WO2002070763A1

WO2002070763A1 - Titanium alloy bar and method for production thereof

Info

Publication number: WO2002070763A1
Application number: PCT/JP2002/001710
Authority: WO
Inventors: Hideaki Fukai; Atsushi Ogawa; Kuninori Minakawa
Original assignee: Jfe Steel Corporation
Priority date: 2001-02-28
Filing date: 2002-02-26
Publication date: 2002-09-12
Also published as: US20030223902A1; EP1382695A1; JPWO2002070763A1; TWI293987B; US20050051245A1; EP1382695A4; RU2003126234A; JP4013761B2; RU2259413C2

Abstract

An α + β type titanium alloy bar which has a substantial chemical composition in mass %: Al: 4 to 5 %, V: 2.5 to 3.5 %, Fe: 1.5 to 2.5 %, Mo: 1.5 to 2.5 % and balance: Ti, and a structure wherein a pro-eutectoid a phase accounts for a volume percentage of 10 % to 90 %, has an average crystal grain size of 10 νm or less, and exhibits an aspect ratio of a grain of 4 or less in the cross section parallel to the rolling direction. The α + β type titanium alloy bar is excellent in ductility, fatigue characteristics and formability.

Description

TECHNICAL FIELD The present invention relates to a titanium alloy bar excellent in ductility, fatigue characteristics and workability, particularly to an a + i3 type titanium alloy bar and a method for manufacturing the same. BACKGROUND ART Titanium alloys are used as structural materials in chemical plants, generators, aircraft, and other fields because of their high strength, lightness, and excellent corrosion resistance. Among them, there are various α +] 3 type titanium alloys that have high strength and relatively good workability.

Products using titanium alloy include various shapes such as thin plates, thick plates and bars. In some cases, the rod is used in its original shape, but in some cases it is processed into a complex shape, such as a threaded part of Porto, or it is used as a forged material. Excellent workability is required in addition to ductility and fatigue properties.

Figure 1 shows a typical method of manufacturing a bar.

The ingot produced by melting is processed into a billet by forging and becomes a rolled material. As shown in Figs. 2Α and 2Β, rolling is performed by heating a billet in a heating furnace and then by a reverse type rolling mill or tandem type rolling mill.If necessary, the billet is reheated to a temperature at which rolling can be performed by an intermediate heating furnace. You.

In the case of rods made of titanium and titanium alloys, especially α + type titanium alloy rods, the temperature of the material to be rolled increases during hot rolling due to the heat generated during processing, so that stable hot rolling cannot be performed and ductility and fatigue properties In fact, it is not possible to obtain a titanium alloy rod having excellent workability. For example, when the temperature of the material to be rolled rises to the i3 transformation point or higher, the 挪戠 Therefore, excellent ductility and fatigue properties cannot be obtained. In addition, since the transformation point is high, the temperature of the material to be rolled hardly becomes higher than the i3 transformation point due to the heat generated during processing. Ductile, fatigue properties and workability cannot be obtained.

As a method of solving the problem of the temperature rise due to the heat generated during processing, Japanese Patent Application Laid-Open No. 59-82101 discloses a method of reducing the cross-sectional reduction rate per rolling pass at 0: zone temperature and + / 3 zone temperature to 40% or less. Is disclosed. Japanese Patent Application Laid-Open No. 58-25465 discloses a method of water-cooling a material to be rolled in order to suppress a rise in temperature due to heat generated during processing. In addition, in Paper 1: “Hot Bar Rolling of Ti-6A1-4V in a Controllable Continuous Mill (Titanium '92 Science and Technology)”, the rolling speed is used to suppress the heat generated during processing. It is described that the speed is reduced to the performance limit of the rolling mill. However, according to the methods disclosed in JP-A-59-82101 and JP-A-58-25465, a titanium alloy bar excellent in ductility, fatigue properties and workability cannot be obtained.

Further, even if the cross-sectional reduction rate is 40% or less per rolling pass according to the method disclosed in JP-A-59-82102, suppression of heat generation during processing may be insufficient depending on the type of alloy. Furthermore, in the method disclosed in Japanese Patent Application Laid-Open No. 58-25465, there are also problems that the material is deteriorated due to hydrogen absorption due to water cooling, and that accurate temperature control becomes difficult due to distortion due to rapid cooling. .

