Rare earth metals and their alloys play the role of deoxidization and desulfurization in steelmaking, which can reduce the content of both to less than 0.001%, change the morphology of inclusions and refine grains, thus improving the processing performance of steel, enhancing strength, toughness, corrosion resistance and oxidation resistance. Rare earth metals and their alloys are used to produce nodular cast iron, high strength gray cast iron and vermicular cast iron. They can change the graphite morphology in cast iron, improve casting technology and improve the mechanical properties of cast iron.