US20180243823A1

US20180243823A1 - Method of manufacturing of a casted part or ingot of a metallic alloy attaining a minimal segragation in the casting process

Info

Publication number: US20180243823A1
Application number: US15/558,753
Authority: US
Inventors: Isaac Valls Anglés
Original assignee: Innomaq 21 Ltda Soc
Current assignee: Innomaq 21 Ltda Soc
Priority date: 2015-03-18
Filing date: 2016-03-18
Publication date: 2018-08-30
Also published as: WO2016146829A1

Abstract

The present invention relates to a method of manufacturing of a casted part or ingot of a metallic alloy attaining a minimal segregation in the casting process, for alloys which are prone to segregate. The method can also be employed to refine the grain and microstructure of the obtained alloys. The method is especially interesting for Fe, Ti, Co or Ni based alloys. The method is very inexpensive and can be applied for the obtaining of very large cross-sections. An additional feature of the method is that it can be employed to capitalize impurities.

Description

FIELD OF THE INVENTION

The present invention relates to a method to minimize the segregation on metallic alloys which are prone to segregate. The method can also be employed to refine the grain and microstructure of the obtained alloys. The method is especially interesting for Fe, Ti, Co or Ni based alloys. The method is very inexpensive and can be applied for obtaining very large cross-sections. An additional feature of the method is that it can be employed to capitalize impurities.

STATE OF THE ART

Materials properties are arguably one of the main limitations to engineering evolution. Often materials with higher mechanical resistance in combination with other properties are desired. Evolution in this area are mostly attained trough improvements in the understanding the effect of alloying and microstructures attainable trough thermo-mechanical processing and lately even more trough the improvement of manufacturing processes.
For very high end applications as is the case in aeronautics, nuclear, military and tooling applications amongst others, a lot of attention is played in maximizing material performance. In this applications often complex (and cost intensive) manufacturing processes are employed to improve purity, refine microstructure or any other means to improve mechanical properties or other aspects like for example polish-ability.
For this purpose, high purity scraps and master alloys are often used despite the added cost, and cost intensive melting processes are employed like vacuum induction melting, or various refining (VD, VAD, VOD, . . . ) or even re-melting strategies (ESR, VAR, . . . ). Particularly interesting is the case of the re-melting strategies for their incidence on the segregation given the confined melting pool.
One of the major problems affecting quality of these alloys when large components are required is segregation. Due to the complex alloying strategies, those alloys are often prone to segregate during cooling in a close to equilibrium regime. Some strategies based on rapid cooling are often used to minimize this segregation. (the already mentioned re-melting strategies or even atomization/powder metallurgy techniques).
It is interesting to notice than these alloys often comprise complex alloying strategies, and it is quite common that they include some micro-alloying strategies also. So often there are small volume fractions of phases with a significant incidence on the properties. Those phases are often integrated by intermetallic phases or ceramic phases like carbides, nitrides borides or mixtures thereof. At the same time, more often than not, other phases in the same order of magnitude when it comes to volume fraction are referred as to impurities or non-metallic inclusions. What makes an element in the ppm to thousands of ppm's level a micro-alloying agent or an impurity depends on the intentionality of its presence. In the same way the main reason leading to the classification of “non-metallic inclusion” or “intentional second phase” is often the main perceived effect on the mechanical properties.
Usage of rare earths as scavengers for some detrimental elements as sulphur and phosphorous is known, since a control over the shape of the inclusions to minimize their effect on fracture toughness due to stress concentration effects, can be implemented. Rare earths are also known for their vigorous reaction with oxygen, so that they can be employed to deoxidize in replacement for Al, Si, Ti . . . . One example of the application of such technology can be found in U.S. Pat. No. 3,816,103. Some of the treatments with rare earths are only thought to be possible or effective for relatively small metallic melt amounts. In this document, rare earths are employed as nucleation seeds for large melting quantities.
Alloys prone to present constitutional undercooling promoting out of the plane columnar solidification front suffer enrichment of the interdendritic liquid leading to macro-segregation which can be massive for big ingots or parts.
Large primary carbide colonies tend to form in cold work tool steels if they are cast in big ingots or parts, unless some remelting technology with smaller melt pool is used like is the case of ESR or VAR.
For alloys that need a heat treatment to attain their properties, often the small scale segregation of certain elements, that because of this very same reason are referred to as impurities, can lead to temper embrittlement of the manufactured parts upon tempering.
It is also well known the negative effect of segregation on fracture toughness of most hot work tool steels leading to premature thermal fatigue in applications with large thermal cycles like is the case of die casting of aluminum based alloys.
Usage of vibration and ultrasonic vibration has been extensively studied for small melts and especially for low melting point alloys. For Fe based alloys and other high melting point alloys it has been limited to small melts or in the case of medium or large melts only for the purpose of helping desgasification or increasing convection in the melt. One such example can be found in US2010263821, where vibration is only used to increase the forced convection rate in the melt, thus meaning lower amplitudes an accelerations are employed in comparison to the present invention so that no significant effect on segregation can be expected, on the other hand the challenges of dealing with shrinkage porosity are avoided and thus in US2010263821 no special measures had to be taken in the form of specific alloy design to minimize density miss-match, controlled cooling after solidification or posterior thermo-mechanical treatments to deal with induced shrinkage porosity.
Usage of remelting practices for big ingots, where the melting pool is much smaller than when casting the whole ingot are common practice. The probably better known technologies are VAR (Vacuum Arc Remelting) and ESR (Electro Slag Remelting). In both inclusion and/or detrimental gases are also taken out of the melt, and the positive effect on segregation reduction comes from the much smaller melting pool enhanced by a forced cooling crucible leading to much faster solidification. The main limitations of these technologies are that they need a very specific shape of the final product attained and the associated cost. Also the usage of powder metallurgy for the manufacturing of tool steel parts is common practice, here the obtaining of the steel powder is often done under conditions where both the melting pool size (just a droplet of molten metal) and the cooling speeds employed during solidification are orders of magnitude greater than in the conventional melting case. The effect on segregation in this case is very notorious, and trough many different consolidation technologies a wide range of sizes can be attained, with some limitations when it comes to size. Mainly cost and often surface oxidation of the powder previous to consolidation are the main drawbacks of this technology.
Usage of gas bubbling to rinse (some inpurities and specially other gases) is a common practice in the melting of both low melting point alloys and high melting point alloys, for small, medium and large castings. In the case of iron and nikel base alloys normally converters are used for this purpose like AOD (Argon-Oxigen-Degasing converter), VOD (Vacuum-Oxigen-Desgasing converter), ladle gas purging treatments are also becoming more and more popular, and such treatments can be applied to almost any kind of molten metal technology including continuous casting. Examples of such technology to remove non-metallic inclusions and reduce the presence of non-desirable gases in the melt can be found in U.S. Pat. No. 3,886,992; U.S. Pat. No. 3,998,261; U.S. Pat. No. 4,015,655 or U.S. Pat. No. 3,779,743 But vigorous gas bubbling sufficient to break columnar growth formations or to increase the undercooling required for solidification, have not been reported. High energy gas bubbling to have a marked effect on the segregation, even less.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a method of manufacture a casted part or ingot of a metallic alloy, avoiding the problem of segregation in materials prone to segregate.
In the context of the present invention a metallic alloy is referred, but not limited to a mainly metallic material as a pure metal, a metallic base alloy, a metallic matrix composite, an alloyed steels, a highly alloyed steels or an intermetallic materials among others. Metallic alloys of especial interest to be manufactured in a casted form with the method of the present invention are Fe, Ti, Co or Ni based alloys.
In an embodiment of the invention the composition of the metallic alloy that can be manufactured with the method of the present invention has the following compositional range:


% C = 0.15-4	% N = 0-0.6	% B = 0-0.6
% Cr <11.0	% Ni = 0-12	% Si = 0-2.4	% Mn = 0-3
% Al = 0-2.5	% Mo = 0-10	% W = 0-10	% Ti = 0-2
% Ta = 0-3	% Zr = 0-3	% Hf = 0-3	% V = 0-12
% Nb = 0-3	% Cu = 0-2	% Co = 0-12,

the rest consisting of iron and trace elements (less than 2%).

For several applications the minimum carbon content of the composition is especially indicated to be at least 0.15% by weight or more, more preferably 0.25% by weight or more, more preferably 0.32% by weight or more and more preferably 0.52% by weight or more. For other applications is specially indicated that the maximum carbon content is preferably less than 2.8%, more preferably less than 1.8%, more preferably less than 1.4, or even more preferably less than 0.9%.
In a preferred embodiment of the invention the metallic alloy casted is a Fe, Ti, Co or Ni based alloy.
In the context of the present invention cast is referred to a method of manufacturing a metallic alloy in which the melt is usually poured into a mold, including but not limited to reusable metallic molds, a temporary non-reusable molds such as sand casting, a plastic mold casting and non-expendable mold casting such as die casting, semi-solid casting or continuous casting among others, wherein the melt of the metallic alloy adopt the desired shape and is allowed to solidify.
This method is especially useful for the production of casted tool steels and ingots, especially for the production of big cast or ingots of 1.5 Tm, 2.2 Tm, 4.3 Tm 8.4 Tm, 10.4 Tm, 15.6 Tm, 20.4 Tm or even 50 Tm or more, to obtain large cross-sections steels and hot work tool steels but can also be used for obtaining cold work steels, steels for plastic injection, stainless steel, high speed steels, supercarburated steels, high strength materials, high conductivity steels or low conductivity steels, among others, in that way that the casted alloys obtained using the method of the present invention are useful in construction, aeronautic, nuclear, military and tooling applications among others.
In a preferred embodiment of the invention the metallic alloy casted using the method of the invention is an ingot
In another preferred embodiment of the invention, the metallic alloy casted using the method of the present invention is a hot work steel.
The method of the present invention is specially indicated for casting large cross section, preferably for cross sections of more than 40.000 mm², preferably for cross sections of more than 230.000 mm², more preferably for cross sections of more than 640.000 mm², or even for cross sections of more than 1.200.000 mm².
The method for manufacturing a casted part or ingot of a metallic alloy of the present invention, comprises pouring a melted metallic alloy in a casting mold and the following steps: a) adding to the melt of the metallic alloy a nucleation promoter, and subjecting the melt of the metallic alloy to at least one of steps b) and c) wherein step b) consist on a vibration process and step c) consist on a gas bubbling process.
In a preferred embodiment the method of the manufacturing a casted part or ingot of a metallic alloy process comprises the following steps:

- a) Adding to the melt of the metallic alloy at least 12 ppm by weight of a nucleation promoter, and
- b) Subjecting the melt of the metallic alloy to vibration with an acceleration of at least 1 m/s²at least until the temperature of the melt is below the theoretical melting point and/or until at least 10% of solid phase is present, and/or
- c) Bubbling to the melt of the metallic alloy a gas flow of at least 1 m³/min per ton of the melt of metallic alloy, at least until the temperature of the melt is below the theoretical melting point and/or until at least 10% of solid phase is present.

