Metal powder for additive manufacturing method, use of metal powder, manufacturing method of a component, and component

Abstract

The invention relates to a metal powder intended for use in an additive manufacturing method, the powder consisting of steel particles, wherein the average diameter of the steel particles is from 5 pm to 150 pm and the steel particles consist of, in mass percentages: C: 0.15% to 1.0%, N: 0.15% to 1.0%, Si: 0.1% to 2.0%, Mn: 10% to 25%, Cr: 5% to 21%, Mo: 0.1% to 3.0%, Ni: < 5%, the balance being iron and unavoidable impurities, the flowability of the metal powder determined according to ISO 4490 being less than 30 sec / 50 g. Reliable high-load components can be manufactured using the metal powder according to the invention by additive manufacturing. The metal powder according to the invention is therefore particularly suitable for manufacturing mechanical parts that are subjected to high loads and medical components for use in or on the human or animal body. The invention also provides a method that reliably enables the metal powder according to the invention to manufacture components with optimized mechanical properties on the basis of an additive manufacturing method.

Description

Technical Field

[0001] This invention relates to a metal powder composed of steel particles for use in additive manufacturing methods. The invention also relates to the use of this metal powder, methods for manufacturing components from this metal powder using additive manufacturing methods, and components manufactured using additive manufacturing methods.

[0002] When “%” data are given below regarding the composition of alloys or steel, unless otherwise explicitly stated, these data refer to mass (“mass” data).

[0003] Unless otherwise explicitly stated, the percentage of certain components in the microstructure of intermediate steel products or steel components is expressed as a percentage by volume (%). The percentage of components in the microstructure is determined by X-ray diffraction, with the microstructure percentage evaluated according to the Rietveld method.

[0004] Unless otherwise specified, all mechanical properties shown herein, including tensile strength Rm, yield strength Rp, and elongation at break A5.65, shall be determined in accordance with DIN 50125.

[0005] The values ​​of notched impact energy and notched impact strength shown in this article are determined according to DIN EN 10045. Background Technology

[0006] Austenitic stainless steels, especially due to their good deformability and excellent corrosion resistance, have wide applications in traditional mechanical engineering and medical technology. A major representative steel among these is the standardized steel X2CrNiMo17-12-2, with material number 1.4404 in the steel list. According to DIN EN 10088-3, steel X2CrNiMo17-12-2 consists of the following components, in mass percent: up to 0.03% C, up to 1.00% Si, up to 2.00% Mn, 16.5% to 18.5% Cr, 2.0% to 2.5% Mo, and 10.0% to 13.0% Ni, with the balance being iron and unavoidable impurities.

[0007] The alloying concept based on austenitic stainless steel must ensure the material's corrosion resistance. This is achieved, in particular, by adding chromium (“Cr”). When the Cr content is greater than 12% by mass, a chromium oxide layer forms on the steel components, preventing corrosion. This chromium oxide layer can be further stabilized by the element molybdenum (“Mo”). Specifically, the presence of Mo in the steel alloy increases resistance to pitting corrosion.

[0008] However, corrosion resistance is only aided when both Cr and Mo are dissolved in the metal matrix. Therefore, the carbon content (“C”) of austenitic stainless steel is limited to a maximum of 0.030% by mass, and the nitrogen content (“N”) is limited to a maximum of 0.011% by mass. Otherwise, there is a risk of chromium carbide or chromium nitride formation, which would lead to localized loss of the steel’s metal matrix.

[0009] Chromium carbide preferably precipitates along grain boundaries, which is actually critical for technical applications. As explained in the literature “Ferrousmaterials–Steeland castiron, H. Berns, W. Theisen, DOI:10.1007 / 978-3-540-79957-3, Springer Verlag”, the above process leads to intergranular corrosion, which in technical applications often results in the complete failure of components made of the corresponding steel.

[0010] However, carbon is not typically classified as a critical element in austenitic stainless steel. C and N can also be used as interstitial elements to improve the properties of austenitic stainless steel. In this way, these elements also contribute to corrosion resistance upon dissolution. This contribution can be estimated using the so-called MARC equation:

[0011] MARC=[%Cr]+3.3*[%Mo]+20*[%N]+20*[%C]-0.5*[%Mn]-0.25*[%Ni]

[0012] (MARC = Alloying determination for corrosion resistance) takes into account the effects of elements with positive (Cr, Mo, N, C) and negative (manganese (“Mn”), nickel (“Ni”)) on corrosion resistance.

[0013] Furthermore, C and N, as substitute elements, enhance the strength of austenitic steel through solid solution strengthening. The so-called "C+N alloyed austenitic stainless steel," with a high proportion of interstitial dissolved atoms, is based on this effect. DE 101 46 616A1 discloses an example of an alloy specification for such steel. It specifies that the austenitic stainless steel consists of the following, in mass %: 12% to 15% Cr, 17% to 21% Mn, <0.7% Si, a total of 0.4% to 0.7% C and N, and a balance of iron limited to less than 1.0% and unavoidable impurities related to manufacturing. The following applies to the ratio formed by the corresponding C content %C and the corresponding N content %N: %C:%N: 0.6 < %C:%N < 1.0. In the solution-annealed state, the steel constructed in this way exhibits significantly higher strength compared to the conventional austenitic stainless steel to which the aforementioned steel, material number 1.4404, belongs.

[0014] The low solubility of nitrogen (N) in molten iron (“Fe”) negates the improved mechanical properties of C+N alloyed austenitic stainless steel, making N alloying difficult. Another method for producing steels with higher N content is known as “melt pressure nitriding.” Pressure nitriding, in turn, requires specialized furnace technology that melts the steel under pressure with the desired amount of nitrogen dissolved in the melt (see, for example, EP 1 196 642 B1).

[0015] Adding manganese (Mn) increases the solubility of nitrogen (N) in the melt. Therefore, a higher Mn content allows for the production of steel with a high N content under atmospheric pressure. Furthermore, both Mn and N are strong austenite stabilizers, so in steels with high Mn and N content, the expensive alloying element nickel (“Ni”) is no longer needed, or is only required to a limited extent as an austenite stabilizer.

