RU2544976C2 - Titanium material - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to titanium materials with high strength and processibility. Titanium material contains iron 0.60 wt % or less and oxygen 0.15 wt % or less, titanium and inevitable impurities are the rest. Material has a non-recrystallised structure formed by processing accompanied by plastic deformation and a recrystallised structure formed by annealing after the above treatment; average size of recrystallised α-grains is 1 mcm or more and 5 mcm or less, and surface area of the non-recrystallised part in a cross section of titanium material is more than 0 to 30%.

EFFECT: material is characterised by high strength and processibility.

2 dwg, 2 tbl, 45 ex

Description

FIELD OF TECHNOLOGY

The present invention relates to a titanium material, and more particularly to a titanium material excellent in strength and processability.

DESCRIPTION OF THE PRIOR ART

Typically, plate-shaped or bar-shaped parts formed from materials such as titanium alloys and pure titanium have been widely used. For example, plate-shaped titanium material (also referred to as “titanium plate” hereinafter) has been widely used for industrial products in which a titanium plate is subjected to various plastic deformation treatments, such as bending, bending and drawing, to form various products. The titanium plate that is subjected to such a treatment requires excellent machinability. Further, recently, a decrease in the thickness of the titanium plate has been required in the sense of reducing the cost of raw materials, reducing the mass of the product, and the like. As a result, an increase in the strength of the titanium plate was increasingly required. However, usually the machinability and strength of a titanium plate are in a compromise ratio and it is time consuming to satisfy these properties at the same time. That is, conventional titanium plates pose a problem in that manufacturing becomes labor intensive (poor workability) with an increase in yield strength.

In relation to the above subject, the following Patent Document 1 shows the workability assessment of thin titanium plates having various components and crystal grain sizes in an exhaust test, and describes that the finer the crystal grain, the better the workability (page 103, from line 5 ) Further, the following Patent Document 1 discloses a method for manufacturing a thin plate of pure titanium and describes the manufacture of a thin plate of pure titanium having a reduced gloss surface, including final annealing at (600-800) ° C × (2-5) minutes, then the implementation of processing by etching and selection of the average grain size of the crystal (hereinafter referred to as the particle size) of the product up to 3-60 microns.

Further, in the following patent document 2, pure titanium for building materials, a pure titanium plate and a method for its manufacture are disclosed, and a titanium material for building materials is described which contains 900 ppm or less oxygen and 100 ppm or more, and 600 ppm or less Fe, where the content of Ni and Cr is limited. Moreover, Patent Document 2 describes a titanium material for building materials having an average crystal grain size of 70 μm or less, which was subjected to etching with an aqueous solution of nitric and hydrofluoric acids after cold rolling and annealing.

However, in these patent documents 1 and 2 there is practically no data that would evaluate a titanium material having a fine crystal grain size of 5 μm or less, and in patent document 2 an example is given in which the crystal grain size is 3 μm, but in at the same time, in paragraph [0026], it is described that “in actual production, the lower limit is about 5 μm,” which is a negative description of the crystal grain size of 5 μm or less.

This is most likely due to the fact that these documents set the goal of obtaining excellent titanium material for construction, which has a low gloss, and workability in bending, deep drawing and the like have not been studied enough.

Further, in the following patent document 4, a titanium plate disclosed is excellent in machinability, which has low strength (yield strength) despite the presence of excellent machinability and cannot simultaneously satisfy both machinability and strength.

LIST OF BIBLIOGRAPHIC REFERENCES

PATENT DOCUMENT

Patent Document 1: Japanese Patent Application Laid-Open No. 63-103056

Patent Document 2: Japanese Patent Application Laid-Open No. 9-3573

Patent Document 3: Japanese Patent Application Laid-Open No. 2006-316323

Patent Document 4: Japanese Patent Application Laid-Open No. 63-60247

NON-PATENT DOCUMENT

Non-Patent Document 1: "Titanium", Vol. 57, No. 2 (published by the Japan Titanium Society, April 2009)

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

An object of the present invention is to provide a titanium plate having high strength and excellent machinability.

