Hot press-forming plated steel sheet, hot press-formed member, and manufacturing methods therefor

Abstract

One aspect of the present invention provides a hot press-forming plated steel sheet having excellent resistance to hydrogen embrittlement, a hot press-formed member, and manufacturing methods therefor.

Description

Galvanized steel sheets for hot forming, hot forming members and their manufacturing methods

[0001] The present invention relates to a hot-forming galvanized steel sheet having excellent hydrogen embrittlement resistance, a hot-forming member, and a method for manufacturing the same.

[0002] Due to the depletion of petroleum resources and growing environmental concerns, regulations on improving automobile fuel efficiency are becoming increasingly stringent. From a material perspective, one way to improve fuel efficiency is to reduce the thickness of steel sheets used. However, reducing thickness can compromise vehicle safety, so increasing the strength of the steel sheets is essential.

[0003] For these reasons, demand for high-strength steel plates has persisted, and various types have been developed. However, due to their inherently high strength, these steel plates suffer from poor workability. Specifically, because the product of strength and elongation tends to remain constant across steel grades, increasing strength leads to a decrease in elongation, a key indicator of workability.

[0004] To address these issues, hot press forming has been proposed. Hot press forming involves processing steel plates at a high temperature suitable for processing and then rapidly cooling them to a lower temperature. This process forms low-temperature structures, such as martensite, within the steel plate, thereby increasing the strength of the final product. This method has the advantage of minimizing workability issues when manufacturing high-strength components.

[0005] When hot press forming is performed, the steel sheet can have a strength of 1000 MPa or more, and in some cases, 1400 MPa or more, and recently, the level of strength requirement has become higher, so there are cases where the steel sheet has a strength of 1800 MPa or more. However, when the strength of the steel sheet increases, it becomes sensitive to hydrogen delayed fracture, and the steel sheet may break even if it contains a small amount of hydrogen. In addition, when an aluminum-plated steel sheet is hot press formed, Fe diffusion occurs from the base iron of the steel sheet to the plating layer on the surface, causing alloying in the plating layer. This alloy layer makes it difficult for hydrogen that has penetrated during the hot press forming to escape, which causes the hydrogen resistance of the hot press formed part to deteriorate.

[0006] According to one aspect of the present invention, a hot-forming plated steel sheet, a hot-forming member, and a manufacturing method thereof having excellent hydrogen embrittlement resistance can be provided.

[0007] The objectives of the present invention are not limited to the above-described scope. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall content of this specification.

[0008] A hot forming plated steel sheet according to one aspect of the present invention may include a base steel sheet; and an Al-based plating layer formed on a surface of the base steel sheet, wherein the Al-based plating layer may include a Fe2Al8Si phase, and the Fe2Al8Si phase may include, in wt%, Fe: 15.0 to 25.0%, Si: 5.00 to 15.0%, Nimax: 0.400% to 5.00%, and the remainder may be composed of Al and unavoidable impurities.

[0009] The above-described Al-based plating layer may be composed of 5.0 to 10% Si, with the remainder being Al and other unavoidable impurities, when the remaining alloy composition excluding Fe diffused from the base steel sheet is 100% in weight %.

[0010] The above-described Fe2Al8Si phase may have an average thickness of 3.0 μm or more in the thickness direction of the Al-based plating layer.

[0011] The above-mentioned steel sheet contains, in wt%, C: 0.060 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.00100 to 0.0300%, S: 0.000100 to 0.0200%, Al: 0.0100 to 0.100%, Cr: 0.0100 to 1.00%, N: 0.001000 to 0.02000%, Ti: 0 to 0.100%, B: 0 to 0.01000%, Cu: 0 to 1.00%, Mo: 0 to 1.00%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, V: 0 to 1.00%, Ca: 0 to 0.0100%, Nb: 0 to 0.100%, Sn: 0 to 1.00%, W: 0 to 1.00%, Sb: 0 to 1.00%, Mg: 0 to 0.100%, Co: 0 to 1.00%, As: 0 to 1.00%, Zr: 0 to 1.00%, Bi: 0 to 1.00% and REM: 0 to 0.300%, and the remainder may be composed of Fe and inevitable impurities.

[0012] A hot-forming galvanized steel sheet according to one embodiment of the present invention may additionally include a Ni flash electroplating layer between the base steel sheet and the Al-based plating layer.

[0013] A method for manufacturing a hot-forming galvanized steel sheet according to another aspect of the present invention may include the steps of: preparing a base steel sheet; performing Ni flash electroplating on the base steel sheet to obtain an electroplated steel sheet; continuously annealing the electroplated steel sheet; immersing the continuously annealed electroplated steel sheet in an aluminum plating bath; controlling the plating adhesion amount of the electroplated steel sheet immersed in the aluminum plating bath with an air knife (A / K); and cooling the electroplated steel sheet to obtain a plated steel sheet.

[0014] The above-mentioned Ni flash electroplating is 150mg / m 2 More than 2500 mg / m 2 It can be done with the following plating attachment amount.

[0015] In addition, in the method for manufacturing a hot-forming plated steel sheet according to an example of the present invention, the K value derived by the following equation 1 may be 2 or more and 4 or less.

[0016] (Equation 1) K = 10 4 ×(a×d) / (b×c×e)

[0017] (In the above formula 1, a represents the Si content (weight %) of the aluminum plating bath, b represents the line speed (mpm), c represents the air knife spacing (mm), d represents the air knife pressure (kPa), and e represents the air knife height (mm).)

[0018] The above-mentioned steel sheet contains, in wt%, C: 0.060 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.00100 to 0.0150%, S: 0.000100 to 0.0200%, Al: 0.0100 to 0.100%, Cr: 0.0100 to 1.00%, N: 0.001000 to 0.02000%, Ti: 0 to 0.100%, B: 0 to 0.01000%, Cu: 0 to 1.00%, Mo: 0 to 1.00%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, V: 0 to 1.00%, Ca: 0 to 0.01%, Nb: 0 to 0.10%, Sn: 0 to 1.00%, W: 0 to 1.00%, Sb: 0 to 1.00%, Mg: 0 to 0.100%, Co: 0 to 1.00%, As: 0 to 1.00%, Zr: 0 to 1.00%, Bi: 0 to 1.00% and REM: 0 to 0.300%, and the remainder may be composed of Fe and inevitable impurities.

