CN108326041B - A kind of helical tapered roll isometric rolling method of large-size titanium alloy ultra-fine grained bar - Google Patents

Abstract

The invention discloses a spiral conical roller equidistant rolling method for large-size titanium alloy ultrafine crystal bars, which relates to the technical field of machining, in particular to a spiral conical roller equidistant rolling method for large-size titanium alloy ultrafine crystal bars, and comprises the following steps of S1 selecting titanium alloy blanks with the diameter D of 40-150mm and the length of 300-plus 5000mm, S2 placing the titanium alloy blanks in a heating furnace to be heated to 800-plus 1120 ℃, S3 transferring the heated titanium alloy blanks from the heating furnace to a guide chute of a skew rolling mill, S4 feeding the titanium alloy blanks in the guide chute of the skew rolling mill, feeding the titanium alloy blanks into a deformation area between an inlet and an outlet of the skew rolling mill, carrying out spiral motion of the titanium alloy blanks in the deformation area until the deformation is finished, S5 repeating the steps S2-S4, carrying out 2-8 times of spiral rolling on the titanium alloy blanks to obtain TC18 titanium alloy integral ultrafine crystal bars, and the invention has the advantages of large penetration depth of the deformation area, continuous multi-continuous and stable multi-torsion and severe rolling, and can obtain ideal three-dimensional composite grain thinning effect.

Description

A kind of helical tapered roll isometric rolling method of large-size titanium alloy ultra-fine grained bar

technical field

The invention relates to the technical field of mechanical processing, in particular to a spiral conical roller equidistant rolling method of a large-sized titanium alloy ultra-fine grain rod.

Background technique

When using plastic deformation to prepare nanoscale materials, its equivalent strain should usually be greater than 6, which is difficult to achieve by traditional plastic processing methods, but can be achieved by applying super plastic deformation method (Severe Plastic Deformation, SPD). Modern SPD began with the combined forming method of high pressure and shear deformation proposed by Bridgemen, and its rapid development began in the former Soviet Union and Western countries in the mid-1970s. Segal developed Equal-Channel Angular Pressing (ECAP), It marks the arrival of the microstructural era of SPD research. In the past 10 years, thousands of research results have been published publicly.

The generally accepted definition of SPD after 2006: a metal forming method that produces super large strain in the block without significantly changing the geometric size of the block, and presents the grain refinement effect of large-angle grain boundaries. 100-1000nm) and nanoscale (less than 100nm), can be called nano-SPD (referred to as nanoSPD). Because nanoSPD materials have a large number of large-angle non-equilibrium grain boundary structures with high density of dislocations and high internal stress, the materials exhibit mechanical behaviors and deformation mechanisms that are different from traditional coarse-grained materials.

Current existing processing technology solutions: typical SPD methods include High Pressure Torsion (HPT), equal channel angular press-ing (ECAP), and Accumulative Roll Bonding (ARB). ), torsional extrusion (Twist Extrusion, TE) and multi-directional forging (Multi-Directional Forging, MDF).

Among them, (1) high-pressure torsional deformation: apply several GPa pressure to the original sample (block or powder) placed in the support groove, and rotate the upper and lower anvils relatively, so that the sample undergoes strong shear deformation and refines the grains. The characteristic of high-pressure torsion is that the workpiece is disc-shaped and small in size, generally 10-20 mm in diameter and 0.2-0.5 mm in thickness.

(2) Equal-diameter angular extrusion deformation: The material is extruded from one end to the other end through two equal-section channels intersecting at a certain angle in the mold, and the change of the moving direction of the material by the bending angle causes it to produce pure shear deformation. The forming process can be repeated with the amount of shear strain increasing with the deformation pass.

(3) Cumulative stacking method: The original sheet is double-stacked after surface treatment, rolled and welded together after heating, and then cut from the middle and sent back to the surface treatment before the next rolling and welding cycle. The plates can be welded together, and the reduction in each pass shall not be less than 50%, but the ARB processing requires strong shear stress conditions, and lubricants cannot be used, which is detrimental to the service life of the rolls.

(4) Torsional extrusion: Beygelzime et al. proposed this process. This method is also a forming technology of grain refinement through shear deformation, extruding the columnar blank through a torsion die. Similar to HPT, there is a problem of uneven deformation, and the grain refinement effect is lower than that of ECAP and HPT.

(5) Multi-directional forging: This process obtains large deformation by changing the direction of free forging multiple times orthogonally. The grain refinement effect of such deformation is significantly lower than that of ECAP and HPT.

