JP7107501B2 - β-type titanium alloy and its manufacturing method - Google Patents

Description

The present invention relates to a β-titanium alloy and a method for producing the same. More specifically, the present invention relates to a β-titanium alloy capable of partially forming a high-hardness surface region and a method for producing the same.

Titanium alloys are attracting attention as practical metals that combine excellent properties such as light weight, high strength, and high corrosion resistance with recyclability that is friendly to the global environment.
Such titanium alloys are used in mechanical parts such as sliding members, cutlery for medical and food use, and the like. As a countermeasure against wear in these applications, there is a demand for a means for imparting good wear resistance to the necessary parts of the titanium alloy. As a more specific means of imparting wear resistance to titanium alloys, a method has been proposed in which a plurality of types of heat treatments are sequentially performed to partially harden the necessary portions (see Patent Document 1). .).

JP 2015-190032 A

In the β-type titanium alloy and the method for producing the same disclosed in Patent Document 1, it is possible to harden a part of the titanium alloy, but it is required to harden the surface of the part to increase the wear resistance. ing.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a β-titanium alloy capable of partially forming a high-hardness surface region, and a method for producing the same.

The present invention is as follows.
1. A manufacturing method for heat-treating a β-type titanium alloy base material to produce a β-type titanium alloy in which an oxygen-immersed layer and a hardened layer are formed in order from the surface side of a part of the base material, wherein the β-type titanium alloy base material is a first heat treatment step of heat-treating at a temperature H _T (° C.) represented by the following formula (1); A second heat treatment step of locally heating, and a third heat treatment step of obtaining the β-titanium alloy by heat-treating the β-titanium alloy base material heat-treated in the second heat-treatment step for 120 hours or more to perform in this order. A method for producing a β-type titanium alloy, characterized by:
_{200≤HT≤βT} - ₇₀ (1)
(In the formula, β _T indicates the β transformation point (°C) of the β-type titanium alloy)
2. During the local heating of the second heat treatment step, the inert gas is continuously blown to the one portion, and the blowing is stopped when the local heating is finished. A method for producing the described β-titanium alloy.
3. The first heat treatment step removes the oxide film formed on the surface of the β-type titanium alloy base material after the heat treatment. or 2. A method for producing a β-type titanium alloy according to 1.
4. The amount of oxygen in each of the oxygen-immersed layer, the hardened layer, and the heat-treated base material after heat treatment of the β-type titanium alloy base material has the highest oxygen amount in the oxygen-immersed layer and decreases sequentially. to 3. A method for producing a β-type titanium alloy according to any one of 1.
5. A β-type titanium alloy comprising a heat-treated base material obtained by heat-treating a β-type titanium alloy base material, and an oxygen-immersed layer and a hardened layer sequentially formed from the surface side of a portion of the heat-treated base material. The β-type titanium alloy, wherein the oxygen content of each of the oxygen-immersed layer, the hardened layer, and the heat-treated base material is the highest in the oxygen-immersed layer and decreases in order. .
6. The β-type titanium alloy base material is Ti-22V-4Al consisting of 22% by mass of V, 4% by mass of Al, and the balance of Ti, and the oxygen-immersed layer is formed from the hardened layer and the heat-treated base material. 5. The amount of vanadium is also low. β-type titanium alloy according to.
7. 5. The one portion is located on the front end side of the base material after the heat treatment. or 6 above. β-type titanium alloy according to.

According to the method for producing a β-titanium alloy of the present invention, the toughness as a structure is maintained and the machinability is excellent. Abrasive. Further, by having the oxygen-immersed layer and the hardened layer in one part, the deformation of one part can be suppressed. By forming these layers, it can be suitably used in various fields (machine parts, food processing equipment, cooking utensils, medical instruments, tools, etc.) where both toughness and wear resistance properties are required.

During the local heating of the second heat treatment step, if the inert gas is continuously blown to the part and the blowing is stopped at the end of the local heating, the surface of the part is heated during the local heating. By cooling with an inert gas only in the third heat treatment step, a semi-hardened layer that becomes an oxygen-impregnated layer and a hardened layer can be easily formed, and an oxygen-impregnated layer and a hardened layer with excellent wear resistance can be formed. Obtainable.
In the first heat treatment step, if the oxide film formed on the surface of the β-type titanium alloy base material is removed after the heat treatment, the removal of the oxide film prevents oxygen from entering the base material in the second heat treatment step. Preparations can be made to facilitate the formation of the oxygen-immersed layer.
When the oxygen-immersed layer, the hardened layer, and the base material after heat treatment of the β-titanium alloy base material have the highest oxygen content and decrease in this order, Equipped with an oxygen-immersed layer with excellent wear resistance, other parts can obtain sufficient toughness.

According to the β-type titanium alloy of the present invention, the elemental amount of oxygen contained in each of the oxygen-immersed layer, the hardened layer, and the heat-treated base material has the highest oxygen content in the oxygen-immersed layer, and decreases sequentially. As a result, an oxygen-immersed layer with excellent wear resistance can be provided, and other portions can obtain sufficient toughness.
In addition, the β-type titanium alloy base material is Ti-22V-4Al consisting of 22% by mass of V, 4% by mass of Al, and the balance of Ti, and the oxygen-immersed layer is composed of the hardened layer and the heat-treated mother. When the amount of vanadium is lower than that of the material, the α-phase is sufficiently precipitated by the first heat treatment step, and a hardened layer having excellent wear resistance can be obtained.
When the part is located on the tip side of the base material after the heat treatment, it is possible to increase the hardness by forming an oxygen-immersed layer and a hardened layer in a part where high hardness is required, such as the cutting edge of a cutting tool. It can be a β-titanium alloy suitable for many applications.

