TWI732435B - Manufacturing method of processed titanium material - Google Patents

Abstract

In the present invention, a rolling roll with a roll diameter of 20 mm or more and 90 mm or less is used to cold-roll or warm-roll the titanium blank at a total reduction of 1.0% or more, thereby imparting strain to the surface layer of the titanium blank. According to the processed titanium material obtained by this manufacturing method, it is possible to reduce the surface defects caused by the delay of hot rolling.

Description

Manufacturing method of processed titanium material

The present invention relates to a manufacturing method of processed titanium material that can reduce surface defects during hot rolling.

Background of the invention The general manufacturing method of the titanium material for hot rolling is as follows, for example. First, use the consumable electrode type arc melting method (VAR: Vacuum Arc Remelting) or the electron beam melting method (EBR: Electron Beam Remelting) to melt and solidify the titanium, thereby manufacturing an ingot. Then, the ingot is decomposed by hot working such as block division, forging, rolling, etc., to produce titanium materials for hot rolling, such as flat billets or small blocks. In addition, in recent years, a technology has been continuously developed to omit the above-mentioned decomposition step by manufacturing a rectangular ingot that can be directly hot-rolled by the electron beam melting method.

However, large ingots used in industry have coarse crystal grains as large as several tens of mm in the solidification structure. If such an ingot is directly hot-rolled without going through the decomposition step, uneven deformation will occur due to coarse crystal grains, and may grow into larger surface defects. In addition, even in the case of a decomposition step, etc., when the processing rate is low or the temperature is inappropriate, the cast structure may remain or the structure may become coarse instead, which may cause surface defects during hot rolling.

If surface flaws occur as described above, the yield in the subsequent descaling step will become very poor, and a hot-rolled titanium material that is not prone to hot-rolled surface flaws is required.

Patent Document 1 proposes the following method: when directly hot working an ingot of titanium material, in order to refine the crystal grains near the surface layer, strain is applied to the surface layer, and then the surface layer is heated to a temperature higher than the recrystallization temperature to deepen the depth from the surface. After recrystallization of 2 mm or more, hot working is performed.

In addition, Patent Documents 2 and 3 describe a titanium material for hot rolling, which uses a steel tool with a radius of curvature of 3 to 30 mm or a steel ball with a radius of 3 to 30 mm to make the titanium material for hot rolling. Plastic deformation occurs on the surface of the material, thereby imparting strain to the surface layer. According to Patent Documents 2 and 3, it is said that by hot rolling such a titanium material for hot rolling, the influence of the coarse solidification structure can be made harmless and surface defects can be reduced.

Prior art literature Patent literature Patent Document 1: Japanese Patent Laid-Open No. 1-156456 Patent Document 2: International Publication No. 2010/090352 Patent Document 3: Japanese Patent Application Publication No. 2018-1249

Summary of the invention The problem to be solved by the invention Patent Document 1 lists forging, roll reduction (specifically, cold rolling using rolls having an outer diameter of 100 mm), and shot blast as means for imparting strain. However, the general spray bead is small because the diameter of the bead is 0.5~1mm, so the amount of strain that can be applied is also small. In addition, during forging or cold rolling using rolls with an outer diameter of 100 mm, so-called dead metal is generated, and the amount of strain near the surface layer decreases and the strain is introduced further inside. Therefore, in order to ensure the required thickness and grain refinement of the recrystallized layer, a very large amount of rolling shrinkage is required, and the cost increases or the equipment load increases, which may be difficult to implement.

In Patent Documents 2 and 3, the strain is applied by hammering or pressing with a steel tool. Therefore, it may take a long time to stably apply the strain to the entire surface, and the efficiency is low. In addition, for high-strength materials, there are cases where the impact energy cannot be transmitted to the inside and the thickness of the required fine-grained structure cannot be ensured. Therefore, there is still room for further improvement.

The present invention was made in view of the above-mentioned circumstances, and its subject is to provide a method for manufacturing a processed titanium material that can reduce surface defects caused by the hot rolling delay.

Means to solve the problem The gist of the present invention for solving the above-mentioned problems is as follows. A manufacturing method for processing titanium materials, which uses rolling rolls with a roll diameter of 20 mm or more and 90 mm or less to cold-roll or warm-roll the titanium blank at a total reduction of 1.0% or more, thereby reducing the amount of titanium The surface layer of the blank imparts strain.

Invention effect According to the present invention, even if the ingot decomposition step is omitted, and the titanium blank is still in the state after casting, the surface flaws generated during hot rolling can be reduced, and excellent hot-rolled and cold-rolled products can be provided.

The form used to implement the invention The embodiments of the present invention will be described below using drawings. Based on the viewpoint of reducing the surface defects caused by hot rolling, the inventors of the present invention aimed at a method of harmlessly making the coarse solidified structure of an ingot with a crystal grain as large as several tens of mm, and the remaining after decomposition. The method of making the influence of the solidified structure harmless has been studied repeatedly, and as a result, the following knowledge and insights have been obtained, and finally the present invention has been completed.

In order to refine the coarse solidified structure or to eliminate the parts affected by the solidified structure, a method of forming a recrystallized layer by a predetermined heat treatment such as heating with a delay in hot rolling after applying strain to the surface layer by cold working can be considered. .

In the present invention, the titanium blank is cold-rolled or warm-rolled using rolls having a roll diameter of 20 mm or more and 90 mm or less, thereby imparting strain to the surface layer of the titanium blank. And it is found that the processed titanium material obtained by this method can significantly suppress the surface defects of the hot rolling delay. By using a rolling roll with a roll diameter of 90mm or less for rolling, the strain-introduced area will not spread in the overall thickness direction of the billet, but will become concentrated on the surface layer of the processed titanium to give shear strain. Subsequent hot rolling delays heating to form a fine recrystallized layer on the surface layer, which can suppress surface defects.

