JP2009161816A - Titanium material - Google Patents

Abstract

An object of the present invention is to obtain a titanium material excellent in formability while suppressing the material from being limited to a special one.
SOLUTION Iron is contained more than 0.1% by mass and 0.5% by mass or less, oxygen is contained by 0.03% by mass or more and 0.1% by mass or less, and the balance is made of titanium and inevitable impurities. The present invention provides a titanium material excellent in formability, characterized in that the crystal grain size is formed so as to have a grain size number of 10 or more.
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Description

  The present invention relates to a titanium material, and more particularly to a titanium material having excellent formability.

Conventionally, a titanium material formed in various forms such as a plate shape or a rod shape using a titanium alloy or pure titanium has been widely used as a material for producing a molded product (titanium product).
For example, in order to manufacture a titanium product, a plate-like titanium material (hereinafter, also referred to as “titanium plate”) is subjected to various processes accompanied by plastic deformation such as bending and drawing.
Titanium plates used for manufacturing such titanium products are required to have excellent formability during these processes.

  The titanium metal used as a raw material for the titanium plate, etc. is formed by reacting chlorine gas with a product obtained by removing iron from a complex oxide of iron and titanium such as ilmenite to form titanium tetrachloride. After the formation, the method of reducing separation by contacting with molten magnesium, for example, the so-called “crawl method” is used.

Further, for example, pure titanium is produced by a method of obtaining an ingot by arc melting of sponge titanium produced by this crawl method. In JIS, pure titanium is 1 depending on the content other than titanium such as iron. From species to four species are specified.
As the material characteristics of this pure titanium, JIS type 1 having the smallest content other than titanium, such as iron, has the lowest strength, and the strength becomes higher as it becomes two types and three types.
However, on the other hand, the formability decreases as the JIS type 2 and the JIS type 3 become, and for example, it is not easy to perform drawing using these.

Therefore, for example, JIS 1 type pure titanium is often used for titanium plates used for applications that require excellent formability (hereinafter also referred to as “for high moldability”). The JIS 1 type pure titanium whose amount is 0.03-0.06 mass% and whose iron content is 0.02-0.06 mass% is mainly used.
Further, it is known that the formability of a titanium material such as a titanium plate is also affected by the crystal grain size of pure titanium constituting the titanium material. It is described that a titanium plate formed with a crystal grain size such that the grain size number is any of 4 to 7 with pure titanium having an oxygen content and an iron content has excellent formability.

By the way, the reduction reaction in the crawl method is usually carried out discontinuously (batch type) in a carbon steel or iron alloy container, and therefore, in the obtained sponge titanium, the sponge titanium at a site close to the container side. Contains a larger amount of iron than sponge titanium in the region close to the center of the container.
Therefore, in order to obtain a titanium plate as described in Patent Document 1, it is possible to use only a limited raw material in the center of the container, and it is difficult to use sponge titanium in a region close to the container side. There is a problem that there is.

As described above, the fact that a titanium material with a low iron content is suitable for high molding is also described in Patent Document 2 below, and in Patent Document 2, the particle size can be reduced by containing iron to some extent. Although a fine structure having a number of 8 or more can be formed on a titanium plate, it is described that ductility is impaired when the crystal grain size of the titanium plate is refined.
Furthermore, in this Patent Document 2, the titanium plate is made so as to have an extremely low oxygen content of 0.01 to 0.03% by mass while containing a certain amount of iron to form a fine structure in the titanium plate. It is described that by forming it, the titanium plate can be softened to ensure good formability.

However, in order to obtain a titanium material as described in Patent Document 2, it is necessary to pay close attention not to cause oxidation during the manufacturing process for producing the titanium material. Usually, since a certain amount of oxygen is contained, there is a problem that an expensive raw material having an extremely small oxygen content must be used.
Therefore, it is difficult to obtain the titanium material described in Patent Document 2 without using a special raw material as well as the titanium material described in Patent Document 1.
That is, conventionally, there is a problem that it is difficult to obtain a titanium material excellent in formability while suppressing the raw material from being limited to a special one.

JP 63-60247 A JP 2006-316323 A

  This invention makes it a subject to obtain the titanium material excellent in the moldability, suppressing that a raw material is limited to a special thing.

  As a result of intensive studies on the formability of titanium material, its components and crystal grain size, the inventor has found that when iron is contained in a larger amount than conventional titanium material, rather, the case having a microstructure is formed. As a result, the present invention has been completed.

  That is, the titanium material excellent in formability according to the present invention contains iron in excess of 0.1% by mass and 0.5% by mass or less, and oxygen is 0.03% by mass or more and 0.1% by mass or less. The balance is made of titanium and inevitable impurities, and the crystal grain size is 10 or more.

According to the present invention, iron is contained in an amount exceeding 0.1% by mass and 0.5% by mass or less, oxygen is contained by 0.03% by mass or more and 0.1% by mass or less, and the balance is titanium and inevitable impurities. Since the raw material which consists of can be used for formation of a titanium material, the restriction | limiting with respect to the raw material used for a titanium material can be eased.
In addition, since the crystal grain size is 10 or more, the titanium material can exhibit excellent formability.
That is, according to the present invention, it is possible to provide a titanium material excellent in formability while suppressing the raw material from being limited to a special one.