Through the application of the method of the present invention several impurities can be capitalized as “micro-alloying agents” and many “non-metallic inclusions” as “intentional second phases”, since they become very important to refine the grain and microstructure and minimize segregation.
The inventor has seen that one way to minimize segregation is to control the size, morphology, volume fraction, solidification temperature with respect to the melt of the metallic alloy and distribution of certain non-metallic particulates otherwise falling into the category of “impurities”; so as to promote their action as nucleation promoters. At the same time some other means to promote simultaneous solidification in the whole volume of the ingot or cast part is preferably employed to avoid excessive columnar growth which often promotes segregation, which can also be attained through a “breaking-as it grows” strategy on the dendritic or out of the plane solidification. Such means include for example vibration (mechanical or electromagnetically among others), intense stirring or gas bubbling. While most of these strategies have been reported inefficient against segregation specially when the solidifying metal body is large, and even more for highly alloyed steels naturally prone to segregation, like is the case of tool steels, the inventor has seen that with the proper choosing of composition and process parameters a very remarkable effect can be attained especially for large bodies and cross sections such as big cast or ingots.
The nucleation sites play a capital role in the present invention. In general terms the volume fraction, size, morphology and nature have to be adapted to the particular metallic alloy cast. Generally when a fine equiaxed microstructure is preferred a high volume fraction with a small size will be preferred for the nucleation sites. In this respect volume fractions of 0.005% by weight or more, preferably 0.01% by weight or more, more preferably 0.05% by weight or more and even 0.2% by weight or more will be desirable for those applications. Also sizes smaller than 180 microns, preferably smaller than 46 microns, more preferably smaller than 8 microns and even smaller than 900 nanometers will be suitable for such applications. For some applications the preferred nucleation sites are carbides, for some other applications borides, nitrides, carbides and/or mixtures thereof, for some other applications the preferred nucleation sites are oxides and/or sulphides or other inclusions with similar morphology.
As inclusion scavenger or nucleation site, as has been described rare earths are preferred in the present invention acting as nucleation promoters. The method of the present invention comprises the use of a nucleation promoter in step a). In a preferred embodiment of the invention a rare earth (hereinafter referred as REE) is used as nucleation promoter.
Rare earth, also rare earth element (REE) as defined by IUPAC, is one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides, as well as scandium and yttrium. Scandium and yttrium are considered rare earth elements because they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties. The seventeen REE known until the moment are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. In the last years their use has been largely increased due to the great new devices and demanding applications in the field of electronics or aerospace industries. In metallurgy, it has been observed that rare earth elements work as scavengers of oxygen and other impurities present inherent of the melting process itself. Therefore, the use of REE might seem suitable for such kind of aim. Depending on certain desired final properties, being able to control the morphology of inclusions present in the steel is of great advantage. On the other hand, the fact that it has also been observed that in general terms such elements do not have a positive effect on hardenability. Still, regardless this fact which indeed is true, the inventors have surprisingly seen that when such elements are combined with other alloying elements in the precise way, the combination of them do have a positive influence on hardenability.
The quantity of REE has to be carefully chosen; the inventors have determined that too less of them do not bring any difference in any remarkable property; on the contrary, too much may have a detrimental effect. It is often desired that the sum of all REE is at least more than 7 ppm, preferably more than 12 ppm, preferably more than 55 ppm, more preferably more than 220 ppm and even more preferably more than 330 ppm or even more than 430 ppm. For special applications, it might be preferable to have even more than 603 ppm. On the other hand, for other applications, it is desirable to have less than 0.6% wt of RRE, preferably less than 0.3% wt, more preferably less than 0.1% wt and even more preferably less than 600 ppm. For special applications it might also be preferable to have less than 350 ppm and even less than 90 ppm. There are some properties which might benefit from having REE in even much higher quantities, for example more than 1% wt, preferably more than 1.5% wt. more preferably more than 1.8% wt. For some applications it can be desirable to have even more than 2% wt and for special instances, it might be also desirable to have even more than 3.4% Wt.
In an embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is at least 0.0007% (7 ppm) by weight of the melt of the metallic alloy (wt). In a preferred embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is at least 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is at least 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is at least 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is at least 0.0120% (120 ppm) by weight of the melt of the metallic alloy (wt).
Therefore, in general terms it is preferred that the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight to the melt of the metallic alloy (wt) to 3.4% by weight of the melt of the metallic alloy (wt). In a preferred embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight to the melt of the metallic alloy (wt) to 3.4% by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight to the melt of the metallic alloy (wt) to 3.4% by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.012% (120 ppm) by weight to the melt of the metallic alloy (wt) to 3.4% by weight of the melt of the metallic alloy (wt).
In an embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt). In other embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 0.0090% (90 ppm) by weight of the melt of the metallic alloy (wt); in other embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 0.022% (220 ppm) by weight of the melt of the metallic alloy (wt); in other embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 0.033% (330 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy and 0.035% (350 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 0.043% (430 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0012% by weight of the melt of the metallic alloy (wt) and 0.0603% (603 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 0.1% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 0.3% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 0.6% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% by weight of the melt of the metallic alloy (wt) and 1.0% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 1.5% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 2.0% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0012% (12 ppm) by weight of the melt of the metallic alloy (wt) and 3.4% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is more than 3.4% by weight of the melt of the metallic alloy (wt).
In an embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt). In other embodiment of the invention the sum of all REE that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 0.0090% (90 ppm) by weight of the melt of the metallic alloy (wt); in other embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 0.022% (220 ppm) by weight of the melt of the metallic alloy (wt); in other embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 0.033% (330 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy and 0.035% (350 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 0.043% (430 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0032% by weight of the melt of the metallic alloy (wt) and 0.0603% (603 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 0.1% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 0.3% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 0.6% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% by weight of the melt of the metallic alloy (wt) and 1.0% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 1.5% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 2.0% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0032% (32 ppm) by weight of the melt of the metallic alloy (wt) and 3.4% by weight of the melt of the metallic alloy (wt).
In an embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 0.0090% (90 ppm) by weight of the melt of the metallic alloy (wt); in other embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 0.022% (220 ppm) by weight of the melt of the metallic alloy (wt); in other embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 0.033% (330 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy and 0.035% (350 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 0.043% (430 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0055% by weight of the melt of the metallic alloy (wt) and 0.0603% (603 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 0.1% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 0.3% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 0.6% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% by weight of the melt of the metallic alloy (wt) and 1.0% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 1.5% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 2.0% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0055% (55 ppm) by weight of the melt of the metallic alloy (wt) and 3.4% by weight of the melt of the metallic alloy (wt).
In an embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0120% (120 ppm) by weight of the melt of the metallic alloy (wt) and 0.022% (220 ppm) by weight of the melt of the metallic alloy (wt); in other embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0120% (120 ppm) by weight of the melt of the metallic alloy (wt) and 0.033% (330 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0120% (120 ppm) by weight of the melt of the metallic alloy and 0.035% (350 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0120% (120 ppm) by weight of the melt of the metallic alloy (wt) and 0.043% (430 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy (wt) is between 0.0120% by weight of the melt of the metallic alloy (wt) and 0.0603% (603 ppm) by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0120% (120 ppm) by weight of the melt of the metallic alloy (wt) and 0.1% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0120% (120 ppm) by weight of the melt of the metallic alloy (wt) and 0.3% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0120% (120 ppm) by weight of the melt of the metallic alloy (wt) and 0.6% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0120% by weight of the melt of the metallic alloy (wt) and 1.0% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0120% (120 ppm) by weight of the melt of the metallic alloy (wt) and 1.5% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.00120% (120 ppm) by weight of the melt of the metallic alloy (wt) and 2.0% by weight of the melt of the metallic alloy (wt); in another embodiment of the invention the sum of all REEs that shall be added to the melt of the metallic alloy is between 0.0120% (120 ppm) by weight of the melt of the metallic alloy (wt) and 3.4% by weight of the melt of the metallic alloy (wt).
