CN115747689A - 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 invention 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-size bar, which is realized by the steps of cogging forging, beta crystal grain circulating recrystallization refinement and homogenization, primary alpha-phase spheroidization and homogenization and finished product forging. The method fully utilizes the modes of two-phase zone pre-deformation and hot material return single-phase zone static recrystallization to solve the problem of homogenization of the beta crystal grains of the Ti-1350 titanium alloy, and simultaneously combines the relationship between the size/uniformity of the recrystallized crystal grains and the pre-deformation amount of the two-phase zone, the section size of a blank, the recrystallization temperature and the recrystallization heat-preservation time, designs different recrystallization heat-preservation times by designing a gradient circulation recrystallization process and combining the growth rule of alloy recrystallization nucleation under different temperature conditions, can refine the beta crystal grains to be less than 1mm, and avoids deformation streamlines and nonuniformity of the beta crystal grain size caused by the nonuniformity of forging because the forging is not carried out in the process of refining the beta crystal grains.
Description
Technical Field
The invention 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 type titanium alloy not only has the characteristics of high specific strength, good hardenability, excellent corrosion resistance and the like, but also is easy to be plastically processed and formed, and can realize excellent strength-plasticity-toughness matching through heat treatment strengthening, so that the high-strength and high-toughness near-beta type titanium alloy is widely applied to the field of aerospace and used for manufacturing large-scale load-bearing components such as aircraft landing gears, frames, beams and the like. With the upgrading of weaponry, higher requirements on the performance of high-strength and high-toughness titanium alloy materials are provided for meeting the design requirements of new-generation airplanes and aero-engines on long service life and high weight reduction.
The Ti-1350 titanium alloy is an ultrahigh-strength near-beta titanium alloy developed by our country in recent years aiming at the development requirement of new generation aircrafts in China, and in order to meet the design requirement, the transverse elongation is more than 5 percent while the room temperature strength of a large-size bar reaches 1350MPa level.
CN20171025920085 discloses a forging method for producing a large-size Ti1350 alloy bar with the diameter of more than 200mm, which specifically comprises the steps of performing cogging forging of three piers and three-drawing above the beta-phase transition temperature, performing three-pier three-drawing above the beta-phase transition temperature, performing reversing pier drawing above the beta-phase transition temperature, performing one-pier one-drawing below the beta-phase transition temperature, performing pier drawing deformation above the beta-phase transition temperature, performing flat and square pier drawing deformation above the beta-phase transition temperature and size and face exchange, performing pier drawing deformation above the beta-phase transition temperature, performing pier drawing deformation below the beta-phase transition temperature, performing elongation forging above the beta-phase transition temperature, and finally performing elongation shaping forging on a finished product below the beta-phase transition temperature. The forging method mainly comprises single-phase region upsetting deformation, alternately uses two-phase region upsetting deformation, and uses flat square upsetting deformation mode for individual fire times, so that the forging permeability of the core of the blank is improved, a twisted beta crystal boundary structure is obtained, a fine acicular alpha phase is obtained by controlling the 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 grain is refined to a certain degree, the beta grain cannot be further refined, and the alpha phase cannot be fully spheroidized because the forging deformation is not uniform, and the alloy plasticity needs to be improved.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a high-plasticity forging method for a Ti-1350 ultrahigh-strength titanium alloy large-size bar, the method can be used for preparing the Ti-1350 ultrahigh-strength titanium alloy large-size bar with the strength reaching 1350MPa and the plasticity still having large margin, and the problem of insufficient plasticity margin of the Ti-1350 ultrahigh-strength titanium alloy is practically solved.
