Process for the additive manufacturing of maraging steels

Abstract

A process for manufacturing an additively-manufactured part from a metal powder having a composition having the following elements, expressed in content by weight: 6%≤Ni≤14%, 5%≤Cr≤10%, 0.5%≤Si≤2.5%, 0.5%≤Ti≤2%, C≤0.04% and optionally containing 0.5%≤Cu≤2%, the balance being Fe and unavoidable impurities resulting from the elaboration, the metal powder having a microstructure including in area fraction more than 98% of a body-centered cubic crystalline phase, the process having a step during which at least a part of the metal powder is melted in an atmosphere substantially composed of an inert gas other than Argon or of a combination of inert gases other than Argon.

Claims

1-8. (canceled)

9. A method for manufacturing an additively-manufactured part from a metal powder having a composition comprising the following elements, expressed in content by weight:
6%≤Ni≤14%
5%≤Cr≤10%
0.5%≤Si≤2.5%
0.5%≤Ti≤2%
C≤0.04% and optionally containing:
0.5%≤Cu≤2% a balance being Fe and unavoidable impurities resulting from processing, the metal powder having a microstructure including in area fraction more than 98% of a body-centered cubic crystalline phase, the method comprising: melting at least a part of the metal powder in an atmosphere substantially composed of an inert gas other than Argon or of a combination of inert gases other than Argon.

10. The method as recited in claim 9 wherein the inert gas other than Argon is Nitrogen.

11. The method as recited in claim 9 wherein the atmosphere comprises less than 1000 ppm of oxygen.

12. The method as recited in claim 9 wherein the inert gas other than Argon or the combination of inert gases other than Argon are in a hermetically sealed chamber.

13. The method as recited in claim 9 wherein the additively-manufactured part is manufactured by Laser Powder Bed Fusion (LPBF).

14. The method as recited in claim 13 wherein the laser power is between 80 and 200 W.

15. The method as recited in claim 13 wherein a Linear Energy Density (LED) is comprised between 175 and 550N.

16. The method as recited in claim 13 wherein a Volumetric Energy Density (VED) is comprised between 100 and 510 J/mm.sup.3.

Description

EXAMPLES

[0064] The following examples and tests presented hereunder are non-restricting in nature and must be considered for purposes of illustration only. They will illustrate the advantageous features of the present invention, the significance of the parameters chosen by inventors after extensive experiments and further establish the properties that can be achieved by the process according to the invention.

[0065] Powder Ref 1:

[0066] Pure elements were mixed so as to obtain a composition comprising 1.15 wt % Si, 0.56 wt % Ti, 0.97 wt % Cu, 7.55 wt % Cr, 7.07 wt % Ni, 0.013 wt % C, the balance being Fe and unavoidable impurities resulting from the elaboration. The composition was heated at a temperature 215° C. above its liquidus temperature (i.e. at 1685° C.) and then atomized by gas atomization in N2 at 20 bar, with a nozzle diameter of 3 mm.

[0067] The metal powder obtained had a sphericity of 0.79 and a particle size distribution such that D.sub.10=27.3 μm, D.sub.50=70.4 μm and D.sub.90=179.7 μm. The metal powder had a good flowability with a Hausner ratio of 1.129 and a Carr Index of 11.012%.

[0068] Powder Ref 2:

[0069] Ferroalloys and pure elements were mixed so as to obtain a composition comprising 0.97 wt % Si, 0.85 wt % Ti, 1.00 wt % Cu, 7.73 wt % Cr, 7.15 wt % Ni, 0.038 wt % C, the balance being Fe and unavoidable impurities resulting from the elaboration. The composition was heated at a temperature 215° C. above its liquidus temperature (i.e. at 1683° C.) and then atomized by gas atomization in N.sub.2 at 20 bar, with a nozzle diameter of 3mm.

[0070] The metal powder obtained had a sphericity of 0.82 and a particle size distribution such that D.sub.10=32.4 μm, D.sub.50=92.7 μm and D.sub.90=250.8 μm. The metal powder had an excellent flowability with a Hausner ratio of 1.098 and a Carr Index of 9.856%.

[0071] Powder Ref 3:

[0072] Ferroalloys and pure elements were mixed so as to obtain a composition comprising 0.95 wt % Si, 0.77 wt % Ti, 1.06 wt % Cu, 7.97 wt % Cr, 7.11 wt % Ni, 0.026 wt % C, the balance being Fe and unavoidable impurities resulting from the elaboration. The composition was heated at a temperature 236° C. above its liquidus temperature (i.e. at 1698° C.) and then atomized by gas atomization in N2 at 20 bar, with a nozzle diameter of 3mm.

[0073] The metal powder obtained had a sphericity of 0.77 and a particle size distribution such that D.sub.10=30.8 μm, D.sub.50=89.8 μm and D.sub.90=246.2 μm. The metal powder had a good flowability with a Hausner ratio of 1.109 and a Carr Index of 11.12%.

[0074] F2 fractions (i.e. particles between 20 and 63 μm) of powders referenced 1 to 3 were then used to manufacture parts by LPBF in the process conditions detailed in Table 1 and with a layer thickness of 20 μm.

[0075] Relative density of the printed parts was measured by first measuring the absolute density by Archimedes method according to ISO3369:2006 and then by calculating the ratio between the absolute density and the theoretical density of the material (possibly obtained from a part casted with the same composition than the printed parts).

[0076] As it is apparent from the relative density values obtained, the parts manufactured under N2 present a very good relative density whatever the process conditions. As soon as Ar is used as inert gas, the relative density of the parts strongly decreases.

TABLE-US-00001 TABLE 1 Ex Powder Inert Power Speed LED Hatch VED Relative # ref gas (W) (mm) (N) (mm) (J/mm.sup.3) density  1* 1 N2 170 800 213 0.09 118 99.56%  2* 1 N2 200 700 286 0.09 159 99.56%  3* 1 N2 200 700 286 0.07 205 99.86%  4* 1 N2 200 500 400 0.08 250 99.75%  5* 1 N2 200 400 500 0.08 312 99.74%  6* 1 N2 200 400 500 0.07 357 99.85%  7* 2 N2 175 900 194 0.08 122 99.90%  8 2 Ar 175 900 194 0.08 122 97.86%  9* 2 N2 185 800 231 0.08 145 99.58% 10* 2 N2 185 600 308 0.08 193 99.39% 11* 2 N2 200 500 400 0.08 250 99.42% 12* 2 N2 170 400 425 0.07 304 99.61% 13* 3 N2 150 400 375 0.08 234 99.58% 14 3 Ar 150 400 375 0.08 234 98.99% 15* 3 N2 170 400 425 0.07 304 99.48% 16 3 Ar 170 400 425 0.07 304 98.36% 17* 3 N2 175 1000 175 0.07 124 99.06% 18 3 Ar 175 1000 175 0.07 124 98.52% 19* 3 N2 175 300 583 0.10 307 99.23% 20 3 Ar 175 300 583 0.10 307 98.86% 21* 3 N2 175 200 875 0.09 505 99.19% 22 3 Ar 175 200 875 0.09 505 98.82% 23* 3 N2 200 900 222 0.06 179 99.19% 24 3 Ar 200 900 222 0.06 179 98.73% *according to the invention