WO2022162814A1 - チタン合金薄板およびチタン合金薄板の製造方法 - Google Patents
チタン合金薄板およびチタン合金薄板の製造方法 Download PDFInfo
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Classifications
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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
- 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
- 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
Definitions
- the present disclosure relates to a titanium alloy sheet and a method for manufacturing a titanium alloy sheet.
- Titanium is a lightweight, high-strength, and corrosion-resistant material that can be applied to the aircraft field from the perspective of weight reduction and improved fuel efficiency. Titanium alloys have been actively developed in accordance with the characteristics required for each component of aircraft.
- Patent Document 1 discloses an ⁇ + ⁇ type titanium alloy wire consisting of 1.4% or more and less than 2.1% Fe, 4.4% or more and less than 5.5% Al, and the balance titanium and impurities. .
- Patent Document 2 discloses an ⁇ + ⁇ -type titanium alloy bar consisting of 0.5% or more and less than 1.4% Fe, 4.4% or more and less than 5.5% Al, and the balance titanium and impurities.
- Patent Document 3 discloses a thin plate manufacturing method in which a pack material is formed by covering one or more plate-shaped core materials with a spacer material and a cover material, and the pack material is rolled to reduce the thickness of the core material.
- a pack material is formed by covering one or more plate-shaped core materials with a spacer material and a cover material, and the pack material is rolled to reduce the thickness of the core material.
- Manufacture of Ti-6Al-4V alloy thin sheets by pack rolling characterized in that each initial thickness is set so that the thickness of the cover material is set so that the ratio of the core material to the pack material is at least 0.25 or more.
- a method is disclosed.
- Patent Document 4 discloses a thin plate manufacturing method in which one or more plate-shaped core materials are covered with a spacer material and a cover material to form a pack material, and the pack material is rolled to reduce the thickness of the core material.
- a method for producing a Ti-6Al-4V alloy thin sheet by pack rolling characterized in that the reduction ratio of the thickness of the pack material before and after decompression is 3 or more, and the rolling rate per pass is 15% or more. is disclosed.
- Patent Document 5 a hot-rolled and annealed titanium alloy sheet composed of Al: 2.5 to 3.5%, V: 2.0 to 3.0%, and the balance Ti and ordinary impurities, in terms of weight percent, is heated.
- a method for producing a titanium alloy sheet comprises cold rolling at a total rolling reduction of 67% or more in the same direction as the interrolling direction, and then annealing at a temperature between 650 and 900°C.
- Patent Document 7 discloses that at least one solid-solution type ⁇ -stabilizing element is 2.0 to 4.5% by mass in Mo equivalent and at least one eutectoid-type ⁇ -stabilizing element is 0.00% in Fe equivalent.
- ⁇ + ⁇ type titanium alloy containing 3 to 2.0% by mass, at least one ⁇ -stabilizing element in Al equivalent of more than 3.0% by mass and 5.5% by mass or less, and the balance being Ti and unavoidable impurities
- the thin plate has an average particle size of the ⁇ phase of 5.0 ⁇ m or less, a maximum particle size of the ⁇ phase of 10.0 ⁇ m or less, an average aspect ratio of the ⁇ phase of 2.0 or less, and an ⁇
- An ⁇ + ⁇ type titanium alloy sheet is disclosed, characterized in that the maximum aspect ratio of the phase is 5.0 or less.
- Patent Document 8 discloses an ⁇ + ⁇ type titanium alloy hot-rolled sheet, wherein (a) the direction of the normal to the rolling surface (thickness direction) of the hot-rolled sheet is ND, the hot-rolling direction is RD, and the hot-rolled sheet width is The direction is TD, the normal direction of the (0001) plane of the ⁇ phase is the c-axis orientation, the angle formed by the c-axis orientation and ND is ⁇ , and the plane including the c-axis orientation and ND is the plane including ND and TD.
- ⁇ is 0 degrees or more and 30 degrees or less
- ⁇ is the (0002) reflection relative intensity of the X-ray from the crystal grain that falls within the entire circumference ( ⁇ 180 degrees to 180 degrees) , where XND is the strongest intensity, and (b2) ⁇ is 80 degrees or more and less than 100 degrees, and ⁇ is ⁇ 10 degrees.
- XTD is 5.0 or more.
- ⁇ be the angle formed by the plane with the plane including ND and TD, and (b1) ⁇ is 0 degrees or more and 30 degrees or less, and ⁇ is within the entire circumference ( ⁇ 180 degrees to 180 degrees)
- X Of the (0002) line reflection relative intensities, the strongest intensity is XND, and (b2) X-ray (0002 ) Among the reflection relative intensities, XTD is the strongest intensity, and (c) XTD/XND is 4.0 or more. disclosed.
- a high-strength ⁇ + ⁇ -type titanium alloy cold-rolled annealed sheet containing O, N and Fe in a range satisfying Q 0.34 to 0.55, the balance being Ti and inevitable impurities, the texture in the sheet surface direction was analyzed, the normal direction of the rolling surface of the cold-rolled annealed sheet was ND, the longitudinal direction was RD, the width direction was TD, the normal direction of the (0001) plane of the ⁇ phase was the c-axis direction, and the c-axis Let ⁇ be the angle formed by the orientation with ND, and ⁇ be the angle formed between the projection line of the c-axi
- Non-Patent Document 1 discloses an ⁇ + ⁇ titanium alloy sheet having anisotropy in strength in the rolling direction and in the direction perpendicular to the rolling direction.
- Non-Patent Document 2 discloses an ⁇ + ⁇ titanium alloy sheet that is hot rolled at a temperature higher than the ⁇ transformation point to reduce the anisotropy of strength in the rolling direction and in the direction perpendicular to the rolling direction.
- an alloy containing a relatively large amount of Al which is an ⁇ -phase solid-solution strengthening element, such as Ti-6Al-4V (64 alloys) are often used.
- the ⁇ + ⁇ type titanium alloy, such as 64 alloy which contains a large amount of Al and has high strength, generally has poor workability and is difficult to cold-roll.
- a titanium alloy is subjected to unidirectional high-speed hot rolling at a temperature in the ⁇ region or in the ⁇ + ⁇ high temperature region where the ⁇ phase ratio is high, during the transformation from the ⁇ phase to the ⁇ phase, a hexagonal shape is formed in the sheet width direction by variant selection.
- a hexagonal close-packed (hcp) c-axis oriented texture (T-texture) is formed. Since the c-axis direction of titanium has higher Young's modulus and strength than other directions, the T-texture is a texture suitable for increasing the strength and Young's modulus in the sheet width direction.
- the temperature of the material during hot rolling drops sharply due to the reduction in sheet thickness, so the high-strength ⁇ phase increases and the high-temperature strength low ⁇ Titanium alloys with phase reduction have significantly increased deformation resistance and may exceed the load capacity of the rolling mill. Therefore, it is difficult to manufacture a thin plate having a thickness of 2.5 mm or less only by hot rolling.
- the present disclosure has been made in view of the above problems, and the purpose of the present disclosure is to utilize T-texture, have high strength in the sheet width direction, and have a high Young's modulus in the sheet width direction.
- An object of the present invention is to provide an Al-containing titanium alloy sheet having a thickness of 2.5 mm or less and a method for producing the same titanium alloy sheet.
- the T-texture in hcp titanium is expected to deform due to slip in the hot rolling direction, so it cannot be concluded that cold rolling in the same direction is difficult.
- the inventors of the present invention have made intensive and detailed studies on the production of a thin plate of 2.5 mm or less by cold rolling using an Al-containing titanium alloy having a T-texture developed by hot rolling.
- a titanium alloy sheet according to an aspect of the present disclosure has, in mass %, Al: more than 4.0% and 6.6% or less, Fe: 0% or more and 2.3% or less, V: 0% or more , 4.5% or less, Si: 0% or more and 0.60% or less, Ni: 0% or more and less than 0.15%, Cr: 0% or more and less than 0.25%, Mn: 0% or more, 0 less than .25%, C: 0% or more and less than 0.080%, N: 0% or more and 0.050% or less, and O: 0% or more and 0.40% or less, and the balance is Ti and impurities,
- the titanium alloy sheet according to [1] above contains, in % by mass, Fe: 0.5% or more and 2.3% or less or V: 2.5% or more and 4.5% or less may be contained.
- Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25% may contain one or more selected from the group consisting of.
- the half width may be 0.20° or more.
- the titanium alloy sheet according to any one of [1] to [5] above has an aspect ratio of more than 3.0 and a band structure extending in the longitudinal direction of the plate, An area ratio of the band structure may be 70% or more.
- the titanium alloy sheet according to any one of [1] to [6] above may have a thickness dimensional accuracy of 5.0% or less with respect to the average thickness.
- a method for producing a titanium alloy sheet according to another aspect of the present disclosure is the method for producing a titanium alloy sheet according to any one of [1] to [7] above, comprising: % by mass, Al: more than 4.0% and 6.6% or less, Fe: 0% or more and 2.3% or less, V: 0% or more and 4.5% or less, Si: 0% or more, 0.5% or less; 60% or less, Ni: 0% or more and less than 0.15%, Cr: 0% or more and less than 0.25%, Mn: 0% or more and less than 0.25%, C: 0% or more and 0.08% less than, N: 0% or more and 0.05% or less, and O: 0% or more and 0.40% or less, a heating step of heating a titanium material with the balance being Ti and impurities; a hot rolling step of unidirectionally hot rolling the titanium material after the heating step; a cold rolling step of performing one or more cold rolling passes in the longitudinal direction of the titanium material after the hot rolling step, The heating temperature of
- the rolling reduction in the hot rolling step is 80.0% or more
- the finishing temperature in the hot rolling step is (T ⁇ -250) ° C. or higher and (T ⁇ -50) ° C. or lower
- the cold rolling process is The rolling reduction per cold rolling pass is 40% or less, and when performing a plurality of the cold rolling passes, an intermediate annealing treatment is included,
- the annealing conditions for the intermediate annealing treatment are The annealing temperature is 500° C. or higher and 750° C.
