CN118272697A

CN118272697A - Medium-strength impact-resistant titanium alloy with yield strength of 800MPa and cold-rolled tube preparation method thereof

Info

Publication number: CN118272697A
Application number: CN202211736428.3A
Authority: CN
Inventors: 孙继锋; 计波; 张春霞; 吴英彦
Original assignee: Baowu Teye Titanium Technology Co ltd
Current assignee: Baowu Teye Titanium Technology Co ltd
Priority date: 2022-12-31
Filing date: 2022-12-31
Publication date: 2024-07-02

Abstract

The invention belongs to the technical field of novel titanium alloy and pipe manufacturing, and particularly relates to a novel medium-strength impact-resistant titanium alloy with yield strength of 800MPa and a cold-rolled pipe manufacturing method thereof. The medium-strength impact-resistant titanium alloy with the yield strength of 800MPa comprises the following chemical components in percentage by weight: 13.5 to 4.5 percent of A, 2 to 3 percent of V, 1 to 2 percent of Fe, 1 to 1.5 percent of Mo, 0.08 to 0.15 percent of O, and the balance of Ti and unavoidable impurity elements. According to the titanium alloy, the titanium alloy seamless tube is prepared through the optimized tube blank preparation process, the combination of oblique rolling perforation and cold rolling; the pipe is subjected to simple annealing treatment, the yield strength is not lower than 800MPa, the elongation is not lower than 12%, and the impact energy is not lower than 50J.

Description

Medium-strength impact-resistant titanium alloy with yield strength of 800MPa and cold-rolled tube preparation method thereof

Technical Field

The invention belongs to the technical field of novel titanium alloy and pipe manufacturing, and particularly relates to a novel medium-strength impact-resistant titanium alloy with yield strength of 800MPa and a cold-rolled pipe manufacturing method thereof.

Background

The titanium alloy has the advantages of small density, high specific strength, excellent impact resistance, strong seawater corrosion resistance, good cold processing performance and the like, and becomes the preferred material for manufacturing marine engineering pipelines. Alpha-titanium alloys, such as pure titanium (brands: TA1, TA 2), TA16, TA18, etc., are used primarily for low pressure fluid delivery lines. Alpha+beta type alloys, such as TC4 (Ti-6A 1-4V), TC23 (Ti-6 Al-4V-Ru), ti80 (Ti-6A 1-3Nb-2Zr-1 Mo) alloys, can be used to prepare drill pipes, oil casings and part of risers for marine exploration with higher strength requirements. Wherein the titanium alloy with the yield strength of 800MPa is mainly TC4 and Ti80. Based on the design concept of 'first leakage and then breaking', the requirement of impact performance is also provided besides the strict strength requirement on the pipe material. TC4 titanium alloy has advantages such as intensity is high, corrosion resistance is good, but its cold workability is poor, is difficult to prepare the heavy-calibre seamless pipe through cold rolling mode to its impact toughness is lower, and when its yield strength is at 800MPa grade, room temperature U type impact energy often only about 40J has prevented the application as the pipe aspect. Ti80 has moderate room temperature strength, good toughness and welding performance, the impact energy is more than 50J, but the alloy contains 3 percent of Nb, and the raw material cost is high.

At present, the processing technology of low-strength and low-alloyed titanium and titanium alloy seamless tubes is mature, and a cold rolling vacuum annealing process is adopted. The forming of the medium-high strength titanium alloy seamless pipe is difficult, and mainly adopts the traditional preparation process of the titanium alloy pipe, comprising the steps of oblique rolling perforation, cold rolling, oblique rolling perforation, warm (hot) rolling, extrusion, cold rolling, extrusion, warm (hot) rolling, boring and radial forging. Wherein, the cost of extrusion, warm rolling and radial forging is high and the surface quality is poor. By adopting a cold rolling mode, the pipe with good surface quality and good dimensional accuracy can be prepared, but for the middle-high strength titanium alloy, the cold processing performance is poor, and the problems of rolling stability, rolling surface cracking and the like exist in the cold rolling forming process of the pipe. In addition, the existing titanium alloy seamless pipe rod blank is generally required to be forged by multiple fires, the production period is long, and the cost is high.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a titanium alloy with medium strength and high impact toughness for ocean engineering and oil and gas fields, wherein the alloy has the yield strength reaching 800MPa, the elongation not lower than 12 percent and the impact energy not lower than 50J. The alloy has excellent hot processing and cold-hot processing properties, can be prepared into a bar blank through a simplified forging process, and can be used for preparing a large-caliber titanium alloy seamless pipe with high surface quality through a combined process of oblique rolling perforation and cold rolling, so that the process flow is simple, and the processing cost is greatly reduced compared with that of a traditional titanium alloy pipe.

