JP6851147B2 - Titanium alloy forged material - Google Patents
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本発明は、チタン合金鍛造材に関し、特に、ニア（ｎｅａｒ）β型チタン合金鍛造材に関する。 The present invention relates to a titanium alloy forged material, and more particularly to a near β-type titanium alloy forged material.
航空機用部品等には、軽量で高強度であることに加えて、高延性、高靭性等であることが要求されることから、α＋β型チタン合金やニアβ型チタン合金が多く使用されている。α＋β型チタン合金は、主相である稠密六方晶（ｈｃｐ構造）のα相と体心立方晶（ｂｃｃ構造）のβ相とが室温で安定に共存して、強度と延性等のバランスに優れており、また、β変態点（Ｔβ）以上の温度域でβ相単相となる。ニアβ型チタン合金は、α＋β型チタン合金と高強度なβ型チタン合金との中間的な金属組織を有しており、α＋β型チタン合金と同様にα相とβ相とが共存する。これらのチタン合金の鍛造材には、Ｔβ以上の温度に到達しないようにＴβ未満の温度域（α＋β二相域）に加熱して鍛造するα＋β鍛造によるものと、Ｔβ以上の温度域（β単相域）に加熱して鍛造するβ鍛造によるものとがある。α＋β鍛造材とβ鍛造材では、形成される材料組織は全く異なり、それに伴い材料特性が異なることが知られている。 Since aircraft parts and the like are required to have high ductility, high toughness, etc. in addition to being lightweight and high strength, α + β type titanium alloys and near β type titanium alloys are often used. .. In the α + β type titanium alloy, the α phase of the dense hexagonal crystal (hcp structure) and the β phase of the body-centered cubic crystal (bcc structure) coexist stably at room temperature, and the balance between strength and ductility is excellent. In addition, it becomes a β phase single phase in a temperature range above the β transformation point (Tβ). The near β-type titanium alloy has an intermediate metal structure between the α + β-type titanium alloy and the high-strength β-type titanium alloy, and the α-phase and the β-phase coexist like the α + β-type titanium alloy. These titanium alloy forgings are forged by α + β forging by heating to a temperature range below Tβ (α + β two-phase range) so as not to reach a temperature above Tβ, and a temperature range above Tβ (β single). There is one by β forging that heats and forges in the phase area). It is known that the material structure formed between the α + β forged material and the β forged material is completely different, and the material properties are different accordingly.
チタン合金の中でも、高強度なニアβ型チタン合金として、Ti-10V-2Fe-3Al合金などが知られている。Ti-10V-2Fe-3Al合金は、その特性をさらに改良するために、いくつかの改良技術が開発されている。例えば、特許文献１には、ニアβ型チタン合金の高強度化特性を維持しつつ冷間加工性を改善する加工前処理方法が開示されている。また、特許文献２には、強度・靭性に優れたニアβ型チタン合金を得るための処理方法が開示されている。 Among the titanium alloys, Ti-10V-2Fe-3Al alloy and the like are known as high-strength near β-type titanium alloys. Several improved techniques have been developed for the Ti-10V-2Fe-3Al alloy to further improve its properties. For example, Patent Document 1 discloses a pre-processing method for improving cold workability while maintaining high strength characteristics of a near β-type titanium alloy. Further, Patent Document 2 discloses a treatment method for obtaining a near β-type titanium alloy having excellent strength and toughness.
しかしながら、航空機用部品には、更なる強度、延性等の機械的特性の向上が要求されている。一般に高強度化を図ると、延性は低下する傾向にある。特許文献１および特許文献２に開示された処理方法は、機械的特性にまだ改良の余地を有するものであった。 However, aircraft parts are required to have further improved mechanical properties such as strength and ductility. Generally, when the strength is increased, the ductility tends to decrease. The processing methods disclosed in Patent Document 1 and Patent Document 2 still have room for improvement in mechanical properties.
さらに、特に大型のチタン合金鍛造材においては、優れた機械的特性を保持しつつ、チタン合金鍛造材の表面部と内部との物性ばらつきをできるだけ低減化させたいという要望があり、新たな目的として持ち上がってきている。ここで、大型のチタン合金鍛造材とは、断面図において１００〜５００ｍｍの大きさの最大内接円を設定することができるチタン合金鍛造材を意味する。 Furthermore, especially for large-sized titanium alloy forged materials, there is a demand to reduce the variation in physical properties between the surface and the inside of the titanium alloy forged material as much as possible while maintaining excellent mechanical properties, as a new purpose. It has been lifted. Here, the large titanium alloy forged material means a titanium alloy forged material in which a maximum inscribed circle having a size of 100 to 500 mm can be set in the cross-sectional view.
本発明は、前記問題点に鑑みてなされたものであり、機械的特性を保持しつつ、大型の鍛造材の表面部と内部との物性ばらつきを低減することが可能なチタン合金鍛造材を提供することを課題とする。 The present invention has been made in view of the above problems, and provides a titanium alloy forged material capable of reducing variations in physical properties between the surface portion and the inside of a large forged material while maintaining mechanical properties. The task is to do.
本発明者らは鋭意研究の結果、一次α相の結晶粒子の形態を微細かつ小さなアスペクト比を有したものに制御し、鍛造材の表面部と内部との差を特定範囲に制御することによって、上記課題を解消し得ることを見出して、本発明に到達したものである。 As a result of diligent research, the present inventors controlled the morphology of the crystal particles of the primary α phase to have a fine and small aspect ratio, and controlled the difference between the surface portion and the inside of the forging material within a specific range. The present invention has been reached by finding that the above problems can be solved.
すなわち、本発明に係るチタン合金鍛造材は、元素Ｘの含有量（質量％）を[Ｘ]としたときに、下記式（１）で表されるＭｏ当量［Ｍｏ］ｅｑが１０以上１３未満であるチタン合金からなるチタン合金鍛造材である。
[Ｍｏ]ｅｑ＝[Ｍｏ]＋[Ｔａ]/５＋[Ｎｂ]/３．６＋[Ｗ]/２．５＋[Ｖ]/１．５＋１．２５[Ｃｒ]＋１．２５[Ｎｉ]＋１．７[Ｍｎ]＋１．７[Ｃｏ]＋２．５[Ｆｅ]・・・（１）
そして、本発明に係るチタン合金鍛造材は、α相とβ相の面積率の合計が９９％以上であり、一次α相の平均粒径が２．５μｍ以下であり、一次α相の平均アスペクト比が３．０以下であり、表面側と内部側の一次α相の面積率の差が７．０％以下である。ここで、前記表面側とは、前記チタン合金鍛造材の表面から１５±１０ｍｍの深さの部分であり、前記内部側とは、前記チタン合金鍛造材の断面に１００〜５００ｍｍの大きさの内接円を設定したときに、前記内接円の中心±１５ｍｍの深さの部分である。
That is, the titanium alloy forged material according to the present invention has a Mo equivalent [Mo] eq represented by the following formula (1) of 10 or more and less than 13 when the content (% by mass) of the element X is [X]. It is a titanium alloy forged material made of a titanium alloy.
