CN1659295A - β-type titanium alloy and manufacturing method thereof - Google Patents

Abstract

The present invention provides a β-type titanium alloy having excellent cold rolling workability, high strength after aging, and excellent property stability. The alloy comprises, by mass%, 15-25% V, 2.5-5% Al, 0.5-4% Sn, 0.20% or less O (oxygen), 0.03% or less H, 0.40% or less Fe, 0.05% or less C, and 0.02% or less N. The alloy is produced by a method characterized by first pickling with an aqueous solution containing 3-40% by mass HF as a main component, and then pickling with an aqueous solution containing 3-6% by mass HF and 5-20% by _mass HNO₃.

Description

β-type titanium alloy and manufacturing method thereof

technical field

The invention relates to a β-type titanium alloy which has low deformation resistance in cold rolling processing in a solid solution state, has excellent deformation ability, and becomes high-strength after aging treatment, and a manufacturing method of the alloy.

Background technique

Due to its low density and high strength, titanium alloy has high specific strength (strength/density) among practical metal materials, and has excellent corrosion resistance. , materials for golf clubs, materials for tableware, etc. are widely used. With its widespread use, further improvement in the properties of titanium alloys or reduction in price is more required.

Titanium alloys are roughly classified into α (hexagonal close-packed: hcp) type, β (body-centered cubic: bcc) type, and α+β type in terms of the crystal structure of phases constituting the metal structure at room temperature. Titanium for industrial use or an alloy with a small amount of Al added is α-type. It is well known as a high-strength alloy. The Ti-6Al-4V alloy used in aircraft and the like is α+β-type. An alloy containing an element that stabilizes the β phase.

Titanium alloys generally have poor cold-rolling workability, which increases manufacturing costs. In pure titanium with a low oxygen content and relatively good cold-rollability, the strength of formed parts is insufficient, and it is difficult to apply it to parts requiring high specific strength. On the other hand, as a high-strength titanium alloy, although the most representative Ti-6Al-4V has high strength, its deformability at room temperature is extremely poor, and the target shape cannot be formed only by hot rolling or cutting, and the manufacturing cost increases. high.

From the above-mentioned circumstances, attention has been paid to β-type titanium alloys having a body-centered cubic crystal structure. The β-type alloy is, for example, Ti-3Al-8V-6Cr-4Mo-4Zr alloy or Ti-15V-3Cr-3Al-3Sn. These β-type alloys have a large deformability in cold rolling when they are subjected to solution treatment to form a β single phase, and after processing, they are subjected to aging treatment to precipitate an α phase, which can improve strength and have ideal properties as a material for precision parts.

However, conventionally known β-type titanium alloys have high deformation resistance even though they have good deformability. Therefore, even in the case of performing cold rolling and forging, dies such as dies or piercers are often cracked or broken with a relatively small number of uses. In addition, in the cold rolling and rolling used for the manufacture of processed materials, the wear of the roller is relatively large, and adhesion is easy to occur in the case of cold rolling and drawing.

As an invention to solve such a problem, Japanese Patent No. 2669004 discloses V: 15 to 25%, Al: 2.5 to 5%, Sn: 0.5 to 4%, oxygen: 0.12% or less, and the rest is Ti and impurities. The invention of the alloy (hereinafter referred to as Ti-20V-4Al-1Sn alloy). Although the deformability of this alloy is approximately the same as that of conventional β-type titanium alloys, it not only has low strength and deformation resistance in the solution treated state, but also has high strength after aging treatment. However, when the alloy of this invention is produced and formed into various parts, the deformability in the β-treated state is not always excellent, and the deformation resistance is not stable. In addition, there is a problem that the variation in strength after aging is large.

Contents of the invention

One of the objects of the present invention is to provide a titanium alloy that can easily and stably realize the characteristics of excellent cold-rolling workability in a solid solution state and high strength after aging treatment.

The second object of the present invention is to provide a pickling method for reducing the H (hydrogen) content in the manufacture of the titanium alloy.

