JPH11335757A - High-strength, high-ductility titanium alloy with excellent resistance to high-temperature atmospheric oxidation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a yield and dimensional precision by adding a specified quantity of Zr to a Ti alloy, which contains Fe liable to oxidation and O in a specified quantity, has high strength and is excellent in ductility so as to improve oxidation resistance at a high temp. in the atmosphere of hot working, etc., and to suppress generation of an oxidized scale. SOLUTION: The high strength, high ductility Ti alloy, which contains, by mass, 0.2-5% Fe, 0.05-0.75% O, further 0.01.e<0.7(> F<e)> -20.e<0.2(> F<e)> ((Fe) is a content in the alloy) Zr, at need 0.01.e<0.5(> F<e)> -5.e<0.5(> F<e)> Si, is obtained. Zr forms a dense Zr oxide layer on the alloy surface which suppresses intrusion of oxygen to improve high temp. atmospheric oxidation resistance, and further, Zr enters into solid solution in the alloy to increase strength, while it is preferable to avoid excessive addition in order to suppress a raw material cost. Si is stably forms a dense ZrSiO4 on an alloy surface to increase high temp. atmospheric oxidation resistance as well as enters into solid solution to improve strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-ductility titanium alloy having excellent oxidation resistance in a high-temperature atmosphere (hereinafter referred to as high-temperature atmospheric oxidation resistance).

[0002]

2. Description of the Related Art Titanium alloys are characterized by high strength despite being lightweight, and excellent fatigue resistance and corrosion resistance. Therefore, aircraft parts, automobile parts,
It is used for various purposes such as sports and leisure tools, medical supplies such as artificial bones, and parts for equipment in the chemical industry.

[0003] Titanium alloys having high strength and excellent ductility include "α + β type" and "β type". Both of them are obtained by adding components such as V, Al, Mo, Cr, Sn and Fe to titanium. An alloy with improved mechanical properties.

[0004] The Ti-5% Al-2.5% Fe alloy is an alloy whose production cost has been reduced by substituting V which is an expensive additive component with Fe which is an element which is relatively inexpensive and harmless to the human body. Are known.

Japanese Patent Application Laid-Open No. 1-252747 discloses that strength and ductility are improved without containing a large amount of alloy components.
A titanium alloy containing 0.1 to 0.8% of Fe, O (oxygen) and N is disclosed.

[0006] International Publication WO96 / 33292 discloses that
Fe: 0.9 to Fe and 0.9 with improved strength and high ductility without containing alloying elements such as Al, V and Mo that increase the production cost.
2.3% with O (oxygen), N and Cr and Ni if necessary
Is disclosed.

[0007] However, these newly developed alloys contain a large amount of Fe which is easily oxidized in the atmosphere at high temperatures. Therefore, it lacks high-temperature atmospheric oxidation resistance.

[0008] The term "high temperature" used herein means "400 to 11".
00 ° C. ”, which corresponds to the heating temperature for hot working and heat treatment.

When the high-temperature atmospheric oxidation resistance is inferior, in a hot working step such as hot rolling or hot forging, or in a heat treatment step for annealing or recrystallization, the yield is reduced due to the formation of oxide scale, and the working is reduced. Problems such as a decrease in the dimensional accuracy of the product and the occurrence of surface flaws due to entrapment of the oxide scale during processing are caused.

[0010] Measures for suppressing atmospheric oxidation include:
Application of an oxidation inhibitor to the surface of the alloy before heating, heating in an inert atmosphere such as Ar gas, etc., are all impractical because they require labor and equipment and increase manufacturing costs.

[0011] TITANIUM '80, Proceedings of the Fourth
International Conference on Titanium, P.2755,
It has been reported that the addition of Zr and Si to titanium is effective in suppressing atmospheric oxidation. However, F which is easily oxidized
The effect of suppressing the oxidation of Zr and Si when e is contained has not been known.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-strength, high-ductility titanium alloy containing Fe that is easily oxidized and having excellent resistance to high-temperature atmospheric oxidation.

