WO2021020532A1 - Titanium alloy plate and exhaust system component of automobiles - Google Patents

Abstract

This titanium alloy plate has a specific chemical composition, while comprising an α phase having an average crystal grain size of from 5 μm to 30 μm and an intermetallic compound in the structure; the intermetallic compound contains a TiSiGe intermetallic compound that contains Ti and one or both of Si and Ge, and optionally contains a TiCu intermetallic compound that contains Cu and Ti; the total area fraction of the TiSiGe intermetallic compound and the TiCu intermetallic compound in the structure is from 1.0% to 5.0%; and the area fraction of the TiSiGe intermetallic compound is 1.0% or more.

Description

Titanium alloy plate and automobile exhaust system parts

The present invention relates to a titanium alloy plate and automobile exhaust system parts.
The present application claims priority based on Japanese Patent Application No. 2019-139944 filed in Japan on July 30, 2019, the contents of which are incorporated herein by reference.

The exhaust system of automobiles and the like is equipped with an exhaust manifold and an exhaust pipe. The exhaust gas discharged from the engine and collected by the exhaust manifold is discharged to the outside from the exhaust port at the rear of the vehicle body via the exhaust pipe. A catalyst device and a muffler (silencer) are arranged in the middle of the exhaust pipe to purify the exhaust gas and muffle the exhaust noise. In the present specification, the entire area from the exhaust manifold to the exhaust pipe to the exhaust port is referred to as an "exhaust device". Further, parts such as an exhaust manifold, an exhaust pipe, a catalyst device, and a muffler that constitute an exhaust device are referred to as "exhaust system parts".

Conventionally, stainless steel with high strength and excellent corrosion resistance and workability has been used for the components of the exhaust system of four-wheeled vehicles and two-wheeled vehicles (hereinafter referred to as automobiles, etc.). However, in recent years, titanium materials, which are lighter than stainless steel, have high strength, and have excellent corrosion resistance, are being used. For example, JIS2 type industrial pure titanium material is used for the exhaust system of a two-wheeled vehicle. Furthermore, recently, titanium alloys having higher heat resistance are being used in place of JIS2 type industrial pure titanium materials.

Especially recently, the exhaust gas temperature has tended to rise. Therefore, the exhaust gas temperature in the exhaust pipe may reach about 800 ° C., and it is required to secure sufficient high temperature strength even in this temperature range. Further, since the exhaust system parts are processed, the material is also required to have excellent workability at room temperature.

Patent Document 1 describes a titanium alloy containing 0.15 to 2% by mass of Si, restricting Al to less than 0.30% by mass, and having excellent high temperature oxidation resistance consisting of residual titanium and unavoidable impurities. ing.
Further, Patent Document 2 is characterized by containing Al: 0.30 to 1.50% and Si: 0.10 to 1.0% on a mass basis, and is excellent in high temperature oxidation resistance and corrosion resistance. Titanium alloys are listed.
Further, Patent Document 3 contains Cu: more than 2.1% to 4.5%, oxygen: 0.04% or less, Fe: 0.06% or less in mass%, and the balance Ti and unavoidable impurities. A heat-resistant titanium alloy for an exhaust device member, which comprises excellent cold workability, is described.
Further, in Patent Document 4, the mass% is Si: 0.1 to 0.6%, Fe: 0.04 to 0.2%, O: 0.02 to 0.15%, and Fe and O. For exhaust system parts with excellent oxidation resistance, consisting of unavoidable impurities having a total content of 0.1% or more, 0.3% or less, balance Ti, and a single content of less than 0.04%. Titanium alloy materials are listed.

However, the titanium alloys described in Patent Document 1, Patent Document 3, and Patent Document 4 are intended to secure high-temperature strength by limiting the chemical composition, and the strength in a high-temperature range of 800 ° C. or higher is not always required. It wasn't enough. Further, although the titanium alloy described in Patent Document 2 can obtain a certain high-temperature strength, the processability at room temperature is not always sufficient.

Japanese Patent Application Laid-Open No. 2007-270199 Japanese Patent Application Laid-Open No. 2005-290548 Japanese Patent Application Laid-Open No. 2009-030140 Japanese Patent Application Laid-Open No. 2013-142183

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a titanium alloy plate and automobile exhaust system parts which are excellent in high temperature strength in a high temperature environment of 800 ° C. or higher and also excellent in workability at room temperature. And.

The gist of the present invention is as follows.
[1] The titanium alloy according to one aspect of the present invention has a chemical composition of 0 to 0.60% Si and 0 to 4.5% Ge, or both, and 0 to 1.0 in mass%. One or more selected from the group consisting of% Al, 0 to 1.0% Zr, and 0 to 2.0% Sn, and 0 to 1.5% Cu are represented by the following formulas. (1) to (3) are contained so as to satisfy, 0 to 1.0% Nb, 0 to 0.080% Fe, Mo, Ta, W, V, Cr, Ni, Mn and Co. And are contained so as to satisfy the following formula (4), Ga: 0 to 10.0%, In: 0 to 10.0%, and Hf: 0 to 10.0%. It is limited to 0.070% or less, the balance is composed of Ti and impurities, and has an α phase having an average crystal grain size of 5 μm or more and 30 μm or less and an intermetallic compound in the structure, and the intermetallic compound is Si. , TiSiGe-based intermetallic compound containing one or both of Ge and Ti, and optionally containing TiCu-based intermetallic compound containing Cu and Ti, said TiSiGe-based intermetallic compound and said TiCu in the structure. The total area fraction of the intermetallic compounds is 1.0% or more and 5.0% or less, and the area fraction of the TiSiGe intermetallic compound is 1.0% or more.
1.5% ≤ [Ge%] + 7.5 x [Si%] ≤ 4.5% ... (1)
[Cu%] + 1.5 x [Zr%] ≤ 1.5% ... (2)
10.0% ≤12 x [Al%] +10 x [Cu%] +3.5 x [Zr%] +6 x [Sn%] ≤36.5% ... (3)
[Mo%] + 0.2 x [Ta%] + 0.285 x [Nb%] + 0.4 x [W%] + 0.67 x [V%] + 1.25 x ([Cr%] + [Ni%] ) + 1.7 x ([Mn%] + [Co%]) + 2.5 x [Fe%] ≤ 0.4% ... (4)
However, in the formulas (1) to (4), [Ge%], [Si%], [Zr%], [Al%], [Sn%], [Mo%], [Ta%], [Nb%]. ], [W%], [V%], [Cr%], [Ni%]), [Mn%], [Co%], [Fe%] are the contents of each element in mass%. , If the element is not contained, 0 is substituted.
[2] In the titanium alloy plate according to the above [1], the average particle size of the TiSiGe-based intermetallic compound may be in the range of 0.1 to 2.0 μm.
[3] In the titanium alloy plate according to the above [1] or [2], 80% or more of the TiSiGe-based intermetallic compound may be present at the grain boundaries of the α phase in terms of the number ratio.
[4] The titanium alloy plate according to [1] above contains Cu having a chemical composition of 0.5% to 1.5% by mass, and the area fraction of the TiCu-based intermetallic compound is 0. It may be more than%.
[5] In the titanium alloy plate according to the above [4], the average particle size of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound may be in the range of 0.1 to 2.0 μm.
[6] In the titanium alloy plate according to the above [4] or [5], 80% or more of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound are at the grain boundaries of the α phase in a number ratio. It may exist.
[7] The automobile exhaust system component according to another aspect of the present invention has a housing made of the titanium alloy plate according to any one of [1] to [6].

According to the above aspect of the present invention, it is possible to provide a titanium alloy plate having excellent high temperature strength in a high temperature environment of 800 ° C. or higher and excellent workability at room temperature, and an automobile exhaust system component including the titanium alloy.

The present inventors have investigated a method for simultaneously improving high-temperature strength and workability.
In order to improve the high temperature strength of the titanium alloy plate, it is usually carried out to contain an alloy element and solid solution strengthen it. However, since the titanium alloy plate having improved high-temperature strength has high strength even at room temperature, the springback during molding is increased, and the workability at room temperature (molding workability) is lowered. For example, in order to automate welding and the like to efficiently produce products such as exhaust devices, it is necessary to reduce the conventional misalignment due to springback.

To suppress springback, it is effective to increase Young's modulus or reduce strength, especially 0.2% proof stress. In order to increase Young's modulus, it is necessary to add Al or O or to develop the texture, but this reduces the ductility of the material and the press workability itself before springback. Therefore, the present inventors have studied a method of increasing the strength at high temperature while lowering the strength at room temperature, and have come to find that an element having a solid solution limit greatly different depending on the temperature is utilized. As a result, the strength is relatively low by precipitating solid solution elements at room temperature during molding, and when used in a high temperature range, the precipitate is partially solid solution to strengthen the solid solution, and the rest. Invented a titanium alloy plate that can secure high-temperature strength by leaving the precipitates in the high-temperature region and maintaining the fine granulation of the α phase to prevent a decrease in strength, and preventing the β-phase from precipitating. I came to do it. In particular, in order to leave precipitates when used in a high temperature region, it is important to deposit more precipitates.

Here, the 0.2% proof stress described above will be described. Titanium alloy plates may or may not show a yield phenomenon in a tensile test. When the yield phenomenon is not shown, the stress corresponding to the yield stress must be defined as the proof stress in order to clarify the boundary between the elastic deformation and the plastic deformation for convenience. In general, since the permanent strain at the time of yielding of steel is about 0.002 (0.2%), the stress at which the permanent strain at the time of unloading becomes 0.2% is called 0.2% proof stress.
As a result of the examination by the present inventors, in the titanium alloy plate according to the present invention, the 0.2% proof stress and the yield stress were equivalent even when the yield phenomenon was exhibited. Therefore, in the present embodiment, this 0.2% proof stress is substituted for the yield stress.

