827MPa-grade high-strength high-toughness titanium alloy drill rod pipe for deep well and large-strain short-process preparation method and application thereof

Abstract

The invention relates to an 827MPa-grade high-strength and high-toughness titanium alloy drill rod pipe for a deep well as well as a large-strain and short-process preparation method and application thereof. The pipe comprises the following components in percentage by weight: 5.5%-6.0% of Al, 3.5%-4.0% of V, 0.5%-1.0% of Mo, 0.5%-1.0% of Zr, 0.2%-1% of Nb, 0.1%-0.5% of Fe, 0.1%-0.3% of Ru, less than or equal to 0.1% of O and the balance of Ti and inevitable impurities. Pressing the ingredients into an electrode according to the weight percentage, and obtaining a cast ingot through a smelting process; the cast ingot is sequentially subjected to cogging forging, homogeneous forging, machining and large-strain extrusion, and an extruded pipe blank is obtained; and sequentially carrying out straightening and sub-temperature annealing heat treatment on the extruded tube blank. The titanium alloy drill rod pipe provided by the invention is good in obdurability matching, has relatively high strength and impact toughness, and also has better corrosion resistance, fatigue resistance and the like, meanwhile, the processing flow is shortened, and the manufacturing cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing titanium alloy drill pipes for harsh energy drills in the petroleum and natural gas industry, and specifically relates to a 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells and a large strain short process preparation method and application thereof. Background Art

[0002] With the continuous deepening of energy exploration and development, deep and ultra-deep oil and gas, and marine methane hydrate have gradually become the main areas for the recovery of oil and gas resources. The increasingly harsh drilling and production environment has put forward higher requirements on the service performance of oil drill pipes. Under complex well conditions, the drill pipe needs to circulate for a longer time at a higher stress level at a smaller radius of curvature. At the same time, it is subjected to the influence of acidic media and high temperature environment. The drill pipe will drastically shorten its service life or even fail and break due to fatigue cracks, wear, corrosion and performance degradation, posing a safety hazard to drilling operations. Complex working conditions such as deep wells, ultra-deep wells, ultra-short radius wells, and sulfur-containing oil and gas wells urgently need to apply high-performance lightweight drill pipe materials with high load-bearing capacity, long life, fatigue resistance, high corrosion resistance, and high temperature resistance. In order to improve the service life of drill pipes and drilling efficiency and reduce the occurrence of failure accidents, titanium alloy materials with the advantages of low density, high strength limit, excellent corrosion resistance and fatigue resistance have begun to be developed at home and abroad for the preparation of oil drill pipes to solve the drilling problems of oil and gas wells in complex working conditions such as deep wells, ultra-deep wells, large displacement wells, sulfur-containing wells, short radius wells, high temperature and high pressure wells.

[0003] However, due to the limitations of the current level of titanium alloy drill pipe processing technology, the preparation of titanium alloy drill pipes mostly adopts process routes such as "oblique rolling piercing-hot rolling" or "extrusion-rolling". Titanium alloy pipes for oil drill pipes still have problems such as insufficient strength and toughness matching, complex processing flow and high cost. The processing technology of large-sized titanium alloy drill pipes is not mature enough, which restricts the application of titanium alloy drill pipes. Therefore, it is urgent to develop a short-process, low-cost, and easy-to-implement industrial high-strength and high-toughness titanium alloy drill pipe preparation technology. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the present invention provides a 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells and its large strain short process preparation method and application. The technical solution of the present invention can achieve a good match between the strength and toughness of the titanium alloy drill pipe, and on the basis of high strength and better fatigue resistance, wear resistance, corrosion resistance and other properties, can achieve excellent performance of impact energy not less than 50J, and can shorten the process flow and reduce costs.

[0005] The technical solution provided by the present invention is as follows:

[0006] The invention discloses a 827MPa high-strength and high-toughness titanium alloy drill pipe for deep wells. The components and contents thereof are respectively as follows, in weight percentage: Al: 5.5%-6.0%, V: 3.5%-4.0%, Mo: 0.5%-1.0%, Zr: 0.5%-1.0%, Nb: 0.2%-1%, Fe: 0.1%-0.5%, Ru: 0.1%-0.3%, O: ≤0.1%, and the balance is Ti and unavoidable impurities.

