TW201916947A - Method for manufacturing hot-rolled titanium plate by having the to-be-rolled surface not irradiated with a beam or plasma while having the lateral surface irradiated with the beam or plasma to form a structure layer - Google Patents

Abstract

A method is provided for manufacturing a titanium plate by subjecting a titanium slab that is directly produced by applying an electron beam melting method or a plasma arc melting method to hot rolling. A surface of the titanium slab that is rolled during hot rolling is taken as a to-be-rolled surface, and a surface that is parallel to the rolling direction and perpendicular to the to-be-rolled surface is taken as a lateral surface, wherein (1) at least a part of the lateral surface of the titanium slab that is on a side of the to-be-rolled surface is melted by having the to-be-rolled surface not irradiated with a beam or plasma while having the lateral surface irradiated with the beam or plasma, and then solidified again, so as to form, in the lateral side, a structure layer that has a circle equivalent diameter less than 1.5mm and a depth of at least 3.0mm from the lateral side; (2) the to-be-rolled surface of the titanium slab that has been formed with the fine grain structure layer is subjected to finishing treatment to make a slab flatness index X smaller than 3.0; and (3) the titanium slab that has been subjected to the finishing treatment is subjected to hot rolling under the condition that a roll contact arc length L applied for the first round of rough rolling is greater than 230mm.

Description

Method for manufacturing titanium hot rolled sheet

[0001] The present invention relates to a method of producing a titanium hot rolled sheet.

[0002] Titanium hot rolled sheets are generally produced by the production method shown below. First, the sponge titanium or titanium scrap obtained by the Kroll method is melted and solidified to become an ingot (melting step). Next, the ingot is applied in a hot state by block rolling or forging, and processed into a flat embryo (opening step) suitable for the shape and size of the hot-rolled titanium hot-rolled sheet. Next, the flat embryo is hot rolled to form a titanium hot rolled sheet. [0003] As a melting method used in the melting step, a non-consumption electrode arc melting method (VAR), an electron beam melting method (EBR), or a plasma arc melting method (PAM) is used. [0004] When a non-consumption electrode arc melting method is used as the melting method, since the shape of the mold is restricted to a cylindrical shape, an opening step is required. When the electron beam melting method or the plasma arc melting method is used as the melting method, since the molten metal melted in a place different from the mold flows into the mold, the degree of freedom of the mold shape is high. Therefore, a rectangular column ingot which can be suitably used for the size of hot rolling of a titanium hot rolled sheet can be cast. When the rectangular columnar ingot is used to produce a titanium hot rolled material, the opening step can be omitted. [0005] As a method of producing a titanium hot-rolled sheet without undergoing an opening step, for example, the techniques described in Patent Documents 1 to 3 are known. [0006] Patent Document 1 discloses that a pure titanium rectangular ingot having a width/thickness of ≧3.5 is heated to a temperature of 900 to 1000 ° C, and a surface temperature of 880 ° C or more at the start of rolling is applied, and a pressing ratio of 10% or more is applied. After the rolling failure of less than 40%, in the temperature range where the surface temperature is less than 880 ° C and the surface temperature immediately after the final rolling is not lower than 650 ° C, the rolling at which the total reduction ratio becomes 70% or more is performed. method. In the method described in Patent Document 1, by suppressing the reduction amount in the β phase stabilization temperature range to a specific value or less, the width of the material is suppressed to be large. As a result, in Patent Document 1, the wrinkles generated on the side surface of the hot-rolled sheet are moved to the surface due to the expansion of the width, and the scar is suppressed. [0007] Patent Document 2 proposes that a steel tool having a tip shape having a radius of curvature of 3 to 30 mm or a steel ball having a radius of 3 to 30 mm is used for the surface of a rectangular ingot to be cold-plastically deformed and imparted with ripples. The contour curve elements have an average height of 0.2 to 1.5 mm and an average length of 3 to 15 mm. According to Patent Document 2, the surface of the rectangular ingot is deformed in a cold state by the steel tool or the steel ball described above, and the surface layer portion is recrystallized when the hot-rolled ingot is heated to reduce the coarse solidified structure. The resulting surface defects. [0008] Patent Document 3 describes a material for hot rolling of titanium, which combines one or more of high frequency induction heating, arc heating, plasma heating, electron beam heating, and laser heating to make an ingot. The surface layer of the surface to be rolled is melted and solidified, and a depth of 1 mm or more from the surface layer is a structure which is melted and solidified. In Patent Document 3, by solidifying and re-solidifying the surface layer of the ingot, a solidified structure having an extremely fine and irregular orientation is obtained, and the surface flaw caused by the influence of the coarse solidified structure is reduced. CITATION LIST Patent Literature [0009] Patent Document 1: Japanese Unexamined Patent Publication No. 7-251202 Patent Document 2: International Publication No. 2010/090352 Patent Document 3: Japanese Laid-Open Patent Publication No. 2007-332420

