Mechanical and chemical surface treatment of golf club heads

Abstract

Described herein is a method for treating a metal golf club head through a series of post-assembly steps to provide a hardened black coating. The method described herein includes a quench-polish-quench (QPQ) process that results in a surface coating with better hardness, uniformity, and porosity characteristics, thereby reducing visible surface deformation and loss of durability.

Description

[Technical Field]

[0001] Cross Reference Priority This application claims the benefit of prior U.S. Provisional Application No. 63 / 383,234, filed November 10, 2022, the contents of which are incorporated herein by reference in their entirety.

[0002] The present disclosure relates generally to golf club heads and methods of heat treating the exterior surface of a golf club head to increase the surface hardness and corrosion resistance of the exterior surface of the golf club head. The methods described herein may relate to golf equipment, and more particularly to face plate and golf club body materials, and manufacturing and heat treating methods. [Background technology]

[0003] Golf club heads can be treated to change the physical and mechanical properties of the club head. Golf club heads undergo several manufacturing processes before arriving at a final product with desired physical specifications. For example, after a golf club head is manufactured by casting or forging, various surface treatments may be applied to achieve desired mechanical and physical properties. After the surface treatment, the loft angle and / or lie angle of the golf club head may be manipulated.

[0004] Both loft angle and lie angle directly affect the ability of a club head to accurately guide a golf ball along a desired target line at a desired launch angle. The loft angle (also referred to as "loft") of a golf club head is the angle formed between the club face and the ground plane when the golf club is set at address. Loft affects the trajectory and spin rate of a golf ball. The lie angle (also referred to as "lie") of a golf club head is the angle formed between the shaft and the ground plane when the golf club is set at address. Without the proper lie angle, a player will not be able to consistently and accurately hit a golf ball along a desired target line at a desired launch angle. Therefore, the loft and lie angle must be adjusted after the club head is set to ensure the desired loft and lie angle are achieved.

[0005] During such bending operations, cosmetic defects such as stress marks and / or structural breaks can occur in the club head. More specifically, tension can cause cracks to form on the outer surface of the club head. Conventional surface treatment methods, such as the known quench-polish-quench process, result in harnesses and material structures that are prone to surface cracks during bending or other physical processes during manufacturing. Therefore, there is a need in the art for a manufacturing process that provides a golf club head with a desired surface hardness while minimizing surface face cracks on the hosel. [Brief explanation of the drawings]

[0006] To facilitate further description of the embodiments, the following drawings are provided:

[0007] [Figure 1] A block diagram of the quench-polish-quench heat treatment process is shown.

[0008] [Figure 2] Show the chemical equation showing the chemical reaction.

[0009] [Figure 3] Show the chemical equation showing the chemical reaction.

[0010] [Figure 4] 1 shows a front view of a golf club head.

[0011] [Figure 5A] FIG. 1 is a diagram showing the appearance of a hosel having a surface-treated region of a golf club head.

[0012] [Figure 5B] FIG. 5B is a view focusing on the appearance of the hosel region of the golf club head of FIG. 5A.

[0013] [Figure 5C] FIG. 5B shows a cross-sectional enlarged view of the hosel region of the golf club head of FIG. 5A, including a surface crack.

[0014] [Figure 5D] FIG. 5B illustrates another cross-sectional enlarged view of the hosel region of the golf club head of FIG. 5A, showing the nitride layer and core.

[0015] [Figure 5E] FIG. 5B illustrates yet another cross-sectional enlarged view of the hosel region of the golf club head of FIG. 5A, showing the core, nitride layer, and first and second oxide layers.

[0016] [Figure 5F] FIG. 5B shows an enlarged side view of a surface crack in the hosel region of the golf club head of FIG. 5A.

[0017] [Figure 5G] 5B shows an enlarged cross-sectional side view of the core in the hosel region of the golf club head of FIG. 5A. FIG.

[0018] [Figure 6A] FIG. 1 is a diagram showing the appearance of a hosel having a surface-treated region of a golf club head.

[0019] [Figure 6B] FIG. 6B is a view focusing on the appearance of the hosel region of the golf club head of FIG. 6A.

[0020] [Figure 6C] FIG. 6B shows a cross-sectional enlarged view of the hosel region of the golf club head of FIG. 6A, including a surface crack.

[0021] [Figure 6D] FIG. 6B illustrates another cross-sectional enlarged view of the hosel region of the golf club head of FIG. 6A, showing the nitride layer and core.

[0022] [Figure 6E] FIG. 6B illustrates yet another cross-sectional enlarged view of the hosel region of the golf club head of FIG. 6A, showing the core, nitride layer, and first and second oxide layers. DETAILED DESCRIPTION OF THE INVENTION

[0023] For simplicity and clarity of illustration, the drawings show general structural aspects, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the present invention. Further, elements in the drawings are not necessarily drawn to scale. For example, the dimensions of some elements in the drawings may be exaggerated relative to other elements to facilitate understanding of embodiments of the present invention. The same reference numerals in different drawings refer to the same elements.

[0024] Described herein are golf club heads with uniform nitride and oxide layers. Forming a smooth, uniform nitride layer that bonds with the actual metal of the golf club head not only significantly improves bonding with the oxide layer, but also facilitates the formation of a more uniform oxide layer thickness. The improved bonding and uniformity reduce porosity caused by agitation in the applied oxide layer. While some porosity near the surface, grades 1-3, is expected and considered acceptable, porosity deep below the surface is undesirable and is mitigated by the QPQ process described herein. Specifically, subsurface porosity, grades 4-5, observed with conventional QPQ processes, is highly visible to users and promotes cracks that reduce the stability of the material, increasing the risk of deformation and failure. Therefore, forming a uniform layer of grade 3 or better reduces both crack formation and growth, resulting in fewer cracks, smaller cracks, and less visible to users. These uniform layers can be achieved by a modified quench-polish-quench process detailed below.

[0025] definition As used herein, terms such as "first," "second," "third," and "fourth" are intended to distinguish between similar elements and do not necessarily denote a particular order or chronological sequence. It should be understood that terms so used are interchangeable under appropriate circumstances, such as when the embodiments described herein are capable of operating in orders other than those illustrated or otherwise set forth herein. Furthermore, the terms "comprise" and "have," as well as variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, device, or apparatus comprising a list of elements is not necessarily limited to those elements but may include elements not expressly listed or other elements inherent in such process, method, system, article, device, or apparatus.

[0026] As used herein, terms such as "left," "right," "front," "rear," "top," "bottom," "upper," "lower," and the like are for convenience of description and do not necessarily describe permanent relative positions. It is to be understood that such terms are interchangeable under appropriate circumstances, for example, where the embodiments of the invention described herein are operable in orientations other than those illustrated or otherwise described herein.

[0027] As used herein, the terms "couple," "coupled," "coupled," and the like should be interpreted broadly and refer to connecting two or more elements or signals electrically, mechanically, and / or otherwise.

[0028] The term "composition" as used herein is defined as the types and relative numbers of elements contained in a material. In the case of an alloy material, the composition represents the weight percentage of each alloying element in the material.

[0029] As used herein, the term "tensile strength" is defined as the maximum strength under a tensile or pulling load that a material can absorb without failure, where failure occurs when a break, crease, or fracture occurs.

[0030] The term "brittle" as used herein is defined as sudden failure without plastic deformation. Brittleness is also defined as the absence of ductility.

[0031] As used herein, "elastic modulus" or "Young's modulus" is the ratio of stress to strain, which is the slope (E) of the stress-strain curve in the elastic region. Elastic modulus is used to describe the stiffness of a material.

[0032] As used herein, the term "yield strength" or "proportional limit" is defined as the point on the stress-strain curve at which a material can be loaded in tension until it undergoes permanent or plastic deformation and the deformation remains when the load is removed.

[0033] As used herein, the term "elongation" or "minimum elongation" is a measure of the amount of stretch or elongation that a material can withstand before it begins to permanently deform.

[0034] The term "quenching," as used herein, is defined as the process of rapidly cooling a metal to obtain specific material properties. Quenching may be accomplished by applying a quenching medium at a predetermined temperature for a predetermined exposure time. Quenching mediums include corrosives, oils, molten salts, and gases. The cooling rate and quenching medium determine the mechanical properties of the metal immediately after quenching.

[0035] As used herein, the term "quench-polish-quench" is defined as a thermochemical process in which nitrogen and carbon are simultaneously diffused onto the surface of a material in the presence of a salt bath.

[0036] As used herein, the term "aging" is defined as a form of heat treatment in which a material is slowly cooled to room temperature for the purpose of increasing its strength.

[0037] As used herein, the term "pit furnace" defines a type of furnace typically used for metallurgical processes requiring low temperatures. Pit furnaces as described herein may be cylindrical in shape and may include an opening at the top of the furnace for insertion of a holding fixture. The pit furnace regulates the atmosphere in which the golf club heads are placed, including, but not limited to, regulating temperature and pressure.

[0038] As used herein, the term "metallurgical process" defines a process for extracting metals into a purer form.

[0039] As used herein, the term "nitriding" is defined as a diffusion-related surface treatment that can increase surface hardness. Nitriding can improve mechanical properties such as wear resistance, minimized deformation, temper resistance, improved fatigue life, and reduced notch sensitivity.

[0040] The term "composite layer" as used herein is defined as a coating formed on a material surface that results directly from the QPQ process. The composite layer may comprise multiple layers, including all nitride and oxide layers formed by the QPQ process.

[0041] Before describing embodiments of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. It is also to be understood that the phraseology and terminology used herein is for the purpose of description and is not to be regarded as limiting. As used herein, the use of "including," "comprising," and "having," as well as variations thereof, is meant to encompass the subsequently listed items and equivalents thereof, as well as additional items. All weight percent (wt%) figures set forth below are total weight percents.

[0042] Provided herein are general terms used to describe material properties for the disclosed materials. These definitions are considered to be industry standard and are provided by ASM International, a professional association of materials scientists and engineers.

[0043] As used herein, the term "geometric center point" or "geometric center" of a striking face may refer to the geometric center point of the striking face's perimeter and the midpoint of the face height of the striking face. In the same example or other examples, the geometric center point may be centered relative to an engineered impact zone, which may be defined by a groove area on the striking face. As an alternative approach, the geometric center point of a striking face may be located according to the definition of a golf governing body, such as the United States Golf Association (USGA).

