Over the last century, improvement in mechanical performance of structural metals has primarily been achieved by creating more and more complex chemical compositions. Such compositional complexity raises costs, creates supply vulnerability, and complicates recycling. As a relatively new metal processing technique, metal 3D-printing provides a possibility to revisit and simplify alloy compositions, achieving alloy plainification, which enables simpler materials to be used versatilely. Here, we demonstrate that high performance simple plain carbon steels can be produced through 3D-printing. Our 3D-printed plain carbon steels achieve tensile and impact properties comparable, or even superior to those of ultra-high strength alloy steels such as Maraging steels. The sequential micro-scale melting and solidification intrinsic to 3D-printing provides sufficient cooling to directly form martensite and/or bainite, strengthening the steels while maintaining microstructural and property homogeneity without dimensional limitations or heat treatment distortion and cracking. By manipulating 3D-printing parameters, we can tailor the microstructure, thereby control the properties for customized applications. This offers a scalable approach to reduce alloy complexity without compromising mechanical performance and highlights the opportunities for the 3D-printing to help drive alloy plainification.
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