in which the increase or decrease of Fe in the section (increase or decrease or increase or decrease), but the Fe content at all points in the section should be in the range of 45 to 80%. In addition, if the corresponding sections in the plating layer appear in several places, it means the concentration gradient of the lowest section (the section farthest from the surface) in the plating layer where the public is mainly generated. According to another embodiment of the present invention, the concentration gradient may be 5% by weight or less. The lower limit of the concentration gradient does not need to be specified, but in general, the concentration gradient generally has a positive value in that the Fe content near the base steel sheet and the Fe content on the surface side are low in the section for calculating the concentration gradient. In one embodiment of the present invention, the lower limit of the concentration gradient may be set to 0% by weight / μm. However, the lower limit is not necessarily limited thereto, and even if the concentration gradient has a negative value, it does not impair the gist of the present invention. In addition, there is typically a point where the Fe content is 80% and 45% in the plating layer and in this case, the above-described Fe content difference is fixed to 35% by weight. In this case, the length of the above-described content section is 7 μm. The above should be sufficient.

The steel sheet of the present invention is a steel sheet for hot press molding, and if used for hot press molding, its composition is not particularly limited. However, according to one aspect of the present invention in terms of weight percent (hereinafter, unless noted otherwise, it is necessary to note that the composition of the steel sheet and the plating layer is based on weight), C: 0.04-0.5%, Si: 0.01-2%, Mn: 0.01-10%, Al: 0.001-1.0%, P: 0.05% or less, S: 0.02% or less and N: 0.02% or less.

C: 0.04-0.5%

C may be added in an appropriate amount as an essential element for increasing the strength of the heat treatment member. That is, in order to ensure sufficient strength of the heat treatment member, the C may be added at least 0.04%. In one embodiment, the lower limit of the C content may be 0.1%. However, if the content is too high, when producing cold rolled material, the cold rolled material is too high when cold-rolled and the cold rolled property is greatly inferior, and the spot weldability is greatly degraded. It may be added at 0.5% or less to ensure weldability. In addition, the C content may be limited to 0.45% or less and 0.4% or less.

Si: 0.01-2%

The Si not only needs to be added as a deoxidizer in steelmaking, but also suppresses carbide formation which most affects the strength of the hot press forming member, and in the hot press forming, carbon is formed on the martensite lath grain boundary after martensite formation. It is an element that plays a role of concentrating and securing residual austenite. Thus, Si may be added in an amount of 0.01% or more. In addition, the upper limit of the Si content may be set to 2% in order to secure sufficient plating properties when aluminum plating the steel sheet after rolling. In one embodiment of the present invention, the Si content may be limited to 1.5% or less.

Mn: 0.01 ~ 10%

The Mn may be added in an amount of 0.01% or more in order to secure a solid solution strengthening effect and to lower the critical cooling rate for securing martensite in the hot press forming member. In addition, the Mn content may be 10% or less in terms of ensuring the hot press forming process workability, reducing manufacturing cost, and improving spot weldability by appropriately maintaining the strength of the steel sheet, and one embodiment of the present invention. Can be 9% or less, or 8% or less.

Al: 0.001-1.0%

The Al may be added in an amount of 0.001% or more since the deoxidation action in steelmaking together with Si may increase the cleanliness of the steel. In addition, the content of Al may be 1.0% or less in order to prevent the Ac3 temperature from becoming too high so that heating required in hot press molding may be performed in an appropriate temperature range.

P: 0.05% or less

P is present as an impurity in the steel, and the smaller the content is, the more advantageous. Therefore, in one embodiment of the present invention, P may be included in an amount of 0.05% or less. In another embodiment of the invention, P may be limited to 0.03% or less. Since less P is an advantageous impurity element, there is no need to specifically set an upper limit of the content. However, in order to lower the P content excessively, the manufacturing cost may increase, and when considering this, the lower limit may be 0.001%.

S: 0.02% or less

S is an impurity in steel, and the maximum content is 0.02% (preferably 0.01% or less) because it is an element that inhibits the ductility, impact property and weldability of the member. In addition, since the manufacturing cost may increase when 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%.

N: 0.02% or less

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

In the present invention, if necessary, in addition to the above-described steel composition, at least one sum selected from the group consisting of Cr, Mo, and W: 0.01 to 4.0%, and at least one sum from the group consisting of Ti, Nb, Zr, and V: 0.001 At least one of ˜0.4%, Cu + Ni: 0.005 to 2.0%, Sb + Sn: 0.001 to 1.0%, and B: 0.0001 to 0.01%.