[0007] In the above alloys:

[0008] The added 5.5% to 6.0% Al can fully dissolve in the α phase, change the critical shear stress in the α phase, increase the number of slip systems in the α phase, and thus improve the yield strength and fracture toughness of the material.

[0009] Refractory metals such as Mo and Al are added in the form of Al-Mo alloys in accordance with the Al-Mo equivalent design criteria to reduce material costs and avoid high-density inclusions during smelting, which has the effects of improving fracture toughness and reducing extrusion difficulty.

[0010] V and Mo are infinitely dissolved in the β phase, which increases the hardenability of the titanium alloy, plays a role in fine grain strengthening, improves the room temperature strength and thermal stability of the alloy, and improves the corrosion resistance and fatigue resistance of the pipe;

[0011] Zr is infinitely dissolved in the α and β phases at the same time, which has little effect on the phase transition point of the alloy material and plays a supplementary strengthening role;

[0012] The addition of Nb element can refine the size of α lamella in the ingot, improve the crack resistance of the ingot, inhibit the growth rate of grains at high temperature, and lay a good foundation for the implementation of the subsequent high-temperature large-strain forging and extrusion process. It is helpful for the formation of twins inside the grains during the hot deformation process, and improves the coordinated deformation ability and the upper limit of the toughness of the material. On the other hand, it increases the activity of Al element, gives full play to the solid solution strengthening effect of Al element, reduces the precipitation of brittle phase, and is beneficial to the improvement of yield strength and impact toughness of the pipe.

[0013] Adding 0.1% to 0.5% Fe not only avoids the occurrence of local segregation, but also effectively refines the original β grains and cluster size, improves material strength, and Fe is relatively cheap, reducing alloy costs;

[0014] Considering that surface corrosion and wear will accelerate the initiation and expansion of cracks in titanium alloy drill pipes and reduce the service life of titanium alloy drill pipes, the addition of Ru elements can improve the corrosion potential and corrosion resistance of the material on the one hand, and enhance the TiO 2 The surface potential of the film layer and the repair ability of the passivation film can improve the wear resistance of the drill pipe;

[0015] The 827MPa high-strength and high-toughness titanium alloy drill pipe for deep wells provided by the above technical solution is based on the technology of Ti-Al-V-Mo-Zr system titanium alloy, while adding trace amounts of Nb, Fe and Ru, and controlling the oxygen content. The obtained titanium alloy material has excellent strength and impact toughness, and has good corrosion resistance and wear resistance, which reduces the cost of raw material input and lays a raw material foundation for the implementation of the short process route.

[0016] The present invention also provides a method for preparing the above-mentioned 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells, comprising the following steps:

[0017] 1) Pressing the ingredients into electrodes according to the weight percentage, and obtaining an ingot through three smelting processes;

[0018] 2) subjecting the ingot obtained in step 1) to blanking forging, homogenizing forging, machining and high-temperature large-strain extrusion in sequence to obtain an extruded tube blank;

[0019] 3) The extruded tube obtained in step 2) is sequentially straightened and subjected to sub-temperature annealing heat treatment to obtain a 827 MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells.

[0020] Based on the above technical solution:

[0021] The vacuum consumable arc furnace uses a three-stage melting method to form ingots, which fully alloys and effectively reduces the impurity content, and improves the strength and toughness of the material through the tissue genetic effect;

[0022] Inverting the ingot for each smelting can significantly reduce the macro segregation of the ingot and improve the uniformity of the original structure of the ingot;

[0023] The "circular-rectangular-circular" method is used for homogeneous forging. The cross-section deformation of the forging blank is more uniform, the metal flow is more sufficient, and the macro-micro segregation can be effectively reduced. The dendrites are broken finer and more uniform, which reduces the probability of material microcracks during forging and subsequent extrusion, and improves the overall life of the pipe. At the same time, compared with the general forging process, the use of homogeneous forging further simplifies the forging process and saves forging time;

[0024] The fine-grained structure obtained by homogeneous forging and the high-temperature β grain refinement brought about by Nb microalloying allow the tube to be extruded at a higher temperature in the β phase region, thus avoiding cracks in the tube due to a large extrusion ratio.

