KR20130099226A - Abrasion-resistant titanium alloy member having excellent fatigue strength - Google Patents

Abstract

In order to provide a titanium alloy member having better abrasion resistance and fatigue strength than a conventional titanium alloy at a low cost, the present invention has a mass% of Al: 4.5% or more and less than 5.5%, Fe: 1.3% or more and less than 2.3%, Si: 0.25%. It is to provide a wear-resistant titanium alloy member having excellent fatigue strength having a hardened layer of oxygen-solid solution in the surface layer of the base material containing not less than 0.50% and not less than O: 0.08% and not more than 0.25%, and the residual portion titanium and unavoidable impurities.

Description

Wear-resistant titanium alloy member with excellent fatigue strength {ABRASION-RESISTANT TITANIUM ALLOY MEMBER HAVING EXCELLENT FATIGUE STRENGTH}

The present invention relates to a wear-resistant titanium alloy member having a hardened layer on the surface layer and having wear resistance when used in contact portions or sliding portions with other members and exhibiting excellent fatigue strength.

Titanium alloys having light weight, high specific strength and excellent corrosion resistance are used in a wide range of applications such as automobile parts and consumer products, in addition to aircraft applications. Among them, Ti-6Al-4V having excellent strength ductility balance is a representative example. On the other hand, in order to reduce the high cost which is one of the factors which hinder the expansion of spreading, the alloy which has the property which can replace Ti-6Al-4V using the cheap Fe as an additional element has been developed.

Moreover, since titanium alloys are inferior in abrasion resistance, they become a problem when used in contact parts with other members or sliding parts. As a method of improving the wear resistance of the product used for the engine parts of automobiles, Patent Literature 1 discloses a method of forming an oxide scale on a surface. However, there is a problem that cracking easily occurs in the oxide scale layer, the surface scale is peeled off, the surface irregularities tend to be large, and the fatigue strength of the member is greatly reduced as compared with the case where such anti-wear treatment is not performed. .

In addition, the creep resistance and the fatigue characteristic need to be good for the member used in a high temperature environment such as an internal combustion engine of an automobile. In Non-Patent Documents 1 and 2, and Patent Documents 2, 3 and 8, a technique of adding Si is disclosed in order to improve creep resistance of a titanium alloy. However, when a large amount of Si is added, Si, which is not completely dissolved in the α phase or the β phase, forms silicide of titanium, coarsens during the heat treatment or during use at high temperature, and the fatigue strength is lowered as a starting point of fatigue fracture. It varies depending on the component and temperature, but the high capacity of Si in the binary system of Ti-Si is about 0.2% at 700 ° C, and about 0.1% at 700 ° C on α + β alloy of Ti-5% Al-2% Fe. It is not employed outside. Therefore, in the use which a fatigue strength becomes a problem, there existed restrictions, such as making Si addition amount less than 0.25%.

The Ti-6Al-1.7Fe-0.1Si alloys described in Non-Patent Document 1 and Non-Patent Document 2 are high-strength and high-rigid alloys, but have a problem in that the amount of Al added is large and the hot workability is inferior. Moreover, although Si is added for the improvement of creep resistance in the high temperature environment up to 480 degreeC, the addition amount is suppressed to 0.13%.

Patent Literature 2 discloses an Al + β-type titanium alloy having a fatigue strength equivalent to that of a conventional Al-Fe-based titanium alloy and having less variation and higher hot workability than that of Al: 4.4% or more and less than 5.5%, An alloy comprising Fe: 0.5% or more and less than 1.4% is disclosed. However, no mention is made of fatigue strength in a condition in which wear resistance is imparted. The amount of Si added is less than 0.25% for the reason that the fatigue strength is lowered.

Patent Document 3 discloses a titanium alloy having fatigue strength equivalent to that of a conventional Al-Fe-based titanium alloy and higher hot or cold workability than that of Al: 4.4% or more and less than 5.5% and Fe: 1.4% or more and less than 2.1%. Alloys are disclosed. However, no mention is made of fatigue strength in the state of providing wear resistance. In addition, about Si addition amount, it becomes less than 0.25% because a fatigue strength falls.