- the annealing temperature T (° C.) and the holding time t (seconds) at the annealing temperature satisfy the following formula (2). 18000 ⁇ (T+273.15) ⁇ (Log 10 (t)+20) ⁇ 22000 Expression (2) [9]
- the annealing temperature is 500° C. or higher and 750° C. or lower, and the final temperature satisfies the formula (2). Annealing may be performed.
- the strength in the sheet width direction is high, and the Young's modulus in the sheet width direction is high, and the sheet thickness is 2.5 mm or less. It is possible to provide a method.
- FIG. 3 is an explanatory diagram for explaining the crystal orientation of ⁇ -phase crystal grains of a titanium plate by Euler angles according to Bunge's notation method.
- 1 is an example of a crystal orientation distribution function obtained by an electron beam backscattering diffraction method for a titanium alloy thin plate according to an embodiment of the present disclosure
- 1 is an optical micrograph showing an example of a band structure. It is a figure which shows an example of the optical microscope photograph of the titanium alloy thin plate which concerns on the same embodiment. It is a schematic diagram for demonstrating the measuring method of average plate
- Titanium alloy sheet> First, a titanium alloy sheet according to this embodiment will be described with reference to the drawings.
- the titanium alloy sheet according to this embodiment has, in mass %, Al: more than 4.0% and 6.6% or less, Fe: 0% or more and 2.3% or less, V: 0% or more and 4.5%.
- Si 0% or more and 0.60% or less
- Ni 0% or more and less than 0.15%
- Cr 0% or more and less than 0.25%
- Mn 0% or more and less than 0.25%
- C 0% or more and less than 0.08%
- N 0% or more and 0.05% or less
- O 0% or more and 0.40% or less
- the balance consists of Ti and impurities.
- the notation "%" represents “% by mass” unless otherwise specified.
- Al is an ⁇ -phase stabilizing element and an element with high solid-solution strengthening ability. Increasing the Al content increases the tensile strength at room temperature and the strength at relatively high temperatures. Al also has the effect of increasing the Young's modulus. Furthermore, if the Al content exceeds 4.0%, the hot-rolled sheet before cold rolling can maintain high cold-rollability. The Al content is preferably 4.5% or more. On the other hand, if the Al content exceeds 6.6%, the cold rolling property of the hot-rolled sheet before cold rolling is significantly reduced, and Al is locally excessively concentrated due to solidification segregation and the like, resulting in Al regularizes. This Al-ordered region reduces the impact toughness of the titanium alloy sheet. Therefore, the Al content is 6.6% or less, preferably 6.5% or less, 6.3% or less, more preferably 6.2% or less.
- Fe is a ⁇ -phase stabilizing element. Since Fe is an element with high solid-solution strengthening ability, increasing the Fe content increases the tensile strength at room temperature. Also, since the ⁇ phase has higher workability than the ⁇ phase, increasing the Fe content improves the workability of the titanium alloy sheet.
- the Fe content is preferably 0.5% or more in order to obtain the desired tensile strength while maintaining the ⁇ phase with good workability at room temperature. Since Fe is not essential in the titanium alloy sheet, the lower limit of its content is 0%. The Fe content is more preferably 0.7% or more.
- the Fe content is preferably 2.3% or less.
- the Fe content is more preferably 2.1% or less, still more preferably 2.0% or less. It should be noted that Fe is less expensive than ⁇ -phase stabilizing elements such as V or Si.
- V is a completely solid-solution type ⁇ -phase stabilizing element, and is an element having a solid-solution strengthening ability.
- the V content is preferably 2.5% or more in order to obtain a solid-solution strengthening ability equivalent to that of Fe described above.
- the V content is more preferably 3.0% or more. Since V is not essential in the titanium alloy sheet, the lower limit of its content is 0%. Substituting V for Fe increases the cost, but since V is less likely to segregate than Fe, variations in properties due to segregation are suppressed. As a result, it becomes easier to obtain stable properties in the longitudinal direction and the width direction of the titanium alloy thin plate. In order to suppress variations in properties due to V segregation, the V content is preferably 4.5% or less. As described above, since V is less likely to segregate than Fe, it is preferable that V be contained in the titanium material when manufacturing a large ingot.
- Si is a ⁇ -phase stabilizing element, it also dissolves in the ⁇ -phase and exhibits high solid-solution strengthening ability.
- Fe may segregate if it is contained in the titanium alloy sheet by more than 2.3%. Therefore, if necessary, Si may be contained in the titanium alloy sheet to increase the strength of the titanium alloy sheet.
- Si has a segregation tendency opposite to that of O described below, and is less likely to solidify and segregate than O. Therefore, by including appropriate amounts of Si and O in the titanium alloy thin sheet, high fatigue strength and tensile strength can be expected to be compatible with
- the Si content is high, an intermetallic compound of Si called silicide is formed, which may reduce the fatigue strength of the titanium alloy sheet.
- the Si content is preferably 0.60% or less.
- the Si content is preferably 0.50% or less, more preferably 0.40% or less, still more preferably 0.30% or less. Since Si is not essential in the titanium alloy plate, the lower limit of its content is 0%, but the Si content may be, for example, 0.10% or more, or 0.15% or more. may be
- Ni like Fe or V, is an element that improves tensile strength and workability.
- the Ni content is preferably less than 0.15%.
- the Ni content is more preferably 0.14% or less and 0.11% or less. Since Ni is not essential in the titanium alloy plate, the lower limit of its content is 0%, but the Ni content may be, for example, 0.01% or more.
- Cr like Fe or V
- the Cr content is preferably less than 0.25%.
- the Cr content is more preferably 0.24% or less, still more preferably 0.21% or less. Since Cr is not essential in the titanium alloy sheet, the lower limit of its content is 0%, but the Cr content may be, for example, 0.01% or more.
- Mn like Fe or V
- the Mn content is preferably less than 0.25%.
- the Mn content is more preferably 0.24% or less, still more preferably 0.20% or less. Since Mn is not essential in the titanium alloy sheet, the lower limit of its content is 0%, but the Mn content may be, for example, 0.01% or more.
- the titanium alloy sheet according to the present embodiment contains either Fe: 0.5 to 2.3% or V: 2.5 to 4.5% as an optional element. preferably.
- the titanium alloy sheet according to the present embodiment contains either Fe: 0.5 to 2.3% or V: 2.5 to 4.5%, is replaced with part of Fe or V, one or two selected from the group consisting of Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25% It is preferable to contain the above.
- the total amount of Fe, Ni, Cr, and Mn is preferably 0.5% or more and 2.3% or less when the species or two or more are contained.
- the total amount of Fe, Ni, Cr, and Mn is 0.5% or more, high tensile strength is obtained, and the ⁇ phase, which has good workability at room temperature, is maintained to improve workability of the titanium alloy sheet.
- the total amount of Fe, Ni, Cr, and Mn is 2.3% or less, segregation of these elements is suppressed, and it is possible to suppress variations in properties of the titanium alloy thin sheet.
- the titanium alloy sheet according to the present embodiment contains V, it is selected from the group consisting of Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25%.
- the total amount of V, Ni, Cr, and Mn is preferably 2.5% or more and 4.5% or less.
- the total amount of V, Ni, Cr, and Mn is 2.5% or more, high tensile strength is obtained, and the ⁇ phase, which has good workability at room temperature, is maintained to improve workability of the titanium alloy sheet.
- the total amount of V, Ni, Cr, and Mn is 4.5% or less, the segregation of these elements is suppressed, making it possible to suppress variations in the properties of the titanium alloy sheet.
- the titanium alloy sheet according to the present embodiment is preferably limited to C: less than 0.080%, N: 0.050% or less, and O: 0.40% or less.
- the content of each element is described below. Since C, N and O are not essential in the titanium alloy sheet, the lower limit of their content is 0%.
- the C content is preferably less than 0.080%.
- C is an unavoidably mixed substance, and its substantial content is usually 0.0001% or more.
- N if contained in a large amount in a titanium alloy sheet, may reduce the ductility or workability of the titanium alloy sheet.
- N is an interstitial element that penetrates into the ⁇ phase to strengthen the solid solution of the titanium material. Therefore, the N content is preferably 0.050% or less.
- N is a substance that is unavoidably mixed, and the substantial content is usually 0.0001% or more.
- O may reduce the ductility or workability of the titanium alloy sheet if it is contained in a large amount in the titanium alloy sheet.
- O is an interstitial element and penetrates into the ⁇ phase to strengthen the solid solution of the titanium material. Therefore, the O content is preferably 0.40% or less, more preferably 0.35% or less, and still more preferably 0.30% or less.
- O is an unavoidably mixed substance, and its substantial content is usually 0.0001% or more.
- the titanium alloy sheet according to the present embodiment contains one or more selected from the group consisting of O, N, Fe, and V
- the content of O in mass% is [O]
- the N content is [N]
- the Fe content is [Fe]
- the V content is [V]
- the Q value represented by the following formula (1) is 0.340 or less.
- the lower limit of the Q value is not particularly limited, the Q value is substantially greater than 0 because O and N are unavoidably mixed.
- Q [O]+(2.77 ⁇ [N])+(0.1 ⁇ [Fe])+(0.025 ⁇ [V]) Equation (1)
- the Q value is an index for estimating the cold-rollability of titanium materials. If the Q value exceeds 0.340, the cold rolling properties may be remarkably lowered. As described above, when O and N are contained in a large amount, the cold rolling property is lowered. In particular, in a system containing more than 4.0% by mass of Al, O may be ordered with Al to form an intermetallic compound, resulting in a decrease in cold-rollability. Fe and V are ⁇ -phase stabilizing elements and basically have the effect of increasing cold-rollability. may reduce The coefficients of [N], [Fe] and [V] are determined in consideration of the degree of influence on deterioration of cold rolling properties.
