Forging method for improving TC18 titanium alloy fine-crystal bright band structure
Through multi-fire forging and heat treatment, the forging temperature and deformation amount are controlled, and the fine crystal bright belt structure of TC18 titanium alloy is transformed into an isometric α phase and formed a basket-like structure, which solves the problem of forging performance not meeting the standards and achieves the improvement of the mechanical properties of forgings.
Patent Information
- Application Number
- CN202510784327.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-12
- Publication Date
- 2025-08-01
AI Technical Summary
TC18 titanium alloy is prone to form fine and bright ribbon tissue during forging, resulting in the performance of the forging not meeting the standards, and it is difficult for traditional forging processes to completely transform into net basket-like tissue, resulting in the strength of the forgings being lower than the standard requirements and causing economic losses.
By using multi-fire forging and heat treatment, the fine and grey ribbon tissue is converted into an isometric α phase by controlling the forging temperature and deformation, and finally forming a net basket-like tissue, including heating to Tβ+ (30-80℃), insulation, water-cooling and large deformation forging, combined with double annealing treatment.
It significantly improves the mechanical properties of forgings, makes them meet the standard requirements, avoids the scrapping of forgings, and reduces economic losses.
Smart Images
Figure CN120394745A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of forging, and specifically to a forging method for improving the fine-grained bright band structure of TC18 titanium alloy. Background Art
[0002] TC18 (BT22) titanium alloy is a typical high-strength near-β type titanium alloy. Due to its excellent hardenability, forging penetration, strength and toughness characteristics, it is widely used in the preparation of main load-bearing structural parts such as large aircraft landing gear crossbeams and fuselage butt joints. The traditional forging process is to heat the TC18 bar to Tβ - 30°C, forge it with a deformation amount of 10 - 40% in multiple heats, and perform water cooling after each heat to finally form a forging. However, due to the characteristics of large deformation resistance, narrow forging process window, and sensitivity of tissue properties to process parameters during the forging of TC18 titanium alloy, it is easy to cause abnormal forging structure or unqualified performance. There is a fine-grained bright band structure in the macrostructure of the TC18 titanium alloy free forging after forging, and the strength of the forging after heat treatment is far lower than the index requirements, resulting in the scrapping of the forging and causing huge economic losses to the enterprise. Moreover, due to multiple heats of forging and water cooling, the fine-grained bright band structure in the forging becomes very stable, and the traditional forging process cannot completely change the fine-grained bright band structure into a basket-weave structure. Summary of the Invention
[0003] The technical problem to be solved by the present invention is to provide a forging method for improving the fine-grained bright band structure of TC18 titanium alloy, which re-forges the free forging with the fine-grained bright band structure to make the mechanical properties of the forging meet the standard requirements.
[0004] The technical solution adopted by the present invention to solve its technical problems is a forging method for improving the fine-grained bright band structure of TC18 titanium alloy, including the following steps:
[0005] S1: Forge the initial forging with the fine-grained bright band structure for n heats to form an initial bar, perform water cooling after each heat of forging to transform the fine-grained bright band structure into equiaxed α phase; when forging each heat, heat the initial forging to Tβ + (30 - 80°C) and keep it warm for the first time T1, T1 = f * Dx, where f is the heating coefficient taken as 0.5 - 0.7, x takes 1, 2, 3... n, and Dx is the maximum cross-sectional thickness of the initial forging at the x-th heat.
[0006] S2: Forge the initial billet for m times to form the final forging. After each forging, water-cool it. The shape and size of the final forging are the same as those of the initial billet. Transform the equiaxed α-phase in the initial billet into a basketweave structure. When forging each time, heat the initial billet to Tβ + (30 - 80°C) and hold for the first time T2, where T2 = f * Dy, f is the heating coefficient with a value of 0.5 - 0.7, y takes 1, 2, 3... m, and Dy is the maximum cross-sectional thickness of the initial billet at the y-th forging time.
