Selective laser melting of H13: microstructure and residual stress

In this research, samples of the H13 steel, a commonly used hot work tool steel in the die/mould manufacturing industry, were additively manufactured using selective laser melting (SLM). Their as-built microstructures were characterised in detail using transmission electron microscopy (TEM) and compared with that of the conventionally manufactured H13 (as-supplied). SLM resulted in the formation of martensite and also its partial decomposition into fine alpha-Fe and Fe3C precipitates along with retained austenite. TEM analyses further revealed that the lattice of the resulting a-Fe phase is slightly distorted due to enhanced Cr, Mo and V contents. Substantially high residual stresses in the range of 940-1420 MPa were detected in the as-built H13 samples compared with its yield strength of similar to 1650 MPa. In addition, it was identified that the high residual stress existed from just about two additive layers (100 mu m) above the substrate along the build direction. The high residual stresses were mainly attributed to the martensitic transformation that occurred during SLM. The research findings of this study suggest that the substantially high residual stresses can be easily problematic in the AM of intricate H13 dies or moulds by SLM.