Spaced apart packs of closely spaced steel or other metallic rods, tubes or other elongate articles are annealed or otherwise heat treated by advancing them step by step by a walking beam mechanism through a chamber having a series of independently temperature controlled zones along the path of travel, the articles being disposed horizontally and transversely of the path of travel. The atmosphere within each zone is recirculated therein independently of the recirculation of atmosphere within adjacent zones and without substantial mixing of the atmosphere within adjacent zones. Packs are introduced into the chamber from a bed of powered rollers adjacent to the inlet end of the chamber partly by pivoting the free ends of extensions of the movable rails of the walking beam mechanism, to lift a pack above the level of the powered rollers so that it can translate with the other packs within the chamber, and partly by pusher heads which slidably engage the movable rail extensions and which are reciprocable with respect thereto. The chamber is preferably utilized to process articles which retain a significant degree of latent heat from a manufacturing or other processing operation to avoid the need for a significant degree of reheating of the articles within the chamber and without substantial intermixing of the atmosphere from adjacent zones.