JP5421796B2 - Titanium alloy billet with excellent defect detection capability in ultrasonic testing - Google Patents
Titanium alloy billet with excellent defect detection capability in ultrasonic testing Download PDFInfo
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本発明は、チタン合金製品の製造工程で得られる中間素材のチタン合金ビレットに係り、超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットに関するものである。 The present invention relates to an intermediate titanium alloy billet obtained in a manufacturing process of a titanium alloy product, and relates to a titanium alloy billet excellent in defect detection capability in an ultrasonic flaw detection test.
Ｔｉ−６Ａｌ−４Ｖ合金に代表される高強度α＋β型チタン合金は、軽量、高強度、高耐食性に加え、溶接性、超塑性、拡散接合性などの利用加工諸特性を有することから、航空機産業を中心に多用されてきた。これらの特性を更に活用すべく、近年では、ゴルフ用品をはじめとしたスポーツ用品にも使用されるようになってきており、自動車部品、土木建築用素材、各種工具類などの民生品分野や、深海やエネルギー開発用途などへの適用拡大も進んでいる。 High-strength α + β-type titanium alloys represented by Ti-6Al-4V alloy have various processing characteristics such as weldability, superplasticity, and diffusion bondability in addition to light weight, high strength, and high corrosion resistance. Has been used extensively. In order to further utilize these characteristics, in recent years it has come to be used for sports equipment such as golf equipment, such as consumer products such as automobile parts, civil engineering materials, various tools, Application to deep seas and energy development applications is also expanding.
チタン合金製品は、まず、原材料の溶解、ビレット鍛造という工程を経て中間素材であるチタン合金ビレットを製造し、そのチタン合金ビレットを、鍛造、熱処理、機械加工することによって製造される。 A titanium alloy product is manufactured by first manufacturing a titanium alloy billet as an intermediate material through steps of melting raw materials and billet forging, and forging, heat treatment, and machining the titanium alloy billet.
航空機向け部材にあっては、疲労強度等の製品特性を害するサブミリメートル以上の内部欠陥の検査は、超音波探傷法によって、ビレットおよび熱処理後の鍛造品の２回の製造段階で実施されるのが一般的である。 For aircraft components, inspection of sub-millimeter internal defects that impair product characteristics such as fatigue strength is performed at the two manufacturing stages of billets and forged products after heat treatment by ultrasonic flaw detection. Is common.
しかし、チタン合金は他の金属素材と比較して超音波探傷試験における欠陥検出能力が低く、特に直径がφ１５０ｍｍ以上の大型のチタン合金ビレットにおいては、φ０．８ｍｍより小さい欠陥を検出することは困難であった。 However, titanium alloys have lower defect detection capabilities in ultrasonic flaw detection tests than other metal materials, and it is difficult to detect defects smaller than φ0.8 mm especially in large titanium alloy billets with a diameter of φ150 mm or more. Met.
従来からのチタン合金ビレットで、超音波探傷試験における欠陥検出能力に優れるビレットとしては、特許文献１、２ならびに非特許文献１に記載のＵＦＧ（Ｕｎｉｆｏｒｍ Ｆｉｎｅ Ｇｒａｉｎ）ビレットを挙げることができる。このＵＦＧビレットは、ビレット製造時の鍛造方法を制御して均一且つ微細な等軸α組織を得ることで、超音波探傷試験における欠陥検出能力を高めたビレットである。しかしながら、このＵＦＧビレットを製造するには、低歪速度での鍛造が必要であり、試験的な製造は行うことができるものの、量産を行うことはできず、実際の製造現場で生産することは不可能であった。また、前記の鍛造方法で大型のＵＦＧビレットを製造することは不可能であった。 Examples of billets that are conventional titanium alloy billets and have excellent defect detection capabilities in ultrasonic flaw detection tests include UFG (Uniform Fine Grain) billets described in Patent Documents 1 and 2 and Non-Patent Document 1. This UFG billet is a billet having improved defect detection capability in an ultrasonic flaw detection test by controlling a forging method at the time of manufacturing the billet to obtain a uniform and fine equiaxed α structure. However, in order to manufacture this UFG billet, forging at a low strain rate is necessary, and although trial manufacture can be performed, mass production cannot be performed and production at an actual manufacturing site is not possible. It was impossible. Moreover, it was impossible to produce a large UFG billet by the forging method described above.
