Abstract: The specification discloses a method and apparatus enabling the formation of a diffusion surface layer on a surface of a metal substrate, typically a ferrous based metal substrate, wherein in a first stage in a first fluidized bed furnace, a diffusion zone is formed extending inwardly from the surface of the metal substrate in which nitrogen has been diffused to form a nitride or carbo nitride inner zone and an outer white layer that is substantially free of porosity, treating the substrate formed in the first stage to prevent formation of or remove any surface oxide on the surface of the substrate, and in a second stage separate from the first stage, holding the thus treated substrate in a fluidized bed furnace operated under an inert atmosphere and fluidized by a flow of inert gas or gases, the substrate in the fluidized bed furnace being treated in the presence of a halide gas and a particulate metal or metal alloy.

Abstract: The specification discloses a method and apparatus enabling the formation of a diffusion surface layer on a surface of a metal substrate, typically a ferrous based metal substrate, wherein in a first stage in a first fluidized bed furnace, a diffusion zone is formed extending inwardly from the surface of the metal substrate in which nitrogen has been diffused to form a nitride or carbo nitride inner zone and an outer white layer that is substantially free of porosity, treating the substrate formed in the first stage to prevent formation of or remove any surface oxide on the surface of the substrate, and in a second stage separate from the first stage, holding the thus treated substrate in a fluidized bed furnace operated under an inert atmosphere and fluidized by a flow of inert gas or gases, the substrate in the fluidized bed furnace being treated in the presence of a halide gas and a particulate metal or metal alloy.

Abstract: A fluidized bed heat treatment apparatus is provided to be heated by combusting fuel gas in a manner to minimize or prevent the exhaust of carbon monoxide, the apparatus including a retort containing refractory particles to be fluidized, a first inlet in a lower region of the retort for introducing fuel/air mixture into the retort, a second inlet in a lower region of the retort for introducing secondary air into the retort, a temperature sensor located above the first and second inlets, a flame initiator located above the refractory particles, an externally located mixer to mix fuel and air in desired proportions and to supply same to the first inlet, and a control device arranged to control said externally located mixer in response to temperatures sensed by said temperature sensor whereby when the temperature sensor is below a predetermined temperature indicative of the bed being substantially not fluidized, a stoichiometric fuel/air mixture is supplied to the first inlet and when the temperature sensor sens