Preparation method of TC18 titanium alloy free forging with large thickness-diameter ratio

Abstract

This invention relates to the field of TC18 titanium alloy processing technology, and discloses a method for preparing TC18 titanium alloy free forgings with a large length-to-thickness ratio, which includes a heating temperature of T. β The forging and heating temperature of the (α+β) two-phase region at -40 to 60℃ is T. β Forging in the β-phase region at +(15~20)℃, with deformation controlled at 15~35% per heat, and reducing the deformation in the width direction of the billet during the flattening forging stage, while increasing the feed rate in the β-phase region forging, thereby reducing the difference in microstructure and properties between the head and tail, thus solving the problem of uneven microstructure in the preparation of TC18 titanium alloy free forgings with large length-to-thickness ratios. The TC18 titanium alloy free forgings with large length-to-thickness ratios prepared by the method of this invention have uniform microstructure and stable properties, and can meet the performance requirements of aircraft forging standards.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy processing technology, and particularly relates to a method for preparing TC18 titanium alloy free forgings with a large length-to-thickness ratio. Background Technology

[0002] The nominal composition of TC18 titanium alloy is Ti-5Al-5Mo-5V-1Cr-1Fe. It is a near-β type titanium alloy and belongs to high strength and toughness titanium alloys. Forgings made from it have the characteristics of high specific strength and significant weight reduction effect. At the same time, it has excellent impact resistance and is widely used in some load-bearing components of aircraft, such as struts, frame beams, landing gear and fuselage.

[0003] The traditional process for free forging of TC18 titanium alloy is currently billet preparation, quasi-β forging (forging heating temperature is T). β +15℃) + double annealing. For free forgings of TC18 titanium alloy with a small length-to-thickness ratio, the anisotropy of the microstructure is small during the quasi-β forging process. However, when the length-to-thickness ratio of the free forging of TC18 titanium alloy is large, problems such as large microstructure anisotropy, poor forging flatness, and significant differences in mechanical properties of the forging in the length direction are likely to occur. Traditional preparation methods often cannot guarantee the uniformity of the microstructure and the stability of the properties of the material. Summary of the Invention

[0004] In view of this, in order to overcome the above-mentioned problems in the prior art, the purpose of this invention is to provide a method for preparing TC18 titanium alloy forgings with a large length-to-thickness ratio. This method can prepare TC18 titanium alloy forgings with a large length-to-thickness ratio that have uniform microstructure and stable performance, and the prepared forgings meet the requirements of aerospace standards.

[0005] To solve the above problems, the present invention adopts the following technical solution:

[0006] On one hand, the present invention provides a method for preparing a TC18 titanium alloy free forging with a large length-to-thickness ratio, which includes the following steps:

[0007] S1 is used to forge TC18 titanium alloy bars in the (α+β) two-phase region:

[0008] The TC18 titanium alloy bar is heated in a furnace to T. β -(40~60)℃, the holding time is ((0.6~1.2)×thickness of the minimum cross section of the billet)min, and the billet is taken out of the furnace for flattening and forging. The deformation amount per heat is controlled at 15%~30%, and the pressing speed is controlled at 5~10mm / s to obtain rectangular billet A.

[0009] S2 involves forging the cuboid blank A obtained in step S1 into the β-phase region:

[0010] The rectangular billet A is preheated to T in a furnace using a stepped heating method. β -(20~60)℃, preheating and holding time is ((0.5~1)×min of the minimum cross-section thickness of the bar) min, then heating is carried out at a heating temperature of T. β +(15~20)℃, holding time is ((0.3~0.5)×min of minimum cross-sectional thickness of bar), after taking it out of the furnace, wrap it with an insulating sleeve, and put it back into the furnace, at T β Heating at a temperature of +(15~20)℃ and holding at that temperature, the billet is drawn into a flat square by pressing down with two staggered hammers. The deformation is controlled at 30~35% to obtain billet B.

[0011] S3 divides the blank B obtained in step S2 into two parts along the width direction to obtain blank C1 and blank C2;

[0012] S4 performs a first annealing treatment on the billet C1 obtained in step S3, wherein the temperature of the first annealing is (T β -35)℃~(T β -30℃, hold at that temperature, furnace cool to 750℃~760℃, hold at that temperature again, remove from the furnace and air cool to room temperature to obtain billet D1;

[0013] S5 performs a second annealing on the billet D1 obtained in step S4. The temperature of the second annealing is 600℃~630℃. After being taken out of the furnace, it is air-cooled to room temperature to obtain TC18 titanium alloy free forging.

