Centrifugal atomization of iron-based alloys
A method for the production of iron-based alloy powders, or particulate materials, through rotating or centrifugal atomization (CA) is disclosed. The invention is suitable for obtaining steel powder, especially tool steel powder, high strength steels and other iron-based alloys of similar properties by means of centrifugal atomization, particularly conducted by means of a rotating element atomization technique. The fine, smooth, low oxygen content and low satellite, or even satellite-free, powder is atomized by a cooled rotating atomization device (e.g. disk, cup, . . . ) with various geometries in an atomization chamber under a preferably non-oxidizing atmosphere.
1. A method for producing alloy powders or particulate material, comprising the steps of:
(a) providing an alloy composition with a melting point above 1040° C., wherein the alloy composition is chosen from alloy compositions within the following chemical composition ranges (wt. %):
% Ceq = 0.001-2.8
% C = 0.001-2.8
% N = 0.0-2.0
% B = 0.0-2
% Cr = 0.0-20.0
% Ni = 0.0-25.0
% Si = 0.0-3.0
% Mn = 0.0-7.0
% Al = 0.0-6.0
% Mo = 0.0-11.0
% W = 0.0-16.0
% Ti = 0.0-3.0
% Ta = 0.0-2.0
% Zr = 0.0-10.0
% Hf = 0.0-4.0
% V = 0.0-15.0
% Nb = 0.0-4.0
% Cu = 0.0-5.0
% Co = 0.0-15.0
% Ce = 0.0-2
% Ca = 0.0-1
% P = 0.0-2
% S = 0.0-2
% As = 0.0-2
% Bi = 0.0-1
% Pb = 0.0-2
% Sb = 0.0-1
% Li = 0.0-1
% Te = 0.0-2
% Zn = 0.0-1
% Cd = 0.0-1
% Sr = 0.0-1
% K = 0.0-1
% Na = 0.0-1
the rest consisting of iron and trace elements;
wherein % Ceq=% C+0.86·% N+1.2·% B and
wherein:
when % Co>0.9 then % V>1.2 and/or % Ni+% Al+% Ti+% Si>0.3 and/or Cr<0.8
when % Cr>9.8 then % Ceq>0.14 and
when % Cr>9.8 then % Mo+% W+% V+% Ti>0.5 and/or % Si+% Al+% Ti+% Ni>0.5
when % Cr<2 then % Mo+% W+% V+% Ti>0.5,
(b) melting the composition, and
(c) atomizing the molten composition by means of centrifugal atomization or rotating atomization with a rotating atomization device having an atomizing rotating element and a nozzle, the rotating element presenting a plurality of protuberances with a radial component, a number and configuration of the protuberances being effective to allow distribution and flow of the molten composition in a normal direction to a surface of a base of the rotating element so as to enable atomization of the molten composition when exiting the nozzle at a feed rate of 55 kg·h −1 or more, the atomizing being carried out with the molten composition exiting the nozzle at the feed rate of 55 kg·h −1 or more.
2. The method according to claim 1 , wherein the rotating element presents protuberances with a profile evolution in the direction normal to the active surface of the rotating element at the line of insertion.
3. The method according to claim 1 , wherein the rotating element presents protuberances with a variable curvature in the direction normal to the active surface of the rotating element at the line of insertion.
4. The method according claim 1 , wherein the rotating element presents protuberances with a variable curvature in the direction parallel to the active surface of the rotating element at the line of insertion.
5. The method according to claim 1 , wherein the protuberances form vanes on the surface of the atomizing rotating element, wherein the vanes have a profile that is contained in a single plane.
6. The method according to claim 1 , wherein the profile of the vanes is determined using analytical mathematical models that predict radial and tangential velocities of the liquid metal as functions of the radius of the rotating element, the liquid kinematic viscosity, the volume flow rate, the metallostatic head, and the rotational speed.
7. The method according to claim 1 , wherein the active surface of the atomizing rotating element in contact with the molten metal is made and/or coated with materials from the group consisting of fused silicon, graphite, fully stabilized zirconia (FSZ), partially stabilized zirconia (PSZ), silicon carbide, silicon nitride, zircon, alumina, magnesia, AlN, BN, MgZrO 3 , SiAlON, AlTiO 3 , ZrO 2 , SiC, MgZrO 3 , CaO, and ZrO 2 .
8. The method according to claim 1 , wherein the material of the atomizing rotating element exhibits a yield strength higher than 460 MPa.
