Water-based processing of high-speed steel utilising starch consolidation

Two different high-speed steel (HSS) powders, M2 and T15 from Osprey Metals were evaluated in water-based shaping by starch consolidation (SC) and sintering in a nitrogen atmosphere. Materials were produced based on various slurry compositions with different solids loading (60–62 vol.%) and starch content (2–5 wt.% based on water). The high solid loadings were possible utilising the stabilising (repulsive) forces provided by a small addition (0.04 wt.%) of a dispersant (polyacrylic acid) that resulted in accurate fluidity and a consolidation of the prepared slurries. Shaped specimens of T15 sintered to near full density and displayed a fine-grained and homogeneous microstructure. Higher nitrogen uptake with increased amounts of added starch was assumed to cause the decrease of measured density (8.20→8.14 g/cm3). Materials based on M2 did not completely densify (<7.88 g/cm3), which was an effect of the different alloy composition. An indicated higher degree of oxidation of this material during the water processing was considered to be an additional factor that might have reduced the sintering performance. The M2 specimens contained pores, which corresponded to the granule shape and size of the added starch.