Golf club head

Abstract

A golf club head showing good ball bouncing performance is provided with good cold workability and age hardenability.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a golf club head (hereinafter referred to as “head”) that is made of a Ti—Al—V—Sn-based β titanium alloy.

DESCRIPTION OF THE PRIOR ART

[0002] In recent years, hollow metallic heads have attracted attention as heads. Titanium alloys are generally used as the material for metallic heads in particular. The reason for this is titanium alloys have those properties which are required for head materials, namely high strength and low specific gravity.

[0003] FIG. 1 is a perspective view illustrating a wood type head. As shown in FIG. 1, the wood type head 1 is mainly composed of a face 2 and the head body 3. The head body 3 is mainly constituted of an upper structure called the crown, a side and a sole. Among the parts constituting a wood type head, the face 2, in particular, is required to have high strength as compared with the head body 3, since the face directly impacts the ball.

[0004] However, increasing the face thickness in order to maintain the strength of the face makes it necessary to reduce the weight of the head body so that the weight of the whole head may be kept within an appropriate range. As a result, it may become difficult to control the center of gravity of the head, or it may become impossible to increase the volume of the head. The face is desired to be thin for the ball bouncing performance. Therefore, the material of the face is required to be high in tensile strength and low in specific gravity.

[0005] Titanium alloys generally used as head materials are a Ti—6Al—4V alloy and a Ti—4.5Al—3V—2Fe—2Mo alloy. These titanium alloys are, however, α+β type alloys, hence are high in deformation resistance in a low temperature range. The face of a wood type head, in particular, is not flat but has a slight curved surface, and the working thereof is difficult.

[0006] There are two methods for making the face. One is casting or forging, the other is press forming of a heated plate. The casting, however, results in a little decrease in tensile strength as compared with the forging or the press forming, and in addition, may cause casting defects. Therefore, for the face to have a sufficient level of strength, it becomes necessary to increase its thickness. In the case of the forging or the press forming as well, working in a high temperature range is necessary for forming a predetermined shape. Titanium alloys have a drawback in that when they are heated at high temperatures, they are readily oxidized.

[0007] Laid-open Japanese Patent Application (JP Kokai) H06-240390 discloses an invention relating to a Ti-based driver head material comprising not less than 10 mass % but less than 25 mass % of V as a fundamental alloying element and containing one or more elements selected from among 2-5 mass % of A, 2-5 mass % of Cr and 2-4 mass % of Sn. This alloy is commonly referred to as Ti—15V—3Al—3Cr—3Sn alloy and is a kind of β type titanium alloy. Since β type titanium alloys can be worked by plastic forming and, further, can be improved in tensile strength by aging treatment, thickness reduction can easily be achieved. Furthermore, they are low in Young's modulus among titanium alloys and therefore allow balls to bounce more, hence they are useful as head materials.

[0008] According to the above-cited publication JP Kokai H06-240390, the reason Al is contained is that Al promotes aging and the material cost of Al—V is lower. It is also described that Cr is contained for improving cold press workability, and Sn is added for preventing the formation of that brittle ω phase which precipitates during aging treatment.

[0009] However, the titanium alloy described in the above-cited JP Kokai H06-240390 has a high Sn content of 2 mass % or above and therefore shows a high Young's modulus and, as a result, the ball bouncing performance declines. Furthermore, the alloy is not satisfactory in cold workability. For example, it tends to readily undergo cracking in edge portions during cold rolling.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a head whose face is made of a titanium alloy, having combined characteristics required of the head face, namely good cold workability, age hardenability and ball bouncing performance.

[0011] The present invention consists in a head specified below. The percentages referring to the contents of components are on the “mass %” basis.

[0012] A golf club head, at least the face of which is made of a titanium alloy containing V: 15 to 25%, Al: 2.5 to 5%, and one or both of Sn: 0.25 to 2.0% and Zr: 0.5 to 4.0%, with the balance being Ti and impurities.

[0013] The content of hydrogen, among the impurities in the face-constituting titanium alloy, is desirably 0.05% or less. The head of the present invention can have a face thickness of 1 to 3.0 mm, a head volume of 200 to 500 cm3 and a head weight of 170 to 220 g.