[0025] During the extrusion process, the forging billet and the inlet / outlet of the extrusion die are chamfered to avoid dead zones at the corners, fully promote metal flow, reduce surface stress concentration, reduce surface defects, make the surface of the extruded tube billet smooth, and reduce the source of fatigue cracks in the tube during service;

[0026] The tube billet extruded by a large extrusion ratio is in a three-dimensional compressive stress state at the microscopic level. Combined with the subsequent sub-temperature annealing heat treatment, this three-dimensional compressive stress state can be retained on the surface of the finished tube, further improving the strength, toughness, wear resistance and fatigue resistance of the tube.

[0027] Through the sub-temperature annealing heat treatment process combined with the large strain extrusion process, a high-strength and high-toughness titanium alloy drill pipe with a certain proportion of primary α and secondary α was obtained. During the sub-temperature annealing process, a part of the primary α phase was retained, with a size of about 2-10um, and a β transformation structure with an average grain size of 10-20μm was formed. The β transformation structure contains lamellar secondary α, which grows inside the β transformation structure according to the Bragg phase relationship, and grows from the boundary to the inside of the β transformation structure. When the pipe is subjected to external stress, the equiaxed α and β transformation structures produce a synergistic effect. When the crack propagates, the crack preferentially propagates along the equiaxed α or the junction of the equiaxed α and β transformation structures. At this time, the equiaxed α undergoes microscopic local deformation twinning, and the β transformation structure also undergoes severe kinking. The synergy of the two releases a large amount of crack tip stress. Secondly, when the crack passes through the β transformation structure, the secondary α cluster inside the β transformation structure deflects the crack propagation path, increasing the energy required for crack propagation. The synergistic effect of the two simultaneously improves the mechanical strength and impact toughness of titanium alloy drill pipe.

[0028] Based on the above technical solution, 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells can be prepared without rolling with a shortened process flow and at a lower cost.

[0029] Specifically, in step 1), the smelting conditions are: furnace temperature 1950-2100° C., furnace vacuum ≤1 Pa, repeated three times, each time the oxide layer is removed by peeling, and the ingot is inverted.

[0030] Specifically, in step 2), the conditions for forging the blank are: temperature of 1000-1150° C., and pressing down 70-80 mm each time.

[0031] Specifically, in step 2), the conditions for homogeneous forging are: temperature of 900° C. to 1000° C., and pressing down 50 to 70 mm each time.

[0032] Specifically, the diameter of the extruded tube obtained after machining is 200 to 300 mm.

[0033] Specifically, in step 2), the conditions for high temperature and large strain extrusion are: temperature of 1000-1100° C.; extrusion ratio of large strain extrusion of 20-40. The outer diameter of the extruded tube obtained after high temperature and large strain extrusion is 70-100 mm, and the wall thickness is 5-15 mm.

[0034] Specifically, during the extrusion deformation process, the forging billet and the extrusion die are chamfered, and after being kept warm in the β phase region, extrusion is performed using an extrusion barrel with a large extrusion ratio.

[0035] Specifically, in step 3), the straightness of the extruded tube after straightening is not greater than 0.8 mm / m.

[0036] Specifically, in step 3), the conditions for the sub-temperature annealing heat treatment are: heating the straightened extruded tube billet at 750-900° C. and keeping the temperature for 0.5-1 h, and finally air cooling to room temperature.

[0037] The present invention also provides a 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells prepared according to the above preparation method.

[0038] The tensile strength of the 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells is ≥930MPa, the yield strength is ≥827MPa, the elongation is ≥10%, and the impact energy is ≥50J.

[0039] The wear efficiency of the 827MPa high-strength and high-toughness titanium alloy drill pipe used in deep wells is less than 0.046g / min in a sulfur-containing mud environment, and the corrosion fatigue life is greater than 10 7 Number of cycles.

[0040] The present invention also provides an application of the above-mentioned 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells, which is used for manufacturing deep well drill pipes.

[0041] The 827MPa high-strength and high-toughness titanium alloy drill pipe for deep wells provided by the present invention is particularly suitable for making deep well drill pipes because of its high strength, high impact energy, good wear resistance and corrosion fatigue resistance. The deep well drill pipe produced has the advantages of good load-bearing performance, high fatigue life and resistance to hydrogen sulfide corrosion.

