JPS60230968A - Manufacture of rolled titanium alloy plate - Google Patents

Abstract

PURPOSE:To obtain a rolled Ti alloy plate of high reliability by carrying out recrystallization annealing in a rolling stage and cross rolling before and after the annealing so as to prevent the formation of a locally isometric crystal structure and to reduce the amount of alpha-phase. CONSTITUTION:The ingot of an alpha- or (alpha+beta)-Ti alloy is broken down and cross rolled (A) in the alpha+beta range at >=1.2 draft and 0.6-1.4 cross ratio. The resulting plate is subjected to recrystallization annealing (B) at the beta transformation point -20 deg.C--100 deg.C, and it is cross rolled (C) in the (alpha+beta) range at >=1.6 draft and 0.6-1.4 cross ratio. The stages B, C may be repeated once or more. By this method a Ti alloy plate having the isometric alpha-crystal structure with no anisotropy can be obtd. The Ti alloy plate has superior strength and ductility.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a titanium alloy rolled sheet, and in particular, cross rolling is performed before and after recrystallization annealing to produce an equiaxed titanium alloy sheet with excellent strength and ductility and no anisotropy. The present invention relates to a method for manufacturing a titanium alloy plate having an α-crystal structure.

Titanium alloys have a high specific strength slope and are excellent in corrosion resistance, so their use is gradually increasing in various types of equipment, including the aerospace field and even terrestrial instruments. Along with this, Ti-AI-V series, Ti-Al-8n yarn, Tl
-Mn yarn, 'i'1-AI-M n series, Ti-AI-M
Many titanium alloys, such as o-V series, have been developed.

Titanium alloy is one of the wheel processed materials, and although there are few reports on its dipping method, generally the structure is improved by rolling.
It is said that by processing as much as possible in the β range, an equiaxed α crystal structure with excellent mechanical properties can be obtained. Furthermore, in connection with structural products, it has been reported that uniform refinement of the structure can be achieved by combining structural processing at a certain processing rate or higher and heat treatment at a temperature in the β region (Japanese Patent Publication No. 1983- No. 8099). In relation to rolled materials,
It has been proposed to make the crystals isotropic and finer by combining at least 70% hot rolling with an equiaxed crystal formation process in which cooling and reheating are performed under specified conditions (Japanese Patent Application Laid-Open No. No. 58-25425).

However, in these methods, the α phase that is not equiaxed partially remains, which causes a problem in the reliability of the product. When manufactured according to this structure, there are significant variations in the structure in the longitudinal direction of dipping and in the cross section. Even when manufactured by rolling, the α phase of titanium alloy is hep
It is known that due to the crystalline structure, large mechanical anisotropy occurs in the rolling direction and the direction perpendicular to the rolling direction. Titanium alloys are used in harsh environments such as high temperatures, high corrosion, and high loads, so high reliability is required of the products.

Basically, the rolling method is more advantageous than the forging method in terms of product quality and manufacturing efficiency, and in order to meet the demands of this industry that will increase in the future, it is necessary to It is necessary to establish a titanium alloy rolling method that largely suppresses or eliminates the residual and does not cause mechanical anisotropy.

In response to these demands, the present invention has developed high-quality titanium that has greatly improved product reliability by reducing the alpha phase that does not form a local equiaxed heavy structure, and has greatly reduced mechanical anisotropy. The object of the present invention is to provide a method for manufacturing rolled alloy plates.

As a result of extensive grinding at 7°C, the present inventors found that: (1) By incorporating recrystallization annealing during rolling, the residual α phase that does not form a local equiaxed heavy structure is greatly suppressed; (2) It has been found that mechanical anisotropy can be greatly reduced by cross rolling. The recrystallization annealing and cross rolling described above must be carried out under specific ranges of temperature and stress conditions. In this way, by cross-rolling back and forth with recrystallization annealing in between, a titanium alloy with an equiaxed α-crystalline structure without locally remaining equiaxed heavy structures, without an α-phase, and without mechanical anisotropy. It becomes possible to manufacture plates. The resulting titanium alloy plate also has improved strength and ductility and can be used with high reliability in high load, high temperature and highly corrosive environments.

In summary, the present invention comprises the steps of: (A) cross-compressing an α-type or α+β-type titanium alloy at a ratio of 12 or more and a cross ratio of α6 to t4 in the α+β region after (a) breakdown; (B) Thereafter, a step of performing recrystallization annealing at a temperature between 20°C and 100°C below the β transformation point, and (C) further, a reduction ratio of 1.6 or more in the α+β region and a cross ratio α
Provided is a method for manufacturing a titanium alloy rolled sheet, which comprises a step of cross rolling under conditions 6 to 1.4, and then heat treatment such as annealing and solution aging treatment depending on the product use.

