Hot-pressed formed part

Abstract

Hot-pressed formed part, comprising: a basic steel sheet; an aluminum alloy layer applied to the base steel sheet, and including the aluminium alloy layer: an alloy layer (I) formed on the base steel sheet and containing 5-30% Al by weight; an alloy layer (II) formed on the alloy layer (I) and containing 30-60% Al by weight; an alloy layer (III) formed on the alloy layer (II) and containing 20-50% Al, 5-20% Si by weight; an alloy layer (IV) which is formed continuously or discontinuously on at least part of a surface of the alloy layer (III) and contains, in weight percent, 30-60% Al, and wherein the proportion of the alloy layer (III) exposed on an outermost surface of the aluminium alloy layer is 10% or more.

Description

[Technical field]

[0001] The present disclosure relates to a hot-pressed part. [State of the art]

[0002] Recently, due to the depletion of petroleum resources and a strong focus on environmental protection, regulations aimed at improving the fuel efficiency of motor vehicles have become stricter. One method for improving fuel efficiency is to reduce the thickness of steel sheets used in vehicles. However, reducing sheet thickness can affect vehicle safety. Therefore, the strength of the steel sheet may also need to be improved.

[0003] For this reason, there is a constant demand for high-strength steel sheets, and various types of steel sheets have been developed. However, because such steel sheets exhibit high strength, their workability can be poor, which can pose a problem. In other words, since the product of strength and elongation tends to have a constant value for each type of steel sheet, the elongation, an indicator of workability, can decrease as the strength of the steel sheet increases, which can be problematic.

[0004] To solve this problem, a hot-press forming process was proposed. Hot-press forming is a method for increasing the strength of a finished product by processing a steel sheet at a high temperature suitable for steel processing, followed by rapid cooling of the steel sheet to a low temperature, thereby forming a low-temperature structure, such as martensite, within the steel sheet. In this case, an advantage can be seen in the reduction of the problem of processability when manufacturing a high-strength component.

[0005] However, since hot pressing heats the steel sheet to a high temperature, surface oxidation can occur, necessitating a post-hot pressing process to remove the oxide, which can pose a problem. The technique described in U.S. Patent No. 6,296,805 was proposed as a solution to this problem. In U.S. Patent No. 6,296,805, a steel sheet coated with aluminum can be hot-pressed or formed at room temperature, as well as heated and rapidly cooled (“heat-treated”). Because the aluminum layer is present on the surface of the steel sheet, the steel sheet cannot oxidize during heating.

[0006] However, in the case of hot forming a steel sheet coated with aluminum, a problem can arise because the material's strength is extremely low due to the high temperature during hot forming, which can lead to significant wear on the die. This is because base iron can diffuse into the aluminum alloy layer while the aluminum-coated steel sheet is heated for hot forming. Consequently, a hard iron and aluminum alloy layer can form on the surface of the steel sheet, and the hardness of this alloy layer can be higher than that of the die material, which is generally made of tool steel. Therefore, the wear on the die during hot forming can be substantial.Accordingly, in the case of hot pressing a steel sheet that has undergone an aluminium coating, a press die may need to be ground or replaced in a short cycle, which can increase the manufacturing costs of a hot pressing part, which can be a problem. [Technical problem]

[0007] The purpose of the present disclosure is to provide a hot-press formed part that can cause less abrasion on a hot-press forming tool during the hot-press forming process.

[0008] The purpose of the present disclosure is not limited to the disclosure above. A person skilled in the art in the field to which the present disclosure belongs will have no difficulty in understanding an additional purpose of the present disclosure from the general aspects contained therein. [Technical solution]

[0009] One aspect of the present disclosure relates to a hot-press formed part comprising a base steel sheet and an aluminum alloy layer formed on the base steel sheet, wherein the aluminum alloy layer comprises an alloy layer (I) formed on the base steel sheet containing 5-30% Al by weight, an alloy layer (II) formed on the alloy layer (I) containing 30-60% Al by weight, an alloy layer (III) formed on the alloy layer (II) containing 20-50% Al and 5-20% Si by weight, and an alloy layer (IV) formed continuously or discontinuously on at least a portion of a surface of the alloy layer (III) containing 30-60% Al, and wherein a proportion of the alloy layer (III) exposed on an outermost surface of the aluminum alloy layer is 10% or more.

[0010] A large number of pores can be formed in the alloy layer (III), and the porosity of the alloy layer (III) can be 5-50%.

[0011] The base steel sheet may contain, by weight percent, 0.04-0.5% C, 0.01-2% Si, 0.1-5% Mn, 0.001-0.05% P, 0.0001-0.02% S, 0.001-1% Al, 0.001-0.02% N and, as a remainder, Fe and other impurities.

[0012] The base steel sheet may also contain, by weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti.

[0013] An explanatory aspect of the present disclosure, which is not claimed, relates to a method for producing a hot-press formed part, wherein the method comprises aluminum coating of a surface of a base steel sheet and annealing the steel sheet, thereby obtaining an aluminum-coated steel sheet; annealing the aluminum-coated steel sheet, thereby obtaining a steel sheet coated with an aluminum-iron alloy; and hot-press forming the aluminum-coated steel sheet, wherein an aluminum coating quantity of 30-200 g / m² 2 , based on a single side surface of the steel sheet, wherein a cooling rate to 250°C is less than 20°C / sec after the aluminium coating, wherein the winding tension is 0.5-5kg / mm 2during annealing, wherein the annealing is carried out in a batch annealing furnace in a heating temperature range of 550-750°C for 30 minutes to 50 hours, wherein, when heating from room temperature to the heating temperature during annealing, the average temperature rise rate is 10-100°C / h and the average temperature rise rate in a 400-500°C range is 1-15°C / h, wherein the difference between an atmospheric temperature in the batch annealing furnace and a temperature of the steel sheet is set at 5-80°C, and wherein heat treatment is carried out in a temperature range of Ac3-950°C during hot pressing, the heating is carried out at a temperature rise rate of 3-18°C / s to a temperature range of 200°C to Ac3-950°C, and heat treatment is carried out for 1-15 minutes as the total heating time. is carried out, and hot pressing is performed.

[0014] If the hot-pressed part is manufactured 500 times using the hot-pressed part manufacturing process, the average wear depth at 10 points of a hot-pressed part can be 15 µm or less. [Beneficial effects]

[0015] According to the present disclosure, in the manufacture of a hot-press formed part, the surface hardness of a plated layer can be lower than that of a hot-press forming die, so that the abrasion of the hot-press forming die can be reduced, thereby increasing the grinding or replacement cycle of the hot-press forming die and improving the manufacturing costs and production efficiency of the hot-press formed part.

