U.S. patent application number 10/916653 was filed with the patent office on 2006-02-16 for case-hardened stainless steel foundry alloy and methods of making the same.
This patent application is currently assigned to Coastcast Corporation. Invention is credited to Jose Monterrosa, Rahbar Nasserrafi, Mike Wyte.
Application Number | 20060032556 10/916653 |
Document ID | / |
Family ID | 34979819 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060032556 |
Kind Code |
A1 |
Nasserrafi; Rahbar ; et
al. |
February 16, 2006 |
Case-hardened stainless steel foundry alloy and methods of making
the same
Abstract
A case-hardened stainless steel part and method of making the
same are disclosed. The part comprises a case defining a first
layer proximate the outer surface of the part and a core defining a
second layer adjacent the case and distal from the outer surface.
The core has a hardness of from about 80 on the Rockwell Hardness B
Scale to about 50 on the Rockwell Hardness C Scale. The case has a
hardness of not less than about 30 equivalence on the Rockwell
Hardness C Scale.
Inventors: |
Nasserrafi; Rahbar; (Chula
Vista, CA) ; Wyte; Mike; (Culver City, CA) ;
Monterrosa; Jose; (Southgate, CA) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Assignee: |
Coastcast Corporation
Rancho Dominguez
CA
|
Family ID: |
34979819 |
Appl. No.: |
10/916653 |
Filed: |
August 11, 2004 |
Current U.S.
Class: |
148/225 ;
148/233; 148/319 |
Current CPC
Class: |
C22C 38/04 20130101;
A63B 53/047 20130101; C21D 6/00 20130101; C22C 38/22 20130101; C22C
38/02 20130101; C21D 1/06 20130101; A63B 53/04 20130101; C21D 1/18
20130101; A63B 60/00 20151001; A63B 2209/00 20130101; C21D 9/00
20130101; C23C 8/22 20130101; C21D 6/04 20130101 |
Class at
Publication: |
148/225 ;
148/233; 148/319 |
International
Class: |
C23C 8/22 20060101
C23C008/22 |
Claims
1. A case-hardened, cast part formed from a stainless steel alloy,
the alloy comprising: chromium in an amount of from about 15.5 to
about 18.5 percent by weight of the alloy; carbon in an amount of
from about 0.13 to about 0.29 percent by weight of the alloy;
manganese in an amount up to about 1.5 percent by weight of the
alloy; silicon in an amount of from about 0.25 to about 1.5 percent
by weight of the alloy; molybdenum in an amount up to about 1.0
percent by weight of the alloy; and iron present in a remaining
amount of the alloy; wherein said cast part has an outer surface
and a case, said case defining a first layer of said part proximate
said surface, said cast part further comprising a core, said core
defining a second layer of said cast part adjacent to said case and
distal from said surface, wherein said core has a hardness of from
about HRB 80 to HRC 50 and said case has a hardness of not less
than about HRC 30 equivalence.
2. The cast part of claim 1, wherein said case further has a
thickness of from about 0.002 inches to about 0.035 inches.
3. The cast part of claim 1, wherein said part has a yield strength
of not more than about 125,000 psi.
4. The cast part of claim 1, wherein said amount of chromium is
from about 15.5 to about 18.0 percent by weight of the alloy.
5. The cast part of claim 1, wherein said amount of chromium is
from about 16.5 to about 18.0 percent by weight of the alloy.
6. The cast part of claim 1, wherein said amount of carbon is from
about 0.13 to about 0.24 percent by weight of the alloy.
7. The cast part of claim 1, wherein said amount of carbon is from
about 0.13 to about 0.21 percent by weight of the alloy.
8. The cast part of claim 1, wherein said amount of manganese is
from about 0.3 to about 1.0 percent by weight of the alloy.
9. The cast part of claim 1, wherein said amount of manganese is
from about 0.3 to about 0.6 percent by weight of the alloy.
10. The cast part of claim 1, wherein said amount of molybdenum is
from about 0.25 to about 0.5 percent by weight of the alloy.
11. The cast part of claim 1, wherein said amount of silicon is
from about 0.3 to about 1.0 percent by weight of the alloy.
12. The cast part of claim 1, wherein said amount of silicon is
from about 0.3 to about 0.8 percent by weight of the alloy.
13. A golf club head formed from the cast part of claim 1.
14. The golf club head of claim 13, comprising a wedge-shaped
striking surface.
15. The cast part of claim 1, wherein the case has a carbon
concentration and the core has a carbon concentration, said case
carbon concentration being higher than said core carbon
concentration.
16. A case-hardened, cast part formed from a stainless steel alloy,
the alloy comprising: chromium in an amount of from about 15.5 to
about 18.5 percent by weight of the alloy; wherein said cast part
has an outer surface and a case defining a first layer proximate
said outer surface, said part further comprising a core defining a
second layer of said part adjacent said case and distal from said
surface, wherein said core has a hardness of from about HRB 80 to
about HRC 50 and said case has a hardness of not less than about
HRC 30 equivalence.