[0019] The above-described aluminum plating bath may contain 5.0 to 10 wt% of Si, with the remainder being Al and other unavoidable impurities.

[0020] A hot-formed member according to another aspect of the present invention may include a base iron; and an alloy plating layer formed on the base iron, and the alloy plating layer may include an Fe2AlSi2 phase.

[0021] The above-described Fe2AlSi2 phase may contain, in wt%, Fe: 25.0 to 60.0%, Si: 10.0 to 20.0%, Nimax: 0.300% to 5.00%, and the remainder may be composed of Al and unavoidable impurities.

[0022] The above-described alloy plating layer may be composed of Si: 1.0 to 15%, Ni: 0.00100 to 1.00%, and the remainder Al and other unavoidable impurities, when the remaining alloy composition excluding the Fe content diffused from the base steel sheet is 100% in weight %.

[0023] The above-described Fe2AlSi2 phase may be 5% by area or more of the total area of ​​the alloy plating layer, and may be formed as a distinct layer in the middle of the alloy plating layer.

[0024] The average maximum thickness value of the Fe2AlSi2 phase described above may be 2.0 μm or more in the direction of the alloy plating layer thickness.

[0025] In addition, the above-described Fe2AlSi2 phase may have a maximum gap of 4.5 μm or less between adjacent Fe2AlSi2 phases when viewed from a cross-section cut through the alloy plating layer.

[0026] A hot-formed member according to an example of the present invention has a hydrogen diffusion coefficient D of the alloy plating layer derived by the following equations 2 and 3. eff,coating The value is 2.5x10 -7 cm 2 s -1 It may be less than or equal to 0.2 ppm, and the amount of diffusible hydrogen may be less than or equal to 0.2 ppm.

[0027] (Formula 2)

[0028] (D in the above equation 2eff is the hydrogen diffusion coefficient of the hot-formed member, L is the thickness of the hot-formed member, t b represents the start time (in seconds) at which hydrogen begins to permeate the hot-formed member during the hydrogen permeation test.

[0029] (Formula 3)

[0030] (D in the above equation 3 eff is the hydrogen diffusion coefficient of the hot-formed member, L is the thickness of the hot-formed member, L sheet is the thickness of the above-mentioned steel, L Coating is the thickness of the above alloy plating layer, D eff,sheet represents the hydrogen diffusion coefficient of the above-mentioned iron.)

[0031] The hot-forming plated steel sheet of the present invention forms Ni on the surface of the steel sheet and sufficiently diffuses the Ni into the Al-based plating layer, thereby forming an Fe2AlSi2 phase at an appropriate level in the alloy plating layer of a hot-formed member obtained after hot press forming. The Fe2AlSi2 phase formed in this manner can reduce the amount of diffusible hydrogen in the alloy plating layer, and therefore the hot-formed member of the present invention including the Fe2AlSi2 phase can have excellent hydrogen embrittlement resistance.

[0032] Figure 1 shows an SEM image photograph of a plating layer formed on a hot-forming plating steel sheet corresponding to Invention Example 6.

[0033] Figure 2 shows an SEM image photograph of a plating layer formed on a hot-formed member corresponding to Invention Example 6.

[0034] Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0035] In this specification, the term "including" is used to indicate that other components may be included rather than excluding other components unless specifically stated to the contrary.

[0036] Additionally, unless otherwise specifically provided in the specification of the present invention, the % unit means weight%.

[0037] Although not essential, it should be noted that the technical solutions according to each aspect of the present invention can also be usefully applied to other aspects of the present invention. Furthermore, the compositions and various useful parameters according to each aspect of the present invention can be appropriately combined with other aspects to achieve beneficial effects.

[0038] The present inventors have conducted in-depth research on the multi-layer alloy phases formed in hot-formed parts obtained by hot press forming of aluminum-plated steel sheets. As a result, the present inventors have discovered that when the Fe2AlSi2 phase among the multi-layer alloy phases is formed in a hot-formed part, the Fe2AlSi2 phase can effectively block hydrogen absorbed within the steel sheet, and thus a hot-formed part including the Fe2AlSi2 phase can secure excellent hydrogen embrittlement resistance.

[0039] As a result of further research into this, the inventors of the present invention have found that, as described above, one effective way to form an Fe2AlSi2 phase at an appropriate level in a hot-formed member is to include Ni on the surface of a steel sheet and sufficiently diffuse the Ni into an Al-based plating layer formed thereon. In addition, the inventors of the present invention have found that, in order to diffuse Ni into the plating layer in this way, the Al-based plating layer needs to include a Fe2Al8Si phase, and have thus completed the present invention.

[0040] Hereinafter, a hot-forming galvanized steel sheet according to one aspect of the present invention will be described in detail.

[0041] [Galvanized steel sheet for hot forming]

[0042] According to one embodiment of the present invention, a hot-forming plated steel sheet may include a base steel sheet; and an Al-based plating layer formed on a surface of the base steel sheet. In addition, the Al-based plating layer may include a Fe2Al8Si phase, and the Fe2Al8Si phase may include, in wt%, Fe: 15.0 to 25.0%, Si: 5.00 to 15.0%, Nimax: 0.400% to 5.00%, and the remainder may be composed of Al and unavoidable impurities.

[0043] Below, each component is explained in detail.

[0044] According to one embodiment of the present invention, the steel sheet (steel sheet) may not be particularly limited as long as it is a steel sheet for hot press forming and is used for hot press forming. However, as a non-limiting example, the steel sheet may contain, in wt%, C: 0.060 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.00100 to 0.0150%, S: 0.000100 to 0.0200%, Al: 0.0100 to 0.100%, Cr: 0.0100 to 1.00%, N: 0.001000 to 0.02000%, Ti: 0 to 1.00% or less, B: 0 to 0.01000%, Cu: 0 to 1.00%, Mo: 0 to 1.00%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, V: 0 to 1.00%, Ca: 0 to 0.01%, Nb: 0 to 0.10%, Sn: 0 to 1.00%, W: 0 to 1.00%, Sb: 0 to 1.00%, Mg: 0 to 0.100%, Co: 0 to 1.00%, As: 0 to 1.00%, Zr: 0 to 1.00%, Bi: 0 to 1.00%, and REM: 0 to 0.300%.