[ Problem to be Solved by the Invention ] However, in the conventional method for producing a titanium hot-rolled sheet, a surface defect called edge ridge occurs in the end portion in the width direction of the rolled surface of the titanium hot-rolled sheet. The occurrence of edge defects is particularly remarkable in the titanium hot rolled sheet produced by omitting the opening step. This is because the pores (pinholes) present on the surface of the ingot are not degraded by the crimping of the opening step. If pores are present in the hot-rolled titanium slab, the pores are present in the pores of the surface to be rolled during hot rolling, or the pores present on the side are wound by the plastic flow of the rolls. The surface is opened at the rolled surface and becomes an edge 瑕疵. [0011] If edge enthalpy occurs in the titanium hot-rolled sheet, it is necessary to increase the amount of the surface of the hot-rolled titanium sheet (the amount of melting) in the pickling step, or to cut the width of the rolled surface in which the edge 瑕疵 is removed. End, and yield is reduced. [0012] It is an object of the present invention to provide a method for producing a titanium hot-rolled sheet which suppresses the occurrence of edge flaws and has a good surface property. Means for Solving the Problem In order to suppress the edge flaw in the titanium hot-rolled sheet, the present inventors have determined that the pores existing in the vicinity of the to-be-rolled surface of the rolled surface and the side surface of the titanium flat blank can be prevented from opening during hot rolling. Yes. As a result of the investigation by the inventors of the present invention, it has been found that a molten re-solidification treatment which satisfies the conditions of the following [1], a finishing treatment satisfying the conditions of the following [2], and the following are performed by the titanium flat embryo before the hot working [ The hot working under the condition of 3] can suppress the edge enthalpy from the pores in the vicinity of the surface of the surface of the titanium flat blank, and the present invention has been conceived as follows. [0014] (1) A method for producing a titanium hot-rolled sheet, which is a method for producing a titanium plate by hot rolling using a titanium flat embryo directly produced by an electron beam melting method or a plasma arc melting method; The titanium slab has a surface to be rolled during hot rolling as a rolled surface, and a surface parallel to the rolling direction and perpendicular to the surface to be rolled is used as a side surface, [1] by not being rolled to the aforementioned surface Irradiating the beam or the plasma, irradiating the beam or the plasma to the side surface, and melting at least one side of the side of the rolled surface of the side surface of the titanium slab, and then solidifying it to form a circle equivalent on the side surface a step of having a particle diameter of 1.5 mm or less and a depth of 3.0 mm or more from the side surface, and [2] finishing the rolled surface of the titanium flat embryo forming the organized layer, and the following is performed ( 1) The step X of the formula is 3.0 or less, and [3] the step of hot rolling the titanium flat embryo after the finishing treatment under the condition that L defined by the following (2) is 230 mm or more; X=(H ₀ , the maximum value of H ₁ and H ₂ ) - (the minimum value of H ₀ , H ₁ and H ₂ ) (1) L = {R(H _{0 -} H ₃ )} ^1/2・・・( 2 However, the definition of the symbols in the above formula is as follows; X: flat embryo flatness index H ₀ : thickness (mm) of the central portion in the width direction of the titanium flat embryo after the finishing treatment H ₁ : the aforementioned finishing treatment Thickness (mm) of the end portion in the width direction of the rear titanium flat embryo (1/8 width position) H ₂ : thickness of the end portion (1/4 width position) in the width direction of the titanium flat embryo after the finishing treatment (mm) L: roll contact arc length (mm) of the first pass of rough rolling R: radius of the roll of the first pass of rough rolling (mm) H ₃ : center part of the width direction of the above-mentioned titanium flat embryo on the first pass side of rough rolling Thickness (mm). (2) The method for producing a titanium hot-rolled sheet according to the above (1), wherein in the step (1), the structure layer is formed on the entire side surface. (3) The method for producing a titanium hot-rolled sheet according to the above (1), wherein in the step (1), the thickness of at least the titanium flat blank is from the surface to be rolled from the side surface The fine particle structure layer is formed in a region up to the position of /6. [0017] (4) The method for producing a titanium hot-rolled sheet according to the above (3), wherein in the step (1), in the side surface, at least the thickness of the titanium flat embryo is from the rolled surface The fine particle structure layer is formed in a region up to 1/3 of the position. (5) The method for producing a titanium hot-rolled sheet according to any one of the above (1), wherein the surface roughness (Ra) of the surface to be rolled is performed in the step (2) It becomes 0.6 μm or more. (6) The method for producing a titanium hot-rolled sheet according to any one of the above (1), wherein, in the step (3), the radius of the roll of the first rough rolling exceeds 650 mm . (7) The method for producing a titanium hot-rolled sheet according to any one of the above (1), wherein, in the step (3), the reduction ratio of the first pass of the rough rolling is 30. %the above. (8) The method for producing a titanium hot-rolled sheet according to any one of the above (1), wherein the surface roughness (Ra) of the roll is 0.6 μm in the step (3). the above. Advantageous Effects of Invention According to the method for producing a titanium hot-rolled sheet according to the present invention, it is possible to suppress the pores existing on the side surface of the titanium flat embryo from being wound into the surface to be rolled during hot rolling, and opening the edge of the rolled surface to cause an edge In the case where the pores are present, even if the pores are present on the rolled surface of the titanium flat embryo, the occurrence of edge defects due to the opening of the pores existing on the rolled surface can be suppressed. Therefore, according to the method for producing a titanium hot-rolled sheet according to the present invention, a titanium hot-rolled sheet having a good surface property can be obtained. As a result, the amount of dissolution of the surface of the titanium hot rolled sheet removed in the pickling step can be reduced. Further, the cutting width of the end portion in the width direction of the rolled surface due to the edge enthalpy can be reduced, and the yield can be increased.

