COMPONENT WITH AN INTEGRATED NICKEL DIFFUSION LAYER

Description

[0001] The invention relates to a component having a steel component, wherein the component is coated with a nickel diffusion layer, wherein the component is a fastening means, such as a screw or a nut.

[0002] Metal components, especially high-strength and ultra-high-strength components, are susceptible to hydrogen embrittlement. Hydrogen embrittlement is caused by the penetration of hydrogen into the metal structure of the components and leads to intergranular cracking when the components are subjected to stress. This phenomenon is known as hydrogen-induced stress corrosion cracking.

[0003] US 2016 / 0168657 A1 relates to a method for producing a surface-treated steel sheet for battery containers, comprising a first method for forming an iron-nickel alloy plating layer on at least one side of the steel sheet, a second method for forming a nickel plating layer on the iron-nickel alloy plating layer; and a third method for performing a heat treatment after forming the nickel plating layer to form, by thermal diffusion, an iron-nickel alloy layer having an outermost surface in which the content of Fe atoms is 12 to 55 atomic % on an outermost layer.

[0004] The present invention is based on the object of reducing the tendency towards hydrogen-induced stress corrosion cracking in steel components, wherein the component is a fastening means.

[0005] This object is achieved with a fastening means having a component made of steel according to claim 1 and a use according to claim 8. Further features, embodiments and advantages emerge from the subclaims, the description and the figures.

[0006] One aspect of the invention may relate to a component with a steel component, wherein the component is a fastening means, wherein the steel component has and / or forms a threaded region, wherein the component is at least partially coated, in particular in the threaded region, with a nickel diffusion layer, wherein the layer thickness of the nickel diffusion layer is 5 - 300 µm, wherein the nickel diffusion layer has a nickel content, based on the total weight of the nickel diffusion layer, of 2 wt.% above the nickel content of the steel up to a maximum concentration, wherein the nickel content in the nickel diffusion layer increases continuously towards the surface of the nickel diffusion layer from 2 wt.% above the nickel content of the steel up to the maximum concentration, and wherein the maximum concentration is 20 - 100 wt.%, wherein the layer thickness of the nickel diffusion layer and the nickel content are measured according to the description. The

[0007] The fastening means is expediently a screw, in particular a high-strength or even an ultra-high-strength screw, or a nut, in particular a high-strength or even an ultra-high-strength nut.

[0008] Also described is a method for producing a component with a steel component, the component being a fastener, comprising the steps: a) Providing a fastening means with a component made of steel, wherein the component (1) has and / or forms a threaded region and / or shaft region, b) Applying a nickel layer comprising ≥ 30 wt.% nickel, based on the total weight of the nickel layer, to the component made of steel, in particular in the threaded region and / or shaft region, and subsequently c) Heating the component and the nickel layer for at least 10 minutes, preferably for at least 20 minutes, to 750 to 950 °C, whereby a nickel diffusion layer is produced on the component made of steel.

[0009] A further aspect of the invention relates to the use of the fastening agent according to the invention for reducing hydrogen embrittlement.

[0010] Surprisingly, the nickel diffusion layer according to the invention acts on steel components as a pronounced barrier against the penetration of hydrogen by diffusion and thereby increases the resistance of the components to hydrogen-induced stress corrosion. The diffusion process and thus the formation of the nickel diffusion layer also improves the adhesion of the nickel layer to the steel, as the nickel layer essentially grows together with the steel of the component. Preventing hydrogen-induced stress corrosion is particularly advantageous and desirable, especially in the case of fasteners, which usually have high and often dynamic axial stress, because these fasteners, which can be screws or nuts, for example, are essential for many assemblies. For example, the failure of a fastener, in particular a high-strength or ultra-high-strength screw, can have drastic consequences for people or machines, such as:B. in an engine head screw, a bridge screw, a cylinder head screw, a chassis screw, and / or a battery fastening screw. In other words, the invention can also relate to a vehicle, an engine, in particular a cylinder head, a chassis assembly, or a battery assembly with a component, in particular a fastening means, having the nickel diffusion layer according to the invention, or to a structure, in particular such as a bridge.

[0011] To produce the nickel diffusion layer, the steel component, for example, a high-strength or ultra-high-strength screw, is coated with a nickel layer. All known coating methods are suitable, in particular electroplating or PVD (physical vapor deposition). Alternatively, or additionally and preferably, the coating can also be carried out by laser melting and / or laser metal deposition. These processes, in particular, allow for particularly cost-effective coating. Furthermore, the coating can also be carried out by deposition welding, which can also be referred to as cladding, to achieve a particularly mechanically resilient coating.

