JPS62207831A - Electron beam melting method - Google Patents

Abstract

PURPOSE:To enable easy adjustment of the oxygen content in an ingot and the production of a low oxygen-content ingot by evacuating a melting atmosphere while introducing a nonoxidizing gas into said atmosphere at the time of melting raw materials contg. an active metal. CONSTITUTION:The raw materials G are melted by irradiating an electron beam B from an electron beam irradiating device 2a on said material while the raw material G contg. the active metal such as Ti or Zr is continuously supplied into a water cooled vessel 4 of an electron beam melting device. The molten metal M formed in such a manner is fed into a water cooled casting mold 8 and is successively cooled to solidify. The ingot I is continuously drawn by a drawing device 9. The inside of a shielding case 1 is evacuated to a vacuum by a discharge system 5 while the nonoxidizing gas such as Ar, He or H2 is introduced through a flow rate regulating valve 12 into the case 1 in the stage of melting.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention melts a raw material containing active metals such as Ti and Zr by irradiating it with an electron beam, and produces an ingot of 11% Zr or an alloy thereof. This invention relates to an electron beam melting method for suppressing the amount of oxygen mixed into cast products as much as possible when producing these products.

[Prior Art] The VAR (vacuum arc remelting) method has been widely used for melting active metals such as Ti. In other words, the VAR method involves forming an active metal into an electrode shape and applying it under high vacuum (10-2 to 10-3
This is a method in which an arc is generated between the electrode and the melting melt in a water-cooled crucible at a temperature of about 10.5 torr (approximately 1.5 torr), thereby melting the electrode.

However, in this method, it is necessary to manufacture an electrode made of an active metal such as Ti prior to arc melting, which has the disadvantage that the process is complicated and productivity and economy are low.

On the other hand, as vacuum technology progresses and electron beam irradiation equipment becomes larger, a melting method using an electron beam has been proposed and is attracting attention. In other words, the electron beam melting method is performed under high vacuum (1
This is a method of melting raw materials by irradiating them with an electron beam at a temperature of about 0-2 to 10-6 torr). With this method, granular raw materials and scraps can be melted in their original form, and the VAR method There is no need for any required electrode manufacturing process. Moreover, since the electron beam can be scanned in any direction by electromagnetic field control, even irregularly shaped ingots can be easily melted.

[Problems to be Solved by the Invention] This electron beam melting method has various advantages as described above, but on the other hand, due to structural constraints, the oxygen content in the molten metal (hereinafter referred to as [0] ) is likely to increase. That is, in the electron beam melting method, VAR
There are more opportunities for molten metal to come into contact with atmospheric gas than in
Furthermore, since the equipment is relatively large and there is a large possibility that air will leak in, active metals such as Ti are easily oxidized and [o] is likely to increase undesirably.

On the other hand, the mechanical properties of active metals such as Ti are greatly influenced by [0], and as shown in FIGS. 2 and 3, the strength and hardness of manufactured products increase as [0] increases. According to component standards for Ti, Zr, etc., [0] is regulated in various ways depending on the application, and [0] is adjusted according to the standards by considering the blending ratio of charging raw materials. . However, in the conventional melting method, there is a problem that [0] increases during melting, which makes it difficult to adjust [0] in manufactured products (ingots). In particular, when it is necessary to melt a low-oxygen-containing ingot, the above-mentioned problem comes into sharp focus.

The present invention has been made in view of these circumstances, and its purpose is to prevent an unwanted increase in [0] even when using raw materials containing active metals such as Ti and Zr. [The purpose of the present invention is to provide an electron beam melting method that facilitates adjustment to within the standard of 0 and enables melting of low-oxygen-containing ingots.

[Means for Solving the Problems] The configuration of the present invention that achieves the above objects is such that when raw materials containing active metals are melted with electron beams, a non-oxidizing gas is introduced into the melting atmosphere and the atmosphere is evacuated. The key point is that it is pulled and dissolved.

[Function] First, the present inventors selected sponge Ti as the melting raw material, and conducted a melting experiment using the apparatus shown in Fig. 4 in order to quantitatively understand the increasing tendency of [0] that occurs during electron beam melting. I did it. The experiment was conducted by evacuating the inside of the shield case 1 using the evacuation system 5, assuming cases in which the amount of air leaking into the shield case 1 was large and small, and the degree of vacuum was low and high. The results are shown in FIG. Note that FIG. 5 also shows the results when air was forcibly introduced through the flow rate regulating valve 12 provided in association with the vacuum gauge P and pressure control device 11 shown in FIG. In FIG. 4, 2 indicates an electron beam irradiation device, 4 indicates a container for dissolving raw material (water-cooled container), and B indicates an electron beam. As is clear from the results in Figure 5, [0] in the Ti ingot after melting.
are all higher than [0] in the sponge Ti, which is the raw material, and the tendency for [0] to increase becomes more pronounced as the degree of vacuum becomes worse, that is, as the amount of air leakage increases.

