CN114147161A

CN114147161A - Drawing forging method for relieving anisotropy of ultrahigh-strength titanium alloy bar

Info

Publication number: CN114147161A
Application number: CN202111507733.0A
Authority: CN
Inventors: 张宏岭; 樊凯; 李超; 朱鸿昌; 邹金佃; 焦毅柱
Original assignee: Hunan Goldsky Titanium Industry Technology Co ltd
Current assignee: Hunan Goldsky Titanium Industry Technology Co ltd
Priority date: 2021-12-10
Filing date: 2021-12-10
Publication date: 2022-03-08
Anticipated expiration: 2041-12-10
Also published as: CN114147161B

Abstract

The invention relates to the technical field of metal thermal deformation forming, and particularly discloses a drawing and forging method for relieving anisotropy of an ultrahigh-strength titanium alloy bar, which is characterized in that in a forming and forging step in a free forging process, a forging blank forged in a two-phase region is drawn for 1-3 times at a temperature of 30-50 ℃ below a phase transition point, air cooling or hot material returning is carried out in the time of the times, then recrystallization treatment is carried out, and finally the forging blank subjected to recrystallization treatment is drawn. The invention effectively improves the recrystallization degree in the forming and forging process, thereby reducing the texture strength of beta crystal grains and relieving the anisotropy of finished bars.

Description

Drawing forging method for relieving anisotropy of ultrahigh-strength titanium alloy bar

Technical Field

The invention relates to the technical field of metal thermal deformation forming, in particular to a drawing forging method for relieving anisotropy of an ultrahigh-strength titanium alloy bar.

Background

At present, the high-strength and high-toughness titanium alloy generally adopts the same free forging mode as the conventional titanium alloy to complete the preparation of bars with various specifications, and the free forging process generally comprises four processes of single-phase region forging, low-high-low-high forging, two-phase region forging and forming forging. Although the application of the free forging method in the field of conventional high-strength and high-toughness titanium alloy is mature, the problems of large anisotropy difference, difficulty in meeting the standard requirement of transverse plasticity, low fracture toughness and the like of a finished bar are caused because the forming forging adopts large-forging-ratio net drawing forging after the two-phase region upsetting-drawing forging is completed.

The deformation resistance of ultra-high-strength titanium alloys (the strength is more than or equal to 1300 MPa) such as TC18 and the like is further increased relative to high-strength and high-toughness titanium alloys, and meanwhile, the recovery and recrystallization processes of the alloys are hindered by the enrichment of more alloy elements in beta grain boundaries, so that the anisotropy of the forged bars is aggravated by adopting the free forging method in the prior art; and the ultra-high-strength titanium alloy such as TC18 has low plasticity margin, so that the anisotropy is further increased, and the qualification rate of the ultra-high-strength titanium alloy is seriously reduced.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a drawing forging method for relieving the anisotropy of an ultrahigh-strength titanium alloy bar.

The invention mainly takes TC18 titanium alloy ingot as raw material, and the whole forging process comprises single-phase region cogging forging, low-high-low-high forging, two-phase region forging and forming drawing forging.

In order to achieve the purpose, the invention adopts the technical scheme that: a drawing forging method for relieving anisotropy of an ultrahigh-strength titanium alloy bar is characterized in that in a forming forging step in a free forging process, a forging blank forged in a two-phase region is drawn out for 1-3 times of heating at a temperature of 30-50 ℃ below a phase transition point, air cooling or hot material returning is carried out between the times of heating, then recrystallization treatment is carried out, and finally the forging blank subjected to recrystallization treatment is drawn out.

