Preparation method of titanium alloy super-thick-wall hot-rolled pipe

Abstract

The invention relates to a preparation method of a titanium alloy super-thick-wall hot-rolled pipe, which comprises the following steps: S1, freely forging a titanium alloy cast ingot into a bar blank, and forging heating number is not less than four; s2, the bar billet is placed in a heating furnace to be heated in a sectional mode; s3, after heating is stopped, the bar is cooled to the room temperature in the furnace; s4, repeating the steps S2-S3 for two to three times; s5, the bar billet is heated again; s6, the heated pipe blank is subjected to cross piercing; s7, the hot-rolled perforated pipe directly enters a heat preservation sleeve; s8, hot air precooling is conducted on the surface of the heat preservation sleeve; s9, the perforated pipe is taken out of the heat preservation sleeve and air-cooled to the room temperature; and S10, the perforated pipe is sequentially subjected to annealing, straightening, machining and flaw detection, and then the finished titanium alloy super-thick-wall seamless pipe is obtained. The titanium alloy super-thick-wall hot-rolled pipe prepared through the method has the dual-state structure morphology, meanwhile, the high surface quality and the high yield are achieved, and more excellent deformation performance is provided for subsequent machining.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy pipe manufacturing, in particular to a method for preparing an ultra-thick-wall hot-rolled titanium alloy pipe. Background Art

[0002] Titanium alloy ultra-thick wall tubes usually refer to titanium alloy tubes with a diameter-to-thickness ratio of less than 5. Compared with traditional extruded tubes, oblique rolling and piercing have the characteristics of high production efficiency, low cost, and high yield rate.

[0003] However, due to the large wall thickness of the thick-walled tube, it is difficult to deform the rolled piece in the radial direction. The difference between the inner diameter of the tube and the diameter of the plug is small, which increases the difficulty of piercing and easily causes the phenomenon of back-stuck. At the same time, due to the large heat generated by deformation, the temperature of the deformation zone rises rapidly, and the instantaneous temperature exceeds the T of the titanium alloy. β Phase transition temperature. During the cooling process after piercing, water quenching is usually used, which results in a faster cooling rate for the outer wall of the thick-walled tube. However, the thermal conductivity of titanium alloy is low, and the deformation temperature rise and heat in the core are high, which cannot be conducted in time. As a result, the microstructure of each part of the tube is unevenly distributed, and coarse Widmanstätten or basketweave structures are very likely to appear. In particular, the brittle phase is prone to form on the surface of the tube, leading to problems such as cracking on the surface of the hot-rolled tube. In addition, it is impossible to obtain a dual-state structure with excellent comprehensive performance, which affects subsequent processing. Summary of the Invention

[0004] To address the above-mentioned issues, the present invention aims to provide a method for producing ultra-thick-wall hot-rolled titanium alloy tubes. By subjecting the titanium alloy tube blank to segmented, step-wise heating, residual stress within the tube blank is eliminated, the α→β phase transition is complete, and the overall uniformity of the tube is improved. Simultaneously, a cooling process combining tubing and hot air pre-cooling is employed to mitigate the impact of rapid cooling caused by air cooling, reduce internal stress and internal and external wall microstructure heterogeneity, and lower the probability of surface cracking in the tube. This improves the tube yield and mechanical properties, resulting in a high-performance dual-modal microstructure.

[0005] The technical solution adopted in the present invention is as follows:

[0006] The present invention provides a method for preparing an ultra-thick-wall hot-rolled titanium alloy tube, which specifically comprises the following steps:

[0007] S1. Free forging the titanium alloy ingot into a bar billet, with the forging number of not less than four times;

[0008] S2, placing the billet in a heating furnace for segmented heating;

[0009] S3. After stopping heating, the bar material is cooled to room temperature in the furnace;

[0010] S4, repeat steps S2-S3 two or three times;

[0011] S5. Heat the rod again to T β-(10~50℃), heating rate 5~10℃ / min, keep warm for 1~2h;

[0012] S6, performing oblique rolling and piercing on the heated tube blank;

[0013] S7, the hot-rolled perforated pipe directly enters the insulation sleeve;

[0014] S8. Pre-cool the surface of the insulation sleeve with hot air;

[0015] S9, taking the perforated pipe out of the insulation sleeve and air-cooling it to room temperature;

[0016] S10. The perforated tube is sequentially annealed, straightened, machined and inspected to obtain a finished titanium alloy ultra-thick wall seamless tube.