FIG. 3 is a schematic cross-sectional view for explaining the vicinity of a hardened surface of a portion of the β-titanium alloy. It is a schematic diagram which shows the example of a 2nd heat processing process. It is a perspective view showing an example of a drill bit. FIG. 3 is a partially enlarged cross-sectional view from GG shown in FIG. 2 to the cutting edge of the drill bit; 5 is a partially enlarged cross-sectional view of the distal end side of FIG. 4; FIG. It is the image which cut|disconnected the front end side of the produced drill bit in the axial direction. FIG. 7 is a partially enlarged view of the distal end side of FIG. 6; It is a graph which shows the change of the amount of oxygen from a hardened surface to a deep part. It is a graph which shows the change of the amount of vanadium from a hardened surface to a deep part. It is an analysis image showing changes in O, Ti, V, and Al in cross sections of an oxygen-immersed layer and a hardened layer of a drill bit. 4 is an analysis image showing changes in O, Ti, V, and Al in the cross section of the base material after heat treatment of the drill bit.

The material presented herein is intended to be illustrative and illustrative of the embodiments of the invention and is believed to be the most effective and readily comprehensible description of the principles and conceptual features of the invention. It is stated for the purpose of providing what it seems. In this regard, no attempt is made to show structural details of the invention beyond those necessary for a fundamental understanding of the invention, and the description in conjunction with the drawings will illustrate some aspects of the invention. It will be clear to those skilled in the art how it is actually implemented.

In the method for producing the present β-titanium alloy, a first heat treatment step, a second heat treatment step, and a third heat treatment step are sequentially performed on a β-titanium alloy base material to form an oxygen-immersed layer and harden in order from the surface side of a part. It is characterized by producing a β-type titanium alloy in which a layer is formed.
The produced β-titanium alloy 1 consists of a heat-treated base material 11 obtained by heat-treating the β-type titanium alloy base material, and a hardened surface 21 which is the surface of a portion 2 of the heat-treated base material 11 in this order. an oxygen-immersed layer 5 and a stiffening layer 6 formed in (see FIG. 1). Also, an oxide coating layer 4 may be formed on the surface of the portion 2 . In this case, an oxide coating layer 4 , an oxygen-immersed layer 5 and a hardened layer 6 are formed in this order from the surface of the part 2 .

The one portion is a portion that is arbitrarily set for the β-titanium alloy, and is a portion that is imparted with wear resistance such that the hardness of the surface is higher than that of the base material 11 after heat treatment. The one site may be one site or two or more sites. Further, as a specific example of the one portion, the front end side of the base material after the heat treatment can be mentioned. The tip side of the heat-treated base material often needs to have high hardness, such as the cutting edge of a cutting tool.

The β-type titanium alloy base material (hereinafter abbreviated as base material) may be a titanium alloy having a β-phase crystal structure, and examples include Al, C, Ga, N, O, Sn, Mo, V, An alloy containing one or more of Nb, Ta, Ru, Cr, Fe, Mn, Cu, Co, Si, Zr, Hf, Ni and W, with the balance being Ti and unavoidable impurities can do. Further, the present base material also includes a near β-type titanium alloy in which the α phase is mixed in the β phase.
More specific β-type titanium alloys include Ti-V-Al, Ti-V-Cr-Al, Ti-Mo-V-Fe-Al, and Ti-Al-V-Cr-Mo-Zr. , Ti-Mo-Zr system, Ti-Mo-Zr-Al system, Ti-Fe system, Ti-Fe-Al system, Ti-Mo-Zr-Sn system, Ti-V-Zr-Al-Sn system, Ti -V-Cr-Al-Sn system, Ti-Al-V-Fe system, Ti-Mo-Nb-Al-Si system, Ti-Fe-Cr-Al system, Ti-Mo-Zr-Fe system, Ti- Mo system, Ti-Nb-Zr-Ta system, T-Nb system, Ti-V-Mo-Cr-Al system, Ti-V-Mo-Cr-Fe-Al system and Ti-Al-Sn-Cr-Mo Binary or higher β-type titanium alloys such as -Zr-Fe can be mentioned.

Further, as a more specific example of the binary or higher β-type titanium alloy, for example, Ti-22V-4Al (hereinafter referred to as mass% omitted), Ti-15V-6Cr-4Al, Ti-13V-11Cr-3Al, Ti-8Mo-8V-2Fe-3Al, Ti-3Al-8V-6Cr-4Mo-4Zr, Ti-15Mo-5Zr , Ti-15Mo-5Zr-3Al, Ti-2-15Fe (for example, Ti-4Fe, Ti-4.5Fe, T-5Fe can be exemplified.), Ti-2-15Fe-1-10Al (for example, Ti-4Fe-1Al, Ti-5Fe-1Al can be exemplified.), Ti-11.5Mo-6Zr-4.5Sn, Ti-11V-11Zr-2Al-2Sn, Ti-15V-3Cr-3Al-3Sn, Ti-1Al-8V-5Fe, Ti-15Mo-2.7Nb-3Al-0.2Si, Ti-4.3Fe-7.1Cr-3Al, Ti-12Mo-6Zr-2Fe, Ti-15Mo, Ti-35Nb-7Zr-5Ta, Ti-45Nb, Ti-5Al-5V-5Mo-3Cr and the like can be mentioned. Examples of near β titanium alloys include Ti-10V-2Fe-3Al, Ti-5V-5Mo-1Cr-1Fe-5Al, and Ti-5Al-2Sn-2Cr-4Mo-4Zr-1Fe.

