Metal Powder for an Additive Manufacturing Process, Uses of the Metal Powder, Method for Producing a Component, and Component

Abstract

The invention relates to a metal powder intended for use in an additive manufacturing process, which consists of steel particles having an average diameter of 5-150 μm and consisting of, in mass %, C: 0.15-1.0%, N: 0.15-1.0%, Si, 0.1-2.0%, Mn: 10-25%, Cr: 5-21%, Mo: 0.1-3.0%, Ni: ≤5%, remainder of iron and unavoidable impurities. The metal powder has a flow rate determined in accordance with DIN EN ISO 4490 of less than 30 sec/50 g. Using a metal powder according to the invention, reliable high-load-bearing components can be produced by additive manufacturing. Accordingly, a metal powder according to the invention is particularly suitable for the manufacture of machine elements that are exposed to high loads and of medical components that are used in or on the human or animal body. The invention also provides a method which reliably allows components with optimised mechanical properties to be manufactured from metal powder according to the invention on the basis of an additive manufacturing process.

Claims

1. A metal powder for use in an additive manufacturing process and consisting of steel particles which have an average diameter of 5-150 μm and consist of, in mass %, C: 0.15-1.0%, N: 0.15-1.0%, Si: 0.1-2.0%, Mn: 10-25%, Cr: 5-21%, Mo: 0.1-3.0%, Ni: ≤5%, with the remainder being iron and unavoidable impurities, wherein the metal powder has a flow rate determined in accordance with DIN EN ISO 4490 of less than 30 sec/50 g.

2. The metal powder according to claim 1, wherein the Mn content of its steel particles is at least 15 mass %.

3. The metal powder according to claim 1, wherein the Cr content of its steel particles is at least 14 mass %.

4. The metal powder according to claim 1 wherein the Ni content of its steel particles is at most 0.1 mass %.

5. The metal powder according to claim 1 wherein the total of the contents of C and N of its steel particles is 0.6-1.5 mass %.

6. A method of additive manufacturing of components for use in or on the human or animal body including the step of using the metal powder as set forth in claim 1.

7. A method for manufacturing a steel component, comprising the following steps: a) melting a steel melt, which consists of, in mass %, C: 0.15-1.0%, N: 0.15-1.0%, Si: 0.1-2.0%, Cr: 5-21%, Mo: 0.1-3.0%, Ni: ≤5%, and of Mn and as the remainder of iron and manufacture-related unavoidable impurities, wherein the Mn content of the melt is 0.5-5% higher than the respective Mn target content % Mn_Z of the component to be manufactured, for which the following applies: 8%≤Mn_Z≤24%. b) atomising the melt melted in work step a) into a metal powder, wherein the steel particles obtained with an average grain size of 5-150 μm are selected for further processing; c) manufacturing the component using an additive manufacturing process in which c.1) at least one solidified volume section of the component to be manufactured is produced from at least one portion of the metal powder; c.2) if necessary, a further portion of the metal powder is applied to the volume section solidified in work step c.1 and c.3) if necessary, work steps c.1 and c.2 are repeated until the component to be manufactured is additively formed in a completely finished manner; d) optional machining to shape the components; e) optional final heat treatment of the component obtained; f) optional mechanical or thermochemical edge layer treatment of the component.

8. The method according to claim 7, wherein the component is held at a temperature of 1000-1250° C. for a duration of 5 min-120 min during the optional heat treatment (work step e)) carried out.

9. The method according to claim 7, wherein the atomisation of the melt in work step b) is carried out as gas atomisation.

10. The method according to claim 7, wherein in work step c.1) a laser beam is used as a heat source, which is directed at the volume section to be heated in each case with an energy density of 20-110 J/mm.sup.3.