- the remainder of the chemical composition of the titanium alloy sheet according to this embodiment may be Ti and impurities.
- Impurities include, for example, H, Cl, Na, Mg, Ca, and B that are mixed in during the refining process and Zr, Sn, Mo, Nb, and Ta that are mixed in from scraps and the like. If the total amount of impurities is 0.5% or less, there is no problem. Also, the H content is 150 ppm or less. B may form coarse precipitates in the ingot. Therefore, even if it is contained as an impurity, it is preferable to suppress the B content as much as possible.
- the titanium alloy plate of the present embodiment preferably has a B content of 0.01% or less.
- V contained in the titanium alloy sheet may be contained in an amount considered to be an impurity.
- Fe contained in the titanium alloy sheet may be contained in an amount regarded as an impurity.
- the titanium alloy sheet according to the present embodiment may contain various elements in place of Ti as long as high strength in the sheet width direction and high Young's modulus can be obtained.
- the elements exemplified as impurities may be contained in an amount equal to or greater than the amount considered as impurities, as long as the titanium alloy sheet has high strength and excellent workability.
- the titanium alloy sheet according to the present embodiment can have the above chemical components. More specifically, the chemical composition of the titanium alloy sheet according to this embodiment may be, for example, Ti-6Al-4V, Ti-6Al-4V ELI, and Ti-5Al-1Fe.
- the maximum integrated orientation indicated by the crystal orientation distribution function f(g) is ⁇ 1: 0 to 30°, ⁇ : 60 to 90°, ⁇ 2: 0 to 60°, and if the degree of integration in the maximum integration direction is 10.0 or more, the tissue has a developed T-texture.
- the titanium alloy sheet according to the present embodiment has a structure with a developed T-texture and contains a large amount of non-recrystallized structure.
- FIG. 1 is an explanatory diagram for explaining the crystal orientation of ⁇ -phase crystal grains of a titanium alloy thin plate in terms of Euler angles according to Bunge's notation method.
- RD rolling direction
- TD strip width direction
- ND normal direction of rolling surface
- Each coordinate axis is arranged so that the origin of each coordinate system coincides, and the hexagonal column indicating hcp is shown so that the center of the (0001) plane of hcp, which is the ⁇ phase of titanium, coincides with the origin. ing.
- the X-axis coincides with the [10-10] direction of the ⁇ phase
- the Y-axis coincides with the [-12-10] direction
- the Z-axis coincides with the [0001] direction (C-axis direction).
- These three angles ⁇ 1, ⁇ , and ⁇ 2 are called Euler angles according to Bunge's notation.
- the Euler angles according to the Bunge notation method define the crystal orientation (such as the C-axis direction) of the ⁇ -phase crystal grains of the titanium alloy thin plate.
- ⁇ 1 is the line of intersection between the RD-TD plane (rolling plane) of the sample coordinate system and the [10-10]-[-12-10] plane of the crystal coordinate system and the RD (rolling plane) of the sample coordinate system. direction).
- ⁇ is the angle between the ND (normal direction of the rolled surface) of the sample coordinate system and the [0001] direction (normal direction of the (0001) plane) of the crystal coordinate system.
- ⁇ 2 is the line of intersection between the RD-TD plane (rolled surface) of the sample coordinate system and the [10-10]-[-12-10] plane of the crystal coordinate system, and the [10-10] direction of the crystal coordinate system. is the angle formed by
- the maximum integration direction and maximum integration degree can be obtained as follows.
- a cross section (L section) perpendicular to the width direction of the titanium alloy thin plate is chemically polished at the center position in the width direction (TD), and the crystal orientation is analyzed using the electron backscatter diffraction (EBSD) method.
- About 5 fields of view are measured in an area of (total plate thickness) ⁇ 200 ⁇ m at a step of 1 ⁇ m for each of the lower surface portion and the central portion of the plate thickness of the titanium alloy thin plate.
- the crystal orientation distribution function f(g) OIM Analysis TM software (Ver.8.1.0) manufactured by TSL Solutions.
- the crystal orientation distribution function f(g) is calculated with an expansion index of 16 and a Gaussian half width of 5° in texture analysis using the spherical harmonics method of the EBSD method. At that time, considering the symmetry of the rolling deformation, the calculation is performed so as to be line symmetrical with respect to each of the thickness direction, the rolling direction, and the width direction.
- the ODF is a three-dimensional distribution plotted in a three-dimensional space (Eulerian space) of ⁇ 1- ⁇ - ⁇ 2 of the measured crystal orientations and expressed by a distribution function.
- FIG. 2 is an example of the crystal orientation distribution function f(g) obtained by the electron beam backscatter diffraction method of the titanium alloy thin plate according to this embodiment. In FIG.
- the Eulerian space in order to display the Eulerian space in two dimensions, the Eulerian space is horizontally sliced every 5 degrees in the direction of angle ⁇ 2, and the obtained cross sections are arranged.
- the maximum integration orientation and maximum integration degree can be calculated.
- the maximum accumulation orientation and maximum accumulation degree are obtained based on the L cross section at the center position in the width direction, but since the texture of the titanium alloy thin plate is uniform in the width direction, The maximum integration direction and the maximum integration degree may be obtained based on the L section.
- Dislocation density Generally, metal materials are work hardened by introducing dislocations. Also in the titanium alloy sheet, the higher the dislocation density, the higher the strength. Since the titanium alloy sheet according to the present embodiment has a structure with a developed T-texture, it contains a large amount of non-recrystallized structure. A non-recrystallized structure is a structure in which a large amount of dislocations are introduced.
- a method of estimating the dislocation density there is a method of estimating the dislocation density from the half width of the diffraction peak obtained by X-ray diffraction (XRD). The larger the half width of the diffraction peak, the higher the dislocation density.
- the dislocation density is calculated by the following method. After the surface of the titanium alloy thin plate is wet-polished using emery paper, the surface is mirror-polished using colloidal silica to obtain a mirror surface. XRD measurement is performed on the surface of the mirror-finished titanium alloy thin plate. The XRD measurement uses CuK ⁇ as a radiation source, and is carried out in the range of 2 ⁇ from 50.0° to 55.0° at a measurement pitch of 0.01° and a measurement speed of 2°/min. The half-value width is calculated by Rigaku integrated powder X-ray analysis software PDXL using X-ray diffraction data measured by Rigaku Smartlab.
- the titanium alloy sheet according to the present embodiment preferably has an aspect ratio of more than 3.0 and a band structure extending in the longitudinal direction of the plate, and the area ratio of the band structure is preferably 70% or more.
- the band structure referred to here is, for example, a structure elongated in the longitudinal direction as shown in the optical micrograph of the band structure in FIG. Specifically, it refers to crystal grains having an aspect ratio of more than 3.0, which is represented by the major axis/minor axis of the crystal grain.
- the titanium alloy sheet according to this embodiment has a band structure elongated in the longitudinal direction of the sheet, as shown in the optical micrograph of the titanium alloy sheet according to this embodiment in FIG.
- a band structure elongated in the longitudinal direction of the plate is formed.
- the band structure has many crystal grain boundaries perpendicular to the plate thickness direction. If the area ratio of the band structure is 70% or more, it is possible to slow down the growth of cracks generated from the plate surface in the plate thickness direction.
- the area ratio of the band structure is more preferably 75% or more, still more preferably 80% or more. Also, all crystal grains may have a band structure, and the upper limit is 100.0%.
- the aspect ratio and area ratio of the band structure can be calculated as follows.
- a cross section (L section) obtained by cutting a titanium alloy thin plate perpendicularly to the width direction (TD) at the center position of the width direction (TD) is chemically polished, and at any five points in the cross section, (total thickness) ⁇
- a region of 200 ⁇ m is measured in steps of 1 ⁇ m, and the crystal orientation is analyzed by the EBSD method. From the crystal orientation analysis result of this EBSD, the aspect ratio is calculated for each crystal grain. After that, the area ratio of crystal grains with an aspect ratio exceeding 3.0 is calculated.
- the aspect ratio and the area ratio of the band structure are calculated based on the L cross section at the center position in the width direction, but since the band structure is uniformly distributed in the width direction, the L The aspect ratio and the area ratio of the band structure may be calculated based on the cross section.
- the 0.2% yield strength in the sheet width direction at room temperature of the titanium alloy sheet according to this embodiment is 800 MPa or more. In the field of aircraft and the like, tensile strength close to the tensile strength at room temperature of Ti-6Al-4V, which is a general-purpose ⁇ + ⁇ -type titanium alloy, is often required. If the 0.2% proof stress in the sheet width direction at room temperature of the titanium alloy sheet is 800 MPa or more, it can be used for applications requiring high strength. The 0.2% yield strength in the sheet width direction at room temperature is preferably 850 MPa or more.
- the 0.2% yield strength in the sheet width direction at room temperature is preferably 1300 MPa or less.
- the 0.2% yield strength in the sheet width direction at room temperature is more preferably 1250 MPa or less.
- the 0.2% yield strength can be measured by a method conforming to JIS Z2241:2011. Specifically, a No.
- 13B tensile test piece (parallel part width 12.5 mm, gauge length 50 mm) specified in JIS Z 2241: 2011 so that the tensile direction is the plate width direction of the titanium alloy thin plate. It can be measured by preparing and performing a tensile test at a strain rate of 0.5% / min
- the Young's modulus in the plate width direction of the titanium alloy thin plate according to this embodiment is 125 GPa or more. If the Young's modulus is 125 GPa or more, it can be used in applications such as the aircraft field, automobile parts, and consumer products that require high synthesis. In particular, if the Young's modulus in the plate width direction is 125 GPa or more, there is an advantage that the weight can be reduced by about 3 to 4% compared to the conventional one. A too high Young's modulus does not pose any problem, but the practical upper limit for titanium is about 150 GPa.
