JPH01222026A - Melting method for titanium and titanium alloy - Google Patents

Abstract

PURPOSE:To melt titanium having high ductility at an ordinary temp. by subjecting titanium and titanium alloy to high-frequency melting in a graphitic crucible while carbon having the specific amounts which are also those of solid solution limit or above into a titanium alpha phase thereto and depositing TIC in a cooling stage. CONSTITUTION:The titanium and titanium alloy are subjected to high-frequency melting in a graphitic crucible. At this time, carbon, 0.5-<1.8wt.%, as well as having the amounts of solid solution limit or above into a titanium alpha phase is incorporated thereto. Carbon which forms solid solution is then deposited as TIC in the cooling stage of the molten metal. As the result, the amounts of carbon which forms solid solution into the alpha phase are reduced. By this method, titanium or titanium alloy having high ductility can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for melting titanium and titanium alloys.

[Prior art] In the past, titanium and titanium alloys were melted by
It is performed using a consumable electrode arc melting method using a water-cooled crucible. In this case, electrodes are manufactured from the material to be melted and then melted. However, if the material is melted to a certain degree, there may be residual melt, or if it is an alloy, problems such as segregation may occur, so the material melted at a certain degree is not used. It was usual to carry out double melting, in which electrodes were used to melt the material again.

In such a melting method, a large number of steps must be performed before producing a sound ingot, making the production process complicated.

To solve this problem, melting methods such as scrap plasma melting method or high frequency melting method are being considered, and the melting method that is attracting attention among them is high frequency melting method.

In order to perform this high frequency melting method, it is necessary to use a crucible made of refractory material, and recently, Cab, BN,
There have been research reports on high-frequency melting methods using refractory crucibles such as %C, but titanium, which is an extremely active metal (
(including titanium alloys), contamination by impurity elements from the crucible caused a problem of reduced ductility at room temperature, making it difficult to put them into practical use. In order to minimize contamination by impurity elements, technological developments such as optimization of refractories and 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 the various problems of the conventional melting methods for titanium and titanium alloys as explained above, the present inventor has conducted intensive research and has made numerous considerations. A method for melting titanium and titanium alloys that does not minimize the content of impurity elements, but instead increases the content to an appropriate range, making scrap melting possible and having high ductility at room temperature. was developed.

[Means for Solving the Problems] The method for melting titanium and titanium alloys according to the present invention is characterized by: 0.5 wt% or more of carbon 1.8 wt% in a graphite crucible
% and above the solid solubility limit in the titanium alpha phase, and then performs high frequency dissolution while causing the solid solute carbon to precipitate as TiC in the cooling process.

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

In the method for melting titanium and titanium alloys according to the present invention, a graphite crucible is used, but in the conventional high-frequency melting method, a CaO crucible is used. and
In normal high-frequency melting, the oxygen content increases to 0.5 wt%, and when titanium contains a large amount of oxygen,
Although the strength increases, the ductility deteriorates extremely, making it unsuitable as a practical material. Further, since oxygen is dissolved in α-phase titanium up to about 15% by volume, it is impossible to improve the ductility even if the oxygen content is intentionally increased further.

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, which has a small solid solubility limit with respect to alpha-phase titanium and has a 0.5 wt%, even if carbon is mixed near the solid solution limit, TiC will not precipitate much and will exist as solid solution carbon, and as with oxygen, the ductility will decrease as the strength increases due to solid solution strengthening. , elongation and aperture at room temperature are zero. However, since it was conventionally believed that carbon should be reduced, the carbon content of high-frequency melted materials using graphite crucibles was suppressed to below the solid solubility limit, which resulted in low ductility. Became.

If carbon is contained in the α phase at the envelopment point in an amount exceeding the solid solubility limit, most of the carbon will precipitate as TiC during the cooling process, so the amount of carbon dissolved in the α phase will decrease and the ductility will decrease. You can get it.

Therefore, lowering the carbon content does not lead to improvement in characteristics, and on the contrary, reducing the carbon content by 0.5vt
The most important requirement is to intentionally contain at least % of The amount should be less than 1.8 wt%.

[Example] An example of the method for melting titanium and titanium alloy according to the present invention will be described.

Example 1 T+-6A in vacuum using a graphite crucible
I-4V scrap material is melted in a high frequency melting furnace (approximately 5 kgf)
The carbon content was varied by changing the melting time, and a room temperature tensile test was conducted when the steel was forged and then annealed. At this time, the forging conditions were heating to a temperature of 950°C,
The training ratio was set to 5. Annealing was performed at a temperature of 700°C for 2 hours.

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

From this Table 1, if the carbon content is 0.5 wt% or more, 1,
It can be seen that high ductility (elongation) is obtained at less than 8 wt%.

Table 1 Example 2 In the same manner as in Example 1, titanium sponge was melted by high frequency melting (approximately 5 kgf), and the produced ingot was forged, annealed, and subjected to a tensile test at room temperature. The forging conditions were heating at a temperature of 800°C and a forging ratio of 5. Annealing is 7
2 hours at a temperature of 00°C.

Table 2 shows the results.

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

Table 2 [Effects of the Invention] As explained above, since the method for melting titanium and titanium alloys according to the present invention has the above configuration, titanium and titanium alloys having high ductility can be manufactured by high frequency melting method. It has the effect of being possible.

Claims (1)

[Claims] 0.5wt% or more of carbon 1.8wt in graphite crucible
Titanium and titanium alloys, characterized in that high-frequency melting is carried out while containing less than % and above the solid solubility limit in the titanium alpha phase, and then the solid solute carbon is precipitated as TiC in the cooling process. How to dissolve.