[0016] Various and useful advantages and effects of the present disclosure are not limited to the above disclosure and will become more easily understood in the course of the disclosure of specific embodiments of the present disclosure. [Brief description of the drawings] Fig. Figure 1 is an image of a cross-sectional area of ​​a plated layer of a hot-pressed part produced according to Example 1, obtained using a scanning electron microscope; and Fig. Figure 2 is a scanning electron microscope image of a cross-sectional area of ​​a plated layer of a hot-pressed part produced according to comparative example 1. [Best Invention Method]

[0017] The following disclosure describes in detail a hot-pressed part according to one aspect of the present disclosure. The present disclosure indicates that the content of individual elements may be given in weight percent unless otherwise specified. Likewise, a ratio of crystals or structures on a surface may be given unless otherwise specified. [Hot-pressed part]

[0018] A hot-pressed part may comprise a base steel sheet and an aluminum alloy layer formed on the base steel sheet, and the aluminum alloy layer may comprise an alloy layer (I) formed on the base steel sheet containing 5-30% Al by weight, an alloy layer (II) formed on the alloy layer (I) containing 30-60% Al by weight, an alloy layer (III) formed on the alloy layer (II) containing 20-50% Al and 5-20% Si by weight; and an alloy layer (IV) formed continuously or discontinuously on at least a part of a surface of the alloy layer (III) and containing 30-60% Al.

[0019] Preferably, each of the alloy layers can contain the components listed below. Alloy layer (I) can contain 5-30 wt% Al, 0-10 wt% Si, and the remainder Fe and other unavoidable impurities included by the alloying process; alloy layer (II) can contain 30-60 wt% Al, 0-5 wt% Si, and the remainder Fe and other unavoidable impurities included by the alloying process; alloy layer (III) can contain 20-50 wt% Al, 5-20 wt% Si, and a remainder Fe and other unavoidable impurities included by the alloying process; and alloy layer (IV) can contain 30-60 wt% Al, 0-5 wt% Si, and a remainder Fe and other unavoidable impurities included by the alloying process.

[0020] If the base steel sheet is coated with aluminum and undergoes heat treatment, the iron from the base steel sheet can diffuse into the aluminum-coated layer with a high aluminum content. In the hot-pressed part of this disclosure, an alloy between aluminum and iron can occur in the clad layer through an annealing treatment for alloying and a heat treatment during hot pressing, and a layer structure consisting of alloy layers (I)-(IV) can be formed depending on the degree of iron alloying.

[0021] The alloy layer (IV) can form continuously or discontinuously on at least part of the surface of the alloy layer (III). That is, the alloy layer (IV) can form on part of the surface of the alloy layer (III) and not on its entire surface.

[0022] Since the alloy layer (IV) forms on at least part of the surface of the alloy layer (III), part of the surface of the alloy layer (III) may also be exposed to an outermost surface of the aluminum alloy layer. This outermost surface may refer to an outermost surface of the aluminum alloy layer on a side opposite the base steel sheet. If an oxide layer forms on the surface of the aluminum alloy layer, the outermost layer may refer to the uppermost surface of the layers other than the oxide layer.

[0023] In this case, the proportion of the alloy layer (III) exposed at the outermost surface of the aluminum alloy layer can preferably be 10% or more. Here, the ratio of the alloy layer (III) exposed at the outermost surface can be defined as the ratio of the length of an area where the alloy layer (III) is exposed to the total length of the outermost surface when considering a cross-sectional area of ​​the aluminum alloy layer, or in some cases, the ratio can be defined as an area ratio of the surface area of ​​the alloy layer (III) exposed at the outermost surface to the surface area of ​​the outermost surface of the aluminum alloy layer.Among the alloy layers, the hardness of alloy layer (II) and alloy layer (IV) can be extremely high, around 900 Hv, while the hardness of alloy layer (I) and alloy layer (III) can be around 300–700 Hv, relatively lower than that of alloy layer (II) and alloy layer (IV). Therefore, if the exposed area of ​​alloy layer (III), with its relatively low hardness, increases on the outermost surface of the aluminum alloy layer that is in contact with the die during hot pressing, the average overall hardness of the outermost surface can decrease, thus reducing die wear.

[0024] If the proportion of the alloy layer (III) exposed to the outermost surface is less than 10%, the difference between the average hardness of the outermost surface and the die hardness may decrease, potentially rendering die wear ineffective. The lower the hardness of the outermost surface of the aluminum alloy layer, the more advantageous it is for preventing die wear, and therefore it may not be necessary to specify an upper limit for the ratio. Preferably, the ratio may be 15% or more, and in some cases, 20% or more.

[0025] A variety of pores can form in alloy layer III. When an aluminum-coated steel sheet is produced by performing an alloy heat treatment in a batch annealing furnace under predetermined conditions, a variety of alloy layers can form in the aluminum-coated steel sheet, and a variety of pores can form on an upper final alloy layer due to a difference in the mutual diffusion coefficients, such as Fe, Al, and Si, between alloy layers with different components.In this case, if an increasing number of pores are formed towards the top of the alloy layer, the porosity within it can be high. When the aluminum-coated steel sheet is heated and hot-pressed, a top alloy layer exhibiting high-density pores can be fractured into small particles by the die. Since the rolling friction that occurs as these small particles roll may be less than the sliding friction between the steel sheet and the die, the lubricity between the die and the steel sheet can increase. Porosity can be defined as the ratio of the pore area to the area of ​​each alloy layer (or the alloy layer itself) when considering the cross-sectional area of ​​the alloy layer (or the alloy layer).

[0026] However, as in Fig.1. Since most areas of alloy layer IV are fractured during hot pressing, it can be difficult to measure the porosity of alloy layer IV in the hot-pressed part. Therefore, the features of the present disclosure can be characterized by the porosity of alloy layer (III), which is less affected by the pressing process and has a close relationship to the porosity of alloy layer (IV) before pressing.

[0027] Accordingly, the porosity of the alloy layer (III) of the hot-pressed part can be 5-50% according to one aspect of the present disclosure. If the porosity is less than 5%, it is difficult to expect a lubricating effect from rolling friction during hot pressing. If the porosity exceeds 50%, the structure of the alloy layer (III) of the hot-pressed part can be excessively weakened, so that the contamination of the die by particles falling out of the plated layer in the die during continuous hot pressing can increase. Therefore, in the present disclosure, the porosity can preferably be 5-50% and in some cases 7-50%.

