JPS6167725A - Method for vacuum arc-melting active metal having high melting point and alloy thereof - Google Patents

Abstract

PURPOSE:To obtain an ingot having superior uniformity by reducing electric current for melting in several stages when a hot top is formed in the last stage of melting, holding the molten metal for a fixed time in each stage, and making the depth of the molten metal pool gradually small. CONSTITUTION:In the vacuum arc melting of an active metal having a high m.p. or an alloy thereof by a consumable electrode system, electric current for melting is reduced in several stages when a hot top is formed in the last stage of melting, and the molten metal is held for a fixed time in each stage. The depth of the molten metal pool is made as small as possible when the power supply is cut, and while the electric current is reduced, the molten metal is properly fed to carry out nearly uniform solidification, so the surface quality of an ingot and the productivity are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a vacuum arc melting method for obtaining an ingot with excellent homogeneity in vacuum arc melting of high melting point active metals such as Ti5Zr and their alloys.

Conventional technology High melting point active metals are usually melted by vacuum arc melting, but this method involves constant melting with a constant current, and in the late stage of melting, 20
This is a so-called hot top process in which the melting current is reduced within a relatively short period of about 60 minutes.

Solidification of molten metal in consumable electrode vacuum arc melting is
In the initial stage, solidification from the bottom of the mold is dominant;
After a certain period of time, the amount of solidification from the mold wall increases significantly. At this stage, the depth of the molten metal pool is constant if the melting rate is constant, solidification progresses sequentially from the bottom to the top, and as the metal is supplied from the consumable electrode, the remaining portion is relatively uniform. , component segregation and shrinkage pores in the center are small.

However, if the molten metal pool is deep when the power is turned off at the end of melting, the components will be segregated and the shrinkage pores will be thick.Therefore, a hot top is carried out in the late stage of melting, but the current must be properly controlled at this time. Homogeneity cannot be improved.

However, the current hot top method, which is generally carried out at the final stage of melting, takes a relatively short time and finishes melting while the molten metal pool is still quite deep.
Both component segregation and shrinkage pores have not been sufficiently reduced.

Therefore, various efforts have been made to reduce the occurrence of shrinkage holes.
No. 21 has a method in which the melting current is gradually lowered by a constant deceleration coefficient from the early stage of melting.

Problems to be Solved by the Invention The above method for reducing the occurrence of shrinkage holes is to prevent the occurrence of shrinkage holes by gradually decreasing the depth of the molten metal boule while preventing solidification from the upper surface of the molten metal pool.

However, in this case, since the hot top time is increased, the melting rate becomes low, productivity deteriorates, and the surface quality of the ingot also deteriorates.

In view of the current situation, this invention performs high current melting until the hot top starts, and after the hot top starts, the molten metal pool is gradually shallowed and the molten metal is appropriately supplied to a state close to uniform solidification, thereby achieving homogeneity. This paper proposes a vacuum arc melting method for high melting point active metals and their alloys to obtain ingots with excellent surface quality.

Means for Solving the Problems This invention provides a consumable electrode type vacuum arc melting method for high melting point active metals and their alloys, in which the melting current is reduced in several stages during the final stage of melting. The depth of the molten metal pool is gradually reduced by holding it for a certain period of time.
The gist is to solidify in a state close to uniform solidification.

Operation Next, the details of this invention will be explained based on FIG. 1. A method according to the present invention is shown in C. For comparison, conventional method A involves hot top for a short period of time T^ after steady melting, and deceleration melting in which the melting current is gradually reduced with a constant speed coefficient from the beginning. Law B was proposed.

In the method of the present invention, in a steady state, a steady current I is determined by the electrode and mold dimensions. When it is time to start the hot top, the current is reduced to ■, and at this current the time T1
only dissolves. Furthermore, the current decreases to ■2 for a time T,
Either the current is melted and the power is turned off, or the current is further reduced to I3, the current is melted for a time T3, and the power is turned off.

As mentioned above, this invention gradually makes the molten metal pool shallower,
In order to ensure the surface quality of the ingot while supplying appropriate hot water, the hot top is installed in several stages (the drawing shows two stages and three stages).
This method employs a dissolution current pattern that occurs over a period of time (as shown in the figure).

The current of the hot top at this time! 7, I2, and I3 are determined by the electrode, mold dimensions, and material, i.e., the level of added elements. The inventors conducted various experiments on component segregation, surface quality, productivity, etc., and found that I, = 0.60 to 0.80.
I.

y, −0.40 to 0.60I.

I learned that l3=0.15 to 0.40I0 is desirable. Also, the time varies depending on the dissolution situation, but according to the experimental results, in the case of 2 steps, T = 20 to 40 molecules, 220 minutes (including adjustment), and in the case of 3 steps, T = 20 to 40 molecules, 2 = 20 ~ 40 molecules, 510 minutes (including adjustment) is desirable.

