A low-cost preparation method for large-size curved forgings of high-temperature titanium alloy

Abstract

This invention belongs to the field of hot working of titanium-based materials, specifically relating to a low-cost method for preparing large-size curved surface forgings of high-temperature titanium alloys. The method includes components such as applicable alloy types, hot working processes, and heat treatment methods, employing two main processes: die forging and annealing. The curved surface forgings obtained by this invention have a single-piece weight of over 600 kg and a maximum projected area of ​​2 m². 2 The above-mentioned room temperature strength and 650℃ strength retention rates can reach 95% and 92% of those of conventionally sized forgings, respectively. The manufacturing cost of curved surface forgings prepared using this invention can be reduced by 10% to 20%, especially for single pieces weighing over 1200 kg and with a maximum projected area of ​​4 m². 2 The advantages of the above forging technology are more obvious. This invention is used in integral or split panel or arm plate structures in aerospace and other fields, meeting the application needs of lightweight, high-temperature resistant materials in high-tech fields such as aerospace.

Description

Technical Field

[0001] The invention belongs to the field of hot processing of titanium-based materials, and in particular relates to a low-cost preparation method of a large-size curved surface forging of a high-temperature titanium alloy. Background Art

[0002] Different periods of aerospace vehicles have different requirements for materials and preparation processes. Early aircraft or aerospace vehicles used aluminum alloy products on a large scale to achieve lightweight structures and improve fuel efficiency, speed, load rate and maneuverability. With the improvement of technical requirements, the strength and temperature resistance of aluminum alloys can no longer meet the requirements, so titanium alloys represented by Ti-6Al-4V gradually replaced aluminum alloys and became the key material for aircraft structures; the development of high Mach number aircraft technology has made traditional low-temperature components high-temperature, that is, the parts of traditional low-Mach number aircraft that work at 200°C or even lower temperatures generally have higher operating temperatures under high Mach number flight conditions, which puts higher requirements on the strength and temperature resistance of materials and structures. In addition, the improvement of aircraft structure and function also requires a more efficient overall structure and higher material performance guarantees.

[0003] Most traditional large-size curved components use plate rib forming technology. Plate rib forming requires the material to have good formability and welding process performance. In addition, plate rib forming is limited by material properties and dimensional accuracy after forming, and the available heat treatment control methods are limited. Therefore, the traditional plate rib forming process is mainly based on shape control, that is, "shape control". Mechanical property control needs to adapt to the needs of the forming process, so it often fails to achieve the ideal performance level that the material can actually achieve.

[0004] High-temperature titanium alloy is a kind of material with specific uses that developed in the 1950s along with the technology of aero-engines. The temperature range of mature high-temperature titanium alloys is currently 350℃~600℃. Compared with other types of titanium alloys, the most notable feature of high-temperature titanium alloys is the high requirements for high endurance and creep performance. The creep and endurance performance of titanium alloy forgings is 3 to 7 times higher than that of plates with the same composition under the same loading conditions. This is one of the reasons why forged products are preferred for high-temperature structural parts.

[0005] For parts that cannot meet the requirements of plate rib forming or whose mechanical properties after plate rib forming cannot meet the requirements, it is necessary to adopt the method of machining after integral forming. However, due to the large size and weight of such parts, the material cost and machining cost are several to dozens of times higher than plate rib forming. Therefore, complex plate rib parts choose to adopt the integral forming process, and cost control is one of the key factors to pay attention to. Summary of the invention

[0006] In view of the application demand for large-sized curved surface components of high-temperature titanium alloys in the aerospace field, the purpose of the present invention is to provide a low-cost preparation method for large-sized curved surface forgings of high-temperature titanium alloys. High-temperature titanium alloy slabs are formed by die forging in high α+β / β two-phase region and low-temperature annealing in two simple processes to obtain large-sized curved surface forgings that meet the requirements of dimensional accuracy and mechanical properties, and the manufacturing cost is reduced by 10% to 20%.

