WO2019155553A1 - チタン合金材 - Google Patents
チタン合金材 Download PDFInfo
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- WO2019155553A1 WO2019155553A1 PCT/JP2018/004216 JP2018004216W WO2019155553A1 WO 2019155553 A1 WO2019155553 A1 WO 2019155553A1 JP 2018004216 W JP2018004216 W JP 2018004216W WO 2019155553 A1 WO2019155553 A1 WO 2019155553A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
- C22F1/18—High-melting or refractory metals or alloys based thereon
- C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C14/00—Alloys based on titanium
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
- C22F1/18—High-melting or refractory metals or alloys based thereon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
Definitions
- the present invention relates to a titanium alloy material excellent in high-temperature strength and moldability that is suitably used for, for example, exhaust system parts.
- stainless steel having excellent corrosion resistance, strength, workability, etc. has been used as a constituent member of exhaust devices of automobiles and motorcycles (hereinafter referred to as automobiles), but in recent years, it is lighter than stainless steel. Titanium materials having high strength and excellent corrosion resistance are being used. For example, a titanium material (so-called industrial pure titanium) defined by JIS type 2 is used for an exhaust device of a motorcycle. Further, recently, a titanium alloy material having higher heat resistance has been used in place of the titanium material specified by JIS class 2. In recent years, a muffler equipped with a catalyst used at a high temperature is also used to remove harmful components of exhaust gas.
- Exhaust devices such as automobiles are provided with an exhaust manifold and an exhaust pipe.
- the exhaust pipe is configured by being divided into several parts in order to put a catalyst device or a muffler (silencer) on which a catalyst is mounted or applied on the way.
- the exhaust manifold, exhaust pipe, and exhaust port are referred to as an “exhaust device” throughout.
- a part constituting the exhaust device is referred to as “exhaust system part”.
- Combustion gas discharged from an engine such as an automobile is collected by an exhaust manifold, and discharged from an exhaust port at the rear of the vehicle via an exhaust pipe. Since the exhaust device is exposed to high temperature exhaust gas, the titanium material constituting the exhaust device is required to have strength and corrosion resistance in a high temperature range. In addition, since the parts of these exhaust devices are complicated in shape, moldability at room temperature is also required.
- Patent Document 1 contains Cu, Sn, Si, and O, the total amount of Cu and Sn is 1.4 to 2.7%, and the balance is excellent in oxidation resistance consisting of Ti and inevitable impurities.
- a heat-resistant titanium alloy material for exhaust system parts is described.
- a titanium alloy having the above components is hot-rolled, further cold-rolled, and annealed at 750 to 830 ° C. to produce a heat-resistant titanium alloy material for exhaust system parts.
- Patent Document 2 describes a heat-resistant titanium alloy plate excellent in cold workability, which contains Cu, O, and Fe, and the balance is Ti and impurities of 0.3% or less.
- the titanium alloy having the above components is subjected to processes such as hot rolling, hot rolled sheet annealing, cold rolling, intermediate annealing, and final annealing, and the final annealing is performed at a temperature of 600 to 650 ° C.
- Patent Document 3 describes a heat-resistant titanium alloy material for exhaust system parts that contains Cu, Si, and O, and the balance is made of Ti and inevitable impurities and has excellent oxidation resistance and formability.
- the titanium alloy having the above components is subjected to steps such as hot rolling, hot rolled sheet annealing, cold rolling, and final annealing, and the final annealing is performed at a temperature of 630 to 700 ° C.
- heat-resistant titanium alloy materials for exhaust system parts with excellent formability.
- the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a titanium alloy material excellent in high-temperature strength and excellent in formability at room temperature and a method for producing the same.
- the gist of the present invention is as follows.
- the area fraction of the ⁇ phase in the structure is 96.0% or more, the area fraction of the intermetallic compound is 1.0% or more, A titanium alloy material in which an average crystal grain size of the ⁇ phase is 10 ⁇ m or more and 100 ⁇ m or less, and an average grain size of the intermetallic compound is 0.1 to 3.0 ⁇ m.
- the present invention it is possible to provide a titanium alloy material that is excellent in high-temperature strength and excellent in moldability at room temperature.
- This titanium alloy material is further excellent in oxidation resistance and appearance after molding.
- the present invention will be described in detail below.
- an alloy element is usually added to strengthen the solution.
- the titanium alloy material with improved high-temperature strength has high strength even at room temperature, the springback at the time of molding increases, and the formability decreases.
- room temperature is 20 ° C. to 30 ° C.
- the room temperature is preferably 25 ° C.
- Titanium alloy materials may or may not show a yield phenomenon in a tensile test.
- the yield phenomenon it is necessary to define the stress corresponding to the yield stress as the proof stress in order to clarify the boundary between the elastic deformation and the plastic deformation for convenience.
- the stress at which the permanent strain at unloading is 0.2% is called 0.2% proof stress. This is substituted for the yield stress in the specification.
- the intermetallic compound In order to ensure formability, it is preferable to increase the ductility by increasing the average crystal grain size of the ⁇ phase. At this time, if the intermetallic compound remains in the structure, the intermetallic compound inhibits the ⁇ -phase grain growth, so annealing is performed at a relatively high temperature range in which the intermetallic compound does not precipitate. It is recommended to promote phase grain growth.
- annealing may be performed for a long time in a temperature range lower than the temperature range in which the ⁇ phase grows. Precipitation of intermetallic compounds can be realized by second annealing (precipitation treatment of intermetallic compounds) described later.
- the intermetallic compound previously precipitated is re-dissolved in the metal structure by annealing, and the room temperature It becomes impossible to secure the moldability in Therefore, it is necessary to first perform annealing to increase the crystal grain size of the ⁇ phase, and then perform annealing to precipitate an intermetallic compound.
- the metal structure of the titanium alloy receives a roll reduction force by being subjected to cold rolling, the structure after cold rolling becomes a structure having a form stretched in the rolling direction. Accordingly, the annealing for controlling the average crystal grain size of the ⁇ phase needs to be performed after cold rolling.
