A free forging method of high-toughness high-organization-uniformity TC11 titanium alloy thin slab

Abstract

The application discloses a free forging method of a high-toughness high-organization-uniformity TC11 titanium alloy thin slab, and specifically comprises the following steps: open-die forging, first-time temperature below a phase transition point forging, single-phase-zone forging, second-time temperature below a phase transition point forging, near-phase-transition-point constant-deformation elongation forging, and finished product constant-deformation deformation heat treatment. Compared with the prior art, the application can obtain a high-toughness high-organization-uniformity thin slab, and has a positive significance for promoting the development of China's aerospace industry.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy forging technology, specifically to a free forging method for titanium alloy slabs, used to prepare high-strength, high-toughness, and high-uniformity TC11 titanium alloy thin (thickness 60mm-120mm) slabs. Background Technology

[0002] As aerospace equipment continues to develop towards higher safety, longer lifespan, and lighter weight, there are urgent requirements for its key main load-bearing structures such as frames, beams, and wall panels to become larger, more integrated, and more complex. Titanium alloys have received much attention due to their excellent properties (high specific strength, high temperature resistance, fatigue resistance, etc.). When selecting materials for titanium alloy structures, in addition to emphasizing static strength and fatigue performance, more attention is paid to damage tolerance characteristics. At present, the TC4-DT damage-tolerant titanium alloy, which is widely used in large main load-bearing structures at home and abroad, has achieved excellent fracture toughness and fatigue crack propagation rate, but its static strength is more than 15% lower than that of TC4, which leads to an increase in structural mass and a reduction in load-bearing capacity. Therefore, the demand for high-strength and high-toughness titanium alloys is becoming increasingly urgent.

[0003] The nominal composition of TC11 titanium alloy is Ti-6.5Al-3.5Mo-1.5Zr-0.3Si. It is an α+β type heat-resistant titanium alloy with good comprehensive performance. It has excellent heat resistance below 500℃. This alloy is mainly used to manufacture compressor disks, blades, drums and other parts for aero engines.

[0004] Currently, there are no patents or papers in China disclosing a forging method for producing high-strength, high-toughness, and highly homogeneous TC11 thin slabs. To ensure microstructure homogeneity, TC11 thin slabs are conventionally forged below the phase transformation point. However, the resulting slabs have an equiaxed microstructure, which cannot meet the requirements for high strength and high toughness (ensuring tensile strength ≥1070 MPa and impact toughness ≤40 J / cm²). 2 Fracture toughness ≤90MPa*m 1 / 2 In theory, forging above the phase transformation point can achieve the required high toughness (impact toughness > 50 J / cm). 2 Fracture toughness > 100 MPa*m 1 / 2 However, it is difficult to achieve the requirements of uniform structure and high strength. The reasons are as follows: In order to achieve the requirement of high toughness, the structure of the produced product must be a basket webbing structure. The basket webbing structure can only be produced when forging above the phase transformation point. If the heating temperature is too high, the heating time is too long, or the deformation is not properly controlled when forging above the phase transformation point, it will cause the lamellar α phase in the basket webbing structure to become thicker and longer. This structure cannot meet the requirements of high strength and high uniformity. If the temperature is too low when forging above the phase transformation point, if the deformation is not properly controlled, or the forging time is too long, a cross-phase region structure will be produced, resulting in a very non-uniform structure that cannot meet the uniformity requirements. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the purpose of this invention is to provide a free forging method for high-strength, high-toughness, and high-uniformity TC11 titanium alloy thin slabs. The slabs produced have a thickness of 60mm-120mm, excellent microstructure uniformity, and superior mechanical properties, making them suitable for industrial production.

[0006] To achieve the above objectives, the raw material of this invention is TC11 titanium alloy ingots with a diameter of Φ680-Φ780mm produced by our company. The production process is as follows: billet forging → forging at a temperature below the first phase transformation point → forging in the single-phase region → forging at a temperature below the second phase transformation point → elongation forging with a fixed deformation amount near the phase transformation point → deformation heat treatment of the finished product with a fixed deformation amount.

[0007] The present invention discloses a free forging method for high-strength, high-toughness, and high-uniformity TC11 titanium alloy thin slabs, characterized by the following steps:

[0008] Step 1) Forging the billet

[0009] The heating temperature is 1100℃-1200℃. After holding at this temperature, the ingot is subjected to one-time upsetting and drawing forging (two upsetting and two drawing), followed by air cooling.