- the Young's modulus in the sheet width direction can be measured by the following method. That is, a No.
- 13B tensile test piece (parallel part width 12.5 mm, gauge length 50 mm) specified in JIS Z 2241: 2011 was prepared so that the tensile direction was the width direction of the titanium alloy thin plate, A strain gauge is attached, and at a strain rate of 10.0%/min, load-unload is repeated 5 times in a stress range from 100 MPa to half of the 0.2% yield strength, and the slope is obtained, and the maximum and minimum values are excluded. Let the average value of three times be a Young's modulus.
- the Vickers hardness HV of the titanium alloy thin plate according to this embodiment is 330 or higher.
- Vickers hardness HV conforms to JIS Z 2244: 2009, mirror-polished a cross section (TD (Transverse direction) surface) perpendicular to the width direction (TD) at the central position of the rolled plate in the width direction (TD), The cross section is measured at 7 points with a load of 500 g and a load time of 15 seconds, and the average value of the 5 points excluding the maximum and minimum values is defined as the Vickers hardness HV.
- the Vickers hardness HV of the titanium alloy thin plate according to this embodiment may be 340 or higher, or 350 or higher.
- the Vickers hardness HV of the titanium alloy thin plate according to the present embodiment may be 430 or less, or may be 420 or less.
- the Vickers hardness of HV330 or more of the titanium alloy thin plate according to this embodiment corresponds to a tensile strength of 1 GPa or more measured by a method conforming to JIS Z2241:2011.
- the TD surface at the central position in the longitudinal direction is used as the measurement surface for the Vickers hardness HV.
- the surface may be used as the measurement surface for the Vickers hardness HV.
- the average plate thickness of the titanium alloy thin plate according to this embodiment is 2.5 mm or less.
- the titanium alloy sheet according to the present embodiment is manufactured by a method including a cold rolling process, so that the average sheet thickness can be 2.5 mm or less.
- the average plate thickness of the titanium alloy thin plate according to the present embodiment is preferably 0.1 mm or more.
- the average plate thickness of the titanium alloy thin plate according to this embodiment is more preferably 0.3 mm or more.
- FIG. 5 is a schematic diagram for explaining a method for measuring the average plate thickness.
- the plate thickness at each position is 1 m in the longitudinal direction at the position of 1/4 of the plate width from the center position of the plate width direction (TD) and both ends in the plate width direction. Measurements are taken at 5 or more locations with the above intervals, and the average value of the measured plate thicknesses is taken as the average plate thickness.
- the thickness dimensional accuracy of the titanium alloy thin plate according to the present embodiment is preferably 5.0% or less with respect to the average plate thickness.
- pack rolling multiple layers of titanium material wrapped in steel material are hot rolled to produce titanium alloy sheets. It is difficult to manufacture thick thin plates.
- the titanium alloy sheet according to the present embodiment is manufactured through cold rolling as described later, the titanium alloy sheet is excellent in thickness dimensional accuracy.
- the dimensional accuracy of the titanium alloy thin plate according to the present embodiment is more preferably 4.0% or less of the average plate thickness, and still more preferably 2.0% or less.
- the titanium alloy sheet according to the present embodiment has been described above.
- the titanium alloy sheet according to the present embodiment described above may be manufactured by any method, but may be manufactured, for example, by the method for manufacturing a titanium alloy sheet described below.
- the method for manufacturing a titanium alloy sheet according to the present embodiment includes a slab manufacturing process for manufacturing a titanium alloy slab that is the material (titanium material) of the titanium alloy sheet, a heating process for heating the titanium alloy slab, and a titanium alloy sheet after the heating process.
- a titanium alloy slab is manufactured.
- a material having the chemical composition described above and manufactured by a known method can be used.
- the method for producing the titanium alloy slab is not particularly limited, and for example, it can be produced according to the following procedure.
- an ingot is produced from sponge titanium by various melting methods such as vacuum arc melting method, electron beam melting method, hearth melting method such as plasma melting method, and the like.
- a titanium alloy slab can be obtained by hot forging the obtained ingot at a temperature in the ⁇ -phase high-temperature range, the ⁇ + ⁇ two-phase range, or the ⁇ -phase single-phase range.
- the titanium alloy slab may be subjected to pretreatment such as cleaning treatment and cutting as necessary.
- pretreatment such as cleaning treatment and cutting as necessary.
- a rectangular shape that can be hot-rolled by the hearth melting method it may be subjected to hot rolling without hot forging or the like.
- the manufactured titanium alloy slab contains more than 4.0% and 6.6% or less of Al, Fe: 0% or more and 2.3% or less, V: 0% or more and 4.5% or less, Si: 0%.
- Ni 0% or more and less than 0.15%
- Cr 0% or more and less than 0.25%
- Mn 0% or more and less than 0.25%
- C 0% or more, It contains less than 0.080%
- N 0% or more and 0.050% or less
- O 0% or more and less than 0.40%.
- the titanium alloy slab is heated to a temperature equal to or higher than the ⁇ transformation point T ⁇ °C ( T ⁇ + 150°C) or lower. If the heating temperature is lower than T ⁇ °C, the titanium alloy slab will be rolled down with a high proportion of the ⁇ phase, and the reduction with a high proportion of the ⁇ phase will be insufficient. Therefore, the T-texture is not sufficiently developed. Also, if the heating temperature exceeds (T ⁇ +150° C.), the possibility of recrystallization of the ⁇ phase during rolling becomes very high. In this case, variant selection does not occur during the phase transformation from the ⁇ phase to the ⁇ phase, so the T-texture is difficult to develop.
- the temperature of the titanium alloy slab referred to here is the surface temperature, which is measured with a radiation thermometer.
- a radiation thermometer For the emissivity of the radiation thermometer, a value calibrated to match the temperature measured using a contact thermocouple on the slab immediately after coming out of the heating furnace is used.
- the ⁇ transformation point T ⁇ means the boundary temperature at which the ⁇ phase begins to form when the titanium alloy is cooled from the ⁇ single phase region.
- T ⁇ can be obtained from the state diagram.
- the state diagram can be obtained, for example, by the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) method.
- the phase diagram of the titanium alloy is obtained by the CALPHAD method using Thermo-Calc, which is an integrated thermodynamic calculation system of Thermo-Calc Software AB, and a predetermined database (TI3), and T ⁇ is calculated. can do.
- Titanium alloys usually form a T-texture during the transformation from the ⁇ phase to the ⁇ phase when unidirectional high-speed hot rolling is performed at a temperature on the high temperature side of the ⁇ region or the ⁇ + ⁇ region having a high ⁇ phase ratio.
- the T-texture can be sufficiently developed by starting hot rolling in a temperature range where the ⁇ -region single phase or the ⁇ -phase fraction is high, for example, at (T ⁇ -50)°C or higher.
- hot rolling is started at a temperature of 950° C. or higher, for example.
- the method for producing a titanium alloy sheet according to the present embodiment includes a hot rolling step of hot rolling a titanium alloy slab in one direction.
- the reduction ratio of the titanium alloy slab in is 80% or more, and the finishing temperature is (T ⁇ -250)° C. or more and (T ⁇ -50)° C. or less.
- T-texture is formed in the titanium alloy hot-rolled sheet obtained by hot-rolling the slab.
- T-texture is excellent in cold-rollability and is effective in increasing strength in the sheet width direction and increasing Young's modulus.
- the finishing temperature is less than (T ⁇ ⁇ 250)° C.
- the titanium alloy slab will be reduced with a high proportion of ⁇ phase, and the reduction with a high proportion of ⁇ phase will be insufficient. Therefore, the T-texture is not sufficiently developed.
- the finishing temperature is less than (T ⁇ ⁇ 250)° C.
- the hot deformation resistance increases sharply and the hot workability decreases, so edge cracks are likely to occur and the yield decreases. .
- the rolling reduction is less than 80.0%, the working strain is not sufficiently introduced, the strain is not introduced uniformly over the entire plate thickness, and the T-texture may not develop sufficiently.
- the hot-rolled titanium alloy sheet In order to make the texture of the hot-rolled titanium alloy sheet a strong T-texture and ensure high anisotropy, it is preferable to heat the titanium alloy slab to the above heating temperature and hold it for 30 minutes or more. By holding the titanium alloy slab at the above heating temperature for 30 minutes or more, the crystal phase of the titanium alloy slab becomes the ⁇ single phase, and the T-texture is formed and developed more easily.
- the heating temperature and finishing temperature are the surface temperatures of the titanium alloy slab, and can be measured by known methods.
- the heating temperature and finishing temperature can be measured using, for example, a radiation thermometer.
- the titanium alloy slab can be continuously hot rolled using known continuous hot rolling equipment.
- a continuous hot rolling facility the titanium alloy slab is hot rolled and then wound by a winding machine to form a titanium alloy hot rolled coil.
- the hot-rolled titanium alloy sheet obtained through the above-described hot-rolling process may be subjected, if necessary, to annealing by a known method, removal of oxide scale by pickling or cutting, or cleaning treatment. good.
- the titanium material after the hot rolling step is subjected to one or more cold rolling passes in the longitudinal direction.
- the rolling reduction per cold rolling pass in the cold rolling process is 40% or less. If the rolling reduction per cold rolling pass is 40% or less, recrystallization is less likely to occur in subsequent intermediate annealing and final annealing, and the T-texture can be maintained.
- the cold rolling pass referred to here refers to cold rolling that is performed continuously. Specifically, the cold rolling pass is performed after the hot rolling process until the titanium material reaches the final product thickness, or after the hot rolling process when the temper rolling process described later is performed after the hot rolling process. It refers to cold rolling from to before the temper rolling process. However, if intermediate annealing is performed in the cold rolling process, the cold rolling after the hot rolling process to the intermediate annealing process, from the intermediate annealing process until the titanium material reaches the final product thickness, or before the temper rolling process cold rolling is called a cold rolling pass. Further, when the intermediate annealing treatment is performed multiple times, the cold rolling from the previous intermediate annealing treatment to the subsequent intermediate annealing treatment is also called a cold rolling pass.
