Higher densities of PM-steels by warm secondary compaction and sizing

Reaching higher densities is one of the biggest challenges for PM products today. This paper presents how new compaction processes like secondary pressing and sizing at elevated temperatures increase density and mechanical properties of sintered steels. A prealloyed iron powder Astaloy CrL with 1.5 % Cr and 0.2 % Mo (Höganäs AB) was used without and with an amount of 0.5 % graphite. The powders were compacted by different methods that combine double press/double sinter, warm compaction for both pressing stages and warm sizing. The compaction and sizing temperatures were ranged from 20 °C to 200 °C. The various processing routes are compared through measurements of density, microstructure and mechanical properties. The results show that elevated temperatures in different compaction stages lead to a significant increase of the relevant properties.