WO2017018516A1 - Titanium composite material and titanium material for hot working - Google Patents

Abstract

Provided is a titanium composite material 1 having a first surface layer part 2, an inner layer part 4, and a second surface layer part 3, wherein: the first surface layer part 2 and the second surface layer part 3 are formed from a titanium alloy; the inner layer part 4 is formed from industrial-use pure titanium having voids; the chemical composition of at least the first surface layer part 2 or the second surface layer part 3 contains a total of 0.08-1.0 mass% of one or more elements selected from Fe, Cr, Ni, Al and Zr, with the remainder being Ti and impurities; the thickness of the first surface layer part 2 and/or the second surface layer part 3 is 5-100 μm and accounts for 20% or less of the total thickness of the titanium composite material 1; and the volume fraction of the voids in a cross section perpendicular to the plate thickness is greater than 0% and no more than 30%.

Description

Titanium composite and titanium material for hot working

The present invention relates to a titanium composite material and a titanium material for hot working.

Titanium material has excellent properties such as corrosion resistance, oxidation resistance, fatigue resistance, hydrogen embrittlement resistance, and neutron blocking properties. These properties can be achieved by adding various alloying elements to titanium.

Industrial titanium cold-rolled sheet materials (for example, pure titanium cold-rolled sheet materials for industrial use) can be used by forming and processing plate materials into a predetermined shape, such as plate heat exchangers and FC separators. ing. For this reason, in addition to formability, industrial titanium cold-rolled sheet materials are also required to be thin by improving fatigue strength and to have a high added environment (under high load).

On the other hand, as with other metal materials, pure titanium has a contradictory relationship between ductility that governs formability and strength (fatigue strength).

Japanese Patent Laid-Open No. 2008-195994 (Patent Document 1) discloses that plasma nitriding is performed on a titanium product made of pure titanium, α-type titanium alloy, β-type titanium alloy, or α + β-type titanium alloy. A compound existing on the surface of the hardened layer by performing a plasma nitriding treatment for forming a hardened layer on the surface of the metal and a fine particle collision treatment for causing one or more kinds of fine particles to collide with the treatment target after the plasma nitriding treatment A method is disclosed in which the fatigue strength is improved by surface modification of a titanium product by removing the layer.

Japanese Patent Application Laid-Open No. 2013-76110 (Patent Document 2) discloses a step A of performing fine particle peening on the surface of a substrate made of a titanium alloy and titanium, a step B of performing a first heat treatment in a temperature zone T1, and a temperature zone. Step C in which the second heat treatment is performed in T2 and Step D in which the third heat treatment is performed in the temperature zone T3 are sequentially provided, satisfying the relationship of T1> T2> T3, and T1 being set to 900 to 1000 ° C. A surface treatment method for a substrate made of a titanium alloy and titanium is disclosed. That is, in this surface treatment method, an amorphous layer, a fine particle layer (α phase, particle size: about 300 nm), a submicron particle layer (α phase, particle) are formed in the vicinity of the surface of the titanium material in this order from the surface side. Diameter: About 500 nm micron particle layer (β phase, particle diameter: about 3000 nm) is formed to improve fatigue strength.

JP 2008-195994 A JP 2013-76110 A

According to the method disclosed in Patent Document 1, in order to use C and N having high solid solution strengthening ability for forming a hardened layer, if these are solid solution, it becomes harder and fatigue strength can be improved, but a rapid ductility decrease is caused. Invited, formability is inferior.

Further, according to the examination results of the present inventors, it is not easy to improve the moldability by this surface treatment method disclosed in Patent Document 2.

Furthermore, the inventions disclosed in Patent Documents 1 and 2 require a special surface treatment for the titanium material, and an increase in manufacturing cost is inevitable.

The present invention reduces the content of alloy elements to be added to improve fatigue resistance (amount of specific alloy elements that express target characteristics), and suppresses the production cost of the titanium material, The object is to obtain a titanium material having desired characteristics at low cost.

The present invention has been made in order to solve the above-mentioned problems, and the gist thereof is the following titanium composite material and titanium material for hot working.

(1) a first surface layer part;
The inner layer,
A titanium composite material comprising a second surface layer portion,
The first surface layer portion and the second surface layer portion are made of a titanium alloy,
The inner layer portion is made of industrial pure titanium having voids,
The chemical composition of at least one of the first surface layer part and the second surface layer part is mass%,
Total of one or more selected from Fe, Cr, Ni, Al and Zr: 0.08 to 1.0%,
The balance: Ti and impurities,
The thickness of the at least one of the first surface layer portion and the second surface layer portion is 5 to 100 μm, and the proportion of the total thickness of the titanium composite material is 20% or less;
The volume ratio in a cross section perpendicular to the thickness direction of the gap is more than 0% and 30% or less.
Titanium composite material.