11. A component that is manufactured by an additive manufacturing process, consists of, in mass %, 0.15-1.0% C, 0.15-1.0% N, 0.1-2.0% Si, 8-24% Mn, 5-21% Cr, 0.15-3.0% Mo, ≤5% Ni and as the remainder of iron and unavoidable impurities, and has a structure consisting of more than 50 vol. % austenite, up to at most 49 vol. % ferrite and as the remainder of ferrite and other manufacture-related unavoidable structural constituents, wherein the proportion of unavoidable structural constituents in the structure of the component is at most 30 vol. %.

12. The component according to claim 11, wherein it has 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 achieves a notch impact energy of at least 30 J and a notch impact strength of at least 50 J/cm.sup.3 in the notch impact test.

13. The component according to claim 12, wherein its surface hardness is at least 250 HV.

14. The component according to claim 11, wherein the heat-treated state in the notch impact test it achieves a notch impact energy of at least 100 J and a notch impact strength of at least 120 J/cm.sup.3.

15. The component according to claim 14, wherein its surface hardness is at least 200 HV.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0111] The invention is explained in greater detail below using exemplary embodiments.

[0112] In order to test the properties of metal powders according to the invention and components manufactured from them by additive manufacturing, nine melts M1-M9 were produced in a first series of tests, the composition of which is indicated in Table 1.

[0113] Due to their minimised Ni content, the melts M1-M9 are suitable for the production of the steel particles of metal powders used to manufacture components intended for use on human or animal bodies.

[0114] The melts M1-M9 have been gas-atomised into steel particles in a conventional manner with an atomising device established in the prior art for this purpose. Nitrogen was used as an atomising gas.

[0115] From the steel particles obtained by the atomising, the particles whose average grain size was 10 μm to 53 μm were selected by sieving and air separation. The flow rate of the thus selected steel particles determined in accordance with DIN EN ISO 4490 was 18 s/50 g.

[0116] In a further step, the metal powders produced were processed using a conventional 3D printing device (3D printer of type M290, see https://www.eos.info/eos-m-290, accessed on 19 Dec. 2019). The metal powders could be processed without any problems and the components produced showed a dense structure, free of pores or cracks. Overall, it was demonstrated that reliable components could be produced from the metal powders in an energy density range of 30-90 J/mm.sup.3.

[0117] Argon was used as the process gas in some of the 3D printing tests and nitrogen in others. Both process gases produced consistently good results.

[0118] A phase analysis of the printed components using X-ray diffractometry revealed that there were no chromium carbides or other precipitates that could negatively influence the corrosion properties.

[0119] The printed components each had a completely austenitic structure (austenite proportion ≥99 vol. %).

[0120] The tensile strengths Rm, the yield strengths Rp, the notch impact energy, the notch impact strengths and the Vickers hardnesses of the printed components were also conventionally determined in accordance with standards.

[0121] Table 2 shows the regions in which the relevant characteristic values were found to have been determined in the horizontal construction direction of the components for the components that were printed from metal powders produced from the melts M1-M9.

[0122] Table 3 shows the regions in which the relevant characteristic values were determined in the vertical construction direction of the components for the components that were printed from metal powders produced from the melts M1-M9.

[0123] In addition, Tables 2 and 3 list the corresponding characteristic values, where available, of the reference material 316L known from the specialist literature (see https://www.fabb-it.de/files/datenblaetter/edelstahl.pdf, found on 16 Jan. 2020), whose composition is also indicated in Table 1.

[0124] The tests show that the mechanical properties of the non-heat-treated components printed from the metal powders according to the invention are not only superior to the mechanical properties of the components produced from the conventional material 316L, but also that high C and N contents lead to significantly improved mechanical properties of the components produced according to the invention.

[0125] For a second series of tests, another melt was melted and also atomised into steel particles in the manner explained above for the melts M1-M9. The composition M10 of the steel particles obtained is indicated in Table 4. From the steel particles, those whose average grain diameter was 10-53 μm were selected by sieving. The flow rate of the metal powder thus obtained was 16.8 s/50 gr with a bulk density of 4.23 g/cm.sup.3.