In order to further reduce the residual α phase that does not result in an anisotropic and equiaxed heavy structure, if necessary, perform the above (B) and (C).
It is also possible to add a step of repeating the step at least once.

The present invention will be explained in detail below.

The titanium alloys to be treated in the present invention are α-type and α+
Any β type may be used. Starting with Tl-6AI-4V, which is a typical α+β type practical alloy, Ti-
6AI-6V-28n.

T1-5AI-2,5V, TI-8Mn%, TI-4A
l-4Mn, Ti-4ATi-4AI-8, Ti-4A
Ti-4AI-4'lI is an example.

Titanium alloy rolled products start from the ingot breakdown process, in which the ingot is first produced by blooming rolling or forging.
After the rolling process, the product is finally rolled according to its purpose.
Dull treatment, solution treatment! Manufactured by performing heat treatment such as heat treatment. As mentioned above, what characterizes the present invention is the rolling process between the ingot breakdown process and the final heat treatment, which consists of the following three steps.

(A) Reduction ratio of 1.2 or more in the α+β region, Rips (
B) Reconsolidation at 20 to 100°C below the β transformation point (C
) Rolling ratio in the α+β region of 1.6 or more, cross ratio of 0.
6 to 1.4 cross rolling 12th floor Here, the rolling ratio and the cross ratio are defined as follows.

First, in step (A), the slab material that has undergone the ingot breakdown process, which is carried out at a reduction ratio of β transformation point or higher in the same direction as the J"1 final pass direction of rolling, undergoes Widmansteten formed in the ingot breakdown process. In order to store strain as a driving force to bring the alpha phase of the shape and the crystal electric field alpha phase generated at the prior beta grain boundaries closer to the equiaxed alpha crystal in the next (B) recrystallization annealing process, the rolling reduction ratio is 12 or more, and Cross rolling is carried out under the conditions of a cross ratio α6 to 14. In cross rolling, the rolling direction is changed by 90° and the rolled material is rolled by 4'l.
The first method is rolling. There is no particular temperature specification for the degree of compaction in the α+β range, but near the β transformation point, the material temperature may rise above the β transformation point due to processing heat, and if the temperature is too low, the processing Therefore, the temperature below the β-friendly point is preferably 50°C to 200°C. The higher the reduction ratio in this (A) stage, the more equiaxed α crystals will be formed in the next (B) stage. However, in this case, it is not necessary to make a completely equiaxed α crystal, and it is possible to destroy the Wittmann-Steten-like α phase and the grain boundary α phase to make it close to an equiaxed α crystal. Yes, and for that purpose, the rolling reduction ratio needs to be at least about 12. The upper limit of the reduction ratio depends on the type of alloy and the temperature, but it is possible to set it up to about 8 to 10 without causing cracks, and usually up to about 15 is sufficient for the reasons mentioned above. In order to eliminate anisotropy in the mechanical properties of the final product, cross rolling should be carried out from step (A). Cross rolling is performed only in stage (C), and (A)
Normal straight rolling at this stage can produce a certain effect, but in order to reliably produce high-quality products with less anisotropy, it is necessary to perform cross rolling from stage (A) onwards. It was 114 IuJi that it was good. The cross rolling ratio is carried out at a cross rolling ratio of 0.6 to 1.4. The closer the cross ratio is to 1, the more effective it is, and outside the above range, the purpose of cross rolling is lost. The (A) stage can be regarded as a pre-(IIli stage) in preparation for the final equiaxed α crystallization.

Subsequently, the material after cross rolling is heated at 20°C below the β transformation point.
undergo recrystallization annealing at temperatures from to 100°C. The β transformation point is determined by the alloy type, but for example, Ti-6AI-4V
For alloys it is about 1000°C, so 980-900°C
Annealing is carried out at a temperature within the range of °C. At temperatures higher than 20° C. below the β change If adjustment point, the proportion of the primary α phase becomes extremely low, deteriorating the mechanical properties of the final product. jl
On the k side, tea I! is lower than 100℃ below the β transformation point! In this case, the polycrystalline P polycrystal is not sufficiently applied to the axis α, and is ineffective. The annealing time may be sufficient to cause fine recrystallization and depends on the alloy type and temperature.

Equiaxed α to the extent that even stages (A) and (B) above alone
Although a titanium alloy plate that can be assembled into a mold can be obtained, it has been found that α phase that does not form an equiaxed product remains in some parts. The reduction ratio in stage (A) should be increased.
The number of remaining α phases that do not form an equiaxed structure will decrease slightly, but this will not be a fundamental solution;
Therefore, in the present invention, (c) cross-rolling is performed again on the L9th floor to sufficiently accumulate internal strain, and in the final heat treatment, equiaxed α crystallization is carried out. This greatly reduces the residual α phase that does not form an equiaxed structure. The effect becomes more pronounced when the rolling reduction ratio is at least 1.6, generally 2 or more, by performing cross rolling in the step (A), and the significance of cross rolling comes into play. What's more, recrystallization is better than simply cross-rolling! By performing cross rolling before and after the IfI stage, the occurrence of anisotropy can be further reduced. In stage (C) as well, the cross ratio needs to be within the range of 0.6 to t4, and the closer it is to 1, the greater the effect. The material temperature in the (C) stage is not particularly specified as long as it is in the α+β range, but as with the (A) stage, the β transformation point is preferably about 50 to 200°C.

