JPS62176666A - Melting method by high energy density beam - Google Patents

Abstract

PURPOSE:To form fine crystal grain structure and to obtain a high-quality ingot having the fine crystal grain structure by successively scanning the top surface of the ingot at a specific area rate and forming molten pools as small as possible. CONSTITUTION:Raw material lumps 10 for melting are melted by electron beams 18, 19 while the lumps are supplied from above to form the ingot 12. The top surface of the ingot 12 is successively scanned at <=5% area rate while said surface is locally melted. The electron beams are respectively deflected 18, 109 by a deflecting coil 20 to melt the surface of the ingot 12 and to form the molten pools 16, 17. The molten pools 16 and 17 and parted form each other and are not continuous. Since the molten pools which are melting parts are successively scanned and moved, solidification is quickly executed and since the molten pools are small, the workability of the fine crystal grain structure in a post stage is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a high energy density beam melting method for producing an ingot having a fine grain structure and excellent workability.

[Technical background of the invention and its problems]

In general, the high energy density beam melting method uses a cooled crucible.The molten raw material rod placed above the crucible and the ingot surface in the crucible are irradiated and melted simultaneously by a high energy density beam, and the molten material is removed from the molten raw material rod. The raw material is melted by dropping it onto the ingot in the crucible, or the surface of the ingot in the crucible is irradiated with a high energy density beam to melt it and then the raw material is added to the solidified ingot. A rod-shaped ingot is manufactured by sequentially pulling the ingot downward or solidifying and growing upward.

In this high energy density beam melting method, an electron beam, a plasma electron beam, a plasma jet, a light beam (including a laser beam), etc. are used as the high energy density beam, and generally special steel, Ni-based alloy, Ti-based alloy, Zr Base alloy or high melting point metal (W, Mo,
It is widely used as a method for melting Nb, Ta, etc.-based alloys.

Regardless of the high energy density beam melting method, in the conventional method, the entire upper surface of the ingot is melted at the same time, and the operation is carried out so that a large amount of melting can be obtained per unit time.

Since such a melting method is adopted, a melting pool is formed throughout the inside of the crucible during melting. Therefore, in proportion to the size of the molten pool, a coarse grain structure is formed that extends largely in the direction where the cooling temperature gradient is maximum. Further, in the center of the ingot, coarse crystal grains are formed that extend in the axial direction of the ingot.

Generally, such impurities in an ingot tend to be concentrated at grain boundaries during solidification. In addition, an ingot with coarse grains has a smaller total area of grain boundaries than an ingot with wide grains. Therefore, if the amount of impurities contained in both is the same, the amount of grain boundaries per unit area The amount of impurities (the concentration of impurities at grain boundaries) is greater in ingots made of coarse grains.

Grain boundaries with a high impurity concentration have low strength, and after the ingot is created, grain boundary cracks are likely to occur during extrusion, forging, and other subsequent processes, resulting in poor workability.
There was a problem in that high-temperature heating was required during processing, resulting in high costs.

[Purpose of the invention]

This invention provides a high-energy-density beam melting method that improves the drawbacks of conventional methods, forms a fine grain structure, and can obtain high-quality ingots with improved workability in subsequent processes. It is.

[Summary of the invention]

The present inventor noticed that the conventional method of melting the entire upper surface of an ingot at the same time resulted in coarsening of the crystal grains, and by making the melt pool during melting as small as possible, the crystal grain structure was refined. We have discovered a high energy density beam melting method.

That is, the present invention provides a high energy density beam melting method in which a raw material is melted by a high energy density beam while being supplied from above, and is sequentially cooled in a cooled crucible to form a rod-shaped ingot. The method is characterized in that the upper surface of the ingot is sequentially scanned and melted while locally dissolving the upper surface to be melted at an area ratio of 5% or less. As a result, the small molten pool, which is the molten part, scans the surface of the ingot while sequentially moving, so that solidification occurs rapidly and, since the molten pool is small, a fine grain structure is obtained.

Furthermore, since the continuity of melting in the axial direction of the ingot is interrupted, the generation of crystal grains that grow long in the axial direction near the center of the ingot is also prevented.

Ingots with finer grains have a larger total area of grain interfaces than ingots with coarse grains, and the concentration of impurities per unit area of grain boundaries is lower. Cracking is reduced and processing temperatures can be lower than for coarse grained ingots.

