JP2000045067A - High purity titanium sheet for titanium target material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a target material dense in a sheet face metallic structure, also uniform in a macro-structure, and capable of forming a titanium-adhered film uniform in film thickness and orientation properties by sputtering by allowing it to have a cold-worked structure and moreover specifying the area ratio of mechanical twin crystals in the optional L cross-section. SOLUTION: A high purity titanium material is hot-rolled, is annealed in the air at need and is thereafter cold-rolled while scale is kept adhered on the surface. At this time, while the revolution speed Rc of a rolling roll is controlled to the range shown by the inequality of Rc<=1.59172-2.2541×106/ D4+4.21766×105/D3-2.54285×104/D2+7.89452×102/D, it is cold-rolled at a draft of >=6%. In this way, a cold rolled sheet having a cold-worked structure, and in which the area ratio of mechanical twin crystals in the total sheet thickness cross-section in the optional L cross-section is >=25% is obtd., and it is moreover subjected to annealing at need to obtain a cold rolled and annealed sheet having a recrystalized structure, and in which the area ratio of the colony structure in the optional face parallel to the sheet face is <10%, and a high purity titanium sheet for a titanium target material is obtd therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity titanium having a dense metal structure on a plate surface and a uniform macro pattern for a titanium target material used for manufacturing a semiconductor device or a display element such as a liquid crystal. The present invention relates to a plate and a method for manufacturing the plate.

[0002]

2. Description of the Related Art Very Large Scale (VLSI)
With the rapid increase in integration of display elements such as integrated circuits and liquid crystals, the commercialization of high-purity titanium, which is a metal with a high melting point and low resistance, as a gate electrode material, diffusion barrier material, wiring material, etc. is being promoted. I have. These titanium materials as electronic materials are mainly formed by sputtering.
For this reason, the demand for a high-purity titanium material for a sputtering target material is rapidly increasing. The purity of titanium materials used for these electronic materials is very important, and high purity is required. For example, Fe, N
Impurity metal elements such as i and Cu cause an increase in leakage current of the semiconductor element, and radioactive elements such as U and Th cause soft errors. Therefore, the incorporation of these elements is severely restricted.

[0003] Such a high-purity titanium material is usually produced by the following steps. First, using a high-purity sponge titanium by a Mg reduction method (Kroll method) or a high-purity titanium precipitate obtained by an iodide method or a molten salt electrolytic purification method as a raw material, a vacuum arc melting furnace (VAR) or an electron beam melting method is used. After melting in an oven (EBR) and evaporating and removing alkali metals having a high vapor pressure, an ingot is obtained.

[0004] The ingot is subjected to various processes according to the shape of the final product. That is, a method of hot rolling an ingot to form a billet, a bar, a plate, a wire, or the like (see JP-A-63-212061), and a method of forging and rolling the ingot to form a shape (Japanese Patent Laid-Open No. JP-A-8-23206, JP-A-5-255842
Is known. Further, in order to prevent contamination (eg, oxidation and absorption of impurity gas components) during processing, there is a method of processing into a predetermined shape by cold working at a temperature near room temperature (see Japanese Patent Application Laid-Open No. 3-130339). ).

[0005] In the cold rolling of titanium, since the titanium and the roll surface are liable to cause seizure, the rolling roll diameter Y is related to the crystal grain size D of the cold rolled material.
Is known so as to be equal to or less than a value obtained from one empirical formula (see Japanese Patent Publication No. 63-48602). According to this technique, it is possible to prevent the occurrence of oil pits due to the fluid characteristics of the lubricating oil existing between the surface of the descaled titanium material and the rolling roll. According to this empirical formula, the roll diameter Y must be selected so as to be substantially inversely proportional to the crystal grain diameter D, that is, as the crystal grain diameter D of the cold-rolled material increases. On the other hand, as another manufacturing method of high-purity titanium material,
After enclosing the above high purity titanium precipitate in a compression container,
There is also a method in which a desired shape is directly obtained by heating and processing with an IP (hot isostatic processing apparatus) (see Japanese Patent Application Laid-Open No. 8-277427).

[0006]

However, the above prior art mainly focuses on the technical focus of processing a high-purity raw material into a shape close to a desired shape as a target material without deteriorating its purity. Therefore, technical innovation is intense, and the required quality level for the target material is increasing. In the VLSI field, there is a case in which the required quality cannot be sufficiently satisfied. The reasons why the required quality of the target material cannot be achieved include, for example, the effects of remaining rolled structure, mixture of coarse crystal grains, non-uniform crystal grain size distribution, presence of unfavorable texture, variation of texture, and the like. However, the actual situation has not been fully examined.