[0014] The T β This represents the β transformation temperature of TC18 titanium alloy.

[0015] Furthermore, in the flattening forging process in step S1, the hot material is recycled 2 to 3 times in the middle, and the heating time of the hot material is ((0.3 to 0.6) × the thickness of the minimum cross section of the bar) min.

[0016] Furthermore, in step S1, the hot material is recycled twice with insulation coefficients of 0.43 and 0.47 respectively.

[0017] Furthermore, in step S2, after holding at a temperature for 30 minutes, a flattened square forging is performed using a 100MN high-speed forging machine with two staggered hammer presses.

[0018] Furthermore, in step S2, the insulation sleeve is rock wool.

[0019] Furthermore, in step S2, the final forging temperature is ≥820℃.

[0020] Furthermore, in step S4, after holding at the temperature for 3.5 hours, the furnace is cooled to 750℃~760℃, then held at the temperature for another 2.5 hours, and finally removed from the furnace and air-cooled to room temperature.

[0021] Furthermore, after step S4, the forging obtained in step S4 is further subjected to sawing, surface turning and polishing to obtain a machined TC18 titanium alloy free forging.

[0022] On the other hand, the present invention also provides a TC18 titanium alloy free forging with a large length-to-thickness ratio, which is prepared by the above-described preparation method.

[0023] Furthermore, the TC18 titanium alloy free forging has a single weight of 90 kg and dimensions of 65 mm thickness × 125 mm width × 2060~2500 mm length.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The method for preparing TC18 titanium alloy free forgings of the present invention breaks the conventional deformation amount in the width direction in the (a+β) two-phase region forging and β phase region forging flattening deformation mode. When flattening the billet during the billet preparation stage, the deformation amount in the width direction of the billet is reduced to obtain an intermediate billet A with a smaller width direction. This increases the feed amount during subsequent β phase region forging and reduces the β forging time, thereby achieving the excellent effect of reducing the anisotropy of the forging and enabling it to meet the performance requirements of the forging standard.

[0026] In addition, the preparation method of this invention increases the amount of deformation in the thickness direction during β forging by using a two-stage staggered hammer pressing method. This reduces the deformation concentration area of ​​the billet, making the billet structure more uniform. It also ensures the amount of deformation below the phase transformation point, improves the alloy strength, and obtains high plasticity and high fracture toughness. Its comprehensive performance is excellent, and the forgings prepared meet the requirements of aviation standards. Attached Figure Description

[0027] Figure 1 This is a low-magnification transverse microstructure of the TC18 titanium alloy free forging prepared in Example 1 of the present invention.

[0028] Figure 2 This is a high-magnification transverse microstructure image of the TC18 titanium alloy free forging prepared in Example 1 of this invention. Detailed Implementation

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0030] In this invention, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0031] Unless otherwise specified, the temperature parameters in this invention can be either constant temperature treatment or variations within a certain temperature range. It should be understood that the constant temperature treatment allows temperature fluctuations within the precision range controlled by the instrument. Fluctuations are permitted within ranges such as ±5℃, ±4℃, ±3℃, ±2℃, and ±1℃.

[0032] This invention provides a method for preparing a TC18 titanium alloy free forging with a large length-to-thickness ratio, characterized by comprising the following steps:

[0033] A method for preparing a TC18 titanium alloy free forging with a large length-to-thickness ratio, characterized by comprising the following steps:

[0034] S1 is used to forge TC18 titanium alloy bars in the (α+β) two-phase region:

[0035] The TC18 titanium alloy bar is heated in a furnace to T. β -(40~60)℃, the holding time is ((0.6~1.2)×thickness of the minimum cross section of the billet)min, and the billet is taken out of the furnace for flattening and forging. The deformation amount per heat is controlled at 15%~30%, and the pressing speed is controlled at 5~10mm / s to obtain rectangular billet A.

[0036] S2 involves forging the cuboid blank A obtained in step S1 into the β-phase region:

[0037] The rectangular billet A is preheated to T in a furnace using a stepped heating method. β -(20~60)℃, preheating and holding time is ((0.5~1)×min of the minimum cross-section thickness of the bar) min, then heating is carried out at a heating temperature of T. β +(15~20)℃, holding time is ((0.3~0.5)×min of minimum cross-sectional thickness of bar), after taking it out of the furnace, wrap it with an insulating sleeve, and put it back into the furnace, at Tβ Heating at a temperature of +(15~20)℃ and holding at that temperature, the billet is drawn into a flat square by pressing down with two staggered hammers. The deformation is controlled at 30~35% to obtain billet B.

