Coated steel sheet for hot pressing with excellent impact properties after hot pressing, hot-pressed part

Abstract

Hot-pressed molded part with excellent impact resistance properties, including: a basic steel sheet; and an alloy layer on a surface of the base steel sheet; where a ratio (C PS / C B ) of a C content (C PS ) of a component surface layer part to a C content (C B ) of the base steel sheet 1.2 or less, where a ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.8 or more, and where the component surface layer part refers to an area up to a depth of 25 µm from the surface of the base steel sheet, excluding the alloy layer.

Description

[Technical field]

[0001] The present disclosure relates to a coated steel sheet for hot press forming, which exhibits excellent impact resistance properties after hot press forming and can preferably be used for automotive parts requiring impact resistance, as well as to a hot press formed part. [State of the art]

[0002] In recent years, due to the depletion of petroleum resources and heightened environmental concerns, regulations aimed at improving the fuel efficiency of motor vehicles have become stricter. Reducing the thickness of steel sheets used in motor vehicles can be one way to improve fuel efficiency; however, this can also compromise vehicle safety. Therefore, in this case, improving the strength of the steel sheets should be prioritized.

[0003] Therefore, there is a constant demand for high-strength steel sheets, and various types of steel sheets have been developed. However, since these steel sheets inherently possess high strength, their workability is poor. Because the product of strength and elongation tends to have a constant value for each steel grade, increasing the strength of the steel sheet can lead to a problem: the elongation, an indicator of workability, decreases.

[0004] To solve this problem, a hot press forming process was proposed. Hot press forming is a process in which a low-temperature structure, such as martensite, is formed in a steel sheet by forming it at a high temperature suitable for the forming process, followed by quenching the steel sheet at a low temperature, resulting in a final product with low thermal strength. The advantage of this method is that the problem of processability in the production of a high-strength component can be minimized.

[0005] A typical technology for such a hot-press formed part is described in Patent Document 1. In Patent Document 1, an Al-Si coated steel sheet is heated to 850°C or higher, hot-rolled, formed by pressing, and then quenched to create a martensitic structure, achieving an ultra-high tensile strength of more than 1600 MPa. Ensuring such ultra-high tensile strength facilitates the production of lightweight vehicles. However, according to Patent Document 1, the impact resistance properties are relatively low due to the high strength, and a phenomenon occurs where, in some cases, depending on the hot-press forming conditions, etc., unusually low impact resistance properties are observed.

[0006] Accordingly, Patent Document 2 proposes a technique for improving the impact strength properties after hot pressing by spheroidizing inclusions through adjustment of the Ca / S ratio and refining the grains by adding an alloying element such as niobium (Nb) to a steel for hot pressing. However, Patent Document 2 relates to controlling inclusions and grain size to improve the notched impact toughness of general steel materials and is considered difficult to apply as a means of improving the low impact strength that occurs during actual hot pressing.

[0007] Therefore, there is a need for the development of a clad or coated steel sheet for hot pressing that exhibits excellent impact properties after hot pressing, as well as a hot pressing part.

[0008] (Patent 1) US Patent Publication No. 6296805

[0009] (Patent 2) Korean Publication No. 10-2010-0047011 [Technical problem]

[0010] One aspect of the present disclosure may provide a plated or coated steel sheet for hot pressing with excellent impact resistance properties after hot pressing and a hot pressing formed part therefor.

[0011] The technical problem of the present disclosure is not limited to the aforementioned points. Additional problems of the present disclosure are described in the overall content of the disclosure, and those who possess ordinary expertise in the field to which the present disclosure relates will have no difficulty understanding the additional problems of the present disclosure based on the content described in the disclosure of the present disclosure. [Technical solution]

[0012] According to one aspect of the present disclosure, a clad or coated steel sheet for hot pressing with excellent impact strength properties after hot pressing comprises: a base steel sheet having, in wt.%: 0.15% to 0.4% carbon (C), 0.1% to 1% silicon (Si), 0.6% to 8% manganese (Mn), 0.001% to 0.05% phosphorus (P), 0.0001% to 0.02% sulfur (S), 0.01% to 0.1% aluminum (Al), 0.001% to 0.02% nitrogen (N), 0.01% to 0.5% chromium (Cr), and, as a remainder, Fe and other impurities; and an alloy plating layer formed of zinc, aluminum, or alloys thereof on a surface of the base steel sheet, wherein a ratio (C S / C B ) of a C content (C S ) of a surface layer part to a C content (C B ) of the base steel sheet is 0.6 or less, and a ratio ((Mn S +Cr S ) / (MnB +Cr B )) of the sum (Mn S +Cr S ) the Mn and Cr contents of the surface layer part to the sum (Mn S +Cr S ) the Mn and Cr content of the base steel sheet is 0.8 or more, wherein the surface layer portion refers to an area up to a depth of 15 µm from the surface of the base steel sheet excluding the plating layer.

[0013] The base steel sheet may also contain 0.0005 to 0.01 wt% boron (B) and 0.01 to 0.05 wt% titanium (Ti) or more.

[0014] The microstructure of the base steel sheet can contain, based on the area fraction, 40% to 100% ferrite and a remainder of 0% to 60% pearlite, bainite or martensite in the surface layer part and 30% to 90% ferrite and a remainder of 10% to 70% pearlite, bainite or martensite in a central part thereof.

[0015] According to another aspect of the present disclosure, a hot press formed member with excellent impact resistance comprises: a base steel sheet containing, in wt.%, 0.15% to 0.4% carbon (C), 0.1% to 1% silicon (Si), 0.6% to 8% manganese (Mn), 0.001% to 0.05% phosphorus (P), 0.0001% to 0.02% sulfur (S), 0.01% to 0.1% aluminum (Al), 0.001% to 0.02% nitrogen (N), 0.01% to 0.5% chromium (Cr), with Fe and other impurities as the remainder; and an alloyed cladding layer formed from a zinc- or aluminum-containing alloy on a surface of the base steel sheet, wherein the ratio (C PS / C B ) of the C content (C PS ) of a component surface layer to the C content (C B ) of the base steel sheet is 1.2 or less, and a ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr PS) the Mn and Cr contents of the component surface layer section to the sum (Mn S +Cr S ) the Mn and Cr content of the base steel sheet is 0.8 or more, wherein the component surface layer refers to an area up to a depth of 25 µm from the surface of the base steel sheet excluding the alloy coating layer.

[0016] The ferrite coverage at a martensitic grain boundary of the surface layer part of the component can be 30% or less.