Based on the results in Figure 5, the amount of air leakage measured after the dissolution experiment (hereinafter referred to as leak rate) is plotted on the horizontal axis, and the amount of oxygen fluctuation Δ[0] before and after dissolution is plotted on the vertical axis. The relationship between the two is shown in FIG. As is clear from the results in Figure 6, as the leak rate to the electron beam melting furnace increases, the amount of [0] in the Ti ingot increases rapidly, and the amount of [0] in the Ti ingot increases during melting. It is understood how important it is to make the size of the crate as small as possible in order to prevent an unwanted increase in [o] inside the shield case 1. To this end, it is considered that airtightness should be sufficiently increased at locations where air may leak into the electron beam melting furnace (hereinafter referred to as leakage), such as flanges and viewing windows. However, as a practical matter, there are many places where there is a possibility of leaks, such as flanges, etc., and the airtightness decreases after long-term operation, so it is actually impossible to completely eliminate leaks. above is impossible.

Therefore, the present inventors conducted various studies in an attempt to establish a method that can prevent an unwanted increase in [0] in the ingot even if leakage to the electron beam melting furnace is limited to some extent. . As a result, Ar.

Inert gas such as He, reducing gas such as H2, or a mixture of both gases (collectively referred to as non-oxidizing gases)
[0] in the ingot is introduced into the shield case 1.
The present inventors have discovered that this is effective in preventing an undesirable increase in

The present inventors conducted an experiment using the apparatus shown in FIG. 7 in order to investigate the effect of introducing non-oxidizing gas. In the experiment, the non-oxidizing gas in the gas cylinder 13 was introduced into the shield case 1 through the flow rate regulating valve 12, the Ti sponge was melted with the internal pressure kept constant, and the amount of oxygen fluctuation in the Ti ingot Δ[ 0] was investigated. The experimental apparatus shown in FIG. 7 has the same structure as the apparatus shown in FIG. 4 except for the gas cylinder 13. The results of the experiment are shown in FIG.

In this experiment, non-oxidizing gas (Ar, He or H2) was used for both large and small leaks.
), which lowers the degree of vacuum than when non-oxidizing gas is not introduced, but in either case, by introducing non-oxidizing gas, the [0 It is understood that an undesirable increase in the amount of non-oxidizing gas can be prevented.The effect of introducing non-oxidizing gas is more pronounced when the leak rate is large.Also, the effect of introducing non-oxidizing gas is more pronounced when the leak rate is large. The higher the amount, the greater the prevention effect against the increase in [01.Furthermore, the prevention effect of inert gases such as Ar and He is almost the same, but the prevention effect of H2, which is a reducing gas, is slightly lower than that of Ar and He. It's getting a high value.

When the Ti metal melt scatters, molecular oxygen (0
Considering the oxidation process caused by 2), [
0] increase mainly due to the diffusion rate of 02 in vacuum and Ti
This is thought to be related to the oxygen partial pressure during the oxidation reaction process. When an inert gas such as Ar or He is introduced, the diffusion rate of 02 in the atmosphere is slowed down and an unwanted increase in [0] in the ingot is suppressed, whereas the reduction of H2, etc. When a reactive gas is introduced, in addition to the effect of reducing the diffusion rate,
Ar
, He, etc. are considered to have a greater effect than when introduced.

The present invention is basically intended to achieve the purpose of preventing an undesired increase in [0] in the ingot, and this purpose can be achieved by adopting the configuration described above. However, another disadvantage of the electron beam melting method is that it originates from impurities in the melted raw material. For example, a small amount of chloride is mixed into a sponge-like active metal such as sponge Ti during the manufacturing process, but when such a sponge-like active metal is used as a raw material for dissolution, the chloride volatilizes during the melting process. An extremely undesirable phenomenon (splash phenomenon) occurs in which the molten metal scatters while exhibiting a foaming state, which not only causes a decrease in the yield of the molten metal, but also causes the scattered droplets to adhere to the inner walls of the melting furnace, electron beam irradiation equipment, etc. This causes operational troubles and makes maintenance work complicated and difficult.

