JP5072725B2 - 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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Description
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 having excellent 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、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 a lower defect detection capability in ultrasonic flaw detection tests than other metal materials, and it is difficult to detect defects smaller than φ0.8 mm in large titanium alloy billets with a diameter of φ150 mm or more. there were.
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.
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、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 even in the case of a large billet having a diameter of φ150 mm or more, as in the case of other metal products, generally used ultrasonic flaw detection It is an object of the present invention to provide a titanium alloy billet that is capable of inspecting finer internal defects than conventional methods and that can be mass-produced and has excellent defect detection capabilities in ultrasonic flaw detection tests. It is.
請求項１記載の発明は、直径がφ１５０ｍｍ以上で略円柱状のＡＭＳ４９２８で規定され且つチタン合金の組織が一次α相、二次α相及びβ相からな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、アスペクト比が２．０以下の一次α相の面積率が、１０％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 according to claim 1 is the axial direction of the central portion of a titanium alloy billet having a diameter of φ150 mm or more and defined by a substantially cylindrical AMS4928 and having a titanium alloy structure composed of a primary α phase, a secondary α phase, and a β phase. In a region where the total area of arbitrary parallel cross-sections is 400,000 μm 2 or more, the area ratio of the primary α phase in the entire structure is 10% or more with an aspect ratio of 2.0 or less. It is a titanium alloy billet with excellent defect detection capability in the ultrasonic flaw detection test.
請求項２記載の発明は、前記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、存在する一次α相の平均アスペクト比が２．０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。 According to a second aspect of the present invention, the average aspect ratio of the primary α-phase present in the region where the total area of an arbitrary cross section parallel to the axial direction of the central portion of the titanium alloy billet is 400,000 μm 2 or more is 2. The titanium alloy billet having an excellent defect detection capability in the ultrasonic flaw detection test according to claim 1, wherein the titanium alloy billet is 0 or less.
請求項３記載の発明は、前記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、存在する一次α相の面積率と平均粒径の関係が、１．０≦一次α相の面積率÷一次α相の平均粒径≦８．０という要件を満たすことを特徴とする請求項１または請求項２に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 3 is characterized in that the area ratio of the primary α phase and the average particle diameter are present in a region where the total area of an arbitrary cross section parallel to the axial direction of the central portion of the titanium alloy billet is 400,000 μm 2 or more. 3 satisfies the requirement that 1.0 ≦ area ratio of primary α phase ÷ average particle diameter of primary α phase ≦ 8.0 in the ultrasonic flaw detection test according to claim 1 or 2. Titanium alloy billet with excellent defect detection capability.
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、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、しかも、量産することが可能である。 According to the titanium alloy billet excellent in defect detection capability in the ultrasonic flaw detection test of the present invention, even a large billet having a diameter of φ150 mm or more is inspected for internal defects by a generally used ultrasonic flaw detection method. Can be carried out without problems, and mass production is possible.
本発明者らは、種々のチタン合金ビレットを製造し、実験により調査することで、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の組織状態ならびにその製造方法を解明するために鋭意研究を進めた。 The inventors of the present invention have made various studies to elucidate the structure of the titanium alloy billet and its manufacturing method by producing various titanium alloy billets and investigating them by experiments, which have excellent defect detection capabilities in ultrasonic testing. Advanced.
その結果、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、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, by promoting the degree of equiaxing of the primary α phase and reducing the aspect ratio of the primary α phase, the colony (the acicular α phase in the same orientation) that is the source of ultrasonic noise during the ultrasonic flaw detection test It was confirmed that a titanium alloy billet having a defect detection capability in an ultrasonic flaw detection test exceeding that of a conventional titanium alloy billet can be obtained.