By the way, raw materials for producing high-purity titanium materials, that is, ingots produced by melting, slabs and billets subjected to rough working, and the like are further forged, rolled, and so on.
When a heat-treated or the like is formed into an expanded material, the macrostructure of the original material is inherited even after the processing step, and the metal structure pattern that can be visually recognized even when processed into the expanded material (hereinafter, referred to as a macro pattern) ) Is usually present. This macro pattern is also considered to be one of the causes that the required quality of the target material as described above cannot be achieved. In addition, the existence of the macro pattern is often overlooked by observation with an optical microscope or the like, and it has not been quantitatively sufficiently grasped conventionally.

Here, the difference between the macro structure and the macro pattern will be described. Usually, the macrostructure in metallography is
It can be obtained by etching using an acid solution (for example, nitric hydrofluoric acid) suitable for revealing a metallographic structure used for developing a cast structure or a processed structure. In the case of a cast or processed structure, the corrosive action of the acid solution causes the metal flow to concentrate processing strains, a grain boundary with a high lattice defect density, a boundary between colonies and a region with almost uniform crystal orientation called a colony, etc. Is preferentially eroded and is visually recognized as a pattern.

On the other hand, the macro pattern means that relatively coarse crystal grains present in the raw material, that is, the ingot or a material obtained by partially processing the ingot, and the colonies contained in the raw material are plastically deformed during the expansion processing. A remnant of changes in shape, size, and their distribution in response to deformation and heat history, refers to those that are recognized as trace patterns when the plate surface of wrought material is polished and macro-etched. In many cases, this macro pattern has an indistinct boundary and is difficult to correspond to a clear metallographic feature as in the macro structure described above.
The inside of the macro pattern contains a microstructure observed with a normal optical microscope, and when observed in a limited narrow area, the microstructure may seem uniform at first glance, but most of this microstructure is Since it inherits the crystallographic orientation of its ancestor macrostructure, a clear macro pattern will be observed at the macroscopic level.

The present inventors have studied the effect of the macro pattern on the quality of the target material. That is,
When sputtering is performed using a target material manufactured from a rolled product having such a non-uniform macro pattern, the distribution of the sputtered particles in the direction of discharge, the distribution of the release rate, and the distribution of the released energy are affected by the crystallographic orientation of the macro pattern. Therefore, it was considered that there was a difference in the speed at which sputtered particles adhere to the substrate, causing problems of nonuniformity of the deposited film thickness and nonuniformity of orientation.

Therefore, the surface of the target material is required to have a uniform macro pattern. In addition, since the surface of the target material becomes rough during use, it is polished and leveled and used continuously, so the titanium material for the target material has not only uniformity in the plate surface but also in the thickness direction. Is also required. Further, the present inventors have separately studied that, in the prior art described in JP-B-63-48602, if the rolling roll diameter is too small with respect to the crystal grain size, the shearing deformation during rolling is concentrated near the surface. Therefore, it has been found that a new problem of breaking at the crystal grain boundary is caused.

Accordingly, an object of the present invention is to provide a semiconductor device or a display element such as a liquid crystal or the like, which has a dense metal structure on a plate surface so that the thickness and orientation of a titanium adhesion film formed by sputtering are uniform. An object of the present invention is to provide a high-purity titanium plate for a titanium target material having a uniform macro pattern and a method for producing the same.

[0013]

SUMMARY OF THE INVENTION The present inventors have found that in the titanium target material, if the macro pattern is non-uniform, the non-uniformity of the film thickness formed by the sputtering method and the non-uniformity of the orientation are caused. As a result of intensive research, the inventor of the present invention has invented a titanium plate for a target material which can be sufficiently used for VLSI and can be industrially manufactured, and a method for manufacturing the same.

That is, the first invention titanium plate of the present invention for solving the above-mentioned problems has a cold worked structure,
A high-purity titanium plate for a titanium target material, wherein a mechanical twin area ratio of a cross section of the entire plate thickness is 25% or more. The second invention titanium plate is a high-purity titanium plate for a titanium target material, wherein the titanium plate has a recrystallized structure and an area ratio of a colony structure on an arbitrary surface parallel to the plate surface is less than 10%.

Next, a first invention method of the present invention for solving the above-mentioned problems is to provide a rolling roll rotation speed Rc (r) during cold rolling.
ps) is controlled in accordance with the roll diameter D (mm) to a range represented by the formula (1), and a cold-rolled structure with a draft of 6% or more is formed to form a cold-worked structure. A method for producing a high-purity titanium plate for a titanium target material, wherein the cold-rolled plate has a mechanical twin area ratio of 25% or more in the entire cross-section in the L cross section.

Rc ≦ 1.59172 −2.2541 × 10 ⁶ / D ⁴ + 4.21766 × 10 ⁵ / D ³ −2.54285 × 10 ⁴ / D ² + 7.89452 × 10 ² / D (1)

[0017] It is preferable to perform cold rolling with the scale formed during hot working attached to the surface. In addition, after the scale generated during hot working is attached to the surface and then annealed in the air, cold rolling can be performed with the scale remaining, and the scale generated during hot working can be applied to the surface. After being annealed in a vacuum creep straightening machine while being attached, cold rolling can be performed with the scale remaining. Further, the cold-rolled material from which the surface scale has been removed is subjected to a diameter D according to the crystal grain size d (μm) of the material.
Cold rolling can also be performed with a rolling roll whose (mm) satisfies the relationship of the expression (2).

