Fig. 1. (a) SEM image of the 304 L SS powders, (b) optical micrograph of the SLMed 304 L SS sample fabricated using optimized parameters showing very low defect density and (c) the schematic of tensile specimens in building direction (vertical sample) and layer directions (horizontal sample).

Fig. 2. Optical micrographs of (a) ‘fish scale’ morphology and (b) columnar grains with melt pool boundary on vertical plane, and (c) laser exposure traces and (d) equiaxed grains on horizontal plane at low and high magnification respectively, in the as-fabricated 304 L SS. The nanoscale cellular subgrains on vertical and horizontal planes are revealed by the SEM micrographs taken at higher magnification and inserted in (b) and (d), respectively.

Fig. 3. EBSD unique grain colour maps of (a) the columnar grains aligned in the building direction on the vertical plane and (b) grains on the horizontal plane. The step size used for the EBSD scan is 1 μm.

Fig. 4. XRD pattern of phase identification in the as fabricated 304 L stainless steel, with step size of 0.02° and 1 s acquisition time per step. Fine scanning is performed in a small range from 45° to 48° with an acquisition time of 10 s per 0.02° step, with the spectrum inserted.

Fig. 5. EBSD results of (a) phase distribution map with the ferrite in green, σ phase in red and austenite matrix in canary as shown by the colour coding; (b) grain boundary map with low-angle grain boundaries in green, high angle grain boundaries (labelled as random boundary in the colour coding) in blue and twin boundary in red colour coding; (c) the inverse pole figure orientation mapping and pole figure of austenite matrix and precipitates of ferrite and σ phase.

Fig. 6. Bright filed TEM images of SLMed 304 L stainless steel: (a) cellular sub-grain structures with dislocation tangles as the cell wall, the associate selective area diffraction (SAD) pattern is taken from the austenite matrix indicated by the red dashed circle; (b) needle like ferrites observed inside the austenite matrix and confirmed by the SAD pattern taken at the location indicated by the red dashed circle; (c) square particles of the σ phase identified by EDS chemical composition.

Fig. 7. Representative stress/strain curves of the SLMed 304 L stainless steel in horizontal and vertical planes.

Fig. 8. SEM images of the fracture surfaces of SLMed 304 L tensile specimens: (a) horizontal sample; (b) vertical sample.

Fig. 9. Fraction of the equilibrium phase versus temperature calculated through Thermal-Calc software according to the specific chemical composition of 304 L stainless steel in this study.

Fig. 10. Comparison of the phase distribution mappings on the horizontal plane (a) and on the vertical plane (b) obtained by the EBSD phase measurement at a high magnification with the step size of 0.075 μm.