更には、一次α相の面積率と平均粒径を制御することで、変形によりビレットに導入される亀裂の進展経路が直線状になりにくくすることができ、従来からのチタン合金ビレットを超える破壊靱性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。 Furthermore, by controlling the area ratio and average particle size of the primary α phase, the crack propagation path introduced into the billet due to deformation can be made less likely to be linear, and the fracture exceeds conventional titanium alloy billets. It was confirmed that a titanium alloy billet having toughness could 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ＡＭＳ４９２８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、アスペクト比が２．０以下の一次α相の面積率が、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。アスペクト比が２．０以下の一次α相の面積率の下限は、１０％以上であれば効果を得ることができる。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 determined that the total area of an arbitrary cross section parallel to the axial direction of the center portion of the titanium alloy billet defined by AMS4928 having a diameter of φ150 mm or more and a substantially cylindrical shape is 400,000 μm 2. In the above region, it was confirmed that the defect detection capability in the ultrasonic flaw detection test was improved as the area ratio of the primary α-phase occupying the whole structure increased to 2.0 or less. An effect can be obtained if the lower limit of the area ratio of the primary α phase having an aspect ratio of 2.0 or less is 10% or more. The lower limit of the area ratio is more preferably 20%, still more preferably 30%.
尚、ＡＭＳ４９２８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とＶを含有し、その含有量は、Ａｌ：５．５〜６．７５質量％、Ｖ：３．５〜４．５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Ｃ：０．１質量％、Ｆｅ：０．３質量％、Ｈ：０．０１２５質量％、Ｎ：０．０５質量％、Ｏ：０．２質量％を含有する。 In addition, the component composition of the titanium alloy billet specified by AMS4928 contains Al and V as main additive elements, and the contents thereof are Al: 5.5 to 6.75 mass%, V: 3.5 to 4.5% by mass, the balance being Ti and inevitable impurities. Inevitable impurities include approximately C: 0.1% by mass, Fe: 0.3% by mass, H: 0.0125% by mass, N: 0.05% by mass, and O: 0.2% by mass.
ここで、略円柱状のＡＭＳ４９２８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 AMS4928 is set to φ150 mm or more because the size is small if the diameter is less than φ150 mm. 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ＡＭＳ４９２８で規定されるチタン合金ビレットの中心部とは、ビレットの中心軸を中心とした直径の１／４の内部範囲のことを示す。こ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。 Further, the center part of the titanium alloy billet defined by the substantially cylindrical AMS4928 indicates an inner range of ¼ of the diameter centering on the billet central axis. Based on the structure in the cross section parallel to the axial direction of the central part, the central part is most likely to cause internal defects, and becomes a source of ultrasonic noise during the ultrasonic flaw detection test after the billet is manufactured. This is because the colony tends to remain and is the most difficult part to inspect the internal defect.
尚、全組織中に占める、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ＡＭＳ４９２８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。 In addition, although the area ratio of the primary α phase with an aspect ratio of 2.0 or less occupying in the entire structure was used as a condition, the structure that is the denominator of the area ratio of the titanium alloy billet defined by AMS4928 of the present invention includes: In addition to the primary α phase and secondary α phase, there is a β phase.
本発明者らは、直径がφ１５０ｍｍ以上で略円柱状のＡＭＳ４９２８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、アスペクト比が２．０以下の一次α相の面積率を１０％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 center part of the titanium alloy billet defined by AMS4928 having a diameter of φ150 mm or more and a substantially cylindrical shape is not less than 400,000 μm 2 , More excellent by prescribing the upper limit of the average aspect ratio of the existing primary α phase after setting the area ratio of the primary α phase in the structure to an aspect ratio of 2.0 or less of the primary α phase to 10% or more It was also confirmed that a titanium alloy billet having a defect detection ability in an ultrasonic flaw detection test can be obtained.
その一次α相の平均アスペクト比の上限は２．０である。一次α相の平均アスペクト比の上限を２．０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１．８、更に好ましくは１．６である。 The upper limit of the average aspect ratio of the primary α phase is 2.0. By setting the upper limit of the average aspect ratio of the primary α phase to 2.0, it is possible to obtain a titanium alloy billet having a superior defect detection capability in an ultrasonic flaw detection test. Further, the upper limit of the average aspect ratio is more preferably 1.8, and still more preferably 1.6.
