JP2004068146A - beta TYPE TITANIUM ALLOY AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a β type titanium alloy which has excellent cold workability, high strength after aging and excellent characteristic stability, and to provide a production method which is suitable for the production of the alloy. <P>SOLUTION: The titanium alloy comprises, by mass, 15 to 25% V, 2.5 to 5% Al, 0.5 to 4% Sn and ≤0.20% O (oxygen), and, as impurities, ≤0.03% H, ≤0.40% Fe, ≤0.05% C and ≤0.02% N. In the production process of the alloy, it is first pickled with an aqueous solution essentially consisting of 3 to 40% HF, and is next pickled with an aqueous solution comprising 3 to 6% HF and 5 to 20% HNO<SB>3</SB>. <P>COPYRIGHT: (C)2004,JPO

Description

【００６３】
【表２】

【００６４】
冷間圧延後、真空中で８５０℃にて５分間加熱して、水冷する焼鈍および溶体化処理を施し、得られた板からＪＩＳ１３号Ｂの引張試験片を採取して、引張強さを測定した。この引張強さの大小から、加工時の変形抵抗が推測できる。
【００６５】
さらに、冷間圧延にて大きな耳割れを生じなかった板を用い、４７５℃にて２０時間加熱の時効処理をおこない、時効後の板からＪＩＳ１３号Ｂの引張試験片を採取し、引張強さおよび伸びを測定した。これらの測定結果も表１および表２に併せて示す。
【００６６】
表１および表２の結果から明らかなように、試験番号１〜２４は、いずれもその主要組成がＴｉ−２０Ｖ−４Ａｌ−１Ｓｎ合金に合致するものであるが、試験番号２０〜３３の材料に比較して、試験番号１〜１９の材料は冷間加工性にすぐれ、かつ時効後の強さおよび伸びがすぐれていることがわかる。これは、従来管理されていなかったＨ、Ｆｅ、ＣおよびＮの含有量を限定することによってもたらされた効果であり、これらの元素の含有量を低く抑えることの重要性が明らかである。
【００６７】
【発明の効果】
本発明によれば、現在用いられているβ型のＴｉ−２０Ｖ−４Ａｌ−１Ｓｎ合金は、より変形抵抗が小さくかつ変形能のすぐれた合金となる。これにより、冷間圧延、および冷間伸線など冷間加工におけるロールやダイスの寿命延長、冷間鍛造時の金型寿命の延長など、高強度のチタン合金製部品の製造コスト低減に大きく寄与することができる。
【００６８】
本発明のチタン合金は、自動車の動弁部品、宇宙航空機用部品等の産業機器用のみならず、例えば、めがねフレームのような日用品、ゴルフクラブヘッド等の運動器具の材料として好適である。
【００６９】
本発明の製造方法によれば、安定した品質のチタン合金の冷間圧延材を製造することができる。
【図面の簡単な説明】
【図１】チタン合金の時効による硬さの変化に及ぼす水素含有量の影響を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a β-type titanium alloy having low deformation resistance in cold working in a solution state, excellent deformability, and high strength after aging treatment, and a method for producing the alloy.
[0002]
[Prior art]
Titanium alloys have low density and high strength, have high specific strength (strength / density) among practical metal materials, and are excellent in corrosion resistance. Therefore, titanium alloys, materials for automobile parts, materials for medical equipment and medical equipment Its use is expanding to materials, eyeglass materials, golf club materials, tableware materials and the like. Accordingly, there is a strong demand for further improvement of properties and reduction in price of titanium alloys.
[0003]
Titanium alloys are roughly classified into α (dense hexagonal: hcp) type, β (body-centered cubic: bcc) type, and α + β type from the crystal structure of the phase constituting the metal structure at normal temperature. Alloys containing a small amount of pure titanium or Al for industrial use are α-type, Ti-6Al-4V alloys, which are well known as high-strength alloys and used in aircraft, are α + β-type, and β-type is β-type more than α + β-type. An alloy with an increased content of phase stabilizing elements.
