Plated steel sheet for hot forming having excellent hydrogen embrittlement resistance, and method for manufacturing hot formed member

Abstract

[Disclosure] [Technical Problem] An aspect of the present disclosure may provide a plated steel sheet for hot forming capable of reducing occurrence of delayed fracture due to hydrogen embrittlement of a hot formed member and having excellent hydrogen embrittlement resistance, a hot formed member manufactured using the same, and a method for manufacturing the same.SOLUTION: And an Al-based plated layer formed on a surface of the base steel sheet, wherein an average content of Ni in the Al-based plated layer is 0.05 to 0.35 wt%. According to another aspect of the present disclosure, a hot press-formed member having excellent hydrogen embrittlement resistance may include a base iron; and an alloy plating layer formed on the base iron, wherein a Ni content at a point (Nimax) having a highest Ni content from a surface of the alloy plating layer to 15 μm in a depth direction is 0.1 to 0.75 wt%.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a hot press forming method for use as an automobile body part, etc. Coated steel sheets for hot forming (heat forming, HPF) and hot formed components, and methods for manufacturing these That is why. [Background technology]

[0002] Recently, hot-formed parts have been used in automobiles for the purpose of improving fuel efficiency by reducing the weight of automobiles and protecting passengers. It is widely used in structural components such as steel sheets, etc., where ultra-high strength or energy absorption capacity is particularly required. It is widely used for bumpers, doors, filler reinforcement, etc. where hot forming is required. When using shaped components, plated steel sheets are often used to ensure corrosion resistance. I am using it.

[0003] A representative example of such hot forming technology is disclosed in Patent Document 1. After heating Al-Si plated steel sheet to 850℃ or more, it is hot formed by pressing and then rapidly cooled. The structure of the member is formed as martensite, and ultra-high strength can be ensured. When using such hot forming technology to ensure ultra-high strength, complex shapes are formed at high temperatures. It can also be easily molded. In addition, the strength is increased by rapid cooling inside the mold, resulting in high strength. At the same time, weight reduction effects can be expected.

[0004] However, the martensite structure is known to have low resistance to hydrogen embrittlement. In particular, parts manufactured after hot forming have residual stress due to rapid cooling after heating, If the amount of diffusible hydrogen in steel increases, delayed fracture due to hydrogen embrittlement may occur. Therefore, there is a drawback in that the application is limited. This is the reality that is required. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 6,296,805 Summary of the Invention [Problem to be solved by the invention]

[0006] One aspect of the present invention is to reduce the occurrence of delayed fracture due to hydrogen embrittlement in hot-formed members. and a hot-formed member manufactured using the hot-formed plated steel sheet, which has excellent resistance to hydrogen embrittlement. It also relates to methods for producing them.

[0007] The object of the present invention is not limited to the above. Those skilled in the art will be able to understand the further object of the present invention from the overall contents of the specification of the present invention. There is no difficulty in understanding it. [Means for solving the problem]

[0008] One aspect of the present invention is a base steel sheet; and an Al-based plating layer formed on the surface of the base steel sheet, The average Ni content in the Al-based plating layer is 0.05 to 0.35 wt %. The present invention relates to a plated steel sheet for hot forming having excellent heat resistance.

[0009] Another aspect of the present invention is a method for manufacturing a steel sheet, comprising the steps of: preparing a base steel sheet; The above prepared base steel sheet is coated with a coating weight of 150 to 2500 mg / m 2 Ni plating with stage; and continuous annealing the Ni-plated cold-rolled steel sheet and plating it with an Al-based coating; The present invention relates to a method for producing a plated steel sheet for hot forming that is excellent in hydrogen embrittlement resistance.

[0010] Another aspect of the present invention is a steel sheet comprising: An alloy plating layer formed on the base steel, From the surface of the alloy plating layer to a depth of 15 μm, the point with the highest Ni content (N Hot-formed alloys with excellent resistance to hydrogen embrittlement, containing 0.1 to 0.75 wt% Ni at imax. It concerns components.

[0011] Another aspect of the present invention is a steel sheet and an Al-based plating formed on the surface of the steel sheet. The average Ni content in the Al-based plating layer is 0.05 to 0.35 wt %. providing a blank; Heating the blank at a temperature in the range of Ac3 to 975°C; and The heated blank is transferred to a press, molded, and cooled at a cooling rate of 20°C / s or more. the stage of doing; The present invention relates to a method for producing a hot-formed member having excellent hydrogen embrittlement resistance, comprising: [Effects of the Invention]

[0012] When the plated steel sheet for hot forming of the present invention is hot formed, the amount of diffusible hydrogen in the steel is reduced. As a result, it is possible to provide a hot-formed part having excellent resistance to hydrogen embrittlement.