[0044] As used herein, the term "ground contact" may refer to a reference plane relative to the surface on which a golf ball rests. The ground contact may be the horizontal plane that contacts the sole at address.

[0045] As used herein, the term "loft plane" may refer to a reference plane that is tangent to the geometric center point of the striking face.

[0046] As used herein, the term "loft angle" may refer to the angle measured between the loft plane and the XY plane (defined below).

[0047] As used herein, the term "face height" may refer to the distance measured parallel to the loft plane between the top of the striking face perimeter and the bottom of the striking face perimeter.

[0048] As used herein, the term "lie angle" may refer to the angle between the hosel axis extending through the hosel and the ground plane. The lie angle is measured from a front view.

[0049] As used herein, the "geometric center height" of a fairway-type golf club head is the height measured perpendicularly from the ground plane to the geometric center point of the golf club head.

[0050] As used herein, the "leading edge" of the club head is the portion of the striking face that is closest to the sole.

[0051] explanation This specification describes golf club heads and various methods for treating golf club heads in a series of steps completed after manufacture with the goal of enhancing the exterior surface (hereinafter "exterior surface") of a metal golf club head by providing a more uniform black coating or finish. A uniform finish significantly improves the uniformity, resilience, and appearance, as well as the bonding ability of layers within the coating. Good bonding and uniformity can reduce the occurrence of porosity due to agitation of the black finish. As discussed above, while near-surface porosity is expected and considered acceptable, porosity extending beyond the region closest to the surface is undesirable because it can result in undesirable deep cracks that are highly visible to users and reduce the stability of the material, increasing the risk of deformation and breakage. If the nitride layer, first oxide layer, and second oxide layer are not uniform, these deep cracks can extend downward into the second oxide layer and primary nitride layer. A uniform finish therefore limits both crack formation and growth, resulting in fewer cracks and fewer cracks visible to the user. This uniform coating is achieved by the improved Quench-Polish-Quench (hereinafter "QPQ") process, which is described in detail below.

[0052] In the QPQ method, applying a QPQ finish to the golf club head 100 after it is formed can result in more uniform surface hardness and improved corrosion resistance on the exterior surface. The uniformity of surface hardness and corrosion resistance can be attributed to the multiple blasting steps applied during the QPQ process. The multiple blasting steps result in a QPQ finish with more uniform thickness layers. The QPQ finish may include a nitride layer 230, a first oxide layer 120, and a second oxide layer 122. The above-described method can result in a golf club head with a QPQ finish having uniform nitride and oxide layers. The multiple blasting steps result in a more uniform nitride layer, followed by a more uniform first oxide layer 120, followed by a more uniform second oxide layer 122 on the exterior surface of the golf club head 100, as shown in FIG. 5E. More specifically, each blasting step flattens the crystallized surfaces of nitride layer 230, first oxide layer 120, and second oxide layer 122. This results in each layer having a more uniform thickness. Visible cracks are not visible at arm's length.

[0053] As mentioned above, the aforementioned QPQ method can be applied to a golf club 100. The golf club may include a golf club head 100, a shaft, and a grip. The golf club head 100 may include a body having a striking face 104, a top rail 110 opposite a sole 106, a toe opposite a heel, and a hosel 102 connected to the club body and having a first end proximate the heel and a second end opposite the first end. The golf club head 100 may further include an outer surface. The QPQ method may be applied to a portion of the golf club head 100 or to the entire golf club head 100. A golf club head 100 treated with the QPQ method described herein reduces surface deformation, improves durability, and increases loft and lie adjustability.

[0054] The following QPQ method may be applied during the manufacturing process to improve surface hardness and corrosion resistance. The QPQ method may include the steps described below and illustrated in FIG. 1 . In a first step, a nitriding salt bath may be aged at a predetermined temperature for a predetermined time. In a second step, the exterior surface of the golf club head may be blasted. In a third step, the golf club head may be placed in a furnace and heated to a predetermined temperature for a predetermined time. In a fourth step, the golf club head may be placed in the nitriding salt bath in the first furnace for a predetermined time. The fourth step may further include forming a nitride layer 230 on the exterior surface of the golf club head. In a fifth step, the temperature of the furnace may be reduced to a predetermined temperature for a predetermined time to form a first oxide layer 120 on the nitride layer 230. In a sixth step, the club head 100 may be removed from the furnace, cooled, and cleaned. In a seventh step, the exterior surface of the golf club head 100 may be blasted. In an eighth step, the club head 100 may be placed in a furnace and heated to a predetermined temperature for a predetermined time. In a ninth step, the club head 100 may be placed again in a nitride salt, and a second oxide layer 122 may be formed on the first oxide layer 120. In a tenth step, the club head 100 may be removed from the furnace, cooled, and cleaned. In an eleventh step, the exterior surface of the golf club head 100 may be blasted. These steps result in the golf club head having a finish with a uniform nitride, first oxide, and second oxide layers 122.

[0055] More specifically, the first step involves aging the golf club head 100 in a nitride salt bath (hereinafter also referred to as the "salt bath") in a first furnace for a predetermined time (hereinafter referred to as the "aging time") at a predetermined temperature (hereinafter referred to as the "aging temperature"). The salt bath may include chemical compositions such as NaCNO, KCNO, Na2CO3, K2CO3, KCl, Li2CO3, and Na2SO4. The salt bath may include a combination of compounds, and the amount of each compound used in the salt bath is characterized by a percentage indicating the proportion of the salt bath attributable to that compound. The percentage of each compound can affect how the exterior surface of the golf club head reacts with the salt bath, and more specifically, how the nitride layer 230, the first oxide layer 120, and the second oxide layer 122 are formed.

[0056] In some embodiments, the salt bath contains 30-60% NaCNO. In some embodiments, the NaCNO percentage may be 30-35%, 35-40%, 40-45%, 45-50%, 50-55%, or 55-60%. In some embodiments, the NaCNO percentage may be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, and 60%. In one embodiment, the NaCNO percentage is 35-55%.

[0057] In some embodiments, the salt bath contains 0.01% to 25% KCNO. In some embodiments, the percentage of KCNO can be 0.01% to 5%, 5% to 10%, 10% to 15%, 15% to 20%, or 20% to 25%. In some embodiments, the percentage of KCNO can be 0.01%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%. In one embodiment, the percentage of KCNO is 0% to 20%. In some embodiments, the percentage of KCNO in the salt bath can be less than 5%, less than 10%, less than 15%, less than 20%, or less than 25%.

[0058] In some embodiments, the salt bath contains 3% to 13% Na2CO3. In some embodiments, the percentage of Na2CO3 can be 3% to 5%, 5% to 7%, 7% to 9%, 9% to 11%, or 11% to 13%. In some embodiments, the percentage of Na2CO3 can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, or 13%. In one embodiment, the percentage of Na2CO3 is 5% to 10%.

[0059] In some embodiments, the salt bath contains 15% to 40% K2CO3. In some embodiments, the percentage of K2CO3 can be 15% to 20%, 20% to 25%, 25% to 30%, 30% to 35%, or 35% to 40%. In some embodiments, the percentage of K2CO3 can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, or 40%. In one embodiment, the percentage of K2CO3 is 20% to 35%.

[0060] In some embodiments, the salt bath contains 0.01% to 20% KCl. In some embodiments, the percentage of KCl may be 0.01% to 5%, 5% to 10%, 10% to 15%, or 15% to 20%. In some embodiments, the percentage of KCl may be 0.01%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%. In some embodiments, the percentage of KCl in the salt bath may be less than 5%, less than 10%, less than 15%, or less than 20%. In one embodiment, the percentage of KCl is 0.01% to 15%.

[0061] In some embodiments, the salt bath contains 0.01% to 15% Li2CO3. In some embodiments, the percentage of Li2CO3 can be 0.01% to 5%, 5% to 10%, or 10% to 15%. In some embodiments, the percentage of Li2CO3 can be 0.01%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. In some embodiments, the percentage of Li2CO3 in the salt bath can be less than 5%, less than 10%, or less than 15%. In one embodiment, the percentage of Li2CO3 is 0.01% to 10%.

[0062] In some embodiments, the salt bath contains 0.01% to 5% Na2SO4. In some embodiments, the percentage of Na2SO4 can be 0.01% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, or 4% to 5%. In some embodiments, the percentage of Na2SO4 can be 0.01%, 1%, 2%, 3%, 4%, or 5%. In some embodiments, the percentage of Na2SO4 in the salt bath can be less than 1%, less than 2%, less than 3%, less than 4%, or less than 5%. In one embodiment, the percentage of Na2SO4 is 0% to 2%. As discussed above, the percentage of the compound can affect how the exterior surface reacts with the salt bath. More specifically, the percentage of the compound can affect how the nitride layer 230 and the first oxide layer 120 are formed, thereby affecting the surface hardness and corrosion resistance of the exterior surface.

[0063] As described above, the salt bath may be aged by heating to the aging temperature for an aging time. The aging time may be 5.00 hours to 7.00 hours. The aging time may be 5.00 hours to 5.25 hours, 5.25 hours to 5.50 hours, 5.50 hours to 5.75 hours, 5.75 hours to 6.00 hours, 6.00 hours to 6.25 hours, 6.25 hours to 6.50 hours, 6.50 hours to 6.75 hours, or 6.75 hours to 7.00 hours. In one embodiment, the aging time is 6.00 hours.

