Golf Club Head

This application is a continuation-in-part of U.S. patent application Ser. No. 18/771,457, which is a non-provisional of U.S. Provisional Application No. 63/614,154, filed on Dec. 22, 2023, the disclosures of each of which are incorporated herein by reference in its entirety.

Golf clubs from a technical perspective undergo a unique set of rigors. For example, golf clubs are evaluated in their ability to meet performance thresholds such as efficient transfer of energy to a golf ball upon impact. Golf clubs are also evaluated in terms of their ability to provide forgiveness on off-centered shots or mis-hits. Further, golf clubs in some cases are evaluated in their ability to impart specific spin characteristics or other attributes to a golf ball upon impact for shaping flight trajectory and/or ball roll characteristics. Apart from performance, club heads are expected to withstand repeated use, e.g. resist wear, rust, and material fatiguing. Some club heads are also expected to permit a degree of adjustability by plastic deformation, e.g. hosel bending to adjust loft and/or lie.

Golf club manufacturers desire to achieve success across all or as many of these aspects of use as possible. But the varied nature of these functional desirables, and provision of limitations, e.g. regarding mass, physical dimensions, and cost, often lead to design conflicts and tradeoffs. For example, increasing the forgiveness of a club head, e.g. by increasing its moment of inertia about preferred axes often comes at the cost of desirable feel. Similarly, adapting a club head to impart beneficial spin and wear resistance may likely involve a material selection that could adversely affect other considerations. For example, conventional materials that offer high hardness, high yield strength and adequate machineability often fall short in other key areas such as malleability or softness, which is preferable regarding the provision of adjustability or bendability.

To minimize the severity of such design trade-offs, manufacturers have considered selectively varying club head materials about the structure of the club head to better match material properties with structural function. For example, iron-type club heads, e.g. wedges, have implemented face inserts of a material different from that of a main body to which the face insert is secured. Accordingly, the face insert may be selected to exhibit properties ideal for impact, such as relatively high hardness, low density, adequate wear resistance, and adequate machineability. Yet, the material of the main body may appropriately depart from those properties and instead be selected to exhibit e.g. a higher density and greater malleability.

Selectively positioning different materials about the structure of a club head, although with apparent benefit, is not without detriment. First, increasing the number of components constituting a club head increases its cost and complexity in manufacture. As a result, margins of error in manufacturing may increase as may locations of failure e.g. given the imposition of adhesives, mechanical fasteners and heat-affected zones resulting from welding or brazing. Also, departure of a club head from solid structure toward componentized structure may result in deleterious loss of feel and poor acoustics or vibratory properties.

An object, therefore, of the present disclosure is to provide material compositions, and implementations thereof, that are in themselves suitable for varied use aspects expected of golf club heads. Accordingly, benefits associated with selectively corresponding material properties with particular club head structure may be achieved, while detriments associated with unduly componentized structure may be minimized or avoided.

In one aspect, a golf club head includes a unitary component formed of a stainless steel material. The unitary component has variable hardness. A first portion of the component exhibits a first hardness H1 no less than 50 HRC. A second portion of the component exhibits a second hardness H2 no greater than 85 HRB.

In another aspect of the present disclosure, a method includes forming a component of a golf club head. The component comprises a stainless steel material. The method includes selectively surface hardening the component such that a first portion of the component exhibits a first hardness H1 no less than 50 HRC and a second portion of the component exhibits a second hardness H2 no greater than 85 HRB.

In another aspect of the present disclosure, a component for a golf club head includes a stainless steel material. The stainless steel material has a Nickel content no greater than 0.25% by mass.

In another aspect of the present disclosure, a component for a golf club head includes a stainless steel material. The stainless steel material has a Carbon content no less than 0.25% by mass.

In another aspect of the present disclosure, a component for a golf club head includes a stainless steel material. The stainless steel material has an austenization temperature no less than 800° C.

These and other features and advantages of the golf club heads, their compositions, and manufacturing methods thereof according to the various aspects of the present disclosure will become more apparent upon consideration of the following description, drawings, and appended claims. The description and drawings described below are for illustrative purposes only and are not intended to limit the scope of the present invention in any manner.