17. The cast part of claim 16, wherein the alloy further comprises
carbon in an amount of from about 0.13 to about 0.29 percent by
weight of the alloy.
18. The cast part of claim 17, wherein said amount of carbon is
from about 0.13 to about 0.21 percent by weight of the alloy.
19. The cast part of claim 16, wherein the alloy further comprises
manganese in an amount up to about 1.5 percent of the alloy.
20. The cast part of claim 19, wherein said amount of manganese is
from about 0.3 to about 0.6 percent by weight of the alloy.
21. The cast part of claim 16, wherein the alloy further comprises
silicon in an amount of from about 0.25 to about 1.5 percent by
weight of the alloy.
22. The cast part of claim 21, wherein said amount of silicon is
from about 0.3 to about 0.8 percent by weight of the alloy.
23. The cast part of claim 16, wherein the alloy further comprises
molybdenum in an amount up to about 1.0 percent by weight of the
alloy.
24. The cast part of claim 23, wherein said amount of molybdenum is
from about 0.25 to about 0.5 percent by weight of the alloy.
25. The cast part of claim 16, wherein said amount of chromium is
from about 16.5 to 18 percent by weight of the alloy.
26. A golf club head formed from the stainless steel cast part of
claim 16.
27. The golf club head of claim 26, wherein said golf club head
comprises a wedge-shaped striking surface.
28. The cast part of claim 16, wherein said case has a thickness of
from about 0.002 inches to about 0.035 inches.
29. The cast part of claim 16, wherein the case has a carbon
concentration and the core has a carbon concentration, said case
carbon concentration being higher than said core carbon
concentration.
30. A method of forming a case-hardened, stainless steel cast part,
comprising the steps of: providing a cast part formed from an alloy
comprising chromium in an amount of from about 15.5 to about 18.5
percent by weight of the alloy; and carburizing said cast part at a
temperature of from about 1600.degree. F. to about 1900.degree. F.
for a period of from about 1 hour to less than about 2 hours.
31. The method of claim 30, further comprising homogenizing said
cast part at a temperature of from about 1900.degree. F. to about
2100.degree. F. for a period of about 1 to about 4 hours.
32. The method of claim 31 wherein said homogenizing temperature is
about 2100.degree. F.
33. The method of claim 31, wherein said period of homogenizing is
about 1.5 hours.
34. The method of claim 30, further comprising preheating said cast
part at a temperature of from about 1100.degree. F. to about
1400.degree. F. for a period of about 30 minutes to 1 hour before
said carburizing step.
35. The method of claim 34, wherein said preheating temperature is
about 1200.degree. F.
36. The method of claim 34, wherein said period of preheating is
about 30 minutes.
37. The method of claim 30, further comprising quenching said cast
part with a fluid having a temperature of from about 100.degree. F.
to about 200.degree. F. for a period of about 5 to about 15
minutes.
38. The method of claim 37, wherein said fluid is oil.
39. The method of claim 30, further comprising cooling said cast
part at a temperature of not more than about -100.degree. F. for a
period of about 1 to about 3 hours.
40. The method of claim 39, wherein said cooling temperature is
about -100.degree. F.
41. The method of claim 39, wherein said cooling period is about 2
hours.
42. The method of claim 30, further comprising tempering said cast
part at a temperature of from about 200 to about 600.degree. F. for
a period of about 1 to about 3 hours.
43. The method of claim 42, wherein said tempering temperature is
about 300.degree. F.
44. The method of claim 30, wherein the alloy further comprises
carbon in an amount of from about 0.13 to about 0.29 percent by
weight of the alloy.
45. The method of claim 44, wherein said amount of carbon is from
about 0.13 to about 0.24 percent by weight of the alloy.
46. The method of claim 44, wherein said amount of carbon is from
about 0.13 to about 0.21 percent by weight of the alloy.
47. The method of claim 30, wherein the alloy further comprises
manganese in an amount up to about 1.5 percent by weight of the
alloy.
48. The method of claim 47, wherein said amount of manganese is
from about 0.3 to about 1.0 percent by weight of the alloy.
49. The method of claim 47, wherein said amount of manganese is
from about 0.3 to about 0.6 percent by weight of the alloy.
50. The method of claim 30, wherein the alloy further comprises
silicon in an amount of from about 0.25 to about 1.5 percent by
weight of the alloy.
51. The method of claim 50, wherein said amount of silicon is from
about 0.3 to about 1.0 percent by weight of the alloy.
52. The method of claim 50, wherein said amount of silicon is from
about 0.3 to about 0.8 percent by weight of the alloy.
53. The method of claim 30, wherein the alloy further comprises
molybdenum in an amount up to about 1.0 percent of the alloy.
54. The method of claim 53, wherein the amount of molybdenum is
from about 0.25 to about 0.5 percent by weight of the alloy.
