Fig. 1. Morphology and particle size distribution of 24CrNiMo alloy steel powder. (a) Morphology; (b) particle size distribution

Fig. 2. Schematic of scanning strategy of SLM forming

Fig. 3. Size of tensile specimen

Fig. 4. XRD patterns of SLM-formed alloy steel and as-cast alloy steel (P=320 W, v=950 mm/s)

Fig. 5. OM morphology of alloy steel. (a) As-cast alloy steel(etched by 4% nital); (b)(c) XOZ cross-sections of SLM-formed alloy steel (etched by 4% nital and Lepera solution, P=320 W, v=950 mm/s)

Fig. 6. TEM images of molten pool zone and heat affected zone of SLM-formed alloy steel (forming parameters: P=320 W, v=950 mm/s). (a)--(c) Molten pool; (d)--(f) heat affected zone

Fig. 7. OM images of XOZ cross-section of SLM-formed alloy steel with different laser parameters (etched by 4% nital)

Fig. 8. SEM images of XOZ cross-section of SLM-formed alloy steel with different laser parameters (etched by 4% nital)

Fig. 9. Relative density of SLM-formed alloy steel with different laser parameters

Fig. 10. Schematics of XOZ cross-section morphology evolution of SLM-formed alloy steel with different parameters. (a) Low energy input; (b) high energy input

Fig. 11. Microhardness of molten pool zone and heat affected zone in XOZ cross-sections of SLM-formed alloy steel with different laser parameters

Fig. 12. Tensile curves of SLM-formed alloy steel and as-cast alloy steel

Fig. 13. Tensile fractures of SLM-formed alloy steel and as-cast alloy steel. (a) Sample 2#; (b) sample 3#; (c) as-cast alloy steel