[0126] Twenty components were printed from the metal powder formed by the steel particles using the aforementioned M290 3D printer. Nitrogen was used as a protective gas. The components were printed with a layer thickness of 40 μm per layer.

[0127] The density, Vickers hardness HV, notch impact energy, yield strength Rp, tensile strength Rm, elongation at break A5.65 were tested on the twenty components in the non-heat-treated state in accordance with standards in the vertical construction direction. The mean values of the results of these examinations are summarised in Table 5 and compared with the corresponding characteristic values of a component printed from the conventional steel 316L, which were taken from the aforementioned citation. Again, a clear superiority of the material provided and processed according to the invention is demonstrated here.

[0128] In addition, the composition and the structure of the components printed from the metal powder formed by the steel particles M10 according to the invention have been examined. This showed that a significant loss of Mn and N occurred due to the 3D printing process used. The average Mn content of the components was around 8% lower than the Mn content of the steel particles of the metal powder. Similarly, the N content of the components declined on average by about 12% during the 3D printing process. However, the Mn and N content remaining in the components was sufficient to ensure the characteristics of a completely austenitic structure (austenite proportion >99 vol. %) in the components.

[0129] Finally, a corrosion test according to SEP 1877 method II was carried out on one of the components printed from metal powder with the steel particles composed according to the invention corresponding to the alloy M10 and for comparison on a component printed from a conventional metal powder, the steel particles of which consisted of the steel 316L. This test is used to test the resistance of highly-alloyed corrosion-resistant materials to intergranular corrosion. Both components passed the test and were therefore resistant to intergranular corrosion.

[0130] Furthermore, the components printed from the metal powder according to the invention and the components printed from the steel 316L used for comparison were subjected to a pitting corrosion test in accordance with ASTM G48, method E. Here too, it was found that the components produced from the metal powder according to the invention had a resistance to pitting corrosion which was at least equal to the conventional metal powders that were printed and used for comparison.

[0131] Finally, the components printed from the metal powder according to the invention with the steel particles composed according to the alloy M10 were subjected to a heat treatment in which they were heated for an annealing duration of 30 minutes to a temperature of 1125° C. and then quenched with water. The notch impact energy has been determined in a standardised manner on the thus heat-treated components. This averaged 129±2 J, which corresponds to approximately 2.4 times the notch impact energy of 52±3 J achieved on average by the non-heat-treated state in the standard notch impact test.

TABLE-US-00001 TABLE 1 Information in mass %, the remainder being Fe and unavoidable impurities 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  

TABLE-US-00002 TABLE 2 Notch Notch impact impact Hardness energy strength Rp Rm Steel [HV] [J] [J/cm.sup.3] [MPa] [MPa] M1 . . . M9 250-450 30-120 50-150 650-1100 650-1300 316L 162 n.d. n.d. 530 ± 60 640 ± 50 * n.d. = not determined

TABLE-US-00003 TABLE 3 Notch Notch impact impact Hardness energy strength Rp Rm Steel [HV] [J] [J/cm.sup.3] [MPa] [MPa] M1 . . . M9 250-450 30-120 50-150 650-1200 650-1300 316L 162 166 ± 12 132 470 ± 90 540 ± 55

TABLE-US-00004 TABLE 4 Alloy M10, information in mass %, remainder being Fe and impurities C + N C N Si Mn Cr Mo Ni Powder 0.942 0.39 0.552 0.22 18.4 19.2 2.25 0.1 Component 0.861 0.38 0.481 0.25 16.9 19.2 2.35 0.1

TABLE-US-00005 TABLE 5 Notch impact Density Hardness energy Rp Rm A 5.65 Steel [g/cm.sup.3] [HV] [J] [MPa] [MPa] [%] M10 7.78 350 ± 4 52 ± 3  915 ± 11 1120 ± 9  30 ± 2 316L 7.92 162 50 ± 10 470 ± 90  540 ± 55 45 ± 1