[0013] The various yet significant advantages and effects of the present invention are not limited to those described above. In the course of describing specific embodiments of the invention, it will be easier to understand. [Brief explanation of the drawings]

[0014] [Figure 1]1 is a graph showing the results of analyzing the Fe and Ni contents of the Al-based coating layer of the coated steel sheet for hot forming of Example 1 in the Examples by glow discharge spectroscopy (GDS). [Figure 2] 1 is a graph showing the results of GDS analysis of the Ni content in the alloy plating layer of the hot-formed member of Example 3 among the Examples, and is a diagram showing the Ni-enriched layer. [Figure 3] 1 is a graph showing the results of GDS analysis of the Ni content in the alloy plating layer of the hot-formed members of Examples 1 to 3 and Comparative Example 2 among the working examples. [Figure 4] 1 is a graph showing the results of measuring the Ni content at the Nimax point and the diffusible hydrogen content of each hot-formed member of Examples 1 to 8 and Comparative Examples 1 and 2 among the working examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] The terms used herein are for the purpose of describing the invention and are not intended to limit the invention. Also, the singular forms used herein are not intended to be used unless the relevant definition clearly indicates otherwise. Plural forms are included unless a contrary meaning is expressed.

[0016] The meaning of "comprise" as used in the specification is to embody a structure and not to include the presence or addition of other structures. It is not something to be excluded.

[0017] Unless otherwise defined, all terms used herein, including technical and scientific terms, The meanings are the same as those generally understood by a person having ordinary skill in the technical field to which the present invention pertains. Dictionary-defined terms have the same meaning as those in the relevant technical literature and the present disclosure. The terms "agreement" and "contract" are interpreted to mean the following:

[0018] The inventors of the present invention have conducted extensive research into hydrogen embrittlement of hot-formed components and have found that A blank (manufactured from a plated steel sheet for hot forming) with a plated layer of aluminum or the like is added to the During the heating stage, it was confirmed that the water vapor present in the heat treatment furnace was adsorbed on the blank surface. Next, the hydrogen generated by dissociating water dissociates into austenite, which has high hydrogen solubility at high temperatures. It is absorbed in the steel with a phase.

[0019] However, when rapid cooling occurs during hot forming and the material changes to martensite, the solubility of hydrogen decreases. The alloy plating layer formed during alloying of the plating layer is difficult to release hydrogen. Therefore, a considerable amount of Diffusible hydrogen content remains in the steel, which increases the possibility of crack formation due to hydrogen delayed fracture. Therefore, it is important to reduce the amount of diffusible hydrogen absorbed during heat treatment. I understand.

[0020] The inventors have investigated the amount of diffusible hydrogen in steel that affects hydrogen embrittlement in hot forming steel. While conducting an analysis of the effect of Ni plating, it was found that the amount of diffusible hydrogen can be reduced. This has led to the present invention.

[0021] The present invention will be described in detail below.

[0022] The plated steel sheet for hot forming, which is one aspect of the present invention, comprises a base steel sheet, a The Al-based plating layer has an Ni content of 0.05 wt % or more. It is preferable that

[0023] The Al-based coating layer, excluding the Ni, is the same as the coated steel sheet for hot forming to which the present invention pertains. It is widely used in hot forming galvanized steel sheets by ordinary skilled artisans in the field of Any Al-based plating that can be used is sufficient, and there are no particular restrictions on the content or type of the components. This includes not only pure Al plating, but also plating that contains some Si in Al. This can be done.

[0024] The Al-based plating layer may include an Al-rich layer and a concentration gradient layer. The above concentration gradient layer is formed during the process of applying Al-based plating to the base steel sheet. This is the section formed by the mutual reaction of the Al plating bath components, containing Fe. It is not easy to clearly distinguish the boundary between the Al-rich layer and the concentration gradient layer. The content of Fe in the Al-rich layer is less than the content of Fe in the concentration gradient layer. For example, when the Fe content in the Al-based plating layer is about 2% by weight or more, It is sometimes understood that the content of Fe diffused in the base steel sheet is higher than that of the coating components. , which can be considered as the boundary between the Al-rich layer and the concentration gradient layer, and the above concentration gradient layer and the base steel sheet The boundary can be considered to be up to the point where the Fe content is about 80 wt %, but it is not necessarily It is not necessarily a clear distinction like this.

