Effect of lanthanum–cerium mixed rare earth on inclusions in U76CrRe eavy rail steel

Abstract

ABSTRACT This study focused on the entire process evolution law of inclusions in steel during heavy rail steel production. By adding rare earths, the number density of inclusions with areas > 1 µm2 decreased from 88.44–78.58 particles/mm2. Moreover, that of inclusions with areas > 5 µm2 decreased from 21.38–6.86 particles/mm2. After La–Ce was added, all Al2O3 inclusions disappeared, and the La–Ce in the molten steel combined with Al2O3 to form CaO–MgO–Al2O3–SiO2–ReO inclusions. The number density of Al-containing inclusions in steel with areas > 1 µm2 decreased from 50.8–11.33 particles/mm2. Sulfur enrichment occurred on the surface of the CaO–MgO–Al2O3–SiO2–ReO inclusions, enabling MnS and CaO–MgO–Al2O3–SiO2–ReO to form composite inclusions that could be removed easily. The number density of MnS inclusions with areas > 1 µm2 decreased from 86.40–49.33 particles/mm2. The tensile strength, hardness, yield strength, and impact toughness of the rare earth heavy rail were improved to varying degrees through the metamorphic effect of the rare earth elements La and Ce on the Al-containing and MnS inclusions. The fractures of the heavy rail steel without and with rare earth elements were mainly brittle and ductile, respectively.