D ≧ 1.033 d ^0.504 (2)

In the second invention method, the titanium plate obtained by the first invention method is annealed in the air or in a vacuum creep straightening machine to form a recrystallized structure and to have an arbitrary surface parallel to the plate surface. A cold-rolled annealed sheet having an area ratio of a colony structure of less than 10% in the above-mentioned method, which is a method for producing a high-purity titanium sheet for a titanium target material.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is basically constructed on the premise of the following manufacturing steps. Normally, high-purity titanium wrought products are manufactured by melting a high-purity raw material in a vacuum arc melting furnace (VAR) or an electron beam remelting furnace (EBR), and then casting it into a cylindrical ingot in a metal state or a rectangular cross-section ingot. . Due to its shape, VAR ingots are rarely used directly as a material for sheet rolling, etc., and the special shape of a forging machine, a large press machine or a slab rolling mill reduces the shape of the cylinder into a flat rectangular cross section. Slabs are often formed. The EBR ingot is an ingot having a columnar or rectangular cross section, and is also formed into a rectangular cross section slab which can be easily operated by a plate rolling mill in a later process by using a forging machine or a slab rolling mill.

These wrought forged slabs and wrought rolled slabs are further hot-worked to a predetermined thickness and, if necessary, are annealed for the purpose of removing strain and adjusting the microstructure.
Material for cold working. This material is cold-worked to obtain the titanium plate of the first invention, and further annealed to obtain the titanium plate of the second invention. In order to obtain a target material, the titanium plate of the present invention is further cut and ground to a finished size to obtain a product.

In the high purity titanium plate for a titanium target material of the present invention, high purity titanium has a purity of 4N (99.9).
9%) or more. At this time, O, N, and H of the gas components are not counted in the purity display. With this purity, when a sputtering target is used, there is no problem caused by impurities such as leak current in the manufactured VLSI.

The titanium plate according to the first invention is a cold-worked plate, has a cold-worked structure, and has a mechanical twin area ratio of 25% or more in an entire L-thick section in any L section. As the cold working, any plastic working method such as forging, drawing, repeated bending, and tension may be employed in addition to rolling. Here, the L section is a plane perpendicular to the plate surface and parallel to the stretching direction of the structure, that is, in the case of a rolled plate, a plane parallel to the rolling direction.

The material for cold working is a material that has been subjected to hot working such as rolling, or has been further annealed. Mechanical twinning is generated by cold working to divide the macro pattern. If the mechanical twin area ratio is 25% or more in the entire thickness section in an arbitrary L section, when sputtering is performed using a target manufactured from the titanium plate, a gate electrode material to be formed, Diffusion barrier material,
A titanium film such as a wiring material has a uniform thickness and orientation, and is used for manufacturing a semiconductor device or a display element such as a liquid crystal, and can be sufficiently used for a VLSI. Then, there is no problem even if the target surface is roughened and polished and leveled and used repeatedly. Moreover, such a first invention titanium plate can be manufactured industrially stably.

The second invention titanium plate is a plate annealed after cold working, has a recrystallized structure, and has an area ratio of colony structure on an arbitrary surface parallel to the plate surface of less than 10%. Here, the area ratio of the colony tissue was defined based on the following technical concept. Although the inside of the macro pattern contains the microstructure observed with a normal optical microscope, the macro pattern has an indistinct boundary, and it is difficult to correspond to a clear metallographic feature as in the macro structure described above. Often. In the present invention, the nonuniform distribution of the crystal orientation on the plate surface was quantitatively evaluated by a judgment method utilizing the color etching method described below.

ASM published Metal Progress March 1985 issue
George F. Vander Voort, p. 31, `` Tint Etchi
Table 1 of the commentary on “ng” introduces color etching methods for titanium and titanium alloys. In this paper, the etching solution of Weck (5 g NH ₄ FHF + 100
mL ・ water or 3g ・ NH ₄ FHF + 4mL ・ HC
(L + 100 mL water), it is described that crystal grains can be colored depending on the crystal orientation when observed with a polarizing microscope.

First, five samples for microscope observation (25 mm in width × 50 mm in length × thickness) were sampled from a plate material to be determined, and a normal microstructure was obtained for a plane parallel to the plate surface at the center of the plate thickness. Is mirror-polished to the same degree as observed with a microscope, and the above-mentioned etching solution of Weck (5 g · NH ₄ FHF + 1) is used.
(00 mL water). Use a Nomarski-type polarizing microscope to increase the distribution of the colored crystal grains by a factor of 25 (10x for the ocular lens, no objective lens without filter)
(2.5x) with a color film (ISO100) and finished in A4 paper size color photo at final magnification of 34x. Imaging was performed in three fields of view for each sample.

