It is the purpose of this study to investigate the effects of shape of pores on toughness and ductility of sintered iron.
Compacts with a density range of 5.9-7.6 g/cm³ were pressed from electrolytic iron powder and pre-sintered at 1100°C for 10 min in hydrogen. Subsequently they were infiltrated with ferrous chloride by soaking for 4 min in its melt at 750°C.
Activated-sintering (or reduction of ferrous chloride) was carried out at 800°C, 950°C and 1100°C for 5 min-3 hr in hydrogen. Impact and tensile properties of these materials with round pores were compared to those of conventionally sintered ones with sharp edged pores.
The results were summarized as follows.
1. The roundness of the pores caused an increase in the charpy shelf energy and made the ductile-brittle transition more evident.
For this reason, the impact strength of the activation-sintered iron was, at 200°C, about two times as large as that of conventionally sintered iron with the same density, but at low temperatures, smaller than that.
2. Activated-sintering increased the ultimate tensile strength and the fracture strain by 10-50% over conventional sintering. But the yield strength was hardly affected by the pore shape.
3. The relative strength and the fracture strain of porous materials were expressed as functions relating not only to the porosity but also to the notch effect of the pores.