Crack-containing hot-stamped steel parts with a thin coating, offering excellent spot-weldability and paint adhesion.

Abstract

Provide a hot-stamped coated steel part comprising a steel substrate having excellent paint adhesion and excellent spot weldability simultaneously, and an aluminum alloy coating on at least one surface of the steel substrate, and a method for manufacturing the same. 【Solution means】In a hot-stamped coated steel part comprising a steel substrate and an aluminum alloy coating including an interdiffusion layer and an outer layer from the steel substrate outward, the total thickness e of the coating coating and the thickness e of the interdiffusion layer IDL satisfy the following conditions. 16 ≦ E pc <40 at JPEG2026123063000040.jpg14115 The hot-stamped coated steel part comprises a non-deformed part having a thickness e of 0.6 mm to 3.5 mm Pflat and at least one deformed part. The linear density dC of cracks in the coating of the non-deformed part is the minimum linear density dC of cracks defined as follows min (e Pflat ) or more. JPEG2026123063000041.jpg8115

Description

[Technical Field]

[0001] The present invention relates to a hot-stamped coated steel part comprising a steel substrate and an aluminum alloy coating on at least one surface of the steel substrate, wherein the coating has an optimized crack density and the part has excellent paint adhesion and excellent spot weldability. The present invention also relates to a method for manufacturing a hot-stamped coated steel part. [Background technology]

[0002] Such components can also be used, for example, in the automotive industry to manufacture structural elements for intrusion prevention or energy absorption functions.

[0003] For this type of application, it is desirable to have steel components that possess high mechanical strength, high impact resistance, good corrosion resistance, and dimensional accuracy. Automotive parts such as front or rear rails, roof rails, and B-pillars, as well as chassis components such as lower control arms and engine cradles, require these properties more specifically.

[0004] To meet these demands, such parts are now generally manufactured by a hot stamping process (also known as press hardening). In the hot stamping process, as disclosed particularly in French Patent Invention No. 2780984 and French Patent Invention No. 2807447, blanks cut from steel sheets pre-coated with metal or a metal alloy are heated in a furnace to a temperature at which the ferrite and cementite microstructure of the low-carbon steel is transformed at least partially into austenite, and then hot-stamped in a mold. During stamping, the part is held in the mold to achieve rapid cooling, resulting in the formation of the desired hardened microstructure and the acquisition of the desired mechanical properties. The pre-coating can be aluminum or an aluminum alloy. During heating in the furnace, the pre-coating alloy alloys with the steel substrate to form a compound that provides protection for the steel surface against decarburization and scale formation.

[0005] Recently, there has been focus on the coating of parts after hot stamping, and how this affects the properties of the parts during use.

[0006] In International Publication No. 2008 / 053273, it was proposed to limit the pre-coating thickness to between 20 and 33 μm at all locations and to control the hot stamping process, particularly the heating rate and austenitization parameters, in order to achieve a desirable continuity and morphology of the continuous layer in the coating of a part and to result in improved weldability. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] French Patent No. 2780984 [Patent Document 2] French Patent No. 2807447 Specification [Patent Document 3] International Publication No. 2008 / 053273 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, it remains desirable to provide hot-stamped steel parts that can be manufactured with lower pre-coating thicknesses and have improved spot weldability and paint adhesion.

[0009] Furthermore, even if paint adhesion can be improved, such improvement is achieved by compromising spot weldability, and therefore, it is still desirable to provide a part that combines excellent paint adhesion with excellent spot weldability.

[0010] Therefore, the present invention aims to provide a hot-stamped coated steel part comprising a steel substrate having excellent paint adhesion and excellent spot weldability, and an aluminum alloy coating on at least one surface of the steel substrate, and a method for manufacturing the same.

[0011] In particular, it is desirable to provide hot-stamped coated steel parts that have at least an undeformed portion and a weld range exceeding 1 kA as measured according to standard SEP 1220-2 (2011), along with excellent paint adhesion. Paint adhesion is evaluated by performing a dry coat test according to standard ISO 2409:2013. If the result of the dry coat test is strictly less than 1, it is considered that the paint adhesion is excellent. [Means for solving the problem]

[0012] For this purpose, the present invention relates to a hot-stamped coated steel part as described in claim 1.

[0013] The hot-stamped coated steel component preferably has one or more of the features of claims 2 to 13.

[0014] The present invention also relates to a method for manufacturing a hot-stamped coated steel part as described in claim 14.

[0015] This method preferably includes one or more features from claims 15 to 24.

[0016] The present invention also relates to the use of hot-stamped coated steel parts according to the present invention or hot-stamped coated steel parts manufactured by the method according to the present invention for the manufacture of chassis or white body parts or suspension arms for automobile vehicles.

[0017] The present invention will be described in detail without limitation with reference to the following figures and illustrated by examples. [Brief explanation of the drawing]

[0018] [Figure 1] This figure schematically shows an example of a hot-stamped coated steel part according to the present invention. [Figure 2] This is a cross-sectional view of the coating of a non-deformable portion of a part according to the present invention, observed in a given field of view. [Figure 3] An example of a cross-section of a coating in an undeformed portion of another part with insufficient crack density is shown. [Modes for carrying out the invention]

[0019] This invention relates to hot-stamped coated steel parts.

[0020] Hot-stamped coated steel parts are non-flat parts manufactured by hot-stamping a blank.

[0021] A steel plate refers to a flat steel sheet. Here, a steel plate refers to a coiled hot-rolled or cold-rolled steel sheet, or a sheet cut from such a coil.

[0022] A steel sheet has a top and bottom surface, also called an upper and bottom surface or top and bottom surface. The distance between these surfaces is specified as the sheet thickness. The thickness can be measured, for example, using micrometers, with the spindle and anvil positioned on the top and bottom surfaces, and the axis between the spindle and anvil perpendicular to the sheet surface. Similarly, the thickness can also be measured on a molded part. Similarly, the thickness can also be measured on a blank and a part.

[0023] A steel blank refers to a flat sheet of steel cut into any shape suitable for its use, or a blank manufactured by cutting two or more steel plate materials, which may have different thicknesses or compositions, into the required shape, assembling them together, and especially welding them together.

[0024] The average thickness of a part or a portion of a part refers to the overall average thickness of the material that makes up the part after it has been formed from a flat sheet into a three-dimensional part.

[0025] Uniform thickness means that the thickness of the blank, part, sheet, or area or portion thereof is constant, and the maximum variation in thickness above or below the average thickness of the blank, part, sheet, or area or portion thereof is no more than 0.1 mm. In particular, uniform thickness means that no spontaneous changes in thickness occurred during manufacturing, especially during the manufacturing of sheets in hot and / or cold rolling, and during the forming process of manufacturing parts.

[0026] In the following, the thickness of a blank, part, sheet, or area or portion thereof having a uniform thickness is defined as the average thickness of that blank, part, sheet, or area or portion thereof.

[0027] Furthermore, the term "thickness" is used to refer to the thickness of a blank, part, sheet, or area or portion thereof of uniform thickness, while "average thickness" is more generally used to refer to the average thickness of a blank, part, sheet, or area or portion thereof, regardless of whether the thickness is uniform or variable.

[0028] Tailored weld blanks are manufactured by assembling several sheets or cut blanks of steel, known as subblanks, together, for example by laser welding, to optimize the performance of the part in its different areas, reduce the overall part weight, reduce the overall part cost, and reduce material scrap. The subblanks forming a tailored weld blank can be assembled with or without overlap, for example, by laser butt welding (no overlap) or by spot welding to each other (with overlap).

[0029] A flexible blank is a type of tailor-welded blank in which at least part of the connection between different sub-blanks is a region that is not rigid, allowing the sub-blanks to move in different directions during the forming process in the corresponding region.

[0030] In contrast to tailor-welded blanks, a monolithic blank refers to a blank consisting of a single sub-blank, without several sub-blanks being joined together.

[0031] A tailor-rolled blank is a blank with variable thickness, i.e., a change in thickness along the blank, obtained by differential rolling during the steel sheet manufacturing process.

[0032] Hot stamping is a forming technique that involves heating a blank to a temperature at which the steel's microstructure transforms to at least partially austenite, stamping the blank to form a blank at a high temperature, and then quenching the formed part to obtain a microstructure with high strength. Hot stamping makes it possible to obtain very high-strength parts with complex shapes and presents many technical advantages.

[0033] Monolithic parts are hot-stamped parts manufactured from monolithic blanks.

[0034] Monolithic components are manufactured, for example, from monolithic blanks having a uniform thickness, or from monolithic tailor-rolled blanks.

[0035] A hot-stamped welded steel part or a hot-stamped laser-welded steel part is a hot-stamped part manufactured from a tailor-welded blank, such as a flexible blank. Thus, a hot-stamped welded steel part comprises two or more hot-stamped subparts and one or more hot-stamped welds that join the hot-stamped subparts together.

[0036] In one embodiment, the hot-stamped coated steel component of the present invention is a monolithic component.

[0037] In another embodiment, the hot-stamped coated steel part is a hot-stamped welded steel part.

[0038] The hot-stamped coated steel parts of the present invention preferably have an average thickness e between 0.6 mm and 3.5 mm. P It has.

[0039] The 0.6mm to 3.5mm range is a common thickness used in the manufacture of structural or reinforcing parts for the automotive industry. This thickness range is also suitable for industrial press-hardening tools, particularly hot stamping presses or molds.

[0040] Furthermore, as detailed below, the thermal process applied to a given steel plate thickness affects the formation of cracks in the coating, particularly in the coating of the flat, non-deformable portion desired in the present invention.

[0041] Preferably, the average thickness e of the hot-stamped coated steel part. P The range is 0.7 mm to 3.0 mm.

[0042] In one embodiment, the hot-stamped coated steel part has a uniform thickness e of 0.6 mm to 3.5 mm, preferably 0.7 mm to 3.0 mm. P It has.

[0043] In another embodiment, the hot-stamped coated steel parts have variable thickness (and therefore non-uniform). In this case, the hot-stamped coated steel parts have different uniform thicknesses, preferably 0.6 mm to 3.5 mm, and preferably 0.7 mm to 3.0 mm. Pi It consists of two or more regions having [a certain characteristic].

[0044] For example, hot-stamped coated steel parts with variable thickness can be manufactured from tailor-rolled blanks with variable thickness obtained by differential rolling during the steel sheet manufacturing process.

[0045] As another example, a hot-stamped coated steel part with variable thickness may be a hot-stamped welded steel part manufactured from a tailor-welded blank made of blanks of different thicknesses.

