Titanium sheet and method for producing the same

Abstract

A titanium sheet having a sheet thickness of 0.2 mm or less and including a hardened layer on a surface, the titanium sheet including a chemical composition containing, in mass percent: Fe: 0.001 to 0.08%; and O: 0.03 to 0.08%, wherein a grain size satisfies following Formulas (1) to (3), a thickness of the hardened layer is 0.1 to 2.0 μm. The titanium sheet has both a sufficient strength and an excellent workability. Formulas (1) to (3) are dave≥2.5 (1), t/dave≥3.0 (2), and t/dmax—1.5 (3), where, in Formulas (1) to (3), t denotes the sheet thickness (μm), dave denotes an average grain size (μm), and dmax denotes a maximum grain size (μm).

1 . A titanium sheet having a sheet thickness of 0.2 mm or less and including a hardened layer on a surface, the titanium sheet having a chemical composition containing, in mass percent:
 Fe: 0.001 to 0.08%; and   O: 0.03 to 0.08%, wherein   a grain size satisfies following Formulas (1) to (3),   a thickness of the hardened layer is 0.1 to 2.0 μm, and   a maximum height Rz is 3.0 μm or less:   d ave ≥2.5 (1)   t/d ave ≥3.0 (2)   t/d max ≥1.5 (3)   where, in Formulas (1) to (3), t denotes the sheet thickness (μm), d ave  denotes an average grain size (μm), and dmax denotes a maximum grain size (μm).   
     
     
         2 . The titanium sheet according to  claim 1 , wherein a number ratio of grains each having a grain size of t/2 or more is 15% or less. 
     
     
         3 . A method for producing the titanium sheet according to  claim 1  having steps of cold rolling and annealing repeated on a titanium product a plurality of times, wherein the titanium product having an average grain size adjusted to 2.0 μm or less is finish cold rolled with a rolling ratio of 50 to 80% and thereafter finish annealed in an inert atmosphere at 570 to 750° C. 
     
     
         4 . A method for producing the titanium sheet according to  claim 2  having steps of cold rolling and annealing repeated on a titanium product a plurality of times, wherein the titanium product having an average grain size adjusted to 2.0 μm or less is finish cold rolled with a rolling ratio of 50 to 80% and thereafter finish annealed in an inert atmosphere at 570 to 750° C.