JPS61284539A - Method for refining alloy to high purity - Google Patents

Abstract

PURPOSE:To rapidly refine an alloy to high purity in a high yield by holding the alloy at the solidus line temp. to the liquidus line temp., adding a refining agent to the alloy while agitating the alloy, and vigorously agitating the alloy to efficiently remove impurities from the alloy. CONSTITUTION:An alloy to be refined is held at the solidus line temp. to the liquidus line temp., and while the alloy is agitated, a refining agent such as Ca-CaF2 is added. The alloy is vigorously agitated by applying high or low frequency power or electromagnetic force or blowing gas, and slag is removed so that impurities do not return from the slag to the alloy. The above-mentioned refining may be repeatedly carried out. Impurity elements such as P, S and As in the alloy are efficiently removed and a high purity alloy is obtd. in a high yield.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention is applicable to alloys such as iron alloys, nickel alloys, chromium alloys, titanium alloys, manganese alloys (including pure metals thereof)
The present invention relates to an efficient refining method for removing impurities from and achieving high purity.

(Prior Art) Conventionally, methods implemented for removing impurities from alloys involve maintaining the alloy from which impurities are to be removed in a completely molten state in a refining vessel, i.e., maintaining the temperature above the melting point of the alloy. It is common to refine it by smelting it.

For example, the present inventors have proposed a method for removing impurity elements from metals or alloys using CaC2 (Japanese Patent Publication No. 59
-034767) or a method of refining hot metal using a refining agent mainly containing CaO (Japanese Patent Publication No. 58-01
However, the solubility of impurities in alloys is generally greater in liquid alloys than in solid alloys, and impurity elements are difficult to remove from an equilibrium perspective. Therefore, since the above method refines the alloy in a completely molten state, there is a natural limit to the efficiency of removing impurity elements.

On the other hand, since the removal of impurity elements from a solid state alloy utilizes the diffusion of the impurity elements in the alloy, it takes a long time to remove the impurity elements. - As an example, Cm
- A method of refining solid alloy grains with CaC22 or Ca-CaF27 lux (Japanese Unexamined Patent Publication No. 49-73321) is known. However, the process is too complex to rapidly refine alloys in large quantities.

Furthermore, an alloy refining method has already been reported that targets an alloy in a solid-liquid coexistence state, concentrates impurities into a liquid, and then separates the liquid alloy from the solid alloy (refining pie fractional solid alloy). Difficulty (A, L, Lux.

M. C. Flemings, ”Refining
by FractionalSoltdificat
1on'', Submitted to Met, B
, May+19781).

However, this method has a poor yield of purified solid alloys.
Furthermore, in order to improve the yield, the separated liquid alloy must be purified repeatedly, and the purification process is complicated, resulting in poor purification efficiency.

Furthermore, because no refining agent is used, even if a liquid with concentrated impurities is repeatedly refined, there will naturally be a difference in impurity concentration between the initially obtained solid alloy and the repeatedly refined solid alloy. , the impurity concentration of the obtained solid alloy gradually becomes high. On the other hand, a zone melting method has been known for a long time to produce alloys by utilizing the distribution of impurity elements between solid and liquid. However, the zone melting method has very poor productivity, cannot refine a large amount of alloy in a short time, and also leaves a large distribution of impurity elements inside the alloy. A portion must be removed, making the use of refined alloy extremely inefficient.

(Problems to be solved by the invention) The present inventors have solved the problem of impurity removal efficiency, long processing time,
As a result of various research efforts to solve the problems of conventional technology such as complicated processes and low productivity, we have invented a method to efficiently and quickly remove impurity elements from alloys. did.

(Means for solving the problem) The present invention maintains the temperature of an alloy from which impurity elements are to be removed below the liquidus temperature of the alloy and above the solidus temperature of the alloy, and while stirring the alloy. The purpose is to remove impurities in the alloy by adding and mixing a refining agent and stirring vigorously.

That is, the present invention allows a solid alloy and a liquid alloy to coexist, first concentrates impurities in the liquid alloy by utilizing solid-liquid distribution, and then utilizes a chemical reaction by using a refining agent. Since only the impurity elements concentrated in the liquid alloy are transferred to the refining agent, the loss of the alloy is extremely small, the refining effect is large, and the process is simple.

The present invention will be explained below.

Generally, impurity elements (silica, sulfur, arsenic, etc.) contained in alloys such as F@-based, Nl-based, and Cr-based alloys must be reduced as much as possible since they significantly impede the mechanical properties of the alloy. When an alloy with an average impurity element concentration P0 in the entire liquid is held between the liquidus temperature (TL) and the solidus temperature (T8) of the alloy, a solid alloy with a low impurity element concentration will crystallize in the liquid metal. do. This is schematically shown in Figure 1).

On the other hand, the concentration of impurity elements in the liquid alloy becomes high because the impurity elements discharged from the solid alloy are concentrated. Therefore,
When this liquid alloy with a high impurity concentration is reacted with a refining agent, even if the refining agent has only the refining ability up to the P0 level shown in FIG. 1<=), impurities can be removed to PR on average. Therefore, the impurity removal rate per unit refining agent υ is greatly improved.