The β-type titanium alloy is an alloy of the metastable β phase produced by rapidly cooling the β phase, which is a high-temperature phase of titanium, to room temperature. Alloy elements for stabilizing the β phase include V, Mo, Nb, Ta, Cr, Fe, Mn, etc., but among them, hardening as a solid solution is small and has little adverse effect on workability. Aging can obtain high-strength and relatively stable cheap elements, including V and Mo. However, Mo has difficulties such as high melting point, easy segregation, and high hot-rolling workability and cold-rolling deformation resistance due to the addition of Mo. Therefore, V is selected and Al is included for increasing the strength during aging treatment. In order to achieve the purpose of suppressing solid solution hardening, a part of Al is substituted with Sn to form a Ti-20V-4Al-1Sn alloy.

In the process of producing many of these alloys, it has been found that cold-rolling workability and aging hardening properties cannot be obtained stably, and the present inventors have conducted various studies in order to understand the cause and find countermeasures. First, the workability and aging properties of V, Al, and Sn, which are the main components, were investigated in combination with varying content ranges. However, when the fluctuations of these main components approached the boundary of the range of the content, except that the influence appeared to some extent, no particularly significant influence on the characteristic change was found.

However, in the course of the above-mentioned investigation, it was clearly found that in the β-type Ti-20V-4Al-1Sn alloy, the content of O (oxygen), H, Fe, C and N, which are generally regarded as impurities of titanium, It has a particularly large influence on the properties of the alloy, that is, the cold-rolling workability and the increase in strength after aging. The respective contents of these impurity elements are regulated by the standards of titanium or titanium alloys such as JIS-H-4600, JIS-H-4605, or JIS-H-4607. However, this regulation does not apply to the β-type Ti-20V-4Al-1Sn alloy to be improved by the present invention.

The actions of the above-mentioned elements are known as follows.

O is an α-phase stabilizing element, and if it is contained in a large amount, it will hinder the single-phase formation of the β-phase by solution treatment, but in addition, it will harden the alloy, increase the deformation resistance, and reduce the deformability. Since H is a β-phase stabilizing element, it delays the aging hardening due to the precipitation of the α-phase, and hinders the improvement of the strength due to aging. Although Fe is a β-phase stabilizing element, it is not suitable to contain a large amount because it increases the strength of the alloy after solution treatment and increases deformation resistance. C forms carbide precipitates, greatly reducing deformation resistance and deformation ability. Although N is dissolved in about 1% of the β phase, it will cause a large decrease in ductility and reduce the deformability.

However, in the case of the β-type Ti-20V-4Al-1Sn alloy, even if the impurities are limited to the range specified by the JIS standard, there are elements that cannot be easily reduced within this range. Within, elements are also found whose amounts have a greater influence on the properties of the alloy. This is because the titanium alloy specified by the HS standard is an α-type or α+β-type alloy, whereas the Ti-20V-4Al-1Sn alloy is a β-type alloy.

For example, β-type alloys absorb hydrogen more easily than α-type alloys or α+β-type alloys. In particular, in the case of a sheet produced by cold rolling with a thickness of 5 mm or less, descaling must be performed after cold rolling in order to obtain a good surface. In this descaling method, there is also a method of mechanically grinding the surface, but this method is slow in processing speed and poor in yield. Therefore, pickling with hydrofluoric acid or fluoronitric acid is usually performed. However, when the β-type Ti-20V-4Al-1Sn alloy is formed into a solid solution for cold rolling, it absorbs hydrogen in pickling which greatly exceeds the boundary amount defined by the above-mentioned JIS standard. Even with various adjustments to pickling conditions, it is difficult to achieve a sufficient reduction thereof. In addition, since the alloy contains a scale-enhancing component, hydrogen absorption increases due to prolonged pickling time.

The β-type alloy can be processed into the desired shape and then subjected to aging treatment to increase its strength. However, the contained hydrogen significantly hinders aging hardening and prolongs the aging treatment time, making it difficult to achieve aging hardening to achieve the target strength. In addition, hydrogen reduces the ductility of the alloy to deteriorate the workability, and also greatly deteriorates the toughness. Although it is possible to dehydrogenate by heating at a high temperature in a vacuum, it requires a long-time treatment, and since degradation occurs during this treatment, it is difficult to put it into practical use.

