JP2009007679A - Titanium alloy and method for producing titanium alloy material - Google Patents

Abstract

Provided are a titanium alloy having sufficient cold workability and excellent superplastic properties, and a method for producing the titanium alloy material.
(1) By mass%, Al: 2.0 to 4.0%, V: 4.0 to 9.0%, Zr: 0 to 2.0% and Sn: 0 to 3.0% As required, Fe: 0.20 to 1.0%, Cr: 0.01 to 1.0%, Cu: 0.01 to 1.0% and Ni: 0.01 to 1.0% A titanium alloy comprising at least one selected from the group consisting of Ti and impurities, wherein Veq obtained from the following formula (1) is in the range of 4.0 to 9.5.
Veq = V + 1.9Cr + 3.75Fe (1)
(2) A method for producing a titanium alloy material, wherein the titanium alloy material is subjected to cold working with a cross-sectional reduction rate of 40% or more.
[Selection figure] None

Description

  The present invention relates to a titanium alloy used for a heat exchanger material and the like, and a method for producing the titanium alloy material, and more particularly to a titanium alloy having excellent cold workability and superplastic characteristics and a method for producing the titanium alloy material.

  A heat exchanger means a device that can transfer heat energy between different types of fluids. For example, it is used for air conditioners, refrigerators, air preheating devices for burners, automobile radiators, chemical industry parts, seawater parts, etc. It has been. In particular, titanium heat exchangers are used for applications that require excellent corrosion resistance, such as the chemical industry and seawater. Further, in order to reduce the size of the heat exchanger, it is necessary to increase the strength of the member used, and as such a heat exchanger material, a lightweight and high strength titanium alloy is used.

  Among titanium alloys, Ti-6Al-4V alloy, as described in Non-Patent Document 1, for example, is widely used as a material for heat exchangers because it has excellent superplastic properties. However, this alloy has poor cold workability. For this reason, for example, when manufacturing a thin plate by cold rolling the Ti-6Al-4V alloy plate scraped off to the coil, there is a drawback that the number of intermediate annealings must be increased.

  Non-Patent Document 2 shows a Ti-9V-2Mo-3Al alloy as a titanium alloy that is excellent in cold workability and excellent in superplastic workability. However, this alloy contains Mo as an essential element, which increases raw material costs. Further, since Mo has a high melting point, undissolved or solidified segregation is likely to occur during melting.

  In Patent Document 1, in mass%, Al: 5.5 to 6.5%, V: 3.5 to 4.5%, O: 0.2% or less, Fe: 0.15 to 3.0% , Cr: 0.15 to 3.0%, Mo: 0.85 to 3.15%, Fe, Cr and Mo are in a range represented by a specific formula, and an average grain of α crystal A titanium alloy having a diameter of 6 μm or less and excellent superplastic workability is described. This alloy is superior to Ti-6Al-4V in superplastic properties, but cold workability is not considered. That is, since this alloy has a high Al content of 5.5% or more, when this alloy is subjected to cold rolling with a cross-sectional reduction rate of 50%, an edge crack occurs at the end of the plate.

  In Patent Document 2, in mass%, Al: 3.0 to 5.0%, V: 2.1 to 3.7%, Mo: 0.85 to 3.15%, O: 0.15% or less In addition, there is described a titanium alloy having excellent workability that contains at least one of Fe, Cr, Ni, and Co, and the content of these elements is within a range represented by a specific formula. . In addition, a manufacturing method of a titanium alloy material with specified hot rolling conditions and a superplastic working method of a titanium alloy material with specified heat treatment conditions are also described. However, since this alloy contains Mo, the same problem as the alloy described in Non-Patent Document 2 occurs.

Japanese Patent Publication No.8-19502 Japanese Patent Publication No. 8-23053 N. Furushiro, three others, "Titanium '80", published by Metallurgical Society of AIME, 1980, pages 993-998 Tsutomu Oka, two others, "What are you studying about titanium materials in Japan," Japan Iron and Steel Institute, December 1, 1989, pp. 58-60

  An object of the present invention is to provide a titanium alloy excellent in cold workability and superplastic characteristics and a method for producing the alloy material.

