WO2004067785A1

WO2004067785A1 - Method for doping melts using metal capsules

Info

Publication number: WO2004067785A1
Application number: PCT/AT2004/000012
Authority: WO
Inventors: Konstantin Chuntonov
Original assignee: Konstantin Technologies Gmbh
Priority date: 2003-01-30
Filing date: 2004-01-19
Publication date: 2004-08-12
Also published as: ATA1432003A; AT412159B

Abstract

The invention relates to a method for doping melts using hermetically sealed, thick-walled capsules whose shells consist of the same material as the melt to be treated. The capsules are thrown into a bath containing the melt, they sink to the bottom since they are denser than the melt, and there they open automatically, thereby releasing the dopant material contained therein under a layer of melt. The inventive method is especially suitable for cases where it is necessary to dope a melt with light-weight and/or chemically active substances.

Description

Process for doping melts using metal capsules

A process for doping melts with the help of hermetically sealed, thick-walled capsules, the sheath of which is made of the same material as a treated melt. If such capsules are thrown into a bath with the melt, they sink to the bottom because their density is greater than the density of the melt, and there they open automatically, releasing the dopant contained under a layer of melt. This method is particularly useful in cases where it is necessary to dope a melt with light and / or chemically active substances.

General state of the art.

A method of doping with small amounts of additives, which change the properties of the material produced in the required direction to a sufficient extent, is used in the metallurgy of many metals and alloys. The compositions of these dopants, the targets and doping methods can vary widely depending on the nature and the destination of the material being treated. The existing technical level of the process used is also different in each specific case.

Such useful dopants can be gases that react with a foreign substance and remove it from the melt, or gases that dissolve in the melt and modify the primary grain formation, such as nitrogen in steels. Such dopants can also be electropositive metals which have an analogous effect, ie either bind an impurity in a melt and remove it from the melt by means of density separation (for example calcium and barium as cleaning agents in the processes of copper, lead etc. refining) or in liquid state go into solution, but they are reflected in the composition of a solidifying disperse phase in the solid state (eg precipitates of LiAl ₃ in an Al matrix of aluminum alloys for the space folding industry), etc.

An analysis of the technologies that exist in this area shows that the main concern in the development of melt doping processes is the possibility of performing the operations at the most convenient time, thereby achieving melt homogeneity and technical simplicity of the process. Most of the difficulties usually arise when adding (introducing?) Either gases or light and chemically active metals to a melt.

E SATZBLAπ (RULE 26) The present invention proposes a simple and comprehensive solution to the problem of introducing small amounts of any substance into any melt.

Technical field.

The present invention relates to the field of metallurgy, whereby it relates to the treatment of melts with special additives for the purpose of producing pure metals or the production of alloys with improved (mechanical, electrical, corrosion-resistant etc.) properties.

Summary of the invention.

A basic idea of the novel method is the idea of a thick-walled and hermetically sealed metal capsule with a doping filling inside, which is released during the softening and breaking open or during the melting of the capsule walls under a melt layer. Because of the special geometry of the capsule, the filling is released gradually and in a directed manner, which makes it easier to mix and evenly distribute the dopant in the melt volume.

Preferred embodiments of the invention are described in the attached claims.

A distinction is made between two aspects of the idea, a chemical and a physical, each contributing to the creation of the general encapsulation model. Taking into account the chemistry of the process, it will be optimal

Capsules are used, which are made of the same material as the treated one

Melt, either directly a doping element (or several elements) or its

Alloy used with the melt material as dopants. Under these conditions, the destruction of the capsule walls takes place by itself as a result of the melting of the crystal substance in its own melt, and a doping element is spread in the melting volume in response to mixing or dilution.

The physical requirements for the capsule are as follows: the weight of the capsule should be greater than its (Archimedean) buoyancy; a capsule wall should have some weak point which should open in front of the main part of the capsule, thus creating an extended and directed "ejection" of dopant into the melt.

The design of the capsules shown in Fig. 1 meets these requirements. The first requirement is taken into account by setting (adjusting) three values, namely the inner volume of a capsule, the filling weight and the change in density in the melt that occurs during solidification, and the second requirement is met by the presence of a thin-walled projection the ends of the capsule.

The doping process is very simple and consists in throwing a capsule 2, which has a jacket of the same composition [L] as the melt (FIG. 2), into a bath 1 filled with melt (L). The capsule is filled with the compound AL, where A is a doping element. Since the capsule has a higher density than the melt, it sinks to the bottom, where the thin-walled projection melts earlier than the middle part, which creates the conditions for a gradual escape of element A into the melt. In the case of gases, dopants are also used in condensed form, but the mechanism of the method has some differences here, which are taken into account in the description of the preferred embodiments.

The described method for doping melts with capsules is characterized by a number of advantages: sterile doping conditions (a dopant is sealed in a hermetically sealed container)

Packaging kept under vacuum and only released under a melt layer);

Availability of an additional background for the even distribution of the

Melt (approximation between the density of a doping element and that of a melt due to the use of AL compounds, slow release of a dopant into the melt due to the capsule design);

Uniformity of the doping process for different melts, readiness of the method for standardization of the doped product; technical simplicity of the procedure for the user. Description of the preferred embodiments.

The technology of doping melts using metal capsules has two main factors: filling a dopant and sealing the capsule under vacuum; defining the geometric parameters of a capsule in each specific case of doping.

Both points are dealt with in more detail below.