[0007] The technical solution of the present invention is:

[0008] A low-cost preparation method for a large-size curved surface forging of a high-temperature titanium alloy includes two main processes of die forging and annealing, and is applicable to TA15, TC11, TC25G, TA32, TA33, TA37 or TA38 high-temperature titanium alloys. The specific steps are as follows:

[0009] 1) Die forging

[0010] The forging billet is heated to a forming temperature in a heating device, the forming temperature is 10°C to 50°C below the α+β / β phase transformation point, and is kept warm for 1 to 5 hours after being heated through. After the holding time is over, the hot forging billet is transferred to a forging die for forming, taken out from the forging die, and transferred to air for cooling;

[0011] 2) Annealing

[0012] The forgings after die forging are loaded into a heat treatment furnace and heated to 600℃~750℃ at a rate not higher than 10℃ / min. After being heated through, they are kept warm for 2~10h.

[0013] The low-cost preparation method of the large-size curved surface forging of high-temperature titanium alloy, the curved surface forging has a unit weight of ≥600kg, a thickness of 30-90mm, and a projection area of ​​≥2m 2 The raw materials used are high-temperature titanium alloy forging or rolling forging billets, and the macrostructure meets the requirements of levels 1 to 3 of GJB2220A-2018 standard.

[0014] The low-cost preparation method of the high-temperature titanium alloy large-size curved surface forgings is as follows: before die forging, the forging blank is heated to a high α+β two-phase region, the heat preservation time after heat penetration is not less than 2 hours, and then the blank is transferred to a forging die and die forged using a press.

[0015] The low-cost preparation method of large-size curved forgings of high-temperature titanium alloy is as follows: during the die forging process, after the press pressure reaches a peak value, the pressure is maintained for more than 20 seconds and then unloaded; the forging blank is kept under pressure for more than 3 minutes in the forging die using the weight of the forging die, and then taken out of the forging die and transferred to air to cool to room temperature.

[0016] In the low-cost preparation method of the high-temperature titanium alloy large-size curved surface forging, during the die forging process, the compression deformation amount in the thickness direction of the forging blank is ≤20%.

[0017] The low-cost preparation method of the high-temperature titanium alloy large-size curved surface forgings is as follows: after the annealing treatment and heat preservation are completed, the forgings are taken out of the furnace and air-cooled to room temperature; or, they are not taken out of the heat treatment furnace, but are naturally or temperature-controlled cooled to below 400°C in the heat treatment furnace, and then taken out of the furnace and air-cooled to room temperature.

[0018] In the low-cost preparation method of the high-temperature titanium alloy large-size curved surface forging, the heating equipment adopts a resistance furnace with a temperature control accuracy of not less than ±10°C.

[0019] The design idea of ​​the present invention is:

[0020] Taking cost control as the starting point, and sacrificing a small amount of mechanical properties under the premise of meeting the demand, the forging preparation process has been significantly simplified as a means to achieve the low-cost control requirements of high-temperature titanium alloy large-size curved surface forgings. The specific idea is to merge the high-temperature heat treatment of the material with the die forging process, and the forging blank is die forged after being heated within the heat treatment temperature range; after the die forging is completed, the pressure is maintained to make the forging die and the forging surface in close contact, and the high thermal conductivity of the forging die material is used to cool the hot forging to below 850℃ at a relatively fast speed, thereby ensuring that the reduction value of the mechanical properties of the forging is within a controllable range; another advantage of this technical measure is that the cooling of the forging is completed under the state of deformation constraint, which is conducive to maintaining the dimensional accuracy of the forging and can save the subsequent correction process; in addition, considering the subsequent machining stress relief annealing, the cooling method of the forging after annealing is changed from air cooling to furnace or temperature control cooling, which saves a stress relief annealing process for subsequent parts processing, thereby reducing the manufacturing cost of forgings by 10-20%.