また、本出願人は、直径がφ１５０ｍｍ以上の大型のビレットであっても、他の金属製品の場合と同様に、一般的に用いられている超音波探傷法で、従来よりも微細な内部欠陥の検査を行うことができ、しかも、量産することが可能な、超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットとして、ＡＭＳ４９２８で規定されるチタン合金ビレットに関する発明を、特願２００８−１５４４６２号として既に提案している。 In addition, the present applicant, even in the case of a large billet having a diameter of φ150 mm or more, as in the case of other metal products, is a generally used ultrasonic flaw detection method, and internal defects smaller than conventional ones. The invention relating to the titanium alloy billet specified by AMS4928 as a titanium alloy billet excellent in defect detection capability in the ultrasonic flaw detection test that can be inspected and mass-produced is disclosed in Japanese Patent Application No. 2008-154462. It has already been proposed as an issue.
しかしながら、このＡＭＳ４９２８で規定されるチタン合金ビレットは、チタン合金ビレットの中では超音波透過性に優れる材料であり、ＡＭＳ４９２８で規定されるチタン合金ビレットより超音波透過性に劣るＡＭＳ４９８１で規定されるチタン合金ビレットに関しては、上記特性を備えた超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットは、まだ開発されていないのが現状であった。 However, the titanium alloy billet specified by AMS4928 is a material having excellent ultrasonic transmission among the titanium alloy billets, and titanium specified by AMS4981 which is inferior in ultrasonic transmission than the titanium alloy billet specified by AMS4928. Regarding the alloy billet, a titanium alloy billet having excellent defect detection capability in the ultrasonic flaw detection test having the above characteristics has not been developed yet.
本発明は、上記従来の問題を解決せんとしてなされたもので、チタン合金の中では超音波透過性が比較的劣る材料であるＡＭＳ４９８１で規定されるチタン合金製で、しかも、直径がφ１５０ｍｍ以上の大型のビレットであっても、他の金属製品の場合と同様に、一般的に用いられている超音波探傷法で、従来よりも微細な内部欠陥の検査を行うことができ、また、量産することが可能な、超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットを提供することを課題とするものである。 The present invention has been made as a solution to the above-described conventional problems, and is made of a titanium alloy defined by AMS4981, which is a material with relatively poor ultrasonic transmission among titanium alloys, and has a diameter of φ150 mm or more. Even for large billets, as in the case of other metal products, it is possible to inspect fine internal defects finer than before by mass-production using the generally used ultrasonic flaw detection method. It is an object of the present invention to provide a titanium alloy billet that has excellent defect detection capability in an ultrasonic flaw detection test.
請求項１記載の発明は、一次α相、二次α相、及び、β相からなる合金組織を有するチタン合金ビレットであって、直径がφ１５０ｍｍ以上で円柱状のＡＭＳ４９８１で規定されるチタン合金ビレットの中心軸を中心とした直径の１／４の内部範囲の軸方向に平行な任意の断面の総面積が４０万μｍ２以上である領域において、全組織中に占める、一次α相の面積率が２０％以上であると共に、アスペクト比が２．０以下の一次α相の面積率が１２％以上であることを特徴とする超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットである。 The invention described in claim 1 is a titanium alloy billet having an alloy structure composed of a primary α phase, a secondary α phase, and a β phase, and having a diameter of 150 mm or more and defined by a cylindrical AMS4981 The area ratio of the primary α phase occupying in the whole structure in the region where the total area of the arbitrary cross section parallel to the axial direction of the inner range of ¼ of the diameter centered on the central axis of the core is 400,000 μm 2 or more Is a titanium alloy billet excellent in defect detection capability in an ultrasonic flaw detection test characterized in that the area ratio of the primary α-phase is not more than 20% and the aspect ratio is not more than 2.0.
請求項２記載の発明は、前記チタン合金ビレットの中心軸を中心とした直径の１／４の内部範囲の軸方向に平行な任意の断面の総面積が４０万μｍ２以上である領域において、存在する一次α相の平均アスペクト比が３．０以下であることを特徴とする請求項１記載の超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットである。 The invention according to claim 2 is a region where the total area of any cross section parallel to the axial direction of the inner range of 1/4 of the diameter centered on the central axis of the titanium alloy billet is 400,000 μm 2 or more, 2. The titanium alloy billet having excellent defect detection capability in the ultrasonic flaw detection test according to claim 1, wherein an average aspect ratio of an existing primary α phase is 3.0 or less.
本発明の超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットによると、チタン合金の中では超音波透過性が比較的劣る材料であるＡＭＳ４９８１で規定されるチタン合金製で、しかも、直径がφ１５０ｍｍ以上の大型のビレットであっても、一般的に用いられている超音波探傷法により、内部欠陥の検査を問題なく行うことができ、また、量産することが可能である。 According to the titanium alloy billet having excellent defect detection capability in the ultrasonic flaw detection test of the present invention, it is made of a titanium alloy specified by AMS4981 which is a material having relatively low ultrasonic permeability among titanium alloys, and has a diameter of Even a large billet having a diameter of 150 mm or more can be inspected for internal defects without problems by a generally used ultrasonic flaw detection method, and can be mass-produced.