In the present invention, the area to be simultaneously melted is set to 5% or less of the upper surface of the ingot to be melted, but if a larger area than this is simultaneously melted, the crystal grains of the resulting ingot may become coarse. This is not desirable because it is significant.

The method of supplying the molten raw material in the present invention is to melt the raw material rod with a part of a high energy density beam that is melting the ingot surface above the crucible, or with a separate high energy density beam. When melting the raw material and dropping it onto the ingot surface, the position of the raw material rod is moved in synchronization with the high energy density beam that is scanning the ingot surface, and the molten raw material dripping from the raw material rod is In addition, in the raw material supply method in which unmelted bulk raw material is supplied to the upper surface of the ingot and the raw material is simultaneously melted on the upper surface of the ingot, the raw material must be supplied near the melting pool. In synchronization with the movement, raw materials that need to be supplied near the molten pool or evenly spread over the upper surface of the ingot may be supplied unevenly to the upper surface of the ingot. This is undesirable because the height becomes uneven, leading to uneven ingot growth.

In addition, in order to interrupt the continuity of melting on the upper surface of the ingot and obtain an ingot with a more *m grained Mi weave, it is necessary to melt a certain part and then move the high energy density beam to the adjacent part by scanning. Before melting that part, it is effective to reduce the beam power once, solidify the previously melted part, and then increase the beam power again to melt the part that has moved.6 However, in this method, the beam power Since there is a time when the temperature is lowered, the time required for melting becomes longer. In order to prevent this, there is a method of scanning the upper surface of the ingot by moving a high energy density beam at intervals so that the molten pool undergoing melting at one point does not adjoin the molten pool undergoing melting at the next point. is valid. Discontinuous melting of the upper surface of the ingot by moving a high-energy-density beam at high speed can also be achieved by the optical beam method, which scans by moving a reflecting mirror using a mechanical method. Easier and faster scanning can be achieved by an electron beam method in which the beam is changed and electrically scanned. This shows that the electron beam method is the most excellent heating method to be applied to this melting method, in combination with the feature that the melting process is performed in a high vacuum and has a particularly excellent purification effect. .

Next, an apparatus for carrying out the method of the present invention will be explained.

The figure shows an example of a case where a water-cooled metal crucible is used to melt a lumpy raw material using an m beam to obtain an ingot.

In the figure, l is an electron iron that generates an electron beam, and is attached to a vacuum chamber 3 via an airtight insulator 2. 4
is a water-cooled metal crucible, and cooling water 5 passes through the inside to cool it. 6 is the bottom surface of the crucible, which is water-cooled like the metal crucible 4, and can be moved up and down by a vertical mechanism 7 driven by a motor 8. Reference numeral 9 denotes a raw material hopper which holds a small lump 10 of the melted raw material inside and intermittently supplies the raw material into the metal crucible through an opening/closing device 11.

13 is the raw material falling from the hopper onto the ingot surface.

The supplied raw material is melted by an electron beam to form an ingot 12. At some point, the electron beam is deflected by the deflection coil 20 into a beam 19, forming a molten pool 17 on the upper surface of the ingot. At the next point, the electron beam is deflected as beam 18 to melt the new ingot surface and the raw material 15 on the ingot, forming a molten pool 16.

The melt pools 16 and 17 are separated from each other and are not continuous, and 14 is an unmelted raw mass on the ingot.

When the entire ingot surface is scanned and melted in this manner, new raw materials are uniformly spread over the ingot surface, and melting is repeated. These devices are installed in the vacuum chamber 3 and evacuated from the vacuum outlet 21 by an exhaust system (not shown).

Note that the supply of current and voltage to the electron gun and the current to the deflection coil is controlled by an electron beam power supply/control device 22. Furthermore, the supply of JM material and the withdrawal of ingots are controlled by the control device 23.

〔Effect of the invention〕

According to the high-energy-density beam melting method of the present invention, by scanning the entire upper surface of the ingot while locally melting in a narrow range, the ingot is made into a fine crystal grain structure, resulting in high-quality products processed by extrusion, forging, etc. Ingots can be obtained.

[Embodiments of the invention]

(Example 1) A large number of cylindrical compacts were made from MO powder with a particle size of approximately 5 μm using an automatic powder compaction machine equipped with a small mold, and then one
Sintering was carried out in a hydrogen stream at 750° C. for 30 minutes to produce a sintered body of the melted raw material with an outer diameter of 2 mm and a length of 4 III m.

