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Based on the heat transfer theory, and the fact that thermal physical parameters, latent heat of phase change and heat transfer coefficient which vary with temperature is taken into considered, a three-dimensional transient temperature field model of 12CrNi2 by Laser Melting Deposition (LMD) is established by using the parametric design language of ANSYS. Optimum process parameters were determined by single-layer and single-track experiments of LMD. Microstructure observation by optical microscope shows that the width of heat affected zone increased with the increase of laser power and decreased with the increase of printing speed. The top of the deposited layer is mainly composed of equiaxed dendrites, and the middle and bottom of the deposited layer are columnar crystals with epitaxial growth characteristics. At the same time, the accuracy and reliability of temperature field model are verified by comparing the morphology of molten pool. The simulation results show that in the process of LMD, the peak temperature of molten pool increases with the increase of layers; the peak temperature of the node increases with the increase of laser power and the decrease of printing speed. The research results in this paper would be reference for LMD of 12CrNi2 alloy steel.

Herein, based on the ABAQUS commercial finite‐element analysis (FEA) software, a set of user subroutines is designed, and then a 3D FEA model is proposed to systematically and quantitatively investigate the effects of laser processing parameters on the evolution of molten pool structure and complicated thermal behavior during the selective laser melting (SLM) additive manufacturing of H13 die steel. The SLM experiments are conducted to verify the accuracy and reliability of simulation and reveal the densification behavior of SLM‐fabricated H13 die steel parts. The underlying thermal mechanism is revealed, and the relationship among laser processing parameters, thermal behavior, and densification is established. It is found that the densification behavior is highly sensitive to the applied volume energy density (VED). The densification level is effectively controlled by adjusting VED, hence obtaining the parts with excellent performance. The SLM‐fabricated specimens with nearly full dense cross sections are obtained, as the applied VED increases to 111 J mm−3. Research results found herein lie a foundation for the actual SLM processing of H13 die steel and provide a theoretical basis and technical support for the laser rapid prototyping of other die steels or even complete die parts.

In this study, the effects of laser volumetric energy density (η) on the metallurgical defect behavior and microstructure evolution of H13 die steel fabricated by selective laser melting (SLM) additive manufacturing are systematically studied, and underlying thermal mechanisms are revealed. The results indicate that the metallurgical defect behavior is significantly affected by the applied η, which is controlled by laser power P and scanning speed v. With increasing P or decreasing v, η increases, the metallurgical defects such as pores and poor fusion initially decrease and then increase, and the density initially increases and then decreases. The typical microstructures induced by SLM are columnar dendrites and equiaxed dendrites. Their growth direction, distribution, and size at different positions in the molten pool are quite different. The size of the columnar crystals with directional full growth is highly correlated with the applied η. As the applied η increases, the length and diameter of the columnar crystals increase, but grains with nonuniform distribution are obtained under a higher η of 122.22 J mm−3. Under the optimized η of 111.11 J mm−3 (P = 200 W, v = 1000 mm/s), the H13 die steel samples fabricated by SLM are near-fully dense and have almost no metallurgical defects (the density reaches 99.13%), and the dense columnar crystals with uniform distribution are obtained. This study may provide a theoretical and experimental basis for the design and optimization of SLM processing parameters and the reliable fabrication of SLM-processed parts with controlled defects and microstructures.

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