[0045] C: 0.060~0.50%

[0046] The above C is an essential element for increasing the strength of a hot-formed member and can be added in an appropriate amount. That is, in order to sufficiently secure the strength of a hot-formed member, the C can be added in an amount of 0.060% or more. According to another embodiment, the lower limit of the C content may be 0.075%. However, if the content is too high, when producing a cold-rolled member, the strength of the hot-rolled member becomes too high when cold-rolling the hot-rolled member, resulting in greatly inferior cold-rollability and greatly reduced spot weldability. Therefore, in order to secure sufficient cold-rollability and spot weldability, the C content may be added to 0.50% or less. In addition, in another embodiment, the C content may be 0.45% or less, and in another embodiment, it may be 0.40% or less.

[0047] Si: 0.050~1.0%

[0048] The above-mentioned Si should not only be added as a deoxidizer in steelmaking, but also plays a role in suppressing the formation of carbides, which has the greatest influence on the strength of hot-formed parts. In the present invention, in order to secure residual austenite by concentrating carbon in the martensite lath grain boundaries after the formation of martensite in hot press forming, it may be added in an amount of 0.050% or more. In addition, in order to secure sufficient plating properties when aluminum plating is performed on a steel sheet after rolling, the upper limit of the Si content may be set to 1.0%. According to another embodiment, the upper limit of the Si content may be 0.80%.

[0049] Mn: 0.50~4.0%

[0050] The above Mn can be added in an amount of 0.50% or more to not only secure a strengthening effect but also lower the critical cooling rate for securing martensite in a hot press-formed member. In addition, the Mn content can be limited to 4.0% or less in order to secure the workability of the hot press-formed process, reduce manufacturing costs, and improve spot weldability by appropriately maintaining the strength of the steel sheet. In addition, in another embodiment, the Mn content can be 3.5% or less.

[0051] P: 0.00100~0.0300%

[0052] The above P exists as an impurity in steel, and the lower its content is, the more advantageous it is. Therefore, in the present invention, the P content can be limited to 0.0150% or less, and according to another embodiment, the P can be limited to 0.0200% or less. Since P is an impurity element that is advantageous the lower the content, there is no need to specifically set a lower limit for its content. However, since there is a concern that manufacturing costs may increase if the P content is excessively lowered, taking this into consideration, the lower limit can be set to 0.00100%.

[0053] S: 0.000100~0.0200%

[0054] The above S is an impurity in steel and is an element that impairs the ductility, impact properties, and weldability of the member. Therefore, the maximum content is limited to 0.0200%, and more preferably, it can be limited to 0.0100% or less. In addition, if the minimum content is less than 0.000100%, the manufacturing cost may increase, so the lower limit of the content can be set to 0.000100%.

[0055] Al: 0.0100~0.100%

[0056] The above Al, together with Si, can improve the cleanliness of steel by performing a deoxidizing effect in steelmaking, and can be added in a content of 0.0100% or more to achieve the above effect. In addition, the content of the above Al can be limited to 0.100% or less to prevent the Ac3 temperature from becoming too high and to allow the heating required for hot press forming to be performed within an appropriate temperature range.

[0057] Cr: 0.0100~1.00%

[0058] The above Cr can be added in an amount of 0.0100% or more to improve hardenability and secure strength and grain refinement through the precipitation strengthening effect. In addition, the content can be limited to 1.00% or less to secure weldability of the member.

[0059] N: 0.001000~0.02000%

[0060] Nitrogen (N) is an element that is inevitably added to steel, and if the content of N exceeds 0.02000%, there is a problem that slab cracks easily occur by combining with Al in the steel to form AlN. Since N is an unavoidable impurity, there is no particular limitation on its lower content. However, since manufacturing costs may be significantly increased in order to control the content of N to less than 0.001000%, it may be 0.001000% or more in consideration of this.

[0061] Ti: 0 to 0.100%

[0062] The above Ti can be added because it is effective in improving the steel sheet of the heat-treated member by forming fine precipitates and in stabilizing the retained austenite and improving the impact toughness by refining the crystal grains. However, if the amount added exceeds 0.100%, not only will the effect be saturated, but excessive addition of alloy iron may also result in an increase in cost. In addition, the above Ti is an element that may or may not be added selectively depending on the purpose, and the base steel sheet of the present invention may not contain the above Ti at all.

[0063] B: 0 to 0.01000%

[0064] The above B is an element that can not only improve hardenability even with a small amount of addition, but also suppress embrittlement of a hot press-formed part caused by grain boundary segregation of P and / or S by segregating at the grain boundaries of old austenite. However, if it exceeds 0.01000%, not only is the effect saturated, but it also causes embrittlement in hot rolling, so the upper limit may be set to 0.01000%, and in another embodiment, the B content may be 0.008000% or less. In addition, the B is an element that may or may not be selectively added depending on the purpose, and the base steel sheet of the present invention may not contain the B at all.

[0065] In addition, it will be apparent to those skilled in the art that, taking into account the target properties of the final product, etc., the composition may further include Cu, Mo, Cr, Ni, V, Ca, Nb, Sn, W, Sb, Mg, Co, As, Zr, Bi, REM, etc., in addition to the aforementioned composition.

[0066] Other than the above-mentioned components, the remaining components include iron (Fe) and unavoidable impurities.

[0067] Meanwhile, as described above, the hot-forming plated steel sheet according to an embodiment of the present invention can secure excellent hydrogen embrittlement resistance of a hot-forming member by including Ni on the surface of the steel sheet and sufficiently diffusing the Ni into an Al-based plating layer formed thereon. As one means for achieving the above object, the hot-forming plated steel sheet according to an embodiment of the present invention may additionally include a Ni flash electroplating layer between the base steel sheet and the Al-based plating layer; however, considering that there may be various methods for including Ni on the surface of the steel sheet, the present invention is not necessarily limited thereto.

