Heat treatment method for improving strength of Ti-6Al-4V titanium alloy forge piece
By controlling the cooling speed in the heat treatment of Ti-6Al-4V titanium alloy forgings, and precipitating fine secondary α phases, the problem of insufficient strength in the prior art is solved, and the forging strength and forming performance are improved.
Patent Information
- Application Number
- CN202510582208.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-07
- Publication Date
- 2025-07-18
AI Technical Summary
The existing heat treatment method of Ti-6Al-4V titanium alloy forgings leads to insufficient strength and difficult to meet the high-demand mechanical properties and forming properties, resulting in problems such as low yield and high manufacturing costs.
The heat treatment method is adopted to cool to 300 to 320°C at a rate of 40 to 60°C/h, and to keep the heat at 0.5 to 1.5 hours, and then air-cooled to room temperature. The cooling rate is controlled to precipitate fine secondary α phases and improve the strength of the forging.
The strength of the forgings, especially the yield strength, is significantly improved, 16-29MPa, improves warping and deformation, and improves forming performance.
Smart Images
Figure CN120330635A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of heat treatment, and specifically relates to a heat treatment method for improving the strength of Ti-6Al-4V titanium alloy forgings. Background Art
[0002] Ti-6Al-4V titanium alloy has excellent comprehensive mechanical properties. It not only has medium room temperature and high temperature strength and high fatigue performance, but also has good creep resistance and thermal stability, as well as excellent fracture toughness and corrosion resistance. This alloy also has excellent process plasticity and is suitable for forming by various pressure processing methods. Therefore, Ti-6Al-4V titanium alloy has become the most widely used titanium alloy today and has been widely used in various fields such as aerospace, petrochemical, ordnance, and shipbuilding.
[0003] With the rapid development of domestic aerospace equipment, the demand for Ti-6Al-4V titanium alloy forgings, especially large-sized Ti-6Al-4V titanium alloy forgings with a thickness greater than 150 mm, is increasing day by day, and higher requirements are also put forward for their various mechanical properties and forming properties. Titanium alloy forgings need to be heat-treated after forging to obtain the required tissue properties. For Ti-6Al-4V titanium alloy forgings, the standard heat treatment system is to hold at a single-step temperature of 704 - 788 °C for a certain time and then air-cool to room temperature. However, this heat treatment system often leads to insufficient strength margin of Ti-6Al-4V titanium alloy forgings or even fails to meet the standard value requirements, resulting in problems such as low yield rate and high manufacturing cost. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to provide a heat treatment method for improving the strength of Ti-6Al-4V titanium alloy forgings, so as to improve the strength of Ti-6Al-4V titanium alloy forgings and the mechanical properties of the forgings.
[0005] The technical solution adopted by the present invention to solve its technical problems is: a heat treatment method for improving the strength of Ti-6Al-4V titanium alloy forgings, including:
[0006] S1. Load the forging into a heat treatment furnace, raise the heating temperature to 725 - 735 °C, and then hold for a holding time of T, where T = [(H - 25.4) mm * 2.4 min / mm + 60 min] rounded up, and H is the effective thickness dimension of the largest cross-section of the forging;
[0007] S2. After the forging is held, cool the forging in the furnace at a rate of 40 - 60 °C / h to 300 - 320 °C and hold for 0.5 - 1.5 h;
[0008] S3. Take the forging out of the furnace and air-cool to room temperature.
[0009] Further, before the step S1, a preheating step of the heat treatment furnace is further included, and the preheating temperature of the heat treatment furnace is not higher than 300 °C.
[0010] Further, in the step S1, the heating rate of the forging is controlled at 80-120 °C / h.
