JP2007239030A - Alpha plus beta type titanium alloy with high specific strength, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lightweight high specific strength alpha plus beta type titanium alloy which has high specific strength equal to or higher than that of Ti-6Al-4V alloys and in which second-class sponge titanium and scrap of Ti-6Al-4V alloys comprising 80% of all the titanium alloys can be used as a raw material, and also to provide its manufacturing method. <P>SOLUTION: The alpha plus beta type titanium alloy with high specific strength has a composition which consists of, by mass, 7.1 to 10% Al, 0.1 to 3.0% Fe, ≤0.5% C, 0.05 to 0.5% O, ≤0.5% N and the balance Ti with inevitable impurities and further contains, if necessary, 0.01 to 2.0% V and further at least one or more elements selected from the group consisting of Cr, Ni and Mo within the range satisfying the condition that the total amount of the group is ≤1 mass%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high specific strength α + β type titanium alloy and a method for producing the same.

  Titanium alloys have a lower specific gravity than iron or the like, a higher specific strength (= strength / specific gravity), and excellent corrosion resistance and heat resistance. Therefore, titanium alloys are used in chemical plants, seawater utilization fields, consumer products fields (sports (golf club head), building materials, medical care, accessories), aircraft fields, and the like.

The titanium alloys are classified into α-type titanium alloys, α + β-type titanium alloys, and β-type titanium alloys, and there are many types of alloys. Among them, a typical one is a Ti-6Al-4V alloy which is an α + β type titanium alloy that occupies about 80% of the whole titanium alloy.
However, the specific gravity of the α + β type titanium alloy (Ti-6Al-4V: 4.45) is less than the specific gravity of iron (7.87), etc. There was a problem that specific gravity was large compared with aluminum alloy (3.01 in A2024).

  Moreover, Ti-6Al-4V alloy has a drawback that its use is limited because of its high price, and it is not sufficient in terms of strength. Therefore, in order to improve this drawback, Patent Documents 1 and 2 disclose titanium alloys for achieving high specific strength and low cost.

  The high-strength Ti alloy of Patent Document 1 is, by weight, Al: 5.00 to 7.00%, V: 1.00 to 3.50%, Fe: more than 0.40 to 1.00%, O: 0.20 to 0.50%, C: 0.05% or less, N: 0.05% or less, V equivalent (V equivalent = V% + 4.2Fe%) is 3.00 to 5.50% And the balance is substantially made of Ti. Further, the high-strength Ti alloy of Patent Document 2 is mass%, Al: 5.50 to 7.00%, Fe: 0.50 to 4.00%, N: 0.02 to 0.10%, and O : 0.05 to 0.40%, with the balance being Ti and inevitable impurities.

JP 2001-115221 A JP 2004-010963 A

  However, the high-strength Ti alloys disclosed in Patent Documents 1 and 2 need to contain a β-stabilizing element such as V or Mo in order to stabilize the β-phase. β-stabilizing elements are expensive and many have high specific gravity. Therefore, these high-strength Ti alloys still have problems in terms of price and weight when applied to consumer products such as golf heads and eyeglass frames, and to the automotive field where fuel efficiency is reduced.

  In particular, a golf head, which is one of titanium consumer parts, is expected to shift from a high-strength material to a Ti-6Al-4V alloy in the future due to the influence of repulsion regulation. Therefore, there is a demand for the development of a lightweight material that has the same strength or specific strength as Ti-6Al-4V alloy.

  The present invention has been made in view of the above circumstances, and aims to provide a lightweight high specific strength α + β type titanium alloy having a high specific strength equal to or higher than that of a Ti-6Al-4V alloy and a method for producing the same. To do.

  In order to solve the above problems, the present inventors have conducted extensive research on a high specific strength α + β type titanium alloy and a method for producing the same, and as a result, in order to reduce the specific gravity of the Ti-6Al-4V alloy, It has been found that the high specific strength α + β type titanium alloy can be increased in specific strength and reduced in price by substituting V for Fe with Al and adding Al which is an α-stabilizing element with a light specific gravity. Then, in order to produce a high specific strength α + β type titanium alloy, it has been found that secondary sponge titanium or titanium alloy (for example, Ti-6Al-4V alloy) scrap may be used as a raw material. Based on this knowledge, the present invention has been made.

In order to solve the above-mentioned problems, the high specific strength α + β type titanium alloy according to the present invention is mass%, Al: 7.1 to 10%, Fe: 0.1 to 3.0%, C: 0.5. %: O: 0.05 to 0.5%, N: 0.5% or less, and the balance is made of Ti and inevitable impurities.
In this case, it is desirable that the high specific strength α + β-type titanium alloy further includes V: 0.01 to 2.0% by mass.

  In this case, the high specific strength α + β type titanium alloy further includes at least one or two or more selected from the group consisting of Cr, Ni and Mo, and the total amount thereof is 1% or less by mass%. It is desirable.