When observing a macro pattern that can be identified by the naked eye with a microscope, the magnification should be about 25 times as described above. (1) Correspondence with the macro pattern, (2) Differentiation of each crystal grain, (3) Crystal It was optimal for discriminating the color difference for each grain. A color photograph obtained by photographing all or a part of the macro pattern portion was taken into a computer using a color scanner, and the color of each crystal grain was determined using image analysis software for metallographic structure. The determination of the object color data depends on the color scanner used.

X from tristimulus values R, G, B in the RGB color system
The tristimulus values of the YZ color system are converted into X, Y, and Z, and
The object color data L ^* , a ^* , b ^* of the L ^* a ^* b ^* color system is obtained by the method specified in SZ 8729, or the object color data L ^* , a ^* , b ^* data is obtained directly. In the present invention, the data obtained by both methods were used without distinction. As a result, the typical crystal orientation of the crystal grains could be measured as the object color (finished in a photograph) of the crystal grains colored by color etching.

In a material in which the macro pattern cannot be discriminated at all with the naked eye, the distribution of colors corresponding to individual crystal grains was random, but in a material in which the macro pattern could be clearly discriminated, crystal grains of similar colors were colonized as a group. It turned out that it was distributed in the shape. As an index of the randomness of the color distribution of each crystal grain, in the present invention, the color difference between the object colors of the individual crystal grains is calculated according to JIS Z8.
730 color difference display method ΔE ^* ab = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δ
b ^* ) ² ] ^1/2 .

When there are two crystal grains, when the color difference ΔE ^* ab of each object color is less than 5.0, it is judged to be similar color, and when it is more than 5.0, it is judged to be different color. If the area of the population formed by adjacent crystal grains having similar object colors is 40,000 μm ² or more, these populations are defined as colony structure, and the macro pattern heterogeneity occupies the entire metal structure on the plate surface. Was defined as the area ratio of the colony tissue.

In a titanium plate annealed after cold working, if the area ratio of the colony structure on an arbitrary surface parallel to the plate surface is less than 10%, sputtering is performed using a target manufactured from this titanium plate. In this case, the formed titanium film such as a gate electrode material, a diffusion barrier material, and a wiring material has a uniform thickness and orientation, and can be sufficiently used for a liquid crystal element and a VLSI.

Next, in the first invention method of the present invention, a hot-worked material is cold-rolled to generate a predetermined amount of mechanical twins over the entire thickness range. It is a method of manufacturing. In the present invention, the cause of the non-uniformity of the high-purity titanium plate is considered to be caused by the macro pattern. When manufacturing a high-purity titanium plate for a titanium target material by cold rolling, a macro pattern existing in a hot-worked material of the material is destroyed in the entire thickness range by generating mechanical twins. As the conditions, the rolling reduction Rc (rps, rotations / second) during the cold rolling is controlled within the range represented by the above equation (1) according to the rolling roll diameter D (mm), and the rolling reduction 6 % Cold rolling is performed.

When plastic working is performed on a material whose main constituent phases are hexagonal, such as high-purity titanium, industrial-use high-purity titanium or a titanium alloy, mechanical twinning occurs in addition to slip deformation. It is known that distortion is caused by a considerable ratio (for example, "Metal titanium and its application", Nikkan Kogyo Shimbun, 1983). At this time, the shape of the mechanical twin is a straight line or a bamboo leaf-shaped band, and is generated by penetrating the crystal grains linearly.

Therefore, not only can a local plastic strain be given much more than the applied average strain, but also relatively large crystal grains constituting the colony structure can be efficiently divided, and the inside of the crystal grains can be efficiently separated. The degree of dispersion of crystal orientation can be increased. Therefore, the macro pattern can be effectively destroyed by the generation of mechanical twins. After mechanical twins are formed, slip deformation mainly causes plastic deformation strain.However, since slip deformation is already active inside sub-crystal grains that have been separated by mechanical twins, the colony structure is reduced. The ability to break is small compared to mechanical twins.

Since titanium has poor thermal conductivity, when the strain rate is increased during plastic working, the heat generated does not diffuse to the outside and the temperature of the material tends to rise. It is also known that the formation of mechanical twins decreases as the material temperature increases.
Therefore, the relationship between the amount of mechanical twins generated and the cold working conditions in a high-purity titanium material was examined in detail. In addition, since the target material is required to have uniformity and denseness of the macro-pattern on the sheet surface also in the sheet thickness direction, the amount of mechanical twins generated is L section, that is, the section including the rolling direction and the sheet thickness direction. Was observed over the entire thickness range to determine the area ratio.