Of the β-type titanium alloys, a β-type titanium alloy containing no tin atoms as a component is more preferable. Such β-type titanium alloys include Al, C, Ga, N, O, Mo, V, Nb, Ta, Ru, Cr, Fe, Mn, Cu, Co, Si, Zr, Hf, Ni, W, etc. It contains one or more types, the balance being Ti and unavoidable impurities, Ti-V-Al system, Ti-V-Cr-Al system, Ti-Mo-V-Fe-Al system, Ti- Al-V-Cr-Mo-Zr system, Ti-Mo-Zr system, Ti-Mo-Zr-Al system, Ti-Fe system, Ti-Fe-Al system, Ti-Al-V-Fe system, Ti- Mo-Nb-Al-Si, Ti-Fe-Cr-Al, Ti-Mo-Zr-Fe, Ti-Mo, Ti-Nb-Zr-Ta, T-Nb and Ti-V- The Mo-Cr-Fe-Al system can be mentioned.
Further, more specific examples of the β-type titanium alloys include Ti-22V-4Al, Ti-15V-6Cr-4Al, Ti-13V-11Cr-3Al, Ti-8Mo-8V-2Fe-3Al, Ti-3Al-8V-6Cr-4Mo-4Zr, Ti-15Mo-5Zr, Ti-15Mo-5Zr-3Al, Ti-2~15Fe, Ti-2~15Fe-1~10Al, Ti-1Al-8V-5Fe, Ti-15Mo-2.7Nb-3Al-0.2Si, Ti-4.3Fe-7.1Cr-3Al, Ti-12Mo-6Zr-2Fe, Ti-15Mo, Ti-35Nb-7Zr-5Ta, Ti-45Nb, Ti-10V- Mention may be made of 2Fe-3Al and Ti-5V-5Mo-1Cr-1Fe-5Al. Among these, Ti-22V-4Al (β transformation point: 730°C), Ti-15V-6Cr-4Al (β transformation point: 730°C), Ti-4Fe (β transformation point: 830°C), Ti-5Fe, Ti-4Fe-1Al, Ti-5Fe-1Al or Ti-15Mo-5Zr-3Al are particularly good examples.

Examples of commercially available base materials include DAT51 (Ti-22V-4Al) manufactured by Daido Steel Co., Ltd., JIS 80 class, KS15-5-3 (Ti-15Mo-5Zr-3Al) manufactured by Kobe Steel, Ltd., and Nippon Steel & Sumitomo Metal Corporation. SSAT-2041CF (Ti-20V-4Al-1Sn), etc. can be mentioned.

The base material to be heat-treated is not particularly limited and can be appropriately selected according to the shape of the required β-titanium alloy product, although a flat shape such as a plate can be mentioned. The size of the base material is not particularly limited. For example, when the β-titanium alloy to be produced is a blade of a kitchen knife, the thickness of the base material can be about 0.5 to 5.0 mm. Moreover, the thickness of the base material in the case of the sliding member can be at least 1 mm or more. However, the thickness of each base material is not limited to the thickness, and a base material having an arbitrary thickness can be used.

(First heat treatment step)
The first heat treatment step is a step of heating a base material to a _temperature HT and then performing solution heat treatment, which is a heat treatment for cooling, to obtain a heat-treated base material (hereinafter referred to as a first heat-treated base material).
The heat treatment may be whole heating for heating the entire base material, and examples thereof include a low-frequency heating furnace, a gas furnace, an electric furnace, and the like.
The heat treatment temperature H _T (° C.) is a temperature that satisfies the following formula (1).
_{200≤HT≤βT} - ₇₀ (1)
(In the formula, β _T indicates the β transformation point (°C) of the β-type titanium alloy)

The β transformation point is the temperature above which the crystal structure of the base material becomes a single β phase when heat treated. In the first heat treatment step of the present invention, the heat treatment is performed so that the heat treatment temperature H _T satisfies the above formula (1) (specifically, at a temperature significantly lower than the β transformation point β _T of the β-type titanium alloy). .
Ordinary solution treatment is performed at a temperature above the β transformation point, which is directly below the melting point, but the first heat treatment step is performed at a temperature below the β transformation point shown in the above formula (1), so that the α phase is uniformly distributed throughout. Titanium alloy that precipitates and changes the crystal structure of the base material to a crystal structure in which the α phase (close-packed cubic crystal) is mixed with the β phase (body-centered cubic crystal), and has a higher hardness than ordinary solution treatment can be obtained.
When the heat treatment temperature H _T is higher than β _T −70° C., the precipitation ratio of the α phase decreases. It is difficult to obtain in the heat treatment step, and there is a possibility that a β single phase (or a crystal structure close to it) may be obtained in the first heat treatment step. On the other hand, if the heat treatment _temperature HT is lower than 200° C., the effect of the heat treatment may not be obtained. Therefore, the heat treatment _temperature HT is defined by the above formula (1). The upper limit of the heat treatment temperature H _T is preferably β _T -80°C, and the lower limit of H _T is more preferably 500°C. If the first heat treatment step is performed in such a temperature range, for example, when the Vickers hardness of the base material is 230 HV, the first heat treated base material with a hardness of 230 to 350 HV can be obtained.