[0004]
Titanium alloys generally have poor cold workability, which increases production costs. Pure titanium, which has relatively good cold workability and low oxygen content, has insufficient strength of a molded part, and is difficult to apply to a part requiring a high specific strength. On the other hand, Ti-6Al-4V, which is the most representative titanium alloy having high strength, has high strength but extremely poor deformability at room temperature, and can be formed into a target shape only by hot working or cutting. Cost increases.
[0005]
Under such circumstances, attention has been paid to β-type titanium alloys having a body-centered cubic crystal structure. The β-type alloy is, for example, a Ti-3Al-8V-6Cr-4Mo-4Zr alloy or Ti-15V-3Cr-3Al-3Sn. These β-type alloys have a large deformability in cold working when subjected to a solution treatment to form a β single phase, and after aging, precipitating and precipitating the α phase, it is possible to increase the strength, It has the desirable properties as a component material.
[0006]
However, conventionally known β-type titanium alloys have high deformation resistance even though they have good deformability. Therefore, for example, when cold forging is performed, a die such as a die or a punch is often cracked or chipped with a small number of uses. Further, in cold rolling for manufacturing a material to be processed, roll wear is large, and in the case of cold drawing, seizure is likely to occur.
[0007]
As an invention for solving such a problem, Patent Document 1 (Japanese Patent No. 2669004) discloses that V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, and oxygen: 0. The invention of an alloy of 12% or less and a balance of Ti and impurities (hereinafter abbreviated as Ti-20V-4Al-1Sn alloy) is disclosed. This alloy has substantially the same deformability as a conventional β-type titanium alloy, but has low strength in a solution treatment state and low deformation resistance, as well as high strength after aging treatment. However, when the alloy of the present invention is produced and molded into various parts, the deformability in the β-treated state is not always stable and excellent, and the deformation resistance is unstable. In addition, there is a disadvantage that the strength after aging varies greatly.
[0008]
[Patent Document]
Japanese Patent No. 2669004
[0009]
[Problems to be solved by the invention]
A first object of the present invention is to provide a titanium alloy that is excellent in cold workability in a solutionized state and that can easily and stably realize characteristics of high strength after aging treatment. .
[0010]
A second object of the present invention is to provide a pickling method for reducing the H (hydrogen) content in producing the above titanium alloy.
[0011]
[Means for Solving the Problems]
β-type titanium alloy is a metastable β-phase alloy that rapidly cools the high-temperature β-phase of titanium and brings it to room temperature. Alloying elements for stabilizing the β phase include V, Mo, Nb, Ta, Cr, Fe, Mn, etc. Among them, hardening due to solid solution is small, and adversely affects workability. V and Mo are relatively inexpensive elements that provide high strength by aging and are relatively inexpensive. However, Mo has a disadvantage that it has a high melting point and is easily segregated, and the addition of Mo increases the hot workability and the deformation resistance of cold working. Therefore, V is selected, and Al is contained from the increase in strength during aging treatment. The Ti-20V-4Al-1Sn alloy replaces part of Al with Sn for the purpose of suppressing solid solution hardening.
[0012]
In the process of producing a large number of these alloys, it was found that there was a problem that cold workability and aging strengthening were not always obtained stably, and the present inventors conducted various studies to elucidate the cause and deal with it. Was performed. First, with respect to V, Al and Sn of the main compositions, the workability and the aging effect were investigated by changing the combination of the content ranges. However, the fluctuation of these main components had no effect on the characteristic change, except that the effect appeared somewhat near the limit of the content range.
[0013]
However, in the course of the above-mentioned investigation, the content of elements generally regarded as titanium impurities, such as O (oxygen), H, Fe, C, and N, in the β-type Ti-20V-4Al-1Sn alloy, It has become clear that the properties of the alloy, that is, the cold workability and the strength after aging, are particularly greatly affected. The content of each of these impurity elements is regulated by standards of titanium and titanium alloys such as JIS-H-4600, JIS-H-4605 or JIS-H-4607. However, the regulation is not intended for β-type Ti-20V-4Al-1Sn alloys to be improved by the present invention.