In this invention, the implementation of the molten metal tube is determined by taking into consideration the depth of the molten metal pool, retained heat, and melting situation when reducing the current, and the depth of the molten metal pool when the power is turned off is By keeping the molten metal as shallow as possible and by properly feeding the molten metal during the process of lowering the current, a state close to uniform solidification is achieved.

Furthermore, even if the molten metal pool is deep, as long as the molten metal is supplied properly, there will be no segregation of components or formation of shrinkage pores. We should aim to improve productivity.

Examples Example 1 Using a compact molded by a hydraulic press, a diameter of 788 mlA and a length of 63 mm was made by plasma beam welding.
A primary electrode of 00 wires and 7200 kg of electric resistance welding was made, and this was double melted using a consumable electrode type vacuum arc melting furnace, and a diameter of 980all, a length of 2100 u71, and a weight of 7150 was made.
KP pure 1,000 tan ingot was produced.

At this time, the secondary melting was all carried out under the same conditions, and the hot top conditions for the secondary melting were varied as shown in FIG. That is, A is a conventional method with a short hot top time, B is a fast melting method in which the melting current is reduced by a constant deceleration coefficient from the beginning of melting to the end, and C is an embodiment of the present invention.

In this case, the hot top time (TA) of conventional method A is 30 minutes, and the hot top time (Tc) of inventive method C is 100 minutes.
It was a minute.

At the same time, each ingot was longitudinally cut into two, and Fe, which had significant segregation, was cut into two.
In addition to adjusting the -C component distribution for O to 1.1, productivity,
Observations of surface quality were made. The results are shown in Table 1.

(Hereinafter F margin) 1'JQ- 1'''''1 Also, based on the above results, the maximum variation from the target value 1a (a
Fig. 2 shows the ingot surface quality index (Fig. b), and production efficiency (CC Fig.).

From the above results, this invention method C has significantly improved component segregation compared to the conventional method A, which uses a short hot top time, and can obtain the same homogeneity as the straight melting method B, which uses a long hot top time. It can be seen that an ingot with excellent productivity and surface quality can be obtained. The macro photograph in Fig. 4 shows the structure of the top part of pure titanium ingots produced by each method A, B, and C described above. It can be seen that this is more homogeneous than the other A and H.

Example 2 Using a compact molded by a hydraulic press, a diameter of 560 mm and a length of 625011 was made by plasma beam welding.
M, the weight of 4860 gin was produced, and this was double melted using a consumable electrode type vacuum arc melting furnace, and the diameter was 73.
Ti-6 of 5 mm, length 2570 mm, weight 48301 c7
AI? -4V alloy manufacturing site.

At this time, all secondary melting was performed under the same conditions, and the hot top conditions for secondary melting were changed as shown in Figure 1.
Conventional corporate hot top time is 43 minutes, invention method C is 10 minutes
It was set to 3 minutes. At the same time, each ingot is longitudinally cut into two, and A4, V, and Fe, which have segregation problems.

The component distribution of O was investigated, and the surface quality was also observed. The results are shown in Table 2.

(See the margins below) Also, based on the above results, the maximum variation from the target value (Figure a), the ingot surface quality index (Figure B), and the production efficiency (Figure 0) are shown in Figure 3.

The results show that the invented method C has significantly improved component segregation compared to the conventional method A, which does not adjust the components, and has the same homogeneity as the slow dissolution method B, which uses a hot top for a long time. It can be seen that an ingot with excellent productivity and surface quality can be obtained.

Effects of the Invention This invention, when performing vacuum arc melting of high-melting point active metals and their alloys, reduces the melting current in several stages at the hot top in the latter half of final melting to solidify in a state close to uniform solidification. As a result, an ingot with excellent homogeneity, surface quality, and productivity can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram showing the secondary melting current pattern in consumable electrode type vacuum arc melting, Figure 2 is a diagram showing the ingot homogeneity, surface quality, and production in Example 1, and Figure 3 is in Example 2. Diagram showing the effect of dissolution pattern on
FIG. 4 is a photograph showing the macrostructure of the top part of the pure natan ingot according to Example 1. A: Conventional method, B: Rapid melting method, C: Invention method, Io: Steady melting current, 11: 1st stage hot top current, T2: 2nd stage hot top current,
T3... 3rd stage hot top 'F style, T1...
1st stage hot top time, T2... 2nd stage hot top time, T3... 3rd stage hot top time, T
A... Total hot top time in A pattern, TB.
...Total hot top time in pattern B, Tc...C
All hot top time in the pattern.

Claims (1)

[Claims] In the consumable electrode vacuum arc melting method for high melting point active metals and their alloys, during the hot top in the late melting stage, the melting current is reduced in several stages and held at each stage for a certain period of time to gradually increase the depth of the molten metal pool. A vacuum arc melting method for high melting point active metals and their alloys, which is characterized by reducing the size and solidifying in a state close to uniform solidification.