JP4704797B2 - Method for producing long ingot of active refractory metal-containing alloy by plasma arc melting - Google Patents

Description

  The present invention relates to a method for producing a long ingot of an alloy containing an active refractory metal such as titanium or zirconium by a plasma arc melting method in an argon atmosphere.

  Conventionally, various titanium alloys containing active refractory metals such as titanium and zirconium, and alloys having excellent practicality such as zircaloy are agglomerated by vacuum arc melting, cold crucible induction melting, electron beam melting or plasma arc melting. Manufactured.

  The above-mentioned vacuum arc melting method is a method in which an alloy rod-shaped body of a predetermined component is used as a consumable electrode and gradually melts and solidifies in a vacuum, but when melting an alloy with a large melting point difference between the alloy components, a low melting point is used. The component falling tends to be an ingot with component segregation preceding the melting of the high melting point component. For example, when a TiAl-based intermetallic compound having a high aluminum content is melted, low melting point aluminum is first melted down, so that the consumable electrode itself is insufficient in mechanical strength due to excessive titanium and falls undissolved. As a result, there is a fatal problem that both metal components are melted without being mixed, and only ingots with large component segregation can be obtained with insufficient alloying.

  The cold crucible induction melting is a method of using a water-cooled copper crucible equipped with a high frequency coil and melting raw materials in a crucible in a vacuum or an inert gas atmosphere. This method can form a homogeneous molten metal bath in the crucible even with a metal component having a high melting point difference, but in the case of an alloy containing a metal element having a high melting point and a high specific gravity such as Mo, W, Nb, Ta, etc. There is a risk that the constituent elements remain undissolved in the product ingot.

Moreover, the said electron beam melting | dissolving method can use a dish-shaped melting | dissolving container (hearth) normally, and can fully alloy a molten metal in the inside. However, as long as Hearth is used, the volume of the molten metal region is small compared to the entire target ingot, so there is a restriction that the compounding material must be prepared in a fine size corresponding to it, and the alloy components are homogeneous There is a difficulty in manufacturing a simple ingot. Further, since this method is performed under a high vacuum, there is a problem that alloy components such as aluminum and tin tend to evaporate, and the component composition of the ingot tends to fluctuate.
On the other hand, the plasma arc melting method can sufficiently alloy the molten metal in the hearth and produce an ingot with little segregation in the shallow molten pool in the hearth. Limited. In addition, as long as the hearth is used, it is very difficult to produce a long ingot having a height with respect to the diameter of 1.5 or more. However, it has already been put into practical use to produce a long ingot by the plasma arc melting method by continuous casting in which the solidified portion is drawn downward while supplying the raw material prepared in a fine granule to the molten metal pool. However, in this method, the metal element having a high melting point and a high specific gravity remains undissolved and remains in the ingot, and the production is unstable.
In addition, in the case of this plasma arc melting method, when argon gas constituting the high-pressure atmosphere in the chamber is caught in the ingot, it becomes difficult to produce an ingot having a uniform mechanical characteristic including a void of several μm. Therefore, it is necessary to reduce the pressure in the chamber. The following Patent Document 1 discloses a method of melting a titanium-based alloy by plasma arc melting and a method of performing it under normal pressure or reduced pressure, and by implementing plasma arc melting twice, raw material procurement Convenient. However, although this method is intended to produce an ingot of a titanium base alloy having a low impurity level, it eliminates fine pores of several μ level inside the ingot and requires highly stable mechanical characteristics. It is not satisfactory as a method for producing a long ingot of titanium alloy.
Patent Documents 2 and 3 below disclose a method in which plasma arc melting is performed under a wide range of atmospheric pressures ranging from low pressure to high pressure such as 0.3 to 10 atmospheres or 0.5 to 10 atmospheres. However, Patent Document 2 is intended to manufacture a vacuum plating vapor deposition source with a small gas component content, and is not a technique suitable for a long ingot. Patent Document 3 discloses that a rare earth element-containing alloy can be produced by continuous casting, but is a method of supplying raw materials in a granular form, and does not necessarily produce a high-quality ingot without void defects. .
Sho 57-145946 Sho 56-13477 Sho 55-28361

  The present invention relates to an alloy containing an active refractory metal element such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Y or a rare earth element as an alloy component by plasma arc melting. It is a method for manufacturing a long ingot, and an object is to reliably prevent the occurrence of component segregation and shrinkage cavities and void defects in the central portion.