[0025] As an example, referring to FIG. 1, a plated steel sheet for hot forming according to Example 1 of the following Examples is shown. Glow Discharge Optical Spectroscopy (Glow Discharge Optical As a result of the analysis using GDS (Geometry for Emission Spectrometry), As a result, the Al-based plating layer is composed of an Al-rich layer and a concentrated layer containing up to 80% by weight of Fe. This can be understood to include a gradient layer.

[0026] In the above-mentioned plated steel sheet for hot forming, the above-mentioned Al-based plating layer has an average Ni content of 0. As shown in FIG. 1, the Al-based plating layer preferably contains 0.5 wt. % or more of the aluminum. It is preferable that the Ni contained in the film is distributed in the depth direction. The Ni content is not constant from the surface of the plated steel sheet to the depth of the plated layer. The content means the average of the results of an analysis in the depth direction of the Al-based plating layer from the surface. As a preferred example of measuring the average of the graph in the GDS analysis Ni profile shown in Figure 1, The Ni contained in the Al-based plating layer can be calculated as an average value, as will be described later. In addition, a Ni-enriched layer is formed in the alloy plating layer formed during the hot forming process. The Ni-enriched layer formed on the substrate is exposed to external hydrogen that may be absorbed during the heat treatment process for hot forming. It prevents hydrogen from penetrating into the steel plate, improving the hydrogen embrittlement resistance of hot-formed components. It plays a role that can be fulfilled.

[0027] If the Ni content is less than 0.05 wt%, a sufficient Ni-enriched layer is not formed during hot forming. This makes it difficult to effectively prevent external hydrogen from being absorbed during the hot forming heat treatment. The higher the Ni content, the greater the effect of preventing external hydrogen. If it exceeds 0.35 wt%, the cost increases due to the increase in Ni coating weight and unevenness in the width direction. Since the Ni content increases, it is difficult to manufacture uniform steel sheets. It is preferred that the content not exceed 0.35% by weight. A more preferred range is 0.055 to 0.335%. Percent by weight.

[0028] In the present invention, the type of the base steel sheet and the alloy composition are not particularly limited. As a preferred example, the present invention The above-mentioned base steel sheet contains, by weight, carbon (C): 0.07 to 0.5%, silicon (Si) : 0.05-1%, Manganese (Mn): 0.5-4%, Phosphorus (P): 0.001-0.0 15%, Sulfur (S): 0.0001-0.02%, Aluminum (Al): 0.01-0 0.1%, Chromium (Cr): 0.01-1%, Nitrogen (N): 0.001-0.02%, Rest Contains iron (Fe) and unavoidable impurities. Titanium (Ti): 0.1% or less (including 0) Boron (B): 0.01% or less (including 0) can be contained. A brief explanation of minutes will be given below.

[0029] Carbon (C): 0.07~0.5% by weight (hereinafter referred to as %) The above-mentioned C is an element that improves the strength and hardening ability of hot-formed parts, and is used for strength adjustment. It is necessary to include it appropriately as an essential element. If the C content is less than 0.07%, the hardening ability will be impaired. When the cooling rate is reduced, sufficient martensite cannot be secured and ferrite Since it is difficult to secure the desired strength in the production, it is preferable to include 0.07% or more, and 0 If it exceeds 0.5%, the strength increases excessively, causing embrittlement and reducing weldability. Therefore, it is preferable not to exceed 0.5%.

[0030] Silicon (Si): 0.05 to 1% The above-mentioned Si is not only necessary to be added as a deoxidizer in steelmaking, but also as a solid solution strengthening element. It is an element that suppresses the formation of carbides and is effective in making the internal structure uniform. It contributes to increasing the strength of the material and is an effective element for homogenizing the material. However, when the content is 0.05%, If the content is less than 1%, the above effect cannot be expected, and if it exceeds 1%, the surface of the steel sheet may deteriorate during annealing. The excessive silicon oxide generated in the film significantly reduces plating properties, so the film should be kept at 1% or less. It is preferable that

[0031] Manganese (Mn): 0.5-4% The above Mn not only ensures the desired strength through its solid solution strengthening effect, but also It is an element necessary for suppressing ferrite formation during hot forming through improving mechanical properties. If the Mn content is less than 0.5%, it is difficult to obtain a sufficient hardening effect, and insufficient hardening occurs. The problem is that excessive use of other expensive alloy elements for performance increases the manufacturing cost. On the other hand, if the Mn content exceeds 4%, the Mn atoms arranged in the rolling direction in the microstructure The band tissue deepens, causing heterogeneity in the internal tissue. Therefore, it is preferable that the value is 4% or less.