Hereinafter, the manufacturing method of the processed titanium material of this embodiment is demonstrated. The processed titanium material (hereinafter also referred to as "processed titanium material of this embodiment") produced by the manufacturing method of the processed titanium material of this embodiment will be described. In the processed titanium material of this embodiment, in the thickness direction of the titanium blank, the difference ΔHV between the Vickers hardness at a position 3 mm from the bottom of the groove and the Vickers hardness at a position 1/2 of the thickness is 20 or more. The processed titanium material with a difference ΔHV of 20 or more is the following: When heat treatment is performed at 800°C for 4 hours, an equivalent circle is formed at least from the bottom of the groove to a depth of 3.0mm. The average particle size is 1.00 The standard deviation of the logarithmic conversion value of the equivalent circle diameter of the crystal grain is less than 1.00. In other words, the processed titanium material of the present embodiment can refine the surface layer structure by heating with a delay in hot rolling, so that it is possible to suppress the occurrence of surface defects during hot working. In addition, the processed titanium material of the present embodiment is preferably a smooth surface with at least a part of the surface having an arithmetic mean roughness Ra of 5.0 μm or less, and is the following: after heat treatment at 800°C for 4 hours, At least in the range from a smooth surface to a depth of 3 mm, crystal grains having an equivalent circle average grain size of 1.00 mm or less are formed, and the standard deviation of the logarithmic conversion value of the equivalent circle grain size of the crystal grains is 1.00 or less. In addition, the titanium blank used in the manufacturing method of the processed titanium material of this embodiment is preferably made of industrial pure titanium or titanium alloy. In addition, as the titanium blank used in the manufacturing method of the processed titanium material of the present embodiment, examples thereof include ingots, flat blanks, medium blocks, or small blocks. Furthermore, the smooth surface of the processed titanium material of this embodiment is preferably a surface that becomes a rolled surface that is hot rolled later.

Fig. 1 shows an example of the titanium blank used in the manufacturing method of the processed titanium material of this embodiment. Titanium blank can be flat blank 1 as shown in Figure 1(a), or medium block 2 as shown in Figure 1(b), or it can be perpendicular to the length as shown in Figure 1(c) The cross section of the direction is a rectangular small block 3, as shown in Fig. 1(d), it can also be a small block 4 with a circular cross section perpendicular to the length direction.

In the processed titanium material of this embodiment, the Vickers hardness at a depth of 3mm from the surface (the position of the line of symbol S in Figure 2) and the depth of 1/2 of the thickness (the position of the line of symbol M in Figure 2) ) The difference in Vickers hardness ΔHV is above 20. In addition, FIG. 2 is a schematic cross-sectional view along the longitudinal direction when the flat blank is used as the titanium blank used in the method of manufacturing the processed titanium material of the present embodiment.

Regarding the flat embryos or middle blocks shown in Fig. 1(a) or Fig. 1(b), the 1/2 depth position of the thickness refers to the position of the thickness t of the flat embryo or 1/2t of the thickness t of the middle block, respectively. As for the small block with a rectangular cross section with an aspect ratio of about 1 shown in Figure 1(c), it is the position of the center of gravity of the cross section of the small block. And, for the small block with a circular cross-section shown in Fig. 1(d), it is the center position of the cross-section of the small block. The thickness t of the flat embryo, the middle block and the small block, and the diameter t of the small block with a circular section should be 90~250mm.

In addition, regarding the flat blank 1 of Fig. 1(a) and the middle block 2 of Fig. 1(b), the surfaces 1a, 2a with the largest area will become the rolled surfaces with a delay in hot rolling, so these surfaces 1a, 2a It is suitable to be a smooth surface with an arithmetic average roughness Ra of 5.0 μm or less. As shown in Figure 1(c), the rectangular small block 3 with the aspect ratio of the cross-sectional shape of about 1, because the four sides 3a along the length of the small block 3 will become hot rolled delayed Therefore, a smooth surface with the arithmetic average roughness Ra of the four surfaces 3a of 5.0 μm or less is preferred. In addition, regarding the small block 4 shown in Figure 1(d) with a circular cross-sectional shape, since the circumferential surface 4a of the small block 4 along the longitudinal direction becomes the rolled surface with a delay in hot rolling, the circumference is A smooth surface having an arithmetic mean roughness Ra of the surface 4a of 5.0 μm or less is preferable. These surfaces 1a to 4a become the rolled surfaces that the rolling rolls contact in the subsequent hot rolling, and are the surfaces that are prone to surface defects. In this embodiment, it is preferable to introduce strain into the surface layers of the surfaces 1a to 4a. The strain introduction is performed by rolling rolls with a roll diameter of 20 mm or more and 90 mm or less. The surfaces 1a to 4a that are reduced by the rolling rolls become smooth surfaces that reflect the surface roughness of the rolling rolls.

To suppress surface defects that can be caused by hot rolling, it is necessary to refine the crystal structure of the processed titanium material. Refining the overall crystal structure of the processed titanium material can of course also suppress surface defects, but for this purpose, a large amount of strain must be applied to the entire blank. In addition, if strain is applied to the entire blank, the crystal grain size may increase after recrystallization, which may result in surface defects. In addition, if necessary, when rolling in the width direction before hot rolling, if the amount of rolling shrinkage in the width direction of the titanium blank in the post-casting state increases, the coarse cast structure may occur. The resulting wrinkles, resulting in surface flaws after hot rolling.