[0017] According to another aspect of the present disclosure, a method for producing a clad steel sheet for hot pressing which exhibits excellent impact strength properties after hot pressing comprises: producing a slab which in wt.-% 0.15% to 0.4% carbon (C), 0.1% to 1% silicon (Si), 0.6% to 8% manganese (Mn), 0.001% to 0.05% phosphorus (P), 0.0001% to 0.02% sulfur (S), 0.01% to 0.1% aluminum (Al), 0.001% to 0.02% nitrogen (N), 0.01% to 0.5% chromium (Cr), and containing Fe and other impurities as the remainder, and heating the slab to a temperature of 1050°C to 1300°C; hot rolling of the heated slab in a hot finishing temperature range of 800°C to 950°C to obtain a hot-rolled steel sheet; Annealing of the hot-rolled steel sheet at 450°C to 750°C after hot finishing rolling is complete; annealing of the coiled hot-rolled steel sheet by heating to 740°C to 860°C under an atmosphere in which the dew point temperature is -10°C to 30°C for 10 to 600 seconds; and immersion of the hot-rolled steel sheet after annealing in a plating bath formed of zinc, aluminum or their alloys to carry out plating.

[0018] The process may further include: cold rolling the hot-rolled steel sheet before it is wound up after hot rolling to obtain cold-rolled steel sheet.

[0019] The slab may also contain 0.00005 to 0.01 wt% boron (B) and 0.01 to 0.05 wt% titanium (Ti) or more.

[0020] According to another aspect of the present disclosure, a method for producing a hot-press formed part with excellent impact resistance properties comprises the following steps: heat treatment of the clad steel sheet for hot pressing, produced by the above-described method for producing a clad steel sheet for hot pressing with excellent impact resistance properties after hot pressing, in a temperature range of Ac3 to 950°C for 1 to 15 minutes; and subsequent performance of the hot pressing. [Beneficial effects]

[0021] According to the present disclosure, a clad steel sheet for hot pressing (forming) can be provided which has excellent impact resistance properties after hot pressing (forming).

[0022] The hot-pressed part, produced by hot-pressing a clad steel sheet for hot-pressing according to the present disclosure, has a bending angle of 60° or more, measured by a VDA238-100 bending test at a tensile strength of 1500 MPa, thereby ensuring excellent impact resistance properties.

[0023] Various and advantageous benefits and effects of the present disclosure are not limited to the above disclosure and will become more easily understood in the course of disclosing specific embodiments of the present disclosure. [Description of the drawings] Fig.1 is the result of an analysis of the concentration of carbon (C), manganese (Mn) and chromium (Cr) in a depth direction of a surface layer part using a GDS prior to hot pressing for the clad steel sheet for hot pressing of Invention Example 1. Fig. Figure 2 is a light microscope photograph showing the structure of a surface layer part of an element after hot pressing of the inventive example 1. Fig. 3 is the result of an analysis of the concentration of carbon (C), manganese (Mn) and chromium (Cr) in a depth direction of a surface layer part using a GDS prior to hot pressing for the clad steel sheet for hot pressing of comparative example 1. Fig. Figure 4 is a light microscope photograph showing the structure of the surface layer part of the element after hot pressing of the comparative example 3. [Preferred examples]

[0024] The following are examples of embodiments of the present disclosure. However, these embodiments can be modified in various other ways, and the scope of the present disclosure is not limited to the embodiments described below. Furthermore, examples of embodiments of the present disclosure are given to explain the present disclosure more fully to persons with average technical knowledge.

[0025] The inventors of the present application found that the bending angle of an uncoated material after hot pressing is significantly better than that of a coated material. Further investigations confirmed that, in the case of uncoated materials, decarburization occurred in a surface layer of a steel sheet during heating for hot pressing, resulting in the formation of a soft ferrite layer on that surface layer and thus leading to excellent bending properties.

[0026] The inventors focused on the idea that the bendability of a hot-pressed (construction) component could be improved by forming a soft layer on the surface layer of the base steel sheet, thereby reducing the carbon content of the surface layer in clad materials. However, it was found that forming a soft ferrite layer in clad materials is difficult, as it is in unclad materials. This is because decarburization during the heating process for hot pressing does not occur to the same extent as in unclad materials, and if the ferrite layer is not consistently formed to a sufficient degree, the bendability is more likely to be impaired.

[0027] The present inventors investigated further in order to overcome the problem and completed the present disclosure after confirming that a clad steel sheet for hot pressing with excellent impact-resistant properties after hot pressing and a hot pressing part can be provided by adjusting a C content in a surface layer part of the base steel sheet to a value below a predetermined level compared to a C content in a middle part of the base steel sheet and controlling the sum of the contents of Mn and Cr in the surface layer part of the base steel sheet to a level above a predetermined level compared to the sum of the contents of Mn and Cr in the middle part by controlling the annealing conditions.

[0028] Below, a clad steel sheet for hot pressing and a hot pressing-formed (construction) part with excellent impact resistance properties after hot pressing are described in detail according to one aspect of the present disclosure.

[0029] Coated steel sheet for hot pressing with excellent impact resistance properties after hot pressing

[0030] A clad steel sheet for hot pressing with excellent impact strength properties after hot pressing, according to one aspect of the present disclosure, comprises: a base steel sheet having, in wt.%, 0.15% to 0.4% carbon (C), 0.1% to 1% silicon (Si), 0.6% to 8% manganese (Mn), 0.001% to 0.05% phosphorus (P), 0.0001% to 0.02% sulfur (S), 0.01% to 0.1% aluminum (Al), 0.001% to 0.02% nitrogen (N), 0.01% to 0.5% chromium (Cr), and, as a remainder, iron (Fe) and other impurities; and a cladding layer formed of zinc, aluminum, or alloys thereof on a surface of the base steel sheet, wherein a ratio (C S / C B ) of a C content (C S ) of a surface layer part to a C content (C B ) of the base steel sheet is 0.6 or less, and a ratio ((Mn S +Cr S ) / (Mn S +Cr S )) of the sum (Mn S +Cr S) the Mn and Cr contents of the surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.8 or more.

[0031] First, the alloy composition of a base steel sheet as defined in this disclosure is described in detail. It should be noted that, unless otherwise specified, the content of the individual elements in this disclosure refers to weight percent (wt%).

[0032] C: 0.15% to 0.4%

[0033] Carbon is an essential element for increasing the strength of a hot-pressed part. If the carbon content is less than 0.15%, it can be difficult to achieve sufficient strength. Conversely, if the carbon content is more than 0.4%, the strength of the hot-rolled material is too high when cold-rolled, so that the cold-rolling properties can be significantly worse and weldability can be considerably restricted. Therefore, in the present disclosure, the carbon content can be limited to 0.15% to 0.4%.