In one aspect of the present disclosure, referring to, a club headis shown. The golf club headincludes a front portionincluding a striking face, a top portionand a sole portionopposite the top portion. The sole portionis configured to rest on a virtual ground plane, e.g. ground plane, when in a reference position. The golf club headfurther include a heel portionand a toe portionopposite the heel portion. A hosel portionextends from heel portion. The hosel portionincludes a hosel bore (not shown) configured to receive a golf shaft (not shown). The golf club head, once combined with a golf shaft may form a golf club. The hosel portiondefines a virtual hosel axisbeing a central axis defined by the hosel bore. The hosel axisin relation to the remaining structure of the club headdefines a club head loft and lie.

As used herein, “reference position” refers to a position of the golf club head, e.g. club head, wherein a hosel centerline lies in an imaginary vertical hosel plane relative to a ground plane, the hosel plane intersects a striking face plane along a line parallel the scorelines, and the scorelinesgenerally extend parallel to the ground plane

Preferably, the club headis an iron-type club head, e.g. having a loft between 20° and 66°. More preferably, the club headis a wedge-type club head, e.g. having a loft between 40° and 66°. Additionally, or alternatively, the club headbears a lie between about 62° and about 66°, more preferably between 61° and 63°. However, the structures and material compositions described herein may readily apply to other types of golf club heads, e.g. woods including drivers, fairway woods, and hybrids, as well as putters, rescue clubs, etc.

The golf club head preferably comprises a steel material, preferably a stainless steel material. Typically, readily-available grades of stainless steel are applied in golf club head construction, particularly for iron-type, including wedge-type, club heads. For example, AISI 431 alloy steel is a commonly used material in golf club heads and components thereof. However, in consideration of the unique set of rigors and constraints associated with golf club heads, particularly wedge-type golf club heads, as well as the desire to minimize the severity of design trade-offs, steel compositions different from conventional materials, say AISI 431, may be advantageous. For all purposes herein, a steel alloy is considered to be a stainless steel if its Chromium content is at least 10.5% by mass.

Preferably, a majority (i.e. greater than 50%) of the club head, by mass, is comprised of such steel, more preferably at least 85% of the club head, even more preferably substantially the entirety of the club head(e.g. accounting for minor auxiliary components such as paints, thin coatings, mouse glue, ferrules, etc.). Alternatively or additionally, such steel preferably constitutes a unitary component of the club head, more preferably a unitary component that includes a first portion forming at least a portion of the striking face, even more preferably also including a second portion forming at least a portion of the hosel portionand yet even more preferably including a third portion forming at least a portion of the rear portionof the club head. The club headis preferably solid in shape having an upper blade portionand lower muscle portionproximate the sole portion. In some aspects, substantially the entirety of the club headis unitarily formed of such steel. As discussed above, reducing the number of the components required in the build of the club headmay provide benefits in reducing manufacturing cost, reducing manufacturing tolerances, and reducing locations susceptible to failure, while maintaining desirable feel, acoustics and vibratory characteristics.

Preferably, though, the composition of the steel described above is selected such that it provides material properties that are particularly beneficial for use in a golf club head. Conventionally available grades of steel have some adequate properties regarding club heads but are also believed to have properties not particularly relevant to golf club head use. For at least these reasons, tailoring steel composition for use associated with club heads may provide benefits with no or little detriment. Also, preferably, tailoring steel composition for use associated with club heads may permit greater flexibility in varying club head properties on a structure-by-structure basis.

As described above, the golf club headis preferably an iron-type club head, more preferably a wedge-type club head. Accordingly, adapting main body material composition to the specific use aspects of such club heads may result in outweighed benefit. Particular attention is drawn to hardness characteristics, wear resistance and density for their believed relevance to wedge-type club heads. However, other characteristics may be taken into consideration also.