- the temperature at which the cold rolling pass is performed may be, for example, 500°C or lower, or 400°C or lower.
- the lower limit of the temperature at which the cold rolling pass is performed is not particularly limited, and the temperature at which the cold rolling pass is performed can be, for example, room temperature or higher. Room temperature here intends 0 degreeC or more.
- the titanium material after the final cold rolling pass may be subjected to a final annealing treatment.
- the final annealing treatment may be performed as appropriate and is not an essential treatment.
- the processing conditions for the intermediate annealing treatment and the final annealing treatment are such that the annealing temperature is 500° C. or higher and 750° C. or lower, and the annealing temperature T (° C.) and the holding time t (seconds) at the annealing temperature are expressed by the following formula (102 ). Note that (T+273.15) ⁇ (Log 10 (t)+20) in the following equation (102) is the Larson-Miller parameter. 18000 ⁇ (T+273.15) ⁇ (Log 10 (t)+20) ⁇ 22000 Expression (102)
- the annealing temperature is less than 500 ° C. or the annealing temperature or holding time does not satisfy the above formula (102), recovery of the metal structure will be insufficient, causing internal cracks or edge cracks during cold rolling. In some cases, the strain accumulation at the surface increases, resulting in recrystallization. On the other hand, if the annealing temperature exceeds 750° C., recrystallization occurs and the T-texture is lost.
- the annealing temperature is 500° C. or higher and 750° C.
- the annealing temperature T (° C.) and the holding time t (seconds) at the annealing temperature satisfy the following formula (102)
- a titanium alloy sheet is manufactured through the above-described cold rolling process. After the cold rolling process, the titanium alloy sheet may be subjected to temper rolling for adjusting mechanical properties or correcting the shape, if necessary. A tensile correction is preferably applied. The rolling reduction in temper rolling is preferably 10% or less, and the elongation of the titanium alloy cold-rolled sheet in tensile straightening is preferably 5% or less. It should be noted that temper rolling and tension straightening may not be performed if unnecessary. The method for manufacturing a titanium alloy sheet according to the present embodiment has been described above.
- the T-texture is generated and developed by the hot rolling process, and the T-texture is maintained by the cold rolling process. is obtained.
- the maximum integrated orientation indicated by the crystal orientation distribution function f(g) is ⁇ 1: 0 to 30°, ⁇ : 60 to 90°, ⁇ 2: 0 to 60°
- a titanium alloy sheet having a degree of integration of the maximum integration orientation of 10.0 or more is obtained.
- This titanium alloy thin plate has, in mass %, Al: more than 4.0% and 6.6% or less, Fe: 0% or more and 2.3% or less, V: 0% or more and 4.5% or less, Si: 0% or more and 0.60% or less, Ni: 0% or more and less than 0.15%, Cr: 0% or more and less than 0.25%, Mn: 0% or more and less than 0.25%, C: 0% and less than 0.080%, N: 0% or more and 0.050% or less, and O: 0% or more and 0.40% or less.
- This titanium alloy sheet has a 0.2% proof stress in the sheet width direction at 25° C. of 800 MPa or more and a Young's modulus in the sheet width direction of 125 GPa or more.
- Example 1 Manufacture of Titanium Alloy Sheet First, after manufacturing a titanium alloy ingot as a raw material for the titanium alloy sheet shown in Table 1 by vacuum arc remelting (VAR: Vacuum Arc Remelting), it is bloomed or forged to a thickness of 150 mm and a width of 800 mm. ⁇ A slab with a length of 5000 mm was manufactured. Elements other than those listed in Table 1 are Ti and impurities. "Q" in Table 1 is a value calculated by the following formula (1).
- the ODF was calculated with an expansion index of 16 and a Gaussian half width of 5° in texture analysis using the spherical harmonics method of the EBSD method. At that time, considering the symmetry of the rolling deformation, the calculation was performed so as to be line symmetrical with respect to each of the thickness direction, the rolling direction, and the width direction.
- the diffraction peak half width of the (102) plane was calculated. Specifically, after the surface of the titanium alloy thin plate is wet-polished using emery paper, the surface is mirror-polished using colloidal silica to obtain a mirror surface. XRD measurement is performed on the surface of the mirror-finished titanium alloy thin plate.
- the XRD measurement was carried out using CuK ⁇ as a radiation source, with a measurement pitch of 0.01° and a measurement speed of 2°/min in the range of 2 ⁇ from 50.0° to 55.0°.
- the half-value width was calculated by Rigaku's integrated powder X-ray analysis software PDXL using X-ray diffraction data measured by Rigaku's Smartlab. If the half width is 0.20° or more, the dislocation density is such that sufficient work hardening can be obtained.
- the 0.2% proof stress ⁇ T in the sheet width direction at 25° C. of the titanium alloy sheets according to each of the invention examples, reference examples and comparative examples was measured according to JIS Z 2241:2011. Specifically, a No. 13B tensile test piece (parallel part width 12.5 mm, gauge length 50 mm) specified in JIS Z 2241: 2011 so that the tensile direction is the plate width direction of the titanium alloy thin plate. A tensile test was performed at a strain rate of 0.5%/min for measurement.
- Young's modulus E in the sheet width direction The Young's modulus E in the sheet width direction of the titanium alloy sheets according to each of the invention examples, reference examples and comparative examples was measured by the following method. That is, a No. 13B tensile test piece (parallel part width 12.5 mm, gauge length 50 mm) specified in JIS Z 2241: 2011 was prepared so that the tensile direction was the width direction of the titanium alloy thin plate, A strain gauge is attached and the strain rate is 10.0% / min, and the load-unload is repeated 5 times in the stress range from 100 MPa to half of the 0.2% proof stress, and the slope is obtained. The Young's modulus was defined as the average value of three times except for the value.
- Vickers hardness HV The Vickers hardness HV is measured in accordance with JIS Z 2244: 2009 by mirror-polishing a cross section (TD (Transverse direction) surface) perpendicular to the width direction of the rolled surface at the central position in the longitudinal direction (RD). The cross section was measured at 7 points with a load of 500 g and a load time of 15 seconds, and the Vickers hardness HV was obtained by excluding the maximum and minimum values and averaging the 5 points.
- TD Transverse direction
- RD longitudinal direction
- Average plate thickness dave The average plate thickness of the titanium alloy sheets according to each invention example, reference example and comparative example was measured by the following method. The thickness of each titanium alloy sheet was measured in the longitudinal direction using an X-ray or a vernier caliper at a distance of 1/4 of the plate width from the center position in the plate width direction and both ends in the plate width direction of each titanium alloy thin plate manufactured. Measurements were taken at 5 or more locations with an interval of 1 m or more, and the average value of the measured plate thicknesses was taken as the average plate thickness.
- the cold-rollability of the titanium alloy sheets according to each invention example, reference example and comparative example was evaluated by the following method. That is, the maximum value of edge cracks after cold rolling was evaluated. Then, when the maximum value of edge cracks after cold rolling is 1 mm or less, the cold rolling property is extremely good "A", and when the maximum value of edge cracks after cold rolling is more than 1 mm and 2 mm or less, the cold rolling property is When the maximum value of edge cracks after cold rolling was more than 2 mm, the cold rolling property was rated as poor "C".
- the maximum integration orientation was in the range of ⁇ 1: 0 to 30°, ⁇ : 60 to 90°, and ⁇ 2: 0 to 60°, and the maximum integration degree was 10.0 or more.
- the half width was 0.20° or more, and the area ratio of the band structure was 70% or more.
- the 0.2% proof stress ⁇ T in the sheet width direction at 25° C. was 800 MPa or more, and the Young's modulus in the sheet width direction was 125 GPa or more.
- the final average plate thickness dave was 1.2 to 1.9 mm, and the dimensional accuracy a was 5.0% or less.
- Comparative Example 10 since the Al content was small, the 0.2% proof stress was as small as 692 MPa, and the Young's modulus in the sheet width direction was as small as 122 GPa. Comparative Example 11 had a high Al content, and surface cracks and severe edge cracks occurred during cold rolling after hot rolling. In Comparative Example 12, the temperature dropped significantly in the second half of hot rolling, and the hot-rolled sheet cracked, so a sheet with a thickness of 2.5 mm could not be produced.
- Invention Examples 1 to 6, 9 to 20, and 25 to 49 have a Q value of 0.340 or less, and these examples are compared with Invention Examples 7, 8, and 21 to 24, which have a Q value of more than 0.340. and showed good cold rolling properties.
- Comparative Examples 1 to 10 deviate from the manufacturing conditions of the method for manufacturing a titanium alloy sheet according to the present disclosure, the maximum accumulation orientation or the degree of accumulation in the maximum accumulation orientation does not satisfy the requirements of the present application, and the Young's modulus in the sheet width direction E was less than 125 GPa.