The technical scheme of the invention is as follows:

The medium-strength high-toughness titanium alloy with yield strength of 800MPa for ocean and oil gas comprises the following chemical components in percentage by weight: 13.5 to 4.5 percent of A, 2 to 3 percent of V, 1 to 2 percent of Fe, 1 to 1.5 percent of Mo, 0.08 to 0.15 percent of O, and the balance of Ti and unavoidable impurity elements.

Further, the A1 equivalent range of the alloy satisfies: 5wt. < [ Al ] eq <5.5wt.%, while Mo equivalent satisfies: 5wt. < [ Mo ] eq <6wt.%.

According to the invention, the yield strength of the marine ship is 800MPa, and the total content of impurity elements (C, N, H and other trace elements) in the titanium alloy is less than 0.05wt.%.

The invention also provides a preparation process of the middle-strength high-toughness titanium alloy with the yield strength of 800MPa for the marine ship, which mainly comprises the following steps: electrode pressing and smelting, ingot cogging, tube blank preparation, finishing, oblique rolling perforation, cold rolling, heat treatment and finished product production.

(1) Electrode pressing and smelting: electrode pressing is completed on a hydraulic press according to the chemical components of the titanium alloy, and cast ingots with uniform components are prepared by secondary and tertiary vacuum consumable smelting of the electrode;

(2) Cogging ingot casting: cogging the cast ingot by adopting a high-low process, firstly upsetting and pulling the cast ingot for 2-3 times at 50-150 ℃ above a phase transition point, controlling the forging ratio of each time to be 1.5-2.0, and adopting air cooling after forging; then forging by upsetting and pulling for 1 time at 30-50 ℃ below the transformation point, wherein the forging ratio is controlled between 1.5 and 2.5, directly returning to a furnace for recrystallization heat treatment after forging, keeping the heat treatment heating temperature at 30-50 ℃ above the beta transformation temperature, discharging after heat preservation for proper time, then forging by upsetting and pulling for 1 time, wherein the forging ratio is controlled between 1.5 and 2.5, and adopting air cooling after forging;

(3) Preparing a tube blank: forging the forging stock obtained in the step (2) at the temperature of 40-60 ℃ below the alloy transformation point for 2-3 times by upsetting and drawing, wherein the forging ratio is controlled between 1.8-2.5, and air cooling is adopted after upsetting and drawing; then performing drawing forging for 1 fire time, wherein the heating temperature is 40-60 ℃ below the beta transformation temperature, the forging ratio is 1.8-2.0, and air cooling is adopted after drawing. Depending on the size of the final tube blank, the forged bar stock may also be subjected to 1-pass forging at 40-60 ℃ below the beta transus temperature to produce a tube blank.

(4) Performing oblique rolling perforation on the rod blank obtained in the step (3), and then sequentially performing inner and outer surface defect trimming, acid washing and annealing treatment to obtain a perforated tube blank; the temperature of the oblique rolling perforation blank is 20-40 ℃ above the beta transformation temperature, and the deformation is 60-70%.

(5) Performing cold rolling treatment on the perforated pipe blank obtained in the step (4) to obtain a cold-rolled pipe blank; cold rolling for 2-3 times, wherein the pass deformation is 20-25%;

(6) Sequentially removing defects on the inner surface and the outer surface, pickling, heat treatment and straightening the cold-rolled tube blank obtained in the step (5) to obtain a titanium alloy tube;

Further, in the above forging process blank heating process, the holding time is calculated as the minimum cross-sectional dimension of the blank x 0.8-1 min/mm.

Further, in the step (6), the pipe is annealed, the heat treatment temperature is 850-900 ℃, the heat treatment time is 1-2 hours, and the pipe is air-cooled.

The yield strength of the annealed titanium alloy pipe is not lower than 800MPa, the elongation is not lower than 12%, and the impact energy is not lower than 50J.

The invention provides a titanium alloy and pipe preparation process design principle as follows:

(1) The invention adopts the alloy design of cheap elements to control the cost of the titanium alloy;

the titanium alloy is designed by adopting low-cost elements such as Fe and the like to partially replace expensive elements such as V and the like, and the raw material cost is reduced on the premise of keeping the alloy performance.

(2) By controlling the components of the titanium alloy, the titanium alloy has higher strength and toughness, excellent hot processing performance and can be cold-rolled into a pipe.