[0042] The present invention achieves good microstructure by coordinated optimization of all processes, targets microalloying component systems such as Nb and Ru, adopts a short-process molding process in combination with a low-temperature short-time heat treatment process, retains the three-dimensional compressive stress state of the surface layer, reduces surface defects of the pipe, simplifies the process flow, saves pipe preparation time, improves processing efficiency, and reduces industrial manufacturing costs while ensuring high strength, high toughness, high wear resistance, and fatigue resistance of the pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is the metallographic structure diagram of the high-strength and high-toughness titanium alloy drill pipe prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0044] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0045] Embodiment 1:

[0046] A high-strength and high-toughness titanium alloy drill pipe material, wherein the components and contents of the titanium alloy drill pipe material are as follows by weight percentage: Al: 5.5%, V: 3.5%, Mo: 1%, Zr: 1%, Nb: 0.2%, Fe: 0.5%, Ru: 0.3%, O: 0.08%, and the remainder is Ti and unavoidable impurities.

[0047] A method for manufacturing a high-strength and high-toughness titanium alloy drill pipe comprises the following steps:

[0048] Step 1, pressing the ingredients into electrodes according to the weight percentage, and obtaining an ingot by smelting three times in a vacuum consumable electric furnace;

[0049] Step 2, the ingot in step 1 is processed by blanking forging and homogenizing forging to obtain a bar of required size;

[0050] Step 3, machining the bar in step 2 to obtain a tube blank, the diameter of the tube blank is 300 mm;

[0051] Step 4: Extruding the tube blank in step 3 through an extruder at high temperature and high strain to obtain an extruded tube blank with an outer diameter of 70 mm and a wall thickness of 9 mm, and the extrusion ratio is 40;

[0052] Step 5, straightening the tube blank that has been extruded and deformed in step 4, and the straightness after straightening is 0.5 mm / m;

[0053] Step 6: performing a sub-temperature annealing heat treatment on the straightened extruded tube blank in step 5. The sub-temperature annealing heat treatment is specifically as follows: heating the straightened tube at 750° C. and keeping the temperature for 1 hour, and then air cooling to room temperature to obtain a titanium alloy drill pipe tube;

[0054] Step seven: performance testing.

[0055] In step 1, the specific conditions for smelting are: furnace temperature 2000°C, furnace vacuum degree 0.8Pa, repeated three times, each time the oxide layer is peeled off and the ingot is inverted.

[0056] In step 2, the specific conditions for forging the blank are: temperature 1100°C, and pressing down 75 mm each time.

[0057] In step 2, the specific conditions of homogeneous forging are: temperature 950°C, and pressing down 60 mm each time.

[0058] In step 4, the specific conditions of high temperature and large strain extrusion are: temperature 1100°C.

[0059] In step 5, the straightness of the extruded tube after straightening is not greater than 0.8 mm / m.

[0060] The mechanical properties of the titanium alloy drill pipe treated by the above method are as follows: tensile strength of 972MPa, yield strength of 870MPa, elongation of 11%, and impact energy of 52J. A dual-state structure containing more equiaxed α and a small amount of fine secondary α is generated, wherein the average diameter of the primary α is about 3.9um, the average diameter of the β transformation structure is about 10um, the volume proportion of the primary α phase is about 36%, and the secondary α in the β transformation structure is parallel to each other and uniformly oriented, with an average width of about 0.25um. The structure can undergo coordinated deformation after being subjected to external force, the equiaxed α deformation twin and the β transformation structure are broken and twisted, effectively releasing the stress concentration of the tip crack, and at the same time having high strength and high impact toughness. The surface of the material is in a triaxial compressive stress state at the microscopic level, and has good wear resistance and fatigue resistance. In a sulfur-containing mud environment, the wear efficiency is 0.04507g / min, and the corrosion fatigue life is 10203885 cycles.

[0061] Embodiment 2:

[0062] A high-strength and high-toughness titanium alloy drill pipe material, wherein the components and contents of the titanium alloy drill pipe material are as follows, in weight percentage: Al: 6.0%, V: 4.0%, Mo: 0.5%, Zr: 0.5%, Nb: 1%, Fe: 0.1%, Ru: 0.1%, O: 0.1%, and the balance is Ti and unavoidable impurities.