[0014]
The following is known about the action of each of the above elements.
[0015]
O is an α-phase stabilizing element. When O is contained in a large amount, it hinders β-phase single-phase formation by solution treatment, but hardens the alloy to increase the deformation resistance and lower the deformability. Since H is a β-phase stabilizing element, it delays age hardening due to α-phase precipitation and hinders strength improvement due to aging. Although Fe is a β-phase stabilizing element, a large amount is not preferable because it increases the strength of the solution-treated alloy and increases the deformation resistance. C forms precipitates of carbides, and greatly reduces both deformation resistance and deformability. N forms a solid solution of about 1% in the β phase, but causes a large decrease in ductility and lowers the deformability.
[0016]
However, in the case of β-type Ti-20V-4Al-1Sn alloy, even if an attempt is made to control impurities within the range regulated by the JIS standard, there are elements that cannot be easily reduced within the range. It has been found that there are elements whose amounts greatly affect the properties of this alloy even if it is limited to the following. This is presumably because the titanium alloy specified by the JIS standard is an α-type or α + β-type alloy, whereas Ti-20V-4Al-1Sn is a β-type alloy.
[0017]
For example, a β-type alloy is much easier to absorb hydrogen than an α-type alloy and an α + β-type alloy. In particular, in the case of a plate manufactured by cold rolling having a thickness of 5 mm or less, descaling must be performed after hot rolling in order to obtain a good surface. This descaling method includes a method of mechanically grinding the surface, but this method has a low processing speed and a low yield. Therefore, it is common to perform pickling with hydrofluoric acid or nitric hydrofluoric acid. However, in the case of a Ti-20V-4Al-1Sn alloy which has been turned into a solution by cold rolling to form β-form, hydrogen which greatly exceeds the limit amount defined by the above JIS standard is absorbed during pickling. It is difficult to sufficiently reduce the pickling conditions even if various methods are devised. In addition, since the above-mentioned alloy contains a component that increases the oxide scale, hydrogen absorption tends to increase due to prolonged pickling time.
[0018]
After processing into a desired shape, the β-type alloy can be subjected to an aging treatment to improve the strength. However, the contained hydrogen significantly inhibits age hardening, prolongs the aging treatment time, and makes it difficult to age harden to the desired strength. In addition, hydrogen lowers the ductility of the alloy, thereby deteriorating the workability, and further significantly lowers the toughness. Dehydrogenation is possible by heating at a high temperature in a vacuum, but it requires a long time treatment, and furthermore, aging occurs during this treatment, so that practical use is difficult.
[0019]
The absorption of hydrogen by pickling for descaling is inevitable in the production process of this Ti-20V-4Al-1Sn alloy plate. Therefore, while adopting the pickling method for minimizing the hydrogen absorption described below, assuming the hydrogen content after pickling still inevitably mixed in, the reduction of the aging speed due to the hydrogen and the workability and We considered that the decrease in toughness could be compensated by controlling the amount of other impurity elements, and investigated the effects of the contents of O, Fe, N, and C. As a result, it was found that a Ti-20V-4Al-1Sn alloy having stable and excellent characteristics can be obtained by regulating the content of each of these elements together with the amount of hydrogen. Based on the results of these studies, the present invention was completed by further clarifying the limit conditions. The gist of the present invention resides in the following titanium alloys (1) to (3) and the titanium alloy production methods (4) and (5).
[0020]
(1) In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.20% or less, H: 0.03% or less, Fe : 0.40% or less, C: 0.05% or less, N: 0.02% or less, the balance being Ti and impurities, β-type titanium alloy characterized by the above-mentioned.
[0021]
(2) In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.12% or less, H: 0.03% or less, Fe: : 0.15% or less, C: 0.03% or less, N: 0.02% or less, with the balance being Ti and impurities, β-type titanium alloy.
[0022]
(3) In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.12% or less, H: 0.03% or less, Fe : 0.15% or less, C: 0.03% or less, N: 0.02% or less, and among each 3% or less of Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd and Si. A β-type titanium alloy containing one or more selected elements, with the balance being Ti and impurities.