The heat treatment time of the first heat treatment step is not particularly limited, and can be appropriately set according to the thickness, type, etc. of the base material to be heat treated. In general, regardless of the thickness and type of the base material, the time is preferably 15 minutes (0.25 hours) or longer, more preferably 1 hour or longer, even more preferably 3 hours or longer, and particularly preferably 24 hours or longer. . Moreover, the upper limit of the heat treatment time is not particularly limited.
The heat treatment atmosphere of the first heat treatment step is not particularly limited, and examples include an oxidizing atmosphere (including an air atmosphere), an inert gas atmosphere (for example, an atmosphere of a rare gas such as argon), and a vacuum. can be done. Moreover, when the first heat treatment step is performed in an oxidizing atmosphere and an oxide film is formed on the surface of the first heat-treated base material, it is preferable to remove the formed oxide film.
The method for cooling the base material after the heat treatment is not particularly limited, and examples thereof include liquid cooling in which the base material is cooled by putting it in water or oil.

(Second heat treatment step)
The second heat treatment step is a step of obtaining a base material (hereinafter referred to as a second heat treated base material) by locally heating a portion of the first heat treated base material obtained in the first heat treatment step in an oxidizing atmosphere. By heating only one part 2 by local heating and then cooling, the one part 2 becomes a β single phase that becomes an oxygen-immersed layer 5 and a hardened layer 6 in order from the surface side by the third heat treatment step. It becomes a hardened layer. At this time, an oxide coating layer 4 may be formed on the surface.
Although the heating temperature of the local heating is not limited, it is presumed that one portion of the first heat-treated base material is heated to 1000° C. or higher (preferably 1300° C. or higher) by the local heating.

As specific heating means for local heating, for example, laser heating, high-frequency induction heating, gas burner heating, electron beam heating, and the like can be used. Among these heating means, at least one selected from the group consisting of laser heating, high-frequency induction heating and gas burner heating can be mentioned as a good example.

Examples of the types of laser heating include CO ₂ laser, YAG laser, excimer laser, UV laser, semiconductor laser, fiber laser, LD laser, and LD-excited solid-state laser heat. Specifically, as an example of conditions for heating by a semiconductor laser as local heating, a laser torch 91 with an output of 50 to 1000 W is moved at a moving speed of 6 mm / s with respect to the first heat treatment base material 12. 2 heating while moving without melting the surface (see FIG. 2).
The high-frequency induction heating may be performed by induction heating with high-frequency current from an AC power source, and commercial products can be used regardless of specific types.
The gas burner heating can be performed by mixing a hydrocarbon gas such as methane, ethane, propane and butane with air as a fuel gas and burning it for heating. can be used.
Electron beam heating can be performed by irradiating an object with an electron beam that is converged at high density in a vacuum to heat the object, and commercial products can be used regardless of the specific type.

During the heat treatment of the second heat treatment step, during the local heating, inert gas can be continuously blown to the part 2 from the nozzle 93 or the like to cool the part other than the heated part (see FIG. 2). . Moreover, it is preferable to stop blowing when the local heating is completed. By spraying only during this local heating, it is possible to prevent coarsening of crystal grains in the semi-hardened layer of the second heat-treated base material and to form a β single phase, thereby facilitating the formation of the oxygen-immersed layer 5 and the hardened layer 6. becomes. Examples of the inert gas used for spraying include rare gases such as argon and nitrogen.
Although the amount of the inert gas to be blown is not particularly limited, for example, when argon gas is to be blown, conditions of 10 to 40 L/min (more preferably 20 to 35 L/min) from a nozzle with a diameter of φ6 mm can be mentioned.
Normally, the surface of titanium readily reacts with oxygen to form TiO ₂ , which forms an oxide coating layer that prevents oxygen from entering, so oxygen is less likely to enter deep layers of the base material. Therefore, by blowing an inert gas onto the heated portion, the partial pressure of oxygen in the vicinity of the heated portion is lowered, thereby suppressing the formation of the oxide coating layer on the surface or suppressing the thickness of the formed oxide coating layer from becoming thicker. This makes it easier for oxygen to penetrate deeper into the base material.
When oxygen penetrates into the base material, it does not combine to form TiO ₂ , but instead dissolves in the titanium alloy (that is, an oxygen-immersed layer is formed). In the case of simply lowering the oxygen partial pressure in the atmosphere, it takes a long time for the oxygen to penetrate, and there is a problem of coarsening of the crystal grains. It is considered that a thick oxygen-immersed layer can be formed and coarsening of crystal grains can be suppressed.

(Third heat treatment step)
In this step, a portion 2 of the second heat-treated base material obtained in the second heat treatment step is heat-treated for 120 hours or more to obtain a β-type titanium alloy 1 having an oxygen-immersed layer 5 and a hardened layer 6 formed thereon. The heat treatment in the third heat treatment step promotes hardening (also referred to as age hardening) of the quasi-hardened layer (β single phase) obtained in the second heat treatment step, forming an oxygen-immersed layer 5 in which oxygen is dissolved. , and the remaining hardened layer 6 . On the other hand, the second heat-treated base material containing two phases of α phase and β phase does not progress hardening due to the heat treatment, and becomes the base material 11 after the heat treatment.
Therefore, while maintaining the toughness as a structure, a β-type titanium alloy having excellent wear resistance (specifically, a β type titanium alloy) is suitably obtained. The heat treatment shown in the third heat treatment step is generally called aging treatment.