SOLUTION

Although the strength (yield strength) of titanium material can be increased by adding mainly oxygen (O) and iron (Fe), but when they are added, ductility will decrease, thereby reducing workability. For example, since titanium material designated as JIS Class 1 has a low oxygen and iron content, a titanium plate using JIS Class 1 material generally has low strength (yield strength), but is excellent in ductility and excellent in machinability. When using JIS grade 2 titanium material having a higher oxygen and iron content than JIS grade 1 titanium material, the resulting titanium material will have a higher strength (yield strength) than titanium material using a grade 1 titanium material JIS, while it will tend to have reduced ductility with reduced machinability. JIS grade 3 and grade 4 titanium materials having a much higher oxygen and iron content have much greater strength (yield strength), but have much more reduced ductility with a strong reduction in workability. That is, the strength (yield strength) and workability have a certain relationship (hereinafter referred to as the equilibrium "strength (yield strength) - workability").

In particular, plate materials and wire materials made by using titanium materials are formed by subjecting the materials to a plastic deformation treatment such as rolling and wire drawing. These plate materials and wire materials subjected to plastic deformation processing generally have an inner part in which the structure to be processed is formed as it is, and therefore they are subjected to a stage called final annealing in order to recrystallize the structure before their delivery to the market. For example, a titanium plate is subjected to a treatment, such as cold rolling, to adjust the thickness to a predetermined value, and then subjected to periodic annealing, continuous annealing, or the like, to recrystallize the treated structure of the inner part to form equiaxed crystal grains (hereinafter referred to as “recrystallized grains” "). These recrystallized grains grow strongly over time annealing and the like, and, in particular, in the period immediately after the initiation of recrystallization, where the particle size of the recrystallized grains is small, the growth rate of the recrystallized grains will be high and they will grow to a large particle size, exceeding 5 microns in a relatively short time. When the recrystallized grains grow to this size, the unrecrystallized part (the processed structure) will not be preserved, and only the equiaxed structure based on the recrystallized grains will generally form in the inner part of the titanium material.

As a result of intensive and extensive studies to achieve the above goal, the authors of the present invention found that an increase in the strength (yield strength) of the titanium material can be achieved by selecting a structure (grinding of crystal grains by preserving the unrecrystallized part), which was not addressed as a means of increasing the strength. Specifically, the inventors of the present invention completed the present invention by subjecting a commercially available pure titanium plate, which was cold rolled to a predetermined thickness, to final annealing in vacuum using an electric furnace; making various titanium plates having various structures on an experimental basis by changing its temperature and time; and evaluating its strength (yield strength) and workability (ductility) using residual elongation and Ericksen's test.

As a result of the assessment, it was found that, although the strength (yield strength) tends to increase and workability (Ericksen number) tends to decrease with decreasing crystal grain size, the Ericksen number does not decrease significantly, provided that the average particle size of the recrystallized grains has a predetermined size or less, and "balance strength (yield strength) - workability" can be improved with conventional titanium materials.

Further, there was a case when, even if the average grain size of the crystal of the recrystallized grains is a predetermined size or less, workability (Ericksen number) is reduced and, therefore, the "equilibrium strength (yield strength) - workability" cannot be improved compared to conventional titanium materials. As a result of a detailed study of the microstructure of this titanium plate, many unrecrystallized parts were observed in addition to the grains recrystallized by final annealing. The "equilibrium strength (yield strength) - workability" was studied on the basis of the amount of unrecrystallized part, and it was found that workability is highly reduced if the fraction of the area of the unrecrystallized part in the cross section of the titanium plate exceeds 30%. It should be noted that in the present description, the non-crystallized part means the part in which the machined structure subjected to plastic processing is stored.

