JPS61250138A - Titanium alloy excelling in cold workability - Google Patents

Abstract

PURPOSE:To obtain a beta single phase-type Ti alloy having improved cold workability by incorporating, as principal components, specific amounts of V, Al, Cr, Fe and Mn to Ti. CONSTITUTION:The Ti alloy consists of, by weight, 8-25% V, 0.5-5% Al, <1.0% Cr, <=1.0% Fe, <=1.0% Mn and the balance essentially Ti, whose hardness after solution heat treatment is limited to <=HrC25. In this way, cold workability can be improved. Moreover, if necessary, when 0.01-3.0% REM and <=5%, in total, of >=1 kind among 0.01-1.0%, each, of Ca, S, Se, Te, Pb and Bi are incorporated to the above composition, machinability can be improved besides cold workability. This Ti alloy can be used in various fields such as material for space planes, automobile material, material for machine structural use, biomaterial, material for general civilian goods, and the like.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention can be used as materials for spacecraft, automobiles, mechanical structural parts, biological materials, materials for general civilian use, etc. This invention relates to a titanium alloy with excellent cold workability.

(Prior Art) Titanium alloys have the same strength as steel and are lightweight, so they have been commonly used as materials for spacecraft. In addition, recently, it has begun to be used as a material for automobiles, a material for mechanical structural parts, a biomaterial, a material for general civilian use, etc.

Among the titanium alloys that have been developed in the past, those with various chemical compositions.

Ti-6A-4V alloy is the most commonly used titanium alloy because it has stable mechanical properties and is easy to use. However, this titanium alloy
Since it contains approximately 80% α phase having a hexagonal crystal structure with low deformability, cold working of 25% or more is difficult.

For this reason, single-phase β-phase titanium alloys having a body-centered cubic crystal structure with good cold workability are attracting attention. As this β phase single phase type titanium alloy, for example, Ti-11,5
%Mo-6%Zr-4,5%Sn.

Ti-13%v-11%Cr-3%AJL, Ti-10
%V-2%Fe-3%Al, etc.

(Problems to be Solved by the Invention) However, although the conventional β-phase single-phase titanium alloy exemplified above can be cold-worked up to about 70%, its hardness is quite high at about HRC 30 or more. Therefore, when cold forging is performed, the life of the mold is short, and when cold wire drawing or cold rolling is performed, seizure with dies and rolls is likely to occur.

This invention was made by focusing on these conventional problems, and the hardness after solution treatment is quite low, approximately HRC25 or less, and when cold forging is performed, the life of the mold is long, and the hardness is very low. The object of the present invention is to provide a β-phase single-phase titanium alloy that is less likely to seize with dies or rolls during wire drawing or cold rolling, and has excellent cold workability.

[Structure of the Invention] (Means for Solving the Problems) The β-phase single-phase titanium alloy according to the present invention has, in weight%,
V: 8-25%, Al: 0.5-5%, Cr: 1.
less than 0%, Fe: 1.0% or less, Mn: 1.0% or less,
and 0.01-3.0% REM and 0.01% as required. O2N2.0% Ca, S, Ss, Te, Pb
, a total of 5% or less of one or more of Bi,
The remaining portion is substantially composed of Ti, and is characterized by being a β-phase single-phase titanium alloy with excellent cold workability.

The reasons for limiting the component range (wt%) of the β-phase single-phase titanium alloy excellent in cold workability according to the present invention will be explained below.

v: 8-25% (2) is the most important element in the present invention.

In order to improve the cold workability of titanium alloys, it is essentially necessary to form a single-phase β-phase structure, but such a single-phase β-phase structure can be improved by adding β-stabilizing elements. achieved. As this β stabilizing element, ' M
o, V, Ta.

There are metal elements such as Nb, Fe, Cr, and Mn, but among these, a β-phase single-phase alloy with low strength is formed only when Mo and V are added; other elements create a β-phase single-phase alloy. When it is made into a microstructure, the hardness becomes larger than HRC25 and cold workability decreases. Furthermore, MO has a high melting point, so it is not easy to manufacture and is expensive, making it impractical.

Therefore, the inventor of the present invention conducted numerous experiments on many of these β-stabilizing elements, and as a result found that only (2) is an element that can improve cold workability without increasing hardness. In these experiments, for example, the relationship between the amount of V added during Ti synthesis and the hardness after solution treatment was investigated.

That is, by button arc melting, T i −4+
Various titanium alloys based on 5%/1l-0.3%Cr and varying the V content were melted into 100g ingots, which were then rolled into straight bars with a diameter of 10mm. For the bar, 900”OXo, 5
Solution treatment was performed under the condition of heating for a time and then cooling with water, and the hardness and cold workability after the solution treatment were examined.

FIG. 1 shows the relationship between the amount of V added to the Ti-4,5%A1-0.3%Cr alloy and the hardness after solution treatment.

As shown in FIG. 1, the hardness decreases as the amount of () added increases, and when the amount added exceeds 8%, the hardness falls below the target HRC of 25. The decrease in hardness continues until the amount of V added is about 20%, and becomes saturated above this point.