[0012] In the subsequent heating step, nickel diffuses into the iron lattice of the steel and iron into the nickel layer. This creates a nickel diffusion layer that is thicker than the original nickel layer. In addition to the iron, any alloying components of the steel also diffuse into the nickel layer. The nickel diffusion layer exhibits a concentration gradient, with the nickel concentration continuously increasing towards the surface of the nickel diffusion layer. The iron concentration continuously decreasing towards the surface of the nickel diffusion layer. Furthermore, the concentration of any alloying components of the steel continuously decreasing towards the surface of the nickel diffusion layer. The surface is in particular the area that borders the nickel diffusion layer distally opposite or facing away from the steel component.The nickel diffusion layer is therefore delimited by the surface, particularly distally opposite the steel component. This surface can itself be coated and / or the surface can, for example, be a free surface that is not coated. In other words, the surface can be exposed or covered by a coating and / or by another component. The surface is therefore, in particular, the area or the resulting interface where the maximum concentration is present.

[0013] A steel component within the meaning of the invention can be understood in particular to mean that at least a portion of the component, i.e., a volume region, is made of steel. It is particularly preferred if at least 80%, preferably at least 90%, and particularly strongly preferred at least 95% of the component's weight consists of steel or is formed by the steel component. This allows particularly good mechanical strength of the component, in particular of the fastening means, to be achieved. In order to increase mechanical strength, it is particularly preferred if the steel component is made in one piece. "Integral" can be understood in particular to mean that at least the one-piece part has been created in a primary forming process and / or is continuous.

[0014] For the purposes of the invention, the nickel diffusion layer is defined as the region of the steel component having a nickel content, based on the total weight of the nickel diffusion layer, from 2 wt.% above the nickel content of the steel up to a maximum concentration, wherein the maximum concentration is 20 - 100 wt.% nickel. If, for example, the steel used does not contain any nickel, the nickel diffusion layer is the layer having a nickel content of 2 wt.% up to the maximum nickel concentration. Pure nickel can be present on the surface of the nickel diffusion layer, i.e. the maximum concentration is then 100 wt.%. In this case, for a steel without a nickel content, the nickel concentration in the nickel diffusion layer is between 2 and 100 wt.%.

[0015] If, in the above-mentioned case, the iron diffuses to the surface of the original nickel layer during diffusion, the maximum concentration is below the original nickel content of the nickel layer, for example, below 100 wt.% if a pure nickel layer was applied. For example, it could be 98 wt.%. In this case, the nickel diffusion layer has a nickel content of 2-98 wt.%.

[0016] If the steel of the component part is an alloyed steel with a nickel content of, for example, 1 wt.%, the nickel content in the nickel diffusion layer is 3 wt.% up to the maximum concentration. If the maximum concentration at the surface is 100 wt.%, the nickel content in the nickel diffusion layer is 3–100 wt.%. If iron and / or other alloying constituents of the substrate or steel component diffuse to the surface during the heating step, resulting in a maximum concentration of 95 wt.% at the surface of the nickel diffusion layer, the nickel content in the nickel diffusion layer is 3–95 wt.%.

[0017] For the purposes of the invention, "coated" with a nickel diffusion layer means that the steel component has a nickel diffusion layer on its outside in cross-section. This means, in particular, that the steel component is bordered in at least one spatial direction by a firmly adhering layer of amorphous material, which is a nickel diffusion layer. Advantageously, the coating can comply with DIN 8580 – particularly in the version applicable as of May 1, 2021.

[0018] The thickness of the nickel diffusion layer depends, among other things, on the thickness of the originally applied nickel layer and the duration and temperature of the heating step. According to the invention, the thickness of the nickel diffusion layer is 1-500 µm, preferably 3-300 µm, particularly preferably 5-150 µm, especially 7-100 µm, and most preferably 10-70 µm. The lower thicknesses of the preferred embodiments of the nickel diffusion layer are particularly advantageous for precisely fitting components.

[0019] The "layer thickness" of the nickel layer and the nickel diffusion layer refers to the average layer thickness, provided the top or bottom surface is uneven. For this purpose, at least three measurements of the layer thickness are taken, preferably six to eight measurements, and the arithmetic mean of the measured values ​​is determined.

