JPS6039134A - Melting method of titanium group metal alloy - Google Patents

Abstract

PURPOSE:To obtain an alloy product of titanium group metals free of defect and having a regulated carbon concn. by using a compact contg. tin added with dispersed low-melting-point carbide consisting essentially of cementite as a concumable electrode, and melting in a vacuum electric arc furnace. CONSTITUTION:The starting material consisting of sponge titanium, alloying components, etc. is mixed by a mixer 1 and pressed into a compact 3 in a pressing stage 2. A rod-shaped compact obtained by linking many compacts together at a welding stage 3 is used as a consumable electrode 71 which is melted in the primary vacuum electric arc furnace 61 to obtain the melt 9 which is molded into an ingot with a mold 8. An electrode 72 of the secondary vacuum electric arc furnace 62 is obtained by linking plural said ingots together. The electrode is melted and molded into the product with a mold 82. In the above-mentioned melting method of the titanium group metal alloy, a compact, added with dispersed low-melting-point carbide consisting essentially of cementite, or consisting of Cr7C3 or Cr3C2, is used to constitute the consumable electrode 71. The carbon concn. in the alloy is regulated in this way, and the generation of the defects in the product due to the remaining unmelted substance of the added carbonaceous agent can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the method of adding carbon for strength adjustment in melting titanium group metal alloys using a consumable electrode vacuum arc furnace (hereinafter referred to as MAR) method. This invention relates to a method for melting titanium group metal alloys, which is compactly dispersed in the form of low melting point carbides such as cementite and chromium carbide, which are easy to melt, and which aims to prevent product defects due to unmelted residuals of added carbon 1 and 11.

Generally, the method for melting titanium group metal alloys is to repeat the melting process twice using the VAR method as shown in the process diagram in Figure 1.
A method of casting has been adopted8.

That is, for example, raw materials consisting of adjusted compositions of nubondititanium, titanium nuclapp, alloy components, etc. are mixed in a mixer (1) and then pressed into a crimped molded product called compact (3) in 2J, followed by a welding process (4). ) A rod-shaped compact (5) made by connecting many of the compacts (3)
) is manufactured. Next, in the primary vacuum arc furnace (6/), the rod-shaped compact (5) is used as a consumable electrode (7/) between the electrode (7/) and the molten metal (9) in the mold (8/). An arc is generated and the arc heat causes the electrode (7
/) is melted and poured into a mold (8/) to obtain a primary incot. Next, a plurality of these secondary ingots are joined together to form an electrode (7, 7) of a secondary vacuum arc furnace (6, 2).
2), and the electrode (72) is cast into a mold (8) in the same manner as above to form a secondary ingot (ingot product).

When melting titanium group metal alloys as described above, the range of the basic components of the product is determined by standards. Although it is easy to make the concentrations of these basic components meet the specifications by appropriately selecting raw materials, it is quite difficult to make the mechanical properties of the finished product, especially the tensile strength, meet the specified values. Therefore, if the tensile strength is slightly insufficient compared to the specified value, the method of adjusting the strength to meet the specified value δ is to use a reinforcing element that can significantly improve the strength by adding Sunset. Carbon, which has an extremely high ability to improve strength, is known as the most effective element for strength adjustment. The maximum concentration of carbon mentioned above is specified by the standard, but for example, T1-e A/! , -4'V combined M
T at most 11,000 J) I) It is a small amount at about ti of u.

However, this carbon generally has a low melting point, and any residue that remains during the melting process will lead to defects in the quality of the finished product, so it was said that it would be difficult to put it into practical use in the first chapter. First of all, in melting by VAR, an electrode made of pressed compacts is melted in layers in an arc furnace, and then solidified in layers in a water-cooled copper mold, so it cannot be used as normal refractory waste. Compared to melting in the vessel, the time spent in the molten state is wedge-like and short.

Therefore, in general, the first condition that should be met regarding the properties of the alloying element to be added is that it be easily soluble.

