Consolidation of water-atomized chromium-nickel-alloyed powder metallurgy steel through novel processing routes

When processing powder metallurgy (PM) steels, the conventional press and sinter route can reach a relative density up to 95%, which is insufficient for applications when dynamic mechanical performance is critical. In this study, a novel route is demonstrated consisting of cold isostatic pressing (CIP) followed by sintering and capsule-free hot isostatic pressing (HIP), allowing to achieve full density PM steels. Water-atomized steel powder admixed with 2 wt.% Ni was subjected to CIP and followed by sintering in 90N2/10H2 atmosphere at 1120 and 1250 degrees C, and in vacuum (10-2 mbar) at 1250 and 1350 degrees C, respectively. At the highest explored CIP pressure of 600 MPa, the three high-temperature sintering runs at 1250 degrees C in 90N2/10H2 atmosphere and vacuum, and 1350 degrees C in vacuum resulted in relative density of similar to 94% and closed surface pores. This condition with necessary closed porosity then allowed subsequent capsule-free HIP after sintering, resulting in full densification of the components.