Method for manufacturing TC21 titanium alloy forge piece with high fracture toughness

Abstract

The invention provides a high-fracture-toughness manufacturing method for a TC21 titanium alloy forge piece. The high-fracture-toughness manufacturing method comprises the following steps that S1, the relation between the TC21 fracture toughness and the original beta grain size is established; s2, testing the relationship between the grain size and the heat preservation time at the temperature; s3, correcting the formula (2) according to the actual condition of the heating furnace on site; S4, calculating the original beta grain size d required to be controlled by the forge piece through the formula (1); substituting the calculated d value into a formula (3) to obtain the required heating temperature and time; s5, heating is conducted according to the calculated heating time, and forging of the forge piece is conducted; and S6, through the air speed of the high-power fan, the cooling rate of the forge piece in the forging temperature range of X DEG C to 700 DEG C is controlled to be 2 DEG C / min to 10 DEG C / min. And a growth model of the grain size of the forge piece during forging heating is established, reasonable control over the grain size is achieved, and high-fracture-toughness manufacturing is achieved.

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. It is widely used in aircraft structural parts due to its good fracture toughness and fatigue crack resistance. 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, and high fracture toughness is of great significance to the service safety of forgings. According to research, the fracture toughness of titanium alloy forged in the β phase region is affected by the size of the original β grains and the primary α lamellae in the crystal, 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 crystal, the greater the ability to hinder cracks, and the higher the fracture toughness. However, the original β grain size of the titanium alloy cannot be controlled too large, otherwise, while the fracture toughness is improved, the section shrinkage and plasticity of the forging at room temperature 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 forging.

[0003] In the actual production process, the original β grain size of the forging is mainly affected by the heating time and heating temperature; however, the size, weight and thickness of TC21 titanium alloy forgings are often large, and the growth behavior and size of the original β grains cannot be accurately controlled like laboratory-grade specimens; therefore, how to control the grain size growth of TC21 forgings is an important way to manufacture them with high fracture toughness. Generally speaking, the grain size growth of metals during isothermal annealing obeys the Beck model; in past studies, Reference 1 (Study on the Grain Growth Behavior of β Single Phase Zone of TC21 Titanium Alloy, 2011) established the growth behavior of the original β grains of TC21 titanium alloy in the β phase zone based on the Beck model by using 6mm×6mm×6mm samples, but the sample size in this study was small. When the model was used to guide the production of TC21 large forgings, it was found that there was an obvious grain size deviation; in addition, after more than 10 years of improvement, the composition and phase transition point of TC21 titanium alloy bars have been optimized, which is somewhat different from the state when the study was published. Summary of the invention

[0004] The technical problem solved by the present invention is to provide a method for manufacturing a TC21 titanium alloy forging with high fracture toughness, establish a growth model of the grain size of the forging 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 the production big data, the relationship between the fracture toughness of TC21 and the original β grain size is established during the quasi-β forging process as follows:

[0008] K IC =0.06d+51.2# (1)

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

[0010] S2. The samples of titanium alloy forgings were kept at β forging temperature of X℃ for different time periods. After cooling, the relationship between grain size and holding time at this temperature was tested. The relationship is as follows:

[0011] d = kt n # (two)

[0012] In formula (2), k is a coefficient related to material and temperature; t is the heating time, in 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] d=(1.05~1.13)kt n # (three)

[0015] In formula (III), 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, according to the KIC value required in the standard, the original β grain size d required to be controlled for the forging is calculated by formula (I); the calculated d value is substituted into formula (III) 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 the wind speed of a high-power electric fan.

[0019] In step S1, the original β grain size 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 of 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 the forging at a certain temperature when TC21 titanium alloy is forged in the β phase region, the grain size of the forging can be predicted. Combined with the boundary conditions of the on-site industrial heating furnace, the prediction model of the β grain size of the TC21 titanium alloy forging during heating is accurately corrected, making the model more accurate.

[0024] 2. By controlling the size of the original β grains, 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 is further described below in conjunction with the accompanying drawings and embodiments.

[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 the production big data, the relationship between the fracture toughness of TC21 and the original β grain size is established during the quasi-β forging process as follows:

[0031] K IC =0.06d+51.2# (1)

[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 kept at β forging temperature of X℃ for different time periods (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 holding time at this temperature is tested:

[0034] d = kt n # (two)

[0035] In formula (2), k is a coefficient related to material and temperature; t is the heating time, in 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] d=(1.05~1.13)kt n # (three)

[0038] In formula (III), 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, according to the KIC value required in the standard, the original β grain size d required to be controlled for the forging is calculated by formula (I); the calculated d value is substituted into formula (III) 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 to be 2°C / min to 10°C / min by the wind speed of a high-power electric fan to ensure that the α lamellae inside the original β grains are not too dense or too sparse.