Further, in order to ensure workability at room temperature, it is preferable to increase the average crystal grain size of the α phase to improve ductility. In order to increase the average crystal grain size of the α phase, it is effective to perform annealing after cold rolling to promote the grain growth of the α phase. However, if an intermetallic compound is formed in the structure during annealing after cold rolling, the intermetallic compound inhibits the grain growth of the α phase. Therefore, it is desirable to perform annealing in a relatively high temperature range where intermetallic compounds do not precipitate.
On the other hand, when the alloying element dissolves in the metal structure, the metal structure is solid-solved and strengthened, the proof stress is improved by 0.2%, springback is likely to occur, and workability at room temperature is hindered. Therefore, in order to ensure processability at room temperature, it is preferable that there is a certain amount of intermetallic compound.
As a result of the study by the present inventors, in order to precipitate the intermetallic compound, the temperature is lower than the temperature range in which the α-phase crystal grains are grown after the α-phase crystal grains are grown by annealing after cold rolling. It has been found that if the second annealing is performed in the region for a long time, a certain amount of intermetallic compound can be precipitated after increasing the average crystal grain size of the α phase.

If the intermetallic compound is precipitated and then annealed to enlarge the crystal grains of the α phase, the previously precipitated intermetallic compound is re-solidified into the metal structure by annealing, and at room temperature. It becomes impossible to secure workability. Therefore, it is necessary to first perform annealing to increase the size of the α-phase crystal grains, and then perform a second annealing to precipitate the intermetallic compound.

Further, since the metal structure of the titanium alloy receives a roll rolling force by being subjected to cold rolling, it becomes a structure composed of crystal grains stretched in the rolling direction. Therefore, annealing for controlling the average crystal grain size of the α phase needs to be performed after cold rolling.

As described above, in order to increase the average crystal grain size of the α phase and then precipitate a certain amount of the intermetallic compound, the first annealing in which the average crystal grain size of the α phase is controlled after cold rolling. Then, it is desirable to perform a second annealing for precipitating the intermetallic compound.

On the other hand, in order to secure high-temperature strength, as described above, it is desirable that the intermetallic compound dissolves in solid solution and strengthens in solid solution when the titanium alloy plate is heated to the operating temperature. However, if all the intermetallic compounds are dissolved, the pinning effect is lost and α-phase grain growth may occur, which may reduce the high-temperature strength. Therefore, the intermetallic compounds should be used so that the α-phase grain growth can be suppressed. It is preferable that it remains to some extent even at high temperatures. In order to exert the effect of solid solution strengthening and to leave the intermetallic compound at a high temperature, it is preferable to precipitate a large amount of the intermetallic compound at room temperature. Further, it is effective to precipitate a kind of intermetallic compound that easily remains at a high temperature. As a result of studies by the present inventors, the constituent elements of a predetermined intermetallic compound are locally concentrated in a solid solution state before the intermetallic compound is precipitated by the second annealing after cold rolling. As a result, it was found that a large amount of intermetallic compounds that tend to remain at high temperatures can be precipitated at room temperature. It was also found that for that purpose, it is preferable to perform annealing at a temperature in the α + β region between hot working and cold rolling to concentrate the solid solution element in the β phase.

The titanium alloy plate obtained through such a step has a relatively large α-phase crystal grain size and has a structure in which a large amount of TiSiGe-based intermetallic compounds that tend to remain at high temperatures are precipitated, and at low temperatures. Workability can be ensured.
Further, since the eutectoid temperature of the intermetallic compound exceeds 800 ° C. for Si and Ge, the intermetallic compound is present even when used at more than 800 ° C., and coarsening of crystal grains can be suppressed. In addition, since it contains alloying elements with a wide solid solution limit such as Al, Zr, and Sn, a part of the intermetallic compound is dissolved in the metal structure at high temperature, and in addition to the solid solution strengthening by Si and Ge. , Al, Zr, Sn can be strengthened by solid solution to improve high temperature strength.
Furthermore, when Cu with a wide solid solution limit is contained, Cu, which was present as a TiCu-based intermetallic compound near room temperature, dissolves a part of the intermetallic compound in the metal structure at high temperature, thereby further strengthening the solid solution. It can be further improved and the high temperature strength can be further improved.

The titanium alloy plate according to the present invention is particularly preferably used as a constituent member of an exhaust system component of an exhaust device such as an automobile or a motorcycle. The exhaust device is manufactured by forming various exhaust system parts by molding a titanium alloy plate and combining these exhaust system parts. After that, the exhaust device is mounted on an automobile or the like and used. By using the exhaust device, the titanium alloy plate, which is a constituent member, is exposed to high-temperature exhaust gas and heated to a high temperature. The titanium alloy plate according to the present invention has low strength because the intermetallic compound is present in the metal structure and the average crystal grain size of the α phase is relatively large. Therefore, the titanium alloy plate according to the present invention is excellent in workability at room temperature and has a small springback during molding.
In addition, after molding, when used as an exhaust device, the titanium alloy plate is exposed to high-temperature exhaust gas and heated to a high temperature, so that the intermetallic compounds in the metal structure that existed during the molding process are dissolved. The solid solution is strengthened and excellent high temperature strength is ensured. In particular, the titanium alloy plate according to the present invention can further increase the high-temperature strength at 800 ° C. or higher.

Hereinafter, the titanium alloy plate according to the embodiment of the present invention (titanium alloy plate according to the present embodiment) will be described in detail.
The titanium alloy plate according to the present embodiment has a chemical composition of 0 to 0.60% Si and 0 to 4.5% Ge, or both, and 0 to 1.0% Al. One or more selected from the group consisting of 0 to 1.0% Zr and 0 to 2.0% Sn, and 0 to 1.5% Cu are used in the following formulas (1) to (3) is contained so as to satisfy, and 0 to 1.0% Nb, 0 to 0.080% Fe, and Mo, Ta, W, V, Cr, Ni, Mn, and Co are described below. It is contained so as to satisfy the formula (4), Ga: 0 to 10.0%, In: 0 to 10.0%, and Hf: 0 to 10.0%, and O: 0.070%. The balance is limited to the following, the balance is composed of Ti and impurities, and the structure has an α phase having an average crystal particle size of 5 μm or more and 30 μm or less and an intermetallic compound, and the intermetallic compound is one of Si and Ge. Alternatively, it contains a TiSiGe-based intermetallic compound containing both and Ti, and optionally contains a TiCu-based intermetallic compound containing Cu and Ti, and the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound in the structure. The total area fraction of the above is 1.0% or more and 5.0% or less, and the area fraction of the TiSiGe-based intermetallic compound is 1.0% or more.
1.5% ≤ [Ge%] + 7.5 x [Si%] ≤ 4.5% ... (1)
[Cu%] + 1.5 x [Zr%] ≤ 1.5% ... (2)
10.0% ≤12 x [Al%] +10 x [Cu%] +3.5 x [Zr%] +6 x [Sn%] ≤36.5% ... (3)
[Mo%] + 0.2 x [Ta%] + 0.285 x [Nb%] + 0.4 x [W%] + 0.67 x [V%] + 1.25 x ([Cr%] + [Ni%] ) + 1.7 x ([Mn%] + [Co%]) + 2.5 x [Fe%] ≤ 0.4% ... (4)
However, in the formulas (1) to (4), [Ge%], [Si%], [Zr%], [Al%], [Sn%], [Mo%], [Ta%], [Nb%]. ], [W%], [V%], [Cr%], [Ni%]), [Mn%], [Co%], [Fe%] are the contents of each element in mass%. , If the element is not contained, 0 is substituted.
In the titanium alloy plate, when the intermetallic compound is a TiSiGe-based intermetallic compound, the average particle size of the TiSiGe-based intermetallic compound may be in the range of 0.1 to 2.0 μm, and the TiSiGe-based intermetallic compound may be in the range of 0.1 to 2.0 μm. 80% or more of the intermetallic compound may be present at the grain boundaries of the α phase.
Further, when the titanium alloy plate contains Cu and the intermetallic compounds are a TiSiGe-based intermetallic compound and a TiCu-based intermetallic compound, the average particle size of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound is , 0.1 to 2.0 μm, and 80% or more of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound are present in the crystal grain boundary of the α phase in a number ratio. May be good.

