Abstract
The mechanism of graphite nodularization and how to control graphite morphologies in sintered products of cast iron swarf powder, Fe-Si-C mixed powders, or Ni-C mixed powders have been investigated.
When the powder contains carbon less than the maximum solubility at the given sintering temperature, all carbon atoms dissolve in solid solution (γ-Fe or Ni-phase) during sintering and precipitate as the graphite into the pores during cooling. Consequently, if the pores in the sintered products are spherical by long-time sintering or powder forging processes, spherical frames for the graphite to grow in nodular morphology, can be provided. Then for example, the products (Imass%C) made from mixtures of cast iron swarf powder and reduced iron powder show the high tensile strength of 95 kgf/mm2 by long-time sintering (1150°C⋅20 hr).
On the other hand, when carbon contents are more than the maximum solubility, no nodular graphite can be obtained because of residual undissolved graphite.
