Research on the mechanism of the rare-earth Ce regulating inclusions in U71Mn heavy rail steel and improving its corrosion resistance

Coarse inclusions in U71Mn heavy rail steel and the local corrosion they cause are the key problems restricting its service life. In this paper, the rare-earth Ce is used to modify the inclusions, and the effects of Ce on the microstructure, inclusion characteristics, and corrosion resistance of the steel are systematically studied. The results show that the addition of Ce significantly refined the pearlite lamellar spacing, which decreased from 0.418 μm to 0.247 μm, and successfully transformed the coarse Al2O3 and MnS inclusions into fine, ellipsoidal CeAlO3 – MnS – CaS composite phases. Electrochemical tests show that after 72 h of corrosion, the impedance modulus of the Ce – containing sample is 217.1 Ω·cm², higher than 195.4 Ω·cm² of the sample without Ce addition. Raman spectroscopy confirms that it can form a protective α – Fe2O3 rust layer earlier. The potential difference between the modified composite inclusions and the matrix is significantly reduced to 50–60 mV, effectively suppressing the micro – galvanic corrosion. This study clarifies the mechanism by which the rare-earth Ce improves the comprehensive corrosion resistance of U71Mn steel by synergistically optimising the microstructure and inclusion characteristics.