更には、直径がφ１５０ｍｍ以上で略円柱状のＡＭＳ４９２８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、アスペクト比が２．０以下の一次α相の面積率を１０％以上とした上で、存在する一次α相の面積率と平均粒径の関係を規定することで、優れた超音波探傷試験における欠陥検出能力を有すると共に、優れた破壊靱性をも有する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。 Furthermore, in a region where the total area of an arbitrary cross section parallel to the axial direction of the central portion of the titanium alloy billet defined by AMS4928 having a diameter of φ150 mm or more and substantially cylindrical shape is 400,000 μm 2 or more, Excellent ultrasonic flaw detection by defining the relationship between the area ratio of the primary α phase existing and the average particle size after setting the area ratio of the primary α phase to 10% or more. It was also confirmed that a titanium alloy billet having a defect detecting ability in the test and having an excellent fracture toughness can be obtained.
一次α相の面積率÷一次α相の平均粒径が大きくなりすぎると、変形によりビレットに導入される亀裂の進展経路が直線状になりやすく、そのため、ビレットの破壊靱性が低くなりすぎ、ビレットに最低限必要な破壊靱性を得ることができない。一方、一次α相の面積率÷一次α相の平均粒径が小さくなりすぎると、超音波ノイズが大きくなり、超音波探傷試験における欠陥検出能力が低下し始める。一次α相の面積率÷一次α相の平均粒径の上限は８．０、より好ましくは６．０である。一方、その下限は１．０、より好ましくは１．５である。 If the average particle size of the primary α phase ÷ the average particle size of the primary α phase becomes too large, the crack propagation path introduced into the billet due to deformation tends to be straight, and therefore the fracture toughness of the billet becomes too low, and the billet In other words, the fracture toughness required at the minimum cannot be obtained. On the other hand, if the area ratio of the primary α phase ÷ the average particle size of the primary α phase becomes too small, the ultrasonic noise increases and the defect detection ability in the ultrasonic flaw detection test starts to decrease. The area ratio of the primary α phase ÷ the upper limit of the average particle size of the primary α phase is 8.0, more preferably 6.0. On the other hand, the lower limit is 1.0, more preferably 1.5.
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、ＡＭＳ４９２８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 AMS4928 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、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ＡＭＳ４９２８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。 Based on such preconditions, the inventors examined the production conditions of the titanium alloy billet of the present invention. In order to produce a titanium alloy billet normally defined by AMS4928, the total forging ratio of forging in the α-β range 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.
尚、請求項３記載の要件を満足するチタン合金ビレットを製造する場合には、上記２）の条件、すなわち、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方法を採用する必要がある。この条件を採用することで、請求項３の要件を満足する、破壊靱性にも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。α−β域での鍛造の総鍛錬比は、３５００００÷Ｒ２＋１．００以上とすることがより好ましく、３５００００÷Ｒ２＋２．００以上とすることが更に好ましい。 In the case of producing a titanium alloy billet that satisfies the requirements described in claim 3, the condition of 2) above, that is, the strain rate at the time of forging is set to a normal level (about 10 −2 s −1 or more), It is necessary to adopt a method in which the total forging ratio of forging in the α-β region is not less than the value obtained from the mathematical formula of 350,000 ÷ R 2 . By adopting this condition, a titanium alloy billet satisfying the requirements of claim 3 and excellent in fracture toughness can be reliably produced. Total forging ratio forged in alpha-beta range, more preferably to 350000 ÷ R 2 +1.00 or more, more preferably it is 350000 ÷ R 2 +2.00 or more.
