JP2003201530A - High-strength titanium alloy with excellent hot workability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium alloy which has cold strength equal to or higher than that of a Ti-6Al-4V alloy used for general purpose as a high-strength titanium alloy and also has excellent hot workability including hot forgeability and subsequent secondary workability and can be efficiently hot-worked into desired shape at a low cost. <P>SOLUTION: In the high-strength titanium alloy with excellent hot workability, tensile strength at room temperature (25°C) after annealing at 700°C is ≥895 MPa and deformation resistance at high-speed tension at 850°C is ≤200 MPa and, further, the ratio between the tensile strength and the deformation resistance is ≥9. <P>COPYRIGHT: (C)2003,JPO

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【発明の属する技術分野】本発明は、実用温度域で高強
度を示すと共に高温時の変形抵抗が小さくて熱間加工性
に優れたチタン合金に関し、このチタン合金は、高強度
と優れた熱間加工性を活かして、例えば航空機分野、自
動車分野、船舶分野などに幅広く利用できる。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium alloy which exhibits high strength in a practical temperature range, small deformation resistance at high temperature and excellent hot workability. The titanium alloy has high strength and excellent heat resistance. Utilizing the inter-workability, it can be widely used in the fields of aircraft, automobiles, ships, etc.

【０００２】[0002]

【従来の技術】Ｔｉ−６Ａｌ−４Ｖ合金に代表されるα
−β型チタン合金は、軽量且つ高強度で優れた耐食性を
有していることから、航空機や自動車、船舶分野などを
始めとする様々の分野で、鉄鋼材料に代わる構造材や外
板材等としての実用化が積極的に進められている。2. Description of the Related Art α represented by Ti-6Al-4V alloy
-Beta-type titanium alloys are lightweight, have high strength, and have excellent corrosion resistance, so they are used as structural materials and outer plate materials in place of steel materials in various fields including the fields of aircraft, automobiles, and ships. Is being actively put into practical use.

【０００３】ところが、高強度のチタン合金はα−β温
度域、即ち熱間加工温度域での変形抵抗が大きくて鍛造
加工性や２次加工性が悪いため、汎用化を進める上で大
きな障害となっている。そのため、熱間加工時の加工回
数と加熱回数を増やし、製品歩留まりを犠牲にして充分
な余肉をつけた状態で熱間加工を行っているのが実情で
あり、熱間プレス加工を行うにしても、適用可能なプレ
ス能力の限界サイズに甘んじている。また棒状や線状に
熱間圧延する場合でも、高速圧延を採用すると大きな変
形抵抗に起因して大きな加工発熱を生じ組織不良を招く
ので低速で圧延せざるを得ず、生産性を高める上で大き
な障害となっている。However, since a high strength titanium alloy has a large deformation resistance in the α-β temperature range, that is, a hot working temperature range and is poor in forgeability and secondary workability, it is a major obstacle in promoting general use. Has become. Therefore, the number of times of hot working and the number of times of heating are increased, and it is the actual situation that hot working is performed with sufficient surplus at the expense of product yield. Even, I'm at the limit of applicable press capacity. Even in the case of hot rolling in the form of a rod or a wire, if high-speed rolling is adopted, large deformation resistance causes a large amount of processing heat and causes a structural failure.Therefore, it has to be rolled at a low speed to improve productivity. It is a big obstacle.

【０００４】[0004]

【発明が解決しようとする課題】本発明は上記のような
事情に着目してなされたものであって、その目的は、高
強度チタン合金として現在最も広範に利用されているＴ
ｉ−６Ａｌ−４Ｖ合金に匹敵し、或いはこれを上回る常
温強度を有すると共に、熱間鍛造やその後の２次加工を
含めた熱間加工性に優れ、所望形状に低コストで効率よ
く熱間加工することのできるチタン合金を提供すること
にある。SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and the purpose thereof is T, which is currently most widely used as a high strength titanium alloy.
It has room temperature strength comparable to or higher than that of i-6Al-4V alloy, and has excellent hot workability including hot forging and subsequent secondary processing, and it is efficient and hot workable to a desired shape at low cost. It is to provide a titanium alloy that can be manufactured.

【０００５】[0005]

【課題を達成するための手段】上記課題を解決すること
のできた本発明に係るチタン合金とは、７００℃で焼鈍
した後の室温（２５℃）での引張強さと、８５０℃での
高速引張りにおける変形抵抗との比が９以上であり、高
い常温強度を有すると共に卓越した熱間加工性を有する
高強度チタン合金である。The titanium alloy according to the present invention, which has been able to solve the above-mentioned problems, has a tensile strength at room temperature (25 ° C.) after annealing at 700 ° C. and a high-speed tensile strength at 850 ° C. It is a high-strength titanium alloy having a ratio of 9 or more with respect to the deformation resistance in Table 1 above, having high room temperature strength and excellent hot workability.

【０００６】本発明にかかる高強度チタン合金のより好
ましい特性は、７００℃焼鈍後の室温（２５℃）での引
張強さで８９５ＭＰａ以上の高強度を有し、且つ、８５
０℃での高速引張りにおける変形抵抗は２００ＭＰａ以
下の低い値を示し、或いは更に、７００℃で焼鈍した後
の５００℃での引張強さが、室温（２５℃）での引張強
さの４５％以上で、実用温度域では充分な耐熱強度を有
しているものであり、こうした特性は、従来の高強度チ
タン合金に見られない特異な特性である。More preferable properties of the high-strength titanium alloy according to the present invention are that it has a high tensile strength of 895 MPa or more at room temperature (25 ° C.) after annealing at 700 ° C.
The deformation resistance in high-speed tension at 0 ° C shows a low value of 200 MPa or less, or the tensile strength at 500 ° C after annealing at 700 ° C is 45% of the tensile strength at room temperature (25 ° C). As described above, it has sufficient heat resistance in a practical temperature range, and such characteristics are peculiar characteristics not found in conventional high strength titanium alloys.

【０００７】本発明の上記チタン合金において更に好ま
しい態様は、α−β型に属し、β変態点が８５０℃超で
あるチタン合金であり、β変態点を８５０℃超とするこ
とにより、チタン合金本来の温度と鍛造性の観点から如
何なる組成であっても、換言すれば純チタンであっても
熱間鍛造が難しくなる８００℃以下での加工を避けるこ
とができ、顕著な加工割れなどを起こすことがなくなる
ので好ましい。A further preferred embodiment of the titanium alloy of the present invention is a titanium alloy which belongs to the α-β type and has a β transformation point of more than 850 ° C., and a titanium alloy having a β transformation point of more than 850 ° C. From any point of view of the original temperature and forgeability, it is possible to avoid processing at 800 ° C or less, which makes hot forging difficult even with pure titanium, in other words pure titanium, causing remarkable processing cracks. It is preferable because it will not occur.