- the titanium alloy material obtained through such a process has a relatively large ⁇ phase crystal grain size and a structure in which an intermetallic compound is precipitated, and can ensure formability at room temperature. .
- the intermetallic compound dissolves in the metal structure at high temperatures, improving 0.2% proof stress and increasing high temperature strength. .
- the titanium alloy material according to the present invention is particularly suitably used as a constituent material for exhaust system parts of exhaust systems such as automobiles and motorcycles.
- the exhaust device is manufactured by forming various types of exhaust system parts by molding a titanium alloy material and combining these exhaust system parts. Thereafter, the exhaust system device is mounted and used in an automobile or the like.
- the titanium alloy material as a constituent member is heated to a high temperature by being exposed to high-temperature exhaust gas.
- the titanium alloy material according to the present invention has a low strength before being heated to a high temperature, that is, at room temperature, because an intermetallic compound is present in the metal structure and the average crystal grain size of the ⁇ phase is relatively large. Thus, the moldability is improved and the springback during the molding process is also reduced.
- the titanium alloy material according to the present invention has a breaking elongation at 25 ° C. of 25.0% or more and a 0.2% proof stress at 25 ° C. of 340 MPa or less as an index of moldability at room temperature. Further, as an index of high temperature strength, the tensile strength at 700 ° C. is set to 60 MPa or more.
- a titanium alloy material according to an embodiment of the present invention will be described in detail.
- the content of each component element will be described.
- “%” for the component is mass%.
- the chemical composition is not an ingot but an analysis value in a titanium alloy material subjected to finish annealing.
- Cu 0.7% to 1.48%
- Cu is an element that has a wide solid solubility limit and improves strength at high temperatures and at room temperature. In order to improve high temperature strength, it is necessary to contain 0.7% or more. When Cu is contained excessively, a large amount of intermetallic compounds such as Ti 2 Cu are precipitated, and ductility is impaired. Furthermore, when it is used, if it exceeds 780 ° C., a ⁇ phase is formed. Furthermore, if the amount of Ti 2 Cu deposited is large, the ⁇ -phase grain growth is hindered to become fine grains, which lowers the ductility at room temperature. Therefore, the upper limit of Cu content is set to 1.4% or less. Therefore, the Cu content is set to 0.7% to 1.4%. The lower limit of Cu may be 0.8%, 0.9%, or 1.0%. Further, the upper limit of Cu may be 1.3%, 1.2% or 1.1%.
- Sn is an element that has a wide solid solubility limit and improves high-temperature strength. In order to improve high temperature strength, it is necessary to contain 0.5% or more of Sn. In addition, Si, which will be described later, improves high-temperature strength and oxidation resistance, but tends to cause segregation when manufacturing products using large ingots, and is unsuitable for using large ingots in order to reduce manufacturing costs. is there. Therefore, it is necessary to reduce the variation in high-temperature strength by adding Sn with small segregation. Incidentally, if excessively containing Sn, to promote the precipitation of intermetallic compounds such as Ti 2 Cu, it is necessary to limit below 1.5%. Therefore, the Sn content is set to 0.5% to 1.5%. The lower limit of Sn may be 0.6%, 0.7%, or 0.8%. Further, the upper limit of Sn may be 1.4%, 1.3%, or 1.2%.
- Si 0.10% to 0.45%
- Si is an element that improves high-temperature strength and oxidation resistance.
- it is necessary to contain 0.10% or more of Si.
- Si is contained excessively, the effect of improving the high-temperature strength and oxidation resistance is reduced with respect to the content, and further, the intermetallic compound (silicide) is precipitated in a large amount, thereby reducing the ductility at room temperature.
- the upper limit is 0.45% or less. Therefore, the Si content is set to 0.10% to 0.45%.
- the lower limit of Si may be 0.15%, 0.20%, or 0.25%. Further, the upper limit of Si may be 0.40%, 0.35%, or 0.30%.
- Nb is an element that improves oxidation resistance. Further, in the addition range of the invention, Nb is an element that is less segregated than Si. Therefore, it is necessary to add Nb in order to reduce variation in oxidation resistance due to segregation of Si. In order to obtain the effect of improving the oxidation resistance, it is necessary to contain 0.05% or more of Nb. When Nb is contained excessively, the effect of improving oxidation resistance with respect to the content is reduced, and a ⁇ phase is easily formed. Furthermore, since Nb is expensive, the upper limit is made 0.50% or less. Therefore, the Nb content is set to 0.05% to 0.50%. The lower limit of Nb may be 0.10%, 0.15%, or 0.20%. The upper limit of Nb may be 0.40%, 0.35%, or 0.30%.
- Fe (Fe: 0.00% to 0.08%) Fe is an element inevitably included. Fe is a ⁇ -stabilizing element, and if it is contained in excess, it tends to form a ⁇ -phase and hinders growth of ⁇ -phase crystal grains. In order to obtain sufficient ductility at room temperature, it is necessary to grow ⁇ -phase crystal grains. Therefore, it is preferable that the Fe content is small. Therefore, the Fe content is set to 0.00% to 0.08%. The upper limit of Fe may be 0.06%, 0.04%, or 0.02%.
- O is an element inevitably included, and improves the strength at room temperature and decreases the ductility. Since there is almost no contribution to the strength at high temperature, it is preferable that the content is small. Therefore, the O content is set to 0.00% to 0.08%.
- the upper limit of O may be 0.06, 0.04%, or 0.02%.
- the balance of the titanium alloy material of this embodiment is Ti and other impurities than the above.
- impurity elements of Fe and O there are C, N, H, Cr, Al, Mo, Zr, Mn, V, and Ni. If the content of these impurities is large, ductility at room temperature decreases. Therefore, it is desirable that the upper limit of each impurity element be 0.05% or less. In addition, the total content of these impurity elements is preferably less than 0.3%.
- the titanium alloy material of the present embodiment may contain one or both of Bi or Ge in a range where the total content is less than 3.0%, instead of a part of Ti.
- the upper limit of one or both of Bi and Ge may be 2.5%, 2.0%, or 1.5%.