[0064] The aging temperature may be 525°C to 605°C. The aging temperature may be 525°C to 535°C, 535°C to 545°C, 545°C to 555°C, 555°C to 565°C, 565°C to 575°C, 575°C to 585°C, 585°C to 595°C, or 595°C to 605°C. The aging temperatures were 525°C, 526°C, 527°C, 528°C, 529°C, 530°C, 531°C, 532°C, 533°C, 534°C, 535°C, 536°C, 537°C, 538°C, 539°C, 540°C, 541°C, 542°C, 543°C, 544°C, 545°C, 546°C, 547°C, 548°C, 549°C, 550°C, 551°C, 552°C, 553°C, 554°C, 555°C, 556°C, 557°C, 558°C, 559°C, 560°C, 561°C, 562°C, 563°C, 564°C, 565°C, 566°C, 567°C, 568°C, 569°C, 570°C, 571°C, 572°C, 573°C, 574°C, 575°C, 576°C, 577°C, 578°C, 579°C, 580°C, 581°C, 582°C, 583°C, 584°C, 585°C, 586°C, 587°C, 588°C, 589°C, 590°C, 591°C, 592°C, 593°C, 594°C, 595°C, 596°C, 5 The aging temperature may be 5°C, 566°C, 567°C, 568°C, 569°C, 570°C, 571°C, 572°C, 573°C, 574°C, 575°C, 576°C, 577°C, 578°C, 579°C, 580°C, 581°C, 582°C, 583°C, 584°C, 585°C, 586°C, 587°C, 588°C, 589°C, 590°C, 591°C, 592°C, 593°C, 594°C, 595°C, 596°C, 597°C, 598°C, 599°C, 600°C, 601°C, 602°C, 603°C, 604°C, or 605°C. In one embodiment, the aging temperature is 565°C.

[0065] Aging the salt bath for a specific time and temperature results in a CNO concentration of 28% to 36%. In some embodiments, the CNO concentration is 28% to 29%, 29% to 30%, 30% to 31%, 31% to 32%, 32% to 33%, 33% to 34%, or 35% to 36%. As shown in FIG. 2, CNO decomposes during aging to provide nitrogen for forming nitride layer 230.

[0066] The second step may include blasting the exterior surface with a medium selected from the group consisting of glass beads, sand, water, aluminum oxide, silicon carbide, steel shot, and any other suitable form of grit. The grit size may range from #60 grit to #320 grit. The grit size may be #60 grit to #80 grit, #80 grit to #100 grit, #100 grit to #120 grit, #120 grit to #140 grit, #140 grit to #160 grit, #160 grit to #180 grit, #180 grit to #200 grit, #200 grit to #220 grit, #220 grit to #240 grit, #240 grit to #260 grit, #260 grit to #280 grit, #280 grit to #300 grit, or #300 grit to #320 grit. In one embodiment, the media may be #80 grit glass beads. In one embodiment, the media may be #220 grit glass beads.

[0067] Furthermore, the blasting treatment may be carried out under pressure, which may be 1 to 5 kg / cm. 2 In some embodiments, the pressure may be 1 kg / cm 2 ~2kg / cm 2 , 2kg / cm 2 ~3kg / cm 2 , 3kg / cm 2 ~4kg / cm 2 , or 4 kg / cm 2 ~5kg / cm 2 The pressure may be 1 kg / cm 2, 2kg / cm 2 , 3kg / cm 2 , 4kg / cm 2 , or 5 kg / cm 2 In one embodiment, the blasting may be performed at a pressure of 2 kg / cm 2 In some embodiments, the second step may include blasting the exterior surface with a first media having a first grit size under a first pressure, followed by blasting the exterior surface with a second media having a second grit size under a second pressure. Blasting can uniform the exterior surface by reducing localized areas of overdeposition of the exterior layer. A uniform exterior surface at this point in the process can allow for more uniform formation of the nitride layer 230 and first oxide layer 120 grown from this surface.

[0068] In some embodiments, the second step may include attaching the golf club head 100 to a holding fixture. In one exemplary embodiment, the holding fixture may comprise a tree fixture. The tree fixture allows for the processing of a large number of golf club heads at any one time.

[0069] The third step may include placing the holding fixture in a second heating furnace and heating the second furnace to a predetermined temperature for a predetermined time. The time and temperature may be selected to ensure that little or no moisture remains on or within the golf club head 100. The predetermined temperature may be between 325°C and 375°C. In one embodiment, the predetermined temperature may be between 325°C and 330°C, 330°C and 335°C, 335°C and 340°C, 340°C and 345°C, 345°C and 350°C, 350°C and 355°C, 355°C and 360°C, 360°C and 365°C, 365°C and 370°C, or 370°C and 375°C. In one example, the predetermined temperature may be 350°C. The predetermined time for heating may be between 25 and 35 minutes. The predetermined time may be 25-26 minutes, 26-27 minutes, 27-28 minutes, 28-29 minutes, 29-30 minutes, 30-31 minutes, 31-32 minutes, 32-33 minutes, 33-34 minutes, or 34-35 minutes. The time and temperature are selected to allow the atmosphere in the pit furnace to reach equilibrium. This step ensures that little or no moisture remains on or within the golf club head 100, which may improve the bonding capabilities of the second oxide layer 122, as described in greater detail below.

[0070] A fourth step may include moving the holding fixture from the second furnace to the first furnace, submerging the holding fixture in a salt bath, and allowing the holding fixture to remain in the first furnace for a predetermined period of time, which may be long enough to form the nitride layer 230 on the exterior surface of the golf club head.

[0071] The predetermined temperature used in the fourth step may be between 500°C and 650°C. In one embodiment, the predetermined temperature may be between 500°C and 525°C, between 525°C and 550°C, between 550°C and 575°C, between 575°C and 600°C, between 625°C and 650°C. In one example, the predetermined temperature may be 580°C. The predetermined time used in the fourth step may be between 35 minutes and 55 minutes. In some embodiments, the predetermined time may be between 35 minutes and 40 minutes, between 40 minutes and 45 minutes, between 45 minutes and 50 minutes, or between 50 minutes and 55 minutes. The time and temperature are selected to ensure complete formation of nitride layer 230.

[0072] The nitride layer 230 is formed by a chemical reaction between the salt bath and the exterior surface. The chemical formula is shown in FIG. 2. As described above in step 1, the salt bath is preheated to a predetermined temperature for a predetermined time. This process dissociates nitrogen from the compound, as shown in FIG. 2. By placing the golf club head 100 in the salt bath and applying additional heat, the nitrogen can be dissipated to the exterior surface. The uniform exterior surface created by the blasting process described above in step 2 facilitates the dissipation of nitrogen to the exterior surface. The dissipation of nitrogen to the exterior surface of the golf club head forms the nitride layer 230.

[0073] The nitride layer 230 may have both mechanical and physical properties that may affect the durability and performance of the final golf club head 100. Such mechanical properties include, but are not limited to, the hardness and uniformity (hereinafter also referred to as "nitride uniformity") of the nitride layer 230. Uniformity may refer to the layer having approximately the same thickness throughout the layer. Uniformity may be quantified by being equal to the difference between the maximum nitride thickness and the minimum nitride thickness. Physical properties may include, but are not limited to, nitride thickness, maximum nitride thickness, and minimum nitride thickness.

[0074] The nitride thickness may be defined as the distance from the point where the nitride layer 230 meets the core 110 to the point where the nitride layer 230 meets the first oxide layer 120. The nitride thickness may be between 0.00025 inches and 0.00060 inches. The nitride thickness may be between 0.00025 inches and 0.00030 inches, between 0.00030 inches and 0.00035 inches, between 0.00035 inches and 0.00040 inches, between 0.00040 inches and 0.00045 inches, between 0.00045 inches and 0.00050 inches, between 0.00050 inches and 0.00055 inches, between 0.00055 inches and 0.00060 inches, or between 0.00060 inches and 0.00065 inches. As discussed above, nitride thickness can affect the durability and performance of a QPQ finish. More specifically, if the nitride thickness is too large, a large amount of force may be required to adjust the loft and lie. This large amount of force may overstress the QPQ finish, resulting in numerous cracks during the loft / lie adjustment process. Furthermore, if the nitride thickness is too small, the finish may not be strong enough and may crack when subjected to force during the loft / lie adjustment process. Furthermore, because QPQ finishes tend to be brittle, a thicker nitride layer 230 increases the likelihood of large cracks 108 and the likelihood of these cracks 108 forming.

[0075] The nitride layer 230 may further comprise a maximum nitride thickness and a minimum nitride thickness. The maximum nitride thickness may be defined as the maximum distance from the point where the nitride layer 230 meets the core 110 to the point where the nitride layer 230 meets the first oxide layer 120. The maximum nitride thickness may be measured in a direction perpendicular to the nitride layer 230 at the measurement point. The minimum nitride thickness may be between 0.00025 inches and 0.00045 inches.

[0076] The minimum nitride thickness may be defined as the smallest distance from where the nitride layer 230 meets the core 110 to where the nitride layer 230 meets the first oxide layer 120. The minimum nitride thickness may be measured in a direction perpendicular to the nitride layer 230 at the measurement point. The maximum nitride thickness may be between 0.00045 inches and 0.00060 inches.

[0077] The nitride layer 230 may further have nitride uniformity, defined herein as the ratio between the maximum thickness and the minimum thickness. The uniformity may be between 1.00 and 1.25. The uniformity may be between 1.00 and 1.05, between 1.05 and 1.10, between 1.10 and 1.15, between 1.15 and 1.20, or between 1.20 and 1.25. The uniformity may be less than 1.25, less than 1.20, less than 1.15, or less than 1.10. The closer the uniformity is to 1, the more uniform the nitride thickness. The nitride uniformity further ensures the uniformity of the first oxide layer 120 by ensuring a uniform and even surface on which the first oxide layer 120 is grown. The uniformity, or lack thereof, of the nitride layer 230 is directly reflected in the uniformity of the first oxide layer 120.

