Heat treatment method for improving impact toughness of WTD1200 titanium alloy

Abstract

The invention discloses a heat treatment method for improving impact toughness of a WTD1200 titanium alloy, which comprises the following steps: 1, preserving heat of a WTD1200 titanium alloy bar at (Ts-20)-(Ts-60) DEG C for 1-2 hours, then cooling the WTD1200 titanium alloy bar to (Ts-100)-(Ts-140) DEG C along with a furnace, preserving heat for 1-2 hours, taking out the WTD1200 titanium alloy bar, and air-cooling the WTD1200 titanium alloy bar to room temperature; 2, carrying out heat preservation at 460-600 DEG C for 4-8 hours, taking out, and carrying out air cooling to room temperature; and thirdly, heat preservation is conducted for 1 h to 4 h at the temperature of 700 DEG C to 750 DEG C, the WTD1200 titanium alloy bar is taken out and air-cooled to the room temperature, and the WTD1200 titanium alloy bar subjected to heat According to the method, multi-stage heat treatment is adopted, the WTD1200 titanium alloy bar is promoted to be separated out to generate a large number of alpha phases and grow to the micron order, meanwhile, the structure uniformity of the WTD1200 titanium alloy bar is improved, the impact toughness of the WTD1200 titanium alloy bar is improved, and the WTD1200 titanium alloy bar is suitable for the extreme service environment.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy heat treatment, and particularly relates to a heat treatment method for improving the impact toughness of WTD1200 titanium alloy. Background Art

[0002] Titanium alloys are widely used in aerospace, weapons, petrochemicals, automobiles, construction, biomedicine, and daily life due to their high specific strength, good corrosion resistance, excellent biocompatibility, and non-magnetic properties. Based on their phase composition, titanium alloys are divided into three categories: α alloys, β alloys, and α+β alloys. β alloys contain a large amount of β-stabilizing elements. These alloys can be strengthened through heat treatment, resulting in high strength and excellent impact resistance. However, due to the large differences in the melting points of β-stabilizing elements, they are prone to local segregation during solidification or thermal deformation, leading to uneven microstructure and affecting the alloy's physical properties.

[0003] WTD1200 titanium alloy is a β-titanium alloy containing a large amount of β-stabilizing elements. Its nominal chemical composition is Ti-5Al-3.5Mo-3Cr-2Fe-1.5Zr-1.5V. This alloy can maintain a tensile strength of 1200MPa while maintaining an elongation of more than 10%, which belongs to the category of high-strength titanium alloys. However, WTD1200 titanium alloy is prone to structural inhomogeneity after hot deformation such as forging or rolling, resulting in low impact toughness. In addition, structural inhomogeneity also poses a major safety hazard to the material's service life. Therefore, it is necessary to improve structural inhomogeneity through appropriate treatment to ensure that the alloy meets the requirements of use. Heat treatment is a simple and efficient post-treatment method that can improve structural uniformity, thereby optimizing performance and improving impact toughness. However, the existing WTD1200 titanium alloy heat treatment process adopts a solid solution + aging method. The structure after heat treatment is unstable, and it is prone to inconsistencies in internal and external structures and local structural inhomogeneity. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned existing technologies and provide a heat treatment method for improving the impact toughness of WTD1200 titanium alloy. This method uses a multi-stage heat treatment to promote the precipitation and growth of a large amount of α phase in the WTD1200 titanium alloy bar to the micron level, effectively improving the microstructure uniformity of the WTD1200 titanium alloy bar and increasing its impact toughness. This solves the problem of uneven microstructure and low impact toughness of the WTD1200 titanium alloy caused by existing heat treatment processes.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a heat treatment method for improving the impact toughness of WTD1200 titanium alloy, characterized in that the method comprises the following steps: Step 1: Place the WTD1200 titanium alloy bar at a temperature of (T s -20)℃~(T s Keep in a resistance furnace at -60℃ for 1h~2h, then cool to (T s -100)℃~(T s -140)℃ and keep warm for 1h~2h, take out and air cool to room temperature, where T s is the phase transition point of WTD1200 titanium alloy bar, in °C; Step 2: Place the WTD1200 titanium alloy bar cooled to room temperature in step 1 in a resistance furnace at a temperature of 460°C to 600°C for 4 to 8 hours, then take it out and air cool it to room temperature; Step 3: Place the WTD1200 titanium alloy rod that has been kept warm and then air-cooled to room temperature in step 2 in a resistance furnace at a temperature of 700°C to 750°C for 1h to 4h, take it out and air-cool it to room temperature to obtain the heat-treated WTD1200 titanium alloy rod.

[0006] Aiming at the problems of uneven structure and low impact toughness of WTD1200 titanium alloy after thermal deformation and unstable structure, inconsistent internal structure and local uneven structure caused by existing solution + aging heat treatment, the present invention first heats the WTD1200 titanium alloy bar at a temperature slightly below the phase transformation point (T s -20)℃~(T s -60)℃ for 1h~2h, then at a temperature far below the phase transition point (T s -100)℃~(T s The WTD1200 titanium alloy rod is kept at -140)℃ for 1h~2h. Through the two-stage heat treatment, the WTD1200 titanium alloy rod is fully transformed, the secondary α phase is precipitated from the β matrix, and the original network grain boundaries are broken or eliminated to the greatest extent; then the WTD1200 titanium alloy rod is kept at 460℃~600℃ for 4h~8h, the metastable β remaining in the WTD1200 titanium alloy rod is transformed into the α phase, and a large amount of α secondary phase is further precipitated to prepare for subsequent heat treatment; finally, the WTD1200 titanium alloy rod is kept at 700℃~750℃ for 1h~4h, so that the secondary α phase precipitated in the previous two heat treatment stages is further grown and homogenized. At the same time, a small amount of new α phase is also formed in this stage, ensuring that there is a large amount of α phase in the alloy, and the diffusion energy is fully activated during the entire heat treatment process of this stage, which promotes the α phase to gradually grow to the micron level, greatly improving the uniformity of the structure in the WTD1200 titanium alloy rod, thereby greatly improving the impact toughness of the WTD1200 titanium alloy rod.

[0007] The aforementioned heat treatment method for improving the impact toughness of WTD1200 titanium alloy is characterized in that the diameter of the WTD1200 titanium alloy bar in step 1 does not exceed 100 mm. By limiting the bar diameter to no more than 100 mm, it is ensured that the α phase can be fully precipitated after the heat treatment.

[0008] The above-mentioned heat treatment method for improving the impact toughness of WTD1200 titanium alloy is characterized in that in step one, the WTD1200 titanium alloy rod is placed in a resistance furnace at a temperature of 840°C and kept warm for 1 hour, and then cooled to 740°C with the furnace and kept warm for 1 hour, in step two, the WTD1200 titanium alloy rod air-cooled to room temperature is placed in a resistance furnace at a temperature of 560°C and kept warm for 6 hours, and in step three, the WTD1200 titanium alloy rod air-cooled to room temperature after keeping warm is placed in a resistance furnace at a temperature of 700°C and kept warm for 1.5 hours.

[0009] The above-mentioned heat treatment method for improving the impact toughness of WTD1200 titanium alloy is characterized in that the structure of the WTD1200 titanium alloy bar after heat treatment in step 3 is uniform and has no segregation, and the impact resistance is 35J / cm 2 Compared with existing titanium alloys, the heat-treated WTD1200 titanium alloy bar of the present invention has both high strength and high impact toughness, which is conducive to application in special service environments.

[0010] Compared with the prior art, the present invention has the following advantages: 1. The present invention adopts multi-stage heat treatment to promote the precipitation of a large amount of α phase in the WTD1200 titanium alloy bar and grow it to the micron level, so that the surface and core structures of the WTD1200 titanium alloy bar are consistent, greatly improving the structural uniformity of the WTD1200 titanium alloy bar, and there is no obvious segregation structure.

[0011] 2. The present invention effectively optimizes the structure of WTD1200 titanium alloy bar and regulates its performance through multi-stage heat treatment, so that the impact toughness of WTD1200 titanium alloy bar is significantly improved, and the performance stability and consistency of WTD1200 titanium alloy bar are improved.

[0012] 3. The present invention can adjust the temperature and time of multi-stage heat treatment to achieve the regulation of the performance of WTD1200 titanium alloy bars to meet the use requirements of different scenarios.

[0013] 4. The multi-stage heat treatment of the present invention is simple to operate, has significant effects, and is easy to promote. It can also optimize the structure and properties of WTD1200 titanium alloy bars that are overheated during the forging process, and has important guiding significance.

[0014] 5. The present invention develops a titanium alloy with high strength and high impact toughness, which has broad market application prospects.

[0015] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a microstructure diagram of the WTD1200 titanium alloy bar after heat treatment in Example 1 of the present invention.

[0017] Figure 2 This is a microstructure diagram of the WTD1200 titanium alloy bar after heat treatment in Comparative Example 1 of the present invention.

[0018] Figure 3 This is a microstructure diagram of the WTD1200 titanium alloy bar after heat treatment in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0019] Example 1 This embodiment includes the following steps: Step 1: Place the WTD1200 titanium alloy bar with a diameter of Φ40mm obtained after forging in a resistance furnace at a temperature of 840℃ and keep it for 1 hour, then cool it to 740℃ and keep it for 1 hour, take it out and air cool it to room temperature, where T s The phase transition point of WTD1200 titanium alloy bar is 860℃; Step 2: Place the WTD1200 titanium alloy bar cooled to room temperature in step 1 in a resistance furnace at 560°C for 6 hours, take it out and air cool it to room temperature; Step 3: Place the WTD1200 titanium alloy rod that has been kept warm and then air-cooled to room temperature in step 2 in a resistance furnace at 700°C for 1.5 hours, take it out and air-cool it to room temperature to obtain a heat-treated WTD1200 titanium alloy rod.

[0020] Figure 1 The microstructure of the WTD1200 titanium alloy bar after heat treatment in this embodiment is shown in FIG. Figure 1 It can be seen that the structure of the WTD1200 titanium alloy bar after heat treatment is uniform and has no segregation. After testing, the tensile strength of the WTD1200 titanium alloy bar after heat treatment is 1058MPa, the elongation after fracture is 22%, and the impact resistance is 50J / cm 2 .

[0021] Example 2 This embodiment includes the following steps: Step 1: Place the WTD1200 titanium alloy bar with a diameter of Φ40mm obtained after forging in a resistance furnace at a temperature of 840℃ and keep it for 2h, then cool it to 760℃ and keep it for 2h, take it out and air cool it to room temperature, where T s The phase transition point of WTD1200 titanium alloy bar is 860℃; Step 2: Place the WTD1200 titanium alloy bar cooled to room temperature in step 1 in a resistance furnace at 600°C for 8 hours, take it out and air cool it to room temperature; Step 3: Place the WTD1200 titanium alloy rod that has been kept warm and then air-cooled to room temperature in step 2 in a resistance furnace at a temperature of 750° C. and keep warm for 4 hours. Take it out and air-cool it to room temperature to obtain a heat-treated WTD1200 titanium alloy rod.

[0022] After testing, the WTD1200 titanium alloy bar after heat treatment in this embodiment has a uniform structure without segregation; at the same time, the impact resistance of the WTD1200 titanium alloy bar after heat treatment is 37J / cm 2 .

[0023] Example 3 This embodiment includes the following steps: Step 1: Place the WTD1200 titanium alloy bar with a diameter of Φ60mm obtained after forging in a resistance furnace at a temperature of 800℃ and keep it for 1 hour, then cool it to 700℃ and keep it for 1 hour, take it out and air cool it to room temperature, where T s The phase transition point of WTD1200 titanium alloy bar is 860℃; Step 2: Place the WTD1200 titanium alloy bar cooled to room temperature in step 1 in a resistance furnace at 460°C for 4 hours, take it out and air cool it to room temperature; Step 3: Place the WTD1200 titanium alloy rod that has been kept warm and then air-cooled to room temperature in step 2 in a resistance furnace at 700°C for 1 hour, take it out and air-cool it to room temperature to obtain a heat-treated WTD1200 titanium alloy rod.

[0024] After testing, the WTD1200 titanium alloy bar after heat treatment in this embodiment has a uniform structure without segregation; at the same time, the impact resistance of the WTD1200 titanium alloy bar after heat treatment is 36J / cm 2 .

[0025] Example 4 This embodiment includes the following steps: Step 1: Place the WTD1200 titanium alloy bar with a diameter of Φ50mm obtained after forging in a resistance furnace at a temperature of 820℃ and keep it for 2 hours, then cool it to 740℃ and keep it for 1 hour, take it out and air cool it to room temperature, where T s The phase transition point of WTD1200 titanium alloy bar is 860℃; Step 2: Place the WTD1200 titanium alloy bar cooled to room temperature in step 1 in a resistance furnace at 560°C for 6 hours, take it out and air cool it to room temperature; Step 3: Place the WTD1200 titanium alloy rod that has been kept warm and then air-cooled to room temperature in step 2 in a resistance furnace at 720°C and keep warm for 2 hours, take it out and air-cool it to room temperature to obtain a heat-treated WTD1200 titanium alloy rod.

[0026] After testing, the WTD1200 titanium alloy bar after heat treatment in this embodiment has a uniform structure without segregation; at the same time, the impact resistance of the WTD1200 titanium alloy bar after heat treatment is 41J / cm 2 .