[0028] The base steel sheet of the present disclosure can be a steel sheet for hot pressing, and if the base steel sheet is used for hot pressing, its composition need not be particularly limited. However, according to one aspect of the present disclosure, the base steel sheet can contain 0.04-0.5 wt% C, 0.01-2 wt% Si, 0.1-5 wt% Mn, 0.001-0.05 wt% P, 0.0001-0.02 wt% S, 0.001-1 wt% Al, 0.001-0.02 wt% N, and, as a remainder, Fe and other impurities. The individual composition systems are described in more detail below. C: 0.04-0.5%

[0029] Carbon (C) can be an essential element for increasing the strength of a part for heat treatment and can be added in appropriate amounts. That is, to ensure sufficient strength of the part for heat treatment, C can be added in an amount of 0.04% or more. Preferably, the lower limit of the C content can be 0.1% or more. However, if the content is too high, the strength of the hot-rolled material may be too high when the hot-rolled material is cold-rolled, so that the cold-rolling properties can be severely deteriorated and weldability can be significantly impaired. Therefore, to ensure sufficient cold-rolling properties and weldability, C can be added in an amount of 0.5% or less. The C content can also be 0.45% or less, and preferably the content can be limited to 0.4% or less. Si: 0.01-2%

[0030] Silicon (Si) can be added as a deoxidizing agent during steel production and can also prevent the formation of carbides, which have the greatest impact on the strength of the hot-pressed part. In the present disclosure, the Si content during hot pressing can be 0.01% or more to ensure retained austenite by concentrating the carbon at the grain boundaries of the martensite flakes after the martensite has formed. If the steel sheet is coated with aluminum after rolling, an upper limit of 2% Si content can be set to ensure adequate coating properties. Preferably, the Si content can be limited to 1.5% or less. Mn: 0.1-5%

[0031] Manganese (Mn) can be added in amounts of 0.1% or more to ensure a strengthening effect of the solid solution and also to reduce the critical cooling rate for securing martensite in the hot-pressed part. Since Mn can appropriately maintain the strength of the steel sheet, it can also ensure the processability of the hot pressing, reduce manufacturing costs, and improve weldability, so that the Mn content can be limited to 5% or less. P: 0.001-0.05%

[0032] Phosphorus (P) can be present as an impurity in steel, and a low P content can be advantageous. Therefore, in the present disclosure, the P content can be limited to 0.05% or less, and preferably to 0.03% or less. The lower the P content, the more advantageous it is as an impurity, so it is not strictly necessary to specify an upper limit. However, an excessively low P content can increase production costs, so a lower limit of 0.001% can be specified in consideration of this. S: 0.0001-0.02%

[0033] S is an impurity found in steel and can impair the ductility, impact strength, and weldability of the component. Therefore, the maximum content can be limited to 0.02%, preferably to 0.01% or less. If the minimum content is less than 0.0001%, manufacturing costs may increase, so a lower limit of 0.0001% may be set. Al: 0.001-1%

[0034] Aluminum, along with silicon, can increase the purity of steel through deoxidation during steelmaking and can be added in amounts of 0.001% or more to achieve the aforementioned effect. Furthermore, the aluminum content can be limited to 1% or less to prevent the Ac3 temperature from rising excessively, thus ensuring that the heating required during hot pressing can be carried out within a suitable temperature range. N: 0.001-0.02%

[0035] Nitrogen (N) can be present as an impurity in steel, and to reduce its susceptibility to cracking during continuous slab casting and to ensure impact strength, a lower N content can be advantageous. Therefore, N can be added at 0.02% or less. It may be necessary to establish a lower limit, but considering the potential increase in production costs, the N content can be set at 0.001% or more.

[0036] In addition to the alloy composition described above, the aluminium-coated steel sheet may, according to one aspect of the present disclosure, contain one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti. B: 0.001-0.01%

[0037] B can improve hardenability even in small amounts and can be segregated at a previous austenite grain boundary, thus preventing brittleness of the hot-pressed part due to grain boundary segregation of P and / or S. Therefore, 0.0001% or more of B can be added. If the content exceeds 0.01%, the effect may become saturated and cause brittleness during hot rolling; therefore, an upper limit of 0.01% may be set, and preferably the B content may be set at 0.005% or less. Cr: 0.01-1%

[0038] Cr can be added to increase strength in solid solution and improve hardenability during hot pressing, similar to manganese. A concentration of 0.01% or more of Cr can be added to achieve this effect. However, to ensure weldability of the component, the concentration may be limited to 1% or less. If the concentration exceeds 1%, the improvement in hardenability may be negligible compared to the amount added, which can be costly. Ti: 0.001-0.2%

[0039] Ti can improve the strength of the heat-treated element by forming fine precipitates and enhance the element's collision behavior by refining the grains. Furthermore, when B is added, it preferentially reacts with N, thus maximizing the effect of the B addition. To achieve the aforementioned effect, Ti can be added in amounts of 0.001% or more. However, the formation of coarse TiN, caused by an increase in the Ti content, can degrade the element's collision performance, and therefore the content may need to be limited to 0.2% or less.

[0040] A residue other than the components described above may contain iron (Fe) and unavoidable impurities, and the addition of any element is not particularly limited as long as the element can be incorporated into the steel sheet for hot pressing.

[0041] When the hot-press formed part is manufactured with the alloy composition and layer structure described above, the proportion of the low-hardness alloy layer (III) on the surface of the aluminum-coated steel sheet can increase during hot pressing, thus reducing the average surface hardness and effectively minimizing die wear caused by hardness differences. In particular, even when the hot-press formed part is manufactured more than 500 times, the average 10-point wear depth of the hot-press formed part can be 15 µm or less.

[0042] Furthermore, a large number of pores can be formed in the alloy layers (III) and (IV), the upper end layers of the aluminium alloy layer, during hot pressing, and the alloy layer (IV) can be fractured due to the pores during pressing, so that a lubricating effect can be achieved through rolling friction and damage to the die can be further prevented.

[0043] An illustrative, unclaimed method for manufacturing a hot-pressed part is described in detail below. The method described below for manufacturing a hot-pressed part can only be an example and does not mean that the hot-pressed part in the present disclosure must be manufactured by this method. Any manufacturing method that satisfies the claims of the present disclosure can readily implement any embodiment of the present disclosure. [Method for producing a hot-pressed part]

[0044] The hot-press formed part in the present disclosure can be obtained by preparing a hot- or cold-rolled base steel sheet, applying an aluminium coating to a surface of the base steel sheet, performing an alloy heat treatment in a batch annealing furnace to obtain an aluminium-coated steel sheet, and carrying out hot-press forming under predetermined conditions.