【０００８】また、上記特性を発揮する本発明の高強度
チタン合金を成分組成の観点からみると、好ましいの
は、α安定化元素としてＡｌを３〜７質量％、Ｃを０．
０８〜０．２５質量％含有し、且つβ安定化元素を、下
記式で示されるＭｏ当量で３．０〜１０質量％含有する
ものである。 Mo当量＝Mo(mass％)+(1/1.5)V(mass%)+1.25Cr(mass%)+
2.5Fe(mass%)From the viewpoint of the component composition of the high strength titanium alloy of the present invention which exhibits the above characteristics, it is preferable that Al is 3 to 7 mass% and C is 0.1% as an α stabilizing element.
The content of the β-stabilizing element is 3.0 to 10 mass% in terms of Mo equivalent represented by the following formula. Mo equivalent = Mo (mass%) + (1 / 1.5) V (mass%) + 1.25Cr (mass%) +
2.5Fe (mass%)

【０００９】より具体的には、α安定化元素としてＡｌ
を３〜７質量％、Ｃを０．０８〜０．２５％含み、β安
定化元素として上記Ｍｏ，Ｖ，Ｃｒ，Ｆｅよりなる群か
ら選択される少なくとも１種、より好ましくはこれらの
うちＣｒとＦｅを、上記Ｍｏ当量で３．５〜８．０質量
％含有するものである。More specifically, Al is used as an α-stabilizing element.
Of 3 to 7% by mass, C of 0.08 to 0.25%, and at least one selected from the group consisting of Mo, V, Cr, and Fe as a β-stabilizing element, and more preferably Cr among these. And Fe in an amount of 3.5 to 8.0 mass% in terms of Mo equivalent.

【００１０】また、更に他の元素として、Ｓｎ：１〜５
質量％、Ｚｒ：１〜５質量％、Ｓｉ：０．２〜０．８質
量％よりなる群から選択される少なくとも１種の元素を
含むチタン合金も好ましいものとして推奨される。Further, as another element, Sn: 1 to 5
A titanium alloy containing at least one element selected from the group consisting of mass%, Zr: 1 to 5 mass% and Si: 0.2 to 0.8 mass% is also recommended as a preferable one.

【００１１】[0011]

【発明の実施の形態】本発明者らは、先に指摘した様な
従来技術の問題点に鑑み、現在、高強度チタン合金とし
て最も広範に利用されているＴｉ−６Ａｌ−４Ｖ合金に
匹敵し、或いはこれを上回る常温強度を有すると共に、
通常の上限使用温度域である約５００℃付近でも充分な
強度を確保しつつ、通常のα−β型チタン合金では熱間
加工性が難しくなる８００℃前後以上の高温での変形抵
抗を下げることで熱間加工性を改善し、強度と熱間加工
性の共に優れたチタン合金を開発すべく、特にチタン合
金組成を中心にして研究を進めてきた。DETAILED DESCRIPTION OF THE INVENTION In view of the problems of the prior art as pointed out above, the inventors of the present invention are comparable to Ti-6Al-4V alloy, which is the most widely used high strength titanium alloy at present. Or, it has room temperature strength higher than this,
Lowering the deformation resistance at a high temperature of around 800 ° C or more, which is difficult to hot work with ordinary α-β titanium alloys, while ensuring sufficient strength even at around 500 ° C, which is the normal upper limit operating temperature range. In order to improve the hot workability, and develop a titanium alloy that has both excellent strength and hot workability, we have been conducting research with particular emphasis on the titanium alloy composition.

【００１２】その結果、後述する如く合金元素の種類や
含有率をうまく調整してやれば、常温〜約５００℃程度
の実用温度域ではＴｉ−６Ａｌ−４Ｖ合金に匹敵し、或
いはこれを上回る強度を有しつつ、卓越した熱間加工性
を有するチタン合金が得られることを知り、上記本発明
に想到したものである。As a result, if the kind and content of the alloying elements are properly adjusted as will be described later, it has strength comparable to or exceeding Ti-6Al-4V alloy in the practical temperature range from room temperature to about 500 ° C. At the same time, the inventors have arrived at the present invention, knowing that a titanium alloy having excellent hot workability can be obtained.

【００１３】こうした高強度と優れた熱間加工性を兼ね
備えたチタン合金は、後述する如く主として合金元素の
種類と量を適切に選択・制御することによって得ること
ができるが、現存するチタン合金には見られない本発明
チタン合金の特殊性は、常温強度と高温条件下での高速
引張りにおける変形抵抗との比に現れる。即ち本発明の
チタン合金は、当該合金を７００℃で２時間加熱焼鈍し
たのち自然放冷したものの室温（２５℃）での引張強度
（ＡＳＴＭ Ｅ８に準拠して求められる値）Ａと、当該
チタン合金を８５０℃×５分間大気雰囲気下で加熱し、
その直後に歪速度１００／ｓｅｃで高速引張試験を行っ
た時の変形抵抗（引張試験片の平行部長さが均一に変形
すると仮定して、歪速度１００／ｓｅｃでの高速引張試
験における最大荷重を、引張試験前の平行部の面積で除
した値）Ｂとの比（Ａ／Ｂ）が９以上を示すところに特
徴を有している。The titanium alloy having both such high strength and excellent hot workability can be obtained mainly by appropriately selecting and controlling the kinds and amounts of alloying elements as described later. The peculiarity of the titanium alloy of the present invention, which is not seen, appears in the ratio between the room temperature strength and the deformation resistance in high-speed tensile under high temperature conditions. That is, the titanium alloy of the present invention has a tensile strength (value determined according to ASTM E8) A at room temperature (25 ° C.), which is obtained by annealing the alloy at 700 ° C. for 2 hours and then allowing it to cool naturally, and the titanium. The alloy is heated at 850 ° C. for 5 minutes in the atmosphere,
Immediately after that, the deformation resistance when performing a high-speed tensile test at a strain rate of 100 / sec (assuming that the parallel portion length of the tensile test piece is uniformly deformed, the maximum load in the high-speed tensile test at a strain rate of 100 / sec is The characteristic (A / B) of the value obtained by dividing by the area of the parallel portion before the tensile test) B is 9 or more.