9. The method according to claim 1 , wherein the material of the atomizing rotating element exhibits a melting temperature higher than 1400° C., a mechanical strength higher than 680 MPa and is coated with a material that promotes a wettability lower than 90° with the alloy that is intended to be atomized.
10. The method according to claim 1 , wherein the geometry of the atomizing rotating element allows the distribution and the flow of the liquid metal in a normal direction to the surface of the base of the rotating element.
11. A steel powder with the following composition, all ranges in wt. %:
% C = 0.001-2.8
% N = 0.0-2.0
% B = 0.0-2
% Cr = 0.0-20.0
% Ni = 0.0-25.0
% Si = 0.0-3.0
% Mn = 0.0-7.0
% Al = 0.0-6.0
% Mo = 0.0-11.0
% W = 0.0-16.0
% Ti = 0.0-3.0
% Ta = 0.0-2.0
% Zr = 0.0-10.0
% Hf = 0.0-4.0
% V = 0.0-15.0
% Nb = 0.0-4.0
% Cu = 0.0-5.0
% Co = 0.0-15.0
% Ce = 0.0-2
% Ca = 0.0-1
% P = 0.0-2
% S = 0.0-2
% As = 0.0-2
% Bi = 0.0-1
% Pb = 0.0-2
% Sb = 0.0-1
% Li = 0.0-1
% Te = 0.0-2
% Zn = 0.0-1
% Cd = 0.0-1
% Sr = 0.0-1
% K = 0.0-1
% Na = 0.0-1
the rest consisting of iron and trace elements;
wherein % Ceq=% C+0.86·% N+1.2·% B and % Ceq is higher than 0.62% and not more than 2.8%;
wherein:
when % Co>0.9 then % V>1.2 and/or % Ni+% Al+% Ti+% Si>0.3 and/or Cr<0.8
when % Cr>9.8 then % Ceq>0.14 and
when % Cr>9.8 then % Mo+% W+% V+% Ti>0.5 and/or % Si+% Al+% Ti+% Ni>0.5
when % Cr<2 then % Mo+% W+% V+% Ti>0.5; and
wherein the steel powder is prepared by centrifugal atomization such that the steel powder has a sphericity of greater than 0.76.
12. The steel powder according to claim 11 , wherein when % C≥2 or % Cr≤10, then % Cr+% Ti+% W+% Mo+% V+% Nb+% Zr+% Hf+% Co≥0.5.
13. The steel powder according to claim 11 , wherein % C<0.1, with the proviso that when % Ni≥0.9 and % Co≥0.9, then % Si<0.4.
14. A steel powder with the following composition, all ranges in wt. %:
% Ceq =
% C = 0.001-2.8
% N = 0.0-2.0
% B = 0.0-2
0.001-2.8
% Cr = 0.0-20.0
% Ni = 0.0-25.0
% Si = 0.0-3.0
% Mn = 0.0-7.0
% Al = 0.0-6.0
% Mo = 0.0-11.0
% W = 0.0-16.0
% Ti = 0.0-3.0
% Ta = 0.0-2.0
% Zr = 0.0-10.0
% Hf = 0.0-4.0
% V = 0.0-15.0
% Nb = 0.0-4.0
% Cu = 0.0-5.0
% Co =
% Ce = 0.0-2
0.0-15.0
% Ca = 0.0-1
% P = 0.0-2
% S = 0.0-2
% As = 0.0-2
% Bi = 0.0-1
% Pb = 0.0-2
% Sb = 0.0-1
% Li = 0.0-1
% Te = 0.0-2
% Zn = 0.0-1
% Cd = 0.0-1
% Sr = 0.0-1
% K = 0.0-1
% Na = 0.0-1
the rest consisting of iron and trace elements;
wherein % Ceq=% C+0.86·% N+1.2·% B;
wherein:
when % Co>0.9 then % V>1.2 and/or % Ni+% Al+% Ti+% Si>0.3 and/or Cr<0.8
when % Cr>9.8 then % Ceq>0.14 and
when % Cr>9.8 then % Mo+% W+% V+% Ti>0.5 and/or % Si+% Al+% Ti+% Ni>0.5
when % Cr<2 then % Mo+% W+% V+% Ti>0.5; and
wherein the steel powder is prepared by centrifugal atomization such that the steel powder has a sphericity of at least 0.92.