In order to stably suppress the surface flaws caused by not only the cast structure but also the wrinkles caused by the increased rolling time in the width direction as described above, it is necessary to make at least the surface layer into a recrystallized structure. The surface layer refers to the area from the surface of the processed titanium material to a depth position with a depth of 3 mm or more. In order to make the surface layer into a recrystallized structure during the heating of hot rolling, strain must be applied to a depth position of 3 mm or more from the surface. As a result of various analyses, the inventors of the present invention have clarified that as long as the equivalent strain at the 3 mm position of the surface layer is 0.2 or more, recrystallization occurs during the heating of hot rolling, resulting in a fine structure. It is also known that the equivalent strain system is related to the Vickers hardness. As long as the Vickers hardness at the depth of 3mm from the surface is greater than 20 relative to the Vickers hardness at the 1/2 thickness position of the processed titanium material, this can be achieved. The value should be above 0.2. The Vickers hardness system at the 1/2 thickness position of the processed titanium material is almost the same as the hardness after casting, so ΔHV corresponds to the increase in surface layer hardness when an equivalent strain of 0.2 or more is introduced into the surface layer. As long as the ΔHV of the processed titanium material is 20 or more, sufficient strain is introduced into the surface layer, and it becomes possible to form fine and uniform recrystallized grains. The larger the ΔHV, the better, and the upper limit is not particularly specified. However, considering the load on the rolling roll, the ΔHV can also be set to 50 or less.

The method of measuring the Vickers hardness is to cut the surface of the titanium material to which the strain is applied. After the cut section (the section perpendicular to the surface) is mirror-polished, the Vickers hardness test is used. Machine to determine. At a depth of 3 mm from the strained surface and 1/2 thickness of the processed titanium material, 7 points were measured with a load of 1 kg, and the average of 5 points after removing the maximum and minimum hardness was calculated. Then calculate the hardness difference (ΔHV) between the 3mm position from the surface and the 1/2 thickness position.

Regarding the processed titanium material of this embodiment, it is only necessary to measure the difference ΔHV between the Vickers hardness at a depth of 3mm (S) from the surface and the Vickers hardness at a depth of 1/2 of the thickness (M) to determine whether it is in It is only necessary to introduce a strained surface into the surface layer, but it can also be determined by measuring the arithmetic average roughness Ra of the surface. The titanium blank before cold rolling or warm rolling is obtained by direct casting of titanium, and conventionally, it is directly supplied to hot rolling after casting. The titanium blank obtained by direct casting has a relatively rough surface with an arithmetic average roughness Ra of 25 μm or more. On the other hand, the processed titanium material of this embodiment is cold-rolled or warm-rolled on the titanium blank, so that at least a part of its surface has a smooth surface reflecting the surface roughness of the roll surface of the rolling roll. . It can be inferred that a smooth surface having an arithmetic mean roughness Ra of 5.0 μm or less is the processed titanium material of the present invention.

In addition, the arithmetic average roughness Ra of the smooth surface is 5.0 μm or less, so that unevenness is reduced, and the risk of defects caused by unevenness can be reduced.

The processed titanium material of this embodiment simulates hot rolling, for example, after heat treatment at a temperature of 800°C for a heating time of 4 hours, at least an equivalent circle is formed from a smooth surface to a depth of 3mm. The average particle size is less than 1.00mm. The grain structure. On the other hand, the standard deviation of the logarithmic conversion value of the equivalent circle diameter of the crystal grains becomes 1.00 or less. The crystal grains formed by simulating the heat treatment of hot rolling become crystal grains with relatively uniform grain size.

The larger the crystal grains, the easier it is to produce surface defects that will occur when the processed titanium blank is hot rolled. After the processed titanium material of this embodiment is heat-treated at 800°C for 4 hours, the equivalent circle average grain size of the crystal grains from the smooth surface to the depth of 3mm is 1.00mm or less, and 0.80mm or less Preferably, it is more preferably less than 0.70 mm. Regarding the average crystal grain size after heating that simulates hot rolling, it must be finer than the cast structure with an average grain size of 10 mm or more. If it is larger than 1.00 mm and coarser, it may still be within the above standard deviation. Produce surface flaws during hot rolling. Since the smaller the equivalent circle average particle size is, the less surface defects will occur, so the lower limit of the equivalent circle average particle size is not specifically defined.

After investigation, it was found that as long as the crystal grain size after the heat treatment at 800°C for 4 hours is within the above range, surface defects will not occur in the hot rolling temperature range of the actual machine. Therefore, the range of the equivalent circle average particle diameter and the standard deviation of the crystal grains is the latter after the strain is applied to the surface layer and the heat treatment at 800° C. for 4 hours.

In addition, for example, when a mixed-grain structure in which fine-grained parts and coarse-grained parts are mixed is formed on the surface of a heated processed titanium material, crystal grains with a large particle size become the starting point and hot rolling defects are likely to occur. Therefore, after heating that simulates hot rolling, it is better if a polycrystalline structure with a relatively small grain size and less variation in grain size can be formed. The processed titanium material of this embodiment preferably has a grain structure whose standard deviation of the logarithmic conversion value of the equivalent circle diameter becomes 1.00 or less by heating at 800°C for 4 hours. When the crystal grain size of the metal material becomes a distribution close to the logarithmic normal distribution, the narrower the logarithmic normal distribution is, the more uniform the crystal grain size is, and the less likely it is to produce surface defects during hot rolling. That is, as long as the crystal grains are fine to a certain extent and the standard deviation of the logarithmic normal distribution is within a certain range or less, a uniform structure will be formed and surface defects will become less likely to occur.

If the standard deviation σ of the distribution of the converted value obtained by converting the equivalent circle diameter D of each crystal grain into the natural logarithm LnD is less than 1.00, when the equivalent circle average diameter is less than 1.00 mm, surface defects will be suppressed produce. The standard deviation is preferably 0.80 or less, more preferably 0.70 or less. The narrower the distribution of the crystal grain size, that is, the smaller the standard deviation σ, the less likely to produce surface flaws, so the lower limit of the standard deviation is not specifically defined.