Specifically, the present invention related to a titanium material for achieving the above object is characterized in that the titanium material has an iron content of 0.60% by mass or less and an oxygen content of 0.15% by mass or less, with the remainder being titanium and inevitable impurities, while the titanium material has a processed structure formed by processing accompanied by plastic deformation, and a crystallized structure formed by annealing after processing, where the titanium material is sph rmirovannym so that the average particle size of the recrystallized structure of the crystal grains is 1 m or more and 5 m or less and the unrecrystallized portion in the area of the cross section of the titanium material is more than 0% and 30% or less.

USEFUL EFFECT OF THE INVENTION

In the present invention, it is possible to create a titanium material having high strength and excellent machinability.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a micrograph showing the microstructure of the titanium plate of the example observed using a transmission electron microscope (the unrecrystallized portion is observed in the portion between the recrystallized grains).

Figure 2 is a graph showing the relationship between yield strength and Ericksen number.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferred embodiment of a titanium material in accordance with the present invention will be described by taking an example of a titanium plate. The titanium plate in the present embodiment is formed from a titanium material having an iron (Fe) content of 0.60% by mass or less and an oxygen content (O) of 0.15% by mass or less, with the remainder being titanium (Ti) and inevitable impurities. The titanium plate is formed by processing, accompanied by plastic deformation followed by annealing, and it has a treated structure in the inner part, which is processed, and a crystallized structure, followed by annealing, where the titanium plate is formed so that the average grain size of the crystal particles of the recrystallized structure is 1 μm or more and 5 μm or less and the area of the non-crystallized part in the cross section of the titanium material is more than 0% and 30% or less.

As described above, iron (Fe) is contained with a percentage of 0.60% by weight or less. It should be noted that the upper limit of Fe is 0.60% by mass, since Fe is a β-phase stabilizing element in the titanium material, and if the Fe content exceeds 0.60% by mass, in the structure constituting the titanium plate, in addition to the α phase, many β phases can form. That is, since, depending on the size of the formed β-phase, ductility is greatly reduced or corrosion resistance is greatly reduced, it is important to maintain the content of Fe contained in the titanium material that forms the titanium plate of the present embodiment at 0.60% by mass or less in terms of forming a titanium plate having high strength and excellent machinability.

It should be noted that, although the lower limit of the Fe content is not necessarily required in the sense of forming a titanium plate having high strength and excellent machinability, expensive and high-purity sponge titanium should be used as raw material if the goal is to use a titanium plate having a Fe content of less than 0 , 01% by mass, which can increase the material cost of a titanium plate. Therefore, the Fe content is preferably 0.01% by mass or more and 0.60% by mass or less in terms of the cost of a titanium plate and the like.

For example, in the Kroll process, titanium material having a Fe content of 0.60% by mass or more usually forms only in a small region near the vessel. Therefore, you can use most of the sponge titanium obtained in the Kroll process, since the titanium plate in the present embodiment has an iron content as a component in the range of 0.01-0.60% by weight. That is, it can be said that the titanium plate of the present embodiment is suitable as a consumer material, since there are practically no restrictions on the use of sponge titanium.

Oxygen (O) is contained in a titanium material with a content of 0.15% by mass or less. The O content in the titanium material forming the titanium plate of the present embodiment is 0.15% by mass or less, since if the O content exceeds 0.15% by mass, the strength of the titanium plate can be excessively increased, preventing it from being sufficiently imparted machinability, even if there is a goal to improve the "strength-workability balance" by reducing the grain size of the crystal, thereby making it difficult to form a titanium plate suitable for processing, such as bending deep or deep drawing.

It should be noted that, although the lower limit of the O content is not specifically indicated, it may be necessary to manufacture a titanium plate using expensive and high-purity sponge titanium as a raw material, if the goal is to set the O content in the titanium material constituting the titanium plate to less than 0.015 % by weight. Therefore, the O content is preferably 0.015% by mass or more and 0.15% by mass or less.