Sum of at least one selected from the group consisting of Cr, Mo and W: 0.01% to 4.0%

The Cr, Mo and W can secure the hardenability and secure the strength and grain refinement through the precipitation strengthening effect, one or more of these may be added 0.01% or more based on the total content. In addition, the content may be limited to 4.0% or less in order to ensure weldability of the member. In addition, if the content of these elements exceeds 4.0%, further increase in effect is also weak, so if the content is limited to 4.0% or less, it is possible to prevent the increase in cost due to the addition of additional elements.

Sum of at least one selected from the group consisting of Ti, Nb, Zr and V: 0.001 to 0.4%

The Ti, Nb and V are effective in improving the steel sheet of the heat-treating member by forming fine precipitates and improving the retained austenite and impact toughness by refining grains, and therefore, at least one of them may be added in an amount of 0.001% or more. have. However, if the added amount exceeds 0.4%, the effect is not only saturated, but excessive cost may be caused by the addition of ferroalloy.

Cu + Ni: 0.005-2.0%

Cu and Ni are elements that form fine precipitates to improve strength. In order to obtain the above-mentioned effects, the sum of one or more of these components may be 0.005% or more. However, if the value exceeds 2.0%, the excessive cost increases, so the upper limit is 2.0%.

Sb + Sn: 0.001-1.0%,

The Sb and Sn may be concentrated on the surface during annealing heat treatment for Al-Si plating to suppress the formation of Si or Mn oxide on the surface to improve plating properties. It may be added 0.001% or more in order to obtain such an effect. However, if the added amount exceeds 1.0%, the upper limit is 1.0% because not only excessive ferroalloy costs but also solid solution at the slab grain boundary may cause coil edge cracks during hot rolling.

B: 0.0001-0.01%

The above-mentioned B is an element which can not only improve hardenability by addition of a small amount but also segregate in the old austenite grain boundary and suppress brittleness of the hot press-molded member due to grain boundary segregation of P or / and S. Therefore, B may be added at least 0.001%. However, if the content exceeds 0.01%, the effect is not only saturated, but also causes brittleness in hot rolling, so the upper limit thereof may be 0.01%, and in one embodiment, the B content may be 0.005% or less.

Iron and unavoidable impurities are mentioned as remainder other than the above-mentioned component, and if it is a component which can be contained in a steel plate for hot forming, it will not specifically limit.

Hereinafter, an example of a method of manufacturing a steel sheet for hot press forming according to an aspect of the present invention will be described. However, the manufacturing method of the steel sheet for hot press forming described below is just one example, and the steel sheet for hot pressing forming of the present invention is not necessarily manufactured by the present manufacturing method, and any method of manufacturing the steel sheet for the present invention satisfies the claims of the present invention. It should be noted that there is no problem in using each of the embodiments of the present invention.

The steel sheet of the present invention can be obtained by using hot-rolled or cold-rolled steel sheet, by performing hot-dip aluminum plating on the surface of the steel sheet and performing annealing treatment on the coated steel sheet.

[Aluminum Plating Process]

In one embodiment of the present invention, a process of preparing a holding steel sheet, aluminum plating and winding the surface of the holding steel sheet under appropriate conditions is performed to obtain an aluminum plated steel sheet (coil).

One side  30 ~ 200g / m Per ² Aluminum plating on the surface of the steel sheet

The surface of the rolled steel sheet may be subjected to aluminum plating. Aluminum plating is usually required by AlSi plating (type 80), containing at least 80% Al and 5-20% Si, optionally with additional elements, or at least 90% Al (type II). Depending on the plating, any plating containing additional elements may be used. Molten aluminum plating may be performed to form a plating layer, and annealing treatment may be performed on the steel sheet before plating. When plating, the appropriate plating amount is 30 ~ 200g / m ² on one side. If the plating amount is too large, it may take an excessive time to alloy to the surface, on the contrary, if the plating amount is too small, it is difficult to obtain sufficient corrosion resistance.

After aluminum plating, the cooling rate up to 250 ℃ is 20 ℃ / sec or less

The cooling rate after the aluminum plating affects the formation of the diffusion suppression layer between the plating layer and the base iron. If the cooling rate is too fast after the aluminum plating, the diffusion suppression layer is not uniformly formed, and thus the alloying behavior of the coil during the subsequent annealing treatment is performed. It can become uneven. Therefore, the cooling rate to 250 degreeC after aluminum plating can be 20 degrees C / sec or less.

After plating Winding  Coiling tension is 0.5 ~ 5 kg Of mm ²  Should be

When winding the steel plate after plating to obtain a coil, the winding tension of the coil can be adjusted. According to the adjustment of the winding tension of the coil, the alloying behavior and the surface quality of the coil may be changed during the subsequent annealing treatment.