As described above, the titanium alloy plate according to the present embodiment does not necessarily contain Cu, and may contain a TiSiGe-based intermetallic compound as an intermetallic compound or a TiSiGe-based intermetallic compound as an intermetallic compound containing Cu. And when it contains a TiCu-based intermetallic compound, it may be paraphrased as follows.
[1'] One or both of Si of 0% by mass or more and 0.60% by mass or less and Ge of 0% by mass or more and 4.5% by mass or less.
One or two or more of Al of 1.0% by mass or less, Zr of 1.0% by mass or less, and Sn of 2.0% by mass or less.
Containing Nb of 1.0% by mass or less (including 0% by mass),
Satisfy the following formulas (1') to (3'),
Fe is limited to 0.080% by mass or less, and O is limited to 0.070% by mass or less.
Further, Mo, Ta, W, V, Cr, Ni, Mn, Co and Fe are restricted so as to satisfy the following formula (4').
The rest consists of Ti and impurities
A TiSiGe-based intermetallic compound having an α phase having an average crystal grain size of 5 μm or more and 30 μm or less and an intermetallic compound in the structure and containing one or both of Si and Ge and Ti is used as the intermetallic compound. Including
The surface integral of the TiSiGe-based intermetallic compound in the structure is 1.0% or more and 5.0% or less.
A titanium alloy plate characterized by that.
1.5% ≤ [Ge%] + 7.5 [Si%] ≤ 4.5% ... (1')
1.5 [Zr%] ≤ 1.5% ... (2')
10.0% ≤12 [Al%] +3.5 [Zr%] +6 [Sn%] ≤36.5% ... (3')
[Mo%] +0.2 [Ta%] +0.285 [Nb%] +0.4 [W%] +0.67 [V%] +1.25 ([Cr%] + [Ni%]) + 1.7 ( [Mn%] + [Co%]) + 2.5 [Fe%] ≤ 0.4% ... (4')
However, in the formulas (1') to (4'), [Ge%], [Si%], [Zr%], [Al%], [Sn%], [Mo%], [Ta%], [ [Nb%], [W%], [V%], [Cr%], [Ni%]), [Mn%], [Co%], [Fe%] are the contents (mass%) of each element. If the element is not contained, 0 is substituted.
[2'] One or both of Si of 0% by mass or more and 0.60% by mass or less and Ge of 0% by mass or more and 4.5% by mass or less.
One or two or more of Al of 1.0% by mass or less, Zr of 1.0% by mass or less, and Sn of 2.0% by mass or less.
Nb of 1.0% by mass or less (including 0% by mass) and
Contains 1.5% by mass or less of Cu and
Satisfy the following formulas (5') to (7'),
Fe is limited to 0.080% by mass or less, and O is limited to 0.070% by mass or less.
Further, Mo, Ta, W, V, Cr, Ni, Mn, Co and Fe are restricted so as to satisfy the following formula (8').
The rest consists of Ti and impurities
A TiSiGe-based intermetallic compound having an α phase having an average crystal grain size of 5 μm or more and 30 μm or less and an intermetallic compound in the structure and containing one or both of Si and Ge and Ti is used as the intermetallic compound. In addition to containing, it contains a TiCu-based intermetallic compound containing Cu and Ti,
The total area fraction of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound in the structure is 1.0% or more and 5.0% or less, and the area fraction of the TiSiGe-based intermetallic compound is 1. It is 0% or more, and the area fraction of the TiCu-based intermetallic compound is more than 0%.
A titanium alloy plate characterized by that.
1.5% ≤ [Ge%] + 7.5 [Si%] ≤ 4.5% ... (5')
[Cu%] + 1.5 [Zr%] ≤ 1.5% ... (6')
10.0% ≤12 [Al%] +10 [Cu%] +3.5 [Zr%] +6 [Sn%] ≤36.5% ... (7')
[Mo%] +0.2 [Ta%] +0.285 [Nb%] +0.4 [W%] +0.67 [V%] +1.25 ([Cr%] + [Ni%]) + 1.7 ( [Mn%] + [Co%]) + 2.5 [Fe%] ≤ 0.4% ... (8')
However, in the formulas (5') to (8'), [Ge%], [Si%], [Cu%], [Zr%], [Al%], [Sn%], [Mo%], [ [Ta%], [Nb%], [W%], [V%], [Cr%], [Ni%]), [Mn%], [Co%], [Fe%] contain each element. It is an amount (mass%), and 0 is substituted when the element is not contained.
[3'] The titanium alloy plate according to [1'], wherein the average particle size of the TiSiGe-based intermetallic compound is in the range of 0.1 to 2 μm.
[4'] The titanium alloy plate according to [2'], wherein the average particle size of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound is in the range of 0.1 to 2 μm.
[5'] The titanium alloy plate according to [1'] or [3'], wherein 80% or more of the TiSiGe-based intermetallic compound is present at the grain boundaries of the α phase in a number ratio.
[6'] The above-mentioned [2'] or [4'], wherein 80% or more of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound are present at the grain boundaries of the α phase in a number ratio. Titanium alloy plate.
[7'] Further, any one or more of Ga, In, and Hf are contained in a range satisfying Ga ≤ 10% by mass, In ≤ 10% by mass, and Hf ≤ 10% by mass, [1']. The titanium alloy plate according to any one of [6'].

That is, when Cu is not contained, the titanium alloy plate contains one or both of Si and Ge, one or more of Al, Zr, and Sn, and 1.0% by mass or less (0% by mass). The content of Si, Ge, Al, Zr, and Sn satisfies the predetermined relational expression, and Fe is 0.080% by mass or less and O is 0.070% by mass or less. Examples thereof include those in which Mo, Ta, W, V, Cr, Ni, Mn, Co and Fe are restricted so as to satisfy a predetermined formula, and the balance has a composition of Ti and impurities.

On the other hand, when Cu is contained, the titanium alloy plate contains one or both of Si and Ge, one or more of Al, Zr and Sn, and 1.0% by mass or less (0% by mass). Nb and Cu are contained, and the contents of Si, Ge, Al, Cu, Zr, and Sn satisfy the predetermined relational expression, Fe is 0.080% by mass or less, and O is 0.070. The composition is limited to% by mass or less, further limited so that Mo, Ta, W, V, Cr, Ni, Mn, Co and Fe satisfy the predetermined formula, and the balance is composed of Ti and impurities. Can be exemplified.

Hereinafter, each element and its content will be described. Here, "%" for the content of each element in the chemical composition is mass%.

(One or both of Si and Ge)
The titanium alloy plate according to the present embodiment needs to have an α phase and an intermetallic compound present in the structure when heated to 800 ° C. or higher. Examples of the element that combines with titanium to form an intermetallic compound include eutectoid elements such as Si, Ni, Cu, Sn, Ge, and Bi. Among these eutectoid elements, the elements having an eutectoid temperature of 800 ° C. or higher are Si and Ge, and the other elements have an eutectoid temperature lower than 800 ° C. Therefore, the titanium alloy plate according to the present embodiment must contain one or both of Si and Ge.

In addition, a part of Si dissolves in the α phase at 800 ° C. or higher, and the solid solution is strengthened to improve the high temperature strength and the oxidation resistance. Similar to Si, Ge dissolves partly in the α phase to strengthen the solid solution and improve the high temperature strength.

When one or both of Si and Ge are contained, it is necessary to satisfy the following formula (1). When both Si and Ge are contained, the lower limit of either one may be set to 0% or more as long as the equation (1) is satisfied. When either Si or Ge is contained, the Si content is 0.20% or more and the Ge content is 1.5% or more so as to satisfy the equation (1).
When Si is contained alone, the Si content is preferably 0.30% or more, more preferably 0.40% or more.
When Ge is contained alone, the Ge content is preferably 2.0% or more, more preferably 3.0% or more.
When both Si and Ge are contained, the Si content is preferably 0.10% or more, more preferably 0.20% or more, still more preferably 0.30% or more. The Ge content is preferably 0.5% or more, more preferably 0.6% or more, and even more preferably 0.8% or more.

1.5% ≤ [Ge%] + 7.5 x [Si%] ≤ 4.5% ... (1)

However, in the formula (1), [Ge%] and [Si%] are the contents (mass%) of each element, and 0 is substituted when the element is not contained.

If the contents of Si and Ge are too small, that is, if [Ge%] + 7.5 × [Si%] in the equation (1) is less than 1.5%, an intermetallic compound (TiSiGe system) stable at 800 ° C. or higher Intermetallic compounds) cannot be formed.

In the titanium alloy plate according to the present embodiment, the β phase is substantially precipitated when the temperature exceeds 830 ° C. due to the influence of other elements and impurity elements. Therefore, the practical upper limit temperature is about 820 ° C. In order to maintain the phase composition of the α phase and the intermetallic compound at 820 ° C., [Ge%] + 7.5 × [Si%] in the formula (1) is preferably 3.0% or more.

However, if the content of Si or Ge is large, the ductility at room temperature will decrease and the workability will be significantly deteriorated. Therefore, [Ge%] + 7.5 × [Si%] in the equation (1) is set to 4.5% or less. Therefore, the Si content is 0.60% or less, and the Ge content is 4.5% or less. The Si content is preferably 0.50% or less, and the Ge content is preferably 4.0% or less.

(One or more of Al, Zr, Sn)
In the titanium alloy plate according to the present embodiment, Si and Ge remain as an intermetallic compound (TiSiGe-based intermetallic compound) at a temperature of 800 ° C. or higher. Therefore, the solid solution amounts of Si and Ge that dissolve in the α phase are the maximum amounts (saturation amounts) of each, and there is a limit to the solid solution strengthening with only Si and Ge. Therefore, the titanium alloy plate according to the present embodiment needs to contain a solid solution strengthening element other than Si and Ge in order to further strengthen the solid solution. In particular, it has a wider solid solution range than Si and Ge, and by containing an element that improves high-temperature strength, it is possible to further increase the strength. However, if an element having a large β-stabilizing ability is contained, the β phase is precipitated at 800 ° C., so it is necessary to contain an element having a small β-stabilizing ability or an α-stabilizing element. Examples of such an element include Al, Zr, and Sn. Therefore, the titanium alloy plate according to the present embodiment contains one or more of Al, Zr, and Sn.
Further, the titanium alloy plate according to the present embodiment may further contain Cu, if necessary.

The titanium alloy contains one or more of Al, Zr, and Sn, and when Cu is contained as required, it is contained so as to satisfy the following equations (2) and (3). ..
If the left side ([Cu%] +1.5 × [Zr%]) of the equation (2) exceeds 1.5%, the β phase may be precipitated at a high temperature of 800 ° C. or higher. The left side of the equation (2) is preferably 1.4% or less, more preferably 1.3% or less.

The middle side of equation (3) (12 x [Al%] + 10 x [Cu%] + 3.5 x [Zr%] + 6 x [Sn%]) is when the solid solution strengthening amount of each element is converted to at%. Since it correlates with the amount of solid solution of, the atomic weight of each element is converted to Cu, and the strengthening ability of each element at high temperature is multiplied to obtain the product. If the middle side of the equation (3) is less than 10.0%, the solid solution strengthening becomes insufficient, and the high temperature strength of 800 ° C. or higher decreases. The middle side of the formula (3) is preferably 11.0% or more, more preferably 12.0% or more, and further preferably 13.0% or more.
On the other hand, if the middle side of the formula (3) exceeds 36.5%, the β phase may precipitate at a high temperature of 800 ° C. or higher. In addition, Al, Cu, and Sn, or Al, Cu, Zr, and Sn are excessively contained, which may reduce ductility at room temperature. The middle side of the equation (3) is preferably 32.0% or less, more preferably 30.0% or less.

[Cu%] + 1.5 x [Zr%] ≤ 1.5% ... (2)

10.0% ≤12 x [Al%] +10 x [Cu%] +3.5 x [Zr%] +6 x [Sn%] ≤36.5% ... (3)

However, in the formulas (2) and (3), [Zr%], [Al%], [Sn%], and [Cu%] are the contents (mass%) of each element and contain the element. If not, substitute 0.

Further, the content of each of Al, Zr, Sn, and Cu is preferably in the range described later.

Al is an element effective for solid solution strengthening and also an α-stabilizing element. When this effect is obtained, the Al content is preferably 0.1% or more.
On the other hand, when the Al content becomes excessive, twinning deformation at room temperature is inhibited, and ductility at room temperature decreases. Therefore, even when Al is contained, the Al content is set to 1.0% or less. The Al content is preferably 0.5% or less. The Al content may be 0% as long as the equations (2) to (3) are satisfied.