1. Close the capsules.

This process is based on the known technical solutions (see, for example, K.A. Chuntonov et al. J. Less-Comm. Met., 1982, Vol. 83, 143). A capsule is filled with a dopant (Fig. 3a), connected to a vacuum system, pumped out, a thin-walled tubular projection (Fig. 3b) is flattened, and without stopping the pumping out the sealing of the capsule in the case of refractory metals in one Short circuit system or in the case of deformable metals, such as Aluminum, copper etc., carried out by pressure welding. The sequence of operations is shown for the first sealing variant in the series of figures A-1, A-2 and A-3. The final product is shown in Fig. 3c.

2. Geometry of the capsules.

The problem of defining the useful volume of a capsule in the case of a cylinder is reduced to defining the diameter of the inner channel of a capsule d with a fixed outer diameter of a capsule D. Based on the balance of three forces, the weight of the capsule, the weight of the filling and the Buoyancy, we achieve the following solution to the problem in dimensionless form:

where pι the density of the melt, p the density of the same melt in the solid state, pj the density of the dopant, k a packing factor of the inner channel of the capsule, corresponding to the ratio of the filling volume to the total volume of the channel, c the buoyancy coefficient, corresponding to the ratio of the weight of one filled capsule for Buoyancy, where the capsule floats when c = 1, propels the capsule to the surface when c <1, the capsule sinks when c> 1.

It can be seen from the formula given above that the more the volume of the melt decreases during solidification, the more effective the process, and it can also be seen that in practice it is more advantageous to use dopants of high density p _d and that To infect the interior volume to the maximum with the doping material.

Brief description of the drawings.

Fig. 1. Design of the capsules: a - one-piece capsule (1 - capsule body or jacket, 2 - inner channel, 3 - thin-walled projection, 4 - filling); b - two-part capsule (1 - countersunk, 2 - metal ampoule, 3 - filling).

Fig. 2. Doping process:

1 - bath with melt (L), 2 - capsule [L] with AL filling.

Fig. 3. Vacuum sealing the capsules: a - initial state, b - flattening the walls of the projection, sealed capsule.

Example 1.

Fe ₂ N powder, which dissolves at 200 ° C to produce gaseous nitrogen, is selected for nitriding molten steel. In this case, a capsule is made of the same steel as that which is being treated. Since pL ps ~ 0.95, pd / ps ~ 0.81 in the example under consideration, we obtain assuming k = 0.8 and c = 1.03 d / D ~ 0.25.

For the convenience of filling a capsule with powder, a steel tube with an inner diameter of 20 mm is taken (type b in Fig. 1) and then the outer diameter of a countersunk body is defined as 80 mm.

After sealing one of the ends of the pipe, a steel plug made of waste (casing) is pressed into the sealed part, then the pipe is filled with Fe N powder, the second end is also closed with a plug made of steel wire or waste, which Pipe is inserted into a sinker, a free one The end is connected to a vacuum system, the inner volume is pumped out, and the capsule is finally closed.

If the capsule is thrown into molten steel, the protruding end of the tube is heated faster than the main part of the capsule. When the temperature at both ends of the tube reaches ~ 900 ° C, gaseous nitrogen, the pressure of which at this point reaches several atmospheres, breaks up the tube wall and the gas begins to flow (with thin jets of gas) into the melt, causing it penetrates through grooves and pores of the internal steel plugs.

A capsule of the type described can produce 15 to 20 volumes of molecular nitrogen per unit of its volume.

Example 2.

Molten steel with sodium can be doped in metal form for the purpose of deoxidation and not with the help of a precursor. For this, a steel capsule (type a in Fig. 1) is filled with sodium. In this case pd / ps ~ 0 _. 1, k = 0.9, and assuming c = 1.02, we get d / D ~ 0.19. This means that each volume unit of the capsule releases 3.5% by volume of metallic sodium into the melt. As with the nitriding of steel (see example 1), sodium begins to penetrate into the melt in the form of metal vapor at temperatures of 900 to 1000 ° C.

Example 3. •

Al-32 at% Li is used to dope aluminum with a eutectic lithium alloy. Its liquidus point is lower than the melting point of pure aluminum. A cylindrical block of the mentioned composition, which has a diameter which corresponds to the diameter of the inner channel of a capsule, is filled into a capsule (type a in Fig. 1), the latter is pumped out and sealed by means of a printing process, i.e. a protrusion is strongly flattened and cut off during pumping out. The diameter of the inner channel is drilled according to d / D ~ 0.55 (pi ps ~ 0.93, pd / ps ~ 0.92, c = 1.02 and k = 0.9). According to the amount of lithium contained, such capsules correspond to homogeneous blocks of the same volume, although they have an average concentration of 7 at% Li.

Claims

Expectations:

1. Means made of metal for doping a melt of a metal L with a dopant A, characterized in that the means has an interior which is hermetically sealed from the environment and contains the dopant A.

2. Agent according to claim 1, characterized in that it has a weak point, which melts when the agent is introduced into the molten metal L and at least partially releases the dopant A into the molten metal L before the agent melts as such.

3. Composition according to one of claims 1 or 2, characterized in that it is designed so that it has an overall density which is higher than that of the molten metal L.

4. Agent according to one of claims 1 or 3, characterized in that the dopant A is in the form of an alloy with the metal L.

5. Agent according to one of claims 1 to 4, characterized in that it has the shape of a capsule.

6. A method for doping a melt of a metal L by introducing a dopant A into the metal melt L, characterized in that the dopant A, enclosed in an agent made of the metal L according to one or more of claims 1 to 5, in the metal melt L is introduced.

7. A process for the preparation of the agent according to any one of claims 1 to 5, characterized in that the dopant A is filled into the agent under vacuum or inert gas.