Golf club

Abstract

At least a part of a head portion of a golf club consists of stainless steel containing throughout 0.1% or more to 0.3% or less by weight of nitrogen. Further, at least a part of the head portion consists of a corrosion-resistant metal having a yield strength of 0.2% of 350 MPa or more to 600 MPa or less, a tensile strength of 500 MPa or more to 800 MPa or less and an elongation after fracture of 40% or more to 60% or less.

Description

[0001] This application claims priority from Japanese Patent Application No. 2000-338616(P) bearing the filing date of Nov. 7, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a golf club, and more particularly to a golf club having a head portion formed of a prescribed composition of material.

[0004] 2. Description of the Background Art

[0005] Conventionally, austenite 18 Cr--8Ni (SUS304 according to Japanese Industrial Standards (JIS) code), ferritic 17Cr stainless steel (SUS430 according to JIS), precipitation hardening 17Cr--4Ni (SUS630 according to JIS) or the like are generally used for a head portion made of stainless steel. S25C of carbon steels for machine structural use is also used.

[0006] Japanese Utility Model Laying-Open No. 2-143969 describes an invention in which nitrogen is introduced into a hitting surface of a head portion by ion implantation or ion beam mixing.

[0007] Further, Japanese Patent Laying-Open No. 6-269520 discloses a method of manufacturing a golf club head, wherein stainless steel hardened by sub-zero treatment is forged into a head shape, which is subjected to solution treatment in a nitrogen atmosphere, followed by sub-zero treatment.

[0008] Still further, Japanese Patent Laying-Open No. 11-206930 discloses a method of manufacturing a golf club head, wherein austenite material is formed into a head, which is subjected to solution treatment in vacuo at 1050-1070--for two hours, followed by cooling in a nitrogen atmosphere.

[0009] SUS304 is preferably used for fabricating an inexpensive head portion. SUS304, however, is not strong enough to wear well, unless a face portion is made thick. This makes it difficult to fabricate a thin large-size head.

[0010] Then, in order to make a face portion and a head portion thin, SUS630 which can be increased in strength by precipitation hardening by means of heat treatment after fabricating a head portion is used.

[0011] SUS630, however, is too hard, resulting in a poor feeling of hitting. Further, a general-size neck portion made of this material is too strong to bend easily, and thus a lie angle cannot be adjusted. In addition, since SUS630 is a precipitation hardening type, it needs to be increased in strength by heat treatment and therefore requires the cost of this heat treatment.

[0012] Although SUS430, 431 have a strength between SUS304 and SUS630, they have a relatively poor corrosion resistance among stainless steel. This causes rusting of a head portion to some extent. In addition, it is difficult to adjust a lie angle.

[0013] S25C is not strong enough to fabricate a thin, large-size head. Further, since it has a poor corrosion resistance, a head surface needs to be plated.

[0014] According to Japanese Utility Model Laying-Open No. 2-143969, a hitting surface is introduced with nitrogen by ion implantation or ion bean mixing. This increases cost, and in addition, only the hitting surface is hardened. It follows that although the strength of the hitting surface becomes high, the strength of a head internal portion remains low. Therefore, when a thin, large-size head is fabricated, the strength is not sufficient.

[0015] According to Japanese Patent Laying-Open No. 6-269520, although a head surface is softened to provide a good feeling of hitting, a head internal portion is too strong to adjust an angle of a neck portion easily. In addition, performing a sub-zero treatment increases cost.

[0016] According to Japanese Patent Laying-Open No. 11-206930, nitrogen penetrates only into the vicinity of a head surface. As a result, although the strength of the head surface becomes high, the strength of a head internal portion remains low. Therefore, when a thin, large-size head is fabricated, the strength is not sufficient.

[0017] Therefore, an object of the present invention is to provide a golf club including a head portion which enables an easy adjustment of an angle of a neck portion, allows for fabrication of a thin, large-size head, and provides a good corrosion resistance.

SUMMARY OF THE INVENTION

[0018] A golf club in accordance with the present invention includes a head portion, at least a part of which consists of stainless steel containing throughout at least 0.1% by weight to at most 0.3% by weight of nitrogen.

