WO2018221992A1

WO2018221992A1 - Steel sheet for hot press formed member having excellent painting adhesion and post-painting corrosion resistance, and method for manufacturing same

Info

Publication number: WO2018221992A1
Application number: PCT/KR2018/006259
Authority: WO
Inventors: 오진근; 김성우; 신현정; 조아라
Original assignee: 주식회사 포스코
Priority date: 2017-06-01
Filing date: 2018-05-31
Publication date: 2018-12-06

Abstract

The present invention relates to a steel sheet for a hot press formed member having excellent painting adhesion and post-painting corrosion resistance, and a method for manufacturing the same. A steel sheet for hot press forming according to one aspect of the present invention comprises a base steel sheet and a plated layer formed on a surface of the base steel sheet, wherein the ratio of an area occupied by pores to the entire area of a surface layer portion may be 10% or more in a cross section of the surface layer portion observed when the plated layer is cut in a thickness direction thereof.

Description

Steel plate for hot press forming member having excellent paint adhesion and corrosion resistance after painting and its manufacturing method

[Revision 13.08.2018 under Rule 26]
The present invention relates to a steel sheet for hot press forming member excellent in coating adhesion and corrosion resistance after painting, and a manufacturing method thereof.

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.

However, even if the aluminum plating layer is present on the surface so that the steel sheet is not oxidized at the time of heating, the member obtained after heating and molding is still exposed to the corrosive environment. Particularly, in the process of heating the plated steel sheet, base iron diffuses into the aluminum plating layer, and a hard Fe-Al-based plating layer is formed on the surface of the steel sheet. In the case of the Fe-Al-based plating layer, cracks occur in the plating layer because it is vulnerable as hard. There is a concern that the steel sheet may be exposed to a corrosive environment.

In order to prevent this, the hot press formed member is provided with a coating layer, which is required to have excellent paint adhesion.

According to one aspect of the present invention there is provided a steel sheet for hot press molding that can produce a hot press molding member excellent in paint adhesion and consequently excellent in corrosion resistance after painting.

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 includes a holding plate and a plated layer formed on the surface of the plate, and the area ratio occupied by the voids in the cross section of the surface layer observed by cutting the plated layer in the thickness direction. It may be more than 10% of the area of the.

In one embodiment of the present invention, the area ratio occupied by the voids in the cross section of the surface layer portion observed by cutting the plating layer in the thickness direction may be 15% or more of the total surface layer portion.

In one embodiment of the present invention, the plating layer may be an aluminum alloy plating layer.

In one embodiment of the present invention, the aluminum alloy plating layer may have an average content of Fe of at least 30% by weight.

In one embodiment of the present invention, the aluminum alloy plating layer may have an average content of Fe of at least 40% 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 the winding tension is 0.5 to 5 kg /. in mm ² and said annealing is carried out at a heating temperature range of 550 ~ 750 ℃ 30 bun ~ 50 hours at a appeal placed, when heated in room temperature during the annealing to the heating temperature, the average temperature increase rate 20 ~ 100 ℃ / h, but the average temperature increase rate of 400 ~ 500 ℃ section 1 ~ 15 ℃ / h, the heating temperature -50 ℃ ~ heating temperature section of the heating rate is 1 ~ 15 ℃ / h, in the above annealing furnace The difference between the atmosphere temperature and the steel sheet temperature is 5 to 80 ° C., and the cooling may be performed at a rate of 50 ° C./h or less to 500 ° C. in the step of cooling the aluminum alloy plated steel sheet.

According to one aspect of the present invention, since the steel sheet for hot press forming contains voids in the surface layer portion, the surface roughness of the member obtained after hot press forming can be greatly increased, resulting in good paint adhesion, and as a result, good post-painting corrosion resistance. You can get it.

1 is a cross-sectional photograph of the cut surface of the plated layer of the steel sheet according to an embodiment of the present invention.