4N5 purity (above 99.995%)
High-purity titanium hot-rolled sheet (thickness: 33 mm) is held in a vacuum creep straightening machine (VCF, Vacuum Creep Flattening equipment) at 400 ° C for 2 hours, and then furnace-cooled by VCF annealing. Cold rolling is performed using a cold rolling mill and a thick plate hot rolling mill with a roll diameter of
The cold rolling condition of 25% or more was investigated. VCF annealing refers to simultaneous hot shape correction and annealing in a VCF device. After singly or laminating materials that are difficult to leveler correction such as thick plate and middle plate, fill the furnace with mica powder, etc., and then apply vacuum while heating, and the atmospheric pressure will act on the plate material to cause slight creep deformation The shape can be corrected to produce a flat plate material.

The roll diameter D of the cold rolling is 60 to 16
90 mm, the roll rotation speed Rc was 0.1 to 10 rps, lubrication was unlubricated, and mineral oil and tallow oil were used in combination with a rolling mill as appropriate. The rolling reduction for each pass was determined in consideration of the roll diameter in order to prevent the roll from being damaged. In order to greatly change the roll diameter of the rolling mill, experiments were performed at room temperature of about 25 ° C. using a small-scale rolling mill on a laboratory scale or a large hot rolling mill for actual production. In the experiment, the total rolling reduction during cold rolling was unified to 25%.

FIG. 1 shows a curve of a critical condition in which the area ratio of mechanical twins is 25% or more, with the roll diameter D and the roll rotation speed Rc of the cold rolling as coordinates. In the region below the curve including this curve, the area ratio of mechanical twins is 25% or more, and this condition is represented by the above formula (1). In the region above the curve, since the strain rate during processing is too high, slip deformation occurs preferentially before twinning occurs, and the area ratio of mechanical twins becomes less than 25%. As described above, the amount of mechanical twins does not depend on the type of plastic working method, but is sensitive to the strain rate during working. It is important to consider manufacturing conditions.

FIG. 2 shows the mechanical twin area ratio observed when cold rolling was performed under various conditions such as roll diameter D, roll rotation speed Rc, and lubrication conditions in the above-described experiment for obtaining the relationship of FIG. The relationship between the maximum value and the rolling reduction is shown. That is, FIG. 2 shows that in order to make the mechanical twin area ratio 25% or more, the rolling reduction needs to be 6% or more. The above experiments were conducted on VCF-annealed hot-rolled sheets.Similar results were obtained for the specimens annealed in air and those not subjected to annealing. In the process, a considerable amount of grinding is required to process the target material into a disk shape and increase its flatness, and it is not always necessary to cold-roll the surface properties required for wrought materials of normal industrial purity. It is not necessary to have it as it is. Therefore, in the cold rolling according to the present invention, it is preferable to use the lubrication effect of the black scale. In other words, after the scale formed in the hot working process is attached to the surface, or with the scale attached, it is annealed in the air or with a VCF (vacuum creep straightening machine),
It is preferable to perform cold rolling while leaving the scale. In this case, since cold rolling gives a kind of mechanical descale effect, the surface can be efficiently descaled by subsequently performing shot blasting and pickling, and the target material can be used as it is.

In the conventional production of a cold rolled titanium sheet of industrial purity, the hot rolled sheet is subjected to mechanical descale such as shot blasting after the hot rolled sheet is subjected to recrystallization annealing for softening before cold rolling. After the treatment and the subsequent pickling treatment, the scale (oxide film,
It is common sense to perform cold rolling after completely removing black scale). This method is mainly used to manufacture a sheet product in which the cold-rolled sheet is directly degreased and then vacuum-annealed to avoid unnecessary oxidation and gas absorption, and the surface properties of the cold-rolled sheet become the product surface as it is. It is by being.

In the method of the present invention, it is preferable to cold-roll the raw material with scale as described above. Materials with scales that have been hot worked or have just been annealed in the air or with VCF have fine-grained parts under the scale due to the concentration of shear deformation during hot working. In addition, it also has an effect of contributing to prevention of cracks at grain boundaries during cold rolling.

However, for unavoidable reasons, for example, when a high-purity titanium product once manufactured for another purpose is used as a target material, the rolled material has already been descaled and cold rolled with the surface black scale removed. Will do.
Also, in the normal wrought material manufacturing process, these are removed together with the black scale in the refining process for making the product, so when cold-working the product once finished, The following problems may occur.

From the viewpoint of providing a target material having a dense metal structure on a plate surface, the inventors of the present invention used a high purity titanium cold rolled material of the 5N level as an EBR (Electron Beam Remelting) having a large crystal grain size. A piece with a thickness of 80 mm cut out from the slab (average crystal grain size on the plate surface: 55 mm), a piece with a thickness of 100 mm cut from the bulk slab (average crystal grain size on the plate surface: 3.3 mm), a hot-rolled sheet ( (Plate thickness: 50 mm) was held at 200 ° C. to 790 ° C. in the air for 30 minutes to 2 hours, then air-cooled, and the surface was mechanically cut (average crystal grain size at the plate surface: 1.1 to 112.0 μm) ) Was performed.

