JPH03170651A - Method for refining structure of beta ti alloy - Google Patents

Abstract

PURPOSE:To remarkably refine recrystallized grain size and to prevent the occurrence of surface roughness at the time of cold working by subjecting a beta Ti alloy in the state of martensitic structure to cold plastic working and then to recrystallization. CONSTITUTION:Light-degree working is applied to a hot rolled plate of beta Ti alloy having a composition consisting of, by weight, 18% V, 4% Sn, and the balance Ti to form a martensitic structure, and the hot rolled plate is cold- rolled at 5-50% draft and further annealed at 800 deg.C to undergo recrystallization. By this method, Ti alloy parts having extremely fine recrystallized grain size as small as <=50mum and free from the occurrence of surface roughness at the time of subsequent secondary working can be produced.

Description

【発明の詳細な説明】 ［産業上の利用分野］ 本発明は冷間加工の可能なβ型Ｔｉ合金を対象とし、冷
間加工時に肌荒れを起こさない程度に再結晶組織を微細
化する方法の改良に関するものである。[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a cold-workable β-type Ti alloy, and describes a method for refining the recrystallized structure to the extent that roughness does not occur during cold working. It is about improvement.

［従来の技術］ β型Ｔｉ合金は、α型Ｔｉ合金と違って冷間加工が可能
であり、しかも加工後の熱処理によって高強度を得るこ
とができるところから、航空機分野の各種機材をはじめ
、船舶や自動車の部品材料としても需要は次第に増大し
てきている．しかしβ型Ｔｉ合金といえども鉄鋼、ＡＩ
やＣｕ等の金属材に比べると冷間加工性は非常に悪く、
冷間加工により肌荒れを起こし易い．そこで肌荒れを軽
減する為の手段として再結晶組織の微細化が検討され、
現在ではβ型Ｔｉ合金にβ単相状態で十分な冷間加工を
加えた後再結晶させる方法が有効であることが確認され
、一部では実用化が進められている．この方法で微細化
を図るには、少なくとも４０％程度以上の圧下率（この
値は使用するβ型Ｔｉ合金の初期粒径によって異なり、
初期粒径が大きいものほどこの値は小さくなる．初期粒
径が８０μｍ程度のものでは４０％以上が必要となる）
で冷間加工を行なう必要があり、初期粒径よりも十分微
細な再結晶粒を得るには、通常６５〜８０％程度の冷間
加工が必要とされる．しかしながら実操業においては十
分な冷間加工が行なえないことも多く、またβ型Ｔｉ合
金は加工率を高めるにつれて伸びが極端に低下し冷間加
工性が悪化するという事情もあって、より少ない加工量
で結晶粒の微細化を達成し得る様な技術の開発が望まれ
る． ［発明が解決しようとする課題］ 本発明は上記の様な事情に着目して成されたものであっ
て、その目的は、従来法よりも小さな冷間加工量で結晶
粒を十分に微細なものとすることができ、それにより肌
荒れのない美麗な冷間加工製品を与えるＴｉ合金の製造
技術を確立しようとするものである。[Prior Art] Unlike α-type Ti alloys, β-type Ti alloys can be cold-worked, and high strength can be obtained by heat treatment after processing, so they are used in various equipment in the aircraft field, etc. The demand for it as a component material for ships and automobiles is gradually increasing. However, even though it is a β-type Ti alloy, steel, AI
Cold workability is very poor compared to metal materials such as or Cu.
Cold processing tends to cause skin roughness. Therefore, refinement of the recrystallized structure was considered as a means to reduce rough skin.
Currently, it has been confirmed that the method of recrystallizing β-type Ti alloys after sufficient cold working in the β-single phase state is effective, and is being put into practical use in some cases. In order to achieve refinement using this method, a reduction rate of at least 40% or higher (this value varies depending on the initial grain size of the β-type Ti alloy used;
The larger the initial particle size, the smaller this value becomes. If the initial particle size is around 80μm, 40% or more is required)
In order to obtain recrystallized grains that are sufficiently finer than the initial grain size, cold working of approximately 65 to 80% is usually required. However, in actual operations, sufficient cold working is often not possible, and as the working rate of β-type Ti alloys increases, the elongation decreases extremely and cold workability worsens. It is desired to develop a technology that can achieve grain refinement by increasing the amount of grains. [Problems to be Solved by the Invention] The present invention has been made with attention to the above-mentioned circumstances, and its purpose is to make crystal grains sufficiently fine with a smaller amount of cold working than conventional methods. The objective is to establish a manufacturing technology for Ti alloys that can produce beautiful cold-worked products without rough skin.

［課題を解決するための手段］ 上記課題を解決することのできた本発明に係る組織微細
化法の構成は、β型Ｔｉ合金に対しマルテンサイト組織
状態の下に冷間で塑性加工を施した後再結晶させるとこ
ろに要旨を有するものである。[Means for Solving the Problems] The structure of the structure refining method according to the present invention that can solve the above problems is that a β-type Ti alloy is subjected to cold plastic working under a martensitic structure state. The gist of this is that it is then recrystallized.