Also, in Figure 2, the diameter is 6 mm x length 11.5 mm.
In Figure 2, which shows the results of a compression test conducted using a specimen of The height is h)]), and the larger this value is, the less likely it is that cracks will occur during cold working.

As shown in FIG. 2, it can be seen that as the amount of V added to the Ti-4°5%A composition increases, the cold workability improves.

As shown in FIGS. 1 and 2, the amount of V added to the titanium alloy is determined from the viewpoint of lowering the hardness after solution treatment and improving cold workability. A more desirable addition amount of (1) is determined by the content of Cr, which is a β-stabilizing element, and is set in the range of 8 to 25% in the titanium alloy according to the present invention. In other words, as is clear from the above, if ■ is less than 8%, α phase remains in the alloy, resulting in poor cold workability, and if it exceeds 25%, age hardening does not occur, resulting in a high temperature during use. Strength cannot be obtained.

A = 0.5 to 5% β-phase single-phase titanium alloys are normally used by cold working after solution treatment and then age hardening treatment, but the addition of AQ requires the aging treatment. Increases later ductility. This effect is particularly well observed at 0.5 to 3.5%.

On the other hand, the effect of Al addition on the hardness of titanium alloy was investigated. That is, Ti-18% by button arc melting
Various titanium alloys based on V-0.3% Cr and varying amounts of Ai were melted into 100g ingots, which were then rolled into straight bars with a diameter of 10mm. Solution treatment was performed under conditions of heating at 700° C. for 0.5 hour and cooling with water, and the hardness after the solution treatment was examined. The results are shown in FIG.

As shown in FIG. 3, it is clear that the hardness increases as the Al content increases. therefore.

If the amount of Al added is too large, only the hardness increases and no improvement in ductility is observed.

By the way, in order to provide a β-phase single-phase titanium alloy at a low cost, it is effective to use Ti-6%AR-4%V scrap as a raw material.

Therefore, the ductility is improved by adding Al as described above.

Due to increased hardness and manufacturing costs.

The amount of Al added was in the range of 0.5 to 5%.

Cr: less than 1.05 Cr is a β-stabilizing element and is effective in changing the crystal structure of the base to a body-centered cubic crystal, but in order to lower the hardness after solution treatment, it is better to use as little as possible. desirable, but
As mentioned above, it has the effect of stabilizing the β phase, so
It is acceptable up to less than 1.0%.

Fe: 1.0% or less, Mn: 1.0% or less, Fe and Mn are both β-stabilizing elements and are effective in changing the crystal structure of the base to a body-centered cubic crystal, but solution treatment In order to reduce the subsequent hardness, it is preferable to reduce the amount as much as possible.However, as mentioned above, the effect of stabilizing the β phase is as follows: When ■ is 1, Mn is 2.4. Fe is 4.3
This is because both of them are larger than V and are also cheaper, so adding them in combination has a great economic effect.

Up to 1.0% of each is acceptable.

REM (One or more rare earth elements = 0.01
~3.0% One or more of Ca, S, Se, Te, Pb, Bi: 0.01~1.0% Total of REM, Ca, S, Se, Te, Pb, Bi: 5
% or less REM, Ca, S, Se, Te, Pb, and Bi are all effective elements for improving the machinability of titanium alloys.

Among these, rare earth elements REM (especially Sc.

Y and lanthanide series (atomic numbers 57-71)
has the effect of forming stable compounds with S, Se, Te, etc., making inclusions granular, improving toughness and ductility, and improving machinability. In order to obtain such an effect, it is contained in an amount of 0.01% or more as necessary. However, if it is contained in a large amount, it will reduce the corrosion resistance and strength of the titanium alloy.

It needs to be 3.0% or less. Also, Ca is S, Se
It is effective in creating stable compounds with Te, Te, etc., controlling the morphology of inclusions, and improving the toughness and machinability of titanium alloys. Contain 0.01% or more. However, if it is contained in a large amount, the corrosion resistance and fatigue strength of the titanium alloy will be reduced, so it is necessary to keep it at 1.0% or less. Furthermore, S
, Se, Te, Pb, and Bi are elements that improve the machinability of titanium alloy as described above, and in order to obtain such an effect, they are contained in an amount of 0.015 or more as necessary. However, if the content is too large, the hot workability of the titanium alloy will be significantly reduced, so each content is set at 1.0% or less. These machinability improving elements are REM, Ca, S, Se, and Te.

If the total amount of Pb and Bi is too large, the corrosion resistance, strength, hot workability, etc. of the titanium alloy will be reduced, so the total amount of these must be 5% or less.

(Example) Kan 1 Yi senju & tortured prince ^ Yotsuso Δtameru ppr (Plas
ma Progressive casting
) Smelted in a furnace, forged into a round bar with a diameter of 50 mm after ingot formation, and then solution treated (heated at 800°C for 0.5 hour and then water cooled)
The test material was prepared by applying the following steps.