[Mo] eq = [Mo] + [Ta] / 5 + [Nb] /3.6+ [W] /2.5+ [V] /1.5+1.25 [Cr] +1.25 [Ni] +1.7 [ Mn] +1.7 [Co] +2.5 [Fe] ... (1)
In the titanium alloy forged material according to the present invention, the total area ratio of the α phase and the β phase is 99% or more, the average particle size of the primary α phase is 2.5 μm or less, and the average aspect of the primary α phase. The ratio is 3.0 or less, and the difference between the area ratios of the primary α phase on the surface side and the internal side is 7.0% or less. Here, the surface side is a portion having a depth of 15 ± 10 mm from the surface of the titanium alloy forged material, and the inner side is a portion having a size of 100 to 500 mm in the cross section of the titanium alloy forged material. When the tangent circle is set, it is a portion having a depth of ± 15 mm at the center of the inscribed circle.
かかる構成のチタン合金鍛造材は、機械的特性を保持しつつ、大型の鍛造材の表面部と内部との物性ばらつきを低減することができる。 The titanium alloy forged material having such a structure can reduce the variation in physical properties between the surface portion and the inside of the large-sized forged material while maintaining the mechanical properties.
また、本発明に係るチタン合金鍛造材は、前記一次α相の面積率が２０％以下であることが好ましい。かかる構成のチタン合金鍛造材は、さらに、強度に優れたものとなる。 Further, the titanium alloy forged material according to the present invention preferably has an area ratio of the primary α phase of 20% or less. The titanium alloy forged material having such a structure is further excellent in strength.
また、本発明に係るチタン合金鍛造材は、二次α相の平均間隔が２００ｎｍ以下であるであることが好ましい。かかる構成のチタン合金鍛造材は、さらに、強度に優れたものとなる。 Further, in the titanium alloy forged material according to the present invention, the average interval of the secondary α phase is preferably 200 nm or less. The titanium alloy forged material having such a structure is further excellent in strength.
本発明のチタン合金鍛造材は、機械的特性を保持しつつ、大型の鍛造材の表面部と内部との物性ばらつきを低減することができる。 The titanium alloy forged material of the present invention can reduce the variation in physical properties between the surface portion and the inside of the large-sized forged material while maintaining the mechanical properties.
以下、本発明の実施の形態について詳細に説明する。
本発明に係るチタン合金鍛造材は、航空機用部品等に用いられ得るチタン合金鍛造材であって、鍛造や熱処理によって金属組織を制御することで、機械的特性に優れたものとすることができる。
Hereinafter, embodiments of the present invention will be described in detail.
The titanium alloy forged material according to the present invention is a titanium alloy forged material that can be used for aircraft parts and the like, and can be made excellent in mechanical properties by controlling the metal structure by forging or heat treatment. ..
〔チタン合金〕
本発明に係るチタン合金は、元素Ｘの含有量（質量％）を[Ｘ]としたときに、下記式（１）で表されるＭｏ（モリブデン）当量［Ｍｏ］ｅｑが１０以上１３未満である。
[Ｍｏ]ｅｑ＝[Ｍｏ]＋[Ｔａ]/５＋[Ｎｂ]/３．６＋[Ｗ]/２．５＋[Ｖ]/１．５＋１．２５[Ｃｒ]＋１．２５[Ｎｉ]＋１．７[Ｍｎ]＋１．７[Ｃｏ]＋２．５[Ｆｅ]・・・（１）
Ｍｏ当量は、チタン合金の各相の安定性を示す指標として、一般的に使用されているものである。Ｍｏ当量の詳細については、G. Lutjering & J. C. Williams, "Titanium", Second Edition, Springer-Verlag, Berlin, 2010, p30または古原、牧, 金属, vol.66（1996）, No.4, p289 等において説明がなされている。
Ｍｏ当量は、強度を確保するために１０以上の値は必要であり、より好ましくは１０．５以上である。一方、熱間鍛造性や延性を良好なものとするために１３未満に制御することが必要であり、より好ましくは１２．５以下である。
[Titanium alloy]
The titanium alloy according to the present invention has a Mo (molybdenum) equivalent [Mo] eq represented by the following formula (1) of 10 or more and less than 13 when the content (mass%) of the element X is [X]. is there.
[Mo] eq = [Mo] + [Ta] / 5 + [Nb] /3.6+ [W] /2.5+ [V] /1.5+1.25 [Cr] +1.25 [Ni] +1.7 [ Mn] +1.7 [Co] +2.5 [Fe] ... (1)
The Mo equivalent is generally used as an index showing the stability of each phase of the titanium alloy. For more information on Mo equivalents, see G. Lutjering & JC Williams, "Titanium", Second Edition, Springer-Verlag, Berlin, 2010, p30 or Furuhara, Maki, Metals, vol.66 (1996), No.4, p289, etc. It is explained in.
The Mo equivalent is required to have a value of 10 or more in order to secure the strength, and more preferably 10.5 or more. On the other hand, in order to improve the hot forgeability and ductility, it is necessary to control it to less than 13, and more preferably 12.5 or less.
上記のＭｏ当量の規定を満足するチタン合金として、ＡＭＳ４９８４に定められたTi-10V-2Fe-3Al合金がある。Ti-10V-2Fe-3Al合金の合金組成は、Ｖ：９．０〜１１．０質量％、Ａｌ：２．６〜３．４質量％、Ｆｅ：１．６〜２．２２質量％を含有し、残部はＴｉおよび不可避的不純物である。不可避的不純物としては、例えば、Ｃ：０．０５質量％以下、Ｎ：０．０５質量％以下、Ｏ：０．１３質量％以下、Ｈ：０．０１５質量％以下、Ｙ：０．００５質量％以下を含有する。ここで、Ｍｏ当量は、式（１）中でTi-10V-2Fe-3Al合金が含有しない元素については、含有量０として計算される。 As a titanium alloy that satisfies the above Mo equivalent specification, there is a Ti-10V-2Fe-3Al alloy defined in AMS4984. The alloy composition of the Ti-10V-2Fe-3Al alloy contains V: 9.0 to 11.0% by mass, Al: 2.6 to 3.4% by mass, and Fe: 1.6 to 2.22% by mass. The rest is Ti and unavoidable impurities. Examples of unavoidable impurities include C: 0.05% by mass or less, N: 0.05% by mass or less, O: 0.13% by mass or less, H: 0.015% by mass or less, and Y: 0.005% by mass. % Or less. Here, the Mo equivalent is calculated assuming that the content of the element not contained in the Ti-10V-2Fe-3Al alloy in the formula (1) is 0.
