JPH06238424A - Method for casting active metal alloy of high melting point - Google Patents

Abstract

PURPOSE:To provide a large-sized alloy ingot which dispenses with the complicated control, and is excellent in the uniformity and the crystallization of the alloy composition. CONSTITUTION:The casting method of the alloy ingot is disclosed where a cooled conductive mold is used and the active metal of high melting point is based. The casting method of the active metallic alloy of high melting point includes the process to melt and stir the metal in a mold by making use of the dielectric heating and the dielectric stirring by the high frequency magnetic field, the process to cool the whole molten metal to the temperature below the melting point and to solidify the alloy, the process to draw the solidified alloy by the prescribed amount and to form the ingot composed of the alloy, and the process to supply into the mold the metallic material whose quantity is equivalent to the weight of the ingot drawn by the prescribed amount, and a large-sized alloy ingot is provided by repeating the series of the processes at least two or more times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting an alloy ingot based on a high melting point active metal such as titanium, zirconium, vanadium, molybdenum and niobium, and more particularly to a method for casting an alloy ingot using a cold crucible. It is about.

[0002]

2. Description of the Related Art In order to industrially melt and cast a high melting point active metal represented by titanium or the like, for example, (1) a consumable electrode type vacuum arc melting (VAR) method, (2) a plasma arc melting method, ( 3) Methods such as electron beam (BE) melting have been used.

Although the above-mentioned conventional melting methods each have a slight difference in their characteristics, they generally adopt a multiple melting system. Especially when casting an alloy ingot based on a high melting point active metal, In order to make the components uniform, we have adopted a system in which melting and casting are repeated.

Nevertheless, the alloy components of the alloy ingot obtained by using these melting methods are not always uniform, and it has been difficult to obtain a good quality ingot. This is because the conventional melting method had almost no effect of stirring the melted alloy material.

Therefore, a dielectric heating melting method has been newly developed in which the effects of shape control, induction heating, and induction stirring can be expected sufficiently by a high frequency magnetic field.

It is expected that this dielectric heating melting method will compete with the most predominant consumable electrode type vacuum arc melting (VAR) method in the near future, and research and development for improving its performance are actively pursued. There is.

As a typical induction heating melting method,
(1) Induct slag melting method, (2) induction skull melting method, (3) cold crucible melting method and the like.

[0008]

The induct slag melting method is characterized in that a slag of calcium fluoride (CaF) is provided in a water-cooled copper mold, and this slag relaxes the drawing resistance between the mold and the ingot. is doing.

According to this induct slag melting method, it is possible to cast a large-sized (50 kg / charge or more) ingot, but it is difficult to avoid contamination from the slag and there is a problem in the quality of the ingot.

In addition, in the induction skull melting method, the alloy material is melted on the skull at the bottom of the furnace without using slag,
This is a method in which the furnace itself is tilted to pour the contents into the mold, and while it is possible to obtain good quality, it was not possible to cast a large ingot.

The cold crucible dissolution method, which has been developed to eliminate the above-mentioned drawbacks of the two dissolution methods, is
By melting, casting, drawing, and adding raw materials simultaneously while controlling them with electromagnetic force, it is intended to obtain a large-sized ingot of high quality.

However, the cold crucible melting method has a problem that the control operation becomes complicated because the power source factor, the extraction factor, the raw material addition factor, etc. that determine the electromagnetic force interact with each other.

Further, since the ingot is continuously pulled out under an unsteady state in which a molten state expanded at a very high temperature and a solidified state contracted by cooling coexist in the mold, the mold is continuously extracted. There is a problem that the drawing balance is easily lost at the contact portion between the ingot and the ingot, and surface defects such as solidification cracks are likely to occur on the ingot surface.

The present invention solves the above-mentioned problems of the induction heating melting method and utilizes cold crucible to obtain a large alloy ingot which does not require complicated control and is excellent in alloy component uniformity. An object of the present invention is to provide a method for casting a high melting point active metal alloy that can be used.

[0015]

SUMMARY OF THE INVENTION The present invention provides a method for casting an ingot of a refractory active metal based alloy using a cooled conductive mold.

In the method of casting a high melting point active metal alloy according to the present invention, the first step and the first step of melting and stirring the metal material in the mold utilizing induction heating and induction stirring by a high frequency magnetic field. After that, a second step of cooling the entire melted metal material below the melting point to solidify the alloy, and after the second step, a predetermined amount of the solidified alloy is drawn out and a third ingot of the alloy is cast. And a fourth step of, after the third step, introducing a metal material in an amount corresponding to the mass of the ingot pulled out by a predetermined amount into the mold,
It is characterized in that a series of steps up to the first, second, third and fourth steps are repeated at least twice.

