Manufacturing method of titanium processed material

Abstract

A manufacturing method of a titanium processed material, which is a method for manufacturing a titanium material by passing a titanium billet through the gap between a pair of rolls, wherein at least one of the rolls in the pair of rolls has a plurality of protrusions arranged in a staggered manner when the surface is developed and viewed from above, and the manufacturing method of the titanium processed material includes a step of forming a plurality of recessed portions on the surface of the titanium billet by pressing the protrusions into the surface of the titanium billet. The protrusion has a spherical pressing surface at its tip. When the height of the pressing surface is set to h (mm), the radius of curvature of the pressing surface of the protrusion is set to R (mm), the center-to-center distance between adjacent protrusions in the passing direction of the titanium billet is set to S (mm), and the pressing amount of the protrusion is set to D (mm), R is in the range of 3 to 30, D is in the range of 2 to 10 and is less than or equal to h, and S is in the range of 2(R²-(R - D)²)¹ / ² to 3(R²-(R - D)²)¹ / ². By using the titanium processed material obtained by this method, surface defects generated during hot rolling can be reduced.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a titanium processed material capable of reducing the generation of surface defects during hot rolling. Background Art

[0002] A method for manufacturing a titanium material for ordinary hot rolling is as follows, for example. First, an ingot is manufactured by melting and solidifying titanium through a consumable electrode type arc melting method (VAR: Vacuum arc remelting) or an electron beam melting method (EBR: Electron beam remelting). Next, the ingot is subjected to breakdown by hot working such as blooming, forging, and rolling to produce a hot-rolled titanium material such as a slab or a billet. In addition, in recent years, a technique has been developed to omit the above breakdown process by manufacturing a rectangular ingot capable of direct hot rolling using an electron beam melting method.

[0003] However, large ingots used industrially have coarse grains reaching several tens of mm in the solidification structure. If such an ingot is directly hot-rolled without going through the breakdown process, there is a situation where non-uniform deformation occurs due to the coarse grains, leading to the development of large surface defects. In addition, even when going through the breakdown process etc., if the working rate in the breakdown process is low or the temperature is inappropriate, there is also a situation where the casting structure remains and the structure becomes coarser instead, resulting in the generation of surface defects during hot rolling.

[0004] If surface defects are generated in this way, the yield in the subsequent descaling process becomes extremely poor, and thus there has been a continuous demand for a hot-rolled titanium material that is less likely to generate hot-rolled surface defects.

[0005] In Patent Document 1, a method is proposed in which when directly hot-working an ingot of a titanium material, in order to refine the grains near the surface layer, after applying strain to the surface layer, it is heated to a temperature above the recrystallization temperature, and after recrystallization of a portion with a depth of 2 mm or more from the surface, hot working is performed.

[0006] In addition, Patent Documents 2 and 3 describe a titanium material for hot working, in which the surface of the titanium material for hot working is plastically deformed by using a steel tool having a curvature radius of 3 mm to 30 mm at the tip or a steel ball having a radius of 3 mm to 30 mm, thereby applying strain to the surface layer portion. According to Patent Documents 2 and 3, by hot-rolling such a titanium material for hot working, the influence of the coarse solidification structure can be made harmless, and surface defects can be reduced.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 1-156456

[0010] Patent Document 2: International Publication No. 2010 / 090352

[0011] Patent Document 3: Japanese Patent Laid-Open No. 2018-1249 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] In Patent Document 1, as methods for imparting strain, forging, rolling, and shot peening can be cited. However, for ordinary shot peening, since the diameter of the shot grains is as small as 0.5 mm to 1 mm, the amount of strain applied is also small. In addition, in the case of forging and rolling, so-called dead zone metal is generated, the amount of strain becomes less or the strain is introduced to a more internal position. Therefore, there are cases where the thickness of the necessary recrystallized layer cannot be ensured and cases where grain refinement is insufficient.

[0014] In Patent Document 2 and Patent Document 3, since strain is imparted by hitting or pressing with a steel tool, in order to stably impart strain to the entire surface, it sometimes takes a long time, resulting in low efficiency. In addition, in the case of high-strength materials, there are also cases where the impact energy does not reach the inside, so that the thickness of the necessary fine-grained structure cannot be ensured. Therefore, there is room for further improvement.

[0015] The present invention has been completed in view of the above circumstances, and its object is to provide a method for efficiently manufacturing a titanium processed material capable of reducing surface defects generated during hot rolling.

[0016] Means for Solving the Problems

[0017] The gist of the present invention for solving the above problems is as follows.

[0018] A method for manufacturing a titanium processed material, which is a method for manufacturing a titanium processed material by passing a titanium billet through the gap between a pair of rolls, wherein,

[0019] at least one of the pair of rolls has a plurality of protrusions arranged in a staggered manner when the surface is developed and viewed from above,

[0020] the method for manufacturing the titanium processed material includes a step of forming a plurality of recessed portions on the surface of the titanium billet by pressing the protrusions into the surface of the titanium billet,

[0021] The protrusion has a spherical pressing surface at its tip. When the height of the pressing surface is set to h (mm), the radius of curvature of the pressing surface is set to R (mm), the center - to - center distance between adjacent protrusions in the passing direction of the titanium blank is set to S (mm), and the press - in amount of the protrusion is set to D (mm),

[0022] the R is in the range of 3 to 30,

[0023] the D is in the range of 2 to 10 and is less than or equal to h,

[0024] the S is in the range of 2(R 2 -(R - D) 2 ) 1 / 2 ~3(R 2 -(R - D) 2 ) 1 / 2 ).

[0025] Effects of the Invention

[0026] According to the present invention, a manufacturing method of a titanium processed material capable of reducing surface defects generated during hot rolling can be provided.

[0027] In addition, according to the present invention, even for a titanium blank in a casting state in which the primary rolling process of the ingot is omitted, it is possible to stably make the surface defects generated during hot rolling slight, and it is possible to efficiently provide excellent hot - rolled and cold - rolled products. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a perspective view showing an example of the shape of the titanium processed material of the present embodiment.

[0029] Figure 2 is a schematic cross - sectional view of the titanium processed material of the present embodiment.

[0030] Figure 3 of (a), Figure 3 of (b) and Figure 3 of (c) are diagrams for explaining the arrangement of the recessed portions in the present embodiment.

[0031] Figure 4 is a schematic cross - sectional view of the titanium processed material of the present embodiment.

[0032] Figure 5 is a schematic side view of the processing machine used in the manufacturing method of the titanium processed material of the present embodiment.

[0033] Figure 6 of (a), Figure 6 of (b) and Figure 6 of (c) are diagrams for explaining the arrangement of the protrusions 6 (6a, 6b, 6c) in the present embodiment.

[0034] Figure 7 of (a), Figure 7 and (b) thereof are enlarged cross-sectional views in the radial direction of the roll for explaining the shape of the protrusions 6 (6a, 6d) in the present embodiment. Detailed Embodiment

[0035] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0036] The present inventors have repeatedly and intensively studied a method for rendering harmless the influence of the coarse solidification structure of an ingot having a grain diameter of several tens of mm, and further the solidification structure remaining after primary rolling, from the viewpoint of reducing surface defects caused by hot rolling, and a titanium processed material adapted to this method, and as a result, obtained the following insights, thereby completing the present invention.

[0037] In order to refine the coarse solidification structure or to eliminate the portion where the influence of the solidification structure remains, a method is considered in which after applying a predetermined strain to the surface of a titanium billet, recrystallization is performed by a predetermined heat treatment such as heating during hot rolling.