[0013]

The gist of the present invention relating to a high-strength, high-ductility titanium alloy excellent in high-temperature atmospheric oxidation resistance is as follows.

(1) In mass%, Fe: 0.2 to 5%, O
(Oxygen): A high-strength, high-ductility titanium alloy containing 0.05 to 0.75% and further containing Zr in the following range and having excellent oxidation resistance in high-temperature air.

Zr (% by mass): 0.01 · e ^{0.7 [Fe]}
20 · e ^{−0.2 [Fe]} Here, [Fe] indicates the content (% by mass) in the alloy,
e indicates the base of the natural logarithm. (2) In mass%, Fe: 0.2 to 5%, O (oxygen):
A high-strength, high-ductility titanium alloy excellent in oxidation resistance in a high-temperature atmosphere, containing 0.05 to 0.75%, and further containing Zr and Si in the following range.

Zr (% by mass): 0.01 · e ^{0.7 [Fe]}
20 · e ^{-0.2 [Fe]} Si (mass%): 0.01 · e ^{0.5 [Fe] to} 5 · e
^{-0.5 [Fe]} where [Fe] indicates the content (% by mass) in the alloy,
e indicates the base of the natural logarithm.
As a result of conducting various experimental studies to improve the high-temperature atmospheric oxidation resistance of a titanium alloy containing e, the following findings were obtained.

A) When Zr is contained in an Fe-containing titanium alloy, the effect of improving the high-temperature atmospheric oxidation resistance of Zr is affected by the Fe content.

B) The lower limit of Zr required to obtain the effect of improving the high-temperature atmospheric oxidation resistance increases as the Fe content increases. However, the upper limit of the Zr content is Fe
If the content is not reduced as the content increases, the ductility deteriorates.

C) That is, when the content of Zr is 0.01
By setting the range of e ^{0.7 [Fe]} to 20 · e ^{−0.2 [Fe]} , high-temperature atmospheric oxidation resistance can be obtained and ductility can be ensured.

D) If the titanium alloy containing Fe and Zr further contains Si, the high-temperature atmospheric oxidation resistance is further improved and the strength is also improved.

E) The lower limit of the amount of Si required to obtain the effect of improving the resistance to high-temperature atmospheric oxidation must be increased as the Fe content increases. However, if the upper limit of the Si content is not reduced as the Fe content increases, the ductility and atmospheric oxidation characteristics deteriorate.

F) That is, when Si is contained, its content must be in the range of 0.01 · e ^{(0.5 [Fe] to} 5 · e ^{−0.5 [Fe])} .

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the chemical composition of the titanium alloy of the present invention will be described below. In addition,% display of a chemical composition shows mass%.

Fe: Fe is an indispensable important alloy element. Fe has an action of forming a β phase or a TiFe phase in the α phase which is a parent phase, and increases the strength by making the structure of the alloy polyphase.

In order to exhibit this effect, 0.2%
It is necessary to contain the above. On the other hand, if the Fe content exceeds 5%, the ductility is significantly reduced. Therefore, the Fe content is set to 0.2 to 5%. Taking into account the balance between strength and ductility, the content is preferably 0.2 to 3.5%.

O (oxygen): O is also an important element indispensable like Fe. O has a function of improving the strength of the alloy by a solid solution strengthening function. To obtain the effect, the O content needs to be 0.05% or more. However, if it exceeds 0.75%, the amount of solid solution of O becomes excessive and ductility decreases. Therefore, the O content is 0.0
5 to 0.75%. In consideration of the balance between strength and ductility, the content is preferably 0.1 to 0.6%.

Zr: Zr is an important element in the alloy of the present invention, and forms a dense Zr oxide layer on the surface of the alloy to prevent oxygen from entering the alloy and improve the high-temperature atmospheric oxidation resistance. Contribute. Further, it has the effect of improving the strength by forming a solid solution in the alloy.