  In order to solve the above-mentioned problems, the method for producing the high specific strength α + β-type titanium alloy according to the present invention is a titanium sponge and / or titanium alloy scrap containing Fe: 0.1 to 2.0% by mass%. Can be used as a raw material.

The high specific strength α + β type titanium alloy according to the present invention replaces expensive V, which is a β-stabilizing element, with cheap Fe, which is a β-stabilizing element, and adds an amount of light and inexpensive Al, which is an α-stabilizing element. Therefore, there is an effect that low cost and high specific strength are achieved.
According to the method for producing a high specific strength α + β type titanium alloy according to the present invention, secondary sponge titanium and / or titanium alloy scrap can be used as a raw material, so that low cost and high specific strength can be achieved. There is an effect that can be done.

The reason for limiting the component composition of the high specific strength α + β type titanium alloy according to the present invention will be described below. In the following, “%” means “% by mass” unless otherwise specified.
Al: 7.1 to 10.0%
Al is an element mainly strengthening the α phase by dissolving in the α phase of the high specific strength α + β type titanium alloy (α stabilizing element). Moreover, since Al is lighter than high specific strength α + β type titanium alloy, it is easy to achieve high specific strength. For these reasons, Al is added in the present invention. The reason why the lower limit of Al is set to 7.1% is that if it is added more than that, the effect of increasing the specific strength is higher than that of the conventional product. On the other hand, the upper limit of Al is set to 10.0% because if an excessive amount of Al is added, the intermetallic compound Ti ₃ Al is precipitated and the alloy becomes brittle.

Fe: 0.1 to 3.0%
Fe is an element that can stabilize the β phase and increase the alloy strength, and is also inexpensive. Therefore, Fe is an element added for the purpose of stabilizing the β phase, increasing the specific strength, and reducing the cost. As this Fe, in addition to a high-purity Fe source (for example, electrolytic iron or the like), a secondary sponge titanium or stainless steel scrap containing a relatively large amount of Fe can be used. The reason why the lower limit of Fe is set to 0.1% is that if the addition amount is less than that, the effect of stabilizing the β phase and increasing the specific strength is reduced. On the other hand, the upper limit of Fe is set to 3.0% because the alloy hardness increases when the added amount is larger than that.

C: 0.5% or less C is an element that solidifies in the α phase and strengthens the α phase (α stabilizing element). C is an element optionally added. When C is contained excessively, ductility is reduced. Therefore, the upper limit of C is preferably 0.5% or less.

O: 0.05 to 0.5%
O is an element that dissolves in the α phase and strengthens the α phase (α stabilizing element). In order to acquire the effect, 0.05% or more is preferable. On the other hand, the upper limit of O is set to 0.5% because the ductility is lowered when the added amount is more than that.

N: 0.5% or less N is an element that solidifies into the α phase and strengthens the α phase (α stabilizing element). N is an element that is optionally added. When N is contained excessively, inclusions such as TiN are formed, and therefore, fatigue cracks are generated as low density inclusions. Therefore, the upper limit of N is preferably 0.5% or less.

V: 0.01 to 2.0%
V is an element that stabilizes the β phase and improves hot formability and heat treatment properties (β phase stabilizing element). V is an element optionally added. Therefore, when adding V, V contained in the scrap of the titanium alloy (for example, Ti-6Al-4V alloy) used as a raw material can be used. The reason why the lower limit of V is set to 0.01% is that if the amount added is less than that, the effect of improving the β-phase stabilization, hot formability, and heat treatment properties is small. On the other hand, the reason why the upper limit of V is set to 2.0% is to avoid an increase in weight and an increase in price.

Cr + Ni + Mo ≦ 1.0%
Cr, Ni and Mo are elements that stabilize the β phase and improve hot formability and heat treatment (β stabilizing element). Therefore, when adding Cr, Ni, Mo, in order to obtain the effect of improving the β phase stabilization effect, hot formability, heat treatment, one or more of Cr, Ni, Mo alone Alternatively, it is added so that the total amount is 1.0% or less. When these elements are added, high-purity products whose components are adjusted may be added intentionally, or those originally contained when using stainless steel scrap or titanium alloy scrap are added incidentally. May be. The reason why one or two or more of Cr, Ni and Mo are used alone or in total is 1.0% or less is that if the content exceeds 1.0%, the weight increases and the price increases.

  Next, a method for producing a high specific strength α + β type titanium alloy according to the present invention will be described. The production method of the high specific strength α + β type titanium alloy according to the present invention is mass%, Al: 7.1 to 10%, Fe: 0.1 to 3.0%, C: 0.5% or less, O: 0.05 to 0.5%, N: 0.5% or less, and if necessary, V: 0.01 to 2.0%, and a group consisting of Cr, Ni and Mo A high specific strength α + β type titanium alloy comprising at least one or two or more selected from the group, the total amount of the group being 1% by mass or less, and the balance being Ti and inevitable impurities In the production method, as a raw material, sponge titanium and / or titanium alloy scrap containing Fe: 0.1 to 2.0% by mass is used as a raw material. As a raw material, one or more of alloy elements, iron alloy scraps such as ordinary sponge titanium and stainless steel, and titanium alloy scraps can be used in combination as necessary.