In order to purify an alloy, the present invention maintains the temperature of the alloy to be refined below the liquidus temperature of the alloy and above the solidus temperature, stirs the alloy, and refines the alloy. This method is characterized in that impurity elements in the alloy are removed by adding and mixing additives and vigorously stirring the mixture. This will be explained in detail below.

When the alloy temperature (TR) is between TL and T, the impurity removal rate is much improved by υ compared to when the alloy temperature is T or higher. Such coexistence of solid and liquid alloys can only be achieved by maintaining the temperature of the alloy to be refined below the liquidus temperature of the alloy and above the solidus temperature of the alloy.

When refining an alloy in this state, stirring of the alloy is very important. In other words, the higher the refining temperature, the greater the chemical reaction rate or the mass transfer rate of impurities in the alloy.
This is advantageous because the time required to remove impurities is short. However, the refining temperature TR in the present invention is TL>TR>T
Since the refining temperature is in the range of s, the refining temperature is lower than that of ordinary alloys, and the reaction rate is slow as shown in Figure 2. However, by stirring the alloy and bringing it into active contact with the refining agent, the rate of impurity removal is greatly improved.

Furthermore, in refining the alloy in which a solid alloy and a liquid alloy coexist, it is preferable that the temperature of the alloy in the refining vessel be as uniform as possible.

If the temperature of the alloy is non-uniform, the alloy will solidify locally, reducing refining efficiency. Therefore, stirring the alloy is very effective in maintaining the temperature of the alloy uniformly within the specified range.

The most effective methods of stirring used according to the method of the present invention are stirring using high frequency, stirring using low frequency, and stirring using electromagnetic force. Stirring may also be used.

In carrying out the method of the present invention, various heating methods can be used to maintain the alloy temperature constant.

By repeatedly carrying out the method of the present invention on the alloy to be refined, an alloy with higher purity can be obtained.

In this case, it is preferable to exclude the slag after the second refining.

The method of the invention can also be carried out under reduced pressure or high vacuum.

After the alloy is highly purified according to the method of the present invention, it may be immediately cast into a target mold, or it may be reheated to raise the alloy temperature above the TL of the alloy before proceeding to the next step. You may let them. In this case, the slag used for refining in the refining vessel is preferably removed so that impurities from the slag do not return to the alloy.

Here, it is preferable to experimentally measure the liquidus temperature TL and solidus temperature T8 of the alloy in advance. Furthermore, if the phase diagram of the alloy is known, from that phase diagram TL and T,
can be read and used.

Note that the method of the present invention can also be used to remove impurities from pure metals. However, in the case of pure metals, TL and T must be equal values, and the melting point is expressed. In this case, it is preferable to maintain the temperature of the metal to be refined at the melting point of the metal, but by keeping it within 3 to 5 degrees Celsius above or below the melting point of the metal, it is possible to have a solid phase and a liquid phase coexist. can be done. In this case, it is preferable to pass the melting point more frequently.

(Example) Next, examples of the present invention will be shown.

Example 1 An alloy of 30 to 9 having the following composition was melted in a low frequency heating furnace and refined using the following refining agent.

Example 2 Alloy 30 with composition 20%Cr -10% N1-F'e
Changes in phosphorus concentration in the alloy over time were measured when the alloy was refined in a low frequency heating furnace and in a resistance heating furnace in an argon atmosphere using Ca-CaF2 as a refining agent. Figure 2 shows the results, and shows the method of the present invention (TL
) 1445℃>T, line ■ in Figure 2) is another method [low frequency heating furnace (low frequency stirring) TR > TL (line ■ in Figure 2)]
and [Resistance heating furnace (no stirring) TL) 1445°C>'
rs (line 111 in FIG. 2)) It is clearly recognized that dephosphorization is carried out in a short time compared to K.

Example 3 30 to 9 of the following metals were melted in a low frequency heating furnace and refined using the following refining agent.

(Effects of the Invention) As is clear from the above explanation, the method of the present invention exhibits a far superior dephosphorizing effect compared to the conventional method.

[Brief explanation of drawings]

Figure 1 (,) is an explanatory diagram showing the concentration distribution of impurity elements in the solid-liquid coexistence region of the alloy, Figure 1 (b) is its schematic diagram, and Figure 2
The figure shows the change in phosphorus concentration over time in the method of the present invention and a comparative example, and FIG. 3 is a phase diagram of the AB binary alloy. Fig. 1 Fig. 2 fil @ square gq FgI (min) - 溌 phase thread spring one hundred hundred foot spring i degree C

Claims (1)

[Claims] When purifying an alloy, the temperature of the alloy to be refined is kept below the liquidus temperature and above the solidus temperature of the alloy, and the alloy is stirred and a refining agent is added and mixed to strengthen it. A refining method for high purification of an alloy, characterized by removing impurity elements in the alloy by stirring.