[0010] Step 2) Forging below the first phase transformation temperature

[0011] The heating temperature is 30-60℃ below the phase transformation point temperature. After holding at the temperature, the billet is subjected to one upsetting and drawing forging (one upsetting and one drawing). After forging, the hot material is returned to the furnace.

[0012] Step 3) Single-phase forging

[0013] The heating temperature is 50-120℃ above the phase transformation point temperature. After holding at the temperature, the billet is subjected to one upsetting and drawing forging (one upsetting and one drawing), and then air-cooled.

[0014] Step 4) Forging below the second phase transformation temperature

[0015] The heating temperature is 30-60℃ below the phase transformation point temperature. After holding at this temperature, the billet is subjected to 1-2 upsetting and drawing forging cycles (one upsetting and one drawing). After forging, it is either air-cooled or returned to the furnace while still hot. Then, the billet is heated and held at 30-60℃ below the phase transformation point temperature for 2-4 drawing and forging cycles. After forging, it is either air-cooled or returned to the furnace while still hot.

[0016] Step 5) Near-phase transformation temperature "constant deformation" elongation forging

[0017] The process employs a three-stage heating method: preheating, heating up, and holding. The preheating stage involves a temperature of 800-850℃ and a heating time of 60-150 minutes. Immediately after preheating, the billet is removed from the furnace and wrapped with insulating asbestos. After wrapping, the hot material is returned to the furnace for the heating stage, which lasts ≤90 minutes, raising the temperature from the preheating temperature to the holding stage temperature. The holding stage temperature is 15-30℃ above the phase transformation point temperature, and the holding time is controlled to 60-90 minutes. After the three-stage heating, the billet undergoes a single-pass elongation forging process, with the elongation deformation strictly controlled at 25%-30%. The total forging time is controlled within 90 seconds, followed by air cooling.

[0018] Step 6) Deformation heat treatment of finished product with "fixed deformation amount"

[0019] The heating temperature is 30-40℃ below the phase transformation point temperature. After holding at the temperature, the billet is forged in one heat and the elongation deformation is strictly controlled to ≤15%. After forging, it is immediately water-cooled and the material transfer time is <30s. After water cooling, it is heated to 500-550℃ and held for 240-480min.

[0020] Furthermore, the upsetting and drawing forging in step 1) above is two upsetting and two drawing, and the holding time is controlled to be [(0.55~0.80)×min minimum cross-sectional size of billet] min, and the deformation of the forging upsetting and drawing is controlled to be 35%-45%.

[0021] Furthermore, in step 2) above, the upsetting and drawing forging is done in one upsetting and one drawing process, and the holding time is controlled to be [(0.60~0.90)×min minimum cross-sectional size of billet] min; and the forging upsetting and drawing deformation is controlled to be 25%-35%.

[0022] Furthermore, in step 3) above, the upsetting and drawing forging is done in one upsetting and one drawing process, and the holding time is controlled to be [(0.35~0.55)×min minimum cross-sectional size of billet] min; and the forging upsetting and drawing deformation is controlled to be 15%-25%.

[0023] Furthermore, in step 4) above, the upsetting and drawing forging is performed in one upsetting and one drawing process. The holding time before upsetting and drawing forging is controlled at [(0.60~0.90)×min minimum cross-sectional size of billet] min, and the upsetting deformation per heat is controlled at 25%-35%. The holding time before drawing forging is [(0.60~0.90)×min minimum cross-sectional size of billet] min, and the drawing deformation per heat is controlled at 20%-35%.

[0024] Furthermore, in step 5) above, the drawing forging is a one-pass direct drawing and forming process, and the material transfer time from the heat preservation furnace to the drawing forging station is ≤60s. In the one-pass drawing forging, no shaping is performed before or after forging.

[0025] Furthermore, in step 6) above, the heat preservation time is controlled as [(0.80~1.20) × minimum cross-sectional dimension of the billet] min.

[0026] As is well known to those skilled in the art, the strength-ductility, strength-toughness, and ductility-toughness relationships of titanium alloys exhibit a negative correlation. The innovation of this invention lies in using engineering practice to harmonize various key influencing factors, thereby producing thin slabs with high strength and toughness, while also possessing relatively high ductility. The specific innovative points of this invention are as follows:

[0027] The TC11 titanium alloy with a uniform and fine "α+β" phase region is obtained by forging with fewer forging cycles: "1100℃~1200℃ forging → forging at a temperature below the first phase transformation point → forging in the single phase region → forging at a temperature below the second phase transformation point". This provides a basic guarantee for the plasticity and uniformity of the final product.

[0028] Through a relatively complex "near-phase transformation point, fixed deformation amount, high-precision drawing and forging" operation, specifically: a) the heating temperature is set at "15℃-30℃ above the phase transformation point temperature", and a "three-stage" heating method is used to shorten the heating time in the single-phase region, thus accurately obtaining uniform and fine β grains; b) by wrapping "insulating asbestos", and precisely controlling sufficient deformation amount, short deformation time, and short material transfer time, and performing one-time drawing and forming operations, the main hot deformation is ensured to be carried out in the β phase region, ensuring that the basket structure is fine and uniform, thereby ensuring fracture toughness and structural uniformity. By comprehensively adjusting various influencing factors at the appropriate point, a fine and uniform titanium alloy "basket structure" that is difficult to obtain with free forging is obtained, thus giving the material high fracture toughness.

[0029] By performing a deformation heat treatment with a fixed amount of deformation on the finished product, not only is the plate shape guaranteed, but more importantly, at this temperature and deformation amount, the uniform basket structure will produce some long strip α phase fractures, which provides a guarantee of material plasticity while ensuring toughness. Immediate water cooling then provides the metastable β phase, followed by a low-temperature heat treatment at 500℃-550℃ to decompose the metastable β phase, which provides a guarantee of high strength while ensuring toughness and plasticity. As a result, the final TC11 titanium alloy slab has "high strength and high toughness" as well as plasticity, thus exhibiting excellent comprehensive performance.

[0030] Compared with existing technologies, this invention can obtain thin slabs with high strength, toughness and high microstructure uniformity, which is of positive significance for promoting the development of my country's aerospace industry. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the three-segment heating curve of the present invention;

[0032] Figure 2The microstructure of the slab in Embodiment 1 of the present invention is shown in the diagram (left: edge; right: core).

[0033] Figure 3 The microstructure of the slab in Embodiment 2 of the present invention is shown in the diagram (left: edge; right: core).

[0034] Figure 4 The microstructure of the comparative slab of this invention is shown (left: edge; right: core). Implementation

[0035] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. The following are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any identical or similar solutions without departing from the concept of the present invention should fall within the scope of protection of the present invention. Furthermore, in the following text, “□” refers to the side length of the square blank, “Φ” refers to the diameter of the blank with a circular cross-section, and “L” refers to the length of the material. Example 1

[0036] The raw material is a TC11 titanium alloy ingot with a diameter of 680mm produced by our company (the ingot's phase transformation point has been tested and found to be 1000℃). The specific forging process flow is shown in Table 1 below:

[0037] Table 1:

[0038]

[0039] Table 2 shows the properties of the finished 60*520*Lmm slab prepared by forging in this embodiment. It can be seen that the strength and toughness (impact toughness and fracture toughness) are excellent, and it also has high plasticity.

[0040] Table 2 Mechanical properties of slabs with dimensions □60*520*Lmm

[0041]

[0042] And from Figure 2 As can be seen from the image, the microstructure of the edge and core of the finished slab prepared in this embodiment is a uniformly woven basket structure. Example 2

[0043] The raw material is a 680mm TC11 titanium alloy ingot produced by our company (the phase transformation point of the ingot is tested to be 1005℃). The specific process flow for forging is shown in Table 3 below:

[0044] Table 3:

[0045]

[0046] Table 4 shows the properties of the finished slab with dimensions of □120*500*Lmm prepared by forging in this embodiment. It can be seen that the strength and toughness (impact toughness and fracture toughness) are excellent, and it also has high plasticity.

[0047] Table 4 Mechanical properties of slabs with dimensions □120*500*Lmm

[0048]

[0049] And from Figure 3 As can be seen from the microstructure of the edge and center of the finished slab in this embodiment, it is a uniformly woven basket structure.

[0050] Comparative Example

[0051] The raw material is a TC11 titanium alloy ingot with a diameter of 680mm produced by our company (the phase transformation point of the ingot is tested to be 1000℃). Except for the heating temperature of the 10th heating cycle being 960℃ and the heating time being 80 minutes, the process is completely consistent with Example 1. The specific process flow of the forging method is shown in Table 5 below:

[0052] Table 5:

[0053]

[0054] Table 6 shows the properties of the finished 60*520*Lmm slab prepared by forging in this embodiment. It can be seen that the strength is comparable to that of Example 1, but the toughness (impact toughness and fracture toughness) is significantly lower than that of Example 1.

[0055] Table 6 Mechanical properties of slabs with dimensions □60*520*Lmm

[0056]

[0057] And from Figure 4 As can be seen from the image, the microstructure of the edge and core of the finished slab prepared in this embodiment is equiaxed.