[0045] First, a process can be carried out to produce the base steel sheet with the alloy composition described above, to apply aluminium to the surface of the base steel sheet under suitable conditions, and to anneal the steel sheet, thereby obtaining an aluminium-coated steel sheet (coil).

[0046] An aluminum coating can be applied to the surface of the rolled steel sheet in a coating quantity of 30-200g / m². 2 The coating process can be carried out on one side. The aluminum coating can be an AlSi coating (containing 80% or more Al and 5-20% Si, and optionally additional elements), commonly known as Type I, or a coating requiring 90% or more Al and optionally containing additional elements, known as Type II, can also be used. Hot-dip aluminum plating can be performed to form a clad layer, and the steel sheet can be annealed prior to coating. An appropriate coating quantity of 30-200 g / m² can be applied. 2on a single side. If the coating amount is too high, it can take an excessively long time for the surface to become alloyed, and if the coating amount is extremely low, it can be difficult to achieve sufficient corrosion resistance.

[0047] Following aluminum plating, cooling to 250°C can be carried out at a rate of 20°C / sec or less. The cooling rate after aluminum plating can influence the formation of the diffusion-inhibiting layer between the coated layer and the base iron. If the cooling rate after aluminum plating is extremely high, the diffusion-inhibiting layer may not form uniformly, and the alloying behavior of a coil during subsequent annealing may become uneven. Therefore, the cooling rate to 250°C after aluminum plating can be set to 20°C / sec or less.

[0048] When a coil is produced by winding the steel sheet after coating, the winding tension of the coil can be set to 0.5-5 kg / mm². 2The annealing voltage of the coil can be adjusted. Depending on the setting of the annealing voltage of the coil, the alloy behavior and the surface quality of the coil can differ during the subsequent annealing treatment.

[0049] Afterwards, the aluminium-coated steel sheet can be produced by an annealing treatment under the conditions described below, resulting in an aluminium-coated steel sheet.

[0050] The aluminum-clad steel sheet (coil) can be heated in a batch annealing furnace (BAF). When the steel sheet is heated, it can be held in a range of 550 to 750 °C for 30 minutes to 50 hours, depending on the target temperature of the heat treatment and the holding time (in the present disclosure, the highest temperature reached by the material in this temperature range can be referred to as the heating temperature), preferably based on the temperature of the steel sheet. The holding time can be the time until cooling begins after the coil temperature has reached the target temperature. If the alloying is insufficient, the clad layer may be stripped during rolling, and therefore the heating temperature for sufficient alloying can be set at 550 °C or higher.To prevent excessive oxide formation on the surface layer and ensure weldability, the heating temperature can also be 750 °C or less. To adequately secure the clad layer and prevent a decrease in productivity, the holding time can be set from 30 minutes to 50 hours. In some cases, the temperature of the steel sheet can be adjusted using a heating curve, where the temperature continues to rise without cooling until the heating temperature is reached, or a heating curve where the temperature, equal to or lower than the target temperature, is maintained for a predetermined time and then allowed to rise.

[0051] When the steel sheet is heated to the heating temperature described above, an average temperature rise rate of 10-100°C / h with respect to the temperature of the steel sheet (coil) can be achieved across the entire temperature range (from room temperature to the heating temperature) to ensure sufficient productivity and uniform alloying of the clad layer throughout the entire steel sheet (coil). However, in one embodiment of the present disclosure, to avoid surface stains caused by rolling oil remaining in the temperature range where the rolling oil mixed in during rolling evaporates, and to ensure sufficient productivity, heating can be carried out with an average temperature rise rate in the range of 400-500°C, which is 1-15°C / h as the temperature increases.

[0052] Furthermore, the temperature difference between the atmosphere and the temperature of the steel sheet in the batch annealing furnace can range from 5 to 80°C. Generally, the batch annealing furnace can be heated by a process where the steel sheet (the coil) is heated by increasing the temperature of the atmosphere in the furnace, rather than by a process where the steel sheet (the coil) is heated directly. In this case, the difference between the atmosphere temperature and the coil temperature cannot be avoided, but to minimize variations in material and coating quality at each location within the steel sheet, the difference between the atmosphere temperature and the steel sheet temperature can be 80°C or less, depending on when the target heat treatment temperature is reached.It may be ideal to reduce the temperature difference as much as possible, but a reduced temperature difference can decrease the rate of temperature rise, making it difficult to meet the condition of the overall average rate of temperature rise. Therefore, taking this into account, the difference may be set at 5°C or more. The temperature of the steel sheet can refer to the temperature measured at a lower section (the bottom section of the coil) of the steel sheet being charged, and the temperature of the atmosphere can refer to the temperature measured in the center of an interior space of the heating furnace.

[0053] After the aluminum-coated steel sheet has been produced using the manufacturing process described above, hot pressing can be performed on it, resulting in a hot-pressed part. In this case, a standard technical procedure can be used for hot pressing. For example, though not limited to, heat treatment can be carried out within a temperature range of Ac3-950°C. Heating can be performed at a temperature increase rate of 3-18°C / s from 200°C to this range. The total heating time can be defined as the time spent heating both during the temperature increase phase and during the heating phase within the Ac3-950°C range. [Preferred embodiment]

[0054] The present disclosure is described in more detail below with reference to exemplary embodiments. It should be noted, however, that these embodiments serve only to specify the present disclosure and do not limit its scope. The scope of the present disclosure can be determined by the circumstances described in the claims and the circumstances derived therefrom. (Example of implementation)

[0055] First, a cold-rolled steel sheet for hot pressing was produced with the composition specified in Table 1 as the base steel sheet, and the surface of the steel sheet was coated with a Type I plating bath containing an Al-9%Si-1.5%Fe composition. During the plating process, the coating quantity was increased to 75 g / m². 2per side, and cooling was carried out at a cooling rate of 10 °C / s to 250 °C after the aluminium coating, and the annealing stress was set to 3 kg / mm². 2 adjusted, resulting in an aluminium-coated steel sheet. [Table 1] element C Si Mn Al P S N Cr Ti B AC3 Salary (%) 0,23 0,2 1,25 0,03 0, 01 0,002 0, 005 0,21 0,034 0, 0022 822°C