[0016] Conventional austenitic stainless steel only specifies the minimum content of N and C. Therefore, C+N alloyed austenitic steel has the following advantages compared to conventional austenitic stainless steel:

[0017] - It has higher strength due to the high proportion of interstitial dissolved atoms C and N (solid solution hardening).

[0018] - Due to the presence of interstitial dissolved atoms, the alloy has a higher tendency for work hardening.

[0019] - It has higher corrosion resistance due to the high proportion of interstitial dissolved atoms C and N.

[0020] - The cost of the alloy is reduced by replacing Ni with Mn.

[0021] - Because Mn is used instead of Ni (to avoid nickel allergy), it has the potential for use in the medical technology field.

[0022] Industrially, attempts to use the aforementioned C+N alloyed austenitic steel in conventional smelting metallurgical manufacturing processes contrast with the fact that the cooling of precast castings (such as lumps, slabs, etc.) made from this steel inevitably produces chromium carbides within the precast castings, which also negatively impacts corrosion resistance. However, to ensure sufficient corrosion resistance, the steel must undergo dissolution annealing during its processing to dissolve the chromium carbides. However, the annealing temperature required for this is above 1100°C, thus practically achievable only through specialized heat treatment furnaces. Another problem with conventional manufacturing processes is that, particularly for thick sections, cooling cannot be rapid enough to prevent the re-formation of chromium carbides.

[0023] Furthermore, due to the strong tendency for work hardening, austenitic steels with high C+N content are difficult or impossible to form or process at room temperature. Instead, they must be hot-formed, where the required temperatures are so high that cooling of the corresponding hot-formed parts again leads to the formation of undesirable chromium carbides. This severely limits the possible processing temperatures for hot forming and the extent of deformation that the steel can be hot-formed. Moreover, hot forming eliminates the possibility of optimizing the mechanical properties of C+N alloyed austenitic steels through work hardening. This means that extensive rework is required, especially in the manufacture of precision components, or in the manufacture of components that cannot be made from steels with specific strength requirements.

[0024] An alternative to conventional molten metallurgy manufacturing routes is powder metallurgy, which is used to manufacture components close to the final shape by pressing metal powder into the desired shape and then compressing it by sintering. Firstly, water-atomized metal powder is used for this purpose because the angular shape of the powder particles (characterized by protruding serrations, etc.) allows the water-atomized metal powder to be easily compressed into the original component, thus enabling the desired dimensional stability of the original component to be achieved without additional assistance.

[0025] Furthermore, for example, see the literature “Characterization of the surface of Fe-19Mn-18Cr-CN during heat treatment in a high vacuum – An XPS study, K. Zusmande et al, Materials Characterization, Vol. 71 (2012), 66-76”, which demonstrates that manganese oxides can exist on the particle surface of gas-atomized powders. These manganese oxides act as diffusion barriers, preventing metal powders containing such MnO oxides on their particle surface from being used for conventional sintering.

[0026] Hot isostatic pressing (“HIP”) is another possible method for compressing metal powders composed of austenitic steel, specifically the C+N alloy type discussed. Despite the presence of an oxide coating, this method also enables the metal powder to be compacted to up to its theoretical density. However, for example, see the literature "Surface Oxide Transformation during HIP of Austenitic Fe-19Mn-18Cr-CN PM steel", E. Hryha et al, Proceedings of the 11th International Conference on Hot Isostatic Pressing, 9-13 June 2014, Stockholm, Sweden. Research reports in the aforementioned publication have shown that the oxide coating of the powder particles negatively impacts the mechanical properties, particularly the toughness, of components made from such metal powders, even when the metal powder is compressed via hot isostatic pressing (HIP). Another disadvantage of HIP is the need for complexly formed capsules to create the final shape in which the metal powder is pressed. This limits the possibility of using HIP technically and economically. Similarly, the forming of the component within the capsule during HIP results in a low cooling rate, leading to the formation of undesirable chromium carbide in the component during cooling after HIP. This chromium carbide must be dissolved again through downstream heat treatment, resulting in the same problems as in conventional manufacturing described above.

[0027] The aforementioned drawbacks of known methods for manufacturing parts that approximate the final shape can be avoided by additive manufacturing methods.

[0028] In this paper, the term "additive manufacturing method" encompasses all manufacturing methods that add material to create components. This addition is typically done in layers. Therefore, the "additive manufacturing method," often referred to in technical terms as a "generative method" or commonly known as "3D printing," contrasts with classical subtractive manufacturing methods such as machining (e.g., milling, drilling, and turning), in which material is removed to shape the components to be manufactured separately. Similarly, additive manufacturing methods generally differ from conventional solid forming methods such as forging, in which the corresponding steel parts are formed while maintaining the quality of the initial or intermediate product.

[0029] The principle of additive manufacturing enables the creation of geometrically complex structures that cannot be achieved or can only be achieved with great difficulty using conventional manufacturing methods such as the aforementioned machining methods or primary forming methods (casting, forging) (see the literature "VDI Status Report "Additive Manufactuing Methods", September 2014, published by Verein Deutscher Ingenieure eV, Fachbereich Produktionstechnik und Fertigungsverfahren (Association of German Engineers, Department of Production Technology and Manufacturing Processes), www.vdi.de / statusadditiv")

[0030] Further definitions of methods encompassed in the general term “additive methods” can be found, for example, in VDI Guidelines 3404 and 3405.

[0031] When additively processing metal powder into components, there is a distinction between the following methods: a method of curing metal powder by melting the metal particles of the powder in a manner that forms a material bonding compound through heat input; and a method of curing by using an adhesive mixed with the powder particles, so that the particles remain in a solid matrix after hardening.

