Selective laser melting and tempering of H13 tool steel for rapid tooling applications

H13 components with a relative density of similar to 99% were additively manufactured using the selective laser melting (SLM) process. The highest density part (relevant density 99%) with the lowest level of porosity (<0.01%) was made with a volumetric energy density of 760 J/mm(3) (152 W laser power, 100 mm/s scanning speed, 40 mu m hatch spacing, and 50 mu m layer thickness). Wrought and additively manufactured samples underwent tempering at 550, 600, and 650 degrees C for 2 h followed by furnace cooling. Additively manufactured samples and wrought H13 samples that were austenitized followed by water quenching were martensitic with similar microhardness values of 708.4 +/- 25.0 HV and 708.1 +/- 12.6 HV, respectively. A tempered martensitic structure was observed in SLM-manufactured and tempered samples. Samples that were additively manufactured and tempered at 550 degrees C showed higher microhardness (728.5 +/- 28.2 HV) than non-tempered SLM-manufactured samples due to an upward shift in the secondary hardening phase. Tempering at 600 and 650 degrees C resulted in coarsening of the carbides and martensite, which led to a reduction in microhardness. Additively manufactured samples maintained higher microhardness values than wrought H13 samples at all tempering temperatures, likely because of higher dislocation density, finer grains present, and higher volume fraction of carbide nanoparticles. (C) 2020 Elsevier B.V. All rights reserved.