55. The method of claim 30, wherein said amount of chromium is from
about 15.5 to about 18.0 percent by weight of the alloy.
56. The method of claim 30, wherein said amount of chromium is from
about 16.5 to about 18.0 percent by weight of the alloy.
57. The method of claim 30, wherein said period of carburizing is
about 1 hour.
58. The method of claim 30, wherein said carburizing temperature is
about 1800.degree. F.
59. A method of forming a golf club head according to the method of
claim 30, wherein said cast part is prepared by forming the alloy
into the shape of a golf club head.
60. A golf club head prepared by the method of claim 59.
61. The method of claim 30, wherein said carburizing step forms a
case in the cast part defining a first layer and a core in the cast
part defining a second layer, wherein said core has a hardness of
from about HRB 80 to about HRC 50 and said case has a hardness of
not less than about HRC 30 equivalence.
62. A method of making a golf club head, comprising: a. providing a
steel alloy comprising chromium in an amount of from about 15.5 to
about 18.5 percent by weight of the alloy; b. forming said alloy
into a part having the shape of a golf club head; c. preheating
said part; d. carburizing said part; e. quenching said part with a
fluid; f. cooling said part; and g. tempering said part.
63. The method of claim 62, wherein said forming step is performed
by investment casting.
64. The method of claim 62, wherein said carburizing step is
conducted at a temperature of from about 1600.degree. F. to
1900.degree. F. for a period of about 1 to 3 hours.
65. The method of claim 64, wherein said carburizing temperature is
about 1800.degree. F. and said period of carburizing is about 1
hour.
66. The method of claim 62, wherein said amount of chromium is from
about 16.5 to about 18 percent of the alloy.
67. The method of claim 62, further comprising homogenizing said
part.
68. The method of claim 62, wherein said preheating step is
conducted at a temperature of from about 1100.degree. F. to about
1400.degree. F. for a period of about 30 minutes to about 1
hour.
69. The method of claim 68, wherein said preheating temperature is
about 1200.degree. F.
70. The method of claim 62, wherein said fluid has a temperature of
from about 100.degree. F. to about 200.degree. F. during said
quenching step.
71. The method of claim 62, wherein said cooling step is conducted
at a temperature of not more than about -100.degree. F. for a
period of about 1 to about 3 hours.
72. The method of claim 71, wherein said cooling temperature is
about -100.degree. F. and said period of cooling is about 2
hours.
73. The method of claim 62, wherein said tempering step is
conducted at a temperature of from about 200.degree. F. to about
600.degree. F. for a period of about 1 to about 3 hours.
74. The method of claim 62, wherein said tempering temperature is
about 300.degree. F.
75. The method of claim 62, wherein said alloy further comprises
carbon in an amount of from about 0.13 to about 0.29 percent by
weight of the alloy.
76. The method of claim 75, wherein said amount of carbon is from
about 0.13 to about 0.21 percent by weight of the alloy.
77. The method of claim 62, wherein said alloy further comprises
manganese in an amount up to about 1.5 percent by weight of the
alloy.
78. The method of claim 62, wherein said amount of manganese is
from about 0.3 to about 0.6 percent by weight of the alloy.
79. The method of claim 62, wherein said alloy further comprises
silicon in an amount of from about 0.25 to about 1.5 percent by
weight of the alloy.
80. The method of claim 79, wherein said amount of silicon is from
about 0.3 to about 0.8 percent by weight of the alloy.
81. The method of claim 62, wherein said alloy further comprises
molybdenum in an amount up to about 1.0 percent by weight of the
alloy.
82. The method of claim 81, wherein said amount of molybdenum is
from about 0.3 to about 0.8 percent by weight of the alloy.
83. The method of claim 62, wherein said amount of chromium is from
about 16.5 to about 18 percent by weight of the alloy.
84. The method of claim 62, wherein said part includes an outer
surface, and wherein said carburizing step forms a case defining a
first layer of said part proximate said outer surface and a core
defining a second layer of said part adjacent to said case and
distal from said surface, and wherein said core has a hardness of
from about HRB 80 to about HRC 50 and said case has a hardness of
not less than about HRC 30 equivalence.
85. The method of claim 62, further comprising polishing said
part.
86. The method of claim 62, wherein said step of forming said alloy
into a part having the shape of a golf club head includes forming
said alloy into a part having a wedge-shaped striking surface.
87. The method of claim 62, wherein said fluid is oil.
88. The method of claim 63, wherein said investment casting
comprises preparing a casting mold by (i) providing a temporary
preform shaped in the form of a golf club head; (ii) surrounding
said preform with a refractory slurry; (iii) hardening said
refractory slurry; (iv) melting said preform; (v) and removing said
melted preform from said hardened refractory slurry, wherein the
hardened refractory slurry is the casting mold.
89. The method of claim 88, wherein said forming step further
comprises heating said alloy and pouring it into said casting
mold.
