JPS6115786B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming crude ingots of active metals or refractory metals or their alloys. From the standpoint of resource conservation, high melting point metals and active metals are used as scrap or products generated in processes such as agglomeration and processing, and in recent years there has been a strong desire to recycle scrap that is not used due to end of life or unnecessary use. Recyclable scraps (hereinafter referred to as recycled raw materials) generated in the manufacturing process and usage of these metals and alloys are remelted in a high vacuum or in a low pressure vacuum purged with high purity inert gas. It is known to form agglomerates. These known melting and agglomeration methods include electron beam (high voltage) melting, vacuum arc (low voltage) melting, arc (low voltage) melting in an inert gas atmosphere, plasma melting, etc. as well as melting of purgin raw materials. means are mainly used. Typical examples of alloys of high melting point active metals are shown in Table 1.

【table】

[Table] Among these, Zircaloy-2, Ti-6Al-
The use of alloys such as 4V is increasing, with the former used for the nuclear power industry, and the latter used for a wide range of mechanical structural materials, mainly in the aircraft industry. Therefore, as the amount of production and usage increases, the amount of scrap generated also increases, and there is a strong desire to recycle it. When remelting recycled raw materials for these alloys, a remelting method that minimizes changes in the composition ratio, which has already been adjusted within the specification range, is strongly desired. For example, Table 2 shows a comparison of the vapor pressures of added elements for the two alloys mentioned above.

[Table] In Zircaloy-2 mentioned above, the vapor pressure of Cr at the melting point of the alloy is approximately 10 ⁵ times that of Zr,
It is easy to understand that selective evaporation of Cr occurs actively when heated and held at high temperatures. When melting virgin raw materials, additional elements are added to the melted raw materials taking into consideration the evaporation loss (yield after melting) of each additional element. It has been reported that the yield during melting of Cr in Zircaloy-2, for example, is 5-40% for high-voltage electron beam melting, 40-60% for low-voltage plasma beam melting, and ≒90% for consumable electrode arc melting. ing. As a method for melting recycled raw materials that have a loose shape, it is possible to use the above-mentioned melting method using a high-voltage electron beam or a low-voltage plasma beam as a heating source, but it is possible to directly form a healthy alloy ingot using these methods. In this case, as mentioned above, the yield of Cr is poor, and therefore it is extremely difficult to adjust the Cr content and maintain uniformity (within specification values and without segregation). Plasma beam melting has a relatively good yield, but in the case of large ingot agglomeration, compositions may be partially outside the desired composition range.
On the other hand, consumable electrode type arc (hereinafter abbreviated as AR)
Now we need to prepare the consumable electrodes. The necessary conditions for a consumable electrode are: 1. It must be connected (fused) in a rod shape to be able to pass a large current. 2. The composition of the connected (fused) part must not change.
Less reduction in added elements. Also, there shall be no contamination by foreign matter (W infusion during TIG welding) and active harmful gases (O ₂ , N ₂ , CO _2, etc.). etc. Conventionally, when melting recycled raw materials for alloys of high melting point metals and active metals such as Zircaloy-2, Ti-6Al-4V, etc., the amount of added elements decreases little.
Moreover, no agglomeration process with almost no contamination or foreign matter was found. The present invention improves these conventional methods and is a method for forming crude ingots of a desired composition from recycled raw materials of active metals, high melting point metals, and alloys of these metals. As specified in the scope, more specifically, the surface layer of the recycled raw material is melted in a vacuum plasma melting furnace equipped with a water-cooled copper hearth (preferably a rectangular cross section), and a consumable electrode for secondary melting is used. Create. In that case, additional elements may be added if necessary. The recycled raw material is charged into a water-cooled copper hearth before melting, and is additionally charged from the raw material input system attached to the melting furnace. In this case, the melting method does not require sufficient melting, and it is sufficient to fuse the material to an extent that satisfies the conditions necessary for a consumable electrode as described above. Using the melting rod thus obtained, consumable electrode type arc melting is performed to obtain a desired rough ingot.
The surface of the obtained rough ingot is cut and finished in exactly the same way as a rough ingot formed from virgin raw materials to obtain a product ingot, which can be used in subsequent processing steps such as forging, rolling, and extrusion. An example of the method of the present invention for forming crude ingots from recycled raw materials of Zircaloy-2 will be described below. Example Table 3 shows the classification, shape, weight, and composition ratio of the prepared recycled raw materials based on their source. The water-cooled copper hearth of the low-voltage plasma beam reactor has a cross section of 140mm x 140mm and a length of 1M800mm.