本発明者らは、ＡＭＳ４９８１で規定されるチタン合金製で、直径がφ１５０ｍｍ以上の大型のビレットを製造し、実験により調査することで、チタン合金の中では超音波透過性が比較的劣る材料であるＡＭＳ４９８１で規定されるチタン合金ビレットであっても、超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットとすることができる発明を見出すために鋭意研究を進めた。 The present inventors manufactured a large billet having a diameter of φ150 mm or more made of a titanium alloy specified by AMS4981 and investigated it by experiment. In order to find an invention in which even a titanium alloy billet defined by a certain AMS4981 can be made into a titanium alloy billet having an excellent defect detection capability in an ultrasonic flaw detection test, research has been advanced.
その結果、一次α相の面積率を増大させることで、超音波探傷試験時の超音波透過能を増大させることができることを見出し、また、一次α相の等軸化度を促進し、一次α相のアスペクト比を小さくすることで、超音波探傷試験時の超音波ノイズの発生源となるコロニー（同一方位の針状α相の集合体）のサイズを小さくすることができることを見出した。これらの要件を採用することで、チタン合金の中では超音波透過性が比較的劣る材料であるＡＭＳ４９８１で規定されるチタン合金製で、しかも、直径がφ１５０ｍｍ以上の大型のビレットであっても、従来からのチタン合金ビレットを超える超音波探傷試験における欠陥検出能力を備えたチタン合金ビレットを得ることができることを確認した。 As a result, it has been found that by increasing the area ratio of the primary α phase, it is possible to increase the ultrasonic transmission power during the ultrasonic flaw detection test, and also promotes the equiaxed degree of the primary α phase, It has been found that by reducing the phase aspect ratio, the size of colonies (aggregates of acicular α-phase in the same direction) that are the source of ultrasonic noise during the ultrasonic flaw detection test can be reduced. By adopting these requirements, even in the case of a large billet with a diameter of φ150 mm or more, it is made of a titanium alloy defined by AMS4981 which is a material with relatively poor ultrasonic transmission among titanium alloys. It was confirmed that a titanium alloy billet having a defect detection capability in an ultrasonic flaw detection test exceeding the conventional titanium alloy billet can be obtained.
以下、本発明を実施形態に基づいて更に詳細に説明する。 Hereinafter, the present invention will be described in more detail based on embodiments.
本発明者らは、鋭意研究を進めた結果、直径がφ１５０ｍｍ以上で略円柱状のＡＭＳ４９８１で規定されるチタン合金ビレットの中心軸を中心とした直径の１／４の内部範囲（以下、中心部という。）の軸方向に平行な任意の断面の総面積が４０万μｍ２以上である領域において、全組織中に占める、一次α相の面積率と、アスペクト比が２．０以下の一次α相の面積率が、共に増加するに伴い、超音波探傷試験における欠陥検出能力が向上することを確認した。一次α相の面積率の下限は２０％、より好ましくは３０％である。また、アスペクト比が２．０以下の一次α相の面積率の下限は、１２％以上であれば効果を得ることができる。この面積率の下限は、より好ましくは２０％、更に好ましくは３０％である。 As a result of diligent research, the present inventors have found that the internal range of 1/4 of the diameter centered on the central axis of the titanium alloy billet defined by AMS4981 having a diameter of φ150 mm or more and a substantially cylindrical shape (hereinafter referred to as the center portion). In the region where the total area of an arbitrary cross section parallel to the axial direction is 400,000 μm 2 or more, the area ratio of the primary α phase in the entire structure and the primary α of the aspect ratio of 2.0 or less. It was confirmed that the defect detection ability in the ultrasonic flaw detection test was improved as the area ratio of the phases increased. The lower limit of the area ratio of the primary α phase is 20%, more preferably 30%. Moreover, an effect can be acquired if the minimum of the area ratio of the primary alpha phase whose aspect ratio is 2.0 or less is 12% or more. The lower limit of this area ratio is more preferably 20%, still more preferably 30%.
尚、ＡＭＳ４９８１で規定されるチタン合金ビレットの成分組成は、主添加元素として、Ａｌ、Ｓｎ、ＺｒおよびＭｏを含有し、その含有量は、Ａｌ：５．５０〜６．５０質量％、Ｓｎ：１．７５〜２．２５質量％、Ｚｒ：３．５０〜４．５０質量％、Ｍｏ：５．５０〜６．５０質量％であって、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、おおよそＮ：０．０４質量％、Ｃ：０．０８質量％、Ｈ：０．０１５質量％、Ｆｅ：０．１５質量％、Ｏ：０．１５質量％を含有する。 In addition, the component composition of the titanium alloy billet specified by AMS4981 contains Al, Sn, Zr and Mo as main additive elements, and the contents thereof are Al: 5.50 to 6.50 mass%, Sn: 1.75 to 2.25 mass%, Zr: 3.50 to 4.50 mass%, Mo: 5.50 to 6.50 mass%, and the balance is Ti and inevitable impurities. As inevitable impurities, N: 0.04 mass%, C: 0.08 mass%, H: 0.015 mass%, Fe: 0.15 mass%, and O: 0.15 mass% are contained.
