JP2797913B2 - High corrosion resistance titanium alloy with excellent cold workability and weldability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly corrosion-resistant titanium alloy used in the chemical industry (such as piping), energy development (such as umbilical tubes, oil well pipes for oil development) and aircraft (such as hydraulic piping).

[0002]

2. Description of the Related Art Titanium has the advantages of high specific strength (strength / specific gravity) and excellent corrosion resistance. Heretofore, titanium alloys have been developed in the direction of individually improving each of these advantages. These improvements include Al, V, Ni
However, sufficient consideration has not been given to the cold workability, and the cold workability is often impaired even if the strength or corrosion resistance is improved.

[0003] Titanium alloys generally have poor cold workability and weldability, and in many cases, must be finished by machining after hot working. However, titanium alloy has poor machinability,
For this reason, the cost is increased due to a decrease in product yield and a prolonged cutting.

[0004] Among titanium and titanium alloys, alloys which can be cold worked include pure Ti which is α-type titanium, Ti-3Al-2.5V which is α + β-type titanium alloy, and many β-type titanium alloys. Can be

[0005] Of these, β-type titanium alloys can be cold-worked, but have a large hot deformation resistance, are difficult to manufacture by conventional processes, and have a high temperature range (100 to 4).
(Approximately 00 ° C.), there is a problem that embrittlement occurs due to precipitation of an α phase and an ω phase, and thermal stability is lacking.

[0006] Ti-3Al-2.5V is a typical cold workable α + β type titanium alloy, the basic component of which is Al
2.5-3.5% by weight, V 2.0-3.0% by weight (this alloy is standardized to AMS). This alloy can be cold-worked like pure Ti, but it has lower strength than many other titanium alloys, and its corrosion resistance is not enough.
Practical applications are being narrowed.

[0007] JP-A-50-25418 discloses Al, Zr, M
Although a titanium alloy containing o, V, Cr, Ni and Fe is shown, this was invented for the purpose of improving strength and fracture toughness, and almost no cold workability or weldability was observed. Not considered at all.

[0008] As is well known, titanium has the advantage of being a material having excellent corrosion resistance. However, use in a severe corrosive environment requires further improvement in corrosion resistance, and high strength is required in some applications. . In response to these requirements, for example, JP-A-61-257448 discloses a titanium alloy to which Al, Ni, Zr, etc. are added to impart high corrosion resistance and high strength by a combined action of Ni and Zr. I have. Also, JP-A-63-17
No. 9033 discloses a titanium alloy which achieves high strength and high corrosion resistance by adding Al, Ni, Mo and the like. However, these titanium alloys have not been sufficiently studied on cold workability and weldability. In particular, in the former invention, the degree of occurrence of edge cracks when the rolling reduction of the cold rolling is 30% is used as a criterion for determining the quality of the cold workability. But this
The rolling reduction of 30% is a considerably low standard, and even at a higher rolling reduction, a titanium alloy having excellent cold workability is not shown.

JP-A-3-166350 and JP-A-3-166350
No. 274238 discloses a β-phase stabilizing element (Fe, Ni, Co, Cr,
There is disclosed a titanium alloy in which the ratio of β phase is increased by the addition of Mo, V) to achieve high cold workability and strength improvement by solid solution strengthening. The present inventors have also disclosed in Japanese Patent Laid-Open No.
In Patent Document 1, a titanium alloy having high strength and high toughness while maintaining good cold workability by adding 0.1% to 10.0% of Nb to a Ti-3Al-2.5V alloy was disclosed. However, in these inventions, corrosion resistance and weldability have not been clarified.

[0010]

SUMMARY OF THE INVENTION Titanium alloys are expected to be used as structural materials for corrosive environments by utilizing the characteristics of high corrosion resistance and high specific strength. However, many titanium alloys are not sufficiently corrosion resistant to withstand use in harsh corrosive environments. Further, in general, when a titanium alloy is used as a structural material due to poor cold workability and weldability, it is necessary to manufacture a product by machining from a hot finished state. As a result, the product yield is reduced and the cost is increased.

The present invention provides a highly corrosion-resistant titanium alloy excellent in cold workability and weldability in order to improve the product yield and reduce the production cost when manufacturing structural members from a titanium alloy. It is done for the purpose of.

The specific goals are as follows.

The cold workability must be at least Ti-3Al-2.5V alloy in a cold workability test described later.

