JPS63105954A - Hot-working method for near beta-type titanium alloy - Google Patents

Abstract

PURPOSE:To manufacture a Near beta-type Ti alloy combining high strength with high toughness and having superior quality, by applying hot working under specific conditions in the course of cooling a Ti alloy from a beta-single phase region. CONSTITUTION:In the course of cooling an ingot of Near beta-type Ti alloy (Ti-5 Al-2Sn-2Zr-4Mo-4Cr) of relatively low alpha-phase content from a beta-single phase region, hot working of about 20% draft is applied in an arbitrary temp. range between the initial and finishing temps. of alpha-phase precipitation to form two- phase structure of alpha+beta, followed further by hot working of about 30%. Successively, the about alloy is subjected to heat treatment such as solution heat treatment, ageing treatment, etc., so that Near beta-type Ti alloy combining high strength with high toughness can be manufactured without causing cutoff- direction dependency to mechanical properties, particularly to fracture toughness.

Description

【発明の詳細な説明】 ［産業上の利用分野コ 本発明は機械的性質特に破！１１靭性に切出し方向依存
性を生じることなく、高強度かつ高靭性を得ることので
きるＮ　ｅａｒβ型チタン合金の熱間加工方法に関する
ものである。[Detailed Description of the Invention] [Industrial Fields of Application] The present invention is applicable to mechanical properties, especially mechanical properties. The present invention relates to a method for hot working a near β type titanium alloy that can obtain high strength and high toughness without causing dependence of toughness on cutting direction.

［従来の技術］ 従来のチタン合金の熱間加工方法においては、均一な等
軸組織を得るために、β単相領域より焼入れしたものを
α＋β温度領域で熱間加工を行っていた。この加工方法
は、Ｔｉ−６ＡＩ−４Ｖ合金等に代表される比較的α相
の多いα＋β合金においては有効であるが、α相の比較
的少ないＮ　ｅａｒβ型合金においては、加熱時β粒界
に沿って析出したα相が加工後にも連続的に残存し、そ
の後の熱処理においても連続性が維持され等軸組織が得
られない（第３図参照）。[Prior Art] In a conventional method for hot working titanium alloys, in order to obtain a uniform equiaxed structure, a material that has been quenched from the β single phase region is hot worked in the α+β temperature range. This processing method is effective for α+β alloys that have a relatively large amount of α phase, such as the Ti-6AI-4V alloy, but in near β type alloys that have a relatively small amount of α phase, it is difficult to process the β grain boundaries during heating. The α phase precipitated along the surface remains continuously even after processing, and the continuity is maintained even in the subsequent heat treatment, so that an equiaxed structure is not obtained (see Fig. 3).

［発明が解決しようとする問題点］ このため機械的性質に切出し方向依存性が生じ、破壊靭
性の切出方向依存性には顕著な影響を及ぼす。たとえば
一方向の鍛造を行ったときに鍛伸方向に沿ってα相が連
続的に存在すると鍛伸方向への亀裂が容易に進展し、鍛
伸方向の高靭性が得られない。[Problems to be Solved by the Invention] For this reason, mechanical properties become dependent on the cutting direction, which has a significant effect on the dependence of fracture toughness on the cutting direction. For example, when forging is performed in one direction, if α phase exists continuously along the forging direction, cracks in the forging direction will easily propagate, making it impossible to obtain high toughness in the forging direction.

そこで本発明においては、従来の加工方法では消失させ
ることのできなかったα相の連続性を阻止することによ
って等軸性を与え、機械的な性質特に破壊靭性に切出し
方向依存性を生じることなく、高強度かつ高靭性を得る
ことのできるＮ　ｅａｒβ型チタン合金の熱間加工方法
の提供を目的としている。Therefore, in the present invention, by preventing the continuity of the α phase, which could not be eliminated by conventional processing methods, equiaxed property is imparted, and mechanical properties, especially fracture toughness, do not depend on the cutting direction. The object of the present invention is to provide a method for hot working a near β type titanium alloy that can obtain high strength and high toughness.

［問題点を解決するための手段］ 上記問題点を解決することのできた本発明とはチタン合
金をβ単相領域より冷却していく過程中でα相の析出が
開始されてからｄ相の析出が完了するまでの間の任意の
段階で熱間加工を加え、α＋β２相領域が形成された後
、更に熱間加工することを構成要旨とするものである。[Means for Solving the Problems] The present invention has solved the above problems. During the process of cooling the titanium alloy from the β single phase region, the precipitation of the α phase begins and then the d phase begins to precipitate. The gist of the structure is to apply hot working at any stage until the precipitation is completed, and to further hot work after the α+β two phase region is formed.

