Method for producing special steels and semifinished products and moulded parts based thereon

Abstract

The invention relates to a method for producing high-nitrogen alloyed iron-based powders, comprising the following steps: a) providing (1100) at least one solid iron-based material with a starting nitrogen amount (NBasis) of 0.2 to 1.5 wt.%, b) providing (1200) a nitrogen-containing atmosphere with an excess pressure (PN) in a working space (2), wherein the excess pressure (PN) is set corresponding to the starting nitrogen amount (NBasis) and to a target nitrogen amount (NZiel) of the iron-based material, c) at least partially melting (1300) the iron-based material to form a melt in the working space (2) at excess pressure (PN), d) atomising (1400) the melt by way of an atomising gas to form an iron-based powder with the target nitrogen amount (NZiel), and wherein the target nitrogen amount (NZiel) of the iron-based powder (30) is in a range from 0.2 wt.% to 1.5 wt.%, in particular from 0.2 wt.% to 1.5 wt.% for martensitic materials and 0.5 wt.% to 1.5 wt.% for austenitic materials.

Description

[0001] Processes for the production of special steels and semi-finished products and molded parts based on them

[0002] The invention relates to methods for producing highly nitrogen-alloyed iron-based powders, as well as to methods for the powder metallurgical production of components from highly nitrogen-alloyed iron-based powders, and to corresponding highly nitrogen-alloyed iron-based powders. Furthermore, the invention relates to the use of nitrogen in the gas atomization of iron-based materials for producing highly nitrogen-alloyed iron-based powders.

[0003] Processes for producing iron-based powders are generally known. Iron-based powders are produced, for example, by mechanical processes in which an iron-based material is converted into a powdery state under the action of mechanical forces. Mechanical processes are very limited in terms of the achievable particle size and shape and exhibit a wide range of fluctuations in particle size distribution. Furthermore, iron-based powders with coarser particle sizes can be produced using the so-called direct reduction process of iron ore followed by grinding. Atomization processes for producing iron-based powders are also known. In atomization processes, an iron-based material is first at least partially melted and then converted from the liquid phase into a powdery state under the action of an atomization medium in a countercurrent process.Atomization processes primarily use liquid or gaseous atomization media. Contact with the atomization medium atomizes the liquid phase and simultaneously cools, thereby converting it into the solid phase. Desired and undesired interactions of a physical and, in some cases, chemical nature occur between the atomization medium and the molten metal, provided the atomization gas is not inert. Due to the high cooling rates of the melt and conversion into the solid state, alloying elements can generally be dissolved in iron-based alloys, often above their solubility limit. However, this does not apply to volatile alloying elements, which under normal conditions, for example, preferentially exist in the gas phase. Therefore, the production of iron-based powders by atomization imposes limitations on the manufacturability of some commercially highly relevant iron-based alloys.

[0004] Austenitic and martensitic steels are of particular interest for a wide range of industrial applications. Austenitic steels are characterized by a face-centered cubic crystal structure and generally very good corrosion resistance. This is achieved in iron-based alloys, among other things, by the addition of the alloying elements chromium and nickel. Particularly in the consumer goods industry, medical technology, and luxury goods such as jewelry or watches, nickel is generally undesirable due to the potential for allergic reactions and limited biocompatibility. For this reason, highly nitrogen-alloyed austenitic steels, so-called AHNS steels, are increasingly being used. In these steels, nickel is either partially or completely replaced by the addition of nitrogen and other alloying elements such as manganese and / or molybdenum.Furthermore, so-called nitrogen formers, chemical substances that decompose during alloy formation and release nitrogen dissolved in the steel, are optionally used in the production of such steels. A particular effort is made to completely eliminate the use of nickel as an austenite former in AHNS steels, although this requires a sufficiently high proportion of nitrogen dissolved in the solid solution, which is not possible with known processes for producing nitrogen-alloyed iron-based powders.

[0005] Martensitic steels also require an initially austenitic microstructure which depends, among other things, on the temperature. Martensite forms from the face-centered cubic lattice of austenite through a diffusionless folding process during rapid cooling to a temperature below the so-called martensite start temperature. This diffusionless folding process ends as soon as the so-called martensite finish temperature is reached. The proportion of carbon or nitrogen incorporated in the microstructure determines the proportion of retained austenite that remains. In steels, the martensitic transformation of the austenitic microstructure leads to an increase in hardness and can cause cracking if the proportion of retained austenite is too low. The diffusionless folding process also requires a rapid cooling rate, a so-called lower critical cooling rate.The proportion of the foreign element dissolved in the microstructure, in this case nitrogen, is crucial for the resulting hardness and shifts the martensite start temperature to lower temperatures compared to the widely used alloying element carbon, depending on the other composition, down to below 200°C. Since nitrogen can only be dissolved in iron-based powders to a limited extent above the equilibrium concentration, the martensite start temperatures of carbon-based steels produced from them are usually between 300°C and 500°C.

[0006] In a variety of processes for the powder-based production of components under the influence of high temperatures and high cooling rates from these temperatures, such as selective laser melting, only steels are used that do not undergo martensitic transformation, or in which martensite formation occurs via a precipitation process (e.g., so-called maraging steels). Due to the high cooling rates already during laser application to temperatures below the martensite start temperature, structural transformations of austenite to martensite would otherwise occur, resulting in cracks due to the locally varying volume changes associated with the structural transformation.Processes for the powder-based production of components using jet-based powder bed processes therefore mainly use steel powders that are either not hardenable or that can only be hardened by subsequent precipitation hardening or case hardening or carbonitriding with a low core carbon content. This in turn does not correspond to the often desired areas of application in both series production and prototype construction. There are also approaches to processing martensitic steels at elevated temperatures in the range of at least 500 °C, i.e. above the martensite start temperature of carbon-based steels, although this requires complex plant technology with build space heating. Alternatively, other powder bed processes can be used. If iron-based powder is to be processed under normal conditions, i.e. up to approx.200 °C, this is usually only possible with carbon-based martensitic steels by accepting the risk of cracking.

[0007] Accordingly, there is great interest in achieving a nitrogen content in the alloy above the solubility limit of nitrogen for both martensitic and austenitic steels in order to produce powder-metallurgically highly nitrogen-alloyed steels, so-called HNS steels. Conventionally produced HNS steels are generally known and are described, for example, in the book "High Nitrogen Steels

[0008] Structure, Properties, Manufacture, Applications" by Valentin G. Gavriljuk, Hans Berns, 2013, Springer Verlag Berlin Heidelberg. HNS steels occur in various microstructures. As ANHS steels, they generally have manganese contents of 8 to 21 wt.%. In the form of a rust-resistant martensitic HNS steel, they contain up to 1.5 wt.% manganese, and in the form of a dual-phase HNS steel with a ferritic and an austenitic microstructure, they contain up to 8 wt.% Mn.

[0009] However, in the production of iron-based powders by atomization, nitrogen cannot currently be readily dissolved to a sufficient degree above the solubility limit due to the necessary melting of a solid iron-based material. For example, CN 110181069 A1 discloses the nitrogenization of dual-phase steel with nickel as an austenite stabilizer or austenitic steel with a high manganese content of over 18 wt.% in the melt under high overpressure of 4 bar or more and subsequent atomization. However, such high overpressures are very complex and cost-intensive in terms of plant technology. Furthermore, there is a need to provide suitable production processes for austenitic-ferritic iron-based powders without nickel as an austenite stabilizer.