[0068] Meanwhile, the Al-based plating layer of the hot-forming plated steel sheet according to an example of the present invention may include a Fe2Al8Si phase, and the Fe2Al8Si phase may include, in wt%, Fe: 15.0 to 25.0%, Si: 5.00 to 15.0%, Nimax: 0.400 to 5.00%, and the remainder may be composed of Al and unavoidable impurities. In this case, Nimax may mean the maximum value of Ni throughout the present specification.

[0069] The above Fe2Al8Si phase can be formed by the reaction between the base steel sheet and the Al-based plating layer immediately after aluminum plating. As described above, the Fe2Al8Si phase can effectively allow electroplated Ni to diffuse into the plating layer. The reason why the Fe2Al8Si phase can help Ni diffusion is because not only is the Ni diffusion rate faster in the Fe2Al8Si phase than in other phases, but also the Ni solubility is high during the alloying process. When Ni is sufficiently diffused into the plating layer, the Fe2AlSi2 phase can be generated at an appropriate level after HPF heat treatment, thereby effectively improving the hydrogen embrittlement resistance of a hot-formed part obtained after hot press forming the plating steel sheet.

[0070] In order to achieve the above-described object, according to one embodiment of the present invention, the Fe2Al8Si phase may have an average thickness of 3.0 μm or more in the thickness direction of the Al-based plating layer. In addition, according to one implementation example of the present invention, the Fe2Al8Si phase may be formed at the interface between the base steel sheet and the Al-based plating layer and may exist in the form of a layer. According to another embodiment, the Fe2Al8Si phase of the plating steel sheet may have an average thickness of 3.2 μm or more, and according to another embodiment, may have an average thickness of 3.6 μm or more. Since the average thickness of the Fe2Al8Si phase is more advantageous in achieving the object of the present invention as it is thicker, the upper limit thereof is not specifically limited. However, if the thickness is made excessively thick, a high temperature needs to be maintained during immersion or cooling in the plating bath, and in this case, considering that a load on the equipment may occur, in one example of the present invention, the upper limit of the average thickness of the Fe2Al8Si phase may be 9.0 μm.

[0071] Meanwhile, according to one embodiment of the present invention, the Al-based plating layer may include Si in an amount of 5.0 to 10% by weight, with the remainder being Al and other unavoidable impurities, when the remaining alloy composition excluding Fe diffused from the base steel sheet is 100%. In addition, as described above, the hot-forming plated steel sheet according to a non-limiting example of the present invention may additionally include a Ni flash electroplating layer between the base steel sheet and the Al-based plating layer, and in this case, the Al-based plating layer may include Ni diffused from the Ni flash electroplating layer. In consideration of this, the alloy composition of the Al-based plating layer described above may be 100%, with the remaining alloy composition excluding Ni diffused from the Ni flash electroplating layer, together with the Fe diffused from the base steel sheet.

[0072] More specifically, in one embodiment of the present invention, Si may be included in an amount of 5.0 to 10 wt%. The Si plays a role in uniformly alloying with Fe within the plating layer, and in order to obtain this effect, it must be included in an amount of at least 5.0%. On the other hand, since Si also plays a role in inhibiting the diffusion of Fe, if it is included in excess of 10%, the diffusion of Fe may be excessively inhibited, making it impossible to obtain the desired plating structure of the present invention. According to another embodiment, the Si content may be 7.0 to 9.8 wt%, and according to yet another embodiment, it may be 8.0 to 9.5 wt%.

[0073] As the Al-based plating layer of the hot-forming plated steel sheet according to one embodiment of the present invention satisfies the above-described alloy composition range, the Fe2Al8Si phase included in the Al-based plating layer may include, in wt%, Fe: 15.0 to 25.0%, Si: 5.00 to 15.0%, Nimax: 0.400% to 5.00%, and the remainder may be composed of Al and unavoidable impurities.

[0074] In particular, the Fe2Al8Si phase can sufficiently diffuse Ni into the Al-based plating layer by setting Nimax to 0.400% or more. In another embodiment, the Nimax may be 0.500% or more. Since a higher content of the Nimax is advantageous in achieving the purpose of the present invention, the upper limit thereof is not specifically limited. However, considering that the Nimax cannot realistically increase above a certain level, the upper limit of the Nimax in the present invention may be 5.00%.

[0075] The Fe content of the above Fe2Al8Si phase may be all or partly derived from the base steel sheet, and derived from the base steel sheet may mean that it has diffused from the Fe component of the base steel sheet and is included in the Fe2Al8Si phase.

[0076] Hereinafter, a method for manufacturing a hot-forming coated steel sheet of the present invention will be described. However, the following method for manufacturing a hot-forming coated steel sheet is merely an example, and it is not necessary for the hot-forming coated steel sheet of the present invention to be manufactured by this manufacturing method. It should be noted that any manufacturing method that satisfies the claims of the present invention can be used to implement each embodiment of the present invention without any problem.

[0077] [Method for manufacturing galvanized steel sheets for hot forming]

[0078] A method for manufacturing a hot-forming galvanized steel sheet according to one embodiment of the present invention may include the steps of: preparing a base steel sheet; performing Ni flash electroplating on the base steel sheet to obtain an electroplated steel sheet; continuously annealing the electroplated steel sheet; immersing the continuously annealed electroplated steel sheet in an aluminum plating bath; controlling the plating adhesion amount of the electroplated steel sheet immersed in the aluminum plating bath with an air knife (A / K); and cooling the electroplated steel sheet to obtain a plated steel sheet.

[0079] Steps to prepare the steel plate

[0080] Prepare a base steel sheet as a plating steel sheet. The base steel sheet may be cold-rolled steel sheet, or in some cases, hot-rolled steel sheet. The composition of the base steel sheet is as described above, so its description is omitted.

[0081] Step for obtaining electroplated steel sheet by nickel flash electroplating

[0082] As described above, the method for manufacturing a plated steel sheet for hot forming according to one embodiment of the present invention can form alloyed Ni in a base steel sheet used during hot press forming in order to form an Fe2AlSi2 phase at an appropriate level in a hot forming member.