The element A1 is the most widely added alloy element in the titanium alloy, belongs to a displacement type alpha phase stabilizing element, has a solid solution strengthening effect on alloy, and increases the room temperature tensile strength by about 50MPa when 1 percent of Al is added. The content of the A1 element is too small, and the strengthening effect of the alloy is not obvious. The content of the A1 element is too high, and an ordered phase Ti3Al (alpha 2) super-structural phase appears in the structure, so that the plasticity and impact toughness of the alloy are obviously reduced, and the workability of the alloy is reduced, so that the alloy cannot be used for preparing pipes; the novel alloy is designed by adopting low aluminum equivalent weight ([ A1] eq), wherein the calculation formula of [ Al ] eq is [ Al ] eq=Al wt. +10+O wt.% (5 wt.% < [ Al ] eq <5.5 wt.%).

By adding a certain amount of beta-phase stabilizing element, a stable beta-phase can be obtained at room temperature, the strengthening effect of which can be related to Mo equivalent ([ Mo ] eq) with the calculated formula [ Mo ] eq = Mo wt. + vwt./1.5+fe wt./0.5. When [ Mo ] eq is higher, the solid solution strengthening effect is good; meanwhile, the total amount of beta phase stabilizing elements is increased, the range of an alloy two-phase region is enlarged, the proportion of beta phase (body-centered cubic structure, bcc) is high when the temperature of the alloy two-phase region is low, the forging deformability is high, and defects such as deformation cracks and the like are not easy to occur. However, when [ Mo ] eq exceeds 6, the welding process performance will be significantly reduced. In addition, the beta phase in the titanium alloy has a body-centered cubic bcc structure, and the plasticity and impact toughness of the titanium alloy are obviously reduced along with the reduction of temperature, so that the content of the beta phase stabilizing element in the alloy is strictly controlled in order to ensure the low-temperature toughness of the alloy. Based on the design principle, the Mo equivalent in the novel alloy meets the following conditions: 5wt. < [ Mo ] eq <6wt.%. Mo, V and low cost Fe are selected for specific additive element selection. The diffusion speed of Mo element in the titanium alloy is relatively slow, the effect of fine grain strengthening can be achieved, brittle intermetallic compounds are not easy to form, and therefore the strength of the titanium alloy is greatly improved. V belongs to one of few alloy elements with the same crystal type beta phase stability, not only can strength be improved, but also can inhibit the formation of a sequential phase Ti3Al (alpha 2) super-structure phase, and alloy embrittlement is avoided in the long-time use process. Fe is the strongest slow eutectoid beta stable element, and has the strengthening effect in all beta stable elements, and the strengthening effect on the solid solution of the titanium alloy is most obvious, so that the strength of the titanium alloy can be obviously improved by adding a proper amount of Fe element. Meanwhile, the price of Fe is cheaper than elements such as V, so that the production cost of the titanium alloy can be reduced to a certain extent. However, when Fe in the titanium alloy exceeds a certain content, a "beta spot" is easily formed, and the alloy performance is significantly adversely affected, so that the content of beta in the titanium alloy of the present invention is strictly controlled, and the content thereof is controlled to be in the range of 1 to 2wt.%.

The titanium alloy product also contains impurity elements such as oxygen, nitrogen, carbon, hydrogen and the like, which belong to interstitial elements, can be in solid solution in alpha phase or beta phase, can exist in a compound form, and has a strengthening effect decreasing in the order of nitrogen, oxygen and carbon. The hardness of titanium is sensitive to interstitial impurity elements, and the higher the impurity content, the higher the hardness of titanium. Wherein the influence of hydrogen on the properties of pure titanium and titanium alloys is to cause hydrogen embrittlement. The strength of nitrogen, oxygen and carbon can be improved, and the plasticity is drastically reduced. Therefore, the contents of oxygen, nitrogen, carbon, and hydrogen are specified in designing the titanium alloy composition. The oxygen-doped titanium alloy is an important strengthening element, and on the premise of ensuring plasticity and toughness, the oxygen content is controlled to be 0.08-0.15% by adopting a low-clearance oxygen element design thought, and the oxygen content of the traditional TC4 alloy is generally controlled to be below 0.2%. The total content of other unavoidable impurity elements (C, N, H and other trace elements) is less than 0.05wt.%.