[0010] Iron-based powders must therefore undergo further processing steps to achieve a nitrogen content above the solubility limit corresponding to conventionally produced HNS steels.

[0011] For example, BASF's Catamold® PANACEA is a ferritic steel powder that is nitrided during sintering or subjected to gas nitriding prior to sintering. Nitriding during sintering limits such powders to further processing by sintering. However, even gas nitriding prior to sintering, which involves nitriding the ferritic steel powder, severely limits further processing. Gas nitriding occurs at temperatures exceeding 500°C. Thus, gas nitriding can cause sintering or agglomeration of the powder even with small particle sizes. The sintered or agglomerated particles must then be broken up again, which negatively impacts their morphology. Furthermore, this type of gas nitriding does not produce a homogeneous microstructure for the powder particles.Thus, such a process is only possible for powders with larger particle sizes (usually more than 25 pm, i.e. average particle sizes of D50 in the range of 40 - 50 pm, depending on the composition).

[0012] Iron-based powders whose nitrogen content is increased by gas nitriding are therefore not suitable, for example, for further processing in the so-called binder jetting process or metal injection molding (MIM), which requires fine average particle sizes of 25 pm or less. Due to these limitations, nickel-containing austenitic iron-based powders, such as the so-called 316L steel (X2CrNiMo 17-12-2 or 1.4404) or the 304L steel, as described in US Pat. No. 5,114,470 A, are usually used for the binder jetting process, provided a property profile with increased corrosion resistance is required for the component to be produced. Furthermore, gas nitriding produces increased nitrides, reducing the proportion of nitrogen dissolved in the solid solution.Furthermore, the nitriding time is relatively long, especially for austenitic high-nitrogen alloyed steels, since such alloys form a passivation layer due to the high chromium content, which delays or even completely prevents the gas phase reaction.

[0013] By adding manganese ("Mn"), the solubility of nitrogen ("N") in a melt can fundamentally be increased. Higher manganese contents therefore enable the production of steels with high N contents under atmospheric pressure, as shown in CN 1 01 134 244 A and US 5 114 470 A. Furthermore, both Mn and N are strong austenite stabilizers, meaning that in steels with high Mn and N contents, the expensive alloying element nickel ("Ni") is no longer required as an austenite stabilizer, or only required to a limited extent. However, since manganese influences plastic formability, its addition is only desirable to a limited extent. For example, in highly nitrogen-alloyed austenitic steels, the manganese content is preferably limited to a maximum of 21%, in highly nitrogen-alloyed dual-phase steels to a maximum of 8%, and in highly nitrogen-alloyed martensitic steels even to a maximum of 1.5%.This places limitations on the addition of manganese to improve nitrogen solubility. Therefore, there is a need for processes that provide sufficient nitrogen solubility for the production of highly nitrogen-alloyed iron-based powders, even at comparatively low manganese contents, such as those found in dual-phase or martensitic steels.

[0014] Furthermore, EP 3 851 551 A1 discloses a process for producing iron-based powders in which melts are alloyed with Mn and S to counteract the process-related loss of manganese and nitrogen. Thus, the manganese content of the melt is 2-4 wt.% above a target manganese content in the powder to be produced. Such a process is limited to certain steel grades due to the high manganese contents, which are particularly necessary for dissolving the nitrogen in the solid solution. Furthermore, the nitrogen content varies within the structure of the powder particles, as nitrogen losses are greater at the particle surface. However, manganese is highly sensitive to oxidation, so that manganese oxides can form in iron-based powders produced in this way. In general, part of the nitrogen required as an austenite former is replaced by the element carbon.It is therefore an object of the present invention to overcome at least one of the disadvantages known from the prior art. In particular, it is an object of the present invention to provide a process for producing a high-nitrogen alloyed iron-based powder, a process for the powder-metallurgical production of components from high-nitrogen alloyed steel (HNS steel), and a corresponding high-nitrogen alloyed iron-based powder, which allow the omission of nickel as an austenite stabilizer and permit simplified plant technology, without requiring a process-related restriction of the achievable particle sizes or the addition of carbon in austenitic steels. Furthermore, the object of the present invention is to provide a process for producing a high-nitrogen alloyed iron-based powder by means of rod atomization.In other words, the object of the present invention is to provide a highly nitrogen-alloyed iron-based powder that can be used for flexible powder metallurgical processes.

[0015] The invention solves the problem solved at the outset in a first aspect by a method according to claim 1.

[0016] In particular, the invention proposes that the method for producing highly nitrogen-alloyed iron-base powders comprises the steps of: a) providing at least one solid iron-base material with an initial nitrogen content which is in particular in a range of 0.2 - 1.5 wt.%, b) providing a nitrogen-containing atmosphere in a work space, b1) setting an overpressure of the nitrogen-containing atmosphere corresponding to the initial nitrogen content and to a target nitrogen content of the iron-base material, wherein the nitrogen partial pressure is in particular above atmospheric pressure, c) at least partially melting the iron-base material to form a melt in the work space, and d) atomizing the melt using an atomization gas to form an iron-base powder with a target nitrogen content, wherein the target nitrogen content of the iron-base powder is in a range of 0.2 wt.% to 1.5 wt.% for martensitic materials and 0.5 wt.% to 1.5 wt.-% dissolved in the solid solution for austenitic materials. In particular, the target nitrogen content of the iron-based powder is at least equal to or higher than the initial nitrogen content. In this context, an iron-based powder is defined as a powder made of an iron-based alloy. A highly nitrogen-alloyed iron-based powder is defined as an iron-based powder whose alloy composition corresponds to that of high-temperature steels.

[0017] Furthermore, atomization refers to the production of metal powders using a media-supported atomization process.

[0018] The components according to the invention are, in particular, machine elements subject to high levels of stress in practice, luxury goods, or components for use in or on the human or animal body produced using a powder metallurgical manufacturing process. The term "component for use in or on the human or animal body" encompasses implants that are permanently installed in the body, such as screws, splints, braces, parts of hip or knee joints, dental abutments or other dental implants firmly anchored in the jaw, and other parts implanted as replacements for natural bones or joints, as well as prostheses that are temporarily or permanently attached to the body, such as parts of dental prosthetics (bridges, partial or full tooth replacements) or tools that are particularly required in dental or general surgery or in minimally invasive applications.Materials for implants or prostheses must be sufficiently corrosion-resistant and exhibit optimized biocompatibility. Consequently, they must not have any harmful effects on the body in or on which the components made from them are inserted, nor trigger any other reactions that could have an adverse impact on well-being or health. At the same time, implant or prosthetic materials must possess sufficient mechanical properties, such as strength, toughness, and the like, for their intended use. An iron-based powder produced according to the invention optimally fulfills this requirement profile and also enables the production of delicate yet stable components using known powder metallurgical manufacturing processes.