[0038] In the present invention, a titanium billet is rolled using a roll having a predetermined protrusion, and the protrusion is pressed into the titanium billet, whereby a plurality of recessed portions (concavo-convex) are formed on the surface of the titanium billet, and strain is imparted to the surface layer of the billet. It has been found that the titanium processed material obtained by this method has a processed structure on the surface layer and can significantly suppress surface defects during hot rolling. Further, in the present invention, by pressing the protrusion into the titanium billet, the titanium billet is physically plastically deformed to form a recessed portion, whereby strain can be stably introduced, and effective and sufficient strain can be introduced to the bottom of the recessed portion. By heating during subsequent hot rolling, fine recrystallization is formed on the surface layer, whereby the generation of surface flaws can be suppressed.

[0039] Hereinafter, a method for manufacturing a titanium processed material according to the present embodiment will be described with reference to the drawings. In addition, in all the following drawings, the thickness and dimensional ratio of each component are adjusted for easy observation of the drawings.

[0040] First, a titanium processed material manufactured by the method for manufacturing a titanium processed material according to the present embodiment (hereinafter also referred to as "the titanium processed material of the present embodiment") will be described. This titanium material has a processed structure on the surface layer and is suitable as a billet for subsequent hot rolling. Further, preferably, in this titanium processed material, the radius of curvature R1 at the bottom of the recessed portion is 3 mm to 30 mm, and the recessed portions are arranged in a staggered pattern in a plan view.

[0041] In addition, for the titanium processed material of the present embodiment, preferably, when the radius of the recessed portion is set to r1 (mm), both the distance P between the centers of adjacent recessed portions and the distance Q between the columns in which the recessed portions are arranged are in the range of (2 × r1) mm to (3 × r1) mm.

[0042] In addition, preferably, the titanium billet used in the manufacturing method of the titanium processed material of the present embodiment is composed of industrial pure titanium or a titanium alloy.

[0043] Furthermore, examples of the titanium billet used in the manufacturing method of the titanium processed material of the present embodiment include ingots, slabs, blooms, or billets. Regarding the shape of the titanium billet, the diameter of the titanium billet having a circular cross-section is 100 mm to 300 mm, preferably 90 mm to 250 mm.

[0044] As described later, the titanium processed material of the present embodiment is manufactured by using a roll with protrusions and pressing the roll into the titanium billet to form recessed portions on the surface of the titanium billet, thereby imparting strain. Details of the manufacturing method will be described later.

[0045] Figure 1 An example of the titanium processed material of the present embodiment is shown. The titanium processed material of the present embodiment can be a slab 1 as shown in Figure 1 (a), a bloom 2 as shown in Figure 1 (b), a billet (rectangular billet) 3 having a rectangular cross-section perpendicular to the length direction as shown in Figure 1 (c), or a billet (circular billet) 4 having a circular cross-section perpendicular to the length direction as shown in Figure 1 (d). In addition, on the surfaces 1a, 2a, 3a, and 4a of the slab 1 in Figure 1 (a), the bloom 2 in Figure 1 (b), the rectangular billet 3 in Figure 1 (c), and the circular billet 4 in Figure 1 (d), a plurality of recessed portions 1b, 2b, 3b, and 4b are formed. In addition, although not shown, when the titanium processed material is any of the rectangular cross-sections in Figure 1 (a) to Figure 1 (c), recessed portions can also be formed on the side surfaces in the length direction.

[0046] Figure 2 Shows a schematic cross-sectional view along the A-A line in Figure 1 (a) to Figure 1 (d). In addition, when cutting along the A-A line in Figure 1 (a) to Figure 1 (d), the cross-sectional structure is in Figure 1(a) to Figure 1 The structures in (d) are the same. Therefore, for the sake of convenience in explanation, the sectional views are collectively shown in Figure 2 .

[0047] In addition, in the slab 1 or bloom 2 shown in (a) of Figure 1 or (b) of Figure 1 , the positions at the 1 / 2 depth of the thickness are the positions at 1 / 2t thickness of the slab thickness t or the bloom thickness t respectively. Further, in the billet 3 with a rectangular cross-section having an aspect ratio of about 1 shown in (c) of Figure 1 , the position at the 1 / 2 depth of the thickness is the centroid position of the billet cross-section, and in the billet 4 with a circular cross-section shown in (d) of Figure 1 , the position at the 1 / 2 depth of the thickness is the center position of the billet cross-section.

[0048] In order to stably suppress the surface defects that may be generated by hot rolling, it is necessary to refine the crystal structure of the titanium processed material. Of course, refining the crystal structure of the entire titanium processed material can also suppress surface defects, but for this purpose, a large amount of strain needs to be imparted to the entire billet. In addition, there are cases where rolling is performed in the width direction before hot rolling as needed. However, if the reduction amount in the width direction of the as-cast titanium billet becomes large, there will be a situation where wrinkles caused by the coarse casting structure are generated, and surface defects will be generated after hot rolling.

[0049] Thus, in order to stably suppress not only the surface defects caused by the casting structure but also the surface defects caused by the wrinkles during rolling in the width direction, it is necessary to make at least the surface layer into a fine recrystallized structure during hot rolling. The surface layer mentioned here refers to the region between the bottom of the recessed portion and the depth position of 3 mm. In addition, the bottom of the recessed portion is the deepest part of the recessed portion. In order to make the surface layer into a fine recrystallized structure during the heating of hot rolling, it is necessary to introduce a predetermined amount of strain from the bottom of the recessed portion to the position at a depth of 3 mm. According to the results of various investigations, the present inventors have clarified that in the region at a depth of 3 mm from the bottom of the recessed portion, if the equivalent strain is 0.2 or more, recrystallization occurs during the heating of hot rolling, forming a fine structure. The thickness of the recrystallized layer obtained in this way is 3 mm or more, and it can suppress surface defects during hot rolling. A thickness of 3 mm or more of the recrystallized layer is sufficient, and there is no particular limitation on the upper limit. However, in order to increase this thickness, it is necessary to increase the stamping load for introducing strain. Therefore, from the viewpoint of the load-bearing limit of the stamping machine, the practical upper limit of the thickness of the recrystallized layer is 25 mm.

[0050] Thus, since the titanium processed material of the present embodiment has a plurality of recessed portions formed on the surface, sufficient strain is introduced into the surface layer of the billet, and during the heating of hot rolling, fine and uniformly sized recrystallization can be formed.

[0051] Next, a preferred form of the recessed portion formed in the titanium processed material of the present embodiment will be described.

[0052] Preferably, as shown in (a) of Figure 1 to (d) of Figure 1 a plurality of recessed portions 1a to 4a are formed on the surface of the titanium processed material of the present embodiment, and the radius of curvature R1 of these recessed portions is set to 3 mm to 30 mm.

[0053] The reason for setting the bottom shape of the recessed portion to a spherical shape with a radius of curvature R1 of 3 mm to 30 mm is as follows: When a protrusion having the above-mentioned radius of curvature is pressed into the titanium blank 1 to form a recessed portion, it is not easy to form a dead zone metal portion near the bottom of the recessed portion, and the metal flow to the surroundings becomes isotropic (concentric circular). That is, by setting the bottom of the recessed portion to a spherical shape, it is easy to introduce strain into the periphery of the recessed portion. In addition, because a recessed portion is formed using a protrusion having a spherical pressing surface with a radius of curvature R of 3 mm to 30 mm at the tip, that is, a protrusion with a ball head at the tip, the shape of the recessed portion is not likely to become a steep pit where the ends of the recessed portion are laminated during hot rolling and develop into surface defects, which will be described in detail later. Therefore, preferably, the bottom shape of the recessed portion is set to a shape with a radius of curvature R1 in the range of 3 mm to 30 mm (a spherical shape corresponding to a protrusion with a ball head at the tip).

