Preheating type heat treatment process for TC18 titanium alloy heavy forgings

Abstract

The present application relates to titanium alloy production forging process technical field, disclose a kind of TC18 titanium alloy large forging preheating type heat treatment process, comprising the following steps, S1 prepares solid solution, and the forging of hot working state is carried out preliminary solid solution at T1 temperature;S2 solid solution treatment, after S1 preliminary solid solution, furnace temperature rises to T2 temperature and keeps warm for a period of time, then furnace temperature is reduced to T3 temperature and keeps warm for a period of time, then cooling, wherein T2 is lower than T β , T1 is lower than T2, T3 is lower than T2;S3 preliminary aging, after S2 cooling, the forging is carried out preliminary aging heat at T4 temperature;S4, aging treatment, after S3 preliminary aging, furnace temperature rises to T5 temperature and keeps warm for a period of time, then cooling, wherein T4 is lower than T5.The present application patent solves the problem of large performance difference between core and edge of TC18 large forging after heat treatment and the problem of comprehensive mechanical property difference in the prior art.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy production forging technology, specifically to a preheating heat treatment process for large TC18 titanium alloy forgings. Background Technology

[0002] Titanium alloys possess high strength, low density, corrosion resistance, and excellent high and low temperature performance, making them widely used in high-tech fields such as aerospace, marine engineering, and national defense. TC18 (nominal composition: Ti-5Al-5Mo-5V-1Cr-1Fe), a typical high-strength and tough near-β-type titanium alloy, exhibits excellent hardenability, forgeability, and overall strength and toughness. After heat treatment, its tensile strength can reach over 1080 MPa, and its hardened thickness can reach 250 mm. Therefore, it is often chosen for manufacturing the main load-bearing structural components of large aircraft, such as the docking frame between the landing gear crossbeam and the fuselage. Large, integrated structural components not only significantly reduce weight, improve structural integrity and reliability, and enhance equipment fatigue life and safety, but also simplify assembly processes and increase production efficiency. Based on these advantages, adopting the design concepts of "integration" and "large-scale" has become a clear development trend in the industry.

[0003] Currently, TC18 forgings are generally heat-treated using a dual annealing method of solution treatment and aging. For example, invention patent CN115976441B discloses a heat treatment method for TC18 titanium alloy, the steps of which are: first, solution heat treatment, heating the TC18 titanium alloy to the β phase transformation temperature T. β After holding at 70℃~130℃ for 1 hour, cool to room temperature with water; T β The first step is the β-phase transformation temperature of the alloy; the second step is a first-stage aging heat treatment, in which the alloy obtained after the first step of cooling is heated to 550℃~600℃, held for 6~8h, and then water-cooled to room temperature; the third step is a second-stage aging heat treatment, in which the alloy obtained after the second step of cooling is heated to 300℃~450℃, held for 2h~4h, and then water-cooled to room temperature. While the aforementioned solution treatment and second-stage aging methods can obtain high-strength, high-ductility TC18 titanium alloys, for large forgings, the poor thermal conductivity of titanium alloys inevitably leads to difficulties in controlling the uniformity of microstructure and properties due to the large size of the forgings. Furthermore, the short holding time of solution aging makes it difficult to ensure complete heat penetration of the core of large forgings, resulting in significant differences in properties between the core and the edges, thus failing to fully release the performance potential of the finished forgings. This problem directly threatens the safety, reliability, and service life of the overall structural components. Therefore, developing a reasonable heat treatment regime suitable for large TC18 forgings is crucial. Summary of the Invention

[0004] The present invention aims to provide a preheating heat treatment process for large TC18 titanium alloy forgings to solve the problem of large differences in the properties of the core and the edge of large TC18 forgings after heat treatment and poor overall mechanical properties in the prior art.

[0005] To solve the above problems, the present invention adopts the following technical solution: a preheating heat treatment process for TC18 titanium alloy large forgings, including the following steps: S1 pre-solution treatment, in which the hot-worked forgings are pre-solution treated at a temperature T1. S2 solution treatment involves heating the forging, after S1 pre-solution treatment, in the furnace to temperature T2 and holding it for a period of time, then cooling it in the furnace to temperature T3 and holding it for a period of time, followed by cooling. T2 is lower than T... β T1 is lower than T2, and T3 is lower than T2; S3 pre-aging involves subjecting the forging cooled by S2 to pre-aging heat at temperature T4. S4 aging treatment involves heating the forgings that have undergone pre-aging in S3 to T5 temperature in the furnace and holding them at that temperature for a period of time, followed by cooling. T4 is lower than T5.

