JPH08282B2 - Method and apparatus for manufacturing alloy ingot - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] For example, each pure metal constituting the alloy, such as NiTi alloy, is relatively mass-produced or has excellent workability, It is available at low cost, the alloy is a difficult-to-work material, and the characteristics are extremely sensitive to composition,
The present invention provides a method and an apparatus for inexpensively producing an alloy ingot when strict control of components is required.

[Conventional technology]

A NiTi alloy containing both Ni and Ti in an amount of about 50 at% is known as an alloy having characteristics such as a shape memory effect and superelasticity, and these characteristics are utilized for various applications. However, the characteristics of the NiTi alloy are extremely sensitive to the composition. For example, when the Ni content changes by only 0.1%, the transformation point exhibiting the shape memory effect changes by 10 ° C to 15 ° C. Therefore, it is necessary to control the composition uniformly and accurately to a target value when the NiTi alloy is melted.

Conventionally, the production of NiTi alloy has been carried out mainly by a high-frequency vacuum induction melting method using a graphite crucible. (Yuichi Suzuki:
According to this method, the molten metal is sufficiently mixed by the high frequency induction stirring effect, so that it is possible to obtain a relatively uniform ingot. However, since Ti is an extremely active element and has a large affinity with C, it is difficult to prevent C from melting into the melt from the crucible, and it is extremely difficult to obtain an ingot with a low C content of 300 ppm or less. .

Recently, a method of using calcia as a material for crucibles has been attempted (Mamoru Hamada, Fumihiro Uraya, Yushin Hanate, Masakazu Miyagi: Osaka Prefectural Institute of Industrial Technology Report, 82 (1983), 20),
In this case, for the same reason as above, it is difficult to prevent O from melting into the melt from the crucible, and an ingot with low O content cannot be obtained.

C and O as impurity elements are preferentially combined with Ti to form Ti.
Since a rich compound is formed, the Ti concentration in the matrix is reduced to change the transformation point of the shape memory effect to the low temperature side, making it difficult to control the transformation point and also degrading workability. Further, if an attempt is made to increase the amount of dissolution in order to increase productivity, the constituent elements tend to segregate during solidification after casting, and there is a restriction on increasing the scale of dissolution.

In addition, an example of a vacuum arc melting method using a consumable electrode has been announced. (Kanto Special Steel Technical Information No.KSM-
In the case of this method, since the melting in the water-cooled copper mold prevents contamination from the crucible, it is difficult to obtain a uniform ingot because the whole ingot is not melted and mixed together at the same time.

Further, in JP-A-60-148660, rod-shaped raw materials having the same length and having the elemental elements matched to the weight ratio of alloying components are superposed with one end thereof aligned, and the plasma beam or the electron beam is applied in an inert gas or vacuum. A method of melting from one end with a beam to cast into a water-cooled copper mold, or the ingot thus obtained is remelted from one end with a plasma beam or an electron beam in an inert gas or vacuum and cast into a water-cooled copper mold The method of doing is proposed. In the present invention, it is necessary to prepare rod-shaped raw materials having the same length and the component elements accurately matched to the weight ratio of the alloy components. That is, it is necessary to prepare a melted material whose length and diameter are strictly adjusted to a predetermined dimension, which is actually a laborious work that requires considerable skill, which is not practical.

Furthermore, considering that the size of the ingot obtained by the method described above is relatively large, the NiTi alloy is an alloy with extremely poor workability, and in many cases it is used with a relatively thin wire rod of 2 mm or less. Then, the processing is difficult and it is a big factor to increase the price of the final product.

