Evolution mechanisms of MgO·Al2O3 inclusions by cerium in spring steel used in fasteners of high-speed railway

Abstract

The effect of rare earth metal addition on the non-metallic inclusions in spring steel used in fastener of high speed railway was investigated by metallographic examination; SEM-EDS and component analysis, aiming at deform those harmful inclusions to improve service life of spring steel. MgO·Al2O3 inclusions were found in present experimental steel, which is also confirmed by the stability diagram of MgO/MgO·Al2O3/Al2O3 from thermodynamic consideration. After Ce addition, the evolution process of Al2O3·MgO inclusions was determined through the surface and line scanning. The effects of time and Ce content on the evolution of Al2O3·MgO inclusions were examined. It was indicated that Al2O3·MgO inclusions were wrapped by rare earth inclusions to form a ring like shape Ce-riched band around the inclusion, which would be useful to improve fatigue and corrosion resistance of spring steel. It was found that diffusion of Ce3+, Al3+ and Mg2+ in inclusions core and intermediate layer would be the limited step during evolutions of inclusions.