Warm compaction of ferrous powders in the 400°C to 520°C range—Part 2: Properties of unalloyed and low-alloy steels

In the first part of this feasibility study, a warm compaction route for ferrous powders has been described that operates in the 400–520°C range. In this second part, warm compacting studies with various types of unalloyed and alloyed steels were done. It showed that short preheating of the powder batch in the tool cavity and in protective atmosphere is sufficient, and also the time at pressure may be fairly short. However, too high green density may result in cracking during sintering, caused by trapped gases formed during carbothermal reduction processes. When comparing warm compaction with cold compacting at high pressures, a significant effect of the alloying route was observed: for elemental powder mixes, warm compaction showed to be preferable regarding the densities attained. For prealloyed grades, in contrast, high-pressure compaction yielded generally higher green densities, although for special prealloyed powder grades trimmed to maximum compactibility, also warm compaction seems to be eligible.