Hardness is an example of a property of which desirable application is unique in the case of golf club heads. On one hand, a striking face, e.g. striking face, preferably comprises a relatively hard surface. Yet, other portions of a club head, e.g. club head, are preferably softer and/or more malleable, e.g. the hosel portion. Such malleability supports adjustability by plastically deforming the club head, e.g. modifying loft and/or lie by hosel bending. This duality in hardness desirability is a unique aspect of golf club head functionality and is believed to justify deviation from conventional material composition.

One concern regarding conventional steels is their limitations in providing for manipulation of hardness. For example, 431 Stainless Steel exhibits an austenization temperature of about 720° C., which in turn enables tempering at a temperature no greater than about 700° C.; exceeding this temperature deleteriously raises the likelihood of austenite transformation and rehardening. Thus, maintaining malleable qualities while achieving a striking face of relatively high hardness may be challenging.

Such limitations on hardening are believed closely correlated with Nickel content in steels, other material constituents notwithstanding. Nickel is believed to be a strong austenite promoter. This in turn is believed to affect, by decreasing, an austenization temperature. In turn, this is believed to raise the minimum achievable hardness by such steel in a quenched and tempered state. For example, 431 Stainless Steel is believed only capable of being softened to about 85 HRB by quenching and tempering. Remedial processes may counteract this deficiency, such as a softening processes that includes holding such steels at temperatures about their austenization temperature and slowly cooling. However, these remedial processes are not without detriment themselves, e.g. reduced wear resistance. Such remedial processes also complicate, and increase the cost of, manufacturing. Thus, a steel composition capable of achieving desirable variation in hardness, by virtue of quenching and tempering, alone, is preferable.

Accordingly, the steel composition of the club headpreferably comprises a Nickel content no greater than 0.5% by mass, more preferably no greater than 0.35% by mass. However, notably, even reducing Nickel composition to no greater than 0.25% by mass, or more preferably about 0.2% by mass, the club headmay be capability of exhibiting superior properties, e.g. hardness variation and wear resistance, with little believed detriment. Accordingly, an exemplary preferably range of Nickel content of the steel composition of the golf club headis between 0.07% and 0.27% by mass. Provided such a Nickel content, the steel can exhibit an austenization temperature no less than 800° C., preferably no less than 850° C., and even more preferably equal to about 870° C. As a result, the steel may likely be capable of being tempered at temperatures of at least 800° C. This may result in a capability to soften the steel to 90 HRB or less after quenching and tempering (e.g. 89 HBR or less), substantially increasing bendability, e.g. to accommodate loft and/or lie adjustment by hosel bending. Preferably, the steel exhibits material properties permitting up to about 4° of angular adjustment of the hosel portion whether in loft adjustment or lie adjustment. Generally, in some alternative aspects, the content of Nickel may be reduced to be below 0.2% without significant detriment, particularly in the case of a wedge-type club head. However, lower limits of Nickel content may correspond to unacceptable impact energy and should be evaluated on that basis.

Hardness characteristics of steel are also believed substantially affected by Carbon content. Other material constituents notwithstanding, increasing Carbon may generally be considered to increase maximum achievable hardness of a steel in a quenched state. For example, 431 Stainless Steel is believed to have a Carbon content of about 0.1% by mass and to exhibit a maximum hardness in a quenched state of around 40 HRC. 8620 Stainless Steel is believed to have a Carbon content of about 0.2% by mass and to exhibit a maximum hardness in a quenched state of about 45 HRC. Preferably, the steel of the club head 100 has a Carbon content of no less than 0.13% by mass, more preferably no less than 0.15% by mass, even more preferably no less than 0.20% by mass, and yet even more preferably no less than 0.25% by mass. Other constituents notwithstanding, the steel of the club headin a quenched state can exhibit a hardness no less than 50 HRC, more preferably no less than 55 HRC, even more preferably no less than 60 HRC and yet even more preferably between 60 HRC and 65 HRC.

In addition to its own direct benefits, Carbon is believed, to a degree, to be an effective substitute for Nickel. Thus Carbon permits the advantageous reduction in Nickel content as described above. In addition to such hardness benefits, such Carbon content ranges are believed to contribute to improved wear resistance and reduced material density.