The method described in Paper 1 is not always applicable to alloys that are subject to T6A4T4V alloys and have a large heating value and are rolled at lower temperatures, as shown below. No fatigue life and workability can be obtained.

Figure 3 shows the relationship between the temperature of the material to be rolled and the rolling time in bar rolling of the Ti-6A4V alloy and the Ti-44.5Al-3V-2Fe-2Mo alloy.

Here, the heating temperature is 950 ° for the Ti-6A4 4V alloy (: for the Ti-4.5A3 3V-2Fe-2Μο 'alloy, the j3 transformation point of which is 100 ° C lower than the Ti-6A4V alloy) The temperature was lowered to 850 ° C by the difference between the three transformation points. Rolling was performed using a reverse mill and a tandem mill, and the rolling speed, rolling reduction, and pass schedule were the same for both alloys. Rolling on a reverse rolling mill Was 2.7 mI sec for both alloys, and rolling ¾i in the tandem rolling mill was 2.25 m / sec for both alloys in the final rolling pass, which was the fastest. The rolling speed is lower than the rolling speed (6 m / sec) described in the above paper 1. The cross-sectional reduction rate is set to 26% at maximum for both alloys.

In the case of rolling a Ti-6A4V alloy, rolling is performed at a temperature sufficiently lower than 1000 ° C, which is the / 3 transformation point of this alloy, and a good value is obtained. On the other hand, in the case of Ti-4.5Al-3V-2Fe-2Mo alloy, the deformation resistance increased due to low-temperature rolling, although the caloric heat temperature was lowered by the low / 3 transformation point. Heat generation increases, and the temperature of the material to be rolled rises to a temperature range exceeding the β transformation point, so that a good structure cannot be obtained. Therefore, excellent ductility, fatigue properties and workability cannot be obtained. This suggests that it is necessary to consider not only rolling conditions but also rolling conditions such as rolling temperature, rolling reduction, and time between rolling passes. DISCLOSURE OF THE INVENTION An object of the present invention is to provide a high-strength titanium alloy rod having excellent ductility, fatigue properties and workability, and a method for producing the same. This purpose is, in mass%, substantially: A1: 4% to 5%, V: 2.5% to 3.5%, Fe: 1.5% to 2.5%, Mo: 1.5% or more, 2.5% or less, balance: Ti, volume fraction of proeutectoid phase is 10% or more and 90% or less, average grain size of proeutectoid α phase is 10m or less, rolling This is achieved by α + / 3 type titanium alloy rods in which the aspect ratio of the grains of the proeutectoid phase in a cross section parallel to the direction is 4 or less.

The a + jS type titanium alloy bar has a process of hot rolling the titanium alloy of the above component so that the surface temperature is always below the β transformation point. It can be manufactured by a method. Brief description of the drawings- FIG. 1 is a diagram showing a typical method of manufacturing a bar.

FIG. 2 is a diagram showing a bar rolling process.

FIG. 3 is a diagram showing the relationship between the temperature of the material to be rolled and the rolling time in bar rolling of the Ti-6A4V alloy and the Ti-44.5Al-3V-2Fe-2Mo alloy.

FIG. 4 is a diagram showing the relationship between the average crystal grain size of the primary 0; phase and the total elongation by a high-temperature tensile test.

Figure 5 is a diagram showing a relationship between fatigue strength at 10 ⁸ times in the fatigue test and the average crystal grain size of Hatsu析Hi phase.

FIG. 6 is a diagram showing changes over time in the temperature of the surface layer portion and the central portion.

FIG. 7 is a diagram showing the relationship between the cross-sectional area of the material to be rolled and the temperature difference between the surface portion and the central portion. BEST MODE FOR CARRYING OUT THE INVENTION First, the present inventors studied what kind of fiber of α + type titanium alloy rod should be made to obtain excellent ductility, fatigue properties and workability. As a result, the following became clear.

+ / 3 type titanium alloys consist of proeutectoid a phase and transformation i3 phase, but have an HCP structure with few slip systems.The volume fraction of a phase becomes extremely large, and transformation with acicular α; phase inside. Since the workability and ductility decrease even when the volume fraction of the β phase is extremely large, the volume fraction of the proeutectoid phase should be 10% or more and 90% or less. If the volume fractions of the sphing phase and the] 3 phase are equal or close to each other during heating in hot working, the workability is further improved, and the volume fraction of the primary a phase is 50% or more. % Or less is desirable.

