A series of new steel alloys were prepared by injecting particle aerosols into molten steel using an experimental set up (bench top furnace equipped with an aerosolizer) designed, built, and commissioned at Cornell. The introduction of the various particles, especially nanoparticles, results in significantly altered microstructure (grain size and morphology). The target metal particles or mixtures of particles are aerosolized first and carried into the molten metal for alloying. Cast iron and 1018 steel are chosen as the raw materials while metal powders (Ti, W, Nb) with different size scale (micron and nano-scale) are alloyed into the molten metals through different approaches (regular alloying and aerosol technology). Compared to the alloys produced by conventional metallurgy (regular alloying and regular size particles), the new alloys exhibit significantly altered microstructures and refinement of grain size, and much better uniform distribution as observed with EDS element mapping. The experiments confirm that the nanoparticle-aerosol technology is a promising approach with good versatility and can realize excellent dispersion of alloyed agents even with trace amount of injection. Moreover, this approach is shown to be more advantageous over conventional metallurgy and seems to have potential in industrial applications.