Annealing Process

An annealing treatment is performed on the aluminum plated steel sheet by the above-described process to obtain an aluminum alloy plated steel sheet.

30 minutes to 50 hours in the range of 550 ~ 750 ℃

Aluminum plated steel sheets (coils) are heated in a batch annealing furnace. When heating the steel sheet, the heat treatment target temperature and the holding time are 30 minutes to 50 minutes at a range of 550 to 750 ° C based on the steel sheet temperature (in the present invention, the highest temperature at which the material reaches this temperature range is called a heating temperature). It is desirable to keep time. The holding time is the time from the coil temperature reaching the target temperature until the cooling start. In one embodiment of the present invention, when the alloying is not sufficiently made, the plating layer may be peeled off during roll leveling, so that the heating temperature may be 550 ° C. or more for sufficient alloying. In addition, the heating temperature may be 750 ° C. or less in order to prevent excessive generation of oxide on the surface layer and to secure spot weldability. In addition, in order to sufficiently secure the plating layer and prevent a decrease in productivity, the holding time may be set to 30 minutes to 50 hours. In one embodiment of the present invention, the temperature of the steel sheet may have a heating pattern in which the temperature continues to rise without a cooling process until the heating temperature is reached.

Heating up to heating temperature with an average temperature increase rate of 20 to 100 ° C / h

When heating the steel sheet at the above-described heating temperature, in order to ensure sufficient productivity and to uniformly alloy the plating layer on all steel sheets (coils), the steel sheet (coil) temperature reference for the entire temperature section (room temperature to heating temperature section) The average temperature increase rate can be 20-100 degreeC / h. In addition, the overall average temperature increase rate can be controlled in the above numerical range, but in one embodiment of the present invention to control the temperature increase rate of a specific temperature section as described later to achieve the problem of the present invention.

Heating at an average temperature increase rate of 400 ~ 500 ℃ section at 1 ~ 15 ℃ / h

In one embodiment of the present invention in order to ensure sufficient productivity while preventing the rolling oil remains in the temperature range during which the rolling oil mixed during rolling is vaporized to cause surface stains, etc., the average temperature increase rate of 400 to 500 ° C. is increased. It can be heated at 1 to 15 ° C / h. In one embodiment of the present invention can be the lower limit of the average temperature increase rate of 400 ~ 500 ℃ section at the time of the temperature increase to 3 ℃ / hr, and in another embodiment the lower limit of the average temperature increase rate of 400 ~ 500 ℃ section at the time of temperature increase It may also be 4 ° C / hr.

The difference between the ambient temperature and the steel plate temperature in the annealing furnace is 5 ~ 80 ℃

In general, the heating of the annealing furnace is a method of heating the steel sheet (coil) by raising the atmosphere temperature in the annealing furnace, rather than directly heating the steel sheet (coil). In this case, the difference between the ambient temperature and the coil temperature is unavoidable, but in order to minimize the variation in material and plating quality for each position in the steel sheet, the difference between the ambient temperature and the steel sheet temperature can be 80 ° C or less based on the time point at which the heat treatment target temperature is reached. have. Ideally, the temperature difference should be as small as possible, but this can be made 5 ° C or higher, since it may be difficult to meet the overall average temperature rise rate conditions by slowing the rate of temperature rise. Here, the temperature of the steel sheet means that the temperature of the loaded steel plate (coil) bottom part (meaning the lowest part of the coil) is measured, and the atmospheric temperature means the temperature measured at the center of the internal space of the heating furnace. .

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it should be noted that the following examples are only intended to illustrate 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)

Manufacture of steel sheet

Inventive Example 1

To prepare a cold rolled steel sheet for hot press molding having the composition of Table 1. The surface of the steel sheet was plated with a type I plating bath having an Al-9% Si-2.5% Fe composition. During plating, the plating amount was adjusted to 50 g / m ² per side, and after cooling the aluminum to 250 ° C. after cooling to 8 ° C./sec, the winding tension was adjusted to 2.8 kg / mm ² .

element C Si Mn Al P S N Additional elements content(%) 0.24 0.1 1.2 0.03 0.008 0.002 0.003 Cr 0.15, B 0.003

The plated steel sheet was heated to 650 ° C. under the following conditions in an annealing furnace.