[0017] Furthermore, in step S2, the segmented heating specifically includes: low-temperature stress relief heating: heating from room temperature to 400-550°C, heating rate 5-8°C / min, keeping warm for 20-30min; continuing heating to T in two stages β -(50~80℃), first stage heating rate 6~10℃ / min to T β -(100~150℃), secondary heating rate 15~20℃ / min, each level keeping 10~15min; quickly heat up to T β +(5~10℃), heating rate ≥20℃ / min, keep warm for 5~10min.

[0018] Furthermore, in step S2, the heating furnace is a vacuum heating furnace with a vacuum degree of ≤10 -3 Pa.

[0019] Furthermore, in step S7, the thermal insulation sleeve is an alumina ceramic tube.

[0020] Furthermore, in step S7, the insulation sleeve needs to be preheated to T before the perforated pipe enters. β -(200~350℃).

[0021] Furthermore, in step S7, the inner diameter D of the thermal insulation sleeve and the outer diameter d of the perforated pipe have the following relationship: D=d+(20-30 mm).

[0022] Furthermore, the step S8 includes blowing hot air onto the surface of the insulation sleeve, the hot air temperature being 120-150°C, and stopping blowing the hot air when the temperature of the tube billet cools to 400-550°C.

[0023] Furthermore, in step S10, the diameter of the finished tube is 70-160 mm, and the diameter-to-thickness ratio is less than 5.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention precisely controls the temperature gradient during the heating process and heats the product above the phase transition temperature T β The above repeated heat treatment method fully eliminates the residual stress in the titanium alloy bar blank and achieves uniform bar structure. After passing through the tube, it directly enters the casing, which has a good thermal insulation effect, reduces the temperature difference between the surface and the core, and is pre-cooled with hot air to slow down the cooling rate, ensuring the formation of a dual-state structure morphology with better performance. At the same time, it can reduce the stress concentration and structural unevenness caused by the perforation process of the titanium alloy thick-walled tube, avoid cracking during perforation, and improve the surface quality and yield of the product. Step heating and repeated heating can reduce the rolling force by about 18 to 22%, extending the life of the roller. The technical solution proposed by the present invention has broad market prospects. It can not only improve the product quality and production efficiency of titanium alloy thick-walled tubes, but also reduce the probability of hot rolling cracking, and effectively improve the product qualification rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the metallographic annealing structure of the titanium alloy tube prepared in Example 1 of the present invention;

[0027] Figure 2 Schematic diagram of the metallographic annealing structure of the titanium alloy tube prepared in Example 2 of the present invention;

[0028] Figure 3 Schematic diagram of the metallographic annealing structure of the titanium alloy tube prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] The present invention proposes a method for preparing ultra-thick-wall hot-rolled titanium alloy tubes. Figure 1 As shown, the specific steps include:

[0031] S1. Free forge the titanium alloy ingot into a bar billet, with the forging number of not less than four times.

[0032] S2. Place the billet in a heating furnace for segmented heating; the heating furnace is a vacuum heating furnace with a vacuum degree of ≤10 -3 Pa; the segmented heating specifically includes:

[0033] (1) Low-temperature stress relief heating: heating from room temperature to 400-550°C at a heating rate of 5-8°C / min and keeping warm for 20-30 minutes; (2) Continue heating in two stages to T β -(50~80℃), first stage heating rate 6~10℃ / min to T β -(100~150℃), secondary heating rate 15~20℃ / min, each stage heat preservation 10~15min; (3) rapid heating to T β +(5~10℃), heating rate ≥20℃ / min, keep warm for 5~10min.

[0034] By adopting segmented heating, heat preservation in the low temperature stage eliminates the residual stress inside the billet, heat preservation in the medium temperature range promotes the uniformity of α→β phase transformation, and heat preservation above the phase transformation point achieves the uniformity of the composition and organization of the billet. At the same time, ultra-short high temperature insulation method is adopted to control the growth of β grains and improve the thermoplasticity of the pipe.

[0035] S3. After stopping heating, the bar material is cooled to room temperature in the furnace.

[0036] S4, repeat steps S2-S3 two or three times;

[0037] Repeated heat treatment can further improve the overall uniformity of the billet and eliminate the residual stress caused by the deformation of the billet.

[0038] S5. Heat the rod again to T β -(10~50℃), heating rate 5~10℃ / min, keep warm for 1~2h.

[0039] S6, performing oblique rolling and piercing on the heated tube blank;

[0040] The perforation is performed at a temperature below the phase change temperature. Considering that thick-walled tubes are difficult to deform and have a significant temperature rise, lowering the perforation temperature can reduce the temperature rise of the core caused by deformation and reduce the temperature difference between the core and the outer wall.