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 scanning electron micrograph (rear scattering electron image) of observing a cross section of a plated layer of a steel sheet manufactured according to Inventive Example 1. FIG.

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

5 is a scanning electron micrograph (backscattered electron image) of observing a cross section of a plated layer of a steel sheet prepared according to Inventive Example 2. FIG.

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

7 is a scanning electron microscope photograph of a cross section of a plated layer of a steel sheet manufactured according to Comparative Example 1. FIG.

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

9 is a scanning electron microscope photograph of a cross section of a plated layer of a steel sheet manufactured by Comparative Example 2. FIG.

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

FIG. 11 is a scanning electron microscope photograph of a cross section of a plated layer of the steel sheet manufactured by Comparative Example 3. FIG.

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.

1 is a cross-sectional photograph of the cut surface of the plated layer of the steel sheet according to an embodiment of the present invention. As can be seen in the drawing, the steel sheet of the present invention is composed of a plated steel plate and a plated layer formed on the surface of the plated steel plate, and has a plurality of pores (pore) in the surface layer portion of the plated layer. This is a phenomenon that cannot be observed in the conventional aluminum plated steel sheet for hot press forming. In the conventional aluminum plated steel sheet, voids are hardly generated in the surface layer by hot-dip aluminum plating, whereas in the steel sheet according to the present embodiment, the surface layer portion of the plated layer is The main feature is that a number of voids are formed. In this embodiment, the surface layer means a region within 10 μm deep from the surface (if the surface layer is rough, the depth is measured from each point of the rough surface).

When a plurality of pores are included in the surface layer of the plated steel sheet, when the steel sheet is hot heated and press-molded, some of the surface layer pores are opened by the stress applied during press working, which increases the roughness of the surface of the plated layer. Do it.

Alloying is performed to the surface of the member for hot press forming obtained by hot press molding an aluminum plated steel plate. The resulting alloy layer is relatively stable compared with the non-alloyed aluminum plating layer, so the reactivity with the phosphate to improve the coating adhesion is weak, and there is little room for improvement of the coating adhesion only by the usual phosphate treatment. Of course, the roughness during the alloying in the hot press molding process increases the adhesion to the paint itself to some level, but there is a limit to the improvement.

Therefore, in this embodiment, in order to improve this, by forming voids in the plating layer in the steel sheet step as described above, the voids are collapsed in future press molding, thereby contributing to increase the roughness.

To this end, the area ratio occupied by the voids in the cross section of the surface layer portion observed by cutting the plating layer of the steel sheet in the thickness direction may be 10% or more with respect to the total surface layer portion, or may be 15% or more. In this case, the surface roughness is improved when the steel sheet is hot press formed, thereby greatly improving the coating adhesion and the corrosion resistance after painting. The upper limit of the surface roughness does not need to be particularly limited in terms of paint adhesion or post-painting corrosion resistance, but the void ratio may be usually determined to be 70% or less or 60% or less. There may be various methods for measuring the void ratio, but in one embodiment of the present invention, a method for measuring the ratio of the portion where the void exists by using an image analyzer may be used.

In the present invention, in order to form a plating layer having a high proportion of voids in the surface layer portion on the surface of the steel sheet, the plating layer may be an aluminum alloy plating layer, and in one embodiment, an Al-Fe alloy plating layer. According to one embodiment of the present invention, the Al—Fe alloy plating layer may be obtained by alloying an Al plated steel sheet under appropriate conditions. That is, in the present invention, when the Al-coated steel sheet is heated under appropriate conditions, diffusion occurs between Al of the plating layer and Fe of the base steel sheet, and Al and Fe are alloyed. In the process, a plurality of voids are formed in the surface layer portion. will be.

In this case, in order to form the voids, the average content of Fe in the plating layer may be 30% by weight or more, more preferably 40% by weight or more, and more preferably 50% by weight or more. That is, since sufficient voiding may occur to obtain voids in the surface layer portion, the average content of Fe in the plating layer may be 30% by weight, 40% by weight or 50% by weight or more. 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.