【００１４】ちなみに図１は、後記実験例で得た本発明
のチタン合金、と、従来の代表的な高強度チタン合
金であるＴｉ−６Ａｌ−４Ｖ合金（従来合金）および
ＪＩＳ２種チタン（純チタン）について、試験温度と
引張強さおよび高速引張り時の変形抵抗の関係を示した
グラフである。尚、常温(２５℃)から５００℃までの間
の引張強さはＡＳＴＭ Ｅ８に準拠して求め、７００℃
から９５０℃までの変形抵抗値は、歪速度１００／ｓｅ
ｃでの高速引張試験によって求めた値を示している。By the way, FIG. 1 shows the titanium alloy of the present invention obtained in an experimental example described later, a Ti-6Al-4V alloy (conventional alloy) which is a typical conventional high-strength titanium alloy, and JIS type 2 titanium (pure titanium). Is a graph showing the relationship between the test temperature, the tensile strength, and the deformation resistance during high-speed tension. The tensile strength from room temperature (25 ° C) to 500 ° C is calculated according to ASTM E8 and is 700 ° C.
Deformation resistance value from 100 to 950 ° C is strain rate 100 / se
The value obtained by the high-speed tensile test at c is shown.

【００１５】この図からも明らかな様に、本発明のチタ
ン合金、と従来合金や純チタンは、何れも試験
温度が高くなるにつれて強度（変形抵抗）が低下してい
くことに変わりはない。また、常温から約５００℃程度
までの温度域（即ち、実際の使用温度域）における強度
低下傾向は、代表的な高強度チタン合金であるＴｉ−６
Ａｌ−４Ｖからなる従来合金と本発明に係るチタン合
金、の間で大きな違いは見られない。As is clear from this figure, the strength (deformation resistance) of the titanium alloy of the present invention, the conventional alloy, and the pure titanium all decrease as the test temperature increases. In addition, the strength decreasing tendency in the temperature range from room temperature to about 500 ° C. (that is, the actual use temperature range) shows that Ti-6 which is a typical high strength titanium alloy.
No significant difference is observed between the conventional alloy composed of Al-4V and the titanium alloy according to the present invention.

【００１６】ところが、熱間加工温度域、殊に８００〜
９５０℃のα−β温度域における変形抵抗を比較する
と、従来合金はかなり高い強度（変形抵抗）を維持し
ているのに対し、本発明チタン合金、の強度（変形
抵抗）は極端に低くなっている。このことから、本発明
のチタン合金は、常温から約５００℃程度までの実用温
度域では高強度を示し、且つ熱間加工温度域では強度が
著しく低下し変形抵抗の大幅低下により優れた熱間加工
性を示すことが分る。However, the hot working temperature range, especially 800 to
Comparing the deformation resistances in the α-β temperature range of 950 ° C., the conventional alloy maintains considerably high strength (deformation resistance), whereas the titanium alloy of the present invention has extremely low strength (deformation resistance). ing. From this, the titanium alloy of the present invention exhibits high strength in a practical temperature range from room temperature to about 500 ° C., and in the hot working temperature range, the strength is remarkably reduced and the deformation resistance is significantly reduced. It turns out that it shows workability.

【００１７】本発明では、こうした常温強度〜５００℃
程度までの高温強度に優れ、且つ熱間加工温度域での低
い変形抵抗（即ち、優れた熱間加工性）を、現存するチ
タン合金に見られない特性として定量化するため、例え
ば後記表１〜３に示す如く実際の測定値を基に、［７０
０℃で２時間加熱焼鈍したのち自然放冷したものの室温
（２５℃）での引張強度］Ａと、［８５０℃×５分間大
気雰囲気で加熱しその直後に歪速度１００／ｓｅｃで高
速引張試験を行った時の変形抵抗］Ｂとの比で、「Ａ／
Ｂ≧９以上」であるものと定めた。本発明においてより
好ましいのは、Ａ／Ｂが１０以上、更に好ましくは１２
以上のものである。In the present invention, such room temperature strength to 500 ° C.
In order to quantify low deformation resistance in the hot working temperature range (that is, excellent hot workability) as a characteristic not found in existing titanium alloys, for example, Table 1 below. Based on actual measured values as shown in
Tensile strength at room temperature (25 ° C) after heat-annealing at 0 ° C for 2 hours and natural cooling] A and [850 ° C x 5 minutes in air atmosphere and immediately after that, high-speed tensile test at 100 / sec strain rate Deformation resistance when
B ≧ 9 or more ”. In the present invention, A / B is preferably 10 or more, more preferably 12
That is all.

【００１８】ちなみに、α−β型の代表的な高強度チタ
ン合金であるＴｉ−６Ａｌ−４Ｖ合金（従来合金）の
上記測定法によって求められるＡ／Ｂの値は、表３から
も明らかな如く［９９４／３１９＝３．１］であり、本
発明で規定する上記「Ａ／Ｂ≧９」の要件を大幅に下回
っている。なお図１や表１〜３には、参考のため従来の
チタン合金に比べて熱間加工の容易なＪＩＳ２種純チタ
ンの特性も併記した。By the way, as is clear from Table 3, the A / B value of the Ti-6Al-4V alloy (conventional alloy), which is a typical α-β type high-strength titanium alloy, obtained by the above measurement method is clear. [994/319 = 3.1], which is far below the requirement of “A / B ≧ 9” defined in the present invention. For reference, FIG. 1 and Tables 1 to 3 also show the characteristics of JIS Class 2 pure titanium, which is easier to hot work than conventional titanium alloys.

【００１９】即ち本発明の高強度チタン合金は、既存の
チタン合金に対し、上記「Ａ／Ｂ≧９」という強度特性
によって特徴付けられ、公知のチタン合金とは明確に区
別される新規な高強度チタン合金である。更に本発明の
高強度チタン合金は、その優れた強度特性や熱間加工
性、或いは更に熱間加工時の組織制御の安定性等を考慮
すると、上記「Ａ／Ｂ≧９」という強度特性に加えて、
下記特性を有するものが好ましい。That is, the high-strength titanium alloy of the present invention is characterized by a strength characteristic of "A / B ≧ 9" described above with respect to the existing titanium alloy, and is a novel high strength which is clearly distinguished from known titanium alloys. It is a strength titanium alloy. Furthermore, the high-strength titanium alloy of the present invention has the above-mentioned strength characteristics of “A / B ≧ 9” in consideration of its excellent strength characteristics, hot workability, stability of structure control during hot working, and the like. in addition,
Those having the following characteristics are preferable.

