Easily segregated titanium alloy component efficient homogenization process

Abstract

The invention relates to the technical field of titanium alloy treatment processes, and discloses an easy-segregation titanium alloy component efficient homogenization process which comprises the following steps: step 1, cogging in a single-phase region, heating a cast ingot to the single-phase region, preserving heat for a period of time, and then forging; (2) repeated remelting and forging: remelting the blank forged in the step (1) for short-time heat preservation, then discharging and forging, repeating the remelting and heat preservation and discharging and forging operations for more than or equal to three times, and finally cooling; thirdly, single-phase region step-by-step cooling forging is carried out, and the recrystallization forging technology below the phase transformation point and above the phase transformation point is carried out on the blank obtained after repeated remelting forging in the second step; and 4, two-phase region forging is carried out, and a product is obtained. The invention solves the problems of long time consumption, high energy consumption and serious segregation problem in the homogenization process of the easily segregated titanium alloy in the prior art.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy processing technology, specifically to a highly efficient homogenization process for the composition of easily segregated titanium alloys. Background Technology

[0002] Titanium alloys possess high specific strength, good ductility, and excellent fracture toughness, leading to their increasing market share in the aerospace field. Among them, near-β and β-type titanium alloys, due to their high strength and toughness, are widely used in the manufacture of critical load-bearing components such as aircraft landing gear, main beams, and shafts. However, the strengthening effect of these titanium alloys largely depends on the alloying effects of elements such as Cr, Fe, and Mo. Common examples of such titanium alloys include TC17 (Ti-5Al-4Mo-4Cr-2Zr-2Sn), TB6 (Ti-10Al-2Fe-3V), and Ti-55531 (Ti-5Al-5Mo-5V-3Cr-1Zr). Most of the aforementioned alloying elements are β-stabilizing elements. In the production process of these types of titanium alloys, the poor solubility of the solid / liquid phases leads to macroscopic and microscopic segregation problems. The increased local element content caused by microscopic segregation significantly lowers the local phase transformation point T. β Titanium alloys are typically in (T β -50℃~(T β Forging is carried out within a narrow range of +30℃, within which temperature changes can significantly affect the microstructure and properties.

[0003] Segregation is an inevitable natural phenomenon in vacuum arc remelting. The industry typically suppresses segregation by reducing the melting rate. However, vacuum arc remelting furnaces are limited by equipment characteristics, with a lower allowable melting rate. Excessively low melting rates can cause problems such as incomplete melting at the molten pool edge and ingot surface delamination, severely impacting subsequent hot deformation processing. Moreover, even with extreme control measures during the melting process, these titanium alloys still exhibit severe segregation. Therefore, the industry often employs high-temperature heat treatment of the ingot to help homogenize the elements. This process generally requires heating at above 1100℃ for more than 30 hours, but suffers from insufficient diffusion rate, high energy consumption, and overheating of the microstructure. Subsequent process improvements have led to a combined process of forging followed by water cooling and then similar high-temperature homogenization. This process achieves better homogenization, but still suffers from drawbacks such as long processing time, high energy consumption, and complex procedures. Furthermore, it cannot adequately resolve the segregation problem for alloys like TB6, which exhibit extremely severe segregation. Summary of the Invention

[0004] The present invention aims to provide an efficient homogenization process for easily segregated titanium alloys, in order to solve the problems of long time consumption, high energy consumption and serious segregation problem in the existing homogenization process for easily segregated titanium alloys.

[0005] The inventors discovered that the high-temperature homogenization heat treatment of ingots / bills is designed based on the principle of spontaneous homogenization diffusion of elements at high temperatures. The solution to Fick's second law regarding the diffusion equation can quantitatively describe this process: the time required to complete homogenization is t = k * d. 2 / D, where k is a material constant; d is the diameter of the segregation region; and D is the diffusion coefficient. It can be noted that as the diffusion rate D increases, t decreases, and the increase in t is also related to the square of the size d of the segregation region. Clearly, as the segregation region becomes larger, the required homogenization heat treatment time increases dramatically. This indicates that high-temperature homogenization heat treatment is always an auxiliary means, and the fundamental solution to segregation still relies on the ingot smelting process. It also shows that when the level of smelting segregation is poor, simply extending the high-temperature homogenization heat treatment time to achieve compositional homogenization is extremely costly and has limited effect.

