IRON-BASED ALLOY POWDER

Abstract

The present invention relates to an iron-based alloy powder wherein the alloy comprises the elements Fe (iron), Cr (chrome) and Mo (molybdenum) and the iron-based alloy powder is produced by an ultra-high liquid atomization process comprising at least two stages as defined below.

Claims

1.-7. (canceled)

8. An iron-based alloy powder wherein the alloy comprises the elements Fe, Cr and Mo and the iron-based alloy powder is produced by an ultra-high liquid atomization process comprising at least two stages, wherein 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 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 liquid 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 individual particles of the iron-based alloy powder.

9. The iron-based alloy powder according to claim 8, wherein i) the liquid jet stream is a water-containing jet stream, preferably the liquid is pure water, and/or ii) the liquid jet stream is applied under a pressure of at least 600 bar, and/or iii) the gas stream is a nitrogen-containing gas stream and/or an inert gas stream.

10. The iron-based alloy powder according to claim 8, wherein i) the iron-based alloy powder is an alloy which comprises Fe at 82.0 wt. % to 86.0 wt. %; Cr at 10.0 wt. % to 12.0 wt. %; Ni at 1.5 wt. % to 2.5 wt. %; Cu at 0.4 wt. % to 0.7 wt. %; Mo at 1.2 wt. % to 1.8 wt. %; C at 0.14 wt. % to 0.18 wt. %; Nb at 0.02 wt. % to 0.05 wt. %; N at 0.04 to 0.07 wt. % and Si at 0 to 1.0 wt. %, or ii) the iron-based alloy powder comprises the elements as follows: Cr is present at 14 wt. % to 19.0 wt. %, Mo is present at 2.0 wt. % to 3.0 wt. %, C is present at 0 to 0.30 wt. %, Ni is present at 8.0 wt. % to 15.0 wt. %, Mn is present at 0 to 2.0 wt. %, Si is present at 0 to 2.0 wt. % and O is present at 0 to 0.50 wt. %, the balance up to 100 wt. % is Fe.

11. The iron-based alloy powder according to claim 8, wherein the iron-based alloy powder contains non-spherical particles, preferably at least 40% of the total amount of particles have a non-spherical shape, wherein the sphericity of the particles having a non-spherical shape is not more than 0.9.

12. 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 8 is employed.

13. A three-dimensional (3D) object obtainable by a process according to claim 12.

14. A use of at least one iron-based alloy powder according to claim 8 within a three-dimensional (3D) printing process.

Description

[0011] According to the present invention, the object is achieved by an iron-based alloy powder wherein the alloy comprises the elements Fe, Cr and Mo and the iron-based alloy powder is produced by an ultra-high liquid atomization process comprising at least two stages, wherein 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 circulates around the molten iron-based alloy powder within this first area and,

[0012] 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 liquid 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 individual particles of the iron-based alloy powder.

[0013] It has surprisingly been found that the iron-based alloy powder according to the present invention, especially if having a non-spherical shape, has a comparable or in some cases even a better performance in terms of flowability compared to corresponding alloy powder predominantly based on particles having a spherical shape. The iron-based alloy powder according to the present invention can be successfully employed within any 3D-printing process technique, in particular within a SLM-printing process.

[0014] The iron-based alloy powder according to the present invention shows a free flowing behavior. The respective powder exhibits a good processability and/or decent build rates. Furthermore, 3D objects printed with the respective iron-based alloy powder according to the present invention exhibit high densities and/or can be characterized as having a highly dispersed fine grained microstructures and/or showing high hardness.

[0015] Furthermore, the iron-based alloy powders according to the present invention usually show a rather low amount of hollow particles. In preferred embodiments of the present invention, the particle size distribution of the respective iron-based alloy powders according to the present invention is well-suited for the processability within the SLM-technique since the particles may have a d10-value of approximately 15 μm and a d90-value of approximately 65 μm (in each case in relation to volume).

[0016] Another advantage can be seen in the fact that the iron-based alloy powder according to the present invention can be distributed in a very homogeneous way in order to form the respective layer when being employed within the respective 3D-printing process, in particular within the SLM-technique. Due to the rather broad particle size distribution, the bulk density of the respective layer is improved/higher compared to particles according to the prior art. By consequence, the shrinkage behavior of the respective layer during the 3D-printing process is reduced causing improved mechanical features, especially in the “as printed” stage (without performing any further heat treatment step). Improved mechanical features can also be seen in respect of the hardness and/or elongation at break.