Therefore, generally when the element to be added is a high melting point element, an alloy with the elements constituting the target alloy, called a low melting point master alloy, is often prepared in advance and used instead. For example, in melting a Ti-6At-4V alloy, since (1) has a high melting point, a low melting point master alloy of At, -V2O:50 is used as a substitute for (2).

However, in the case of carbon, the above-mentioned target alloy is 173
Conventionally, graphite or T1 alloys were generally used with Tic, Zr, etc.
ZrC and the like were used as alloys.

These Tic and ZrC were then made into fine powders, but the only way to do so was to make them into fine powders of graphite, sprinkle them on a 7-pound tube, and use them in an easily soluble form. But this time
-C, ZrC, C, etc. H all have melting points of 3000"c or higher"
Since it is a carbide with a high melting point, even if the target a degree of addition to the target alloy is a relaxed condition that the saturated solubility of h00 is sufficient, it will be sufficiently melted in the short stay as mentioned above. When the melting process is not completed, a portion remains unmelted, and this residue can cause scratches and other defects, resulting in defects in the finished product.

As described above, although the effectiveness of carbon addition in improving strength is well known, the reality is that it has not been used in practice due to problems when put into practical use.

In view of the above, the present invention adds strength-adjusting carbon in the form of a low melting point carbide to the melting of titanium group metal alloys by VAR to reduce as much as possible the occurrence of defects in products due to unmelted carbide residues. This is an attempt to provide a method for melting titanium group metal alloys that facilitates the use of carbon for strength adjustment. The present inventors have conducted various research studies on low melting point carbides that can be practically used in melting titanium group metal alloys by UVAR. I did it. As a result, we discovered the following facts. That is, first of all, by forming carbon in the form of cementite (Fe3C), a low melting point of 1225°C can be obtained. Therefore, the Fe5C with high purity is extremely unstable and is not suitable for practical use.2) E, Fe5CIc Mn 'f
x Vr and by containing Cr in the range of 0% to 30%, stability to the extent that it does not cause any practical problems can be obtained, and the strength improvement ability is almost the same as that of conventional T1-C, ZrC, etc. It was also discovered that the concentration of alloy components could be controlled without exceeding the specifications.

Also, carbon can be made into a low melting point carbide by taking the form of chromium carbide, but in particular Cr7C3 has a melting point of 1"1.
780'j:, Cr3C,2 (d1890℃ is suitable, and if chromium carbide has such a small amount of Cr, even if it is added to adjust the C concentration, the amount of Cr will be small, so the degree of Cr increase will be 8th grade, O in alloy formulation
Since an increase in r concentration exceeding the standard can be avoided, it is sufficiently effective as a carbon agent for strength adjustment [L and the above F(3jC
Similarly, it was found that it could pass J↓ from the point of view of alloy component concentration as well.

- Also, as for the particle size of Fe5C, Cr7C3, and Cr3C2, by pulverizing all of them into fine powders of 0.05 or less, the ease of dissolution is greatly improved, and the dissolution of the electrode in VA-F is extremely short. Complete dissolution is obtained even during melting while staying in the bath water for hours, and undissolved portions remain.
- We also found 41 cases where there was no such thing.

The present invention has been made based on the above findings, and its gist is as follows: (1) In the melting of titanium group metal alloys in a consumable electrode type vacuum arc furnace, A method for melting titanium group metal alloys characterized by adjusting the carbon concentration in the alloy using a compact to which melting point carbides are dispersed (2) Melting titanium group metal alloys using a consumable electrode type vacuum arc furnace, Consumable electrode VCCr
A method for melting a titanium group metal alloy, which is characterized by adjusting the carbon concentration in the valley metal using a compact to which a low melting point carbide consisting of 7C3 or C]TJC,2 and a mixture thereof is dispersed.

Next, a method for melting a titanium group metal alloy according to the present invention will be explained based on the drawings.

For example, when carbon is used as a strength-adjusting element in the melting process shown in FIG. 1, carbon is added as follows.