Patent document 4 can be produced in an industrially inexpensive manner, and is an alpha + beta titanium alloy having a mechanical property equivalent to that of Ti-6Al-4V alloy, Al: 5.5 to 7.0%, Fe: 0.5 to 4.0%, An alloy consisting of O: 0.5% or less is disclosed. However, there is a problem in that the amount of Al is added, hot and cold workability is inferior, and when high Fe is used, the nonuniformity of characteristics due to Fe segregation and the stiffness reduction as a member due to a decrease in Young's modulus have occurred.

Patent Literature 5 describes an α + β type titanium alloy for casting that is higher in strength than Ti-6Al-4V and has excellent castability, and includes Al: 5.0 to 7.0%, Fe + Cr + Ni: 0.5 to 10.0%, and C + N. A titanium alloy is disclosed which has a tensile strength of 890 MPa or more and a melting point of 1650 ° C. or less in a state of + O: 0.01 to 0.5% and casting. Although this titanium alloy is an alloy which can obtain the favorable fluidity | liquidity at the time of melt | fusion, and the outstanding strength after solidification, there existed a subject that a coagulation | solidification structure becomes coarse easily, and fatigue strength falls.

Patent Document 6 discloses a high strength α having room temperature strength and fatigue strength equivalent to Ti-6Al-4V and less than Al: 4.4 to 5.5%, Fe: 1.4 to 2.1%, Mo: 1.5 to 5.5%, and Si: 0.1%. A + β type alloy is disclosed. Patent Literature 7 discloses an engine valve using the alloy, and discloses a technique of forming a hard layer such as an oxide on the surface layer to improve wear resistance. However, since the titanium alloys of patent documents 6 and 7 contain a large amount of Mo which is expensive and large price fluctuation, there existed a subject that it was difficult to manufacture stably at low cost. Moreover, since this titanium alloy contains a large amount of Mo, specific gravity is higher than Ti-6Al-4V, Young's modulus is also equivalent to Ti-6Al-4V, and it is inadequate in the lightening effect in the member which requires rigidity. It was.

Patent Document 8 discloses a method for producing a titanium alloy valve, and discloses a method of oxidizing and nitriding a surface layer by heating a Ti-6Al-4V alloy valve in an atmosphere of nitrogen and oxygen as an α + β type titanium alloy. have. This improves the wear resistance of the face portion and the end surface, but is expensive because Ti-6Al-4V alloy is used, and the stiffness and fatigue resistance are insufficient.

Patent Literature 9 discloses a Ti alloy having improved workability of a Ti-6Al-4V alloy, wherein the Al equivalent is 3 to 6.5%, and at least one of the electrolytic solid solution β stabilizing elements is 2.0 to 4.5% as the Mo equivalent; It has been disclosed that 0.3 to 2% of the vacancy-type β-stabilizing element is contained in Fe equivalent. However, Mo, V, Ta, Nb, etc. as the high solid solution β-stabilizing element have a high cost, and therefore have a disadvantage of high cost.

Patent Document 10 discloses a heat resistant titanium alloy comprising components such as Al: 5.5 to 6.5%, Sn: 1.5 to 3.0%, Zr: 0.7 to 5.0%, Mo: 0.3 to 3.0%, Si: 0.15 to 0.50% have. Thus, the reason for adding a large amount of Si is to assume use in the temperature range of 500-600 degreeC or more, and to improve creep resistance. The titanium alloy of patent document 8 adds Sn, Zr, and Mo in large quantities in order to obtain high temperature strength in the temperature range, and in addition to high alloy cost, there existed a subject that hot workability was very bad and manufacturing cost was high. . In addition, Zr is an element that easily forms silicide in the form of (Ti.Zr) xSiy, and has a problem that it is easy to cause a decrease in fatigue strength. In addition, in patent document 8, sufficient examination is not performed about wear resistance, For example, when forming a hardened layer as described in patent document 6 for the purpose of improving wear resistance, silicide is formed as mentioned above. As a result, the fatigue characteristics are greatly reduced.