If, however, Carbon content is too high, deleterious effects may result. For example, manufacturing issues such as problems with weldability and solidification may be presented. Also, Carbon content, in association with Nickel and other constituents, is believed to contribute to the steel's austenization temperature. Specifically, a relatively high Carbon content may lower austenization temperature as it is believed to be a strong austenite promoter. As a result, the steel may be deleteriously limited in its above-mentioned capability to be softened by tempering to a hardness no greater than 90 HRB. Thus, the steel of the club headpreferably has a Carbon content between 0.13% and 0.50% by mass, more preferably between 0.22% and 0.50% by mass, even more preferably between 0.22% and 0.27% by mass. However, higher Carbon contents, e.g. in a range of 0.45% to 0.50%, may be particularly preferable in cases where capability of achieving higher hardnesses are prioritized over lower minimum hardness, e.g. for purposes of adjustability as described above.

Notwithstanding other factors correlated with wear resistance, increased hardness itself is believed correlated in part with greater wear resistance. Thus, the capability of quenching the above steel to achieve a higher hardness in turn may increase wear resistance and strength. This may be particularly true in the case of specific heat treat processes such as laser etching or laser peening in combination with the Carbon contents described above.

The content of Chromium is also believed to contribute to material properties of steel uniquely relevant to golf club heads. This is particularly true regarding hardness and wear resistance, including resistance to rust. Preferably, the content of Chromium present in the steel of club headis selected primarily based on improving these properties, as described below in further detail.

As described above, the club headpreferably exhibits a relative high

hardness at striking face locations, and relative low hardness at other locations, e.g. the hosel portionand/or the rear portion. Chromium, in addition to Nickel and Carbon as described above, may contribute to achieving these desired club head properties. For example, steel composition, apart from its per se hardness properties, may also indirectly affect hardness. For example, steel composition may dictate which surface processing options, e.g. surface hardening or case hardening, may be effectively applied and their degree of success. For example, in some aspects, the striking faceundergoes a surface hardening process, preferably a nitriding process. In some aspects, other surface hardening processes may be applied, either in substitution or in addition to nitriding, such as carburizing, carbonitriding, normalizing, case hardening, induction hardening, cyaniding, flame hardening and laser hardening. However, nitriding is preferable as it is believed to be cost-effective and to achieve the most satisfactory results. Because of the presence of Chromium, a nitriding process is capable of permitting Chromium Nitride to form on the striking face. In turn, this permits the striking face 102 to exhibit a surface hardness of no less than 1200 HV (0.05). Otherwise, e.g. for a conventional carbon steel, maximum achievable hardness may be significantly less, e.g. about 800 HV (0.05).

Nitriding may also bear drawbacks. For example, nitriding stainless steel has been shown to decrease corrosion resistance. However, considering the overall use characteristics of a club head, particularly the wedge-type club headof, the hardness benefits achieved by virtue of steel composition and surface hardening, e.g. nitriding, are believed to outweigh this potential detriment.

Regarding rust, preferably, the steel composition is adapted to reduce or minimize propagation of rust or natural oxidation. In some alternative aspects, rusting or oxidizing of the striking faceof the club headmay be viewed as a positive development. For example, a niche market exists for golf club heads with striking faces exhibiting rust or having characteristics specifically selected to promote rust. Such client base of golfers favors the particular texture, appearance, and/or surface roughness characteristics associated with a rusted face. However, in general, preferably, the club headis configured to reduce the onset or propagation of rust. It is believed that club heads susceptible to rust wear faster than club heads not so susceptible. This may be because rust on a striking face is believed to wear faster than regions not exhibiting rust, resulting in a greater rate of volume loss of the rusted club head. This is of particular concern regarding scoreline structure. The presence of Chromium in the steel reduces the onset and propagation of rust, thus likely reducing rate of wear.

Based on the above considerations, the steel implemented in the club headpreferably includes Chromium in an amount no less than 13% by mass, more preferably no less than 14% by mass, even more preferably no less than 16% by mass. Additionally, or alternatively, the steel includes Chromium in an amount no greater than 21% by mass, more preferably no greater than 18% by mass. A preferable range of Chromium content in the steel of golf club headis between 16.5% and 18.0% by mass. A Chromium content that is too high may frustrate the steel's transition to martensitic crystalline structure, may result in a steel that is too brittle, and/or may deleteriously result in sigma phase formation during tempering.