[0054] When the radius of curvature R1 of the spherical shape at the bottom of the recessed portion is less than 3 mm, it may become a steep pit that develops into a surface defect, or it may not be possible to sufficiently introduce strain in the depth direction of the surface layer of the titanium processed material, resulting in a shallow surface layer thickness where the structure is refined, and as a result, surface defects are generated. Therefore, preferably, the radius of curvature R1 at the bottom of the recessed portion is set to 3 mm or more.

[0055] On the other hand, when the radius of curvature R1 of the recessed portion exceeds 30 mm, there is a risk that the dead zone metal portion becomes large and it is not possible to impart sufficient strain to the surface layer of the titanium processed material. Therefore, preferably, the radius of curvature R1 of the recessed portion is set to 30 mm or less. In this way, by setting the radius of curvature R1 of the recessed portion to 30 mm or less, the dead zone metal portion can be made smaller, and strain can be concentrated and introduced into the surface layer of the titanium processed material to a sufficient depth.

[0056] Next, regarding the preferred arrangement of the recessed portions formed in the titanium processed material of the present embodiment, a case where a slab ( Figure 1 of (a)) is used as the type of titanium blank will be described with reference to the drawings.

[0057] Figure 3 of (a) to Figure 3Figure (c) is a diagram for explaining the arrangement of the recessed portions in the present embodiment, and is a schematic view of the recessed portions 1b, 1b', 1b'' when looking down on the titanium processed material (slab 1) shown in (a) of Figure 1 . In addition, Figure 3 In (a) to Figure 3 In (c), the reference numerals X1 to X3 indicate the arrangement columns of the recessed portions.

[0058] In addition, Figure 4 Figure is a cross-sectional view of the recessed portion for explaining the shape of the recessed portion in the present embodiment, and is a cross-sectional view taken along the line B-B in (a) of Figure 3 .

[0059] As shown in Figure 3 In (a), when looking down on the slab 1, each protrusion column X1, X2, X3 in which a plurality of recessed portions 1b are regularly arranged in one column are arranged in the width direction or the length direction of the slab 1, and the plurality of recessed portions 1b are alternately arranged in the width direction or the length direction of the slab 1 with respect to each other. That is, the recessed portions 1b are arranged in a staggered shape when looking down. The recessed portion 1b having such an arrangement is formed by a roller with protrusions having the arrangement, and by pressing the protrusions into the surface 1a of the slab 1, uniform strain can be efficiently introduced into the rolled surface of the slab 1. In addition, the arrangement direction of the protrusion columns X1, X2, X3 can be any one of the width direction and the length direction of the slab 1, and can also be a direction having a certain angle with the width direction (or the length direction). In addition, for the sake of convenience of explanation, a method with three protrusion columns is described, but the number of these columns can be appropriately determined according to the size (diameter, width, etc.) of the slab 1, the roller with protrusions used when forming the recessed portion, the size of the protrusions, etc.

[0060] In addition, the recessed portions may be arranged at a certain distance from each other as shown in Figure 3 In (a) and Figure 4 , or may be arranged such that the columns arranged in the width direction or the length direction of the slab are in contact with each other in a state where the adjacent recessed portions 1b' in the same column are separated from each other as shown in Figure 3 In (b). In addition, they may be arranged in contact with each other without gaps such that all the recessed portions 1b'' are in contact as shown in Figure 3 In (c).

[0061] Next, the distance P between the centers of adjacent recessed portions among the plurality of recessed portions arranged in the same column, and the distance between the columns (distance between recessed portion columns) Q will be described. As shown in Figure 3 In (a) to Figure 3 In (c), Figure 4As shown, the center-to-center distance P means the distance between the centers of adjacent recesses in the same column (for example, on column X1, column X2, etc.) when looking down at the recesses 1b, 1b', 1b''. In addition, the distance Q between recess columns represents the distance between the central axes of adjacent recess columns (for example, column X1 and column X2).

[0062] In the present embodiment, it is preferable that when the radius of the recess is set to r1 (mm), both the center-to-center distance P (mm) and the distance Q between recess columns (mm) are set to be not less than (2 × r1) and not more than (3 × r1).

[0063] When the center-to-center distance P and the distance Q between recess columns are smaller than (2 × r1), there is a concern that metal flow is inhibited, resulting in insufficient strain introduced around the recesses. On the other hand, when the center-to-center distance P and the distance Q between recess columns are larger than (3 × r1), the interval between adjacent recesses becomes excessively large, so the introduced strain becomes insufficient, and as a result, surface defects after hot rolling may sometimes not be sufficiently suppressed.

[0064] Above, the slab 1 of (a) exemplified Figure 1 has been used to illustrate the preferred form of the recesses in the present embodiment. In Figure 1 the bloom 2 of (b), Figure 1 the rectangular billet 3 of (c) and Figure 1 the round billet 4 of (d) also have recesses of the same form as described above.

[0065] The titanium billet in the present embodiment is a titanium ingot for hot rolling. Examples of the titanium billet include ingots, slabs, blooms, billets, etc. such as the following (A) or (B). That is, the titanium billet does not include a titanium plate that has been hot-rolled or cold-rolled to a thickness smaller than a predetermined thickness. Therefore, in the case of a cuboid or cube-shaped titanium billet, a titanium billet with a thickness of 100 mm or more is targeted, and in the case of a cylindrical titanium billet, a titanium billet with a diameter of 90 mm or more is targeted. The titanium billet (B) is composed of a solidified structure obtained by melting and casting titanium and has a cast structure with coarse grains having a grain diameter of 10 mm or more.

[0066] (A) A titanium billet obtained by further performing primary rolling on an ingot obtained by temporarily melting titanium by the consumable electrode type arc melting method (VAR: Vacuum Arc Remelting), electron beam melting method (EBR: Electron Beam Remelting), plasma arc melting method (PAM: Plasma Arc Melting), etc. and then solidifying it through hot working such as blooming, forging, and rolling to form shapes such as slabs and billets.

[0067] (B) A titanium billet is obtained as follows: when solidifying after temporarily melting titanium by electron beam melting or plasma arc melting, a rectangular ingot of a size capable of being directly hot-rolled is formed, and the primary rolling process of the above (A) is omitted.

[0068] In the electron beam melting method, since the irradiated electron beam can be focused by polarized light, heat can be easily supplied even in a narrow area between the mold and the molten titanium, so that the surface of the casting can be well controlled. In addition, the degree of freedom of the cross-sectional shape of the mold is relatively high. Therefore, preferably, a rectangular or cylindrical ingot of a size capable of being directly hot-rolled as in the above (B) is melted using an electron beam melting furnace. In addition, in the plasma arc melting method, although the heating principle is different from that of the electron beam melting method, the same effect as that of the electron beam melting method can be obtained.

[0069] Preferably, the titanium billet is composed of industrial pure titanium or a titanium alloy.

[0070] Industrial pure titanium includes industrial pure titanium specified by 1 to 4 types of JIS H4600 standard, and Grade 1 to 4 corresponding to ASTM265B standard, Grade I (WL3.7025), Grade II (WL3.7035), Grade III (WL3.7055) of DIN 17850 standard. That is, the industrial pure titanium targeted in the present invention is composed of C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% or less, Fe: 0.5% or less by mass%, and the balance is Ti. Hereinafter, "%" regarding the content of each element means "mass%".

[0071] On the other hand, for low alloys and α-type titanium alloys, the alloy can be appropriately used in necessary applications. More preferably, a low alloy with an alloy component of 5% or less is substantially preferred. For example, a highly corrosion-resistant alloy containing Pd < 0.15%, Ru < 0.10%, and also containing rare earth elements < 0.02%, a heat-resistant alloy containing a total of less than 5% of Cu, Al, Si, Sn, Nb, Fe, etc. can be exemplified.