The 0.2% proof stress of the welded portion at room temperature that exhibits weldability is 600 MPa or more, and the 0.2% proof stress of the base material portion at room temperature is 600 MPa or more.

The breaking strength of the weld at room temperature is 90% or more of that of the base metal.

From the practical point of application to structural materials, etc., a lower limit is set for the elongation indicating weldability, and the tensile elongation of the base material and the weld at room temperature is 10.0% or more and 5.0% or more, respectively. .

In the bending test described later, no crack occurs in the welded portion.

The corrosion resistance is at least twice that of pure titanium in a corrosion resistance test described later.

[0019]

Means for Solving the Problems The present inventors studied the effects of various additional elements on cold workability, strength, weldability and corrosion resistance, and advanced the corrosion resistance, cold workability, strength and weldability. Developed a titanium alloy balanced to

The gist of the present invention resides in the following titanium alloy.

(1) Al: 1.5 to 4.5% by weight, V: 1.
High corrosion resistance titanium alloy containing 5 to 4.5% and Mo: 0.1% to less than 2.5%, with the balance being Ti and unavoidable impurities and having excellent cold workability and weldability.

(2) In addition to the components described in (1) above,
A highly corrosion-resistant titanium alloy containing 0.1 to 10.0% by weight of Zr, with the balance being Ti and unavoidable impurities, and having excellent cold workability and weldability.

[0023]

The titanium alloy of the present invention is obtained by adding Al, V and Mo to Ti by several%, and further adding Zr as necessary, thereby further improving strength, cold workability and weldability. is there. The reason for limiting the chemical composition as described above will be described. Hereinafter,% means% by weight.

Al: 1.5 to 4.5% Al is an α-phase stabilizing element. Although it is included for the purpose of solid solution strengthening and corrosion resistance improvement, to obtain the target strength and corrosion resistance, Al
Must be contained at least 1.5%. On the other hand, when the Al content is
If it exceeds 4.5%, the cold workability is reduced, so that cracks occur during cold work. Therefore, the range of the Al content is 1.5 to
4.5%. Preferred is the range 2.5-3.5%.

V: 1.5 to 4.5% V is a β-phase stabilizing element. Although it is contained for the purpose of solid solution strengthening, it is necessary to contain 1.5% or more to obtain the target strength. On the other hand, when the V content exceeds 4.5%, the cold workability and corrosion resistance deteriorate. Therefore, the range of the V content is 1.5 to
4.5%.

The preferred range is 2.5-3.5%.
V is an element that deteriorates the weldability like Mo, but its degree is smaller than that of Mo, and there is no problem as long as it is within the above range.

Mo: 0.1% to less than 2.5% Mo contributes to improvement of cold workability, strength and corrosion resistance, but its effect is small when the content of Mo is less than 0.1%. However, when Mo is contained in a large amount, the weldability is deteriorated, and considering that there is a concern that segregation may occur due to the high melting point metal and that elongation is reduced, the Mo content is suppressed to less than 2.5%. Should. Therefore, the range of the Mo content is 0.
1% to less than 2.5%. A preferred lower limit is 0.8%.

V and Mo may be added as a single metal, but may be an Al-V master alloy, an Al-Mo master alloy or an Al-Mo- alloy.
It may be added in the form of a V master alloy.

Zr: 0.1-10.0% Zr contributes to improvement of corrosion resistance, cold workability and strength,
Particularly, since it is an element having a large effect of improving cold workability (see FIG. 2 described later), it is contained as necessary. Zr content
Below 0.1%, the effect is small. On the other hand, if it exceeds 10.0%, the corrosion resistance and strength are increased, but the elongation, cold workability and weldability are significantly deteriorated. For this reason, the range when Zr is contained should be 0.1 to 10.0%. Preferred is a range of 0.5-7.0%.

Others: Inevitable impurities include C, H,
It refers to O, N, Fe, Y, etc., but there is no particular problem as long as it is a normal content level.

Fe is inevitably incorporated because it is contained in the sponge Ti and the additive element raw material to some extent, but there is no problem if it is 0.5% or less. Fe has a high degree of solid solution strengthening, and even a small amount contributes to the improvement of strength. However, if its content exceeds 0.5%, it reacts with Ti to form an intermetallic compound and significantly deteriorates cold workability. Further, it is not preferable because it degrades corrosion resistance and causes generation of β fleck (macrosegregation of Fe) due to segregation in the ingot. Therefore, the Fe content is preferably set to 0.5% or less.