[0038] S3 divides the blank B obtained in step S2 into two parts along the width direction to obtain blank C1 and blank C2;

[0039] S4 performs a first annealing treatment on the billet C1 obtained in step S3, wherein the temperature of the first annealing is (T β -35)℃~(T β -30℃, hold at that temperature, furnace cool to 750℃~760℃, hold at that temperature again, remove from the furnace and air cool to room temperature to obtain billet D1;

[0040] S5 performs a second annealing on the billet D1 obtained in step S4. The temperature of the second annealing is 600℃~630℃. After being taken out of the furnace, it is air-cooled to room temperature to obtain TC18 titanium alloy free forging.

[0041] The T β This represents the β transformation temperature of TC18 titanium alloy.

[0042] In some embodiments, the present invention provides a method for preparing a TC18 titanium alloy free forging with a large length-to-thickness ratio, comprising the following steps:

[0043] S1 is used to forge TC18 titanium alloy bars in the (α+β) two-phase region:

[0044] The TC18 titanium alloy bar is heated in a furnace to T. β -(40~60)℃, holding time is ((0.6~1.2)×min thickness of minimum cross section of bar) min, after taking it out of the furnace, it is drawn into a flat square forging, the deformation amount per heat is controlled at 15%~30%, and the hot material is recycled 2~3 times in the middle, the hot material is heated for ((0.3~0.6)×min thickness of minimum cross section of bar) min, and the pressing speed is controlled at 5~10mm / s to obtain rectangular billet A;

[0045] S2 involves forging the cuboid blank A obtained in step S1 into the β-phase region:

[0046] The rectangular billet A is preheated to T in a furnace using a stepped heating method. β -(20~60)℃, preheating and holding time is ((0.5~1)×min of the minimum cross-section thickness of the bar) min, then heating is carried out at a heating temperature of T. β +(15~20)℃, holding time is ((0.3~0.5)×min of minimum cross-sectional thickness of bar), after taking it out of the furnace, wrap it with an insulating sleeve, and put it back into the furnace, at T βHeating at a temperature of +(15~20)℃, holding for 30 minutes, and then using a 100MN fast forging machine to draw flat square forging by two staggered hammer pressing, with the deformation controlled at 30~35%, and the final forging temperature ≥820℃, to obtain billet B;

[0047] S3 divides the blank B obtained in step S2 into two parts along the width direction to obtain blank C1 and blank C2;

[0048] S4 performs a first annealing treatment on the billet C1 obtained in step S3, wherein the temperature of the first annealing is (T β -35)℃~(T β -30℃, hold for 3.5h, furnace cool to 750℃~760℃, hold for another 2.5h, remove from furnace and air cool to room temperature to obtain billet D1;

[0049] S5 performs a secondary annealing treatment on the billet D1 obtained in step S4. The temperature of the secondary annealing is 600℃~630℃. After exiting the furnace, it is air-cooled to room temperature to obtain a TC18 titanium alloy free forging.

[0050] The T β This represents the β transformation temperature of TC18 titanium alloy.

[0051] In other embodiments, the present invention provides a TC18 titanium alloy free forging with a large length-to-thickness ratio prepared by the above preparation method, which has a single weight of 90 kg and dimensions of 65 mm thickness × 125 mm width × 2060~2500 mm length.

[0052] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

[0053] Example 1

[0054] A method for preparing TC18 titanium alloy free forgings with a large length-to-thickness ratio, using φ250mm bars for billet preparation and quasi-β forging.

[0055] S1 is used to forge TC18 titanium alloy bars in the (α+β) two-phase region.

[0056] The billet is prepared on a 25MN high-speed forging mill. A section of the billet, weighing 280kg and measuring φ250mm×1235mm, is cut from a finished TC18 titanium alloy bar with a diameter of φ250mm×L and forged in one pass. The billet is first heated to 50℃ below the phase transformation point and held for 250min (holding coefficient is 1, holding time is (minimum cross-sectional size of billet × holding coefficient)). After exiting the furnace, it is forged into a flat square shape, with the deformation controlled at 25%, the pressing speed at 10mm / s, the reduction at 40-60mm, and the feed rate at 130-200mm. The billet is forged to a thickness of 188mm (billet size: 188×250×1293mm) and then returned to the furnace. The reheating time is 80 minutes (holding coefficient is 0.43). After exiting the furnace, the billet is flattened, with deformation controlled at 21%. The pressing speed is 10 mm / s, the reduction is 30-40 mm, and the feed rate is 100-160 mm. The billet is forged to a thickness of 149 mm (billet size: 149×260×1569 mm) and then reheated. The reheating time is 70 minutes (holding coefficient is 0.47). After exiting the furnace, the billet is flattened, with deformation controlled at 16%. The pressing speed is 10 mm / s, the reduction is 25-35 mm, and the feed rate is 70-120 mm. The final forging billet size is 125×260×1862 mm. The final forging temperature throughout the entire forging process is controlled above 700℃.