Further, it is important that inevitable impurities such as carbon (C), nitrogen (N) and hydrogen (H) are each contained in an amount corresponding to JIH class 2 or less in order to ensure good workability in production. More specifically, it is important that the content of C, N and H is less than 0.02% by weight for each. Further, the content of C is preferably 0.01% by mass or less, the content of N is preferably 0.01% by mass or less, the content of H is preferably 0.01% by mass or less. Although the lower limit is not specific to the above content of C, N and H, from the point of view of machinability of the titanium plate, the production cost of the titanium plate can increase significantly if it is intended to completely remove this content. From the point of view of preventing such an increase in cost, the content of C is preferably 0.0005% by mass or more, the content of N is preferably 0.0005% by mass or more, the content of H is preferably 0.0005% by mass or more.

As described above, the titanium plate of the present invention has a machined structure and a recrystallized structure in its inner part and is formed so that the average particle size of the crystal grains of the recrystallized structure is 1 μm or more and 5 μm or less, and the surface area of the unrecrystallized structure is transverse the cross section of the titanium plate is greater than 0% and 30% or less.

The upper limit of the average particle size of the recrystallized structure is 5 μm or less, since if the average crystal grain size of the equiaxed α-grains obtained by recrystallization exceeds 5 μm, the effect of grinding the crystal grains will be small, making it difficult to achieve a “strength-workability equilibrium " Further, the lower limit is 1 μm, since if the titanium plate is subjected to processing (rolling, forging and the like) in actual production (industrially suitable method) followed by annealing to obtain an average crystal grain size of less than 1 μm, the fraction of the area of the unrecrystallized part (machined structure), which will be described below, will increase, which extremely increases the strength, but significantly reduces machinability, making it difficult to achieve an excellent "balance of strength - machining tidiness. "

The non-crystallized portion is formed from a treated structure in which a titanium plate is plastically deformed by processing (cold rolling, forging and the like) to compress crystal grains, and the strength of the titanium plate can be increased by allowing the treated structure to be stored in the titanium plate. A titanium plate containing a machined structure formed by cold rolling or the like has high strength, while its ductility is very small. Therefore, the treated structure was conventionally recrystallized by annealing to form an equiaxed structure and sufficient annealing time was provided to such an extent that the treated structure was not stored in the titanium plate. On the other hand, with respect to the titanium plate in the present embodiment, the treated structure is allowed to remain in the titanium plate by using annealing conditions, which will be described later, and moreover, the particle size of the recrystallized grains is controlled as described above.

In the sense of obtaining an excellent “strength-workability equilibrium”, it is important that the non-crystallized part (machined structure) is created so that the proportion of its area in the cross section of the titanium plate is 30% or less. If the area fraction of the non-crystallized portion is more than 30%, the strength of the titanium plate will be greater, but the ductility will be reduced, making it difficult to ensure excellent machinability of the titanium plate. As a result, it may not be possible to achieve an excellent “strength-workability balance." The area fraction of the non-crystallized portion is preferably 10% or less in the sense of more reliably providing the titanium plate with an excellent "strength-workability balance". It should be noted that, although the lower limit is not specifically limited, the particle size of the recrystallized grains will increase dramatically if the unrecrystallized part is lost (area fraction is 0%). Therefore, the area fraction of the non-crystallized portion is preferably 0.1% or more, in which the particle size of the recrystallized grains can be more reliably controlled within the range as described above.

A method for controlling the particle size of recrystallized grains and forming an unrecrystallized portion as described above includes a method in which a titanium plate is brought to the desired thickness in a conventional rolling process and the like, and then subjected to final annealing in a predetermined state.

