Heterogeneous structure architected by additive manufacturing: facile route towards strong and ductile steel

Here we reported a novel approach to architect heterostructure in steels with superior mechanical properties by laser powder bed fusion (LPBF). By taking advantage of intrinsic heat treatment during LPBF, microstructure architecting on the scale of molten pool was realized in a ferritic/martensitic steel. The resulting microstructure consists of coarse ferrite, fine martensite and retained austenite with multiscale heterogeneity. Compared to the counterpart steel fabricated by casting and forging, the LPBFed steel exhibits remarkable enhancement in both strength (from 727.6 to 1408.6 MPa) and uniform elongation (from 6.2% to 9.3%). Progressive plasticity of the heterostructure and hetero-deformation induced hardening contribute to the superior synergy in strength and ductility.