(19)
(11) EP 3 797 898 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
31.03.2021 Bulletin 2021/13

(21) Application number: 19199984.6

(22) Date of filing: 26.09.2019
(51) International Patent Classification (IPC): 
B22D 11/108(2006.01)
 C21C 7/00(2006.01)
(84) Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR
Designated Extension States:
BA ME
Designated Validation States:
KH MA MD TN

(71) Applicant: AB Sandvik Materials Technology
811 81 Sandviken (SE)

(72) Inventors:
  • WALDÈN, Bertil
    811 61 Sandviken (SE)
  • Paliwal, Manas
    411014 Pune (IN)

(74) Representative: Sandvik 
Sandvik Intellectual Property AB
811 81 Sandviken
811 81 Sandviken (SE)

   


(54) A MOULD FLUX AND THE USE THEREOF


(57) A mould flux having a composition of, in weight%: and wherein the melting point of the mould flux is less than or equal to 1300°C.


Description

TECHNICAL FIELD



[0001] The present disclosure relates to a mould flux and to a method of manufacturing a nickel-base alloy.

BACKGROUND



[0002] When manufacturing nickel-base alloys, especially nickel-base alloys containing titanium, a problem has been noticed in connection to the Vacuum Arc Re-melting process (VAR) following the moulding of a piece of the alloy. as it has been seen that the arc may become unstable and, as a result thereof, the process sometimes stops. Such unwanted stops of the process are caused by the fact that a portion in the moulded piece has a substantially lower electric conductivity than the rest of the moulded piece, resulting in an unstable arc or extinction of the arc.

[0003] It is therefore an aspect of the present disclosure to provide a solution or at least reduce the above-mentioned problem.

SUMMARY



[0004] The present disclosure therefore provides a mould flux having a composition of, in weight%
SiO2 10-25;
CaO 15-35;
Al2O3 1-7;
Na2O 18-30;
K2O 15-25;
Fe2O3 0-5;
C 0-4;
TiO2 0-2;
MnO 0-2;
MgO 0-2;
Li2O 0-10;
and wherein the melting point of the mould flux is less than or equal to 1300°C.

[0005] Mould fluxes are synthetic slags constituted by a complex mix of oxides, minerals and carbonaceous materials. The main oxides are silica (SiO2), calcium oxide (CaO), sodium oxide (Na2O), alumina (Al2O3) and magnesium oxide (MgO).

[0006] The liquid slag formed by the flux constitutes a barrier to avoid steel re-oxidation by contact with air and the entrapment of other gases, such as nitrogen. The fluxes can be added through the top of the mould on the liquid steel, manually or automatically.

[0007] According to one embodiment, the mould flux is provided as a powder having the above-mentioned or below-mentioned composition. The flux will then melt in contact with the molten alloy.

[0008] It has been found been surprisingly found that the use of the present mould flux when moulding Ni-base alloys, especially those nickel base alloys containing Ti will prevent or suppress the formation of portions of lower electric conductivity in the moulded piece, such that the above-mentioned problem during a subsequent VAR process is remedied.

[0009] When the nickel base alloy contains Ti, the presence of CaO in the mould flux and the Ti content in the nickel alloy will be responsible for the formation of Perovskite. Hence, the present composition limits the CaO content in the mould powder compared to conventional mould fluxes.

[0010] Additionally, if CaO content is lowered, then in order to control the various thermo-physical properties of mould powder such as melting point, density and viscosity, the content of SiO2 should be lowered as well.

[0011] Furthermore, it has been found that local portions in moulded pieces of a Ni-base alloy, especially those containing titanium have a lower electric conductivity than the rest of the piece. This is due to the fact that said portions comprise a Perovskite phase. The Perovskite phase formation is assumed to be as follows: SiO2+Ti→TiO2+Si. As a result, TiO2 may together with CaO form Perovskite as a solution of Ca2Ti2O5 and Ca2Ti2O6. As mentioned herein, CaO in the flux contributes to the formation of Perovskite. The mould flux according to the present disclosure suppresses the formation of a Perovskite phase compared to mould fluxes of prior art. A relatively low content of SiO2 in the present mould flux powder and a relatively high content of alkali oxides (Na2O and K2O), and possibly also the effect of Li2O and MgO, is assumed to suppress the formation of Perovskite.

[0012] According to one embodiment of the mould flux as defined hereinabove or hereinafter, at least a part of Na2O, SiO2 and Al2O3 present in the mould flux are in the form of Sodium Feldspar (Na0.33Al0.35Si1.13O2.95). According to further embodiments, at least 25%, or at least 40% of Na2O, SiO2 and Al2O3 present in the mould flux are in the form of Sodium Feldspar (Na0.33Al0.35Si1.13O2.95). According to further embodiments, at least 50%, or at least 90% of the Na2O present in the mould flux is in the form of Sodium Feldspar, (Na0.33Al0.35Si1.13O2.95).

