Development of corrosion. Fatigue resistant diffusion. Bonded pump impellers from stainless PM steels

For manufacturing of only a small number of corrosion and/or abrasion resistant pump impellers the application of the casting technology would be too expensive and time consuming. However, the PM technology offers an economical production alternative. The upper and lower parts of the impellers were cold-isostatically pressed, presintered, machined and assembled by sinter-joining during final sintering. As this impeller has to operate in corrosive environment the basic material was the prealloyed austenitic PM' steel Fe-18.0 per cent Cr-10.0 per cent Ni-2.0 per cent Mo-0.03 per cent C-0.8 per cent Si (similar to AISI 316). By admixing of 2.0 per cent Cu with 0.3 and 0.7 per cent P, respectively, the material was modified in order to control the shrinkage of the upper and lower disks of the impeller during sinterjoining. The operational safety of the new impeller was proved in a closed pump test loop in tap and artificial seawater under severe operational conditions without any signs of corrosion fatigue and cracks. For corrosive environments more severe than seawater this production concept can be applied by using more corrosion resistant materials like Hastelloy.