[0072] More specifically, as low alloys, there are, for example, high corrosion-resistant alloys (ASTM Grade 7, 11, 16, 26, 13, 30, 33 or their corresponding JIS grades, alloys containing various elements in small amounts), Ti-0.5Cu, Ti-1.0Cu, Ti-1.0Cu-0.5Nb, Ti-1.0Cu-1.0Sn-0.3Si-0.25Nb, Ti-0.5Al-0.45Si, Ti-0.9Al-0.35Si, etc. In addition, as α-type titanium alloys, there are, for example, Ti-5Al-2.5Sn, Ti-6Al-2Sn-4Zr-2Mo, Ti-6Al-2.75Sn-4Zr-0.4Mo-0.45Si, etc.

[0073] As α+β-type titanium alloys, there are, for example, Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-6Al-7V, Ti-3Al-2.5V, Ti-3Al-5V, Ti-5Al-2Sn-2Zr-4Mo-4Cr, Ti-6Al-2Sn-4Zr-6Mo, Ti-1Fe-0.35O, Ti-1.5Fe-0.5O, Ti-5Al-1Fe, Ti-5Al-1Fe-0.3Si, Ti-5Al-2Fe, Ti-5Al-2Fe-0.3Si, Ti-5Al-2Fe-3Mo, Ti-4.5Al-2Fe-2V-3Mo, etc.

[0074] Furthermore, as β-type titanium alloys, there are, for example, Ti-11.5Mo-6Zr-4.5Sn, Ti-8V-3Al-6Cr-4Mo-4Zr, Ti-10V-2Fe-3Mo, Ti-13V-11Cr-3Al, Ti-15V-3Al-3Cr-3Sn, Ti-6.8Mo-4.5Fe-1.5Al, Ti-20V-4Al-1Sn, Ti-22V-4Al, etc.

[0075] For the titanium alloy of the present invention, for example, by containing one or more elements selected from O: 0% to 0.5%, N: 0% to 0.2%, C: 0% to 2.0%, Al: 0% to 8.0%, Sn: 0% to 10.0%, Zr: 0% to 20.0%, Mo: 0% to 25.0%, Ta: 0% to 5.0%, V: 0% to 30.0%, Nb: 0% to 40.0%, Si: 0% to 2.0%, Fe: 0% to 5.0%, Cr: 0% to 10.0%, Cu: 0% to 3.0%, Co: 0% to 3.0%, Ni: 0% to 2.0%, platinum group elements: 0% to 0.5%, rare earth elements: 0% to 0.5%, B: 0% to 5.0% and Mn: 0% to 10.0% in an amount exceeding 0%, it is possible to impart a target function to the surface of the titanium processed material.

[0076] Elements other than the above and capable of being contained in titanium are elements that, as general knowledge of metallic materials, can be expected to improve strength, etc. through solid solution strengthening and precipitation strengthening (including cases where they do not dissolve and cases where precipitates are formed). Examples of such elements include elements with atomic numbers from hydrogen (1) to astatine (85) (excluding noble gas elements of Group 18), and a total of up to about 5% is allowed.

[0077] The remaining part other than the above is Ti and impurities. As impurities, they can be contained within a range that does not hinder the target properties. Other impurities mainly include impurity elements mixed in from raw materials and scrap, and elements mixed in during the manufacturing process. As examples, C, N, O, Fe, H, etc. are representative elements. In addition, there are elements such as Mg, Cl, etc. mixed in from raw materials, and elements such as Si, Al, S, etc. mixed in during the manufacturing process. If the content of the above elements is about 2% or less, it can be considered within the range that does not hinder the target properties of this application.

[0078] In addition, the titanium alloy of the present invention may also contain, for example, one or more elements selected from O: 0.01% to 0.5%, N: 0.01% to 0.2%, C: 0.01% to 2.0%, Al: 0.1% to 8.0%, Sn: 0.1% to 10.0%, Zr: 0.5% to 20.0%, Mo: 0.1% to 25.0%, Ta: 0.1% to 5.0%, V: 1.0% to 30.0%, Nb: 0.1% to 40.0%, Si: 0.1% to 2.0%, Fe: 0.01% to 5.0%, Cr: 0.1% to 10.0%, Cu: 0.3% to 3.0%, Co: 0.05% to 3.0%, Ni: 0.05% to 2.0%, platinum group elements: 0.01% to 0.5%, rare earth elements: 0.001% to 0.5%, B: 0.01% to 5.0%, and Mn: 0.1% to 10.0%.

[0079] More preferably, the titanium alloy of the present invention contains one or more elements selected from O: 0.02% to 0.4%, N: 0.01% to 0.15%, C: 0.01% to 1.0%, Al: 0.2% to 6.0%, Sn: 0.15% to 5.0%, Zr: 0.5% to 10.0%, Mo: 0.2% to 20.0%, Ta: 0.1% to 3.0%, V: 2.0% to 25.0%, Nb: 0.15% to 5.0%, Si: 0.1% to 1.0%, Fe: 0.05% to 2.0%, Cr: 0.2% to 5.0%, Cu: 0.3% to 2.0%, Co: 0.05% to 2.0%, Ni: 0.1% to 1.0%, platinum group elements: 0.02% to 0.4%, rare earth elements: 0.001% to 0.3%, B: 0.1% to 5.0% and Mn: 0.2% to 8.0%. Further preferably, the titanium alloy of the present invention contains one or more elements selected from O: 0.03% to 0.3%, N: 0.01% to 0.1%, C: 0.01% to 0.5%, Al: 0.4% to 5.0%, Sn: 0.2% to 3.0%, Zr: 0.5% to 5.0%, Mo: 0.5% to 15.0%, Ta: 0.2% to 2.0%, V: 5.0% to 20.0%, Nb: 0.2% to 2.0%, Si: 0.15% to 0.8%, Fe: 0.1% to 1.0%, Cr: 0.2% to 3.0%, Cu: 0.3% to 1.5%, Co: 0.1% to 1.0%, Ni: 0.1% to 0.8%, platinum group elements: 0.03% to 0.2%, rare earth elements: 0.001% to 0.1%, B: 0.2% to 3.0% and Mn: 0.2% to 5.0%.

[0080] Here, as the platinum group elements, specifically, Ru, Rh, Pd, Os, Ir and Pt can be cited, and one or more elements among the above elements can be contained. In the case of containing two or more platinum group elements, the content of the above platinum group elements means the total amount of the platinum group elements. In addition, as the rare earth elements (REM), specifically, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu can be cited, and one or more elements among the above elements can be contained. In the case of containing two or more rare earth elements, for example, a mixture or compound of rare earth elements such as a mischmetal alloy (Mm) or a neodymium praseodymium alloy can be used. In addition, in the case of containing two or more rare earth elements, the content of the above rare earth elements means the total amount of the rare earth elements.

[0081] Next, the manufacturing method of the titanium processed material of the present embodiment will be described.

[0082] The manufacturing method of the titanium processed material of the present embodiment is a manufacturing method of a titanium processed material in which a titanium billet is passed through the gap between a pair of rolls to form a plurality of recessed portions on the surface of the titanium billet. In the manufacturing method of the titanium processed material of the present embodiment, as at least one of the pair of rolls, a roll having a plurality of protrusions arranged in a staggered manner when the surface is developed and viewed from above is used. By using such a roll having a plurality of protrusions on the surface and pressing the protrusions into the surface of the titanium billet, recessed portions are formed, and strain is imparted to the surface layer portion of the billet. Generally, when attempting to impart strain by forging, large-diameter roll forging of an ingot, etc., metal flow does not occur in the portion in contact with the die, but a portion called dead zone metal is generated. Since the amount of strain in the dead zone metal portion is small, if strain is imparted by forging or large-diameter rolls, strain is introduced not into the surface layer portion but into a portion deeper inside, and thus the structure of the surface layer portion cannot be refined.