In a preferred embodiment of the invention the nucleation promoter in step a) is selected from SC, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and/or Lu and/or mixtures thereof.
Among all existing REEs, the inventors have seen that the most interesting ones for reducing segregation in the casted metallic alloys are Ce, La, Sm, Y, Nd and Gd, in pure form or in the form of oxide. In a preferred embodiment of the invention the nucleation promoter used in the method of manufacturing a casted metallic alloy of the present invention is selected from the group consisting on Ce, La, Sm, Y, Nd and/or Gd in pure form and/or in the form of oxide and/or mixtures thereof.
For the case of % La, in some applications it is preferred to have at least 4 ppm, preferably more than 10 ppm, more preferably more than 23 ppm and even more preferably more than 100 ppm. For other applications the inventors have seen that it is desirable to have at least 0.1% wt, preferably more than 0.5% wt, more preferably more than 0.9% wt and even more preferably more than 1% wt. For special cases, it is desirable to have even higher amount, for example more than 1.5% wt, more than 2% wt and even more than 4.5% wt. If % La is not used as the only REE and it is combined with other REEs, then it is desirable that % La accounts to at least 30% by weight of the total amount of REEs, preferably more than 45% by weight of the total amount of REEs, more preferably more than 67% by weight of the total amount of REEs and even more preferably more than 80% by weight of the total amount of the REEs. In some instances, it is preferred that % La accounts for even more than 91% by weight of the total amount of the REEs and the rest remain as trace elements.
In a preferred embodiment of the invention the % La that shall be added to the melt of the metallic alloy in step a) is at least 0.0004% (4 ppm) by weight of the melt of the metallic alloy. In another embodiment of the invention the % La that shall be added to the melt of the metallic alloy in step a) is between 0.0004% (4 ppm) by weight of the melt of the metallic alloy and 4.5% by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the % La that shall be added to the melt of the metallic alloy in step a) is at least 4.5% by weight of the melt of the metallic alloy (wt).
For the case of % Ce, for some applications it is preferred to have at least 5 ppm, preferably more than 15 ppm, more preferably more than 53 ppm and even more preferably more than 150 ppm. For some applications the inventors have seen that it is desirable to have at least 0.09% wt, preferably more than 0.2% wt, more preferably more than 0.7% wt and even more preferably more than 0.9% wt. For special cases, it is desirable to have even higher amount, for example more than 1% wt, more than 1.5% wt and even more than 3% wt. If % Ce is not used as the only REE and it is combined with other REE, then it is preferred that % La accounts to at least 25% by weight of the total amount of REEs, preferably more than 47% by weight of the total amount of REEs, more preferably more than 73% by weight of the total amount of REEs and even more preferably more than 91% by weight of the total amount of the REEs. In some instances, it is desirable that % Ce accounts for even more than 95% by weight of the total amount of the REEs and the rest remain as trace elements. There is also a variety of what is called Ce-mischmetal or mischmetal, which is an alloy of REE; it is mainly composed of Ce and La (typical composition is about 50% by weight Ce, about 45% by weight La, with traces of Nd and Pr). If this Ce-mischmetal is preferred to be used, then it is preferable to use about 0.5% by weight of the melt of the metallic alloy, preferably more than 1.6% by weight of the melt of the metallic alloy, more preferably more than 3.1% by weight of the melt of the metallic alloy and even more preferably more than 4.5% by weight of the melt of the metallic alloy.
In a preferred embodiment of the invention the % Ce that shall be added to the melt of the metallic alloy in step a) is at least 0.0005% (5 ppm) by weight of the melt of the metallic alloy. In another embodiment of the invention the % Ce that shall be added to the melt of the metallic alloy in step a) is between 0.0005% (5 ppm) by weight of the melt of the metallic alloy and 4.5% by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the % Ce that shall be added to the melt of the metallic alloy in step a) is at least 4.5% by weight of the melt of the metallic alloy (wt).
For the case of % Sm, for some applications it is preferred to have at least 2 ppm, preferably more than 9 ppm, more preferably more than 43 ppm and even more preferably more than 90 ppm. For some applications the inventors have seen that it is desirable to have at least 0.02% wt, preferably more than 0.2% wt, more preferably more than 0.51%₁, wt and even more preferably more than 0.9% wt. For special cases, it is desirable to have even higher amount, for example more than 1.0% wt, more than 1.3% wt and even more than 3% wt. If % Sm is not uses as the only REE and it is combined with other REE, then it is desirable that % Sm accounts to at least 10% by weight of the total amount of REEs, preferably more than 15% by weight of the total amount of REEs, more preferably more than 22% by weight of the total amount of REEs and even more preferably more than 45% by weight of the total amount of the REEs. In some instances, it is preferred that % Sm accounts for even more than 53% by weight of the total amount of the REEs and the rest remain as trace elements.
In a preferred embodiment of the invention the % Sm that shall be added to the melt of the metallic alloy in step a) is at least 0.0002% (2 ppm) by weight of the melt of the metallic alloy. In another embodiment of the invention the Sm that shall be added to the melt of the metallic alloy in step a) is between 0.0002% (2 ppm) by weight of the melt of the metallic alloy and 3% by weight of the melted metallic alloy (wt). In another preferred embodiment of the invention the % Sm that shall be added to the melt of the metallic alloy in step a) is at least 3% by weight of the melt of the metallic alloy (wt).
For the case of % Y, for some applications it is preferred to have at least (9 ppm, preferably more than 34 ppm, more preferably more than 67 ppm and even more preferably more than 200 ppm. For some applications the inventors have seen that it is desirable to have at least 0.12% wt, preferably more than 0.22% wt, more preferably more than 0.9% wt and even more preferably more than 1% wt. For special cases, it is desirable to have even higher amount, for example more than 1.5% wt, more than 2% wt and even more than 3% wt. If % Y is not uses as the only REE and it is combined with other REE, then it is desirable that % Y accounts to at least 30% by weight of the total amount of REEs, preferably more than 45% by weight of the total amount of REEs, more preferably more than 67% by weight of the total amount of REEs and even more preferably more than 80% by weight of the total amount of the REEs. In some instances, it is preferred that % Y accounts for even more than 91% by weight of the total amount of the REEs and the rest remain as trace elements.
In a preferred embodiment of the invention the % Y that shall be added to the melt of the metallic alloy in step a) is at least 0.0009% (9 ppm) by weight of the melt of the metallic alloy. In another preferred embodiment of the invention the % Y that shall be added to the melt of the metallic alloy in step a) is between 0.0009% (9 ppm) by weight of the melt of the metallic alloy and 3% by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the % Y that shall be added to the melt of the metallic alloy in step a) is at least 3% by weight of the melt of the metallic alloy (wt).
For the case of % Gd, for some applications it is preferred to have at least 2 ppm, preferably more than 27 ppm, more preferably more than 53 ppm and even more preferably more than 98 ppm. For some applications the inventors have seen that it is desirable to have at least 0.01% wt, preferably more than 0.1% wt, more preferably more than 0.29% wt and even more preferably more than 0.88% wt. For special cases, it is desirable to have even higher amount, for example more than 0.9% wt, more than 1.7% wt and even more than 3% wt. If % Gd is not used as the only REE and it is combined with other REE, then it is desirable that % Gd accounts to at least 14% by weight of the total amount of REEs, preferably more than 26% by weight of the total amount of REEs, more preferably more than 37% by weight of the total amount of REEs and even more preferably more than 45% by weight of the total amount of the REEs. In some instances, it is preferred that % Gd accounts for even more than 69% by weight of the total amount of the REEs and the rest remain as trace elements.
In a preferred embodiment of the invention the % Gd that shall be added to the melt of the metallic alloy in step a) is at least 0.0002% (2 ppm) by weight of the melt of the metallic alloy. In another preferred embodiment of the invention the % Gd that shall be added to the melt of the metallic alloy in step a) is between 0.0002% (2 ppm) by weight of the melt of the metallic alloy and 3% by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the % Gd that shall be added to the melt of the metallic alloy in step a) is at least 3% by weight of the melt of the metallic alloy (wt).
For the case of % Nd, for some applications it is preferred to have at least 16 ppm, preferably more than 38 ppm, more preferably more than 98 ppm and even more preferably more than 167 ppm. For some applications the inventors have seen that it is desirable to have at least 0.04% wt preferably more than 0.14% wt, more preferably more than 0.48% wt and even more preferably more than 1.34%, wt. For special cases, it is desirable to have even higher amount, for example more than 1.5% wt, more than 2% wt and even more than 3% wt. If % Nd is not used as the only REE and it is combined with other REE, then it is desirable that % Nd accounts to at least 35% by weight of the total amount of REEs, preferably more than 49% by weight of the total amount of REEs, more preferably more than 71% by weight of the total amount of REEs and even more preferably more than 83% by weight of the total amount of the REEs. In some instances, it is preferred that % Nd accounts for even more than 93% by weight of the total amount of the REEs and the rest remain as trace elements.
In a preferred embodiment of the invention the % Nd that shall be added to the melt of the metallic alloy in step a) is at least 0.0016% (16 ppm) by weight of the melt of the metallic alloy. In another preferred embodiment of the invention the % Nd that shall be added to the melt of the metallic alloy in step a) is between 0.0016% (16 ppm) by weight of the melt of the metallic alloy and 3% by weight of the melt of the metallic alloy (wt). In another preferred embodiment of the invention the Nd shall be added to the melt of the metallic alloy in step a) is at least 3% by weight of the melt of the metallic alloy (wt).
The REE can be used in the present application in any form such as ferro alloys, in pure form and in oxide form among others. In a preferred embodiment of the invention, the REEs are selected in their ferro alloy and/or pure form and/or in their oxide form and/or mixtures thereof:
For some applications Al, Ti and/or Si can be used as replacement of the rare earths (REE). The effect is normally less pronounced but it might have positive effects on other relevant properties including cost. These elements can be used alone or in combination with the same amounts described for the rare earths in the preceding paragraphs. But when those elements are used the most common is to do it in moderate amounts, usually less than 2%, preferably less than 0, 8%, more preferably less than 0.2%, and even less than 0.08%. Also Zr and Hf can be used for this purpose with the same amounts, from 0.08% to 2% for some applications especially when less spherical morphologies are acceptable.
