A method for manufacturing TC21 titanium alloy forgings with high fracture toughness

Abstract

The present invention provides a method for manufacturing a TC21 titanium alloy forging with high fracture toughness, comprising the following steps: S1. establishing a relationship between the TC21 fracture toughness and the original β grain size; S2. testing the relationship between the grain size and the heating time at the temperature; S3. modifying formula (2) based on the actual conditions of the heating furnace on site; S4. calculating the original β grain size d required for the forging using formula (1); substituting the calculated d value into formula (3) to obtain the required heating temperature and time; S5. heating the forging according to the calculated heating time; and S6. controlling the cooling rate of the forging within the forging temperature range of X°C to 700°C to 2°C / min to 10°C / min by using the wind speed of a high-power electric fan. A grain size growth model for the forging during forging heating is established to achieve reasonable control of the grain size and achieve high fracture toughness manufacturing.

Description

Technical Field

[0001] The invention relates to the technical field of nonferrous metal hot processing, in particular to a method for manufacturing a TC21 titanium alloy forging with high fracture toughness. Background Art

[0002] TC21 titanium alloy is a damage tolerant titanium alloy. Due to its good fracture toughness and fatigue crack resistance, it is widely used in aircraft structural parts. In the engineering manufacturing process, TC21 titanium alloy structural parts are usually forged in the β phase region. Fracture toughness is an important indicator of the service life of TC21 titanium alloy forgings. High fracture toughness is of great significance to the service safety of forgings. According to research, the fracture toughness of titanium alloys forged in the β phase region is affected by the size of the original β grains and the primary α lamellae in the grains, and the former is the main influencing factor. Generally speaking, the larger the original β grains, the more complete the precipitation of the lamellae in the grains, the greater the ability to hinder cracks, and the higher the fracture toughness. However, the original β grain size of titanium alloy cannot be controlled too large, otherwise, while the fracture toughness increases, the cross-sectional shrinkage rate and plasticity of the forging under room temperature tensile stress will decrease. Therefore, precise control of the original β grain size during the forging process is of great significance to the control of the fracture toughness and tensile properties of the forgings.

[0003] In actual production, the original β grain size of forgings is primarily affected by heating time and temperature. However, TC21 titanium alloy forgings are often large in size, weight, and thickness, making it difficult to precisely control the growth behavior and size of their original β grains as in laboratory-grade specimens. Therefore, controlling the grain size growth of TC21 forgings is a key approach to achieving high fracture toughness. Generally speaking, the grain size growth of metals during isothermal annealing follows the Beck model. Previous research, including Reference 1 (Study on Grain Growth Behavior in the β Single-Phase Region of TC21 Titanium Alloy, 2011), used a 6mm×6mm×6mm sample to establish the growth behavior of the original β grains in the β phase region of TC21 titanium alloy based on the Beck model. However, the sample size in this study was relatively small, and significant grain size deviations were observed when this model was used to guide the production of large TC21 forgings. Furthermore, after more than a decade of refinement, the composition and phase transformation points of TC21 titanium alloy bars have been optimized, resulting in some deviations from the state at the time of publication. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a method for manufacturing TC21 titanium alloy forgings with high fracture toughness, establish a growth model of the grain size of the forgings during forging heating, realize reasonable control of the grain size, and achieve manufacturing with high fracture toughness.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A method for manufacturing a TC21 titanium alloy forging with high fracture toughness comprises the following steps:

[0007] S1. Based on production big data, the relationship between TC21 fracture toughness and original β grain size during quasi-β forging is established as follows:

[0008] (one)

[0009] In formula (1), KIC is the fracture toughness value; d is the original β grain size, unit is μm;

[0010] S2. Titanium alloy forging samples were heated at a β forging temperature of X°C for different times. After cooling, the relationship between grain size and heating time at this temperature was tested. The relationship is as follows:

[0011] (two)

[0012] In formula (2), k is a coefficient related to material and temperature; t is the heating time, unit is min; n is the grain growth coefficient;