[0078] The fifth step may include ramping down the furnace temperature to a predetermined temperature over a predetermined time period to form the first oxide layer 120 on the nitride layer 230, as described above. The predetermined temperature may be between 345°C and 415°C. In some embodiments, the predetermined temperature may be between 345°C and 350°C, 350°C and 355°C, 355°C and 360°C, 360°C and 365°C, 365°C and 370°C, 370°C and 375°C, 375°C and 380°C, 380°C and 385°C, 385°C and 390°C, 390°C and 395°C, 395°C and 400°C, 400°C and 405°C, or 405°C and 410°C. The predetermined temperatures are 345°C, 346°C, 347°C, 348°C, 349°C, 350°C, 351°C, 352°C, 353°C, 354°C, 355°C, 356°C, 357°C, 358°C, 359°C, 360°C, 361°C, 362°C, 363°C, 364°C, 365°C, 366°C, 367°C, 368°C, 369°C, 370°C, 371°C, 372°C, 373°C, 374°C, 375°C, 376°C, 377°C, 378°C, 379°C, and 380°C. , 381°C, 382°C, 383°C, 384°C, 385°C, 386°C, 387°C, 388°C, 389°C, 390°C, 391°C, 392°C, 393°C, 394°C, 395°C, 396°C, 397°C, 398°C, 399°C, 400°C, 401°C, 402°C, 403°C, 404°C, 405°C, 406°C, 407°C, 408°C, 409°C, 410°C, 411°C, 412°C, 413°C, 414°C, or 415°C. In one embodiment, the predetermined temperature may be 410°C. In another embodiment, the predetermined temperature may be 350°C. The predetermined time may be between 25 and 35 minutes. The predetermined time may be 25-26 minutes, 26-27 minutes, 27-28 minutes, 28-29 minutes, 29-30 minutes, 30-31 minutes, 31-32 minutes, 32-33 minutes, 33-34 minutes, or 34-35 minutes. In one embodiment, the predetermined time is 30 minutes. The time and temperature are selected to completely form the first oxide layer 120. As described above, a chemical reaction may occur such that the first oxide layer 120 is formed on the outer surface of the club head over the nitride layer 230. The relevant chemical reactions are illustrated in FIG. 3.

[0079] The first oxide layer 120 may have both mechanical and physical properties that may affect the durability and performance of the final golf club head 100. Such mechanical properties include, but are not limited to, the hardness and uniformity of the first oxide layer 120. The physical properties include, but are not limited to, the maximum first oxide thickness, the minimum first oxide thickness, and the uniformity of the first oxide layer 120 (hereinafter also referred to as "first oxide uniformity").

[0080] The first oxide thickness can be defined as the distance from the point where the first oxide layer 120 meets the nitride layer 230 to the point where the first oxide layer 120 meets the second oxide layer 122. The first oxide thickness can be between 0.000045 inches and 0.000115 inches. The first oxide thickness can be between 0.000045 inches and 0.000055 inches, between 0.000055 inches and 0.000065 inches, between 0.000065 inches and 0.000075 inches, between 0.000075 inches and 0.000085 inches, between 0.000085 inches and 0.000095 inches, between 0.000095 inches and 0.000105 inches, or between 0.000105 inches and 0.000115 inches. The first oxide thickness may be less than 0.000115 inches, less than 0.000105 inches, less than 0.000095 inches, less than 0.000085 inches, less than 0.00075 inches, or less than 0.000065 inches.

[0081] The first oxide maximum thickness can be defined as the maximum distance from the point where the first oxide layer 120 meets the nitride layer 230 to the point where the first oxide layer 120 meets the second oxide layer 122. The first oxide maximum thickness can be measured in a direction perpendicular to the nitride layer 230 at the measurement point. The first oxide maximum thickness can be between 0.000075 inches and 0.000115 inches.

[0082] The first oxide minimum thickness may be defined as the smallest distance from the point where first oxide layer 120 meets nitride layer 230 to the point where first oxide layer 120 meets second oxide layer 122. The first oxide minimum thickness may be measured in a direction perpendicular to nitride layer 230 at the measurement point. The first oxide minimum thickness may be between 0.000050 inches and 0.000075 inches.

[0083] First oxide uniformity may refer to a layer thickness that is approximately the same throughout the layer. First oxide uniformity may be quantified by being equal to the difference between the first oxide maximum thickness and the first oxide minimum thickness. This uniformity may be between 1.00 and 1.85. The uniformity may be between 1.00 and 1.15, 1.15 and 1.30, 1.30 and 1.45, 1.45 and 1.60, 1.60 and 1.65, 1.65 and 1.80, or 1.80 and 1.95. The uniformity may be less than 1.95, less than 1.80, less than 1.65, or less than 1.50. The closer the uniformity is to 1, the more uniform the first oxide thickness is.

[0084] A sixth step may include removing the holding fixture from the first furnace and cooling the club head 100 to a predetermined temperature. In some embodiments, the club head 100 may be cooled by air-cooling. In other embodiments, the club head 100 may be cooled by partially or completely immersing the club head 100 in a medium. The medium may be a gas or a liquid. In one embodiment, the medium is an inert gas. The predetermined temperature may be between 60°C and 100°C. In some embodiments, the predetermined temperature may be between 60°C and 65°C, 65°C and 70°C, 70°C and 75°C, 75°C and 80°C, 80°C and 85°C, 90°C and 95°C, or 95°C and 100°C.

[0085] The club head 100 may be allowed to cool for a specified period of time. This period may be between 20 and 40 minutes. In some embodiments, the cooling may occur for 20 to 25 minutes, 25 to 30 minutes, 30 to 35 minutes, or 35 to 40 minutes. After the club head 100 has cooled, the club head 100 may be rinsed with water and removed from the holding fixture.

[0086] The seventh step may include blasting the exterior surface to ensure uniformity across the first oxide layer 120. This step may include blasting the golf club with a medium selected from the group consisting of glass beads, sand, aluminum oxide, silicon carbide, steel shot, and any other suitable form of grit. The medium may further comprise a grit size. The grit size may be between #60 grit and #320 grit. The grit size may be #60 grit to #80 grit, #80 grit to #100 grit, #100 grit to #120 grit, #120 grit to #140 grit, #140 grit to #160 grit, #160 grit to #180 grit, #180 grit to #200 grit, #200 grit to #220 grit, #220 grit to #240 grit, #240 grit to #260 grit, #260 grit to #280 grit, #280 grit to #300 grit, or #300 grit to #320 grit. In one exemplary embodiment, the media may be #80 grit glass beads. In one exemplary embodiment, the media may be #220 grit glass beads.

[0087] Furthermore, the blasting process may be carried out under a specific pressure, which may be 1 to 5 kg / cm. 2 In some embodiments, the pressure may be 1 kg / cm 2 ~2kg / cm 2 , 2kg / cm 2 ~3kg / cm 2 , 3kg / cm 2 ~4kg / cm 2 , or 4 kg / cm 2 ~5kg / cm2 In one exemplary embodiment, the blasting may be performed at a pressure of 2.5 kg / cm 2 In some embodiments, the eighth step may include blasting the exterior surface with a first media having a first grit size under a first pressure, and then blasting the exterior surface with a second media having a second grit size under a second pressure. In one exemplary embodiment, the eighth step is performed at a pressure of 2.5 kg / cm. 2 Blasting the exterior surface with #80 grit glass beads under a pressure of 2.5 kg / cm 2 and blasting the exterior surface with #220 grit glass beads under a pressure of 1000 psi. As discussed above, blasting ensures uniformity of the first oxide layer 120. A uniform first oxide layer 120 allows for more uniform formation of the second oxide layer 122, resulting in uniform strength across the entire exterior surface of the golf club head.

[0088] The seventh step may further include visually inspecting the golf club head 100 to ensure uniformity. As discussed above, ensuring uniformity in this step ensures that the second oxide layer 122 is more uniformly formed, and therefore has uniform strength across the entire exterior surface of the golf club head. This step may be performed on each layer (nitride, first oxide, and second oxide) to ensure uniformity (close to 1), as each layer interacts with the other to inhibit crack migration.

[0089] In some embodiments, the seventh step may further include attaching the golf club head 100 to a holding fixture. In one exemplary embodiment, the holding fixture may comprise a tree fixture. As previously mentioned, the tree fixture allows for the processing of a large number of golf club heads at any one time.

[0090] An eighth step may include placing the holding fixture in a second heating furnace and heating the second furnace to a predetermined temperature for a predetermined time. The time and temperature may be selected to prevent moisture from remaining on or within the golf club head 100. The predetermined temperature may be between 325°C and 375°C. In one embodiment, the predetermined temperature may be between 325°C and 330°C, 330°C and 335°C, 335°C and 340°C, 340°C and 345°C, 345°C and 350°C, 350°C and 355°C, 355°C and 360°C, 360°C and 365°C, 365°C and 370°C, or 370°C and 375°C. In one example, the predetermined temperature may be 350°C. The predetermined time may be between 25 and 35 minutes. In one embodiment, the predetermined time may be 25-26 minutes, 26-27 minutes, 27-28 minutes, 28-29 minutes, 29-30 minutes, 30-31 minutes, 31-32 minutes, 32-33 minutes, 33-34 minutes, or 34-35 minutes. The time and temperature are selected to allow the atmosphere in the pit furnace to reach equilibrium. This step ensures that little or no moisture is present on or within the golf club head 100, which may improve the bonding capabilities of the second oxide layer 122, as described in greater detail below.

[0091] A ninth step may include transferring the holding fixture from the second furnace to the first furnace and maintaining the holding fixture in the first furnace for a predetermined period of time, which may be long enough to form a second oxide layer 122 on the exterior surface of the golf club head. A chemical equation illustrating the chemical reactions that occur during this step is shown in FIG. 3.

[0092] The second oxide layer 122 may have both mechanical and physical properties that can affect the durability and performance of the final golf club head 100. This layer is exposed to the elements and provides the visual aesthetics of the QPQ finish of the golf club head 100. The mechanical properties include, but are not limited to, the hardness and thickness of the second oxide layer 122. The physical properties include, but are not limited to, the second oxide maximum thickness, the second oxide minimum thickness, and the uniformity of the second oxide layer 122 (hereinafter also referred to as "second oxide uniformity"). The second oxide uniformity may refer to a layer thickness that is approximately the same throughout the layer. The second oxide uniformity can be quantified by being equal to the difference between the second oxide maximum thickness and the second oxide minimum thickness.

[0093] The second oxide layer 122 may have both mechanical and physical properties that may affect the durability and performance of the final golf club head 100. Such mechanical properties include, but are not limited to, the hardness and uniformity of the second oxide layer 122 (hereinafter also referred to as "second oxide uniformity"). Second oxide uniformity may refer to a layer thickness that is approximately the same throughout the layer. Second oxide uniformity may be quantified by being equal to the difference between the second oxide maximum thickness and the second oxide minimum thickness. Physical properties include, but are not limited to, the second oxide thickness, the second oxide maximum thickness, and the second oxide minimum thickness.