Ti-10V-2Fe-3Al合金の場合、β相の固溶強化やβ相を安定化させるために、Ｖ：９．０質量％以上、Ｆｅ：１．６質量％以上が必要であり、α相の固溶強化やα相を安定化させるためにＡｌ：２．６質量％以上が必要である。また、過剰な添加は熱間鍛造性や延性を損なう恐れがあるため、Ｖ：１１．０質量％以下、Ａｌ：３．４質量％以下、Ｆｅ：２．２２質量％以下に制御する。また、不可避不純物が増えると素材が脆化する恐れがあるため、上述の通り上限値以下に制御する。 In the case of Ti-10V-2Fe-3Al alloy, V: 9.0% by mass or more and Fe: 1.6% by mass or more are required in order to strengthen the solid solution of the β phase and stabilize the β phase. Al: 2.6% by mass or more is required to strengthen the solid solution of the phase and stabilize the α phase. Further, since excessive addition may impair hot forging property and ductility, control is performed to V: 11.0% by mass or less, Al: 3.4% by mass or less, and Fe: 2.22% by mass or less. Further, if the amount of unavoidable impurities increases, the material may become embrittled. Therefore, control the value to the upper limit or less as described above.
Ｍｏ当量が１０以上１３未満であるチタン合金としては、その他に、Ti-5Al-5V-5Mo-3Cr合金等を例示することができる。 Other examples of titanium alloys having a Mo equivalent of 10 or more and less than 13 include Ti-5Al-5V-5Mo-3Cr alloys.
〔金属組織〕
本発明のチタン合金鍛造材はニアβ型チタン合金鍛造材であり、その金属組織は、主にα相とβ相からなり、α相は、一次α相と二次α相からなる。本発明のチタン合金鍛造材の金属組織は、一次α相の平均粒径が２．５μｍ以下であり、一次α相の平均アスペクト比が３．０以下であり、表面側と内部側の一次α相の面積率の差が７．０％以下である。また、一次α相の面積率が２０％以下であることが好ましい。また、二次α相の平均間隔が２００ｎｍ以下であることが好ましい。
以下、各特性について順次説明する。
[Metal structure]
The titanium alloy forged material of the present invention is a near β type titanium alloy forged material, and its metal structure is mainly composed of α phase and β phase, and α phase is composed of primary α phase and secondary α phase. In the metal structure of the titanium alloy forged material of the present invention, the average particle size of the primary α phase is 2.5 μm or less, the average aspect ratio of the primary α phase is 3.0 or less, and the primary α on the surface side and the internal side. The difference in the area ratio of the phases is 7.0% or less. Further, it is preferable that the area ratio of the primary α phase is 20% or less. Further, it is preferable that the average interval of the secondary α phase is 200 nm or less.
Hereinafter, each characteristic will be described in sequence.
本発明のチタン合金鍛造材の金属組織は、実質的にα相およびβ相からなり、α相とβ相の面積率の合計は９９％以上である。更にα相は、一次α相と二次α相に分類される。二次α相とは、時効工程において析出してくるα相のことであり、一次α相とは、二次α相以外のα相のことである。α相およびβ相以外の組織としては、炭化物や介在物等を微量含有することがある。 The metal structure of the titanium alloy forged material of the present invention is substantially composed of α phase and β phase, and the total area ratio of α phase and β phase is 99% or more. Further, the α phase is classified into a primary α phase and a secondary α phase. The secondary α phase is an α phase that is precipitated in the aging process, and the primary α phase is an α phase other than the secondary α phase. The structures other than the α phase and the β phase may contain a trace amount of carbides, inclusions, and the like.
（一次α相の平均粒径）
本発明のチタン合金鍛造材の金属組織において、一次α相と二次α相とは、粒径が異なる。そこで、倍率４００倍の光学顕微鏡を用いて観察したときのα相の粒径によって、一次α相と二次α相とを区別して規定することとする。すなわち、倍率４００倍の光学顕微鏡で観察したときに、粒径が０．５μｍ以上の閉じた領域のα相を一次α相と定義する。一次α相以外の領域は、二次α相およびβ相を含む領域となる。ここで、粒径は、円相当径として求められる。また、α相およびβ相以外の組織は除外している。
(Average particle size of primary α phase)
In the metal structure of the titanium alloy forged material of the present invention, the primary α phase and the secondary α phase have different particle sizes. Therefore, the primary α phase and the secondary α phase are defined separately according to the particle size of the α phase when observed with an optical microscope having a magnification of 400 times. That is, when observed with an optical microscope having a magnification of 400 times, the α phase in a closed region having a particle size of 0.5 μm or more is defined as the primary α phase. The region other than the primary α phase is a region including the secondary α phase and the β phase. Here, the particle size is obtained as a circle-equivalent diameter. In addition, tissues other than α phase and β phase are excluded.
チタン合金鍛造材の機械的特性のばらつきを抑制するため、金属組織中の一次α相の平均粒径を２．５μｍ以下に制御する。一次α相の平均粒径が２．５μｍを超えると、延性が低下し易く、ばらつきも生じ易くなる。一次α相の平均粒径は、好ましくは２．３μｍ以下である。一次α相の平均粒径は、金属組織の倍率４００倍の光学顕微鏡写真を画像解析することによって求められる。一次α相の平均粒径を２．５μｍ以下に制御するには、鍛造を所定の条件で行う方法があるが、詳細は後記する。 In order to suppress variations in the mechanical properties of the titanium alloy forged material, the average particle size of the primary α phase in the metal structure is controlled to 2.5 μm or less. When the average particle size of the primary α phase exceeds 2.5 μm, the ductility is likely to decrease and variation is likely to occur. The average particle size of the primary α phase is preferably 2.3 μm or less. The average particle size of the primary α-phase can be determined by image analysis of an optical micrograph of a metal structure at a magnification of 400 times. In order to control the average particle size of the primary α phase to 2.5 μm or less, there is a method of forging under predetermined conditions, which will be described in detail later.
（一次α相の平均アスペクト比）
チタン合金鍛造材の機械的特性のばらつきを抑制するため、金属組織中の一次α相の平均アスペクト比を３．０以下に制御する。一次α相の平均アスペクト比が３．０を超えると、延性が低下し易く、特性ばらつきも生じ易くなる。すなわち、一次α相のアスペクト比が小さい球状の形態に制御すると、特性ばらつきが少なくなり、安定して延性を確保することができる。一次α相の平均アスペクト比は、好ましくは、２．７以下である。一次α相の平均アスペクト比は、金属組織の倍率４００倍の光学顕微鏡写真を画像解析することによって求められる。一次α相の平均アスペクト比を３．０以下に制御するには、鍛造を所定の条件で行う方法があるが、詳細は後記する。
(Average aspect ratio of primary α phase)
In order to suppress variations in the mechanical properties of the titanium alloy forged material, the average aspect ratio of the primary α phase in the metal structure is controlled to 3.0 or less. When the average aspect ratio of the primary α phase exceeds 3.0, the ductility tends to decrease and the characteristics tend to vary. That is, if the shape is controlled to be spherical with a small aspect ratio of the primary α phase, the variation in characteristics is reduced and the ductility can be stably ensured. The average aspect ratio of the primary α phase is preferably 2.7 or less. The average aspect ratio of the primary α-phase can be determined by image analysis of an optical micrograph of a metal structure at a magnification of 400 times. In order to control the average aspect ratio of the primary α phase to 3.0 or less, there is a method of forging under predetermined conditions, but the details will be described later.