Figure 4 shows the relationship between the average crystal grain size of the proeutectoid phase and the total elongation by a high-temperature tensile test. If the average crystal grain size of the proeutectoid phase exceeds 10 m, the total elongation in the high-temperature tensile test decreases sharply. In addition, the workability decreases accordingly.

Figure 5 shows the relationship between the fatigue strength at 10 ⁸ times in the fatigue test and the average crystal grain size of Hatsu析Hi phase. If the average grain size of the proeutectoid phase exceeds 10 m, the fatigue strength decreases. Further, when the average crystal grain size of the primary phase is smaller than 6 m, higher fatigue strength can be obtained.

When a bar is forged, rough surface is generated on a free deformation surface not in contact with the mold due to the shape of the crystal grains, that is, the aspect ratio of the crystal grains. Generally, in the case of a rod, the crystal grains tend to spread in the rolling direction. In particular, in the case of upset forging, the expanded structure appears on the side surface of the bar that becomes the free-deformation surface.To prevent roughening of the product after forging, the aspect ratio during forging must be large. Specifically, the aspect ratio of the crystal grains of the primary e-phase a in the cross section parallel to the rolling direction of the rod needs to be 4 or less so as not to be excessive.

From the above, the volume fraction of primary a-phase a is 10% or more and 90% or less, more preferably 50% or more and 80% or less, and the average crystal grain size of the primary a-phase a is 10 m or less, more preferably 6 or less. If the aspect ratio of the crystal grains of the proeutectoid a phase in the cross section parallel to the rolling direction is 4 or less, a high-strength titanium alloy bar excellent in ductility, fatigue properties and workability can be obtained.

The a + 3 type titanium alloy bar material having such a fiber is substantially in mass%, A1: 4% to 5%, V: 2.5 to 3.5%, Fe: 1.5 % Or more and 2.5% or less, Mo: 1.5% or more and 2.5% or less, and the balance: It must be a component composed of Ti. The reasons for limiting the content of each element will be described below.

A1: It is an essential element for stabilizing the phase and also contributes to high strength. If it is less than 4, high strength is not sufficiently achieved, and if it exceeds 5%, ductility deteriorates.

V:] An element that stabilizes the three phases and also contributes to high strength. If it is less than 2.5%, high strength is not sufficiently achieved, and) the three phases are not stable. If it exceeds 3.5%, the transformation temperature range is reduced due to the decrease of the 0 transformation point, and the cost is increased. Invite.

Mo: An element that stabilizes the / 3 phase and also contributes to high-strength siding. If it is less than 1.5%, the high strength steel is not sufficiently achieved, and the jS phase is not stable. If it exceeds 2.5%, the processing temperature range becomes narrow due to the decrease in β transformation point and the cost increases. Invite.

Fe: An element that stabilizes the / 3 phase and also contributes to high strength. In addition, it has the effect of improving the workability with a high diffusion rate, but if it is less than 1.5%, it is not sufficient And the J3 phase is not stable, and excellent workability cannot be obtained. If it exceeds 2.5%, the / 3 transformation point will decrease and the processing temperature range will be narrowed, and the characteristics will also deteriorate due to segregation.

The α + 3 type titanium alloy bar of the present invention is obtained by adjusting the rolling conditions such as heating temperature, rolling temperature range, rolling reduction, rolling speed, inter-pass time, etc. It can be manufactured by hot rolling so that the surface temperature is always below the (3) transformation point while suppressing the temperature rise due to heat generation. For example, the / 3 transformation point is Τ3. (: << +] Type 3 tidan alloy is heated so that the surface temperature is in the range of (Τβ-150) ° C or more and ° C or less, and the heated type titanium alloy is being rolled. When the surface temperature of the material to be rolled is (T) S-300) ° C or more (Cβ-50) ° C or less, the finishing surface temperature is (T / 3-300) ° C or more (Τ-100) This is a method having a step of hot rolling so that the temperature falls within the range of ° C or lower.