Patent Document 11 discloses a valve having a hardened layer formed by solid-solving oxygen in a low-strength Ti alloy, and Ti-Fe: 0.04 to 2.40% -O: 0.08 to 0.20% is disclosed as a Ti alloy . However, since the base material strength is inadequate, the use of the application which requires high strength and high fatigue strength has a drawback that it is difficult.

Japanese Patent Application Laid-open No. 62-256956 Japanese Patent No. 3076697 Japanese Patent No. 3076696 Japanese Patent No. 3306878 Japanese Patent Application Publication No. 2010-7166 Japanese Patent Application Laid-Open No. 2005-320618 Japanese Patent Application Publication No. 2007-100666 Japanese Patent Application Laid-open No. Hei 6-041715 Japanese Patent Application Laid-open No. 2000-273598 Japanese Patent Application Laid-open No. Hei 2-22435 Japanese Patent Application Laid-open No. Hei 7-269316

P.Bania, Metallugy and Technology of Practical Titanium Alloys, p.9, TMS, Warrendale, PA (1994) F.H.FROES and I.L.CAPLAN, TITANIUM'92 SCIENCE AND TECHNOLOGY, p.2787

Conventionally, the technique which simultaneously satisfies the wear resistance and the fatigue characteristics in a titanium alloy without adding Mo has not been disclosed.

In order to improve the abrasion resistance of the titanium alloy member, for example, it is conceivable to perform abrasion resistance treatment to form a cured layer by oxidation, nitriding and carbonization at the surface layer portion. However, there has been a problem that the fatigue strength of the member decreases when such an anti-wear treatment is performed.

Therefore, this invention advantageously solves the said subject and provides the wear-resistant titanium alloy member which is more excellent in fatigue strength than the conventional alloy at low cost.

MEANS TO SOLVE THE PROBLEM In order to achieve the said objective, in order to achieve the said objective, as a reinforcement element, Fe which is cheaper than V and Mo, and Si which has a high reinforcement capability by addition of a small amount are added, and the surface layer is improved in order to improve the influence on hot workability and abrasion resistance. The fatigue strength of the titanium alloy in which the hardened layer in which oxygen was dissolved was formed was carefully investigated.

MEANS TO SOLVE THE PROBLEM The present inventors made the index of hot workability for industrially cheap manufacture into 40% or more of (beta) phase ratio in (beta) transformation temperature 1000 degrees C or less and 900 degreeC. The reason for using these as an index is that in general, when forging from ingot to billet, or during hot working from a raw material to a part shape, it is heated to a β single phase region having a high deformability, to a two-phase region below the β transformation temperature during processing. The temperature is lowered. If the heating temperature exceeds 1000 ° C., the surface properties due to oxidation deteriorate, the yield decreases due to scale generation, and the increase in cutting load leads to a significant increase in production cost. Moreover, when the ratio of (beta) phase is less than 40% by the temperature fall during a process, it is because a crack will generate easily during a process.

The hardened layer in which the solid solution of oxygen is dissolved in the surface layer of the titanium alloy after being formed into a member shape by processing in hot rolling, for example, is dissolved in oxygen by thermal diffusion, or any one of nitrogen and carbon or It can form by two types and solid solution of oxygen.

MEANS TO SOLVE THE PROBLEM The present inventors found that the fatigue strength at the time of forming the hardened layer which oxygen solidified to the surface layer about the fatigue strength of a titanium alloy is 360 MPa or more exceeding 10% of 330 MPa which is the fatigue strength of the conventional Ti-6Al-4V alloy. It was taken as an index.

As a result, it has been found that titanium alloys excellent in fatigue strength, hot workability and wear resistance can be produced by adjusting the component ranges of Al, Fe, O, and Si to an appropriate amount.

The subject of this invention is as follows.

(1) In mass%, Al: 4.5% or more and less than 5.5%, Fe: 1.3% or more and less than 2.3%, Si: 0.25% or more and less than 0.50%, O: 0.08% or more and less than 0.25%, and remainder titanium and inevitable The wear-resistant titanium alloy member excellent in fatigue strength characterized by having a hardened layer in which oxygen dissolved in the surface layer of the titanium alloy base material which consists of impurities.

(2) The wear-resistant titanium alloy having excellent fatigue strength according to (1), wherein the cured layer is one or two of nitrogen and carbon and oxygen is dissolved in the surface layer of the base material. absence.