BRIEF DESCRIPTION OF THE DRAWING

[0014] FIG. 1 is a perspective view illustrating a wood type head.

[0015] (Explanation of Symbols)

[0016] 1.—wood type head, 2.—face, 3.—head body, 4.—hosel.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0017] In the following, the effects of the components of the titanium alloy, constituting the head of the present invention, and the grounds for restriction of the contents thereof are explained.

[0018] (a) V: 15 to 25%

[0019] V solutes in the titanium alloy matrix and makes the structure of the matrix a β single phase at room temperature, hence it is an element effective in facilitating cold working. When the content of V is less than 15% however, the solution heat treatment will fail to convert the structure to the β single phase. Instead, a martensitic structure will be formed, whereby the cold workability will be deteriorated. Further, even during the solution heat treatment, the α phase will exist abundantly, hence the Young's modulus will increase and the ball bouncing performance will decrease. Conversely, when the V content exceeds 25%, the structure becomes the β phase but the deformation resistance in the step of cold working increases and, at the same time, the age hardenability deteriorates, so that it becomes necessary to prolong the aging time, causing an increase in production cost. In addition, V is an expensive element, therefore, from the material cost reduction viewpoint, an excessive content thereof is not desirable. Accordingly, the V content should be kept within the range of 15 to 25%.

[0020] Mo, Cr, Fe, Mn etc. are also known as β phase-stabilizing elements. However, among titanium alloys containing such elements, only those containing V are low in strength in a solid solution state, hardly allow any segregation of components and also show good cold workability (cold rollability and cold forgeability).

[0021] (b) Al: 2.5 to 5%

[0022] Al is an element most effective in strengthening the a phase. The titanium alloy used in making the head of the present invention shows a metastable β single phase in the solid solution state and, when it is subjected to aging treatment, the a phase precipitates in the β phase, whereby the strength is improved. In order to attain the high strength through the a phase precipitation, it is effective to not only disperse the fine α phase precipitate but also strengthen the precipitate itself. Additionally, Aluminum contained in the alloy is effective to prevent the precipitation of the ω phase and also to promote the precipitation of a phase. For producing the above effects, the Al content is required to be not less than 2.5%. Conversely, when the Al content exceeds 5%, the hardness in the solution heat-treated condition becomes high, the ductility decreases, and the cold workability decreases. In addition, the Young's modulus increases and the ball bouncing performance decreases. Therefore, the Al content should be 2.5 to 5%.

[0023] (c) Sn: 0.25 to 2.0% and Zr: 0.5 to 4.0%

[0024] The alloy of the present invention contains one or both of Sn and Zr. These are elements which markedly improve the cold workability of the titanium alloy. Furthermore, these elements promote and stabilize the age precipitation of the a phase and, accordingly, inhibit the formation of the α phase, therefore, the temperature range for appropriate aging treatment can be widened. They are also effective in improving the hardness after the aging treatment. Furthermore, as compared with Al, Sn and Zr will not harden the alloy matrix. Therefore, by replacing part of Al with Sn and/or Zr, it becomes possible to improve the cold workability, and also prevents the deformation resistance from increasing. For producing such effects, the Sn content is required to be not less than 0.25%, and the Zr content not less than 0.5%. However, when the Sn or Zr content exceeds these amounts, the β single phase matrix in the solution heat treated condition is hardened and the cold workability decreases. In addition, the Young's modulus increases and the hitting performance deteriorates. These influences are more significant with Sn as compared with Zr, so that the upper limit to the Sn content is set at 2.0% and the upper limit to the Zr content is set at 4.0%. Amore preferred upper limit is 1.8% for Sn and 3.0% for Zn.

[0025] The alloy to be used in making the head of the present invention contains the above chemical components, with the balance being Ti and impurities. The content of hydrogen among the impurities is desirably 0.05% or less. The reasons are as follows.

[0026] (d) Hydrogen: not more than 0.05%

[0027] Hydrogen is a β phase stabilizing element and, when its content is excessive, the age precipitation is retarded, hence it is desired that the hydrogen content be as low as possible. Therefore, the hydrogen content is desirably restricted to 0.05% or less.

