Method for improving fatigue properties of titanium alloy seamless tubes

Abstract

The present invention relates to a method for improving the fatigue properties of a titanium alloy seamless tube, comprising the steps of: step S1 mixing raw materials, pressing them into a plurality of electrode blocks, and welding the plurality of electrode blocks to obtain a consumable electrode; step S2 melting and refining the consumable electrode two or three times in a vacuum consumable electrode arc melting furnace to obtain a titanium alloy ingot; step S3 performing multiple upsetting, drawing, and spheroidizing processes on the ingot to form a titanium alloy round bar; step S4 precision forging the round bar with two or fewer heat treatments; step S5 annealing and stress relief followed by turning and drilling to obtain a titanium alloy seamless tube raw material; step S6 performing multiple cold rolling to obtain a titanium alloy seamless tube semi-finished product; step S7 vacuum annealing and pickling; step S8 electro-magnetic combined polishing; and step S9 shot blasting. The present invention effectively improves the rotating bending fatigue properties of the titanium alloy seamless tube, enabling it to pass a 20 million cycle test.

Description

[Technical Field]

[0001] (cross reference) This application claims the benefit of priority from a Chinese patent application bearing application number 202311618077.0 and entitled "Method for improving the fatigue properties of titanium alloy seamless pipes," filed with the State Intellectual Property Office of the People's Republic of China on November 30, 2023, the entire contents of which are incorporated herein by reference.

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

[0003] Titanium alloy seamless pipes have good room temperature mechanical properties and corrosion resistance, and are widely used in technical fields such as aviation, nuclear power generation, and oil exploration. Rotating bending fatigue properties are an important indicator of titanium alloy seamless pipes. Titanium alloy seamless pipes used in aviation hydraulic piping systems in particular are required to pass a 107-cycle test without any failures during the test period.

[0004] There are many factors that affect the fatigue properties of titanium alloy seamless pipes. However, at present, strict control of these factors is not carried out in the manufacturing process of titanium alloy seamless pipes. Therefore, it is difficult for titanium alloy seamless pipes to pass the rotating bending fatigue property test. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above problems, and aims to provide a method for improving the fatigue properties of a titanium alloy seamless pipe, which can effectively improve the rotating bending fatigue properties of a titanium alloy seamless pipe. [Means for solving the problem]

[0006] The technical approach of the present invention is as follows.

[0007] The method for improving the fatigue properties of a titanium alloy seamless tube according to the present invention comprises the following steps: a step S1 of mixing materials, forming them into a plurality of electrode blocks by pressing, and welding the plurality of electrode blocks to obtain consumable electrodes; Step S2: melting and refining the consumable electrode obtained in step S1 in a vacuum consumable electrode arc melting furnace two or three times to obtain a titanium alloy ingot; The ingot obtained in step S2 is subjected to upsetting, drawing, and spheroidizing processes through multiple heat treatments, and then formed into a titanium alloy round bar. Three upsetting and drawing processes are required in the intermediate heat treatment, and upsetting and drawing are performed in each direction so that one upsetting and drawing is performed in each of the x, y, and z directions of the billet, and then spheroidizing is performed in the final heat treatment to form into a round bar. Step S3. Step S4: precision forging the round bar obtained in step S3 by heat treatment twice or less to obtain a round bar with higher dimensional accuracy, finer structure, and uniform radial structure; Step S5: After annealing and removing distortions from the round bar processed in step S4, the round bar is subjected to turning and drilling to obtain a titanium alloy seamless pipe raw material. Step S6: subjecting the titanium alloy seamless pipe raw material obtained in step S5 to multiple stages of cold rolling to form a titanium alloy seamless pipe semi-finished product; Step S7: vacuum annealing and pickling are sequentially performed on the titanium alloy seamless pipe semi-finished product obtained in step S6; Step S8: performing electrolytic-magnetic composite polishing on the pipe material treated in step S7; and step S9 of subjecting the titanium alloy seamless tube treated in step S8 to shot blasting.