[0083] As a non-limiting way to implement this, a method for manufacturing a hot-forming galvanized steel sheet according to one embodiment of the present invention may include a step of obtaining an electroplated steel sheet by performing Ni flash electroplating on the base steel sheet.

[0084] At this time, the Ni flash electroplating is 150 mg / m 2 More than 2500 mg / m 2 The plating can be performed with the following plating amount. That is, the method for manufacturing a hot-forming plating steel sheet according to one embodiment of the present invention is 150 mg / m 2 By performing Ni flash electroplating with a plating amount of 200 mg / m, the Fe2AlSi2 phase can be formed at an appropriate level in the alloy plating layer of the hot-formed member, thereby improving the hydrogen embrittlement resistance of the hot-formed member. According to another embodiment, the Ni flash electroplating is performed with a plating amount of 200 mg / m. 2 The plating amount can be applied at the above amount, and according to another embodiment, 250 mg / m 2 It can be done with the above plating attachment amount.

[0085] On the other hand, the Ni flash electroplating is 2500mg / m 2 If the plating amount is excessive, the production speed may be reduced or the electroplating deviation may significantly increase due to excessive use of current for electroplating. Therefore, one embodiment of the present invention sets the upper limit of the plating amount of the Ni flash electroplating to 2500 mg / m. 2 According to another embodiment, the Ni flash electroplating can be performed at 2000 mg / m 2 It can be done with the following plating attachment amount.

[0086] Continuous annealing stage

[0087] Next, according to a non-limiting embodiment of the present invention, the electroplated steel sheet can be continuously annealed.

[0088] More specifically, according to one example of the present invention, the continuous annealing may be performed at 700°C to 900°C. If the continuous annealing temperature is lower than 700°C, it is difficult for the rolled structure produced in the cold rolling process to recover and recrystallize, whereas if it exceeds 900°C, the annealing equipment may deteriorate, which may increase manufacturing costs due to frequent equipment replacement, etc.

[0089] In addition, the continuous annealing can be performed for 1 to 1000 seconds within the temperature range described above. If the annealing treatment time is less than 1 second, the annealing treatment effect cannot be obtained, while if it exceeds 1000 seconds, there is a risk of reduced productivity.

[0090] Step of immersing in an aluminum plating bath

[0091] According to one embodiment of the present invention, the continuously annealed electroplated steel sheet may be immersed in an aluminum plating bath. At this time, the aluminum plating bath may contain 5.0 to 10 wt% of Si, with the remainder being Al and other unavoidable impurities.

[0092] Step for controlling the amount of plating adhesion using an air knife (A / K)

[0093] In one embodiment of the present invention, the amount of plating adhesion of the electroplated steel sheet immersed in the aluminum plating bath can be controlled by an air knife (Air Knife, A / K). Through this step, one embodiment of the present invention can sufficiently cool the surface of the Al-based plating layer to prevent problems such as roll seizure of the cooling equipment, and at the same time, can appropriately maintain the temperature inside the Al-based plating layer. In addition, one embodiment of the present invention can appropriately maintain the temperature inside the Al-based plating layer in this way to form a Fe2Al8Si phase above a certain level, thereby alloying Ni within the Al-based plating layer.

[0094] In order to achieve the above-described purpose, according to one embodiment of the present invention, the K value derived by the following equation 1 may be 2 or more and 4 or less.

[0095] (Equation 1) K = 10 4 ×(a×d) / (b×c×e)

[0096] (In the above formula 1, a represents the Si content (weight %) of the aluminum plating bath, b represents the line speed (mpm), c represents the air knife spacing (mm), d represents the air knife pressure (kPa), and e represents the air knife height (mm).)

[0097] If the K value is less than 2, the surface of the Al-based plating layer may not be sufficiently cooled, which may result in poor roll adhesion and may cause cooling equipment problems. On the other hand, if the K value exceeds 4, the amount of air injected may increase excessively, which may result in excessive increase in process costs, and since cooling occurs excessively inside the plating layer, alloying of Ni within the plating layer may not be easy. In another embodiment, the K value may be 2.04 to 3.96, and in yet another embodiment, the K value may be 2.11 to 3.79.

[0098] A step of cooling the electroplated steel sheet to obtain a plated steel sheet.

[0099] Next, the electroplated steel sheet can be cooled to produce a plated steel sheet. Detailed cooling conditions, such as the cooling rate and cooling stop temperature, are not specifically limited, as they can be appropriately designed by a skilled technician for the specific purpose.

[0100] Meanwhile, according to another embodiment of the present invention, a hot-formed member obtained by hot press forming the hot-formed plated steel sheet of the present invention described above can be provided. In this case, the hot press forming can be performed using a method generally used in the relevant technical field, for example, the hot-formed plated steel sheet according to the present invention can be heated in a temperature range of 880 to 950°C for 3 to 10 minutes, and then the heated steel sheet can be hot-formed into a desired shape using a press and then rapidly cooled, but is not limited thereto.

[0101] Hereinafter, a hot-formed member obtained by hot press forming the hot-formed plated steel sheet of the present invention according to the above-described method will be described in detail.

[0102] [Hot-formed parts]

[0103] As described above, when the hot-forming plated steel sheet of the present invention is hot-press formed, a hot-forming member can be obtained. When the HPF heat treatment is performed in this manner, alloying of the plating layer containing Ni occurs, and accordingly, an Fe2AlSi2 phase can be formed together with an intermediate layer (FeAl(Si)).

[0104] That is, a hot-formed member according to one embodiment of the present invention may include a base iron; and an alloy plating layer formed on the base iron, and the alloy plating layer may include an Fe2AlSi2 phase.

[0105] As a non-limiting example, the Fe2AlSi2 phase included in the alloy plating layer can be formed as a distinct layer in the middle of the alloy plating layer.

[0106] The Fe2AlSi2 phase formed in this way effectively blocks the absorbed hydrogen and has a hydrogen diffusion rate (D) within the plating layer. eff,coating ) can be lowered to reduce the amount of diffusible hydrogen after HPF heat treatment.

