Selective laser melting (SLM) of CX stainless steel: Theoretical calculation, process optimization and strengthening mechanism

In the present work, selective laser melting (SLM) technology was utilized for manufacturing CX stainless steel samples under a series of laser parameters. The effect of laser linear energy density on the microstructure characteristics, phase distribution, crystallographic orientation and mechanical properties of these CX stainless steel samples were investigated theoretically and experimentally via scanning electron microscope (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). Based on the systematic study, the SLM CX stainless steel sample with best surface roughness (Ra = 4.05 ± 1.8 μm) and relative density (Rd = 99.72 %±0.22 %) under the optimal linear density (η = 245 J/m) can be obtained. SLM CX stainless steel was primarily constituted by a large number of fine martensite (α’ phase) structures (i.e., cell structures, cellular dendrites and blocky grains) and a small quantity of austenite (γ phase) structures. The preferred crystallographic orientation (i.e., direction) can be determined in the XZ plane of the SLM CX sample. Furthermore, under the optimal linear energy density, the good combinations with the highest ultimate tensile strength (UTS = 1068.0 %±5.9 %) and the best total elongation (TE = 15.70 %±0.26 %) of the SLM CX sample can be attained. Dislocation strengthening dominates the strengthening mechanism of the SLM CX sample in as-built state.