Al, Ti, SI, Zr and/or Hf can be used in the present application in any chemical form. In a preferred embodiment of the invention, Al, Ti, SI, Zr and/or Hf are selected in their ferro alloy form and/or pure form and/or in their oxide form.
In a preferred embodiment of the invention, the nucleation promoter in step a) is selected from the group consisting on SC, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ti, Si, Zr and/or Hf in ferro alloy and/or pure and/or oxide form and/or mixtures thereof.
In another preferred embodiment of the invention, the nucleation promoter in a) is selected from Al, Ti, Si, Zr and/or Hf in ferro alloy and/or pure and/or oxide form and/or mixtures thereof.
In another preferred embodiment Al, Ti, Si, Zr and/or Hf are added to the melt of the metallic alloy as nucleation promoters in step a) from 0.08% by weight of the melt of the metallic alloy to 2% by weight of the melt of the metallic alloy. In another preferred embodiment Al, Ti, Si, Zr and/or Hf are added to the melt of the metallic alloy as nucleation promoters in step a) in an amount of less than 0.08% by weight of the melt of the metallic alloy.
In another preferred embodiment of the invention, the nucleation promoter in step a) is selected from the group consisting on SC, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ti and/or Si in ferro alloy and/or pure and/or oxide form and/or mixtures thereof.
The method of the present invention, often promotes simultaneous solidification (not always, a typical counter-example is the case in which only breakage during growth of dendrites during solidification is sought for) which negatively affects the strategies often applied to group and control shrinkage porosity. Many alloys have a lower density in fluid state than they do in solid state which leads to a volume reduction upon solidification which can lead to the so called “shrinkage porosity” if it is not properly driven to form a macro internal solidification cavity in a desired position as could be the “hot top” of an ingot. It can also be overcome by having some liquid reservoirs that provide the missing material for the new state. In the case of the present invention the preferred ways to proceed are basically three. Besides the conventional liquid reservoir strategy which becomes more challenging the more simultaneous the solidification becomes, at least two more strategies are often employed. In fact any known strategy to minimize the effects of the difference of density of liquid and solid for some alloys, can be employed in the present invention. One of the preferred strategies is based on the minimization cancellation or sign changing of the volume miss-match trough proper metallurgical design of the alloy (through existing models, simulation and proper usage of the experimental results available in the literature). Probably the most trivial example could be adjusting the chemical composition of a low alloyed steel to avoid both the delta->gamma transformation and the peritectic reaction (which happens at about 0.6% C). Another strategy, especially for pieces that can undergo thermo-mechanical treatments (as is the case amongst others of all ingots to be processed into bars, and many cast parts that can be forged or at least heat treated after casting) is to minimize the effect of the volume mismatch trough proper thermos-mechanical treatment. As an example, as far as brittleness is not excessive and porosity not interconnected (to avoid oxidation of the voids or internal solidification cavities free surfaces), ingots can have their “shrinkage porosity” closed, and thus eliminated through a proper hot deformation step (forging, rolling and extrusion among others). Under hot deformation is understood any process that can cause permanent material flow and which takes place at a temperature at which diffusion is possible for the alloy being deformed and thus an internal void can be completely closed.
In a preferred embodiment of the invention the method of manufacturing a casted part or ingot of a metallic alloy of the invention, comprises adding a nucleation promoter and subjecting the melt of the metallic alloy to a vibration process during the solidification.
The vibration process of step b) can be made using any vibrator existing by any technological method available, as for example but not limited to ultrasonic vibration, magneto-restrictive vibration or piezoelectric vibration among others. In a preferred embodiment of the invention the vibrator used in step b) consists on a magneto restrictive generator.
The inventor has noticed that ultrasonic vibration has to be handled with care since it might be quite relevant in some instances to minimize segregation but it can also have the contrary effect. So only for some alloys ultrasounds or any other instance of “sonic” vibration makes sense. When the vibration is introduced with a sonotrode it has to be taken into account also the nature of the vibration generator. It was observed with surprise than despite the growing tendency in the industry to use piezoelectric generators, amongst others due to their greater efficiency, for most cases in the present invention it is magneto-restrictive generators that bring an advantage in terms of segregation reduction. This is believed to be mostly due to the temperatures involved and the heat management bringing along some reliability problems due to thermal shock amongst others. There are though a group of alloys, especially those with smaller internal friction, for which piezoelectric generated vibration can be advantageously used. Also the frequency used and amplitude determines whether the ultrasonic vibrations contribute to the reduction of segregation, have no noticeable effect or are even detrimental for a given system.
As has been mentioned the way the vibration is applied is very important in the present invention. The vibration parameters have to be adjusted to every composition as a function of its segregation propensity and melting temperature range amongst others, but some general remarks can be made regarding some of the vibration parameters.
Inventor has found that magneto-restrictive generators bring an advantage in terms of segregation reduction and only for alloys with smaller internal friction, preferably with an internal friction value piezoelectric generated vibration is useful.
When subjecting the melt of the metallic alloy to a vibration, the acceleration shall be adjusted to minimize segregation and avoid the contrary effect. The range of acceleration used can be adjusted for each metallic alloy especially in the case of very large castings, as for example those exceeding 6 tm, preferably exceeding 11 tm, more preferably exceeding 32 tm and even exceeding 52 tm it can be convenient to not exceed certain acceleration values, in this case accelerations below 48 m/s2, preferably below 28 m/s², and even below 18 m/s²can be used.
For some applications what is crucial is to have a sufficient acceleration, in those cases often accelerations above 4 m/s², preferably above 10 m/s², more preferably above 22 m/s²and even above 32 m/s².
In an embodiment of the invention the acceleration used is between 1 m/s²and 32 m/s², in a preferred embodiment the acceleration used is between 1 m/s²and 22 m/s², in other preferred embodiment the acceleration used is between 1 m/s²to 18 m/s², in other preferred embodiment the acceleration used is between 1 m/s²and 10 m/s², in other preferred embodiment the acceleration used is between 1 m/s²and 4 m/s².
In a preferred embodiment of the invention the acceleration used in the vibration step b) is at least 1 m/s².
In a preferred embodiment of the invention the acceleration used in the vibration step b) is at least 4 m/s².
In another preferred embodiment of the invention the acceleration used in the vibration step b) is between 1 m/s²and 32 m/s².
In another preferred embodiment of the invention the acceleration used in the vibration step b) is between 4 m/s²and 32 m/s².
For some applications quite large amplitude levels are desirable, often above 1 mm, preferably above 2 mm, more preferably above 5 mm and even above 12 mm. In a preferred embodiment of the invention the amplitude used for vibration in step b) is at least 1 mm.
It has also been observed that larger amplitudes seem to have a better effect upon segregation, thus amplifiers play a very important role in the present invention.
Frequency is far less capital than could be expected for some applications of the present invention and yet quite crucial for others. In this respect some applications benefit from moderate frequencies often below 2000 Hz, preferably below 98 Hz, more preferably below 58 Hz and even below 18 Hz. Some other applications benefit from relatively higher frequencies. Then often more than 8 Hz, preferably more than 22 Hz, more preferably more than 43 Hz and even more than 63 Hz are used.
In an embodiment of the invention the vibration frequency in step b) used is between 8 Hz to 200 Hz, in a preferred embodiment the frequency is between 8 to 60 Hz, in other preferred embodiment the frequency used is more than 63 Hz.
For several alloys with a density of 6 kg/m3 or more, ultrasonic vibration is advantageous, when using frequencies below 39 KHz, preferably below 31 KHz, preferably bellow 23 KHz and more preferably bellow 18 KHz.
In a preferred embodiment of the invention vibration is applied at least until the temperature of the melt reaches the theoretical melting point, preferably until an undercooling of at least 8 K is reached more preferably until an undercooling of at least 12K is reached, and even until an undercooling of 110 K is reached. In other preferred embodiment of the invention it is more convenient to orient the minimum vibration exposure with the amount of solid phase present due to solidification. In a preferred embodiment of the invention vibration is maintained in the melt of the metallic alloy until at least 10% solid phase is present, preferably until at least 22% solid phase is present, more preferably until at least 42% solid phase is present, and even until at least 62% solid phase is present. In some cases the vibration can be maintained beyond solidification completion of the melt of the metallic alloy, but that is rarely economically meaningful.
In the context of the present invention the theoretical melting point is defined as the temperature at which first solid content appears in the molten metallic alloy. This temperature can be determined using thermo analytical methods with the generally used empirically based formulas and thermodynamic simulation software, as for example but not limited to ThermoCalc, a software package for the calculation of thermodynamic and phase equilibria based on thermodynamic data which is supplied in a database, using the most updated database or by means of thermal analysis using DSC.
DSC or differential scanning calorimetry is a thermo analytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. Both the sample and reference are maintained at nearly the same temperature throughout the experiment.
In the context of the present invention undercooling is defined as the process of cooling a metal below the theoretical melting point without obtaining the transformation of liquid to solid.
The determination of the solid phase content in the melt of the metallic alloy during the solidification process can be estimated using thermodynamic simulation software as for example but not limited to ThermoCalc, a software package for the calculation of thermodynamic and phase equilibria based on thermodynamic data which is supplied in a database, using the most updated database.
In a preferred embodiment the method of manufacturing a casted part or ingot of a metallic alloy of the invention, comprises the following steps:

- a) Adding to the melt of the metallic alloy at least 12 ppm of a nucleation promoter, and
- b) Subjecting the melt of the metallic alloy to vibration with an acceleration of at least 1 m/s²until the temperature of the melt is below the theoretical melting point and/or until at least 10% of solid phase is present.

In another preferred embodiment of the invention the method of manufacturing a casted part or ingot of a metallic alloy of the invention, comprises adding a nucleation promoter and bubbling to the melt of the metallic alloy a gas flow.
The gas bubbling can be achieved by any technological method available. Two of the more typical ways consist on the introduction of a lance in the melt where the gas is flushed, or the usage of a porous ceramic on the ingot or melt container, through which the gas is flushed. What is capital for the present invention is that the gas bubbling should be very vigorous much more than the typical levels used for degasification or rinsing purposes. Normally more than 1 m³/min/ton (cubic meter of gas per minute and tone of melted metallic alloy), preferably more than 6 m³/min/ton, more preferably more than 12 m³/min/ton and even more than 28 m³/min/ton. For big casts or molds the positioning of the gas inlets is very important, and thus eventually more than one lance or inlet can be used to assure enough stirring in the melt over the whole cast or ingot. Mostly neutral gases are employed for the bubbling purposes (principally Ar or N₂), but some reactive gases can be used also to simultaneously attain some metallurgical effect (like would be the usage of a mixture of O₂with the Ar to accomplish the burning of some impurities like % S to reduce its content, or the regulation of the % C content, or even the control of the temperature of the melt. Other gases or mixtures can be used when looking for other simultaneous effects. In some cases, when possible it is interesting to introduce the gas with a high pressure to make the bubbling more energetic. In a preferred embodiment of the invention the pressure of the gas bubbled in step (c) is at least 2 bar.
In a preferred embodiment of the invention the bubbled gas in step c) is selected from Ar, N₂, O₂and/or mixtures thereof
It is often recommendable in the present invention to apply the gas bubbling until the desired temperature of the melt is obtained. Often gas bubbling will be applied at least until the temperature of the melt reaches the theoretical melting temperature, preferably until an undercooling of at least 8 K is reached more preferably until an undercooling of at least 12K is reached, and even until an undercooling of 110 K is reached. Sometimes is more convenient to orient the minimum gas bubbling exposure with the amount of solid phase present due to solidification. In those cases often gas bubbling will be maintain until at least 10% solid phase is present, preferably until at least 22% solid phase is present, more preferably until at least 42% solid phase is present, and even until at least 62% solid phase is present In some cases one can maintain the gas bubbling beyond solidification completion, but that is rarely economically meaningful.
In a preferred embodiment of the invention the method of manufacturing a casted part or ingot of a metallic alloy, the casting process comprising the following steps:

- a) Adding to the melt of the metallic alloy at least 12 ppm of a nucleation promoter, and
- c) Bubbling to the melt of the metallic alloy a gas flow from of at least 1 m³/min per ton of the melt of metallic alloy, at least until the temperature of the melt is below the theoretical melting point and/or until at least 10% of solid phase is present.

In another preferred embodiment of the invention the method of manufacturing a casted part or ingot of a metallic alloy, comprises adding a nucleation promoter; subject the melt of the metallic alloy to a vibration process during the solidification process and bubbling to the melt of the metallic alloy a gas flow during the solidification process.
In another preferred embodiment the method of the manufacturing a casted part or ingot of a metallic alloy process comprises the following steps:

- a) Adding to the melt of the metallic alloy at least 12 ppm of a nucleation promoter, and
- b) Subjecting the melt of the metallic alloy to vibration with an acceleration of at least 1 m/s²at least until the melt of the metallic alloy reaches a temperature between 8K and 110 k bellow the theoretical melting temperature and/or until at least 10% of solid phase is present, and/or
- c) Bubbling to the melt of the metallic alloy a gas flow of at least 1 m³/min per ton of the melt of metallic alloy, at least until the melt of the metallic alloy reaches a temperature between 8K and 110 k bellow the theoretical melting temperature and/or until at least 10% of solid phase is present.

