Method for improving fatigue performance of titanium alloy seamless tube

Abstract

A method for improving the fatigue performance of a titanium alloy seamless tube. The method comprises: S1, mixing raw materials, pressing same into a plurality of electrode blocks, and welding the plurality of the electrode blocks to obtain a consumable electrode; S2, smelting the consumable electrode 2-3 times by using a vacuum consumable electrode arc furnace, so as to obtain a titanium alloy cast ingot; S3, upsetting and drawing the cast ingot multiple times and rolling same into a titanium alloy bar; S4, subjecting the bar to precision forging, with the amount of times of heating being no more than twice; S5, annealing and straightening same, followed by turning and drilling treatments, so as to obtain a rough blank of a titanium alloy seamless tube; S6, subjecting same to multi-pass cold rolling, so as to obtain a semi-finished titanium alloy seamless tube product; S7, performing vacuum annealing and acid pickling; S8, performing electrolytic-magnetic composite polishing; and S9, performing a shot blasting treatment. The method can effectively improve the rotating bending fatigue performance, and the titanium alloy seamless tube can endure 20 million test cycles.

Description

A method for improving fatigue performance of titanium alloy seamless pipe

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 30, 2023, with application number 202311618077.0 and invention name “A Method for Improving Fatigue Performance of Titanium Alloy Seamless Pipes”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of titanium alloy processing, and in particular to a method for improving the fatigue performance of a titanium alloy seamless pipe. Background Art

[0003] Titanium alloy seamless pipes have excellent room-temperature mechanical properties and corrosion resistance, making them widely used in aerospace, nuclear power, oilfield, and other technical fields. Rotary bending fatigue performance is a key performance indicator for titanium alloy seamless pipes, particularly those used in aviation hydraulic piping systems. These pipes must pass 107 cycles of testing, with no failures allowed.

[0004] Since there are many factors that affect the fatigue performance of titanium alloy seamless pipes, there is currently no strict control over each factor during the preparation process of titanium alloy seamless pipes, which makes it difficult for the rotary bending fatigue performance of titanium alloy seamless pipes to pass the assessment.

[0005] Summary of the Invention

[0006] In view of the above problems, the purpose of the present invention is to provide a method for improving the fatigue performance of titanium alloy seamless pipes, which can effectively improve the rotary bending fatigue performance of titanium alloy seamless pipes.

[0007] The technical solution adopted in the present invention is as follows:

[0008] The present invention proposes a method for improving the fatigue performance of a titanium alloy seamless pipe, comprising the following steps:

[0009] S1: mixing raw materials and pressing them into multiple electrode blocks, and welding the multiple electrode blocks to obtain consumable electrodes;

[0010] S2: melting the consumable electrode obtained in step S1 2-3 times in a vacuum consumable arc furnace to obtain a titanium alloy ingot;

[0011] S3: The ingot obtained in step S2 is subjected to multiple fires of upsetting and rounding to form a titanium alloy bar, wherein the middle fire needs to be subjected to three upsetting and three drawing, and the upsetting and drawing adopts reversing upsetting to ensure that the square billet has one upsetting in each direction of xyz. The last fire is subjected to drawing and rounding to form a bar;

[0012] S4: The bar obtained in step S3 is subjected to no more than two heats of fine forging to obtain a bar with higher dimensional accuracy and finer structure, and the bar has a certain radial texture;

[0013] S5: annealing and straightening the bar material after the treatment in step S4, and then performing lathing and drilling to obtain a titanium alloy seamless tube rough blank;

[0014] S6: cold rolling the titanium alloy seamless tube rough billet obtained in step S5 into a titanium alloy seamless tube semi-finished product in multiple passes;

[0015] S7: vacuum annealing and pickling the semi-finished seamless pipe obtained in step S6 in sequence;

[0016] S8: Electrolytic-magnetic composite polishing is performed on the pipe treated in step S7;

[0017] S9: Shot peening is performed on the titanium alloy seamless pipe processed in step S8.

[0018] Furthermore, the oxygen content of the titanium alloy ingot is between 0.08-0.12%, and the rare earth element Tb is added, and its content is between 0.001-0.05%.

[0019] Furthermore, in step S3, the ingot is placed at 880° C.-1100° C. and kept warm for 4.5 h-5 h before performing multiple upsetting operations.

