Abstract: A continuous heat treatment furnace has an entrance, a preheat zone, a thermal treatment zone, a cooling zone and an exit. Curtains are provided at the entrance and exit respectively. Nitrogen and hydrogen (or other reducing gas) are supplied to the furnace to create a non-oxidizing or reducing atmosphere in the thermal treatment and cooling zones. Elongate workpieces such as tubes are advanced through the furnace and thereby heat treated (e.g. annealed). As the workpieces pass through the curtains so the tendency for air to leak into the furnace is increased. To counteract this tendency, position sensing plates are adapted to actuate a signal generator controlling a valve which in turn controls flow of e.g. nitrogen to the furnace. The arrangement is such that the flow of nitrogen to the furnace is increased wherever a workpiece is sensed, thereby enabling the essentially reducing or non-oxidizing character of the atmosphere to be sustained.

Abstract: Ferrous metal is treated by austenitic nitro-carburizing in a heat treatment furnace. A suitable atmosphere is created by admitting to the furnace nitrogen; ammonia; and a liquid or vaporous organic compound of carbon, hydrogen and oxygen. The atmosphere is maintained at a temperature in the range 690.degree. to 750.degree. C. The organic compound is typically methanol and the atmosphere typically comprises nitrogen, carbon monoxide, hydrogen and free ammonia as well as small amounts of methane, carbon dioxide and water vapor.After being removed from the furnace, the ferrous metal is quenched. It has an outer surface layer of white, scuff-resistant, epsilon compound and an inner carbo-nitrided case containing austenitic and martensitic zone. The ferrous metal may then be treated to convert austenite to martensite or lower bainite.

Abstract: In order to decarburize ferrous metal without recourse to an exothermic generator, an inert gas (typically nitrogen), water and a liquid or vaporous compound of carbon, hydrogen and oxygen (typically methanol) are admitted to a working chamber of the heat treatment furnace in which the metal is situated. The decarburization is preferably performed at 700.degree. to 800.degree. C. The methanol and water react to form a non-oxidizing, decarburizing atmosphere at the decarburizing temperature. The metal may be oxidized at a temperature below 600.degree. C. in another chamber of the furnace, the atmosphere from the decarburizing chamber being passed into the oxidizing chamber.