Claims
- 1. A stainless steel screw having a corrosion-resistant portion, the screw comprising:
- a core of austenitic stainless steel,
- a hard layer over the entire surface of the austenitic stainless steel core, the hard layer having a thickness of 30-150 .mu.m and a hardness of 320-650 Hv and comprising a solid solution of N, Fe-C and austenitic stainless steel, and
- an ultra hard layer over a portion of the hard layer so as to leave a neck portion or a head portion of the screw of the hard layer forming an external surface of the screw, the ultra hard layer having a thickness of 15-30 .mu.m and a hardness of 1200-1400 Hv and comprising intermetal compounds including an intermetal compound selected from the group consisting of CrN, Cr.sub.2 N, and F.sub.2-3 N;
- the ultra hard layer and the neck portion or head portion of the hard layer together forming the external surface of the screw.
- 2. A stainless steel screw having a corrosion-resistant portion, the screw comprising:
- a core of austenitic stainless steel,
- a hard layer over the entire surface of the austenitic stainless steel core, the hard layer having a thickness of 30-150 .mu.m and a hardness of 320-650 Hv and comprising a solid solution of C, N, Fe-C and austenitic stainless steel; and
- an ultra hard layer over a portion of the hard layer so as to leave a neck portion or a head portion of the screw of the hard layer forming an external surface of the screw, the ultra hard layer having a thickness of 15-30 .mu.m and a hardness of 1200-1400 Hv and comprising intermetal compounds including an intermetal compound selected from the group consisting of CrN, Cr.sub.2 N, and F.sub.2-3 N;
- the ultra hard layer and the exposed neck portion or head portion of the hard layer together forming the external surface of the screw.
- 3. An austenitic stainless steel screw including a corrosion-resistant neck portion or a head portion made by the process of heating an austenitic stainless steel screw in a fluorine-containing atmosphere at a temperature sufficient to form a fluoride layer on the surface of the austenitic stainless steel screw;
- beating the austenitic stainless steel screw coated with the fluoride layer in a nitriding atmosphere at a temperature sufficient to transform the fluoride layer to a nitride layer having a thickness of 45-180 .mu.m; and
- removing 15-30 .mu.m of the surface of the nitride layer of a neck portion of a hard portion of the nitrided austenitic stainless steel screw to be made corrosion-resistant.
- 4. An austenitic stainless steel screw including a corrosion-resistant neck portion or a head portion made by the process of heating an austenitic stainless steel screw in a fluorine-containing atmosphere at a temperature sufficient to form a fluoride layer on the surface of the austenitic stainless steel screw;
- heating the austenitic stainless steel screw coated with the fluoride layer in a nitriding atmosphere at a temperature sufficient to transform the fluoride layer to a carbonitride layer having a thickness of 45-180 .mu.m; and
- removing 15-30 .mu.m of the surface of the nitride layer of a neck portion or a head portion of the nitrided austenitic stainless screw to be made corrosion-resistant.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2-267729 |
Oct 1990 |
JPX |
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Parent Case Info
This is a continuation application of Ser. No. 07/669,440, filed Mar. 13, 1991, which in turn is a continuation-in-part of Ser. No. 479,013, filed Feb. 12, 1990, now U.S. Pat. No. 5,013,371.
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
4184899 |
Blas et al. |
Jan 1980 |
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Foreign Referenced Citations (2)
Number |
Date |
Country |
62-40319 |
Mar 1987 |
JPX |
2006833 |
May 1979 |
GBX |
Continuations (1)
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Number |
Date |
Country |
Parent |
669440 |
Mar 1991 |
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Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
479013 |
Feb 1990 |
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