[0006] The principles and beneficial effects of this application are as follows: In this application, a preliminary heat treatment is added before both solution treatment and aging treatment, and the temperature range of the preliminary heat treatment is effectively controlled so that the preliminary solution treatment temperature T1 in S1 is lower than the solution treatment temperature T2 in S2, and the preliminary aging temperature T4 in S2 is lower than the aging temperature T5 in S4. In this application, heating and holding at a temperature below the solution treatment temperature achieves the preliminary heat treatment, ensuring sufficient hot head in the core of the forging. During solution treatment, the forging is heated to T1. β The following temperature range (T2) is used for insulation (T β The β-phase transformation temperature of TC18 titanium alloy is used to fully dissolve the α-phase in the β matrix, followed by rapid cooling to obtain and retain the metastable phase. Pre-aging involves preheating the solution-treated forging below the aging temperature to promote the rapid decomposition of the metastable phase during subsequent aging, thereby strengthening the material. Aging treatment involves holding the solution-treated alloy at a lower temperature to promote the precipitation of fine, uniform, and dispersed secondary α-phase, significantly improving the forging's properties.

[0007] Furthermore, the stepped heating process in this application, from pre-treatment to subsequent solution treatment and aging, has a dual effect: firstly, it eliminates residual stress from forging through pre-treatment; secondly, the stepped heating effectively alleviates the problem of uneven heating between the core and edges caused by the low thermal conductivity of titanium alloys, thus ensuring overall heat penetration of the forging and fully exploiting the material's performance potential, improving its mechanical properties after heat treatment, making it particularly suitable for the preparation of large forgings. Therefore, the TC18 forging achieves excellent mechanical properties and microstructure while ensuring a high degree of consistency in the microstructure and properties between the core and edges, fully stimulating the material's performance potential. Compared to the prior art's method of multiple solution failures, this application directly completes solution treatment and aging by heating in the furnace after pre-treatment. This not only improves the uniformity of heating between the core and edges of the titanium alloy, thus enhancing the consistency of the microstructure and properties between the core and edges, but also effectively controls its comprehensive mechanical properties, enabling it to meet service standards.

[0008] Furthermore, in this application, during the S2 solution treatment, the forging is first heated to T2 temperature for solution treatment, and then directly cooled to T3 temperature in the furnace for solution strengthening treatment. This can effectively eliminate the component segregation formed during the first solution treatment or hot working process, especially the unstable β phase enriched and precipitated at the grain boundaries. By holding the temperature at high temperature, these elements are re-dissolved into the matrix, suppressing the formation of coarse α phase or grain boundary precipitates, optimizing the uniformity of the microstructure and grain refinement, and improving mechanical properties.

[0009] Preferably, as an improvement, the temperature range of T1 is 750℃~820℃, the temperature range of T2 is 820℃~850℃, the temperature range of T3 is 740~760℃, the temperature range of T4 is 400℃~500℃, and the temperature range of T5 is 500℃~650℃.

[0010] Preferably, as an improvement, the holding time for pre-solidification at temperature T1 in S1 is 1 to 3 hours.

[0011] Preferably, as an improvement, the holding time for pre-aging at temperature T4 in S3 is 1 to 3 hours.

[0012] Preferably, as an improvement, the thickness of the forgings in S1 and S3 is 100-300 mm.

[0013] Preferably, as an improvement, the number of forgings in S1-S4 is multiple, and the material spacing between the multiple forgings in the heating furnace is greater than or equal to 150mm.

[0014] Preferably, as an improvement, both S2 and S4 are cooled by air cooling.

[0015] Preferably, as an improvement, the ambient temperature range for cooling S2 and S4 after exiting the furnace is 0℃~50℃, and the distance between adjacent forgings is greater than or equal to 300mm.

[0016] Preferably, as an improvement, in step S4, the difference in tensile strength and yield strength between the core and edge of the forging after cooling is within 30 MPa, the difference in elongation after fracture and reduction of area is less than 3% and 5% respectively, and the difference in impact toughness is less than 5 J / cm. 2 The fracture toughness difference is less than 5 MPa·m 1 / 2 .

[0017] Preferably, as an improvement, in S2, the holding time at temperature T2 is 1-3 hours, and the holding time at temperature T3 is 1-3 hours; in S4, the holding time at temperature T5 is 2-6 hours.