Another type of existing processing technology solutions: derivative methods. The basic forming principles are the same as the above methods, and many new SPD forming technologies are derived. These methods try to simplify tool design, reduce energy consumption, increase yield, increase workpiece size, and upgrade automation. etc., which include:

(1) ECAP derivative method: Repeated bending and straightening (RCS), the blank is placed between the bending devices, and as the upper die moves down, the blank is bent and becomes wavy; then two flat plates are used for straightening, Bending is performed again, and through repeated repetitions, sufficient deformation is accumulated and the material structure is refined without significantly changing the size of the blank.

(2) Cyclic closed die forging (CCDF), the die consists of a lower die of a certain section cavity and a punch of the same section that moves vertically in the cavity. A fully lubricated sample with graphite lubricant is placed in the lower die and heated to a certain temperature. The workpiece is pressed into the lower die by the punch, and after being taken out, it is rotated 90° around the Z axis in the same direction, and the lower die is reinserted to deform. In this way, the workpiece is rotated 90° around the Z axis between successive passes. In this way, 1, 3 and 5 compressions were experienced, respectively.

(3) Reciprocating extrusion (CEC), the die consists of two cavities, a compression belt and a punch placed in the two cavities. The cross-sectional areas of the two cavities are equal, and they are connected on the same axis by a compression belt in the middle. During the extrusion process, the sample reaches the compression belt under the action of the punch. At this time, the sample will be subjected to positive extrusion deformation, and the extruded workpiece will be upsetting under the action of the punch of another die cavity. deformed. Then, the punch on the other side pushes the workpiece back in reverse according to the above process to complete an extrusion cycle. The above process is repeated until the desired strain is obtained.

(4) The plate is continuously sheared and deformed. The device uses the upper die, the lower die and the lower roller to form two intersecting channels with a small difference in cross-sectional area. The plate is fed into the cavity, and the plate undergoes strong plastic deformation at the corner of the cavity, and is then extruded from the other side of the cavity. Grooves are machined on the surface of the feed roll to increase friction. Due to the fact that the cross-sectional area of the material remains unchanged before and after deformation, the plate can be repeatedly deformed in multiple passes in the same mold.

(5) Elliptical spiral equal channel extrusion method (ECEA), under the action of the extrusion force, the billet is subjected to upsetting (circle-ellipse transformation), torsion (elliptical cross-section twist) and reverse upsetting (ellipse —circle transformation) process changes back to round bar. The metal mainly produces plastic flow in the cross section and accumulates strain. The shape of the mold takes advantage of the particularity of the round and oval shape, and the cavity has no sharp corners, making the metal easy to flow. The combination of multiple deformation modes in one process is realized.

(6) Continuous Friction Angular Extrusion (CFAE), which drives the rollers to rotate and applies pressure P to the workpiece against its supports. The first extrusion channel is formed between the drive roll and the workpiece support, and the second channel is a short slot in the stationary die assembly. The sheet workpiece is processed one to eight times, and the maximum equivalent true strain can reach 5.3, and the sheet orientation is always kept constant.

A HPT-derived method suitable for high pressure torsion of tubes (HPTT), where the tube is located in a rigid disk, the mandrel is placed in the tube, and is compressed in its elastic state with a compressor. Due to the axial compression of the mandrel, it expands in the radial direction, and the expansion is limited by the tube and the disc, creating a large hydrostatic stress in the tube and creating a large friction force on both sides of the tube. Deformation of the tube is achieved by rotating the disk with external torque while keeping the mandrel stationary. During the torsion process, the deformation mode is local shear, the normal direction of the shear plane is the radial direction of the tube, and the shear direction is parallel to the circumferential direction.

A TE-derived method, superhigh torsion (STS), localizes the torsional strain (TS) region by localized heating and cooling that makes the region less resistant to deformation than the other two parts. Simultaneously with the creation of the TS zone, the rod is moved along the longitudinal axis, thus continuously producing super large plastic strains throughout the rod. This new process STS includes rods that create localized soft zones and regions of movement in the longitudinal direction relative to the rest of the rod. An important feature of STS is that the cross-sectional dimensions of the rod remain unchanged under strain.