Hereinafter, with regard to a preferred embodiment of the present invention, components contained in the titanium material of the present embodiment will be described first.
In addition to titanium, the titanium material of the present embodiment contains iron and oxygen.
In addition to these, inevitable impurities are contained.

The iron is contained in the titanium material of the present embodiment in any content within the range of more than 0.1% by mass and 0.5% by mass or less.
In general, in a titanium alloy, iron is a β-stabilizing element, and some of the solid solution forms a β-phase, and further exists as TiFe by heat treatment or the like, thereby inhibiting the growth of crystal grains. Therefore, conventionally, when a large amount of iron is contained in the titanium material, the crystal grain size becomes smaller (the flow number becomes larger), and the strength of the titanium alloy and the workability of the polishing process can be improved. It was thought that the index indicating ductility (molding processability) such as Eriksen value would decrease.
However, as will be described later, when the content of iron in the titanium material is larger than that of the conventional titanium material, it is possible to improve the formability by forming a microstructure having a small crystal grain size. .

It should be noted that the iron content in the titanium material of the present embodiment has a value exceeding 0.1% by mass when the iron content is 0.1% or less in the reduction reaction vessel in the crawl method. This is because sponge titanium containing a large amount of iron, such as nearby sponge titanium, may not be usable.
In addition, when the iron content is 0.1% or less, the α phase is a single phase, or even if it becomes two phases of α + β, the β phase becomes very small, and the particle size number is increased. Thus, it becomes difficult to obtain the effect of the present invention that the moldability is improved.

  In addition, the iron content in the titanium material of the present embodiment is 0.5% by mass or less when the iron content exceeds 0.5% of the β phase in the two phases of α + β. This is because the β ratio remains even in the case where the volume ratio is increased to a predetermined level or more and the room temperature is reached after the finish annealing is finished, which adversely affects the formability such as a decrease in ductility.

The oxygen is contained in the titanium material of the present embodiment in any content within the range of 0.03% by mass or more and 0.1% by mass or less.
Note that the oxygen content in the titanium material of the present embodiment is 0.03% by mass or more, and it is difficult to use a general raw material if the oxygen content is to be less than 0.03% by mass. Not only that, but there is a risk that great care must be taken to prevent oxidation during the production of the titanium material.
In addition, when the oxygen content is reduced, the strength of the titanium material is lowered, and it may be difficult to impart sufficient strength to a product (molded product) manufactured using the titanium material.

  In addition, the oxygen content in the titanium material of the present embodiment is 0.1% by mass or less because when the oxygen content is a value exceeding 0.1% by mass, the molded product produced from the titanium material This is because the ductility of the titanium material is lowered while the strength can be improved, and it becomes difficult to impart sufficiently excellent formability to the titanium material.

This will be explained in more detail. Oxygen has a function of improving the strength by dissolving in titanium, and depends on manufacturing conditions. For example, the strength of a titanium material containing 0.03% by mass of oxygen is 305 MPa. It will be about.
For example, the strength of the titanium material containing 0.1% by mass of oxygen is about 410 MPa, and the strength of the titanium material containing 0.3% by mass of oxygen is about 710 MPa.
On the other hand, the ductility decreases as the oxygen content increases and depends on the production conditions. For example, the elongation of a titanium material containing 0.03% by mass of oxygen is about 58% in the rolling direction, whereas oxygen The elongation of the titanium material containing 0.3% by mass is about 22% in the rolling direction.

  Examples of the inevitable impurities include impurities usually contained in industrial titanium other than iron and oxygen, such as hydrogen and nitrogen. These contents in the titanium material of the present embodiment are usually JIS H. The content is defined as 4600 pure titanium JIS 4 types, and preferably the content corresponding to JIS 2 types.

  In the present embodiment, the form of the titanium material is not particularly limited as long as it is formed of a raw material containing the above components, and various forms such as a plate shape, a rod shape, and a linear shape are employed. Can do.

However, the titanium material of the present embodiment needs to be formed so that the particle size number is 10 or more.
The reason why the grain size number of the titanium material in the present embodiment is set to the grain size number 10 or more is that when the grain size number is less than 10 and the crystal grain size is increased, the Erichsen value is decreased, which is accompanied by plastic deformation such as drawing. This is because the moldability for processing may be reduced.
More specifically, when the particle size number is less than 10, the Erichsen value may be lowered, for example, less than 10 mm.

From such a viewpoint of formability, it is preferable to form the titanium material so that the particle size number becomes a larger value, but if the particle size number is increased too much, the production for obtaining the titanium material There is a risk that the labor of the process increases.
From such a viewpoint, the titanium material is preferably formed so that the crystal grain size is 14 or less.
That is, the crystal grain size of the titanium material in the present embodiment is preferably any value in the range of the particle size number of 10-14.