(3) The invention combines the process characteristics of the oblique rolling perforation, optimizes the conventional forging and radial forging deformation process for preparing the tube blank, reduces multiple deformation procedures in the tube blank preparation process, obtains the blank with a two-phase region structure with fine beta grains, and has the advantages of recrystalization refinement of the beta grains in the heating and rolling process of the single-phase region of the oblique rolling perforation, good plasticity of the blank in the subsequent cold rolling deformation process, combination of the characteristics of alloy, difficult cracking in the tube cold rolling process, high surface quality, high precision and high yield.

The cross-rolling perforation is one of the main deformation processes of the large-diameter titanium alloy hot-rolled seamless pipe. In the process of oblique rolling perforation, the deformation condition is bad, and the product is extremely easy to generate defects such as outward folding, inward folding, inner and outer surface cracks and the like; meanwhile, the optimal deformation temperature interval of the titanium alloy is narrow, the deformation amount is large in the process of oblique rolling perforation, and the material enters a temperature interval in which the plasticity is sharply reduced due to the temperature rise of the thermomechanical effect (generally reaching about 100 ℃), so that the selection of the heating temperature of the oblique rolling perforation blank is extremely important. In order to ensure that the rolling process is not blocked and prevent the blank from growing seriously, the invention selects 20-40 ℃ above the phase transition point to carry out oblique rolling perforation, so as to obtain a uniform structure composed of a certain number of fine basket and beta-converting matrix, and prepares excellent structure form for the subsequent cold rolling process.

In the cold rolling process, the single-pass deformation is unsuitable to be too large, cracks or cracks are easy to occur when the single-pass deformation is too large, and the rolling deformation effect cannot be achieved when the single-pass deformation is too small.

According to the titanium alloy, the titanium alloy seamless tube is prepared through the optimized tube blank preparation process, the combination of oblique rolling perforation and cold rolling; the pipe is subjected to simple annealing treatment, the yield strength is not lower than 800MPa, the elongation is not lower than 12%, and the impact energy is not lower than 50J.

The beneficial technical effect of this patent:

1. The invention provides a medium-strength impact-resistant titanium alloy with yield strength of 800MPa, wherein the yield strength is not lower than 800MPa, the elongation is not lower than 12%, and the impact energy is not lower than 50J. The alloy has better hot working and cold working performance than TC4, and the impact toughness of the alloy is higher than that of TC 4; compared with Ti80, the alloy does not contain noble Nb and has lower raw material cost.

2. The medium-strength high-impact-toughness titanium alloy has the advantages of simple components, low cost, difficult segregation in smelting, better deformability in the hot working deformation process, difficult occurrence of defects such as cracks and the like, and can simplify the manufacturing and forging process of the tube blank; the method has excellent cold workability, can prepare the pipe through oblique rolling perforation and cold rolling, has high yield and simple process flow, reduces the processing cost, and greatly reduces the processing cost compared with the traditional titanium alloy pipe.

Drawings

Fig. 1 shows a pipe with a gauge Φ89×6.5mmobtained in example 1, with a length greater than 10 meters.

FIG. 2 shows the microstructure of the tube made from alloy example #1 after 900 ℃/1 hour annealing.

Detailed Description

Specific embodiments of the present invention will be described in further detail below with reference to examples 1 to 3:

(1) Ingot smelting

Raw materials such as commercially available titanium sponge, aluminum vanadium, aluminum wire, aluminum molybdenum, aluminum iron and the like are prepared into electrode blocks according to the component proportions of table 1, the electrode blocks are welded into vacuum consumable electrodes in a vacuum plasma box, then three times of vacuum consumable smelting are carried out to prepare cast ingots, and the phase change points of the cast ingots are respectively 930, 920 and 925 ℃ measured by a metallographic method.

TABLE 1 actual measurement composition (wt%)

	C	V	Al	Fe	Mo	N	H	O
									Example #1	0.01	2.52	4.07	1.41	1.20	0.003	0.0006	0.10
Example #2	0.01	2.10	3.60	1.80	1.05	0.004	0.0006	0.14
									Example #3	0.01	2.90	4.40	1.10	1.45	0.004	0.0006	0.08

(2) Tube blank preparation

Cogging the cast ingot by adopting a high-low process, firstly upsetting and forging the cast ingot at 150 ℃ above a phase transition point, controlling the forging ratio between 1.5 and 2.0, then cooling to a single-phase region of 50 ℃ above the phase transition point, and forging the cast ingot, wherein the forging ratio is controlled between 1.5 and 2.0; then forging by upsetting and pulling for 2 times at 30-50 ℃ below the transformation point, wherein the forging ratio is controlled to be 1.5-2.5, directly returning to a furnace for recrystallization heat treatment after forging, keeping the heat treatment heating temperature to be 30-50 ℃ above the beta transformation temperature, discharging after heat preservation for proper time, then performing drawing for 1 time, controlling the forging ratio to be 1.5-2.0, and adopting air cooling after forging.