[0020] The maximum concentration of nickel in the nickel diffusion layer is 20-100 wt.%. 40-100 wt.% is preferred, further preferred is 70-100 wt.%, particularly preferred is 70-99.5 wt.%, in particular 80-99.2 wt.%, and most preferred is 90-99.0 wt.%. These maximum concentrations of nickel in the nickel diffusion layer lead to a particularly advantageous design with regard to hydrogen embrittlement.

[0021] The nickel content in the nickel diffusion layer increases continuously toward the surface of the nickel diffusion layer. The increase occurs from 2 wt.% above the nickel content of the steel up to the maximum concentration, for example, 70–99.5 wt.%. Preferably, the nickel content in the nickel diffusion layer increases perpendicularly toward the surface of the nickel diffusion layer. Furthermore, it is preferred that the nickel content in the nickel diffusion layer increases continuously perpendicularly toward the surface of the nickel diffusion layer.

[0022] To further adapt the surface of the component with a steel component to the respective application, it is preferred that a further layer be applied to the nickel diffusion layer, in particular selected from a nickel layer, a corrosion protection layer, a wear protection layer, and a sliding layer. Phosphate layers, zinc-nickel layers, and zinc flakes are preferred, especially when the component is a fastener, advantageously a screw or bolt. These layers are particularly advantageous with regard to improving corrosion resistance and / or friction properties.

[0023] Advantageously, the steel component is coated with the nickel diffusion layer in areas with increased notch effect and / or adjacent areas to areas with increased notch effect, in particular in areas of a thread, under a head, e.g. of a screw, notches or grooves. Areas with an increased notch effect are in particular areas which have a notch effect factor of more than 1.1, preferably more than 1.4, particularly preferably more than 1.9 and particularly strongly preferably more than 2.1. In an area of ​​a thread, a groove or under a (screw) head or in the transition to the screw head, an area with increased notch effect within the meaning of the invention is therefore advantageously to be seen. An area adjacent to an area with increased notch effect is to be seen as an area which is a maximum of 10 mm, preferably a maximum of 5 mm and particularly preferably a maximum of 2 mm, away from the area with increased notch effect.Alternatively, an adjacent region to a region with increased notch effect may also be present if it is spaced from the region with increased notch effect by a maximum of 10%, preferably a maximum of 5%, particularly preferably a maximum of 2%, of the largest main dimension of the steel component.

[0024] A nickel layer in the sense of the present invention is preferably a layer whose nickel content, based on the total weight of the nickel layer, is ≥ 30 wt.%, more preferably ≥ 50 wt.%, even more preferably ≥ 70 wt.%, in particular ≥ 90 wt.% and most preferably 100 wt.%.

[0025] The nickel layer may comprise a nickel alloy, preferably a Ni-Co, Ni-Mn, and / or Ni-Co-Mn alloy. In these nickel layers, also referred to as nickel alloy layers, the nickel content, based on the total weight of the layer, is ≥ 30 wt.%, more preferably ≥ 50 wt.%, and even more preferably ≥ 70 wt.%.

[0026] The steel of the component part can be a high-alloy steel or a low-alloy steel, with a low-alloy steel being preferred. Alternatively or additionally, the steel, in particular low-alloy steel, can also be an unalloyed steel. A low-alloy steel is understood within the meaning of the invention to be a steel whose total proportion of alloying elements does not exceed 5 wt. %, in particular of the alloying elements Cr, Mo, V, Ni, Mn, Al, B and Ti, based on the total weight of the steel. The term low-alloy steel within the meaning of the invention also includes micro-alloyed steels. A high-alloy steel is understood within the meaning of the invention to be a steel whose total proportion of alloying constituents is greater than 5 wt. %, in particular of the alloying elements Cr, Mo, V, Ni, Mn, Al, B and Ti, based on the total weight of the steel. An unalloyed steel is understood within the meaning of the invention to be a steel which contains up to 0.8 wt.-% carbon and less than 1 wt.% manganese, based on the total weight of the steel.

[0027] In a preferred embodiment of the invention, the steel of the component part is a low-alloy steel with a nickel content of < 1 wt.%, based on the total weight of the steel component. Furthermore, the steel is preferably a high-strength or ultra-high-strength steel. The advantage of low-alloy steel is that it can be particularly well tempered and, simultaneously or alternatively, can provide a particularly high degree of strength, so that the advantages achieved by the invention, particularly with regard to hydrogen embrittlement, can be particularly well realized.

