JPH1085804A - Manufacture of seamless tube consisting of alpha-type or alpha+beta type titanium alloy containing substance for inhibiting coarsening of structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a seamless tube which consists of an α-type or α+βtype titanium alloy containing an inhibstor of the coarsening of structure, whose strength and ductility are higher in the same order in both directions of the length direction and peripheral direction and which has small anisotropy. SOLUTION: After a solid billet or bloom of the α-type or α+β type titanium alloy containing the substance for inhibiting the coarsening of structure is heated to the temp. range of not lower than the β-transformation temp., combined rolling of rolling for imparting a material flow in the peripheral direction of tube-making and rolling for imparting the material flow in the length direction of tube-making is executed and, in that combined rolling, the ratio RH/RL of the total sum RH of the reduction of area by the rolling for imparting the material flow in the peripheral direction to the total sum RL of the reduction of area by the rolling for imparting the material flow in the length direction is defined as the range of 0.5-2.0. In this way, the inhibition of the coarsening of structure and reduction of anisotropy are achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an α-form or α + β
The present invention relates to a method for producing a seamless pipe made of a titanium alloy. More specifically, the present invention relates to a method for producing a seamless tube having a small material anisotropy from an α-type or α + β-type titanium alloy containing a substance that suppresses coarsening of a structure.

[0002]

2. Description of the Related Art In recent years, titanium alloys having three major properties of light weight, high strength, and high corrosion resistance have been used in recent years to take advantage of these characteristics.
It has begun to be applied to extreme environments at high depths, high temperatures, high pressures, and high corrosion, such as geothermal development, offshore oil and gas fields, and further expansion of titanium alloy applications is expected. Among titanium alloys, α-type and α + β-type titanium alloys, which have a high track record in aircraft applications, and small amounts of P
Highly corrosion-resistant α + β-type titanium alloys further enhanced in corrosion resistance by adding a platinum group element such as d or Ru are regarded as particularly promising as excellent materials for extreme environments.

[0003] In the above-mentioned applications, the pipe has a main product shape. As a method for manufacturing a pipe made of a titanium alloy, there is the following method. That is, 1) a method of bending and welding a plate, 2) a method of punching by a hot press, and further extruding or stretching by a press to form a pipe to a predetermined size (press method); 3) a drilling-stretching-standard- There is a method (rolling method) in which rolling processes such as drawing, polishing tube and fixed form are sequentially and continuously performed to form a tube (rolling method).

In the method 1), a strong steel plate mill is used to perform processing at a temperature not higher than the β transformation point having high deformation resistance to obtain a fine equiaxed structure excellent in strength and ductility. On the other hand, it has the advantage of being able to be performed, but has the disadvantage that it has a welded part in which characteristic deterioration is unavoidable. In contrast,
The methods 2) and 3) can produce seamless pipes,
There is no weld where there is concern about deterioration of properties, and even in the above-mentioned extreme environment applications where repair and parts replacement are extremely difficult, it has the advantage of being able to be used stably for a long time, but the temperature range below the β transformation point However, even with the use of a powerful steel manufacturing facility, titanium alloys with high deformation resistance cannot be sufficiently processed, and all or most of the processing has low deformation resistance but rapid diffusion β
It must be performed at the transformation point or higher, the structure becomes coarse, and the strength /
There was a problem that ductility deteriorated.

[0005] On the other hand, as a method for preventing the structure from being coarsened even when heated and processed to a temperature higher than the β transformation point at which diffusion is rapid, for example, Y ₂ O ₃ , Dy ₂ O ₃ , Nd
A method of containing a rare earth element oxide such as ₂ O ₃ , Lu ₂ O ₃ , and Er ₂ O ₃ or a boride of titanium such as TiB is disclosed in “Sixth World Conference on Titani” in 1989.
um Proceedings Part II ”(Les Editions de Physique
Issuance, p. 831-836). In addition, titanium carbide such as TiC or silicide, or SAE Technical Paper Series No.
As described in 910425, it is reported that sulfides of rare earth elements such as Ce and La also have an effect of suppressing the coarsening of the structure.