[0032] Because of the short exposure time to the heat source, heat input-based additive manufacturing methods can achieve such high cooling rates that chromium carbide does not form in the manufactured components. The types of austenitic steels discussed in this paper are particularly suitable for additive manufacturing because they do not undergo any phase transformation during heating and cooling. Therefore, the steel X2CrNiMo17-12-2 (material number 1.4404), mentioned initially, has itself been identified as one of the standard steels for manufacturing metal powders for 3D printing. However, the mechanical properties obtained by this steel at room temperature during printing are insufficient for many applications. Summary of the Invention

[0033] In view of the background of the prior art, the object of the present invention is to provide a metal powder suitable for additive manufacturing, which can reliably manufacture high-load components.

[0034] In addition, the advantageous uses of the metal powder provided should be pointed out.

[0035] A method should also be proposed that enables the reliable manufacture of components with optimized mechanical properties based on an additive manufacturing method utilizing the provided metal powder.

[0036] Finally, it should be noted that when manufactured using additive manufacturing methods, the resulting components exhibit optimized mechanical properties.

[0037] The metal powder used to achieve this purpose consists of steel particles and has at least the following characteristics:

[0038] - The average diameter of the steel particles ranges from 5 μm to 150 μm, and

[0039] - The steel particles consist of the following, in percentage by mass:

[0040] C: 0.15% to 1.0%,

[0041] N: 0.15% to 1.0%,

[0042] Si: 0.1% to 2.0%,

[0043] Mn: 10% to 25%

[0044] Cr: 5% to 21%,

[0045] Mo: 0.1% to 3.0%,

[0046] Ni: ≤5%,

[0047] The balance consists of iron and unavoidable impurities.

[0048] -The flowability of the metal powder, as determined according to DIN ENISO 4490, is less than 30 sec / 50 g.

[0049] According to the present invention, the method for achieving the above-mentioned objective includes at least the following processing steps:

[0050] a) Melt a steel melt, the steel melt being composed of the following, in percentage by mass:

[0051] C: 0.15% to 1.0%,

[0052] N: 0.15% to 1.0%,

[0053] Si: 0.1% to 2.0%,

[0054] Cr: 5% to 21%,

[0055] Mo: 0.1% to 3.0%,

[0056] Ni: ≤5%,

[0057] And Mn,

[0058] The balance consists of iron and unavoidable manufacturing-related impurities.

[0059] The Mn content of the melt is 0.5% to 5% higher than the corresponding target Mn content %Mn_Z of the component to be manufactured, and the following condition applies: 8% ≤ Mn_Z ≤ 24%;

[0060] b) The melt obtained in processing step a) is atomized into metal powder, wherein steel particles with an average particle size of 5 μm to 150 μm are selected from the obtained steel particles for further processing;

[0061] c) The component is manufactured using an additive manufacturing method, wherein

[0062] c.1) At least one solidified volume cross-section of the component to be manufactured is made from at least a portion of the metal powder;

[0063] c.2) Apply another portion of the metal powder to the solidified volume section of the processing step c.1;

[0064] as well as

[0065] c.3) Repeat steps c.1 and c.2 until the component to be manufactured is additively formed in a fully completed manner.

[0066] It goes without saying that, when implementing the methods according to the invention and their variations and the extended options explained herein, those skilled in the art will add processing steps not explicitly mentioned in the context of the invention, which are generally applied based on their practical experience when implementing such methods.

[0067] Finally, according to the present invention, the above-mentioned objective is also achieved by a component having at least the following characteristics and manufactured by an additive manufacturing method:

[0068] The component

[0069] - Manufactured using additive manufacturing methods.

[0070] - Composed of the following, in mass percent: 0.15% to 1.0% C, 0.15% to 1.0% N, 0.1% to 2.0% Si, 8% to 24% Mn, 5% to 21% Cr, 0.15% to 3.0% Mo, ≤5% Ni, and the balance being iron and unavoidable impurities.

[0071] -Has a microstructure consisting of more than 50% by volume austenite, up to 49% by volume ferrite, with the balance being ferrite and other unavoidable microstructure components related to manufacturing, wherein the proportion of unavoidable microstructure components in the microstructure of the component is up to 30% by volume.

[0072] In particular, such components according to the invention can be manufactured from metal powder obtained according to the invention by applying the method according to the invention.

[0073] In particular, the components according to the invention are mechanical parts subjected to high stress in practice or components used in or on the human or animal body, manufactured by an additive manufacturing method particularly suitable for metal powders according to the invention.

[0074] The present invention also includes other advantageous embodiments, which are identical to the general idea of ​​the invention and will be explained in detail below. Detailed Implementation

[0075] In this document, the term "components for use in or on the human or animal body" includes implants permanently placed in the body, such as screws, splints, braces, hip or knee joint components, dental abutments, or other dental implants firmly fixed in the jaw, and other components implanted as replacements for natural bone or joints, as well as prostheses temporarily or permanently fixed to the body, such as prosthetic restorations (bridges, partial or complete dentures) or tools specifically required in dental or general surgical treatments. Materials used for implants or prostheses must possess sufficient corrosion resistance and optimized biocompatibility. Therefore, these materials must not have harmful effects on the body in which or on which components made of that material are used, nor should they provoke any other reactions that may adversely affect comfort and health. Simultaneously, implant or prosthetic materials must possess mechanical properties sufficient for their respective intended uses, such as strength and toughness. The metal powder (whose particles are configured as described above within the alloy framework specified according to the invention) optimally meets the above requirements and also enables the manufacture of fine and stable components using known 3D printing processes, which can safely withstand the stresses generated during their use in the body. Therefore, for example, components for general and dental surgical purposes, such as screws, nails, bolts, joint components, etc., and surgical instruments, such as surgical instruments, can be manufactured from the metal powder according to the invention via additive manufacturing.