[0034] Si: 0.1% to 1%

[0035] Silicon (Si), added as a deoxidizing agent during steel production, strengthens solid solutions and prevents carbide formation. Furthermore, Si contributes to increased strength of hot-pressed parts and ensures material uniformity. If the Si content is less than 0.1%, the aforementioned effects are insufficient. If the Si content exceeds 1%, the properties of aluminum coatings can be significantly impaired by silicon oxide forming on the surface of the steel sheet during annealing. Therefore, in this disclosure, the Si content can be limited to 0.1% to 1%.

[0036] Mn: 0.6% to 8%

[0037] Manganese (Mn) is an element added to ensure a work hardening effect in solid solutions and to lower the critical cooling rate required to secure martensite in the hot-pressed part. To achieve the aforementioned effect, Mn must be added in an amount of 0.6% or more. However, if the Mn content exceeds 8%, the cold-rolling properties may be reduced due to increased strength of the steel sheet prior to hot pressing, the cost of the ferroalloy may increase, and weldability may be impaired. Therefore, in this disclosure, the Mn content can be limited to 0.6% to 8%.

[0038] P: 0.001% to 0.05%

[0039] Phosphorus (P) is present as an impurity in steel, and a lower content is advantageous. Accordingly, in the present disclosure, the P content can be limited to 0.05% or less, and preferably to 0.03% or less. Since a lower P content is advantageous, it is not necessary to specify a particular lower limit for the content. However, an excessive reduction in the P content can lead to an increase in production costs, which is why the lower limit of the P content can be set at 0.001%.

[0040] S: 0.0001% to 0.02%

[0041] Sulfur (S) is an impurity in steel and an element that impairs the ductility, impact strength, and weldability of the component. Therefore, the maximum S content is limited to 0.02% and preferably to 0.01% or less. Furthermore, manufacturing costs can increase if the minimum S content is less than 0.0001%, so a lower limit for the S content can be set at 0.0001%.

[0042] Al: 0.01% to 0.1%

[0043] Aluminum can increase the purity of the steel by deoxidizing it together with silicon. 0.01% or more of aluminum can be added to achieve the aforementioned effect. However, if the aluminum content exceeds 0.1%, the high-temperature ductility may deteriorate due to excessive AlN formed during the casting process, leading to cracking in the slab. Therefore, an upper limit for the content of 0.1% or less may be established. In the present disclosure, the aluminum content is therefore preferably between 0.01% and 0.1%.

[0044] N: 0.001% to 0.02%

[0045] Nitrogen (N) is an element present as an impurity in steel. At an N content exceeding 0.02%, high-temperature ductility can deteriorate due to excessive AlN formation during the casting process, leading to slab cracking. To reduce the susceptibility to cracking during continuous slab casting and to ensure impact toughness, the N content can therefore be 0.02% or less. A lower limit cannot be explicitly specified, but considering the potential increase in production costs, the lower limit for the N content can be set at 0.001% or more. Therefore, within the scope of this disclosure, the N content is preferably between 0.001% and 0.02%.

[0046] Cr: 0.01% to 0.5%

[0047] Cr is an element added to enhance the effects of solid solution strengthening and hardenability during hot pressing, similar to Mn, and can be added in amounts of 0.01% or more to achieve the aforementioned effect. However, if the Mn content exceeds 0.5%, while hardenability may be adequately ensured, the properties may become saturated, and the cost of producing the steel sheet may increase. Therefore, the Cr content in the present disclosure is preferably 0.01% to 0.5%.

[0048] The base steel sheet of the clad steel sheet for hot pressing according to one aspect of the present disclosure may, in addition to the aforementioned components, contain one or more of 0.0005% to 0.01% boron (B) and 0.01% to 0.05% titanium (Ti).

[0049] B: 0.0005% to 0.01%

[0050] B is an element that improves hardenability even at small addition levels and segregates along the grain boundaries of the pre-tenite to suppress embrittlement of the hot-pressed part due to grain boundary segregation of P and / or S. It can be added in an amount of 0.0005% or more to achieve the aforementioned effect. However, if the B content exceeds 0.01%, the effect is saturated and embrittlement occurs during hot rolling. Therefore, an upper limit for the B content can be set at 0.01%, and preferably, the B content can be set at 0.005% or less. In the present disclosure, the B content is therefore preferably 0.0005% to 0.01%.

[0051] Ti: 0.01% to 0.05%

[0052] Titanium is added to combine with the nitrogen remaining as an impurity in the steel to form TiN, thereby maintaining the solid solution B, which is essential for ensuring hardenability. If the titanium content is less than 0.01%, it can be difficult to sufficiently achieve the aforementioned effect, and if the titanium content is more than 0.05%, the properties may become saturated and the cost of producing the steel sheet increases. Therefore, in the present disclosure, the titanium content is preferably between 0.01% and 0.05%.

[0053] The remainder, apart from the components mentioned above, is iron (Fe), and the addition of any other component is not limited as long as it can be contained within the steel sheet used for hot pressing. Furthermore, in a general manufacturing process, unintentional impurities originating from raw materials or the environment may inevitably be introduced, which cannot be ruled out. Since these impurities are known to those skilled in the art in the manufacturing process, they are not explicitly mentioned in this disclosure.

[0054] The clad steel sheet for hot pressing, exhibiting excellent impact resistance properties after hot pressing according to one aspect of the present disclosure, comprises a cladding layer of zinc, aluminum, or their alloys formed on a surface of the base steel sheet. The cladding layer imparts corrosion resistance to the component in its final part and serves to prevent decarburization and scaling of the base steel sheet during heating for hot pressing.

[0055] In the present disclosure, the type of plating layer is not particularly limited, and any plating layer applied to a steel sheet for hot pressing dies from the related prior art may be used without restriction in the present disclosure. In a non-restrictive embodiment, the plating layer may consist of zinc, aluminum, or alloys thereof, and in particular, the plating layer may be a hot-dip galvanized layer, an electrogalvanized layer, a zinc alloy plating layer, an aluminum plating layer, or an aluminum alloy plating layer.

[0056] According to one aspect of the present disclosure, the plating layer may contain components that may be present during the manufacturing process in an area that does not affect the purpose of the present disclosure, and in particular may contain other unavoidable impurities.

[0057] Furthermore, the coating thickness can range from 5µm to 100µm. If the coating thickness is less than 5µm, it can be difficult to achieve sufficient corrosion resistance in the hot-pressed part, and if the thickness is more than 100µm, the heating time for hot pressing can be excessively extended, and the manufacturing costs can be excessively increased for the sake of the improved corrosion resistance.