The method of measuring the crystal grain size is to cut the strained surface of the titanium material by cutting, and after chemically polishing the cut cross section, the electron backscatter diffraction method (EBSD (Electron Back Scattering)) is used. Diffraction Pattern)), measure in a 5mm×5mm area with a step distance of 5-20μm, and measure a field of view of 2-10. Then, calculate the equivalent circle diameter (area A=π×(particle size D/2) ² ) for the crystal grain size based on the crystal grain area measured by EBSD, and calculate the logarithmic normal distribution standard based on the crystal grain size distribution差σ。 Difference σ.

In the processed titanium material of this embodiment, due to the shear strain applied by cold rolling or warm rolling, the surface layer is recrystallized during the heating of hot rolling, and the surface layer is recrystallized from the surface to 3 mm or more and less than 25 mm. crystallization. That is, the range in which recrystallization is formed is at least the surface to the depth of 3 mm or more, preferably the surface to the depth of 6 mm or more. In addition, the range in which recrystallization is formed is from the surface to a depth of less than 25 mm at the maximum. The processed titanium material of this embodiment becomes the above-mentioned structure state by hot rolling. If the range in which recrystallization is formed is less than 3 mm in depth from the surface, the generation of coarse surface defects of 20 mm or more cannot be suppressed. In addition, if the range in which recrystallization is formed extends from the surface to a range with a depth of 25 mm or more, strain will be dispersed, and the crystal grain size after hot rolling will become coarser, which may cause surface defects. It should be less than 20mm. In addition, the range of formation of recrystallization can be confirmed by microscope observation after performing a heat treatment equivalent to the heating of the hot-rolling delay on the cross-section of the processed titanium material that has been cold-rolled or warm-rolled.

If the processed titanium material of the present embodiment is hot rolled, the surface defects of the titanium material after hot rolling become very slight and are suppressed to the extent that there are no problems. On the other hand, if the method of the present invention is not applied and strain is not introduced into the surface layer, and the processed titanium material with the coarse solidified structure still in the as-cast state is hot rolled, a lot of lengths of 20 mm or more will be produced after the hot rolling. Coarse surface defects.

The titanium blank used in the manufacturing method of the processed titanium material of this embodiment is a hot-rolled titanium cast slab, for example, the following (A) or (B) ingots, flat blanks, medium blocks and Small pieces of material are used as titanium blanks. That is, the titanium plate system that has been rolled to a thickness smaller than a predetermined thickness by hot rolling or cold rolling is excluded from the titanium blank. Therefore, if it is a rectangular or cubic titanium blank, the thickness is, for example, 100 mm or more, and if it is a cylindrical titanium blank, the diameter is, for example, 90 mm or more. The titanium blank (B) is composed of a solidified structure obtained by melting and casting titanium, and has a structure in a state after casting with coarse crystal grains having a crystal grain size of 10 mm or more.

(A) A titanium blank, which uses electron beam melting (EBR: Electron Beam Remelting) or plasma arc melting (PAM: Plasma Arc Melting) to temporarily melt titanium and then solidify it to obtain an ingot. The ingot is decomposed by thermal processing such as block division, forging, rolling, etc., and formed into titanium blanks in the shape of flat blanks and small blocks.

(B) A titanium blank, which is obtained by omitting the decomposition step of (A) above when the titanium is temporarily melted and solidified by the electron beam melting method to form a rectangular ingot of a size that can be directly hot-rolled Titanium blank.

In the electron beam melting method, the irradiated electron beam can be concentrated by polarized light, so even if it is a narrow area between the mold and the molten titanium, it is easy to supply heat, so that the surface of the casting can be well controlled. Moreover, the degree of freedom of the cross-sectional shape of the mold is high. Therefore, it is preferable to use an electron beam melting furnace to melt a rectangular or cylindrical ingot of a size that can be directly supplied to hot rolling as described in (B). As for the plasma arc melting method, although the heating principle is different from the electron beam melting method, the same effect as the electron beam melting method can still be obtained.

The titanium blank is preferably made of industrial pure titanium or titanium alloy. Industrial pure titanium shall include the industrial pure titanium specified in the following specifications: JIS H4600 standard 1~4, and corresponding ASTM 265B standard grade (Grade) 1~4, DIN 17850 standard grade I ( WL3.7025), Class II (WL3.7035), Class III (WL3.7055). That is, the industrial pure titanium targeted in the present invention is C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% or less, and Fe: 0.5% or less in mass%, and the remainder Partly composed of Ti. Hereinafter, the "%" related to the content of each element means "mass%".

On the other hand, the α-type titanium alloy only needs to use an appropriate alloy for the desired application. Preferably, it is a low alloy having an alloy composition of 5% or less. For example, high corrosion resistance alloys, heat resistant alloys, etc. can be exemplified. The high corrosion resistance alloys are added with Pd <0.15%, Ru <0.10% and rare earth elements <0.02%, and the heat resistant alloys are added with Cu, Al, Si, Sn, Nb and Fe are added in a total of less than 5%. More specifically, as α-type titanium alloys, there are, for example, high corrosion resistance alloys (ASTM grades 7, 11, 16, 26, 13, 30, and 33, or corresponding JIS types or less containing various elements), 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, Ti- 3Al-2.5V, Ti-5Al-2.5Sn, Ti-6Al-2Sn-4Zr-2Mo, Ti-6Al-2.75Sn-4Zr-0.4Mo-0.45Si, etc.

α+β titanium alloys include, for example: Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-6Al-7V, 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-0.3 Si, Ti-5Al-2Fe-3Mo, Ti-4.5Al-2Fe-2V-3Mo, etc.

In addition, β-type titanium alloys include, 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.

The titanium alloy of the present invention, for example, by containing one or more elements selected from the following and containing more than 0%, the target function can be given to the surface of the processed titanium material: O: 0~0.5%, N: 0~0.2%, C : 0~2.0%, Al: 0~8.0%, Sn: 0~10.0%, Zr: 0~20.0%, Mo: 0~25.0%, Ta: 0~5.0%, V: 0~30.0%, Nb: 0~40.0%, Si: 0~2.0%, Fe: 0~5.0%, Cr: 0~10.0%, Cu: 0~3.0%, Co: 0~3.0%, Ni: 0~2.0%, platinum group elements ：0~0.5%, rare earth elements: 0~0.5%, B: 0~5.0% and Mn: 0~10.0%.