ここで、略円柱状のＡＭＳ４９８１で規定されるチタン合金ビレットの直径をφ１５０ｍｍ以上としたのは、直径がφ１５０ｍｍ未満であれば、サイズが小さいことから、特に本発明のような組織制御を行わなくても超音波探傷法によって、内部欠陥の検査を行うことが可能であるという理由からである。 Here, the diameter of the titanium alloy billet defined by the substantially cylindrical AMS4981 is set to φ150 mm or more because the size is small if the diameter is less than φ150 mm, and thus the structure control as in the present invention is not particularly performed. However, this is because the internal defect can be inspected by the ultrasonic flaw detection method.
また、チタン合金ビレットの中心部の軸方向に平行な任意の断面の総面積が４０万μｍ２以上である領域を要件としたのは、その総面積が４０万μｍ２未満であると、得られるデータが少な過ぎ、正確な数値を得ることができない可能性が懸念されるからである。 In addition, the requirement that the total area of an arbitrary cross section parallel to the axial direction of the center part of the titanium alloy billet is 400,000 μm 2 or more is that the total area is less than 400,000 μm 2. This is because there is a concern that there is too little data to be obtained, and it may not be possible to obtain an accurate numerical value.
また、略円柱状のＡＭＳ４９８１で規定されるチタン合金ビレットの中心部の軸方向に平行な断面における組織を基準としたのは、中心部が最も内部欠陥が発生しやすく、また、ビレット製造後において超音波探傷試験時の超音波ノイズの発生源となるコロニーが残存しやすいため、最も内部欠陥の検査が行い難い部位であるという理由からである。 The structure in the cross section parallel to the axial direction of the central portion of the titanium alloy billet defined by the substantially cylindrical AMS4981 is used as a reference. The central portion is most likely to cause internal defects. This is because the colony that is the source of ultrasonic noise during the ultrasonic flaw detection test is likely to remain, so that it is the most difficult part to inspect the internal defect.
尚、全組織中に占める、一次α相の面積率と、アスペクト比が２．０以下の一次α相の面積率を条件としたが、本発明のＡＭＳ４９８１で規定されるチタン合金ビレットの面積率の分母である組織には、この一次α相と二次α相のほか、β相が存在する。 It should be noted that the area ratio of the primary α phase and the area ratio of the primary α phase having an aspect ratio of 2.0 or less occupying the entire structure were used as conditions. The area ratio of the titanium alloy billet defined by AMS4981 of the present invention. In addition to the primary α phase and the secondary α phase, the β phase is present in the tissue that is the denominator.
本発明者らは、直径がφ１５０ｍｍ以上で略円柱状のＡＭＳ４９８１で規定されるチタン合金ビレットの中心部の軸方向に平行な任意の断面の総面積が４０万μｍ２以上である領域において、全組織中に占める、一次α相の面積率が２０％以上、且つ、アスペクト比が２．０以下の一次α相の面積率を１２％以上とした上で、更に、存在する一次α相の平均アスペクト比の上限を規定することで、より優れた超音波探傷試験における欠陥検出能力のチタン合金ビレットを得ることができることも確認した。 In the region where the total area of an arbitrary cross section parallel to the axial direction of the central part of the titanium alloy billet defined by AMS4981 having a diameter of φ150 mm or more and a substantially cylindrical shape is 400,000 μm 2 or more, The primary alpha phase area ratio in the structure is 20% or more and the primary alpha phase area ratio is 12% or more with an aspect ratio of 2.0 or less. It was also confirmed that by defining the upper limit of the aspect ratio, it is possible to obtain a titanium alloy billet having a better defect detection ability in an ultrasonic flaw detection test.
その一次α相の平均アスペクト比の上限は３．０である。一次α相の平均アスペクト比の上限を３．０とすることで、より優れた超音波探傷試験における欠陥検出能力のチタン合金ビレットを得ることができる。また、その平均アスペクト比の上限は、より好ましくは２．５、更に好ましくは２．０である。 The upper limit of the average aspect ratio of the primary α phase is 3.0. By setting the upper limit of the average aspect ratio of the primary α phase to 3.0, it is possible to obtain a titanium alloy billet having a better defect detection ability in an ultrasonic flaw detection test. Moreover, the upper limit of the average aspect ratio is more preferably 2.5, and still more preferably 2.0.
