CN115747689B - High-plasticity forging method for Ti-1350 ultrahigh-strength titanium alloy large-size bar - Google Patents
High-plasticity forging method for Ti-1350 ultrahigh-strength titanium alloy large-size bar Download PDFInfo
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Abstract
The application relates to the technical field of titanium alloy forging, and discloses a high-plasticity forging method for a Ti-1350 ultrahigh-strength titanium alloy large-specification bar, which is realized through the steps of cogging forging, beta grain cyclic recrystallization refining and homogenizing, primary alpha phase spheroidizing and homogenizing, and finished product forging. The application fully utilizes the mode of pre-deformation of the two-phase region and static recrystallization of the hot material return furnace single-phase region to solve the problem of homogenizing the Ti-1350 titanium alloy beta grains, combines the relation between the size/uniformity of the recrystallized grains and the pre-deformation of the two-phase region, the cross section size of the blank, the recrystallization temperature and the recrystallization heat preservation time, designs gradient circulation recrystallization technology and alloy recrystallization nucleation growth rules under different temperature conditions, designs different recrystallization heat preservation time, refines the beta grains to less than 1mm, and avoids deformation streamline and non-uniformity of the beta grain size caused by the non-uniformity of forging because the beta grains are not forged in the refining process.
Description
Technical Field
The application relates to the technical field of titanium alloy forging, in particular to a high-plasticity forging method for a Ti-1350 ultrahigh-strength titanium alloy large-size bar.
Background
The high-strength and high-toughness near-beta titanium alloy has the characteristics of high specific strength, good hardenability, excellent corrosion resistance and the like, is easy to carry out plastic forming, can realize excellent strength-plasticity-toughness matching through heat treatment strengthening, and is widely applied to the field of aerospace and used for manufacturing large-scale bearing components such as landing gear, frame, beam and the like of an airplane. Along with the upgrading of weapon equipment, in order to meet the design requirements of new generation aircraft and aeroengines on long service life and high weight reduction, higher requirements on the performance of high-strength and high-toughness titanium alloy materials are also provided.
The Ti-1350 titanium alloy is an ultra-high strength and toughness near-beta titanium alloy which is developed in recent years aiming at the development requirement of new-generation aircrafts in China, and the transverse elongation is more than 5 percent while the room-temperature strength of large-specification bars is required to reach 1350MPa level in order to meet the design requirement.
CN20171025920085 discloses a forging method for producing large-sized Ti1350 alloy bars with phi above 200mm, specifically, performing cogging forging with three piers and three pullouts above beta-phase transition temperature, performing reversing pier pullouts above beta-phase transition temperature, performing one pier and one pier pullout below beta-phase transition temperature, performing pier pullout deformation above beta-phase transition temperature, flat and square pier pullout deformation and size surface interchange above beta-phase transition temperature, performing pier pullout deformation below beta-phase transition temperature, performing elongation forging above beta-phase transition temperature, and finally performing elongation shaping forging of finished products below beta-phase transition temperature. The forging method mainly comprises single-phase region upsetting deformation, two-phase region upsetting deformation is used alternately, and flat square upsetting deformation modes are used for individual fires, so that the forging permeability of the core part of the blank is improved, a distorted beta grain boundary structure is obtained, a fine needle-shaped alpha phase is obtained by controlling a heating system and pass deformation amount of the single-phase region upsetting deformation, and the fracture toughness value of the material is improved. However, when the grains are refined to a certain degree, the beta grains cannot be further refined, and the alpha phase cannot be fully spheroidized due to uneven forging deformation, so that the alloy plasticity is required to be improved.
Disclosure of Invention
Aiming at the defects of the prior art, the application aims to provide a high-plasticity forging method for Ti-1350 ultrahigh-strength titanium alloy large-specification bars, which can prepare the Ti-1350 ultrahigh-strength titanium alloy large-specification bars with high plastic margin when the strength reaches 1350MPa level, and can practically solve the problem of insufficient plastic margin of the Ti-1350 ultrahigh-strength titanium alloy.