  In order to achieve the above object, the present inventors have completed the present invention as a result of repeated research based on a Ti-3Al-2.5V alloy, which is considered to be excellent in cold workability.

  The gist of the present invention is a titanium alloy shown in the following (1) and (2) and a method for producing a titanium alloy material shown in the following (3).

  (1) By mass%, Al: 2.0-4.0%, V: 4.0-9.0%, Zr: 0-2.0% and Sn: 0-3.0%, the balance being A titanium alloy comprising Ti and impurities.

(2) By mass%, Al: 2.0-4.0%, V: 4.0-9.0%, Zr: 0-2.0% and Sn: 0-3.0%, One or more selected from Fe: 0.20-1.0%, Cr: 0.01-1.0%, Cu: 0.01-1.0% and Ni: 0.01-1.0% And the balance is Ti and impurities, and Veq obtained from the following formula (1) is in the range of 4.0 to 9.5.
Veq = V + 1.9Cr + 3.75Fe (1)
However, the symbol on the right side of the formula (1) means the content of each element.

  (3) A method for producing a titanium alloy material, comprising subjecting the titanium alloy according to the above (1) or (2) to cold working with a cross-sectional reduction rate of 40% or more.

  The titanium alloy of the present invention has sufficient cold workability and excellent superplastic properties. Therefore, a coil can be manufactured by cold rolling using the titanium alloy of the present invention, and a superplastic forming material having a uniform thickness distribution can be manufactured. Thereby, the titanium alloy thin plate can be easily manufactured at low cost, and the application field of the titanium alloy thin plate can be expanded.

  First, the chemical composition of the titanium alloy of the present invention and the reason for limitation will be described. In the following description, “%” for each component means “mass%”.

Al: 2.0-4.0%
Al is an element that plays an extremely important role in increasing the strength of the titanium alloy. Al is also an element effective for stabilizing the α phase of the titanium alloy. Superplastic properties are manifested in a temperature region where the ratio of α phase to β phase is around 50:50. However, if the Al content is low, this temperature region is narrowed, so that stable superplastic properties are obtained. It becomes difficult. In order to obtain superplastic characteristics in a wide temperature range, the Al content needs to be 2.0% or more. However, the cold workability decreases as the Al content increases. In particular, when a cold working with a cross-sectional reduction rate of about 50% is performed on a titanium alloy having an Al content exceeding 4.0%, an edge crack occurs at the end of the plate. For this reason, the content of Al is set to 2.0 to 4.0%.

V: 4.0-9.0%
V is an element effective for stabilizing the β phase of the titanium alloy, and has the effect of increasing the β phase ratio in the temperature range of 800 to 850 ° C. In particular, when V is contained in an amount of 4.0% or more, the temperature range in which the ratio of the α phase to the β phase is around 50:50 can be expanded. However, if the content of V exceeds 9.0%, the oxidation resistance characteristics of the titanium alloy material are deteriorated. This is because the oxide of V has sublimability, and when a titanium alloy having a V content exceeding 9.0% is exposed to a high temperature, the scale generated on the alloy surface is not dense, and oxygen This is because the permeability is high. For this reason, it becomes easy to generate | occur | produce a crack on the alloy surface, and high temperature ductility falls. Therefore, the content of V is set to 4.0 to 9.0%.

Zr: 0 to 2.0%
Zr is an element that does not need to be added, but if Zr is added, it contributes to strengthening of the titanium alloy by its solid solution strengthening action. Further, when a titanium alloy containing Zr is exposed to a high temperature, a strong Zr oxide is formed on the surface and the inside of the alloy is prevented from being oxidized. For this reason, in the deformation | transformation at high temperature of a titanium alloy, generation | occurrence | production of a crack can be prevented and elongation can be increased, Therefore The superplastic characteristic of a titanium alloy can be improved. These effects are large at 0.5% or more. On the other hand, if the content of Zr exceeds 2.0%, the effect of suppressing the oxidation is saturated, and the cost increases because Zr is an expensive element. Therefore, when Zr is contained, the content is preferably 2.0% or less.