- Bi 0.1% to 2.0%
- Bi has a certain solid solubility limit at a high temperature, and may be contained by 0.1% or more in order to improve the high temperature strength.
- Bi produces an intermetallic compound like Cu and Si, and lowers the ductility at room temperature, so the upper limit is made 2.0% or less.
- the lower limit of Bi may be 0.2%, 0.3%, or 0.4%.
- the upper limit of Bi may be 1.5%, 1.0%, or 0.8%.
- Ge has a certain solid solubility limit at a high temperature, and may be contained in an amount of 0.1% or more in order to improve the high temperature strength.
- Ge produces an intermetallic compound like Cu and Si, and lowers the ductility at room temperature, so the upper limit is made 1.5% or less.
- the lower limit of Bi may be 0.2%, 0.3%, or 0.4%.
- the upper limit of Bi may be 1.2%, 1.0%, or 0.8%.
- the solid solubility limits are both small, so when 2.0%, which is the upper limit of each element, is added (a total of 4.0%), an intermetallic compound is formed. Therefore, unless the total addition amount of Bi and Ge is 3.0% or less, ductility deteriorates due to a large amount of intermetallic compounds.
- the titanium alloy material of the present embodiment includes the above-described basic element, and the balance is a chemical composition composed of Ti and impurities, or at least one selected from the above-described basic element and the above-described selective element. And the balance has a chemical composition comprising Ti and impurities.
- the titanium alloy material of the present embodiment suppresses solid solution strengthening, lowers 0.2% proof stress, and improves forming processability by precipitating intermetallic compounds in the metal structure at room temperature.
- the area fraction of the intermetallic compound may be 3.0% or less, or 2.0% or less.
- the area fraction of the ⁇ phase is set to 96.0% or more.
- the lower limit of the ⁇ phase area fraction may be 97.0% or 98.0%.
- the measurement of the area fraction here is performed by image analysis of the reflected electron image in a region having a thickness of 500 ⁇ m ⁇ 500 ⁇ m (250,000 ⁇ m 2 ) or more in the center of the L cross section using a scanning electron microscope. Even if the measurement area is not one visual field, a total of two or more visual fields may be secured at 250,000 ⁇ m 2 or more.
- a white area or a black area is present than the matrix, and the area fraction is obtained as an intermetallic compound. These white areas or black areas appear in the grain boundaries or grains of the ⁇ phase. In the black part, an element having a small atomic number is concentrated, for example, a Ti—Si intermetallic compound.
- the white region is concentrated with an element having a large atomic number, such as a Ti—Cu intermetallic compound.
- the titanium alloy material may have a ⁇ phase in addition to the ⁇ phase and the intermetallic compound.
- the ⁇ phase is displayed as a white region in the reflected electron image. In this white region, it is difficult to separate the intermetallic compound and the ⁇ phase only by the reflected electron image. In order to separate, it is necessary to confirm the presence or absence of Fe enrichment in the ⁇ phase by EPMA (Electron Probe Micro Analyzer) or EDX (Energy Dispersive X-ray spectroscopy).
- the ⁇ phase does not exist, or even if it exists, the area fraction is 0.2% or less.
- the ⁇ phase may be recognized as the second phase together with the intermetallic compound. That is, when the ⁇ phase is included, the area fraction of the ⁇ phase may be included in the area fraction of the intermetallic compound.
- the titanium alloy material of this embodiment improves the ductility at room temperature and decreases the 0.2% proof stress by increasing the crystal grain size of the ⁇ phase. Therefore, the average crystal grain size of the ⁇ phase that is the main phase needs to be 10 ⁇ m or more. If it is smaller than 10 ⁇ m, the 0.2% proof stress may be too high or the elongation may be insufficient. More preferably, it is 12 micrometers or more, More preferably, it is 15 micrometers or more. The larger the average crystal grain size, the better the ductility at room temperature, but if it exceeds 100 ⁇ m, wrinkles may occur due to molding, and the appearance may be impaired. Therefore, the upper limit of the average crystal grain size of the ⁇ phase needs to be 100 ⁇ m.
- the thickness is desirably 70 ⁇ m or less, and more desirably 50 ⁇ m or less.
- D ( ⁇ m) (D 1 + D 2 + D 3 + D 4 + D 5 ) / 5 (2)
- the amount of solid solution of the intermetallic compound in the ⁇ phase is reduced by the precipitation of the intermetallic compound at a predetermined area fraction, and the 0.2% yield strength at room temperature is reduced. .
- the deposited intermetallic compound is again dissolved in the ⁇ phase by being exposed to a high temperature, so that the high temperature strength is improved. If a coarse intermetallic compound is deposited, it is difficult to form a solid solution when exposed to a high temperature, and sufficient high-temperature strength cannot be obtained. Therefore, the average particle size of the intermetallic compound needs to be 3.0 ⁇ m or less. .
- the lower limit of the average particle size of the intermetallic compound is set to 0.1 ⁇ m.
- the intermetallic compound in the present embodiment Ti 2 Cu, or titanium silicide, an intermetallic compound of titanium and other metal elements, of course, also include intermetallic compounds of metal elements each other than titanium.
- a scanning electron microscope is used to observe the particle size of the intermetallic compound. The measurement range is the same as the case of the area fraction of the intermetallic compound, but when measuring each intermetallic compound, it is preferable to use 1000 times as a guide, or measurement at a higher magnification.
- FIG. 1 ingot production, hot rolling, descaling, cold rolling, and finish annealing (annealing 1 + annealing 2) are indispensable processes. Forging / bundling rolling, hot-rolled sheet annealing, intermediate annealing / cold rolling The shape correction is a process performed as necessary.
- Hot rolling As a material to be hot-rolled, an ingot having the above-described chemical composition cast by a method such as vacuum arc melting or electron beam melting is used. In addition, you may add forging and a lump rolling before hot rolling. Forging / slab rolling is performed by heating to 1000 ° C. or higher (desirably 1050 ° C. or higher). Hot rolling is performed by heating at 800 to 1100 ° C. If the hot rolling temperature at this time is less than 800 ° C., the deformation resistance increases, and hot rolling becomes difficult. If the temperature exceeds 1100 ° C., the oxidation is intense, and the yield is lowered due to the increase of scale intrusion and scale portion by hot rolling.