[0013] According to one embodiment of the mould flux as defined hereinabove or hereinafter, at least a part of K2O, SiO2 and Al2O3 present in the mould flux is present in the form of Potassium Feldspar (K0.33Al0.35Si1.13O2.95). According to further embodiments at least 25%, or at least 40% of K2O, SiO2 and Al2O3 present in the mould flux is present in the form of Potassium Feldspar (K0.33Al0.35Si1.13O2.95). According to further embodiments, at least 50%, or at least 90%, of the K2O present in the mould flux is present in the form of Potassium Feldspar (K0.33Al0.35Si1.13O2.95).

[0014] According to one embodiment, the content of Na2O in the mould flux is 18-25 weight%.

[0015] According to one embodiment, the content of K2O in the mould flux is 15-22 weight%.

[0016] According to one embodiment, the content of TiO2 in the mould flux is >0.05 weight%.

[0017] According to one embodiment, the content of Li2O in the mould flux is >1.0 weight%.

[0018] According to one embodiment, the ratio of SiO2/(CaO+Al2O3)>1.

[0019] According to one embodiment, the ratio of CaO and SiO2 (CaO/SiO2)- is in the range of 3:4 to 4:3, such as 1:1. These oxides are important to control the viscosity and the melting point of the mould flux. A CaO content greater than 35 weight% will promote the formation of Perovskite and CaO less than 15 % might induce high viscosity in the molten mould powder. The content of SiO2 should be controlled on the basis of CaO.

[0020] Na2O, K2O and Li2O will stabilize Ti in the melt and thereby as mentioned above will contribute to the prevention of Perovskite formation. This is best results are achieved when each of Na2O and K2O is present in an amount of 18-22 weight%, preferably around 20 weight%, in the mould mixture. In addition, these alkali oxides promote the formation of Nepheline phase which is beneficial during casting. A very high content of these oxides will make the flux mould too fluid and a too low content would result in formation of Perovskite phase.

[0021] The objective of the present disclosure is also achieved by means of a method of moulding a piece of a Ni-base alloy wherein a mould flux as defined hereinabove or hereinafter is applied on a surface of the molten alloy during moulding thereof.

[0022] According to one embodiment, the Ni-base alloy comprises, in weight%:
C <0.05;
Cr 17-23;
Ni 35-63;
Mo 2.5-9.5;
Ti 0.3-3.0;
Al 0-0.7;
Si 0-0.5;
Nb 0-4.5;
Cu 0-3;
Mn 0-0.1;
S 0-0.003;
P: 0-0.02;
balance Fe.



Claims

1. A mould flux having a composition of, in weight%:
SiO2 15-25;
CaO 15-35;
Al2O3 1-7;
Na2O 18-30;
K2O 15-25;
Fe2O3 0-5;
C 0-4;
TiO2 0-2;
MnO 0-2;
MgO 0-2;
Li2O 0-10;
and wherein the melting point of the mould flux is less than or equal to 1300°C.
 
2. The mould flux according to claim 1, wherein at least a part of Na2O, SiO2 and Al2O3 present in the mould flux is present in the form of Sodium Feldspar, Na0.33Al0.35Si1.13O2.95.
 
3. The mould flux according to claim 1 or 2, wherein at least a part of K2O, SiO2 and Al2O3 present in the mould flux is present in the form of Potassium Feldspar, K0.33Al0.35Si1.13O2.95.
 
4. The mould flux according to any one of claims 1-3, wherein at least 50% of the Na2O present in the mould flux is in the form of Sodium Feldspar, Na0.33Al0.35Si1.13O2.95.
 
5. The mould flux according to any one of claims 1-4, wherein at least 50%, of the K2O present in the mould flux is present in the form of Potassium Feldspar, K0.33Al0.35Si1.13O2.95.
 
6. The mould flux according to any one of claims 1-5, wherein the content of Na2O, in weight%, is 18-25.
 
7. The mould flux according to any one of claims 1-6, wherein the content of K2O, in weight %, is 15-22.
 
8. The mould flux according to any one of claims 1-7, wherein the content of TiO2 is >0.05 weight%.
 
9. The mould flux according to any one of claims 1-8, wherein the content of Li2O is >1.0 weight%.
 
10. The mould flux according to any one of claims 1-9, wherein SiO2/(CaO+Al2O3)>1.
 
11. The mould flux according to any one of claims 1-10, wherein the ratio between CaO and SiO2 is in the range of 3:4 - 4:3.
 
12. The mould flux according to any one of claims 1-11, wherein the mould flux is a powder having the composition according to any one of claims 1-11.
 
13. A method of manufacturing a nickel-base alloy, wherein a mould flux according to any one of claims 1-12 is applied on a surface of the molten nickel-base alloy during moulding thereof.
 
14. A method according to claim 13, wherein said Ni-base alloy comprises, in weight%:
C <0.05;
Cr 17-13;
Ni 35-63;
Mo 2.5-9.5;
Ti 0.3-3.0;
Al 0-0.7;
Si 0-0.5;
Nb 0-4.5;
Cu 0-3;
Mn 0-0.1;
S 0-0.003;
P: 0-0.02;
balance Fe.

 





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