Absorption of hydrogen by pickling for descaling should be avoided during the manufacture of the Ti-20V-4Al-1Sn alloy sheet. Therefore, on the premise that the pickling method that suppresses hydrogen absorption to a minimum is adopted later, and the hydrogen content after pickling that is inevitably mixed in it is premised, whether it can be achieved by controlling the amount of other impurity elements The effects of the contents of O, Fe, N, and C to compensate for the decrease in aging rate and the decrease in workability and toughness due to hydrogen were investigated. As a result, it has been found that a Ti-20V-4Al-1Sn alloy with excellent characteristics can be obtained stably by limiting the content of each of these elements together with hydrogen. Based on these research results, the boundary conditions were further clarified, and the present invention was completed. The gist of the present invention lies in the following (1) to (3) titanium alloys and (4) and (5) methods of producing titanium alloys.

(1) A β-type titanium alloy, characterized in that, in terms of mass %, V: 15-25%, Al: 2.5-5%, Sn: 0.5-4%, 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 the remainder is composed of Ti and impurities.

(2) A β-type titanium alloy, characterized in that, in terms of mass %, V: 15-25%, Al: 2.5-5%, Sn: 0.5-4%, 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 the remainder is composed of Ti and impurities.

(3) A β-type titanium alloy, characterized in that, by mass %, V: 15-25%, Al: 2.5-5%, Sn: 0.5-4%, 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 one selected from Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd and Si less than 3% each As above, the remainder is composed of Ti and impurities.

(4) A method for producing a β-type titanium alloy, characterized in that V: 15-25%, Al: 2.5-5%, Sn: 0.5-4%, 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 the remainder is a β-type titanium alloy composed of Ti and impurities. First, 3 to 40% by mass of HF is used as the main component. Pickling with an aqueous solution of 3-6% by mass of HF and 5-20% by mass of _HNO3 .

(5) A method for producing a β-type titanium alloy, characterized in that, in mass %, V: 15-25%, Al: 2.5-5%, Sn: 0.5-4%, 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 less than 3% each selected from Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd, and Si More than one kind of β-type titanium alloy whose remaining part is composed of Ti and impurities is first pickled with an aqueous solution containing 3 to 40% by mass of HF as the main component, and then pickled with 3 to 6% by mass of HF and 5 to 20% by mass % HNO ₃ aqueous acid pickling.

Description of drawings

FIG. 1 is a graph showing the effect of hydrogen content on changes in hardness of titanium alloys due to aging.

Detailed ways

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 measured by mass %.

V: 15-25%

V is an important element for stabilizing the β phase and making the structure of the alloy at room temperature into a β single phase. If it is less than 15%, a martensitic structure will be generated when solution treatment is performed from a high-temperature β-phase state by rapid cooling such as water cooling, and the cold-rolling workability will be greatly deteriorated. If it exceeds 25%, the aging hardenability of the β-type alloy will be deteriorated, the time required for aging treatment will be prolonged, and sufficient strengthening cannot be obtained after aging treatment. In addition, the deformation resistance of the cold rolling process of the alloy also increases.

Al: 2.5-5%

Although the β-type alloy is finally strengthened by aging treatment, it contains Al in order to obtain a sufficient strength increase at this time. In addition, it also has the effect of suppressing the precipitation of the ω phase that embrittles the alloy and accelerating the precipitation of the α phase during the aging treatment. Such an effect is not sufficient if the content is less than 2.5%, and if it exceeds 5%, the hardness in the β state increases and the cold rolling workability decreases. Therefore, it is set at 2.5 to 5%.

Sn: 0.5-4%

Although Sn has the same function as Al mentioned above, since it does not increase the hardness in the β state like Al, an increase in deformation resistance can be suppressed by reducing Al and substituting it with Sn. Such an effect of Sn is not conspicuous if 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 increases, so it is limited to 4%.

O (oxygen): 0.20% or less

O reduces the deformability of the alloy, causes cracks during high-strength cold rolling, and increases the deformation resistance. The smaller the amount, the better, but it is set at 0.20% or less as a borderline amount that does not cause significant adverse effects. Furthermore, it is more preferable to set it as 0.12 % or less.