The heating means for the heat treatment may be any means capable of heating the entire base material as in the first heat treatment step. Moreover, the same heating means as in the first heat treatment step may be used, or a different heating means may be used.
The heat treatment temperature in the third heat treatment step is preferably 200 to 500.degree. C., more preferably 200 to 450.degree.
The heat treatment time can be 120 hours or longer. By setting the heat treatment time of the third heat treatment process within this range, the hardness of the oxygen-immersed layer 5 becomes 400 HV or more, and the wear resistance is improved. The upper limit of the heat treatment time is not particularly limited, but it is preferable to set the upper limit of the time for overaging to reduce the hardness, and the time can be set to about 1000 hours, for example.

Examples of the atmosphere in the third heat treatment step include an oxidizing atmosphere (including an air atmosphere), an inert gas atmosphere (for example, an atmosphere of a rare gas such as argon), and a vacuum.

(Oxide coating layer)
The oxide coating layer 4 formed by the above manufacturing method is formed on the surface layer of the part 2 and is an oxide layer mainly composed of TiO ₂ formed by oxidation of titanium. The thickness of the oxide coating layer 4 is appropriately set according to the application, and can be, for example, 20 μm or less, preferably 5 μm or less. By suppressing the thickness to the above range, abrasion resistance can be maintained without exfoliation of the oxide coating layer 4 .

(Oxygen immersion layer)
The oxygen-immersed layer 5 is a titanium alloy layer formed on the surface or on the deep layer side of the oxide coating layer 4 and in which oxygen is dissolved in the crystal structure of the β phase.
The hardness of the oxygen-immersed layer 5 is appropriately set according to the application, but it can be usually 500 to 850 HV (more preferably 550 to 800 HV). The thickness of the oxygen-immersed layer 5 can be 5 to 100 μm (more preferably 10 to 70 μm, particularly preferably 10 to 50 μm).

(Hardened layer)
The hardened layer 6 formed by the above-described manufacturing method is a titanium alloy layer having a β-phase crystal structure, which is formed on the deep layer side of the oxygen-immersed layer 5 . The hardness of the hardened layer 6 is appropriately set, but it can usually be 400 to 550 HV. The thickness of the hardened layer 6 is appropriately set according to the application, and may be, for example, 30 μm to 3.5 mm.
When a load is applied to one part 2 and surface force is applied to the oxide coating layer 4 and the oxygen-immersed layer 5, if the oxygen-immersed layer 5 is directly formed on the post-heat treatment base material 11 having high toughness, The base material 11 is deformed by the surface force, and force is applied to the boundaries of each layer, making it easier for the oxygen-immersed layer 5 to separate from the base material 11 after heat treatment, or for the oxide film layer 4 to separate from the oxygen-immersed layer 5 . . On the other hand, in the present titanium alloy, since the oxygen-immersed layer 5 is formed on the hardened layer 6 having a hardness higher than that of the base material 11 after heat treatment, the hardened layer 6 is less likely to be deformed even when surface force is applied. It is possible to prevent peeling of the oxygen-immersed layer 5 and the oxide film layer 4 .

(Base material after heat treatment)
The post-heat treatment base material 11 of the β-type titanium alloy 1 is a titanium alloy layer in which the crystal structure is a mixture of the β-phase (body-centered cubic) and the α-phase (close-packed cubic).
The hardness of the base material 11 after the heat treatment is appropriately set, but the Vickers hardness can be usually 200 to 380 HV (more preferably 230 to 350 HV).

The amount of oxygen contained in each of the oxygen-immersed layer 5 and the hardened layer 6 and the post-heat treatment base material 11 is highest in the oxygen-immersed layer 5 and decreases in this order.
The proportion of oxygen dissolved in the oxygen-immersed layer 5 and the hardened layer 6 can be appropriately selected. It can contain up to 5% by mass. As a good example, the oxygen-immersed layer 5 contains 4 to 6.9% by mass of oxygen atoms (particularly preferably 4.4 to 6.6% by mass), and the hardened layer 6 contains 1.8 to 4.0% by mass of oxygen atoms. 4% by weight (particularly preferably 2.0 to 4.4% by weight).

Further, when the β-type titanium alloy base material is Ti-22V-4Al, the oxygen-immersed layer 5 can have a lower vanadium element content than the hardened layer 6 and the heat-treated base material 11 . At this time, the oxygen-immersed layer 5 can contain 21 to 23% by mass of vanadium atoms, and the hardened layer 6 can contain 21.5 to 25% by mass of vanadium atoms. As a good example, the oxygen-immersed layer 5 contains 21.5 to 22.5% by mass of vanadium atoms (particularly preferably 21.8 to 22.2% by mass), and the hardened layer 6 contains 21.8 to 21.8% by mass of vanadium atoms. 24% by mass (particularly preferably 22-23% by mass).

The present β-type titanium alloy may be provided with an arbitrary surface treatment film on the surface of the part 2 . In this case, a surface treatment film, an oxygen-immersed layer 5 and a hardened layer 6 are formed in this order from the surface of the part 2 . The surface treatment film is appropriately selected according to the application, and examples thereof include diamond-like carbon (DLC) deposited by PVD and CVD, TiN, TiC, etc., in addition to the anodized film.