【００２０】７００℃で焼鈍した後の室温（２５℃）
での引張強さが８９５ＭＰａ以上であること。この特性
は、高強度チタン合金としての位置付けをより明確にす
る上で望ましい特性であり、前述した既存の代表的な高
強度チタン合金であるＴｉ−６Ａｌ−４Ｖ合金のＡＳＴ
Ｍ規格で定められる強度の下限値が８９５ＭＰａである
ことから、この既存合金に匹敵する特性を満たす条件と
して定めた。ちなみに、後記実施例として挙げた本発明
に係る高強度チタン合金の常温強度は、通常のＴｉ−６
Ａｌ−４Ｖ焼鈍材と同等の１０００ＭＰａ前後の値を示
している。Room temperature (25 ° C.) after annealing at 700 ° C.
Tensile strength at 895 MPa or more. This characteristic is a desirable characteristic for clarifying the positioning as a high-strength titanium alloy, and is the AST of Ti-6Al-4V alloy which is the existing representative high-strength titanium alloy described above.
Since the lower limit of the strength defined by the M standard is 895 MPa, it was defined as a condition satisfying the characteristics comparable to this existing alloy. By the way, the room-temperature strength of the high-strength titanium alloy according to the present invention, which is given as an example below, is the same as that of ordinary Ti-6
The value around 1000 MPa, which is equivalent to that of the Al-4V annealed material, is shown.

【００２１】８５０℃での高速引張りにおける変形抵
抗が２００ＭＰａ以下であること。この特性は、既存の
高強度チタン合金には見られない卓越した熱間加工性を
より具体的に数値化した値である。通常の鍛造温度を想
定し、該温度条件下で充分に変形抵抗が小さく安定して
優れた加工性を保障するには、上記温度条件下での変形
抵抗が２００ＭＰａ以下、より好ましくは１５０ＭＰａ
以下、更に好ましくは１００ＭＰａ以下であることが望
ましい。ちなみに、後記実施例に示した本発明合金の該
変形抵抗値は何れも１００ＭＰａ以下である。The deformation resistance in high-speed tension at 850 ° C. is 200 MPa or less. This property is a more specific numerical value of the outstanding hot workability that is not found in existing high-strength titanium alloys. Assuming a normal forging temperature, the deformation resistance under the above temperature conditions is 200 MPa or less, and more preferably 150 MPa, in order to ensure a sufficiently small deformation resistance and stable and excellent workability under the temperature conditions.
Hereafter, it is desirable that the pressure is 100 MPa or less. Incidentally, the deformation resistance values of the alloys of the present invention shown in Examples below are all 100 MPa or less.

【００２２】７００℃で焼鈍した後の５００℃での引
張強さが、室温（２５℃）での引張強さの４５％以上で
あること。この強度特性は、本発明合金を実用化する際
に曝される高温条件下での強度保持性、即ち実用上の耐
熱特性を表す指標として定めたもので、常温強度に対し
５００℃レベルの高温条件下でも強度の低下が少なく、
耐熱強度特性に優れたものであることを表している。よ
り高レベルの耐熱強度特性を確保するには、５０％以
上、更に好ましくは５５％以上を維持することが望まし
い。ちなみに、後記実施例に挙げた本発明合金、は
何れも５５％以上を有している。The tensile strength at 500 ° C. after annealing at 700 ° C. is 45% or more of the tensile strength at room temperature (25 ° C.). This strength property is defined as an index showing the strength retention under high temperature conditions to which the alloy of the present invention is put into practical use, that is, the heat resistance property in practical use, and it is a high temperature of 500 ° C at room temperature strength. There is little decrease in strength even under conditions,
It shows that it has excellent heat resistance characteristics. In order to secure a higher level of heat resistance strength, it is desirable to maintain 50% or more, and more preferably 55% or more. By the way, each of the alloys of the present invention described in Examples below has 55% or more.

【００２３】β変態点が８５０℃超であること。この
変態点は、熱間加工途上で被加工材が降温した場合で
も、熱間加工を安定して継続可能にするための特性とし
て定めたもので、最低でも８５０℃以上の加熱温度を確
保して熱間加工を行うには、β変態点が８５０℃超、よ
り好ましくは９００℃以上であることが望ましい。ちな
みにβ変態点が８５０℃以下のものでは、等軸組織を得
るのに加熱温度を８５０℃（β変態点）以下の比較的低
温にしなければならず、如何なる組織であれ鍛造性が著
しく劣化し、鍛造時に割れなどを引き起こし易くなる。The β transformation point is higher than 850 ° C. This transformation point is defined as a characteristic that enables the hot working to be continued stably even when the temperature of the workpiece is lowered during the hot working, and a heating temperature of at least 850 ° C or higher is secured. In order to perform hot working by heating, it is desirable that the β transformation point is higher than 850 ° C., more preferably 900 ° C. or higher. By the way, if the β transformation point is 850 ° C or lower, the heating temperature must be set to a relatively low temperature of 850 ° C (β transformation point) or lower in order to obtain an equiaxed structure, and any structure will significantly deteriorate the forgeability. , It becomes easy to cause cracks during forging.

【００２４】α−β型であること。本発明のチタン合
金は、強度−延性バランスと耐熱性を良好なものとする
ための要件として、α−β型に属するものであることが
望ましい。しかして、α型チタン合金となる組成では熱
間変形抵抗が大きくなり易く、またβ型チタン合金とな
る組成では耐熱性に劣るものとなり易く、何れも本発明
で意図する高強度・高加工性チタン合金としての要求特
性になじみ難いものとなる。Being α-β type. The titanium alloy of the present invention preferably belongs to the α-β type as a requirement for achieving good strength-ductility balance and heat resistance. However, a composition that becomes an α-type titanium alloy tends to have a large hot deformation resistance, and a composition that becomes a β-type titanium alloy tends to have poor heat resistance, and both have high strength and high workability intended by the present invention. It becomes difficult to adapt to the required characteristics as a titanium alloy.

【００２５】上記強度特性を示す高強度チタン合金の製
法は特に制限されないが、本発明者らが実験により確認
したところでは合金元素の種類と含有量が重要になると
思われる。現時点で具体的な合金元素の種類や含有量を
特定することはできないが、以下に示す成分組成の要件
を満たすチタン合金は、本発明で定める前記強度特性を
満たす高性能のものになることを確認している。The production method of the high-strength titanium alloy exhibiting the above-mentioned strength characteristics is not particularly limited, but the types and contents of alloying elements seem to be important, as confirmed by the present inventors through experiments. Although it is not possible to specify the type and content of specific alloying elements at this time, titanium alloys that satisfy the requirements for the composition of components shown below are those with high performance that satisfy the strength characteristics defined in the present invention. I'm confirming.