H: 0.03% or less

H not only delays the precipitation of the α phase during the aging treatment, reduces the increase in strength due to aging, but also deteriorates the ductility and toughness, so the less the H, the better. However, in the β-type Ti-20V-4Al-1Sn alloy that easily absorbs hydrogen, there are absorptions other than the pickling process, and especially for thin plates, it is difficult to reduce to An amount of 0.005% or less. Therefore, although the lower limit value is not particularly limited, the upper limit value adopts a boundary where the influence is not large, and is set to 0.03%. More preferably, it is 0.01% or less.

An example of investigation on the influence of hydrogen content on aging hardening is shown below.

The alloy composition is V: 20.0%, Al: 3.2%, Sn: 1.0%, O: 0.11%, H: 0.015%, Fe: 0.10%, C: 0.01%, N: 0.01%, the rest: Ti and impurities The hot-rolled calendered sheet with a thickness of 5mm was subjected to solution treatment, and after steel shot peening, the hydrogen content was changed by changing the pickling time, and aging treatment was carried out at 450°C. The solution treatment is a treatment of heating in air at 850° C. for 5 minutes, followed by water cooling.

The results of the investigation on hardness changes caused by aging time are shown in Fig. 1 . The hardness Hv is a Vickers hardness with a test load of 1 kgf.

It can be seen from Fig. 1 that when the hydrogen content is 0.015% or 0.025%, the target hardness is reached and saturated due to 12 hours of aging treatment. On the contrary, even when the hydrogen content was 0.040% or 0.065%, sufficient hardness was not achieved even after 20 hours of treatment. In the case of these alloys, to achieve the hardness obtained in alloys with a hydrogen content of 0.015% or 0.025%, a rather long aging treatment of more than 20 hours is necessary, which lacks practicality. Also, when the hydrogen content is 0.100%, hardening is basically impossible as shown in the figure.

According to the above experimental results, it can be seen that the H content of the alloy is preferably kept below 0.03%.

Fe: 0.40% or less

Fe, like hydrogen, stabilizes the β phase, delays hardening by aging treatment, and increases deformation resistance, so the less the better. As described above, since it is difficult to avoid the inclusion of hydrogen, it is at most 0.40% as a boundary amount that does not bring about a significant increase in deformation resistance. Furthermore, the more preferable Fe content is 0.15% or less.

C: less than 0.05%

Since C greatly reduces the ductility, that is, the deformability, the less the better. As a limit amount that does not bring about a significant reduction in deformability, it is at most 0.05%. More preferably 0.03% or less.

N: 0.02% or less

Since N greatly reduces the deformability, the less the better. As a limit amount that does not bring about a significant reduction in deformability, it is set to 0.02%.

The O, Fe, C and N impurity elements not only originate from the sponge titanium of the raw material, but also enter into the titanium alloy during subsequent alloy melting or high-temperature heating to increase, but cannot be reduced to the level of the raw material. below its content. Therefore, it is necessary to select sponge titanium with less content of these impurities as a raw material, and to reduce pollution in the manufacturing process as much as possible.

Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd and Si

In addition to V, Al, and Sn, the alloy of the present invention may also contain less than 3% of Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd, and Si within the range that does not impair the effect of the present invention. Choose more than one. These components do not impair other properties such as deformability of the alloy of the present invention, but contribute to the improvement of the strength of the alloy after aging treatment. A more preferable content of each component is 0.1 to 1%.

The average crystal grain size when the β-type alloy is formed by solution treatment is preferably 20 to 130 μm. This is because, if it is less than 20 μm, the deformation resistance becomes large and processing is difficult, while when it is larger than 130 μm, the deformability decreases, cracks are likely to occur during processing, and insufficient strength also occurs after aging. In addition, although the aging treatment is usually carried out at 400 to 500° C., by setting the crystal particle size of the β phase within the above range, the particle size of the α phase precipitated by aging becomes the ideal range of 0.02 to 500° C. 0.2μm, the strength and toughness are also very good.

The above-mentioned preferred average crystal grain size can be obtained by employing the following production conditions.