また、鍛造後に、α−β温度域での熱処理を１回以上実施することが好ましい。更には、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。 Moreover, it is preferable to perform the heat treatment in the α-β temperature range at least once after 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−４Ｖ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およびφ３０５ｍｍで略円柱状の、ＡＭＳ４９２８で規定されるチタン合金ビレットの一例であるＴｉ−６Ａｌ−４Ｖ合金ビレットを製造した。一部のＴｉ−６Ａｌ−４Ｖ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α−β鍛造後の熱処理温度（鍛造温度）と処理時間（鍛造時間）、ならびに歪速度を表１に示す。 In the test of this example, first, a φ840 mm Ti-6Al-4V ingot is β-forged, and then subjected to a process of α-β forging → β heat treatment → α-β forging, and the diameters are approximately 205 mm and φ305 mm. A columnar Ti-6Al-4V alloy billet, which is an example of a titanium alloy billet defined by AMS4928, was manufactured. Some Ti-6Al-4V 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 heat treatment temperature (forging temperature) and processing time (forging time) after the final α-β forging, and the strain rate.
以下の試験結果で具体的に示すが、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。 As specifically shown in the following test results, from Table 1, the total forging ratio of forging in the α-β region is equal to or greater than the numerical value obtained from the mathematical formula of 350,000 ÷ R 2 (R is the billet diameter, the unit is mm). Thus, it can be seen that a titanium alloy billet excellent in defect detection capability in an ultrasonic flaw detection test that satisfies the requirements of the present invention can be reliably produced.
試験では、図１に示すＴｉ−６Ａｌ−４Ｖ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, a sample for tissue observation was collected by cutting from 10 arbitrary positions in an arbitrary cross section parallel to the axial direction of the central portion of the Ti-6Al-4V 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、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、一次α相の平均粒径を夫々求めた。尚、一次α相の平均粒径は円相当径を採用した。一次α相の面積率÷一次α相の平均粒径については、以上の得られた結果から計算して求めた。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 area ratio of the primary α phase, the average aspect ratio of the primary α phase, the primary α phase of each field of view using the image analysis software Image-Pro PLUS The average particle size of the phase was determined for each. In addition, the equivalent circle diameter was employ | adopted for the average particle diameter of the primary alpha phase. The area ratio of the primary α phase ÷ the average particle size of the primary α phase was calculated from the obtained results. 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−４Ｖ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。なお、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 sample of a cubic shape of 30 mm is cut by cutting from 10 arbitrary positions in the axial direction of the center portion of the Ti-6Al-4V alloy billet 1 shown in FIG. An ultrasonic flaw detection test (C scope method) was performed using 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。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. The obtained results are shown in Table 1.
また、請求項３記載の要件を満たすチタン合金ビレットが破壊靱性に優れることは、破壊靱性試験により確認した。破壊靱性試験はＪＩＳ−Ｒ１６０７で制定される方法により実施し、破壊靱性値を求めた。得られた結果を表１に示す。 Moreover, it was confirmed by a fracture toughness test that a titanium alloy billet satisfying the requirements of claim 3 is excellent in fracture toughness. The fracture toughness test was carried out by the method established by JIS-R1607, and the fracture toughness value was determined. The obtained results are shown in Table 1.
発明例１〜５，８〜１０は全て、ＡＭＳ４９２８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、アスペクト比が２．０以下の一次α相の面積率が、１０％以上である。その中でも、発明例２，３，５，８は、その面積率がより好ましいとした２０％以上、発明例４は、その面積率が更に好ましいとした３０％以上である。 Inventive Examples 1-5, 8-10 are all in the entire structure in the region where the total area of any cross section parallel to the axial direction of the center part of the titanium alloy billet defined by AMS4928 is 400,000 μm 2 or more. The area ratio of the primary α phase that occupies an aspect ratio of 2.0 or less is 10% or more. Among them, Invention Examples 2, 3, 5 and 8 are 20% or more that the area ratio is more preferable, and Invention Example 4 is 30% or more that the area ratio is more preferable.