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 inhibits 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 boundary after martensite formation. It concentrates to secure 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 strength and crystallization through improving the hardenability, and the precipitation strengthening effect, these one or more 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 ²² 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 plating Winding Tension 0.5 ~ 5 kg Of mm ²² 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.

[Annealed]

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 ℃

The aluminum plated steel sheet (coil) is heated in a batch annealing furnace. When heating the steel sheet, the target heat treatment temperature and the holding time are in the range of 550 to 750 ° C based on the steel sheet temperature (in the present invention, this temperature range). It is preferable to maintain the maximum temperature reached by the material at 30 minutes to 50 hours at the heating temperature), wherein the holding time is the time from the coil temperature to the target temperature until the cooling start. In one embodiment, if the alloying is not sufficient, 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 order to ensure spot weldability, the heating temperature may be 750 ° C. or lower, and sufficient plating layer productivity and productivity In order to prevent degradation, 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 pattern in which the temperature is continuously raised without cooling until the heating temperature is reached. Can be.

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. In another embodiment of the present invention, the average temperature increase rate of the entire temperature section may be set at 70 ° C /.

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 4 ℃ / 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 5 ° C / hr.

At elevated temperature Heating temperature-50 ℃ ~ heating temperature average Elevated temperature Heating at speed of 1 ~ 15 ℃ / h

In order to prevent sticking during the alloying (surface defects where the surface of the coil is alloyed and sticking) and to allow the voids to be formed sufficiently, to ensure sufficient productivity, the average temperature rise rate of the heating temperature -50 ° C to the heating temperature range during heating It can be heated at 1-15 degreeC / h. In one embodiment of the present invention, the lower limit of the average temperature increase rate of the section may be set at 4 ° C./h. In another embodiment, the lower limit of the average temperature increase rate of the section may be set at 5 ° C./h.

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 atmosphere temperature and the steel sheet temperature cannot be avoided. However, the difference between the atmosphere temperature and the coil temperature can be set to 80 ° C or less based on the time point at which the heat treatment target temperature is reached in order to minimize the variation of the material and plating quality for each position in the steel sheet. have. Ideally, the temperature difference should be as small as possible, but this can be as high as 5 ° C, 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. .

[Cooling process]

After annealing, cool down to 500 ℃ at a rate of 50 ℃ / h or less

After maintaining a certain time at the target temperature, the aluminum alloy plated steel sheet (coil) is cooled. As the cooling method, various methods, such as furnace cooling, air cooling, and water cooling, can be applied. There is no particular limitation on the average cooling rate of the entire cooling section, and it may be rapidly cooled to improve productivity. However, in order to prevent sticking defects and ensure material uniformity and to form voids sufficiently, the cooling rate of the temperature section up to 500 ° C. after heating may be 50 ° C./h or less. The lower limit is not particularly limited, but may be 1 ° C / h or more in consideration of productivity.

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 coating amount was adjusted to 70 g / m ² per side, and the coil was wound by adjusting the winding tension after plating to 2.2 kg / mm ² .

원소element	CC	SiSi	MnMn	AlAl	PP	SS	NN	추가 원소Additional elements
함량(%)content(%)	0.210.21	0.20.2	1.31.3	0.030.03	0.010.01	0.0030.003	0.0050.005	Ti 0.03, B 0.002, Cr 0.2Ti 0.03, B 0.002, Cr 0.2

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: 20 ° C / h

Average temperature rise rate of 400 ~ 500 ℃ temperature range: 10 ℃ / h

Average temperature rise rate of 600 ~ 650 ℃ temperature range: 10 ℃ / h

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

After heating, the plate was maintained at the same temperature for 10 hours, after which the steel sheet was cooled to an average cooling rate of 40 ° C./h up to 500 ° C., and then cooled to an average cooling rate of 55 ° C./h up to 100 ° C. 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 calculated based on this was 51.5 wt%. As shown in FIG. 3, the cross-sectional shape of the steel sheet was formed with a plating layer formed on the outer surface of the base steel sheet, and the area ratio of the voids formed in the portion corresponding to the surface layer portion from the surface of the formed plating layer to the 10 µm thickness direction was 22.8%. there was.