【００２６】即ち、本発明にかかるチタン合金の好まし
い成分組成は、α安定化元素としてＡｌを３〜７質量％
（より好ましくは３．５〜５．５質量％）、Ｃを０．０
８〜０．２５質量％（より好ましくは０．１０〜０．２
２質量％）含有し、且つβ安定化元素を、下記式で示さ
れるＭｏ当量で３．０〜１０質量％（より好ましくは
３．５〜８．０質量％）含有するものである。 Mo当量＝Mo(mass％)+(1/1.5)V(mass%)+1.25Cr(mass%)+
2.5Fe(mass%)That is, the preferable composition of the titanium alloy according to the present invention is 3 to 7 mass% of Al as an α-stabilizing element.
(More preferably 3.5 to 5.5 mass%), C is 0.0
8 to 0.25 mass% (more preferably 0.10 to 0.2
2 mass%) and also contains a β-stabilizing element in an Mo equivalent of 3.0 to 10 mass% (more preferably 3.5 to 8.0 mass%) represented by the following formula. Mo equivalent = Mo (mass%) + (1 / 1.5) V (mass%) + 1.25Cr (mass%) +
2.5Fe (mass%)

【００２７】より具体的には、α安定化元素としてＡｌ
を３〜７質量％（より好ましくは３．５〜５．５質量
％）、Ｃを０．０８〜０．２５％（より好ましくは０．
１０〜０．２２質量％、更に好ましくは０．１５〜０．
２０質量％）含み、β安定化元素として、Ｍｏ，Ｖ，Ｃ
ｒ，Ｆｅから選ばれる少なくとも１種、より好ましくは
これらのうち少なくともＣｒとＦｅを、上記Ｍｏ当量で
３．５〜８．０質量％含有するものである。また、これ
らの元素に加えて、Ｓｎ：１〜５質量％、Ｚｒ：１〜５
質量％、Ｓｉ：０．２〜０．８質量％よりなる群から選
択される少なくとも１種の元素を含むチタン合金も、優
れた性能を発揮し得ることを確認している。More specifically, Al is used as an α-stabilizing element.
Of 3 to 7% by mass (more preferably 3.5 to 5.5% by mass) and C of 0.08 to 0.25% (more preferably 0.
10 to 0.22% by mass, more preferably 0.15 to 0.
20 mass%), and as a β-stabilizing element, Mo, V, C
At least one selected from r and Fe, and more preferably at least Cr and Fe are contained in an amount of 3.5 to 8.0 mass% in terms of Mo equivalent. In addition to these elements, Sn: 1 to 5 mass%, Zr: 1 to 5
It has been confirmed that a titanium alloy containing at least one element selected from the group consisting of mass% and Si: 0.2 to 0.8 mass% can also exhibit excellent performance.

【００２８】なお、上記で推奨する含有元素の好ましい
含有量を定めた理由は下記の通りである。まずＡｌ含量
は、Ｔｉ−６Ａｌ−４Ｖ相当の強度を確保するために下
限値を推奨し、また上限値については、熱間加工条件下
において変形抵抗の上昇と熱間延性の低下を抑えること
のできる許容限として推奨している。またＣ量も、Ｔｉ
−６Ａｌ−４Ｖ相当の強度を確保するために下限値を推
奨し、また上限値については、ＴｉＣの多量析出により
熱間延性を劣化させることのない許容限として推奨して
いる。The reason why the preferable content of the content element recommended above is determined is as follows. First, for the Al content, a lower limit value is recommended in order to secure strength equivalent to Ti-6Al-4V, and an upper limit value is to suppress an increase in deformation resistance and a decrease in hot ductility under hot working conditions. Recommended as a permissible limit. Also, the amount of C is Ti
The lower limit is recommended in order to secure strength equivalent to -6Al-4V, and the upper limit is recommended as an allowable limit that does not deteriorate hot ductility due to precipitation of a large amount of TiC.

【００２９】またＭｏ当量の下限を定めたのは、同様に
Ｔｉ−６Ａｌ−４Ｖ相当の強度を確保するためであり、
上限値については、熱間加工時の変形抵抗を上昇させず
且つβ変態点を下げ過ぎないための要件として推奨して
いる。更にＳｎ，Ｚｒ，Ｓｉについては、常温〜５００
℃レベルの温度域における強度上昇効果を発揮し得る量
として下限を規定し、一方、上限値については、Ｓｎ，
Ｚｒの場合は熱間延性、Ｓｉの場合は常温延性を夫々劣
化させることのない量として推奨している。Further, the lower limit of the Mo equivalent is set in order to secure the strength equivalent to Ti-6Al-4V in the same manner.
The upper limit is recommended as a requirement for not increasing the deformation resistance during hot working and not lowering the β transformation point too much. Further, for Sn, Zr, and Si, the room temperature to 500
The lower limit is defined as the amount capable of exerting the strength increasing effect in the temperature range of the ° C level, while the upper limit is Sn,
In the case of Zr, the hot ductility is recommended, and in the case of Si, the room temperature ductility is recommended.

【００３０】本発明で好ましく使用されるチタン合金の
具体例としては、後記実施例でも明らかにする如く、
「Ｔｉ−５Ａｌ−６．２５Ｃｒ−０．２Ｃ合金」や「Ｔ
ｉ−５Ａｌ−０．５Ｍｏ−２．４Ｖ−２Ｆｅ−０．２Ｃ
合金」等が例示される。また、Ｓｎ，Ｚｒ，Ｓｉ等を含
むチタン合金の具体例としては、「Ｔｉ−６Ａｌ−４Ｓ
ｎ−４Ｃｒ−０．５Ｆｅ−０．２Ｓｉ−０．２Ｃ」や
「Ｔｉ−６Ａｌ−４Ｓｎ−６Ｃｒ−０．５Ｆｅ−０．２
Ｓｉ−０．２Ｃ」等が例示される。これら合金元素の作
用は、合金元素の種類や２種以上の元素の複合添加、更
にはそれらの添加量によってもかなり変動するので、そ
れら合金元素の種類や複合添加、或いは好適添加量など
は、用いる合金元素に応じて適宜に選択・決定すればよ
い。Specific examples of the titanium alloy preferably used in the present invention are as shown in Examples below.
"Ti-5Al-6.25Cr-0.2C alloy" and "T
i-5Al-0.5Mo-2.4V-2Fe-0.2C
“Alloy” and the like are exemplified. Further, as a specific example of the titanium alloy containing Sn, Zr, Si, etc., "Ti-6Al-4S"
n-4Cr-0.5Fe-0.2Si-0.2C "and" Ti-6Al-4Sn-6Cr-0.5Fe-0.2.
Si-0.2C "etc. are illustrated. The action of these alloying elements varies considerably depending on the type of alloying elements, the combined addition of two or more elements, and the addition amount thereof, so the type and combined addition of these alloying elements, or a suitable addition amount, It may be appropriately selected and determined according to the alloy element used.