[0028] Regarding oxygen as an impurity in the titanium alloy, defined by the present invention, the content thereof should be low so that cold workability, in particular cold press workability, can be maintained; hence, the content thereof is preferably not more than 0.25%. As for Fe, it is a β phase stabilizing element but excessively increases the hardness after solution heat treatment, so that its content should be not more than 0.3% and desirably as low as possible.

[0029] The head of the present invention is one in which at least the face is made of the above-defined titanium alloy. In other words, the body portion other than the face may be made of the titanium alloy specified herein or of a conventional titanium alloy, for example a Ti—6Al—4V alloy. This is because the golf club performance depends mainly on the face with which the ball comes into direct contact, hence it is only necessary to use the above titanium alloy in that face portion.

[0030] In cases where an alloy, other than the above titanium alloy, is used in the body portion other than the face, the welding materials to be used for joining the face and the body may be the same in composition as the above titanium alloy used in making the face, the titanium alloy used in making the body portion other than the face, or an intermediate in composition between the two.

[0031] In order to improve the ball bouncing performance_of the head, it is effective to make the face thickness as thin as possible. When any of the conventional titanium alloys are used in making the face and the thickness thereof is reduced, it becomes difficult to maintain the required strength. On the contrary, the head of the present invention can maintain the required strength even when the face thickness is significantly reduced to 3.0 mm or less and even further to 2.8 mm or less. From the strength viewpoint, the lower limit of the face thickness is set at 1 mm.

[0032] For increasing the driving distance and improving directional accuracy of the ball, the head volume is desirably to be not less than 200 cm3. On the other hand, it is necessary to maintain the strength of the head itself. When the conventional titanium alloys are used for head materials, the head should be rather thick in order to maintain strength. Therefore, the head becomes large-sized and the weight increases and exceeds, for example, 220 g. Such a high weight is inadequate for appropriate use of a golf club. For increasing the head volume to cope with the above situation, while keeping the head weight at a low level, it is necessary to reduce the head thickness (in particular, the thickness of the face having a comparatively high weight). When the conventional titanium alloys are used, the strength required of the head cannot be maintained.

[0033] On the contrary, when the titanium alloy defined herein is used, the face thickness can be reduced while maintaining its high strength. Therefore, a head volume of 200 cm3 can be attained while suppressing the weight of the whole head to 220 g or less. However, the head volume must be determined under consideration of the proper balance between the weight and the strength of the head. Thus, the upper limit of the head volume is set at 500 cm3. When the head weight is insufficient, no sufficient moment of inertia can be obtained and the driving distance of the ball decreases. Hence, the lower limit of the head is set at 170 g.

[0034] The term “head” includes, within the meaning thereof, the face, head body and hosel for connection with a shaft, as shown in FIG. 1.

[0035] The head of the present invention can be produced, for example, in the following manner.

[0036] First, a raw material with an adjusted chemical composition is melted by the VAR (vacuum arc remelting) method and an ingot is made. The ingot is hot-rolled, and the sheet obtained is subjected to solution heat treatment (e.g. 930° C.×5 minutes) and then cold-rolled to give a 1 to 3-mm-thick sheet for making faces. Then, this cold-rolled sheet with residual strain is formed into faces having a predetermined shape by a cold or warm pressing. Each face is then welded to the other part, followed by aging treatment.

[0037] The aging treatment may be carried out prior to assembling by welding. In making a head having a special structure, the aging treatment is desirably carried out after the second solution heat treatment, following the working to the desired face form by cold or warm pressing. This is because a higher level of ductility can be obtained as compared with a head produced without the second solution heat treatment.

[0038] It is also possible to produce faces, having a predetermined shape and form, by working the above ingot to a bar by forging and, after solution heat treatment, subjecting the bar to hot forging or cold forging. In making the head of the present invention using the head formed in such process, it is also recommended that the aging treatment be carried out after forging or assembling, by welding. In making the face by cold forging, it is recommended that the solution heat treatment be carried out immediately before aging treatment, similar to the case of making the face by cold rolling.

EXAMPLES

[0039] The present invention is further described by the following examples.