Further, the drawing forging method for relieving the anisotropy of the ultrahigh-strength titanium alloy bar is specifically realized by the following steps:

step 1), finishing single-phase region forging, low-high-low-high forging and two-phase region forging of the ultrahigh-strength titanium alloy cast ingot according to a conventional ultrahigh-strength titanium alloy free forging process;

step 2), forging the forging stock obtained by forging the two-phase region in the step 1) in T_βCarrying out 1-3 fire drawing at (30-50) DEG C, wherein the deformation of single fire drawing is 30-50%, air cooling or hot material returning is adopted in the time of pass, and air cooling or water cooling is carried out after forging;

step 3) carrying out recrystallization treatment on the forged blank obtained in the step 2), wherein the treatment mode is T_βHeating the bar at the temperature of 10-50 ℃, and performing drawing forging on the blank with the deformation of 0-25% after heating to realize recrystallization of the blank;

step 4), putting the forged blank obtained in the step 3) at T_βCarrying out 1-5 times of fire drawing at the temperature of (30-50) DEG C, wherein the deformation of the single time of fire drawing is 10% -40%, and the accumulated deformation of the bar is not lower than 30% in the stage;

and 5) rounding the forging blank obtained in the step 4), wherein the round-throwing elongation deformation amount is 10-20%, and finally the two-phase region forging bar with low anisotropy and fuzzy beta crystal boundary is obtained.

Further, the above steps 2) and 3) are a complete reconnection process, which is repeated N times to enter step 4), where N is an integer greater than or equal to 1.

Further, the heating coefficient in the step 2) is 0.3-0.7; the heating coefficient in the step 3) is 0.3-0.7; the heating coefficient in the step 4) is 0.6-0.7.

Compared with the prior art, the invention has the beneficial effects that:

according to the invention, the recrystallization treatment is carried out in the forming and forging process in the existing free forging process, so that the recrystallization degree in the forming and forging process is effectively improved, the texture strength of beta grains is reduced, and the anisotropy of finished bars is relieved.

Drawings

FIG. 1 is a comparison of a process line of the present invention with a prior art forging process line, wherein (a) is the forging process line of the present invention and (b) is the prior art forging process line;

FIG. 2 is a macroscopic structure and a macroscopic structure of the bar prepared in comparative example one (wherein the macroscopic structure is shown on the left and the macroscopic structure is shown on the right);

FIG. 3 shows the macrostructure and the macrostructure of the bar prepared in the first example of the present invention (in which the macrostructure is shown on the left and the macrostructure is shown on the right);

FIG. 4 is a macroscopic structure and a macroscopic structure of the bar prepared in the second embodiment of the present invention (wherein the macroscopic structure is shown on the left and the macroscopic structure is shown on the right);

FIG. 5 is a macroscopic structure and a macroscopic structure of the bar prepared in the third example of the present invention (wherein the macroscopic structure is shown on the left and the macroscopic structure is shown on the right);

FIG. 6 is a macroscopic structure and a macroscopic structure of the bar prepared in the fourth example of the present invention (wherein the macroscopic structure is shown on the left and the macroscopic structure is shown on the right);

FIG. 7 is a macroscopic structure and a macroscopic structure of the rods prepared in the fifth example of the present invention (wherein the macroscopic structure is shown on the left and the macroscopic structure is shown on the right).

Detailed Description

The invention will now be further described with reference to the accompanying drawings and specific embodiments. The following are only preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any equivalent or similar arrangement without departing from the spirit of the invention is intended to fall within the scope of the invention. And hereinafter: "o" refers to the thickness of a billet with a regular octagonal billet cross-section, and "o" refers to the diameter of a billet with a circular cross-section; "L" refers to the length of the billet; t is_βIs the phase transition point temperature.

The main reason for generating the anisotropy is that the difference of transverse and longitudinal grain boundary densities caused by the unidirectional elongation of beta grains in the drawing process of the bar is large, and the anisotropy can be effectively eliminated through dynamic recovery and dynamic recrystallization. However, in the two-phase region forging process, the dynamic recovery and dynamic recrystallization processes are influenced by the dislocation migration speed, and the dislocation migration is influenced by the pinning effect of the Coriolis gas clusters in the thermal deformation process (the mechanism of the effect is that alloy elements are dissolved into a Ti substrate in the form of solid solution or intermittent solid solution, and due to the difference of the atomic sizes of the alloy elements and basic elements, the lattice structure of the Ti substrate is distorted, and the distortion can form the migration of the Coriolis gas cluster pinning dislocations. Thus, in order to alleviate the anisotropy of the rod material, the effect of the Coriolis gas masses on the inhibition of dislocation glide must be reduced. The pinning effect of the Coriolis gas mass is negatively related to the diffusion speed of atoms in the alloy, so that the improvement of the diffusion speed of the atoms in the thermal deformation process is an effective means for improving the recrystallization level and relieving the anisotropy of the bar.