[0076] Furthermore, the metal powder according to the invention is suitable for manufacturing high-load and highly corrosion-resistant mechanical parts, such as pump housings or other finely shaped mechanical components. The forming of these components is subject to specific requirements due to particular flow engineering demands, and such forming cannot be achieved using conventional forming, reforming, or subtractive manufacturing methods. Specifically, the strong work-hardening tendency of the steel used according to the invention can be used to manufacture components that, despite minimizing size, can actually withstand high compressive stresses, etc.

[0077] Therefore, the metal powder for additive manufacturing provided according to the present invention is composed of steel particles, wherein

[0078] - The average diameter of the steel particles ranges from 5 μm to 150 μm.

[0079] and

[0080] - The steel particles consist of the following, in percentage by mass:

[0081] C: 0.15% to 1.0%,

[0082] N: 0.15% to 1.0%,

[0083] Si: 0.1% to 2.0%,

[0084] Mn: 10% to 25%

[0085] Cr: 5% to 21%,

[0086] Mo: 0.1% to 3.0%,

[0087] Ni: ≤5%,

[0088] The balance consists of iron and unavoidable impurities.

[0089] -The flowability of the metal powder, as determined according to DIN ENISO 4490, is less than 30 sec / 50 g.

[0090] As explained in the introductory section, the high carbon (“C”) and nitrogen (“N”) content of the steel particles in the metal powder according to the invention contributes to the strength, work hardening, and corrosion resistance of components manufactured from the metal powder according to the invention by additive manufacturing. To ensure this, the invention specifies a total C and N content of 0.3% by mass to 2% by mass, wherein the C content and N content are 0.15% by mass to 1% by mass, respectively. In terms of strength properties, processing characteristics, and corrosion resistance, a C or N content of at least 0.3% by mass has proven particularly advantageous, wherein a C or N content of up to 0.7% by mass in the steel particles of the metal powder ensures a particularly advantageous combination of high strength values, good toughness, and equally good elongation at break. Overall, the C and N content of the steel particles in the metal powder according to the invention is advantageously limited to 0.6% by mass to 1.4% by mass.

[0091] The melt for producing the steel particles of the metal powder according to the invention, and the resulting steel particles themselves, contain 0.1% to 2% by mass of silicon (“Si”) to adjust the melting point and viscosity of the melt during the atomization of the melt into steel particles, so that the melt can be reliably atomized into steel particles. Si is also necessary for melt deoxidation during steelmaking. A Si content of at least 0.15% by mass is particularly suitable, wherein the positive effects of the presence of Si can be utilized particularly effectively when the Si content is at most 0.6% by mass.

[0092] Manganese (“Mn”) is included in the steel particles of the metal powder according to the invention at a content of 10% to 25% by mass to ensure that the microstructure of the component manufactured from the metal powder according to the invention is, technically speaking, at least primarily and preferably entirely composed of austenite. Thus, the manganese content is set such that the austenitic phase in the microstructure is stabilized not only by the coexisting C, N, and Mn, but also by a sufficient proportion of austenite in the microstructure even in the solidified state of the component, while simultaneously compensating for the effect of the contents of chromium (“Cr”), molybdenum (“Mo”), and silicon (Si) provided according to the invention in the alloy of the steel particles of the metal powder on ferrite stabilization. Mn is also necessary to increase the nitrogen solubility of the melt. In this way, the high N content provided according to the invention can be achieved at atmospheric pressure.

[0093] Importantly, according to the invention, the Mn content of the steel particles in the metal powder according to the invention is determined such that, although a portion of the Mn content present in the steel particles is lost during the manufacturing of the metal powder and additive manufacturing processes, an austenite content still exists in the component obtained by additive manufacturing, which is sufficient to form the desired predominant, and particularly fully austenitic, microstructure. In this case, the invention is based on the common knowledge that there is a Mn loss of 0.5% to 2.5% by mass during additive manufacturing, where actual testing has shown that the Mn loss that occurs is typically 1.5 ± 0.5% by mass.

[0094] To ensure that the microstructure of the components manufactured from the metal powder according to the invention is technically entirely austenitic, and therefore the components under discussion are indeed non-magnetic, taking into account the Mn loss that occurs during additive manufacturing, the Mn content of the metal powder can be set such that greater than 10% by mass, and particularly greater than 13% by mass, Mn is reliably present in the obtained components. Actual tests shown herein demonstrate that, with the Mn content of the steel particles of the metal powder according to the invention being at least 13% by mass, and particularly at least 15% by mass, the Mn content is reliably present in components manufactured by additive manufacturing from the metal powder according to the invention, thus guaranteeing a fully austenitic microstructure. Therefore, particularly when components for human or animal bodies are to be manufactured by additive manufacturing from metal powder, the Mn content provided in the steel particles of the metal powder according to the invention is at least 15% by mass.

[0095] According to the invention, the microstructure is considered to be "fully austenitic," wherein the total proportion of technically unavoidable microstructure components other than austenite in the microstructure of the component is at most 10% by volume. In this case, the proportion of other microstructure components is preferably kept as low as possible, such that the proportion of other microstructure components is particularly preferably less than 5% by volume.

[0096] The chromium (“Cr”) content of the steel particles in the metal powder according to the invention is from 5% to 21% by mass, thereby ensuring sufficient corrosion resistance of components formed from the metal powder according to the invention by appropriate additive manufacturing methods, when combined with a molybdenum (“Mo”) content of 0.5% to 3.0% by mass. When it is necessary to ensure sufficient corrosion resistance of components manufactured for use in the human or animal body or in other highly corrosive environments, the Cr content in the steel particles of the metal powder may be specified to be at least 14% by mass for this purpose.

[0097] When mechanical parts are manufactured from metal powders that meet specific toughness requirements, the nickel (“Ni”) content in the steel particles of the metal powder according to the invention may be up to 5% by mass. However, when components for use on or inside the human or animal body are manufactured from the metal powder according to the invention, the Ni content should be set as low as possible, but in any case should be limited to up to 0.1% by mass, so that although the presence of Ni is technically unavoidable due to the manufacturing method, the components manufactured from the metal powder according to the invention will not cause allergic reactions upon contact with the human or animal body.