[0058] Meanwhile, in the case of the clad steel sheet for hot pressing dies according to the present disclosure, the ratio (C) is S / C B) of the C content (C S ) of a surface layer section to a C content (C B ) of the base steel sheet (hereinafter referred to as "ratio (C) S / C B )“ denotes) 0.6 or less. The surface layer area refers to a region from the surface of the base steel sheet without the plating layer down to a depth of 15 µm.

[0059] Furthermore, according to one aspect of the present disclosure, the ratio (C) in the clad steel sheet for hot pressing can be B / C S ) of the C content (C S ) of the surface layer part to the C content (C B ) of the base steel sheet preferably 0.5 or less, more preferably 0.4 or less and most preferably 0.35 or less.

[0060] If the ratio (C S / C BIf the ratio (C) is set to less than 0.6, a relatively soft martensite phase with a low carbon content can form in the surface layer portion, in contrast to the hard martensite phase that forms in the center of the base steel sheet after hot pressing. Since the soft martensite phase forms on the surface layer portion of the coated steel sheet, the hardness of the surface layer portion decreases, thus ensuring excellent bending properties. If the ratio (C) S / C B If the ratio exceeds 0.6, it can be difficult to achieve the effect of improving flexural strength through softening of the surface layer after hot pressing. A lower limit of the ratio (C S / C B) cannot be particularly limited. However, if the carbon content in the surface layer is too low, the element's strength may decrease, or its fatigue properties may be worse after hot pressing, so the lower limit of the ratio (C) S / C B ) can be set to 0.05 or more, but is not limited to that.

[0061] Furthermore, in the case of the clad steel sheet for hot pressing, according to one aspect of the present disclosure, a ratio ((Mn) can be achieved. S +Cr S ) / (Mn B +Cr B )) of the sum (Mn S +Cr S ) the Mn and Cr contents of the surface layer part to the sum (Mn B +Cr B ) the Mn and Cr contents of the base steel sheet (hereinafter referred to as “(ratio (Mn S +Cr S ) / (Mn B +Cr B))“ denotes) 0.8 or more. Here, the surface layer fraction refers to an area from the surface of the base steel sheet without the plating layer down to a depth of 15 µm.

[0062] According to one aspect of the present revelation, the relationship ((Mn) can be S +Cr S ) / (Mn B +Cr B )) of the sum (Mn S +Cr S ) the Mn and Cr contents of the surface layer part to sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is preferably 0.85 or more, and more preferably 0.87 or more.

[0063] If the ratio ((Mn S +Cr S ) / (Mn B +Cr BIf the π is less than 0.8, the hardenability of the surface layer portion during hot pressing may be insufficient, so that ferrite can form partially on the surface of the element. Since ferrite that forms partially at the hard martensitic grain boundary significantly impairs the flexural strength, the ratio ((Mn S +Cr S ) / (Mn B +Cr B )) preferably 0.8 or more. The upper limit of the ratio ((Mn S +Cr S ) / (Mn B +Cr B The ratio ()) does not need to be limited, but if the Mn and Cr contents in the surface layer are too high, the hardness of the surface layer after hot pressing may increase and the flexibility may worsen. Therefore, the upper limit of the ratio ((Mn) S +Cr S ) / (Mn B +Cr B )) 2 or less, but is not limited to that.

[0064] The microstructure of the base steel sheet does not need to be particularly restricted. However, the microstructure of the surface layer portion of the base steel sheet can contain 40% to 100% ferrite and a remainder of 0% to 60% pearlite, bainite, or martensite. Furthermore, the microstructure of a central portion of the base steel can contain 30% to 90% ferrite and a remainder of 10% to 70% pearlite, bainite, or martensite.

[0065] Hot-pressed (construction) component with excellent impact resistance properties.

[0066] In the meantime, a hot-press formed (construction) part with excellent impact resistance properties can be produced by heat-treating the coated steel sheet for hot pressing with the above-mentioned configuration in a temperature range of Ac3 to 950°C for 1 to 15 minutes and then carrying out the hot pressing on it.

[0067] A hot-pressed part with excellent impact resistance properties according to one aspect of the present disclosure comprises a base steel sheet with the same alloy composition as that of the base steel sheet of the coated or clad steel sheet and an alloyed cladding layer formed from a zinc or aluminum-enclosing alloy on a surface of the base steel sheet, wherein a ratio (C PS / C B ) of a C content (C PS ) of a component surface layer part to a C content (C B ) of the base steel sheet is 1.2 or less, and a ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr PS ) the Mn and Cr content of the (construction) part surface layer portion or surface layer portion of the (construction) part (member surface layer portion) to the sum (Mn S +Cr S) the Mn and Cr content of the base steel sheet (hereinafter referred to as the “ratio ((Mn-+Cr) PS ) / (Mn B +Cr B ))“) is 0.8 or more. Here, the part of the surface layer refers to an area from the surface of the base steel sheet without the alloy layer down to a depth of 25 µm.

[0068] Meanwhile, according to one aspect of the present disclosure, the ratio (C) in the hot-pressed part can be PS / C B ) of the C content (C PS ) of the surface layer part of the (construction) part to the C content (C B ) of the base steel sheet preferably 1.1 or less, and more preferably 1.05 or less.

[0069] Furthermore, according to one aspect of the present disclosure, the ratio ((Mn) can be found in the hot-pressed part. PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr PS) of the Mn and Cr content of the component surface layer part to the sum (Mn S +Cr S ) of the Mn and er content of the base steel sheet preferably 0.9 or more, and more preferably 0.93 or more.

[0070] When the clad steel sheet is heated for hot pressing, the thickness of the cladding layer generally increases because the cladding layer and the base iron are alloyed, and because the cladding layer has a very low solubility of C, C that was not dissolved during the alloying process is concentrated in the surface layer part, thus increasing the C content of the surface layer part, and the high C content of the surface layer part increases the hardness of the surface layer part and worsens the bendability.

[0071] In the production of a hot-pressed part by hot-pressing the coated steel sheet for hot-pressing according to one aspect of the present disclosure, the ratio (C) is PS / C B ) of the C content (C PS ) of the surface layer part of the (construction) part to C content (C B ) of the base steel sheet 1.2 or less, so that an excessive increase in the hardness of the surface layer of the molded part can be prevented, even if C is concentrated in the surface region of the molded part. Furthermore, since the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr PS ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B) the Mn and Cr content of the base steel sheet is 0.8 or more, the hardenability is sufficient and thus the formation of ferrite can be prevented, so that the ferrite coverage rate at the martensitic grain boundary in the surface layer part of the component (area occupied by ferrite in the martensitic grain boundary when a cross-section is observed) can be 30% or less, and as a result excellent bendability with sufficient strength can be ensured.