[0057] S2 performs β-phase region forging on the forged billet obtained in step S1.

[0058] The forged billet obtained in step S1 was forged in the β-phase region using a 100MN high-speed forging mill. The forged billet was loaded into the furnace and heated to 30°C below the phase transformation point, held for 90 minutes (holding coefficient 0.72), then heated to 18°C ​​above the phase transformation point and held for 50 minutes (holding coefficient 0.4). After reaching the desired temperature, the billet was removed from the furnace, coated with cotton, and then returned to the furnace. After returning to the furnace, it was held for another 30 minutes. After removal from the furnace, the billet was flattened and forged, with the deformation controlled at 32%. The pressing speed was 10 mm / s. The reduction was done in two stages, with a feed rate of 400–500 mm. The first stage involved 5–6 hammer blows, and the second stage involved 5–6 hammer blows. After the billet was turned around, it was pressed again in two stages, with the first stage involving 1 hammer blow and the second stage involving 2–4 hammer blows. Finally, the billet is shaped, first in the width direction with 7 hammer blows, then in the thickness direction with 6 hammer blows. After turning it around, the thickness is shaped first with 2-3 hammer blows, then the width direction is shaped again, followed by the thickness direction, repeating this process twice. The final forged billet dimensions are 85×300×2332mm, and the final forging temperature is controlled above 820℃. The billet is then leveled and straightened using its residual heat. During straightening, the billet is placed parallel to the lower anvil, allowing the upper anvil to press down entirely.

[0059] During this forging process, select the heating furnace closest to the forging machine for heating and heat preservation, with a furnace load of ≤2; the heat preservation cannot be extended, and the process must be completed within 10 minutes after the heat preservation time.

[0060] To reduce the performance differences between the beginning and end of the forging, the forging time in the final β-phase region needs to be reduced. In flattened square forging, the feed rate needs to be increased. However, when the feed rate is increased, the billet barely moves along its length, while moving more along its width. Therefore, the billet dimensions after forming need to be longer in the length direction and narrower in the width direction.

[0061] S3 heat treatment

[0062] Before heat treatment, the billet is divided evenly along its width. After slitting, the billet size is 85(0, +5)mm × 145(-5, +0)mm × L. The billet is then subjected to heat treatment. A heat treatment furnace with controllable cooling rate is used for heat treatment. The heat treatment regime is as follows: First annealing: 840℃ / 3.5h, furnace cooling to 750℃ / 2.5h (furnace cooling rate is 0.5℃ / min), leveling and straightening after removal from the furnace, and then air cooling; Second annealing: 610℃ / 5h, AC.

[0063] S4 machining

[0064] Machining requirements: Thickness 65(0,+5)mm × Width 125(0,+5)mm × Length 2060(0,+5)mm; the surface roughness of all four major surfaces in the width and height directions must be Ra≤1.6μm; after grinding, surface defects must not exceed the negative tolerance of the forging.

[0065] The finished forgings have dimensions of 65mm×125mm×2060mm.

[0066] The microstructure of the forging prepared in Example 1 was observed under low magnification. Figure 1 As shown, the low-magnification microstructure of the forging is uniform, free from cracks, inclusions, segregation, shrinkage cavities, porosity, delamination, fine-grained bright bands (rings), and other metallurgical defects. The streamlines of the forging conform to the specifications of the forging drawing, with no obvious turbulence or severe eddies. The streamlines of the free forging show no obvious cut-off, meeting aerospace standard requirements.

[0067] Table 1 shows the mechanical property test results of the forgings prepared in Example 1.

[0068]

[0069]

[0070] In the table, ST represents vertical direction, LT represents horizontal direction, and L represents vertical direction.

[0071] Ultrasonic testing was performed on the forgings prepared in Example 1, and the results were uniform and consistent, all meeting the requirement of φ1.2-12dB or higher.

[0072] Example 2

[0073] The difference between Example 2 and Example 1 is that the billet is polished between the completion of forging and the start of quasi-β forging, and the surface defects of the billet are inspected and polished to obtain forgings of better quality.