Drawing the forged blank after the cogging at the temperature of 40-60 ℃ below the alloy transformation point for 1 fire time, forging the forging ratio of 1.8-2.0, and air cooling after drawing to finally obtain a black bar with the size of phi 155mm, and turning the bar to remove surface defects. Preparing a phi 120mm tube blank by adopting diameter forging, wherein the heating temperature of the blank is 40-60 ℃ below the phase transition point, the temperature keeping time is 2.5 hours, carrying out hot straightening after the diameter forging, and turning the tube blank into phi 114mm.

(3) Phi 89 x 6.5mm tubular product produced by perforation and cold rolling trial production

The heating temperature is set at 940 ℃ in consideration of equipment safety, product molding and organization, and the initial temperature of perforation can reach 920 ℃ or above after certain heat preservation and temperature equalization. Adopting a 120 puncher to thermally punch a phi 114mm optical rod to a phi 115 mm intermediate blank, and then carrying out 2-pass cold rolling to obtain a phi 89 mm 6.5mm pipe; the cold rolling process of the pipe adopts a lubricant composed of special graphite and emulsion in proportion for lubrication, and the deformation of the cold rolling is 22%. In the cold rolling process of the pipe, vacuum annealing of the intermediate pipe is required in each pass, pickling treatment is carried out simultaneously, the surface quality of the pipe blank is overhauled, defects such as cracks are removed, and the subsequent cold rolling is ensured to be carried out smoothly. The intermediate annealing adopts a vacuum annealing furnace, the vacuum degree of the annealing furnace is not lower than 5 multiplied by 10 < -2 > Pa, the annealing temperature is 650-700 ℃, and the heat preservation time is 60-120 min.

(4) Finishing and treatment of finished pipe surfaces

And (3) annealing the obtained finished pipe to adjust the final microstructure of the titanium alloy so as to improve the comprehensive mechanical properties of the titanium alloy. If the annealing temperature is too low, the recrystallization is incomplete, and the stability of the subsequent use is affected; when the temperature is too high, crystal grains grow up, and the performance is further affected. Straightening the titanium alloy pipe subjected to heat treatment by adopting a straightener, wherein the straightness of the straightened pipe is less than or equal to 2mm/m; and (5) after straightening, cutting the head and removing the tail by using a pipe cutting machine. The final tube was prepared in a phi 89 x 6.5mm specification as shown in figure 1.

Table 2 shows the mechanical properties of the titanium alloy of invention example #1 under 4 heat treatment conditions, preferably with the heat treatment process: 850-900 ℃/1h, and air cooling to obtain better strong plastic matching. At this time, the tensile strength Rm is 978-1009 MPa, the yield strength Rp0.2 is 816-830 MPa, the elongation A is 13-14%, the area reduction Z is 47-52%, and the impact Ku2 is 56-71J. FIG. 2 shows the microstructure of the tube after heat preservation at 900 ℃ for 1 hour and cold annealing treatment, and the microstructure consists of primary a-phase and b-phase transformation structures.

TABLE 2 tensile Properties and impact Properties of titanium alloys under 4 Heat treatment regimes according to example #1 of the present invention

Table 3 shows the mechanical properties of the titanium alloy of invention example #2 under 4 heat treatment conditions, preferably with the heat treatment process: 850-900 ℃/1h, and air cooling to obtain better strong plastic matching. At this time, the tensile strength Rm is 990-1020 MPa, the yield strength Rp0.2 is 830-843 MPa, the elongation A is 13%, the area reduction Z is 44-48%, and the impact Ku2 is 55-67J.

TABLE 3 tensile Properties and impact Properties of titanium alloys under 4 Heat treatment regimes according to example #2 of the present invention

Table 4 shows the mechanical properties of titanium alloy #3 of the invention under 4 heat treatment conditions, preferably with the heat treatment process: 850-900 ℃/1h, and air cooling to obtain better strong plastic matching. At this time, the tensile strength Rm is 985 to 1011MPa, the yield strength Rp0.2 is 820 to 833MPa, the elongation A is 15 to 18%, the area reduction Z is 57 to 61%, and the impact Ku2 is 76 to 82J.