[0018] This application also has the following technical effects: 1. In this scheme, the time for pre-solution treatment and pre-aging is 1 to 3 hours, and the thickness of the forgings in S1 and S3 is 100 to 300 mm. The time range for pre-solution treatment and pre-aging is appropriate, which can effectively ensure that the titanium alloy of the large forgings with a thickness range of 100 to 300 mm can be fully preheated, so as to obtain large TC18 forgings with uniform structure and excellent performance.

[0019] 2. In this scheme, there are multiple forgings in S1-S4. Multiple forgings can be heat-treated simultaneously in each process step, which improves the preparation and forming efficiency of TC18 large forgings. Moreover, during the heating process in the furnace, the distance between adjacent forgings (i.e., the material spacing) is greater than or equal to 150mm to ensure that all forgings can be heated evenly and fully.

[0020] 3. In this scheme, when multiple forgings are heat-treated at the same time, air cooling is used during the cooling process after S2 and S4, and the ambient temperature is between 0℃ and 50℃. The distance between adjacent forgings during cooling is greater than or equal to 300mm to avoid mutual interference between the cooling processes of adjacent forgings, so that all forgings can be cooled quickly and stably.

[0021] 4. Using the technical solution of this application, after cooling in step S4, the difference in tensile strength and yield strength between the core and edge of the forging is within 30 MPa, the difference in elongation after fracture and reduction of area is less than 3% and 5% respectively, and the difference in impact toughness is less than 5 J / cm. 2 The fracture toughness difference is less than 5 MPa·m 1 / 2This ensures that the overall performance of TC18 titanium alloy in large forgings is consistent and stable, resulting in TC18 large forgings with uniform microstructure and excellent performance. The final product has tensile strength in the L, LT, and ST directions of ≥1120MPa, yield strength in the L, LT, and ST directions of ≥1040MPa, elongation after fracture and reduction of area of ​​≥8% and 22%, respectively. Attached Figure Description

[0022] Figure 1 The images show the microstructure of a 300mm thick TC18 forging (Example 11) after undergoing the pre-heat treatment process of this invention, measured at 500x (left) and 200x (right) magnification at D / 4.

[0023] Figure 2 The images are SEM images of a 300mm thick TC18 forging (Example 11) after being processed by the pre-heat treatment process of the present invention, measured at 300x (left) and 500x (right) magnification at D / 4.

[0024] Figure 3 The images show the microstructure of a 250mm thick TC18 forging (Example 3) after undergoing the pre-heat treatment process of this invention, measured at 500x (left) and 200x (right) magnification at D / 4.

[0025] Figure 4 The images are SEM images of a 250mm thick TC18 forging (Example 3) after being processed by the pre-heat treatment process of the present invention, magnified at D / 4 by 200x (left) and 500x (right). Detailed Implementation

[0026] The following detailed description illustrates the specific implementation method: Example 1: A preheating heat treatment process for large TC18 titanium alloy forgings, comprising the following steps: S1 pre-solution treatment involves pre-solution treatment of the hot-worked forgings at temperature T1, which ranges from 750℃ to 820℃. The holding time for pre-solution treatment at temperature T1 is 1 to 3 hours. The thickness of the forgings entering the furnace during this process is 100 to 300 mm.

[0027] S2 solution treatment involves heating the forgings (after S1 solution treatment) in the furnace to temperature T2 and holding them at that temperature for a period of time. The temperature range for T2 is 820℃~850℃, and the holding time is 1~3 hours. Then, the forgings are cooled in the furnace to temperature T3 and held at that temperature for a period of time. The temperature range for T3 is 740~760℃, and the holding time is 1~3 hours. Finally, the forgings are cooled by air cooling. T2 is lower than T... β T1 is lower than T2, and T3 is lower than T2.

[0028] S3 pre-aging involves subjecting the forgings cooled in S2 to pre-aging heat treatment at a temperature of T4, which ranges from 400℃ to 500℃. The holding time for pre-aging at T4 is 1 to 3 hours. The thickness of the forgings entering the furnace during this process is 100 to 300 mm.