In order to achieve the purpose, the invention adopts the technical scheme that: a high-plasticity forging method for a Ti-1350 ultrahigh-strength titanium alloy large-size bar is realized by the steps of cogging forging, beta crystal grain circulating recrystallization refinement and homogenization, primary alpha phase spheroidization and homogenization and finished product forging, and specifically comprises the following steps:
step 1), cogging and forging:
heating Ti-1350 titanium alloy ingots with phi of 650-phi 800mm to a temperature higher than the beta transition temperature of 300-400 ℃, taking out of a furnace, performing rolling shaping, controlling the rolling reduction at 30-50mm, and then performing 2-upsetting and 2-drawing deformation, wherein the upsetting deformation is controlled at 35-45%;
the hot working plasticity of the as-cast structure is generally poor, and the alloying element of Ti-1350 is as high as 20%, in order to improve the component uniformity of the cast ingot, the finished product is smelted by adopting a low-current shallow molten pool, so that more cold interlayers and subcutaneous blowholes exist on the surface of the cast ingot. A large number of experiments show that before large-deformation upsetting-drawing forging is carried out on an ingot, the ingot is pre-deformed by adopting the rolling reduction of 30 to 50mm, on one hand, the hot working plasticity of the ingot can be obviously improved, on the other hand, through carrying out quick rounding shaping on the surface, a cold interlayer and subcutaneous air holes which are remained on the surface of the ingot can be forged and closed, the surface quality of a forging blank is greatly improved, cracking is further reduced, and the yield is improved.
Step 2), circulating recrystallization refining and homogenization of beta grains:
step 2.1: 1 upsetting the forging stock completed in the step 1) at a temperature of 30-50 ℃ below the beta transition temperature for 1 drawing deformation, controlling the upsetting deformation at 35-40%, forging the stock to a flat square, ensuring that the minimum section size h of the flat square is not more than 500mm, returning the hot stock to a furnace above the beta transition temperature after forging is completed for 150-180 ℃, and keeping the temperature for recrystallization according to t = k 1 H is calculated, where k 1 K is a recrystallization holding factor 1 Controlling the value to be 0.4-0.8 min/mm, taking h as the minimum section size of the blank, immediately discharging the blank after heat preservation is finished, and air-cooling the blank to room temperature;
step 2.2: 1 upsetting the forging stock completed in the step 2.1 at the temperature of 30-50 ℃ below the beta transition temperature for 1 drawing deformation, controlling the upsetting deformation at 30-35%, forging the blank to four sides, returning the hot material to the temperature of 70-100 ℃ above the beta transition temperature after forging is completed, preserving heat, recrystallizing and preserving heat for t = k 2 H is calculated, where k 2 For recrystallization of the thermal insulation coefficient, k 2 Controlling the value to be between 0.5 and 0.9min/mm, immediately discharging the furnace after the heat preservation is finished, and air-cooling the furnace to the room temperature;
step 2.3: 1 upsetting at 30 to 50 ℃ below the beta transition temperature and 1 drawing deformation, controlling the upsetting deformation at 25 to 30%, forging the blank to eight directions, returning the hot material to the beta transition temperature for 30 to 50 ℃ after forging, preserving heat, recrystallizing and preserving heat for t = k 3 H is calculated, where k 3 For recrystallization of the thermal insulation coefficient, k 3 Controlling the value to be between 0.6 and 1.0min/mm, immediately discharging the furnace after the heat preservation is finished, and air-cooling the furnace to room temperature;
step 3), primary alpha phase spheroidizing and homogenizing:
step 3.1: carrying out 1-time upsetting and 1-drawing deformation on the forging stock finished in the step 2) at 6-8 fire times at the temperature of 30-50 ℃ below the beta transition temperature, wherein the upsetting deformation is controlled to be 30-40%;
step 3.2: carrying out hot drawing deformation on the forging stock finished in the step 3.1 for 1 to 3 times at the temperature of 30 to 50 ℃ below the beta transformation temperature, wherein the drawing deformation is controlled to be 25 to 35 percent;
step 4), forging of finished products:
performing 1-time rolling and shaping forging on the blank finished in the step 3) at the temperature of 30-50 ℃ below the beta transition temperature, controlling the shaping deformation to be 15-20%, and forging the blank to a proper specification size.