In order to suppress high-temperature atmospheric oxidation, a strong Zr oxide layer must be formed on the surface of the alloy to prevent oxygen from entering the alloy. Since the generation of Fe oxides becomes active in proportion to the increase in the Fe content, it is necessary to increase the lower limit of the Zr content as the Fe content increases. In order to obtain the effect of improving the high-temperature atmospheric oxidation resistance and strength of Zr, the Zr content must be 0.01 · e ^{0.7 [Fe]} %.
It is necessary to do above. On the other hand, when the Zr content is 20 · e
^{If the} content exceeds ^{-0.2 [Fe]} %, the ductility of the alloy decreases. Therefore, the Zr content is 0.01 · e ^{0.7 [Fe] to} 20 · e.
^{-0.2 [Fe]} %.

FIG. 1 is a diagram showing the range of the Zr content specified in the present invention.

The upper and lower limits are obtained by repeating various experiments. Within the allowable range of the Zr content according to the Fe content, the higher the Zr content, the greater the effect of improving high-temperature atmospheric oxidation resistance and strength. However, since excessive addition of Zr increases the cost of raw materials, the Zr content should be reduced to an amount that provides high-temperature atmospheric oxidation resistance and strength required in manufacturing conditions and product specifications, and excessive addition should be avoided. Is good.

Si: Si is an element to be contained when more excellent high-temperature atmospheric oxidation resistance and strength are required.

Si forms stable and dense ZrSiO ₄ on the alloy surface, suppresses the penetration of oxygen into the alloy, and contributes to the improvement of high-temperature atmospheric oxidation resistance. Further, it has the effect of improving the strength of the alloy by being dissolved in the alloy.

As described above, since the generation of Fe oxides becomes active due to the increase of the Fe content, it is necessary to form a strong Si oxide layer on the alloy surface in order to suppress the high-temperature atmospheric oxidation of Fe. Good. Therefore, it is necessary to increase the lower limit of the Si content in accordance with the increase in the Fe content.
Therefore, in order to obtain the effect of improving the high-temperature atmospheric oxidation resistance and strength of Si, the Si content needs to be 5 · e ^{−0.5 [Fe]} % or more. On the other hand, if the Si content exceeds a certain range, the ductility of the alloy is lowered and, at the same time, the low melting point (110
(Approximately 0 ° C.), an Fe / Si composite oxide is generated, and the Si oxide layer becomes brittle, so that atmospheric oxidation characteristics are significantly deteriorated. If the upper limit of the Si content is not reduced as the Fe content increases, ductility and high-temperature atmospheric oxidation resistance deteriorate. Therefore, the upper limit of Si is 0.01 ·
e ^{0.5 [Fe]} %.

FIG. 2 shows the range of the Si content defined in the present invention.

Other elements: In addition to Fe, O, and Zr, Al, Cr, Mn, Ni, C, N, and the like can be contained as necessary. The functions and preferable contents of these elements are as follows. .

Al: Al has the effect of improving the strength of the alloy by solid solution strengthening. Therefore, when it is necessary to further improve the strength of the alloy, it is preferable to contain Al.

In order to obtain this strength improving effect, the Al content is preferably set to 0.01% or more. However, A
If the l content exceeds 6.5%, the ductility of the alloy decreases.
Therefore, when Al is contained, 0.01-6.
5%, preferably 0.01 to 5%, more preferably 0.01 to 3.5%.

Cr, Mn, Ni, C and N: All of these elements have a function of improving the strength of the alloy by forming a solid solution in the alloy. When it is necessary to exert the above effects, Cr, Mn, Ni, C and N are all 0.01%.
% Is preferably contained. However, if the contents of Cr, Mn and Ni exceed 0.5% and the contents of C and N exceed 0.2%, the solid solution amounts of these elements become excessive, so that the ductility of the alloy decreases. I do.

[0039]

EXAMPLE The chemical composition shown in Tables 1 and 2 was 85 mm in length, 75 mm in width,
An ingot having a thickness of 15 mm was produced. After heating these 35 types of ingots to 950 ° C., they were hot-rolled into 3 mm thick plates. Next, the hot-rolled sheet was heated to 850 ° C.
Annealing was performed in the atmosphere for 0 minutes. The steel plate surface was cut to remove the oxide scale formed on the surface of the titanium alloy plate, and the following room temperature tensile test and evaluation test of high-temperature atmospheric oxidation resistance were performed.