[0107] In order to obtain the above-described effect, according to one embodiment of the present invention, the Fe2AlSi2 phase may be 5 area% or more with respect to the entire area of ​​the alloy plating layer. If the Fe2AlSi2 phase is less than 5 area%, the hydrogen diffusion rate within the plating layer may not be effectively reduced, and thus a hot-formed part including the same may be vulnerable to hydrogen embrittlement. According to another embodiment, the Fe2AlSi2 phase may be 5.1 area% or more with respect to the entire area of ​​the alloy plating layer, and according to another embodiment, it may be 5.9 area% or more. The present invention does not specifically limit the upper limit of the area fraction of the Fe2AlSi2 phase, but as an example, the area fraction of the Fe2AlSi2 phase may be 15 area% or less.

[0108] Likewise, for the purpose of providing a hot-forming member with excellent hydrogen embrittlement resistance by forming the Fe2AlSi2 phase at an appropriate level, the average maximum thickness of the Fe2AlSi2 phase in the alloy plating layer thickness direction may be 2.0 μm or more. In another embodiment, the average maximum thickness may be 2.5 μm or more, and in another embodiment, it may be 2.7 μm or more. The average maximum thickness may be obtained by observing the Fe2AlSi2 phase through SEM image analysis, repeating the operation of measuring the maximum thickness of the observed Fe2AlSi2 phase several times, and then averaging the values. The present invention does not specifically limit the upper limit of the average maximum thickness of the Fe2AlSi2 phase, but as an example, the average maximum thickness of the Fe2AlSi2 phase may be 10.0 μm or less.

[0109] According to one example of the present invention, the Fe2AlSi2 phase may have a maximum spacing between adjacent Fe2AlSi2 phases of 4.5 μm or less when viewed in a cross-section cut through the alloy plating layer. In this case, the maximum spacing between adjacent Fe2AlSi2 phases means the largest value among the minimum values ​​of the straight-line distance between each adjacent Fe2AlSi2 phase existing within the observation area. In this way, one embodiment of the present invention can prevent the problem of hydrogen passing between adjacent Fe2AlSi2 phases by controlling the maximum spacing between adjacent Fe2AlSi2 phases. More preferably, it may be 4.3 μm or less.

[0110] Meanwhile, as a non-limiting example, the alloy plating layer may include, in weight %, Si: 1.0 to 15%, Ni: 0.00100 to 1.00%, the remainder Al, and other unavoidable impurities, when the remaining alloy composition excluding the Fe content diffused from the base steel sheet is 100%.

[0111] Accordingly, the Fe2AlSi2 phase may include, by weight %, Fe: 25.0 to 60.0%, Si: 10.0 to 20.0%, Nimax: 0.300 to 5.00%, and the remainder may be composed of Al and unavoidable impurities. In this way, a hot-formed member including the Fe2AlSi2 phase in the alloy plating layer can improve hydrogen embrittlement of steel by reducing the amount of diffusible hydrogen after HPF heat treatment, as described above. More specifically, according to a non-limiting embodiment, the amount of diffusible hydrogen in the alloy plating layer may be 0.2 ppm or less, and the hydrogen diffusion coefficient D eff,coating The value is 2.5x10 -7 cm 2 s -1 It may be as follows. At this time, the hydrogen diffusion coefficient D of the alloy plating layer eff,coating The value can be derived by the following equations 2 and 3.

[0112] (Formula 2)

[0113] (D in the above equation 2 eff is the hydrogen diffusion coefficient of the hot-formed member, L is the thickness of the hot-formed member, t b represents the start time (in seconds) at which hydrogen begins to permeate the hot-formed member during the hydrogen permeation test.

[0114] (Formula 3)

[0115] (D in the above equation 3 eff is the hydrogen diffusion coefficient of the hot-formed member, L is the thickness of the hot-formed member, L sheet is the thickness of the above-mentioned steel, L Coating is the thickness of the above alloy plating layer, D eff,sheet represents the hydrogen diffusion coefficient of the above-mentioned iron.)

[0116] Hydrogen diffusion coefficient D eff can be measured according to a hydrogen permeation test. Specifically, the thickness and hydrogen permeability can be measured for the hot-formed member including the alloy plating layer, and the base steel from which the alloy plating layer has been removed by surface polishing, etc. Then, by applying the measured values ​​to the above equations, the hydrogen diffusion coefficient D of the alloy plating layer eff,coating can be obtained.

[0117] In this way, the hot-formed member according to the present invention can delay the diffusion of hydrogen within the alloy plating layer after HPF heat treatment, thereby ensuring excellent hydrogen embrittlement resistance. Accordingly, the hot-formed member according to the present invention can prevent fracture of the steel sheet due to hydrogen embrittlement after hot press forming.

[0118] Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are intended only to illustrate and further illustrate the present invention and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters set forth in the patent claims and matters reasonably inferred therefrom.

[0119] (Example)

[0120] First, 22MnB5 steel plates with the composition range of Table 1 were prepared and cold rolled. After that, 300 g / m of the cold rolled steel plates were 2 Ni flash electroplating was performed with a plating amount of . Then, continuous annealing was performed at a target temperature of 750℃ to 820℃. Thereafter, the steel sheet was immersed in an aluminum plating bath containing 9.5 wt% of Si and the remainder containing Al and inevitable impurities, and during the process, the plating amount was controlled using an air knife under the conditions of Table 2. Then, the steel sheet was cooled to obtain a plated steel sheet. The average thickness of the Fe2Al8Si phase of the obtained hot-forming plated steel sheet was measured and is shown in Table 2 below. At this time, the average thickness of the Fe2Al8Si phase was derived by observing the specimen through SEM photography, measuring the thickness at 10 points at intervals of 1 μm in the vertical direction of the thickness, and then calculating the average value thereof.

