The relationship between tensile strength and porosity in sintered compacts has been investigated with carbonyl iron powder. It was shown that the variation in the measured tensile strength with porosity could be expressed by dividing the whole range into three stages, that is, the low density range, the middle density range, and the high density range. Then, the relations of tensile strength and porosity in those three ranges can be represented by the following equation forms as a function of porosity alone.
For the low density range,
S=S'0-k1P(P1<P≤P0)
where S is the tensile strength, P, the prosity, P0, the green porosity, and S'0, k1 and P1, empirical constants. For the middle density range,
S=S0 exp(-bP) (P2<P≤P1)
where S is the tensile strength, P, the porosity, and S0, b, P1 and P2, empirical constants. For the high density range,
S=(Ss+k2Pa)exp(-bP)(P≤P2)
where S is the tensile strength, P, the porosity, and Ss, k2, a, b and P2, empirical constants.
The empirical constants contained in the above equation forms were determined from the experimental results. Thereby, the following equation forms representing the relations of tensile strength and porosity in the sintered carbonyl iron were obtained; when the compacting pressure is 4 t/cm2, for the low density range,
S=141-495P [kg/mm2] (0.24<P≤0.28),
for the middle density range,
S=40.1exp(-3.7P) [kg/mm2] (0.11<P≤0.24), and
for the high density range,
S=(22.6+94.7P0.8)exp(-3.7P) [kg/mm2] (P≤0.11).