[0028] In a preferred embodiment of the invention, the microstructure of the steel component in the component is at least predominantly martensitic, bainitic, and / or dual-phase (residual austenite, ferrite, and / or martensite). Preferably, the microstructure of the steel component in the component is at least 80 wt.%, in particular at least 90 wt.%, martensitic, bainitic, and / or dual-phase (residual austenite, ferrite, and / or martensite), in each case based on the total weight of the steel component. These microstructures impart particularly high strength and toughness to the component according to the invention. These microstructures can be subjected to high and often dynamic axial stress, so that the reduction of hydrogen embrittlement is particularly advantageous for them. The microstructure in the nickel diffusion layer can differ from the microstructure of the remaining steel component (the so-called base material).The element distribution in the nickel diffusion layer is advantageously characterized by a high concentration of two elements, namely iron and nickel. Depending on the composition of the steel component, the other alloying elements can be present as dissolved elements or as intermetallic precipitates in the nickel diffusion layer.

[0029] The component according to the invention is preferably a high-strength or ultra-high-strength component, in particular with strengths above 1000 MPa, preferably above 1200 MPa, particularly preferably above 1400 MPa, and particularly highly preferably above 1600 MPa. Preferred high-strength and ultra-high-strength components are high-strength or ultra-high-strength screws or fasteners, springs, leaf springs, disc springs and chain drives, formed components, and / or structural components. Further or alternatively, the component according to the invention, in particular the high-strength or ultra-high-strength component, is preferably a welded component, an additively manufactured component, or a case-hardened component. Particularly in welded components, high hydrogen embrittlement can occur due to welding, so the invention can be particularly well-suited for use here.For a case-hardened component, the component is additionally case-hardened during production, particularly by carburizing, nitriding, or nitrocarburizing. The component is then coated with nickel, as described here.

[0030] A formed component is understood in particular to be a component which has been formed by means of a forming step, in particular a cold forming process. Especially in the case of a formed component, in particular a cold formed component, it is particularly advantageous to avoid brittleness, in particular hydrogen embrittlement, because formed components already exhibit a certain degree of brittleness due to the accumulated Wald dislocations. A structural component within the meaning of the invention exists in particular when the component is a load-bearing component. This structural component has in particular two load introduction sections, which advantageously contain load-introducing structures, such asmounting recesses or openings, and a transmission region arranged between the load introduction sections, which transmission region can and / or transmits a load, in particular a bending load and / or tensile load, from one load introduction section to the other load introduction section. Advantageously, at least one, preferably all load introduction sections, and / or the transmission region are equipped with the nickel diffusion layer according to the invention. The design of the component such that the steel has a strength of over 1000 MPa, preferably over 1200 MPa, particularly preferably over 1400 MPa and particularly strongly preferably over 1600 MPa, is particularly advantageous because hydrogen embrittlement is becoming increasingly critical in these strength classes, so that the invention can exploit its advantages precisely at these strengths.

[0031] The fastening means according to the invention can in particular be force-fitting fastening means, such as screws, bolts or nuts. Force-fitting fastening means are characterized in particular by the fact that they have a threaded portion for clamping or fastening, in particular with an external thread or an internal thread. For example, the threaded portion can therefore be an external thread or an internal thread. Advantageously, this threaded portion is introduced into a component of the fastening means which is made of steel. In other words, the steel component can have a threaded portion which can be coated with the nickel diffusion layer set out above and below. Expediently, in particular at least three, preferably at least five, and particularly preferably all threads of the threaded portion are coated with the nickel diffusion layer.Advantageously, at least the distal end threads are those threads which are coated with the nickel diffusion layer. The end threads are in particular the threads which form one end of the threaded section or the end regions of the threaded section or the thread run-out. Alternatively or additionally, the nickel diffusion layer can also preferably be present in a shaft region. The shaft region is in particular a region of the fastening means which lies between the head, in particular the screw head, and the threaded section of the fastening means and mechanically connects them to one another. Preferably, the shaft region can be threadless and / or designed as a cylindrical section. The diameter of the shaft can be greater than, less than, or equal to the thread diameter in the threaded section. By applying orBy forming a nickel diffusion layer—as described above and below—in the shaft area, the mechanical properties of the fastener can be positively influenced according to the invention. The screws are advantageously high-strength or ultra-high-strength screws.

[0032] The steel component in the component according to the invention is at least partially coated with a nickel diffusion layer, i.e. the component is partially or completely coated with a nickel diffusion layer.