（表面側と内部側の一次α相の面積率の差）
大型のチタン合金鍛造材においては、鍛造材の表面側と内部側との間の機械的特性のばらつきが問題となる。ここで、大型のチタン合金鍛造材とは、断面図において１００〜５００ｍｍの大きさの最大内接円を設定することができるチタン合金鍛造材を意味する。また、チタン合金鍛造材の表面側とは、鍛造材の表面付近であり、鍛造材の表面から１５±１０ｍｍの深さの部分を意味する。また、チタン合金鍛造材の内部側とは、鍛造材の中心付近であり、鍛造材の断面に１００〜５００ｍｍの大きさの内接円を設定したときに、内接円の中心±１５ｍｍの深さの部分を意味する。ここで、鍛造材の断面の内接円とは、鍛造材の断面において、表側表面と裏側表面の両者に接する円のことを意味する。
(Difference in area ratio of primary α phase between surface side and inner side)
In a large titanium alloy forged material, variation in mechanical properties between the surface side and the inner side of the forged material becomes a problem. Here, the large titanium alloy forged material means a titanium alloy forged material in which a maximum inscribed circle having a size of 100 to 500 mm can be set in the cross-sectional view. Further, the surface side of the titanium alloy forged material means a portion near the surface of the forged material and a depth of 15 ± 10 mm from the surface of the forged material. The inner side of the titanium alloy forged material is near the center of the forged material, and when an inscribed circle having a size of 100 to 500 mm is set on the cross section of the forged material, the depth of the center of the inscribed circle is ± 15 mm. It means the part of the forging. Here, the inscribed circle in the cross section of the forging material means a circle in contact with both the front surface and the back surface in the cross section of the forging material.
チタン合金鍛造材の機械的特性のばらつきを抑制するため、表面側と内部側の一次α相の面積率の差を７．０％以下に制御する。表面側と内部側の一次α相の面積率の差が７．０％を超えると、強度と延性のばらつきが生じ易くなる。表面側と内部側の一次α相の面積率の差は、好ましくは６．０％以下である。表面側と内部側の一次α相の面積率は、金属組織の倍率４００倍の光学顕微鏡写真を画像解析することによって求められる。表面側と内部側の一次α相の面積率の差を７．０％以下に制御するには、溶体化処理の温度を所定の条件で行う方法があるが、詳細は後記する。 In order to suppress variations in the mechanical properties of the titanium alloy forged material, the difference in the area ratio of the primary α phase on the surface side and the internal side is controlled to 7.0% or less. If the difference in area ratio between the primary α phase on the surface side and the area ratio on the inner side exceeds 7.0%, variations in strength and ductility are likely to occur. The difference in area ratio between the primary α phase on the surface side and the area ratio on the inner side is preferably 6.0% or less. The area ratio of the primary α phase on the surface side and the inner side can be obtained by image analysis of an optical micrograph of a metal structure at a magnification of 400 times. In order to control the difference in the area ratio of the primary α phase on the surface side and the inner side to 7.0% or less, there is a method in which the temperature of the solution treatment is performed under a predetermined condition, but the details will be described later.
（一次α相の面積率）
チタン合金鍛造材の延性を確保しつつ強度を高めるために、一次α相の面積率を２０％以下に制御することが好ましい。一方、延性を確保する上で一次α相の面積率は一定量必要であり、通常は一次α相の面積率５％以上が目安である。一次α相の面積率は、金属組織の倍率４００倍の光学顕微鏡写真を画像解析することによって求められる。一次α相の面積率を２０％以下に制御するには、溶体化処理の温度を所定の条件で行う方法があるが、詳細は後記する。
(Area ratio of primary α phase)
In order to increase the strength while ensuring the ductility of the titanium alloy forged material, it is preferable to control the area ratio of the primary α phase to 20% or less. On the other hand, a certain amount of the area ratio of the primary α phase is required to ensure ductility, and usually, the area ratio of the primary α phase is 5% or more as a guide. The area ratio of the primary α phase is obtained by image analysis of an optical micrograph of a metal structure at a magnification of 400 times. In order to control the area ratio of the primary α phase to 20% or less, there is a method in which the temperature of the solution treatment is performed under predetermined conditions, but the details will be described later.
（二次α相の平均間隔）
本発明のチタン合金鍛造材の金属組織において、二次α相は、一次α相以外の領域を、ＦＥ−ＳＥＭ（電界放射型走査電子顕微鏡）を用いて倍率３万倍に拡大することによって観察することができる。このとき、二次α相とβ相とは、相互に入り組んだ不規則な形状を有しているが、画像の色相から両者を区別して認識することができる。
(Average interval of secondary α phase)
In the metallographic structure of the titanium alloy forged material of the present invention, the secondary α phase is observed by magnifying the region other than the primary α phase at a magnification of 30,000 times using an FE-SEM (field emission scanning electron microscope). can do. At this time, the secondary α phase and the β phase have irregular shapes intertwined with each other, but both can be distinguished and recognized from the hue of the image.
チタン合金鍛造材の延性を確保しつつ強度を高めるために、二次α相の平均間隔を２００ｎｍ以下に制御することが好ましい。二次α相の平均間隔は、より好ましくは１８０ｎｍ以下である。一方、二次α相の平均間隔が著しく小さいと、鍛造材が脆化する恐れがあるため、二次α相の平均間隔は１００ｎｍ以上が好ましい。二次α相の平均間隔は、金属組織の倍率３万倍のＦＥ−ＳＥＭによる顕微鏡写真を画像解析することによって求められる。二次α相の平均間隔は、後記するように、時効処理の保持温度によって制御することができる。 In order to increase the strength while ensuring the ductility of the titanium alloy forged material, it is preferable to control the average interval of the secondary α phase to 200 nm or less. The average spacing of the secondary α phase is more preferably 180 nm or less. On the other hand, if the average spacing of the secondary α phases is extremely small, the forged material may be embrittled. Therefore, the average spacing of the secondary α phases is preferably 100 nm or more. The average spacing of the secondary α phase is determined by image analysis of a micrograph of the metal structure by FE-SEM at a magnification of 30,000 times. The average interval of the secondary α phase can be controlled by the holding temperature of the aging treatment, as described later.
以上のように、本発明のチタン合金鍛造材は、特定の化学組成を有し、その金属組織を一次α相および二次α相によって規定される上記の特性を満足する特定の形態とすることによって、機械的特性を保持しつつ、表面部と内部との物性ばらつきの少ないものとすることができる。 As described above, the titanium alloy forged material of the present invention has a specific chemical composition, and its metal structure is in a specific form satisfying the above-mentioned characteristics defined by the primary α phase and the secondary α phase. Therefore, it is possible to reduce the variation in physical properties between the surface portion and the inside while maintaining the mechanical properties.
〔チタン合金鍛造材の製造方法〕
次に、本発明で規定する組織を得るための製造方法の一例について説明する。
上記の金属組織を有するチタン合金鍛造材は、以下に記載するチタン合金鍛造材の製造方法を適用することによって、製造することが可能である。本発明のチタン合金鍛造材の製造方法は、鍛造工程、溶体化工程、時効工程の各工程において、以下に記載する特定の加工条件で加工を行うことを特徴としている。
[Manufacturing method of titanium alloy forged material]
Next, an example of a manufacturing method for obtaining the structure specified in the present invention will be described.