In addition, manufacture of NiTi alloy by powder metallurgy is also attempted. (WAJohnson, JADominque and SHReichman:
J.de Phys., 43, Suppl.No.12 (1982), C4-285) In this case, the transformation point is within ± 2K by mixing and sintering two or more kinds of powders with known transformation points. It is reported that it is possible to control. However, in this method, the homogenization of the alloy is performed by diffusion in the same phase, so the reaction rate is slow, a long heat treatment is required for homogenization, and the transformation point of the alloy powder that can be used as a raw material is used to suppress microsegregation. There is also a restriction on the temperature range. Further, in order to bring the density close to the true density, it is necessary to use a special processing means such as a high temperature isostatic press (HIP), which is difficult to say industrially.

[Purpose of the present invention]

The present invention, as a result of various investigations in view of these, the components can be uniformly and accurately controlled to the target composition throughout the material,
Moreover, it is possible to prevent the mixing of impurity elements, such as NiTi alloy,
It is intended to provide a new method and apparatus for producing an alloy ingot which contains a large amount of active elements and has a large dependence on the chemical composition of the characteristics and which is difficult to process.

One of the present inventions is to prepare two or more kinds of pure metal or alloy wires so that the chemical composition calculated from the supply amount per unit time becomes equal to the chemical composition of the alloy to be melted. Adjust the supply rate and supply into a water-cooled metal mold, melt them using a heating source such as tungsten arc, plasma arc or electron beam, and further solidify to continuously produce alloy ingots. It is characterized by that. In the method of the present invention, since the wire material is used as the raw material for melting, the supply amount per unit time to the melting pulley can be accurately controlled, and the raw material having a uniform chemical component can always be supplied in the melting pool. Therefore, it is possible to obtain an ingot which has no segregation and has extremely small variation over the entire ingot.

The raw material wire is, for example, a pure metal wire made of the constituent elements of the alloy to be melted, which is available at a relatively low cost because it is mass-produced and has good workability. If necessary, the alloy to be melted may be
In the case of an alloy of the original system or higher, an alloy wire composed of two or more kinds of constituent elements of the alloy and having good workability can be used as a raw material wire rod.

For example, in the case of NiTi shape memory alloy, the titanium wire rod as a raw material may be TW28 or higher purity titanium wire rod defined by JIS H 4670. Also,
JIS is a nickel wire that is commercially available mainly for electron tubes.
High-purity nickel wire rods of VNiW or higher specified in H 4511 are available, and they can be used.

The diameter of these raw material wire rods is preferably selected from the range of 0.2 to 6.0 mm.

If it is 0.2 mm or less, not only is it expensive, but it is difficult to supply the wire rod to the mold, and the impurity concentration is generally high due to contamination from the lubricant during wire drawing of the wire rod. This is because it becomes difficult to obtain a lump. Also, if it is 6.0 mm or more, it is still difficult to stably supply the wire, and it is easy to cause problems with the uniform solubility on the mold or in the mold. It is desirable to set within. In addition, the diameter of the wire rod as the raw material is required to have little variation in the length direction. However, as described above and JP-A-60-
Since it is not necessary to accurately match the weight per unit length of each wire with the weight ratio of the alloy components as in the case of Japanese Patent No. 148660, the range of selection of the wire used as a raw material is wide and industrially advantageous.

Another aspect of the present invention relates to an apparatus used in the method of the present invention, which will be described in detail below with reference to the drawings.

One of the devices according to the present invention is, as shown in FIG. 1, a metal water-cooled mold 1 having a groove on its outer peripheral portion and rotating orthogonally to a horizontal plane. Mainly composed of an apparatus 2 for supplying a raw material wire rod to a water-cooled mold, a heat source 3 for heating and melting the supplied raw material wire material and its power source 4, and an ingot drawing device 5 for continuously extracting a solidified alloy ingot. To be done.

In this example, the raw material wire rod is continuously melted on a water-cooled mold to be alloyed and solidified. In this case, as the water-cooled mold, one having a groove having a desired shape on the outer peripheral surface of a cylindrical body is used, and the alloy ingot solidified in the groove is continuously drawn out. The device for supplying the wire must be capable of accurately supplying the raw material wire in an amount suitable for the dissolution rate in a fixed amount.
A wire rod may be grasped by a pair of carrier rolls and fed through a guide pipe as in a welding rod feeder or welding rod feeder.