[0033] In a particularly preferred embodiment of the invention, the component is a high-strength or ultra-high-strength screw. A high-strength screw is understood to be a screw with a tensile strength of at least 800 MPa. High-strength screws are, for example, screws of strength classes 8.8, 10.9, and 12.9. In particular, the strength classes of the invention correspond to ISO 898-1 in the version valid as of January 2021. An ultra-high-strength screw is understood to be a screw with a tensile strength, in particular of at least 1200 MPa and / or advantageously of 1400 MPa. Ultra-high-strength screws include screws in strength classes 12.8, 12.9, 14.8, 14.9, 15.8, 15.9, 16.8, 16.9, 17.8, and 12.8U, 12.9U, 14.8U, 14.9U, 15.8U, 15.9U, 16.8U, and 17.8U. A high-strength screw is a screw that is at least high-strength, but can also be ultra-high-strength.Preferably, it is a high-strength or ultra-high-strength screw with a strength of over 1000 MPa. The component of the component or screw having the nickel diffusion layer is particularly preferred, namely the shaft and / or the threaded area of ​​the screw, because this is precisely where strong dynamic loads occur during operation of the screw, increasing the screw's susceptibility to hydrogen embrittlement, which can be prevented or at least significantly reduced by the invention. The screw can have a head with tool engagement surfaces, wherein these tool engagement surfaces together form, in particular, an internal or external hexagon. It is particularly preferred if the entire screw is coated with the nickel diffusion layer.

[0034] In a preferred embodiment of the invention, the component with a component made of steel is a fastening means, wherein the component has and / or forms a threaded region and / or a shaft region, wherein the component is at least partially coated with a nickel diffusion layer, in particular in the threaded region and / or in the shaft region, wherein the layer thickness of the nickel diffusion layer is 1 - 500 µm, wherein the nickel diffusion layer has a nickel content, based on the total weight of the nickel diffusion layer, of 2 wt.% above the nickel content of the steel up to a maximum concentration, wherein the nickel content in the nickel diffusion layer increases continuously towards the surface of the nickel diffusion layer from 2 wt.% above the nickel content of the steel up to the maximum concentration, and wherein the maximum concentration is 20 - 100 wt.%, preferably 40 - 100 wt.-%, preferably wherein the steel is a low-alloy steel or an unalloyed steel.

[0035] As described above, the fastening means is preferably a high-strength or ultra-high-strength fastener, in particular a screw or nut.

[0036] A method for producing the component according to the invention is also described. The method according to the invention comprises the following steps: a) providing a component, wherein the component is a fastener, with a steel component, b) applying a nickel layer comprising ≥ 30 wt.% nickel, based on the total weight of the nickel layer, to the steel component, and c) heating the component and the nickel layer for at least 20 minutes to 750 to 950 °C, thereby producing a nickel diffusion layer on the steel component.

[0037] The above-mentioned steps a), b), and c) are performed in this order. As described above, the thickness of the nickel diffusion layer depends, among other things, on the thickness of the originally applied nickel layer and the duration and temperature of the heating step. The nickel layer applied in step b) preferably has a thickness of 0.1-100 micrometers (µm), more preferably 0.5-80 µm, even more preferably 1-50 µm, particularly preferably 1.5-30 µm, and in particular 2.5-15 µm.

[0038] The heating step preferably lasts at least 10 minutes, preferably at least 15 minutes, and particularly preferably at least 20 minutes. Furthermore, it is preferred that the heating takes place for 10-600 minutes, particularly preferably for 15-400 minutes, and most preferably for 20-180 minutes. The heating takes place at 750-950°C for the specified periods, preferably at 800-950°C, particularly preferably at 820-920°C, and especially at 830-900°C. This achieves advantageous interdiffusion between iron and nickel to form the nickel diffusion layer, which counteracts hydrogen embrittlement.

[0039] After the heating step c), further steps may follow, in particular a tempering step d). Alternatively or additionally, the tempering step may preferably also take place during and / or simultaneously with or together with the heating step c). In other words, the tempering and heating can take place together in a single step. This allows for a particularly rapid and cost-effective creation of the nickel diffusion layer, particularly in the case of a low-alloy steel. For example, martensitic tempering (preferably by quenching in oil, air, and / or water) or bainitic treatment (preferably in a salt bath) can be carried out. Martensitic tempering or bainitic treatment take place under the usual conditions.