In order to achieve the above purpose, the application adopts the following technical scheme: a high-plasticity forging method for Ti-1350 ultrahigh-strength titanium alloy large-specification bars is realized through the steps of cogging forging, beta grain cyclic recrystallization refinement and homogenization, primary alpha phase spheroidization and homogenization and finished product forging, and specifically comprises the following steps:
step 1), cogging forging:
heating a Ti-1350 titanium alloy cast ingot with the diameter of phi of 650-800 mm to 300-400 ℃ above the beta transformation temperature, discharging, carrying out rolling shaping, controlling rolling reduction to be 30-50 mm, and then carrying out 2-upsetting 2-drawing deformation, wherein the upsetting deformation is controlled to be 35-45%;
the hot working plasticity of the as-cast structure is generally poor, and alloying elements of Ti-1350 are up to 20%, so that the smelting of a finished product adopts a small-current shallow molten pool to smelt in order to improve the component uniformity of the ingot, and more cold barriers and subcutaneous air holes are formed on the surface of the ingot. According to the application, a large number of experiments show that before the large-deformation upsetting forging is performed on the cast ingot, the cast ingot is pre-deformed by adopting the reduction of 30-50 mm, so that on one hand, the hot working plasticity of the cast ingot can be obviously improved, on the other hand, the cold interlayer and the subcutaneous air holes remained on the surface of the cast ingot can be closed by rapidly rounding and shaping the surface, the surface quality of the forged blank is greatly improved, the cracking is further reduced, and the yield is improved.
Step 2), circulating recrystallization refinement and homogenization of beta grains:
step 2.1: carrying out 1 upsetting and 1 drawing deformation on the forging stock finished in the step 1) at the temperature of 30-50 ℃ below the beta transformation temperature, controlling the upsetting deformation to be 35-40%, forging the blank to be flat, wherein the minimum cross section dimension h of the flat is not more than 500mm, returning hot stock to the furnace to the temperature of 150-180 ℃ above the beta transformation temperature after the forging is finished, carrying out heat preservation, and carrying out recrystallization heat preservation for the time of t=k 1 H performs the calculation, where k 1 To recrystallize the heat preservation coefficient, k 1 The value is controlled to be 0.4-0.8 min/mm, h is the minimum cross section size of the blank, and the blank is immediately discharged from the furnace and air-cooled to room temperature after heat preservation is finished;
step 2.2: carrying out 1 upsetting and 1 drawing deformation on the forging stock finished in the step 2.1 at the temperature of 30-50 ℃ below the beta transformation temperature, controlling the upsetting deformation to be 30-35%, forging the blank to be square, returning hot materials to the furnace to 70-100 ℃ above the beta transformation temperature after forging, carrying out heat preservation, and carrying out recrystallization heat preservation for the time of t=k 2 H performs the calculation, where k 2 To recrystallize the heat preservation coefficient, k 2 The value is controlled to be 0.5-0.9 min/mm, and the furnace is immediately taken out after the heat preservation is finished, and the furnace is air cooled to the room temperature;
step 2.3: carrying out 1 upsetting and 1 drawing deformation on the forging stock finished in the step 2.2 at the temperature of 30-50 ℃ below the beta transformation temperature, controlling the upsetting deformation to be 25-30%, forging the blank to eight directions, returning hot materials to the furnace to the temperature of 30-50 ℃ above the beta transformation temperature after forging, carrying out heat preservation, and carrying out recrystallization heat preservation for the time of t=k 3 H performs the calculation, where k 3 To recrystallize the heat preservation coefficient, k 3 The value is controlled to be 0.6-1.0 min/mm, and the furnace is immediately taken out after the heat preservation is finished, and the furnace is cooled to the room temperature in an air way;
step 3), primary alpha phase spheroidization and homogenization:
step 3.1: carrying out 1 upsetting and 1 drawing deformation on the forging stock finished in the step 2) at the temperature of 30-50 ℃ below the beta transformation temperature for 6-8 times, wherein the upsetting deformation is controlled to be 30-40%;
step 3.2: performing 1-3 times of elongation deformation on the forging stock finished in the step 3.1 at the temperature of 30-50 ℃ below the beta transformation temperature, wherein the elongation deformation is controlled to be 25-35%;
step 4), forging a finished product:
and (3) performing 1-time rounding shaping forging on the blank obtained in the step (3) at the temperature of 30-50 ℃ below the beta transformation temperature, controlling the shaping deformation to be 15-20%, and forging the blank to a proper specification and size.