Therefore, the inventors of the present invention have developed an electron beam melting method that does not cause a drop in yield due to the splash phenomenon even when such a sponge-like active metal is used as a raw material, and can ensure stable operability. , which has already been filed 1 (Japanese Patent Application No. 60-218721). The above techniques are techniques for recovering molten metal (hereinafter referred to as droplets) scattered by the splash phenomenon, but even with these techniques, the problem of an increase in [0] in the ingot is unavoidable. It is also possible to combine the above technique with the configuration of the present invention. In this case, consideration must also be given to [o] in the collected droplets.

Therefore, the present inventors conducted an experiment similar to the experiment described above (see FIG. 4) to investigate the increase in [0] in the droplet. First, using the experimental apparatus shown in Fig. 9, a sponge Ti
was dissolved. The difference between this experimental apparatus and the apparatus shown in FIG. 4 is that a gold steel 14 is installed upright to surround the electron beam irradiation area in the water-cooled container 4, and the gold steel 14 is used to direct droplets. The droplets were collected and analyzed for [0] in the droplets. In this experiment, similar to the experiment adopted in FIG. The results were also investigated when air was forced in through the tube. The results are shown in Figure 10, and the [0] in the droplets scattered by the splash phenomenon is higher than the [01] of the Ti sponge, and the lower the degree of vacuum, that is, the more leakage, the more [0] 0]
The degree of increase is remarkable. These trends are consistent with the results shown in FIG. 5 above.

Furthermore, based on the results shown in Figure 10, when the leak rate measured after the dissolution experiment is plotted on the horizontal axis and the oxygen fluctuation amount Δ[0] before and after dissolution is plotted on the vertical axis, the relationship is as follows:
As shown in Figure 1, in this case as well, as with the results shown in Figure 6 above (in the case of the amount of oxygen fluctuation in the ingot), as the leakage to the electron beam melting furnace increases, [0] into the droplet increases rapidly.

Next, the present inventors conducted experiments similar to those shown in FIGS. 7 and 8 above in order to investigate the influence of non-oxidizing gas on the increase in [0] in the droplets. The result is the 12th
As shown in the figure. As is clear from the results shown in Figure 12, the present invention can be effectively applied even when active metals such as sponge Ti are used and droplets generated by the splash phenomenon during the melting process are recovered in some way. can.

[Example] FIG. 1 is a schematic explanatory diagram showing an example of an electron beam melting apparatus configured to carry out the method of the present invention. In FIG. 1, 1 is a shield case and 2a.

2b is an electron beam irradiation device, 3 is a raw material supply hopper, 4
5 is a water-cooled container, 5 is a vacuum exhaust system, 8 is a water-cooled mold, 9 is a slab drawing device, 11 is a pressure control device, 12 is a flow rate adjustment valve,
B indicates an electron beam, G indicates a raw material containing an active metal, M indicates a molten metal, ■ indicates a slab, and P indicates a vacuum gauge. In the electron beam melting apparatus shown in FIG.
The raw material G is melted by irradiating the electron beam B from the electron beam irradiation device 2a, and the resulting molten metal M is cooled by water from the overflow port 4a provided at the other end of the water-cooled container 4. The slab I is sent to a mold 8 and sequentially cooled and solidified, and the slab I is continuously pulled out by a slab drawing device 9. Note that the electron beam B irradiated from the electron beam irradiation device 2b retains heat of the molten metal M on the surface layer of the water-cooled container 4 and the water-cooled mold 8,
It plays the role of ensuring smooth flow of molten metal M.

During melting, a non-oxidizing gas such as Ar, He, or N2 is introduced into the shield case 1 (inside the melting atmosphere) through the flow rate adjustment valve 12, and the inside of the shield case 1 is evacuated by the vacuum exhaust system 5. do. When carrying out such an electron beam melting method, the degree of vacuum when non-oxidizing gas is introduced is determined in advance by measuring the glue crate in the melting apparatus, and then the vacuum level of kr etc. is determined based on the set value. The amount of non-oxidizing gas introduced may be adjusted using the pressure control device 11 and the flow rate adjustment valve 12. By employing this configuration, it is possible to prevent an unwanted increase in [0] in the molten metal M and, by extension, in the ingot.

The non-oxidizing gases introduced here include Ar, He,
An inert gas such as Ne or a reducing gas such as N2 is preferable; for example, using N2 may increase the nitrogen content [N], and CO or co2 may increase the carbon content [C].
and [01 may occur, which is not preferable. However, there may be cases where there is no problem even if [N] is high, so the type of non-oxidizing gas may be appropriately selected depending on the intended use of the product, required characteristics, etc. Also, the larger the amount of non-oxidizing gas introduced, the more effective it is in preventing an increase in O. However, if the degree of vacuum is too poor, the heat loss when the electron beam B advances will increase, so the vacuum It is preferable to suppress the amount of the seed valve oxidizing gas introduced so that the temperature does not fall below about 10-2 torr.