[0020] Furthermore, in step S4, the finishing forging temperature is [T-(100-200)]°C, the holding time is 1.5-3h, T is the phase transition point of the titanium alloy, and the deformation amount after the fire is between 40% and 55%.

[0021] Furthermore, in step S5, the annealing temperature is [T-(150-250)]°C, and the temperature is kept for 1.5-3 hours.

[0022] Furthermore, in step S6, the intermediate annealing temperature of the multiple cold rolling passes is [T-(200-300)]°C, the holding time is 1-2h, the ratio Q of the relative wall reduction to the relative diameter reduction in the last two passes is between 1.5-2, the cold rolling deformation in the last two passes is between 40%-50%, and Q ≥ 1 for the remaining passes.

[0023] Furthermore, in step S7, the vacuum annealing temperature is [T-(350-500)]°C, and the holding time is 1-2 hours.

[0024] Furthermore, in step S8, the electrolyte is 10% NaNO3 solution; the magnetic abrasive particles are stainless steel powder with a particle size of 100-200 μm, and the roughness of the inner and outer surfaces of the pipe after polishing is ≤0.09 μm.

[0025] Furthermore, in step S9, the pellets are stainless steel pellets with a diameter of 20-50 μm. After treatment, the residual stress on the inner and outer surfaces of the pipe is compressive stress, ranging from -150 MPa to 300 MPa.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention optimizes the titanium alloy composition and uses reverse upsetting and precision forging to produce titanium alloy bars with a defined radial texture. The bars are then machined to produce cold-rolled tube billets. By controlling the Q value during the subsequent cold rolling process, the CSR value of the resulting titanium alloy seamless tube is guaranteed to maintain a consistent relationship with the tube's outer diameter. Finally, electrolytic-magnetic composite polishing and shot peening are combined to ensure surface roughness and compressive stress. This comprehensive preparation method improves the rotary bending fatigue performance of titanium alloy seamless tubes, enabling them to pass 20 million cycle tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is a schematic diagram of the metallographic structure of a pipe according to Example 1 of the present invention;

[0029] FIG2 is a pole figure of the pipe of Example 1 of the present invention;

[0030] FIG3 is a schematic diagram of the surface morphology of the pipe according to Example 1 of the present invention;

[0031] FIG4 is a schematic diagram of the metallographic structure of a pipe according to Example 2 of the present invention;

[0032] FIG5 is a pole figure of the pipe of Example 2 of the present invention;

[0033] FIG6 is a schematic diagram of the surface morphology of the pipe according to Example 2 of the present invention. DETAILED DESCRIPTION

[0034] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0035] The present invention proposes a method for improving the fatigue performance of titanium alloy seamless pipes, and the specific implementation process is as follows:

[0036] S1: mixing raw materials and pressing them into multiple electrode blocks, and welding the multiple electrode blocks to obtain consumable electrodes;

[0037] S2: The consumable electrode obtained in step S1 is melted 2-3 times in a vacuum consumable arc furnace to obtain a titanium alloy ingot;

[0038] The oxygen content in the titanium alloy ingot is controlled to be between 0.08% and 0.12%, and the rare earth element Tb is added to a content between 0.001% and 0.05% to improve the ductility of the alloy; the above percentages are all mass percentages;

[0039] S3: The ingot obtained in step S2 is kept at 880°C-1100°C for 4.5h-5h, and then subjected to multiple fires of upsetting and rounding to form a titanium alloy bar. The middle fire needs to be subjected to three upsetting and three drawing, and the upsetting and drawing adopts reversing upsetting to ensure that the billet is upset once in each direction of xyz. The last fire is subjected to drawing and rounding to form a bar.

[0040] S4: The bar obtained in step S3 is subjected to no more than two heats of finish forging at a temperature of [T-(100-200)]°C for 1.5-3 hours, where T is the phase transition point of the titanium alloy and the deformation per heat is between 40% and 55%. This results in a bar with higher dimensional accuracy, finer microstructure, and a certain radial texture.

[0041] S5: annealing and straightening the bar after the treatment in step S4 at a temperature of [T-(150-250)]°C for 1.5-3 hours; and performing lathing and drilling after annealing and straightening to obtain a titanium alloy seamless tube rough blank.

