Titanium alloy sheet, titanium alloy coil, method for manufacturing titanium alloy sheet, and method for manufacturing titanium alloy coil

Abstract

This titanium alloy sheet contains predetermined chemical components, an area ratio of an α-phase is 80% or more, an area ratio of the α-phase having an equivalent circle diameter of 1 μm or more is more than 53%, and in a (0001) pole figure in a sheet thickness direction, an angle formed between the sheet thickness direction and a direction indicating a peak of intensity calculated by texture analysis in a case in which a series rank is 16 and the Gaussian half width is 5° for an inverse pole figure using a spherical harmonics method of an electron backscatter diffraction method is 65° or less, and the average sheet thickness is 2.5 mm or less.

1 . A titanium alloy sheet containing, in % 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 and 0.60% or less;   C: 0% or more and less than 0.080%;   N: 0% or more and 0.050% or less;   O: 0% or more and 0.40% 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%; and   a remainder of Ti and impurities,   wherein an area ratio of an α-phase is 80% or more,   an area ratio of an α-phase having an equivalent circle diameter of 1 μm or more is more than 53%, and   in a (0001) pole figure in a sheet thickness direction, an angle formed between the sheet thickness direction and a direction indicating a peak of intensity calculated by texture analysis in a case in which Series Rank is 16 and a Gaussian half width is 5° for an inverse pole figure using a spherical harmonics method of an electron backscatter diffraction method is 65° or less, and   an average sheet thickness is 2.5 mm or less.   
     
     
         2 . The titanium alloy sheet according to  claim 1  having a microstructure including an equiaxed structure with an aspect ratio of 3.0 or less and a longitudinally elongated band structure with an aspect ratio of more than 3.0,
 wherein the equiaxed structure has an average grain size of 0.1 μm or more and 20.0 μm or less, and 
 an area ratio of the band structure with respect to an area of the microstructure is or less. 
 
     
     
         3 . The titanium alloy sheet according to  claim 1  containing, in % by mass, either Fe: 0.5% or more and 2.3% or less or V: 2.5% or more and 4.5% or less. 
     
     
         4 . The titanium alloy sheet according to  claim 1  containing, in % by mass, one element or two or more elements selected from the group including Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25% in place of a part of the Fe or the V. 
     
     
         5 . The titanium alloy sheet according to  claim 1 , wherein the smaller of a 0.2% proof stress in a longitudinal direction at 25° C. and a proof stress in a width direction at 25° C. is 700 MPa or more and 1200 MPa or less. 
     
     
         6 . The titanium alloy sheet according to  claim 1 ,
 wherein, in a (0001) pole figure in a sheet thickness direction, an angle formed between a width direction and a direction indicating a peak of intensity calculated by texture analysis in a case in which Series Rank is 16 and a Gaussian half width is 5° for an inverse pole figure using a spherical harmonics method of an electron backscatter diffraction method is 10° or less, and   a ratio of a 0.2% proof stress in the width direction to a 0.2% proof stress in a longitudinal direction is 1.05 or more and 1.18 or less.   
     
     
         7 . The titanium alloy sheet according to  claim 1 ,
 wherein, in a (0001) pole figure in a sheet thickness direction, an angle formed between the sheet thickness direction and a direction indicating a peak of intensity calculated by texture analysis in a case in which Series Rank is 16 and a Gaussian half width is 5° for an inverse pole figure using a spherical harmonics method of an electron backscatter diffraction method is 35° or less, and   a ratio of a 0.2% proof stress in a width direction to a 0.2% proof stress in a longitudinal direction is 0.85 or more and 1.10 or less.   
     
     
         8 . The titanium alloy sheet according to  claim 1 , wherein a dimensional accuracy of a sheet thickness is 5.0% or less with respect to the average sheet thickness. 
     
     
         9 . A titanium alloy coil containing, in % 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 and 0.60% or less;   C: 0% or more and less than 0.080%;   N: 0% or more and 0.050% or less;   O: 0% or more and 0.40% 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%; and   a remainder of Ti and impurities,   wherein an area ratio of an α-phase is 80% or more, an area ratio of an α-phase having an equivalent circle diameter of 1 μm or more is more than 53%, and   in a (0001) pole figure in a sheet thickness direction, an angle formed between the sheet thickness direction and a direction indicating a peak of intensity calculated by texture analysis in a case in which Series Rank is 16 and a Gaussian half width is 5° for an inverse pole figure using a spherical harmonics method of an electron backscatter diffraction method is 65° or less, and   an average sheet thickness is 2.5 mm or less.   
     
     
         10 . A method for manufacturing the titanium alloy sheet according to  claim 1 , comprising:
 performing one or more cold rolling passes in a longitudinal direction of a titanium material containing, in % 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 and 0.60% or less, C: 0% or more and less than 0.080%, N: 0% or more and 0.050% or less, O: 0% or more and 0.40% 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%, and a remainder of Ti and impurities; and   annealing the titanium material after a final cold rolling pass,   wherein a rolling rate per cold rolling pass in the cold rolling process is more than 30%, and a total rolling rate is 60% or more.   
     
     
         11 . The method for manufacturing the titanium alloy sheet according to claim wherein the cold rolling process includes an intermediate annealing process of annealing the titanium material between a plurality of cold rolling passes in the case of performing the plurality of cold rolling passes, and annealing conditions for the intermediate annealing process and the final annealing process are conditions in which an annealing temperature is 600° C. or higher and (T β −50)° C. or lower, and the annealing temperature T (° C.) and a holding time t (seconds) at the annealing temperature satisfy the following formula (1),
   22000≤( T+ 273.15)×(Log 10 ( t )+20)≤27000   Formula (1)
 
 where, T β  is a β transformation point (° C.). 
 
     
     
         12 . A method for manufacturing the titanium alloy sheet according to  claim 1 , comprising:
 performing a cold rolling pass in a longitudinal direction and a width direction of a titanium material containing, in % 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 and 0.60% or less, C: 0% or more and less than 0.080%, N: 0% or more and 0.050% or less, 0: 0% or more and 0.40% 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%, and a remainder of Ti and impurities; and   annealing the titanium material after the cold cross-rolling process,   wherein a total rolling rate in the cold cross-rolling process is 60% or more, and   a cross-rolling ratio, which is a ratio of a rolling rate in the longitudinal direction to a rolling rate in the width direction, is 0.05 or more and 20.00 or less.   
     
     
         13 . The method for manufacturing the titanium alloy sheet according to  claim 12 , wherein the cold cross-rolling process includes an intermediate annealing process of annealing the titanium material between a plurality of cold rolling passes in the case of performing the plurality of cold rolling passes, and annealing conditions for the intermediate annealing process and the final annealing process are conditions in which an annealing temperature is 600° C. or higher and (T β −50)° C. or lower, and the annealing temperature T (° C.) and a holding time t (seconds) at the annealing temperature satisfy the following formula (1),
   22000≤( T+ 273.15)×(Log 10 ( t )+20)≤27000   Formula (1)
 
 where, T β  is a β transformation point (° C.). 
 
     
     
         14 . A method for manufacturing the titanium alloy coil according to  claim 9 , comprising:
 performing one or more cold rolling passes in a longitudinal direction of a titanium material containing, in % 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 and 0.60% or less, C: 0% or more and less than 0.080%, N: 0% or more and 0.050% or less, 0: 0% or more and 0.40% 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%, and a remainder of Ti and impurities; and   annealing the titanium material after a final cold rolling wherein a rolling rate per cold rolling pass in the cold rolling process is more than 30%, and a total rolling rate is 60% or more.