Among the elements other than the above, the elements that can be contained in titanium are based on the general common sense of metal materials, and the strength due to solid solution strengthening and precipitation strengthening (in the case of insolubilization and the formation of precipitates) can be expected. The element of promotion and so on. These elements can be exemplified from hydrogen (1) to marrow (85) in the atomic number (except for the inert gas elements of group 18 elements), and can be tolerated up to about 5% in total.

The remainder other than the above is Ti and impurities. Impurities can be contained within the range that does not hinder the target characteristics. Other impurities mainly include impurity elements mixed from raw materials or waste materials and elements mixed in manufacturing. For example, C, N, O, Fe, and H are representative elements There are also elements such as Mg and Cl mixed in from raw materials, or elements such as Si, Al, and S mixed in manufacturing. If the above element is less than 2%, it can be considered that it does not hinder the scope of the target characteristics of this case.

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

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

Here, the platinum group element specifically includes Ru, Rh, Pd, Os, Ir, and Pt, and one or more of these may be contained. When two or more types of platinum group elements are contained, the content of the aforementioned platinum group elements refers to the total amount of platinum group elements. In addition, the rare earth elements (REM) specifically include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and may contain these One or more of them. When two or more rare earth elements are contained, mixtures or compounds of rare earth elements such as rare earth metal alloys (Mm) and neodymium alloys can also be used. In addition, when two or more kinds of rare earth elements are contained, the content of the above rare earth elements refers to the total amount of rare earth elements.

Next, the manufacturing method of the processed titanium material of this embodiment is demonstrated. In the manufacturing method of this embodiment, the titanium blank is cold-rolled or warm-rolled using rolls having a roll diameter of 20 mm or more and 90 mm or less, thereby imparting strain to the surface layer of the titanium blank. Specifically, in the titanium blank, at least the rolling roll is brought into contact with the surface that becomes the rolled surface after hot rolling to introduce strain.

When the titanium blank is flat blank 1 or medium block 2, as shown in Figure 1, the largest area of the titanium blank surface 1a, 2a will become the rolled surface, so it is only necessary to make the rolling roll 5 contact the surface It can be cold rolled in the same way. More specifically, as shown in Fig. 3 or Fig. 4, the titanium blank (flat blank 1 or medium block 2) is passed between two rolling rolls 5 arranged at predetermined intervals, thereby performing rolling. Just extend it. Fig. 3 series titanium blank is an example of flat blank 1, and Fig. 4 series titanium blank is an example of medium block 2.

In addition, when the titanium blank is a small block, the entire surface extending in the longitudinal direction may become a rolled surface. Therefore, for example, in the case of a small block 3 with a rectangular cross-section, as shown in FIG. 5, the small blocks are passed through a pair of horizontal rolls 5a (rolling rolls) and a pair of vertical rolls arranged at predetermined intervals in sequence as shown in FIG. 5b (rolling roll), and rolling can be performed by this. In addition, if it is a small block 4 with a circular cross section, for example, as shown in FIG. 6, the small block 4 is rotated while passing through the truncated cone-shaped rolling rolls 5c arranged in three directions on the outer periphery of the small block. In between, rolling can be carried out by this.

The rolling direction of the cold rolling delay or the warm rolling delay is preferably set to be along the length direction of the titanium blank, that is, along the rolling direction of the subsequent hot rolling. The processed titanium material of this embodiment has a relatively large length L along the rolling direction of the hot rolling delay time relative to its thickness t, so it is delayed during cold rolling or warm rolling time, as shown in Fig. 3(c) or Fig. 4( As shown in c), the so-called double barreling phenomenon is prone to occur at the end faces 1b and 2b in the length direction of the titanium blank, which only extends on the surface and does not extend in the center in the thickness direction of the titanium blank. If the double barrel swelling and deformation occurs, the surface layer will be overlapped on the end face of the titanium blank in the length direction. Even if the double-barrel swelling deformation occurs on the end faces 1b, 2b in the length direction of the titanium blank, the yield reduction is still small, but if the double-barrel swelling deformation occurs on the width direction end faces, the yield will be greatly reduced. Therefore, in order to suppress the decrease in yield, it is better to roll along the length direction instead of along the width direction of the titanium blank. However, as long as the problem of productivity reduction does not occur, cold rolling may be performed using the width direction of the titanium blank.

The smaller the roll diameter of the rolling roll 5 for the delayed cold rolling, the larger the amount of shear strain introduced into the surface layer. The roll diameter of the rolling roll 5 must be 90 mm or less. By using a small diameter rolling roll 5 with a diameter of 90 mm or less to cold-roll or warm-roll the titanium blank, a sufficient depth of shear strain can be applied to the surface of the titanium blank, so that the subsequent hot rolling can be delayed. The crystal grains are sufficiently refined. If the diameter of the rolling roll 5 is greater than 90 mm, strain will be introduced into the entire thickness direction of the titanium blank, and the amount of shear strain introduced into the surface layer will be relatively small. In addition, if the roll diameter is larger than 90mm, a so-called stagnant metal area may not be plastically deformed in the vicinity of the surface layer. As a result, the amount of strain on the surface layer will become insufficient, and the grains cannot be sufficiently refined during the subsequent hot rolling delay, which may cause surface defects during the hot rolling delay. The roll diameter is preferably 80 mm or less, more preferably 70 mm or less. The lower limit of the roll diameter of the rolling roll 5 is preferably set to 20 mm or more. By making the roll diameter more than 20mm, the rigidity of the rolling roll will become large enough, and the elastic deformation of the rolling roll in the cold rolling delay or the warm rolling delay is suppressed, and it becomes possible for the cold rolling delay or the warm rolling delay time. Shear strain is uniformly introduced across the entire rolled surface.