[0021] The advantages and beneficial effects of the present invention are:

[0022] 1. The present invention can form large-sized curved forgings of high-temperature titanium alloy with high deformation resistance characteristics;

[0023] 2. The dimensional accuracy of large-sized curved forgings of the present invention is well controlled;

[0024] 3. The manufacturing cost of curved forgings prepared by the technology of the present invention can be reduced by 10% to 20%. For single piece weight of more than 1200kg and maximum projection area of ​​4m 2 The above forging technology advantages are more obvious;

[0025] 4. The mechanical properties of the present invention, especially the room temperature and high temperature strength, can reach more than 90% of the ideal level of the material;

[0026] 5. The technical principle of the present invention is applicable to most titanium alloys such as TA15, TC11, TC25G, TA32, TA33, TA37 and TA38, and is used in integral or split panels or arm structures in aerospace and other fields, meeting the application needs of lightweight and high-temperature resistant materials in high-tech fields such as aerospace. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1-Figure 2 Schematic diagram of the typical geometric shape of a typical curved surface forging of the present invention. DETAILED DESCRIPTION

[0028] In the specific implementation process, the present invention proposes a low-cost preparation method for a large-size curved surface forging of a high-temperature titanium alloy, including components such as applicable alloy type, hot working process and heat treatment method, and includes the following steps:

[0029] 1) If Figure 1-Figure 2 As shown, the die forging blank is a high-temperature titanium alloy forging blank with a thickness of 30 to 100 mm, and the macrostructure of the forging blank meets the requirements of levels 1 to 3 of the GJB 2220A-2018 standard;

[0030] 2) Before die forging, the forging blank is heated to the α+β two-phase region, and the heat preservation time is not less than 2h after heat penetration, and then transferred to the forging die and formed by a press; the high α+β two-phase region means the material α+β / β phase transition point (T β ) to T β -50℃ temperature range.

[0031] 3) The forging blank is heated to the forming temperature in the heating equipment, and the forming temperature is 10°C to 50°C below the α+β / β phase transformation point. After being heated through, the blank is kept warm for 1 to 5 hours. After the holding time is over, the hot forging blank is transferred to the forging die for forming, and then taken out from the forging die and transferred to the air for cooling;

[0032] During the die forging process, the press pressure is maintained for more than 20 seconds after reaching the peak value, and then unloaded; the forging blank is kept under pressure for more than 3 minutes in the forging die by the weight of the forging die, and then taken out of the forging die and transferred to the air to cool to room temperature;

[0033] 4) After die forging, the forgings are charged into the furnace at a temperature below 500°C (preferably 300°C), and then heated to 600°C-750°C at a rate not higher than 10°C / min. After being heated through, they are kept warm for 2-10 hours. After the end of the heat preservation, the power is turned off, and then they are air-cooled, temperature-controlled cooled, or cooled with the furnace to below 400°C (preferably 300°C) after the power is turned off, and then taken out of the furnace and air-cooled to room temperature.

[0034] The characteristics of the above preparation method are: 1) the process flow is short, including only two main processes: die forging and post-forming annealing; 2) the post-forming annealing process is combined with the rough machining stress relief annealing process of the parts, which further shortens the process flow and reduces the manufacturing cost. The large-sized curved forgings obtained by the present invention have a single piece weight of more than 600kg, a thickness of 30 to 100mm, and a maximum projection area of ​​2m 2 The room temperature strength and 650℃ strength retention rates can reach 95% and 92% respectively.

[0035] Below, the present invention is further described in detail by examples.

[0036] Embodiment 1:

[0037] The experimental material is TA38 alloy forging billet or rolled slab, with a size of 3200mm×660mm×80mm, a weight of 780kg, and an α+β / β phase transition temperature of 1038℃. The preparation process route is divided into two steps: hot forming in the high α+β two-phase region and annealing heat treatment:

[0038] 1) Hot forming: The forming temperature is 990℃, and the heating is carried out in an electric furnace that complies with GJB 904AIII. After the temperature rises to 1025℃, the heat-through time is 50min and the holding time is 120min. The preheating temperature of the forging die is 300℃. After the forging billet is held in the forging die, it is formed by a die forging press. After the stress reaches the maximum value during the forming process, the pressure is maintained for 20s, and then unloaded. The forging billet continues to be held under the weight of the forging die for 180s, and then it is taken out of the forging die and transferred to the atmosphere for air cooling to room temperature.