[0032] Phosphorus (P): 0.001 to 0.015% The above P exists as an impurity in steel, and its minimum content must be less than 0.001%. is undesirable because it requires a lot of manufacturing cost, and the maximum content should not exceed 0.015%. This will result in a deterioration in the weldability of the hot-formed components and in the material properties due to high-temperature grain boundary segregation. It is preferable not to exceed 15%.

[0033] Sulfur (S): 0.0001 to 0.02% The above S is an element that acts as an impurity and inhibits the ductility, impact properties and weldability of components. The maximum content is preferably 0.02%. The minimum content is less than 0.0001%. However, in order to achieve this, the manufacturing cost increases significantly, which is not preferable.

[0034] Aluminum (Al): 0.01 to 0.1% The above-mentioned Al is an element that acts as a deoxidizer together with Si during steelmaking to increase the cleanliness of steel. If the content is less than 0.01%, it is difficult to obtain this effect, and if it exceeds 0.1%, In this case, excessive AlN precipitates formed during the continuous casting process reduce the high temperature ductility. The upper limit is 0.1% because cracks in the rubbed area may occur, causing manufacturing problems. It is preferable that:

[0035] Chromium (Cr): 0.01 to 1% Cr, like Mn, ensures the hardening ability of steel and suppresses the formation of ferrite after hot forming. If the Cr content is less than 0.01%, the above effect cannot be achieved. It is difficult to ensure this, and if it exceeds 1%, the effect of improving hardening ability relative to the amount added is small. In addition, excessive formation of coarse iron carbides may cause cracks when stress is applied. Therefore, it is preferable not to exceed 1% as this will cause deterioration of the material.

[0036] Nitrogen (N): 0.001-0.02% The above N is contained in steel as an impurity. In order to keep the above N content below 0.001%, It involves excessive manufacturing costs, and when its content exceeds 0.02%, it is as Since cracks in the slab due to AlN formation are likely to occur, the content should not exceed 0.02%. It is preferable.

[0037] Titanium (Ti): 0.1% or less (including 0) The above Ti combines with nitrogen remaining as an impurity in the steel to form TiN, which improves hardness. It is possible to protect B, which is used to ensure chemical activity, from becoming a compound. Ti may also be included. In addition, TiC precipitates are formed to strengthen the precipitation and grain size. However, if the content exceeds 0.1%, the coarse T Since a large amount of NiO is formed and deteriorates the quality of the steel, the upper limit should not exceed 0.1%. It is preferable that:

[0038] Boron (B): 0.01% or less (including 0) The above-mentioned B is an element that can effectively improve hardenability, and The segregation of impurities P and / or S at grain boundaries increases the brittleness of hot-formed components. However, if the above B is more than 0.01%, If exceeded, Fe 23 The formation of CB6 complex compounds can cause embrittlement during hot rolling. Therefore, the upper limit is preferably 0.01%.

[0039] The remainder consists of iron (Fe) and unavoidable impurities. Unavoidable impurities are intentionally generated during the normal steel manufacturing process. It is not possible to completely eliminate these substances, and they may be mixed in without being removed. Any engineer in the field of steel manufacturing can easily understand the meaning of this. However, this does not mean that addition of other compositions than the above-mentioned steel compositions is completely excluded.

[0040] Next, a method for producing a plated steel sheet for hot forming, which is another embodiment of the present invention, will be described in detail. The manufacturing method to be described is a preferred example of manufacturing the above-mentioned plated steel sheet for hot forming. However, it does not necessarily have to be manufactured in this manner.

[0041] The manufacturing method includes the steps of preparing a base steel sheet; plating a surface of the prepared base steel sheet with Ni; and a step of continuously annealing the Ni-plated base steel sheet and then plating it with an Al-based coating. Includes.

[0042] The base steel sheet is as described above, and the process of preparing the base steel sheet is carried out by using the steel composition described above. After heating the steel slab that satisfies the above, it is hot rolled, coiled, and cold rolled to obtain the steel.

[0043] A steel slab satisfying the above-mentioned composition is heated to 1050 to 1300°C and then hot-rolled. If the heating temperature is less than 1050°C, the steel slab structure will not be homogenized sufficiently, and the precipitation origin will When using elements, it is difficult to redissolve them, and if the temperature exceeds 1300°C, an excessive oxide layer will form. This increases the manufacturing cost for removing the oxide layer, and surface defects occur after hot rolling. This increases the likelihood of

[0044] The finish rolling temperature of the hot rolling is preferably in the range of 800 to 950°C. If the above finish rolling temperature is less than 800°C, rolling in the two-phase region progresses, and ferrite forms in the surface layer of the steel sheet. On the other hand, when the temperature exceeds 950℃, the grain size of the hot rolled steel is increased. Coarsening of the grains may occur.