[0046] Hot-stamped coated steel parts comprise a steel substrate (also called a steel base material) having two main surfaces.

[0047] The steel in the substrate is hot-stamping steel, that is, steel that hardens after austenitization and can be rapidly cooled by quenching.

[0048] In one embodiment, the component is manufactured from a monolithic blank, and the steel substrate is made from a single piece of steel.

[0049] In another embodiment, the component is a hot-stamped welded steel component, and the steel substrate consists of two or more regions (or sub-components) which can be made of the same or different steels and may have the same or different microstructures.

[0050] In the following, the microstructure and composition of a steel substrate refers to the microstructure and composition of the steel substrate (if the substrate is made of a single piece of steel), or the microstructure or composition of one or more regions or sub-components of the steel substrate.

[0051] The composition of the steel depends on the desired mechanical properties of the part. However, preferably, in the steel substrate, or in each region of the steel substrate, the steel is present in weight %. 0.062% ≤ C ≤ 0.4% 0.4% ≤ Mn ≤ 3.9% 0.10% ≤ Si ≤ 1.5% 0.005% ≤ Al ≤ 1.0% 0.001% ≤ Cr ≤ 2.0% 0.001% ≤ Ti ≤ 0.2% 0.0005% ≤ B ≤ 0.010% Ni ≤ 2% Nb ≤ 0.1% Mo ≤ 0.65% W ≤ 0.30% N ≤ 0.010% 0.0001% ≤ S ≤ 0.05% 0.0001% ≤ P ≤ 0.1% Ca ≤ 0.005% It has a composition that includes [a certain component], with the remainder of the composition consisting of iron and unavoidable impurities resulting from processing.

[0052] The level of impurities generated from the processing depends on the manufacturing route used. For example, when using a blast furnace route with low levels of steel scrap (recycled steel), the level of impurities remains very low. On the other hand, when refining steel using an electric furnace with a very high proportion of recycled scrap steel, the level of impurities increases significantly. In the latter case, for example, the level of Cu can rise to 0.25%, Ni to 0.25%, Sn to 0.05%, As to 0.03%, Sb to 0.03%, and Pb to 0.03%.

[0053] Therefore, in one embodiment, the steel contains up to 0.25% Cu, up to 0.05% Sn, up to 0.03% As, up to 0.03% Sb, and / or up to 0.03% Pb as unavoidable impurities.

[0054] The above composition is advantageous for achieving high mechanical properties, particularly tensile strength (TS) in the range of 950 MPa to 2100 MPa.

[0055] Tensile strength is measured according to the ISO standard NF EN ISO 6892-1, published in October 2009. Tensile test specimens are cut from the flat portion of the hot-stamped part.

[0056] In the following, unless otherwise specified, the content of each element is expressed as a weight percentage.

[0057] The carbon content depends on the desired tensile strength TS of the hot-stamped coated steel part.

[0058] Below a carbon content of less than 0.062%, it is difficult to obtain a tensile strength of at least 950 MPa after hot stamping under any cooling conditions. Above 0.4%, in combination with other elements of the composition, the adhesion of the coating after hot stamping may not be satisfactory, and the resistance to delayed cracking and toughness of the steel may decrease. In one embodiment, the carbon content is up to 0.38%.

[0059] The carbon (C) content depends on the desired tensile strength TS of the hot-stamped part, which is manufactured by hot-stamping steel sheets. In one embodiment, the C content is 0.062% to 0.095%. If a higher tensile strength is desired, the C content can be increased to a range of 0.15% to 0.30% at around 1500 MPa. If it is necessary to further increase the tensile strength to at least 1800 MPa, the C content can be added up to a content of 0.4%.

[0060] Apart from its deoxidizing role, manganese has an important effect on hardenability, especially when its content is at least 0.4%. Above 3.9%, the stabilization of austenite by Mn may become too important, which can lead to the formation of excessively prominent striped structures. Preferably, the Mn content is a maximum of 3.0%.

[0061] Silicon is added in a content of at least 0.10% to aid in the deoxidation of molten steel and contribute to the hardening of the steel by precipitation in the solid solution. However, its content is generally limited to avoid the excessive formation of silicon oxide, which impairs the coating properties of the steel. Therefore, the silicon content is generally 1.5% or less, for example, 0.80% or less.

[0062] Aluminum may be added as a deoxidizer in a content of at least 0.005%. Furthermore, Al can protect boron by bonding with N if the titanium content is insufficient. The Al content is preferably at least 0.01%. To avoid oxidation problems and ferrite formation during hot stamping, the Al content is generally 1.0% or less. Preferably, the Al content is up to 0.1%.

[0063] Cr may be added to enhance the hardenability of the steel and contribute to achieving the desired tensile strength after hot stamping. When Cr is added, its content is 0.01% or more, preferably 0.1% or more, and a maximum of 2.0%. If no Cr is added, the Cr content may be present as an impurity at a low level of about 0.001%.

[0064] When titanium is added, its content is preferably at least 0.008% and a maximum of 0.2%. When the Ti content is between 0.008% and 0.2%, precipitation occurs at very high temperatures in the form of TiN, and then at lower temperatures in the form of fine TiC in austenite, leading to hardening. Furthermore, when titanium is added in addition to boron, titanium inhibits the bonding of boron with nitrogen, while nitrogen bonds with titanium. Therefore, the titanium content is preferably 3.42%. * The Ti content is higher than that of N, where N is the N content by weight percentage in the composition. However, the Ti content should preferably remain at 0.2% or less, preferably 0.1% or less, and more preferably at a maximum of 0.05%, in order to avoid the precipitation of coarse TiN precipitates. If no Ti is added, Ti is present as an impurity in a content of at least 0.001%.

[0065] Boron is added to enhance the hardenability of the steel in a content of at least 0.0005% and a maximum of 0.010%. Preferably, the B content is a maximum of 0.004%.

[0066] In one embodiment, Ni can be added in a content of up to 2%, generally at least 0.25%, preferably up to 0.5%, to reduce susceptibility to delayed fracture by concentrating on the surface of the component. If not added, Ni may be present as an impurity in a low content of about 0.001%. Depending on the manufacturing route used, the Ni content as an impurity can be as high as 0.25% (e.g., when manufacturing steel with a high proportion of recycled scrap steel) or as high as 0.1% (e.g., when using lower levels of steel scrap).

[0067] To obtain precipitation hardening and fine structures such as austenite grain size, up to 0.1% niobium may be added. Nb further improves the ductility of the steel. When Nb is added, its content is preferably at least 0.01%. The Nb content is preferably a maximum of 0.06% to avoid the formation of coarse (Ti,Nb)(C,N) precipitates.

[0068] Molybdenum can be added in a maximum content of 0.65%. When Mo is added, its content is preferably at least 0.05%. Mo is preferably added together with Nb and Ti to form a co-precipitation that is very stable at high temperatures. Mo may also be added to increase the toughness of the steel by acting as a grain boundary strengthener in a solid solution state. Optimal effects are obtained when the Mo content is between 0.15% and 0.25%.

[0069] W may be added to enhance the hardenability and hardening properties of the steel by forming tungsten carbide. If W is added, its content should be between 0.001% and 0.30%.

[0070] Sulfur, phosphorus, and nitrogen are generally present in steel composition as impurities.

[0071] The nitrogen content is generally at least 0.0005%. To prevent the precipitation of coarse TiN precipitates, the N content is generally at most 0.010%, preferably at most 0.005%.

[0072] In excess amounts, sulfur and phosphorus reduce ductility. Therefore, their content is limited to 0.05% and 0.1%, respectively.

[0073] In particular, the presence of sulfur (S) in molten steel can lead to the formation of MnS precipitates, which are detrimental to its properties. Preferably, the S content is at most 0.01%, and more preferably at most 0.005%. Achieving a very low S content, i.e., less than 0.0001%, is very costly and unprofitable. Therefore, the S content is generally 0.0001% or higher.

[0074] Preferably, the phosphorus content is a maximum of 0.05%, and more preferably a maximum of 0.02%. Achieving a very low P content, i.e., less than 0.0001%, is very costly. Therefore, the P content is generally 0.0001% or higher.

[0075] Steel may undergo globularization treatment with calcium sulfides, and the globularization of MnS has the effect of improving the bending angle. Therefore, the steel composition may contain at least 0.0001% and up to 0.005% Ca.

[0076] The remainder of the steel's composition consists of iron and impurities resulting from the processing. As detailed above, these impurities may include less than 0.25% Cu, less than 0.05% Sn, less than 0.03% As, less than 0.03% Sb, and / or less than 0.03% Pb.

[0077] The composition of the steel can be selected according to the desired mechanical properties, particularly in terms of strength and ductility.

[0078] In particular, when a tensile strength in the range of 950 to 1200 MPa is desired along with a bending angle greater than 75° (measured according to the VDA 238-100 bending standard of July 2020), the steel of the steel substrate or at least one area of ​​the steel substrate, in the whole of the part or in at least one area of ​​the part, is preferably, by weight %, 0.062% ≤ C ≤ 0.095% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.020% ≤ Al ≤ 0.070% 0.02% ≤ Cr ≤ 0.1% 1.5% ≤ (C + Mn + Si + Cr) ≤ 2.7% 0.0035% ≤ Ti ≤ 0.072% 0.0002% ≤ B ≤ 0.004% 0.04% ≤ Nb ≤ 0.06% 0.044% ≤ (Nb + Ti) ≤ 0.09% 0.001% ≤ N ≤ 0.009% 0.0005% ≤ S ≤ 0.003% 0.0001% ≤ P ≤ 0.020% Ca ≤ 0.005%, The composition contains a first preferred composition, the remainder of which consists of iron and unavoidable impurities resulting from processing.

[0079] On the other hand, when a tensile strength of at least 1400 MPa is required, the steel of the steel substrate or at least one region of the steel substrate is preferably, by weight %, 0.15% ≤ C ≤ 0.30% 0.5% ≤ Mn ≤ 3.0% 0.10% ≤ Si ≤ 0.50% 0.005% ≤ Al ≤ 0.1% 0.01% ≤ Cr ≤ 1.0% 0.001% ≤ Ti ≤ 0.2% 0.0002% ≤ B ≤ 0.010% 0.0005% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.05% 0.0001% ≤ P ≤ 0.1% Ca ≤ 0.005% The composition contains a second preferred composition, the remainder of which consists of Fe and unavoidable impurities resulting from processing.