- Hot-rolled sheet annealing is performed for the purpose of facilitating cold rolling by reducing the strain of the titanium alloy material after hot rolling. However, this step is not necessarily performed, and may be performed when the cold rolling property is insufficient. Hot-rolled sheet annealing is performed at 750 to 850 ° C. in order to suppress excessive oxidation and suppress decrease in yield. There is no particular limitation on the annealing time, but holding for about 1 to 60 minutes is sufficient.
- Cold rolling is performed after descaling after hot rolling or hot-rolled sheet annealing.
- the descaling may be a general method, for example, a method in which the surface layer is removed by pickling with a mixed acid of nitric acid and hydrofluoric acid after shot blasting.
- the cold rolling rate is preferably 50% or more.
- the cold rolling rate exceeds 95% and cold rolling is performed, an ear crack that greatly reduces the yield is generated, so the upper limit of the cold rolling rate is 95% or less. More preferably, it is 90% or less, More preferably, it is 85% or less.
- the cold rolling rate after the intermediate annealing may be 50% or more.
- the intermediate annealing is desirably performed at 750 to 850 ° C. as in the case of hot rolled sheet annealing.
- finish annealing is performed on the titanium alloy material after cold rolling.
- the first annealing is performed at 750 to 830 ° C.
- the second annealing is further performed at 550 to 720 ° C.
- cold rolling is not performed between the first annealing and the second annealing.
- the first annealing (hereinafter referred to as annealing 1) is performed for the purpose of coarsening the ⁇ -phase crystal grains while dissolving the intermetallic compound. For that purpose, it is necessary to perform annealing at 750 ° C. or higher.
- the titanium alloy material of the present embodiment contains a large amount of alloying elements in order to increase the high-temperature strength. At temperatures below 750 ° C., intermetallic compounds precipitate, and ⁇ -phase grain growth is hindered and coarsened. becomes difficult. Therefore, a long time is required for coarsening, and the deposited intermetallic compound becomes coarse.
- annealing 1 is given by continuous annealing. Therefore, in order to control the average crystal grain size of the ⁇ phase within a predetermined range, annealing 1 is performed at 750 ° C. to 830 ° C. by continuous annealing.
- a preferred range is 770 to 820 ° C, and a more preferred range is 780 to 810 ° C.
- Cooling after annealing 1 may be performed by air cooling or furnace cooling because the deposition rate of Ti 2 Cu, which is one of intermetallic compounds, is extremely slow.
- the average cooling rate up to 550 ° C. or less is preferably 0.5 ° C./s, more preferably 1 ° C./s.
- the temperature is lower than 550 ° C., the precipitation reaction becomes very slow. Therefore, the cooling rate in the region lower than 550 ° C. need not be particularly noted. Even when the annealing temperature is maintained for less than 1 minute, the intermetallic compound starts to dissolve, and crystal grains in the ⁇ phase can be grown.
- annealing 1 is performed for about 1 minute as a guideline, and it is preferable to adjust according to the equipment so that the average crystal grain size of ⁇ phase is in a desired range (10 ⁇ m to 100 ⁇ m).
- the annealing time of annealing 1 may be 1 to 5 minutes.
- annealing 2 When the temperature of annealing 2 exceeds 720 ° C., the solid solubility limit in the ⁇ phase of Cu or Si increases, so the amount of precipitation of intermetallic compounds decreases, and a sufficient 0.2% yield strength reduction effect is obtained. Absent. On the other hand, when the temperature is lower than 550 ° C., the diffusion of the elements is suppressed, so that the precipitation of the intermetallic compound becomes insufficient or the precipitated intermetallic compound becomes fine and the 0.2% yield strength is increased. Therefore, annealing 2 is performed within a range of 550 to 720 ° C. Moreover, in order to fully precipitate an intermetallic compound, the annealing time of annealing 2 needs to be 4 hours or more.
- the upper limit of the annealing time is not particularly limited, but is preferably 50 hours or less, more preferably 40 hours or less from the viewpoint of productivity.
- the intermetallic compound is already sufficiently precipitated, and even if the cooling rate is slow, the amount of precipitation of the intermetallic compound is only slightly increased. is there.
- annealing 2 at 550 ° C. or higher and 720 ° C. or lower is performed.
- the annealing 2 may be performed by cooling to near room temperature after the annealing 1 and then heating.
- FIG.2 (b) after annealing 1, you may cool to the temperature range of annealing 2, and you may anneal 2 as it is.
- annealing 1 when performing annealing 1 for a long time (so-called furnace cooling) in the heating furnace, it passes through the region of 550 to 720 ° C. that is the annealing temperature of annealing 2, In this case, the region of 550 to 720 ° C. cannot be maintained for 4 hours or more, and the temperature range is passed in less than 4 hours. Therefore, it is difficult to sufficiently precipitate the intermetallic compound only by performing furnace cooling after annealing 1.
- the titanium alloy material according to this embodiment is manufactured.
- the titanium alloy material of the present embodiment a titanium alloy material excellent in high-temperature strength and formability at room temperature.
- the titanium alloy material of the present embodiment is manufactured by subjecting an ingot having a predetermined chemical component to hot rolling and cold rolling, and then performing two-stage annealing. By the first annealing, the crystal grains of the ⁇ phase in the titanium alloy are 10 ⁇ m or more, and by the second annealing, the area fraction of the intermetallic compound is 1.0% or more, and the area fraction of the ⁇ phase is 96. 0% or more.
- the titanium alloy material of the present embodiment has such a metal structure, and contains an additive element having a wide solid solubility limit. Therefore, while maintaining high temperature strength, the titanium alloy material has 0.2 at room temperature. % Proof stress can be suppressed and molding processability can be improved.
- the conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited.
