JP2000273598A - Manufacture of high strength coil cold rolled titanium alloy sheet excellent in workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of adopting a coil rolling process enabling continuous production and applicable to an Al-containing α+β Ti alloy and further capable of providing a Ti alloy combining excellent workability with strength by means of subsequent annealing. SOLUTION: At the time of annealing a coil cold rolled sheet of Al-containing α+β Ti alloy, annealing is performed while selecting the heating temperature at annealing among the temperatures avoiding the temperature region where a brittle hexagonal crystal appears, within the temperature range between the temperature at which work hardening at cold rolling is relaxed and Tβ. By this procedure, the elongation of the coil cold rolled Ti alloy sheet in T- direction can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cold-rolled Ti alloy sheet having high strength and excellent workability. In particular, the present invention provides excellent workability by appropriately controlling the annealing conditions after coil cold-rolling. The present invention relates to a method for manufacturing a high-strength coil cold-rolled Ti alloy sheet.

[0002]

2. Description of the Related Art Ti alloys are widely used in the fields of aerospace industry and chemical industry in recent years because they are lightweight and have excellent strength, toughness and corrosion resistance. However, Ti alloys are inherently poor workable materials, and therefore have a major drawback that the cost for forming is significantly higher than other materials. For example, Ti-6Al-4V alloy, which is a typical α + β type titanium alloy, is a difficult-to-work material and has poor cold workability, and it is said that it is practically impossible to manufacture a sheet material by coil cold rolling.

[0003] When a Ti-6Al-4V alloy is processed into a plate shape, a technique called pack rolling is adopted. That is, pack rolling refers to Ti obtained by hot rolling.
This is a method in which -6Al-4V alloy sheets are stacked in layers and placed in a mild steel box, and a thin sheet is manufactured by hot rolling while keeping the temperature below a predetermined temperature. In this method, a pack is manufactured. In addition to the need for mild steel cover and pack welding, the application of a release agent to prevent diffusion bonding of titanium alloy sheets is extremely complicated and requires a lot of cost compared to cold rolling. In addition, since the temperature range suitable for hot rolling is limited, there are many restrictions on working.

On the other hand, JP-A-3-274238 and JP-A-3-166350 disclose Al, Ti in a Ti base material.
The content of V and Mo is specified, and Fe, Ni, C
By containing an appropriate amount of at least one alloying element selected from o and Cr, the alloy has the same strength as the Ti-6Al-4V alloy, and also has a superplastic workability and a hot workability higher than those of the Ti-6Al-4V alloy. It is described that an excellent titanium alloy can be obtained.

Further, Japanese Patent Application Laid-Open No. 7-54081 and
No. 54083 discloses an Al content of 1.0 to 4.5%.
And the V content is 1.5-4.5.
%, The content of Mo is defined as 0.1 to 2.5%, or further contains a small amount of Fe or Ni, thereby maintaining a high strength and improving the cold workability of a Ti alloy. I have.

[0006] This Ti alloy is excellent in that it has both cold workability and high strength, and also has improved weldability. However, the demands of consumers have become more severe in recent years, and further improvement is desired.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances. In particular, the present invention is directed to an α + β type Ti alloy containing Al and adopting a coil rolling method capable of continuous production. An object of the present invention is to provide a method capable of obtaining a Ti alloy having both excellent workability and strength by subsequent annealing.

[0008]

Means for Solving the Problems The manufacturing method of the present invention which can solve the above-mentioned problems is achieved by a cold-rolled α + β coil containing Al.
In annealing the type Ti alloy sheet, the heating temperature at the time of annealing should be set to a temperature range in which a brittle hexagonal crystal appears in a temperature range not less than a temperature at which work hardening during coil rolling is relaxed and not more than Tβ. The gist lies in that the elongation in the T direction of the coil cold-rolled Ti alloy sheet is improved by annealing from a temperature to be avoided.

Although the chemical composition of the α + β type Ti alloy applied to the present invention is not particularly limited, it has a workability capable of cold rolling as an original hot rolled material, and has a suitable temperature range in the subsequent cold rolling. In order to obtain a Ti alloy having both excellent workability and high strength by a combination of annealing, it is particularly preferable that the Al equivalent is 3 to 6.5% and the solid solution β
At least one stabilizing element has a Mo equivalent of 2.0 to 4.
5% and at least one of the eutectoid β-stabilizing elements contains 0.3 to 2% by Fe equivalent, or 0.01 to 0.15% of C as another element, and 0 to 0% of Si. .
It is a Ti alloy containing 5%.