The titanium alloy forged material having the above metal structure can be produced by applying the method for producing a titanium alloy forged material described below. The method for producing a titanium alloy forged material of the present invention is characterized in that each step of the forging step, the solution hardening step, and the aging step is performed under the specific processing conditions described below.
（チタン合金）
本発明のニアβ型チタン合金は、元素Ｘの含有量（質量％）を[Ｘ]としたときに、下記式（１）で表されるＭｏ当量［Ｍｏ］ｅｑが１０以上１３未満であるチタン合金からなる。
[Ｍｏ]ｅｑ＝[Ｍｏ]＋[Ｔａ]/５＋[Ｎｂ]/３．６＋[Ｗ]/２．５＋[Ｖ]/１．５＋１．２５[Ｃｒ]＋１．２５[Ｎｉ]＋１．７[Ｍｎ]＋１．７[Ｃｏ]＋２．５[Ｆｅ]・・・（１）
(Titanium alloy)
The near β-type titanium alloy of the present invention has a Mo equivalent [Mo] eq represented by the following formula (1) of 10 or more and less than 13 when the content (mass%) of the element X is [X]. Made of titanium alloy.
[Mo] eq = [Mo] + [Ta] / 5 + [Nb] /3.6+ [W] /2.5+ [V] /1.5+1.25 [Cr] +1.25 [Ni] +1.7 [ Mn] +1.7 [Co] +2.5 [Fe] ... (1)
本発明に係るチタン合金鍛造材は、前記組成のチタン合金からなるインゴットをビレットに鍛造し、溶体化処理、時効処理を行って所望の製品形状に製造される。尚、下記に記載した製造条件以外の製造工程、製造条件については、公知の条件を適宜適用して行うことによって、チタン合金鍛造材を得ることができる。 Titanium alloy forging according to the present invention is to forge an ingot of titanium alloy of the composition billet, solution heat treatment, is fabricated into a desired product shape by performing the aging treatment. A titanium alloy forged material can be obtained by appropriately applying known conditions to the manufacturing process and manufacturing conditions other than the manufacturing conditions described below.
（鍛造工程）
鍛造工程では、β変態域（Ｔβ〜（Ｔβ＋２００℃）程度）に加熱して鍛造を行い、鍛造材としての形状を整える。その後、α＋β温度域（（Ｔβ−３００℃）〜Ｔβ程度）に加熱して、α＋β域での相当歪量が累積で２〜１０となるように鍛造する（以下、累積された相当歪量を「累積歪量ε」と記載する。）。加熱時間は１〜８ｈｒ程度である。累積歪量εを２以上へ増やすことによって、α相を微細にし、かつ球状の形状に作りこむ。尚、累積歪量εを高くするためには、複数回に分けて加熱と鍛造を繰返せばよい。累積歪量εは１０を超えてもよいが、効果が飽和するため２〜１０とする。累積歪量εは好ましくは、３以上である。
(Forging process)
In the forging step, forging is performed by heating to a β transformation region (about Tβ to (Tβ + 200 ° C.)) to prepare the shape of the forging material. After that, it is heated to the α + β temperature range ((Tβ-300 ° C.) to Tβ) and forged so that the cumulative equivalent strain amount in the α + β range is 2 to 10 (hereinafter, the accumulated equivalent strain amount is used). Described as "cumulative strain amount ε"). The heating time is about 1 to 8 hr. By increasing the cumulative strain amount ε to 2 or more, the α phase is made finer and formed into a spherical shape. In order to increase the cumulative strain amount ε, heating and forging may be repeated in a plurality of times. The cumulative strain amount ε may exceed 10, but it is set to 2 to 10 because the effect is saturated. The cumulative strain amount ε is preferably 3 or more.
ここで、相当歪量は、相当塑性ひずみ量ともいう。試験片採取位置におけるα＋β域での相当歪量を市販のＦＥＭ解析ソフト（例えば、TRANSVALOR社製解析ソフト「FORGE 2011」）を用いて解析することによって測定することができる。また、累積歪量εについても同様に、鍛造を複数回行った際の累積された相当塑性ひずみ量を、市販のＦＥＭ解析ソフトを用いて解析することによって測定することができる。 Here, the equivalent strain amount is also referred to as an equivalent plastic strain amount. The amount of equivalent strain in the α + β region at the test piece sampling position can be measured by analyzing it using commercially available FEM analysis software (for example, TRANSVALOR analysis software “FORGE 2011”). Similarly, the cumulative strain amount ε can be measured by analyzing the cumulative equivalent plastic strain amount when forging is performed a plurality of times using commercially available FEM analysis software.
一方、加熱時間が増えると、一次α相が粗大となるため、トータルの累積加熱時間（７００℃以上での保持時間）は、１００ｈｒ以下に制御する。累積加熱時間は、好ましくは９０ｈｒ以下である。このように、累積歪量εはできるだけ大きくし、かつ累積加熱時間はできるだけ小さくするという条件にて鍛造を行うことで、一次α相の粗大化を抑制することができる。 On the other hand, as the heating time increases, the primary α phase becomes coarse, so the total cumulative heating time (holding time at 700 ° C. or higher) is controlled to 100 hr or less. The cumulative heating time is preferably 90 hr or less. As described above, by forging under the condition that the cumulative strain amount ε is made as large as possible and the cumulative heating time is made as short as possible, the coarsening of the primary α phase can be suppressed.
また、鍛造終了温度は４００℃以上に制御する。鍛造終了温度が４００℃未満であると、一次α相が針状の形態となり易い（すなわちアスペクト比が大きい）ため、延性低下や延性のばらつきが生じ易くなる。 Further, the forging end temperature is controlled to 400 ° C. or higher. When the forging end temperature is less than 400 ° C., the primary α phase tends to have a needle-like shape (that is, the aspect ratio is large), so that ductility is likely to decrease and ductility is likely to vary.
（溶体化工程）
鍛造後に、溶体化処理を行う。溶体化処理は、（Ｔβ−７０℃）を超える温度であって、（Ｔβ−２０℃）以下の温度に加熱することが好ましい。保持温度が（Ｔβ−７０℃）以下の温度の場合、一次α相の面積率が高くなり易く、強度が低下し易い。また、保持温度が（Ｔβ−２０℃）を超える場合、表面側と内部側の一次α相の面積率の差が大きくなり易く、機械的特性のばらつきが大きくなり易い。溶体化処理の保持時間は、好ましくは６０〜２４０ｍｉｎである。その後の時効工程で強度を確保するため、加熱保持後は、水冷する。
(Solution process)
After forging, solution treatment is performed. The solution treatment is preferably heated to a temperature higher than (Tβ-70 ° C.) and lower than (Tβ-20 ° C.). When the holding temperature is (Tβ-70 ° C.) or less, the area ratio of the primary α phase tends to increase and the strength tends to decrease. Further, when the holding temperature exceeds (Tβ-20 ° C.), the difference in the area ratio between the primary α phase on the surface side and the internal side tends to be large, and the variation in mechanical characteristics tends to be large. The retention time of the solution treatment is preferably 60 to 240 min. In order to secure the strength in the subsequent aging process, it is cooled with water after being heated and held.