The annealing technique, which can be used in the final annealing, can be roughly divided into a continuous type and a batch type. Among them, the continuous continuous type annealing is an annealing method by expanding a cold rolled coil and passing a titanium plate at a constant speed through the annealing furnace, and the method can control the time to maintain the heating temperature using the speed of the plate. In the final annealing of conventional titanium plates, in the case of a continuous type, the heating temperature is 700-800 ° C and the heating time is from several tens of seconds to about 2 minutes. On the other hand, the periodic type of final annealing is the heating of the titanium plate coil in the annealing furnace in the state of the coil itself, where the titanium plate is slowly heated in order to reduce the difference in heat application between the outer part and the inner part of the coil, and its heating rate is also is extremely slow. In the final annealing of conventional titanium plates, in the case of a batch type, the heating temperature is 550-650 ° C and the heating time is from about 3 hours to 30 hours.

On the other hand, the final annealing carried out in the manufacture of the titanium plate of the present embodiment is preferably carried out, for example, in a continuous system under heating conditions at a temperature of 580 ° C. or more and less than 600 ° C., for 1 minute or more and 10 minutes or less, or under heating conditions at a temperature of 600 ° C or more and 650 ° C or less, for 10 seconds or more and 2 minutes or less. A period of time of 10 seconds or more is selected as the preferred heating condition, because if the temperature maintenance time is less than 10 seconds, the correct range of operating conditions, such as the speed of the plate and the heating temperature to effect a predetermined annealing of the titanium plate, will be extremely narrow, which requires high-precision regulation of the device or its operation. On the other hand, a condition of 10 minutes or more is preferable as the heating time, because if the holding time exceeds 10 minutes, the speed of the plate must be reduced, thereby reducing productivity.

Further, a temperature of 580 ° C. or more is selected as the preferred condition for the heating temperature, because if the heating temperature is less than 580 ° C., it will be difficult to cause a predetermined recrystallization in the titanium plate for a holding time of 10 minutes or less, and the fraction of the area is unrecrystallized parts will in many cases exceed 30%. Moreover, a heating temperature of 650 ° C. or less is chosen because, if the temperature is more than 650 ° C., the recrystallization of the titanium plate can be completed even within 10 seconds and the recrystallized grains can grow to an average particle size of 5 μm or more.

Further, the final annealing carried out in the manufacture of the titanium plate of the present embodiment is preferably carried out under heating conditions at a temperature of 420 ° C. or more and less than 550 ° C., for 3 hours or more and 50 hours or less, when it is periodic type. A condition of 3 hours or more is preferable as a heating time, because if the heating time is less than 3 hours, the temperature of the inside of the roll may not reach a predetermined temperature depending on the size of the roll. On the other hand, a condition of 50 hours or less is preferable as the heating time, because if the heating time exceeds 50 hours, then the time required for annealing will be excessively long, thereby reducing the productivity of the titanium plate.

Further, a heating temperature of 420 ° C. is preferable because if the heating temperature is less than 420 ° C., it will be difficult to cause a predetermined recrystallization in the titanium plate for a holding time of 50 hours or less, and the area fraction of the unrecrystallized portion will in many cases exceed thirty%. Or it is due to the fact that it is necessary to have several annealing furnaces (heating equipment) in order to provide a predetermined production volume, which increases the cost of equipment and requires a large space for installing annealing furnaces. It should be noted that in the batch type, since the titanium plate is heated in a roll state, the rate of temperature increase differs between the outer part and the inner part of the roll and the time before the temperature reaches the target temperature is also different. Depending on the roll size, heating temperature and heating ability of the annealing furnace, the time before the temperature reaches the target temperature, in general, differs by tens of minutes - several hours. Therefore, it is important to heat the roll to a temperature range where the size of the recrystallized grains does not differ much, even if the heating time is somewhat different, i.e. it is important to the temperature range where the growth rate of the recrystallized grains is low.

Further, the heating temperature is preferably less than 550 ° C, because due to the fact that the growth rate of the recrystallized crystal grains is high at a temperature of 550 ° C or more, when the heating time is reduced in accordance with the outer part of the roll, the target temperature is the inner part of the roll may not be achieved, leading to a state where an unrecrystallized part that is not recrystallized may be present in an amount exceeding 30%; on the contrary, when the heating time is increased in accordance with the inside of the roll, the recrystallized grains may excessively grow in the outside of the roll, resulting in an average crystal grain size of 5 μm or more.