[0006] These effects are mainly due to suppression of coarsening of β grains, that is, suppression of movement of β grain boundaries.
An α-type or α + β-type titanium alloy containing such a substance that suppresses the coarsening of the structure does not coarsen even when processed at a temperature equal to or higher than the β transformation point. It has the advantage that it can be manufactured without coarsening.

[0007]

However, α-type or α + containing a substance that suppresses tissue coarsening as described above.
A seamless tube made of β-type titanium alloy is different from ordinary α-type or α + β-type alloys that do not contain these substances, and the characteristics in the length direction and circumferential direction of the tube are extremely different. Have a fatal disadvantage that one of the characteristics is extremely deteriorated.

Regarding the anisotropy of the material, a normal α-type or α + β which does not contain a substance which suppresses tissue coarsening is used.
It has been known that when anisotropy occurs in a type titanium alloy, it can be eliminated by heating and holding again in a β single phase temperature region higher than the β transformation point. However, in an α-type or α + β-type titanium alloy containing a substance that suppresses the coarsening of the structure as described above, the anisotropy hardly disappears even when heated to a temperature equal to or higher than the β transformation point. In some cases, the problem may be solved by heating to an extremely high temperature range, for example, at a temperature of 1300 ° C. or higher. In that case, however, the problem is that the structure is coarsened and the effect of adding a substance that suppresses the coarsening of the structure is lost. There was a point.

In view of the above problems, an object of the present invention is to provide an α-form or α-form containing a substance that suppresses tissue coarsening.
In a method of manufacturing a seamless tube using a + β-type titanium alloy, the strength and ductility are as high in both the longitudinal direction and the circumferential direction, while fully exerting the effect of the substance that suppresses the coarsening of the structure. An object of the present invention is to provide a method for manufacturing an isotropic small seamless tube.

[0010]

According to the present invention, there is provided a method for producing a seamless pipe made of an α-type or α + β-type titanium alloy containing a substance which suppresses the structure coarsening. Containing a substance that suppresses
After heating a solid billet or bloom of the α-type or α + β-type titanium alloy to a temperature range higher than the β transformation point, rolling is performed to give a material flow in the circumferential direction of the pipe making, Rolling combined with rolling to give flow,
In the combination rolling, a ratio RH of a total area reduction ratio (RH) by rolling to give a material flow in the circumferential direction and a total area reduction rate (RL) by rolling to give a material flow in the length direction.
/ RL is in the range of 0.5 to 2.0, characterized in that the seamless pipe is made of an α-type or α + β-type titanium alloy containing a material having a small material anisotropy and containing a substance which suppresses coarsening of the structure. It is a manufacturing method. The above-described rolling for imparting the material flow in the circumferential direction of the pipe making is suitable for rolling by inclined rolls, and the rolling for imparting the material flow in the longitudinal direction of the pipe making is suitable for rolling by caliber rolls. The effect of the present invention is best exhibited when the substance that suppresses the coarsening of the structure is one or more of a boride of Ti, an oxide of a rare earth element, and a sulfide of a rare earth element.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a seamless tube is manufactured from an α-type or α + β-type titanium alloy containing a substance that suppresses coarsening of the structure. An α-type titanium alloy is an alloy in which an α phase accounts for 95% or more at room temperature in an equilibrium state,
Ti-5Al-2.5Sn and Ti-5Al-2.5Sn ELI in which the concentration of an intrusion type impurity element is reduced are known as typical alloys. The α + β-type titanium alloy is a titanium alloy having a main phase of about 75 to 95% of an α phase at room temperature in an equilibrium state, and the balance being substantially a β phase. , Is a type of alloy that undergoes martensite transformation in whole or in part. Typical α + β type titanium alloys include Ti-3Al-2.5
V, Ti-6Al-4V, Ti-6Al-4V EL
I, Ti-6Al-6V-2Sn, Ti-6Al-2S
n-4Zr-6Mo, Ti-4.5Al-3V-2Mo
-2Fe and the like. In addition, recently developed Ti containing about 0.9 to 2.3% of Fe and further adding about 0.1 to 0.6% of oxygen and nitrogen in total.
-Fe-ON-based α + β-type titanium alloys also belong to α + β-type titanium alloys. Such Ti-Fe-ON-based α + β
In some cases, the type titanium alloy contains 0.25% or less of Ni and Cr as impurities. Various types of α or α
+ Β-type alloy in order to increase the corrosion resistance.
An alloy to which about 5% of a platinum group element is added also belongs to the α-type or α + β-type titanium alloy.