These cold-rolled materials were cold-rolled at room temperature of about 25 ° C. by using a non-lubricated laboratory-scale small rolling mill or a large-scale hot rolling mill for actual production, with the rolling roll diameter being greatly changed to 60 to 1690 mm. did. The total rolling reduction during cold rolling was unified to 40%. Further, the surface of the rolled material was mirror-finished by pickling and buffing after mechanical cutting to make it easier to detect the occurrence of cracks. As a result of examining the surface of the cold-rolled sheet after rolling by using a stereoscopic microscope for cracks at grain boundaries and examining rolling conditions under which cracks do not occur, a rolling roll was applied to the crystal grain size d (μm) of the cold-rolled material. It has been found that by selecting the diameter D (mm) so as to satisfy the above equation (2), grain boundary cracking can be prevented.

In the method of the present invention, the rate of occurrence of mechanical twins due to processing heat is prevented from being reduced by limiting the number of rotations of a rolling roll in order to maximize the generation of mechanical twins during cold working. ing. On the other hand, in conventional cold rolling of wrought titanium and titanium low alloy, in the acceleration stage until the rolling speed reaches a steady state and the deceleration stage until the end of the rolling, the rolling roll rotation speed is temporarily It may be within the scope of the present method. However, in the method of the present invention, the number of rotations of the roll at the stage when the rolling speed reaches a steady state is defined.

Next, the second invention method will be described. The second invention method of the present invention is a method for producing the second invention titanium sheet by annealing the titanium plate obtained by the first invention method in the air or in a vacuum creep straightening machine. First
By performing cold working according to the invention method to make the mechanical twin area ratio of the entire sheet thickness section in the L section 25% or more, the colony structure existing in the cold-rolled material is mechanically broken, and Become. It is considered that when this is recrystallized and annealed, the dispersion of the crystal orientation in the macrostructure proceeds, and the unevenness of the macro pattern is eliminated. From such a viewpoint, the present inventors examined the relationship between the area ratio of mechanical twins generated during cold rolling and the uniformity of the macro pattern after recrystallization.

That is, a hot-rolled sheet (plate thickness: 20 mm) of high-purity titanium having a purity of 4N5 (99.995% or more) with a black scale and 500 ° C. in air.
Hot rolled as it is after being annealed for 30 minutes
The annealed plate was directly subjected to cold rolling by a four-high rolling mill having a work roll diameter of 270 mm. The rotation speed of the rolling roll is
The rolling was performed at 0.5 rps, unlubricated, and subjected to a reduction of 0.5 mm on each pass on average, cold-rolled in a total reduction ratio of 5 to 80%, and sampled every 5%. It was noted that each pass was immersed in water at room temperature (25 ° C.) so that the temperature of the plate became constant.

[0049] The mechanical twin area ratios of all cross sections of the cold rolled sheet having different rolling reductions in the L section were measured at three places, and the average value was obtained. Furthermore, the cold rolled sheet is 350 ° C. × 30 in the air.
After holding for a minute, the sample was annealed by air cooling and ground in parallel with the plate surface to a depth of 5 mm, and then the uniformity of the macro pattern was determined using the area ratio of the colony tissue defined as described above as an index.
The macro pattern uniformity was determined as follows according to the colony tissue area ratio.

Rating ×: Colony tissue area ratio 30% or more to 100% Rating Δ: Colony tissue area ratio 10% to less than 30% Rating ○: Colony tissue area ratio 5% to less than 10% Rating ◎: Colony tissue area A rating of 0 or more to less than 5% was evaluated on a four-point scale, and 以上 or more passed.

FIG. 3 shows the relationship between the mechanical twin area ratio in the cold rolled sheet and the macro pattern uniformity score. As the twin area ratio increases, the uniformity of the macro pattern is improved. Is shown. From FIG. 3, the twin area ratio in the cold rolled sheet is 2
It can be seen that those with 5% or more have a macro pattern uniformity at an acceptable level. In this test, the shape of the cold rolled material was corrected through a cold roll leveler so that surface grinding could be performed.However, as long as the sheet thickness was not changed, the generation of additional twins due to the cold roll leveler correction was extremely large. It was confirmed in another experiment that it was small.

It can be seen from FIG. 3 that the effect of dividing the colony structure by the introduction of mechanical twins is determined only by the proportion of the mechanical twins irrespective of the presence or absence of annealing of the hot-rolled sheet and the amount of reduction in cold rolling. In addition, the above results were obtained by conducting studies using one of the plastic working methods called rolling, but it is not the plastic working method called rolling that is effective in eliminating the macro pattern,
The amount of generated mechanical twins has a great influence, and basically does not depend on the processing method.

The material subjected to cold rolling with the scale attached in the first invention method is often work-hardened,
There is a case where it is difficult to bend at the correction stage at the time of manufacturing the target material and the workability is poor. Also, if there is residual stress, distortion is likely to occur in the cutting stage after straightening. In such a case, the problem is solved by softening by annealing after cold rolling by the second invention method.