In another preferred embodiment the method of the manufacturing a casted part or ingot of a metallic alloy process comprise the following steps:

- a) Adding to the melt of the metallic alloy between 12 ppm and 3.4% by weight of a nucleation promoter, and
- b) Subjecting the melt of the metallic alloy to vibration with an acceleration between 1 m/s²and 32 m/s²at least until the melt of the metallic alloy is below the theoretical melting point of the metallic alloy and/or until at least 10% solid phase is present, and/or
- c) Bubbling to the melt of the metallic alloy a gas flow between 1 m³/min and 28 m³/min per ton of the melt of the metallic alloy, at least until the melt of the metallic alloy is below the theoretical melting point of the metallic alloy and/or until at least 10% solid phase is present

In another preferred embodiment the method of the manufacturing a casted part or ingot of a metallic alloy process comprises the following steps:

It was observed that following the method of the present invention the segregation levels attained were much lower than those predicted by the most widely used models like the modifications of the Clyne-Karz model (like is the case for Ohnaka, Voller and Beckermann and Won and Thomas among others). In fact it is common when following the present invention, to reduce the segregation levels to less than 80%, preferably less than a 60% more preferably less than a 40% and even less than a 10% for at least one solute element, preferably at least 2 solute elements, more preferably at least 4 solute elements and even at least 6 solute elements with respect to the segregation predicted by the Won and Thomas model (as published in Metallurgical and Materials Transactions A, volume 32A month 2001-3).
In a preferred embodiment the method of the present invention reduces the segregation levels for at least one component to less than 80%.

EXAMPLES

Example 1

Three alloys within the following composition range:

the rest consisting of iron and trace elements (less than 2%),
where melt in an electric furnace. 20 minutes before pouring a rare earth mix mainly consisting on Ce and La with some minor quantities of other Actinides was added to the melt. Prior to pouring the composition was checked and rare earths controlled to be above 400 ppm given the sulphur and phosphorous content around 0.006% and 0.008% respectively. The casting ingot was placed on a vibrating table where with an amplitude of 2 mm and an acceleration of 2.5 m/s²were applied. The ingot had also a porous insert on the bottom where Ar was very vigorously flushed. When an undercooling of 20 K was reached, the gas bubbling was stopped, followed by a stop of the vibration 2 minutes later. In each case an alloy with the same nominal composition, was melt on the same equipment but desoxidation was made with Al and Ti but no rare earths, and final contents for both Al and Ti were kept below the 10 ppm level. No vibration or gas bubbling was applied to the melt. The alloy with no vibration, gas bubbling and scavengers presented columnar growth with very apparent segregation in the last solidified interdendritic liquid. The ingots with scavengers and where vibration and gas bubbling were applied presented an equiaxed grain structure with no apparent segregation.

Example 2

A metallic alloy within the following composition range:
% C = 0.35 % B = 0.0005 (5 ppm)

% Cr <2.0 % Ni = 0.4 % Si = <0.8

% Mo = 3.8 % W = 1.2 % Mn = <0.8

% Zr = 0.07 % V = 0.55

% Nb = 0.07%

the rest consisting of iron and trace elements (less than 2%),
where melt in an electric furnace, before pouring a rare earth mix mainly consisting on Ce and La with some minor quantities of other Actinides was added to the melt. Prior to pouring the composition was checked and rare earths controlled to be above 200 ppm. The casting metallic alloy was placed on a vibrating table where with an amplitude of 4 mm and an acceleration of 11 m/s²were applied. When an undercooling of 38 K was reached the vibration was stopped. No gas bubbling was applied to the melt. The metallic alloy with rare earths as nucleation promoters and where vibration were applied presented a mostly an equiaxed grain structure with very little segregation.

Claims

1. A method of manufacturing a casted metallic alloy, wherein the casting process comprises the following steps:

a) Adding to the melt of the metallic alloy at least 12 ppm of a nucleation promoter, and

b) Subjecting the melt of the metallic alloy to vibration with an acceleration of at least 1 m/s2 at least until the melt of the metallic alloy is below the theoretical melting point of the metallic alloy and/or until at least 10% solid phase is present, and/or

c) Bubbling to the melt of the metallic alloy a gas flow of at least 1 m3/min per ton of the melt of the metallic alloy, at least until the melt of the metallic alloy is below the theoretical melting point of the metallic alloy and/or until at least 10% solid phase is present

2. The method of claim 1, wherein the nucleation promoter in step a) is selected from the group consisting on: Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ti and Si and mixtures thereof.

3. The method of claim 1, wherein the nucleation promoter in step a) is selected from the group consisting on: Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu and mixtures thereof.

4. The method of claim 1, wherein the nucleation promoter in step a) is selected from the group consisting on Ce, La, Sm, Y, Ne and/or Ge and mixtures thereof.

5. The method according to claim 1, wherein the nucleation promoter in step a) consist on a mixture of La and at least one of Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ti and Si, characterized in that La is at least 40% of the total amount of the REEs.

6. The method of claim 1, wherein the nucleation promoter in step a) consist on a mixture of Ce and at least one of Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ti and/or Si, characterized in that Ce is at least 40% by weight of the total amount of the REEs.

7. The method of claim 1, wherein the nucleation promoter in step a) consist on a mixture of Nd and at least one of Sc, Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ti and/or Si, characterized in that Nd is at least 40% by weight of the total amount of the REEs.

8. The method according to claim 1, wherein the nucleation promoter in step a) is in its ferro alloy and/or pure and/or oxide form and/or mixtures thereof.

9. The method according to claim 1, wherein the nucleation promoter is added to the melt of the metallic alloy between 12 ppm and 3.4% by weight.

10. The method according to claim 1, wherein steps b) and/or c) are applied at least until the melt of the metallic alloy reaches a temperature between 8K and 110 k below the theoretical melting temperature.

11. The method according to claim 1, wherein the acceleration in step b) is between 1 m/s²and 32 m/s².

12. The method according to claim 1, wherein the gas flow in step c) is between 1 m³/min and 28 m³/min.

13. The method according to claim 1, wherein the vibration in step b) is made using a magneto-restrictive generator.

14. The method according to claim 1, wherein the amplitude used for vibration in step b) is at least 1 mm.

15. The method according to claim 1, wherein the vibration frequency in step b) is between 8 and 60 Hz.

16. The method of claim 1, wherein the bubbled gas in step b) is selected from Ar, N2, O2 and/or mixtures thereof.

17. The method of claim 1, wherein the pressure of the bubbled gas in step c) is at least 2 bar.

18. The method of claim 1, wherein the metallic alloy casted is a Fe, Ti, Co or Ni based alloy.

19. The method of claim 1, characterized in that reduces the segregation levels for at least one component to less than 80%.