[0042] S6: The titanium alloy seamless tube rough billet obtained in step S5 is subjected to multiple cold rolling passes to form a titanium alloy seamless tube semi-finished product. The outer diameter of the tube is ≤ 25 mm. The intermediate annealing temperature is [T-(200-300)]°C, and the holding time is 1-2 hours. The ratio Q of the relative wall reduction to the relative diameter reduction in the last two passes is between 1.5-2. The cold rolling deformation in the last two passes is between 40%-50%, and Q in the remaining passes is ≥ 1. The implementation of steps S4 and S6 can ensure that the CSR value of the tube is between 1.4 and 2.4.

[0043] S7: vacuum annealing and pickling the semi-finished seamless pipe obtained in step S6 in sequence; wherein the vacuum annealing temperature is [T-(350-500)]°C and the holding time is 1-2 hours;

[0044] S8: The tube treated in step S7 is subjected to electrolytic-magnetic composite polishing, wherein the electrolyte is a 10% NaNO3 solution, which can form a passivation film with low hardness on the surface of the tube; the magnetic abrasive particles are stainless steel powder with a particle size of 100-200 μm, which can initially improve the surface roughness of the tube. Too small a particle size is not conducive to the grinding efficiency. After polishing, the roughness of the inner and outer surfaces of the tube is ≤ 0.09 μm;

[0045] S9: Shot peening is performed on the titanium alloy seamless tube after step S8. Stainless steel shot is used, with a diameter of 20-50 μm. Due to the thin wall of the tube, larger shot sizes can damage the tube surface. After treatment, the residual stress on the inner and outer surfaces of the tube is compressive, ranging from -150 MPa to 300 MPa. This partially offsets the tensile stress experienced by the tube during rotational bending fatigue, improving its performance. Excessive surface residual stress can affect the mechanical properties of the tube itself.

[0046] The present invention will be further described below by specific examples and comparative examples:

[0047] Example 1:

[0048] The production specification is TA18 titanium alloy seamless pipe with a diameter of 20×1.6mm.

[0049] The production process is as follows: raw materials → electrode → Φ660mm ingot, oxygen content 0.08%, Tb content 0.03% → machining → 1100℃ upsetting forging (reversing upsetting) → 950℃ upsetting forging (reversing upsetting) → 890℃ upsetting forging (reversing upsetting) → 880℃ upsetting forging (drawing and rolling) to Φ140 bar → finishing forging first fire to Φ100 bar → finishing forging second fire to Φ60 Bar → 750℃ / 2h annealing and straightening → machining into Φ58*9 ​​tube billet → cold rolled into Φ42*5.7 → 700℃ / 2h vacuum annealing → cold rolled into Φ33*3.8 → 700℃ / 2h vacuum annealing → cold rolled into Φ26*2.5 → 600℃ / 2h vacuum annealing → cold rolled into Φ20*1.6 → 500℃ / 2h vacuum annealing → straightening and pickling → electrolytic-magnetic composite polishing → shot peening.

[0050] The TA18 titanium alloy seamless tube prepared in this embodiment has a CSR value of 2.0, an inner surface roughness of 0.07 μm, an outer surface roughness of 0.05 μm, an inner surface residual compressive stress of -232 MPa, an outer surface residual compressive stress of -275 MPa, and is fatigue-resistant after 20 million rotational bending cycles.

[0051] Example 2:

[0052] The production specification is TA18 titanium alloy seamless pipe with a diameter of 12×1.1mm.

[0053] The production process adopted is as follows: raw materials → electrode → Φ750mm ingot, oxygen content 0.01%, Tb content 0.008% → machining → 1100℃ upsetting forging (reversing upsetting) → 950℃ upsetting forging (reversing upsetting) → 890℃ upsetting forging (reversing upsetting) → 880℃ upsetting forging (drawing and rolling) to Φ110 bar → finishing forging first fire to Φ80 bar → finishing forging second fire to Φ52 bar → 750℃ / 2h annealing Straightening → machining into Φ48*6.5 tube billet → cold rolling into Φ35*4.5 → vacuum annealing at 700℃ / 2h → cold rolling into Φ27*3.2 → vacuum annealing at 700℃ / 2h → cold rolling into Φ19*2.5 → vacuum annealing at 600℃ / 2h → cold rolling into Φ15*1.7 → vacuum annealing at 500℃ / 2h → cold rolling into Φ12*1.1 → vacuum annealing at 500℃ / 2h → straightening and pickling → electrolytic-magnetic composite polishing → shot peening.

