Magnetic Properties and Microstructure of High-Density Sintered Iron Formed by Warm Compaction Using Die Wall Lubrication

Sintered iron is a useful soft magnetic material. However, its magnetic flux density is smaller than that of wrought magnetic iron, due to the low density of the sintered material. In order to increase the sintered density, we developed a new warm compaction technique using die wall lubrication (WC-DWL) with lithium stearate. With this method, a very high-density sintered body can be fabricated. Pure iron powder compacted at 1176 MPa and sintered at 1523K showed the following properties: sintered density = 7.76 Mg.m - 3 , maximum permeability (μ m ) = 5300, magnetic flux density; B 1 6 0 = 1.16T, B 2 4 0 = 1.28T, B 4 0 0 = 1.40T, B 2 k = 1.60T, and coercivity ( b H c ) = 110 A.m - 1 . Some of the sintered iron showed an anisotropic dimensional change and anisometric microstructure, which were linked to abnormal grain growth of up to several mm in length. This anomaly was more pronounced the higher the green density of the specimens.