In addition to the considerations described above affecting rust reduction and wear, the Chromium contents described above—in association with the described Carbon and Nickel contents—desirably reduce overall steel density. The density of a metallic material is primarily affected by two attributes: (1) the composition of the alloy; and (2) the formation in which its atoms are arranged.

A simplified method to estimate the actual density of an alloy is to calculate density as derived solely from constituent content information, herein referred to as an alloy's “theoretical density.” Because theoretical density provides useful aggregate information about an alloy's composition, it is considered a useful material property in its own right, regardless of whether it may differ from an actual, measured density of the same alloy. Theoretical density is determined by taking the percent by weight of each constituent element and divide it by the density of the constituent element to return the total volume of each element. Then, assume a 100 g sample and divided by the sum of the volumes as shown in Equation 1 below:

The other key contributor (i.e. (2) as described above) to steel density is the structure in which the atoms are arranged or the structure's crystal structure. For this reason, in part, an alloy's actual density may differ from its theoretical density describe above. The steel of the club head, based on its constituent compositions described above, once tempered and/or quenched, is preferably a mixture of Ferrite, which has body centered cubic structure (BCC), and Martensite—or substantially entirely, or entirely—Martensite. Martensite exhibits body centered tetragonal (BCT) structure in the quenched state and body centered cubic (BCC) structure in the tempered state. Thus, the relative proportions of Martensite's crystal structure is dependent on the amount of tempering after quenching. BCC and BCT structures have an atomic packing factor, i.e. amount of atom volume per unit cell, of 0.68. Because the packing factors for BCC and BCT structures are similar, overall material density is believed primarily governed by composition of the alloy.

Another common metallic crystal structure is face centered cubic (FCC) which has an atomic packing factor greater than BCC or BCT, of 0.74, indicative of a close packed structure. Austenite has an FCC structure so it will generally have a higher density than the blended composition of the steel of the club head, even though its theoretical density according to the above Equation 1 would be lower.

Based on the above, the actual density of the steel is preferably no greater than 7.85 g/cm, more preferably no greater than 7.67 g/cmand even more preferably no greater than 7.60 g/cm. Reducing density increases discretionary mass of the club head, i.e. mass not primarily required for the structural integrity of the club head thus capable of being placed in locations for purposes of enhancing the various mass properties of the club head, e.g. the location of the center of gravity and moments of inertia about relevant axes passing through the center of gravity.

The constituent composition of Nitrogen in the steel of the club headis also significant. Nitrogen may affect steels in a similar manner as does Carbon. This is due to their similar size, i.e. Nitrogen and Carbon may both be considered interstitial elements. Accordingly, as with Carbon, Nitrogen is a strong austenite promoter. Thus, increasing Nitrogen composition beyond a certain point may deleteriously result in increased minimum quenched and tempered hardness. Further, if too high in content, Nitrogen may result in partitioning problems of the steel during welding and solidification due to its small size and relatively high diffusion rates. Further, if too high in content, Nitrogen may also result in the steel alloy's loss of ductility, undesirable toughness, and corrosion resistance by the formation of CrN. Nitrogen may influence the maximum strength of stainless steels, albeit to a believed lesser extent than Carbon.

Based on the above considerations, the steel of the club headpreferably includes Nitrogen content in an amount no greater than 0.035% by mass, more preferably no greater than 0.15% by mass, even more preferably within the range of about 0% to 0.06% by mass. Because of its shared characteristics with Carbon, the combined content of Carbon and Nitrogen also bears significance. Preferably, this combined content in the steel of the club headis no less than 0.13%, more preferably no less than 0.17% by mass, even more preferably no less than 0.19% by mass, yet even more preferably no less than 0.24% by mass. As an example, a preferably range of Nitrogen content in the steel composition of the golf club headis between 0.0% and 0.06%. Additionally, or alternatively, the combined content of Nitrogen and Carbon in the steel of club head 100 is within the range of 0.13% to 0.75% by mass, more preferably within the range of 0.24% to 0.35% by mass. In this case, if such content is too low, the steel may not be capable of hardening to a desirable degree, may exhibit reduced wear residence and may exhibit undesirably high density.