次に、本発明のチタン合金ビレットの製造条件について説明する。 Next, manufacturing conditions for the titanium alloy billet of the present invention will be described.
通常、ＡＭＳ４９８１で規定されるチタン合金ビレットは、β鍛造→α−β鍛造→β熱処理→α−β鍛造の各工程を経て製造されるが、原材料の化学組成や工程の順序並びに工程毎の諸条件という複数の条件によって、製造されるチタン合金ビレットの物性や組織状態は変化するので、一連の製造工程として総合的に条件を選択して決定すべきであって、必ずしも工程の順序や工程毎の条件を厳密に規定することは適切ではない。 Usually, the titanium alloy billet specified by AMS4981 is manufactured through each process of β forging → α-β forging → β heat treatment → α-β forging. Since the physical properties and structural state of the titanium alloy billet to be manufactured change depending on a plurality of conditions called conditions, the conditions should be selected and determined comprehensively as a series of manufacturing processes. It is not appropriate to strictly define the conditions.
そのような前提条件をもとに、本発明者らは本発明のチタン合金ビレットの製造条件を検討した。通常ＡＭＳ４９８１で規定されるチタン合金ビレットを製造するには、α−β域での鍛造の総鍛錬比を、３５００００÷Ｒ２（Ｒはビレット直径で、その単位はｍｍ）という数式から得られる数値未満程度とするか、鍛造時の歪速度を、１０−２ｓ−１以上程度とすることで製造されているが、本発明の要件を満たす超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットを製造するためには、１）α−β域での鍛造の総鍛錬比を通常程度（３５００００÷Ｒ２という数式から得られる数値未満程度）として、歪速度を１０−２ｓ−１未満とする。或いは、２）鍛造時の歪速度については通常程度（１０−２ｓ−１以上程度）として、α−β域での鍛造の総鍛錬比を３５００００÷Ｒ２という数式から得られる数値以上とすること、のいずれかを採用すれば良いことを確認した。更には、これに併せて、最終のα−β域での鍛造回数を３回以上とすることが必要であることを確認した。 Based on such preconditions, the present inventors examined the production conditions of the titanium alloy billet of the present invention. In order to manufacture a titanium alloy billet normally defined by AMS4981, the total forging ratio of forging in the α-β region is 350,000 ÷ R 2 (where R is the billet diameter and the unit is mm). Titanium alloy having excellent defect detection ability in an ultrasonic flaw detection test that is manufactured by setting the strain rate to less than or less than 10 −2 s −1 at the forging strain rate. In order to produce a billet, 1) The total forging ratio of forging in the α-β region is set to a normal level (less than the value obtained from the formula of 350,000 ÷ R 2 ), and the strain rate is less than 10 −2 s −1. And Alternatively, 2) The strain rate during forging is set to a normal level (about 10 −2 s −1 or higher), and the total forging ratio of forging in the α-β range is set to a value obtained from a mathematical formula of 350,000 ÷ R 2. It was confirmed that either one of them could be adopted. In addition to this, it was confirmed that the number of forgings in the final α-β region needs to be 3 or more.
更には、これに併せて、最終鍛造後に、９２０℃以下のα−β温度域で熱処理を加えても良い。また、β熱処理後の冷却中に鍛造を加えても良い。また、更には、α−β鍛造における鍛造前の均熱保持時間を通常よりも長時間としても良い。これらの条件を適切に組み合わせることで、本発明の要件を満たし、更に超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットを製造することができる。 In addition to this, heat treatment may be applied in the α-β temperature range of 920 ° C. or lower after final forging. Further, forging may be added during cooling after β heat treatment. Furthermore, the soaking time before forging in α-β forging may be longer than usual. By appropriately combining these conditions, it is possible to produce a titanium alloy billet that satisfies the requirements of the present invention and further has an excellent defect detection capability in an ultrasonic flaw detection test.
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、本発明の趣旨に適合し得る範囲で適宜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。 Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, but may be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention. These are all included in the technical scope of the present invention.