[0039] 2) Annealing treatment: Annealing temperature is 700℃. Use GJB 904A III electric furnace for heating, load the furnace at 500℃, heat up to 700℃ at a heating rate of 8℃ / min, heat-through time is 30min, and heat preservation time is 240min; after heat preservation, cool to 300℃ with the furnace and air cool to room temperature.

[0040] Embodiment 2:

[0041] The experimental material is TA38 alloy forged or rolled slab, with a size of 2800mm×1000mm×90mm, a weight of 1160kg, and an α+β / β phase transition temperature of 1035℃. The preparation process route is divided into two steps: hot forming in the high α+β two-phase region and annealing heat treatment:

[0042] 1) Hot forming: The forming temperature is 1015℃, and the heating is carried out in an electric furnace conforming to GJB 904A Class III. After the temperature rises to 1020℃, the heat penetration time is 60min and the holding time is 120min; the preheating temperature of the forging die is 300℃. After the forging billet is held in the forging die, it is transferred to the forging die and formed by the die forging press; after the stress reaches the maximum value during the forming process, the pressure is maintained for 40s, and then unloaded; the forging billet continues to be held under the weight of the forging die for 300s, and then it is taken out of the forging die and transferred to the atmosphere for air cooling to room temperature;

[0043] 2) Annealing treatment: Annealing temperature is 720℃. Use electric furnace that meets GJB 904AIII class to heat, load the furnace at 500℃, heat up to 720℃ at a heating rate of 8℃ / min, heat-through time is 30min, and heat preservation time is 180min; after heat preservation, cool to 400℃ and air cool to room temperature.

[0044] Embodiment 3:

[0045] The experimental material is TA38 alloy forged or rolled slab with a size of 3100mm×1600mm×75mm, a weight of 1660kg, and an α+β / β phase transition temperature of 1042℃. The preparation process route is divided into two steps: hot forming in the high α+β two-phase region and annealing heat treatment:

[0046] 1) Hot forming: The forming temperature is 1018℃, and the heating is carried out in an electric furnace conforming to GJB 904A Class III. After the temperature rises to 1020℃, the heat penetration time is 60min and the holding time is 120min; the preheating temperature of the forging die is 300℃. After the forging billet is held in the forging die, it is transferred to the forging die and formed by the die forging press; during the forming process, the stress reaches the maximum value and the pressure is maintained for 60s, and then unloaded; the forging billet continues to be held under the weight of the forging die for 2400s, and then it is taken out of the forging die and transferred to the atmosphere for air cooling to room temperature;

[0047] 2) Annealing treatment: Annealing temperature is 680℃. Use GJB 904A III electric furnace for heating, load the furnace at 500℃, heat up to 680℃ at a heating rate of 8℃ / min, heat-through time is 35min, and heat preservation time is 360min; after heat preservation, cool to 200℃ with the furnace and air cool to room temperature.

[0048] Tables 1 and 2 show the room temperature tensile and high temperature tensile properties of three embodiments and two comparative examples. The TA38 material used in comparative example 1 in the table has a length of 180 mm, a width of 140 mm, and a thickness of 80 mm. The heat treatment state is 30°C for 2 hours at the α+β / β phase transition point and then water quenched. The TA38 material size and solution treatment temperature used in comparative example 2 are the same as those in embodiment 1, but the cooling method is air cooling. It can be seen from the table that the strength level of the large-sized curved forgings prepared by the process of this application is between the water quenching and air cooling of the small-sized samples. In order to achieve structural weight reduction, high-temperature titanium alloy components for aerospace need to pursue the highest possible strength level, and for this purpose, a quenching cooling method is required; but after quenching, the components are very easy to deform and cause over-dimensioning; if air cooling is used, although the deformation of the parts will be reduced, the strength will be reduced to an unacceptable level. By adopting the method and process of the present application, the mechanical properties of the material, especially the tensile strength, are maintained to the greatest extent while ensuring that the deformation of the parts meets the dimensional tolerance requirements. At the same time, because at least two processes, heat treatment and correction, are omitted, the process is significantly simplified, achieving low-cost manufacturing.