[0056] Subsequently, an alloy heat treatment of the coated steel sheet was carried out in a batch annealing furnace under the conditions specified in Table 2, and hot pressing was performed 500 times on each sample, resulting in a hot-pressed part. In comparative example 1, however, the alloy heat treatment was not performed on the aluminum-coated steel sheet described above, and hot pressing was carried out under the conditions specified in Table 2, resulting in a hot-pressed part. [Table 2] classification Conditions for alloy heat treatment Conditions for hot pressing Temperature (°C) Average temperature rise rate (°C / h) Average temperature rise rate in the temperature range 400-500 °C (°C / h) Temperature difference between atmosphere and steel sheet at heating temperature (°C) Time (h) Rate of temperature increase (°C / s) Temperature (°C) Total heating time (min) Inventive Example 1 630 21 6 25 14 5, 8 930 5 Inventive Example 2 590 25 10 30 30 8,5 900 6 Imaginative Example 3 680 27 12 25 8 6,2 930 5 Compare - - - - - 3,4 930 5 Ending example 1 Comparative Example 2 500 35 20 25 8 4, 7 900 6

[0057] Subsequently, the component was produced 500 times using the press mold employed in each example and comparative example of the invention. The wear depth was measured at 10 random points, and the average values ​​are listed in Table 3 below. From the 500 products of each example, ten random samples were taken, and their cross-sectional areas were examined using a scanning electron microscope to confirm the coverage of the outermost layer of the alloy layer (III). The average coverage values ​​are listed in Table 3 below. Furthermore, the porosity of the alloy layer (III) was measured, and the results are listed in Table 3 below. In the same embodiment (example according to the invention or comparative example), it was found that the deviation between the coverage of the outermost layer and the porosity of the alloy layer (III) was not large. [Table 3] Classification Percentage of alloy layer(III) on the outermost surface (%) Average abrasion depth of the press mold after 500 production runs (µm) Porosity of the alloy layer (III) (%) Inventive example 1 35 7 7,2 Inventive Example 2 12 9 5, 7 Imaginative Example 3 47 4 13,1 Comparative Example 1 7 39 1, 7 Comparison 9 23 3,2 handdesExample2

[0058] As shown in Table 3, for Examples 1 to 3 according to the invention, where the area fraction of the alloy layer (III) exposed on the outermost surface is 10% or more and the porosity is 5% or more, it was confirmed that even after the hot-press formed part was produced 500 times according to Examples 1 to 3, the average wear depth of the die was 15 µm or less, thus effectively preventing wear of the hot-press forming die. In Comparative Example 1, a general Al-Si-coated steel sheet was hot-pressed, and the area fraction of the alloy layer (III) exposed on the outermost surface was less than 10%, and the porosity was low, so that the wear of the die increased significantly compared to the example according to the invention.

[0059] As in Comparative Example 2, the alloy heat treatment of the aluminum layer was also carried out, but the temperature of the alloy heat treatment was low, so the alloying was not sufficiently carried out. Accordingly, it was confirmed that, since the area fraction of the alloy layer (III) on the outermost surface was less than 10% and the porosity was low, the abrasion of the press mold increased significantly, as in Comparative Example 1.

[0060] Although the embodiments have been illustrated and described above, it is obvious to the person skilled in the art that changes and variations can be made without departing from the scope of the embodiment as defined by the attached claims.

[0061] The invention is described in more detail with reference to the following aspects: [ASPECTS][ASPECT 1]

[0062] Hot-pressed formed part, comprising: a basic steel sheet; and an aluminum alloy layer applied to the base steel sheet, including the aluminium alloy layer: an alloy layer (I) formed on the base steel sheet and containing 5-30% Al by weight; an alloy layer (II) formed on the alloy layer (I) and containing 30 to 60% Al by weight; an alloy layer (III) formed on the alloy layer (II) and containing, in weight percent, 20-50% Al and 5-20% Si; and an alloy layer (IV) that is formed continuously or discontinuously on at least part of a surface of the alloy layer (III) and contains 30-60% Al, and wherein the proportion of the alloy layer (III) exposed on an outermost surface of the aluminium alloy layer is 10% or more. [ASPECT 2]

[0063] The hot-pressed part according to aspect 1, where a large number of pores are formed in the alloy layer (III), and where the porosity of the alloy layer (III) is 5-50%. [ASPECT 3]

[0064] Hot-pressed part according to aspect 1, wherein the base steel sheet contains in wt% 0.04 to 0.5% C, 0.01 to 2% Si, 0.1 to 5% Mn, 0.001 to 0.05% P, 0.0001 to 0.02% S, 0.001 to 1% Al, 0.001 to 0.02% N and as balance Fe and other impurities. [ASPECT 4]

[0065] The hot-pressed part according to aspect 3, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 6,296,805

[0005]

