JPS63118023A - Melting method for titanium - Google Patents

Abstract

PURPOSE:To enable efficient remelting by using cutting waste without any foreign material, which causes material defect, by obtaining the cutting wastes of Ti-base metal as the remelting raw material by using ceramic tool having specific material and density. CONSTITUTION:The cutting wastes of pure Ti or Ti alloy are obtd. by using the tool having oxiding, nitriding or oxy-nitriding ceramic as main composition and <=4.5g/cm<2> density and this cutting wastes are used as remelting raw material. Then, as the tool material to be available, the ceramic, such as Al2O3, Si3N4, cubic system BN, SIALON (Si-Al-O-N series), etc., as main composition, is recommended. The cutting wastes obtd. by using the above tool are available for the remelting raw material, since the material of the above tool mixed in the cutting wastes is easily melted in the molten Ti. Further, in case of density of the tool material exceeds 4.5kg/cm<2>, the tool material sometimes is not perfectly melted but settles in the molten Ti and in case of being <=4.5kg/cm<2>, the tool material has enough time to melt and if it remains without melting, it floats up and is separated.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for dissolving titanium.

(Prior Art) The method of melting titanium that is currently the most widely used industrially is the consumable electrode vacuum arc remelting method.

The material to be dissolved is mainly compact titanium sponge molded and welded electrodes are used. By the way, the production of this titanium sponge consumes a lot of energy and is expensive, so it is necessary to efficiently digest scrap.

However, in order to utilize scrap, measures must be taken in the melting system to prevent material defects caused by dissimilar metals that may be mixed into the scrap raw material.

One of the sources of this scrap is chips generated by cutting operations such as turning and milling of titanium ingots and titanium products. However, since titanium has a lower degree of heat transfer and a lower specific heat per unit volume than steel, it is difficult for the heat generated during cutting to be released through the work material. Therefore, the tool tip temperature can easily be reduced to 10
The temperature rises to nearly 00'c.

(Problem to be solved by the invention) Therefore, for the reasons mentioned above, carbide tools (WC-CO) are usually used as cutting tools for titanium, but when cutting tools made of such materials are used, At around 1000°C, titanium forms a eutectic with iron group elements, forming brittle intermetallic compounds and causing defects, resulting in tool material being mixed into the chips. However, when these chips are used as raw materials for remelting, the carbide components are not completely dissolved and remain as high-density inclusions, which affect the shape of the material, so the cutting chips are rarely used as remelting scraps. is the current situation.

The present invention has been made to solve the above-mentioned problems, and provides a method for efficiently using and remelting titanium chips free of foreign substances that would cause material defects.

(Means for solving the problem) The present inventors investigated the machinability of various tool materials and the solubility in molten titanium in order to avoid mixing of cemented carbide components into titanium chips, and found that titanium Due to the relationship with the density of , pure titanium or titanium alloy chips cut with a tool whose main component is oxide, nitride, or oxynitride ceramics with a density of 4.5 g/cffl or less should be used as a remelting raw material. The present invention was established based on the discovery that this method is effective in obtaining melt-molded material free of material defects.

That is, the present invention has an oxide, nitride, or oxynitride ceramic as its main component, and has a density of 4.5 g/cll! The gist of this method is to obtain cutting waste of pure titanium or titanium alloy using the following tool, and to use this cutting waste as a raw material for remelting.

Here, the tool material applicable to the present invention is AI! 0
．． 3. Ceramics whose main components include Si3N4, C-BN (cubic BN), and Sialon (Si-AI-0-N system) can be mentioned.

However, in the present invention, the chips obtained by cutting with a tool mainly composed of oxide, nitride, or oxynitride ceramics are effective as raw materials for remelting because of these tool materials mixed in the chips. This is because it easily dissolves in molten titanium.

This is thought to be due to the large amount of oxygen and nitrogen solidly dissolved in titanium. For example, SiJ.

is dissolved in the Ti1 hot water by the decomposition reaction 5iJ4-3Si + 4N.

On the other hand, tool materials made of carbides such as WC and borides such as TiB2 have a small amount of solid solution of carbon and boron in Ti, so they are not dissolved and remain as high-density inclusions.

In addition, in the present invention, the density of the tool material is set to 4.5 g/
The reason why it is limited to less than cnt is that if it exceeds 4.5 g/c+J, the tool material will settle in the molten titanium, making it impossible to obtain sufficient dissolution time and the melt may remain. However, if it is 4.5 g/cJ or less, it will float in the molten metal, allowing sufficient time for dissolution, and even if there is any remaining molten metal, it can be floated and separated.

(Function) The present invention obtains cutting waste of pure titanium or titanium alloy using a tool containing oxide, nitride, or oxynitride ceramics as a main component and having a density of 4.5 g/cI11 or less. Since titanium is used as a re-melted raw material, there is no foreign matter that could cause material defects in the titanium chips.

(Example) Next, the results of an experiment conducted to confirm the high cost of the method of the present invention will be described.

Chips obtained by cutting pure titanium using a Si□N4-based tool and a carbide tool were respectively crushed and pickled. Of these, the titanium chips obtained by cutting with the carbide tool were further subjected to magnetic separation to remove the carbide component. However,
Each chip was compacted, welded and used as an electrode for vacuum arc melting to obtain an ingot weighing approximately 1 ton. In addition, an ingot made from titanium sponge was also produced as a comparison material.

As a result, foreign matter was observed under a microscope in the ingot in which the cutting chips from the carbide tool had been dissolved, even though it had gone through the magnetic separation process.

When this foreign substance was investigated using an X-ray microanalyzer (EPMA), it was found to be WC.

On the other hand, no high-density inclusions were observed in the ingot in which chips obtained by cutting with a 5ilN four-base tool were dissolved and in the ingot in which sponge titanium was dissolved.

Ti thin plate (L3mm) made by rolling these melted materials
As a result of ultrasonic flaw detection, three defective areas were detected per 10m in the thin plate that was rolled by melting chips obtained by cutting with a carbide tool, and these defective areas contained W of about 70 μm.
C existed.

On the other hand, no defective parts were detected in plate 71, which was rolled by melting chips and titanium sponge obtained by cutting with a 5iJ4-based tool.

Note that although this example uses a consumable vacuum arc remelting method, it is not limited to this;
Of course, it is also possible to use a plasma beam melting method, a plasma beam melting method, an electron beam melting method, or the like.

(Effects of the Invention) As explained above, the present invention has an oxide, a nitride, or an oxynitride ceramic as a main component, and has a density of 4.5 g/
cn! The following tool is used to obtain pure titanium or titanium alloy cutting waste, and this cutting waste is used as a raw material for remelting, so there is no foreign matter that could cause material defects in the titanium chips. In other words, since the chips used in the method of the present invention are high-grade titanium scraps, they can be efficiently remelted without going through an impurity removal process such as magnetic separation.

Claims (1)

[Claims] (1) Cuttings of pure titanium or titanium alloy are obtained using a tool mainly composed of oxide, nitride, or oxynitride ceramics and having a density of 4.5 g/cm^3 or less, and the cuttings are remelted. A method for dissolving titanium as a raw material.