90. The method of claim 67, wherein said homogenizing step is
conducted at a temperature of from about 1900.degree. F. to about
2100.degree. F. for a period of from about 1 to 4 hours.
91. The method of claim 67, wherein said homogenizing step is
conducted at a temperature of about 2100.degree. F. for a period of
about 1.5 hours.
92. A method of making a golf club head, comprising: a. preparing a
casting mold by (i) providing a temporary preform shaped in the
form of a golf club head, (ii) surrounding said preform with a
refractory slurry, (iii) hardening said refractory slurry, (iv)
melting said preform, and (iv) removing said melted preform from
said hardened refractory slurry, wherein the hardened refractory
slurry is the casting mold; b. combining chromium in an amount of
from about 16.5 to about 18.0 percent by weight, carbon in an
amount of from about 0.13 to about 0.21 percent by weight,
manganese in an amount of from about 0.3 to about 0.6 percent by
weight, silicon in an amount of from about 0.3 to about 0.8 percent
by weight and molybdenum in an amount of from about 0.25 to about
0.5 percent by weight, with iron present in a remaining amount; c.
melting the combined ingredients to form a mixture; d. pouring the
mixture into said casting mold to form a cast part; e. removing
said cast part from said casting mold, said cast part having an
outer surface; f. homogenizing the cast part at a temperature of
about 2100.degree. F. for about 1.5 hours; g. preheating the cast
part at a temperature of about 1200.degree. F. for a period of
about 30 minutes to about 1 hour; h. carburizing said cast part at
a temperature of about 1800.degree. F. for about 1 hour, thereby
forming a case having a carbon concentration, said case defining a
first layer of said cast part proximate said outer surface, and a
core having a carbon concentration, said core defining a second
layer of said cast part adjacent to said case and distal from said
surface, said case carbon concentration being higher than said core
carbon concentration; i. quenching said cast part with a fluid
having a temperature of from about 100.degree. F. to about
200.degree. F. for a period of about 5 to about 15 minutes; j.
cooling said cast part at a temperature of about -100.degree. F.
for about 2 hours; k. tempering said cast part at a temperature of
about 300.degree. F. for about 1 to about 3 hours; and l. polishing
said part; wherein said core has a hardness of from about HRB 80 to
about HRC 50, said case has a hardness of not less than about HRC
30 equivalence and said part has a yield strength of not more than
about 125,000 psi.
93. A golf club head prepared by: a. preparing a casting mold by
(i) providing a temporary preform shaped in the form of a golf club
head, (ii) surrounding said preform with a refractory slurry, (iii)
hardening said refractory slurry, (iv) melting said preform, and
(iv) removing said melted wax mold from said hardened refractory
slurry, wherein the hardness refractory slurry is the casting mold;
b. combining chromium in an amount of from about 16.5 to about 18.0
percent by weight, carbon in an amount of from about 0.13 to about
0.21 percent by weight, manganese in an amount of from about 0.3 to
about 0.6 percent by weight, silicon in an amount of from about 0.3
to about 0.8 percent by weight and molybdenum in an amount of from
about 0.25 to about 0.5 percent by weight, with iron present in a
remaining amount; c. melting the combined ingredients to form a
mixture; d. pouring the mixture into said casting mold to form a
cast part; e. removing said cast part from said casting mold, said
cast part having an outer surface; f. homogenizing the cast part at
a temperature of about 2100.degree. F. for about 1.5 hours; g.
preheating the cast part at a temperature of about 1200.degree. F.
for a period of about 30 minutes to about 1 hour; h. carburizing
the cast part at a temperature of about 1800.degree. F. for about 1
hour, thereby forming a case having a carbon concentration, said
case defining a first layer of said cast part proximate said outer
surface, and a core having a carbon concentration, said core
defining a second layer of said cast part adjacent to said case and
distal from said surface, said case carbon concentration being
higher than said core carbon concentration; i. quenching said cast
part with a fluid having a temperature of from about 100.degree. F.
to 200.degree. F. for a period of about 5 to 15 minutes; j. cooling
said cast part at a temperature of about -100.degree. F. for about
2 hours; k. tempering said cast part at a temperature of about
300.degree. F. for about 1 to about 3 hours; and l. polishing said
part; wherein said core has a hardness of from about HRB 80 to
about HRC 50, said case has a hardness of not less than about HRC
30 equivalence, and said part has a yield strength of not more than
about 125,000 psi.
94. A case-hardened, stainless steel cast part prepared by: a.
providing a casting mold; b. combining chromium in an amount of
from about 16.5 to about 18.0 percent by weight, carbon in an
amount of from about 0.13 to about 0.21 percent by weight,
manganese in an amount of from about 0.3 to about 0.6 percent by
weight, silicon in an amount of from about 0.3 to about 0.8 percent
by weight and molybdenum in an amount of from about 0.25 to about
0.5 percent by weight, with iron present in a remaining amount; c.
melting the combined ingredients to form a stainless steel mixture;
d. pouring the stainless steel mixture into said casting mold to
form a cast part; e. removing said cast part from said casting
mold, said cast part having a surface; f. homogenizing the cast
part at a temperature of about 2100.degree. F. for about 1.5 hours;
g. preheating the cast part at a temperature of about 1200.degree.