[0098] Impurities in the steel particles of the metal powder according to the invention include all alloying elements that inevitably enter the steel during steel manufacturing and processing, but not explicitly mentioned herein. However, the content of these alloying elements is in such a low degree in any case that they do not affect the properties of the steel alloyed in the manner according to the invention. Naturally, the level of impurities should therefore be kept as low as possible. However, for technical and economic reasons, it is considered that steel particles of the metal powder according to the invention with a total impurity content of at most 2% by mass, preferably at most 1% by mass, and particularly preferably less than 1% by mass, are not detrimental to the effects and performance sought according to the invention. In cases where the metal powder according to the invention is intended to manufacture components for human or animal use, in addition to the Ni content, the total content of cadmium (“Cd”), beryllium (“Be”), and lead (“Pb”) as undesirable impurities should be limited to at most 0.02% by mass.

[0099] Because the flowability of the metal powder according to the invention, as defined by DIN ENISO 4490, must be less than 30 sec / 50 g, this metal powder possesses a flowability that makes it optimally suited for conventional 3D printing processes. A flowability of at most 20 sec / 50 g is particularly suitable.

[0100] The bulk density of the metal powder according to the present invention shall be at least 3 g / cm³. 3 To ensure optimal processability. A bulk density range of 3 g / cm³ is particularly suitable for implementation. 3 Up to 6g / cm 3 .

[0101] According to the above description of the present invention, the method for manufacturing steel components according to the present invention includes the following steps:

[0102] a) Melt a steel melt, the steel melt being composed of the following, in percentage by mass:

[0103] C: 0.15% to 1.0%,

[0104] N: 0.15% to 1.0%,

[0105] Si: 0.1% to 2.0%,

[0106] Cr: 5% to 21%,

[0107] Mo: 0.1% to 3.0%,

[0108] Ni: ≤5%,

[0109] And Mn,

[0110] The balance consists of iron and unavoidable manufacturing-related impurities.

[0111] The Mn content of the melt is 0.5% to 5% higher than the corresponding target Mn content %Mn_Z of the component to be manufactured, and the following condition applies: 8% ≤ Mn_Z ≤ 24%;

[0112] b) The melt molten in processing step a) is atomized into metal powder, wherein steel particles with an average particle size of 5 μm to 150 μm are selected from the obtained steel particles for further processing;

[0113] c) Components are manufactured using additive manufacturing methods, wherein

[0114] c.1) At least one of the components to be manufactured is made from at least a portion of metal powder.

[0115] The solidified volume cross-section;

[0116] c.2) If necessary, apply another portion of the metal powder to the solidified volume section in processing step c.1;

[0117] as well as

[0118] c.3) If necessary, repeat steps c.1 and c.2 until the component to be manufactured is additively formed in a fully completed manner;

[0119] d) Optionally, machining is performed to shape the component;

[0120] e) Optionally, the obtained component is subjected to final heat treatment;

[0121] f) Optionally, the component may be subjected to a mechanical or thermochemical surface treatment.

[0122] The method according to the invention specifies the Mn content of the melt to be atomized into the metal powder according to the invention, the Mn content of the melt being 2% to 4% by mass higher than the Mn content present in the component manufactured according to the invention, so that the component has the desired mechanical properties and that the component has the same desired at least major austenitic structure.

[0123] In this context, the present invention is based on the common knowledge that significant Mn loss occurs not only during additive manufacturing processes as already mentioned, but also when atomizing the melt into metal powder. In practice, the Mn loss is typically in the range of 1.5 ± 0.5% by mass. Compared to the alloy of the final component manufactured according to the invention, the melt has a sufficient Mn content through over-alloying according to the invention, thus actively compensating for all Mn losses that may occur during the manufacture and processing of the metal powder according to the invention.

[0124] Steel particles of metal powder are manufactured in a conventional manner using a suitable atomization method, such as gas or water atomization. When necessary, powder particles of suitable size are selected from the obtained powder particles by sieving for further processing according to the invention. Here, particles with an average diameter of 5 μm to 150 μm have proven suitable for the purposes of the invention. Therefore, the diameter of the particles selected according to the invention, through sieving and additional air separation (when necessary), is 5 μm to 150 μm, which is the average of all particles (see, for example, Zogg, Martin: Einführungin dieMechanische Verfahrenstechnik, 3rd, revised Edition Stuttgart: Teubner, 1993 ISBN 3-519-16319-5, https: / / de.wikipedia.org / wiki / Siebanalyse, published on November 1, 2018, or see Lexikon Produktionstechnik Verfahrenstechnik / ed. Heinz M. Hiersig, Düsseldorf: VDI-Verl., 1995, ISBN 3-18-401373-1, terms “Siebanalyse” and “Sieben”).

[0125] Depending on the method of melt atomization in processing step b) and the execution method of additive manufacturing, nitrogen (N) loss also occurs during the manufacture and processing of the metal powder according to the invention due to the low nitrogen solubility of the molten metal. Taking this into account, the present invention sets the N content of the melt to ensure that sufficient N is present in the final component under various conditions, so that N has a positive impact on the performance of the component. The N content can be precisely adjusted by comparing the N content of the melt with the target N content of the component, wherein the target N content of the component typically ranges from 0.15%N by mass to 1.0%N by mass, particularly from 0.2%N by mass to 0.7%N by mass, while the N content of the melt is over-alloyed to 0.1%N by mass to 0.2%N by mass.

[0126] Metal powders according to the invention can be produced particularly well by gas atomization of the alloyed melt according to the invention. In this case, it is preferable to use a gas that is inert to the melt to avoid oxidation of the metal particles. In particular, when the metal powder solidifies by heat input, during the additive processing of the metal powder according to the invention, greater nitrogen loss can be avoided by processing in a protective gas atmosphere composed of, for example, nitrogen or argon (“Ar”).