[0049] Table 1 shows the room temperature tensile properties

[0050] Sample status <![CDATA[R m ,MPa]]> <![CDATA[R p0.2 ,MPa]]> A，％ Z，％ Example 1 1070 1001 6.0 9 Example 2 1059 998 10.0 16 Example 3 1047 979 10.0 15 Comparative Example 1 1120 1022 7.5 12 Comparative Example 2 1011 907 11.0 21

[0051] Table 2 shows the tensile properties at 650℃

[0052]

[0053]

[0054] It should be pointed out that although the three embodiments provided in this application are all for TA38 alloy, the heat treatment method of this alloy is similar to that of TC25G, TA32, TA33, TA37 and TA38, and all require solution aging heat treatment or high and low temperature double annealing system. Therefore, the method of this application can be referred to to prepare components of the same or similar size and shape.

[0055] To sum up, based on theoretical analysis and experimental research, the present invention proposes a low-cost preparation method for large-size curved surface forgings of high-temperature titanium alloys according to the application needs of large-size curved surface products of high-temperature titanium alloys in the fields of aviation and aerospace. This method can effectively shorten the process flow, improve the forming accuracy of forgings, and reduce the overall material and hot processing costs by 10% to 20%. It can be used for the production of high-temperature resistant structural parts for aircraft or aerospace vehicles, and has broad prospects for promotion and application.

Claims

1. A low-cost preparation method for large-size curved surface forgings of high-temperature titanium alloy, characterized in that: It includes two main processes: die forging and annealing. It is suitable for TA15, TC11, TC25G, TA32, TA33, TA37 or TA38 high-temperature titanium alloys. The specific steps are as follows: 1) Die forging The forging billet is heated to the forming temperature in the heating equipment, and the forming temperature is 10℃~50℃ below the α+β / β phase transformation point. After being heated through, it is kept warm for 1~5h. After the holding time is over, the hot forging billet is transferred to the forging die for forming, taken out from the forging die, and transferred to the air for cooling; During the die forging process, the press pressure is maintained for more than 20 seconds after reaching the peak value, and then unloaded; the forging blank is kept under pressure for more than 3 minutes in the forging die by the weight of the forging die, and then taken out of the forging die and transferred to the air to cool to room temperature; During the die forging process, the compression deformation in the thickness direction of the forging billet is ≤20%; 2) Annealing After die forging, the forging is placed in a heat treatment furnace and heated to 600℃~750℃ at a rate not higher than 10℃ / min. After being heated thoroughly, it is kept warm for 2~10h. After the annealing treatment is completed, the furnace is taken out of the furnace and air-cooled to room temperature; or, the furnace is not taken out of the heat treatment furnace, and the furnace is naturally or temperature-controlled cooled to below 400°C, and then the furnace is taken out of the furnace and air-cooled to room temperature; Curved forgings: unit weight ≥ 600kg, thickness 30~90mm, projection area ≥ 2m 2 The raw materials used are high-temperature titanium alloy forging or rolling forging billets, and the macrostructure meets the requirements of levels 1 to 3 of GJB 2220A-2018 standard.

2. The low-cost preparation method for high-temperature titanium alloy large-size curved surface forgings according to claim 1, characterized in that: Before die forging, the forging blank is heated to the high α+β two-phase region, and the holding time after heat penetration is not less than 2 hours. It is then transferred to the forging die and die forged using a press.

3. The low-cost preparation method for high-temperature titanium alloy large-size curved surface forgings according to claim 1, characterized in that: The heating equipment adopts a resistance furnace with a temperature control accuracy of not less than ±10℃.

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