- the present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
- No. No. 10 is excluded. 1-1-No. 1-3, no. 2-1. 2-3, no. 3-1. 3-2, no. 4, no. 5-1, No. 5 5-2, no. 6-1, no. 6-2, no. 7-No. 9, no. 11-No. 14, no. 15-1 to No. 15-3, no. 16-1 to No. 16-3, no. 17-1, no. 17-2, no. 18-1 ⁇ No. 18-22, no. 19-1 ⁇ No. 19-5, no. 20-1, no. 20-2, no. 21-No. No. 30 was prepared using an ingot of about 0.6 kg obtained by vacuum arc button melting. No. 10 was produced using an ingot of about 20 kg by vacuum arc melting. Each produced ingot was hot-rolled at 1000 ° C. to obtain a hot-rolled sheet having a thickness of 10 mm. Thereafter, hot rolling at 860 ° C. was performed to obtain a hot rolled sheet having a thickness of 4 mm.
- the tensile test at room temperature was conducted by using an ASTM half-size tensile test piece (parallel part width 6.25 mm, parallel part length 32 mm, distance between gauge points 25 mm) from the above-described thin plate. ) And the strain rate was 0.5% / min up to 1.5% strain and then 30% / min until fracture.
- the ductility and springback at room temperature were evaluated by the elongation at break and 0.2% proof stress at room temperature. A case where the elongation at break at room temperature was 25.0% or more and the 0.2% proof stress at room temperature was 340 MPa or less was determined to be acceptable because the ductility was sufficient and the spring back was small.
- the tensile test was carried out in a room maintained at an average temperature of 25 ° C. ( ⁇ 2 ° C.) by an air conditioner.
- the ⁇ phase area fraction was obtained by image processing of the ⁇ phase area fraction.
- the area fraction of the intermetallic compound was obtained from the area of the portion other than the ⁇ phase.
- the average particle size of the intermetallic compound was obtained by calculating the area per particle from the number of particles other than the ⁇ phase and the area of the portion other than the ⁇ phase, and approximating the square.
- the ⁇ -phase crystal grain size is an average crystal grain size obtained by a cutting method. When the average grain size of the ⁇ phase obtained by the above method is 10 ⁇ m to 100 ⁇ m, the case where the area fraction of the ⁇ phase is 96% or more and the case where the area fraction of the intermetallic compound is 1.0% or more.
- Table 1 shows the results of the tensile test and the structure observation.
- surface shows having remove
- the overhang height may be lowered to 13 mm or 10 mm, and judgment may be made by comparative evaluation with a conventional material (JIS H4600 type 2 titanium).
- the conventional material is formed by hot-rolling by hot-rolling (thickness 4-5mm) manufactured from an ingot having the chemical composition of JIS H4600 second type titanium by shot blasting and pickling. A cold-rolled portion having no wrinkles was cold-rolled to a thickness of 1 mm, and then the rolling oil was washed and removed with acetone or an alkaline solution, and then subjected to vacuum annealing at 650 ° C. for 8 hours to obtain a plate material.
- oxidation test In the oxidation test, the surface of the plate thickness x 20 mm x 40 mm is wet-polished with emery paper # 600, and the value obtained by dividing the increase in weight after holding at 800 ° C. for 100 hours in the atmosphere by the surface area of the test piece (oxidation increase) is evaluated. did. During the test, the surface of the test piece was sufficiently exposed to the atmosphere by leaning the test piece against a container or the like. A case where the increase in oxidation was 50 g / m 2 or less was judged to be excellent in oxidation resistance. The increase in oxidation is an index representing oxidation resistance, and the smaller the value, the better the oxidation resistance.
- Oxidation increases weight because oxygen combines with titanium. When the oxide scale peels off, it decreases. When the scale peels off, the peel scale is also collected and weighed. Therefore, the test is performed by putting it in a container that can be recovered even if the scale is peeled off.
- No. 16-2, no. 18-2, no. 18-3, no. No. 18-22 was annealed 1 (solution treatment) but not annealed 2 (intermetallic compound precipitation), so the intermetallic compound did not precipitate so much and the 0.2% yield strength was too high.
- No. No. 18-2 is the holding time No. 18-2. Since it was shorter than 18-3, it was fine-grained, and as a result, the 0.2% yield strength was higher.
- No. 16-3, no. 18-4 ⁇ No. No. 18-20 is an example in which annealing 2 was performed without performing annealing 1.
- No. 18-4, no. 18-5, no. 18-6, no. 18-7, no. 18-10, no. 18-12, no. 18-16, no. 18-20 was conducted at a temperature higher than 720 ° C., and the average crystal grain size of the ⁇ phase was 10 ⁇ m or more.
- no. 18-4, no. 18-5, no. 18-6, no. 18-7, no. 18-10, no. 18-12, no. 18-16 has insufficient precipitation of intermetallic compounds and has a high 0.2% yield strength.
- No. 18-4, no. 18-5, no. 18-12, no. In 18-20 a small amount of intermetallic compounds existed before annealing 2, and annealing 2 was performed at 730 ° C., where intermetallic compounds did not precipitate finely. As a result, the high temperature strength decreased.
- No. No. 18-8 was annealed 2 only, so the average crystal grain size of the ⁇ phase was less than 10 ⁇ m, so the 0.2% yield strength was high.
- the temperature of annealing 1 was lower than 750 ° C., so that it could not be sufficiently dissolved, pinned by an intermetallic compound, and the average crystal grain size of ⁇ phase was less than 10 ⁇ m.
- the 0.2% proof stress was 340 MPa or less due to the precipitation of the intermetallic compound, but the elongation was less than 25%.
- No. 17-2 became fine because the annealing time in annealing 1 was short, and increased in strength and further reduced in ductility.
- No. No. 29 has an elongation of less than 25% because a large amount of intermetallic compounds were precipitated because the Ge content was too high. No. In No. 30, since the Bi content is too large, an intermetallic compound is excessively precipitated and the elongation is less than 25%.