Although the alloy or alloy plate of the present invention is produced by forging and smelting a raw material having a desired composition, hot-rolling it, cold-rolling it, and then performing solution treatment, it is excellent in cold-rolling workability, that is, in deformability. In addition, for the above-mentioned β-type alloy having a low deformation resistance and an average crystal grain size, it is preferable to set the production conditions as follows.

The heating temperature of raw materials for hot rolling and calendering can be 900-1050°C. This is because, when the temperature is lower than 900°C, the deformation resistance of hot rolling processing is relatively large, and the burden on the processing equipment will be too large, and when it exceeds 1050°C, not only the oxidation during heating will be severe, which will reduce the utilization rate of materials, but also The coarsening of crystal grains also affects the properties of the alloy after processing. In addition, the temperature during hot rolling is preferably in the range of 750 to 1050° C. above the β transformation even if there is a temperature drop between deformation processing and deformation processing waiting time and a temperature rise due to processing heat.

After the hot rolling process, rapid cooling with an average cooling rate of 30° C./min or more such as water cooling may be used. This is because if slow cooling is performed, the α-phase is precipitated and hardened, making handling of the rolled material difficult, and there is a possibility that the sheet wound into a coil cannot be unrolled. When carrying out cold rolling, cold rolling, etc. in the subsequent steps, in order to obtain sufficient softening, for example, pass through a continuous pickling and annealing apparatus (HAP), perform solution treatment and descale. Solution treatment, that is, beta treatment, is best heated to 750-950°C and then water-cooled. This is because, at this time, if the temperature is less than 750°C, it may not be sufficient to form the β-phase one phase, and if it exceeds 950°C, the crystal grains may be coarsened. The heating time for the solution treatment may be 1 to 30 minutes for sufficient solid solution and avoiding useless heating.

The conditions for the average crystal grain size to be less than 20 μm are when the temperature of the hot rolling process is near or lower than the β transformation temperature, and when the temperature in HAP reaches about 750° C. Therefore, it is best to avoid such conditions. However, when high strength after aging treatment is to be obtained even if the cold rolling workability is somewhat sacrificed, the hot rolling processing temperature can be set below the β transformation, and the temperature in HAP can be set at around 750°C so that the average crystal grain The diameter is less than 20 μm, for example, 10 μm.

In descaling, grinding with a belt grinder or the like is preferable in view of no hydrogen absorption, but it is poor in productivity and high in cost. Therefore, descaling by pickling should be carried out so as not to mix hydrogen as much as possible.

Pickling conditions for producing a plate with a beautiful surface by cold rolling while suppressing hydrogen absorption as much as possible and not only fully descaling but also removing the α shell may be set as follows, for example. Also, the α shell refers to a hard and brittle oxygen-enriched layer on the surface of the β-type titanium alloy where oxygen can penetrate.

①Before pickling, perform shot blasting.

② Pickling is carried out within 10 minutes at 20 to 70°C in an aqueous solution containing 3 to 40% by mass of HF as the main component.

③ Pickling is carried out within 20 minutes at 20-70°C in an aqueous solution of fluoronitric acid containing 3-6% by mass of HF and 5-20% by mass of HNO ₃ .

Although the shot peening treatment of ① may not be carried out, the pickling time can be shortened when light shot peening treatment is carried out. Is used to add cracks in scale.

The aqueous solution of ② may contain, in addition to 3 to 40% by mass of HF as the main component, nitric acid, hydrogen peroxide, etc. which have reducing properties and suppress hydrogen absorption. For example, waste liquid (mainly composed of hydrofluoric acid and containing subcomponents such as acetic acid) generated in a semiconductor manufacturing process can also be used.

The aqueous solution of ③ may contain reductive secondary components such as hydrogen peroxide and impurities such as acetic acid in addition to the fluoronitric acid aqueous solution of 3-6% by mass of HF and 5-20% by mass of _HNO3 .