[0008] Furthermore, the titanium alloy ingot has an oxygen content in the range of 0.08 to 0.12%, and an additionally added rare earth element Tb content in the range of 0.001 to 0.05%.

[0009] Furthermore, in the step S3, the ingot is kept at a temperature of 880°C to 1100°C for 4.5 to 5 hours before multiple upsetting and drawing processes are carried out.

[0010] Furthermore, in step S4, the precision forging is performed at a temperature of [T-(100-200)]°C (where T is the titanium alloy phase transition point), the temperature retention time is 1.5-3 hours, and the deformation amount in each heat treatment is in the range of 40-55%.

[0011] Furthermore, in the step S5, the annealing is performed at a temperature of [T-(150 to 250)]°C for a holding time of 1.5 to 3 hours.

[0012] Furthermore, in step S6, the multiple-stage cold rolling has an intermediate annealing temperature of [T-(200-300)]°C, a holding time of 1-2 hours, a ratio Q of the relative wall thickness reduction to the relative tube diameter reduction in the last two stages is in the range of 1.5-2, the deformation amount in the last two stages of cold rolling is in the range of 40%-50%, and Q≧1 in the remaining stages.

[0013] Furthermore, in the step S7, the vacuum annealing is carried out at a temperature of [T-(350 to 500)]°C for a temperature retention time of 1 to 2 hours.

[0014] Furthermore, in step S8, a 10% NaNO3 solution is used as the electrolyte, stainless steel powder with a particle size of 100 to 200 μm is used as the magnetic abrasive particles, and the surface roughness of the inner and outer surfaces of the pipe material after polishing is 0.09 μm or less.

[0015] Furthermore, in step S9, stainless steel beads having a diameter of 20 to 50 μm are used as shot blasting beads, and the residual stress on the inner and outer surfaces of the pipe material after treatment is a compressive stress in the range of −150 MPa to −300 MPa. [Effects of the Invention]

[0016] Compared with the prior art, the present invention has the following advantageous effects.

[0017] In this invention, the titanium alloy composition is optimized, and a titanium alloy round bar with a consistent radial structure is obtained through multidirectional upsetting, drawing, and precision forging. The round bar is then machined to obtain a cold-rolled tube blank. Subsequent control of the Q value during the cold rolling process ensures that the CSR value and outer diameter of the resulting titanium alloy seamless tube satisfy a specific relationship. Finally, electrolytic-magnetic composite polishing and shot blasting are used in combination to ensure the tube's surface roughness and compressive stress. This integrated manufacturing method improves the rotating bending fatigue properties of the titanium alloy seamless tube, enabling it to pass a 20 million cycle test. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of the metallographic structure of a pipe material according to Example 1 of the present invention. [Figure 2] FIG. 2 is a pole figure of the pipe material of Example 1 according to the present invention. [Figure 3] 1 is a schematic diagram of the surface morphology of a pipe material according to Example 1 of the present invention. [Figure 4] FIG. 2 is a schematic diagram of the metallographic structure of a pipe material according to Example 2 of the present invention. [Figure 5] FIG. 10 is a pole figure of a pipe material according to a second embodiment of the present invention. [Figure 6] FIG. 4 is a schematic diagram of the surface morphology of a pipe material according to Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] For convenience in understanding the present application, the present application will be described in more detail below with reference to the accompanying drawings. In these drawings, preferred embodiments of the present application are shown. It should be noted that the present application is not limited to the examples set forth herein, but may be realized in many different forms. These embodiments are provided to enable a deeper and more complete understanding of the disclosure of the present application.

[0020] The specific steps of the method for improving the fatigue properties of a titanium alloy seamless pipe according to the present invention are as follows:

[0021] In step S1, materials are mixed and pressed into a plurality of electrode blocks, which are then welded together to obtain consumable electrodes.