(3) The wear-resistant titanium alloy member excellent in fatigue strength as described in said (1) or (2) characterized by the said Vickers hardness of cross section being 450 HV or more in 10 micrometer depth from the surface.

The titanium alloy member of the present invention has abrasion resistance, fatigue strength and hot workability exceeding that of a conventional titanium alloy, and is inexpensive. As a result, the titanium alloy member of the present invention has a wider industrial use as a member of sliding parts such as engine valves and connecting rods for automobiles than conventional high strength titanium alloys. It is possible to obtain a wide range of effects such as fuel efficiency improvement. In addition, the titanium alloy member of the present invention can be used in a wide range, including parts of sliding parts, and the effect thereof can be obtained widely. Therefore, the industrial effect is immeasurable.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the development, first, based on the Ti-5% Al-1 to 2% Fe-based alloy developed as a low-cost Fe-containing high strength α + β type titanium alloy, the strength, Young's modulus and β transformation temperature due to addition of Si and oxygen were The effect of

As a result, it was found that both Si and oxygen improve the strength and Young's modulus, but Si does not affect the β transformation temperature, while oxygen addition has a large effect of increasing the β transformation temperature. Fe lowers β transformation temperature and Young's modulus together.

Next, the evaluation method of abrasion resistance is demonstrated. Abrasion resistance is, in the axial direction of the rod member, after adding the tensile load 300MPa, the surface of a member, to collide a SCM435 material under a load of 98N (10kgf), the conditions of a vibration frequency of 500Hz, the number of 1 × 10 ⁷ times after having, on the surface It evaluated by the presence or absence of the crack.

Next, the fatigue strength is described. The fatigue strength is obtained by processing a titanium alloy into a test piece shape, and then performing a wear-resistant treatment described below to form a hardened layer of oxygen-solid solution in the surface layer of the base material. ^It evaluated by the breaking strength in ^seven times.

As a result, when the surface layer of a base material has a hardened layer, compared with the case where there is no hardened layer, when the Si content of a base material is less than 0.25%, fatigue strength falls about 100-150 MPa, but when Si content of a base material is 0.25% or more, The phenomenon which the fatigue strength improves was seen.

Usually, when there is a hardened layer in the surface layer of the base material which consists of a titanium alloy, fatigue strength falls compared with the case where there is no hardened layer in the surface layer. Although this reason is unclear, it is thought that it is because a micro crack easily forms on a surface layer part, and becomes a starting point of fatigue.

When there is a hardened layer in the surface layer of a base material, the mechanism which improves a fatigue strength when increasing the Si addition amount of a base material is unclear, but when considering, the following mechanism can be considered. In the 1 × 10 ⁷ repeated test used for evaluating general fatigue strength, fatigue failure of titanium alloy occurs from the surface layer as a starting point. In particular, if coarse precipitates or the like of silicide are present in the surface layer, breakage occurs from the starting point.

This time, the microstructure of the cross-sectional surface layer part of the test piece whose Si content of the base material which consists of a titanium alloy is 0.25% or more was investigated in detail. As a result, the layer which does not exist silicide was seen in the surface layer part of the base material in which oxygen is dissolved and the hardened layer is formed. This is because oxygen as the α stabilizing element penetrates from the outside by an oxidation treatment for forming a hardened layer, so that the proportion of the α phase increases and the region of the β phase is decreased, and Si as the β stabilizing element has moved in the scale or inside the base metal. I think it is because. The depth of the layer without the silicide is shallower than the depth of the hardened layer of oxygen, but at least 3 µm or more from the surface, and is considered to be sufficient to avoid becoming a starting point of the fatigue crack.

Silicide is normally observed here as thickening of Si by mapping analysis of EPMA. More specifically, it is necessary to perform electron beam diffraction by a transmission electron microscope. In the case of the test piece which has a hardened layer in the surface layer of the base material which consists of a titanium alloy whose Si content of this time is 0.25% or more, it was confirmed that the silicide which exists inside a base material is 0.1 micrometer or more in size.

