In order to improve the performance of 45 steel, Fe-Cr-Mo-B-C amorphous composite coatings were fabricated on 45 steel substrates using a synergistic technique of laser cladding (LC) followed by laser remelting (LR). To further refine the microstructure of the coatings, laser remelting was applied with varying scanning speeds. The influence of different laser scanning speeds during laser remelting on the microstructure (including amorphous content, porosity, and phase composition) and properties of the coatings, including Vickers hardness, tribological behavior, and corrosion resistance, was systematically investigated in this study. Scanning electron microscopy (SEM), x-ray diffraction (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) were employed to characterize the microstructure, phase composition, amorphous/nanocrystalline coexistence, and thermal stability, respectively, and the wear and corrosion morphologies were analyzed to evaluate the surface integrity. The results indicate that a scanning speed of 20 mm/s is optimal, as it significantly enhances the amorphous content of the coatings (up to 48%), reduces porosity (to 0.474%), improves their microstructure, and strengthens their mechanical properties (maximum Vickers hardness of 1520.36 HV and minimum wear volume of 0.00315 mm3) as well as corrosion resistance (corrosion current density as low as 7.876 × 10−7 A/cm2 and corrosion potential of  −215 mV in 3.5 wt.% NaCl solution). This study provides valuable insights into optimizing laser processing parameters to enhance the performance of Fe-based amorphous composite coatings for demanding industrial applications such as automotive, petrochemical, and marine engineering.