The action principle of the invention is as follows:
under the condition of definite alloy grade and chemical composition proportion, the main factors influencing the strength and plasticity of the alloy are beta crystal grain size and alpha phase shape distribution. It is generally advantageous to refine the beta grain size to improve both the strength and plasticity of the alloy. The morphological distribution of the alpha phase mainly comprises the size, the morphology and the distribution of a primary alpha phase and a 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 accumulated deformation of the alloy in the two-phase region, the more sufficient the primary alpha phase spheroidization is, and the better the plasticity of the alloy is.
The traditional method for refining the beta grain size of the titanium alloy is mainly characterized in that a titanium alloy forging stock is repeatedly forged and deformed by multiple times of fire in a single-phase region or low-high alternation, cast grains can be well crushed and refined in the early stage, when the grains are refined to a certain degree, the beta grains are difficult to be further refined by increasing the upsetting forging times of the single-phase region, and the uniformity of the beta grains is relatively poor due to the fact that the forging deformation is not uniform. The method solves the problem of homogenization of beta grains of the Ti-1350 titanium alloy by fully utilizing the modes of two-phase zone pre-deformation and hot material return single-phase zone static recrystallization, simultaneously combines the relationship between the size/uniformity of recrystallized grains and the pre-deformation amount, the section size of a blank, the recrystallization temperature and the recrystallization heat preservation time of the two-phase zone, designs different recrystallization heat preservation times by designing a gradient circulation recrystallization process and combining the nucleation and growth rules of alloy recrystallization under different temperature conditions, can refine the beta grains to be less than 1mm, avoids the nonuniformity of deformation streamlines and beta grain sizes caused by the nonuniformity of forging because the beta grains are not forged and deformed in the refinement process, obviously improves the tissue refinement and homogenization effects, and lays a foundation for further improving the plasticity of the Ti-1350 ultrahigh-strength titanium alloy.
After the single-phase region forging is completed, the titanium alloy enters a two-phase region to be properly forged so as to improve the plasticity of the alloy. The titanium alloy is in lamellar or needle-like installation in the nascent alpha phase that the two-phase region naturally separates out, and along with the increase of the forging heat number in the two-phase region, the alpha phase is gradually broken and spheroidized, and the alloy plasticity is also gradually improved. The nodulizing is considered to be completed when the aspect ratio of the primary alpha phase is less than or equal to 2, so that an equiaxed structure is obtained, for the conventional medium-strength or high-strength titanium alloy large-size bar, the alloy strength after heat treatment is generally not more than 1200MPa, and the common equiaxed structure generally has excellent plasticity. For a Ti-1350 ultrahigh-strength titanium alloy large-size bar, the strength after heat treatment is required to reach 1350MPa, and under the strength level, the transverse elongation of a common equiaxial structure bar is only 3 to 6 percent, even obvious brittle fracture occurs. A large number of experiments show that the alloy structure can be changed from a common equiaxial structure with the primary alpha phase length-width ratio of less than or equal to 2 into a spherical structure with the primary alpha phase length-width ratio of less than 1.5 by increasing the forging heat number of the two-phase region from 2 to 4 to 6 to 8 and matching with a measure for improving the deformation uniformity, all primary alpha phases are in a uniform sphere shape, and no obvious edge angle exists.
Preferably, the heating and heat-preserving coefficient is 0.5 to 0.7min/mm when the blank in the step 1) is charged into the furnace, and the heating and heat-preserving coefficient is 0.6 to 0.8min/mm when the blank in the steps 3) and 4) is charged into the furnace.