[0094] The second oxide thickness can be defined as the distance from the point where the second oxide layer 122 meets the first oxide layer 120 to the point where the second oxide layer 122 meets the exterior surface. The second oxide thickness can be between 0.000045 inches and 0.000115 inches. The second oxide thickness can be between 0.000045 inches and 0.000055 inches, between 0.000055 inches and 0.000065 inches, between 0.000065 inches and 0.000075 inches, between 0.000075 inches and 0.000085 inches, between 0.000085 inches and 0.000095 inches, between 0.000095 inches and 0.000105 inches, or between 0.000105 inches and 0.000115 inches. The second oxide thickness may be less than 0.000115 inches, less than 0.000105 inches, less than 0.000105 inches, less than 0.000095 inches, less than 0.000085 inches, less than 0.000075 inches, or less than 0.000065 inches.

[0095] The second oxide maximum thickness can be defined as the maximum distance from the point where the second oxide layer 122 meets the first oxide layer 120 to the point where the second oxide layer 122 meets the exterior surface. The second oxide maximum thickness can be measured in a direction perpendicular to the second oxide layer 122 at the measurement point. The second oxide maximum thickness can be between 0.000075 inches and 0.000115 inches.

[0096] The second oxide minimum thickness may be defined as the smallest distance from the point where the second oxide layer 122 meets the first oxide layer 120 to the point where the second oxide layer 122 meets the exterior surface. The second oxide minimum thickness may be measured in a direction perpendicular to the nitride layer 230 at the measurement point. The second oxide minimum thickness may be between 0.000050 inches and 0.000075 inches.

[0097] As previously described, the second oxide layer 122 has a second oxide uniformity. The second oxide uniformity can be defined as the ratio between the second oxide maximum thickness and the second oxide minimum thickness. The uniformity can be between 1.00 and 1.65. The uniformity can be between 1.00 and 1.15, between 1.15 and 1.30, between 1.30 and 1.45, between 1.45 and 1.60, or between 1.60 and 1.65. The uniformity can be less than 1.65, less than 1.50, less than 1.45, or less than 1.30. The closer the uniformity is to 1, the more uniform the second oxide thickness is.

[0098] A tenth step may include removing the holding fixture from the first oven and cooling the club head 100 to a predetermined temperature. In some embodiments, the club head 100 may be cooled by air-cooling. In other embodiments, the club head 100 may be cooled by partially or completely immersing the club head 100 in a medium. The predetermined temperature may be between 60°C and 100°C. In some embodiments, the predetermined temperature may be between 60°C and 65°C, between 65°C and 70°C, between 70°C and 75°C, between 80°C and 85°C, between 90°C and 95°C, or between 95°C and 100°C.

[0099] The club head 100 may be allowed to cool for a period of time. The period of time may be between 20 and 40 minutes. In some embodiments, the cooling may occur for 20 to 25 minutes, 25 to 30 minutes, 30 to 35 minutes, or 35 to 40 minutes. After the club head 100 has cooled, the club head 100 may be rinsed with water and removed from the holding fixture.

[0100] In some embodiments, the tenth step may further include air-drying the club head 100. The club head 100 may be air-dried until it reaches room temperature. In some embodiments, the room temperature may be between 20°C and 35°C. In some embodiments, the room temperature may be between 20°C and 25°C, between 25°C and 30°C, or between 30°C and 35°C.

[0101] An eleventh step may include blasting the exterior surface to ensure uniformity across the second oxide layer 122. This step may include blasting the golf club with a medium selected from the group consisting of glass beads, sand, aluminum oxide, silicon carbide, steel shot, and any other suitable form of grit. The grit size may range from #60 grit to #320 grit. The grit size may be #60 grit to #80 grit, #80 grit to #100 grit, #100 grit to #120 grit, #120 grit to #140 grit, #140 grit to #160 grit, #160 grit to #180 grit, #180 grit to #200 grit, #200 grit to #220 grit, #220 grit to #240 grit, #240 grit to #260 grit, #260 grit to #280 grit, #280 grit to #300 grit, or #300 grit to #320 grit. In one exemplary embodiment, the media may be #220 grit glass beads.

[0102] Furthermore, the blasting treatment may be carried out under pressure, which may be 1 to 5 kg / cm. 2 In one embodiment, the pressure may be 1 kg / cm 2 ~2kg / cm 2 , 2kg / cm 2 ~3kg / cm 2 , 3kg / cm 2 ~4kg / cm 2 , or 4 kg / cm 2 ~5kg / cm 2 In one exemplary embodiment, the blasting treatment may be 2 kg / cm 2 In another exemplary embodiment, the blasting is carried out under a pressure of 3 kg / cm. 2In some embodiments, the fifteenth step may include blasting the exterior surface with a first media having a first grit size under a first pressure, and then blasting the exterior surface with a second media having a second grit size under a second pressure. As discussed above, blasting can ensure uniformity throughout the second oxide layer 122, resulting in uniform strength throughout the exterior surface of the golf club head.

[0103] In some embodiments, step 11 may further include visually inspecting each golf club head 100 to ensure uniformity, similar to step 9. The uniformity of second oxide layer 122 ensures a uniform surface hardness, eliminating or minimizing the formation of cracks 108 during loft / lie adjustment.

[0104] One embodiment of the method is as follows: 1) aging the nitride salt at a temperature of 565°C for 6 hours; 2) blasting the exterior surface of the golf club head; 3) mounting the golf club head in a holding fixture; 4) placing the holding fixture in a second furnace and heating the second furnace to 350°C for 30 minutes; 5) transferring the holding fixture from the second furnace to the first furnace and maintaining the furnace at 580°C for 45 minutes to form a nitride layer; 6) reducing the furnace temperature to 410°C and maintaining it there for 30 minutes to form a first oxide layer on the nitride layer; 7) removing the holding fixture from the first furnace, cooling the club head to temperature, cleaning the club head, and removing the club head from the holding fixture; 10) reattaching the golf club head to the holding fixture; 11) placing the holding fixture in a second furnace and heating the second furnace to 410°C for 45 minutes to form a second oxide layer; 12) transferring the holding fixture from the second furnace to the first furnace and allowing the holding fixture to remain in the first furnace for a predetermined time; 13) removing the holding fixture from the first furnace and allowing the club head to cool to a predetermined temperature and cleaning the club head; 14) allowing the golf club head to air dry; 15) blasting the exterior of the golf club head; 16) visually inspecting the golf club head to ensure exterior uniformity.

[0105] The above-described method can provide increased uniformity in the formation of each of the nitride layer 230, the first oxide layer 120, and the second oxide layer 122. The increased uniformity of these layers, and more specifically, the increased uniformity of the layer thicknesses, can provide increased layer integrity, leading to improved mechanical properties of the exterior surface of the golf club head.

[0106] Improving uniformity in the formation of the nitride layer 230, first oxide layer 120, and second oxide layer 122 improves the hardness uniformity of the QPQ finish. The hardness of the QPQ finish may be 55HRC to 65HRC. The hardness of the QPQ finish may be 55HRC to 60HRC, or 60HRC to 65HRC. The hardness may be 55HRC, 56HRC, 57HRC, 58HRC, 59HRC, 60HRC, 61HRC, 62HRC, 63HRC, 64HRC, or 65HRC. The QPQ finish described herein may provide a 27% hardness improvement. The QPQ finish described herein can provide up to 36% better hardness variation, improving hardness uniformity across the QPQ finish. [Table 1] Table 1: Diagrams for grades 1-5 illustrating the extent and depth of porosity within the composite layer.

[0107] The above-described method can produce a golf club head having a graded composite layer or layers. The composite layer grade or layer grade can refer to the QPQ finish, more specifically, the nitride layer 230, the first oxide layer 120, and the second oxide layer 122. The composite layer grade represents the degree and distribution of porosity within the composite layer. Grades 1, 2, and 3 are considered to have an acceptable level of porosity. Grades 4 and 5 are considered to have too much porosity to reliably prevent undesirable surface deformation. Specifically, Grades 1 and 2 represent high-density composite layers with little or no porosity on the surface. Grade 3 refers to a high-density composite layer in which the porosity gradually decreases from the top layer toward the interior of the material. Grades 4 and 5 refer to a composite layer in which porosity accounts for two-thirds or more of the composite layer. In some examples, the golf club heads described herein may include a Grade 3 composite layer. In some examples, the golf club heads described herein may include a Grade 2 composite layer. In some examples, the golf club heads described herein may include a Grade 1 composite layer. The golf club heads described herein may include a Grade 1, Grade 2, or Grade 3 composite layer. The golf club heads described herein do not include a Grade 4 or Grade 5 composite layer.

[0108] The grade of the composite layer depends on the porosity level in the top half of the composite layer (which includes at least part of the first oxide layer 120 and the second oxide layer 122) and the porosity level in the bottom half of the composite layer (which includes at least part of the nitride layer 130). High surface and near-surface porosity levels are an expected effect of the QPQ process, which can result in surface deformation, including the formation of microcracks. The significant difference in the severity of surface deformation and microcracks and larger cracks is due to the significant difference in porosity deeper than the top half of the composite layer.

[0109] Pores in the lower half of the composite layer can create gaps that allow microcracks formed on the surface to extend deep into the material. Therefore, it is desirable to have few or no porosity in the lower half of the composite layer. The porosity of the lower half of the composite layer may be 0% to 5%. The porosity of the lower half of the composite layer may be 0% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, or 4% to 5%. The porosity of the lower half of the composite layer may be less than 5%, less than 3%, less than 2%, or less than 1%. A low porosity in the lower half of the composite layer greatly reduces the likelihood that microcracks formed in the upper half will connect with gaps formed by pores in the lower half, thereby greatly reducing the likelihood of cracks deepening and extending into the lower half, becoming visible at arm's length.

[0110] The porosity of the top half of the composite layer may be 40% to 65%. The porosity of the top half of the composite layer may be 40% to 45%, 45% to 55%, 55% to 60%, or 60% to 65%. Higher porosity levels in the top half of the composite layer are an expected effect of the QPQ process and may result in surface deformation, including the formation of microcracks, but the microcracks do not extend deep into the bottom half of the composite layer.