Example 1

[0040] Ingots were prepared by melting titanium alloys having respective compositions specified in Table 1 by the VAR method. These ingots were subjected to hot forging and hot rolling under ordinary conditions, then to solution heat treatment (930° C.×5 minutes), descaling treatment (washing with hydrofluoric/nitric acid) and finally to cold rolling to a thickness of 2.7 mm. In the step of descaling, the oxygen content in each alloy was adjusted by immersing in hydrofluoric acid. Face-shaped pieces were punched out from these sheets and worked to acquire a predetermined curved surface, and each was joined, by welding, with a crown, side and sole prepared separately, to give a wood type head. The produced heads were further subjected to aging treatment at 500° C. for 5 hours, and the face thickness was adjusted to 2.6 mm by surface polishing. The products thus obtained were used as test specimens. The volume of each head manufactured was 400 cm3, and the weight thereof was 185 g.

	TABLE 1
	Chemical constituents (% by mass), balance: Ti	Cold	Durability
No.	V	Al	Sn	Zr	H	O	Fe	workability	test	Example
1	13.0*	3.2	1.0	—	0.012	0.085	0.101	Cracking (E, S)	Cracking	for comparison
2	15.0	3.2	1.0	—	0.011	0.089	0.095	Good	Passed	of Invention
3	20.2	3.2	1.0	—	0.012	0.080	0.112	Good	Passed	of Invention
4	25.0	3.0	1.0	—	0.010	0.092	0.098	Good	Passed	of Invention
5	27.5*	3.2	1.1	—	0.010	0.080	0.094	Good	Depression	for comparison
6	20.0	2.0*	1.0	—	0.011	0.083	0.115	Good	Depression	for comparison
7	20.0	2.5	1.0	—	0.012	0.085	0.102	Good	Passed	of Invention
8	20.2	4.8	1.0	—	0.013	0.091	0.090	Good	Passed	of Invention
9	20.1	6.0*	1.0	—	0.009	0.077	0.093	Cracking (E, S)	Cracking	for comparison
10	20.2	3.2	1.0	—	0.045	0.080	0.107	Good	Passed	of Invention
11	20.2	3.2	1.0	—	0.055	0.090	0.121	Good	Passed**	of Invention
12	20.2	3.2	*	*	0.012	0.085	0.105	Good	Depression	for comparison
13	20.0	3.3	0.4	—	0.011	0.090	0.090	Good	Passed	of Invention
14	20.1	3.0	1.8	—	0.010	0.082	0.113	Good	Passed	of Invention
15	20.0	3.2	3.0*	—	0.011	0.081	0.099	Cracking (E)	Passed	for comparison
16	20.2	2.9	—	0.6	0.013	0.087	0.090	Good	Passed	of Invention
17	20.0	3.0	—	3.0	0.013	0.088	0.120	Good	Passed	of Invention
18	20.4	3.2	—	5.0*	0.010	0.089	0.117	Cracking (E)	Passed	for comparison
19	20.2	4.0	*	*	0.012	0.090	0.100	Cracking (E, S)	Cracking	for comparison
20	20.2	3.2	0.5	1.0	0.010	0.099	0.090	Good	Passed	of Invention
Notes:
The symbol “*” means that the chemical composition was out of the scope of the present invention.
The symbol “**” means that slight depression occurred.
Under the heading “Cold workability”:
“E” indicates that edge cracking occurred and
“E, S” indicates that cracking occurred in edge and surface layer.

[0041] Under the heading “cold workability” in the table, these are the results obtained upon examination for edge and surface layer cracking on the sheets obtained by cold rolling of 5.0 mm thick hot rolled sheets into sheets of 2.7 mm thick. Under the heading “durability test”, there are the results obtained by equipping each head with a shaft and causing the central part thereof to repeatedly collide with a ball at a head speed of 50 m/s. The evaluation was made according to the following criteria: when neither depression nor cracking occurred on the face surface after 3,000 repetitions of the above collision, the specimen was regarded as passing the test. When depression and/or cracking occurred, the specimen was regarded as failing to pass the test.