[0072] Since, as described above, the hot-pressed part, according to one aspect of the present disclosure, has a ratio (C S / C B ) of 1.2 or less and the ratio ((Mn PS +Cr PS ) / (Mn S +Cr SIf the requirement of 0.8 or more is met, the bending angle measured in a VDA 238-100 bending test at a tensile strength of 1500 MPa will be 60° or more, thus ensuring excellent impact resistance properties. However, if the tensile strength increases, e.g., if the tensile strength of the hot-pressed part is 1800 MPa or more, the bending angle criterion for determining excellent impact resistance properties can be lowered.

[0073] Next, an illustrative, unclaimed method for producing a clad steel sheet for hot pressing and a hot pressing-formed part with excellent impact resistance properties after hot pressing is described in detail.

[0074] Method for producing a clad steel sheet for hot pressing with excellent impact resistance properties after hot pressing

[0075] A method for producing a clad steel sheet for hot pressing with excellent impact strength properties after hot pressing, according to another aspect of the present disclosure, comprises heating a slab satisfying the above-mentioned alloy composition to 1050°C to 1300°C; hot finish rolling the heated slab in a temperature range of 800°C to 950°C to obtain a hot-rolled steel sheet; annealing the hot-rolled steel sheet at 450°C to 750°C after completion of the hot finish rolling; annealing the coiled hot-rolled steel sheet by heating it to 740°C to 860°C under an atmosphere in which the dew point temperature is -10°C to 30°C for 10 to 600 seconds; and the immersion of the annealed hot-rolled steel sheet into a plating bath made of zinc, aluminium or their alloys to carry out the plating. Step of the slab heating

[0076] First, the slab, which corresponds to the aforementioned alloy composition, is heated to between 1050°C and 1300°C. If the heating temperature of the slab is below 1050°C, it can be difficult to homogenize the slab structure, and if the temperature exceeds 1300°C, an excessive oxide layer can form. step of hot rolling

[0077] The heated slab is hot-rolled to a final temperature of 800°C to 950°C to produce a hot-rolled steel sheet. If the final hot-rolling temperature is below 800°C, controlling the shape of the sheet can be difficult because a duplex grain structure develops in the surface layer of the steel sheet due to rolling in two-phase zones, and if the temperature exceeds 950°C, the grains become coarse. Cooling and coiling step

[0078] After completion of the hot rolling process, the hot-rolled steel sheet is coiled at temperatures between 450°C and 750°C. At coiling temperatures below 450°C, material variations in width increase, leading to strip breakage and shape defects during cold rolling. Conversely, if the coiling temperature exceeds 750°C, the carbides become coarse, resulting in reduced bendability. step of cold rolling

[0079] If necessary, a further step in the production of cold-rolled steel sheet can be carried out before annealing by cold rolling the coiled hot-rolled steel sheet. Cold rolling serves to more precisely control the thickness of the steel sheet, and annealing and cladding can be carried out directly without cold rolling. In this case, cold rolling can be performed with a reduction rate of 30% to 80%. Step of glowing

[0080] Annealing is carried out for 10 to 600 seconds under an atmosphere with a dew point temperature of -10 to 30°C by heating the coiled hot-rolled steel sheet to 740°C to 860°C. If the annealing temperature is less than 740°C or the annealing time is less than 10 seconds, the microstructure may not recrystallize sufficiently, resulting in poor sheet form, or the post-coating strength may be too high, potentially leading to tool wear during the stamping process. Furthermore, carbon diffusion during annealing is insufficient, making it difficult to determine the carbon-to-carbon ratio. S / C B ) of the C content (C S ) of the surface layer part to the C content (C B) of the base steel sheet to ensure a ratio of 0.6 or less. If the annealing temperature exceeds 860°C or the annealing time exceeds 600 seconds, a large amount of annealing oxide can form on the surface of the steel sheet during annealing, leading to coating delamination or deterioration of coating adhesion. Furthermore, Mn, Cr, etc., form in the base steel sheet at an interface between the coating layer and the base steel sheet or at a grain boundary of the base steel sheet, making it difficult to achieve a ratio of 0.8 or greater than the ratio ((Mn ) S +Cr S ) / (Mn B +Cr B )) of the sum (Mn S +Cr S ) the Mn and Cr contents of the surface layer part to the sum (Mn B +Cr B) the levels of Mn and Cr in the base steel sheet, which leads to a lack of hardenability of the surface layer part, and accordingly, ferrite may partially form in the surface layer part after hot pressing, which impairs the flexibility.

[0081] In the present disclosure, it is very important to control the dew point temperature of the annealing atmosphere in order to control the ratio of the C, Mn, and Cr contents in the surface layer to the base material component of the base steel sheet. If the dew point temperature of the annealing atmosphere is less than -10°C, the decarburization reaction may be insufficient, and the effect on the improved ductility may be negligible. Conversely, if the dew point temperature exceeds 30°C, the hardenability of the surface layer may decrease due to excessive internal oxidation, leading to partial ferrite formation and impairing the bending ability.

[0082] Furthermore, according to one aspect of the present disclosure, annealing can be carried out for 10 to 100 seconds under an atmosphere in which the dew point temperature is 10 to 30°C by heating the wound hot-rolled steel sheet to 800 to 840°C (800-840°C). step of the coating

[0083] After annealing, the annealed hot-rolled steel sheet is immersed in a coating bath of zinc, aluminum, or alloys thereof for coating. In the present disclosure, the components of the coating bath used in forming the coating layer are not specifically limited. However, as a non-limiting example, the coating bath used in the present disclosure may consist of zinc, a zinc alloy, aluminum, or an aluminum alloy. Furthermore, the coating conditions can be applied without restriction to the present disclosure, provided that the coating conditions are commonly applied to hot-pressed steel sheets and are therefore not specifically mentioned in the present disclosure.Furthermore, according to one aspect of the present disclosure, the coating bath may contain other unavoidable impurities, and the zinc alloy and the aluminum alloy may also contain components that are commonly found in an area that does not affect the subject matter of the present disclosure, and in particular, other unavoidable impurities.