TABLE 4 tensile Properties and impact Properties of titanium alloys under 4 Heat treatment regimes according to example #3 of the present invention

Example 2 is based on example 1, in which the Al and V contents were reduced and the Fe and O contents were increased, and it was found from comparison of tables 2 and 3 that the strength of the alloy was increased (under the same heat treatment conditions) and the plasticity and toughness were decreased due to the increase in the solid solution strengthening effect of Fe and O elements. Example 3 is that the content of Al and V is improved and the content of Fe and O is reduced based on the content of example 1, and the strength of the alloy is not changed greatly and the plasticity and toughness are improved as shown in comparison of tables 2 and 4.

It will be appreciated by persons skilled in the art that the above embodiments are provided for illustration only and not as a definition of the limits of the invention, and that variations and modifications of the above described embodiments will fall within the scope of the appended claims.

Claims

1. The medium-strength impact-resistant titanium alloy with the yield strength of 800MPa is characterized by comprising the following chemical components in percentage by weight: 13.5 to 4.5 percent of A, 2 to 3 percent of V, 1 to 2 percent of Fe, 1 to 1.5 percent of Mo, 0.08 to 0.15 percent of O, and the balance of Ti and unavoidable impurity elements.

2. A medium strength impact resistant titanium alloy having a yield strength of 800MPa according to claim 1, wherein: the A1 equivalent range of the alloy satisfies the following conditions: 5wt. < [ Al ] eq <5.5wt.%, while Mo equivalent satisfies: 5wt. < [ Mo ] eq <6wt.%.

3. A medium strength impact resistant titanium alloy having a yield strength of 800MPa according to claim 1, wherein: the total content of impurity elements in the titanium alloy is less than 0.05wt.%.

4. A medium strength impact resistant titanium alloy having a yield strength of 800MPa according to claim 3, wherein: the impurity element is C, N, H trace elements.

5. A method for preparing a cold-rolled high impact titanium alloy with a yield strength of 800MPa according to any one of claims 1-4, characterized in that: the dominant process comprises the following steps: electrode pressing and smelting, ingot cogging, tube blank preparation, finishing, oblique rolling perforation, cold rolling, heat treatment and finished product production.

6. The method for manufacturing a cold-rolled tube of a strong impact-resistant titanium alloy with yield strength of 800MPa according to claim 5, wherein: the method comprises the following specific steps:

(3) Preparing a tube blank: forging the forging stock obtained in the step (2) at the temperature of 40-60 ℃ below the alloy transformation point for 2-3 times by upsetting and drawing, wherein the forging ratio is controlled between 1.8-2.5, and air cooling is adopted after upsetting and drawing; then performing drawing forging for 1 fire time, wherein the heating temperature is 40-60 ℃ below the beta transformation temperature, the forging ratio is 1.8-2.0, and air cooling is adopted after drawing;

(4) Performing oblique rolling perforation on the tube blank obtained in the step (3), and then sequentially performing inner and outer surface defect trimming, acid washing and annealing treatment to obtain a perforated tube blank; the temperature of the cross-rolled perforated blank is 20-40 ℃ above the beta transformation temperature, and the deformation is 60-70%;

(6) And (3) sequentially removing defects on the inner surface and the outer surface of the cold-rolled tube blank obtained in the step (5), pickling, heat treatment and straightening to obtain the titanium alloy tube.

7. The method for manufacturing a cold rolling tube of a titanium alloy with a high impact resistance at a yield strength of 800MPa according to claim 6, wherein in the step (3), the forged bar stock is further subjected to 1-fire radial forging at a temperature of 40 to 60 ℃ below the beta transus temperature, depending on the size of the final tube stock, to prepare the tube stock.

8. The method for manufacturing a cold-rolled tube of a strong impact-resistant titanium alloy having a yield strength of 800MPa according to claim 6, wherein the heat-retaining time in the step (2) is calculated as the minimum cross-sectional dimension of the billet x 0.8-1 min/mm during the heating of the billet in the forging process.

9. The method for producing a cold-rolled tube of a titanium alloy with a yield strength of 800MPa and a high impact resistance according to claim 6, wherein in the step (6), the tube is annealed at a temperature of 850 to 900 ℃ for 1 to 2 hours and air-cooled.

10. A titanium alloy seamless tube prepared by the method for preparing a cold-rolled tube of a strong impact-resistant titanium alloy with yield strength of 800MPa according to any one of claims 5 to 9, wherein the tube is subjected to simple annealing treatment, the yield strength is not lower than 800MPa, the elongation is not lower than 12%, and the impact energy is not lower than 50J.