Form of implementing the invention [0024] In the method for producing a titanium hot-rolled sheet according to the present embodiment, the titanium flat embryo directly produced by the electron beam melting method or the plasma arc melting method is subjected to melt re-solidification treatment and finishing treatment, and then subjected to A titanium plate is produced by hot rolling. Hereinafter, each step will be described with reference to Figs. 1 to 6 . 1. Manufacturing Conditions of Titanium Flat Embryo When manufacturing the titanium hot rolled sheet of the present embodiment, a titanium flat embryo directly produced by an electron beam melting method or a plasma arc melting method is used. Here, as the titanium flat embryo, a rectangular columnar ingot or a flat embryo which can be suitably used for the hot rolling of a titanium hot rolled sheet can be used, and those manufactured by various methods can be used. Specifically, as the titanium flat embryo, a rectangular columnar ingot manufactured by an electron beam melting method or a plasma arc melting method can be used. [0027] In the case of titanium having a high alloy composition, the rolling reaction force becomes large in the temperature condition of the α phase domain or the α + β phase domain. Therefore, it is not easy to manufacture a titanium hot rolled sheet having only an α phase or a high alloy composed of an α phase and a β phase. Therefore, when the high alloy composition of titanium is hot rolled under high pressure, it is preferably carried out in the β phase domain. However, when the high alloy composition of titanium is hot rolled in the β phase domain, the occurrence of edge defects is small. Therefore, the titanium flat embryo used in the present embodiment is preferably titanium having a Ti content of 99% by mass or more (also referred to as industrial pure titanium) or a low alloy composition in which the main constituent layer is an α phase (also referred to as titanium). Titanium alloy). However, as the titanium flat embryo, titanium of the α phase and the β phase and titanium of the β phase may be used as needed. [0028] The chemical composition of the titanium flat embryo depends on the chemical composition or weight ratio of the titanium sponge and/or titanium scrap used as the raw material, the chemical composition of the added auxiliary material and its weight ratio. Therefore, in order to obtain the chemical composition of the target titanium flat embryo, the chemical composition of the sponge titanium and titanium scrap and the auxiliary material can be grasped in advance by chemical analysis or the like, and the weight of each raw material required can be determined according to the chemical composition. Further, an element (for example, chlorine or magnesium) which is volatilized and removed by melting of the electron beam is not contained in the titanium flat embryo even if it is contained in the raw material. Hereinafter, the "%" of the content of each element means "% by mass". [0029] The chemical composition of the titanium squash of the present invention is, for example, O: 0 to 1.0%, Fe: 0 to 5.0%, Al: 0 to 5.0%, Sn: 0 to 5.0%, and Zr: 0 to 5.0%. Mo: 0 to 2.5%, Ta: 0 to 2.5%, V: 0 to 2.5%, Nb: 0 to 2%, Si: 0 to 2.5%, Cr: 0 to 2.5%, Cu: 0 to 2.5%, Co : 0 to 2.5%, Ni: 0 to 2.5%, platinum group elements: 0 to 0.2%, REM: 0 to 0.1%, B: 0 to 3%, N: 0 to 1%, C: 0 to 1%, H: 0 to 0.015%, and the remainder is titanium and impurities. [0030] The platinum group element is specifically one or more selected from Ru, Rh, Pd, Os, Ir, and Pt, and the content of the platinum group element means the total content of the above elements. Further, REM is a general term for a total of 17 elements of Sc, Y, and a lanthanoid element, and the content of REM means the total amount of the above elements. [0031] O, Fe, Al, Sn, Zr, Mo, Ta, V, Nb, Si, Cr, Cu, Co, Ni, a platinum group element, REM and B are not required, and the lower limit of each content is 0%. The lower limit of the content of each of O, Fe, Al, Sn, Zr, Mo, Ta, V, Nb, Si, Cr, Cu, Co, Ni, platinum group elements, REM and B can be set to 0.01%, 0.05%, 0.1%, 0.2% or 0.5%. [0032] The upper limit of O may be set to 0.80%, 0.50%, 0.30%, or 0.10%. The upper limit of Fe can be set to 3%, 2% or 1%. The upper limit of the content of Al can be set to 3%, 2% or 1%. The upper limit of the content of Sn can be set to 3%, 2% or 1%. The upper limit of the content of Zr can be set to 3%, 2% or 1%. The upper limit of the content of Mo can be set to 2%, 1.5%, 1% or 0.5%. The upper limit of the content of Ta can be set to 2%, 1.5%, 1% or 0.5%. The upper limit of the content of V can be set to 2%, 1.5%, 1% or 0.5%. The upper limit of the content of Nb can be set to 1.5%, 1%, 0.5% or 0.3%. The upper limit of the content of Si can be set to 2%, 1.5%, 1% or 0.5%. The upper limit of the Cr content may be set to 2%, 1.5%, 1% or 0.5%. The upper limit of Cu can be set to 2%, 1.5%, 1% or 0.5%. The upper limit of the content of Co can be set to 2%, 1.5%, 1% or 0.5%. The upper limit of the content of Ni can be set to 2%, 1.5%, 1% or 0.5%. The upper limit of the content of the platinum group element can be set to 0.4%, 0.3%, 0.2% or 0.1%. The upper limit of the content of REM can be set to 0.05%, 0.03% or 0.02%. The upper limit of the content of B can be set to 2%, 1%, 0.5% or 0.3%. The upper limit of N can be set to 0.08%, 0.05%, 0.03% or 0.01%. The upper limit of C can be set to 0.08%, 0.05%, 0.03% or 0.01%. The upper limit of H can be set to 0.012%, 0.010%, 0.007% or 0.005%. The titanium flat embryo of the present invention is preferably produced in such a manner as to satisfy the chemical composition range specified by various specifications. In the following, the ASTM standard or the AMS standard is also included, but the representative specifications are mainly exemplified by the JIS standard. The present invention is capable of using the manufacture of titanium of such specifications. [0034] Examples of the specifications of the titanium include the first type to the fourth type specified in JIS H4600 (2012), and the third to fourth grades of the Grad 1 to 4 and the DIN 17850 specifications specified in ASTM B265. Titanium specified in 7035 and 3.7055. [0035] As the titanium having a low alloy composition in which the main constituent phase is the α phase, the alloying element is preferably 5.0% or less in total, and the remainder is Ti and impurities. Here, as the alloying element, Al such as an α-stabilizing element, Sn or Zr of a neutral element, Fe, Cr, Cu, Ni, V, Mo, Ni, Si, Co, Ta of a β-stabilizing element can be exemplified. Etc., Pd, Ru, etc. of a platinum group element, Mm (fine alloy) of a rare earth element, Y, etc., O, C, N, etc. of a gas element. The preferred content of the α-stabilizing element or the neutral element is 0 to 5.0%, and the preferred content of the β-stabilizing element is 0 to 2.5%. Further, the preferred content of the rare earth element is 0 to 0.5%, and the preferable content of the gas element such as O, C, or N is 0 to 1.0%. Any content refers to the total content when a plurality of elements are added. [0036] For example, there is a corrosion-resistant alloy of Pd or Ru containing 0.02 to 0.2% of a platinum group element in Ti, and further contains 0.02 to 0.2% of a platinum group element of Pd or Ru, and further contains 0.001 to 0.1% of A corrosion resistant alloy of Mm or Y composed of a rare earth element, or a heat resistant alloy of Al, Cu, or Sn having a large solid solution amount in the α phase of 0.1 to 2.5%, respectively. [0037] As shown in FIG. 2, the titanium flat blank 10 of the material of the titanium hot rolled sheet is slightly rectangular. The surface which is substantially perpendicular to the thickness direction of the titanium flat blank 10 (in other words, the two faces whose normal lines are substantially parallel with respect to the thickness direction of the titanium flat blank) is referred to as the rolled surface of the rolled surface at the time of hot rolling. 10C, 10D. As shown in Fig. 2, the rolled faces 10C, 10D of the titanium flat blank are substantially rectangular. Further, a surface substantially parallel to the thickness direction of the titanium flat blank 10 (in other words, a surface normal to the thickness of the titanium flat blank) is referred to as a side surface. The side of the titanium flat embryo 10 is of two types. One side surface is a side surface substantially parallel to the long side of the rectangular shape formed by the rolled surfaces 10C and 10D (in other words, the normal line is substantially parallel to the short side of the rectangular shape formed by the rolled surface). Such a side surface is referred to as a long side (indicated by symbols 10A, 10B in Fig. 2). That is, the side surface parallel to the rolling direction D in the hot rolling step is a long side surface. The other side surface is a side surface substantially parallel to the short side of the rectangular shape formed by the rolled surfaces 10C and 10D (in other words, the normal line is substantially parallel to the long side of the rectangular shape formed by the rolled surface). Such a side is referred to as a short side. Further, the side faces 10A and 10B parallel to the rolling direction D of the titanium flat blank 10 used in the present embodiment mean the above-mentioned "long side faces". In the following description, when the "side" of the titanium flat embryo is described, the "long side" of the titanium flat embryo is used unless otherwise specified. 