The action principle of the application is as follows:
under the condition of determining alloy brands and chemical composition ratios, the main factors influencing alloy strength and plasticity are beta grain size and alpha phase morphology distribution. Refining the beta grain size generally facilitates improving both the strength and plasticity of the alloy. The morphology distribution of the alpha phase mainly comprises the size, the morphology and the distribution of the primary alpha phase and the secondary alpha phase, wherein the primary alpha phase mainly influences the plasticity of the alloy, the secondary alpha phase mainly influences the strength of the alloy, the morphology of the primary alpha phase is mainly influenced by a deformation process, and the secondary alpha phase is mainly influenced by a heat treatment system. Generally, the larger the cumulative deformation of the alloy in the two-phase region, the more fully the primary alpha phase is spheroidized, and the better the plasticity of the alloy.
The traditional method for refining the size of the beta grains of the titanium alloy mainly comprises the steps of repeatedly forging and deforming the titanium alloy forging stock in a single-phase area or alternately in low and high modes for multiple times, wherein the method can better crush and refine the as-cast grains in the early stage, but after the grains are refined to a certain degree, the beta grains are difficult to refine further by increasing forging heat in the single-phase area, and the uniformity of the beta grains is relatively poor because the forging deformation is uneven. The application fully utilizes the mode of the two-phase area pre-deformation and the hot material return single-phase area static recrystallization to solve the problem of homogenizing the Ti-1350 titanium alloy beta grains, combines the relation between the size/uniformity of the recrystallized grains and the pre-deformation quantity of the two-phase area, the section size of the blank, the recrystallization temperature and the recrystallization heat preservation time, designs different recrystallization heat preservation time by designing a gradient circulation recrystallization process and combining the alloy recrystallization nucleation growth rules under different temperature conditions, can refine the beta grains to be less than 1mm, avoids the deformation streamline and the non-uniformity of the beta grain size caused by the non-uniformity of forging, remarkably improves the tissue refining and homogenizing effects, and lays a foundation for further improving the plasticity of the Ti-1350 ultra-high strength titanium alloy.
After the titanium alloy is forged in the single-phase region, the titanium alloy enters the two-phase region for proper forging so as to improve the plasticity of the alloy. The primary alpha phase naturally precipitated in the two-phase region of the titanium alloy is lamellar or pin-packed, and the alpha phase is gradually crushed and spheroidized along with the increase of forging fire in the two-phase region, so that the alloy plasticity is also gradually improved. The primary alpha phase length-width ratio is less than or equal to 2, namely the spheroidization is considered to be completed, an equiaxed structure is obtained, the alloy strength after heat treatment is generally not more than 1200MPa for the conventional medium-strength or high-strength titanium alloy large-size bar, and the common equiaxed structure generally has excellent plasticity. For Ti-1350 ultrahigh-strength titanium alloy large-size bars, the strength required after heat treatment reaches 1350MPa, and under the strength level, the transverse elongation of the common equiaxed structure bars is only 3-6%, even obvious brittle failure occurs. According to the application, a large number of experiments show that by increasing the forging firing time of the two-phase region from 2-4 fires to 6-8 fires and simultaneously matching with measures for improving deformation uniformity, the alloy structure can be changed from a common equiaxed structure with the aspect ratio of the primary alpha phase less than or equal to 2 into a spherical structure with the aspect ratio of the primary alpha phase less than 1.5, and all the primary alpha phases are uniformly spherical without obvious edges.
Preferably, when the blanks in the step 1) are charged, the heating and heat preservation coefficient is 0.5-0.7 min/mm, and when the blanks in the step 3) and the step 4) are charged, the heating and heat preservation coefficient is 0.6-0.8 min/mm.
