JPH02236233A - Method for producing TiAl alloy ingot - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for melting a TiAl alloy ingot by a vacuum arc remelting method. [Conventional technology] TiAl-based alloys such as TiAl and TisAl are lightweight and have high strength at high temperatures, so they are attracting attention as high-temperature elongation materials that require lightweight properties, and research and development is being conducted on them. ．． When melting these alloys, there is a large difference in melting point between Ti and AI, and since Ti is an active metal, it must be melted by high-frequency induction heating using expensive calcia-based refractories, or by water cooling. Special melting methods are used, such as vacuum arc remelting using a steel mold, plasma beam melting, and electron beam melting. The vacuum arc remelting method involves mixing Ti and A1 according to their alloy compositions, joining them by welding to a compacted material using a hydraulic press, etc., using this as an electrode, melting it by arc discharge in a vacuum, and melting it in a crucible. In this method, the ingot is obtained by solidifying the ingot while forming a pool. In addition, in the plasma beam melting method and electron beam melting method, the raw material supplied on the hearth is melted using a plasma beam or an electron beam depending on the alloy composition, and the melted material is dripped into a water-cooled steel mold.
In this method, the ingot is pulled out from below the mold in accordance with the dissolution rate of the raw materials. In the high frequency induction heating method as disclosed in JP-A-63-183189, a calcia-based refractory is used to prevent contamination caused by the refractory during high-temperature melting.

[Problems to be solved by the invention] However, the following problems occur in the conventional method. That is, ■In JP-A No. 63-183189, TiA
Since I-series alloys are active, even if they are melted using calcia-based refractories, the molten metal may become contaminated if the temperature of the molten metal is high, the melting time is long, or the oxygen partial pressure in the melting atmosphere is high. , the oxygen concentration in the molten metal increases. ■Plasma beam melting method. In the electron beam melting method, it is difficult to pull out the ingot because the shell of the TiAl alloy solidified in the mold (the surface portion of the ingot formed at the initial stage of solidification) does not have sufficient strength at high temperatures. ■Even in the vacuum arc remelting method using a water-cooled copper mold, the shell strength is insufficient and cracks occur in the ingot. The third country is an explanatory diagram of the conventional technology. In the vacuum arc remelting furnace 1, an electrode 11 is suspended from a stinger rod 2, and direct current is supplied from a direct current power source 3 via a power supply circuit 4, and a direct current arc 13 is generated between the lower end of the electrode 11 and the melting boule 12. This heat sequentially melts the electricity, and droplets 15 drip to form a molten pool 12. This molten boule 12 is cooled by a water-cooled copper mold 7,
An ingot 14 is formed. The water-cooled copper mold is part of the water-cooled jacket 5 and is cooled by cooling water 6. During this cooling, the temperature gradient between the molten pool and the water-cooled copper mold is extremely large, and it is thought that large thermal stress is generated inside the shell, and this thermal stress causes cracks in the ingot. The purpose of the present invention is to solve the above problems and provide a method for melting a sound ingot using a vacuum arc remelting method. [Means for solving the problem] T i A by vacuum arc remelting method according to the present invention
The method for producing a TiAl alloy ingot involves inserting a carbon sleeve into a water-cooled metal mold and vacuum melting the alloy material within the sleeve. [Function] In the present invention, TiAl by vacuum arc remelting method
The method for producing alloy ingots involves inserting a carbon sleeve into a water-cooled metal mold and melting the alloy material in vacuum within the sleeve, so the temperature gradient at the interface between the molten metal and the carbon sleeve is small and the shell is melted. Since excessive thermal stress is not applied to the ingot, cracks do not occur in the ingot. Embodiment] FIG. 1 is an explanatory diagram showing an embodiment of the present invention. The overall structure is the same as that shown in FIG. 3, but a carbon bottom plate 9 and a carbon sleeve 8 are inserted into a water-cooled copper mold 7. Figure 2 is an enlarged view of the main parts of Figure 1. The melting process will be explained below with reference to Figures 1 and 2. A bottom torsion having a diameter smaller than the inner diameter of the mold is placed at the bottom of the water-cooled copper mold 7, and the inner diameter is placed on the bottom plate.
Place a cylindrical carbon sleeve 8 larger than the outside diameter of ll. Place 10 pieces of initial ignition material (titanium sponge; the same material as the electrodes) on the bottom plate. t[itll, t
Generates an arc by flowing a current. The following ingot forming process is similar to that of the prior art, but the molten pool 12 is in contact with the carbon material, the temperature gradient at the interface between the two is small, and excessive thermal stress is not applied to the shell. Therefore, no cracks occur during solidification. In other words, in the present invention, a vacuum arc remelting furnace is used, and the work steps in the melting method are no different from the vacuum arc remelting method. The results of melting a TiAI alloy (At; 37 wt.%) ingot using the method of the present invention are shown below. A predetermined amount of aluminum grains and titanium sponge are mixed and compression molded, and then argon arc welded to create a block with a diameter of 10III1 and a length of 1000 mm.
A primary electrode with a diameter of 138 mm is formed by the method of the present invention.
A primary ingot with a length of 450 am was obtained. (1 pressure 28V.t?IE3200A, degree of vacuum 10-2To
rr) The carbon sleeve used at this time had an inner diameter of 1
40 IIm, outer diameter 172! It was II+. Next, two of these primary ingots were joined by plasma arc welding to form a primary electrode with a diameter of 138 mm and a length of 900 mm, and by the method of the present invention, a primary electrode with a diameter of 174 mm and a length of 5 mm was formed.
A secondary ingot of 0 + u was obtained. (Voltage 28v, current 4400A, vacuum 10-2Torr) The carbon sleeve used at this time had an inner diameter of 176 mm and an outer diameter of 196 mm. The surface skin of this secondary ingot is beautiful,
No trace of cracking was observed, and as a result of analyzing the chemical components of the skin and center of the top, middle, and bottom parts of this ingot, a homogeneous distribution of components was obtained as shown in Table 1. Table 1 (AI wt.%) In this example, the shape of the carbon sleeve is circular, but the present invention is not limited to this. However, a split structure may be used as long as there is no problem. [Effects of the Invention] As described above, according to the present invention, existing equipment can be replaced by introducing a carbon sleeve into the water-cooled copper mold of a vacuum arc remelting furnace. It has the effect of easily melting TiAI alloy ingots without causing cracks.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG.
An enlarged view of the main part of the figure, and Figure 3 is an explanatory diagram of the prior art. l...vacuum arc remelting furnace,

Claims (1)

[Claims] A method for producing a TiAl alloy ingot by a vacuum arc remelting method, which comprises inserting a carbon sleeve into a water-cooled metal mold and vacuum melting the alloy material within the sleeve. Method for melting ingots.