[0022] In step S2, the consumable electrode obtained in step S1 is melted and refined two or three times in a vacuum consumable electrode arc melting furnace to obtain a titanium alloy ingot.

[0023] The oxygen content in the titanium alloy ingot components is controlled to be in the range of 0.08 to 0.12%, and the content of the additionally added rare earth element Tb is controlled to be in the range of 0.001 to 0.05%, thereby improving the ductility of the alloy. Here, the percentages are mass percentages.

[0024] In step S3, the ingot obtained in step S2 is kept at 800-1100°C for 4.5-5 hours, and then subjected to multiple heat treatments of upsetting, drawing, and spheroidizing to form a titanium alloy round bar. Among these, three upsetting and drawing steps are required in the intermediate heat treatments, and upsetting and drawing are performed in each direction so that one upsetting and drawing step is performed in each of the x, y, and z directions of the billet, and the final heat treatment is performed to form the round bar by spheroidizing.

[0025] In step S4, the round bar obtained in step S3 is precision forged at a temperature of [T-(100-200)]°C (where T is the titanium alloy phase transition point), with a heat retention time of 1.5-3 hours and a deformation amount of 40-55%, with two or fewer heat treatments performed to obtain a round bar with higher dimensional accuracy, a finer structure and a consistent radial structure.

[0026] In step S5, the round bar processed in step S4 is annealed and stress-relieved under the conditions of an annealing temperature of [T-(150 to 250)]°C and a temperature retention time of 1.5 to 3 hours, and after the annealing and stress-relieving treatment, it is subjected to turning and drilling to obtain a titanium alloy seamless pipe raw material.

[0027] In step S6, the titanium alloy seamless pipe raw material obtained in step S5 is cold-rolled in multiple stages to form a titanium alloy seamless pipe semi-finished product. Here, the outer diameter of the pipe material is set to 25 mm or less, the intermediate annealing temperature is [T-(200-300)]°C, the warm-holding time is set to 1-2 hours, the ratio Q of the relative wall thickness reduction to the relative pipe diameter reduction in the last two stages is set to 1.5-2, the deformation amount in the last two cold rolling stages is set to 40%-50%, and Q in the remaining stages is set to 1 or more. By performing steps S4 and S6, it is possible to ensure that the CSR value of the pipe material is 1.4-2.4.

[0028] In step S7, the titanium alloy seamless pipe semi-finished product obtained in step S6 is subjected to vacuum annealing and pickling in this order. Here, the vacuum annealing is performed at a temperature of [T-(350-500)]°C for an incubation time of 1-2 hours.

[0029] In step S8, the pipe material processed in step S7 is subjected to electrolytic-magnetic hybrid polishing. Here, a 10% NaNO3 solution is used as the electrolyte, forming a low-hardness passivation film on the surface of the pipe material. The surface roughness of the pipe material can be initially increased by using stainless steel powder with a particle size of 100 to 200 μm as the magnetic abrasive particles; too small a particle size is detrimental to the polishing efficiency. After polishing, the surface roughness of the inner and outer surfaces of the pipe material is 0.09 μm or less.

[0030] In step S9, the titanium alloy seamless tube processed in step S8 is shot-blasted. Stainless steel beads with a diameter of 20 to 50 μm are used for shot-blasting. Because the tube wall is thin, excessively large particle sizes would damage the surface of the tube. After the process, the residual stress on the inner and outer surfaces of the tube is compressive stress in the range of -150 MPa to -300 MPa. This offsets the tensile stress experienced in some tubes during rotating bending fatigue tests, improving their performance. On the other hand, excessively high surface residual stress can adversely affect the mechanical performance of the tube itself.

[0031] The present invention will be described in more detail below with reference to specific examples and comparative examples.

[0032] [Example 1] The following manufacturing process steps were adopted to manufacture TA18 titanium alloy seamless tubes with dimensions of Φ20×1.6 mm.