[0019] The inventors contemplate to provide a material for a head portion, wherein 1) an angle of a neck portion is easily adjusted when it has a normal neck diameter, 2) the head portion can be reduced in thickness and increased in size, and 3) the head portion has a good corrosion resistance. Then, it has been found that such a material for a head portion that can satisfy all the above characteristics can result by mixing nitrogen into stainless steel at the stage of a raw material before forging or casting to vary the strength of the material according to a nitrogen content. More specifically, it has been found that inclusion of at least 0.1% by weight to at most 0.3% by weight of nitrogen throughout stainless steel can attain, for example, a yield strength of 0.2% of 350 MPa-470 MPa, a tensile strength of 630 MPa-800 MPa, and an elongation after fracture of 40%-57% as shown in Table 1. As a result, by using the above mentioned material for a neck portion, the angle adjustment of the neck portion becomes easy even when it has a normal neck diameter, and such a strength can be attained that allows for a thin, large-size head portion. Further, the use of stainless steel as a base material can ensure corrosion resistance.

[0020] The aforementioned stainless steel preferably includes at least 0% by weight preferably 0.001% by weight) to at most 0.08% by weight of carbon, at least 0% by weight (preferably 0.001% by weight) to at most 1.00% by weight of silicon, at least 0% by weight preferably 0.001% by weight) to at most 2.5% by weight of manganese, at least 0% by weight (preferably 0.001% by weight) to at most 0.045% by weight of phosphorus, at least 0% by weight (preferably 0.001% by weight) to at most 0.03% by weight of sulfur, at least 0% by weight (preferably 0.001% by weight) to at most 0.15% by weight of niobium, at least 18% by weight to at most 20% by weight of chromium, and at least 7% by weight to at most 10.5% by weight of nickel, with the remainder consisting of iron and inevitable impurity.

[0021] As described above, when SUS304 material is employed as stainless steel serving as a base material, nitrogen atoms permeate throughout the atoms constituting SUS304 material, resulting in a particularly preferred value of yield strength of 0.2%, tensile strength, elongation after fracture and the like of the material, as shown in Table 1. Furthermore, inclusion of a large amount of nickel and chromium attains an excellent corrosion resistance.

[0022] Preferably, the head portion has a face portion and a neck portion, at least one of which consists of the aforementioned stainless steel.

[0023] Further, preferably, the head portion has a hollow structure, and has a face portion consisting of the aforementioned stainless steel, and the thickness of the face portion is at least 1 mm to at most 2.5 mm.

[0024] Since the material of the present invention has a relatively high strength as described above, fabrication of the face portion with this material can ensure a desired strength even when the thickness of the face portion is reduced to 1 to 3.0 mm. In addition, the face portion can be increased in size. Therefore, the face portion itself can easily flex as the area of that part of the face portion which can flex at the time of actually hitting a ball (an effective face area) is increased, thereby improving the restitution characteristics of the face portion.

[0025] Furthermore, the thickness of the peripheral portion of the face portion may be made smaller than the thickness of the center portion of the face portion. The use of the material in accordance with the present invention can ensure a desired strength even when the thickness of the peripheral portion of the face portion is reduced. Therefore, the face portion can be easily flexed, thereby improving the restitution characteristics of the face portion.

[0026] The dimensional parts of the neck portion are shown in FIG. 1. The length of the neck portion is represented by length L extending from the end portion of the neck to the ridgeline by the side of a heel where the neck and a sole face join. The neck portion shown in FIG. 1 preferably has an outer diameter D of at least 8.5 mm to at most 12.5 mm, and an inner diameter d of at least 9 mm to at most 10 mm, and the neck portion preferably has a length L of at least 30 mm to at most 80 mm.

[0027] By using the material in accordance with the present invention, the neck portion can be sized similar to a normal golf club, while the neck portion can be manually bent using tools or the like relatively easily so that the lie angle or the loft angle of the neck portion can be adjusted.

[0028] A golf club in accordance with another aspect of the present invention includes a head portion, at least a part of which consists of a corrosion-resistant metal with a yield strength of 0.2% of at least 350 MPa to at most 600 MPa, a tensile strength of at least 500 MPa to at most 800 MPa and an elongation after fracture of at least 40% to at most 60%. A corrosion-resistant metal herein refers to a metal which has an excellent corrosion resistance, such as stainless steel.