（時効工程）
溶体化処理後に、時効処理を行う。時効処理は、４８０℃〜５２０℃の温度に保持することが好ましい。この温度範囲よりも低い場合は、二次α相が微細化し脆化の恐れがある、また、この温度範囲よりも高い場合は、二次α相の平均間隔が２００ｎｍを超えて、強度が低下し易い。時効処理の保持時間は、好ましくは２〜１２ｈｒである。
(Aging process)
After the solution treatment, aging treatment is performed. The aging treatment is preferably maintained at a temperature of 480 ° C to 520 ° C. If it is lower than this temperature range, the secondary α phase may become finer and embrittled, and if it is higher than this temperature range, the average interval of the secondary α phase exceeds 200 nm and the strength decreases. Easy to do. The holding time of the aging treatment is preferably 2 to 12 hr.
本発明に係るチタン合金鍛造材は、機械的特性を保持しつつ、大型の鍛造材であっても、鍛造材の表面部と内部における強度や延性等の特性ばらつきが少ないものである。強度および延性のばらつきが抑制されることで、大型の複雑形状の部品をより高い信頼性で設計することができる。例えば、極端に高強度な場所が存在することによって、鍛造材が脆化したり、加工性（切削加工性等）が低下するといったような問題が生じることが少なくなり、均一な特性を有した製品とすることができる。 The titanium alloy forged material according to the present invention retains mechanical properties, and even if it is a large-sized forged material, there is little variation in characteristics such as strength and ductility between the surface portion and the inside of the forged material. By suppressing variations in strength and ductility, large, complex-shaped parts can be designed with higher reliability. For example, the presence of an extremely high-strength place reduces problems such as brittleness of the forged material and deterioration of workability (cutting workability, etc.), and a product having uniform characteristics. Can be.
以下に、本発明の効果を確認した実施例を、本発明の要件を満たさない比較例と対比して具体的に説明する。尚、本発明は以下の実施例に限定されるものではない。 Hereinafter, examples in which the effects of the present invention have been confirmed will be specifically described in comparison with comparative examples that do not satisfy the requirements of the present invention. The present invention is not limited to the following examples.
〔試験材の作製〕
ＡＭＳ４９８４で規定されるTi-10V-2Fe-3Al合金（Ｔβ：８１０℃、Ｍｏ当量１１．７）からなるビレットを用いて、β変態点の８１０℃以上の温度で鍛造後に、表１に記載の各条件で、鍛伸してφ１８０ｍｍの鍛造材とし、その後熱処理を行った。表１には、α＋β域での仕上げ鍛造における累積歪量εを示した。
[Preparation of test material]
Table 1 shows after forging with a billet made of a Ti-10V-2Fe-3Al alloy (Tβ: 810 ° C., Mo equivalent 11.7) specified by AMS4984 at a temperature of 810 ° C. or higher at the β transformation point. Under each condition, it was forged to obtain a forged material having a diameter of 180 mm, and then heat-treated. Table 1 shows the cumulative strain amount ε in the finish forging in the α + β region.
鍛造後の素材を使って、溶体化処理および時効処理を表１に記載の条件で行った。溶体化の加熱保持後は、水冷した。時効処理は、所定温度に加熱保持後、空冷にて室温まで冷却した。溶体化処理や時効処理の時間は、表１に記載の加熱温度の炉に入れてからの時間とした。 Using the forged material, solution treatment and aging treatment were performed under the conditions shown in Table 1. After heating and holding the solution, it was cooled with water. The aging treatment was carried out by heating and holding at a predetermined temperature, and then cooling to room temperature by air cooling. The time for the solution treatment and the aging treatment was the time after being placed in the furnace at the heating temperature shown in Table 1.
〔試験材の評価〕
得られた鍛造材（試験材Ｎｏ.１〜９）の表面側と内部側からそれぞれ引張試験用試験片と組織観察用ブロックを切り出して評価に供した。このとき、物性がばらつく端部を避けるため、引張試験用試験片と組織観察用ブロックを切り出す位置は、鍛造材の長さ方向（Ｌ方向、鍛伸方向）の各端部から５０ｍｍ以上内側となる位置で切り出した。さらに、前記範囲内の鍛造材の任意の位置において、鍛造材の幅方向および厚さ方向における断面平面が得られるように、長さ方向と直角方向であって、厚さ方向と平行に切断した。得られた断面において最大内接円が得られる位置で最大内接円を描いた。表面側の試験片は、試験片の中心位置が当該最大内接円において、表面から１５±１０ｍｍの深さとなる場所から採取した。一方、内部側の試験片は、試験片の中心位置が当該最大内接円の中心±１５ｍｍの深さとなる場所から採取した。図２は、鍛造材の断面における最大内接円と特性の評価位置を示す模式的断面図である。
[Evaluation of test material]
A tensile test test piece and a structure observation block were cut out from the surface side and the inner side of the obtained forged material (test materials Nos. 1 to 9) and used for evaluation. At this time, in order to avoid the end portion where the physical properties vary, the position where the tensile test test piece and the structure observation block are cut out is 50 mm or more inside from each end portion in the length direction (L direction, forging direction) of the forging material. It was cut out at the position where. Further, it was cut in the direction perpendicular to the length direction and parallel to the thickness direction so that a cross-sectional plane in the width direction and the thickness direction of the forging material could be obtained at an arbitrary position of the forging material within the above range. .. The maximum inscribed circle was drawn at the position where the maximum inscribed circle was obtained in the obtained cross section. The test piece on the front surface side was taken from a place where the center position of the test piece was 15 ± 10 mm from the surface in the maximum inscribed circle. On the other hand, the test piece on the inner side was taken from a place where the center position of the test piece was ± 15 mm at the center of the maximum inscribed circle. FIG. 2 is a schematic cross-sectional view showing the maximum inscribed circle and the evaluation position of the characteristics in the cross section of the forged material.
尚、当該鍛造材の切断位置は、当該鍛造材において、断面の内接円として最大の内接円が得られる位置、すなわち厚みが最大となる位置で切断することが好ましい。当該鍛造材の最大の内接円が得られる位置で試験材を採取することによって、当該鍛造材の代表的物性や最大の物性ばらつきを評価することができるからである。 The cutting position of the forged material is preferably a position where the maximum inscribed circle of the cross section is obtained, that is, a position where the thickness is maximum. This is because the representative physical properties and the maximum variation in physical properties of the forged material can be evaluated by collecting the test material at a position where the maximum inscribed circle of the forged material can be obtained.
Ｎｏ.１〜９の試験材から得られた個々の試験片について、以下に記載する評価条件によって、各種物性を測定・評価し、それらの平均値を求めた。評価結果は表２に示した。
尚、試験材Ｎｏ.１〜９はいずれも、ニアβ型チタン合金鍛造材であり、α相とβ相の面積率の合計が９９％以上であった。
For each test piece obtained from the test materials No. 1 to 9, various physical properties were measured and evaluated according to the evaluation conditions described below, and the average value thereof was obtained. The evaluation results are shown in Table 2.