O also has a high degree of solid solution strengthening, and even a small amount contributes to strength improvement, but on the other hand, it deteriorates cold workability.
Therefore, it is desirable that the O content be 0.2% or less.

With the above chemical composition, a titanium alloy having the above-mentioned target strength, elongation, cold workability, weldability and corrosion resistance can be obtained.

The alloy of the present invention can be applied to a structural material for a corrosive environment or the like due to these characteristics. In particular, it is used as a material for an umbilical tube which is required to have weldability, strength, cold workability and corrosion resistance. It is suitable. The umbilical tube is a control pipe that connects an oil field on the sea floor and a platform on the sea, through which electric wires for controlling hydraulic pressure are passed.

[0035]

EXAMPLE An alloy having the composition shown in Tables 1 and 2 was melted by a vacuum melting method to obtain a cylindrical ingot having a diameter of 120 mm and a length of 300 mm. Alloy Nos. 1 to 13 in Table 1 are examples of the present invention, Alloy Nos. 14 to 22 in Table 2 are comparative examples of compositions outside the scope of the present invention, and alloys Nos. 23 and 24 in Table 2 are for existing cold work Pure Ti, Ti-3Al
-2.5V alloy.

[0036]

[Table 1]

[0037]

[Table 2]

After heating these ingots to 1100 ° C., forging is performed at 850 ° C. or more, and the thickness is 60 mm × width 70 mm × length.
It was 680 mm square. After that, hot rolling (heating at 900 ℃, 7
(Launched at 50 ° C) to obtain a plate having a thickness of 15 mm and a width of 70 mm, and then annealed at 750 ° C.

The hot workability was evaluated as poor when the cracks occurred due to the hot forging and hot rolling, and evaluated as poor when the cracks did not occur.

From each of the test materials thus obtained, a cold-rolled test piece (thickness 12 mm × width 35 mm × length 200 mm), a cold upsetting test piece (φ6 mm × length 9 mm) and hydrochloric acid Corrosion test pieces (thickness 10 mm × width 20 mm × length 20 mm) were cut out and subjected to cold workability and corrosion resistance tests.

TIG welding (one pass each on both sides in an Ar atmosphere, welding rod) was also cut from the hot-rolled sheet material to the test material (thickness 3 mm x width 70 mm) cut from the hot-rolled sheet material. After that, a plate tensile test piece having dimensions of 2 mm in thickness, 6.25 mm in width and 32 mm in length was cut out from the welded portion and the base material portion, respectively, and the tensile strength was measured. Further, a bending test piece (2 mm thick × 15 mm wide × 100 mm long) was cut out to examine the bending workability of the welded portion of each test material, and a bending test was performed.

Next, the details of each test will be described.

[Cold rolling test] 12 mm thick x 35 mm wide x length
The 200mm test piece was reduced by 0.5mm per pass with a roll, and the limit of cold working was when the ear cracks with a length of 3mm or more from the edge of the plate occurred within 5cm along the side of the plate. And calculated according to the following equation (1).

[0044]

(Equation 1)

[Cold upsetting test] φ6 mm × length 9
mm, the test piece was subjected to cold upsetting with a processing for master tester at a strain rate of 1.0 × 10 ⁻² sec ⁻¹ ,
The working ratio at which cracks occurred was defined as the limit cold working ratio. In addition,
This upsetting test is performed three times for each alloy,
The average value was defined as a limit cold working degree and calculated according to the following equation (2).

[0046]

(Equation 2)

[Hydrochloric acid corrosion test] 10 mm thick x 20 mm wide x length
The test piece of 20 mm was immersed in a 5 wt% HCl boiling solution for 20 hours to measure the corrosion loss, and the corrosion loss was evaluated by converting the corrosion loss to mm / year.

[Tensile test] The parallel part cut out from the base material and the welded part dimensions: The above test piece having a thickness of 2 mm, a width of 6.25 mm and a length of 32 mm was subjected to 0.5% strain / min up to 0.2% proof stress and after proof stress. Is 15%
A tensile rate of strain / min was applied to break, and the strength was measured to evaluate the weldability. This tensile test was performed twice at room temperature, and the strength and elongation were compared on average.