As described above, when there is a hardened layer in which oxygen is dissolved in the surface layer of the base material made of a titanium alloy having a Si content of 0.25% or more, Si of the surface layer is thinned, and the formation of silicide on the surface layer is suppressed, and thus the starting point of fatigue failure. On the other hand, Si in a base material contributes to the strength improvement of a base material. Therefore, the fall of fatigue strength is suppressed and it is thought that fatigue strength improves.

Further, when a hardened layer of oxygen-Soluble is formed in the surface layer of the base material made of a titanium alloy containing Fe and having a Si content of 0.25% or more, and the proportion of the α phase is increased and the region of the β phase is reduced, the Fe phase is in the α phase. Since the solid solution amount of remarkably is small, the solid solution strengthening ability is remarkably lowered, and the higher capacity of Si to the α phase is larger than Fe, and the decrease in the solid solution strengthening ability is also considered to contribute to the improvement of the fatigue strength.

The element which forms a hardened layer is not limited to oxygen, The hardened layer may be the one in which one type or two types of nitrogen and carbon, and oxygen are solid-solution in the surface layer of a base material. Nitrogen and carbon are alpha stabilizing elements which are solid solution in titanium similarly to oxygen, and it is thought that the same mechanism as oxygen acts in the titanium alloy.

In the titanium alloy member of the first embodiment of the present invention, the content ratio of the constituent elements of the base material and a hardened layer of oxygen-solid solution are formed in the surface layer of the base material.

Al is an α-stabilizing element, and by solid solution in α phase, the strength of the titanium alloy member increases with increasing content. However, when a base material contains 5.5% or more of Al, hot workability will deteriorate. Therefore, content of Al of a base material was made into 4.5% or more and less than 5.5%. As for the upper limit of content of Al, less than 5.3% is more preferable. Moreover, as for the minimum of content of Al, 4.8% or more is more preferable.

Fe is a vacancy-type β stabilizing element, and by solid solution in the β phase, the room temperature strength of the titanium alloy member increases with increasing content, and the β transformation temperature is lowered. In order to secure the strength and lower the β transformation temperature, the base material needs to contain 1.3% or more of Fe. However, when the base material contains 2.3% or more of Fe, segregation becomes a problem when the solvent is formed into a large ingot. Therefore, content of Fe of a base material was made into 1.3% or more and less than 2.3%. As for the upper limit of content of Fe, less than 2.1% is more preferable. Moreover, 1.5% or more is preferable and, as for the minimum of content of Fe, it is more preferable to set it as 1.6% or more.

Si is a β stabilizing element, and the strength increases with increasing content. In order to ensure the fatigue strength at the time of providing abrasion resistance, it is necessary for the base material to contain 0.25% or more of Si.

On the other hand, when a base material contains 0.50% or more of Si, toughness will fall. Therefore, content of Si of a base material was made into 0.25% or more and less than 0.50%. As for the upper limit of content of Si, less than 0.45% is more preferable. Further, in order to increase the strength of the base material, the lower limit value of Si content is more preferably 0.28% or more.

O is an element that enhances the α phase. In order to express the effect, it is necessary to make content of O of a base material into 0.05% or more. However, when O is contained in an amount of 0.25% or more, the formation of the α ₂ phase is promoted to cause embrittlement, or the β transformation temperature is increased to increase the heat treatment cost. For this reason, content of O of a base material was made into 0.05% or more and less than 0.25%. Preferably, it is 0.08% or more and less than 0.22%. More preferably, they are 0.12% or more and less than 0.20%.

In the titanium alloy member of the second embodiment of the present invention, the hardened layer is one or two or one of nitrogen and carbon, and oxygen is dissolved in the surface layer of the base material.

Oxygen, nitrogen, and carbon are all alpha stabilizing elements which are solid solution in titanium, and are considered to suppress fatigue strength reduction by reducing the Si concentration of the surface layer by suppressing the formation of silicide by solid solution in the surface layer.

In the titanium alloy member of the third embodiment of the present invention, the Vickers hardness of the cross section is assumed to be 450 HV or more at a depth of 10 µm from the surface.