In the present specification, the "high melting point active metal" has a melting point of 1500 to 3000 ° C., and easily reacts with gas components such as oxygen and nitrogen in the atmosphere at high temperature, and also in vacuum. Purity is significantly reduced by causing a reduction reaction with refractory materials stable at high temperatures, such as alumina (Al ₂ O ₃ ) and silica (SiO ₂ ),
It can be defined as a metal that has a property that the characteristics inherent to the metal are significantly deteriorated.

The high melting point active metal in the present invention includes
Representative examples include titanium (Ti), zirconium (Zr), vanadium (V), molybdenum (Mo), niobium (Nb), and the like.

In the present invention, the alloy based on the high melting point active metal is, for example, 90 wt% Ti-6.
wt% Al-4 wt% V, 76 wt% Ti-15 wt%
V-3wt% Cr-3wt% Sn-3wt% Al, 75
wt% Ti-3 wt% Al-8 wt% V-6 wt% Cr
-4 wt% Mo-4 wt% Zr, 73 wt% Ti-13
wt% V-11 wt% Cr-3 wt% Al, 64 wt%
Ti-36 wt% Al, 46 wt% Ti-54 wt% N
Alloys such as i and 34 wt% Ti-66 wt% Nb can be preferably mentioned.

In the present invention, as the cooled conductive mold, a cylindrical water-cooled copper mold having vertical strips (see FIG. 2) as shown in the following examples can be preferably used.

Further, in the present invention, the high frequency magnetic field can be easily realized by the high frequency coil arranged around the above-mentioned mold.

In the present invention, when the solidified alloy is drawn in the third step, at least 1/10 or more of the drawn ingot is melted again together with the metallic material charged in the fourth step. It is important to properly set the predetermined amount of withdrawal in advance. This is 1/10 from the upper end of the cooled and solidified ingot in the second step.
This is because casting defects such as surface solidification cracks and solidification shrinkage holes that occur during solidification are likely to occur in the above parts, and it is necessary to dissolve these parts again to eliminate the defects.

In the third step, it is preferable that the predetermined amount for pulling down the solidified alloy is set to 1/2 or less of the inner diameter of the conductive mold. If the predetermined amount to be pulled out is set as above, at least 1/10 or more of the ingot is melted again together with the metal material put in in the fourth step, so that a large ingot with few surface defects such as solidification cracks can be obtained. Can be formed.

Further, in the present invention, in the first step, the time period for melting and stirring the metal material is 10 seconds or more, and in the second step, the time period for cooling the entire melted metal material to the melting point or less is 10 seconds or more. It is preferable that the time is at least seconds. Here, it is preferable that the time period for melting and stirring is 10 seconds or more. If the time period is less than 10 seconds, for example, when alloying elements such as Al and V are added to titanium (Ti), molten metal is This is because the alloy element components added in the ingot are segregated due to insufficient stirring.

Further, it is preferable that the time period for cooling the entire melted metal material to be equal to or lower than the melting point is 10 seconds or longer. When the time is less than 10 seconds, the induced current applied to the molten metal sharply decreases and the melted metal is melted. The balance of the conductive mold,
This is because the molten metal adheres particularly between the strips of the conductive mold, making it impossible to pull out a predetermined amount of the ingot in the third step.

[0026]

The operation mechanism of the method for casting a high melting point active metal alloy according to the present invention will be described in the order of steps with reference to FIG.

In the method of casting a high melting point active metal alloy according to the present invention, as shown in FIG. 3 (a), a cylindrical conductive mold having strips in the vertical direction is used. Add metal. Next, as shown in FIG. 3B, the metal material is melted and stirred in the mold using induction heating and induction stirring by a high frequency magnetic field.
This makes it possible to eliminate the unmelted residue of the metal material and to uniformly mix the alloy components. Next, as shown in FIG. 3C, the entire melted metal material is once cooled to the melting point or lower to solidify the alloy. Further, as shown in FIG. 3D, the solidified alloy is drawn out by a predetermined amount and an ingot made of the alloy is cast. After that, a metal material in an amount corresponding to the ingot pulled out by a predetermined amount is put into the conductive mold.

As described above, in the present invention, the steps of melting, casting, drawing, and adding raw materials are not all performed simultaneously as in the prior art, but the steps of melting, casting, cooling, drawing, and adding raw materials are sequentially performed. It is carried out intermittently with time differences.