[0084] Method for producing a hot-pressed part with excellent impact resistance properties

[0085] A hot-pressed part with excellent impact strength properties can be produced by hot-pressing the clad steel sheet for hot-pressing, which is manufactured by the manufacturing process described above in this disclosure. The hot-pressing can be carried out according to a generally accepted method. However, as a non-limiting example, the clad steel sheet for hot-pressing can be heat-treated in a temperature range of Ac3 to 950°C for 1 to 15 minutes and then pressed to perform the hot-pressing. [Examples of implementation]

[0086] The present disclosure is described in more detail below by means of examples. However, it should be noted that the following examples serve only for illustration and are not intended to limit the scope of this disclosure. This is because the scope of this disclosure is determined by the facts described in the claims and the facts derived therefrom. (Example)

[0087] First, a slab with the alloy composition shown in Table 1 was produced, heated, hot-rolled, and wound under the manufacturing conditions shown in Table 2 to produce a hot-rolled steel sheet. Then, the produced steel sheet was processed under the conditions shown in Table 2. Fig. The parts were annealed under the annealing conditions shown in section 2 and then immersed in a galvanizing bath, and then the coating was applied such that the coating quantity per side was 70 g / m². 2fraud in order to produce a coated steel sheet. [Table 1] Classification C Si Mn P S Al N Cr Ti B Steel A 0,21 0,25 1,3 0,01 0,002 0,035 0,005 0,22 0,03 0,0022 Steel B 0,2 0,1 2,5 0,009 0,001 0,03 0,004 0,1 - - [Table 2] Classification Steel grade Slab heating temperature (°C) Final temperature during hot rolling (°C) Temperature during glowing (°C) Glowing condition Heating temperature (°C) Holding time (sec.) Dew point temperature (°C) IE 1 A 1250 900 560 820 42 15 IE2 B 1200 880 500 800 65 10 CE 1 A 1250 900 560 820 42 -15 CE 2 A 1250 900 560 700 45 10 CE 3 B 1200 880 500 800 65 40 CE 4 B 1200 880 500 870 620 15 IE*: Invention example CE*: Comparison example

[0088] For the clad steel sheets of the invention examples and the comparative examples, which were produced according to the manufacturing conditions mentioned above, the concentrations of carbon (C), manganese (Mn), and chromium (Cr) were analyzed to a sufficient depth from a surface layer using a glow discharge spectrometer (GDS) (GDS 850A from USA LECO) capable of quantitatively analyzing various components. An average content for an area corresponding to a portion of the surface layer was analyzed from the GDS results by integration, and the results are presented in Table 3 below.In general, GDS analysis is performed in the depth direction over a circular area of ​​2 mm to 6 mm, so it can be difficult to determine an exact interface between the coating and the base steel sheet in the form of a concentration profile for the depth direction, but in the present disclosure a point where the Zn content was 1% was defined as the interface between the coating and the base steel sheet based on various optical and SEM analysis results, etc. [Table 3] Classification Steel grade C B C S Ratio (Cs / CB) Mn B +Cr B Mn S +Cr S ratio ((Mn S +Cr S ) / (Mn B +Cr B )) IE1 A 0,21 0,03 0,14 1,52 1,32 0,87 IE 2 B 0,2 0,07 0,35 2,6 2,43 0,93 CE 1 A 0,21 0,2 0,95 1,52 1,49 0,98 CE 2 A 0,21 0,19 0,90 1,52 1,5 0,99 CE 3 B 0,2 0,02 0,10 2,6 1,74 0,67 CE 4 B 0,2 0,01 0,05 2,6 1,52 0,58 IE*: Invention example CE*: Comparison example

[0089] Furthermore, a hot-press formed part was produced by hot pressing the coated steel sheets of the examples according to the invention and the comparative examples under the conditions described in Table 4. Tensile and bending tests (VDA 238-100) were carried out by taking a sample from a flat section of the produced hot-press formed part. The concentration analysis of C, Mn, and Cr was performed by GDS analysis in the depth direction, and the degree of ferrite coverage at a martensitic grain boundary of a portion of the surface layer of a component was evaluated by observing a cross-section with an optical microscope. The results are summarized in Table 4. [Table 4] classification State of hot pressing ratio (C PS / C B ) ratio (Mn PS +Cr PS ) / (Mn B +Cr B )) Detection range: Ferrite content (%) Tensile strength (MPa) Bending angle (degrees) Heating temperature (°C) Heating time (min.) IE 1 900 6 0, 95 0,93 0,5 1502 72 IE 2 930 5 1,05 0,97 2,7 1527 67 CE 1 930 5 1,52 0,98 0,2 1508 53 CE 2 900 6 1,29 0,99 1,3 1511 51 CE 3 900 6 0,9 0,76 36 1478 42 CE 4 930 5 0,88 0,65 48 1427 47 IE*: Invention example CE*: Comparison example

[0090] The clad steel sheets of Invention Examples 1 and 2, produced according to the conditions of the present disclosure, met a ratio (C S / C B) of 0.6 or less and a ratio ((Mn S +Cr S ) / (Mn B +Cr B )) of 0.8 or more. Accordingly, the hot-pressed part produced by hot-pressing the clad steel sheets of Invention Examples 1 and 2 fulfills a ratio (C PS / C B ) of 1.2 or less and a ratio ((Mn PS +Cr PS ) / (Mn S +Cr S )) of 0.8 or more, and accordingly the ferrite coverage at the martensitic grain boundary of the surface layer part was 30% or less, and the bending angle was 60° or more at a tensile strength of 1500 MPa, indicating good bending properties.

[0091] Comparative example 1 is a case in which the dew point temperature during annealing was less than -10°C, and comparative example 2 is a case in which the heating temperature was not reached during annealing. In both comparative examples 1 and 2, the ratio (C S / C B ) of the coated steel sheet was above 0.6, and accordingly the ratio (C PS / C B ) in the hot-pressed part also exceeded 1.2, which led to poor bending properties.

[0092] Comparison example 3 is a case in which the dew point temperature exceeded 30°C during annealing, and comparison example 4 is a case in which the annealing was excessive. In both comparison examples 3 and 4, a ratio (C S / C B ) the coated steel sheets the conditions of the present disclosure, but the ratio ((Mn S +Cr S ) / (Mn B CrB )) was less than 0.8 and the ratio ((Mn PS +Cr PS ) / (Mn S +Cr S The )) of the hot-pressed part was less than 0.8. As a result, the ferrite content at the martensitic grain boundary of the surface layer of the component exceeded 30%, and the tensile strength was relatively low compared to the other examples, and the flexibility was also severely impaired.

