Abstract: A method of hardening steel so that it may have a surface layer with sufficient hardness to permit fabrication into machinery parts with a minimum of strain developed therein. The method comprises heating steel at a temperature in a range not lower than 100.degree. C. below its A.sub.1 transformation point (about 630.degree. C.) and not higher than 50.degree. C. thereabove (about 780.degree. C.) in an atmosphere consisting solely of ammonia gas, or composed of ammonia gas and at least one of organic liquids, petroleum gases, endothermic gases and neutral gases, while ammonia gas is being supplied continuously at a lower flow rate, or at a higher flow rate followed by a diffusion treatment to austenitize a surface layer of the steel by penetration of nitrogen thereinto, and quenching the steel to transform the austenitized surface layer into a martensite layer.

Abstract: A process for case hardening martensitic stainless steels comprising the steps of forming non-explosive and neutral or weakly reducing atmosphere consisting essentially of 97.5% to 95% by volume of nitrogen gas, 0.5% to 1.5% by volume of carbon monoxide and 2% to 3.5% by volume of hydrogen gas. The carbon monoxide and hydrogen gases are produced by heat decomposition of an organic solvent mixed with the nitrogen gas. The martensitic stainless steel is heated in this atmosphere at a solution heat treatment temperature in the range 900.degree. C. to 1100.degree. C. for a period required to cause nitriding of a surface thereof to a predetermined depth. The steel is then quenched at a temperature within the range of 150.degree. C. to room temperature, the quenching gas being selected from the group consisting of nitrogen gas and the resulting gaseous atmosphere. As a result of this process, resistance against planar pressure by loads and the strength of the martensitic stainless steel are increased.

Abstract: This invention relates to a method of carbonitriding an iron-containing article. The method comprises the steps of subjecting the article to a carbonitriding atmosphere which atmosphere contains ammonia and an oxygen-containing organic solvent. The ratio of the oxygen atoms to the carbon atoms in the solvent is from about 0.5 to 1.5; and maintaining the article in the carbonitriding atmosphere until at least the surface of the article has increased its carbon and nitrogen content a predetermined amount.Inasmuch as the carbonitriding treatment of the instant invention has a propensity to produce "HCN" which is well-known noxious gas, as well as NH.sub.3 and CO, it is also within the method of the instant invention to mix the gases used initially to contact the iron-containing article with a fuel gas and remove such a mixture of gases from the furnace where the mixture is subsequently burned thereby decomposing and detoxifying the HCN contained in the exhaust gas.

Abstract: The method of this invention is directed to the heat treatment of an iron-containing article and comprises the steps of subjecting the article to an atmosphere comprising specific amounts of nitrogen, carbon, hydrogen, and carbon monoxide and heating this article in this atmosphere. The furnace comprises first and second interconnected chambers, with the first chamber being a heating chamber and the second chamber being a cooling chamber. The first chamber is selectively joined to the second chamber by a gate means. The heating chamber has a heating plate disposed therein arranged and configured to support an article thereon. The heating chamber further has heating means for heating the chamber disposed therein. The cooling chamber has means for positioning the article therein and at least one nozzle for selectively introducing nitrogen gas into the cooling chamber.

Abstract: A gas carburizing furnace wherein the liquid organic composition is introduced into the furnace through a perforated container contained therein. The perforated container comprises a thermal plate at the bottom and perforated walls made from a catalytic material. Therefore, the liquid organic composition entering the container through the dropping port is vaporized when it comes in contact with the hot thermal plate and is cracked while passing through the perforations in the catalytic material.