(2) The crystal grain size of the α phase in the at least one of the first surface layer part and the second surface layer part is 15 μm or less.
The titanium composite material according to (1) above.

(3) The chemical composition of the industrial pure titanium is mass%,
C: 0.1% or less,
H: 0.015% or less,
O: 0.4% or less,
N: 0.07% or less,
Fe: 0.5% or less,
Balance: Ti and impurities,
The titanium composite material according to (1) or (2) above.

(4) The fatigue strength ratio is 0.65 or more.
The titanium composite material according to any one of (1) to (3) above.

(5) The elongation at break in the width direction during rolling is 25% or more,
The titanium composite material according to any one of (1) to (4) above.

(6) a housing;
One or more types selected from sponge titanium, briquettes compressed with sponge titanium, and industrial pure titanium scrap filled in the housing,
Part of the housing, the part constituting the surface layer after hot working is made of a titanium alloy,
The chemical composition of the titanium alloy is mass%,
Total of one or more selected from Fe, Cr, Ni, Al and Zr: 0.08 to 1.0%,
Balance: Ti and impurities,
Titanium material for hot working.

Since the titanium composite material according to the present invention has a surface layer portion made of a titanium alloy and an inner layer portion made of industrial pure titanium, the whole is equivalent to a titanium material made of the same titanium alloy. Although it has fatigue resistance, it can be manufactured at low cost.

FIG. 1 is an explanatory view showing an example of the configuration of a titanium composite material according to the present invention. FIG. 2 is an explanatory view showing the structure of a titanium material that is a material for hot working of a titanium composite material according to the present invention. FIG. 3 is an explanatory view showing a plane bending fatigue test material. FIG. 4 shows an example of a tissue photograph produced by the method shown in this specification.

The inventors of the present invention have made extensive studies in order to solve the above problems, and by alloying only the surface layer portion of the titanium plate of the final product, the amount of a specific alloy element that expresses the target characteristics is reduced, In addition, as a result of intensive studies to suppress the production cost of titanium material, a relatively inexpensive material such as sponge titanium is filled and sealed under reduced pressure in a case made of a titanium alloy material. The present inventors have found a method of hot working a titanium material to form a titanium composite material.

The present invention has been made based on the above findings. Hereinafter, a titanium composite material according to the present invention and a titanium material for hot working thereof will be described with reference to the drawings. In the following description, “%” regarding the content of each element means “mass%” unless otherwise specified.

1. Titanium composite 1-1. Overall Configuration As shown in FIG. 1, a titanium composite material 1 according to the present invention is a titanium composite material 1 including a first surface layer portion 2, an inner layer portion 4, and a second surface layer portion 3. The part 2 and the second surface layer part 3 are made of a titanium alloy, and the inner layer part 4 is made of industrial pure titanium having voids. As described above, the fatigue resistance of the titanium composite material is ensured by the surface layer portions (the first surface layer portion 2 and the second surface layer portion 3) in contact with the external environment. And the 1st surface layer part 2 and the 2nd surface layer part 3 are comprised with the titanium alloy which is excellent in various performances compared with industrial pure titanium.

The entire titanium composite 1 has the same characteristics as a titanium material made of the same titanium alloy, but can be manufactured at a low cost.

1-2. First surface layer and second surface layer (thickness)
If the thickness of the surface layer portion in contact with the external environment among the first surface layer portion 2 and the second surface layer portion 3 is too thin, sufficient fatigue resistance cannot be obtained. Although the thickness of the 1st surface layer part 2 and the 2nd surface layer part 3 changes with the thickness of the raw material used for manufacture, or a subsequent processing rate, if it is 5 micrometers or more, a sufficient effect will be exhibited. Therefore, the thickness of at least one of the first surface layer portion 2 and the second surface layer portion 3 (at least the surface layer portion in contact with the external environment) is preferably 5 μm or more, and more preferably 10 μm or more. Further, the thickness of the first surface layer portion 2 and the second surface layer portion 3 with respect to the total thickness of the titanium composite material 1 is preferably 1% or more.

On the other hand, when the first surface layer portion 2 and the second surface layer portion 3 are thick, there is no problem in fatigue resistance, but the formability is lowered. Moreover, since the ratio of the titanium alloy in the entire titanium composite material is increased, the cost merit is reduced. For this reason, the thicknesses of the first surface layer portion 2 and the second surface layer portion 3 are each desirably 100 μm or less, and more desirably 50 μm or less. The thicknesses of the first surface layer portion 2 and the second surface layer portion 3 with respect to the total thickness of the titanium composite material 1 are each preferably 20% or less, and more preferably 10% or less.