Here, the reason for heating the surface temperature before rolling to (T / 3-150) ° C or more and Ίβ ° C or less is that if it is less than (T / 3-150), This is because the temperature drop increases, causing cracking sensitivity and deformation resistance to increase.If the temperature exceeds Τβ ° C, the structure of the rolled material becomes β mainly composed of needles, and ductility and workability deteriorate. . The reason why the surface temperature of the material to be rolled during rolling is (圧延) 3-300) ° C or more and (Τ-50) ° C or less is that (Ti3-300) ° C or less This is because the workability is reduced and problems such as cracks occur. If the temperature exceeds (Ίβ-50) ° C, the temperature rise due to the heat generated during the process causes coarsening of crystal grains and formation of a needle-like structure. Furthermore, the reason why the finished surface temperature, which is the surface temperature immediately after the rolled material has completed the final rolling pass, is in the range of -300) ° C or more and (T 3-100) ° C or less is αβ-300) ° c If it is less than the above, cracking sensitivity and deformation resistance will increase, and if it exceeds (Tjs-loo) ° c, crystal grains will be coarse.

Although hot rolling is performed in a plurality of rolling passes, it is preferable to reduce the rolling reduction per rolling pass to 40% or less in order to prevent a temperature rise due to heat generated during processing.

When hot rolling is performed using a reverse type rolling mill, the rolling speed is preferably set to 6 m / sec or less in order to prevent a temperature rise due to heat generated during processing. In addition, when using a tandem type rolling mill, it is preferable to set the rolling length ¾ ^ to 1.5 mIsec or less. After each rolling pass, the material to be rolled is cooled from the surface. Therefore, even if the temperature rises due to the heat generated during processing, the temperature of the surface layer of the material to be rolled will decrease to some extent by the next rolling pass. However, as shown in Fig. 6, when the diameter of the material to be rolled is large (106 diameters), the temperature drop at the center of the material to be rolled is small, so the surface layer and the center of the material to be rolled are small. A large temperature difference appears. If the temperature drop in the central part is small, it undergoes the next rolling pass before the temperature in the central part falls, and the temperature rises further due to the heat generated during processing. If this phenomenon continues, the center will be rolled at a higher temperature than the initial temperature. For this reason, when the diameter of the material to be rolled is large, it is necessary to cool down the central part with sufficient time between rolling passes.

Accordingly, the present inventors have studied in detail the temperature difference between the surface portion and the central portion, as shown in FIG. 7, the temperature difference in the cross-sectional area of the rolling direction and perpendicular direction of the rolled material is 3500 mm ² or more When the material to be rolled having such a large cross-sectional area is rolled so that the cross-sectional area becomes S-picture ² , the time to start the next rolling is 0.167XS ^1/2 sec or more. Has been found to be preferable in that a temperature difference can be reduced and a rod having uniform characteristics is produced.

In the production method of the present invention, since rolling is performed so that the surface temperature of the material to be rolled is always 13 or less, the surface temperature of the material to be rolled may vary depending on the time between rolling passes and the diameter of the material to be rolled. During rolling, the temperature may deviate from the appropriate rolling temperature range to a lower temperature side. In such a case, it is also possible to reheat by high frequency heating equipment. · Example 1

Rolled material of 125 thigh angle was cut out from titanium alloys AO1 (within the scope of the present invention) and A02 (outside the scope of the present invention) of the chemical composition shown in Table 1 and A02 (within the scope of the present invention). Under the indicated rolling conditions B01-B18, rods having a diameter of 0 strokes or 50 bars were manufactured. The time between rolling passes in Table 2 is 〇 when the time between rolling passes is 0.167 XS ^1/2 sec or more in all rolling passes and X when not. Indicated by Also, Table 3-Table 20 show the cross-sectional area S, rolling reduction, 0.167 XS ^1/2 time between rolling passes, surface temperature and rolled body of the material to be rolled in each rolling pass under each rolling condition. In the rolling equipment column in the table, R represents a reverse rolling mill, and T represents a tandem rolling mill. Tensile tests were performed on the manufactured rods after annealing at 700 ° C or more and 720 ° C or less, and the yield strength (0.2 ¾PS), tensile strength (UTS), extension (El), and drawing (RA) were measured. In addition, a smoothness test (condition: Kt = 1) and a notch test (condition: Kt = 3) were performed to measure the fatigue strength. Furthermore, in order to examine the fine fibers, the microstructure at the center of the rod and at the 1/4 position (1 / 4D) of the diameter was observed, and the crystal grain size of the primary α phase, its volume fraction and rolling direction Next, the aspect ratio of the crystal grains in the parallel section was measured.