【００３１】しかし、本発明で推奨する上記成分組成の
チタン合金に共通する化学成分は、代表的な高強度チタ
ン合金であるＴｉ−６Ａｌ−４Ｖ合金に対してややＡｌ
含量が少な目で、且つ少量のＣを含んでいる点である。
そしてこれらＡｌやＣの作用は次の様に推測される。即
ちＡｌやＣは周知の通りα安定化元素であり、一般的に
は高温強度の上昇に寄与する。しかしこれらの含有率を
適切に制御すれば、室温から５００℃レベルの温度まで
は温度上昇に伴う大幅な強度低下を起こさないが、より
高温の熱間加工温度域では強度上昇を抑え、変形抵抗を
大幅に低下させることが可能となる。特にＣは、室温か
ら５００℃レベルの温度域までは固溶強化に寄与する
が、熱間加工温度域では強化に寄与しなくなると考えら
れる。更にＣは、微量の添加でβ変態点を大幅に上昇さ
せる作用も有しているため、本発明にとって極めて有用
な元素であると考えられる。However, the chemical composition common to the titanium alloys of the above-mentioned composition recommended in the present invention is a little Al compared with Ti-6Al-4V alloy which is a typical high strength titanium alloy.
That is, the content is small and a small amount of C is contained.
And the action of these Al and C is presumed as follows. That is, Al and C are α-stabilizing elements as is well known, and generally contribute to the increase in high temperature strength. However, if these contents are properly controlled, the strength does not drop significantly with increasing temperature from room temperature to the temperature of 500 ° C, but in the higher hot working temperature range, the strength increase is suppressed and the deformation resistance increases. Can be significantly reduced. In particular, C contributes to solid solution strengthening from room temperature to a temperature range of 500 ° C., but is considered not to contribute to strengthening in the hot working temperature range. Further, since C also has the effect of significantly increasing the β transformation point by the addition of a trace amount, it is considered to be an extremely useful element for the present invention.

【００３２】また、上記チタン合金を用いた熱間加工材
の製造条件も特に制限されないが、好ましい条件として
は、前記成分組成の好ましい要件を満たすチタン合金
を、常法に従って溶製し鋳造した後、該鋳塊を常法より
もやや低い温度域、好ましくは当該チタン合金のβ変態
温度（Ｔβ）を基準にしてＴβ〜（Ｔβ＋２００℃）、
より好ましくはＴβ〜（Ｔβ＋１００℃）に加熱してか
ら、７０〜８０％程度の加工率で荒鍛造し、次いで、好
ましくは（Ｔβ−５０℃）〜８００℃程度の温度域で、
７０〜８０％程度の加工率で仕上げ加工を施す方法であ
る。該仕上げ加工の後は、必要により７００〜８００℃
×６０〜１２０分程度で焼鈍することも有効である。The production conditions of the hot-worked material using the above titanium alloy are not particularly limited, but a preferable condition is that after melting and casting a titanium alloy satisfying the preferable requirements of the above-mentioned composition according to a usual method. , Tβ to (Tβ + 200 ° C) based on the β transformation temperature (Tβ) of the titanium alloy.
More preferably, it is heated to Tβ- (Tβ + 100 ° C), then rough forged at a working rate of about 70-80%, and then preferably in a temperature range of (Tβ-50 ° C) -800 ° C.
This is a method of performing finishing at a processing rate of about 70 to 80%. After the finishing, if necessary, 700 to 800 ° C
It is also effective to anneal for about 60 to 120 minutes.

【００３３】尚、断面サイズが比較的小さいチタン合金
鋳塊の場合は、鋳造時の冷却速度が速いため鋳塊の結晶
粒は比較的小さくなる。従ってこの様な場合は高温での
荒鍛造を省略し、鋳塊をそのまま低温、即ちＴｉ−Ｃの
２元系で言うところの包析温度以下に加熱してから仕上
げ鍛造することも有効である。In the case of a titanium alloy ingot having a relatively small cross-sectional size, the crystal grain of the ingot is relatively small because the cooling rate during casting is high. Therefore, in such a case, it is also effective to omit the rough forging at a high temperature and to heat the ingot as it is at a low temperature, that is, below the encapsulation temperature of the binary system of Ti-C before finish forging. .

【００３４】[0034]

【実施例】以下、実施例を挙げて本発明をより具体的に
説明するが、本発明はもとより下記実施例によって制限
を受けるものではなく、前・後記の趣旨に適合し得る範
囲で適当に変更を加えて実施することも可能であり、そ
れらは何れも本発明の技術的範囲に含まれる。EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and may be appropriately applied within a range compatible with the gist of the preceding and the following. Modifications can be made and implemented, and all of them are included in the technical scope of the present invention.

【００３５】実施例１ 本発明にかかる代表的なチタン合金として、Ｔｉ−５Ａ
ｌ−６．２５Ｃｒ−０．２Ｃ合金（β変態点：９１５
℃）と、Ｔｉ−５Ａｌ−０．５Ｍｏ−２．４Ｖ−２Ｆｅ
−０．２Ｃ合金（変態点：９６７℃）を、コールドク
ルーシブルインダクション溶解法（ＣＣＩＭ）により溶
製・鋳造して２５ｋｇ鋳塊を製造し、この鋳塊を、通常
よりやや低めの好ましい加熱温度として１０００℃に加
熱した後、８０％の加工率で荒鍛造する。次いで８５０
℃に加熱し、７５％の加工率で仕上げ鍛造し、７００℃
×２時間加熱→空冷で焼鈍を施すことにより鍛造丸棒を
作製した。Example 1 As a typical titanium alloy according to the present invention, Ti-5A
1-6.25Cr-0.2C alloy (β transformation point: 915
C) and Ti-5Al-0.5Mo-2.4V-2Fe
A −0.2 C alloy (transformation point: 967 ° C.) is melted and cast by a cold crucible induction melting method (CCIM) to produce a 25 kg ingot, and this ingot is set as a preferable heating temperature slightly lower than usual. After heating to 1000 ° C., rough forging is performed at a working rate of 80%. Then 850
Heated to ℃, finish forged with a processing rate of 75%, 700 ℃
A forged round bar was prepared by annealing for 2 hours and then air cooling.