(Chemical composition)
The titanium composite material 1 according to the present invention contains the following various alloy elements in order to increase the fatigue resistance of at least one of the first surface layer portion 2 and the second surface layer portion 3 (at least the surface layer portion in contact with the external environment). It is necessary to let

One or more selected from Fe, Cr, Ni, Al and Zr: 0.08 to 1.0%
Since the starting point of fatigue failure is the surface of the plate material, in order to obtain high fatigue resistance while maintaining the formability, it is preferable that the crystal grain size of the α phase is 15 μm or less. The crystal grain size of the α phase is more preferably 10 μm or less, and further preferably 5 μm or less.

In order to set the α phase crystal grain size to 15 μm or less and to obtain high fatigue resistance, the total content of Fe, Cr, Ni, Al and Zr is set to 0.08% or more. On the other hand, if the total content of these elements exceeds 1.0%, ductility such as elongation or formability may be greatly reduced. Therefore, the total content of one or more selected from Fe, Cr, Ni, Al and Zr is set to 0.08 to 1.0%.

The balance other than the above is Ti and impurities. Impurities can be contained as long as the target characteristics are not impaired, and other impurities are mainly impurity elements mixed from scrap, such as Sn, Mo, V, Mn, Nb, Si, Cu, Co, Pd, Ru, There are Ta, Y, La, Ce, and the like, and together with general impurity elements C, N, O, and H, a total amount of 5% or less is acceptable.

(Mechanical properties)
The titanium composite material 1 has high fatigue strength while maintaining excellent formability, and the fatigue strength ratio (10 ⁷ times fatigue strength / tensile strength) is 0.65 or more. The higher the fatigue strength ratio, the better the fatigue characteristics. Titanium materials generally have a numerical value of 0.5 to 0.6. It can be said that the fatigue characteristics are excellent, and if it is 0.70 or more, it is further excellent.

In addition, the titanium composite 1 has a breaking elongation of 25% or more in the direction perpendicular to the rolling direction. In the molding process, the elongation is greatly affected, and the larger the elongation, the better the moldability.

1-3. Inner layer (chemical component)
The pure titanium component of the inner layer portion 4 of the titanium composite material 1 depends on the component of the sponge titanium used when manufacturing, as will be described later. In the titanium composite material 1 according to the present invention, JIS class 1, JIS class 2, JIS class 3 or JIS class 4 industrial pure titanium can be used among the pure titanium specified in JIS. That is, it contains 0.1% or less C, 0.015% or less H, 0.4% or less O, 0.07% or less N, 0.5% or less Fe, and the balance is Ti. Pure titanium for industrial use.

When these JIS 1-4 kinds of industrial pure titanium are used, a titanium material that has sufficient workability, does not generate cracks, and is integrated with the surface titanium alloy after hot working can be obtained. However, since titanium is an active metal, the surface area per mass increases when the average particle diameter of sponge titanium becomes 0.1 mm or less, and O catch-up (concentration) becomes unavoidable under actual operation. It should be noted.

The O content of the inner layer portion of the titanium composite material can be adjusted according to desired mechanical properties, and may be contained up to a maximum of 0.4% when high strength is required. If the O content exceeds 0.4%, cracks and the like may occur, and a titanium material integrated with the surface titanium alloy after hot working may not be obtained. On the other hand, when ductility is required rather than strength, it is preferable to lower the O content, preferably 0.1% or less, more preferably 0.05% or less.

(Porosity)
The titanium composite material 1 according to the present invention is manufactured by hot working and cold working using a titanium material 5 described later as a raw material. At this time, the gap formed in the pure titanium portion in the titanium material 5 is pressure-bonded with the hot working and the cold working, but is not completely removed and a part remains in the inner layer portion 4. When there are too many voids in the inner layer portion 4, mechanical properties (strength and ductility) as a bulk metal are lowered.

However, in order to completely press the gap, a large reduction is required, and the shape (thickness) of the titanium composite material 1 to be manufactured is limited, which may further increase the manufacturing cost. On the other hand, when the voids are contained to such an extent that the mechanical properties (strength, ductility, etc.) sufficient to maintain the structure as the titanium composite material 1 are contained, the density of the internal titanium is lowered, and thus the titanium composite material 1 is manufactured. Weight reduction of the titanium composite material 1 can be expected.

At this time, if the porosity in the inner layer portion 4 is 30% or less, the inner layer portion 4, the first surface layer portion 2, and the second surface layer portion 3 are manufactured as a titanium composite material 1. In order to efficiently manufacture the titanium composite material 1, it is desirable to perform hot and cold processing beyond a certain amount, and the porosity in this case is 10% or less.

