JPH04143236A - High strength alpha type titanium alloy excellent in cold workability - Google Patents

Abstract

PURPOSE:To improve the strength and cold workability of an alpha type titanium alloy by incorporating prescribed ratios of V, Fe, Cr, Ni and Co as well as O and Al into Ti. CONSTITUTION:This alpha type titanium alloy is formed by a compsn. in the range satisfying, by weight, (V/13)+(Fe/20)+(Cr/17)+(Ni/31)+(Co/23) <=0.1% as well as <=0.6% O, <=4% Al and (5/2)O+(1/3)Al <=0.9% and the balance Ti. This titanium allay not only has high strength but also is free from the generation of cracks and ghost lines at the time of cold forming.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention not only has high strength but also has excellent cold formability, and is suitable for use in cold forming, for example, pipes for heat exchangers, panel parts for automobiles and aircraft, etc. The present invention relates to an α-type titanium alloy suitable as a manufacturing material for machining.

[Prior Art and Problems to be Solved by the Invention] Titanium has been widely used for heat exchanger pipes since it has excellent corrosion resistance. Since pure titanium has good cold workability, this heat exchanger pipe is manufactured by pipe-forming a pure titanium cold-rolled plate. Moreover, due to such good cold workability, pure titanium has been used for panel parts and the like. However, the pure titanium thin sheets used for such applications are either J131 type or J2 type, which have particularly good workability, or they have a low 0.2% proof stress, and even JIS type 2, which has a higher value, cannot be used. 0 obtained
, the 2% yield strength is only 30 kg/2 pieces at most. Currently, 0.7mm material is often used for heat exchanger pipes, but there is a demand for thinner walls to increase the heat exchange efficiency, and the strength of pure titanium as described above is insufficient. It is enough.

On the other hand, titanium alloys have the highest specific strength among practical metal materials, and have thus far been used extensively, especially as aircraft parts, but in recent years, their application not only to these uses but also to general industrial uses has been considered. However, although titanium alloys have superior strength compared to pure titanium, they generally have poor cold rollability and cold formability, and therefore, improving these properties is a major issue in expanding the use of titanium alloys. In general, various defects appear during cold forming, but cold forming of titanium alloys causes problems such as "cracks" and, when no cracks occur, the occurrence of defects called "ghost lines." When ghost lines occur, not only the appearance is significantly impaired and the commercial value is reduced, but also the plate thickness becomes uneven, resulting in poor strength of the product.

This invention was made in view of such circumstances, and
The object of the present invention is to provide an α-type titanium alloy having a 0.2% yield strength of 30 kg/112 or more and excellent cold formability without cracking or ghost lines during cold forming.

[Means for Solving the Problems] The high-strength α-type titanium alloy with excellent cold formability according to the present invention has the following composition (V/13) + (Fe/20) + (in weight %).
Cr/17) Ten (Ni/31) + (Co/23) is 0
．． 10% or less, and O≦0.6%, 11≦4.0
%, and (5/2)0+ (1/3)AI≧0.90%
0 and AI within the range that satisfies the requirements, and the remainder is substantially Ti.
It is characterized by consisting of.

In addition, for the sake of simplicity, (V/13) + (Fe/20)
+ (Cr/17)+ (Ni/31)+(Co/
23) is expressed as EQI.

[Function] As a result of research and consideration in order to suppress the generation of ghost lines during cold forming of titanium alloy thin sheets for forming processing, the present inventors found that V, Fe, which are β-stable elements in titanium,
It has been newly discovered that the generation of ghost lines can be prevented by controlling the contents of Cr, Ni, and Co to below a certain value.

The content of V, Fe, Cr, Ni, and Co here is EQI>
When the relationship is 0.10% by weight, the occurrence of ghost lines is observed. This is because when the content of β-stabilizing elements is high, segregation of these β-stabilizing elements inevitably occurs due to the manufacturing history, resulting in a microstructure in which three types of α-crystals with different hardness are mixed unevenly. This is because it occurs in cold-formed materials.