FIG. 13 is a schematic explanatory diagram showing another embodiment of the present invention, and the physical structure is the same as the example in FIG. 1. However, in this example, as shown in the figure, a heat-resistant water-cooled metal wall 17 is erected on the upper part of the water-cooled container 4 so as to surround the electron beam irradiation area from the electron beam irradiation device 2a. In this example, raw material G
This effect becomes remarkable when a sponge-like active metal is used in the water-cooled metal wall 17, and the water-cooled metal wall 17 captures the molten metal M (droplets) scattered by the splash phenomenon when the sponge-like active metal is melted. The collected metal is periodically irradiated with an electron beam to melt it and flow down into the lower water-cooled container 4, thereby preventing loss of active metal due to scattering. are doing. As mentioned above, the electron beam irradiated from the electron beam irradiation device 2b serves to retain heat of the molten metal M in the water-cooled container 4 and the surface layer of the water-cooled mold 8, and to ensure the smooth flow of the molten metal M. However, at this point, there is no longer a splash phenomenon, so there is no need to install a water-cooled metal wall F. Reference numeral 19 in FIG. 13 indicates a chloride trap provided in the upper opening of the water-cooled metal wall 17, if necessary. In other words, the splash phenomenon is caused by chlorides (MgC12 and N
These chlorides are generated by the evaporation of aC1), and these chlorides may adhere to the inner wall of the shield case 1 and obstruct high vacuuming, or may damage the oil in the oil diffusion pump, rotary pump, etc. of the vacuum exhaust system 5. It causes many problems such as pollution. In particular, Mgct2 has high hygroscopicity, so if the inside of the casing is exposed to the atmosphere during a suspension of operation, it will rapidly absorb moisture, which will significantly impede evacuation when restarting operation. In order to avoid such problems caused by chloride adhesion, in this example, a chloride trap 19 is disposed in the upper opening surrounded by a water-cooled metal wall 17 as shown in the figure, so that chloride can be adsorbed and removed. It consists of The other configurations, such as the pressure control device 11 and the flow rate regulating valve 12, are the same as in the example shown in FIG. This can prevent an involuntary increase.

FIG. 14 is a schematic explanatory diagram showing still another embodiment of the present invention, except that the droplet collection method is changed.
This is substantially the same as the example shown in the figure. That is, in this example, a collection wall 18 made of the same material as the dissolving active metal is provided in place of the heat-resistant water-cooled metal wall 17, and droplets attached to the collection wall 18 during melting are redissolved together with the collection wall 18. This is to collect the droplets. Even with such a configuration, the same effects as the embodiment shown in FIG. 13 can be achieved.

[Effects of the Invention] As described above, according to the present invention, by employing the above-described configuration, even when raw materials containing active metals such as Ti and Zr are used, the [0
] can be prevented from increasing unexpectedly. As a result, it became easy to adjust [0] in the ingot to within the specification, and it became possible to melt the ingot with low oxygen content.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram showing an example of an electron beam melting apparatus used to carry out the method of the present invention, and Figs. 2 and 3 show the influence of [0] on the strength and hardness of manufactured products. The graph, Figure 4 is a schematic illustration of the experimental equipment used to investigate how much [0] in the ingot increases during the electron beam melting process, and Figure 5 is the experimental equipment shown in Figure 4. A graph showing the relationship between [0] in the ingot and the degree of vacuum when using a non-oxidizing gas. A schematic explanatory diagram of the experimental equipment used to investigate the effect of introducing
Figure 9 is a graph showing the results of an experiment conducted using the experimental equipment shown in the figure. A schematic explanatory diagram, FIG. 10 is a graph showing the relationship between [0] in a droplet and the degree of vacuum obtained using the experimental apparatus shown in FIG. 9, and FIG. 11 is a graph showing the relationship between [0] in a droplet and the degree of vacuum, and FIG. Figure 12 is a graph showing the relationship between [0] in droplets and the leak rate.
FIG. 3 is a schematic explanatory diagram showing another embodiment of the present invention, and FIG. 14 is a schematic explanatory diagram showing still another embodiment of the present invention. 1... Shield case 2.2a, 2b... Electron beam irradiation device 3... Raw material supply hopper

Claims (1)

[Claims] 1. An electron beam melting method that comprises introducing a non-oxidizing gas into a melting atmosphere and evacuation of the atmosphere when melting a raw material containing an active metal with an electron beam.