Nitride casehardening process and the nitrided product thereof
First Claim
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1. A method of nitriding ferrous alloys to harden a surface portion thereof, comprising the combination and sequence of distinct steps of:
- (a) first heating a ferrous alloy article to a high temperature of below about 496°
C., and subjecting said article to an atmosphere comprising anhydrous ammonia;
(b) then displacing at least a portion of the anhydrous ammonia of the atmosphere about the article by the addition of dissociated ammonia;
(c) thereafter heating the article to a temperature of at least about 535°
C.; and
(d) then reducing the level of dissociated ammonia in the atmosphere about the article.
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Abstract
A method of nitriding ferrous alloys for improving the quality and integrity of the resultant case or hardened surface portion formed thereby, comprising the application of a specific combination of sequenced temperature and nitrogen conditions.
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Citations
18 Claims
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1. A method of nitriding ferrous alloys to harden a surface portion thereof, comprising the combination and sequence of distinct steps of:
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(a) first heating a ferrous alloy article to a high temperature of below about 496°
C., and subjecting said article to an atmosphere comprising anhydrous ammonia;(b) then displacing at least a portion of the anhydrous ammonia of the atmosphere about the article by the addition of dissociated ammonia; (c) thereafter heating the article to a temperature of at least about 535°
C.; and(d) then reducing the level of dissociated ammonia in the atmosphere about the article. - View Dependent Claims (2, 3, 4, 5)
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6. A method of nitriding ferrous alloys to harden a surface portion thereof, comprising the combination and sequence of distinct steps of:
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(a) heating a ferrous alloy article to a preceding high temperature stage of below about 496°
C., and subjecting said heated article to an atmosphere comprising anhydrous ammonia;(b) then providing an ammonia atmosphere about the article of greater than about 80% ammonia dissociation by the addition of dissociated ammonia; (c) thereafter heating the article to a subsequent temperature stage of higher than about 535°
C.; and(d) then providing an ammonia atmosphere about the article of about 65 to 75% ammonia dissociation. - View Dependent Claims (7, 8, 9, 10)
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11. A method of nitriding chrome-containing ferrous alloys to harden a surface portion thereof, comprising the combination and sequence of distinct steps of:
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(a) heating a chrome-containing ferrous alloy article to a preceding temperature stage of about 480°
to about 496°
C., and subjecting said heated article to an atmosphere comprising anhydrous ammonia;(b) then displacing at least a portion of the anhydrous ammonia of the atmosphere about the article by the addition of dissociated ammonia in amount providing an ammonia dissociation greater than about 80% in the atmosphere about the article. (c) thereafter heating the article to a subsequent temperature stage of about 570°
to about 858°
C.; and(d) then reducing the ammonia dissociation of the atmosphere about the article to about 65 to about 75%. - View Dependent Claims (12, 13, 14, 15)
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16. A method of nitriding chrome-containing ferrous alloys to harden a surface portion thereof, comprising the combination and sequence of distinct steps of:
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(a) heating a chrome-containing ferrous alloy article to a preceding temperature stage of about 480°
to about 496°
C., and holding the article at said temperature over a period of at least about one-half hour while subjecting said heated article to an atmosphere comprising anhydrous ammonia;(b) then displacing at least a portion of the anhydrous ammonia of the atmosphere about the article by the addition of dissociated ammonia in amount providing an ammonia dissociation greater than about 80% in the atmosphere about the article; (c) thereafter heating the article to a subsequent temperature stage of about 570°
to about 585°
C.; and(d) then reducing the ammonia dissociation of the atmosphere about the article to about 65 to about 75% by proportioning amounts of anhydrous ammonia and dissociated ammonia provided to the atmosphere about the article. - View Dependent Claims (17, 18)
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Specification