Sn: 0 to 3.0%
Sn is an element that does not need to be added, but Sn does not contribute to stabilization of the α phase or β phase, but contributes to strengthening of the titanium alloy. In order to obtain such an Sn effect, it is preferable to contain 0.2% or more. However, when Sn is contained in an amount exceeding 3.0%, a low melting point region is formed in the solidification process, so that cracking occurs based on this low melting point region. Therefore, when it contains Sn, it is good to make the content into 3.0% or less.

  The titanium alloy of the present invention has the chemical components described above, and the residue is made of Ti and impurities, but instead of a part of Ti, Fe: 0.20 to 1.0%, Cr: 0 One or more of 0.01 to 1.0%, Cu: 0.01 to 1.0% and Ni: 0.01 to 1.0% may be included. This is due to the following reason.

  Fe and Cr are elements contained as impurities in titanium sponge, which is a titanium raw material, or in an aluminum / vanadium alloy, which is an additive raw material. For this reason, even if these elements are not positively added, Fe is contained in the titanium alloy in less than 0.20% and Cr in less than 0.01%. All of these elements are β-phase stabilizing elements and have the same effects as V, but are cheaper than V. Therefore, if these elements are positively added, the cost can be reduced. Therefore, it is desirable to contain 0.20% or more of Fe and 0.01% or more of Cr. However, Fe and Cr are eutectoid elements that form intermetallic compounds in titanium alloys. When Fe and Cr are contained in excess of 1.0%, they cause embrittlement due to excessive precipitation of intermetallic compounds. .

  Cu and Ni are β-stabilizing elements like V, and are effective elements for increasing the β-phase ratio in the temperature range of 800 to 850 ° C. Moreover, since these elements are elements cheaper than V, they can be added as substitute elements for V. In order to obtain this effect, it is desirable to contain Cu 0.01% or more and Ni 0.01% or more. However, since Cu and Ni are eutectoid elements for titanium, inclusion of these elements in an amount exceeding 1.0% each makes an intermetallic compound and reduces cold workability.

  Therefore, when the titanium alloy of the present invention contains one or more of these elements, Fe is 0.20 to 1.0%, Cr is 0.01 to 1.0%, Cu is 0.00. 01-1.0%, Ni was 0.01-1.0%.

Veq (= V + 1.9Cr + 3.75Fe): 4.0 to 9.5
As an index indicating the stability of the β phase of the titanium alloy, there is Veq represented by the following (1). However, the symbol on the right side of the formula (1) means the content of each element.
Veq = V + 1.9Cr + 3.75Fe (1)

When this Veq is less than 4.0, the β-phase ratio in the temperature range of 800 to 850 ° C. becomes low, and the superplastic characteristics in this temperature range are hardly exhibited. On the other hand, when Veq exceeds 9.5, the ratio of the α phase decreases, the superplastic properties in the temperature range of 800 to 850 ° C. deteriorate, the specific gravity of the alloy itself increases, and the titanium alloy is lightweight. The characteristics of will be impaired. Therefore, when Fe and / or Cr is contained in the titanium alloy of the present invention, it is necessary to limit Veq obtained from the above formula (1) to a range of 4.0 to 9.5.

  The titanium alloy of the present invention contains the above-mentioned components, and the balance is composed of Ti and impurities. Major impurities include O (oxygen), C (carbon), N (nitrogen), and H (hydrogen). O is an impurity contained in the sponge titanium and the V raw material, and C and N are impurities contained in the sponge titanium. H is an impurity that is absorbed from the atmosphere during heating or absorbed in the pickling process. The smaller these impurities, the better. However, it is acceptable that O is up to 0.2%, C is up to 0.01%, N is up to 0.01%, and H is up to 0.01%.