【００３６】この鍛造材を用いて、室温から５００℃ま
での引張強度（ＡＳＴＭ Ｅ８に準拠）を測定した。ま
た、上記鋳塊から図２に示す寸法・形状の試験片を切出
し、各試験片を大気雰囲気下に７００℃〜９５０℃で５
分間加熱し、その直後に、高速引張試験機（富士電波工
機社製商品名「サーメックマスターＺ」）を用いて、歪
速度１００／ｓｅｃで高速引張り試験を行い、変形抵抗
を求めた。なお変形抵抗値は、該高速引張り試験で得た
最大荷重を引張試験前の平行部の面積で除して算出し
た。結果を表１に示す。Using this forged material, the tensile strength (according to ASTM E8) from room temperature to 500 ° C. was measured. Further, test pieces having the dimensions and shapes shown in FIG. 2 were cut out from the ingot, and each test piece was subjected to 5 at 700 ° C. to 950 ° C. in an air atmosphere.
After heating for a minute, immediately after that, a high-speed tensile test was performed using a high-speed tensile tester (trade name “Thermec Master Z” manufactured by Fuji Denwa Koki Co., Ltd.) at a strain rate of 100 / sec to determine the deformation resistance. The deformation resistance value was calculated by dividing the maximum load obtained in the high-speed tensile test by the area of the parallel portion before the tensile test. The results are shown in Table 1.

【００３７】また、上記で得た各鋳片、を使用し、
上記の条件で荒鍛造、仕上げ鍛造および等軸晶化のため
の焼鈍を行い、各々について、７００℃で２時間加熱焼
鈍した後、０．１〜０．２℃／ｓｅｃの速度で冷却し、
島津製作所製の引張試験機（商品名「ＡＧ−Ｅ２３０ｋ
Ｎ オートグラフ引張試験機」）を用いて、室温（２５
℃）〜５００℃での引張強度をＡＳＴＭ Ｅ８に準拠し
て求めた。結果を表２に示す。Further, using the cast pieces obtained above,
Rough forging, finish forging and annealing for equiaxed crystallization are performed under the above conditions, and each of them is heated and annealed at 700 ° C. for 2 hours, and then cooled at a rate of 0.1 to 0.2 ° C./sec.
Shimadzu tensile tester (trade name "AG-E230k
N Autograph Tensile Tester ”) at room temperature (25
C.) to 500.degree. C. tensile strength was determined according to ASTM E8. The results are shown in Table 2.

【００３８】[0038]

【表１】 [Table 1]

【００３９】[0039]

【表２】 [Table 2]

【００４０】図１は、上記表１，２の結果を、試験温度
（℃）と引張強さ（常温〜５００℃）および変形抵抗
（７００℃〜９５０℃）の関係として図示したものであ
る。なお表１，２及び図１には、従来の代表的なチタン
合金であるＴｉ−６Ａｌ−４Ｖ合金（従来合金）とＪ
ＩＳ２種チタン（純チタン）の測定結果を併記した。FIG. 1 shows the results of the above Tables 1 and 2 as the relationship between the test temperature (° C.), the tensile strength (normal temperature to 500 ° C.) and the deformation resistance (700 ° C. to 950 ° C.). In Tables 1 and 2 and FIG. 1, J-6Al-4V alloy (conventional alloy), which is a typical conventional titanium alloy, and J
The measurement results of IS2 type titanium (pure titanium) are also shown.

【００４１】表１，２及び図１からも明らかな様に、代
表的な高強度チタン合金である従来合金は、常温〜５
００℃の実用温度域で高強度を有している反面、熱間加
工温度域である７００〜９５０℃の高温域でもかなり高
強度を維持しており、変形抵抗が大きいため熱間加工性
に欠ける。As is clear from Tables 1 and 2 and FIG. 1, the conventional alloy, which is a typical high strength titanium alloy, has room temperature to 5
While it has high strength in the practical temperature range of 00 ° C, it also maintains high strength in the high temperature range of 700 to 950 ° C, which is the hot working temperature range, and it has a high deformation resistance, which makes it hot workable. Lack.

【００４２】これらに対し本発明のチタン合金、
は、常温〜５００℃の実用温度域では従来合金を上回
る高強度を有しており、しかも熱間加工が想定される８
００〜９５０℃の高温域での変形抵抗は、易加工性の純
チタンと同程度に低く、熱間加工性においても非常に
優れたものであることが分る。On the other hand, the titanium alloy of the present invention,
Has a higher strength than conventional alloys in the practical temperature range of normal temperature to 500 ° C, and hot working is expected 8
It can be seen that the deformation resistance in the high temperature range of 00 to 950 ° C. is as low as that of pure titanium which is easily workable, and it is also very excellent in hot workability.

【００４３】即ち、実用温度域での強度および熱間加工
温度域での変形抵抗について、本発明の規定要件を満た
すチタン合金、と従来合金や純チタンを比較す
ると、下記表３に示す通りであり、本発明のチタン合金
、はいずれも高強度と優れた熱間加工性を兼備して
いることが分る。That is, when comparing the titanium alloy satisfying the requirements of the present invention with respect to the strength in the practical temperature range and the deformation resistance in the hot working temperature range, the conventional alloy and pure titanium are shown in Table 3 below. Therefore, it can be seen that each of the titanium alloys of the present invention has both high strength and excellent hot workability.

【００４４】[0044]

【表３】 [Table 3]

【００４５】実施例２ 室温から５００℃までの高強度化に主眼を置いたチタン
合金の例として、表４に示す符号ａ，ｂの合金を使用
し、それ以外は前記実施例１と全く同様にして溶製→鋳
造→鍛造→焼鈍を行い、得られた各焼鈍材について、同
様にして常温（２５℃）および高温（５００℃）引張強
度、並びに８５０℃での高速引張り時における変形抵抗
を測定し、表４に併記する結果を得た。また表４には、
比較のため前掲の代表的な従来合金であるＴｉ−６Ａｌ
−４Ｖ合金を用いた場合の値も併記した。Example 2 As an example of a titanium alloy focused on increasing the strength from room temperature to 500 ° C., the alloys indicated by the symbols a and b shown in Table 4 were used, and otherwise the same as Example 1 above. Then, melting, casting, forging, and annealing were performed, and for each of the obtained annealed materials, the room temperature (25 ° C.) and high temperature (500 ° C.) tensile strength and the deformation resistance during high-speed drawing at 850 ° C. were similarly determined. The measurement was performed and the results shown in Table 4 were obtained. Also, in Table 4,
For comparison, Ti-6Al, which is a typical conventional alloy described above, is used.
The value when using a -4V alloy is also shown.