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 coating amount was adjusted to 80g / m ² per side, and the coil was wound by adjusting the winding tension after plating to 2kg / mm ² .

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

Overall average temperature rise rate up to 700 ° C: 20 ° C / h

Average temperature rise rate in the temperature range of 400 ~ 500 ℃: 12 ℃ / h

Average temperature rise rate of 650 ~ 700 ℃ temperature range: 8 ℃ / h

Temperature difference between atmosphere and coil at heating temperature: 40 ° C

After heating was maintained at the same temperature for 1 hour, and then the steel sheet was cooled to an average cooling rate of 30 ℃ / h to 500 ℃, then cooled to an average cooling rate of 57 ℃ / h to 100 ℃ 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. 4 was obtained, and the average Fe content calculated based on this was 53.7 wt%. As shown in FIG. 5, the cross-sectional shape of the steel sheet was formed with a plating layer formed on the outer surface of the base steel sheet, and the area ratio of the voids formed in the portion corresponding to the surface layer portion from the surface of the formed plating layer to the 10 μm thickness direction was 28.5%. there was.

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 shown in FIG. 6 was obtained, and the average Fe content calculated based on this was 23.6 wt%. As shown in FIG. 7, the cross-sectional shape of the steel sheet was that a plating layer was formed on the outer surface of the base steel sheet, and almost no voids were formed in the portion corresponding to the surface layer portion from the surface of the formed plating layer to a point of 10 μm in the thickness direction. there was. The area ratio of the formed voids was 0%.

Comparative Example 2

In the same manner as in Inventive Example 2, 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. 8 was obtained, and the average Fe content calculated based on this was 21% by weight. As shown in Fig. 9, in the cross-sectional shape of the steel sheet, a plating layer was formed on the outer surface of the steel sheet, and almost no void was formed in the portion corresponding to the surface layer portion from the surface of the formed plating layer to a point of 10 µm in the thickness direction. there was. The area ratio of the formed voids was 0%.

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 90 g / m ² per side, and the coil was wound by adjusting the winding tension after plating to 2 kg / mm ² .

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

Overall average temperature rise rate up to 650 ° C: 50 ° C / h

Average temperature rise rate of 400 ~ 500 ℃ temperature range: 10 ℃ / h

Average temperature rise rate in the 600 ~ 650 ℃ temperature range: 70 ℃ / h

After heating, the plate was maintained at the same temperature for 10 hours, after which the steel sheet was cooled to an average cooling rate of 45 ° C./h up to 500 ° C., and then cooled to an average cooling rate of 60 ° C./h up to 100 ° C. 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. 10 was obtained, and the average Fe content was 48.4 wt% based on this. As shown in FIG. 11, the cross-sectional shape of the steel sheet was formed with a plating layer formed on the outer surface of the base steel sheet, and the area ratio of the voids formed in the portion corresponding to the surface layer portion from the surface of the formed plating layer to a thickness point of 10 μm was 3.5%. there was.

Hot Press molding

The steel sheets of Inventive Examples 1 and 2 and Comparative Examples 1 to 3 were heated to 950 ° C. and maintained at the above temperature for 5 minutes, and then subjected to hot press molding to quench while pressing by a press to obtain a hot press molding member.

The cross section of the obtained member was observed to observe the surface roughness Ra, and the results are shown in Table 2 below.