  Next, the manufacturing method of the titanium alloy material of the present invention will be described by taking the case of manufacturing a thin plate as an example. For titanium alloy materials, ingots produced by a normal melting method such as VAR are made into slabs by hot forging or rolling, hot coils are produced by hot rolling, and the final thickness is obtained by cold rolling. It is finished and finished by final annealing. Of these, the cold rolling process has a great influence on the product characteristics. In particular, it has excellent superplastic properties at high temperatures by performing cold working (cold rolling) with a cross-section reduction rate of 40% or more. A titanium alloy material can be obtained. This is due to the following reasons.

  That is, when the cross-section reduction rate in cold rolling is increased, the crystal grain size in the titanium alloy material, particularly the grain size of the pro-eutectoid α phase is reduced. And if the crystal grain diameter in a titanium alloy material becomes small, since the elongation when giving superplastic deformation at high temperature will become large, the titanium alloy material which is excellent in the superplastic property at high temperature can be manufactured. Thus, when the cross-section reduction rate in cold rolling is increased, the elongation when superplastic deformation is applied at high temperature rapidly increases until the cross-section reduction rate is around 40%, and in the region of 40% or more, Change is getting smaller. Therefore, in the manufacturing method of the titanium alloy material of the present invention, cold working with a cross-section reduction rate of 40% or more is performed. Although there is no restriction | limiting in particular in the upper limit of a cross-section reduction rate, When cold rolling exceeding 80% is given, an ear crack will generate | occur | produce in the edge part of a board. Therefore, it is desirable to limit the cross-sectional reduction rate in cold working to 80% or less. However, when performing the intermediate annealing for the purpose of recovering the ductility of the material, the cold working may be performed under the condition that the cross-section reduction rate exceeds 80%.

The cross-sectional reduction rate can be obtained from the following equation (a).
Cross-sectional reduction rate (%) = {(cross-sectional area before processing−cross-sectional area after processing) / cross-sectional area before processing} × 100 (a)

Example 1
Using an arc melting furnace in plasma, a button ingot having a width of 50 mm, a thickness of 15 mm, and a length of 80 mm was produced. After heating the button ingot between 850 ° C., hot rolling with a thickness of 5 mm was performed. A plate was made. After this hot-rolled sheet is annealed at 750 ° C. for 10 minutes, the oxide scale is removed by shot brass and pickling, and the surface is further cut by machining to a thickness of 4 mm for cold rolling. The material was made. This cold-rolling material was cold-rolled to produce a cold-rolled plate having a thickness of 2 mm. At this time, as an evaluation of cold-rollability, the occurrence of cracks at the surface edge of the cold-rolled plate was visually observed.

  Furthermore, for those in which no cracks occurred during the cold rolling, heat treatment was performed in an argon atmosphere at 700 ° C. for 30 minutes, and after rolling to 1.5 mm by cold rolling, again in an argon atmosphere. A heat treatment was performed at 700 ° C. for 30 minutes to obtain a test material. A plate-shaped test piece having a thickness of 1.5 mm and a width of 12.5 mm was taken from the specimen so that the length direction of the test piece and the rolling direction were parallel to each other. A tensile test was performed at a test temperature of 800 ° C. and a tensile speed of 9 mm / min, and the elongation at break was measured by setting the distance between the test marks of this tensile test piece to 20 mm.

  Table 1 shows the chemical composition, cold-rollability evaluation and breaking elongation of the cold-rolled sheet.

  As shown in Table 1, an alloy that satisfies the chemical composition defined in the present invention can be cold-rolled and has excellent superplastic elongation.

(Example 2)
Under the same manufacturing conditions as in Example 1, a cold rolling material having a thickness of 4 mm containing Al: 3.0%, V: 5.0%, the balance being Ti and impurities was produced.

