Effect of compaction conditions on the properties of magnetically soft materials sintered from iron powder

Abstract

The effect of compaction on the porosity and magnetic properties of materials sintered from iron powder is studied. It is shown that porosity, when it is more than 6.5%, is the major factor that determines the magnetic flux density of the material. With lower porosity, the magnetic properties are greatly influenced by another structural factor-strain accumulated during additional compaction.The magnetic properties of materials (B max , B r , μ max , H c , R) are greatly dependent on their composition and production conditions. They in turn determine the density, structure, and residual mechanical stresses. It is noted in [1-3] that the porosity of magnetically soft materials substantially influences their magnetic properties. In particular, according to [2], the magnetic flux density of a porous material is proportional to its density in a first approximation.It is ascertained in [4] that the magnetic permeability of magnetically soft materials is a linear function of porosity if the porosity is high and nonlinear if low. At the same time, the density of a powder part depends on the initial porosity of the compact and sintering temperature, but it is usually impossible to reach quite high density after single pressing and sintering. For the sintered billets to be denser, they are additionally compacted; the porosity of the final product primarily depends on deformation pattern and strain. However, the plastic strain of the base material accumulated during additional compaction of the billets affects structurally-sensitive magnetic properties because of the increase in residual stresses [1].For example, according to [5], magnetic properties weakly depend on density when it is 73 to 98%; this is because two opposite effects compensate each other (increase in the amount of material per volume unit is accompanied by the increase in internal stresses). It is concluded that material does not need to be very dense to reach high magnetic properties. The magnetic properties of the material annealed after additional compaction are somewhat better than those without annealing since residual stresses decrease in the particles and compact as a whole [5].It is currently impossible to uniquely assess the effect of porosity and cold hardening on the magnetic properties of magnetically soft powder materials. Therefore, the objective of this paper is to examine how the compaction conditions influence the porosity and magnetic properties of materials sintered from iron powder.

A short review on the effect of compaction pressure on properties of materials obtained via powder metalurgy

“…Sintered iron powder magnetic and density properties are reported (BAGLYUK et al, 2009). For the condition of porosity higher than 6.5%, the porosity itself is the main parameter that influences the magnetic flux density of the sintered.…”