In order to solve the above problems, the present invention
(1) A raw material rod made of an active refractory metal-containing alloy previously prepared by melting is melted by a plasma arc in an argon gas atmosphere of 30 Torr to 200 Torr, and the molten metal pool is held in a water-cooled copper crucible. while cooling and solidifying while resulting stirring flow in the rotational direction to the molten metal pool by energizing a direct current to coils which are mounted on the outer circumference of the water-cooled copper crucible, a movable bottom plate of the copper crucible per minute 50mm following speed A method for producing a long ingot of an active refractory metal-containing alloy by plasma arc melting, characterized by being drawn downward;
(2) The active refractory metal by plasma arc melting according to claim 1, wherein the active refractory metal is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Y or a rare earth element. A method for producing a long ingot of a contained alloy,
(3) The raw material rod made of an active refractory metal-containing alloy is prepared by melting and preparing in advance by a cold crucible induction melting method, a vacuum arc melting method, an electron beam melting method or a plasma arc melting method. A method for producing a long ingot of an active refractory metal-containing alloy by plasma arc melting of
(4) The active refractory metal-containing alloy by plasma arc melting according to claim 1, 2 or 3, wherein the production object is a long ingot having a diameter or a ratio of the height to the length of one side of 1.5 or more. Manufacturing method of long ingot,
(5) The long ingot of an active refractory metal-containing alloy by plasma arc melting according to claim 1, wherein the raw material rod is fed forward toward the plasma arc while rotating around its long axis. Manufacturing method.

In the present invention, when melting a long ingot of an active refractory metal-containing alloy by plasma arc melting, the pressure of the argon gas atmosphere is set in the range of 30 Torr to 200 Torr, and the core mounted on the outer periphery of the water-cooled copper crucible is used . In order to control the pulling speed of the ingot, which is solidified by cooling while generating a stirring flow in the rotating direction in the molten metal pool by applying a direct current to the steel plate, under the condition of 50 mm / min or less. As a result, there is no solidification segregation or component segregation, and a sound high quality long ingot having no void in the center can be easily manufactured.

The present invention relates to a long ingot of alloys containing an active refractory metal element such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Y or rare earth as an alloy component. It is a manufacturing method. The most specific target alloys are TiAl-based alloys that are intermetallic compound alloys, and active high melting point metal-containing alloys such as NbTi, NiTi, VTiCr, Cr, or ZrAlCuNi alloys.

  And this invention aims at manufacture of the long ingot of the said alloy made into the column shape or prismatic shape whose ingot height is 1.5 times or more with respect to the diameter or length of one side of an ingot. .

  In order to carry out the present invention, first, raw materials prepared in the alloy composition of the target product ingot are melted to prepare a round bar shape. This raw material rod may be manufactured by any melting method, but it may be melted by any one of cold crucible induction melting, vacuum arc melting, electron beam melting or plasma arc melting.

  In the present invention, the raw material rod is melted into a long ingot by plasma arc melting. For this purpose, the plasma arc melting apparatus illustrated in FIGS. This device uses a water-cooled copper crucible (1) equipped with a high-frequency coil on the outer periphery, and in particular, a device designed so that its bottom plate (2) can be driven in the vertical direction. Moreover, the raw material feeder (4) which can mount the raw material rod (3) in the horizontal direction is designed to be able to drive the raw material rod (3) in the horizontal direction, and these devices are not shown in a vacuum chamber (not shown). It is installed inside. On the other hand, a plasma torch (5) is provided directly above the copper crucible (1), and the raw material bar (3) is melted using this as a heat source by converting the argon helium mixed gas supplied from above into plasma.