The β-titanium alloy can be used in various fields where both toughness and wear resistance properties are required.
The article comprising the β-titanium alloy is not particularly limited, and the β-titanium alloy can be used for articles that generally use metals. Examples of articles having a β-titanium alloy include machine parts, food processing equipment, cooking utensils, medical instruments, and tools.

Examples of the mechanical parts include sliding members used for automobile parts, aircraft parts, and the like. Automotive parts include engine parts, connecting rods, valves, and the like. Aircraft parts include engine parts. The sliding member is a β-titanium alloy having a hardened surface 21 at a sliding contact portion, and includes, for example, bearings, bearing balls, rollers, vanes for compressors, gas turbine blades, and cam rollers.
Examples of the food processing equipment include a meat slicer, a vegetable cutter, a mixer, and the like, which are equipment using a β-titanium alloy having a hardened surface 21 such as a cutting edge for processing food.
Examples of the cooking utensils include kitchen knives, cooking scissors, skewers, pots, frying pans, and the like, which are utensils using a β-titanium alloy with a cutting edge or the like having a hardened surface 21 .
Examples of the medical instrument include a knife, scissors, an injection needle, a drill bit, and the like, which are instruments using a β-titanium alloy having a hardened surface 21 such as a cutting edge.

The tool is a tool using a β-titanium alloy with a cutting edge or the like having a hardened surface 21, and includes various cutting tools (bite, milling cutter, drill bit, etc.).
The drill bit 7 includes a shaft portion 71 and a cutting edge portion 75 which is a portion 2 provided at the tip of the shaft portion 71 (see FIGS. 3 to 5). The drill bit 7 can be suitably used for medical and dental purposes where compatibility with the human body is desired.

The first portion 2 can include an extension portion 73 within a predetermined range from the cutting edge portion 75 of the shaft portion 71 . The extended portion 73 separates the boundary between the oxygen-immersed layer 5 and the post-heat-treatment base material 11 from the cutting location, so that the oxygen-immersed layer 5 of the cutting edge portion 75 is less likely to be chipped from the boundary, and the durability of the drill bit 7 is improved. can be improved. The length (extended length) from the cutting edge portion 75 where the extended portion 73 is formed can be, for example, 0.3 to 12 mm (more preferably 1 to 7 mm).

In addition, in the applications of food processing equipment, cooking utensils, medical instruments and tools having cutting edges such as drill bits, there is a demand for re-forming and reusing cutting edges when the cutting edges are worn.
Each article for the above application having a β-type titanium alloy (or a β-type titanium alloy portion in an article having a β-type titanium alloy) is manufactured by processing the base material to reshape the shape of the cutting edge, and then applying the β-type titanium alloy. By performing the second heat treatment step and the third heat treatment step of the alloy manufacturing method in this order, an oxygen-immersed layer and a hardened layer are formed on the hardened surface, and a high-hardness cutting edge can be re-formed. The conditions of the second heat treatment step and the third heat treatment step to be performed may be the same as or different from those of the second heat treatment step and the third heat treatment step when producing the present β-titanium alloy.

(Example 1)
As Example 1, a drill bit for medical or dental use was produced. The drill bit 7 is a drill bit made by heat-treating a β-titanium alloy Ti-22V-4Al as a base material. As shown in FIGS. A cutting edge portion 75 provided on the tip side of 71 and serving as the one portion 2 is provided. Further, the cutting edge portion 75 is provided with a sharp end portion 76 positioned on the axis of the shaft portion 71 . Furthermore, the extension length of the extension portion 73 was set to about 2 mm from the end of the cutting edge portion 75 .

Such a drill bit 7 was produced as follows.
(1) Base Material Forming Step First, a round bar (about 2 mm in diameter) of β-type titanium alloy Ti-22V-4Al (DAT51 manufactured by Daido Steel Co., Ltd.) is processed to form the shaft portion 71 and the cutting edge portion 75. A preform having a shape was produced.
(2) First heat treatment step After that, as the first heat treatment step, the base material is heat treated for 0.5 hours in a low-frequency heating furnace in an air atmosphere at about 650°C to obtain a first heat-treated base material. rice field. After the heat treatment was completed, the first heat-treated base material was submerged in water and cooled to room temperature, and the oxide film formed on the surface due to the heat treatment was removed by shot blasting. The shot blasting was carried out under conditions of a nozzle diameter of φ8 mm and a pressure of 0.5 MPa, using alumina particles having a particle size of F46 conforming to JIS R6001. Also, after shot blasting, it was washed with acetone.

(3) Second heat treatment step Next, as a second heat treatment step, the range up to the cutting edge portion 75 and the extended portion 73, which are the part 2 of the first heat treated base material, is subjected to heat treatment by irradiating a laser. got The heat treatment in the second heat treatment step is carried out by using a 720 W semiconductor laser (LDL160-1000, manufactured by Laser Line Co., Ltd.) with a focal length of 100 mm, a defocus of 15 mm, a spot diameter of 1 mm, and a surface temperature of 1000 ° C. or higher. The irradiation was carried out at a moving speed of 6 mm/s under the condition that the inclination angle θ was 10 degrees. During the laser irradiation, argon gas was blown to the laser irradiation portion at 20 L/min from the nozzle 93 directed toward the surface of the portion 2 . Immediately after the end of the laser irradiation, the blowing of argon gas was stopped, and natural slow cooling was performed until the temperature reached room temperature.

