Method for producing hot-rolled titanium plate

A method for producing a titanium plate by performing hot rolling on a titanium slab that is directly produced by using an electron beam re-melting process or a plasma arc melting process, comprising:

• when a face of the titanium slab to be rolled when the slab is subjected to hot rolling is defined as a “surface to be rolled”, and a face that is parallel to a rolling direction and is perpendicular to the surface to be rolled is defined as a “side surface”,
• [1] a step of melting at least one part on the surface to be rolled side of the side surface of the titanium slab by radiating a beam or plasma toward the side surface without radiating a beam or plasma toward the surface to be rolled, and thereafter causing re-solidification to form a microstructure layer having an equivalent circular grain diameter of 1.5 mm or less to a position at a depth of at least 3.0 mm from a surface of the side surface in at least one part of the side surface;
• [2] a step of performing a finishing process on the surface to be rolled of the titanium slab in which the microstructure layer is formed to bring X defined by formula (1) below to 3.0 or less;
• and
• [3] a step of subjecting the titanium slab after the finishing process to hot rolling under a condition in which L defined by (2) below is 230 mm or more;
• X=(largest value among H0, H1 and H2)−(smallest value among H0, H1 and H2) (1)
• L={R(H0−H3)}1/2 (2)
• where, the meaning of the symbols in the above formulae is as follows:
• X:
• slab flatness index
• H0:
• thickness of a central part in a width direction of the titanium slab after the finishing process (mm)
• H1:
• thickness of an end part (position at ⅛ of the width) in a width direction of the titanium slab after the finishing process (mm)
• H2:
• thickness of an end part (position at ¼ of the width) in a width direction of the titanium slab after the finishing process (mm)
• L:
• length of arc of contact of a roll in a first pass of rough rolling (mm)
• R:
• radius of a rolling roll in a first pass of rough rolling (mm)
• H3:
• thickness of a central part in the width direction of the titanium slab on a delivery side in a first pass of rough rolling (mm);
• wherein, in the step of [1], in the side surface, the microstructure layer is formed in a region from the surface to be rolled to a position at least ⅙ of the thickness of the titanium slab.