Table 21 shows the results. The absence of the crystal grain size in the microstructures in the table means that the site consisted only of the β-structure mainly composed of acicular a, and no equiaxed pro-eutectoid α-phase could be observed.

When the heating temperature of the surface was lower than (T j3 -150) ° C, the surface temperature of the material to be rolled was too low, and the rolling load was too high to roll. If the heating temperature is higher than T) S ° C, the surface temperature of the rolled material is too high even if the time between rolling passes is within the range of the present invention, as in the rolling conditions B02 and B11. The heat generated causes the surface temperature of the material to be rolled to exceed Tj6, and the sag at the center becomes jS fibers mainly composed of needle-like α, deteriorating ductility and fatigue properties. If the finished surface temperature is lower than (T) 3-300) ° C, the temperature of the material to be rolled is too low, the workability is reduced, and cracks occur during rolling. On the other hand, when the surface temperature is higher than (T) 3-100), as in the rolling conditions # 04, # 05 and # 07, the microstructure cannot be refined and the ductility and fatigue properties deteriorate.

If the surface temperature of the material to be rolled is lower than (T j8-300) ° C, the surface temperature of the material to be rolled is too low and cracks occur during rolling. When the surface temperature of the material to be rolled is higher than (Ί β-50) ° C, the center of the roll and the 1 / 4D yarn 1¾ are stitched as in the rolling conditions B02-B05, B07 and B11. It becomes a β-yarn mainly composed of a shape and has poor ductility and fatigue properties.

When the rolling reduction in one rolling pass exceeded 40%, the heat generated during processing increased, and the temperature of the material to be rolled exceeded Τβ, making it impossible to achieve finer ∞.

When the rolling speed exceeds 6 m / sec using a reverse type rolling mill as in rolling condition Β, and when the tandem type rolling mill as in rolling condition B15, the rolling ¾! Exceeds 1.5 m / sec. As a result, the heat generated during processing increased, the surface temperature of the material to be rolled exceeded TjS, and the structure could not be miniaturized. When the time between rolling passes is out of the range of the present invention, the surface temperature of the material to be rolled rises due to the heat generated from the processing, and the temperature of the material to be rolled exceeds T) 8. Could not be achieved.

In the bar manufactured using A01 whose chemical composition is within the range of the present invention and under the rolling conditions of BOK B06, B08, B09, B16, B17 and B18, a uniform fine yarn having a crystal grain size of proeutectoid phase of 10 or less. Are observed, and excellent ductility and fatigue properties are obtained. These have more excellent ductility and fatigue properties with elongation of 15% or more, drawing of 40% or more, smooth fatigue strength of 500 MPa or more, and notch (Kt = 3) fatigue strength of 200 MPa. Furthermore, as in rolling conditions B01, B06, B08 and B09, α + type titanium alloys in which the volume fraction of proeutectoid α phase is 50% or more and 80% or less and the average crystal grain size of proeutectoid phase is 6 m or less The rods provide even better ductility and fatigue properties with an elongation of at least 20%, a drawing of at least 50, a smooth fatigue strength of at least 550 MPa and a notched (Kt = 3) fatigue strength of 200 MPa. On the other hand, in the bar manufactured using rolling conditions B10 and B12 using A02 whose chemical composition is out of the range of the present invention, since the rolling conditions were within the range of the present invention, the heat generation during processing was suppressed. Since the particle size exceeds 10, sufficient ductility and fatigue strength cannot be obtained. Example 2

A cylindrical test piece of Φ8 thigh × 12 thigh was collected from the radial center of the bar manufactured under the rolling conditions B0-B18 in Example 1 and heated to 800 ° C., compressed by 70%, and compressed. The hot forgeability was evaluated by examining the surface for cracks and rough surfaces.

The results are shown in Table 21.