[0023]
(4) In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.20% or less, H: 0.03% or less, Fe : 0.40% or less, C: 0.05% or less, N: 0.02% or less, with the balance being a β-type titanium alloy comprising Ti and impurities, first containing 3 to 40% by mass of HF as a main component Pickling with aqueous solution, then 3-6% by weight HF and 5-20% by weight HNO ₃ A method for producing a β-type titanium alloy, comprising pickling with an aqueous solution containing
[0024]
(5) In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.20% or less, H: 0.03% or less, Fe : 0.40% or less, C: 0.05% or less, N: 0.02% or less, and among Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd and Si each less than 3%. A β-type titanium alloy containing one or more selected elements, with the balance being Ti and impurities, is first pickled with an aqueous solution mainly containing 3 to 40% by mass of HF, and then 3 to 6% by mass of HF and 5% by mass. ~ 20% by mass of HNO ₃ A method for producing a β-type titanium alloy, comprising pickling with an aqueous solution containing
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
The reasons for limiting the constituent elements of the β-type titanium alloy of the present invention are as follows. In addition, the content of each component is shown by mass%.
[0026]
V: 15 to 25%
V is an important element for stabilizing the β phase and changing the structure of the alloy to a β single phase at room temperature. When the content is less than 15%, a martensitic structure is generated during solution treatment by rapid cooling such as water cooling from a high-temperature β-phase state, and the cold workability is greatly deteriorated. If the content exceeds 25%, the age hardening property of the β-type alloy is deteriorated, the time required for the aging treatment is lengthened, and sufficient strengthening may not be obtained even after the aging treatment. In addition, the deformation resistance of the cold working of the alloy increases.
[0027]
Al: 2.5 to 5%
The β-type alloy is finally strengthened by aging treatment, in which case Al is contained in order to obtain a sufficient strength increase. In addition, there is also an effect of suppressing the precipitation of the ω phase that embrittles the alloy by the aging treatment and promoting the precipitation of the α phase. If the effect is less than 2.5%, the effect is insufficient, and if it exceeds 5%, the hardness in the β state increases, and the cold workability is reduced. Therefore, it is set to 2.5 to 5%.
[0028]
Sn: 0.5-4%
Sn has the same function as Al described above, but does not increase the hardness in the β state as much as Al. Therefore, by reducing Al and replacing it with Sn, an increase in deformation resistance can be suppressed. Such an effect of Sn becomes poor when the content is small, so the content is made 0.5% or more. On the other hand, when the Sn content increases, the hardness of the β-formed alloy also increases.
[0029]
O (oxygen): 0.20% or less
O lowers the deformability of the alloy, causes cracking when performing cold working with high strength, and increases the deformation resistance. The smaller the amount, the better, but it is set to 0.20% or less, which is a limit amount at which adverse effects are not conspicuous. It is more desirable that the content be 0.12% or less.
[0030]
H: 0.03% or less
H retards the precipitation of the α phase during the aging treatment and not only reduces the increase in strength due to aging, but also deteriorates ductility and toughness. However, in the case of a β-type Ti-20V-4Al-1Sn alloy which easily absorbs hydrogen, there is also absorption in a process other than the pickling process. Particularly in the case of a thin plate, it is essential to perform pickling and descaling. It is difficult to reduce the amount to less than 005%. Therefore, the lower limit is not particularly defined, but the upper limit is set to 0.03% as a limit at which the effect is not large. More preferably, it is 0.01% or less.
[0031]
An investigation example of the effect of the hydrogen content on age hardening is shown below.
[0032]
Alloy composition: V: 20.0%, Al: 3.2%, Sn: 1.0%, 〇: 0.11%, H: 0.015%, Fe: 0.10%, C: 0.01 %, N: 0.01%, balance: Ti and a 5 mm thick hot-rolled plate as an impurity are subjected to a solution treatment, and after a steel shot blast, the hydrogen content is changed by changing the pickling time, Aging treatment was performed at 450 ° C. The solution treatment is a treatment of heating at 850 ° C. for 5 minutes in the air and then cooling with water.
