Effects of Apparent Density on Compacting Behavior of Atomized Iron Powder

Abstract

Apparent density (AD) has a close correlation with green density of a compacted body because AD is one of important scales indicating the filling structure of powder particles in a die. In this study, to clarify the effect of AD on green density, an annealed atomized iron powder of quite high AD (3.95 Mg/m3) was prepared, and its compacting behavior was investigated by comparing a low AD (3.05 Mg/m3) powder. The high AD powder was made by sieving commercial atomized powder into 5 sizes, and blending them to provide the particle size distribution of the lowest porosity, which was simulated by the calculation using Multi-component randomly packed bed model. The green densities of the high AD powder compacted at 686 MPa/130°C was 7.55 Mg/m3, which was higher than that of the low AD powder.The compacting processes were analyzed in accordance with Cooper-Eaton type formula. The analysis showed that particles deformation started at lower pressure in the low AD powder in comparison with the high AD powder. Micro-Vickers hardness of particles in the compacted green of the low AD powder was wholly higher than that of the high AD powder. Because, in the low AD powder, the powder particles could be packed roughly and inhomogeneously in a die, and compacting stress should concentrate in locally densed area, work hardening of particles could start at lower applied pressure and progress more. In compacting process, work hardened particles should suppress particle deformation, resulting in the lower green density. This result makes it clear that the increase in AD is effective on uniform and dense powder packing in a die, which results in high green density by delaying the start of work hardening.