[0012] The substance which suppresses the coarsening of the structure suppresses the coarsening of the β grains even when the α-type or α + β-type titanium is heated to a temperature higher than the β transformation point and processed, thereby suppressing the coarsening of the structure. Refers to a substance that has an effect. The substance having such action and effect, as described in the section of "conventional art", oxides of rare earth elements such as Y ₂ O ₃ and Er ₂ O _3, borides Ti, such as TiB, TiC Ti carbides and silicides, rare earth sulfides such as La and Ce, and the like. Any one or two of these
It can contain more than one species. Among various coarsening suppressing substances, in particular, boride of Ti, oxide of rare earth element,
The sulfide of a rare earth element has a particularly large effect of suppressing the coarsening of the structure, and the present invention can be effectively applied to an α-type or α + β-type alloy containing these substances. As a method for adding the above substances, each substance may be added directly, or may be added in another form, and may be crystallized or precipitated during or after solidification, and the addition method is limited. Not something.

The present inventors have analyzed the cause of the material anisotropy of a seamless pipe made of an α-type or α + β-type titanium alloy containing such a substance that suppresses the coarsening of the structure, and analyzed the following. Obtained knowledge. That is, 1) The addition of the substance that suppresses the coarsening of the structure significantly suppresses the coarsening of the β-grain, remarkably delays the recrystallization of the β-grain, and leaves much of the processed structure and the structure in the recovered state. From such unrecrystallized β grains that are insufficiently recrystallized, during cooling, an α-phase texture with a remarkably oriented crystal orientation is formed in a specific direction related to the processing direction, and the α phase becomes symmetric. Due to the poorest dense hexagonal system, large material anisotropy occurs. 2) In a normal α-type or α + β-type titanium alloy to which a substance that suppresses microstructure coarsening is not added, when reheating to a temperature range higher than the β transformation point, the processing strain in the β grains causes recrystallization or grain growth. And during the subsequent cooling, an α phase having a random orientation precipitates and the anisotropy is eliminated. However, in an α-type or α + β-type titanium alloy containing a substance that suppresses the coarsening of the structure, recrystallization or grain growth does not occur even when reheated to a temperature higher than the β transformation point, and thus the α phase precipitated during cooling Is not randomized.

The present inventors have studied the above findings in more detail, and have studied the technology for producing a seamless pipe. As a result, 3) by controlling the orientation distribution of the processing strain remaining in the β phase. In addition, it is possible to reduce the anisotropy of the material properties by controlling the preferential precipitation orientation of the α phase generated during cooling, that is, the α phase texture. 4) When a seamless tube is manufactured by a combination of appropriate rolling conditions, it is possible to easily control the orientation distribution of the processing strain remaining in the β phase. I found that.

Therefore, in the present invention, a solid billet or bloom of an α-type or α + β-type titanium alloy containing a substance that suppresses the coarsening of a structure is heated to a temperature range not lower than the β transformation point, and then the pipe is formed. A seamless pipe is manufactured by performing a combined rolling of a rolling that gives a material flow in a circumferential direction and a rolling that gives a material flow in a length direction of the pipe.
This is essential for controlling the orientation distribution of the strain remaining in the β phase. As explained in the "Background" section,
As a method of manufacturing a seamless pipe, a press method, a rolling method, and the like can be cited. Among these methods, the press method simply generates a flow of the material in the length direction of the pipe, and changes the orientation distribution of the strain in the β phase. It is impossible to control. Also, in the rolling method, the material flow in the case where the whole rolling step or most of the steps consist only of the rolling method using the inclined rolls occurs spirally with a slight inclination in the circumferential direction,
Alternatively, on the contrary, when only the process using the caliber roll is used, the flow of the material occurs in the length direction and is a simple flow in one direction. It is impossible to control.