The hardness and depth of the cured layer are mirror polished on the cross section, and the Vickers hardness is measured at a load of 10 gf. Since oxygen invades from the surface layer, the hardness of the surface decreases as the surface hardness reaches the maximum and the inside of the base material. It is preferable that it is HV450 or more, and, as for Vickers hardness in the 10 micrometers depth from the surface of a hardened layer, it is more preferable that it is HV500 or more. When the Vickers hardness of the said hardened layer is HV450 or more, the abrasion resistance improvement effect by providing a hardened layer in the surface layer of a base material is obtained more effectively.

In the titanium alloy member of the present invention, the microstructure of the base metal is preferably a needle-like structure. When the microstructure of a base material is a needle-like structure, it becomes a titanium alloy member excellent in creep resistance. In addition, when the microstructure of a base material is a needle-like structure, creep deformation of a member at the time of performing anti-wear process, such as an oxidation process for forming a hardened layer which gives abrasion resistance, at high temperature is suppressed.

The titanium alloy member of the present invention can have excellent fatigue strength and wear resistance.

The titanium alloy member of the present invention can be produced by a method for producing a titanium alloy and a surface treatment method which are usually used. The typical manufacturing process of the titanium alloy member of this invention is as follows.

First, the mixing of impurities is suppressed by the dissolution method in which a sponge titanium or an alloy material is used as a raw material, arc melting or electron beam melting in vacuum, and casting into a water-cooled copper mold, so that the components of the base material of the titanium alloy member of the present invention Ingot. Here, O can be added at the time of dissolution by using titanium oxide or sponge titanium having a high oxygen concentration. After heating this ingot in the (alpha) + (beta) area | region or (beta) area | region or more of 950 degreeC, it forges to a billet shape and surface-cuts, and hot-rolls at the heating temperature of 950 degreeC or more. Thereby, the base material which consists of a bar material of phi 12-20 mm which is an example of the shape of the titanium alloy member of this invention can be obtained.

Next, to the surface layer of the base material in the shape of the titanium alloy member of the present invention, a wear-resistant treatment for dissolving oxygen, or one or two kinds of nitrogen and carbon, and a wear-resistant treatment for dissolving oxygen are performed. In the abrasion resistant treatment, for example, oxidation, carburization and nitriding by the thermal diffusion method can be used in combination as necessary. When the thermal diffusion method is carried out as the abrasion resistant treatment, specifically, for example, oxidation is carried out in an oxygen-containing gas such as air, nitriding is carried out in a nitrogen-containing gas mainly composed of nitrogen, and carburization includes carbon such as carbon dioxide, carbon monoxide and methane. It is preferable to use the method of performing the heat processing which hold | maintains from 700 degreeC to 900 degreeC for 1 hour to 8 hours in gas. By performing the anti-wear treatment, the α + β titanium alloy member of the present invention having a hardened layer in which oxygen is dissolved in the surface layer of the base material can be obtained.

In this embodiment, before performing the abrasion-resistant process which forms the hardened layer which oxygen dissolved in the surface layer of a base material, the base material in the shape of a titanium alloy member is heated to the temperature more than (beta) transformation temperature, and after that, it is air-cooled or more It is preferable to perform cooling at a speed (solution treatment). By performing the solution treatment, the α phase precipitates in the sphere β phase of the base material, and the microstructure of the base material becomes a needle-like structure. Therefore, by performing the solution treatment before performing the wear resistant treatment, creep deformation of the member due to the wear resistant treatment can be suppressed.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1)

Titanium alloys of the components Nos. 1 to 12 shown in Table 1 were produced by the vacuum arc melting method, and each was about 200 kg ingot. Each of these ingots was forged and hot rolled to obtain a round bar having a diameter of 15 mm.

The round bar of raw materials No. 1 to 15 was heated at a β transformation temperature of + 60 ° C. shown in Table 2 for 20 minutes to perform a solution solution for cooling by blowing nitrogen gas into the furnace, and the microstructure was made into acicular tissue. It was. Then, the round bar was processed and the base material of the shape of the fatigue test piece of parallel part diameter 4mm, gage distance 20mm, and diameter 15mm was obtained. Then, the abrasion-resistant process which forms the hardened layer which dissolved oxygen in the surface layer of a base material by the heat processing in air | atmosphere of 800 degreeC and 1 hour was obtained, and the fatigue test piece was obtained.