Next, the hardness of each sample material after solution treatment was measured, and a machinability test for evaluating machinability and a compression test for evaluating cold workability were conducted. Among these, the hardness was measured using the Rockwell C scale. In addition, the machinability test was conducted under the conditions shown in Table 2, and the 1000mm life speed under these conditions was determined, and the comparison was made when the value of the conventional material 6% Al-4% V-Ti alloy was set as 100. In other words, the drill life speed ratio was evaluated. Furthermore, in the compression test, as shown in Figure 4, the cold workability was evaluated by determining the deformation resistance when compressing a specimen with a diameter of 6 mm and a height of 11.5 mm to a height of h). did.

The results of hardness measurement and machinability test are shown in Table 1, and the ratio 1
The results of the I11 test are shown in FIG.

Table 2 As shown in red in Table 1, the titanium alloy according to the present invention (No.
, 1 to 11), the hardness after solution treatment is HR
C25 or less, and according to the compression test results shown in FIG. 5, the titanium alloys (Nos. 1 to 3) according to the present invention are conventional materials Ti-6All-4V CNo.

12) OJ: and Ti-13V-11Cr-3Al(N
This shows that the deformation resistance is considerably lower than that of 13), and cracks are less likely to occur on the surface. That is, the titanium alloys (Nos. 1 to 3) according to the present invention have extremely good cold workability, and as shown in Table 1, have a low drill life speed ratio and excellent machinability. . Further, in the titanium alloy according to the present invention, R
E.M.

In the case of alloys (No. 4 to 11) containing one or more of Ca, S, Se, Te, Pb, and Bi (7), the fifth
As shown in the figure, surface cracks and haze are more likely to occur, but the conventional material Ti-6A-4V (N
The drill life speed ratio is considerably higher than the conventional material (No. 12.13), which improves not only cold workability but also machinability. It is extremely excellent.

Next, the age hardening characteristics of the titanium alloys shown in No. 7 in Table 1 were investigated. The results are shown in FIG.

As shown in Figure 6, the hardness of this titanium alloy increases when it is subjected to solution treatment and then aging treatment at temperatures above 700°C, and the increase in hardness is greatest when the aging temperature is 400°C. If the solution treatment temperature is 900℃, HR
It was confirmed that the C16 material had an HRC of 34 and had excellent cold workability after solution treatment, as well as high strength after aging treatment. It was also confirmed that when cold working was performed after solution treatment, the hardness after aging treatment was further increased by the amount of hardness due to cold working.

[Effects of the Invention] As explained above, the β-phase single-phase titanium alloy according to the present invention has v: 8 to 25%, Jl: 0 in weight%.
．． 5-5%, Cr: less than 1.05.

Fe: 1.0% or less, Mn: 1.0% or less, and if necessary, 0.01 to 3.0% REM and 0.0%
1-1.0% Ca, s, se.

One or two of T e , P b , B i
Since it is composed of less than 5% Ti in total and the remainder is substantially Ti, it has significantly superior cold workability compared to the currently used Ti-6AJL-4V, and when cold worked. It has a long mold life, is less likely to seize with dies and rolls during cold wire drawing or cold rolling, and is extremely superior in the manufacturability of parts and products. Therefore, by taking advantage of titanium alloy's features such as light weight, corrosion resistance, and high strength, it can be used in a wide range of fields such as aerospace materials, automobile materials, mechanical structural materials, biomaterials, and materials for general civilian use. For example, more specifically, a valve in an automobile engine.

By applying it to valve retainers, valve springs, eyeglass frames, etc., it is possible to obtain the advantages of being lightweight and strong, and the cost advantages of good manufacturability. has excellent effects.

[Brief explanation of the drawing]

Figures 1 and 2 are Ti-4,5%AJI-0,3%
A graph showing an example of the results of investigating the relationship between V content, hardness, and critical compressibility of a Cr-based titanium alloy,
Figure 3 is a graph showing an example of the relationship between the AfL content and hardness of a titanium alloy based on Ti-18%V-0.3%Cr. An explanatory diagram showing the shape of each test piece used in the test before and after the compression test, Figure 5 is a graph showing the deformation resistance and deformation limit of each test piece determined by the compression test, and Figure 6 is the hardness depending on the aging temperature. 3 is a graph showing an example of the results of investigating the influence on Patent applicant Daido Steel Co., Ltd. Representative Patent Attorney Yutaka Oshio Figure 4 (a) (b) Figure 5

Claims (1)

[Claims] (1) In weight%, V: 8 to 25%, Al: 0.5 to 5%, Cr: less than 1.0%, Fe: 1.0% or less, Mn: 1.0 % or less, and the remainder substantially consists of Ti. A titanium alloy with excellent cold workability. (2) A titanium alloy with excellent cold workability according to claim (1), which has a hardness of H_RC25 or less after solution treatment. (3) In weight%, V: 8 to 25%, Al: 0.5 to 5%, Cr: less than 1.0%, Fe: 1.0% or less, Mn: 1.0% or less, and 0. 01-3.0%
of REM and 0.01-1.0% of Ca, S, Se,
A titanium alloy having excellent machinability and cold workability, characterized in that the total content of one or more of Te, Pb, and Bi is 5% or less, and the remainder is substantially composed of Ti. (4) A titanium alloy with excellent machinability and cold workability according to claim (3), which has a hardness of H_RC25 or less after solution treatment.