[0007] S3: Place the final forging in a heating furnace for heat treatment. Heat the final forging to 820 - 850°C and hold for 1 - 3 hours. Then cool the heating furnace to 740 - 760°C, hold for 1 - 3 hours and then water-cool. Finally, place the final forging in the heating furnace, heat it to 600 - 620°C, hold for 2 - 6h, and then air-cool it out of the furnace.
[0008] Further, in step S1, if the fine-grained bright band structure has not completely transformed into the equiaxed α-phase, heat the initial billet to Tβ + (30 - 80°C), then upset and draw out. The material after upsetting and drawing out has the same shape and size as the initial billet until the fine-grained bright band structure completely transforms into the equiaxed α-phase.
[0009] Further, in step S1, the deformation amount for each forging is 20 - 40%.
[0010] Further, in step S2, the deformation amount for each forging is 50 - 70%.
[0011] After step S3, take samples at the center position of the final forging, including microscopic specimens, fracture toughness specimens, and tensile specimens.
[0012] The beneficial effects of the present invention are as follows: First, by heating the initial forging with a fine-grained bright band structure to Tβ + (30 - 80°C), the stability of the fine-grained bright band structure is reduced, and under the action of a large deformation amount of 20 - 40%, the fine-grained bright band structure is transformed into the equiaxed α-phase. Then, the bar is forged into a forging under high-temperature and large-deformation conditions, and heat treatment, physical and chemical tests are carried out. The mechanical properties and macro and microstructures of the forging meet the standard requirements. Description of the Drawings
[0013] Figure 1 is a schematic diagram of the macrostructure of the initial forging;
[0014] Figure 2 is a schematic diagram of the macro and microstructures of the bar;
[0015] Figure 3 is a schematic diagram of the macro and microstructures of the final forging;
[0016] Figure 4 is a schematic diagram of the sampling position. Detailed Embodiments
[0017] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.
[0018] As Figure 1 shown, a forging method for improving the fine-grained bright band structure of TC18 titanium alloy according to the present invention includes the following steps:
[0019] S1: The initial forging with a fine-grained bright band structure is forged for n heats to form an initial billet. After each heat forging, it is water-cooled to transform the fine-grained bright band structure into equiaxed α phase. When forging each heat, the initial forging is heated to Tβ+(30 - 80°C) and held for the first time T1, where T1 = f*Dx, f is the heating coefficient taken as 0.5 - 0.7, x takes 1, 2, 3... n, and Dx is the maximum cross-sectional thickness of the initial forging at the x-th heat. Since the fine-grained bright band structure becomes very stable after the previous process, heating the initial forging of each heat to Tβ+(30 - 80°C) and increasing the forging temperature can reduce the bonding force between the grains of the fine-grained bright band structure, dissolve and break the fine-grained bright band structure during the forging process of each heat, and transform the fine-grained bright band structure into equiaxed α phase. The size of the initial billet is the same as that of the billet initially formed into the initial forging, so that the same forging equipment and auxiliary equipment can be used when the initial billet is formed into the final forging later.
[0020] S2: The initial billet is forged for m heats to form the final forging. After each heat forging, it is water-cooled. The final forging is the same in shape and size as the initial forging. The equiaxed α phase in the initial billet is changed into a basketweave structure. When forging each heat, the initial billet is heated to Tβ+(30 - 80°C) and held for the first time T2, where T2 = f*Dy, f is the heating coefficient taken as 0.5 - 0.7, y takes 1, 2, 3... m, and Dy is the maximum cross-sectional thickness of the initial billet at the y-th heat. Since the initial billet is formed by forging the initial forging with a fine-grained bright band structure, the stability of the equiaxed α phase in the initial billet is not high. If the traditional forging process below the phase transformation point is used, due to the low forging temperature, the equiaxed α phase in the initial billet may be transformed into a fine-grained bright band structure. Therefore, by heating the initial billet to Tβ+(30 - 80°C) when forging each heat, the stability of the equiaxed α phase is ensured, and further the equiaxed α phase in the initial billet is changed into a basketweave structure to make its structure normal.