[0093] Although exemplary embodiments of the present disclosure have been shown and described, it will be obvious to the person skilled in the art that modifications and variations can be made without deviating from the scope of the present invention. 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] KR 10-2010-0047011

[0009]

Claims

[1] Hot-pressed part with excellent impact resistance properties, comprising: a basic steel sheet; and an alloy layer on a surface of the base steel sheet; where a ratio (C PS / C B ) of a C content (C PS ) of a component surface layer part to a C content (C B ) of the base steel sheet is 1.2 or less, where a ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.8 or more, and where the component surface layer part refers to an area up to a depth of 25 µm from the surface of the base steel sheet, excluding the alloy layer. [2] Hot-pressed part according to claim 1, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 1.1 or less. [3] Hot-pressed part according to one of claims 1 to 2, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 1.05 or less. [4] Hot-pressed part according to any one of claims 1 to 3, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 0.95 or less. [5] Hot-pressed part according to any one of claims 1 to 4, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.9 or more. [6] Hot-pressed part according to any one of claims 1 to 5, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.93 or more. [7] Hot-pressed part according to any one of claims 1 to 6, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.97 or more. [8] Hot-pressed part according to any one of claims 1 to 7, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 2 or less. [9] Hot-pressed part according to any one of claims 1 to 8, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 30% or less. [10] Hot-pressed formed part according to any one of claims 1 to 9, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 2.7% or less. [11] Hot-pressed part according to any one of claims 1 to 10, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 0.5% or less. [12] Hot-pressed part according to any one of claims 1 to 11, wherein the tensile strength of the hot-pressed part is 1500 MPa or more. [13] Hot-pressed part according to any one of claims 1 to 12, wherein the tensile strength of the hot-pressed part is 1502 MPa or more. [14] Hot-pressed part according to any one of claims 1 to 13, wherein the tensile strength of the hot-pressed part is 1527 MPa or more. [15] Hot-pressed part according to any one of claims 1 to 14, wherein the tensile strength of the hot-pressed part is 1800 MPa or more. [16] Hot-pressed part according to any one of claims 1 to 15, wherein the bending angle of the hot-pressed part at a tensile strength of 1500 MPa, measured by a bending test according to VDA238-100, is 60° or more. [17] Hot-pressed part according to any one of claims 1 to 16, wherein a bending angle of the hot-pressed part is 67° or more. [18] Hot-pressed part according to any one of claims 1 to 17, wherein the alloy layer is formed from an alloy containing zinc or aluminium. [19] Hot-pressed part according to any one of claims 1 to 18, wherein the base steel sheet comprises, in weight percent, 0.15% to 0.4% carbon (C), 0.1% to 1% silicon (Si), 0.6% to 8% manganese (Mn), 0.001% to 0.05% phosphorus (P), 0.0001% to 0.02% sulfur (S), 0.01% to 0.1% aluminium (Al), 0.001% to 0.02% nitrogen (N), 0.01% to 0.5% chromium (Cr), and as a remainder Fe and other impurities. [20] Hot-pressed part according to claim 19, wherein the base steel sheet further contains, in weight percent, one or more of the following elements: 0.0005% to 0.01% boron (B) and 0.01% to 0.05% titanium (Ti). [21] Hot-pressed part according to claim 19, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.0005% to 0.01% boron (B) and 0.01% to 0.05% titanium (Ti), as well as Fe and other impurities as the remainder, such that the sum equals 100 weight percent. [22] Hot-pressed part with excellent impact resistance properties, comprising: a basic steel sheet; and an alloy layer on a surface of the base steel sheet; where a ratio (C PS / C B ) of a C content (C PS ) of a component surface layer part to a C content (C B ) of the base steel sheet is 1.2 or less, where a ratio ((MnPS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr content of the Component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.8 or more, and wherein the component surface layer part refers to an area up to a depth of 25 µm from the surface of the base steel sheet excluding the alloy layer, and where the surface of the base steel sheet and the alloy layer is a point where the aluminium content according to GDS analysis is 1%. [23] Hot-pressed part according to claim 22, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 1.1 or less. [24] Hot-pressed part according to one of claims 22 to 23, wherein the ratio (CPS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 1.05 or less. [25] Hot-pressed part according to one of claims 22 to 24, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 0.95 or less. [26] Hot-pressed part according to one of claims 22 to 25, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.9 or more. [27] Hot-pressed part according to one of claims 22 to 26, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B)) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.93 or more. [28] Hot-pressed part according to one of claims 22 to 27, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.97 or more. [29] Hot-pressed part according to any one of claims 22 to 28, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 2 or less. [30] Hot-pressed part according to any one of claims 22 to 29, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 30% or less. [31] Hot-pressed part according to any one of claims 22 to 30, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 2.7% or less. [32] Hot-pressed part according to any one of claims 22 to 31, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 0.5% or less. [33] Hot-pressed part according to any one of claims 22 to 32, wherein the tensile strength of the hot-pressed part is 1500 MPa or more. [34] Hot-pressed part according to any one of claims 22 to 33, wherein the tensile strength of the hot-pressed part is 1502 MPa or more. [35] Hot-pressed part according to any one of claims 22 to 34, wherein the tensile strength of the hot-pressed part is 1527 MPa or more. [36] Hot-pressed part according to any one of claims 22 to 35, wherein the tensile strength of the hot-pressed part is 1800 MPa or more. [37] Hot-press formed part according to any one of claims 22 to 36, wherein a bending angle of the hot-press formed part is 60° or more. [38] Hot-press formed part according to any one of claims 22 to 37, wherein a bending angle of the hot-press formed part is 67° or more. [39] Hot-pressed part according to any one of claims 22 to 38, wherein the alloy layer is formed from an alloy containing zinc or aluminium. [40] Hot-pressed part according to any one of claims 22 to 39, wherein the base steel sheet comprises, in weight percent, 0.15% to 0.4% carbon (C), 0.1% to 1% silicon (Si), 0.6% to 8% manganese (Mn), 0.001% to 0.05% phosphorus (P), 0.0001% to 0.02% sulfur (S), 0.01% to 0.1% aluminium (Al), 0.001% to 0.02% nitrogen (N), 0.01% to 0.5% chromium (Cr), and as a remainder Fe and other impurities. [41] Hot-pressed part according to claim 40, wherein the base steel sheet further contains, in weight percent, one or more of the following elements: 0.0005% to 0.01% boron (B) and 0.01% to 0.05% titanium (Ti). [42] Hot-pressed part according to claim 40, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.0005% to 0.01% boron (B) and 0.01% to 0.05% titanium (Ti), as well as Fe and other impurities as the remainder, such that the sum equals 100 weight percent. [43] Hot-pressed part with excellent impact resistance