[0029] At the time of actually hitting a ball with the above noted golf club with a normal diameter, the neck portion is bent when the component material of the neck portion has a yield strength of 0.2% of less than 200 MPa and a tensile strength of less than 500 MPa. On the other hand, when the yield strength of 0.2% is more than 600 MPa and the tensile strength is more than 800 MPa, it is difficult to bend the neck portion manually using tools or the like. Further, when the yield strength of 0.2% and the tensile strength are within the above mentioned ranges but the elongation after fracture is less than 30%, the neck portion is less likely to deform, which makes it difficult to adjust the angle of the neck portion. Therefore, when yield strength of 0.2%, tensile strength and elongation after fracture are within the above ranges, the neck portion can be prevented from bending at the time of hitting a ball, while the angle of the neck portion can be adjusted relatively easily. In addition, since the strength of the material is relatively high, the head portion can be reduced in thickness and increased in size, and also be assured of corrosion resistance.

[0030] The aforementioned yield strength of 0.2% is preferably at most 400 MPa to at least 600 MPa, and the tensile strength is preferably at least 600 MPa to at most 800 MPa.

[0031] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is an illustration indicating the dimensions of the neck portion in the head portion.

[0033] FIG. 2 is an exploded perspective view of the head portion in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] In the following, an embodiment of the present invention will be described. The present invention relates to a material for forming a head portion of a golf club, and is aimed to achieve the desired characteristics by using stainless steel, which is a metal having a good corrosion resistance, as a base material, and properly adjusting the composition of the base material.

[0035] The present invention is applicable for any golf club whether it is an iron type or a wood type. Shapes of a head portion, shaft and grip of a golf club may be conventional ones used generally, and therefore these are not shown herein.

[0036] In accordance with the present invention, at least a part of a head portion of a golf club consists of stainless steel containing throughout 0.1% or more to 0.3% or less by weight of nitrogen.

[0037] Since nitrogen is mixed into stainless steel at the stage of a raw material before forging or casting, nitrogen is present not only in the surface of but also throughout the stainless steel.

[0038] A technique of mixing nitrogen will now be described. Stainless steel which was melted in an electric furnace (molten metal) is transferred as it is to a refinery. Then, in the refinery, the chemical composition is adjusted to an intended component standard range with removal of impurity. Refining of this stainless steel is normally performed in an anti-oxidization atmosphere to inhibit oxidization reaction of the included chromium. At this point, nitrogen gas is blown into the molten metal so that the molten metal undergoes solid-solution treatment with nitrogen, resulting in the stainless steel containing a large amount of nitrogen.

[0039] Nitrogen which is mixed into stainless steel as described above disperses in the stainless steel as substitutional type atoms. This increases the strength of stainless steel.

[0040] The inventors considered how much nitrogen could be mixed into stainless steel to produce such a material for a head portion in that 1) an angle of a neck portion could be easily adjusted when it had a normal neck diameter, 2) the head portion could be reduced in thickness and increased in size, and 3) the head portion had a good corrosion resistance.

[0041] The following Table 1 shows the relation of a nitrogen content with the yield strength of 0.2%, tensile strength and elongation after fracture of the material. Note that SUS304 material was used as a base material.

1TABLE 1 nitrogen content (% by weight) 0 0.1 0.2 0.3 yield strength of 0.2% (MPa) 260 350 420 470 tensile strength (MPa) 600 630 750 800 elongation after fracture (%) 64 57 49 40

[0042] As shown in Table 1, as the nitrogen content increases, the yield strength of 0.2% and tensile strength of the material increase and therefore the strength of the stainless steel increases. On the other hand, the elongation after fracture decreases as the nitrogen content increases.

[0043] The nitrogen content, however, has a limit so that it is difficult to mix more than 0.3% by weight. Further, even if the nitrogen content exceeds 0.3% by weight, the strength does not increase accordingly. In addition, as the elongation of the material decreases, possible damage or crack is more likely to cause breakage. Still further, an excess amount of a nitrogen content deteriorates weldability.

[0044] Then, nitrogen content in stainless steel is determined to be 0.1% or more to 0.3% or less by weight (preferably about 0.2% by weight). This attained a yield strength of 0.2% of 350 MPa-470 MPa, a tensile strength of 630 MPa-800 MPa, and an elongation after fracture of 40%-57% as shown in Table 1.

[0045] The above noted ranges of the yield strength of 0.2% and the like can increase the strength of the material appropriately, so that the angle of the neck portion can easily be adjusted when it has a normal neck diameter, and in addition, a head portion can be reduced in thickness and increased in size. Further, the use of stainless steel as a base material can ensure corrosion resistance.