The heating and heat preservation coefficients in the steps 1), 3) and 4) ensure that the center of the blank is basically heat-through (so-called basic heat-through is that the temperature of the center of the blank is 5-10 ℃ lower than that of the edge, and the center of the blank can generate a certain temperature rise in the subsequent forging process to make up the deficiency of the temperature of the center of the heating process, so that the integral temperature field and the deformation uniformity of the blank in the forging process are ensured), but the blank does not obviously grow up. The heat conductivity of the Ti-1350 alloy is lower than the phase transition temperature and higher than the phase transition temperature, so that the heat insulating coefficient is slightly higher than the phase transition temperature. Short heat preservation time, incomplete heat penetration of the center of the blank, large difference of deformation resistance of different parts caused by temperature field difference, and aggravated non-uniformity of deformation. The energy consumption is wasted due to the overlong heat preservation time, and the single-phase region still has the risk of growing crystal grains, so the heat preservation coefficient range needs to be strictly controlled.
Preferably, in the step 1), the step 3) and the step 4), a one-stage heating mode is adopted for heating the blank each time, the blank is subjected to warm charging, and air cooling treatment is performed after forging is completed. The one-stage heating refers to that the charging temperature is the heat preservation temperature, preheating is not needed, if the heating heat preservation temperature is 1000 ℃, the temperature of the heating furnace can be increased to 1000 ℃, the blank is directly charged after the temperature of the heating furnace is reached, and the heat preservation time is calculated after the temperature of the heating furnace is stabilized to 1000 ℃.
Compared with two-section type and three-section type heating curves, the one-section type heating mode can avoid frequent heating and cooling of the heating furnace in 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. This application combines finite element simulation and a large amount of experiments to verify the syllogic heating heat preservation coefficient who is applicable to Ti-1350 alloy that groped out, compares in two segmentations of tradition and syllogic heating methods, and the effect of one segmentations heating is comparable, but whole heat time is shorter, and avoided frequently to go up the latency of cooling process and the injury that leads to the fact the heating furnace, and production efficiency can promote more than 20%, and heating furnace life can promote more than 30%.
Preferably, the upsetting forging rate in the step 1) is controlled to be 20 to 25mm/s, and the drawing forging rate is controlled to be 25 to 30mm/s; in the steps 2, 3 and 4, the upsetting forging rate is controlled to be less than 3 to 8mm/s, and the elongation forging rate is controlled to be 20 to 25mm/s.
The Ti-1350 titanium alloy has low phase transition temperature and great deformation resistance, and the forging process has temperature raising to make the blank temperature field uneven and to intensify deformation unevenness. The deformation resistance, the pass deformation and the pass deformation rate of the alloy jointly determine the forging temperature rise degree of the alloy. The deformation of the upsetting pass is large, the deformation of the drawing-out pass is usually small, the temperature rise of the blank is strictly controlled while the forging efficiency is improved, and the upsetting rate is lower than the drawing-out rate; the forging above the phase transition temperature has small deformation resistance, relatively low temperature rise and no worry about tissue overheating, while the forging below the phase transition temperature has large deformation resistance and high temperature rise, and when the temperature rise is close to or exceeds the phase transition temperature, overheating or overburning tissues can appear to cause product rejection. Thus, the forging rate below the phase transition temperature is controlled to be lower than the phase transition temperature. The forging rate control in the application is obtained through simulation and experimental groping verification of a large number of finite elements, and the forging rate in different steps is matched with the forging temperature and pass deformation.
Preferably, the blank is forged to eight directions after each fire forging in the step 3.1.
And 3.1, forging in a two-phase region, controlling the upsetting deformation within the range of 30-40% and the upsetting rate within the range of 3-8mm/s according to the technical requirements of the application, wherein for a large-size forging blank, the upsetting process needs 2-3 min, and if a square or flat square is used in the process, the edge is easy to darken rapidly due to too fast temperature drop, so that the nonuniformity of the blank is increased. Compared with a square or flat square, the octagonal upsetting die has the advantages that no obvious edges and corners exist around a blank, the phenomenon that the edges and corners are quickly darkened due to too fast temperature drop in the process of slow upsetting does not occur, the cross section of the octagonal is larger in size under the same cross section area, bending or double bulging are not prone to occurring in the upsetting process, and the deformation uniformity is superior to that of the square or flat square.