【００４６】[0046]

【表４】 [Table 4]

【００４７】表４からも明らかな様に、本発明の規定要
件を満たす符号ａ，ｂのチタン合金は、代表的な高強度
チタン合金である符号ｃの従来合金に較べて、常温で格
段に優れた引張強度を有しているにも拘わらず、８５０
℃における変形抵抗は低く優れた熱間加工性を有してい
ることが分る。As is clear from Table 4, the titanium alloys a and b satisfying the requirements of the present invention are much more remarkable at room temperature than the conventional alloy of the symbol c which is a typical high strength titanium alloy. 850 despite having excellent tensile strength
It can be seen that the deformation resistance at ° C is low and that it has excellent hot workability.

【００４８】[0048]

【発明の効果】本発明は以上の様に構成されており、常
温〜５００℃の実用温度域で高強度を有すると共に、熱
間加工温度域での変形抵抗が低くて優れた熱間加工性を
有しており、高い熱間加工性の下で高強度のチタン合金
部材を与えるチタン合金を提供し得ることになった。EFFECTS OF THE INVENTION The present invention is constituted as described above, has high strength in a practical temperature range of normal temperature to 500 ° C., and has a low deformation resistance in a hot working temperature range and an excellent hot workability. Therefore, it is possible to provide a titanium alloy having a high strength and providing a high strength titanium alloy member under high hot workability.

【００４９】また本発明の高強度チタン合金は、上記の
様に熱間加工温度域での変形抵抗が低いことから、１回
当たりの加工率（熱間鍛造時の鍛造比、熱延時の減面率
や圧下率など）を大きく取ることができ、所望サイズ、
厚さ、直径の加工品を少ない加工回数で生産性良く得る
ことができる。更には、熱間加工時の抵抗発熱が少な
く、熱間加工時の温度上昇も低く抑えられるので、当該
チタン合金のβ変態点を考慮して高めの加工温度を採用
した場合でも高温変態を起こすことなく、所望の強度特
性を備えた加工製品を容易に得ることが可能となる。Further, since the high strength titanium alloy of the present invention has a low deformation resistance in the hot working temperature range as described above, the working ratio per one time (forging ratio during hot forging, reduction in hot rolling) is reduced. It is possible to take large values such as surface ratio and reduction ratio.
It is possible to obtain a product having a thickness and a diameter with a small number of times of processing and high productivity. Furthermore, since resistance heat generation during hot working is small and the temperature rise during hot working can be suppressed to a low level, high temperature transformation occurs even if a high working temperature is adopted considering the β transformation point of the titanium alloy. Without this, it is possible to easily obtain a processed product having desired strength characteristics.

【図面の簡単な説明】[Brief description of drawings]

【図１】本発明の高強度チタン合金と従来合金の試験温
度と引張強さ(および変形抵抗)の関係を示すグラフであ
る。FIG. 1 is a graph showing the relationship between test temperature and tensile strength (and deformation resistance) of a high strength titanium alloy of the present invention and a conventional alloy.

【図２】高温域での変形抵抗測定用試験片の形状・寸法
を示す説明図である。FIG. 2 is an explanatory diagram showing the shape and dimensions of a test piece for measuring deformation resistance in a high temperature range.

───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.⁷ 識別記号 ＦＩ テーマコート゛(参考） Ｃ２２Ｆ 1/00 ６８３ Ｃ２２Ｆ 1/00 ６８３ ６９１ ６９１Ｂ ６９１Ｃ ６９２ ６９２Ａ ６９２Ｚ ６９４ ６９４Ａ ６９４Ｂ ─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22F 1/00 683 C22F 1/00 683 691 691B 691C 692 692A 692Z 694 694A 694B

Claims (8)

【特許請求の範囲】[Claims] 【請求項１】 ７００℃で焼鈍した後の室温（２５℃）
での引張強さと、８５０℃での高速引張りにおける変形
抵抗との比が９以上であることを特徴とする熱間加工性
に優れた高強度チタン合金。1. Room temperature (25 ° C.) after annealing at 700 ° C.
A high-strength titanium alloy with excellent hot workability, characterized in that the ratio of the tensile strength at room temperature to the deformation resistance during high-speed tensile at 850 ° C. is 9 or more. 【請求項２】 ７００℃で焼鈍した後の室温（２５℃）
での引張強さが８９５ＭＰａ以上である請求項１に記載
の高強度チタン合金。2. Room temperature (25 ° C.) after annealing at 700 ° C.
The high-strength titanium alloy according to claim 1, which has a tensile strength of 895 MPa or more. 【請求項３】 ８５０℃での高速引張りにおける変形抵
抗が２００ＭＰａ以下である請求項１または２に記載の
高強度チタン合金。3. The high-strength titanium alloy according to claim 1, which has a deformation resistance of 200 MPa or less in high-speed tension at 850 ° C. 【請求項４】 ７００℃で焼鈍した後の５００℃での引
張強さが、室温（２５℃）での引張強さの４５％以上で
ある請求項１〜３のいずれかに記載の高強度チタン合
金。4. The high strength according to claim 1, wherein the tensile strength at 500 ° C. after annealing at 700 ° C. is 45% or more of the tensile strength at room temperature (25 ° C.). Titanium alloy. 【請求項５】 β変態点が８５０℃超である請求項１〜
４のいずれかに記載の高強度チタン合金。5. The β transformation point is higher than 850 ° C.
The high-strength titanium alloy according to any one of 4 above. 【請求項６】 α−β型である請求項１〜５のいずれか
に記載の高強度チタン合金。6. The high-strength titanium alloy according to claim 1, which is α-β type. 【請求項７】 α安定化元素としてＡｌを３〜７質量
％、Ｃを０．０８〜０．２５質量％含有し、且つβ安定
化元素を、下記式で示されるＭｏ当量で３．０〜１０質
量％含有するものである請求項６に記載の高強度チタン
合金。 Mo当量＝Mo(mass％)+(1/1.5)V(mass%)+1.25Cr(mass%)+
2.5Fe(mass%)7. The α-stabilizing element contains 3 to 7 mass% of Al and 0.08 to 0.25 mass% of C, and the β-stabilizing element is 3.0 in terms of Mo equivalent represented by the following formula. The high-strength titanium alloy according to claim 6, which contains 10 to 10 mass%. Mo equivalent = Mo (mass%) + (1 / 1.5) V (mass%) + 1.25Cr (mass%) +
2.5Fe (mass%) 【請求項８】 更に他の元素として、Ｓｎ：１〜５質量
％、Ｚｒ：１〜５質量％、Ｓｉ：０．２〜０．８質量％
よりなる群から選択される少なくとも１種の元素を含む
ものである請求項６または７に記載の高強度チタン合
金。8. As other elements, Sn: 1 to 5% by mass, Zr: 1 to 5% by mass, Si: 0.2 to 0.8% by mass.
The high-strength titanium alloy according to claim 6 or 7, containing at least one element selected from the group consisting of: