| 摘要 |
PURPOSE:To improve considerably resistance to wear and corrosion by subjecting parts to a heating treatment in steam to form an oxide film thereon then heating the parts in a reducing gaseous atmosphere and heating the parts in an ammonia gaseous atmosphere to nitride the surface. CONSTITUTION:Ferrous sintered parts are first contained in a heating furnace kept at 500-570 deg.C, prior to surface nitriding of said parts, and steam under 5- 500mm. water column steam pressure is introduced into the furnace for 30-90min to form an oxide film on the surfaces of the parts and the pore walls near the surface. The parts are then heated for about 30min at 450-550 deg.C in a reducing gas such as, for example, the cracked gas of ammonia to reduce part or the whole of the oxide film on the surface of the parts except the oxide film of the pore walls near the surface which are held without reduced. The temp. in the furnace is maintained at 500-600 deg.C in succession thereto and gaseous ammonia kept under 5-100mm. water column pressure is introduced into the furnace to nitride the surface of the ferrous sintered parts. |
