US 4,306,918 AGranted

Process for carburizing ferrous metals

AssigneeAir Products and Chemicals, Inc.

InventorsJelle H. Kaspersma, Robert J. Peartree

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Abstract

A process for carburizing steel in a furnace under an atmosphere derived from the decomposition of an oxygenated hydrocarbon containing up to three carbon atoms, no more than one carbon to carbon bond, and a carbon to oxygen ratio of from 1 to 2 such as alcohols, aldehydes, ethers, esters and mixtures thereof. The oxygenated hydrocarbon injected into the furnace produces an atmosphere under which an initial rapid stage of carburization takes place. After the initial rapid stage of carburization gaseous nitrogen is blended into the oxygenated hydrocarbon atmosphere throughout the remainder of the process with a concurrent reduction in the rate of injection of oxygenated hydrocarbon while maintaining volumetric flow through the furnace during the entire carburizing cycle. During the entire carburizing cycle, the carbon potential of the furnace atmosphere can be controlled by addition of a hydrocarbon gas enriching or carburizing agent.

Claims22

Dependent claims

A method of carburizing a ferrous article comprising the steps of:

a. charging the articles to be treated into a furnace maintained at a temperature in excess of 1500.degree. F. (816.degree. C.);
b. injecting into the furnace an oxygenated hydrocarbon containing up to three carbon atoms, no more than one carbon to carbon bond, a carbon to oxygen ratio of from 1 to 2 and a boiling point no greater than 100.degree. C., said oxygenated hydrocarbon selected from the group consisting of alcohols, aldehydes, esters, ethers and mixtures thereof to react and form a carburizing atmosphere in said furnace;
c. establishing and maintaining a rate of injection of said oxygenated hydrocarbon and adding a hydrocarbon gas to maintain a carbon potential of between 0.8 and 1.1% in said furnace atmosphere for at least that portion of the total carburizing process where rapid carburizing occurs;
d. subsequently reducing the rate of oxygenated hydrocarbon injection while maintaining a total injection rate by injecting nitrogen into said furnace to maintain said furnace atmosphere at a carbon potential similar to that for a conventional carburizing atmosphere and for a period of time to complete carburization of said articles to the desired case depth;
and
e. discharging said articles from said furnace and cooling at a rate determined by the desired physical properties of said article.

3 more elements

Dependencies are inferred from the claim text.