[0080] If an even higher tensile strength of 1800 MPa or more is required, the composition is preferably, in weight percent, 0.3% ≤ C ≤ 0.4% 0.5% ≤ Mn ≤ 1.0% 0.40% ≤ Si ≤ 0.80% 0.01% ≤ Al ≤ 0.1% 0.1% ≤ Cr ≤ 1.0% 0.008% ≤ Ti ≤ 0.03% 0.0005% ≤ B ≤ 0.003% Ni ≤ 0.5% 0.01% ≤ Nb ≤ 0.1% 0.1% ≤ Mo ≤ 0.5% N ≤ 0.005% 0.0001% ≤ S ≤ 0.004% 0.0001% ≤ P ≤ 0.02% Ca ≤ 0.0010% The composition, according to a third preferred composition including the above, consists of iron and unavoidable impurities resulting from processing.

[0081] The steel substrate of hot-stamped coated steel parts generally has a microstructure consisting of, by volume fraction, at least 60% martensite, up to 20% bainite, up to 5% ferrite, and up to 15% austenite.

[0082] The martensite fraction can be as high as 100%, while the bainite, ferrite, and austenite fractions can each be as low as 0%.

[0083] This description of the microstructure applies to the majority of the steel substrate, meaning that this microstructure is present in at least 95% of the volume of the steel substrate, preferably the entire volume of the steel substrate.

[0084] The microstructure is determined by the following method: A specimen is cut from a hot-stamped coated steel part, polished as detailed below, and etched at Nital 2% (10 seconds) to reveal the microstructure. The cross-section is then examined with a 500x optical microscope, and if it is necessary to distinguish between martensite and bainite, a scanning electron microscope (SEM) (backscattered electron mode, 500x magnification, EHT (electron high voltage) = 15.00 kV, scale 10 micrometers) is used. The volume fraction of each component (martensite, bainite, ferrite, austenite) is measured by image analysis using a method known to the public.

[0085] In one embodiment, the austenite fraction is up to 5% of the volume, and / or the bainite fraction is up to 10% of the volume.

[0086] In one embodiment, the microstructure consists of, by volume, at least 80% martensite, up to 10% bainite, up to 5% austenite, and up to 5% ferrite.

[0087] In a preferred embodiment, the microstructure is essentially martensite, i.e., by volume, consisting of at least 95% martensite and up to 5% bainite and / or ferrite.

[0088] More preferably, the microstructure is entirely martensite.

[0089] The hot-stamped coated steel component comprises a non-deformable portion and at least one deformable portion.

[0090] In one embodiment, the hot-stamped coated steel component includes two or more non-deformable portions.

[0091] In fact, during stamping, particularly hot stamping, to manufacture parts, one or more parts of the blank remain undeformed, while others deform to reach the final non-planar geometric shape of the part. The undeformed parts, or each undeformed part, are not deformed during hot stamping and, if any, also during the previous cold pre-deformation of the blank.

[0092] "Not deformed" means that during the stamping process, the non-deformed portion underwent an equivalent deformation of up to 0.01.

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[0093] For example, the main deformation of a given molded part

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[0094] For example, if the above methods cannot be applied because only a portion of a fully molded part is available or can be processed, or to evaluate deformation very locally in a specific region such as an edge, electron backscatter diffraction (EBSD) measurements can be performed in combination with scanning electron microscopy (SEM) observation. This depends on the correlation between deformation and local crystal orientation shifts. For example, the following reference gives an example of such a measurement: "Kamaya M. Assessment of local deformation using EBSD: quantification of accuracy of measurement and definition of local gradient. Ultramicroscopy. 2011 Jul;111(8):1189-99.doi:10.1016 / j.ultramic.2011.02.004.Epub 2011 Feb 21.PMID:21763236".

[0095] Another methodology that can be applied to determine the main deformation of a molded part is to measure the thickness of the deformed material within the molded region and compare it to the thickness of the undeformed region.

[0096] The non-deformable portion, or each non-deformable portion, is a flat portion of the part.

[0097] An undeformable portion, or each undeformable portion, is, for example, a flange of a part or a flat portion located between two deformable portions of a part. As an example, in a hat-shaped part, the flat portion may further include the flat top of the hat-shaped stamped part.

[0098] An example of such a component is schematically shown in Figure 1.

[0099] Figure 1 shows a hot-stamped coated steel component 1 welded to a flat component 2 by multiple spot welds 3. In this example, the spot welds 3 are located on the flange 8 of the hot-stamped coated steel component 1.

[0100] An exemplary hot-stamped coated steel part 1 is a hat-shaped part (or "omega" shaped part) comprising a flat top 4, two first curves 5 (or radii) extending from two opposing longitudinal edges of the flat top 4, two side walls 6 each extending from the longitudinal edges of the first curves 6, two second curves 7 each extending outward from the longitudinal edges of the side walls 6, and two flat flanges 8 each extending from the longitudinal edges of the second curves 7 to the outer edge of part 1. Thus, the flanges 8 form the edge of part 1.

[0101] In this example, the flange 8 and the flat top 4 are flat, non-deformable portions of the hot-stamped coated steel part 1.

[0102] Non-deformed portions can be distinguished from deformed portions by their shape and / or by observing cracks in the coating of these portions.

[0103] In fact, as detailed below, the coating on the deformed portion contains broad cracks that are either absent or barely present in the coating on the non-deformed portion.

[0104] Each non-deformed part is not subjected to deformation, but it undergoes the same thermal cycle as the deformed part.

[0105] The hot-stamped coated steel part of the present invention differs from a flat blank manufactured by austenitization and quenching without deformation, not only in that it includes at least one deformed portion resulting from hot stamping, but also in that the entire hot-stamped coated steel part undergoes a thermal cycle due to hot stamping that is different from the thermal cycle that a non-deformed steel sheet undergoes.

[0106] In particular, each non-deformable part, although not subjected to deformation, experiences the same thermal cycle as the deformable parts in hot stamping during heating, transfer to the mold, and holding within the mold.

[0107] Therefore, in a hot-stamped coated steel part, the deformed portion or each deformed portion is deformed during hot stamping, while the non-deformed portion or each non-deformed portion is not deformed but undergoes the same thermal cycle as the deformed portion during hot stamping.

[0108] The hot-stamped coated steel parts of the present invention obtained by the in-mold hot stamping process are also different from samples produced by heating in an experimental furnace or any non-surface contact technique, such as a Gleeble machine, which are uniaxially deformed in the furnace. In fact, such samples do not have undeformed portions and are subjected to uniaxial deformation (tensile deformation), whereas in hot stamping, the deformation is not uniform throughout the part but three-dimensional. Furthermore, the thermal cycle that hot-stamped coated steel parts undergo is different from the thermal cycle that undergoes in an experimental furnace without in-mold transfer or stamping.

[0109] The flat, non-deformable portion of the part, or each flat, non-deformable portion, has a uniform thickness e of 0.6 mm to 3.5 mm, preferably 0.7 mm to 3.0 mm. pflat This is the part that has it.

[0110] For example, flanges of different thicknesses e pflat(1) and e pflat(2) If it consists of two regions having , then each of these regions is a distinct, non-deformable part.

[0111] When the hot-stamped coated steel part has a uniform thickness, the thickness of the flat non-deformed part (or each non-deformed part) is the thickness e of the hot-stamped coated steel part P is equal to.

[0112] When the hot-stamped coated steel part has a variable thickness and includes two or more non-deformed parts, the thickness of the non-deformed parts is e Pflat(i) is shown by, where i = 1...n are the indices associated with each non-deformed part, n is the number of non-deformed parts, and the thicknesses of the non-deformed parts may be different from each other or the same.

[0113] The thickness e pflat can be measured, for example, using a micrometer.

[0114] The hot-stamped coated steel part comprises a coating on at least the surface of the steel substrate.

[0115] The coating is an aluminum alloy coating.

[0116] This coating contains aluminum and iron, and preferably further contains silicon.

[0117] The coating advantageously contains more than 50% aluminum.

[0118] For example, the coating contains from 8 to 12 wt% Si and from 3 to 5 wt% Fe, with the balance being Al and unavoidable impurities.

[0119] The coating results from the interdiffusion between the aluminum alloy precoating and the steel during hot stamping.

[0120] The coating comprises an interdiffusion layer that is located closest to the inside of the coating, i.e., in contact with the steel substrate.

[0121] The interdiffusion layer generally has an Fe content of at least 80% and up to 95%, and an Al content of 4% to 20%, with up to 2% Si.

[0122] In one embodiment, the interdiffusion layer has a composition consisting of 86-95% Fe, 4-12% Al, and 0-2% Si.

[0123] The coating further comprises an outer layer that extends from the diffusion layer to the surface of the coating.

[0124] The outer layer generally contains or consists of intermetallic compounds of Fe, Al, and possibly Si.

[0125] The outer layer may consist of a single layer, or it may consist of a sublayer of a different intermetallic compound.

[0126] For example, the outer layer consists of 1 to 4 sublayers.

[0127] However, in the present invention, the inventors have found that the objective of the present invention is achieved if the linear density of cracks conforms to the following conditions, regardless of what the layers in the coating are, in particular, what their composition and number are.

[0128] In the hot-stamped coated steel part according to the present invention, the total thickness of the coating is e coating and the thickness of the interdiffusion layer e IDL It satisfies the following conditions. 16≦E pc <40 In,

number

[0129] E pc If the value is less than 16, the coating may not adequately protect the part for its intended use, E pcIf the value is 40 or higher, the desired excellent spot weldability and paint adhesion may not be guaranteed, as detailed below.

[0130] In the hot-stamped coated steel part according to the present invention, the coating is 16 ≤ E in at least one non-deformable portion of the hot-stamped coated steel part. pc Provided that <40, the coating has a thickness e of the non-deformable portion. pflat The minimum linear density of the crack depends on dC min (e pflat These are cracks having a linear density dC of ) or greater, and are defined as follows:

number

[0131] In this formula,

number

[0132] Here, the "linear density of cracks," which indicates the number of cracks per millimeter, is naturally a linear density, not a volume density, in that it measures the number of cracks present in the cross-section of the coating over a given length in a direction parallel to the surface of the steel substrate.

[0133] In fact, the inventors conducted intensive research to solve the problem of improving spot weldability and paint adhesion, and surprisingly, contrary to the established idea that cracks are detrimental to the properties of hot-stamped coated steel parts, they discovered that both spot weldability and paint adhesion dramatically increase when the linear density of cracks exceeds a threshold.

