A METHOD OF MAKING SAME, AND A METHOD OF USING SAME FOR MAKING A GOLF CLUB HEAD

BACKGROUND OF THE INVENTION:

FIELD OF THE INVENTION:

This invention relates to stainless steel strip material and in particular to a stainless steel strip article having very high tensile strength, a method of making same, and a method of using the strip material for making a golf club head.

DESCRIPTION OF THE RELATED ART:

Golf club manufacturers are constantly looking for a high strength faceplate material. Very high strength allows the faceplate section to be made thinner, and therefore lighter, which provides designers more leeway in club head design. In addition, corrosion-resistant materials are preferable to non-stainless materials because surface coatings or plating, which could be removed during use, are not required.

Current solutions to this problem include the use of standard PH stainless steel alloys such as the CUSTOM 455 alloy and newly designed stainless alloys such as the CUSTOM 465 and CUSTOM 475 alloys. However, the CUSTOM 455 and CUSTOM 465 alloys do not provide the strength levels desired in new club designs. The CUSTOM 475 alloy provides very high strength, but it is also highly alloyed, making it both expensive for the club manufacturer as well as less forgiving in the golf club manufacturing process.

In addition, many club heads are typically manufactured using a cast body with a faceplate. The cast body material is typically formed of a precipitation hardenable stainless steel such as 17-4 PH or 15-5 PH stainless steel. Golf clubs are typically manufactured by welding the faceplate to the cast body and then heat treating the entire assembly to develop final properties. The alloys typically used for the cast body of the club have solution temperatures of about 1900 ⁰ F (1038 ⁰ C) ₁ whereas the known faceplate materials have solution temperatures ranging from 155O ⁰ F to 1800°F (843 ⁰ C to 982 ⁰ C). This mismatch in heat treating temperatures results in either the club body, or the faceplate material, or possibly both, providing less than optimum properties in the as-heat treated condition after assembly of the club head. In addition, the CUSTOM 475 alloy often requires a different manufacturing process altogether, because the alloy cannot be re-solutioned after club head assembly.

BRIEF SUMMARY OF THE INVENTION:

The disadvantages of the known materials are overcome to a large degree by a stainless steel strip article according to this invention. In accordance with the one aspect of the present invention, there is provided a stainless steel strip article that is formed from a corrosion resistant alloy comprising, in weight percent, about:

C 0.03 max.

Mn 1.0 max.

Si 0.75 max.

P 0.040 max.

S 0.020 max.

Cr 10.9-11.1

Ni 10.9-11.1

Mo 0.9-1.1

Ti 1.5-1.6

Al 0.25 max.

Nb 0.7-0.8

Cu 1 max.

B 0.010 max.

N 0.030 max. and the balance is iron and usual impurities. The elongated thin strip article provides a room temperature tensile strength of at least about 280 ksi (1930.5 MPa) in the solution treated and age hardened condition.

In accordance with another aspect of this invention there is provided a method of making a thin strip article. The method comprises the steps of casting a corrosion resistant alloy having the weight percent composition set forth above to form an ingot. The ingot is hot worked to form an elongated strip material. The strip material is then heat treated under conditions of time and temperature to provide an ultimate tensile strength of at least about 280 ksi (1930.5 MPa) at room temperature.

In accordance with a further aspect of this invention there is provided a method of making a golf club head. The method includes the step of casting a corrosion resistant alloy having the weight percent composition set forth above to form an ingot. The ingot is hot worked to form an elongated strip article which is then heat treated under conditions of time and temperature to benefit the machinability and processability of the strip material. The strip material is then machined to form a faceplate for a golf club head. The method includes the further step of forming a golf club head body from a corrosion resistant precipitation hardenable steel alloy. The faceplate is bonded to golf club head body. The assembly is then heat treated under conditions of time and temperature sufficient to provide a desired level of hardness and strength in the golf club head body and an ultimate tensile strength of at least about 280 ksi (1930.5 MPa) at room temperature in the faceplate.

BRIEF DESCRIPTION OF THE DRAWING:

The drawing is a graph of tensile strength as a function of aging temperature.

DETAILED DESCRIPTION:

A preferred embodiment of the invention includes an elongated strip article having the following composition in weight percent:

C 0.03 max.

Mn 1.0 max.

Si 0.75 max.

P 0.040 max

S 0.020 max

Cr 10.9-11.1

Ni 10.9-11.1

Mo 0.9-1.1

Ti 1.5-1.6

Al 0.25 max. Nb 0.7-0.8

Cu 1 max.

B 0.010 max.

N 0.030 max.

The balance is iron and the usual impurities.

The alloy composition is preferably melted using vacuum induction melting (VIM). The steel is cast into one or more ingot molds. For additional cleanness, the alloy is vacuum arc remelted (VAR) after the VIM step. After solidification, the alloy is formed into strip by intermediate pressing of the ingot to form a billet and then hot rolling the billet to form elongated strip. Alternatively, the strip material can be formed by hot rolling the ingot from a starting temperature of about 1900 ⁰ F to 225O ⁰ F (1038°C to 1232 ⁰ C). The strip can be provided in the overaged condition by heating at about 1100°F to 135O ⁰ F (593 ⁰ C to 732 ⁰ C) for about 2 to 8 hours and then cooling in air. Alternatively, and for better machinability and processability, the strip material is heated at about 1900°F to 195O ⁰ F (1038 ⁰ C to 1065 ⁰ C) for about 1 hour, cooled in air, refrigerated at about -100 ⁰ F (-73.3 ⁰ C) for about 8 hours, and then warmed in air to room temperature. Preferably, the strip material is cold rolled to final or near final thickness prior to being heat treated. The strip material according to this invention can be solution treated in a continuous furnace with times and temperatures adjusted accordingly. For the golf club application, the strip material is processed to a thickness of about 0.02-0.16 inches (0.5-4 mm), preferably about 0.10-0.12 inches (2.5-3.0 mm).