[0040]

[Table 1]

[0041]

[Table 2]

Reference numerals 1 to 25 shown in Table 1 are examples of the present invention, and reference numerals A to M are comparative examples. The relationship between the Fe and Zr contents of the alloys shown in Tables 1 and 2 is as shown in FIG. The relationship between Fe and Si content is as shown in FIG.

The test conditions and measurement items were as follows.

(1) Room Temperature Tensile Test Test Method: JIS Z2241 Specimen: Plate-shaped Specimen (1/2 size of No. 13B specified in JIS Z2201, thickness 2 mm) Measurement: Tensile strength, Elongation (2) Evaluation test for high-temperature atmospheric oxidation resistance Test piece: Plate-shaped test piece (length: 25 mm, width: 20 mm, thickness: 2 mm) Heating condition: 900 ° C., 1 hour, in air (test piece in alumina container) And heating and holding in a heating element type electric furnace) Measurement: Increase in oxidation (measurement of weight change before and after heating with an electronic balance) The measurement results are summarized in Tables 1 and 2. The criteria for each evaluation in the table were as follows.

Tensile strength ：: 800 MPa or more Elongation ：: 5% or more ▲: Less than 5% Oxidation resistance ：: 10 g / m ² ：: ²⁰ gm ² or less ：: 100 g
/ M ² or more As is clear from Table 1, with respect to the reference numerals 1 to 25 of the examples of the present invention, the increase in oxidation is 16 g / m ² or less, and they are excellent in high-temperature atmospheric oxidation resistance.

The tensile strength in the tensile test was 800
At least MPa and an elongation of at least 6%, all of which are practically sufficient performance.

In the examples of the present invention, samples 11 to 21 and 24 and 25 are examples in which Zr and Si are combined and contained. In these cases, among the examples of the present invention, the oxidation weight gain is relatively small, and thus it is suitable for applications requiring higher-temperature atmospheric acid resistance.

On the other hand, the samples A to J of the comparative examples are inferior in either the oxidation weight increase or the elongation.

Samples A to C have too low a Zr content.
In each case, the increase in oxidation is as large as 100 g / m ² or more. Samples DF have too high a Zr content, and Samples GI have Sr.
Since the i content is too large, the elongation is as low as 2% or less.

[0050]

The alloy of the present invention is excellent in high-temperature atmospheric oxidation resistance, and also excellent in strength and ductility, despite containing Fe which is easily oxidized. Therefore,
Since the decrease in yield due to oxidation is drastically reduced and there is no indentation surface flaw during rolling caused by scale generated during heating, a high quality titanium alloy product can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a range of a Zr content specified in the present invention and a relationship between Fe and Zr content of an alloy used in an example.

FIG. 2 is a diagram showing the range of the Si content specified in the present invention and the relationship between the Fe and Si contents of the alloy used in the examples.

Claims (2)

[Claims] (1) In mass%, Fe: 0.2 to 5%, O (oxygen): 0.05 to 0.75%, and Zr in the following range. High-strength, high-ductility titanium alloy with excellent oxidation resistance in high-temperature atmosphere. Zr (% by mass): 0.01 · e ^{0.7 [Fe]} to 20 · e
^{-0.2 [Fe]} where [Fe] indicates the content (% by mass) in the alloy,
e indicates the base of the natural logarithm 2. The composition contains, by mass%, Fe: 0.2 to 5% and O (oxygen): 0.05 to 0.75%, and further comprises Zr and Si.
A high-strength, high-ductility titanium alloy excellent in oxidation resistance in a high-temperature atmosphere in the following range. Zr (% by mass): 0.01 · e ^{0.7 [Fe]} to 20 · e
^{-0.2 [Fe]} Si (mass%): 0.01 e ^{0.5 [Fe] to} 5 e
^{-0.5 [Fe]} where [Fe] indicates the content (% by mass) in the alloy,
e indicates the base of the natural logarithm