Zr is an element that is effective in strengthening solid solution and has a small β-stabilizing ability. When this effect is obtained, the Zr content is preferably 0.1% or more, more preferably 0.2% or more.
If the Zr content is 1.0% or less, the β phase is not formed even at 820 ° C. Therefore, the Zr content is set to 1.0% or less. The Zr content may be 0% as long as the equations (2) to (3) are satisfied.

Sn is an element that is effective for strengthening solid solution and has a small β-stabilizing ability. When this effect is obtained, the Sn content is preferably 0.5% or more, more preferably 0.6% or more, and further preferably 0.7% or more.
Further, Sn is an element that forms an intermetallic compound like Si and Ge, and is an element that reduces ductility at room temperature. However, in addition to being difficult to form, almost all of the intermetallic compounds containing Sn and Ti are solid-solved without remaining even if they exist at a high temperature of 800 ° C. or higher. That is, Sn improves the high temperature strength by strengthening the solid solution. A β phase does not occur even if Sn is contained in an amount of 10.0% or more, but if Sn is contained in an excessive amount, twinning deformation at room temperature is inhibited and ductility is lowered. Therefore, the Sn content is set to 2.0% or less. The Sn content is preferably 1.5% or less, more preferably 1.4% or less. The Sn content may be 0% as long as the equations (2) to (3) are satisfied.

Cu is an element that is effective in strengthening solid solution and has a small β-stabilizing ability. Further, Cu is an element that combines with Ti to form an intermetallic compound such as Ti ₂ Cu, like Si and Ge, and is an element that improves ductility at room temperature. However, almost all of the intermetallic compounds containing Cu and Ti (TiCu-based intermetallic compounds) do not remain at a high temperature of 800 ° C. or higher and are solid-dissolved.
In order to obtain the above effects, Cu may be contained in the titanium alloy plate according to the present embodiment. In that case, the Cu content is preferably 0.5% or more, more preferably 0.7% or more, and even more preferably 0.8% or more.
If the Cu content is 1.5% or less, the β phase is not formed even at 820 ° C. Therefore, the Cu content is set to 1.5% or less. The Cu content is preferably 1.3% or less, more preferably 1.2% or less.

Further, the titanium alloy plate containing substantially no Cu is superior in high temperature salt damage resistance to the titanium alloy plate containing Cu, and is more suitable for use in an environment in which snowmelt salt is sprayed. This is a phenomenon in which high-temperature salt damage causes chlorine contained in snowmelt salt to react with titanium oxide at high temperatures to promote oxidation in the atmosphere, and when it contains Cu that promotes the reaction with chlorine, This is because oxidation is further promoted as compared with the case where it is not contained.
Therefore, from the viewpoint of high temperature salt damage resistance, the Cu content is preferably less than 0.7%. It is more preferably less than 0.5%, further preferably 0.3% or less, still more preferably 0.1% or less.
The Cu content may be 0%.

(Nb: 0 to 1.0%)
Nb is an element that improves oxidation resistance. Therefore, it may be contained (it may not be contained) as needed. In order to obtain the effect of improving the oxidation resistance, it is preferable to contain Nb in an amount of 0.05% or more.
On the other hand, when the Nb content becomes excessive, the effect of improving the oxidation resistance with respect to the content becomes small, and the β phase is easily formed. In addition, Nb is an expensive element. Therefore, even when it is contained, the Nb content is set to 1.0% or less. The Nb content is preferably 0.5% or less, more preferably 0.4% or less.

(Fe: 0 to 0.080%)
Fe is an element irreversibly contained in the titanium alloy and is a β-stabilizing element. If Fe is excessively contained, the β phase is likely to be formed, and the growth of α-phase crystal grains is hindered. In order to obtain sufficient ductility at room temperature, it is necessary to grow α-phase crystal grains, so a low Fe content is preferable. If the Fe content exceeds 0.080%, the above-mentioned adverse effects become remarkable, so the Fe content needs to be limited to 0.080% or less. The Fe content is preferably 0.070% or less, more preferably 0.060% or less. The Fe content is preferably 0% as it is smaller, but the production cost is high in order to reduce it to less than 0.001%. Therefore, the content of 0.001% or more is allowed, and the Fe content may be 0.001% or more.

(Mo, Ta, W, V, Cr, Ni, Mn, Co)
Mo, Ta, W, V, Cr, Ni, Mn, and Co are elements that stabilize the β phase like Fe and Nb. Therefore, it is necessary to reduce it as much as possible. The content of these elements, together with the Fe content and the Nb content, needs to be limited to a range that satisfies the following equation (4). If the left side of Eq. (4) exceeds 0.4%, the β phase tends to precipitate, which is not preferable.
The lower limit of the left side of Eq. (4) need not be limited, but is substantially 0.01%.

[Mo%] + 0.2 x [Ta%] + 0.285 x [Nb%] + 0.4 x [W%] + 0.67 x [V%] + 1.25 x ([Cr%] + [Ni%] ) + 1.7 x ([Mn%] + [Co%]) + 2.5 x [Fe%] ≤ 0.4% ... (4)

In equation (4), [Mo%], [Ta%], [Nb%], [W%], [V%], [Cr%], [Ni%]), [Mn%], [Co%]. ] And [Fe%] are the contents (mass%) of each element, and 0 is substituted when the element is not contained.

(O: 0.070% or less)
O (oxygen) is an element irreversibly contained in the titanium alloy. If O is contained in excess, the strength at room temperature is improved and the ductility is lowered. Since O has almost no contribution to the strength at high temperature, it is preferable that the O content is small.
If the O content exceeds 0.070%, the above-mentioned adverse effects become remarkable, so the O content is set to 0.070% or less. The O content is preferably 0.065% or less, more preferably 0.060% or less. The smaller the O content, the more preferable it is, so it may be 0%, but in order to reduce it to less than 0.001%, the manufacturing cost becomes high. Therefore, the content of 0.001% or more is allowed, and the O content may be 0.001% or more.

(Ga, In, Hf)
Ga, In, and Hf are elements effective for solid solution strengthening, and one or more of them may be contained as necessary. In order to exert the effect of strengthening the solid solution, it is preferable to contain at least 0.1% or more of each element. On the other hand, these elements are expensive and increase the specific gravity of the titanium alloy plate. Therefore, even when it is contained, the Ga content, the In content, and the Hf content are each set to 10.0% or less. The Ga content, In content, and Hf content are each preferably 5.0% or less, more preferably 1.0% or less, and even more preferably 0.5% or less.

The rest of the chemical composition of the titanium alloy plate according to this embodiment is Ti and impurities other than the above.

The chemical composition of the titanium alloy plate according to this embodiment can be obtained by the following method.
Collect the test piece so as to include the total thickness of the titanium alloy plate. However, when analyzing carbon, a total thickness of 10% is removed from each surface. Acetone ultrasonic cleaning is performed before analysis. Oxygen is an inert gas molten infrared absorption method, nitrogen and hydrogen are inert gas molten thermoconductivity methods, carbon is a high-frequency combustion infrared absorption method, and other contained metals are JIS H1632-1: 2014. After decomposition, analysis is performed by an induction-bonded plasma (ICP) emission analysis method to determine the chemical composition of each element.

Next, the structure of the titanium alloy plate according to the present embodiment will be described.
The titanium alloy plate according to the present embodiment has an α phase having an average crystal grain size of 5 μm or more and 30 μm or less and an intermetallic compound in the structure.
When the titanium alloy plate according to the present embodiment does not contain Cu, the intermetallic compound includes a TiSiGe-based intermetallic compound containing one or both of Si and Ge and Ti. In this case, the surface integral of the TiSiGe-based intermetallic compound in the structure is 1.0% or more and 5.0% or less.
On the other hand, when Cu is contained, the intermetallic compound includes a TiSiGe-based intermetallic compound containing one or both of Si and Ge and Ti, and a TiCu-based intermetallic compound containing Cu and Ti. In this case, the total area fraction of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound in the structure is more than 1.0% and 5.0% or less, and the area fraction of the TiSiGe-based intermetallic compound is 1.0. % Or more, and the area fraction of the TiCu-based intermetallic compound is more than 0%.
That is, in the titanium alloy plate according to the present embodiment, the total area fraction of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound is 1.0% or more and 5.0% or less, and the TiSiGe-based compound is used. The area fraction of the intermetallic compound is 1.0% or more. However, when Cu is not contained, the TiCu-based intermetallic compound does not occur, and the surface integral is 0%.
Since it is difficult to measure the volume fraction of intermetallic compounds, it is evaluated by area fraction.
Hereinafter, the details of the structure of the titanium alloy plate according to the present embodiment will be described.

[Intermetallic compound]
The titanium alloy plate according to the present embodiment contains a TiSiGe-based intermetallic compound.
The TiSiGe-based intermetallic compound is an intermetallic compound containing one or both of Si and Ge and Ti, and more preferably an intermetallic compound composed of one or both of Si and Ge and Ti. The TiSiGe-based intermetallic compound may contain a metal element that is partially substitutable with Si and Ge. For example, as TiSiGe intermetallic _{compound, TiSi a, TiGe b, TiSi} c Ge d (a ~ d is a positive real number) can be exemplified the like, more _{specifically, TiSi, Ti 3 Si, Ti} 5 Si 3, Ti ₅ Ge ₃ , TiZrSi and the like can be exemplified.

The TiSiGe-based intermetallic compound exists relatively stably in the structure of the titanium alloy in the temperature range of about room temperature to about 830 ° C. Although a part of the TiSiGe-based intermetallic compound dissolves in a solid solution at 800 ° C. or higher, a sufficient amount can be left in a high temperature range of 800 ° C. or higher by precipitating a large amount at room temperature.
The remaining TiSiGe-based intermetallic compound can prevent α-phase grain growth at high temperatures. Further, by solid-solving a part of the TiSiGe-based intermetallic compound, the solid-solution strengthening of the titanium alloy can be achieved, and the high-temperature strength can be increased. Further, since the TiSiGe-based intermetallic compound is present in the structure at room temperature, the springback of the titanium alloy is suppressed and the workability is improved.