[0006] As mentioned in the background section, there is currently a process where forging is followed by high-temperature homogenization heat treatment, which is more effective than simple heat treatment. For example, invention patent CN117816881A discloses a low-cost method for preparing large-size forged plates of TC18 titanium alloy. First, in step 1, the titanium alloy ingot is forged 2-4 times, with heating and holding during forging followed by upsetting and drawing. Then, in step 2, it is held at temperatures above and below the phase transformation point and forged 4-6 times. This process involves forging first, followed by high-temperature homogenization treatment. This is because the numerous dislocations, grain boundaries, and subgrain boundaries present after forging deformation are rapid diffusion channels for elements. The diffusion rate of elements such as Fe and Cr at these defects is more than two orders of magnitude higher than when they diffuse within the crystal lattice, resulting in better homogenization. However, this current process is merely a simple combination of deformation and high-temperature homogenization heat treatment, and the homogenization effect remains limited. Furthermore, prolonged high-temperature heating after deformation can easily lead to abnormal grain growth, which is difficult to improve in subsequent forging and cannot fully solve the segregation problem.

[0007] In reality, when titanium alloys undergo hot deformation in the single-phase region above 1000℃, their recrystallization rate is extremely fast, often completed within minutes. After recrystallization, the aforementioned dislocation-assisted diffusion effect is significantly weakened, and the subsequent tens of hours of heat preservation remain inefficient and slow diffusion, resulting in low cost-effectiveness and the risk of abnormal grain growth. To address this, the inventors believe that the traditional processing method can be modified. After high-speed crystallization following single-phase region hot deformation, there is no need to wait for a long, inefficient diffusion process, saving significant time while sacrificing a small diffusion effect. Furthermore, the number of high-speed crystallization cycles in the single-phase region hot deformation process can be increased to improve homogenization, thereby improving the overall effect and reducing processing time.

[0008] Based on the inventor's conceptual design described above, the present invention adopts the following technical solution: a highly efficient homogenization process for the composition of easily segregating titanium alloys, comprising the following steps: Step 1: Single-phase region billet preparation. The ingot is heated to the single-phase region, held at that temperature for a period of time, and then forged. Step 2: Repeated re-forging. After the billet forged in Step 1 is forged, it is re-forged in the furnace for a short time and then taken out of the furnace for forging. The re-forging and taking out of the furnace operations are repeated three times or more. Finally, it is cooled. Step 3: Step-by-step cooling forging in the single-phase region. The billet after multiple re-forgings in Step 2 is subjected to recrystallization forging processes below and above the phase transformation point. Step 4: Forging in the two-phase region to obtain the product.

[0009] The principle of this scheme is as follows: Step one is the same as the conventional single-phase zone heating and holding forging process in existing technologies, utilizing high temperature to enhance the thermal diffusion ability of atoms and improve the uniformity of the composition and structure of the ingot; in step two, the billet after single-phase zone blanking in step one is returned to the furnace for short-term holding and then forged, and this short-term holding and forging process is repeated at least three times. Compared with the existing technology of holding the ingot at high temperature for tens of hours (for example, conventional processes require heat treatment for more than 30 hours), this innovative short-term holding and forging process in step two effectively utilizes the fact that "titanium alloys can withstand temperatures of 1000℃ and above..." During hot deformation in the single-phase region, the titanium alloy exhibits a very fast recrystallization rate, often completing the recrystallization process within minutes. During the short-term holding period in step two, the titanium alloy can rapidly recrystallize without the need for the subsequent tens of hours of slow diffusion. This effectively utilizes only the high-speed recrystallization phase, discarding the very long subsequent slow diffusion phase. Repeating the short-term holding period and forging multiple times further enhances the recrystallization effect. Finally, after the step three of progressively cooling forging in the single-phase region and the step four of reforging in the two-phase region, a highly efficient and homogeneous titanium alloy product can be obtained.

[0010] Therefore, step two of this application differs from the conventional one-time long-term high-temperature treatment method. Instead, it adopts a multiple-furnace holding and forging method, which allows the billet to recrystallize at high speed multiple times. Since the holding time of each furnace reheat is short, even if the furnace reheating and forging are repeated multiple times, it can save a lot of time compared with the long-term high-temperature treatment in the prior art. The process in this application can also efficiently homogenize the composition of titanium alloys, which is particularly suitable for the efficient homogenization of titanium alloys such as TB6 with extremely severe segregation. It effectively reduces the time for composition homogenization, saves energy consumption costs, and can effectively ensure the effect of composition homogenization.

[0011] Preferably, as an improvement, the short-term heat preservation time of the billet during each return to the furnace in step two is less than or equal to 1 hour.

[0012] Preferably, as an improvement, the temperature of the billet being kept warm in the furnace during step two is greater than or equal to 1100℃.

[0013] Preferably, as an improvement, the forging upsetting deformation range during forging after short-term heat preservation in step two is 15-30%.

[0014] Preferably, as an improvement, the polishing is performed after cooling in step two.

[0015] Preferably, as an improvement, during the step-by-step cooling forging in the single-phase region in step three, the temperature decreases by 100–200°C.

[0016] Preferably, as an improvement, in step three, during the progressively decreasing temperature forging process, the forging upsetting deformation range is 25% to 50%.