[0054]

EXAMPLES The present invention will be further described below with reference to examples.

Example 1 A hot rolled sheet (thickness: 32 mm) with 4N5 high-purity titanium scale attached thereto, and it was kept in a vacuum creep straightening machine at 360 ° C. for 4 hours, and then subjected to furnace cooling annealing. Again, the hot rolled annealed plate with scale was lubricated at room temperature 2 with a 200 mm work roll diameter experimental 4-high rolling mill.
The cold rolling was performed at 8 ° C., and the rolling reduction was changed in a range of 5% to 80%. The number of rotations of the rolling roll was 1.3 rps. The average value of the total twin thickness of the twin generation area ratio in the L section of these samples was measured. 300 ° C in cold creep straightening machine
After holding for 4 hours, the furnace is annealed by cooling, and 2mm below the scale surface
And then subjected to # 320 polishing and etched with a normal nitric acid-based macro-corrosion solution to visually determine the macro pattern. As a result, as shown in Table 1, when the mechanical twin area ratio was 25% or more, the macro pattern judgment passed, but when the mechanical twin area ratio was less than 25%, the macro pattern judgment failed regardless of the presence or absence of hot-rolled sheet annealing. Was.

[0056]

[Table 1]

Example 2 A hot rolled plate (plate thickness 27 mm) of 5N5 level high-purity titanium was placed in the air at 300 ° C. for 30 minutes.
Annealing at 450 ° C. × 30 minutes and holding at 600 ° C. × 4 hours in a vacuum creep straightening machine, then furnace-cooled annealing, and a cold rolling mill for experimental use having a roll diameter of 60 to 1690 mm in the state of black scale and for actual production Cold rolling was performed at room temperature of about 27 ° C. while changing the number of rolls using a large-sized hot plate mill of No. 1 to investigate the area ratio of occurrence of mechanical twins. Lubrication was used without lubrication, using mineral oil and tallow oil in combination with a rolling mill as appropriate. The rolling reduction for each pass was set at 5 to 11% in consideration of the roll diameter in order to prevent the roll from being damaged. In addition, the total reduction rate at the time of cold rolling was unified to 33%. As a result, as shown in Table 2, those in the range of the formula (1) had a twin area ratio of 25% or more.

[0058]

[Table 2]

(Example 3) A 50 mm-thick slice (average crystal grain size on the plate surface: 52 mm) cut from an EBR (electron beam remelting) thin slab of 4N5 level high-purity titanium as a cold-rolled material, hot A piece with a thickness of 50 mm cut out from the forged slab is kept at 500 ° C. for 30 minutes in the air, then air-cooled (average crystal grain size on the plate surface is 4.1 mm), and a hot-rolled sheet (50 mm in thickness) is heated to 500 ° C. in the air. Air cooling (average crystal grain size at plate surface: 333 μm), holding at 840 ° C. × 5 hours in vacuum creep straightener, furnace cooling (average crystal grain size at plate surface: 333 μm), holding at 880 ° C. × 11 hours Furnace-cooled (average crystal grain size on the plate surface is 520 μm), the surface of which is mechanically cut, pickled, and mirror-polished is lubricated and the rolling roll diameter and the number of rotations of the rolling roll are changed without lubrication. Cold rolled. The total rolling reduction during cold rolling was unified to 60%. From Table 3, the roll diameter D (mm) is expressed as (2) with respect to the crystal grain diameter d (μm).
It has been found that selection to satisfy the equation is effective in preventing grain boundary cracking.

[0060]

[Table 3]

(Example 4) Hot-rolled sheets of 5N, 4N5, and 4N levels of high-purity titanium as-black (plate thickness 25 mm to 52 mm,
270 ° C to 475 while vacuum degassing them further in a vacuum creep straightening furnace.
An annealed plate with black scale was used which was heated and held at 30 ° C. for 30 minutes to 4 hours to simultaneously perform shape correction and annealing. The non-lubricated cold rolling at a total reduction of 40% was performed at room temperature of about 42 ° C. by changing the rolling roll diameter and the number of rotations of the rolling roll. Even when the vacuum creep treatment was performed, only a part of the black scale of the hot-rolled sheet was discolored, and there was no significant change in the thickness of the scale. After cold rolling, a sample was taken from a portion and the area ratio of occurrence of mechanical twins was measured. After cold rolling, each of the cold rolled sheets was subjected to normal air annealing (555 ° C. × 30 minutes heating and air cooling after holding) and annealing in a vacuum creep straightening machine (450 ° C. × 4 hours holding and furnace cooling), The macro pattern of the plate surface was scored by the method described above.
As shown in Table 4, there was no difference in the evaluation of flaws in any of the annealings. When the twinned area ratio was controlled in accordance with the above findings, improvement of the macro pattern could be confirmed.