When the titanium alloy plate according to the present embodiment contains Cu, it further contains not only the TiSiGe-based intermetallic compound but also the TiCu-based intermetallic compound as the intermetallic compound. The TiCu-based intermetallic compound is an intermetallic compound containing Cu and Ti, and more preferably an intermetallic compound composed of Cu and Ti. Examples of the TiCu-based intermetallic compound include Ti ₂ Cu and the like.

The TiCu-based intermetallic compound exists relatively stably in the structure of the titanium alloy in the temperature range of about room temperature to about 790 ° C. The presence of the TiCu-based intermetallic compound in the structure increases the ductility of the titanium alloy and improves the workability.
On the other hand, when the temperature exceeds 790 ° C., Cu is solid-solved in the structure to strengthen the solid solution. Further, depending on the Cu content, the β phase is precipitated.

[Surface integral of intermetallic compound and surface integral of α phase]
The titanium alloy plate according to the present embodiment suppresses solid solution strengthening and reduces 0.2% resistance by precipitating the above-mentioned intermetallic compound in the metal structure at room temperature, thereby improving workability. Let me. In order to obtain this effect, it is necessary that the TiSiGe-based intermetallic compound is precipitated at 1.0% or more in total of the area fraction in the titanium alloy plate containing no Cu. It is preferably 2.0% or more, and more preferably 3.0% or more. However, if an excessive amount of the intermetallic compound is precipitated, the ductility at room temperature may be lowered due to precipitation strengthening. Therefore, the total area fraction of the TiSiGe-based intermetallic compound is set to 5.0% or less.
On the other hand, in the titanium alloy plate containing Cu, it is necessary that 1.0% or more of the TiSiGe-based intermetallic compound is precipitated, and at the same time, it is preferable that more than 0% of the TiCu-based intermetallic compound is precipitated. That is, it is preferable that the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound are precipitated in an area fraction of more than 1.0% in total.
However, if a large amount of these intermetallic compounds are precipitated, the ductility at room temperature may decrease due to precipitation strengthening. Therefore, the total area fraction of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound is set to 5.0% or less.
The titanium alloy plate according to the present embodiment contains a large amount of TiSiGe-based intermetallic compounds, so that when exposed to a high temperature of 800 ° C. or higher, a part of the titanium alloy plate is solid-solved to strengthen the solid solution, and the rest remains. Therefore, it is possible to suppress the grain growth of the α phase and suppress the decrease in high temperature intensity.
Further, since the TiCu-based intermetallic compound is contained when Cu is contained, the lower limit value is set to 0% for the titanium alloy plate containing Cu, and the lower limit value exceeds 0% for the titanium alloy plate containing Cu. And.

The balance other than the intermetallic compound is the α phase, and the surface integral of the α phase is 95.0% or more and 99.0% or less. Generally, the titanium alloy plate may have a β phase, but the titanium alloy plate according to the present embodiment does not have a β phase, or even if it exists, it is extremely small with respect to the amount of the intermetallic compound. Therefore, when the β phase is included, it may be included in the surface integral of the intermetallic compound. Further, as long as it does not inhibit the coarsening of α-phase crystal grains, it does not exclude the inclusion of a very small amount of β-phase.

In the titanium alloy plate according to the present embodiment, when the structure of the L cross section (cross section parallel to the rolling direction and the plate thickness direction) of the titanium alloy plate is elementally mapped, one or both of Si and Ge are larger than the average composition. The region in which Ti is contained and Ti is detected at the same time is specified as a TiSiGe-based intermetallic compound.
Specifically, the element distribution is measured by an energy dispersive X-ray spectroscope (EDX) or a wavelength dispersive X-ray spectroscope (WDS) attached to a scanning electron microscope (SEM). The measurement is performed by scanning the measurement area: 50 μm × 50 μm at intervals of 0.2 μm at an acceleration voltage of 15 kV. At this time, it is specified that the region in which Si and Ge are concentrated more than the parent phase without overlapping with the Fe-concentrated region is the TiSiGe-based intermetallic compound. As a guideline for "more concentrated than the mother phase", the concentration in mass% is 15 times or more that of the mother phase. The concentrated region of Fe is the β phase.
As described above, the TiSiGe-based intermetallic compound can be specified, and the area fraction of the TiSiGe-based intermetallic compound in the structure can be obtained based on the measured area and the size of the specified (detected) region.
Further, when the cross section of the structure of the titanium alloy plate is elementally mapped, the region where Cu and Ti are detected at the same time is specified as a TiCu-based intermetallic compound. In addition, the surface integral of the TiCu-based intermetallic compound in the structure can be determined based on the size of the detected region.

The titanium alloy plate according to the present embodiment may contain an intermetallic compound other than the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound as long as the processability at room temperature and the high-temperature strength are not impaired. The practical upper limit of the intermetallic compound other than the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound is 0.5%.

For the area fraction of the α phase, the cross section of the structure of the titanium alloy plate is elementally mapped in the same manner as described above, and the area specified as the TiSiGe-based intermetallic compound or the TiCu-based intermetallic compound is subtracted from the measured area. It is calculated by dividing the difference by the measured area. When a trace amount of β phase is present, the β phase is included in the surface integral of the intermetallic compound.

[Average particle size of intermetallic compounds]
In the titanium alloy plate according to the present embodiment, at room temperature, TiSiGe-based intermetallic compounds and TiCu-based intermetallic compounds are precipitated in a predetermined area fraction, so that the amount of solid solution of the intermetallic compounds in the α phase is small. 0.2% lower endurance. On the other hand, when the precipitated intermetallic compound is exposed to a high temperature, it dissolves in the α phase again, so that high high temperature strength can be obtained.
However, if a coarse intermetallic compound is precipitated, it is difficult to dissolve in a solid solution when exposed to a high temperature, and sufficient high temperature strength may not be obtained. Therefore, in the titanium alloy plate containing no Cu, the average particle size of the TiSiGe-based intermetallic compound is preferably 2.0 μm or less. More preferably, it is 1.0 μm or less. However, if the intermetallic compound is dispersed too finely, the effect of precipitation strengthening at room temperature becomes large, and the ductility decreases. Further, if the intermetallic compound is dispersed too finely, the intermetallic compound is dissolved at a high temperature of 800 ° C. or higher, the residual ratio of the intermetallic compound is lowered, and the pinning effect of the crystal grains is reduced. There is concern that the phase will grow. Therefore, the average particle size of the intermetallic compound is preferably 0.1 μm or more.

On the other hand, in the titanium alloy plate containing Cu, the average particle size of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound is preferably 2.0 μm or less, more preferably 1.0 μm or less. However, if these intermetallic compounds are dispersed too finely, the effect of precipitation strengthening at room temperature becomes large, and ductility decreases. Further, if these intermetallic compounds are dispersed too finely, the intermetallic compound is dissolved at a high temperature of 800 ° C. or higher, the residual ratio of the intermetallic compound is lowered, and the pinning effect of the crystal grains is reduced. There is concern that the α phase will grow. Therefore, it is preferable that the average particle size of these intermetallic compounds is 0.1 μm or more.

[Existence region of intermetallic compounds]
The TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound are present in the α-phase crystal grains or at the grain boundaries.
In the titanium alloy plate containing no Cu, it is preferable that 80% or more of TiSiGe-based intermetallic compounds are present at the grain boundaries of the α phase in the number ratio. It is more preferable that the TiSiGe-based intermetallic compound having a number ratio of 90% or more is present at the grain boundaries of the α phase. Since most of the intermetallic compounds are present at the grain boundaries, the intermetallic compounds are likely to remain at the grain boundaries when heated to a high temperature of 800 ° C. or higher, and the grain growth due to high temperature heating is suppressed by the pinning effect. be able to. When the number ratio of TiSiGe-based intermetallic compounds existing at the crystal grain boundaries is less than 80%, the intermetallic compounds remaining at the crystal grain boundaries during high-temperature heating decrease, making it difficult to suppress the grain growth of α-phase crystal grains. May become.

On the other hand, in the titanium alloy plate containing Cu, it is preferable that the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound, which are 80% or more in number ratio, are present at the grain boundaries of the α phase. It is more preferable that the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound having a number ratio of 90% or more are present at the grain boundaries of the α phase. Since most of the intermetallic compounds are present at the grain boundaries, the intermetallic compounds are likely to remain at the grain boundaries when heated to a high temperature of 800 ° C. or higher, and the grain growth due to high temperature heating is suppressed by the pinning effect. be able to. When the number ratio of the intermetallic compounds existing at the crystal grain boundaries is less than 80%, the intermetallic compounds remaining at the crystal grain boundaries during high temperature heating decrease, making it difficult to suppress the grain growth of α-phase crystal grains. There is.

[Average crystal grain size of α phase]
The smaller the crystal grain size of the α phase, the higher the strength, but the ductility at room temperature decreases, the 0.2% proof stress increases, and the processability decreases. Since the titanium alloy plate according to this embodiment is applied to exhaust system parts, it is desirable to secure workability at room temperature to some extent. Therefore, the crystal grain size of the α phase is 5 μm or more. As a result, workability at room temperature can be ensured. The crystal grain size of the α phase is preferably 10 μm or more.
On the other hand, the larger the crystal grain size, the better the ductility at room temperature, but if the crystal grain size is excessively large, wrinkles may occur due to molding and the appearance may be impaired. Further, if the crystal particle size is larger than necessary, the crystal may grow further in a high temperature state of 800 ° C. or higher, and sufficient high temperature strength may not be obtained. Therefore, the average crystal grain size of the α phase is set to 30 μm or less. It is preferably 25 μm or less.

The titanium alloy plate according to this embodiment is assumed to be applied to exhaust system parts, and the plate thickness is preferably 2.0 mm or less. It is more preferably 1.8 mm or less, still more preferably 0.8 mm or less. On the other hand, from the viewpoint of manufacturing, the plate thickness is preferably 0.5 mm or more, more preferably 0.7 mm or more, and further preferably 0.9 mm or more.

Further, the automobile exhaust system parts according to the present embodiment use the titanium alloy plate according to the present embodiment described above for the housing.