(4) Third Heat Treatment Step After that, as the third heat treatment step, the second heat treatment base material was heat treated in a low-frequency heating furnace in an air atmosphere at about 300° C. for 120 hours to obtain a β-type titanium alloy. After the heat treatment was completed, natural slow cooling was performed until the temperature reached room temperature.

FIGS. 6 and 7 show longitudinally sectioned images of the prepared drill bit 7 made of β-type titanium alloy. The oxide coating layer 4, the oxygen-immersed layer 5, and the hardened surface 21 formed in order from the hardened surface 21 of the cutting edge portion 75 and the extension portion 73, which are a portion 2 within a range of 2 mm from the tip of the drill bit 7 shown in FIGS. Layer 6 showed a color different from that of base material 11 after heat treatment, and its thickness was about 5 μm for oxide coating layer 4 and about 40 μm for oxygen-immersed layer 5 . In addition, the remaining portion of the one portion 2 was entirely the hardened layer 6 .

In the prepared drill bit 7, the Vickers hardness of the surface of the oxide coating layer 4, the oxygen-immersed layer 5, the hardened layer 6, and the heat-treated base material 11 was measured.
The Vickers hardness of the surface of the oxide coating layer 4 (cutting edge portion 75) is about 590 HV, and it is understood that a hole can be drilled into a human bone. Further, when measured after exposing the oxygen-immersed layer 5 by polishing to a position 30 μm from the surface, the Vickers hardness was about 500 to about 520 HV.
Furthermore, the Vickers hardness of the base material 11 after heat treatment was about 240 HV when measured at a position of 0.5 mm from the surface. In addition, the post-heat treatment base material 11 has a crystal structure in which the α phase is mixed in the β phase, and has toughness that does not break due to piercing.

Such a drill bit 7 is produced by heat-treating a base material of a β-titanium alloy, and since it does not have small pieces such as cemented carbide tips attached thereto, the small pieces do not come off from the joints. , suitable for applications such as surgery. Also, by using a titanium alloy, there is little interaction with the human body.
Furthermore, using a drill bit 7, after drilling five holes in a cortical bone sheet (SAW3401-04, manufactured by Avis Co., Ltd.), which is a 6 mm-thick pressure shaping plate made of epoxy resin and short glass fibers. When the cutting edge portion 75 was observed, the peeling of the oxide coating layer 4 was not observed and it was good. On the other hand, as a comparative example, a SUS420J2 drill bit of the same shape was used to drill a hole in the same manner, and then the cutting edge 75 was observed.

Quantitative analysis was performed in order to confirm the difference in oxygen content between the oxygen-immersed layer 5 and the hardened layer 6 of the prepared drill bit 7 . For this quantitative analysis, line analysis and surface analysis were performed using an electron probe microanalyzer (JXA-8530, manufactured by JEOL Ltd.). 8 and 9 are line analysis graphs showing changes in oxygen content and vanadium content from the hardened surface 21 of the drill bit 7 (example) and the surface of the base material 11 after heat treatment (comparative example) to 100 μm. 10 and 11 are surface analysis graphs showing changes in O, Ti, V, and Al from the surface of the drill bit 7 (upper part of the drawing) to the deep part (lower part of the drawing).

As shown in FIG. 8, the amount of oxygen in the example is 6.6% by mass and 6.9% by mass at depths of 5 μm and 10 μm from the surface corresponding to the oxygen-immersed layer 5 . 3.9 to 2.7% by mass at a depth of 50 μm or more corresponding to , and 2.7% by mass or less at a depth of 55 μm or more corresponding to the base material 11 after heat treatment. It can be seen that they are formed.
On the other hand, in the comparative example in which the second heat treatment step was not performed, the oxygen content did not change significantly regardless of the depth, and was within the range of 1.4 to 1.8% by mass.
The reason why the amount of oxygen changed greatly depending on the presence or absence of the second heat treatment process is that the crystal structure of the surface layer of the part 2 became a single β phase due to the second heat treatment process, and the oxide film was easily formed. it is conceivable that.

As a result of checking the image of the measurement result of the surface analysis, it was found that in the example, it decreased from the surface oxide coating layer 4 (upper in FIG. 10) to the deep heat-treated base material 11 (lower in FIG. 10). Recognize. On the other hand, as shown in FIG. 11, it can be seen that the amount of oxygen in the comparative example does not change significantly regardless of the location.

As shown in FIG. 9, the amount of vanadium gradually increases from 21.8% by mass in the surface layer to 23% by mass in the deep layer (100 μm). On the other hand, as shown in FIG. 10, it can be seen that the amount of vanadium in the comparative example does not change significantly regardless of the location.
Such a difference is considered to be due to the fact that the α-phase precipitates in the first heat treatment step, and vanadium is concentrated in the β-phase portion remaining in the second heat treatment step due to its influence.

In this way, the oxygen-immersed layer 5, in which the amount of oxygen is increased by solid solution from the hardened layer 6, increases the hardness of the one portion 2 while the oxide coating layer 4 and the oxygen-immersed layer 5 increase the toughness through the hardened layer 6. Since it is formed on the base material 11 after heat treatment, the oxide coating layer 4 and the oxygen-immersed layer 5 can be a β-type titanium alloy that is difficult to peel off. Further, in the drill bit using such a β-type titanium alloy, the hardness of the cutting edge portion 75 can be increased, and the toughness of the shaft portion 71 can be increased by the post-heat treatment base material 11 having toughness. drill bit.
In addition, the boundary between the oxide coating layer 4 and the oxygen-immersed layer 5 and the post-heat treatment base material 11 is located at the extended portion 73, which is away from the cutting edge portion 75 for cutting and does not come into direct contact with the cutting object during cutting. Since the oxide coating layer 4 and the oxygen-immersed layer 5 are less likely to be chipped from the boundary, the durability of the drill bit can be improved.