As described above, select the porosity depending on the application, such as lowering the porosity when mechanical properties as a bulk metal are important, and increasing the porosity when priority is given to weight reduction of the material. Is possible. At this time, the porosity in the inner layer portion 4 is desirably more than 0% and not more than 30%, and more desirably more than 0% and not more than 10%.

(Porosity calculation method)
The ratio (void ratio) of the voids remaining in the inner layer portion 4 of the titanium composite material 1 is calculated as follows. After embedding in the resin so that the cross section of the titanium material can be observed, the observation surface is buffed with a diamond or alumina suspension to give a mirror finish. An optical micrograph of the central part of the plate thickness is taken at a magnification of 500 times using the sample for observation that has been mirror-finished. The area ratio of the voids observed in the photographed optical micrograph is measured, and the 20 measurement results are averaged to calculate the void ratio. The microscope used for the observation is not a problem even with a normal optical microscope, but it is desirable to use it because it can be observed more clearly by using a differential interference microscope capable of observing polarized light.

2. FIG. 2 is an explanatory diagram showing the structure of a hot working titanium material 5 that is a hot working material of the titanium composite 1. The titanium composite material 1 in which the first surface layer portion 2 and the second surface layer portion 3 are made of a titanium alloy and the inner layer portion 4 is made of pure titanium is, for example, a titanium alloy material having various characteristics as shown in FIG. The entire periphery is sealed to form a housing 6, and the inside of the housing 6 is filled with a titanium lump 7. The inside of the housing 6 is decompressed to form a titanium material 5, and this titanium material 5 is heated as a material for hot working. Manufactured by hot working. Below, the detail of each structure of a raw material is demonstrated.

2-1. Titanium lump (chemical component)
The titanium block 7 filled in the titanium material 5 for hot working according to the present invention is a normal titanium block manufactured by a smelting process such as a conventional crawl method, and the components thereof are JIS type 1, JIS type 2, JIS 3 type. Industrial pure titanium corresponding to seeds or JIS type 4 can be used.

(shape)
The titanium block 7 includes one or more selected from sponge titanium, briquettes obtained by compressing sponge titanium, and industrial pure titanium scrap. The size of the titanium block 7 is preferably 30 mm or less in terms of average particle size. When the average particle size is larger than 30 mm, there are problems during handling such as difficulty in handling during transportation and difficulty in placing in titanium material, resulting in poor work efficiency. Moreover, the filling rate at the time of filling in the housing | casing 6 may become low, and the density of the titanium composite material 1 manufactured by hot processing may become low, and it may become a factor which causes characteristics deterioration, such as ductility.

On the other hand, if the size of the titanium block 7 is too small, not only may the dust become a problem when filling the housing 6 and the work may be hindered, but also the surface area per mass becomes large and handling is in progress. Concentration of O may occur. For this reason, it is preferable that the average particle diameter of the titanium lump 7 is 0.1 mm or more, and it is more preferable that it is 1 mm or more.

In addition, it is possible to use the pure titanium powder which gave the MM (Mechanical Milling) process as a very fine powder with an average particle diameter of 0.1 mm or less. The MM process is a process in which powder and hard balls are put in a pot and sealed, and a pot mill is vibrated to refine the powder. Since the surface of the fine powder after MM treatment is in an active state, it is necessary to handle it by inert gasification so as not to absorb O and N in the atmosphere when recovering pure titanium powder from the pot.

In addition, when pure titanium having a low concentration of O and N is treated with MM, the powder is pressed against each other because of high ductility, or pure titanium is pressed against a hard ball or pot surface. Therefore, the problem that the yield of the pure titanium powder obtained by MM processing is bad arises. For these reasons, production of pure titanium powder by MM treatment requires a great deal of labor and cost, and is not suitable for mass production.

There is also a method for producing titanium fine powder from sponge titanium by hydrodehydrogenation. However, since the surface area per mass increases and the O concentration tends to increase due to surface oxidation, it becomes difficult to control the material. Therefore, the present invention using sponge titanium as it is is superior in terms of quality and cost.

In addition, when using sponge titanium as a briquette by press molding, a part or all of sponge titanium may be replaced with scrap (pure titanium scrap) or titanium powder.

2-2. Housing (Chemical component)
The titanium alloy of the alloy component described above is used so as to form a titanium alloy of the first surface layer portion 2 and the second surface layer portion 3 of the titanium composite material 1 that is the final product.