[0033]
The result of examining the change in hardness due to the aging time was as shown in FIG. The hardness Hv is a Vickers hardness at a test load of 1 kgf.
[0034]
As can be seen from FIG. 1, when the hydrogen content is 0.015% or 0.025%, the target hardness is reached by aging treatment for 12 hours, and the hardness is saturated. On the other hand, if the hydrogen content is 0.040% or 0.065% even after the treatment for 20 hours, the hardness will not be sufficient. In the case of these alloys, a long aging treatment far exceeding 20 hours is required to reach the hardness obtained with alloys having a hydrogen content of 0.015% or 0.025%. Poor sex. When the hydrogen content is 0.100%, it cannot be hardened almost as shown.
[0035]
From the above test results, it is understood that the content of H in the alloy is desirably suppressed to 0.03% or less.
[0036]
Fe: 0.40% or less
Fe stabilizes the β phase similarly to hydrogen, delays hardening by aging treatment, and further increases the deformation resistance. Since the inclusion of hydrogen is unavoidable as described above, the limit amount that does not cause a significant increase in deformation resistance is set to at most 0.40%. Note that a more desirable Fe content is 0.15% or less.
[0037]
C: 0.05% or less
C greatly reduces ductility, that is, deformability, so the smaller the better, the better. The limit amount that does not cause a significant decrease in deformability is at most 0.05%. 0.03% or less is more desirable.
[0038]
N: 0.02% or less
N greatly reduces the deformability, so the smaller the better, the better. The limit amount that does not cause a significant decrease in deformability is up to 0.02%.
[0039]
The above-described impurity elements of O, Fe, C and N are not only derived from the raw material sponge titanium, but also taken into the titanium alloy in the course of the subsequent melting and high-temperature heating of the alloy, and are not increased. Even if it does, it cannot be reduced below its content in the raw material. Therefore, it is necessary to select titanium sponge having a small content of these impurities as a raw material, and further reduce contamination in the production process as much as possible.
[0040]
Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd and Si
The alloy of the present invention includes, in addition to V, Al and Sn, Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd and Si each having a content of less than 3% as long as the effects of the present invention are not impaired. One or more selected materials may be contained. These components contribute to the improvement of the strength of the alloy after aging treatment without impairing the deformability and other properties of the alloy of the present invention. A more desirable content of each component is 0.1 to 1%.
[0041]
The average crystal grain size when the solution treatment is performed to form a β-type alloy is desirably 20 to 130 μm. This is because, if it is less than 20 μm, the deformation resistance becomes large and processing becomes difficult, and if it is more than 130 μm, the deformability is reduced and cracks are liable to occur when processed, resulting in insufficient strength even after aging. . The aging treatment is usually performed at 400 to 500 ° C., but by setting the crystal grain size of the β phase in the above range, the grain size of the α phase precipitated by aging is preferably in the range of 0.02 to 0 °. .2 μm, resulting in excellent strength and toughness.
[0042]
The above desirable average crystal grain size can be obtained by employing the following manufacturing conditions.
[0043]
The alloy or alloy plate of the present invention is manufactured by forging a material ingot to a required composition, hot rolling, cold rolling, and then performing a solution treatment. In order to obtain a β-type alloy having the above-mentioned average crystal grain size which is excellent in performance and low in deformation resistance, it is desirable to make the production conditions as follows.
[0044]
The material heating temperature of the hot rolling is preferably set to 900 to 1050C. This is because if the temperature is lower than 900 ° C., the deformation resistance in hot working is large, and the load on the processing equipment becomes excessive. If the temperature exceeds 1050 ° C., the oxidation during heating becomes severe, and the yield only decreases. In addition, the crystal grains are coarsened, which affects the alloy properties after processing. In addition, the temperature during hot working should be within the range of 750 to 1050 ° C., which is equal to or higher than β transus, even if there is a temperature drop during the waiting time between deformation processing and deformation processing, or a temperature rise due to processing heat. Is desirable.