[0019] By providing an overpressure in the working space in which the iron-based material is at least partially melted to form a melt, nitrogen dissolves within the melt above the solubility limit, which would correspond to normal atmospheric pressure. By setting the overpressure as a function of the initial nitrogen content and the particle size, it is possible according to the invention to prevent the atmospheric pressure in the working space from becoming over-dimensioned. The inventor recognized that by providing iron-based alloys with an initial nitrogen content which is in particular in a range of 0.2 wt.% to 1.5 wt.%, even a slight overpressure of the nitrogen-containing atmosphere is sufficient to compensate for the escape of nitrogen from the melt and to achieve a target nitrogen content in a range of 0.2 wt.% to 1.5 wt.% for martensitic materials and 0.5 wt.% to 1.5 wt.-% for austenitic materials. It should be understood that the target nitrogen content for austenitic steels and dual-phase steels refers to the content of nitrogen dissolved in the solid solution, as this content is crucial for the effect of nitrogen in stabilizing the austenitic microstructure. The overpressure creates an external force on the melt, causing the nitrogen to be forcibly dissolved in the melt. In addition to the level of the overpressure, the partial pressure of the nitrogen is of particular importance. The partial pressure of the nitrogen is also above atmospheric pressure. This is already the case in a pure nitrogen atmosphere due to the overpressure, but must also be ensured when using gas mixtures in the working space. It ensures that the required amount of nitrogen is dissolved in the melt.The atmosphere therefore comprises nitrogen with a nitrogen partial pressure greater than atmospheric pressure, in particular greater than or equal to 1 bar, in particular at least 1.5 bar. According to the invention, the maximum overpressure is 3 bar.

[0020] Due to the overpressure of the nitrogen-containing atmosphere in the work space and the associated forced solution of the nitrogen, the process according to the invention also allows the production of highly nitrogen-alloyed iron-base powders without the presence of comparatively high manganese or carbon contents in the iron-base material. This also makes it possible to dispense with nickel as an alloying element. It should be understood that the iron-base powder according to the invention has a target nickel content of preferably less than 1.5%, in particular 0%, although impurities can always be present. Thus, the process according to the invention can be used to produce, in particular, iron-base powders with a nitrogen content in a range of 0.2 wt.% to 1.5 wt.% and a comparatively low Mn content of preferably a maximum of 8 wt.%. However, manganese contents of up to 21% are also possible, particularly with austenitic steels.In particular, martensitic iron-based powders of this composition can be advantageously produced using the process according to the invention.

[0021] The process according to the invention allows a target nitrogen content of the iron-based powder to be set, independent of other alloying elements such as manganese, that is higher than the initial nitrogen content or at least corresponds to the initial nitrogen content. Thus, even at low overpressures, the escape of nitrogen during melting is compensated for by the overpressure in the nitrogen atmosphere in the work chamber. Depending on the level of the overpressure, the initial nitrogen content of the solid iron-based material, and the desired particle size, the process according to the invention can also be used to set a target nitrogen content of the iron-based powder that is above the initial nitrogen content. The target nitrogen content increases with the level of the overpressure and also with decreasing particle size.According to the invention, a highly nitrogen-alloyed iron-based powder produced in this way can be consolidated directly into a powder-manufactured component without any further secondary treatment. Secondary treatment is understood here to mean all processing steps downstream of powder production that are not involved in the shaping of the component and thus take place before consolidation.

[0022] The content of additional alloying elements, in particular manganese, in the provided iron-based material preferably corresponds essentially—i.e., less process-related fluctuations—to the content of alloying elements in the iron-based powder or the iron-based powder plus additional alloying elements added in solid form before heating. The iron-based material can also be over-alloyed with certain alloying elements, whereby the content of the over-alloyed alloying elements is reduced again during steps c) and / or d).

[0023] If melting and atomization take place in a shared working chamber, an overpressure above the partial pressure of nitrogen also prevents the formation of larger gas pores during atomization. This is particularly advantageous for rod or block atomization.

[0024] Preferably, melting takes place in the working chamber and atomization takes place entirely in a sealed space. In the case of crucible atomization, the working chamber, which can be referred to here as the melting chamber, and the atomization chamber are housed in a common, sealed housing. In the case of rod atomization, melting and atomization take place together in the working chamber. By carrying out melting and atomization in a sealed space, i.e. a space sealed against ambient media, the purity of the produced powder is increased and overall process reliability is improved. According to a preferred embodiment, the atomization gas comprises nitrogen. In conventional atomization processes, nitrogen is usually used solely for cost reasons. There is a cost discrepancy of several hundred percent between nitrogen and argon.In the powder metallurgical production of AISI 316L, for example, atomization with nitrogen results in the formation of chromium nitrides in addition to the austenite through a reaction with the nitrogen. This leads to poorer corrosion resistance due to chromium depletion in the austenitic matrix. The inventors advantageously recognized that for the production of highly nitrogen-alloyed iron-based powders, which, as described above, preferably contain manganese and optionally additionally molybdenum as alloying elements, the use of nitrogen as the atomization gas does not adversely affect the corrosion properties. In particular, the use of nitrogen as the atomization gas can reduce the escape of nitrogen dissolved in the melt during solidification.

[0025] More preferably, the method comprises the step of adjusting the initial nitrogen content in the iron-based material by at least one of the following sub-steps:

[0026] Providing the iron-based material with a nitrogen content corresponding to the initial nitrogen content,

[0027] Providing a plurality of iron-based materials whose average nitrogen content corresponds to the initial nitrogen content,

[0028] Providing at least the iron-based material and at least one individual alloy component, wherein at least one of the individual alloy components comprises a nitrogen generator, for example, silicon nitride. The inventors advantageously recognized that the initial nitrogen content of the iron-based material co-determines the target nitrogen content of the iron-based powder. By adjusting the initial nitrogen content according to at least one of these sub-steps, the target nitrogen content can thus be specifically influenced. Furthermore, adjusting the initial nitrogen content based on an average nitrogen content of various iron-based materials enables the use of material combinations and increases the selection of usable iron-based materials.By providing an iron-based material in an alloy component containing a nitrogen former, the nitrogen content in an iron-based material alloyed with only a low nitrogen content can also be increased. This enables the process to be carried out with only slight overpressures in the working chamber. It is further preferred that the overpressure in the working chamber in step c) is kept within a maximum pressure fluctuation range of + / - 20%. In particular, the overpressure is kept essentially constant, thus exhibiting only process-related fluctuations. The pressure in the working chamber has a decisive influence on the target nitrogen content of the iron-based powder. For industrial applications, this should not fluctuate by more than 0.05% nitrogen. A pressure fluctuation range of + / - 20% allows such a small fluctuation in the target nitrogen content in the iron-based powder, depending on the desired particle size.

[0029] More preferably, the iron-based powder has a particle size in a range from 0.1 pm to 100 pm, wherein the target nitrogen content of the iron-based powder particles is maintained within a concentration fluctuation range of a maximum of 0.05 wt.%. A corresponding particle size with a maximum pressure fluctuation range of + / - 20% reliably enables the target nitrogen content to be kept essentially constant and within a concentration fluctuation range of a maximum of 0.05 wt.%. Particle sizes in a range from 0.1 pm to 100 pm also permit a variety of processes for the powder-metallurgical further processing of the iron-based powder. To adjust the desired ranges of the particle sizes present in the iron-based powder for the respective further processing, the process for producing highly nitrogen-alloyed iron-based powders can additionally comprise a classification step after atomization.With such subsequent classification of the powder, the iron-based powder can be divided into different sub-fractions.

[0030] In this context, particle size refers to the size of the individual powder particles. Such particle size is always subject to process-related fluctuations, resulting in a particle size distribution within a powder.