(shape)
Since the shape of the titanium alloy material used as the housing 6 depends on the shape of the titanium material 5 used as the hot working material, there is no particular shape, and a plate material or a tube material can be used. However, in order to provide the titanium composite 1 manufactured through the manufacturing processes such as hot working, cold working and annealing with high functionality by alloying the surface layer and excellent surface properties, The thickness of the titanium alloy material used is important.

When the thickness is as thin as less than 1 mm, the housing 6 breaks during the hot working due to plastic deformation, the vacuum breaks, and the internal titanium mass 7 is oxidized. Further, the undulations of the titanium mass 7 filled in the titanium material 5 are transferred to the surface of the titanium material 5, and a large surface undulation is generated on the surface of the titanium material 5 during hot working. As a result, the manufactured titanium composite material 1 adversely affects the mechanical properties such as surface properties and ductility, and further fatigue resistance.

In addition, even when no surface defects occur during hot working and cold working, the thickness of the titanium alloy portion is locally reduced in the manufactured titanium composite 1 and sufficient fatigue resistance is exhibited. It may not be possible. Moreover, since the weight of the titanium lump 7 filled inside cannot be supported when the casing 6 becomes excessively thin, the rigidity of the titanium material 5 is insufficiently deformed during holding or processing at room temperature or hot. .

If the thickness of the titanium alloy material used for the housing 6 is 1 mm or more, it is possible to perform hot working without causing these problems, and the titanium composite material 1 having excellent surface properties and fatigue resistance can be obtained. Can be manufactured. The thickness of the titanium alloy material is more preferably 2 mm or more.

On the other hand, if the thickness of the titanium alloy material becomes too thick, the proportion of the casing 6 in the manufactured hot-working titanium material 5 increases, and the proportion of the titanium mass 7 in the titanium material 5 relatively increases. Therefore, the yield decreases and the cost increases.

2-3. Next, the titanium material 5 manufactured using the titanium block 7 and the housing 6 will be described.

(shape)
The shape of the titanium material 5 is not limited to a specific shape, but is determined by the shape of the titanium composite material 1 to be manufactured. A rectangular parallelepiped titanium material 5 is manufactured for the purpose of manufacturing a plate material, and a cylindrical or octagonal columnar titanium material 5 is manufactured for the purpose of manufacturing a round bar, wire or extruded material. Is done. The size of the titanium material 5 is determined by the size (thickness, width, length) of the product and the production amount (weight).

(internal)
A titanium lump 7 is filled in the inside of the titanium material 5 that is sealed and surrounded by the housing 6. Since the titanium mass 7 is a massive particle, there is a space (gap) between the particles. In order to improve the handleability of the titanium lump 7 and reduce these gaps, the titanium lump 7 may be previously compression-molded and then placed in the titanium material 5. If air remains in the gap in the titanium material 5, the titanium lump 7 is oxidized and nitrided during heating before hot working, and the ductility of the manufactured titanium composite material 1 is reduced. For this reason, the inside of the titanium material 5 is depressurized to a high degree of vacuum.

(Degree of vacuum)
In order to prevent oxidation / nitridation of the titanium lump 7 during hot working, the degree of vacuum inside the titanium material 5 is set to 10 Pa or less, preferably 1 Pa or less. When the internal pressure (absolute pressure) of the titanium material 5 is greater than 10 Pa, the titanium mass 7 is oxidized or nitrided by the remaining air. Although the lower limit is not particularly defined, in order to extremely reduce the degree of vacuum, it leads to an increase in manufacturing cost such as improvement of the air tightness of the device and enhancement of the vacuum exhaust device, so it is necessary to make it less than 1 × 10 ⁻³ Pa Absent.

(welding)
As a method for welding the casing 6, arc welding such as TIG welding or MIG welding, electron beam welding, laser welding, or the like can be used, and the method is not particularly limited. However, the welding atmosphere is a vacuum atmosphere or an inert gas atmosphere so that the surfaces of the titanium block 7 and the housing 6 are not oxidized or nitrided. When welding the joint of the housing | casing 6 last, it is preferable to put the titanium material 5 in the container (chamber) of a vacuum atmosphere, and to weld, and to keep the inside of the titanium material 5 in a vacuum.

3. Next, a manufacturing method of the titanium composite 1 that performs hot working using the titanium material 5 of the present invention as a raw material for hot working will be described.

The titanium composite material (product) 1 is formed by performing hot working using the titanium material 5 as a hot working material. The hot working method can be selected depending on the shape of the product.

When manufacturing a plate material, a rectangular parallelepiped (slab) titanium material 5 is heated and hot-rolled to obtain a titanium plate. If necessary, after the hot rolling, the surface oxide layer may be removed by pickling or the like after hot rolling, and then cold rolling may be performed to further reduce the thickness.