2. Conditions of Melt Resolidification Treatment The melt resolidification treatment for titanium flat embryos must satisfy the conditions of the following [1]. [1] By irradiating a beam or a plasma to the surface to be rolled, irradiating a beam or a plasma onto the side surface, and melting at least one side of the side of the rolled surface of the side surface of the titanium flat embryo, and then co-solidifying On the other hand, a layer having a circular equivalent particle diameter of 1.5 mm or less is formed from a surface of the side surface to a position of at least 3.0 mm in depth. This tissue layer is a structure formed by changing from a β phase to an α phase at the time of remelting and solidification, and is a finer structure than the parent phase, and is hereinafter referred to as a fine particle structure layer. [0041] Further, the titanium flat embryo directly produced by the electron beam or plasma arc melting method is slowly cooled in a vacuum, and is a mother phase which is not subjected to the melt resolidification treatment, and is a circle or the like. A very large cast structure with a particle size of several mm. On the other hand, the side surface of such a titanium flat embryo is cooled relatively quickly by the heat removal from the flat embryo upon re-solidification after being melted by the melt resolidification treatment. Therefore, the fine grain structure layer becomes a finer structure than the mother phase. The circular equivalent particle diameter of the fine particle structure layer is preferably 1.2 mm or less, more preferably 1.0 mm or less. The circular equivalent particle diameter in the fine grain structure layer is not hindered even if it is small, but 5 μm is a substantial lower limit. The lower limit of the circular equivalent particle diameter of the fine particle structure layer may also be 1 μm. By forming such a fine grain structure layer, the pores existing on the side surface of the titanium flat embryo can be made harmless. [0042] Further, the crystal grain size of the fine particle structure layer is a T section of the titanium slab that can be polished (parallel to the thickness direction of the titanium flat embryo and perpendicular to the side surface) by EBSD (electron backscatter diffraction pattern) Electron back scattered diffraction pattern). In this measurement, when the crystal orientation difference between the adjacent measurement points is 5 or more, it is regarded as different crystal grains, and the area A of each crystal grain is obtained, and it is possible to obtain A=p ́(L/2). ² Calculate the circle equivalent particle size L. [0043] When the titanium flat blank is hot rolled, one of the side faces is wound around the rolled surface because the width of the central portion is enlarged. Therefore, if the defect exists in the side surface portion, edge ridges often occur at the end portion of the plate width, and since the portion must be cut largely, the yield is lowered. This winding is in the case where the winding is large, and is about 1/3 to 1/6 of the thickness of the flat embryo. For example, when the thickness of the flat embryo is about 200 to 260 mm, it is about several tens of mm. Therefore, the portion that is wound around the surface to be rolled is a portion close to the surface to be rolled (near the surface to be rolled) even in the side surface, and the edge of the rolled surface can be suppressed even if the side surface is not completely melted and solidified. It happened. Therefore, it is only necessary to form a fine particle structure layer in at least one of the side faces of the rolled surface. More specifically, when at least one of the side faces of the side of the rolled surface is melted and solidified, when the thickness of the titanium flat blank is regarded as t, it is preferably a region from the rolled surface to the 1/3 t position. A fine grained layer is formed in the middle. That is, it is preferable to melt and resolidify at least the range from the upper end and the lower end to 1/3t. That is, even if a region of molten re-solidified which is not more than 1/3 t is applied to the center of the sheet thickness, the edge enthalpy of the surface to be rolled can be suppressed. Moreover, since the melt re-solidification of the side surface is only a part, the processing time can be shortened, and productivity can be improved. However, since the fine-grained structure layer is provided in a too narrow range, and the effect of suppressing the edge entanglement is not obtained, the fine-grained layer at the time of at least one side of the side of the rolled surface is provided. It may be formed in a region from the above-mentioned rolled surface to a 1/6 t position. [0044] On the other hand, the side surface may be completely melted and solidified. At this time, in addition to suppressing the edge entanglement due to the above-described winding of the rolled surface, the crack at the end portion of the sheet can be suppressed. The cracking system deteriorates the yield. Further, when the titanium material having a relatively high strength is cold-rolled after hot rolling, the plate is broken by using the crack as a starting point. This can be suppressed by melting and resolidifying the side surface. It is determined according to the product size (thickness) or the manufacturing step (with or without cold rolling, etc.) that only one side of the side surface of the side to be rolled or which is to be fully melted and resolidified. [0045] In this step, it is specified that the rolled surface of the titanium flat embryo is not melted. The reason for this is that if the rolled surface of the titanium flat blank is melted and solidified, irregularities are generated on the surface. In particular, in the present invention, since hot rolling is applied so that the contact arc length is 230 mm or more, the plastic flow during hot rolling is likely to occur largely in the sheet width direction. Therefore, if the surface to be rolled is melted and solidified, a linear hot rolling flaw occurs on the surface. Therefore, the re-solidification of the rolled surface is not performed in the patent of the present invention. 2 is a view for explaining an example of a melting re-solidification step in the method for producing a titanium hot-rolled sheet according to the embodiment. In the melt resolidification step, the melt resolidification treatment of irradiating the beam or the plasma to the surface to be rolled 10C, 10D is not performed, and the beam or the plasma is irradiated to the side faces 10A, 10B to make the titanium flat embryo 10 At least one of the side faces 10A and 10B parallel to the rolling direction D is melted and solidified at least on one side of the rolled faces 10C and 10D to form a finer structure than the base material. At this time, the depth from the side faces 10A and 10B of the fine particle structure layer is 3.0 mm or more. In the melt resolidification treatment of the side faces 10A and 10B, a part of the end region of the to-be-rolled surfaces 10C and 10D adjacent to the side faces 10A and 10B (for example, an area from the end portion to 10 mm or 5 mm) is used. Melt and resolidify to form a tissue layer similar to the fine grain structure layer, but this is tolerated. In the present embodiment, as a heating method used to melt and resolidify the side faces 10A and 10B parallel to the rolling direction D of the titanium flat blank 10, arc heating (TIG (Tungsten Inert Gas)) and carbon dioxide can be used. Laser heating such as laser, plasma heating, plasma arc heating, induction heating, electron beam heating, etc. In particular, when plasma heating and electron beam heating are used, since the amount of heat input can be increased, the unevenness of the surface of the casting of the cast rectangular columnar ingot can be easily smoothed. Further, when plasma heating and electron beam heating are used, the melt resolidification step can be easily performed in a non-oxidizing environment. Therefore, plasma heating and electron beam heating are suitable as a method of melting and solidifying the titanium flat embryo 10 composed of an active metal. In order to suppress the surface oxidation of the titanium flat blank 10, when the melting and resolidification step is carried out in a vacuum, the degree of vacuum in the furnace to be subjected to the melt resolidification treatment is preferably set to 3 × 10 ^-3 Support the following high vacuum. [0048] The melt resolidification step of the present embodiment may be carried out only once, and may be increased as many times as necessary. However, the more the number of melt resolidification steps, the longer the treatment time required for the melt resolidification step, resulting in reduced productivity and increased cost. Therefore, the number of times of the melt resolidification step is preferably 1 or 2 times. In the present embodiment, at least one of the side faces 10A and 10B of the side faces 10A and 10B parallel to the rolling direction D of the titanium flat blank 10 is melted and solidified to form a fine grain structure layer. . In the titanium flat embryo 10 having the fine particle structure layer of the present embodiment, since the size of the fine particle structure layer and the base material structure are greatly different, it is easy to observe the cross section orthogonal to the rolling direction by a microscope. the difference. The fine particle structure layer is composed of a molten resolidified layer which is solidified after being melted in the melt resolidification step and a heat affected layer (HAZ layer) in the melt resolidification step. In the present embodiment, a fine particle structure layer having a depth of 3.0 mm or more is formed on at least one of the side faces 10A and 10B on the side of the rolled faces 10C and 10D by performing the melt resolidification step. The depth of the fine particle structure layer is preferably 4.0 mm or more. Since the depth of the fine particle structure layer is 3.0 mm or more, the pores present in the side surface of the titanium flat embryo 10 can be made harmless. In addition, when the depth of the fine-grained structure layer is 3.0 mm or more, when the cast rectangular column-shaped ingot is directly used as the titanium flat blank 10, the unevenness of the surface of the casting in the side surface of the titanium flat blank 10 can be reduced. On the other hand, when the depth of the fine-grained structure layer is less than 3.0 mm, the pores present in the side surface of the titanium flat blank 10 are wound around the rolled surface due to plastic flow by hot rolling, and it is not sufficiently suppressed. An edge flaw in the rolling surface