[0134] The inventors also found that, with respect to the linear density of cracks, the relevant portion of the part was an undeformed portion (for example, the flat top of a hat-shaped part as shown in Figure 1) that, despite undergoing the same thermal cycle as the deformed portion, was located on the flange of a hot-stamped part or in a flat area between two deformed portions of the part and therefore did not undergo deformation.

[0135] In fact, in the deformed areas, the coating undergoes deformation during stamping, which leads to cracks in the coating due to the difference in expansion between the substrate and the coating, and depending on the deformation temperature and applied deformation rate at each location. However, the inventors have found that having numerous cracks in some deformed areas is insufficient to guarantee excellent spot weldability and excellent paint adhesion, at least in the sense that it does not guarantee such properties in other parts of the hot-stamped coated steel part.

[0136] Preferably, the non-deformable portion is located within the flange of the part, which is the area most likely to be spot-welded, so it is particularly desirable that this portion has excellent spot-weldability (as well as excellent paint adhesion).

[0137] The inventors further discovered that the threshold for the linear density of cracks is not an absolute value, but depends on the thickness of the non-deformed portion, and that a higher linear density of cracks is required as the thickness of the non-deformed portion decreases in order to achieve the desired spot weldability and paint adhesion.

[0138] Based on these studies, the inventors concluded that the coating of the component is 16 ≤ E pc If <40, the linear density of cracks in the coating in the non-deformed portion is dC min We found that excellent spot weldability and paint adhesion are achieved when these conditions are met.

[0139] Preferably, the linear density of cracks in the coating is at most 4 * dC min Preferably up to 3 * dCmin It remains the same.

[0140] Preferably, the hot-stamped coated steel part includes two or more non-deformable portions, and the linear density of cracks dC(i) in each non-deformable portion is equal to the thickness e of this non-deformable portion. pflat (i) Related to,

number

[0141] Therefore, each undeformed portion has a thickness of 0.6 mm to 3.5 mm. pflat (i) has such that i=1...n is the index associated with each non-deformable part, n≧2 is the number of non-deformable parts, and thickness e pflat The linear density of cracks in the coating at each non-deformed portion of (i) is dC(i):

number

number

number

[0142] This formula is valid whether all the non-deformable parts are the same thickness or different thicknesses.

[0143] Cracks in the coating extend from the surface of the coating to the surface of the steel substrate (i.e., the interface between the steel substrate and the coating) in a direction approximately perpendicular to the coating surface, and to a depth of at least 5 μm. The cracks have a width of less than 2 μm (in the direction parallel to the surface of the steel substrate).

[0144] Therefore, cracks are distinguished from possible gaps in a coating with a width greater than 2 μm, cracks in deformed areas which may also have a width greater than 2 μm, and voids or coating defects that affect the coating over a depth of less than 5 μm.

[0145] Furthermore, as mentioned above, in the non-deformed areas, cracks generally have a maximum width of 1 μm. In particular, the average width of the largest cracks, which are cracks with a width greater than 90% of the cracks in the coating, is less than 1 μm. In other words, the average width of the 10% of the observed cracks with the largest width is less than 1 μm. Here, the average width of the largest cracks represents the average value calculated from the widths of all the largest cracks.

[0146] In contrast, in the deformed areas, the coating has more cracks with widths greater than 1 μm, and thus the average crack width is generally greater than 1 μm. In either case, the deformed area, or each deformed area, has an average crack width greater than 1 μm, with cracks having a width greater than 90% of the crack width.

[0147] Preferably, the coating on the non-deformed portion does not have gaps or cracks having a width of 2 μm or more.

[0148] The linear density of cracks is determined by a bright-field optical microscope as the ratio of the number of cracks observed over the entire length of at least 5 mm of observation (in a direction parallel to the surface of the steel substrate) in the cross-section of the non-deformed portion, to this total length (i.e., the number of cracks divided by the total length).

[0149] In particular, the linear density of cracks in the coating is determined by observing cross-sections of the coating on two samples taken from the undeformed portion of a hot-stamped coated steel part using a 500x bright-field microscope across multiple fields of view, such that the total length of the field of view (parallel to the surface of the steel substrate) is at least 5 mm. The linear density of cracks is then determined as the ratio of the number of observed cracks to the total length of the field of view.

[0150] In fact, the inventors have determined that in order to ensure the target excellent spot weldability and excellent paint adhesion, at least dC is applied over a small portion of the coating. min They found that having a crack with a linear density of at least dC is not sufficient. They further found that in order to achieve these properties, at least dC measured over a length of at least 5 mm is required. min We found that it is necessary for the crack to have a certain linear density.

[0151] The average width of the largest crack is determined by measuring the width of all cracks observed over the observed length, identifying the largest cracks from these measurements, and calculating the average width of these largest cracks.

[0152] In detail, the characteristics of the coating described above are determined as follows:

[0153] First, prepare a sample by taking it from the component.

[0154] To that end, a sample of the appropriate size of 20 × 30 mm is prepared by cutting the hot-stamped coated steel part in the middle of its length at the non-deformed portion.

[0155] The cutting process is carried out carefully using a hard iron cutting wheel (e.g., Struers 60A25) or, preferably, a micro-cutting device, to avoid excessive stress that could damage the sample.

[0156] Next, the sample is washed (preferably in an ultrasonic bath) and dried with ethanol and compressed air.

[0157] Next, the sample is cold-mounted with resin. Cold mounting is chosen over hot mounting because the gap between the resin and the sample is very small or nonexistent. This is important because gaps can cause several preparatory problems such as etching, scratching, or coating damage. The resin is preferably liquid EpoFix(R) resin mixed with Epofix Hardener(R). Polymerization takes 10 hours. Two protective metal sheets (guard plates) are provided on both sides of the sample to protect the coating from surface damage during polishing. Each time, the two samples are mounted together to ensure that these two samples are subjected to the same polishing.

[0158] Next, the sample is carefully polished. Polishing is a critical step in evaluating the characteristics of the coating, as improper polishing can result in defects in the coating. These defects include the adhesion of diamond particles, damage to the coating such as delamination, and, more importantly, cracks in the coating, especially longitudinal cracks. Longitudinal cracks, which extend in a direction approximately parallel to the surface of the steel substrate, can reflect preparation problems and must be avoided during polishing to ensure reliable results when counting the number of cracks.

[0159] Polishing is divided into three main stages: disc polishing, diamond polishing, and oxide polishing. To remove polishing contamination, the sample must be washed and dried after each polishing step and checked with an optical microscope.

[0160] First, the sample is polished on a SiC paper P320 polishing disc for 120 seconds, using a sample holder rotation speed of 150 RPM (revolutions / minute) and a disk rotation speed of 100 RPM, both rotating in the same direction. A force of 15 N is applied, and the sample is washed with water.

[0161] Next, a 9 μm diamond abrasive is used to remove material from the surface without causing scratches or deformation. This step is important to ensure the flatness of the polished surface. The rotation speed is the same as in the previous step, but the sample rotation is in the opposite direction to the disc rotation. This stage is set to 300 seconds and uses a force of 20 N. The polishing disc is dampened with lubricant in an optimal amount (0.5 mL / 30 seconds) to ensure better material removal. The sample is washed with water.

[0162] The final step is oxide polishing using a colloidal silica solution (1 mL / 5 seconds). This step is performed for 90 seconds with the sample holder rotating in the same direction at a speed of 150 RPM and the disk rotating at a speed of 60 RPM. The applied force is 20 N. The sample is first washed with water, followed by ethanol.

[0163] Next, the sample is etched with nital (2%, 5-10 seconds) to clarify the microstructure of the steel and the steel / coating interface.

[0164] Total thickness of coating e coating and the thickness of the interdiffusion layer e IDL To determine this, the sample is imaged using a scanning electron microscope (SEM) (backscattered electron mode, magnification 500x, preferably a working distance (WD) of 10 mm, electron high voltage (EHT) = 15.00 kV, scale 10 micrometers) to show cross-sections of the coating and at least a portion of the base steel.

[0165] From the image, the interdiffusion layer can be identified as the layer of light closest to the steel substrate.

[0166] The total thickness of the coating (including the interdiffusion layer) and the thickness of the interdiffusion layer are measured at five spots spaced 15 μm apart horizontally.

[0167] Next, the total thickness of the coating and the thickness of the interdiffusion layer are calculated as the average of the obtained values. Therefore, the total thickness of the coating e coating and the thickness of the interdiffusion layer eIDL This is the average thickness.

[0168] Furthermore, the composition of the interdiffusion layer can be determined as follows.

[0169] The sample is observed using a scanning electron microscope (SEM) to display the cross-section of the coating and at least a portion of the base steel.

[0170] Energy-dispersive spectroscopy (EDS) is used to determine the composition of 10 spots by considering two vertically separated spots within the interdiffusion layer at five different horizontal locations.

[0171] Next, the composition of the interdiffusion layer is calculated as the average of the obtained values.

[0172] If necessary, the composition of the entire coating can be measured using EDS.

[0173] The linear density of cracks in the coating of the non-deformed portion is determined as follows:

[0174] Two samples mounted on the same resin were imaged with a bright-field optical microscope (500x magnification), showing cross-sections of the coating and at least a portion of the steel substrate at multiple locations on the sample.

[0175] Next, for each sample, 10 separate, non-overlapping fields of view are randomly selected and observed. Each field of view has a length of at least 250 μm (parallel to the surface of the steel substrate).

[0176] Therefore, the total length of the observation, which is the total length of the field of view of the two samples (in the direction parallel to the surface of the steel substrate), is 5 mm or more (250 μm). * 2 * 10) is.

[0177] In each field of view, first, it is confirmed that there are no longitudinal cracks extending in a direction substantially parallel to the surface of the steel substrate. If there are longitudinal cracks, the presence of such cracks means that the sample preparation (cutting, polishing) was erroneously performed at this location, so the field of view is ignored and replaced.

[0178] Next, in each field of view, cracks extending in the direction of the steel substrate, substantially perpendicular to the surface of the steel substrate, are identified starting from the top surface of the coating.

[0179] <00009​​​​​​​​​​​​​​​​​​​​​​​​To achieve this, for each crack, the width is measured at three locations located at the center of the crack and at a distance of 2 μm on either side of the center. The average of these three measurements is determined as the crack width.

[0186] Next, cracks larger than the maximum width, i.e., 90% of the width of the cracks in the coating, are identified. Thus, these cracks represent 10% of the cracks with the maximum width. The average width of these cracks is then calculated by dividing the sum of their individual widths by their number.