When manufacturing a round bar or wire, a cylindrical or polygonal (billet) titanium material 5 is heated and hot-rolled or hot extruded to form a titanium round bar or wire. Further, as necessary, after the hot working, the oxide layer may be removed by pickling or the like, and then cold-rolled and further thinned as in the conventional process.

Furthermore, when manufacturing an extruded profile, a cylindrical or polygonal (billet) titanium material 5 is heated and subjected to hot extrusion to obtain various cross-sectional titanium profiles.

The heating temperature before hot working may be the same heating temperature as when hot working a normal titanium slab or billet. Although it varies depending on the size of the titanium material 5 or the degree of hot working (working rate), it is preferably set to 600 ° C. or more and 1200 ° C. or less. If the heating temperature is too low, the high-temperature strength of the titanium material 5 becomes too high, causing cracks during hot working, and joining of the titanium block 7 and the casing (titanium alloy part) 6 becomes insufficient. On the other hand, if the heating temperature is too high, the structure of the obtained titanium composite material 1 becomes rough, so that sufficient material properties cannot be obtained, and the surface casing (titanium alloy portion) 6 is thinned by oxidation. End up. If the heating temperature is 600 to 1200 ° C., hot working can be performed without such a problem.

The degree of processing during hot processing, that is, the processing rate, can be selected to control the porosity in the titanium composite 1. The processing rate here is a ratio (percentage) obtained by dividing the difference between the cross-sectional area of the titanium material 5 and the cross-sectional area of the titanium composite material 1 after hot working by the cross-sectional area of the titanium material 5.

When the processing rate is low, the gap between the titanium masses 7 inside the titanium material 5 is not sufficiently crimped, and therefore remains as a void after hot working. The titanium composite material 1 containing many such voids is lighter by the amount of voids contained. However, since there are many voids present inside, the mechanical properties are not sufficiently exhibited. On the other hand, as the processing rate increases, the porosity decreases and the mechanical properties improve. For this reason, when the mechanical characteristics of the titanium composite material 1 to be manufactured are regarded as important, a higher processing rate is preferable.

Specifically, when the processing rate is 90% or more, the gap between the grain boundaries of the titanium mass 7 inside the titanium material 5 can be sufficiently bonded, and the voids of the titanium composite material 1 can be reduced. A higher processing rate is preferable in order to surely eliminate the voids in the titanium composite material 1, but the cross-sectional area of the titanium material 5 must be increased, and hot processing must be repeated many times. No longer. As a result, problems such as a long manufacturing time occur, and therefore, the processing rate is preferably 99.9% or less.

Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.

As shown in FIGS. 1 and 2, a titanium ingot 7 was filled into a titanium alloy plate 6 to obtain a titanium material 5, and a method of rolling the titanium material 5 was performed to prepare a test piece.

The total thickness of the titanium material 5 is 125 mm, the total content of Fe, Cr, Ni, Al, and Zr in the housing 6 is 0.03 to 1.12%. The chemical composition of the inner titanium mass 7 is O In the range of 0.043 to 0.301%, Fe: 0.028 to 0.088%, C: 0.01% or less, H: 0.003 or less, and N: 0.006% or less. In order to partially compare the influence of the hot rolling rate, titanium materials 5 having a total thickness of 25 mm and 50 mm were also produced.

Specifically, a casing 6 is produced on the outer periphery using a titanium alloy plate having an adjusted Fe, Cr, Ni, Al, Zr concentration and thickness, and sponge titanium is compression-molded inside the casing 6. The compressed body (briquette) was filled, and then the lid of the titanium material 5 was welded.

A briquette is prepared by mixing 10% or 30% of a titanium material 5 that is not filled with briquettes and filled with sponge titanium as it is, a pure titanium plate having the same composition as sponge titanium, and cut to about 25 mm square. A filled titanium material 5 was produced.

As the welding method, in order to prevent oxidation and nitridation of the titanium block 7 during hot working, electron beam welding was performed in a vacuum atmosphere in which the degree of vacuum inside the titanium material 5 was 10 Pa or less.

Then, after hot rolling to a thickness of 5 mm, descaling (shot blasting and pickling), cold rolling and annealing were performed to obtain a titanium composite material 1. In addition, the thickness of the 1st surface layer part 2 and the 2nd surface layer part 3 which make an element concentration area | region (titanium alloy) was adjusted with the thickness of the outer titanium alloy board 6, and the surface removal amount at the time of descaling.

About each test material which is titanium composite material 1, (alpha) phase crystal grain diameter in each position, tensile strength, elongation, fatigue strength, and the moldability were evaluated on the conditions shown below.

(Α phase crystal grain size)
The thickness of the 1st surface layer part 2 and the 2nd surface layer part 3 was measured by EPMA. In the structure photograph taken with an optical microscope, the average crystal grain size of the α phase at the position of 1 to 10% of the plate thickness was calculated in the inner layer portion and the surface layer portion by a cutting method according to JIS G 0551 (2005).

(Tensile strength, elongation)
Prepare a tensile test material with a parallel part of 6.25 x 32 mm, a distance between gauge points of 25 mm, a chuck part width of 10 mm, and a total length of 80 mm (half the size of JIS13-B tensile test material). The tensile test was performed at a tensile rate of 30% / min after the yield strength at 0.5% / min. Here, the tensile strength and the total elongation in the direction perpendicular to the rolling direction were evaluated.

(Fatigue strength)
Using a plane bending fatigue test material shown in FIG. 3 and a plane bending test machine manufactured by Tokyo Henki, a fatigue test was performed under the conditions of a stress ratio R = −1 and a frequency of 25 Hz. Here, the number of repetitions until breakage at each stress amplitude was determined to create a stress fatigue curve, and the fatigue limit (fatigue strength) that did not break even after repeated bending 10 ⁷ times was evaluated.

(Formability)
A ball head overhang test was performed on a titanium plate processed into a 90 mm × 90 m × 0.5 mm shape using a ball head punch of φ40 mm in a deep drawing tester manufactured by Tokyo Tester, model number SAS-350D. The overhang test is performed by applying high viscosity oil (# 660) manufactured by Nippon Tool Oil Co., Ltd., placing a poly sheet on it, preventing the punch and titanium plate from touching directly, and the overhang height when the test material breaks. It was evaluated by comparing the thickness.

The overhang height in the ball head overhang test is strongly affected by the oxygen concentration, so that the moldability is 21.0 mm or more for JIS type 1, 19.0 mm or more for JIS type 2 and 13.0 mm or more for JIS type 3 ( (Circle mark in the table). In the case of less than this, it was considered unsatisfactory (x mark in the table).

(Metal structure)
FIG. 4 shows an example of a tissue photograph when produced by the above method. 4 (a) shows test no. 1 (comparative example, general titanium material), and FIG. 9 (example of the present invention), and FIG. 16 (example of the present invention), and FIG. 22 is a structure photograph of 22 (example of the present invention).

4 (b) to 4 (d) are examples of the present invention, and the thicknesses of the first surface layer portion 2 and the second surface layer portion 3 are different.

The test results are summarized in Tables 1 and 2. Table 1 shows a case where industrial pure titanium corresponding to JIS type 1 is used as the titanium mass 7, and Table 2 shows a case where industrial pure titanium corresponding to JIS 2, 3 type is used as the titanium mass 7. In Tables 1 and 2, the symbols N1 to N4 in the column “Level of material form used inside the casing” indicate the following types and ratios.
N1: Briquette using 100% sponge titanium N2: 100% titanium sponge remains
N3: Briquette mixed with 90% sponge titanium and 10% scrap with the same composition N4: Briquette mixed with 70% sponge titanium and 30% scrap with the same composition

Test No. in Table 1 Nos. 7 to 19, 21 to 24, 26 to 30, and 33 to 40 are examples of the present invention that satisfy all the conditions defined in the present invention. Reference numerals 1 to 6, 20, 25, 31 and 32 are comparative examples which do not satisfy the conditions defined in the present invention.

Test No. 1 to 3 are titanium alloy plates corresponding to JIS Class 1, and have formability and fatigue strength which are standards for evaluating the formability and fatigue strength of the examples of the present invention. Test No. The fatigue strength ratios of 1 to 3 are 0.63, 0.63, and 0.55, respectively, which are typical values.

Test No. 7 to 19, 21 to 24, 26 to 30 and 33 to 40, elongation: 30 to 46%, tensile strength: 295 to 341 MPa, fatigue strength: 197 to 251 MPa, fatigue strength ratio: 0.67 to 0.78 The overhang height: 21.0 to 21.7 mm of mechanical properties is obtained, which indicates that both the formability and the fatigue strength are excellent.

In contrast, test no. No. 4 is unsatisfactory with a fatigue strength ratio of 0.63 because the Fe content of the first surface layer portion 2 and the second surface layer portion 3 is below the range of the present invention.

Test No. 5 and 6 are unsatisfactory at 20% and 18%, respectively, because the Fe content of the first surface layer portion 2 and the second surface layer portion 3 exceeds the range of the present invention.

Test No. No. 20 has a fatigue strength ratio of 0.63 because the thickness of the first surface layer portion 2 and the second surface layer portion 3 is 3 μm and the thickness / total plate thickness × 100 is 0.5%, which is below the range of the present invention. And unsatisfactory.