  In order to carry out plasma arc melting using the raw material rod with the above equipment, first, a plate-shaped starter plate (6) having the same composition as the raw material rod (3) is placed on the bottom plate in the copper crucible (1) ( 2) Place on top. Then, after evacuating the chamber, the argon helium mixed gas supplied to the plasma torch (5) is converted into plasma and dissolved in a state where argon gas is introduced and the chamber is always kept at 30 Torr to 200 Torr. Holds the plasma arc of the heat source.

  The reason why the present invention controls the atmosphere in the chamber to 30 Torr or more is to prevent the plasma arc from becoming unstable during the melting operation and being interrupted, thereby preventing the melting from being interrupted. Therefore, it is necessary to set the pressure to 30 Torr or more. However, when the atmosphere becomes 200 Torr or more, argon gas is engulfed in the ingot and many voids of several μm remain, and the homogeneous mechanical properties of the ingot are impaired. This is not preferable because of fear.

  With the above atmosphere maintained, the raw material feeder (4) is driven to move the raw material rod (3) horizontally, and the tip portion thereof is inserted into the plasma arc, so that the surface layer portion melts and drops. It falls and creates a molten metal pool in the copper crucible. If the raw material feeder (4) is designed so that it can be driven horizontally and at the same time the raw material rod (3) can rotate around its central axis, the raw material rod (3) can be uniformly and reliably as a whole in both operations. Can dissolve.

  A long ingot can be continuously produced by lowering the bottom plate (2) of the copper crucible (1) while melting the raw material rod (3) while the molten metal is placed. That is, by this pulling-down operation, the molten metal held in the copper crucible (1) is lowered into the crucible while gradually solidifying under the cooling action of the water-cooled copper crucible, and at the same time, changed into a solid state and ingot. The part which became becomes surely pulled down from the crucible and grows into a product ingot.

  The present invention is characterized in that the ingot drawing speed by lowering the bottom plate (2) of the copper crucible is controlled to 50 mm or less. Because this operation cools and melts the molten metal and draws it downward while solidifying, if the speed is too high, a portion of the molten metal may leak out of the crucible due to insufficient cooling, and therefore 50 mm per minute. Hereinafter, it is desirably controlled within a range of 20 mm or less per minute. However, since the productivity is hindered when the drawing speed is too low, it is preferable to maintain the drawing speed at 1 mm or more. Although it is conceivable that the ingot is directly water-cooled like continuous casting of aluminum or copper, the alloy containing the active refractory metal targeted by the present invention must be avoided from being oxidized. Therefore, it is indispensable to appropriately control the drawing speed according to the cooling situation.

On the other hand, the outer circumference of the copper crucible Yes equipped with coils, by energizing a direct current thereto, caused agitation flow in the rotational direction to the melt pool can uniformly heat supply into the mold, the withdrawal ingot The effect that the surface quality becomes constant can be expected.

The melting and drawing operation is continued in this way, and the ingot drawing operation is stopped when the raw material rod (3) supplied by the raw material feeder (4) reaches a predetermined position as shown in FIG. However, in the process of finishing the casting, an operation for reducing the amount of heat of the plasma arc in a stepwise manner is performed. By doing so, the final part of the ingot is gradually solidified, and it is possible to prevent the formation of shrinkage cavities in the ingot, and finally a continuous long ingot without solidification defects and component segregation is continuously produced. it can.
(Example)
As an example of the present invention, an ingot of TiAl-based (50/50 at%) intermetallic compound alloy having a diameter of 160 mm and a length of 600 mm to 700 mm was manufactured using the equipment of FIG. The equipment specifications and operating conditions at this time are as follows.