Therefore, it is specified that EQI≦0.10% by weight. Note that the ratio of the effects of these β stabilizing elements is V:Fe:Cr:Ni
:Co=1/13:1/20:1/17:1/31
: Since it is 1/23, these contents are calculated as E above.
QI was specified.

On the other hand, i and O are elements that achieve high strength by being added to titanium. However, if these amounts exceed 4.0% by weight and 0.6% by weight, respectively, although high strength is achieved, cold rollability deteriorates. Therefore, 4.
Zero weight is defined as 1% or less, and 0 is defined as 0.6 weight% or less. Also, the content of AI and 0 is (5/2)O+ (1/3)
If AI <0.90 wt%, target 3
Since 0.2% yield strength of 0kg/■■2 or more cannot be obtained,
(5/2) O+ (1/3) AI! ≧0.90% by weight
stipulates.

[Example] Examples of the present invention will be described below.

Ingots (numbers 1 to 82) having the composition shown in Table 1 were produced by VAR melting, and heated to 1000°C.
It was hot forged into a slab with a thickness of 16m5. Next, these slabs were hot-rolled at 80[)° C. to produce a hot-rolled plate having a thickness of 311 mm. Then, scale was removed from these hot-rolled plates using a coil grinder to obtain a cold-rolled material having a plate thickness of 2.21 mm.

Thereafter, it was cold rolled by 50% and visually inspected for the occurrence of cracks after cold rolling. In Table 1, the presence or absence of cracking is indicated by 0 (no cracking) and x (cracking). Furthermore, the cold-rolled material in which no cracking was observed was subjected to vacuum annealing at 650° C. for 1 hour, and its mechanical properties and the occurrence of ghost lines were investigated. Mechanical properties were determined by taking a JIS 13B test piece (parallel part: 12.5-1, GL: 50 wet I) parallel to the rolling direction, and subjecting this test piece to a tensile test to determine its 0.2% yield strength. This was determined through measurement. In addition, the occurrence of ghost lines was investigated using bending test pieces taken in the direction perpendicular to rolling.
A bending test was conducted with a bending radius of 20T (T: plate thickness), and the presence or absence of ghost lines was visually determined. In Table 1, the presence or absence of ghost lines is indicated by O (ghost lines not occurring) and × (ghost lines occurring).

Table 1 shows the results of these tests. Also, Al and O
The relationship between the content and properties is shown in Figure 1.

First, for V, Fe, Cr, and Ni Co, the first
As shown in the table, it was confirmed that ghost lines were generated when EQI exceeded 0.10% (expressed as weight %, hereinafter the same).

Next, regarding AΩ and O, as shown in Table 1 and FIG. 1, it was confirmed that cold cracking occurs when Ajll>4.0%, O>0, and 696. On the other hand, (5/2
)O+ (1/3)Al 0.0% in the range <0.90%.
It was confirmed that the 2% proof stress was a low value of less than 30 kg/as2.

On the other hand, when EQ1≦0.10% and 0≦0.6%
, AI? ≦4,0%, (5/2)O+(1/3)All
For those having a composition within the range of the present invention, which is ≧0.9%, only cracks occurred during cold rolling, and no ghost lines were observed.

moreover, 0° 2% yield strength is 30 kg/■12 Good as above It showed great strength.

[Effect of the invention] According to this invention, the 0.2% yield strength is 30 kg/-12
As described above, it is possible to provide an α-type titanium alloy that exhibits good strength and has excellent cold forming properties without cracking or ghost lines during cold forming.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the content of Al and 0 in a titanium alloy and its properties.

Claims (1)

[Claims] In weight%, (V/13) + (Fe/20) + (Cr/1
7)+(Ni/31)+(Co/23) is 0.10% or less, and O≦0.6%, Al≦4.0%, and (
5/2) High-strength alpha titanium with excellent cold formability, containing O and Al in a range that satisfies O + (1/3) Al≧0.90%, with the remainder substantially consisting of Ti. alloy.