[0011] The beneficial effects of the present invention are as follows: The heat treatment method of the Ti-6Al-4V titanium alloy forging of the present invention first heats the forging temperature to 725-735 °C and then holds it, and then furnace cools it to 300-320 °C at a rate of 40-60 °C / h, holds it for 0.5-1.5 h, and finally air cools it, so that part of the α phase will be transformed into the β phase when the forging is held at the first stage (725-735 °C). When cooling, by adopting a slow cooling rate of 40-60 °C / h to control the cooling rate, a certain amount of fine secondary α phase can be precipitated from the β phase, thereby improving the strength of the forging. When the forging is cooled to 300-320 °C and then held, and then air cooled, the temperature stress during the cooling process of the forging can be effectively controlled, and the warping deformation of the forging can be improved. Description of the Drawings
[0012] Figure 1 is the flow chart of the present invention;
[0013] Figure 2 is the metallographic structure photograph of Example 1;
[0014] Figure 3 is the secondary electron photograph of Example 1;
[0015] Figure 4 is the metallographic structure photograph of Comparative Example 1;
[0016] Figure 5 is the secondary electron photograph of Comparative Example 1;
[0017] Figure 6 is the metallographic structure photograph of Example 2;
[0018] Figure 7 is the secondary electron photograph of Example 2;
[0019] Figure 8 is the metallographic structure photograph of Comparative Example 2;
[0020] Figure 9 is the secondary electron photograph of Comparative Example 2. Detailed Embodiments
[0021] The present invention will be further described below with reference to the drawings and embodiments.
[0022] As Figure 1As shown in the figure, a heat treatment method for improving the strength of Ti-6Al-4V titanium alloy forgings according to the present invention includes:
[0023] S1. Load the forging into a heating furnace and raise the heating temperature to 725 - 735 °C, then hold for a holding time of T, where T = [(H - 25.4) mm * 2.4 min / mm + 60 min] rounded up, and H is the effective thickness dimension of the largest cross-section of the forging;
[0024] S2. After the forging is held, cool the forging in the furnace at a rate of 40 - 60 °C / h to 300 - 320 °C, and hold for 0.5 - 1.5 h;
[0025] S3. Take the forging out of the furnace and air-cool it to room temperature.
[0026] In the heat treatment method of the Ti-6Al-4V titanium alloy forging of the present invention, part of the α phase will transform into the β phase during holding at the first stage (725 - 735 °C). During cooling, by slowly cooling at a rate of 40 - 60 °C / h to control the cooling rate, a certain amount of fine secondary α phase can be precipitated from the β phase, thereby improving the strength of the forging. Experiments show that the strength of the forging treated by the heat treatment method of the present invention is increased by 16 - 29 Mpa.
[0027] In the present invention, the temperature range of room temperature is 20 - 30 °C.
[0028] In order to improve the heat treatment efficiency, a preheating step of the heat treatment furnace is also included before the step S1. In the present invention, preferably, the preheating temperature of the heat treatment furnace is not higher than 300 °C, so that the forging is heated more evenly, reducing the temperature stress caused by uneven heating and causing deformation of the forging.
[0029] In the present invention, preferably, in the step S1, the heating rate of the forging is controlled at 80 - 120 °C / h to ensure that the forging can be heated evenly, reducing the temperature stress caused by uneven heating and causing deformation of the forging.
[0030] Example 1:
[0031] The forging material is Ti-6Al-4V, and the outer contour dimensions of the forging are 1800 (length) * 350 (width) * 195 (height) mm. The heat treatment steps after the forging is completed are as follows:
[0032] Step 1. Heat the temperature of the heat treatment furnace to 250 °C;
[0033] Step 2: Load the forging into the heat treatment furnace, heat it to 725°C at a heating rate of 100°C / h, and then hold for a holding time of T. T = round([(H - 25.4) mm * 2.4 min / mm + 60 min]), and T is 467 min;
[0034] Step 3: After the forging is held, cool the forging in the furnace to 300°C at a rate of 40°C / h, and then air-cool the forging to room temperature.
[0035] Comparative Example 1:
[0036] The forging material is Ti-6Al-4V, and the outer contour dimensions of the forging are 1800 (length) * 350 (width) * 195 (height) mm. The heat treatment steps after forging of this forging are as follows:
[0037] Step 1: Heat the temperature of the heat treatment furnace to 725°C;
[0038] Step 2: Load the forging into the heat treatment furnace. Wait for the furnace temperature to return to 725°C, and then hold for a holding time of T. T = round([(H - 25.4) mm * 2.4 min / mm + 60 min]), and T is 467 min;
[0039] Step 3: After the forging is held, take the forging out of the furnace and cool it to room temperature in the air.