due to the opening. In order to efficiently carry out the melt resolidification step, the depth of the fine particle structure layer is preferably 20.0 mm or less, more preferably 10.0 mm or less. The depth of the fine particle structure layer in the present embodiment means the depth measured by the method shown below. From the titanium flat embryo after the melt resolidification step, a sample having the side surface side as a observation surface was taken in a cross section perpendicular to the side surface. The obtained sample was embedded in a resin as needed, and the surface was mirror-polished by mechanical polishing, and the surface was visually observed by a hydrofluoric acid solution, and the depth of the fine particle structure layer was measured by microscopic observation of a field of view of 30 × 30 mm or more. Further, when the fine-grained tissue layer is deep, the field of view is increased in the depth direction, and a microscope photograph is connected in series to measure the depth of the fine-grained tissue layer. Then, the average value is calculated from the depth of the fine grain structure layer at any five places, and is regarded as the depth of the fine grain structure layer. Next, as an example of the melt resolidification step of the present embodiment, a case where the side faces 10A and 10B parallel to the rolling direction D of the titanium flat blank 10 are melted and solidified by electron beam heating is exemplified. ,Be explained. [0054] First, as shown in FIG. 2, the titanium flat embryo 10 is provided such that the side faces 10A, 10B are slightly horizontal. Next, in the side faces 10A, 10B of the titanium flat blank 10, for the upwardly disposed face (indicated by symbol 10A in Fig. 2), an electron beam is irradiated from an electron beam irradiation gun 12 as a heating means to heat the surface. At least one of the sides 10A on the side of the rolled surface 10D is melted and solidified. [0055] For the side 10A of the titanium flat blank 10, the area and shape of the illuminated area 14 of the electron beam can be made by high-frequency means by adjusting the focus of the electron beam and/or using an electromagnetic lens. The vibration (oscillation) is adjusted to form a beam or the like. [0056] With respect to the side surface 10A of the titanium flat blank 10, the area of the irradiation region 14 of the electron beam is remarkably small as compared with the entire area of the side surface 10A to be melted and resolidified. Therefore, it is preferable that the electron beam irradiation gun 12 is continuously moved to the side surface 10A of the titanium flat blank 10, or the side surface 10A of the titanium flat blank 10 is continuously moved while irradiating the electron beam with the electron beam 12, and irradiation is performed. Electron beam. [0057] With respect to the side surface 10A, the moving direction of the electron beam irradiation gun 12 is not particularly limited. For example, as shown in FIG. 2, the electron beam irradiation gun 12 can be moved in the rolling direction D of the titanium flat blank 10 (the longitudinal direction of the titanium flat blank 10) (indicated by an arrow A in FIG. 2). Irradiate the electron beam. Thereby, the side face 10A is continuously heated in a strip shape in the width W (the diameter W in the case of a circular beam or a beam). When the electron beam irradiation gun 12 reaches the longitudinal end of the titanium flat blank 10, the electron beam irradiation gun 12 is moved by a predetermined size portion in the thickness direction of the titanium flat blank 10. Then, the electron beam irradiation gun 12 is continuously moved in the opposite direction to the movement in the longitudinal direction with respect to the unheated region disposed on the side of the strip-shaped heated region on the side surface 10A. The strip side heats the side 10A. [0058] In this manner, the movement of the electron beam irradiation gun 12 in the longitudinal direction of the titanium flat blank 10 and the movement of the designated portion toward the thickness direction of the titanium flat blank 10 are repeated, and at least the heated side surface 10A is rolled. One or the whole of the 10D side. When the side surface 10A of the titanium flat blank 10 is irradiated with an electron beam and heated, when the surface temperature of the side surface 10A becomes the melting point of titanium (usually about 1670 ° C or more), the surface layer of the side surface 10A is melted. Thereby, as shown in FIG. 3, the unevenness 10P of the surface of the casting existing in the side surface 10A of the titanium flat blank 10, or the defect 10Q of a fine hole etc. are harmless. Then, after melting, it is cooled by heat removal from the base material (the inside of the titanium flat blank 10), and when it reaches the solidification temperature or lower, it solidifies to become the molten resolidified layer 16. In this manner, in the side surface 10A, the fine particle structure layer 20 composed of the molten re-solidified layer 16 and the heat-affected layer (HAZ layer) 18 corresponding to the depth of the heat input amount of the electron beam is formed. The heat-affected layer (HAZ layer) 18 is formed by heating at the time of forming the molten re-solidified layer 16, and the region on the side of the base material side of the molten re-solidified layer 16 becomes a temperature equal to or higher than the β-deformation point, and is used for transformation into a β phase. [0061] Furthermore, as shown in FIGS. 3 and 4, the depth of the molten re-solidified layer 16 and the heat-affected layer (HAZ layer) 18 formed by electron beam heating (the depth of the fine-grained structure layer 20) is not fixed. In the central portion of the irradiation region 14 of the 18-electron beam of the molten re-solidified layer 16 and the heat-affected layer (HAZ layer), the depth is the largest, and the end portion of the irradiated region 14 is shallower in depth, and becomes the base material side in the cross-sectional view. Convex curved shape. Therefore, in order to increase the depth of the molten re-solidified layer 16 and the heat-affected layer (HAZ layer) 18 formed by electron beam heating (the depth of the fine-grained structure layer 20) to 3.0 mm or more, it is necessary to adjust the electrons in the strip-shaped irradiation. The interval between the beams. For example, as described above, the movement of the electron beam irradiation gun 12 in the longitudinal direction of the titanium flat blank and the movement of the designated size portion in the thickness direction of the titanium flat blank 10 are repeated, and when the entire side surface is continuously heated, When the movement of the electron beam irradiation gun 12 in the thickness direction of the titanium flat blank 10 is set to a size of 1/2 or less of the melt width, the depth of the fine particle structure layer 20 can be made substantially constant. In the present embodiment, it is preferable to control the heat input amount of the electron beam and the irradiation interval of the electron beam so that the side surface 10A is melted so that the depth of the fine particle structure layer 20 is 3.0 mm or more. Coagulate. The difference between the maximum depth and the minimum depth of the fine-grained structure layer 20 is preferably 1.0 mm or less per observation field. Next, the titanium flat blank 10 is placed so that the side surface 10B is upward, and similarly to the side surface 10A, the electron beam is irradiated from the electron beam irradiation gun 12 of one unit, and the surface is melted and solidified. By the above steps, in the side faces 10A, 10B parallel to the rolling direction D of the titanium flat blank 10, a fine grain structure layer 20 having a depth of 3.0 mm or more formed of a finer structure than the base material structure is formed. . 3. Conditions of Finishing Treatment The finishing treatment of the titanium squash after the melt resolidification treatment must satisfy the following [2]. [2] The rolled surface of the titanium flat embryo on which the fine grain structure layer is formed is subjected to finishing treatment so that X defined by the following formula (1) is 3.0 or less. X=(H ₀ , H ₁ And H ₂ Maximum)-(H ₀ , H ₁ And H ₂ Minimum value) (1) However, the definition of the symbols in the above formula is as follows; X: Flat embryo flatness index H ₀ : thickness (mm) of the central portion in the width direction of the titanium flat embryo after the finishing treatment H ₁ Thickness (mm) of the end portion (1/8 width position) in the width direction of the titanium flat embryo after the above finishing treatment H ₂ : thickness (mm) of the end portion (1/4 width position) in the width direction of the titanium flat embryo after the finishing treatment. FIG. 1 is a section of a titanium flat embryo manufactured by electron beam melting or plasma arc melting. Model diagram. In the electron beam melting method or the plasma arc melting method, the titanium melt flows into the mold and is pulled out to produce a titanium flat embryo. At this time, the titanium flat germ system is restrained by the four sides in the mold to have the same shape as the mold shape, but is unconstrained if it leaves the mold. At the time, in the central portion of the titanium squash, the pool remained, and bulging occurred in the central portion of the titanium slab due to the pressure from the inside to the outside. Therefore, as shown in FIG. 1, the titanium flat blank 10 is formed in a drum shape in which the center portion 11a is slightly raised from the end portion 11b in the width direction. Therefore, when hot rolling is performed in such a shape, the contact arc length of the roll changes in the center portion 11a and the end portion 11b, and the contact arc length of the end portion 11b becomes short. In this case, in the vicinity of the end portion 11b, the pores are opened and edge defects occur. If the difference in thickness between the central portion 11a and the end portion 11b is at most 3.0 mm, the contact arc length can be securely secured. Therefore, the