Microstructure and mechanical characterization of rapidly solidified Cr-C tool steel: Annealing effects

•D2 tool steel was produced using rapid solidification followed by isochronal annealing.•Significant retained and supersaturated austenite was observed.•Larger process cooling rates delay the onset of phase transformation.•A maximum hardness of 620 HV0.1 was achieved, when annealing at 550 °C.

The effect of isochronal annealing on D2 tool steel powder, rapidly solidified via both Impulse Atomization and Water Atomization, has been evaluated using high-resolution scanning electron microscopy and Vickers microhardness. The amount of supersaturation of the alloying elements inside the retained austenite phase as a function of eutectic undercooling was calculated. The fraction of austenite transformed to ferrite at different annealing temperatures (from 350 °C to 810 °C) was also determined, using Rietveld analysis. The results show that although the particles with larger eutectic undercooling have larger supersaturation of alloying elements within the retained austenite phase, they have a smaller fraction of austenite to ferrite transformation at the temperature in which transformation starts. The maximum hardness was achieved at an annealing temperature of 550 °C, due to the formation of fine and well-distributed carbides.

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