[0031] The atomization gas preferably comprises nitrogen. More preferably, the atomization gas comprises nitrogen with a partial pressure of at least 1 bar. The use of nitrogen offers cost advantages over the use of noble gases, for example, and does not adversely affect the atmosphere in the working chamber during atomization and melting in a shared working chamber, such as in rod or block atomization. Furthermore, the impact of the nitrogen-containing atomization gas advantageously promotes the nitrogen concentration.

[0032] According to a preferred embodiment, the iron-based material is provided in step a) as a rod or block, and in step c) only a partial melting of the iron-based material takes place, with steps c) and d) being carried out in the work space. By melting the iron-based material directly on the rod or block, the design effort for a device required to carry out the process is simplified. The partial melting of the iron-based material in step c) can preferably take place by induction. Induction enables local melting of an iron-based material in the form of a block or rod through targeted, locally acting temperature application. In this embodiment, the starting nitrogen content of the iron-based material can either already correspond to the target nitrogen content of the iron-based powder or be lower than the target nitrogen content.Partial melting means that only a part of the volume of the iron-based material is melted.

[0033] According to an alternative preferred embodiment, the melting of the iron-based material in step c) takes place in a crucible and the iron-based material is completely melted and led from the working chamber into an atomization chamber for carrying out step d).

[0034] Preferably, the at least one iron-based material has an initial nitrogen content of, in particular, 0.2 to 1.5 wt.% and, as further alloying constituents, 12 to 30 wt.% chromium and 8 to 21 wt.% manganese, wherein the highly nitrogen-alloyed iron-based powder preferably has an austenitic structure and / or is designed to form an austenitic structure in a process for the powder-metallurgical production of components. A corresponding initial nitrogen content as well as corresponding contents of the alloying elements chromium and manganese allow the formation of an austenitic structure of the iron-based powder after atomization due to the resulting cooling rates of at least 10 4K / s. Due to the austenite stabilizers present in the iron-based material, it is preferably furthermore designed to form an austenitic microstructure in a process for the powder metallurgical production of components. There are many different processes for the powder metallurgical production of components. Well-known examples include cold isostatic or coaxial pressing, which is combined with subsequent sintering at temperatures of approximately 2 / 3 to 4 / 5 of the melting temperature (in °K). Also used are so-called hot isostatic pressing, both for the actual consolidation and for a subsequent densification process, or additive manufacturing processes such as selective laser beam melting (SLM, also known as LPBF, Laser Powder Bed Fusion) or electron beam melting (EBM). This list is not exhaustive.What these processes have in common is that the iron-based powder can be converted into a liquid phase, at least temporarily and if necessary partially.

[0035] The term "additive manufacturing" encompasses all manufacturing processes in which a material is added to create a component. This addition usually occurs layer by layer or in a deposition process. "Additive manufacturing processes," which are often referred to in technical terms as "generative processes" or generally as "3D printing," thus contrast with traditional subtractive manufacturing processes, such as machining (e.g., milling, drilling, and turning), in which material is removed to give the component its shape. Additive processes also differ fundamentally from conventional bulk forming processes, such as forging and the like, in which the respective steel part is formed from a starting or intermediate product while retaining its mass.More detailed definitions of the processes summarized under the general term "additive processes" can be found, for example, in VDI guidelines 3404 and 3405.

[0036] In the additive processing of metal powders to form components in a powder bed, a distinction is made between processes in which the solidification of the metal powder occurs by the addition of heat, which melts the metal particles of the powder so that they form cohesive bonds, and processes in which the solidification is achieved with the help of a binder that is mixed with the powder particles so that the particles are held in a solid composite matrix after curing.

[0037] According to a further preferred embodiment, the iron-based material has an initial nitrogen content of in particular 0.2 to 1.2 wt.% and up to 1.5 wt.% manganese, in particular up to 1 wt.% manganese, wherein the highly nitrogen-alloyed iron-based powder is designed to be used in a process for the powder metallurgical production of components with a cooling rate of at least 10 4 K / s to at least partially form a martensitic structure. The iron-based material preferably contains 10 to 17 wt.% chromium, wherein the highly nitrogen-alloyed iron-based powder is designed to form a rust-resistant martensitic steel. Alternatively, the iron-based material preferably contains 0.8 to 1.8 wt.% chromium, wherein the highly nitrogen-alloyed iron-based powder is designed to form a non-stainless martensitic steel.

[0038] Alternatively, the at least one iron-based material has an initial nitrogen content of in particular 0.2 to 1 wt.%, 15 to 27 wt.% Cr, up to 8 wt.% Mn and / or Mo and / or Ni, and the highly nitrogen-alloyed iron-based powder forms a dual-phase steel with a ferritic structure and an austenitic structure and / or is designed to form a dual-phase steel with a ferritic structure and an austenitic structure in a process for the powder metallurgical production of components. Dual-phase steels are steels whose structure consists of a ferritic matrix in which a predominantly strength-increasing martensitic second phase is embedded in islands at the grain boundaries with a proportion of usually 10 to 40%. Dual-phase steel has a relatively low yield strength, which is favorable for possible subsequent forming processes, as well as high tensile strength, elongation, and n-value.These properties are advantageous for complex deep-drawn parts. Dual-phase steel also exhibits a pronounced bake-hardening effect.

[0039] It should be understood that the structure of the iron-based powder always contains unavoidable structural components or impurities due to the manufacturing process, in particular minor elements.

[0040] In a second aspect, the invention relates to a method for the powder metallurgical production of components from highly nitrogen-alloyed iron-based powders. The invention achieves the aforementioned object according to the second aspect by a method according to claim 13.

[0041] In particular, the invention proposes that the method comprises the steps:

[0042] Providing a high-nitrogen alloyed iron-based powder produced in a process according to the first aspect of the invention, and

[0043] Carrying out at least one processing step under the action of temperature and / or pressure and / or radiation and / or electrical charge or electrical discharge to produce a near-net-shape component from the provided highly nitrogen-alloyed iron-based powder. By providing a highly nitrogen-alloyed iron-based powder produced in a method according to the first aspect of the invention, the method for powder-metallurgical production of components according to the second aspect of the invention incorporates the advantages mentioned above. Advantages and preferred embodiments according to the first aspect of the invention are likewise advantages and preferred embodiments according to the second aspect of the invention, and vice versa.

[0044] By providing a suitably manufactured, highly nitrogen-alloyed iron-base powder, the temperature range and radiation usable in the process, as well as the level of electrical charge or discharge, are less limited. This is due, among other things, to the fact that the process according to the invention allows highly nitrogen-alloyed iron-base powders to be provided in a wide range of particle sizes for specific applications. Furthermore, the ability to adjust the target nitrogen content of the iron-base powder can influence the minimum cooling rate as well as the martensite start and martensite finish temperatures, thus avoiding unwanted microstructural transformations.

[0045] The process can preferably also include a processing step that combines the effects of temperature and / or pressure and / or radiation and / or electrical charge and / or electrical discharge, or a plurality of processing steps can be performed in which, for example, only one of these variables is effective. Cold isostatic pressing is known, in which a near-net-shape or semi-finished material composite is produced under pressure, which can then be converted into a component in a second processing step under the influence of temperature in a sintering process.