[0046] Stainless steel serving as a base material is preferably SUS304, including at least 0% (preferably 0.001%) to at most 0.08% by weight of carbon, at least 0% (preferably 0.001%) to at most 1.00% by weight of silicon, at least 0% (preferably 0.001%) to at most 2.5% by weight of manganese, at least 0% (preferably 0.001%) to at most 0.045% by weight of phosphorus, at least 0% (preferably 0.001%) to at most 0.03% by weight of sulfur, at least 0% (preferably 0.001%) to at most 0.15% by weight of niobium, at least 18% to at most 20% by weight of chromium, and at least 7% to at most 10.5% by weight of nickel, with the remainder consisting of iron and inevitable impurity.

[0047] By employing SUS304 material as stainless steel serving as a base material as described above, the yield strength of 0.2%, tensile strength, elongation after fracture and the like fall within the particularly preferred ranges as shown in Table 1. Further, inclusion of a large amount of chromium and nickel attains an excellent corrosion resistance.

[0048] A head portion was fabricated using a material, in which the present invention described above was embodied, (an embodiment), which was compared with a head portion using a conventional stainless steel in terms of yield strength of 0.2%, tensile strength, corrosion prevention, feeling of hitting, and easiness of the angle adjustment of the neck portion (neck angle adjustment). The result is shown in Table 2 below.

2 TABLE 2 neck neck yield tensile corrosion feeling angle bending strength strength preven- of adjust- in (MPa) (MPa) tion hitting ment hitting embodiment 400 750 no S25C 280 460 x no SUS3O4 210 550 yes SUS431 650 850 ? ? x no SUS630 750 950 x x no

[0049] A method of manufacturing in accordance with the aforementioned embodiment will now be described. First, using a material (JIS SUS304N2) in which about 0.2% by weight of nitrogen is mixed in SUS304 by the aforementioned technique, a face side portion 3 into which a face portion and a neck portion are integrated as shown in FIG. 2 is fabricated by forging. On the other hand, a back side portion 4 is fabricated using SUS304 material by forging.

[0050] At this point, as shown in FIG. 2, the thickness of center part 3a of the face portion is made to 2.5 mm, upper part 3b of the face portion is to 2.1 mm, and lower part 3c of the face portion 3c is to 2.3 mm. The outer diameter of the neck portion is 12.5 mm, the inner diameter thereof is 9.5 mm, and the length thereof is 50 mm.

[0051] Then, using a welding rod of SUS304, the face side portion and the back side portion are welded together. Note that after welding, thermal treatment is not performed.

[0052] As shown in Table 2, the yield strength of 0.2% and tensile strength of the head portion manufactured through the above steps are greater than those of SUS304 and S25C, and smaller than those of SUS431 and SUS630.

[0053] In other words, it should be understood that the strength is appropriately increased. Therefore, when a neck portion is formed of the aforementioned material, the neck portion can be sized similar to a normal golf club while the neck portion can be manually bent using tools or the like relatively easily so that the lie angle and the loft angle of the neck portion can be easily adjusted.

[0054] It is noted that the outer diameter of the neck portion may be at least 8.5 mm to at most 12.5 mm, the inner diameter thereof may be at least 9 mm to at most 10 mm, and the length thereof may be at least 30 mm to at most 80 mm.

[0055] Furthermore, since the material in accordance with the present invention has a relatively high strength, it is possible to provide a head portion in a hollow structure and to reduce the thickness of a face portion to 3.0 mm or less while increasing the size of the face portion.

[0056] Accordingly, the face portion itself can easily flex as the area of that part of the face portion that can flex at the time of hitting a ball (an effective face area) is increased, thereby improving the restitution characteristics of the face portion.

[0057] It is noted that the thickness of the face portion may be 1 mm or more to 3.0 mm or less. The use of the material in accordance with the present invention can reduce the thickness of the face portion to this extent.

[0058] Furthermore, when the thickness of the peripheral portion of the face portion is made smaller than that of the center portion of the face portion as the aforementioned embodiment, the face portion tends to flex more easily, and therefore the restitution characteristics of the face portion can further be improved.

[0059] A golf club having a head portion fabricated using the material of the present invention was evaluated by having a professional player hit a ball with this club. As a result, it is appreciated with an impression that "feeling of hitting is very good", though Table 2 just shows,.

[0060] Since SUS304 is used as a base material, the corrosion resistance (corrosion prevention) of the head portion of the present embodiment is excellent as shown in Table 2.

[0061] It is noted that although the face portion and the neck portion are integrated in the aforementioned embodiment, at least one of the face portion and the neck portion may consist of the material of the present invention. Alternatively, the neck portion and the back portion may be integrated.

