The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Oct. 27, 1987
Filed:
Oct. 07, 1986
Michel Madsac, Sceaux, FR;
Rene Mauvoisin, Paris, FR;
L'Air Liquide, Paris, FR;
Abstract
A heat process for producing corrosion resistant steel articles, comprising a first step during which the articles placed in a furnace are nitrided in a gaseous atmosphere to produce on their surface a first layer consisting essentially of epsilon type iron nitride, followed by a second stage during which the articles are exposed to an oxidizing atmosphere to form a second, oxide-rich layer on the surface of the articles. According to the invention, during the first step, an atmosphere comprising 20 to 70% by volume of ammonia NH.sub.3, 1 to 5% by volume of nitrous oxide N.sub.2 O and 25 to 79% by volume of nitrogen N.sub.2 is introduced into the furnace, the concentration ratio of ammonia to nitrous oxide [NH.sub.3 ]/[N.sub.2 O] in the introduced atmosphere being greater than 5 so that the furnace atmosphere is not oxidizing, and during the second step, an atmosphere comprising 0 to 25% by volume NH.sub.3, 0 to 5% by volume N.sub.2 O and 70 to 100% by volume N.sub.2 is introduced into the furnace, the concentration ratio of ammonia to nitrous oxide in the atmosphere introduced in the second step being such that 0.ltoreq.[NH.sub.3 ]/[N.sub.2 O].ltoreq.5, the furnace atmosphere being renewed at a rate of 2 to 5 such that the atmosphere gradually becomes oxidizing. The steel articles thus produced feature a base layer of epsilon type iron nitride over the core, an intermediate layer of iron oxinitride having a thickness of 2 to 12 microns and an outermost surface layer of iron oxide having a thickness of 1 to 7 microns.