[0017] Preferably, as an improvement, during the two-phase zone forging in step four, the forging is carried out in the two-phase zone 4 to 8 times, and the billet is finally drawn to the predetermined specifications.

[0018] Preferably, as an improvement, in step one the ingot is heated to a temperature greater than or equal to 1150°C in the single-phase region.

[0019] Preferably, as an improvement, the forging upsetting deformation range during forging in step one is 20-40%.

[0020] The beneficial effects of this plan are: 1. In this scheme, in step two, the temperature range during short-term heat preservation in the furnace is controlled to be greater than or equal to 1100℃, and the forging upsetting deformation range during forging after short-term heat preservation in the furnace is controlled to be 15-30%, so as to prevent the billet from cracking severely due to repeated furnace forging.

[0021] 2. When forging the single-phase region in step two, the ingot is heated to a temperature range of 1100°C or higher and held for less than 1 hour. In step two, forging is carried out in no less than 3 forging cycles. The forging upsetting deformation range is 15% to 30% during forging, so that the billet can have suitable deformation and temperature conditions. After heating, the alloying elements diffuse rapidly in the solid phase and become homogenized.

[0022] 3. In step three, a single-phase zone step-down cooling forging process is adopted. The billet after multiple re-forgings in step two is subjected to recrystallization forging processes below and above the phase transformation point. During the single-phase zone step-down cooling forging, the temperature decreases by 100-200℃ at each stage, and the forging upsetting deformation range is 25-50% at each temperature stage. This allows the billet structure to be refined step-by-step multiple times to achieve the goal of uniform structure and controllable texture, effectively improving the strength, toughness and machinability of the titanium alloy. Attached Figure Description

[0023] Figure 1 This is a low-magnification tissue photograph of the finished β-spot from Embodiment 1 of the present invention.

[0024] Figure 2 This is a low-magnification tissue photograph of the finished β-spot from Comparative Example 1 of the present invention.

[0025] Figure 3 This is a high-magnification tissue photograph of the finished β-spot from Embodiment 1 of the present invention.

[0026] Figure 4 This is a high-magnification tissue photograph of the finished β-spot from Comparative Example 1 of the present invention.

[0027] Figure 5 This is a low-magnification photograph of the finished R-state tissue from Embodiment 1 of the present invention.

[0028] Figure 6 This is a low-magnification image of the finished R-state tissue from Comparative Example 1 of this invention. Detailed Implementation

[0029] The following detailed description illustrates the specific implementation method: Example 1 This first embodiment describes a highly efficient process for homogenizing the composition of easily segregating titanium alloys, comprising the following steps: Step 1: Single-phase zone billet preparation. Heat the ingot to the single-phase zone at a temperature of ≥1150℃, then perform one forging pass, with the forging upsetting deformation ranging from 20% to 40%. Step 2: Repeated re-forging. After the billet forged in Step 1 is forged, it is re-forged in the furnace for a short time and then taken out of the furnace for forging. The temperature of the re-forging is greater than or equal to 1100℃ and the holding time of each re-forging is less than or equal to 1 hour. The above re-forging and forging operations are repeated more than or equal to three times. Finally, it is cooled by air cooling and the billet is polished after air cooling. Step 3: Step-by-step cooling forging in the single-phase region. The billet after multiple remelting forgings in Step 2 is subjected to recrystallization forging processes below and above the phase transformation point. During step-by-step cooling forging in the single-phase region, the temperature decreases by 100-200℃ at each stage, and the forging upsetting deformation ranges from 25% to 50% at each temperature stage. Step 4: Two-phase zone forging. The billet is forged 4 to 8 times in the two-phase zone and finally drawn to the predetermined specifications to obtain the product.

[0030] Specifically, this embodiment uses the near-β titanium alloy TB6 as an example. The nominal composition of TB6 titanium alloy is Ti-10Al-2Fe-3V, and the empirical average β transformation temperature is 800℃ (i.e., T). β (The value is 800℃), and the process steps are as follows: Step 1: Single-phase zone billet preparation. Heat the ingot with dimensions of Φ650×1000mm to 1150℃ and hold for 8 hours. Then perform two upsetting and two drawing operations with a forging upsetting deformation of 30%. After forging, return it to the furnace.

[0031] Step 2: Forging in the furnace multiple times, holding at 1150℃ for 1 hour, then removing from the furnace for upsetting and drawing forging. Perform two upsetting and two drawing operations with an upsetting deformation of 25%, and repeat the forging process four times after holding in the furnace. Finally, air cool and grind.