Unlike the known high strength stainless steel alloys such as the CUSTOM 475 stainless alloy, the alloy strip according to this invention can be double solution treated with no significant loss in properties, particularly no loss of strength. In other words, the stainless steel strip material of this invention can be provided in the solution treated plus refrigerated condition, processed into components, and then re-solutioned, re- refrigerated, and age hardened after being assembled into a golf club head to provide the desired high strength and hardness. As an example of the elongated strip article according to the present invention, a small heat was melted and processed. The 400 Ib (181.4 kg) heat was melted by VIM + VAR and cast as an 8-inch (20.3 cm) diameter ingot. The weight percent composition of the VAR ingot is given below in Table I. The balance of the alloy was iron and usual impurities.

Table I

The ingot was homogenized at about 2300 ⁰ F (126O ⁰ C) for 16 hours, and then pressed to a 4-in x 8-in (10 cm x 20.3 cm) billet from a starting temperature of about 2000 ⁰ F (1093°C). The billet was hot rolled to 7.5 in. wide x 0.15 in. thick (19 cm wide x 3.8 mm thick) strip from a starting temperature of about 225O ⁰ F (1232 ⁰ C). The strip was then ground to 0.135 in. (3.4 mm) thick and then cold rolled to 0.1103 in. (2.8 mm) thick. The strip was given an overaging treatment by heating at about 1146 ⁰ F (619 ⁰ C) for 5.5 hours. After cooling to room temperature, the strip material was ground to a final thickness of 0.1083 in (2.75 mm).

Standard strip tensile blanks were rough cut in the longitudinal and transverse orientations from the overaged strip. Groups of the blanks were solution treated at 185O ⁰ F (1010 ⁰ C), 1900 ⁰ F (1038 ⁰ C) ₁ 195O ⁰ F (1065°C), and 2000°F (1093X), respectively, for 1 hour and air cooled. The solution treated blanks were deep chilled at -100 ⁰ F (-73.3 ⁰ C) for 8 hours and then warmed in air to room temperature. The blanks were then rough machined to provide a gage section about Vz inch wide x 2 inches long (1.27 cm wide x 5.08 cm long). Groups of the rough machined blanks from each solution treatment were aged at temperatures ranging from about 900 ⁰ F (482 ⁰ C) to about 975 ⁰ F (524 ⁰ C) for 4 hours and then air cooled. The test specimens were finish machined after aging and tested at room temperature. The results of room temperature tensile and hardness testing are presented in Tables 2 - 4 below including the solution treatment temperature (Solution Temp.) and the aging temperature (Age Temp.) in ⁰ F ( ⁰ C) ₁ the 0.2% offset yield strength (Y.S.) and ultimate tensile strength (U.T.S.) in ksi (MPa), and the Rockwell C-scale hardness (Hardness) as HRC.

Table 2

Table 3

Table 4

* Strength data was lost for these samples. However, the test operator recalls that the U.T.S. for the H900 samples was above 280 ksi (1930.5 MPa) and that the U.T.S. for the H950 samples was slightly under 280 ksi (1930.5 MPa).

Metallographic analysis of the test specimens showed that the material solution treated at 185O ⁰ F (1038 ⁰ C) and 1900 ⁰ F (1038°C) had a grain size of about ASTM 8. The material solution treated at 195O ⁰ F (1065°) had a grain size of about ASTM 7-8. The material solution treated at 2000°F (1093 ⁰ C) had a grain size of about ASTM 2-3. Here and throughout this application, the ASTM grain size means average grain size as determined in accordance with ASTM Standard Test Procedure E-112.

The results presented in Tables 2, 3, and 4 show that the preferred solution temperature is about 1900 ⁰ F (1038 ⁰ C) to about 195O ⁰ F (1065 ⁰ C). Likewise, the preferred aging temperature is about 900 ⁰ F to 925 ⁰ F (482 ⁰ C to 496 ⁰ C) in order for the material to provide the desired 280 ksi (1930.5 MPa) U.T.S. A graph of U.T.S. versus solution and aging temperature combinations is shown in the drawing.

The data presented in the tables show that a strip article made from the alloy composition described in this application is capable of attaining an U.T.S, 280 ksi (1930.5 MPa) or higher. The strip material is much less heavily alloyed than other stainless compositions capable of that strength level, resulting in a lower alloy cost. In addition, the strip material is capable of being solution heat treated more than once without sacrificing strength or toughness properties. The strip material of this invention is preferably solution heat treated at a temperature in range of about 1900-1950 ⁰ F (1038-1065 ⁰ C), making golf club faceplates of this composition fully compatible with the solution treating temperature for the precipitation hardenable stainless casting alloys most often used for the body of golf club head. Therefore, the faceplate and the club head body can be solution treated and age hardened in the assembled configuration to develop maximum hardness and strength, not only in the body of the club head, but also in the faceplate which makes contact with a golf ball.

It will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It is understood, therefore, that the invention is not limited to the particular embodiments that are described, but is intended to cover all modifications and changes within the scope and spirit of the invention as described above and set forth in the appended claims.