[0045] After hot rolling, coiling is carried out at a temperature in the range of 500 to 700°C. If the temperature is lower than 100°C, martensite will be formed in the whole or part of the steel sheet, making it difficult to control the coil shape. Not only is it difficult to control, but the excessive increase in strength of the hot-rolled steel sheet reduces the subsequent cold rolling properties. On the other hand, if the temperature exceeds 700°C, excessive coarse carbides are formed. , cracks are generated when stress occurs in hot-formed parts, resulting in a decrease in crashworthiness. There is a risk.

[0046] After this, a cold rolling process is carried out. However, before the cold rolling, the steel is subjected to an acid treatment to remove surface oxides. If necessary, the steel sheet can be plated without cold rolling. It can be used as a base steel sheet for hot forming.

[0047] The cold rolling reduction rate during the cold rolling is 30 It is preferable to carry out the rolling reduction at a rate of up to 80%.

[0048] The surface of the base steel sheet prepared as described above is plated with Ni. Ni flash plating can be applied before annealing. It is one of the electroplating methods used in the electroplating process, and the amount of current during electroplating is The Ni plating is carried out by adjusting the temperature and humidity. 500 mg / m 2 It is preferable to apply the coating amount of 100%.

[0049] The Ni plating coating weight in the above Ni plating is 150 to 2500 mg / m 2 That's it It is preferable that the Ni plating coating weight is 150 mg / m 2 If it is less than 10 ... Therefore, the effect of the present invention cannot be fully achieved because Ni cannot be concentrated in the plating layer by heat treatment for this purpose. 500 mg / m 2 If the value exceeds this, excessive current concentration during electroplating may cause damage to the steel sheet interior. Not only does this cause localized non-plating, but it also causes excessive use of the electroplating solution for Ni application. The cost of production increases excessively due to the use of 2500 mg / m 2 You can do the following: On the other hand, a more preferable Ni plating coverage is 200 to 2000 mg / m 2 is preferred stomach.

[0050] The Ni-plated base steel sheet is then continuously annealed and coated with Al. Annealing temperature The annealing temperature is preferably 740 to 860°C. When the annealing temperature is less than 740°C, The recrystallization of the cold-rolled structure is not completed sufficiently, resulting in poor sheet shape and poor finish after plating. The strength of the die may be too high, which may cause die wear during the blanking process. If the temperature exceeds 860°C, the formation of surface oxides during the annealing process will be promoted, resulting in the deterioration of the Al-based plating. In addition, the atmosphere during annealing heat treatment must be non-oxidizing. A reactive atmosphere is preferred, and a hydrogen-nitrogen mixed gas or the like can be used. The dew point of the atmospheric gas is preferably -75 to -20°C. In order to keep the dew point temperature below -75°C, additional equipment is required to control the dew point temperature. This raises the problem of increased manufacturing costs, and if the temperature exceeds -20°C, the steel being annealed Annealing oxides can form on the surface of the sheet, resulting in poor surface quality such as unplated surfaces.

[0051] After the annealing, an Al-based plating is applied. The present invention applies to any plating layer that is applied to a plated steel sheet for hot forming. can also be applied without restriction.

[0052] The Al-based plating is preferably carried out by immersion in an Al-based plating bath. The plating bath composition is silicon (Si): 6 to 12 wt % and iron (Fe): 1 to 4 wt % The remainder preferably contains aluminum (Al) and unavoidable impurities.

[0053] The coating weight for the above Al-based plating is 20 to 140 g / m per side 2 It is preferable to be The plating weight per side is 20g / m 2 If the temperature is less than 1000 K, the corrosion resistance of the hot-formed part will be poor. On the other hand, it is difficult to ensure the required strength. 2 If it exceeds this limit, the excess plating will be This not only increases the manufacturing cost, but also makes it difficult to evenly coat the plating layer across the entire width and length of the coil. It's not easy to do.

[0054] Next, a hot-formed member, which is another embodiment of the present invention, will be described in detail. The hot-formed member can be obtained by hot-forming the above-mentioned plated steel sheet for hot forming. can.

