METHOD FOR EXECUTING REDUCTION-ANNEALING TO METAL POWDER

PURPOSE:To shorten treating time in a reduction-annealing chamber in a furnace and treating time in preheating and cooling processes by separating reduction- reaction process to easy-to-reducing oxide from reaction process to difficult-to- reducing oxide in metal powder. CONSTITUTION:At the time of executing reduction-annealing to the metal powder (steel powder) under atmosphere of reduced pressure by preheating, reduction-annealing and cooling, the steel powder is charged into pans 8 and charged in a tray 7 together with the pans 8 and heated in a preheating chamber 1 through an inlet door 4 in the furnace at 800 - 1,000 deg.C. Then, only the reducing reaction to the easy-to-reducing oxide in the steel powder is developed. Successively, the tray 7 is charged in the reduction-annealing chamber 2 through a movable door 5 and held at >=1,000 deg.C to execute the reduction-annealing mainly to the difficult-to-reducing oxide, and after cooling it in the cooling chamber 3 through a movable door 6, the obtd. sintered steel powder is crushed to make the product steel powder. By this method, partial pressures of CO and CO2 produced with reaction in the chambers 1, 2 are lowered, and the reducing reaction velocity can be made to high.