Thus, in the method for casting a high melting point active metal alloy according to the present invention, the ingot drawing step is not under the unsteady state in which the molten state and the solidified state coexist as in the conventional case, but the shrinkage after cooling and solidification. It will be carried out stably under the steady state. Therefore, the resistance of the contact portion between the mold and the ingot can be suppressed to be small, and the drawing can be made much easier than in the past. Therefore, the occurrence of surface defects such as solidification cracks on the surface of the cast ingot is significantly suppressed.

Further, in the method for casting a high melting point active metal alloy according to the present invention, since no slag or the like is used, the risk of contaminating the ingot is extremely small.

Further, in the method for casting a high melting point active metal alloy according to the present invention, after the metal material is re-introduced after the drawing step,
Since the alloy is solidified, part of the metal material that was thrown in when melting the metal material does not remain unmelted as in the past, and the part of the extracted ingot and the metal material that was put in are efficiently It will blend well. Therefore,
It is possible to continuously cast a good quality ingot having a fine casting structure and having extremely little segregation of alloy components.

Further, in the present invention, melting is performed by electromagnetic force,
Since only the stirring needs to be controlled, the control operation can be simplified compared to the conventional case.

[0033]

【Example】

 Examples Hereinafter, examples based on the present invention will be described.

FIG. 1 is a sectional view showing the structure of the casting apparatus used in this embodiment, and FIG. 2 is a partially cutaway perspective view of the cylindrical water-cooled copper mold shown in FIG.

Here, the structure of the casting apparatus will be briefly described. Referring to FIGS. 1 and 2, a cylindrical water-cooled copper mold 6 is provided in a vacuum chamber 1 having an exhaust port 3 and a gas supply port 4 and having an optical window. A raw material charging chamber 2 for charging a molten raw material into the mold 6 is inserted in the vacuum chamber 1.

As shown in FIG. 2, an upper portion of a cylindrical water-cooled copper mold 6 provided with a plurality of slits 9 in the vertical direction,
The melting furnace 5 is composed of the high-frequency coil 7 provided around it. The melting raw material charged in the melting furnace 5 is melted, and the melted raw material 11 has a dome shape. Further, the melted raw material 11 is gradually cooled below the mold 6.
In order to draw out the ingot 12 solidified by cooling as an ingot, a drawing rod 10 is inserted from below into the mold 6. A pull-out roller 8 is installed to adjust the pull-out of the pull-out rod 10.

A titanium alloy (75 wt% Ti-3 wt) was used by using the casting apparatus equipped with the cylindrical water-cooled copper mold as described above.
% Al-8 wt% V-6 wt% Cr-4 wt% Mo-4
wt% Zr) Ingot shall be cast.

For the melting raw material, pure JIS sponge titanium of JIS standard 2 is used as the main raw material, and flaky (50 mm under) Al alloy, flaky or pelletized Mo, Cr, and Zr are added as the raw material. did.

In this example, operating parameters were determined from the mathematical model as shown in Table 1.

[0040]

[Table 1]

After the above-mentioned melting raw material is charged into the melting furnace 5 from the raw material charging chamber 2, the vacuum chamber 1 is evacuated to a pressure of 0.01 Torr by a vacuum exhaust device (not shown). Then, the vacuum chamber 1 is filled with argon gas from the gas supply port 4, and the pressure inside the vacuum chamber 1 is set to 100 To.
The atmosphere was adjusted to rr. Next, the melting raw material introduced by the induction power from the high frequency coil 7 was heated and melted. After the molten raw material was raised in a dome shape, it was cooled and cast, and the ingot was pulled out below the mold 6. further,
After withdrawing the ingot, a molten raw material having a mass corresponding to the withdrawn ingot was re-input.

In this embodiment, the melting step, the cooling casting step,
A series of steps including a drawing step and a raw material adding step was set as one cycle, and 12 cycles were performed at a rate of about 10 minutes per cycle to cast an alloy ingot.

Example 1 The amount of drawing is equal to the inner diameter of the cylindrical water-cooled copper mold 6 150
Finally, an alloy ingot having a weight of 150 kg was cast.

Example 2 An alloy ingot having a weight of 75 kg was finally cast by setting the amount of drawing to 75 cm, which corresponds to one half of the inner diameter of the cylindrical water-cooled copper mold 6.

Comparative Example A titanium alloy ingot was cast using a casting apparatus equipped with a cylindrical water-cooled copper mold similar to the above-mentioned examples.

However, in the comparative example, the operating parameters were determined from the mathematical model as shown in Table 2, and the melting, casting, raw material addition, and continuous drawing of the ingot of the alloy material were carried out simultaneously according to the ordinary cold crucible melting method. I decided to do it.