구분division	표면 조도(Ra)Surface roughness (Ra)
발명예 1Inventive Example 1	2.012.01
발명예 2Inventive Example 2	2.232.23
비교예 1Comparative Example 1	1.121.12
비교예 2Comparative Example 2	1.271.27
비교예 3Comparative Example 3	1.481.48

As can be seen in Table 2, Inventive Example 1 and Inventive Example 2 have a surface roughness (Ra) of 2.01 and 2.23㎛, respectively, Comparative Example 1, Comparative Example 2 and Comparative Example 3 has a surface roughness (Ra) of 1.12, 1.27 And 1.48 μm.

Phosphate treatment and electrodeposition coating were performed on the members obtained from the respective examples and comparative examples, crosses were formed on the surface of the steel sheet, and then a cyclic corrosion test was carried out to cause blisters on the crosses. Was observed. The composite corrosion test was carried out in a cycle of 24 hours of 'wet atmosphere exposure 2 hours-salt spray exposure 2 hours-drying 1 hour-wet atmosphere exposure 6 hours-drying 2 hours-wet atmosphere exposure 6 hours-drying 2 hours-cooling 3 hours'. It was time and maintained a total of 50 cycles. Inventive Examples 1 and 2 were all the maximum width of the blister 1mm or less, while Comparative Examples 1, 2 and 3 are the maximum width of the blister 3.2, 2.9 and 2.4mm respectively, it can be confirmed that the corrosion resistance is poor after coating compared to the invention example there was.

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

Claims

A steel plate and a plating layer formed on a surface of the steel plate,

A steel sheet for hot press forming member having excellent coating adhesiveness and corrosion resistance after coating, wherein an area ratio occupied by the voids in the cross section of the surface layer portion observed by cutting the plating layer in the thickness direction is 10% or more of the total surface layer portion.
The steel sheet for hot press-molded member according to claim 1, wherein an area ratio of voids in the cross section of the surface layer portion observed by cutting the plating layer in the thickness direction is 15% or more relative to the area of the entire surface layer portion.
The steel sheet for hot press forming member according to claim 1, wherein the plating layer is an aluminum alloy plating layer.
4. The steel sheet for hot press forming member according to claim 3, wherein the aluminum alloy plating layer has excellent paint adhesion and corrosion resistance after coating, in which the average content of Fe is 30% by weight or more.
4. The steel sheet for hot press forming member according to claim 3, wherein the aluminum alloy plating layer is excellent in paint adhesion and corrosion resistance after coating, in which the average content of Fe is 40% 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 a composition containing% or less, N: 0.02% or less, balance Fe and other unavoidable impurities, and excellent coating adhesion and corrosion resistance after painting.
The composition of claim 6, wherein the composition of the steel sheet is in weight percent, at least one selected from the group consisting of Cr, Mo, and W: 0.01 to 4.0%, at least one member from the group consisting of Ti, Nb, Zr, and V. Total: 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% Hot press forming with excellent paint adhesion and corrosion resistance after painting Steel plate for member.
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,

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 is 1 ~ 15 ℃ / h, heating temperature-50 ℃ ~ The temperature increase rate of the heating temperature range is 1 ~ 15 ℃ / h,

The difference between the ambient annealing furnace atmosphere temperature and the steel sheet temperature is 5 ~ 80 ℃,

The method of manufacturing a steel sheet for hot press molding member having excellent coating adhesion and corrosion resistance after cooling at a rate of 50 ° C./h or less to 500 ° C. in the step of cooling the aluminum alloy plated steel sheet.
9. The steel sheet according to claim 8, wherein the base steel sheet is in weight percent 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 a composition containing% or less, N: 0.02% or less, balance Fe and other unavoidable impurities, and excellent coating adhesion and postcorrosion resistance.
The composition of claim 9, wherein the composition of the steel sheet is in weight percent, at least one sum selected from the group consisting of Cr, Mo, and W: 0.01 to 4.0%, at least one member from the group consisting of Ti, Nb, Zr, and V. Total: 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% Hot press forming with excellent paint adhesion and corrosion resistance after painting Method for manufacturing steel sheet for member.