F. for a period of about 30 minutes to about 1 hour; h. carburizing
the cast part at a temperature of about 1800.degree. F. for about 1
hour thereby forming a case having a carbon concentration, said
case defining a first layer of said cast part proximate said
surface, and a core having a carbon concentration, said core
defining a second layer of said cast part adjacent to said case and
distal from said surface, said case carbon concentration being
higher than said core carbon concentration; i. quenching said cast
part with oil having a temperature of from about 100.degree. F. to
about 200.degree. F. for a period of about 5 to about 15 minutes;
j. cooling said cast part at a temperature of about -100.degree. F.
for about 2 hours; k. tempering said cast part at a temperature of
about 300.degree. F. for about 1 to about 3 hours; and l. polishing
said cast part; wherein said core has a hardness of from about HRB
80 to about HRC 50, said case has a hardness of not less than about
HRC 30 equivalence, and said part has a yield strength of not more
than about 125,000 psi.
95. A method of case hardening a steel cast part, comprising: a.
providing a cast steel part having an outer surface; b.
homogenizing said part at a temperature of about 2100.degree. F.
for about 1.5 hours; c. preheating said part at a temperature of
about 1200.degree. F. for a period of about 30 minutes to about 1
hour; d. carburizing said part at a temperature of about
1800.degree. F. for about 1 hour, thereby forming a case defining a
first layer and a core defining a second layer; e. quenching said
part with oil having a temperature of from about 100.degree. F. to
about 200.degree. F. for a period of about 5 to about 15 minutes;
f. refrigerating said part at a temperature of about -100.degree.
F. for about 2 hours; g. tempering said part at a temperature of
about 300.degree. F. for about 1 to about 3 hours; and h. polishing
said cast steel part; wherein said core has a hardness of from
about HRB 80 to about HRC 50 and said case has a hardness of not
less than about HRC 30 equivalence.
96. The cast part of claim 1, wherein said core has a hardness of
from about HRC 20 to about HRC 34.
97. The cast part of claim 1, wherein said case has a hardness of
not less than about HRC 50 equivalence.
98. The cast part of claim 16, wherein said core has a hardness of
from about HRC 20 to about HRC 34.
99. The cast part of claim 16, wherein said case has a hardness of
not less than about HRC 50 equivalence.
Description
FIELD OF THE INVENTION
[0001] The present application relates to hardenable stainless
steels and, more particularly, to case hardened stainless steels
suitable for the manufacture of golf club heads.
BACKGROUND OF THE INVENTION
[0002] Many steels suffer from a number of drawbacks when used to
manufacture irons and wedges for golf club heads. For example, golf
professionals generally like clubs with a balance of corrosion
resistance and "feel," which relates to the balance of surface
hardness and core hardness, as well as a high degree of polish. The
core hardness is generally responsible for the feel of the club,
while the surface hardness is generally responsible for the
aesthetic appearance of the club, as well as its corrosion
resistance and scratch resistance. The lack of stainless casting
alloys with the desired properties has forced golf club designers
to use chrome plated alloys for such applications. However, chrome
plating is expensive and environmentally undesirable. Thus, a need
has arisen for an alloy and method of manufacture which addresses
the foregoing problems.
SUMMARY OF THE PREFERRED EMBODIMENTS
[0003] In accordance with one aspect of the present invention, a
case-hardened stainless steel part is provided. The part is formed
from a stainless-steel alloy, wherein the alloy generally comprises
chromimum in an amount of from about 15.5 to about 18.5 percent by
weight of the alloy and preferably includes carbon in an amount of
from about 0.13 to about 0.29 percent by weight of the alloy,
manganese in an amount of up to about 1.5 percent by weight of the
alloy, silicon in an amount of from about 0.25 to about 1.5 percent
by weight of the alloy and molybdenum in an amount up to about 1.0
percent by weight of the alloy, with iron present in a remaining
amount based on the total weight of the alloy.
[0004] The cast part preferably has an outer surface and a case
that defines a first layer proximate the outer surface. The cast
part further comprises a core that defines a second layer distal
from the outer surface. The core preferably has a hardness from
about HRB 80 (Rockwell Hardness B Scale) to about HRC 50 (Rockwell
Hardness C Scale) and more preferably has a hardness from about HRC
20 to about HRC 34. The case preferably has a hardness of not less
than about HRC 30 equivalence, and more preferably has a hardness
of not less than about HRC 50 equivalence. It is also preferred
that the case and core each have a carbon concentration, with the
carbon concentration in the case being higher than that in the
core.
