The influence of DED process parameters and heat-treatment cycle on the microstructure and hardness of AISI D2 tool steel

Abstract

The impact of both the laser directed energy deposition (DED) process parameters and post-deposition heat-treatment cycles on the microstructural characteristics and hardness are evaluated for cladding AISI D2 tool steel onto annealed AISI D2 substrates. The influences of powder feed rate, and laser scanning speed were assessed. After laser deposition, the DED samples were subjected to various tempering heat-treatment cycles. The microstructural and compositional characteristics of both the ‘as-printed’ and heat-treated DED processed samples were investigated using scanning electron microscopy with energy dispersive X-ray spectroscopy, confocal laser scanning microscopy, and X-ray diffraction. The indentation and scratch hardness responses were assessed to evaluate the effects of various heat-treatment schedules, with comparison made to wrought D2. It was demonstrated that the microstructure of the DED processed samples had a dendritic morphology with columnar grains. Moreover, the hardness values of the DED fabricated parts were found to be higher than an annealed wrought D2, but lower than the quenched D2. Subsequent tempering of the DED printed parts resulted in a final hardness, essentially equivalent to the as-quenched level.