前記した超音波探傷試験で得られた評価値は、発明例の中で、全組織中に占める、アスペクト比が２．０以下の一次α相の面積率が、最も低い１３％の発明例９でも１．１０であり、その面積率を、本発明で規定した値とすることで、現行材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ることを確認した。また、その面積率が２０％台の発明例２，４，５，８では、評価値は１．８０〜２．５０、更には、その面積率が３０％以上の発明例４では、評価値は２．３０〜３．１０であり、全組織中に占める、アスペクト比が２．０以下の一次α相の面積率が、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がこの試験結果から確認できた。 The evaluation value obtained by the ultrasonic flaw detection test described above is an invention example 9 in which the area ratio of the primary α phase having an aspect ratio of 2.0 or less in the entire tissue is the lowest 13% among the invention examples. However, it was 1.10, and it was confirmed that by setting the area ratio 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. Further, in the invention examples of the area ratio of 20 percent 2, 4, 5, 8, the evaluation value is 1.80 to 2.50, furthermore, in the invention example 4 the area ratio is 30% or more, evaluation The value is 2.30 to 3.10, and the defect detection capability in the ultrasonic flaw detection test is improved as the area ratio of the primary α-phase occupying the whole tissue and the aspect ratio is 2.0 or less increases. This was confirmed from the test results.
また、一次α相の平均アスペクト比が２．０を超える発明例９と発明例１０では、評価値は１．１０と１．１５であり、請求項２記載の要件を満たす他の発明例より低いことが分かる。すなわち、請求項２記載の要件を満たすことで、超音波探傷試験における欠陥検出能力が更に向上することがこの試験結果から確認できた。 Further, in Invention Example 9 and Invention Example 10 in which the average aspect ratio of the primary α phase exceeds 2.0, the evaluation values are 1.10 and 1.15, compared with other invention examples that satisfy the requirements of claim 2 It turns out that it is low. That is, it can be confirmed from the test results that the defect detection capability in the ultrasonic flaw detection test is further improved by satisfying the requirements of claim 2.
更には、前記した破壊靱性試験で得られた破壊靱性値は、請求項記載の要件を満たす発明例１〜５，８〜１０のすべてにおいて、ビレットに必要な最低限の破壊靱性値である４０ＭＰａ・ｍ１／２を超えることが試験結果から確認できた。 Furthermore, the fracture toughness value obtained by the above-described fracture toughness test is 40 MPa, which is the minimum fracture toughness value required for billets in all of the inventive examples 1 to 5 and 8 to 10 that satisfy the requirements of the claims. -It was confirmed from the test results that it exceeded m1 / 2 .
また、発明例１１はビレット径が、他の発明例とは異なりφ３０５ｍｍであるが、請求項１で規定した要件、更には請求項３で規定した要件を具備しており、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、かつ、ビレットに必要な最低限の破壊靱性値を超えることを確認した。 Inventive Example 11 has a billet diameter of 305 mm, unlike the other Inventive Examples, but has the requirements specified in claim 1 and further the requirements specified in claim 3, and an ultrasonic flaw detection test. It was confirmed that the defect detection capability in the case can be excellent and exceeds the minimum fracture toughness value required for the billet.
また、発明例１３は、全組織中に占める、アスペクト比が２．０以下の一次α相の面積率は９６％であり、超音波探傷試験で得られた評価値は６．５０である。従って、超音波探傷試験における欠陥検出能力は優れている。しかしながら、請求項３記載の要件は満足していないため、破壊靱性値は３０ＭＰａ・ｍ１／２であり、ビレットに必要な最低限の破壊靱性は有しないことが試験結果から確認できた。 In Invention Example 13, the area ratio of the primary α phase having an aspect ratio of 2.0 or less in all tissues was 96%, and the evaluation value obtained in the ultrasonic flaw detection test was 6.50. Therefore, the defect detection capability in the ultrasonic flaw detection test is excellent. However, since the requirement of claim 3 is not satisfied, the fracture toughness value is 30 MPa · m 1/2 , and it was confirmed from the test results that the billet does not have the minimum fracture toughness necessary for the billet.
