High-speed machining tool-steel chips as an outstanding raw material for indirect additive manufacturing?

Abstract

Sustainable recycling approaches are emerging topics for environmental safety of manufacturing technologies. Chips generated in high–speed machining (HSM) of as-quenched steels have a potential re-use for more sustainable and cost-efficient manufacturing routes, such as powder production from chip milling for additive manufacturing (AM). The objective of this study was to characterise tool-steel chips generated by HSM of an AISI-SAE H13 as-quenched workpiece and evaluate their potential use for powder production, as an alternative process to atomisation. Microhardness tests reveal that this type of waste has a suitable hardness for milling, which could be attributed to its microstructure. Chips were also analysed by X-ray diffraction, scanning and transmission electron microscopies, and transmission electron backscattering diffraction (t-EBSD) mapping. The microstructure of the areas adjacent to the adiabatic shear band (ASB), where intense material flow takes place, consists of thin martensite laths with high dislocation density and low angle grain boundaries (LAGB) or sub-grain regions. ASB consists of ultrafine and nanocrystalline grains. The results provide new insight on the grain-refining mechanism assisted by progressive martensite lath subdivision into small and near-equiaxed grains, as a direct result of intense strain accumulation and recrystallisation, endorsing HSM tool-steel chips as superior (nanocrystalline) and low-cost raw material for powder production.

Keywords

• Tool-steel chip
• Grain-refinement
• Nanocrystalline
• t-EBSD
• Additive manufacturing