The test materials Nos. 1 to 9 were all near β type titanium alloy forged materials, and the total area ratio of the α phase and the β phase was 99% or more.
（引張試験）
試験材の長さ方向と引張試験片の荷重軸方向が平行になるように、各試験材毎に２個ずつ試験片を採取した。引張試験ではＡＳＴＭ規格のＥ８に準拠して実施した。試験片サイズはＡＳＴＭ Ｅ８のSpecimen2とした。
(Tensile test)
Two test pieces were collected for each test material so that the length direction of the test material and the load axis direction of the tensile test piece were parallel to each other. The tensile test was carried out in accordance with ASTM standard E8. The size of the test piece was Spectrum 2 of ASTM E8.
表面側及び内部側の平均の強度（引張強さ、ＴＳ）と延性（伸び、ＥＬ）を求めた（特性平均値）。また、特性ばらつきを、強度差／内部強度、および延性差／内部延性として評価した。ここで、強度差とは、表面側の特性平均値と内部側の特性平均値の差であり、延性差とは、表面側の特性平均値と内部側の特性平均値の差である。これを内部の特性平均値で除して、どれだけの割合（％）でばらつきが生じるかを評価した。 The average strength (tensile strength, TS) and ductility (elongation, EL) on the surface side and the inner side were determined (characteristic average value). In addition, the characteristic variation was evaluated as strength difference / internal strength and ductility difference / internal ductility. Here, the strength difference is the difference between the characteristic average value on the surface side and the characteristic average value on the inner side, and the ductility difference is the difference between the characteristic average value on the surface side and the characteristic average value on the inner side. This was divided by the average value of the internal characteristics to evaluate the rate of variation (%).
測定の結果、強度差／内部強度の数値が１０％以下のものを合格、および延性差／内部延性の数値が３０％以下のものを合格とした。また、強度（ＴＳ）は、１２００ＭＰａ以上のとき、延性（ＥＬ）は、８％以上のとき合格と判定した。 As a result of the measurement, those having a strength difference / internal strength value of 10% or less were accepted, and those having a ductility difference / internal ductility value of 30% or less were accepted. Further, when the strength (TS) was 1200 MPa or more and the ductility (EL) was 8% or more, it was judged to be acceptable.
（組織観察）
＜試料調製＞
鍛造材のＬ方向（光学顕微鏡で観察した際にβ結晶粒の伸張方向で判別できる）に平行な断面が観察できるように、引張試験片採取位置のすぐ隣の深さが同等の位置から、各試験材毎に表面側と内部側において、各２試験片ずつ組織観察用のブロックを切出した。
樹脂包埋、研磨および腐食（フッ硝酸溶液）を実施し組織観察用のサンプルとし、光学顕微鏡（OLYMPUS社製、GX71）観察、ＦＥ−ＳＥＭ（日立製作所社製、SU-70）観察を実施した。
(Tissue observation)
<Sample preparation>
From a position with the same depth immediately next to the tensile test piece collection position, so that a cross section parallel to the L direction of the forging material (which can be identified by the elongation direction of β crystal grains when observed with an optical microscope) can be observed. A block for observing the structure was cut out from each of the two test pieces on the front side and the inner side of each test material.
Resin embedding, polishing and corrosion (fluorinated nitric acid solution) were carried out to prepare samples for microstructure observation, and optical microscope (OLYMPUS, GX71) observation and FE-SEM (Hitachi, SU-70) observation were carried out. ..
＜一次α相の粒径、アスペクト比、面積率の測定＞
光学顕微鏡にて、倍率４００倍で観察した。円相当径で０．５μｍ以上に判別される領域を一次α相とし、一次α相以外の領域は一次α相以外の二次α相やβ相などの領域とした。各試験片において、各５枚の写真をランダムに取得し、一次α相の粒径（＝円相当径）、アスペクト比、面積率を画像解析（画像解析ソフトウェア；日本ローパー社製、Image-Pro Plus、ver.7.0）により求めた。尚、一次α相は鍛造や熱処理によって徐々にくびれ（凹み）が生じ、更には分断されていくが、くびれが生じていても互いに重なっている一次α相については一つの一次α相としてカウントした。
<Measurement of particle size, aspect ratio, and area ratio of primary α phase>
It was observed with an optical microscope at a magnification of 400 times. The region determined to have a diameter equivalent to a circle of 0.5 μm or more was defined as the primary α phase, and the region other than the primary α phase was defined as a region such as a secondary α phase or β phase other than the primary α phase. For each test piece, 5 photographs are randomly acquired, and the particle size (= circle equivalent diameter), aspect ratio, and area ratio of the primary α phase are analyzed by image analysis (image analysis software; Image-Pro manufactured by Nippon Roper Co., Ltd.). Obtained by Plus, ver.7.0). The primary α phase gradually develops a constriction (dent) due to forging or heat treatment, and is further divided. However, even if the constriction occurs, the primary α phases that overlap each other are counted as one primary α phase. ..
解析結果から、一次α相の平均粒径（各４試験片×５枚の写真の平均）、平均アスペクト比（各４試験片×５枚の写真の平均）、平均面積率（各４試験片×５枚の写真の平均）、表面側と内部側の一次α相の面積率の差（内部側２試験片の平均面積率と表面側２試験片の平均面積率の差）を算出した。 From the analysis results, the average particle size of the primary α phase (4 test pieces each x 5 photographs average), average aspect ratio (4 test pieces each x 5 photographs average), average area ratio (4 test pieces each) (Average of 5 photographs), the difference in the area ratio of the primary α phase between the surface side and the internal side (the difference between the average area ratio of the two internal test pieces and the average area ratio of the two surface side test pieces) was calculated.
＜二次α相の平均間隔の測定＞
各試験材の各試験片毎に、倍率３万倍のＦＥ−ＳＥＭにより観察を行い、一次α相以外の領域（β相と二次α相が含まれる領域）において、各５枚の写真をランダムに撮影した。
写真を元に、水平方向及び垂直方向に写真の端から端まで線分を各５本、等間隔に引き、線分が二次α相と交わる点をカウントした。その後、（線分長さの合算）÷（カウント数の総数）から、二次α相の平均間隔を算出した。図１に二次α相の平均間隔を算出する方法を示す模式図を示した。線分ｌと二次α相Ｐとの交点Ｘ１〜Ｘ５をカウントした。
尚、測定の際、まれに極端に微細なα相や極端に微細なβ相の領域が存在する場合があるが、画像解析ソフトにて円相当径が５ｎｍ以上とカウントされるα相・β相をカウント対象とした。ここで、円相当径の算出にあたっては、図１の交点Ｘ４、Ｘ５を通る二次α相のような場合、二次α相の中に含まれるβ相（白色）の領域は円相当径を算出する際の計算対象としていない（つまり黒色の領域のみの面積から円相当径を求めた。）
解析結果から、二次α相の平均間隔（各試験材毎に４試験片×５枚の写真の平均）を算出した。
<Measurement of average interval of secondary α phase>
For each test piece of each test material, observation was performed by FE-SEM at a magnification of 30,000, and 5 photographs were taken in each region other than the primary α phase (the region containing the β phase and the secondary α phase). Taken at random.