本実施例の試験では、まず、φ８４０ｍｍのＴｉ−６Ａｌ−２Ｓｎ−４Ｚｒ−６Ｍｏ鋳塊をβ鍛造し、その後、α−β鍛造→β熱処理→α−β鍛造という工程を経て、直径がφ２０５ｍｍで略円柱状の、ＡＭＳ４９８１で規定されるチタン合金ビレットの一例であるＴｉ−６Ａｌ−２Ｓｎ−４Ｚｒ−６Ｍｏ合金ビレットを製造した。一部のＴｉ−６Ａｌ−２Ｓｎ−４Ｚｒ−６Ｍｏ合金ビレットには、最終α−β鍛造後に熱処理を加えた。α−β域での鍛造の総鍛錬比、最終のα−β域での鍛造回数、最終α−β鍛造後の熱処理温度（鍛造温度）と処理時間（鍛造時間）、並びに歪速度を表１に示す。 In the test of this example, a Ti-6Al-2Sn-4Zr-6Mo ingot having a diameter of 840 mm is first forged and then subjected to a process of α-β forging → β heat treatment → α-β forging, and the diameter is φ205 mm. A substantially cylindrical Ti-6Al-2Sn-4Zr-6Mo alloy billet, which is an example of a titanium alloy billet defined by AMS4981, was manufactured. Some Ti-6Al-2Sn-4Zr-6Mo alloy billets were heat treated after the final α-β forging. Table 1 shows the total forging ratio of forging in the α-β region, the number of forgings in the final α-β region, the heat treatment temperature (forging temperature) and processing time (forging time) after the final α-β forging, and the strain rate. Shown in
また、表１からα−β域での鍛造の総鍛錬比を、３５００００÷Ｒ２（Ｒはビレット直径で、その単位はｍｍ）という数式から得られる数値以上とすることで、本発明の要件を満たす超音波探傷試験における欠陥検出能力に優れたチタン合金ビレットを確実に製造することができることが分かる。 In addition, the total forging ratio of forging in the α-β range from Table 1 is set to be equal to or greater than a numerical value obtained from a mathematical formula of 350,000 ÷ R 2 (R is a billet diameter, and its unit is mm). It can be seen that a titanium alloy billet excellent in defect detection capability in an ultrasonic flaw detection test that satisfies the above can be reliably manufactured.
試験では、図１に示すＴｉ−６Ａｌ−２Ｓｎ−４Ｚｒ−６Ｍｏ合金ビレット１の中心部の軸方向に平行な任意の断面において、任意の１０箇所から切断することによって、組織観察用サンプルを採取した。その任意の１０箇所の断面の総面積は４３７５００μｍ２である。その断面を仕上げ研磨並びにエッチングすることにより観察面に仕上げ、光学顕微鏡にて４００倍の倍率で組織観察した。４００倍の倍率で観察した理由は、４００倍が、広範囲の微細組織の観察ができる最適の倍率であるからである。 In the test, samples for tissue observation were collected by cutting from arbitrary 10 locations in an arbitrary cross section parallel to the axial direction of the central portion of the center portion of the Ti-6Al-2Sn-4Zr-6Mo alloy billet 1 shown in FIG. . The total area of the cross-sections at the arbitrary 10 points is 437500 μm 2 . The cross section was finished, polished and etched to finish the observation surface, and the structure was observed with an optical microscope at a magnification of 400 times. The reason for observing at a magnification of 400 times is that 400 times is the optimum magnification at which a wide range of fine structures can be observed.
その観察結果の写真の一例を図２に示す。写真には、略球形の一次α相と、針状の二次α相が確認できる。β相は、α相の境界部の黒色部である。 An example of a photograph of the observation result is shown in FIG. The photograph shows a substantially spherical primary α phase and a needle-like secondary α phase. The β phase is a black portion at the boundary of the α phase.
それら１０箇所の組織観察用サンプルの断面写真を適宜拡大、印刷し、ＯＨＰシートにアスペクト比が２．０以下の一次α相のみをトレースした。トレースしたＯＨＰシートをスキャナによりパソコンに取り込み、画像解析ソフトＩｍａｇｅ−Ｐｒｏ ＰＬＵＳを用いて各視野の、一次α相の面積率、アスペクト比が２．０以下の一次α相の面積率、一次α相の平均アスペクト比を夫々求めた。得られた結果を表１に示す。 The cross-sectional photographs of the 10 tissue observation samples were appropriately enlarged and printed, and only the primary α phase having an aspect ratio of 2.0 or less was traced on the OHP sheet. The traced OHP sheet is taken into a personal computer by a scanner, and the primary alpha phase area ratio and primary alpha phase area ratio of the primary alpha phase and aspect ratio of 2.0 or less for each visual field using image analysis software Image-Pro PLUS. The average aspect ratio was obtained. The obtained results are shown in Table 1.