[0013] S3. According to the actual situation of the heating furnace on site, the revised formula (II) is as follows:

[0014] (three)

[0015] In formula (3), 1.05~1.13 is the correction coefficient of the heating furnace during the actual heating process of TC21 large forgings;

[0016] S4. Before forging heating, calculate the original β grain size d required for the forging using formula (1) based on the KIC value required in the standard; substitute the calculated d value into formula (3) to obtain the required heating temperature and time;

[0017] S5. Heating is performed according to the calculated heating time to forge the forging;

[0018] S6. On the basis of steps S3 to S5, after forging is completed, the cooling rate of the forging in the forging temperature range of X°C to 700°C is controlled to be 2°C / min to 10°C / min by using the wind speed of a high-power electric fan.

[0019] In step S1 , the size of the original β grains is 50 mm < d < 800 μm.

[0020] In step S2, the size of the sample is 20 mm×20 mm×20 mm.

[0021] In step S3, the correction coefficients 1.05 to 1.13 are used for forgings with a weight greater than 30 kg and a thickness greater than 50 mm.

[0022] The beneficial effects of the present invention are:

[0023] 1. By accurately establishing the growth relationship of the β grain size of TC21 titanium alloy forgings at a certain temperature when forging in the β phase region, the grain size of the forgings can be predicted. Combined with the boundary conditions of the on-site industrial heating furnace, the prediction model of the β grain size of TC21 titanium alloy forgings during heating was accurately corrected, making the model more accurate.

[0024] 2. By controlling the original β grain size, the cooling rate is further controlled to control the size of the primary α lamellae within the original β grains of the forging, thereby achieving coordinated control of high fracture toughness and high tensile properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the microstructure diagram of the forging in Example 1;

[0026] Figure 2 This is the microstructure diagram of the forging in Example 2. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and examples.

[0028] Example 1

[0029] A method for manufacturing a TC21 titanium alloy forging with high fracture toughness comprises the following steps:

[0030] S1. Based on production big data, the relationship between TC21 fracture toughness and original β grain size during quasi-β forging is established as follows:

[0031] (one)

[0032] In formula (1), KIC is the fracture toughness value; d is the original β grain size, unit is μm;

[0033] S2. Titanium alloy forging samples were heated at β forging temperature of X℃ for different times (T β +10℃、T β +20℃、T β +30℃, Tβ is the β phase transition point), after cooling, the relationship between the grain size and the heating time at this temperature is:

[0034] (two)

[0035] In formula (2), k is a coefficient related to material and temperature; t is the heating time, unit is min; n is the grain growth coefficient;

[0036] S3. According to the actual situation of the heating furnace on site, the revised formula (II) is as follows:

[0037] (three)

[0038] In formula (3), 1.05~1.13 is the correction coefficient of the heating furnace during the actual heating process of TC21 large forgings;

[0039] S4. Before forging heating, calculate the original β grain size d required for the forging using formula (1) based on the KIC value required in the standard; substitute the calculated d value into formula (3) to obtain the required heating temperature and time;

[0040] S5. Heating is performed according to the calculated heating time to forge the forging;

[0041] S6. On the basis of steps S3 to S5, after forging is completed, the cooling rate of the forging in the forging temperature range of X°C to 700°C is controlled by the wind speed of a high-power electric fan to be 2°C / min to 10°C / min, to ensure that the α lamellae inside the original β grains are not too dense or too sparse.

[0042] In step S1 , the size of the original β grains is 50 mm < d < 800 μm.

[0043] In step S2, the size of the sample is 20 mm×20 mm×20 mm.

[0044] In step S3, the correction coefficients 1.05 to 1.13 are used for forgings with a weight greater than 30 kg and a thickness greater than 50 mm.

[0045] By accurately establishing the growth relationship of the β grain size of TC21 titanium alloy forgings at a certain temperature when forging in the β phase region, the grain size of the forgings can be predicted. Combined with the boundary conditions of the on-site industrial heating furnace, the prediction model of the β grain size of TC21 titanium alloy forgings during heating was accurately corrected, making the model more accurate.