On the other hand, rolling is performed by appropriately combining rolling for providing a material flow in the circumferential direction (and a direction having a slight angle with the circumferential direction) of the pipe making and rolling for providing a material flow in the longitudinal direction. When the tube is formed, a flow in two directions can be given, and since the angles are almost orthogonal, it is possible to control the azimuthal distribution of strain in the β phase by changing the ratio of the two.

In the present invention, the ratio of the combination of the rolling for providing the flow of the material in the circumferential direction of the pipe making and the rolling for providing the flow of the material in the longitudinal direction is defined by the reduction in area. In a predetermined combination of the two, the sum of the reduction in area (RH) of the rolling that gives the flow of the material in the circumferential direction and the sum of the reduction (RL) of the reduction in the rolling that gives the flow of the material in the longitudinal direction The ratio RH / RL is 0.5
To 2.0. By defining the ratio in this range, the orientation distribution of the processing strain remaining in the β phase becomes appropriate, and a texture in which the crystal orientation of the α phase is appropriately oriented in both the circumferential direction and the length direction is generated. . When such a texture occurs, the characteristic difference between the length direction and the circumferential direction decreases. The ratio RH / RL of the sum of the area reduction rates of both is 0.5 to
If it is out of the range of 2.0, the orientation distribution of the strain in the β phase is biased in the circumferential direction or the length direction, and the orientation accumulation of the α phase precipitated during cooling is also biased. , The anisotropy of the material becomes remarkable, for example, the ductility in the opposite direction decreases.

As the above-mentioned rolling for imparting the material flow in the circumferential direction of the pipe making, rolling with inclined rolls is preferable, and as the rolling for imparting the material flow in the longitudinal direction, rolling with a caliber roll is preferred. is there. In addition, "rolling method"
The production of seamless pipes by means of drilling, drawing, polishing pipes, shaping, drawing, etc. consists of various rolling processes,
The present invention does not define the rolling mode in each of these steps in a fixed manner.Depending on the rolling mill, there are cases where a step such as piercing or stretching of an inclined roll system is performed, and cases where the caliber roll system is used. . In the case of piercing using a caliber roll, the rolled material may be pressed from behind in an auxiliary manner. For example, the perforation is performed with an inclined roll, and the steps after stretching may be performed with a caliber roll, and conversely, the perforation may be performed with a caliber roll, and the steps after stretching may be performed with an inclined roll. As long as the ratio of the total of the area reduction rates of the two is within the range of the present invention, the effect of the present invention is sufficiently exhibited.

In the present invention, the heating temperature of the solid billet or bloom is set to the β transformation point or higher. This is because all or most of the processing is performed at a temperature equal to or higher than the β transformation point where the deformation resistance is low. As described in the section of “Prior Art”, the deformation resistance is reduced in the α + β region below the β transformation point. This is based on the equipment restriction that it cannot be sufficiently processed even if a strong seamless steel pipe manufacturing equipment is used because it is extremely high. However, it is possible to process at a temperature below the β transformation point for a small amount of processing.Because the temperature decreases with the progress of processing, even if part of the pipe forming process is below the β transformation point, most of the processing will be β transformation. It just needs to be done above the point.

Further, in the present invention, the steps such as heat treatment, straightening, and refining after pipe forming are not restricted. That is, it is possible to perform various heat treatments such as annealing, solution aging, and solution aging, and perform various refining processes such as hot, cold correction, grinding, cutting, and pickling. It is possible to do. Further, in the present invention, it is possible to perform reheating in the middle of the pipe forming process, and then to further perform a rolling step. It is the object of the present invention: “α-type or α + to which a substance that suppresses tissue coarsening is added.
In β-type titanium alloys, the recrystallization and grain growth of β grains are extremely unlikely, so the effect of the previous processing hardly disappears even if reheated, and almost the same effect as continuous processing. Because it is obtained. When the processing amount after the reheating is small, the reheating temperature may be in the α + β region below the β transformation point.

[0021]

The present invention will be described in more detail with reference to the following examples. FIG. 1 shows an outline of the tube mill used in the test. Mill A has an inclined roll type perforation, and Mill B has a caliber roll type perforation. Mill C
Is a rolling mill that reheats a raw material formed in a mill B to form a smaller-diameter tube.