[0055] The hot-formed member includes a base steel and an alloy plating layer formed on the base steel, The Ni content of the alloy plating layer was measured from the surface to 15 μm, and it was found that The Ni content at the highest point (Nimax) is preferably 0.1 wt% or more. One example of a method for confirming Nimax is glow discharge spectroscopy. scharge Optical Emission Spectrometry, GD This can be confirmed by analyzing the graph obtained from the results of S). If the Ni content is less than 0.1 wt%, the Ni-enriched layer is not formed sufficiently, and the Ni-enriched layer is not formed sufficiently during hot forming. It is difficult to effectively prevent external hydrogen absorption, making it difficult to ensure hydrogen embrittlement resistance. The higher the Ni content in Nimax, the greater the effect of suppressing hydrogen absorption. However, if the content is excessive, there is a concern that the cost will increase due to the increase in Ni adhesion amount, and Since there is a risk of environmental problems occurring, it is preferable that the content does not exceed 0.75% by weight.

[0056] The alloy plating layer is formed by heating the Al-based plating layer during hot forming. In the present invention, the alloy plating layer is formed by the mutual reaction of the components, the base iron, etc. There are no particular restrictions on the layer.

[0057] On the other hand, it is preferable that the alloy plating layer contains a Ni-enriched layer. There are various methods for this purpose. As a preferred example, a method for forming a part on the surface of the alloy plating layer is Glow Discharge Optical Emission Spectroscopy (Glow Discharge Optical Emission Spectroscopy) Concentration profiles derived using GDS (Geographical Data Spectrometry) In the above concentration profile graph, the Ni content From the highest point (Nimax) to the surface of the above-mentioned material, the first point where the slope of the graph becomes 0 The point (Nio) and the Nimax in the depth direction of the component have the same content as the Nio. The width between the points (Nio') having the Ni enriched layer can be defined as the Ni enriched layer.

[0058] FIG. 2 shows the Ni content of the hot-formed part of Example 3 of the invention analyzed by GDS. The concentration profile graph is shown in Figure 2. From this, a Ni-enriched layer can be confirmed.

[0059] The thickness of the Ni-enriched layer is not particularly limited, and may vary depending on the heat treatment conditions during plating and hot forming. As a specific example, the thickness of the Ni-enriched layer is 1 to 15 μm. If the thickness of the Ni-enriched layer is less than 1 μm, sufficient hydrogen embrittlement resistance is not achieved. It is difficult to ensure the desired results, and if the thickness exceeds 15 μm, excessive Ni flash plating will occur. This may increase costs and cause environmental problems during welding.

[0060] The amount of diffusible hydrogen in the hot-formed part is preferably 0.3 ppm by weight or less. The amount of diffusible hydrogen in hot-formed parts was measured using the Thermal Desortion Analysis (TDA). The measurement can be performed using a thermolysis device. The temperature is increased at a rate of ℃ / s and the time is maintained so that the diffusible hydrogen peak appears sufficiently. The hydrogen diffusion curve is measured and the value obtained by integrating this curve is is.

[0061] The alloy composition of the base steel sheet for hot forming and the base steel for hot forming components differs. Although the difference is not large, it is preferable to distinguish between them because there may be differences in the microstructure. Therefore, in the present invention, the base steel sheet is also a plated steel sheet for hot forming. On the other hand, the base steel of hot-formed coated steel sheets is In the case of plates, the structure is ferrite and pearlite, but it is formed through hot forming. In the base steel of the hot-formed parts, martensite is formed as the main phase, and some of it is bainite. can be formed.

[0062] Hereinafter, a method for producing a hot-formed part according to another embodiment of the present invention will be described. For this purpose, the steel sheet includes a base steel sheet and an Al-based plating layer formed on the surface of the base steel sheet, Provide a blank with an average Ni content of 0.05 to 0.35 wt% in the l-based plating layer. As an example of providing the blank, the above-mentioned plated steel sheet for hot forming is used to form the blank. Ranks can be manufactured.

[0063] The blank provided above is heated to a temperature above the austenite single phase region, more specifically, Ac3 It is preferable to heat the film at a temperature in the range of 1000 to 975°C. The presence of untransformed ferrite in the two-phase region ensures strength and crash resistance. On the other hand, if the heating temperature exceeds 975°C, excessive oxides will form on the surface of the component. As a result, it becomes difficult to ensure spot weldability, and the manufacturing cost increases due to the need to maintain high temperatures. The blank thus heated is preferably maintained at the above temperature range for 1 to 1000 seconds. If the holding time is less than 1 second, it is difficult to achieve uniform temperature distribution over the entire blank, and the material temperature at different positions is low. If the time exceeds 1000 seconds, excessive oxide formation on the surface may cause quality deviation. This not only makes it difficult to ensure the proper spot weldability, but also increases the manufacturing costs of the components. The above Ar3 can be derived using the following formula: Ar3=902-255C+19Si-11Mn-5Cr[℃] (The above C, Si, Mn, and Cr refer to the content of each component.)