When transitioning from the (B) stage to the (C) stage, the material may be cooled once to a crystalline state, or it may be directly cooled to the (C)J stage.
You may move to the second floor.

As explained above, the mechanism of suppressing the residual α phase that does not form an equiaxed structure in the present invention is that internal strain is stored in step (A) and the Wittmann-Steten-like α phase and grain boundary α phase are suppressed. In step (B), the internal strain is stored again, and in the subsequent final heat treatment, equiaxed α crystallization is performed twice. This is to eliminate as much as possible the remaining α phase that does not form an equiaxed structure. At the same time, cross rolling is performed before and after recrystallization annealing to achieve mechanical isotropy of the material. Cross rolling contributes not only to isotropy of the material but also to equiaxed α crystallization, and recrystallization annealing during cross rolling not only suppresses the remaining α phase that does not form an equiaxed structure, but also contributes to It also plays an important role in reducing polarity. In this respect, in the present invention, the superimposed effect of the combination of recrystallization annealing and cross rolling before and after recrystallization annealing achieves more complete elimination of the α phase that does not result in an equiaxed structure and the elimination of mechanical anisotropy. It will be done.

From this meaning, stage (A) → stage CB) → stage (C) →
As shown in step (B) → stage (C) → final heat treatment,
It will be appreciated that by repeating steps (B) and (C) at least once, the objectives of the invention may be more fully realized.

Example 1 and Comparative Examples Regarding Ti-6AI-4V, which is a typical practical alloy of α+β type, the following five tests were conducted on a slab with a thickness of 160 fins forged in the β region. Note that the β transformation point of this material was 1000°C.

(1) Process according to the present invention (Example 1) Reduction ratio 4.80 Cross ratio 0.99 (2) Case where only cross rolling is performed (Comparative Example 1) 950
°C heating rolling (160 fl → 25 dew) Reduction ratio 6.4
0 Cross ratio 1.00 (3) Straight rolling process (Comparative example 2) 950°C heat rolling (160 fins → 25 fins) Reduction ratio &40 Cross rolling None Rolling of (1), +2) and (3) through the above steps Each material was subjected to solution aging treatment as the final heat treatment. The solution aging treatment conditions are general conditions stipulated in the AMg standard: 955°C x 5hr water quenching, followed by 568°C
It was air-cooled for 6 hours at ℃.

Photo 1 shows the results of the subsequent observation of the MikuOMi of each material. The observation plane is a cross section parallel to the final rolling direction. The product produced by the process of the present invention shown in the photo (&) has a fine equiaxed α crystal structure. On the other hand, in the cross-rolling process and the straight-rolling process, α phases which do not form an equiaxed structure as seen in photographs (b) and (e) are observed here and there.

In addition, the tensile test results for each material are shown in Table 1.

[Brief explanation of the drawing]

Attached photos t'' {(a), (b) and (c) are Example 1, Comparative Example 1 twist ratio; bite example 2 Ode showing gold f-'i #jl weave {1; i mirror photo The name of the agent is Jinhiro Kurauchi,' Shisuke Hashi] clQ

Claims (1)

[Claims] 1) After ingot breakdown of an α-type or α+β-type titanium alloy, (A) cross-rolling the α-type or α+β-type titanium alloy at a reduction ratio of 12 or more and a cross ratio of 16 to t4 in the α+β region; B) Thereafter, a step of recrystallization annealing is performed at a temperature between 20"C and 100C below the β transformation point, and (C) further, a reduction ratio of 16 or more and a cross ratio of 0.
A method for manufacturing a titanium alloy rolled sheet, which comprises a step of cross rolling at a temperature of 6 to 4 t4, followed by heat treatment such as annealing and solution aging treatment depending on the product use. 2) After ingot breakdown of the α-type or α+β-type titanium alloy, (A) a step of cross rolling in the α+β region at a reduction ratio of 1.2 or more and a cross ratio of α6 to t4, and CB) then β 20°C to 100°C below transformation point
(C) Further, in the α+β region, the reduction ratio is 16 or more and the cross ratio α is
A step of cross-rolling at 6 to t4, and (D) a step of repeating steps (B) and (C) at least once, followed by heat treatment depending on the product use such as annealing and solution aging treatment. A method for manufacturing a titanium alloy rolled plate, the method comprising: