The author reported previously that the Young's modulus of sintered iron compacts measured by the resonance method was affected by the pore shape, rather than by the pore size and number. The purpose of this study is attempts to express quantitatively the effect of pore shape on Young's modulus and evaluate the degree of spheroidizing of pores in sintered iron compacts added by alloying elements such as P and Si. The results are summarized as follows:
Using the proposed pore shape factor, η, which is mainly based upon the Hashin's elastic theory, the relation between Young's modulus of compacts, E, and the porosity, s, can be simply and successfully expressed as E/E0=(1-ε)/(1 +ηε), where E0 is Young's modulus of bulk material. In the case of sintered iron compacts, the value of η takes about 1 for the spherical shape of pores, and 2 to 3 for the pores with rounded edges. Thus, the value of η increases as the pore shape becomes irregular and angular.
For a given amount of porosity, Young's modulus of Fe-P compacts sintered above 1050°C (eutectic temperature of Fe-Fe3P) is higher than that of Fe compacts alone, which is due to the appearance of spheroidized pores by the liquid phase sintering. Addition of 3 wt%Si to atomized iron powders is somewhat effective on the spheroidization of pores as compared to that of 0.4 wt%P for the same sintering conditions, e.g. 1150°C×1hr.
Young's modulus of Fe-2.5%Si-0.3%P compact increases with increasing sintering temperature, and the elastic behavior of the specimen sintered at 1200°C for 1 hr is comparable with that of the carbonyl sintered iron, and the value of η of the former reaches nearly 1. Moreover, it was found that sintered iron compact treated by the gas sulfurizing shows a considerably spheroidized pore structure.