[0021] S3: Place the final forging in a heating furnace for heat treatment. Heat the final forging to 820 - 850 °C and hold for 1 - 3 hours. Then cool the heating furnace to 740 - 760 °C, hold for 1 - 3 hours and then water-cool. Finally, place the final forging in the heating furnace, heat it to 600 - 620 °C and hold for 2 - 6 h, and then air-cool it out of the furnace. The heat treatment system of TC18 is double annealing. The first annealing is primary annealing, mainly to make the alloy recrystallize and dissolve the metastable phase at 30 - 60 °C below Tβ. During the secondary annealing, the metastable phase decomposes.
[0022] Further, in step S1, if the fine-grained bright band structure has not completely changed into equiaxed α phase, heat the initial billet to Tβ+(30 - 80 °C), then upset and draw it. The material after upsetting and drawing has the same shape and size as the initial billet until the fine-grained bright band structure completely changes into equiaxed α phase.
[0023] Further, in step S1, the deformation amount for each forging pass is 20 - 40%. Controlling the deformation amount within 20 - 40% can break up the abnormal structure faster and make the structure normal.
[0024] Further, in step S2, the deformation amount for each forging pass is 50 - 70%. Adopting a large deformation amount of 50 - 70% makes the slip between equiaxed α phases more rapid and the forming efficiency of the basket-like structure higher.
[0025] After step S3, samples are taken at the center position of the final forging, including microscopic specimens, fracture toughness specimens and tensile specimens.
[0026] Example 1
[0027] The initial forging is square, made of TC18, with dimensions of 560×340×140 mm. The phase transformation point Tβ is 872 °C. Place the initial forging with fine-grained bright band structure in a heating furnace, heat it to Tβ+30 °C, that is, 902 °C, and hold. Forge the initial forging in 3 passes, with the deformation amount controlled at 20% for each pass until the initial forging becomes an initial billet with dimensions of Φ300×430 mm. After each forging pass, use water-cooling as the cooling method.
[0028] Perform forging deformation on the initial billet. Select the forging temperature as Tβ+30 °C, that is, 902 °C, and hold. Forge it into the final forging in 2 passes, with the deformation amount controlled at 50%. The dimensions of the final forging are the same as those of the initial forging, both being 560×340×140 mm. After each forging, use water-cooling as the cooling method.
[0029] The final forging is placed in a heating furnace for heat treatment. The final forging is heated to 820 °C and held for 1 hour. Then the heating furnace is cooled to 740 °C, held for 1 hour and then water-cooled. Finally, the final forging is placed in the heating furnace, heated to 600 °C and held for 2 h, and then air-cooled out of the furnace.
[0030] Samples are taken at the center of the final forging, including microscopic specimens, fracture toughness specimens and tensile specimens, and tested separately.
[0031] Example 2
[0032] The initial forging is square, made of TC18, with dimensions of 560×340×140 mm. The phase transformation point Tβ is 872 °C. The initial forging with a fine-grained bright band structure is placed in a heating furnace and heated to Tβ + 50 °C, that is, 922 °C, and held. The initial forging is forged in two heats, with the deformation per heat controlled at about 30% until the initial forging is changed into an initial bar stock with dimensions of Φ300×430 mm. After each heat of forging, water cooling is used as the cooling method.
[0033] The initial bar stock is forged and deformed. The forging temperature is selected as Tβ + 50 °C, that is, 922 °C, and held. It is forged into the final forging in two heats, with the deformation controlled at 60%. The dimensions of the final forging are the same as those of the initial forging, both being 560×340×140 mm. After each heat of forging, water cooling is used as the cooling method.
[0034] The final forging is placed in a heating furnace for heat treatment. The final forging is heated to 830 °C and held for 2 hours. Then the heating furnace is cooled to 750 °C, held for 2 hours and then water-cooled. Finally, the final forging is placed in the heating furnace, heated to 610 °C and held for 4 h, and then air-cooled out of the furnace.
[0035] Samples are taken at the center of the final forging, including microscopic specimens, fracture toughness specimens and tensile specimens, and tested separately.
