JPS63183139A - Melting method for ti-al alloy - Google Patents

Abstract

PURPOSE:To manufacture a Ti-Al alloy excellent in quality, by placing metallic titanium in a crucible composed of graphite or calcareous refractory, by heating the above to a specific temp. in an inert-gas atmosphere, and by adding pure Al. CONSTITUTION:Ti 25 is put in a graphite or calcia crucible 2 free from erosion by molten Ti, etc., and unreactive to Ti, and the inside of a vacuum vessel 1 in which the above crucible 2 is placed is formed into high vacuum or subjected to introduction of an Ar gas from an inlet 11, and then heated by means of an induction coil 3 provided to the outside periphery of the crucible. At the point of time when a temp. in a range of 1,300-1,670 deg.C (the melting point of Ti) is reached, Al in a vessel 6 evacuated from an outlet 7 is added into the crucible 2 by means of a conveying trough 9. In this way, the evaporation losses, due to superheating, of Al heaving low melting point are removed and the absorption of oxygen in calcia of the crucible 2 by Ti-Al alloy is prevented, so that Ti-Al alloy excellent in purity and composition ratio can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for melting a Ti--An alloy by high-frequency induction heating.

[Conventional technology]

T1) Al, TiAj! Ti-AJ! The alloys are
For example, it has attracted attention as an alloy for high temperatures, and development is progressing. As a melting method, there is a large difference in melting point between Ti and Al,
In addition, the difference in specific gravity is large, and both elements are active metals, so general melting methods such as high-frequency induction heating cannot be applied to melt Ti-Al alloys, and consumable electrode melting methods, plasma Special methods such as beam melting and electron beam melting are used.

The consumable electrode melting method involves mixing Ti and Al according to their alloy compositions, pressing them together, connecting the compacts by welding, melting the resulting electrode into a crucible using an arc, and solidifying it while pooling. In addition, in the plasma beam melting method and electron beam melting method, the raw material supplied on the hearth is melted with a plasma beam or electron beam depending on the alloy composition and sent into the mold. It is pulled downward from the bottom at a rate that depends on the rate of dissolution.

[Problem that the invention seeks to solve]

In all of these methods, a forced water-cooled steel bridge body is used as a crucible or mold.

However, in the former consumable electrode melting method, the molten raw material that melts through is gradually solidified within the crucible.
Since the molten pool is essentially small compared to the ingot size and component segregation is unavoidable, there is a problem of non-uniformity of the components.

Furthermore, in the latter plasma beam melting method and electron beam melting method, in addition to this problem, there is also the problem that the molten pool solidifies quickly at the mold wall, making it difficult to pull out the ingot.

In addition, in the former melting method, the steps from electrode molding to melting are complicated and manufacturing costs are high.

Ti and Al inherently have poor weldability and have low electrode strength, so there is a high risk of the bridge falling during melting.The above weldability decreases as the Al ratio increases, so Alloys have problems such as the impossibility of electrode molding.

The present invention provides a melting method that solves all of these problems by introducing high-frequency induction heating.

[Means for solving problems]

If high-frequency induction heating could be introduced to melt Ti-Ajt alloys, electrode forming would be unnecessary, and since a large amount of raw material could be completely melted at once in the crucible, non-uniformity of ingredients would not occur, and the ingot could be Since there is no need to pull out, problems caused by pulling out are also solved. In other words, the above-mentioned problems can be solved at once by introducing high-frequency induction heating.

However, in high-frequency induction heating, water-cooled copper crucibles cannot be used due to the heating method, and crucibles made of refractories must be used. However, magnesia or magnesia chromite, which is generally used as this refractory, When quality materials come into contact with molten Ti or Ti alloys,
It is unusable because it erodes in a short time and has a metallurgical effect on the T is T s alloy in the crucible.

Therefore, the present applicant has developed a crucible that can melt TI and 'l'i alloys by high-frequency induction heating, and has previously filed an application for this crucible and a method for melting T is T alloys using this crucible (Japanese Patent Application Laid-Open No. 1982-132345 and Japanese Patent Application Publication No. 1983
8-133338), this crucible uses a calcareous refractory (calcia) such as Ca oxide, which is not easily corroded by molten Ti or molten T1 alloy, and is not easily corroded by Ti or its alloy components. There is almost no reaction.

However, when Ti and An were charged into this crucible and heated by induction, Aj+ melted when the temperature of the charged raw materials reached approximately 660°C, and the subsequent temperature rise overheated the molten Al and caused it to evaporate. In addition, a reaction between Al and the calcareous refractory started, which consumed the heat input, making it difficult to raise the temperature of the charged raw material, and the melting had to be stopped. The temperature of the charged raw material at the stage when melting was stopped was 1500℃
Although it was nearby, AN had almost disappeared, although no progress was observed in the state of Ti.

The inventors of the present invention repeatedly conducted extensive experimental research on countermeasures against this problem, and found that it is effective to delay the charging of Al with respect to the charging of Ti. However, after dissolving Ti, A
If 1 is added, there is a risk of an increase in oxygen in the alloy due to the reaction between the molten Ti and the refractory, and a change in composition due to evaporation of Al.