If the above annealing is performed using a Ti alloy having the above alloy composition, the tensile strength after annealing is 900 M
It shows an elongation percentage of not less than Pa and not less than 4%, and the [elongation percentage in L direction (coil rolling direction)] / [elongation percentage in T direction (direction perpendicular to coil rolling direction)] is 0.4 to 1.0. T
An i-alloy plate can be easily obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the present invention, when an Al-containing cold-rolled Ti alloy sheet containing an α + β phase is annealed, the heating temperature during the annealing is reduced by reducing the work hardening during the cold rolling of the coil. The annealing temperature is selected from a temperature range in which a fragile hexagonal crystal appears as much as possible in a temperature range not lower than Tb and not higher than Tβ. By improving the elongation in the T direction (in the direction perpendicular to the cold rolling direction of the coil), which causes an extreme decrease in ductility in the coil cold rolling step, the workability was improved while maintaining high strength. The configuration, operation, and effect of the present invention will be described in detail below in the course of experiments.

The present inventors have developed an α + β-type Ti alloy which is a cold-rollable α + β-type Ti alloy developed by the present inventors.
Influence of annealing conditions after coil cold rolling on ductility and strength in the L direction (same direction as coil rolling) and T direction of the Ti alloy for -2Mo-1.6V-4.5Al alloy I've been working hard to do this.

As a result, as shown in FIGS. 1 and 2 described below, the proof stress and tensile strength are not significantly affected by the annealing temperature. It was confirmed that the temperature showed a specific tendency. That is, in the above alloy system, a certain annealing temperature (around 850 ° C. in FIG. 1 and around 800 ° C. in FIG. 2).
, The elongation in the T direction shows a minimum value, and shows an increasing tendency in the annealing temperature range before and after that.

As a result of further pursuing the reasons for the above-mentioned peculiar tendency, the following facts have become clear.

That is, annealing after coil cold rolling is generally performed as a process for relaxing work hardening generated by coil cold rolling by recrystallization by heating and recovering ductility in the T direction, which has been largely reduced by cold rolling. It is considered that the ductility improvement effect by such recrystallization increases as the annealing temperature increases.

Incidentally, the dashed line shown in FIG. 3 is a conceptual diagram showing the relationship between the annealing temperature and the ductility generally recognized. In the low temperature region where the annealing temperature after cold rolling is about 650 ° C. or less, the ductility in the T direction is reduced. Almost no improvement effect was observed, but when the annealing temperature was increased to about 700 ° C. or more, a slight recovery of ductility was observed. Thereafter, as the annealing temperature was increased, the recovery of ductility progressed. It is considered that, when the content is increased above, recrystallization occurs, anisotropy is eliminated, and ductility is remarkably improved.

However, when the relationship between the annealing temperature and the elongation rate after coil cold rolling of the alloy type α + β type Ti alloy capable of coil cold rolling was examined by experiments, as shown by solid lines A and B in FIG. In both the L-direction elongation (solid line A) and the T-direction elongation (solid line B), the ductility recovers as the temperature rises and the elongation rate increases up to an annealing temperature of about 800 ° C. as in the conventional recognition. However, when the annealing temperature is further increased, the elongation rate once drops sharply, and then when the annealing temperature is further increased, the elongation rate shows a peculiar tendency to rapidly rise again. Ti
It was confirmed that the phenomenon was remarkably exhibited in the case of an alloy.

Moreover, such a tendency is caused by α as shown in FIG.
This can be explained by the phase diagram of the + β type Ti alloy and the structural change of the Ti alloy. That is, FIG. 4 is an explanatory diagram showing the relationship between the ductility of the transformed β phase (that is, the α phase) in the Ti + alloy in comparison with the phase diagram of the α + β type Ti alloy, in which the amount of the β stabilizing element is relatively small. The α phase has a relatively ductile hexagonal structure, but as the amount of β-stabilizing element increases, it becomes brittle hexagonal at a certain amount and the ductility decreases rapidly. Will come. Thereafter, when the amount of the β-stabilizing element further increases, it becomes an orthorhombic crystal having relatively high ductility, and the yield stress and the tensile strength are reduced, but the ductility again shows an increasing tendency. That is, in the α + β-type Ti alloy, the ductility remarkably changes due to the difference in the crystal structure accompanying the change in the amount of β-stabilizing element, and it is possible to control the alloy composition so that a brittle hexagonal crystal which appears immediately before the appearance of the orthorhombic crystal is hardly generated. It becomes important.