(Test 1) α + β type titanium alloy Ti-6A
The l-4V into TiB ₂ 0.1 wt% alloy added with and dissolved vacuum arc twice, Ti-6Al-4V alloy TiB is dispersed in the matrix (Ti-6Al-4V + Ti
The ingot of B) was produced. Β transition point of this alloy is 990 ℃
It is. Here, TiB is generated by reacting TiB ₂ with Ti. This ingot is subjected to slab rolling to a diameter of 2
Bloom with a circular cross section of 50 mm, a seamless pipe having an outer diameter of 251.7 mm and a thickness of 16.5 mm by the press method under the conditions shown in Table 1, and the diameter of the gauge section in the longitudinal direction and circumferential direction of the pipe. A round bar tensile test specimen having a length of 6.35 mm and a length of 30 mm was cut out and subjected to a tensile test to measure 0.2% proof stress and elongation.

Table 5 shows the test results. Test No. 1 was performed using Ti-containing TiB as a substance that suppresses tissue coarsening.
This is a case where 6Al-4V + TiB is formed by a press method at a temperature equal to or higher than the β transformation point and annealed at 750 ° C. The characteristics in the longitudinal direction and the circumferential direction of the pipe are extremely different, and the material anisotropy is strongly shown. The circumferential direction has extremely high strength and the ductility is extremely low in comparison with the longitudinal direction. It is an index that indicates the anisotropy of strength.
The 2% proof stress ratio (L / H) was 0.79 with an isotropic value of 1.
It greatly deviates from 00. Test No. 2 is a case where the pipe was formed in the same process, heated to the β transformation point or higher, and further subjected to stabilization annealing. In the case of ordinary α-type and α + β-type titanium alloys to which no substance that suppresses microstructural coarsening has been added, the anisotropy is eliminated by such heat treatment. The anisotropy is hardly eliminated.

[0024]

[Table 1]

(Test 2) Ti-6Al used in Test 1
In addition to -4V + TiB, Y ₂ O ₃ in the Ti-6Al-4V
Was melted twice in a vacuum arc with 0.1% by weight of
Y ₂ O ₃ in the Ti-6Al-4V matrix was prepared an ingot of the dispersed alloy (Ti-6Al-4V + Y 2 O 3). The β transformation point of this alloy is 990 ° C. These ingots were formed into blooms having a rectangular cross section of 210 mm × 210 mm by slab rolling, and the method shown in Table 2 was used according to the method of mill B,
A seamless pipe with an outer diameter of 251.7 mm and a thickness of 16.5 mm was used.
A 5 mm, 30 mm long round bar tensile test piece was cut out and subjected to a tensile test to measure 0.2% proof stress and elongation. All heat treatments are air cooled after treatment at 750 ° C.-1 hr.

Table 5 shows the test results. Test number 3 is T
In this example, the i-6Al-4V + TiB bloom was heated to 950 ° C. in the α + β region below the β transformation point to attempt pipe making. However, the deformation resistance was high, and even the perforation process could not be performed.
Test No. 4 shows that the heating temperature of the bloom is 1 above the β transformation point.
At 050 ° C., the perforation process was performed in the β region, and the subsequent stretching process was performed in the α + β region below the β transformation point. Although perforation was possible, stretching at a temperature below the β transformation point where deformation resistance was high was impossible. However, as shown in Test Nos. 5 and 6, the bloom is heated above the β transformation point, most of the processing is performed in the temperature range above the β transformation point, and a small amount of processing is performed at a temperature below the β transformation point. Tube was possible.
In Test Nos. 5 and 6, the ratio of the total reduction in the rolling process using the inclined rolls to the total reduction in the rolling process using the caliber rolls was within the scope of the present invention. As shown in the figure, the strength ratio in the length direction and the circumferential direction was small in the range of 1.00 ± 0.10, and the elongation was a high value of 10% or more in both directions. That is, the effect of adding the substance that suppresses the coarsening of the structure is sufficiently exhibited, and the strength and ductility are as high in both the length direction and the circumferential direction, and a seamless pipe with small anisotropy can be manufactured. Was.

