Abstract
Cylindrical compacts, φ10×h10 mm, for the size measurement and cubic compacts, 10 mm in size, for the dilatometry were formed of an electrolytic iron powder by die-wall lubricating alone, or by admixing 0.3-1.5 wt% of zinc-stearate.
During pressing at 200-800 MPa the diameters of the cylindrical compacts and the die-cavity were larger than the original diameter of die-cavity size by 0.01-0.07%. The ejection of compact from the die was accompanied by some radial spring-back in the compact; that is, some 0.04-0.17% of expansion in comparison with the original die size.
During de-waxing at 600°C (873K) for 30 min and sintering at 1100°C (1373K) for 60 min in dissociated ammonia, the compacts expanded in the radial direction only when they contained zinc-stearate and were heated rapidly at the rate of several hundred degrees per minute. While those compacted by die-wall lubricating alone, and/or heated slowly at l0°C/min exhibited some shrinkage almost of the same order as the expansion by the spring-back. No correlation, however, was found between the expansion and the shrinkage.
On the dilatometer, the compacts were heated slowly at 10°C/min in hydrogen. Some of the compacts containing zinc-stearate, expanded in the lateral direction and shrank in the pressing direction simultaneously during the early stage of de-waxing.