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Abstract
Description
質量%で
Cu:0.7%~1.4%、
Sn:0.5%~1.5%、
Si:0.10%~0.45%、
Nb:0.05%~0.50%、
Fe:0.001%~0.08%、
O:0.001%~0.08%
を含有し、残部がTi及び不純物からなり、
組織中のα相の面積分率が96.0%以上であり、金属間化合物の面積分率が1.0%以上であり、
前記α相の平均結晶粒径が10μm以上100μm以下であり、前記金属間化合物の平均粒径が0.1~3.0μmである、チタン合金材。
更に、質量%で、
Bi:0.1~2.0%、
Ge:0.1~1.5%
のいずれか一方または両方を含有し、
これらの合計量が3.0%未満である、[1]に記載のチタン合金材。
25℃での破断伸びが25.0%以上、かつ、25℃での0.2%耐力が340MPa以下であり、700℃での引張強度が60MPa以上である、[1]に記載のチタン合金材。
チタン合金材の高温強度を向上させるためには、合金元素を添加して固溶強化させることが通常行われる。しかし、高温強度が向上したチタン合金材は、室温でも高強度になるため、成形加工時のスプリングバックが大きくなり、成形性が低下する。例えば、溶接などを自動化して排気装置等の製品を効率的に生産するためには、スプリングバックによる位置ずれを小さくする必要がある。なお、本明細書において室温とは、20℃~30℃である。室温は、好ましくは25℃である。
まず、各成分元素の含有量について説明する。ここで、成分についての「%」は質量%である。また、化学組成はインゴットではなく、仕上げ焼鈍まで施されたチタン合金材での分析値である。
Cuは、固溶限が広く、高温強度及び室温での強度を向上させる元素である。高温強度を向上させるためには、0.7%以上含有する必要がある。Cuを過剰に含有すると、Ti2Cuなどの金属間化合物が多量に析出し、延性が損なわれる。さらに、使用される際には780℃を超えるとβ相が形成されるようになるため、高温強度が低下する懸念がある。さらに、Ti2Cuの析出量が多いと、α相の粒成長が阻害され細粒となり、室温での延性を低下させてしまう。そのため、Cu含有量の上限を1.4%以下とする。したがって、Cuの含有量を0.7%~1.4%とする。Cuの下限は、0.8%、0.9%又は1.0%でもよい。又、Cuの上限は、1.3%、1.2%又は1.1%でもよい。
Snは、固溶限が広く、高温強度を向上させる元素である。高温強度を向上させるためには、Snを0.5%以上含有する必要がある。また、後述するSiは高温強度と耐酸化性を向上させるが、大型鋳塊を用いて製品を製造する場合に偏析を生じやすく、製造コストを抑制するために大型鋳塊を用いるには不向きである。そのため、偏析が小さいSnを添加することで高温強度のばらつきを低減する必要がある。なお、Snを過剰に含有すると、Ti2Cuなどの金属間化合物の析出を促進するため、1.5%以下に制限する必要がある。したがって、Sn含有量を0.5%~1.5%とする。Snの下限は、0.6%、0.7%又は0.8%でもよい。又、Snの上限は、1.4%、1.3%又は1.2%でもよい。
Siは、高温強度及び耐酸化性を向上させる元素である。ただし、偏析も考慮すると、これらの効果を得るには、Siを0.10%以上含有する必要がある。Siを過剰に含有すると、高温強度及び耐酸化性の向上効果が含有量に対して小さくなり、さらに、金属間化合物(シリサイド)を多量に析出し、室温での延性を低下させてしまうため、上限を0.45%以下とする。したがって、Si含有量を0.10%~0.45%とする。Siの下限は、0.15%、0.20%又は0.25%でもよい。又、Siの上限は、0.40%、0.35%又は0.30%でもよい。
Nbは、耐酸化性を向上させる元素である。また、発明の添加範囲においてNbはSiに比べて偏析が小さい元素である。そのため、Siの偏析による耐酸化性のばらつきを低減するためにNbも添加する必要がある。耐酸化性の向上効果を得るには、Nbを0.05%以上含有する必要がある。Nbを過剰に含有すると、含有量に対して耐酸化性の向上効果が小さくなり、また、β相を形成しやすくなる。さらにNbは高価であることから、上限を0.50%以下とする。したがって、Nb含有量を0.05%~0.50%とする。Nbの下限は、0.10%、0.15%又は0.20%でもよい。又、Nbの上限は、0.40%、0.35%又は0.30%でもよい。
Feは、不可避的に含まれる元素である。また、Feはβ安定化元素であり、過剰に含まれるとβ相を形成しやすく、α相の結晶粒の成長を妨げる。室温において十分な延性を得るためには、α相の結晶粒を成長させる必要があるため、Fe含有量は少ないほうが好ましい。したがって、Fe含有量は0.00%~0.08%とする。Feの上限は、0.06%、0.04%又は0.02%でもよい。
Oは、不可避的に含まれる元素であり、室温での強度を向上させ、延性を低下させる。高温での強度に対する寄与はほとんどないため、含有量は少ないほうが好ましい。したがって、O含有量を0.00%~0.08%とする。Oの上限は、0.06、0.04%又は0.02%でもよい。
本実施形態のチタン合金材は、Tiの一部に代えて、BiまたはGeのうち一方または両方を、含有量の合計が3.0%未満の範囲で含有してもよい。BiまたはGeのうち一方または両方Cuの上限は、2.5%、2.0%又は1.5%でもよい。
Biは、高温ではある程度の固溶限を有しており、高温強度を向上させるために0.1%以上含有してもよい。しかし、Biは、CuやSiと同様に金属間化合物を生じ、室温での延性を低下させるため、上限を2.0%以下とする。Biの下限は、0.2%、0.3%又は0.4%でもよい。又、Biの上限は、1.5%、1.0%又は0.8%でもよい。