[0127] Similarly, when manufacturing metal powders via gas atomization, greater nitrogen loss can be avoided when N or Ar is used as the atomizing gas. The value of nitrogen as a processing gas in both additive manufacturing and gas atomization has been specifically demonstrated because its use offsets nitrogen degassing from the steel during the short-duration melting phases of atomization or additive manufacturing processes.

[0128] Recent developments indicate that, as an alternative to gas atomization via conventional water atomization, the metal powder according to the invention can also be manufactured from the alloyed steel melt according to the invention, which satisfies the requirements for further processing.

[0129] The mechanical properties of components manufactured according to the invention can be improved by optionally performing heat treatment (processing step e). Thus, the corresponding components can be annealed at temperatures from 1000°C to 1250°C for 5 to 120 minutes, with annealing durations of 10 to 30 minutes and annealing temperatures from 1100°C to 1150°C proving particularly useful.

[0130] The metal powder according to the invention can be processed using a 3D printing apparatus known and provided in the prior art in additive manufacturing according to the invention. Therefore, in additive manufacturing, the metal powder processed according to the invention can be cured by heat input, wherein in processing step c.1), at least a first portion of the volumetric cross-section undergoes a time-limited heat input, followed by cooling, such that steel particles of the metal powder present in the heated volumetric cross-section and respectively adjacent to each other form a material bond, and are cured to the corresponding volumetric cross-section of the component to be manufactured after cooling. Tests have shown that when a laser beam is used as a heat source in processing step c.1), the laser beam at 30 J / mm... 3 Up to 90J / mm 3 When the energy density is directed towards the volume cross-section to be heated separately, good processing success can be safely achieved.

[0131] However, alternatively, additive manufacturing such as the known binder jetting can also be performed, in which powder particles are bonded together by a suitable binder to form a solid component (see reference https: / / de.wikipedia.org / wiki / Binder_Jetting, published January 16, 2020).

[0132] Based on the above explanation, the feature of the component according to the present invention further lies in its

[0133] - Manufactured using additive manufacturing methods.

[0134] - Composed of the following, in mass percent: 0.15% to 1.0% C, 0.15% to 1.0% N, 0.1% to 2.0% Si, 8% to 24% Mn, 5% to 21% Cr, 0.15% to 3.0% Mo, ≤5% Ni, and the balance being iron and unavoidable impurities.

[0135] -Has a microstructure consisting of more than 50% by volume austenite, up to 49% by volume ferrite, with the balance being ferrite and other unavoidable microstructure components related to manufacturing, wherein the proportion of unavoidable microstructure components in the microstructure of the component is up to 30% by volume.

[0136] In the manufacture of mechanical components such as pump housings and finely shaped parts for machinery, vehicle bodies, or vehicle chassis from the metal powder according to the invention, it may be sufficient in many applications for the microstructure of the manufactured components to be primarily composed of austenite, i.e., greater than 50 vol%, particularly greater than 60 vol%, or at least 80 vol% austenite in various cases, while the balance of the microstructure is ferrite and up to 30 vol% of other unavoidable microstructure components. The other unavoidable components comprising up to 30 vol% of the microstructure include chromium carbide, chromium nitride, and σ phase. Preferably, the proportion of other unavoidable components related to manufacturing is limited to up to 20 vol%, particularly up to 15 vol%, or especially preferably up to 5 vol%, to achieve optimized mechanical properties of the components.

[0137] When the ferrite content in the microstructure of the component according to the invention is at most 15% by volume, particularly at most 10% by volume, this can help improve toughness while maintaining consistently high strength. This combination of properties may be particularly beneficial when the component according to the invention is exposed to high alternating loads in practical use, or when it should be able to absorb high dynamic forces, such as in the case of collision-related components in a vehicle body or chassis.

[0138] On the other hand, when the components provided according to the invention are used for medical purposes, it has proven particularly advantageous when the austenite content of the tissue is at least 95% by volume, and especially at least 98% by volume, making the components safe and non-magnetic.

[0139] The tensile strength Rm of the component according to the invention in the non-heat-treated state is typically at least 650 MPa, and the yield strength Rp is typically at least 650 MPa. Furthermore, in this state, the notched impact energy of the component is at least 30 J, and the notched impact strength is at least 50 J / cm². 3 In practice, the notched impact energy typically reached is at least 40 J, and the notched impact strength is at least 60 J / cm². 3In the unhardened state, the surface hardness measured on the free surface of the component according to the invention is typically at least 200 HV, particularly at least 250 HV. The elongation at break (A5.65) of the component according to the invention in the untreated state is typically at least 15%.

[0140] As described above, the mechanical properties of the components manufactured according to the invention can be further improved by optionally providing heat treatment. In the notched impact test, the notched impact energy of the component is at least 100 J, and the notched impact strength is at least 120 J / cm². 3 The surface hardness measured on the free surface of the component according to the invention is typically at least 200 HV, and there is no surface layer hardening.

[0141] In this context, it is known that the mechanical properties of components manufactured by the additive manufacturing method of the type discussed are anisotropic. Therefore, in various cases, the limiting values ​​shown above are those values ​​that must conform to the relevant mechanical properties, regardless of whether they are determined in the horizontal or vertical direction of the corresponding component. The "vertical" construction direction refers to the extension of the component in the direction of layer-by-layer construction during the additive manufacturing process, while the "horizontal" construction direction refers to the extension in the direction aligned with the transverse side of the component.

[0142] Due to the composition of the steel particles in the metal powder according to the invention, the alloy provided according to the invention can be surface hardened in a conventional manner after 3D printing, which can be particularly achieved by plasma nitriding. The high chromium content in the alloy leads to the formation of chromium carbide or chromium nitride layers and a corresponding increase in hardness in the near-surface region. These properties are particularly advantageous for components subjected to dynamic loads or wear.