[0121] Alloy composition (weight %)CMnSiPSAlNCrB22MnB50.221.250.250.0100.00300.0300.0060.200.0025

[0122] Separation line speed (mpm) Air knife (A / K) K value Fe2Al8Si phase A / K gap (mm) A / K pressure (kPa) A / K height (mm) Thickness (μm) Invention example 1758139002.297.8 Invention example 2757148003.175.1 Comparative example 1756.5157004.182.6 Invention example 3907.5128002.118.6 Invention example 4906.5146003.793.6 Comparative example 2906156004.401.9 Invention example 51008127002.048.7 Invention example 61006.5137002.715.9 Invention example 71006156003.963.2 Comparative Example 31005.5156004.322.0 Invention Example 81156.5116002.338.2 Invention Example 91156147002.755.5 Invention Example 101155.5136003.254.3 Comparative Example 41155156004.132.4

[0123] After that, the manufactured hot-forming plated steel sheet was heated at 900℃ for 6 minutes, and then the heated steel sheet was hot-formed into a desired shape using a press to manufacture a hot-formed member. The alloy plating layer of the manufactured hot-formed member was composed of Si: 9.0%, Ni: 0.17%, and the remainder Al and other unavoidable impurities, as calculated by the GDS profile, when the remaining alloy composition excluding the Fe content diffused from the base steel sheet is 100%. Thereafter, the area fraction of the Fe2AlSi2 phase relative to the total area fraction of the alloy plating layer of the manufactured hot-formed member, the average maximum thickness of the Fe2AlSi2 phase, and the maximum value of the spacing between adjacent phases, D eff,coating And the amount of diffusion hydrogen was measured and shown in Table 3 below.

[0124] More specifically, the area fraction of the Fe2AlSi2 phase in the alloy plating layer was measured by distinguishing the Fe2AlSi2 phase through SEM observation and analyzing the SEM image. At this time, the magnification was 1000 times. In addition, the average maximum thickness of the Fe2AlSi2 phase and the maximum spacing between adjacent phases were also measured for the Fe2AlSi2 phase observed through SEM observation. The maximum thickness of the Fe2AlSi2 phase and the maximum spacing between adjacent phases were each measured 5 times, and the averages are shown in Table 3 below.

[0125] And, a hydrogen permeation test was performed on the manufactured hot-formed parts to determine the start time (t) at which hydrogen permeation begins. b ) is measured, and the thickness (L) of the hot-formed member is measured and substituted into Equation 2 below to obtain D eff Then, the alloy plating layer was removed from the hot-formed member through surface polishing, etc., and the same procedure as for the hot-formed member was performed on the base steel to produce D. eff,sheet Value and L sheet The values ​​were measured. In this way, by substituting the measured values ​​into Equation 3 below, D eff,coating The values ​​were calculated and shown in Table 3.

[0126] (Formula 2)

[0127] (D in the above equation 2 eff is the hydrogen diffusion coefficient of the entire specimen including the alloy plating layer, L is the thickness of the entire specimen, t b represents the start time (in seconds) at which hydrogen begins to permeate during the hydrogen permeation test.

[0128] (Formula 3)

[0129] (D in the above equation 3 eff is the hydrogen diffusion coefficient of the entire specimen including the alloy plating layer, L is the thickness of the entire specimen, L sheet is the thickness of the steel sheet, L CoatingThickness of silver alloy plating layer, D eff,sheet represents the hydrogen diffusion coefficient of the iron.)

[0130] Finally, the manufactured hot-formed part was immersed in liquid nitrogen for 12 hours, then heated at a rate of +5 / °C to the target temperature of 300°C and maintained for 30 minutes to perform TDA analysis, thereby detecting the amount of diffused hydrogen. The TDA analysis was performed using equipment from Bruker, Germany.

[0131] Classification Fe2AlSi2 phase D eff,coating (x10 -7 cm 2 s -1 ) Amount of diffusion hydrogen (ppm) Area fraction (area %) Maximum thickness average (μm) Maximum spacing between adjacent phases (μm) Invention example 110.86.30 2.01 0.09 Invention example 27.34.13.12.38 0.17 Comparative example 13.11.9 7.12.65 0.30 Invention example 311.16.40 1.77 0.08 Invention example 45.93.33.72.3 10.16 Comparative example 21.5 1.08.72.78 0.35 Invention example 511.36.90 1.58 0.11 Invention example 68.65.02.62.13 0.15 Invention example 75.12.74.32.48 0.19 Comparative example 30.90.410.92.800.31 Invention example 810.56.201.900.14 Invention example 98.74.92.42.050.16 Invention example 107.04.03.32.410.18 Comparative example 42.61.67.82.600.28

[0132] Looking at Table 2 above, the hot-forming galvanized steel sheets of Comparative Examples 1 to 4 had K values ​​derived by Equation 1 presented in the present invention exceeding the range presented in the present invention, and thus the Al-based plating layer was excessively cooled, and thus the Fe2Al8Si phase containing Ni was not sufficiently diffused.

[0133] In addition, looking at Table 3, it can be confirmed that the hot-formed parts of Comparative Examples 1 to 4, in which the Fe2Al8Si phase was not sufficiently diffused as described above, did not properly form the Fe2AlSi2 phase on the intermediate layer. Accordingly, the Fe2AlSi2 phase did not effectively function as a barrier for the diffusible hydrogen of the alloy plating layer, and the hydrogen diffusion coefficient was 2.5x10 -7 cm 2 s -1 In addition, the amount of diffusible hydrogen exceeded 0.2 ppm after heat treatment, causing hydrogen embrittlement.

[0134] On the other hand, it can be confirmed that invention examples 1 to 3, which satisfy all the conditions proposed in the present invention, have excellent hydrogen embrittlement resistance.

[0135] Figure 1 shows an SEM image photograph of a plating layer formed on a hot-forming plating steel sheet corresponding to Invention Example 6, and at this time, the composition ratio of the Fe2Al8Si phase formed on the plating layer formed on the hot-forming plating steel sheet was, in wt%, Fe: 19%, Si: 11%, and Nimax: 0.42%.

[0136] Figure 2 shows an SEM image photograph of a plating layer formed on a hot-formed member corresponding to Invention Example 6. At this time, the composition ratio of the Fe2AlSi2 phase formed on the plating layer formed on the hot-formed member was Fe: 45.97%, Si: 13.33%, and Nimax: 0.34% in wt%.

Claims

1. Steel plate; and Including an Al-based plating layer formed on the surface of the above steel plate, The above Al-based plating layer includes a Fe2Al8Si phase, The above Fe2Al8Si phase contains, in wt%, Fe: 15.0 to 25.0%, Si: 5.00 to 15.0%, and Nimax: 0.400 to 5.00%. The above Fe2Al8Si phase is a hot-forming plated steel sheet composed of residual Al and inevitable impurities having an average thickness of 3.0 μm or more in the thickness direction of the Al-based plating layer.