It should be noted that the final annealing of either a continuous type or a batch type is preferably carried out in a vacuum or in an inert gas atmosphere. A titanium plate having an excellent strength-workability balance can be obtained by adjusting the average particle size of the recrystallization and the residual percentage of the unrecrystallized part (treated structure) with annealing conditions as described above.

It should be noted that, although this is not described in detail in the present description, the known approach in a conventional titanium plate and method for manufacturing a titanium plate can also be applied in the present invention in a range that does not attenuate the effect of the present invention in a significant way. Further, although the titanium plate is indicated as an example of the titanium material of the present embodiment, various forms of titanium material, such as wire material, bar material, tubular material, are the same as the titanium plate, since excellent “balance strength” is exhibited - workability "and these titanium materials also fall within the scope implied by the present invention.

EXAMPLES

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to them.

Rating 1

Samples No. 1-45

Production of test fragments

An ingot (140 mm in diameter) was made using small-sized vacuum arc welding and the ingot was heated to 1050 ° C and then forged to produce a workpiece having a thickness of 50 mm. The billet was hot rolled at 850 ° C to a thickness of 5 mm and then annealed at 750 ° C and the burrs on the surface of the annealed billet were removed by shot peening and etching to prepare the plate material. The plate material was further cold rolled to obtain a sample in the form of a plate (titanium plate) having a thickness of 0.5 mm. A titanium plate having a thickness of 0.5 mm was finally annealed at a temperature of 400-800 ° C for 48 hours or less in an atmosphere of gaseous argon to obtain a test fragment in which the crystal grains were adjusted.

Component measurement

The amounts of iron and oxygen contained in the titanium plate were measured using the plate material after hot rolling, from which the surface burrs were cut. The iron content was measured in accordance with JIS H1614 and the oxygen content was measured in accordance with JIS H1620.

Tensile strength

Further, the tensile strength of the test piece (titanium plate) in which the crystal grain size was adjusted as described above was measured in accordance with JIS Z2241.

Workability Assessment

Next, the machinability of the test fragment (titanium plate) in which the crystal grain size was adjusted as described above was evaluated. The evaluation was carried out by measuring the Ericksen number using graphite lubricant as a lubricant in accordance with JIS Z2247.

Structure study

The microstructure of the titanium plate was observed to obtain structural photographs of crystal grains (recrystallized α grains) and the unrecrystallized part (processed structure). It should be noted that an optical microscope or transmission electron microscope was used for observation. An example of a structural photograph observed using a transmission electron microscope is shown in FIG. 1 (microstructure of sample No. 28). In this structural photograph, the recrystallized α-grains and the non-crystallized part are observed (In the photograph shown in FIG. 1, the place designated as “A” is the un-crystallized part). This photograph was examined for an area other than the unrecrystallized portion, using image analysis software to determine the average area of the recrystallized α-grains; and the diameter of a circle having the same area as the average area was determined by calculation to establish the average particle size of the recrystallized grains. Further, the area fraction of the non-crystallized part was determined from the area of the non-crystallized part. The results of the above are shown in table 1.

