IRON-BASED ALLOY POWDER CONTAINING NON-SPHERICAL PARTICLES

Abstract

The present invention relates to an iron-based alloy powder containing non-spherical particles wherein the alloy comprises the elements Fe (iron), Cr (chrome) and Mo (molybdenum), and at least 40% of the total amount of particles have a non-spherical shape. In said iron-based alloy powder, Cr is present at 10.0 wt. % to 18.3 wt. %, Mo is present at 0.5 wt. % to 2.5 wt. %, C is present at 0 to 0.30 wt. %, Ni is present at 0 to 4.0 wt. %, Cu is present at 0 to 4.0 wt. %, Nb is present at 0 to 0.7 wt. %, Si is present at 0 to 0.7 wt. % and N is present at 0 to 0.20 wt. %, the balance up to 100 wt. % is Fe.

Claims

1.-11. (canceled)

12. An iron-based alloy powder containing non-spherical particles wherein the alloy comprises the elements Fe, Cr and Mo, and at least 40% of the total amount of particles have a non-spherical shape, wherein Cr is present at 10.0 wt. % to 18.3 wt. %, Mo is present at 0.5 wt. % to 2.5 wt. %, C is present at 0 to 0.30 wt. %, Ni is present at 0 to 4.0 wt. %, Cu is present at 0 to 4.0 wt. %, Nb is present at 0 to 0.7 wt. %, Si is present at 0 to 0.7 wt. % and N is present at 0 to 0.20 wt. %, the balance up to 100 wt. % is Fe, wherein the sphericity of the particles having a non-spherical shape is not more than 0.9.

13. The iron-based alloy powder according to claim 12, wherein (i) at least 50%, of the total amount of particles have a non-spherical shape, or (ii) the total amount of particles having a non-spherical shape is in the range of at least 40 to 70%,.

14. The iron-based alloy powder according to claim 12, wherein (i) at least 70% of the total amount of particles have a non-spherical shape, or (ii) the total amount of particles having a non-spherical shape is in the range of 45 to 60%

15. The iron-based alloy powder according to claim 12, wherein (i) at least 95% of the total amount of particles have a non-spherical shape, or (ii) the total amount of particles having a non-spherical shape is in the range of 50 to 55%

16. The iron-based alloy powder according to claim 12, wherein (i) at least 99% of the total amount of particles have a non-spherical shape, or (ii) the total amount of particles having a non-spherical shape is in the range of 50 to 55%.

17. The iron-based alloy powder according to claim 12, wherein the particles have a diameter in the range of 1 to 200 microns.

18. The iron-based alloy powder according to claim 12, wherein the particles have a diameter in the range of 3 to 70 microns.

19. The iron-based alloy powder according to claim 12, wherein the particles have a diameter in the range of 15 to 53 microns.

20. A process for producing an iron-based alloy powder according to claim 12, wherein the iron-based alloy powder is provided in a molten state and an atomization step is carried out with a stream of the molten iron-based alloy powder.

21. The process according to claim 20, wherein the atomization step is carried out as an ultrahigh pressure liquid atomization by jetting at least one liquid with a pressure of at least 300 bar.

22. The process according to claim 20, wherein the atomization step is carried out as an ultrahigh pressure liquid atomization by jetting at least one liquid with a pressure of at least 600 bar onto the stream of the molten iron-based alloy powder.

23. The process according to claim 20, wherein the liquid contains water, and/or the ultrahigh pressure liquid atomization is carried out by an atomization process comprising at least two stages, preferably, within a first stage of this atomization process, a stream of the molten iron-based alloy powder is fed through a nozzle into a first area located between the nozzle and a choke and a gas stream, which is preferably a nitrogen-containing gas stream and/or an inert gas stream, circulates around the molten iron-based alloy powder within this first area and, within a second stage of this atomization process, the stream of the molten iron-based alloy powder is fed to a second area located beyond the choke, where the stream of the molten iron-based alloy powder is contacted with a water-containing jet stream under a pressure of at least 300 bar, causing a break up and solidification of the stream of the molten iron-based alloy powder into the respective particles, wherein at least 50% of the total amount of the particles have a non-spherical shape.

24. The process according to claim 23, wherein the liquid is water, and the water-containing jet stream is under a pressure of at least 600 bar.

25. A use of at least one iron-based alloy powder according to claim 12 within a three-dimensional (3D) printing process.

26. A process for producing a three-dimensional (3D) object wherein the 3D object is formed layer by layer and within each layer at least one iron-based alloy powder according to claim 12 is employed.

27. The process according to claim 26, wherein in each layer the employed at least one iron-based alloy powder is molten by applying energy on the surface of the iron-based alloy powder with a laser beam,

28. The process according to claim 26, wherein in each layer the employed at least one iron-based alloy powder is molten by applying energy on the surface of the iron-based alloy powder with an electron beam.