According to the application, the heating and heat preservation coefficients in the steps 1), 3) and 4) ensure the basic heat penetration of the central part of the blank (namely, the basic heat penetration is that the temperature of the central part of the blank is 5-10 ℃ lower than that of the side parts, and a certain temperature rise is generated in the central part in the subsequent forging process so as to make up the deficiency of the temperature of the central part in the heating process, thereby ensuring the uniformity of the whole temperature field and deformation of the blank in the forging process, but the whole blank does not have obvious grain growth. The heat conduction coefficient of the Ti-1350 alloy below the phase transition temperature is smaller than that of the Ti-1350 alloy above the phase transition temperature, so that the heat preservation coefficient is slightly larger than that of the Ti-1350 alloy above the phase transition temperature. The heat preservation time is short, the core of the blank is not heated thoroughly, and the deformation resistance difference of different parts is large due to the difference of temperature fields, so that the non-uniformity of deformation is increased. The energy consumption is wasted due to the overlong heat preservation time, and the risk of grain growth exists in the single-phase region, so that the heat preservation coefficient range is strictly controlled.
Preferably, in the steps 1), 3) and 4), the blank is heated by one-stage heating method to Wen Zhuanglu each time, and air cooling treatment is performed after forging. The one-stage heating means that the charging temperature is the heat preservation temperature, and the heating furnace temperature can be raised to 1000 ℃ without preheating, for example, the heating heat preservation temperature is 1000 ℃, blanks are directly charged into the furnace after the heating furnace reaches the temperature, and the heat preservation time is calculated after the furnace temperature is stabilized again to 1000 ℃.
Compared with two-section heating curves and three-section heating curves, the one-section heating mode can avoid frequent heating and cooling of the heating furnace during engineering continuous production, shortens the waiting time of the heating and cooling process, greatly improves the production efficiency and prolongs the service life of the heating furnace. Compared with the traditional two-section type and three-section type heating modes, the one-section type heating and heat preservation coefficient suitable for the Ti-1350 alloy is obtained by combining finite element simulation and a large number of experimental verification, the one-section type heating and heat preservation coefficient has the advantages that the one-section type heating effect is equivalent, the whole heating time is shorter, the waiting time in the frequent temperature rise and reduction process and the damage to a heating furnace are avoided, the production efficiency can be improved by more than 20%, and the service life of the heating furnace can be improved by more than 30%.
Preferably, in the step 1), the upsetting forging rate is controlled to be 20-25 mm/s, and the drawing forging rate is controlled to be 25-30 mm/s; and 2, controlling the upsetting forging speed in the steps 2, 3 and 4 to be 3-8 mm/s, and controlling the drawing forging speed to be 20-25 mm/s.
The Ti-1350 titanium alloy has low phase transition temperature and extremely high deformation resistance, the temperature field of the blank is uneven due to temperature rise in the forging process, the deformation unevenness is aggravated, and the temperature rise is severe until obvious coarse crystals or overheat structures appear (the overheat structures mainly appear in the two-phase region forging process), so that the temperature rise of the blank needs to be strictly controlled in order to ensure the uniformity of the forging structure. The deformation resistance, the pass deformation amount and the pass deformation rate of the alloy jointly determine the forging temperature rise degree of the alloy. The upsetting pass deformation is larger, the drawing pass deformation is smaller, the blank temperature rise is strictly controlled while the forging efficiency is improved, and the upsetting speed is lower than the drawing speed; the forging deformation resistance above the phase transition temperature is small, the temperature rise is relatively not serious, and the problem of overheating of the tissue is avoided, the forging deformation resistance below the phase transition temperature is large, the temperature rise is serious, and when the temperature rise is close to or exceeds the phase transition temperature, overheating or overburning of the tissue can occur, so that the product is scrapped. Thus the forging rate control below the phase transition temperature is lower than above the phase transition temperature. The forging rate control in the application is obtained through a large number of finite element simulation and experimental groping verification, and the forging rate in different steps is matched with the forging temperature and the pass deformation.