[0005] In another aspect of the present invention, a method of
making a case-hardened stainless steel part is provided. The method
comprises providing a cast part formed from a stainless steel
alloy, wherein the alloy comprises chromium, generally in an amount
of from about 15.5 to about 18.5 percent by weight of the alloy,
and carburizing the part. Preferably the carburization is conducted
at a temperature of from about 1600.degree. F. to about
1900.degree. F. for a period of from about 1 hour to less than
about 2 hours.
[0006] In another aspect of the present invention, a method of
making a golf club head is provided. According to the method, a
steel alloy comprising chromium in an amount from about 15.5 to
about 18.5 percent by weight of the alloy is formed into a part
having a shape of a golf club head. Preferably, the part is
preheated, carburized, quenched, cooled, and tempered. More
preferably, it includes an outer surface and has a case defining a
first layer proximate the outer surface and a core defining a
second layer adjacent the first layer and distal from the outer
surface, wherein the core has a hardness which is preferably from
about HRB 80 to about HRC 50, and more preferably from about HRC 20
to about HRC 34. The case has a hardness which is preferably not
less than about HRC 30 equivalence and is more preferably not less
than about HRC 50 equivalence.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The invention may be more readily understood by referring to
the accompanying drawing in which:
[0008] FIG. 1 is a perspective view of a golf club head in
accordance with a preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0009] The present invention is directed to stainless steel alloy
parts and methods of making the same. One particular part for which
the invention is well-suited is in the manufacture of golf club
heads.
[0010] An embodiment of a case-hardened stainless steel part in
accordance with the present invention will now be described.
According to this embodiment, the part is formed from a stainless
steel alloy that generally comprises chromium in an amount of from
about 15.5 to about 18.5 percent by weight of the alloy, carbon in
an amount of from about 0.13 to about 0.29 percent by weight of the
alloy, manganese in an amount of up to about 1.5 percent by weight
of the alloy, silicon in an amount of from about 0.25 to about 1.5
percent by weight of the alloy and molybdenum in an amount up to
about 1.0 percent by weight of the alloy, with iron present in a
remaining amount of the alloy, except for trace impurities
typically found in commercial grades of stainless steels. For
example, the alloy may include trace elements of up to about 0.03
weight percent sulfur, up to about 0.02 weight, and up to about
0.03 weight percent nitrogen.
[0011] The alloy more preferably comprises chromium in an amount of
from about 16.5 to about 18.5 percent by weight of the alloy,
carbon in an amount of from about 0.13 to about 0.24 percent by
weight of the alloy, manganese in an amount of from about 0.3 to
about 1.0 percent by weight of the alloy, molybdenum in an amount
of from about 0.25 to about 0.5 percent by weight of the alloy, and
silicon in an amount of from about 0.3 to about 1.0 percent by
weight of the alloy. It is especially preferred that the amount of
chromium is from about 16.5 to about 18.0 percent by weight of the
alloy, the amount of carbon is from about 0.13 to about 0.21
percent by weight of the alloy, the amount of manganese is from
about 0.3 to about 0.6 percent by weight of the alloy, the amount
of molybdenum is from about 0.25 to about 0.5 percent by weight of
the alloy and the amount of silicon is from about 0.3 to about 0.8
percent by weight of the alloy.
[0012] According to this embodiment, the cast part has an outer
surface and a case that defines a first layer proximate the outer
surface. The cast part further includes a core that defines a
second layer distal from the outer surface.
[0013] The layers comprising the case and core are preferably
defined in the part as a result of carburizing the part at a
temperature of from about 1600.degree. F. to about 1900.degree. F.
for a period of from about 1 hour to less than about 2 hours. A
carburization temperature of about 1800.degree. F. and a
carburization period of about 1 hour are especially preferred.
According to this embodiment, the part is preferably homogenized
prior to carburization at a temperature of from about 1900.degree.
F. to about 2100.degree. F. for a period of about 1 to about 4
hours. A homogenization temperature of about 2100.degree. F. and a
homogenization period of about 1.5 hours are especially preferred.
The carburization process will modify the carbon content of the
part by providing a locally higher carbon concentration closer to
the outer surface of the part. However, the weight percentages of
carbon recited herein refer to the condition of the cast steel part
before it is carburized.
[0014] Prior to carburizing it, the part is preferably preheated at
a temperature of from about 1100.degree. F. to about 1400.degree.
F. for a period commensurate with the thickness of the part, most
preferably between about 30 minutes and about 1 hour. More
preferably, the preheating step follows the homogenization step and
precedes the carburization step. A preheat temperature of about
1200.degree. F. is especially preferred.
[0015] The part is also preferably quenched from the preheated
temperature in a fluid, which is preferably oil. The quenching more
preferably follows the carburization step and is conducted at a
fluid temperature of from about 100.degree. F. to about 200.degree.