一方、現行材相当の比較例１４と、比較例１５は、全組織中に占める、アスペクト比が２．０以下の一次α相の面積率が、夫々９％と０％であり、超音波探傷試験で得られた評価値は、夫々１．００と０．５５であった。その面積率が、本発明で規定した下限値未満のビレットでは、超音波探傷試験における欠陥検出能力は優れるものとすることができないことを確認した。 On the other hand, in Comparative Example 14 and Comparative Example 15 corresponding to the current material, the area ratio of the primary α-phase occupying the entire structure is 9% and 0%, respectively, with an aspect ratio of 2.0 or less. The evaluation values obtained in the test were 1.00 and 0.55, respectively. It was confirmed that the billet whose area ratio is less than the lower limit defined in the present invention cannot be excellent in the defect detection ability in the ultrasonic flaw detection test.
一部重複して説明するが、発明例１〜５，８は、Ｔｉ−６Ａｌ−４Ｖ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、存在する一次α相の平均アスペクト比が、請求項２の記載を満足する２．０以下である。その中でも、発明例２，５，８は、その平均アスペクト比がより好ましいとした１．８以下、発明例３，４は、その平均アスペクト比が更に好ましいとした１．６以下である。 Although partially redundantly described, Invention Examples 1 to 5 and 8 are in a region where the total area of an arbitrary cross section parallel to the axial direction of the center portion of the Ti-6Al-4V alloy billet is 400,000 μm 2 or more. The average aspect ratio of the existing primary α phase is 2.0 or less that satisfies the description of claim 2. Among them, Invention Examples 2, 5, and 8 have a mean aspect ratio of 1.8 or less, and Invention Examples 3 and 4 have a mean aspect ratio of 1.6 or less.
これら発明例１〜５，８は、全組織中に占める、アスペクト比が２．０以下の一次α相の面積率が夫々異なるため、一概には判断することができないが、Ｔｉ−６Ａｌ−４Ｖ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、存在する一次α相の平均アスペクト比が小さくなるほど、超音波探傷試験における欠陥検出能力が向上する傾向があることが試験結果から確認できた。 Since these invention examples 1 to 5 and 8 have different aspect ratios of the primary α phase with an aspect ratio of 2.0 or less in the entire structure, they cannot be generally determined, but Ti-6Al-4V In a region where the total area of an arbitrary cross section parallel to the axial direction of the center portion of the alloy billet is 400,000 μm 2 or more, the smaller the average aspect ratio of the primary α phase existing, the more the defect detection capability in the ultrasonic flaw detection test is. It was confirmed from the test results that there was a tendency to improve.
また、発明例１〜５，８〜１０は、Ｔｉ−６Ａｌ−４Ｖ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、存在する一次α相の面積率と平均粒径の関係が、１．０≦一次α相の面積率÷一次α相の平均粒径≦８．０という要件も満たしており、この要件を満たすことにより、超音波探傷試験における欠陥検出能力に加え、破壊靱性が向上することが試験結果から確認できた。 Further, Invention Example 1～5,8～10 is, Ti-6Al-4V in the region the total area of any cross-section parallel to the axial direction of the center portion is 400,000 [mu] m 2 or more alloy billet One existing primary α The relationship between the area ratio of the phase and the average particle diameter also satisfies the requirement that 1.0 ≦ area ratio of the primary α phase ÷ average particle diameter of the primary α phase ≦ 8.0. From the test results, it was confirmed that the fracture toughness was improved in addition to the defect detection ability in the flaw detection test.
１…Ｔｉ−６Ａｌ−４Ｖ合金ビレット
２…軸方向の縦断面
1 ... Ti-6Al-4V alloy billet 2 ... Axial longitudinal section
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