[0033] The manufacturing process steps are as follows: Raw material → Electrode → Φ660mm cast ingot (oxygen content: 0.08%, Tb content: 0.03%) → Machining → Upset and draw forging at 1100℃ (upset and drawing with different orientation) → Upset and draw forging at 950℃ (upset and drawing with different orientation) → Upset and draw forging at 890℃ (upset and drawing with different orientation) → Upset and draw forging at 880℃ (drawing and spheroidizing) to produce a Φ140 round bar → Precision forging to produce a Φ1 Production of 00 round bar → Production of Φ60 round bar by precision forging in the second heat treatment → Annealing and distortion removal at 750℃ / 2h → Production of Φ58×9 tube blank by machining → Cold rolling to Φ42×5.7 → Vacuum annealing at 700℃ / 2h → Cold rolling to Φ33×3.8 → Vacuum annealing at 700℃ / 2h → Cold rolling to Φ26×2.5 → Vacuum annealing at 600℃ / 2h → Cold rolling to Φ20×1.6 → Vacuum annealing at 500℃ / 2h → Distortion removal and pickling → Electrolytic-magnetic combined polishing → Shot blasting.

[0034] The TA18 titanium alloy seamless pipe manufactured in this example had a CSR value of 2.0, an inner surface roughness of 0.07 μm, an outer surface roughness of 0.05 μm, an inner residual compressive stress of -232 MPa, and an outer residual compressive stress of -275 MPa. It passed a rotating bending fatigue test of 20 million cycles.

[0035] [Example 2] The following manufacturing process steps were adopted to manufacture TA18 titanium alloy seamless tubes with a size of Φ12 × 1.1 mm.

[0036] The manufacturing process steps are as follows: Raw material → Electrode → Φ750mm cast ingot (oxygen content: 0.01%, Tb content: 0.008%) → Machining → Upset and draw forging at 1100℃ (upset and draw with different orientation) → Upset and draw forging at 950℃ (upset and draw with different orientation) → Upset and draw forging at 890℃ (upset and draw with different orientation) → Upset and draw forging at 880℃ (spheroidizing) to produce a Φ110 round bar → Precision forging to produce a Φ80 round bar in the first heat treatment → Second heat treatment Precision forging to produce a Φ52 round bar → annealing and straightening at 750℃ / 2h → machining to produce a Φ48×6.5 tube blank → cold rolling to Φ35×4.5 → vacuum annealing at 700℃ / 2h → cold rolling to Φ27×3.2 → vacuum annealing at 700℃ / 2h → cold rolling to Φ19×2.5 → vacuum annealing at 600℃ / 2h → cold rolling to Φ15×1.7 → vacuum annealing at 500℃ / 2h → cold rolling to Φ12×1.1 → vacuum annealing at 500℃ / 2h → straightening and pickling → electrolytic-magnetic combined polishing → shot blasting.

[0037] The TA18 titanium alloy seamless pipe manufactured in this example had a CSR value of 1.8, an inner surface roughness of 0.1 μm, an outer surface roughness of 0.08 μm, an inner residual compressive stress of -215 MPa, and an outer residual compressive stress of -187 MPa. It passed a rotating bending fatigue test of 20 million cycles.

[0038] Any matter not described in detail in the present invention is well known in the art. The technical features in the above-described embodiments can be combined in any manner. For the sake of convenience, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be understood that it is within the scope described in this specification.

[0039] The above examples merely illustrate some embodiments of the present application, and although more specific and detailed descriptions have been provided, they should not be understood as limiting the scope of the present invention patent. Those skilled in the art should understand that some modifications and improvements can be made without departing from the spirit of the present application, and these fall within the scope of protection of the present application. Therefore, the scope of protection of the present invention patent should be governed by the appended claims.