[0032] Step 3: Forging in the single-phase region with progressively decreasing temperature. After holding at 1050℃ for 7 hours, perform two upsetting and two drawing operations with a forging upsetting deformation of 35%. Return to the furnace, hold at 950℃ for 4 hours, and perform two upsetting and two drawing operations with a forging upsetting deformation of 35%. Cool and grind. Then, hold at 760℃ for 7 hours, perform upsetting with a forging upsetting deformation of 30%, and hold at 860℃ for 4 hours, followed by drawing with a forging upsetting deformation of 30%. Finally, air cool and grind.

[0033] Step 4: Two-phase zone forging. The two-phase zone is heated and forged to complete 6 upsetting and drawing processes with a deformation of 30% each, and then drawn to a product bar with a specification of Φ350mm. β spots are then detected.

[0034] Comparative Example 1: Step 1: Heat the ingot with dimensions of Φ650×1000mm to 1150℃ and hold for 50h, and perform two upsetting and two drawing processes with a forging upsetting deformation of 30%, followed by air cooling. Step 2: Forging in the single-phase region with progressively decreasing temperature. After holding at 1050℃ for 7 hours, perform two upsetting and two drawing operations with a forging upsetting deformation of 35%. Return to the furnace, hold at 950℃ for 4 hours, and perform two upsetting and two drawing operations with a forging upsetting deformation of 35%. Cool and grind. Then, hold at 760℃ for 7 hours, perform upsetting with a forging upsetting deformation of 30%, and hold at 860℃ for 4 hours, followed by drawing with a forging upsetting deformation of 30%. Finally, air cool and grind.

[0035] Step 3: Two-phase zone forging. The two-phase zone is heated and forged to complete 6 upsetting and drawing processes with a deformation of 30% each, and then drawn to a product bar with a specification of Φ350mm. β spots are then detected.

[0036] according to Figure 1 and Figure 2 The comparison shows that in Example 1, no bright β spots were observed in the low-magnification microstructure of the finished bar material, while in Comparative Example 1, obvious bright spots were observed. Figure 3 and Figure 4 After high-magnification microstructure examination, it was confirmed that the αp phase content in the bright spots of Comparative Example 1 was less than 5%, indicating β spots, while the αp phase content in Example 1 was 7-10%, with no localized areas below 5%, proving that the titanium alloy treated using the method of Example 1 had better compositional uniformity. Simultaneously, combined with... Figure 5 and Figure 6 After low-magnification examination of the R-state microstructure, it was found that the microstructure of Example 1 was uniform and fine, while the microstructure of Comparative Example 1 was relatively coarse and contained some large grains, further proving that the method can effectively improve the uniformity of composition.

[0037] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A process for efficiently homogenizing the composition of easily segregating titanium alloys, comprising the following steps: Step 1: Single-phase region billet preparation. The ingot is heated to the single-phase region, held at that temperature for a period of time, and then forged. Step 2: Repeated re-forging. After the billet forged in Step 1 is forged, it is re-forged in the furnace for a short time and then taken out of the furnace for forging. The re-forging and taking out of the furnace operations are repeated three times or more. Finally, it is cooled. Step 3: Step-by-step cooling forging in the single-phase region. The billet after multiple re-forgings in Step 2 is subjected to recrystallization forging processes below and above the phase transformation point. Step 4: Forging in the two-phase region to obtain the product; The efficient homogenization process for easily segregated titanium alloy composition according to claim 1 is characterized in that: In step two, the holding time for each return of the billet to the furnace is less than or equal to 1 hour.

2. The efficient homogenization process for easily segregated titanium alloy composition according to claim 1, characterized in that: In step two, the temperature for heat preservation of the billet during return to the furnace is greater than or equal to 1100℃.

3. The efficient homogenization process for the composition of easily segregating titanium alloys according to claim 1, characterized in that: In step two, the forging upsetting deformation range during forging after short-term heat preservation in the furnace is 15-30%.

4. The efficient homogenization process for easily segregated titanium alloy composition according to claim 1, characterized in that: Step two involves polishing after cooling.

5. The efficient homogenization process for the composition of easily segregating titanium alloys according to claim 1, characterized in that: In step three, during the single-phase region forging process, the temperature decreases by 100–200°C at each stage.

6. The efficient homogenization process for the composition of easily segregating titanium alloys according to claim 1, characterized in that: In step three, during the progressively decreasing temperature forging process, the forging upsetting deformation ranges from 25% to 50%.

7. The efficient homogenization process for easily segregated titanium alloy composition according to claim 1, characterized in that: In step four, during the two-phase zone forging process, the billet is forged 4 to 8 times in the two-phase zone and finally drawn to the predetermined specifications.

8. The efficient homogenization process for easily segregated titanium alloy composition according to claim 1, characterized in that: In step one, the ingot is heated to a temperature greater than or equal to 1150°C in the single-phase region.

9. The efficient homogenization process for easily segregated titanium alloy composition according to claim 1, characterized in that: In step one, the forging upsetting deformation range is 20-40%.

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