[Table] The melting conditions in a vacuum plasma melting furnace are current
The pressure during melting is within the range of 1×10 ^-2 Torr at 1.5KA and 65V voltage. (Substituted with Ar gas) The end of the forged material, which accounts for about 60% of the total melted raw material, is charged in a water-cooled copper hearth before melting, and the remaining 40% is the pipe end, rolled The recycled raw material at the end of the plate is cut into pieces of 50 mm or less in length and charged to the raw material supply system together with the compressed cut pieces.
Regarding Cr, in order to compensate for the evaporation loss of about 15%, Zr-Cr alloy button (mixing ratio (weight%) 80Zr-
Charge 20 pieces of 20Cr (one piece weighs 15g) to the additive element supply system. Plasma beam melting first melts the surface layer of the charged raw material (end of the forged material) in the hearth, and then additionally charges the raw material and additive elements (Zr-Cr alloy button) to melt the surface layer of these materials. .
The charge for the main melting of the additive element buttons is 10, and one button is charged every 180 mm from the hearth end position of 90 mm. All recycled material was dissolved in 48 minutes. The weight after dissolution is 209.8Kg. The weight loss in this plasma beam melting was an extremely small value of 0.095%. The molten rod has a molten part that spans the entire length and ranges from 12 to 25% of each cross section, and the molten part is retained in the molten metal without being overheated and melts into the gap at the bottom. Useful for fusing unmelted lumps. The plasma beam melted rod was then melted in a consumable electrode type arc melting furnace using a 300 mm water-cooled copper mold.The conditions are shown below. Ingot Weight 192.8Kg Dimensions Diameter 296mm x Length 437mm Consumable electrode unmelted Weight 15.4Kg Arc current 7.0KA Arc voltage 33V Pressure during melting 1 to 3 x 10 ^-3 torr The center of the top, middle and bottom of the obtained ingot Collect a sample for analysis from the surrounding area, and
The component ratio was determined by line analysis. The results are shown in Table 4. Furthermore, the average value of O ₂ for the raw material was 1170 p.pm, but the average value for the ingot produced by consumable electrode arc melting was 1090 p.pm, indicating that there was no contamination in this process.

[Table] Table 5 shows the yield of added elements in crude ingots produced by consumable electrode arc melting (plasma beam melting and consumable electrode arc melting) from recycled raw materials according to the method of the present invention.

[Table] Amount correction is included. In Table 5, when comparing Cr with the conventional method, which has a high vapor pressure and is easy to evaporate, the yield of Cr is 0.05 to 0.4 in high-voltage electron beam melting, and 0.4 to 0.4 in low-voltage plasma beam melting, as mentioned above. It was found that the yield was much better than that of 0.4 to 0.6, and that the ingot was homogeneous in all parts. Additive elements other than Cr: Sn, Fe, and Ni are each 95%
The above yield is shown, and it is therefore clear that adjustment of the component ratio is extremely easy to implement in the present invention. Although the example of Zircaloy-2 has been described in detail above, it can be similarly applied to active metals, high melting point metals, and alloys of these metals such as Ti-6Al-4V alloy, Ta alloy, Nb alloy, etc. Metals (pure metals) have advantages such as being free from contamination when making consumable electrodes and having extremely low evaporation loss.

Claims (1)

[Claims] 1. A vacuum plasma melting furnace having a recycled raw material of active metals such as titanium and zirconium, high melting point metals such as tantalum, niobium, molybdenum, and tungsten, or alloys based on these metals, and a water-cooled copper hearth. A method for producing active metals, high-melting point metals, or alloys of these metals, which consists of a process of melting the surface layer of the recycled raw material to form a rod-like agglomerate, and a process of vacuum arc melting using this rod-like body as a consumable electrode. A method of making ingots. 2. The method for agglomerating a crude ingot according to claim 1, wherein the surface layer portion of the recycled raw material in the agglomeration step is dissolved to about 12 to 25% of the cross section of the raw material. 3. The method for forming a coarse ingot according to claim 1, wherein the composition is adjusted in a vacuum plasma melting step in producing the coarse ingot of the alloy based on the metal.