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Abstract
Description
一方で、チタン合金をβ域またはβ相割合の高いα+β高温域の温度で一方向の高速の熱間圧延を行うと、β相からα相への変態時に、バリアント選択によって板幅方向に六方最密充填構造(hexagonal close-packed、hcp)のc軸が配向した集合組織(T-texture)が形成される。チタンのc軸方向が他方向に比べて高いヤング率、強度を有するため、T-textureは、板幅方向の高強度化や高ヤング率化に適した集合組織である。しかし、熱間圧延により薄いチタン合金板を製造しようとすると、板厚の減少により熱間圧延時の材料の温度が急激に低下するため、高強度のα相が増加し、高温強度の低いβ相が減少するチタン合金は著しく変形抵抗が増大し、圧延機の許容荷重を超えることがある。そのため、熱間圧延のみでは板厚2.5mm以下の薄板を製造することが困難である。また、冷間圧延での加工硬化の軟化を目的とした高温の焼鈍により、再結晶集合組織が形成した場合、本集合組織は容易に消失する。このため、従来は板厚2.5mm以下の薄板では、本集合組織は有効活用されてこなかった。これらにより、従来、Alを多く含有しかつT-textureが発達した高強度、高ヤング率のチタン合金薄板を製造することは困難と考えられていた。
[1] 本開示の一態様に係るチタン合金薄板は、質量%で、Al:4.0%超、6.6%以下、Fe:0%以上、2.3%以下、V:0%以上、4.5%以下、Si:0%以上、0.60%以下、Ni:0%以上、0.15%未満、Cr:0%以上、0.25%未満、Mn:0%以上、0.25%未満、C:0%以上、0.080%未満、N:0%以上、0.050%以下、および、O:0%以上、0.40%以下、を含有し、残部がTiおよび不純物からなり、
α相の結晶方位をBungeの表記方法によるオイラー角g={φ1,Φ,φ2}で表した場合に、後方散乱電子線回折法の球面調和関数法を用いたTexture解析において、展開指数を16とし、ガウス半値幅を5°として算出される結晶方位分布関数f(g)で示される最大集積方位がφ1:0~30°、Φ:60~90°、φ2:0~60°の範囲にあり、前記最大集積方位の集積度が10.0以上であり、
25℃における板幅方向の0.2%耐力が800MPa以上であり、
板幅方向のヤング率が125GPa以上であり、
平均板厚が2.5mm以下である。
[2] 上記[1]に記載のチタン合金薄板は、質量%で、
Fe:0.5%以上、2.3%以下またはV:2.5%以上、4.5%以下
を含有してもよい。
[3] 上記[2]に記載のチタン合金薄板は、前記Feまたは前記Vの一部に替えて、質量%で、
Ni:0.15%未満、
Cr:0.25%未満、および、
Mn:0.25%未満、からなる群より選択される1種または2種以上を含有してもよい。
[4] 上記[2]または[3]に記載のチタン合金薄板は、前記Tiの一部に替えて、O、N、Fe、およびVからなる群より選択される1種または2種以上を含有する場合、質量%での、Oの含有量を[O]、Nの含有量を[N]、Feの含有量を[Fe]、Vの含有量を[V]としたときに、下記式(1)で示されるQが0.340以下であってもよい。
Q=[O]+(2.77×[N])+(0.1×[Fe])+(0.025×[V]) …式(1)
[5] 上記[1]~[4]のいずれか1項に記載のチタン合金薄板は、CuKαを線源とするX線回折法によって検出される2θ=53.3±1°における回折ピークの半値幅が0.20°以上であってもよい。
[6] 上記[1]~[5]のいずれか1項に記載のチタン合金薄板は、アスペクト比が3.0超であり板長手方向に伸長したバンド組織を有し、
前記バンド組織の面積率が70%以上であってもよい。
[7] 上記[1]~[6]のいずれか1項に記載のチタン合金薄板は、板厚の寸法精度が前記平均板厚に対して5.0%以下であってもよい。
質量%で、Al:4.0%超、6.6%以下、Fe:0%以上、2.3%以下、V:0%以上、4.5%以下、Si:0%以上、0.60%以下、Ni:0%以上、0.15%未満、Cr:0%以上、0.25%未満、Mn:0%以上、0.25%未満、C:0%以上、0.08%未満、N:0%以上、0.05%以下、および、O:0%以上、0.40%以下、を含有し、残部がTiおよび不純物からなるチタン素材を加熱する加熱工程と、
前記加熱工程後の前記チタン素材を一方向に熱間圧延する熱間圧延工程と、
前記熱間圧延工程後の前記チタン素材に対して当該チタン素材の長手方向に1回以上の冷間圧延パスを行う冷間圧延工程と、を有し、
前記加熱工程における前記チタン素材の加熱温度は、β変態点をTβ(℃)としたとき、Tβ℃以上(Tβ+150)℃以下であり、
前記熱間圧延工程における圧下率は、80.0%以上であり、
前記熱間圧延工程における仕上温度は、(Tβ-250)℃以上(Tβ-50)℃以下であり、
前記冷間圧延工程は、
冷間圧延パス1回当たりの圧延率が40%以下であり、複数の前記冷間圧延パスを行う場合は中間焼鈍処理を含み、
前記中間焼鈍処理の焼鈍条件は、
焼鈍温度が500℃以上750℃以下であり、かつ、
前記焼鈍温度T(℃)と、前記焼鈍温度における保持時間t(秒)とが、下記式(2)を満足する。
18000≦(T+273.15)×(Log10(t)+20)<22000 …式(2)
[9] 上記[8]に記載のチタン合金薄板の製造方法では、最後の前記冷間圧延パス後に、焼鈍温度が500℃以上750℃以下であり、かつ、前記式(2)を満足する最終焼鈍を施してもよい。
まず、図面を参照して、本実施形態に係るチタン合金薄板について説明する。
本実施形態に係るチタン合金薄板が含有する化学成分を説明する。本実施形態に係るチタン合金薄板は、質量%で、Al:4.0%超、6.6%以下、Fe:0%以上、2.3%以下、V:0%以上、4.5%以下、Si:0%以上、0.60%以下、Ni:0%以上、0.15%未満、Cr:0%以上、0.25%未満、Mn:0%以上、0.25%未満、C:0%以上、0.08%未満、N:0%以上、0.05%以下、および、O:0%以上、0.40%以下、を含有し、残部がTiおよび不純物からなる。なお、以下では化学成分の説明において特に断りのない限り、「%」との表記は「質量%」を表わすものとする。
Q=[O]+(2.77×[N])+(0.1×[Fe])+(0.025×[V]) …式(1)
次に、本実施形態に係るチタン合金薄板の金属組織について説明する。
まず、チタン合金薄板の集合組織の結晶方位について説明する。チタン合金は、β域またはβ相割合の高いα+β高温域の温度で、一方向に高速で熱間圧延を行うと、β相からα相への相変態時に、バリアント選択則により板幅方向にhcpのc軸が配向した集合組織(T-texture)を形成する。T-textureは、圧延変形を受けた未再結晶のβ相がα相に変態する際に形成する集合組織である。T-textureは、板幅方向の強度とヤング率を向上させる。α相の結晶方位をBungeの表記方法によるオイラー角g={φ1,Φ,φ2}で表した場合に、結晶方位分布関数f(g)により示される最大集積方位がφ1:0~30°、Φ:60~90°、φ2:0~60°の範囲にあり、前記最大集積方位の集積度が10.0以上であれば、T-textureが発達した組織である。本実施形態に係るチタン合金薄板は、T-textureが発達した組織であり、未再結晶組織を多く含んでいる。
金属材料は、一般に、転位を導入することで硬化する加工硬化が生じる。チタン合金薄板においても、転位密度が高いほど強度は高くなる。本実施形態に係るチタン合金薄板は、T-textureが発達した組織であるため、未再結晶組織を多く含む。未再結晶組織は、多量の転位が導入されている組織である。この転位密度を見積もる手法として、X線回折法(XRD;X-Ray Diffraction)により得られる回折ピークの半値幅から転位密度を見積もる方法がある。回折ピークの半値幅が大きいほど転位密度は高い。十分な加工硬化を得るためには、CuKαを線源とするX線回折によって検出される2θ=53.3±1°の位置に表れる(102)面の回折ピーク半値幅が0.20°以上であることが好ましい。一方、転位密度が高すぎると、強度が高くなりすぎ、切欠き感受性が高くなり、板破断が生じる可能性がある。そのため、(102)面の回折ピーク半値幅が1.00°以下であることが好ましく、0.80°以下であることがより好ましい。
本実施形態に係るチタン合金薄板は、アスペクト比が3.0超であり板長手方向に伸長したバンド組織を有し、当該バンド組織の面積率が70%以上であることが好ましい。ここで言うバンド組織とは、例えば、図3のバンド組織の光学顕微鏡写真に示すような、長手方向に伸長した組織である。具体的には、結晶粒の長軸/短軸で表されるアスペクト比が3.0超の結晶粒のことを言う。本実施形態に係るチタン合金薄板は、図4の本実施形態に係るチタン合金薄板の光学顕微鏡写真に示すように、板長手方向に伸長したバンド組織を有する。チタン合金は、α+β域やβ域の温度で熱間圧延を行うと、板長手方向に伸長したバンド組織が形成される。バンド組織は、板厚方向に対して垂直な結晶粒界を多く有している。バンド組織の面積率が70%以上であれば、板表面から発生したき裂の板厚方向への進展を遅くすることができる。バンド組織の面積率は、より好ましくは、75%以上、更に好ましくは80%以上である。また、すべての結晶粒がバンド組織でもよく、上限は100.0%である。
本実施形態に係るチタン合金薄板の室温における板幅方向の0.2%耐力は、800MPa以上である。航空機分野等では、汎用のα+β型チタン合金であるTi-6Al-4Vの室温での引張強度に近い引張強度が要求されることが多い。チタン合金薄板の室温における板幅方向の0.2%耐力が800MPa以上であれば、高い強度が求められる用途に用いることが可能である。室温における板幅方向の0.2%耐力は、好ましくは、850MPa以上である。一方、強度が高すぎると、冷間圧延前の熱延板の強度も高いため、熱延板を冷間圧延しづらくなり、複数パスの冷間圧延を要しコスト増となる場合がある。また、強度が高すぎると、切欠き感受性が高くなり、板破断が生じる可能性がある。よって、室温における板幅方向の0.2%耐力は、1300MPa以下であることが好ましい。室温における板幅方向の0.2%耐力は、より好ましくは、1250MPa以下である。0.2%耐力は、JIS Z2241:2011に準拠した方法で測定することができる。具体的には、引張方向が、チタン合金薄板の板幅方向になるようにJIS Z 2241:2011に規定される13B号引張試験片(平行部の幅12.5mm、標点間距離50mm)を作製し、ひずみ速度0.5%/minで引張試験を行うことで測定することができる