[Production method]
Next, a preferable manufacturing method of the titanium alloy plate according to the present embodiment will be described.
The titanium alloy plate according to this embodiment can be manufactured by a manufacturing method including the following steps.
(I) A step of performing hot working on an ingot made of a titanium alloy having the above-mentioned chemical composition (hot working step),
(II) A step of annealing a titanium alloy plate obtained by hot working at 820 to 850 ° C. for 1.0 minute or more (hot-rolled plate annealing step).
(III) After that, a step of cooling to 550 ° C. or lower at an average cooling rate of 5 ° C./sec or higher (cooling step).
(IV) A step of performing cold rolling on a cooled titanium alloy plate (cold rolling step),
(V) A step of subjecting a titanium alloy plate after cold rolling to annealing at 750 to 850 ° C. for 20 seconds or longer (first annealing step).
(VI) A step of subjecting a titanium alloy plate after the first annealing step to annealing at 650 to 730 ° C. for 1 hour or longer (second annealing step).
Hereinafter, each step will be described.

[Hot working process]
In the hot working process, the material is hot-worked to obtain a hot-rolled plate (titanium alloy plate). As the material to be hot-processed, an ingot having the above-mentioned chemical composition manufactured by vacuum arc melting, electron beam melting, or the like is used. Since the chemical composition does not change in the manufacturing process, it is within the above range even when analyzed with a product. The ingot may be used as a hot working material by adding ingot rolling or forging before hot working.
As the hot working, for example, hot rolling can be exemplified. In this case, it is preferable to heat the ingot to 800 to 1100 ° C. for hot rolling. When the hot rolling temperature is lower than 800 ° C., the deformation resistance becomes large and hot rolling becomes difficult. On the other hand, if the temperature exceeds 1100 ° C., the oxidation is severe, and the scale is pushed in by hot rolling and the scale portion is increased, so that the yield is lowered.

[Hot rolled plate annealing process]
Next, the titanium alloy plate after hot rolling is annealed by hot rolling plate holding at 820 to 850 ° C. for 1.0 minute or more. By performing hot-rolled sheet annealing, the titanium alloy plate after hot rolling is dissolved to reduce intermetallic compounds, and cold rolling to be performed later becomes easy.
Further, by performing hot-rolled sheet annealing, the structure can be brought into a two-phase state of α phase and β phase, and the β stabilizing element can be concentrated in β phase. In addition, since elements other than Al and oxygen are more likely to be concentrated in the β phase than in the α phase, Si and Ge are also concentrated in the β phase by hot rolling plate annealing. By sufficiently concentrating Si, Ge, and Cu in the β phase in hot-rolled sheet annealing, more TiSiGe-based intermetallic compounds and TiCu-based intermetallic compounds are precipitated in annealing after cold rolling, in particular. More TiSiGe-based intermetallic compounds will be precipitated.

By setting the annealing temperature of the hot-rolled plate annealing to 820 ° C. or higher, a two-phase state of α phase and β phase can be obtained. If the annealing temperature is less than 820 ° C., the β phase may not be precipitated. Further, by setting the annealing temperature to 850 ° C. or lower, excessive precipitation of the β phase can be suppressed. When the β phase is excessively precipitated and the area fraction of the β phase is increased, the concentration of Si, Ge, and Cu concentrated in the β phase is lowered, and the precipitation amount of the TiSiGe-based intermetallic compound is reduced, which is preferable. Absent.
The annealing time for hot-rolled plate annealing is preferably 1.0 minutes or longer, more preferably 1.5 minutes or longer, and even more preferably 2.0 minutes or longer. The longer the annealing time, the more Si, Ge, and Cu can be concentrated in the β phase. However, if the annealing time is too long, the productivity will decrease. Therefore, the annealing time is preferably 10 hours or less.

[Cooling process]
Next, the titanium alloy plate after hot rolling plate annealing is cooled to 550 ° C. or lower at an average cooling rate of 5 ° C./sec or more. By cooling to 550 ° C. or lower under these conditions, the β phase is transformed into the α phase, and Si, Ge, and Cu concentrated in the β phase are prevented from being precipitated as a metal compound. By not precipitating the intermetallic compound before the cold rolling, the cold rolling can be smoothly performed. The α phase transformed from the β phase is in a slightly unstable state because the solid solution element is excessively concentrated.

[Cold rolling process]
If necessary, the titanium alloy plate after the cooling step is descaled and then cold-rolled. In cold rolling, the cold rolling ratio is preferably 50% or more in order to obtain a uniform structure. On the other hand, when the cold rolling rate exceeds 95% and cold rolling is performed, ear cracks that greatly reduce the yield occur. Therefore, the cold rolling ratio is preferably 95% or less. It is more preferably 90% or less, still more preferably 85% or less. When intermediate annealing is performed, the cold rolling ratio after intermediate annealing may be 50% or more.
The cold rolling ratio indicates the cumulative rolling reduction rate when a plurality of rolling passes are performed, or the rolling reduction ratio of a rolling pass only once. From the viewpoint of manufacturability, the cold rolling ratio in one pass is preferably 20% or less.

[First annealing process]
[Second annealing process]
Next, the titanium alloy plate after cold rolling is subjected to the first annealing held at 750 to 850 ° C. for 20 seconds or longer, and further subjected to the second annealing held at 650 to 730 ° C. for 1 hour or longer. By performing the annealing twice, the desired metal structure can be obtained.

<First annealing>
In the first annealing (hereinafter referred to as annealing 1 or finish annealing 1), the crystal structure stretched in the rolling direction by cold rolling is recrystallized, and the grain size of the α phase crystal grains is reduced by recrystallization. adjust. In addition, the β phase transformed into the α phase by quenching after annealing with the hot-rolled plate is reprecipitated. The β phase is reprecipitated in the region where the alloying elements are concentrated by hot rolling sheet annealing. At this time, the intermetallic compound is prevented from being precipitated as much as possible, and Si, Ge, and Cu are further concentrated.
Annealing is required at 750 ° C. or higher in order to adjust the particle size of the α-phase crystal grains and to reprecipitate the β-phase. The titanium alloy plate according to the present embodiment contains a large amount of alloying elements in order to increase the high temperature strength, β phase does not precipitate at a temperature lower than 750 ° C., and the particle size of α phase crystal grains is adjusted. Will be damaged. On the other hand, when the annealing temperature exceeds 850 ° C., the number of β phases increases, which makes it difficult to adjust the crystal grains of the α phase. In addition, since the β phase increases and the region where Si and Ge are concentrated increases, the amount of intermetallic compounds precipitated in annealing 2 may increase, which may reduce ductility.
In this way, in order to make the crystal grain size of the α phase a predetermined particle size and to precipitate the β phase, annealing 1 is carried out at 750 ° C. to 850 ° C. In order to control the structure to a desired state by annealing 1, the annealing time is preferably 20 seconds (0.3 minutes) or more. If the annealing time (retention time) is less than 20 seconds, the concentration of Si, Ge, and Cu becomes insufficient, and the adjustment of the particle size of the α-phase crystal grains becomes incomplete. The annealing time is more preferably 1.0 minute or more. On the other hand, it is not necessary to limit the upper limit of the annealing time, but if the annealing time is 5.0 minutes or more, the productivity is lowered. Therefore, the annealing time is preferably less than 5.0 minutes.
In the cooling after annealing 1, since the precipitation rate of Ti ₂ Cu, which is one of the intermetallic compounds, is extremely slow, there is no big problem even with air cooling or furnace cooling.

<Second annealing (precipitation treatment of intermetallic compounds)>
In the titanium alloy plate after performing the annealing 1, the intermetallic compound hardly precipitates, and even if it precipitates, the area fraction of the intermetallic compound is less than 0.5%. If the intermetallic compound remains in the solid solution, the proof stress increases by 0.2% due to the solid solution strengthening, so that the processability is not excellent. Therefore, the intermetallic compound is precipitated in a predetermined surface integral ratio, the solid solution strengthening is suppressed, and the 0.2% proof stress is lowered. In the method for producing a titanium alloy plate according to the present embodiment, in order to precipitate the intermetallic compound at a predetermined area fraction, an annealing 1 is followed by a second annealing at an annealing temperature of 650 to 730 ° C. (hereinafter, annealing 2 or Finish annealing 2) is applied.

When the temperature of annealing 2 exceeds 730 ° C., the intermetallic compound is less likely to precipitate. Further, when the temperature is lower than 650 ° C., the TiSiGe-based intermetallic compound is not sufficiently precipitated, and the grain growth of the intermetallic compound is not promoted. Therefore, annealing 2 is preferably performed in the range of 650 to 730 ° C. More preferably, it is in the range of 670 ° C. to 720 ° C.
Further, in order to sufficiently precipitate the intermetallic compound, the annealing time of annealing 2 is preferably 1.0 hour or more. More preferably, it is 2.0 hours or more. The upper limit of the annealing time is not particularly limited, but from the viewpoint of productivity, 50 hours or less is preferable, and 40 hours or less is more preferable.

In the method for producing a titanium alloy plate according to the present embodiment, annealing 1 at 750 ° C. or higher and 850 ° C. or lower is followed by annealing 2 at 650 ° C. or higher and 730 ° C. or lower. After annealing 1, the film is cooled to near room temperature and then heated. Then, annealing 2 may be performed. Further, after annealing 1, it may be cooled to the temperature range of annealing 2 and annealing 2 may be performed as it is.

When annealing 1 is performed and then cooling is performed for a long time in the heating furnace (so-called furnace cooling), the temperature passes through the annealing temperature range of 650 to 730 ° C. in this case. , The range of 650 to 730 ° C. cannot be maintained for 1.0 hour or more, and passes through this temperature range in less than 1.0 hour. Therefore, it is difficult to sufficiently precipitate the intermetallic compound only by cooling in a furnace after annealing 1.

By annealing 2, TiSiGe-based intermetallic compounds are mainly precipitated, and when Cu is contained in the titanium alloy plate, TiCu-based intermetallic compounds are precipitated. Si, Ge and Cu constituting these intermetallic compounds are in a state of being concentrated in the β phase by the steps from hot-rolled plate annealing to annealing 1. By performing annealing 2 following annealing 1, these elements are precipitated as intermetallic compounds, and the β phase is almost eliminated. Since the β phase exists at the grain boundaries of the α phase, most of these intermetallic compounds are precipitated at the grain boundaries of the α phase. In order to suppress the grain growth of the α phase at high temperature, it is desirable that 80% or more of the intermetallic compounds are present at the grain boundaries of the α phase in terms of the number ratio.