［作用コ 熱間加工を与えないという条件によって準安定的にβ単
相を保持せしめたチタン合金をα＋β２相温度領域で加
熱保持すると、α相は優先的にβ粒界に析出し、粒界析
出したα相はβ粒界に沿って連続性を示す。この状態に
対し等軸組織を得るべく加工を加えるのが従来の技術で
あるが、β粒界に連続的に析出したα相の連続性はこの
加工によっても容易に消失させることはできない。[Effect] When a titanium alloy in which a single β phase is maintained quasi-stablely under the condition of no hot working is heated and held in the α + β two phase temperature range, the α phase preferentially precipitates at the β grain boundaries, and the α phase precipitates at the β grain boundaries. The precipitated α phase shows continuity along the β grain boundaries. The conventional technique is to process this state to obtain an equiaxed structure, but the continuity of the α phase that is continuously precipitated at the β grain boundaries cannot be easily eliminated even by this process.

ところが、本発明の場合はチタン合金をβ単相領域より
α相の析出が完了するまでの冷却過程で熱間加工してお
り、このときβ粒内に一時的に剪断歪が導入される結果
、α相の多くはその歪部分（旧β粒内）に優先的に析出
してくる。このためβ粒界でのα相の連続的析出が阻止
され、強固な連続的α相は形成されなくなる。この場合
の熱間加工量は特に規定しないが２０％程度でも十分な
効果が得られる。However, in the case of the present invention, the titanium alloy is hot worked in the cooling process from the β single phase region until the precipitation of the α phase is completed, and at this time, shear strain is temporarily introduced into the β grains. , most of the α phase preferentially precipitates in the strained areas (inside the former β grains). Therefore, continuous precipitation of the α phase at the β grain boundaries is prevented, and a strong continuous α phase is no longer formed. Although the amount of hot working in this case is not particularly specified, a sufficient effect can be obtained even with about 20%.

しかし、この加工のみでは初析α相は板状もしくは針状
であり、通常行うその後の溶体化および時効処理におい
てもその形状は維持されるのみならず、この初析α相が
β粒界に集中し、再び連続性が形成されることがある。However, with this processing alone, the pro-eutectoid α phase remains plate-like or acicular, and this shape is not only maintained even in the subsequent solution treatment and aging treatment that are normally performed, but also the pro-eutectoid α phase forms at the β grain boundaries. Concentration may occur and continuity may be formed again.

このため初析のα相をさらに等軸化するための熱間加工
が必要となる。これがα＋β２相領域が形成された後の
熱間加工である。このα＋β２相領域での熱間加工によ
り、安定した等軸組織のＮ　ｅａｒβ型のチタン合金が
得られる。この熱間加工温度はα＋β２相領域であれば
基本的には問題はなしくが、変態点直下では初析α相量
が少ないので組織不均一化をもたらすので好ましくない
、またより低温側は、チタン合金の加工変形能の不足か
ら自ずと規制される。したがってα＋β２相領域での熱
間加工は変態点より１５〜１１５℃低い温度で行うのが
好ましい、この場合の加工量は製品形状とのかねあいで
決まる部分も多いが約３０％以上であることが望ましい
、また等軸化をさらに促進するという観点から最初の熱
間加工が終った後、α＋β２相領域での熱間加工を行な
うまでにα＋β２相領域での溶体化処理を施すことも有
効である。Therefore, hot working is required to further make the pro-eutectoid α phase equiaxed. This is hot working after the α+β two phase region is formed. By hot working in this α+β two phase region, a near β type titanium alloy with a stable equiaxed structure is obtained. There is basically no problem with this hot working temperature if it is in the α + β two phase region, but just below the transformation point, the amount of pro-eutectoid α phase is small, resulting in a non-uniform structure, which is undesirable. This is naturally regulated due to the lack of processing deformability of the alloy. Therefore, hot working in the α+β two phase region is preferably performed at a temperature 15 to 115°C lower than the transformation point.The amount of processing in this case is often determined by the balance with the product shape, but it is recommended that it be approximately 30% or more. From the viewpoint of further promoting equiaxed formation, it is desirable and effective to perform solution treatment in the α+β two-phase region after the initial hot working and before hot working in the α+β two-phase region. .