[0083] Therefore, the present inventors studied a method of preventing the generation of dead zone metal and efficiently and uniformly imparting strain to the surface layer of the titanium billet so that no coarse grain portion is generated, and found that if the following method is used for treatment, strain can be efficiently imparted to the surface layer.

[0084] Hereinafter, the manufacturing method of the titanium processed material of the present embodiment will be described in detail.

[0085] The manufacturing method of the titanium processed material of the present embodiment is carried out under the following conditions: the protrusion has a spherical pressing surface at its tip, when the height of the pressing surface is set to h (mm), the radius of curvature of the pressing surface is set to R (mm), the center-to-center distance between the adjacent protrusions in the passing direction of the titanium billet is set to S (mm), and the penetration amount of the protrusion is set to D (mm), R is in the range of 3 to 30, D is in the range of 2 to 10 and is less than or equal to h, and S is in the range of 2(R 2 -(R-D) 2 ) 1 / 2 ~3(R 2 -(R-D) 2 ) 1 / 2 range.

[0086] Preferably, in the manufacturing method of the titanium processed material of the present embodiment, the distance L between the columns in which the protrusions are arranged is in the range of 2(R 2 -(R-D) 2 ) 1 / 2 ~3(R 2 -(R-D) 2 ) 1 / 2 range.

[0087] Further, preferably, in the method for manufacturing the titanium processed material of the present embodiment, the step of forming the recessed portion is performed at a temperature of 0°C or higher and 500°C or lower on the surface layer of the titanium billet.

[0088] Furthermore, preferably, in the method for manufacturing the titanium processed material of the present embodiment, the titanium billet before the step of forming the recessed portion is manufactured by using an electron beam melting method or a plasma arc melting method.

[0089] In addition, preferably, in the method for manufacturing the titanium processed material of the present embodiment, the titanium billet is composed of industrial pure titanium or a titanium alloy.

[0090] In addition, preferably, in the method for manufacturing the titanium processed material of the present embodiment, the titanium billet is a slab, a bloom, or a billet.

[0091] As the processing machine used in the method for manufacturing the titanium processed material of the present embodiment, a twin-roll processing machine equipped with a pair of rolls 2 will be exemplified for explanation. Figure 5 Fig. shows a schematic side view of the twin-roll processing machine. In addition, in the following description, the case where a slab ( Figure 1 (a)) is used as the type of the titanium billet, which is the object to be processed, will be exemplified. In addition, the thick arrow in the figure is the conveying direction of the titanium billet (slab) 1, and the thin arrow indicates the rotation direction of the roll 2.

[0092] As Figure 5 shown, the present embodiment is a method of performing processing while conveying the titanium billet (slab) 1 between a pair of rolls 5a. Specifically, the present embodiment is a method in which the titanium billet 1 is conveyed between a pair of rolls 5a having a plurality of protrusions 6 with a tip shape having a radius of curvature R of 3 mm to 30 mm, and at the same time, the protrusions 6 are pressed into the surface 1a of the titanium billet 1, so that the surface 1a is plastically deformed by a predetermined amount to form a recessed portion 1b on the surface 1a, thereby imparting strain to the surface layer of the titanium billet 1. In addition, in the titanium billet 1, it is sufficient to form the recessed portion 1b on the surface that will become the rolled surface at least during the hot rolling in the later process to introduce strain. That is, the formation surface of the recessed portion 1b may be only the surface of a part of the billet or the entire surface. Therefore, it is sufficient that at least one of the pair of rolls 5a is formed with the aforementioned protrusions 6.

[0093] According to this manufacturing method, it is possible to easily and efficiently manufacture a titanium processed material that can significantly suppress surface defects during hot rolling.

[0094] In addition, in the present embodiment, when conveying between the rollers 5a having protrusions 6 on the surface and forming a recessed portion 1b on the surface 1a of the titanium billet 1, the number of conveyances (the number of passes between the rollers) can be either 1 or set to two or more. That is, similar to reverse rolling, it is possible to convey once between the rollers 5a to form a recessed portion on the surface, and then set the conveyance direction of the second time to the direction opposite to that of the first time, and then convey between the rollers 5a again and press the protrusion 6 against the titanium billet. In addition, such a pressing process is not particularly limited, and the number can be determined within the range where no crack occurs in the titanium billet.

[0095] In addition, the shape of the titanium billet to be processed in the present embodiment can be Figure 1 the slab shown in (a) of Figure 1 or the bloom shown in (b) of Figure 1 or the small bloom 3 with a rectangular cross-section perpendicular to the length direction shown in (c) of Figure 1 or the small bloom 4 with a circular cross-section perpendicular to the length direction shown in (d) of

[0096] In the case where the titanium billet is a slab or a bloom, the surface with the largest area in the titanium billet becomes the surface to be rolled during hot rolling. Therefore, it is sufficient to form a recessed portion at least on this surface. In addition, in the case where the titanium billet is a small bloom, the entire surface extending along its length direction may become the surface to be rolled. Therefore, for example, in the case of a small bloom with a rectangular cross-section, it is preferable to form a recessed portion on its entire surface to introduce strain into the entire surface of the titanium billet. For example, in the case of using Figure 1 the small bloom 4 with a circular cross-section shown in (d) of

[0097] as the titanium billet, it is preferable to perform processing using cylindrical or conical rollers provided with a plurality of predetermined protrusions, such as the Mannesmann rolling method. Specifically, for example, it is preferable to introduce strain by forming a recessed portion on the surface of the small bloom using the following method: arranging a plurality of cylindrical (or conical) rollers (for example, 3 rollers) on the outer periphery of the circular small bloom 4, and causing the circular small bloom 4 to roll and rotate while advancing in the conveyance direction. Figure 5 In this way, in the present embodiment, a double-roller type processing machine shown in

[0098] is exemplified, but in the method for manufacturing a titanium billet of the present invention, regardless of the type of the processing machine, the number of rollers, etc., the Mannesmann rolling method or the like as described above can be adopted, and the number of rollers can also be 3 or more. Even in such a case, it is sufficient that the protrusion 6 of the present embodiment is formed on at least one roller.

[0098] As Figure 5As shown, a plurality of protrusions 6 are provided on the surface of the roller 5a, and the protrusions 6 have a tip shape with a radius of curvature R of 3 mm to 30 mm. In addition, the plurality of protrusions 6 are arranged in a staggered pattern when the surface of the roller 5a is developed and viewed from above.

[0099] The reason for setting the pressing surface of the tip of the protrusion 6 to a spherical shape with a radius of curvature R of 3 mm to 30 mm (i.e., a ball head) is that when the protrusion 6 is pressed into the titanium blank 1 to form the recessed portion 1b, it is not easy to form a dead metal portion near the bottom of the recessed portion 1b, and the metal flow around becomes isotropic (concentric circular). That is, because by setting the tip of the protrusion 6 to a ball head, it is easy to introduce strain to the periphery of the recessed portion 1b formed after pressing. In addition, because by setting the tip shape of the pressed protrusion 6 to a ball head, the shape of the recessed portion 1b is not likely to become a steep pit where the ends of the recessed portion 1b are stacked and developed into surface defects during hot rolling. For example, when the tip shape of the protrusion is set to a rectangle, a quadrangular pyramid, or a triangular pyramid, there must be a flat portion and angular portions with angular shapes on the protrusion. When using such protrusions to form recessed portions, a dead metal portion may sometimes be formed on the flat portion. In addition, there is a concern that due to the angular portions with angular shapes in the recessed portion, the metal flow is restricted, and the introduction of strain in the depth direction of the blank is hindered. Therefore, the pressing surface of the tip of the protrusion 6 provided on the roller 5a is a spherical shape (ball head) in the range of a radius of curvature R of 3 mm to 30 mm.

