Upgrading mechanical property and corrosion resistance of a low cost 45 steel by remelting a Cr film of ∼1μm in thickness

It is well-known that the overall mechanical or chemical properties of the metallic material could be tailored by introducing either grain size gradient or chemical gradient. In this work, we, taking one of the widely used low cost 45 steel as a model material, demonstrated that both mechanical properties and corrosion resistance can be greatly upgraded by laser remelting a Cr film of ∼1 μm in thickness. The yield strength was increased by ∼110 MPa and the elongation was almost unchanged in contrast to the Cr-free substrate. The corrosion resistance was also enhanced with a higher self-corrosion voltage (increased by 0.1 V) and a lower self-corrosion current (decreased by 80 nA/cm2). The upgraded strength-ductility synergy derives from the laser induced rapid melting and solidification, where the top surface layer incorporates both grain size gradient and chemical gradient. Greatly refined grain size and micro-alloying of Cr in the form of both solid solution and nanoprecipitates contribute to the enhanced strength, while higher concentration of Cr resulting in the formation of passivation film, accounts for the superior corrosion resistance. The findings in this work provide a strategy for optimizing the mechanical and chemical properties through surface medications, making metallic materials multi-functional.