[0047]

[Table 2]

Example 1 Drawing speed 15 mm / min, raw material addition speed 1.25 kg
/ Minute, the required time is about 120 minutes, and the final weight is 15
A 0 kg alloy ingot was cast.

Example 2 Extraction rate 7.5 mm / min, raw material addition rate 0.625 k
g / min, the required time is about 120 minutes, and the final weight is 7
A 5 kg alloy ingot was cast.

Conventional Example In the conventional example, the known consumable electrode type vacuum arc melting (VA) is used.
R) method, using a double melting system, diameter 150 m
A titanium alloy ingot weighing m and weighing 75 kg was cast.

The solidification cracks, blowholes, and unmelted residue were evaluated as the surface properties of the alloy ingots obtained in each of the examples, comparative examples, and conventional examples, and the results are shown in Table 3.

[0052]

[Table 3]

Further, solidification shrinkage holes and component segregation were evaluated as internal qualities of the alloy ingots obtained in each of Examples, Comparative Examples and Conventional Examples, and the results are shown in Table 4. However, regarding the component segregation, the results obtained by sampling the obtained alloy ingot in the radial direction and the longitudinal direction of the central portion at intervals of 20 mm and analyzing the results are evaluated by the segregation rate (maximum analysis value / average analysis value). And

[0054]

[Table 4]

As is clear from the results shown in Table 3, the alloy ingots obtained in Examples 1 and 2 of the example have solidification cracks and cracks on the surface as compared with the alloy ingots obtained in Examples 1 and 2 of the comparative example. It was found that there was no unmelted residue and the like, and the surface properties were extremely excellent. It is considered that this is because the contact resistance between the mold and the ingot was suppressed to be small in the drawing step in this example.

Further, as is clear from the results in Table 4, in the alloy ingot obtained in this example, the segregation rate of alloy components is higher than in the alloy ingot of the conventional example obtained by the conventional method having no stirring effect. It is needless to say that the segregation rate is further increased in both the radial direction and the longitudinal direction of the central portion of the alloy ingot of the comparative example obtained by continuous drawing using a cylindrical water-cooled copper mold. It turned out to be kept small. From this, it was found that in this example, a large ingot with less segregation of alloy components and excellent internal quality was obtained.

Further, comparing Example 1 and Example 2 in Example, ingot 2 of higher quality than Example 1 is obtained in Example 2 in which the amount of drawn molten material after cooling and casting is half the inner diameter of the mold 6. Was obtained.

[0058]

According to the casting method for a high melting point active metal alloy according to the present invention, a high quality and large size alloy made of an alloy based on a high melting point active metal such as titanium having high purity and excellent alloy component uniformity and crystallinity is used. The ingot can be manufactured stably. Therefore, according to the present invention, the production capacity of the high melting point active metal alloy can be expanded and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a casting apparatus used in an example according to the present invention.

FIG. 2 is a partially cutaway perspective view of the cylindrical water-cooled copper mold shown in FIG.

FIG. 3 is a schematic view showing a casting method according to the present invention in the order of steps.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Raw material input chamber 3 Exhaust port 4 Gas supply port 5 Melting furnace 6 Water-cooled copper mold 7 High frequency coil 8 Extraction roller 10 Extraction rod 11 Melted raw material 12 Solidified raw material Shows the part.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H05B 6/10 371 8915-3K

Claims (3)

[Claims] 1. A method for casting an ingot made of an alloy based on a high melting point active metal using a cooled cylindrical conductive mold having strips in the vertical direction, wherein a high frequency magnetic field is applied in the mold. A first step of melting and stirring a metal material using dielectric heating and dielectric stirring, and a second step of cooling the entire melted metal material to a temperature below its melting point to solidify an alloy after the first step. And, after the second step, withdrawing the solidified alloy by a predetermined amount,
A third step of casting an ingot made of an alloy, and a fourth step of, after the third step, introducing a metal material in an amount corresponding to the mass of the ingot extracted by the predetermined amount into the mold, A method for casting a high melting point active metal alloy, characterized in that a series of steps leading to the first, second, third and fourth steps are repeated at least twice. 2. The height according to claim 1, wherein in the third step, a predetermined amount for drawing out the solidified alloy is set to a length of 1/2 or less of an inner diameter of the mold. Casting method for melting point active metal alloy. 3. In the first step, the time period for melting and stirring the metal material is 10 seconds or more, and in the second step, the time period for cooling the entire melted metal material to the melting point or less is 10 seconds or more. The method for casting a high melting point active metal alloy according to claim 1, wherein the casting time is at least 2 seconds.