[0042] In step S1, the original β grain size 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 of 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 the forging at a certain temperature when TC21 titanium alloy is forged in the β phase region, the grain size of the forging 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 is accurately corrected, making the model more accurate.

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

[0047] Example 2

[0048] The maximum effective section thickness of a forging is 80 mm, and the forging weight is 150 kg. 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 = 80MPa.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 the production big data, the relationship between the fracture toughness of TC21 and the original β grain size during quasi-β forging is established as follows:

[0051] K IC =0.06d+51.2#

[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. Use a 20mm×20mm×20mm sample, keep it at a β forging temperature of X℃ for different time periods, and after cooling, test the relationship between the grain size and the holding time at this temperature. The relationship is as follows:

[0054] d = kt n #

[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 for different times. After cooling, the relationship between the grain size and the holding time at this temperature was tested, and the results were:

[0056] d=71.8t 0.46

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

[0058] 480 = (1.07 × 71.8) t 0.46 #(3)

[0059] The t was obtained to be 54 min.

[0060] S4. Before forging heating, according to the KIC value required in the standard, the original β grain size d required to be controlled for the forging is calculated by formula (I); the calculated d value is substituted into formula (III) 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 for forging.

[0064] S6. On the basis of steps S3 to S5, after forging is completed, the cooling rate of the forging in the range of forging temperature X°C to 700°C is controlled to be 2°C / min to 10°C / min by the flux of a high-power electric fan, so as 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 wind speed of the fan 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]

[0070] Example 3

[0071] The maximum effective section thickness of a forging is 140 mm, and the forging weight is 550 kg. IC The value is adjusted to 105MPa.m 1 / 2 , the manufacturing steps are as follows:

[0072] A method for manufacturing a TC21 titanium alloy forging with high fracture toughness comprises the following steps:

[0073] S1. Based on the production big data, the relationship between the fracture toughness of TC21 and the original β grain size during quasi-β forging is established as follows:

[0074] K IC =0.06d+51.2#

[0075] According to formula (1), the KIC value is calculated to be 105MPa.m 1 / 2 When the original β grain size is d, the d value needs to be controlled to 896μm.

[0076] S2: A sample of 20mm×20mm×20mm was used, and the β forging temperature was X℃, and the temperature was kept for different times. After cooling, the relationship between the grain size and the holding time at the temperature was tested as follows:

[0077] d = kt n #

[0078] 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 for different times. After cooling, the relationship between the grain size and the holding time at this temperature was tested, and the results were obtained;

[0079] d=71.8t 0.46

[0080] S3: According to the production of the forging heating furnace, the revised form (II) is:

[0081] 896 = (1.06 × 71.8) t 0.46 #

[0082] The obtained t is 215min.

[0083] S4: Before forging heating, according to the KIC value required in the standard, the original β grain size d required to be controlled for the forging is calculated by formula (1); the calculated d value is substituted into formula (3) to estimate the required heating temperature and time.

[0084] According to the calculation results, the effective insulation time of the forging is 215min.

[0085] S5: heating according to the calculated heating time, and then forging the forging;

[0086] 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 for forging.

[0087] 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 the wind speed of a high-power electric fan, so as to ensure that the α-lamellae inside the original β-grains are not too dense or too sparse.

[0088] 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.

[0089] After the forging is forged, its microstructure is as follows Figure 2 As shown; after measurement, 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.

[0090] Table 2 shows the tensile properties and fracture toughness of the forgings in Example 3 at the core position.

[0091]

[0092] 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 protection scope of the present invention.

Claims

1. A method for manufacturing a TC21 titanium alloy forging with high fracture toughness, characterized in that: The following steps are involved: S1. Based on production data, the relationship between TC21 fracture toughness and original β grain size during quasi-β forging is established as follows: K IC = 0.06d + 51.2 #(One) In formula (1), KIC is the fracture toughness value; d is the original β grain size, unit is μm; S2. The samples of titanium alloy forgings were kept at β forging temperature of X℃ for different time periods. After cooling, the relationship between grain size and holding time at this temperature was tested. The relationship is as follows: d=ktn#(two) In formula (2), k is a coefficient related to material and temperature; t is the heating time, in 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: d = (1.05 to 1.13)kt n #(III) In formula (III), 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 KIC value required in the standard, the original β grain size d required to be controlled for the forging is calculated by formula (I); the calculated d value is substituted into formula (III) to obtain the required heating temperature and 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 the wind speed of a high-power electric fan.

2. The method for manufacturing a TC21 titanium alloy forging with high fracture toughness as claimed in claim 1, characterized in that: In step S1, the original β grain size is 50 mm<d<800 μm.

3. The method for manufacturing a TC21 titanium alloy forging with high fracture toughness as claimed in claim 1, characterized in that: 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 as claimed in claim 1, characterized in that: In step S3, the correction coefficients of 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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