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US4718908A
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High-strength, cold-forged type 316L stainless steel for orthopedic implant
Assignee: Smith and Nephew Inc
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Filing: 1984-06-04
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Granted: 1988-01-12
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Expires: 2004-06-04
Abstract
Abstract A surgical implant manufactured from austenitic stainless steel by cold-forging has improved mechanical properties and corrosion fatigue resistance. The grain-size index for the cold-forged 316L stainless steel is increased from an ASTM grain-size index of about 8 to an ASTM grain-size index of about 14 by cold-forging the steel into the desired shape. Further improvement in mechanical properties and corrosion fatigue resistance is obtained by stress relieving the material after cold-forging into the desired configuration. The microstructure of the cold-forged material is characterized by the absence of visible slip planes at 600× magnification, in contrast with visible slip planes present in the microstructure of the austenitic stainless steel starting material.
Inventors
- 👤 Robert E. Wigginton
- 👤 Barry Gordon
- 👤 Imogene Baswell
- 👤 Steve Garner
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 20:24
CPC Classifications
A; A61; A61L; A61L27/00; A61L27/02; A61L27/04; A61L27/042; A61F; A61F2/00; A61F2/02; A61F2/30; A61F2/32; A61F2/36; C; C21; C21D; C21D7/00; C21D7/02; C21D7/10; C21D8/00; A61F2310/00; A61F2310/00005; A61F2310/00011; A61F2310/00017; Y; Y10; Y10S; Y10S72/00; Y10S72/70
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
73 words
A corrosion resistant, austenitic, stainless steel prosthetic device, adapted to be implanted in animals, and formed as a result of a method comprising the step of cold forging a starting material consisting essentially of biocompatible 316L stainless steel with a maximum carbon content of about 0.03% until it has a microstructure comprising an ASTM grain-size index above about 14 and having an absence of discernible slip planes at a magnification of about 600×.
Claim 2
Dependent Claim
73 words
A corrosion resistant, austenitic, stainless steel prosthetic device, adapted to be implanted in animals, and formed as a result of a method comprising the step of cold forging a starting material consisting essentially of biocompatible 316L stainless steel with a maximum carbon content of about 0.03% until it has a microstructure comprising an ASTM grain-size index above about 14 and having an absence of discernible slip planes at a magnification of about 600×.
Claim 3
Dependent Claim
41 words
The method of claim 1 wherein the cold-forging step is practiced to alter the ASTM grain-size index of the material from about 8 for the starting material to an ASTM grain-size index of about 14 or higher for the forged material.
Claim 4
Dependent Claim
57 words
The method of claim 2 wherein the starting material is a length of bar stock and the cold forging step includes: initially forging opposite end portions of the bar stock; bending the initially forged bar stock about an intermediate portion thereof; and further forging one end portion of the initially forged, bent stock to a predetermined shape.
Claim 5
Dependent Claim
25 words
The method of claim 3 wherein the initially forging step of the cold forging process includes a rapid reduction in diameter of the starting bar.
Claim 6
Dependent Claim
28 words
The method of claim 3 wherein the further forging step of the cold forging step includes pressing the one end portion of the stock with a shaped die.
Claim 7
Dependent Claim
54 words
The method of claim 5, further comprising the step of: stress relieving the forged material after the rapid reduction step, wherein the stress relieving step includes heating the material to the temperature of about 750° F. (399° C.); and maintaining the material at the temperature for about two hours, followed by ambient air cooling.
Claim 8
Dependent Claim
17 words
The method of claim 6 wherein the cold forging step is practiced to form a surgical implant.
Claim 9
Dependent Claim
13 words
The method of claim 7 wherein the surgical implant is a hip plate.
Claim 10
Dependent Claim
16 words
The method of claim 8 wherein the starting material is formed of Type 316L stainless steel.
Claim 11
Dependent Claim
19 words
The method of claim 9 wherein the pressing step includes applying a force greater than about 700 U.S. tons.
Claim 12
Independent Claim
101 words
A method of manufacturing a surgical implant device from bar stock Type 316L stainless steel starting material below its recrystallization temperature, comprising the steps of: rapidly reducing opposite end portions of the starting material, leaving an intermediate portion unreduced; bending the reduced bar about the intermediate portion to form a predetermined angle between the opposite end portions; pressing one of the end portions into a suitable configuration; and wherein the rapid reduction and pressing steps result in the device having an ASTM grain-size index above about 14 and having an absence of discernable slip planes at a magnification of about 600×.
Claim 13
Independent Claim
101 words
A method of manufacturing a surgical implant device from bar stock Type 316L stainless steel starting material below its recrystallization temperature, comprising the steps of: rapidly reducing opposite end portions of the starting material, leaving an intermediate portion unreduced; bending the reduced bar about the intermediate portion to form a predetermined angle between the opposite end portions; pressing one of the end portions into a suitable configuration; and wherein the rapid reduction and pressing steps result in the device having an ASTM grain-size index above about 14 and having an absence of discernable slip planes at a magnification of about 600×.
Claim 14
Dependent Claim
16 words
The method of claim 11, wherein the device is stress relieved after the cold forging steps.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1991-01-11 | 1991-07-13 | 1992-01-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-01-11 | 1995-07-13 | 1996-01-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-01-11 | 1999-07-13 | 2000-01-12 | $7700.00 | Window Closed / Lapsed |