There are relatively few patent reports on the ultrafine grain process of titanium alloys at home and abroad. In the patent [CN 103014574 A], Zhou Kechao et al. of Central South University mentioned a preparation method of TC18 ultra-fine grain titanium alloy, which mentioned detailed heat treatment and ultra-fine grain process parameters of multi-pass upsetting. This process uses multi-directional upsetting for deformation, which belongs to the traditional forging method. Due to the small range and penetration depth of the deformation zone in a single pass, in order to obtain an ultra-fine grain structure, more than 8-10 passes of repeated deformation are generally required. The period is long, the efficiency is low, and there is generally obvious deformation inhomogeneity.

Wang Liqiang et al. of Shanghai Jiaotong University mentioned in the patent [CN 103572186 A] a method for preparing ultra-fine-grained titanium-based composite materials by using equal-diameter curved channel deformation. This method has been proposed in the background of this patent, although severe plastic deformation can be repeated , but the deformed size is 10X10X100mm, which is difficult to meet industrial-grade needs. Du Suigeng of Northwestern Polytechnical University mentioned a preparation method of ultrafine-grained materials in the patent [CN 1446935 A]. This method mainly focuses on the generation of ultrafine grains on the surface. Although the degree of deformation is high and it can be repeatedly deformed, it is limited to the preparation of surface nanocrystals, and cannot achieve the overall ultrafine grain from the core to the surface.

Liu Guohuai et al. of Northeastern University mentioned a preparation method of an equal-thickness ultrafine-grained TC4 titanium alloy sheet in the patent [CN 107030111 A]. This method is similar to the cumulative stack rolling in the introduction of the patent background. This process requires strong shear stress conditions, the load is large, and the size conditions are limited. Only sheets can be prepared, but bars cannot be prepared. From the paper reports on the ultrafine grain process of titanium alloys, most of them use ECAP and HPT to deform titanium alloys. The size of the products involved is small, and it is difficult to produce large-sized bulk materials with industrial-grade overall ultrafine grains.

Comprehensive analysis shows that the titanium alloy ultra-fine grain processes mentioned in the existing patents or papers all use traditional HPT, ECAP and ARB methods to prepare small-sized uniform ultra-fine grain materials under extremely high loads. It is difficult to prepare large-scale materials with industrial-grade monolithic ultrafine grains by laboratory development.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a helical conical roll equidistant rolling method for large-sized titanium alloy ultra-fine grain bars, so as to solve the problems of limited size, large load and low efficiency proposed in the above background technology.

The present invention is a spiral conical roller equidistant rolling method of a large-size titanium alloy ultra-fine grain rod, comprising the following steps:

S1: Select a titanium alloy billet with a diameter D of 40-150mm and a length of 300-5000mm;

S2: Place the above titanium alloy billet in a heating furnace and heat it to 800-1120°C, and the heating time is: the diameter of the titanium alloy billet D×(0.6~0.8)min;

S3: Transfer the heated titanium alloy billet from the heating furnace to the guide trough of the skew rolling mill, and the transfer time is 5-20s;

S4: Feeding is carried out in the guide groove of the skew rolling mill, and the titanium alloy billet is sent to the deformation zone between the entrance and the exit of the skew rolling mill. The titanium alloy billet moves spirally in the deformation zone until the deformation ends, and the TC18 titanium with a diameter of Dm is obtained. Alloy bar and bar, where m is the number of rollings, the diameter of the TC18 titanium alloy bar obtained by rolling once is D1, the diameter of the TC18 titanium alloy bar obtained by rolling twice is D2, and so on;

S5: Repeat the above steps S2-S4, and perform 2-8 spiral rolling on the titanium alloy billet to obtain a TC18 titanium alloy integral ultra-fine grain rod;

The skew rolling mill is a two-roll skew rolling mill, the rolls are all single-tapered rolls, the rolls are provided with spiral grooves, and the precession direction of the spiral grooves is the same as the precession direction of the titanium alloy billet rolling process, The cone angle γ1 is 17-19 degrees, and the arc radius r of the roll bite into the titanium alloy billet is 60-400mm, the roll feeding angle α is 19-21 degrees, and the rolling angle β of the roll is 17-19 degrees. The roll distance Dg between each roll is 87%-95% of the diameter D of the titanium alloy billet, and the roll speed n is 30-55r/min;

The titanium alloy blank is a large-sized TC18 titanium alloy bar;

The heating time of the repeated rolling process in the S5 step is the diameter of the TC18 titanium alloy bar Dm×(0.3-0.4) min.

Preferably, the small end face of the roll is set as a circular arc surface, and the radius of the circular arc surface is 60-400 mm.

