SUMMARY

Cyclical temperature changes in additive manufacturing due to overlapping weld beads across multiple deposition layers result in high hardness values, leading to machining difficulties from an increase in required cutting forces. The present study explores the viability of localized laser-based treatments to thermally soften deposited materials by defocusing the beam caustic and dispersing energy over a larger area. A five-axis machine tool equipped with a blown powder laser directed energy deposition system was utilized for this work. H13 samples were manufactured using nominally correct deposition parameters, resulting in hardness values greater than 600 HV. Laser power, offset distance, and exposure time were varied to locally soften the as-printed samples to varying degrees. Parameter combinations that sufficiently softened the prints resulted in hardness reduction to 270 HV. When exposure time was increased from 5 minutes to 15 minutes, a change in temper penetration depth of up to \SI{1.1}{\mm} depending on the power and offset parameter combination was observed. Microstructure observations revealed separate regions within the locally tempered zone to track martensitic phase transformations. Discrete point hardness maps were overlaid with matching micrographs to correlate hardness reduction to solid state phase transformation of the microstructure. The present results have shown the effectiveness of using laser heat treatment to locally temper deposited tool steels with the ultimate goal of reducing hardness.