[0017] The above mentioned advantages can be even further improved within some embodiments of the present invention in case the iron-based alloy powder is prepared by a process, wherein the atomization step is carried out as an ultra-high pressure liquid atomization with higher water pressures, preferably with a water pressure of at least 300 bar, more preferably of at least 600 bar. Further advantages can also be seen in higher space-time yield and/or lower process costs, especially within the latter embodiments.

[0018] Within the context of the present invention the term “non-spherical shape” or “particles having a non-spherical shape” means that the sphericity of the respective particle is not more than 0.9. The sphericity of a particle is defined as the ratio of the surface area of a sphere (with the same volume as the given particle) to the surface area of the particle. By contrast, a particle is considered as having a spherical shape in case its sphericity is more than 0.9. The sphericity of a particle can be determined by methods known to a skilled person. A suitable test method is, for example, an optical test method by particle characterizing systems (e.g. Camsizer®).

[0019] In a preferred embodiment, the sphericity (SPHT) is determined according to ISO 9276-6, wherein the sphericity (SPHT) is defined by formula (I)

[00001]$\begin{array}{cc}\mathrm{SPHT}=\frac{4\pi A}{p^2}={\mathrm{Circularity}}^2& \left(I\right)\end{array}$

[0020] wherein

[0021] p is the measured perimeter/circumference of a particle projection and A is the measured area covered by a particle projection. The proportion of non-spherical particles is defined as the proportion of particles whose sphericity is not more than 0.9, based on volume (Q3 (SPHT)).

[0022] The invention is specified in more detail as follows.

[0023] A first subject matter according to the present invention is an iron-based alloy powder wherein the alloy comprises the elements Fe, Cr and Mo and the iron-based alloy powder is produced by an ultra-high liquid atomization process comprising at least two stages, wherein

[0024] 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 circulates around the molten iron-based alloy powder within this first area and,

[0025] 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 liquid 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 individual particles of the iron-based alloy powder.

[0026] Metal-based alloy powders as such including iron-based alloy powders are known to a person skilled in the art. This also applies to process for the production of such iron-based alloy powders as well as the specific shape of such alloy powders (for example in form of particles). The iron-based alloy powders according to the present invention comprise as mandatory (metal) elements Fe (iron), Cr (chrome) and Mo (molybdenum). Besides these three mandatory elements, the iron-based alloy powders according to the present invention may comprise further elements such as C (carbon), Ni (nickel), S (sulfur), O (oxygen), Nb (niobium), Si (silicon), Cu (copper) or N (nitrogen).

[0027] In one embodiment of the present invention it is preferred that the iron-based alloy powder is an alloy which comprises Fe at 82.0 wt. % to 86.0 wt. %; Cr at 10.0 wt. % to 12.0 wt. %; Ni at 1.5 wt. % to 2.5 wt. %; Cu at 0.4 wt. % to 0.7 wt. %; Mo at 1.2 wt. % to 1.8 wt. %; C at 0.14 wt. % to 0.18 wt. %; Nb at 0.02 wt. % to 0.05 wt. %; N at 0.04 to 0.07 wt. % and Si at 0 to 1.0 wt. %.

[0028] In a further embodiment of the present invention, the iron-based alloy powder preferably comprises the elements as follows:

[0029] Cr is present at 14 wt. % to 19.0 wt. %, Mo is present at 2.0 wt. % to 3.0 wt. %, C is present at 0 to 0.30 wt. %, Ni is present at 8.0 wt. % to 15.0 wt. %, Mn is present at 0 to 2.0 wt. %, Si is present at 0 to 2.0 wt. % and O is present at 0 to 0.50 wt. %, the balance up to 100 wt. % is Fe.

[0030] It is also preferred, that the iron-based alloy powder according to the present invention is an alloy which indicates a tensile strength of at least 1000 MPa, an elongation of at least 1.0% and a hardness (HV) of at least 450.

[0031] In another embodiment, it is preferred that the iron-based alloy powder according to the present invention is an alloy which indicates a tensile strength of at least 1000 MPa, an elongation of at least 0.5% and a hardness (HV) of at least 450.