Bars manufactured under rolling conditions B01, B06, B08, B09, B16, ΒΠ, and B18 in which the microfilament falls within the scope of the present invention did not cause cracking or roughening, and obtained good hot forgeability. . On the other hand, rods manufactured under rolling conditions B10 and B12 in which the crystal grain size of the pro-eutectoid α phase exceeded 10 m did not crack, but roughened the surface. In addition, both the cracks and the rough surface occurred in the bars manufactured under the rolling conditions Β02, Β03, Β04, Β05, Β07, Bll, Β14, and B15 in which the center and the 1 / 4D part consisted of only / 3 phase. . Further, the crystal grain size and the volume fraction of the pro-eutectoid α phase are within the range of the present invention, but the aspect ratio of the crystal grains in a cross section parallel to the rolling direction is determined. With rolling condition B13 exceeding 4, the surface roughness still occurred _c

table 1

The unit is mass%

Table 2

Underlined values indicate that they are outside the scope of the present invention.

'tfc extension: ■ ■ Number of passes Cross-sectional area Reduction rate 0.167V S Time between strips Rolling speed

(.mm) (%) sec) sec) vm / sec) rc)

15625

1 16.8 25 2.7 790 R

13000 19.0

2 15.4 25 2.7 796 R

1 1000 17.5

3 13.6 25 2.7 801 R

9500 16.3

4 15.8 25 2.7 803 R

8000 14.9

5 18.8 25 2.7 81 1 R

6500 13.5

6 20.0 25 2.7 801 R

5200 12.0

7 20.2 25 2.7 779

4150 10.8

8 20.5 25 2.7 761 R

3300 9.6

g 25.8 25 2.7 738 R

2450 8.3

10 24.5 25 2.7 719 R

1850 7.2

1 1 21.6 5 .0-35h ..: 721 T

1450 6.4

12 20.7 5 0,466 732 T

1150 5.7

13 21.7 5 Q.581 739 T

900 5.0

14 22.2 5 0.733 745 T

700 4.4

15 21.4 5 0.871 741 T

550 3.9

16 23.6 5 0.982 730 T

420 3.4

17 23.8 1.125 714 τ

320

-tfciik condition: BtW

Lotus number cross section l ± f 毕 0.167 S 1, f * days between strips, tt roll: 1≤ degree rolling

(mm (%) (sec) (sec) (m / sec) C)

15625

1 16.8 25 2.7 890 R

13000 19.0

2 15.4 25 2.7 894 R

11000 17.5

3 13.6 25 2.7 899 R

9500 16.3

4 15.8 25 2.7 906 R

8000 14.9

5 18.8 25 2.7 911 R

6500 13.5

6 20.0 25 2.7 902 R

5200 12.0

7 20.2 25 2.7 889 R

4150 10.8

8 20.5 25 2.7 881 R

3300 9.6

9 25.8 25 2.7 867 R

2450 8.3

10 24.5 25. 2.7; 860 R

1850 7.2

1 1 21.6 5.0; 350 852

1450 6.4

12 20.75:, 0.466.839 T

1150 5.7

13 21.7 5 .0.5 & 1 830 T

900 5.0

14 22.2 5 o,? 3a 820 T

700 4.4

15 21.4 5 0.871; ■ 803 T

550 3.9

16 23.6 5 .0.982 784 T

420 3.4

17 23.8 1.t25 764 T

320

W

18 Table 9

Sialla

OlLlO / ZOdT / lDd

One fcv: l2 OAV

o

Table 21

0.2%

PS UTS El RA Fatigue strength Microstructure Forging properties Rolling conditions Flat;-Bone test Notch test 1 / 4D center Cracked rough skin Remarks Grain size fraction To ass "Cut grain size to fraction" Occurrence Occurrence

(MPa) (MPa) (¾) () (Kt = 1) (Kt = 3) (Aim) (%) ratio (U m) (%) ratio

B01 931 1030 20.4 51.9 565 230 2.5 66 1.5 2.7 66 1.8 None None Example of the present invention

B02 885 1009 3.5 12.3 350 120 3.7 59 4.1 —— —— —— Peri fc Comparative Example

B03 879 1010 4.1 13.5 355 125 3.4 58. 4.4 —— —— Peri feu Comparative example

B04 881 101 1 4.1 1 1.6 365 1 15 —— —— '—— —— .——,

B05 874 1014 3.8 1 1.1 360 100 3.8 29; 4.2 —— —— ~-.