Therefore, when adding Al, the Ti temperature inside the crucible is T.
It has been found that a range from near the melting point of the t-Al alloy to near the melting point of pure Ti is good. If Al is added when the Ti temperature is within this range, the melting of Al and the alloying of Ti and Al will proceed simultaneously, and the molten metal will not reach sparheating, increasing the amount of oxygen in the alloy. is suppressed, and the yield of Al is greatly improved.

The present invention was made based on this knowledge, and involves placing pure Ti in a crucible lined with a graphite refractory, a calcareous refractory, or a calcareous refractory on the inside, and subjecting it to high-frequency induction heating in a vacuum or argon atmosphere. The gist is a method for melting a Ti-Al alloy, which is characterized in that Al is added to the crucible and melted when the temperature of pure Ti in the crucible is 1300° C. or higher and lower than the melting point.

The furnace used in the melting method of the present invention is a high frequency induction heating type furnace.

The crucible installed in the furnace is made of calcareous refractory or has an inner surface lined with calcareous refractory. In addition to the above-mentioned Ca oxide (calcia), calcareous refractories include CaO-MgO1CaO-C, CaO-Mg0-C
etc. In addition, other than calcareous refractories, C is 90 to 9
A crucible made of graphite refractory containing 9% by weight can also be used.

This is because Ti and Al are near the melting point of Ti-Al alloy.
This is because there is little reaction between the metal and the refractory. A binder or the like may be added to the calcareous refractory or graphite refractory as necessary.

Heating is carried out in vacuum or in an argon atmosphere in order to prevent oxidation of the charge and to eliminate metallurgical influences on the charge.

The addition of Al was performed when the temperature of the Ti bag in the paddy bag in the crucible was 130°C.
It is carried out when the temperature is above 0°C and below the melting point. The reason is that Ti
-TtA, which is the lowest melting point compound among Ajl alloys
The melting point of Js is around 1350℃, and if Al is added when the temperature of Ti in the crucible is lower than this temperature, Ajl will melt at about 660℃, but the melting point of TiAl will decrease even with subsequent heating. Because of the high temperature, alloying with Ti does not proceed, and the molten Al is overheated and evaporates, and the Al
This is because the reaction between the refractories and the refractories is accelerated, and the inventors' tendency is remarkable, making them impossible to dissolve. Conversely, when Ti exceeds its melting point (1670°C), that is, when it is in a molten state, A
According to the investigation by the present inventors, when 1 is added, the molten metal becomes superheated due to the low melting point of the Ti-Al alloy, and the amount of oxygen in the alloy increases due to the reaction with the refractory. Strictly speaking, there are some differences depending on the type of alloy, but Ti
When the temperature exceeds the melting point, the amount of oxygen increases significantly, causing quality problems.

The amount of Al added is Ti-An! The amount is determined in consideration of the yield (95 to 98%) in accordance with the melting target composition of the system alloy.

After adding Al, the target Ti-Al alloy can be obtained by performing the same operation as normal induction heating melting.

〔Example〕

FIG. 1 shows an example of furnace equipment suitable for the melting method of the present invention.

1 is the main airtight container with crucible 2 installed inside.
is surrounded by a heating coil 3.

The crucible 2 is a container made of a general refractory material with a calcia lining 4 provided on the inner surface thereof, and is placed on a pedestal 5. The heating coil 3 is a water-cooled coil that is supplied with high-frequency alternating current through a cable (not shown).
The raw material 25 in the crucible 2 is heated by induction.

Reference numeral 6 denotes an Al charging chamber with an airtight structure provided above the main vacuum vessel, which is connected to a vacuum exhaust system (not shown) by an exhaust lower, and is also connected to the main vacuum via a connecting ramp 9 equipped with a lock valve 8. It communicates with the container. Inside this connecting slope 9,
A diagonal conveyance gutter lO is provided whose rear end protrudes from the diagonal path 9 into the main vacuum vessel and whose tip faces the mouth of the crucible 2.
The Al inside slides down on the gutter 10 and is charged into the crucible 2.

Note that 1) is an argon introduction pipe provided at the bottom of the main vacuum vessel 1, 12 is an exhaust pipe provided at the top of the main vacuum vessel 1, and 13.
14 is a pressure regulating valve, 15 is a sample collector for collecting a sample inside the crucible 2, and 16 is a thermometer for measuring the temperature of the raw material inside the crucible 2.

17 is a sub-vacuum container that houses the mold 18, and an exhaust pipe 1
9, it is connected to a vacuum exhaust system (not shown). The sub-vacuum container 17 also has a sliding door 2 that fits into a slit 20 and moves up and down with excellent airtightness.
1 to the main vacuum vessel l. Further, on the opposite side of this opening/closing 5t21, there is provided an outlet 22 for carrying the mold 1B out of the container, and this outlet 22 is equipped with a vertically sliding opening/closing a23 having excellent airtightness similar to the opening/closing m21 described above.