The total rolling reduction ratio (rolling reduction) of the cold rolling delay or the warm rolling delay must be 1.0% or more. By making the total rolling reduction ratio 1.0% or more, sufficient shear strain can be introduced, and the occurrence of surface defects can be sufficiently suppressed after the hot rolling of the processed titanium material. The higher the reduction ratio is, the greater the shear strain introduced into the surface layer becomes, and the more surface flaws are suppressed. There is no need to specify the upper limit of the reduction ratio. If the reduction ratio becomes extremely large, only the surface layer in contact with the rolling roll 5 of the titanium blank will be greatly extended, and the end face shape of the titanium blank will be disordered. Therefore, the upper limit of the total reduction ratio is preferably set to 10%. In addition, the number of rolling passes for imparting strain is unlimited. It may be one time or two or more times.

If the surface roughness of the rolling roll 5 is too large, the surface properties of the processed titanium material may deteriorate. Therefore, the surface roughness Ra of the rolling roll 5 is preferably 5.0 μm or less. The surface roughness of the rolling roll 5 is preferably 0.6 μm or more in terms of arithmetic average roughness Ra, and more preferably 1.0 μm or more. If the arithmetic average roughness Ra of the surface of the rolling roll 5 is 0.6 μm or more, it becomes easier to impart strain to the surface layer due to slight irregularities generated on the surface of the roll.

When the rolling roll 5 is used to roll the titanium blank, cold rolling without heating the titanium blank can be performed, or warm rolling can be performed after the titanium blank is heated up to 500°C or lower.

In the present embodiment, it is assumed that the surface of the rolled surface that will become the processed titanium material after the hot rolling time is cold or warm is imparted with strain. In order to reduce the surface flaws that occur during the hot rolling delay, it is necessary to form a recrystallized structure to a certain depth. Particularly, in the case of a high-hardness blank, it is difficult for strain to enter the inside of the titanium blank. In order to impart strain to a deeper position in the surface layer, it is necessary to apply a large load to the rolling. However, it has recently been learned that the imparted strain causes the ductility near the surface layer to decrease, and cracks occur on the surface. Therefore, in order to stably impart strain to a deep position and increase the ductility of the surface layer, it is also effective to increase the temperature to a certain extent to lower the strength of the titanium blank itself. On the other hand, for low-strength titanium blanks, it is better to concentrate strain on the surface layer to make the surface layer structure finer, so it is better to impart strain at room temperature. That is, cold rolling is better.

On the other hand, if it is rolled at a high temperature higher than 500°C, the strain imparted by the rolling disappears on the spot, and it may become impossible to recrystallize during subsequent heating. In addition, at a temperature higher than 500°C, an oxide film may be formed on the surface of the titanium blank. The oxide film is pressed in during warm rolling to cause surface defects, which may develop into surface defects during subsequent hot rolling. As long as the temperature is below 500°C, the above-mentioned problems will not occur, so the upper limit is preferably below 500°C.

In addition, depending on the type of alloy, the temperature zone where the strength and ductility of the titanium blank become higher is different, and it is not only necessary to perform it at a higher temperature. For example, in the case of industrial pure titanium, the twin deformation of titanium, which is an important deformation mechanism, will be active around room temperature, but it will not occur at a temperature of about 400 to 500°C. The twin crystal deforms, so the ductility is lower than that at room temperature, but it becomes easy to crack. On the other hand, in Al-rich alloy systems, this twin-crystal deformation hardly occurs near room temperature, so it is impossible to ensure ductility by heating to 500°C or lower. Therefore, it is only necessary to select a temperature range that does not cause cracks on the surface after rolling and obtains an appropriate recrystallized structure and surface state.

By applying the processed titanium material of the present invention, surface defects after hot rolling are obviously suppressed. By applying the present invention to a rectangular or cylindrical ingot (still a solidified structure after casting), even if it does not undergo decomposition steps such as block rolling, it can be hot rolled into a plate, strip coil or bar wire At the same time, it still exerts the effect of suppressing surface defects to the extent that there are no problems.

The heating temperature during the hot rolling process of the titanium material of this embodiment is preferably set in the range of 800°C to 950°C to reduce deformation resistance. In addition, in order to suppress the scale produced when the flat embryo is heated, the heating temperature is preferably lower than the β transformation point.

As described above, the processed titanium material produced according to this embodiment is not only suitable for supply to hot rolling, but also the surface defects of the hot rolled material produced by hot rolling are significantly suppressed, and it can be used even if cold rolling is subsequently performed. Yan can also produce sound effects of products.

As explained above, according to the present embodiment, even if the ingot decomposition step is omitted, the titanium blank is still in the state after casting, the surface flaws generated during hot rolling can be reduced, and excellent hot rolling can be provided. , Cold rolled products.

In addition, if the present embodiment is applied to a titanium blank that has undergone a decomposition step, surface defects caused by a delay in hot rolling will be extremely reduced. As a result, it is possible to further increase the yield of the rust-removing step of the hot-rolled plate or rod wire and the final product. Example

Hereinafter, the present invention will be explained in more detail using examples.

Example 1 [Test No. 1~14 (Table 1)] The electron beam melting method (EBR) is used to cast a 1050mm wide×250mm thick×6000mm long flat blank (titanium blank). The flat blank (titanium blank) is composed of pure titanium from JIS1 to JIS4. The shape of the titanium blank after casting is as shown in Figure 1(a). The surface (corresponding to the two surfaces of the surface 1a in Fig. 1(a) and Fig. 2) that becomes the rolled surface of the titanium blank after casting is cold rolled by a pair of rolling rolls. In this way, a processed titanium material is made.