Preferably, the pass ovality coefficient is the ratio of the guide plate distance D _d to the roll distance Dg. In step S4, the titanium alloy billet is rolled in the deformation zone with a pass ovality coefficient of 1.25-1.4.

Preferably, in the process of rolling the titanium alloy billet, the roll distance Dg between the two rolls is fixed, which is beneficial to realize multiple passes of repeated rolling.

Preferably, the pitch ι of the helical rolling groove is 6-15mm, and the tooth height h is 6-15mm.

Preferably, during the repeated rolling process in step S5, the shape of the deformation zone remains unchanged.

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

(1) The deformation zone has a large penetration depth, and a large-scale overall ultra-fine grain structure can be obtained. The plastic deformation inside the material during skew rolling consists of two parts, one is the compression deformation between the rolls, which is periodic intermittent deformation, and the other is the continuous torsional deformation. The superposition of compression and torsion deformation produces three-dimensional severe plastic deformation in the deformation zone during the skew rolling process, which is obviously different from that of conventional forging; (2) The diameter of the bar remains unchanged before and after skew rolling, and multi-pass rolling can be performed. There is widening in the skew rolling process, and the equivalent diameter in the cross section of the superalloy billet remains unchanged; (3) continuous and stable local deformation, the rolling load is small, and the deformation process is stable. During the skew rolling process, the actual contact area between the workpiece and the superalloy billet is only a small part of the surface area of the superalloy billet, which is a local contact deformation, so the load is small; (4) The compression-torsion composite three-dimensional severe deformation can obtain ideal grains Refinement effect.

Description of drawings

Figure 1 is a schematic diagram of the roll of the present invention.

Figure 2 is a schematic diagram of the original structure grains.

FIG. 3 is a schematic diagram showing that the number of rollings is 2 in the first embodiment of the present invention.

FIG. 4 is a schematic diagram showing that the number of rollings is 6 times in the first embodiment of the present invention.

Fig. 5 is the relative position of each die during the skew rolling process of the present invention.

FIG. 6 is a plan view of the relative positions of the dies during the skew rolling process of the present invention.

FIG. 7 is a left side view of the relative positions of the various dies during the skew rolling process of the present invention.

FIG. 8 is a schematic diagram of the deformation zone during the skew rolling process of the present invention.

Reference numerals: 1-roller, 2-titanium alloy billet, 3-guide plate.

Detailed ways

The present invention is a spiral conical roller equidistant rolling method of a large-size titanium alloy ultra-fine grain rod, comprising the following steps:

S1: Select a titanium alloy blank 2 with a diameter D of 40-150mm and a length of 300-5000mm;

S2: Place the above-mentioned titanium alloy billet 2 in a heating furnace and heat it to 800-1120°C, and the heating time is: the diameter of the titanium alloy billet 2 × (0.6~0.8) min;

S3: transfer the heated titanium alloy billet 2 from the heating furnace to the guide groove of the skew rolling mill, and the transfer time is 5-20s;

S4: Feeding is carried out in the guide groove of the skew rolling mill, and the titanium alloy billet 2 is sent into the deformation zone between the entrance and the outlet of the skew rolling mill. TC18 titanium alloy bar and bar, where m is the number of rollings, the diameter of the TC18 titanium alloy bar obtained by rolling once is D1, the diameter of the TC18 titanium alloy bar obtained by rolling twice is D2, and so on;

S5: Repeat the above steps S2-S4, and perform 2-8 spiral rolling on the titanium alloy billet 2 to obtain a TC18 titanium alloy integral ultra-fine grain rod;

The skew rolling mill is a two-roll skew rolling mill, the rolls 1 are all single-conical rolls 1, the roll 1 is provided with a spiral groove, and the precession direction of the spiral groove is the same as that of the titanium alloy billet 2 during the rolling process. The precession direction is the same, the cone angle γ1 is 17-19 degrees, the arc radius r of the roll 1 biting into the titanium alloy billet 2 is 60-400mm, the feeding angle α of the roll 1 is 19-21 degrees, the rolling of the roll 1 is 19-21 degrees. The rolling angle β is 17-19 degrees, the roll distance Dg between the two rolls 1 is 87%-95% of the diameter D of the titanium alloy billet 2, and the rotational speed n of the roll 1 is 30-55r/min;

The titanium alloy blank 2 is a large-sized TC18 titanium alloy bar;

The heating time of the repeated rolling process in the S5 step is the diameter of the TC18 titanium alloy bar Dm×(0.3-0.4) min.

