| Summary: | A study has been made of a new particulate forging process in which pellets are used instead of conventional powder. The experimental procedure was first to produce iron oxide pellets prepared from a mixture of iron oxide superconcentrate powder and an organic binder. After drying, the oxide pellets were reduced and sintered in hydrogen to produce porous sponge iron pellets. Preforms were made from these pellets and subsequently hot forged in a closed die at 1100°C to produce forged discs. The discs were called 'sponge iron pellet forgings'. One of the purposes of the investigation was to determine whether the new route gave a product which had mechanical properties at least equal to the equivalent powder forged product even though it was made from a potentially cheap and relatively impure raw material. Thus, forgings were also made from pelletised iron powder and iron powder, and the results compared. Mechanical properties appear to be better or similar to that of iron powder forgings. The effects of process variables, such as pellet size, preform density, type of deformation and annealing treatment, on the final properties were studied. Among these, preform density (varying between 50-95% theoretical) and annealing treatment (1 hour at 700°C in H2) had significant effects on the final properties. Microscopically the product is characterised by a fine grain size and a large number of uniformly distributed fine inclusions. The inclusions derived from residual impurities in the concentrate, most of which were originally in the magnetite lattice. The number, size and size distribution of the inclusions are determined. The inclusions impart a substantial grain-refinement strengthening to the iron matrix during annealing.
|
|---|