[0029] S4 aging treatment involves heating the forgings that have undergone pre-aging (S3) in the furnace to temperature T5 and holding them at that temperature for a period of time. The temperature range for T5 is 500℃~650℃, and the holding time is 2~6 hours. Then, the forgings are cooled by air cooling, with T4 being lower than T5. After cooling, the difference in tensile strength and yield strength between the core and edges of the forging is within 30MPa, the difference in elongation after fracture and reduction of area is less than 3% and 5% respectively, and the difference in impact toughness is less than 5J / cm². 2 The fracture toughness difference is less than 5 MPa·m 1 / 2 .

[0030] The specific implementation steps are as follows: S1 Pre-solution treatment: Place the TC18 forging with a thickness of 250mm in the hot-worked state in a box-type resistance furnace. After the furnace temperature rises to T1 temperature of 810℃ and stabilizes, hold it at this temperature for 2 hours to perform pre-solution treatment.

[0031] S2 solution treatment involves heating the forgings after S1 solution treatment in the furnace from 810°C (T1) to 840°C (T2). After the furnace temperature stabilizes, the forgings are held at this temperature for 3 hours. Then, the forgings are cooled in the furnace to 760°C (T3). After the furnace temperature stabilizes, the forgings are held at this temperature for 2.5 hours to perform solution strengthening treatment. Finally, the forgings are removed from the furnace and placed on channel steel for air cooling.

[0032] For S3 pre-aging, the forgings after S2 air cooling are placed in a box-type resistance furnace. After the furnace temperature rises to T4 temperature of 400℃, they are held for 1 hour to complete the pre-aging treatment.

[0033] S4 aging treatment involves heating the forgings that have undergone pre-aging treatment (S3) from 400℃ (T4) to 617℃ (T5) in the furnace. After the furnace temperature stabilizes, it is held at this temperature for 6 hours for aging strengthening. The forgings are then air-cooled on a channel steel. According to Example 1, the compressive strength, yield strength, elongation after fracture, reduction of area, and fracture toughness of the core and edges of the heat-treated TC18 forgings are as follows: 1. Core: R m =1150MPa, R p0.2 =1065MPa, A=16%, Z=27%, αku=45J / cm 2 K IC =57.6 MPa·m 1 / 2 2. Edge: R m =1155MPa, R p0.2=1084MPa, A=13%, Z=24%, αku=43J / cm 2 K IC =55.6 MPa·m 1 / 2 .

[0034] The process steps of Examples 2-11 are the same, with only the process parameters differing, as shown in Table 1 below: Table 1 Process parameters for Examples 1-11

[0035] The performance parameter test results of Examples 1-11 are shown in Table 2 below: Table 2 Performance parameter test results of Examples 1-11

[0036] A comparison of Table 1 and Table 2 shows that: 1. Through Examples 1-3, a stepped heating and holding method was adopted, and a pre-heat treatment was added before solution treatment and aging. This resulted in more uniform heating of the large TC18 forgings during heat treatment, significantly improving the consistency of the microstructure and properties between the core and the edges. The difference in tensile strength and yield strength between the core and the edges was within 30 MPa, the difference in elongation after fracture and reduction of area was less than 3% and 5%, respectively, and the difference in impact toughness was less than 5 J / cm. 2 The fracture toughness difference is less than 5 MPa·m 1 / 2 Forgings exhibit excellent overall mechanical properties. While reducing the temperature and time of pre-solution treatment, solution treatment, pre-aging, and aging processes can significantly improve the strength of TC18 forgings, it will inevitably reduce their plasticity, impact toughness, and fracture toughness. Therefore, rationally controlling the heat treatment process parameters is crucial to achieving the superior comprehensive performance of finished forgings.

[0037] 2. A comparison of Examples 6 and 7 shows that reducing the temperature and time of aging and solution treatments, while omitting the pre-solution and pre-aging steps, will further reduce the overall mechanical properties of the forgings. This fully demonstrates that adding pre-solution and pre-aging steps helps to improve the overall performance of the forgings.

[0038] 3. As can be seen from the comparison between Examples 8 and 9, adding pre-aging treatment before aging treatment alone can significantly improve the elongation after fracture and the reduction of area of ​​the material, so that the TC18 forging can effectively improve the toughness and plastic deformation capacity of the material when the difference between compressive strength and yield strength is small.

[0039] 4. As can be seen from the comparison between Examples 10 and 11, the addition of solution treatment and aging pre-heat treatment can effectively improve the compressive strength, yield strength, elongation after fracture and reduction of area of ​​TC18 forgings. That is, the method can simultaneously improve the strength, plasticity and toughness of forgings and comprehensively improve the performance of materials.