B06 921 1020 20.0 50.8 560 5.4 60 2.1 5.8 68 2.2

B07 887 1005 3.7 12.1 5.9 31 4.3 --- C U J Comparative example

B08 930 1030 20.5 52.3 ark 1.7 67 1.9 1.9 69 2.3

B09 929 1027 20.1 50.1 u in 4.1 4.1 1.7 1.7 4.9 64 2.1

B10 91 1 1019 14.8 43.3 480 185 1 1.4 89 2.8 12.0 88 3.2 No Yes Comparative example

B1 1 863 1012 3.6 9.8 230 95 13.2 85 <2: 9 Yes Yes Comparative example

B12 902 101 1 13.8 42.1 440 175 14.5 80 3.0 15.0 89 3.4 No Yes Comparative example

B13 899 987 12.1 38.2 395 155 5.5 85 4.2 5.8 87 4.5 None Comparative example

B14 884 971 13.7 34.5 345 1 15, :: 5.2 84: 4.2 Yes-Yes Comparative example

B15 .894 955 1 1.9 33.3 340 120 5.3 81 .4.3 Yes Yes it comparative example

B16 910 1014 17.4 40.1 505 205, 6.2 63 2.5 6.4 60 2.7 None None Takaaki Moto

B1 7 914 1021 18.3 42.3 510 205 5.8 64 2.7 6.3 61 2.9 None None Example of the present invention

B18 902 1008 15.6 40.1 500 200 6.5 60 3.1 6.6 60 3.3 None None Example of the present invention

Claims

The scope of the claims

1. Substantially, mass rc, A1: 4 to 5 mm, V: 2.5 to 3.5 mm, Fe: 1.5 to 2.5, Mo: 1.5 to 2.5, balance: Ti The volume fraction of the precipitated α-phase is 10 to 90%, the average crystal grain size of the primary α-phase is 10 / m or less, and the phase of the primary α-phase crystal grains in a cross section parallel to the rolling direction. "+) 3 type titanium alloy bar with cut ratio of 4 or less.

2. The α + -type titanium alloy rod according to claim 1, wherein the volume fraction of the pro-eutectoid phase is not less than 50 ° and not more than 80 °, and the average crystal grain size of the pro-eutect α phase is not more than 6 tm.

3. Substantially, by mass A, A1: 4 to 5 ¾, V: 2.5 to 3.5 ¾, Fe: 1.5 to 2.5 、, Mo: 1.5 to 2.5 、, balance: Ti + A method for producing an α + 0 type titanium alloy bar, comprising a step of hot rolling a type 3 titanium alloy so that its surface temperature is always 13 or lower.

4. a step of heating an α + β type titanium alloy having a β transformation point of ^ β ^ so that the surface temperature is -150) and 上 is in the following range:

When the surface temperature of the material to be rolled during the rolling of the heated α + -type titanium alloy is in the range of (Τ / 3-300) or more and (Τ3-50) or less, the surface temperature immediately after the final rolling pass is completed. Hot-rolling such that a given surface temperature is above (Τ-300) and above (Τ / 3-100) and below

3. The method for producing an α +] 3 type titanium alloy rod according to claim 3, comprising:

5. The method for producing an α + / 3 type titanium alloy rod according to claim 4, wherein the reduction ratio per rolling pass is 40 ° or less in the hot rolling step.

6. When hot rolling is performed with a reverse type rolling mill, make sure that rolling i ^ is 6 m / sec or less. A method for producing an α + iS type titanium alloy bar according to claim 4.

7. The method of claim 4 wherein the rolling speed is 1.5 m / sec or less when hot rolling is performed using a tandem rolling mill.

8. In the hot rolling process, when a material to be rolled having a cross-sectional area perpendicular to the rolling direction of 3500 mm ² or more is rolled so that the cross-sectional area becomes S bandage ² , the next rolling is started. 4. The method for producing a + / 3 type titanium alloy bar according to claim 4, wherein the time until the time is 0.167XS ^1/2 sec or more.

9. The method according to claim 4, wherein the material to be rolled is reheated during rolling in the hot rolling step.