flatness index X defined by the above formula (1) is set to 3.0 or less. The flatness index X is preferably set to 2.8 or less, and more preferably set to 2.6 or less. The smaller the flatness index X is, the better, but in consideration of manufacturability, 0.5 is a substantial lower limit. In the present embodiment, as a method of finishing the rolled surfaces 10C and 10D, a method of performing a grinding process such as a grinding machine and/or a cutting process such as a milling machine or a planer can be mentioned. The grinding processing system can be divided into cutting machining such as milling machining or planer machining. As the finishing treatment step, after the cutting process, the final processing can be performed by a grinding process such as a grinder. In the present embodiment, it is preferable that the rolled surface 10C and 10D of the titanium flat blank 10 having the fine particle structure layer 20 are subjected to finishing treatment to have a surface roughness (Ra) of 0.6 μm or more, and more preferably 0.8 μm or more. When the surface roughness (Ra) of the surface to be rolled 10C and 10D is 0.6 μm or more, the binding force of the titanium flat blank 10 caused by the roll of the titanium flat blank 10 is increased in the hot rolling step, and further Suppresses the occurrence of edge defects. When the surface roughness Ra is too large, hot rolling is caused by the unevenness, and the surface property is deteriorated. Therefore, it is preferably 100 μm or less, and more preferably 50 μm or less. 4. Conditions of Hot Rolling For the hot rolling of the titanium slab after the finishing treatment, the following [3] must be satisfied. [3] a step of hot rolling the titanium flat embryo after the finishing treatment under the condition that L defined by the following (2) is 230 mm or more; L={R(H) ₀ -H ₃ )} ^1/2 ・・・(2) However, the definition of the symbols in the above formula is as follows; L: the roll contact arc length of the first pass of rough rolling (mm) R: the radius of the roll of the first pass of rough rolling (mm) H ₀ : thickness (mm) of the central portion in the width direction of the titanium flat embryo after the finishing treatment H ₃ : Thickness (mm) of the center portion in the width direction of the titanium flat blank on the first pass side of the rough rolling At this time, the contact area between the roll and the titanium flat blank is sufficiently ensured in the first pass of the rough rolling. Therefore, the binding force of the titanium flat embryo caused by the roll of the titanium flat embryo is sufficiently obtained. As a result, even if the pores are present on the rolled surface of the titanium flat blank, the opening of the pores existing in the rolled surface can be suppressed, and the occurrence of edge defects can be suppressed. [0070] Hereinafter, a method of producing a titanium hot rolled sheet of the present invention will be described in more detail. [0071] As the hot rolling method in the hot rolling step, a well-known method can be used, and there is no particular limitation. When a thin plate of a hot-rolled titanium sheet is used as a product, roll rolling is usually employed. Moreover, when a thin plate is used as a product, the thickness of the titanium hot-rolled sheet is usually about 3 to 8 mm. [0072] The heating conditions in the hot rolling step can be set to well-known conditions. For example, in the same manner as ordinary titanium hot rolling, it can be heated at a temperature of 720 to 920 ° C for 60 to 420 minutes, hot rolling is started in this temperature range, and heat is terminated at a temperature of room temperature or higher according to the capacity of the hot rolling mill or the like. Rolling. [ Fig. 5] Fig. 5 is a view for explaining an example of a hot rolling step in the method for producing a titanium hot rolled sheet according to the embodiment. Fig. 5 is a schematic cross-sectional view showing a state in which the titanium slab 10 having the fine-grained structure layer 20 is rolled by the rolls 24 and 24 of the rolling mill in the roll zone of the first pass. In the hot rolling step of the present embodiment, the roll contact arc length L is set to 230 mm or more, and hot rolling of the first rough rolling of the titanium flat blank 10 having the fine particle structure layer 20 is performed. The roll contact arc length L is the length of the contact portion of the roll 24 with the titanium flat blank 10 when the rolls 24 and 24 of the roll mill are viewed in cross section, and is expressed by the above formula (1). [0075] The edge lanthanum of the titanium hot rolled sheet occurs due to hot rolling and the titanium squash 10 protrudes to the side. Therefore, the edge lanthanum tends to occur in the initial stage of rough rolling in which the reduction ratio is large. In particular, the edge lanthanum is likely to occur in the first pass of the rough rolling, and after the second pass, the edge enthalpy hardly occurs. Therefore, the roll contact arc length L can be set to 230 mm or more only in the first pass of the rough rolling. When the roll contact arc length L is 230 mm or more, hot rolling of the first rolling of the titanium flat blank 10 is performed, and the contact area between the rolls 24 and 24 and the titanium flat blank 10 can be sufficiently ensured. Therefore, the binding force of the titanium flat blank 10 caused by the rolls 24 and 24 sandwiching the titanium flat blank 10 is sufficiently obtained, and unevenness occurring in the rolled surfaces 10C and 10D can be reduced. As a result, even if the pores are present in the rolled faces 10C and 10D of the titanium flat blank 10, the pore openings existing in the rolled faces 10C and 10D can be suppressed, and the occurrence of edge defects can be suppressed. In order to increase the restraining force of the titanium flat blank 10 by the rolls 24, 24, the roll contact arc length L is more preferably 250 mm or more. Further, if the roller contact arc length L is too large, the load per unit area becomes small, and the restraining force becomes weak. Therefore, the roller contact arc length L is preferably 400 mm or less. The roll contact arc length L is as shown in the above formula (1), and is lengthened by increasing the radius R of the roll and the reduction ratio. [0078] In order to ensure that the roller contacts the arc length L, the radius R of the roll 24 is preferably more than 650 mm, more preferably 750 mm or more. However, if the radius R of the roll 24 is large, the rolling equipment becomes large-scale, and therefore the radius R of the roll 24 is preferably 1200 mm or less. The reduction ratio of the first pass of the rough rolling is preferably 30% or more, more preferably 35% or more, and particularly preferably 40% or more. Since the reduction ratio of the first pass of the rough rolling is set to 30% or more, it is easy to ensure the contact arc length L of the roll, and at the same time, the pore opening existing in the vicinity of the rolled faces 10C and 10D of the titanium flat blank 10 can be suppressed, and the edge is further suppressed. It happened. However, if the reduction ratio of the first pass of the rough rolling exceeds 50%, a rolling equipment capable of applying a large load is required, and the rolling equipment becomes large-scale. Therefore, the reduction ratio of the first pass of the rough rolling is preferably 50% or less. The surface roughness (Ra) of the roll 24 is preferably 0.6 μm or more, and more preferably 0.8 μm or more. When the surface roughness (Ra) of the roll 24 is 0.6 μm or more, the binding force of the titanium flat blank 10 caused by the rolls 24 and 24 which sandwich the titanium flat blank 10 becomes high, and the occurrence of edge defects is further suppressed. However, if the surface roughness (Ra) of the roll 24 is too large, the surface property shape of the hot rolled sheet may deteriorate. Therefore, the surface roughness (Ra) of the roll 24 is preferably 1.5 μm or less. In the method for producing a titanium hot-rolled sheet according to the present embodiment, the side faces 10A and 10B parallel to the rolling direction D of the titanium flat blank 10 are melted and solidified, and a depth of 3.0 mm or more is formed in the side faces 10A and 10B. Since the fine particle structure layer 20 is formed, the pores existing in the side faces 10A and 10B of the titanium flat embryo 10 are rendered harmless. Therefore, it is possible to suppress the pores existing in the side faces 10A and 10B of the titanium flat blank 10 from being wound into the rolled faces 10C and 10D during hot rolling, and opening in the rolled faces 10C and 10D to cause edge flaws. Further, in the method for producing a titanium hot-rolled sheet according to the present embodiment, the roll contact arc length L is set to 230 mm or more, and the heat of the first pass of the rough rolling of the titanium flat blank 10 having the fine particle structure layer 20 is performed. Rolling. Therefore, the restraining force of the titanium flat blank 10 caused by the rolls 24 and 24 sandwiching the titanium flat blank 10 is sufficiently obtained. As a result, even if the pores are present on the rolled faces 10C and 10D of the titanium flat blank 10, the pore openings existing in the rolled faces 10C and 10D are suppressed, and the occurrence of edge flaws is suppressed. Therefore, according to the method for producing a titanium hot-rolled sheet of the present embodiment, a titanium hot-rolled sheet having a good surface property can be obtained. As a result, the amount of removal of the surface removed when pickling the titanium hot rolled sheet can be reduced. Further, when the end portion in the width direction of the rolled surface due to the edge enthalpy is cut off from the titanium hot rolled sheet, the width of the cut and removed can be reduced. Therefore, the yield of the material for the titanium hot rolled sheet is increased. Further, in the method for producing a titanium hot-rolled sheet according to the present embodiment, since the titanium hot-rolled sheet having a good surface property is obtained