The above description details preferable steel composition embodiments for use in golf club head. Table 1 below summarizes several exemplary steel compositions corresponding to the above description. Exemplary Steel A corresponds to a first, general example of the steel used in golf club head.

A more detailed assessment of the chemical composition of Exemplary Steel A is shown below in Table #2. Some properties of club headare shown in, for alternative cases in which the golf club headis composed of known steels as well as the exemplary steel described herein.

Based on the above constituent contents, the exemplary steel composition of golf club headis capable, after quenching, tempering and case hardening, of exhibiting a maximum hardness of no less than 50 HRC, more preferably no less than 55 HRC, yet even more preferably within the range of 60 HRC and 65 HRC. With regard to the Vickers hardness scale, such maximum hardness is preferably no less than 500 HV1 (or no less than 650 HV0.05, more preferably no less than 700 HV0.05). The same steel composition of the golf club head, by virtue of its constituent composition, is capable of exhibiting a minimum hardness of no greater than 90 HRB, more preferably no greater than 8 5HRB. With regard to the Vickers hardness scale, such minimum hardness is preferably no greater than 185 HV1 (or no greater than 260 HV0.05,more preferably no greater than 250 HV0.05). Preferably, the component of the club headcomprised of this steel includes a first location on the striking faceof the club head, preferably a second location at a hosel portion, and preferably a third location at a rear portionof the club head. In such embodiments, e.g. by virtue of selective surface processing, preferably, the first location has a hardness no less than 50 HRC more preferably no less than 55 HRC, even more preferably within the range of 60 HRC to 65 HRC. Alternative or additionally, the steel component's maximum hardness preferably coincides with the first location, e.g. is located on the striking face. Preferably, the second location (and optionally the third location) has a hardness no greater than 90 HRB, more preferably no greater than 85 HRB. Alternatively or additionally, the steel component's minimum thickness is preferably located on a portion other than the striking face, and preferably located at the hosel portion. However, in some aspects, the location of minimum hardness of the steel component is on the rear portionor another portion of the club head.

In addition or alternatively, a ratio of the steel's maximum hardness (capable by virtue of quenching) to the steel's minimum hardness (capable by virtue of quenching and tempering) determined where both maximum and minimum values are expressed in quantities in association with the Rockwell C Hardness (HRV) Scale) is preferably no less than 4.5, more preferably no less than 6, even more preferably no less than 9, yet even more preferably no less than 12. In some particular embodiments, preferably such ratio is within the range of 12 to 16.25. Expressed another way, the ratio of such maximum hardness to such minimum hardness is preferably no less than 0.5 HRC/HRB (i.e. where maximum hardness is measured and expressed using the HRC scale and minimum hardness is measured and expressed using the HRB scale). Expressed another way, the ratio of such maximum hardness to such minimum hardness is preferably no less than 2.5, more preferably no less than 2.6 (i.e. where maximum hardness and minimum hardness are measured and expressed using the HV1 scale).

illustrates a process flow chartdescribing preferable steps taken in the formation of the club headusing the exemplary steel composition aspects described herein. While the steps of processare organized sequentially and preferably intended to occur chronologically in the sequence shown, it is contemplated that one or more steps may occur in a different sequence or be omitted. Further, in some aspects, additional steps or processes may occur chronologically before, after, or between any process step shown and described.

In step, an intermediate club head body is formed by casting, e.g. investment or lost-wax casting. Next, optionally, in step, welding is applied to add material and/or repair any regions of the intermediate cast club head body due to artifacts or defects of the casting process. For example, welding material may be applied as filler for regions exhibiting porosity issues. The welding material is preferably a stainless steel material. However, other materials may alternatively be used but, if so, preferably in combination with additional post-processing.

Next, optionally, in step, the intermediate club head body is polished preferably removing any remnants of gates or other artifacts resulting from the casting process.