[0062]

[Table 4]

In the present invention, as an embodiment, the annealing was performed with respect to atmospheric annealing and annealing in a vacuum creep straightening machine. However, oxidation and gas absorption during annealing should be avoided as much as possible. Performing in a reduced pressure atmosphere does not impair the technical idea of the present invention. The choice of the annealing atmosphere should be made based on economic indicators, even if it gets tired. As in the third embodiment, when using a material obtained by cutting a material from a slab, it is not always necessary to perform annealing after cutting, and the slab may be annealed in advance and then a cold-rolled material may be cut.

Further, in the present invention, the colony structure is destroyed by the generation of mechanical twins, and the effect is produced if a predetermined amount of mechanical twins is generated. It does not need to be performed near room temperature. For example, it is needless to say that the same effect can be obtained if a predetermined twin content is produced even by working in a warm region lower than about 200 ° C., and should be included in the present invention.

[0065]

The present invention examines in detail a method for eliminating macro patterns contained in a high-purity titanium target material, and cold-rolls the material in the manufacturing process of a high-purity titanium plate for a titanium target material. Focusing on the process, the amount of mechanical twinning over the entire sheet thickness during cold rolling is controlled by controlling the rolling roll, rolling roll rotation speed, and rolling material grain size.
An object of the present invention is to provide a manufacturing method capable of destroying and eliminating a macro pattern inherited in a processing step from an original material at once, and a high-purity titanium plate for the target material. The present invention has a great economic effect of improving the quality of the target material, the quality of the target material, the production efficiency and the yield, and the uniform and dense microstructure and macrostructure of conventional titanium and low titanium alloy wrought materials. Its industrial value is great because its technical ideas can be applied to the development of products.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a roll diameter and a roll rotation speed in cold rolling in the method of the present invention.

FIG. 2 is a graph showing a relationship between a total draft in cold rolling and a mechanical twin area ratio generated in a cold-rolled sheet.

FIG. 3 is a graph showing a relationship between a twin area ratio when a hot-rolled sheet and a material annealed in the air are cold-rolled at various total rolling reductions and a macro pattern score of the material annealed the cold-rolled sheet. is there.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C22F 1/00 613 C22F 1/00 613 623 623 683 683 684 684C 685 685Z 686 686Z 694 694 694A 694Z (72) Inventor Yu Kawahara In addition, 1-1 Nichihata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works (72) Inventor Isao Nagai 1-1-1, Tobita-cho, Tobata-ku, Kitakyushu, Fukuoka New Nippon Steel Corporation Yawata Inside the steelworks (72) Inventor Masao Chiba 2-6-3 Otemachi, Chiyoda-ku, Tokyo F-term in Nippon Steel Corporation (reference) 4K029 BA17 BD01 DC03 DC07 4M104 BB14 DD40 HH20

Claims (8)

[Claims] 1. A high-purity titanium plate for a titanium target material having a cold-worked structure and having a mechanical twin area ratio of 25% or more in an entire L-thickness cross-section in an arbitrary L cross-section. 2. A high-purity titanium plate for a titanium target material, which has a recrystallized structure and an area ratio of a colony structure on an arbitrary surface parallel to the plate surface is less than 10%. 3. The roll rotation speed Rc (r) during cold rolling.
ps) is controlled in accordance with the roll diameter D (mm) to a range represented by the formula (1), and a cold-rolled structure with a draft of 6% or more is formed to form a cold-worked structure. A method for producing a high-purity titanium sheet for a titanium target material, wherein the cold-rolled sheet has a mechanical twin area ratio of 25% or more in the entire sheet thickness section in the L section. Rc ≦ 1.59172 −2.2541 × 10 ⁶ / D ⁴ + 4.21766 × 10 ⁵ / D ³ −2.54285 × 10 ⁴ / D ² + 7.89452 × 10 ² / D (1) 4. The method for producing a high-purity titanium plate for a titanium target material according to claim 3, wherein the scale produced during hot working is cold-rolled while being attached to the surface. 5. The titanium target material according to claim 3, wherein after the scale formed during hot working is attached to the surface, annealing is performed in the air, and then cold rolling is performed with the scale remaining. Production method of high purity titanium plate for use. 6. After performing annealing in a vacuum creep straightening machine with the scale formed during hot working attached to the surface,
4. The method for producing a high-purity titanium plate for a titanium target material according to claim 3, wherein cold rolling is performed while the scale remains. 7. A cold-rolled material from which surface scale has been removed is subjected to a diameter D (mm) according to a crystal grain size d (μm) of the material.
7. The method for producing a high-purity titanium plate for a titanium target material according to claim 3, wherein cold rolling is performed with a rolling roll that satisfies the relationship of the expression (2). D ≧ 1.033 d ^0.504 (2) 8. The titanium plate according to claim 3, 4, 5, 6, or 7 is annealed in the air or in a vacuum creep straightening machine to form a recrystallized structure, and any surface parallel to the plate surface. A method for producing a high-purity titanium plate for a titanium target material, comprising a cold-rolled annealed plate having an area ratio of colony structure of less than 10%.