[0040] Heating step c) can thus be a separate heating step, for example, in a furnace, or the heating step can take place during the quenching and tempering of the component, for example, during the austenitization of the steel. Preferably, the heating step takes place during the quenching and tempering of the component.

[0041] A method for manufacturing a component is also described, comprising the steps: a) Providing a component with a steel component, wherein the component is a fastening means and the component has and / or forms a threaded region and / or shaft region, wherein the steel is a low-alloy steel or an unalloyed steel, b) Applying a nickel layer comprising 40 - 100 wt.% nickel, based on the total weight of the nickel layer, to the steel component, in particular in the threaded region and / or shaft region, and c) Heating the component and the nickel layer for at least 10 minutes, preferably at least 20 minutes, to 750 to 950 °C, whereby a nickel diffusion layer is produced on the steel component.

[0042] In the method, the preferred and particularly preferred features of the component are also preferred and particularly preferred.

[0043] The invention also relates to the use of the fastening means according to the invention for preventing or reducing hydrogen embrittlement. The use preferably comprises the use of the described, preferred components for preventing or reducing hydrogen embrittlement, for example a fastening means with a threaded region. This particularly relates to the reduction or prevention of hydrogen embrittlement in the component caused by hydrogen that can penetrate from the outside, for example during the intended use of the component. This can be the case, for example, when the component according to the invention, for example a fastening means, is used in a corrosive environment. The nickel diffusion layer according to the invention then particularly effectively protects the component against hydrogen embrittlement by reducing or preventing the penetration of hydrogen into the component.

[0044] A preferred embodiment of the invention relates to the use of the fastening means according to the invention in a battery assembly or a fuel cell. Batteries or fuel cells often generate relatively large amounts of hydrogen, and in these cases, the nickel diffusion layer according to the invention can particularly advantageously prevent hydrogen embrittlement.

[0045] The invention also relates to a battery assembly and / or fuel cell comprising a fastening means according to the invention, in particular a fastening means according to the invention. Here, the above-described advantages of avoiding hydrogen embrittlement are achieved particularly effectively due to the relatively high amounts of hydrogen generated in battery assemblies or fuel cells.

[0046] The above-described advantageous embodiments of the method are also advantageous for this preferred method, in particular the mentioned preferred and particularly preferred layer thicknesses, temperatures, heating times and / or advantageous components, etc.

[0047] The microstructure of the steel component before heating step c) can be ferritic, ferritic-pearlitic, bainitic, GKZ-annealed, or a mixed microstructure. After quenching and tempering step d), the microstructure of the component can, in a preferred embodiment, be martensitic, bainitic, ferritic-martensitic, or dual-phase (retained austenite, ferrite, and / or martensite).

[0048] It is understood that the features mentioned above and those to be explained below can be used not only in the specified combinations, but also in other combinations or alone, without departing from the scope of the present invention. The advantages of features or combinations of several features mentioned are merely exemplary and can be used alternatively or cumulatively. The combination of features of different embodiments of the invention or of features of different patent claims is possible, deviating from the selected references to the patent claims.

[0049] The following example further explains the invention. Measurement method for layer thickness determination:

[0050] The thickness of the nickel layer is preferably measured with a micrometer, for example, using the method according to ASTM C664-10 (as published in 2020, Test Method A). This essentially involves measuring the thickness of the component before and after plating, and the difference is used to determine the layer thickness.

[0051] The thickness of the nickel diffusion layer can be determined by first measuring the thickness of the component after it has been coated with the nickel layer and the nickel diffusion layer has been formed through the heating step. The nickel diffusion layer is then removed, for example by grinding, and the composition of the material is analyzed, for example by chemical analysis of the removed material or chemical analysis of the remaining surface material. Examples of analysis methods that can be used are wet chemical processes or atomic force microscopy (AFM). Material is removed as long as the removed material has a nickel content of at least 2 wt.% higher than the nickel content of the steel, based on the total weight of the nickel diffusion layer. After the nickel diffusion layer has been removed, the nickel content of the steel on the surface of the component is just below 2 wt.-% above the nickel content of the steel, and the thickness of the component is measured again with a micrometer. The difference determines the thickness of the nickel diffusion layer.