Table 1 Sample No. The content of O (wt.%) Fe content (wt.%) Annealing conditions The average grain size of the crystal of recrystallized grains (μm) The fraction of the area of the unrecrystallized part (%) Yield Strength (MPa) Ericksen number (mm) Temperature Time one 0,021 0.017 450 8 hour 2,3 25 190 13.9 2 0,021 0.017 600 1 min 3.9 2 162 14.5 3 0.024 0.253 600 110 sec 2.2 16 352 10.9 four 0.024 0.253 630 110 sec 2,8 eleven 305 11.7 5 0.024 0.253 650 1 min 3.4 5 268 12.1 6 0,030 0,022 450 8 hour 2.0 23 240 12.9 7 0,030 0,022 450 48 hour 2.6 2 229 13.1 8 0,030 0,022 480 8 hour 2,3 10 236 13.0 9 0,030 0,022 480 24 hour 2,8 5 230 13,2 10 0,030 0,022 480 32 hour 2.9 3 224 13.3 eleven 0,030 0,022 480 48 hour 3,1 one 225 13.3 12 0,030 0,022 500 8 hour 3.3 3 217 13,4 13 0,030 0,022 520 4 hour 4,5 0.5 210 13.6 fourteen 0,030 0,022 600 1 min 3,5 2 205 13,4 fifteen 0,035 0,027 600 10 sec 3.6 fifteen 261 12.3 16 0,035 0,027 600 30 sec 4.1 3 255 12.5 17 0,035 0,027 600 1 min 4.2 one 262 12,4 eighteen 0,035 0,027 630 10 sec 4.4 2 264 12,4 19 0,035 0,027 630 30 sec 4.7 one 250 13.3 twenty 0,053 0.217 650 1 min 4.2 3 310 11.5 21 0,066 0.377 650 1 min 3.4 four 336 11.0 22 0,066 0.377 650 10 sec 4.9 one 301 11.7 23 0,068 0.059 450 8 hour 1.8 21 428 9,4 24 0,068 0.059 500 8 hour 3.2 2 356 10.7 25 0,068 0.059 600 1 min 3.3 2 345 10.8 26 0,068 0.059 650 10 sec 4.9 0.2 313 12.1 27 0,042 0.024 425 24 hour 1.8 26 360 10,4 28 0,042 0.024 450 24 hour 2.6 13 304 12.0 29th 0,042 0.024 480 24 hour 3.3 four 264 12.0 thirty 0,042 0.024 500 24 hour 4.6 1,5 240 12.5 31 0,021 0.017 600 4 hour 26 0 107 14.0 32 0,030 0,022 600 1 hour 12 0 172 12.7 33 0,030 0,022 600 4 hour 23 0 159 13.0 34 0,030 0,022 750 1 min 46 0 148 13,2 35 0,035 0,027 800 1 min 82 0 146 13,4 36 0,053 0.217 800 5 minutes 17,2 0 430 8.0 37 0,066 0.377 800 15 hour 21 0 266 9.2 38 0,068 0.059 750 1 min 42 0 199 11.7 39 0,068 0.059 800 1 min fifty 0 189 12,2 40 0,068 0.059 800 15 minutes 75 0 192 11.5 41 0.160 0,065 750 10 min 28 0 346 8.2 42 0.209 0.104 750 10 min 22 0 411 7.6 43 0,030 0,022 450 1 hour 1.8 43 263 8.6 44 0,066 0.377 500 1 hour 2,3 35 238 10,4 45 0,042 0.024 400 24 hour 1,5 45 414 6.9

Each of the above samples No. 1-30 has an average recrystallized grain size of 5 μm or less, and an unrecrystallized part is observed in each of these samples with an area fraction of less than 30% in the cross section of the titanium plate; and samples nos. 31-42 are in a state where the unrecrystallized portion is not retained, like ordinary titanium plates. Further, samples No. 43-45 were obtained by adjusting the annealing conditions in such a way that the unrecrystallized part was purposely allowed to remain, where the unrecrystallized part was allowed to remain in a state where the area fraction exceeds 30%. The above samples No. 1-30 and No. 31-42 were obtained by adjusting the grain size of the crystal (equivalent to the circumference of the average grain size of the α phase) and the amount of unrecrystallized part with the difference between the annealing conditions regardless of the use of titanium materials in which the oxygen content and the iron contents are almost the same. As shown in table 1, the average particle size can be suppressed to a small and a high yield strength is manifested by maintaining the unrecrystallized part. In the above estimate, machinability (Ericksen number) generally tends to decrease as the yield strength increases, but when samples having comparable machinability (Ericksen number) are compared to each other, it is found that the yield strength of these samples is increased, and these the samples have high strength due to the presence of the non-crystallized part (for example, see comparison of sample No. 1 with No. 31, No. 9 with No. 34 and No. 15 with No. 39). That is, it was found that when the crystal grains are 5 microns or less in size and the unrecrystallized portion is present in an amount of 30% or less, the “equilibrium tensile strength - workability” is good. On the other hand, when the area of the unrecrystallized portion is more than 30% after the final annealing, workability (Ericksen number) is greatly reduced, as shown in samples No. 43-45. These results also showed that the present invention can provide a titanium plate having high strength and excellent machinability.