properties, comprising: a basic steel sheet; and an alloy layer on a surface of the base steel sheet; where a ratio (C PS / C B ) of a C content (C PS ) of a component surface layer part to a C content (C B ) of the base steel sheet is 1.2 or less, where a ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr content of the Component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.8 or more, and where the component surface layer part refers to an area up to a depth of 25 µm from an interface between the base steel sheet and the alloy layer. [44] Hot-pressed part according to claim 43, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 1.1 or less. [45] Hot-pressed part according to one of claims 43 to 44, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 1.05 or less. [46] Hot-pressed part according to any one of claims 43 to 45, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 0.95 or less. [47] Hot-pressed part according to any one of claims 43 to 46, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.9 or more. [48] ​​Hot-pressed part according to any one of claims 43 to 47, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.93 or more. [49] Hot-pressed part according to any one of claims 43 to 48, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.97 or more. [50] Hot-pressed part according to any one of claims 43 to 49, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 2 or less. [51] Hot-pressed part according to any one of claims 43 to 50, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 30% or less. [52] Hot-pressed part according to any one of claims 43 to 51, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 2.7% or less. [53] Hot-pressed part according to any one of claims 43 to 52, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 0.5% or less. [54] Hot-pressed part according to any one of claims 43 to 53, wherein the tensile strength of the hot-pressed part is 1500 MPa or more. [55] Hot-pressed part according to any one of claims 43 to 54, wherein the tensile strength of the hot-pressed part is 1502 MPa or more. [56] Hot-pressed part according to any one of claims 43 to 55, wherein the tensile strength of the hot-pressed part is 1527 MPa or more. [57] Hot-pressed part according to any one of claims 43 to 56, wherein the tensile strength of the hot-pressed part is 1800 MPa or more. [58] Hot-pressed part according to any one of claims 43 to 57, wherein a bending angle of the hot-pressed part is 60° or more. [59] Hot-press formed part according to any one of claims 43 to 58, wherein a bending angle of the hot-press formed part is 67° or more. [60] Hot-pressed part according to any one of claims 43 to 59, wherein the alloy layer is formed from an alloy containing zinc or aluminium. [61] Hot-pressed part according to any one of claims 43 to 60, wherein the base steel sheet comprises, in weight percent, 0.15% to 0.4% carbon (C), 0.1% to 1% silicon (Si), 0.6% to 8% manganese (Mn), 0.001% to 0.05% phosphorus (P), 0.0001% to 0.02% sulfur (S), 0.01% to 0.1% aluminium (Al), 0.001% to 0.02% nitrogen (N), 0.01% to 0.5% chromium (Cr), and as a remainder Fe and other impurities. [62] Hot-pressed part according to claim 61, wherein the base steel sheet further contains, in weight percent, one or more of the following elements: 0.0005% to 0.01% boron (B) and 0.01% to 0.05% titanium (Ti). [63] Hot-pressed part according to claim 61, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.0005% to 0.01% boron (B) and 0.01% to 0.05% titanium (Ti), as well as Fe and other impurities as the remainder, such that the sum equals 100 weight percent. [64] Hot-pressed part with excellent impact resistance properties, comprising: a basic steel sheet; and an alloy layer on a surface of the base steel sheet; where a ratio (C PS / C B ) of a C content (C PS ) of a component surface layer part to a C content (C B ) of the base steel sheet is 1.2 or less, where a ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr content of the Component surface layer part to the sum (Mn B +Cr B) the Mn and Cr content of the base steel sheet is 0.8 or more, and where the component surface layer part refers to an area up to a depth of 25 µm from an interface between the base steel sheet and the alloy layer, where the interface between the base steel sheet and the alloy layer is a point where the aluminium content according to GDS analysis is 1%. [65] Hot-pressed part according to claim 64, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 1.1 or less. [66] Hot-pressed part according to one of claims 64 to 65, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 1.05 or less. [67] Hot-pressed part according to any one of claims 64 to 66, wherein the ratio (C PS / C B ) of the C content (C PS ) of the component surface layer part to the C content (C B ) of the base steel sheet is 0.95 or less. [68] Hot-pressed part according to any one of claims 64 to 67, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.9 or more. [69] Hot-pressed part according to any one of claims 64 to 68, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B) the Mn and Cr content of the base steel sheet is 0.93 or more. [70] Hot-pressed part according to any one of claims 64 to 69, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 0.97 or more. [71] Hot-pressed part according to any one of claims 64 to 70, wherein the ratio ((Mn PS +Cr PS ) / (Mn B +Cr B )) of the sum (Mn PS +Cr S ) the Mn and Cr contents of the component surface layer part to the sum (Mn B +Cr B ) the Mn and Cr content of the base steel sheet is 2 or less. [72] Hot-pressed part according to any one of claims 64 to 71, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 30% or less. [73] Hot-pressed part according to any one of claims 64 to 72, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 2.7% or less. [74] Hot-pressed part according to any one of claims 64 to 73, wherein the ferrite coverage at a martensitic grain boundary of the component surface layer part is 0.5% or less. [75] Hot-pressed part according to any one of claims 64 to 74, wherein the tensile strength of the hot-pressed part is 1500 MPa or more. [76] Hot-pressed part according to any one of claims 64 to 75, wherein the tensile strength of the hot-pressed part is 1502 MPa or more. [77] Hot-pressed part according to any one of claims 64 to 76, wherein the tensile strength of the hot-pressed part is 1527 MPa or more. [78] Hot-pressed part according to any one of claims 64 to 77, wherein the tensile strength of the hot-pressed part is 1800 MPa or more. [79] Hot-press formed part according to any one of claims 64 to 78, wherein a bending angle of the hot-press formed part is 60° or more. [80] Hot-press formed part according to any one of claims 64 to 79, wherein a bending angle of the hot-press formed part is 67° or more. [81] Hot-pressed part according to any one of claims 64 to 80, wherein the alloy layer is formed from an alloy containing zinc or aluminium. [82] Hot-pressed part according to any one of claims 64 to 81, wherein the base steel sheet comprises, in weight percent, 0.15% to 0.4% carbon (C), 0.1% to 1% silicon (Si), 0.6% to 8% manganese (Mn), 0.001% to 0.05% phosphorus (P), 0.0001% to 0.02% sulfur (S), 0.01% to 0.1% aluminium (Al), 0.001% to 0.02% nitrogen (N), 0.01% to 0.5% chromium (Cr), and as a remainder Fe and other impurities. [83] Hot-pressed part according to claim 82, wherein the base steel sheet further contains, in weight percent, one or more of the following elements: 0.0005% to 0.01% boron (B) and 0.01% to 0.05% titanium (Ti). [84] Hot-pressed part according to claim 82, wherein the base steel sheet also contains, in weight percent, one or more of the following elements: 0.0005% to 0.01% boron (B) and 0.01% to 0.05% titanium (Ti), as well as Fe and other impurities as the remainder, such that the sum equals 100 weight percent.

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