[0052] Alternatively, the thickness of the nickel diffusion layer can be determined using the method according to ASTM C664-10 (as published in 2020, Test Method B). This essentially involves measuring the layer thickness in a cross-section using an optical microscope. It is also possible to determine the thickness of the nickel diffusion layer in a cross-section using energy-dispersive X-ray spectroscopy (EDS, EDX, EDXS, or XEDS). Example:

[0053] Production of a nickel diffusion layer and its influence on hydrogen-induced stress corrosion cracking. A component with a nickel diffusion layer is manufactured from steel as a substrate material using axial cold forming. The starting material is fed to the forming machine in the form of a wire coil. The formed product has the geometry of a screw. This is followed by cleaning in a sodium hydroxide solution and inhibited HCl to remove the lubricant (phosphate) required for forming, thus preventing the diffusion of phosphorus into the substrate during subsequent heat treatment. The surface is activated using 10% sulfuric acid. A nickel layer is then applied by electrodeposition using a conventional nickel bath (55°C for 15 min, current density 0.8–1 A / dm²).A 2-3 µm Ni layer is created (determined according to the method described above). This is followed by rinsing in deionized water and drying.

[0054] For better adhesion, an additional nickel layer <1µm thick can be applied before the nickel layer, e.g. in the so-called Ni-Strike process.

[0055] After the coating is applied, the component is austenitized for 30 minutes in a protective gas atmosphere at a temperature of 850°C for quenching and tempering. During this time, the nickel interdiffusion occurs into the substrate material and vice versa. A zone is formed with a gradient in nickel concentration. To achieve the desired microstructure and mechanical properties of the component, quenching is performed immediately after austenitization. During the quenching process, a suitable microstructure is established. Within the diffusion layer, the material transforms according to its local nickel concentration. The resulting component had a tensile strength of 1600 MPa–1650 MPa.

[0056] Experimental assessment of the influence of the nickel diffusion layer on hydrogen-induced stress corrosion cracking: The phenomenon of hydrogen-induced stress corrosion cracking in high-strength steel materials generally requires three external influencing factors. These are: 1. Material susceptible to hydrogen-induced stress corrosion cracking 2. High mechanical tensile or bending stresses in the component 3. Hydrogen availability in the environment

[0057] To evaluate the material's behavior with regard to hydrogen-induced stress corrosion cracking, a test setup that reproducibly replicates the two remaining factors is therefore suitable. The test setup according to DIN EN ISO 7539-7 is used for the assessment.

[0058] The evaluation according to DIN EN ISO 7539-7 Chapter 7.3 according to the "Integral of the nominal stress / strain curve" has proven particularly precise. In each case, the system consisting of the above-mentioned influencing factors in the state without hydrogen in the environment is compared with the system with hydrogen in the environment for characterization. After evaluating the characteristic value of the "Integral of the nominal stress / strain curve," a value for the total deformation energy absorbed by the component is obtained for each of the two states. Using the formula HE = 1 − W Bh Verformungsenergie mit H − Beladung W Bu Verformungsenergie ohne H − Beladung The so-called HE value is determined from the two determined deformation energies. The HE value can range between 0 and 1. A value of HE=0 means no influence on the material properties, while HE=1 means failure under hydrogen without load (the latter is a theoretical extreme value and not possible in reality). The integrals of the nominal stress / strain curve for W Bh and W Bu are shown schematically for the above-mentioned screw components in Fig: 2 shown. Materials required to conduct the test:

[0059] 1. Components in the condition to be tested 2. 37% HCl 3. Deionized water 4. Instrumented tensile / compression testing machine

[0060] The test to characterize the screws with integrated nickel diffusion layer is carried out by determining the reference value without hydrogen exposure, W Bu. This is determined using the average value of three specimens tested at a strain rate of 0.0067 1 / s in the instrumented tensile / compression testing machine. W Bu = 268 J was determined.

[0061] To determine the deformation energy under the influence of hydrogen (W Bh), three samples from an identical production batch as above were immersed in 37% HCl for 10 minutes to introduce hydrogen through the cathodic partial reaction of acid corrosion. Immediately afterwards, the treated samples were tested in an instrumented tensile / compression testing machine at an elongation rate of 0.02 mm / min (total test duration 4 hours) to determine W Bh. W Bh = 246 J was determined.

[0062] Overall, a susceptibility to hydrogen-induced stress corrosion cracking of HE=0.08 was determined.

[0063] In the Fig. 2 and 3 the comparison between the known components and the component according to the invention with integrated nickel diffusion layer is shown.