・ Power output: Up to 100kW
・ Operating current: 700-950A
・ Inner diameter of water-cooled copper crucible: 160mm
・ Water cooling capacity of water-cooled copper crucible: 100 L / min
・ Copper crucible bottom plate: Water-cooled copper bottom plate with pull-out mechanism ・ Plasma gas: Ar1-He5 mixed gas (flow rate: about 60 L / min)
・ Vacuum chamber: 2m ³
First, a TiAl-based metal raw material was melted by a cold crucible melting method to produce a round bar-shaped ingot having a diameter of 120 mm and a length of 1000 mm as a raw material rod, and this was mounted on a raw material feeder in a horizontal direction. In addition, a drawing start board was manufactured from a TiAl material having the same composition as that of the raw material rod and mounted on the drawing mechanism at the bottom of the crucible.
Then, after evacuating the vacuum chamber to 1 Torr with a booster pump, high-purity argon, up to 200 Torr in Example 1, up to 150 Torr in Example 2, up to 80 Torr in Example 3, up to 30 Torr in Example 4, respectively. Filled and replaced with inert gas atmosphere.
Next, the plasma torch was activated to generate a plasma arc with an argon-helium mixed gas, and while rotating the raw material rod, the tip portion was inserted by driving the raw material feeder. By this operation, the surface layer portion at the tip of the raw material rod was melted and dropped as a droplet to form a pool in the copper crucible. Simultaneously with this operation, the coil on the outer periphery of the copper crucible was energized to cause a stirring flow in the rotational direction in the pool, and even heat was supplied into the mold to control the surface quality of the ingot to be constant.
And in each Example, as shown in Table 1, the operation which pulls down a molten metal pool at the speed of 2-50 mm / min was implemented, and the long ingot of (phi) 160mm x 700Lmm was obtained.
On the other hand, for comparison, when the pressure in the vacuum chamber is 900 Torr and the extraction speed is 70 mm / min for comparison (Comparative Example 1), the pressure is 250 Torr and the extraction speed is 2 mm / min. The same melting was performed in the case of (Comparative Example 2), and also in the case of the same pressure of 80 Torr and the drawing speed of 2 mm / min (Comparative Example 3).
Table 1 shows the quality of each of the seven ingots. Thus, the fact that the melting effect according to the present invention is excellent can be well understood.

An outline of the plasma arc melting equipment is shown. Schematic which shows the condition at the time of casting by the said equipment.

(1) Water-cooled copper crucible (4) Raw material feeder (2) Crucible bottom board (5) Plasma torch (3) Raw material bar (6) Start board

Claims (5)

A raw material rod made of an active refractory metal-containing alloy prepared in advance is melted by a plasma arc in an argon gas atmosphere of 30 Torr to 200 Torr, and the molten metal pool is held in a water-cooled copper crucible. while cooling and solidifying while causing agitation flow in the rotational direction to the molten metal pool by energizing a direct current to coils that is provided on the outer periphery of the crucible, pulling down the movable bottom plate of the copper crucible per minute 50mm following speed A method for producing a long ingot of an active refractory metal-containing alloy by plasma arc melting.   The active refractory metal-containing alloy according to claim 1, wherein the active refractory metal is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Y, or a rare earth element. Manufacturing method of long ingot.   The plasma arc according to claim 1 or 2, wherein the raw material rod made of an active refractory metal-containing alloy is prepared in advance by a cold crucible induction melting method, a vacuum arc melting method, an electron beam melting method or a plasma arc melting method. A method for producing a long ingot of an active refractory metal-containing alloy by melting.   The long casting of an active refractory metal-containing alloy by plasma arc melting according to claim 1, wherein a long ingot having a diameter or a ratio of a height to a side length of 1.5 or more is a production object. A method of manufacturing a lump.   The method for producing a long ingot of an active refractory metal-containing alloy by plasma arc melting according to claim 1, wherein the raw material rod is forwardly fed toward the plasma arc while rotating around its long axis. .

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