Pickling is first carried out in an aqueous solution mainly composed of hydrofluoric acid in ②. Pickling with hydrofluoric acid is effective in removing scale, but hydrogen absorption is particularly large when removing the α shell by pickling. Therefore, stay at the level where the α shell remains within 10 minutes at the longest, and then carry out the pickling in ③ below. The oxygen-enriched layer under the oxide skin, that is, the α shell, can be effectively removed by using fluorine nitric acid solution. Pickling using fluorine nitric acid solution utilizes the reducing action of nitric acid. Although it has the advantage of less hydrogen absorption, when there are many oxide scales, the time required for removal is prolonged, and there is a possibility that corrosion may occur locally and the surface may be roughened. Therefore, after pickling with an aqueous solution mainly composed of hydrofluoric acid of ②, pickling with a fluorine nitric acid solution of ③ is performed. However, since the hydrogen absorption increases after a long time even if the fluoronitric acid solution is used, it is preferable to set it within 20 minutes.

In the above pickling, the temperature is set at 20-70°C because, at a temperature lower than 20°C, it will take too much time to remove the scale or oxygen-enriched layer, and when it exceeds 70°C, the surface will be rough. The oxidation becomes serious, and the evaporation of oxygen also increases. When the concentration of HF is less than 3% by mass in both the solution of ② and the solution of ③, the reaction rate becomes too slow. On the other hand, if it exceeds 40% by mass in the solution of ②, the reaction becomes too violent, causing problems in terms of safety, and it becomes difficult to adjust the amount of corrosion. In the solution of ③, when it exceeds 6% by mass, surface roughening after pickling becomes serious. In addition, adding 5 to 20% by mass of HNO ₃ to the solution of ③ is because this has the effect of suppressing hydrogen absorption, but if it is less than 5% by mass, the effect is insufficient, and when it exceeds 20% by mass, the effect is saturated And form a waste.

Since the amount of hydrogen increases rapidly if the immersion time of pickling is long, the generation of scale during heating is suppressed as much as possible. When there are many scales, mechanical descaling methods such as grinding can be used at the same time.

Cold rolling processing In order to make the crystal grain size below 130μm in the β treatment after processing, it is best to have a processing rate of 30% or more (if it is a plate, the compression elongation rate is 30% or more, and if it is a bar, the area reduction rate is 30% above). It doesn't matter if the processing rate is large, but the upper limit is naturally limited due to work hardening, which makes it impossible to process.

The β-phase transformation after cold rolling, including annealing, may be performed by solution treatment in which the steel is heated to 750 to 900° C. and then cooled at a cooling rate equal to or higher than air cooling. The reason why the heating rate of 750 to 900°C is preferable is the same as that of the heating temperature range of the solution treatment before cold rolling. If it is too low, the β-phase transformation will be insufficient, and if it is too high, the crystal grains will be coarse. change. If the heating time is too short or too long, the β-phase transformation will be insufficient or the crystal grains will be coarsened in the same way, so it may be set to 1 to 30 minutes. Furthermore, the heating of the solution treatment after the cold rolling and rolling is preferably performed in a vacuum or in an inert gas such as high-purity Ar and He. This is because heating under surface oxidation conditions requires pickling with fluoronitric acid or the like in order to remove the oxide coating, that is, descaling. As a result, hydrogen penetrates into the alloy, and the hydrogen content exceeds the limit value.

After hot rolling, cold rolling is usually performed after solution treatment, but it can also be processed into a desired shape in a cold rolled state, and then aging treatment can be performed. In this case, a component with fine crystal grains and high strength can be formed.

The aging treatment for strengthening of the β-type alloy of the present invention is preferably set at 400 to 500°C. Although the fine α-phase is precipitated by aging, and thus can be strengthened, if it is below 400°C, it will take a long time for aging hardening, and the ductility after strengthening will be extremely reduced and the toughness will be poor, while at 500°C In the case of above, coarse α-phase grains are formed, and the strength decreases.

Example

Titanium alloys having the compositions shown in Table 1 and Table 2 were melted in a water-cooled copper crucible consumable electrode vacuum arc melting furnace (VAR) to form an ingot with a diameter of 140 mm. These ingots were heated at 1000° C. and hot-rolled forged into hot-rolled rolled raw materials with a thickness of 50 mm and a width of 150 mm. The raw material was heated to 950° C., hot-rolled and rolled, and rolled at 800° C., immediately cooled to 300° C. at an average cooling rate of 200° C./min with water spray cooling, and then left to cool. The solution treatment of "heating at 880° C. for 10 minutes and then cooling with water" was performed on this hot rolled sheet.