[0064] Further advantages and features of the present invention will become apparent from the following description with reference to the figures. Individual features of the illustrated embodiments may also be used in other embodiments, unless expressly excluded. It shows: Figure 1 shows a component according to the invention; Figure 2 shows a tensile-elongation diagram for a device according to the invention; and Figure 3 shows a tensile-elongation diagram for a device not according to the invention; In the figure 1 A component according to the invention is shown. The component has a component 1 made of steel. The component can in particular be a fastening means or a spring. The component 1 is at least partially coated with a nickel diffusion layer 10, wherein the layer thickness of the nickel diffusion layer is 1 to 500 µm. The arrow in the nickel diffusion layer 10 of the Figure 1 indicates the decrease in the concentration of nickel in the nickel diffusion layer 10 as well as the thickness direction, in which in particular the thickness of the nickel diffusion layer 10 can be determined. The nickel diffusion layer is distally opposite to the component 1 of Steel is limited by the surface 12. This surface 12 can itself be coated.

[0065] In the Figure 2A tension-strain diagram is shown, which resulted from a product according to the invention or a device according to the invention. In the diagram, the nominal stress - in Figure 2 Indicated in MPa, plotted against strain (%). From this tension-strain diagram, the HE value can be determined, or the absorbed (specific) deformation energy can be determined.

[0066] The HE value is calculated using the formula: HE = 1 − W Bh Verformungsenergie mit H − Beladung W Bu Verformungsenergie ohne H − Beladung

[0067] The W Bh value is the absorbed (specific) deformation energy of the component when the component was treated with hydrogen. The W Bu value, on the other hand, is the absorbed deformation energy when the component was not treated with hydrogen. Figure 2As can be seen schematically, the absorbed deformation energy of the component treated with hydrogen is only slightly lower than the absorbed energy of the component that was not treated with hydrogen. In other words, no or at most only slight embrittlement occurred due to the hydrogen.

[0068] In the Figure 3 Another tensile-strain diagram of a test is shown, where the components used for the test did not correspond to the invention. Figure 3 can be seen, the plastic energy absorbed by the component treated with hydrogen is significantly lower than that of the component that was not treated with hydrogen. Figures 2 and 3In the diagrams shown, the fracture of the component with hydrogen treatment or the failure is marked with an asterisk. The fracture of the component that was not treated with hydrogen is marked with a cross. Figures 2 and 3 The same scales were used to enable comparison.

Claims

1. Component with a steel constituent (1), where the component is a fastener, wherein the component (1) has and / or forms a threaded area and / or shank area, wherein the component (1) is at least partially coated with a nickel diffusion layer (10), in particular in the threaded area and / or shank area, wherein the layer thickness of the nickel diffusion layer (10) is 5 - 300 µm, wherein the nickel diffusion layer (10) has a nickel content, based on the total weight of the nickel diffusion layer, of 2 wt.-% above the nickel content of the steel up to a maximum concentration, wherein the nickel content in the nickel diffusion layer (10) increases continuously in the direction of the surface (12) of the nickel diffusion layer (10) from 2 wt.-% above the nickel content of the steel to the maximum concentration, and wherein the maximum concentration is 20 - 100 wt.-%, wherein the layer thickness of the nickel diffusion layer (10) and the nickel content are measured according to the present description.

2. Component according to claim 1, characterized in that the maximum concentration is 70 - 99.5 wt.-%, preferably 80 - 99.2 wt.-%.

3. Component according to any one of the preceding claims, characterized in that the nickel content in the nickel diffusion layer (10) increases perpendicularly in the direction of the surface (12) of the nickel diffusion layer (10).

4. Component according to any one of the preceding claims, characterized in that a further layer is applied to the nickel diffusion layer (10), selected from nickel layer comprising ≥ 90 wt.-% nickel, based on the total weight of the nickel layer, corrosion protection layer, wear protection layer and sliding layer.

5. Component according to any one of the preceding claims, characterized in that the steel is a low-alloy steel, a micro-alloy steel or an unalloyed steel.

6. Component according to any one of the preceding claims, characterized in that the component is selected from the group consisting of high-strength and ultra-high-strength components, welded components, additive-manufactured components, formed components and / or case-hardened components.

7. Component according to any one of the preceding claims, characterized in that the component is a high-strength or ultra-high-strength component selected from the group consisting of screws, springs, leaf springs, disc springs and chain drives.

8. Use of a component according to any one of claims 1 to 7 for reducing hydrogen embrittlement, in particular use in a battery arrangement and / or a fuel cell.

9. Battery arrangement or fuel cell comprising a mounting means according to any one of claims 1 to 7.