[0032] The iron-based alloy powder according to the present invention contains individual particles of the respective iron-based alloy powder. Preferably, the iron-based alloy powder according to the present invention is completely present as particles. The shape of the respective particles may be both spherical and non-spherical. However, it is preferred that the iron-based alloy powder according to the second aspect of the present invention contains non-spherical particles. Preferably, at least 40% of the total amount of particles have a non-spherical shape.

[0033] In a first embodiment of the present invention it is preferred that the iron-based powder is a powder containing particles, wherein at least 50%, preferably at least 70%, more preferably at least 95%, most preferably at least 99% of the total amount of particles have a non-spherical shape.

[0034] In another preferred embodiment of the present invention, the iron-based alloy powder contains particles, wherein the total amount of particles having a non-spherical shape is in the range of at least 40 to 70%, more preferably in the range of more than 45 to 60%, most preferably in the range of at least 50 to 55%.

[0035] In another preferred embodiment of the present invention, the iron-based alloy powder contains particles, wherein the total amount of particles having a non-spherical shape is in the range of at least 40 to 70%, more preferably in the range of more than 45 to 65%, most preferably in the range of at least 50 to 60%.

[0036] The particles of the iron-based alloy powders according to the present invention are not limited to a specific diameter. However, it is preferred that the particles have a diameter in the range of 1 to 200 microns, more preferably from 3 to 70 microns, and most preferably from 15 to 53 microns.

[0037] It is also preferred that the particles of the iron-based alloy powder according to the present invention have a particle size distribution with a d10-value of at least 15 microns and a d90-value of not more than 65 microns, preferably related on a volume based Q.sub.3-distribution.

[0038] The iron-based alloy powder according to the present invention is preferably produced by an ultra-high liquid atomization process, wherein [0039] i) the liquid jet stream is a water-containing jet stream, preferably the liquid is pure water, and/or [0040] ii) the liquid jet stream is applied under a pressure of at least 600 bar, and/or [0041] iii) the gas stream is a nitrogen-containing gas stream and/or an inert gas stream.

[0042] Even more preferably, all three above-mentioned options i), ii) and iii) are present within said atomization process according to the present invention.

[0043] Another subject matter of the present invention is a process as such for producing an iron-based alloy powder according to the present invention as described above. By consequence, the present invention also relates to a process for producing an iron-based alloy powder wherein the alloy comprises the elements Fe, Cr and Mo and the iron-based alloy powder is produced by an ultra-high liquid atomization process comprising at least two stages, wherein

[0044] 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 circulates around the molten iron-based alloy powder within this first area and,

[0045] 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 liquid 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 individual particles of the iron-based alloy powder.

[0046] Another subject matter according to the present invention is the use of the at least one iron-based alloy powder as described above within a three-dimensional (3D) printing process and/or in a process for producing a three-dimensional (3D) object.

[0047] Three-dimensional (3D) printing process is as such as well as three-dimensional (3D) objects as such are known to a person skilled in the art. Preferably, the at least one iron-based alloy powders according to the present invention are employed within a 3D-printing process in connection of a laser beam or an electron beam technique. It is particularly preferred, that the iron-based alloy powders according to the present invention are employed of in a selective laser melting (SLM) process. As SLM-process as well as other laser beam or electron beam based 3D-printing techniques are known to a person skilled in the art.

[0048] Another subject matter according to the present invention is 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 as described above is employed.

[0049] Within this process it is preferred that 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,

[0050] preferably the energy is applied by a laser beam or an electron beam, more preferably by a laser beam.

[0051] It is even more preferred, that the inventive process is carried out as a SLM process as described for example in WO 2019/025471.

[0052] Therefore, a process is preferred, 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): [0053] (i) applying a first layer of at least one iron-based alloy powder onto a surface, [0054] (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, [0055] (iii) solidifying the first molten layer obtained in step (ii), [0056] (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.

[0057] Another subject matter of the present invention is a three-dimensional (3D) object as such obtainable by a process according to the present invention as described above by employing at least one iron-based alloy powder according to the present invention as described above.

[0058] A further subject of the present invention is the use of at least one iron-based alloy powder according to the present invention within a three-dimensional (3D) printing process and/or in a process for producing a three-dimensional (3D) object.