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US-20260125783-A1 - Metal powder for additive manufacturing

US20260125783A1US 20260125783 A1US20260125783 A1US 20260125783A1US-20260125783-A1

Abstract

A metal powder for additive manufacturing having a composition including the following elements, expressed in content by weight 15%≤Mn≤35%, 6%≤Al≤15%, 0.5%≤C≤1.8%, 1.6%≤Si≤3.5%, P≤0.013%, S≤0.015%, N≤0.100%, and optionally containing Ni≤8.5 wt. % and/or Cr≤2.5 wt. % and/or B≤0.1 wt. % and/or one or more elements chosen among Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0 wt. %, the balance being iron and unavoidable impurities resulting from the elaboration. It also deals with a process for manufacturing such powder and for manufacturing a printed part out of it.

Inventors

  • Manuel SÁNCHEZ PONCELA
  • Rosalia REMENTERIA FERNANDEZ
  • Laura DEL RIO FERNANDEZ
  • Verónica SUAREZ FERNANDEZ

Assignees

  • ARCELORMITTAL

Dates

Publication Date
20260507
Application Date
20231011
Priority Date
20221019

Claims (17)

  1. 1 - 12 . (canceled)
  2. 13 . A metal powder for additive manufacturing having a composition comprising the following elements, expressed in content by weight: 15 ⁢ % ≤ Mn ≤ 35 ⁢ % ; 6 ⁢ % ≤ Al ≤ 15 ⁢ % ; 0.5 % ≤ C ≤ 1.8 % ; 1.6 % ≤ Si ≤ 3.5 % ; P ≤ 0.013 % ; S ≤ 0.015 % ; N ≤ 0.1 % ; and optionally containing at least one of the following: Ni≤8.5 wt. %; Cr≤2.5 wt. %; B≤0.1 wt. % and one or more elements chosen from at least one of the group consisting of: Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0 wt. %; and a balance being iron and unavoidable impurities resulting from the elaboration.
  3. 14 . The metal powder according to claim 13 wherein the powder particles have an austenitic microstructure including optionally up to 1 weight % of kappa carbides (Fe,Mn) 3 AlCx, up to 1 weight % of AlN, and up to 20 weight % of ferrite.
  4. 15 . The metal powder according to claim 13 wherein the density of the metal powder is below 7.0 g/cm 3 .
  5. 16 . The metal powder according to claim 13 wherein an average particle size ranks from 1 to 150 μm.
  6. 17 . The metal powder according to claim 16 wherein the average particle size ranks from 1 to 20 μm.
  7. 18 . The metal powder according to claim 16 wherein the average particle size ranks from 20 to 63 μm.
  8. 19 . The metal powder according to claim 16 wherein the average particle size ranks from 60 to 150 μm.
  9. 20 . A process for manufacturing a metal powder for additive manufacturing, comprising: melting elements or metal-alloys at a temperature at least 100° C. above the liquidus temperature to obtain a molten composition, the molten composition being the composition as recited in claim 13 ; and atomizing the molten composition through a nozzle with a gas pressurized from 10 to 30 bar.
  10. 21 . A process for manufacturing a printed part by additive manufacturing wherein the metal powder as recited in claim 13 is printed by Laser Powder Bed Fusion.
  11. 22 . The process according to claim 21 including: a first step of forming a powder layer with a thickness below 100 μm; and a second step where a focused laser beam forms a shaped layer by melting at least part of the powder layer in an atmosphere substantially composed of an inert gas.
  12. 23 . The process according to claim 21 wherein: a laser power is limited to maximum 500 W, a scan speed is from 300 to 2000 mm/s, a Linear Energy Density is from 190 to 500 J/m, a the hatch spacing is from 50 to 120 μm, and a Volumetric Energy Density is from 100 to 330 J/mm 3 .
  13. 24 . A printed part obtained by the process according to claim 21 , the printed part having a cellular solidification structure with an equivalent diameter below 2 μm.
  14. 25 . A process for manufacturing a printed part by additive manufacturing wherein the metal powder obtained as recited in claim 20 is printed by Laser Powder Bed Fusion.
  15. 26 . The process according to claim 25 including: a first step of forming a powder layer with a thickness below 100 μm; and a second step where a focused laser beam forms a shaped layer by melting at least part of the powder layer in an atmosphere substantially composed of an inert gas.
  16. 27 . The process according to claim 25 wherein: a laser power is limited to maximum 500 W, a scan speed is from 300 to 2000 mm/s, a Linear Energy Density is from 190 to 500 J/m, a the hatch spacing is from 50 to 120 μm, and a Volumetric Energy Density is from 100 to 330 J/mm 3 .
  17. 28 . A printed part obtained by the process according to claim 25 , the printed part having a cellular solidification structure with an equivalent diameter below 2 μm.