[0100] When the radius of curvature R of the spherical pressing surface (ball head) at the tip of the protrusion 6 is less than 3 mm, when the pressing amount D of the protrusion 6 is large (for example, 2 mm or more), a steep pit that develops into a surface defect will be formed. On the other hand, if the pressing amount D is reduced (for example, less than 2 mm) so as not to generate a steep pit, the strain cannot be sufficiently introduced into the depth direction of the surface layer of the blank, and the thickness of the surface layer where the structure is refined is shallow, resulting in surface defects. Therefore, the radius of curvature R is set to 3 mm or more.

[0101] On the other hand, when the radius of curvature R exceeds 30 mm, the dead metal portion becomes large, and sufficient strain cannot be imparted to the surface layer of the blank. Therefore, the radius of curvature R is set to 30 mm or less. In this way, by setting the radius of curvature R to 30 mm or less, the dead metal portion can be made smaller, and the strain can be concentrated and introduced into the surface layer of the blank to a sufficient depth. In addition, if the radius of curvature R is small, it is easily affected by the wear of the protrusion 6. Therefore, the lower limit of the radius of curvature R is preferably 5 mm. In addition, if the radius of curvature R is large, the load on the roller 5a increases. Therefore, the upper limit of the radius of curvature R is preferably 15 mm.

[0102] In the present embodiment, a roll 5a having protrusions 6 with the above-described shape is used, and by pressing the protrusions 6 into the titanium blank 1, a recessed portion 1b is formed to introduce strain. However, the pressing amount D at this time is set to be 2 mm to 10 mm and not more than the pressing surface height h (mm) of the protrusion.

[0103] In order to sufficiently suppress surface defects after hot rolling, it is effective to preliminarily refine the surface layer with a depth of 3 mm or more from the surface of the titanium workpiece before hot rolling. In the present embodiment, in order to refine the surface layer with a depth of 3 mm or more from the surface of the titanium blank, it is necessary to apply a deformation with a pressing amount of 2 mm or more from the surface of the blank. That is, the depth of the recessed portion 1b formed by pressing the protrusion 6 is set to be 2 mm or more. On the other hand, if the pressing amount D exceeds the pressing surface height h of the protrusion 6, in addition to the possibility of forming steep pits that develop into surface defects, there will be no place for metal flow. Therefore, the pressing amount D of the protrusion 6 is set to be in the range of 2 mm to 10 mm and not more than the pressing surface height h of the protrusion.

[0104] In order to introduce sufficient strain into the surface layer of the blank and refine the surface layer structure after hot rolling, the protrusion 6 is pressed with a pressing amount D of 2 mm or more. However, in order to obtain this pressing amount D, preferably, the height H of the protrusion 6 exceeds the target pressing amount D. If the height H of the protrusion 3 is too low, there is a concern that a sufficient pressing amount D cannot be ensured. From the above viewpoints, the height H of the protrusion 6 can also be set to a height exceeding the pressing surface height h of the protrusion 6 (refer to (b) described later Figure 7 ). In addition, the spherical pressing surface provided at the tip of the protrusion 6d may be a shape having a relationship of pressing surface height h = radius of curvature R, that is, a hemispherical shape, but may also be a shape having a relationship of pressing surface height h < radius of curvature R. In addition, the spherical shape means a shape that constitutes a part of a spherical surface. For example, as Figure 7 shown in (a) of Figure 7 and (b) of

[0105] Next, the arrangement of the protrusions 6 on the roll 5a will be described.

[0106] Figure 6 Figures (a) to Figure 6 Figures (c) are diagrams for explaining the arrangement of the protrusions 6 (6a, 6b, 6c) in the present embodiment, and are schematic diagrams of the protrusions 6a, 6b, 6c when the surface of the roll 5a is developed and viewed from above. In addition, Figure 6 Figures (a) to Figure 6 Figures (c) the reference numerals Y1 to Y3 respectively represent protrusion rows.

[0107] In addition, Figure 7 Figures (a) ofFigure 7 Figure (b) is an enlarged cross-sectional view in the radial direction of the roller for explaining the shape of the protrusions 6 (6a, 6d) in the present embodiment. In particular, Figure 7 Figure (a) is a cross-sectional view taken along the C-C line of Figure 6 Figure (a).

[0108] As Figure 6 shown in Figures (a) to Figure 6 Figure (c), when the surface of the roller 5a is developed and viewed from above, each row of protrusions Y1, Y2, Y3, in which a plurality of protrusions 6 (6a, 6b, 6c) are regularly arranged in one row, are arranged along the width direction or the circumferential direction of the roller 5a, and the plurality of protrusions 6 (6a, 6b, 6c) are alternately arranged along the width direction or the circumferential direction of the roller 5a. That is, the protrusions 6 are arranged in a staggered pattern when viewed from above. By pressing the protrusions 6 arranged in such an arrangement pattern into the surface 1a of the blank 1 to form the recessed portions 1b, uniform strain can be efficiently introduced into the rolled surface of the blank 1. In addition, the arrangement direction of the rows of protrusions Y1, Y2, Y3 can be either the circumferential direction or the width direction of the roller 5a, and can also be a direction having a certain angle with the circumferential direction (or the width direction). In addition, for the sake of convenience of explanation, a method with three rows of protrusions is described, but regarding the number of rows, it can also be appropriately determined according to the size (diameter, width, etc.) of the roller used, the size of the protrusions 6, etc.

[0109] In addition, the protrusions 6 can be arranged at a certain distance from each other as shown in Figure 6 Figure (a) and Figure 7 Figure (a), or can be arranged such that the adjacent protrusions 6b are separated from each other and the rows arranged in the circumferential direction or the width direction of the roller are in contact with each other as shown in Figure 6 Figure (b). In addition, they can also be arranged in contact with each other without gaps as shown in Figure 6 Figure (c) such that all the protrusions 6c are in contact.

[0110] In addition, Figure 7 Figure (b) is also an example in which the protrusions are arranged separately without contact with each other as in Figure 7 Figure (a), but as described above, for the shape of the protrusion 6d, the height H can also exceed the radius of curvature R of the protrusion 6d. In this case, the protrusion height H has a portion exceeding the radius of curvature R, that is, a portion (cylindrical portion) p perpendicular to the roller surface.

[0111] Next, the center-to-center distance S between adjacent protrusions 6 among the plurality of protrusions 6 arranged in the same row and the distance between columns (distance between rows of protrusions) L are described. As Figure 6 shown in Figures (a) to Figure 6 Figure (c), Figure 7 Figure (a),Figure 7 As shown in (b), the center-to-center distance S refers to the distance between the centers of adjacent protrusions 6 in the same column (e.g., on column Y1 or column Y2, etc.) when looking down at the protrusions 6. In addition, the inter-column distance L of the protrusions represents the distance between the central axes of adjacent protrusion columns (e.g., Y1 and Y2). In addition, the inter-column distance L of the protrusions is the distance along the rotation direction of the roll.

[0112] In the present embodiment, the protrusions 6 are arranged in such a manner that the center-to-center distance S is in the range of 2(R 2 -(R - D) 2 ) 1 / 2 to 3(R 2 -(R - D) 2 ) 1 / 2 (where R is the radius of curvature and D is the amount of indentation). That is, when the radius of the protrusion 6 when looking down is set to r, preferably, the center-to-center distance S is in the range of 2r or more and 3r or less.