Claims

1. A method of free forging a high-ductility high-homogeneity TC11 titanium alloy sheet billet, characterized by, The process is achieved by the following steps: Step 1), cogging forging The heating temperature is 1100-1200℃, and after holding, the ingot is subjected to 1-time upsetting and drawing forging, and is air-cooled after forging; Step 2), forging below the first phase transition point temperature The heating temperature is 30-60℃ below the phase transition point temperature, and after holding, the blank is subjected to 1-time upsetting and drawing forging, and hot charging is adopted after forging; Step 3), single-phase zone forging The heating temperature is 50-120℃ above the phase transition point temperature, and after holding, the blank is subjected to 1-time upsetting and drawing forging, and is air-cooled after forging; Step 4), forging below the second phase transition point temperature The heating temperature is 30-60℃ below the phase transition point temperature, and after holding, the blank is subjected to 1-2-time upsetting and drawing forging, and is air-cooled or hot charging after forging; then the blank is subjected to 2-4-time lengthening forging at a heating temperature of 30-60℃ below the phase transition point temperature, and is air-cooled or hot charging after forging; Step 5), near-phase transition point temperature "constant deformation amount" lengthening forging The three-stage heating of preheating, heating and holding is adopted, wherein the preheating temperature is 800-850℃, and the heating time is 60-150min; after preheating, the blank is immediately taken out of the furnace for holding asbestos wrapping, and after wrapping, the blank is hot charged for the heating stage; the heating stage time is ≤90min, and the temperature is raised from the preheating temperature to the holding stage temperature; the holding stage temperature is 15-30℃ above the phase transition point temperature, and the holding time is controlled to be 60-90min; after the three-stage heating is completed, the blank is subjected to 1-time lengthening forging, wherein the lengthening deformation amount is strictly controlled to be 25%-30%, and the total forging time is controlled to be within 90s, and the blank is air-cooled after forging; Step 6), finished product "constant deformation amount" deformation heat treatment The heating temperature is 30-40℃ below the phase transition point temperature, and after holding, the blank is subjected to 1-time lengthening forging, and the lengthening deformation amount is strictly controlled to be ≤15%; the blank is immediately water-cooled after forging, the material transfer time is <30s, and after water cooling, the blank is heated to 500-550℃ and held for 240-480min.

2. The free forging method of a high-ductility high-homogeneity TC11 titanium alloy sheet billet according to claim 1, characterized in that, The upsetting and drawing forging in step 1) is two-up and two-down, and the holding time is controlled to be [(0.55-0.80)×the minimum cross-sectional dimension of the blank]min, and the upsetting and lengthening deformation amount is controlled to be 35%-45%.

3. The free forging method of a high-ductility high-homogeneity TC11 titanium alloy sheet billet according to claim 1, characterized in that, The upsetting and drawing forging in step 2) is one-up and one-down, and the holding time is controlled to be [(0.60-0.90)×the minimum cross-sectional dimension of the blank]min; and the upsetting and lengthening deformation amount is controlled to be 25%-35%.

4. The free forging method of a high-ductility high-homogeneity TC11 titanium alloy sheet billet according to claim 1, characterized in that, The upsetting and drawing forging in step 3) is one-up and one-down, and the holding time is controlled to be [(0.35-0.55)×the minimum cross-sectional dimension of the blank]min; and the upsetting and lengthening deformation amount is controlled to be 15%-25%.

5. The free forging method of a high-ductility high-homogeneity TC11 titanium alloy sheet billet according to claim 1, characterized in that, The upsetting and drawing in the step 4) is one upsetting and drawing, wherein the holding time before the upsetting and drawing is controlled to be [(0.60-0.90)×the minimum cross-sectional dimension of the blank] min, and the upsetting deformation per heating is controlled to be 25%-35%; and the holding time before the drawing is [(0.60-0.90)×the minimum cross-sectional dimension of the blank] min, and the drawing deformation per heating is controlled to be 20%-35%.

6. The free forging method of a high-ductility high-homogeneity TC11 titanium alloy sheet billet according to claim 1, characterized in that, The drawing in the step 5) is one-time direct drawing forming, the material transfer time from the holding furnace to the drawing station is ≤60 s, and the blank is not shaped before and after the drawing in one heating.

7. The free forging method of a high-toughness high-homogeneity TC11 titanium alloy sheet billet according to claim 1, characterized in that, In the step 6), the holding time is controlled to be [(0.80-1.20)×the minimum cross-sectional dimension of the blank] min.

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