[0046] It is further preferred that carrying out at least one processing step comprises pressing, in particular extrusion or uniaxial or coaxial single or multiple pressing in matrices, preferably cold isostatic pressing (Cold Isostatic Pressing, CIP), warm isostatic pressing (WIP) or hot isostatic pressing (HIP).

[0047] It is further preferred that at least one processing step comprises sintering under a vacuum or protective gas atmosphere, in particular microwave sintering, gravity sintering, or sintering under simultaneous mechanical pressure and an electrical discharge, the SPS (spark plasma sintering) process. Since the process according to the invention for producing the highly nitrogen-alloyed iron-based powder can avoid agglomerations resulting from gas nitriding of the powder for nitriding, or even an irregular and / or sharp-edged morphology of the particles resulting from breakage or other mechanical post-processing, the provided powders are particularly suitable for shaping and sintering processes.The uniform globular formation guarantees good processability in terms of pourability and flowability, and the avoidance of chromium carbides within the structure of such powders prevents premature cracking in components during forming.

[0048] It is further preferred that the performance of at least one processing step includes powder forging. Powder forging is characterized by high design flexibility and very good performance with good geometric precision. The iron-based powder is first pressed, preferably having a compaction density of 6-7.5 g / cm 3and subsequently sintered. After sintering, the component is fed directly into a forging press, but can also be reheated to forging temperature. There, it is further densified by forming. Since highly nitrogen-alloyed iron-based powders, particularly those with a martensitic transformation of the microstructure, are also excellently suited for highly stressed precision parts, such as transmission components, the provision of the powder by a method according to the invention and the use of powder forging as a processing step enables such applications.

[0049] It is further preferred that at least one processing step be carried out using a powder casting process, in particular slip or strip casting. Since the process according to the invention can produce powders with fine particle sizes of 30 μm or less, these iron-based powders are particularly suitable for casting processes in general, as the flowability of the injection molding compound can be sufficiently ensured.

[0050] It is further preferred that at least one processing step comprises screen printing. It is further preferred that at least one processing step comprises extrusion. Due to the wide range of adjustment options for the particle size distribution and the globular structure of the particles, these are also particularly suitable for extrusion processes or screen printing.

[0051] It is further preferred that at least one processing step comprises powder bed or powder deposition processes using laser, electron beam, LED, or plasma-based energy sources. Since the inventive method allows the martensite start and finish temperatures of martensitic powder types to be influenced by the incorporated nitrogen, unintentional martensitic transformation and the associated crack formation, e.g., due to excessively rapid process-related cooling in the range of approximately 100-250 °C, can be avoided in these processes.

[0052] It is further preferred that carrying out at least one processing step comprises binder- or paste-based additive manufacturing processes, in particular binder jetting, material jetting, fused filament fabrication (FFF), MoldJet technology, gel casting or modified stereolithography (lithography-based metal manufacturing LMM),

[0053] It is further preferred that at least one processing step involves powder injection molding (PIM), in particular metal injection molding (MIM). Since the process according to the invention can produce powders with fine particle sizes of 30 μm or less, these iron-based powders are particularly suitable for powder injection molding, as the flowability of the injection molding compound is sufficiently ensured, and the fineness of the powder ensures high sintering activity.

[0054] According to a third aspect, the invention also relates to a process for powder metallurgical coating with highly nitrogen-alloyed iron-based powders, comprising the steps:

[0055] Providing a high-nitrogen alloyed iron-based powder produced in a process according to the first aspect of the invention,

[0056] Carrying out at least one coating step for applying a layer based on the provided iron-based powder to a component. By providing a highly nitrogen-alloyed iron-based powder produced in a method according to the first aspect of the invention, the method for powder-metallurgical coating according to the third aspect of the invention takes advantage of the aforementioned advantages. Advantages and preferred embodiments according to the first aspect of the invention are also advantages and preferred embodiments according to the third aspect of the invention, and vice versa.

[0057] Preferably, performing at least one coating step comprises at least one of the following coating processes: powder deposition welding; flame spraying; plasma spraying; high-velocity flame spraying (HVOF); high-velocity flame spraying with air (HVAF); plasma powder deposition welding (PTA); laser deposition welding; cold spraying. In a fourth aspect, the invention relates to the use of a device for melting iron-based materials under an overpressure in a method according to the first aspect of the invention for producing highly nitrogen-alloyed iron-based powders. The use of a device for melting iron-based materials under an overpressure in a method according to the first aspect of the invention makes the invention, according to the third aspect, adopt the advantages mentioned above.Advantages and preferred embodiments according to the first aspect of the invention are also advantages and preferred embodiments according to the third aspect of the invention and vice versa.

[0058] According to a fifth aspect, the invention provides a highly nitrogen-alloyed iron-base powder comprising particles of an iron-base material with a globular structure, wherein the iron-base material comprises 0.2 wt.% to 1.5 wt.% nitrogen and up to 10 wt.% Mn, in particular up to 8 wt.% Mn. A highly nitrogen-alloyed iron-base powder produced in the process according to the invention has an alloy composition which corresponds to that of HNS steels and makes use of the advantages described above with regard to the first aspect of the invention. Advantages and preferred embodiments of the first aspect of the invention are likewise advantages and preferred embodiments of the iron-base powder according to the fifth aspect of the invention.

[0059] The particles preferably have an at least partially martensitic structure, wherein the iron-based material comprises 0.2 wt.% to 1.5 wt.% nitrogen, up to 1.5 wt.% Mn, in particular up to 1 wt.% Mn. Preferably, the iron-based material further comprises 10 to 17 wt.% Cr, and the highly nitrogen-alloyed iron-based powder forms a rust-resistant martensitic steel. Alternatively, the iron-based material preferably comprises 0.8 to 1.8 wt.% Cr, and the highly nitrogen-alloyed iron-based powder forms a non-rust-resistant martensitic steel. In an alternative embodiment, the iron-based powder comprises particles of a dual-phase steel with a globular structure and ferritic and austenitic microstructure, wherein the dual-phase steel has an initial nitrogen content of 0.2 to 1 wt.%, 15 to 27 wt.% Cr, and up to 8 wt.% Mn and / or Mo and / or Ni. The particles preferably have a target nickel content of less than 1.5%, in particular 0.

[0060] Furthermore, the invention relates to highly nitrogen-alloyed iron-base powders comprising particles with a globular structure. In particular, the invention proposes that the iron-base powder is a highly nitrogen-alloyed iron-base powder and is produced in a process according to the first aspect of the invention. The iron-base powder has a nitrogen content in a range from 0.2 wt.% to 1.5 wt.%, in particular from 0.2 wt.% to 1.5 wt.% for a martensitic material and 0.5 wt.% to 1.5 wt.% for an austenitic material. Furthermore, the iron-base powder preferably has a minor element content of less than 0.3%. Furthermore, the particles preferably have particle sizes between 0.1 pm and 400 pm, preferably between 0.1 pm and 355 pm.

[0061] In particular, an iron-based powder produced in this way has a nitrogen content that is above the natural solubility limit of nitrogen in the corresponding microstructure. A correspondingly produced iron-based powder particularly preferably has particle sizes of less than 100 pm. Minor elements are referred to here as secondary elements that are not involved in the actual alloy formation. These include, for example, oxygen and sulfur.