F. for a period of about 5 minutes to about 15 minutes. It is
especially preferred to conduct the quenching at a fluid
temperature of about 200.degree. F. for a period of about 10
minutes.
[0016] In addition, the part is preferably cooled. More preferably,
the cooling follows the quenching and is conducted at a temperature
of not more than about -100.degree. F. for a period of about 1 to
about 3 hours. A temperature of about -100.degree. F. and a period
of about 2 hours are especially preferred. It is especially
preferred that the cooling be performed using known refrigeration
processes.
[0017] According to this embodiment, the part is also preferably
tempered. More preferably, the tempering follows the cooling step
and is conducted at a temperature of from about 200 to about
600.degree. F. for a period of from about 1 to about 3 hours. A
temperature of about 300.degree. F. and a period of about 2 hours
are especially preferred. If necessary to achieve the desired core
and case hardness, this tempering step can be repeated by again
tempering the part at about 600.degree. F., and if necessary, at
about 1400.degree. F.
[0018] The part is preferably polished after tempering. The
polishing generally removes from about 0.002 to about 0.006 inches,
preferably removes from about 0.002 to about 0.004 inches and more
preferably removes from about 0.002 to about 0.003 inches from the
surface of the casting.
[0019] The methods and compositions disclosed herein will generally
produce a core having a hardness that is preferably from about HRB
80 to about HRC 50, and more preferably from about HRC 20 to about
HRC 34. After tempering and polishing, the methods and compositions
disclosed herein will generally produce a case having a hardness
that is preferably not less than about HRC 30 equivalence, and more
preferably not less than about HRC 50 equivalence. Parts having a
core hardness in the foregoing ranges will typically have a yield
strength of not more than about 125,000 psi. Without wishing to be
bound by any theory, it is believed that the composition, the
degree of carburization and the tempering conditions all contribute
to the core hardness and yield strength. The post-polishing
thickness of the case as measured from the outer surface of the
part is preferably from about 0.002 to about 0.035 inches, more
preferably from about 0.002 to about 0.030 inches, and is
preferably uniform throughout the part.
[0020] As mentioned above, the alloys and processing methods
described herein are especially suited for making golf club heads.
An embodiment of a method for making a golf club head in accordance
with the present invention will now be described. According to this
embodiment, a steel alloy comprising chromium in an amount
generally ranging from about 15.5 to about 18.5 percent of the
alloy is formed into the shape of a golf club head, preferably one
with a wedge-shaped striking surface. Preferably, an investment
casting process is used to form a mold for shaping the alloy into
the shape of a golf club head.
[0021] More preferably, the investment casting process comprises
providing a temporary preform--for example, a wax preform--shaped
in the form of a golf club head and surrounding the preform with a
refractory slurry and refractory stucco. Several layers of slurry
and stucco are preferably applied until the required thickness is
obtained. The completed shell is then placed into an autoclave for
removal of the wax preform. The shell is then placed into a preheat
oven and its temperature is raised until the required temperature
for pouring the steel alloy is reached. The steel alloy is then
melted and poured into the preheated mold. After sufficient
cooling, the part is then removed from the hardened slurry
mold.
[0022] Following removal from the mold, the part is case-hardened
by carburizing it, preferably after preheating it. Following
carburization, the part is preferably quenched from its preheated
temperature with a fluid, preferably an oil, and then cooled. The
part is preferably tempered and polished following the cooling step
to produce the final part. Although a variety of temperatures and
times can be used for each of the foregoing steps, the temperatures
and times set forth above for the steps of preheating, carburizing,
quenching, cooling and tempering are preferred. It is further
preferred to homogenize the golf club head, more preferably prior
to the preheating step and using the temperatures and periods set
forth above.
[0023] Referring to FIG. 1, a golf club head prepared in accordance
with a preferred embodiment of the present invention is depicted.
Golf club 10 generally comprises a head 30 and a shaft 20 (only a
portion of which is depicted in FIG. 1). Head 30 includes an outer
surface 40. Face 35 comprises a portion of outer surface 40 used to
strike a golf ball. Golf club heads prepared according to this
embodiment of the invention will preferably comprise a case 50
defining a first layer proximate the outer surface 40. They will
also preferably comprise a core 50 defining a second layer adjacent
the case 50 and distal from the outer surface 40. The core 60 will
preferably have a hardness of from about HRB 80 to about HRC 50,
and more preferably from about HRC 20 to about HRC 34. The case 50
will preferably have a hardness of not less than about HRC 30
equivalence and more preferably not less than about HRC 50
equivalence. Preferably, head 30 will have a yield strength of not
more than about 125,000 psi. The post-polishing thickness of the
case 50 as measured from the outer surface 40 of the part is
preferably from about 0.002 to about 0.035 inches, more preferably
from about 0.002 to about 0.030 inches, and is preferably uniform
throughout head 30.