even if the opening step is omitted, the step of opening the blank can be omitted, and the productivity can be improved. However, in the method for producing a titanium hot-rolled sheet according to the present embodiment, even if a cast rectangular column-shaped ingot is directly used as the titanium flat blank 10, the titanium flat embryo 10 can be alleviated by performing the melt re-solidification step. The unevenness 10P of the surface of the casting in the side faces 10A, 10B. Therefore, in addition to the melt resolidification step, the step of smoothing the surface of the casting in the side faces 10A, 10B of the titanium flat blank 10 is not required. As described above, the method for producing a titanium hot-rolled sheet according to the present embodiment is extremely effective in reducing the manufacturing cost, and the industrial effect is immeasurable. Further, the method for producing the titanium hot-rolled sheet of the present invention is not limited to the production method of the above embodiment. [0087] For example, in the above-described embodiment, the case where the side faces 10A and 10B of the titanium flat blank 10 are slightly horizontal and is melted and solidified is described as an example, but it may be as shown in FIG. It is shown that the side faces 10A, 10B of the titanium flat blank 10 are arranged to be slightly perpendicular to the ground, and are melted and solidified. [0088] In the above-described embodiment, the case where the electron beam irradiation gun 12 is moved in the rolling direction D of the titanium flat blank 10 (the longitudinal direction of the titanium flat blank 10) is irradiated with an electron beam. For example, the electron beam may be irradiated while continuously moving in a direction orthogonal to the rolling direction D (the thickness direction of the titanium flat blank 10). [0089] In the above-described embodiment, the case where the electron beam irradiation gun 12 of one of the side faces 10A and 10B of the titanium flat blank 10 is used as a heating device and the electron beam is irradiated is described as an example, but the heating device is described. The system may be used alone or in multiple numbers, and a plurality of heating devices may be used to simultaneously heat a plurality of regions. Example [0090] Hereinafter, the present invention will be specifically described by way of examples. [0091] The titanium having the chemical compositions shown in Table 1, Table 4, and Table 7 is melted and solidified by electron beam melting (EBM) or plasma arc melting (PAM) to produce a cast rectangle. Columnar ingot, used as a titanium flat embryo (width 1000mm). Next, the side surface of the titanium flat embryo (parallel to the rolling direction and perpendicular to the surface of the surface to be rolled) was subjected to melting and resolidification treatment under various conditions. Then, finishing treatment is carried out under various conditions, and hot rolling is performed to obtain a titanium hot rolled sheet. [0092] In the above-described melt resolidification treatment, the heating systems on the side surfaces are each carried out by the method shown below. While the heating device is moved in the longitudinal direction of the titanium flat embryo, the side surface is heated continuously in a strip shape. When the heating device reaches the end portion in the longitudinal direction of the titanium flat blank, the heating device is moved by a dimension portion of 1/2 of the melting width in the thickness direction of the titanium flat blank. Then, the unheated region disposed beside the band-shaped heated region on the side surface is continuously heated in a strip shape while moving the heating device in a direction opposite to the movement in the longitudinal direction of the previous time. In this manner, the movement of the heating device toward the longitudinal direction of the titanium flat blank and the movement of the 1/2 dimension of the melt width in the thickness direction of the titanium flat embryo are repeated, and the designated area of the side surface (whole or rolled surface) is heated. One side of the side). The titanium slabs after the melt resolidification treatment are each cut at a position 200 mm from the end portion in the rolling direction (the portion at the rear end during hot rolling) in a direction orthogonal to the rolling direction. A cut surface orthogonal to the rolling direction was taken as a sample of the observation surface. The obtained sample was embedded in a resin, and the surface was observed by mechanical polishing to form a mirror surface, and etching was performed by a hydrofluoric acid solution of hydrogen fluoride, and a field of view of 30 × 30 mm was observed under a microscope. As a result, in all of the titanium flat embryos, it was confirmed that at least one of the side faces of the rolled surface side formed a fine particle structure layer composed of a structure finer than the base material structure. Further, the observation surface of each sample was polished, and the depth of the fine particle structure layer and the circular equivalent particle diameter were measured by EBSD (Electron back scattered diffraction pattern). The measurement of the circular equivalent particle diameter is regarded as a different crystal grain when the crystal orientation difference between adjacent measurement points is 5° or more, and the area A of each crystal grain is obtained, from A=p ́(L/2). ² Calculate the circle equivalent particle size L. Then, the average value of the fine grain structure layer and the circular equivalent particle diameter of any five places is calculated as the depth of the fine grain structure layer and the circle equivalent particle diameter. [0094] Next, the rolling surface of the titanium flat embryo after the melting and resolidification step is finished by a finishing treatment method (grinding processing (grinding processing) or cutting processing (milling processing)) to have a thickness of 200 to ～ 300mm. Thereafter, the surface roughness (Ra) of any five places in the rolled surface of the titanium flat blank was measured using a surface roughness meter, and the average value thereof was determined. Further, the thickness of the central portion and the end portion in the width direction of the titanium flat embryo after the finishing treatment was measured, and the flatness flatness index was obtained. Next, the obtained titanium flat slab after the finishing treatment was heated at a temperature of 820 ° C for 240 minutes, and then subjected to hot rolling including rough rolling under various conditions to produce a titanium hot rolled sheet (belt coil). [0096] The surface roughness (Ra) of the rolls was determined by the method shown below. The surface roughness (Ra) of any five places on the surface of the roll was measured using a surface roughness meter, and the average value thereof was determined. Moreover, the rolling reduction rate of the first pass of the rough rolling was calculated from the thickness of the original plate and the thickness of the first rolling after rough rolling. The roll contact arc length of the first pass of the rough rolling was calculated from the radius of the roll, the thickness of the original plate, and the thickness of the roll after the first pass of the rough rolling using the above formula (1). Next, the strip-shaped web was pickled by a continuous pickling line composed of hydrofluoric acid hydrofluoric acid, and melted on each side by about 50 μm. Then, the end portion in the width direction of the rolled surface of the strip-shaped web was subjected to visual observation of the surface flaw, and the degree of edge flaw was evaluated for the entire length of the strip roll based on the following criteria. [0098] Slight (Evaluation A): No edge defects were observed, or edge defects of less than 5 mm were observed. (Evaluation: Good) Slightly large 瑕疵 (Evaluation B): 5 mm or more, and edge defects of less than 10 mm were observed. (Evaluation: Good) Deep 瑕疵 (Evaluation C): Edge 瑕疵 of 10 mm or more was observed. (Evaluation: Defect) Table 2 and Table 3 show the manufacturing conditions and evaluation of the material for hot rolling shown in Table 1, and Table 5 and Table 6 show the manufacturing conditions and evaluation of the material for hot rolling shown in Table 4. Tables 8 and 9 show the manufacturing conditions and evaluation of the material for hot rolling shown in Table 7. [0099] [0100] [0101] [0102] [0103] [0104] [0105] [0106] [0107] [0108] In addition, in Tables 3, 6 and 9, "the surface roughness of the roll" means "the surface roughness of the roll of the first pass of the rough rolling", and the "roller radius" means the rough rolling "The radius of one roll", "Original thickness" means "the thickness of the center of the width direction of the titanium flat embryo after finishing", and "thickness after rolling" means "the first pass of rough rolling""The thickness of the center portion of the titanium flat blank in the width direction" and "roller contact arc length" means "the roll contact arc length of the first pass of the rough rolling". As shown in Tables 1 to 9, the depths of the No. 1 and 2 fine particle structure layers were insufficient, and the depth of the fine particle structure layer was less than 3 mm. The circle equivalent particle diameter of the No. 4 system fine grain structure layer was too large as 1.60 mm. No. 8 is a flatness index X in the rolled surface after finishing treatment of 4.0. No. 9 and 10 series rough rolling The first roller has a small contact arc length. As a result, No. 1 and 2, 4, and 8 to 10 deep crucibles exist in the width direction end portion of the rolled surface of the titanium hot-rolled sheet, and the quality of the titanium hot-rolled sheet is inferior. With respect to this, No. 3, 5 to 7, and 11 to 51 satisfying the conditions specified in the present invention are all "slight" or "slightly large" in the width direction end portion of the rolled surface of the titanium hot-rolled sheet. The surface properties of the titanium hot rolled sheet are good.