本発明の要件を満たすチタン合金ビレットが超音波探傷試験における欠陥検出能力に優れることは、ＳＮ比（底面エコー高さ÷ノイズ高さ）を測定することで確認した。その測定方法には水侵法を採用した。まず、図１に示すＴｉ−６Ａｌ−２Ｓｎ−４Ｚｒ−６Ｍｏ合金ビレット１の中心部の軸方向の任意の１０箇所から、□３０ｍｍの立方体形状のサンプルを切断することにより採取し、表面を６Ｓ仕上げした後に、図３に示す試験装置で、超音波探傷試験（Ｃスコープ法）を実施した。尚、超音波探傷試験における超音波入射方向は、図１に示す２方向とした。 It was confirmed by measuring the SN ratio (bottom echo height ÷ noise height) that the titanium alloy billet satisfying the requirements of the present invention was excellent in defect detection capability in the ultrasonic flaw detection test. The water immersion method was adopted as the measurement method. First, a 30 mm cubic sample was taken from any 10 axial locations in the center of the Ti-6Al-2Sn-4Zr-6Mo alloy billet 1 shown in FIG. 1, and the surface was finished with 6S. Then, an ultrasonic flaw detection test (C scope method) was carried out with the test apparatus shown in FIG. The ultrasonic incident directions in the ultrasonic flaw detection test were two directions shown in FIG.
この試験で、立方体形状のサンプルのＳＮ比を測定算出し、全１０サンプルから得られた合計２０面（＝２面×１０サンプル）のＳＮ比のうち、その最小値をサンプルのＳＮ比とした。更に、従来の製造ビレット（現行材）と試験で求めたサンプルのＳＮ比から換算ＳＮ比（＝サンプルのＳＮ比÷現行材のＳＮ比）を算出し、この換算ＳＮ比をＳＮ比の評価値とした。この試験では換算ＳＮ比が１．２５以上であれば合格とする。得られた結果を表１に示す。 In this test, the SN ratio of the cube-shaped sample was measured and calculated, and among the SN ratios of a total of 20 planes (= 2 planes × 10 samples) obtained from all 10 samples, the minimum value was taken as the SN ratio of the samples. . Furthermore, the converted SN ratio (= sample SN ratio ÷ current material SN ratio) is calculated from the SN ratio of the conventional manufacturing billet (current material) and the sample obtained in the test, and this converted SN ratio is an evaluation value of the SN ratio. It was. In this test, if the converted S / N ratio is 1.25 or more, the test is accepted. The obtained results are shown in Table 1.
また、超音波透過能としてＢ１エコー高さを測定した。まず、図１に示すＴｉ−６Ａｌ−２Ｓｎ−４Ｚｒ−６Ｍｏ合金ビレット１の中心部の軸方向の任意の１０箇所から、□３０ｍｍの立方体形状のサンプルを切断することにより採取し、表面を６Ｓ仕上げした後に、図３に示す試験装置で、超音波探傷試験（Ａスコープ法）によりサンプルの中心部を測定した。その際、まず、現行材（比較例５）のサンプル底面からのエコー高さ（Ｂ１エコー高さ）の平均値が８０％になるよう調整し、その後、他のサンプルの測定も実施した。超音波透過能は、Ｂ１エコー高さが７５％以上であれば合格とする。得られた結果を表１に示す。 Further, the B1 echo height was measured as the ultrasonic transmission ability. First, a 30 mm cubic sample was taken from any 10 axial locations in the center of the Ti-6Al-2Sn-4Zr-6Mo alloy billet 1 shown in FIG. 1, and the surface was finished with 6S. Then, the central part of the sample was measured by an ultrasonic flaw detection test (A scope method) with the test apparatus shown in FIG. At that time, first, the average value of the echo height (B1 echo height) from the sample bottom surface of the current material (Comparative Example 5) was adjusted to 80%, and then the measurement of other samples was also performed. The ultrasonic transmission ability is accepted if the B1 echo height is 75% or more. The obtained results are shown in Table 1.
Ｎｏ．１〜８は、ＡＭＳ４９８１で規定されるチタン合金ビレットの中心部の軸方向に平行な任意の断面の総面積が４０万μｍ２以上である領域において、全組織中に占める、一次α相の面積率が２０％以上であると共に、アスペクト比が２．０以下の一次α相の面積率が１２％以上である。また、一次α相の平均アスペクト比は３．０以下である。 No. 1 to 8 are areas of the primary α phase occupied in the entire structure in a region where the total area of an arbitrary cross section parallel to the axial direction of the center portion of the titanium alloy billet defined by AMS4981 is 400,000 μm 2 or more. The ratio is 20% or more, and the area ratio of the primary α phase having an aspect ratio of 2.0 or less is 12% or more. The average aspect ratio of the primary α phase is 3.0 or less.