Preferably, the blank is forged to eight directions after each forging in step 3.1.
Step 3.1 is two-phase zone forging, the upsetting deformation is controlled to be in the range of 30-40%, the upsetting speed is controlled to be in the range of 3-8 mm/s, and for large-size forging stock, the upsetting process usually needs 2-3 min, and if square or flat square is used in the process, edges and corners are extremely easy to darken rapidly due to too fast temperature drop, so that the non-uniformity of the blank is aggravated. Compared with square or flat square, the eight directions have no obvious edges and corners around the blank, the phenomenon that edges and corners are quickly darkened due to too fast temperature drop in the slow upsetting process is avoided, the eight directions are larger in cross section size under the same cross section area, bending or double-drum is not easy to occur in the upsetting process, and the deformation uniformity is superior to that of the square or flat square.
The diameter specification of the large-specification bar is more than or equal to phi 200mm.
The application has the following beneficial effects:
after the forging process is optimized according to the method disclosed by the application, the primary alpha phase spheroidizing effect and uniformity of the bar are improved, and the alloy plasticity is further improved.
Drawings
FIG. 1 is a high-power organization chart of a bar obtained by a prior art method;
FIG. 2 is a high-power organization chart of a bar obtained by the method of the application.
Detailed Description
The present application will be described in detail with reference to preferred embodiments so that advantages and features of the present application can be more easily understood by those skilled in the art, thereby making clear and unambiguous definitions of the scope of the present application. Any identical or similar solution without departing from the inventive concept shall fall within the scope of protection of the present application. And not described in detail herein, all in a manner conventional in the art. And hereinafter: "Φ" refers to the diameter of a blank having a circular cross-section; "L" refers to the length of the blank; t is insulation time (unit min), k is insulation coefficient (unit min/mm), h is minimum section size (unit mm) of the blank, and when the insulation coefficient is given, the calculation method of the blank insulation time t is t=k×h.
The strength and plastic design index requirements of the large-specification bar with the diameter of 200mm or more of the Ti-1350 titanium alloy are shown in the table 1:
materials: ti-1350 titanium alloy, phase transition point: the ingot specification is phi 680 multiplied by Lmm, the single ingot weighs about 2.4 tons, and the finished bar specification is phi 350 multiplied by Lmm.
Example 1
Step 1): cogging forging:
adding Ti-1350 titanium alloy cast ingot with phi 680 x-1400 mm (the meaning of 'approximately equal' in the specification) to 300-400 ℃ above beta transition temperature, adopting Wen Zhuanglu, starting timing when the furnace temperature is restored to the range of +/-10 ℃ and controlling the heat preservation coefficient to be in the range of 0.5-0.7 min/mm, carrying out rounding shaping after heat preservation, controlling the rolling reduction to be 30-50 mm, and then carrying out 2-upsetting 2-drawing deformation, wherein the upsetting deformation is controlled to be 35-45%, the upsetting reduction rate is controlled to be 20-25 mm/s, the drawing reduction rate is controlled to be 25-30 mm/s, and carrying out air cooling after forging.
Step 2): and (3) circulating recrystallization refinement and homogenization of beta grains:
step 2.1: heating the forging stock finished in the step 1) to 30-50 ℃ below the beta transition temperature, adopting until Wen Zhuanglu, starting timing when the furnace temperature is restored to the range of +/-10 ℃ of the set temperature, controlling the heat preservation coefficient to be in the range of 0.6-0.8 min/mm, discharging from the furnace for 1 upsetting and 1 drawing deformation after the heat preservation is finished, controlling the upsetting deformation to be 35-40%, controlling the upsetting reduction rate to be 3-8 mm/s, controlling the drawing reduction rate to be 20-25 mm/s, forging the blank to a flat square with the minimum section size not exceeding 500mm, returning the hot stock to the range of +/-10 ℃ above the beta transition temperature for heat preservation after the forging is finished, starting timing when the furnace temperature is restored to the range of +/-10 ℃ of the set temperature, and recrystallizing for heat preservation time according to t=k 1 H performs the calculation, where k 1 To recrystallize the heat preservation coefficient, k 1 The value is controlled to be between 0.4 and 0.8min/mm,h is the minimum cross-section size of the blank, and the blank is immediately discharged from the furnace and air-cooled to room temperature after heat preservation.