Claims

1. a step S1 of mixing materials, forming them into a plurality of electrode blocks by pressing, and welding the plurality of electrode blocks to obtain consumable electrodes; Step S2: melting and refining the consumable electrode obtained in step S1 in a vacuum consumable electrode arc melting furnace two or three times to obtain a titanium alloy ingot; The ingot obtained in step S2 is subjected to upsetting, drawing, and spheroidizing processes through multiple heat treatments to form it into a titanium alloy round bar, and three upsetting and drawing processes are required in the intermediate heat treatments, and the upsetting and drawing processes are performed by changing the direction so that one upsetting and drawing is performed in each of the x, y, and z directions of the billet, and then a final heat treatment is performed to form it into a round bar. Step S4: precision forging the round bar obtained in step S3 by heat treatment twice or less to obtain a round bar with higher dimensional accuracy, finer structure, and uniform radial structure; Step S5: annealing and removing distortion of the round bar processed in step S4, and then turning and drilling the round bar to obtain a titanium alloy seamless pipe raw material. Step S6: performing multiple stages of cold rolling on the titanium alloy seamless pipe raw material obtained in step S5 to form a titanium alloy seamless pipe semi-finished product; a step S7 in which the titanium alloy seamless pipe semi-finished product obtained in the step S6 is vacuum annealed and pickled in sequence; A step S8 of performing electrolytic-magnetic composite polishing on the pipe material treated in the step S7; and step S9 of subjecting the titanium alloy seamless tube treated in step S8 to shot blasting.

2. 2. The method for improving the fatigue properties of a titanium alloy seamless pipe as claimed in claim 1, wherein the titanium alloy ingot has an oxygen content in the range of 0.08 to 0.12%, and the content of the additionally added rare earth element Tb in the range of 0.001 to 0.05%.

3. 2. The method for improving the fatigue properties of a titanium alloy seamless tube as claimed in claim 1, wherein in step S3, before performing multiple upsetting and drawing, the ingot is kept at a temperature of 880°C to 1100°C for 4.5 to 5 hours.

4. 2. The method for improving the fatigue properties of a titanium alloy seamless tube according to claim 1, wherein in step S4, the precision forging is performed at a temperature of [T-(100-200)]°C (where T is the titanium alloy phase transition point), the heat-holding time is 1.5-3 hours, and the deformation amount in each heat treatment is in the range of 40-55%.

5. The method for improving the fatigue properties of a titanium alloy seamless tube according to claim 1, characterized in that in step S5, the annealing temperature is [T-(150-250)]°C, and the heat-holding time is 1.5-3 hours.

6. 2. The method for improving the fatigue properties of a titanium alloy seamless tube according to claim 1, wherein in step S6, the multi-stage cold rolling has an intermediate annealing temperature of [T-(200-300)]°C, a holding time of 1-2 hours, a ratio Q of the relative wall thickness reduction to the relative tube diameter reduction in the last two stages is in the range of 1.5-2, a deformation amount in the last two cold rolling stages is in the range of 40%-50%, and Q in the remaining stages is 1 or more.

7. 2. The method for improving the fatigue properties of a titanium alloy seamless tube according to claim 1, wherein in step S7, the vacuum annealing is performed at a temperature of [T-(350-500)]°C and the heat-holding time is 1-2 hours.

8. In step S8, 10% NaNO was used as the electrolyte. ３ The method for improving the fatigue properties of a titanium alloy seamless tube according to claim 1, characterized in that the solution is used, the magnetic abrasive particles are stainless steel powder with a particle size of 100-200 μm, and the surface roughness of the inner and outer surfaces of the tube material after polishing is 0.09 μm or less.

9. 2. The method for improving the fatigue properties of a titanium alloy seamless tube as claimed in claim 1, wherein in step S9, stainless steel beads having a diameter of 20 to 50 μm are used as shot blasting beads, and the residual stress on the inner and outer surfaces of the tube after treatment is a compressive stress in the range of -150 MPa to -300 MPa.

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