[0113] When the center-to-center distance S is smaller than 2(R 2 -(R - D) 2 ) 1 / 2 (smaller than 2r), there is a concern that the amount of indentation D of the protrusion 6 cannot be sufficiently ensured, resulting in insufficient strain. Furthermore, when the center-to-center distance S is smaller than 2(R 2 -(R - D) 2 ) 1 / 2 (smaller than 2r), there is a concern that when the protrusion 6 is indented, the surrounding recessed portions become an obstacle to metal flow, restricting the space for metal flow and thus unable to impart sufficient strain. On the other hand, when the center-to-center distance S is larger than 3(R 2 -(R - D) 2 ) 1 / 2 (larger than 3r), since the interval between adjacent protrusions 6 is excessively increased, the strain introduced by the indentation of the protrusion 6 becomes insufficient, and as a result, sometimes the surface defects after hot rolling cannot be sufficiently suppressed.

[0114] In addition, even when the center-to-center distance S is 2r or more, that is, even when there is a certain degree of gap between adjacent protrusions 6, the portion indented by the protrusion 6 is accompanied by metal flow to the surrounding, so that in addition to being able to sufficiently introduce strain around the surface layer portion of the formed recessed portion 1b, strain can also be sufficiently introduced in this gap portion.

[0115] Furthermore, in the present embodiment, preferably, the distance L between the protrusion columns is set in the range of 2(R 2 -(R - D) 2 ) 1 / 2 to 3(R2 -(R - D) 2 ) 1 / 2 Within the range. That is, when the radius when looking down at the projection 6 is set as r, preferably, the distance L between the projection rows is within the range of 2r or more and 3r or less.

[0116] When the distance L between the projection rows is smaller than 2(R 2 -(R - D) 2 ) 1 / 2 (smaller than 2r), a certain amount of strain can be imparted, but there are cases where the amount of this strain is insufficient. In addition, there are concerns about an increase in the processing load and load of the roll. Therefore, preferably, the distance L between the projection rows is set to 2(R 2 -(R - D) 2 ) 1 / 2 or more. On the other hand, when the distance L between the projection rows is larger than 3(R 2 -(R - D) 2 ) 1 / 2 (larger than 3r), since the interval between adjacent projection rows increases excessively, the amount of strain introduced by the pressing-in of the projection 6 becomes insufficient, and as a result, it may sometimes not be possible to sufficiently suppress surface defects after hot rolling. Therefore, preferably, the distance L between the projection rows is set to 3(R 2 -(R - D) 2 ) 1 / 2 or less.

[0117] In the present embodiment, by using the roll 5a having the projection 6 described above, it is possible to ensure the above-mentioned pressing-in amount D and perform the processing of forming the recessed portion 1b in the blank 1.

[0118] For the processing using such a roll 5a, if the above-mentioned pressing-in amount D can be ensured, it can be performed once, but considering the capabilities and specifications of the processing machine, it can also be performed multiple times, as long as the total pressing-in amount D can be ensured to be within the above range.

[0119] In addition, in the present embodiment, as a method of processing the blank 1, compared with the method of pressing down like forging, by adopting the Figure 5 rolling method shown, the metal flow becomes easier, and there is an effect of not easily forming the above-mentioned dead zone metal.

[0120] In addition, if a roll 5a that covers the entire width of the blank 1 is used, the strain can be efficiently introduced. In addition, in the present embodiment, since the projection 6 only presses in the contacted portion, compared with pressing in the entire width of the titanium blank using a flat roll or die without projections, even a smaller load can introduce the required strain.

[0121] When forming a plurality of recessed portions on the surface of the titanium billet using the roller 5a with the protrusions 6, it can be carried out at room temperature without heating the titanium billet, or it can be carried out after heating the titanium billet to a maximum of 500 °C or less.

[0122] In the present embodiment, strain is imparted to the surface of the titanium workpiece that becomes the rolled surface at room temperature to warm rolling temperature. In order to reduce surface defects generated during hot rolling, it is necessary to form a recrystallized structure with a certain depth. Especially in the case of a high-hardness titanium billet, it is difficult for strain to enter the interior of the titanium billet. In order to impart strain to a deeper position in the surface layer, it is necessary to impart the processing of forming irregularities with a large load. However, it has been newly found that when strain is imparted, the ductility in the vicinity of the surface layer is reduced, resulting in cracks on the surface. Therefore, in order to stably impart strain to a deeper position and improve the ductility of the surface layer, it is also effective to raise the temperature to a certain extent to reduce the strength of the titanium billet itself. On the other hand, for a titanium billet with not so high strength, concentrating the strain on the surface layer can make the structure of the surface layer finer, so it is preferable to impart strain at room temperature.

[0123] On the other hand, if the processing of forming the recessed portions is carried out at a high temperature exceeding 500 °C, there is a situation where the strain imparted by the processing immediately disappears, and thus recrystallization cannot be carried out during subsequent heating. In addition, when the temperature exceeds 500 °C, an oxidation cured layer sometimes forms on the surface of the titanium billet, and there is a concern that this oxidation cured layer is pressed in during processing to generate surface defects, which develop into surface flaws during subsequent hot rolling. If it is 500 °C or less, the above problems do not occur. Therefore, it is preferable that the upper limit is 500 °C or less.

[0124] In addition, the temperature range in which the strength and ductility of the titanium billet increase varies depending on the alloy type, so it is not sufficient to perform processing at a higher temperature. For example, in the case of commercially pure titanium, near room temperature, twinning deformation, which is one of the important deformation mechanisms of titanium, actively occurs. However, at around 400°C to 500°C, this twinning deformation does not occur, so the ductility decreases compared to room temperature, and cracks are more likely to occur. On the other hand, in the case of alloys containing a large amount of Al, this twinning deformation hardly occurs even near room temperature. Therefore, by heating to below 500°C, ductility can be ensured. In addition, β-type titanium alloys have the characteristic that if heated at 300°C to 500°C for a long time, the strength increases due to age hardening, and the ductility decreases. In addition, if the titanium billet is made to be at a high temperature and the material strength is extremely weakened, there is a concern that the undulation (depth) of the shape of the recessed part on the surface becomes too large during plastic deformation, and surface defects are generated due to this undulation. Therefore, according to the variety and type of the titanium billet, it is sufficient to select a temperature range in which cracks do not occur on the surface after rolling and an appropriate recrystallized structure and surface state can be obtained.

[0125] As described above, in the manufacturing method of the present embodiment, while conveying the titanium billet between a pair of rolls having a plurality of protrusions, the protrusions are pressed into the surface of the titanium billet, whereby the titanium billet is plastically deformed by a predetermined amount to form recessed parts on the surface. As a result, strain can be efficiently and stably introduced into the surface layer of the billet. And, by heating during subsequent hot rolling, fine recrystallization is formed on the surface layer, whereby the generation of surface defects can be suppressed.

[0126] In addition, the surface defects after hot rolling can be significantly suppressed in the titanium processed material obtained by the manufacturing method of the present embodiment. By applying the present invention to rectangular or cylindrical ingots, even without performing primary rolling processes such as blooming rolling, when hot rolling plates, strip coils, or bars, the surface defects can be suppressed to a level where there are no problems.

[0127] In order to reduce the deformation resistance, the heating temperature during hot rolling of the titanium processed material of the present embodiment is preferably set in the range of 800°C to 950°C. Furthermore, in order to suppress the scale generated during slab heating, the heating temperature is preferably lower than the β transformation point. Here, the β transformation point refers to the lower limit temperature at which the titanium billet becomes a single-phase β phase as it is heated.

[0128] In this way, the titanium processed material manufactured according to the present embodiment has the following effects: not only is it suitable for hot rolling, but also the surface defects of the hot-rolled material manufactured by hot rolling are significantly suppressed. After that, even if cold rolling is performed, a sound product can be manufactured.

[0129] In addition, according to the present embodiment, even for a titanium billet in a cast state in which the blooming process of the ingot is omitted, surface defects generated during hot rolling can be made minor, and excellent hot-rolled and cold-rolled products can be provided.