Step 2.2: heating the forging stock finished in the step 2.1 to 30-50 ℃ below beta transition temperature, adopting Wen Zhuanglu, starting timing when the furnace temperature is restored to the range of +/-10 ℃ of the set temperature, controlling the heat preservation coefficient to be in the range of 0.6-0.8 min/mm, discharging the forging stock to perform 1 upsetting and 1 drawing deformation after the heat preservation is finished, controlling the upsetting deformation amount to be 30-35%, controlling the upsetting reduction rate to be 3-8 mm/s, controlling the drawing reduction rate to be 20-25 mm/s, forging the blank to be square, returning the hot stock to 70-100 ℃ above beta transition temperature for heat preservation after the forging is finished, starting timing when the furnace temperature is restored to the range of +/-10 ℃ of the set temperature, and recrystallizing the heat preservation time according to t=k 2 H performs the calculation, where k 2 To recrystallize the heat preservation coefficient, k 2 The value is controlled to be 0.5-0.9 min/mm, and the furnace is immediately taken out after the heat preservation is finished, and the air cooling is carried out to the room temperature.
Step 2.3: heating the forging stock finished in the step 2.2 to 30-50 ℃ below the beta transformation temperature, adopting the temperature to Wen Zhuanglu, starting timing when the furnace temperature is restored to the range of +/-10 ℃ of the set temperature, controlling the heat preservation coefficient to be in the range of 0.6-0.8 min/mm, discharging the forging stock to perform 1 upsetting and 1 drawing deformation after the heat preservation is finished, controlling the upsetting deformation amount to be 25-30%, controlling the upsetting reduction rate to be 3-8 mm/s, controlling the drawing reduction rate to be 20-25 mm/s, forging the blank to eight directions, returning the hot stock to the temperature of 30-50 ℃ above the beta transformation temperature for heat preservation after the forging is finished, starting timing when the furnace temperature is restored to the range of +/-10 ℃ of the set temperature, and recrystallizing the heat preservation time according to t=k 3 H performs the calculation, where k 3 To recrystallize the heat preservation coefficient, k 3 The value is controlled to be 0.6-1.0 min/mm, and the furnace is immediately taken out after the heat preservation is finished, and the furnace is cooled to the room temperature.
Step 3): primary alpha phase spheroidization and homogenization:
step 3.1: heating the forging stock finished in the step 2 to 30-50 ℃ below the beta transformation temperature, adopting Wen Zhuanglu, starting timing when the furnace temperature is restored to the range of the preset temperature +/-10 ℃, controlling the heat preservation coefficient at the range of 0.6-0.8 min/mm each time, performing 1 upsetting and 1 drawing deformation for 8 times, controlling the upsetting deformation at 30-40% each time, controlling the upsetting reduction rate at 3-8 mm/s, controlling the drawing reduction rate at 20-25 mm/s, forging the blank to eight directions each time, and then air cooling the blank to room temperature.
Step 3.2: heating the forging stock finished in the step 3.1 to 30-50 ℃ below the beta transformation temperature, adopting Wen Zhuanglu, starting timing when the furnace temperature is restored to the range of the set temperature plus or minus 10 ℃, controlling the heat preservation coefficient to be in the range of 0.6-0.8 min/mm, performing drawing deformation for 2 times, controlling the drawing deformation to be 25-35%, controlling the drawing reduction rate to be 20-25 mm/s, and air-cooling the blank to room temperature after each time of forging.
Step 4): forging a finished product:
and (3) starting timing when the temperature of the blank finished in the step (3) is 30-50 ℃ below the beta transformation temperature to Wen Zhuanglu and the furnace temperature is restored to the set temperature +/-10 ℃, controlling the heat preservation coefficient to be in the range of 0.6-0.8 min/mm, performing 1-fire round rolling shaping forging after discharging, controlling the shaping deformation to be 15-20%, controlling the shaping pressing rate to be in the range of 20-25 mm/s, forging the blank to a bar with the size of approximately phi 350mm, and performing air cooling after forging.