[0143] In one variant of the metal powder according to the invention, which is particularly suitable for the actual manufacture of mechanical parts, the steel particles consist of the following, in mass %: 0.35% to 0.45% C, 0.55% to 0.65% N, 0.2% to 0.3% Si, 20.0% to 21.0% Mn, 17.5% to 18.5% Cr, 1.9% to 2.1% Mo, up to 1.0% Ni, and the balance being iron and up to 1.0% by mass of unavoidable impurities, wherein the impurities include those that are present in undesirable amounts: ≤0.02% P, ≤0.02% S, ≤0.05% Nb, ≤0.05% W, ≤0.05% V, ≤0.1% O, ≤0.01% B and ≤0.1% Al.

[0144] The steel variant of the metal powder according to the invention, which is particularly suitable for manufacturing components for use on or inside the human or animal body, differs from the alloy described in the preceding paragraph only in that the Ni content is limited to at most 0.1% by mass, preferably less than 0.1% by mass.

[0145] The invention will now be explained in more detail using exemplary embodiments.

[0146] To test the performance of the metal powder according to the invention and components made from the metal powder according to the invention by additive manufacturing, nine melts M1 to M9 were manufactured in a first series of tests, the composition of which is shown in Table 1.

[0147] Because they minimize Ni content, melts M1 to M9 are suitable for producing steel particles from such metal powders, which are used to manufacture components intended for use on human or animal bodies.

[0148] The molten gases M1 to M9 are atomized into steel particles using an atomizing device established in the prior art in a conventional manner. Nitrogen is used as the atomizing gas.

[0149] From the steel particles obtained by atomization, particles with an average size of 10 μm to 53 μm are selected by sieving and air separation. According to DIN ENISO 4490, the flowability of the steel particles selected in this way is ≤18 s / 50 g.

[0150] In a further step, the manufactured metal powder was processed using a conventional 3D printing apparatus (M290 3D printer, see https: / / www.eos.info / eos-m-290, published December 19, 2019). The metal powder could be processed without question, and the manufactured components exhibited a dense structure without pores or cracks. Overall, it has been demonstrated that energy densities in the range of 30 J / mm² can be achieved. 3 Up to 90J / mm 3 Reliable components are manufactured from metal powder.

[0151] Argon was used as the processing gas in some 3D printing tests, and nitrogen was used in others. Both processing gases consistently produced good results.

[0152] Phase analysis of the printed components using X-ray diffraction showed that there were no chromium carbide or other precipitates that negatively affected corrosion resistance.

[0153] Each printed component has a fully austenitic microstructure (austenite content ≥ 99% by volume).

[0154] The tensile strength Rm, yield strength Rp, notched impact energy, notched impact strength, and Vickers hardness of the printed components are also determined in a conventional manner according to standards.

[0155] Table 2 shows the range of relevant characteristic values ​​that have been determined in the horizontal construction direction of the components for metal powder printed from melts M1 to M9.

[0156] Table 3 shows the range of relevant characteristic values ​​determined in the vertical construction direction of the component for components printed from metal powder manufactured from melts M1 to M9.

[0157] In addition, Tables 2 and 3 list the available characteristic values ​​of reference material 316L obtained from professional literature (see the literature https: / / www.fabb-it.de / files / datenblaetter / edelstahl.pdf, published on January 16, 2020), and the composition of reference material 316L is also shown in Table 1.

[0158] Tests show that the machinability of the untreated components printed from the metal powder according to the present invention is not only superior to that of components made from conventional material 316L, but the high C and N content also results in significantly improved mechanical properties of the components manufactured according to the present invention.

[0159] For the second series of tests, another melt was melted and atomized into steel particles in the same manner as described above for melts M1 to M9. The composition M10 of the obtained steel particles is shown in Table 4. Steel particles with an average particle size of 10 μm to 53 μm were selected from these particles by sieving. The resulting metal powder had a flowability of 16.8 s / 50 gr and a bulk density of 4.23 g / cm³. 3 .

[0160] Using the aforementioned M290 3D printer, twenty components were printed from metal powder formed from steel particles. Nitrogen gas was used as a protective gas. The components were printed with a layer thickness of 40 μm per layer.

[0161] In the vertical structural direction, the density, Vickers hardness (HV), notched impact energy, yield strength (Rp), tensile strength (Rm), and elongation at break (A5.65) of twenty components in a non-heat-treated state were tested according to standards. The average values ​​of these test results are summarized in Table 5 and compared with the corresponding property values ​​of components printed from conventional 316L steel from the aforementioned cited literature. Again, the significant superiority of the material provided and processed according to the present invention is demonstrated here.

[0162] Furthermore, the composition and microstructure of components printed from metal powder formed from steel particles M10 according to the present invention were examined. The results showed a significant loss of Mn and N due to the 3D printing process used. The average Mn content of the component was approximately 8% lower than that of the steel particles in the metal powder. Similarly, the N content of the component decreased by an average of approximately 12% during the 3D printing process. However, the Mn and N content retained in the component was sufficient to ensure the characteristic of a fully austenitic microstructure (austenite content > 99% by volume) in the component.

[0163] Finally, a component printed with metal powder having steel particles corresponding to alloy M10 according to the present invention and a comparative component printed with conventional metal powder having steel particles composed of steel 316L were subjected to corrosion tests according to SEP 1877 Method II. This test is used to test the resistance of highly alloyed corrosion-resistant materials to intergranular corrosion. Both components passed the test and therefore resisted intergranular corrosion.

[0164] Furthermore, according to ASTM G48 Method E, pitting corrosion tests were performed on components printed with the metal powder according to the invention and, for comparison, on components printed with 316L steel. It was also found that components made with the metal powder according to the invention have at least the same pitting corrosion resistance as those printed with conventional metal powder used for comparison.

[0165] Finally, the component printed from the metal powder according to the invention, which consists of steel particles with a composition according to alloy M10, was heat-treated by heating the component to a temperature of 1125°C, annealing for 30 minutes, and then water-quenching. The notched impact energy of the component heat-treated in this manner was measured in a standardized manner, and the result was an average of 129 ± 2 J, which is approximately 2.4 times the average notched impact energy of 52 ± 3 J obtained in the standard notched impact test from the non-heat-treated state.