Further, when comparing the precipitation behavior of the intermetallic compound between the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound, the TiCu-based intermetallic compound is more likely to precipitate at a relatively low temperature than the TiSiGe-based intermetallic compound. Further, the amount of the TiCu-based intermetallic compound deposited is small in the precipitation temperature range of the TiSiGe-based intermetallic compound. Therefore, by annealing at a temperature of 650 ° C. or higher and 730 ° C. or lower for 1.0 hour or longer in annealing 2, more TiSiGe-based intermetallic compounds are precipitated than TiCu-based intermetallic compounds.

Preferred requirements for the average particle size of the TiSiGe intermetallic compound to be 2.0 μm or less include the following production conditions and chemical composition requirements. It is not necessary to meet all of these requirements, it is sufficient to meet one requirement.
As the manufacturing conditions, firstly, the holding time should be relatively short within the range satisfying the holding times of the hot-rolled plate annealing step and the first annealing step, and secondly, the annealing temperature of the second annealing step should be set. The annealing temperature should be relatively low within the range to be satisfied. The number of intermetallic compounds deposited affects the particle size. Further, as a requirement of the chemical composition, Si, Ge, and Cu constituting the intermetallic compound are contained in a relatively large amount within a range satisfying the above-mentioned chemical composition.

Preferred requirements for the TiSiGe-based intermetallic compound to be present at the α-phase grain boundary in terms of the number ratio include the following requirements such as production conditions. It is not necessary to meet all of these requirements, it is sufficient to meet one requirement.
As manufacturing conditions, firstly, the holding time of the hot-rolled sheet annealing process is satisfied but the holding time is relatively long, and secondly, the annealing temperature of the second annealing process is satisfied, but the annealing temperatures are compared. To raise the target.
In addition, as another aspect, there are requirements for a chemical composition and a production method. If the chemical composition is relatively large within the range satisfying the formula (1), the intermetallic compound is likely to precipitate in the grains. On the other hand, by raising the annealing temperature in the first annealing step to a range that satisfies the annealing temperature, a β phase, which is a nucleus in which the metal-metal compound is precipitated, is formed, and the TiSiGe-based metal-metal compound has a grain boundary. The rate of precipitation increases.

By the above steps, the titanium alloy plate according to this embodiment is manufactured.

According to the titanium alloy plate according to the present embodiment, it is possible to provide a titanium alloy plate having excellent high-temperature strength and workability at room temperature.
Further, the titanium alloy plate according to the present embodiment is produced by subjecting an ingot having a predetermined chemical component to hot rolling and cold rolling, and then subjecting it to two-step annealing. In the first annealing, the crystal grain size of the α phase in the titanium alloy plate is adjusted to 5 to 30 μm. Then, in the second annealing, the intermetallic compound is precipitated to set the area fraction of the TiSiGe-based intermetallic compound and / or the TiCu-based intermetallic compound to 1.0% or more and 5.0% or less.
Since the titanium alloy plate according to the present embodiment has such a metal structure and contains an alloy element having a wide solid solution limit, the titanium alloy plate has a high temperature strength and is 0. 2% proof stress can be suppressed and workability can be improved.

Titanium alloy No. having the chemical composition shown in Tables 1A to 1C. 1 to No. 84 was made into an ingot by melting the vacuum arc button. The produced ingot was hot-rolled at 1000 ° C. to obtain a hot-rolled plate having a thickness of 10 mm. Then, hot rolling at 860 ° C. was performed to obtain a hot-rolled plate (titanium alloy plate) having a thickness of 4 mm. In Tables 1A to 1C, the description of the content of Mo, Ta, W, V, Cr, Ni, Mn, and Co as impurities is omitted, and the result of the formula (4) calculated based on the content of these elements is obtained. Shown.

Then, the descaling step or the hot rolling sheet annealing at the temperatures and times shown in Tables 2A to 2C is performed, and then the descaling step is performed, and then the cold rolling with the cold rolling ratio set to 75% is performed. , A thin plate having a thickness of 1.0 mm was used. The cold rolling ratio is the cumulative cold rolling ratio obtained by performing a plurality of rolling passes. Then, finish annealing 1 and finish annealing 2 were performed at the annealing temperatures and annealing times shown in Tables 2A to 2C. In this way, No. Titanium alloy plates of 1 to 84 were manufactured. After the step of finish annealing 1, it was air-cooled, and after the step of finish annealing 2, it was furnace-cooled. No. 1 produced by the above steps. 1 to No. For 84, a room temperature tensile test, a high temperature tensile test, an oxidation increase measurement, and a microstructure observation were carried out by the following methods. The results are shown in Tables 3A to 3C.

[Room temperature tensile test]
The tensile test at room temperature was carried out as follows.
From the above titanium alloy plate, an ASTM half-size tensile test piece (parallel portion width 6.25 mm, parallel portion length 32 mm, distance between gauge points 25 mm) whose longitudinal direction was parallel to the rolling direction was collected. A tensile test was performed on this test piece at a strain rate of 0.5% / min up to a strain of 1.5% and then 30% / min until breakage. Evaluation of ductility and springback at room temperature is expressed as elongation at break at room temperature (denoted as elongation at break in Tables 3A to 3C) and 0.2% proof stress at room temperature (denoted as 0.2% proof stress in Tables 3A to 3C). ). When the breaking elongation at room temperature was 25.0% or more and the 0.2% proof stress was 340 MPa or less, it was judged to be acceptable as having sufficient ductility and small springback.

[High temperature tensile test]
The tensile test at high temperature was carried out as follows.
From the above titanium alloy plate, a tensile test piece (parallel portion width 10 mm, parallel portion length and distance between gauge points 30 mm) whose longitudinal direction was parallel to the rolling direction was collected. A tensile test was performed on this test piece at a strain rate of 0.3% / min up to a strain of 1.5% and then 7.5% / min until breakage. The test atmosphere was carried out in the air at 800 ° C., and the test was carried out after being held in the test atmosphere for 30 minutes so that the test piece sufficiently reached the test temperature.
When the tensile strength at 800 ° C. (denoted as high temperature strength in Tables 3A to 3C) was 37 MPa or more, it was judged to be excellent in high temperature strength and passed.

[Oxidation increase]
Oxidation increase is an important property of titanium, which is easily oxidized, when it is used for high temperature applications such as exhaust systems. As the oxidation progresses, the wall thinning causes problems such as insufficient strength and opening of holes. Therefore, the amount of increase in oxidation, which is an index indicating the ease of oxidation, must be below a certain value.
To increase the amount of oxidation, a 20 mm × 20 mm test piece is taken from the above titanium alloy plate, the surface is polished with emery paper # 600, and the surface is exposed to static air at 800 ° C. for 100 hours to increase the mass after exposure. It was measured and evaluated by the value obtained by dividing the increased mass by the surface area of the tensile test piece (increased mass (mg) / surface area of the test piece (cm ² ), hereinafter referred to as "oxidation increase"). 4.5 mg / cm ² or less was accepted.

[Tissue observation]
The L cross section (cross section parallel to the rolling direction and the plate thickness direction) of the titanium alloy plate was observed with a scanning electron microscope (SEM), and the α phase and the intermetallic compound were discriminated from the reflected electron image. Since the intermetallic compound is white or black as compared with the α phase which is the matrix phase and is a fine precipitate, it can be distinguished from the α phase from this feature. From this backscattered electron image, the average crystal grain size of the α phase was determined by the cutting method. More specifically, a test piece of 1.0 mm (the same thickness as the plate thickness) × 15.0 mm was prepared from the L cross section of the titanium alloy plate. The test piece was corroded with a mixed aqueous solution of nitric acid and hydrofluoric acid, and observed with a scanning electron microscope (SEM) to obtain a reflected electron image. The average crystal grain size of the α phase was determined from the backscattered electron image by the cutting method. In the cutting method used here, the number of crystal grains to be cut by one line segment is 10 or more, 5 or more of one or more line segments are drawn in the rolling direction, and the number of crystal grains to be cut is 100 or more. .. Further, the line segments were arranged equally in the plate thickness direction of the test piece. The average crystal grain size of the α phase was determined by arithmetic mean from the crystal grain size of each cleaved α phase.

The intermetallic compound was discriminated as follows. In the TiSiGe-based intermetallic compound, when the L cross section of the titanium alloy plate was elementally mapped by the WDS (wavelength dispersion type X-ray spectrometer) attached to the SEM, one or both of Si or Ge and Ti were detected at the same time. The region was identified as a TiSiGe-based intermetallic compound. In addition, the surface integral of the TiSiGe-based intermetallic compound in the structure was determined based on the size of the detected region.
Further, in the TiCu-based intermetallic compound, the region in which Cu and Ti were simultaneously detected when the L cross section of the titanium alloy plate was elementally mapped by WDS was identified as the TiCu-based intermetallic compound. In addition, the surface integral of the TiCu-based intermetallic compound in the structure was determined based on the size of the detected region.
Furthermore, the average particle size of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound was determined from the element mapping and the reflected electron image.
Furthermore, the number ratio of TiSiGe-based intermetallic compounds and TiCu-based intermetallic compounds present in the grain boundaries of the α phase was determined from the element mapping and the reflected electron image. In the measurement, the beam diameter was set to φ0.2 μm or less, the step size was set to 0.2 μm, and the measurement field of view was set to 2 or more fields in a square region having a side of 50 to 100 μm at the center of the plate thickness of the L cross section.

The α grain size in Tables 3A to 3C is the average crystal grain size of the α phase, and the total area fraction is the total area fraction of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound, and the intermetallic compound average grain. The diameter is the average grain size of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound, the Ti (Si, Ge) area fraction is the area fraction of the TiSiGe-based intermetallic compound, and the TiCu-based intermetallic compound is the TiCu-based intermetallic compound. It is the area division of the intermetallic compound, and the grain boundary ratio is the number ratio of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound existing in the grain boundary of the α phase.

With reference to Tables 1A to 3C, the chemical composition of the examples of the present invention is within the range of the chemical composition of the heat-resistant titanium alloy material according to the present embodiment, and as shown in Tables 3A to 3C, the average of α phases. Both the grain size and the volume fraction of the intermetallic compound satisfy the target. As a result, the performance required for the titanium alloy plate of the present invention was satisfied.
For No. 80, a high-temperature tensile test was performed even under the condition that the test atmosphere was 820 ° C (other conditions are the same as in the case of 800 ° C). As a result, the tensile strength at 820 ° C. was 38 MPa, and the tensile strength at 820 ° C. was sufficient.