As is clear from the trends shown in FIGS.
The ductility of the α + β-type Ti alloy after the cold rolling of the coil is not solely determined by the annealing temperature for recrystallization for relaxing work hardening, but is also significantly affected by the crystal structure of the Ti alloy. . As a combined effect of these, even when the annealing temperature for recrystallization is increased as shown in FIG. 3, when the transformed β phase at that time becomes mainly fragile hexagonal α, the ductility rapidly decreases, Further, after the brittle hexagonal structure is changed to a highly ductile orthorhombic structure, it is considered that ductility is rapidly recovered due to the progress of recrystallization by annealing again.

As described above, in the present invention, the fact that the ductility after coil rolling is not uniquely determined by the annealing temperature for recrystallization but is significantly affected by the difference in the crystal structure of the Ti alloy. In short, when annealing the coil-rolled α + β-type Ti alloy to reduce work hardening and increase ductility, the annealing temperature is set to the brittle phase due to the appearance of the brittle hexagonal crystal. It is characterized in that by controlling the generation region as much as possible, the elongation is surely increased to obtain excellent workability.

At this time, as shown in, for example, a region X in FIG. 4, even in a region where the alloy composition of the β phase shows a weak hexagonal crystal during annealing heating, the temperature range at which the weak hexagonal crystal appears is gradually reduced. When cooled (furnace cooled), the structural change of the Ti alloy changes along the β transus (Tβ), and the appearance of brittle hexagonal crystals is suppressed. If normal cooling is performed while avoiding the temperature range, a high-ductility annealed material can be obtained.

The α + β-type Ti alloy thus annealed while avoiding the embrittlement zone as described above has a tensile strength of 900MPa.
It shows an elongation of 4% or more at a level or higher, and T
The anisotropy, that is, (L-direction elongation) / (T-direction elongation) is about 0.4 to 1.0 due to the significant recovery of the elongation in the direction, and excellent processing in both the vertical and horizontal directions. It is possible to obtain an annealed material having good properties.

This tendency is a phenomenon common to all α + β-type Ti alloys containing Al. Therefore, the present invention is applied to all the α + β-type Ti alloys containing Al. Particularly preferred alloy compositions for more effectively utilizing the improvement (cost reduction) and the elongation-strength balance on a practical scale are as follows.

That is, among the α + β-type Ti alloys used in the present invention, a particularly preferable base composition has an Al equivalent of 3 to 6.5%, more preferably 3.5 to 5.5%.
And at least one of the total solid solution type β-stabilizing elements such as Mo, V, Ta, and Nb is 2.0% or more in Mo equivalent.
5% or less, more preferably 2.5% or more and 3.5% or less, and eutectoid β such as Fe, Cr, Ni, and Co.
0.3% or more and 2% or less, more preferably 0.4% or more, 1.5% or more in Fe equivalent of at least one stabilizing element
An α + β-type Ti alloy containing:

In the above, the Al equivalent, the Mo equivalent, and the Fe equivalent refer to the amounts represented by the following formulas, and the reason for determining their preferred ranges is as follows. Al equivalent = Al + 1/3 · Sn + 1/6 · Zr Mo equivalent = Mo + 1 / 1.5 · V + 1/5 · Ta + 1 / 1.36 · Nb Fe equivalent = Fe + 1/2 · Cr + 1/2 · Ni + 1 / 1.5 · Co + 1 /
1.5 · Mn.

Al equivalent: 3 to 6.5% Al is an element that contributes to strength improvement as an α-stabilizing element. If the Al content is less than 3%, the Ti alloy becomes insufficient in strength. However, when the Al content exceeds 6.5%, the cold workability decreases, and the number of cold rolling and annealing until rolling to a predetermined thickness increases, which leads to an increase in cost. Considering the balance between strength and workability, the lower limit of the more preferable Al content is 3.5%, and the more preferable upper limit is 5.5%.
In the present invention, since Sn and Zr also exert the same action as Al, when they contain these elements, they are defined as the Al equivalent represented by the above formula, including those elements. .