Geは、高温ではある程度の固溶限を有しており、高温強度を向上させるために0.1%以上含有してもよい。しかし、Geは、CuやSiと同様に金属間化合物を生じ、室温での延性を低下させるため、上限を1.5%以下とする。Biの下限は、0.2%、0.3%又は0.4%でもよい。又、Biの上限は、1.2%、1.0%又は0.8%でもよい。BiとGeを複合添加する場合、固溶限はどちらも小さくなるため、各元素の上限である2.0%ずつ添加(合計4.0%)すると金属間化合物が形成される。そのため、BiとGeの合計添加量は3.0%以下でなければ、多量の金属間化合物によって延性が劣化する。
本実施形態のチタン合金材は、室温において、金属組織中に金属間化合物を析出させることによって、固溶強化を抑制し、0.2%耐力を低下させ、成形加工性を向上させる。この効果を得るためには、チタン合金材中に金属間化合物が、面積分率で1.0%以上析出している必要がある。ただし、金属間化合物が多量に析出しすぎると、析出強化により室温での延性を低下させる場合があるので、金属間化合物の面積分率を4.0%以下とする。金属間化合物の面積分率は、3.0%以下、又は、2.0%以下でもよい。また、α相の面積分率を96.0%以上とする。α相の面積分率の下限は、97.0%、98.0%でもよい。
本実施形態のチタン合金材は、α相の結晶粒径を大きくすることにより、室温での延性を向上させ、0.2%耐力を低下させる。そのため、主相であるα相の平均結晶粒径が、10μm以上である必要がある。10μmよりも小さいと0.2%耐力が高くなりすぎる場合や伸びが不十分となる場合がある。より好ましくは12μm以上であり、更に好ましくは15μm以上である。平均結晶粒径が大きいほど室温での延性に優れるが、100μmを超えると、成形によってしわが発生し、外観を損ねる可能性がある。したがって、α相の平均結晶粒径の上限を100μmとする必要がある。望ましくは70μm以下であり、より望ましくは50μm以下である。
Dn (μm)=Ln / Xn (1)
D (μm) = (D1+D2+D3+D4+D5)/5 (2)
本実施形態のチタン合金材は、金属間化合物が所定の面積分率で析出することにより、α相中の金属間化合物の固溶量が減少し、室温での0.2%耐力が低下する。析出した金属間化合物は、高温に曝されることで、再度α相中に固溶するため、高温強度が向上する。粗大な金属間化合物が析出していると、高温に曝された時に固溶しにくく、十分な高温強度が得られないため、金属間化合物の平均粒径を3.0μm以下とする必要がある。しかし、微細分散しすぎると、析出強化の効果が大きくなり、延性が低下してしまう。そのため、金属間化合物の平均粒径の下限を0.1μmとする。なお、本実施形態における金属間化合物には、Ti2Cu、チタンシリサイドなど、チタンとその他の金属元素からなる金属間化合物は勿論、チタン以外の金属元素同士の金属間化合物も含まれる。金属間化合物の粒径を観察するためには走査型電子顕微鏡を用いる。測定範囲は金属間化合物の面積分率の場合と同じであるが、各々の金属間化合物を測定する場合は1000倍を目安に行うのが良く、より高倍率での測定でも良い。
次に、本実施形態によるチタン合金材の製造方法の一例について、図1を参照にして説明する。製造工程の流れを図1に示す。図1中、インゴット製造、熱間圧延、脱スケール、冷間圧延、仕上げ焼鈍(焼鈍1+焼鈍2)は必須の工程であり、鍛造・分塊圧延、熱延板焼鈍、中間焼鈍・冷間圧延、形状矯正は必要に応じて行う工程である。
熱間圧延する素材は、真空アーク溶解や電子ビーム溶解などの方法で鋳造された、上述の化学組成を有するインゴットを用いる。なお、鍛造・分塊圧延を熱間圧延の前に加えてもよい。鍛造・分塊圧延は1000℃以上(望ましくは1050℃以上)に加熱して行う。熱間圧延は800~1100℃で加熱し圧延を行う。この時の熱間圧延温度は800℃を下回ると変形抵抗が大きくなり、熱間圧延が困難になる。1100℃を超えると、酸化が激しく、熱間圧延によるスケール押し込みやスケール部分が多くなることにより、歩留まりが低下する。
熱延板焼鈍は、熱間圧延後のチタン合金材のひずみを低減することにより、冷間圧延をしやすくする目的で行う。ただし、この工程は必ずしも行う必要は無く、冷間圧延性が不足する場合に実施すればよい。熱延板焼鈍は、過剰な酸化を抑制し、歩留まりの低下を抑制するために、750~850℃で行う。焼鈍時間に特に制限は無いが、1分~60分程度の保持で十分である。
冷間圧延は熱間圧延もしくは熱延板焼鈍後の脱スケールを行った後に行う。脱スケールは一般的な方法でよく、たとえばショットブラストを行った後に硝酸とふっ酸の混酸による酸洗によって表層を除去する方法である。冷間圧延では均一な組織を得るために、冷間での総圧延率(冷間圧延率)を高くする必要があり、冷間圧延率は50%以上が望ましい。一方で、冷間圧延率が95%を超えて冷間圧延をすると、歩留まりを大きく低下させるような耳割れを生じるため、冷間圧延率の上限は95%以下とする。より好ましくは90%以下であり、さらに好ましくは85%以下である。中間焼鈍を施す場合は、中間焼鈍後の冷間圧延で50%以上の冷間圧延率とすればよい。なお、中間焼鈍は熱延板焼鈍と同様に750~850℃で行うことが望ましい。
1回目の焼鈍(以下、焼鈍1という)は、金属間化合物を固溶させつつ、α相の結晶粒を粗粒化させる目的で行う。そのためには、750℃以上で焼鈍を行う必要がある。本実施形態のチタン合金材は、高温強度を高めるために合金元素を多量に含有しており、750℃を下回る温度では金属間化合物が析出し、α相の粒成長が阻害され、粗粒化が困難になる。そのため、粗粒化のために長時間が必要となり、析出した金属間化合物が粗大化する。さらに2回目の焼鈍においても、すでに存在する金属間化合物が成長するため、粗大な金属間化合物を形成することになる。一方、焼鈍温度が830℃を超えると、β相が形成されるため、α相の結晶粒成長が阻害される。また、750℃以上では、バッチ式焼鈍を行うとコイル同士の接触部で接合し、焼付きを生じるため不適切である。そのため、連続式焼鈍によって焼鈍1が施される。したがって、α相の平均結晶粒径を所定の範囲に制御するために、焼鈍1は連続式焼鈍によって750℃~830℃で実施する。好ましい範囲は770~820℃であり、より好ましい範囲は780~810℃である。焼鈍1後の冷却は、金属間化合物の一つであるTi2Cuの析出速度が極めて遅いことから、空冷や炉冷程度でもよい。好ましくは550℃以下までの平均冷却速度が0.5℃/sであり、より好ましくは1℃/sである。550℃を下回ると析出反応は非常に遅くなるため、550℃よりも低い領域の冷却速度は特に注意する必要はない。上記焼鈍温度において、1分未満の保持でも金属間化合物は固溶しはじめ、α相中の結晶粒が成長可能な状態となる。そのため、焼鈍1は1分程度を目安に行い、α相の平均結晶粒径が所望の範囲(10μm~100μm)になるように設備に応じて調整するとよい。焼鈍1の焼鈍時間は、具体的には1~5分であればよい。