(Example 2)
Next, after the cutting edge portion 75 of the drill bit 7 of Example 1 was ground to remove all of the oxide coating layer 4 and the oxygen-immersed layer 5, the shape of the cutting edge portion 75 was reshaped. After that, the second heat treatment step and the third heat treatment step were sequentially performed under the same conditions as in Example 1, and a drill bit 7' in which the oxide coating layer 4, the oxygen-immersed layer 5 and the hardened layer 6 were re-formed was manufactured. When the Vickers hardness of the oxide coating layer 4 was measured, the drill bit 7' having the cutting edge portion 75 re-formed in this way had a Vickers hardness of about 590 HV, and could be reused as the drill bit 7 without repeating the first heat treatment step. I found out.

It should be noted that the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the present invention according to the purpose and application. An embodiment of the present β-titanium alloy and its manufacturing method is a drill bit 7, but it is not limited to this, and any cutlery such as a kitchen knife, a scalpel, scissors, a food cutter, or a machine part may be used. may Also, the drill bit 7 may or may not have the sharp end 76 .

1; β-type titanium alloy, 11; base material after heat treatment, 2; one part, 21; hardened surface, 4; oxide coating layer, 5;
7; drill bit, 71; shank, 72; discharge groove, 73; extension, 75; cutting edge, 76;

Claims (6)

A production method for heat-treating a β-type titanium alloy base material to produce a β-type titanium alloy in which an oxide coating layer, an oxygen-immersed layer and a hardened layer are formed in order from the surface side of a part of the base material,
a first heat treatment step of heat-treating the β-type titanium alloy base material at a temperature H _T (° C.) represented by the following formula (1);
locally heating the portion of the heat-treated β-type titanium alloy base material at a temperature of 1000° C. or higher in an oxidizing atmosphere ;
During the local heating, the inert gas is continuously blown to cool the part other than the one heated part, and the blow is stopped at the end of the local heating,
a second heat treatment step in which the atmosphere in the vicinity of the heated portion is the oxidizing atmosphere containing an inert gas ;
a third heat treatment step of obtaining the β-type titanium alloy by heat-treating the β-type titanium alloy base material heat-treated in the second heat-treatment step at a temperature of 200 to 500° C. for 120 hours or longer , and
A method for producing a β-type titanium alloy , wherein the hardness of the oxygen-immersed layer is higher than the hardness of the hardened layer, and the hardness of the hardened layer is higher than the hardness of the heat-treated base material .
_{200≤HT≤βT} - ₇₀ (1)
(In the formula, β _T indicates the β transformation point (°C) of the β-type titanium alloy) 2. The method for producing a β-titanium alloy according to claim 1 , wherein the inert gas is blown at an amount of 10 to 40 L/min . 2. The method for producing a β-type titanium alloy according to claim 1 , wherein the oxygen-immersed layer has a thickness of 5 to 50 μm, and the oxide coating layer has a thickness of 5 μm or less . A base material made of a titanium alloy in which an α phase is mixed in a β phase, an oxygen-immersed layer formed in a part of the base material, and a hardened layer formed on the base material side of the oxygen-immersed layer β type titanium alloy,
The oxygen-immersed layer is a titanium alloy layer in which oxygen is dissolved in the crystal structure of the β phase,
The amount of oxygen contained in the oxygen-immersed layer is larger than the amount of oxygen contained in the hardened layer, and the amount of oxygen contained in the hardened layer is larger than the amount of oxygen contained in the heat-treated base material,
the amount of oxygen at the boundary between the oxygen-immersed layer and the hardened layer continuously decreases from the oxygen-immersed layer to the hardened layer;
The hardness of the oxygen-immersed layer is greater than the hardness of the hardened layer, and the hardness of the hardened layer is greater than the hardness of the heat-treated base material,
A β-type titanium alloy, wherein the oxygen-immersed layer has a thickness of 5 to 50 μm . A drill bit comprising a round bar-shaped shank and a cutting edge provided on the distal end side of the shank,
The shaft portion is made of the base material according to claim 4,
5. A drill bit, wherein said cutting edge portion has an oxygen-impregnated layer formed on said one portion according to claim 4 and a hardened layer formed on said base material side of said oxygen-impregnated layer. A method for reusing a drill bit according to claim 5,
removing the oxygen-immersed layer from the part of the used drill bit to form a new cutting edge shape from which the oxygen-immersed layer has been removed;
After that, a new part of the base material on which the shape of the new cutting edge is formed is locally heated at a temperature of 1000 ° C. or higher in an oxidizing atmosphere, and during the local heating, the part other than the heated part is heated. a second heat treatment step in which an inert gas is continuously blown to cool the portion, the blowing is stopped when the local heating is completed, and the atmosphere near the heated portion is the oxidizing atmosphere containing the inert gas;
and a third heat treatment step of obtaining a β-type titanium alloy by heat treating the base material heat-treated in the second heat treatment step at a temperature of 200 to 500° C. for 120 hours or longer, and is formed on the new part from which the oxygen-immersed layer has been removed.

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