本発明におけるチタン合金の加工方法は前述の如く、最
初の熱間加工によって旧β粒内にα相を均一に分散析出
させ、得られたα＋β２相領域に対する熱間加工によっ
てα相をさらに等軸化させチタン合金の等軸組織を安定
化させるというものであるが、この加工方法はチタン合
金の組成によってなんら影響を受けるものではない。も
っともα＋β２相領域からの溶体化処理によりβ相が別
の相に変態するようなチタン合金に対しては、他の要因
が組織形態に影響を及ぼすため適用はむずかしい、この
ため、本発明は後の溶体化処理および時効処理によって
も約４５％以内のα相と残部が主としてβ相よりなるチ
タン合金、すなわち比較的α相の少ないＮ　ｅａｒβ型
チタン合金への適用に限定される。As described above, the method for processing titanium alloys in the present invention involves first hot working to uniformly disperse and precipitate the α phase within the prior β grains, and then hot working the resulting α+β two-phase region to further convert the α phase to equiaxed This processing method is not influenced in any way by the composition of the titanium alloy. However, it is difficult to apply the present invention to titanium alloys in which the β phase transforms into another phase by solution treatment from the α + β two phase region because other factors affect the structure morphology. Even after solution treatment and aging treatment, the application is limited to titanium alloys consisting of approximately 45% α phase and the remainder mainly β phase, that is, near β type titanium alloys with relatively little α phase.

［実施例および比較例］ 実施例Ｉ Ｎ　ｅａｒβ型合金であるＴｉ−５ＡＩＴｉ−５ＡＩ−
２Ｓｎ−２Ｚｒ−４（変態点：８６５℃）の９０Ｘ９０
Ｘ１００　（ａｒｍ）のブロックを８７０℃より約７５
０℃までの冷却過程において２０％加工し、８３０℃に
て３０％再加工した。その後、８００℃で４時間の溶体
化処理と６２０℃で８時間の時効処理を行った時の組織
状態を第２図に示す。[Examples and Comparative Examples] Example I N ear β type alloy Ti-5AITi-5AI-
90X90 of 2Sn-2Zr-4 (transformation point: 865°C)
X100 (arm) block from 870℃ to about 75℃
20% was processed during the cooling process to 0°C, and 30% was reprocessed at 830°C. Thereafter, the structure was subjected to solution treatment at 800° C. for 4 hours and aging treatment at 620° C. for 8 hours, and the state of the structure is shown in FIG.

比較例１ 前記実施例１と同素材および同形状のブロックを８３０
℃にて８０％加工した後、８００℃で４時間の溶体化処
理と６２０℃で８時間の時効処理を行った。得られた合
金の組織状態を第３図に示す。Comparative Example 1 830 blocks of the same material and the same shape as in Example 1 were used.
After 80% processing at 800°C, solution treatment was performed at 800°C for 4 hours and aging treatment at 620°C for 8 hours. The structure of the obtained alloy is shown in FIG.

第２図及び第３図より明らかなように実施例１のもので
は、比較例１のもののようにβ粒界に沿った連続的なα
相が存在せず、α相が均一に点在した状態の等軸組織と
なっている。As is clear from FIGS. 2 and 3, in Example 1, continuous α along the β grain boundary as in Comparative Example 1.
It has an equiaxed structure in which no phase exists and the α phase is uniformly scattered.

この実施例１および比較例１によって熱間加工された試
料における破壊靭性の切出方向依存性を評価するため 第１図にに！ｃ（Ｌ）：亀裂が鍛伸方向に進む場合の破
壊靭性値 ｘｔｃ（Ｔ）：亀裂が鍛伸方向と直交する方向に進む場
合の破壊靭性 値 Ｋｘｃ　（Ｌ）　／　Ｋ’＋ｃ　（Ｔ）値の値をそれぞ
れ示す、実施例１のＫｘｃ（Ｌ）は比較例１に比べて大
きく向上しており、Ｋ＋ｃ（Ｌ）／Ｋｘｃ（Ｔ）の値も
比較例１ではＯ６，７であるのに対し、実施例１では０
．９以上と大きく改善されている。尚破壊靭性試験はＡ
ＳＴＭＥ３９９に従って行った。In order to evaluate the dependence of the fracture toughness on the cutting direction in the hot-worked samples according to Example 1 and Comparative Example 1, Figure 1 is shown. c(L): Fracture toughness value when the crack progresses in the forging and elongation direction xtc (T): Fracture toughness value when the crack progresses in a direction perpendicular to the forging and elongation direction The Kxc(L) of Example 1, which shows the values of , is greatly improved compared to Comparative Example 1, and the value of K+c(L)/Kxc(T) is also O6, 7 in Comparative Example 1. On the other hand, in Example 1, 0
．． 9 or higher, which is a big improvement. The fracture toughness test was A.
It was carried out according to STME399.