The diameter specification of the large-size bar related by the invention is more than or equal to phi 200mm.
The invention has the following beneficial effects:
after the forging process is optimized according to the method, the primary alpha phase spheroidization effect and uniformity of the bar are improved, and the alloy plasticity is further improved.
Drawings
FIG. 1 is a high magnification organization chart of a bar obtained by a prior art method;
FIG. 2 is a high magnification organization chart of the bar obtained by the method of the invention.
Detailed Description
The present invention is described in detail below with reference to preferred embodiments so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making more clear and definite definitions of the scope of the present invention. Any arrangement, which is the same or similar, without departing from the spirit of the invention, is intended to be within the scope of the present invention. And not described in detail herein, are performed in a manner conventional in the art. And, hereinafter: "Φ" refers to the diameter of a billet that is circular in cross-section; "L" refers to the length of the billet; t is the holding time (unit min), k is the holding coefficient (unit min/mm), h is the minimum section size (unit mm) of the blank, and when the holding coefficient is given, the calculation method of the holding time t of the blank is t = k × h.
The design index requirements of the strength and the plasticity of the large-size bar with the diameter of more than 200mm of the Ti-1350 titanium alloy are shown in the table 1:
materials: ti-1350 titanium alloy, transformation point: the ingot casting specification is phi 680 XLmm at 840 ℃, the weight of a single ingot is about 2.4 tons, and the specification of a finished bar is phi 350 XLmm.
Example one
Step 1): cogging and forging:
adding Ti-1350 titanium alloy ingots with phi 680 to 1400mm (wherein, the range of is about equal to the meaning of the term), to a beta transition temperature of more than 300 to 400 ℃, adopting a warm charging furnace, starting timing when the furnace temperature is restored to a set temperature of +/-10 ℃, controlling the heat preservation coefficient to be in the range of 0.5 to 0.7min/mm, carrying out rolling circle shaping after finishing heat preservation, controlling the rolling circle reduction rate to be 30 to 50mm, then carrying out 2 upsetting and 2 drawing deformation, wherein, the upsetting deformation rate is controlled to be 35 to 45 percent, the upsetting deformation rate is controlled to be 20 to 25mm/s, the drawing length reduction rate is controlled to be 25 to 30mm/s, and air cooling is carried out after forging.
Step 2): refining and homogenizing the beta grains by circulating recrystallization:
step 2.1: heating the forging stock finished in the step 1) to a temperature of 30-50 ℃ below the beta transition temperature, adopting a warm charging furnace, and recovering the furnace temperature to a set temperature of +/-10 DEG CTiming when the range is started, controlling the heat preservation coefficient within the range of 0.6-0.8min/mm, discharging the blank after the heat preservation, performing 1 heading 1 drawing deformation, controlling the upsetting deformation within the range of 35-40%, controlling the upsetting reduction rate within the range of 3-8mm/s, controlling the drawing reduction rate within the range of 20-25mm/s, forging the blank to a flat side with the minimum section size not exceeding 500mm, returning the hot material to the beta transformation temperature above 150-180 ℃ after the forging is completed, keeping the temperature when the furnace temperature is recovered to the range of +/-10 ℃, timing when the temperature of the recrystallization is recovered to the set temperature, and timing when the temperature of the recrystallization is kept for the time of t = k 1 H is calculated, where k 1 For recrystallization of the thermal insulation coefficient, k 1 Controlling the value to be 0.4-0.8 min/mm, taking h as the minimum section size of the blank, immediately discharging the blank after heat preservation, and air-cooling the blank to the room temperature.