2. In paragraph 1, A hot-forming galvanized steel sheet, wherein the Al-based plating layer contains Si at 5.0 to 10% by weight, when the remaining alloy composition excluding Fe diffused from the base steel sheet is 100%, and the remainder is Al and other unavoidable impurities.

3. In paragraph 1, The above steel plate contains, in wt%, C: 0.060 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.00100 to 0.0300%, S: 0.000100 to 0.0200%, Al: 0.0100 to 0.100%, Cr: 0.0100 to 1.00%, N: 0.001000 to 0.02000%, Ti: 0 to 0.100%, B: 0 to 0.01000%, Cu: 0 to 1.00%, Mo: 0 to 1.00%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, V: 0 to 1.00%, Ca: 0 to A hot-forming galvanized steel sheet comprising: 0.0100%, Nb: 0 to 0.100%, Sn: 0 to 1.00%, W: 0 to 1.00%, Sb: 0 to 1.00%, Mg: 0 to 0.100%, Co: 0 to 1.00%, As: 0 to 1.00%, Zr: 0 to 1.00%, Bi: 0 to 1.00% and REM: 0 to 0.300%, the remainder being Fe and unavoidable impurities.

4. In paragraph 1, A hot-forming galvanized steel sheet additionally comprising a Ni flash electroplating layer between the above-mentioned steel sheet and the Al-based galvanized layer.

5. Step for preparing the steel plate; A step of obtaining an electroplated steel sheet by performing Ni flash electroplating on the above-mentioned steel sheet; A step of continuously annealing the above electroplated steel sheet; A step of immersing the continuously annealed electroplated steel sheet in an aluminum plating bath; A step of controlling the plating adhesion amount of the electroplated steel sheet immersed in an aluminum plating bath using an air knife (A / K); and A step of cooling the electroplated steel sheet to obtain a plated steel sheet; A method for manufacturing a hot-forming galvanized steel sheet having a K value of 2 or more and 4 or less, derived by the following equation 1. (Formula 1) K = 10 4 ×(a×d) / (b×c×e) (In the above Equation 1, a represents the Si content (weight %) of the aluminum plating bath, b represents the line speed (mpm), c represents the air knife spacing (mm), d represents the air knife pressure (kPa), and e represents the air knife height (mm).) 6. In paragraph 5, The above Ni flash electroplating is 150mg / m 2 More than 2500mg / m 2 A method for manufacturing a hot-forming galvanized steel sheet with the following galvanized coating amount.

7. In paragraph 5, The above steel plate contains, in wt%, C: 0.060 to 0.50%, Si: 0.050 to 1.0%, Mn: 0.50 to 4.0%, P: 0.00100 to 0.0300%, S: 0.000100 to 0.0200%, Al: 0.0100 to 0.100%, Cr: 0.0100 to 1.00%, N: 0.001000 to 0.02000%, Ti: 0 to 0.100%, B: 0 to 0.01000%, Cu: 0 to 1.00%, Mo: 0 to 1.00%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, V: 0 to 1.00%, Ca: 0 to A method for manufacturing a hot-formable plated steel sheet, comprising: 0.01%, Nb: 0 to 0.10%, Sn: 0 to 1.00%, W: 0 to 1.00%, Sb: 0 to 1.00%, Mg: 0 to 0.100%, Co: 0 to 1.00%, As: 0 to 1.00%, Zr: 0 to 1.00%, Bi: 0 to 1.00%, and REM: 0 to 0.300%, the remainder being Fe and unavoidable impurities.

8. In paragraph 5, A method for manufacturing a hot-forming galvanized steel sheet, wherein the above aluminum plating bath contains 5.0 to 10 wt% of Si, the remainder being Al and other unavoidable impurities.

9. So Ji-cheol; and Including an alloy plating layer formed on the above-mentioned steel, The above alloy plating layer includes a Fe2AlSi2 phase, The above Fe2AlSi2 phase contains, in weight %, Fe: 25.0 to 60.0%, Si: 10.0 to 20.0%, Nimax: 0.300 to 5.00%, and the remainder is Al and inevitable impurities. A hot-formed member in which the Fe2AlSi2 phase is at least 5 area% of the total area of ​​the alloy plating layer.

10. In paragraph 9, A hot-formed member comprising the alloy plating layer, in wt%, of Si: 1.0 to 15%, Ni: 0.00100 to 1.00%, and the remainder Al and other unavoidable impurities, when the remaining alloy composition excluding the Fe content diffused from the base steel sheet is 100%.

11. In paragraph 9, A hot-formed member in which the above Fe2AlSi2 phase is formed as a distinct layer in the middle of an alloy plating layer.

12. In paragraph 9, A hot-formed member having an average maximum thickness of the Fe2AlSi2 phase of 2.0 μm or more in the direction of the alloy plating layer thickness.

13. In paragraph 9, The above Fe2AlSi2 phase is a hot-formed member in which the maximum gap between adjacent Fe2AlSi2 phases is 4.5 μm or less when viewed in a cross-section cut through the alloy plating layer.

14. In paragraph 9, Hydrogen diffusion coefficient D of the alloy plating layer derived by the following equations 2 and 3 eff,coating The value is 2.5x10 -7 cm 2 s -1 The following hot-formed parts: (Formula 2) (D in the above formula 2 eff is the hydrogen diffusion coefficient of the hot-formed member, L is the thickness of the hot-formed member, t b represents the start time (in seconds) at which hydrogen begins to permeate through the hot-formed member during the hydrogen permeation test. (Formula 3) (D in the above formula 3 eff is the hydrogen diffusion coefficient of the hot-formed member, L is the thickness of the hot-formed member, L sheet is the thickness of the above-mentioned steel, L Coating is the thickness of the alloy plating layer, D eff,sheet represents the hydrogen diffusion coefficient of the above-mentioned iron.) 15. In paragraph 9, Hot-formed parts having a diffusible hydrogen content of 0.2 ppm or less.

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