[0040] The forgings of Example 1 and Comparative Example 1 were subjected to microstructure observation and room temperature tensile tests. 4 groups of tensile specimens were tested for each case. The metallographic microstructure photos of the forgings in Example 1 are as Figure 2 shown. Darker-colored microstructures appeared at the junctions of the α phases. Further magnified observation was carried out using a scanning electron microscope, as Figure 3 shown. Nanoscale lamellar α phases precipitated in the β phase at the α-phase junctions. The metallographic microstructure photos of the forgings in Comparative Example 1 are as Figure 4 shown. Its microstructure is a typical duplex microstructure of titanium alloy, and no Figure 2 darker-colored microstructures were found in the metallographic photos. Further magnified observation was carried out using a scanning electron microscope, as Figure 5 shown. No nanoscale α phases appeared in the remaining β phase.
[0041] The results of the tensile tests are shown in the following table. It can be seen from the following table that under the condition that the plastic indexes elongation rate δ4 and reduction of area ψ are comparable, the strength indexes of the forgings of the present invention: yield strength σ0.2 and tensile strength σb, are both superior to those of the forgings in the comparative example. In particular, the yield strength σ0.2 of the forging is increased by 18 - 29 MPa.
[0042]
[0043] Example 2:
[0044] The forging material is Ti-6Al-4V, and the outer contour dimensions of the forging are 900 (length) * 300 (width) * 150 (height) mm. The heat treatment steps after the forging is completed are as follows:
[0045] Step 1: Heat the temperature of the heat treatment furnace to 300 °C;
[0046] Step 2: Load the forging into the heat treatment furnace, heat it to 735 °C at a heating rate of 100 °C / h, and then hold it. The holding time T, T = round([(H - 25.4) mm * 2.4 min / mm + 60 min]), and T is 360 min;
[0047] Step 3: After the forging is held, cool the forging in the furnace to 320 °C at a rate of 60 °C / h, and then air-cool the forging to room temperature.
[0048] Comparative Example 2:
[0049] The forging material is Ti-6Al-4V, and the outer contour dimensions of the forging are 900 (length) * 300 (width) * 150 (height) mm. The heat treatment steps after the forging is completed are as follows:
[0050] Step 1: Heat the temperature of the heat treatment furnace to 735 °C;
[0051] Step 2: Load the forging into the heat treatment furnace, wait for the furnace temperature to return to 735 °C, and then hold it. The holding time T, T = round([(H - 25.4) mm * 2.4 min / mm + 60 min]), and T is 360 min;
[0052] Step 3: After the forging is held, take the forging out of the furnace and cool it to room temperature in the air.
[0053] Perform a room temperature tensile test on the Ti-6Al-4V titanium alloy forgings after heat treatment according to the above two schemes, and test 4 groups of specimens for each example. From the Figures 6 to 9 microstructure observation results attached, nano-precipitation phases are also formed in the forgings after furnace cooling. As can be seen from the following table, under the condition that the plastic indexes elongation rate δ4 and reduction of area ψ are equivalent, the strength indexes of the forgings of the present invention: yield strength σ0.2 and tensile strength σb, are both superior to those of the comparative example forgings. In particular, the yield strength σ0.2 of the forgings is increased by 16 - 22 MPa in strength. Therefore, this heat treatment process system has the value of popularization and application for improving the strength performance.
[0054]
Claims
1. A heat treatment method for improving the strength of Ti-6Al-4V titanium alloy forgings, characterized in that, Including: S1. Load the forging into the heat treatment furnace and heat it to a temperature of 725 - 735 °C, then hold for a holding time of T, where T = [(H - 25.4) mm * 2.4 min / mm + 60 min] rounded up, and H is the effective thickness dimension of the largest cross-section of the forging; S2. After the forging is held, cool the forging in the furnace at a rate of 40 - 60 °C / h to 300 - 320 °C and hold for 0.5 - 1.5 h; S3. Take the forging out of the furnace and air-cool it to room temperature.
2. The heat treatment method for improving the strength of Ti-6Al-4V titanium alloy forgings as described in claim 1, characterized in that, Before the step S1, it also includes a preheating step for the heat treatment furnace, and the preheating temperature of the heat treatment furnace is not higher than 300 °C.
3. A heat treatment method for improving the strength of Ti-6Al-4V titanium alloy forgings as described in claim 1, characterized in that, In the step S1, the heating rate of the forging is controlled at 80 - 120 °C / h.
4. A heat treatment method for improving the strength of Ti-6Al-4V titanium alloy forgings as described in claim 1, characterized in that, The room temperature is 20 - 30 °C.