After cutting so as to include the strain-imparted surface of the processed titanium material, the cut cross section was mirror-polished, and then the Vickers hardness was measured using a Vickers hardness tester. Measure 7 points at a depth of 3mm from the strained surface and 1/2 thickness of the processed titanium material with a load of 1kg, and calculate the average of the 5 points after removing the maximum and minimum hardness, and calculate from the surface The difference in hardness between the 3mm position and the 1/2 thickness position (ΔHV).

The average equivalent circle diameter and standard deviation of the recrystallized structure of the surface layer of the processed titanium material after heating at 800°C for 4 hours are measured according to the following procedure. First, the processed titanium material before hot rolling was heat-treated under the condition of heating for 4 hours at an reaching temperature of 800°C in an Ar gas atmosphere. Next, the processed titanium material after the heat treatment is cut to include the strained surface by rolling, and the cut cross section is chemically polished, and then electron backscattered diffraction (EBSD) is used. (Electron Back Scattering Diffraction Pattern)), measured in a 5mm×5mm area with a step distance of 5-20μm and measured a field of view of about 2-10. Then, for the crystal grain size, the equivalent circle diameter is calculated based on the grain area measured by EBSD (area A=π×(particle size D/2) ² ), and the logarithmic normal distribution is calculated based on the crystal grain size distribution The standard deviation σ.

Next, after inserting the processed titanium material into a furnace at 820°C, heating for about 240 minutes, and using a continuous lath hot rolling mill to produce a 5mm thick hot-rolled sheet, it is wound into a coil. Next, bead spraying is performed on the hot-rolled sheet, and it passes through a continuous pickling production line composed of nitric-hydrofluoric acid to dissolve about 50 μm per single side. Then, the two rolled surfaces were visually observed to evaluate the occurrence of surface defects.

Regarding the evaluation of surface flaws, in the rolled surface of the hot-rolled sheet after passing through the continuous pickling line, if the number of surface flaws of 10 mm or ^{more exceeds 0.3 per 1 m 2, it} is judged as unacceptable (evaluation D), 0.3 The following are evaluated as qualified (evaluation A~C). When the number of surface flaws per 1 m ² is 0.05 or less, it is evaluated as evaluation A, more than 0.05 and less than 0.2 are evaluated as evaluation B, and more than 0.2 and less than 0.3 are evaluated as evaluation C. In addition, as an observation field of surface flaws, it is desirable to investigate the rolled surface of the entire hot-rolled sheet, but it is also possible to randomly select a surface of 100 m ² or more of the rolled surface for investigation. As for the method of evaluating the surface defects of hot-rolled round bars, etc., it is only necessary to perform the method according to the above-mentioned method of evaluating the surface defects of the hot-rolled sheet. The results are shown in Table 1. In addition, FIG. 7 shows the crystal grain size distribution after logarithm conversion of No. 8 (Example) as an example. The vertical axis is relative to the probability of occurrence of all crystal grains measured.

The comparative example of No. 1 did not roll the surface of the flat blank which was still in the state after casting, and directly hot rolled it. Therefore, the surface of the hot-rolled sheet after hot rolling and pickling has many large surface defects.

No. 2 and 3 series of comparative examples. After cutting and finishing the flat blank surface which was still in the state after casting, cold rolling was performed. The roll diameters of No. 2 and 3 are large, and the total rolling shrinkage is small. Therefore, the amount of strain in the surface layer is insufficient, and the surface of the hot-rolled sheet after hot rolling and pickling has many defects.

No. 4 to 14 are the examples, the roll diameter and the total rolling reduction meet the scope of the present invention, and the amount of surface strain is sufficient, and the surface properties of the hot rolled sheet after hot rolling and pickling are good.

[Table 1]

Example 2 [Test No. 15-18 (Table 2)] The plasma arc melting method (PAM) is used to cast JIS1 type and ASTM2~4 pure titanium flat blanks (titanium blanks) of 1050mm wide × 250mm thick × 5500mm long. The shape of the titanium blank after casting is as shown in Figure 1(a). For the surface of the titanium blank after casting that becomes the rolled surface (equivalent to the surface 1a of Figure 1 (a) and Figure 2) that becomes the delayed hot rolling surface, use a pair of rolling rolls as shown in Figure 3 Cold rolled, thereby making processed titanium material.

Next, after inserting the processed titanium material into a furnace at 820°C, heating for about 240 minutes, and using a continuous lath hot rolling mill to produce a 5mm thick hot-rolled sheet, it is wound into a coil. Next, the hot-rolled sheet was sprayed with beads, and passed through a continuous pickling line composed of nitric acid-hydrofluoric acid, so as to dissolve and shave about 50 μm per single side. Then, the two rolled surfaces were visually observed to evaluate the occurrence of surface defects.

As shown in Table 2, No. 15 to 18 series of examples, the roll diameter and the total rolling reduction meet the scope of the present invention, and the amount of surface strain is sufficient. The surface of the hot-rolled sheet after hot rolling and pickling Good traits.

[Table 2]

Example 3 [Test Nos. 19-27 (Table 3)] Use electron beam melting method (EBR) or plasma arc melting method (PAM) to cast a titanium alloy flat blank of 1050mm wide×250mm thick×5000mm long. The shape of the titanium blank after casting is as shown in Figure 1(a). For the surface of the titanium blank after casting that becomes the rolled surface (equivalent to the surface 1a of Figure 1 (a) and Figure 2) that becomes the delayed hot rolling surface, use a pair of rolling rolls as shown in Figure 3 Cold rolled, thereby making processed titanium material.

Next, after inserting the processed titanium material into a furnace at 820°C, heating for about 240 minutes, and using a continuous lath hot rolling mill to produce a 5mm thick hot-rolled sheet, it is wound into a coil. Next, the hot-rolled sheet was sprayed with beads, and passed through a continuous pickling line composed of nitric acid-hydrofluoric acid, so as to dissolve and shave about 50 μm per single side. Then, the two rolled surfaces were visually observed to evaluate the occurrence of surface defects.