[0064] The heated blank is transferred to a press for forming and cooling. The cooling rate is preferably 20°C / s or more. During cooling, ferrite phases are introduced and formed at the grain boundaries, improving physical properties such as strength and impact resistance. The process of transferring, molding and cooling the blank is not particularly limited, and The techniques commonly used for hot forming can be applied as they are. [Example]

[0065] Examples of the present invention will be described in detail below. The following examples are provided for the purpose of understanding the present invention. It is not intended to interpret the scope of the present invention.

[0066] (Example) First, a steel slab satisfying the steel composition (unit: weight %) in Table 1 below was cut to a thickness of 60 mm. The remainder of the steel composition not listed in Table 1 was Fe and unavoidable The steel slab thus prepared was heated to 1200°C and maintained for 1 hour. The sheet was hot rolled, finished at a hot rolling temperature of 900°C, and coiled at a temperature of 600°C. After that, cold rolling was carried out to produce cold-rolled steel sheets with a thickness of 1.5 mm.

[0067] The cold-rolled steel sheet was subjected to Ni plating by Ni flash treatment. The amount of plating is shown in Table 1. The Ni flash treatment is performed by electroplating using Ni electrolyte. Specifically, the amount of current during electroplating was adjusted to control the deposition weight.

[0068] The Ni flash treated cold rolled steel sheet was annealed and mixed with 9% by weight of Si, 2% by weight of Fe, and the remaining The plating temperature is approximately 660°C using an Al-based plating bath containing Al and unavoidable impurities. Adhesion amount per side: 75g / m 2 The continuous annealing was carried out at a temperature of 800°C.

[0069] Average content of Ni distributed in the Al-based coating layer of the coated steel sheet manufactured as above The results are shown in Table 2. As mentioned above, the Al-based plating layer is composed of the plating layer and the concentration gradient layer ( The measurement was performed including the point where the Fe content in the Al-based coating layer was 80% by weight or less, and GDS Glow discharge spectroscopy (G) was performed using the 850A (model name, manufactured by LECO) DC and RF equipment. low discharge optical emission spectrum The analysis was carried out using data from the data collection system (try, GDS).

[0070] In addition, to check the adhesion of the Ni electroplating, the plated steel sheets were visually inspected. The long axis length of the part that had peeled off from the steel plate was measured and evaluated according to the following criteria. did. ○: The major axis length of the detached area is 3 mm or less ×: The longitudinal length of the detached area exceeds 3 mm

[0071] A blank was produced using the above-mentioned plated steel sheet, which was then heated to 900°C and maintained at that temperature for 6 minutes. Within 10 seconds, the material was transferred to a mold and cooled at a rate of 20-40°C / s. In the hot-formed member thus produced, the surface of the alloy plating layer was cooled at a cooling rate of 1000 kJ / cm. The Ni content at the point with the highest Ni content (Nimax) from the surface to 15 μm in the depth direction was The results of the GDS analysis are shown in Table 2. The amount of diffusible hydrogen in the components was also measured. are shown in Table 2.

[0072] [Table 1]

[0073] [Table 2]

[0074] On the other hand, FIG. 1 shows the Fe and Al-based coating layer of the coated steel sheet for hot forming of Example 1. 2 is a graph showing the results of GDS analysis of the content of Ni and the content of Inventive Examples 1 to 3 and Comparative Example 2. 1 is a graph showing the results of a GDS analysis of the Ni content in the alloy plating layer of the hot-formed member. 3 is the Ni in the alloy plating layer of the hot-formed members of the above-mentioned Examples 1 to 8 and Comparative Examples 1 and 2. 1 is a graph showing the maximum content and the amount of diffusible hydrogen.

[0075] As can be seen from the results of Table 2 and Figures 1 to 4 obtained in the above examples, The invention examples falling within the scope of the present invention are plated steel sheets with excellent coating adhesion, which are hot-formed. It is clear that the alloy has excellent resistance to hydrogen embrittlement.

[0076] However, the ratios in which Ni flash plating is omitted or performed in small amounts are outside the scope of the present invention. In Comparative Examples 1 and 2, sufficient Ni was not secured in the alloy plating layer after hot forming, and the Ni content was not sufficient as required by the present invention. It was found that it is difficult to ensure the required hydrogen embrittlement resistance.