[Weld Bending Test] The test piece having a thickness of 2 mm, a width of 15 mm and a length of 100 mm was cut out from a weld of each test material and bent at 90 ° C. with a bending radius of 2 mm. After the bending test,
A 20-fold observation of the bent portion was performed with an optical microscope, and the presence or absence of cracks was investigated to evaluate weldability. FIG. 1 is a diagram showing the shape of the test piece.

The results of the above evaluation tests are shown in Tables 3 and 4 and FIG.

[0051]

[Table 3]

[0052]

[Table 4 (1)]

[0053]

[Table 4 (2)]

The following is clear from the results of Tables 3 and 4.

According to the results of alloys Nos. 1 to 3 and Nos. 14 and 15, although Al greatly contributes to strength improvement by solid solution strengthening, the effect is small if the content is small (alloy No. 14 , Al is 0.5% and the strength is low). Also, excessive Al content lowers the cold workability (see Alloy No. 15 for 6.
0%, indicating poor cold workability).

According to the results of alloys Nos. 4 and 5, and Nos. 16 and 17, V also contributes to the improvement in strength by solid solution strengthening. However, the effect is small when the content is small (alloy No. 16
, V is 0.5% and the strength is low). Also, excessive V
The content decreases the cold workability (the alloy No. 17 also has 6.0%, and the cold workability is lower than that of the Ti-3Al-2.5V alloy).

According to the results of alloys Nos. 6 and 7 and Nos. 18 and 19, Mo contributes to the improvement of cold workability, strength and corrosion resistance. However, according to the results of Alloy No. 18, when the Mo content is less than 0.1%, the contribution to the improvement of the above three properties is small. Also, excessive Mo content causes a decrease in weldability, which is not preferable (alloy No. 19
In this case, Mo is 4.0%, and the bending property of the weld is low.)

According to the results of alloys Nos. 8, 9 and 21, although oxygen greatly contributes to strength improvement, it lowers cold workability and weldability. However, there is no problem if the amount is normal (less than 0.2%).

According to the results of alloys Nos. 10 and 20, Fe has a great influence on the strength similarly to oxygen, and has a bad influence on the cold workability. In addition, the corrosion resistance deteriorates, but the Fe content is reduced to 0.
There is no problem if it is less than 5%.

FIG. 2 shows the results of the cold upsetting test.
It is a figure showing an example of the influence of the Zr content on the critical cold work degree. The base composition of the titanium alloy in this case is Al: 3.0
%, V: 3.0%, Mo: 1.5%, O: 0.1%, Fe: 0.1%, bal .: T
i. As shown in the drawing, the limit cold working degree increases in the range where the Zr content is determined by the present invention.

As shown in Tables 3 and 4, and FIG.
According to the results of No. 2, No. 11 to 13 and No. 22, Zr contributes to the improvement of strength, corrosion resistance and cold workability, but contains excessive Zr (for example, Zr in alloy No. 22: 13%) reduces cold workability, elongation and weldability. However, within the range defined by the present invention, there is an effect of improving strength and corrosion resistance without impairing cold workability and weldability.

The existing pure Ti or Ti-3Al-
The 2.5V alloy has lower strength and lower corrosion resistance than the alloy of the present invention.

[0063]

The alloy of the present invention is a high-strength and high-corrosion-resistant titanium alloy having excellent cold workability and weldability (weld strength). Since the weldability is good, it is possible to manufacture a titanium alloy tube material suitable for use in a corrosive environment atmosphere in fields such as chemical industry, energy development, general industry, etc. at a low cost without mechanical cutting. .

[Brief description of the drawings]

FIG. 1 is a view showing the shape of a test piece in a weld bending test.

FIG. 2 is a diagram showing an example of the effect of the Zr content on the critical cold work degree in the case of a cold upsetting test.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C22C 14/00

Claims (2)

(57) [Claims] (1) Al: 1.5 to 4.5%, V: 1.5 to 4.5% by weight
4.5% and Mo: 0.1% to less than 2.5%, with the balance being
High corrosion resistance titanium alloy with excellent cold workability and weldability consisting of Ti and unavoidable impurities. 2. The composition according to claim 1, further comprising, by weight%, 0.1 to 10.0% by weight of Zr, with the balance comprising Ti and unavoidable impurities having excellent cold workability and weldability. Corrosion resistant titanium alloy.