［作用］ β型Ｔｉ合金の多くは、すべり変形によって塑性変形す
るのが支配的であるとされている。この場合のすべり変
形は粒界近傍で優先的に生じ、この部分に格子欠陥が集
中してその後の再結晶サイトとなるところから、該サイ
トが局所的に存在することとなり、この状態で再結晶熱
処理を行なつても再結晶粒を十分に小さなものとするこ
とができない。従って再結晶組織を微細化するには初期
結晶の粒界のみならず粒内にも不均一変形を起こさせて
再結晶サイトを密に導入することが必要であり、その為
の手段として、従来例では前述の如くβ単相状態のＴｉ
合金に冷間加工を施し、格子欠陥を密に与えることによ
って再結晶サイトを増大していたのである。しかし再結
晶サイトを満足のいく程度まで増大するには、前述の如
く冷間加工時の圧下量を相当高くしなければならないと
いう問題があった． ところが本発明者らが再結晶粒を微細化すべく種々研究
を進めるうちβ型Ｔｉ合金を一旦マルテンサイト組織状
態とし、その後玲間加工してから再結晶させると、従来
の半分以下の冷間加工量で再結晶粒を著しく微細化し得
ることが確認された．これは、β型Ｔｉ合金をマルテン
サイト組織状態とすると粒界はもとより粒内にもマルテ
ンサイト晶の結晶界面が多数存在することとなり、塑性
変形時に粒界はもとより粒内でも不均一変形が起こって
再結晶サイトとなり、同等の加工量であっても従来例に
比べて再結晶サイトが密に導入されるものと考えられる
。[Function] Most β-type Ti alloys are said to undergo plastic deformation predominantly through sliding deformation. In this case, slip deformation occurs preferentially near the grain boundaries, and lattice defects concentrate in these areas and become recrystallization sites, so these sites exist locally, and in this state recrystallization occurs. Even if heat treatment is performed, recrystallized grains cannot be made sufficiently small. Therefore, in order to refine the recrystallized structure, it is necessary to introduce recrystallization sites densely by causing non-uniform deformation not only at the grain boundaries of the initial crystal but also within the grains. In the example, as mentioned above, Ti is in the β single phase state.
The number of recrystallization sites was increased by subjecting the alloy to cold working to create dense lattice defects. However, in order to increase the number of recrystallization sites to a satisfactory degree, there was a problem in that, as mentioned above, the reduction amount during cold working had to be considerably increased. However, as the present inventors conducted various studies to refine the recrystallized grains, they discovered that once the β-type Ti alloy was brought into a martensitic structure state, and then subjected to cold working and then recrystallized, the cold working was less than half of the conventional method. It was confirmed that the recrystallized grains could be significantly refined by increasing the amount. This is because when a β-type Ti alloy has a martensitic structure, there are many crystal interfaces of martensitic crystals not only at the grain boundaries but also within the grains, and non-uniform deformation occurs not only at the grain boundaries but also within the grains during plastic deformation. It is thought that even with the same amount of processing, recrystallization sites are introduced more densely than in the conventional example.

本発明で使用されるβ型Ｔｉ合金は、室温でマルテンサ
イト組織となり得るものであればその種類は一切問われ
ない。The type of β-type Ti alloy used in the present invention is not particularly limited as long as it can form a martensitic structure at room temperature.

