Part deflection and residual stresses in laser powder bed fusion of H13 tool steel

Abstract

This study aims at a comprehensive investigation of residual stresses in laser powder bed fusion processed H13 tool steel through experiment and part-level simulation. Twin-cantilever beams and cubic coupons were printed in a wide range of process parameters to characterize residual stresses under preheated and non-preheated conditions. Results revealed the significant role of martensitic phase transformation, process parameters, densification level, and preheating condition on the residual stress regime and beam deflections. The residual stress regime was governed by the competition between the tensile and compressive stresses caused by the solidification/cooling contraction and martensitic phase transformation, respectively. The compressive residual stresses on the top surface turned into tensile immediately below the last consolidated layer. Higher heat inputs led to the increased magnitude of compressive residual stresses on the top surface of non-preheated samples. For parts having relative densities higher than 97%, the residual stresses were found to be independent of the densification level. Deflection modeling results indicated that for steels experiencing martensitic phase transformation, the martensite start temperature needs to be set as the relaxation temperature to accurately predict the beam deflection. This study proves that 200 °C of preheating eliminates not only cracks but also the need for stress-relief post-processing.