Effect of Gadolinium on the Deformation of Sulfides and Mechanical Properties of an Al-Killed Resulfurized Steel

The rare earth element Gd was added into a resulfurized steel to enhance its performance. Non-metallic inclusions in the steel, the hardness and the microstructure of the steel were analyzed. The addition of Gd resulted in the formation of Gd–O–S and Gd–S inclusions which served as cores of MnS inclusions so that the resistance to the deformation of inclusions was improved. When the content of the total gadolinium (T.Gd) increased from 0 to 198 ppm, the hardness of the steel matrix increased from 60.4 to 80.4 HRA. The microstructure predominantly consisted of a substantial number of pearlites with a minor presence of ferrites distributed in a network-like pattern. The distribution of ferrites along the grain boundary was weakened when the T.Gd content in the steel was 79 ppm. The tensile fracture of the steel exhibited a mixed ductile-brittle pattern while its impact fracture displayed brittle characteristics.