[0041] S7, the hot-rolled perforated tube is directly put into the insulation sleeve; wherein, the insulation sleeve is an alumina ceramic tube; the inner diameter D of the insulation sleeve and the outer diameter d of the perforated tube have the following relationship: D = d + (20 ~ 30mm); the insulation sleeve needs to be preheated to T before the perforated tube enters β -(200~350℃);

[0042] The casing method is used to prevent the perforated thick-walled tube from directly contacting the air, causing a large temperature difference between the inner and outer walls, thereby producing abnormal tissue, and achieving the effect of uniform and slow cooling of the thick-walled tube.

[0043] S8. Pre-cool the surface of the insulation sleeve with hot air: blow hot air to the surface of the insulation sleeve at a temperature of 120-150°C. Stop blowing the hot air when the tube temperature cools to 400-550°C.

[0044] By pre-cooling with hot air, the problem of significant temperature difference between the inner and outer walls caused by cooling is further reduced, providing sufficient cooling time for the phase change of the perforated tube.

[0045] S9. Remove the perforated pipe from the insulation sleeve and air-cool it to room temperature.

[0046] S10 and perforated tubes are successively annealed, straightened, machined and inspected to obtain finished titanium alloy ultra-thick wall seamless tubes; the diameter of the finished tubes is 70 to 160 mm, and the diameter-to-thickness ratio is less than 5; the material of the finished tubes can be TA15, TA10, TC4 and other brands.

[0047] The titanium alloy ultra-thick wall tube prepared by the method of the present invention has a dual-state microstructure, and at the same time has high surface quality and yield rate, providing more superior deformation performance for subsequent processing.

[0048] The effects of the present invention will be further described below by means of specific examples and comparative examples:

[0049] Example 1

[0050] S1. The TC4 titanium alloy ingot is free forged into Φ85 mm billet by four times.

[0051] S2. Place the billet into a vacuum heating furnace for staged heating: (1) Low-temperature stress relief heating: Heat from room temperature to 400°C at a heating rate of 5°C / min and hold for 20 minutes. (2) Continue heating to 930°C in two stages: a first stage heating rate of 6°C / min to 880°C and a second stage heating rate of 20°C / min to 930°C, each stage holding for 10 minutes. (3) Rapidly heat to 990°C at a heating rate of 20°C / min and hold for 5 minutes.

[0052] S3. After stopping heating, the bar material is cooled to room temperature in the furnace.

[0053] S4. Repeat steps S2-S3 twice.

[0054] S5. Heat the rod again to 970°C at a heating rate of 10°C / min and keep warm for 2 hours.

[0055] S6. The heated tube billet is subjected to oblique rolling and punching to form a Φ89×20mm tube.

[0056] S7. The hot-rolled perforated tube is directly placed into the alumina ceramic sleeve. The sleeve needs to be preheated to 780°C in advance. The inner diameter of the sleeve is D = 110 mm.

[0057] S8. Pre-cool the surface of the casing with hot air and blow hot air onto the casing surface. The hot air temperature is 120℃. Stop blowing the hot air when the surface temperature of the tube cools to 400℃.

[0058] S9. Remove the perforated tube from the casing and air-cool it to room temperature.

[0059] S10. The perforated tube is annealed at 850°C for 2h, straightened, machined, and inspected to obtain a titanium alloy seamless tube.

[0060] The metallographic annealing structure of the titanium alloy seamless tube prepared in this embodiment is as follows: Figure 1 shown.

[0061] Example 2

[0062] S1. The TC4 titanium alloy ingot is free forged into Φ85 mm billet through five times.

[0063] S2. Place the billet into a vacuum heating furnace for staged heating: (1) Low-temperature stress relief heating: Heat from room temperature to 550°C at a heating rate of 8°C / min and hold for 30 minutes. (2) Continue heating to 900°C in two stages: a first stage heating rate of 10°C / min to 830°C and a second stage heating rate of 15°C / min to 900°C, each stage holding for 15 minutes. (3) Rapidly heat to 985°C at a heating rate of 25°C / min and hold for 10 minutes.

[0064] S3. After stopping heating, the bar material is cooled to room temperature in the furnace.

[0065] S4. Repeat steps S2-S3 three times.

[0066] S5. Heat the rod again to 930°C at a heating rate of 5°C / min and keep warm for 1 hour.

[0067] S6. The heated tube billet is subjected to oblique rolling and punching to form a Φ89×25mm tube.

[0068] S7. The hot-rolled perforated tube is directly placed into the alumina ceramic sleeve. The sleeve needs to be preheated to 630°C in advance. The inner diameter of the sleeve is D = 120 mm.