[0045]
After hot working, rapid cooling with an average cooling rate of 30 ° C./min or more, such as water cooling, is preferred. This is because, when the cooling is performed slowly, the α phase precipitates and hardens, which makes it difficult to handle the rolled material, and the rolled plate may not be developed. When performing cold rolling, cold drawing or the like in the next step, in order to obtain sufficient softening, for example, the solution is subjected to a solution treatment through a continuous pickling annealing apparatus (HAP) and descaling is performed. In the solution treatment, that is, the β treatment, it is desirable to heat to 750 to 950 ° C. and then water-cool. In this case, if the temperature is lower than 750 ° C., it may be insufficient to form a single β phase, and if it exceeds 950 ° C., crystal grains may be coarsened. The heating time of the solution treatment is preferably set to 1 to 30 minutes in order to sufficiently form a solution and avoid unnecessary heating.
[0046]
The average crystal grain size becomes smaller than 20 μm when the hot working temperature is close to β transus or lower, and the temperature at HAP is close to 750 ° C. Therefore, it is desirable to avoid such conditions. However, when high strength after aging treatment is required even if the cold workability is somewhat sacrificed, the hot working temperature is set to β transus or less, the temperature at HAP is set to around 750 ° C., and the average crystal grain size is reduced. It may be smaller than 20 μm, for example, 10 μm.
[0047]
For descaling, grinding with a coil grinder or the like is desirable because there is no absorption of hydrogen, but productivity is poor and cost is high. Therefore, descaling by pickling is performed, but it is necessary to carry out as little hydrogen contamination as possible.
[0048]
Hydrogen absorption is suppressed as much as possible, and not only sufficient descaling but also removal of the α case can be performed, and pickling conditions for producing a plate having a beautiful surface by cold rolling are preferably as follows, for example, as follows. . The α case is a hard and brittle oxygen-enriched layer formed by the penetration of oxygen into the surface of the β titanium alloy.
(1) Prior to pickling, a shot blast is applied.
{Circle over (2)} Pickling is performed within 10 minutes with an aqueous solution containing 20 to 70 ° C. and 3 to 40% by mass of HF as a main component.
{Circle around (3)} 20 to 70 ° C., 3 to 6% by mass of HF and 5 to 20% by mass of HNO ₃ Pickling with a hydrofluoric acid aqueous solution containing
[0049]
The shot blast of (1) does not need to be performed, but the pickling time can be shortened by applying light shot blast. This is because cracks enter the oxide scale.
[0050]
The aqueous solution of the above (2) may contain nitric acid, hydrogen peroxide or the like, which has a reducing property and suppresses hydrogen absorption, in addition to 3 to 40% by mass of HF as a main component. For example, a waste liquid from a semiconductor manufacturing process (hydrofluoric acid as a main component and secondary components such as acetic acid) can be used.
[0051]
The aqueous solution of the above (3) is also composed of 3 to 6% by mass of HF and 5 to 20% by mass of HNO. ₃ In addition, it may contain secondary components having a reducing property such as hydrogen peroxide and impurities such as acetic acid.
[0052]
The pickling is first performed with the aqueous solution containing hydrofluoric acid as a main component in (2). Pickling with hydrofluoric acid is effective in removing oxide scale, but when pickling and removing the α case, hydrogen absorption is particularly large. Therefore, the acid case is kept to the extent that the α case remains within 10 minutes at the longest, and then the next (3) pickling is performed. The oxygen-enriched layer formed under the oxide scale, that is, the α case, can be efficiently removed by the nitric acid solution. Pickling with a hydrofluoric acid solution has the advantage of reducing hydrogen absorption due to the reducing action of nitric acid. is there. Therefore, after (2) pickling with an aqueous solution mainly containing hydrofluoric acid, (3) pickling with a hydrofluoric acid solution is performed. However, even with a hydrofluoric acid solution, hydrogen absorption increases over a long period of time.