Step 2.2: heating the forging stock finished in the step 2.1 to a temperature which is 30-50 ℃ below the beta transition temperature, using a temperature charging furnace, starting timing when the furnace temperature returns to a set temperature range of +/-10 ℃, controlling the heat preservation coefficient to be in a range of 0.6-0.8min/mm, taking out the forging stock from the furnace after the heat preservation is finished, performing 1-upsetting-1-drawing deformation, controlling the upsetting deformation to be 30-35%, controlling the upsetting reduction rate to be in a range of 3-8mm/s, controlling the drawing reduction rate to be in a range of 20-25mm/s, forging the blank to be square, returning the hot material to a temperature which is 70-100 ℃ above the beta transition temperature after the forging is finished, performing heat preservation, starting timing when the furnace temperature returns to the set temperature range of +/-10 ℃, and performing recrystallization heat preservation for a time according to t = k 2 H is calculated, where k 2 K is a recrystallization holding factor 2 Controlling the value to be between 0.5 and 0.9min/mm, immediately discharging the furnace after the heat preservation is finished, and air-cooling the furnace to the room temperature.
Step 2.3: heating the forging stock finished in the step 2.2 to be below the beta transition temperature by 30-50 ℃, using a temperature charging furnace, starting timing when the furnace temperature returns to the set temperature within the range of +/-10 ℃, controlling the heat preservation coefficient within the range of 0.6-0.8min/mm, taking out the forging stock from the furnace after the heat preservation is finished, carrying out 1-upsetting-1-drawing deformation, controlling the upsetting deformation to be 25-30%, controlling the upsetting reduction rate to be within the range of 3-8mm/s, controlling the drawing reduction rate to be within the range of 20-25mm/s, forging the blank to eight directions, returning the hot material to be above the beta transition temperature by 30-50 ℃ after the forging is finished, carrying out heat preservation when the furnace temperature returns to the set temperature within the range of +/-10 ℃, starting timing, and carrying out recrystallization heat preservation for a time according to t = k 3 H is calculated, where k 3 Heat retention coefficient for recrystallization，k 3 Controlling the value between 0.6 and 1.0min/mm, immediately discharging the furnace after heat preservation is finished, and air-cooling to room temperature.
And step 3): primary alpha phase spheroidization and homogenization:
step 3.1: heating the forging stock finished in the step 2 to be 30-50 ℃ below the beta transition temperature, adopting a warm-up furnace, starting timing when the furnace temperature is recovered to be within the range of +/-10 ℃, controlling the heat preservation coefficient within the range of 0.6-0.8min/mm each time, carrying out 1-upsetting-1-drawing deformation for 8 times in total, controlling the upsetting deformation within the range of 30-40% each time, controlling the upsetting reduction rate within the range of 3-8mm/s, controlling the drawing reduction rate within the range of 20-25mm/s, forging the stock to eight directions each time, and then air-cooling the stock to the room temperature.
Step 3.2: heating the forging stock finished in the step 3.1 to a temperature of 30-50 ℃ below the beta transition temperature, using a warm-up furnace, starting timing when the furnace temperature returns to a set temperature range of +/-10 ℃, controlling the thermal insulation coefficient to be in a range of 0.6-0.8min/mm, carrying out drawing deformation for 2 times in total, controlling the drawing deformation to be in a range of 25-35%, controlling the drawing reduction rate to be in a range of 20-25mm/s, and cooling the blank to room temperature after each time of the drawing.
Step 4): forging a finished product:
and (2) casting the blank finished in the step 3) below a beta transition temperature by 30 to 50 ℃, using a temperature furnace, starting timing when the furnace temperature returns to a set temperature range of +/-10 ℃, controlling the heat preservation coefficient to be within 0.6 to 0.8min/mm, performing 1-fire rounding shaping forging after discharging, controlling the shaping deformation to be within 15 to 20%, controlling the shaping pressing rate to be within 20 to 25mm/s, forging the blank to a bar material with the size of phi 350mm, and cooling in air after forging.