[0062] Although the desired characteristics of stainless steel is achieved by mixing an adequate amount of nitrogen into stainless steel in accordance with the aforementioned embodiment, it is assumed that any metal material which can satisfy the condition described below will bring about the aforementioned effect specific to the present invention.

[0063] More specifically, it is assumed that any corrosion-resistant metal can bring about the effect specific to the present invention as long as it has a yield strength of 0.2% of at least 350 MPa to at most 600 MPa, a tensile strength of at least 500 MPa to at most 800 MPa, and an elongation after fracture of at least 40% to at most 60%. A corrosion-resistant metal herein refers to a metal which has an excellent corrosion resistance, such as stainless steel.

[0064] An iron based material having a yield strength of 0.2% of 0-600 MPa, a tensile strength of 0-800 MPa, and an elongation after fracture of 30% or more enables a neck portion with a normal neck diameter to be bent manually using tools or the like. A yield strength of 0.2% of less than 200 MPa, however, causes bending of the neck portion in hitting a ball actually.

[0065] Further, a yield strength of 0.2% of more than 600 MPa, and a tensile strength of more than 800 MPa make it difficult to bend the neck portion manually even by means of tools or the like. In addition, when a yield strength of 0.2% and a tensile strength are within the above noted ranges but an elongation after fracture is less than 30%, the neck portion is less likely to deform, which makes it difficult to adjust the angle of the neck portion.

[0066] Therefore, when the yield strength of 0.2%, tensile strength and elongation after fracture are set to be within above noted ranges, bending of the neck portion can be prevented when hitting a ball actually, while the angle of the neck portion can be adjusted relatively easily. Furthermore, the relatively high strength allows for a thin, large-size head portion, and the use of a corrosion-resistant metal can ensure the corrosion resistance of the head portion.

[0067] The above noted yield strength of 0.2% is preferably at least 400 MPa to at most 600 MPa, and the tensile strength is preferably at least 600 MPa to at most 800 MPa. This makes the effect of the present invention more prominent.

[0068] According to the present invention, the desired value of the strength of the material for the head portion can be achieved, so that the angle of the neck portion can be easily adjusted when it has a normal neck diameter, and the head portion can be reduced in thickness and increased in size. Furthermore, the use of a material having an excellent corrosion resistance as a base material of the head portion can ensure corrosion resistance.

[0069] Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims

What is claimed is:

1. A golf club comprising a head portion, wherein at least a part of said head portion consists of stainless steel containing throughout at least 0.1% by weight to at most 0.3% by weight of nitrogen.

2. The golf club according to claim 1, wherein said stainless steel includes at most 0.08% by weight of carbon, at most 1.00% by weight of silicon, at most 2.5% by weight of manganese, at most 0.045% by weight of phosphorus, at most 0.03% by weight of sulfur, at most 0.15% by weight of niobium, at least 18% by weight to at most 20% by weight of chromium, and at least 7% by weight to at most 10.5% by weight of nickel, with the remainder consisting of iron and inevitable impurity.

3. The golf club according to claim 1, wherein said head portion has a face portion and a neck portion, and at least one of said face portion and said neck portion consists of said stainless steel.

4. The golf club according to claim 3, wherein thickness of a peripheral portion of said face portion is made smaller than thickness of a center portion of said face portion.

5. The golf club according to claim 1, wherein said head portion has a hollow structure and has a face portion consisting of said stainless steel, and thickness of said face portion is at least 1 mm to at most 2.5 mm.

6. The golf club according to claim 5, wherein thickness of a peripheral portion of said face portion is made smaller than thickness of a center portion of said face portion.

7. The golf club according to claim 3, wherein said neck portion has an outer diameter of at least 8.5 mm to at most 12.5 mm and an inner diameter of at least 9 mm to at most 10 mm, and said neck portion has a length of at least 30 mm to at most 80 mm.

8. A golf club comprising a head portion, wherein at least a part of said head portion consists of a corrosion-resistant material having a yield strength of 0.2% of at least 350 MPa to at most 600 MPa, a tensile strength of at least 500 MPa to at most 800 MPa and an elongation after fracture of at least 40% to at most 60%.

9. The golf club according to claim 8, wherein said yield strength of 0.2% is at least 400 MPa to at most 600 MPa, and said tensile strength is at least 600 MPa to at most 800 MPa.