上記焼鈍1を実施した後のチタン合金材は、金属間化合物がほとんど析出せず、析出したとしても金属間化合物の面積分率は1.0%未満である。金属間化合物が固溶したままでは、固溶強化により0.2%耐力が高くなるため、成形加工性に優れない。したがって、金属間化合物を所定の面積分率で析出させ、固溶強化を抑制し、0.2%耐力を低くする。本実施形態では、金属間化合物を所定の面積分率で析出させるために、焼鈍1の後に550~720℃で2回目の焼鈍(以下、焼鈍2という)を施す。
室温(25℃)での引張試験は、上記の薄板から、長手方向が圧延方向に対して平行のASTMハーフサイズ引張試験片(平行部幅6.25mm、平行部長さ32mm、標点間距離25mm)を採取し、ひずみ速度を、ひずみ1.5%までを0.5%/min、その後破断までを30%/minで行った。室温における延性及びスプリングバックの評価は、室温での破断伸び及び0.2%耐力で評価した。室温での破断伸びが25.0%以上であり、かつ、室温での0.2%耐力が340MPa以下である場合を、延性が十分でありスプリングバックが小さいとして合格と判定した。なお、引張試験は空調設備によって平均温度25℃(±2℃)に保たれた室内で実施した。
高温での引張試験は、上記の薄板から、長手方向が圧延方向に対して平行の引張試験片(平行部幅10mm、平行部長さ及び標点間距離30mm)を採取し、ひずみ速度を、ひずみ1.5%までを0.3%/min、その後破断までを7.5%/minで行った。試験雰囲気は、700℃の大気中で行い、試験片が十分に試験温度に達するように、試験雰囲気中に30分間保持した後、試験を行った。高温での引張強度が60MPa以上の場合を、高温強度に優れるとし、合格と判定した。
上記薄板のL断面(TD面)を光学顕微鏡により観察し、α相の平均結晶粒径を切断法によって求めた。走査型電子顕微鏡により観察した反射電子像での組織中のコントラストからα相と金属間化合物とを判別した。
厚さ50μmのテフロンシートを潤滑剤として用いた球頭張出し試験を張出し高さが15mmとなるまで行い、外観のシワの発生程度を観察し、ABCDの4段階で評価した(「テフロン」は登録商標)。Aは従来材(JIS H4600 第2種チタン)と同等の外観を有するもの、Bは従来材よりも外観上は劣るが製品化した後の研磨によって除去可能なもの、Cは研磨前にブラストなどの工程が必要となるもの、Dはブラストなどを行っても研磨で除去できないものとした。Dは不合格である。なお、15mmで破断する場合は13mmもしくは10mmまで張り出し高さを低くし、従来材(JIS H4600 第2種チタン)との比較評価によって判断してもよい。なお、従来材はJIS H4600 第二種チタンの化学組成を有する鋳塊から製造された熱延板(厚さ4~5mm)をショットブラストおよび酸洗によって脱スケールし、熱間圧延までで形成された疵がない部分を厚さ1mmまでの冷間圧延した後に、アセトンもしくはアルカリ溶液で圧延油を洗浄除去した後、650℃で8h真空焼鈍を施した板材とした。
酸化試験は板厚×20mm×40mm程度の表面をエメリー紙#600番で湿式研磨し、大気中で800℃、100h保持後の重量増加を試験片の表面積で除した値(酸化増量)で評価した。なお、試験時には試験片を容器などに立てかけることで試験片の表面が十分に大気にさらされるようにした。酸化増量が50g/m2以下の場合を耐酸化性に優れると判断した。なお、酸化増量は耐酸化性を表す指標であり、小さいほど耐酸化性に優れる。酸化すると酸素がチタンと結合するため重量が増加する。酸化スケールが剥離する場合には減少するが、スケール剥離した場合は剥離スケールも回収して重量測定する。そのため、スケールが剥離しても回収できるような容器に入れるなどして試験を行う。
Claims (3)
- 質量%で
Cu:0.7%~1.4%、
Sn:0.5%~1.5%、
Si:0.10%~0.45%、
Nb:0.05%~0.50%、
Fe:0.00%~0.08%、
O:0.00%~0.08%
を含有し、残部がTi及び不純物からなり、
組織中のα相の面積分率が96.0%以上であり、金属間化合物の面積分率が1.0%以上であり、
前記α相の平均結晶粒径が10μm以上100μm以下であり、前記金属間化合物の平均粒径が0.1~3.0μmである、チタン合金材。 - 更に、質量%で、
Bi:0.1~2.0%、
Ge:0.1~1.5%
のいずれか一方または両方を含有し、
これらの合計量が3.0%未満である、請求項1に記載のチタン合金材。 - 25℃での破断伸びが25.0%以上、かつ、25℃での0.2%耐力が340MPa以下であり、700℃での引張強度が60MPa以上である、請求項1に記載のチタン合金材。
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PCT/JP2018/004216 WO2019155553A1 (ja) | 2018-02-07 | 2018-02-07 | チタン合金材 |
US16/962,356 US11390935B2 (en) | 2018-02-07 | 2018-02-07 | Titanium alloy material |
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