JPH07109014B2 - Method for melting titanium and titanium alloys - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for melting titanium and titanium alloys.

[Prior Art] Conventionally, melting of titanium and titanium alloys has been performed by a consumable electrode type arc melting method using a water-cooled crucible. In this case, the material is melted after the electrode is manufactured using the material to be melted, but there is a problem of segregation or the like in the case of an unmelted material in the case of once melting or in the case of an alloy,
It was usual to carry out double melting in which the once melted material is used as an electrode to dissolve again.

In such a melting method, a large number of steps have to be performed until a sound ingot is manufactured, and the manufacturing process is complicated.

To solve this problem, for example, a melting method such as a scrap plasma melting method or a high frequency melting method has been studied, and the melting method that has been drawing attention is the high frequency melting method.

In order to carry out this high-frequency melting method, it is necessary to use a crucible made of refractory material. Recently, CaO, BN, C
There have been research reports on the high-frequency melting method that uses refractory crucibles such as titanium, but in the case of titanium (including titanium alloys), which is an extremely active metal, ductility decreases at room temperature due to contamination by impurity elements from the crucible Became a problem and it was difficult to put it into practical use. In order to minimize the contamination by this impurity element, for example, technological developments such as optimization of refractory or shortening of melting time have been carried out, but sufficient results have not been obtained.

[Problems to be Solved by the Invention] In view of various problems of the conventional methods for melting titanium and titanium alloys as described above, the present invention has been earnestly studied by the present inventors, and as a result of repeated studies, Instead of suppressing the content of the impurity element to the minimum, on the contrary, by increasing the content within an appropriate range, for example, a melting method of titanium and titanium alloys that enables scrap melting and has high ductility at room temperature. Was developed.

[Means for Solving the Problems] A feature of the method for melting titanium and titanium alloys according to the present invention is that the carbon content in the graphite crucible is 0.5 wt% or more and less than 1.8 wt% and the solid content in the titanium α phase is high. This is to perform high frequency melting while containing an amount equal to or more than the melting limit, and then precipitate the solid solution carbon as TiC in the cooling process.

The method for melting titanium and titanium alloy according to the present invention will be described in detail below.

In the titanium and titanium alloy melting method according to the present invention, a graphite crucible is used, but in the conventional high-frequency melting method, a CaO crucible is used.
When aO crucible is used, the pollutant is oxygen, and the oxygen content increases to 0.5 wt% in normal high frequency melting.If a large amount of oxygen is contained in titanium, the strength increases but the ductility does not increase. Since it deteriorates extremely, it is not suitable as a practical material. Also, oxygen is about 15 wt% for α phase titanium.
However, even if the oxygen content is increased intentionally, it is impossible to improve the ductility.

However, when a graphite crucible is used as in the method for melting titanium and titanium alloys according to the present invention, the contaminant is carbon, and this carbon has a small solid solubility limit with respect to α-phase titanium, and at the encapsulation temperature, 0.5% by weight, TiC does not precipitate even when carbon is mixed up to near the solid solution limit, exists as solid solution carbon, and as with oxygen, the ductility decreases as the strength increases due to solid solution strengthening, and Growth in
The diaphragm becomes zero. However, since it was thought that carbon should be lowered in the past, the carbon content of the high-frequency melting material using a graphite crucible was suppressed below the solid solubility limit, which on the contrary resulted in low ductility. Became.

Then, when carbon is contained in the α phase at the encapsulation point in an amount higher than the solid solution limit, most of the carbon precipitates as TiC during the cooling process, so the solid solution amount of carbon in the α phase decreases and the ductility increases. You can get it.

Therefore, lowering the carbon content does not lead to improvement of the characteristics, but rather the intentional inclusion of a carbon content of 0.5 wt% is the most important requirement. Originally non-ductile TiC
Since a large amount is precipitated during the cooling process, the ductility is reduced, so the carbon content must be less than 1.8 wt%.

[Examples] Examples of the method for melting titanium and titanium alloys according to the present invention will be described.

Example 1 Using a graphite crucible, Ti-6Al-4 in vacuum
V scrap material is melted in a high frequency melting furnace (about 5 kgf) and the melting time is changed to change the carbon content,
A room temperature tensile test was performed when annealing was performed after forging. At this time, the forging conditions were heating to a temperature of 950 ° C. and a forging ratio of 5. The annealing was performed at a temperature of 700 ° C. for 2 hours.

Table 1 shows the chemical analysis results of carbon and the tensile properties at room temperature.

It can be seen from Table 1 that high ductility (elongation) is obtained when the carbon content is 0.5 wt% or more and less than 1.8 wt%.

Example 2 In the same manner as in Example 1, titanium sponge was melted by a high frequency melting method (about 5 kgf), and the manufactured ingot was forged,
It was annealed and a tensile test was performed at room temperature. Forging condition is 800 ℃
It is heated at the temperature of, and the training ratio is 5. Annealing is at a temperature of 700 ° C. for 2 hours.

The results are shown in Table 2.

It can be seen that high ductility is obtained when the carbon content is 0.5 wt% or more and less than 1.8 wt%.

[Effects of the Invention] As described above, since the method for melting titanium and titanium alloy according to the present invention has the above-described structure, it is possible to manufacture titanium and titanium alloy having high ductility by the high frequency melting method. have.

Claims (1)

[Claims] 1. Carbon 0.5 wt% or more 1.8 in a graphite crucible
Titanium and titanium characterized by performing high frequency melting while containing less than wt% and more than the solid solubility limit in the titanium α phase, and then precipitating the solid solution carbon as TiC in the cooling process. Method of melting alloy.