The authors reported previously the sponge iron powder for powder metallurgy which was prepared from pyrite by means of a sequence of the following operations: flotation, roasting and treating with nitric acid, reduction of the purified pyrite cinder with hydrogen, and rolling and annealing of the reduced iron powder.
Furthermore, an attempt was made to cut the cost by employing H₂-Co gas mixture as a reducing agent. And the authors has succeeded in improving the apparent density and the compressibility of the reduced iron powder by repeating the processes of powder rolling, grinding and annealling.
Consequently, they obtained the reduced iron powder having little carbon content and other impurites. The result showed that repeated powder rolling and annealling were effective for densification, and that it was preferable to anneal the powder at a comparatively lower temperature for the improvement of compressibility.
Iron powder obtained had compressibility as high as electrolytic iron powder, and the other properties were also satisfactory.