これらＮｏ．１〜８は、前記した超音波探傷試験で得られた評価値（換算ＳＮ比）は、１．３〜１．８であり、一次α相の面積率と、アスペクト比が２．０以下の一次α相の面積率を、本発明で規定した値とすることで、現行材（Ｎｏ．１２）よりも超音波探傷試験における欠陥検出能力が優れるものとすることができ、更には、換算ＳＮ比を合格判定基準の１．２５以上とすることができることを確認した。また、超音波透過能（Ｂ１エコー高さ）は、７８〜８０％であり、合格判定基準の７５％を上回り、現行材（Ｎｏ．１２）と同等のＢ１エコー高さを確保することができたといえる。 These No. 1 to 8 , the evaluation values (converted SN ratio) obtained in the above-described ultrasonic flaw detection test are 1.3 to 1.8, and the area ratio of the primary α phase and the aspect ratio are 2.0 or less. By setting the area ratio of the primary α phase to the value specified in the present invention, the defect detection capability in the ultrasonic flaw detection test can be made superior to that of the current material (No. 12). It was confirmed that the ratio could be 1.25 or more of the acceptance criterion. Moreover, the ultrasonic transmission power (B1 echo height) is 78-80%, exceeds 75% of the acceptance criteria, and can ensure the B1 echo height equivalent to the current material (No. 12). It can be said that.
一方、Ｎｏ．１０は、最終α−β鍛造後の熱処理（焼鈍）温度が９３０℃と高すぎたため、一次α相の面積率が１７％と低くなってしまった事例である。その結果、超音波透過能（Ｂ１エコー高さ）が６９％と低くなってしまった。 On the other hand, no. No. 10 is an example in which the heat treatment (annealing) temperature after the final α-β forging was too high at 930 ° C., and the area ratio of the primary α phase was as low as 17%. As a result, the ultrasonic transmission ability (B1 echo height) was as low as 69%.
また、Ｎｏ．１１は、最終α−β鍛造後の熱処理（焼鈍）を実施しなかったため、アスペクト比が２．０以下の一次α相の面積率が１１％と低くなってしまった事例である。その結果、超音波探傷試験で得られた評価値（換算ＳＮ比）が１．２０で現行材（Ｎｏ．１２）よりは高かったものの、合格判定基準の１．２５より低かった。 No. No. 11 is an example in which the heat treatment (annealing) after the final α-β forging was not performed, and thus the area ratio of the primary α phase having an aspect ratio of 2.0 or less was as low as 11%. As a result, the evaluation value (converted S / N ratio) obtained in the ultrasonic flaw detection test was 1.20, which was higher than the current material (No. 12), but was lower than the acceptance criterion 1.25.
以上の結果は、一次α相、二次α相、及び、β相からなる合金組織を有するチタン合金ビレットであって、直径がφ１５０ｍｍ以上で円柱状のＡＭＳ４９８１で規定されるチタン合金ビレットの中心部の軸方向に平行な任意の断面の総面積が４０万μｍ２以上である領域において、全組織中に占める、一次α相の面積率を２０％以上とすると共に、アスペクト比が２．０以下の一次α相の面積率を１２％以上とすることで、超音波探傷試験における欠陥検出能力が優れたチタン合金ビレットが得られることを示している。 The above result is a titanium alloy billet having an alloy structure composed of a primary α phase, a secondary α phase, and a β phase, and the center portion of the titanium alloy billet having a diameter of φ150 mm or more and defined by a cylindrical AMS4981 In the region where the total area of any cross-section parallel to the axial direction is 400,000 μm 2 or more, the area ratio of the primary α phase in the entire structure is 20% or more and the aspect ratio is 2.0 or less. It is shown that a titanium alloy billet having excellent defect detection capability in an ultrasonic flaw detection test can be obtained by setting the area ratio of the primary α phase to 12% or more.
１…Ｔｉ−６Ａｌ−２Ｓｎ−４Ｚｒ−６Ｍｏ合金ビレット
２…軸方向の縦断面
1 ... Ti-6Al-2Sn-4Zr-6Mo alloy billet 2 ... Axial longitudinal section
Claims (2)
直径がφ１５０ｍｍ以上で円柱状のＡＭＳ４９８１で規定されるチタン合金ビレットの中心軸を中心とした直径の１／４の内部範囲の軸方向に平行な任意の断面の総面積が４０万μｍ２以上である領域において、全組織中に占める、一次α相の面積率が２０％以上であると共に、アスペクト比が２．０以下の一次α相の面積率が１２％以上であることを特徴とする超音波探傷試験における欠陥検出能力に優れたチタン合金ビレット。 A titanium alloy billet having an alloy structure consisting of a primary α phase, a secondary α phase, and a β phase,
The total area of any cross section parallel to the axial direction of the inner range of ¼ of the diameter centered on the central axis of the titanium alloy billet defined by the cylindrical AMS4981 with a diameter of φ150 mm or more is 400,000 μm 2 or more In one region, the area ratio of the primary α phase in the entire structure is 20% or more, and the area ratio of the primary α phase having an aspect ratio of 2.0 or less is 12% or more. Titanium alloy billet with excellent defect detection capability in ultrasonic testing.
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