Based on the photograph, five line segments were drawn horizontally and vertically from one end of the photograph to the other at equal intervals, and the points at which the line segments intersected the secondary α phase were counted. After that, the average interval of the secondary α phase was calculated from (total of line segment lengths) ÷ (total number of counts). FIG. 1 shows a schematic diagram showing a method of calculating the average interval of the secondary α phase. The intersections X1 to X5 of the line segment l and the secondary α phase P were counted.
In rare cases, there may be extremely fine α phase or extremely fine β phase regions during measurement, but the α phase / β whose circle equivalent diameter is counted as 5 nm or more by image analysis software. The phase was counted. Here, in calculating the equivalent circle diameter, in the case of the secondary α phase passing through the intersections X4 and X5 in FIG. 1, the β phase (white) region included in the secondary α phase has the equivalent circle diameter. Not included in the calculation when calculating (that is, the equivalent circle diameter was obtained from the area of only the black area).
From the analysis results, the average interval of the secondary α phase (the average of 4 test pieces × 5 photographs for each test material) was calculated.
試験材Ｎｏ．５〜９は、いずれも本発明のＭｏ当量を満足し、前記の特定の製造条件を用いて製造されたものである。試験材Ｎｏ．５〜９は、一次α相の平均粒径、一次α相の平均アスペクト比および表面側と内部側の一次α相の面積率の差において、本発明の規定を満足するものである。そのため、いずれの試験材も、平均強度と平均延性に優れ、表面部と内部における強度と延性の特性ばらつきにおいても優れたものであった。
但し、試験材Ｎｏ．５は、溶体化処理の加熱温度が低目の温度であるため、一次α相の面積率が２０％を超え、他の試験材に比べて、強度がやや低いものであった。試験材Ｎｏ．６は、時効処理の加熱温度が好ましい温度範囲に比べてやや高いため、二次α相の平均間隔が２００ｎｍを超え、他の試験材に比べて、強度がやや低いものであった。
Test material No. All of 5 to 9 satisfy the Mo equivalent of the present invention and are produced using the above-mentioned specific production conditions. Test material No. 5 to 9 satisfy the provisions of the present invention in terms of the average particle size of the primary α phase, the average aspect ratio of the primary α phase, and the difference in the area ratio of the primary α phase between the surface side and the internal side. Therefore, all of the test materials were excellent in average strength and average ductility, and also excellent in variation in strength and ductility characteristics between the surface portion and the inside.
However, the test material No. In No. 5, since the heating temperature of the solution treatment was a low temperature, the area ratio of the primary α phase exceeded 20%, and the strength was slightly lower than that of other test materials. Test material No. In No. 6, since the heating temperature of the aging treatment was slightly higher than the preferable temperature range, the average interval of the secondary α phase exceeded 200 nm, and the strength was slightly lower than that of the other test materials.
試験材Ｎｏ．１は、溶体化工程における加熱温度が好ましい温度範囲に比べて高いため、表面側と内部側の一次α相の面積率の差が大きくなり、表面部と内部における強度と延性の特性ばらつきにおいて劣るものであった。
試験材Ｎｏ．２は、α＋β域鍛造工程における累積歪量εが小さいため、一次α相の平均アスペクト比が３．０を超え、延性の特性ばらつきにおいて劣るものとなった。
試験材Ｎｏ．３は、α＋β域鍛造工程における累積加熱時間が１００ｈｒを超えているため、一次α相の平均粒径が２．５μｍを超えており、延性の特性ばらつきにおいて劣るものとなった。
試験材Ｎｏ．４は、α＋β域鍛造工程における鍛造終了温度が好ましい温度範囲に比べて低いため、一次α相の平均アスペクト比が３．０を超え、表面部と内部における強度と延性の特性ばらつきにおいて劣るものであった。
Test material No. In No. 1, since the heating temperature in the solution formation step is higher than the preferable temperature range, the difference in the area ratio of the primary α phase between the surface side and the internal side becomes large, and the strength and ductility characteristics vary between the surface portion and the internal portion. It was a thing.
Test material No. In No. 2, since the cumulative strain amount ε in the α + β region forging step was small, the average aspect ratio of the primary α phase exceeded 3.0, and the variation in ductility characteristics was inferior.
Test material No. In No. 3, since the cumulative heating time in the α + β region forging step exceeded 100 hr, the average particle size of the primary α phase exceeded 2.5 μm, which was inferior in the variation in ductility characteristics.
Test material No. In No. 4, since the forging end temperature in the α + β region forging step is lower than the preferable temperature range, the average aspect ratio of the primary α phase exceeds 3.0, and the strength and ductility characteristics vary between the surface and the inside. there were.
Ｐ 二次α相
Ｘ１、Ｘ２、Ｘ３、Ｘ４、Ｘ５ 交点
ｌ 線分
P secondary α phase X1, X2, X3, X4, X5 intersection l line segment
Claims (3)
[Ｍｏ]ｅｑ＝[Ｍｏ]＋[Ｔａ]/５＋[Ｎｂ]/３．６＋[Ｗ]/２．５＋[Ｖ]/１．５＋１．２５[Ｃｒ]＋１．２５[Ｎｉ]＋１．７[Ｍｎ]＋１．７[Ｃｏ]＋２．５[Ｆｅ]・・・（１）
前記チタン合金がＡＭＳ４９８４に定められたTi-10V-2Fe-3Al合金であり、
α相とβ相の面積率の合計が９９％以上であり、
一次α相の平均粒径が２．５μｍ以下であり、
一次α相の平均アスペクト比が３．０以下であり、
表面側と内部側の一次α相の面積率の差が７．０％以下であることを特徴とするチタン合金鍛造材。
ここで、前記表面側とは、前記チタン合金鍛造材の表面から１５±１０ｍｍの深さの部分であり、
前記内部側とは、前記チタン合金鍛造材の断面に１００〜５００ｍｍの大きさの内接円を設定したときに、前記内接円の中心±１５ｍｍの深さの部分である。 A titanium alloy forged material made of a titanium alloy having a Mo equivalent [Mo] eq represented by the following formula (1) of 10 or more and less than 13 when the content (mass%) of the element X is [X]. hand,
[Mo] eq = [Mo] + [Ta] / 5 + [Nb] /3.6+ [W] /2.5+ [V] /1.5+1.25 [Cr] +1.25 [Ni] +1.7 [ Mn] +1.7 [Co] +2.5 [Fe] ... (1)
The titanium alloy is a Ti-10V-2Fe-3Al alloy defined in AMS4984.
The total area ratio of α phase and β phase is 99% or more,
The average particle size of the primary α phase is 2.5 μm or less,
The average aspect ratio of the primary α phase is 3.0 or less,
Titanium alloy forging difference between the surface side and the area ratio of the internal side of the primary α phase is characterized der Rukoto 7.0% or less.
Here, the surface side is a portion having a depth of 15 ± 10 mm from the surface of the titanium alloy forged material.
The inner side is a portion having a depth of ± 15 mm at the center of the inscribed circle when an inscribed circle having a size of 100 to 500 mm is set on the cross section of the titanium alloy forged material.
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