Characterization of MnS Particles in Heavy Rail Steels Using Different Methods

Characterization of the MnS particles in continuous casting (CC) blooms and rolled rails of U75V steel using the methods of traditional two‐dimensional (2D) microscope observation, three‐dimensional (3D) micro‐CT detection, and electrolytic extraction is performed. MnS particles from the surface to the interior, inside of columnar dendritic zone, and the equiaxed zone of the CC bloom are discussed. The morphology of MnS changes from elliptical and spherical near the surface of bloom to strip‐like, petal‐like, polyhedral, and irregular in the center of bloom gradually. The size of both pure MnS particles and complex inclusions which consist of a MnS outer layer and an oxide core increase from the edge to the center of bloom. However, MnS is elongated along the rolling direction during rolling process. The morphology of the cross section of the elongated MnS particles presents as globular and flaggy shape in the head and bottom of rail, and spindle shape in the waist of rail. The precipitation of MnS particles is studied on the basis of thermodynamics, the calculating results show that MnS particles are generated towards the end of solidification (solid fraction fS = 0.94), the amount of MnS particles are affected by the initial concentration of Mn and S in molten steel during solidification. The morphology of MnS changed from elliptical and spherical near the surface of bloom to strip‐like, petal‐like, polyhedral, and irregular in the center of bloom gradually. The size of both pure MnS particles and complex inclusions which consisted of a MnS outer layer and an oxide core increased from the edge to the center of bloom.