またこれらのβ型Ｔｉ合金をマルテンサイト組織状態と
する手段も特に制限されないが、一般的手法としては、
合金組成を調整することによってマルテンサイト変態点
を室温付近のものとし、これをβ単相域より室温まで急
冷した後サブゼロ処理に付し、或は軽加工を加えてマル
テンサイト組織状態とする方法等が例示される． ［実施例］ Ｔｉ−１８Ｖ−４Ｓｎ合金（合金■）およびＴｉ−１　
５Ｖ−３Ｃｒ−３Ｓｎ−３Ａ１合金（合金■）を夫々溶
製し、熱間加工により厚さ５ＩＩＩ１の熱延板■．■を
製造した．得られた各供試板■．■はいずれもβ阜相で
あるが、前者■は盟性加工により加工誘起マルテンサイ
ト変態を示し、後者は■はすべり変形を示すことを確認
した後、両者に対し第１表に示す如く所定の冷間加工（
圧延）を加え、次いで８００℃の焼鈍に付して再結晶せ
しめ、完全に再結晶した時点での粒径を切片法によって
測定し、冷間加工量と再結晶粒径の関係を調べた。尚、
供試材の初期粒径はいずれも約８０μｍであった． 結果を第１表に示す． 第 １ 表 第１表からも明らかである様に、β単相でも加工誘起マ
ルテンサイト変態を起こさずすべり変形のみを生じるＴ
ｉ合金■と加工誘起マルテンサイト変態を生じるＴｉ合
金■を比較した場合、前者ではすべり変形により格子欠
陥が粗に与えられ再結晶サイトが結晶粒界のすべり部に
しか導入されないため、再結晶粒径を十分に小さくする
には加工量をかなり大きくしなければならないのＣ対し
、後者では冷間加工の初期にマルテンサイト変態状態と
なるため、加工によって与えられる欠陥が粒界のみなら
ずマルテンサイト晶の界面にも生じて再結晶サイトが著
しく増大するため、加工量を少なめに抑えた場合でも再
結晶粒径は格段に小さくなっている．そして初期粒径８
０μｍに対したとえば約５０μｍの再結晶粒径を得よう
とした場合、比較例では玲間加工量を５０％にまで高め
なければならない（実験Ｎｏ．７）のに対し、本発明で
あればその１７１　０以下の冷間加工量（５％：実験Ｎ
ｏ．１）で済むことが分かる。Furthermore, there are no particular restrictions on the means for making these β-type Ti alloys into a martensitic structure, but as a general method,
A method of adjusting the alloy composition to bring the martensitic transformation point to around room temperature, rapidly cooling it from the β single phase region to room temperature, and then subjecting it to sub-zero treatment or adding light processing to create a martensitic structure state. Examples include: [Example] Ti-18V-4Sn alloy (alloy ■) and Ti-1
5V-3Cr-3Sn-3A1 alloy (alloy ■) was melted and hot-worked to form a hot-rolled sheet with a thickness of 5III1. ■ was manufactured. Each sample board obtained ■. Both ■ are in the β-phase, but after confirming that the former ■ shows deformation-induced martensitic transformation due to interlocking processing, and the latter ■ shows slip deformation, the predetermined conditions for both were determined as shown in Table 1. cold working (
Rolling), followed by annealing at 800°C to recrystallize, and the grain size at the time of complete recrystallization was measured by the intercept method to examine the relationship between the amount of cold work and the recrystallized grain size. still,
The initial particle size of all sample materials was approximately 80 μm. The results are shown in Table 1. Table 1 As is clear from Table 1, even with a single β phase T
When comparing the i alloy ■ and the Ti alloy ■ that undergoes deformation-induced martensitic transformation, the former has coarse lattice defects due to slip deformation and recrystallization sites are introduced only in the slip areas of the grain boundaries, so the recrystallization grains In order to make the diameter sufficiently small, the amount of processing must be considerably large. However, in the latter case, martensitic transformation occurs in the early stage of cold working, so defects caused by processing occur not only at grain boundaries but also at martensite. Since the recrystallization sites also occur at the crystal interfaces and the number of recrystallization sites increases significantly, the recrystallization grain size becomes significantly smaller even when the amount of processing is kept small. and initial particle size 8
For example, when trying to obtain a recrystallized grain size of approximately 50 μm compared to 0 μm, in the comparative example, the amount of machining must be increased to 50% (Experiment No. 7), whereas in the present invention, the 171 Amount of cold working less than 0 (5%: Experiment N
o. It turns out that 1) is sufficient.

［発明の効果］ 本発明は以上の様に構戒されており、β型Ｔｉ合金に対
しβ単相状態で加工してすべり変形により再結晶サイト
を導入するのではなく、マルテンサイト組織状態で塑性
加工して再結晶サイトを導入することによって、再結晶
サイトを全体に亘って密に導入することができ、従って
これを再結晶熱処理することにより再結晶粒径を著しく
微細なものとすることができる．殊に本発明によれば、
従来例に比べて非常に少ない加工量で再結晶サイトを多
数導入することができ、低加工量でもその後の２次加工
で肌荒れを起こすことのない微細な組織のＴｉ合金を容
易に得ることができる。[Effects of the Invention] The present invention is designed as described above, and instead of processing a β-type Ti alloy in a β single phase state and introducing recrystallization sites through sliding deformation, it is processed in a martensitic structure state. By introducing recrystallization sites through plastic working, it is possible to introduce recrystallization sites densely throughout the material, and by subjecting this to recrystallization heat treatment, the recrystallization grain size can be made extremely fine. Can be done. In particular, according to the invention:
It is possible to introduce a large number of recrystallization sites with a very small amount of processing compared to conventional methods, and even with a small amount of processing, it is possible to easily obtain a Ti alloy with a fine structure that does not cause roughness during subsequent secondary processing. can.

Claims (1)

【特許請求の範囲】[Claims] 　β型Ｔｉ合金に対しマルテンサイト組織状態の下に冷
間で塑性加工を施した後再結晶させることを特徴とする
β型Ｔｉ合金の組織微細化方法。A method for refining the structure of a β-type Ti alloy, which comprises subjecting the β-type Ti alloy to cold plastic working in a martensitic state and then recrystallizing it.