[0187] If the number of cracks is such that 90% of the cracks are not integers, the 90% result of the number of cracks is rounded to the nearest integer (for example, 90% of 108 cracks is considered to be 97 cracks, and 90% of 135 cracks is considered to be 122 cracks).

[0188] The hot-stamped coated steel component according to the present invention has a weld range of more than 1 kA, measured according to standard SEP 1220-2 (2011), at least in the non-deformed portion.

[0189] Hot-stamped coated steel parts also have excellent paint adhesion, and at least in the non-deformed portions, when subjected to dry paint application, the dry paint adhesion is strictly less than 1.

[0190] Next, a method for manufacturing hot-stamped coated steel parts according to the present invention is disclosed.

[0191] This method generally involves preparing a steel blank having an average thickness of 0.6 to 3.5 mm, preferably 0.7 to 3.0 mm. This thickness is generally the average thickness of the hot-stamped coated steel parts that are to be manufactured from the blank. P It is the same as this.

[0192] The blank is provided with a pre-coating of aluminum or an aluminum alloy on at least one surface, the pre-coating having an average thickness in the range of 8.0 μm to 19.90 μm.

[0193] Preferably, the blank has an aluminum or aluminum alloy pre-coating on each of its two main surfaces, with the pre-coating having an average thickness in the range of 8.0 μm to 19.90 μm.

[0194] This pre-coating can be aluminum or an aluminum alloy (containing more than 50% aluminum).

[0195] Advantageously, the pre-coating is an aluminum-silicon alloy containing 7% to 15% silicon, 2% to 4% iron, and optionally 0.0015% to 0.0030% calcium by weight, with the remainder being aluminum and unavoidable impurities resulting from processing.

[0196] Preferably, the pre-coating contains, by weight, 8% to 11% Si, 2% to 4% Fe, and optionally 0.0015% to 0.0030% Ca, with the remainder being Al and impurities resulting from smelting.

[0197] Pre-coating is generally obtained by hot-dip plating in an Al or Al alloy bath.

[0198] In one embodiment, the blank is a monolithic blank, that is, a blank consisting of a single subblank obtained by cutting a pre-coated steel sheet.

[0199] A monolithic blank is, for example, a tailor-rolled blank, i.e., a blank with variable thickness obtained by differential rolling during the steel sheet manufacturing process.

[0200] In another embodiment, the blank is a tailor-welded blank manufactured by assembling multiple blanks cut from different pre-coated steel sheets known as subblanks, particularly by welding them together by laser welding, for example.

[0201] In one embodiment, the blank has a uniform thickness of 0.6 mm to 3.5 mm, preferably 0.7 mm to 3.0 mm.

[0202] In another embodiment, the blank is a tailor - rolled blank or a tailor - welded blank, and the blank has a variable thickness.

[0203] In this case, the blank consists of two or more regions each having a different thickness e of 0.6 mm to 3.5 mm, preferably 0.7 mm to 3.0 mm. Bi Each region of the blank having a given thickness e Bi corresponds to a region of the final hot - stamped coated steel part having a thickness e Pi .

[0204] In any case, the blank comprises a flat portion having a uniform thickness e defined to be the non - deformed portion of the hot - stamped coated steel part after the hot - stamping process. The thickness e Bflat is also 0.6 mm to 3.5 mm, preferably 0.7 mm to 3.0 mm. Bflat

[0205] ​​​​​​​​​​​​​​​​​​​​​​The thickness is between 0.6 mm and 3.5 mm, preferably between 0.7 mm and 3.0 mm. Furthermore, each thickness e Bflat(i) The thickness e of the corresponding non-deformable portion of the part. Pflat(i) It is equal to.

[0209] If the blank thickness is uniform, then the thickness e Bflat , or each thickness e where applicable Bflat(i) The thickness of the blank is e B It is equal to.

[0210] If the blank, or if the blank is a tailor-welded blank, each subblank is preferably made of steel having the composition disclosed above, particularly according to the first, second, or third preferred composition. The subblanks may have the same steel composition or different steel compositions.

[0211] The blanks or each sub-blank are manufactured, for example, as follows:

[0212] Semi-finished products in the form of slabs, thin slabs, and / or ingots that can be further hot-rolled are preferably provided in the steel composition described above. The thickness of these semi-finished products is typically in the range of 50 to 250 mm.

[0213] If necessary, this semi-finished product is heated to a temperature generally in the range of 1100°C to 1300°C, and then hot-rolled at a finish rolling temperature preferably in the range of 880°C to 950°C to obtain a hot-rolled steel sheet. The hot-rolled steel sheet is wound at a temperature Tc of 750°C or lower, generally above the steel temperature Ms.

[0214] At this stage, the thickness of the hot-rolled steel sheet may be in a typical range of 1.5 to 4 mm. Depending on the thickness of the hot-rolled steel sheet and the desired sheet thickness, the steel sheet may be pickled under normal conditions and further cold-rolled, or it may be directly annealed in the process described below.

[0215] If the blank to be manufactured is a tailor-rolled blank, the steel sheet can be manufactured by differential rolling (or continuous flexible rolling), that is, by a process in which the thickness of the sheet obtained after rolling is variable in the rolling direction in relation to the load applied to the sheet through the rollers during the rolling process.

[0216] After hot or cold rolling, in preparation for coating, the steel sheet is typically annealed at a temperature between Ac1 and Ac3, generally in the range of 700-850°C, and if cold rolling was performed, the crystal grains are recrystallized. The sheet is then hot-dip plated in an Al or Al alloy bath at a temperature of generally about 670-680°C (the exact temperature depends on the composition of the bath).

[0217] A preferred pre-coating is Al-Si, which is obtained by molten plating the sheet in a bath containing 7% to 15% by weight of Si, 2% to 4% of Fe, and optionally 0.0015% to 0.0030% of Ca, with the remainder being Al and impurities resulting from smelting.

[0218] Preferably, the bath contains, by weight, 8% to 11% Si, 2% to 4% Fe, and optionally 0.0015% to 0.0030% Ca, with the remainder being Al and impurities resulting from smelting.

[0219] Afterward, the pre-coated steel sheets are cooled to room temperature.

[0220] Pre-coated steel sheets are cut to obtain blanks (or sub-blanks), but the geometry of the blanks is related to the final geometry of the hot-stamped coated steel parts.

[0221] If the blank from which the parts are manufactured is a tailor-welded blank, the sub-blanks manufactured as described above are welded to each other.

[0222] In one embodiment, the subblanks have the same composition. In another embodiment, the subblanks have different compositions. This is particularly true when different mechanical properties are required at different locations in the final part. As an example, the composition of the steel in the first subblank is selected from the three preferred compositions described above, and the composition of the second subblank is selected from two other preferred compositions, or within the same preferred composition as the first subblank, but having a different specific composition.

[0223] In one embodiment, the subblanks have the same uniform thickness. In another embodiment, the subblanks have different thicknesses.

[0224] Optionally, the blank can be cold-formed and pre-deformed before the heating and hot-stamping processes in the mold. This cold pre-deformation reduces the amount of deformation in the subsequent hot-stamping process. In any case, the portion of the blank designated to be the non-deformable portion of the hot-stamped coated steel part after the hot-stamping process is not deformed during such cold pre-deformation. Therefore, this portion of the blank remains flat. On the other hand, the portion of the blank that will subsequently be deformed during hot-stamping is only partially deformed during cold pre-deformation. As a result, it is ensured that the cold pre-deformation does not affect the target coating properties.

[0225] Next, the blank (flat or cold pre-deformed) is subjected to a temperature range of 850-970°C in the furnace. heat It is heated.

[0226] Heating is performed so that the temperature of the blank reaches the melting temperature T of the pre-coating. melt The first heating stage is maintained below the melting temperature T of the pre-coating, and the temperature of the blank is maintained below the melting temperature T of the pre-coating. melt That concludes the explanation regarding the thermal temperature T. heat It comprises a second heating stage that rises to a certain temperature.

[0227] The heating method is not limited and may be based on radiation, conduction, induction, or resistance.

[0228] The time spent by the blank between each of these two stages can be adjusted by controlling the furnace, particularly by using a furnace with different sections having independent settings, for example, with respect to power and temperature, so that the heating rate in each of these sections can be adjusted independently of each other. For example, if a high heating rate is desired in the first heating stage, the first section of the furnace can be set to a high temperature and high power to ensure such rapid heating. Then the final heating temperature T heat If a low heating rate is desired, the melting temperature of the pre-coating should be T melt To ensure a longer time beyond this point, multiple sections are used, allowing for a slight increase in furnace temperature between sections. Conversely, the melting temperature T of the pre-coating... melt and heating temperature T heat If a shorter heating time is desired, a high temperature can be set in the furnace section, and the blank can reach the target heating temperature T before this temperature is reached. heat It can be moved to the section.

[0229] Furthermore, those skilled in the art know, for example, how to determine the melting temperature of a pre-coating whose composition is known, using a three-component phase diagram.

[0230] Next, the heated blank is heated to a heating temperature T in order to obtain a complete austenitic structure in the steel. heat It is held there.

[0231] Preferably, the total residence time in the furnace, including heating and holding, is in the range of 1.5 to 15 minutes.

[0232] Next, the heated blank is transferred to a mold (or hot stamping press). The transfer time is preferably up to 15 seconds, more preferably up to 10 seconds or up to 8 seconds.

[0233] Next, the die is closed to punch the blank into parts, and the temperature of the blank when the die is closed is T close It will be recorded as such.

[0234] Preferably, the time elapsed between transferring the heated blank to the mold and closing the mold is less than 8 seconds.

[0235] Heating and holding induce interdiffusion between the pre-coating and the steel substrate. In particular, during heating and holding, iron diffuses from the steel substrate towards the coating, and aluminum diffuses from the coating towards the steel substrate. This interdiffusion leads to the formation of an interdiffused layer of the coating.

[0236] Furthermore, depending on the composition of the pre-coating, one or more intermetallic phases can be generated by interdiffusion on the interdiffusion layer (and therefore within the outer layer of the part) in the form of a solid solution.

[0237] According to the present invention, heating, holding, transfer, mold closing and cooling inside the mold are performed in dC min To achieve the above linear crack density dC in the coating of the non-deformed portion of the hot-stamped steel part, the thickness e of the flat portion of the blank converted to the non-deformed portion during hot stamping is Bflat It is controlled as a function of [something].