[0062] The invention is described below with reference to the accompanying figures, in which:

[0063] Fig. 1 shows a method for producing high-nitrogen alloyed iron-based powders according to a first embodiment;

[0064] Fig. 2 shows a method for producing high-nitrogen alloyed iron-based powders according to a second embodiment;

[0065] Fig. 3 shows a process for the powder metallurgical production of components from highly nitrogen-alloyed iron-based powders;

[0066] Fig. 4 shows a device for the production of high nitrogen alloyed

[0067] Iron-based powders according to a first embodiment;

[0068] Fig. 5 shows a device for producing high nitrogen alloyed

[0069] Iron-based powders according to a second embodiment;

[0070] Fig. 6 is a diagram showing target nitrogen contents depending on nitrogen

[0071] Overpressure shows;

[0072] Fig. 7a is a micrograph of a structure of a component produced using a method according to Fig. 3; Fig. 7b is a micrograph of the structure according to Fig. 7a.

[0073] The method 1000 shown in Fig. 1 for producing highly nitrogen alloyed iron-based powders comprises, in a first step 1100, providing at least one solid iron-based material 10 (cf. Fig. 4 and Fig. 5) with an initial nitrogen content Nßasis (cf. Fig. 4 and Fig. 5).

[0074] In a second step 1200, which can also be performed parallel to the first step 1100, the method 1000 comprises providing an overpressure PN (see Fig. 4) in a working chamber 2 (see Fig. 4 and Fig. 5). It is preferred that the overpressure PN corresponds to the initial nitrogen content Nßasis (see Fig. 4 and Fig. 5) or a desired target nitrogen content Nziei (see Fig. 4 and Fig. 5) of the iron-based powder 30 to be produced. A further influencing variable in this context is the desired particle size S (see Fig. 4 and Fig. 5) of the iron-based powder 30 to be produced.

[0075] In a third step 1300, the method 1000 comprises melting the iron-based material 10 to form a melt 12 (cf. Fig. 4 and Fig. 5) in the working chamber 2 under overpressure PN.

[0076] Furthermore, in a fourth step 1400, the method 1000 comprises atomizing the melt 12 by an atomizing gas 20 (see Fig. 4 and Fig. 5) to form the iron-based powder 30.

[0077] The method preferably comprises, in a preceding step 1010, adjusting the initial nitrogen content in the provided iron-based material. Adjusting the initial nitrogen content preferably comprises one or more substeps.

[0078] In a first sub-step 1011, this adjustment 1010 comprises the provision of a single iron base material 10 having the initial nitrogen content Nßasis.

[0079] Alternatively or additionally, the provision 1010 comprises in a further sub-step 1012 the provision of a plurality of iron-based materials 10.1, 10.2 (cf. Fig. 4 and Fig. 5) whose average nitrogen content Nßasis (cf. Fig. 4 and Fig. 5) corresponds to the initial nitrogen content Nßasis.

[0080] Alternatively or additionally, adjusting the initial nitrogen content in step 1010 further comprises, as sub-step 1013, providing at least the iron-based material and at least one individual alloy component 12 comprising a nitrogen former 14. Through these sub-steps, the required initial nitrogen content Nßasis in the iron-based material 10 can be adjusted. A combination of these sub-steps can also be performed.

[0081] Fig. 2 shows a method 1000' for producing a highly nitrogen-alloyed iron-based powder according to a second embodiment. The method 1000' differs from the method 1000 shown in Fig. 1 according to the first embodiment only by the preceding step 1010 for adjusting the initial nitrogen content Nßasis in the iron-based material 10. The remaining identical method steps have identical reference numerals in Fig. 1 and Fig. 2, and reference is made in full to the description of the method 1000 according to Fig. 1, and only the differences are discussed.

[0082] In Fig. 2, the adjustment 1010 of the initial nitrogen content in the iron-based material 10 in a sub-step 1014 comprises providing at least the iron-based material 10 with a reduced initial nitrogen content N'ßasis (cf. Fig. 4) which is below the initial nitrogen content Nßasis and further the injection 1015 of additional nitrogen N (cf. Fig. 4) into the melt 12 in step 1300. By injecting additional nitrogen into the melt which is formed from the iron-based material 10 with the reduced initial nitrogen content N ßasis, the nitrogen content corresponds to the minimum necessary initial nitrogen content Nßasis.

[0083] Fig. 3 shows a method 2000 for the powder-metallurgical production of components 40 from highly nitrogen-alloyed iron-based powders 30 (cf. Figs. 4 and 5). The method 2000 comprises, in a first step 2100, providing a highly nitrogen-alloyed iron-based powder 30 produced in a process 1000, 1000' according to Fig. 1 or Fig. 2. In a second step 2200, the method 2000 comprises performing at least one processing step under the action of temperature T and / or pressure P and / or radiation Q and / or electrical charge E or electrical discharge to produce the near-net-shape component 40 from the provided iron-based powder 30.

[0084] It is preferred that the processing step comprises one or more substeps. In a first substep 2210, the method 2000 preferably comprises pressing, which can be carried out only under pressure P or under pressure P and temperature influence T.

[0085] In a second optional sub-step 2220, the processing steps include sintering under vacuum or a protective gas atmosphere. In a third optional sub-step 2230, the processing steps include powder forging 2230, or in a fourth sub-step 2240, a casting process, in particular a powder injection molding process.

[0086] Further optional sub-steps include screen printing in sub-step 2250, extrusion in sub-step 2260 and powder bed or powder deposition processes in sub-step 2270 using laser, electron beam, LED or plasma-based energy sources.

[0087] As a further optional sub-step 2280, the method 2000 comprises

[0088] Processing step: binder- or paste-based additive manufacturing processes.

[0089] Fig. 4 shows a first embodiment of a device 1 for producing high-nitrogen alloyed iron-based powders 30.

[0090] The device 1 comprises a working chamber 2, which can also be referred to as a melting chamber in the present case, and an atomization chamber 4. The atomization chamber 4 and the melting chamber 2 are preferably spatially separated. A crucible 6 is arranged in the melting chamber 2 and is heated by an induction coil 8. An overpressure PN prevails in the melting chamber 2, which is kept essentially constant. The overpressure PN is greater than atmospheric pressure and, in particular, amounts to a maximum of 3 bar, so that the process can be carried out in a system not specifically designed for high-pressure applications.

[0091] In the crucible 6, iron-based materials 10 having an initial nitrogen content Nßasis are melted to form a melt 12. This can preferably be achieved by melting a plurality of iron-based materials having an average initial nitrogen content N basis corresponding to the initial nitrogen content Nßasis.

[0092] Alternatively or additionally, the average initial nitrogen content N based on the majority of iron-based materials 10.1 , 10.2 may be different from the required

[0093] Initial nitrogen content Nßasis may differ or a provided iron-based material may have a nitrogen content Nßasis that differs from the required initial nitrogen content Nßasis.

[0094] In these cases, it is advantageous that, in addition to iron-based materials 10, further alloy components 12 are melted in the crucible 6 to form a melt 12, which includes nitrogen formers 14. Alternatively, additional nitrogen N can also be blown into the melt 12.