[0036] Example 3
[0037] The initial forging is square, made of TC18, with dimensions of 560×340×140 mm. The phase transformation point Tβ is 872 °C. The initial forging with a fine-grained bright band structure is placed in a heating furnace and heated to Tβ + 80 °C, that is, 952 °C, and held. The initial forging is forged in two heats, with the deformation per heat controlled at 40% until the initial forging is changed into an initial bar stock with dimensions of Φ300×430 mm. After each heat of forging, water cooling is used as the cooling method.
[0038] The initial bar is subjected to forging deformation. The forging temperature is selected as Tβ + 80°C, i.e., 952°C, and it is kept warm. It is forged into the final forging in two heats, and the deformation amount is controlled at 70%. The dimensions of the final forging are the same as those of the initial forging, both being 560×340×140 mm. After each heat of forging, water cooling is used as the cooling method.
[0039] The final forging is placed in a heating furnace for heat treatment. The final forging is heated to 850°C and kept warm for 3 hours. The heating furnace is cooled to 760°C, and after keeping warm for 3 hours, it is water cooled. Finally, the final forging is placed in the heating furnace and heated to 620°C and kept warm for 6 h, and then air cooled out of the furnace.
[0040] Samples are taken at the center position of the final forging, including microscopic specimens, fracture toughness specimens, and tensile specimens, and they are respectively tested.
[0041] The following table shows the mechanical properties of the forgings processed by this method and the initial forgings. It can be concluded that the mechanical properties of the forgings processed by this method are significantly higher than those of the initial forgings.
[0042]
[0043]
[0044] The embodiments of this specific implementation manner are all preferred embodiments of the present invention. Without limiting the protection scope of the present invention accordingly, therefore: All equivalent changes made according to the structure, shape, and principle of the present invention shall be covered within the protection scope of the present invention.
Claims
1. A forging method for improving the fine-grained bright band structure of TC18 titanium alloy, characterized in that, It includes the following steps: S1: The initial forging with a fine-grained bright band structure is forged for n heats to form an initial bar. After each heat forging, it is water-cooled to transform the fine-grained bright band structure into equiaxed α phase. When forging each heat, the initial forging is heated to Tβ+(30 - 80°C) and held for the first holding time T1, where T1 = f*Dx, f is the heating coefficient taken as 0.5 - 0.7, x takes 1, 2, 3... n, and Dx is the maximum cross-sectional thickness of the initial forging at the x-th heat; S2: The initial bar is forged for m heats to form the final forging. After each heat forging, it is water-cooled. The final forging has the same shape and size as the initial forging. The equiaxed α phase in the initial bar is changed into a basketweave structure. When forging each heat, the initial bar is heated to Tβ+(30 - 80°C) and held for the first holding time T2, where T2 = f*Dy, f is the heating coefficient taken as 0.5 - 0.7, y takes 1, 2, 3... m, and Dy is the maximum cross-sectional thickness of the initial bar at the y-th heat; S3: The final forging is placed in a heating furnace for heat treatment. The final forging is heated to 820 - 850°C and held for 1 - 3 hours, then the heating furnace is cooled to 740 - 760°C, held for 1 - 3 hours and then water-cooled; finally, the final forging is placed in the heating furnace and heated to 600 - 620°C, held for 2 - 6h, and then air-cooled out of the furnace.
2. The forging method for improving the fine-grained bright band structure of TC18 titanium alloy according to claim 1, characterized in that, In step S1, if the fine-grained bright band structure has not been completely transformed into equiaxed α phase, the initial bar is heated to Tβ+(30 - 80°C), then upset and drawn out. The material after upsetting and drawing out has the same shape and size as the initial bar until the fine-grained bright band structure is completely transformed into equiaxed α phase.
3. A forging method for improving the fine-grained bright band structure of TC18 titanium alloy as described in claim 1, characterized in that, In step S1, the deformation amount for each heat forging is 20 - 40%.
4. A forging method for improving the fine-grained bright band structure of TC18 titanium alloy as described in claim 1, characterized in that, In step S2, the deformation amount for each heat forging is 50 - 70%.
5. A forging method for improving the fine-grained bright band structure of TC18 titanium alloy according to claim 1, characterized in that, After step S3, samples are taken at the center position of the final forging, including microscopic specimens, fracture toughness specimens and tensile specimens.