If necessary, two or more supply devices are arranged and the raw material wire rods are simultaneously supplied and melted.

As shown in FIG. 2, the cross-sectional shape of the bottom of the groove of the water-cooled mold is preferably semicircular and its diameter is preferably 5 mm to 20 mm. By doing so, by controlling the feed rate of the raw material wire rod and the withdrawal rate of the molten ingot, the ingot utilizes the surface tension of the alloy in the molten state, and the cross-sectional shape is approximately 5 mm in diameter. It is possible to make a circle of 20 mm, which is convenient for subsequent processing. By setting the peripheral speed and the ingot drawing speed to be approximately the same, stable operation becomes possible.

Since the melting and heating device rapidly melts the active metal, it is necessary to have an atmosphere controllable and high energy density. As a melting and heating source for that, plasma arc,
Electron beam, tungsten arc, etc. are suitable, and the melting atmosphere can be an inert gas atmosphere or a vacuum, depending on the type of heating method, the metal to be melted, the activity of the alloy, and other characteristics.

Another one of the devices according to the present invention uses a water-cooled metal mold 1 having a vertical through hole as a mold, as shown in FIG. In this case, by controlling the supply amount of the wire rod as the raw material per unit time and the drawing speed of the ingot, the level of the molten metal surface can be kept constant and stable operation can be performed.

If the inner diameter of the through hole of the water-cooled mold is less than 4 mm, it is difficult to produce an alloy ingot with good surface properties. Can be lowered to enable stable manufacturing.

As the melting and heating source, the device for supplying the raw material wire rod, and the ingot drawing device, the same device as the above-mentioned device can be used.

Next, an example in which the present invention is applied to a NiTi shape memory alloy will be described.

The alloy for which the manufacturing method and apparatus of the present invention are applicable is Ti
It is not limited to Ni alloys only. It can also be applied to other alloy systems, for example, NbTi alloy as a superconducting material.

[Example 1] Using a device shown in Fig. 1 using a transfer type plasma arc as a heating source, a pure nickel wire having a diameter of 2.0 mm and a pure titanium wire having a diameter of 2.0 mm were used as raw material rods, and a pure titanium wire was formed on the mold. It was supplied and sequentially melted and solidified at a current of 130A. The cross-sectional shape of the groove bottom of the mold used at this time was a semicircle with a diameter of 10 mm, the supply rate of both wires used as raw materials was 300 mm / min for pure nickel, 483 mm / min for pure titanium, and NiTi after melting. By setting the drawing speed of the alloy wire rod to 30 mm / min, it was possible to stably obtain an ingot with a cross section of 10 mm in diameter.

In this way, the NiTi alloy ingot thus obtained, 900 ℃
After refining for 2 hours at 5 minutes, samples were taken from 5 locations at intervals of 1 m in the length direction, analysis of impurity elements C and O and martensitic transformation start temperature (Ms point) by differential scanning calorimeter (DSC).
Was measured. The results are shown in Table 1. The transformation temperature was measured after the sample was cut out and heat-treated at 500 ° C. for 1 hour.

As is clear from Table 1, the variation of the transformation temperature of the NiTi alloy ingot according to the method of the present invention is within 5 ° C. Yes Very small. By the way, it is difficult to suppress C to 300 ppm or less by a melting method using a vacuum high-frequency induction melting furnace using a graphite crucible, which is a conventional manufacturing method of NiTi alloy, while it is possible to reduce C by using a calcial crucible.
It is said to be difficult to keep the value below 600ppm. Comparing these values, it can be seen that the C and O concentrations of the NiTi alloy according to the present invention are sufficiently reduced.