[0111]

10‧‧‧Titanium flat embryo

10A, 10B‧‧‧ side

10C, 10D‧‧‧ rolled noodles

10P‧‧‧ bumps on the surface of castings

10Q‧‧‧ Defects

12‧‧‧Electronic beam irradiation gun

14‧‧‧ illuminated area

16‧‧‧fused resolidified layer

18‧‧‧ Heat affected zone (HAZ layer)

20‧‧‧ Fine grain layer

24‧‧‧ Rolls

D‧‧‧Rolling direction

L‧‧‧Roll contact arc length

1 is a model diagram showing a cross section of a titanium flat embryo manufactured by an electron beam melting method or a plasma arc melting method. Fig. 2 is a view for explaining an example of a melting re-solidification step in the method for producing a titanium hot-rolled sheet according to the embodiment. Fig. 3 is a view for explaining an example of a melt resolidification step. Fig. 4 is a view for explaining an example of a melt resolidification step. Fig. 5 is a view for explaining an example of a hot rolling step in the method for producing a titanium hot-rolled sheet according to the embodiment. Fig. 6 is a view for explaining another example of the melt resolidification step in the method for producing a titanium hot rolled sheet according to the embodiment.

Claims (8)

A method for producing a titanium hot-rolled sheet, which is a method for producing a titanium sheet by hot rolling using a titanium flat embryo directly produced by an electron beam melting method or a plasma arc melting method; and comprising: the titanium flat embryo described above The surface rolled by hot rolling is regarded as the rolled surface, and the surface parallel to the rolling direction and perpendicular to the surface to be rolled is regarded as the side surface, [1] by not irradiating the above-mentioned rolled surface with a beam or a plasma. Irradiating the beam or the plasma to the side surface, and melting at least one of the side faces of the titanium slab to be re-solidified, and at least a part of the side surface, from the side The surface is at least 3.0 mm in depth to form a tissue layer having a circular equivalent particle diameter of 1.5 mm or less, and [2] finishing the previously rolled surface of the titanium flat embryo forming the organized layer. And the step of hot rolling the titanium flat embryo after the finishing treatment under the condition that X defined by the following formula (1) is 3.0 or less and [3] is L or more defined by the following (2) of 230 mm or more _{; X = (H 0, H} 1 and H ₂ of the maximum value) - (H _0, H ₁ and H ₂ is the minimum) · · (1) L = {R (H 0 -H 3)} 1/2 · · · (2) However, the above definition of the symbols in the formula as follows based; X: flat embryo flatness index H _0: the fine Thickness (mm) of the central portion in the width direction of the titanium flat embryo after the treatment H ₁ : thickness (mm) of the end portion (1/8 width position) in the width direction of the titanium flat embryo after the finishing treatment H ₂ : Thickness (mm) of the end portion (1/4 width position) in the width direction of the titanium flat embryo after finishing treatment L: Roll contact arc length (mm) of the first pass of the rough rolling R: Roll of the first pass of the rough rolling Radius (mm) H ₃ : thickness (mm) of the central portion in the width direction of the titanium flat blank on the first pass side of the rough rolling. The method for producing a titanium hot-rolled sheet according to claim 1, wherein in the step (1), the tissue layer is formed on the entire side surface. The method for producing a titanium hot-rolled sheet according to claim 1, wherein in the step (1), at a position from the rolled surface to at least 1/6 of a thickness of the titanium flat blank In the region, the aforementioned fine grain structure layer is formed. The method for producing a titanium hot-rolled sheet according to claim 3, wherein in the step (1), the side surface is at least 1/3 of the thickness of the titanium flat blank from the rolled surface In the region, the aforementioned fine grain structure layer is formed. The method for producing a titanium hot-rolled sheet according to any one of claims 1 to 4, wherein in the step (2), the surface roughness (Ra) of the surface to be rolled is 0.6 μm or more. The method for producing a titanium hot-rolled sheet according to any one of claims 1 to 5, wherein in the step (3), the radius of the roll of the first rough rolling exceeds 650 mm. The method for producing a titanium hot-rolled sheet according to any one of claims 1 to 6, wherein in the step (3), the rolling reduction of the first pass of the rough rolling is 30% or more. The method for producing a titanium hot-rolled sheet according to any one of claims 1 to 7, wherein in the step (3), the surface roughness (Ra) of the roll is 0.6 μm or more.