[0238] In particular, the present inventors have found a desired linear density of cracks in the coating of the non-deformable portion, i.e., dC min The relevant factor for achieving the above crack linear density dC is not the time spent in the furnace, but the blank temperature T when the mold is closed. close Combined with the melting temperature T of the pre-coating in the hot stamping process, melt Time spent by the blank beyond t M They discovered that...

[0239] This time t M This refers to the heating in the second stage above (T above)melt ) Heating temperature T heat Holding time T at heat , transfer time, and the time (before and after stamping) consumed by the blank in the mold until the molded blank reaches temperature T melt during cooling are included.

[0240] This time t M can be determined and controlled during the hot stamping process by monitoring the temperature of the blank during heating and adjusting the time consumed beyond T melt as detailed above, by controlling the holding time t heat at heating temperature T heat , and by controlling the time consumed by the blank during transfer to the mold and during cooling in the mold to T melt .

[0241] The inventors have found that in order to obtain a crack line density of at least dC min , the temperature T close must be in the range of 720 to 820 °C, and the time t melt consumed beyond the melting temperature T M of the pre - coating must be in the range between the minimum time t Bflat and the maximum time t heat which depend on the thickness e melt of the flat part of the blank defined to be the non - deformed part, the heating temperature T Mmin , and the melting temperature T Mmax of the pre - coating.

[0242] The minimum time t Mmin and the maximum time t Mmax are defined as follows. [Equation] and [Equation]

[0243] In these formulas, t Mmin and t Mmax are expressed in seconds, T heat represents the heating temperature of the blank in °C, T melt represents the melting temperature of the pre - coating in °C, and e Bflat represents the thickness of the flat part of the blank, determined so as not to be deformed during hot stamping and thus to become the non - deformed part of the component, in mm.

[0244] In fact, the inventors have found that by satisfying these conditions, after hot stamping and cooling, a hot - stamped coated steel component can be achieved such that the linear density of cracks in the coating of the non - deformed part is dC min or more.

[0245] On the other hand, when the time t M does not satisfy the above - mentioned relationship, and / or when the temperature T close is above 820°C and below 720°C, the linear density of cracks becomes insufficient, and it is impossible to achieve both excellent spot weldability and excellent paint adhesion.

[0246] In particular, when it is less than the minimum time t Mmin , the linear density of cracks is insufficient, and neither the paint adhesion nor the spot weldability is satisfactory.

[0247] On the other hand, when it exceeds the maximum time t Mmax , the linear density of cracks becomes insufficient, and even if the paint adhesion can be improved by increasing the time exceeding the melting temperature, the spot weldability becomes too low.

[0248] Naturally,

Number

Number

number

number

[0249] In one embodiment, a uniform thickness e B A blank having a thickness e of the blank portion that is determined to be the non-deformable part of the component. Bflat Equal to, therefore, t Mmin and t Mmax It will be as follows:

number

number

[0250] When the blank has a variable thickness, preferably, time t according to the required characteristics. M is, thickness e Bi For the additional blank portion / region that has time t Mmin (e Bi ) and time t Mmax (e Bi ) may be adjusted to be included between them.

[0251] In that case, t Mmin and t Mmax The value of is blank e Bi This can be calculated for each of the parts that are considered as a function of the thickness of this part. Next, time t M This is the calculated minimum time t Mmin The maximum value and the calculated maximum time t MmaxIt is selected between the minimum value and the specified value.

number

[0252] t Mmin and t Mmax The value of is an increasing function of thickness, which can be simplified as follows:

number

[0253] In other words, the minimum linear density dC of cracks in two or more parts of a component manufactured from two or more parts of a blank having different thicknesses. min If it is desired to ensure a linear density of cracks exceeding a certain value, then time t M This is the minimum time t defined for the thickest part. Mmin and the maximum time t defined for the thinnest part Mmax It falls within the range between [the specified range].

[0254] Preferably, the hot stamping is performed with a thickness e such that i=1...n Bflat When this is done to form a hot-stamped coated steel part containing two or more non-deformable parts by hot-stamping a blank such that two or more parts having (i) are not deformed, time t M The minimum time t required for the thickest part is Mmin and the maximum time t required for the thinnest part Mmax It falls within the range between [the specified range].

number

[0255] In that case, all the flat portions of the blank that are considered, corresponding to the non-deformable parts of the component, are their actual thickness e Bflat(i) The minimum time t corresponding to Mmin and maximum time t Mmax Time t within the range between M It is guaranteed to be manufactured in [location / location].

[0256] More preferably, the blank has a minimum thickness e Bmin and maximum thickness e Bmax It has time t M is, maximum thickness e Bmax The minimum time required t Mmin and minimum thickness e Bmin The maximum time required t Mmax It falls within the range between [the specified range].

number

[0257] In that case, all areas of the blank correspond to the minimum time t of their actual thickness. Mmin and maximum time t Mmax Time t within the range between M It is guaranteed to be hot-stamped.

[0258] Preferably, the blank temperature T when the mold is closed. close It is at least 740°C.

[0259] In one embodiment, temperature T close The maximum temperature is 800°C.

[0260] In particular, temperatures below 800℃ T close up to 4 * dC min This enables achieving a high linear density of cracks and reduces the risk of powdering.

[0261] The heated blank is hot-stamped in the mold and then hardened in the mold.

[0262] As detailed above, with hot stamping, one or more parts of the blank remain unchanged, while at least one part is deformed by the hot stamping process.

[0263] The undeformed portion of the blank becomes the undeformed portion of the hot-stamped coated steel part obtained by the process.

[0264] The deformed portion of the blank forms the deformed portion of the hot-stamped coated steel part.

[0265] The modes and amounts of deformation in the deformed areas vary from place to place due to the geometry of the final part and the molding tool. For example, some areas may expand, while others are constrained and deformed. Whatever the modes of deformation outlined above, equivalent deformation

number

number

number

number

number

[0266] In the non-deformable portion, equivalent deformation

number

[0267] Next, the hot-stamped blank is held in the mold to ensure an appropriate cooling rate and to avoid distortion of the part due to shrinkage and phase transformation.

[0268] The hot-stamped blank is cooled primarily by conduction through heat transfer with the mold. The mold may include a coolant circulation system to increase the cooling rate, or a heating cartridge to decrease the cooling rate. Thus, the cooling rate can be adjusted by implementing such means.

[0269] The hot-stamped blanks are cooled to a temperature of less than 400°C.

[0270] The applicable cooling rate depends on the composition of the steel as well as the desired structural and mechanical properties.

[0271] temperature T heat The average cooling rate from 0°C to 400°C (including cooling during transfer and cooling within the mold) is generally at least 27°C / second, preferably at least 50°C / second, and usually less than 200°C / second.

[0272] Preferably, the blank is cooled in the mold from the temperature of the blank when the mold is closed down to 400°C at an average cooling rate of at least 30°C / second, more preferably at least 50°C / second.

[0273] For example, if the steel has a composition according to the first preferred composition described above, the hot-stamped blank is first cooled, preferably in a temperature range of 750 to 450°C, at a first average cooling rate in the range of 40 to 360°C / second. In this range, a transformation from austenite to martensite, and possibly to bainite, occurs. In a further step, the hot-stamped blank is cooled in a temperature range including 450°C to 250°C at an average cooling rate of 15 to 150°C / second, which is slower than the first cooling rate.

[0274] If the steel has a composition of the second preferred composition, the hot-stamped blank is preferably cooled in the mold at an average cooling rate of at least 30°C / second to a temperature of less than 400°C from the furnace outlet in order to achieve a structure that is essentially made of martensite.

[0275] If the steel has a composition of a third preferred composition, the hot-stamped blank is preferably cooled in the mold to obtain a structure consisting of martensite, or martensite and bainite.

[0276] In either case, the hot-stamped blank is cooled in the mold to a temperature of less than 400°C, and then cooled to room temperature to obtain the hot-stamped coated steel part.

[0277] Examples Steel having the composition shown in Table 1, expressed as a weight percentage, with a uniform thickness of 1.8 mm or 1.2 mm e B It is provided in the form of a blank cut from a pre-coated steel sheet having [a specific characteristic].

[0278] The blanks were pre-coated on both sides with an Al-Si pre-coating having a composition of 8% to 11% Si, 2% to 4% Fe, with the remainder being Al and impurities resulting from smelting. All pre-coatings were melted at a temperature of 577°C. melt He possessed it.

[0279] For comparison, the pre-coating thickness was adjusted to a range of 8.0–19.90 μm for steel A and to a range of 19.91–40 μm for steel B.

[0280] [Table 1]

[0281] The remainder of the composition consists of iron and unavoidable impurities (including Cu, whose content is reported above).

[0282] These pre-coated steel sheets are cut into blanks.

[0283] Next, the blank is placed in the furnace at temperature T heat Heat with T heat It was maintained at that temperature and then transferred into the mold within 8 seconds.

[0284] Next, the blank was hot-stamped in a mold to produce a part with deformed and flat, undeformed portions. In both cases, the blank temperature T close The mold was closed when the temperature reached 750°C.

[0285] Next, the hot-stamped blank was cooled in the mold to a temperature of less than 400°C, then removed from the mold and cooled to room temperature to obtain a hot-stamped coated steel part.

[0286] Heating, holding, transferring, and cooling within the mold are performed by pre-coating T melt Various times t exceeding the melting temperature M It was adjusted to reach that point.

[0287] For each example, the melting temperature T of the pre-coating melt The time consumed by the blank beyond t M This is reported in Table 2, with the minimum time t Mmin and maximum time t Mmax It is compared to this.

[0288] Minimum time t Mmin and maximum time t Mmax The thickness of the blank is e B This is calculated using the above formula, and it is equal to the thickness of the blank portion where the non-deformable part occurs.

[0289] [Table 2]

[0290] Next, the hot-stamped blank was cooled to a temperature of less than 400°C in the mold to obtain a hot-stamped coated steel part having a martensitic structure.

[0291] Hot-stamped coated steel parts are manufactured using blanks with a thickness of e B A uniform thickness e equal to P (and e P =e Pflat (So ​​that it becomes so).

[0292] Samples were taken from the non-deformed parts of each component and prepared as described above.

[0293] Total thickness of coating e coating and the thickness of the interdiffusion layer e IDL This was determined using the protocol disclosed above, as well as the linear density of cracks in the coating.

[0294] The linear density of cracks in the coating of the non-deformed portion was determined in both cases by observing 10 fields of view for each of the two samples, with a total observation length of 5.29 mm for the two samples.

[0295] The total thickness of the measured coating e coating and the thickness of the interdiffusion layer e IDL Therefore, E was determined according to the above formula. pc The values ​​are reported in Table 3 below.