[0063] A method for manufacturing a high-strength and tough titanium alloy drill pipe comprises the following steps:

[0064] Step 1, pressing the ingredients into electrodes according to the weight percentage, and obtaining an ingot by smelting three times in a vacuum consumable electric furnace;

[0065] Step 2, the ingot in step 1 is processed by blanking forging and homogenizing forging to obtain a bar of required size;

[0066] Step 3, machining the bar in step 2 to obtain a tube blank, the diameter of the tube blank is 200 mm;

[0067] Step 4: Extruding the tube blank in step 3 through an extruder at high temperature and high strain to obtain an extruded tube blank with an outer diameter of 70 mm and a wall thickness of 5 mm, and the extrusion ratio is 28;

[0068] Step 5, straightening the tube blank that has been extruded and deformed in step 4, and the straightness after straightening is 0.8 mm / m;

[0069] Step 6: Perform a sub-temperature annealing heat treatment on the straightened extruded tube blank in step 5 to obtain a high-strength and high-toughness titanium alloy drill pipe. The sub-temperature annealing heat treatment is specifically as follows: heating the straightened tube at 900°C and keeping it warm for 0.5h, and finally air cooling it to room temperature;

[0070] Step seven: performance testing.

[0071] In step 1, the specific conditions for smelting are: furnace temperature 2000°C, furnace vacuum degree 0.8Pa, repeated three times, each time the oxide layer is peeled off and the ingot is inverted.

[0072] In step 2, the specific conditions for forging the blank are: temperature 1100°C, and pressing down 75 mm each time.

[0073] In step 2, the specific conditions of homogeneous forging are: temperature 950°C, and pressing down 60 mm each time.

[0074] In step 4, the specific conditions of high temperature and large strain extrusion are: heating temperature 1050°C.

[0075] In step 5, the straightness of the extruded tube after straightening is not greater than 0.8 mm / m.

[0076] The mechanical properties of the titanium alloy drill pipe treated by the above method are as follows: tensile strength of 985MPa, yield strength of 890MPa, elongation of 16%, and impact energy of 57J. More Nb elements are added in the composition design, and a larger extrusion ratio, higher annealing temperature and shorter annealing time are used in the production process. The residual triaxial compressive stress intensity of the surface of the pipe is relatively large, and the grains are finer at the microscopic level. The organizational characteristics are a dual-state organization composed of equiaxed α phase and lamellar secondary α, in which the average diameter of the primary α phase is about 6um, the average diameter of the β transformation organization is about 18um, and the volume proportion of the primary α phase is about 24%. The secondary α phases in the β transformation organization are parallel to each other and uniformly oriented, with an average width of about 0.65um. It has good service performance. In a sulfur-containing mud environment, the wear efficiency is 0.0448g / min, and the corrosion fatigue life is 10060312 cycles.

[0077] Embodiment 3:

[0078] A titanium alloy drill pipe has the following components and contents by weight: Al: 5.8%, V: 3.9%, Mo: 0.8%, Zr: 0.8%, Nb: 0.5%, Fe: 0.3%, Ru: 0.2%, O: 0.05%, and the remainder is Ti and unavoidable impurities.

[0079] A method for manufacturing a high-strength and high-toughness titanium alloy drill pipe comprises the following steps:

[0080] Step 1, pressing the ingredients into electrodes according to the weight percentage, and obtaining an ingot by smelting three times in a vacuum consumable electric furnace;

[0081] Step 2, the ingot in step 1 is processed by blanking forging and homogenizing forging to obtain a bar of required size;

[0082] Step 3, machining the bar in step 2 to obtain a tube blank, the diameter of the tube blank is 200 mm;

[0083] Step 4: Extruding the tube blank in step 3 by high temperature and large strain extrusion in an extruder to obtain an extruded tube blank with an outer diameter of 70 mm and a wall thickness of 7 mm, and an extrusion ratio of 20;

[0084] Step 5, straightening the tube blank that has been extruded and deformed in step 4, and the straightness after straightening is 0.5 mm / m;

[0085] Step 6: performing a sub-temperature annealing heat treatment on the straightened extruded tube blank in step 5. The sub-temperature annealing heat treatment is specifically as follows: heating the straightened tube at 850° C. and keeping the temperature for 0.75 h, and then air cooling to room temperature to obtain a titanium alloy drill pipe tube;

[0086] Step seven: performance testing.

[0087] In step 1, the specific conditions for smelting are: furnace temperature 2000°C, furnace vacuum degree 0.8Pa, repeated three times, each time the oxide layer is peeled off and the ingot is inverted.

[0088] In step 2, the specific conditions for forging the blank are: temperature 1100°C, and pressing down 75 mm each time.

[0089] In step 2, the specific conditions of homogeneous forging are: temperature 950°C, and pressing down 60 mm each time.