Comparative example 1 (namely TC18 titanium alloy bar conventional ultra-high strength titanium alloy free forging process)

Step one, smelting TC18 titanium alloy into a cast ingot with a phi 760mm specification;

step two, performing single-phase region cogging forging, low-high-low-high forging and two-phase region homogenization forging on the ingot obtained in the step one with reference to table 1, wherein the specification of the forged blank is 560 × Lmm;

table 1:

step three, the forged blank obtained in the step two is placed in T_βCarrying out 7 times of forming and drawing forging at the temperature of minus 40 ℃, wherein the specific technological parameters of each time of forming and drawing forging are shown in the following table 2, and finally drawing to obtain the final size phi 210 multiplied by Lmm;

table 2:

comparative example one bar finally prepared had a macrostructure and a macrostructure as shown in fig. 2, and mechanical properties as shown in table 2.

Example one

The drawing forging method for relieving the anisotropy of the ultrahigh-strength titanium alloy bar is specifically completed by the following steps:

step 1), preparing an ingot with the specification of phi 760mm according to the step one in the comparative example 1, and preparing a forging blank with the specification of 560X Lmm according to the step two in the comparative example 1;

step 2), the forging stock prepared in the step 1) is heated at T according to the heating coefficient of 0.6_βHeating at 40 ℃, then drawing the blank subjected to heating to 440mm x L after 1 heating and 40% net drawing amount, and air cooling after forging;

step 3), placing the forging stock prepared in the step 2) in T_βKeeping the temperature at +30 ℃ according to a heating coefficient of 0.5, drawing out 10 percent of net drawing length to 420mm multiplied by L after finishing heating for 1 fire time, and air cooling after forging;

step 4), the forging stock prepared in the step 3) is heated at T according to the heating coefficient of 0.6_βHeating at-40 ℃, then drawing the blank subjected to heating to 330mm x L with 1 fire time and 40% of net drawing amount, and air cooling after forging;

step 5), placing the forging stock prepared in the step 4) in T_βKeeping the temperature at +30 ℃ according to a heating coefficient of 0.5, drawing out 10 percent of net drawing length to 310mm X L after finishing heating for 1 fire time, and air cooling after forging;

step 6), placing the forging stock prepared in the step 5) in T_βHeating at-40 ℃ according to a heating coefficient of 0.6, subsequently drawing the blank subjected to heating to 260mm x L after 1 heating and 30% net drawing length, and air cooling after forging;

step 7), placing the forging stock prepared in the step 6) in T_βHeating at-40 ℃ according to a heating coefficient of 0.6Then, the blank after being heated is drawn to 260mm multiplied by L after 1 heating and 20 percent of net drawing length, and is air-cooled after being forged;

step 8), the blank prepared in the step 7) is placed in T_βHeating at-40 deg.C according to a heating coefficient of 0.6, then making round to phi 220mm × L, and machining to obtain the invented product with phi 210mm × L bar material.

Example two the final bar material prepared according to the example is shown in fig. 2, and the parameters of the fire technique and the anisotropy index of the final bar material are shown in the following table 3:

table 3:

example two

step 2), the forging stock prepared in the step 1) is heated at T according to the heating coefficient of 0.6_βHeating at 40 ℃, then drawing the blank subjected to heating to 440mm x L after 1-time heating and 40% of net drawing amount, and returning the forged hot material to the furnace;

step 3), the forging stock prepared in the step 2) is heated at T according to the heating coefficient of 0.3_βHeating at-40 ℃, then drawing the blank subjected to heating to 370mm x L with 1 fire and 30% of net length, and air cooling after forging;

step 4), placing the forging stock prepared in the step 3) in T_βKeeping the temperature at +30 ℃ according to a heating coefficient of 0.5, drawing out 10 percent of net drawing length to 350mm multiplied by L after finishing heating for 1 heating time, and air cooling after forging;