Claims

[1] Hot-pressed part comprising: a basic steel sheet; an aluminum alloy layer applied to the base steel sheet, and including the aluminium alloy layer: an alloy layer (I) formed on the base steel sheet and containing 5-30% Al by weight; an alloy layer (II) formed on the alloy layer (I) and containing 30-60% Al by weight; an alloy layer (III) formed on the alloy layer (II) and containing 20-50% Al, 5-20% Si by weight; an alloy layer (IV) which is formed continuously or discontinuously on at least part of a surface of the alloy layer (III) and contains, in weight percent, 30-60% Al, and wherein the proportion of the alloy layer (III) exposed on an outermost surface of the aluminium alloy layer is 10% or more. [2] Hot-pressed part according to claim 1, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 15% or more. [3] Hot-pressed part according to one of claims 1 to 2, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 20% or more. [4] Hot-pressed part according to any of the preceding claims, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 47% or less. [5] Hot-pressed part according to any of the preceding claims, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 35% or less. [6] Hot-pressed part according to one of the preceding claims, wherein a plurality of pores are formed in the alloy layer (III). [7] Hot-pressed part according to one of the preceding claims, wherein a plurality of pores are formed in the alloy layer (IV). [8] Hot-pressed part according to any of the preceding claims, wherein the porosity of the alloy layer (III) is 5-50%. [9] Hot-pressed part according to any of the preceding claims, wherein the porosity of the alloy layer (III) is 7-50%. [10] Hot-pressed part according to any of the preceding claims, wherein the porosity of the alloy layer (III) is 13.1% or less. [11] Hot-pressed part according to any of the preceding claims, wherein the porosity of the alloy layer (III) is 7.2% or less. [12] Hot-pressed part according to any of the preceding claims, wherein the porosity of the alloy layer (III) is 5.7% or less. [13] Hot-pressed part according to one of the preceding claims, wherein the hardness of the alloy layer (III) is less than the hardness of the alloy layer (II). [14] Hot-pressed part according to one of the preceding claims, wherein the hardness of the alloy layer (III) is less than the hardness of the alloy layer (IV). [15] Hot-pressed part according to one of the preceding claims, wherein the hardness of the alloy layer (I) is less than the hardness of the alloy layer (II). [16] Hot-pressed part according to one of the preceding claims, wherein the hardness of the alloy layer (I) is less than the hardness of the alloy layer (IV). [17] Hot-pressed part according to one of the preceding claims, wherein the hardness of the alloy layer (III) is 300-700 Hv. [18] Hot-pressed part according to one of the preceding claims, wherein an oxide layer is formed on the aluminium alloy layer. [19] Hot-pressed part according to any of the preceding claims, wherein the base steel sheet contains, by weight, 0.04 to 0.5% C, 0.01 to 2% Si, 0.1 to 5% Mn, 0.001 to 0.05% P, 0.0001 to 0.02% S, 0.001 to 1% Al, 0.001 to 0.02% N and, as a remainder, Fe and other impurities. [20] Hot-pressed part according to claim 19, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti. [21] Hot-pressed part according to claim 19, wherein the base steel sheet also contains, by weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti, as well as Fe and other impurities as the remainder, such that the sum equals 100% by weight. [22] Hot-pressed part comprising: a basic steel sheet; an aluminum alloy layer applied to the base steel sheet, and including the aluminium alloy layer: an alloy layer (I) formed on the base steel sheet, consisting of 5-30% Al by weight and Fe as the remainder and contains unavoidable impurities trapped by the alloying process; an alloy layer (II) formed on the alloy layer (I) and consisting of 30-60% Al by weight and Fe as the remainder and contains unavoidable impurities trapped by the alloying process; an alloy layer (III) formed on the alloy layer (II) and containing, by weight percent, 20-50% Al, 5-20% Si and, as a remainder, Fe and unavoidable impurities that are included by the alloying; an alloy layer (IV) which is formed continuously or discontinuously on at least part of a surface of the alloy layer (III) and contains, in weight percent, 30-60% Al and as a remainder Fe and unavoidable impurities that are included by the alloying, and wherein the proportion of the alloy layer (III) exposed on an outermost surface of the aluminium alloy layer is 10% or more. [23] Hot-pressed part according to claim 22, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 15% or more. [24] Hot-pressed part according to one of claims 22 to 23, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 20% or more. [25] Hot-pressed part according to any one of claims 22 to 24, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 47% or less. [26] Hot-pressed part according to any one of claims 22 to 25, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 35% or less. [27] Hot-pressed part according to one of claims 22 to 26, wherein a plurality of pores are formed in the alloy layer (III). [28] Hot-pressed part according to one of claims 22 to 27, wherein a plurality of pores are formed in the alloy layer (IV). [29] Hot-pressed part according to any one of claims 22 to 28, wherein the porosity of the alloy layer (III) is 5-50%. [30] Hot-pressed part according to any one of claims 22 to 29, wherein the porosity of the alloy layer (III) is 7-50%. [31] Hot-pressed part according to any one of claims 22 to 30, wherein the porosity of the alloy layer (III) is 13.1% or less. [32] Hot-pressed part according to any one of claims 22 to 31, wherein the porosity of the alloy layer (III) is 7.2% or less. [33] Hot-pressed part according to any one of claims 22 to 32, wherein the porosity of the alloy layer (III) is 5.7% or less. [34] Hot-pressed part according to one of claims 22 to 33, wherein the hardness of the alloy layer (III) is less than the hardness of the alloy layer (II). [35] Hot-pressed part according to any one of claims 22 to 34, wherein the hardness of the alloy layer (III) is less than the hardness of the alloy layer (IV). [36] Hot-pressed part according to any one of claims 22 to 35, wherein the hardness of the alloy layer (I) is less than the hardness of the alloy layer (II). [37] Hot-pressed part according to any one of claims 22 to 36, wherein the hardness of the alloy layer (I) is less than the hardness of the alloy layer (IV). [38] Hot-pressed part according to any one of claims 22 to 37, wherein the hardness of the alloy layer (III) is 300-700 Hv. [39] Hot-pressed part according to any one of claims 22 to 38, wherein an oxide layer is formed on the aluminium alloy layer. [40] Hot-pressed part according to any one of claims 22 to 39, wherein the base steel sheet contains, by weight percent, 0.04 to 0.5% C, 0.01 to 2% Si, 0.1 to 5% Mn, 0.001 to 0.05% P, 0.0001 to 0.02% S, 0.001 to 1% Al, 0.001 to 0.02% N and, as a remainder, Fe and other impurities. [41] Hot-pressed part according to claim 40, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti. [42] Hot-pressed part according to claim 40, wherein the base steel sheet also contains, by weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti, as well as Fe and other impurities as the remainder, such that the sum equals 100% by weight. [43] Hot-pressed part comprising: a basic steel sheet; an aluminum alloy layer applied to the base steel sheet, and including the aluminium alloy layer: an alloy layer (I) formed on the base steel sheet containing, by weight percent, 5-30% Al, 0-10% Si and as the remainder Fe and unavoidable impurities included by the