Test No. 7 shows that Ti-6Al-4V + containing Y ₂ O ₃ as a substance for suppressing the coarsening of the structure.
This is an example in which the present invention is applied to Y ₂ O ₃ . In this case as well, the tube had high strength and high ductility in both the length direction and the circumferential direction, and had small anisotropy. However, in Test No. 8, the ratio of the sum of the reductions in the rolling process using the inclined rolls and the sum of the reductions in the rolling process using the caliber rolls was out of the range specified in the present invention. Therefore, the strength in the length direction became higher than the strength in the circumferential direction by 20% or more, and the ductility in the length direction became extremely low.

[0028]

[Table 2]

(Test 3) Ti-6 used in Tests 1 and 2
In addition to Al-4V + TiB, α-type titanium alloy Ti-5A
l-2.5Sn alloys where the Er ₂ O ₃ was added 0.1% by weight dissolved vacuum arc twice, Ti-5Al-2.5Sn
Alloy Er ₂ O ₃ is dispersed in a matrix (Ti-5A
1-2.5Sn + Er ₂ O ₃ ) was produced. The β transformation point of this alloy is 1030 ° C. These ingots were formed into billets having a circular cross section of 170 mm in diameter by ingot rolling, and had an outer diameter of 1 mm according to the conditions shown in Table 3 using a mill A method shown in FIG.
A seamless pipe having a thickness of 61.4 mm and a thickness of 7.0 mm was obtained. In the length direction, gauge part width 12.5mm, thickness 4mm, length 80
Cut out a tensile test piece of 0.2 mm and perform a tensile test.
The yield strength and elongation were measured. Since a similar test piece cannot be collected in the circumferential direction, as shown in FIG. 2, an arc-shaped sample having a width of 30 mm is cut out, heated to 600 ° C., and then warm-corrected, and subjected to a tensile test similar to the length direction. A piece was taken and 0.2% proof stress and elongation were measured by a tensile test.

Table 5 shows the test results. Test No. 9 is an example in the case where the Ti-6Al-4V + TiB used in Test 2 was formed by a pipe mill different from that in Test 2. Unlike the case of Test 2, the inclined roll is used in the punching step and the caliber roll is used in the stretching step. However, since the ratio of the sum of the area reduction rates of both is within the range specified in the present invention, Tubes with high strength and high ductility in both the width direction and the circumferential direction and low anisotropy could be produced. Test number 10 is the same as test number 9
In this case, the solution aging treatment was performed in place of the annealing performed in the above step. Since the rolling conditions were appropriate, a tube having high strength, high ductility and small anisotropy was obtained in both the length direction and the circumferential direction regardless of the type of heat treatment. Test No. 11 shows that Er ₂ O was used as a substance for suppressing tissue coarsening.
_{3 Ti-5Al-2.5Sn + Er 2} O 3 containing an an example of applying the present invention. Also in this case, a tube having high strength, high ductility and low anisotropy in both the longitudinal direction and the circumferential direction is obtained.

[0031]

[Table 3]

(Test 4) An alloy obtained by adding 0.5% by weight of cerium group rare earth element (mainly containing Ce and La) and 0.15% by weight of S to Ti-6Al-4V, Ti-6
Alloy obtained by adding 5% by weight of TiC to Al-4V, α + β
0.1% of B ₄ C in Ti-3Al-2.5V
Alloy containing 0.05% by weight of Y and 0.05% by weight of Y. Similarly, 0.1% by weight of B ₄ C, 0.3% by weight of a rare earth element (REM) of cerium, and 0.3% by weight of S are added to Ti-3Al-2.5V. An alloy (Ti-6Al-4V + REM) in which four kinds of alloys containing 0.09% by weight were melted by vacuum arc melting twice and REM ₃ S ₄ (REM: rare earth element) was dispersed in a Ti-6Al-4V matrix. ₃ S ₄ ), Ti
Alloy in which TiC is dispersed in a -6Al-4V matrix (Ti-6Al-4V + TiC), Ti-3Al-2.
5V TiB in the matrix and Y ₂ O ₃ is dispersed alloy (Ti-3Al-2.5V + TiB + Y 2 O 3), Ti
-3Al-2.5V matrix with TiB and REM ₃ S
₄ dispersed alloy (Ti-3Al-2.5V + TiB +
An ingot of REM ₃ S ₄ ) was produced. Here, TiB is B
₄ are C and the substance which Ti is produced by the reaction, Y ₂ O ₃ is a substance produced by the reaction of oxygen in Y and _{Ti-3Al-2.5V, REM 3} S 4 cerium genus rare earth elements Is a substance crystallized by the reaction between S and S. The β transformation points of the above four alloys are 990 ° C., 1010 ° C., 910 ° C., 9
20 ° C.