step 5), the forging stock prepared in the step 4) is heated at T according to the heating coefficient of 0.6_βHeating at-40 deg.C, and then passing the heated blank1 fire, 40 percent of net drawing length is drawn to 270mm multiplied by L, and air cooling is carried out after forging;

step 6), placing the forging stock prepared in the step 5) in T_βKeeping the temperature at +30 ℃ according to a heating coefficient of 0.5, drawing out 10 percent of net length of drawing to 260mm X L after finishing heating for 1 fire time, and air cooling after forging;

step 7), placing the forging stock prepared in the step 6) in T_βHeating at-40 ℃ according to a heating coefficient of 0.6, subsequently drawing the blank subjected to heating to 235mm L with 1 firing time and 20% of net length, and air-cooling after forging;

Example two the final bar material prepared according to the example is shown in fig. 2, and the parameters of the fire technique and the anisotropy index of the final bar material related to the example are shown in the following table 4:

table 4:

EXAMPLE III

step 3), placing the forging stock prepared in the step 2) in T_βKeeping the temperature at +30 ℃ according to a heating coefficient of 0.5, and drawing up to 420 ℃ after finishing heating by 1 fire time and 10 percent of net drawing-up amountmm multiplied by L, and air cooling is carried out after forging;

step 4), the forging stock prepared in the step 3) is heated at T according to the heating coefficient of 0.6_βHeating at-40 ℃, then drawing the blank subjected to heating to 300mm x L by 1 fire time and 40% of net drawing amount, and air cooling after forging;

step 5), placing the forging stock prepared in the step 4) in T_βKeeping the temperature at minus 40 ℃ according to a heating coefficient of 0.6, drawing out 30 percent of net drawing length to 260mm X L after finishing heating for 1 firing time, and air cooling after forging;

step 6), placing the forging stock prepared in the step 5) in T_βHeating at-40 ℃ with a heating coefficient of 0.6, subsequently drawing the heated blank to 235mm L with 1 firing and 25% net length, and air cooling after forging;

step 7), the blank prepared in the step 6) is placed in T_βHeating at-40 deg.C according to a heating coefficient of 0.6, then making round to phi 220mm × L, and machining to obtain the invented product with phi 210mm × L bar material.

The macrostructure and the macrostructure of the bar finally prepared by the above example are shown in fig. 5, and the technical parameters of each fire number and the anisotropy index of the final bar related to the example are shown in the following table 5:

table 5:

example four

step 3), placing the forging stock prepared in the step 2) in T_βKeeping the temperature at +30 ℃ according to a heating coefficient of 0.5, drawing out 20% of net length of drawing to 400mm X L after finishing heating for 1 fire time, and air-cooling after forging;

step 4), the forging stock prepared in the step 3) is heated at T according to the heating coefficient of 0.6_βHeating at-40 ℃, then drawing the blank subjected to heating to 310mm x L after 1-time heating and 40% of net drawing amount, and air cooling after forging;

step 5), placing the forging stock prepared in the step 4) in T_βKeeping the temperature at +30 ℃ according to a heating coefficient of 0.5, drawing out to 275mm x L after finishing heating by 1 fire time and 20 percent of net drawing amount, and air cooling after forging;

The macrostructure and the macrostructure of the bar finally prepared by the above example are shown in fig. 6, and the technical parameters of each fire number and the anisotropy index of the final bar related to the example are shown in the following table 6:

table 6:

EXAMPLE five

step 2) mixingThe forging stock prepared in the step 1) has a heating coefficient of 0.6 at T_βHeating at 40 ℃, then drawing the blank subjected to heating to 440mm x L after 1-time heating and 40% net drawing amount, and cooling by water after forging;

step 7), placing the forging stock prepared in the step 6) in T_βHeating at-40 ℃ according to a heating coefficient of 0.6, subsequently drawing the blank subjected to heating to 260mm x L after 1 heating and 20% net drawing length, and air cooling after forging;

