Swagelok Company

Case Western Reserve University

Steven V Marx

Peter C Williams

Sunniva R Collins

Frank Ernst

Anna V Agaponova

Gerhard H Schiroky

Anna V Agoponova

A workpiece made from a self passivating metal and having one or more surface regions defining a Beilby layer as a result of a previous metal shaping operation is activated for subsequent low temperature gas hardening by exposing the workpiece to the vapors produced by heating an oxygen-free nitrogen halide salt.

Enhanced activation of self-passivating metals

Low temperature gas carburization of stainless steel using acetylene as the carburizing specie is carried out under soft vacuum conditions in the presence of hydrogen or other companion gas. Carburization is made to go faster by including HCl or other carbon-free, halogen-containing activating compound in the carburizing gas being fed to the carburization reactor.

Concurrent flow of activating gas in low temperature carburization

Low temperature carburization of stainless steel using acetylene as the carburizing specie is carried out under soft vacuum conditions in the presence of hydrogen or other companion gas. As a result, formation of soot and the undesirable thermal oxide film that normally occurs during low temperature carburization is eliminated virtually completely.

Low temperature carburization under soft vacuum

An iron-containing workpiece is case hardened by low temperature carburization during which one or more process steps&mdash;including adjusting the carburization temperature, adjusting the concentration of carburization specie in the carburization gas and reactivating the surfaces to be carburized&mdash;is carried out to enhance the overall rate and uniformity of carburization with minimized soot generation, whereby carburization can be completed faster than possible in the past.

Modified low temperature case hardening processes

A method for case hardening a chromium bearing nickel or ferrous based alloy, for example stainless steel, article, the method including the steps of activating the surface of the article; and carburizing the activated surface at a temperature below that temperature which would promote the formation of carbides. In one embodiment the surface is activated by disposing a layer of iron over the surface of the article.

Low temperature case hardening processes

A selectively case hardened steel article by low temperature carburization includes a body made of a chromium bearing nickel or ferrous based alloy (for example, stainless steel), a first portion of the body having a first hardness characteristic, and a second portion of the body having a second hardness characteristic; the second portion being less than the entire body and substantially free of carbides. One method for selective case hardening by low temperature carburization includes the steps of applying a carbon blocking mask over surface areas of the article that are not going to be carburized; activating those surface areas that are to be carburized; diffusing carbon into the activated surface areas at a temperature below which carbides readily form; and removing the carbon blocking mask.

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University Heights, OH, United States of America

Steven V Marx