[Example 2] Using a device shown in Fig. 2 in which a plasma arc was used as a heating source, a pure nickel wire having a diameter of 2.0 mm and a pure titanium wire having a diameter of 2.0 mm were used as a raw material and supplied onto a mold. They were sequentially dissolved and solidified. The diameter of the through hole of the water-cooled copper mold used at this time was 20 mm at the upper part, and the feeding speed of both wires used as raw materials was 1200 mm / min for pure nickel and 193 for pure titanium.
By setting the drawing speed of the NiTi alloy wire rod to 0 mm / min and the melted NiTi alloy wire to 30 mm / min, it was possible to obtain a wire rod having a cross section of about 20 mm in diameter in this case as well.

In this way, with respect to the obtained NiTi alloy ingot, samples were taken from 5 locations at intervals of 1 m in the lengthwise direction in the same manner as in Example 1 to analyze the impurity elements C and O and measure the transformation temperature using the DSC method. did. The results are shown in Table 2.

As is clear from Table 2, the variation in transformation temperature of the NiTi alloy wire according to the method of the present invention is within 6 ° C., which is extremely small. Further, it can be seen that the C and O concentrations are also sufficiently reduced.

[Effects of the Invention] According to the apparatus and the manufacturing method of the present invention, it is possible to accurately control the amount of the alloy component elements melted in, and it is possible to manufacture a small-diameter alloy ingot without segregation of the target composition Is. Further, the present invention is a melting method using a water-cooled metal mold, such as melting using a conventional graphite crucible,
The problem of contamination due to the reaction between the molten metal and the crucible material does not occur, and it is possible to manufacture an alloy ingot having excellent characteristics. Also,
According to the present invention, since an alloy ingot having a diameter of 20 mmφ or less can be directly produced, if necessary, it is possible to omit the intermediate steps such as forging and hot rolling which were necessary in the case of the conventional melt casting method,
It is possible to reduce the processing cost and improve the yield.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a manufacturing apparatus for a small-diameter alloy ingot according to the present invention when a plasma arc is used as a heating source, and FIG. 2 is a bottom shape of a groove of a mold of the manufacturing apparatus in FIG. FIG. 3 is a cross-sectional view showing an example, and FIG. 3 is a schematic view showing another example of an apparatus for producing a small-diameter alloy ingot according to the present invention. 1 ... Water-cooled metal mold 2 ... Raw wire supply device 3 ... Heating source 4 ... Power supply 5 ... Alloy ingot drawing device 6 ... Alloy ingot 7 ... W electrode 8 ... Wire rod 9 ... Cooling water 10 Ar shielding gas 11 Plasma arc 12 Main power supply 13 Pilot power supply 14 High frequency oscillation device 15 Antioxidant cover

Claims (4)

[Claims] 1. A wire material of two or more kinds of pure metals or alloys is used as a raw material so that the chemical composition calculated from the supply amount per unit time thereof is equal to the chemical composition of the alloy to be melted. Manufacture of alloy ingots characterized by adjusting the feed rate of each wire, melting and solidifying these wires together in a water-cooled metal mold using a heating source, and then continuously drawing Method. 2. The method for producing an alloy ingot according to claim 1, wherein the raw material wire is nickel and titanium and the alloy to be melted is a NiTi alloy. 3. A metal water-cooled mold having a groove on its outer periphery and rotating orthogonal to a horizontal plane; a device capable of adjusting a supply speed; and a device for supplying a raw material wire rod to the metal water-cooled mold. An apparatus for producing an alloy ingot, comprising: a heat source for heating and melting the formed raw material wire rod; and an ingot extracting device for continuously extracting a solidified alloy ingot. 4. A water-cooled metal mold having a rigid through hole, a device capable of adjusting the feed rate, a device for feeding a raw material wire into the metal water-cooled mold, and a heating and melting of the fed raw material wire. An apparatus for producing an alloy ingot, comprising: a heat source for heating and an ingot extracting device for continuously extracting a solidified alloy ingot.