Nitrogen assisted hardening of an article

Abstract

A method of heat-treating an article is described. The method includes the steps of depassivating the article at a temperature in a range from about 200 degrees Centigrade to about 300 degrees centigrade, at a pressure in a range from about 0.1 millibar to about 10 millibar in an atmosphere comprising hydrogen and an inert gas, to produce a hot article, heating the hot article to a temperature in a range from about 300 degrees centigrade to about 400 degrees centigrade, at a pressure in a range from about 1 millibar to about 10 millibar in an atmosphere comprising hydrogen, inert gas, nitrogen and a hydrocarbon to produce a preliminary heat-treated article, and maintaining the preliminary heat-treated article at a temperature in a range from about 300 degrees centigrade to about 400 degrees centigrade at a pressure in a range from about 1 millibar to about 10 millibar in an atmosphere comprising hydrogen, inert gas, nitrogen and a hydrocarbon, for a time period in a range from about 10 hours to about 30 hours, to produce the heat-treated article. The heat-treated article retains the appearance of the article prior to heat-treatment.

Dependencies are inferred from the claim text.