[0027] Comparative Example 1 This comparative example comprises the following steps: Step 1: Place the WTD1200 titanium alloy bar with a diameter of Φ40mm obtained after forging in a resistance furnace at a temperature of 840℃ and keep it for 1 hour, then cool it to 740℃ and keep it for 1 hour, take it out and air cool it to room temperature, where T s The phase transition point of WTD1200 titanium alloy bar is 860℃; Step 2: Place the WTD1200 titanium alloy bar cooled to room temperature in step 1 in a resistance furnace at 560°C for 6 hours, take it out and air cool it to room temperature; Step 3: Place the WTD1200 titanium alloy rod that has been kept warm and then air-cooled to room temperature in step 2 in a resistance furnace at 650°C for 2 hours, take it out and air-cool it to room temperature to obtain a heat-treated WTD1200 titanium alloy rod.

[0028] Figure 2 The microstructure of the WTD1200 titanium alloy bar after heat treatment in this comparative example, wherein (a) represents the surface structure and (b) represents the core structure. Figure 2 It can be seen that compared with Example 1, due to the different heat treatment temperature and time in the final stage, the surface and core structures of the WTD1200 titanium alloy bar after the heat treatment are inconsistent, and there is a segregated structure; after testing, the impact resistance of the WTD1200 titanium alloy bar after the heat treatment is 28J / cm 2 , which is much lower than that in Example 1.

[0029] Comparative Example 2 This comparative example comprises the following steps: Step 1: Place the WTD1200 titanium alloy bar with a diameter of Φ50mm obtained after forging in a resistance furnace at a temperature of 840℃ and keep it for 1 hour, then cool it to 740℃ and keep it for 1 hour, take it out and air cool it to room temperature, where T s The phase transition point of WTD1200 titanium alloy bar is 860℃; Step 2: Place the WTD1200 titanium alloy rod air-cooled to room temperature in step 1 in a resistance furnace at a temperature of 560° C. and keep it warm for 6 hours, take it out and air-cool it to room temperature to obtain a heat-treated WTD1200 titanium alloy rod.

[0030] Figure 3The microstructure of the WTD1200 titanium alloy bar after heat treatment in this comparative example, wherein Figure (a) is the low-magnification structure and Figure (b) is the high-magnification structure of the uneven part. Figure 3 It can be seen that compared with Example 1, due to the lack of the final stage of heat treatment, the surface and core structures of the WTD1200 titanium alloy bar after heat treatment are inconsistent, and there is a segregated structure; after testing, the impact resistance of the WTD1200 titanium alloy bar after heat treatment is 23J / cm 2 , which is much lower than that in Example 1.

[0031] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A heat treatment method for improving the impact toughness of WTD1200 titanium alloy, characterized in that: The method comprises the following steps: Step 1: Place the WTD1200 titanium alloy bar at a temperature of (T s -20)℃~(T s Keep in a resistance furnace at -60℃ for 1h~2h, then cool to (T s -100)℃~(T s -140)℃ and keep warm for 1h~2h, take out and air cool to room temperature, where T s is the phase transition point of WTD1200 titanium alloy bar, in °C; Step 2: Place the WTD1200 titanium alloy bar cooled to room temperature in step 1 in a resistance furnace at a temperature of 460°C to 600°C for 4 to 8 hours, then take it out and air cool it to room temperature; Step 3: Place the WTD1200 titanium alloy rod that has been kept warm and then air-cooled to room temperature in step 2 in a resistance furnace at a temperature of 700°C to 750°C for 1h to 4h, take it out and air-cool it to room temperature to obtain the heat-treated WTD1200 titanium alloy rod.

2. A heat treatment method for improving the impact toughness of WTD1200 titanium alloy according to claim 1, characterized in that: The diameter of the WTD1200 titanium alloy rod described in step 1 does not exceed 100 mm.

3. A heat treatment method for improving the impact toughness of WTD1200 titanium alloy according to claim 1, characterized in that: In step 1, the WTD1200 titanium alloy rod is placed in a resistance furnace at a temperature of 840°C and kept warm for 1 hour, then cooled to 740°C with the furnace and kept warm for 1 hour. In step 2, the WTD1200 titanium alloy rod that has been air-cooled to room temperature is placed in a resistance furnace at a temperature of 560°C and kept warm for 6 hours. In step 3, the WTD1200 titanium alloy rod that has been air-cooled to room temperature after keeping warm is placed in a resistance furnace at a temperature of 700°C and kept warm for 1.5 hours.

4. A heat treatment method for improving the impact toughness of WTD1200 titanium alloy according to claim 1, characterized in that: The WTD1200 titanium alloy bar after heat treatment in step 3 has a uniform structure without segregation and an impact resistance of 35 J / cm 2 above.

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