Comparative example
Step 1: heating Ti-1350 titanium alloy ingots with the specification of phi 680 x-1400 mm to 1150 ℃, performing 1-time fire 3-time upsetting and 3-drawing forging, controlling the upsetting deformation within 30-45%, and air-cooling after forging;
step 2: heating the blank finished in the step 1 to a temperature 50-250 ℃ above the phase transition temperature, performing 2-time upsetting and 2-time drawing forging for 3 times, controlling the upsetting deformation in each time to be 30-45%, and performing air cooling after each time of forging;
and 3, step 3: heating the blank finished in the step 2 to be below the phase transition temperature by 30-50 ℃, performing 1 upsetting and 1 drawing forging for 2 times, controlling the upsetting deformation amount to be 30-40% each time, and performing air cooling after each time of forging;
and 4, step 4: heating the blank finished in the step 3 to a temperature 50-100 ℃ above the phase transition temperature, performing 2-time 2-upsetting and 2-drawing forging, controlling the upsetting deformation in each time within 30-45%, and performing air cooling after each time of forging;
and 5: heating the blank finished in the step 4 to be below the phase transition temperature by 30-50 ℃, performing 1 upsetting and 1 drawing forging for 4 times, controlling the upsetting deformation amount to be 30-40% each time, and performing air cooling after forging for each time;
and 6: heating the blank finished in the step 5 to be below the phase transition temperature by 30-50 ℃, performing 1 upsetting for 4 times and 1 drawing forging, controlling the upsetting deformation amount to be 30-40% each time, performing air cooling after forging each time;
and 7: heating the blank finished in the step 6 to be below the phase transition temperature for 2 times of hot drawing forging, controlling the hot drawing deformation amount to be 30 to 40 percent, drawing the blank to be a blank with an eight-square section, and cooling in air after hot forging;
and step 8: and (3) heating the blank finished in the step (7) to a temperature below the phase transition temperature of 30-50 ℃, performing 1-time rolling, shaping and forging, controlling the elongation deformation within 10-20%, drawing and shaping the blank into a bar with the size of about phi 350mm, and cooling in air after forging.
The free ends of the bars forged by the two different methods of the above examples and comparative examples are cut off, then samples with the diameter of 350 multiplied by 100mm are cut from the ends of the bars of two batches respectively, and after heat treatment is carried out according to 825 ℃/2h, FC to 780 ℃/2h +520 ℃/8h and AC, the high power tissues and the mechanical properties of the bars of two batches are respectively shown in figure 1 and table 2.
As can be seen from the comparison in fig. 1, the high-power primary alpha phase of the bar obtained by the prior art method (i.e., the comparative method) is mainly equiaxed, a small amount of short bar-shaped primary alpha phase remains, and the primary alpha phases of the bar forged by the method of the present application are all uniformly spherical, and have aspect ratios of less than 1.5.
From a comparison of the mechanical properties in Table 2, it is clear that the tensile strength of the bars obtained according to the comparative example and the method of the present application is substantially equivalent, but that the yield strength, elongation and reduction of area of the bars obtained according to the method of the present application are significantly higher than those of the bars obtained according to the comparative example.