alloying; an alloy layer (II) formed on the alloy layer (I) and containing, by weight percent, 30-60% Al, 0-5% Si and, as a remainder, Fe and unavoidable impurities included by the alloying; an alloy layer (III) formed on the alloy layer (II) and containing, by weight percent, 20-50% Al, 5-20% Si and, as a remainder, Fe and unavoidable impurities that are included by the alloying; an alloy layer (IV) which is formed continuously or discontinuously on at least part of a surface of the alloy layer (III) and contains, in weight percent, 30-60% Al, 0-5% Si and as a remainder Fe and unavoidable impurities that are included by the alloying, and wherein the proportion of the alloy layer (III) exposed on an outermost surface of the aluminium alloy layer is 10% or more. [44] Hot-pressed part according to claim 43, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 15% or more. [45] Hot-pressed part according to any one of claims 43 to 44, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 20% or more. [46] Hot-pressed part according to any one of claims 43 to 45, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 47% or less. [47] Hot-pressed part according to any one of claims 43 to 46, wherein the proportion of the alloy layer (III) exposed on the outermost surface of the aluminium alloy layer is 35% or less. [48] ​​Hot-pressed part according to any one of claims 43 to 47, wherein a plurality of pores are formed in the alloy layer (III). [49] Hot-pressed part according to any one of claims 43 to 48, wherein a plurality of pores are formed in the alloy layer (IV). [50] Hot-pressed part according to any one of claims 43 to 49, wherein the porosity of the alloy layer (III) is 5-50%. [51] Hot-pressed part according to any one of claims 43 to 50, wherein the porosity of the alloy layer (III) is 7-50%. [52] Hot-pressed part according to any one of claims 43 to 51, wherein the porosity of the alloy layer (III) is 13.1% or less. [53] Hot-pressed part according to any one of claims 43 to 52, wherein the porosity of the alloy layer (III) is 7.2% or less. [54] Hot-pressed part according to any one of claims 43 to 53, wherein the porosity of the alloy layer (III) is 5.7% or less. [55] Hot-pressed part according to one of claims 43 to 54, wherein the hardness of the alloy layer (III) is less than the hardness of the alloy layer (II). [56] Hot-pressed part according to any one of claims 43 to 55, wherein the hardness of the alloy layer (III) is less than the hardness of the alloy layer (IV). [57] Hot-pressed part according to any one of claims 43 to 56, wherein the hardness of the alloy layer (I) is less than the hardness of the alloy layer (II). [58] Hot-pressed part according to any one of claims 43 to 57, wherein the hardness of the alloy layer (I) is less than the hardness of the alloy layer (IV). [59] Hot-pressed part according to any one of claims 43 to 58, wherein the hardness of the alloy layer (III) is 300-700 Hv. [60] Hot-pressed part according to any one of claims 43 to 59, wherein an oxide layer is formed on the aluminium alloy layer. [61] Hot-pressed part according to any one of claims 43 to 60, wherein the base steel sheet contains, by weight, 0.04 to 0.5% C, 0.01 to 2% Si, 0.1 to 5% Mn, 0.001 to 0.05% P, 0.0001 to 0.02% S, 0.001 to 1% Al, 0.001 to 0.02% N and, as a remainder, Fe and other impurities. [62] Hot-pressed part according to claim 61, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti. [63] Hot-pressed part according to claim 61, wherein the base steel sheet also contains, by weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti, as well as Fe and other impurities as the remainder, such that the sum equals 100% by weight. [64] Hot-pressed part comprising: a basic steel sheet; an aluminum alloy layer applied to the base steel sheet, and including the aluminium alloy layer: an alloy section (I) formed on the base steel sheet and containing 5-30% Al by weight and Fe as the remainder and contains unavoidable impurities; an alloy section (II) formed on the alloy section (I) and consisting of 30-60% Al by weight and Fe as the remainder and contains unavoidable impurities; an alloy section (III) formed on the alloy section (II) and containing, by weight percent, 20-50% Al, 5-20% Si and, as a remainder, Fe and unavoidable impurities; an alloy section (IV) which is formed continuously or discontinuously on at least part of a surface of the alloy section (III) and contains, in weight percent, 30-60% Al and as a remainder Fe and unavoidable impurities, and wherein the proportion of the alloy section (III) exposed on an outermost surface of the aluminium alloy layer is 10% or more. [65] Hot-pressed part according to claim 64, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 15% or more. [66] Hot-pressed part according to any one of claims 64 to 65, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 20% or more. [67] Hot-pressed part according to any one of claims 64 to 66, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 47% or less. [68] Hot-pressed part according to any one of claims 64 to 67, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 35% or less. [69] Hot-pressed part according to any one of claims 64 to 68, wherein a plurality of pores are formed in the alloy section (III). [70] Hot-pressed part according to any one of claims 64 to 69, wherein a plurality of pores are formed in the alloy section (IV). [71] Hot-pressed part according to any one of claims 64 to 70, wherein the porosity of the alloy section (III) is 5-50%. [72] Hot-pressed part according to any one of claims 64 to 71, wherein the porosity of the alloy section (III) is 7-50%. [73] Hot-pressed part according to any one of claims 64 to 72, wherein the porosity of the alloy section (III) is 13.1% or less. [74] Hot-pressed part according to any one of claims 64 to 73, wherein the porosity of the alloy section (III) is 7.2% or less. [75] Hot-pressed part according to any one of claims 64 to 74, wherein the porosity of the alloy section (III) is 5.7% or less. [76] Hot-pressed part according to any one of claims 64 to 75, wherein the hardness of the alloy section (III) is less than the hardness of the alloy section (II). [77] Hot-pressed part according to any one of claims 64 to 76, wherein the hardness of alloy section (III) is less than the hardness of alloy section (IV). [78] Hot-pressed part according to any one of claims 64 to 77, wherein the hardness of alloy section (I) is less than the hardness of alloy section (II). [79] Hot-pressed part according to any one of claims 64 to 78, wherein the hardness of alloy section (I) is less than the hardness of alloy section (IV). [80] Hot-pressed part according to any one of claims 64 to 79, wherein the hardness of the alloy section (III) is 300-700 Hv. [81] Hot-pressed part according to any one of claims 64 to 80, wherein an oxide layer is formed on the aluminium alloy layer. [82] Hot-pressed part according to any one of claims 64 to 81, wherein the base steel sheet contains, by weight percent, 0.04 to 0.5% C, 0.01 to 2% Si, 0.1 to 5% Mn, 0.001 to 0.05% P, 0.0001 to 0.02% S, 0.001 to 1% Al, 0.001 to 0.02% N and, as a remainder, Fe and other impurities. [83] Hot-pressed part according to claim 82, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti. [84] Hot-pressed part according to claim 82, wherein the base steel sheet also contains, by weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti, as well as Fe and other impurities as the remainder, such that the sum equals 100% by weight. [85] Hot-pressed part comprising: a basic steel sheet; an aluminum alloy layer applied to the base steel sheet, and including the aluminium alloy layer: an alloy section (I) formed on the base steel sheet and containing 5-30% Al by weight and Fe as the remainder and contains unavoidable impurities trapped