Abstract
We have already reported that lithium stearate as the die wall lubricant enabled warm compaction at the pressure range up to 2000 MPa without the internal lubricant and that the high green density of almost pore free density was obtained. Since this high green density results in the high sintered density and the low dimensional change, the cost reduction of finish machining besides the improvement of mechanical properties are expected. However in some low alloy sintered steels, the high pressure warm compaction above 1200 MPa followed by high temperature sintering causes the blister which results in the decrease in the density during the sintering. In this study, inhibition of the blister is investigated and the beneficial effects of the small amount additives of the easily oxidizable metal elements are revealed. As a result of controlling the blister, the low alloy sintered steels highly densified more than 7.7 g/cm3 are realized and extremely good mechanical properties are obtained.