Table 2 shows the comparison of the mechanical properties of the bars obtained by the comparative example method and the technical method of this patent:
Claims (5)
- the high-plasticity forging method of the Ti-1350 ultrahigh-strength titanium alloy large-size bar is characterized by comprising the following steps:step 1), cogging and forging:heating Ti-1350 titanium alloy ingots with phi of 650-phi 800mm to a temperature higher than the beta transition temperature of 300-400 ℃, taking out of a furnace, performing rolling shaping, controlling the rolling reduction at 30-50mm, and then performing 2-upsetting and 2-drawing deformation, wherein the upsetting deformation is controlled at 35-45%;step 2), circulating, recrystallizing, refining and homogenizing 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 transition temperature, controlling the upsetting deformation at 35-40%, forging the stock to a flat square, ensuring that the minimum section size h of the flat square is not more than 500mm, returning the hot stock to the temperature of 150-180 ℃ above the beta transition temperature after the forging is finished, carrying out heat preservation, and recrystallizing for heat preservation time according to t = k 1 H is calculated, where k 1 K is a recrystallization holding factor 1 Controlling the value to be 0.4-0.8 min/mm, wherein h is the minimum section size of the blank, immediately discharging the blank after heat preservation is finished, and air-cooling the blank to room temperature;step 2.2: carrying out 1-upsetting-1-drawing deformation on the forging stock finished in the step 2.1 at the temperature of 30-50 ℃ below the beta transition temperature, controlling the upsetting deformation at 30-35%, forging the stock to the square, returning the hot material to the furnace to be 70-100 ℃ above the beta transition temperature after the forging is finished, carrying out heat preservation, and recrystallizing for heat preservation time according to t = k 2 H is calculated, where k 2 K is a recrystallization holding factor 2 Controlling the value to be between 0.5 and 0.9min/mm, immediately discharging the furnace after the heat preservation is finished, and air-cooling the furnace to the room temperature;step 2.3: carrying out 1 upsetting 1 drawing deformation on the forging stock finished in the step 2.2 at the temperature of below 30-50 ℃ and upsetting deformationControlling the temperature to be 25 to 30%, forging the blank to an eighth direction, after forging, returning the hot material to the temperature which is 30 to 50 ℃ higher than the beta transition temperature for heat preservation, and recrystallizing for heat preservation time according to t = k 3 H is calculated, where k 3 K is a recrystallization holding factor 3 Controlling the value to be between 0.6 and 1.0min/mm, immediately discharging the furnace after the heat preservation is finished, and air-cooling the furnace to room temperature;step 3), primary alpha phase spheroidizing and homogenizing:step 3.1: carrying out 1 upsetting 1 and 1 drawing deformation on the forging stock finished in the step 2) at the temperature of 30 to 50 ℃ below the beta transition temperature, wherein the upsetting deformation is controlled at 30 to 40%;step 3.2: carrying out hot drawing deformation on the forging stock finished in the step 3.1 for 1 to 3 times at the temperature of 30 to 50 ℃ below the beta transformation temperature, wherein the drawing deformation is controlled to be 25 to 35 percent;step 4), forging of finished products:and (4) performing 1-time rolling, shaping and forging on the blank finished in the step 3) at the temperature of below the beta transition temperature and 30-50 ℃, controlling the shaping deformation to be 15-20%, and forging the blank to a proper specification size.
- 2. The high-plasticity forging method for the Ti-1350 ultrahigh-strength titanium alloy large-specification bar according to claim 1, wherein the heating and heat-preservation coefficient is 0.5 to 0.7min/mm when the blank in the step 1) is charged into the furnace, and the heating and heat-preservation coefficient is 0.6 to 0.8min/mm when the blank in the steps 3) and 4) is charged into the furnace.
- 3. The high-plasticity forging method for the large-size Ti-1350 ultra-high-strength titanium alloy bar according to claim 1, wherein in the steps 1), 3) and 4), a one-stage heating mode is adopted for heating the blank each time, the blank is charged into a furnace at a warm temperature, and air cooling treatment is performed after forging.
- 4. The high-plasticity forging method for the large-size Ti-1350 ultrahigh-strength titanium alloy bar according to claim 1, wherein the upsetting forging rate in the step 1) is controlled to be 20 to 25mm/s, and the drawing forging rate is controlled to be 25 to 30mm/s; in the step 2), the step 3) and the step 4), the upsetting forging rate is controlled to be less than 3 to 8mm/s, and the elongation forging rate is controlled to be 20 to 25mm/s.
- 5. The high-plasticity forging method for the large-size Ti-1350 ultra-high-strength titanium alloy bar according to claim 1, wherein the blank is forged to eight directions after each fire forging in step 3.1.
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| CN117696669A (en) * | 2023-12-27 | 2024-03-15 | 北京钢研高纳科技股份有限公司 | Thin bar for Ti2AlNb alloy bolt and preparation method thereof |
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