Mo equivalent: 2.0 to 4.5% Mo is a β-stabilizing element and increases the volume ratio of the β-phase, and forms a solid solution with the β-phase to contribute to an increase in strength. Also,
It also has the property of forming a fine equiaxed crystal structure by forming a solid solution in the Ti base material, and is an extremely useful element from the viewpoint of improving the balance between strength and ductility. The content of Mo should be 2.0% or more, more preferably 2.5% or more in order to effectively exert the action of Mo. However, if the content is too large, the corrosion resistance of the Ti alloy increases, and the annealing during the cold rolling is performed. It becomes difficult to remove the formed oxide scale and the base metal in which oxygen, which is called α-case, is dissolved, which not only impairs the workability but also reduces the Ti.
Since the density of the whole alloy is increased, and the characteristic of the high specific strength inherent in the Ti alloy is impaired, it should be suppressed to 4.5% or less, more preferably 3.5% or less. V, T
Since a and Nb also have the same effect as Mo, the Mo equivalent of the above formula is defined including these same elements.

Fe equivalent: 0.3 to 2% Fe has an effect of lowering the deformation resistance at the time of working, and contributes to cold workability. In addition, Fe precipitates at the crystal grain boundaries to increase the crystal grains at high temperatures. It has the effect of suppressing and preventing the embrittlement of the Ti alloy. To effectively exhibit such an effect, Fe should be contained at 0.3% or more, more preferably 0.4% or more. However, if the Fe content is too large, segregation during the production of ingots becomes conspicuous, causing quality stability to be impaired. Therefore, 2% or less, more preferably 1.5%
It should be kept below. Since Cr, Ni, Co, and Mn also have the same effect as Fe, they are defined by the Fe equivalent of the above formula including these same effective elements.

In the present invention, the component composition of the base Ti alloy is as described above.
Ti- (4-5%) Al- (1.5-3%) Mo- (1-2%) V- (0.3
~ 2.0%) Fe (especially Ti-4.5% Al-2% Mo-1.6% V
-0.5% Fe).

Incidentally, even with the same α + β type Ti alloy,
The embrittlement temperature range slightly changes depending on the composition of the component. Therefore, in practicing the present invention, the embrittlement temperature range is checked in advance according to the component composition of the Ti alloy to be applied. The annealing temperature may be controlled so as to be out of the temperature range, whereby an annealed material having high strength and improved elongation in the T direction can be reliably obtained.

Further, when 0.1 to 1.5% of Si is contained in the α + β-type Ti alloy having the above base composition, the strength characteristics of the Ti alloy and the welding characteristics can be improved without reducing the ductility required for coiling. The properties (strength and ductility) of the heat-affected zone can be further enhanced. If C is positively contained in an amount of 0.01 to 0.15%, excellent cold workability is not impaired. It is preferable because strength and ductility are further improved.

That is, Si exerts an action of improving strength properties without any adverse effect on the cold rolling properties of the α + β type Ti alloy, and also exerts an action of increasing strength and ductility in the weld heat affected zone. C has the effect of significantly increasing the strength while maintaining excellent ductility of the Ti alloy base material,
By adding an appropriate amount of C, it is possible to obtain an α + β-type Ti alloy with further enhanced strength and ductility.

In order to more effectively exert the above-mentioned effect of Si, it is desirable to contain 0.1% or more, more preferably 0.2% or more. Since it becomes difficult, the content is preferably suppressed to 1.5% or less, more preferably 1.0% or less. In order to effectively exert the effect of C, the content is 0.01% or more, more preferably 0.02% or more, and 0.15% or less, more preferably 0.12% or less. If it is less than 0.01%, the above effect of C cannot be effectively utilized, and if it exceeds 0.15%, the cold-rolling property is impaired by precipitation hardening of carbide.

In addition to the above Si and C, a small amount of O (oxygen)
Is preferable because the strength can be further increased without substantially affecting the ductility of the Ti alloy base material. These effects of oxygen are manifested in very small amounts,
In order to exhibit the effect more effectively, the content is preferably about 0.07% or more, more preferably about 0.1% or more. However, if the oxygen content is too large, the cold workability is reduced, and the ductility is also reduced due to an excessive increase in strength. Therefore, the oxygen content is 0.25% or less, more preferably 0.18% or less. It is better to suppress.

In the present invention, the preferable composition of the Ti alloy has been described from the above viewpoints. The preferable range of the typical content of the elements contained in the Ti alloy will be described in more detail as follows.

In the Ti alloy of the present invention, trace elements other than the above may be mixed in as traces as other unavoidable impurity elements. Is acceptable.