[0111] Applying the method described herein not only improves the hardness uniformity and wear resistance of the outer surface of the golf club head, but also maintains the softness and ductility of the core 110, which is extremely important for a golf club head in order to maintain flexibility for loft / lie adjustment and to maintain desirable feel and sound characteristics. Applying this QPQ method results in a golf club head 100 with an outer surface that can withstand the forces applied at impact and during the loft / lie adjustment process without affecting the feel of the golf club head 100 at impact.

[0112] Heat treating metals increases their hardness but also increases their porosity. Porosity increases the likelihood of cracks 108 by forming gaps in the material. Porosity near the surface can result in microcracks. However, the deeper the material is below the surface, the more porosity present, and the deeper the cracks propagate into the material, resulting in longer and wider cracks. Specifically, when microcracks connect with gaps created by pores, they gain volume (depth and width) from the gaps. These long, wide cracks tend to merge or connect with each other and extend further along the surface, increasing their visibility and reducing their integrity. High porosity beyond the surface region increases the likelihood of deep cracks because gaps form more easily within the material. While low porosity can result in cracks that extend to the same maximum depth as cracks in highly porous materials, the number of deep cracks is significantly reduced, thereby maintaining durability.

[0113] A typical QPQ process results in a hardened surface that contains highly porous regions that extend deep into the material. The QPQ process described above produces a desirable hardened surface while retaining the high porosity that results in increased hardness near the surface. This desirably results in cracks that are less likely to extend deep below the surface or far beyond the surface. When bent, a QPQ-treated surface is more likely to exhibit a series of microcracks rather than a wide, deep crack, allowing for the retention of elasticity while providing the hardness obtained from the QPQ process.

[0114] example Example I: Comparison between conventional and exemplary layers This section describes a physical property comparison between a control golf club head made using a conventional QPQ process detailed in Table 2 below and an exemplary golf club head made using a QPQ process detailed in Table 3 below. More specifically, this example illustrates the differences in thickness and uniformity of the nitride layer, first oxide layer, and second oxide layer. [Table 2] Table 2: Steps 1-16 of the conventional QPQ process [Table 3] Table 3: Steps 1-17 of the QPQ method described herein

[0115] Magnified images of the exterior surfaces of the golf club heads were taken, as shown in Figures 5E and 6E. Figure 5E shows a magnified image of an exemplary golf club head, and Figure 6E shows a magnified image of a control golf club head. Using each image, the depths of the nitride layer, first oxide layer, and second oxide layer at selected points were measured. These values ​​were then used to calculate the thicknesses of the nitride layer, first oxide layer, and second oxide layer at each selected point. Because there were four selected points, four data points were obtained for each layer. These four data points were used to determine the minimum and maximum thickness values ​​for each layer of each club head. The ratio of the maximum thickness to the minimum thickness was then used to determine uniformity. Additionally, the standard deviation of the four data points was calculated to indicate the thickness variation of each layer of each golf club head. The results are shown in Tables 4, 5, and 6 below. [Table 4] Table 4: Comparison of nitride layers between control club heads and exemplary golf club heads

[0116] As shown in Table 4 above, the exemplary golf club heads exhibited 34.99% better nitride layer uniformity than the control golf club heads. The uniformity of the nitride layer further ensures uniformity of the first and second oxide layers by providing a consistent surface for the first oxide layer to stretch and grow. The uniformity of the nitride layer can be directly reflected in the first and second oxide layers. Furthermore, the exemplary golf club heads exhibited 67.83% better standard deviation of nitride layer thickness than the control golf club heads. Because standard deviation measures the magnitude of thickness variation, the significantly better standard deviation of nitride layer thickness further indicates the uniformity of the nitride layer thickness. [Table 5] Table 5: Comparison of First Oxide Layer Between Control and Exemplary Golf Club Heads

[0117] As shown in Table 5 above, the example golf club heads experienced a 1.93% decrease in first oxide layer uniformity. However, the example golf club heads had a 40.23% better standard deviation of first oxide layer thickness compared to the control golf club heads. Because the first oxide layer thickness standard deviation was significantly better than the control golf club heads, the decrease in uniformity was considered negligible. As previously mentioned, the standard deviation measures the magnitude of thickness variation, and therefore the standard deviation of the first oxide layer thickness is an indication of the uniformity of the first oxide layer thickness.

[0118] Additionally, as shown in Table 5 above, the average thickness of the exemplary first oxide layer is much smaller than the control first oxide layer. The smaller average thickness results in a thinner first oxide layer that is less brittle and less prone to large cracks. [Table 6] Table 6: Comparison of Second Oxide Layer Between Control and Exemplary Golf Club Heads

[0119] As shown in Table 6 above, the exemplary golf club heads had a 12.08% better second oxide layer uniformity. Additionally, the exemplary golf club heads had a 19.05% better standard deviation in second oxide layer thickness compared to the control golf club heads. Because standard deviation measures the amount of thickness variation, the significantly better standard deviation in second oxide layer thickness compared to the control golf club heads further demonstrates the uniformity of the second oxide layer thickness.

[0120] Additionally, as shown in Table 6 above, the average thickness of the exemplary second oxide layer is much smaller than the control second oxide layer. The smaller average thickness results in a thinner second oxide layer that is less brittle and less prone to large cracks.

[0121] In conclusion, the additional blasting step of the QPQ process described herein has been found to improve the uniformity of each of the nitride, first oxide, and second oxide layers. This improved uniformity promotes bonding between the layers, reduces porosity, and increases hardness, as detailed in Examples II and V below. Specifically, the smooth surface provided by the blasting step reduces the formation of defects between the layers of the composite layer, thereby reducing the likelihood of deep cracks forming, as detailed in Examples III and IV below.

[0122] Example II: Comparison of porosity in composite layers formed by the QPQ method described herein and traditional QPQ methods Example II describes a comparison of the extent and depth of porosity within composite or finish layers applied to the surface of a golf club head using the method described herein and a conventional QPQ method. Two samples (hereinafter referred to as "Example Club Head 1" and "Example Club Head 2") of an exemplary embodiment of a golf club head having a one-piece hosel structure made from 8620 steel alloy and subjected to a post-manufacture QPQ process, as described above and detailed in FIG. 1, are described. Specifically, the exemplary golf club heads were processed using the steps detailed in Table 3 of Example I above.

[0123] The depth and extent of high porosity in Exemplary Club Head 1 and Exemplary Club Head 2 were compared to two samples of similar golf club heads that underwent conventional QPQ processing (hereinafter referred to as "Control Club Head 1" and "Control Club Head 2"). The conventional QPQ processing consisted of the steps set forth in Table 2 of Example I above. [Table 7] Table 7: Summary of composite layer grades and porosity for control and exemplary club heads

[0124] Referring to Table 7 above, Control Club Head 1 and Control Club Head 2 exhibit high levels of porosity in the top half of the composite layer, at 39% and 47%, respectively. Exemplary Club Head 1 and Exemplary Club Head 2 similarly exhibit high levels of porosity in the top half of the composite layer, at 59% and 45%, respectively. High surface and near-surface porosity levels are an expected effect of any QPQ process and can result in surface deformation, including the formation of microcracks. The significant difference in the severity of surface deformation and cracks larger than microcracks is due to the significant difference in porosity deeper than the top half of the composite layer.

[0125] Referring again to Table 7, Control Club Head 1 and Control Club Head 2 exhibit moderate levels of porosity in the lower half of the composite layer, at 15% and 13%, respectively. Exemplary Club Head 1 and Exemplary Club Head 2 exhibit very low levels of porosity in the lower half of the composite layer, at 1% and less than 1%, respectively, which is significantly lower than the lower half of the composite layer in Control Club Head 1 and Control Club Head 2. Porosity in the lower half of the composite layer creates gaps that allow microcracks formed at the surface to extend deeper into the material. While the high porosity is consistent across all tested club heads, microcracks are expected to form on the surface, but they do not significantly affect the strength of the coating and are not clearly visible to the user. The extremely low porosity of Exemplary Club Head 1 and Exemplary Club Head 2 results in a highly resilient composite layer that resists surface deformation and inhibits the formation of deep cracks.

[0126] Each sample was graded based on the degree of porosity found within the composite layer. These grades are hereafter referred to as "oxidized loose layer grades" or "composite layer grades." Referring to Table 1, grades 1, 2, and 3 are considered acceptable porosity. Grades 4 and 5 are considered too porosity-rich to reliably prevent undesirable surface deformation. Specifically, grades 1 and 2 represent dense composite layers with little or no microporosity on the surface, which can lead to the propagation and deepening of microcracks. Grade 3 represents dense composite layers with a gradual decrease in microporosity from the top layer toward the interior of the material. Grades 4 and 5 represent composite layers in which more than two-thirds of the composite layer is occupied by microporosity, resulting in cracks visible at arm's length. As shown in Table 7 above, both Control Club Head 1 and Control Club Head 2 had composite layers with a grade of 4, which was deemed defective, while Exemplary Club Head 1 and Exemplary Club Head 2 had composite layers with an acceptable grade of 3. Thus, previous QPQ methods have not been able to produce coatings with acceptable levels of porosity in materials. The QPQ method described herein produces material coatings with acceptable porosity levels while still providing a desirable hardened surface, providing users with the resilience necessary to limit surface deformation when bent.

[0127] Example III: Comparison of bendability and surface deformation in coatings formed by the QPQ method described herein and conventional QPQ methods Example III describes the occurrence of substantial visible surface deformation caused by stresses on club heads processed with the QPQ method described herein. Specifically, Example III discusses test data regarding bending a hosel to adjust loft and lie angles and the formation of visible cracks in the bent area.

[0128] Described herein is a sample of one exemplary embodiment of a golf club head (hereinafter "exemplary club head") having a one-piece hosel construction made from 8620 steel alloy and subjected to post-manufacture QPQ processing, as described above and detailed in Figure 1. Specifically, the exemplary golf club head was processed according to the steps detailed in Table 3 of Example I above.

