Abstract: Fluidized bed apparatus 1 for use in heat treating metal articles in a bed of fluidized particles 6 includes a heat insulated structure 2 and a removable module 4. The module is a metallic assembly integrating a vessel 5 for receiving the fluidizable particles, a bottom plate 8 of the vessel having a plurality of gas inlet nozzles 9, and a gas plenum chamber 11 fed by a gas admission conduit comprising a gas duct 12 and an entry pipe 13. Each nozzle 9 comprises a vertical inlet pipe 25 and a distinct cap 26 of specific channel design mounted on top of the pipe for deflecting a fluidizing gas flow into the particle bed 6.