[0090] In step 4, the specific conditions of high temperature and large strain extrusion are: temperature 1000°C.

[0091] In step 5, the straightness of the extruded tube after straightening is not greater than 0.8 mm / m.

[0092] The mechanical properties of the titanium alloy drill pipe treated by the above method are as follows: tensile strength is 952MPa, yield strength is 882MPa, elongation is 14.5%, impact energy is 55J, wear efficiency is 0.0426g / min in a sulfur-containing mud environment, and corrosion fatigue life is 10134791 cycles.

[0093] Figure 1 This is the metallographic structure diagram of the high-strength and high-toughness titanium alloy drill pipe prepared in Example 1 of the present invention. Figure 1As shown in the figure, the microstructure of the high-strength and high-toughness titanium alloy drill pipe is a dual-state structure composed of primary equiaxed α and β transformation structures. The average diameter of the primary α is about 3.9um, the average diameter of the β transformation structure is about 10um, and the volume proportion of the primary α phase is about 36%. The secondary α in the β transformation structure are parallel to each other and uniformly oriented, with an average width of about 0.25μm, and the primary α is evenly distributed inside the material. In terms of material composition design, the present invention gives full play to the solid solution strengthening effect of Al element, cooperates with Mo to reduce material cost, reduce defects and reduce extrusion difficulty; V, Mo, Zr, Nb and the like are added to refine the structure, increase grain boundaries and supplement the strengthening effect, especially the addition of Nb element, which can refine the size of α lamellae in the ingot, improve the cracking resistance of the ingot, inhibit the growth rate of grains at high temperature, improve the foundation for the implementation of subsequent high-temperature large-strain forging and extrusion processes, help the formation of twins inside the grains during thermal deformation, improve the coordinated deformation ability and the upper limit of toughness of the material, and improve the activity of Al element, give full play to the solid solution strengthening effect of Al element, reduce the precipitation of brittle phase, and benefit the improvement of yield strength and impact toughness of the pipe; a small amount of cheap Fe is added to achieve the best solid solution strengthening concentration and reduce the cost of raw materials; Ru element is added to improve the corrosion resistance and wear resistance of the material. In terms of pipe preparation technology, the proposed short-term sub-temperature annealing heat treatment system (750-900℃ insulation for 0.5-1h, air cooling to room temperature) obtains a dual-state structure composed of primary α and β transformation structures, which plays a synergistic role and increases the energy required for crack initiation and expansion caused by tension, fatigue, etc. At the same time, short-term sub-temperature annealing retains the three-dimensional compressive stress on the microscopic scale of the material and has good mechanical properties. Compared with the comparative example, the embodiment implemented in accordance with the technical requirements, on the basis of ensuring good tensile and yield strength of the pipe, obtains excellent performance of impact energy not less than 50J, and achieves a good match between strength and toughness. In terms of process, high-temperature large-strain extrusion process and short-term sub-temperature degradation are adopted. Through simple heat treatment in the extrusion state, the pipe can meet the required specifications and performance requirements without rolling, and the service performance of the material is improved at the whole process level, which greatly reduces the cost.

[0094] Comparative Example 1

[0095] A titanium alloy drill pipe has the following components and contents by weight: Al: 5.8%, V: 3.9%, Mo: 0.8%, Zr: 0.8%, Nb: 0.5%, Fe: 0.3%, Ru: 0.2%, O: 0.05%, and the remainder is Ti and unavoidable impurities.

[0096] A method for manufacturing a high-strength and high-toughness titanium alloy drill pipe comprises the following steps:

[0097] Step 1, pressing the ingredients into electrodes according to the weight percentage, and obtaining an ingot by smelting three times in a vacuum consumable electric furnace;

[0098] Step 2, the ingot in step 1 is processed by blanking forging and homogenizing forging to obtain a bar of required size;

[0099] Step 3, machining the bar in step 2 to obtain a tube blank, the diameter of the tube blank is 200 mm;

[0100] Step 4: Extruding the tube blank in step 3 by high temperature and large strain extrusion in an extruder to obtain an extruded tube blank with an outer diameter of 70 mm and a wall thickness of 7 mm, and an extrusion ratio of 20;

[0101] Step 5, straightening the tube blank that has been extruded and deformed in step 4, and the straightness after straightening is 0.5 mm / m;

[0102] Step 6: performing high temperature annealing heat treatment on the straightened extruded tube blank in step 5, specifically: heating the straightened tube to 1010° C., keeping the temperature for 1.5 hours, and then air cooling to room temperature to obtain a titanium alloy drill pipe;

[0103] Step seven: performance testing.