When using cementite as a carbon additive for strength adjustment, add Mn or or from 0 to 30% in Fe2C.
When using cementite I, which has been adjusted by adding chromium carbide, use 0r7C3 or Cr3.
C, and CI''7CJ, Cr5Cx (D mixtures are used, and it is necessary for each of these additives to have a particle size of Q, 5 or less.

As for the addition method, when producing the compact (3) from raw materials by pressing in the pressing step (2) in Figure 1, the adjusting element may be dispersed and charged in the middle stage of the compact (3). In addition, the raw material and the adjusting element are charged and mixed together in the mixing step (1), and the raw material is mixed with the adjusting agent. 1il
l! After uniformly dispersing and adding the base material, it may be continuously fed to the press process, and the method of addition is not particularly limited. Since there is a possibility that melting within a short residence time during arc melting may be hindered, it is particularly desirable that the carbon agent be added in an appropriately dispersed manner.

Next, the present invention will be described in detail with reference to Examples.

Example 1 Target composition (7) shown in Table IK An ingot of 400mm x 150011111t of Ti-6At-4V alloy was
Cementite, Cr7C3, Cr3 was used as a carbon agent for strength adjustment to obtain a target value of carbon content based on an uninvented method when melting using the VAR shown in Figure 1.
Table 2-1 shows Nuponji Tj-1 AI-V alloy, pure At plate, etc. for obtaining C, 2 and target values of Ti, At, and V components. A shite compact material was prepared using the compounding ratios shown in Table 2-TI and Table 2-■.

Table 2-I Table 2-M Table 2-m Each compact was arc melted and Table 3-
Ingot test materials of the present invention examples having the components shown in Table I, Table 3-π, and Table s-m were obtained.

For comparison, melting was performed using the same compact material as in Table 2-I above, except that it did not contain cementite.
An ingot sample material of a comparative example with the components shown in was obtained.

Table 8-I Table 3-I [Tables a-m From the comparison between the invention example and the comparative example, the following was confirmed δ. That is, in Table 4 of the comparative example, since no strength-adjusting carbon was added, the carbon content remained at 0.01% at 0 minutes in the ingot, failing to reach the target value of 0.02X. On the other hand, the sample materials shown in Table 8-I, Table 3-II, and Tables a-m of the present invention examples all achieved the target value of C of 0.02%, and Table 3-■, Table As shown in Table 3-■ and Table 3-■, there was almost no variation in the components in the height direction of the ingot.

In addition, the above ingot of the present invention was forged into a 10 On$ billet, and each billet had 100111 parts at a pitch of 1 m.
When the C# of the longitudinal section of length δ was investigated, there was no segregation of C, and the method of the present invention produced extremely healthy Ti-13At-4 that satisfied the target component value and the desired tensile strength value.
An ingot product of V alloy could be obtained.

As described above, the method for melting titanium group metal alloys of the present invention is such that carbon for strength adjustment is added in the form of a low melting point compound that is easily soluble in the production of titanium group metal alloys by the VAR method. This has made it possible to avoid defects in product quality due to unmelted residues due to the addition of carbon, improving the quality of melting titanium group metal alloys.
It is particularly effective in improving tensile strength.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a process diagram of melting a titanium group metal alloy using the VAR method. ■ = mixer, 2: press process, 3: compact, 4: welding process, 5: rod-shaped compact, 6/2 primary vacuum arc furnace, 6: secondary vacuum arc furnace, 7/, 7.2: electrode, 8/
, 8J: Mold No. 1 Figure-211-

Claims (2)

[Claims] (1) In a method for melting titanium group metal alloys using a consumable electrode type vacuum arc furnace, the carbon concentration in the alloy is adjusted by melting using a compact in which a low melting point carbide whose main component is cementite is added to the consumable electrode. A method for melting titanium group metal alloys. (2) In the method of melting titanium group metal alloys using a consumable electrode type vacuum arc kettle, the consumable electrode is made of Cr7C,y or Cr.
1. A method for melting a titanium group metal alloy, which comprises melting using a compact to which a low melting point carbide consisting of 3C, 2 and a mixture thereof is added in a dispersed manner to adjust the carbon concentration in the alloy.