As shown in Table 3, No.19~27 are examples. The roll diameter and total reduction of the rolls meet the scope of the present invention, and the amount of surface strain is sufficient. The surface of the hot-rolled sheet after hot rolling and pickling Good surface properties. In addition, in the alloy composition of the titanium blank in Table 3, "Mm" is a rare earth metal alloy (alloy containing rare earth elements).

[table 3]

Example 4 [Test No. 28~37 (Table 4)] Use electron beam melting method (EBR) or plasma arc melting method (PAM) to cast flat blanks (titanium blanks) with a width of 1050mm×250mm×5000mm in length. The flat blanks (titanium blanks) are from JIS 1~4 It is made of pure titanium or titanium alloy. The shape of the titanium blank after casting is as shown in Figure 1(a). For the surface of the titanium blank after casting that becomes the rolled surface (corresponding to the two surfaces of the surface 1a in FIG. 2) that becomes the hot rolling delay time, the pair of rolling rolls shown in FIG. 3 are used for warm rolling, thereby Made of processed titanium. The heating temperature of the titanium blank after warm rolling is shown in Table 4.

Next, after inserting the processed titanium material into a furnace at 820°C, heating for about 240 minutes, and using a continuous lath hot rolling mill to produce a 5mm thick hot-rolled sheet, it is wound into a coil. Next, the hot-rolled sheet was sprayed with beads, and passed through a continuous pickling line composed of nitric acid-hydrofluoric acid, so as to dissolve and shave about 50 μm per single side. Then, the two rolled surfaces were visually observed to evaluate the occurrence of surface defects.

As shown in Table 4, Nos. 28 to 37 are examples. The roll diameters and total reduction of the rolls meet the scope of the present invention, and the amount of surface strain is sufficient. The surface of the hot-rolled sheet after hot rolling and pickling Good surface properties.

[Table 4]

Example 5 [Test No. 38~40 (Table 5)] Use electron beam melting method (EBR) to cast 400mm wide × 400mm thick × 5500mm long titanium block, 200mm wide × 200mm thick × 5500mm long titanium small block (square small block) and 200mm diameter × 5500mm long Titanium small block (round small block), the titanium medium block is composed of JIS2 pure titanium, and the titanium small block (square small block) is composed of JIS2 pure titanium and its cross-section is rectangular, The small titanium block (round small block) is composed of JIS2 pure titanium and has a circular cross section. The shape of the titanium blank after casting is shown in Fig. 1(b), Fig. 1(c) and Fig. 1(d) respectively. For the surface of the titanium blank after casting that becomes the rolled surface with a hot rolling delay (corresponding to the surface of Figure 1 (b), Figure 1 (c) and Figure 1 (d) and the surface of Figure 2 surface 2a~4a) , Respectively, using the rolling rolls shown in Figure 4, Figure 5 and Figure 6 to perform cold rolling, thereby making processed titanium materials.

Next, after inserting the processed titanium material into a furnace at 820°C, heating for about 240 minutes, and using a continuous hot rolling mill to produce a hot-rolled round bar with a diameter of 10 mm, it is wound into a coil. Next, the hot-rolled round bar was sprayed and immersed in a nitric acid-hydrofluoric acid bath to melt and shave the surface by about 50 μm. Then, the rolled surface was visually observed, and the condition of the occurrence of surface defects was evaluated.

As shown in Table 5, No.38~40 are examples. The roll diameter and total rolling shrinkage meet the scope of the present invention, and the amount of surface strain is sufficient. The surface of the hot-rolled round bar after hot rolling and pickling The surface properties are good.

[table 5]

1: Flat embryo 2: Medium block 3,4: small pieces 5: Rolling roll 1a, 2a, 3a, 4a: surface 1b, 2b: the end face in the length direction 5a: Horizontal roller 5b: upright roll 5c: truncated cone type rolling roll L: length M: 1/2 depth position of thickness S: 3mm depth position from the surface t: thickness (diameter)

Fig. 1 is a perspective view showing an example of the shape of a titanium blank according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view of a processed titanium material according to an embodiment of the present invention. Fig. 3 is a diagram illustrating a method of manufacturing a processed titanium material according to an embodiment of the present invention, (a) is a schematic plan view, (b) is a schematic side view, and (c) is a side view illustrating the shape of the processed titanium material after rolling Schematic. Fig. 4 is a diagram illustrating a method of manufacturing a processed titanium material according to an embodiment of the present invention, (a) is a schematic plan view, (b) is a schematic side view, and (c) is a side view illustrating the shape of the processed titanium material after rolling Schematic. Fig. 5 is a diagram illustrating a method of manufacturing a processed titanium material according to an embodiment of the present invention, (a) is a schematic plan view, (b) is a schematic side view, and (c) is a schematic front view. Fig. 6 is a diagram illustrating a method of manufacturing a processed titanium material according to an embodiment of the present invention, (a) is a schematic plan view, and (b) is a schematic front view. Fig. 7 is a graph showing the grain size distribution of No. 8 (Example) after logarithmic conversion.

1: Flat embryo

1a: surface

1b: The end face in the length direction

5: Rolling roll

L: length

t: thickness (diameter)

Claims (3)

A manufacturing method for processing titanium materials, which uses rolling rolls with a roll diameter of 20 mm or more and 90 mm or less, and cold rolling or warm rolling of the titanium blank with a total reduction of 1.0% or more and 10% or less, This imparts strain to the surface layer of the titanium blank. The method for manufacturing a processed titanium material according to claim 1, wherein the arithmetic average roughness Ra of the surface of the aforementioned rolling roll is 5.0 μm or less. The method for manufacturing a processed titanium material of claim 1 or 2, wherein the aforementioned titanium blank is a titanium cast piece.

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