The fatigue test pieces of Nos. 1 to 15 thus obtained were subjected to a fatigue test under the conditions shown below, and evaluated as shown below. The results are shown in Table 2.

The fatigue test was conducted up to 1 × 10 ⁷ times at the maximum stress of 360 MPa, the stress ratio R = -1, 3600 rpm, and room temperature in the ono-type rotation bending fatigue test. The case where O was not broken up to 1x10 ⁷ times and the case where it was broken were evaluated as Ｘ.

In addition, about the fatigue test pieces of Nos. 1-15, it measured so that a base material might show the ratio of the (beta) phase in 900 degreeC below. The sample cut out from the same raw material was hold | maintained at 900 degreeC for 1 hour, and then water cooled, and the area | region of the cornerstone alpha phase and transformation beta phase of a cross-sectional microstructure was measured, and it calculated | required from the ratio. The results are shown in Table 2.

In addition, the fatigue test pieces of Nos. 1 to 15 were evaluated so as to show workability in hot rolling below. That is, the case where cracking did not generate | occur | produced in hot rolling and O and the case where a crack generate | occur | produced were evaluated by Ｘ. The results are shown in Table 2.

Nos. 1 to 8 are examples of the present invention, and Nos. 9 to 15 are comparative examples in which the component (constituent element of the base material) of any of the materials is out of the scope of the present invention. The underline is drawn to the numerical value which deviates from the scope of the present invention.

The invention examples of Nos. 1 to 8 all have a β transformation temperature of 1000 ° C. or less, a ratio of β phase at 900 ° C. of the base material to 40% or more, no cracking due to hot working, and a fatigue strength of 360 MPa or more after abrasion resistance treatment. Good hot workability and fatigue strength were shown.

In Comparative Example No. 9, the Al content was out of the lower limit, and in Fe. 10, the Fe content was out of the lower limit, and all of them had insufficient fatigue strength after the abrasion resistance treatment. In addition, in No. 11 of the comparative example, the amount of Al deviated from the upper limit and the amount of Si deviated from the lower limit, resulting in a lack of hot workability and fatigue strength. In No. 12, the amount of Si was out of the lower limit and the fatigue strength after the abrasion resistance treatment was insufficient. No. 13 was out of the upper limit of Al amount and lacked hot workability. No. 14 is outside the upper limit, and No. 10, No. 11, No. 13, and No. 14 have β transformation temperatures of more than 1000 ° C., and the proportion of β phase at 900 ° C. of the base material is less than 40%. Therefore, hot workability was inadequate. In No. 15, the amount of Si was out of the upper limit and the fatigue strength was insufficient.

(Example 2)

The round bar of raw material No. 5 of Table 1 was used for test piece No. 16-19. In Test Piece No. 20, a rolled round bar of Ti-6Al-4V was used for comparison.

About the round bar of raw material No. 5, the same solution treatment as Example 1 was performed, and the base material processed into the same shape as Example 1 using the microstructure as a needle-like structure was obtained. After that, heat treatment was performed at 770 ° C for 5 hours in a carbon-containing gas atmosphere to perform abrasion resistance to form a cured layer in which carbon and oxygen were dissolved in the surface layer of the base material, thereby obtaining a fatigue test piece of No. 16.

Nitrogen and oxygen are dissolved in the surface layer of the base material by subjecting the base material having the same shape as in Example 1 obtained in the same manner as in Test Piece No. 16 to 770 ° C. for 5 hours in a nitrogen gas atmosphere containing a small amount of oxygen. The abrasion-resistant process of forming the hardened layer was performed, and the fatigue test piece of No. 17 was obtained.

The round bar of the material No. 5 was subjected to a solution treatment for heating and air-cooling at a β transformation temperature of -30 ° C. for 60 minutes to prepare a microstructure as a mixed structure composed of a cornerstone α phase and a transformation β phase. The base material processed into the same shape as this was obtained. Then, the wear-resistant process which forms the hardened layer which oxygen solidified to the surface layer of a base material was performed by performing oxidation treatment at 760 degreeC for 1 hour, and the fatigue test piece of No. 18 was obtained.