Overall average temperature rise rate up to 650 ° C: 25 ° C / h

Average temperature rise rate of 400 ~ 500 ℃ temperature range: 5 ℃ / h

Temperature difference between atmosphere and steel plate at heating temperature: 15 ℃

After heating was maintained at the same temperature for 20 hours, the steel sheet was then cooled by air to obtain a hot press forming steel sheet.

As a result of analyzing the plated layer of the steel sheet using a GDS analyzer, a component profile of the form as shown in FIG. 2 was obtained, and the average Fe content was calculated based on 59.4% by weight. In addition, the concentration gradient in the Fe content range of 45 to 80% by weight in the plating layer was 3.6% / 탆.

Inventive Example 2

On the surface of the steel sheet having the composition shown in Table 1, the surface of the steel sheet was plated with a type I plating bath having an Al-9% Si-2.5% Fe composition. During plating, the plating amount was adjusted to 70 g / m ² per side, and after cooling the aluminum to 250 ° C. after cooling to 11 ° C./sec, the winding tension was adjusted to 3.2 kg / mm ² .

The plated steel plate was then heated to 700 ° C. under the following conditions in an annealing furnace.

Total average temperature rise rate up to 700 ° C: 30 ° C / h

Average temperature rise rate of 400 ~ 500 ℃ temperature range: 7 ℃ / h

Temperature difference between atmosphere and steel plate at heating temperature: 30 ° C

After heating was maintained at the same temperature for 10 hours, the steel sheet was then cooled by air to obtain a hot press forming steel sheet.

As a result of analyzing the plated layer of the steel sheet using a GDS analyzer, it was possible to obtain a component profile as shown in FIG. 3, and the average Fe content calculated based on this was 63.7 wt%. In addition, the concentration gradient in the Fe content range of 45 to 80% by weight in the plating layer was 1.5% / 탆.

Comparative Example 1

In the same manner as in Inventive Example 1, only the plating was performed, but the heating and cooling were not performed.

As a result of analyzing the plated layer of the steel sheet using a GDS analyzer, a component profile of the form as shown in FIG. 4 was obtained, and the average Fe content calculated based on this was 22.6 wt%. Incidentally, the concentration gradient in the Fe content range of 45 to 80% by weight was 10.1% / µm.

Comparative Example 2

An aluminum plated steel sheet was prepared in the same manner as Inventive Example 2, but with no plating but heating and cooling.

As a result of analyzing the plated layer of the steel sheet using a GDS analyzer, a component profile of the form as shown in FIG. 5 was obtained, and the average Fe content calculated based on this was 18.3 wt%. Incidentally, the concentration gradient in the section in which the Fe content was 45 to 80% by weight in the plating layer was 11.1% / µm.

Comparative Example 3

On the surface of the steel sheet having the composition shown in Table 1, the surface of the steel sheet was plated with a type I plating bath having an Al-9% Si-2.5% Fe composition. During plating, the coating amount was adjusted to 70 g / m ² per side, and after the aluminum plating, the cooling rate to 250 ° C. was cooled to 25 ° C./sec, and the winding tension was adjusted to 3.8 kg / mm ² .

The plated steel plate was then heated to 600 ° C. under the following conditions in an annealing furnace.

Overall average temperature rise rate up to 600 ° C: 150 ° C / h

Average temperature increase rate in 400 ~ 500 ℃ temperature range: 100 ℃ / h

Temperature difference between atmosphere and coil at heating temperature: 50 ° C

After heating was maintained at the same temperature for 2 hours, the steel sheet was then cooled by air to obtain a hot press forming steel sheet.

As a result of analyzing the plated layer of the steel sheet using a GDS analyzer, a component profile having the form shown in FIG. 6 was obtained, and the average Fe content calculated based on this was 36.6 wt%. Incidentally, the concentration gradient of the Fe content of 45 to 80% by weight in the plating layer was 8% / 탆.

Hot  Press molding

The steel sheets of Inventive Examples 1 and 2 and Comparative Examples 1, 2 and 3 were heated to 950 ° C. at a heating rate of 6.2 ° C./s, and then maintained at the temperature for 5 minutes. Then, hot press molding was quenched by press. Was performed to obtain a hot press-molded member.

A part of the obtained member was taken out and the cross section was observed, and the number of cavities per unit area was measured at a position from the boundary between the steel plate and the plated layer to a point up to 15 µm (lower portion of the plated layer cross section).