[0054] The TA18 titanium alloy seamless tube prepared in this embodiment has a CSR value of 1.8, an inner surface roughness of 0.1 μm, an outer surface roughness of 0.08 μm, an inner surface residual compressive stress of -215 MPa, an outer surface residual compressive stress of -187 MPa, and is fatigue-resistant after 20 million rotational bending cycles.

[0055] Matters not described in detail in this invention are all known technologies.

[0056] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A method for improving the fatigue performance of a titanium alloy seamless pipe, characterized in that: The following steps are involved: S1: mixing the raw materials and pressing them into a plurality of electrode blocks, and welding the plurality of electrode blocks to obtain a consumable electrode; S2: melting the consumable electrode obtained in step S1 for 2-3 times in a vacuum consumable arc furnace to obtain a titanium alloy ingot; S3: The ingot obtained in step S2 is subjected to multiple fire upsetting and rolling to form a titanium alloy bar, wherein the middle fire needs to be subjected to three upsetting and three drawing, and the upsetting and drawing adopts reversing upsetting and drawing to ensure that the square billet has one upsetting and drawing in each direction xyz, and the last fire is subjected to drawing and rolling to form a bar; S4: performing no more than two heat forgings on the bar obtained in step S3 to obtain a bar with higher dimensional accuracy and finer structure, and the bar has a certain radial texture; S5: annealing and straightening the bar material after the treatment in step S4, and then performing lathing and drilling after annealing and straightening to obtain a titanium alloy seamless tube rough blank; S6: cold rolling the titanium alloy seamless tube rough blank obtained in step S5 into a titanium alloy seamless tube semi-finished product in multiple passes; S7: vacuum annealing and pickling the seamless pipe semi-finished product obtained in step S6 in sequence; S8: electrolytic-magnetic composite polishing is performed on the tube treated in step S7; S9: Shot peening is performed on the titanium alloy seamless pipe after the treatment in step S8.

2. The method for improving fatigue performance of titanium alloy seamless pipe according to claim 1, characterized in that: The oxygen content of the titanium alloy ingot is between 0.08% and 0.12%, and the rare earth element Tb is added, and its content is between 0.001% and 0.05%.

3. The method for improving fatigue performance of titanium alloy seamless pipe according to claim 1, characterized in that: In the step S3, the ingot is placed at 880°C-1100°C for 4.5h-5h before multiple upsetting and drawing.

4. The method for improving fatigue performance of titanium alloy seamless pipe according to claim 1, characterized in that: In the step S4, the fine forging temperature is [T-(100-200)]°C, the holding time is 1.5-3h, T is the phase transition point of the titanium alloy, and the deformation amount of the fire is between 40% and 55%.

5. The method for improving fatigue performance of titanium alloy seamless pipe according to claim 1, characterized in that: In the step S5, the annealing temperature is [T-(150-250)]°C, and the temperature is kept for 1.5-3 hours.

6. The method for improving fatigue performance of titanium alloy seamless pipe according to claim 1, characterized in that: In step S6, the intermediate annealing temperature of the multiple cold rolling passes is [T-(200-300)]°C, the holding time is 1-2h, the ratio Q of the relative wall reduction to the relative diameter reduction of the last two passes is between 1.5-2, the cold rolling deformation of the last two passes is between 40%-50%, and Q≥1 for the remaining passes.

7. The method for improving fatigue performance of titanium alloy seamless pipe according to claim 1, characterized in that: In the step S7, the vacuum annealing temperature is [T-(350-500)]°C, and the insulation time is 1-2h.

8. The method for improving fatigue performance of titanium alloy seamless pipe according to claim 1, characterized in that: In the step S8, the electrolyte is 10% NaNO3 solution; the magnetic abrasive particles are stainless steel powder with a particle size of 100-200 μm, and the roughness of the inner and outer surfaces of the pipe after polishing is ≤0.09 μm.

9. The method for improving fatigue performance of titanium alloy seamless pipe according to claim 1, characterized in that: In the step S9, the pellets are made of stainless steel pellets with a diameter of 20-50 μm. After the treatment, the residual stress on the inner and outer surfaces of the pipe is compressive stress, ranging from -150 MPa to 300 MPa.

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