[0166] Table 1

[0167] powder C+N C N Si Mn Cr Mo Ni M1 0.6 0.3 0.3 0.1 15.0 14 0.5 ≤0.1 M2 0.7 0.3 0.4 0.2 16.0 15 1.0 ≤0.1 M3 0.8 0.3 0.5 0.3 17.0 16 1.5 ≤0.1 M4 0.9 0.4 0.5 0.4 18.0 17 2.0 ≤0.1 M5 1.0 0.4 0.6 0.5 19.0 18 2.5 ≤0.1 M6 1.1 0.5 0.6 0.6 20.0 19 3.0 ≤0.1 M7 1.2 0.5 0.7 0.1 21.0 20 3.0 ≤0.1 M8 1.3 0.6 0.7 0.15 22.0 21 3.0 ≤0.1 M9 1.4 0.7 0.7 0.2 23.0 21 3.0 ≤0.1 316L - <0.03 <0.1 <0.75 <2.0 18 2.7 14

[0168] Data are expressed as a percentage by mass, with the balance being Fe and unavoidable impurities.

[0169] Table 2

[0170]

[0171]

[0172] *)nd = Undetermined

[0173] Table 3

[0174]

[0175] Table 4

[0176]

[0177] Alloy M10, data in mass percent, balance Fe and unavoidable impurities.

[0178] Table 5

[0179]

Claims

1. Metal powder for use in an additive manufacturing method and consisting of steel particles, wherein - the average diameter of the steel particles is from 5 pm to 150 pm, and - the steel particles consist of, in mass-%, C: 0.15% to 1.0%, N: 0.15% to 1.0%, Si: 0.1% to 2.0%, Mn: 10% to 25%, Cr: 5% to 21%, Mo: 0.1% to 3.0%, Ni: < 5%, the balance being iron and unavoidable impurities, - wherein the flowability of the metal powder, determined according to DIN EN ISO 4490, is less than 30 sec / 50 g.

2. The metal powder according to claim 1, characterized in that The Mn content of the steel particles of the metal powder is at least 15 mass-%.

3. The metal powder according to any one of the preceding claims, characterized in that, The Cr content of the steel particles of the metal powder is at least 14 mass-%.

4. Metal powder according to the preceding claim 1 or 2, characterized in that The Ni content of the steel particles of the metal powder is at most 0.1 mass-%.

5. Metal powder according to the preceding claim 1 or 2, characterized in that The total content of C and N of the steel particles of the metal powder is from 0.6 mass-% to 1.5 mass-%.

6. Use of the metal powder obtained according to claim 2, 3 or 4 in the additive manufacturing of a component for or on the human or animal body.

7. A method for manufacturing a steel component, comprising the following steps: a) melting a steel melt, which consists of, in mass-%, C: 0.15% to 1.0%, N: 0.15% to 1.0%, Si: 0.1% to 2.0%, Cr: 5% to 21%, Mo: 0.1% to 3.0%, Ni: < 5%, and Mn, and the balance being iron and unavoidable impurities related to the manufacture, wherein the Mn content of the melt is from 0.5% to 5% higher than the respective Mn target content %Mn_Z of the component to be manufactured, for which the following condition applies: 8% < Mn_Z < 24%; b) atomizing the melt melted in process step a) to a metal powder, wherein from the resulting steel particles steel particles having an average particle size of from 5 pm to 150 pm are selected for further processing; c) manufacturing the component using an additive manufacturing method, wherein c.1) at least one solidified volume section of the component to be manufactured is manufactured from at least a portion of the metal powder; c.2) a further portion of the metal powder is applied to the solidified volume section in process step c.1); and c.3) process steps c.1) and c.2) are repeated until the component to be manufactured is additively shaped in a completely finished manner.

8. The method of claim 7, wherein, The method further comprises a step d) of machining to shape the component.

9. The method of claim 7, wherein, The method further comprises a step e) of subjecting the obtained component to a final heat treatment.

10. The method of claim 7, wherein, The method further comprises a step f) of subjecting the component to a mechanical or thermo-chemical surface layer treatment.

11. The method of claim 9, wherein, During the heat treatment, the component is held at a temperature of from 1000 °C to 1250 °C for 5 min to 120 min.

12. The method of any one of claims 7 or 8, wherein, The atomization of the melt in process step b) is carried out by gas atomization.

13. The method of any one of claims 7 or 8, wherein, In the machining step c.1 ) a laser beam is used as heat source, wherein the laser beam is in each case guided with an energy density of 20 J / mm 3 to 110 J / mm 3 to the volume cross section to be heated.

14. A component, - manufactured by an additive manufacturing method, - consists, in mass-%, of 0.15% to 1.0% C, 0.15% to 1.0% N, 0.1% to 2.0% Si, 8% to 24% Mn, 5% to 21% Cr, 0.15% to 3.0% Mo, < 5% Ni, and the balance being iron and unavoidable impurities, and - has a microstructure consisting of more than 50 vol-% austenite, at most 49 vol-% ferrite, and the balance being ferrite and unavoidable other microstructural constituents related to the manufacturing, wherein the unavoidable microstructural constituents in the microstructure of the component amount to at most 30 vol-%.

15. The structure of claim 14, wherein said member having a tensile strength Rm of at least 650 MPa and a yield strength Rp of at least 650 MPa in the non-heat treated state, and a notched impact energy of at least 30 J and a notched impact strength of at least 50 J / cm in a notched impact test 3 .

16. The structure of claim 15, wherein The surface hardness of the component is at least 250 HV.

17. The construction of any of claim 15, wherein, The component achieves a notched impact energy of at least 100 J and a notched impact strength of at least 120 J / cm in the heat treated condition in the notched impact test 3 .

18. The structure of claim 17, wherein The surface hardness of the component is at least 200 HV.

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