[0104] In step 1, the specific conditions for smelting are: furnace temperature 2000°C, furnace vacuum degree 0.8Pa, repeated three times, each time the oxide layer is peeled off and the ingot is inverted.

[0105] In step 2, the specific conditions for forging the blank are: temperature 1100°C, and pressing down 75 mm each time.

[0106] In step 2, the specific conditions of homogeneous forging are: temperature 950°C, and pressing down 60 mm each time.

[0107] In step 4, the specific conditions of high temperature and large strain extrusion are: temperature 1000°C.

[0108] In step 5, the straightness of the extruded tube after straightening is not greater than 0.8 mm / m.

[0109] The mechanical properties of the titanium alloy drill pipe treated by the above method are as follows: tensile strength is 890MPa, yield strength is 817MPa, elongation is 9%, and impact energy is 47J.

[0110] By comparison with Example 1, it can be seen that changes in the tube extrusion ratio and the heat treatment process of the tube after straightening will lead to significant changes in the tensile strength, yield strength, elongation and impact energy.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A 827MPa grade high strength and high toughness titanium alloy drill pipe for deep wells. It is characterized in that In terms of weight percentage, the components and their contents are: Al: 5.5%-6.0%, V: 3.5%-4.0%, Mo: 0.5%-1.0%, Zr: 0.5%-1.0%, Nb: 0.2%-1%, Fe: 0.1%-0.5%, Ru: 0.1%-0.3%, O: ≤0.1%, and the balance is Ti and unavoidable impurities.

2. A method for preparing the 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells according to claim 1, It is characterized in that The following steps are involved: 1) Pressing the ingredients into electrodes according to the weight percentage, and obtaining an ingot through three smelting processes; 2) subjecting the ingot obtained in step 1) to blanking forging, homogenizing forging, machining and high-temperature large-strain extrusion in sequence to obtain an extruded tube blank; 3) The extruded tube obtained in step 2) is sequentially straightened and subjected to sub-temperature annealing heat treatment to obtain a 827 MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells.

3. The method for preparing the 827MPa high-strength and high-toughness titanium alloy drill pipe for deep wells according to claim 2, It is characterized in that In step 2), the conditions for homogeneous forging are: temperature of 900°C to 1000°C; pressing down 50 to 70 mm each time.

4. The method for preparing the 827MPa high-strength and high-toughness titanium alloy drill pipe for deep wells according to claim 3, It is characterized in that In step 2), the conditions for high temperature and large strain extrusion are: temperature of 1000-1100; extrusion ratio of large strain extrusion of 20-40.

5. The method for preparing the 827MPa high-strength and high-toughness titanium alloy drill pipe for deep wells according to claim 4, It is characterized in that In step 3), the conditions for the sub-temperature annealing heat treatment are: heating the straightened extruded tube billet at 750-900° C. and keeping the temperature for 0.5-1 h, and finally air cooling to room temperature.

6. A method for preparing a 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells according to any one of claims 2 to 5, It is characterized in that In step 2): The diameter of the extruded tube obtained after machining is 200-300 mm; The outer diameter of the extruded tube obtained after high-temperature and large-strain extrusion is 70 to 100 mm, and the wall thickness is 5 to 15 mm.

7. A method for preparing a 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells according to any one of claims 2 to 5, It is characterized in that In step 3), the straightness of the extruded tube after straightening is not greater than 0.8 mm / m.

8. A 827MPa grade high-strength and high-toughness titanium alloy drill pipe for deep wells prepared according to the preparation method according to any one of claims 2 to 7.

9. The 827MPa high-strength and high-toughness titanium alloy drill pipe for deep wells according to claim 8, Features: Tensile strength ≥930MPa, yield strength ≥827MPa, elongation ≥10%, impact energy ≥50J; In sulfur-containing mud environment, the wear efficiency is less than 0.046g / min and the corrosion fatigue life is greater than 10 7 Number of cycles.

10. An application of the 827MPa high-strength and high-toughness titanium alloy drill pipe for deep wells according to claim 1, 8 or 9, Features: Used to make drill pipes for deep wells.

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