[0053]
In the above pickling, the temperature is set to 20 to 70 ° C. When the temperature is lower than 20 ° C., it takes too much time to remove the scale and the oxygen-enriched layer, and when the temperature exceeds 70 ° C., the surface becomes extremely rough and the acid evaporates. Is also increased. If the concentration of HF is less than 3% by mass in both the solution (2) and the solution (3), the reaction rate becomes too slow. On the other hand, in the case of the solution (2), if the content exceeds 40% by mass, the reaction becomes too violent, causing a problem in safety and making it difficult to adjust the amount of corrosion. In the case of the solution (3), if it exceeds 6% by mass, the surface roughness after pickling becomes excessive. The solution of (3) contains 5 to 20% by mass of HNO. ₃ However, this is because hydrogen absorption is suppressed. If the amount is less than 5% by mass, the effect is not sufficient. If the amount exceeds 20% by mass, the effect is saturated and is wasted.
[0054]
If the immersion time of the pickling becomes longer, the amount of hydrogen increases rapidly, so that the generation of scale during heating is suppressed as much as possible. If the scale is large, a mechanical scale removing method such as grinding may be used together.
[0055]
In cold working, since the grain size is reduced to 130 μm or less by β treatment after working, the working rate is 30% or more (rolling elongation rate is 30% or more for a sheet, and the area reduction rate is 30% or more for a strip). desirable. The processing rate may be large, but the upper limit is naturally limited by the inability to process due to work hardening.
[0056]
The β phase formation after cold rolling is preferably carried out by a solution treatment in which the material is heated to 750 to 900 ° C. and then cooled at a cooling rate equal to or higher than air cooling, also during annealing. The reason why the heating temperature of 750 to 900 ° C. is desirable is that, as in the case of the above-mentioned heating temperature range in the solution treatment before cold working, if it is too low, β phase formation becomes insufficient, and if it is too high, crystal grains become coarse. Because you do. If the heating time is too short or too long, similarly, the β phase is insufficiently formed and the crystal grains are coarsened. Therefore, the heating time is preferably set to 1 to 30 minutes. The heating in the solution treatment after the cold rolling is desirably performed in a vacuum or in an inert gas such as high-purity Ar or He. Heating under conditions where the surface is oxidized requires removal of the oxide film, that is, pickling with hydrofluoric acid or the like for descaling. As a result, hydrogen enters the alloy and the hydrogen content exceeds the specified value. It is because.
[0057]
After hot rolling, cold rolling is usually performed after a solution treatment, but it may be processed into a desired shape in a cold rolled state and then subjected to aging treatment. In this case, a component having fine crystal grains and high strength can be obtained.
[0058]
The aging treatment for strengthening of the β-type alloy of the present invention is preferably performed at 400 to 500 ° C. This is because a fine α phase precipitates due to aging and thereby strengthening is performed. However, at 400 ° C. or less, a long time is required for age hardening, ductility after strengthening is extremely reduced, and toughness is deteriorated. If the temperature is higher than 0 ° C., coarse α-phase grains are formed and the strength is reduced.
[0059]
【Example】
A titanium alloy having a composition shown in Tables 1 and 2 was melted by a water-cooled copper crucible consumable electrode type vacuum arc melting furnace (VAR) to obtain an ingot having a diameter of 140 mm. These ingots were heated to 1000 ° C. and hot forged to obtain a hot-rolled material having a thickness of 50 mm and a width of 150 mm. This material was heated to 950 ° C., hot-rolled, finished rolling at 800 ° C., immediately cooled to 300 ° C. at an average cooling rate of 200 ° C./min by water spray cooling, and then allowed to cool. This hot rolled sheet was subjected to a solution treatment of “heating at 880 ° C. for 10 minutes and then water cooling”.
[0060]
After the solution treatment, shot blasting, immersion in a 4% by mass HF aqueous solution of hydrofluoric acid at 30 ° C. for 4 minutes, followed by HNO ₃ : 10% by mass, HF: 4% by mass, immersed in hydrofluoric acid at a temperature of 30 ° C for 10 minutes to remove the scale and the oxygen-enriched layer, further grind both surfaces, and then perform 80% cold rolling. The thickness was 3 mm.