[0024] As mentioned above, the steel alloy used for manufacturing
golf club heads in accordance with this embodiment generally
comprises chromium in an amount of from about 15.5 to about 18.5
percent by weight of the alloy. A chromium content of about 15.5 to
about 18 percent by weight of the alloy is more preferred, and a
chromium content of about 16.5 to about 18 percent by weight of the
alloy is especially preferred. Preferably, the alloy further
comprises carbon in an amount of from about 0.13 to about 0.29
percent by weight of the alloy. An amount of from about 0.13 to
about 0.24 percent by weight of the alloy is more preferred, and an
amount from about 0.13 to about 0.21 percent by weight of the alloy
is especially preferred.
[0025] The alloy also preferably comprises manganese in an amount
up to about 1.5 percent by weight of the alloy. An amount of from
about 0.3 to about 1.0 percent by weight of the alloy is more
preferred, and an amount of from about 0.3 to about 0.6 percent by
weight of the alloy is especially preferred.
[0026] In addition, the alloy preferably comprises molybdenum in an
amount up to about 1 percent by weight of the alloy, and more
preferably from about 0.25 to about 0.5 percent by weight of the
alloy. It also preferably comprises silicon in an amount of from
about 0.25 to about 1.5 percent by weight of the alloy. An amount
of from about 0.3 to about 1.0 percent by weight of the alloy is
more preferred, and an amount of about 0.3 to about 0.8 percent by
weight of the alloy is especially preferred.
[0027] The invention may be better understood by the following
specific examples of case-hardened stainless steel parts prepared
in accordance with the present invention. Set forth below in Table
1 are experimental results for four samples of alloys that were
case-hardened in accordance with an embodiment of the present
invention. The samples were homogenized for 1.5 hours at a
temperature of 2100.degree. F. and then preheated at a temperature
of 1200.degree. F. for 30 minutes. The samples were then carburized
at 1800.degree. F. for 1 hour. The carbon potentials were set to
obtain a desired case hardness of HRC 62 at a pre-polishing depth
of 0.004 inches from the surface. Following carburization, the
samples were cooled at -100.degree. F. for 2 hours and tempered at
300.degree. F. for 2 hours to achieve the desired core and surface
hardness. The post-tempering hardnesses are shown as "Core Hardness
After Carburization" in Table 1. The parts were subsequently heated
to 600.degree. F. and 1400.degree. F. to further refine the core
hardness. TABLE-US-00001 TABLE 1 Core Hardness Core Hardness Core
Hardness Alloy After After Heating After Heating Element Wt %
Carburization at 600.degree. F. at 1400.degree. F. Sample 1 HRC
29.83 HRC 20.7 HRB 85.9 C 0.16 Si 0.61 Cr 16.97 Mo 0.34 Mn 0.31
Sample 2 HRC 36.2 HRC 30.8 HRB 94.2 C 0.24 Si 0.62 Cr 16.88 Mo 0.39
Mn 0.30 Sample 3 HRC 47.9 HRC 38.8 HRB 96.2 C 0.29 Si 0.62 Cr 16.73
Mo 0.37 Mn 0.30 Sample 4 HRB 97.1 HRB 87.2 HRB 82.9 C 0.13 Si 0.60
Cr 17.15 Mo 0.34 Mn 0.34
[0028] As shown in Table 2, following carburization, the surface
hardness of Samples 1 and 4 was HRC 62 at a depth of 0.004 inches
from the cast surfaces as measured using a 500 g load (Knoop
Hardness). After carburization, samples 1 and 4 were polished to
remove approximately 0.004 inches of the alloy. After polishing,
the samples were sectioned and the transverse microhardness of the
sample surfaces was measured at various depths from the surface of
the sample. Using known visual techniques, the case depth in Sample
1 was determined to be approximately 0.006 inches, and the case
depth in Sample 4 was determined to be approximately 0.035 inches.
As indicated in Table 2, the samples had a case hardness of greater
than HRC 30 equivalence.
[0029] Table 2 includes the transverse microhardness results and
their corresponding depths from the surface of the sample. The
negative signs are used to indicate that the depths are measured
from the surface of the part after polishing. TABLE-US-00002 TABLE
2 Surface Hardness Surface Hardness Sample and Depth (in.) After
Polishing No. Before Polishing at Depth Depth (in.) 4 HRC 62/0.004
HRC 51 -0.002 4 HRC 51 -0.003 4 HRC 38 -0.005 4 HRC 25 -0.009 4 HRB
98 -0.012 4 HRB 98 -0.016 4 HRB 98 -0.035 1 HRC 62/0.004 HRC 32
-0.012 1 HRC 32 -0.016 1 HRC 32 -0.035
[0030] The foregoing embodiments are merely examples of the present
invention. Those skilled in the art may make numerous uses of, and
departures from, such embodiments without departing from the spirit
and the scope of the present invention. Accordingly, the scope of
the present invention is not to be limited to or defined by such
embodiments in any way, but rather, is defined solely by the
following claims.
* * * * *