[0069] S8. Pre-cool the surface of the casing with hot air and blow hot air onto the surface of the casing. The hot air temperature is 150℃. Stop blowing the hot air when the surface temperature of the tube cools to 550℃.

[0070] S9. Remove the perforated tube from the casing and air-cool it to room temperature.

[0071] S10. The perforated tube is annealed at 850°C for 2h, straightened, machined, and inspected to obtain a titanium alloy seamless tube.

[0072] The metallographic annealing structure of the titanium alloy seamless tube prepared in this embodiment is as follows: Figure 2 shown.

[0073] Comparative Example 1

[0074] S1. The TC4 ingot is free forged into Φ85mm forged rods by 4 times.

[0075] The S2 and TC4 forging bars were heated to 930 °C at a heating rate of 20 °C / min.

[0076] S3. After the forged rod is taken out of the furnace, it is subjected to oblique rolling and punching to prepare a Φ89×25mm titanium alloy tube.

[0077] S4. The perforated tube enters the water tank and is cooled by water quenching.

[0078] S5. The perforated tube is annealed at 850℃ for 2h, straightened, machined and inspected to obtain a titanium alloy seamless tube.

[0079] The metallographic annealing structure of the titanium alloy seamless pipe prepared in this comparative example is as follows: Figure 3 shown.

[0080] The tensile properties of the titanium alloy seamless pipes prepared in Example 1, Example 2 and Comparative Example 1 are shown in the following table:

[0081] <![CDATA[R p0.2 / MPa]]> <![CDATA[R m / MPa]]> A / ％ Example 1 875 965 17 Example 2 903 984 16 Comparative Example 1 768 831 13

[0082] Matters not described in detail in this invention are all known technologies.

[0083] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for preparing ultra-thick-wall hot-rolled titanium alloy tubes, characterized in that: The process comprises the following steps: S1. Free forging the titanium alloy ingot into a bar billet, with the forging number of not less than four times; S2, placing the billet in a heating furnace for segmented heating; S3. After stopping heating, the bar material is cooled to room temperature in the furnace; S4, repeat steps S2-S3 two or three times; S5. Heat the rod again to T β -(10~50℃), heating rate 5~10℃ / min, keep warm for 1~2h; S6, performing oblique rolling and piercing on the heated tube blank; S7, the hot-rolled perforated pipe directly enters the insulation sleeve; S8. Pre-cool the surface of the insulation sleeve with hot air; S9, taking the perforated pipe out of the insulation sleeve and air-cooling it to room temperature; S10. The perforated tube is sequentially annealed, straightened, machined and inspected to obtain a finished titanium alloy ultra-thick wall seamless tube.

2. The method for preparing an ultra-thick-wall hot-rolled titanium alloy tube according to claim 1, characterized in that: In step S2, the segmented heating specifically includes: low-temperature stress relief heating: heating from room temperature to 400-550°C, heating rate 5-8°C / min, keeping warm for 20-30min; continuing heating to T in two stages; β -(50~80℃), first stage heating rate 6~10℃ / min to T β -(100~150℃), secondary heating rate 15~20℃ / min, each level keeping 10~15min; quickly heat up to T β +(5~10℃), heating rate ≥20℃ / min, keep warm for 5~10min.

3. The method for preparing an ultra-thick-wall hot-rolled titanium alloy tube according to claim 1, characterized in that: In step S2, the heating furnace is a vacuum heating furnace with a vacuum degree of ≤10 -3 Pa.

4. The method for preparing an ultra-thick-wall hot-rolled titanium alloy tube according to claim 1, wherein: In step S7, the thermal insulation sleeve is an alumina ceramic tube.

5. The method for preparing an ultra-thick-wall hot-rolled titanium alloy tube according to claim 1, characterized in that: In step S7, the insulation sleeve needs to be preheated to T before the perforated pipe enters. β -(200~350℃).

6. The method for preparing an ultra-thick-wall hot-rolled titanium alloy tube according to claim 1, characterized in that: In step S7, the inner diameter D of the thermal insulation sleeve and the outer diameter d of the perforated pipe have the following relationship: D=d+(20-30 mm).

7. The method for preparing an ultra-thick-wall hot-rolled titanium alloy tube according to claim 1, characterized in that: The step S8 includes blowing hot air onto the surface of the insulation sleeve, the hot air temperature is 120-150°C, and the blowing of the hot air is stopped when the temperature of the tube billet cools to 400-550°C.

8. The method for preparing an ultra-thick-wall hot-rolled titanium alloy tube according to claim 1, characterized in that: In step S10, the diameter of the finished pipe is 70-160 mm, and the diameter-to-thickness ratio is less than 5.

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