[0040] 5. As can be seen from the comparison of Examples 4-9, by adjusting and optimizing the pre-heat treatment and solution aging regime, the synergy of material strength, plasticity, and toughness can be further improved, its performance potential can be fully explored, and the overall mechanical properties of the forging can be effectively improved. After pre-heat treatment, the tensile and yield strength of the 130mm thick forging increased by about 20MPa, the elongation after fracture and the reduction of area increased by about 2% and 8% respectively, and the impact toughness and fracture toughness increased by about 5J / cm. 2 and 5MPa·m 1 / 2 Forgings with thicknesses of 110mm and 210mm, by adjusting the pre-heat treatment process, have reduced strength but increased plasticity and toughness, thereby improving the overall service performance of the forgings.

[0041] Example 12: The difference between Example 12 and Example 1 is that in Example 12, the number of forgings in S1-S4 is multiple, such as five, six, ten, or other integers, so as to enable the efficient batch production of TC18 large forgings to meet production needs. When the number of forgings is multiple, the material spacing between multiple forgings in the heating furnace is greater than or equal to 150 mm, preferably 200 mm. The ambient temperature range for cooling after exiting the furnace in S2 and S4 is 0℃~50℃, preferably 25℃. The spacing between adjacent forgings is greater than or equal to 300 mm, preferably 500 mm, to ensure that the heat treatment and cooling process of a single forging is not affected by adjacent forgings, thereby improving the stability of forging performance during the batch forging production process.

[0042] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A preheating heat treatment process for large TC18 titanium alloy forgings, characterized in that: Includes the following steps, S1 pre-solution treatment involves pre-solution treatment of the hot-worked forging at temperature T1. S2 solution treatment involves heating the forging, after S1 pre-solution treatment, in the furnace to temperature T2 and holding it for a period of time, then cooling it in the furnace to temperature T3 and holding it for a period of time, followed by cooling. T2 is lower than T... β T1 is lower than T2, and T3 is lower than T2; S3 pre-aging involves performing a pre-aging heat treatment on the forgings cooled in S2 at a temperature of T4. S4, aging treatment, involves heating the forging after pre-aging in S3 to T5 temperature in the furnace and holding it at that temperature for a period of time, then cooling it, where T4 is lower than T5.

2. The preheating heat treatment process for TC18 titanium alloy large forgings according to claim 1, characterized in that: The temperature range for T1 is 750℃~820℃, the temperature range for T2 is 820℃~850℃, the temperature range for T3 is 740~760℃, the temperature range for T4 is 400℃~500℃, and the temperature range for T5 is 500℃~650℃.

3. The preheating heat treatment process for TC18 titanium alloy large forgings according to claim 2, characterized in that: The holding time for pre-solidification in S1 at temperature T1 is 1 to 3 hours.

4. The preheating heat treatment process for large TC18 titanium alloy forgings according to claim 2, characterized in that: In S3, the holding time for pre-aging at temperature T4 is 1 to 3 hours.

5. The preheating heat treatment process for TC18 titanium alloy large forgings according to claim 1, characterized in that: The thickness of the forgings in S1 and S3 is 100-300 mm.

6. The preheating heat treatment process for TC18 titanium alloy large forgings according to claim 5, characterized in that: The number of forgings in S1-S4 is multiple, and the material spacing between multiple forgings in the heating furnace is greater than or equal to 150mm.

7. The preheating heat treatment process for TC18 titanium alloy large forgings according to claim 1, characterized in that: Both S2 and S4 are cooled by air after being removed from the furnace.

8. The preheating heat treatment process for TC18 titanium alloy large forgings according to claim 7, characterized in that: The ambient temperature range for S2 and S4 after cooling is 0℃~50℃, and the spacing between adjacent forgings is greater than or equal to 300mm.

9. The preheating heat treatment process for TC18 titanium alloy large forgings according to claim 8, characterized in that: In step S4, after cooling, the difference in tensile strength and yield strength between the core and edge of the forging is within 30 MPa, the difference in elongation after fracture and reduction of area is less than 3% and 5% respectively, and the difference in impact toughness is less than 5 J / cm. 2 The fracture toughness difference is less than 5 MPa·m 1 / 2 .

10. The preheating heat treatment process for TC18 titanium alloy large forgings according to claim 1, characterized in that: In S2, the holding time at temperature T2 is 1–3 hours, and the holding time at temperature T3 is 1–3 hours; in S4, the holding time at temperature T5 is 2–6 hours.

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