実施例２ Ｎ　ｅａｒβ型合金であるＴｉ−１０Ｖ−２Ｆｅ　−３
Ａ１　（変態点二８００℃）の９０Ｘ９０Ｘ９０（ｍｍ
）のブロックを８２０℃から約７３０℃までの冷却過程
において２０％加工し、７６０℃にて３０％再加工した
。その後、７４０℃で１時間の溶体化処理と５１０℃で
８時間の時効処理を行った時の組織状態を第４図に示す
。Example 2 N ear β type alloy Ti-10V-2Fe-3
A1 (transformation point 2800℃) 90X90X90 (mm
) was processed by 20% during the cooling process from 820°C to about 730°C, and reprocessed by 30% at 760°C. Thereafter, the structure was subjected to solution treatment at 740° C. for 1 hour and aging treatment at 510° C. for 8 hours, and the state of the structure is shown in FIG.

比較例２ 前記実施例２と同素材および同形状のブロックを従来法
に従い８５０℃のβ単相領域より焼入れし、７６０℃に
て８０％加工した後、７４０℃で１時間の溶体化処理と
５１０℃で８時間の時効処理を行った。得られた合金組
織状態を第５図に示す。Comparative Example 2 A block of the same material and shape as in Example 2 was quenched from the β single phase region at 850°C according to the conventional method, processed to 80% at 760°C, and then subjected to solution treatment at 740°C for 1 hour. Aging treatment was performed at 510°C for 8 hours. The obtained alloy structure is shown in FIG.

第４図及び第５図より明らかなように比較例２のもので
はα相の連続性が見られるが実施例２のものでは全体的
に等軸組織となっており、本方法の有効性が示される。As is clear from Figures 4 and 5, continuity of the α phase is observed in Comparative Example 2, but the overall equiaxed structure is observed in Example 2, which indicates the effectiveness of this method. shown.

［発明の効果］ 以上のよう−に本発明方法によって得られるＮ　ｅａｒ
β型チタン合金は、α相の析出がβ粒界に沿った連続的
なものとならず等軸組織を形成するので、機械的性質特
に破壊靭性に切出し方向依存性を生じることなく、高強
度かつ高靭性のものとなる。[Effect of the invention] As described above, the near-ear obtained by the method of the present invention
In β-type titanium alloys, the precipitation of the α phase is not continuous along the β grain boundaries and forms an equiaxed structure, so the mechanical properties, especially the fracture toughness, do not depend on the cutting direction and have high strength. It also has high toughness.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は本発明方法による実施例および従来方法による
比較例における「亀裂が鍛伸方向に進む場合の破壊靭性
値ＫＩＣ（Ｌ）、亀裂が鍛伸方向に直交する方向に進む
場合の破壊靭性値ＫＩＣ（Ｔ）およびに＋ｃ（Ｌ）／に
！ｃ（Ｔ）値」を示す図であり、第２．４図は実施例、
第３．５図は比較例の金属組織を示す電子顕微鏡写真で
ある。 第１図 例　　　　　　例 すぐ＝コ 匈ｖ＋ｔマ（ｘ）Figure 1 shows the "fracture toughness value KIC (L) when the crack propagates in the forging direction, and the fracture toughness value KIC (L) when the crack propagates in the direction orthogonal to the forging direction, in an example according to the method of the present invention and a comparative example according to the conventional method. FIG. 2.4 is a diagram showing the value KIC(T) and +c(L)/to!c(T) value, and FIG. 2.4 is an example.
Figure 3.5 is an electron micrograph showing the metal structure of a comparative example. Figure 1 Example Example immediately = ko匈v+tma(x)

Claims (1)

【特許請求の範囲】[Claims] チタン合金をβ単相領域より冷却していく過程中でのα
相の析出が開始されてからｄ相の析出が完了するまでの
間の任意の階段で熱間加工を加え、α＋β２相領域が形
成された後、更に熱間加工することを特徴とするＮｅａ
ｒβ型チタン合金の熱間加工方法。α during the process of cooling the titanium alloy from the β single phase region
Nea is characterized in that hot working is applied at any step between the start of phase precipitation and the completion of d-phase precipitation, and further hot working is carried out after the α+β two phase region is formed.
Hot working method for rβ type titanium alloy.