[0095] The melt 12 is fed from the melting chamber 2 into the atomization chamber 4. Furthermore, an atomization medium, in this case an atomization gas 20 in the form of nitrogen N, is fed into the atomization chamber 4 via lines 9 as an atomization jet 22 through a nozzle 23. The atomization gas 20 impinges on the melt 12 in the form of an atomization jet and, through rapid cooling and atomization, forms the melt 12 into a highly nitrogen-alloyed iron-based powder with a globular structure. The highly nitrogen-alloyed iron-based powder 30 has a target nitrogen content N.

[0096] It should be understood that in addition to an induction coil 8, further heating devices can also be used to temper the crucible 6 in the melting chamber.

[0097] Fig. 5 shows a second embodiment of an apparatus T according to the invention for producing high-nitrogen alloyed iron-based powders 30. Identical or similar elements have identical reference numerals in Fig. 4 and Fig. 5 and reference is made to the description of the embodiment according to Fig. 4.

[0098] The device 1' differs from the device according to Fig. 4 in that the working chamber 2 in this case also includes the atomization chamber 4. Thus, melting and atomization take place in a common working chamber 2, with the overpressure PN prevailing.

[0099] Instead of being placed in a crucible, the iron-based material 10 in the embodiment according to Fig. 5 is provided as a rod 16 or block 18 and partially melted directly on the rod 16 or block 18 via the induction coil 8. The local melting forms the melt 12, which drips down and strikes an atomizing jet 22 of the atomizing gas 20 emitted by a nozzle 23.

[0100] Fig. 6 shows a diagram illustrating the relationship between the overpressure PN and the particle size and the resulting target nitrogen content Nziei for the material 1.3616 (brand name P900).

[0101] The diagram shows only two measuring points, so that a supposedly linear relationship appears to arise. It should be noted that a linear relationship between the overpressure PN and the target nitrogen content Nziei does not necessarily exist. However, the diagram shows that a target nitrogen content can be achieved at an overpressure of just 1 bar, which is above an initial nitrogen content Nßasis of, for example, 0.64 wt.%. This is the case with a pure nitrogen atmosphere, so that the nitrogen partial pressure corresponds to at least 1 bar and is thus only slightly above atmospheric pressure. The decisive factor here is the appropriate level of the overpressure, depending on the particle size and the initial nitrogen content, which should always be at least 0.2 wt.%.

[0102] The bottom line refers to a highly nitrogen-alloyed iron-base powder 30 with a desired S3 particle size of more than 45 pm, the middle line S2 refers to a highly nitrogen-alloyed iron-base powder 30 with a particle size in the range of 15 pm to 45 pm, and the upper line S1 refers to an iron-base powder 30 with a desired particle size of less than 15 pm. With a reduced particle size of the iron-base powder 30 to be produced, the target nitrogen content Nziei increases at a constant overpressure PN and a constant initial nitrogen content Nßasis.

[0103] By varying process parameters such as the shape and arrangement of the nozzles, pressure, velocity and flow rate of the atomizing gas, thickness of the liquid metal jet, etc., the particle size can be adjusted within a wide range. The particle shape is primarily determined by the solidification rate and varies from spherical to spherical when a gas with a low heat capacity is used.

[0104] Overall, it can be seen from Fig. 6 that with an overpressure PN of maximum 3 bar, the corresponding target nitrogen contents, as required for the production of highly nitrogen-alloyed iron-based powders, can be achieved.

[0105] Figures 7a and 7b show a micrograph of a structure of a component 40 (see Figure 3) that was manufactured using a highly nitrogen-alloyed iron-based powder. Such an iron-based powder can be produced using a process according to Figure 1 or Figure 2.

[0106] Fig. 7a shows the micrograph at a lower magnification (scale bar corresponds to 100 pm), and Fig. 7b shows the microstructure at a higher magnification (scale bar corresponds to 20 pm). The iron-based powder shown has a target nickel content Niziei of 0 wt.%.

[0107] In the present example, steel 1 .4452 is provided as the iron-based material.

[0108] This steel, also known as P2000, has an initial nitrogen content of 0.75 to 1 wt.%. It also contains 2.5 to 4.5 wt.% molybdenum and 12 to 16 wt.% manganese as an austenite stabilizer. Further details on the alloy composition can be found in the relevant data sheets.

[0109] The iron-based material 30 was preferably melted in a device as shown by way of example in Fig. 4, at a nitrogen overpressure of at least 0.5 bar, in this case in particular 1 bar, and atomized with nitrogen N as the atomization gas 20. The particle size S of the powder present was in a range from 0.1 to 100 pm. The produced iron-based powder 30 had a nitrogen content of 0.78 wt.%. Furthermore, it is a highly nitrogen-alloyed iron-based powder with a globular morphology.

[0110] As shown in Figs. 7a and 7b, no undesirable precipitates were present, and a twin microstructure typical of austenitic materials was obtained. The powder provided was produced in one processing step, in this case a consolidation step, via binder jetting, followed by a subsequent processing step, namely sintering.

[0111] It should be understood that further processing steps or alternative processing steps are also contemplated. The powder produced according to the invention is particularly advantageous in binder- or sinter-based processes, as this requires the use of powders with a particle size of preferably less than 30 pm. High-nitrogen alloyed powders with a nitrogen content of, for example, 0.78 wt.% in this case have not yet been able to be produced in such a particle size range and with a correspondingly low content of minor elements.

[0112] List of reference symbols

[0113] 1 , 1 ' device

[0114] 2 work space

[0115] 4 Atomization chamber

[0116] 6 crucibles

[0117] 8 Induction coil

[0118] 9 lines

[0119] 10 Iron-based material

[0120] 10.1 , 10.2 Majority of iron-based materials

[0121] 12 Melt

[0122] 14 nitrogen formers

[0123] 16 bars

[0124] 18 blocks

[0125] 20 atomizing gas

[0126] 22 atomization jet

[0127] 23 Nozzle

[0128] 30 iron-based powders

[0129] 40 components

[0130] 1000, 1000' Process for producing iron-based powders

[0131] 2000 processes for powder metallurgical production

[0132] E load

[0133] N Nitrogen

[0134] P pressure

[0135] PN overpressure

[0136] Q radiation

[0137] S particle size

[0138] Nßasis initial nitrogen content

[0139] N ßasis reduced initial nitrogen content

[0140] Niziei target nickel content

[0141] NBasis average initial nitrogen content

[0142] T Temperature

Claims

Claims 1 . A method for producing highly nitrogen-alloyed iron-based powders, comprising the steps of: a) providing (1100) at least one solid iron-based material with an initial nitrogen content (Nßasis) which is in particular in a range of 0.2 to 1.5 wt.- % b) providing (1200) a nitrogen-containing atmosphere in a working space (2), b1) setting an overpressure (PN) of the nitrogen-containing atmosphere in the working space (2) corresponding to the initial nitrogen content (Nßasis) and to a target nitrogen content (Nziei) of the iron-based material, wherein the nitrogen partial pressure is in particular above atmospheric pressure, c) at least partially melting (1300) the iron-based material to a melt in the working space (2) under overpressure (PN), d) atomizing (1400) the melt by an atomizing gas to an iron-based powder with the target nitrogen content (Nziei), and wherein the target nitrogen content (Nziei) of the iron-based powder (30) is in a range from 0.2 wt.% to 1.5 wt.%, in particular from 0.2 wt.% to 1.5 wt.% for martensitic materials and 0.5 wt% to 1.5 wt% dissolved in the solid solution for austenitic materials.