After solution treatment, after performing shot peening, immerse in HF: 4% by mass, 30°C hydrofluoric acid aqueous solution for 4 minutes, and then in HNO ₃ : 10% by mass, HF: 4% by mass, temperature 30°C Dip in fluoronitric acid for 10 minutes to remove the scale and oxygen-enriched layer, and then after grinding both surfaces, perform 80% cold rolling to form a thickness of 3 mm.

The amount of hydrogen in the table is the value obtained by analyzing the samples taken after cold rolling. From the occurrence of edge cracks during the cold rolling, the deformability of the β-type alloy after solid solution was determined. Furthermore, in Experiment Nos. 20, 21, and 30, the time for immersion in HF: 4% by mass, 30° C. hydrofluoric acid was set to approximately 15 minutes to increase the amount of hydrogen.

After cold rolling, heating at 850° C. for 5 minutes in vacuum, water-cooling annealing and solution treatment were performed, and tensile test pieces of JIS No. 13 B were taken from the obtained sheet to measure the tensile strength. From the magnitude of the tensile strength, the deformation resistance during processing can be estimated.

In addition, using a plate that does not produce large edge cracks during cold rolling, aging treatment was performed at 475°C for 20 hours, and a tensile test piece of JIS No. 13 B was taken from the aged plate to measure the tensile strength. Tensile strength and extensibility. These measurement results are shown in Table 1 and Table 2 together.

From the results in Table 1 and Table 2, it can be clearly seen that although the main components of experiment numbers 1 to 24 conform to Ti-20V-4Al-1Sn alloy, compared with the materials of experiment numbers 20 to 33, the experimental numbers 1 to 19 The material is more excellent in cold rolling processability, and the strength and elongation after aging are very good. This is an effect brought about by limiting the contents of H, Fe, C, and N, which have not been controlled in the past, and clarified the importance of keeping the contents of these elements low.

Industrial Utilization Possibility

According to the present invention, the currently used β-type Ti-20V-4Al-1Sn alloy is formed into an alloy with lower deformation resistance and better deformability. In this way, it can greatly contribute to the prolongation of the life of the rolls or dies of cold rolling such as cold rolling and cold rolling, the prolongation of the life of dies during cold rolling and forging, and the manufacturing cost of high-strength titanium alloy parts. decrease.

The titanium alloy of the present invention can be used not only for industrial machines such as valve parts for automobiles and space shuttle parts, but also for daily necessities such as eyeglasses, and materials for sports equipment such as golf clubs.

According to the manufacturing method of the present invention, it is possible to manufacture a titanium alloy cold-rolled rolled material with stable quality.

Table 1 experiment number Chemical composition (mass%) [the remainder is Fe and impurities] ※Cold rolling crack After solid solution After aging Remark V Al sn o h Fe C N other Tensile strength (MPa) Crystal particle size (μm) Tensile strength (MPa) Elongation (%) 12345678910111213141516171819 16.020.024.220.020.020.020.020.020.020.220.220.220.220.220.220.220.220.220.2 3.23.23.22.54.03.03.03.23.23.43.43.33.33.33.33.33.33.33.3 1.01.01.21.01.11.91.01.01.01.01.01.01.01.01.01.01.01.01.0 0.100.110.090.090.110.100.080.110.110.100.100.100.100.100.100.100.100.100.10 0.0200.0150.0100.0220.0210.0180.0280.0150.0200.0060.0070.0080.0070.0200.0210.0200.0210.0200.021 0.100.110.110.100.090.090.100.100.050.110.110.110.130.110.130.110.130.110.13 0.010.010.020.010.010.010.010.010.020.020.010.010.010.010.010.010.010.010.01 0.010.010.020.010.010.010.010.010.020.010.010.020.020.020.020.020.020.020.02 -------------Zr: 0.3Cr: 0.4Mo: 0.3Pd: 0.1Cr: 0.4Zr: 0.3Cr: 0.2Zr: 0.2Cr: 0.2Nb: 0.2 ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ 735700725676725720685700685700705695695720740730740745745 90807080607070607060607070656565656560 1250123012201200132012501230127012651285128512801280129012901290129012951300 12.512.612.913.010.512.114.512.512.312.813.012.812.912.812.912.812.512.512.3 Examples of the present invention """"""""""""""""""""

[-] is the impurity level.