29. The process according to claim 19, wherein the 3D object is produced by a selective laser melting (SLM) process, preferably the selective laser melting (SLM) process comprises the steps (i) to (iv): (i) applying a first layer of at least one iron-based alloy powder onto a surface, (ii) scanning the first layer of the at least one iron-based alloy powder with a focused laser beam at a temperature sufficient to melt at least part of the first layer of the at least one iron-based alloy powder throughout its layer thickness to obtain a first molten layer, (iii) solidifying the first molten layer obtained in step (ii), (iv) repeating process steps (i), (ii) and (iii) with a pattern of scanning effective to form the respective 3D object or at least a part thereof.

30. A three-dimensional (3D) object obtainable by a process according to claim 19.

Description

EXAMPLES

Inventive Example E1

[0059] Production of the Iron-Based Alloy Powder Containing Non-Spherical Particles

[0060] An iron-based alloy powder containing non-spherical particles was produced by providing an iron-based alloy powder with the composition listed in table 1 in a molten state and by carrying out an atomization step with a stream of the molten iron-based alloy powder.

TABLE-US-00001 TABLE 1 Fe Cr Mo Ni Si C Example [wt. %] [wt. %] [wt. %] [wt. %] [wt. %] [wt. %] E1 85.53 11.0 1.0 1.7 0.6 0.17

[0061] The atomization step was carried out as an ultrahigh pressure liquid atomization by jetting water with a pressure of 600 bar onto the stream of the molten iron-based alloy powder.

[0062] The obtained iron-based alloy powder contained roundish to irregularly shaped particles, wherein a cut, comprising particles having a diameter in the range of 15 to 53 microns, was characterized by the following methods:

[0063] Particle Size Distribution

[0064] To determine the particle size distribution, reported as the d10, d50 and d90 values, the obtained iron-based alloy powder was analysed in dry form. The d10, d50 and d90 values were determined by laser diffraction using a Malvern Master Sizer 2000.

[0065] Sphericity Measurements

[0066] The proportion of non-spherical particles was optically determined by a particle characterizing system (Camsizer®). It is defined as the proportion of particles whose sphericity is not more than 0.9, based on volume (Q3(SPHT)). The sphericity (SPHT) was determined according to ISO 9276-6, wherein the sphericity (SPHT) is defined by formula (I).

[0067] Bulk Density, Tapped Density, Hausner Factor

[0068] In addition, the bulk density according to DIN EN ISO 60 and the tapped density according to DIN EN ISO 787-11 were determined. The Hausner factor is the ratio of tapped density to bulk density.

[0069] The results of the above-mentioned characterizations can be taken from table 2.

TABLE-US-00002 TABLE 2 Proportion of non- Bulk Tamped spherical density density Hausner d10 d50 d90 particles Example [g/cm.sup.3] [g/cm.sup.3] factor [μm] [μm] [μm] [%] E1 3.33 3.95 1.19 17 33 66 50-60

[0070] As can be seen from table 2, due to the rather broad particle size distribution, the bulk density of the iron-based alloy powder is improved/higher compared to particles according to the prior art, resulting in a reduced Hausener factor. As further can be seen from table 2 and FIG. 1, at least 50 to 60% of the total amount of particles have a non-spherical shape, which means that they have a sphericity not more than 0.9.

[0071] In order to proof the processability of the inventive iron-based alloy powder containing non-spherical particles in a 3D-printing process technique, the inventive powder was tested in a powder bed fusion printer.

[0072] Powder Bed Fusion Printer Experiments

[0073] The inventive iron-based alloy powder was introduced with a layer thickness of 30 μm into the cavity at the temperature specified in table 3. The iron-based alloy powder was subsequently exposed to a laser with the laser power output specified in table 3 and the hatch distance specified, with a speed of the laser over the sample during exposure of 500 to 550 mm/s. Powder bed fusion printing typically involves scanning in stripes. The hatch distance gives the distance between the centres of the stripes, i.e. between the two centres of the laser beam for two stripes.

TABLE-US-00003 TABLE 3 Temperature Laser power Laser speed Hatch Example [° C.] output [W] [mm/s] distance [mm] E1 200 150-350 500-550 0.15

[0074] Subsequently, the properties of the 3D-printed objects obtained were determined. The 3D-printed objects obtained were tested in the dry state. In addition, Charpy bars were produced, which were likewise tested in dry form.

[0075] Tensile strength, yield strength and elongation at break were determined according to DIN EN ISO 6892-1.

[0076] Hardness (HV) was tested according to DIN EN ISO 6507-4.

[0077] The mechanical properties of the 3D-printed objects were determined before (E1a) and after a heat treatment (E1b). For heat treatment, the 3D-printed objects were heated up to 550° C. with a heating rate of 4° C./min under nitrogen atmosphere and kept at 550° C. for 1 h.

[0078] The results are given in table 4. The errors are based on standard deviation.

TABLE-US-00004 TABLE 4 Charpy Impact Tensile Elongation Yield Hardness Energy Strength at Break strength Example (HV) [J] [MPa] [%] [MPa] E1a 490 (±5) 17 (±4) 1670 (±10) 10 (±3)  800 (±20) E1b 400 (±5) 54 (±4) 1250 (±10) 15 (±3) 1070 (±20)

[0079] As can be seen from table 2, the 3D-printed objects comprising the inventive iron-based alloy are characterized by high strength, hardness and ductility at the same time.