The small end face of the roll 1 is set as an arc surface, and the radius of the arc surface is 60-400mm.

The pass ovality coefficient is the ratio of the guide plate distance D _d to the roll distance Dg. In step S4, the titanium alloy billet 2 is rolled with a pass ovality coefficient of 1.25-1.4 in the deformation zone.

During the rolling process of the titanium alloy billet 2, the roll distance Dg between the two rolls 1 is fixed, which is beneficial to realize multiple passes of repeated rolling.

The pitch ι of the helical rolling groove is 6~15mm, and the tooth height h is 6~15mm.

During the repeated rolling process in step S5, the shape of the deformation zone remains unchanged.

In the present invention, the small end face of the roll 1 is an arc surface, which can quickly change the cylindrical titanium alloy billet 2 into an elliptical cylinder, providing sufficient deformation for constant roll gap spiral rolling; the main shape of the roll 1 is a single cone , the taper angle is equal to the rolling angle. Compared with the ordinary roll 1, the length of the outer diameter compression deformation zone is increased to 2 times the length. Rolling with a larger ellipticity coefficient, after the titanium alloy billet 2 is pulled into the roll 1, the cross section becomes an ellipse. During the spiral advancement process, since the radius of the long axis of the ellipse is greater than the distance between the rolls 1, the titanium alloy billet 2 has been subjected to the roll. The small deformation amount of 1 is compressed, and the deformation zone rotates one circle at any point, and is compressed twice by the roll 1; the spiral rolling can be repeated many times. The resulting rolled piece can be repeatedly rolled under the same deformation parameters, so that a larger amount of deformation can be obtained; by using a large feed angle and a large rolling angle, a more stable helical forward power can be obtained, so that the To meet the needs of large plastic deformation, and through the assisted deformation of the helical rolling groove on the tapered roll, on the basis of the original deformation, a small range of compression and bending shear deformation is superimposed, and finally super large plastic deformation is realized, and the grain refinement is achieved. the role of particles.

Generally, the type of material processing is distinguished by the recrystallization temperature. Above the recrystallization temperature is hot processing, and below the recrystallization temperature is cold processing. In the existing technology, cold processing is used to prepare ultrafine grains. Small grains, but such grains have poor thermal stability and cannot be heat treated. The purpose of this patent is to obtain grains that can be heat treated, that is, to obtain ultrafine grains by means of recrystallization by accumulating large deformation, thereby distinguishing them from traditional cold working.

Therefore, this patent provides a realistic choice for the industrialized preparation of large-sized TC18 integral ultra-fine grained rods.

Example 1:

Using the above technical parameters, the design and processing of the spiral rolling roll 1 is shown in Figure 1;

S1: Titanium alloy TC18 is selected as the main deformation parameters, the diameter D is 100mm, and the length is 800mm; the bite arc radius r of the spiral roll 1 is 60mm, the taper angle γ1 of the tapered roll is 18°, and the feeding angle α is 20°. The rolling angle β is 18°, the pitch ι of the spiral roll 1 is 13 mm, the tooth height h is 9 mm, the pitch Dg of the rolling roll 1 is 88% of the diameter D of the billet, the ellipticity coefficient is 1.25, and the rotational speed n of the roll 1 is 32 r/min;

S2: Heat the titanium alloy cylindrical billet to 850°C in a heating furnace, and the heating time is 80 minutes;

S3: Transfer the heated billet from the heating furnace to the guide trough of the skew rolling mill, and the transfer time is 10s;

S4: The billet moves spirally in the deformation zone until the deformation ends;

S5: Repeated rolling 2 times and 6 times sampling analysis, it has a significant effect on the grain refinement of titanium alloy, the grain size is small, and the heating time of the repeated rolling process is: TC18 titanium alloy bar diameter Dm × (0.3 ~0.4) min, where m is the number of rollings, the diameter of the TC18 titanium alloy bar obtained by rolling once is D1, and rolling twice is to use the TC18 titanium alloy bar with a diameter of D1 as the billet for re-rolling, The diameter of the obtained TC18 titanium alloy bar is D2, and so on. During the re-rolling process, the shape of the deformation zone remains unchanged.

