Atmosphere compositions and methods of using same for surface treating ferrous metals
AssigneeAir Products and Chemicals, Inc.
InventorEdward J. Arndt
Life of this patent
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Abstract
Atmosphere compositions and processes utilizing the compositions for heat treating ferrous metal articles under a controlled furnace atmosphere to either maintain or change the surface chemistry of the article being treated are disclosed in the following specification. The invention features atmosphere compositions or mixtures which are blended from normally gaseous components outside the furnace and the mixture or blend is injected into the furnace to provide a carburizing, decarburizing, carbonitriding or neutral hardening atmosphere inside the furnace.
Claims19
A gaseous mixture prepared at ambient temperature suitable for injecting into a ferrous metal treating furnace maintained at a temperature in excess of 1500.degree. F. wherein ferrous metal parts are heated in a furnace atmosphere created by the gas mixture injected into the furnace, the atmosphere being variable to perform a treatment selected from the group consisting of carburizing, decarburizing, neutral hardening and carbonitriding, said mixture consisting essentially of 62 to 98% by volume substantially pure nitrogen;
- 1.5 to 30% by volume natural gas being substantially methane;
- 0.2 to 15% by volume substantially pure carbon dioxide;
- the natural gas and carbon dioxide being present in a ratio of 0.5 to 15.0 natural gas/carbon dioxide;
- and
- 0.0 to 10% by volume substantially pure ammonia.
A method of heat treating ferrous articles in a furnace raised to an elevated temperature and under a furnace atmosphere that can be varied to be classified as carburizing, decarburizing, neutral or carbonitriding in character comprising the steps of:
- a. charging the articles to be treated into a furnace maintained at a temperature in excess of 1500.degree. F.;
- b. mixing outside the furnace at ambient temperature a gas composition consisting essentially of 65 to 98% by volume nitrogen, 1.5 to 30% by volume natural gas being substantially methane;
- 0.2 to 15% by volume substantially pure carbon dioxide, 0.0 to 10% by volume substantially pure ammonia, the natural gas and carbon dioxide being present in a ratio of 0.5 to 15.0 natural gas/carbon dioxide;
- c. injecting said mixture into said furnace to form a furnace atmosphere as the articles are being heated;
- d. maintaining said articles at a temperature in the presence of said furnace atmosphere until said parts are in thermal equilibrium with said furnace;
- e. continuing said heating under atmosphere until said parts have been treated by said atmosphere according to the nature of the atmosphere present in said furance;
- and
- f. cooling said articles to ambient temperature.
Dependencies are inferred from the claim text.