The fatigue of No. 19 which made the surface grind | pulverized when the surface was processed into the shape of the fatigue test piece, without performing the abrasion-resistant process which forms a hardened layer to the base material of Example 1 obtained similarly to Test piece No. 18. A test piece was obtained.

About the rolled round bar of Ti-6Al-4V, the solution treatment which heated and air-cooled for 20 minutes at the temperature of (beta) transformation temperature +60 degreeC was performed, and the base material processed to the same shape as Example 1 was obtained. Thereafter, an oxidation treatment was performed at 800 ° C. for 1 hour in an air atmosphere to perform abrasion resistance to form a hardened layer of oxygen-solid solution in the surface layer of the base material, thereby obtaining a fatigue test piece of No. 20.

The fatigue test pieces of Nos. 16 to 20 were evaluated by the above-described wear resistance evaluation method. As a result, Table 3 shows O where cracks did not occur and cracks occurred.

In Test Nos. 16 to 18 of the present invention, no cracking occurred. On the other hand, the crack generate | occur | produced in the test No. 19 which does not have a hardened layer on the surface, and the test piece No. 20 in which the component of a base material is out of this invention range.

In addition, the fatigue test pieces of Nos. 16 to 18 were subjected to the fatigue test and evaluated in the same manner as in Example 1. The results are shown in Table 3.

All the test pieces No. 16-18 showed favorable fatigue strength in 360 Pa or more of fatigue strength after abrasion-resistant treatment.

(Example 3)

The round bar of Table 1 raw material No. 5 was used for test piece No. 21-23.

About the round bar of raw material No. 5, the same solution treatment as Example 1 was performed, and the base material processed into the same shape as Example 1 using the microstructure as a needle-like structure was obtained. Then, the heat-resistant process which forms the hardened layer which solid-solution oxygen was formed in the surface layer of a base material by performing heat processing of the temperature and time shown below in air | atmosphere was performed.

The test piece of No. 21 was the example which performed the heat processing for 1 hour at 740 degreeC, and as shown in Table 4, the Vickers hardness of 10 micrometers depth was 420HV. The test piece of No. 22 was the example which performed the heat processing for 1 hour at 770 degreeC, and the Vickers hardness of 10 micrometers depth was 470 HV. The test piece of No. 23 was the example which performed the heat processing of 800 degreeC for 1 hour, and the Vickers hardness of 10 micrometers depth was 530HV.

In addition, the Vickers hardness of the test piece Nos. 21-23 mirror-polished the cross section of the test piece, and measured on the conditions of 10 gf load.

About test pieces No. 21-23, abrasion resistance was evaluated by the above-mentioned evaluation method. Moreover, the amount of abrasion before and after evaluation of abrasion resistance was measured about each test piece No. 21-23. In addition, about each test piece No. 21-23, it carried out similarly to Example 1, and evaluated by the fatigue test. The results are shown in Table 4.

As a result of evaluation of abrasion resistance, all of the specimens Nos. 21 to 23 did not crack, but the wear amount was more than 50 µm, No. 22 to less than 20 to 50 µm, and No. 23 to less than 20 µm. Fatigue strength showed favorable fatigue strength in both test pieces of 360 MPa or more.

Claims (3)

In mass%, Al: 4.5% or more and less than 5.5%, Fe: 1.3% or more and less than 2.3%, Si: 0.25% or more and less than 0.50%, O: 0.08% or more and less than 0.25%, and remainder consists of titanium and inevitable impurities The wear-resistant titanium alloy member excellent in fatigue strength characterized by having a hardened layer in which oxygen dissolved in the surface layer of a titanium alloy base material. The wear-resistant titanium alloy member having excellent fatigue strength according to claim 1, wherein the cured layer is one or two of nitrogen and carbon, and oxygen is dissolved in the surface layer of the base material. The said hardened layer is a Vickers hardness of a cross section of 450 HV or more in 10 micrometer depth from the surface, The wear-resistant titanium alloy member excellent in the fatigue strength of Claim 1 or 2 characterized by the above-mentioned.