[0046] By controlling the original β grain size and further controlling the cooling rate, the size of the primary α lamellae within the original β grains of the forging can be controlled, thereby achieving coordinated control of high fracture toughness and high tensile properties.

[0047] Example 2

[0048] The maximum effective section thickness of a forging is 80mm, and the forging weight is 150kg. The standard requires that the fracture toughness K of a TC21 titanium alloy forging be IC Value ≥65MPa.m 1 / 2 , but the forgings actually need to reach K IC Value = 80 MPa.m 1 / 2, in order to ensure safe delivery, the main steps of manufacturing are as follows:

[0049] A method for manufacturing a TC21 titanium alloy forging with high fracture toughness comprises the following steps:

[0050] S1. Based on production data, the relationship between the fracture toughness of TC21 and the original β grain size during quasi-β forging is established as follows:

[0051]

[0052] The calculated KIC value is 80MPa.m 1 / 2 When the original β grain size d value needs to be controlled as: 480μm≤dactual≤800μm.

[0053] S2. Using a 20mm×20mm×20mm sample, heat it at a β forging temperature of X°C for different times. After cooling, test the relationship between grain size and heating time at this temperature. The relationship is as follows:

[0054]

[0055] The phase transformation point T of the forging β is 968℃, and the forging temperature to be selected is T β +30℃, so a 20mm×20mm×20mm sample was used, and the β forging temperature was 998℃, and the temperature was kept at different times. After cooling, the relationship between the grain size and the holding time at this temperature was tested, and the results were:

[0056]

[0057] S3. According to the actual situation of the heating furnace on site, the revised form (II) is:

[0058]

[0059] The obtained t is 54 min.

[0060] S4. Before forging heating, calculate the original β grain size d required for the forging according to the KIC value required in the standard using formula (1); substitute the calculated d value into formula (3) to estimate the required heating temperature and time.

[0061] According to the calculation results, the effective insulation time of the forging is 54 minutes.

[0062] S5. Heating is performed according to the calculated heating time, and then forging is performed;

[0063] The pre-forged billet is heated at 998°C. After the effective heating time of the core reaches 54 minutes, it is taken out of the furnace and forged into shape.

[0064] S6. Based on steps S3 to S5, after forging is completed, the cooling rate of the forging in the range of forging temperature from X°C to 700°C is controlled to be 2°C / min to 10°C / min by using a high-power electric fan to ensure that the α lamellae inside the original β grains are not too dense or too sparse.

[0065] After forging is completed, the forgings are quickly transferred to the material rack, and then the fan speed is adjusted to ensure that the cooling rate of the forgings in the range of 998℃ to 700℃ is between 5℃ / min and 7℃ / min.

[0066] After the forging is forged, its microstructure is as follows Figure 1 As shown; after measurement, the average original β grain size of the forging is 495μm, and the K IC The performance and tensile properties meet the standard requirements, and K IC The performance margin is relatively high, as shown in Table 1.

[0067] Table 1 shows the tensile properties and fracture toughness of the forging at the core position in Example 2.

[0068]

[0069] Example 3

[0070] The maximum effective section thickness of a forging is 140 mm and the weight of the forging is 550 kg. IC The value is adjusted to 105MPa.m 1 / 2 , the manufacturing steps are as follows:

[0071] A method for manufacturing a TC21 titanium alloy forging with high fracture toughness comprises the following steps:

[0072] S1. Based on production data, the relationship between the fracture toughness of TC21 and the original β grain size during quasi-β forging is established as follows:

[0073]

[0074] According to formula (1), the KIC value is calculated to be 105MPa.m 1 / 2 When the original β grain size d value needs to be controlled to 896μm.

