Laser additive manufacturing of hot work tool steel by means of a starting powder containing partly spherical pure elements and ferroalloys

Abstract

Until now, additive manufacturing of high-performance materials such as martensitic hardenable tool steels is rarely investigated. This work addresses the introduction of an alternative alloying strategy for hot work tool steel powder, provided for laser powder bed fusion (L-PBF). The focus is on the question whether a powder mixture of spherical iron powder mixed with mechanically crushed ferroalloy particles can be processed by L-PBF, instead of using cost-intensive pre-alloyed gas-atomized powder, and to investigate the material properties associated with it. The particle morphology, packing density and flowability of this L-PBF powder feedstock is compared to gas-atomized spherical pre-alloyed steel powder and the results are correlated to the defect density, the resulting microstructure and the chemical homogeneity. Finally the resulting surface hardness is compared to a conventionally casted material as a reference state. It shows that the L-PBF fabrication of high-dense parts by means of both starting powders is technically feasible. Even though the alternative alloying concept promotes local chemical inhomogeneities within the microstructure, the overall porosity and the appearance of micro cracks are reduced.