2. Method according to claim 1, characterized in that the atmosphere comprises nitrogen with a nitrogen partial pressure greater than 1 bar, in particular at least 1.5 bar, and / or the overpressure (PN) is a maximum of 3 bar.

3. The method according to claim 1 or 2, further comprising the step: Adjusting (1010) the initial nitrogen content in the iron-based material by at least one of the following sub-steps: Providing (1011) a single iron-based material (10) having the initial nitrogen content, Providing (1012) a plurality of iron-based materials (10.1, 10.2), the average nitrogen content (N Basis ) corresponds to the initial nitrogen content, Providing (1013) the at least one iron-based material (10) and at least one individual alloy component (12), wherein at least one of the individual alloy components comprises a nitrogen former (14).

4. The method according to claim 1, 2 or 3, characterized in that the nitrogen overpressure (PN) in the working chamber (2) in step c) is kept within a maximum pressure fluctuation range of + / - 20%, in particular constant 5. The method according to claim 4, characterized in that the iron-based powder (10) has a particle size (S) in a range from 0.1 pm to 100 pm, wherein the target nitrogen content of the iron-based powder (30) varies in a concentration fluctuation range of at most 0.05 wt.%.

6. Process according to one of the preceding claims, characterized in that the iron-based powder has a target nickel content (Niziei) of at most 1.5 wt.%, in particular of 0 wt.%.

7. Method according to one of the preceding claims, characterized in that the iron-based material is provided in step a) as a rod or block and in step c) only partial melting of the iron-based material takes place, wherein steps c) and d) are carried out in the working space (2).

8. The method according to claim 7, characterized in that the partial melting of the iron-based material in step c) is carried out by induction.

9. Method according to one of claims 1 to 6, characterized in that the melting of the iron-based material (10) in step c) takes place in a crucible (6) and the iron-based material is completely melted, the melt (12) being led from the working chamber (2) into an atomization chamber (4) for carrying out step d).

10. Method according to one of the preceding claims, characterized in that the at least one iron-based material has an initial nitrogen content of 0.2 to 1.5 wt.%, 12 to 30 wt.% chromium and 8 to 25 wt.% manganese and the highly nitrogen-alloyed iron-based powder has a has an austenitic structure and / or is designed to form an austenitic structure in a process for the powder metallurgical production of components.

11. Method according to one of claims 1 to 9, characterized in that the at least one iron-based material has an initial nitrogen content of 0.2 to 1.2 wt.% and up to 1.5 wt.% Mn, in particular up to 1 wt.% Mn, and the highly nitrogen-alloyed iron-based powder is designed to be used in a process for the powder metallurgical production of components with a cooling rate of more than 10 4K / sec, to at least partially form a martensitic structure, and wherein the iron-based material preferably comprises 10 to 17 wt.% Cr and the highly nitrogen-alloyed iron-based powder forms a rust-resistant martensitic steel, or wherein the iron-based material preferably comprises 0.8 to 1.8 wt.% Cr and the highly nitrogen-alloyed iron-based powder forms a non-stainless martensitic steel.

12. The method according to any one of claims 1 to 9, characterized in that the at least one iron-based material has an initial nitrogen content of 0.2 to 1 wt.%, 15 to 27 wt.% Cr, up to 8 wt.% Mn and / or Mo and / or Ni and the highly nitrogen-alloyed iron-based powder forms a dual-phase steel with a ferritic structure and an austenitic structure and / or is designed to form a dual-phase steel with a ferritic structure and an austenitic structure in a method for the powder metallurgical production of components.

13. A process (2000) for the powder metallurgical production of components (40) from highly nitrogen-alloyed iron-based powders, comprising the steps: Providing (2100) a high-nitrogen alloyed iron-based powder produced in a process according to any one of claims 1 to 12, Carrying out (2200) at least one processing step under the action of temperature and / or pressure and / or radiation and / or electrical charge or electrical discharge to produce a component, in particular one close to the net shape, from the provided iron-based powder.

14. Method according to claim 13, characterized in that carrying out the at least one processing step comprises at least one of the following shaping processes: Presses (2210), in particular extrusion or uniaxial or coaxial single or multiple pressing in dies, preferably cold isostatic pressing (Cold Isostatic Pressing, CIP), warm isostatic pressing (WIP), or hot isostatic pressing (HIP), Sintering (2220) under vacuum or protective gas atmosphere, in particular microwave sintering, gravity sintering or SPS (spark plasma sintering) processes, Powder forging (2230), Powder casting processes (2240), in particular slip and strip casting or powder injection molding, preferably metal injection molding (MIM), Screen printing (2250), Extrude (2260), Powder bed or powder deposition processes (2270) using laser, electron beam, LED, or plasma-based energy sources, binder- or paste-based additive manufacturing processes (2280), in particular binder jetting, material jetting, fused filament fabrication (FFF), MoldJet technology, gel casting or modified stereolithography (lithography-based metal manufacturing LMM).

15. Process (2000) for powder metallurgical coating with highly nitrogen-alloyed iron-based powders, comprising the steps: Providing (2100) a high-nitrogen alloyed iron-based powder produced in a process according to any one of claims 1 to 12, Carrying out (2200) at least one coating step for applying a layer based on the provided iron-based powder to a component.

16. The method according to claim 15, characterized in that carrying out at least one coating step comprises at least one of the following coating processes: powder deposition welding; flame spraying; plasma spraying; high-velocity flame spraying (HVOF); high-velocity flame spraying with air (HVAF); plasma powder deposition welding (PTA); laser deposition welding; cold spraying.

17. Use of a device (1) for melting iron-based materials under an overpressure (PN) in a process (1000, 1000') according to one of claims 1 to 12 for producing highly nitrogen-alloyed iron-based powders (30).

18. Highly nitrogen alloyed iron-based powder comprising particles of a high-nitrogen alloyed iron-based material with a globular structure, wherein the iron-based material comprises 0.2 wt.% to 1.5 wt.% nitrogen, and up to 10 wt.% Mn, in particular up to 8 wt.% Mn.

19. Iron-based powder according to claim 18, wherein the particles have an at least partially martensitic structure, wherein the iron-based material comprises 0.2 wt.% to 1.5 wt.% nitrogen, up to 1.5 wt.% Mn, in particular up to 1 wt.% Mn, wherein the iron-based material preferably comprises 10 to 17 wt.% Cr and the highly nitrogen-alloyed iron-based powder forms a rust-resistant martensitic steel, or wherein the iron-based material preferably comprises 0.8 to 1.8 wt.% Cr and the highly nitrogen-alloyed iron-based powder forms a non-stainless martensitic steel.

20. Iron-based powder according to claim 18, comprising particles of a dual-phase steel having a globular structure and ferritic and austenitic microstructure, wherein the dual-phase steel has an initial nitrogen content of 0.2 to 1 wt.%, 15 to 27 wt.% Cr, up to 8 wt.% Mn and / or Mo and / or Ni.

21. Iron-based powder comprising particles with a globular structure, characterized in that the iron-based powder is a highly nitrogen-alloyed iron-based powder and is produced in a process according to one of claims 1 to 12, wherein the iron-based powder has a nitrogen content in a range from 0.2 wt.% to 1.5 wt.%, in particular from 0.2 wt.% to 1.5 wt.% for a martensitic material and 0.5 wt.% to 1.5 wt.% for an austenitic material

Images