[0075] S2: A 20mm×20mm×20mm sample was heated at a β forging temperature of X°C for different times. After cooling, the relationship between grain size and heating time at the temperature was measured as follows:

[0076]

[0077] The phase transformation point T of the forging βis 968℃, and the forging temperature to be selected is T β +30℃, so a 20mm×20mm×20mm sample was used, heated at a β forging temperature of 998℃ for different times, and after cooling, the relationship between grain size and heating time at this temperature was tested to obtain;

[0078]

[0079] S3: Based on the production conditions of the forging heating furnace, Form (II) is revised as follows:

[0080]

[0081] The obtained t is 215 min.

[0082] S4: Before forging heating, calculate the original β grain size d required for the forging using formula (1) based on the KIC value required in the standard; substitute the calculated d value into formula (3) to estimate the required heating temperature and time.

[0083] According to the calculation results, the effective heating time of the forging is 215 minutes.

[0084] S5: heating according to the calculated heating time, and then forging the forging;

[0085] The pre-forged billet is heated at 998°C. After the effective heating time of the core reaches 214 minutes, it is taken out of the furnace and forged into shape.

[0086] S6: Based on steps S3 to S5, after forging is completed, the cooling rate of the forging in the forging temperature range of X°C to 700°C is controlled by the wind speed of a high-power electric fan to be 2°C / min to 10°C / min, to ensure that the α lamellae inside the original β grains are not too dense or too sparse.

[0087] After forging is completed, the forgings are quickly transferred to the material rack, and then the fan flux is adjusted to ensure that the cooling rate of the forgings in the range of 998℃ to 700℃ is between 7℃ / min and 10℃ / min.

[0088] After the forging is forged, its microstructure is as follows Figure 2 As shown in Table 2, the average original β grain size of the forging is 900-1000μm. Although the KIC performance of the forging is high, the cross-sectional shrinkage rate of the forging is unqualified and the elongation of the forging is low, as shown in Table 2.

[0089] Table 2 shows the tensile properties and fracture toughness of the forgings in Example 3 at the core position.

[0090] project Tensile strength (MPa) Yield strength (MPa) Elongation(%) Sectional shrinkage (%) <![CDATA[Fracture toughness (MPa.m 1 / 2 )]]> Test average 1099 1008 10.5 9.8 103 Require ≥1060 ≥930 ≥7 ≥10 /

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for manufacturing TC21 titanium alloy forgings with high fracture toughness, characterized by: The following steps are involved: S1. Based on production data, the relationship between the fracture toughness of TC21 and the original β grain size during quasi-β forging is established as follows: (one) In formula (1), K IC is the fracture toughness value; d is the original β grain size, unit is μm; S2. Titanium alloy forging samples were heated at a β forging temperature of X°C for different times. After cooling, the relationship between grain size and heating time at this temperature was tested. The relationship is as follows: (two) In formula (2), k is a coefficient related to material and temperature; t is the heating time, unit is min; n is the grain growth coefficient; S3. According to the actual situation of the heating furnace on site, the revised formula (II) is as follows: (three) In formula (3), 1.05~1.13 is the correction coefficient of the heating furnace during the actual heating process of TC21 large forgings; S4. Before forging heating, according to the K required in the standard IC The original β grain size d required to be controlled for the forging is calculated using formula (1); the calculated d value is substituted into formula (3) to obtain the required heating time; S5. Heating is performed according to the calculated heating time to forge the forging; S6. On the basis of steps S3 to S5, after forging is completed, the cooling rate of the forging in the forging temperature range of X°C to 700°C is controlled to be 2°C / min to 10°C / min by using the wind speed of a high-power electric fan.

2. The method for manufacturing a TC21 titanium alloy forging with high fracture toughness according to claim 1, wherein: In step S1 , the original β grain size is 50 μm<d<800 μm.

3. The method for manufacturing a TC21 titanium alloy forging with high fracture toughness according to claim 1, wherein: In step S2, the size of the sample is 20 mm×20 mm×20 mm.

4. The method for manufacturing a TC21 titanium alloy forging with high fracture toughness according to claim 1, wherein: In step S3, the correction coefficients 1.05 to 1.13 are used for forgings with a weight greater than 30 kg and a thickness greater than 50 mm.

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