  This cold-rolling material was subjected to cold rolling with different cross-sectional reduction rates to produce cold-rolled plates having thicknesses of 3.5 mm, 3.0 mm, 2.5 mm, 2.0 mm, and 1.5 mm. These cold-rolled plates were heat-treated at 700 ° C. for 30 minutes in an argon atmosphere, and then the parallel part had a thickness of 1.0 mm and a width of 12 so that the length direction of the test piece was parallel to the rolling direction. A 5 mm plate specimen was collected. A tensile test was performed at a test temperature of 800 ° C. and a tensile speed of 9 mm / min, and the elongation at break was measured by setting the distance between the test marks of this tensile test piece to 20 mm.

  Furthermore, after conducting a heat treatment at 700 ° C. for 30 minutes in an argon atmosphere on a cold-rolled sheet having a thickness of 2.0 mm in order to investigate the influence of the cross-section reduction rate in the cold rolling after the intermediate annealing on the superplastic properties. After rolling again to a thickness of 1.5 mm or 1.0 mm by cold rolling, a heat treatment was performed at 700 ° C. for 30 minutes in an argon atmosphere to obtain a test material. A plate-shaped test piece having a parallel portion of 1.0 mm in thickness and 12.5 mm in width was sampled from the test material, and the same tensile test as described above was performed to measure the elongation at break. These cross-sectional reduction rates and elongation at break are shown in Table 2.

  As shown in Table 2, since the chemical composition was in the range defined by the present invention in any of the examples, the elongation at break exceeded 200%, and excellent superplastic characteristics were obtained. In particular, the elongation at break increases as the cross-section reduction rate increases, and the elongation at break hardly changes when the cross-section reduction rate is 40% or more. No. From the results of 39 and 40, it can be seen that even if the cold rolling rate after the intermediate annealing is low, the elongation at break is good if the cross-sectional reduction rate before the intermediate annealing is 40% or more.

  The titanium alloy of the present invention has sufficient cold workability and excellent superplastic properties. Therefore, a coil can be manufactured by cold rolling using the titanium alloy of the present invention, and a superplastic forming material having a uniform thickness distribution can be manufactured. Thereby, the titanium alloy thin plate can be easily manufactured at low cost, and the application field of the titanium alloy thin plate can be expanded.

Claims (4)

  In mass%, Al: 2.0 to 4.0%, V: 4.0 to 9.0%, Zr: 0 to 2.0% and Sn: 0 to 3.0%, the balance being Ti and impurities A titanium alloy characterized by comprising: In mass%, Al: 2.0 to 4.0%, V: 4.0 to 9.0%, Zr: 0 to 2.0% and Sn: 0 to 3.0%, and Fe: 0 20-1.0%, Cr: 0.01-1.0%, Cu: 0.01-1.0% and Ni: 0.01-1.0% or more selected from one type, A titanium alloy, wherein the balance is Ti and impurities, and Veq obtained from the following formula (1) is in the range of 4.0 to 9.5.
Veq = V + 1.9Cr + 3.75Fe (1)
However, the element symbol on the right side of the formula (1) means the content (% by mass) of the element.   In mass%, Al: 2.0 to 4.0%, V: 4.0 to 9.0%, Zr: 0 to 2.0% and Sn: 0 to 3.0%, the balance being Ti and impurities A method for producing a titanium alloy material, comprising subjecting a titanium alloy made of a material to cold working with a cross-sectional reduction rate of 40% or more. In mass%, Al: 2.0 to 4.0%, V: 4.0 to 9.0%, Zr: 0 to 2.0% and Sn: 0 to 3.0%, and Fe: 0 20-1.0%, Cr: 0.01-1.0%, Cu: 0.01-1.0% and Ni: 0.01-1.0% or more selected from one type, A titanium alloy whose balance is made of Ti and impurities and Veq obtained from the following formula (1) is in the range of 4.0 to 9.5 is subjected to cold working with a cross-section reduction rate of 40% or more. A method for producing a titanium alloy material.
Veq = V + 1.9Cr + 3.75Fe (1)
However, the element symbol on the right side of the formula (1) means the content (% by mass) of the element.