※Crack evaluation ○: No cracks △: Small edge cracks ×: Large edge cracks

Table 2 experiment number Chemical composition (mass%) [the remainder is Fe and impurities] ※Cold rolling crack After solid solution After aging Remark V Al sn o h Fe C N other Tensile strength (MPa) Crystal particle size (μm) Tensile strength (MPa) Elongation (%) 2021222324252627282930313233 20.020.020.020.020.0*12.020.120.120.1*27.120.020.015.0*4.0 3.23.23.23.23.23.0*6.03.03.03.03.03.03.0*6.0 1.01.01.01.01.01.01.0*5.01.01.01.21.23.0*- 0.110.110.110.110.110.100.100.10*0.300.100.100.100.120.12 *0.042*0.0600.0200.0220.0180.0200.0150.0100.0220.021*0.0600.0200.0170.015 *0.410.10*0.450.100.110.120.120.110.090.110.110.110.110.10 *0.060.020.02*0.070.010.010.010.010.010.020.020.020.010.01 *0.050.010.020.02*0.120.010.010.010.010.020.020.020.010.01 -----------*Zr: 4.0*Cr: 3.0- △○○△△××△×○○×○× 8107107907607609009308009007806959108201060 50706560701006060606065659055 10909051100 Unexpected Unexpected Unexpected 1250 Unexpected 1100900 Unexpected 1280 Unexpected 9.514.812.1 EXCEPTION EXCEPTION EXCEPTION 6.5 EXCEPTION 18.515.0 EXCEPTION 11.0 EXCEPTION Comparative example """"""""""""""

The * mark indicates that it is outside the scope of the present invention. [-] is the impurity level.

※Crack evaluation ○: No cracks △: Small edge cracks ×: Large edge cracks

Claims (5)

1. beta titanium alloy, it is characterized in that, in quality % by V:15～25%, Al:2.5～5%, Sn:0.5～4%, below the O:0.20%, below the H:0.03%, below the Fe:0.40%, below the C:0.05%, below the N:0.02%, remainder is that Ti and impurity constitute.

2. beta titanium alloy, it is characterized in that, in quality % by V:15～25%, Al:2.5～5%, Sn:0.5～4%, below the O:0.12%, below the H:0.03%, below the Fe:0.15%, below the C:0.03%, below the N:0.02%, remainder is that Ti and impurity constitute.

3. beta titanium alloy, it is characterized in that, in quality % comprise V:15～25%, Al:2.5～5%, Sn:0.5～4%, below the O:0.20%, below the H:0.03%, below the Fe:0.40%, below the C:0.05%, below the N:0.02% and respectively less than 3% among Zr, Mo, Nb, Ta, Cr, Mn, Ni, Pd and the Si more than one of being selected from, remainder is made of Ti and impurity.

4. the manufacture method of a beta titanium alloy, it is characterized in that, will in quality % by V:15～25%, Al:2.5～5%, Sn:0.5～4%, below the O:0.20%, below the H:0.03%, below the Fe:0.40%, below the C:0.05%, below the N:0.02%, remainder is the beta titanium alloy that Ti and impurity constitute, at first the HF in order to 3～40 quality % is the solution acid pickling of principal constituent, then with containing the HF of 3～6 quality % and the HNO of 5～20 quality % ₃Solution acid pickling.

5. the manufacture method of a beta titanium alloy, it is characterized in that, to comprise V:15～25% in quality %, Al:2.5～5%, Sn:0.5～4%, below the O:0.20%, below the H:0.03%, below the Fe:0.40%, below the C:0.05%, N:0.02% is following and respectively less than 3% the Zr that is selected from, Mo, Nb, Ta, Cr, Mn, Ni, among Pd and the Si more than one, the beta titanium alloy that remainder is made of Ti and impurity, at first the HF in order to 3～40 quality % is the solution acid pickling of principal constituent, then with containing the HF of 3～6 quality % and the HNO of 5～20 quality % ₃Solution acid pickling.