Description

The present invention relates to a metal powder for the manufacturing of steel parts and in particular for their additive manufacturing. The present invention also relates to the method for manufacturing the metal powder. BACKGROUND Environmental restrictions are forcing automakers to continuously reduce the CO2 emissions of their vehicles. To do that, automakers are looking at every way to reduce the weight of motor vehicles. SUMMARY OF THE INVENTION This can in particular be achieved by reducing the density of the steels used for manufacturing parts, by alloying them with other, lighter metals than iron. Steels containing high levels of manganese aluminum and carbon, often referred to as triplex steels, can show density levels below 7.4 g/cm3. Their solidified structure shows an austenitic structure possibly comprising kappa carbide (Fe,Mn)3AlCx and ferrite. However, they are difficult to manufacture by conventional casting methods due to their high aluminum and carbon amounts. They also exhibit some macro-segregations of manganese, carbon and/or aluminum, generating bands when they are laminated and possibly forming brittle phases leading to cracks. It is an object of the present invention to remedy the drawbacks of the prior art by providing a new way to obtain parts with low density without manufacturability issues. The present invention provides a metal powder for additive manufacturing having a composition comprising the following elements, expressed in content by weight: 15⁢%≤Mn≤35⁢%6⁢%≤Al≤15⁢%0.5 %≤C≤1.8 %1.6 %≤Si≤3.5 %P≤0.013 %S≤0.015 %N≤0.1 %and optionally containing Ni≤8.5 wt. % and/or Cr≤2.5 wt. % and/or B≤0.1 wt. % and/or one or more elements chosen among Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0 wt. %, the balance being iron and unavoidable impurities resulting from the elaboration. The metal powder according to the invention may also have the optional features listed below, considered individually or in combination: the powder particles have an austenitic microstructure comprising up to 1 weight % of kappa carbides (Fe,Mn)3AlCx and up to 20 weight % of ferrite and up to 1 weight % of AlN,the powder has a density below 7.0 g/cm3,the average particle size ranks from 1 to 150 μm,the average particle size ranks from 1 to 20 μm,the average particle size ranks from 20 to 63 μm,the average particle size ranks from 60 to 150 μm. The present invention also provides a process for manufacturing a metal powder for additive manufacturing, comprising: a) Melting elements and/or metal-alloys at a temperature at least 100° C. above the liquidus temperature so as to obtain a molten composition as described above, and,b) Atomizing the molten composition through a nozzle the diameter of which is at most 4 mm, with a gas pressurized from 10 to 30 bar. The present invention also provides a process for manufacturing a printed part by additive manufacturing wherein a powder according to the invention is printed by Laser Powder Bed Fusion. The printing process according to the invention may also have the optional features listed below, considered individually or in combination: the process comprises a first step of forming a powder layer with a thickness below 100 μm and a second step where a focused laser beam forms a shaped layer by melting at least part of the powder layer in an atmosphere substantially composed of an inert gas,the process is set with the following parameters: the laser power is limited to maximum 500 W,the scan speed is from 300 to 2000 mm/s,the Linear Energy Density is from 190 to 500 J/m,the hatch spacing is from 50 to 120 μm,The Volumetric Energy Density is from 100 to 330 J/mm3. The present invention also provides a printed part obtained according to the invention having a cellular solidification structure with an equivalent diameter below 2 μm. DETAILED DESCRIPTION The present invention will be better understood by reading the following description, which is provided purely for purposes of explanation and is in no way intended to be restrictive. Manganese is present in the composition according to the invention at a content of 15 to 35 wt. %. Manganese is an essential alloying element for such grade, mainly due to the fact that alloying with very high amounts of manganese and carbon stabilizes, in the final part, the austenite down to room temperature, which can then tolerate high amounts of aluminum without being destabilized and transformed into too much ferrite or into martensite. To enable the alloy to have a superior ductility, the manganese content has to be equal or higher to 15 wt. %. However, when the manganese content is over 35 wt. %, the precipitation of β-Mn phase will deteriorate the ductility of the alloy. Therefore, the manganese content should be controlled to be equal or greater than 15 wt. %, but lower than equal to 35 wt. %. In a preferred embodiment, it is equal or greater than 15.5 wt. % or even than 16.0 wt. %. Its amount is more prefera