本実施形態に係るチタン合金薄板の板幅方向のヤング率は、125GPa以上である。ヤング率が125GPa以上であれば、高い合成が要求される航空機分野や自動車用部品、民生品等の用途に使用することが可能となる。特に、板幅方向のヤング率が125GPa以上であれば、従来よりも3~4%程度軽量化できるという利点がある。ヤング率が高過ぎることで不都合はないが、チタンでは現実的には150GPa程度が上限である。板幅方向のヤング率は、以下の方法で測定することができる。すなわち、引張方向が、チタン合金薄板の板幅方向になるようにJIS Z 2241:2011に規定される13B号引張試験片(平行部の幅12.5mm、標点間距離50mm)を作製し、歪ゲージを張り付けてひずみ速度10.0%/minで、100MPaから0.2%耐力の半分までの応力範囲で負荷-除荷を5回繰り返し、その傾きを求め、最大値と最小値を除いた3回の平均値をヤング率とする。
本実施形態に係るチタン合金薄板のビッカース硬さHVは、330以上である。ビッカース硬さHVは、JIS Z 2244:2009に準拠し、圧延板における板幅方向(TD)中央位置で、板幅方向に対して垂直な断面(TD(Transverse direction)面)を鏡面研磨し、当該断面について、荷重500g、負荷時間15秒として、7か所測定し、最大値と最小値を除いた5点の平均値をビッカース硬さHVとする。本実施形態に係るチタン合金薄板のビッカース硬さHVは、340以上であってもよいし、350以上であってもよい。また、本実施形態に係るチタン合金薄板のビッカース硬さHVは、430以下であってもよいし、420以下であってもよい。なお、本実施形態に係るチタン合金薄板のビッカース硬さHV330以上は、JIS Z2241:2011に準拠した方法で測定した引張強さ1GPa以上に相当する。なお、上記では、長手方向中央位置でのTD面をビッカース硬さHVの測定面としているが、チタン合金薄板のビッカース硬さHVの長手方向でのばらつきは小さいので、任意の長手方向位置におけるTD面をビッカース硬さHVの測定面としてもよい。
本実施形態に係るチタン合金薄板の平均板厚は、2.5mm以下である。通常の熱間圧延を行う場合、板厚が薄くなると温度が急激に低下することで変形抵抗が増大する。これにより、高強度材を熱間圧延する場合、圧延機の許容荷重を超えることがあり、平均板厚を2.5mm以下にすることが難しい。一方で、詳細は後述するが、本実施形態に係るチタン合金薄板は、冷間圧延工程を含む方法で製造されるため、平均板厚が2.5mm以下とすることが可能である。また、本実施形態に係るチタン合金薄板の平均板厚の下限には特に制限はないものの、上記の強度を有するようなチタン合金では、現実的には平均板厚は0.1mm以上であることが多い。そのため、本実施形態に係るチタン合金薄板の平均板厚は、0.1mm以上であることが好ましい。本実施形態に係るチタン合金薄板の平均板厚は、より好ましくは、0.3mm以上である。
本実施形態に係るチタン合金薄板の板厚寸法精度は、平均板厚に対して5.0%以下であることが好ましい。パック圧延では、複数積層され、鋼材で包まれたチタン材を熱間圧延して、チタン合金薄板を製造するが、温度分布によって複数積層されたチタン材の変形抵抗が大きく変化するため、均一な板厚の薄板を製造することが難しい。しかしながら、本実施形態に係るチタン合金薄板は、後述するように冷間圧延を経て製造されるため、板厚寸法精度に優れたチタン合金薄板となる。本実施形態に係るチタン合金薄板の寸法精度は、より好ましくは、平均板厚に対して4.0%以下であり、より一層好ましくは、2.0%以下である。
a’=(d-dave)/dave×100 …式(101)
本実施形態に係るチタン合金薄板の製造方法は、チタン合金薄板の素材(チタン素材)となるチタン合金スラブを製造するスラブ製造工程と、チタン合金スラブを加熱する加熱工程と、加熱工程後のチタン合金スラブを熱間圧延する熱間圧延工程と、熱間圧延工程後のチタン素材を冷間圧延する冷間圧延工程と、必要に応じて、冷間圧延工程後のチタン素材を調質圧延または引張矯正する調質圧延・引張矯正工程とを含む。以下、本実施形態に係るチタン合金薄板の製造方法の各工程について説明する。
スラブ製造工程では、チタン合金スラブを製造する。素材としては、上述した化学組成を有し、公知の方法により製造された素材を用いることができる。チタン合金スラブの製造方法は、特段制限されず、例えば、以下の手順で製造することができる。例えば、スポンジチタンから真空アーク溶解法や電子ビーム溶解法またはプラズマ溶解法等のハース溶解法等の各種溶解法によりインゴットを作製する。次に、得られたインゴットをα相高温域やα+β二相域、β相単相域の温度で熱間鍛造することにより、チタン合金スラブを得ることができる。なお、チタン合金スラブには、必要に応じて洗浄処理、切削等の前処理が施されていてもよい。また、ハース溶解法で熱延可能な矩形とした場合は、熱間鍛造等を行わず熱間圧延に供してもよい。製造されたチタン合金スラブは、Alを4.0%超、6.6%以下、Fe:0%以上、2.3%以下、V:0%以上、4.5%以下、Si:0%以上、0.60%以下、Ni:0%以上、0.15%未満、Cr:0%以上、0.25%未満、Mn:0%以上、0.25%未満、C:0%以上、0.080%未満、N:0%以上、0.050%以下、および、O:0%以上、0.40%未満、を含有する。
本工程では、チタン合金スラブをβ変態点Tβ℃以上(Tβ+150℃)以下の温度に加熱する。加熱温度がTβ℃未満の場合、α相の割合が高い状態でチタン合金スラブが圧下されることになり、β相の割合が高い状態での圧下が不十分となる。そのため、T-textureが十分に発達しない。また、加熱温度が(Tβ+150℃)を超えると、圧延中にβ相が再結晶する可能性が非常に高くなる。この場合、β相からα相への相変態時にバリアント選択が生じないため、T-textureは発達し難い。さらには、チタン合金スラブ表面の酸化が激しくなり、熱間圧延後に熱延板表面にヘゲやキズを生じ易くなる。ここでいうチタン合金スラブの温度は、表面温度であり、放射温度計で測定する。放射温度計の放射率には、加熱炉から出てきた直後のスラブに対して、接触式の熱電対を用いて測定した温度と一致するように校正した値を用いる。
チタン合金は、通常、β域またはβ相割合の高いα+β域の高温側の温度で一方向の高速熱延を行うと、β相からα相への変態時に、T-textureを形成する。β域単相もしくはβ相分率が高い温度域、例えば、(Tβ―50)℃以上で熱間圧延を開始することで、十分にT-textureを発達させることができる。チタン合金スラブの組成によりβ変態点は異なるが、例えば、950℃以上の温度で熱間圧延を開始する。また、T-textureを発達させるためには、β相割合の高い温度域で高い圧下率で圧延を行い、β相の集合組織を発達させ、またβ相の再結晶を抑制することも重要である。T-textureを形成し、発達させるために、本実施形態に係るチタン合金薄板の製造方法においては、チタン合金スラブを一方向に熱間圧延する熱間圧延工程を有し、当該熱間圧延工程におけるチタン合金スラブの圧下率が80%以上であり、仕上温度が(Tβ-250)℃以上(Tβ-50)℃以下である。これにより、スラブが熱間圧延されて得られたチタン合金熱延板にT-textureが形成される。T-textureは、冷間圧延性に優れかつ板幅方向の高強度化や高ヤング率化に有効である。
本工程では、熱間圧延工程後のチタン素材を長手方向に1回以上の冷間圧延パスを実施する。冷間圧延工程における冷間圧延パス1回当たりの圧延率が40%以下である。冷間圧延パス1回当たりの圧延率が40%以下であれば、その後の中間焼鈍や最終焼鈍で再結晶が生じにくく、T-textureを保つことができる。
なお、下記式(102)の(T+273.15)×(Log10(t)+20)は、ラーソンミラーパラメータである。
18000≦(T+273.15)×(Log10(t)+20)<22000 …(102)式
上記冷間圧延工程を経てチタン合金薄板が製造されるが、冷間圧延工程後のチタン合金薄板は、必要に応じて、機械的特性を調整するための調質圧延または形状を矯正するための引張矯正が施されることが好ましい。調質圧延における圧下率は10%以下が好ましく、引張矯正におけるチタン合金冷延板の伸び率は5%以下であることが好ましい。なお、調質圧延および引張矯正は、必要がない場合は実施しなくてもよい。以上、本実施形態に係るチタン合金薄板の製造方法について説明した。
1. チタン合金薄板の製造
まず、真空アーク溶解(VAR:Vacuum Arc Remelting)にて表1に示すチタン合金薄板の素材となるチタン合金インゴットを製造した後、分塊圧延または鍛造により厚さ150mm×幅800mm×長さ5000mmのスラブを製造した。なお、表1に記載の元素以外は、Tiおよび不純物である。また、表1中の「Q」は、下記式(1)により算出した値である。
Q=[O]+(2.77×[N])+(0.1×[Fe])+(0.025×[V]) …式(1)
なお、式中、[O]は質量%でのO含有量、[N]は質量%でのN含有量、[Fe]は質量%でのFe含有量、および[V]は質量%でのV含有量である。
各発明例および比較例に係るチタン合金薄板について、以下の項目の評価を行った。
