EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Supersolidus sintering is a process variant in powder metallurgy that is known to promote densification during sintering in a particularly efficient way. For powder metallurgy precision parts, high density would be particularly attractive of combined with the associated mechanical properties. In the present study, supersolidus sintering was studied on PM plain carbon steels and Mo alloyed grades, both with varying carbon content. ThermoCalc simulations predicted that fairly high temperatures are required for reaching high density/low porosity levels. Higher carbon contents significantly decrease the required temperature and also widen the phase field solid-liquid, easing control of the sintering process, the Mo alloyed steels being more tolerant here. Dilatometric runs combined with metallography confirmed these findings but also showed that slightly too low temperatures result rather in pore coarsening than pore elimination. In case of proper sintering, however, density levels >7.7 g.cm-3 are possible. On the other hand, sintering to almost full density also eliminates the grain stabilizing effect of the pores, and, as a consequence of the high temperatures, very coarse microstructures result. These however can be refined by classical heat treating procedures which also remove the problem of proeutectoid carbides at the grain boundaries that emerge at higher carbon levels. In general, the availability of sintering furnaces that provide excellent temperature and carbon control offers the chance to use supersolidus sintering also for production of highly loaded PM parts.