[0074] In addition, to ensure the overall performance of the forgings, the heat treatment process adopted in Example 2 is a single annealing process: the forgings are charged into the furnace at the specified temperature, heated to 840°C, held for 3.5 hours, and the furnace cooling rate is controlled at 0.67°C / min (i.e., the time to cool from 840°C to 760°C is 120 minutes). The forgings are then held at 760°C for 2.5 hours, leveled and straightened after being removed from the furnace, and then air-cooled. The second annealing process is: the forgings are charged into the furnace at the specified temperature, heated to 608°C for 5 hours, and then air-cooled.

[0075] Table 2 Mechanical properties of the forgings prepared in Example 2

[0076]

[0077] As shown in Table 2, the forgings prepared in Example 2 have good mechanical properties, and their microstructure is uniform and their performance is stable, meeting the requirements of aviation standards.

[0078] It should be noted that the embodiments described above are merely preferred embodiments of the present invention. For those skilled in the art, various modifications, improvements, and equivalent substitutions can be made to the present invention without departing from its principles, and such modifications, improvements, and equivalent substitutions are also considered to fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a TC18 titanium alloy free forging with a large length-to-thickness ratio, characterized in that, Includes the following steps: S1 is used to forge TC18 titanium alloy bars in the (α+β) two-phase region: The TC18 titanium alloy bar is heated in a furnace to T. β -(40~60)℃, the holding time is ((0.6~1.2)×thickness of the minimum cross section of the billet)min, and the billet is taken out of the furnace for flattening and forging. The deformation amount per heat is controlled at 15%~30%, and the pressing speed is controlled at 5~10mm / s to obtain rectangular billet A. S2 involves forging the cuboid blank A obtained in step S1 into the β-phase region: The rectangular billet A is preheated to T in a furnace using a stepped heating method. β -(20~60)℃, preheating and holding time is ((0.5~1)×min of the minimum cross-section thickness of the bar) min, then heating is carried out at a heating temperature of T. β +(15~20)℃, holding time is ((0.3~0.5)×min of minimum cross-sectional thickness of bar), after taking it out of the furnace, wrap it with an insulating sleeve, and put it back into the furnace, at T β Heating at a temperature of +(15~20)℃, and then holding at that temperature, the blank is drawn into a flat square by pressing down with two staggered hammers. The deformation is controlled at 30~35%, and the pressing speed is 10mm / s to obtain the blank B. In step S2, after holding at a temperature for 30 minutes, a flat square is forged using a 100MN high-speed forging machine with two staggered hammer presses; in step S2, the final forging temperature is ≥820℃; in step S2, the insulation sleeve is rock wool. S3 divides the blank B obtained in step S2 into two parts along the width direction to obtain blank C1 and blank C2; S4 performs a first annealing treatment on the billet C1 obtained in step S3, wherein the temperature of the first annealing is (T β -35)℃~(T β -30℃, hold at that temperature, furnace cool to 750℃~760℃, hold at that temperature again, remove from the furnace and air cool to room temperature to obtain billet D1; S5 performs a second annealing on the billet D1 obtained in step S4. The temperature of the second annealing is 600℃~630℃. After being taken out of the furnace, it is air-cooled to room temperature to obtain TC18 titanium alloy free forging. The T β The lowest temperature at which TC18 titanium alloy completely transforms into the β phase during heating is called the β transformation temperature. The TC18 titanium alloy free forging with a large length-to-thickness ratio prepared according to the above preparation method has a single weight of 90 kg and a specification of 65 mm thickness × 125 mm width × 2060~2500 mm length.

2. The method for preparing a TC18 titanium alloy free forging with a large length-to-thickness ratio according to claim 1, characterized in that, In the flattening forging process in step S1, the hot material is recycled 2 to 3 times in the middle. The heating time for the hot material recycling is ((0.3 to 0.6) × the thickness of the minimum cross section of the bar) min.

3. The method for preparing a TC18 titanium alloy free forging with a large length-to-thickness ratio according to claim 2, characterized in that, In step S1, the hot material is recycled twice, with insulation coefficients of 0.43 and 0.47 respectively.

4. The method for preparing a TC18 titanium alloy free forging with a large length-to-thickness ratio according to claim 1, characterized in that, In step S4, after holding at the temperature for 3.5 hours, the furnace is cooled to 750℃~760℃, then held at the temperature for another 2.5 hours, and finally removed from the furnace and air-cooled to room temperature.

5. The method for preparing a TC18 titanium alloy free forging with a large length-to-thickness ratio according to claim 1, characterized in that, After step S4, the forging obtained in step S4 is further subjected to sawing, surface turning and polishing to obtain a machined TC18 titanium alloy free forging.

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