by the alloying process; an alloy section (II) formed on the alloy section (I) and consisting of 30-60% Al by weight and Fe as the remainder and contains unavoidable impurities trapped by the alloying process; an alloy section (III) formed on the alloy section (II) and containing, by weight percent, 20-50% Al, 5-20% Si and, as a remainder, Fe and unavoidable impurities included by the alloying; an alloy section (IV) which is formed continuously or discontinuously on at least part of a surface of the alloy section (III) and contains, in weight percent, 30-60% Al and as a remainder Fe and unavoidable impurities included by the alloying, and wherein the proportion of the alloy section (III) exposed on an outermost surface of the aluminium alloy layer is 10% or more. [86] Hot-pressed part according to claim 85, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 15% or more. [87] Hot-pressed part according to any one of claims 85 to 86, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 20% or more. [88] Hot-pressed part according to any one of claims 85 to 87, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 47% or less. [89] Hot-pressed part according to any one of claims 85 to 88, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 35% or less. [90] Hot-pressed part according to any one of claims 85 to 89, wherein a plurality of pores are formed in the alloy section (III). [91] Hot-pressed part according to any one of claims 85 to 90, wherein a plurality of pores are formed in the alloy section (IV). [92] Hot-pressed part according to any one of claims 85 to 91, wherein the porosity of the alloy section (III) is 5-50%. [93] Hot-pressed part according to any one of claims 85 to 92, wherein the porosity of the alloy section (III) is 7-50%. [94] Hot-pressed part according to any one of claims 85 to 93, wherein the porosity of the alloy section (III) is 13.1% or less. [95] Hot-pressed part according to any one of claims 85 to 94, wherein the porosity of the alloy section (III) is 7.2% or less. [96] Hot-pressed part according to any one of claims 85 to 95, wherein the porosity of the alloy section (III) is 5.7% or less. [97] Hot-pressed part according to any one of claims 85 to 96, wherein the hardness of the alloy section (III) is less than the hardness of the alloy section (II). [98] Hot-pressed part according to any one of claims 85 to 97, wherein the hardness of alloy section (III) is less than the hardness of alloy section (IV). [99] Hot-pressed part according to any one of claims 85 to 98, wherein the hardness of alloy section (I) is less than the hardness of alloy section (II). [100] Hot-pressed part according to any one of claims 85 to 99, wherein the hardness of alloy section (I) is less than the hardness of alloy section (IV). [101] Hot-pressed part according to any one of claims 85 to 100, wherein the hardness of the alloy section (III) is 300-700 Hv. [102] Hot-pressed part according to any one of claims 85 to 101, wherein an oxide layer is formed on the aluminium alloy layer. [103] Hot-pressed part according to any one of claims 85 to 102, wherein the base steel sheet contains, by weight percent, 0.04 to 0.5% C, 0.01 to 2% Si, 0.1 to 5% Mn, 0.001 to 0.05% P, 0.0001 to 0.02% S, 0.001 to 1% Al, 0.001 to 0.02% N and, as a remainder, Fe and other impurities. [104] Hot-pressed part according to claim 103, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti. [105] Hot-pressed part according to claim 103, wherein the base steel sheet also contains, by weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti, as well as Fe and other impurities as the remainder, such that the sum equals 100% by weight. [106] Hot-pressed part comprising: a basic steel sheet; an aluminum alloy layer applied to the base steel sheet, and including the aluminium alloy layer: an alloy section (I) formed on the base steel sheet containing, by weight percent, 5-30% Al, 0-10% Si and as the remainder Fe and unavoidable impurities included by the alloying; an alloy section (II) formed on the alloy section (I) and containing, by weight percent, 30-60% Al, 0-5% Si and as the remainder Fe and unavoidable impurities included by the alloying; an alloy section (III) formed on the alloy section (II) and containing, by weight percent, 20-50% Al, 5-20% Si and, as a remainder, Fe and unavoidable impurities included by the alloying; an alloy section (IV) which is formed continuously or discontinuously on at least part of a surface of the alloy section (III) and contains, in weight percent, 30-60% Al, 0-5% Si and as a remainder Fe and unavoidable impurities included by the alloying, and wherein the proportion of the alloy section (III) exposed on an outermost surface of the aluminium alloy layer is 10% or more. [107] Hot-pressed part according to claim 106, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 15% or more. [108] Hot-pressed part according to any one of claims 106 to 107, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 20% or more. [109] Hot-pressed part according to any one of claims 106 to 108, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 47% or less. [110] Hot-pressed part according to any one of claims 106 to 109, wherein the proportion of the alloy section (III) exposed on the outermost surface of the aluminium alloy layer is 35% or less. [111] Hot-pressed part according to one of claims 106 to 110, wherein a plurality of pores are formed in the alloy section (III). [112] Hot-pressed part according to any one of claims 106 to 111, wherein a plurality of pores are formed in the alloy section (IV). [113] Hot-pressed part according to any one of claims 106 to 112, wherein the porosity of the alloy section (III) is 5-50%. [114] Hot-pressed part according to any one of claims 106 to 113, wherein the porosity of the alloy section (III) is 7-50%. [115] Hot-pressed part according to any one of claims 106 to 114, wherein the porosity of the alloy section (III) is 13.1% or less. [116] Hot-pressed part according to any one of claims 106 to 115, wherein the porosity of the alloy section (III) is 7.2% or less. [117] Hot-pressed part according to any one of claims 106 to 116, wherein the porosity of the alloy section (III) is 5.7% or less. [118] Hot-pressed part according to any one of claims 106 to 117, wherein the hardness of the alloy section (III) is less than the hardness of the alloy section (II). [119] Hot-pressed part according to any one of claims 106 to 118, wherein the hardness of alloy section (III) is less than the hardness of alloy section (IV). [120] Hot-pressed part according to any one of claims 106 to 119, wherein the hardness of alloy section (I) is less than the hardness of alloy section (II). [121] Hot-pressed part according to any one of claims 106 to 120, wherein the hardness of alloy section (I) is less than the hardness of alloy section (IV). [122] Hot-pressed part according to any one of claims 106 to 121, wherein the hardness of the alloy section (III) is 300-700 Hv. [123] Hot-pressed part according to any one of claims 106 to 122, wherein an oxide layer is formed on the aluminium alloy layer. [124] Hot-pressed part according to any one of claims 106 to 123, wherein the base steel sheet contains, by weight percent, 0.04 to 0.5% C, 0.01 to 2% Si, 0.1 to 5% Mn, 0.001 to 0.05% P, 0.0001 to 0.02% S, 0.001 to 1% Al, 0.001 to 0.02% N and, as a remainder, Fe and other impurities. [125] Hot-pressed part according to claim 124, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti. [126] Hot-pressed part according to claim 124, wherein the base steel sheet also contains, by weight percent, one or more of the following elements: 0.001-0.01% B, 0.01-1% Cr and 0.001-0.2% Ti, as well as Fe and other impurities as the remainder, such that the sum equals 100% by weight.

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