These ingots were rolled into a 210 mm ×
A bloom having a rectangular cross section of 210 mm, a seamless tube having an outer diameter of 178 mm and a thickness of 13 mm according to the conditions shown in Table 4 in the form of Mill B and Mill C, and a 6.35 mm diameter gauge and a length from the length direction. Cut out 30mm tensile test piece,
A tensile test was performed to measure 0.2% proof stress and elongation.
In addition, since it is difficult to collect the same tensile test specimen in the circumferential direction,
Warm straightening was performed in the same manner as in Test 3, and thereafter, the same test piece collection and test as in the longitudinal direction were performed. All the heat treatments are air-cooled annealing treatments at 750 ° C.-1 hr.
The temperature of reheating when moving from the mill B to the mill C is β
The temperature is above the transformation point.

Table 5 shows the test results. In Table 5, the test numbers 12, 13, 14, 16 which are the examples of the present invention are shown.
Are tubes having high strength, high ductility, and low anisotropy in both the longitudinal direction and the circumferential direction. However, in Test No. 15, the 0.2% proof stress in the length direction was only 80% in the circumferential direction, and the circumferential elongation was a remarkably low value from the matrix composition (Ti-3Al-2.5V). Was. This is because the ratio of the sum of the reductions in the rolling process using the inclined rolls and the sum of the reductions in the rolling process using the caliber rolls was out of the range specified in the present invention.

[0035]

[Table 4]

[0036]

[Table 5]

[0037]

As described above, according to the present invention, in a method for manufacturing a seamless pipe made of an α-type or α + β-type titanium alloy containing a substance that suppresses the coarsening of the structure, the material in the circumferential direction of the pipe-making is manufactured. Since the combination of the rolling for imparting the flow (preferably inclined roll rolling) and the rolling for imparting the material flow in the length direction (preferably caliber roll rolling) was used, the ratio was determined by the reduction in area. Strength and ductility are equally high in both the longitudinal and circumferential directions,
An α-type or α + β-type titanium alloy seamless tube having a small material anisotropy and containing a substance that suppresses the coarsening of a structure can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of a flow of a tube mill applied to a test.

FIG. 2 is a schematic diagram showing a method of collecting a tensile test specimen from a circumferential direction.

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[Procedure amendment]

[Submission date] October 1, 1996

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

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Claims (3)

[Claims] 1. An α-containing substance that suppresses tissue coarsening.
In a method for producing a seamless tube made of a titanium alloy or an α + β titanium alloy, a solid billet or bloom of an α-type and an α + β-type titanium alloy containing a substance that suppresses the coarsening of the structure is heated to a temperature range above the β transformation point. After doing
Rolling to give a material flow in the circumferential direction of the pipe making and rolling to give a material flow in the length direction of the pipe making a combined rolling, in the combined rolling by rolling to give the material flow in the circumferential direction The ratio RH / RL of the total area reduction rate (RH) to the total area reduction rate (RL) by rolling to impart a material flow in the length direction is in the range of 0.5 to 2.0. A method for producing a seamless tube made of an α-type or α + β-type titanium alloy containing a material having a small material anisotropy and suppressing a material coarsening. 2. The rolling for imparting a material flow in the circumferential direction of the pipe making is rolling by an inclined roll, and the rolling for imparting a material flow in the longitudinal direction of the pipe making is rolling by a caliber roll. A method for producing a seamless tube made of an α-type or α + β-type titanium alloy containing a substance having a small material anisotropy and suppressing a coarsening of the structure. 3. The material according to claim 1, wherein the substance that suppresses the coarsening of the structure is one or more of a boride of Ti, an oxide of a rare earth element, and a sulfide of a rare earth element. A method for producing a seamless tube made of an α-type or α + β-type titanium alloy containing a substance having a small anisotropy and suppressing a structure coarsening.