[0077] On the other hand, in Comparative Examples 2 and 3, in which the amount of Ni flash plating was excessive, hydrogen embrittlement resistance was not ensured. However, due to the burning phenomenon inside the steel sheet during plating, unplated areas may occur. It was confirmed that the adhesion was poor.

Claims

1. Base steel sheet; and an Al-based plating layer formed on a surface of the base steel sheet, The average Ni content in the Al-based plating layer is 0.05 to 0.35 wt %. Hydrogen embrittlement resistance Highly corrosion-resistant hot forming plated steel sheet.

2. The base steel sheet contains, in weight percent, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5-4%, P: 0.001-0.015%, S: 0.0001-0.02%, Al: 0.01 to 0.1%, Cr: 0.01 to 1%, N: 0.001 to 0.02%, Ti:

0. 1% or less, B: 0.01% or less, and the remainder including Fe and inevitable impurities. The plated steel sheet for hot forming has excellent resistance to hydrogen embrittlement as described above.

3. 2. The water-resistant coating according to claim 1, wherein the Al-based plating layer includes an Al-rich layer and a concentration gradient layer. A hot-forming plated steel sheet with excellent resistance to brittleness.

4. preparing a base steel sheet; The prepared base steel sheet is coated with a coating weight of 150 to 2500 mg / m ２ Ni plating with stage; and The hydrogen-resistant steel sheet is subjected to continuous annealing and then to Al-based plating. A method for manufacturing plated steel sheets for hot forming that have excellent brittleness.

5. The step of preparing the base steel sheet includes: In weight percent, C: 0.07 to 0.5%, Si: 0.05 to 1%, Mn: 0.5 to 4%, P :0.001~0.015%, S:0.0001~0.02%, Al:0.01~0.1 %, Cr: 0.01-1%, N: 0.001-0.02%, Ti: 0.1% or less, B: 0 providing a steel slab containing not more than 0.01% of Cu, the remainder being Fe and unavoidable impurities; heating the steel slab to 1050-1300°C; The heated steel slab is finish hot-rolled in the temperature range of 800 to 950°C to produce a hot-rolled steel sheet. producing Coiling the hot-rolled steel sheet at a temperature in the range of 500 to 700°C; and a step of pickling the steel sheet after the coiling and cold rolling it at a reduction ratio of 30 to 80%. A method for producing the plated steel sheet for hot forming having excellent hydrogen embrittlement resistance described above.

6. The continuous annealing is performed at a temperature range of 740 to 860°C and a dew point temperature of -75 to -25°C. Item 5. A method for producing a plated steel sheet for hot forming having excellent hydrogen embrittlement resistance according to Item 4.

7. bare steel; and An alloy plating layer formed on the base steel, The point where the Ni content is highest (N imax) has a Ni content of 0.1 to 0.75 wt % and is excellent in hydrogen embrittlement resistance. Inter-molded member.

8. the alloy plating layer includes a Ni-enriched layer, The Ni-enriched layer was observed by glow discharge spectroscopy. The alloy plating was measured using GDS (Glass Emission Spectrometry). The point where the Ni content is highest in the concentration profile graph from which the Ni content of the layer is derived. The point (Nio) where the slope of the graph becomes 0 from (Nimax) toward the surface of the member and the point before A point (Nio') having the same content as the Nio in the depth direction of the member from the Nimax 8. The hot-formed member having excellent hydrogen embrittlement resistance according to claim 7, wherein the width is between 0.1 mm and 1.0 mm.

9. The heat-resistant alloy having excellent hydrogen embrittlement resistance according to claim 8, wherein the thickness of the Ni-enriched layer is 1 to 15 μm. Inter-molded member.

10. The resistance steel according to claim 7, wherein the amount of diffusible hydrogen in the hot-formed member is 0.3 ppm by weight or less. Hot-formed components with excellent resistance to hydrogen embrittlement.

11. The hot-rolled steel having excellent hydrogen embrittlement resistance according to claim 7, wherein the main phase of the base steel is martensite. Molded parts.

12. The steel sheet includes a base steel sheet and an Al-based plating layer formed on the surface of the base steel sheet, providing a blank having an average Ni content of 0.05 to 0.35 wt% in the plating layer; Heating the blank at a temperature ranging from Ac3 to 975°C; and The heated blank is transferred to a press, molded, and cooled at a cooling rate of 20°C / s or more. a step of:

13. The hot workpiece having excellent hydrogen embrittlement resistance according to claim 12, wherein the temperature range is maintained for 1 to 1000 seconds. Method for manufacturing a molded part.

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