Based on the above example, the original structure is shown in Figure 2. In the figure, β grains are dominant, and the average size of the β grains is 80um. The method of the present invention is adopted. Figure 3 is a typical titanium alloy grain diagram with 2 rolling times. , the grain size is about 8um, and the grain refinement degree is 90%; Figure 4 is the grain diagram of the titanium alloy with 6 rolling times, in which the grain size is about 2.5um, and the grain refinement degree is 96.88%. . The working principle is shown in FIG. 8 , and the positional relationship between the roll 1 and the guide plate 3 is shown in FIG. 5 , FIG. 6 and FIG. 7 .

To sum up, the present invention provides a method for rolling a large-size TC18 titanium alloy integral ultra-fine-grained bar with helical tapered rolls with equal roll spacing, by designing the shape of the helical tapered rolls and maintaining the roll spacing in the deformation zone. Unchanged, the pass ovality coefficient in the super deformation zone is used for repeated multi-pass rolling, and the super plastic deformation is gradually accumulated; moreover, this method can carry out multi-pass spiral rolling. For different types of titanium alloys, the rolling times are Within the range of 2-8, the effect on grain refinement of titanium alloy is the best, and the overall ultrafine grain size obtained is the smallest. This process is suitable for continuous severe plastic deformation of titanium alloy bars of various sizes and types under low load. It is used to prepare the overall fine-grained/ultra-fine-grained rods of 1000~3000nm. It can overcome the shortcomings of the existing severe plastic deformation process that the load is large and only small-sized workpieces can be processed.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (5)

1. a helical conical roller equidistant rolling method of a large-size titanium alloy ultra-fine grain rod, is characterized in that, comprises the following steps: S1: Select a titanium alloy billet (2) with a diameter D of 40-150mm and a length of 300-5000mm; S2: Place the above titanium alloy billet (2) in a heating furnace and heat it to 800-1120°C, and the heating time is: the diameter of the titanium alloy billet (2) D × (0.6~0.8) min; S3: transfer the heated titanium alloy billet (2) from the heating furnace to the guide trough of the skew rolling mill, and the transfer time is 5-20s; S4: Feeding is carried out in the guide groove of the skew rolling mill, and the titanium alloy billet (2) is fed into the deformation zone between the entrance and the exit of the skew rolling mill, and the titanium alloy billet (2) spirally moves in the deformation zone until the deformation ends to obtain the diameter is the titanium alloy bar of Dm, where m is the number of rollings; S5: Repeat the above steps S2-S4, and perform 2-8 spiral rolling on the titanium alloy billet (2) to obtain a TC18 titanium alloy integral ultra-fine-grained bar; The skew rolling mill is a two-roll skew rolling mill, the rolls (1) are all single-conical rolls (1), the rolls (1) are provided with a spiral groove, and the screw precession direction of the spiral groove is the same as that of the titanium alloy blank ( 2) During the rolling process, the precession direction is the same, the taper angle γ1 is 17-19 degrees, and the arc radius r of the roll (1) biting into the titanium alloy billet (2) is 60-400mm, and the roll (1) feeds The angle α is 19-21 degrees, the rolling angle β of the roll (1) is 17-19 degrees, and the roll distance Dg between the two rolls (1) is 87%-95% of the diameter D of the titanium alloy billet (2). , the speed n of the roll (1) is 30-55r/min; The titanium alloy blank (2) is a large-sized TC18 titanium alloy bar; In the step S5, the heating time of the repeated rolling process is the diameter of the TC18 titanium alloy bar Dm × (0.3-0.4) min; During the rolling process of the titanium alloy billet (2), the roll distance Dg between the two rolls (1) is fixed. 2. A method for equidistant rolling of a large-size titanium alloy ultra-fine grained rod with helical conical rolls according to claim 1, wherein the small end face of the roll (1) is set as a circular arc surface, and the circular The arc radius is 60-400mm. 3. the helical conical roller equidistant rolling method of a kind of large-size titanium alloy ultrafine grain rod as claimed in claim 1, it is characterized in that, pass ellipticity coefficient is the ratio of guide plate distance D _d and roll distance Dg , in step S4, the titanium alloy billet (2) is rolled in the deformation zone with a pass ovality coefficient of 1.25-1.4. 4. the helical conical roller isometric rolling method of a kind of large-size titanium alloy ultra-fine grain rod as claimed in claim 1, it is characterized in that, the pitch ι of described helical rolling groove is 6～15mm, and the tooth height. h is 6~15mm. 5 . The method for equidistant rolling of a large-size titanium alloy ultrafine-grained bar according to claim 1 , wherein the shape of the deformation zone remains unchanged during the repeated rolling process in step S5 . 6 .

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