In addition, after bonding the two members of the same invention or comparative example with the structural adhesive with the adhesive surface of the member 25.4mm x 12.7mm, the 90% of the allowable adhesive strength of the adhesive in the direction perpendicular to the adhesive surface A load was applied and the adhesion surface was observed to be separated.

division Number of voids per lower cross-sectional area of 1000 μm ² Adhesive surface detached Inventive Example 1 Public not observed Not separated Inventive Example 2 Public not observed Not separated Comparative Example 1 16.3 Detached Comparative Example 2 18.1 Detached Comparative Example 3 10.6 Partially separated

As can be seen in Table 2, the hot press formed members produced from the steel sheets of Inventive Example 1 and Inventive Example 2 hardly generated voids, whereas the hot press formed members manufactured from the steel sheets of Comparative Examples 1 and 2 had a cross-sectional area of 1000. More than 16.3 pores were generated per μm ² , and as a result, the adhesive surface was separated. However, as a result of observing the adhesive surface, it was found that the separation occurred in the plating layer, not in the adhesive layer. In Comparative Example 3, although the number of pores was smaller than that of Comparative Example 1 or 2, a large number of pores existed, the adhesive surface was not separated when a load was applied. However, after the test, the adhesive surface was removed after the removal of the adhesive using a solvent, and as a result, some separation in the plating layer was observed.

Therefore, as suggested by the present invention, it could be confirmed that securing the Fe content in the steel sheet for hot press forming to a predetermined level or more is advantageous for securing the plating adhesion.

Claims (8)

Aluminum alloy plated steel sheet, The average content of Fe in the plating layer is 40% by weight or more, A steel sheet for hot press forming member having excellent plating adhesion with a concentration gradient of 7 wt% / µm or less in a section in which the Fe content is 45 to 80% in the plating layer from the surface of the plating layer in the thickness direction. The steel sheet for hot press forming member according to claim 1, wherein the concentration gradient is 5% by weight or less. The steel sheet for hot press forming member according to claim 1, wherein the aluminum alloy plating layer has an excellent plating adhesiveness with an average content of Fe of 50% by weight or more. According to claim 1, wherein the steel sheet is in the weight% C: 0.04-0.5%, Si: 0.01-2%, Mn: 0.01-10%, Al: 0.001-1.0%, P: 0.05% or less, S: 0.02 A steel sheet for hot press forming member having excellent plating adhesion having a composition containing% or less, N: 0.02% or less, balance Fe and other unavoidable impurities. The composition of claim 4, wherein the composition of the steel sheet is in weight percent, one or more sums selected from the group consisting of Cr, Mo, and W: 0.01-4.0%, one or more kinds in the group consisting of Ti, Nb, Zr, and V. A steel sheet for hot press forming member having excellent plating adhesiveness, further comprising at least one of 0.001 to 0.4%, Cu + Ni: 0.005 to 2.0%, Sb + Sn: 0.001 to 1.0%, and B: 0.0001 to 0.01%. Aluminum plating and winding the surface of the base steel sheet to obtain an aluminum plated steel sheet; Annealing the aluminum plated steel sheet to obtain an aluminum alloy plated steel sheet; And A method of manufacturing a steel sheet for a hot press formed member comprising the step of cooling an aluminum alloy plated steel sheet, The aluminum plating amount is 30 ~ 200g / m ² on one side of the steel sheet, After aluminum plating, the cooling rate up to 250 ° C. should be 20 ° C./sec or less, Winding tension is 0.5 ~ 5kg / mm ² when winding up, The annealing is carried out in a heating temperature range of 550 ~ 750 ℃ in an annealing furnace for 30 minutes to 50 hours, When the annealing is heated from room temperature to the heating temperature, the average temperature increase rate to 20 ~ 100 ℃ / h, the average temperature increase rate of 400 ~ 500 ℃ section to 1 ~ 15 ℃ / h, The manufacturing method of the steel plate for hot press molding members excellent in plating adhesiveness which makes the difference between the said annealing furnace atmosphere temperature and steel plate temperature into 5-80 degreeC. 7. The steel sheet according to claim 6, wherein the base steel sheet is in weight% of C: 0.04-0.5%, Si: 0.01-2%, Mn: 0.01-10%, Al: 0.001-1.0%, P: 0.05% or less, S: 0.02 A method for producing a steel sheet for hot press forming member having excellent plating adhesion having a composition containing% or less, N: 0.02% or less, balance Fe and other unavoidable impurities. The composition of claim 7, wherein the composition of the steel sheet is in weight percent, one or more sums selected from the group consisting of Cr, Mo, and W: 0.01-4.0%, one or more kinds in the group consisting of Ti, Nb, Zr, and V. Sum of 0.001 to 0.4%, Cu + Ni: 0.005 to 2.0%, Sb + Sn: 0.001 to 1.0%, and B: 0.0001 to 0.01% Manufacturing method.

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