The crystal grain size of the titanium material can be adjusted according to the conditions at the time of manufacturing the titanium material. For example, after the cold rolling, finish annealing is performed to recrystallize the rolled structure, and then the crystal is grown. Can be adjusted.
The crystal grain size can be adjusted by the annealing time and its temperature. Normally, the higher the annealing temperature, the longer the annealing time, the more the crystal growth proceeds, and a structure with a smaller grain size number (large crystal grains) is formed in the titanium material. .

Further, the iron content also affects the adjustment of the crystal grain size.
More specifically, it is known that when the iron content in pure titanium is increased, the crystal grain size becomes smaller (the crystal grain size becomes larger).
For example, when the iron content is changed from 0.04% by mass to 0.27% by mass in the range of oxygen content of 0.09 to 0.11% by mass, after 50% cold rolling, 800 ° C. × 10 It has been reported that the average grain size changes from about 63 μm to about 14 μm when performing annealing for a minute (Toyoru Kondo, Shinjiro Suzuki: Sumitomo Metals Magazine, Vol. 8, No. 4, p201) Fig. 42).
In general, titanium containing 0.06% by mass or more of iron has a two-phase structure of an α phase and a β phase when held at a temperature of 595 ° C. or higher.
When iron is less than 0.06% by mass, the β phase is slightly crystallized in a part of the temperature range of 500 to 800 ° C., but most of it is an α phase single phase.
In the conventional high-molding titanium material, when the iron content is less than 0.06% by mass or when the oxygen content is extremely low oxygen of 0.01 to 0.03% by mass and contains a large amount of iron However, since the iron content is 0.1% by mass or less, most of it becomes an α-phase single phase during annealing.
Therefore, the growth rate of the crystals (α grains) is large, and the crystal grain size is rapidly increased (grain size number is decreased) as the annealing time elapses.
On the other hand, since the titanium material of the present embodiment has the iron content and the oxygen content as described above, it has an α + β two-phase structure during annealing.
Therefore, since the growth of α grains is suppressed to β grains, the crystal grain size is suppressed from rapidly increasing (the particle size number is decreased).
That is, the titanium material of the present embodiment contains 0.03% by mass or more and 0.1% by mass or less of oxygen and iron exceeds 0.1% by mass and 0.5% by mass or less. Thus, it is easy to adjust the crystal grain size to grain size number 10 or more by annealing, and not only can the restriction on the raw material be relaxed, but also has an effect that the production is easy.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

(Examples 1-19, Comparative Examples 1-7, Conventional Examples 1-6)
(Production of titanium plate)
An ingot was produced using a small vacuum arc melting furnace, and the ingot was forged at 1150 ° C. to produce a slab having a thickness of 50 mm.
The slab was hot rolled to a thickness of 5 mm at 850 ° C., annealed at 750 ° C., the surface scale was removed, and a plate-like titanium material (titanium plate) having a thickness of 0.5 mm was produced by cold rolling.
The titanium plate was subjected to finish annealing at a temperature of 600 to 850 ° C. for 1 minute to 10 hours in a vacuum atmosphere to adjust the crystal grain size.
In addition, about the sample extract | collected from the board from which the scale of the surface was removed, iron content was measured according to JIS H1614 and oxygen content was measured according to JIS H1620.
The results are shown in Table 1.
Further, Table 1 shows the results of measuring the crystal grain size (grain size number) at the substantially central part of the cross section of the titanium plate by the cross line segment method of JIS G0551.
Moreover, the evaluation result described as a comparative example (No. 39-44 of Table 1) in patent document 2 (Unexamined-Japanese-Patent No. 2006-316323) is shown collectively in Table 1 as the prior art examples 1-6.

(Evaluation)
(Erichsen value)
The titanium plate produced as described above was cut into 90 mm squares to form test pieces, and the test pieces were measured for Erichsen values according to JIS Z2247. The results are shown in Table 1.
Note that graphite grease was used as the lubricant, and the occurrence of cracks was visually determined.
Further, the titanium plate of each Example after the measurement of the Erichsen value exhibited a good appearance without observing rough skin.

As can be seen from the results shown in Table 1, unlike the conventional example, in the titanium material containing iron in a value exceeding 0.1 mass%, the formability is improved by increasing the particle size number. It can be made.
Therefore, for the titanium material of the present invention, sponge titanium containing a large amount of iron, such as sponge titanium in the vicinity of the reduction reaction vessel in the crawl method, can be used for formation.
Further, it can be formed without using a special raw material such as an extremely low oxygen material.
That is, according to the present invention, it is possible to provide a titanium material excellent in formability while suppressing the raw material from being limited to a special one.

Claims (1)

  Iron is contained in an amount exceeding 0.1% by mass and 0.5% by mass or less, oxygen is contained in an amount of 0.03% by mass or more and 0.1% by mass or less, and the balance is composed of titanium and inevitable impurities, and the crystal grain size is A titanium material excellent in formability characterized by being formed to have a particle size number of 10 or more.