[0130] In addition, when the present embodiment is applied to a titanium billet that has undergone the blooming process, surface defects generated during hot rolling are extremely minor. As a result, the descaling process of the plate and bar after hot rolling and the yield rate of the final product can be further improved.

[0131] Examples

[0132] Hereinafter, the present invention will be described in more detail by way of examples.

[0133] <Example 1>

[0134] First, titanium billets having the component compositions shown in Table 1 (commercially pure titanium) and Table 2 (titanium alloy) were cast by an electron beam melting method (EBR) or a plasma arc melting method (PAM) to form a substantially rectangular ingot having a coarse solidified structure in a cast state. In addition, for the billet symbol M9 in Table 1, the ingot was forged to obtain it. In addition, "Mm" of the alloy components of the titanium billets in Table 2 is a mischmetal alloy (an alloy containing rare earth elements).

[0135] Next, titanium billets having a thickness of about 120 mm, a width of about 250 mm, and a length of about 450 mm were cut out from the ingots other than the symbol M9 and machined. For the symbol M9, a titanium billet having a thickness of about 120 mm, a width of about 250 mm, and a length of about 450 mm was cut out from the forged billet and machined. In addition, each of the cut billets was cut out in such a manner that the positional relationship of the cut portions was consistent with respect to the ingot and the depth position from the surface of the ingot was substantially the same.

[0136] For the surface (one side) of the cut billets (M1 to M18) that becomes the rolled surface during subsequent hot rolling, a twin-roll processing machine using a roll having protrusions with the shapes and arrangements shown in Table 3A, Table 4A, and Table 5A (refer to Figure 5 ) was used to form recessed portions on the billet surface to produce titanium processed materials. The processing conditions such as the indentation amount (D) and the processing temperature were varied as shown in Table 3A, Table 4A, and Table 5A. In addition, the protrusions are arranged in a staggered pattern in the top views shown in (a) to Figure 6 of Figure 6 of (c). In addition, billet A2 was processed using a roll with a diameter of 300 mm (without protrusions).

[0137] Next, after heating the titanium processed material at a temperature below the β transformation point for about two hours, it was hot-rolled to a thickness of about 6 mm using a continuous hot strip mill. Shot peening was performed on the hot-rolled plate, and then the hot-rolled plate was pickled by passing it through a continuous pickling line composed of nitric acid - hydrofluoric acid to remove the scale. Thereafter, surface defects generated were marked by visual observation, and the generation status of the surface defects was evaluated. Here, the β transformation point refers to the lower limit temperature at which the titanium billet becomes a single-phase β phase as it is heated.

[0138] Specifically, in the hot-rolled plate after passing through the continuous pickling line, except for the unstable parts at the front and rear ends in the rolling direction, the length was divided at 200 mm intervals, and the ratio obtained by dividing the number of intervals where surface defects were detected by the total number of intervals (40 intervals) was defined as the surface defect incidence rate. Based on the surface defect incidence rate, 0% was evaluated as "◎", more than 0% and 5% or less with minute surface defects of about 1 mm were evaluated as "○", and more than 5% or larger surface defects of about 10 mm or more were evaluated as "×". In addition, "◎" and "○" are qualified, and "×" is unqualified.

[0139] Examples and comparative examples of industrial pure titanium are shown side by side in Table 3B, and examples and comparative examples of titanium alloys are shown side by side in Table 4B. The processing temperature of the rolls was room temperature in all cases.

[0140] In addition, Table 5B shows an example in which the temperature of the billet was heated to 100°C to 400°C during roll processing and concavo-convex forming processing based on the roll was performed.

[0141] As can be seen from Tables 3A to 5B, if a billet is rolled using a roll with protrusions arranged within the scope of the present invention to form recessed parts, the surface defect incidence rate is as low as 5% or less, and can be reduced to 0% within a more preferable condition range.

[0142] On the other hand, it can be seen that in comparative examples where the billet is held without processing, the roll surface has no protrusions, or the radius of curvature (R), indentation amount (D), and distance between protrusion centers (S) are outside the scope of the present invention, the surface defect incidence rate is relatively high.

[0143] In particular, in A14 and A15 where the distance between protrusion centers (S) is outside the range of 2(R 2 -(R - D) 2 ) 1 / 2 ~3(R 2 -(R - D) 2 ) 1 / 2 (the range of 2r1 to 3r1), compared with A1 where there is no processing and A2 where rolling is performed using a roll without protrusions, although the surface defect incidence rate is reduced to about 20%, it does not reach 5% or less.

[0144] In addition, as can be seen from C1 to C20 as examples, when the processing temperature is 100°C to 400°C, the same effects as those obtained at room temperature can also be obtained.

[0145] A10 and A17 as examples are examples in which pressing is performed twice using a roll having a predetermined protrusion arranged thereon, and the effects of the present invention can be obtained.

[0146] A33 as a comparative example is a case where hot rolling is performed on a billet obtained by forging an ingot of M9, and the surface flaw incidence rate is as high as 48%. In contrast, in A41 as an example, by rolling this billet using a roll having a predetermined protrusion arranged thereon, an effect of reducing the surface flaw incidence rate to 0% can be obtained.

[0147] [Table 1]

[0148] Table 1

[0149]

[0150] EBR; Electron Beam Melting

[0151] PAM; Plasma Arc Melting

[0152] [Table 2]

[0153] Table 2

[0154]

[0155] EBR; Electron Beam Melting

[0156] PAM; Plasma Arc Melting

[0157] [Table 3A]

[0158] Table 3A

[0159]

[0160] [Table 3B]

[0161] Table 3B

[0162]

[0163] [Table 4A]

[0164] Table 4A

[0165]

[0166] [Table 4B]

[0167] Table 4B

[0168]

[0169] [Table 5A]

[0170] Table 5A

[0171]

[0172] [Table 5B]

[0173] Table 5B

[0174]

[0175] Description of Reference Numerals

[0176] 1, 2, 3, 4, titanium billet (slab, bloom, billet); 1a, 2a, 3a, 4a, surface; 1b, 2b, 3b, 4b, recessed portion; 1b1, 2b1, 3b1, 4b1, bottom of the recessed portion; 5a, roller; 6, 6a, 6b, 6c, 6d, protrusion.

Claims

1. A manufacturing method of a titanium processed material, which is a manufacturing method of a titanium processed material that passes a titanium billet through the gap between a pair of rolls, wherein, at least one of the pair of rolls has a plurality of protrusions arranged in a staggered manner when the surface is developed and viewed from above, the manufacturing method of the titanium processed material includes a step of forming a plurality of recessed portions on the surface of the titanium billet by pressing the protrusions into the surface of the titanium billet, when the height of the pressing surface of the protrusion is set as h, the radius of curvature of the pressing surface is set as R, the center-to-center distance between adjacent protrusions in the passing direction of the titanium billet is set as S, and the pressing amount of the protrusion is set as D, the R is in the range of 3 to 30, the D is in the range of 2 to 10 and is not more than h, The S is within 2(R 2 -(R - D) 2 ) 1 / 2 ~ 3(R 2 -(R - D) 2 ) 1 / 2 range. the units of the h, the R, the D, and the S are mm.

2. The manufacturing method of the titanium processed material according to claim 1, wherein, when the distance between each column in which the protrusions are arranged is set as L, The L is within 2(R 2 -(R-D) 2 ) 1 / 2 ~3(R 2 -(R-D) 2 ) 1 / 2 range. the unit of the L is mm.

3. The manufacturing method of the titanium processed material according to claim 1 or 2, wherein, the step of forming the recessed portions is performed at a temperature of 0 °C or higher and 500 °C or lower on the surface of the titanium billet.

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