Test No. No. 25 has a high manufacturing cost because the thickness of the first surface layer portion 2 and the second surface layer portion 3 is 128 μm and the thickness / total plate thickness × 100 exceeds 25.6% in the range of the present invention.

Test No. No. 31 is unsatisfactory with a fatigue strength ratio of 0.62, because the Al content of the first surface layer portion 2 and the second surface layer portion 3 is below the range of the present invention.

Furthermore, test no. No. 32 has an unfavorable elongation of 22% because the Al content of the first surface layer portion 2 and the second surface layer portion 3 exceeds the range of the present invention.

Test No. in Table 2 Nos. 46 to 51, 53, 54, and 59 to 66 are examples of the present invention that satisfy all the conditions defined in the present invention. Nos. 41 to 45, 52 and 55 to 58 are comparative examples which do not satisfy the conditions defined in the present invention.

Test No. Nos. 41 and 42 are titanium alloy plates corresponding to JIS class 2, and test nos. 55 and 56 are titanium alloy plates corresponding to JIS class 3. Test No. Each of 41, 42, 55 and 56 has formability and fatigue strength which are standards for evaluating the formability and fatigue strength of the examples of the present invention. Test No. The fatigue strength ratios of 41 and 42 are 0.58 and 0.59, respectively. The fatigue strength ratios for 55 and 56 are 0.59 and 0.58, respectively. Both are general values.

Test No. 47-51, 53, 54 and 59-65 have elongation of 25-33%, tensile strength: 341-614 MPa, fatigue strength: 255-421 MPa, fatigue strength ratio: 0.65-0.77, overhang height The mechanical properties of 10.0 to 20.6 mm are obtained, and it can be seen that both formability and fatigue strength are excellent.

In contrast, test no. No. 43 is unsatisfactory with a fatigue strength ratio of 0.57 because the Fe content of the first surface layer portion 2 and the second surface layer portion 3 is below the range of the present invention.

Test No. 44 and 45 are unsatisfactory at 20% and 16%, respectively, because the Fe content of the first surface layer portion 2 and the second surface layer portion 3 exceeds the range of the present invention.

Test No. No. 52 has a high manufacturing cost because the thickness of the first surface layer portion 2 and the second surface layer portion 3 is 160 μm, which exceeds the range of the present invention.

Test No. No. 57 is unsatisfactory with a fatigue strength ratio of 0.59 because the Fe content of the first surface layer portion 2 and the second surface layer portion 3 is below the range of the present invention.

Test No. No. 58 is unsatisfactory at 19% because the Fe content of the first surface layer portion 2 and the second surface layer portion 3 exceeds the range of the present invention.

1. Titanium composite material First surface layer part3. Second surface layer 4. Inner layer part 5. 5. Titanium material for hot working Case 7. Titanium lump

Claims (6)

A first surface layer,
The inner layer,
A titanium composite material comprising a second surface layer portion,
The first surface layer portion and the second surface layer portion are made of a titanium alloy,
The inner layer portion is made of industrial pure titanium having voids,
The chemical composition of at least one of the first surface layer part and the second surface layer part is mass%,
Total of one or more selected from Fe, Cr, Ni, Al and Zr: 0.08 to 1.0%,
The balance: Ti and impurities,
The thickness of the at least one of the first surface layer portion and the second surface layer portion is 5 to 100 μm, and the proportion of the total thickness of the titanium composite material is 20% or less;
The volume ratio in a cross section perpendicular to the thickness direction of the gap is more than 0% and 30% or less.
Titanium composite material. The crystal grain size of the α phase in the at least one of the first surface layer part and the second surface layer part is 15 μm or less,
The titanium composite according to claim 1. The chemical composition of the industrial pure titanium is mass%,
C: 0.1% or less,
H: 0.015% or less,
O: 0.4% or less,
N: 0.07% or less,
Fe: 0.5% or less,
Balance: Ti and impurities,
The titanium composite material according to claim 1 or 2. The fatigue strength ratio is 0.65 or more,
The titanium composite material according to any one of claims 1 to 3. The elongation at break in the width direction during rolling is 25% or more,
The titanium composite material according to any one of claims 1 to 4. A housing,
One or more types selected from sponge titanium, briquettes compressed with sponge titanium, and industrial pure titanium scrap filled in the housing,
Part of the housing, the part constituting the surface layer after hot working is made of a titanium alloy,
The chemical composition of the titanium alloy is mass%,
Total of one or more selected from Fe, Cr, Ni, Al and Zr: 0.08 to 1.0%,
Balance: Ti and impurities,
Titanium material for hot working.

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