Comparative example
Step 1: heating a Ti-1350 titanium alloy cast ingot with the specification of phi 680 x-1400 mm to 1150 ℃ for forging by 3 upsetting and 3 drawing with 1 firing time, controlling the upsetting deformation to be 30-45%, and performing air cooling after forging;
step 2: heating the blank finished in the step 1 to 50-250 ℃ above the phase transition temperature, performing 2 upsetting and 2 drawing forging for 3 times, controlling upsetting deformation amount for each time to be 30-45%, and performing air cooling after each time of forging;
step 3: heating the blank finished in the step 2 to 30-50 ℃ below the phase transition temperature, performing 2-time upsetting 1-drawing forging, controlling upsetting deformation amount at 30-40% each time, and performing air cooling after each time of forging;
step 4: heating the blank finished in the step 3 to 50-100 ℃ above the phase transition temperature, performing 2-time upsetting and 2-drawing forging, controlling upsetting deformation amount at 30-45% each time, and performing air cooling after each time of forging;
step 5: heating the blank finished in the step 4 to 30-50 ℃ below the phase transition temperature, performing 4-time upsetting 1-drawing forging, controlling upsetting deformation amount at 30-40% each time, and performing air cooling after each time of forging;
step 6: heating the blank finished in the step 5 to 30-50 ℃ below the phase transition temperature, performing 4-time upsetting 1-drawing forging, controlling upsetting deformation amount at 30-40% each time, and performing air cooling after each time of forging;
step 7: heating the blank finished in the step 6 to 30-50 ℃ below the phase transition temperature, performing 2-time drawing forging, controlling the drawing deformation of each time to be 30-40%, drawing the blank to a blank with the cross section in all directions, and performing air cooling after each time of forging;
step 8: and (3) heating the blank finished in the step (7) to 30-50 ℃ below the phase transition temperature, carrying out 1-fire round rolling shaping forging, controlling the elongation deformation to be 10-20%, and shaping the blank into a bar with the size of about phi 350mm, and carrying out air cooling after forging.
The free ends of the bars forged by the two different methods of the example and the comparative example are cut, then phi 350X 100mm samples are cut from the ends of the bars of the two batches, and after heat treatment is carried out according to 825 ℃/2h, FC to 780 ℃/2 h+520 ℃/8h and AC, the high-power tissues and the mechanical properties of the bars of the two batches are respectively shown in the figure 1 and the table 2.
As can be seen from comparison of FIG. 1, the raw alpha phase of the bar Gao Beichu obtained by the prior art method (i.e. the comparative example method) is mainly of equiaxed structure, a small amount of short bar-shaped raw alpha phase remains, and all the raw alpha phases of the forged bar are uniformly spherical and have an aspect ratio of less than 1.5.
As can be seen from the comparison of the mechanical properties in Table 2, the tensile strength of the bars obtained by the comparative example method and the inventive method is substantially equivalent, but the yield strength, the elongation and the reduction of area of the bars obtained by the inventive method are significantly higher than those of the comparative example method.