[0042] As shown in Table 1, in the specimen No. 1, which had α+β structure because V content was below the range specified herein, cracking occurred in edge and surface layer portions during cold rolling, and cracking also occurred in the durability test. With the specimens No. 5, whose V content was above the range specified herein, No. 6, whose Al content was below the range specified herein, and No. 12, which contained neither Sn nor Zr, aging did not result in any improvement in strength, but depression occurred in the durability test.

[0043] With the specimens No. 19, in which the Al content was increased in place of addition of Sn and Zr, and No. 9, whose Al content was above the range specified herein, cracking occurred in edge and surface layer portions during cold rolling and, further, cracking occurred in the durability test as well. With Nos. 15 and 18, whose Sn or Zr content exceeded the range specified herein, edge cracking occurred during cold rolling.

[0044] On the other hand, the specimens Nos. 2, 3, 4, 7, 8, 10, 11, 13, 14, 16, 17 and 20, whose respective chemical compositions were within the range specified herein, were all superior in cold workability and durability. With No. 11, whose hydrogen content in the titanium alloy was 0.055%, slight depression occurred but at a problem-free level. As revealed above, when the titanium alloy having a chemical composition within the range specified herein is used, the head face can be reduced in thickness and therefore the head can be provided with excellent ball bouncing performance.

Example 2

[0045] Ingots were prepared by melting the titanium alloy having the composition No. 3 specified in Table 1 by the VAR method. These ingots were subjected to hot forging and hot rolling under ordinary conditions, then to solution heat treatment (930° C.×5 minutes), descaling treatment (washing with hydrofluoric/nitric acid) and finally to cold rolling to give three kinds of sheets, 3.1 mm, 2.9 mm and 2.7 mm in thickness, respectively. Pieces having a necessary size were cut out from these sheets and worked to a predetermined curved surface, and each was joined, by welding, with a head body prepared separately, to give a wood type head. The produced heads were further subjected aging at 500° C. for 5 hours, and the face thickness was adjusted to 3.0 mm, 2.8 mm and 2.6 mm by surface polishing. The obtained three kinds of specimens were used as test specimens. Separately, three kinds of wood type heads, 3.0 mm. 2.8 mm and 2.6 mm in face thickness, respectively, were produced in the same manner as mentioned above except that a round bar made of a commercial Ti—6% Al—4% V alloy was hot forged. These heads were used as test specimens No.21. The test specimens were subjected to durability testing in the same manner as mentioned above. The results are shown in Table 2.

	TABLE 2
	Chemical constituents (% by mass),	Durability test
	balance: Ti	Face thickness:	Face thickness:	Face thickness:
No.	V	Al	Sn	Zr	H	O	Fe	3.0 mm	2.8 mm	2.6 mm
3	20.2	3.2	1.0	—	0.012	0.080	0.112	Passed	Passed	Passed
21	4.0*	6.0*	*	*	0.005	0.101	0.099	Passed	Cracking after	Cracking after
									2,500 collisions	500 collisions
Notes: The symbol “*” means that the chemical composition was out of the scope of the present invention.

[0046] The specimens No.3, produced from the alloy whose chemical composition, was within the range specified herein passed the durability test irrespective of face thickness whereas. With the specimens No.21, produced using the Ti—6Al—4V alloy, cracking occurred after 2,500 collisions when the face thickness was 2.8 mm and, when the face thickness was 2.6 mm, cracking occurred after no more than 500 collisions.

[0047] As explained above, it is possible, according to the present invention, to produce heads having both high strength and good ball bouncing performance.

Claims

1. A golf club head at least the face of which is made of a titanium alloy consisting of, by mass %, V: 15 to 25%, Al: 2.5 to 5%, and one or both of Sn: 0.25 to 2.0% and Zr: 0.5 to 4.0%, with the balance being Ti and impurities.

2. A golf club head at least the face of which is made of a titanium alloy consisting of, by mass %, V: 15 to 25%, Al: 2.5 to 5%, and one or both of Sn: 0.25 to 2.0% and Zr: 0.5 to 4.0%, with the balance being Ti and impurities, the content of hydrogen as an impurity being not more than 0.05%.

3. A golf club head according to claim 1 or 2, said head having a volume of 200 to 500 cm3 and a weight of 170 to 220 g, with the thickness of the face being 1 to 3.0 mm.