[0129] When a club head hosel is forcibly bent after manufacture, the applied force deforms the material, leaving a visible mark at the bent area. The amount of deformation on the material's surface after bending was analyzed and recorded on a qualitative feedback scale. The hosels of 18 exemplary club heads were forcibly bent within a range of 3° to 5° from the neutral starting position. In this manner, the exemplary club heads were measured for upright and flat-lie adjustments, and open and closed loft adjustments. Table 8 below details the extent of the attempted bends and an assessment of the resulting surface deformation. [Table 8] Table 8: Bend at limit of visibility at arm's length

[0130] The values ​​recorded in the table indicate the amount of loft change before surface deformation becomes substantially noticeable at arm's length. Because the loft and lie angle bending of manufactured club heads can be inaccurate, slight variations in the degree of bending are due to human error in the bending process and are negligible overall. As shown in Table 8, all of the exemplary club heads could be bent well beyond 3 degrees without leaving evidence of surface deformation that was noticeable at arm's length. Not only were the exemplary club heads not visibly affected by the applied force, but they also maintained their ability to bend successfully to the desired angle without breaking.

[0131] Example IV: Surface Comparison Example IV provides a qualitative comparison (i.e., crack propagation and surface characteristics) showing the effect on crack propagation and surface characteristics of applying the QPQ method described herein. Specifically, Example IV compares images taken after bending the hosel showing surface deformation in the hosel region.

[0132] The visibility, frequency, and size of cracks were observed and qualitatively analyzed for exemplary club heads treated with the QPQ method described herein and control club heads that underwent a typical QPQ process. The exemplary club heads treated with the QPQ method described herein (hereinafter referred to as "exemplary club heads") included a one-piece hosel structure made from 8620 steel alloy and were subjected to a post-manufacture QPQ process, as described in the steps detailed above in FIG. 1. Specifically, the exemplary golf club heads were treated with the steps summarized in Table 3 of Example I above.

[0133] The extent of cracking observed on the surface of the exemplary club head was compared to the extent of cracking on a similar golf club head that underwent a conventional QPQ process (hereinafter referred to as the "control club head"). The conventional QPQ process consisted of the steps set forth in Table 2 of Example I above. Images of the surface deformation of the exemplary club head after bending the hosel are shown in Figures 5A-5G. Images of the surface deformation of the control club head after bending the hosel are also shown in Figures 6A-6G.

[0134] Figures 5A (exemplary club head) and 6A (control club head) display the hosel region as seen with the naked eye (without post-processing effects or magnification) and clearly demonstrate the differences in the degree of surface deformation experienced. When viewed at arm's length, the exemplary club head, as shown in Figure 5A, exhibited little to no surface deformation. Specifically, while the hosel of the exemplary club head exhibited slight deformation, the cracks were superficial (i.e., visible at closer than arm's length) and would have little or no effect on the performance or durability of the club head. The hosel of the exemplary club head exhibited virtually no deep cracks or cracks surrounding the hosel. This was also the case for the control club head. The mild surface deformation of the hosel of the exemplary club head was not readily visible at arm's length and was only detectable upon closer inspection. In contrast, Figure 6A exhibits significant surface deformation. The two white paint lines were applied for testing purposes and can be ignored. The cracks in the hosel area of ​​the control clubheads appeared to be of significant impact, specifically calling into question the durability and resilience of the control clubheads, as two cracks in particular were highly visible, appeared to be deep, and encircled the hosel for a significant distance.

[0135] Figures 5B (exemplary club head) and 6B (control club head) show enlarged images of the same hosel region shown in Figures 5A and 6A, but with specialized lighting to fluoresce the surface deformation. Comparing Figures 5B and 6B, it is readily apparent that the control club head experienced a greater level of cracking, as quantified by frequency, length, and width. The exemplary club head exhibits little crack fluorescence, revealing a uniform surface with virtually no surface deformation. The cracks seen in the control club head in Figure 6B are significant and significantly impact the appearance of the hosel after bending. These substantial cracks impact the integrity of the coating and the user's confidence in the durability of the club head. Again, this is due to the uneven nitride, first oxide, and second oxide layers (see Example 2).

[0136] Figure 5C (exemplary club head) and Figure 6C (control club head) are photomicrographs magnified at 100x and show the most severe cracks observed in cross-sectional slides of the hosel region after bending. The cracks seen in Figure 5C are clean and uniform, with the cracks on the left being fairly deep, while the cracks on the right are shallower, revealing the sparse presence of deep cracks. In contrast, the cracks seen in Figure 6C are jagged and rough, indicating the presence of more impurities deeper below the surface. Both cracks are deep, due to the high frequency of deep cracks occurring across the surface. Additionally, the exemplary club head exhibited a smoother, more uniform outer surface, while the control club head exhibited a more uneven outer surface. Finally, the cracks in the control club head significantly affected the surface level, as measured by the difference in surface height immediately to the right and left of each crack, indicating instability in the composite layer and resulting shifts that could cause further surface deformation and potentially compromise the integrity of the coating and material.

[0137] Figure 5D (exemplary club head) and Figure 6D (control club head) are photomicrographs taken after bending. These photomicrographs demonstrate the coverage and depth of the composite layer. It is readily apparent that the exemplary club head has a very smooth and uniform nitride layer 130 (white line) and outer surface. This uniformity promotes strong bonding of the accompanying oxide layer, resulting in a hard surface that is aesthetically pleasing and resistant to surface deformation. The thickness or depth of the composite layer of the control club head varies across the image, resulting in inconsistencies in the subsurface protection provided by the QPQ process in terms of hardness and strength. The surface of the control club head contains multiple pits, which cause stress concentrations (i.e., do not distribute stress evenly across a smooth surface). These pits can lead to the formation of cracks in the surface. The cracks then tend to propagate deep into the composite layer due to porosity and imperfections within each layer that make up the composite layer.

[0138] The composite layer and the individual layers (nitride and oxide layers) that make up the composite layer appear much smoother and more uniform with fewer impurities when the substrate is treated with the QPQ method described herein compared to when the substrate is treated with conventional QPQ methods. The frequency and severity of cracks visible to the naked eye, when viewed at arm's length or under magnification, are significantly reduced when the QPQ treatment described herein is applied to a material surface compared to when the surface is treated with conventional QPQ treatment methods.

[0139] Example V: Surface Hardness Comparison Between Coatings Formed by the QPQ Method Described Herein and by Conventional QPQ Methods Example V compares hardness measurements recorded on the coating surfaces of treated golf club heads for two samples (hereinafter "exemplary club head 1" and "exemplary club head 2") of an exemplary embodiment of a golf club head having a one-piece hosel construction made from 8620 steel alloy and subjected to post-manufacture QPQ processing, as described above and detailed in FIG. 1. Specifically, the exemplary golf club heads were processed using the steps detailed in Table 3 of Example I above.

[0140] The hardness of exemplary club head 1 and exemplary club head 2 was compared to the hardness of two samples of similar golf club heads that underwent conventional QPQ processing (hereinafter referred to as "control club head 1" and "control club head 2"). The conventional QPQ processing consisted of the steps set forth in Table 2 of Example I above. [Table 9] Table 9: Bending at the limit of visibility [Table 10] Table 10: Bending degree at the limit of visibility

[0141] Referring to Tables 9 and 10 above, the hardness of the QPQ coating for each of the control and exemplary club head samples was analyzed using the HRC Rockwell scale. Data was collected from five measurements at different locations on the surface and averaged to determine an average hardness across the surface. Compared to control club head 1 and control club head 2, exemplary club head 1 and exemplary club head 2 had substantially greater hardness. Specifically, the hardness of the coatings on exemplary club head 1 and exemplary club head 2 formed by the QPQ method described herein was 27% greater than the hardness of the coatings on control club head 1 and control club head 2 formed by the conventional QPQ method.

[0142] The hardness values ​​recorded for each of the five measurements may indicate the uniformity of hardness across the surface. Compared to control club heads processed with a conventional QPQ method, the range of hardness values ​​collected across the five measurements for the exemplary club heads processed with the QPQ method described herein was reduced by 36.7% to 54.5%. On average, the QPQ method described herein reduced the variability in the surface hardness values ​​measured for exemplary club head 1 and exemplary club head 2 by more than 46%.

[0143] It was found that the maximum deviation from the mean value was significantly smaller for example club head 1 and example club head 2 compared to control club head 1 and control club head 2. For example club head 1 and example club head 2, the hardness measurements deviated from the mean by 1.85% to 2.25% and 1.59% to 1.72%, respectively. For control club head 1 and control club head 2, the hardness measurements deviated from the mean by 4.74% to 4.94% and 4.96% to 5.95%, respectively. The improved hardness and hardness uniformity not only improves the wear resistance of the outer surface of the golf club head, but also maintains the softness and ductility of core 110.

[0144] Substituting one or more claimed elements constitutes a rearrangement, not a repair. Furthermore, benefits, other advantages, and solutions to problems have been described with respect to particular embodiments. However, these benefits, advantages, solutions to problems, and one or more elements that may give rise to or make more pronounced the benefits, advantages, or solutions, should not be construed as a critical, necessary, or essential feature or element of any or all of the claims, unless such benefit, advantage, solution, or element is expressly recited in the claims.

[0145] Because the Rules of Golf may change from time to time (e.g., new Rules may be adopted, and old Rules may be repealed or amended, by golf standards organizations and / or governing bodies such as the United States Golf Association (USGA) or the Royal and American Golf Association (R&A)), golf equipment relating to the apparatus, methods, and articles of manufacture described herein may or may not conform to the Rules of Golf at any particular time. Accordingly, golf equipment relating to the apparatus, methods, and articles of manufacture described herein may be advertised, offered for sale, and / or sold as conforming or non-conforming golf equipment. The apparatus, methods, and articles of manufacture described herein are not limited in this respect.

[0146] Although the above examples may be described in relation to iron-type golf clubs, the devices, methods, and articles of manufacture described herein may also be applicable to other types of golf clubs, such as driver wood-type golf clubs, fairway wood-type golf clubs, hybrid-type golf clubs, iron-type golf clubs, wedge-type golf clubs, or putter-type golf clubs. Alternatively, the devices, methods, and articles of manufacture described herein may also be applicable to other types of sports equipment, such as hockey sticks, tennis rackets, fishing rods, ski poles, etc.

[0147] Furthermore, the embodiments and limitations disclosed herein are not available to the public under the doctrine of equivalents if such embodiments and / or limitations (1) are not expressly recited in the claims, and (2) are equivalent or potentially equivalent to elements and / or limitations expressly recited in the claims under the doctrine of equivalents.