The macrostructure and the macrostructure of the finally prepared bar are shown in fig. 7, and the technical parameters of each fire number and the final anisotropy index of the bar related to the embodiment are shown in the following table 7:

table 7:

combining examples one to five and comparative example 1, it can be seen that in the case where the cogging single-phase region forging, the low-high-low-high forging, and the two-phase region homogenization forging were the same:

comparing the third embodiment with the comparative example 1, in the drawing and forging process, the net two-phase drawing and forging is adjusted to increase the primary recrystallization forging, the recrystallization technological parameters are within the parameter range of the invention, the anisotropy of the prepared ultrahigh-strength titanium alloy bar is obviously improved, and the principle is as follows: after the high forging ratio is drawn out for the 9 th fire, the heat is preserved above T beta, the recrystallization process of the material is promoted, the elongated beta grains are converted into equiaxed polygonal grains again, the recrystallization uniformity is improved through small deformation, the difference of the grain boundary density between the transverse direction and the longitudinal direction of the bar is weakened, the crack initiation and the expansion difference between the transverse direction and the longitudinal direction of the bar are reduced, and the anisotropy of the bar is reduced.

According to the first embodiment and the third embodiment, two recrystallization and one recrystallization are selected in the drawing process, and the improvement effect of the two recrystallization on the anisotropy of the bar is more remarkable, and the principle is as follows: after two times of recrystallization, beta crystal grains of the blank are further refined on the basis of recrystallization again, and the finer crystal grains tend to be deformed through crystal grain rolling coordination in the drawing process instead of crystal grain drawing, so that the orientation of the crystal grains is reduced. Meanwhile, after the deformation of part of the two-phase region is adjusted to be recrystallization deformation, the net elongation in the forming process is reduced, and the improvement of anisotropy is facilitated.

According to the first embodiment and the second embodiment, the increase of the drawing length of the two-phase region before the recrystallization is beneficial to further improving the anisotropy of the ultrahigh-strength titanium alloy bar, and the principle is as follows: after the elongation of the two-phase region is increased, the accumulated deformation energy storage of the bar before recrystallization is increased, which is beneficial to more fully carrying out crystal re-connection.

According to the first and fourth examples, the effect of increasing the amount of deformation in the recrystallization stage on recrystallization was not significant because: the deformation during recrystallization improves the uniformity of the structure, but does not greatly affect the grain size.

According to the first embodiment and the fifth embodiment, the cooling mode of the two-phase zone drawing-out fire number before recrystallization is adjusted from air cooling to water cooling, so that the anisotropy of the ultrahigh-strength titanium alloy bar is further improved, and the principle is as follows: after the water cooling is adopted, the recovery effect of the structure in the cooling process is reduced, the accumulated deformation energy storage of the bar before recrystallization is increased, and the crystal re-connection is more fully performed.

Claims

1. A drawing forging method for relieving anisotropy of an ultrahigh-strength titanium alloy bar is characterized in that in a forming forging step in a free forging process, a forging blank forged in a two-phase region is drawn out for 1-3 times of heating at a temperature of 30-50 ℃ below a phase transition point, air cooling or hot material returning is carried out between the times of heating, then recrystallization treatment is carried out, and finally the forging blank subjected to recrystallization treatment is drawn out.

2. The drawing forging method for relieving the anisotropy of the ultrahigh-strength titanium alloy bar according to claim 1 is specifically realized by the following steps:

step 2), forging the forging stock obtained by forging the two-phase region in the step 1) in T_βCarrying out drawing at the temperature of (30-50) DEG C for 1-3 times of fire, wherein the deformation of the drawing at the single time of fire is 30-50%, air cooling or hot material returning is adopted in the fire, and air cooling or water cooling is carried out after forging;

3. The method for drawing and forging the ultrahigh-strength titanium alloy bar according to claim 2, wherein the step 2) and the step 3) are a complete re-joining process, and the process is repeated N times to enter the step 4), wherein N is an integer greater than or equal to 1.

4. The drawing forging method for relieving the anisotropy of the ultrahigh-strength titanium alloy bar according to claim 2, wherein the heating coefficient in the step 2) is 0.3-0.7; the heating coefficient in the step 3) is 0.3-0.7; the heating coefficient in the step 4) is 0.6-0.7.