No. No. 5 did not satisfy the equation (3), and the high temperature strength became insufficient.
No. In No. 7, Si and Ge were not contained, the Al content was excessive, and the equation (1) was not satisfied. Therefore, the TiSiGe-based intermetallic compound did not precipitate, and the high-temperature strength became insufficient.
No. Since Nos. 11 and 12 did not contain Si and Ge, TiSiGe-based intermetallic compounds did not precipitate, resulting in insufficient high-temperature strength. In addition, No. The α particle size of Nos. 11 and 12 was coarse, and the appearance after the tensile test was inferior.

No. No. 8 did not satisfy the equation (3), the annealing temperature of the hot-rolled plate was low, and the annealing time of annealing 1 was long. As a result, the high temperature strength became insufficient.
No. No. 9 did not satisfy the equation (3), and the high temperature strength became insufficient.
No. In No. 10, the amount of Fe was excessive and did not satisfy the equations (3) and (4), and the high temperature strength, 0.2% proof stress and elongation at break were insufficient.

No. No. 15 did not satisfy the formula (1), and the Si content was excessive, so that the 0.2% proof stress and the elongation at break were insufficient.
No. No. 16 did not satisfy the equation (2), and the β phase was precipitated and the high temperature strength became insufficient.

No. No. 18 did not satisfy the equation (3), and the elongation at break was insufficient.
No. In No. 28, Al, Zr, and Sn were not contained, the formula (1) was not satisfied, and the Ge content was insufficient. Therefore, the TiSiGe-based intermetallic compound was not sufficiently precipitated, and the high temperature strength was insufficient. ..

No. In No. 29, Al, Zr, and Sn were not contained, the formula (1) was not satisfied, and the Ge content was excessive, so that the elongation at break was insufficient.
No. In No. 32, the upper limit of the equation (2) was exceeded, so that the β phase was precipitated and the high temperature strength became insufficient.

No. Since No. 36 was below the lower limit of Eq. (3), the high temperature strength became insufficient.
No. Since 37 exceeded the upper limit of the formula (3), the β phase was precipitated and the high temperature strength became insufficient.

No. No. 38 did not contain Al, Zr, and Sn, and the β phase was precipitated, resulting in insufficient high-temperature strength.
No. No. 46 did not satisfy the equation (3), and the elongation at break was insufficient.
No. No. 47 did not satisfy the equation (4), and the β phase was precipitated and the high temperature strength became insufficient.

No. In 49, 54, and 55, the chemical composition of the titanium alloy was within the range of the invention, but the annealing temperature of finish annealing 1 was high, and the total area fraction of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound exceeded the upper limit. Therefore, the elongation at break became insufficient.

No. In 51, 52, and 53, Al, Zr, and Sn were not contained, the annealing temperature of the finish annealing 2 was low, the area fraction of the TiSiGe intermetallic compound was low, and the high temperature strength was insufficient.
No. In No. 57, the chemical composition of the titanium alloy was within the range of the invention, but the hot-rolled plate was not annealed. As a result, the surface integral of the TiSiGe-based intermetallic compound became low, and the high-temperature strength was insufficient.
No. In 58, 59, and 68, the chemical composition of the titanium alloy was within the range of the invention, but the hot-rolled plate annealing temperature was low. As a result, the surface integral of the TiSiGe-based intermetallic compound became low, and the high-temperature strength was insufficient. No. 58 and 68 also had a high 0.2% proof stress.
No. In Nos. 60 and 69, the chemical composition of the titanium alloy was within the range of the invention, but the hot-rolled plate annealing temperature was high. As a result, the surface integral ratio of the TiSiGe-based intermetallic compound was low, the proof stress was high by 0.2%, and the high temperature strength was insufficient.
No. In 61 and 70, the chemical composition of the titanium alloy was within the range of the invention, but the annealing time of the hot-rolled plate was short. As a result, the surface integral ratio of the TiSiGe-based intermetallic compound was low, the proof stress was high by 0.2%, and the high temperature strength was insufficient.
No. In No. 62, the chemical composition of the titanium alloy was within the range of the invention, but the temperature of annealing 1 was high. As a result, the average particle size of the α phase was small, the proof stress was high by 0.2%, and the elongation was low.
No. In 63 and 71, the chemical composition of the titanium alloy was within the range of the invention, but the temperature of annealing 1 was low. As a result, the average particle size of the α phase was small, the proof stress was high by 0.2%, and the elongation was low. In addition, there were few intermetallic compounds, and the high-temperature strength was low.
No. In No. 64, the chemical composition of the titanium alloy was within the range of the invention, but the annealing time of annealing 1 was short. As a result, the average particle size of the α phase was small, the proof stress was high by 0.2%, and the elongation was low.
No. In 65 and 72, the chemical composition of the titanium alloy was within the range of the invention, but the temperature of annealing 2 was high. As a result, the surface integral ratio of the TiSiGe-based intermetallic compound was low, the proof stress was high by 0.2%, and the high temperature strength was insufficient.
No. In 66 and 73, the chemical composition of the titanium alloy was within the range of the invention, but the temperature of annealing 2 was low. As a result, the surface integral of the TiSiGe-based intermetallic compound became low, and the high-temperature strength was insufficient. No. At 66, the yield strength was also high by 0.2%.
No. In 67 and 74, the chemical composition of the titanium alloy was within the range of the invention, but the annealing time 2 was short. As a result, the surface integral of the TiSiGe-based intermetallic compound became low, and the high-temperature strength was insufficient.
No. No. 75 did not satisfy the formula (1), and the area fraction of the TiSiGe-based intermetallic compound was low. As a result, the high temperature strength was low.
No. In No. 76, the Si content was excessive and the equation (1) was not satisfied, so that the area fraction of the SiGe intermetallic compound became excessive and the average crystal grain size of the α phase became small. As a result, the yield strength was high by 0.2% and the elongation was low.
No. 77 had an excessive Zr content and did not satisfy the formula (2). As a result, a large amount of β phase was precipitated and the high temperature strength was low.
No. Reference numeral 81 denotes a titanium alloy plate corresponding to Table 1 and No. 3 of Patent Document 2 prepared in accordance with the description of Patent Document 2. No. In No. 81, the hot-rolled plate annealing temperature is low, and the first annealing step is not performed. As a result, the surface integral ratio of the TiSiGe-based intermetallic compound was low, and the proof stress was high by 0.2%.
No. Since the Sn content of 83 was excessive, the 0.2% proof stress and elongation at break were insufficient.
No. In No. 84, the Cu content was excessive, the equation (2) was not satisfied, and the high temperature strength was insufficient.

According to the present invention, it is possible to provide a titanium alloy plate having excellent high temperature strength in a high temperature environment of 800 ° C. or higher and excellent workability at room temperature, and an automobile exhaust system component including the titanium alloy.

Claims (7)

1. The chemical composition is mass%,
   One or both of 0-0.60% Si and 0-4.5% Ge,
   One or more selected from the group consisting of 0-1.0% Al, 0-1.0% Zr, and 0-2.0% Sn.
   0 to 1.5% of Cu is contained so as to satisfy the following formulas (1) to (3).
   It contains 0 to 1.0% Nb, 0 to 0.080% Fe, and Mo, Ta, W, V, Cr, Ni, Mn and Co so as to satisfy the following formula (4). ,
   Ga: 0 to 10.0%,
   In: 0 to 10.0% and Hf: 0 to 10.0%.
   O: Limited to 0.070% or less,
   The rest consists of Ti and impurities
   It has an α phase with an average crystal grain size of 5 μm or more and 30 μm or less and an intermetallic compound in the structure.
   The intermetallic compound includes a TiSiGe-based intermetallic compound containing one or both of Si and Ge and Ti, and optionally contains a TiCu-based intermetallic compound containing Cu and Ti.
   The total area fraction of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound in the structure is 1.0% or more and 5.0% or less, and the area fraction of the TiSiGe-based intermetallic compound is 1.0% or more and 5.0% or less. , 1.0% or more,
   Titanium alloy plate.
   1.5% ≤ [Ge%] + 7.5 x [Si%] ≤ 4.5% (1)
   [Cu%] + 1.5 x [Zr%] ≤ 1.5% (2)
   10.0% ≤12 x [Al%] +10 x [Cu%] +3.5 x [Zr%] +6 x [Sn%] ≤36.5% (3)
   [Mo%] + 0.2 x [Ta%] + 0.285 x [Nb%] + 0.4 x [W%] + 0.67 x [V%] + 1.25 x ([Cr%] + [Ni%] ) + 1.7 x ([Mn%] + [Co%]) + 2.5 x [Fe%] ≤ 0.4% (4)
   However, in the formulas (1) to (4), [Ge%], [Si%], [Zr%], [Al%], [Sn%], [Mo%], [Ta%], [Nb%]. ], [W%], [V%], [Cr%], [Ni%]), [Mn%], [Co%], [Fe%] are the contents of each element in mass%. , If the element is not contained, 0 is substituted.
2. The titanium alloy plate according to claim 1, wherein the average particle size of the TiSiGe-based intermetallic compound is in the range of 0.1 to 2.0 μm.
3. The titanium alloy plate according to claim 1 or 2, wherein 80% or more of the TiSiGe-based intermetallic compound is present at the grain boundaries of the α phase in terms of the number ratio.
4. When the chemical composition is mass%,
   Contains 0.5% to 1.5% Cu
   The surface integral of the TiCu-based intermetallic compound is more than 0%.
   The titanium alloy plate according to claim 1.
5. The titanium alloy plate according to claim 4, wherein the average particle size of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound is in the range of 0.1 to 2.0 μm.
6. The titanium alloy plate according to claim 4 or 5, wherein 80% or more of the TiSiGe-based intermetallic compound and the TiCu-based intermetallic compound are present at the grain boundaries of the α phase in terms of the number ratio.
7. An automobile exhaust system component in which the housing is made of the titanium alloy plate according to any one of claims 1 to 6.