An annealed material obtained by using an α + β type Ti alloy satisfying the above component composition and appropriately controlling the annealing conditions after coil cold rolling so as to satisfy the above requirements is as follows:
As described above, the tensile strength is 900 MPa or more, the T-direction elongation is 4% or more, and the (L-direction elongation) / (T-direction elongation) is 0.4 to 1.0. In both the T and L directions, the alloy has excellent ductility not found in the conventional Ti-6Al-4V alloy, and thus has various shapes by cold working, for example, a thin plate, a corrugated plate, It can be easily processed into a pipe shape.

Incidentally, for example, Ti-4.5% Al-2% M
FIG. 4 shows the relationship between the annealing temperature and the elongation when the cold-rolled sheet made of α + β-type Ti alloy of o-1.6% V-0.5% Fe is annealed.
The brittle hexagonal crystal appears around 850 ° C. Therefore, when annealing a coil cold-rolled Ti alloy having this component composition, it is preferable to remove the temperature range where the brittle hexagonal crystal is formed, preferably from 760 to 825 ° C, or from 875 to Tβ
It is necessary to control the annealing temperature in the above temperature range.

By adopting annealing conditions in an appropriate temperature range for a cold-rolled coil made of a Ti alloy having the above component composition, a tensile strength of 900 MPa or more, a T-direction elongation of 4% or more, and An annealed material having (L-direction elongation) / (T-direction elongation) of 0.4 to 1.0 can be obtained.

Incidentally, even with the same α + β type Ti alloy,
The fragile hexagonal formation temperature range slightly changes depending on the composition of the component, and therefore, in practicing the present invention, the temperature range is checked in advance according to the composition of the Ti alloy to be applied. The annealing temperature may be controlled so as to be out of the temperature range, whereby an annealed material having high strength and improved elongation in the T direction can be reliably obtained.

At this time, depending on the type of the cold-worked product, it may be necessary to perform rolling at the above-mentioned high working ratio,
In this case, one or a plurality of soft annealing treatments may be performed during rolling, and cold rolling may be performed to an arbitrary thickness while relaxing work hardening. In any case, the Ti alloy of the present invention has a higher elongation than the conventional α + β-type Ti alloy, so that coil rolling can be performed without the need for pack rolling as described above. By annealing, excellent workability can be exhibited while maintaining high strength.

The Ti alloy of the present invention thus obtained can be processed into an arbitrary shape such as a plate, a rod, or a tube by utilizing its excellent workability. It has both strength and ductility, and further has good weldability and the weld heat affected zone shows a high level of ductility, so applications where welding is performed before processing into the final product, such as plate materials for heat exchangers, It can be widely and effectively used as Ti golf head materials, welded tubes, various wires, rods, ultrafine wires, and the like.

[0043]

EXAMPLES Hereinafter, the structure and operation and effect of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and the present invention is applicable to the above and following points. The present invention can be appropriately modified and implemented within the scope of the invention, and all of them are included in the technical scope of the present invention.

Experimental Example 1 Inductoskull melting of a Ti alloy ingot (80 mm ^t × 200 mm ^w × 300 mm ^L ) of Ti-2% Mo-1.6% V-0.5% Fe-4.5% Al-0.3Si-0.03% C And then in the β temperature range (about 1100
° C), and then subjected to slab rolling to a plate having a thickness of 40 mm, and then held in a β temperature range (about 1100 ° C) for 30 minutes, followed by air cooling. Next, the α + β region below the β transformation point (900
To 920 ° C.) to produce a hot-rolled sheet having a thickness of 4.5 mm.

Next, after annealing at 760 ° C. for 30 minutes, shot blasting and pickling were performed to obtain a cold-rolled material. This is further subjected to [40% cold rolling + 760 ° C. × 5 minute annealing] × 2 treatments, and after performing 40% cold rolling,
Annealing was performed under the conditions shown in Table 1, and each annealed material was pickled to remove an oxide layer on the surface, and then 0.2% proof stress, tensile strength and T, L direction elongation were measured. The results are shown in Table 1 and FIG.
Shown in

[0046]

[Table 1] As is clear from Table 1 and FIG. 1, in the component type α + β-type Ti alloy used in the present example, the brittle hexagonal crystal is formed in the annealing temperature range around 850 ° C., so that the elongation in the direction perpendicular to the rolling direction (T direction) is increased. It can be confirmed that the temperature is remarkably low. If the annealing is performed in a temperature range of 750 to 830 ° C. or 900 to 950 ° C. excluding the annealing temperature range, excellent elongation is maintained while maintaining high tensile strength and 0.2% proof stress. It can be seen that an annealed material having a high modulus can be obtained.