[0296] The linear density dC of a crack is equal to the minimum linear density dC of a crack. min This is also reported in Table 3.

[0297] Paint adhesion was evaluated for each part as follows:

[0298] Samples were taken from the non-deformed parts of each component.

[0299] The sample was first degreased and then washed with Gardoclean(R) 5176 and a surfactant at 55°C for 6 minutes. Refining was performed with Gardolene(R) ZL6.

[0300] The phosphate treatment process was performed by immersing the sample in a bath containing a solution of Gardobond(R)R24 TA and additives at 50°C for 3 minutes.

[0301] Next, the sample was immersed in a bath containing an aqueous solution of PPG Industries' Pigment Paste(R) W9712-N6 and Resin blend(R) W7911-N6, and a 20 μm e-coating layer was deposited by applying a nominal voltage at 30°C for a total of 180 seconds with a voltage rise time of 30 seconds. The sample was then wiped off and cured in an oven at 175°C for 30 minutes.

[0302] Next, a dry paint adhesion test was performed on the first set of samples by cross-hatching the e-coating layer with a cutter (scratching at 1 mm intervals), peeling off the e-coating layer with adhesive tape (460 N / m), and evaluating the amount of e-coating removed by the naked eye according to ISO 2409:2013. 0 means excellent, in other words, little to no paint was removed, and 5 means very poor, in other words, a large amount of paint (>65%) was removed.

[0303] Furthermore, spot weldability was evaluated by determining the weld range for each specimen according to standard SEP 1220-2 (2011).

[0304] For Example 4, which has a thickness of 1.2 mm, the following parameters were used. -Electrode:F1-16-20-5.5 - Welding force: 4kN - Welding current: Medium frequency DC - Welding time: 320ms per pulse -Holding time: 200ms

[0305] For Examples 1-3, which have a thickness of 1.8 mm, the following parameters were used. -Electrode:F1-20-20-8 - Welding force: 5kN - Welding current: Medium frequency DC - Welding time: 3 pulses of 200ms each (pause time 40ms) -Holding time: 300ms

[0306] The dry paint adhesion and weld range evaluated in this manner are reported in Table 3.

[0307] [Table 3]

[0308] Referring to Tables 2 and 3, Examples 1 and 2 were manufactured using the method according to the present invention, with an E of 16 to less than 40. pc The value is such that the linear density of the crack is the minimum linear density of the crack dC min That's all.

[0309] Figure 2 shows a cross-sectional view of the coating of Example 2, as seen in one of the fields of view observed to evaluate the linear density of cracks. In this image, presented for illustrative purposes only, multiple cracks extending from the surface of the coating toward the steel substrate are observed.

[0310] Naturally, as mentioned above, the linear density of the cracks in Example 2 was not determined based on this single field of view, but rather by observing 20 fields of view and determining the linear density of the cracks over a sufficient observation length in dC. min This was determined by confirming that the crack density was greater than or equal to 10.8 cracks / mm.

[0311] In the embodiments of the present invention, it was observed that the cracks were distributed almost uniformly across the coating of the flat, undeformed portion, but this was not observed in Comparative Example 4, which is described below.

[0312] Furthermore, in the non-deformed areas, it was confirmed that the average width of the widest crack (i.e., the width of the cracks was greater than 90% of the total cracks) was less than 1 μm. In addition, no cracks or gaps with a width of 2 μm or more were observed in Examples 1 and 2.

[0313] In contrast, Figure 3 shows the coating on a non-deformable portion of a component not according to the present invention, which has only a few cracks.

[0314] As a result, both of these examples 1 and 2 exhibit excellent dry paint adhesion, meaning that in both cases the dry paint adhesion was less than 1, or actually 0, and that the paint was not removed at all or only slightly during the test, as well as excellent spot weldability, with a weld range of over 1 kA.

[0315] Therefore, Examples 1 and 2 are dC min The hot-stamped coated steel parts according to the present invention, having the above-mentioned linear density of cracks, have been demonstrated to achieve excellent paint adhesion and spot weldability.

[0316] In contrast, comparative example 3 exceeded the melting temperature of the pre-coating for too long a time t M It was manufactured in dC. min It has a lower linear crack density. As a result, Example 3 does not have satisfactory spot weldability, and the weld range is far below 1 kA.

[0317] Example 4 was manufactured from a pre-coated steel sheet with a pre-coating thickness exceeding 19.90 μm. Therefore, time t M T in hot stamping Mmin and T Mmax Although it was included between, Example 4 is more than 40 E pc It has a value of dC min It has a lower linear crack density than T. Mmin and T Mmax The value of T is closely related to the thickness of the pre-coating, Mmin and TMmax The time t included between and M Having such a coating is insufficient to achieve the target linear density of cracks, and the pre-coating thickness does not fall between 8.0 and 19.90 μm.

[0318] As a result, Example 4 does not have satisfactory paint adhesion.

[0319] Therefore, the example is E pc The value is between 16 and less than 40, and the non-deformable portion of the part has a coating of dC min If the linear density of the cracks is as described above, then it is confirmed that excellent spot weldability and excellent paint adhesion are achieved, at least in this portion.

[0320] Furthermore, the examples show a temperature T exceeding the melting temperature of the coating. close Furthermore, by adjusting the process so that the time spent on the blank is properly controlled, it has been demonstrated that the desired sufficient linear density of the cracks, and therefore the desired properties, can be achieved.

[0321] Therefore, steel components manufactured according to the present invention can be advantageously used in the manufacture of chassis or white body components or suspension arms for automobile vehicles.

Claims

1. A hot-stamped coated steel part comprising a steel substrate and an aluminum alloy coating on at least one surface of the steel substrate, wherein the coating comprises an interdiffusion layer and an outer layer that proceed outward from the steel substrate, and the total thickness of the coating e ｃｏａｔｉｎｇ and the thickness e of the interdiffusion layer ＩＤＬ The following conditions apply: 16≦E ｐｃ <40 In [Math 1] Satisfying the conditions, e ＩＤＬ The thickness of the interdiffusion layer is shown in μm, e ｃｏａｔｉｎｇ This indicates the total thickness of the coating in μm. Hot-stamped coated steel parts are available in thicknesses of 0.6 mm to 3.5 mm. Ｐｆｌａｔ The coating comprises a non-deformable portion and at least one deformable portion, wherein the linear density dC of cracks in the coating in the non-deformable portion is defined as the minimum linear density dC of cracks as follows: ｍｉｎ (e Ｐｆｌａｔ ) That is all, [Math 2] where dC and dC ｍｉｎ (e Ｐｆｌａｔ ) is represented by the number of cracks per 1 mm, and e ｐｆｌａｔ represents the thickness of the non-deformed part in mm, Hot-stamped coated steel parts.

2. The linear density dC of cracks in the coating in the non-deformed portion is 4 ＊ dC ｍｉｎ (e Ｐｆｌａｔ The hot-stamped coated steel part according to claim 1, wherein the part is as follows:

3. Hot-stamped coated steel parts have a uniform thickness e in the range of 0.6 mm to 3.5 mm. Ｐ A hot-stamped coated steel part according to claim 1 or 2, having the following characteristics:

4. Hot-stamped coated steel parts have variable thickness, and each hot-stamped coated steel part has a different thickness e in the range of 0.6 mm to 3.5 mm. Ｐｉ The hot-stamped coated steel part consists of two or more regions having an average thickness e in the range of 0.6 mm to 3.5 mm. Ｐ A hot-stamped coated steel part according to claim 1 or 2, having the following characteristics:

5. Hot-stamped coated steel parts, each with a thickness of 0.6 mm to 3.5 mm e ｐｆｌａｔ The coating comprises two or more non-deformable portions having (i), wherein the linear density of cracks in the coating in each non-deformable portion is dC(i). ｍｉｎ (e ｐｆｌａｔ (i) The above, [Math 3] In the formula, e ｐｆｌａｔ (i) shows the thickness of the non-deformable portion to be considered in mm, i = 1...n, n ≥ 2, and dC(i) and dC ｍｉｎ (e ｐｆｌａｔ (i) is expressed as the number of cracks per 1 mm, and each is equal to the thickness e Ｐｆｌａｔ A hot-stamped coated steel part according to any one of claims 1 to 4, showing the linear density of cracks and the minimum linear density of cracks in the coating of the non-deformable portion considered in (i).

6. The hot-stamped coated steel part according to any one of claims 1 to 5, wherein, in cross-section, cracks in the coating of the non-deformed portion extend from the top surface of the coating toward the steel substrate to a depth of at least 5 μm in a direction substantially perpendicular to the surface of the steel substrate, and each crack has a width of less than 2 μm in a direction substantially parallel to the surface of the steel substrate.

7. The hot-stamped coated steel component according to any one of claims 1 to 6, wherein the linear density of cracks is determined as the ratio of the total number of cracks observed in several cross-sections of the non-deformed portion with a bright-field optical microscope over the entire length of observation of at least 5 mm in a direction parallel to the surface of the steel substrate to the entire length of observation.

8. The hot-stamped coated steel component according to any one of claims 1 to 7, wherein the hot-stamped coated steel component is a monolithic component, or a hot-stamped welded component comprising at least two hot-stamped coated subcomponents and at least one hot-stamped weld that joins the hot-stamped coated subcomponents together.

9. The hot-stamped coated steel component according to claim 8, wherein each hot-stamped coated steel component or each hot-stamped coated subcomponent has a structure consisting of, by volume, at least 60% martensite, up to 20% bainite, up to 5% ferrite, and up to 15% austenite.

10. The amount of steel in a hot-stamped coated steel part, or in each hot-stamped coated subpart, is, by weight %, 0.062% ≤ C ≤ 0.4% 0.4% ≤ Mn ≤ 3.9% 0.10% ≤ Si ≤ 1.5% 0.005% ≤ Al ≤ 1.0% 0.001% ≤ Cr ≤ 2.0% 0.001% ≤ Ti ≤ 0.2% 0.0005% ≤ B ≤ 0.010% Ni ≤ 2% Nb ≤ 0.1% Mo ≤ 0.65% W ≤ 0.30% N ≤ 0.010% 0.0001% ≤ S ≤ 0.05% 0.0001% ≤ P ≤ 0.1% Ca ≤ 0.005% It has a chemical composition containing, The hot-stamped coated steel part according to claim 8 or 9, wherein the remainder of the composition consists of iron and unavoidable impurities resulting from the processing.