  In order to produce a high specific strength α + β type titanium alloy according to the present invention, sponge titanium containing 0.1 to 2.0% Fe is used as a raw material because Fe is the main additive element (Fe: 0.0. This is because a low-quality sponge titanium containing Fe can be used as a raw material. Further, since Fe is dispersed in sponge titanium, an effect of reducing segregation can be obtained when an alloy is used.

Furthermore, when a titanium alloy scrap, for example, a Ti-6Al-4V alloy scrap, is used as a raw material for producing a high specific strength α + β type titanium alloy according to the present invention, a titanium alloy to which an appropriate amount of V is added is obtained. It is done.
Furthermore, in order to produce the high specific strength α + β type titanium alloy according to the present invention, iron alloy scrap such as stainless steel can be used as a raw material. Therefore, manufacturing cost can be reduced. Moreover, since the iron alloy scrap may contain Ni, Cr, and Mo, these are mixed in the titanium alloy obtained when the iron alloy scrap containing these is used as a raw material. If the content of these elements is within a predetermined range, the β phase can be stabilized, hot formability and heat treatment can be improved without deteriorating the characteristics.

  Next, a method for producing a high specific strength α + β type titanium alloy according to an embodiment of the present invention will be described. In addition, this embodiment is only a mere illustration and does not limit this invention.

(Preparation of test piece)
Table 1 summarizes each example and each comparative example. For each of these Examples and Comparative Examples, secondary sponge titanium containing 0.58% Fe and 0.07% O, Al pellet, TiO ₂ for adjusting oxygen content, and electrolytic iron for adjusting Fe content And one or more of ordinary sponge titanium, stainless steel scrap and titanium alloy scrap (Ti-6Al-4V alloy scrap) containing 0.024% Fe and 0.028% O, A predetermined amount was weighed so that each component composition shown in 1 was obtained.

Next, for each example and each comparative example, each raw material weighed in a predetermined amount is put into a plasma skull furnace and melted and cast. The ingot was melted. When the component composition of each ingot was confirmed, it was as shown in Table 1.
Next, each ingot was heated to 1000 ° C., and a round bar having a diameter of 20 mm was produced by hot forging. Furthermore, each round bar was air-cooled by applying a heat treatment at 750 ° C. for 2 hours. Thereafter, No. 3 tensile test piece (diameter 6.25 mm, gauge distance 25 mm) defined in ASTM E8 was produced from each round bar after the heat treatment by machining, and each obtained test piece was used in each Example and It was set as the test piece about each comparative example.
(Evaluation test and evaluation)
The tensile test was performed using an Instron type tensile tester with a crosshead speed of 5 × 10 ⁻⁵ m / s. The results are shown in Table 1. The specific strength was obtained by measuring and calculating the specific gravity by a water immersion method.

Examples 1-6 were good results because the tensile strength exceeded 900 MPa and the specific strength exceeded 200. This is because 7.1 to 10.0% of Al that is relatively light and increases the strength of the α phase is contained, and 0.1 to 3.0% of Fe that increases the strength of the β phase is contained.
In Comparative Examples 1 and 2, the tensile strength of Comparative Example 1 was relatively high, but the tensile strength of Comparative Example 2 was less than 900 MPa, and each of Comparative Examples 1 and 2 had a specific strength of 200 or less. Therefore, it was a bad result. Moreover, since the comparative example 3 raise | generated the forge crack, the measurement of tensile strength and specific strength was not able to be performed. In particular, Comparative Example 3 contains a large amount of Al. From this, it has been found that if too much Al is contained, it cannot be rejected.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

  Since the high specific strength α + β type titanium alloy and the manufacturing method thereof according to the present invention achieve a reduction in weight and a high specific strength while realizing a reduction in cost, the field of consumer products (sports (golf club head), It can be applied in a wide range of fields such as automobile materials, chemical plants, seawater use fields, building materials, medical care, jewelry), aircraft fields, and the like.

Claims (4)

  In mass%, Al: 7.1 to 10%, Fe: 0.1 to 3.0%, C: 0.5% or less, O: 0.05 to 0.5%, N: 0.5% or less A high specific strength α + β-type titanium alloy comprising the balance of Ti and inevitable impurities.   The high specific strength α + β type titanium alloy according to claim 1, further comprising V: 0.01 to 2.0% by mass.   Furthermore, at least 1 type or 2 types or more chosen from the group which consists of Cr, Ni, and Mo is included, and those total amount is 1% or less by mass%, The high of Claim 1 or 2 characterized by the above-mentioned. Specific strength α + β type titanium alloy. In the manufacturing method of the high specific strength α + β-type titanium alloy according to any one of claims 1 to 3,
A method for producing a high specific strength α + β-type titanium alloy characterized by using sponge titanium and / or titanium alloy scrap containing Fe: 0.1 to 2.0% by mass as a raw material.