Grade 2

Samples No. A-H

Real machine test

Test Roll Production

An ingot (750 mm in diameter) was made by vacuum arc welding, and the ingot was heated to 850-1000 ° C and then forged to produce a workpiece having a thickness of 170 mm. The billet was heated to 850 ° C and then hot rolled to a thickness of 3.5 mm, and the hot-rolled plate was annealed at a temperature of 750 ° C, followed by deburring on the surface of the annealed billet by bead-blasting and etching to prepare a hot-rolled coil. The hot rolled coil was cold rolled to obtain a cold rolled coil having a thickness of 0.4-0.8 mm. Oil and fat, such as cold rolling oil, was removed from the cold-rolled coil by refining, and the resulting cold-rolled coil was introduced into the vacuum annealing furnace. The inside of the vacuum annealing furnace, which housed the cold-rolled coil, was pumped out, and then filled with argon gas, and the cold-rolled coil was annealed in a periodic type furnace, in which it was heated to 450-650 ° C, and held for 4-36 hours to adjust the size of the recrystallized grains. In order to evaluate the “component measurement”, “tensile strength measurement”, “workability assessment” and “structural study” in the same manner as in the above assessment 1, samples of the required size were taken from the obtained titanium plate and subjected to evaluations as described above. The results are shown in table 2.

table 2 Sample No. The content of O (wt.%) Fe content (wt.%) Annealing conditions The average grain size of the crystal of recrystallized grains (μm) The fraction of the area of the unrecrystallized part (%) Yield Strength (MPa) Ericksen number (mm) Temperature Time A 0,028 0.0179 500 24 hour 3.6 one 213 13.5 B 0,032 0.024 480 24 hour 2.6 5 232 13.1 C 0,035 0,022 480 24 hour 2,4 four 248 12.8 D 0.058 00234 450 36 hour 2,3 3 385 10.1 E 0,068 0,033 450 36 hour 2,4 four 401 9.9 F 0,022 0.014 600 4 hour 25 0 110 14.0 G 0,030 0.018 630 24 hour 45 0 149 13,2 H 0,041 0,028 650 4 hour 55 0 166 12.8

Each of the above samples No. A-E has an average recrystallized grain size of 5 μm or less, and an unrecrystallized part is observed in each of these samples with an area fraction of less than 30% in the cross section of the titanium plate; and samples No. F-H are in a state where the unrecrystallized portion is not retained, like ordinary titanium plates. In the above samples No. A, B and C, titanium plates were obtained having a yield strength of 200 MPa or more and having excellent machinability in which the Ericksen number is about 13 mm. Further, in samples Nos. D and E, titanium plates were obtained, not only having high strength, in which the yield strength was about 400 MPa, but also having good machinability, in which the Ericksen number was about 10 mm. On the other hand, samples No. F-H are excellent in machinability, but have insufficient strength in which the yield strength is less than 200 MPa. These results also showed that the present invention can provide a titanium plate having high strength and excellent machinability.

Claims (1)

Titanium material, characterized in that it contains iron 0.60 mass% or less and oxygen 0.15 mass% or less, titanium and unavoidable impurities are the rest and have an unrecrystallized structure formed by processing accompanied by plastic deformation and recrystallized a structure formed after annealing by said treatment, the average size of the recrystallized α grains being 1 μm or more and 5 μm or less, and the area of the unrecrystallized part in the cross section of the titanium material ulation from greater than 0% to 30%.

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