11. The steel in a hot-stamped coated steel part, or in at least one hot-stamped coated subpart, is, by weight %, 0.062% ≤ C ≤ 0.095% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.020% ≤ Al ≤ 0.070% 0.02% ≤ Cr ≤ 0.1% 1.5%≦(C+Mn+Si+Cr)≦2.7% 0.0035% ≤ Ti ≤ 0.072% 0.0002% ≤ B ≤ 0.004% 0.04% ≤ Nb ≤ 0.06% 0.044%≦(Nb+Ti)≦0.09% 0.001% ≤ N ≤ 0.009% 0.0005% ≤ S ≤ 0.003% 0.0001% ≤ P ≤ 0.020% Ca ≤ 0.005%, It has a chemical composition containing, The hot-stamped coated steel part according to claim 10, wherein the remainder of the composition consists of iron and unavoidable impurities resulting from the processing.

12. The steel in a hot-stamped coated steel part, or in at least one hot-stamped coated subpart, is, by weight %, 0.15% ≤ C ≤ 0.30% 0.5% ≤ Mn ≤ 3.0% 0.10% ≤ Si ≤ 0.50% 0.005% ≤ Al ≤ 0.1% 0.01% ≤ Cr ≤ 1.0% 0.001% ≤ Ti ≤ 0.2% 0.0002% ≤ B ≤ 0.010% 0.0005% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.05% 0.0001% ≤ P ≤ 0.1% Ca ≤ 0.005% It has a chemical composition containing, The hot-stamped coated steel part according to claim 10, the remainder being Fe and unavoidable impurities resulting from the processing.

13. The steel in a hot-stamped coated steel part, or in at least one hot-stamped coated subpart, is, by weight %, 0.3% ≤ C ≤ 0.4% 0.5% ≤ Mn ≤ 1.0% 0.40% ≤ Si ≤ 0.80% 0.01% ≤ Al ≤ 0.1% 0.1% ≤ Cr ≤ 1.0% 0.008% ≤ Ti ≤ 0.03% 0.0005% ≤ B ≤ 0.003% Ni ≤ 0.5% 0.01% ≤ Nb ≤ 0.1% 0.1% ≤ Mo ≤ 0.5% N ≤ 0.005% 0.0001% ≤ S ≤ 0.004% 0.0001% ≤ P ≤ 0.02% Ca ≤ 0.0010% It has a chemical composition containing, The hot-stamped coated steel part according to claim 10, wherein the remainder of the composition consists of iron and unavoidable impurities resulting from the processing.

14. A method for manufacturing hot-stamped coated steel parts, comprising the following series of steps: -Average thickness e of 0.6 mm to 3.5 mm Ｂ A step of providing a steel blank having, the steel blank having an aluminum or aluminum alloy pre-coating on at least one side, and the pre-coating having an average thickness between 8.0 μm and 19.90 μm, - To obtain a complete austenitic structure in the steel blank, the steel blank is heated in a furnace at a temperature T in the range of 850°C to 970°C. ｈｅａｔ Heat to a temperature T ｈｅａｔ The process of holding in, - The heated blank is transferred to the mold, and then the mold is closed. -0.6 mm to 3.5 mm thickness e Ｂｆｌａｔ A process of hot stamping a blank in a mold such that the flat portion of the blank having a certain feature does not undergo deformation, and at least a portion of the blank is deformed by hot stamping, thereby obtaining a hot-stamped blank having an undeformed portion and at least one deformed portion, - A process of cooling a hot-stamped blank to a temperature of less than 400°C to obtain a hot-stamped coated steel part, Includes, Blank temperature T when the mold is closed ｃｌｏｓｅ The melting temperature of the pre-coating is in the range of 720°C to 820°C, during heating, holding, transfer, and hot stamping. ｍｅｌｔ Time spent by the blank beyond t Ｍ The minimum time t is Ｍｍｉｎ and maximum time t Ｍｍａｘ It is within that range, [Math 4] and [Math 5] In the formula, t Ｍｍｉｎ and t Ｍｍａｘ It is expressed in seconds, T ｈｅａｔ The value indicates the heating temperature of the blank in °C, and T ｍｅｌｔ This indicates the melting temperature of the pre-coating in °C, and e Ｂｆｌａｔ This indicates the thickness in mm of the blank portion that has not been deformed. method.

15. The method according to claim 14, wherein the pre-coating is an aluminum alloy pre-coating containing, by weight, 7% to 15% silicon, 2% to 4% iron, and optionally 0.0015% to 0.0030% calcium, with the remainder being aluminum and unavoidable impurities.

16. The method according to claim 15, wherein the pre-coating is an aluminum alloy pre-coating containing, by weight, 8% to 11% silicon, 2% to 4% iron, and optionally 0.0015% to 0.0030% calcium, with the remainder being aluminum and unavoidable impurities.

17. In hot stamping of blanks within a mold, each has a thickness of 0.6 mm to 3.5 mm e Ｂｆｌａｔ (i) Two or more flat portions of the blank having are not deformed, and the melting temperature of the pre-coating T ｍｅｌｔ Time spent due to a blank period exceeding t Ｍ The minimum time t required for the flat portion having the highest thickness is Ｍｍｉｎ (Max(e Ｂｆｌａｔ（ｉ） ) and the maximum time t required for the flat portion with the lowest thickness Ｍｍａｘ (Min(e Ｂｆｌａｔ（ｉ） The method according to any one of claims 14 to 16, which falls within the range of )).

18. The blank has a minimum thickness e during hot stamping of the blank in the mold. Ｂｍｉｎ From maximum thickness e Ｂｍａｘ It has a variable thickness in the range up to and the melting temperature of the pre-coating T ｍｅｌｔ The time spent in a blank period beyond that point Ｍ is, maximum thickness e Ｂｍａｘ The minimum time required t Ｍｍｉｎ (e Ｂｍａｘ ) and minimum thickness e Ｂｍｉｎ The maximum time required t Ｍｍａｘ (e Ｂｍｉｎ The method according to any one of claims 14 to 17, which is in the range between )

19. The method according to any one of claims 14 to 18, wherein the steel blank is a monolithic blank, a tailor-rolled blank, or a tailor-welded blank manufactured by welding together at least two subblanks.

20. The blank or each sub-blank is, in weight %, 0.062% ≤ C ≤ 0.4% 0.4% ≤ Mn ≤ 3.9% 0.10% ≤ Si ≤ 1.5% 0.005% ≤ Al ≤ 1.0% 0.001% ≤ Cr ≤ 2.0% 0.001% ≤ Ti ≤ 0.2% 0.0005% ≤ B ≤ 0.010% Ni ≤ 2% Nb ≤ 0.1% Mo ≤ 0.65% W ≤ 0.30% N ≤ 0.010% 0.0001% ≤ S ≤ 0.05% 0.0001% ≤ P ≤ 0.1% Ca ≤ 0.005% It has a chemical composition containing, The method according to claim 19, wherein the remainder of the composition consists of iron and unavoidable impurities resulting from processing, and is manufactured by cutting a pre-coated steel sheet.

21. The chemical composition of the blank or at least one subblank is, in weight percent, 0.062% ≤ C ≤ 0.095% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.020% ≤ Al ≤ 0.070% 0.02% ≤ Cr ≤ 0.1% 1.5%≦(C+Mn+Si+Cr)≦2.7% 0.0035% ≤ Ti ≤ 0.072% 0.0002% ≤ B ≤ 0.004% 0.04% ≤ Nb ≤ 0.06% 0.044%≦(Nb+Ti)≦0.09% 0.001% ≤ N ≤ 0.009% 0.0005% ≤ S ≤ 0.003% 0.0001% ≤ P ≤ 0.020% Ca ≤ 0.005%, It contains, The method according to claim 20, wherein the remainder of the composition consists of iron and unavoidable impurities resulting from processing.

22. The chemical composition of the blank or at least one subblank is, in weight percent, 0.15% ≤ C ≤ 0.30% 0.5% ≤ Mn ≤ 3.0% 0.10% ≤ Si ≤ 0.50% 0.005% ≤ Al ≤ 0.1% 0.01% ≤ Cr ≤ 1.0% 0.001% ≤ Ti ≤ 0.2% 0.0002% ≤ B ≤ 0.010% 0.0005% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.05% 0.0001% ≤ P ≤ 0.1% Ca ≤ 0.005% It contains, The method according to claim 20, wherein the remainder is Fe and unavoidable impurities resulting from processing.

23. The chemical composition of the blank or at least one subblank is, in weight percent, 0.3% ≤ C ≤ 0.4% 0.5% ≤ Mn ≤ 1.0% 0.40% ≤ Si ≤ 0.80% 0.01% ≤ Al ≤ 0.1% 0.1% ≤ Cr ≤ 1.0% 0.008% ≤ Ti ≤ 0.03% 0.0005% ≤ B ≤ 0.003% Ni ≤ 0.5% 0.01% ≤ Nb ≤ 0.1% 0.1% ≤ Mo ≤ 0.5% N ≤ 0.005% 0.0001% ≤ S ≤ 0.004% 0.0001% ≤ P ≤ 0.02% Ca ≤ 0.0010% It contains, The method according to claim 20, wherein the remainder of the composition consists of iron and unavoidable impurities resulting from processing.

24. The process of providing the blank or each sub-blank consists of the following sequential steps, namely: - Process for providing steel semi-finished products, - Depending on the circumstances, the semi-finished product may be reheated to a temperature of 1100°C to 1300°C. - A process of hot-rolling semi-finished products to obtain hot-rolled steel sheets, A process of winding hot-rolled steel sheets at a winding temperature of -750°C or lower, - Depending on the circumstances, the process may involve pickling the hot-rolled steel sheet, - Depending on the circumstances, the process may involve cold-rolling hot-rolled steel sheets to obtain cold-rolled steel sheets. - A step of heating a hot-rolled or cold-rolled steel sheet to an annealing temperature between Ac1 and Ac3, A process of molten plating a steel sheet in an Al or Al alloy bath at a temperature of -670°C to 680°C, - A process of cooling the pre-coated steel sheet to room temperature, - A process of cutting pre-coated steel sheets to obtain blanks or sub-blanks, - Depending on the circumstances, a sub-blank may be welded together to produce a tailor-welded blank. The method according to any one of claims 19 to 23, including the method described in any one of claims 19 to 23.

25. Use of a hot-stamped coated steel part according to any one of claims 1 to 13, or a hot-stamped coated steel part manufactured by the method according to any one of claims 14 to 24, for the manufacture of a chassis or white body part or suspension arm for an automobile vehicle.

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