各発明例および比較例に係るチタン板の集積度が最大となる方位および最大集積度は、以下のようにして測定、算出した。チタン合金薄板の幅方向(TD)中央位置で、板幅方向に垂直な断面を化学研磨し、EBSDを用いて結晶方位解析を行った。(全板厚)×200μmの領域を、ステップ1μmで5視野程度測定した。そのデータについて、TSLソリューションズ製のOIM AnalysisTMソフトウェア(Ver.8.1.0)を用いてODFを算出し、このODFから、集積度のピーク位置および最大集積度を算出した。ODFは、EBSD法の球面調和関数法を用いたTexture解析において、展開指数を16とし、ガウス半値幅を5°として算出した。その際に、圧延変形の対称性を考慮し、板厚方向、圧延方向、板幅方向それぞれに対して線対称となるように、計算を行った。
転位密度とXRDによって検出される回折ピークの半値幅とは相関があるため、本実施例では、CuKαを線源とするXRDによって検出される2θ=53.3±1°の位置に表れる(102)面の回折ピーク半値幅を算出した。具体的には、チタン合金薄板の表面をエメリー紙を用いて湿式研磨した後、当該表面をコロイダルシリカを用いて鏡面研磨して鏡面とする。鏡面としたチタン合金薄板の表面についてXRD測定を実施する。XRD測定はCuKαを線源とし、2θが50.0°から55.0°までの範囲を測定ピッチ0.01°、測定速度2°/分で実施した。半値幅はRigaku製Smartlabにより測定されたX線回折データを用い、Rigaku製統合粉末X線解析ソフトウェアPDXLにより算出した。半値幅が0.20°以上であれば、十分な加工硬化が得られる程度の転位密度である。
各試料を板幅中央の位置で板幅方向に対し垂直に切断した断面を化学研磨し、その断面の(全板厚)×200μmの領域を、ステップ1μmで5視野程度を対象に、EBSD法による結晶方位解析を行い、結晶粒のそれぞれについてアスペクト比を算出し、アスペクト比が3.0超の結晶粒の面積率を算出した。
各発明例、参考例および比較例に係るチタン合金薄板の25℃における板幅方向の0.2%耐力σTについては、JIS Z 2241:2011に準拠して測定した。具体的には、引張方向が、チタン合金薄板の板幅方向になるようにJIS Z 2241:2011に規定される13B号引張試験片(平行部の幅12.5mm、標点間距離50mm)を作製し、ひずみ速度0.5%/minで引張試験を行い測定した。
各発明例、参考例および比較例に係るチタン合金薄板の板幅方向のヤング率Eを以下の方法で測定した。すなわち、引張方向が、チタン合金薄板の板幅方向になるようにJIS Z 2241:2011に規定される13B号引張試験片(平行部の幅12.5mm、標点間距離50mm)を作製し、歪ゲージを張り付けてひずみ速度10.0%/minで、100MPaから0.2%耐力の半分までの応力範囲で負荷-除荷を5回繰り返し、その傾きを求め、その際、最大値と最小値を除いた3回の平均値をヤング率とした。
ビッカース硬さHVは、JIS Z 2244:2009に準拠し、長手方向(RD)中央位置で、圧延面における板幅方向に沿って垂直な断面(TD(Transverse direction)面)を鏡面研磨し、当該断面について、荷重500g、負荷時間15秒として、7か所測定し、最大値と最小値を除いた5点の平均値をビッカース硬さHVとした。
各発明例、参考例および比較例に係るチタン合金薄板の平均板厚を以下の方法で測定した。製造された各チタン合金薄板の板幅方向中央位置および板幅方向の両端からそれぞれ板幅の1/4の距離の位置について、各位置の板厚をX線またはノギスを用いて、長手方向に1m以上の間隔を空けて5か所以上測定し、測定した板厚の平均値を平均板厚とした。
各発明例、参考例および比較例に係るチタン合金薄板の板厚寸法精度は、上記の方法で実際に測定された板厚dと、上記の平均板厚daveとを用い、下記式(101)により算出されたa’の最大値を寸法精度aとした。
a’=(d-dave)/dave×100 …式(101)
各発明例、参考例および比較例に係るチタン合金薄板の冷間圧延性を以下の方法で評価した。すなわち、冷間圧延後の耳割れの最大値で評価した。そして、冷間圧延後の耳割れの最大値が1mm以下である場合、冷延性は極めて良好「A」とし、冷間圧延後の耳割れの最大値1mm超2mm以下である場合、冷延性は良好「B」とし、冷間圧延後の耳割れの最大値が2mm超である場合、冷延性は不良「C」とした。
上記の評価結果を表3-1および表3-2に示す。なお、表3中の「φ1」、「Φ」および「φ2」は、Bungeの表記方法に基づく角度である。
Claims (9)
- 質量%で、
Al:4.0%超、6.6%以下、
Fe:0%以上、2.3%以下、
V:0%以上、4.5%以下、
Si:0%以上、0.60%以下、
Ni:0%以上、0.15%未満、
Cr:0%以上、0.25%未満、
Mn:0%以上、0.25%未満、
C:0%以上、0.080%未満、
N:0%以上、0.050%以下、および、
O:0%以上、0.40%以下、
を含有し、残部がTiおよび不純物からなり、
α相の結晶方位をBungeの表記方法によるオイラー角g={φ1,Φ,φ2}で表した場合に、後方散乱電子線回折法の球面調和関数法を用いたTexture解析において、展開指数を16とし、ガウス半値幅を5°として算出される結晶方位分布関数f(g)で示される最大集積方位がφ1:0~30°、Φ:60~90°、φ2:0~60°の範囲にあり、前記最大集積方位の集積度が10.0以上であり、
25℃における板幅方向の0.2%耐力が800MPa以上であり、
板幅方向のヤング率が125GPa以上であり、
平均板厚が2.5mm以下である、
チタン合金薄板。 - 質量%で、
Fe:0.5%以上、2.3%以下またはV:2.5%以上、4.5%以下を含有する、請求項1に記載のチタン合金薄板。 - 前記Feまたは前記Vの一部に替えて、質量%で、
Ni:0.15%未満、
Cr:0.25%未満、および、
Mn:0.25%未満、からなる群より選択される1種または2種以上を含有する、請求項2に記載のチタン合金薄板。 - 前記Tiの一部に替えて、O、N、Fe、およびVからなる群より選択される1種または2種以上を含有する場合、質量%での、Oの含有量を[O]、Nの含有量を[N]、Feの含有量を[Fe]、Vの含有量を[V]としたときに、下記式(1)で示されるQが0.340以下である、請求項2または3に記載のチタン合金薄板。
Q=[O]+(2.77×[N])+(0.1×[Fe])+(0.025×[V]) …式(1) - CuKαを線源とするX線回折法によって検出される2θ=53.3±1°における回折ピークの半値幅が0.20°以上である、請求項1~4のいずれか1項に記載のチタン合金薄板。
- アスペクト比が3.0超であり板長手方向に伸長したバンド組織を有し、
前記バンド組織の面積率が70%以上である、請求項1~5のいずれか1項に記載のチタン合金薄板。 - 板厚の寸法精度が前記平均板厚に対して5.0%以下である、請求項1~6のいずれか1項に記載のチタン合金薄板。
- 請求項1~7のいずれか1項に記載のチタン合金薄板の製造方法であって、質量%で、Al:4.0%超、6.6%以下、Fe:0%以上、2.3%以下、V:0%以上、4.5%以下、Si:0%以上、0.60%以下、Ni:0%以上、0.15%未満、Cr:0%以上、0.25%未満、Mn:0%以上、0.25%未満、C:0%以上、0.08%未満、N:0%以上、0.05%以下、および、O:0%以上、0.40%以下、を含有し、残部がTiおよび不純物からなるチタン素材を加熱する加熱工程と、
前記加熱工程後の前記チタン素材を一方向に熱間圧延する熱間圧延工程と、
前記熱間圧延工程後の前記チタン素材に対して当該チタン素材の長手方向に1回以上の冷間圧延パスを行う冷間圧延工程と、を有し、
前記加熱工程における前記チタン素材の加熱温度は、β変態点をTβ(℃)としたとき、Tβ℃以上(Tβ+150)℃以下であり、
前記熱間圧延工程における圧下率は、80.0%以上であり、
前記熱間圧延工程における仕上温度は、(Tβ-250)℃以上(Tβ-50)℃以下であり、
前記冷間圧延工程は、
冷間圧延パス1回当たりの圧延率が40%以下であり、複数の前記冷間圧延パスを行う場合は中間焼鈍処理を含み、
前記中間焼鈍処理の焼鈍条件は、
焼鈍温度が500℃以上750℃以下であり、かつ、
前記焼鈍温度T(℃)と、前記焼鈍温度における保持時間t(秒)とが、下記式(2)を満足する、チタン合金薄板の製造方法。
18000≦(T+273.15)×(Log10(t)+20)<22000 …式(2) - 最後の前記冷間圧延パス後に、焼鈍温度が500℃以上750℃以下であり、かつ、前記式(2)を満足する最終焼鈍を施す、請求項8に記載のチタン合金薄板の製造方法。
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US9587770B2 (en) * | 2011-12-20 | 2017-03-07 | Nippon Steel & Sumitomo Metal Corporation | α + β type titanium alloy sheet for welded pipe, manufacturing method thereof, and α + β type titanium alloy welded pipe product |
JP6187679B2 (ja) * | 2014-04-10 | 2017-08-30 | 新日鐵住金株式会社 | 管長手方向の強度、剛性に優れたα+β型チタン合金溶接管およびその製造方法 |
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See also references of EP4286550A4 |
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US20240002981A1 (en) | 2024-01-04 |
EP4286550A1 (en) | 2023-12-06 |
JPWO2022162814A1 (ja) | 2022-08-04 |
KR20230118978A (ko) | 2023-08-14 |
EP4286550A4 (en) | 2024-03-06 |
CN116724136A (zh) | 2023-09-08 |
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