Optimization of laser energy density and scanning strategy on the forming quality of 24CrNiMo low alloy steel manufactured by SLM

Abstract

Selective laser melting (SLM) is among the best technologies to realize near-net forming of metal parts. The process involves the matching of various process parameters to achieve the full density of the products. This study was dedicated to understanding the influence of laser energy density and various scanning strategies on the formability of the SLM-fabricated 24CrNiMo specimens, which were characterized in terms of densification, surface quality and microstructure. Firstly, the experiments focused on the adjustment of laser energy density, which was aimed at determining an optimal parameter for the 24CrNiMo steel with the minimum porosity and optimum microstructure. The experimental results illustrated that the relative density of the specimen was promoted to 99.14% and its surface roughness decreased to 19.002 μm by applying the energy density of 56.00 J/mm3. In addition, the microstructure was mainly composed of lower bainite with high strength, and the irregularly oriented grains ensured the homogeneity of the specimen. Subsequently, the residual stress distribution and warping deformation of the specimens prepared by various scanning strategies were thoroughly analyzed to clarify the most suitable strategy for 24CrNiMo steel. It was observed that the specimen prepared by orthogonal scanning strategy exhibited no obvious defects, relatively stable residual stress distribution and optimal surface quality, which could be regarded as a reference for preparing high-quality 24CrNiMo steel via SLM.