[0061]
The hydrogen content in the table is a value obtained by collecting and analyzing a sample after cold rolling. The deformability of the solution-formed β-type alloy was determined from the occurrence of edge cracks during the cold rolling. In Test Nos. 20, 21 and 30, the amount of hydrogen was increased by immersing in HF: 4% by mass and hydrofluoric acid at 30 ° C. for about 15 minutes.
[0062]
[Table 1]

[0063]
[Table 2]

[0064]
After cold rolling, it is heated at 850 ° C. for 5 minutes in a vacuum, subjected to water-cooled annealing and solution treatment, and a tensile test piece of JIS No. 13B is collected from the obtained plate to measure the tensile strength. did. From the magnitude of the tensile strength, the deformation resistance during processing can be estimated.
[0065]
Further, using a plate that did not cause large ear cracks by cold rolling, aging treatment was performed at 475 ° C. for 20 hours, and a tensile test piece of JIS No. 13B was collected from the aged plate to obtain a tensile strength. And elongation were measured. These measurement results are also shown in Tables 1 and 2.
[0066]
As is clear from the results of Tables 1 and 2, Test Nos. 1 to 24 all have the main composition that matches the Ti-20V-4Al-1Sn alloy, but the test Nos. In comparison, it can be seen that the materials of Test Nos. 1 to 19 have excellent cold workability, and have excellent strength and elongation after aging. This is an effect brought about by limiting the contents of H, Fe, C and N, which has not been managed conventionally, and it is clear that the importance of keeping the contents of these elements low is obvious.
[0067]
【The invention's effect】
According to the present invention, the currently used β-type Ti-20V-4Al-1Sn alloy is an alloy having smaller deformation resistance and excellent deformability. This greatly contributes to the reduction of manufacturing costs for high-strength titanium alloy parts, such as extending the life of rolls and dies in cold rolling such as cold rolling and cold drawing, and extending the life of dies during cold forging. can do.
[0068]
The titanium alloy of the present invention is suitable not only for industrial equipment such as valve train parts for automobiles and parts for space aircraft, but also as materials for daily necessities such as eyeglass frames and sports equipment such as golf club heads.
[0069]
ADVANTAGE OF THE INVENTION According to the manufacturing method of this invention, the cold rolled material of a stable quality titanium alloy can be manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram showing the effect of hydrogen content on a change in hardness due to aging of a titanium alloy.

Claims (5)

In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.20% or less, H: 0.03% or less, Fe: 0. A β-type titanium alloy comprising 40% or less, C: 0.05% or less, and N: 0.02% or less, with the balance being Ti and impurities. In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.12% or less, H: 0.03% or less, Fe: 0. A β-type titanium alloy comprising 15% or less, C: 0.03% or less, and N: 0.02% or less, with the balance being Ti and impurities. In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.20% or less, H: 0.03% or less, Fe: 0. 1 selected from among Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd, and Si each having a content of 40% or less, C: 0.05% or less, and N: 0.02% or less, each of which is less than 3%. A β-type titanium alloy containing at least one species and the balance consisting of Ti and impurities. In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.20% or less, H: 0.03% or less, Fe: 0. A β-type titanium alloy containing 40% or less, C: 0.05% or less, N: 0.02% or less, and the balance being Ti and impurities is firstly acidified with an aqueous solution mainly containing 3 to 40% by mass of HF. Washing, and then pickling with an aqueous solution containing ₃ to 6% by mass of HF and 5 to 20% by mass of HNO3. In mass%, V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, O: 0.20% or less, H: 0.03% or less, Fe: 0. 1 selected from among Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd, and Si each having 40% or less, C: 0.05% or less, and N: 0.02% or less, and each having less than 3%. A β-type titanium alloy containing at least seeds and the balance consisting of Ti and impurities is first pickled with an aqueous solution mainly containing 3 to 40% by mass of HF, and then 3 to 6% by mass of HF and 5 to 20% by mass. % By pickling with an aqueous solution containing HNO ₃ %.

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