JPH0583623B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

This invention uses titanium alloys containing elements with high melting points and low solubility such as tantalum, molybdenum, and vanadium.
This article relates to consumable electrodes made of compact titanium alloys used in melting in consumable electrode type melting furnaces such as VAR (vacuum arc melting furnace) and EB (electron beam furnace).

[Conventional technology]

In general, a consumable electrode made of a compact titanium alloy is melted in a chamber, and at the same time, it is accumulated in a water-cooled copper mold placed below it and solidified sequentially from below, eventually becoming a titanium alloy ingot. However, elements such as tantalum, molybdenum, and tungsten, which are much denser than titanium and have higher melting points, remain in the ingot as unmolten material without being sufficiently melted during the process from melting in the consumable electrode to solidification in the copper mold. It often happens. It is common for titanium alloy ingots to be further melted into secondary and tertiary ingots during the process to prevent segregation, but if such unmolten ingots occur in the primary ingot, it will cause problems in the secondary and tertiary ingots. In many cases, these problems are not resolved, and this results in problems as high-density inclusions on the finished product. In order to deal with such problems, various methods have been implemented in the past. In general, there are methods of blending a low-melting-point master alloy containing additive elements in place of the pure components, and a method of preparing a compact by mixing titanium sponge and powdered alloy additive elements. As a method, for example, a method is known in which a consumable electrode for alloy melting is prepared by uniformly mixing 80 to 400 meshes of additive element powder and titanium sponge (Japanese Patent Publication No. 17413/1983). .

[Problem to be solved by the invention]

However, the conventional method has the following problems. In the conventional method, when attempting to use a master alloy, it becomes impossible to use commercially available Al--Mo master alloys, etc., when the alloy contains a large amount of high melting point elements, such as a β-type alloy. Further, it requires a large amount of man-hours and costs to produce a master alloy specially adapted to these alloys, and therefore it is advantageous to mix the additive elements in pure form. In addition, as a method for blending pure components, it is considered effective to mix the metal powder as an additive element and titanium sponge, as shown above, but in general, the smaller the particle size of pure metal powder, the more expensive it is. Moreover, impurities such as oxygen are likely to be mixed in. On the other hand, when the amount of added elements is increased, even relatively large grain size particles often remain undissolved in a low-concentration alloy system. Furthermore, if the particle size of the additive element is uniformly determined to be 80 to 400 meshes, some undissolved elements may be left undissolved depending on the additive element. This invention was made in order to solve the above-mentioned conventional problems, and provides a titanium alloy consumable electrode in which high melting point constituent elements are blended into the titanium compact constituting the titanium alloy consumable electrode in such a way that no undissolved residue is left. This is what I would like to propose.

[Means to solve the problem]

This invention determines the maximum particle size that can be dissolved without any undissolved residue depending on the type and concentration of the added element, and
Based on the knowledge that it is most effective to mix this, the maximum particle size of the powder of the pure component of the high melting point additive element is set to be equal to or less than the value determined by the following formula (1). It is.

[Chemical] d: Maximum particle size of metal powder of added element (μm) ρ _A : Density of added element (g/cm ³ ) ρ _O : Density of titanium (g/cm ³ ) C ^O _A : Ingot alloy Target concentration of component (wt%) C* _A : Concentration of alloy component at which the liquidus temperature is 2000℃ in a binary alloy consisting of titanium and alloy component (wt%) D _A : In molten titanium at 2000℃ Diffusion coefficient of alloy components (cm ² /sec) K: coefficient determined by the melting furnace The basis for deriving equation (1) is as follows. In the boundary layer between the Ti molten metal and the additive element metal particles, the mutual diffusion amount of Ti and the additive element is determined as the mass transfer of the additive element, and this is assumed to be equal to the dissolved amount of the additive element particles, and the particle size of the additive element metal powder is d. If we set _A , the relationship in equation (2) holds true. ρ _A d(1/6πd ³ / _A )/dt=-α・πd ² _A (C* _A −C
^O _A )...(2) Here, if the diffusion coefficient of the added element in Ti is D _A , the shearwood number Sh is theoretically given by equation (3). Sh=α・d _A /D _A =2.0 ...(3) From equations (2) and (3), the temporal change in particle diameter can be found using equation (4). _dA = _√A

Claims (1)

[Claims] 1. A consumable electrode for melting titanium alloy containing a high-melting point metal, characterized in that the particle size of the metal powder of the high-melting point additive element is equal to or less than the value determined by the following formula (1). Titanium alloy consumable electrode containing high melting point metal. [Chemical] d: Maximum particle size of metal powder of added element (μm) ρ _A : Density of added element (g/cm ³ ) ρ _O : Density of titanium (g/cm ³ ) C ^O _A : Ingot alloy Target concentration of component (wt%) C* _A : Concentration of alloy component at which the liquidus temperature is 2000℃ in a binary alloy consisting of titanium and alloy component (wt%) D _A : In molten titanium at 2000℃ Diffusion coefficient of alloy components (cm ² /sec) K: Coefficient determined by the melting furnace.