Steel foams have been receiving a growing interest due to the unique structural properties. The space holder technique provides a high degree of freedom and allows to produce this kind of materials varying in a wide range of porosity. However, the accurate prediction of final porosities has been a difficult problem in this technique. Therefore, a nonlinear equation between spacer content (φ1) and porosity (P) of the sintered steel foams was established in this study when macropores, micropores and their volumetric change were taken into account at the same time, that was P = (aφ1+b)/(cφ1+d). Then, validation of the theoretical relationship was carried out using the experimental data by authors and other researchers. The results showed that the porosity could be well predicted by the nonlinear relationship with varied preparing parameters. One set of coefficients in the model equation, i.e., a, b, c, d, corresponds to a certain preparing condition, while these values changed in different preparing conditions.

Porous irons with only micropores were produced through powder metallurgy route. Corn starch of small particle size (5-15μm) was utilized to regulate the densification of green compacts. The structural and mechanical properties of porous irons sintered at different temperatures were evaluated. The porosities increased with increasing the starch content, which reduced compressive strength and increased volumetric shrinkage. The compressive yield stress increased with increasing sintering temperature. It was also found that the effect of sintering temperature on the microstructure and compressive properties was more obvious when green compacts were less densified. Moreover, volumetric shrinkage of porous irons without adding starch remains in a quite low level for different sintering temperatures.