Table 2 shows the mechanical properties of bars obtained by the comparative example method and the technical method of the patent:
Claims (5)
- the high-plasticity forging method for the Ti-1350 ultrahigh-strength titanium alloy large-specification bar is characterized by comprising the following steps of:step 1), cogging forging:heating a Ti-1350 titanium alloy cast ingot with the diameter of phi of 650-800 mm to 300-400 ℃ above the beta transformation temperature, discharging, carrying out rolling shaping, controlling rolling reduction to be 30-50 mm, and then carrying out 2-upsetting 2-drawing deformation, wherein the upsetting deformation is controlled to be 35-45%;step 2), circulating recrystallization refinement and homogenization of beta grains:step 2.1: carrying out 1 upsetting and 1 drawing deformation on the forging stock finished in the step 1) at the temperature of 30-50 ℃ below the beta transformation temperature, controlling the upsetting deformation to be 35-40%, forging the blank to be flat, wherein the minimum cross section dimension h of the flat is not more than 500mm, returning hot stock to the furnace to the temperature of 150-180 ℃ above the beta transformation temperature after the forging is finished, carrying out heat preservation, and carrying out recrystallization heat preservation for the time of t=k 1 H performs the calculation, where k 1 To recrystallize the heat preservation coefficient, k 1 The value is controlled to be 0.4-0.8 min/mm, h is the minimum cross section size of the blank, and the blank is immediately discharged from the furnace and air-cooled to room temperature after heat preservation is finished;step 2.2: carrying out 1 upsetting and 1 drawing deformation on the forging stock finished in the step 2.1 at the temperature of 30-50 ℃ below the beta transformation temperature, controlling the upsetting deformation to be 30-35%, forging the blank to be square, returning hot materials to the furnace to 70-100 ℃ above the beta transformation temperature after forging, carrying out heat preservation, and carrying out recrystallization heat preservation for the time of t=k 2 H performs the calculation, where k 2 To recrystallize the heat preservation coefficient, k 2 The value is controlled to be 0.5-0.9 min/mm, and the furnace is immediately taken out after the heat preservation is finished, and the furnace is air cooled to the room temperature;step 2.3: carrying out 1 upsetting and 1 drawing deformation on the forging stock finished in the step 2.2 at the temperature of 30-50 ℃ below the beta transformation temperature, controlling the upsetting deformation to be 25-30%, forging the blank to eight directions, returning hot materials to the furnace to the temperature of 30-50 ℃ above the beta transformation temperature after forging, carrying out heat preservation, and carrying out recrystallization heat preservation for the time of t=k 3 H performs the calculation, where k 3 To recrystallize the heat preservation coefficient, k 3 The value is controlled to be 0.6-1.0 min/mm, and the furnace is immediately taken out after the heat preservation is finished, and the furnace is cooled to the room temperature in an air way;step 3), primary alpha phase spheroidization and homogenization:step 3.1: carrying out 1 upsetting and 1 drawing deformation on the forging stock finished in the step 2) at the temperature of 30-50 ℃ below the beta transformation temperature for 6-8 times, wherein the upsetting deformation is controlled to be 30-40%;step 3.2: performing 1-3 times of elongation deformation on the forging stock finished in the step 3.1 at the temperature of 30-50 ℃ below the beta transformation temperature, wherein the elongation deformation is controlled to be 25-35%;step 4), forging a finished product:and (3) performing 1-time rounding shaping forging on the blank obtained in the step (3) at the temperature of 30-50 ℃ below the beta transformation temperature, controlling the shaping deformation to be 15-20%, and forging the blank to a proper specification and size.
- 2. The method for forging the Ti-1350 ultrahigh-strength titanium alloy large-size bar with high plasticity according to claim 1, wherein the heating and heat preservation coefficient is 0.5-0.7 min/mm when the blank in the step 1) is charged, and the heating and heat preservation coefficient is 0.6-0.8 min/mm when the blank in the step 3) and the blank in the step 4) is charged.
- 3. The method for forging large-sized bars of Ti-1350 ultra-high strength titanium alloy according to claim 1, wherein the blanks in the steps 1), 3) and 4) are heated by one-stage heating to Wen Zhuanglu each time, and air-cooled after forging.
- 4. The high-plasticity forging method of the Ti-1350 ultrahigh-strength titanium alloy large-size bar according to claim 1, wherein the upsetting forging rate in the step 1) is controlled to be 20-25 mm/s, and the drawing forging rate is controlled to be 25-30 mm/s; the upsetting forging rate in the steps 2), 3) and 4) is controlled to be 3-8 mm/s, and the drawing forging rate is controlled to be 20-25 mm/s.
- 5. The method for high plasticity forging of Ti-1350 ultra-high strength titanium alloy large gauge bar according to claim 1, wherein the blank is forged to eight directions after each forging in step 3.1.
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