Experimental Example 2 Ti alloy ingot of Ti-3.5% Mo-0.5% Fe-4.5% Al-0.3Si (80 m
The ^{m t × 200mm w × 300mm L} ) was prepared in-duct skull melting, after slabbing the thick plate 40mm from then heated to beta temperature range (about 1100 ° C.), beta temperature range (about (1100 ° C.) Hold for 30 minutes by heating and then cool with air. Next, the α + β region below the β transformation point (900 to 920)
° C) to produce a hot-rolled sheet having a thickness of 4.5 mm.

Next, after annealing at 760 ° C. for 30 minutes, shot blasting and pickling were performed to obtain a cold-rolled material. This is further subjected to [40% cold rolling + 760 ° C. × 5 minute annealing] × 2 treatments, and after performing 40% cold rolling,
Annealing was performed under the conditions shown in Table 1, and each annealed material was pickled to remove an oxide layer on the surface, and then 0.2% proof stress, tensile strength and T, L direction elongation were measured. The results are shown in Table 2 and FIG.
Shown in

[0049]

[Table 2] As is clear from Table 2 and FIG. 2, in the α + β-type Ti alloy of the component system used in this example, the elongation in the direction perpendicular to the rolling direction (T direction) due to the formation of brittle hexagonal crystals in the annealing temperature range around 800 ° C. It can be confirmed that the temperature is remarkably lowered. If annealing is performed at a temperature of 760 ° C. or less or 820 to 950 ° C. or more excluding the annealing temperature range, excellent elongation is maintained while maintaining high tensile strength and 0.2% proof stress. An annealed material having a high rate can be obtained.

[0050]

The present invention is constituted as described above, and α
+ Β type Ti alloy as a base composition, and a specific amount of C,
Alternatively, by further containing a small amount of oxygen, it has a strength not inferior to the most widely used titanium alloy, Ti-6Al-4V alloy, and significantly improves the cold workability lacking in the alloy. Thus, it has become possible to provide a titanium alloy capable of cold rolling of a coil and having both excellent strength and ductility.

Therefore, the titanium alloy of the present invention can be widely used for various applications by utilizing its characteristics. In particular, by utilizing its excellent strength and ductility and utilizing its excellent cold rolling property, it can be used for, for example, aircraft. It can be used very effectively as a body material.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between annealing temperature, strength, and elongation obtained in an experimental example.

FIG. 2 is a graph showing the relationship between annealing temperature, strength, and elongation obtained in another experimental example.

FIG. 3 is a conceptual diagram showing a relationship between an annealing temperature and an elongation rate confirmed by the present inventors.

FIG. 4 shows a phase diagram of an α + β type Ti alloy.
FIG. 4 is an explanatory diagram showing a ductility relationship of a transformed β phase (that is, an α phase) in the Ti alloy.

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Claims (5)

[Claims] When annealing a cold-rolled α + β-type Ti alloy sheet containing Al, the heating temperature at the time of annealing is set to a temperature within a range from a temperature at which work hardening at the time of coil rolling is eased to Tβ or less. Excellent workability characterized by improving the elongation in the T direction of the cold-rolled Ti alloy sheet by annealing from a temperature that avoids the temperature range where fragile hexagonal crystals appear as much as possible. Of high-strength coil cold-rolled Ti alloy sheet. 2. The Ti alloy has an Al equivalent of 3 to 6.5% (meaning mass%, the same applies hereinafter), and the solid solution β
At least one stabilizing element has a Mo equivalent of 2.0 to 4.
5% and the eutectoid β-stabilizing element is 0.3 to 2% by Fe equivalent.
2. The method according to claim 1, wherein the method comprises: 3. The method according to claim 2, wherein the Ti alloy further contains 0.01 to 0.15% of C as another element. 4. The Ti alloy according to claim 2, further comprising 0.1 to 1.5% of Si as another element.
The production method according to any one of the above. 5. Tensile strength after annealing is 900 MPa or more and shows an elongation of 4% or more, and [Elongation in L direction (coil rolling direction)] / [T direction (in a direction perpendicular to the coil rolling direction). The method according to any one of claims 1 to 4, wherein a Ti alloy sheet having an elongation percentage of 0.4 to 1.0 is obtained.