[0148] Various features and advantages of the disclosure are set forth in the following sections and claims.

[0149] Item 1 1. A method of treating a golf club head, comprising: aging a nitride salt in a first furnace for a predetermined time; blasting an exterior surface of the golf club head; placing a holding fixture in a second furnace and heating the second furnace to a predetermined temperature for a predetermined time; transferring the holding fixture from the second furnace to the first furnace and allowing the holding fixture to remain in the first furnace for a predetermined time, wherein a nitride layer forms on the exterior surface; lowering the temperature of the first furnace to a predetermined temperature for a predetermined time, wherein a first oxide layer grows on the nitride layer; removing the holding fixture from the first furnace; cooling the golf club head to the predetermined temperature; and cleaning the golf club head. , removing the golf club head from the holding fixture; blasting the exterior surface of the golf club head; placing the holding fixture in a second furnace and heating the second furnace to a predetermined temperature for a predetermined time; moving the holding fixture from the second furnace to the first furnace and allowing the holding fixture to remain in the first furnace for a predetermined time, wherein a second oxide layer grows on the first oxide layer; removing the holding fixture from the first furnace, cooling the golf club head to a predetermined temperature, cleaning the golf club head; and blasting the exterior surface of the golf club head, wherein the nitride layer, the first oxide layer, and the second oxide layer are uniform.

[0150] Section 2 10. The method of claim 1, wherein the nitride salt comprises a CNO concentration of 28% to 36%.

[0151] Section 3 10. The method of claim 1, wherein the blasting in step (b) is performed with #220 grit glass beads.

[0152] Section 4 The method of claim 1 , wherein the nitride layer comprises a nitride thickness of between 0.00025 inches and 0.00060 inches.

[0153] Section 5 5. The method of claim 4, wherein the nitride layer comprises a nitride maximum thickness and a nitride minimum thickness, the nitride minimum thickness being between 0.00025 inches and 0.00045 inches, and the nitride maximum thickness being between 0.00045 inches and 0.00060 inches.

[0154] Section 6 The method of claim 5 , wherein the nitride layer comprises a nitride uniformity that is less than 1.25.

[0155] Section 7 The method of claim 1 , wherein the first oxide layer comprises a first oxide thickness that is less than 0.000115 inches.

[0156] Section 8 8. The method of claim 7, wherein the first oxide layer comprises a first oxide maximum thickness and a first oxide minimum thickness, the first oxide maximum thickness being between 0.000075 inches and 0.000115 inches, and the first oxide minimum thickness being between 0.000050 inches and 0.000075 inches.

[0157] Section 9 The method of claim 8 , wherein the first oxide layer comprises a first oxide uniformity that is less than 1.85.

[0158] Section 10 The method of claim 1 , wherein the second oxide layer comprises a second oxide thickness that is less than 0.000115 inches.

[0159] Section 11 11. The method of claim 10, wherein the second oxide layer comprises a second oxide maximum thickness and a second oxide minimum thickness, the second oxide maximum thickness being between 0.000075 inches and 0.000115 inches, and the second oxide minimum thickness being between 0.000050 inches and 0.000075 inches.

[0160] Section 12 The method of claim 11 , wherein the second oxide layer comprises a second oxide uniformity that is less than 1.65.

[0161] Section 13 1. A golf club head comprising: a body having a top rail facing the sole and a toe facing the heel; a hosel connected to the club body and having a first end proximate the heel and a second end opposite the first end; and an outer surface having a QPQ finish, the QPQ finish comprising a nitride layer, a first oxide layer, and a second oxide layer, the outer surface having a Grade 3 QPQ finish, the nitride layer having a nitride uniformity of 1.00 to 1.25, the first oxide layer having a first oxide uniformity of 1.00 to 1.25, and the second oxide layer having a second oxide uniformity of 1.00 to 1.25.

[0162] Section 14 14. The golf club head according to claim 13, wherein the QPQ finish has a hardness of 55HRC to 65HRC.

[0163] Section 15 14. The golf club head of claim 13, wherein the nitride layer comprises a nitride thickness between 0.00025 inches and 0.00060 inches.

[0164] Section 16 14. The golf club head of claim 13, wherein the nitride layer has a nitride maximum thickness and a nitride minimum thickness, the nitride minimum thickness being between 0.00025 inches and 0.00045 inches, and the nitride maximum thickness being between 0.00045 inches and 0.00060 inches.

[0165] Section 17 14. The golf club head of claim 13, wherein the first oxide layer comprises a first oxide thickness that is less than 0.000115 inches.

[0166] Section 18 14. The golf club head of claim 13, wherein the first oxide layer has a first oxide maximum thickness and a first oxide minimum thickness, the first oxide maximum thickness being between 0.000075 inches and 0.000115 inches, and the first oxide minimum thickness being between 0.000050 inches and 0.000075 inches.

[0167] Section 19 14. The golf club head of claim 13, wherein the second oxide layer comprises a second oxide thickness that is less than 0.000115.

[0168] Section 20 14. The golf club head of claim 13, wherein the second oxide layer has a second oxide maximum thickness and a second oxide minimum thickness, the second oxide maximum thickness being between 0.000075 inches and 0.000115 inches, and the second oxide minimum thickness being between 0.000050 inches and 0.000075 inches.

Claims

1. 1. A method of treating a golf club head, comprising: The method comprises: (a) aging the nitride salt in a first furnace for a predetermined time; (b) blasting the exterior surface of the golf club head; (c) placing the holding fixture in a second furnace and heating the second furnace to a predetermined temperature for a predetermined period of time; (d) moving the holding fixture from the second furnace to the first furnace and allowing the holding fixture to remain in the first furnace for a predetermined period of time, wherein a nitride layer is formed on the exterior surface; (e) decreasing the temperature of the first furnace to a predetermined temperature over a predetermined time period, wherein a first oxide layer grows on the nitride layer; (f) removing the holding fixture from the first oven, cooling the golf club head to a predetermined temperature, cleaning the golf club head, and removing the golf club head from the holding fixture; (g) blasting the exterior surface of the golf club head; (h) placing the holding fixture into the second furnace and heating the second furnace to a predetermined temperature for a predetermined time; (i) moving the holding fixture from the second furnace to the first furnace and allowing the holding fixture to remain in the first furnace for a predetermined time, wherein a second oxide layer is grown on the first oxide layer; (j) removing the holding fixture from the first oven, cooling the golf club head to a predetermined temperature, and cleaning the golf club head; (k) blasting the exterior surface of the golf club head, wherein the nitride layer, the first oxide layer, and the second oxide layer are uniform.

2. The method of claim 1 , wherein the nitride salt comprises a CNO concentration of 28% to 36%.

3. 10. The method of claim 1, wherein the blasting in step (b) is performed with #220 grit glass beads.

4. The method of claim 1 , wherein the nitride layer comprises a nitride thickness of between 0.00025 inches and 0.00060 inches.

5. the nitride layer having a nitride maximum thickness and a nitride minimum thickness; the nitride minimum thickness is between 0.00025 inches and 0.00045 inches; The method of claim 4, wherein the nitride maximum thickness is between 0.00045 inches and 0.00060 inches.

6. The method of claim 5 , wherein the nitride layer comprises a nitride uniformity that is less than 1.

25.

7. The method of claim 1 , wherein the first oxide layer comprises a first oxide thickness that is less than 0.000115 inches.

8. the first oxide layer comprises a first oxide maximum thickness and a first oxide minimum thickness; the first oxide maximum thickness is between 0.000075 inches and 0.000115 inches; The method of claim 7, wherein the first oxide minimum thickness is between 0.000050 inches and 0.000075 inches.

9. The method of claim 8 , wherein the first oxide layer comprises a first oxide uniformity that is less than 1.

85.

10. The method of claim 1 , wherein the second oxide layer comprises a second oxide thickness that is less than 0.000115 inches.

11. the second oxide layer comprises a second oxide maximum thickness and a second oxide minimum thickness; the second oxide maximum thickness is between 0.000075 inches and 0.000115 inches; The method of claim 10, wherein the second oxide minimum thickness is between 0.000050 inches and 0.000075 inches.

12. The method of claim 11 , wherein the second oxide layer comprises a second oxide uniformity that is less than 1.

65.

13. A golf club head, a body having a top rail opposite the sole and a toe opposite the heel; a hosel connected to the body and having a first end adjacent the heel and a second end opposite the first end; an exterior surface having a QPQ finish; the QPQ finish comprises a nitride layer, a first oxide layer, and a second oxide layer; the exterior surface has a Grade 3 QPQ finish; the nitride layer has a nitride uniformity of 1.00 to 1.25; the first oxide layer having a first oxide uniformity of 1.00 to 1.25; The golf club head, wherein the second oxide layer has a second oxide uniformity of 1.00 to 1.

25.

14. 14. The golf club head of claim 13, wherein the QPQ finish has a hardness of 55 HRC to 65 HRC.

15. The golf club head of claim 13, wherein the nitride layer comprises a nitride thickness of between 0.00025 inches and 0.00060 inches.

16. the nitride layer having a nitride maximum thickness and a nitride minimum thickness; the nitride minimum thickness is between 0.00025 inches and 0.00045 inches; The golf club head of claim 13, wherein the nitride maximum thickness is between 0.00045 inches and 0.00060 inches.

17. The golf club head of claim 13 , wherein the first oxide layer comprises a first oxide thickness that is less than 0.000115 inches.

18. the first oxide layer comprises a first oxide maximum thickness and a first oxide minimum thickness; the first oxide maximum thickness is between 0.000075 inches and 0.000115 inches; 14. The golf club head of claim 13, wherein the first oxide minimum thickness is between 0.000050 inches and 0.000075 inches.

19. The golf club head of claim 13 , wherein the second oxide layer comprises a second oxide thickness that is less than 0.000115 inches.

20. the second oxide layer comprises a second oxide maximum thickness and a second oxide minimum thickness; the second oxide maximum thickness is between 0.000075 inches and 0.000115 inches; 14. The golf club head of claim 13, wherein the second oxide minimum thickness is between 0.000050 inches and 0.000075 inches.

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