Next, electron beam melting was performed in a vacuum of 10-' Torr using a water-cooled steel crucible with a movable bottom and an inner diameter of 60III m. In this case, the accelerating voltage and electron current were 50 KV and 410 mA at the center of the ingot. 50KV in the surrounding area of
, 420 mA, and a molten metal pool with an area percentage of 3 to 4% was locally formed on the upper surface of the ingot. The electron beam is moved continuously to avoid melting more than 4% of the area at a time, and the upper surface of the ingot is scanned, and the raw material is intermittently and evenly spread over the ingot surface while melting and forming a rod-shaped material. The ingot was produced by cutting off the upper part of the ingot by 5 mm and the lower part by 51I11,
The surrounding area was peeled to a thickness of 1 mm. When this ingot was analyzed, impurities were found to be 25 ppm by weight of C and 5 ppm by weight of O□.

The macrostructure of this ingot was observed by wA and its average particle diameter was measured, and the results are shown in Table 1.

In addition, block-shaped test pieces measuring 25 nu++ length x 50 cm width x 20 x height were cut out from the peeled ingot and heated to 1000°C, 1100°C, 1250°C, and 1400°C, respectively.
It was heated at 0.degree. C. and compressed by 50% in the height direction using a high-speed forging machine, and the state of crack generation was examined, and the results are shown in Table 2.

(Example 2) Using the same raw materials and equipment as in Example 1, melting was performed using the same electron current and acceleration voltage. The scanning method of the electron beam is different from that in Example 1, in that the upper surface parts of the ingots that are not adjacent to each other are successively scanned and melted locally, and the melting is performed while the raw material is uniformly and intermittently scattered over the upper surface of the ingot. A rod-shaped ingot was produced.

When this ingot was analyzed, the impurity was 30 heavy iron ρρ.
■ and 0□ were 6 ppm by weight. A test piece was cut out from the ingot in the same manner as in Example 1, and macrostructure observation and high temperature plastic workability tests were performed. The results obtained are shown in Tables 1 and 2.

(Comparative example 1) Melting was performed using the same raw material equipment as in Example 1.

When the entire surface of the ingot was scanned at high speed at an accelerating voltage of 50 V and an electron current of 1470 mA, a continuous molten metal pool was formed over the entire surface. A rod-shaped ingot was manufactured by continuously supplying raw materials and melting the mixture. Analysis of this ingot revealed that the amount of impurities was 20 ppm by weight for C and 3 ppm by weight for PPfil Ox.

Test pieces were cut out from the ingot in the same manner as in Example 1, and tests for macro mats and high temperature plastic workability were conducted.

The results obtained are shown in Tables 1 and 2.

Table 1 Table 2 0: None ×: Yes 1... Electron gun, 2... Insulator.

3... Vacuum chamber, 3... Water-cooled metal crucible,
5... Crucible cooling water, 6... Mobile crucible bottom plate, 7... Bottom plate moving mechanism, 8... Motor, 9...
...Raw material hopper, 10...Dissolved raw material mass, 11
...Raw material supply port opening/closing device.

12... Ingot, 13... Falling melted raw material lump, 14... Unmelted melted raw material lump that will become the ingot surface, 15... Melted raw material lump that is melting, 16... Existing. Molten metal pool at a point in time, 17... Molten metal pool at another point in time, 18... Electron beam at a certain point in time, 19.
...electron beam at another time, 20...electron beam deflection coil, 21...vacuum inlet, 22...electron beam power supply and control device, 23...
Raw material supply and ingot withdrawal control device.

Agent: Patent Attorney Noriyuki Chika Same Bamboo Flower Kikuo

Claims (4)

[Claims] (1) In a high-energy-density beam melting method in which a high-energy-density beam melts the raw material while supplying it from above and forms a rod-shaped ingot while cooling it in a crucible, the upper surface of the ingot to be melted is A high energy density beam melting method characterized by sequentially scanning and melting the upper surface of an ingot while locally melting at an area ratio of 5% or less. (2) A high energy density beam is scanned from one melted part of the upper surface of the ingot to an adjacent part, and before melting that part, the output of the beam is temporarily weakened, and after the melted part has solidified. A high energy density beam melting method according to claim 1, characterized in that adjacent portions are melted. (3) It is confirmed that the molten part of the upper surface of the ingot that is being melted by the high energy density beam at one point in time and the molten part that has moved at the next time are separated from each other by the solid state ingot part and are not continuous. A high energy density beam melting method according to claim 1, characterized in: (4) The high energy density beam melting method according to claim 1, wherein the high energy density beam is an electron beam.