The mold 18 is movably provided on the rail 24,
The crucible 2 and this mold 1B have approximately the same capacity.

To carry out the melting method of the present invention using the furnace equipment shown in FIG.
First, a predetermined amount of pure Ti is charged into the crucible 2.

Next, the opening/closing door 21 is closed, and the main vacuum vessel 1 and the Al charging chamber 6 are evacuated from the exhaust pipes 12 and 7, respectively, to create a vacuum atmosphere. Further, if necessary, argon gas is filled into the main vacuum vessel 1 and the Al charging chamber 6 from the argon introduction pipe 1) and the exhaust lower of the charging chamber 1 to create an argon gas atmosphere.

Thereafter, the Ti in the crucible 2 is heated by induction using the heating coil 3 in a vacuum or argon gas atmosphere, and when the Ti temperature reaches 1300 to 1700°C, the required amount of Al is added to Aj! It is slid down from the charging chamber 6 on the feed channel 1O and charged into the crucible 2.

On the other hand, in parallel with the above-mentioned melting, in the sub-vacuum container 17 that houses the mold 18, the outlet door 23 is closed and the exhaust is evacuated from the exhaust pipe 19 to create a vacuum atmosphere, and if necessary, an argon gas atmosphere is created. put.

After the above-mentioned melting is completed, the opening/closing door 21 is immediately opened to transport the mold 18 to a position close to the crucible 2 in the main vacuum vessel 1, and the crucible 2 is lifted and tilted by a lifting tilter (not shown). and cast it into the mold 18 therein6.
The above is one cycle of dissolution.

The results of actual melting according to the above procedure using the furnace equipment whose structure is shown in FIG. 1 will be described below.

Crucible 2 has a calcia lining with a thickness of 40 to 50 tm on the inner surface, an inner diameter of 120 to 130 m5, and a depth of 250 mm.
Finished it at 1. Heating coil 3 has an output of 0 KW and a frequency of 5.
It belongs to KS.

First, 90m x 200m (5.7 kg) of pure Ti is charged into the crucible 2 outside the main vacuum vessel 1, and this is charged into the container 1. After sealing the container 1, inside the vessel The atmosphere was evacuated to 5.times.10" Pa, and then argon was introduced until the pressure within the vessel was about 50 m water column above atmospheric pressure.

Next, the pure Ti in the crucible 2 is heated by high frequency induction using the heating coil 3, and the temperature of pure Ti is 160°C as measured by a two-color thermometer.
When the temperature reached 0° C., 3.2 kir of shot Al was added from the Al charging chamber.

After adding Al, it melted to a III-tone in about 1 minute, and after keeping it in the crucible 2 for 5 minutes, a graphite mold 18 (120 mm
φ).

The top, middle, and bottom parts of the Ti-Aji alloy ingot obtained in this way were examined for the skin,
Table 1 shows the results of investigating the composition of each component in the center, and the quality was uniform in each part, and the increase in oxygen content was only about 0.05%. Moreover, the yield of Al was also good at 98%.

For comparison, the temperature of pure Ti when adding Al was set to 100
As shown in Table 2, the results of melting tests conducted at various temperatures between 0 and 1750°C show that below 1300°C, melting becomes impossible due to the evaporation of Al and the reaction between Al and the refractory. , above 1700°C, the yield of Al decreases due to superheating of the molten metal, and the amount of oxygen in the alloy increases. The most smooth melting is possible in a range of 0 to 50°C higher than the melting point of the Ti-AJ alloy. By the way, the melting point of this alloy system is 1650℃ for Ti3Al, TiAj! So 14
80°C, TiAl, 1360°C.

In addition, in the melting method of the present invention, the entire amount of raw materials can be completely melted at once in the crucible, and non-uniformity of components does not occur, so it is easy to add third elements such as V, Nb, Mn, and W. It is.

Table 1 Table 2 [Effects of the Invention] As is clear from the above explanation, the melting method of the present invention can be applied to the conventional consumable electrode method, plasma beam method, or electron beam method. jI Ti-Aj had no choice but to turn to a crude dissolution method
The melting of l-based alloys can be easily carried out using high-frequency induction heating, which allows a large amount of raw material to be completely melted at once, which has great effects in terms of both efficiency and quality.
Since compact electric bridges and water-cooled copper molds are not used, all problems caused by electrode formation and the use of water-cooled copper molds are solved, and overall the melting process is extremely efficient and economical, which improves product quality and cost. The effects are huge.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing the structure of an example of furnace equipment suitable for carrying out the melting method of the present invention. In the figure, l: main vacuum vessel, 2 nil acupuncture point, 3: heating coil,
6: Al charging chamber, 17: Secondary wing empty container, 18: Mold.

Claims (1)

[Claims] (1) Pure Ti is placed in a crucible whose inner surface is lined with graphite refractory, calcareous refractory, or calcareous refractory, and heated by high-frequency induction heating in a vacuum or argon atmosphere to raise the temperature of pure Ti in the crucible. is 1300℃
A method for melting a Ti-Al alloy, characterized in that Al is added into a crucible and melted when the temperature is below the melting point.